1,282 research outputs found
A Hybrid Model for QCD Deconfining Phase Boundary
Intensive search for a proper and realistic equations of state (EOS) is still
continued for studying the phase diagram existing between quark gluon plasma
(QGP) and hadron gas (HG) phases. Lattice calculations provide such EOS for the
strongly interacting matter at finite temperature () and vanishing baryon
chemical potential (). These calculations are of limited use at finite
due to the appearance of notorious sign problem. In the recent past,
we had constructed a hybrid model description for the QGP as well as HG phases
where we make use of a new excluded-volume model for HG and a
thermodynamically-consistent quasiparticle model for the QGP phase and used
them further to get QCD phase boundary and a critical point. Since then many
lattice calculations have appeared showing various thermal and transport
properties of QCD matter at finite and . We test our hybrid
model by reproducing the entire data for strongly interacting matter and
predict our results at finite so that they can be tested in future.
Finally we demonstrate the utility of the model in fixing the precise location,
the order of the phase transition and the nature of CP existing on the QCD
phase diagram. We thus emphasize the suitability of the hybrid model as
formulated here in providing a realistic EOS for the strongly interacting
matter.Comment: 22 pages, 10 figures. corrected version published in Physical Review
D. arXiv admin note: substantial text overlap with arXiv:1201.044
Temperature dependent sound velocity in hydrodynamic equations for relativistic heavy-ion collisions
We analyze the effects of different forms of the sound-velocity function
cs(T) on the hydrodynamic evolution of matter formed in the central region of
relativistic heavy-ion collisions. At high temperatures (above the critical
temperature Tc) the sound velocity is calculated from the recent lattice
simulations of QCD, while in the low temperature region it is obtained from the
hadron gas model. In the intermediate region we use different interpolations
characterized by the values of the sound velocity at the local maximum (at T =
0.4 Tc) and local minimum (at T = Tc). In all considered cases the temperature
dependent sound velocity functions yield the entropy density, which is
consistent with the lattice QCD simulations at high temperature. Our
calculations show that the presence of a distinct minimum of the sound velocity
leads to a very long (about 20 fm/c) evolution time of the system, which is not
compatible with the recent estimates based on the HBT interferometry. Hence, we
conclude that the hydrodynamic description is favored in the case where the
cross-over phase transition renders the smooth sound velocity function with a
possible shallow minimum at Tc.Comment: 6 pages, 3 figures, talk given at SQM'07 Levoca, Slovaki
Torqued fireballs in relativistic heavy-ion collisions
We show that the fluctuations in the wounded-nucleon model of the initial
stage of relativistic heavy-ion collisions, together with the natural
assumption that the forward (backward) moving wounded nucleons emit particles
preferably in the forward (backward) direction, lead to an event-by-event
torqued fireball. The principal axes associated with the transverse shape are
rotated in the forward region in the opposite direction than in the backward
region. On the average, the standard deviation of the relative torque angle
between the forward and backward rapidity regions is about 20deg for the
central and 10deg for the mid-peripheral collisions. The hydrodynamic expansion
of a torqued fireball leads to a torqued collective flow, yielding, in turn,
torqued principal axes of the transverse-momentum distributions at different
rapidities. We propose experimental measures, based on cumulants involving
particles in different rapidity regions, which should allow for a quantitative
determination of the effect from the data. To estimate the non-flow
contributions from resonance decays we run Monte Carlo simulations with
THERMINATOR. If the event-by-event torque effect is found in the data, it will
support the assumptions concerning the fluctuations in the early stage of the
fireball formation, as well as the hypothesis of the asymmetric rapidity shape
of the emission functions of the moving sources in the nucleus-nucleus
collisions.Comment: Grant reference adde
Impedance of a Rectangular Beam Tube with Small Corrugations
We consider the impedance of a structure with rectangular, periodic
corrugations on two opposing sides of a rectangular beam tube. Using the method
of field matching, we find the modes in such a structure. We then limit
ourselves to the the case of small corrugations, but where the depth of
corrugation is not small compared to the period. For such a structure we
generate analytical approximate solutions for the wave number , group
velocity , and loss factor for the lowest (the dominant) mode
which, when compared with the results of the complete numerical solution,
agreed well. We find: if , where is the beam pipe width and is
the beam pipe half-height, then one mode dominates the impedance, with
( is the depth of corrugation),
, and , which (when replacing by
) is the same scaling as was found for small corrugations in a {\it round}
beam pipe. Our results disagree in an important way with a recent paper of
Mostacci {\it et al.} [A. Mostacci {\it et al.}, Phys. Rev. ST-AB, {\bf 5},
044401 (2002)], where, for the rectangular structure, the authors obtained a
synchronous mode with the same frequency , but with .
