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Publisher: Oxford University Press (OUP)
Date: 25-03-2015
DOI: 10.1093/MNRAS/STV381
Publisher: Oxford University Press (OUP)
Date: 21-12-2020
Abstract: The Parkes telescope has been monitoring 286 radio pulsars approximately monthly since 2007 at an observing frequency of 1.4 GHz. The wide dispersion measure (DM) range of the pulsar s le and the uniformity of the observing procedure make the data set extremely valuable for studies of flux density variability and the interstellar medium (ISM). Here, we present flux density measurements and modulation indices of these pulsars over this period. We derive the structure function from the light curves and discuss the contributions to it from measurement noise, intrinsic variability, and interstellar scintillation. Despite a large scatter, we show that the modulation index is inversely correlated with DM, and can be generally described by a power law with an index of ∼−0.7 covering DMs from ∼10 to 1000 cm−3 pc. We present refractive time-scales and/or lower limits for a group of 42 pulsars. These often have values significantly different from theoretical expectations, indicating the complex nature of the ISM along in idual lines of sight. In particular, local structures and non-Kolmogorov density fluctuations are likely playing important roles in the observed flux density variation of many of these pulsars.
Publisher: American Astronomical Society
Date: 03-2011
Publisher: Oxford University Press (OUP)
Date: 08-06-2012
Publisher: Elsevier BV
Date: 12-1983
DOI: 10.1016/0165-3806(83)90213-4
Abstract: This study examines the relationship between plasma proteins in blood and in CSF in the developing brain of sheep fetuses between 30 and 60 days gestation. Five proteins account for the very high concentration of protein in fetal CSF (over 1000 mg/100 mg/100 ml at 30 days): alpha-feto-protein, fetuin, albumin, alpha 1-antitrypsin and transferrin the concentration of each protein is similar in lateral and IVth ventricular CSF at 30 days. By 40 days there is considerable decrease in protein concentration in lateral ventricular CSF. At this age in the IVth ventricle the overall total was unchanged, although there were changes in concentration of in idual proteins. At 60 days the concentration of each protein in both compartments had fallen below that at 40 days the marked concentration difference between lateral and IVth ventricular CSF was still present. Experiments using i.v. [125I]- or [3H] labeled plasma proteins in 30-40-day fetuses showed that very little protein penetrated into lateral ventricular CSF by 3-5 h after injection in the same experiments [125I]albumin reached a CSF lasma ratio of about 15% in the IVth ventricle (compared with 55% for the natural steady state). Autoradiographic studies carried out on material from the same animals did not give evidence for transfer of labeled protein across the choroid plexuses although any such penetration may have been below the threshold of the method. Other explanations for the high concentration of protein in CSF that were considered include penetration via cerebral vessels and synthesis of plasma proteins by choroid plexus epithelial cells or neurons within the brain.
Publisher: Oxford University Press (OUP)
Date: 16-06-2016
Publisher: American Astronomical Society
Date: 27-11-2012
Publisher: Oxford University Press (OUP)
Date: 04-2011
Publisher: Oxford University Press (OUP)
Date: 04-12-2019
Abstract: By analysing the data acquired from the Parkes 64-m radio telescope at 1369 MHz, we report on the phase-stationary non-drift litude modulation observed in PSR J1048−5832. The high-sensitivity observations revealed that the central and trailing components of the pulse profile of this pulsar switch between a strong mode and a weak mode periodically. However, the leading component remains unchanged. Polarization properties of the strong and weak modes are investigated. Considering the similarity to mode changing, we argue that the periodic litude modulation in PSR J1048−5832 is periodic mode changing. The fluctuation spectral analysis showed that the modulation period is very short (∼2.1 s or 17P1), where P1 is the rotation period of the pulsar. We find that this periodic litude modulation is hard to explain by existing models that account for the periodic phenomena in pulsars like sub-pulse drifting.
Publisher: Oxford University Press (OUP)
Date: 17-09-2014
Publisher: American Physical Society (APS)
Date: 05-11-2018
Publisher: Oxford University Press (OUP)
Date: 27-07-2023
Abstract: We present a comprehensive study of the rotational and emission properties of PSR J0738−4042 using a combination of observations taken by the Deep Space Network, Hartebeesthoek, Parkes (Murriyang) and Molonglo observatories between 1972 and 2023. Our timing of the pulsar is motivated by previously reported profile/spin-down events that occurred in 2005 September and 2015 December, which result in an anomalously large braking index of n = 23 300 ± 1800. Using a Gaussian process regression framework, we develop continuous models for the evolution of the pulsar spin-down rate ($\\dot{\\nu }$) and profile shape. We find that the pulse profile variations are similar regardless of radio observing frequency and polarization. Small-scale differences can be ascribed to changes in the interstellar medium along the line of sight and frequency-dependent changes in magnetospheric radio emission height. No new correlated spin-down or profile events were identified in our extended data set. However, we found that the disappearance of a bright emission component in the leading edge of archival profiles between 1981 and 1988 was not associated with a substantial change in $\\dot{\\nu }$. This marks a notable departure from the previous profile/spin-down events in this pulsar. We discuss the challenges these observations pose for physical models and conclude that interactions between the pulsar and in-falling asteroids or a form of magnetospheric state-switching with a long periodicity are plausible explanations.
Publisher: AIP
Date: 2011
DOI: 10.1063/1.3615151
Publisher: American Astronomical Society
Date: 02-2023
Abstract: In 2018 an ultra–wide-bandwidth low-frequency (UWL) receiver was installed on the 64 m Parkes Radio Telescope, enabling observations with an instantaneous frequency coverage from 704 to 4032 MHz. Here we present the analysis of a 3 yr data set of 35 ms pulsars observed with the UWL by the Parkes Pulsar Timing Array, using wide-band timing methods. The two key differences compared to typical narrowband methods are (1) generation of two-dimensional templates accounting for pulse shape evolution with frequency and (2) simultaneous measurements of the pulse time of arrival (TOA) and dispersion measure (DM). This is the first time that wide-band timing has been applied to a uniform data set collected with a single large fractional bandwidth receiver, for which such techniques were originally developed. As a result of our study, we present a set of profile evolution models and new timing solutions, including initial noise analysis. Precision of our TOA and DM measurements is in the range of 0.005–2.08 μ s and (0.043–14.24) × 10 −4 cm −3 pc, respectively, with 94% of the pulsars achieving a median TOA uncertainty of less than 1 μ s.
Publisher: Oxford University Press (OUP)
Date: 25-03-2017
DOI: 10.1093/MNRAS/STX729
Publisher: Springer Science and Business Media LLC
Date: 15-03-2016
Publisher: The American Association of Immunologists
Date: 2015
Abstract: Inflammasomes are large protein complexes induced by a wide range of microbial, stress, and environmental stimuli that function to induce cell death and inflammatory cytokine processing. Formation of an inflammasome involves dramatic relocalization of the inflammasome adapter protein apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) into a single speck. We have developed a flow cytometric assay for inflammasome formation, time of flight inflammasome evaluation, which detects the change in ASC distribution within the cell. The transit of ASC into the speck is detected by a decreased width or increased height of the pulse of emitted fluorescence. This assay can be used to quantify native inflammasome formation in subsets of mixed cell populations ex vivo. It can also provide a rapid and sensitive technique for investigating molecular interactions in inflammasome formation, by comparison of wild-type and mutant proteins in inflammasome reconstitution experiments.
