15,535 research outputs found
Geant4 Applications for Modeling Molecular Transport in Complex Vacuum Geometries
We discuss a novel use of the Geant4 simulation toolkit to model molecular
transport in a vacuum environment, in the molecular flow regime. The Geant4
toolkit was originally developed by the high energy physics community to
simulate the interactions of elementary particles within complex detector
systems. Here its capabilities are utilized to model molecular vacuum transport
in geometries where other techniques are impractical. The techniques are
verified with an application representing a simple vacuum geometry that has
been studied previously both analytically and by basic Monte Carlo simulation.
We discuss the use of an application with a very complicated geometry, that of
the Large Synoptic Survey Telescope camera cryostat, to determine probabilities
of transport of contaminant molecules to optical surfaces where control of
contamination is crucial.Comment: 7 pages, 4 figures, 2 tables, to appear in IJMSSC, updated to
accepted versio
Infrared regularization of baryon chiral perturbation theory reformulated
We formulate the infrared regularization of Becher and Leutwyler in a form
analogous to our recently proposed extended on-mass-shell renormalization. In
our formulation, IR regularization can be applied straightforwardly to
multi-loop diagrams with an arbitrary number of particles with arbitrary
masses.Comment: 10 pages, ReVTEX 4, no figure
Wide-field weak lensing by RXJ1347-1145
We present an analysis of weak lensing observations for RXJ1347-1145 over a
43' X 43' field taken in B and R filters on the Blanco 4m telescope at CTIO.
RXJ1347-1145 is a massive cluster at redshift z=0.45. Using a population of
galaxies with 20<R<26, we detect a weak lensing signal at the p<0.0005 level,
finding best-fit parameters of \sigma_v=1400^{+130}_{-140} km s^{-1} for a
singular isothermal sphere model and r_{200} = 3.5^{+0.8}_{-0.2} Mpc with c =
15^{+64}_{-10} for a NFW model in an \Omega_m = 0.3, \Omega_\Lambda = 0.7
cosmology. In addition, a mass to light ratio M/L_R =90 \pm 20 M_\odot /
L_{R\odot} was determined. These values are consistent with the previous weak
lensing study of RXJ1347--1145 by Fischer and Tyson, 1997, giving strong
evidence that systemic bias was not introduced by the relatively small field of
view in that study. Our best-fit parameter values are also consistent with
recent X-ray studies by Allen et al, 2002 and Ettori et al, 2001, but are not
consistent with recent optical velocity dispersion measurements by Cohen and
Kneib, 2002.Comment: accepted to ApJ, tentative publication 10 May 2005, v624
Is MS1054-03 an exceptional cluster? A new investigation of ROSAT/HRI X-ray data
We reanalyzed the ROSAT/HRI observation of MS1054-03, optimizing the channel
HRI selection and including a new exposure of 68 ksec. From a wavelet analysis
of the HRI image we identify the main cluster component and find evidence for
substructure in the west, which might either be a group of galaxies falling
onto the cluster or a foreground source. Our 1-D and 2-D analysis of the data
show that the cluster can be fitted well by a classical betamodel centered only
20arcsec away from the central cD galaxy. The core radius and beta values
derived from the spherical model(beta = 0.96_-0.22^+0.48) and the elliptical
model (beta = 0.73+/-0.18) are consistent. We derived the gas mass and total
mass of the cluster from the betamodel fit and the previously published ASCA
temperature (12.3^{+3.1}_{-2.2} keV). The gas mass fraction at the virial
radius is fgas = (14[-3,+2.5]+/-3)% for Omega_0=1, where the errors in brackets
come from the uncertainty on the temperature and the remaining errors from the
HRI imaging data. The gas mass fraction computed for the best fit ASCA
temperature is significantly lower than found for nearby hot clusters,
fgas=20.1pm 1.6%. This local value can be matched if the actual virial
temperature of MS1054-032 were close to the lower ASCA limit (~10keV) with an
even lower value of 8 keV giving the best agreement. Such a bias between the
virial and measured temperature could be due to the presence of shock waves in
the intracluster medium stemming from recent mergers. Another possibility, that
reconciles a high temperature with the local gas mass fraction, is the
existence of a non zero cosmological constant.Comment: 12 pages, 5 figures, accepted for publication in Ap
The complex galaxy cluster Abell 514: New results obtained with the XMM - Newton satellite
We study the X-ray morphology and dynamics of the galaxy cluster Abell 514.
Also, the relation between the X-ray properties and Faraday Rotation measures
of this cluster are investigated in order to study the connection of magnetic
fields and the intra-cluster medium. We use two combined XMM - Newton pointings
that are split into three distinct observations. The data allow us to evaluate
the overall cluster properties like temperature and metallicity with high
accuracy. Additionally, a temperature map and the metallicity distribution are
computed, which are used to study the dynamical state of the cluster in detail.
Abell 514 represents an interesting merger cluster with many substructures
visible in the X-ray image and in the temperature and abundance distributions.
The new XMM - Newton data of Abell 514 confirm the relation between the X-ray
brightness and the sigma of the Rotation Measure (S_X - sigma_RM relation)
proposed by Dolag et al. (2001).Comment: 9 pages, 13 figures, accepted for publication in A&
Polarization of electric field noise near metallic surfaces
Electric field noise in proximity to metallic surfaces is a poorly understood
phenomenon that appears in different areas of physics. Trapped ion quantum
information processors are particular susceptible to this noise, leading to
motional decoherence which ultimately limits the fidelity of quantum
operations. On the other hand they present an ideal tool to study this effect,
opening new possibilities in surface science. In this work we analyze and
measure the polarization of the noise field in a micro-fabricated ion trap for
various noise sources. We find that technical noise sources and noise emanating
directly from the surface give rise to different degrees of polarization which
allows us to differentiate between the two noise sources. Based on this, we
demonstrate a method to infer the magnitude of surface noise in the presence of
technical noise
Chandra Observation of the Merging Cluster A168: A Late Stage in the Evolution of a Cold Front
We present Chandra observations of the cool cluster A168, for which previous
X-ray imaging and optical studies indicated a merger of two subclusters nearly
in the plane of the sky. We derive a temperature map for A168, which shows that
the merger has proceeded beyond the core passage and is near subcluster
turnaround. It also reveals an unusual feature -- the gas core of one of the
subclusters forms a tongue-like structure extending ahead (in the direction of
motion) of the subcluster center. The coolest cluster gas is found in a
crescent-shaped region at the tip of this tongue, and forms a cold front in
pressure equilibrium with the external gas. In contrast with this feature's
forward location, previously observed merger cold fronts (e.g., A3667,
1E0657--56) lagged behind their host subclusters, as expected in the presense
of ram pressure. We propose that A168 illustrates a much later stage in the
evolution of a cold front, when its host subcluster approaches the apocenter of
the merger orbit where the ram pressure on its gas drops sharply. As a result,
a large chunk of the subcluster gas ``slingshots'' past the dark matter center,
becomes unbound from the subcluster and expands adiabatically, as seen in some
recent hydrodynamic simulations.Comment: 4 pages, 3 figures, to be published in ApJ Letter
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