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ASTROFISICA

The Cosmic Microwave Background Bipolar Power Spectrum:
We study the statistical isotropy (SI) of temperature fluctuations of the CMB as distinct from Gaussianity. We present a detailed formalism of the bipolar power spectrum (BiPS) which was introduced as a fast method of measuring the statistical isotropy by Hajian & Souradeep 2003. The method exploits the existence of patterns in the real space correlations of the CMB temperature field. We discuss the applications of BiPS in constraining the topology of the universe and other theoretical scenarios of SI violation. Unlike the traditional methods of search for cosmic topology, this method is computationally fast.
PHYSICS OF SUPERNOVAE
The origin of cosmic rays (CR) is supposed to be closely connected with supernovae (SNe) which create the conditions favorable for various hanisms of the CR acceleration to operate effectively. First, modern ideas about the physics of the SN explosion are briefly discussed: the explosive thermonuclear burning in degenerate white dwarfs resulting in Type Ia SNe and the gravitational collapse of stellar cores giving rise to other types of SNe (Ib, Ic, IIL,IIP). Next, we survey some global properties of the SNe of different types: the total explosion energy distribution of various components kinetic energy of the hydrodynamic flow, electromagnetic radiation, temporal behavior of the neutrino emission and individual energies of different neutrino flavors).
Plasma Frequency Shift Due to a Slowly Rotating
We investigate the e ects of a slowly rotating compact gravitational source on electron oscillations in a homogeneous electrically neutral plasma in the absence of an external electric or magnetic field. Neglecting the random thermal motion of the electrons we assume the gravitoelectro-magnetic approximation to the general theory of relativity for the gravitational field. It is shown that there is a shift in the plasma frequency and hence in the dielectric constant of the plasma due to the gravitomagnetic force.
Regimes of Stability and Scaling Relations.
We report on our theoretical and numerical results concerning the transport mechanisms in the asteroid belt. We first derive a simple kinetic model of chaotic difusion and show how it gives rise to some simple correlations (but not laws) between the removal time (the time for an asteroid to experience a qualitative change of dynamical behavior and enter a wide chaotic zone) and the Lyapunov time.
Linear Theory of Thin, Radially-Stratified Disks
We consider the nonaxisymmetric linear theory of radially-stratified disks. We work in a shearing-sheet-like approximation, where the vertical structure of the disk is neglected, and develop equations for the evolution of a plane-wave perturbation comoving with the shear flow (a shearing wave, or “shwave”). We calculate a complete solution set for compressive and incompressive short-wavelength perturbations in both the stratified and unstratified shearing-sheet models. We develop expressions for the latetime asymptotic evolution of an individual shwave as well as for the expectation value of the energy for an ensemble of shwaves that are initially distributed isotropically in k-space.
Cosmic evolution of the galaxy mass and luminosity functions by morphological type from multi-wavele
We constrain the evolution of the galaxy mass and luminosity functions from the analysis of (pub-lic) multi-wavelength data in the Chandra Deep Field South (CDFS) area, obtained from the GOODS and other projects, and including very deep high-resolution imaging by HST/ACS. Our reference catalogue of faint high-redshift galaxies, which we have thoroughly tested for completeness and reliability, comes from a deep image by IRAC on the Spitzer Observatory. These imaging data in the field are complemented with extensive optical spectroscopy by the ESO VLT/FORS2 and VIMOS spectrographs, while deep K-band VLT/ISAAC imaging is also used to derive further complementary statistical constraints and to assist the source identification and SED analysis.
Nonhelical turbulent dynamos: shocks and shear
Small scale turbulent dynamo action in compressible transonic turbulence is discussed. It is shown that the critical value of the magnetic Reynolds number displays a bimodal behavior and changes from a typical value of 35 for small Mach numbers to about 80 for larger Mach numbers. The transition between the two regimes is relatively sharp. The direct simulations are then compared with simulations where shocks are captured using a shock viscosity that becomes large at locations where there are shocks. In the presence of shear it is shown that large scale dynamo action is possible.
