3,679 research outputs found
A high Reynolds number numerical solution of the Navier-Stokes equations in stream function-vorticity form
Problems encoutered in investigations of high Reynolds number, incompressible flow are reviewed. A numerical solution computer program was modified to solve the stream function-vorticity form of the Navier-Stokes equations. Using a body fitted coordinate system with a U-shaped outer boundary, a simulation of incompressible flow at a Reynolds number of one million and a body angle of attack of zero was achieved
Freeze-Out Time in Ultrarelativistic Heavy Ion Collisions from Coulomb Effects in Transverse Pion Spectra
The influence of the nuclear Coulomb field on transverse spectra of
and measured in reactions at 158 A GeV has been investigated.
Pion trajectories are calculated in the field of an expanding fireball. The
observed enhancement of the ratio at small momenta depends on the
temperature and transverse expansion velocity of the source, the rapidity
distribution of the net positive charge, and mainly the time of the freeze-out.Comment: 11 pages including 2 figure
Numerical solution of the Navier-Stokes equations for arbitrary two-dimensional multi-element airfoils
The development of a numerical simulation of time dependent, turbulent, compressible flow about two dimensional multi-element airfoils of arbitrary shape is described. The basis of this simulation is a technique of automatic numerical generation of coordinate systems fitted to the multiple bodies regardless of their number or shape. Procedures developed whereby the coordinate lines are automatically concentrated in the boundary layer at any Reynolds number are discussed. The compressible turbulent solution involves an algebraic eddy viscosity turbulence model. The laminar version was run for transonic flow at free stream Mach numbers up to 0.9
(Anti)Proton and Pion Source Sizes and Phase Space Densities in Heavy Ion Collisions
NA44 has measured mid-rapidity deuteron spectra from AA collisions at
sqrt{s}=18GeV/A at the CERN SPS. Combining these spectra with published proton,
antiproton and antideuteron data allows us to calculate, within a coalescence
framework, proton and antiproton source sizes and phase space densities. These
results are compared to pion source sizes and densities, pA results and to
lower energy (AGS) data. The antiproton source is larger than the proton source
at sqrt{s}=18GeV/A. The phase space densities of pions and protons are not
constant but grow with system size. Both pi+ and proton radii decrease with
transverse mass and increase with sqrt{s}. Pions and protons do not freeze-out
independently. The nature of their interaction changes as sqrt{s}, and the
pion/proton ratio increases.Comment: 4 pages, Latex 2.09, 3 eps figures. Changes for January 2001. The
proton source size is now calculated assuming a more realistic Hulthen,
rather than Gaussian, wavefunction. A new figure shows the effect of this
change which is important for small radii. A second new figure shows the
results of RQMD calculations of the proton source size and phase density.
Because of correlations between position and momentum coalesence does not
show the full proton source size. The paper has been streamlined and
readability improve
On the Equation of State of Nuclear Matter in 158A GeV Pb+Pb Collisions
Within a hydrodynamical approach we investigate the sensitivity of single
inclusive momentum spectra of hadrons in 158A GeV Pb+Pb collisions to three
different equations of state of nuclear matter. Two of the equations of state
are based on lattice QCD results and include a phase transition to a
quark-gluon plasma. The third equation of state has been extracted from the
microscopic transport code RQMD under the assumption of complete local
thermalization. All three equations of state provide reasonable fits to data
taken by the NA44 and NA49 Collaborations. The initial conditions before the
evolution of the fireballs and the space-time evolution pictures differ
dramatically for the three equations of state when the same freeze-out
temperature is used in all calculations. However, the softest of the equations
of state results in transverse mass spectra that are too steep in the central
rapidity region. We conclude that the transverse particle momenta are
determined by the effective softness of the equation of state during the
fireball expansion.Comment: 4 pages, including 4 figures and 2 tables. For a PostScript file of
the manuscript, you can also goto http://t2.lanl.gov/schlei/eprint.htm
