Nucleation Rate of Hadron Bubbles in Baryon-Free Quark-Gluon Plasma

We evaluate the factor $\kappa$ appearing in Langer's expression for the nucleation rate extended to the case of hadron bubbles forming in zero baryon number cooled quark-gluon plasma. We consider both the absence and presence of viscosity and show that viscous effects introduce only small changes in the value of $\kappa$Comment: 9 pages, revtex, no figures Full postscript version available at via the WWW at http://nucth.physics.wisc.edu/preprints/ or by via from ftp://nucth.physics.wisc.edu/pub/preprints/mad-nt-95-06.p

Dynamic wormholes, anti-trapped surfaces, and energy conditions

Adapting and extending a suggestion due to Page, we define a wormhole throat to be a marginally anti-trapped surface, that is, a closed two-dimensional spatial hypersurface such that one of the two future-directed null geodesic congruences orthogonal to it is just beginning to diverge. Typically a dynamic wormhole will possess two such throats, corresponding to the two orthogonal null geodesic congruences, and these two throats will not coincide, (though they do coalesce into a single throat in the static limit). The divergence property of the null geodesics at the marginally anti-trapped surface generalizes the ``flare-out'' condition for an arbitrary wormhole. We derive theorems regarding violations of the null energy condition (NEC) at and near these throats and find that, even for wormholes with arbitrary time-dependence, the violation of the NEC is a generic property of wormhole throats. We also discuss wormhole throats in the presence of fully antisymmetric torsion and find that the energy condition violations cannot be dumped into the torsion degrees of freedom. Finally by means of a concrete example we demonstrate that even temporary suspension of energy-condition violations is incompatible with the flare-out property of dynamic throats.Comment: 32 pages in plain LaTex, no figures. Additional text and references adde

Black Men Who Have Sex with Men and Lifetime HIV Testing: Characterizing the Reasons and Consequences of Having Never Tested for HIV

HIV testing remains a critical point of entry to HIV treatment services and now biomedical prevention as well. Yet despite the high HIV prevalence among Black men who have sex with men (MSM), insufficient attention has been given to factors associated with those Black MSM in the United States who have never received an HIV test in their lifetime. Promoting Our Worth, Equality, & Resilience (POWER) is a cross-sectional observational study that recruited Black MSM at Black Pride events across six cities in the United States from 2014 to 2017. Participants completed an anonymous questionnaire and were offered free, confidential HIV testing. Of the 4174 Black MSM without a prior HIV diagnosis, 404 (9.68%) had never tested for HIV (mean age = 31.03 years). Lower education and greater internalized homophobia were associated with never having tested for HIV. Higher age (AOR = 1.05, 95%, 1.02–1.07) and assumption of HIV-positivity (AOR = 3.24, 95% CI 1.53–6.84) were both associated with increased odds of an HIV-positive test result (n = 119; 36%). To compare, HIV prevalence among Black MSM who had received at least one HIV test before study participation was 23%. While a minority of Black MSM had never received an HIV test, this group had a significantly higher likelihood of HIV infection. Alternative HIV testing strategies are needed to facilitate HIV testing initiation among Black MSM for whom conventional HIV testing modalities are insufficient

Is Quantum Chaos Weaker Than Classical Chaos?

We investigate chaotic behavior in a 2-D Hamiltonian system - oscillators with anharmonic coupling. We compare the classical system with quantum system. Via the quantum action, we construct Poincar\'{e} sections and compute Lyapunov exponents for the quantum system. We find that the quantum system is globally less chaotic than the classical system. We also observe with increasing energy the distribution of Lyapunov exponts approaching a Gaussian with a strong correlation between its mean value and energy.Comment: text (LaTeX) + 7 figs.(ps

Slow relaxation in weakly open vertex-splitting rational polygons

The problem of splitting effects by vertex angles is discussed for nonintegrable rational polygonal billiards. A statistical analysis of the decay dynamics in weakly open polygons is given through the orbit survival probability. Two distinct channels for the late-time relaxation of type 1/t^delta are established. The primary channel, associated with the universal relaxation of ''regular'' orbits, with delta = 1, is common for both the closed and open, chaotic and nonchaotic billiards. The secondary relaxation channel, with delta > 1, is originated from ''irregular'' orbits and is due to the rationality of vertices.Comment: Key words: Dynamics of systems of particles, control of chaos, channels of relaxation. 21 pages, 4 figure

Injection drug use, unknown HIV positive status, and self-reported current PrEP use among Black men who have sex with men attending U.S. Black pride events, 2014–2017

