2,733 research outputs found

    Atom-atom ionization mechanism in Argon-Xenon mixtures

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    The atom-atom ionization process occurring in high-purity argon-xenon mixtures has been investigated by means of a conventional shock tube employing a microwave probe to monitor the electron-generation rate. All tests were conducted at approximately atmospheric pressure and at temperatures in the range between 5000° and 9000°K, corresponding to a neutral-particle density of 7.0 X 10^(17) cm^(-3). The cross-sectional slope constant for xenon ionized by collision with an argon atom is 1.8 X 10^(-20) cm^2/eV±20%, that is, equal to that for xenon ionized by collision with another xenon atom. The data for the reaction of argon ionizing xenon are consistent with an activation energy of 8.315 eV, that is, of the xenon-xenon, atom-atom ionization process. No data were obtained for xenon ionizing argon. Good correlation was obtained between the cross sections for electron elastic momentum exchange derived from the microwave experiment and those obtained from beam experiments. The argon-xenon ionization cross section implies that, for atom-atom processes in the noble gases at pressures ~ 1 atm and temperatures ~2/3 eV, the ionization cross section is independent of the electronic structure of the projectile atom

    Atom-atom ionization cross sections of the noble gases-Argon, Krypton, and Xenon

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    An experimental investigation of the initial phase of shock produced ionization in argon, krypton, and xenon has been conducted in order to elucidate the atom-atom ionization reaction and to determine the atom-atom ionization cross sections. A high-purity shock tube was employed to heat these gases to temperatures in the range from 5000° to 9000°K at neutral particle densities of 4.4 X 10^(17), 7.0 X 10^(17), and 13.3 X 10^(17) cm^(-3), and impurity levels of approximately 10^(-6) A K-band (24-GHz) microwave system situated so that the microwave-beam propagation direction was normal to the shock tube, monitored the ionization relaxation process occurring immediately after the passage of the shock front. Electron density was calculated from the microwave data using a plane-wave-plane-plasma slab interaction theory corrected for near field effects associated with the coupling of the microwave energy to the plasma. These data, adjusted to compensate for the effects of shock attenuation, verified that the dominant electron-generation process involve a two-step, atom-atom ionization reaction, the first step (excitation to the first excited states) being rate determining. The quadratic dependence on neutral density associated with this reaction was experimentally demonstrated (with an uncertainty of ± 15%). The cross section, characterized as having a constant slope from threshold (first excited energy level), represented as the cross-sectional slope constant C, was found to be equal to 1.2 X 10^(-19)±15% cm^2/eV, 1.4 X 10^(-19)±15% cm^2/eV, and 1.8 X 10^(-20)±15% cm^2/eV for argon, krypton, and xenon, respectively. The electron-atom elastic momentum-exchange cross sections derived from the microwave data correlated quite well with Maxwell-averaged beam data, the agreement for the case of argon being ±20%; krypton, ±30%; and xenon, within a factor of 2

    The relationship between leisure activities and psychological resources that support a sustainable career: The role of leisure seriousness and work-leisure similarity

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    While leisure plays an increasingly important role in individuals' lives, little is known about its potential to influence career sustainability. Drawing on Conservation of Resources (COR) theory, we investigate whether investing extra time into leisure will have a positive or negative impact on career sustainability by either generating or depleting resources. Specifically, we examine the effects of time spent on leisure on the career-related resources of resilience and self-efficacy using data on within-person changes over the course of 7 monthly surveys. We propose that the effects of leisure on resources depend on the interplay between a) the approach individuals take to their leisure activity, in particular the level of “seriousness” of a leisure activity (i.e., the extent to which individuals identify with, and persevere in, their activity), and b) the similarity between work and leisure (i.e., the extent to which work and leisure involve similar demands and skills). We found that time spent on leisure over and above an individual's average was positively related to work-related self-efficacy, but only when the individual's leisure activities were high in seriousness and low in work-leisure similarity, or when they were low in seriousness and high in similarity. Investing time in leisure was negatively associated with self-efficacy when leisure activities were high in seriousness and similar to an individual's work. Our findings paint a complex picture of the potential influence of leisure on career sustainability and highlight the need to take a nuanced approach when studying the effects of leisure

    The Evolution of Cuspy Triaxial Galaxies Harboring Central Black Holes

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    We use numerical simulations to study the evolution of triaxial elliptical galaxies with central black holes. In contrast to earlier numerical studies which used galaxy models with central density ``cores,'' our galaxies have steep central cusps, like those observed in real ellipticals. As a black hole grows in these cuspy triaxial galaxies, the inner regions become rounder owing to chaos induced in the orbit families which populate the model. At larger radii, however, the models maintain their triaxiality, and orbital analyses show that centrophilic orbits there resist stochasticity over many dynamical times. While black hole induced evolution is strong in the inner regions of these galaxies, and reaches out beyond the nominal ``sphere of influence'' of a black hole, our simulations do not show evidence for a rapid {\it global} transformation of the host. The triaxiality of observed elliptical galaxies is therefore not inconsistent with the presence of supermassive black holes at their centers.Comment: 15 pages, 7 figures (1 color). Accepted for publication in Ap

