2,121 research outputs found
Revision of Pycnandra subgenus Sebertia (Sapotaceae) and a generic key to the family in New Caledonia
The satellite genus Sebertia (Sapotaceae, Chrysophylloideae) in New Caledonia is here recognized as Pycnandra subgenus Sebertia, a group comprising only two species. Pycnandra canaliculata is described and illustrated as new from the south part of Grande Terre where it occurs in maquis vegetation and humid forest on ultramafic soils, often along watercourses. This species is well known among many biologists but misidentified until now as Sebertia gatopensis, a synonym of P. blanchonii that resides in northwest Grande Terre. In New Caledonia, Pycnandra is the only sapotaceous genus with flowers that lack staminodes and Pycnandra subgenus Sebertia is characterized by small white flowers and fruits lacking stylar remnants. The fruits are characteristic with a scale-like epidermis that is translucent and peels off in P. acuminata versus brown and persistent in P canaliculata. Using field data and applying IUCN criteria, we assess the preliminary threat as Least Concern (LC) for P. acuminata and Vulnerable (VU) for P. canaliculata
System-size dependence
The final state in The final state in heavy-ion collisions has a higher
degree of strangeness saturation than the one produced in collisions between
elementary particles like p-p or p-. A systematic analysis of this
phenomenon is made for C-C, Si-Si and Pb-Pb collisions at the CERN SPS collider
and for collisions at RHIC and at AGS energies. Strangeness saturation
is shown to increase smoothly with the number of participants at AGS, CERN and
RHIC energies.Comment: 5 pages, 5 figures, presented at SQM2003 conferenc
Strange particle production at RHIC in a single-freeze-out model
Strange particle ratios and pT-spectra are calculated in a thermal model with
single freeze-out, previously used successfully to describe non-strange
particle production at RHIC. The model and the recently released data for phi,
Lambda, anti-Lambda, and K*(892) are in very satisfactory agreement, showing
that the thermal approach can be used to describe the strangeness production at
RHIC.Comment: We have added the comparison of the model predictions to the newly
released Lambda and K*(892) pT-spectra from STA
The PreAmplifier ShAper for the ALICE TPC-Detector
In this paper the PreAmplifier ShAper (PASA) for the Time Projection Chamber
(TPC) of the ALICE experiment at LHC is presented. The ALICE TPC PASA is an
ASIC that integrates 16 identical channels, each consisting of Charge Sensitive
Amplifiers (CSA) followed by a Pole-Zero network, self-adaptive bias network,
two second-order bridged-T filters, two non-inverting level shifters and a
start-up circuit. The circuit is optimized for a detector capacitance of 18-25
pF. For an input capacitance of 25 pF, the PASA features a conversion gain of
12.74 mV/fC, a peaking time of 160 ns, a FWHM of 190 ns, a power consumption of
11.65 mW/ch and an equivalent noise charge of 244e + 17e/pF. The circuit
recovers smoothly to the baseline in about 600 ns. An integral non-linearity of
0.19% with an output swing of about 2.1 V is also achieved. The total area of
the chip is 18 mm and is implemented in AMS's C35B3C1 0.35 micron CMOS
technology. Detailed characterization test were performed on about 48000 PASA
circuits before mounting them on the ALICE TPC front-end cards. After more than
two years of operation of the ALICE TPC with p-p and Pb-Pb collisions, the PASA
has demonstrated to fulfill all requirements
Aspects of thermal and chemical equilibration of hadronic matter
We study thermal and chemical equilibration in 'infinite' hadron matter as
well as in finite size relativistic nucleus-nucleus collisions using a BUU
cascade transport model that contains resonance and string degrees-of-freedom.
The 'infinite' hadron matter is simulated within a cubic box with periodic
boundary conditions. The various equilibration times depend on baryon density
and energy density and are much shorter for particles consisting of light
quarks then for particles including strangeness. For kaons and antikaons the
chemical equilibration time is found to be larger than 40 fm/c for all
baryon and energy densities considered. The inclusion of continuum excitations,
i.e. hadron 'strings', leads to a limiting temperature of 150 MeV.
We, furthermore, study the expansion of a hadronic fireball after
equilibration. The slope parameters of the particles after expansion increase
with their mass; the pions leave the fireball much faster then nucleons and
accelerate subsequently heavier hadrons by rescattering ('pion wind'). If the
system before expansion is close to the limiting temperature , the slope
parameters for all particles after expansion practically do not depend on
(initial) energy and baryon density. Finally, the equilibration in relativistic
nucleus-nucleus collision is considered. Since the reaction time here is much
shorter than the equilibration time for strangeness, a chemical equilibrium of
strange particles in heavy-ion collisions is not supported by our transport
calculations. However, the various particle spectra can approximately be
described within the blast model.Comment: 39 pages, LaTeX, including 18 postscript figures, Nucl. Phys. A, in
pres
Particle Ratios as a Probe of the QCD Critical Temperature
We show how the measured particle ratios can be used to provide non-trivial
information about the critical temperature of the QCD phase transition. This is
obtained by including the effects of highly massive Hagedorn resonances on
statistical models, which are used to describe hadronic yields. The inclusion
of Hagedorn states creates a dependence of the thermal fits on the Hagedorn
temperature, , which is assumed to be equal to , and leads to an
overall improvement of thermal fits. We find that for Au+Au collisions at RHIC
at GeV the best square fit measure, , occurs at
MeV and produces a chemical freeze-out temperature of 172.6 MeV
and a baryon chemical potential of 39.7 MeV.Comment: 6 pages, 4 figure
Fluctuations and the QCD phase diagram
In this contribution the role of quantum fluctuations for the QCD phase
diagram is discussed. This concerns in particular the importance of the matter
back-reaction to the gluonic sector. The impact of these fluctuations on the
location of the confinement/deconfinement and the chiral transition lines as
well as their interrelation are investigated. Consequences of our findings for
the size of a possible quarkyonic phase and location of a critical endpoint in
the phase diagram are drawn.Comment: 7 pages, 3 figures, to appear in Physics of Atomic Nucle
Collective flow and two-pion correlations from a relativistic hydrodynamic model with early chemical freeze out
We investigate the effect of early chemical freeze-out on radial flow,
elliptic flow and HBT radii by using a fully three dimensional hydrodynamic
model. When we take account of the early chemical freeze-out, the space-time
evolution of temperature in the hadron phase is considerably different from the
conventional model in which chemical equilibrium is always assumed. As a
result, we find that radial and elliptic flows are suppressed and that the
lifetime and the spatial size of the fluid are reduced. We analyze the p_t
spectrum, the differential elliptic flow, and the HBT radii at the RHIC energy
by using hydrodynamics with chemically non-equilibrium equation of state.Comment: One subsection and two figures adde
Status of Chemical Equilibrium in Relativistic Heavy Ion Collisions
Recent work on chemical equilibrium in heavy ion collisions is reviewed. The
energy dependence of thermal parameters is discussed. The centrality dependence
of thermal parameters at SPS energies is presented.Comment: 7 pages, 7 Postscript figure
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