993 research outputs found
Bifurcations in the theory of current transfer to cathodes of dc discharges and observations of transitions between different modes
General scenarios of transitions between different spot patterns on
electrodes of dc gas discharges and their relation to bifurcations of
steady-state solutions are analyzed. In the case of cathodes of arc discharges,
it is shown that any transition between different modes of current transfer is
related to a bifurcation of steady-state solutions. In particular, transitions
between diffuse and spot modes on axially symmetric cathodes, frequently
observed in the experiment, represent an indication of the presence of
pitchfork or fold bifurcations of steady-state solutions. Experimental
observations of transitions on cathodes of dc glow microdischarges are analyzed
and those potentially related to bifurcations of steady-state solutions are
identified. The relevant bifurcations are investigated numerically and the
computed patterns are found to conform to those observed in the course of the
corresponding transitions in the experiment
Modelling cathode spots in glow discharges in the cathode boundary layer geometry
Self-organized patterns of cathode spots in glow discharges are computed in the cathode
boundary layer geometry, which is the one employed in most of the experiments reported
in the literature. The model comprises conservation and transport equations of electrons
and a single ion species, written in the drift-diffusion and local-field approximations, and
Poisson’s equation. Multiple solutions existing for the same value of the discharge current and
describing modes with different configurations of cathode spots are computed by means of a
stationary solver. The computed solutions are compared to their counterparts for plane-parallel
electrodes, and experiments. All of the computed spot patterns have been observed in the
experiment.info:eu-repo/semantics/publishedVersio
3D modelling of self-organized patterns of spots on anodes of DC glow discharge
Self-organized patterns of spots on a at metallic anode in a cylindrical glow
dis- charge tube are simulated self-consistently. A standard model of a glow
discharge is used, comprising conservation and transport equations for a single
species of ion and electrons, written with the use of the drift-diffusion and
local-field approximations, and the Poisson equation. The computation domain is
the region from the anode to the discharge column; only processes in the
near-anode region are considered. Multiple solutions, existing in the same
range of discharge current and describing modes with and without anode spots,
are computed by means of a stationary solver. The computed spots exhibited
unexpected behavior. A reversal of the local anode current density in the
middle of each of the spots was found, i.e. mini-cathodes are formed inside the
spots. The solutions do not fit into the conventional pattern of
self-organization in bistable nonlinear dissipative systems; e.g. the modes are
not joined by bifurcations
Computing DC discharges in a wide range of currents with COMSOL MultiPhysics: time-dependent solvers vs. stationary solvers
The benefits of the usage of stationary over time-dependent solvers of COMSOL Multiphysics in
the modelling of DC discharges are explored and demonstrated using as examples glow and high pressure arc discharges; in particular, it is investigated whether time-dependent solvers can be used
for a systematic computation of different modes of these discharges. It has been found that most
modes of both glow and high-pressure arc discharges cannot be computed in the whole range of
their existence by a time-dependent solver. Further, time-dependent solvers are unsuitable for a
computation of all the states belonging to the retrograde sections of the current-voltage
characteristics of the modes, so the discharge manifests hysteresis, which, in principle, can be
observed in the experiment.info:eu-repo/semantics/publishedVersio
Toward a Reliable Wave Hindcast/Forecast in the Bering Sea
1. To validate the quality of available wind products through application of the WAM model Cycle 4.5 and satellite observations.
