3,220 research outputs found
The Visibility of Galactic Bars and Spiral Structure At High Redshifts
We investigate the visibility of galactic bars and spiral structure in the
distant Universe by artificially redshifting 101 B-band CCD images of local
spiral galaxies from the Ohio State University Bright Spiral Galaxy Survey. Our
artificially redshifted images correspond to Hubble Space Telescope I-band
observations of the local galaxy sample seen at z=0.7, with integration times
matching those of both the very deep Northern Hubble Deep Field data, and the
much shallower Flanking Field observations. The expected visibility of galactic
bars is probed in two ways: (1) using traditional visual classification, and
(2) by charting the changing shape of the galaxy distribution in "Hubble
space", a quantitative two-parameter description of galactic structure that
maps closely on to Hubble's original tuning fork. Both analyses suggest that
over 2/3 of strongly barred luminous local spirals i.e. objects classified as
SB in the Third Reference Catalog) would still be classified as strongly barred
at z=0.7 in the Hubble Deep Field data. Under the same conditions, most weakly
barred spirals (classified SAB in the Third Reference Catalog) would be
classified as regular spirals. The corresponding visibility of spiral structure
is assessed visually, by comparing luminosity classifications for the
artificially redshifted sample with the corresponding luminosity
classifications from the Revised Shapley Ames Catalog. We find that for
exposures times similar to that of the Hubble Deep Field spiral structure
should be detectable in most luminous low-inclination spiral galaxies at z=0.7
in which it is present. [ABRIDGED]Comment: Accepted for publication in The Astronomical Journa
The Poisson Bracket for Poisson Forms in Multisymplectic Field Theory
We present a general definition of the Poisson bracket between differential
forms on the extended multiphase space appearing in the geometric formulation
of first order classical field theories and, more generally, on exact
multisymplectic manifolds. It is well defined for a certain class of
differential forms that we propose to call Poisson forms and turns the space of
Poisson forms into a Lie superalgebra.Comment: 40 pages LaTe
Explorations in Hubble Space: A Quantitative Tuning Fork
In order to establish an objective framework for studying galaxy morphology,
we have developed a quantitative two-parameter description of galactic
structure that maps closely on to Hubble's original tuning fork. Any galaxy can
be placed in this "Hubble space", where the x-coordinate measures position
along the early-to-late sequence, while the y-coordinate measures in a
quantitative way the degree to which the galaxy is barred. The parameters
defining Hubble space are sufficiently robust to allow the formation of
Hubble's tuning fork to be mapped out to high redshifts. In the present paper,
we describe a preliminary investigation of the distribution of local galaxies
in Hubble space, based on the CCD imaging atlas of Frei et al. (1996). We find
that barred, weakly-barred, and unbarred galaxies are remarkably well-separated
on this diagnostic diagram. The spiral sequence is clearly bimodal and indeed
approximates a tuning fork: strongly-barred and unbarred spirals do not simply
constitute the extrema of a smooth unimodal distribution of bar strength, but
rather populate two parallel sequences. Strongly barred galaxies lie on a
remarkably tight sequence, strongly suggesting the presence of an underlying
unifying physical process. Rather surprisingly, weakly barred systems do not
seem to correspond to objects bridging the parameter space between unbarred and
strongly barred galaxies, but instead form an extension of the regular spiral
sequence. This relation lends support to models in which the bulges of
late-type spirals originate from secular processes driven by bars.Comment: Accepted for publication in The Astronomical Journal. Figure 2 is too
large to be embedded in the paper, and has been included as a JPEG imag
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Increased risk of depression in non-depressed HIV infected men with sleep disturbance: Prospective findings from the Multicenter AIDS Cohort Study.
