14,474 research outputs found
Ballerina - Pirouettes in Search of Gamma Bursts
The cosmological origin of gamma ray bursts has now been established with
reasonable certainty. Many more bursts will need to be studied to establish the
typical distance scale, and to map out the large diversity in properties which
have been indicated by the first handful of events. We are proposing Ballerina,
a small satellite to provide accurate positions and new data on the gamma-ray
bursts. We anticipate a detection rate an order of magnitude larger than
obtained from Beppo-SAX.Comment: A&AS in press, proceedings of the Workshop "Gamma Ray Bursts in the
Afterglow Era" in Rome, November 199
Frequency response in surface-potential driven electro-hydrodynamics
Using a Fourier approach we offer a general solution to calculations of slip
velocity within the circuit description of the electro-hydrodynamics in a
binary electrolyte confined by a plane surface with a modulated surface
potential. We consider the case with a spatially constant intrinsic surface
capacitance where the net flow rate is in general zero while harmonic rolls as
well as time-averaged vortex-like components may exist depending on the spatial
symmetry and extension of the surface potential. In general the system displays
a resonance behavior at a frequency corresponding to the inverse RC time of the
system. Different surface potentials share the common feature that the
resonance frequency is inversely proportional to the characteristic length
scale of the surface potential. For the asymptotic frequency dependence above
resonance we find a 1/omega^2 power law for surface potentials with either an
even or an odd symmetry. Below resonance we also find a power law omega^alpha
with alpha being positive and dependent of the properties of the surface
potential. Comparing a tanh potential and a sech potential we qualitatively
find the same slip velocity, but for the below-resonance frequency response the
two potentials display different power law asymptotics with alpha=1 and
alpha~2, respectively.Comment: 4 pages including 1 figure. Accepted for PR
Calibration of the Mass-Temperature Relation for Clusters of Galaxies Using Weak Gravitational Lensing
The main uncertainty in current determinations of the power spectrum
normalization, sigma_8, from abundances of X-ray luminous galaxy clusters
arises from the calibration of the mass-temperature relation. We use our weak
lensing mass determinations of 30 clusters from the hitherto largest sample of
clusters with lensing masses, combined with X-ray temperature data from the
literature, to calibrate the normalization of this relation at a temperature of
8 keV, M_{500c,8 keV}=(8.7 +/- 1.6) h^{-1} 10^{14} M_sun. This normalization is
consistent with previous lensing-based results based on smaller cluster
samples, and with some predictions from numerical simulations, but higher than
most normalizations based on X-ray derived cluster masses. Assuming the
theoretically expected slope alpha=3/2 of the mass-temperature relation, we
derive sigma_8 = 0.88 +/-0.09 for a spatially-flat LambdaCDM universe with
Omega_m = 0.3. The main systematic errors on the lensing masses result from
extrapolating the cluster masses beyond the field-of-view used for the
gravitational lensing measurements, and from the separation of
cluster/background galaxies, contributing each with a scatter of 20%. Taking
this into account, there is still significant intrinsic scatter in the
mass-temperature relation indicating that this relation may not be very tight,
at least at the high mass end. Furthermore, we find that dynamically relaxed
clusters are 75 +/-40% hotter than non-relaxed clusters.Comment: 8 pages, 4 figures, revised version submitted to Ap
Deformation of LeBrun's ALE metrics with negative mass
In this article we investigate deformations of a scalar-flat K\"ahler metric
on the total space of complex line bundles over CP^1 constructed by C. LeBrun.
