1,896 research outputs found
Autofib Redshift Survey: II -- The Evolution of the Galaxy Luminosity Function by Spectral Type
We determine the evolution of the galaxy luminosity function (LF) as a
function of spectral type using the Autofib redshift survey, a compendium of
over 1700 galaxy redshifts in various magnitude-limited samples spanning
b_J=11.5-24.0. To carry out this analysis we have developed a cross-correlation
technique which classifies faint galaxy spectra into one of six types based on
local galaxy templates. Tests and simulations show that this technique yields
classifications correct to within one type for more than 90% of the galaxies in
our sample. We have also developed extensions of the step-wise maximum
likelihood method and the STY parametric method for estimating LFs which are
applicable to recovering an evolving LF from multiple samples. We find that:
(i) The spectra and LF of E/S0 galaxies show no appreciable evolution out to at
least z ~ 0.5. (ii) Early-type spirals show modest evolution, characterised by
a gradual steepening of the faint end of their LF with redshift. (iii) Out to z
~ 0.5, the overall evolution of the galaxy population is dominated by changes
seen in late-type spirals. The characteristic luminosity (L^*) of these
galaxies appears to brighten with redshift and there are signs of strong
density evolution (a rapid increase in \phi^*). These effects appear to be
luminosity dependent so that the LF steepens at higher redshift. These trends
are accompanied by a steep increase in the median [OII] equivalent width,
implying a rapid increase in the star-formation rate with redshift at fixed
luminosity---a given star-formation rate is found at higher redshift in
galaxies of higher luminosity. We find that these conclusions are robust with
respect to spectral classification errors and the luminosity function
estimator.Comment: LaTeX, 22 pages, 22 figure
Building the Infrastructure: The Effects of Role Identification Behaviors on Team Cognition Development and Performance
The primary purpose of this study was to extend theory and research regarding the emergence of mental models and transactive memory in teams. Utilizing Kozlowski et al.âs (1999) model of team compilation, we examine the effect of role identification behaviors and argue that such behaviors represent the initial building blocks of team cognition during the role compilation phase of team development. We then hypothesized that team mental models and transactive memory would convey the effects of these behaviors onto team performance in the team compilation phase of development. Results from 60 teams working on a command and control simulation supported our hypotheses
Line Emitting Galaxies Beyond a Redshift of 7: An Improved Method for Estimating the Evolving Neutrality of the Intergalactic Medium
The redshift-dependent fraction of color-selected galaxies revealing Lyman
alpha emission has become the most valuable constraint on the evolving
neutrality of the early intergalactic medium. However, in addition to resonant
scattering by neutral gas, the visibility of Lyman alpha is also dependent on
the intrinsic properties of the host galaxy, including its stellar population,
dust content and the nature of outflowing gas. Taking advantage of significant
progress we have made in determining the line emitting properties of galaxies, we propose an improved method, based on using the measured
slopes of the rest-frame ultraviolet continua of galaxies, to interpret the
growing body of near-infrared spectra of galaxies in order to take into
account these host galaxy dependencies. In a first application of our new
method, we demonstrate its potential via a new spectroscopic survey of
galaxies undertaken with the Keck MOSFIRE spectrograph. Together with earlier
published data our data provides improved estimates of the evolving visibility
of Lyman alpha, particularly at redshift . As a byproduct, we also
present a new line emitting galaxy at a redshift which supersedes an
earlier redshift record. We discuss the improving constraints on the evolving
neutral fraction over and the implications for cosmic reionization.Comment: To be submitted to Ap
Health outcomes in patients using no-prescription online pharmacies to purchase prescription drugs
