10,961 research outputs found
Fragmentation paths in dynamical models
We undertake a quantitative comparison of multi-fragmentation reactions, as
modeled by two different approaches: the Antisymmetrized Molecular Dynamics
(AMD) and the momentum-dependent stochastic mean-field (SMF) model. Fragment
observables and pre-equilibrium (nucleon and light cluster) emission are
analyzed, in connection to the underlying compression-expansion dynamics in
each model. Considering reactions between neutron-rich systems, observables
related to the isotopic properties of emitted particles and fragments are also
discussed, as a function of the parametrization employed for the isovector part
of the nuclear interaction. We find that the reaction path, particularly the
mechanism of fragmentation, is different in the two models and reflects on some
properties of the reaction products, including their isospin content. This
should be taken into account in the study of the density dependence of the
symmetry energy from such collisions.Comment: 11 pages, 13 figures, submitted to Phys. Rev.
The Changing Composition of American-Citizen PhDs
We describe patterns in the composition of American-citizen doctorate recipients from the early 1960s to 2000. The propensity of bachelorâs degree recipients to earn PhDs varied widely during the 1960s and 1970s, especially for men, but has been relatively constant since the early 1980s. PhD propensity varies widely across students from different types of BA institutions, with higher propensities among those attending research universities and selective liberal-arts colleges. The share of PhDs awarded to women increased dramatically over the past 40 years and was driven largely by increases in the number of women earning BAs
NEW PARTICLES AND INTERACTIONS
We analyze the manifestations of new matter particles predicted by models of
new physics beyond the Standard Model, at present and future high--energy
colliders. We consider both the production of these new particles and some of
their indirect signatures at and colliders as well as TeV \ee
colliders with their \ee, e \gamma, \gamma \gamma and modes. The
report is arranged into four main sections plus an overview. These sections
will deal separately with exotic and excited fermions, difermions, and new
interactions.Comment: 64 pages, latex, 30 figures (not included). The full *.ps file
including the figures can be obtained via anonymous ftp at
ftp://lpsvsh.lps.umontreal.ca/hep_th/dpf.ps . To appear as a chapter in
"Electroweak Symmetry Breaking and Beyond the Standard Model", edited by T.
Barklow, S. Dawson, H.E. Haber and S. Siegrist, World Scientifi
Observation of the Inverse Cotton-Mouton Effect
We report the observation of the Inverse Cotton-Mouton Effect (ICME) i.e. a
magnetization induced in a medium by non resonant linearly polarized light
propagating in the presence of a transverse magnetic field. We present a
detailed study of the ICME in a TGG crystal showing the dependence of the
measured effect on the light intensity, the optical polarization, and on the
external magnetic field. We derive a relation between the Cotton-Mouton and
Inverse Cotton-Mouton effects that is roughly in agreement with existing
experimental data. Our results open the way to applications of the ICME in
optical devices
Comparison of dynamical multifragmentation models
Multifragmentation scenarios, as predicted by antisymmetrized molecular
dynamics (AMD) or momentum-dependent stochastic mean-field (BGBD) calculations
are compared. While in the BGBD case fragment emission is clearly linked to the
spinodal decomposition mechanism, i.e. to mean-field instabilities, in AMD
many-body correlations have a stronger impact on the fragmentation dynamics and
clusters start to appear at earlier times. As a consequence, fragments are
formed on shorter time scales in AMD, on about equal footing of light particle
pre-equilibrium emission. Conversely, in BGBD pre-equilibrium and fragment
emissions happen on different time scales and are related to different
mechanisms
Quenched Computation of the Complexity of the Sherrington-Kirkpatrick Model
The quenched computation of the complexity in the
Sherrington-Kirkpatrick model is presented. A modified Full Replica
Symmetry Breaking Ansatz is introduced in order to study the complexity
dependence on the free energy. Such an Ansatz corresponds to require
Becchi-Rouet-Stora-Tyutin supersymmetry. The complexity computed this way is
the Legendre transform of the free energy averaged over the quenched disorder.
The stability analysis shows that this complexity is inconsistent at any free
energy level but the equilibirum one. The further problem of building a
physically well defined solution not invariant under supersymmetry and
predicting an extensive number of metastable states is also discussed.Comment: 19 pages, 13 figures. Some formulas added corrected, changes in
discussion and conclusion, one figure adde
Dependency-aware unequal erasure protection codes
Classical unequal erasure protection schemes split data to be protected into classes which are encoded independently. The unequal protection scheme presented in this paper is based on an erasure code which encodes all the data together according to the existing dependencies. A simple algorithm generates dynamically the generator matrix of the erasure code according to the packets streams structure, i.e., the dependencies between the packets, and the rate of the code. This proposed erasure code was applied to a packetized MPEG4 stream transmitted over a packet erasure channel and compared with other classical protection schemes in terms of PSNR and MOS. It is shown that the proposed code allows keeping a high video quality-level in a larger packet loss rate range than the other protection schemes
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