In particular, we find that the metric is included in a one-dimensional family
of such metrics on the four-manifold, where the complex structure in the
deformation is not the standard one.Comment: 20 pages, no figure. V2: added two references, filled a gap in the
proof of Theorem 1.2. V3: corrected a wrong statement about Kuranishi family
of a Hirzebruch surface stated in the last paragraph in the proof of Theorem
1.2, and fixed a relevant error in the proof. Also added a reference [24]
about Kuranishi family of Hirzebruch surface
Slow-light enhanced optical detection in liquid-infiltrated photonic crystals
Slow-light enhanced optical detection in liquid-infiltrated photonic crystals
is theoretically studied. Using a scattering-matrix approach and the
Wigner-Smith delay time concept, we show that optical absorbance benefits both
from slow-light phenomena as well as a high filling factor of the energy
residing in the liquid. Utilizing strongly dispersive photonic crystal
structures, we numerically demonstrate how liquid-infiltrated photonic crystals
facilitate enhanced light-matter interactions, by potentially up to an order of
magnitude. The proposed concept provides strong opportunities for improving
existing miniaturized absorbance cells for optical detection in lab-on-a-chip
systems.Comment: Paper accepted for the "Special Issue OWTNM 2007" edited by A.
Lavrinenko and P. J. Robert
A mapping approach to synchronization in the "Zajfman trap": stability conditions and the synchronization mechanism
We present a two particle model to explain the mechanism that stabilizes a
bunch of positively charged ions in an "ion trap resonator" [Pedersen etal,
Phys. Rev. Lett. 87 (2001) 055001]. The model decomposes the motion of the two
ions into two mappings for the free motion in different parts of the trap and
one for a compressing momentum kick. The ions' interaction is modelled by a
time delay, which then changes the balance between adjacent momentum kicks.
Through these mappings we identify the microscopic process that is responsible
for synchronization and give the conditions for that regime.Comment: 12 pages, 9 figures; submitted to Phys Rev
Bubble coalescence in breathing DNA: Two vicious walkers in opposite potentials
We investigate the coalescence of two DNA-bubbles initially located at weak
segments and separated by a more stable barrier region in a designed construct
of double-stranded DNA. The characteristic time for bubble coalescence and the
corresponding distribution are derived, as well as the distribution of
coalescence positions along the barrier. Below the melting temperature, we find
a Kramers-type barrier crossing behaviour, while at high temperatures, the
bubble corners perform drift-diffusion towards coalescence. The results are
obtained by mapping the bubble dynamics on the problem of two vicious walkers
in opposite potentials.Comment: 7 pages, 4 figure
Tur\'an Graphs, Stability Number, and Fibonacci Index
The Fibonacci index of a graph is the number of its stable sets. This
parameter is widely studied and has applications in chemical graph theory. In
this paper, we establish tight upper bounds for the Fibonacci index in terms of
the stability number and the order of general graphs and connected graphs.
Tur\'an graphs frequently appear in extremal graph theory. We show that Tur\'an
graphs and a connected variant of them are also extremal for these particular
problems.Comment: 11 pages, 3 figure
Optical and near-infrared observations of the GRB 970616 error box
We report on near-infrared and optical observations of the GRB 970616 error
box and of the X-ray sources discovered by ASCA and ROSAT in the region. No
optical transient was found either within the IPN band or in the X-ray error
boxes, similarly to other bursts, and we suggest that either considerable
intrinsic absorption was present (like GRB 970828) or that the optical
transient displayed a very fast decline (like GRB 980326 and GRB 980519).Comment: 2 pages with one encapsulated PostScript figure included. Uses
Astronomy & Astrophysics LaTeX macros. Accepted for publication in Astronomy
& Astrophysics Supplement Serie
Correlation-induced conductance suppression at level degeneracy in a quantum dot
The large, level-dependent g-factors in an InSb nanowire quantum dot allow
for the occurrence of a variety of level crossings in the dot. While we observe
the standard conductance enhancement in the Coulomb blockade region for aligned
levels with different spins due to the Kondo effect, a vanishing of the
conductance is found at the alignment of levels with equal spins. This
conductance suppression appears as a canyon cutting through the web of direct
tunneling lines and an enclosed Coulomb blockade region. In the center of the
Coulomb blockade region, we observe the predicted correlation-induced
resonance, which now turns out to be part of a larger scenario. Our findings
are supported by numerical and analytical calculations.Comment: 5 pages, 4 figure
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