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"Skidmore, J."
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Collapse dynamics of spherical cavities in a solid under shock loading
Extraordinary states of highly localised pressure and temperature can be generated upon the collapse of impulsively driven cavities. Direct observation of this phenomenon in solids has proved challenging, but recent advances in high-speed synchrotron radiography now permit the study of highly transient, subsurface events in real time. We present a study on the shock-induced collapse of spherical cavities in a solid polymethyl methacrylate medium, driven to shock states between 0.49 and 16.60 GPa. Utilising multi-MHz phase contrast radiography, extended sequences of the collapse process have been captured, revealing new details of interface motion, material failure and jet instability formation. Results reveal a rich array of collapse characteristics dominated by strength effects at low shock pressures and leading to a hydrodynamic response at the highest loading conditions.
Journal Article
Observations of pressure anisotropy effects within semi-collisional magnetized plasma bubbles
Magnetized plasma interactions are ubiquitous in astrophysical and laboratory plasmas. Various physical effects have been shown to be important within colliding plasma flows influenced by opposing magnetic fields, however, experimental verification of the mechanisms within the interaction region has remained elusive. Here we discuss a laser-plasma experiment whereby experimental results verify that Biermann battery generated magnetic fields are advected by Nernst flows and anisotropic pressure effects dominate these flows in a reconnection region. These fields are mapped using time-resolved proton probing in multiple directions. Various experimental, modelling and analytical techniques demonstrate the importance of anisotropic pressure in semi-collisional, high-
β
plasmas, causing a reduction in the magnitude of the reconnecting fields when compared to resistive processes. Anisotropic pressure dynamics are crucial in collisionless plasmas, but are often neglected in collisional plasmas. We show pressure anisotropy to be essential in maintaining the interaction layer, redistributing magnetic fields even for semi-collisional, high energy density physics (HEDP) regimes.
Magnetic fields can be reorganized by plasma flows and lead to effects such as magnetic reconnection. Here the authors explore the evolution of magnetized-plasma bubbles in a semi-collisional regime and the role of pressure anisotropy in influencing the flow of the laser-produced plasma.
Journal Article
A Relational-Cultural Approach to Examining Concealment among Latter-Day Saint Sexual Minorities
Sexual minorities often conceal their sexual identity from others to avoid distal stressors. Such concealment efforts occur more frequently among sexual minorities in religious settings where rejection and discrimination are more likely. Using a sample of 392 Latter-day Saint (“Mormon”) sexual minorities, we assess (a) the effect of religious affiliation on concealment efforts, (b) the relationship between social support, authenticity, and religious commitment on concealment, and (c) the moderating effect of authenticity on religious commitment and concealment. Multi-level model analyses revealed that religious affiliation alone accounted for over half (51.7%) of the variation in concealment efforts for Latter-day Saint sexual minorities. Social support directly was related to less concealment, whereas religious commitment was related to more concealment, with authenticity moderating the impact of religious commitment on concealment efforts. The present study provides insight into how religious sexual minorities may approach relationships and inadvertently wound their chances to connect with others.
Journal Article
Persistent monitoring of insect-pests on sticky traps through hierarchical transfer learning and slicing-aided hyper inference
Effective monitoring of insect-pests is vital for safeguarding agricultural yields and ensuring food security. Recent advances in computer vision and machine learning have opened up significant possibilities of automated persistent monitoring of insect-pests through reliable detection and counting of insects in setups such as yellow sticky traps. However, this task is fraught with complexities, encompassing challenges such as, laborious dataset annotation, recognizing small insect-pests in low-resolution or distant images, and the intricate variations across insect-pests life stages and species classes.
To tackle these obstacles, this work investigates combining two solutions, Hierarchical Transfer Learning (HTL) and Slicing-Aided Hyper Inference (SAHI), along with applying a detection model. HTL pioneers a multi-step knowledge transfer paradigm, harnessing intermediary in-domain datasets to facilitate model adaptation. Moreover, slicing-aided hyper inference subdivides images into overlapping patches, conducting independent object detection on each patch before merging outcomes for precise, comprehensive results.
The outcomes underscore the substantial improvement achievable in detection results by integrating a diverse and expansive in-domain dataset within the HTL method, complemented by the utilization of SAHI.
We also present a hardware and software infrastructure for deploying such models for real-life applications. Our results can assist researchers and practitioners looking for solutions for insect-pest detection and quantification on yellow sticky traps.
Journal Article
Laboratory analogue of a supersonic accretion column in a binary star system
Astrophysical flows exhibit rich behaviour resulting from the interplay of different forms of energy—gravitational, thermal, magnetic and radiative. For magnetic cataclysmic variable stars, material from a late, main sequence star is pulled onto a highly magnetized (
B
>10 MG) white dwarf. The magnetic field is sufficiently large to direct the flow as an accretion column onto the poles of the white dwarf, a star subclass known as AM Herculis. A stationary radiative shock is expected to form 100–1,000 km above the surface of the white dwarf, far too small to be resolved with current telescopes. Here we report the results of a laboratory experiment showing the evolution of a reverse shock when both ionization and radiative losses are important. We find that the stand-off position of the shock agrees with radiation hydrodynamic simulations and is consistent, when scaled to AM Herculis star systems, with theoretical predictions.
