Resonant Raman scattering off neutral quantum dots

Resonant inelastic (Raman) light scattering off neutral GaAs quantum dots which contain a mean number, N=42, of electron-hole pairs is computed. We find Raman amplitudes corresponding to strongly collective final states (charge-density excitations) of similar magnitude as the amplitudes related to weakly collective or single-particle excitations. As a function of the incident laser frequency or the magnetic field, they are rapidly varying amplitudes. It is argued that strong Raman peaks should come out in the spin-density channels, not related to valence-band mixing effects in the intermediate states.Comment: Accepted in Physical Review

Electric field and exciton structure in CdSe nanocrystals

Quantum Stark effect in semiconductor nanocrystals is theoretically investigated, using the effective mass formalism within a $4\times 4$ Baldereschi-Lipari Hamiltonian model for the hole states. General expressions are reported for the hole eigenfunctions at zero electric field. Electron and hole single particle energies as functions of the electric field ($\mathbf{E}_{QD}$) are reported. Stark shift and binding energy of the excitonic levels are obtained by full diagonalization of the correlated electron-hole Hamiltonian in presence of the external field. Particularly, the structure of the lower excitonic states and their symmetry properties in CdSe nanocrystals are studied. It is found that the dependence of the exciton binding energy upon the applied field is strongly reduced for small quantum dot radius. Optical selection rules for absorption and luminescence are obtained. The electric-field induced quenching of the optical spectra as a function of $\mathbf{E}_{QD}$ is studied in terms of the exciton dipole matrix element. It is predicted that photoluminescence spectra present anomalous field dependence of the emission lines. These results agree in magnitude with experimental observation and with the main features of photoluminescence experiments in nanostructures.Comment: 9 pages, 7 figures, 1 tabl

Determining the nuclear neutron distribution from Coherent Elastic neutrino-Nucleus Scattering: current results and future prospects

Coherent Elastic neutrino-Nucleus Scattering (CEνNS), a process recently measured for the first time at ORNL's Spallation Neutron Source, is directly sensitive to the weak form factor of the nucleus. The European Spallation Source (ESS), presently under construction, will generate the most intense pulsed neutrino flux suitable for the detection of CEνNS. In this paper we quantify its potential to determine the root mean square radius of the point-neutron distribution, for a variety of target nuclei and a suite of detectors. To put our results in context we also derive, for the first time, a constraint on this parameter from the analysis of the energy and timing data of the CsI detector at the COHERENT experiment

Cuantificación mediante estudio estereológico del sistema microfisural del granito de El Berrocal (Sistema Central, Toledo, España)

This paper describes an exarnple of the use of stereological techniques for the quantification of some characteristics of the microcrack network of rocks, in this case the El Berrocal granite (Sistema Central, Toledo, Spain). From data measured in sections, therefore 2-D, 3-D characteristics of the microcrack network have been obtained. The quantified characteristics are the microcrack density (in terms of the frequency distribution of the specific surface of microcracks in relation to their apertures) and the relative frequency of the microcrack aperture. These procedures have been applied to images under scanning electron microscopy, so microcracks with apparent apertures over 0,l pm. have been measured. The so called "vertical sections" have been prepared to assure a correct sampling. From the measurement of the apparent apertures of microcracks and applying stereological procedures, the real apertures and the specific surface of each class of microcracks are obtained. Besides of the characteristics of the microcrack network of the rock as a whole, data of the microcracks associated to each of the main minerals (quartz, feldspars and micas) are presented separately, allowing the interpretation of the contribution of each mineral to the microfractography of the rock. In El Berrocal granite, the microcracks with a real aperture less than 1 m are the most abundant. The microcracks are more important in quartz and, above all, in feldspars (with more than 60% of the total network of the rock), than in micas. When considering the microcrack density of each mineral, and taking into account the mineral composition of the rock too, the feldspar is also the more cracked mineral in the rock. Nevertheless, the frequency distribution of the specific surface in relation to the microcrack aperture is quite similar in any of the three mirierals. It is intended with this paper to show the possibilities of the stereology that, using simple, fast and economic procedures, provides quantitative information about the characteristics of the microcrack network of rocks that can be very useful in many geological studies

On the specificity of renin

originalFil: Fasciolo, Juan C.. Instituto de Fisiología. Facultad de Medicina. Universidad de Buenos Aires; ArgentinaFil: Leloir, Luis Federico. Instituto de Fisiología. Facultad de Medicina. Universidad de Buenos Aires; ArgentinaFil: Muñoz, Juan M.. Instituto de Fisiología. Facultad de Medicina. Universidad de Buenos Aires; ArgentinaFil: Braun Menéndez, Eduardo. Instituto de Fisiología. Facultad de Medicina. Universidad de Buenos Aires; ArgentinaBlanco y negro3 páginas en pdfLFL-PI-O-ART. Artículos científicosUnidad documental simpleAR-HYL-201

Star-forming dwarf galaxies in the Virgo cluster: the link between molecular gas, atomic gas, and dust

