37,706 research outputs found
The effects of shock waves on meteorites Final report
Shock wave effects on iron and iron-nickel alloys in meteorites analyzed by phase diagrams and residual effects due to shock loadin
Novel Bose-Einstein Interference in the Passage of a Fast Particle in a Dense Medium
When an energetic particle collides coherently with many medium particles at
high energies, the Bose-Einstein symmetry with respect to the interchange of
the exchanged virtual bosons leads to a destructive interference of the Feynman
amplitudes in most regions of the phase space but a constructive interference
in some other regions of the phase space. As a consequence, the recoiling
medium particles have a tendency to come out collectively along the direction
of the incident fast particle, each carrying a substantial fraction of the
incident longitudinal momentum. Such an interference appearing as collective
recoils of scatterers along the incident particle direction may have been
observed in angular correlations of hadrons associated with a high-
trigger in high-energy AuAu collisions at RHIC.Comment: 10 pages, 2 figures, invited talk presented at the 35th Symposium on
Nuclear Physics, Cocoyoc, Mexico, January 3, 2012, to be published in IOP
Conference Serie
The Interference Term between the Spin and Orbital Contributions to M1 Transitions
We study the cross-correlation between the spin and orbital parts of magnetic
dipole transitions M1 in both isoscalar and isovector channels. In particular,
we closely examine certain cases where is very close to , implying a cancellation of the summed
interference terms. We gain some insight into this problem by considering
special cases approaching the SU(3) limit, and by examining the behaviour of
single-particle transitions at the beginning and towards the end of the s-d
shell.Comment: 9 pages of latex file and no figure
Pion Interferometry for Hydrodynamical Expanding Source with a Finite Baryon Density
We calculate the two-pion correlation function for an expanding hadron source
with a finite baryon density. The space-time evolution of the source is
described by relativistic hydrodynamics and the Hanbury-Brown-Twiss (HBT)
radius is extracted after effects of collective expansion and multiple
scattering on the HBT interferometry have been taken into account, using
quantum probability amplitudes in a path-integral formalism. We find that this
radius is substantially smaller than the HBT radius extracted from the
freeze-out configuration.Comment: 4 pages, 2 figure
Elliptic Flow from a Transversally Thermalized Fireball
The agreement of elliptic flow data at RHIC at central rapidity with the
hydrodynamic model has led to the conclusion of very rapid thermalization. This
conclusion is based on the intuitive argument that hydrodynamics, which assumes
instantaneous local thermalization, produces the largest possible elliptic flow
values and that the data seem to saturate this limit. We here investigate the
question whether incompletely thermalized viscous systems may actually produce
more elliptic flow than ideal hydrodynamics. Motivated by the extremely fast
primordial longitudinal expansion of the reaction zone, we investigate a toy
model which exhibits thermalization only in the transverse directions but
undergoes collisionless free-streaming expansion in the longitudinal direction.
For collisions at RHIC energies, elliptic flow results from the model are
compared with those from hydrodynamics. With the final particle yield and
\kt-distribution fixed, the transversally thermalized model is shown not to
be able to produce the measured amount of elliptic flow. This investigation
provides further support for very rapid local kinetic equilibration at RHIC. It
also yields interesting novel results for the elliptic flow of massless
particles such as direct photons.Comment: revtex4, 15 pages + 10 embedded EPS figure
Universal Behavior in Large-scale Aggregation of Independent Noisy Observations
Aggregation of noisy observations involves a difficult tradeoff between
observation quality, which can be increased by increasing the number of
observations, and aggregation quality which decreases if the number of
observations is too large. We clarify this behavior for a protypical system in
which arbitrarily large numbers of observations exceeding the system capacity
can be aggregated using lossy data compression. We show the existence of a
scaling relation between the collective error and the system capacity, and show
that large scale lossy aggregation can outperform lossless aggregation above a
critical level of observation noise. Further, we show that universal results
for scaling and critical value of noise which are independent of system
capacity can be obtained by considering asymptotic behavior when the system
capacity increases toward infinity.Comment: 10 pages, 3 figure
Extremal Optimization of Graph Partitioning at the Percolation Threshold
The benefits of a recently proposed method to approximate hard optimization
problems are demonstrated on the graph partitioning problem. The performance of
this new method, called Extremal Optimization, is compared to Simulated
Annealing in extensive numerical simulations. While generally a complex
(NP-hard) problem, the optimization of the graph partitions is particularly
difficult for sparse graphs with average connectivities near the percolation
threshold. At this threshold, the relative error of Simulated Annealing for
large graphs is found to diverge relative to Extremal Optimization at equalized
runtime. On the other hand, Extremal Optimization, based on the extremal
dynamics of self-organized critical systems, reproduces known results about
optimal partitions at this critical point quite well.Comment: 7 pages, RevTex, 9 ps-figures included, as to appear in Journal of
Physics
Heteropolymer Sequence Design and Preferential Solvation of Hydrophilic Monomers: One More Application of Random Energy Model
In this paper, we study the role of surface of the globule and the role of
interactions with the solvent for designed sequence heteropolymers using random
energy model (REM). We investigate the ground state energy and surface monomer
composition distribution. By comparing the freezing transition in random and
designed sequence heteropolymers, we discuss the effects of design. Based on
our results, we are able to show under which conditions solvation effect
improves the quality of sequence design. Finally, we study sequence space
entropy and discuss the number of available sequences as a function of imposed
requirements for the design quality
Interferometry signatures for QCD first-order phase transition in heavy ion collisions at GSI-FAIR energies
Using the technique of quantum transport of the interfering pair we examine
the Hanbury-Brown-Twiss (HBT) interferometry signatures for the
particle-emitting sources of pions and kaons produced in the heavy ion
collisions at GSI-FAIR energies. The evolution of the sources is described by
relativistic hydrodynamics with the system equation of state of the first-order
phase transition from quark-gluon plasma (QGP) to hadronic matter. We use
quantum probability amplitudes in a path-integral formalism to calculate the
two-particle correlation functions, where the effects of particle decay and
multiple scattering are taken into consideration. We find that the HBT radii of
kaons are smaller than those of pions for the same initial conditions. Both the
HBT radii of pions and kaons increase with the system initial energy density.
The HBT lifetimes of the pion and kaon sources are sensitive to the initial
energy density. They are significantly prolonged when the initial energy
density is tuned to the phase boundary between the QGP and mixed phase. This
prolongations of the HBT lifetimes of pions and kaons may likely be observed in
the heavy ion collisions with an incident energy in the GSI-FAIR energy range.Comment: 16 pages, 4 figure
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