Stable fourfold configurations for small vacancy clusters in silicon from ab initio calculations

Using density-functional-theory calculations, we have identified new stable configurations for tri-, tetra-, and penta-vacancies in silicon. These new configurations consist of combinations of a ring-hexavacancy with three, two, or one interstitial atoms, respectively, such that all atoms remain fourfold. As a result, their formation energies are lower by 0.6, 1.0, and 0.6 eV, respectively, than the ``part of a hexagonal ring'' configurations, believed up to now to be the lowest-energy states

Genomic Analysis of Stress Response Against Arsenic in \u3cem\u3eCaenorhabditis elegans\u3c/em\u3e

Arsenic, a known human carcinogen, is widely distributed around the world and found in particularly high concentrations in certain regions including Southwestern US, Eastern Europe, India, China, Taiwan and Mexico. Chronic arsenic poisoning affects millions of people worldwide and is associated with increased risk of many diseases including arthrosclerosis, diabetes and cancer. In this study, we explored genome level global responses to high and low levels of arsenic exposure in Caenorhabditis elegans using Affymetrix expression microarrays. This experimental design allows us to do microarray analysis of dose-response relationships of global gene expression patterns. High dose (0.03%) exposure caused stronger global gene expression changes in comparison with low dose (0.003%) exposure, suggesting a positive dose-response correlation. Biological processes such as oxidative stress, and iron metabolism, which were previously reported to be involved in arsenic toxicity studies using cultured cells, experimental animals, and humans, were found to be affected in C. elegans. We performed genome-wide gene expression comparisons between our microarray data and publicly available C. elegans microarray datasets of cadmium, and sediment exposure samples of German rivers Rhine and Elbe. Bioinformatics analysis of arsenic-responsive regulatory networks were done using FastMEDUSA program. FastMEDUSA analysis identified cancer-related genes, particularly genes associated with leukemia, such as dnj-11, which encodes a protein orthologous to the mammalian ZRF1/MIDA1/MPP11/DNAJC2 family of ribosome-associated molecular chaperones. We analyzed the protective functions of several of the identified genes using RNAi. Our study indicates that C. elegans could be a substitute model to study the mechanism of metal toxicity using high-throughput expression data and bioinformatics tools such as FastMEDUSA

Exact quantum states of a general time-dependent quadratic system from classical action

A generalization of driven harmonic oscillator with time-dependent mass and frequency, by adding total time-derivative terms to the Lagrangian, is considered. The generalization which gives a general quadratic Hamiltonian system does not change the classical equation of motion. Based on the observation by Feynman and Hibbs, the propagators (kernels) of the systems are calculated from the classical action, in terms of solutions of the classical equation of motion: two homogeneous and one particular solutions. The kernels are then used to find wave functions which satisfy the Schr\"{o}dinger equation. One of the wave functions is shown to be that of a Gaussian pure state. In every case considered, we prove that the kernel does not depend on the way of choosing the classical solutions, while the wave functions depend on the choice. The generalization which gives a rather complicated quadratic Hamiltonian is simply interpreted as acting an unitary transformation to the driven harmonic oscillator system in the Hamiltonian formulation.Comment: Submitted to Phys. Rev.

Genomic Analysis of Immune Response against Vibrio Cholerae Hemolysin in Caenorhabditis elegans

Vibrio cholerae cytolysin (VCC) is among the accessory V. cholerae virulence factors that may contribute to disease pathogenesis in humans. VCC, encoded by hlyA gene, belongs to the most common class of bacterial toxins, known as poreforming toxins (PFTs). V. cholerae infects and kills Caenorhabditis elegans via cholerae toxin independent manner. VCC is required for the lethality, growth retardation and intestinal cell vacuolation during the infection. However, little is known about the host gene expression responses against VCC. To address this question we performed a microarray study in C. elegans exposed to V. cholerae strains with intact and deleted hlyA genes. Many of the VCC regulated genes identified, including C-type lectins, Prion-like (glutamine [Q]/asparagine [N]-rich)-domain containing genes, genes regulated by insulin/ IGF-1-mediated signaling (IIS) pathway, were previously reported as mediators of innate immune response against other bacteria in C. elegans. Protective function of the subset of the genes up-regulated by VCC was confirmed using RNAi. By means of a machine learning algorithm called FastMEDUSA, we identified several putative VCC induced immune regulatory transcriptional factors and transcription factor binding motifs. Our results suggest that VCC is a major virulence factor, which induces a wide variety of immune response- related genes during V. cholerae infection in C. elegans

Statistics of Gravitational Microlensing Magnification. I. Two-Dimensional Lens Distribution

