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The mRNA-1273 vaccine was approved for emergency use in December 2020; trial participants who received placebo were informed of the results and offered vaccination. At the close of the blinded phase of the trial, the vaccine efficacy in preventing Covid-19 illness was 93.2%, and the efficacy against severe disease was 98.2%. No new safety issues were identified.

It is demonstrated that Bragg coherent diffraction imaging can be used to visualize dislocation propagation in three dimensions during the repeated growth and dissolution of calcite crystals. Atomic-level defects such as dislocations play key roles in determining the macroscopic properties of crystalline materials 1 , 2 . Their effects range from increased chemical reactivity 3 , 4 to enhanced mechanical properties 5 , 6 . Dislocations have been widely studied using traditional techniques such as X-ray diffraction and optical imaging. Recent advances have enabled atomic force microscopy to study single dislocations 7 in two dimensions, while transmission electron microscopy (TEM) can now visualize strain fields in three dimensions with near-atomic resolution 8 , 9 , 10 . However, these techniques cannot offer three-dimensional imaging of the formation or movement of dislocations during dynamic processes. Here, we describe how Bragg coherent diffraction imaging (BCDI; refs  11 , 12 ) can be used to visualize in three dimensions, the entire network of dislocations present within an individual calcite crystal during repeated growth and dissolution cycles. These investigations demonstrate the potential of BCDI for studying the mechanisms underlying the response of crystalline materials to external stimuli.

Focussed Ion Beam (FIB) milling is a mainstay of nano-scale machining. By manipulating a tightly focussed beam of energetic ions, often gallium (Ga + ), FIB can sculpt nanostructures via localised sputtering. This ability to cut solid matter on the nano-scale revolutionised sample preparation across the life, earth and materials sciences. Despite its widespread usage, detailed understanding of the FIB-induced structural damage, intrinsic to the technique, remains elusive. Here we examine the defects caused by FIB in initially pristine objects. Using Bragg Coherent X-ray Diffraction Imaging (BCDI), we are able to spatially-resolve the full lattice strain tensor in FIB-milled gold nano-crystals. We find that every use of FIB causes large lattice distortions. Even very low ion doses, typical of FIB imaging and previously thought negligible, have a dramatic effect. Our results are consistent with a damage microstructure dominated by vacancies, highlighting the importance of free-surfaces in determining which defects are retained. At larger ion fluences, used during FIB-milling, we observe an extended dislocation network that causes stresses far beyond the bulk tensile strength of gold. These observations provide new fundamental insight into the nature of the damage created and the defects that lead to a surprisingly inhomogeneous morphology.

Objectives Latinos are disproportionately vulnerable to severe COVID-19 due to workplace exposure, multigenerational households, and existing health disparities. Rolling out COVID-19 vaccines among vulnerable Latinos is critical to address disparities. This study explores vaccine perceptions of Latino families to inform culturally centered strategies for vaccine dissemination. Method Semistructured telephone interviews with Latino families (22 mothers and 24 youth, 13–18 years old) explored COVID-19 vaccine perceptions including (1) sources of information, (2) trust of vaccine effectiveness and willingness to get vaccinated, and (3) access to the vaccine distribution. We identified thematic patterns using immersion–crystallization. Results We found that (1) 41% expressed optimism and willingness to receive the vaccine coupled with concerns about side effects; (2) 45% expressed hesitancy or would refuse vaccination based on mistrust, myths, fear of being used as “guinea pigs,” and the perceived role of politics in vaccine development; (3) families “digested” information gathered from social media, the news, and radio through intergenerational communication; and (4) participants called for community-led advocacy and “leading by example” to dispel fear and misinformation. Optimistic participants saw the vaccine as a way to protect their families, allowing youth to return to schools and providing safer conditions for frontline essential workers. Conclusions Culturally centered vaccine promotion campaigns may consider the Latino family unit as their target audience by providing information that can be discussed among parents and youth, engaging a range of health providers and advocates that includes traditional practitioners and community health workers, and disseminating information at key venues, such as schools, churches, and supermarkets.

