The Origin of \lya Absorption Systems at z>1z>1---Implications from the Hubble Deep Field

The Hubble Deep Field images have provided us with a unique chance to relate statistical properties of high-redshift galaxies to statistical properties of \lya absorption systems. Combining an {\em empirical} measure of the galaxy surface density versus redshift with an {\em empirical} measure of the gaseous extent of galaxies, we predict the number density of \lya absorption systems that originate in extended gaseous envelopes of galaxies versus redshift. We show that at least 50% and as much as 100% of observed \lya absorption systems of W\apg0.32 \AA can be explained by extended gaseous envelops of galaxies. Therefore, we conclude that known galaxies of known gaseous extent must produce a significant fraction and perhaps all of \lya absorption systems over a large redshift range.Comment: 12 pages, 3 figures, accepted for publication in the Astrophysical Journal, April 10, 2000 issu

Implanted muon spin spectroscopy on 2-O-adamantane: a model system that mimics the liquid

The transition taking place between two metastable phases in 2-O-adamantane, namely the [Formula: see text] cubic, rotator phase and the lower temperature P21/c, Z  =  4 substitutionally disordered crystal is studied by means of muon spin rotation and relaxation techniques. Measurements carried out under zero, weak transverse and longitudinal fields reveal a temperature dependence of the relaxation parameters strikingly similar to those exhibited by structural glass[Formula: see text]liquid transitions (Bermejo et al 2004 Phys. Rev. B 70 214202; Cabrillo et al 2003 Phys. Rev. B 67 184201). The observed behaviour manifests itself as a square root singularity in the relaxation rates pointing towards some critical temperature which for amorphous systems is located some tens of degrees above that shown as the characteristic transition temperature if studied by thermodynamic means. The implications of such findings in the context of current theoretical approaches concerning the canonical liquid-glass transition are discussed.Postprint (author's final draft

The Star Formation Rate Intensity Distribution Function--Implications for the Cosmic Star Formation Rate History of the Universe

We address the effects of cosmological surface brightness dimming on observations of faint galaxies by examining the distribution of "unobscured" star formation rate intensities versus redshift. We use the star formation rate intensity distribution function to assess the ultraviolet luminosity density versus redshift, based on our photometry and photometric redshift measurements of faint galaxies in the HDF and the HDF--S WFPC2 and NICMOS fields. We find that (1) previous measurements have missed a dominant fraction of the ultraviolet luminosity density of the universe at high redshifts by neglecting cosmological surface brightness dimming effects, which are important at redshifts larger than z = 2, (2) the incidence of the highest intensity star forming regions increases monotonically with redshift, and (3) the ultraviolet luminosity density plausibly increases monotonically with redshift through the highest redshifts observed. By measuring the spectrum of the luminosity density versus redshift, we also find that (4) previous measurements of the ultraviolet luminosity density at redshifts z < 2 must be reduced by a factor 2 to allow for the spectrum of the luminosity density between rest-frame wavelengths 1500 and 2800 A. And by comparing with observations of high-redshift damped Lyman-alpha absorption systems detected toward background QSOs, we further find that (5) the distribution of star formation rate intensities matches the distribution of neutral hydrogen column densities at redshifts z = 2 through 5, which establishes a quantitative connection between high-redshift galaxies and high column density gas and suggests that high-redshift damped Lyman-alpha absorption systems trace lower star formation rate intensity regions of the same galaxies detected in star light in the HDF and HDF--S.Comment: 28 pages, 9 figures; accepted for publication in the Astrophysical Journa

