946 research outputs found
Nonequilibrium stochastic processes: Time dependence of entropy flux and entropy production
Based on the Fokker-Planck and the entropy balance equations we have studied
the relaxation of a dissipative dynamical system driven by external
Ornstein-Uhlenbeck noise processes in absence and presence of nonequilibrium
constraint in terms of the thermodynamically inspired quantities like entropy
flux and entropy production. The interplay of nonequilibrium constraint,
dissipation and noise reveals some interesting extremal nature in the time
dependence of entropy flux and entropy production.Comment: RevTex, 17 pages, 9 figures. To appear in Phys. Rev.
The noise properties of stochastic processes and entropy production
Based on a Fokker-Planck description of external Ornstein-Uhlenbeck noise and
cross-correlated noise processes driving a dynamical system we examine the
interplay of the properties of noise processes and the dissipative
characteristic of the dynamical system in the steady state entropy production
and flux. Our analysis is illustrated with appropriate examples.Comment: RevTex, 1 figure, To appear in Phys. Rev.
A semiclassical theory of quantum noise in open chaotic systems
We consider the quantum evolution of classically chaotic systems in contact
with surroundings. Based on -scaling of an equation for time evolution
of the Wigner's quasi-probability distribution function in presence of
dissipation and thermal diffusion we derive a semiclassical equation for
quantum fluctuations. This identifies an early regime of evolution dominated by
fluctuations in the curvature of the potential due to classical chaos and
dissipation. A stochastic treatment of this classical fluctuations leads us to
a Fokker-Planck equation which is reminiscent of Kramers' equation for
thermally activated processes. This reveals an interplay of three aspects of
evolution of quantum noise in weakly dissipative open systems; the reversible
Liouville flow, the irreversible chaotic diffusion which is characteristic of
the system itself, and irreversible dissipation induced by the external
reservoir. It has been demonstrated that in the dissipation-free case a
competition between Liouville flow in the contracting direction of phase space
and chaotic diffusion sets a critical width in the Wigner function for quantum
fluctuations. We also show how the initial quantum noise gets amplified by
classical chaos and ultimately equilibrated under the influence of dissipation.
We establish that there exists a critical limit to the expansion of phase
space. The limit is determined by chaotic diffusion and dissipation. Making use
of appropriate quantum-classical correspondence we verify the semiclassical
analysis by the fully quantum simulation in a chaotic quartic oscillator.Comment: Plain Latex, 27 pages, 6 ps figure, To appear in Physica
Periodic force induced stabilization or destabilization of the denatured state of a protein
We have studied the effects of an external sinusoidal force in protein
folding kinetics. The externally applied force field acts on the each amino
acid residues of polypeptide chains. Our simulation results show that mean
protein folding time first increases with driving frequency and then decreases
passing through a maximum. With further increase of the driving frequency the
mean folding time starts increasing as the noise-induced hoping event (from the
denatured state to the native state) begins to experience many oscillations
over the mean barrier crossing time period. Thus unlike one-dimensional barrier
crossing problems, the external oscillating force field induces both
\emph{stabilization or destabilization of the denatured state} of a protein. We
have also studied the parametric dependence of the folding dynamics on
temperature, viscosity, non-Markovian character of bath in presence of the
external field
Generalized quantum Fokker-Planck, diffusion and Smoluchowski equations with true probability distribution functions
Traditionally, the quantum Brownian motion is described by Fokker-Planck or
diffusion equations in terms of quasi-probability distribution functions, e.g.,
Wigner functions. These often become singular or negative in the full quantum
regime. In this paper a simple approach to non-Markovian theory of quantum
Brownian motion using {\it true probability distribution functions} is
presented. Based on an initial coherent state representation of the bath
oscillators and an equilibrium canonical distribution of the quantum mechanical
mean values of their co-ordinates and momenta we derive a generalized quantum
Langevin equation in -numbers and show that the latter is amenable to a
theoretical analysis in terms of the classical theory of non-Markovian
dynamics. The corresponding Fokker-Planck, diffusion and the Smoluchowski
equations are the {\it exact} quantum analogues of their classical
counterparts. The present work is {\it independent} of path integral
