Peter Robinson

Waveform and envelope field statistics for waves with stochastically driven amplitudes

Publisher: AIP Publishing

Date: 03-2010

DOI: 10.1063/1.3353092

Towards a quantitative theory for 2-3 kHz radio emission from beyond the heliopause

Publisher: Elsevier BV

Date: 2004

DOI: 10.1016/J.ASR.2003.02.060

Data-driven solar wind model and prediction of type II bursts

Publisher: American Geophysical Union (AGU)

Date: 02-2007

DOI: 10.1029/2006GL028522

Beam-driven three-dimensional electromagnetic strong turbulence

Publisher: AIP Publishing

Date: 08-2012

DOI: 10.1063/1.4740058

Abstract: Large scale beam-driven electromagnetic strong turbulence is investigated by numerically solving the three-dimensional electromagnetic Zakharov equations, where turbulence is driven at nonzero wavenumbers k. For electron thermal speeds ve/c ≳ 0.1, a significant fraction of driven Langmuir waves undergo electromagnetic decay into electromagnetic waves and ion-acoustic waves so that transverse waves contribute significantly to the total energy density. It is shown that as ve/c increases, the wavenumber and energy density of transverse waves produced increase. For ve/c≲0.1, beam-driven turbulence is approximately electrostatic. An approximately periodic cycle is observed, similar to previous two-dimensional electrostatic simulations, in which Langmuir waves are driven to larger mean energy densities until a series of backscatters occurs, shifting the Langmuir waves out of resonance with the driver and decreasing the wavenumber of the Langmuir waves. A low-k condensate results from which wave packets form and collapse, decreasing the mean energy density. Averaging over many of these periods, the statistical properties are calculated and the scaling behavior of the mean energy density is shown to agree well with the electrostatic two-component model prediction. When driven at nonzero k the scaling behavior is shown to depend weakly on ve/c, in contrast to when strong turbulence is driven at k = 0, where the scalings depend more strongly on ve/c.

Sleep Propensity under Forced Desynchrony in a Model of Arousal State Dynamics

Publisher: SAGE Publications

Date: 18-07-2016

DOI: 10.1177/0748730416658806

Abstract: An improvement to our current quantitative model of arousal state dynamics is presented that more accurately predicts sleep propensity as measured with sleep dynamics depending on circadian phase and prior wakefulness. A nonlinear relationship between the circadian variables within the dynamic circadian oscillator model is introduced to account for the skewed shape of the circadian rhythm of alertness that peaks just prior to the onset of the biological night (the “wake maintenance zone”) and has a minimum toward the end of the biological night. The revised circadian drive thus provides a strong inhibitory input to the sleep-active neuronal population in the evening, counteracting the excitatory effects of the increased homeostatic sleep drive as originally proposed in the opponent process model of sleep-wake regulation. The revised model successfully predicts the sleep propensity profile as reflected in the dynamics of the total sleep time, sleep onset latency, wake/sleep ratio, and sleep efficiency during a wide range of experimental protocols. Specifically, all of these sleep measures are predicted for forced desynchrony schedules with day lengths ranging from 1.5 to 42.85 h and scheduled time in bed from 0.5 to 14.27 h. The revised model is expected to facilitate more accurate predictions of sleep under normal conditions as well as during circadian misalignment, for ex le, during shiftwork and jetlag.

Frequency Fine Structures of Type III Bursts Due to Localized Medium-Scale Density Structures Along Paths of Type III Beams

Publisher: Springer Science and Business Media LLC

Date: 11-05-2012

DOI: 10.1007/S11207-012-0001-1

Fundamental and harmonic radiation in type III solar radio bursts

Publisher: Springer Science and Business Media LLC

Date: 10-1994

DOI: 10.1007/BF00681103

Second harmonic electromagnetic emission via beam-driven Langmuir waves

Publisher: AIP Publishing

Date: 2005

DOI: 10.1063/1.1812274

Spatiotemporally varying visual hallucinations: I. Corticothalamic theory

Publisher: Elsevier BV

Date: 09-2014

DOI: 10.1016/J.JTBI.2014.05.025

Abstract: The thalamus is introduced to a recent model of the visual cortex to examine its effect on pattern formation in general and the generation of temporally oscillating patterns in particular. By successively adding more physiological details to a basic corticothalamic model, it is determined which features are responsible for which effects. In particular, with the addition of a thalamic population, several changes occur in the spatiotemporal power spectrum: power increases at resonances of the corticothalamic loop, while the loop acts as a spatiotemporal low-pass filter, and synaptic and dendritic dynamics temporally low-pass filter the activity more generally. Investigation of the effect of altering parameters and gains reveals new parameter regimes where activity that corresponds to hallucinations is induced by both spatially homogeneous and inhomogeneous temporally oscillating modes. This suggests that the thalamus and corticothalamic loops are essential components of a model of oscillating visual hallucinations.

Effects of spatial variations in coronal electron and ion temperatures on type III bursts. II. variations in ion temperature

Publisher: American Astronomical Society

Date: 24-02-2011

DOI: 10.1088/0004-637X/730/1/21

Dependence of absence seizure dynamics on physiological parameter evolution

Publisher: Elsevier BV

Date: 10-2018

DOI: 10.1016/J.JTBI.2018.05.029

Abstract: A neural field model of the corticothalamic system is applied to investigate the temporal and spectral characteristics of absence seizures in the presence of a temporally varying connection strength between the cerebral cortex and thalamus. Increasing connection strength drives the system into an absence seizure-like state once a threshold is passed and a supercritical Hopf bifurcation occurs. The dynamics and spectral characteristics of the resulting model seizures are explored as functions of maximum connection strength, time above threshold, and the rate at which the connection strength increases (r rate). Our results enable spectral and temporal characteristics of seizures to be related to changes in the underlying physiological evolution of connections via nonlinear dynamics and neural field theory. Spectral analysis reveals that the power of the harmonics and the duration of the oscillations increase as the maximum connection strength and the time above threshold increase. It is also found that the time to reach the stable limit-cycle seizure oscillation from the instability threshold decreases with the square root of the r rate.

Modeling 1 AU solar wind observations to estimate azimuthal magnetic fields at the solar source surface

Publisher: American Geophysical Union (AGU)

Date: 17-12-2011

DOI: 10.1029/2011GL049578

Laboratory evidence for stochastic plasma-wave growth

Publisher: American Physical Society (APS)

Date: 14-11-2007

DOI: 10.1103/PHYSREVLETT.99.205004

Quasilinear dynamics of a cloud of hot electrons propagating through a plasma in the presence of an externally applied uniform electric field

Publisher: AIP Publishing

Date: 12-2007

DOI: 10.1063/1.2819314

Abstract: The propagation of a cloud of hot electrons through a plasma and the generation of Langmuir waves are investigated in the presence of an externally applied uniform electric field. Using numerical simulations of the quasilinear equations the evolution of the electron distribution function and the spectral density of Langmuir waves are monitored in coordinate and velocity space. It is found that the Langmuir waves are enhanced in the presence of the electric field and the distribution functions of the beam and Langmuir waves diffuse toward large velocities. The overall self-similar characteristic of the system is preserved in the presence of the electric field. The average beam velocity is no longer constant and increases with time along its trajectory, but the acceleration is much less than that of free streaming particles. The beam number density plateaus in coordinate space and large scale, small litude fluctuations develop on the top of this plateau. The level of the fluctuations depends on the strength of the electric field. We also investigated the influence of the external electric field on the evolution of gas-dynamical parameters such as the height of the plateau in the beam distribution function in velocity space, its upper velocity boundary, and the local velocity spread of the beam. Due to the finite quasilinear relaxation time and spatial inhomogeneity of the electron beam, different parts of the beam are in different states of relaxation. In the region of partial relaxation the plateau is specified by both upper and lower velocity boundaries. The upper boundary of plateau increases linearly with the strength of the electric field but the lower boundary is independent of it. Contrary to the free streaming of a beam in an electric field or quasilinear relaxation in the absence of the electric field, the local velocity spread of the beam increases during its propagation. Some of the electrons at the back of the beam are also transferred by the electric field to its front, so that the height of plateau increases at large distances.

Automatic recognition of coronal type ii radio bursts: The automated radio burst identification system method and first observations

Publisher: American Astronomical Society

Date: 22-01-2010

DOI: 10.1088/2041-8205/710/1/L58

Langmuir snakes and electrostatic decay in the solar wind

Publisher: American Geophysical Union (AGU)

Date: 28-05-2013

DOI: 10.1002/GRL.50475

Wave-number spectrum of electroencephalographic signals

Publisher: American Physical Society (APS)

Date: 16-12-2002

DOI: 10.1103/PHYSREVE.66.061905

Wake-sleep transition as a noisy bifurcation

Publisher: American Physical Society (APS)

Date: 15-08-2016

DOI: 10.1103/PHYSREVE.94.022412

Spatiotemporal BOLD dynamics from a poroelastic hemodynamic model

Publisher: Elsevier BV

Date: 08-2010

DOI: 10.1016/J.JTBI.2010.05.026

Abstract: A quantitative theory is developed for the relationship between stimulus and the resulting blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) signal, including both spatial and temporal dynamics for the first time. The brain tissue is modeled as a porous elastic medium, whose interconnected pores represent the vasculature. The model explicitly incorporates conservation of blood mass, interconversion of oxygenated and deoxygenated hemoglobin, force balance within the blood and of blood pressure with vessel walls, and blood flow modulation due to neuronal activity. In appropriate limits it is shown to reproduce prior Balloon models of hemodynamic response, which do not include spatial variations. The regime of validity of such models is thereby clarified by elucidating their assumptions, and when these break down, for ex le when voxel sizes become small.

Biophysical Mechanisms of Multistability in Resting-State Cortical Rhythms

Publisher: Society for Neuroscience

Date: 27-04-2011

DOI: 10.1523/JNEUROSCI.6693-10.2011

Abstract: The human alpha (8–12 Hz) rhythm is one of the most prominent, robust, and widely studied attributes of ongoing cortical activity. Contrary to the prevalent notion that it simply “waxes and wanes,” spontaneous alpha activity bursts erratically between two distinct modes of activity. We now establish a mechanism for this multistable phenomenon in resting-state cortical recordings by characterizing the complex dynamics of a biophysical model of macroscopic corticothalamic activity. This is achieved by studying the predicted activity of cortical and thalamic neuronal populations in this model as a function of its dynamic stability and the role of nonspecific synaptic noise. We hence find that fluctuating noisy inputs into thalamic neurons elicit spontaneous bursts between low- and high- litude alpha oscillations when the system is near a particular type of dynamical instability, namely a subcritical Hopf bifurcation. When the postsynaptic potentials associated with these noisy inputs are modulated by cortical feedback, the SD of power within each of these modes scale in proportion to their mean, showing remarkable concordance with empirical data. Our state-dependent corticothalamic model hence exhibits multistability and scale-invariant fluctuations—key features of resting-state cortical activity and indeed, of human perception, cognition, and behavior—thus providing a unified account of these apparently ergent phenomena.

NEUROPHYSIOLOGICALLY-BASED MEAN-FIELD MODELLING OF TONIC CORTICAL ACTIVITY IN POST-TRAUMATIC STRESS DISORDER (PTSD), SCHIZOPHRENIA, FIRST EPISODE SCHIZOPHRENIA AND ATTENTION DEFICIT HYPERACTIVITY DISO

Publisher: World Scientific Pub Co Pte Lt

Date: 12-2004

DOI: 10.1142/S0219635204000592

Abstract: A recently developed quantitative model of cortical activity is used that permits data comparison with experiment using a quantitative and standardized means. The model incorporates properties of neurophysiology including axonal transmission delays, synaptodendritic rates, range-dependent connectivities, excitatory and inhibitory neural populations, and intrathalamic, intracortical, corticocortical and corticothalamic pathways. This study tests the ability of the model to determine unique physiological properties in a number of different data sets varying in mean age and pathology. The model is used to fit in idual electroencephalographic (EEG) spectra from post-traumatic stress disorder (PTSD), schizophrenia, first episode schizophrenia (FESz), attention deficit hyperactivity disorder (ADHD), and their age/sex matched controls. The results demonstrate that the model is able to distinguish each group in terms of a unique cluster of abnormal parameter deviations. The abnormal physiology inferred from these parameters is also consistent with known theoretical and experimental findings from each disorder. The model is also found to be sensitive to the effects of medication in the schizophrenia and FESz group, further supporting the validity of the model.

A Unifying Explanation of Primary Generalized Seizures Through Nonlinear Brain Modeling and Bifurcation Analysis

Publisher: Oxford University Press (OUP)

Date: 09-11-2005

DOI: 10.1093/CERCOR/BHJ072

Abstract: The aim of this paper is to explain critical features of the human primary generalized epilepsies by investigating the dynamical bifurcations of a nonlinear model of the brain's mean field dynamics. The model treats the cortex as a medium for the propagation of waves of electrical activity, incorporating key physiological processes such as propagation delays, membrane physiology, and corticothalamic feedback. Previous analyses have demonstrated its descriptive validity in a wide range of healthy states and yielded specific predictions with regards to seizure phenomena. We show that mapping the structure of the nonlinear bifurcation set predicts a number of crucial dynamic processes, including the onset of periodic and chaotic dynamics as well as multistability. Quantitative study of electrophysiological data supports the validity of these predictions. Hence, we argue that the core electrophysiological and cognitive differences between tonic-clonic and absence seizures are predicted and interrelated by the global bifurcation diagram of the model's dynamics. The present study is the first to present a unifying explanation of these generalized seizures using the bifurcation analysis of a dynamical model of the brain.

Exact evaluation of the quadratic longitudinal response function for an unmagnetized Maxwellian plasma

Publisher: AIP Publishing

Date: 07-2012

DOI: 10.1063/1.4737603

Biophysically based method to deconvolve spatiotemporal neurovascular signals from fMRI data

Publisher: Elsevier BV

Date: 10-2018

DOI: 10.1016/J.JNEUMETH.2018.07.009

Abstract: Functional magnetic resonance imaging (fMRI) is commonly used to infer hemodynamic changes in the brain after increased neural activity, measuring the blood oxygen level-dependent (BOLD) signal. An important challenge in the analyses of fMRI data is to develop methods that can accurately deconvolve the BOLD signal to extract the driving neural activity and the underlying cerebrovascular effects. A biophysically based method is developed, which combines an extensively verified physiological hemodynamic model with a Wiener filter, to deconvolve the BOLD signal. The method is able to simultaneously obtain spatiotemporal images of underlying neurovascular signals, including neural activity, cerebral blood flow, cerebral blood volume, and deoxygenated hemoglobin concentration. The method is tested on simulated data and applied to various experimental data to demonstrate its stability, accuracy, and utility. The resulting profiles of the deconvolved signals are consistent with measurements reported in the literature, obtained via multiple neuroimaging modalities. The method provides new testable predictions of the spatiotemporal relations of the deconvolved signals for future studies. This demonstrates the ability of the method to quantify and analyze the neurovascular mechanisms that underlie fMRI, thereby expanding its potential uses.

Prediction and verification of nonlinear sleep spindle harmonic oscillations

Publisher: Elsevier BV

Date: 03-2014

DOI: 10.1016/J.JTBI.2013.11.013

Abstract: This paper examines nonlinear effects in a neural field model of the corticothalamic system to predict the EEG power spectrum of sleep spindles. Nonlinearity in the thalamic relay nuclei gives rise to a spindle harmonic visible in the cortical EEG. By deriving an analytic expression for nonlinear spectrum, the power in the spindle harmonic is predicted to scale quadratically with the power in the spindle oscillation. By isolating sleep spindles from background sleep in experimental EEG data, the spindle harmonic is directly observed.

