Melting of two‐dimensional colloidal crystals: A simulation study of the Yukawa system

The two‐dimensional melting transition of charged polystyrene spheres in aqueous colloidal suspension has been studied by molecular dynamics simulation of a screened Coulomb system. Some central predictions of the Kosterlitz–Thouless–Halperin–Nelson–Young theory of defect‐mediated melting are confirmed, such as an apparent divergence of the correlation lengths for translational and bond‐orientational order at different thermodynamic state points, but there are also predictions of the theory that are violated. The defect topology is very complex, with oscillation periods of the defect density of many million time steps duration. The need for extensive sampling and, to a lesser degree, the choice of potential function continue to be the crucial issues for any attempt to generate a hexatic structure by means of computer simulation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71272/2/JCPSA6-100-4-3114-1.pd

Remediation of RDX- and HMX-Contaminated Groundwater Using Organic Mulch Permeable Reactive Barriers

Organic mulch is a complex organic material that is typically populated with its own consortium of microorganisms. The organisms in mulch breakdown complex organics to soluble carbon, which can then be used by these and other microorganisms as an electron donor for treating RDX and HMX via reductive pathways. A bench-scale treatability study with organic mulch was conducted for the treatment of RDX- and HMX-contaminated groundwater obtained from a plume at the Pueblo Chemical Depot (PCD) in Pueblo, Colorado. The site-specific cleanup criteria of 0.55 ppb RDX and 602 ppb HMX were used as the logical goals of the study. Column flow-through tests were run to steady-state at the average site seepage velocity, using a 70%:30% (vol.:vol.) mulch:pea gravel packing to approach the formation\u27s permeability. Significant results included: (1) Complete removal of 90 ppb influent RDX and 8 ppb influent HMX in steady-state mulch column effluent; (2) pseudo-first-order steady-state kinetic rate constant, k, of 0.20 to 0.27 h-1 based on RDX data, using triplicate parallel column runs; (3) accumulation of reduced RDX intermediates in the steady-state column effluent at less than 2% of the influent RDX mass; (4) no binding of RDX to the column fill material; and (5) no leaching of RDX, HMX or reduction intermediates from the column fill material. The results of the bench-scale study will be used to design and implement a pilot-scale organic mulch/pea gravel permeable reactive barrier (PRB) at the site

Religiousness and Perceived God Perfectionism Among Elite Athletes

Little research has been conducted examining the link between athletes’ religious beliefs and practices and coping with the pressures related to elite competition. The purpose of the study was to investigate athletes’ global self-worth and perfectionistic concerns as key variables that link religiousness and perceived God perfectionism to dealing with performance failure and appraisals of upcoming competition. Self-report data was collected from a sample of 99 elite athletes (Mdn age = 22, 48% female, 89% believed in God) that were currently competing at a NCAA D1, professional or Olympic level. We used structural equation modeling to test direct and indirect pathways of two separate theoretical models and bootstrapping for determining the significance of indirect effects. Self-worth and perfectionistic concerns were important in understanding the link between religious variables and outcomes in both models. Specifically, high levels of athlete religiousness were related to high levels of self-worth, which in turn was related to low levels of shame when recalling a disappointing performance. In contrast, perceived God perfectionism discrepancy (i.e. gap in perceived standards from God and the athletes’ performance) was related to shame via a positive relation to perfectionistic concern. Religiousness was also directly related to feelings of comfort from God, whereas perceived God perfectionism was directly related to athletes’ anger towards God after experiencing disappointment. For the second model, religiousness was linked to high levels of challenge appraisals and low levels of stress and threat appraisals of competition through high levels of global self-worth. On the other hand, perceived God perfectionism discrepancy was related to all three appraisals of competition through high perfectionistic concern and low self-worth. Overall, our findings suggest that religiousness can serve as an important resource for athletes or contribute to psychological difficulties. Implications of our findings for practitioners are discussed

Stress relaxation and misfit dislocation nucleation in the growth of misfitting films: A molecular dynamics simulation study

