Dynamics of a Pair of Interacting Spins Coupled to an Environmental Sea

We solve for the dynamics of a pair of spins, coupled to each other and also to an environmental sea of oscillators. The environment mediates an indirect interaction between the spins, causing both mutual coherence effects and dissipation. This model describes a wide variety of physical systems, ranging from 2 coupled microscopic systems (eg., magnetic impurities, bromophores, etc), to 2 coupled macroscopic quantum systems. We obtain analytic results for 3 regimes, viz., (i) The locked regime, where the 2 spins lock together; (ii) The correlated relaxation regime (mutually correlated incoherent relaxation); and (iii) The mutual coherence regime, with correlated damped oscillations. These results cover most of the parameter space of the system.Comment: 49 pages, To appear in Int J. Mod. Phys.

A Note in the Skyrme Model with Higher Derivative Terms

Another stabilizer term is used in the classical Hamiltonian of the Skyrme Model that permits in a much simple way the generalization of the higher-order terms in the pion derivative field. Improved numerical results are obtained.Comment: Latex. Figure not include; available upon request. 7 pages, report

Dynamics and Kinetic Roughening of Interfaces in Two-Dimensional Forced Wetting

We consider the dynamics and kinetic roughening of wetting fronts in the case of forced wetting driven by a constant mass flux into a 2D disordered medium. We employ a coarse-grained phase field model with local conservation of density, which has been developed earlier for spontaneous imbibition driven by a capillary forces. The forced flow creates interfaces that propagate at a constant average velocity. We first derive a linearized equation of motion for the interface fluctuations using projection methods. From this we extract a time-independent crossover length $\xi_\times$, which separates two regimes of dissipative behavior and governs the kinetic roughening of the interfaces by giving an upper cutoff for the extent of the fluctuations. By numerically integrating the phase field model, we find that the interfaces are superrough with a roughness exponent of $\chi = 1.35 \pm 0.05$, a growth exponent of $\beta = 0.50 \pm 0.02$, and $\xi_\times \sim v^{-1/2}$ as a function of the velocity. These results are in good agreement with recent experiments on Hele-Shaw cells. We also make a direct numerical comparison between the solutions of the full phase field model and the corresponding linearized interface equation. Good agreement is found in spatial correlations, while the temporal correlations in the two models are somewhat different.Comment: 9 pages, 4 figures, submitted to Eur.Phys.J.

Propagation on networks: an exact alternative perspective

By generating the specifics of a network structure only when needed (on-the-fly), we derive a simple stochastic process that exactly models the time evolution of susceptible-infectious dynamics on finite-size networks. The small number of dynamical variables of this birth-death Markov process greatly simplifies analytical calculations. We show how a dual analytical description, treating large scale epidemics with a Gaussian approximations and small outbreaks with a branching process, provides an accurate approximation of the distribution even for rather small networks. The approach also offers important computational advantages and generalizes to a vast class of systems.Comment: 8 pages, 4 figure

Interface dynamics and kinetic roughening in fractals

We consider the dynamics and kinetic roughening of single-valued interfaces in two-dimensional fractal media. Assuming that the local height difference distribution function of the fronts obeys Levý statistics with a well-defined power-law decay exponent, we derive analytic expressions for the local scaling exponents. We also show that the kinetic roughening of the interfaces displays anomalous scaling and multiscaling in the relevant correlation functions. For invasion percolation models, the exponents can be obtained from the fractal geometry of percolation clusters. Our predictions are in excellent agreement with numerical simulations.Peer reviewe

Randomized Controlled Trial of an Internet Application to Reduce HIV Transmission Behavior Among HIV Infected Men Who have Sex with Men.

We conducted a prospective, randomized controlled trial of an internet-based safer-sex intervention to reduce HIV transmission risk behaviors. HIV-infected men who have sex with men (n = 179) were randomized to receive a monthly internet survey alone or a monthly survey plus tailored risk reduction messages over 12 months. The primary outcome was the cumulative sexually transmitted infection (STI) incidence over 12 months. Secondary outcomes included self-reported unprotected sex with an at risk partner and disclosure of HIV status to partners. In a modified intent to treat analysis, there was no difference in 12-month STI incidence between the intervention and control arms (30 vs. 25 %, respectively; p = 0.5). Unprotected sex decreased and disclosure increased over time in both study arms. These improvements suggest that addition of the risk-reduction messages provided little benefit beyond the self-monitoring of risky behavior via regular self-report risk behavior assessments (as was done in both study arms)

Interface Equations for Capillary Rise in Random Environment

We consider the influence of quenched noise upon interface dynamics in 2D and 3D capillary rise with rough walls by using phase-field approach, where the local conservation of mass in the bulk is explicitly included. In the 2D case the disorder is assumed to be in the effective mobility coefficient, while in the 3D case we explicitly consider the influence of locally fluctuating geometry along a solid wall using a generalized curvilinear coordinate transformation. To obtain the equations of motion for meniscus and contact lines, we develop a systematic projection formalism which allows inclusion of disorder. Using this formalism, we derive linearized equations of motion for the meniscus and contact line variables, which become local in the Fourier space representation. These dispersion relations contain effective noise that is linearly proportional to the velocity. The deterministic parts of our dispersion relations agree with results obtained from other similar studies in the proper limits. However, the forms of the noise terms derived here are quantitatively different from the other studies

Antiretroviral therapy experience, satisfaction, and preferences among a diverse sample of young adults living with HIV

Youth and young adults living with HIV (YLWH) have a high HIV infection rate and suboptimal oral medication adherence. Biomedical researchers hope that long-acting antiretroviral therapy (LAART) modalities can help those who struggle with daily oral adherence. While adults living with HIV have expressed interest in LAART, little research has explored perspectives of YLWH. This study explores ART experiences and perspectives on LAART through qualitative interviews with twenty diverse YLWH (18–29) in the United States. Data were analyzed using framework analysis. Most participants were satisfied with their current ART yet had experienced side effects or had struggled with daily adherence. Preferences for improving daily oral ART included making pills smaller and reformulating ART into flavored chewable gummies. Most expressed enthusiasm for LAART, although needle aversion and previous injection drug use were potential barriers for some. Approximately half were interested in an ART patch, though its visibility and fear of stigmatization was concerning. Few expressed interest in implantable ART, calling it unappealing. Although younger people are most likely to benefit from these advancements in HIV treatment, additional research is needed to identify gaps in uptake and to further explore perspectives of YLWH to improve the success of new treatment modalities