Baryon phase-space density in heavy-ion collisions
The baryon phase-space density at mid-rapidity from central heavy-ion
collisions is estimated from proton spectra with interferometry and deuteron
coalescence measurements. It is found that the mid-rapidity phase-space density
of baryons is significantly lower at the SPS than the AGS, while those of total
particles (pion + baryon) are comparable. Thermal and chemical equilibrium
model calculations tend to over-estimate the phase-space densities at both
energies.Comment: 5 pages, 2 tables, no figure. RevTeX style. Accepted for publication
in Phys. Rev. C Rapid Communicatio
Pathogenic Variants in Fucokinase Cause a Congenital Disorder of Glycosylation
FUK encodes fucokinase, the only enzyme capable of converting L-fucose to fucose-1-phosphate, which will ultimately be used for synthesizing GDP-fucose, the donor substrate for all fucosyltransferases. Although it is essential for fucose salvage, this pathway is thought to make only a minor contribution to the total amount of GDP-fucose. A second pathway, the major de novo pathway, involves conversion of GDP-mannose to GDP-fucose. Here we describe two unrelated individuals who have pathogenic variants in FUK and who presented with severe developmental delays, encephalopathy, intractable seizures, and hypotonia. The first individual was compound heterozygous for c.667T>C (p.Ser223Pro) and c.2047C>T (p.Arg683Cys), and the second individual was homozygous for c.2980A>C (p.Lys994Gln). Skin fibroblasts from the first individual confirmed the variants as loss of function and showed significant decreases in total GDP-[3H] fucose and [3H] fucose-1-phosphate. There was also a decrease in the incorporation of [5,6-3H]-fucose into fucosylated glycoproteins. Lys994 has previously been shown to be an important site for ubiquitin conjugation. Here, we show that loss-of-function variants in FUK cause a congenital glycosylation disorder characterized by a defective fucose-salvage pathway
Systematic Study of the Kaon to Pion Multiplicity Ratios in Heavy-Ion Collisions
We present a systematic study of the kaon to pion multiplicity ratios (K+/pi+
and K-/pi-) in heavy-ion collisions from AGS to RHIC energy using the
Relativistic Quantum Molecular Dynamics (RQMD) model. The model satisfactorily
describes the available experimental data on K+/pi+ and K-/pi-. Within the
model, we find that the strong increase of the ratios with the number of
participants is mainly due to hadronic rescattering of produced mesons with
ingoing baryons and their resonances. The enhancement of K/pi in heavy-ion
collisions with respect to elementary p+p interactions is larger at AGS energy
than SPS energy, and decreases smoothly with bombarding energy. The total
multiplicity ratios at RHIC energy are predicted by RQMD to be K+/pi+ = 0.19
and K-/pi- = 0.15.Comment: 10 pages, 8 figures, RevTeX style. A section is added to discuss
effects of rope formatio
Two-kaon correlations in central Pb + Pb collisions at 158 A GeV/c
Two-particle interferometry of positive kaons is studied in Pb + Pb
collisions at mean transverse momenta and 0.91 GeV/c. A
three-dimensional analysis was applied to the lower data, while a
two-dimensional analysis was used for the higher data. We find that the
source size parameters are consistent with the scaling curve observed in
pion correlation measurements in the same collisions, and that the duration
time of kaon emission is consistent with zero within the experimental
sensitivity.Comment: 4 pages incl. 1 table and 3 fig's; RevTeX; accepted for publication
in PR
Elliptical flow -- a signature for early pressure in ultrarelativistic nucleus-nucleus collisions
Elliptical energy flow patterns in non-central Au(11.7AGeV) on Au reactions
have been studied employing the RQMD model. The strength of these azimuthal
asymmetries is calculated comparing the results in two different modes of RQMD
(mean field and cascade). It is found that the elliptical flow which is readily
observable with current experimental detectors may help to distinguish
different reasonable expansion scenarios for baryon-dense matter. The final
asymmetries are very sensitive to the pressure at maximum compression, because
they involve a partial cancelation between early squeeze-out and subsequent
flow in the reaction plane. This cancelation can be expected to occur in a
broad energy region covered by the current heavy ion fixed-target programs at
BNL and at CERN.Comment: 14 pages LaTeX including 3 postscript figure
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