Warm Molecular Gas Traced with CO J = 7->6 in the Galaxy’s Central 2 pc: Dynamical Heat
We present an 11′resolution map of the central two parsecs of the Galaxy in the CO J=7->6 rotational transition. The CO emission shows rotation about Sgr A*, but also evidence for non-circular turbulent motion and a clumpy morphology.
Comments on ´´Sudden future singularities´´.
Barrow just presented an interesting letter which shows that a singularity can occur at a finite future time in an expanding Friedmann universeIntroduce aquí la descripción del enlace.
Discovering the microJy Radio VLBI Sky via ´´Full-beam´´ Self-calibration.
We demonstrate that at 1.4 GHz the combined response of sources detected serendipitously in deep, wide-field VLBI images is sufficient to permit self-calibration techniques to be employed. This technique of “full-beam” VLBI self-calibration permits coherent VLBI observations to be successfully conducted in any random direction on the sky, thereby enabling very faint radio sources to be detected. Via full beam self-calibration.
Real vs. simulated relativistic jets.
Intensive VLBI monitoring programs of jets in AGN are showing the existence of intricate emission patterns, such as upstream
motions or slow moving and quasi-stationary componentes trailing superluminal features. Relativistic hydrodynamic and emission simulations of jets are in very good agreement with these observations, proving as a powerful tool for the understanding of the physical processes taking place in the jets of AGN, microquasars and GRBs. These simulations show that the variability of the jet emission is the result of a complex combination of phase motions, viewing angle selection effects, and non-linear interactions between perturbations and the underlying jet and/or ambient medium.
A COSMIC MILESTONE I: CONSTRAINTS FROM METAL-POOR HALO STARS ON THE COSMOLOGICAL REIONIZATION EPOCH.
Theoretical studies and current observations of the high-redshift intergalactic medium (IGM) indicate that at least two cosmic transitions may occur when the universe reaches gas metallicities of about 10−3Z. hese are the cosmological reionization of the IGM, and the transition from a primordial to present-day mode of star formation. We quantify this relation through calculations of the ionizing radiation produced in association with the elements carbon, oxygen and silicon observed in Galactic metal-poor halo stars, which are likely second-generation objects formed in the wake of primordial supernovae.
Radio-loud and Radio-quiet X-ray Binaries.
The three basic ingredients - a spinning ompact object, an accretion disc and a collimated relativistic jet - make microquasars a galactic scaled-down version of the radio-loud AGN. That explains the large interest attributed to this new class of objects, which up to now consists of less than 20 members. Microquasars belong to the much larger class of X-ray binary systems, where there exits a compact object together with its X-ray emitting accretion disc, but the relativistic jet is missing. When does an X-ray binary system evolve into a microquasar? Ideal for studying such kind of a transition is the periodic microquasar LSI +61◦303 formed by a compact object accreting from the equatorial wind of a Be star and with more than one event of super-critical accretion and ejection along the eccentric orbit.
VLBI observations of young Type II supernovae.
We give an overview of circumstellar interaction in young Type II supernovae, as seen through the eyes of very-long-baseline interferometry (VLBI) observations. The resolution attained by such observations (<1 mas) is a powerful tool to probe the interaction that takes place after a supernova goes off. The direct imaging of a supernova permits, in principle, to estimate the deceleration of its expansion, and to obtain information on the ejecta and circumstellar density profiles, as well as estimates of the magnetic field intensity and relativistic particle energy density in the supernova.
Continuum EVN and MERLIN observations of Ultra Luminous.
Radio imaging of ULIR galaxies is ideal to explore the connection between the starburst and the AGN phenomenon since it is unaffected by dust obscuration, and provides the required high angular resolution to distinguish between an AGN and starburst emission. We have made combined 18cm radio continuum, EVN and MERLIN observations of 13 ULIRGs that have the parsec and deci-parsec scale resolution necessary to distinguish between an AGN and supernovae remnants at the centres of these galaxies, and assess the contribution of each to the total energy distribution. Images of four galaxies are presented here.Introduce aquí la descripción del enlace.
