7,911 research outputs found
Medium corrections in the formation of light charged particles in heavy ion reactions
Within a microscopic statistical description of heavy ion collisions, we
investigate the effect of the medium on the formation of light clusters. The
dominant medium effects are self-energy corrections and Pauli blocking that
produce the Mott effect for composite particles and enhanced reaction rates in
the collision integrals. Microscopic description of composites in the medium
follows the Dyson equation approach combined with the cluster mean-field
expansion. The resulting effective few-body problem is solved within a properly
modified Alt-Grassberger-Sandhas formalism. The results are incorporated in a
Boltzmann-Uehling-Uhlenbeck simulation for heavy ion collisions. The number and
spectra of light charged particles emerging from a heavy ion collision changes
in a significant manner in effect of the medium modification of production and
absorption processes.Comment: 16 pages, 6 figure
Few-Body States in Fermi-Systems and Condensation Phenomena
Residual interactions in many particle systems lead to strong correlations. A
multitude of spectacular phenomenae in many particle systems are connected to
correlation effects in such systems, e.g. pairing, superconductivity,
superfluidity, Bose-Einstein condensation etc. Here we focus on few-body bound
states in a many-body surrounding.Comment: 10 pages, proceedings 1st Asian-Pacific Few-Body Conference, needs
fbssuppl.sty of Few-Body System
Dynamics of photoinduced Charge Density Wave-metal phase transition in K0.3MoO3
We present first systematic studies of the photoinduced phase transition from
the ground charge density wave (CDW) state to the normal metallic (M) state in
the prototype quasi-1D CDW system K0.3MoO3. Ultrafast non-thermal CDW melting
is achieved at the absorbed energy density that corresponds to the electronic
energy difference between the metallic and CDW states. The results imply that
on the sub-picosecond timescale when melting and subsequent initial recovery of
the electronic order takes place the lattice remains unperturbed.Comment: Phys. Rev. Lett., accepted for publicatio
Preparation of zirconium from zirconium tetrafluoride
Increased interest in zirconium as a material of construction has resulted in numerous attempts to develop more economical processes for its production. Currently the Kroll Process, which reduces zirconium tetrachloride with magnesium, is used. A process developed at the Ames Laboratory of the Atomic Energy Commission involves the bomb reduction of zirconium tetrafluoride with calcium. By substituting magnesium for calcium, the cost of producing zirconium by this process might be considerably reduced
Photoinduced melting of superconductivity in the high-Tc superconductor La2-xSrxCuO4 probed by time-resolved optical and THz techniques
Dynamics of depletion and recovery of superconducting state in La2-xSrxCuO_4
thin films is investigated utilizing optical pump-probe and optical pump - THz
probe techniques as a function of temperature and excitation fluence. The
absorbed energy density required to suppress superconductivity is found to be
about 8 times higher than the thermodynamically determined condensation energy
density and nearly temperature independent between 4 and 25 K. These findings
indicate that during the time when superconducting state suppression takes
place (~0.7 ps), a large part (nearly 90%) of the energy is transferred to the
phonons with energy lower than twice the maximum value of of the SC gap and
only 10% is spent on Cooper pair breaking.Comment: 8 pages, 5 figure
Investigations of solutions of Einstein's field equations close to lambda-Taub-NUT
We present investigations of a class of solutions of Einstein's field
equations close to the family of lambda-Taub-NUT spacetimes. The studies are
done using a numerical code introduced by the author elsewhere. One of the main
technical complication is due to the S3-topology of the Cauchy surfaces.
Complementing these numerical results with heuristic arguments, we are able to
yield some first insights into the strong cosmic censorship issue and the
conjectures by Belinskii, Khalatnikov, and Lifschitz in this class of
spacetimes. In particular, the current investigations suggest that strong
cosmic censorship holds in this class. We further identify open issues in our
current approach and point to future research projects.Comment: 24 pages, 12 figures, uses psfrag and hyperref; replaced with
published version, only minor corrections of typos and reference
Smooth Gowdy symmetric generalized Taub-NUT solutions
We study a class of S3 Gowdy vacuum models with a regular past Cauchy horizon
which we call smooth Gowdy symmetric generalized Taub-NUT solutions. In
particular, we prove existence of such solutions by formulating a singular
initial value problem with asymptotic data on the past Cauchy horizon. The
result of our investigations is that a future Cauchy horizon exists for generic
asymptotic data. Moreover, we derive an explicit expression for the metric on
the future Cauchy horizon in terms of the asymptotic data on the past horizon.
This complements earlier results about S2xS1 Gowdy models.Comment: 56 pages, 1 figure. The new version contains a detailed explanation
of the Fuchsian method on the 2-spher
Quasilinear hyperbolic Fuchsian systems and AVTD behavior in T2-symmetric vacuum spacetimes
We set up the singular initial value problem for quasilinear hyperbolic
Fuchsian systems of first order and establish an existence and uniqueness
theory for this problem with smooth data and smooth coefficients (and with even
lower regularity). We apply this theory in order to show the existence of
smooth (generally not analytic) T2-symmetric solutions to the vacuum Einstein
equations, which exhibit AVTD (asymptotically velocity term dominated) behavior
in the neighborhood of their singularities and are polarized or half-polarized.Comment: 78 page
Analysis of Different Types of Regret in Continuous Noisy Optimization
The performance measure of an algorithm is a crucial part of its analysis.
The performance can be determined by the study on the convergence rate of the
algorithm in question. It is necessary to study some (hopefully convergent)
sequence that will measure how "good" is the approximated optimum compared to
the real optimum. The concept of Regret is widely used in the bandit literature
for assessing the performance of an algorithm. The same concept is also used in
the framework of optimization algorithms, sometimes under other names or
without a specific name. And the numerical evaluation of convergence rate of
noisy algorithms often involves approximations of regrets. We discuss here two
types of approximations of Simple Regret used in practice for the evaluation of
algorithms for noisy optimization. We use specific algorithms of different
nature and the noisy sphere function to show the following results. The
approximation of Simple Regret, termed here Approximate Simple Regret, used in
some optimization testbeds, fails to estimate the Simple Regret convergence
rate. We also discuss a recent new approximation of Simple Regret, that we term
Robust Simple Regret, and show its advantages and disadvantages.Comment: Genetic and Evolutionary Computation Conference 2016, Jul 2016,
Denver, United States. 201
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