S/WAVES: The Radio and Plasma Wave Investigation on the STEREO Mission

Publisher: Springer Science and Business Media LLC

Date: 07-02-2008

DOI: 10.1007/S11214-007-9298-8

Spatiotemporal correlation functions in beam-driven plasmas with fluctuations

Publisher: AIP Publishing

Date: 12-2007

DOI: 10.1063/1.2819678

Abstract: Using a reduced-parameter model of wave-particle interactions in a beam-driven plasma, the linear spatiotemporal correlation functions of wave and particle quantities are derived. These are found to have an oscillatory structure with characteristic spatial and temporal scales reflecting the dynamics of energy exchange between particles and waves. The effects of various system parameters on these characteristic scales and the correlation functions are investigated. The correlation scales are shown to erge in some limiting cases, implying the possibility of criticality in the system. A comparison with fully nonlinear numerical simulations is carried out, and the criterion for validity of the linear correlation functions is derived and verified. The nonlinear simulation results are shown to converge to the linear prediction in appropriate limits dictated by this criterion. The correlation functions obtained provide a useful tool for studying dynamical properties of beam-driven plasma-wave systems with fluctuating parameters.

Quantitative theory of deep brain stimulation of the subthalamic nucleus for the suppression of pathological rhythms in Parkinson’s disease

Publisher: Public Library of Science (PLoS)

Date: 29-05-2018

DOI: 10.1371/JOURNAL.PCBI.1006217

Real-time automated EEG tracking of brain states using neural field theory

Publisher: Elsevier BV

Date: 2016

DOI: 10.1016/J.JNEUMETH.2015.09.026

Abstract: A real-time fitting system is developed and used to fit the predictions of an established physiologically-based neural field model to electroencephalographic spectra, yielding a trajectory in a physiological parameter space that parametrizes intracortical, intrathalamic, and corticothalamic feedbacks as the arousal state evolves continuously over time. This avoids traditional sleep/wake staging (e.g., using Rechtschaffen-Kales stages), which is fundamentally limited because it forces classification of continuous dynamics into a few discrete categories that are neither physiologically informative nor in idualized. The classification is also subject to substantial interobserver disagreement because traditional staging relies in part on subjective evaluations. The fitting routine objectively and robustly tracks arousal parameters over the course of a full night of sleep, and runs in real-time on a desktop computer. The system developed here supersedes discrete staging systems by representing arousal states in terms of physiology, and provides an objective measure of arousal state which solves the problem of interobserver disagreement. Discrete stages from traditional schemes can be expressed in terms of model parameters for backward compatibility with prior studies.

Age trends and sex differences of alpha rhythms including split alpha peaks

Publisher: Elsevier BV

Date: 08-2011

DOI: 10.1016/J.CLINPH.2011.01.040

Abstract: To investigate age trends, sex differences, and splitting of alpha peaks of the EEG spectrum in the healthy population. An automated multi-site algorithm was used to parametrize the alpha rhythm in 1498 healthy subjects aged 6-86 years. Alpha peaks identified from multiple electrode sites were organized into clusters of similar frequencies whose sex differences and age trends were investigated. Significant age-related trends were observed for frequency, position, and litude of dominant alpha peaks. Occipital sites had alpha clusters of higher average frequency, higher power, and greater presence across the scalp. Frequency and power differences were found between the sexes. Observed increases in alpha frequency in children and decreases in the elderly were consistent with those from earlier studies. A large fraction of participants (≈ 44%) showed multiple distinct alpha rhythm thus investigations which only examine the alpha frequency with the highest peak power can produce misleading results. The strong dependence of alpha frequency on age and anterior-posterior position indicates use of a fixed alpha frequency band is insufficient to capture the full characteristics of the alpha rhythm. This study establishes alpha rhythm parameter ranges (including power and frequency) in the healthy population, and quantifies the variation in alpha frequency across the scalp. The automated characterization enables objective evaluations of alpha band activities over large s les. These findings are potentially useful in testing theories of alpha generation, where splitting of the alpha rhythm has been theoretically predicted to occur in in iduals with large differences in axon length between anterior and posterior corticothalamic loops.

A unified model of melatonin, 6‐sulfatoxymelatonin, and sleep dynamics

Publisher: Wiley

Date: 08-03-2018

DOI: 10.1111/JPI.12474

Abstract: A biophysical model of the key aspects of melatonin synthesis and excretion has been developed, which is able to predict experimental dynamics of melatonin in plasma and saliva, and of its urinary metabolite 6-sulfatoxymelatonin (aMT6s). This new model is coupled to an established model of arousal dynamics, which predicts sleep and circadian dynamics based on light exposure and times of wakefulness. The combined model thus predicts melatonin levels over the sleep-wake/dark-light cycle and enables prediction of melatonin-based circadian phase markers, such as dim light melatonin onset (DLMO) and aMT6s acrophase under conditions of normal sleep and circadian misalignment. The model is calibrated and tested against group average data from 10 published experimental studies and is found to reproduce quantitatively the key dynamics of melatonin and aMT6s, including the timing of release and litude, as well as response to controlled lighting and shift work.

Arousal state feedback as a potential physiological generator of the ultradian REM/NREM sleep cycle

Publisher: Elsevier BV

Date: 02-2013

DOI: 10.1016/J.JTBI.2012.11.029

Modeling distributed axonal delays in mean-field brain dynamics

Publisher: American Physical Society (APS)

Date: 03-11-2008

DOI: 10.1103/PHYSREVE.78.051901

Dynamics of beam-driven Langmuir and ion-acoustic waves including electrostatic decay

Publisher: AIP Publishing

Date: 18-06-2003

DOI: 10.1063/1.1574515

Abstract: The evolution of Langmuir waves and ion-acoustic waves stimulated by a hot electron beam in an initially homogeneous plasma is investigated numerically in time, position, and wave number space. Quasilinear interactions between the beam particles and Langmuir waves, nonlinear interactions between the Langmuir and ion-acoustic waves through Langmuir decay processes, and spontaneous emission are taken into account in the kinetic theory employed. For illustrative parameters of those in the solar wind near 1 a.u., nonlinear Langmuir decays are observed to transfer the beam-driven Langmuir waves rapidly out of resonance. The scattered Langmuir waves then undergo further decays, moving sequentially toward small wave numbers, until decay is kinematically prohibited. The main features of the evolution of Langmuir and ion-acoustic waves are spatially inhomogeneous. The scattered Langmuir spectra increase and eventually reach or exceed the beam-driven Langmuir spectra at a given spatial location (except in regions where further decays proceed). The ion-acoustic waves are relatively weak and subject to d ing at the later stages of their evolution. The development of fine structures in the product Langmuir and ion-acoustic waves are observed, due to depletion of their energy by decay and dominant d ing effects, respectively. The propagation of the beam is essentially unaffected by the operation of the decay process. The decay process is thus slaved to the primary beam–plasma evolution, as assumed in previous studies. A variation of the ratio of electron temperature to ion temperature is found to affect not only the ion-acoustic wave levels through effects on the d ing rate, but also the dynamics of decay via effects on the decay rate. The latter was not addressed in previous studies. Furthermore, spontaneous emission of ion-acoustic waves is found to affect the dynamics of decay, thus its inclusion is necessary to correctly model the Langmuir and ion-acoustic spectra.

Type II radio emission predictions: Multiple shock ripples and dynamic spectra

Publisher: American Geophysical Union (AGU)

Date: 10-2003

DOI: 10.1029/2003JA009960

Calculation of electromagnetic properties of regular and random arrays of metallic and dielectric cylinders

Publisher: American Physical Society (APS)

Date: 12-1999

DOI: 10.1103/PHYSREVE.60.7614

Abstract: A method is developed to calculate electromagnetic properties of arrays of metallic and dielectric cylinders. It incorporates and exploits cylindrical boundary conditions and Rayleigh identities for efficient, high-accuracy calculation of scattering off in idual layers that are stacked into arrays using scattering matrices. The method enables absorption, dispersion, and randomness to be incorporated efficiently, and reproduces known results with vastly improved speed and accuracy. It is used to demonstrate existence of states introduced into photonic band gaps of a dielectric array by disorder, and anomalous absorption behavior in arrays of aluminum cylinders.

Diffusion and anomalous diffusion of light in two-dimensional photonic crystals

Publisher: American Physical Society (APS)

Date: 14-03-2003

DOI: 10.1103/PHYSREVE.67.036605

Three-dimensional electromagnetic strong turbulence. II. Wave packet collapse and structure of wave packets during strong turbulence

Publisher: AIP Publishing

Date: 07-2011

DOI: 10.1063/1.3603969

Abstract: Large-scale simulations of wave packet collapse are performed by numerically solving the three-dimensional (3D) electromagnetic Zakharov equations, focusing on in idual wave packet collapses and on wave packets that form in continuously driven strong turbulence. The collapse threshold is shown to decrease as the electron thermal speed νe/c increases and as the temperature ratio Ti/Te of ions to electrons decreases. Energy lost during wave packet collapse and dissipation is shown to depend on νe/c. The dynamics of density perturbations after collapse are studied in 3D electromagnetic strong turbulence for a range of Ti/Te. The structures of the Langmuir, transverse, and total electric field components of wave packets during strong turbulence are investigated over a range of νe/c. For νe/c≲0.17, strong turbulence is approximately electrostatic and wave packets have very similar structure to purely electrostatic wave packets. For νe/c≳0.17, transverse modes become trapped in density wells and contribute significantly to the structure of the total electric field. At all νe/c, the Langmuir energy density contours of wave packets are predominantly oblate (pancake shaped). The transverse energy density contours of wave packets are predominantly prolate (sausage shaped), with the major axis being perpendicular to the major axes of the Langmuir component. This results in the wave packet becoming more nearly spherical as νe/c increases, and in turn generates more spherical density wells during collapse. The results obtained are compared with previous 3D electrostatic results and 2D electromagnetic results.

Exploring sleepiness and entrainment on permanent shift schedules in a physiologically based model

Publisher: SAGE Publications

Date: 02-2012

DOI: 10.1177/0748730411419934

Abstract: The effects of permanent shift work on entrainment and sleepiness are examined using a mathematical model that combines a model of sleep-wake switch in the brain with a model of the human circadian pacemaker entrained by light and nonphotic inputs. The model is applied to 8-hour permanent shift schedules to understand the basic mechanisms underlying changes of entrainment and sleepiness. Average sleepiness is shown to increase during the first days on the night and evening schedules, that is, shift start times between 0000 to 0700 h and 1500 to 2200 h, respectively. After the initial increase, sleepiness decreases and stabilizes via circadian re-entrainment to the cues provided by the shifts. The increase in sleepiness until entrainment is achieved is strongly correlated with the phase difference between a circadian oscillator entrained to the ambient light and one entrained to the shift schedule. The higher this phase difference, the larger the initial increase in sleepiness. When entrainment is achieved, sleepiness stabilizes and is the same for different shift onsets within the night or evening schedules. The simulations reveal the presence of a critical shift onset around 2300 h that separates schedules, leading to phase advance (night shifts) and phase delay (evening shifts) of the circadian pacemaker. Shifts starting around this time take longest to entrain and are expected to be the worst for long-term sleepiness and well-being of the workers. Surprisingly, we have found that the circadian pacemaker entrains faster to night schedules than to evening ones. This is explained by the longer photoperiod on night schedules compared to evening. In practice, this phenomenon is difficult to see due to days off on which workers switch to free sleep-wake activity. With weekends, the model predicts that entrainment is never achieved on evening and night schedules unless the workers follow the same sleep routine during weekends as during work days. Overall, the model supports experimental observations, providing new insights into the mechanisms and allowing the examination of conditions that are not accessible experimentally.

Experimental observation of a theoretically predicted nonlinear sleep spindle harmonic in human EEG

Publisher: Elsevier BV

Date: 10-2014

DOI: 10.1016/J.CLINPH.2014.01.025

Abstract: To investigate the properties of a sleep spindle harmonic oscillation previously predicted by a theoretical neural field model of the brain. Spindle oscillations were extracted from EEG data from nine subjects using an automated algorithm. The power and frequency of the spindle oscillation and the harmonic oscillation were compared across subjects. The bicoherence of the EEG was calculated to identify nonlinear coupling. All subjects displayed a spindle harmonic at almost exactly twice the frequency of the spindle. The power of the harmonic scaled nonlinearly with that of the spindle peak, consistent with model predictions. Bicoherence was observed at the spindle frequency, confirming the nonlinear origin of the harmonic oscillation. The properties of the sleep spindle harmonic were consistent with the theoretical modeling of the sleep spindle harmonic as a nonlinear phenomenon. Most models of sleep spindle generation are unable to produce a spindle harmonic oscillation, so the observation and theoretical explanation of the harmonic is a significant step in understanding the mechanisms of sleep spindle generation. Unlike seizures, sleep spindles produce nonlinear effects that can be observed in healthy controls, and unlike the alpha oscillation, there is no linearly generated harmonic that can obscure nonlinear effects. This makes the spindle harmonic a good candidate for future investigation of nonlinearity in the brain.

Suppression of Parkinsonian Beta Oscillations by Deep Brain Stimulation: Determination of Effective Protocols

Publisher: Frontiers Media SA

Date: 11-12-2018

DOI: 10.3389/FNCOM.2018.00098

Mammalian Rest/Activity Patterns Explained by Physiologically Based Modeling

Publisher: Public Library of Science (PLoS)

Date: 05-09-2013

DOI: 10.1371/JOURNAL.PCBI.1003213

Critical dynamics of Hopf bifurcations in the corticothalamic system: Transitions from normal arousal states to epileptic seizures

Publisher: American Physical Society (APS)

Date: 25-04-2017

DOI: 10.1103/PHYSREVE.95.042410

Neural mechanisms of the EEG alpha-BOLD anticorrelation

Publisher: Elsevier BV

Date: 11-2018

DOI: 10.1016/J.NEUROIMAGE.2018.07.031

Abstract: An experimentally tested neural field theory of the corticothalamic system is used to model brain activity and resulting experimental EEG data, and to elucidate the neural mechanisms and physiological basis of alpha-BOLD anticorrelation observed in concurrent EEG and fMRI measurements. Several studies have proposed that the anticorrelation originates from a causal link between changes in the alpha power and BOLD signal. However, the results in this study reveal that fluctuations in alpha and BOLD power do not generate one another but instead respectively result from high- and low-frequency components of the same underlying cortical activity, and that they are inversely correlated via variations in the strengths of corticothalamic and intrathalamic feedback, thereby explaining their anticorrelation.

Modal analysis of corticothalamic dynamics, electroencephalographic spectra, and evoked potentials

Publisher: American Physical Society (APS)

Date: 29-03-2001

DOI: 10.1103/PHYSREVE.63.041909

Self-organized Criticality in Termite Architecture: a Role for Crowding in Ensuring Ordered Nest Expansion

Publisher: Elsevier BV

Date: 06-1999

DOI: 10.1006/JTBI.1999.0917

Simulations of coronal type III solar radio bursts: 3. Effects of beam and coronal parameters

Publisher: American Geophysical Union (AGU)

Date: 02-2009

DOI: 10.1029/2008JA013687

Constraints on nonlinear and stochastic growth theories for type III solar radio bursts from the corona to 1 AU

Publisher: American Astronomical Society

Date: 10-12-1998

DOI: 10.1086/306486

Adaptation to Shift Work: Physiologically Based Modeling of the Effects of Lighting and Shifts' Start Time

Publisher: Public Library of Science (PLoS)

Date: 04-01-2013

DOI: 10.1371/JOURNAL.PONE.0053379

Mode coupling due to twisting of magnetic field lines

Publisher: Springer Science and Business Media LLC

Date: 04-1995

DOI: 10.1007/BF00680839

A new EEG biomarker of neurobehavioural impairment and sleepiness in sleep apnea patients and controls during extended wakefulness

Publisher: Elsevier BV

Date: 08-2013

DOI: 10.1016/J.CLINPH.2013.02.022

Abstract: To explore the use of detrended fluctuation analysis (DFA) scaling exponent of the awake electroencephalogram (EEG) as a new alternative biomarker of neurobehavioural impairment and sleepiness in obstructive sleep apnea (OSA). Eight patients with moderate-severe OSA and nine non-OSA controls underwent a 40-h extended wakefulness challenge with resting awake EEG, neurobehavioural performance (driving simulator and psychomotor vigilance task) and subjective sleepiness recorded every 2-h. The DFA scaling exponent and power spectra of the EEG were calculated at each time point and their correlation with sleepiness and performance were quantified. DFA scaling exponent and power spectra biomarkers significantly correlated with simultaneously tested performance and self-rated sleepiness across the testing period in OSA patients and controls. Baseline (8am) DFA scaling exponent but not power spectra were markers of impaired simulated driving after 24-h extended wakefulness in OSA (r=0.738, p=0.037). OSA patients had a higher scaling exponent and delta power during wakefulness than controls. The DFA scaling exponent of the awake EEG performed as well as conventional power spectra as a marker of impaired performance and sleepiness resulting from sleep loss. DFA may potentially identify patients at risk of neurobehavioural impairment and assess treatment effectiveness.

