1,770 research outputs found
Observers and Measurements in Noncommutative Spacetimes
We propose a "Copenhagen interpretation" for spacetime noncommutativity. The
goal is to be able to predict results of simple experiments involving signal
propagation directly from commutation relations. A model predicting an energy
dependence of the speed of photons of the order E/E_Planck is discussed in
detail. Such effects can be detectable by the GLAST telescope, to be launched
in 2006.Comment: 10 pp; v2: equivalence of observers explicitely stated; v3: minor
changes, references and remarks added, burst spreading with energy emphasized
as a signature rather than nois
The SISO CSPI PDG standard for commercial off-the-shelf simulation package interoperability reference models
For many years discrete-event simulation has been used to analyze production and logistics problems in manufactur-ing and defense. Commercial-off-the-shelf Simulation Packages (CSPs), visual interactive modelling environ-ments such as Arena, Anylogic, Flexsim, Simul8, Witness, etc., support the development, experimentation and visua-lization of simulation models. There have been various attempts to create distributed simulations with these CSPs and their tools, some with the High Level Architecture (HLA). These are complex and it is quite difficult to assess how a set of models/CSP are actually interoperating. As the first in a series of standards aimed at standardizing how the HLA is used to support CSP distributed simula-tions, the Simulation Interoperability Standards Organiza-tion’s (SISO) CSP Interoperability Product Development Group (CSPI PDG) has developed and standardized a set of Interoperability Reference Models (IRM) that are in-tended to clearly identify the interoperability capabilities of CSP distributed simulations
Characterization of the Benchmark Binary NLTT 33370
We report the confirmation of the binary nature of the nearby, very low-mass
system NLTT 33370 with adaptive optics imaging and present resolved
near-infrared photometry and integrated light optical and near-infrared
spectroscopy to characterize the system. VLT-NaCo and LBTI-LMIRCam images show
significant orbital motion between 2013 February and 2013 April. Optical
spectra reveal weak, gravity sensitive alkali lines and strong lithium 6708
Angstrom absorption that indicate the system is younger than field age.
VLT-SINFONI near-IR spectra also show weak, gravity sensitive features and
spectral morphology that is consistent with other young, very low-mass dwarfs.
We combine the constraints from all age diagnostics to estimate a system age of
~30-200 Myr. The 1.2-4.7 micron spectral energy distribution of the components
point toward T_eff=3200 +/- 500 K and T_eff=3100 +/- 500 K for NLTT 33370 A and
B, respectively. The observed spectra, derived temperatures, and estimated age
combine to constrain the component spectral types to the range M6-M8.
Evolutionary models predict masses of 113 +/- 8 M_Jup and 106 +/- 7 M_Jup from
the estimated luminosities of the components. KPNO-Phoenix spectra allow us to
estimate the systemic radial velocity of the binary. The Galactic kinematics of
NLTT 33370AB are broadly consistent with other young stars in the Solar
neighborhood. However, definitive membership in a young, kinematic group cannot
be assigned at this time and further follow-up observations are necessary to
fully constrain the system's kinematics. The proximity, age, and late-spectral
type of this binary make it very novel and an ideal target for rapid, complete
orbit determination. The system is one of only a few model calibration
benchmarks at young ages and very low-masses.Comment: 25 pages, 3 tables, 13 figures, accepted for publication in The
Astrophysical Journa
Very High Energy Gamma-Ray Emission from the Blazar Markarian 421
Very high energy gamma-ray emission from the BL Lac object Markarian 421 has
been detected over three observing seasons on 59 nights between April 1992 and
June 1994 with the Whipple 10-meter imaging Cherenkov telescope. During its
initial detection in 1992, its flux above 500 GeV was
1.610photons cm s. Observations in 1993 confirmed
this level of emission. For observations made between December 1993 and April
1994, its intensity was a factor of 2.20.5 lower. Observations on 14 and
15 May, 1994 showed an increase over this quiescent level by a factor of
10 (Kerrick et al. 1995). This strong outburst suggests that 4 episodes
of increased flux measurements on similar time scales in 1992 and 1994 may be
attributed to somewhat weaker outbursts. The variability of the TeV gamma-ray
emission from Markarian 421 stands in contrast to EGRET observations (Lin et
al. 1994) which show no evidence for variability.Comment: gzip compressed tar file including LaTeX text and 4 postscript
figures (14 pages total incl. 4 tables), accepted for publication in the