Stationary radiative shocks are expected to form above the surface of highly-magnetized white dwarves in binary systems, but this cannot be resolved by telescopes. Here, the authors report a laboratory experiment showing the evolution of a reverse shock when both ionization and radiative losses are important.
Journal Article
“He Just Wanted Me to Do What Was Best for Me”: Latter-Day Saint Clergy’s Counsel to Sexual and Gender Minorities and Its Impact
The purpose of this study was to understand counsel given to sexual and gender minority individuals by clergy in the Church of Jesus Christ of Latter-day Saints (CJCLDS), the impact of that counsel, and individuals’ perceptions of meetings with clergy. Twenty-five current and former members of the CJCLDS who identify as sexual and gender minorities (SGM) participated in 30–60 min semi-structured interviews focused on their interactions with clergy in the CJCLDS. Participants reported receiving various forms of counsel, including encouragement to adhere to church doctrine, counsel focused on self-acceptance, messages that clergy would support congregants’ agency and self-determination, counsel focused on increasing faith, and no answers. Participants reported a variety of perceptions of meetings with clergy including wishing clergy were more educated on the experiences of SGMs, hurtful experiences, expectations of mistreatment, recognition that clergy are doing their best, and gratitude for clergy. Interactions with clergy had long-lasting and far-reaching consequences including loss of trust in religious leaders, restriction of church membership, disengagement from faith, engagement with faith, nuanced or lost beliefs, and impacts on mental health. Results suggest that Latter-day Saints clergy working with SGM individuals may be experienced as most effective when they provide safe and supportive spaces for congregants to share their experiences, use approaches that focus on self-determination and agency, seek education/training from CJCLDS-specific LGBTQ+ organizations, and recognize that many SGM congregants approach interactions with clergy with trepidation and fears of mistreatment.
Journal Article
“I’ll Give Them All the Time They Need”: How LGBTQ+ Teens Build Positive Relationships with Their Active, Latter-Day Saint Parents
Strong and supportive relationships with parents are key to promoting the mental health of LGBTQ+ teens. Overwhelmingly, studies have focused on ways to improve parental acceptance, largely neglecting understanding the parent–teen dyad as a unit and ignoring teens’ contributions to their relationships with their parents. To address this gap, we conducted 19 separate interviews with LGBTQ+ teens and their Latter-day Saint (LDS) parents (38 total interviews) to explore the ways that teens contributed to the development of positive relationships. Additionally, we explored teen-related factors that presented challenges to the parent–teen relationship. Thematic analyses suggested that LGBTQ+ teens engaged in several behaviors that benefitted their relationships with their LDS parents, including having authentic and meaningful conversations, fostering family connections, engaging in casual communication, being open about LGBTQ+ identity, and giving parents time and grace. Participants reported several common teen-related factors that presented challenges to the relationship, including communication and connection difficulties, challenges related to general development, and parents and teens avoiding LGBTQ+ and religious topics. Results suggest that while several of these factors may be relevant for parent–teen relationships more broadly, many were specific to LGBTQ+ teens with active, LDS parents. These findings highlight the ways that LGBTQ+ teens manage to foster positive relationships with their parents despite potential conflict between their LGBTQ+ identities and their parents’ religious beliefs.
Journal Article
Whole-beam self-focusing in fusion-relevant plasma
Fast ignition inertial confinement fusion requires the production of a low-density channel in plasma with density scale-lengths of several hundred microns. The channel assists in the propagation of an ultra-intense laser pulse used to generate fast electrons which form a hot spot on the side of pre-compressed fusion fuel. We present a systematic characterization of an expanding laser-produced plasma using optical interferometry, benchmarked against three-dimensional hydrodynamic simulations. Magnetic fields associated with channel formation are probed using proton radiography, and compared to magnetic field structures generated in full-scale particle-in-cell simulations. We present observations of long-lived, straight channels produced by the Habara–Kodama–Tanaka whole-beam self-focusing mechanism, overcoming a critical barrier on the path to realizing fast ignition. This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 2)’.
Journal Article
Preparations for a European R&D roadmap for an inertial fusion demo reactor
A European consortium of 15 laboratories across nine nations have worked together under the EUROFusion Enabling Research grants for the past decade with three principle objectives. These are: (a) investigating obstacles to ignition on megaJoule-class laser facilities; (b) investigating novel alternative approaches to ignition, including basic studies for fast ignition (both electron and ion-driven), auxiliary heating, shock ignition, etc.; and (c) developing technologies that will be required in the future for a fusion reactor. A brief overview of these activities, presented here, along with new calculations relates the concept of auxiliary heating of inertial fusion targets, and provides possible future directions of research and development for the updated European Roadmap that is due at the end of 2020. This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 2)’.
Journal Article