Modes and their transitions in microstructured optical fibres

Publisher: IEEE

Date: 2003

DOI: 10.1109/LEOSST.2003.1224275

Microstructured optical fiber phase diagrams and operating regimes: toward deterministic MOF design

Publisher: SPIE

Date: 09-07-2004

DOI: 10.1117/12.520867

strong Langmuir turbulence at Jupiter?

Publisher: American Geophysical Union (AGU)

Date: 02-06-1992

DOI: 10.1029/92GL01171

Automatic recognition of type III solar radio bursts: Automated radio burst identification system method and first observations

Publisher: American Geophysical Union (AGU)

Date: 04-2009

DOI: 10.1029/2008SW000425

Maximum Langmuir fields in planetary foreshocks determined from the electrostatic decay threshold

Publisher: American Geophysical Union (AGU)

Date: 10-1995

DOI: 10.1029/95GL01779

Electromagnetic localization in one-dimensional stacks with random loss and gain

Publisher: American Physical Society (APS)

Date: 08-1996

DOI: 10.1103/PHYSREVB.54.3916

Thermal and driven stochastic growth of Langmuir waves in the solar wind and earth's foreshock

Publisher: American Geophysical Union (AGU)

Date: 2000

DOI: 10.1029/1999GL010717

Self-organized Criticality in Ant Brood Tending

Publisher: Elsevier BV

Date: 03-2003

DOI: 10.1006/JTBI.2003.3046

Abstract: A new stochastic lattice gas model of ant brood tending is formulated to examine the role played by repulsive ant-ant interactions in the even distribution of care among brood members. The deterministic limit of the model is known to be self-organized critical. Numerical simulations of the model show that the ant-ant repulsion facilitates an even distribution of brood care in the middle of the brood. This provides a possible explanation for the fact that ants sort their brood so that the youngest brood (which are most in need of care) are placed in the middle. Simulations show that the uniformity of brood care distribution is optimal when ants operate in a regime intermediate between completely random and completely deterministic. A certain degree of randomness helps ants to avoid becoming trapped in suboptimal configurations but does not destroy the long-range correlations that are inherent to self-organized critical systems.

Theory for 2-3 kHz radiation from the outer heliosphere

Publisher: American Geophysical Union (AGU)

Date: 06-2004

DOI: 10.1029/2003JA010117

Self-Organized Criticality and Emergent Oscillations in Models of Termite Architecture with Crowding

Publisher: Elsevier BV

Date: 03-2003

DOI: 10.1006/JTBI.2003.3047

Abstract: The termite architecture model of O'Toole et'al. (1999) is extended to incorporate arbitrary halting time-scales. It is shown that this also means that the assumption of synchronous building must be relaxed. Numerical simulations show that ordered nest architecture emerges under a wide range of time-scales but also that there is an optimal region of halting times. This optimal region is explained by the emergence of synchronized periods of termite activity. The correlation length of the building distribution is shown to erge providing strong evidence that the model is self-organized critical.

Nonuniform corticothalamic continuum model of electroencephalographic spectra with application to split-alpha peaks

Publisher: American Physical Society (APS)

Date: 28-08-2003

DOI: 10.1103/PHYSREVE.68.021922

Modeling absence seizure dynamics: Implications for basic mechanisms and measurement of thalamocortical and corticothalamic latencies

Publisher: Elsevier BV

Date: 07-2008

DOI: 10.1016/J.JTBI.2008.03.005

Abstract: A successful physiologically based continuum model of the corticothalamic system is applied to determine the relative contributions of axonal and intrinsic cellular delays to the waveforms of absence seizures. The predicted period of the absence seizure depends linearly on model parameters describing thalamocortical, corticothalamic, intracortical, and synaptodendritic delays, and these dependences are linked to the seizure mechanism by showing how time intervals between peaks in the waveforms depend on the parameters. Counterintuitively, it is found that a peak in the local field potential recorded in the thalamic relay nuclei can precede the peak in the cortical field that drove it, without violating causality, but rendering naive interpretation of time intervals between peaks invalid. We argue that a thalamocortical loop mechanism for absence seizures is consistent with intrathalamic cellular properties being the leading determinant of the frequency of spike-wave discharges in rat genetic models, with the combination of network and cellular properties providing a natural explanation for the lower frequency of human absence seizures. Finally, our results imply that the seizure frequency is not determined by the fastest thalamocortical and corticothalamic fibers, but rather depends on an effective weighted conduction velocity of all pathways present.

A Quantitative Model of Sleep-Wake Dynamics Based on the Physiology of the Brainstem Ascending Arousal System

Publisher: SAGE Publications

Date: 04-2007

DOI: 10.1177/0748730406297512

Abstract: A quantitative, physiology-based model of the ascending arousal system is developed, using continuum neuronal population modeling, which involves averaging properties such as firing rates across neurons in each population. The model includes the ventrolateral preoptic area (VLPO), where circadian and homeostatic drives enter the system, the monoaminergic and cholinergic nuclei of the ascending arousal system, and their interconnections. The human sleep-wake cycle is governed by the activities of these nuclei, which modulate the behavioral state of the brain via diffuse neuromodulatory projections. The model parameters are not free since they correspond to physiological observables. Approximate parameter bounds are obtained by requiring consistency with physiological and behavioral measures, and the model replicates the human sleep-wake cycle, with physiologically reasonable voltages and firing rates. Mutual inhibition between the wake-promoting monoaminergic group and sleep-promoting VLPO causes ``flip-flop'' behavior, with most time spent in 2 stable steady states corresponding to wake and sleep, with transitions between them on a timescale of a few minutes. The model predicts hysteresis in the sleep-wake cycle, with a region of bistability of the wake and sleep states. Reducing the monoaminergic-VLPO mutual inhibition results in a smaller hysteresis loop. This makes the model more prone to wake-sleep transitions in both directions and makes the states less distinguishable, as in narcolepsy. The model behavior is robust across the constrained parameter ranges, but with sufficient flexibility to describe a wide range of observed phenomena.

Propagation of a cloud of hot electrons in the regime of fast relaxation

Publisher: AIP Publishing

Date: 04-2005

DOI: 10.1063/1.1884616

Field distributions and shapes of Langmuir wave packets observed by Ulysses in an interplanetary type III burst source region

Publisher: American Geophysical Union (AGU)

Date: 05-2007

DOI: 10.1029/2006JA011873

Human Cortical Traveling Waves: Dynamical Properties and Correlations with Responses

Publisher: Public Library of Science (PLoS)

Date: 04-06-2012

DOI: 10.1371/JOURNAL.PONE.0038392

Structure of Langmuir and electromagnetic collapsing wave packets in two-dimensional strong plasma turbulence

Publisher: AIP Publishing

Date: 07-2007

DOI: 10.1063/1.2749495

Abstract: Nucleating and collapsing wave packets relevant to electromagnetic strong plasma turbulence are studied theoretically in two dimensions. Model collapsing Langmuir and transverse potentials are constructed as superpositions of approximate eigenstates of a spherically symmetric density well. Electrostatic and electromagnetic potentials containing only components with azimuthal quantum numbers m=0, 1, 2 are found to give a good representation of the electric fields of nucleating collapsing wave packets in turbulence simulations. The length scales of these trapped states are related to the electron thermal speed ve and the length scale of the density well. It is shown analytically that the electromagnetic trapped states change with ve and that for ve≲0.17c they are delocalized, in accord with recent simulations. In this case, the Langmuir mode collapses independently, as in electrostatic plasma turbulence. For ve≳0.17c, the Langmuir and transverse modes remain coupled during collapse, with autocorrelation lengths in a constant ratio. An investigation of energy transfer to packets localized in density wells shows that the strongest power transfer to the nucleating state occurs for Langmuir waves. Energy transitions between different trapped and free states for collapsing wave packets are studied, and the transition rate from trapped Langmuir to free plane electromagnetic waves is calculated and related to the emission of electromagnetic waves at the plasma frequency.

Sleep deprivation in a quantitative physiologically based model of the ascending arousal system

Publisher: Elsevier BV

Date: 12-2008

DOI: 10.1016/J.JTBI.2008.08.022

Abstract: A physiologically based quantitative model of the human ascending arousal system is used to study sleep deprivation after being calibrated on a small set of experimentally based criteria. The model includes the sleep-wake switch of mutual inhibition between nuclei which use monoaminergic neuromodulators, and the ventrolateral preoptic area. The system is driven by the circadian rhythm and sleep homeostasis. We use a small number of experimentally derived criteria to calibrate the model for sleep deprivation, then investigate model predictions for other experiments, demonstrating the scope of application. Calibration gives an improved parameter set, in which the form of the homeostatic drive is better constrained, and its weighting relative to the circadian drive is increased. Within the newly constrained parameter ranges, the model predicts repayment of sleep debt consistent with experiment in both quantity and distribution, asymptoting to a maximum repayment for very long deprivations. Recovery is found to depend on circadian phase, and the model predicts that it is most efficient to recover during normal sleeping phases of the circadian cycle, in terms of the amount of recovery sleep required. The form of the homeostatic drive suggests that periods of wake during recovery from sleep deprivation are phases of relative recovery, in the sense that the homeostatic drive continues to converge toward baseline levels. This undermines the concept of sleep debt, and is in agreement with experimentally restricted recovery protocols. Finally, we compare our model to the two-process model, and demonstrate the power of physiologically based modeling by correctly predicting sleep latency times following deprivation from experimental data.

Statistics of polarization and Stokes parameters: Multiple orthonormal wave populations

Publisher: AIP Publishing

Date: 2006

DOI: 10.1063/1.2154684

Abstract: A stochastic analysis is developed for the superposition of multiple, fully polarized, electric-field vectors. Each vector is described by a polarization ellipse, with fixed axial ratio and polarization angle, and probability distribution functions (pdfs) for the field strength and phase. These wave populations are then superposed in orthonormal modes of polarization, representing the normal modes of a medium. Central results of this work include analytic and Monte Carlo methods to calculate the pdfs of the measurable Stokes parameters I, U, Q, and V, and degrees of polarization, of the superposed waves. Predictions are computed for the superposition of some characteristic wave populations, and several striking and counterintuitive results produced. These include nonzero probabilities for U, Q, and V at U=0, Q=0, and V=0, irrespective of the constituent wave polarizations and field distributions. For wave populations with identical polarization ellipses, a power-law enhancement of the pdf of the intensity I at low I is found, which is independent of the constituent electric-field distributions. Generation of elliptically polarized light from components which each have an opposite sense of polarization is shown to be possible. A description of the asymptotic limits of the pdfs of the Stokes parameters is obtained, and the appearance of fine structure in the pdfs of the degrees of polarization is demonstrated. Together, these results demonstrate the necessity of systematic analysis when predicting pdfs for the Stokes parameters and degrees of polarization: qualitative results cannot be correctly inferred from intuition alone.

Multiple electron beam propagation and Langmuir wave generation in plasmas

Publisher: AIP Publishing

Date: 19-06-2002

DOI: 10.1063/1.1485973

Abstract: The propagation of multiple electron beams in a plasma and the generation of Langmuir waves via a streaming instability is investigated numerically using quasilinear theory. The generation of waves by two equal copropagating beams injected at different times is studied in detail. The two beams are observed merging into one far from the injection points. Meanwhile, waves are enhanced in the vicinity of the mean beam speed of the leading beam, and are suppressed in a localized region after the injection of the trailing beam. Effects of beam injection parameters on the generation of the waves are studied. In particular, for the injection of two beams, the temperature, initial number density, and location of the injected particles are found to be relevant to fine structures in wave levels. It is also observed that the mechanism of beam merging is via interactions between beam particles and associated waves, i.e., fast particles in a trailing beam lose energy to waves generated initially by the leading beam, while slow particles in the leading beam absorb energy from waves driven by the trailing beam, which eventually leads to the elimination of systematic speed differences between the two beams. This mechanism of energy exchange generalizes the version studied in previous works, in which fast particles in a single beam lose energy that is later reabsorbed by slower particles. The characteristics of wave generation for multiple beam injections are found to be similar to the basic case of two beams. Finally, the applicability of this work to type III solar radio storms and shock associated type III-like bursts is commented upon.

Spatiotemporal dynamics of pattern formation in the primary visual cortex and hallucinations

Publisher: Springer Science and Business Media LLC

Date: 06-06-2009

DOI: 10.1007/S00422-009-0315-8

Abstract: The existence of visual hallucinations with prominent temporal oscillations is well documented in conditions such as Charles Bonnett Syndrome. To explore these phenomena, a continuum model of cortical activity that includes additional physiological features of axonal propagation and synapto-dendritic time constants, is used to study the generation of hallucinations featuring both temporal and spatial oscillations. A detailed comparison of the physiological features of this model with those of two others used previously in the modeling of hallucinations is made, and differences, particularly regarding temporal dynamics, relevant to pattern formation are analyzed. Linear analysis and numerical calculation are then employed to examine the pattern forming behavior of this new model for two different forms of spatiotemporal coupling between neurons. Numerical calculations reveal an oscillating mode whose frequency depends on synaptic, dendritic, and axonal time constants not previously simultaneously included in such analyses. Its properties are qualitatively consistent with descriptions of a number of physiological disorders and conditions with temporal dynamics, but the analysis implies that corticothalamic effects will need to be incorporated to treat the consequences quantitatively.

Statistics of beam-driven waves in plasmas with ambient fluctuations: Reduced-parameter approach

Publisher: AIP Publishing

Date: 09-2008

DOI: 10.1063/1.2977979

Abstract: A reduced-parameter (RP) model of quasilinear wave-plasma interactions is used to analyze statistical properties of beam-driven waves in plasmas with ambient density fluctuations. The probability distribution of wave energies in such a system is shown to have a relatively narrow peak just above the thermal wave level, and a power-law tail at high energies, the latter becoming progressively more evident for increasing characteristic litude of the ambient fluctuations. To better understand the physics behind these statistical features of the waves, a simplified model of stochastically driven thermal waves is developed on the basis of the RP model. An approximate analytic solution for stationary statistical distribution of wave energies W is constructed, showing a good agreement with that of the original RP model. The “peak” and “tail” features of the wave energy distribution are shown to be a result of contributions of two groups of wave clumps: those subject to either very slow or very fast random variations of total wave growth rate (due to fluctuations of ambient plasma density), respectively. In the case of significant ambient plasma fluctuations, the overall wave energy distribution is shown to have a clear power-law tail at high energies, P(W)∝W−α, with nontrivial exponent 1& α& , while for weak fluctuations it is close to the lognormal distribution predicted by pure stochastic growth theory. The model’s wave statistics resemble the statistics of plasma waves observed by the Ulysses spacecraft in some interplanetary type III burst sources. This resemblance is discussed qualitatively, and it is suggested that the stochastically driven thermal waves might be a candidate for explaining the power-law tails in the observed wave statistics without invoking mechanisms such as self-organized criticality or nonlinear wave collapse.

A physiologically based model of orexinergic stabilization of sleep and wake

Publisher: Public Library of Science (PLoS)

Date: 20-03-2014

DOI: 10.1371/JOURNAL.PONE.0091982

Automated characterization of multiple alpha peaks in multi-site electroencephalograms

Publisher: Elsevier BV

Date: 03-2008

DOI: 10.1016/J.JNEUMETH.2007.11.001

Abstract: The identification of alpha rhythm in the human electroencephalogram (EEG) is generally a laborious task involving visual inspection of the spectrum. Moreover the occurrence of multiple alpha rhythms is often overlooked. This paper seeks to automate the process of identifying alpha peaks and quantifying their frequency, litude and width as a function of position on the scalp. Experimental EEG was fitted with parameterized spectra spanning the alpha range, with results categorized by multi-site criteria into three distinct classes: no distinguishable alpha peak, a single alpha peak, and two alpha peaks. The technique avoids visual bias, integrates spatial information, and is automated. We show that multiple alpha peaks are a common feature of many spectra.