Objective: Black gay, bisexual, and other men who have sex with men (BMSM) are at elevated risk for HIV infection in the United States. BMSM who inject drugs may be face even higher HIV risk. Methods: Random time-location sampling was used to survey BMSM attending Black Pride events in 6 U.S. cities about HIV risk and protective behaviors, including injection drug use, prior HIV testing, and pre-exposure prophylaxis (PrEP). 3429 individuals who reported a HIV negative/unknown serostatus at enrollment were included in the analysis. HIV status was determined by in-field rapid HIV testing. Results: 3.6% of BMSM had injected drugs in their lifetime and 58.5% of BMSM who had injected drugs reported sharing syringes in the past six months. BMSM who had injected drugs more commonly reported current PrEP use than BMSM who had never injected (32.5% vs. 8.2%, p < 0.001). BMSM who had injected drugs were 3.6-fold (95% CI: 2.4, 5.4) more likely to report currently using PrEP than BMSM who had never injected after adjustment for sociodemographic, substance use, and sexual risk characteristics. Among BMSM who reported ever injecting drugs (n = 123), 31.7% tested HIV positive. HIV prevalence did not differ by self-reported PrEP use among BMSM who had injected drugs (p = 0.59). Conclusions: BMSM who inject drugs who reported currently using PrEP were no less likely to test positive for HIV than those who did not use PrEP. Wrap-around services to support consistent PrEP use and long-acting PrEP formulations may improve the effectiveness of PrEP among BMSM who inject drugs

Syndemic Health Disparities and Sexually Transmitted Infection Burden Among Black Men Who Have Sex with Men Engaged in Sex Work in the U.S.

Black men who have sex with men (MSM) engaged in sex work (BMSM-SW) experience elevated HIV and sexually transmitted infection (STI) prevalence. Further, BMSM-SW have been shown to have higher rates of syndemic psychosocial health conditions which contribute to HIV risk behavior and incidence, and poorer care outcomes than other groups of men who have sex with men. However, syndemic perspectives have not been applied to understanding past-year STI burden among BMSM-SW in the U.S. Sexually active Black MSM ≥ 18 years old were recruited from Black Pride events in six U.S. cities (n = 4421) between 2014 and 2017. Multivariable logistic regressions assessed correlates of past-year sex work engagement; whether BMSM-SW had higher odds of syndemic conditions; and whether BMSM-SW had higher odds of self-reported, past-year STI diagnoses. Structural equation models assessed relationships between sex work engagement, syndemic conditions, and STI controlled for sociodemographics and number of sexual partners. A total of 254 (5.7%) Black MSM reported past-year sex work, of whom 45.3% were HIV positive. BMSM-SW were significantly more likely to be Hispanic, to report past-year bisexual behavior, and to report annual income < $10,000. In multivariable models, BMSM-SW were significantly more likely to report intimate partner violence, assault victimization, polydrug use, and depression symptoms; they were also more likely to report past-year gonorrhea, chlamydia, and syphilis. Syndemic conditions mediated the relationship between past-year sex work and past-year STI burden, constituting a significant indirect effect. BMSM-SW in the U.S. face severe biopsychosocial health disparities. Interventions developed for BMSM engaged in sex work are lacking. Our results suggest that interventions containing safer sex work education and sex-positive biobehavioral HIV/STI prevention alongside substance use, mental health, employment, and education components will be most effective

Singular solutions of fully nonlinear elliptic equations and applications

We study the properties of solutions of fully nonlinear, positively homogeneous elliptic equations near boundary points of Lipschitz domains at which the solution may be singular. We show that these equations have two positive solutions in each cone of $\mathbb{R}^n$, and the solutions are unique in an appropriate sense. We introduce a new method for analyzing the behavior of solutions near certain Lipschitz boundary points, which permits us to classify isolated boundary singularities of solutions which are bounded from either above or below. We also obtain a sharp Phragm\'en-Lindel\"of result as well as a principle of positive singularities in certain Lipschitz domains.Comment: 41 pages, 2 figure

Prevalence and Correlates of PrEP Awareness and Use Among Black Men Who Have Sex with Men and Women (MSMW) in the United States

Men who have sex with men and women (MSMW), including those who are Black, experience HIV-related disparities compared to men who have sex with men only (MSMO). Few studies have assessed the prevalence and correlates of pre-exposure prophylaxis (PrEP) awareness and use among Black MSMW. We recruited MSM ≥ 18 attending Black Gay Pride events between 2014–2017. We conducted multivariable logistic regressions to assess differences in PrEP awareness and use among HIV-negative Black MSM (n = 2398) and within Black MSMW (n = 419). MSMW were less likely than MSMO to report PrEP awareness (p < 0.001). Among PrEP-aware MSM, MSMW were more likely than MSMO to report PrEP use (p < 0.05). MSMW receiving gay community support were more likely to be PrEP-aware (p < 0.01). MSMW reporting any past-year STI diagnoses were more likely to report PrEP use (p < 0.01). Findings suggest that PrEP awareness campaigns tailored for Black MSMW, concomitant with STI-to-PrEP interventions, will facilitate greater PrEP uptake in this population

Orthogonality conditions and asymptotic stability in the Stefan problem with surface tension

We prove nonlinear asymptotic stability of steady spheres in the two-phase Stefan problem with surface tension. Our method relies on the introduction of appropriate orthogonality conditions in conjunction with a high-order energy method.Comment: 25 pages, important references added, two remarks added, typos correcte