BACKGROUND: Many prescription drugs are freely available for purchase on the Internet without a legitimate prescription from a physician. OBJECTIVE: This study focused on the motivations for using no-prescription online pharmacies (NPOPs) to purchase prescription drugs rather than using the traditional doctor-patient-pharmacy model. We also studied whether users of NPOP-purchased drugs had poorer health outcomes than those who obtain the same drug through legitimate health care channels. METHODS: We selected tramadol as a representative drug to address our objective because it is widely prescribed as an unscheduled opioid analgesic and can easily be purchased from NPOPs. Using search engine marketing (SEM), we placed advertisements on search result pages stemming from the keyword âtramadolâ and related terms and phrases. Participants, who either used the traditional doctor-patient-pharmacy model to obtain tramadol (traditional users, n=349) or purchased it on the Web without a prescription from their local doctor (ie, nontraditional users, n=96), were then asked to complete an online survey. RESULTS: Respondents in both groups were primarily white, female, and in their mid-forties (nontraditional users) to upper forties (traditional users). Nearly all nontraditional users indicated that their tramadol use was motivated by a need to treat pain (95%, 91/96) that they perceived was not managed appropriately through legitimate health care channels. A majority of nontraditional users (55%, 41/75) indicated they used NPOPs because they did not have access to sufficient doses of tramadol to relieve pain. In addition, 29% (22/75) of nontraditional users indicated that the NPOPs were a far cheaper alternative than seeing a physician, paying for an office visit, and filling a prescription at a local pharmacy, which is often at noninsured rates for those who lack medical insurance (37%, 35/96, of NPOP users). The remainder of participants (16%, 12/96) cited other motivations (eg, anonymity) for using NPOPs. In terms of health outcomes, nontraditional users experienced a significantly (P<.01) greater number and severity of adverse events, including life-threatening seizures: 7% (7/96) of nontraditional users reported seizures, while none of the traditional users reported seizures. CONCLUSIONS: Although online pharmacies can offer distinct advantages in terms of convenience and cost, users of these ârogueâ pharmacies that offer drugs with no prescription or doctor supervision do so at great risk to their health, as evidenced by much higher rates of adverse events. The most logical explanation for these findings is that the lack of physician oversight of dosage schedules, contraindicated conditions, and concomitant medications, were responsible for the increased intensity and frequency of adverse events in the nontraditional users. Although we only examined tramadol, it is logical to postulate that similar results would be observed with dozens of equally accessible prescription drugs. As such, the geometric growth in the use of online pharmacies around the world should prompt intense medical and regulatory discussion about their role in the provision of medical care
Qjets: A Non-Deterministic Approach to Tree-Based Jet Substructure
Jet substructure is typically studied using clustering algorithms, such as
kT, which arrange the jets' constituents into trees. Instead of considering a
single tree per jet, we propose that multiple trees should be considered,
weighted by an appropriate metric. Then each jet in each event produces a
distribution for an observable, rather than a single value. Advantages of this
approach include: 1) observables have significantly increased statistical
stability; and, 2) new observables, such as the variance of the distribution,
provide new handles for signal and background discrimination. For example, we
find that employing a set of trees substantially reduces the observed
fluctuations in the pruned mass distribution, enhancing the likelihood of new
particle discovery for a given integrated luminosity. Furthermore, the
resulting pruned mass distributions for (background) QCD jets are found to be
substantially wider than that for (signal) jets with intrinsic mass scales,
e.g. jets containing a W decay. A cut on this width yields a substantial
enhancement in significance relative to a cut on the standard pruned jet mass
alone. In particular the luminosity needed for a given significance requirement
decreases by a factor of two relative to standard pruning.Comment: Minor changes to match journal versio
Spatially Continuous Depletion Algorithm for Monte Carlo Simulations
To correctly predict reactor behavior during cycle operations, the evolution of nuclide number densities throughout the core must be accurately modeled. The time-varying spatial distribution of nuclide number densities is typically resolved by discretizing the Monte Carlo geometry into smaller cells over which number densities are assumed to be spatially invariant.
