Crystallization of a classical two-dimensional electron system: Positional and orientational orders

Crystallization of a classical two-dimensional one-component plasma (electrons interacting with the Coulomb repulsion in a uniform neutralizing positive background) is investigated with a molecular dynamics simulation. The positional and the orientational correlation functions are calculated for the first time. We have found an indication that the solid phase has a quasi-long-range (power-law) positional order along with a long-range orientational order. This indicates that, although the long-range Coulomb interaction is outside the scope of Mermin's theorem, the absence of ordinary crystalline order at finite temperatures applies to the electron system as well. The `hexatic' phase, which is predicted between the liquid and the solid phases by the Kosterlitz-Thouless-Halperin-Nelson-Young theory, is also discussed.Comment: 3 pages, 4 figures; Corrected typos; Double columne

Ab Initio Molecular Dynamics Simulation of Liquid Ga_xAs_{1-x} Alloys

We report the results of ab initio molecular dynamics simulations of liquid Ga_xAs_{1-x} alloys at five different concentrations, at a temperature of 1600 K, just above the melting point of GaAs. The liquid is predicted to be metallic at all concentrations between x = 0.2 and x = 0.8, with a weak resistivity maximum near x = 0.5, consistent with the Faber-Ziman expression. The electronic density of states is finite at the Fermi energy for all concentrations; there is, however, a significant pseudogap especially in the As-rich samples. The Ga-rich density of states more closely resembles that of a free-electron metal. The partial structure factors show only a weak indication of chemical short-range order. There is also some residue of the covalent bonding found in the solid, which shows up in the bond-angle distribution functions of the liquid state. Finally, the atomic diffusion coefficients at 1600K are calculated to be 2.1 \times 10^{-4} cm^2/sec for Ga ions in Ga_{0.8}As_{0.2} and 1.7 \times 10^{-4} cm^2/sec for As ions in Ga_{0.2}As_{0.8}.Comment: 29 pages, 10 eps figures, accepted for publication in Phys. Rev.

Effect of stress-triaxiality on void growth in dynamic fracture of metals: a molecular dynamics study

The effect of stress-triaxiality on growth of a void in a three dimensional single-crystal face-centered-cubic (FCC) lattice has been studied. Molecular dynamics (MD) simulations using an embedded-atom (EAM) potential for copper have been performed at room temperature and using strain controlling with high strain rates ranging from 10^7/sec to 10^10/sec. Strain-rates of these magnitudes can be studied experimentally, e.g. using shock waves induced by laser ablation. Void growth has been simulated in three different conditions, namely uniaxial, biaxial, and triaxial expansion. The response of the system in the three cases have been compared in terms of the void growth rate, the detailed void shape evolution, and the stress-strain behavior including the development of plastic strain. Also macroscopic observables as plastic work and porosity have been computed from the atomistic level. The stress thresholds for void growth are found to be comparable with spall strength values determined by dynamic fracture experiments. The conventional macroscopic assumption that the mean plastic strain results from the growth of the void is validated. The evolution of the system in the uniaxial case is found to exhibit four different regimes: elastic expansion; plastic yielding, when the mean stress is nearly constant, but the stress-triaxiality increases rapidly together with exponential growth of the void; saturation of the stress-triaxiality; and finally the failure.Comment: 35 figures, which are small (and blurry) due to the space limitations; submitted (with original figures) to Physical Review B. Final versio

Hormone therapy and fractures in postmenopausal women

Background:Fracture rates have been reported to be higher among older women living with HIV (WLWH) than HIV- women. Hormone therapy with estrogen can reduce vasomotor symptoms (VMS) associated with menopause and prevent fractures. As data are limited on the benefits of hormone therapy use in WLWH, we examined associations of hormone therapy, use and fractures.Methods:A prospective study of 1765 (1350 WLWH and 415 HIV-) postmenopausal Women's Interagency HIV Study (WIHS) participants was performed, including self-reported hormone therapy, use and fracture data from 2003 to 2017. Proportional hazard models determined predictors of new fractures at any site or at typical fragility fracture sites (hip, spine, wrist).Results:At the first postmenopausal visit, the median (IQR) age of WLWH was slightly younger than HIV- women [49.8 (46.4-53) vs. 50.7 (47.5-54), P = 0.0002] and a smaller proportion of WLWH reported presence of VMS (17% vs. 26%, P < 0.0001). A greater proportion of WLWH than HIV- women reported hormone therapy use (8% vs. 4%, P = 0.007) at the first postmenopausal visit. In multivariate analyses, white race and smoking were significant predictors of incident fracture at any site but hormone therapy (P = 0.69) and HIV status (P = 0.53) were not.Conclusion:Our study did not find evidence of benefit or harm with regards to fracture outcomes in postmenopausal WLWH receiving hormone therapy. Further research is needed to determine whether hormone therapy has benefits beyond treatment of VMS, such as prevention of adverse aging-associated outcomes

