10,360 research outputs found
Induced N=2 composite supersymmetry in 2+1 dimensions
Starting from N=1 scalar supermultiplets in 2+1 dimensions, we build
explicitly the composite superpartners which define a N=2 superalgebra induced
by the initial N=1 supersymmetry. The occurrence of this extension is linked to
the topologically conserved current out of which the composite superpartners
are constructed.Comment: 11 pages LATEX, no figure
Gravitational Self-Force Correction to the Binding Energy of Compact Binary Systems
Using the first law of binary black-hole mechanics, we compute the binding
energy E and total angular momentum J of two non-spinning compact objects
moving on circular orbits with frequency Omega, at leading order beyond the
test-particle approximation. By minimizing E(Omega) we recover the exact
frequency shift of the Schwarzschild innermost stable circular orbit induced by
the conservative piece of the gravitational self-force. Comparing our results
for the coordinate invariant relation E(J) to those recently obtained from
numerical simulations of comparable-mass non-spinning black-hole binaries, we
find a remarkably good agreement, even in the strong-field regime. Our findings
confirm that the domain of validity of perturbative calculations may extend
well beyond the extreme mass-ratio limit.Comment: 5 pages, 1 figure; matches the published versio
Celebrating Cercignani's conjecture for the Boltzmann equation
Cercignani's conjecture assumes a linear inequality between the entropy and
entropy production functionals for Boltzmann's nonlinear integral operator in
rarefied gas dynamics. Related to the field of logarithmic Sobolev inequalities
and spectral gap inequalities, this issue has been at the core of the renewal
of the mathematical theory of convergence to thermodynamical equilibrium for
rarefied gases over the past decade. In this review paper, we survey the
various positive and negative results which were obtained since the conjecture
was proposed in the 1980s.Comment: This paper is dedicated to the memory of the late Carlo Cercignani,
powerful mind and great scientist, one of the founders of the modern theory
of the Boltzmann equation. 24 pages. V2: correction of some typos and one
ref. adde
Genetic mapping of a new heart rate QTL on chromosome 8 of spontaneously hypertensive rats
BACKGROUND: Tachycardia is commonly observed in hypertensive patients, predominantly mediated by regulatory mechanisms integrated within the autonomic nervous system. The genetic loci and genes associated with increased heart rate in hypertension, however, have not yet been identified. METHODS: An F2 intercross of Spontaneously Hypertensive Rats (SHR) × Brown Norway (BN) linkage analysis of quantitative trait loci mapping was utilized to identify candidate genes associated with an increased heart rate in arterial hypertension. RESULTS: Basal heart rate in SHR was higher compared to that of normotensive BN rats (365 ± 3 vs. 314 ± 6 bpm, p < 0.05 for SHR and BN, respectively). A total genome scan identified one quantitative trait locus in a 6.78 cM interval on rat chromosome 8 (8q22–q24) that was responsible for elevated heart rate. This interval contained 241 genes, of which 65 are known genes. CONCLUSION: Our data suggest that an influential genetic region located on the rat chromosome 8 contributes to the regulation of heart rate. Candidate genes that have previously been associated with tachycardia and/or hypertension were found within this QTL, strengthening our hypothesis that these genes are, potentially, associated with the increase in heart rate in a hypertension rat model
Gravitational Lensing of the X-Ray Background by Clusters of Galaxies
Gravitational lensing by clusters of galaxies affects the cosmic X-ray
background (XRB) by altering the observed density and flux distribution of
background X-ray sources. At faint detection flux thresholds, the resolved
X-ray sources appear brighter and diluted, while the unresolved component of
the XRB appears dimmer and more anisotropic, due to lensing. The diffuse X-ray
intensity in the outer halos of clusters might be lower than the sky-averaged
XRB, after the subtraction of resolved sources. Detection of the lensing signal
with a wide-field X-ray telescope could probe the mass distribution of a
cluster out to its virialization boundary. In particular, we show that the
lensing signature imprinted on the resolved component of the XRB by the cluster
A1689, should be difficult but possible to detect out to 8' at the 2-4 sigma
level, after 10^6 seconds of observation with the forthcoming AXAF satellite.
The lensing signal is fairly insensitive to the lens redshift in the range
0.1<z<0.6. The amplitude of the lensing signal is however sensitive to the
faint end slope of the number-flux relation for unresolved X-ray sources, and
can thus help constrain models of the XRB. A search for X-ray arcs or arclets
could identify the fraction of all faint sources which originate from extended
emission of distant galaxies. The probability for a 3 sigma detection of an
arclet which is stretched by a factor of about 3 after a 10^6 seconds
observation of A1689 with AXAF, is roughly comparable to the fraction of all
background X-ray sources that have an intrinsic size of order 1''.Comment: 41 LaTeX pages, 11 postscript figures, 1 table, in AASTeX v4.0
format. To appear in ApJ, April 1, 1997, Vol. 47
Quantum-limited metrology and Bose-Einstein condensates
We discuss a quantum-metrology protocol designed to estimate a physical
parameter in a Bose-Einstein condensate of N atoms, and we show that the
measurement uncertainty can decrease faster than 1/N. The 1/N scaling is
usually thought to be the best possible in any measurement scheme. From the
perspective of quantum information theory, we outline the main idea that leads
to a measurement uncertainty that scales better than 1/N. We examine in detail
some potential problems and challenges that arise in implementing such a
measurement protocol using a Bose-Einstein condensate. We discuss how some of
these issues can be dealt with by using lower-dimensional condensates trapped
in nonharmonic potentials.Comment: 32 pages, 1 figure, updated reference
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