Dynamical Reconnection and Stability Constraints on Cortical Network Architecture

Publisher: American Physical Society (APS)

Date: 04-09-2009

DOI: 10.1103/PHYSREVLETT.103.108104

A minimal physiologically based model of the HPA axis under influence of the sleep-wake cycles.

Publisher: Georg Thieme Verlag KG

Date: 18-04-2013

DOI: 10.1055/S-0033-1333763

Abstract: The hypothalamic-pituitary-adrenal axis (also called the HPA or stress axis) exhibits distinct circadian and ultradian rhythms in cortisol release that cannot be explained solely by the feedback loops from cortisol to the control systems in the paraventricular nucleus (PVN) and pituitary gland. The HPA axis is intimately connected with other brain functions. In particular, it is strongly affected by the sleep-wake cycles via direct and indirect effects of the circadian and homeostatic mechanisms. For ex le, the HPA axis has direct inputs from the master circadian clock in the suprachiasmatic nuclei (SCN), and from the various sleep-wake related neuronal populations, which themselves are under the effects of the circadian and homeostatic processes. In this paper a first step towards a physiologically based mathematical model of the HPA-axis under effects of the sleep-wake cycles is presented. This model accounts for 3 major characteristics of daily cortisol profile in the blood: i) abrupt increase of cortisol concentration in response to awakening, the so-called cortisol-awakening response (CAR) ii) reduced cortisol levels during daytime with underlying ultradian oscillations and iii) suppression of cortisol release during sleep.

Electromagnetic localization in dispersive stratified media with random loss and gain

Publisher: American Physical Society (APS)

Date: 06-1998

DOI: 10.1103/PHYSREVB.57.13535

NFTsim: Theory and Simulation of Multiscale Neural Field Dynamics

Publisher: Public Library of Science (PLoS)

Date: 22-08-2018

DOI: 10.1371/JOURNAL.PCBI.1006387

Necessity of the sleep–wake cycle for synaptic homeostasis: system-level analysis of plasticity in the corticothalamic system

Publisher: The Royal Society

Date: 10-2018

DOI: 10.1098/RSOS.171952

Abstract: Neural field theory is used to study the system-level effects of plasticity in the corticothalamic system, where arousal states are represented parametrically by the connection strengths of the system, among other physiologically based parameters. It is found that the plasticity dynamics have no fixed points or closed cycles in the parameter space of the connection strengths, but parameter subregions exist where flows have opposite signs. Remarkably, these subregions coincide with previously identified regions that correspond to wake and slow-wave sleep, thus demonstrating state dependence of the sign of synaptic modification. We then show that a closed cycle in the parameter space is possible when the plasticity dynamics are driven by the ascending arousal system, which cycles the brain between sleep and wake to complete a closed loop that includes arcs through the opposite-flow subregions. Thus, it is concluded that both wake and sleep are necessary, and together are able to stabilize connection weights in the brain over the daily cycle, thereby providing quantitative realization of the synaptic homeostasis hypothesis.

Modeling the impact of impulsive stimuli on sleep-wake dynamics

Publisher: American Physical Society (APS)

Date: 20-11-2008

DOI: 10.1103/PHYSREVE.78.051920

Type II solar radio bursts: 2. Detailed comparison of theory with observations

Publisher: American Geophysical Union (AGU)

Date: 06-2012

DOI: 10.1029/2011JA016755

Numerical simulations of type-III solar radio bursts

Publisher: American Physical Society (APS)

Date: 13-04-2006

DOI: 10.1103/PHYSREVLETT.96.145005

Type II solar radio bursts: Modeling and extraction of shock parameters

Publisher: American Geophysical Union (AGU)

Date: 03-2012

DOI: 10.1029/2011JA016754

Response-mode decomposition of spatio-temporal haemodynamics

Publisher: The Royal Society

Date: 05-2016

DOI: 10.1098/RSIF.2016.0253

Abstract: The blood oxygen-level dependent (BOLD) response to a neural stimulus is analysed using the transfer function derived from a physiologically based poroelastic model of cortical tissue. The transfer function is decomposed into components that correspond to distinct poles, each related to a response mode with a natural frequency and dispersion relation together these yield the total BOLD response. The properties of the decomposed components provide a deeper understanding of the nature of the BOLD response, via the components' frequency dependences, spatial and temporal power spectra, and resonances. The transfer function components are then used to separate the BOLD response to a localized impulse stimulus, termed the Green function or spatio-temporal haemodynamic response function, into component responses that are explicitly related to underlying physiological quantities. The analytical results also provide a quantitative tool to calculate the linear BOLD response to an arbitrary neural drive, which is faster to implement than direct Fourier transform methods. The results of this study can be used to interpret functional magnetic resonance imaging data in new ways based on physiology, to enhance deconvolution methods and to design experimental protocols that can selectively enhance or suppress particular responses, to probe specific physiological phenomena.

Bistability and Non-Gaussian Fluctuations in Spontaneous Cortical Activity

Publisher: Society for Neuroscience

Date: 07-2009

DOI: 10.1523/JNEUROSCI.0754-09.2009

Nonzero azimuthal magnetic fields at the solar source surface: Extraction, model, and implications

Publisher: American Geophysical Union (AGU)

Date: 10-2012

DOI: 10.1029/2012JA017705

BIOPHYSICAL MODELING OF TONIC CORTICAL ELECTRICAL ACTIVITY IN ATTENTION DEFICIT HYPERACTIVITY DISORDER

Publisher: Informa UK Limited

Date: 2005

DOI: 10.1080/00207450590934499

Abstract: Psychophysiological theories characterize Attention Deficit Hyperactivity Disorder (ADHD) in terms of cortical hypoarousal and a lack of inhibition of irrelevant sensory input, drawing on evidence of abnormal electroencephalographic (EEG) delta-theta activity. To investigate the mechanisms underlying this disorder a biophysical model of the cortex was used to fit and replicate the EEGs from 54 ADHD adolescents and their control subjects. The EEG abnormalities in ADHD were accounted for by the model's neurophysiological parameters as follows: (i) dendritic response times were increased, (ii) intrathalamic activity involving the thalamic reticular nucleus (TRN) was increased, consistent with enhanced delta-theta activity, and (iii) intracortical activity was increased, consistent with slow wave (<1 Hz) abnormalities. The longer dendritic response time is consistent with the increase in the activity of inhibitory cells types, particularly in the TRN, and therefore reduced arousal. The increase in intracortical activity may also reflect an increase in background activity or cortical noise within neocortical circuits. In terms of neurochemistry, these findings may be accounted for by disturbances in the cholinergic and/or noradrenergic systems. To the knowledge of the authors, this is the first study to use a detailed biophysical model of the brain to elucidate the neurophysiological mechanisms underlying tonic abnormalities in ADHD.

Quantitative physiologically based modeling of subjective fatigue during sleep deprivation

Publisher: Elsevier BV

Date: 05-2010

DOI: 10.1016/J.JTBI.2010.02.028

Abstract: A quantitative physiologically based model of the sleep-wake switch is used to predict variations in subjective fatigue-related measures during total sleep deprivation. The model includes the mutual inhibition of the sleep-active neurons in the hypothalamic ventrolateral preoptic area (VLPO) and the wake-active monoaminergic brainstem populations (MA), as well as circadian and homeostatic drives. We simulate sleep deprivation by introducing a drive to the MA, which we call wake effort, to maintain the system in a wakeful state. Physiologically this drive is proposed to be afferent from the cortex or the orexin group of the lateral hypothalamus. It is hypothesized that the need to exert this effort to maintain wakefulness at high homeostatic sleep pressure correlates with subjective fatigue levels. The model's output indeed exhibits good agreement with existing clinical time series of subjective fatigue-related measures, supporting this hypothesis. Subjective fatigue, adrenaline, and body temperature variations during two 72h sleep deprivation protocols are reproduced by the model. By distinguishing a motivation-dependent orexinergic contribution to the wake-effort drive, the model can be extended to interpret variation in performance levels during sleep deprivation in a way that is qualitatively consistent with existing, clinically derived results. The ex le of sleep deprivation thus demonstrates the ability of physiologically based sleep modeling to predict psychological measures from the underlying physiological interactions that produce them.

New regimes of stochastic wave growth: Theory, simulation, and comparison with data

Publisher: AIP Publishing

Date: 11-2006

DOI: 10.1063/1.2363174

Abstract: Stochastic growth theory (SGT) of bursty waves is generalized and it is shown that the theory of “elementary bursts,” previously used to describe bursty emission in certain solar plasmas, is a limiting case of the generalized theory. New regimes of strong and weak stochastic growth are found, the boundaries separating the regimes are elucidated, and a reduced-parameter quasilinear model is used to constrain growth dynamics. The analytic results are then compared with simulations using the reduced-parameter model. Upon re-analysis of data from situations previously studied using SGT or other theories, including spacecraft data and results of particle-in-cell and quasilinear simulations, good agreement is found with the predictions of the generalized theory. In particular, data collapse of stochastic wave statistics is accomplished onto a universal curve with no free parameters.

Effects of rotation interval on sleepiness and circadian dynamics on forward rotating 3-shift systems

Publisher: SAGE Publications

Date: 02-2014

DOI: 10.1177/0748730413516837

Abstract: A physiologically based mathematical model of sleep-wake cycles is used to examine the effects of shift rotation interval (RI) (i.e., the number of days spent on each shift) on sleepiness and circadian dynamics on forward rotating 3-shift schedules. The effects of the schedule start time on the mean shift sleepiness are also demonstrated but are weak compared to the effects of RI. The dynamics are studied for a parameter set adjusted to match a most common natural sleep pattern (i.e., sleep between 0000 and 0800) and for common light conditions (i.e., 350 lux of shift lighting, 200 lux of daylight, 100 lux of artificial lighting during nighttime, and 0 lux during sleep). Mean shift sleepiness on a rotating schedule is found to increase with RI, reach maximum at intermediate RI=6 d, and then decrease. Complete entrainment to shifts within the schedules is not achieved at RI≤10 d. However, circadian oscillations synchronize to the rotation cycles, with RI=1,2 d and RI≥6 d demonstrating regular periodic changes of the circadian rhythm. At rapid rotation, circadian phase stays within a small 4-h interval, whereas slow rotation leads to around-the-clock transitions of the circadian phase with constantly delayed sleep times. Schedules with RI=3-5 d are not able to entrain the circadian rhythms, even in the absence of external circadian disturbances like social commitments and days off. To understand the circadian dynamics on the rotating shift schedules, a shift response map is developed, showing the direction of circadian change (i.e., delay or advance) depending on the relation between the shift start time and actual circadian phase. The map predicts that the un-entrained dynamics come from multiple transitions between advance and delay behavior on the shifts in the schedules. These are primarily caused by the imbalance between the amount of delay and advance on the different shift types within the schedule. Finally, it is argued that shift response maps can aid in the development of shift schedules with desired circadian characteristics.

Potential formulation of sleep dynamics

Publisher: American Physical Society (APS)

Date: 24-02-2009

DOI: 10.1103/PHYSREVE.79.021913

Numerical simulation of electron distributions upstream and downstream of high Mach number quasi-perpendicular collisionless shocks

Publisher: American Geophysical Union (AGU)

Date: 08-2008

DOI: 10.1029/2008JA013268

Simulation of energetic electron bursts upstream of re-forming shocks

Publisher: American Astronomical Society

Date: 10-12-2007

DOI: 10.1086/522686

Physiologically based quantitative modeling of unihemispheric sleep

Publisher: Elsevier BV

Date: 12-2012

DOI: 10.1016/J.JTBI.2012.08.031

Abstract: Unihemispheric sleep has been observed in numerous species, including birds and aquatic mammals. While knowledge of its functional role has been improved in recent years, the physiological mechanisms that generate this behavior remain poorly understood. Here, unihemispheric sleep is simulated using a physiologically based quantitative model of the mammalian ascending arousal system. The model includes mutual inhibition between wake-promoting monoaminergic nuclei (MA) and sleep-promoting ventrolateral preoptic nuclei (VLPO), driven by circadian and homeostatic drives as well as cholinergic and orexinergic input to MA. The model is extended here to incorporate two distinct hemispheres and their interconnections. It is postulated that inhibitory connections between VLPO nuclei in opposite hemispheres are responsible for unihemispheric sleep, and it is shown that contralateral inhibitory connections promote unihemispheric sleep while ipsilateral inhibitory connections promote bihemispheric sleep. The frequency of alternating unihemispheric sleep bouts is chiefly determined by sleep homeostasis and its corresponding time constant. It is shown that the model reproduces dolphin sleep, and that the sleep regimes of humans, cetaceans, and fur seals, the latter both terrestrially and in a marine environment, require only modest changes in contralateral connection strength and homeostatic time constant. It is further demonstrated that fur seals can potentially switch between their terrestrial bihemispheric and aquatic unihemispheric sleep patterns by varying just the contralateral connection strength. These results provide experimentally testable predictions regarding the differences between species that sleep bihemispherically and unihemispherically.

Effects of overshoots on electron distributions upstream and downstream of quasi-perpendicular collisionless shocks

Publisher: American Geophysical Union (AGU)

Date: 05-2007

DOI: 10.1029/2006JA011684

Mammalian Sleep Dynamics: How Diverse Features Arise from a Common Physiological Framework

Publisher: Public Library of Science (PLoS)

Date: 24-06-2010

DOI: 10.1371/JOURNAL.PCBI.1000826

Hybrid simulation of reforming shocks with electron mass and pressure tensor effects

Publisher: American Geophysical Union (AGU)

Date: 2007

DOI: 10.1029/2006GL028447

Incorporation of caffeine into a quantitative model of fatigue and sleep

Publisher: Elsevier BV

Date: 03-2011

DOI: 10.1016/J.JTBI.2010.12.018

Abstract: A recent physiologically based model of human sleep is extended to incorporate the effects of caffeine on sleep-wake timing and fatigue. The model includes the sleep-active neurons of the hypothalamic ventrolateral preoptic area (VLPO), the wake-active monoaminergic brainstem populations (MA), their interactions with cholinergic/orexinergic (ACh/Orx) input to MA, and circadian and homeostatic drives. We model two effects of caffeine on the brain due to competitive antagonism of adenosine (Ad): (i) a reduction in the homeostatic drive and (ii) an increase in cholinergic activity. By comparing the model output to experimental data, constraints are determined on the parameters that describe the action of caffeine on the brain. In accord with experiment, the ranges of these parameters imply significant variability in caffeine sensitivity between in iduals, with caffeine's effectiveness in reducing fatigue being highly dependent on an in idual's tolerance, and past caffeine and sleep history. Although there are wide in idual differences in caffeine sensitivity and thus in parameter values, once the model is calibrated for an in idual it can be used to make quantitative predictions for that in idual. A number of applications of the model are examined, using exemplar parameter values, including: (i) quantitative estimation of the sleep loss and the delay to sleep onset after taking caffeine for various doses and times (ii) an analysis of the system's stable states showing that the wake state during sleep deprivation is stabilized after taking caffeine and (iii) comparing model output successfully to experimental values of subjective fatigue reported in a total sleep deprivation study examining the reduction of fatigue with caffeine. This model provides a framework for quantitatively assessing optimal strategies for using caffeine, on an in idual basis, to maintain performance during sleep deprivation.

Numerical modeling of type III solar radio bursts in the inhomogeneous solar corona and interplanetary medium

Publisher: AIP Publishing

Date: 09-2006

DOI: 10.1063/1.2355660

Abstract: The first numerical calculations are presented for type III solar radio bursts in the inhomogeneous solar corona and interplanetary medium that include microscale quasilinear and nonlinear processes, intermediate-scale driven ambient density fluctuations, and large-scale evolution of electron beams, Langmuir and ion-sound waves, and fundamental and harmonic electromagnetic emission. Bidirectional coronal radiation driven by oppositely directed beams is asymmetric between the upward and downward directions due to downward beam narrowing in velocity space, and harmonic emission dominates fundamental emission, consistent with observations and theoretical analysis. In the interplanetary medium, fundamental and/or harmonic emission can be important depending on beam parameters and plasma conditions. Furthermore, Langmuir waves are bursty, ion-sound waves also show some degree of irregularity, while electromagnetic radiations are relatively smooth, all qualitatively consistent with observations. Moreover, the statistics of Langmuir wave energy agree well with the predictions of stochastic growth theory, indicating that the beam-Langmuir wave system evolves to a stochastic growth state.