Packet Loss in High Data Rate Internet Data Transfer for eVLBI.
VLBI is gradually moving to the point where Gbps data rates are becoming routine. A number of experiments have shown that the internet can be used at data rates of several hundred Mbps on production networks. However use of the network is accompanied by packet loss. The paper discusses the statistics of packet loss as found by recent tests and investigates the expected effect of packet loss on correlator performance and signal to noise ratio on eVLBI observations. The relative merits of UDP versus TCP are also discussed.
Cryogenic Filters for RFI Mitigation in Radioastronomy.
RFI mitigation in Radioastronomy can be achieved adopting cryogenic filters in appropriate typologies. A study has been conducted in L, C and X band with the evaluation of the filter architecture in copper, with theoretical estimation, computer simulations, prototypes realization, laboratory measurements. Such work has been preliminary to the realization of HTS samples with the purpose of a similar complete characterization approach.
Long-range interactions between dark-matter particles in a model with a cosmological, spontaneously-
In a cosmological model with a chiral symmetry, there are two, dynamically- & related spin-zero fields, a scalar & and a pseudoscalar b. These fields have self-interactions. Spontaneous symmetry breaking results in a very massive 5×1011 GeV, and a nearly massless, (Goldstone-like)seudoscalar particle with 0 < mb< 2.7×10&#8722;6 eV. One or both particles can be part of dark matter.
CONSTRAINTS ON THE CARDASSIAN EXPANSION FROM THE COSMIC LENS ALL-SKY SURVEY GRAVITATIONAL LENS STATI
The existence of a dark energy component has usually been invoked as the most plausible way to explain the recent observational results. However, it is also well known that effects arising from new physics (e.g. extra dimensions) can mimic the gravitational effects of a dark energy through a modification of the Friedmann equation.
Evidence for unusual events in high energy cosmic ray interactions.
Anomalous events with a large transverse momenta PT were found for all secondary particles in an analysis of experimental data on cosmic ray interactions at E0 >5·1013eV. In order to clarify the underlying mechanism of these events, the intermittency analysis of interactions with both large and usual transverse momentum was performed. It is shown that behavior of intermittency indices &(q) as a function of rank factorial momentum q for such interactions is very peculiar. The indices show slight growth for the events with large transverse momenta for all secondary particles in contrast with the fast growth for events with normal average transverse momenta for final particles.
Rates of Horizontal Tau Air-Showers observable by satellites.
Up-going and Horizontal Tau Air-Showers, UpTaus and HorTaus, may trace Ultra High Energy Neutrino Tau Earth Skimming at the edge of the horizon. We show that such events even for minimal GZK neutrino fluxes could be detected by space telescopes such as the EUSO project: These Horizontal Tau Showers will track very long fan-like, multifinger showers whose signature would be revealed by EUSO, OWL experiments. Moreover the additional imprint of their young secondaries (µ± and bundles with e± pair flashes) might allow to disentangle their nature from the old UHECR secondaries in horizontal showers.
Discovery of magnetic fields in central stars of planetary nebulae.
For the first time we have directly detected magnetic fields in central stars of planetary nebulae by means of spectro-polarimetry with FORS1 at the VLT. In all four objects of our sample we found kilogauss magnetic fields, in NGC1360 and LSS 1362 with very high significance, while in EGB 5 and Abell 36 the existence of a magnetic field is probable but with less certainty. This discovery supports the hypothesis that the non-spherical symmetry of most planetary nebulae is caused by magnetic fields in AGB stars.