techniques. The theory as developed here is a natural extension of its
classical version and is valid for arbitrary temperature and friction
(Smoluchowski equation being considered in the overdamped limit).Comment: RevTex, 16 pages, 7 figures, To appear in Physical Review E (minor
revision
Awareness of vaccination status and its predictors among working people in Switzerland
BACKGROUND: Adult vaccination status may be difficult to obtain, often requiring providers to rely on individual patient recall. To determine vaccination status awareness and the sociodemographic predictors of awareness for tetanus, hepatitis A and B, tick born encephalitis (TBE) and influenza vaccination. METHODS: Multivariate analyses were used to evaluate a questionnaire survey of 10 321 employees (4070 women and 6251 men aged 15–72 years) of two companies in Switzerland. RESULTS: Among 10 321 respondents, 75.5% reported knowing their tetanus vaccination status, 64.1% hepatitis A, 61.1% hepatitis B, 64.3% TBE and 71.9% influenza. Between 1 in 4 and 1 in 3 employees were not aware of their vaccination status. Differences in awareness for the five vaccinations considered correlated with gender and language. These differences persisted in multivariate analyses. CONCLUSION: Women employees, German-speaking employees and employees who paid more attention to their diet were more often aware of their vaccination status. A more reliable and readily accessible data source for vaccination status is needed in order to capitalize on opportunities to update vaccinations among Swiss employees
Kinetics of self-induced aggregation of Brownian particles: non-Markovian and non-Gaussian features
In this paper we have studied a model for self-induced aggregation in
Brownian particle incorporating the non-Markovian and non-Gaussian character of
the associated random noise process. In this model the time evolution of each
individual is guided by an over-damped Langevin equation of motion with a
non-local drift resulting from the local unbalance distributions of the other
individuals. Our simulation result shows that colored nose can induce the
cluster formation even at large noise strength. Another observation is that
critical noise strength grows very rapidly with increase of noise correlation
time for Gaussian noise than non Gaussian one. However, at long time limit the
cluster number in aggregation process decreases with time following a power
law. The exponent in the power law increases remarkable for switching from
Markovian to non Markovian noise process
Microbiological analysis of skin and soft tissue infections in cancer patients at Apeksha Hospital, Sri Lanka
Background: Skin and soft tissue infections (SSTIs) in patients with malignancies are common and frequently have serious consequences. These infections are caused by a wide range of microorganisms with variable anti-microbial susceptibilities.Objectives: To analyse skin and soft tissue infections in cancer patients at Apeksha Hospital with regard to causative agents, antibiotic susceptibility and associated factors.Methods: A descriptive cross sectional study was carried out for 18-month period. Specimens from adult cancer patients admitted to Apeksha Hospital, Maharagama with SSTIs were analysed. Aerobic and anaerobic bacterial culture, fungal culture, species identification and antibiotic susceptibility testing were performed. Clinical data were obtained from patient records.Results: A total of 85 patients were included with a male: female ratio of 1:1.1.Majority (75%) were >50 years old. Out of the 80 aerobic bacterial isolates most (69%) were Gram negatives, majority being Enterobateriaceae (42/80) followed by Pseudomonas (11/80). Escherichia coli was the commonest bacterial species. Staphylococcus aureus was the commonestGram positive organism (22/80). No strict anaerobic bacteria were yielded however, 3 fungi (two Candida albicans, one Fusarium species) were isolated. Enterobacteria showed lowest resistance to amikacin (7%) and meropenem (10%). Pseudomonas species had highest resistance to ticarcillin-clavulanate (64%). Methicillin resistant Staphylococcus aureus (MRSA) rate was 61%. None had resistance to anti-MRSA agents. Gram-negative bacteria caused 74% of wound infections while 54% of the abscesses were caused by Gram positives. Gram negatives were prevalent (73%) in patients with solid organ cancers and Gram positives in haematological malignancies (83%). Gram-negative infections (69%) predominate in patients on radiotherapy while chemoptherapy had similar rates of infections by the two types of organisms.Conclusion: SSTIs in the cancer patients at Apeksha Hospital, Maharagama are mainly caused by Gram negative bacteria however, Gram positives predominate in haematological malignancies. Multi-drug resistance is prevalent in all commonly isolated pathogens.Acknowledgements: University of Sri Jayewardenepura research grant ASP/01/R/MED/2016/61 (Centre for Cancer Research
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