    Measuring longitudinal amplitudes for electroproduction of pseudoscalar mesons using recoil polarization in parallel kinematics

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    We propose a new method for measuring longitudinal amplitudes for electroproduction of pseudoscalar mesons that exploits a symmetry relation for polarization observables in parallel kinematics. This polarization technique does not require variation of electron scattering kinematics and avoids the major sources of systematic errors in Rosenbluth separation.Comment: intended for Phys. Rev. C as a Brief Repor

    Hot QCD equations of state and RHIC

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    We show how hot QCD equations of states can be adapted to make definite predictions for quark-gluon plasma at RHIC. We consider equations of state up to O(g5)O(g^5) and O[g6(ln(1/g)+δ)]O[g^6(ln(1/g)+\delta)]. Our method involves the extraction of equilibrium distribution functions for gluons and quarks from these equations of state by capturing the the interaction effects entirely in the effective chemical potentials. We further utilize these distribution functions to study the screening length in hot QCD and dissociation phenomenon of heavy quarkonia states by combining this understanding with the semi-classical transport theory.Comment: Based on poster presented during quark matter-2008(4-10 Feb 2008) Jaipur India; 4 Pages, 2 eps fig

    Asthma Knowledge, Control, and Administration Techniques in Hispanic Caregivers of Pediatrics

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    Objectives: The objectives of this study were to (1) describe asthma knowledge, control, and administration techniques in Hispanic caregivers of pediatric asthma patients in primary care clinics and (2) determine the association between asthma knowledge and control. Methods: A pilot, cross-sectional study was conducted by administering a survey to Spanish-speaking primary caregivers of children under 12 years old with a current diagnosis of asthma. The survey contained: demographic questions (8 items), a modified version of the Asthma Control Test (ACT, 5 self-assessment items, 5-point, Likert-type scale), knowledge (21 items, correct/incorrect response), and inhaler use (1 item, rank ordering steps for using inhaler). Descriptive statistics were performed for all items, and a Pearson correlation analysis was utilized to assess the association between asthma knowledge and control in SPSS v. 22.0 (Armonk, NY), with α =0.05. Results: Of the 12 caregivers, who completed the survey, all were parents of the patients. Seven patients (58%) had controlled asthma. On the asthma knowledge portion of the survey, three caregivers of these patients (25%) scored over 75%, three (25%) scored under 50%, and six (50%) scored between 50-75%. There was a statistically-significant, positive correlation between asthma knowledge and asthma control (r=0.668, p=0.017). No caregivers were able to correctly order the eight step sequence of using an inhaler. Conclusion: A positive correlation between asthma knowledge and asthma control was found in caregivers of asthmatic pediatric patients. Inhaler technique, recognition of asthma triggers, and understanding situations necessitating a physician visit were areas in which participants showed a knowledge deficiency

    The Fisk-Vanderbilt Master’s-to-Ph.D. Bridge Program: Recognizing, Enlisting, and Cultivating Unrealized or Unrecognized Potential in Underrepresented Minority Students

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    The Fisk-Vanderbilt Masters-to-Ph.D. Bridge Program is a model for substantially increasing the number of underrepresented minority students earning doctoral degrees in the physical sciences. The program presently leads the nation in master’s degrees in physics for African-Americans, and is one of the top ten producers of physics master’s degrees among all U.S. citizens. The program is on pace to become the nation’s top producer of underrepresented minority Ph.Ds. in physics, astronomy, and materials science. We summarize the main features of the program, including two of its core strategies: Partnering a minority-serving institution and a major research university through collaborative research, and using the master’s degree as a pathway to the Ph.D. We discuss our methods for recognizing and selecting for unrealized potential in students during the admissions process, and for cultivating this potential to develop successful scientists and leaders

    Hard-Loop Effective Action for Anisotropic Plasmas

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    We generalize the hard-thermal-loop effective action of the equilibrium quark-gluon plasma to a non-equilibrium system which is space-time homogeneous but for which the parton momentum distribution is anisotropic. We show that the manifestly gauge-invariant Braaten-Pisarski form of the effective action can be straightforwardly generalized and we verify that it then generates all n-point functions following from collisionless gauge-covariant transport theory for a homogeneous anisotropic plasma. On the other hand, the Taylor-Wong form of the hard-thermal-loop effective action has a more complicated generalization to the anisotropic case. Already in the simplest case of anisotropic distribution functions, it involves an additional term that is gauge invariant by itself, but nontrivial also in the static limit.Comment: 12 pages. Version 3: typo in (15) corrected, note added discussing metric conventions use
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