3,306 research outputs found
Orbital operation for large automated satellites
Orbital operations concepts for the shuttle launched Large Automated Satellites (LAS) are discussed. It includes the orbital operations elements and the major options for accomplishing each element. This study is based on the preliminary payload information available in Level I and II documents and on orbital operations methods used on past programs, both manned and unmanned. It includes a definition of detailed trade studies which need to be performed as satellite design details and organization responsibilities are defined. The major objectives of this study were to define operational methods and requirements for the long duration LAS missions which are effective and primarily economical to implement
Strange Hadrons from the ALCOR Rehadronization Model
Hadron multiplicities --- especially for strange particles --- are calculated
in the framework of the algebraic coalescence rehadronization model (ALCOR),
which counts for redistribution of quarks into hadrons for relativistic
heavy-ion collisions. The influence of Bjorken flow on the final hadronic
composition are incorporated in the model. A comparison is made with the CERN
SPS NA35 and experiments. The analysis of these experiments with
ALCOR shows a strangeness enhancement for S+S collisions and a possible
formation of a sort of semi-deconfined state of the matter. Predictions for
Pb+Pb collisions (NA49) are also presented.Comment: 14 pages, LaTeX, Review to appear in Proceedings of Strangeness'95,
Tucson, Arizona, Jan. 4--6 1995. (American Institute of Physics
Faces of quark matter
Based on an analysis in the framework of a coalescence hadronization model
(ALCOR) we conclude that in heavy ion collisions at CERN SPS and RHIC energies
a new type of matter, the massive quark-antiquark matter is produced.Comment: Talk given at Budapest Workshop on Quark and Hadron Dynamics in
Relativistic Heavy Ion Collisions (BP 2002) Budapest, Hungary, 3-7 Mar 2002.
12 pages in Latex, 8 PS figure. Submitted to Heavy Ion Physics. Note added in
proo
3-D Simulations of Protostellar Jets in Stratified Ambient Media
We present fully three-dimensional hydrodynamical simulations of radiative
cooling jets propagating into stratified isothermal ambient media with
power-law density and pressure distributions. The parameters used are mainly
suitable for protostellar jets but results applicable to extragalactic jets are
also presented. Comparisons are made with previous simulations of jets through
homogeneous media. We find that for radiative cooling jets propagating into
regions where the ambient medium has an increasing density (and pressure)
gradient, the ambient gas tends to compress the cold, low-pressure cocoon of
shocked material that surrounds the beam and destroy the bow shock-like
structure at the head. The compressing medium collimates the jet and promotes
the development of Kelvin-Helmholtz instabilities which cause beam focusing,
wiggling and the formation of internal traveling shocks,
, via pinching along the beam. This remarkably resembles the structure of
some observed systems (e.g. Haro 6-5B northern and HH 24G jets). These effects
are larger for jets with smaller density ratio between jet and environment
(tested for =1, 3, and 10) and larger Mach number
(tested for 12 and 24, where is the jet velocity and the
ambient sound speed). In an ambient medium of decreasing density (and
pressure), the beam is poorly collimated and relaxes, becoming faint. This
could explain ''invisible'' jet sections, like the gap between the parent
source and collimated beam (e.g., in HH30 jet). Although, on average, jets
propagating into an increasing (decreasing) density environment are decelerated
(accelerated) by the increasing (decreasing) ram pressure of the ambient
medium, we find that their propagation velocities have an oscillating pattern.Comment: 33 pp, LaTeX file, 13 figures upon request. To appear in the
Astrophys. J., vol 471, nov. 10t
Correlation between nucleotide composition and folding energy of coding sequences with special attention to wobble bases
Background: The secondary structure and complexity of mRNA influences its
accessibility to regulatory molecules (proteins, micro-RNAs), its stability and
its level of expression. The mobile elements of the RNA sequence, the wobble
bases, are expected to regulate the formation of structures encompassing coding
sequences.
Results: The sequence/folding energy (FE) relationship was studied by
statistical, bioinformatic methods in 90 CDS containing 26,370 codons. I found
that the FE (dG) associated with coding sequences is significant and negative
(407 kcal/1000 bases, mean +/- S.E.M.) indicating that these sequences are able
to form structures. However, the FE has only a small free component, less than
10% of the total. The contribution of the 1st and 3rd codon bases to the FE is
larger than the contribution of the 2nd (central) bases. It is possible to
achieve a ~ 4-fold change in FE by altering the wobble bases in synonymous
codons. The sequence/FE relationship can be described with a simple algorithm,
and the total FE can be predicted solely from the sequence composition of the
nucleic acid. The contributions of different synonymous codons to the FE are
additive and one codon cannot replace another. The accumulated contributions of
synonymous codons of an amino acid to the total folding energy of an mRNA is
strongly correlated to the relative amount of that amino acid in the translated
protein.
Conclusion: Synonymous codons are not interchangable with regard to their
role in determining the mRNA FE and the relative amounts of amino acids in the
translated protein, even if they are indistinguishable in respect of amino acid
coding.Comment: 14 pages including 6 figures and 1 tabl
Pions and kaons from stringy quark matter
Different hadron transverse momentum spectra are calculated in a
non-extensive statistical, quark-coalescence model. For the low-pT part a
gluonic string contribution is conjectured, its length distribution and
fractality are fitted to RHIC data.Comment: Contribution to SQM2008 (Beijing
Nuclear liquid-gas phase transition within the lattice gas model
We study the nuclear liquid-gas phase transition on the basis of a
two-component lattice gas model. A Metropolis type of sampling method is used
to generate microscopic states in the canonical ensemble. The effective
equation of state and fragment mass distributions are evaluated in a wide range
of temperatures and densities. A definition of the phase coexistence region
appropriate for mesoscopic systems is proposed. The caloric curve resulting
from different types of freeze-out conditions are presented.Comment: 13 pages including 4 figure
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