43,702 research outputs found
Spectral-discrete solitons and localization in frequency space
We report families of discrete optical solitons in frequency space, or
spectral-discrete solitons existing in a dispersive Raman medium, where
individual side-bands are coupled by coherence. The associated time-domain
patterns correspond to either trains of ultrashort pulses, or weakly modulated
waves. We describe the physics behind the spectral localization and study
soliton bifurcations, stability and dynamics.Comment: 4 pages, 4 figures, submitted to Opt. Let
A model for the accidental catalysis of protein unfolding in vivo
Activated processes such as protein unfolding are highly sensitive to
heterogeneity in the environment. We study a highly simplified model of a
protein in a random heterogeneous environment, a model of the in vivo
environment. It is found that if the heterogeneity is sufficiently large the
total rate of the process is essentially a random variable; this may be the
cause of the species-to-species variability in the rate of prion protein
conversion found by Deleault et al. [Nature, 425 (2003) 717].Comment: 5 pages, 2 figure
QCD-supression by Black Hole Production at the LHC
Possible consequences of the production of small black holes at the LHC for
different scenarios with large extra dimensions are investigated. The effects
from black hole production on some standard jet observables are examined,
concentrating on the reduction of the QCD cross section. It is found that black
hole production of partons interacting on a short enough distance indeed seem
to generate a drastic drop in the QCD cross section. However from an
experimental point of view this will in most cases be camouflaged by energetic
radiation from the black holes
Generation of continuous-wave THz radiation by use of quantum interference
We propose a scheme for generation of continuous-wave THz radiation. The
scheme requires a medium where three discrete states in a
configuration can be selected, with the THz-frequency transition between the
two lower metastable states. We consider the propagation of three-frequency
continuous-wave electromagnetic (e.m.) radiation through a medium.
Under resonant excitation, the medium absorption can be strongly reduced due to
quantum interference of transitions, while the nonlinear susceptibility is
enhanced. This leads to very efficient energy transfer between the e.m. waves
providing a possibility for THz generation. We demonstrate that the photon
conversion efficiency is approaching unity in this technique.Comment: 18 pages, 4 figure
Storage of light in atomic vapor
We report an experiment in which a light pulse is decelerated and trapped in
a vapor of Rb atoms, stored for a controlled period of time, and then released
on demand. We accomplish this storage of light by dynamically reducing the
group velocity of the light pulse to zero, so that the coherent excitation of
the light is reversibly mapped into a collective Zeeman (spin) coherence of the
Rb vapor
Linearizability with Ownership Transfer
Linearizability is a commonly accepted notion of correctness for libraries of
concurrent algorithms. Unfortunately, it assumes a complete isolation between a
library and its client, with interactions limited to passing values of a given
data type. This is inappropriate for common programming languages, where
libraries and their clients can communicate via the heap, transferring the
ownership of data structures, and can even run in a shared address space
without any memory protection. In this paper, we present the first definition
of linearizability that lifts this limitation and establish an Abstraction
Theorem: while proving a property of a client of a concurrent library, we can
soundly replace the library by its abstract implementation related to the
original one by our generalisation of linearizability. This allows abstracting
from the details of the library implementation while reasoning about the
client. We also prove that linearizability with ownership transfer can be
derived from the classical one if the library does not access some of data
structures transferred to it by the client
Stream gaging control structure for the Rio Grande conveyance channel near Bernardo, New Mexico
CER61EVR42.June 1961.Includes bibliographical references (page 23)
Quantum nano-electromechanics with electrons, quasiparticles and Cooper pairs: effective bath descriptions and strong feedback effects
Using a quantum noise approach, we discuss the physics of both normal metal
and superconducting single electron transistors (SET) coupled to mechanical
resonators. Particular attention is paid to the regime where transport occurs
via incoherent Cooper-pair tunneling (either via the Josephson quasiparticle
(JQP) or double Josephson quasiparticle (DJQP) process). We show that,
surprisingly, the back-action of tunneling Cooper pairs (or superconducting
quasiparticles) can be used to significantly cool the oscillator. We also
discuss the physical origin of negative damping effects in this system, and how
they can lead to a regime of strong electro-mechanical feedback, where despite
a weak SET - oscillator coupling, the motion of the oscillator strongly effects
the tunneling of the Cooper pairs. We show that in this regime, the oscillator
is characterized by an energy-dependent effective temperature. Finally, we
discuss the strong analogy between back-action effects of incoherent
Cooper-pair tunneling and ponderomotive effects in an optical cavity with a
moveable mirror; in our case, tunneling Cooper pairs play the role of the
cavity photons.Comment: 27 pages, 7 figures; submitted to the New Journal of Physics focus
issue on Nano-electromechanical Systems; error in references correcte
Deep ROSAT-HRI observations of the NGC 1399/NGC 1404 region: morphology and structure of the X-ray halo
We present the analysis of a deep (167 ks) ROSAT HRI observation of the cD
galaxy NGC 1399 in the Fornax cluster. Using both HRI and, at larger radii,
archival PSPC data, we find that the radial behavior of the X-ray surface
brightness profile is not consistent with a simple Beta model and suggests
instead three distinct components. We use a multi-component bidimensional model
to study in detail these three components that we identify respectively with
the cooling flow region, the galactic and the cluster halo. From these data we
derive a binding mass distribution in agreement with that suggested by optical
dynamical indicators, with an inner core dominated by luminous matter and an
extended dark halo differently distributed on galactic and cluster scales. The
HRI data and a preliminary analysis of Chandra public data, allow us to detect
significant density fluctuations in the halo. We discuss possible
non-equilibrium scenarios to explain the hot halo structure, including tidal
interactions with neighboring galaxies, ram stripping from the intra-cluster
medium and merging events. In the innermost region of NGC 1399, the comparison
between the X-ray and radio emission suggests that the radio emitting plasma is
displacing and producing shocks in the hot X-ray emitting gas. We found that
the NGC 1404 halo is well represented by a single symmetric Beta model and
follows the stellar light profile within the inner 8 kpc. The mass distribution
is similar to the `central' component of the NGC 1399 halo. At larger radii ram
pressure stripping from the intra-cluster medium produces strong asymmetries in
the gas distribution. Finally we discuss the properties of the point source
population finding evidence of correlation between the source excess and NGC
1399.Comment: 34 pages in aastex5.0 format, including 28 B&W and 4 color figures.
Uses LaTex packages: subfigure, lscape and psfig. Accepted for publication in
ApJ. High resolution version can be found at:
http://www.na.astro.it/~paolillo/publications.htm
Magnetoelectric Effects on Composite Nano Granular Films
Employing a new experimental technique to measure magnetoelectric response
functions, we have measured the magnetoelectric effect in composite films of
nano granular metallic iron in anatase titanium dioxide at temperatures below
50 K. A magnetoelectric resistance is defined as the ratio of a transverse
voltage to bias current as a function of the magnetic field. In contrast to the
anomalous Hall resistance measured above 50 K, the magnetoelectic resistance
below 50 K is significantly larger and exhibits an even symmetry with respect
to magnetic field reversal . The measurement technique required
attached electrodes in the plane of the film composite in order to measure
voltage as a function of bias current and external magnetic field. To our
knowledge, the composite films are unique in terms of showing magnetoelectric
effects at low temperatures, 50 K, and anomalous Hall effects at high
temperatures, 50 K.Comment: ReVTeX, 2 figures, 3 page
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