Macroscopic acoustoelectric charge transport in graphene

Copyright © 2013 AIP PublishingWe demonstrate macroscopic acoustoelectric transport in graphene, transferred onto piezoelectric lithium niobate substrates, between electrodes up to 500 μm apart. Using double finger interdigital transducers we have characterised the acoustoelectric current as a function of both surface acoustic wave intensity and frequency. The results are consistent with a relatively simple classical relaxation model, in which the acoustoelectric current is proportional to both the surface acoustic wave intensity and the attenuation of the wave caused by the charge transport.Royal Societ

Reduced entomopathogen abundance in <i>Myrmica</i> ant nests-testing a possible immunological benefit of myrmecophily using <i>Galleria mellonella</i> as a model

Social insects such as ants have evolved collective rather than individual immune defence strategies against diseases and parasites at the level of their societies (colonies), known as social immunity. Ants frequently host other arthropods, so-called myrmecophiles, in their nests. Here, we tested the hypothesis that myrmecophily may partly arise from selection for exploiting the ants’ social immunity. We used larvae of the wax moth Galleria mellonella as ‘model myrmecophiles’ (baits) to test this hypothesis. We found significantly reduced abundance of entomopathogens in ant nests compared with the surrounding environment. Specific entomopathogen groups (Isaria fumosorosea and nematodes) were also found to be significantly less abundant inside than outside ant nests, whereas one entomopathogen (Beauveria brongniartii) was significantly more abundant inside nests. We therefore hypothesize that immunological benefits of entering ant nests may provide us a new explanation of why natural selection acts in favour of such a life-history strategy

Thermal emission from large area chemical vapor deposited graphene devices

Copyright © 2013 AIP PublishingThe spatial variation of thermal emission from large area graphene grown by chemical vapor deposition, transferred onto SiO2/Si substrates and fabricated into field effect transistor structures, has been investigated using infra-red microscopy. A peak in thermal emission occurs, the position of which can be altered by reversal of the current direction. The experimental results are compared with a one dimensional finite element model, which accounts for Joule heating and electrostatic effects, and it is found that the thermal emission is governed by the charge distribution in the graphene and maximum Joule heating occurs at the point of minimum charge density.This research was supported by the Engineering and Physical Sciences Research Council, and the European Union under the FET-open grant GOSFELEngineering and Physical Sciences Research Council (EPSRC)European Unio

Cooperation and Self-Regulation in a Model of Agents Playing Different Games

A simple model for cooperation between "selfish" agents, which play an extended version of the Prisoner's Dilemma(PD) game, in which they use arbitrary payoffs, is presented and studied. A continuous variable, representing the probability of cooperation, $p_k(t) \in$ [0,1], is assigned to each agent $k$ at time $t$. At each time step $t$ a pair of agents, chosen at random, interact by playing the game. The players update their $p_k(t)$ using a criteria based on the comparison of their utilities with the simplest estimate for expected income. The agents have no memory and use strategies not based on direct reciprocity nor 'tags'. Depending on the payoff matrix, the systems self-organizes - after a transient - into stationary states characterized by their average probability of cooperation $\bar{p}_{eq}$ and average equilibrium per-capita-income $\bar{p}_{eq},\bar{U}_\infty$. It turns out that the model exhibit some results that contradict the intuition. In particular, some games which - {\it a priory}- seems to favor defection most, may produce a relatively high degree of cooperation. Conversely, other games, which one would bet that lead to maximum cooperation, indeed are not the optimal for producing cooperation.Comment: 11 pages, 3 figures, keybords: Complex adaptive systems, Agent-based models, Social system

Phase-Field Approach for Faceted Solidification

We extend the phase-field approach to model the solidification of faceted materials. Our approach consists of using an approximate gamma-plot with rounded cusps that can approach arbitrarily closely the true gamma-plot with sharp cusps that correspond to faceted orientations. The phase-field equations are solved in the thin-interface limit with local equilibrium at the solid-liquid interface [A. Karma and W.-J. Rappel, Phys. Rev. E53, R3017 (1996)]. The convergence of our approach is first demonstrated for equilibrium shapes. The growth of faceted needle crystals in an undercooled melt is then studied as a function of undercooling and the cusp amplitude delta for a gamma-plot of the form 1+delta(|sin(theta)|+|cos(theta)|). The phase-field results are consistent with the scaling law "Lambda inversely proportional to the square root of V" observed experimentally, where Lambda is the facet length and V is the growth rate. In addition, the variation of V and Lambda with delta is found to be reasonably well predicted by an approximate sharp-interface analytical theory that includes capillary effects and assumes circular and parabolic forms for the front and trailing rough parts of the needle crystal, respectively.Comment: 1O pages, 2 tables, 17 figure

