Crossover between the Dense Electron-Hole Phase and the BCS Excitonic Phase in Quantum Dots

Second order perturbation theory and a Lipkin-Nogami scheme combined with an exact Monte Carlo projection after variation are applied to compute the ground-state energy of $6\le N\le 210$ electron-hole pairs confined in a parabolic two-dimensional quantum dot. The energy shows nice scaling properties as N or the confinement strength is varied. A crossover from the high-density electron-hole phase to the BCS excitonic phase is found at a density which is roughly four times the close-packing density of excitons.Comment: Improved variational and projection calculations. 17 pages, 3 ps figures. Accepted for publication in Int. J. Mod. Phys.

Dispersive spherical optical model of neutron scattering from Al27 up to 250 MeV

A spherical optical model potential (OMP) containing a dispersive term is used to fit the available experimental database of angular distribution and total cross section data for n + Al27 covering the energy range 0.1- 250 MeV using relativistic kinematics and a relativistic extension of the Schroedinger equation. A dispersive OMP with parameters that show a smooth energy dependence and energy independent geometry are determined from fits to the entire data set. A very good overall agreement between experimental data and predictions is achieved up to 150 MeV. Inclusion of nonlocality effects in the absorptive volume potential allows to achieve an excellent agreement up to 250 MeV.Comment: 13 figures (11 eps and 2 jpg), 3 table

Gamma ray detector modules

A radiation detector assembly has a semiconductor detector array substrate of CdZnTe or CdTe, having a plurality of detector cell pads on a first surface thereof, the pads having a contact metallization and a solder barrier metallization. An interposer card has planar dimensions no larger than planar dimensions of the semiconductor detector array substrate, a plurality of interconnect pads on a first surface thereof, at least one readout semiconductor chip and at least one connector on a second surface thereof, each having planar dimensions no larger than the planar dimensions of the interposer card. Solder columns extend from contacts on the interposer first surface to the plurality of pads on the semiconductor detector array substrate first surface, the solder columns having at least one solder having a melting point or liquidus less than 120 degrees C. An encapsulant is disposed between the interposer circuit card first surface and the semiconductor detector array substrate first surface, encapsulating the solder columns, the encapsulant curing at a temperature no greater than 120 degrees C

Native breeds of the oaxaqueña Mixteca of México

The Mixteca region is one of the most important areas of the Pacific Mexico with respect to the extensive farming, where the special richness of the Creole population of hens, sheep, goats, cattle, pigs and in a lower wake horses, turkeys and honey bees. Instead of this richness and its socio-economic importance in this region, few scientific studies have been developed about these animals. In this communication, we are developing a description of the most important population existing in this region, pointing out some aspects about their origin, geographical localization, management system, etc. Presently, the lines proposed by FAO for the conservation of the genetic resources is sensitising Mexico and all Latin-America for the conservation of their own resources. In this way, we can stand out the decay of this region in the enclosing of their breed in the international scientific community, what it is shown in the absence of most of them in publications such us the world watch list or the DAD-IS program.La Mixteca es una de las regiones ganaderas extensivas más importantes del México Pacífico, destacada por su gran riqueza en poblaciones criollas de gallinas, ovinos, caprinos, bovinos, porcinos y en menor medida equinos, pavos y abejas. A pesar de esta riqueza y de su importante repercusión socio-económica en esta región, son escasos los estudios científicos realizados sobre estos animales. En este trabajo se realiza una descripción de las principales poblaciones existentes, precisando algunos aspectos sobre su origen, ubicación geográfica, sistema de manejo, producción y opciones de futuro. En la actualidad las líneas impuestas por el programa global de la FAO para la conservación de los recursos genéticos está sensibilizando a México y a toda América Latina en pro de la conservación de sus propios recursos. En este sentido cabe destacar el retraso de esta región en incorporar sus razas a la comunidad científica internacional, lo que queda demostrado por la ausencia de la mayoría de ellos en publicaciones como el World Watch List o el programa DAD-IS

Congélation du sperme de verrat. Races autochtones in peril de disparition (résultats préliminaires)

Dans les races porcines Chato Murciano et Ibérico, le méthode pour congeler l'sperme propose par Thilmant (1997) (A) à ameilloré les résultats obtenus aprés l'emploi du méthode de Westendorf (1975) (B). Dans cette comunication, en employant la Coloration Vital (eosine-nigrosine) (T.V.) et l'état de l'acrosome (NAR) sur six verrats appartenant a races autochtones espagnoles et un verrat croisé, nous avons trouvé résultats moyennes de 59 p.100 vers 47 p.100 dans T.V. et de 59 p.100 vers 33 p.100 dans NAR, pour A et B respectivement.En las razas porcinas Chato Murciano e Ibérico la aplicación del método de congelación de semen porcino propuesto por Thilmant (1997) (A) ha mejorado los resultados alcanzados con el método propuesto por Westendorf (1975) (B). Considerando, a efectos de este trabajo, la tinción vital (T.V.) y el estado del acrosoma (N.A.R.), en seis verracos pertenecientes a razas autóctonas españolas y un verraco cruzado. Hemos encontrado valores medios de 59 p.100 y 47 p.100 para T.V. y de 59 p.100 y 33 p.100 para N.A.R., para los métodos A y B respectivamente. En la inseminación con semen descongelado utilizando el mejor de los métodos estudiados in vitro, se alcanzan valores de gestación cercanos a la monta natural

Level densities of transitional Sm nuclei

Experimentally determined level densities of the transitional isotopes 148, 149, 150, 152Sm at excitation energies below and around the neutron binding energy are compared with microcanonical calculations based on a Monte Carlo approach to noncollective level densities, folded with a collective enhancement estimated in the frame of the interacting boson model (IBM). The IBM parameters are adjusted so as to reproduce the low-lying discrete levels of both parities, with the exception of the odd-mass nucleus, 149Sm, where complete decoupling of the unpaired neutron from the core is assumed