1,024 research outputs found
Student Exchange in Japan: Why and How to Provide Engineering Students with an International Experience
In the last years, to improve the performance of prediction of radioactive contamination, an increasing number of studies have explored and exploited the potentials of geostatistical methods. However, traditional methods like kriging and cokriging are optimal only in the case in which the data may be assumed Gaussian and do not properly cope with data measurements that are discrete, nonnegative or show some degree of skewness, as in many environmental applications concerned with radioactivity measurements. To deal with geostatistical skewed data, we consider a model-based approach in which measurements are modeled with the help of a latent Gaussian structure and some recent classes of skewed distributions extending the normal one. For our model we investigate the implied spatial autocorrelation structure and the marginal distributions of the observable variables. In particular we show that all finite-dimensional marginal distributions of the observable variables belong to the family of the unified skew-normal distribution. Estimation of some of the unknown parameters of the model can be carried out by employing a Monte Carlo expectation maximization procedure, whereas predictions of both latent and observed (at unsampled sites) variables, can be supplied by Markov chain Monte Carlo algorithms
Capture Velocity for a Magneto-Optical Trap in a Broad Range of Light Intensity
In a recent paper, we have used the dark-spot Zeeman tuned slowing technique
[Phys. Rev. A 62, 013404-1, (2000)] to measure the capture velocity as a
function of laser intensity for a sodium magneto optical trap. Due to technical
limitation we explored only the low light intensity regime, from 0 to 27
mW/cm^2. Now we complement that work measuring the capture velocity in a
broader range of light intensities (from 0 to 400 mW/cm^2). New features,
observed in this range, are important to understant the escape velocity
behavior, which has been intensively used in the interpretation of cold
collisions. In particular, we show in this brief report that the capture
velocity has a maximum as function of the trap laser intensity, which would
imply a minimum in the trap loss rates.Comment: 2 pages, 2 figure
Magnetic Field Tomography
Neutral atoms may be trapped via the interaction of their magnetic dipole
moment with magnetic field gradients. One of the possible schemes is the
cloverleaf trap. It is often desirable to have at hand a fast and precise
technique for measuring the magnetic field distribution. We introduce a novel
diagnostic tool for instantaneous imaging the equipotential lines of a magnetic
field within a region of space (the vacuum recipient) that is not accessible to
massive probes. Our technique is based on spatially resolved observation of the
fluorescence emitted by a hot beam of sodium atoms crossing a thin slice of
resonant laser light within the magnetic field region to be investigated. The
inhomogeneous magnetic field spatially modulates the resonance condition
between the Zeeman-shifted hyperfine sublevels and the laser light and
therefore the amount of scattered photons. We demonstrate this technique by
mapping the field of our cloverleaf trap in three dimensions under various
conditions.Comment: 8 pages, 8 figure
Emergence of turbulence in an oscillating Bose-Einstein condensate
We report on the experimental observation of vortices tangle in an atomic BEC
of Rb-87 atoms when an external oscillatory perturbation is introduced in the
trap. The vortices tangle configuration is a signature of the presence of a
turbulent regime in the cloud. We also show that this turbulent cloud has
suppression of the aspect ratio inversion typically observed in quantum
degenerate bosonic gases during free expansion. Instead, the cloud expands
keeping the ratio between their axis constant. Turbulence in atomic superfluids
may constitute an alternative system to investigate decay mechanisms as well as
to test fundamental theoretical aspects in this field.Comment: accepted for Phys. Rev. Let
Tumor cellular and microenvironmental cues controlling invadopodia formation
During the metastatic progression, invading cells might achieve degradation and subsequent invasion into the extracellular matrix (ECM) and the underlying vasculature using invadopodia, F-actin-based and force-supporting protrusive membrane structures, operating focalized proteolysis. Their formation is a dynamic process requiring the combined and synergistic activity of ECM-modifying proteins with cellular receptors, and the interplay with factors from the tumor microenvironment (TME). Significant advances have been made in understanding how invadopodia are assembled and how they progress in degradative protrusions, as well as their disassembly, and the cooperation between cellular signals and ECM conditions governing invadopodia formation and activity, holding promise to translation into the identification of molecular targets for therapeutic interventions. These findings have revealed the existence of biochemical and mechanical interactions not only between the actin cores of invadopodia and specific intracellular structures, including the cell nucleus, the microtubular network, and vesicular trafficking players, but also with elements of the TME, such as stromal cells, ECM components, mechanical forces, and metabolic conditions. These interactions reflect the complexity and intricate regulation of invadopodia and suggest that many aspects of their formation and function remain to be determined. In this review, we will provide a brief description of invadopodia and tackle the most recent findings on their regulation by cellular signaling as well as by inputs from the TME. The identification and interplay between these inputs will offer a deeper mechanistic understanding of cell invasion during the metastatic process and will help the development of more effective therapeutic strategies
Ramsey fringes formation during excitation of topological modes in a Bose-Einstein condensate
The Ramsey fringes formation during the excitation of topological coherent
modes of a Bose-Einstein condensate by an external modulating field is
considered. The Ramsey fringes appear when a series of pulses of the excitation
field is applied. In both Rabi and Ramsey interrogations, there is a shift of
the population maximum transfer due to the strong non-linearity present in the
system. It is found that the Ramsey pattern itself retains information about
the accumulated relative phase between both ground and excited coherent modes.Comment: Latex file, 12 pages, 5 figure
Photoassociative ionization of Na inside a storage ring
Motivated by recent interest in low dimensional arrays of atoms, we
experimentally investigated the way cold collisional processes are affected by
the geometry of the considered atomic sample. More specifically, we studied the
case of photoassociative ionization (PAI) both in a storage ring where
collision is more unidirectional in character and in a trap with clear
undefinition of collision axis. First, creating a ring shaped trap (atomotron)
we investigated two-color PAI dependence with intensity and polarization of a
probing laser. The intensity dependence of the PAI rate was also measured in a
magneto-optical trap presenting equivalent temperature and density conditions.
Indeed, the results show that in the ring trap, the value of the PAI rate
constant is much lower and does not show evidences of saturation, unlike in the
case of the 3D-MOT. Cold atomic collisions in storage ring may represent new
possibilities for study.Comment: 5 pages, 5 figures; Accepted by Optics Communicatio
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