675 research outputs found
The Cauchy problem for the 3-D Vlasov-Poisson system with point charges
In this paper we establish global existence and uniqueness of the solution to
the three-dimensional Vlasov-Poisson system in presence of point charges in
case of repulsive interaction. The present analysis extends an analogeous
two-dimensional result by Caprino and Marchioro [On the plasma-charge model, to
appear in Kinetic and Related Models (2010)].Comment: 28 page
Gamma-ray emission expected from Kepler's SNR
Nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova
remnants (SNRs) is used to investigate the properties of Kepler's SNR and, in
particular, to predict the gamma-ray spectrum expected from this SNR.
Observations of the nonthermal radio and X-ray emission spectra as well as
theoretical constraints for the total supernova (SN) explosion energy E_sn are
used to constrain the astronomical and particle acceleration parameters of the
system. Under the assumption that Kepler's SN is a type Ia SN we determine for
any given explosion energy E_sn and source distance d the mass density of the
ambient interstellar medium (ISM) from a fit to the observed SNR size and
expansion speed. This makes it possible to make predictions for the expected
gamma-ray flux. Exploring the expected distance range we find that for a
typical explosion energy E_sn=10^51 erg the expected energy flux of TeV
gamma-rays varies from 2x10^{-11} to 10^{-13} erg/(cm^2 s) when the distance
changes from d=3.4 kpc to 7 kpc. In all cases the gamma-ray emission is
dominated by \pi^0-decay gamma-rays due to nuclear CRs. Therefore Kepler's SNR
represents a very promising target for instruments like H.E.S.S., CANGAROO and
GLAST. A non-detection of gamma-rays would mean that the actual source distance
is larger than 7 kpc.Comment: 6 pages, 4 figures. Accepted for publication in Astronomy and
Astrophysics, minor typos correcte
Clusters of Galaxies: magnetic fields and nonthermal emission
The nonthermal particle content of galaxy clusters should in part have a
cosmological component generated during the early starburst phase of the member
galaxies. This is reviewed in the framework of a simple cluster formation model
suggested previously. It implies a nonthermal energy fraction of about 10
percent for the Intracluster gas. We also propose a mechanism for the early
generation of Intracluster magnetic fields in terms of Galactic Winds. It
results in typical field strengths of about 0.1 microGauss. Such comparatively
weak fields are consistent with an inverse Compton origin of the excess EUV and
hard X-ray emission of the Coma cluster, given the radio synchrotron emission.
The required relativistic electrons must have been accelerated rather recently,
less than a few billion years ago, presumably in cluster accretion shocks. This
is in contrast to the hadronic nonthermal component which accumulates on
cosmological time scales, and whose pion-decay TeV gamma-ray emission is
expected to be larger, or of the same order as the inverse Compton TeV
emission. This gamma-radiation characterizes the energetic history of cluster
formation and should be observable with future arrays of imaging atmospheric
Cherenkov telescopes.Comment: 16 pages, 8 figures; invited talk presented at the VERITAS Workshop
on TeV Astrophysics of Extragalactic Sources, submitted to Astroparticle
Physic
A 3' â 5' XPB helicase defect in repair/transcription factor TFIIH of xeroderma pigmentosum group B affects both DNA repair and transcription
XPB is a subunit of the basal transcription factor TFIIH, which is also involved in nucleotide excision repair (NER) and potentially in cell cycle regulation. A frameshift mutation in the 3'-end of the XPB gene is responsible for a concurrence of two disorders: xeroderma pigmentosum (XP) and Cockayne's syndrome (CS). We have isolated TFIIH from cells derived from a patient (XP11BE) who carries this frameshift mutation (TFI-IHmut) and from the mother of this patient (TFIIHwt) to determine the biochemical consequences of the mutation. Although identical in composition and stoichiometry to TFIIHwt, TFIIHmut shows a reduced 3' â 5' XPB helicase activity. A decrease in helicase and DNA-dependent ATPase activities was also observed with the mutated recombinant XPB protein. The XPB mutation causes a severe NER defect. In addition, we provide evidence for a decrease in basal transcription activity in vitro. The latter defect may provide an explanation for many of the XP and CS symptoms that are difficult to rationalize based solely on an NER defect. Thus, this work presents the first detailed analysis of a naturally occurring mutation in a basal transcription factor and supports the concept that the combined XP/CS clinical entity is actually the result of a combined transcription/repair deficiency.</p