ObjectiveSleep disturbance is a known risk factor for depression, but it is not known whether sleep disturbance contributes to greater risk of depression in those infected with human immunodeficiency virus (HIV+) as compared to those uninfected with HIV (HIV-).MethodsUsing data from the Multicenter AIDS Cohort Study, a population-based prospective study of men who have sex with men (MSM), self-reported sleep disturbance (>2âŻweeks) and depressive symptoms (Clinical Epidemiologic Scale for Depression, CES-D) were assessed every 6âŻmonths over 12âŻyears of follow-up. Adjusted mixed effects logistic regression analyses tested whether sleep disturbance predicted depression (CES-DâŻâ„âŻ16) at the immediate subsequent visit, and so on over 12âŻyears, in non-depressed HIV+(NâŻ=âŻ1054; 9556 person-visits) and non-depressed HIV- (NâŻ=âŻ1217; 12,680 person-visits). In HIV+ vs. HIV- MSM, linearly estimated average incidence of depression and normalized cumulative rate of depression over 12âŻyears were compared.ResultsIn the HIV+ MSM, sleep disturbance was associated with a significant increase in depression 6âŻmonths later (ORâŻ=âŻ1.6; 95% CI, 1.30, 1.96), which was significantly greater (PâŻ<âŻ.05) than in HIV- MSM (ORâŻ=âŻ1.16; 95% CI, 0.94, 1.44). HIV status and sleep disturbance interacted (PâŻ<âŻ.001), such that incidence of depression and normalized cumulative rate of depression were greater in HIV+ with sleep disturbance than in HIV+ without sleep disturbance and HIV- groups (all P'sâŻ<âŻ0.001).ConclusionsHIV+ persons who report sleep disturbance represent a high risk group to be monitored for depression, and possibly targeted for insomnia treatment to prevent depression. FUND: National Institute of Allergy and Infectious Diseases
Trust, regulatory processes and NICE decision-making: Appraising cost-effectiveness models through appraising people and systems.
This article presents an ethnographic study of regulatory decision-making regarding the cost-effectiveness of expensive medicines at the National Institute for Health and Care Excellence (NICE) in England. We explored trust as one important mechanism by which problems of complexity and uncertainty were resolved. Existing studies note the salience of trust for regulatory decisions, by which the appraisal of people becomes a proxy for appraising technologies themselves. Although such (dis)trust in manufacturers was one important influence, we describe a more intricate web of (dis)trust relations also involving various expert advisors, fellow committee members and committee Chairs. Within these complex chains of relations, we found examples of both more blind-acquiescent and more critical-investigative forms of trust as well as, at times, pronounced distrust. Difficulties in overcoming uncertainty through other means obliged trust in some contexts, although not in others. (Dis)trust was constructed through inferences involving abstract systems alongside actorsâ oral and written presentations-of-self. Systemic features and âforced optionsâ to trust indicate potential insidious processes of regulatory capture
Molecular transport junctions: Current from electronic excitations in the leads
Using a model comprising a 2-level bridge connecting free electron reservoirs
we show that coupling of a molecular bridge to electron-hole excitations in the
leads can markedly effect the source-drain current through a molecular
junction.In some cases, e.g. molecules that exhibit strong charge transfer
transitions, the contribution from electron-hole excitations can exceed the
Landauer elastic current and dominate the observed conduction.Comment: 4 pages, 2 figures, submitted to PR
Partisan impacts on the economy: evidence from prediction markets and close elections
Analyses of the effects of election outcomes on the economy have been hampered by the problem that economic outcomes also influence elections. We sidestep these problems by analyzing movements in economic indicators caused by clearly exogenous changes in expectations about the likely winner during election day. Analyzing high frequency financial fluctuations following the release of flawed exit poll data on election day 2004, and then during the vote count we find that markets anticipated higher equity prices, interest rates and oil prices, and a stronger dollar under a George W. Bush presidency than under John Kerry. A similar RepublicanâDemocrat differential was also observed for the 2000 BushâGore contest. Prediction market based analyses of all presidential elections since 1880 also reveal a similar pattern of partisan impacts, suggesting that electing a Republican president raises equity valuations by 2â3 percent, and that since Ronald Reagan, Republican presidents have tended to raise bond yields
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