6,610 research outputs found
Emission Line Galaxies in the STIS Parallel Survey II: Star Formation Density
We present the luminosity function of [OII]-emitting galaxies at a median
redshift of z=0.9, as measured in the deep spectroscopic data in the STIS
Parallel Survey (SPS). The luminosity function shows strong evolution from the
local value, as expected. By using random lines of sight, the SPS measurement
complements previous deep single field studies. We calculate the density of
inferred star formation at this redshift by converting from [OII] to H-alpha
line flux as a function of absolute magnitude and find rho_dot=0.043 +/- 0.014
Msun/yr/Mpc^3 at a median redshift z~0.9 within the range 0.46<z<1.415 (H_0 =
70 km/s/Mpc, Omega_M=0.3, Omega_Lambda=0.7. This density is consistent with a
(1+z)^4 evolution in global star formation since z~1. To reconcile the density
with similar measurements made by surveys targeting H-alpha may require
substantial extinction correction.Comment: 16 preprint pages including 5 figures; accepted for publication in
Ap
Characterization of non-local gates
A non-local unitary transformation of two qubits occurs when some Hamiltonian
interaction couples them. Here we characterize the amount, as measured by time,
of interaction required to perform two--qubit gates, when also arbitrarily
fast, local unitary transformations can be applied on each qubit. The minimal
required time of interaction, or interaction cost, defines an operational
notion of the degree of non--locality of gates. We characterize a partial order
structure based on this notion. We also investigate the interaction cost of
several communication tasks, and determine which gates are able to accomplish
them. This classifies two--qubit gates into four categories, differing in their
capability to transmit classical, as well as quantum, bits of information.Comment: revtex, 14 pages, no pictures; proof of result 1 simplified
significantl
Measurements of the Diffuse Ultraviolet Background and the Terrestrial Airglow with the Space Telescope Imaging Spectrograph
Far-UV observations in and near the Hubble Deep Fields demonstrate that the
Space Telescope Imaging Spectrograph (STIS) can potentially obtain unique and
precise measurements of the diffuse far-ultraviolet background. Although STIS
is not the ideal instrument for such measurements, high-resolution images allow
Galactic and extragalactic objects to be masked to very faint magnitudes, thus
ensuring a measurement of the truly diffuse UV signal. The programs we have
analyzed were not designed for this scientific purpose, but would be sufficient
to obtain a very sensitive measurement if it were not for a weak but
larger-than-expected signal from airglow in the STIS 1450-1900 A bandpass. Our
analysis shows that STIS far-UV crystal quartz observations taken near the limb
during orbital day can detect a faint airglow signal, most likely from NI\1493,
that is comparable to the dark rate and inseparable from the far-UV background.
Discarding all but the night data from these datasets gives a diffuse
far-ultraviolet background measurement of 501 +/- 103 ph/cm2/sec/ster/A, along
a line of sight with very low Galactic neutral hydrogen column (N_HI = 1.5E20
cm-2) and extinction (E(B-V)=0.01 mag). This result is in good agreement with
earlier measurements of the far-UV background, and should not include any
significant contribution from airglow. We present our findings as a warning to
other groups who may use the STIS far-UV camera to observe faint extended
targets, and to demonstrate how this measurement may be properly obtained with
STIS.Comment: 7 pages, Latex. 4 figures. Uses corrected version of emulateapj.sty
and apjfonts.sty (included). Accepted for publication in A
Combining work and child care: The experiences of mothers in Accra, Ghana
Work-family research has focused predominantly on Western women. Yet the forms of economic labour in which women are typically involved and the meaning of motherhood are context-specific. This paper aims to explore the experience of combining economic activity and child care of mothers with young children using urban Ghana as a case study. Semi-structured interviews (n=24) were conducted in three locations in the Accra Metropolitan Area. Transcripts were analysed using the general inductive approach. The results found womenâs experience of role conflict to be bi-directional. With regard to role enhancement, economic activity allowed women to provide materially for their children. The combination of work and child care had negative consequences for womenâs wellbeing. This research questions policy makersâ strategy of frequently targeting women in their roles either as generators of income, or as the primary care-takers of children by highlighting the reality of womenâs simultaneous performance of these roles
Women over 40, foreigners of color, and other missing persons in globalizing mediascapes: understanding marketing images as mirrors of intersectionality
Media diversity studies regularly invoke the notion of marketing images as mirrors of racism and sexism. This article develops a higher-order concept of marketing images as âmirrors of intersectionality.â Drawing on a seven-dimensional study of coverperson diversity in a globalizing mediascape, the emergent concept highlights that marketing images reflect not just racism and sexism, but all categorical forms of marginalization, including ableism, ageism, colorism, fatism, and heterosexism, as well as intersectional forms of marginalization, such as sexist ageism and racist multiculturalism. Fueled by the legacies of history, aspirational marketing logics, and an industry-wide distribution of discriminatory work, marketing images help to perpetuate multiple, cumulative, and enduring advantages for privileged groups and disadvantages for marginalized groups. In this sense, marketing images, as mirrors of intersectionality, are complicit agents in the structuration of inequitable societies
Measurement of Cosmic Shear with the Space Telescope Imaging Spectrograph
Weak lensing by large-scale structure allows a direct measure of the dark