Publisher: Cambridge University Press (CUP)
Date: 09-2017
DOI: 10.1017/S1743921317008559
Abstract: PSR B1828–11 is a young pulsar once thought to be undergoing free precession and recently found instead to be switching magnetospheric states in tandem with spin-down changes. Here we show the two extreme states of the mode-changing found for this pulsar and comment briefly on its interpretation.
Publisher: Oxford University Press (OUP)
Date: 12-10-2019
Abstract: In this paper, we describe the International Pulsar Timing Array second data release, which includes recent pulsar timing data obtained by three regional consortia: the European Pulsar Timing Array, the North American Nanohertz Observatory for Gravitational Waves, and the Parkes Pulsar Timing Array. We analyse and where possible combine high-precision timing data for 65 millisecond pulsars which are regularly observed by these groups. A basic noise analysis, including the processes which are both correlated and uncorrelated in time, provides noise models and timing ephemerides for the pulsars. We find that the timing precisions of pulsars are generally improved compared to the previous data release, mainly due to the addition of new data in the combination. The main purpose of this work is to create the most up-to-date IPTA data release. These data are publicly available for searches for low-frequency gravitational waves and other pulsar science.
Publisher: Oxford University Press (OUP)
Date: 28-07-2016
Publisher: Oxford University Press (OUP)
Date: 17-06-2017
Publisher: Oxford University Press (OUP)
Date: 24-12-2017
Publisher: Springer Science and Business Media LLC
Date: 08-12-2015
DOI: 10.1038/NGEO2305
Publisher: Oxford University Press (OUP)
Date: 13-08-2012
Publisher: American Astronomical Society
Date: 29-06-2023
Abstract: Pulsar timing arrays aim to detect nanohertz-frequency gravitational waves (GWs). A background of GWs modulates pulsar arrival times and manifests as a stochastic process, common to all pulsars, with a signature spatial correlation. Here we describe a search for an isotropic stochastic gravitational-wave background (GWB) using observations of 30 millisecond pulsars from the third data release of the Parkes Pulsar Timing Array (PPTA), which spans 18 yr. Using current Bayesian inference techniques we recover and characterize a common-spectrum noise process. Represented as a strain spectrum h c = A ( f / 1 yr − 1 ) α , we measure A = 3.1 − 0.9 + 1.3 × 10 − 15 and α = −0.45 ± 0.20, respectively (median and 68% credible interval). For a spectral index of α = −2/3, corresponding to an isotropic background of GWs radiated by inspiraling supermassive black hole binaries, we recover an litude of A = 2.04 − 0.22 + 0.25 × 10 − 15 . However, we demonstrate that the apparent signal strength is time-dependent, as the first half of our data set can be used to place an upper limit on A that is in tension with the inferred common-spectrum litude using the complete data set. We search for spatial correlations in the observations by hierarchically analyzing in idual pulsar pairs, which also allows for significance validation through randomizing pulsar positions on the sky. For a process with α = −2/3, we measure spatial correlations consistent with a GWB, with an estimated false-alarm probability of p ≲ 0.02 (approx. 2 σ ). The long timing baselines of the PPTA and the access to southern pulsars will continue to play an important role in the International Pulsar Timing Array.
Publisher: American Astronomical Society
Date: 29-06-2023
Abstract: The noise in millisecond pulsar (MSP) timing data can include contributions from observing instruments, the interstellar medium, the solar wind, solar system ephemeris errors, and the pulsars themselves. The noise environment must be accurately characterized in order to form the null hypothesis from which signal models can be compared, including the signature induced by nanohertz-frequency gravitational waves (GWs). Here we describe the noise models developed for each of the MSPs in the Parkes Pulsar Timing Array (PPTA) third data release, which have been used as the basis of a search for the isotropic stochastic GW background. We model pulsar spin noise, dispersion measure variations, scattering variations, events in the pulsar magnetospheres, solar wind variability, and instrumental effects. We also search for new timing model parameters and detected Shapiro delays in PSR J0614−3329 and PSR J1902−5105. The noise and timing models are validated by testing the normalized and whitened timing residuals for Gaussianity and residual correlations with time. We demonstrate that the choice of noise models significantly affects the inferred properties of a common-spectrum process. Using our detailed models, the recovered common-spectrum noise in the PPTA is consistent with a power law with a spectral index of γ = 13/3, the value predicted for a stochastic GW background from a population of supermassive black hole binaries driven solely by GW emission.
Publisher: American Astronomical Society
Date: 14-07-2020
Publisher: American Association for the Advancement of Science (AAAS)
Date: 18-10-2013
Abstract: Gravitational waves, predicted by General Relativity, are expected to be produced when very massive bodies, such as black holes, merge together. Shannon et al. (p. 334 ) used data from the Parkes Pulsar Timing Array project to estimate the gravitational wave background produced by pairs of supermassive black holes (those with masses between 10 6 and 10 11 that of the Sun) in merging galaxies. The results can be used to test models of the supermassive black hole population.
Publisher: Oxford University Press (OUP)
Date: 21-12-2012
Publisher: American Astronomical Society
Date: 02-04-2012
Publisher: Informa UK Limited
Date: 19-04-2018
DOI: 10.1080/07391102.2017.1313780
Abstract: Ligand field molecular mechanics (LFMM) parameters have been benchmarked for copper (II) bound to the amyloid-β
Publisher: American Astronomical Society
Date: 20-05-2019
Abstract: We describe PSR J1926−0652, a pulsar recently discovered with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Using sensitive single-pulse detections from FAST and long-term timing observations from the Parkes 64 m radio telescope, we probed phenomena on both long and short timescales. The FAST observations covered a wide frequency range from 270 to 800 MHz, enabling in idual pulses to be studied in detail. The pulsar exhibits at least four profile components, short-term nulling lasting from 4 to 450 pulses, complex subpulse drifting behaviors and intermittency on scales of tens of minutes. While the average band spacing P 3 is relatively constant across different bursts and components, significant variations in the separation of adjacent bands are seen, especially near the beginning and end of a burst. Band shapes and slopes are quite variable, especially for the trailing components and for the shorter bursts. We show that for each burst the last detectable pulse prior to emission ceasing has different properties compared to other pulses. These complexities pose challenges for the classic carousel-type models.