A 3' â 5' XPB helicase defect in repair/transcription factor TFIIH of xeroderma pigmentosum group B affects both DNA repair and transcription
XPB is a subunit of the basal transcription factor TFIIH, which is also involved in nucleotide excision repair (NER) and potentially in cell cycle regulation. A frameshift mutation in the 3'-end of the XPB gene is responsible for a concurrence of two disorders: xeroderma pigmentosum (XP) and Cockayne's syndrome (CS). We have isolated TFIIH from cells derived from a patient (XP11BE) who carries this frameshift mutation (TFI-IHmut) and from the mother of this patient (TFIIHwt) to determine the biochemical consequences of the mutation. Although identical in composition and stoichiometry to TFIIHwt, TFIIHmut shows a reduced 3' â 5' XPB helicase activity. A decrease in helicase and DNA-dependent ATPase activities was also observed with the mutated recombinant XPB protein. The XPB mutation causes a severe NER defect. In addition, we provide evidence for a decrease in basal transcription activity in vitro. The latter defect may provide an explanation for many of the XP and CS symptoms that are difficult to rationalize based solely on an NER defect. Thus, this work presents the first detailed analysis of a naturally occurring mutation in a basal transcription factor and supports the concept that the combined XP/CS clinical entity is actually the result of a combined transcription/repair deficiency.</p
The Case for Quantum Key Distribution
Quantum key distribution (QKD) promises secure key agreement by using quantum
mechanical systems. We argue that QKD will be an important part of future
cryptographic infrastructures. It can provide long-term confidentiality for
encrypted information without reliance on computational assumptions. Although
QKD still requires authentication to prevent man-in-the-middle attacks, it can
make use of either information-theoretically secure symmetric key
authentication or computationally secure public key authentication: even when
using public key authentication, we argue that QKD still offers stronger
security than classical key agreement.Comment: 12 pages, 1 figure; to appear in proceedings of QuantumComm 2009
Workshop on Quantum and Classical Information Security; version 2 minor
content revision
Neutron beam test of CsI crystal for dark matter search
We have studied the response of Tl-doped and Na-doped CsI crystals to nuclear
recoils and 's below 10 keV. The response of CsI crystals to nuclear
recoil was studied with mono-energetic neutrons produced by the
H(p,n)He reaction. This was compared to the response to Compton
electrons scattered by 662 keV -ray. Pulse shape discrimination between
the response to these 's and nuclear recoils was studied, and quality
factors were estimated. The quenching factors for nuclear recoils were derived
for both CsI(Na) and CsI(Tl) crystals.Comment: 21pages, 14figures, submitted to NIM
Role of Inter-Electron Interaction in the Pseudo-Gap Opening in High T Tunneling Experiments
The analysis of tunneling experiments showing the pseudogap type behavior is
carried out based on the idea of the renormalization of density of states due
to the inter-electron interaction in the Cooper channel (superconducting
fluctuations contribution in tunneling current). It is demonstrated that the
observed kink of the zero-bias conductance of junctions in
the vicinity of can be explained in terms of fluctuation theory in a
quite wide range of temperature above , using the values of microscopic
parameters of the electron spectrum taken from independent
experiments. The approach proposed also permits to explain qualitatively the
shape of the tunneling anomalies in and gives a correct estimate for
the pseudogap position and amplitude observed in the experiments on
junctions.Comment: 5 pages, 3 figure
Measurement of the decay width of He
We have precisely measured decay width of \5LHe and
demonstrated significantly larger - overlap than expected
from the central repulsion - potential, which is derived from
YNG \Lambda$-nucleon interaction.Comment: 4 pages, 3 figure
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