Finally, we find that if is large compared to then many nearby modes
contribute to the impedance, resulting in a wakefield that Landau damps.Comment: 18 pages, 6 figures, 1 bibliography fil
Transverse hydrodynamics with sudden hadronization -- production of strangeness
We consider a physical scenario for ultra-relativistic heavy-ion collisions
where, at the early stage, only transverse degrees of freedom of partons are
thermalized, while the longitudinal motion is described by free streaming. When
the energy density of the partonic system drops to a certain critical value,
the partons hadronize and the newly formed hadronic system freezes out. This
sudden change is described with the help of the Landau matching conditions
followed by the simulations done with THERMINATOR. The proposed scenario
reproduces well the transverse-momentum spectra, the elliptic flow coefficient
v2, and the HBT radii of pions and kaons studied at RHIC (Au+Au collisions at
the top beam energy). It also reproduces quite well the transverse-momentum
spectra of hyperons.Comment: talk presented by WF at the Strangeness in Quark Matter Conference,
Buzios, Brazil, Sept. 27 - oct. 2, 200
Immune mobilising T cell receptors redirect polyclonal CD8+ T cells in chronic HIV infection to form immunological synapses
T cell exhaustion develops in human immunodeficiency virus (HIV) infection due to chronic viral antigenic stimulation. This adaptive response primarily affects virus-specific CD8+ T cells, which may remain dysfunctional despite viral load-reducing antiretroviral therapy; however, abnormalities may also be evident in non-HIV-specific populations. Both could limit the efficacy of cell therapies against viral reservoirs. Here, we show that bulk (polyclonal) CD8+ T cells from people living with HIV (PLWH) express proposed markers of dysfunctional HIV-specific T cells at high levels yet form lytic immunological synapses (IS) and eliminate primary resting infected (HIV Gaglo) CD4+ T cells, when redirected by potent bispecific T cell-retargeting molecules, Immune mobilising monoclonal T cell receptors (TCR) Against Virus (ImmTAV). While PLWH CD8+ T cells are functionally impaired when compared to CD8+ T cells from HIV-naïve donors, ImmTAV redirection enables them to eliminate Gaglo CD4+ T cells that are insensitive to autologous HIV-specific cytolytic T cells. ImmTAV molecules may therefore be able to target HIV reservoirs, which represent a major barrier to a cure
Orbital evidence for more widespread carbonate-bearing rocks on Mars
Carbonates are key minerals for understanding ancient Martian environments because they are indicators of potentially habitable, neutral-to-alkaline water and may be an important reservoir for paleoatmospheric CO_2. Previous remote sensing studies have identified mostly Mg-rich carbonates, both in Martian dust and in a Late Noachian rock unit circumferential to the Isidis basin. Here we report evidence for older Fe- and/or Ca-rich carbonates exposed from the subsurface by impact craters and troughs. These carbonates are found in and around the Huygens basin northwest of Hellas, in western Noachis Terra between the Argyre basin and Valles Marineris, and in other isolated locations spread widely across the planet. In all cases they cooccur with or near phyllosilicates, and in Huygens basin specifically they occupy layered rocks exhumed from up to ~5 km depth. We discuss factors that might explain their observed regional distribution, arguments for why carbonates may be even more widespread in Noachian materials than presently appreciated and what could be gained by targeting these carbonates for further study with future orbital or landed missions to Mars
On the formation of Hubble flow in Little Bangs
A dynamical appearance of scaling solutions in the relativistic hydrodynamics
applied to describe ultra-relativistic heavy-ion collisions is studied. We
consider the boost-invariant cylindrically symmetric systems and the effects of
the phase transition are taken into account by using a temperature dependent
sound velocity inferred from the lattice simulations of QCD. We find that the
transverse flow acquires the scaling form r/t within the short evolution times,
10 - 15 fm, only if the initial transverse flow originating from the
pre-equilibrium collective behavior is present at the initial stage of the
hydrodynamic evolution. The amount of such pre-equilibrium flow is correlated
with the initial pressure gradient; larger gradients require smaller initial
flow. The results of the numerical calculations support the phenomenological
parameterizations used in the Blast-Wave, Buda-Lund, and Cracow models of the
freeze-out process.Comment: 11 page
Evidence of Limited Recruitment of Pallid Sturgeon in the Lower Missouri River
Pallid Sturgeon Scaphirhynchus albus are endemic to the Missouri and Mississippi river basins and are rare throughout their range. The species was listed as federally endangered with little to no evidence of natural recruitment. Since population augmentation was initiated as a recovery objective in the early 1990s, thousands of hatchery-origin Pallid Sturgeon have been stocked in the lower Missouri River (Gavins Point Dam [river kilometer 1,305.1] to the confluence of the Mississippi River [river kilometer 0.0]). Efforts to discriminate natural reproduction and recruitment of wild-origin Pallid Sturgeon from hatchery-origin fish has been hampered by tag loss in hatchery-origin sturgeon, inconsistent documentation of hatchery parental crosses, and the failure to collect tissue samples for genotyping all broodstock. However, the recent reconstruction of missing parental genotypes from known hatchery-origin progeny and from cryopreserved milt made it possible to examine Pallid Sturgeon recruitment. Therefore, our objectives were to 1) determine the likelihood that unmarked Pallid Sturgeon captured from the lower Missouri River were the result of natural recruitment and 2) examine the length distribution of wild- and hatchery-origin fish to determine if a difference exists by origin and examine the life-stage distribution. Genetic analysis showed that from 2003 to 2015, 358 ‘‘presumptive wild-origin’’ Pallid Sturgeon were captured in the lower Missouri River and the comparison between the length distributions of wild- and hatchery-origin fish did not provide any additional clarification into potential wildorigin fish. Low recruitment may be due to a small breeding population, high mortality of early life stages, hybridization with Shovelnose Sturgeon Scaphirhynchus platorynchus, or transport of drifting free embryos or larvae into inhospitable habitats. Determining what factors are limiting recruitment is the important next step for the recovery of Pallid Sturgeon in the lower Missouri River
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