A Measurement of Stimulated Emission From 83m-Kr(m)

This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Unidentified EGRET Sources and the Extragalactic Gamma-Ray Background

The large majority of EGRET point sources remain to this day without an identified low-energy counterpart. Whatever the nature of the EGRET unidentified sources, faint unresolved objects of the same class must have a contribution to the diffuse gamma-ray background: if most unidentified objects are extragalactic, faint unresolved sources of the same class contribute to the background, as a distinct extragalactic population; on the other hand, if most unidentified sources are Galactic, their counterparts in external galaxies will contribute to the unresolved emission from these systems. Understanding this component of the gamma-ray background, along with other guaranteed contributions from known sources, is essential in any attempt to use gamma-ray observations to constrain exotic high-energy physics. Here, we follow an empirical approach to estimate whether a potential contribution of unidentified sources to the extragalactic gamma-ray background is likely to be important, and we find that it is. Additionally, we comment on how the anticipated GLAST measurement of the diffuse gamma-ray background will change, depending on the nature of the majority of these sources.Comment: 6 pages, 3 figures, to appear in proceedings of "The Multi-Messenger Approach to High Energy Gamma-Ray Sources", Barcelona, 4-7 July 2006; comments welcom

Gamma-Ray Luminosity Function of Blazars and the Cosmic Gamma-Ray Background: Evidence for the Luminosity Dependent Density Evolution

We present a comprehensive study for the gamma-ray luminosity function (GLF) of blazars and their contribution to the extragalactic diffuse gamma-ray background (EGRB). Radio and gamma-ray luminosity correlation is introduced to take into account the radio detectability which is important for the blazar identification. Previous studies considered only pure luminosity evolution (PLE) or pure density evolution, but we introduce the luminosity dependent density evolution (LDDE) model, which is favored from the evolution of X-ray luminosity function (XLF) of AGNs. The model parameters are constrained by likelihood analyses about the observed redshift and gamma-ray flux distributions of the EGRET blazars. We find that the LDDE model gives a better fit to the observed distributions than the PLE model, indicating that the LDDE model is also appropriate for gamma-ray blazars, and that the jet activity is universally correlated with the accretion history of AGNs. The normalization between the GLF and XLF is consistent with the unified picture of AGNs, when the beaming and a reasonable duty cycle of jet activity are taken into account. We then find that only 25--50% of the EGRB can be explained by unresolved blazars with the best-fit LDDE parameters. Unresolved blazars can account for all the EGRB only with a steeper index of the faint-end slope of the GLF, which is marginally consistent with the EGRET data but inconsistent with that of the XLF. Therefore unresolved AGNs cannot be the dominant source of the EGRB, unless there is a new population of gamma-ray emitting AGNs that evolves differently from the XLF of AGNs. Predictions for the GLAST mission are made, and we find that the best-fit LDDE model predicts about 3000 blazars in the entire sky, which is considerably fewer than a previous estimate.Comment: 13 pages, 12 figures, accepted by ApJ; minor typos corrected and some figures revised, main conclusions essentially unchange

Diffuse inverse Compton and synchrotron emission from dark matter annihilations in galactic satellites

Annihilating dark matter particles produce roughly as much power in electrons and positrons as in gamma ray photons. The charged particles lose essentially all of their energy to inverse Compton and synchrotron processes in the galactic environment. We discuss the diffuse signature of dark matter annihilations in satellites of the Milky Way (which may be optically dark with few or no stars), providing a tail of emission trailing the satellite in its orbit. Inverse Compton processes provide X-rays and gamma rays, and synchrotron emission at radio wavelengths might be seen. We discuss the possibility of detecting these signals with current and future observations, in particular EGRET and GLAST for the gamma rays.Comment: 13 pages, 5 figure

The clustering of ultra-high energy cosmic rays and their sources

The sky distribution of cosmic rays with energies above the 'GZK cutoff' holds important clues to their origin. The AGASA data, although consistent with isotropy, shows evidence for small-angle clustering, and it has been argued that such clusters are aligned with BL Lacertae objects, implicating these as sources. It has also been suggested that clusters can arise if the cosmic rays come from the decays of very massive relic particles in the Galactic halo, due to the expected clumping of cold dark matter. We examine these claims and show that both are in fact not justified.Comment: 13 pages, 8 figures, version in press at Phys. Rev.