CIENCIA DE LOS MATERIALES
CÁLCULO DE LA FUNCIÓN DIELÉCTRICA EFECTIVA EN PELÍCULAS DELGADAS DE SILI
Se modeló el silicio poroso como un medio compuesto de dos fases, conformado por partículas de silicio monocristalino inmersas en una matriz homogénea de aire. Los poros del material se simularón deformando las partículas, inicialmente esféricas, hasta obtener elipsoides de alta excentricidad. Se calculó la función dieléctrica efectiva en películas delgadas de silicio poroso utilizando teorías de medio efectivo (Maxwell-Garnett, Bruggeman y Landau-Lifshitz-Looyenga (LLL).
PARTICIPACIÓN DEL FONÓN LO EN LA RELAJACIÓN TÉRMICA DE PORTADORES CALIEN
Portadores calientes fueron generados por bombeo óptico en películas de GaAs;Ge y GaAs:Sn crecidas por epitaxia en fase líquida y con distintas concentraciones de impurezas. Estos portadores alcanzan entre ellos un causi-equilibrio a través de distintos procesos de relajación, con lo cual se puede definir una temperatura del portador caliente (Tp).
ANÁLISIS POR FTIR DE DIAMANTE Y DLC
Se presenta un estudio comparativo entre películas delgadas de diamante y de carbono tipo diamante (DLC) depositadas en un plasma con alto contenido de hidrógeno. La caracterización de las películas se efectuó por microscopia de fuerza atómica (AFM), espectroscopia Raman y espectroscopia infrarroja con transformada rápida de Fourier FTIR).
APLICACIÓN ACTUAL DE LA TÉCNICA DE DIFRACCIÓN DE RAYOS X PARA LA CARACTERIZACI&
La difracción de rayos X (DRX) es una técnica analítica de uso frecuente en productos farmacéuticos de estado sólido en la que se determinan parámetros asociados con la estructura cristalina tales como, fases presentes, orientación preferencial, tamaño de grano, porcentaje de cristalinidad; a partir de las cuales se siguen modelos de interpretación que permiten inferir características propias de un determinado producto, entre las que se tienen la detección y cuantificación de componentes activos y polimorfismos, determinación de cambios adversos para la estructura final del medicamento cuando es expuesto a condiciones del medio (alta o baja temperatura, grado de humedad, flujo de gases).
ESTUDIO DE TRANSICIONES DE FASE E INCONMENSURABILIDAD EN EL CRISTAL DE Rb2CoBr4 POR MEDIO DE LA TECN
Muchas estructuras asociadas a las perovskitas cuya formula ideal es ABX3 exhiben propiedades similares tales como inconmensurabilidad, ferroelectricidad, ferromagnetismo, formación de pares de Cooper, el efecto Jahn Teller y la superconductividad entre otras. A este grupo pertenecen algunas sales de la familia A2BX4. El compuesto de interés en el presente trabajo es el cristal de Rb2CoBr4, que fue crecido utilizando el Método de Brigman Modificado.
MAGNETIC AND MAGNETOTRANSPORT PROPERTIES OF La0.67Ca0.33MnO3-&#948; THIN FILMS
La0.67Ca0.33MnO3-&#948; manganites thin films were deposited In Situ using a highpressure dc-sputtering process. Pure oxygen at a pressure of 3.5 mbar was used as sputtering gas. The films were grown on different single crystal substrates. Electrical characterization showed a metal-insulating transition between 150 K and 280 K dependent of the substrate.
FÍSICA DEL PLASMA.
FÍSICA NUCLEAR.
Nuclei from QCD : Strategy, Challenges and Status.
Perhaps the greatest challenge facing those of us working in the area of strong interaction physics is to be able to rigorously compute the properties and interactions of nuclei. The many decades of theoretical and experimental investigations in nuclear physics have, in many instances, provided a very precise phenomenology of the strong interactions in the non-perturbative regime. However, at this point in time we have little understanding of much of this phenomenology in terms of the underlying theory of the strong interactions, Quantum Chromo Dynamics (QCD).