Underestimation of Potentially Traumatic Events Resulting From Underreporting of Physical and Sexual Violence Among People Entering Care for HIV in Cameroon

Objective: Measures ascertaining exposure to potentially traumatic events (PTEs) frequently ask respondents about experienced physical and sexual violence. However, little is known about the performance of physical and sexual violence questions on PTE assessments and its effect on PTE classification overall. We estimated underreporting of physical and sexual violence on a PTE assessment among individuals entering HIV care in Cameroon. Method: We compared reports of physical and sexual violence captured via a behaviorally specific measure of intimate partner violence (IPV; Demographic and Health Survey [DHS] domestic violence module = referent) to those captured via two single-item questions that assessed exposure to physical and sexual PTEs during one’s adult life to determine the degree of underreporting on the single-item PTE assessment questions. We explored correlates of underreporting on the PTE assessment using Pearson’s chisquared tests. Results: Overall, 99 (23%) and 113 (27%) of 426 total participants reported instances of sexual and physical violence in their most recent partnership on the behaviorally specific DHS IPV module, respectively. Of those reporting sexual and physical IPV on the DHS module, just 6% (n = 6) and 52% (n = 59) reported sexual and physical violence as an adult on the single-item PTE assessment questions, respectively. Underreporting of physical violence on the PTE assessment was associated with lower educational attainment (p <.05) and reporting being punched (p <.01) or having one’s hair pulled or arm twisted (p <.05) by one’s most recent partner. Conclusions: PTE assessment tools should assess exposure to behaviorally specific acts of violence to ensure appropriate referral to services among survivors of IPV

Mental health and initiation of antiretroviral treatment at enrolment into HIV care in Cameroon under a national “treat all” policy: a cross-sectional analysis

Introduction: Rapid antiretroviral treatment (ART) initiation reduces time from HIV infection to viral suppression, decreasing HIV transmission risk. Mental health symptoms may influence timing of ART initiation. This study estimated the prevalence of ART initiation at enrolment into HIV care and the relationship between mental health and ART initiation at enrolment into HIV care. Methods: We conducted interviews with 426 individuals initiating HIV care in Cameroon between June 2019 and March 2020 to estimate the association between mental health and timing of ART initiation. Depression (Patient Health Questionnaire-9; cut-point 10), anxiety (Generalized Anxiety Disorder-7; cut-point 10), post-traumatic stress disorder (PTSD) (PTSD Checklist for DSM-5; cut-point 31) and harmful alcohol use (Alcohol Use Disorders Identification Test; cut-point 16) were dichotomized to represent those with and without each exposure at first HIV care appointment. Date of ART initiation (date ART prescribed) was ascertained from medical records. Separate multivariable log-binomial regression models were used to estimate the association between mental health exposures and ART initiation at enrolment into care. Results and discussion: Overall, 87% initiated ART at enrolment into HIV care. Approximately 20% reported depressive symptoms, 15% reported PTSD symptoms, 12% reported anxiety symptoms and 13% reported harmful alcohol use. In multivariable analyses, individuals with moderate to severe depressive symptoms had 1.7 (95% confidence interval [CI] 1.1, 2.7) times the prevalence of not initiating ART at enrolment into HIV care compared to those with no or mild depressive symptoms. Those with symptoms of PTSD, compared to those without, had 1.9 (95% CI 1.2, 2.9) times the prevalence of not initiating ART at enrolment into HIV care. Symptoms of anxiety or harmful drinking were not associated with ART initiation at enrolment into HIV care in multivariable models. Conclusions: Symptoms of depression and PTSD were associated with lower prevalence of ART initiation at enrolment into HIV care among this sample of individuals initiating HIV care in Cameroon under a “treat all” policy. Research should examine barriers to timely ART initiation, whether incorporating mental health services into HIV care improves timely ART initiation, and whether untreated symptoms of depression and PTSD drive suboptimal HIV care outcomes

Correlates of self-reported history of mental health help-seeking: a cross-sectional study among individuals with symptoms of a mental or substance use disorder initiating care for HIV in Cameroon

