1,023 research outputs found
Magnetic particles confined in a modulated channel: structural transitions tunable by tilting a magnetic field
The ground state of colloidal magnetic particles in a modulated channel are
investigated as function of the tilt angle of an applied magnetic field. The
particles are confined by a parabolic potential in the transversal direction
while in the axial direction a periodic substrate potential is present. By
using Monte Carlo (MC) simulations, we construct a phase diagram for the
different crystal structures as a function of the magnetic field orientation,
strength of the modulated potential and the commensurability factor of the
system. Interestingly, we found first and second order phase transitions
between different crystal structures, which can be manipulated by the
orientation of the external magnetic field. A re-entrant behavior is found
between two- and four-chain configurations, with continuous second order
transitions. Novel configurations are found consisting of frozen in solitons.
By changing the orientation and/or strength of the magnetic field and/or the
strength and the spatial frequency of the periodic substrate potential, the
system transits through different phases.Comment: Submitted to Phys. Rev. E (10 pages, 12 figures
Simplifying the mosaic description of DNA sequences
By using the Jensen-Shannon divergence, genomic DNA can be divided into
compositionally distinct domains through a standard recursive segmentation
procedure. Each domain, while significantly different from its neighbours, may
however share compositional similarity with one or more distant
(non--neighbouring) domains. We thus obtain a coarse--grained description of
the given DNA string in terms of a smaller set of distinct domain labels. This
yields a minimal domain description of a given DNA sequence, significantly
reducing its organizational complexity. This procedure gives a new means of
evaluating genomic complexity as one examines organisms ranging from bacteria
to human. The mosaic organization of DNA sequences could have originated from
the insertion of fragments of one genome (the parasite) inside another (the
host), and we present numerical experiments that are suggestive of this
scenario.Comment: 16 pages, 1 figure, Accepted for publication in Phys. Rev.
Finite-sample frequency distributions originating from an equiprobability distribution
Given an equidistribution for probabilities p(i)=1/N, i=1..N. What is the
expected corresponding rank ordered frequency distribution f(i), i=1..N, if an
ensemble of M events is drawn?Comment: 4 pages, 4 figure
Feed-forward Space Vector Modulation for Single-Phase Multilevel Cascade Converters with any DC voltage ratio
Modulation techniques for multilevel converters
can create distorted output voltages and currents if the DC link
voltages are unbalanced. This situation can be avoided if the
instantaneous DC voltage error is not taken into account in the
modulation process. This paper proposes a feed-forward space
vector modulation method for a single-phase multilevel cascade
converter. Using this modulation technique, the modulated output
voltage of the power converter always generates the reference
determined by the controller even in worst case voltage unbalance
conditions. In addition the possibility of optimizing the DC
voltage ratio between the H-bridges of the power converter is
introduced. Experimental results from a 5kVA prototype are
presented in order to validate the proposed modulation technique
Stabilized Schemes for the Hydrostatic Stokes Equations
Some new stable finite element (FE) schemes are presented for the hydrostatic Stokes
system or primitive equations of the ocean. It is known that the stability of the mixed formulation ap-
proximation for primitive equations requires the well-known Ladyzhenskaya–Babuˇska–Brezzi condi-
tion related to the Stokes problem and an extra inf-sup condition relating the pressure and the vertical
velocity.
The main goal of this paper is to avoid this extra condition by adding a residual stabilizing term to the
vertical momentum equation. Then, the stability for Stokes-stable FE combinations is extended to
the primitive equations and some error estimates are provided using Taylor–Hood P2 –P1 or miniele-
ment (P1 +bubble)–P1 FE approximations, showing the optimal convergence rate in the P2 –P1 case.
These results are also extended to the anisotropic (nonhydrostatic) problem. On the other hand,
by adding another residual term to the continuity equation, a better approximation of the vertical
derivative of pressure is obtained. In this case, stability and error estimates including this better
approximation are deduced, where optimal convergence rate is deduced in the (P 1 +bubble)–P1 case.
Finally, some numerical experiments are presented supporting previous results
A three-level common-mode voltage eliminated inverter with single dc supply using flying capacitor inverter and cascaded H-bridge
A three-level common-mode voltage eliminated in-
verter with single dc supply using flying capacitor inverter and
cascaded H-bridge has been proposed in this paper. The three
phase space vector polygon formed by this configuration and the
polygon formed by the common-mode eliminated states have been
discussed. The entire system is simulated in Simulink and the re-
sults are experimentally verified. This system has an advantage that
if one of devices in the H-bridge fails, the system can still be oper-
ated as a normal three-level inverter at full power. This inverter has
many other advantages like use of single dc supply, making it pos-
sible for a back-to-back grid-tied converter application, improved
reliability, etc
New stopping criteria for segmenting DNA sequences
We propose a solution on the stopping criterion in segmenting inhomogeneous
DNA sequences with complex statistical patterns. This new stopping criterion is
based on Bayesian Information Criterion (BIC) in the model selection framework.
When this stopping criterion is applied to a left telomere sequence of yeast
Saccharomyces cerevisiae and the complete genome sequence of bacterium
Escherichia coli, borders of biologically meaningful units were identified
(e.g. subtelomeric units, replication origin, and replication terminus), and a
more reasonable number of domains was obtained. We also introduce a measure
called segmentation strength which can be used to control the delineation of
large domains. The relationship between the average domain size and the
threshold of segmentation strength is determined for several genome sequences.Comment: 4 pages, 4 figures, Physical Review Letters, to appea
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