8,493 research outputs found
Trajectory Splitting by Restricted Replication
New algorithms for efficient trajectory splitting are presented. By derandomizing
these techniques that are derived from randomized quasi-Monte Carlo integration,
trajectory splitting for the quasi-Monte Carlo method becomes available
JohnnyVon: Self-Replicating Automata in Continuous Two-Dimensional Space
JohnnyVon is an implementation of self-replicating automata in continuous two-dimensional space. Two types of particles drift about in a virtual liquid. The particles are automata with discrete internal states but continuous external relationships. Their internal states are governed by finite state machines but their external relationships are governed by a simulated physics that includes brownian motion, viscosity, and spring-like attractive and repulsive forces. The particles can be assembled into patterns that can encode arbitrary strings of bits. We demonstrate that, if an arbitrary “seed” pattern is put in a “soup” of separate individual particles, the pattern will replicate by assembling the individual particles into copies of itself. We also show that, given sufficient time, a soup of separate individual particles will eventually spontaneously form self-replicating patterns. We discuss the implications of JohnnyVon for research in nanotechnology, theoretical biology, and artificial life
Stochastic Methods for Zero Energy Quantum Scattering
We investigate the use of stochastic methods for zero energy quantum
scattering based on a path integral approach. With the application to the
scattering of a projectile from a nuclear many body target in mind, we use the
potential scattering of a particle as a test for the accuracy and efficiency of
several methods. To be able to deal with complex potentials, we introduce a
path sampling action and a modified scattering observable. The approaches
considered are the random walk, where the points of a path are sequentially
generated, and the Langevin algorithm, which updates an entire path. Several
improvements are investigated. A cluster algorithm for dealing with scattering
problems is finally proposed, which shows the best accuracy and stability.Comment: 40 pages LaTeX, 1 Postscript file containig 20 figures; execute
main.tex file, which automatically will include other file
Self-Replicating Machines in Continuous Space with Virtual Physics
JohnnyVon is an implementation of self-replicating machines in
continuous two-dimensional space. Two types of particles drift
about in a virtual liquid. The particles are automata with
discrete internal states but continuous external relationships.
Their internal states are governed by finite state machines but
their external relationships are governed by a simulated physics
that includes Brownian motion, viscosity, and spring-like attractive
and repulsive forces. The particles can be assembled into patterns
that can encode arbitrary strings of bits. We demonstrate that, if
an arbitrary "seed" pattern is put in a "soup" of separate individual
particles, the pattern will replicate by assembling the individual
particles into copies of itself. We also show that, given sufficient
time, a soup of separate individual particles will eventually
spontaneously form self-replicating patterns. We discuss the implications
of JohnnyVon for research in nanotechnology, theoretical biology, and
artificial life
Variance Reduction Techniques in Monte Carlo Methods
Monte Carlo methods are simulation algorithms to estimate a numerical quantity in a statistical model of a real system. These algorithms are executed by computer programs. Variance reduction techniques (VRT) are needed, even though computer speed has been increasing dramatically, ever since the introduction of computers. This increased computer power has stimulated simulation analysts to develop ever more realistic models, so that the net result has not been faster execution of simulation experiments; e.g., some modern simulation models need hours or days for a single ’run’ (one replication of one scenario or combination of simulation input values). Moreover there are some simulation models that represent rare events which have extremely small probabilities of occurrence), so even modern computer would take ’for ever’ (centuries) to execute a single run - were it not that special VRT can reduce theses excessively long runtimes to practical magnitudes.common random numbers;antithetic random numbers;importance sampling;control variates;conditioning;stratied sampling;splitting;quasi Monte Carlo
Subthreshold oscillations in a map-based neuron model
Self-sustained subthreshold oscillations in a discrete-time model of neuronal
behavior are considered. We discuss bifurcation scenarios explaining the birth
of these oscillations and their transformation into tonic spikes. Specific
features of these transitions caused by the discrete-time dynamics of the model
and the influence of external noise are discussed.Comment: To be published in Physics Letters
Analysis of Interphase Chromatin Motion in HeLa Cells
Motion of particles under influencing forces may be observed under light microscopy techniques. Variations in mobility of particles may give relevant biophysical information. Automated high resolution single particle tracking techniques were used to characterize interphase chromatin mobility in the cell nucleus. Interphase chromatin undergo replication prior to cell division with the assistance of replication proteins (machinery) which modify chromatin mobility. Using dual color imaging of flourescently tagged chromatin and proliferating cell nuclear antigen (PCNA) were followed through interphase. Chromatin motion was modelled as a two dimensional random walk. Reduction in chromatin mobility was observed during S phase was dependent on proximity to the replication machinery. Mobility during G1 and G2 phase is independent of proximity to GFP-PCNA maxima and is higher than during S phase. These results suggest that replication selectively inhibits chromatin mobility. Local proximity to replication machinery however, cannot account for the entire mobility difference. By modelling the mean square displacement as a power law, sub-diffusive behavior was observed in S phase chromatin whereas non S phase exhibited normal diffusional characteristics
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