232 research outputs found
Simulation of the enhanced traffic alert and collision avoidance system (TCAS 2)
The OSU aircraft code is used to analyze and simulate the TCAS 2 circular array which is mounted on the fuselage of a Boeing 737 aircraft. It is shown that the sum and difference patterns radiated by the circular array are distorted by the various structures of the aircraft, i.e., wings, tail, etc. Furthermore, monopulse curves are calculated and plotted for several beam positions and THETA angles. As expected, the worst cases of distortion occur when the beams are pointed toward the tail of the aircraft
Charmonium and open charm production in nuclear collisions at SPS/FAIR energies and the possible influence of a hot hadronic medium
We provide predictions for charmonium and open charm production in nuclear
collisions at SPS/FAIR energies within the framework of the statistical
hadronization model. The increasing importance at lower energies of Lambda_c
production is demonstrated and provides a challenge for future experiments. We
also demonstrate that, because of the large charm quark mass and the different
timescales for charm quark and charmed hadron production, possible
modifications of charmed hadrons in the hot hadronic medium do not lead to
measurable changes in cross sections for D-meson production. A possible
influence of medium effects can be seen, however, in yields of charmonium.
These effects are visible at all energies and results are presented for the
energy range between charm threshold and RHIC energy.Comment: 12 pages, 4 figures; v2: slightly revised text and updated
calculations; v3: slightly enhanced discussion, one more ref.; data file with
calculations will be available at
http://www-linux.gsi.de/~andronic/physics/charm
Statistical hadronization of charm at SPS, RHIC and LHC
We study the production of charmonia and charmed hadrons for nucleus-nucleus
collisions at SPS, RHIC, and LHC energies within the framework of the
statistical hadronization model. Results from this model are compared to the
observed centrality dependence of J/psi production at SPS energy. We further
provide predictions for the centrality dependence of the production of open and
hidden charm mesons at RHIC and LHC.Comment: Contribution to Quark Matter 2002, 4 pages, 3 figures; revised
version including charmed hyperons (omitted in v1
Hadron Spectra and QGP Hadronization in Au+Au Collisions at RHIC
The transverse mass spectra of Omega hyperons and phi mesons measured
recently by STAR Collaboration in Au+Au collisions at sqrt(s_NN) = 130 GeV are
described within a hydrodynamic model of the quark gluon plasma expansion and
hadronization. The flow parameters at the plasma hadronization extracted by
fitting these data are used to predict the transverse mass spectra of J/psi and
psi' mesons.Comment: 4 pages, 4 figures, Fig. 3 correcte
A model-independent analysis of the dependence of the anomalous J/psi suppression on the number of participant nucleons
A recently published experimental dependence of the J/psi to Drell-Yan ratio
on the measured, by a zero degree calorimeter, forward energy E_ZDC in Pb+Pb
collisions at the CERN SPS is analyzed. Using a model-independent approach it
is shown that the data are at variance with an earlier published experimental
dependence of the same quantity on the transverse energy of neutral hadrons
E_T. The discrepancy is related to a moderate centrality region: 100 < N_p <
200 (N_p is the number of participant nucleons) and is peculiar only to the
data obtained within the `minimum bias' analysis (using the `theoretical
Drell-Yan'). This could result from systematic experimental errors in the
minimum bias sample. A possible source of the errors is discussed.Comment: 10 pages, LaTeX, 3 PS-figures. V2: Misprints are correcte
Evidence for charmonium generation at the phase boundary in ultra-relativistic nuclear collisions
We investigate the transition from suppression to enhancement of J/psi mesons
produced in ultra-relativistic nuclear collisions in the framework of the
statistical hadronization model. The calculations are confronted with the most
recent data from the RHIC accelerator. This comparison yields first direct
evidence for generation of J/psi mesons at the phase boundary. Based on the
success of this approach we make specific predictions for LHC energy.Comment: 5 pages, 2 figures; final version accepted for publication in Phys.
Lett. B (Fig.1 containd a new set of calculations
Heavy flavor kinetics at the hadronization transition
We investigate the in-medium modification of the charmonium breakup processes
due to the Mott effect for light (pi, rho) and open-charm (D, D*)
quark-antiquark bound states at the chiral/deconfinement phase transition. The
Mott effect for the D-mesons effectively reduces the threshold for charmonium
breakup cross sections, which is suggested as an explanation of the anomalous
J/psi suppression phenomenon in the NA50 experiment. Further implications of
finite-temperature mesonic correlations for the hadronization of heavy flavors
in heavy-ion collisions are discussed.Comment: 4 pages, 2 figures, Contribution to SQM2001 Conference, submitted to
J. Phys.
Charmonium from Statistical Hadronization of Heavy Quarks -- a Probe for Deconfinement in the Quark-Gluon Plasma
We review the statistical hadronization picture for charmonium production in
ultra-relativistic nuclear collisions. Our starting point is a brief reminder
of the status of the thermal model description of hadron production at high
energy. Within this framework an excellent account is achieved of all data for
hadrons built of (u,d,s) valence quarks using temperature, baryo-chemical
potential and volume as thermal parameters. The large charm quark mass brings
in a new (non-thermal) scale which is explicitely taken into account by fixing
the total number of charm quarks produced in the collision. Emphasis is placed
on the description of the physical basis for the resulting statistical
hadronization model. We discuss the evidence for statistical hadronization of
charmonia by analysis of recent data from the SPS and RHIC accelerators.
Furthermore we discuss an extension of this model towards lower beam energies
and develop arguments about the prospects to observe medium modifications of
open and hidden charm hadrons. With the imminent start of the LHC accelerator
at CERN, exciting prospects for charmonium production studies at the very high
energy frontier come into reach. We present arguments that, at such energies,
charmonium production becomes a fingerprint of deconfinement: even if no
charmonia survive in the quark-gluon plasma, statistical hadronization at the
QCD phase boundary of the many tens of charm quarks expected in a single
central Pb-Pb collision could lead to an enhanced, rather than suppressed
production probability when compared to results for nucleon-nucleon reactions
scaled by the number of hard collisions in the Pb-Pb system.Comment: review article, 27 pages, Landoldt review volume "Relativistic Heavy
Ion Physics", Reinhard Stock, edito
Characterization of Flexible RF Microcoil Dedicated to Surface Mri
In Magnetic Resonance Imaging (MRI), to achieve sufficient Signal to Noise
Ratio (SNR), the electrical performance of the RF coil is critical. We
developed a device (microcoil) based on the original concept of monolithic
resonator. This paper presents the used fabrication process based on
micromoulding. The dielectric substrates are flexible thin films of polymer,
which allow the microcoil to be form fitted to none-plane surface. Electrical
characterizations of the RF coils are first performed and results are compared
to the attempted values. Proton MRI of a saline phantom using a flexible RF
coil of 15 mm in diameter is performed. When the coil is conformed to the
phantom surface, a SNR gain up to 2 is achieved as compared to identical but
planar RF coil. Finally, the flexible coil is used in vivo to perform MRI with
high spatial resolution on a mouse using a small animal dedicated scanner
operating at in a 2.35 T.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Progress in the determination of the cross section
Improving previous calculations, we compute the cross section using QCD sum rules. Our sum rules for the , , and hadronic
matrix elements are constructed by using vaccum-pion correlation functions, and
we work up to twist-4 in the soft-pion limit. Our results suggest that, using
meson exchange models is perfectly acceptable, provided that they include form
factors and that they respect chiral symmetry. After doing a thermal average we
get mb at T=150\MeV.Comment: 22 pages, RevTeX4 including 7 figures in ps file
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