Difference in Structure and Electronic Properties of Oxygen Vacancies in α-Quartz and α-Cristobalite Phases of SiO2

α-cristobalite (α-C) is a polymorph of silica, mainly found in space exploration and geochemistry research. Due to similar densities, α-C is often used as a proxy for amorphous SiO2, particularly in computer simulations of SiO2 surfaces and interfaces. However, little is known about the properties of α-C and its basic oxygen defects. Using density functional theory (DFT) simulations we provide a comprehensive report on the properties of perfect structure and oxygen vacancies in α-C. The calculated properties of α-C are compared with those of the better-characterized α-quartz (α-Q). Our results demonstrated that the positively charged O vacancy in α-C is most stable in the dimer configuration, in contrast to α-Q, which favors the puckered configuration. A back-projected configuration was also predicted in both polymorphs. We calculated the optical transition energies and isotropic hyperfine constants for O vacancies in both α-Q and α-C, and compared our findings with the results of previous studies and experiments. This work, thus, offers one of the first in-depth investigations of the properties of oxygen vacancies in α-C

Defects in WS2 monolayer calculated with a nonlocal functional: any difference from GGA?

Density Functional Theory (DFT) with Generalized Gradient Approximation (GGA) functionals is commonly used to predict defect properties in 2D transition metal dichalcogenides (TMDs). Since GGA functionals often underestimate bandgaps of semiconductors and incorrectly describe the character of electron localization in defects and their level positions within the band-gap, it is important to assess the accuracy of these predictions. To this end, we used the non-local density functional PBE0-TC-LRC to calculate the properties of a wide range of intrinsic defects in monolayer WS2. The properties, such as geometry, in-gap states, charge transition levels, electronic structure and the electron/hole localization of the lowest formation energy defects are discussed in detail. They are broadly similar to those predicted by the GGA PBE functional but exhibit numerous quantitative differences caused by the degree of electron and hole localization in charged states. For some anti-site defects, more significant differences are seen, with both changes in defect geometries (differences of up to 0.5 Å) as well as defect level positions within the band gap of WS2. This work provides an insight into the performance of functionals chosen for future DFT calculations of transition metal dichalcogenides with respect to the desired defect properties

Perceived Mental Illness Stigma Among Youth in Psychiatric Outpatient Treatment

This research explores the experiences of mental illness stigma in 24 youth (58.3% male, 13–24 years, 75% Latino) in psychiatric outpatient treatment. Using Link and Phelan’s (2001) model of stigmatization, we conducted thematic analysis of the interview texts, examining experiences of stigma at individual and structural levels, in addition to the youths’ social-psychological processes. Youth in psychiatric treatment acknowledged that their larger cultural context holds pejorative viewpoints toward those with mental illness and reported experiences of stigma within their families and social networks. Our results also offer insight into the social-psychological processes of stigma, highlighting how labeling may influence their self-concept and the strategies in which youth engage to manage a stigmatized identity. We discuss differences in stigma experiences by gender, age, and diagnosis. Findings provide new information on the stigma experiences of youth in psychiatric treatment and suggest that a multilevel approach to reduce stigma is warranted

Eosinophils Are Important for Protection, Immunoregulation and Pathology during Infection with Nematode Microfilariae

Eosinophil responses typify both allergic and parasitic helminth disease. In helminthic disease, the role of eosinophils can be both protective in immune responses and destructive in pathological responses. To investigate whether eosinophils are involved in both protection and pathology during filarial nematode infection, we explored the role of eosinophils and their granule proteins, eosinophil peroxidase (EPO) and major basic protein-1 (MBP-1), during infection with Brugia malayi microfilariae. Using eosinophil-deficient mice (PHIL), we further clarify the role of eosinophils in clearance of microfilariae during primary, but not challenge infection in vivo. Deletion of EPO or MBP-1 alone was insufficient to abrogate parasite clearance suggesting that either these molecules are redundant or eosinophils act indirectly in parasite clearance via augmentation of other protective responses. Absence of eosinophils increased mast cell recruitment, but not other cell types, into the broncho-alveolar lavage fluid during challenge infection. In addition absence of eosinophils or EPO alone, augmented parasite-induced IgE responses, as measured by ELISA, demonstrating that eosinophils are involved in regulation of IgE. Whole body plethysmography indicated that nematode-induced changes in airway physiology were reduced in challenge infection in the absence of eosinophils and also during primary infection in the absence of EPO alone. However lack of eosinophils or MBP-1 actually increased goblet cell mucus production. We did not find any major differences in cytokine responses in the absence of eosinophils, EPO or MBP-1. These results reveal that eosinophils actively participate in regulation of IgE and goblet cell mucus production via granule secretion during nematode-induced pathology and highlight their importance both as effector cells, as damage-inducing cells and as supervisory cells that shape both innate and adaptive immunity

A model for adapting evidence-based behavioral interventions to a new culture: HIV prevention for psychiatric patients in Rio de Janeiro, Brazil

As in other countries worldwide, adults with severe mental illness in Brazil have elevated rates of HIV infection relative to the general population. However, no HIV prevention interventions have been tested for efficacy with psychiatric patients in Brazil. We conducted participatory research with local providers, community leaders, patient advocates, and patients using an intervention adaptation process designed to balance fidelity to efficacious interventions developed elsewhere with fit to a new context and culture. Our process for adapting these interventions comprised four steps: (1) optimizing fidelity; (2) optimizing fit; (3) balancing fidelity and fit; and (4) pilot testing and refining the intervention. This paper describes how these steps were carried out to produce a Brazilian HIV prevention intervention for people with severe mental illness. Our process may serve as a model for adapting existing efficacious interventions to new groups and cultures, whether at a local, national, or international level

Homogenization via formal multiscale asymptotics and volume averaging: How do the two techniques compare?

A wide variety of techniques have been developed to homogenize transport equations in multiscale and multiphase systems. This has yielded a rich and diverse field, but has also resulted in the emergence of isolated scientific communities and disconnected bodies of literature. Here, our goal is to bridge the gap between formal multiscale asymptotics and the volume averaging theory. We illustrate the methodologies via a simple example application describing a parabolic transport problem and, in so doing, compare their respective advantages/disadvantages from a practical point of view. This paper is also intended as a pedagogical guide and may be viewed as a tutorial for graduate students as we provide historical context, detail subtle points with great care, and reference many fundamental works

Bostonia: The Boston University Alumni Magazine. Volume 14

Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs