892 research outputs found

    Molecular dynamics simulations of bubble nucleation in dark matter detectors

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    Bubble chambers and droplet detectors used in dosimetry and dark matter particle search experiments use a superheated metastable liquid in which nuclear recoils trigger bubble nucleation. This process is described by the classical heat spike model of F. Seitz [Phys. Fluids (1958-1988) 1, 2 (1958)], which uses classical nucleation theory to estimate the amount and the localization of the deposited energy required for bubble formation. Here we report on direct molecular dynamics simulations of heat-spike-induced bubble formation. They allow us to test the nanoscale process described in the classical heat spike model. 40 simulations were performed, each containing about 20 million atoms, which interact by a truncated force-shifted Lennard-Jones potential. We find that the energy per length unit needed for bubble nucleation agrees quite well with theoretical predictions, but the allowed spike length and the required total energy are about twice as large as predicted. This could be explained by the rapid energy diffusion measured in the simulation: contrary to the assumption in the classical model, we observe significantly faster heat diffusion than the bubble formation time scale. Finally we examine {\alpha}-particle tracks, which are much longer than those of neutrons and potential dark matter particles. Empirically, {\alpha} events were recently found to result in louder acoustic signals than neutron events. This distinction is crucial for the background rejection in dark matter searches. We show that a large number of individual bubbles can form along an {\alpha} track, which explains the observed larger acoustic amplitudes.Comment: 7 pages, 5 figures, accepted for publication in Phys. Rev. E, matches published versio

    Nanobrazing of Inconel 718 and Ti-6Al-4V

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    For high temperature brazing applications, several design considerations must be evaluated including metallurgical compatibility, mechanical stability, wettability, and many others. One of the obstacles to high temperature brazing is minimizing the melting temperature of the brazing material without sacrificing high operating temperature. Traditionally, this is accomplished by adding melting point depressants such as boron and silicon. However, the addition of boron and silicon exposes the base material to the formation of brittle boride and silicide intermetallic phases and/or low melting eutectic phases. Nanomaterials experience size-dependent melting point depression without the use of melting point depressants via the Gibbs-Thomson effect. Until the studies discussed in this dissertation, nanomaterials as the sole brazing material are seldom investigated. In this dissertation, we discuss nanomaterial brazing (nanobrazing) material performance when joining Inconel 718 and Ti-6Al-4V.In the dissertation studies, we compare the mechanical strength of Cu-Ag and Ag nanomaterials and high entropy alloy nanoparticles for laser brazing Inconel 718 to their bulk counterparts. It was found that the Cu-Ag nanomaterials outperformed a commercially available bulk Cu-Ag brazing alloy in terms of strength due to subgrain Hall-Petch strengthening. The bulk high entropy alloy produced a stronger brazing joint than the nanoparticles; however, the nanoparticles had a much lower brazing temperature. We also investigated Ni/Al reactive multilayer films as a self-powered brazing material for joining Ti-6Al-4V. Due to a lack of interdiffusion between the BAlSi-4 and the reactive multilayer film prevents the joint from achieving high strength. In our study of Ni nanomaterials, we established that Ni can outperform BNi-2 commercial brazing material under the same vacuum brazing conditions. High heating rate, high maximum temperature, and high grain boundary diffusivity were identified as critical factors in the nanobrazing process of Ni nanomaterials.Through these studies, we provide evidence for two hypotheses: (1) Surface melting and diffusion are critical processes for successful nanojoining (2) (Sub)Grain boundary strengthening is an important mechanism for high bonding strength of nanojoints. Furthermore, the research in this dissertation provides a firm foundation for future nanobrazing studies and provides valuable insight to fundamental investigations and technical improvements for optimizing nanobrazing procedures

    Graduate recital in composition

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    This graduate composition recital took place on 5 February 2019 at 8:00 pm in Davis Hall. The compositions on the program included: Washington Variations for Solo Violin, Utopy for Alto Saxophone and Piano, Freedom Concerto for Clarinet Quintet, and Four Songs on Liberty. This abstract will summarize the structural, rhythmic, and harmonic conception of each work

    IX: Story About the Law of Non-Discrimination - Documentary

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    The purpose of this project is to provide historical awareness for how Title IX, the anti-gender discrimination law in education, evolved to where it is today and the impact it has on universities in the United States. Strong-willed individuals sought change in the late 1960s and 1970s to prevent gender discrimination in education, thus beginning the creation of the law and making it a powerful tool for women’s rights. As Title IX expanded its reach, universities have been shaped by gender discrimination in athletics, sexual assault, harassment and rape. This project outlines the evolution of Title IX through research based on documentation of events and personal stories from the 1960s to now. This project seeks to dissect Title IX’s struggles of today, with the hopes of bringing understanding and possible ideas to the viewers that can spark a change within the culture of college campuses

    What Kind of Black are You?