New hadrons as ultra-high energy cosmic rays

Ultra-high energy cosmic ray (UHECR) protons produced by uniformly distributed astrophysical sources contradict the energy spectrum measured by both the AGASA and HiRes experiments, assuming the small scale clustering of UHECR observed by AGASA is caused by point-like sources. In that case, the small number of sources leads to a sharp exponential cutoff at the energy E<10^{20} eV in the UHECR spectrum. New hadrons with mass 1.5-3 GeV can solve this cutoff problem. For the first time we discuss the production of such hadrons in proton collisions with infrared/optical photons in astrophysical sources. This production mechanism, in contrast to proton-proton collisions, requires the acceleration of protons only to energies E<10^{21} eV. The diffuse gamma-ray and neutrino fluxes in this model obey all existing experimental limits. We predict large UHE neutrino fluxes well above the sensitivity of the next generation of high-energy neutrino experiments. As an example we study hadrons containing a light bottom squark. These models can be tested by accelerator experiments, UHECR observatories and neutrino telescopes.Comment: 17 pages, revtex style; v2: shortened, as to appear in PR

Stress and coping patterns of participants and non-participants in self-help groups for parents of the mentally ill

The authors examined differences in stress and coping patterns as well as in situationally-related variables between participants and non-participants in self-help groups for parents of the mentally ill in Israel. Participants, who were higher on socio-economic status indicators, reported coping patterns that tended to be both more active and interactive. They also reported greater concerns around psycho-social issues than non-participants. The authors discuss the possible interrelationships among these findings.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44305/1/10597_2004_Article_BF00752453.pd

The Influence of Age and Sex on Genetic Associations with Adult Body Size and Shape : A Large-Scale Genome-Wide Interaction Study

Genome-wide association studies (GWAS) have identified more than 100 genetic variants contributing to BMI, a measure of body size, or waist-to-hip ratio (adjusted for BMI, WHRadjBMI), a measure of body shape. Body size and shape change as people grow older and these changes differ substantially between men and women. To systematically screen for age-and/or sex-specific effects of genetic variants on BMI and WHRadjBMI, we performed meta-analyses of 114 studies (up to 320,485 individuals of European descent) with genome-wide chip and/or Metabochip data by the Genetic Investigation of Anthropometric Traits (GIANT) Consortium. Each study tested the association of up to similar to 2.8M SNPs with BMI and WHRadjBMI in four strata (men 50y, women 50y) and summary statistics were combined in stratum-specific meta-analyses. We then screened for variants that showed age-specific effects (G x AGE), sex-specific effects (G x SEX) or age-specific effects that differed between men and women (G x AGE x SEX). For BMI, we identified 15 loci (11 previously established for main effects, four novel) that showed significant (FDR= 50y). No sex-dependent effects were identified for BMI. For WHRadjBMI, we identified 44 loci (27 previously established for main effects, 17 novel) with sex-specific effects, of which 28 showed larger effects in women than in men, five showed larger effects in men than in women, and 11 showed opposite effects between sexes. No age-dependent effects were identified for WHRadjBMI. This is the first genome-wide interaction meta-analysis to report convincing evidence of age-dependent genetic effects on BMI. In addition, we confirm the sex-specificity of genetic effects on WHRadjBMI. These results may providefurther insights into the biology that underlies weight change with age or the sexually dimorphism of body shape.Peer reviewe

FEASIBILITY OF PRODUCING PATHOGEN-FREE AROID ROOT CROPS COMMERCIALLY BY MICROPROPAGATION

The potential of micropropagation as a means to control disease and to accelerate germplasm buildup has been demonstrated for many different kinds of vegetatively propagated plants, including the aroid root crops, Colocasia and Xanthosoma. However, because of labor costs and the necessity of expensive facilities, the direct commercial application of this technology has been limited to those plants, such as the foliage aroid Dieffenbachia. with relatively high cash values per propagating unit. Based upon computer models using industrygenerated data, we have determined that cost efficiencies are already near their theoretical optima for micropropagation using adventitious and axillary shoot proliferation technologies. Accordingly, alternative means must be deployed for commercial production of aroid root crops and other relatively low cash value aroids, such as Caladium. Robotics and synthetic seed technologies offer promise, but are still early in the developmental stage. Currently, the financial benefits of root crop micropropagation can only be realized when plants derived from this technology are field-grown and multiplied by conventional methods to numbers large enough to drop the cost per propagating unit to commercially acceptable levels. In instances where disease control is a primary objective, it may be necessary to establish blocks of mother plants isolated from major sources of inoculum