Nonlinear harmonic generation in the corticothalamic system

Publisher: Elsevier BV

Date: 2019

DOI: 10.1016/J.JTBI.2018.10.013

Abstract: Neural field theory of the corticothalamic system is applied to quantitatively analyze harmonic generation in normal sleep and wake states. The linear power spectrum is derived analytically via the transfer function and is then convolved with itself and other factors to calculate the nonlinear power spectrum analytically via a recent perturbation expansion. Analysis shows that strong spectral peaks generate a harmonic at twice the original frequency with peak power proportional to the square of that of the original peak. Fits to the data enable absolute normalization to be determined, with the conclusion that the experimentally observed spindle harmonic peak is nonlinear. Using this normalization, the same analysis is applied to the wake state and nonlinear contributions to the alpha and beta peaks are quantified.

Physiologically based arousal state estimation and dynamics

Publisher: Elsevier BV

Date: 09-2015

DOI: 10.1016/J.JNEUMETH.2015.06.002

Abstract: A neural field model of the brain is used to represent brain states using physiologically based parameters rather than arbitrary, discrete sleep stages. Each brain state is represented as a point in a physiologically parametrized space. Over time, changes in brain state cause these points to trace continuous trajectories, unlike the artificial discrete jumps in sleep stage that occur with traditional sleep staging. The discrete Rechtschaffen and Kales sleep stages are associated with regions in the physiological parameter space based on their electroencephalographic features, which enables interpretation of traditional sleep stages in terms of physiological trajectories. Wake states are found to be associated with strong positive corticothalamic feedback compared to sleep. The existence of physiologically valid trajectories between brain states in the model is demonstrated. Actual trajectories for an in idual can be determined by fitting the model using EEG alone, and enable analysis of the physiological differences between subjects.

Probing the Mechanisms of Chronotype Using Quantitative Modeling

Publisher: SAGE Publications

Date: 19-05-2010

DOI: 10.1177/0748730410369208

Abstract: The physiological mechanisms underlying interin idual differences in chronotype have yet to be established, although evidence suggests both circadian and homeostatic processes are involved. A physiologically based model is developed by combining models of the sleep-wake switch and circadian pacemaker, providing a means of examining how interactions between these systems affect chronotype. Specifically, chronotype is shown to depend on the relative influences of homeostatic and circadian drives, with a stronger homeostatic drive causing morningness. Changes to intrinsic circadian and homeostatic properties, including homeostatic clearance and production rates, and circadian period and litude, are also shown to affect chronotype. These results provide a framework for explaining several experimentally observed phenomena, including age-related morningness, adolescent eveningness, and familial advanced and delayed sleep-phase disorders. Additionally, experimental studies have shown that healthy adults on the extremes of the morningness-eveningness spectrum fall into two subtypes: those whose circadian phase markers are unaffected by chronotype, and those whose circadian phase markers track their chronotype. The model demonstrates that this spectrum likely results from interin idual differences in homeostatic kinetics in the first group, and differences in circadian period in the second group. Physiologically based modeling can thus guide diagnosis of sleep pathologies.

Energy approach to rivalry dynamics, soliton stability, and pattern formation in neuronal networks

Publisher: American Physical Society (APS)

Date: 31-10-2007

DOI: 10.1103/PHYSREVE.76.046224

Electrostatic Decay in a Weakly Magnetized Plasma

Publisher: American Physical Society (APS)

Date: 30-04-2013

DOI: 10.1103/PHYSREVLETT.110.185001

Coupled Langmuir and nonlinear ion acoustic waves in the presence of non-thermal electrons

Publisher: Cambridge University Press (CUP)

Date: 04-2009

DOI: 10.1017/S0022377808007435

Abstract: A new set of equations describing the coupling of high-frequency electrostatic waves with ion fluctuations is obtained taking into account a non-thermal electron distribution. It is shown that there exist stationary envelope solitons which have qualitatively different structures from the solutions reported earlier. In particular, the Langmuir field envelopes are found with similar width and strong field intensities in comparison to the isothermal case. It is also shown that the presence of the fast or non-thermal electrons significantly modifies the nature of Langmuir solitons in the transition from a single-hump solution to a double-hump solution as the Mach number increases to unity. The low-frequency electrostatic potential associated with the high-frequency Langmuir field has the usual single-dip symmetric structure whose litude increases with increasing Mach number. Furthermore, the dip at the center of the double-hump Langmuir soliton is found to become smaller as the proportion of non-thermal electrons increases.

Spike-rate adaptation and neuronal bursting in a mean-field model of brain activity

Publisher: Springer Science and Business Media LLC

Date: 05-2007

DOI: 10.1007/S00422-007-0157-1

Abstract: Spike-rate adaptation is investigated within a mean-field model of brain activity. Two different mechanisms of negative feedback are considered one involving modulation of the mean firing threshold, and the other, modulation of the mean synaptic strength. Adaptation to a constant stimulus is shown to take place for both mechanisms, and limit-cycle oscillations in the firing rate corresponding to bursts of neuronal activity are investigated. These oscillations are found to result from a Hopf bifurcation when the equilibrium lies between the local maximum and local minimum of a given nullcline. Oscillations with litudes significantly below the maximum firing rate are found over a narrow range of possible equilibriums.

Propagation and absorption of cyclotron maser radiation in solar microwave spike bursts

Publisher: Springer Science and Business Media LLC

Date: 06-1993

DOI: 10.1007/BF00690659

Conditions for plasma emission in the solar wind and very local interstellar medium (VLISM)

Publisher: American Geophysical Union (AGU)

Date: 11-2005

DOI: 10.1029/2005JA011267

Warm electromagnetic lower hybrid wave dispersion relation

Publisher: AIP Publishing

Date: 05-2009

DOI: 10.1063/1.3132628

Abstract: Lower hybrid (LH) waves can interact resonantly with both electrons and ions transferring energy between the species. For this reason the properties of LH waves are of interest. Most treatments of LH waves include either electromagnetic (EM) or warm plasma effects but not both. Here a new analytic dispersion relation for LH waves, including both EM and warm plasma effects, is derived and shown to be more consistent than the previous analytic dispersion relations with numerical results. These comparisons show a very good agreement of the real part of the frequency and reasonable agreement of the imaginary part for a wide range of parameters. It is found that ion magnetization effects, which have been neglected in all previous analytic treatments of LH waves, are surprisingly important. When ion magnetization effects become important the continuous LH mode breaks up into a series of segments of ion Bernstein modes.

Soliton Model of Competitive Neural Dynamics during Binocular Rivalry

Publisher: American Physical Society (APS)

Date: 23-06-2009

DOI: 10.1103/PHYSREVLETT.102.258701

Theoretically predicted properties of type II radio emission from an interplanetary foreshock

Publisher: American Geophysical Union (AGU)

Date: 03-2003

DOI: 10.1029/2002JA009508

Type II solar radio bursts: Theory and space weather implications

Publisher: Springer Science and Business Media LLC

Date: 2003

DOI: 10.1023/A:1025503201687

First-order thermal correction to the quadratic response tensor and rate for second harmonic plasma emission

Publisher: AIP Publishing

Date: 02-2011

DOI: 10.1063/1.3554700

Abstract: Three-wave interactions in plasmas are described, in the framework of kinetic theory, by the quadratic response tensor (QRT). The cold-plasma QRT is a common approximation for interactions between three fast waves. Here, the first-order thermal correction (FOTC) to the cold-plasma QRT is derived for interactions between three fast waves in a warm unmagnetized collisionless plasma, whose particles have an arbitrary isotropic distribution function. The FOTC to the cold-plasma QRT is shown to depend on the second moment of the distribution function, the phase speeds of the waves, and the interaction geometry. Previous calculations of the rate for second harmonic plasma emission (via Langmuir-wave coalescence) assume the cold-plasma QRT. The FOTC to the cold-plasma QRT is used here to calculate the FOTC to the second harmonic emission rate, and its importance is assessed in various physical situations. The FOTC significantly increases the rate when the ratio of the Langmuir phase speed to the electron thermal speed is less than about 3.

Exact evaluation of the rates of electrostatic decay and scattering off thermal ions for an unmagnetized Maxwellian plasma

Publisher: AIP Publishing

Date: 08-2013

DOI: 10.1063/1.4819032

Abstract: Electrostatic decay of Langmuir waves into Langmuir and ion sound waves (L→L′+S) and scattering of Langmuir waves off thermal ions (L+i→L′+i′, also called “nonlinear Landau d ing”) are important nonlinear weak-turbulence processes. The rates for these processes depend on the quadratic longitudinal response function α(2) (or, equivalently, the quadratic longitudinal susceptibility χ(2)), which describes the second-order response of a plasma to electrostatic wave fields. Previous calculations of these rates for an unmagnetized Maxwellian plasma have relied upon an approximate form for α(2) that is valid where two of the wave fields are fast (i.e., vϕ=ω/k≫Ve where ω is the angular frequency, k is the wavenumber, and Ve is the electron thermal speed) and one is slow (vϕ≪Ve). Recently, an exact expression was derived for α(2) that is valid for any phase speeds of the three waves in an unmagnetized Maxwellian plasma. Here, this exact α(2) is applied to the calculation of the three-dimensional rates for electrostatic decay and scattering off thermal ions, and the resulting exact rates are compared with the approximate rates. The calculations are performed using previously derived three-dimensional rates for electrostatic decay given in terms of a general α(2), and newly derived three-dimensional rates for scattering off thermal ions the scattering rate is derived assuming a Maxwellian ion distribution, and both rates are derived assuming arc distributions for the wave spectra. For most space plasma conditions, the approximate rate is found to be accurate to better than 20% however, for sufficiently low Langmuir phase speeds (vϕ/Ve≈3) appropriate to some spatial domains of the foreshock regions of planetary bow shocks and type II solar radio bursts, the use of the exact rate may be necessary for accurate calculations. The relative rates of electrostatic decay and scattering off thermal ions are calculated for a range of parameters using the exact expressions for the rates electrostatic decay is found to have the larger growth rate over the whole range of parameters, consistent with previous approximate calculations.

Multielectrode electroencephalogram power spectra: Theory and application to approximate correction of volume conduction effects

Publisher: American Physical Society (APS)

Date: 31-05-2006

DOI: 10.1103/PHYSREVE.73.051918

Field statistics of two vectorially superposed wave populations

Publisher: American Physical Society (APS)

Date: 30-12-2002

DOI: 10.1103/PHYSREVE.66.066614

Microstructured optical fibers: where�??s the edge?

Publisher: The Optical Society

Date: 04-11-2002

DOI: 10.1364/OE.10.001285

Abstract: We establish that Microstructured Optical Fibers (MOFs) have a fundamental mode cutoff, marking the transition between modal confinement and non-confinement, and give insight into the nature of this transition through two asymptotic models that provide a mapping to conventional fibers. A small parameter space region where neither of these asymptotic models holds exists for the fundamental mode but not for the second mode we show that designs exploiting unique MOF characteristics tend to concentrate in this preferred region.

Extraordinary-Mode Radiation Produced by Linear-Mode Conversion of Langmuir Waves

Publisher: American Physical Society (APS)

Date: 06-07-2007

DOI: 10.1103/PHYSREVLETT.99.015003

Deconvolution of neural dynamics from fMRI data using a spatiotemporal hemodynamic response function

Publisher: Elsevier BV

Date: 07-2014

DOI: 10.1016/J.NEUROIMAGE.2014.03.001

Abstract: Functional magnetic resonance imaging (fMRI) is a powerful and broadly used means of non-invasively mapping human brain activity. However fMRI is an indirect measure that rests upon a mapping from neuronal activity to the blood oxygen level dependent (BOLD) signal via hemodynamic effects. The quality of estimated neuronal activity hinges on the validity of the hemodynamic model employed. Recent work has demonstrated that the hemodynamic response has non-separable spatiotemporal dynamics, a key property that is not implemented in existing fMRI analysis frameworks. Here both simulated and empirical data are used to demonstrate that using a physiologically based model of the spatiotemporal hemodynamic response function (stHRF) results in a quantitative improvement of the estimated neuronal response relative to unphysical space-time separable forms. To achieve this, an integrated spatial and temporal deconvolution is established using a recently developed stHRF. Simulated data allows the variation of key parameters such as noise and the spatial complexity of the neuronal drive, while knowing the neuronal input. The results demonstrate that the use of a spatiotemporally integrated HRF can avoid "ghost" neuronal responses that can otherwise be falsely inferred. Applying the spatiotemporal deconvolution to high resolution fMRI data allows the recovery of neuronal responses that are consistent with independent electrophysiological measures.

Mode conversion of Langmuir to electromagnetic waves at magnetic field-aligned density inhomogeneities: Simulations, theory, and applications to the solar wind and the corona

Publisher: AIP Publishing

Date: 10-2008

DOI: 10.1063/1.2994719

Abstract: Linear mode conversion of Langmuir waves to radiation near the plasma frequency at density gradients is potentially relevant to multiple solar radio emissions, ionospheric radar experiments, laboratory plasma devices, and pulsars. Here we study mode conversion in warm magnetized plasmas using a numerical electron fluid simulation code with the density gradient parallel to the ambient magnetic field B0 for a range of incident Langmuir wavevectors. Our results include: (1) both o- and x-mode waves are produced for Ω=(ωL∕c)1∕3(ωc∕ω)≲1, contrary to previous ideas. Only the o mode is produced for Ω≳1.5. Here ωc is the (angular) electron cyclotron frequency, ω is the angular wave frequency, L is the length scale of the (linear) density gradient, and c is the speed of light. A WKB-style analysis accounts semiquantitatively for the production and relative conversion efficiencies of the o and x modes in the simulations. (2) In the unmagnetized limit, equal amounts of o- and x-mode radiation are produced. (3) The mode conversion window narrows as Ω increases. (4) As Ω increases the total electromagnetic field changes from linear to circular polarization, with the o- and x-mode signals remaining circularly polarized. (5) The conversion efficiency to the x mode decreases monotonically as Ω increases while the o-mode conversion efficiency oscillates due to an interference phenomenon between incoming and reflected Langmuir/z modes. (6) The maximum total conversion efficiencies for wave power from the Langmuir/z mode to radiation are of order 50%–70%. They depend strongly on the wave frequency when close to the background plasma frequency but weakly on the electron temperature T0 and β=T0∕mc2. The corresponding energy conversion efficiencies are favored since they allow separation into o and x modes, use directly measured experimental quantities, and generalize easily for wave packets. The total energy conversion efficiency differs from the power conversion efficiency by the ratio of the group speeds for each mode, is less than 10% for the value of β=0.01 simulated, and decreases linearly with β. Since β≈10−5–10−4 in the solar wind and corona, this β dependence is important in applications. (7) The interference effect and the disappearance of the x mode at Ω≳1 can be accounted for semiquantitatively using a WKB-type analysis. (8) Constraints on density turbulence are developed for the x mode to be generated and be able to propagate from the source. (9) Standard parameters for the corona and the solar wind near 1 AU suggest that linear mode conversion should produce both o- and x-mode radiation for solar and interplanetary radio bursts. It is therefore possible that linear mode conversion under these conditions might explain the weak total circular polarizations of type II and III solar radio bursts.

Dynamic pattern formation and collisions in networks of excitable elements

Publisher: American Physical Society (APS)

Date: 04-05-2012

DOI: 10.1103/PHYSREVE.85.055101

Decimetric type III bursts: Generation and propagation

Publisher: American Astronomical Society

Date: 10-08-2011

DOI: 10.1088/2041-8205/738/1/L9

Dynamics of epileptic seizures: Evolution, spreading, and suppression

Publisher: Elsevier BV

Date: 04-2009

DOI: 10.1016/J.JTBI.2008.12.009

Abstract: Dynamical properties of epileptic seizures are investigated using a recent compact continuum model for electric activity of the brain. Large litude limit cycles resembling electroencephalograms during epilepsy emerge when the system loses linear stability. Seizures that are confined to an onset area, or spread synchronously to other areas via spatial coupling, are studied and argued to be associated with clinical partial and secondarily generalized seizures, respectively. Suppression of such seizures is also demonstrated, which implies potential for future clinical applications.

