1,076 research outputs found
Possible role of the phagocytic proteinases, cathepsin B and elastas, in orthotopic liver transplantation
Kein Inhaltsverzeichnis
Self-synchronization and dissipation-induced threshold in collective atomic recoil lasing
Networks of globally coupled oscillators exhibit phase transitions from incoherent to coherent states. Atoms interacting with the counterpropagating modes of a unidirectionally pumped high-finesse ring cavity form such a globally coupled network. The coupling mechanism is provided by collective atomic recoil lasing, i.e., cooperative Bragg scattering of laser light at an atomic density grating, which is self-induced by the laser light. Under the rule of an additional friction force, the atomic ensemble is expected to undergo a phase transition to a state of synchronized atomic motion. We present the experimental investigation of this phase transition by studying the threshold behavior of this lasing process
Ultra-cold atoms in an optical cavity: two-mode laser locking to the cavity avoiding radiation pressure
The combination of ultra-cold atomic clouds with the light fields of optical
cavities provides a powerful model system for the development of new types of
laser cooling and for studying cooperative phenomena. These experiments
critically depend on the precise tuning of an incident pump laser with respect
to a cavity resonance. Here, we present a simple and reliable experimental
tuning scheme based on a two-mode laser spectrometer. The scheme uses a first
laser for probing higher-order transversal modes of the cavity having an
intensity minimum near the cavity's optical axis, where the atoms are confined
by a magnetic trap. In this way the cavity resonance is observed without
exposing the atoms to unwanted radiation pressure. A second laser, which is
phase-locked to the first one and tuned close to a fundamental cavity mode
drives the coherent atom-field dynamics.Comment: 7 pages, 7 figure
Cooperative Scattering by Cold Atoms
We have studied the interplay between disorder and cooperative scattering for
single scattering limit in the presence of a driving laser. Analytical results
have been derived and we have observed cooperative scattering effects in a
variety of experiments, ranging from thermal atoms in an optical dipole trap,
atoms released from a dark MOT and atoms in a BEC, consistent with our
theoretical predictions.Comment: submitted for special issue of PQE 201
The role of Mie scattering in the seeding of matter-wave superradiance
Matter-wave superradiance is based on the interplay between ultracold atoms
coherently organized in momentum space and a backscattered wave. Here, we show
that this mechanism may be triggered by Mie scattering from the atomic cloud.
We show how the laser light populates the modes of the cloud, and thus imprints
a phase gradient on the excited atomic dipoles. The interference with the atoms
in the ground state results in a grating, that in turn generates coherent
emission, contributing to the backward light wave onset. The atomic recoil
'halos' created by the scattered light exhibit a strong anisotropy, in contrast
to single-atom scattering
Experimental perspectives for systems based on long-range interactions
The possibility of observing phenomena peculiar to long-range interactions,
and more specifically in the so-called Quasi-Stationary State (QSS) regime is
investigated within the framework of two devices, namely the Free-Electron
Laser (FEL) and the Collective Atomic Recoil Laser (CARL). The QSS dynamics has
been mostly studied using the Hamiltonian Mean-Field (HMF) toy model,
demonstrating in particular the presence of first versus second order phase
transitions from magnetized to unmagnetized regimes in the case of HMF. Here,
we give evidence of the strong connections between the HMF model and the
dynamics of the two mentioned devices, and we discuss the perspectives to
observe some specific QSS features experimentally. In particular, a dynamical
analog of the phase transition is present in the FEL and in the CARL in its
conservative regime. Regarding the dissipative CARL, a formal link is
established with the HMF model. For both FEL and CARL, calculations are
performed with reference to existing experimental devices, namely the
FERMI@Elettra FEL under construction at Sincrotrone Trieste (Italy) and the
CARL system at LENS in Florence (Italy)
Ensemble of Hankel Matrices for Face Emotion Recognition
In this paper, a face emotion is considered as the result of the composition
of multiple concurrent signals, each corresponding to the movements of a
specific facial muscle. These concurrent signals are represented by means of a
set of multi-scale appearance features that might be correlated with one or
more concurrent signals. The extraction of these appearance features from a
sequence of face images yields to a set of time series. This paper proposes to
use the dynamics regulating each appearance feature time series to recognize
among different face emotions. To this purpose, an ensemble of Hankel matrices
corresponding to the extracted time series is used for emotion classification
within a framework that combines nearest neighbor and a majority vote schema.
Experimental results on a public available dataset shows that the adopted
representation is promising and yields state-of-the-art accuracy in emotion
classification.Comment: Paper to appear in Proc. of ICIAP 2015. arXiv admin note: text
overlap with arXiv:1506.0500
Kyste hydatique du masséter: a propos d’un cas
La localisation cervico faciale et particulièrement musculaire massétérine est exceptionnelle même en zone d’endémie. Le kyste hydatique au niveau de cette localisation pose un problème de diagnostic et des difficultés thérapeutiques du fait de la présence de filets nerveux du VII. Les auteurs rapportent un cas rare de localisation primaire d’un kyste hydatique au niveau du muscle masséter.Mots clès : Kyste hydatique, face, masséter, imagerie, chirurgie
Highly versatile atomic micro traps generated by multifrequency magnetic field modulation
We propose the realization of custom-designed adiabatic potentials for cold
atoms based on multimode radio frequency radiation in combination with static
inhomogeneous magnetic fields. For example, the use of radio frequency combs
gives rise to periodic potentials acting as gratings for cold atoms. In strong
magnetic field gradients the lattice constant can be well below 1 micrometer.
By changing the frequencies of the comb in time the gratings can easily be
propagated in space, which may prove useful for Bragg scattering atomic matter
waves. Furthermore, almost arbitrarily shaped potential are possible such as
disordered potentials on a scale of several 100 nm or lattices with a spatially
varying lattice constant. The potentials can be made state selective and, in
the case of atomic mixtures, also species selective. This opens new
perspectives for generating tailored quantum systems based on ultra cold single
atoms or degenerate atomic and molecular quantum gases.Comment: 12 pages, 6 figure
- …