1,966 research outputs found
Levy Flights in Inhomogeneous Media
We investigate the impact of external periodic potentials on superdiffusive
random walks known as Levy flights and show that even strongly superdiffusive
transport is substantially affected by the external field. Unlike ordinary
random walks, Levy flights are surprisingly sensitive to the shape of the
potential while their asymptotic behavior ceases to depend on the Levy index
. Our analysis is based on a novel generalization of the Fokker-Planck
equation suitable for systems in thermal equilibrium. Thus, the results
presented are applicable to the large class of situations in which
superdiffusion is caused by topological complexity, such as diffusion on folded
polymers and scale-free networks.Comment: 4 pages, 4 figure
Particle Dispersion on Rapidly Folding Random Hetero-Polymers
We investigate the dynamics of a particle moving randomly along a disordered
hetero-polymer subjected to rapid conformational changes which induce
superdiffusive motion in chemical coordinates. We study the antagonistic
interplay between the enhanced diffusion and the quenched disorder. The
dispersion speed exhibits universal behavior independent of the folding
statistics. On the other hand it is strongly affected by the structure of the
disordered potential. The results may serve as a reference point for a number
of translocation phenomena observed in biological cells, such as protein
dynamics on DNA strands.Comment: 4 pages, 4 figure
STEPS - an approach for human mobility modeling
In this paper we introduce Spatio-TEmporal Parametric Stepping (STEPS) - a simple parametric mobility model which can cover a large spectrum of human mobility patterns. STEPS makes abstraction of spatio-temporal preferences in human mobility by using a power law to rule the nodes movement. Nodes in STEPS have preferential attachment to favorite locations where they spend most of their time. Via simulations, we show that STEPS is able, not only to express the peer to peer properties such as inter-ontact/contact time and to reflect accurately realistic routing performance, but also to express the structural properties of the underlying interaction graph such as small-world phenomenon. Moreover, STEPS is easy to implement, exible to configure and also theoretically tractable
Relativistic Ring-Diagram Nuclear Matter Calculations
A relativistic extension of the particle-particle hole-hole ring-diagram
many-body formalism is developed by using the Dirac equation for
single-particle motion in the medium. Applying this new formalism, calculations
are performed for nuclear matter. The results show that the saturation density
is improved and the equation of state becomes softer as compared to
corresponding Dirac-Brueckner-Hartree-Fock calculations. Using the Bonn A
potential, nuclear matter is predicted to saturate at an energy per nucleon of
--15.30 MeV and a density equivalent to a Fermi momentum of 1.38 fm, in
excellent agreement with empirical information. The compression modulus is 152
MeV at the saturation point.Comment: 23 pages text (LaTex) and 2 figures (paper, will be faxed upon
request), UI-NTH-92-0
Relativistic heavy ion collisions with realistic non-equilibrium mean fields
We study the influence of non-equilibrium phase space effects on the dynamics
of heavy ion reactions within the relativistic BUU approach. We use realistic
Dirac-Brueckner-Hartree-Fock (DBHF) mean fields determined for
two-Fermi-ellipsoid configurations, i.e. for colliding nuclear matter, in a
local phase space configuration approximation (LCA). We compare to DBHF mean
fields in the local density approximation (LDA) and to the non-linear Walecka
model. The results are further compared to flow data of the reaction on
at 400 MeV per nucleon measured by the FOPI collaboration. We find that
the DBHF fields reproduce the experiment if the configuration dependence is
taken into account. This has also implications on the determination of the
equation of state from heavy ion collisions.Comment: Physics Letters B in press; 10 pages, Postscript file replaced by
Latex file and 3 Postscript figure
The role of caretakers in disease dynamics
One of the key challenges in modeling the dynamics of contagion phenomena is
to understand how the structure of social interactions shapes the time course
of a disease. Complex network theory has provided significant advances in this
context. However, awareness of an epidemic in a population typically yields
behavioral changes that correspond to changes in the network structure on which
the disease evolves. This feedback mechanism has not been investigated in
depth. For example, one would intuitively expect susceptible individuals to
avoid other infecteds. However, doctors treating patients or parents tending
sick children may also increase the amount of contact made with an infecteds,
in an effort to speed up recovery but also exposing themselves to higher risks
of infection. We study the role of these caretaker links in an adaptive network
models where individuals react to a disease by increasing or decreasing the
amount of contact they make with infected individuals. We find that pure
avoidance, with only few caretaker links, is the best strategy for curtailing
an SIS disease in networks that possess a large topological variability. In
more homogeneous networks, disease prevalence is decreased for low
concentrations of caretakers whereas a high prevalence emerges if caretaker
concentration passes a well defined critical value.Comment: 8 pages, 9 figure
Momentum-Dependent Mean Field Based Upon the Dirac-Brueckner Approach for Nuclear Matter
A momentum-dependent mean field potential, suitable for application in the
transport-model description of nucleus-nucleus collisions, is derived in a
microscopic way. The derivation is based upon the Bonn meson-exchange model for
the nucleon-nucleon interaction and the Dirac-Brueckner approach for nuclear
matter. The properties of the microscopic mean field are examined and compared
with phenomenological parametrizations which are commonly used in
transport-model calculations.Comment: 15 pages text (RevTex) and 4 figures (postscript in a separate
uuencoded file), UI-NTH-930
Оценка средней скорости на 10-и метровой глубине для разрезов с высокоскоростным верхним слоем при микрорайонировании
Описываются способы оценки средней скорости поперечной волны на 10-и метровой глубине для разрезов, верхняя часть которых представлена уплотненным насыпным грунтом или мерзлыми породами
Equation of state for nuclear matter based on density dependent effective interaction
An interesting method of obtaining equation of state for nuclear matter, from
a density dependent M3Y interaction, by minimizing the energy per nucleon is
described. The density dependence parameters of the interaction are obtained by
reproducing the saturation energy per nucleon and the saturation density of
spin and isospin symmetric cold infinite nuclear matter. The nuclear matter
equation of state thus obtained is then used to calculate the pressure, the
energy density, the nuclear incompressibility and the velocity of sound in
nuclear medium. The results obtained are in good agreement with experimental
data and provide a unified description of radioactivity, scattering and nuclear
matter.Comment: 10 pages including 2 figure
Quark condensate in nuclear matter based on Nuclear Schwinger-Dyson formalism
The effects of higher order corrections of ring diagrams for the quark
condensate are studied by using the bare vertex Nuclear Schwinger Dyson
formalism based on - model. At the high density the quark
condensate is reduced by the higher order contribution of ring diagrams more
than the mean field theory or the Hartree-Fock
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