724 research outputs found
Modulation of Superconducting Properties by Ferroelectric Polarization in Confined FE-S-FE Films
We show that the electric polarization at the interface with ultrathin
superconducting (S) films sandwiched between ferroelectric (FE) layers allows
achievement of substantially stronger modulation of inner carrier density and
superconducting transition temperature as compared to FE-S bilayers typically
used in superconducting FETs. We find that not only the larger penetration
depths but also the pairing symmetry should be responsible for the fact that
the electric field effect in high temperature superconductors is much stronger
than in conventional systems. Discussing the advantages of multilayers, we
propose a novel design concept for superconducting electric field-effect
transistors based on ferroelectric films.Comment: 5 pages RevTex4, 6 figure
ab inito local vibrational modes of light impurities in silicon
We have developed a formulation of density functional perturbation theory for
the calculation of vibrational frequencies in molecules and solids, which uses
numerical atomic orbitals as a basis set for the electronic states. The
(harmonic) dynamical matrix is extracted directly from the first order change
in the density matrix with respect to infinitesimal atomic displacements from
the equilibrium configuration. We have applied this method to study the
vibrational properties of a number of hydrogen-related complexes and light
impurities in silicon. The diagonalization of the dynamical matrix provides the
vibrational modes and frequencies, including the local vibrational modes (LVMs)
associated with the defects. In addition to tests on simple molecules, results
for interstitial hydrogen, hydrogen dimers, vacancy-hydrogen and
self-interstitial-hydrogen complexes, the boron-hydrogen pair, substitutional
C, and several O-related defects in c-Si are presented. The average error
relative to experiment for the aprox.60 predicted LVMs is about 2% with most
highly harmonic modes being extremely close and the more anharmonic ones within
5-6% of the measured values.Comment: 18 pages, 1 figur
Assessment of the conservation status of natural and semi-natural patches associated with urban areas through habitat suitability indices
Urban environments rely on the surrounding natural ecosystems remnants as providers of ecosystem functions, therefore these areas not only support a unique biodiversity but also have a social value for maintaining public health and wellbeing. For this reason, urbanization is considered to be one the biggest threats to ecosystems, leading to native biodiversity simplification and, thus, to a detriment of the provided ecosystem services. Moreover, this change in land use results in high levels of landscape fragmentation and modification in areas surrounding the habitat remnants which, in consequence, become inadequate for many native species. In this context, it is important that urban planners have the information to assess the possible consequences of future changes in land use in order to increase the landscape chances of supporting both, native biodiversity and the needs of a growing human population. The objective of the present work is to evaluate the ecological integrity of natural and semi-natural vegetation patches immersed in an urban area in order to generate a conceptual framework for landscape assessment that allows urban planners to envision the best choice for city development at a given place. To do so, we developed a quantitative integral environmental evaluation index that includes ecological characterization, geological characterization, and environmental characterization (presence of anthropic disturbance) of the assessed area. We conclude that the index we have generated in this work is suitable to be used as a management tool to allow an unbiased valuation and to identify managing situations that require a short term response.Fil: Natale, Evangelina Sandra. Fundación Conservación y Desarrollo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Villalba, G.. Fundación Conservación y Desarrollo; ArgentinaFil: Junquera, J. E.. Fundación Conservación y Desarrollo; ArgentinaFil: Zalba, Sergio Martín. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia. Grupo de Estudios en Conservación y Manejo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
Sexual Maturity and Spawning of the Greenland Halibut (Reinhardtius hippoglossoides) From Flemish Pass Area
10 páginas, 4 figuras, 3 tablas.-- Scientific Council MeetingPeer reviewe
Band selection and disentanglement using maximally-localized Wannier functions: the cases of Co impurities in bulk copper and the Cu (111) surface
We have adapted the maximally-localized Wannier function approach of [I.
Souza, N. Marzari and D. Vanderbilt, Phys. Rev. B 65, 035109 (2002)] to the
density functional theory based Siesta method [J. M. Soler et al., J. Phys.:
Cond. Mat. 14, 2745 (2002)] and applied it to the study of Co substitutional
impurities in bulk copper as well as to the Cu (111) surface. In the Co
impurity case, we have reduced the problem to the Co d-electrons and the Cu
sp-band, permitting us to obtain an Anderson-like Hamiltonian from well defined
density functional parameters in a fully orthonormal basis set. In order to
test the quality of the Wannier approach to surfaces, we have studied the
electronic structure of the Cu (111) surface by again transforming the density
functional problem into the Wannier representation. An excellent description of
the Shockley surface state is attained, permitting us to be confident in the
application of this method to future studies of magnetic adsorbates in the
presence of an extended surface state
A European Advanced Technology Programme for ADS Accelerator Development
Consecutive to the work of the European Technical Working Group on ADS, the Preliminary Design Study of an Experimental ADS was launched in 2001 as a 5th Framework Program EC project. A special working package was dedicated to the accelerator design, and in particular taking into account that the issue of “beam trips” could be a potential “show-stopper” for ADS technology in general. A reference solution, based on a linear superconducting accelerator with its associated doubly achromatic beam line has been worked out up to some detail. For very high reliability, the proposed design is intrinsically fault tolerant, relying especially on highly modular “de-rated” components associated to a fast digital feedback system. A programme for the remaining R&D, focused on experimental reliability demonstration of prototypical components, has been elaborated. This R&D will be performed in the 6th Framework Program EC project EUROTRANS, which presently is just starting
Neutron Irradiation Tests of Calibrated Cryogenic Sensors at Low Temperatures
This paper presents the advancement of a program being carried out in view of selecting the cryogenic temperature sensors to be used in the LHC accelerator. About 10,000 sensors will be installed around the 26.6 km LHC ring, and most of them will be exposed to high radiation doses during the accelerator lifetime. The following thermometric sensors : carbon resistors, thin films, and platinum resistors, have been exposed to high neutron fluences (>10 n/cm) at the ISN (Grenoble, France) Cryogenic Irradiation Test Facility. A cryostat is placed in a shielded irradiation vault where a 20 MeV deuteron beam hits a Be target, resulting in a well collimated and intense neutron beam. The cryostat, the on-line acquisition system, the temperature references and the main characteristics of the irradiation facility are described. The main interest of this set-up is its ability to monitor online the evolution of the sensors by comparing its readout with temperature references that are in principle insensitive to the neutron radiation (i.e. Argon gas bulbs when working at about 84 K, and below 4.5 K, either helium gas bulbs or the saturation pressure of the superfluid helium bath). The resistance shifts of the different sensors at liquid helium temperatures are presented
Neutron Irradiation Tests in Superfluid Helium of LHC Cryogenic Thermometers
For control and monitoring purposes, about 10,000 individually calibrated cryogenic temperature sensors will be installed along the 26.7 km LHC. In order to reduce maintenance constraints these sensor s should be as immune as possible to the high neutron fluence environment. For selecting the sensor to be used, a radiation hardness evaluation program at cryogenic conditions is being performed in an irradiation vault of the ISN SARA Cyclotron (Grenoble, France). The set-up is capable of simulating the whole life of a LHC thermometer: same total neutron dose (1015 n.cm-2), irradiation at low tempe rature (1.8 K) and thermal cycles. Bath temperature and sensor resistance are monitored on-line. This paper presents the latest results of this program
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