2. To analyze effects of high resolution atmospheric model downscaling and data assimilation.
3. To analyze summer surface wave condition in the Bering Sea during the years, 2007-2011.
4. To explore the possibility of developing a new algorithm for a dynamically constrained minimizing function without employing the adjoint of the dynamical system
Numerical simulations of stellar SiO maser variability. Investigation of the effect of shocks
A stellar hydrodynamic pulsation model has been combined with a SiO maser
model in an attempt to calculate the temporal variability of SiO maser emission
in the circumstellar envelope (CE) of a model AGB star. This study investigates
whether the variations in local physical conditions brought about by shocks are
the predominant contributing factor to SiO maser variability because, in this
work, the radiative part of the pump is constant. We find that some aspects of
the variability are not consistent with a pump provided by shock-enhanced
collisions alone. In these simulations, gas parcels of relatively enhanced SiO
abundance are distributed in a model CE by a Monte Carlo method, at a single
epoch of the stellar cycle. From this epoch on, Lagrangian motions of
individual parcels are calculated according to the velocity fields encountered
in the model CE during the stellar pulsation cycle. The potentially masing gas
parcels therefore experience different densities and temperatures, and have
varying line-of-sight velocity gradients throughout the stellar cycle, which
may or may not be suitable to produce maser emission. At each epoch (separated
by 16.6 days), emission lines from the parcels are combined to produce
synthetic spectra and VLBI-type images. We report here the results for v=1,
J=1-0 (43-GHz) and J=2-1 (86-GHz) masers.Comment: 16 pages, 8 figures, accepted by A&
Toward a simulation approach for alkene ring-closing metathesis : scope and limitations of a model for RCM
A published model for revealing solvent effects on the ring-closing metathesis (RCM) reaction of di-Et diallylmalonate 7 has been evaluated over a wider range of conditions, to assess its suitability for new applications. Unfortunately, the model is too flexible and the published rate consts. do not agree with exptl. studies in the literature. However, by fixing the values of important rate consts. and restricting the concn. ranges studied, useful conclusions can be drawn about the relative rates of RCM of different substrates, precatalyst concn. can be simulated accurately and the effect of precatalyst loading can be anticipated. Progress has also been made toward applying the model to precatalyst evaluation, but further modifications to the model are necessary to achieve much broader aims
Age-related changes in global motion coherence: conflicting haemodynamic and perceptual responses
Our aim was to use both behavioural and neuroimaging data to identify indicators of perceptual decline in motion processing. We employed a global motion coherence task and functional Near Infrared Spectroscopy (fNIRS). Healthy adults (n = 72, 18-85) were recruited into the following groups: young (n = 28, mean age = 28), middle-aged (n = 22, mean age = 50), and older adults (n = 23, mean age = 70). Participants were assessed on their motion coherence thresholds at 3 different speeds using a psychophysical design. As expected, we report age group differences in motion processing as demonstrated by higher motion coherence thresholds in older adults. Crucially, we add correlational data showing that global motion perception declines linearly as a function of age. The associated fNIRS recordings provide a clear physiological correlate of global motion perception. The crux of this study lies in the robust linear correlation between age and haemodynamic response for both measures of oxygenation. We hypothesise that there is an increase in neural recruitment, necessitating an increase in metabolic need and blood flow, which presents as a higher oxygenated haemoglobin response. We report age-related changes in motion perception with poorer behavioural performance (high motion coherence thresholds) associated with an increased haemodynamic response
Development and cross-national investigation of a model explaining participation in WHO-recommended and placebo behaviours to prevent COVID-19 infection
To protect themselves from COVID-19, people follow the recommendations of the authorities, but they also resort to placebos. To stop the virus, it is important to understand the factors underlying both types of preventive behaviour. This study examined whether our model (developed based on the Health Belief Model and the Transactional Model of Stress) can explain participation in WHO-recommended and placebo actions during the pandemic. Model was tested on a sample of 3346 participants from Italy, Japan, Poland, Korea, Sweden, and the US. It was broadly supported: objective risk and cues to action showed both direct and indirect (through perceived threat) associations with preventive behaviours. Moreover, locus of control, decision balance, health anxiety and preventive coping moderated these relationships. Numerous differences were also found between countries. We conclude that beliefs about control over health and perceived benefits of actions are critical to the development of interventions to improve adherence to recommendations
FGF receptor genes and breast cancer susceptibility: results from the Breast Cancer Association Consortium
Background:Breast cancer is one of the most common malignancies in women. Genome-wide association studies have identified FGFR2 as a breast cancer susceptibility gene. Common variation in other fibroblast growth factor (FGF) receptors might also modify risk. We tested this hypothesis by studying genotyped single-nucleotide polymorphisms (SNPs) and imputed SNPs in FGFR1, FGFR3, FGFR4 and FGFRL1 in the Breast Cancer Association Consortium.
Methods:Data were combined from 49 studies, including 53 835 cases and 50 156 controls, of which 89 050 (46 450 cases and 42 600 controls) were of European ancestry, 12 893 (6269 cases and 6624 controls) of Asian and 2048 (1116 cases and 932 controls) of African ancestry. Associations with risk of breast cancer, overall and by disease sub-type, were assessed using unconditional logistic regression.
Results:Little evidence of association with breast cancer risk was observed for SNPs in the FGF receptor genes. The strongest evidence in European women was for rs743682 in FGFR3; the estimated per-allele odds ratio was 1.05 (95 confidence interval=1.02-1.09, P=0.0020), which is substantially lower than that observed for SNPs in FGFR2.
Conclusion:Our results suggest that common variants in the other FGF receptors are not associated with risk of breast cancer to the degree observed for FGFR2. © 2014 Cancer Research UK
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