Driven Disordered Polymorphic Solids: Phases and Phase Transitions, Dynamical Coexistence and Peak Effect Anomalies

We study a model for the depinning and driven steady state phases of a solid tuned across a polymorphic phase transition between ground states of triangular and square symmetry. These include pinned states which may have dominantly triangular or square correlations, a plastically flowing liquid-like phase, a moving phase with hexatic correlations, flowing triangular and square states and a dynamic coexistence regime characterized by the complex interconversion of locally square and triangular regions. We locate these phases in a dynamical phase diagram. We demonstrate that the apparent power-law orientational correlations we obtain in our moving hexatic phase arise from circularly averaging an orientational correlation function with qualitatively different behaviour in the longitudinal (drive) and transverse directions. The intermediate coexistence regime exhibits several novel properties, including substantial enhancement in the current noise, an unusual power-law spectrum of current fluctuations and striking metastability effects. This noise arises from the fluctuations of the interface separating locally square and triangular ordered regions. We demonstrate the breakdown of effective ``shaking temperature'' treatments in the coexistence regime by showing that such shaking temperatures are non-monotonic functions of the drive in this regime. Finally we discuss the relevance of these simulations to the anomalous behaviour seen in the peak effect regime of vortex lines in the disordered mixed phase of type-II superconductors. We propose that this anomalous behavior is directly linked to the behavior exhibited in our simulations in the dynamical coexistence regime, thus suggesting a possible solution to the problem of the origin of peak effect anomalies.Comment: 22 pages, double column, higher quality figures available from author

Effect of fluid-colloid interactions on the mobility of a thermophoretic microswimmer in non-ideal fluids

Janus colloids propelled by light, e.g., thermophoretic particles, offer promising prospects as artificial microswimmers. However, their swimming behavior and its dependence on fluid properties and fluid-colloid interactions remain poorly understood. Here, we investigate the behavior of a thermophoretic Janus colloid in its own temperature gradient using numerical simulations. The dissipative particle dynamics method with energy conservation is used to investigate the behavior in non-ideal and ideal-gas like fluids for different fluid-colloid interactions, boundary conditions, and temperature-controlling strategies. The fluid-colloid interactions appear to have a strong effect on the colloid behavior, since they directly affect heat exchange between the colloid surface and the fluid. The simulation results show that a reduction of the heat exchange at the fluid-colloid interface leads to an enhancement of colloid's thermophoretic mobility. The colloid behavior is found to be different in non-ideal and ideal fluids, suggesting that fluid compressibility plays a significant role. The flow field around the colloid surface is found to be dominated by a source-dipole, in agreement with the recent theoretical and simulation predictions. Finally, different temperature-control strategies do not appear to have a strong effect on the colloid's swimming velocity

Chemotactic predator-prey dynamics

A discrete chemotactic predator-prey model is proposed in which the prey secrets a diffusing chemical which is sensed by the predator and vice versa. Two dynamical states corresponding to catching and escaping are identified and it is shown that steady hunting is unstable. For the escape process, the predator-prey distance is diffusive for short times but exhibits a transient subdiffusive behavior which scales as a power law $t^{1/3}$ with time $t$ and ultimately crosses over to diffusion again. This allows to classify the motility and dynamics of various predatory bacteria and phagocytes. In particular, there is a distinct region in the parameter space where they prove to be infallible predators.Comment: 4 pages, 4 figure

Driven Disordered Periodic Media with an Underlying Structural Phase Transition

We investigate the driven states of a two-dimensional crystal whose ground state can be tuned through a square-triangular transition. The depinning of such a system from a quenched random background potential occurs via a complex sequence of dynamical states, which include plastic flow states, hexatics, dynamically stabilized triangle and square phases and intermediate regimes of phase coexistence. These results are relevant to transport experiments in the mixed phase of several superconductors which exhibit such structural transitions as well as to driven colloidal systems whose interactions can be tuned via surface modifications.Comment: Two-column, 4 pages, figures include

Chronic musculoskeletal pain among elderly individuals in a rural area of West Bengal: A mixed-method study

Introduction: The high prevalence among elderly individuals and potential adverse impact on their overall life quality make chronic musculoskeletal pain a significant public health concern. Chronic musculoskeletal pain is an important cause of self-medication, which must be addressed to avoid various side effects and improve elderly health. This study aimed to determine the prevalence of chronic musculoskeletal pain and its associated factors among individuals (age ≥60 years) in rural West Bengal and explore their perspectives and perceived barriers regarding pain and its management. Methods: This mixed-method study was conducted in rural West Bengal from December 2021 to June 2022. The quantitative strand was conducted by interviewing 255 elderly participants (age ≥60 years) using a structured questionnaire. The qualitative strand was conducted via in-depth interviews of 10 patients with chronic pain. Quantitative data were analyzed using SPSS version 16, and chronic pain-related factors were analyzed using logistic regression models. Qualitative data were analyzed thematically. Results: Among the participants, 56.8% reported chronic musculoskeletal pain. The most frequently affected site was the knee joint. Comorbidity (adjusted odds ratio [aOR]=7.47, 95% confidence interval [CI]=3.2–17.5), age (aOR=5.16, 95% CI=2.2–13.5), depression (aOR=2.96, 95% CI=1.2–6.7) and over-the-counter drug usage (aOR=2.51, 95% CI=1.1–6.4) were significantly associated with chronic pain. Analgesic dependency, lack of motivation to adopt lifestyle modifications, lack of knowledge on analgesic side effects were considered pain management barriers. Conclusion: Managing comorbidities, providing mental support, generating awareness of analgesic side effects, strengthening healthcare facilities should be prioritized for holistic chronic musculoskeletal pain management

Determinants of Modern Contraceptive Usage among Married Women: A Mixed-Methods Study in a Rural Community of India

Objective: A woman’s multifaceted feelings, knowledge, and perceptions of their intimate relations greatly influence their contraceptive behavior. In addition, women empowerment has been increasingly recognized as a key factor in family planning and reproductive health outcomes. This study aimed to assess modern contraceptive usage and its determinants among currently married women of reproductive-age (WRA) in rural Bengal. Materials and Methods: This mixed-method study was conducted in a rural area of Hooghly District, West Bengal from April to September 2021. The quantitative strand of the study was conducted by interviewing 210 currently married WRA. The qualitative strand was conducted via focussed group discussions among husbands/mothersin-law and in-depth interviews with healthcare workers. SPSS software was utilized for quantitative data analysis and factors associated with contraceptive usage were analyzed using logistic regression models. Qualitative data were analyzed thematically. Result: Currently 114 (54.8%) study participants were using modern contraceptive methods. Education (aOR=7.65, 95% CI=1.85-31.67), empowerment through freedom from family domination (aOR=5.56, 95% CI=1.30-23.66), attitude on contraception (aOR=4.67, 95% CI=1.26-17.19), and family planning counselling (aOR=4.41, 95% CI=1.12-17.33) were found to be significantly associated with modern contraceptive usage. Lack of couple counselling, family support, and knowledge gap was identified as the major barriers to contraceptive usage. Conclusion: Since a woman’s decision-making ability significantly affects their sexual and reproductive health outcomes, effective measures should be undertaken to empower them by creating awareness regarding their rights and freedom to make strategic life choices. Couple counselling should be prioritized to enhance male involvement and eliminate perceived barriers