A new catalog of photometric redshifts in the Hubble Deep Field

Using the newly available infrared images of the Hubble Deep Field in the J, H, and K bands and an optimal photometric method, we have refined a technique to estimate the redshifts of 1067 galaxies. A detailed comparison of our results with the spectroscopic redshifts in those cases where the latter are available shows that this technique gives very good results for bright enough objects (AB(8140) < 26.0). From a study of the distribution of residuals (Dz(rms)/(1+z) ~ 0.1 at all redshifts) we conclude that the observed errors are mainly due to cosmic variance. This very important result allows for the assessment of errors in quantities to be directly or indirectly measured from the catalog. We present some of the statistical properties of the ensemble of galaxies in the catalog, and finish by presenting a list of bright high-redshift (z ~ 5) candidates extracted from our catalog, together with recent spectroscopic redshift determinations confirming that two of them are at z=5.34 and z=5.60.Comment: 28 pages, 12PS+4JPEG figures, aaspp style. Accepted for publication in The Astrophysical Journal. The catalog, together with a clickable map of the HDF, Tables 4 and 5 (HTML, LaTeX or ASCII format), and the figures, are available at http://bat.phys.unsw.edu.au/~fsoto/hdfcat.htm

The E-SCREEN assay as a tool to identify estrogens: an update on estrogenic environmental pollutants.

Estrogens are defined by their ability to induce the proliferation of cells of the female genital tract. The wide chemical diversity of estrogenic compounds precludes an accurate prediction of estrogenic activity on the basis of chemical structure. Rodent bioassays are not suited for the large-scale screening of chemicals before their release into the environment because of their cost, complexity, and ethical concerns. The E-SCREEN assay was developed to assess the estrogenicity of environmental chemicals using the proliferative effect of estrogens on their target cells as an end point. This quantitative assay compares the cell number achieved by similar inocula of MCF-7 cells in the absence of estrogens (negative control) and in the presence of 17 beta-estradiol (positive control) and a range of concentrations of chemicals suspected to be estrogenic. Among the compounds tested, several "new" estrogens were found; alkylphenols, phthalates, some PCB congeners and hydroxylated PCBs, and the insecticides dieldrin, endosulfan, and toxaphene were estrogenic by the E-SCREEN assay. In addition, these compounds competed with estradiol for binding to the estrogen receptor and increased the levels of progesterone receptor and pS2 in MCF-7 cells, as expected from estrogen mimics. Recombinant human growth factors (bFGF, EGF, IGF-1) and insulin did not increase in cell yields. The aims of the work summarized in this paper were a) to validate the E-SCREEN assay; b) to screen a variety of chemicals present in the environment to identify those that may be causing reproductive effects in wildlife and humans; c) to assess whether environmental estrogens may act cumulatively; and finally d) to discuss the reliability of this and other assays to screen chemicals for their estrogenicity before they are released into the environment

Mechanism of catalysis and inhibition of Mycobacterium tuberculosis SapM, implications for the development of novel antivirulence drugs.

Mycobacterium tuberculosis (Mtb) SapM is a secreted virulence factor critical for intracellular survival of the pathogen. The role of SapM in phagosome maturation arrest in host macrophages suggests its potential as a drug target to assist in the clearance of tuberculosis infection. However, the mechanism of action of SapM at the molecular level remains unknown. In this study, we provide new insights into the mechanism of catalysis, substrate specificity and inhibition of SapM, and we identify the critical residues for catalysis and substrate binding. Our findings demonstrate that SapM is an atypical monoester alkaline phosphatase, with a serine-based mechanism of catalysis probably metal-dependent. Particularly relevant to SapM function and pathogenesis, is its activity towards PI(4,5)P2 and PI3P, two phosphoinositides that function at the early stages of microbial phagocytosis and phagosome formation. This suggests that SapM may have a pleiotropic role with a wider importance on Mtb infection than initially thought. Finally, we have identified two inhibitors of SapM, L-ascorbic acid and 2-phospho-L-ascorbic, which define two different mechanisms by which the catalytic activity of this phosphatase could be regulated. Critically, we demonstrate that 2-phospho-L-ascorbic reduces mycobacterial survival in macrophage infections, hence confirming the potential of SapM as a therapeutic drug target