Publisher: Cambridge University Press (CUP)
Date: 2020
DOI: 10.1017/PASA.2020.11
Abstract: We describe 14 yr of public data from the Parkes Pulsar Timing Array (PPTA), an ongoing project that is producing precise measurements of pulse times of arrival from 26 millisecond pulsars using the 64-m Parkes radio telescope with a cadence of approximately 3 weeks in three observing bands. A comprehensive description of the pulsar observing systems employed at the telescope since 2004 is provided, including the calibration methodology and an analysis of the stability of system components. We attempt to provide full accounting of the reduction from the raw measured Stokes parameters to pulse times of arrival to aid third parties in reproducing our results. This conversion is encapsulated in a processing pipeline designed to track provenance. Our data products include pulse times of arrival for each of the pulsars along with an initial set of pulsar parameters and noise models. The calibrated pulse profiles and timing template profiles are also available. These data represent almost 21 000 h of recorded data spanning over 14 yr. After accounting for processes that induce time-correlated noise, 22 of the pulsars have weighted root-mean-square timing residuals of $ \\!\\!1\\,\\mu\\text{s}$ in at least one radio band. The data should allow end users to quickly undertake their own gravitational wave analyses, for ex le, without having to understand the intricacies of pulsar polarisation calibration or attain a mastery of radio frequency interference mitigation as is required when analysing raw data files.
Publisher: Oxford University Press (OUP)
Date: 14-06-2018
Publisher: American Astronomical Society
Date: 02-12-2011
Publisher: American Astronomical Society
Date: 05-06-2012
Publisher: American Astronomical Society
Date: 08-10-2012
Publisher: Oxford University Press (OUP)
Date: 26-05-2016
Publisher: Oxford University Press (OUP)
Date: 28-06-2019
Abstract: The Parkes Pulsar Timing Array (PPTA) project monitors two dozen millisecond pulsars (MSPs) in order to undertake a variety of fundamental physics experiments using the Parkes 64-m radio telescope. Since 2017 June, we have been undertaking commensal searches for fast radio bursts (FRBs) during the MSP observations. Here, we report the discovery of four FRBs (171209, 180309, 180311, and 180714). The detected events include an FRB with the highest signal-to-noise ratio ever detected at the Parkes Observatory, which exhibits unusual spectral properties. All four FRBs are highly polarized. We discuss the future of commensal searches for FRBs at Parkes.
Publisher: Oxford University Press (OUP)
Date: 09-12-2016
Publisher: American Astronomical Society
Date: 08-2021
Publisher: Oxford University Press (OUP)
Date: 22-02-2018
DOI: 10.1093/MNRAS/STY470
Publisher: American Astronomical Society
Date: 18-01-2013
Publisher: Oxford University Press (OUP)
Date: 21-07-2014
Publisher: American Astronomical Society
Date: 11-2022
Abstract: High-sensitivity interstellar scintillation and polarization observations of PSR B0656+14 made at three epochs over a year using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) show that the scattering is dominated by two different compact regions. We identify the one nearer to the pulsar with the shell of the Monogem Ring, thereby confirming the association. The other is probably associated with the Local Bubble. We find that the observed position angles of the pulsar spin axis and the spatial velocity are significantly different, with a separation of 19.°3 ± 0.°8, inconsistent with a previously published near-perfect alignment of 1° ± 2°. The two independent scattering regions are clearly defined in the secondary spectra, which show two strong forward parabolic arcs. The arc curvatures imply that the scattering screens corresponding to the outer and inner arcs are located approximately 28 pc from PSR B0656+14 and 185 pc from the Earth, respectively. Comparison of the observed Doppler profiles with electromagnetic simulations shows that both scattering regions are mildly anisotropic. For the outer arc, we estimate the anisotropy A R to be approximately 1.3, with the scattering irregularities aligned parallel to the pulsar velocity. For the outer arc, we compare the observed delay profiles with delay profiles computed from a theoretical strong-scattering model. Our results suggest that the spatial spectrum of the scattering irregularities in the Monogem Ring is flatter than Kolmogorov, but further observations are required to confirm this.
Publisher: EDP Sciences
Date: 03-2023
DOI: 10.1051/0004-6361/202244418
Abstract: Context. PSR J1910−5959A is a binary millisecond pulsar in a 0.837 day circular orbit around a helium white dwarf (HeWD) companion. The position of this pulsar is 6.3 arcmin (∼74 core radii) away from the optical centre of the globular cluster (GC) NGC 6752. Given the large offset, the association of the pulsar with the GC has been debated. Aims. We aim to obtain precise measurements of the masses of the stars in the system along with secular orbital parameters, which will help identify if the system belongs to the GC. Methods. We have made use of archival Parkes 64 m ‘Murriyang’ telescope data and carried out observations with the MeerKAT telescope with different backends and receivers over the last two decades. Pulse times of arrival were obtained from these using standard pulsar data reduction techniques and analysed using state-of-the-art Bayesian pulsar timing techniques. We also performed an analysis of the pulsar’s total intensity and polarisation profile to understand the interstellar scattering along the line of sight, and we determined the pulsar’s geometry by fitting the rotating vector model to the polarisation data. Results. We obtain precise measurements of several post-Keplerian parameters: the range, r = 0.202(6) T ⊙ , and shape, s = 0.999823(4), of the Shapiro delay, from which we infer: the orbital inclination to be 88.9 −0.14 +0.15 deg the masses of the pulsar and the companion to be 1.55(7) M ⊙ and 0.202(6) M ⊙ , respectively a secular change in the orbital period Ṗ b = −53 −6.0 +7.4 × 10 −15 s s −1 that proves the GC association and a secular change in the projected semi-major axis of the pulsar, ẋ = −40.7 −8.2 +7.3 × 10 −16 s s −1 , likely caused by the spin–orbit interaction from a misaligned HeWD spin, at odds with the likely isolated binary evolution of the system. We also discuss some theoretical models for the structure and evolution of white dwarfs in neutron star–white dwarf binaries, using PSR J1910−5959A’s companion as a test bed. Conclusions. PSR J1910−5959A is a rare system for which several parameters of both the pulsar and the HeWD companion can be accurately measured. As such, it is a test bed for discriminating between alternative models of HeWD structure and cooling.
Publisher: IOP Publishing
Date: 04-11-2013
Publisher: Elsevier BV
Date: 08-2017
DOI: 10.1016/J.JINORGBIO.2017.05.003
Abstract: Ligand field molecular mechanics (LFMM) and semi-empirical Parametric Model 7 (PM7) methods are applied to a series of six Pt
Publisher: Springer Science and Business Media LLC
Date: 12-2015
Publisher: Oxford University Press (OUP)
Date: 06-11-2020
Abstract: Pulsar timing array projects measure the pulse arrival times of millisecond pulsars for the primary purpose of detecting nanohertz-frequency gravitational waves. The measurements include contributions from a number of astrophysical and instrumental processes, which can either be deterministic or stochastic. It is necessary to develop robust statistical and physical models for these noise processes because incorrect models diminish sensitivity and may cause a spurious gravitational wave detection. Here we characterize noise processes for the 26 pulsars in the second data release of the Parkes Pulsar Timing Array using Bayesian inference. In addition to well-studied noise sources found previously in pulsar timing array data sets such as achromatic timing noise and dispersion measure variations, we identify new noise sources including time-correlated chromatic noise that we attribute to variations in pulse scattering. We also identify ‘exponential dip’ events in four pulsars, which we attribute to magnetospheric effects as evidenced by pulse profile shape changes observed for three of the pulsars. This includes an event in PSR J1713+0747, which had previously been attributed to interstellar propagation. We present noise models to be used in searches for gravitational waves. We outline a robust methodology to evaluate the performance of noise models and identify unknown signals in the data. The detection of variations in pulse profiles highlights the need to develop efficient profile domain timing methods.