The nuclide number densities in these smaller cells are integrated through time using reaction rate tallies on the same discretized geometry. However, detailed distributions of nuclide number densities in a full three dimensional simulation can require a prohibitive amount of tallies, and the spatial
discretization of the base geometry makes coupling to external multiphysics tools difficult. In this paper a method for solving for spatially continuous number density distributions during depletion calculations
will be described. The spatially continuous number densities can be used in the transport method proposed by Brown and Martin which allows for transporting neutrons through a material with continuously varying properties such as temperature and nuclide number densities. Coupled with the ability of Functional Expansion Tallies (FETs) [2] to represent tallied quantities as continuous functions, it is possible to both solve for and make use of spatially continuous nuclide number densities. The need for this capability was alluded to by Brown et. al., but no solution has yet been proposed. With a continuous depletion method, recent work which utilized
FETs and continuous material tracking to incorporate multiphysics
feedback in Monte Carlo simulations can be extended to simulations that include depletion analysis.United States. Department of Energy (Nuclear Energy University Programs Graduate Fellowship
New Constraints on Cosmic Reionization from the 2012 Hubble Ultra Deep Field Campaign
Understanding cosmic reionization requires the identification and characterization of early sources of hydrogen-ionizing photons. The 2012 Hubble Ultra Deep Field (UDF12) campaign has acquired the deepest infrared images with the Wide Field Camera 3 aboard Hubble Space Telescope and, for the first time, systematically explored the galaxy population deep into the era when cosmic microwave background (CMB) data indicate reionization was underway. The UDF12 campaign thus provides the best constraints to date on the abundance, luminosity distribution, and spectral properties of early star-forming galaxies. We synthesize the new UDF12 results with the most recent constraints from CMB observations to infer redshift-dependent ultraviolet (UV) luminosity densities, reionization histories, and electron scattering optical depth evolution consistent with the available data. Under reasonable assumptions about the escape fraction of hydrogen-ionizing photons and the intergalactic medium clumping factor, we find that to fully reionize the universe by redshift z ~ 6 the population of star-forming galaxies at redshifts z ~ 7-9 likely must extend in luminosity below the UDF12 limits to absolute UV magnitudes of M UV ~ â13 or fainter. Moreover, low levels of star formation extending to redshifts z ~ 15-25, as suggested by the normal UV colors of z â 7-8 galaxies and the smooth decline in abundance with redshift observed by UDF12 to z â 10, are additionally likely required to reproduce the optical depth to electron scattering inferred from CMB observations
Star Formation in Emission-Line Galaxies Between Redshifts of 0.8 and 1.6
Optical spectra of 14 emission-line galaxies representative of the 1999
NICMOS parallel grism Ha survey of McCarthy et al. are presented. Of the 14, 9
have emission lines confirming the redshifts found in the grism survey. The
higher resolution of our optical spectra improves the redshift accuracy by a
factor of 5. The [O II]/Ha values of our sample are found to be more than two
times lower than expected from Jansen et al. This [O II]/Ha ratio discrepancy
is most likely explained by additional reddening in our Ha-selected sample [on
average, as much as an extra E(B-V) = 0.6], as well as to a possible stronger
dependence of the [O II]/Ha ratio on galaxy luminosity than is found in local
galaxies. The result is that star formation rates (SFRs) calculated from [O
II]3727 emission, uncorrected for extinction, are found to be on average 4 +/-
2 times lower than the SFRs calculated from Ha emission. Classification of
emission-line galaxies as starburst or Seyfert galaxies based on comparison of
the ratios [O II]/Hb and [Ne III]3869/Hb is discussed. New Seyfert 1
diagnostics using the Ha line luminosity, H-band absolute magnitude, and Ha
equivalent widths are also presented. One galaxy is classified as a Seyfert 1
based on its broad emission lines, implying a comoving number density for
Seyfert 1s of 2.5{+5.9, -2.1} times 10^{-5} Mpc^{-3}. This commoving number
density is a factor of 2.4{+5.5,-2.0} times higher than estimated by other
surveys.Comment: 51 pages, 18 figures; Accepted for publication in the Astrophysical
Journal; Revised version with minor changes and an additional reference which
gives further support to our conclusion
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