Background: Mental health and substance use disorders (MSDs) increase the risk of poor human immunodeficiency virus (HIV) care outcomes among people living with HIV (PLWH). Receipt of mental health care may improve these adverse outcomes. We aimed to identify correlates of prior mental health help-seeking among PLWH with symptoms of an MSD in Cameroon. Methods: We characterize prior mental health help-seeking from formal (mental health specialist/general medical provider) and informal (traditional healer/religious leader) sources among 161 people with symptoms of depression (Patient Health Questionnaire-9 scores> 9), anxiety (General Anxiety Disorder-7 scores> 9), probable post-traumatic stress disorder (PTSD Checklist for DSM-5 scores> 30), or possible alcohol use disorder (Alcohol Use Disorders Identification Test scores≥16) who were newly entering HIV care at three healthcare facilities in Cameroon between June 2019 and March 2020. Help-seeking was defined as ever speaking to a formal or informal source about emotional problems, sadness, or the way they were feeling or behaving. We estimated the association between sociodemographic and psychosocial measures and lifetime mental health help-seeking from each type of source using log-binomial regression. Results: Overall, 55.3% of 161 PLWH with MSD symptoms reported prior mental health help-seeking, with 24.2% and 46.0% seeking help from formal and informal sources, respectively. Religious leaders were the most common source of help (40.4%), followed by general medical professionals (22.4%), traditional healers (16.8%), and mental health specialists (7.4%). Individuals with higher depressive, anxiety, and trauma symptom severity scores were more likely to have sought help than those with lower scores. Individuals with possible alcohol use disorder were the least likely to have sought help. Prior help-seeking was more common among those reporting a higher number of lifetime traumatic events (prevalence ratio [PR]: 1.06; 95% confidence interval [CI]: 1.01, 1.11) and those with a history of emotional intimate partner violence (PR: 1.34; 95% CI: 1.01, 1.80). Conclusions: Prior mental health help-seeking was associated with psychosocial stressors. Help-seeking from informal networks was more common than formal help-seeking. Training in the provision of evidence-based mental health support for informal networks could improve access to mental health care for PLWH with MSDs in Cameroon

Prevalence of potentially traumatic events and symptoms of depression, anxiety, hazardous alcohol use, and post-traumatic stress disorder among people with HIV initiating HIV care in Cameroon

Background: This study explored the relationship between specific types of potentially traumatic events (PTEs) and symptoms of mental health disorders among people with HIV (PWH) in Cameroon. Methods: We conducted a cross-sectional study with 426 PWH in Cameroon between 2019–2020. Multivariable log binominal regression was used to estimate the association between exposure (yes/no) to six distinct types of PTE and symptoms of depression (Patient Health Questionnaire-9 score > 9), PTSD (PTSD Checklist for DSM-5 score > 30), anxiety (Generalized Anxiety Disorder-7 scale score > 9), and hazardous alcohol use (Alcohol Use Disorders Identification Test score > 7 for men; > 6 for women). Results: A majority of study participants (96%) reported exposure to at least one PTE, with a median of 4 PTEs (interquartile range: 2–5). The most commonly reported PTEs were seeing someone seriously injured or killed (45%), family members hitting or harming one another as a child (43%), physical assault or abuse from an intimate partner (42%) and witnessing physical assault or abuse (41%). In multivariable analyses, the prevalence of PTSD symptoms was significantly higher among those who reported experiencing PTEs during childhood, violent PTEs during adulthood, and the death of a child. The prevalence of anxiety symptoms was significantly higher among those who reported experiencing both PTEs during childhood and violent PTEs during adulthood. No significant positive associations were observed between specific PTEs explored and symptoms of depression or hazardous alcohol use after adjustment. Conclusions: PTEs were common among this sample of PWH in Cameroon and associated with PTSD and anxiety symptoms. Research is needed to foster primary prevention of PTEs and to address the mental health sequelae of PTEs among PWH

Prevalence of stressful life events and associations with symptoms of depression, anxiety, and post-traumatic stress disorder among people entering care for HIV in Cameroon

Background: Exposure to stressors increases the risk of mental health disorders. People living with HIV (PLWH) are particularly affected by poor mental health which can contribute to adverse HIV treatment outcomes. Methods: We estimated the prevalence of recent stressful life events (modified Life Events Survey) among a cohort of PLWH entering HIV care at three public health care facilities in Cameroon and quantified the association of seven types of stressful life events with symptoms of depression (Patient Health Questionnaire-9 scores>9), anxiety (General Anxiety Disorder-7 scores>9), and PTSD (PTSD Checklist for DSM-5 scores>30) using separate log-binomial regression models. Results: Of 426 PLWH enrolling in care, a majority were women (59%), in relationships (58%), and aged 21 to 39 years (58%). Recent death of a family member (39%) and severe illness of a family member (34%) were the most commonly reported stressful life events. In multivariable analyses, more stressful life event types, a negative relationship change, death or illness of a friend/family member, experience of violence, work-related difficulties, and feeling unsafe in one's neighborhood were independently associated with at least one of the mental health outcomes assessed. The greatest magnitude of association was observed between work-related difficulties and PTSD (adjusted prevalence ratio: 3.1; 95% confidence interval: 2.0–4.8). Limitations: Given the design of our study, findings are subject to recall and social desirability bias. Conclusions: Stressful life events were common among this population of PLWH entering care in Cameroon. Evidence-based interventions that improve coping, stress management, and mental health are needed