Publisher: American Physical Society (APS)
Date: 22-02-2022
Publisher: Oxford University Press (OUP)
Date: 25-01-2013
DOI: 10.1093/MNRAS/STS657
Publisher: Oxford University Press (OUP)
Date: 10-2018
Publisher: American Astronomical Society
Date: 06-2022
Abstract: Pulsar timing array experiments have recently reported strong evidence for a common-spectrum stochastic process with a strain spectral index consistent with that expected of a nanohertz-frequency gravitational-wave background, but with negligible yet non-zero evidence for spatial correlations required for a definitive detection. However, it was pointed out by the Parkes Pulsar Timing Array (PPTA) collaboration that the same models used in recent analyses resulted in strong evidence for a common-spectrum process in simulations where none is present. In this work, we introduce a methodology to distinguish pulsar power spectra with the same litude from noise power spectra of similar but distinct litudes. The former is the signature of a spatially uncorrelated pulsar term of a nanohertz gravitational-wave background, whereas the latter could represent ensemble pulsar noise properties. We test the methodology on simulated data sets. We find that the reported common process in PPTA pulsars is indeed consistent with the spectral feature of a pulsar term. We recommend this methodology as one of the validity tests that the real astrophysical and cosmological backgrounds should pass, as well as for inferences about the spatially uncorrelated component of the background.
Publisher: Cambridge University Press (CUP)
Date: 08-2012
DOI: 10.1017/S1743921312024908
Abstract: As part of the Parkes Pulsar Timing Array (PPTA) project, frequent observations of 20 millisecond pulsars are made using the Parkes 64-m radio telescope. Variations in the mean position angle of the 20 millisecond pulsars can be studied by the PPTA data being recorded in full-polarization mode. We briefly discuss these results.
Publisher: Elsevier BV
Date: 09-1999
Publisher: Oxford University Press (OUP)
Date: 05-2015
DOI: 10.1093/MNRAS/STV804
Publisher: American Astronomical Society
Date: 07-07-2011
Publisher: CSIRO
Date: 2018
Publisher: Cambridge University Press (CUP)
Date: 2023
DOI: 10.1017/PASA.2023.36
Abstract: We present the third data release from the Parkes Pulsar Timing Array (PPTA) project. The release contains observations of 32 pulsars obtained using the 64-m Parkes “Murriyang” radio telescope. The data span is up to 18 years with a typical cadence of 3 weeks. This data release is formed by combining an updated version of our second data release with ∼ 3 years of more recent data primarily obtained using an ultra-wide-bandwidth receiver system that operates between 704 and 4032 MHz. We provide calibrated pulse profiles, flux-density dynamic spectra, pulse times of arrival, and initial pulsar timing models. We describe methods for processing such wide-bandwidth observations, and compare this data release with our previous release.
Publisher: Wiley
Date: 13-07-2012
Abstract: Diazido Pt(IV) complexes are inert stable prodrugs that can be photoactivated to produce Pt(II) species with promising anticancer activity. Our studies of the photochemistry of Pt(IV) complexes, [Pt(X)(2) (Y)(2) (Z)(2) ](0/-1) (X=N-ligands (NH(3) , pyridine, etc.)/S(CH(3) )(2) /H(-) , Y=(pseudo)halogen (N(3) (-) , I(-) ), Z=OR(-) , R=H, Ac) by time-dependent density functional theory (TDDFT) show close agreement with spectroscopic data. Broad exploration of cis/trans geometries, trans influences, the nature of the OR(-) and (pseudo)halogen ligands, electron-withdrawing/donating/delocalising substituents on the N-ligands, and intramolecular H bonds shows that: 1) the design of platinum(IV) complexes with intense bands shifted towards longer wavelengths (from 289 to ∼330 nm) can be achieved by introducing intramolecular H bonds involving the OH ligands and 2-hydroxyquinoline or by iodido ligands 2) mesomeric electron-withdrawing substituents on pyridine result in low-energy absorption with significant intensity in the visible region and 3) the distinct makeup of the molecular orbitals involved in the electronic transitions for cis/trans-{Pt(N(3) )(2) } isomers results in different photoproducts. In general, the comparison of the optimised geometries shows that Pt(IV) complexes with longer PtL bonds are more likely to undergo photoreduction with longer-wavelength light. The novel complex trans,trans,trans-[Pt(N(3) )(2) (OH)(2) (NH(3) )(4-nitropyridine)] with predicted absorption in the visible region has been synthesised. The experimental UV/Vis spectrum in aqueous solution correlates well with the intense band in the computed spectrum, whereas the overlay in the low-energy region can be improved by a solvent model. This combined computational and experimental study shows that TDDFT can be used to tune the coordination environment for optimising photoactive Pt(IV) compounds as anticancer agents.
Publisher: American Astronomical Society
Date: 22-08-2017
Publisher: Oxford University Press (OUP)
Date: 05-03-2012
Publisher: American Astronomical Society
Date: 20-09-2013
Publisher: Cambridge University Press (CUP)
Date: 2020
DOI: 10.1017/PASA.2020.2
Abstract: We describe an ultra-wide-bandwidth, low-frequency receiver recently installed on the Parkes radio telescope. The receiver system provides continuous frequency coverage from 704 to 4032 MHz. For much of the band ( ${\\sim}60\\%$ ), the system temperature is approximately 22 K and the receiver system remains in a linear regime even in the presence of strong mobile phone transmissions. We discuss the scientific and technical aspects of the new receiver, including its astronomical objectives, as well as the feed, receiver, digitiser, and signal processor design. We describe the pipeline routines that form the archive-ready data products and how those data files can be accessed from the archives. The system performance is quantified, including the system noise and linearity, beam shape, antenna efficiency, polarisation calibration, and timing stability.
Publisher: Oxford University Press (OUP)
Date: 20-11-2014
Publisher: World Scientific Pub Co Pte Lt
Date: 2013
DOI: 10.1142/S0218271813410071
Abstract: More than 2000 pulsars are now known. These pulsars may be ided into a number of different classes according to their period, period derivative, binary properties, emission characteristics and so on. Some important classes have relatively few members, e.g. double-neutron-star binary systems, and so continued searches for currently unknown pulsars are important. Such searches are being undertaken at various observatories around the world. Somewhat unexpectedly, the Fermi Gamma-ray Observatory, has proved to be an efficient pulsar detector, especially for millisecond pulsars (MSPs). The great stability of pulsar periods, especially for MSPs, leads to a number of important applications of pulsar timing. The detection and study of relativistic orbit perturbations in double-neutron-star systems has proved to be a powerful tool with measurements of the original binary pulsar, PSR B1913+16, and more recently the double pulsar, PSR J0737-3039A/B, showing that Einstein's general theory of relativity accurately describes these gravitational interactions. Direct detection of gravitational waves using pulsar timing is close to being achieved with the development of pulsar timing arrays (PTAs) in Europe, North America and Australia. Combining data from these PTAs to form the International Pulsar Timing Array (IPTA) will lead to improved significance of such a detection. Ultimately, detailed study of gravitational-wave sources will be possible using future large radio telescopes such as FAST and the SKA.
