1,344 research outputs found
Universality of Long-Range Correlations in Expansion-Randomization Systems
We study the stochastic dynamics of sequences evolving by single site
mutations, segmental duplications, deletions, and random insertions. These
processes are relevant for the evolution of genomic DNA. They define a
universality class of non-equilibrium 1D expansion-randomization systems with
generic stationary long-range correlations in a regime of growing sequence
length. We obtain explicitly the two-point correlation function of the sequence
composition and the distribution function of the composition bias in sequences
of finite length. The characteristic exponent of these quantities is
determined by the ratio of two effective rates, which are explicitly calculated
for several specific sequence evolution dynamics of the universality class.
Depending on the value of , we find two different scaling regimes, which
are distinguished by the detectability of the initial composition bias. All
analytic results are accurately verified by numerical simulations. We also
discuss the non-stationary build-up and decay of correlations, as well as more
complex evolutionary scenarios, where the rates of the processes vary in time.
Our findings provide a possible example for the emergence of universality in
molecular biology.Comment: 23 pages, 15 figure
General-Relativistic Thomas-Fermi model
A system of self-gravitating massive fermions is studied in the framework of
the general-relativistic Thomas-Fermi model. We study the properties of the
free energy functional and its relation to Einstein's field equations. A
self-gravitating fermion gas we then describe by a set of Thomas-Fermi type
self-consistency equations.Comment: 7 pages, LaTex, to appear in Gen. Rel. Gra
2D and 3D Core-Collapse Supernovae Simulation Results Obtained with the CHIMERA Code
Much progress in realistic modeling of core-collapse supernovae has occurred
recently through the availability of multi-teraflop machines and the increasing
sophistication of supernova codes. These improvements are enabling simulations
with enough realism that the explosion mechanism, long a mystery, may soon be
delineated. We briefly describe the CHIMERA code, a supernova code we have
developed to simulate core-collapse supernovae in 1, 2, and 3 spatial
dimensions. We then describe the results of an ongoing suite of 2D simulations
initiated from a 12, 15, 20, and 25 solar mass progenitor. These have all
exhibited explosions and are currently in the expanding phase with the shock at
between 5,000 and 20,000 km. We also briefly describe an ongoing simulation in
3 spatial dimensions initiated from the 15 solar mass progenitor.Comment: 5 pages, 3 figure
Semi-Hard Scattering Unraveled from Collective Dynamics by Two-Pion Azimuthal Correlations in 158 A GeV/c Pb + Au Collisions
Elliptic flow and two-particle azimuthal correlations of charged hadrons and
high- pions ( 1 GeV/) have been measured close to mid-rapidity in
158A GeV/ Pb+Au collisions by the CERES experiment. Elliptic flow ()
rises linearly with to a value of about 10% at 2 GeV/. Beyond
1.5 GeV/, the slope decreases considerably, possibly indicating
a saturation of at high . Two-pion azimuthal anisotropies for
1.2 GeV/ exceed the elliptic flow values by about 60% in mid-central
collisions. These non-flow contributions are attributed to near-side and
back-to-back jet-like correlations, the latter exhibiting centrality dependent
broadening.Comment: Submitted to Phys. Rev. Letters, 4 pages, 5 figure
e+e--pair production in Pb-Au collisions at 158 GeV per nucleon
We present the combined results on electron-pair production in 158 GeV/n
{Pb-Au} (= 17.2 GeV) collisions taken at the CERN SPS in 1995 and
1996, and give a detailed account of the data analysis. The enhancement over
the reference of neutral meson decays amounts to a factor of 2.31 for semi-central collisions (28%
) when yields are integrated over 200 MeV/ in
invariant mass. The measured yield, its stronger-than-linear scaling with
, and the dominance of low pair strongly suggest an
interpretation as {\it thermal radiation} from pion annihilation in the
hadronic fireball. The shape of the excess centring at 500
MeV/, however, cannot be described without strong medium modifications of
the meson. The results are put into perspective by comparison to
predictions from Brown-Rho scaling governed by chiral symmetry restoration, and
from the spectral-function many-body treatment in which the approach to the
phase boundary is less explicit.Comment: 39 pages, 40 figures, to appear in Eur.Phys.J.C. (2005
Recent results from Pb-Au collisions at 158 GeV/c per nucleon obtained with the CERES spectrometer
During the 1996 lead run time, CERES has accumulated 42 million events,
corresponding to a factor of 5 more statistics than in 1995 and 2.5 million
events of a special photon-run. We report on the results of the low-mass
ee-pair analysis. Since the most critical item is the poor
signal-to-background ratio we also discuss the understanding of this
background, in absolute terms, with the help of a detailed Monte Carlo
simulation. We show preliminary results of the photon analysis and summarize
the results of the hadron analysis preliminarily reported on already at QM'97Comment: 10 pages, 9 figures, Proceedings of the XIV Int. Conf. on
Nucleus-Nucleus Collisions,Quark Matter 99, Torino, Italy, May 10 - 15, 199
Flow and non-flow event anisotropies at the SPS
A study of differential elliptic event anisotropies (v_2) of charged
particles and high-pt pions in 158 AGeV/c Pb+Au collisions is presented.
Results from correlations with respect to the event plane and from two-particle
azimuthal correlations are compared. The latter give systematically higher v_2
values at pt>1.2GeV/c providing possibly an evidence of a non-flow semihard
component.Comment: 4 pages, 6 figures, Quark Matter 2002, Nantes, to appear in Nucl.
Phys.
- …