366 research outputs found

    Assembly of the Inner Perivitelline Layer, a Homo log of the Mammalian Zona Pellucida: An Immunohistochemical and Ultrastructural Study

    Get PDF
    The avian inner perivitelline layer (IPVL), a homologous structure to the mammalian zona pellucida, is deposited between the granulosa cells and the oocyte cell membrane during folliculogenesis. The glycoprotein meshwork of the IPVL forms a 3-dimensional matrix and possesses important functions in the fertilization process: it contributes to the binding of avian spermatozoa to the oocyte and induces acrosomal exocytosis. In contrast to the zona pellucida of mammals, the IPVL does not prevent the physiological polyspermy found in birds. Previous studies have shown that in the Japanese quail (Cotumix japonica) at least 5 glycoproteins are constituents of the IPVL (ZP1, ZP2, ZP3, ZP4, and ZPD). In this study, we investigated the spatiotennporal assembly pattern of the IPVL during folliculogenesis using immunohistochemical and ultrastructural methods. The obtained results clearly show that these glycoproteins are incorporated into the IPVL at distinct points during follicular development, supporting the hypothesis that ZP2 and ZP4 form a type of prematrix into which ZP1, ZP3, and ZPD are integrated at a later stage of development. Copyright (C) 2011 S. Karger AG, Base

    Transiting Exoplanets with JWST

    Full text link
    The era of exoplanet characterization is upon us. For a subset of exoplanets -- the transiting planets -- physical properties can be measured, including mass, radius, and atmosphere characteristics. Indeed, measuring the atmospheres of a further subset of transiting planets, the hot Jupiters, is now routine with the Spitzer Space Telescope. The James Webb Space Telescope (JWST) will continue Spitzer's legacy with its large mirror size and precise thermal stability. JWST is poised for the significant achievement of identifying habitable planets around bright M through G stars--rocky planets lacking extensive gas envelopes, with water vapor and signs of chemical disequilibrium in their atmospheres. Favorable transiting planet systems, are, however, anticipated to be rare and their atmosphere observations will require tens to hundreds of hours of JWST time per planet. We review what is known about the physical characteristics of transiting planets, summarize lessons learned from Spitzer high-contrast exoplanet measurements, and give several examples of potential JWST observations.Comment: 22 pages, 11 figures. In press in "Astrophysics in the Next Decade: JWST and Concurrent Facilities, Astrophysics & Space Science Library, Thronson, H. A., Tielens, A., Stiavelli, M., eds., Springer: Dordrecht (2008)." The original publication will be available at http://www.springerlink.co

    The Political Economy of US Military Spending

    Full text link
    The causes of the dramatic rise in military spending in the post-war era have been the subject of much political and academic controversy. No extant formulation seems to provide a compelling explanation of the dynamics involved in the levels of, and rates of change in, such spending. In light of this, the authors develop a new model, based mainly on a political-business cycle argument, to account for these dynamics. The basic proposition in this model is that variations in national defense spending arise from political considerations which are related to real and desired conditions within the national economy. Applying this model to the experience of the United States 1948-1976, the authors show that it has a large measure of empirical validity. If one removes the effects of war-time mobilization, it is clear that for the United States the principal driving forces in military spending dynamics were (1) the perceived utility of such spending in stabilizing aggregate demand, (2) the political or electoral value of the perceived economic effects arising out of such spending, and (3) the pressures of institutional-constituency demands.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68958/2/10.1177_002234337901600202.pd

    Precison Measurements of the Mass, the Widths of ψ(3770)\psi(3770) Resonance and the Cross Section σ[e+eψ(3770)]\sigma[e^+e^-\to \psi(3770)] at Ecm=3.7724E_{\rm cm}=3.7724 GeV

    Full text link
    By analyzing the RR values measured at 68 energy points in the energy region between 3.650 and 3.872 GeV reported in our previous paper, we have precisely measured the mass, the total width, the leptonic width and the leptonic decay branching fraction of the ψ(3770)\psi(3770) to be Mψ(3770)=3772.4±0.4±0.3{M}_{\psi(3770)}=3772.4 \pm 0.4 \pm 0.3 MeV, Γψ(3770)tot=28.6±1.2±0.2\Gamma_{\psi(3770)}^{\rm tot} = 28.6 \pm 1.2 \pm 0.2 MeV, Γψ(3770)ee=279±11±13\Gamma_{\psi(3770)}^{ee} = 279 \pm 11 \pm 13 eV and B[ψ(3770)e+e]=(0.98±0.04±0.04)×105B[\psi(3770)\to e^+e^-]=(0.98\pm 0.04\pm 0.04)\times 10^{-5}, respectively, which result in the observed cross section σobs[e+eψ(3770)]=7.25±0.27±0.34\sigma^{\rm obs}[e^+e^-\to \psi(3770)]=7.25\pm 0.27 \pm 0.34 nb at s=3772.4\sqrt{s}=3772.4 MeV. We have also measured Ruds=2.121±0.023±0.084R_{\rm uds}=2.121\pm 0.023 \pm 0.084 for the continuum light hadron production in the region from 3.650 to 3.872 GeV.Comment: 5 pages, 2 figure

    Updated precision measurement of the average lifetime of B hadrons

    Get PDF
    The measurement of the average lifetime of B hadrons using inclusively reconstructed secondary vertices has been updated using both an improved processing of previous data and additional statistics from new data. This has reduced the statistical and systematic uncertainties and gives \tau_{\mathrm{B}} = 1.582 \pm 0.011\ \mathrm{(stat.)} \pm 0.027\ \mathrm{(syst.)}\ \mathrm{ps.} Combining this result with the previous result based on charged particle impact parameter distributions yields \tau_{\mathrm{B}} = 1.575 \pm 0.010\ \mathrm{(stat.)} \pm 0.026\ \mathrm{(syst.)}\ \mathrm{ps.

    Limits on the production of scalar leptoquarks from Z (0) decays at LEP

    Get PDF
    A search has been made for pairs and for single production of scalar leptoquarks of the first and second generations using a data sample of 392000 Z0 decays from the DELPHI detector at LEP 1. No signal was found and limits on the leptoquark mass, production cross section and branching ratio were set. A mass limit at 95% confidence level of 45.5 GeV/c2 was obtained for leptoquark pair production. The search for the production of a single leptoquark probed the mass region above this limit and its results exclude first and second generation leptoquarks D0 with masses below 65 GeV/c2 and 73 GeV/c2 respectively, at 95% confidence level, assuming that the D0lq Yukawa coupling alpha(lambda) is equal to the electromagnetic one. An upper limit is also given on the coupling alpha(lambda) as a function of the leptoquark mass m(D0)
    corecore