2,315 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
Visualising the past – an evaluation of processes and sequences for fingermark recovery from old documents
This study aimed to collect data on the effectiveness of most of the fingermark visualisation reagents currently used on porous surfaces on fingermarks aged for up to 90 years, significantly extending the timescales for which such information exists. A limited subset of the variables associated with processing of old fingermarks was explored, with a focus on the use of 1,8 diazafluoren-9-one (DFO), 1,2-indandione, ninhydrin, and physical developer. These techniques were used in sequence on batches of cheques between 11 and 32 years old, and on documents dating from the 1920s and 1940s. The potential for applying a physical developer enhancement process (blue toning) as the final step in the sequence was also explored. The benefits of using processing sequences on porous items were clearly demonstrated, with all processes in the sequence adding value in terms of additional marks found on the cheques up to 32 years old. In addition, physical developer was found to be capable of developing fingermarks up to 90 years old, whereas the amino acid reagents appear less effective on documents of 70 years and older. An experimental physical developer formulation with reduced environmental impact was found to be as effective as the existing process in these experiments. Blue toning was found to visualise an additional 10-25% of marks, and its wider use after silver-based deposition processes is recommended based on the evidence from this study.Peer reviewedFinal Accepted Versio
Strange quark matter: mapping QCD lattice results to finite baryon density by a quasi-particle model
A quasi-particle model is presented which describes QCD lattice results for
the 0, 2 and 4 quark-flavor equation of state. The results are mapped to finite
baryo-chemical potentials. As an application of the model we make a prediction
of deconfined matter with appropriate inclusion of strange quarks and consider
pure quark stars.Comment: invited talk at Strangeness 2000, Berkeley; prepared version for the
proceedings, 5 page
Gluonic Dissociation Revisited : I. Fugacity, Flux And Formation Time Effects
We revisit the standard treatment [Xu, Kharzeev, Satz and Wang, Phys. Rev. C
{\bf 53}, 3051 (1996)] of suppression due to gluonic bombardment in an
equilibrating quark-gluon plasma. Effects arising from gluon fugacity, relative
flux, and meson formation time are correctly incorporated in
the formulation of the gluon number density, velocity-weighted cross section,
and the survival probability. Our new formulae are applied to numerically study
the pattern of suppression in the central rapidity region at RHIC/LHC
energies. The temperature and transverse momentum dependence of our graphs have
noticeable differences from those of Xu et al.Comment: 15 pages, 6 figure
The Instanton/Sphaleron Mechanism of Prompt Gluon Production in High Energy Heavy Ion Collisions at RHIC
We argue that if the growing part of hadron-hadron cross section (described
phenomenologically by the supercritical soft Pomeron) is due to
instanton/sphaleron mechanism, one should find certain qualitative features of
the produced cluster which differ from the usual string fragmentation.
Furthermore, we suggest that this mechanism should be even more important for
heavy ion collisions in the RHIC energy domain. Large number of parton-parton
collisions should result in hundreds of produced sphaleron-like gluomagnetic
clusters per unit rapidity. Unlike perturbative gluons (or mini-jets), these
{\em classically unstable} objects promptly decay into several gluons and
quarks in mini-explosions, leading to very rapid entropy generation. This may
help to explain why the QGP seem to be produced at RHIC so early. We further
argue that this mechanism cannot be important at higher energies (LHC), where
perturbative description should apply.Comment: Revised and enlarged version, sent to Phys.Lett.
Yang-Mills Radiation in Ultra-relativistic Nuclear Collisions
The classical Yang-Mills radiation computed in the McLerran-Venugopalan model
is shown to be equivalent to the gluon bremsstrahlung distribution to lowest
order in pQCD. The classical distribution is also shown to match smoothly onto
the conventional pQCD mini-jet distribution at a scale characteristic of the
initial parton transverse density of the system. The atomic number and energy
dependence of that scale is computed from available structure function
information. The limits of applicability of the classical Yang-Mills
description of nuclear collisions at RHIC and LHC energies are discussed.Comment: 21 pages (Latex) including 2 postscript figures via psfi
Lifetime of a Disoriented Chiral Condensate
The lifetime of a disoriented chiral condensate formed within a heat bath of
pions is calculated assuming temperatures and densities attainable at present
and future heavy-ion colliders. A generalization of the reduction formula to
include coherent states allows us to derive a formula for the decay rate. We
predict the half-life to be between 4 and 7 fm/c, depending on the assumed pion
density. We also calculate the lifetime in the presence of higher resonances
and baryons, which shortens the lifetime by at most 20%.Comment: 9 pages, 3 figures, REVTeX, Eq. (3) modifie
Angular analysis of bremsstrahlung in alpha decay
A new quantum electrodynamical method of calculations of bremsstrahlung
spectra in the -decay of heavy nuclei taking into account the angle
between the directions of -particle motion (or its tunneling) and
photon emission is presented. The angular bremsstrahlung spectra for
have been obtained for the first time. According to calculations,
the bremsstrahlung in the -decay of this nucleus depends extremely
weakly on the angle. Taking into account nuclear forces, such dependence is not
changed visibly. An analytical formula of the angular dependence of the
bremsstrahlung spectra is proposed and gives its harmonic behavior. The
extremal values of the angle, at which the bremsstrahlung has maximal and
minimal values, has been found.Comment: 15 pages, 1 file of figure in EPS format, LaTeX v.2e with EPJ style.
In the new variant of the paper: 1) more attention is given to a convergence
problem of computer calculations of the bremsstrahlung spectra; 2) a new
section with inclusion of Woods-Saxon component in construction of the total
realistic -nucleus potential into our model (with our first
brermsstrahlung spectra for at such potential) is included into
the paper; 3) possible ways of further improvement of the quantum-mechanical
models are pointed ou
Jets and the shaping of the giant bipolar envelope of the planetary nebula KjPn 8
A hydrodynamic model involving cooling gas in the stagnation region of a
collimated outflow is proposed for the formation of the giant parsec-scale
bipolar envelope that surrounds the planetary nebula KjPn 8. Analytical
calculations and numerical simulations are presented to evaluate the model. The
envelope is considered to consist mainly of environmental gas swept-up by
shocks driven by an episodic, collimated, bipolar outflow. In this model, which
we call the ``free stagnation knot'' mechanism, the swept-up ambient gas
located in the stagnation region of the bow-shock cools to produce a high
density knot. This knot moves along with the bow-shock. When the central
outflow ceases, pressurization of the interior of the envelope stops and its
expansion slows down. The stagnation knot, however, has sufficient momentum to
propagate freely further along the axis, producing a distinct nose at the end
of the lobe. The model is found to successfully reproduce the peculiar shape
and global kinematics of the giant bipolar envelope of KjPn 8.Comment: 20 pages + 8 figures (in 1 tar-file 0.67 Mb
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