3,786 research outputs found
Electromagnetic Form Factors in the hypercentral CQM
We report on the recent results of the hypercentral Constituent Quark Model
(hCQM). The model contains a spin independent three-quark interaction which is
inspired by Lattice QCD calculations and reproduces the average energy values
of the SU(6) multiplets. The splittings are obtained with a SU(6)-breaking
interaction, which can include also an isospin dependent term. Concerning
Constituent Quark models, we have shown for the first time that the decreasing
of the ratio of the elastic form factors of the proton is due to relativistic
effects using relativistic corrections to the e.m. current and boosts. Now the
elastic nucleon form factors have been recalculated, using a relativistic
version of the hCQM and a relativistic quark current showing a very detailed
reproduction of all the four form factor existing data over the complete range
of 0-4 . Futhermore, the model has been used for predictions concerning
the electromagnetic transverse and longitudinal transition form factors giving
a good description of the medium behaviour. We show that the
discrepancies in the reproduction of the helicity amplitudes at low are
due to pion loops. We have calculated the helicity amplitudes for all the 3 and
4 star resonances opening the possibility of application to the evaluation of
cross sections.Comment: 5 pages, 7 figures, Invited talk at the ICTP 4th International
Conference on Perspectives in Hadronic Physics, Trieste, Italy, 12-16 May
2003. Accepted by Eur. Phys. J.
Sizing gold nanoparticles by optical extinction spectroscopy
The measurement of optical extinction is used to determine the size of nearly spherical gold nanoparticles suspended in solution, produced by a 'reverse micelles' process. The contrast between the maximum and the minimum in the extinction spectra around 450 and 520 nm shows a linear dependence with the mean radius of the gold particles less than 3 nm; however, the method can be used to size particles up to 7 nm. Experimental results for extinction spectra can be fitted by Mie's theory if the optical constants from bulk material values are modified by introducing the limitation of the mean free path due to collisions of conduction electrons with the boundary of the nanoparticles.Facultad de Ciencias ExactasCentro de Investigaciones Óptica
Sizing gold nanoparticles by optical extinction spectroscopy
The measurement of optical extinction is used to determine the size of nearly spherical gold nanoparticles suspended in solution, produced by a 'reverse micelles' process. The contrast between the maximum and the minimum in the extinction spectra around 450 and 520 nm shows a linear dependence with the mean radius of the gold particles less than 3 nm; however, the method can be used to size particles up to 7 nm. Experimental results for extinction spectra can be fitted by Mie's theory if the optical constants from bulk material values are modified by introducing the limitation of the mean free path due to collisions of conduction electrons with the boundary of the nanoparticles.Facultad de Ciencias ExactasCentro de Investigaciones Óptica
Splitting neutrino masses and showering into Sky
Neutrino masses might be as light as a few time the atmospheric neutrino mass
splitting. High Energy ZeV cosmic neutrinos (in Z-Showering model) might hit
relic ones at each mass in different resonance energies in our nearby Universe.
This non-degenerated density and energy must split UHE Z-boson secondaries (in
Z-Burst model) leading to multi injection of UHECR nucleons within future
extreme AUGER energy. Secondaries of Z-Burst as neutral gamma, below a few tens
EeV are better surviving local GZK cut-off and they might explain recent Hires
BL-Lac UHECR correlations at small angles. A different high energy resonance
must lead to Glashow's anti-neutrino showers while hitting electrons in matter.
In air, Glashow's anti-neutrino showers lead to collimated and directional
air-showers offering a new Neutrino Astronomy. At greater energy around PeV,
Tau escaping mountains and Earth and decaying in flight are effectively
showering in air sky. These Horizontal showering is splitting by geomagnetic
field in forked shapes. Such air-showers secondaries release amplified and
beamed gamma bursts (like observed TGF), made also by muon and electron pair
bundles, with their accompanying rich Cherenkov flashes. Also planet' s largest
(Saturn, Jupiter) atmosphere limbs offer an ideal screen for UHE GZK and
Z-burst tau neutrino, because their largest sizes. Titan thick atmosphere and
small radius are optimal for discovering up-going resonant Glashow resonant
showers. Earth detection of Neutrino showering by twin Magic Telescopes on top
mountains, or by balloons and satellites arrays facing the limbs are the
simplest and cheapest way toward UHE Neutrino Astronomy .Comment: 4 pages, 7 figures; an author's name correction and Journal Referenc
Repuesta ferro-piezoeléctrica de KNN-LTS poroso
La obtención de materiales monofásicos con respuesta ferroeléctrica y (anti-)ferromagnética simultánea y acoplada resulta problemática debido a limitaciones intrínsecas de tipo físico, estructural y electrónico. En este sentido una alternativa más realista, y en cierto modo con mayor flexibilidad a la hora de diseñar futuros dispositivos multiferroicos, consiste en preparar materiales compuestos en los cuales el acoplamiento magnetoeléctrico se puede alcanzar explotando los efectos interfaciales entre fases disimilares. Tal es el caso de los materiales compuestos basados en BaTiO3 (fase ferroeléctrica) y NiFe2O4 (fase magnética), que ya se han empezado a preparar fundamentalmente por medio de técnicas de deposición altamente energéticas. Sin embargo de cara a su aplicación práctica, sería interesante poder preparar esos materiales por métodos más sostenibles y menos costosos. De acuerdo con ello, en este trabajo se presenta un estudio preliminar en torno a la evolución microestructural experimentada por los materiales basados en NiFe2O4-BaTiO3 cuando son preparados mediante una técnica de procesamiento suave en disolución como es la síntesis hidrotermal. En concreto se ha analizado la influencia que diversos parámetros característicos del procesamiento hidrotermal pueden tener sobre la generación y distribución de fases e interfases durante la posterior consolidación térmica de estos materiales compuestos
