68,676 research outputs found
Signatures of non-gaussianity in the isocurvature modes of primordial black hole dark matter
Primordial black holes (PBHs) are black holes which may have formed very
early on during the radiation dominated era in the early universe. We present
here a method by which the large scale perturbations in the density of
primordial black holes may be used to place tight constraints on
non-gaussianity if PBHs account for dark matter (DM). The presence of
local-type non-gaussianity is known to have a significant effect on the
abundance of primordial black holes, and modal coupling from the observed CMB
scale modes can significantly alter the number density of PBHs that form within
different regions of the universe, which appear as DM isocurvature modes. Using
the recent \emph{Planck} constraints on isocurvature perturbations, we show
that PBHs are excluded as DM candidates for even very small local-type
non-gaussianity, and remarkably the constraint on
is almost as strong. Even small non-gaussianity is excluded if DM is
composed of PBHs. If local non-Gaussianity is ever detected on CMB scales, the
constraints on the fraction of the universe collapsing into PBHs (which are
massive enough to have not yet evaporated) will become much tighter.Comment: 23 pages, 11 figures. V2: minor corrections and changes, matches
published versio
Effect of aluminum phosphate additions on composition of three-component plasma-sprayed solid lubricant
Image analysis (IA) and electron microprobe X-ray analysis (EMXA) were used to characterize a plasma-sprayed, self-lubricating coating, NASA LUBE PS106, specified by weight percent as 35NiCr-35Ag-30CaF2. To minimize segregation of the powder mixture during the plasma-spraying procedure, monoaluminum phosphate was added to form agglomerate particles. Three concentrations of AlPO4 were added to the mixtures: 1.25, 2.5, and 6.25 percent by weight. Analysis showed that 1.25 wt% AlPO4 yielded a CaF2 deficiency, 2.5 wt% kept the coating closest to specification, and 6.25 wt% yielded excess CaF2 as well as more impurities and voids and a deficiency in silver. Photomicrographs and X-ray maps are presented. The methods of IA and EMXA complement each other, and the reasonable agreement in the results increases the confidence in determining the coating composition
Late time evolution of brane gas cosmology and compact internal dimensions
We study the late-time behavior of a universe in the framework of brane gas
cosmology. We investigate the evolution of a universe with a gas of
supergravity particles and a gas of branes. Considering the case when different
dimensions are anisotropically wrapped by various branes, we have derived
Friedman-like equations governing the dynamics of wrapped and unwrapped
subvolumes. We point out that the compact internal dimensions are wrapped by
three or higher dimensional branes.Comment: 16 pages, typos, references, comment on the possibility of
stabilizing the internal dimensions with fluxe
Association of Intraocular Pressure With Human Immunodeficiency Virus
PURPOSE: Prior studies have shown an association between human immunodeficiency virus (HIV) and reduced intraocular pressures (IOP). The purpose of this study was to determine if patients with HIV on highly active antiretroviral therapy (HAART) had any difference in their IOP compared with patients without HIV or with HIV who are not on HAART. DESIGN: Retrospective cross-sectional study. METHODS: We included 400 patients from our academic eye center between 2000 and 2016. Group 1 (G1) consisted of patients with HIV on HAART (n = 176), Group 2 (G2) consisted of patients with HIV who were not on HAART (n = 48), and Group 3 (G3) consisted of controls without HIV (n = 176). An analysis of variance (ANOVA) was performed to compare mean IOP values. Multivariate linear and logistic regression models were performed to assess factors impacting IOP. Difference in IOP was the primary outcome being measured. RESULTS: The mean IOPs in mm Hg were 13.7 +/- 5.1 (G1), 13.1 +/- 3.6 (G2), and 17.3 +/- 3.8 (G3), P \u3c .01. In regression modeling, having a CD4 count CONCLUSIONS: Absolute CD4 counts may play a role in IOP fluctuations. This association was found in patients with HIV regardless of whether patients were on HAART
Deep Near-Infrared Surface Photometry and Properties of Local Volume Dwarf Irregular Galaxies
We present deep H-band surface photometry and analysis of 40 Local Volume
galaxies, a sample primarily composed of dwarf irregulars in the Cen A group,
obtained using the IRIS2 detector at the 3.9m Anglo-Australian Telescope. We
probe to a surface brightness of ~25 mag arcsec, reaching a 40 times
lower stellar density than the Two Micron All Sky Survey (2MASS). Employing
extremely careful and rigorous cleaning techniques to remove contaminating
sources, we perform surface photometry on 33 detected galaxies deriving the
observed total magnitude, effective surface brightness and best fitting
S\'ersic parameters. We make image quality and surface photometry comparisons
to 2MASS and VISTA Hemispheric Survey (VHS) demonstrating that deep targeted
surveys are still the most reliable means of obtaining accurate surface
photometry. We investigate the B-H colours with respect to mass for Local
Volume galaxies, finding that the colours of dwarf irregulars are significantly
varied, eliminating the possibility of using optical-NIR colour transformations
to facilitate comparison to the more widely available optical data sets. The
structure-luminosity relationships are investigated for our `clean' sample of
dwarf irregulars. We demonstrate that a significant fraction of the Local
Volume dwarf irregular population have underlying structural properties similar
to both Local Volume and Virgo Cluster dwarf ellipticals. Linear regressions to
structure-luminosity relationships for the Local Volume galaxies and Virgo
Cluster dwarf ellipticals show significant differences in both slope and
scatter around the established trend lines, suggesting that environment might
regulate the structural scaling relationships of dwarf galaxies in comparison
to their more isolated counterparts.Comment: 27 pages, 14 figures, 5 table
Forbidden Ca 2 in the sun unmasked by way of Venus
Eleven high-dispersion spectra of Venus, taken with blue Doppler shifts have permitted the unmasking of the 7323.88A forbidden line of Ca II from terrestrial absorption. An equivalent width is obtained of 7.4 + or - 0.4mA for this line in integrated sunlight. Our value of W sub lambda is smaller than previous values and much more accurate. The HSRA solar model gives a solar calcium abundance of A sub Ca = 6.21
A Data Exchange Standard for Optical (Visible/IR) Interferometry
This paper describes the OI Exchange Format, a standard for exchanging
calibrated data from optical (visible/infrared) stellar interferometers. The
standard is based on the Flexible Image Transport System (FITS), and supports
storage of the optical interferometric observables including squared visibility
and closure phase -- data products not included in radio interferometry
standards such as UV-FITS. The format has already gained the support of most
currently-operating optical interferometer projects, including COAST, NPOI,
IOTA, CHARA, VLTI, PTI, and the Keck Interferometer, and is endorsed by the IAU
Working Group on Optical Interferometry. Software is available for reading,
writing and merging OI Exchange Format files.Comment: 26 pages, 1 figur
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