Wavenumber-explicit continuity and coercivity estimates in acoustic scattering by planar screens

We study the classical first-kind boundary integral equation reformulations of time-harmonic acoustic scattering by planar sound-soft (Dirichlet) and sound-hard (Neumann) screens. We prove continuity and coercivity of the relevant boundary integral operators (the acoustic single-layer and hypersingular operators respectively) in appropriate fractional Sobolev spaces, with wavenumber-explicit bounds on the continuity and coercivity constants. Our analysis is based on spectral representations for the boundary integral operators, and builds on results of Ha-Duong (Jpn J Ind Appl Math 7:489--513 (1990) and Integr Equat Oper Th 15:427--453 (1992)).Comment: v2 has minor corrections compared to v1. arXiv admin note: substantial text overlap with arXiv:1401.280

Structures and waves in a nonlinear heat-conducting medium

The paper is an overview of the main contributions of a Bulgarian team of researchers to the problem of finding the possible structures and waves in the open nonlinear heat conducting medium, described by a reaction-diffusion equation. Being posed and actively worked out by the Russian school of A. A. Samarskii and S.P. Kurdyumov since the seventies of the last century, this problem still contains open and challenging questions.Comment: 23 pages, 13 figures, the final publication will appear in Springer Proceedings in Mathematics and Statistics, Numerical Methods for PDEs: Theory, Algorithms and their Application

Macroscopic Car Condensation in a Parking Garage

An asymmetric exclusion process type process, where cars move forward along a closed road that starts and terminates at a parking garage, displays dynamic phase transitions into two types of condensate phases where the garage becomes macroscopically occupied. The total car density $\rho_o$ and the exit probability $\alpha$ are the two control parameters. At the transition, the number of parked cars $N_p$ diverges in both cases, with the length of the road $N_s$, as $N_p\sim N_s^{y_p}$ with $y_p=1/2$. Towards the transition, the number of parked cars vanishes as $N_p\sim \epsilon^\beta$ with $\beta=1$, $\epsilon=|\alpha -\alpha^*|$ or $\epsilon=|\rho^*_o -\rho_o|$ being the distance from the transition. The transition into the normal phase represents also the onset of transmission of information through the garage. This gives rise to unusual parked car autocorrelations and car density profiles near the garage, which depend strongly on the group velocity of the fluctuations along the road.Comment: 12 pages including 15 figures; published version in PR

Estimating the Effect of Depression on HIV Transmission Risk Behaviors Among People Who Inject Drugs in Vietnam: A Causal Approach

The burden of depression and HIV is high among people who inject drugs (PWID), yet the effect of depression on transmission risk behaviors is not well understood in this population. Using causal inference methods, we analyzed data from 455 PWID living with HIV in Vietnam 2009–2013. Study visits every 6 months over 2 years measured depressive symptoms in the past week and injecting and sexual behaviors in the prior 3 months. Severe depressive symptoms (vs. mild/no symptoms) increased injection equipment sharing (risk difference [RD] = 3.9 percentage points, 95% CI −1.7, 9.6) but not condomless sex (RD = −1.8, 95% CI −6.4, 2.8) as reported 6 months later. The cross-sectional association with injection equipment sharing at the same visit (RD = 6.2, 95% CI 1.4, 11.0) was stronger than the longitudinal effect. Interventions on depression among PWID may decrease sharing of injection equipment and the corresponding risk of HIV transmission. Clinical trial registration ClinicalTrials.gov NCT01689545

The role of depression in secondary HIV transmission among people who inject drugs in Vietnam: A mathematical modeling analysis

Background Among people who inject drugs (PWID), depression burden is high and may interfere with HIV prevention efforts. Although depression is known to affect injecting behaviors and HIV treatment, its overall impact on HIV transmission has not been quantified. Using mathematical modeling, we sought to estimate secondary HIV transmissions and identify differences by depression among PWID. Methods We analyzed longitudinal data from 455 PWID living with HIV in Vietnam during 2009–2013. Using a Bernoulli process model with individual-level viral load and behavioral data from baseline and 6-month follow-up visits, we estimated secondary HIV transmission events from participants to their potentially susceptible injecting partners. To evaluate differences by depression, we compared modeled transmissions per 1,000 PWID across depressive symptom categories (severe, mild, or no symptoms) in the three months before each visit. Results We estimated a median of 41.2 (2.5th, 97.5th percentiles: 33.2–49.2) secondary transmissions from all reported acts of sharing injection equipment with 833 injecting partners in the three months before baseline. Nearly half (41%) of modeled transmissions arose from fewer than 5% of participants in that period. Modeled transmissions per 1,000 PWID in that period were highest for severe depressive symptoms (100.4, 80.6–120.2) vs. mild (87.0, 68.2–109.4) or no symptoms (78.9, 63.4–94.1). Transmission estimates fell to near-zero at the 6-month visit. Conclusions Secondary transmissions were predicted to increase with depression severity, although most arose from a small number of participants. Our findings suggest that effective depression interventions could have the important added benefit of reducing HIV transmission among PWID. This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose

