2,970 research outputs found
Dirac fermions in a power-law-correlated random vector potential
We study localization properties of two-dimensional Dirac fermions subject to
a power-law-correlated random vector potential describing, e.g., the effect of
"ripples" in graphene. By using a variety of techniques (low-order perturbation
theory, self-consistent Born approximation, replicas, and supersymmetry) we
make a case for a possible complete localization of all the electronic states
and compute the density of states.Comment: Latex, 4+ page
On the structure of non-full-rank perfect codes
The Krotov combining construction of perfect 1-error-correcting binary codes
from 2000 and a theorem of Heden saying that every non-full-rank perfect
1-error-correcting binary code can be constructed by this combining
construction is generalized to the -ary case. Simply, every non-full-rank
perfect code is the union of a well-defined family of -components
, where belongs to an "outer" perfect code , and these
components are at distance three from each other. Components from distinct
codes can thus freely be combined to obtain new perfect codes. The Phelps
general product construction of perfect binary code from 1984 is generalized to
obtain -components, and new lower bounds on the number of perfect
1-error-correcting -ary codes are presented.Comment: 8 page
Experimental Studies of Compensation of Beam-Beam Effects with Tevatron Electron Lenses
Applying the space-charge forces of a low-energy electron beam can lead to a significant improvement of the beam-particle lifetime limit arising from the beam-beam interaction in a high-energy collider [1]. In this article we present the results of various beam experiments with electron lenses, novel instruments developed for the beam-beam compensation at the Tevatron, which collides 980-GeV proton and antiproton beams. We study the dependencies of the particle betatron tunes on the electron beam current, energy and position; we explore the effects of electron-beam imperfections and noises; and we quantify the improvements of the high-energy beam intensity and the collider luminosity lifetime obtained by the action of the Tevatron Electron Lenses.Applying the space-charge forces of a low-energy electron beam can lead to a significant improvement of the beam-particle lifetime limit arising from the beam-beam interaction in a high-energy collider [1]. In this article we present the results of various beam experiments with electron lenses, novel instruments developed for the beam-beam compensation at the Tevatron, which collides 980-GeV proton and antiproton beams. We study the dependencies of the particle betatron tunes on the electron beam current, energy and position/ we explore the effects of electron-beam imperfections and noises/ and we quantify the improvements of the high-energy beam intensity and the collider luminosity lifetime obtained by the action of the Tevatron Electron Lenses
Nonequilibrium wetting
When a nonequilibrium growing interface in the presence of a wall is
considered a nonequilibrium wetting transition may take place. This transition
can be studied trough Langevin equations or discrete growth models. In the
first case, the Kardar-Parisi-Zhang equation, which defines a very robust
universality class for nonequilibrium moving interfaces, with a soft-wall
potential is considered. While in the second, microscopic models, in the
corresponding universality class, with evaporation and deposition of particles
in the presence of hard-wall are studied. Equilibrium wetting is related to a
particular case of the problem, it corresponds to the Edwards-Wilkinson
equation with a potential in the continuum approach or to the fulfillment of
detailed balance in the microscopic models. In this review we present the
analytical and numerical methods used to investigate the problem and the very
rich behavior that is observed with them.Comment: Review, 36 pages, 16 figure
Non-equilibrium Phase Transitions with Long-Range Interactions
This review article gives an overview of recent progress in the field of
non-equilibrium phase transitions into absorbing states with long-range
interactions. It focuses on two possible types of long-range interactions. The
first one is to replace nearest-neighbor couplings by unrestricted Levy flights
with a power-law distribution P(r) ~ r^(-d-sigma) controlled by an exponent
sigma. Similarly, the temporal evolution can be modified by introducing waiting
times Dt between subsequent moves which are distributed algebraically as P(Dt)~
(Dt)^(-1-kappa). It turns out that such systems with Levy-distributed
long-range interactions still exhibit a continuous phase transition with
critical exponents varying continuously with sigma and/or kappa in certain
ranges of the parameter space. In a field-theoretical framework such
algebraically distributed long-range interactions can be accounted for by
replacing the differential operators nabla^2 and d/dt with fractional
derivatives nabla^sigma and (d/dt)^kappa. As another possibility, one may
introduce algebraically decaying long-range interactions which cannot exceed
the actual distance to the nearest particle. Such interactions are motivated by
studies of non-equilibrium growth processes and may be interpreted as Levy
flights cut off at the actual distance to the nearest particle. In the
continuum limit such truncated Levy flights can be described to leading order
by terms involving fractional powers of the density field while the
differential operators remain short-ranged.Comment: LaTeX, 39 pages, 13 figures, minor revision
Exploring the Galaxy at TeV energies: Latest results from the H.E.S.S. Galactic Plane Survey
The High Energy Stereoscopic System (H.E.S.S.) is an array of four imaging
atmospheric-Cherenkov telescopes located in Namibia and designed to detect
extensive air showers initiated by gamma-rays in the very-high-energy domain.
It is an ideal instrument for surveying the Galactic plane in search of new
sources, thanks to its location in the Southern Hemisphere, its excellent
sensitivity, and its large field-of-view. The efforts of the H.E.S.S. Galactic
Plane Survey, the first comprehensive survey of the inner Galaxy at TeV
energies, have contributed to the discovery of an unexpectedly large and
diverse population of over 60 sources of VHE gamma rays within its current
range of l=250 to 65 degrees in longitude and |b|<=3.5 degrees in latitude. The
population of VHE gamma-ray emitters is dominated by the pulsar wind nebula and
supernova remnant source classes, although nearly a third remain unidentified
or confused.
The sensitivity of H.E.S.S. to sources in the inner Galaxy has improved
significantly over the past two years, from continued survey observations,
dedicated follow-up observations of interesting source candidates, and from the
development of advanced methods for discrimination of gamma-ray-induced showers
from the dominant background of hadron-induced showers. The latest maps of the
Galaxy at TeV energies will be presented, and a few remarkable new sources will
be highlighted.Comment: 4 pages, 2 figures, appears in the Proceedings of the 32nd
International Cosmic Ray Conference (ICRC 2011), Beijing, China, 11th to 18th
August 201
On the origin of the Boson peak in globular proteins
We study the Boson Peak phenomenology experimentally observed in globular
proteins by means of elastic network models. These models are suitable for an
analytic treatment in the framework of Euclidean Random Matrix theory, whose
predictions can be numerically tested on real proteins structures. We find that
the emergence of the Boson Peak is strictly related to an intrinsic mechanical
instability of the protein, in close similarity to what is thought to happen in
glasses. The biological implications of this conclusion are also discussed by
focusing on a representative case study.Comment: Proceedings of the X International Workshop on Disordered Systems,
Molveno (2006
- …