556 research outputs found
TRIDYN_FZR User Manual
The present report contains the User Manual of the FZR version of the dynamic binary-collision computer simulation code TRIDYN. The present version of the code is based on TRIDYN Vs. 4.0 by W.Möller and W.Eckstein, Department of Surface Physics, Max-Planck Institute of Plasma Physics, Boltzmannstraße 2, 85748 Garching, Germany (1989). Modifications, in particular for PC implementation, quasi-dynamic display and the input dialog have been performed at the Institute of Ion Beam Physics and Materials Research by V.Kharlamov, T.Schwieger, M.Posselt, and W.Möller (1995-2001)
X-ray analysis of the proper motion and pulsar wind nebula for PSR J1741-2054
We obtained six observations of PSR J1741-2054 using the ACIS-S
detector totaling 300 ks. By registering this new epoch of observations
to an archival observation taken 3.2 years earlier using X-ray point sources in
the field of view, we have measured the pulsar proper motion at in a direction consistent with the symmetry axis of the
observed H nebula. We investigated the inferred past trajectory of the
pulsar but find no compelling association with OB associations in which the
progenitor may have originated. We confirm previous measurements of the pulsar
spectrum as an absorbed power law with photon index =2.680.04,
plus a blackbody with an emission radius of (4.5 km,
for a DM-estimated distance of kpc and a temperature of
eV. Emission from the compact nebula is well described by an
absorbed power law model with a photon index of = 1.670.06, while
the diffuse emission seen as a trail extending northeast of the pulsar shows no
evidence of synchrotron cooling. We also applied image deconvolution techniques
to search for small-scale structures in the immediate vicinity of the pulsar,
but found no conclusive evidence for such structures.Comment: 7 pages, 8 figures, 4 Tables; Accepted by Ap
Development of long-life, low-noise linear bearings for atmospheric interferometry
This paper describes the development of dry-lubricated linear bearings for use on the Michelson interferometer for passive atmospheric sounding (MIPAS). Two candidate bearing systems were developed and tested. In the first, use was made of linear roller (needle) bearings equipped with a pulley-and-cable arrangement to prevent cage drift and to minimize roller slip. The second design was of a roller-guided bearing system in which guidance was provided by all bearings rolling along guide rods. The paper focuses on the development of these linear bearings systems and describes the approach taken in terms of bearing design, lubrication methods, screening programs, and thermal-vacuum testing. Development difficulties are highlighted and the solutions ultimately adopted are described
Constraints on the Equation-of-State of neutron stars from nearby neutron star observations
We try to constrain the Equation-of-State (EoS) of supra-nuclear-density
matter in neutron stars (NSs) by observations of nearby NSs. There are seven
thermally emitting NSs known from X-ray and optical observations, the so-called
Magnificent Seven (M7), which are young (up to few Myrs), nearby (within a few
hundred pc), and radio-quiet with blackbody-like X-ray spectra, so that we can
observe their surfaces. As bright X-ray sources, we can determine their
rotational (pulse) period and their period derivative from X-ray timing. From
XMM and/or Chandra X-ray spectra, we can determine their temperature. With
precise astrometric observations using the Hubble Space Telescope, we can
determine their parallax (i.e. distance) and optical flux. From flux, distance,
and temperature, one can derive the emitting area - with assumptions about the
atmosphere and/or temperature distribution on the surface. This was recently
done by us for the two brightest M7 NSs RXJ1856 and RXJ0720. Then, from
identifying absorption lines in X-ray spectra, one can also try to determine
gravitational redshift. Also, from rotational phase-resolved spectroscopy, we
have for the first time determined the compactness (mass/radius) of the M7 NS
RBS1223. If also applied to RXJ1856, radius (from luminosity and temperature)
and compactness (from X-ray data) will yield the mass and radius - for the
first time for an isolated single neutron star. We will present our
observations and recent results.Comment: refereed NPA5 conference proceedings, in pres
Deep Chandra Observations of the Pulsar Wind Nebula Created by PSR B0355+54
We report on Chandra X-ray Observatory (CXO) observations of the pulsar wind
nebula (PWN) associated with PSR B0355+54 (eight observations with a 395 ks
total exposure, performed over an 8 month period). We investigated the spatial
and spectral properties of the emission coincident with the pulsar, compact
nebula (CN), and extended tail. We find that the CN morphology can be
interpreted in a way that suggests a small angle between the pulsar spin axis
and our line-of-sight, as inferred from the radio data. On larger scales,
emission from the 7' (2 pc) tail is clearly seen. We also found hints of two
faint extensions nearly orthogonal to the direction of the pulsar's proper
motion. The spectrum extracted at the pulsar position can be described with an
absorbed power-law + blackbody model. The nonthermal component can be
attributed to magnetospheric emission, while the thermal component can be
attributed to emission from either a hot spot (e.g., a polar cap) or the entire
neutron star surface. Surprisingly, the spectrum of the tail shows only a
slight hint of cooling with increasing distance from the pulsar. This implies
either a low magnetic field with fast flow speed, or particle re-acceleration
within the tail. We estimate physical properties of the PWN and compare the
morphologies of the CN and the extended tail with those of other bow shock PWNe
observed with long CXO exposures.Comment: 11 pages, 8 figure
Small Angle Scattering by Fractal Aggregates: A Numerical Investigation of the Crossover Between the Fractal Regime and the Porod Regime
Fractal aggregates are built on a computer using off-lattice cluster-cluster
aggregation models. The aggregates are made of spherical particles of different
sizes distributed according to a Gaussian-like distribution characterised by a
mean and a standard deviation . The wave vector dependent
scattered intensity is computed in order to study the influence of the
particle polydispersity on the crossover between the fractal regime and the
Porod regime. It is shown that, given , the location of the
crossover decreases as increases. The dependence of on
can be understood from the evolution of the shape of the center-to-center
interparticle-distance distribution function.Comment: RevTex, 4 pages + 6 postscript figures, compressed using "uufiles",
published in Phys. Rev. B 50, 1305 (1994
An Efficient Molecular Dynamics Scheme for the Calculation of Dopant Profiles due to Ion Implantation
We present a highly efficient molecular dynamics scheme for calculating the
concentration depth profile of dopants in ion irradiated materials. The scheme
incorporates several methods for reducing the computational overhead, plus a
rare event algorithm that allows statistically reliable results to be obtained
over a range of several orders of magnitude in the dopant concentration.
We give examples of using this scheme for calculating concentration profiles
of dopants in crystalline silicon. Here we can predict the experimental profile
over five orders of magnitude for both channeling and non-channeling implants
at energies up to 100s of keV.
The scheme has advantages over binary collision approximation (BCA)
simulations, in that it does not rely on a large set of empirically fitted
parameters. Although our scheme has a greater computational overhead than the
BCA, it is far superior in the low ion energy regime, where the BCA scheme
becomes invalid.Comment: 17 pages, 21 figures, 2 tables. See: http://bifrost.lanl.gov/~reed
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