3,248 research outputs found
Experimental and theoretical studies of sequence effects on the fluctuation and melting of short DNA molecules
Understanding the melting of short DNA sequences probes DNA at the scale of
the genetic code and raises questions which are very different from those posed
by very long sequences, which have been extensively studied. We investigate
this problem by combining experiments and theory. A new experimental method
allows us to make a mapping of the opening of the guanines along the sequence
as a function of temperature. The results indicate that non-local effects may
be important in DNA because an AT-rich region is able to influence the opening
of a base pair which is about 10 base pairs away. An earlier mesoscopic model
of DNA is modified to correctly describe the time scales associated to the
opening of individual base pairs well below melting, and to properly take into
account the sequence. Using this model to analyze some characteristic sequences
for which detailed experimental data on the melting is available [Montrichok et
al. 2003 Europhys. Lett. {\bf 62} 452], we show that we have to introduce
non-local effects of AT-rich regions to get acceptable results. This brings a
second indication that the influence of these highly fluctuating regions of DNA
on their neighborhood can extend to some distance.Comment: To be published in J. Phys. Condensed Matte
Continuous phase transition in polydisperse hard-sphere mixture
In a previous paper (J. Zhang {\it et al.}, J. Chem. Phys. {\bf 110}, 5318
(1999)) we introduced a model for polydisperse hard sphere mixtures that is
able to adjust its particle-size distribution. Here we give the explanation of
the questions that arose in the previous description and present a consistent
theory of the phase transition in this system, based on the Percus-Yevick
equation of state. The transition is continuous, and like Bose-Einstein
condensation a macroscopic aggregate is formed due to the microscopic
interactions. A BMCSL-like treatment leads to the same conclusion with slightly
more accurate predictions.Comment: 7 pages including 5 figures in revte
Experiences with a simplified microsimulation for the Dallas/Fort Worth area
We describe a simple framework for micro simulation of city traffic. A medium
sized excerpt of Dallas was used to examine different levels of simulation
fidelity of a cellular automaton method for the traffic flow simulation and a
simple intersection model. We point out problems arising with the granular
structure of the underlying rules of motion.Comment: accepted by Int.J.Mod.Phys.C, 20 pages, 14 figure
A Cellular Automaton Model for Bi-Directionnal Traffic
We investigate a cellular automaton (CA) model of traffic on a bi-directional
two-lane road. Our model is an extension of the one-lane CA model of {Nagel and
Schreckenberg 1992}, modified to account for interactions mediated by passing,
and for a distribution of vehicle speeds. We chose values for the various
parameters to approximate the behavior of real traffic. The density-flow
diagram for the bi-directional model is compared to that of a one-lane model,
showing the interaction of the two lanes. Results were also compared to
experimental data, showing close agreement. This model helps bridge the gap
between simplified cellular automata models and the complexity of real-world
traffic.Comment: 4 pages 6 figures. Accepted Phys Rev
Non-scattering Metasurface-bound Cavities for Field Localization, Enhancement, and Suppression
We propose and analyse metasurface-bound invisible (non-scattering) partially
open cavities where the inside field distribution can be engineered. It is
demonstrated both theoretically and experimentally that the cavities exhibit
unidirectional invisibility at the operating frequency with enhanced or
suppressed field at different positions inside the cavity volume. Several
examples of applications of the designed cavities are proposed and analyzed, in
particular, cloaking sensors and obstacles, enhancement of emission, and
"invisible waveguides". The non-scattering mode excited in the proposed cavity
is driven by the incident wave and resembles an ideal bound state in the
continuum of electromagnetic frequency spectrum. In contrast to known bound
states in the continuum, the mode can stay localized in the cavity infinitely
long, provided that the incident wave illuminates the cavity
Cluster density functional theory for lattice models based on the theory of Mobius functions
Rosenfeld's fundamental measure theory for lattice models is given a rigorous
formulation in terms of the theory of Mobius functions of partially ordered
sets. The free-energy density functional is expressed as an expansion in a
finite set of lattice clusters. This set is endowed a partial order, so that
the coefficients of the cluster expansion are connected to its Mobius function.
Because of this, it is rigorously proven that a unique such expansion exists
for any lattice model. The low-density analysis of the free-energy functional
motivates a redefinition of the basic clusters (zero-dimensional cavities)
which guarantees a correct zero-density limit of the pair and triplet direct
correlation functions. This new definition extends Rosenfeld's theory to
lattice model with any kind of short-range interaction (repulsive or
attractive, hard or soft, one- or multi-component...). Finally, a proof is
given that these functionals have a consistent dimensional reduction, i.e. the
functional for dimension d' can be obtained from that for dimension d (d'<d) if
the latter is evaluated at a density profile confined to a d'-dimensional
subset.Comment: 21 pages, 2 figures, uses iopart.cls, as well as diagrams.sty
(included
Coherent Retroreflective Metasurfaces
Inhomogeneous metasurfaces have shown possibilities for unprecedented control
of wave propagation and scattering. While it is conventional to shine a single
incident plane wave from one side of these metastructures, illuminating by
several waves simultaneously from both sides may enhance possibilities to
control scattered waves, which results in additional functionalities and novel
applications. Here, we unveil how using coherent plane-wave illumination of a
properly designed inhomogeneous metasurface sheet it is possible to realize
controllable retroreflection. We call these metasurfaces as "coherent
retroreflectors" and explain the method for realizing them both in theory and
practice. We show that coherent retroreflectors can be used for filtering
undesired modes and creation of field-localization regions in waveguides. The
latter application is in resemblance to bound states in the radiation
continuum.Comment: 6 pages, 4 figure
Effects of CPT and Lorentz Invariance Violation on Pulsar Kicks
The breakdown of Lorentz's and CPT invariance, as described by the Extension
of the Standard Model, gives rise to a modification of the dispersion relation
of particles. Consequences of such a modification are reviewed in the framework
of pulsar kicks induced by neutrino oscillations (active-sterile conversion). A
peculiar feature of the modified energy-momentum relations is the occurrence of
terms of the form \delta {\bbox \Pi}\cdot {\bf {\hat p}}, where \delta
{\bbox \Pi} accounts for the difference of spatial components of flavor
depending coefficients which lead to the departure of the Lorentz symmetry, and
, being the neutrino momentum. Owing to the
relative orientation of with respect to \delta {\bbox \Pi}, the
{\it coupling} \delta {\bbox \Pi}\cdot {\bf {\hat p}} may induce the
mechanism to generate the observed pulsar velocities. Topics related to the
velocity distribution of pulsars are also discussed.Comment: 10 pages, 1 figur
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