Astrophysical Journal. Contact address is [email protected]
Late-night salivary cortisol may be valuable for assessing treatment response in patients with Cushing’s disease: 12-month, Phase III pasireotide study
Measuring salivary cortisol is a simple, convenient
and accurate technique with potential value in monitoring
patients with hypercortisolism. This analysis reports
changes in late-night salivary cortisol (LNSC) during a
12-month, multicentre, Phase III study of patients with
Cushing’s disease who were randomized to pasireotide 600
or 900 lg sc bid. LNSC assessment was an exploratory
objective based on a single, optional measurement at
midnight ± 1 h on the same day as one of the 24-h urinary
free cortisol (UFC) measurements. Of 162 enrolled
patients, baseline LNSC was measured in 93. Sixty-seven
patients had levels above the upper limit of normal (ULN);
median baseline levels were 19.7 and 20.7 nmol/L in the
groups subsequently randomized to 600 lg (n = 40) and
900 lg (n = 27), respectively. Median LNSC levels
decreased from baseline to month 12; median changes in
patients who had baseline LNSC [ULN in the 600 and
900 lg groups were -13.4 nmol/L (–52.6 %; n = 19) and
-11.8 nmol/L (–56.1 %; n = 14), respectively. LNSC
normalized at months 6 and 12 in 25/67 (37.3 %) and 13/67
(19.4 %) patients, respectively; 10/25 and 8/13 patients
also had normalized UFC, and 7/25 and 4/13 had partial
UFC control (UFC [ULN and C50 % decrease from
baseline). There was a moderate correlation (r = 0.55) on
the log scale between individual patient LNSC and UFC
values when all time points were pooled. Pasireotide
decreased LNSC levels during 12 months of treatment.
Salivary cortisol may be a simple, convenient biomarker
for assessing treatment response in patients with Cushing’s disease
A Survey for Massive Giant Planets in Debris Disks with Evacuated Inner Cavities
The commonality of collisionally replenished debris around main sequence
stars suggests that minor bodies are frequent around Sun-like stars. Whether or
not debris disks in general are accompanied by planets is yet unknown, but
debris disks with large inner cavities - perhaps dynamically cleared - are
considered to be prime candidates for hosting large-separation massive giant
planets. We present here a high-contrast VLT/NACO angular differential imaging
survey for eight such cold debris disks. We investigated the presence of
massive giant planets in the range of orbital radii where the inner edge of the
dust debris is expected. Our observations are sensitive to planets and brown
dwarfs with masses >3 to 7 Jupiter mass, depending on the age and distance of
the target star. Our observations did not identify any planet candidates. We
compare the derived planet mass upper limits to the minimum planet mass
required to dynamically clear the inner disks. While we cannot exclude that
single giant planets are responsible for clearing out the inner debris disks,
our observations constrain the parameter space available for such planets. The
non-detection of massive planets in these evacuated debris disks further
reinforces the notion that the giant planet population is confined to the inner
disk (<15 AU).Comment: Accepted for publication in Ap
New Limits to the Infrared Background: Bounds on Radiative Neutrino Decay and on Contributions of Very Massive Objects to the Dark Matter Problem
From considering the effect of γ-γ interactions on recently observed TeV gamma-ray spectra, improved limits are set to the density of extragalactic infrared photons which are robust and essentially model independent. The resulting limits are more than an order of magnitude more restrictive than direct observations in the 0.025–0.3 eV regime. These limits are used to improve constraints on radiative neutrino decay in the mass range above 0.05 eV and to rule out very massive objects as providing the dark matter needed to explain galaxy rotation curves. Lower bounds on the maximum distance which TeV gamma rays may probe are also derived
VERITAS: the Very Energetic Radiation Imaging Telescope Array System
The Very Energetic Radiation Imaging Telescope Array System (VERITAS)
represents an important step forward in the study of extreme astrophysical
processes in the universe. It combines the power of the atmospheric Cherenkov
imaging technique using a large optical reflector with the power of
stereoscopic observatories using arrays of separated telescopes looking at the
same shower. The seven identical telescopes in VERITAS, each of aperture 10 m,
will be deployed in a filled hexagonal pattern of side 80 m; each telescope
will have a camera consisting of 499 pixels with a field of view of 3.5 deg
VERITAS will substantially increase the catalog of very high energy (E >
100GeV) gamma-ray sources and greatly improve measurements of established
sources.Comment: 44 pages, 16 figure
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