Publisher: American Chemical Society (ACS)
Date: 10-02-2017
DOI: 10.1021/ACS.INORGCHEM.6B02793
Abstract: Six-coordinate, rigorously octahedral d
Publisher: EDP Sciences
Date: 11-2022
DOI: 10.1051/0004-6361/202244825
Abstract: The double pulsar PSR J0737−3039A/B has offered a wealth of gravitational experiments in the strong-field regime, all of which general relativity has passed with flying colours. In particular, among current gravity experiments that test photon propagation, the double pulsar probes the strongest spacetime curvature. Observations with MeerKAT and, in the future, the Square Kilometre Array (SKA) can greatly improve the accuracy of current tests and facilitate tests of next-to-leading-order (NLO) contributions in both orbital motion and signal propagation. We present our timing analysis of new observations of PSR J0737−3039A, made using the MeerKAT telescope over the last three years. The increased timing precision offered by MeerKAT yields a measurement of Shapiro delay parameter s that it twice as good, and an improved mass measurements compared to previous studies. In addition, our results provide an independent confirmation of the NLO signal propagation effects and already surpass the previous measurement from 16 yr data by a factor of 1.65. These effects include the retardation effect due to the movement of the companion and the deflection of the signal by the gravitational field of the companion. We also investigate the novel effects that have been expected. For instance, we search for potential profile variations near superior conjunctions caused by shifts of the line of sight due to latitudinal signal deflection, and we find insignificant evidence with our current data. With simulations, we find that the latitudinal deflection delay is unlikely to be measured with timing because of its correlation with Shapiro delay. Furthermore, although it is currently not possible to detect the expected lensing correction to the Shapiro delay, our simulations suggest that this effect may be measured with the full SKA. Finally, we provide an improved analytical description for the signal propagation in the double pulsar system that meets the timing precision expected from future instruments such as the full SKA.
Publisher: American Astronomical Society
Date: 28-03-2013
Publisher: American Astronomical Society
Date: 09-2023
Publisher: Springer Science and Business Media LLC
Date: 11-07-2023
Publisher: Cambridge University Press (CUP)
Date: 2013
Abstract: A ‘pulsar timing array’ (PTA), in which observations of a large s le of pulsars spread across the celestial sphere are combined, allows investigation of ‘global’ phenomena such as a background of gravitational waves or instabilities in atomic timescales that produce correlated timing residuals in the pulsars of the array. The Parkes Pulsar Timing Array (PPTA) is an implementation of the PTA concept based on observations with the Parkes 64-m radio telescope. A s le of 20 ms pulsars is being observed at three radio-frequency bands, 50 cm (~700 MHz), 20 cm (~1400 MHz), and 10 cm (~3100 MHz), with observations at intervals of two to three weeks. Regular observations commenced in early 2005. This paper describes the systems used for the PPTA observations and data processing, including calibration and timing analysis. The strategy behind the choice of pulsars, observing parameters, and analysis methods is discussed. Results are presented for PPTA data in the three bands taken between 2005 March and 2011 March. For 10 of the 20 pulsars, rms timing residuals are less than 1 μs for the best band after fitting for pulse frequency and its first time derivative. Significant ‘red’ timing noise is detected in about half of the s le. We discuss the implications of these results on future projects including the International Pulsar Timing Array and a PTA based on the Square Kilometre Array. We also present an ‘extended PPTA’ data set that combines PPTA data with earlier Parkes timing data for these pulsars.
Publisher: Oxford University Press (OUP)
Date: 05-04-2017
DOI: 10.1093/MNRAS/STX837
Publisher: Oxford University Press (OUP)
Date: 15-02-2016
DOI: 10.1093/MNRAS/STW347
Publisher: Oxford University Press (OUP)
Date: 19-02-2016
DOI: 10.1093/MNRAS/STW395
Publisher: Oxford University Press (OUP)
Date: 11-01-2023
Abstract: The radio polarization properties of the pulsar population are only superficially captured by the conventional picture of pulsar radio emission. We study the broadband polarization of 271 young radio pulsars, focusing particularly on circular polarization, using high-quality observations made with the Ultra-Wideband Low receiver on Murriyang, the Parkes radio telescope. We seek to encapsulate polarization behaviour on a population scale by defining broad categories for frequency- and phase-dependent polarization evolution, studying the co-occurrences of these categorizations and comparing them with average polarization measurements and spin-down energy ($\\dot{E}$). This work shows that deviations of the linear polarization position angle from the rotating vector model are linked to the presence of circular polarization features and to frequency evolution of the polarization. Polarization fraction, circular polarization contribution, and profile complexity all evolve with $\\dot{E}$ across the population, with the profiles of high-$\\dot{E}$ pulsars being simple and highly linearly polarized. The relationship between polarization fraction and circular contribution is also seen to evolve such that highly polarized profiles show less variation in circular contribution with frequency than less strongly polarized profiles. This evolution is seen both across the population and across frequency for in idual sources. Understanding pulsar radio polarization requires detailed study of in idual sources and collective understanding of population-level trends. For the former, we provide visualizations of their phase- and frequency-resolved polarization parameters. For the latter, we have highlighted the importance of including the impact of circular polarization and of $\\dot{E}$.
Publisher: American Astronomical Society
Date: 08-11-2019
Publisher: Elsevier BV
Date: 11-2013
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C2DT32650G
Abstract: A series of 18-electron complexes of general formula [Ru(p-cym)(1,2-dicarba-closo-dodecaborane-1,2-dithiolato)(L)] (p-cym = para-cymene L = 4-dimethylaminopyridine (2), nicotinamide (3), 3-ethynylpyridine (4), N-methylimidazole (5), 4-cyanopyridine (6), and pyridine (7)) were synthesised by reactions between the 16-electron precursor [Ru(p-cym)(1,2-dicarba-closo-dodecaborane-1,2-dithiolato)] (1) and corresponding heterocyclic bases. X-ray crystal structures of complexes 2 and 5 were determined. In dichloromethane and chloroform solutions at ambient temperature, the 18-electron complexes 2-7 are in equilibrium with the 16-electron precursor 1. Each equilibrium is displaced towards the formation of the blue 16-electron or yellow 18-electron complex by increasing or decreasing the temperature of the solution, respectively, which results in controlled and reversible thermochromism. Binding constants (K) and Gibbs free energies (ΔG°) of the six equilibria have been determined by a combination of experiments (Job plots, UV-visible titrations, NMR studies) and also by computation (time-dependent density functional theory, TD-DFT). A linear free energy relationship for log K versus pK(a) for the pyridine and imidazole ligands was established. The predicted strong interactions of 1 with other aromatic amine ligands, such as hetamine derivatives, were verified experimentally. This appears to be the first report of reversible 16/18-electron interconversions with associated thermochromic properties for a well-known family of complexes.
