ORCID Profile
0000-0002-9900-9712
Current Organisation
Curtin University
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Atomic molecular and optical physics | Atomic and molecular physics |
Publisher: IOP Publishing
Date: 06-2022
Abstract: Many laboratory and industrial plasma applications require accurate modeling techniques to understand the interplay between microscopic and macroscopic processes. A prime ex le of this interplay is how particle and Monte Carlo (MC) simulation codes describe angular scattering of electrons following elastic scattering events. The forward peaked nature of high energy electron elastic scattering is relatively trivial to accurately describe in plasma simulations. However, for lower energy collisions, which produce near isotropic or backward peaked differential cross sections, there is not a strong consensus among the plasma modeling community on how to best describe these angular scattering trends. In this study, we propose a systematic method to approximate the aforementioned non-trivial angular scattering behavior with a formula that can be readily implemented in particle-in-cell (PIC) and/or MC plasma simulation codes. The present approach is specifically applied to fusion relevant atomic hydrogen and helium, as well as for molecular hydrogen, and results are also applicable to the atomic isotopes and homonuclear molecular isotopologues of these species. Comparisons between the present angular distribution function and benchmark scattering data were used to validate the proposed models. In addition, two-term Boltzmann calculations and PIC direct simulation MC simulations revealed that the proposed angular distribution function is accurate, agreeing very well with benchmark convergent close-coupling scattering calculations, and electron transport measurements. These studies confirmed that the present angular distribution function model can be utilized without the need of renormalization to the momentum transfer cross section (as opposed to using the elastic scattering integrated cross section), which has been suggested by several studies in order to correct for deficient angular scattering models, and to agree with transport measurements. Hence, the present anisotropic angular scattering model can be utilized to accurately model the momentum transfer as well as the electron trajectories of elastic collisions.
Publisher: American Physical Society (APS)
Date: 18-08-2017
Publisher: American Physical Society (APS)
Date: 02-06-2023
Publisher: American Physical Society (APS)
Date: 31-10-2022
Publisher: MDPI AG
Date: 06-08-2019
DOI: 10.3390/ATOMS7030075
Abstract: We present convergent close-coupling (CCC) calculations of electron-impact dissociation of vibrationally-excited molecular hydrogen into neutral fragments. This work follows from our previous results for dissociation of molecular hydrogen in the ground vibrational level [Scarlett et al., Eur. Phys. J. D 72, 34 (2018)], which were obtained from calculations performed in a spherical coordinate system. The present calculations, performed utilizing a spheroidal formulation of the molecular CCC method, reproduce the previous dissociation cross sections for the ground vibrational level, while allowing the extension to scattering on excited levels.
Publisher: EDP Sciences
Date: 02-2022
DOI: 10.1051/0004-6361/202142560
Abstract: Context. Low-energy cosmic rays ( TeV) play a fundamental role in the chemical and dynamical evolution of molecular clouds, as they control the ionisation, dissociation, and excitation of H 2 . Their characterisation is therefore important both for the interpretation of observations and for the development of theoretical models. However, the methods used so far for estimating the cosmic-ray ionisation rate in molecular clouds have several limitations due to uncertainties in the adopted chemical networks. Aims. We refine and extend a previously proposed method to estimate the cosmic-ray ionisation rate in molecular clouds by observing rovibrational transitions of H 2 at near-infrared wavelengths, which are mainly excited by secondary cosmic-ray electrons. Methods. Combining models of interstellar cosmic-ray propagation and attenuation in molecular clouds with the rigorous calculation of the expected secondary electron spectrum and updated electron-H 2 excitation cross sections, we derive the intensity of the four H 2 rovibrational transitions observable in cold dense gas: (1−0)O(2), (1−0)Q(2), (1−0)S(0), and (1−0)O(4). Results. The proposed method allows the estimation of the cosmic-ray ionisation rate for a given observed line intensity and H 2 column density. We are also able to deduce the shape of the low-energy cosmic-ray proton spectrum impinging upon the molecular cloud. In addition, we present a look-up plot and a web-based application that can be used to constrain the low-energy spectral slope of the interstellar cosmic-ray proton spectrum. We finally comment on the capability of the James Webb Space Telescope to detect these near-infrared H 2 lines, which will make it possible to derive, for the first time, spatial variation in the cosmic-ray ionisation rate in dense gas. Besides the implications for the interpretation of the chemical-dynamic evolution of a molecular cloud, it will finally be possible to test competing models of cosmic-ray propagation and attenuation in the interstellar medium, as well as compare cosmic-ray spectra in different Galactic regions.
