2,165 research outputs found
Spin-wave instabilities in spin-transfer-driven magnetization dynamics
We study the stability of magnetization precessions induced in spin-transfer
devices by the injection of spin-polarized electric currents. Instability
conditions are derived by introducing a generalized, far-from-equilibrium
interpretation of spin-waves. It is shown that instabilities are generated by
distinct groups of magnetostatically coupled spin-waves. Stability diagrams are
constructed as a function of external magnetic field and injected
spin-polarized current. These diagrams show that applying larger fields and
currents has a stabilizing effect on magnetization precessions. Analytical
results are compared with numerical simulations of spin-transfer-driven
magnetization dynamics.Comment: 4 pages, 2 figure
A lattice of double wells for manipulating pairs of cold atoms
We describe the design and implementation of a 2D optical lattice of double
wells suitable for isolating and manipulating an array of individual pairs of
atoms in an optical lattice. Atoms in the square lattice can be placed in a
double well with any of their four nearest neighbors. The properties of the
double well (the barrier height and relative energy offset of the paired sites)
can be dynamically controlled. The topology of the lattice is phase stable
against phase noise imparted by vibrational noise on mirrors. We demonstrate
the dynamic control of the lattice by showing the coherent splitting of atoms
from single wells into double wells and observing the resulting double-slit
atom diffraction pattern. This lattice can be used to test controlled neutral
atom motion among lattice sites and should allow for testing controlled
two-qubit gates.Comment: 9 pages, 11 figures Accepted for publication in Physical Review
RAO-II: an AUV for underwater inspection
AIRSUB is a research project funded by the Spanish Ministry of Science
and Technology whose aim is to explore the industrial applications of
underwater robots. The Systems, Robotics and Vision Group (SRV) from
the University of the Balearic Islands (UIB) is responsible for the subproject
of cable/pipeline inspection [1]. To this purpose, an Autonomous
Underwater Vehicle (AUV) is under development as a platform to test the
vision algorithms, control strategies and software architectures devised
in the last years. This paper describes the main characteristics of the new
platform, which is based on a commercial Remotely Operated Vehicle
(ROV). The original vehicle has been deeply modifi ed in structure as well
as in its electric, electronic and sensorial facets to obtain fully autonomous
operation
Tumour heterogeneity: principles and practical consequences
Two major reasons compel us to study tumour heterogeneity: firstly, it represents the basis of acquired therapy resistance, and secondly it may be one of the major sources of the low level of reproducibility in clinical cancer research. The present review focuses on the heterogeneity of neoplastic disease, both within the primary tumour, and between primary tumour and metastases. We discuss different levels of heterogeneity and the current understanding of the phenomenon, as well as imminent developments relevant for clinical research and diagnostic pathology. It is necessary to develop new tools to study heterogeneity and new biomarkers for heterogeneity. Established and new in situ methods will be very useful. In future studies, not only clonal heterogeneity needs to be addressed, but also non-clonal phenotypic heterogeneity which might be important for therapy resistance.
We also review heterogeneity established in major tumour types, in order to explore potential similarities that might help to define new strategies for targeted therapy
Les forĂȘts Ă Alnus cordata en Italie mĂ©ridionale - Comparaison avec les groupements de Corse
Le but de cet article est dâapporter des informations sur les groupements forestiers Ă Alnus cordata Desf. des massifs montagneux de la partie occidentale de lâItalie mĂ©ridionale. Cette essence centro-mĂ©diterranĂ©enne est prĂ©sente en Corse et sur certains versants sud italiens. Dans cette rĂ©gion, elle constitue de vĂ©ritables groupements forestiers, peu Ă©tendus certes, mais bien individualisĂ©s. Câest pourquoi ces groupements sont rattachĂ©s aux grandes unitĂ©s de vĂ©gĂ©tation prĂ©sentes dans cette rĂ©gion. Leurs affinitĂ©s sont discutĂ©es et leur position dans lâĂ©tagement de la vĂ©gĂ©tation bien prĂ©cisĂ©e. Quelques considĂ©rations sur la composition floristique de ces formations permettent de mieux apprĂ©hender les affinitĂ©s biogĂ©ographiques de ces aulnaies
Trente ans d'apport de la recherche sur les forĂȘts mĂ©diterranĂ©ennes
Cet article prĂ©sente un bilan des apports de la recherche Ă©cologique dans le cadre gĂ©nĂ©ral des forĂȘts mĂ©diterranĂ©ennes durant des trois derniĂšres dĂ©cennies. Il convient de prĂ©ciser qu'il s'agit essentiellement de recherche Ă©cologique, car il existe des champs de recherche qui n'y sont pas abordĂ©s
SynthĂšse des acquis du colloque "Changements climatiques et forĂȘt mĂ©diterranĂ©enne" de 2007 -
En novembre 2007, l'Association ForĂȘt MĂ©diterranĂ©enne organisait un colloque original associant effets du changement climatique et forĂȘts mĂ©diterranĂ©ennes. Cette manifestation connut un grand succĂšs, attirant plus de 400 participants de toutes catĂ©gories professionnelles et d'origines gĂ©ographiques variĂ©es, justifiant ainsi la dĂ©cision de recommencer l'expĂ©rience en 2010, pour faire un point sur l'Ă©volution des connaissances thĂ©oriques et pratiques. L'auteur rappelle ici briĂšvement les principales idĂ©es dĂ©veloppĂ©es en 2007
Quelques aspects des forĂȘts d'Afrique du nord.
L'article a pour objet d'évoquer l'éventail des entités forestiÚres d'Afrique du nord. Leur hétérogénéité ainsi que leur vulnérabilité constituent leur caractéristique moyenne
Atom interferometry measurement of the electric polarizability of lithium
Using an atom interferometer, we have measured the static electric
polarizability of Li m atomic units with a 0.66% uncertainty. Our experiment, which
is similar to an experiment done on sodium in 1995 by D. Pritchard and
co-workers, consists in applying an electric field on one of the two
interfering beams and measuring the resulting phase-shift. With respect to D.
Pritchard's experiment, we have made several improvements which are described
in detail in this paper: the capacitor design is such that the electric field
can be calculated analytically; the phase sensitivity of our interferometer is
substantially better, near 16 mrad/; finally our interferometer is
species selective it so that impurities present in our atomic beam (other
alkali atoms or lithium dimers) do not perturb our measurement. The extreme
sensitivity of atom interferometry is well illustrated by our experiment: our
measurement amounts to measuring a slight increase of the atom
velocity when it enters the electric field region and our present
sensitivity is sufficient to detect a variation .Comment: 14 page
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