Neurophysiological changes with age probed by inverse modeling of EEG spectra

Publisher: Elsevier BV

Date: 2010

DOI: 10.1016/J.CLINPH.2009.09.021

Abstract: To investigate age-associated changes in physiologically-based EEG spectral parameters in the healthy population. Eyes-closed EEG spectra of 1498 healthy subjects aged 6-86 years were fitted to a mean-field model of thalamocortical dynamics in a cross-sectional study. Parameters were synaptodendritic rates, cortical wave decay rates, connection strengths (gains), axonal delays for thalamocortical loops, and power normalizations. Age trends were approximated using smooth asymptotically linear functions with a single turning point. We also considered sex differences and relationships between model parameters and traditional quantitative EEG measures. The cross-sectional data suggest that changes tend to be most rapid in childhood, generally leveling off at age 15-20 years. Most gains decrease in magnitude with age, as does power normalization. Axonal and dendritic delays decrease in childhood and then increase. Axonal delays and gains show small but significant sex differences. Mean-field brain modeling allows interpretation of age-associated EEG trends in terms of physiological processes, including the growth and regression of white matter, influencing axonal delays, and the establishment and pruning of synaptic connections, influencing gains. This study demonstrates the feasibility of inverse modeling of EEG spectra as a noninvasive method for investigating large-scale corticothalamic dynamics, and provides a basis for future comparisons.

Eigenmodes of brain activity: Neural field theory predictions and comparison with experiment

Publisher: Elsevier BV

Date: 11-2016

DOI: 10.1016/J.NEUROIMAGE.2016.04.050

Abstract: Neural field theory of the corticothalamic system is applied to predict and analyze the activity eigenmodes of the bihemispheric brain, focusing particularly on their spatial structure. The eigenmodes of a single brain hemisphere are found to be close analogs of spherical harmonics, which are the natural modes of the sphere. Instead of multiple eigenvalues being equal, as in the spherical case, cortical folding splits them to have distinct values. Inclusion of interhemispheric connections between homologous regions via the corpus callosum leads to further splitting that depends on symmetry or antisymmetry of activity between brain hemispheres, and the strength and sign of the interhemispheric connections. Symmetry properties of the lowest observed eigenmodes strongly constrain the interhemispheric connectivity strengths and unihemispheric mode spectra, and it is predicted that most spontaneous brain activity will be symmetric between hemispheres, consistent with observations. Comparison with the eigenmodes of an experimental anatomical connectivity matrix confirms these results, permits the relative strengths of intrahemispheric and interhemispheric connectivities to be approximately inferred from their eigenvalues, and lays the foundation for further experimental tests. The results are consistent with brain activity being in corticothalamic eigenmodes, rather than discrete "networks" and open the way to new approaches to brain analysis.

Automatic recognition of complex magnetic regions on the Sun in GONG magnetogram images and prediction of flares: Techniques for the flare warning program Flarecast

Publisher: American Geophysical Union (AGU)

Date: 11-2011

DOI: 10.1029/2011SW000703

Quasilinear calculation of Langmuir wave generation and beam propagation in the presence of density fluctuations

Publisher: AIP Publishing

Date: 08-2006

DOI: 10.1063/1.2218331

Abstract: The generation of beam-driven Langmuir waves and the propagation of an electron beam in the presence of ambient density fluctuations are numerically studied using quasilinear calculations in one spatial dimension. The random spatiotemporal density fluctuations are driven externally as ion-sound-like turbulence. The effects of Langmuir wave scattering off density inhomogeneities in three spatial dimensions are represented through effective d ing of the Langmuir waves, and are included in the quasilinear model. The numerical results are explored for illustrative parameters, and Langmuir wave field statistics are compared with stochastic growth theory (SGT) predictions. Due to the combined effects of quasilinear interaction with the beam and scattering off density fluctuations, the Langmuir waves show burstiness and the levels are generally lower than when the density is homogeneous, qualitatively consistent with previous predictions. Apart from early evolution, the average beam speed is approximately the same as in the homogeneous case, but relaxation of the beam is significantly retarded. Both features are in qualitative agreement with earlier predictions. Moreover, the beam distribution function displays relatively smooth variations, which implies that the burstiness in the wave levels originates predominantly from the randomness in the d ing rate due to density perturbations, rather than from the stochasticity in the beam growth rate. The statistics of the Langmuir wave field show good agreement with SGT predictions, thus indicating the beam-Langmuir wave system is in a SGT state. Furthermore, variations of the density fluctuation parameters are found to affect the evolution of both beam and Langmuir waves.

Firing patterns in a conductance-based neuron model: bifurcation, phase diagram, and chaos

Publisher: Springer Science and Business Media LLC

Date: 19-09-2012

DOI: 10.1007/S00422-012-0520-8

Abstract: Responding to various stimuli, some neurons either remain resting or can fire several distinct patterns of action potentials, such as spiking, bursting, subthreshold oscillations, and chaotic firing. In particular, Wilson's conductance-based neocortical neuron model, derived from the Hodgkin-Huxley model, is explored to understand underlying mechanisms of the firing patterns. Phase diagrams describing boundaries between the domains of different firing patterns are obtained via extensive numerical computations. The boundaries are further studied by standard instability analyses, which demonstrates that the chaotic neural firing could develop via period-doubling and/or period- adding cascades. Sequences of the firing patterns often observed in many neural experiments are also discussed in the phase diagram framework developed. Our results lay the groundwork for wider use of the model, especially for incorporating it into neural field modeling of the brain.

Terrestrial foreshock Langmuir waves: STEREO observations, theoretical modeling, and quasi-linear simulations

Publisher: American Geophysical Union (AGU)

Date: 12-2009

DOI: 10.1029/2009JA014493

Three-dimensional electromagnetic strong turbulence. I. Scalings, spectra, and field statistics

Publisher: AIP Publishing

Date: 06-2011

DOI: 10.1063/1.3592147

Abstract: The first fully three-dimensional (3D) simulations of large-scale electromagnetic strong turbulence (EMST) are performed by numerically solving the electromagnetic Zakharov equations for electron thermal speeds νe with νe/c≥0.025. The results of these simulations are presented, focusing on scaling behavior, energy density spectra, and field statistics of the Langmuir (longitudinal) and transverse components of the electric fields during steady-state strong turbulence, where multiple wave packets collapse simultaneously and the system is approximately statistically steady in time. It is shown that for νe/c≳0.17 strong turbulence is approximately electrostatic and can be explained using the electrostatic two-component model. For ve/c≳0.17 the power-law behaviors of the scalings, spectra, and field statistics differ from the electrostatic predictions and results because νe/c is sufficiently high to allow transverse modes to become trapped in density wells. The results are compared with those of past 3D electrostatic strong turbulence (ESST) simulations and 2D EMST simulations. For number density perturbations, the scaling behavior, spectra, and field statistics are shown to be only weakly dependent on νe/c, whereas the Langmuir and transverse scalings, spectra, and field statistics are shown to be strongly dependent on νe/c. Three-dimensional EMST is shown to have features in common with 2D EMST, such as a two-component structure and trapping of transverse modes which are dependent on νe/c.

Simulations of coronal type III solar radio bursts: 1. Simulation model

Publisher: American Geophysical Union (AGU)

Date: 06-2008

DOI: 10.1029/2007JA012957

Simulations of coronal type III solar radio bursts: 2. Dynamic spectrum for typical parameters

Publisher: American Geophysical Union (AGU)

Date: 06-2008

DOI: 10.1029/2007JA012958

A resistive instability of lower hybrid-like waves in regions with parallel currents

Publisher: AIP Publishing

Date: 08-2011

DOI: 10.1063/1.3619820

Abstract: The resistive instabilities and dispersion of obliquely propagating waves near the lower hybrid (LH) frequency are studied in plasma carrying a current parallel to the magnetic field. Possible applications of these instabilities include magnetic reconnection regions where LH-like waves may accelerate and heat both ions and electrons. A resistive instability is found in one of the four LH-like wave modes for electron drift speeds several times greater than the electron thermal speed for representative parameters. Numerical fully electromagnetic kinetic calculations of the solutions to the linear dispersion equation are compared with more approximate analytic calculations and show good agreement. The analytic results indicate that ion magnetization effects play a critical role in the resistive instability.

Biophysical modeling of neural plasticity induced by transcranial magnetic stimulation

Publisher: Elsevier BV

Date: 06-2018

DOI: 10.1016/J.CLINPH.2018.03.018

Abstract: Transcranial magnetic stimulation (TMS) is a widely used noninvasive brain stimulation method capable of inducing plastic reorganisation of cortical circuits in humans. Changes in neural activity following TMS are often attributed to synaptic plasticity via process of long-term potentiation and depression (LTP/LTD). However, the precise way in which synaptic processes such as LTP/LTD modulate the activity of large populations of neurons, as stimulated en masse by TMS, are unclear. The recent development of biophysical models, which incorporate the physiological properties of TMS-induced plasticity mathematically, provide an excellent framework for reconciling synaptic and macroscopic plasticity. This article overviews the TMS paradigms used to induce plasticity, and their limitations. It then describes the development of biophysically-based numerical models of the mechanisms underlying LTP/LTD on population-level neuronal activity, and the application of these models to TMS plasticity paradigms, including theta burst and paired associative stimulation. Finally, it outlines how modeling can complement experimental work to improve mechanistic understandings and optimize outcomes of TMS-induced plasticity.

Theory for low‐frequency modulated Langmuir wave packets

Publisher: American Geophysical Union (AGU)

Date: 20-11-1992

DOI: 10.1029/92GL02632

Quantitative modelling of sleep dynamics.

Publisher: The Royal Society

Date: 13-10-2011

DOI: 10.1098/RSTA.2011.0120

Abstract: Arousal is largely controlled by the ascending arousal system of the hypothalamus and brainstem, which projects to the corticothalamic system responsible for electroencephalographic (EEG) signatures of sleep. Quantitative physiologically based modelling of brainstem dynamics theory is described here, using realistic parameters, and links to EEG are outlined. Verification against a wide range of experimental data is described, including arousal dynamics under normal conditions, sleep deprivation, stimuli, stimulants and jetlag, plus key features of wake and sleep EEGs.

Propagation of a cloud of hot electrons through a plasma in the presence of Langmuir scattering by ambient density fluctuations

Publisher: AIP Publishing

Date: 2007

DOI: 10.1063/1.2423253

Abstract: Gas-dynamic theory is generalized to incorporate the effects of beam-driven Langmuir waves scattering off ambient density fluctuations, and the consequent effects on the propagation of a cloud of hot electrons in an inhomogeneous plasma. Assuming Langmuir scattering as the limit of nonlinear three-wave interactions with fluctuations that are weak, low-frequency, long-wavelength ion-sound waves, the net effect of scattering is equivalent to effective d ing of the Langmuir waves. Under the assumption of self-similarity in the evolution of the beam and Langmuir wave distribution functions, gas-dynamic theory shows that the effects of Langmuir scattering on the beam distribution are equivalent to a perturbation in the injection profile of the beam. Analytical expressions are obtained for the height of the plateau of the beam distribution function, wave spectral number density, total wave and particle energy density, and the beam number density. The main results of gas-dynamic theory are then compared with simulation results from numerical solutions of quasilinear equations. The relaxation of the beam in velocity space is retarded in the presence of density fluctuations and the magnitude of the upper velocity boundary is less than that in the absence of fluctuations. There are four different regimes for the height of the plateau, corresponding to different stages of relaxation of the beam in velocity space. Moreover, Langmuir scattering results in transfer of electrons from moderate velocity to low velocity this effect produces an enhancement in the beam number density at small distances near the injection site and a corresponding decrease at large distances. There are sharp decreases in the profiles of the beam and total wave energy densities, which are related to dissipation of energy at large phase velocities. Due to a slower velocity space diffusion of the beam distribution in the presence of scattering effects, the spatial width of the beam is reduced while its mean velocity of propagation increases slightly.

Three-dimensional electromagnetic strong turbulence: Dependence of the statistics and dynamics of strong turbulence on the electron to ion temperature ratio

Publisher: AIP Publishing

Date: 02-2012

DOI: 10.1063/1.3684672

Abstract: The temperature ratio Ti/Te of ions to electrons affects both the ion-d ing rate and the ion-acoustic speed in plasmas. The effects of changing the ion-d ing rate and ion-acoustic speed are investigated for electrostatic strong turbulence and electromagnetic strong turbulence in three dimensions. When ion d ing is strong, density wells relax in place and act as nucleation sites for the formation of new wave packets. In this case, the density perturbations are primarily density wells supported by the ponderomotive force. For weak ion d ing, corresponding to low Ti/Te, ion-acoustic waves are launched radially outwards when wave packets dissipate at burnout, thereby increasing the level of density perturbations in the system and thus raising the level of scattering of Langmuir waves off density perturbations. Density wells no longer relax in place so renucleation at recent collapse sites no longer occurs, instead wave packets form in background low density regions, such as superpositions of troughs of propagating ion-acoustic waves. This transition is found to occur at Ti/Te ≈ 0.1. The change in behavior with Ti/Te is shown to change the bulk statistical properties, scaling behavior, spectra, and field statistics of strong turbulence. For Ti/Te& rsim0.1, the electrostatic results approach the predictions of the two-component model of Robinson and Newman, and good agreement is found for Ti/Te& rsim0.15.

Construction of multivariate surrogate sets from nonlinear data using the wavelet transform

Publisher: Elsevier BV

Date: 08-2003

DOI: 10.1016/S0167-2789(03)00136-2

Stochastic growth of localized plasma waves

Publisher: AIP Publishing

Date: 05-2001

DOI: 10.1063/1.1345505

Abstract: Localized bursty plasma waves are detected by spacecraft in many space plasmas. The large spatiotemporal scales involved imply that beam and other instabilities relax to marginal stability and that mean wave energies are low. Stochastic wave growth occurs when ambient fluctuations perturb the system, causing fluctuations about marginal stability. This yields regions where growth is enhanced and others where d ing is increased bursts are associated with enhanced growth and can occur even when the mean growth rate is negative. In stochastic growth, energy loss from the source is suppressed relative to secular growth, preserving it far longer than otherwise possible. Linear stochastic growth can operate at wave levels below thresholds of nonlinear wave-clumping mechanisms such as strong-turbulence modulational instability and is not subject to their coherence and wavelength limits. These mechanisms can be distinguished by statistics of the fields, whose strengths are lognormally distributed if stochastically growing and power-law distributed in strong turbulence. Recent applications of stochastic growth theory (SGT) are described, involving bursty plasma waves and unstable particle distributions in type III solar radio sources, the Earth’s foreshock, magnetosheath, and polar cap regions. It is shown that when combined with wave–wave processes, SGT also accounts for associated radio emissions.

Field statistics and correlation functions for stochastically growing waves

Publisher: AIP Publishing

Date: 04-2007

DOI: 10.1063/1.2715572

Abstract: Bursty waves are common in laboratory and space plasmas. This paper simulates the generation of bursty waves using stochastic differential equations, calculating the field statistics and correlation functions with and without thermal effects, linear instability, nonlinear processes, intrinsic spatiotemporal inhomogeneities (clumps), and different s ling techniques. Driven thermal waves are shown to have field statistics that agree very well with an analytic prediction (typically power-law above a low field peak near the thermal level, but whose peak can be moved to high fields with appropriate fine tuning of parameters) and are robust against changes in s ling and inclusion of clumping effects. Purely stochastically growing waves, expected to have the log normal statistics observed in multiple applications, only do so under stringent conditions and inclusion of spatiotemporal clumping effects. These conditions have similar forms to ones derived previously using analytic arguments. Deviations from a log normal can be due to s ling and clumping effects, rather than due to the nonlinear and convolution effects inferred previously. Correlation functions are predicted and observed to have an exponential decrease at small lags, with time constant equal to the inverse effective growth rate, provided stochastic effects are relatively small and sufficient averaging is possible. Extraction of the wave, stochastic, and clump parameters from observed field statistics and correlation functions appears viable. An evolutionary transition must exist between driven thermal waves and stochastically driven waves, since their field statistics have different functional forms, dependencies, and sensitivity to clump effects, but still requires identification.