Publisher: American Astronomical Society
Date: 22-06-2020
Publisher: American Astronomical Society
Date: 23-01-2019
Publisher: American Astronomical Society
Date: 28-07-2022
Abstract: We report the discovery of a new 5.78 ms period millisecond pulsar (MSP), PSR J1740−5340B (NGC 6397B), in an eclipsing binary system discovered with the Parkes radio telescope (now also known as Murriyang) in Australia and confirmed with the MeerKAT radio telescope in South Africa. The measured orbital period, 1.97 days, is the longest among all eclipsing binaries in globular clusters (GCs) and consistent with that of the coincident X-ray source U18, previously suggested to be a “hidden MSP.” Our XMM-Newton observations during NGC 6397B’s radio-quiescent epochs detected no X-ray flares. NGC 6397B is either a transitional MSP or an eclipsing binary in its initial stage of mass transfer after the companion star left the main sequence. The discovery of NGC 6397B potentially reveals a subgroup of extremely faint and heavily obscured binary pulsars, thus providing a plausible explanation for the apparent dearth of binary neutron stars in core-collapsed GCs as well as a critical constraint on the evolution of GCs.
Publisher: Cambridge University Press (CUP)
Date: 08-2012
DOI: 10.1017/S1743921312024131
Abstract: An Ensemble Pulsar Time Scale (EPT) is derived based on the Pulsar Timing Array. It is interesting to compare the EPT with the TT terrestrial time scale, and get many new realization on the pulsar time scale and the algorithm. Some future interesting applications of the EPT are described and discussed.
Publisher: American Physical Society (APS)
Date: 15-12-2021
Publisher: Springer Science and Business Media LLC
Date: 18-06-2018
DOI: 10.1007/S12035-018-1179-5
Abstract: The regulation of Trk receptors is critical for orchestrating multiple signalling pathways required for developing and maintaining neuronal networks. Activation of Trk receptors results in signalling, internalisation and subsequent degradation of the protein. Although ubiquitination of TrkA by Nedd4-2 has been identified as an important degradation pathway, much less is known about the pathways regulating the degradation of TrkB and TrkC. Critical to the interaction between TrkA and Nedd4-2 is a PPxY motif present within TrkA but absent in TrkB and TrkC. Given the absence of this interaction motif, it remains to be determined how TrkB and TrkC are ubiquitinated. Here we report that the adaptor protein Ndfip1 can interact with all three Trk receptors and show for TrkB the recruitment of Nedd4-2 through PPxY motifs present in Ndfip1. Ndfip1 mediates the ubiquitination of TrkB, resulting in receptor trafficking predominantly on Rab7 containing late endosomes, highlighting a pathway for TrkB degradation at the lysosome. In vitro, overexpression of Ndfip1 increased TrkB ubiquitination and decreased viability of BDNF-dependent primary neurons. In vivo, conditional genetic deletion of Ndfip1 increased TrkB in the brain and resulted in enlargement of the granular cell layer of the dentate gyrus.
Publisher: American Astronomical Society
Date: 10-11-2015
Publisher: Oxford University Press (OUP)
Date: 09-04-2020
Abstract: In Paper I of this series, we detected a significant value of the braking index (n) for 19 young, high-$\\dot{E}$ radio pulsars using ∼10 yr of timing observations from the 64-m Parkes radio telescope. Here, we investigate this result in more detail using a Bayesian pulsar timing framework to model timing noise and to perform selection to distinguish between models containing exponential glitch recovery and braking index signatures. We show that consistent values of n are maintained with the addition of substantial archival data, even in the presence of glitches. We provide strong arguments that our measurements are unlikely due to exponential recovery signals from unseen glitches even though glitches play a key role in the evolution of a pulsar’s spin frequency. We conclude that, at least over decadal time-scales, the value of n can be significantly larger than the canonical 3 and discuss the implications for the evolution of pulsars.
Publisher: Oxford University Press (OUP)
Date: 29-08-2015
DOI: 10.1093/MNRAS/STV508
Publisher: American Astronomical Society
Date: 25-03-2019
Publisher: Oxford University Press (OUP)
Date: 03-12-2012
DOI: 10.1093/MNRAS/STS359
Publisher: Oxford University Press (OUP)
Date: 21-09-2021
Abstract: We report on a timing programme of 74 young pulsars that have been observed by the Parkes 64-m radio telescope over the past decade. Using modern Bayesian timing techniques, we have measured the properties of 124 glitches in 52 of these pulsars, of which 74 are new. We demonstrate that the glitch s le is complete to fractional increases in spin frequency greater than $\\Delta \\nu ^{90{{\\ \\rm per\\ cent}}}_{\\mathrm{ g}}/\\nu \\approx 8.1 \\times 10^{-9}$ . We measure values of the braking index, n, in 33 pulsars. In most of these pulsars, their rotational evolution is dominated by episodes of spin-down with n & 10, punctuated by step changes in the spin-down rate at the time of a large glitch. The step changes are such that, averaged over the glitches, the long-term n is small. We find a near one-to-one relationship between the interglitch value of n and the change in spin-down of the previous glitch ided by the interglitch time interval. We discuss the results in the context of a range of physical models.
Publisher: Springer Science and Business Media LLC
Date: 09-2017
Publisher: Oxford University Press (OUP)
Date: 04-06-2014
DOI: 10.1093/MNRAS/STU779
Publisher: Elsevier BV
Date: 2013
Publisher: American Association for the Advancement of Science (AAAS)
Date: 25-09-2015
Abstract: Gravitational waves are expected to be generated by the interaction of the massive bodies in black-hole binary systems. As gravitational waves distort spacetime, it should be possible to verify their existence as they interfere with the pulses emitted by millisecond pulsars. However, after monitoring 24 pulsars with the Parkes radio telescope for 12 years, Shannon et al. found no detectable variation in pulsar records. This nondetection result indicates that a new detection strategy for gravitational waves is needed. Science , this issue p. 1522
Publisher: Oxford University Press (OUP)
Date: 23-08-2018
Publisher: American Astronomical Society
Date: 25-10-0012
Publisher: Springer Science and Business Media LLC
Date: 06-05-2021
Publisher: Cambridge University Press (CUP)
Date: 08-2012
DOI: 10.1017/S1743921313000021
Abstract: We investigate the changes in polarization position angle in radiation from pulsar A around the eclipse in the Double Pulsar system PSR J0737-3039A/B at the 20 cm and 50 cm wavelengths using the Parkes 64-m radio telescope. The changes are ~ 2σ during and shortly after the eclipse at 20 cm but less significant at 50 cm. We show that the changes in position angle during the eclipse can be modelled by differential synchrotron absorption in the eclipse regions. Position angle changes after the eclipse are interpreted as Faraday rotation in the magnetotail of pulsar B. Implied charge densities are consistent with the Goldreich-Julian density, suggesting that the particle energies in the magnetotail are mildly relativistic.
