4,292 research outputs found
Resonance production in heavy ion collisions
Recent results of resonance production from RHIC at
200 GeV and SPS at 17 GeV are presented and discussed in
terms of the evolution and freeze-out conditions of a hot and dense fireball
medium. Yields and spectra are compared with thermal model predictions at
chemical freeze-out. Deviations in the low transverse momentum region of the
resonance spectrum of the hadronic decay channel, suggest a strongly
interaction hadronic phase between chemical and kinetic freeze-out. Microscopic
models including resonance rescattering and regeneration are able to describe
the trend of the data. The magnitude of the regeneration cross sections for
different inverse decay channels are discussed. Model calculations which
include elastic hadronic interactions between chemical freeze-out and thermal
freeze-out based on the K(892)/K and (1520)/ ratios suggest a
time between two freeze-outs surfaces of 4 fm/c. The difference
in momentum distributions and yields for the (1020) resonance
reconstructed from the leptonic and hadronic decay channels at SPS energy are
discussed taking into account the impact of a hadronic phase and possible
medium modifications.Comment: 8 pages, 4 figures, conference proceedings (SQM2004
What do we learn from Resonance Production in Heavy Ion Collisions?
Resonances with their short life time and strong coupling to the dense and
hot medium are suggested as a signature of the early stage of the fireball
created in a heavy ion collision \cite{rap00,lut01,lut02}. The comparison of
resonances with different lifetimes and quark contents may give information
about time evolution and density and temperature of during the expanding of
fireball medium. Resonances in elementary reactions have been measured since
1960. Resonance production in elementary collisions compared with heavy ion
collisions where we expect to create a hot and dense medium may show the direct
of influence of the medium on the resonances. This paper shows a selection of
the recent resonance measurements from SPS and RHIC heavy ion colliders.Comment: 10 pages, 8 figures, HotQuarks 2004 conference proceeding
Recurrent cerebellar architecture solves the motor-error problem
Current views of cerebellar function have been heavily influenced by the models of Marr and Albus, who suggested that the climbing fibre input to the cerebellum acts as a teaching signal for motor learning. It is commonly assumed that this teaching signal must be motor error (the difference between actual and correct motor command), but this approach requires complex neural structures to estimate unobservable motor error from its observed sensory consequences.
We have proposed elsewhere a recurrent decorrelation control architecture in which Marr-Albus models learn without requiring motor error. Here, we prove convergence for this architecture and demonstrate important advantages for the modular control of systems with multiple degrees of freedom. These results are illustrated by modelling adaptive plant compensation for the three-dimensional vestibular ocular reflex. This provides a functional role for recurrent cerebellar connectivity, which may be a generic anatomical feature of projections between regions of cerebral and cerebellar cortex
Statistical hadronization phenomenology in fluctuations at ultra-relativistic energies
We discuss the information that can be obtained from an analysis of
fluctuations in heavy ion collisions within the context of the statistical
model of particle production. We then examine the recently published
experimental data on ratio fluctuations, and use it to obtain constraints on
the statistical properties (physically relevant ensemble, degree of chemical
equilibration, scaling across energies and system sizes) and freeze-out
dynamics (amount of reinteraction between chemical and thermal freeze-out) of
the system.Comment: Proceedings, SQM2009. Fig. 4, the main results figure, was wrong due
to editing mistake, now correcte
The Dynamics of T-Cell Receptor Repertoire Diversity Following Thymus Transplantation for DiGeorge Anomaly
T cell populations are regulated both by signals specific to the T-cell receptor
(TCR) and by signals and resources, such as cytokines and space, that act
independently of TCR specificity. Although it has been demonstrated that
disruption of either of these pathways has a profound effect on T-cell
development, we do not yet have an understanding of the dynamical interactions
of these pathways in their joint shaping of the T cell repertoire. Complete
DiGeorge Anomaly is a developmental abnormality that results in the failure of
the thymus to develop, absence of T cells, and profound immune deficiency. After
receiving thymic tissue grafts, patients suffering from DiGeorge anomaly develop
T cells derived from their own precursors but matured in the donor tissue. We
