3,727 research outputs found
How I treat thrombotic thrombocytopenic purpura and atypical haemolytic uraemic syndrome
Thrombotic thrombocytopenic purpura (TTP) and atypical haemolytic uraemic syndrome (aHUS) are acute, rare life-threatening thrombotic microangiopathies that require rapid diagnosis and treatment. They are defined by microangiopathic haemolytic anaemia and thrombocytopenia, with renal involvement primarily in aHUS and neurological and cardiological sequelae in TTP. Prompt treatment for most cases of both conditions is with plasma exchange initially and monoclonal therapy (rituximab in TTP and eculizumab in aHUS) as the mainstay of therapy. Here we discuss the diagnosis and therapy for both disorders
Lorentz Invariance Violation and the Observed Spectrum of Ultrahigh Energy Cosmic Rays
There has been much interest in possible violations of Lorentz invariance,
particularly motivated by quantum gravity theories. It has been suggested that
a small amount of Lorentz invariance violation (LIV) could turn off photomeson
interactions of ultrahigh energy cosmic rays (UHECRs) with photons of the
cosmic background radiation and thereby eliminate the resulting sharp
steepening in the spectrum of the highest energy CRs predicted by Greisen
Zatsepin and Kuzmin (GZK). Recent measurements of the UHECR spectrum reported
by the HiRes and Auger collaborations, however, indicate the presence of the
GZK effect. We present the results of a detailed calculation of the
modification of the UHECR spectrum caused by LIV using the formalism of Coleman
and Glashow. We then compare these results with the experimental UHECR data
from Auger and HiRes. Based on these data, we find a best fit amount of LIV of
,consistent with an upper limit of . This possible amount of LIV can lead to a recovery of the cosmic ray
spectrum at higher energies than presently observed. Such an LIV recovery
effect can be tested observationally using future detectors.Comment: corrected proof version to be published in Astroparticle Physic
Is the Universe More Transparent to Gamma Rays Than Previously Thought?
The MAGIC collaboration has recently reported the detection of the strong
gamma-ray blazar 3C279 during a 1-2 day flare. They have used their spectral
observations to draw conclusions regarding upper limits on the opacity of the
Universe to high energy gamma-rays and, by implication, upper limits on the
extragalactic mid-infrared background radiation. In this paper we examine the
effect of gamma-ray absorption by the extragalactic infrared radiation on
intrinsic spectra for this blazar and compare our results with the
observational data on 3C279. We find agreement with our previous results,
contrary to the recent assertion of the MAGIC group that the Universe is more
transparent to \gray s than our calculations indicate. Our analysis indicates
that in the energy range between ~80 and ~500 GeV, 3C279 has a best-fit
intrinsic spectrum with a spectral index ~1.78 using our fast evolution model
and ~2.19 using our baseline model. However, we also find that spectral indices
in the range of 0.0 to 3.0 are almost as equally acceptable as the best fit
spectral indices. Assuming the same intrinsic spectral index for this flare as
for the 1991 flare from 3C279 observed by EGRET, viz., 2.02, which lies between
our best fit indices, we estimate that the MAGIC flare was ~3 times brighter
than the EGRET flare observed 15 years earlier.Comment: version accepted for publication in ApJ Letter
Collapsible reflector Patent
Self erecting parabolic reflector design for use in spac
Corrected Table for the Parametric Coefficients for the Optical Depth of the Universe to Gamma-rays at Various Redshifts
Table 1 in our paper, ApJ 648, 774 (2006) entitled "Intergalactic Photon
Spectra from the Far IR to the UV Lyman Limit for 0 < z < 6 and the Optical
Depth of the Universe to High Energy Gamma-Rays" had erroneous numbers for the
coefficients fitting the parametric form for the optical depth of the universe
to gamma-rays. The correct values for these parameters as described in the
original text are given here in a corrected table for various redshifts for the
baseline model (upper row) and fast evolution (lower row) for each individual
redshift. The parametric approximation is good for optical depths between 0.01
and 100 and for gamma-ray energies up to ~2 TeV for all redshifts but also for
energies up to ~10 TeV for redshifts less than 1.Comment: Table 1 corrected and new gamma-ray energy range of validity give
A dynamic scheme for generating number squeezing in Bose-Einstein condensates through nonlinear interactions
We develop a scheme to generate number squeezing in a Bose-Einstein
condensate by utilizing interference between two hyperfine levels and nonlinear
atomic interactions. We describe the scheme using a multimode quantum field
model and find agreement with a simple analytic model in certain regimes. We
demonstrate that the scheme gives strong squeezing for realistic choices of
parameters and atomic species. The number squeezing can result in noise well
below the quantum limit, even if the initial noise on the system is classical
and much greater than that of a poisson distribution.Comment: 4 pages, 3 figure
Intergalactic Photon Spectra from the Far IR to the UV Lyman Limit for and the Optical Depth of the Universe to High Energy Gamma-Rays
We calculate the intergalactic photon density as a function of both energy
and redshift for 0 < z < 6 for photon energies from .003 eV to the Lyman limit
cutoff at 13.6 eV in a Lambda-CDM universe with and
. Our galaxy evolution model gives results which are
consistent with Spitzer deep number counts and the spectral energy distribution
of the extragalactic background radiation. We use our photon density results to
extend previous work on the absorption of high energy gamma-rays in
intergalactic space owing to interactions with low energy photons and the 2.7 K
cosmic background radiation. We calculate the optical depth of the universe,
tau, for gamma-rays having energies from 4 GeV to 100 TeV emitted by sources at
redshifts from ~0 to 5. We also give an analytic fit with numerical
coefficients for approximating . As an example of the
application of our results, we calculate the absorbed spectrum of the blazar
PKS 2155-304 at z = 0.117 and compare it with the spectrum observed by the
H.E.S.S. air Cherenkov gamma-ray telescope array.Comment: final version to be published in Ap
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