Degree of Polypharmacy and Cognitive Function in Older Women with HIV

The number of people with HIV (PWH) experiencing age-associated comorbidities including those treated with medications and cognitive impairment is increasing. We examined associations between polypharmacy and cognition in older women with HIV (WWH) given their vulnerability to this comorbidity. Cross-sectional analysis capitalizing on Women's Interagency HIV Study data collected between 2014 and 2017. WWH meeting the following criteria were analyzed: age ≥50 years; availability of self-reported non-antiretroviral therapy (ART) medications data; and neuropsychological data. The number of non-ART medications used regularly in the prior 6 months was summed. Polypharmacy was categorized as none/low (0-4), moderate (5-9), or severe (≥10). Multivariable linear regression analyses examined polypharmacy-cognition (T-score) associations in the total sample and among virally suppressed (VS; < 20 copies/mL)-WWH after covariate adjustment for enrollment site, income, depressive symptoms, substance use (smoking, heavy alcohol, marijuana, crack, cocaine, and/or heroin), the Veterans Aging Cohort Study index (indicators of HIV disease and organ system function, hepatitis C virus serostatus), ART use, nadir CD4 count, and specific ART drugs (efavirenz, integrase inhibitors). We included 637 women (median age = 55 years; 72% Black). Ninety-four percent reported ART use in the past 6 months and 75% had HIV RNA <20 copies/mL. Comorbidity prevalence was high (61% hypertension; 26% diabetes). Moderate and severe polypharmacy in WWH were 34% and 24%. In WWH, severe polypharmacy was associated with poorer executive function (p = .007) and processing speed (p = .01). The same pattern of findings remained among VS-WWH. Moderate polypharmacy was not associated with cognition. Moderate and severe polypharmacy were common and associated with poorer executive function and processing speed in WWH. Severe polypharmacy may be a major contributor to the persistence of domain-specific cognitive complications in older WWH above and beyond the conditions that these medications are used to treat

White Blood Cell Counts, Lymphocyte Subsets, and Incident Diabetes Mellitus in Women Living with and without HIV

Diabetes mellitus (DM) is associated with expansion of proinflammatory lymphocyte subsets. We investigated the relationship of total white blood cell (WBC) count and lymphocyte subsets with incident DM in the Women's Interagency HIV Study (WIHS). Higher CD4 and CD8 T cell counts, lymphocyte count, and total WBC count were associated with incident DM among both women with and without HIV, although the association of CD8 was not statistically significant among women without HIV

Menopausal Hormone Therapy and Subclinical Cardiovascular Disease in Women With and Without Human Immunodeficiency Virus

Background: Estrogen-based hormone therapy (HT) may have beneficial cardiovascular effects when initiated in early menopause. This has not been examined in women with human immunodeficiency virus (HIV), who have heightened immune activation and cardiovascular risks. Methods: Among 609 postmenopausal women (1234 person-visits) in the Women's Interagency HIV Study, we examined the relationship of ever HT use (oral, patch, or vaginal) with subclinical atherosclerosis: carotid artery intima-media thickness (CIMT), distensibility, and plaque assessed via repeated B-mode ultrasound imaging (2004-2013). We also examined associations of HT with cross-sectional biomarkers of immune activation and D-dimer. Statistical models were adjusted for sociodemographic, behavioral, and cardiometabolic factors. Results: Women (mean age, 51 years; 80% HIV positive) who ever used HT at baseline were older, and more likely to be non-Hispanic White and report higher income, than never-users. Women who ever used HT had 43% lower prevalence of plaque (prevalence ratio, 0.57 [95% confidence interval {CI},. 40-.80]; P <. 01), 2.51 μm less progression of CIMT per year (95% CI, -4.60, to -.41; P =. 02), and marginally lower incidence of plaque over approximately 7 years (risk ratio, 0.38 [95% CI,. 14-1.03; P =. 06), compared with never-users, adjusting for covariates; ever HT use was not associated with distensibility. These findings were similar for women with and without HIV. Ever HT use was associated with lower serum D-dimer, but not with biomarkers of immune activation after covariate adjustment. Conclusions: HT may confer a subclinical cardiovascular benefit in women with HIV. These results begin to fill a knowledge gap in menopausal care for women with HIV, in whom uptake of HT is very low