Energy of the quasi-free electron in argon, krypton and xenon

Abstract Recent field ionization measurements of various high-n molecular Rydberg states doped into argon, krypton and xenon perturbers are presented as a function of perturber number density up to the density of the triple point liquid. These data are modeled to within ±0.3% of experiment on both critical and noncritical isotherms using a new theoretical treatment that includes: (i) the polarization of the perturber by the dopant cation, (ii) the polarization of the perturber by the quasi-free electron that arises from field ionization of the dopant, and (iii) the kinetic energy of the quasi-free electron. The polarization terms are determined by a standard statistical mechanical treatment. However, the kinetic energy of the quasi-free electron is calculated within a new local Wigner-Seitz model that contains only one adjustable parameter. This treatment provides an accurate model of the energy of the bottom of the conduction band (V 0 ) in argon, krypton and xenon from the dilute gas up to the density of the triple point liquid, on both critical and noncritical isotherms. The use of supercritical fluids in environmental remediation, in the treatment of high-level hazardous wastes and in tailoring chemical reactions for specific product yields necessitates a better understanding of density and temperature effects on the properties of neutral and charged species solvated in these fluids. We have recently studied the perturber induced shift ∆ D (ρ P ) of dopant ionization energyand the quasi-free electron energy V 0 (ρ P ) -in the rare gases Ar [1-3], Kr Experimental information on the dopants and perturbers used in these studies and the procedures used to ensure homogeneous mixing of samples in the gas handling system have been described previously The quasi-free electron energy V 0 (ρ P ) in a dense perturbing gas can be extracted from ∆ D (ρ P ), which is determined from field ionization studies, using [1-5] where P + (ρ P ) is the ensemble average dopant ionic core/perturber polarization energy, and ρ P is the perturber number density. P + (ρ P ) is calculated from a standard statistical mechanical treatment via [1-5] In eq. (2) g PD (r) is the perturber/dopant radial distribution function, and w + (r) is the perturber/ion interaction potentia

Xenon low-n Rydberg states in supercritical argon near the critical point

Abstract We present vacuum ultraviolet absorption spectra and an asymmetric line shape simulation of the 6s and 6s Rydberg states (including the blue satellite bands) of xenon doped into argon, from low argon number density to the density of the triple point liquid, at both noncritical temperatures and near (+0.5 • C) the critical isotherm of argon (i.e., −122.3 • C). The argon induced shift in the simulated primary transition of the Xe 6s and 6s Rydberg states is presented as a function of argon number density for noncritical temperatures and along an isotherm near the critical temperature. This shift demonstrates a perturber critical point effect on the transition energies of low-n dopant Rydberg states

JD-Next: A Valid and Reliable Tool to Predict Diverse Students’ Success in Law School

Admissions tests have increasingly come under attack by those seeking to broaden access and reduce disparities in higher education. Meanwhile, in other sectors there is a movement towards “work-sample” or “proximal” testing. Especially for underrepresented students, the goal is to measure not just the accumulated knowledge and skills that they would bring to a new academic program, but also their ability to grow and learn through the program. The JD-Next is a fully-online, non-credit, 7-10 week course to train potential JD students in case reading and analysis skills, prior to their first year of law school. This study tests the validity and reliability of the JD-Next exam as a potential admissions tool for juris doctor programs of education. (In a companion article, we report on the efficacy of the course for preparing students for law school.) In 2019, we recruited a national sample of potential JD students, enriched for racial/ethnic diversity, along with a sample of volunteers at one university (N=62). In 2020, we partnered with 17 law schools around the country to recruit a cohort of their incoming law students (N=238). At the end of the course, students were incentivized to take and perform well on an exam that we graded with a standardized methodology. We collected first-semester grades as an outcome variable. We found that the exam was a valid and reliable predictor of law school performance, comparable to legacy exams (LSAT or GRE) now used by law schools. For schools ranked outside the top-50 we found that the legacy exams lacked significant incremental validity in our sample, but the JD-Next exam provided a significant advantage. We also replicated known, substantial racial and ethnic disparities on the legacy exam scores, but estimate smaller, non-significant score disparities on the JD-Next exam. Together this research suggests that, as an admissions tool, the JD-Next exam may reduce the risk that capable students will be excluded from legal education and the legal profession

Micromechanical finite element modelling of thermo-mechanical fatigue for P91 steels

In this paper, the cyclic plasticity and fatigue crack initiation behaviour of a tempered martensite ferritic steel under thermo-mechanical fatigue conditions is examined by means of micromechanical finite element modelling. The crystal plasticity-based model explicitly reflects the microstructure of the material, measured by electronic backscatter diffraction. The predicted cyclic thermo-mechanical response agrees well with experiments under both in-phase and out-of-phase conditions. A thermo-mechanical fatigue indicator parameter, with stress triaxiality and temperature taken into account, is developed to predict fatigue crack initiation. In the fatigue crack initiation simulation, the out-of-phase thermo-mechanical response is identified to be more dangerous than in-phase response, which is consistent with experimental failure data. It is shown that the behaviour of thermo-mechanical fatigue can be effectively predicted at the microstructural level and this can lead to a more accurate assessment procedure for power plant components

Experimental and modelling study of fatigue crack initiation in an aluminium beam with a hole under 4-point bending