The evolution of morphology and internal strain under high pressure fundamentally alters the physical property, structural stability, phase transition and deformation mechanism of materials. Until now, only averaged strain distributions have been studied. Bragg coherent X-ray diffraction imaging is highly sensitive to the internal strain distribution of individual crystals but requires coherent illumination, which can be compromised by the complex high-pressure sample environment. Here we report the successful de-convolution of these effects with the recently developed mutual coherent function method to reveal the three-dimensional strain distribution inside a 400 nm gold single crystal during compression within a diamond-anvil cell. The three-dimensional morphology and evolution of the strain under pressures up to 6.4 GPa were obtained with better than 30 nm spatial resolution. In addition to providing a new approach for high-pressure nanotechnology and rheology studies, we draw fundamental conclusions about the origin of the anomalous compressibility of nanocrystals. Extreme pressure can induce significant changes in a material’s mechanical response, but characterizing the evolution of these changes as they take place is challenging. Yang et al . demonstrate the use of coherent X-ray diffraction imaging to follow changes in the three-dimensional shape and strain fields within gold particles under pressure.

We report an experimental ptychography measurement performed in fly-scan mode. With a visible-light laser source, we demonstrate a 5-fold reduction of data acquisition time. By including multiple mutually incoherent modes into the incident illumination, high quality images were successfully reconstructed from blurry diffraction patterns. This approach significantly increases the throughput of ptychography, especially for three-dimensional applications and the visualization of dynamic systems.

Zeolites are three-dimensional aluminosilicates having unique properties from the size and connectivity of their sub-nanometer pores, the Si/Al ratio of the anionic framework, and the charge-balancing cations. The inhomogeneous distribution of the cations affects their catalytic performances because it influences the intra-crystalline diffusion rates of the reactants and products. However, the structural deformation regarding inhomogeneous active regions during the catalysis is not yet observed by conventional analytical tools. Here we employ in situ X-ray free electron laser-based time-resolved coherent X-ray diffraction imaging to investigate the internal deformations originating from the inhomogeneous Cu ion distributions in Cu-exchanged ZSM-5 zeolite crystals during the deoxygenation of nitrogen oxides with propene. We show that the interactions between the reactants and the active sites lead to an unusual strain distribution, confirmed by density functional theory simulations. These observations provide insights into the role of structural inhomogeneity in zeolites during catalysis and will assist the future design of zeolites for their applications. Study of structural inhomogeneities in zeolites is important but limited by conventional techniques. Here the authors employ in situ free-electron-laser-based time-resolved coherent X-ray diffraction imaging to visualize the effect of these inhomogeneities during catalytic deoxygenation of NOx.

Background: Pre-exposure prophylaxis (PrEP) is an important tool for HIV prevention in Latin America and the Caribbean (LAC). Yet, little is known about the PrEP policies landscape in the region. Addressing this gap, this scoping review assessed current PrEP policies throughout LAC to better understand existing PrEP implementation gaps and identify opportunities to improve access. Methods: We conducted a scoping review, using a modified PRISMA extension, through 28 July 2022, to identify country-level PrEP policies. Data were collected in English, Spanish, French, and Portuguese utilizing online platforms for screening and data extraction (Google Forms, Zotero, and Excel). Extracted data were divided by data source, including country-level government policies, gray literature, and peer-reviewed literature, with at least one full-text reviewer and data extractor per publication. An iterative summative content analysis was performed to compare and interpret themes across phases and data sources. Results: Of the 33 countries in LAC, 22 (67%) had policies approving daily oral PrEP for HIV prevention, which outlined specific key populations, including men who have sex with men, transgender women, sex workers, and serodiscordant couples. Generic tenofovir disoproxil fumarate/emtricitabine has been approved in 15 of the 33 countries, and 13 of the 33 countries have incorporated PrEP into their public health system. No countries were found to have approved cabotegravir. Costing data were reported by only one country, Ecuador, in its national health ministry guidelines. Findings also document a lag between the media/gray-literature announcement of PrEP and implementation of policies. Conclusion: Findings underscore significant advances in PrEP policies in the region and signal opportunities for greater PrEP implementation. Since 2017, an increasing number of countries have begun to provide PrEP to communities at heightened need, although significant gaps remain. Policy approval is a key step to further increasing access to PrEP in LAC, necessary to reduce the burden of HIV in LAC, specifically among marginalized populations.