The low-temperature growth and relaxation of misfitting films are analyzed on the basis of two-dimensional molecular dynamics simulations using Lennard–Jones potentials. The temporal evolution of the surface morphology and the mechanisms for misfit dislocation nucleation and stress relaxation are monitored. Pseudomorphic film growth is observed up to a critical thickness. In some cases, the formation of voids within the film relaxes some of the stress. At the critical thickness, dislocations nucleate and relax most of the misfit. The critical thickness increases with decreasing lattice mismatch and depends on the sign of the misfit. The critical thickness of compressively strained films is smaller than that of films with the same magnitude of misfit, but in tension. The mechanism of dislocation nucleation is different in tension and compression and, in all cases, is associated with the roughness of the film surface. In the compressive misfit case, dislocations nucleate by squeezing-out an atom at the base of surface depressions. In the tensile misfit case, however, the nucleation of misfit dislocations involves the concerted motion of a relatively large number of atoms, leading to insertion of an extra lattice (plane) row into an already continuous film. These results show that the critical thickness depends intimately on the film morphology which, in turn, is determined as an integral part of the film growth process. © 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70519/2/JAPIAU-83-1-217-1.pd

Misfit effects in adhesion calculations

The work of adhesion of bimaterial interfaces is commonly computed using quantum mechanical methods in which the two materials are strained into coherency. There is no relaxation of the coherency by the formation of an array of interfacial misfit dislocations, contrary to what is commonly observed for essentially all systems other than very thin films. In this paper, we investigate the errors introduced into the work of adhesion associated with the assumption of coherency. Series of atomistic simulations in two and three dimensions are performed using a simple Lennard-Jones-type model potential. We demonstrate that the assumption of coherency introduces errors that increase rapidly with misfit (for small misfit) and can easily be of the order of several tens of percent. We trace the source of these errors to the neglect of the elastic fields of misfit dislocations and to the variation in the number of bonds per unit interfacial area with misfit when coherency is assumed. Suggestions are made to minimize and/or correct for this error.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49084/2/ms8205.pd

Growth in Patience in Christian Moral Wisdom and Contemporary Positive Psychology

Moral education requires interdisciplinary engagement across philosophy, psychology, and education. Positive psychologists regularly acknowledge the breadth and depth of wisdom regarding the cultivation of virtues present in philosophical and religious texts and consult such writings when creating constructs, but they are less prone to integrate scientific findings with historical texts as inquiry proceeds. Thus, we provide a comparative analysis of the advice given in Lorenzo Scupoli’s The Spiritual Combat, from traditional Christian moral wisdom literature and the research findings from positive psychology on the cultivation of the virtue of patience. Points of convergence relate to the utility of engaging activities that include cognitive reappraisal, habit formation through daily practice, activating positive motivation, prayer, mantra/transcendental meditation, and cultivating elevation through meditation on moral exemplars. Areas of divergence include the advisability of suppression, the role of motivation, and necessity of spiritual intervention, which suggest areas for future inquiry in moral education

Study of the pd→3HeK+K−pd\to ^3\textrm{He} K^+K^- and pd→3Heϕpd\to ^3\textrm{He} \phi reactions close to threshold

Two--kaon production in proton--deuteron collisions has been studied at three energies close to threshold using a calibrated magnetic spectrograph to measure the final $^3$He and a vertex detector to measure the $K^+K^-$ pair. Differential and total cross sections are presented for the production of $\phi$--mesons, decaying through $\phi\to K^+K^-$, as well as for prompt $K^+K^-$ production. The prompt production seems to follow phase space in both its differential distributions and in its energy dependence. The amplitude for the $pd\to ^3${He}$\phi$ reaction varies little for excess energies below 22 MeV and the value is consistent with that obtained from a threshold measurement. The angular distribution of the $K^+K^-$ decay pair shows that near threshold the $\phi$--mesons are dominantly produced with polarization $m=0$ along the initial proton direction. No conclusive evidence for $f_0(980)$ production is found in the data.Comment: 13 figure