matter distribution. We have used parallel images taken with the Space
Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope to measure
weak lensing, or cosmic shear. We measure the shapes of 26036 galaxies in 1292
STIS fields and measure the shear variance at a scale of 0.51 arcminutes. The
charge transfer efficiency (CTE) of STIS has degraded over time and introduces
a spurious ellipticity into galaxy shapes during the readout process. We
correct for this effect as a function of signal to noise and CCD position. We
further show that the detected cosmic shear signal is nearly constant in time
over the approximately four years of observation. We detect cosmic shear at the
5.1 sigma level, and our measurement of the shear variance is consistent with
theoretical predictions in a LambdaCDM universe. This provides a measure of the
normalization of the mass power spectrum sigma_8=(1.02 +- 0.16)
(0.3/Omega_m)^{0.46} (0.21/Gamma)^{0.18}$. The one-sigma error includes noise,
cosmic variance, systematics and the redshift uncertainty of the source
galaxies. This is consistent with previous cosmic shear measurements, but tends
to favor those with a high value of sigma_8. It is also consistent with the
recent determination of sigma_8 from the Wilkinson Microwave Anisotropy Probe
(WMAP) experiment.Comment: 9 pages, 5 figure, 1 table, Accepted to Ap
Accuracy of core mass estimates in simulated observations of dust emission
We study the reliability of mass estimates obtained for molecular cloud cores
using sub-millimetre and infrared dust emission. We use magnetohydrodynamic
simulations and radiative transfer to produce synthetic observations with
spatial resolution and noise levels typical of Herschel surveys. We estimate
dust colour temperatures using different pairs of intensities, calculate column
densities and compare the estimated masses with the true values. We compare
these results to the case when all five Herschel wavelengths are available. We
investigate the effects of spatial variations of dust properties and the
influence of embedded heating sources. Wrong assumptions of dust opacity and
its spectral index beta can cause significant systematic errors in mass
estimates. These are mainly multiplicative and leave the slope of the mass
spectrum intact, unless cores with very high optical depth are included.
Temperature variations bias colour temperature estimates and, in quiescent
cores with optical depths higher than for normal stable cores, masses can be
underestimated by up to one order of magnitude. When heated by internal
radiation sources the observations recover the true mass spectra. The shape,
although not the position, of the mass spectrum is reliable against
observational errors and biases introduced in the analysis. This changes only
if the cores have optical depths much higher than expected for basic
hydrostatic equilibrium conditions. Observations underestimate the value of
beta whenever there are temperature variations along the line of sight. A bias
can also be observed when the true beta varies with wavelength. Internal
heating sources produce an inverse correlation between colour temperature and
beta that may be difficult to separate from any intrinsic beta(T) relation of
the dust grains. This suggests caution when interpreting the observed mass
spectra and the spectral indices.Comment: Revised version, 17 pages, 17 figures, submitted to A&
Cross infection control measures and the treatment of patients at risk of Creutzfeldt Jakob disease in UK general dental practice
AIMS: To determine the suitability of key infection control measures currently employed in UK dental practice for delivery of dental care to patients at risk of prion diseases. MATERIALS AND METHODS: Subjects: Five hundred dental surgeons currently registered with the General Dental Council of the UK. Data collection: Structured postal questionnaire. Analysis: Frequencies, cross-tabulations and chi-squared analysis. RESULTS: The valid response rate to the questionnaire was 69%. 33% of practices had no policy on general disinfection and sterilisation procedures. Only 10 of the 327 responding practices (3%) possessed a vacuum autoclave. 49% of dentists reported using the BDA medical history form but less than 25% asked the specific questions recommended by the BDA to identify patients at risk of iatrogenic or familial CJD. However, 63% of practitioners would refer such patients, if identified, to a secondary care facility. Of the 107 practitioners who were prepared to provide dental treatment, 75 (70%) would do so using routine infection control procedures. CONCLUSIONS: Most of the dental practices surveyed were not actively seeking to identify patients at risk of prion diseases. In many cases, recommended procedures for providing safe dental care for such patients were not in place
âWe were there tooâ:There is much to learn from embedding auto/biography in the knowing and doing of prison research
QCD Corrections to Scalar Production via Heavy Quark Fusion at Hadron Colliders
We recently proposed that, due to the top-quark-mass enhanced Yukawa
coupling, the s-channel production of a charged scalar or pseudo-scalar from
heavy quark fusion can be an important new mechanism for discovering
non-standard spin-0 particles. In this work, we present the complete O(alpha_s)
QCD corrections to this s-channel production process at hadron colliders,
including the results of QCD resummation over multiple soft-gluon emission. The
systematic QCD-improved production and decay rates at the FermiLab Tevatron and
the CERN LHC are given for the charged top-pions in the topcolor models and for
the charged Higgs bosons in the generic two Higgs doublet model. The direct
extension to the production of the neutral (pseudo-)scalars via bb\bar fusion
is studied in the minimal supersymmetric standard model (MSSM) with large
tan(beta), and in the topcolor model with large bottom Yukawa coupling.Comment: Version to be published in Phys.Rev.D. Discussion on Rb added plus
minor improvements. Conclusions not changed. Latex2e, 40 pages, 16 figure
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