Publisher: American Physical Society (APS)
Date: 10-12-2018
Publisher: IOP Publishing
Date: 08-01-2021
Abstract: Collisional radiative (CR) models for molecular hydrogen are of high relevance for performing qualitative and quantitative analysis of excited-state population densities measured in plasmas or predicting the dependence of plasma emission on parameter variations. Although the development of such models for H 2 started decades ago, major uncertainties still exist regarding the most important set of input parameters, namely the cross sections for electron-impact excitation. The deviations between cross sections from different datasets are particularly pronounced in the energy region close to the threshold energy, strongly increasing the uncertainty of CR models applied to low-temperature plasmas. This paper presents experimental validation of a set of newly calculated non ro-vibrationally resolved electron-impact cross sections calculated for the triplet system of H 2 using the molecular convergent close-coupling method in the adiabatic-nuclei formulation. These cross sections are implemented into a CR model based on the flexible solver Yacora. A first comparison of CR calculations with the different datasets to experimentally-determined population densities is performed at a planar ICP discharge for varying pressure (between 1 and 10 Pa) and RF power (between 700 and 1100 W). For the experimentally-accessible electron temperature and density range (2.5–10 eV and 1.8–3.3 × 10 16 m −3 , respectively), very good agreement between the model and experiment is obtained using the new data set, in contrast to previously used cross sections.
Publisher: IOP Publishing
Date: 11-2021
Abstract: A Monte Carlo simulation of electron energy deposition in a gas of molecular hydrogen has been conducted with the aim of producing an ab initio estimate of energy deposition parameters such as the mean energy per ion pair. A set of cross sections obtained using the molecular convergent close-coupling method were used as input. At high incident electron energies the mean energy per ion pair was calculated to be 36.3 eV, agreeing with the recommended value of 36.5 ± 0.3 eV. This represents the first fully ab initio calculation of the mean energy per ion pair using a self consistent data set.
Publisher: American Physical Society (APS)
Date: 19-02-2021
Publisher: Elsevier BV
Date: 2021
Publisher: American Physical Society (APS)
Date: 03-2021
Publisher: American Physical Society (APS)
Date: 24-11-2021
Publisher: IOP Publishing
Date: 27-06-2018
Publisher: Elsevier BV
Date: 05-2021
Publisher: American Physical Society (APS)
Date: 24-05-2018
Publisher: IOP Publishing
Date: 18-06-2020
Abstract: We present benchmark integrated and differential cross-sections for electron collisions with H 2 using two different theoretical approaches, namely, the R-matrix and molecular convergent close-coupling. This is similar to comparative studies conducted on electron–atom collisions for H, He and Mg. Electron impact excitation to the b 3 Σ u + , a 3 Σ g + , B 1 Σ u + , c 3 Π u , E F 1 Σ g + , C 1 Π u , e 3 Σ u + , h 3 Σ g + , B ′ 1 Σ u + and d 3 Π u excited electronic states are considered. Calculations are presented in both the fixed nuclei and adiabatic nuclei approximations, where the latter is shown only for the b 3 Σ u + state. Good agreement is found for all transitions presented. Where available, we compare with existing experimental and recommended data.
Publisher: IOP Publishing
Date: 03-12-2020
Publisher: American Physical Society (APS)
Date: 17-03-2023
Publisher: Elsevier BV
Date: 11-2022
Publisher: American Physical Society (APS)
Date: 21-12-2017
Publisher: Springer Science and Business Media LLC
Date: 10-2023
Publisher: American Physical Society (APS)
Date: 12-10-2021
Publisher: Elsevier BV
Date: 05-2023
Publisher: Cold Spring Harbor Laboratory
Date: 06-04-2021
DOI: 10.1101/2021.04.05.437453
Abstract: Age-dependent differences in the clinical response to SARS-CoV-2 infection is well-documented 1–3 however the underlying molecular mechanisms involved are poorly understood. We infected fully differentiated human nasal epithelium cultures derived from healthy children (1-12 years old), young adults (26-34 years old) and older adults (56-62 years old) with SARS-COV-2 to identify age-related cell-intrinsic differences that may influence viral entry, replication and host defence response. We integrated imaging, transcriptomics, proteomics and biochemical assays revealing age-related changes in transcriptional regulation that impact viral replication, effectiveness of host responses and therapeutic drug targets. Viral load was lowest in infected older adult cultures despite the highest expression of SARS-CoV-2 entry and detection factors. We showed this was likely due to lower expression of hijacked host machinery essential for viral replication. Unlike the nasal epithelium of young adults and children, global host response and induction of the interferon signalling was profoundly impaired in older adults, which preferentially expressed proinflammatory cytokines mirroring the “cytokine storm” seen in severe COVID-19 4,5 . In silico screening of our virus-host-drug network identified drug classes with higher efficacy in older adults. Collectively, our data suggests that cellular alterations that occur during ageing impact the ability for the host nasal epithelium to respond to SARS-CoV-2 infection which could guide future therapeutic strategies.
Publisher: Springer Science and Business Media LLC
Date: 02-2018
Publisher: Springer Science and Business Media LLC
Date: 02-2020
Publisher: American Physical Society (APS)
Date: 04-09-2018
Publisher: IOP Publishing
Date: 25-02-2019
Start Date: 2024
End Date: 12-2026
Amount: $349,987.00
Funder: Australian Research Council
View Funded Activity