Dielectric confinement of excitons in type-I and type-II semiconductor nanorods

We theoretically study the effect of the dielectric environment on the exciton ground state of CdSe and CdTe/CdSe/CdTe nanorods. We show that insulating environments enhance the exciton recombination rate and blueshift the emission peak by tens of meV. These effects are particularly pronounced for type-II nanorods. In these structures, the dielectric confinement may even modify the spatial distribution of electron and hole charges. A critical electric field is required to separate electrons from holes, whose value increases with the insulating strength of the surroundings.Comment: Journal of Physics: Condensed Matter (in press

Investigation of acceptor levels and hole scattering mechanisms in p-gallium selenide by means of transport measurements under pressure

The effect of pressure on acceptor levels and hole scattering mechanisms in p-GaSe is investigated through Hall effect and resistivity measurements under quasi-hydrostatic conditions up to 4 GPa. The pressure dependence of the hole concentration is interpreted through a carrier statistics equation with a single (nitrogen) or double (tin) acceptor whose ionization energies decrease under pressure due to the dielectric constant increase. The pressure effect on the hole mobility is also accounted for by considering the pressure dependencies of both the phonon frequencies and the hole-phonon coupling constants involved in the scattering rates.Comment: 13 pages, Latex, 4 ps figures. to appear in High Pressure Research 69 (1997

Implementation of a resistance training on young football players

El objetivo de este estudio, es comprobar el efecto de un programa de 20 sesiones de entrenamiento específico de fuerza en futbolistas jóvenes Participaron 38 sujetos en el estudio, divididos en un grupo experimental (GE) y un grupo control (GC). Al GE se le administró un entrenamiento de fútbol y un trabajo específico de fuerza; mientras el GC sólo efectuó práctica de fútbol. Ambos fueron evaluados al inicio y al final del programa, con el objetivo de conocer su fuerza dinámica máxima en los flexores y extensores de la rodilla; su masa muscular en las extremidades inferiores; el porcentaje de grasa; y, por último, la velocidad en las pruebas de 10 y 20 metros. Únicamente el GE mejora de forma muy significativa la fuerza dinámica máxima (p<0,01). No se encuentran diferencias en la masa muscular, ni en la velocidad. El GE y el GC incrementan el porcentaje de grasa corporalThe aim of this study is to check the effect of a specific training strength program on young footballers. 38 players took place in the study; they were divided into an experimental group (EG) and a control group (CG). The EG added a specific strength work to their football workout, whereas the CG just practised football. Both of them were assessed at the beginning and at the end of the program to know their maximum dynamic strength in their flexor and extensor muscles of their knees; their muscle mass in their lower extremities; their body mass and fat percentage; and their speed in the 10 and 20 metres trials. Just the EG improves remarkably their maximum dynamic strength … No differences in their muscle mass or in their movement strength are found. The EG and the CG increase their MBRate and their body fa

Biodegradable polyesters reinforced with triclosan loaded polylactide micro/nanofibers: Properties, release and biocompatibility

Mechanical properties and drug release behavior were studied for three biodegradable polyester matrices (polycaprolactone, poly(nonamethylene azelate) and the copolymer derived from 1,9-nonanediol and an equimolar mixture of azelaic and pimelic acids) reinforced with polylactide (PLA) fibers. Electrospinning was used to produce suitable mats constituted by fibers of different diameters (i.e. from micro- to nanoscale) and a homogeneous dispersion of a representative hydrophobic drug (i.e. triclosan). Fabrics were prepared by a molding process, which allowed cold crystallization of PLA micro/nanofibers and hot crystallization of the polyester matrices. The orientation of PLA molecules during electrospinning favored the crystallization process, which was slightly enhanced when the diameter decreased. Incorporation of PLA micro/nanofibers led to a significant increase in the elastic modulus and tensile strength, and in general to a decrease in the strain at break. The brittle fracture was clearer when high molecular weight samples with high plastic deformation were employed. Large differences in the release behavior were detected depending on the loading process, fiber diameter size and hydrophobicity of the polyester matrix. The release of samples with the drug only loaded into the reinforcing fibers was initially fast and then became slow and sustained, resulting in longer lasting antimicrobial activity. Biocompatibility of all samples studied was demonstrated by adhesion and proliferation assays using HEp-2 cell cultures

Charge control in laterally coupled double quantum dots

We investigate the electronic and optical properties of InAs double quantum dots grown on GaAs (001) and laterally aligned along the [110] crystal direction. The emission spectrum has been investigated as a function of a lateral electric field applied along the quantum dot pair mutual axis. The number of confined electrons can be controlled with the external bias leading to sharp energy shifts which we use to identify the emission from neutral and charged exciton complexes. Quantum tunnelling of these electrons is proposed to explain the reversed ordering of the trion emission lines as compared to that of excitons in our system.Comment: 4 pages, 4 figures submitted to PRB Rapid Com

La enseñanza en España: como se distribuyen los alumnos entre los distintos tipos de estudios

En nuestro deseo de informar sobre la marcha de la enseñanza española, como ya hemos venido haciendo en los números 43 y 46 de esta misma Revista, ampliamos aquellos trabajos con los últimos datos, al tiempo que presentamos un pequeño estudio de cada enseñanza por separado, siguiendo su evolución en el pasado y considerando para un futuro próximo su posible proyección, de acuerdo con la tendencia actual ele las series

Isospin phases of vertically coupled double quantum rings under the influence of perpendicular magnetic fields

Vertically coupled double quantum rings submitted to a perpendicular magnetic field $B$ are addressed within the local spin-density functional theory. We describe the structure of quantum ring molecules containing up to 40 electrons considering different inter-ring distances and intensities of the applied magnetic field. When the rings are quantum mechanically strongly coupled, only bonding states are occupied and the addition spectrum of the artificial molecules resembles that of a single quantum ring, with some small differences appearing as an effect of the magnetic field. Despite the latter has the tendency to flatten the spectra, in the strong coupling limit some clear peaks are still found even when $B\neq 0$ that can be interpretated from the single-particle energy levels analogously as at zero applied field, namely in terms of closed-shell and Hund's-rule configurations. Increasing the inter-ring distance, the occupation of the first antibonding orbitals washes out such structures and the addition spectra become flatter and irregular. In the weak coupling regime, numerous isospin oscillations are found as a function of $B$.Comment: 27 pages, 11 figures. To be published in Phys. Rev.