Particle dynamics in a symmetrically driven underdamped inhomogeneous periodic potential system

We numerically solve the underdamped Langevin equation to obtain the trajectories of a particle in a sinusoidal potential driven by a temporally sinusoidal force in a medium with coefficient of friction periodic in space as the potential but with a phase difference. With the appropriate choice of system parameters, like the mean friction coefficient and the period of the applied field, only two kinds of periodic trajectories are obtained for all possible initial conditions at low noise strengths: one with a large amplitude and a large phase lag with respect to the applied field and the other with a small amplitude and a small phase lag. Thus, the periodic potential system is effectively mapped dynamically into a bistable system. Though the directional asymmetry, brought about only by the frictional inhomogeneity, is weak we find both the phenomena of stochastic resonance, with ready explanation in terms of the two dynamical states of trajectories, and ratchet effect simultaneously in the same parameter space. We analyse the results in detail attempting to find plausible explanations for each.Comment: The paper has been submitted to Physical Review

Brownian rectifiers in the presence of temporally asymmetric unbiased forces

The efficiency of energy transduction in a temporally asymmetric rocked ratchet is studied. Time asymmetry favours current in one direction and suppresses it in the opposite direction due to which large efficiency ~ 50% is readily obtained. The spatial asymmetry in the potential together with system inhomogeneity may help in further enhancing the efficiency. Fine tuning of system parameters considered leads to multiple current reversals even in the adiabatic regime

Multiple current reversals in forced inhomogeneous ratchets

Transport properties of overdamped Brownian paricles in a rocked thermal ratchet with space dependent friction coefficient is studied. By tuning the parameters, the direction of current exhibit multiple reversals, both as a function of the thermal noise strength as well as the amplitude of rocking force. Current reversals also occur under deterministic conditions and exhibits intriguing structure. All these features arise due to mutual interplay between potential asymmetry,noise, driving frequency and inhomogeneous friction.Comment: 6 figure

Asymmetric motion in a double-well under the action of zero-mean Gaussian white noise and periodic forcing

Residence times of a particle in both the wells of a double-well system, under the action of zero-mean Gaussian white noise and zero-averaged but temporally asymmetric periodic forcings, are recorded in a numerical simulation. The difference between the relative mean residence times in the two wells shows monotonic variation as a function of asymmetry in the periodic forcing and for a given asymmetry the difference becomes largest at an optimum value of the noise strength. Moreover, the passages from one well to the other become less synchronous at small noise strength as the asymmetry parameter (defined below) differs from zero, but at relatively larger noise strengths the passages become more synchronous with asymmetry in the field sweep. We propose that asymmetric periodic forcing (with zero mean) could provide a simple but sensible physical model for unidirectional motion in a symmetric periodic system aided by a symmetric Gaussian white noise.Comment: Appeared in PRE March 1997, figures available on reques

Joint estimation of CD4+ cell progression and survival in untreated individuals with HIV-1 infection

Objective: We compiled the largest dataset of seroconverter cohorts to date from 25 countries across Africa, North America, Europe, and Southeast/East (SE/E) Asia to simultaneously estimate transition rates between CD4+ cell stages and death, in antiretroviral therapy (ART)-naive HIV-1-infected individuals. Design: A hidden Markov model incorporating a misclassification matrix was used to represent natural short-term fluctuations and measurement errors in CD4+ cell counts. Covariates were included to estimate the transition rates and survival probabilities for each subgroup. Results: The median follow-up time for 16 373 eligible individuals was 4.1 years (interquartile range 1.7–7.1), and the mean age at seroconversion was 31.1 years (SD 8.8). A total of 14 525 individuals had recorded CD4+ cell counts pre-ART, 1885 died, and 6947 initiated ART. Median (interquartile range) survival for men aged 20 years at seroconversion was 13.0 (12.4–13.4), 11.6 (10.9–12.3), and 8.3 years (7.9–8.9) in Europe/North America, Africa, and SE/E Asia, respectively. Mortality rates increase with age (hazard ratio 2.22, 95% confidence interval 1.84–2.67 for >45 years compared with <25 years) and vary by region (hazard ratio 2.68, 1.75–4.12 for Africa and 1.88, 1.50–2.35 for Asia compared with Europe/North America). CD4+ cell decline was significantly faster in Asian cohorts compared with Europe/North America (hazard ratio 1.45, 1.36–1.54). Conclusion: Mortality and CD4+ cell progression rates exhibited regional and age-specific differences, with decreased survival in African and SE/E Asian cohorts compared with Europe/North America and in older age groups. This extensive dataset reveals heterogeneities between regions and ages, which should be incorporated into future HIV models

Effects of Snail Density on Growth, Reproduction and Survival of Biomphalaria alexandrina Exposed to Schistosoma mansoni

The effects of snail density on Biomphalaria alexandrina parasitized with Schistosoma mansoni were investigated. Laboratory experiments were used to quantify the impact of high density on snail growth, fecundity, and survival. Density-dependent birth rates of snails were determined to inform mathematical models, which, until now, have assumed a linear relationship between density and fecundity. The experiments show that the rate of egg-laying followed a negative exponential distribution with increasing density and this was significantly affected by exposure to parasitic infection. High density also affected the weight of snails and survival to a greater degree than exposure to parasitic infection. Although snail growth rates were initially constrained by high density, they retained the potential for growth suggesting a reversible density-dependent mechanism. These experimental data can be used to parameterise models and confirm that snail populations are regulated by nonlinear density-dependent mechanisms

THERAPEUTIC MANAGEMENT OF PRAVAHIKA (AMOEBIC DYSENTERY) THROUGH AYURVEDIC REGIMEN: A CASE STUDY

Hurry, worry and curry are the three factors which causes intestinal upsets frequently and leads to gastrointestinal problems in modern life. Pravahika (Amoebic dysentery) is also one of the important and oftenly occurring Vyadhis of Annavaha and Pureeshvaha Srotasas in current time. Pravahika is the Pakwasahayagata kaphajavikara with symptoms of Sarakta mala, Sapravahana mala, Sakapha mala, Daah, Jwara, Bhrama Daurbalya, Anannabhilsha, Sweda and Trishna. A case report of a patient with a history of loose motion with mucous discharge for the 6 months visited Ayurveda OPD, is presented in this study. Routine stool examination, blood glucose, serum lipid profile and liver function test were performed. The patient was treated with Ayurvedic medicine Kutajghan vati (1 gm), Bilvadi churna with Takra (6 gm) and, Chitrakadi Gutika (250 mg) in divided doses for 1 month. The patient was followed up for every 7th day and there was significant improvement in the clinical features after 1 month of treatment with the Ayurvedic medicines. There were no side effects reported. This case study demonstrates the therapeutic efficacy of Bilvadi churna, Kutajghan vati and Chitrakadi Gutika in the rapid management of Pravahika.