Multiscale simulations of type III solar radio emission via beam-driven Langmuir waves

Publisher: AIP

Date: 2007

DOI: 10.1063/1.2778942

Imprints of coronal temperature disturbances on type III bursts

Publisher: EDP Sciences

Date: 02-2010

DOI: 10.1051/0004-6361/200913893

Wave damping as a critical phenomenon

Publisher: AIP Publishing

Date: 16-09-2004

DOI: 10.1063/1.1785789

Abstract: The evolution of a monochromatic Langmuir wave in a collisionless plasma is studied using Vlasov simulations for a wide range of initial litudes. Three types of initial electron distributions are considered: Maxwellian, Lorentzian, and dilute warm Maxwellian plus dense cold component. It is shown that there exists a critical initial litude ε* that separates the d ing and nond ing asymptotic regimes. Depending on the initial litude there are three main types of asymptotic evolution: (i) monotonic linear Landau d ing below the threshold, ε≪ε* (ii) the critical case ε≈ε*, when the field d s algebraically as E(t)∝t−3.26 (iii) at ε& ε* initial d ing followed by a period of subsequent exponential growth and then irregular oscillations about a nonzero litude. This threshold is well described as a critical phenomenon, showing power-law dependencies on the distance from the threshold not only for field quantities, which are expected of second-order phase transitions in thermodynamics, but also for temporal ones. The critical exponent for both the initial d ing and growth phases differ from those expected if the threshold is caused by O’Neil’s particle trapping in the wave potential. However, trapping affects the critical exponents well above the threshold and explains the characteristic frequency of oscillations above the threshold. It is found that for a Maxwellian plasma the threshold litude ε* corresponds to the condition that the trapping (bounce) frequency ωb equals the modulus of the theoretical Landau d ing rate |γL| at the threshold, qc=ωb/|γL|≈1. For Lorentzian and Maxwellian-plus-cold component plasmas this ratio is qLor≈0.84 and qCM≈0.83, respectively. The temporal and the field scalings are thus interrelated, suggesting that the inclusion of the temporal dimension is vital for critical phenomena in collisionless plasmas, in contrast to thermodynamic systems where the very small characteristic time to achieve equilibrium removes time from the scaling.

Electric field distributions for Langmuir waves in planetary foreshocks

Publisher: American Geophysical Union (AGU)

Date: 08-2004

DOI: 10.1029/2004JA010408

Requirements for testing stochastic wave growth in laboratory plasmas using beam-plasma experiments

Publisher: IOP Publishing

Date: 04-06-2008

DOI: 10.1088/0741-3335/50/7/074019

Corticothalamic dynamics: Structure of parameter space, spectra, instabilities, and reduced model

Publisher: American Physical Society (APS)

Date: 12-01-2012

DOI: 10.1103/PHYSREVE.85.011910

Shock-like haemodynamic responses induced in the primary visual cortex by moving visual stimuli

Publisher: The Royal Society

Date: 12-2016

DOI: 10.1098/RSIF.2016.0576

Abstract: It is shown that recently discovered haemodynamic waves can form shock-like fronts when driven by stimuli that excite the cortex in a patch that moves faster than the haemodynamic wave velocity. If stimuli are chosen in order to induce shock-like behaviour, the resulting blood oxygen level-dependent (BOLD) response is enhanced, thereby improving the signal to noise ratio of measurements made with functional magnetic resonance imaging. A spatio-temporal haemodynamic model is extended to calculate the BOLD response and determine the main properties of waves induced by moving stimuli. From this, the optimal conditions for stimulating shock-like responses are determined, and ways of inducing these responses in experiments are demonstrated in a pilot study.

Evidence for gently sloping plasma density profiles in the deep corona: Type III observations

Publisher: American Astronomical Society

Date: 11-11-2010

DOI: 10.1088/0004-637X/724/2/1099

Eigenmode structure in solar-wind langmuir waves

Publisher: American Physical Society (APS)

Date: 29-07-2008

DOI: 10.1103/PHYSREVLETT.101.051101

Unified Modeling and Analysis of Primary Generalized Seizures

Publisher: Elsevier

Date: 2008

DOI: 10.1016/B978-012373649-9.50027-2

Inconsistency of Ulysses millisecond Langmuir spikes with wave collapse in type III radio sources

Publisher: American Geophysical Union (AGU)

Date: 15-12-1995

DOI: 10.1029/95GL03513

New constraints and energy conversion efficiencies for plasma emission

Publisher: AIP Publishing

Date: 18-07-2003

DOI: 10.1063/1.1589491

Abstract: Radio emission near the electron plasma frequency fp and 2 fp due to electron beams is important in many laboratory and space applications. Langmuir waves produced as a result of these beams undergo various interactions leading to radio emission. Two categories of such interactions are decay processes involving ion acoustic waves and processes involving scattering off thermal ions (STI). In this paper energy conversion efficiencies for STI emission processes are derived. These are then compared with existing expressions for emission via decay. It is found that decay dominates STI processes when decay is able to proceed. Conditions are derived for emission near fp, and 2 fp by decay processes. These depend on whether significant nonthermal levels of L′ or S waves are produced by the initial nonlinear processes. These conditions are determined by comparing nonlinear growth rates with Landau d ing rates. It is found that where the ratio of the beam speed to the electron thermal speed exceeds roughly 3–6, L′-waves persist and emission near 2 fp can proceed. It is also found that when beams are sufficiently dense, cold, and fast, S-waves persist and emission near fp involving decay processes can proceed.

Dynamics of fundamental electromagnetic emission via beam-driven Langmuir waves

Publisher: AIP Publishing

Date: 05-2005

DOI: 10.1063/1.1906214

Abstract: The nonlinear process of electromagnetic Langmuir decay, which leads to radio emission near the plasma frequency, is studied for situations in which Langmuir waves are directly driven by an electron beam and indirectly generated via electrostatic Langmuir decays. The electromagnetic Langmuir decay is stimulated by the presence of ion-acoustic waves. An approximate method is devised for studying this emission process with axial symmetry (along the direction of beam propagation) in three spatial dimensions, based upon the Langmuir and ion-acoustic wave dynamics in one spatial dimension. Numerical studies of the fundamental electromagnetic emission starting from electron dynamics are then carried out via quasilinear theory, and the results are explored for illustrative parameters. The evolution of the fundamental transverse waves shows the combined effects of local emission and propagation away from the source. At a given location, the emission rate shows a series of peaks associated with successive electromagnetic decays of the Langmuir waves, which are either driven by the beam or produced by successive electrostatic decays. The emission rate for a given electromagnetic decay decreases with time, following an initial increase. In addition, the emission rate for a specific electromagnetic decay shows approximate dipolar form, consistent with previous analytical work. Consequently, the fundamental transverse waves emitted locally propagate approximately symmetrically in both the forward and the backward directions. Variation of the background electron to ion temperature ratio, beam injection parameters, and angular widths of the Langmuir and ion-acoustic spectra are found to affect the emission rate and, hence, the fundamental transverse wave levels. Furthermore detailed studies show that the wave numbers of the maximum emission rates are also in good agreement with an approximate prediction for simple model Langmuir and ion-acoustic spectra.

Effects of disorder in two-dimensional photonic crystal waveguides

Publisher: American Physical Society (APS)

Date: 22-08-2003

DOI: 10.1103/PHYSREVE.68.026611

The Dynamic Brain: From Spiking Neurons to Neural Masses and Cortical Fields

Publisher: Public Library of Science (PLoS)

Date: 29-08-2008

DOI: 10.1371/JOURNAL.PCBI.1000092

Spatiotemporal pattern formation in two-dimensional neural circuits: roles of refractoriness and noise

Publisher: Springer Science and Business Media LLC

Date: 18-09-2012

DOI: 10.1007/S00422-012-0518-2

Abstract: Refractoriness is one of the most fundamental states of neural firing activity, in which neurons that have just fired are unable to produce another spike, regardless of the strength of afferent stimuli. Another essential and unavoidable feature of neural systems is the existence of noise. To study the role of these essential factors in spatiotemporal pattern formation in neural systems, a spatially expended neural network model is constructed, with the dynamics of its in idual neurons capturing the three most essential states of the neural firing behavior: firing, refractory and resting, and the network topology consistent with the widely observed center-surround coupling manner in the real brain. By changing the refractory period with and without noise in a systematic way in the network, it is shown numerically and analytically that without refractoriness, or when the refractory period is smaller than a certain value, the collective activity pattern of the system consists of localized, oscillating patterns. However, when the refractory period is greater than a certain value, crescent-shaped, localized propagating patterns emerge in the presence of noise. It is further illustrated that the formation of the dynamical spiking patterns is due to a symmetry breaking mechanism, refractoriness-induced symmetry breaking that is generated by the interplay of noise and refractoriness in the network model. This refractoriness-induced symmetry breaking provides a novel perspective on the emergence of localized, spiking wave patterns or spike timing sequences as ubiquitously observed in real neural systems it therefore suggests that refractoriness may benefit neural systems in their temporal information processing, rather than limiting the performance of neurons, as has been conventionally thought. Our results also highlight the importance of considering noise in studying spatially extended neural systems, where it may facilitate the formation of spatiotemporal order.

Stochastic growth theory of spatially-averaged distributions of Langmuir fields in Earth's foreshock

Publisher: American Geophysical Union (AGU)

Date: 15-09-2001

DOI: 10.1029/2000GL012709

Reactive instabilities of lower hybrid-like waves in regions with parallel currents

Publisher: AIP Publishing

Date: 05-2011

DOI: 10.1063/1.3589800

Abstract: The dispersion and reactive instabilities of obliquely propagating waves near the lower hybrid (LH) frequency are studied in plasma carrying a current parallel to the magnetic field. Possible applications of these instabilities include magnetic reconnection regions, where LH-like waves may accelerate and heat both ions and electrons. In plasmas with a bulk drift of electrons relative to the ions at speed vd along the magnetic field, the forward and backward propagating LH modes are shown to be replaced by four LH-like modes. Reactive instabilities are discovered here for a forward propagating mode with Re(ω)≈k∥vd/2 and a backward propagating mode with Re(ω) & ~5Ωi. Numerical warm, fully electromagnetic, kinetic calculations are compared with cold plasma calculations and agree well, confirming that the discovered instabilities are reactive. In the cold plasma limit, the forward and backward propagating instabilities occur for vd below and above some thresholds, respectively.

Effects of disorder on wave propagation in two-dimensional photonic crystals

Publisher: American Physical Society (APS)

Date: 11-1999

DOI: 10.1103/PHYSREVE.60.6118

Abstract: The electromagnetic transmittance of disordered two-dimensional photonic crystals composed of circular cylinders is investigated as a function of wavelength and polarization. At short wavelengths, the transmittance shows a band structure similar to that found in the optical absorption spectrum of amorphous semiconductors, with impurity states increasingly appearing on the long wavelength side of the band gaps as the degree of disorder is increased. In the long-wavelength limit, Anderson localization of waves is found, provided that the wavelength is not so large that the random photonic crystal can be viewed as homogeneous. The localization properties in this regime are studied and an analytic expression for the dependence of the localization length on wavelength is derived. In the limit of extremely long wavelengths, the system homogenizes and can be replaced by an equivalent one with uniform effective refractive index, whose form is derived for both polarizations. Analysis of the crossover between localization and homogenization is also presented.

Prediction of Cognitive Performance and Subjective Sleepiness Using a Model of Arousal Dynamics

Publisher: SAGE Publications

Date: 04-2018

DOI: 10.1177/0748730418758454

Abstract: A model of arousal dynamics is applied to predict objective performance and subjective sleepiness measures, including lapses and reaction time on a visual Performance Vigilance Test (vPVT), performance on a mathematical addition task (ADD), and the Karolinska Sleepiness Scale (KSS). The arousal dynamics model is comprised of a physiologically based flip-flop switch between the wake- and sleep-active neuronal populations and a dynamic circadian oscillator, thus allowing prediction of sleep propensity. Published group-level experimental constant routine (CR) and forced desynchrony (FD) data are used to calibrate the model to predict performance and sleepiness. Only the studies using dim light (<15 lux) during alertness measurements and controlling for sleep and entrainment before the start of the protocol are selected for modeling. This is done to avoid the direct alerting effects of light and effects of prior sleep debt and circadian misalignment on the data. The results show that linear combination of circadian and homeostatic drives is sufficient to predict dynamics of a variety of sleepiness and performance measures during CR and FD protocols, with sleep-wake cycles ranging from 20 to 42.85 h and a 2:1 wake-to-sleep ratio. New metrics relating model outputs to performance and sleepiness data are developed and tested against group average outcomes from 7 (vPVT lapses), 5 (ADD), and 8 (KSS) experimental protocols, showing good quantitative and qualitative agreement with the data (root mean squared error of 0.38, 0.19, and 0.35, respectively). The weights of the homeostatic and circadian effects are found to be different between the measures, with KSS having stronger homeostatic influence compared with the objective measures of performance. Using FD data in addition to CR data allows us to challenge the model in conditions of both acute sleep deprivation and structured circadian misalignment, ensuring that the role of the circadian and homeostatic drives in performance is properly captured.

Unified neural field theory of brain dynamics underlying oscillations in Parkinson’s disease and generalized epilepsies

Publisher: Elsevier BV

Date: 09-2017

DOI: 10.1016/J.JTBI.2017.06.016

Abstract: The mechanisms underlying pathologically synchronized neural oscillations in Parkinson's disease (PD) and generalized epilepsies are explored in parallel via a physiologically-based neural field model of the corticothalamic-basal ganglia (CTBG) system. The basal ganglia (BG) are approximated as a single effective population and their roles in the modulation of oscillatory dynamics of the corticothalamic (CT) system and vice versa are analyzed. In addition to normal EEG rhythms, enhanced activity around 4 Hz and 20 Hz exists in the model, consistent with the characteristic frequencies observed in PD. These rhythms result from resonances in loops formed between the BG and CT populations, analogous to those that underlie epileptic oscillations in a previous CT model, and which are still present in the combined CTBG system. Dopamine depletion is argued to weaken the d ening of these loop resonances in PD, and network connections then explain the significant coherence observed between BG, thalamic, and cortical population activity around 4-8 Hz and 20 Hz. Parallels between the afferent and efferent connection sites of the thalamic reticular nucleus (TRN) and BG predict low dopamine to correspond to a reduced likelihood of tonic-clonic (grand mal) seizures, which agrees with experimental findings. Furthermore, the model predicts an increased likelihood of absence (petit mal) seizure resulting from pathologically low dopamine levels in accordance with experimental observations. Suppression of absence seizure activity is demonstrated when afferent and efferent BG connections to the CT system are strengthened, which is consistent with other CTBG modeling studies. The BG are demonstrated to have a suppressive effect on activity of the CTBG system near tonic-clonic seizure states, which provides insight into the reported efficacy of current treatments in BG circuits. Sleep states of the TRN are also found to suppress pathological PD activity in accordance with observations. Overall, the findings demonstrate strong parallels between coherent oscillations in generalized epilepsies and PD, and provide insights into possible comorbidities.

Thalamocortical changes in major depression probed by deconvolution and physiology-based modeling

Publisher: Elsevier BV

Date: 02-2011

DOI: 10.1016/J.NEUROIMAGE.2010.11.008

Abstract: Auditory event-related potentials (ERPs) have been extensively studied in patients with depression, but most studies have focused on purely phenomenological analysis methods, such as component scoring. In contrast, this study applies two recently developed physiology-based methods-fitting using a thalamocortical model of neuronal activity and waveform deconvolution - to data from a selective-attention task in four subject groups (49 patients with melancholic depression, 34 patients with non-melancholic depression, 111 participants with subclinical depressed mood, and 98 healthy controls), to yield insight into physiological differences in attentional processing between participants with major depression and controls. This approach found evidence that: participants with depressed mood, regardless of clinical status, shift from excitation in the thalamocortical system towards inhibition that clinically depressed participants have decreased relative response litude between target and standard waveforms and that patients with melancholic depression also have increased thalamocortical delays. These findings suggest possible physiological mechanisms underlying different depression subtypes, and may eventually prove useful in motivating new physiology-based diagnostic methods.