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    Second-Class Licensure: The Use of Conditional Admission Programs for Bar Applicant with Mental Health and Substance Abuse Histories

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    The permissibility of inquiries about mental health and substance abuse treatment histories on bar applications was actively debated in the years after the passage of the Americans with Disabilities Act (“ADA”). Two decades after those debates began, the law remains unclear and the question is, for the most part, no longer discussed. However, the increasing use of conditional admission for applicants with treatment histories requires a renewed scrutiny of whether state bars should be allowed to use or request this information. Conditional admission programs, which allow applicants to be admitted to the bar subject to monitoring or supervision conditions, have been promoted as a way to admit disabled applicants who would previously have been denied while protecting the public from potentially impaired attorneys. However, conditional admission is often used for applicants with mental health or substance abuse histories who are not impaired and who would have previously been fully licensed. As currently operated, these programs divert qualified applicants with disabilities into an unequal licensure program. This second-class licensure of applicants who are fit to practice law on the basis of their disability clearly violates the ADA and further deters law students from seeking treatment. Both the ADA and these policy concerns require that the use of these programs be reevaluated

    Childern Witnessing Domestic Violence

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    Statement of Problem: Although witnessing violence in the family may account for many symptoms brought to the attention of the primary care providers, such violence is seldom identified as an issue. The purpose of this study was to assess the incidence of children witnessing violence in the home, as self reported by victims of domestic violence in a clinical setting. Method: The study was a retrospective chart review. Data was gathered from a survey administered to individuals identified in the emergency department as victims of domestic violence. The survey addressed demographics, child witnesses to violence, and co-factors of violence including child abuse, alcohol use and weapons in the home. Results: Out of the 120 participants, the highest proportion was categorized as single/divorced. This study found that 75% of the children witnessed domestic violence in the home, as self-reported by victims of domestic violence. The mean age of the children was 8.4 years. The incidence of concurrent child abuse was 19%. The victims of domestic violence self-reported a much higher rate of alcohol use by the perpetrator as compared to their own alcohol use. Conclusion: The findings indicate that children as witnesses to domestic violence is alarmingly high. Universal screening by health care providers ensures that not only are adult victims identified, but also the needs of the children are not overlooked. It is mandatory to identify children living in violent homes so their emotional and physical health can be preserved at the earliest developmental age possible

    If it looks like it, moves like it, and sounds like it, Then it probably is Contemporary Colonization

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    Generation and analysis of p23- and calnexin-deficient mice

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    This thesis provides in vivo information about two proteins - p23 and calnexin - which play major roles in the early secretory pathway of mammalian cells. The aim was to gain further understanding about the function of these proteins by generating mice deficient in the expression of p23 and calnexin. p23 is a member of the integral p24 protein family. These proteins are highly abundant in the endoplasmic reticulum and Golgi apparatus and are thought to play a role in protein transport and vesicle formation. Disruption of both p23 alleles results in early embryonic lethality. Inactivation of one allele leads not only to reduced levels of p23 itself but also of other family members. The reduction in steady state protein levels also leads to an altered subcellular distribution of p23 as well as p26 (another family member) in p23 heterozygous cells. In addition, structural changes in the Golgi apparatus, in particular dilated saccules, were observed. These changes in p23 heterozygous mice have functional consequences, resulting in specific defects in the secretion of some plasma proteins. Calnexin is a molecular chaperone molecule which is involved in the correct folding of newly synthesised polypeptide chains in the ER. 40% of the calnexin homozygous deficient mice died shortly after birth, the remaining 60% developed a severe neuronal phenotype and had to be sacrificed within 2 months. They were about one third smaller than their littermates and displayed motor disorders which included shaking of the body and a wobbly unsteady gait. Histological examination of brain, cerebellum, spinal cord, neuromuscular junctions and muscle did not reveal any abnormalities in the calnexin-deficient mice. Although these mice showed clear neurodegenerative symptoms, the molecular basis for the phenotype has not yet been characterised
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