JPCam: A 1.2Gpixel camera for the J-PAS survey

JPCam is a 14-CCD mosaic camera, using the new e2v 9k-by-9k 10microm-pixel 16-channel detectors, to be deployed on a dedicated 2.55m wide-field telescope at the OAJ (Observatorio Astrofisico de Javalambre) in Aragon, Spain. The camera is designed to perform a Baryon Acoustic Oscillations (BAO) survey of the northern sky. The J-PAS survey strategy will use 54 relatively narrow-band (~13.8nm) filters equi-spaced between 370 and 920nm plus 3 broad-band filters to achieve unprecedented photometric red-shift accuracies for faint galaxies over ~8000 square degrees of sky. The cryostat, detector mosaic and read electronics is being supplied by e2v under contract to J-PAS while the mechanical structure, housing the shutter and filter assembly, is being designed and constructed by a Brazilian consortium led by INPE (Instituto Nacional de Pesquisas Espaciais). Four sets of 14 filters are placed in the ambient environment, just above the dewar window but directly in line with the detectors, leading to a mosaic having ~10mm gaps between each CCD. The massive 500mm aperture shutter is expected to be supplied by the Argelander-Institut fur Astronomie, Bonn. We will present an overview of JPCam, from the filter configuration through to the CCD mosaic camera. A brief outline of the main J-PAS science projects will be included.Comment: 11 pages and 9 figure

A Uniform Analysis of the Ly-alpha Forest at z=0 - 5: V. The extragalactic ionizing background at low redshift

In Paper III of our series "A Uniform Analysis of the Ly-alpha forest at z=0 - 5", we presented a set of 270 quasar spectra from the archives of the Faint Object Spectrograph on the Hubble Space Telescope. A total of 151 of these spectra, yielding 906 lines, are suitable for using the proximity effect signature to measure J(\nu_0), the mean intensity of the hydrogen-ionizing background radiation field, at low redshift. Using a maximum likelihood technique and the best estimates possible for each QSO's Lyman limit flux and systemic redshift, we find J(\nu_0)= 7.6^+9.4_-3.0 x 10^-23 ergs s^-1 cm^-2 Hz^-1 sr^-1 at at 0.03 < z < 1.67. This is in good agreement with the mean intensity expected from models of the background which incorporate only the known quasar population. When the sample is divided into two subsamples, consisting of lines with z 1, the values of J(\nu_0) found are 6.5^+38._-1.6 x 10^-23 ergs s^-1 cm^-2 Hz^-1 sr^-1, and 1.0^+3.8_-0.2 x 10^-22 ergs s^-1 cm^-2 Hz^-1 sr^-1, respectively, indicating that the mean intensity of the background is evolving over the redshift range of this data set. Relaxing the assumption that the spectral shapes of the sample spectra and the background are identical, the best fit HI photoionization rates are found to be 6.7 x 10^-13 s^-1 for all redshifts, and 1.9 x 10^-13 s^-1 and 1.3 x 10^-12 s^-1 for z 1, respectively. This work confirms that the evolution of the number density of Ly-alpha lines is driven by a decrease in the ionizing background from z ~ 2 to z ~ 0 as well as by the formation of structure in the intergalactic medium. (Abridged)Comment: 71 LaTeX pages, 20 encapsulated Postscript figures, Accepted for publication in ApJ, Figure 4 available at http://lithops.as.arizona.edu/~jill/QuasarSpectra/ or http://hea-www.harvard.edu/QEDT/QuasarSpectra

Sperm Hyperactivation and Capacitation Induced By Light Stimuli in Cryopreserved Semen

In mammals, such as rabbits, there are some factors involved in possible fertilization, from complex changes in the membrane of the sperm to obstruction or non-existent of vas deferens, which creates problems in the number and quality of sperm. In this work, we report the effects of rabbit sperm motility and capacitation of cryopreserved semen samples under light stimuli. The sperm velocities were correlated with the percentage of capacitated and non-capacitated sperm seen with a fluorescent dye. Consequently, we analyzed the specific correlations between irradiation times, supplied energy, and fertility parameters. KEYWORDS THAT SEARCHED RELATED TO THE ARTICLE ON THE WEB sperm meaning, capacitation, human sperm, capacitation occurs in, what is sperm, capacitation of sperm, sperm lifetime, fertilization definition, fertilization meaning, capacitation meaning, mechanism of fertilization,sperm capacitation, capacitate meaning, fertilization takes place in, capacitate, capacitation of sperm occurs in, capacitation of sperms, capacitated, definition of fertilizatio