(Abridged) In this paper we refine the theory of microlensing for a planar distribution of point masses. We derive the macroimage magnification distribution P(A) at high magnification (A-1 >> tau^2) for a low optical depth (tau << 1) lens distribution by modeling the illumination pattern as a superposition of the patterns due to individual ``point mass plus weak shear'' lenses. We show that a point mass plus weak shear lens produces an astroid- shaped caustic and that the magnification cross-section obeys a simple scaling property. By convolving this cross-section with the shear distribution, we obtain a caustic-induced feature in P(A) which also exhibits a simple scaling property. This feature results in a 20% enhancement in P(A) at A approx 2/tau. In the low magnification (A-1 << 1) limit, the macroimage consists of a bright primary image and a large number of faint secondary images formed close to each of the point masses. Taking into account the correlations between the primary and secondary images, we derive P(A) for low A. The low-A distribution has a peak of amplitude ~ 1/tau^2 at A-1 ~ tau^2 and matches smoothly to the high-A distribution. We combine the high- and low-A results and obtain a practical semi-analytic expression for P(A). This semi-analytic distribution is in qualitative agreement with previous numerical results, but the latter show stronger caustic-induced features at moderate A for tau as small as 0.1. We resolve this discrepancy by re-examining the criterion for low optical depth. A simple argument shows that the fraction of caustics of individual lenses that merge with those of their neighbors is approx 1-exp(-8 tau). For tau=0.1, the fraction is surprisingly high: approx 55%. For the purpose of computing P(A) in the manner we did, low optical depth corresponds to tau << 1/8.Comment: 35 pages, including 6 figures; uses AASTeX v4.0 macros; submitted to Ap

A Longitudinal Analysis of the Mediating Role of Substance Use in the Relationship between Work Commitment and Antisocial Behavior among Formerly Incarcerated Young Adults

This study (N = 1,289) aims to provide a better understanding of the association among work commitment, substance use, antisocial behavior, and race by 1) examining the effect of work commitment on antisocial behavior; 2) investigating the role of substance use as a mediator between work commitment and antisocial behavior; and 3) identifying racial differences in the substance use mediated relationship between the two factors. The study’s data was drawn from the Pathways to Desistance Study, a longitudinal project following juvenile offenders. The association between work commitment and antisocial behavior was analyzed using a random effects model; the substance use mediated relationship between the two factors was analyzed using structural equation modeling; and the racial difference in the mediated relationship was analyzed using subgroup analyses. The random effects model revealed results that clearly supported the notion and the study’s hypothesis about the role of work on reducing antisocial behavior, after controlling for substance use and demographic covariates. This indicated work might guide individuals to lead prosocial lives and help them keep conventional norms, which, in turn, results in less antisocial behavior. Second, in the cross-sectional mediational analyses included in the longitudinal mediation model, work commitment was associated with higher levels of substance use; which, in turn, was related to a higher level of antisocial behavior. That is, work commitment was associated with higher levels of antisocial behavior through the presence of substance use, which contrasted the hypothesis. This may imply that the deterrence effect of work on substance use is weaker among juveniles transitioning into young adults, like the sample in this study, than adults described in other studies. Lastly, the current study did not find evidence to support racial differences in the substance use mediated relationship between work commitment and antisocial behavior in terms of the direction and magnitude of the coefficients, which was also in contrast to the study’s hypothesis. Future criminal desistance research should further investigate the effect of work on criminal behavior while considering the motivations of substance use among formerly incarcerated youth since substance use seemed to dominate all other factors in the analyses

A comparative analysis of Simplified General Circulation Models of the atmosphere of Venus

Within the context of a working group supported by ISSI (Bern, Switzerland), we have made an intercomparison work between Global Circulation Models using simpli?ed parameterizations for radiative forcing and other physical processes. Even with similar schemes and parameters, the different GCMs produce different circulations, illustrating interesting differences between dynamical model cores

Unitary relations in time-dependent harmonic oscillators

For a harmonic oscillator with time-dependent (positive) mass and frequency, an unitary operator is shown to transform the quantum states of the system to those of a harmonic oscillator system of unit mass and time-dependent frequency, as well as operators. For a driven harmonic oscillator, it is also shown that, there are unitary transformations which give the driven system from the system of same mass and frequency without driving force. The transformation for a driven oscillator depends on the solution of classical equation of motion of the driven system. These transformations, thus, give a simple way of finding exact wave functions of a driven harmonic oscillator system, provided the quantum states of the corresponding system of unit mass are given.Comment: Submitted to J. Phys.

Neighborhood conditions matter for the employment of young people who have been involved in the justice system

Young people who have been involved with the criminal justice system are much more likely to be unemployed than those who have not. In new research, Lewis H. Lee, Minseop Kim, Catherine Carlson, Taylor Ellis, Karen Johnson, and Angela Pretz examined the role of neighborhoods in the employment of justice-involved young adults. They find that young adults who perceive worsening neighborhood conditions tend to work less for formal jobs, whereas a justice-involved young adult who has the same perception is more likely to work more for informal or under-the-table jobs