There is a fundamental interest in studying photoinduced dynamics in nanoparticles and nanostructures as it provides insight into their mechanical and thermal properties out of equilibrium and during phase transitions. Nanoparticles can display significantly different properties from the bulk, which is due to the interplay between their size, morphology, crystallinity, defect concentration, and surface properties. Particularly interesting scenarios arise when nanoparticles undergo phase transitions, such as melting induced by an optical laser. Current theoretical evidence suggests that nanoparticles can undergo reversible nonhomogenous melting with the formation of a core-shell structure consisting of a liquid outer layer. To date, studies from ensembles of nanoparticles have tentatively suggested that such mechanisms are present. Here we demonstrate imaging transient melting and softening of the acoustic phonon modes of an individual gold nanocrystal, using an X-ray free electron laser. The results demonstrate that the transient melting is reversible and nonhomogenous, consistent with a core-shell model of melting. The results have implications for understanding transient processes in nanoparticles and determining their elastic properties as they undergo phase transitions. Significance Despite phase transitions, such as melting, being ubiquitous in nature, understanding what occurs at the nanoscale (such as in nanocrystals) has so far remained challenging. With ensemble studies of nanocrystals it is often difficult to discriminate between intrinsic size-dependent properties and effects due to sample size and shape dispersity. Here, using an X-ray free electron laser we image the reversible melting of an individual nanocrystal induced by an ultrashort laser. It is revealed that the melting occurs transiently, repeatably, and inhomogeneously. This is consistent with a core-shell model where the exterior is melted and a solid core remains. These findings reveal, unambiguously, that core-shell melting occurs, which has important implications for understanding nanoscale phenomena.

Introduction Social networks contribute to normative reinforcement of HIV prevention strategies, knowledge sharing, and social capital, but little research has characterized the social networks of transgender women (TW) in Latin America. We conducted a mixed methods analysis of three network clusters of TW in Lima, Peru, to evaluate network composition, types of support exchanged, and patterns of communication. Methods We recruited TW residing in or affiliated with three “ casas trans ” (houses shared among TW) in Lima between April-May 2018. Eligible participants were 18 or older, self-reported HIV-negative, and reported recent intercourse with a cis-male partner. Participants completed demographic questionnaires, social network interviews, and semi-structured interviews to assess egocentric network structures, support exchanged, and communication patterns. Quantitative and qualitative data were analyzed using Stata v14.1 and Atlas.ti, respectively. Results Of 20 TW, median age was 26 years and 100% reported involvement in commercial sex work. Respondents identified 161 individuals they interacted with in the past month (alters), of whom 33% were TW and 52% family members. 70% of respondents reported receiving emotional support from family, while 30% received financial support and instrumental support from family. Of the 13 (65%) respondents who nominated someone as a source of HIV prevention support (HPS), the majority (69%) nominated other TW. In a GEE regression analysis adjusted for respondent education and region of birth, being a family member was associated with lower likelihood of providing financial support (aOR 0.21, CI 0.08–0.54), instrumental support (aOR 0.16, CI 0.06–0.39), and HPS (aOR 0.18, CI 0.05–0.64). In qualitative interviews, most respondents identified a cis-female family member as their most trusted and closest network member, but other TW were more often considered sources of day-to-day support, including HPS. Conclusion TW have diverse social networks where other TW are key sources of knowledge sharing and support, and family members may also represent important and influential components. Within these complex networks, TW may selectively solicit and provide support from different network alters according to specific contexts and needs. HIV prevention messaging could consider incorporating network-based interventions with TW community input and outreach efforts for supportive family members.