Theoretical modeling for the stereo mission

Publisher: Springer Science and Business Media LLC

Date: 11-2006

DOI: 10.1007/S11214-006-9027-8

Quantitative theory of driven nonlinear brain dynamics

Publisher: Elsevier BV

Date: 09-2012

DOI: 10.1016/J.NEUROIMAGE.2012.05.054

Abstract: Strong periodic stimuli such as bright flashing lights evoke nonlinear responses in the brain and interact nonlinearly with ongoing cortical activity, but the underlying mechanisms for these phenomena are poorly understood at present. The dominant features of these experimentally observed dynamics are reproduced by the dynamics of a quantitative neural field model subject to periodic drive. Model power spectra over a range of drive frequencies show agreement with multiple features of experimental measurements, exhibiting nonlinear effects including entrainment over a range of frequencies around the natural alpha frequency f(α), subharmonic entrainment near 2f(α), and harmonic generation. Further analysis of the driven dynamics as a function of the drive parameters reveals rich nonlinear dynamics that is predicted to be observable in future experiments at high drive litude, including period doubling, bistable phase-locking, hysteresis, wave mixing, and chaos indicated by positive Lyapunov exponents. Moreover, photosensitive seizures are predicted for physiologically realistic model parameters yielding bistability between healthy and seizure dynamics. These results demonstrate the applicability of neural field models to the new regime of periodically driven nonlinear dynamics, enabling interpretation of experimental data in terms of specific generating mechanisms and providing new tests of the theory.

Intrinsic variability and field statistics for the Vela pulsar - III. Two-component fits and detailed assessment of stochastic growth theory

Publisher: Oxford University Press (OUP)

Date: 08-2003

DOI: 10.1046/J.1365-8711.2003.06701.X

Hemodynamic Traveling Waves in Human Visual Cortex

Publisher: Public Library of Science (PLoS)

Date: 22-03-2012

DOI: 10.1371/JOURNAL.PCBI.1002435

Dynamic patterns and their interactions in networks of excitable elements

Publisher: American Physical Society (APS)

Date: 30-10-2013

DOI: 10.1103/PHYSREVE.88.042821

The spatiotemporal hemodynamic response function for depth-dependent functional imaging of human cortex

Publisher: Elsevier BV

Date: 10-2016

DOI: 10.1016/J.NEUROIMAGE.2016.06.019

Abstract: The gray matter of human cortex is characterized by depth-dependent differences in neuronal activity and connections (Shipp, 2007) as well as in the associated vasculature (Duvernoy et al., 1981). The resolution limit of functional magnetic resonance imaging (fMRI) measurements is now below a millimeter, promising the non-invasive measurement of these properties in awake and behaving humans (Muckli et al., 2015 Olman et al., 2012 Ress et al., 2007). To advance this endeavor, we present a detailed spatiotemporal hemodynamic response function (HRF) reconstructed through the use of high-resolution, submillimeter fMRI. We decomposed the HRF into directions tangential and perpendicular to the cortical surface and found that key spatial properties of the HRF change significantly with depth from the cortical surface. Notably, we found that the spatial spread of the HRF increases linearly from 4.8mm at the gray/white matter boundary to 6.6mm near the cortical surface. Using a hemodynamic model, we posit that this effect can be explained by the depth profile of the cortical vasculature, and as such, must be taken into account to properly estimate the underlying neuronal responses at different cortical depths.

Spatiotemporal hemodynamic response functions derived from physiology

Publisher: Elsevier BV

Date: 04-2014

DOI: 10.1016/J.JTBI.2013.12.027

Abstract: Probing neural activity with functional magnetic resonance imaging (fMRI) relies upon understanding the hemodynamic response to changes in neural activity. Although existing studies have extensively characterized the temporal hemodynamic response, less is understood about the spatial and spatiotemporal hemodynamic responses. This study systematically characterizes the spatiotemporal response by deriving the hemodynamic response due to a short localized neural drive, i.e., the spatiotemporal hemodynamic response function (stHRF) from a physiological model of hemodynamics based on a poroelastic model of cortical tissue. In this study, the model's boundary conditions are clarified and a resulting nonlinear hemodynamic wave equation is derived. From this wave equation, d ed linear hemodynamic waves are predicted from the stHRF. The main features of these waves depend on two physiological parameters: wave propagation speed, which depends on mean cortical stiffness, and d ing which depends on effective viscosity. Some of these predictions were applied and validated in a companion study (Aquino et al., 2012). The advantages of having such a theory for the stHRF include improving the interpretation of spatiotemporal dynamics in fMRI data improving estimates of neural activity with fMRI spatiotemporal deconvolution and enabling wave interactions between hemodynamic waves to be predicted and exploited to improve the signal to noise ratio of fMRI.

Statistics of polarization and Stokes parameters of stochastic waves

Publisher: American Physical Society (APS)

Date: 30-09-2004

DOI: 10.1103/PHYSREVE.70.036619

Calcium dependent plasticity applied to repetitive transcranial magnetic stimulation with a neural field model

Publisher: Springer Science and Business Media LLC

Date: 04-06-2016

DOI: 10.1007/S10827-016-0607-7

Abstract: The calcium dependent plasticity (CaDP) approach to the modeling of synaptic weight change is applied using a neural field approach to realistic repetitive transcranial magnetic stimulation (rTMS) protocols. A spatially-symmetric nonlinear neural field model consisting of populations of excitatory and inhibitory neurons is used. The plasticity between excitatory cell populations is then evaluated using a CaDP approach that incorporates metaplasticity. The direction and size of the plasticity (potentiation or depression) depends on both the litude of stimulation and duration of the protocol. The breaks in the inhibitory theta-burst stimulation protocol are crucial to ensuring that the stimulation bursts are potentiating in nature. Tuning the parameters of a spike-timing dependent plasticity (STDP) window with a Monte Carlo approach to maximize agreement between STDP predictions and the CaDP results reproduces a realistically-shaped window with two regions of depression in agreement with the existing literature. Developing understanding of how TMS interacts with cells at a network level may be important for future investigation.

Evidence for reformation of the Uranian bow shock: Hybrid simulations and comparisons with Voyager data

Publisher: American Geophysical Union (AGU)

Date: 04-2011

DOI: 10.1029/2010JA016057

Quasilinear-based simulations of bidirectional type III bursts

Publisher: American Geophysical Union (AGU)

Date: 10-2008

DOI: 10.1029/2008JA013255

Unified theory of monochromatic and broadband modulational and decay instabilities of Langmuir waves

Publisher: AIP Publishing

Date: 19-09-2002

DOI: 10.1063/1.1503358

Abstract: Modulational and decay instabilities driven by pump Langmuir waves are investigated using a nonlinear dispersion equation that incorporates both classes of instability simultaneously, along with the effects of finite bandwidth of the pump. A rational-function approximation of the plasma density response is then introduced to convert this equation into polynomial form. The resulting equation is used to explore the five instability types: decay, modulational, subsonic modulational, supersonic modulational, and modified decay. Growth rates, corresponding wave numbers, stability boundaries, and instability thresholds for the various instabilities are obtained analytically and verified numerically. In the case of a monochromatic pump the results generalize and clarify the limits of validity of many results in the literature. For broadband pumps, existing results for the growth rate of decay instabilities are reproduced, and it is confirmed that broadband modulational and subsonic-modulational interactions are necessarily stable. New results for the behavior of supersonic modulational instabilities are found, and it is also shown that both supersonic modulational and modified decay instabilities have random phase counterparts, the former conclusion contrasting with implications in the literature. The parameter-space transition between modulational and decay instability classes is found to be much sharper than between instability types within either of these classes.

Theory of corticothalamic brain activity in a spherical geometry: Spectra, coherence, and correlation

Publisher: American Physical Society (APS)

Date: 21-11-2017

DOI: 10.1103/PHYSREVE.96.052410

Neurophysical Modeling of Brain Dynamics

Publisher: Springer Science and Business Media LLC

Date: 24-06-2003

DOI: 10.1038/SJ.NPP.1300143

Effects of astrocytic dynamics on spatiotemporal hemodynamics: Modeling and enhanced data analysis

Publisher: Elsevier BV

Date: 02-2017

DOI: 10.1016/J.NEUROIMAGE.2016.10.023

Abstract: The effects of astrocytic dynamics on the blood oxygen-level dependent (BOLD) response are modeled. The dynamics are represented via an astrocytic response function that approximates the effects of astrocytic activity, including delay between neural activity and hemodynamic response. The astrocytic response function is incorporated into a spatiotemporal hemodynamic model to predict the BOLD response measured using functional magnetic resonance imaging (fMRI). Adding astrocytic dynamics is shown to significantly improve the ability of the model to robustly reproduce the spatiotemporal properties of the experimental data such as characteristic frequency and time-to-peak. Moreover, the results are consistent across different astrocytic response functions, thus a simple impulsive form suffices to model the effective time delay of astrocytic responses. Finally, the results yield improved estimates of previously reported hemodynamic parameters, such as natural frequency and decay rate of the flow signal, which are consistent with experimentally verified physiological limits. The techniques developed in this study will contribute to improved analysis of BOLD-fMRI data.

Changes in mode properties versus mode conversion for waves in Earth's auroral ionosphere

Publisher: American Geophysical Union (AGU)

Date: 12-2011

DOI: 10.1029/2011JA016956

Physiologically based calculation of steady-state evoked potentials and cortical wave velocities

Publisher: Springer Science and Business Media LLC

Date: 26-10-2007

DOI: 10.1007/S00422-007-0191-Z

Abstract: Steady-state evoked potentials (SSEPs) elicited by sinusoidal stimuli are predicted from a physiologically-based model, including bielectrode and volume conduction effects. Comparison with visual SSEPs yields constraints on phase and latency of the retinothalamic transfer function that are consistent with experiment. Predictions of phase velocities measured as SSEPs cross the cortex are consistent with low values measured for slow waves in sleep, while resonant behavior induced by corticothalamic loops, especially near the alpha peak, contributes to wide scatter in waking-state phase velocity measurements comparable to effects from volume conduction. The common use of bielectrode derivations to compensate for volume conduction effects is examined and shown to be incomplete, tending to lead to underestimates of phase velocity, especially at low frequencies and near the alpha peak, due to incorrect elimination of true long-wavelength contributions to the SSEP.

Evidence for wind-like regions, acceleration of shocks in the deep corona, and relevance of 1/f dynamic spectra to coronal type II bursts

Publisher: American Astronomical Society

Date: 26-03-2008

DOI: 10.1086/587980

K-complexes, spindles, and ERPs as impulse responses: unification via neural field theory

Publisher: Springer Science and Business Media LLC

Date: 03-2017

DOI: 10.1007/S00422-017-0713-2

Abstract: To interrelate K-complexes, spindles, evoked response potentials (ERPs), and spontaneous electroencephalography (EEG) using neural field theory (NFT), physiology-based NFT of the corticothalamic system is used to model cortical excitatory and inhibitory populations and thalamic relay and reticular nuclei. The impulse response function of the model is used to predict the responses to impulses, which are compared with transient waveforms in sleep studies. Fits to empirical data then allow underlying brain physiology to be inferred and compared with other waves. Spontaneous K-complexes, spindles, and other transient waveforms can be reproduced using NFT by treating them as evoked responses to impulsive stimuli with brain parameters appropriate to spontaneous EEG in sleep stage 2. Using this approach, spontaneous K-complexes and sleep spindles can be analyzed using the same single theory as previously been used to account for waking ERPs and other EEG phenomena. As a result, NFT can explain a wide variety of transient waveforms that have only been phenomenologically classified to date. This enables noninvasive fitting to be used to infer underlying physiological parameters. This physiology-based model reproduces the time series of different transient EEG waveforms it has previously reproduced experimental EEG spectra, and waking ERPs, and many other observations, thereby unifying transient sleep waveforms with these phenomena.

New regimes of stochastic wave growth

Publisher: American Physical Society (APS)

Date: 12-2004

DOI: 10.1103/PHYSREVLETT.93.235003

Steady States and Global Dynamics of Electrical Activity in the Cerebral Cortex.

Publisher: American Physical Society (APS)

Date: 09-1998

DOI: 10.1103/PHYSREVE.58.3557

Propagation of radiation in fluctuating multiscale plasmas. II. Kinetic simulations

Publisher: AIP Publishing

Date: 11-2012

DOI: 10.1063/1.4767641

Abstract: A numerical algorithm is developed and tested that implements the kinetic treatment of electromagnetic radiation propagating through plasmas whose properties have small scale fluctuations, which was developed in a companion paper. This method incorporates the effects of refraction, d ing, mode structure, and other aspects of large-scale propagation of electromagnetic waves on the distribution function of quanta in position and wave vector, with small-scale effects of nonuniformities, including scattering and mode conversion approximated as causing drift and diffusion in wave vector. Numerical solution of the kinetic equation yields the distribution function of radiation quanta in space, time, and wave vector. Simulations verify the convergence, accuracy, and speed of the methods used to treat each term in the equation. The simulations also illustrate the main physical effects and place the results in a form that can be used in future applications.

Propagation of radiation in fluctuating multiscale plasmas. I. Kinetic theory

Publisher: AIP Publishing

Date: 11-2012

DOI: 10.1063/1.4767640

Abstract: A theory for propagation of radiation in a large scale plasma with small scale fluctuations is developed using a kinetic description in terms of the probability distribution function of the radiation in space, time, and wavevector space. Large scale effects associated with spatial variations in the plasma density and refractive index of the plasma wave modes and small scale effects such as scattering of radiation by density clumps in fluctuating plasma, spontaneous emission, d ing, and mode conversion are included in a multiscale kinetic description of the radiation. Expressions for the Stokes parameters in terms of the probability distribution function of the radiation are used to enable radiation properties such as intensity and polarization to be calculated.

Prediction of background levels for the Wind WAVES instrument and implications for the galactic background radiation

Publisher: American Geophysical Union (AGU)

Date: 06-2010

DOI: 10.1029/2009JA014714

Discovery Projects - Grant ID: DP0342542

Start Date: 02-2003

End Date: 12-2008

Amount: $455,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0877816

Start Date: 12-2008

End Date: 12-2011

Amount: $290,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP110101587

Start Date: 08-2011

End Date: 12-2013

Amount: $330,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP130100437

Start Date: 03-2013

End Date: 09-2016

Amount: $375,000.00

Funder: Australian Research Council

Federation Fellowships - Grant ID: FF0883155

Start Date: 12-2008

End Date: 12-2013

Amount: $819,365.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0208527

Start Date: 06-2002

End Date: 12-2005

Amount: $527,000.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP0667442

Start Date: 07-2006

End Date: 12-2010

Amount: $208,500.00

Funder: Australian Research Council

Australian Laureate Fellowships - Grant ID: FL140100025

Start Date: 02-2015

End Date: 12-2020

Amount: $2,617,462.00

Funder: Australian Research Council

Federation Fellowships - Grant ID: FF0348240

Start Date: 09-2003

End Date: 12-2008

Amount: $1,450,370.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE0668467

Start Date: 02-2006

End Date: 06-2008

Amount: $620,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP170101778

Start Date: 2017

End Date: 12-2019

Amount: $370,500.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP0346991

Start Date: 2003

End Date: 11-2005

Amount: $184,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0556288

Start Date: 09-2005

End Date: 12-2008

Amount: $300,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0879522

Start Date: 08-2008

End Date: 10-2011

Amount: $470,000.00

Funder: Australian Research Council

Special Research Initiatives - Grant ID: SR0354494

Start Date: 2004

End Date: 02-2004

Amount: $10,000.00

Funder: Australian Research Council

Special Research Initiatives - Grant ID: SR0354716

Start Date: 12-2003

End Date: 12-2004

Amount: $10,000.00

Funder: Australian Research Council

ARC Centres Of Excellence - Grant ID: CE140100007

Start Date: 06-2014

End Date: 12-2021

Amount: $20,000,000.00

Funder: Australian Research Council

Research Networks - Grant ID: RN0460006

Start Date: 07-2004

End Date: 06-2009

Amount: $1,500,000.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP100200742

Start Date: 03-2011

End Date: 12-2013

Amount: $345,000.00

Funder: Australian Research Council