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The detrimental effects of hydrogen and helium on structural materials undergoing irradiation are well documented, if not well understood. There is experimental evidence to suggest that a synergistic effect between the two elements exists, which results in increased damage when both are present. This situation is expected in the next generation of fusion and fission reactors, so a fundamental understanding of these synergistic interactions is needed to predict materials performance. We perform atomistic simulations of hydrogen and helium bubbles in body-centered cubic iron to determine the mechanism behind this effect. We first develop an interatomic potential suitable for describing the interactions between hydrogen and helium. Through analysis of the energetics and structure of these bubbles, we explain the observed synergy as a consequence of bubble growth through helium induced loop punching, aided by the presence of hydrogen, instead of as a direct interaction between hydrogen and helium. The hydrogen benefits from an increased area of free surface on which to bind.

BackgroundPublic housing residents have a high risk of chronic disease, which may be related to neighborhood environmental factors. Our objective was to understand how public housing residents perceive that the social and built environments might influence their health and wellbeing.MethodsWe conducted focus groups of residents from a low-income public housing community in Baltimore, MD to assess their perceptions of health and neighborhood attributes, resources, and social structure. Focus groups were audio-recorded and transcribed verbatim. Two investigators independently coded transcripts for thematic content using editing style analysis technique.ResultsTwenty-eight residents participated in six focus groups. All were African American and the majority were women. Most had lived in public housing for more than 5 years. We identified four themes: public housing’s unhealthy physical environment limits health and wellbeing, the city environment limits opportunities for healthy lifestyle choices, lack of trust in relationships contributes to social isolation, and increased neighborhood social capital could improve wellbeing.ConclusionsChanges in housing and city policies might lead to improved environmental health conditions for public housing residents. Policymakers and researchers may consider promoting community cohesiveness to attempt to empower residents in facilitating neighborhood change.

Vikram Patel and other global mental health leaders call for a special session of the UN General Assembly to discuss and debate action needed on mental, neurological, and substance use disorders, which have been left off the international NCDs agenda.

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Hydrogen may be trapped in voids in iron, leading to undesirable material properties. In this paper, the energetics of small hydrogen-vacancy clusters in body centered cubic iron are investigated. Results from two interatomic potentials are compared. We use molecular dynamics and Monte Carlo methods to find the minimum energy configurations of voids of up to ten vacancies containing up to 50 hydrogen atoms with ratios of hydrogen to vacancy of 10 or less. The formation energies and binding energies of defects to these clusters are calculated. Our results indicate that the hydrogen stabilizes bubbles by causing vacancies to be more tightly bound to clusters, while neighboring irons are less tightly bound. Hydrogen itself becomes less well bound to clusters as the inventory increases. The more physically relevant potential indicates a maximum supported ratio of hydrogen atoms to vacancies of about 4.

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The behavior of hydrogen in iron and iron alloys is of interest in many fields of physics and materials science. To enable large-scale molecular dynamics simulations of systems with Fe-H interactions, we develop, based on densityfunctional theory calculations, an interatomic Fe-H potential in the TersoffBrenner formalism. The obtained analytical potential is suitable for simulations of H in bulk Fe as well as for modeling small FeH molecules, and it can be directly combined with our previously constructed potential for the stainless steel Fe-Cr-C system. This will allow simulations of, e.g., hydrocarbon molecule chemistry on steel surfaces. In the current work, we apply the potential to simulating hydrogen-induced embrittlement in monocrystalline bulk Fe and in an Fe bicrystal with a grain boundary. In both cases, hydrogen is found to soften the material.