1,139 research outputs found
The SiRi Particle-Telescope System
A silicon particle-telescope system for light-ion nuclear reactions is
described. In particular, the system is designed to be optimized for level
density and gamma-ray strength function measurements with the so-called Oslo
method. Eight trapezoidal modules are mounted at 5 cm distance from the target,
covering 8 forward angles between theta = 40 and 54 degrees. The thin front dE
detectors (130 micrometer) are segmented into eight pads, determining the
reaction angle for the outgoing charged ejectile. Guard rings on the thick back
E detectors (1550 micrometer) guarantee low leakage current at high depletion
voltage.Comment: 6 pages, 8 figure
Temporal and dimensional effects in evolutionary graph theory
The spread in time of a mutation through a population is studied analytically
and computationally in fully-connected networks and on spatial lattices. The
time, t_*, for a favourable mutation to dominate scales with population size N
as N^{(D+1)/D} in D-dimensional hypercubic lattices and as N ln N in
fully-connected graphs. It is shown that the surface of the interface between
mutants and non-mutants is crucial in predicting the dynamics of the system.
Network topology has a significant effect on the equilibrium fitness of a
simple population model incorporating multiple mutations and sexual
reproduction. Includes supplementary information.Comment: 6 pages, 4 figures Replaced after final round of peer revie
String breaking in Lattice QCD
The separation of a heavy quark and antiquark pair leads to the formation of
a tube of flux, or string, which should break in the presence of light
quark-antiquark pairs. This expected zero temperature phenomenon has proven
elusive in simulations of lattice QCD. We present simulation results that show
that the string does break in the confining phase at nonzero temperature.Comment: LATTICE98(hightemp), 3 pages, 4 figures, LaTe
Observation of large scissors resonance strength in actinides
The orbital M1-scissors resonance (SR) has been measured for the first time
in the quasi-continuum of actinides. Particle-gamma coincidences are recorded
with deuteron and 3He induced reactions on 232Th. The residual nuclei
231,232,233Th and 232,233Pa show an unexpectedly strong integrated strength of
in the Egamma=1.0 - 3.5 MeV region. The increased
gamma-decay probability in actinides due to the SR is important for
cross-section calculations for future fuel cycles of fast nuclear reactors and
may also have impact on stellar nucleosynthesis.Comment: 5 pages and 4 figure
Maximum principle and mutation thresholds for four-letter sequence evolution
A four-state mutation-selection model for the evolution of populations of
DNA-sequences is investigated with particular interest in the phenomenon of
error thresholds. The mutation model considered is the Kimura 3ST mutation
scheme, fitness functions, which determine the selection process, come from the
permutation-invariant class. Error thresholds can be found for various fitness
functions, the phase diagrams are more interesting than for equivalent
two-state models. Results for (small) finite sequence lengths are compared with
those for infinite sequence length, obtained via a maximum principle that is
equivalent to the principle of minimal free energy in physics.Comment: 25 pages, 16 figure
Fully adaptive multiresolution schemes for strongly degenerate parabolic equations with discontinuous flux
A fully adaptive finite volume multiresolution scheme for one-dimensional
strongly degenerate parabolic equations with discontinuous flux is presented.
The numerical scheme is based on a finite volume discretization using the
Engquist--Osher approximation for the flux and explicit time--stepping. An
adaptivemultiresolution scheme with cell averages is then used to speed up CPU
time and meet memory requirements. A particular feature of our scheme is the
storage of the multiresolution representation of the solution in a dynamic
graded tree, for the sake of data compression and to facilitate navigation.
Applications to traffic flow with driver reaction and a clarifier--thickener
model illustrate the efficiency of this method
Schwinger Boson Formulation and Solution of the Crow-Kimura and Eigen Models of Quasispecies Theory
We express the Crow-Kimura and Eigen models of quasispecies theory in a
functional integral representation. We formulate the spin coherent state
functional integrals using the Schwinger Boson method. In this formulation, we
are able to deduce the long-time behavior of these models for arbitrary
replication and degradation functions.
We discuss the phase transitions that occur in these models as a function of
mutation rate. We derive for these models the leading order corrections to the
infinite genome length limit.Comment: 37 pages; 4 figures; to appear in J. Stat. Phy
Single-crossover dynamics: finite versus infinite populations
Populations evolving under the joint influence of recombination and
resampling (traditionally known as genetic drift) are investigated. First, we
summarise and adapt a deterministic approach, as valid for infinite
populations, which assumes continuous time and single crossover events. The
corresponding nonlinear system of differential equations permits a closed
solution, both in terms of the type frequencies and via linkage disequilibria
of all orders. To include stochastic effects, we then consider the
corresponding finite-population model, the Moran model with single crossovers,
and examine it both analytically and by means of simulations. Particular
emphasis is on the connection with the deterministic solution. If there is only
recombination and every pair of recombined offspring replaces their pair of
parents (i.e., there is no resampling), then the {\em expected} type
frequencies in the finite population, of arbitrary size, equal the type
frequencies in the infinite population. If resampling is included, the
stochastic process converges, in the infinite-population limit, to the
deterministic dynamics, which turns out to be a good approximation already for
populations of moderate size.Comment: 21 pages, 4 figure
Multimedia Vocabularies on the Semantic Web
This document gives an overview on the state-of-the-art of multimedia metadata formats. Initially, practical relevant vocabularies for developers of Semantic Web applications are listed according to their modality scope. In the second part of this document, the focus is set on the integration of the multimedia vocabularies into the Semantic Web, that is to say, formal representations of the vocabularies are discussed
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