12,095 research outputs found
versus in Type IIB supergravity
We obtain the complete local solutions with 16 supersymmetries to Type IIB
supergravity on a space-time of the form warped over a
Riemann surface in terms of two locally holmorphic functions on
. We construct the general Ansatz for the bosonic supergravity fields
and supersymmetry generators compatible with the isometry
algebra of space-time, which extends to the corresponding real form of the
exceptional Lie superalgebra . We reduce the BPS equations to this
Ansatz, obtain their general local solutions, and show that these local
solutions solve the full Type IIB supergravity field equations and Bianchi
identities. We contrast the solution with the closely
related case and present our results for both in parallel.
Finally, we present a preliminary analysis of positivity and regularity
conditions for , but postpone the construction of globally
regular solutions to a subsequent paper.Comment: 50 page
Interstellar water chemistry: from laboratory to observations
Water is observed throughout the universe, from diffuse interstellar clouds
to protoplanetary disks around young stars, and from comets in our own solar
system and exoplanetary atmospheres to galaxies at high redshifts. This review
summarizes the spectroscopy and excitation of water in interstellar space as
well as the basic chemical processes that form and destroy water under
interstellar conditions. Three major routes to water formation are identified:
low temperature ion-molecule chemistry, high-temperature neutral-neutral
chemistry and gas-ice chemistry. The rate coefficients of several important
processes entering the networks are discussed in detail; several of them have
been determined only in the last decade through laboratory experiments and
theoretical calculations. Astronomical examples of each of the different
chemical routes are presented using data from powerful new telescopes, in
particular the Herschel Space Observatory. Basic chemical physics studies
remain critically important to analyze astronomical data.Comment: Authors' manuscript 138 pages, 34 figures, 4 tables, published in a
Thematic Issue "Astrochemistry" in Chemical Reviews (December 2013), volume
113, 9043-9085 following peer review by the American Chemical Society. The
published paper is available as open access at
http://pubs.acs.org/doi/abs/10.1021/cr400317
The GHOSTS survey. II. The diversity of Halo Color and Metallicity Profiles of Massive Disk Galaxies
We study the stellar halo color properties of six nearby massive highly
inclined disk galaxies using Hubble Space Telescope Advanced Camera for Surveys
and Wide Field Camera 3 observations in both F606W and F814W filters from the
GHOSTS survey. The observed fields, placed both along the minor and major axis
of each galaxy, probe the stellar outskirts out to projected distances of ~
50-70 kpc from their galactic centre along the minor axis. The 50% completeness
levels of the color magnitude diagrams are typically at two mag below the tip
of the red giant branch. We find that all galaxies have extended stellar halos
out to ~ 50 kpc and two out to ~ 70 kpc. We determined the halo color
distribution and color profile for each galaxy using the median colors of stars
in the RGB. Within each galaxy we find variations in the median colors as a
function of radius which likely indicates population variations, reflecting
that their outskirts were built from several small accreted objects. We find
that half of the galaxies (NGC 0891, NGC 4565, and NGC 7814) present a clear
negative color gradient, reflecting a declining metallicity in their halos; the
other have no significant color or population gradient. In addition,
notwithstanding the modest sample size of galaxies, there is no strong
correlation between their halo color/metallicity or gradient with galaxy's
properties such as rotational velocity or stellar mass. The diversity in halo
color profiles observed in the GHOSTS galaxies qualitatively supports the
predicted galaxy-to-galaxy scatter in halo stellar properties; a consequence of
the stochasticity inherent in the assembling history of galaxies.Comment: Accepted by MNRAS, 31 pages, 18 figures. Appendix added and some
editions to match accepted version. Conclusions unchange
Mitral Annular and Coronary Artery Calcification Are Associated with Mortality in HIV-Infected Individuals.
BackgroundHIV infection increases cardiovascular risk. Coronary artery calcification (CAC) and mitral annular calcification (MAC) identify patients at risk for cardiovascular disease (CVD). The purpose of this study was to examine the association between MAC, CAC and mortality in HIV-infected individuals.Methods and resultsWe studied 152 asymptomatic HIV-infected individuals with transthoracic echocardiography (TTE) and computed tomography (CT). MAC was identified on TTE using standardized criteria. Presence of CAC, CAC score and CAC percentiles were determined using the modified Agatston criteria. Mortality data was obtained from the Social Security and National Death Indices (SSDI/NDI). The median age was 49 years; 87% were male. The median duration of HIV was 16 years; 84% took antiretroviral therapy; 64% had an undetectable viral load. CVD risk factors included hypertension (35%), smoking (62%) and dyslipidemia (35%). Twenty-five percent of individuals had MAC, and 42% had CAC. Over a median follow-up of 8 years, 11 subjects died. Subjects with CAC had significantly higher mortality compared to those with MAC only or no MAC. The Harrell's C-statistic of CAC was 0.66 and increased to 0.75 when MAC was added (p = 0.05). MAC, prior CVD, age and HIV viral load were independently associated with higher age- and gender-adjusted CAC percentiles in an adjusted model (p < 0.05 for all).ConclusionIn HIV patients, the presence of MAC, traditional risk factors and HIV viral load were independently associated with CAC. Presence of CAC and MAC may be useful in identifying HIV-infected individuals at higher risk for death
- …