10,376 research outputs found
Evolution of pion HBT radii from RHIC to LHC -- Predictions from ideal hydrodynamics
We present hydrodynamic predictions for the charged pion HBT radii for a
range of initial conditions covering those presumably reached in Pb+Pb
collisions at the LHC. We study central (b=0) and semi-central (b=7fm)
collisions and show the expected increase of the HBT radii and their azimuthal
oscillations. The predicted trends in the oscillation amplitudes reflect a
change of the final source shape from out-of-plane to in-plane deformation as
the initial entropy density is increased.Comment: 6 pages, incl. 5 figures. Contribution to the CERN Theory Institute
Workshop "Heavy Ion Collisions at the LHC -- Last Call for Predictions",
CERN, 14 May - 8 June 2007, to appear in J. Phys.
Hydrodynamic simulation of elliptic flow
We use a hydrodynamic model to study the space-time evolution transverse to
the beam direction in ultrarelativistic heavy-ion collisions with nonzero
impact parameters. We focus on the influence of early pressure on the
development of radial and elliptic flow. We show that at high energies elliptic
flow is generated only during the initial stages of the expansion while radial
flow continues to grow until freeze-out. Quantitative comparisons with SPS data
from semiperipheral Pb+Pb collisions suggest the applicability of
hydrodynamical concepts already 1 fm/c after impact.Comment: 4 pages, 5 figures, proceedings for Quark Matter 9
Design study of special purpose systems for the lunar surface
Design of special purpose systems for lunar surface operation
Chronic Progressive External Ophthalmoplegia Is Associated with a Novel Mutation in the Mitochondrial tRNA(Asn) Gene
Chronic progressive external ophthalmoplegia (CPEO) is caused by a decreased oxidative phosphorylation (OXPHOS) activity due to large-scale deletions of the mitochondrial genome in 50 % of the patients. The deletions encompass structural OXPHOS genes as well as tRNA genes, required for their expression so that the pathogenesis could be due to the deleted OXPHOS subunits or to an impaired mitochondrial translation. We have analyzed the mitochondrial genome of a patient presenting with CPEO for single base substitutions and discovered a novel heteroplasmic mutation in the tRNAAsn gene at position 5692 that converts a highly conserved adenine into a guanine. This mutation is unique because it is located at the transition of the anticodon loop to the anticodon stem and it leads to an additional base pair, thus reducing the number of loop-forming nucleotides from seven to five. Our findings suggest that CPEO can be caused by a single base substition in a mitochondrial tRNA gene so that the mitochondrial protein synthesis becomes the rate limiting step in OXPHOS fidelity
High-j single-particle neutron states outside the N=82 core
The behaviour of the i13/2 and h9/2 single-neutron strength was studied with
the (4He,3He) reaction on 138Ba, 140Ce, 142Nd and 144Sm targets at a beam
energy of 51 MeV. The separation between the single-neutron states i13/2 and
h9/2 was measured in N =83 nuclei with changing proton number. To this end
spectroscopic factors for states populated in high-l transfer were extracted
from the data. Some mixing of l=5 and 6 strength was observed with states that
are formed by coupling the f7/2 state to the 2+ and 3- vibrational states and
the mixing matrix elements were found to be remarkably constant. The centroids
of the strength indicate a systematic change in the energies of the i13/2 and
h9/2 single-neutron states with increasing proton number that is in
quantitative agreement with the effects expected from the tensor interaction.Comment: 12 pages of text, 3 diagram
Whitening of the Quark-Gluon Plasma
Parton-parton collisions do not neutralize local color charges in the
quark-gluon plasma as they only redistribute the charges among momentum modes.
We discuss color diffusion and color conductivity as the processes responsible
for the neutralization of the plasma. For this purpose, we first compute the
conductivity and diffusion coefficients in the plasma that is significantly
colorful. Then, the time evolution of the color density due to the conductivity
and diffusion is studied. The conductivity is shown to be much more efficient
than the diffusion in neutralizing the plasma at the scale longer than the
screening length. Estimates of the characteristic time scales, which are based
on close to global equilibrium computations, suggest that first the plasma
becomes white and then the momentum degrees of freedom thermalize.Comment: 9 pages, revised, to appear in Phys. Rev.
Flow effects on the freeze-out phase-space density in heavy ion collisions
The strong longitudinal expansion of the reaction zone formed in relativistic
heavy-ion collisions is found to significantly reduce the spatially averaged
pion phase-space density, compared to naive estimates based on thermal
distributions. This has important implications for data interpretation and
leads to larger values for the extracted pion chemical potential at kinetic
freeze-out.Comment: 5 pages, 3 figures included via epsfig, added discussion of different
transverse density profiles, 1 new figur
Hydrodynamics at RHIC -- how well does it work, where and how does it break down?
I review the successes and limitations of the ideal fluid dynamic model in
describing hadron emission spectra from Au+Au collisions at the Relativistic
Heavy Ion Collider (RHIC).Comment: 8 pages, 4 figures. Invited talk presented at Strange Quark Matter
2004 (Cape Town, Sep. 15-20, 2004). Proceedings to appear in Journal of
Physics
Fluctuations from dissipation in a hot non-Abelian plasma
We consider a transport equation of the Boltzmann-Langevin type for
non-Abelian plasmas close to equilibrium to derive the spectral functions of
the underlying microscopic fluctuations from the entropy. The correlator of the
stochastic source is obtained from the dissipative processes in the plasma.
This approach, based on classical transport theory, exploits the well-known
link between a linearized collision integral, the entropy and the spectral
functions. Applied to the ultra-soft modes of a hot non-Abelian (classical or
quantum) plasma, the resulting spectral functions agree with earlier findings
obtained from the microscopic theory. As a by-product, it follows that
B\"odeker's effective theory is consistent with the fluctuation-dissipation
theorem.Comment: 9 pages, revtex, no figures, identical to published versio
Dynamical freeze-out condition in ultrarelativistic heavy ion collisions
We determine the decoupling surfaces for the hydrodynamic description of
heavy ion collisions at RHIC and LHC by comparing the local hydrodynamic
expansion rate with the microscopic pion-pion scattering rate. The pion
spectra for nuclear collisions at RHIC and LHC are computed by applying the
Cooper-Frye procedure on the dynamical-decoupling surfaces, and compared with
those obtained from the constant-temperature freeze-out surfaces. Comparison
with RHIC data shows that the system indeed decouples when the expansion rate
becomes comparable with the pion scattering rate. The dynamical decoupling
based on the rates comparison also suggests that the effective decoupling
temperature in central heavy ion collisions remains practically unchanged from
RHIC to LHC.Comment: 7 pages, 9 figure
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