Slip band formation and crack initiation during cyclic fatigue were investigated by in-situ experiments and non-local CPFEM simulations systematically. Experimental techniques including EBSD, digital image correlation (DIC) and SEM have been used to obtain consistent grain orientations, local strains, as well as the locations where slip bands and micro-cracks form on the sample surface. The realistic microstructure based on the EBSD map has been generated and used for finite element modelling. An advanced non-local crystal plasticity model, which considers the isotropic and kinematic hardening of the plastic strain gradient, has been adopted. The simulation results match well the corresponding experimental results. It was found that total strain and averaged slip on all slip systems, combined with accumulated slip on specific slip planes help predict the location and orientation of slip bands and micro-crack initiation correctly. Furthermore, a fatigue indicating parameter based on competition between maximum slip and the total slip has been proposed to reproduce the experimental observations

Quantifying the profile and progression of impairments, activity, participation, and quality of life in people with Parkinson disease : protocol for a prospective cohort study

Background Despite the finding that Parkinson disease (PD) occurs in more than one in every 1000 people older than 60 years, there have been few attempts to quantify how deficits in impairments, activity, participation, and quality of life progress in this debilitating condition. It is unclear which tools are most appropriate for measuring change over time in PD. Methods and design This protocol describes a prospective analysis of changes in impairments, activity, participation, and quality of life over a 12 month period together with an economic analysis of costs associated with PD. One-hundred participants will be included, provided they have idiopathic PD rated I-IV on the modified Hoehn & Yahr (1967) scale and fulfil the inclusion criteria. The study aims to determine which clinical and economic measures best quantify the natural history and progression of PD in a sample of people receiving services from the Victorian Comprehensive Parkinson\u27s Program, Australia. When the data become available, the results will be expressed as baseline scores and changes over 3 months and 12 months for impairment, activity, participation, and quality of life together with a cost analysis. Discussion This study has the potential to identify baseline characteristics of PD for different Hoehn & Yahr stages, to determine the influence of disease duration on performance, and to calculate the costs associated with idiopathic PD. Valid clinical and economic measures for quantifying the natural history and progression of PD will also be identified

A broadly implementable research course in phage discovery and genomics for first-year undergraduate students

Engaging large numbers of undergraduates in authentic scientific discovery is desirable but difficult to achieve. We have developed a general model in which faculty and teaching assistants from diverse academic institutions are trained to teach a research course for first-year undergraduate students focused on bacteriophage discovery and genomics. The course is situated within a broader scientific context aimed at understanding viral diversity, such that faculty and students are collaborators with established researchers in the field. The Howard Hughes Medical Institute (HHMI) Science Education Alliance Phage Hunters Advancing Genomics and Evolutionary Science (SEA-PHAGES) course has been widely implemented and has been taken by over 4,800 students at 73 institutions. We show here that this alliance-sourced model not only substantially advances the field of phage genomics but also stimulates students\u27 interest in science, positively influences academic achievement, and enhances persistence in science, technology, engineering, and mathematics (STEM) disciplines. Broad application of this model by integrating other research areas with large numbers of early-career undergraduate students has the potential to be transformative in science education and research training

Discovery of a Modified Tetrapolar Sexual Cycle in Cryptococcus amylolentus and the Evolution of MAT in the Cryptococcus Species Complex

Sexual reproduction in fungi is governed by a specialized genomic region called the mating-type locus (MAT). The human fungal pathogenic and basidiomycetous yeast Cryptococcus neoformans has evolved a bipolar mating system (a, α) in which the MAT locus is unusually large (>100 kb) and encodes >20 genes including homeodomain (HD) and pheromone/receptor (P/R) genes. To understand how this unique bipolar mating system evolved, we investigated MAT in the closely related species Tsuchiyaea wingfieldii and Cryptococcus amylolentus and discovered two physically unlinked loci encoding the HD and P/R genes. Interestingly, the HD (B) locus sex-specific region is restricted (∼2 kb) and encodes two linked and divergently oriented homeodomain genes in contrast to the solo HD genes (SXI1α, SXI2a) of C. neoformans and Cryptococcus gattii. The P/R (A) locus contains the pheromone and pheromone receptor genes but has expanded considerably compared to other outgroup species (Cryptococcus heveanensis) and is linked to many of the genes also found in the MAT locus of the pathogenic Cryptococcus species. Our discovery of a heterothallic sexual cycle for C. amylolentus allowed us to establish the biological roles of the sex-determining regions. Matings between two strains of opposite mating-types (A1B1×A2B2) produced dikaryotic hyphae with fused clamp connections, basidia, and basidiospores. Genotyping progeny using markers linked and unlinked to MAT revealed that meiosis and uniparental mitochondrial inheritance occur during the sexual cycle of C. amylolentus. The sexual cycle is tetrapolar and produces fertile progeny of four mating-types (A1B1, A1B2, A2B1, and A2B2), but a high proportion of progeny are infertile, and fertility is biased towards one parental mating-type (A1B1). Our studies reveal insights into the plasticity and transitions in both mechanisms of sex determination (bipolar versus tetrapolar) and sexual reproduction (outcrossing versus inbreeding) with implications for similar evolutionary transitions and processes in fungi, plants, and animals