3,780 research outputs found
Effect of large mountain ranges on atmospheric flow patterns as seen from TIROS satellites
Includes bibliographical references
High Resolution X-ray Spectra of the Brightest OB Stars in the Cygnus OB2 Association
The Cygnus OB2 Association contains some of the most luminous OB stars in our
Galaxy, the brightest of which are also among the most luminous in X-rays. We
have obtained a Chandra High Energy Transmission Grating Spectrometer (HETGS)
observation centered on Cyg OB2 No. 8a, the most luminous X-ray source in the
Association. Although our analysis will focus on the X-ray properties of Cyg
OB2 No. 8a, we also present limited analyses of three other OB stars (Cyg OB2
Nos. 5, 9, and 12). Applying standard diagnostic techniques as used in previous
studies of early-type stars, we find that the X-ray properties of Cyg OB2 No.
8a are very similar to those of other OB stars that have been observed using
high-resolution X-ray spectroscopy. From analyses of the He-like ion "fir"
emission lines, we derive radial distances of the He-like line emission sources
and find these fir-inferred radii are consistent with their corresponding X-ray
continuum optical depth unity radii. Contrary to other O-star results, the
emission lines of Cyg OB2 No. 8a show a large range in line centroid shifts
(roughly -800 to +250 km/s). We discuss the implications of our results in
light of the fact that Cyg OB2 No. 8a is a member of a rather tight stellar
cluster, and shocks could arise at interfaces with the winds of these other
stars.Comment: 36 pages (including 4 tables and 12 figures). LaTeX. Submitted to Ap
Transport theories for heavy ion collisions in the 1 AGeV regime
We compare multiplicities as well as rapidity and transverse momentum distributions of protons, pions and kaons calculated within presently available transport approaches for heavy ion collisions around 1 AGeV. For this purpose, three reactions have been selected: Au+Au at 1 and 1.48 AGeV and Ni+Ni at 1.93 AGeV
Strangeness dynamics and transverse pressure in relativistic nucleus-nucleus collisions
We investigate hadron production as well as transverse hadron spectra from
proton-proton, proton-nucleus and nucleus-nucleus collisions from 2 GeV
to 21.3 TeV within two independent transport approaches (HSD and UrQMD)
that are based on quark, diquark, string and hadronic degrees of freedom. The
comparison to experimental data on transverse mass spectra from , and
C+C (or Si+Si) reactions shows the reliability of the transport models for
light systems. For central Au+Au (Pb+Pb) collisions at bombarding energies
above 5 AGeV, furthermore, the measured transverse mass
spectra have a larger inverse slope parameter than expected from the default
calculations. We investigate various scenarios to explore their potential
effects on the spectra. In particular the initial state Cronin effect
is found to play a substantial role at top SPS and RHIC energies. However, the
maximum in the ratio at 20 to 30 AGeV is missed by ~40% and
the approximately constant slope of the spectra at SPS energies is not
reproduced either. Our systematic analysis suggests that the additional
pressure - as expected from lattice QCD calculations at finite quark chemical
potential and temperature - should be generated by strong
interactions in the early pre-hadronic/partonic phase of central Au+Au (Pb+Pb)
collisions.Comment: 20 pages, 15 figures, Phys. Rev. C, in pres
Dissociative recombination and electron-impact de-excitation in CH photon emission under ITER divertor-relevant plasma conditions
For understanding carbon erosion and redeposition in nuclear fusion devices,
it is important to understand the transport and chemical break-up of
hydrocarbon molecules in edge plasmas, often diagnosed by emission of the CH
A^2\Delta - X^2\Pi Ger\"o band around 430 nm. The CH A-level can be excited
either by electron-impact or by dissociative recombination (D.R.) of
hydrocarbon ions. These processes were included in the 3D Monte Carlo impurity
transport code ERO. A series of methane injection experiments was performed in
the high-density, low-temperature linear plasma generator Pilot-PSI, and
simulated emission intensity profiles were benchmarked against these
experiments. It was confirmed that excitation by D.R. dominates at T_e < 1.5
eV. The results indicate that the fraction of D.R. events that lead to a CH
radical in the A-level and consequent photon emission is at least 10%.
Additionally, quenching of the excited CH radicals by electron impact
de-excitation was included in the modeling. This quenching is shown to be
significant: depending on the electron density, it reduces the effective CH
emission by a factor of 1.4 at n_e=1.3*10^20 m^-3, to 2.8 at n_e=9.3*10^20
m^-3. Its inclusion significantly improved agreement between experiment and
modeling
Hole motion in the Ising antiferromagnet: an application of the recursion method
We study hole motion in the Ising antiferromagnet using the recursion method.
Using the retraceable path approximation we find the hole's Green's function as
well as its wavefunction for arbitrary values of . The effect of small
transverse interaction also is taken into account. Our results provide some
additional insight into the self-consistent Born approximation.Comment: 8 pages, RevTex, no figures. Accepted for publication in Phys.Rev.
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