Evolución microestructural en la preparación de materiales compuestos NiFe2O4-BaTiO3 por vía hidrotermal
La obtención de materiales monofásicos con respuesta ferroeléctrica y (anti-)ferromagnética simultánea y acoplada resulta problemática debido a limitaciones intrínsecas de tipo físico, estructural y electrónico. En este sentido una alternativa más realista, y en cierto modo con mayor flexibilidad a la hora de diseñar futuros dispositivos multiferroicos, consiste en preparar materiales compuestos en los cuales el acoplamiento magnetoeléctrico se puede alcanzar explotando los efectos interfaciales entre fases disimilares. Tal es el caso de los materiales compuestos basados en BaTiO3 (fase ferroeléctrica) y NiFe2O4 (fase magnética), que ya se han empezado a preparar fundamentalmente por medio de técnicas de deposición altamente energéticas. Sin embargo de cara a su aplicación práctica, sería interesante poder preparar esos materiales por métodos más sostenibles y menos costosos. De acuerdo con ello, en este trabajo se presenta un estudio preliminar en torno a la evolución microestructural experimentada por los materiales basados en NiFe2O4-BaTiO3 cuando son preparados mediante una técnica de procesamiento suave en disolución como es la síntesis hidrotermal. En concreto se ha analizado la influencia que diversos parámetros característicos del procesamiento hidrotermal pueden tener sobre la generación y distribución de fases e interfases durante la posterior consolidación térmica de estos materiales compuestos
Low CO/CO<sub>2</sub> ratios of comet 67P measured at the Abydos landing site by the <i>Ptolemy</i> mass spectrometer
Comets are generally considered to contain the best-preserved material from the beginning of our planetary system, although the mechanism of their formation and subsequent evolution are still poorly understood. Here we report the direct in situ measurement of H2O, CO, and CO2 by the Ptolemy mass spectrometer onboard the Philae lander, part of the European Space Agency’s Rosetta mission, at the Abydos site of the Jupiter-family comet 67P/Churyumov-Gerasimenko. A CO/CO2 ratio of around 0.07 ± 0.04 is found at the surface of the comet, a value substantially lower than the one measured by ROSINA in the coma. Such a major difference is a potential indication of heterogeneity of the nucleus and not of changes in the CO/CO2 ratio of the coma with radial distance
VNIR spectral analyses of powdered mixtures with ExoMars-Ma_Miss instrument
Ma_Miss (Mars Multispectral Imager for Subsurface Studies) experiment onboard of ExoMars 2018 mission to Mars will study the Martian subsurface down to a depth of 2 meters [1]. Ma_Miss is a miniaturized spectrometer, integrated within the drilling system of the ExoMars rover; it will perform visible and near infrared spectroscopy in the 0.4-2.2 μm range, acquiring signal from the excavated borehole wall. The spectroscopic characterization of the subsurface rocks will give us important information about mineralogy, petrology and geological processes; moreover it will give insights about materials that have not been altered by surface processes such as erosion, weathering or oxidation. Spectroscopic measurements have been performed on different types of rock/mineral mixtures with the Ma_Miss laboratory model (breadboard). <P /
Sizing gold nanoparticles by optical extinction spectroscopy
The measurement of optical extinction is used to determine the size of nearly spherical gold nanoparticles suspended in solution, produced by a 'reverse micelles' process. The contrast between the maximum and the minimum in the extinction spectra around 450 and 520 nm shows a linear dependence with the mean radius of the gold particles less than 3 nm; however, the method can be used to size particles up to 7 nm. Experimental results for extinction spectra can be fitted by Mie's theory if the optical constants from bulk material values are modified by introducing the limitation of the mean free path due to collisions of conduction electrons with the boundary of the nanoparticles.Facultad de Ciencias ExactasCentro de Investigaciones Óptica
Thermal evolution of CaO-doped HfO2 films and powders
Solid solutions of ZrO2 and HfO2 are potential electrolyte materials for intermediate-temperature SOFC because both are oxygen-ion conductors. The main challenge for these compounds is to reduce the relatively high value of the activation energies vacancies diffusion, which is influenced by several factors. In this work the thermal evolution of CaO-HfO2 materials have been investigated. (CaO)y-Hf(1-y)O(2-y) (y 0.06, 0.14 y 0.2) coatings and powders were synthesized by chemical solution deposition (CSD). Films were deposited onto alumina substrates by Dip Coating technique, the burning of organic waste was carried out at 500 °C under normal atmosphere and then the films were thermally treated at intervals of temperature rising to a maximum temperature of 1250 °C. By means Glazing Incidence X-ray Diffraction (ρ-2θ configuration) the phases were studied in the annealed films. On the other hand, the thermal evolution and crystallization process of powders were analyzed in-situ by HT-XRD. The phenomena crystallization occurred in films and powders were analyzed. The activation energies of diffusion of oxygen vacancies of HfO2-14 mole% CaO and HfO2-20 mole% CaO films were measured from the thermal evolution of the relaxation constant measured by Perturbed Angular Correlation Technique.Facultad de Ciencias ExactasFacultad de Ciencias Agrarias y Forestale
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