We present $^{12}$CO(1-0) and $^{12}$CO(2-1) observations of a sample of 20 star-forming dwarfs selected from the Herschel Virgo Cluster Survey, with oxygen abundances ranging from 12 + log(O/H) ~ 8.1 to 8.8. CO emission is observed in ten galaxies and marginally detected in another one. CO fluxes correlate with the FIR 250 $\mu$m emission, and the dwarfs follow the same linear relation that holds for more massive spiral galaxies extended to a wider dynamical range. We compare different methods to estimate H2 molecular masses, namely a metallicity-dependent CO-to-H2 conversion factor and one dependent on H-band luminosity. The molecular-to-stellar mass ratio remains nearly constant at stellar masses <~ 10$^9$ M$_{\odot}$, contrary to the atomic hydrogen fraction, M$_{HI}$/M$_*$, which increases inversely with M$_*$. The flattening of the M$_{H_2}$/M$_*$ ratio at low stellar masses does not seem to be related to the effects of the cluster environment because it occurs for both HI-deficient and HI-normal dwarfs. The molecular-to-atomic ratio is more tightly correlated with stellar surface density than metallicity, confirming that the interstellar gas pressure plays a key role in determining the balance between the two gaseous components of the interstellar medium. Virgo dwarfs follow the same linear trend between molecular gas mass and star formation rate as more massive spirals, but gas depletion timescales, $\tau_{dep}$, are not constant and range between 100 Myr and 6 Gyr. The interaction with the Virgo cluster environment is removing the atomic gas and dust components of the dwarfs, but the molecular gas appears to be less affected at the current stage of evolution within the cluster. However, the correlation between HI deficiency and the molecular gas depletion time suggests that the lack of gas replenishment from the outer regions of the disc is lowering the star formation activity.Comment: 19 pages, 11 figures, accepted for publication in Astronomy & Astrophysic

Genetic Diversity among Wild Common Beans from Northwestern Argentina Based on Morpho-agronomic and RAPD Data

The genetic diversity among 10 wild populations of common bean Phaseolus; vulgaris var. aborigineus was analyzed by means of RAPD markers and morpho-agronomic data. The study was performed on populations collected from different sites located in the provinces of Jujuy, Salta and Tucuman in northwestern Argentina. Ten quantitative traits and 33 random primers were scored. Clustering based on morpho-agronomic traits and RAPD markers generated similar phenograms that grouped bean populations based on their site of collection. The levels of diversity observed among populations were low suggesting they have a common ancestor. The levels of diversity shown by morpho-agronomic traits were higher compared to those of molecular markers, most probably due to the effect of the environment. Furthermore, a 480-bp DNA band identified a group of wild populations collected from similar sites. Breeding strategies need to exploit this diversity to broaden the genetic base of commercial beans to develop high yield cultivars.Instituto de Fisiología Vegeta

Influencia del proceso de esterilización en la mojabilidad del titanio modificado superficialmente

El objetivo de este trabajo es estudiar el cambio en las propiedades energéticas de muestras de titanio comercialmente puro debido a distintos tratamientos superficiales y a distintos métodos de esterilización; con la finalidad de entender cómo afectan estos cambios a los procesos biológicos de los implantes de titanio. Los distintos tratamientos superficiales utilizados fueron: la formación de rugosidad mediante la proyección de partículas abrasivas, el granallado, y la esterilización mediante autoclave, óxido de etileno o radiación gamma. Tanto el nivel de rugosidad generada como la naturaleza de las partículas del granallado influyen en el carácter energético de las muestras; incrementando el carácter hidrofóbico con el aumento de la rugosidad y con la utilización de alúmina. Los contaminantes debidos al proceso de autoclave hidrofobizan las superficies; contrariamente a la esterilización por óxido de etileno que disminuye el valor del ángulo de contacto. La modificación de las superficies tratadas fue examinada con una serie de técnicas analíticas superficiales que incluyen el microscopio electrónico de barrido (SEM), la interferometría óptica y la medición del ángulo de contacto para poder realizar una caracterización topográfica, cualitativa y cuantitiva, y una caracterización energética, respectivamente.The aim of this work is to study the energetic properties of commercially pure titanium samples due to different surface treatments and different sterilization methods; with the purpose to understand how these changes affect to the biological processes of titanium implants. The different surface treatments were: roughness obtained by shot blasting, and sterilization by steam autoclaving, ethylene oxide or gamma radiation. Roughness level and the nature of the abrasive particles of shot blasting influence energetically the samples; increasing the hydrophobic behaviour with the increase of the surface roughness and the alumina use. The contamination due to steam autoclaving hydrophobizes the surface; contrary to sterilization by ethylene oxide, which reduces the contact angle value. The modification of treated surfaces was examined with a series of surface analytical techniques that include the scanning electron microscopy (SEM), the white light interferometer microscopy and the static contact angle measurement in order to determine a qualitative and quantitative topographic characterization and an energetic characterization