Depression, antiretroviral therapy initiation, and HIV viral suppression among people who inject drugs in Vietnam

Background: The burden of depression is high among people who inject drugs (PWID) and may contribute to the spread of HIV through poor treatment engagement and persistent viremia. We estimated the effects of depression on antiretroviral therapy (ART) initiation and viral suppression among PWID living with HIV. Methods: Longitudinal data were collected from 455 PWID living with HIV in Vietnam during 2009–2013. We estimated the 6- and 12-month cumulative incidence of ART initiation and viral suppression, accounting for time-varying confounding, competing events, and missing data. The cumulative incidence difference (CID) contrasted the incidence of each outcome had participants always vs. never experienced severe depressive symptoms across study visits to date. Results: Severe depressive symptoms decreased the cumulative incidence of ART initiation, with CID values comparing always vs. never having severe depressive symptoms of -7.5 percentage points (95% CI: -17.2, 2.2) at 6 months and -7.1 (95% CI: -17.9, 3.7) at 12 months. There was no appreciable difference in the cumulative incidence of viral suppression at 6 months (CID = 0.3, 95% CI: -11.3, 11.9) or 12 months (CID = 2.0, 95% CI: -21.8, 25.8). Limitations: Discrepancies between the ART initiation and viral suppression outcomes could be due to under-reporting of ART use and missing data on viral load. Conclusions: Future work probing the seemingly antagonistic effect of depression on treatment uptake – but not viral suppression – will inform the design of interventions promoting HIV clinical outcomes and reducing onward transmission among PWID

Depressive Symptoms at HIV Testing and Two-Year All-Cause Mortality Among Men Who Inject Drugs in Vietnam

People who inject drugs (PWID) with HIV experience an elevated risk of death. A potentially important determinant of survival is the high burden of depression. This study examined the relationship of depressive symptoms at HIV testing with 2-year all-cause mortality among newly diagnosed HIV-positive PWID in Vietnam. At HIV testing, 141 PWID (42%) experienced severe depressive symptoms, and over the 2 years following diagnosis, 82 PWID (24%) died. Controlling for potential confounders, the 2-year risk of death among those with depressive symptoms was 9.7% (95% CI − 1.2, 20.6%) higher than the risk among those without depressive symptoms. This increased risk of mortality for PWID with depressive symptoms was relatively consistent throughout the 2-year period: at 6, 12, and 18 months, the risk difference was 12.6% (5.5–19.7%), 13.9% (4.6–23.2%), and 11.0% (0.9–21.1%), respectively. HIV diagnosis may provide an important opportunity for depression screening and treatment, subsequently improving survival in this key population. Trial registry: ClinicalTrials.gov NCT01689545

Longitudinal Analysis of Depressive Symptoms, Perceived Social Support, and Alcohol Use among HIV-Infected Men Who Inject Drugs in Northern Vietnam

Background: Limited research examines depressive symptoms, alcohol use, and social support among HIV-infected people who inject drugs. Objectives: Using longitudinal data, we investigated whether perceived social support moderates the relationship between depressive symptoms and alcohol use among HIV-infected men who inject drugs in Vietnam. Methods: Data were collected from participants (N = 455; mean age 35 years) in a four-arm randomized controlled trial in Thai Nguyen, Vietnam. Data were collected at baseline, 6, 12, 18, and 24 months with 94% retention excluding dead (N = 103) or incarcerated (N = 37) participants. Multilevel growth models were used to assess whether: (1) depressive symptoms predict when risk of alcohol use is elevated (within-person effects); (2) depressive symptoms predict who is at risk for alcohol use (between-person effects); and (3) within- and between-person perceived social support moderates the depressive symptoms-alcohol relationship. Results: Participants reported high but declining levels of depressive symptoms and alcohol use. Participants with higher depressive symptoms drank less on average (B = −0.0819, 95% CI −0.133, −0.0307), but within-person, a given individual was more likely to drink when they were feeling more depressed than usual (B = 0.136, 95% CI 0.0880, 0.185). The positive relationship between within-person depressive symptoms and alcohol use grew stronger at higher levels of within-person perceived social support. Conclusions: HIV-infected men who inject drugs have increased alcohol use when they are experiencing higher depressive symptoms than usual, while those with higher average depressive symptoms over time report less alcohol use. Social support strengthens the positive relationship between within-person depressive symptoms and alcohol use

Modeling Translation in Protein Synthesis with TASEP: A Tutorial and Recent Developments

The phenomenon of protein synthesis has been modeled in terms of totally asymmetric simple exclusion processes (TASEP) since 1968. In this article, we provide a tutorial of the biological and mathematical aspects of this approach. We also summarize several new results, concerned with limited resources in the cell and simple estimates for the current (protein production rate) of a TASEP with inhomogeneous hopping rates, reflecting the characteristics of real genes.Comment: 25 pages, 7 figure