Publisher: American Astronomical Society
Date: 16-01-2017
Publisher: Cambridge University Press (CUP)
Date: 09-2017
DOI: 10.1017/S1743921317009607
Abstract: The first known pulsar glitch was discovered in the Vela pulsar at both Parkes and Goldstone in March 1969. Since then the number of known glitches has grown enormously, with more than 520 glitches now known in more than 180 pulsars. Details of glitch parameters and post-glitch recoveries are described and some implications for the physics of neutron stars are discussed.
Publisher: Oxford University Press (OUP)
Date: 28-07-2014
Publisher: American Astronomical Society
Date: 25-11-2020
Publisher: American Astronomical Society
Date: 16-01-2018
Publisher: Oxford University Press (OUP)
Date: 02-03-2019
Publisher: Oxford University Press (OUP)
Date: 03-08-2022
Abstract: Pulsar timing array collaborations have recently reported evidence for a noise process with a common spectrum among the millisecond pulsars in the arrays. The spectral properties of this common-noise process are consistent with expectations for an isotropic gravitational-wave background (GWB) from inspiralling supermassive black hole binaries. However, recent simulation analyses based on Parkes Pulsar Timing Array data indicate that such a detection may arise spuriously. In this paper, we use simulated pulsar timing array data sets to further test the robustness of the inference methods for spectral and spatial correlations from a GWB. Expanding on our previous results, we find strong support (Bayes factors exceeding 105) for the presence of a common-spectrum noise process in data sets where no common process is present, under a wide range of timing noise prescriptions per pulsar. We show that these results are highly sensitive to the choice of Bayesian priors on timing noise parameters, with priors that more closely match the injected distributions of timing noise parameters resulting in diminished support for a common-spectrum noise process. These results emphasize shortcomings in current methods for inferring the presence of a common-spectrum process, and imply that the detection of a common process is not a reliable precursor to detection of the GWB. Future searches for the nanohertz GWB should remain focused on detecting spatial correlations, and make use of more tailored specifications for a common-spectrum noise process.
Publisher: Oxford University Press (OUP)
Date: 14-03-2012
Publisher: Public Library of Science (PLoS)
Date: 06-03-2018
Publisher: Oxford University Press (OUP)
Date: 02-12-2020
Abstract: Cosmic strings are potential gravitational-wave (GW) sources that can be probed by pulsar timing arrays (PTAs). In this work we develop a detection algorithm for a GW burst from a cusp on a cosmic string, and apply it to Parkes PTA data. We find four events with a false alarm probability less than 1 per cent. However further investigation shows that all of these are likely to be spurious. As there are no convincing detections we place upper limits on the GW litude for different event durations. From these bounds we place limits on the cosmic string tension of Gμ ∼ 10−5, and highlight that this bound is independent from those obtained using other techniques. We discuss the physical implications of our results and the prospect of probing cosmic strings in the era of Square Kilometre Array.
Publisher: EDP Sciences
Date: 08-2016
Publisher: Oxford University Press (OUP)
Date: 14-09-2010
Publisher: American Astronomical Society
Date: 03-12-2012
Publisher: American Physical Society (APS)
Date: 31-10-2022
Publisher: American Astronomical Society
Date: 23-03-2018
Publisher: Oxford University Press (OUP)
Date: 04-11-2019
Abstract: We have constructed a new time-scale, TT(IPTA16), based on observations of radio pulsars presented in the first data release from the International Pulsar Timing Array (IPTA). We used two analysis techniques with independent estimates of the noise models for the pulsar observations and different algorithms for obtaining the pulsar time-scale. The two analyses agree within the estimated uncertainties and both agree with TT(BIPM17), a post-corrected time-scale produced by the Bureau International des Poids et Mesures (BIPM). We show that both methods could detect significant errors in TT(BIPM17) if they were present. We estimate the stability of the atomic clocks from which TT(BIPM17) is derived using observations of four rubidium fountain clocks at the US Naval Observatory. Comparing the power spectrum of TT(IPTA16) with that of these fountain clocks suggests that pulsar-based time-scales are unlikely to contribute to the stability of the best time-scales over the next decade, but they will remain a valuable independent check on atomic time-scales. We also find that the stability of the pulsar-based time-scale is likely to be limited by our knowledge of solar-system dynamics, and that errors in TT(BIPM17) will not be a limiting factor for the primary goal of the IPTA, which is to search for the signatures of nano-Hertz gravitational waves.
Publisher: Oxford University Press (OUP)
Date: 09-12-2014
Publisher: Oxford University Press (OUP)
Date: 29-08-2012
Publisher: Oxford University Press (OUP)
Date: 22-12-2012
DOI: 10.1093/MNRAS/STS486
Publisher: Cambridge University Press (CUP)
Date: 09-2017
DOI: 10.1017/S1743921317009334
Abstract: Multi-decade observing c aigns of the globular clusters 47 Tucanae and M15 have led to an outstanding number of discoveries. Here, we report on the latest results of the long-term observations of the pulsars in these two clusters. For most of the pulsars in 47 Tucanae we have measured, among other things, their higher-order spin period derivatives, which have in turn provided stringent constraints on the physical parameters of the cluster, such as its distance and gravitational potential. For M15, we have studied the relativistic spin precession effect in PSR B2127+11C. We have used full-Stokes observations to model the precession effect, and to constrain the system geometry. We find that the visible beam of the pulsar is swiftly moving away from our line of sight and may very soon become undetectable. On the other hand, we expect to see the opposite emission beam sometime between 2041 and 2053.
Publisher: Wiley
Date: 29-01-2018
Publisher: Oxford University Press (OUP)
Date: 06-12-2012
DOI: 10.1093/MNRAS/STS366
Publisher: Oxford University Press (OUP)
Date: 12-04-2016
DOI: 10.1093/MNRAS/STW842
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2PY20217D
Publisher: IOP Publishing
Date: 29-06-2023
Abstract: Observing and timing a group of millisecond pulsars with high rotational stability enables the direct detection of gravitational waves (GWs). The GW signals can be identified from the spatial correlations encoded in the times-of-arrival of widely spaced pulsar-pairs. The Chinese Pulsar Timing Array (CPTA) is a collaboration aiming at the direct GW detection with observations carried out using Chinese radio telescopes. This short article serves as a “table of contents” for a forthcoming series of papers related to the CPTA Data Release 1 (CPTA DR1) which uses observations from the Five-hundred-meter Aperture Spherical radio Telescope. Here, after summarizing the time span and accuracy of CPTA DR1, we report the key results of our statistical inference finding a correlated signal with litude log A c = − 14.4 − 2.8 + 1.0 for spectral index in the range of α ∈ [ − 1.8, 1.5] assuming a GW background (GWB) induced quadrupolar correlation. The search for the Hellings–Downs (HD) correlation curve is also presented, where some evidence for the HD correlation has been found that a 4.6 σ statistical significance is achieved using the discrete frequency method around the frequency of 14 nHz. We expect that the future International Pulsar Timing Array data analysis and the next CPTA data release will be more sensitive to the nHz GWB, which could verify the current results.