followed three DiGeorge patients after thymus transplantation to utilize the
remarkable opportunity these subjects provide to elucidate human T-cell
developmental regulation. Our goal is the determination of the respective roles
of TCR-specific vs. TCR-nonspecific regulatory signals in the growth of these
emerging T-cell populations. During the course of the study, we measured
peripheral blood T-cell concentrations, TCRβ V
gene-segment usage and CDR3-length spectratypes over two years or more for each
of the subjects. We find, through statistical analysis based on a novel
stochastic population-dynamic T-cell model, that the carrying capacity
corresponding to TCR-specific resources is approximately 1000-fold larger than
that of TCR-nonspecific resources, implying that the size of the peripheral
T-cell pool at steady state is determined almost entirely by TCR-nonspecific
mechanisms. Nevertheless, the diversity of the TCR repertoire depends crucially
on TCR-specific regulation. The estimated strength of this TCR-specific
regulation is sufficient to ensure rapid establishment of TCR repertoire
diversity in the early phase of T cell population growth, and to maintain TCR
repertoire diversity in the face of substantial clonal expansion-induced
perturbation from the steady state
The mass and energy budget of Cassiopeia A
Further analysis of X-ray spectroscopy results recently obtained from the MOS
CCD cameras on-board XMM-Newton provides a detailed description of the hot and
cool X-ray emitting plasma in Cas A. Measurement of the Doppler broadening of
the X-ray lines is consistent with the expected ion velocities, ~1500 km/s
along the line of sight, in the post shock plasma. Assuming a constant total
pressure throughout the remnant we estimate the total remnant mass as 10 Msun
and the total thermal energy as 7E43 J. We derive the differential mass
distribution as a function of ionisation age for both X-ray emitting
components. This distribution is consistent with a hot component dominated by
swept up mass heated by the primary shock and a cool component which are
ablated clumpy ejecta material which were and are still being heated by
interaction with the preheated swept up material. We calculate a balanced mass
and energy budget for the supernova explosion giving 1E44 J in ejected mass;
approximately 0.4 Msun of the ejecta were diffuse with an initial rms velocity
of 15000 km/s while the remaining ~1.8 Msun were clumpy with an initial rms
velocity of ~2400 km/s. Using the Doppler velocity measurements of the X-ray
spectral lines we can project the mass into spherical coordinates about the
remnant. This provides quantitative evidence for mass and energy beaming in the
supernova explosion. The mass and energy occupy less than 4.5 sr (<40 % of the
available solid angle) around the remnant and 64 % of the mass occurs in two
jets within 45 degrees of a jet axis. We calculate a swept up mass of 7.9 Msun
in the emitting plasma and estimate that the total mass lost from the
progenitor prior to the explosion could be as high as ~20 Msun.Comment: 8 pages, 7 figures, submitted to Astronomy & Astrophysic
Use of Lichen and Moss in Assessment of Forest Contamination with Heavy Metals in Praded and Glacensis Euroregions (Poland and Czech Republic)
The concentrations of selected metals—Cr, Ni, Cu, Zn, Cd, and Pb—were determined in the samples of Hypogymnia physodes lichen and Pleurozium schreberi moss collected in Polish and Czech Euroregions Praded and Glacensis. More specifically, the samples were collected in Bory Stobrawskie, Bory Niemodlińskie, and Kotlina Kłodzka (Poland) and in Jeseniki (Czech Republic). The concentration of metals in the samples was measured using the atomic absorption spectrometry (flame AAS technique and electrothermal atomization AAS technique). The results were used to calculate the comparison factor (CF) that quantifies the difference in concentration of a given bioavailable analyte × accumulated in lichens and mosses: CF = 2 (cx,lichen − cx,moss) (cx,lichen + cx,moss)−1. The values of CF greater than 0.62 indicate the most probable location of heavy metals deposited in the considered area. In this work, the method was used to show a significant contribution of urban emissions to the deposition of heavy metals in the area of Bory Stobrawskie and in the vicinity of Kłodzko City
Increased aquaporin 1 water channel expression inhuman brain tumours
Aquaporin 1 is a water channel protein. There was little aquaporin 1 immunoreactivity in normal brain parenchyma. In astrocytomas, aquaporin 1 was expressed in microvessel endothelia and neoplastic astrocytes. In metastatic carcinomas, aquaporin 1 was present in microvessel endothelia and reactive astrocytes. Aquaporin 1 may participate in the formation of brain tumour oedema
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