Publisher: Oxford University Press (OUP)
Date: 18-11-2015
Publisher: American Astronomical Society
Date: 12-2020
Abstract: We report the first wideband monitoring observations of PSR J1803−3002A, a relatively bright millisecond pulsar (MSP) in the globular cluster NGC 6522 with a spin period of 7.1 ms and no known binary companion. These observations were performed using the Parkes 64 m radio telescope with the Ultra-Wideband Low receiver system, which covers 704–4032 MHz. We confirm that PSR J1803−3002A is an isolated MSP located near the cluster center and probe the emission properties of the pulsar over the wide observed band. The mean pulse profile consists of three components, with the outer components becoming more prominent at higher frequencies, and a mean spectral index for the pulsed emission of −1.66 ± 0.07 over the observed band. The fractional linear and circular polarization increase with increasing frequency, which is unusual for pulsars. We determine a Faraday rotation measure of −107 ± 6 rad m −2 for the pulsar. PSR J1803−3002A is a distant pulsar in the Galactic plane, but our observations show no evidence of pulse broadening due to interstellar scattering. These results demonstrate the power of ultra-wideband receivers and signal processing systems.
Publisher: Oxford University Press (OUP)
Date: 09-12-2015
Publisher: Springer Science and Business Media LLC
Date: 2002
Publisher: American Astronomical Society
Date: 26-03-2012
Publisher: No publisher found
Date: 2019
DOI: 10.1093/MNRAS/STZ647
Publisher: Oxford University Press (OUP)
Date: 07-03-2019
DOI: 10.1093/MNRAS/STZ650
Publisher: IOP Publishing
Date: 02-2019
Publisher: American Astronomical Society
Date: 10-11-2014
Publisher: American Astronomical Society
Date: 08-11-2012
Publisher: World Scientific Pub Co Pte Lt
Date: 27-04-2015
DOI: 10.1142/S0218271815300189
Abstract: Pulsars are wonderful gravitational probes. Their tiny size and stellar mass give their rotation periods a stability comparable to that of atomic frequency standards. This is especially true of the rapidly rotating "millisecond pulsars" (MSPs). Many of these rapidly rotating pulsars are in orbit with another star, allowing pulsar timing to probe relativistic perturbations to the orbital motion. Pulsars have provided the most stringent tests of theories of relativistic gravitation, especially in the strong-field regime, and have shown that Einstein's general theory of relativity is an accurate description of the observed motions. Many other gravitational theories are effectively ruled out or at least severely constrained by these results. MSPs can also be used to form a "Pulsar Timing Array" (PTA). PTAs are Galactic-scale interferometers that have the potential to directly detect nanohertz gravitational waves from astrophysical sources. Orbiting super-massive black holes in the cores of distant galaxies are the sources most likely to be detectable. Although no evidence for gravitational waves has yet been found in PTA data sets, the latest limits are seriously constraining current ideas on galaxy and black-hole evolution in the early universe.
Publisher: Oxford University Press (OUP)
Date: 21-03-2023
Abstract: The International Pulsar Timing Array 2nd data release is the combination of data sets from worldwide collaborations. In this study, we search for continuous waves: gravitational wave signals produced by in idual supermassive black hole binaries in the local universe. We consider binaries on circular orbits and neglect the evolution of orbital frequency over the observational span. We find no evidence for such signals and set sky averaged 95 per cent upper limits on their litude h95. The most sensitive frequency is 10 nHz with h95 = 9.1 × 10−15. We achieved the best upper limit to date at low and high frequencies of the PTA band thanks to improved effective cadence of observations. In our analysis, we have taken into account the recently discovered common red noise process, which has an impact at low frequencies. We also find that the peculiar noise features present in some pulsars data must be taken into account to reduce the false alarm. We show that using custom noise models is essential in searching for continuous gravitational wave signals and setting the upper limit.
Publisher: Oxford University Press (OUP)
Date: 23-09-2011
Publisher: American Astronomical Society
Date: 27-07-2015
Publisher: MDPI AG
Date: 15-04-2019
DOI: 10.3390/PHARMACEUTICS11040182
Abstract: Electrospinning technologies have been applied in the field of tissue engineering as materials, with nanoscale-structures and high porosity, can be easily prepared via this method to bio-mimic the natural extracellular matrix (ECM). Tissue engineering aims to fabricate functional biomaterials for the repairment and regeneration of defective tissue. In addition to the structural simulation for accelerating the repair process and achieving a high-quality regeneration, the combination of biomaterials and bioactive molecules is required for an ideal tissue-engineering scaffold. Due to the ersity in materials and method selection for electrospinning, a great flexibility in drug delivery systems can be achieved. Various drugs including antibiotic agents, vitamins, peptides, and proteins can be incorporated into electrospun scaffolds using different electrospinning techniques and drug-loading methods. This is a review of recent research on electrospun nanofibrous scaffolds for tissue-engineering applications, the development of preparation methods, and the delivery of various bioactive molecules. These studies are based on the fabrication of electrospun biomaterials for the repair of blood vessels, nerve tissues, cartilage, bone defects, and the treatment of aneurysms and skin wounds, as well as their applications related to oral mucosa and dental fields. In these studies, due to the optimal selection of drugs and loading methods based on electrospinning, in vitro and in vivo experiments demonstrated that these scaffolds exhibited desirable effects for the repair and treatment of damaged tissue and, thus, have excellent potential for clinical application.
Publisher: Hindawi Limited
Date: 30-08-2018
DOI: 10.1155/2018/7214974
Publisher: Oxford University Press (OUP)
Date: 12-2015
Publisher: American Physical Society (APS)
Date: 13-12-2021
Publisher: American Astronomical Society
Date: 22-08-2016
Publisher: Elsevier BV
Date: 11-1993
Publisher: American Physical Society (APS)
Date: 31-03-2016
Publisher: American Astronomical Society
Date: 10-2020
Abstract: We have observed PSR B1534+12 (J1537+1155), a pulsar with a neutron star companion, using the Five-hundred-meter Aperture Spherical radio Telescope. We found that this pulsar shows two distinct emission states: a weak state with a wide pulse profile and a burst state with a narrow pulse profile. The weak state is always present. We cannot, with our current data, determine whether the pulse energy of the weak state follows a normal or a log-normal distribution. The burst state energy distribution follows a power law. The litude of the single-pulse emission in the burst state varies significantly the peak flux intensity of the brightest pulse is 334 times stronger than that of the average pulse. We also examined the timing precision achievable using only bright pulses, which showed no demonstrable improvement because of pulse jitter and therefore quantified the jitter noise level for this pulsar.
Location: Australia
Location: United States of America
Location: United States of America
No related grants have been discovered for Richard Manchester.