Neutrino Electromagnetic Form Factors Effect on the Neutrino Cross Section in Dense Matter
The sensitivity of the differential cross section of the interaction between neutrino-electron with dense matter to the possibly nonzero neutrino electromagnetic properties has been investigated. Here, the relativistic mean field model inspired by effective field theory has been used to describe non strange dense matter, both with and without the neutrino trapping. We have found that the cross section becomes more sensitive to the constituent distribution of the matter, once electromagnetic properties of the neutrino are taken into account.
Status of the ATF extraction line laser-wire.
A new laser-wire is being installed in the extraction line of the ATF at KEK. This device aims at demonstrating that laser wires can be used to measure micrometre scale beam size.
Statistical mechanics and Vlasov equation allow for a simplified Hamiltonian description of Single-P
A reduced Hamiltonian formulation to reproduce the saturated regime of a Single Pass Free Electron Laser, around perfect tuning, is here discussed. Asymptotically, Nm particles are found to organize in a dense cluster, that evolves as an individual massive unit. The remaining particles fill the surrounding uniform sea, spanning a finite portion of phase space, approximately delimited by the average momenta w+ and w-. These quantities enter the model as external parameters, which can be self-consistently determined within the proposed theoretical framework. To this aim, we make use of a statistical mechanics treatment of the Vlasov equation, that governs the initial amplification process. Simulations of the reduced dynamics are shown to successfully capture the oscillating regime observed within the original N-body picture.
L´evy–Student Distributions for Halos in Accelerator Beams.
We describe the transverse beam distribution in particle accelerators within the controlled, stochastic dynamical scheme of the Stochastic Mechanics (SM) which produces time reversal invariant diffusion processes. This leads to a linearized theory summarized in a Shchr¨odinger–like (S–l) equation. The space charge effects have been introduced in a recent paper by coupling this S–l equation with the Maxwell equations. We analyze the space charge effects to understand how the dynamics produces the actual beam distributions, and in particular we show how the stationary, self–consistent solutions are related to the (external, and space–charge) potentials both when we suppose that the external field is harmonic constant focusing), and when we a priori prescribe the shape of the stationary solution.
The International Linear Collider beam dumps.
The ILC beam dumps are a key part of the accelerator design. At Snowmass 2005, the current status of the beam dump designs were reviewed, and the options for the overall dump layout considered. This paper describes the available dump options for the baseline and the alternatives and considers issues for the dumps that require resolution.
Asymptotic Analysis of Ultra-relativistic Charge.
This article offers a new approach for analysing the dynamic behaviour of distributions of charged particles in an electromagnetic field. After discussing the limitations inherent in the Lorentz-Dirac equation for a single point particle a simple model is proposed for a charged continuum interacting self-consistently with the Maxwell field in vacuo. The model is developed using intrinsic tensor field theory and exploits to the full the symmetry and light-cone structure of Minkowski spacetime. This permits the construction of a regular stress-energy tensor whose vanishing divergence determines a system of non-linear partial differential equations for the velocity and self-fields of accelerated charge. Within this covariant framework a particular perturbation scheme is motivated by an exact class of solutions to this system describing the evolution of a charged fluid under the combined effects of both self and external electromagnetic fields. The scheme yields an asymptotic approximation in terms of inhomogeneous linear equations for the self-consistent Maxwell field, charge current and time-like velocity field of the charged fluid and is defined as an ultra-relativistic configuration.
On parameterizations of the Nordheim function.
Several parameterizations of tabulated values of the Nordheim function v(y) and its complementary function t(y) are proposed. The function v(y) plays essential role in description of field emission.
PROPIEDADES MAGNÉTICAS Y ESTRUCTURALES DE ALEACIONES PRODUCIDAS POR ALEAMIENTO MECANICO.
En este trabajo reportamos las propiedades magnéticas y estructurales obtenidas por espectroscopia Mössbauer y difracción de rayos X, de aleaciones de hierro aluminio producido por aleamiento mecánico. Se estudiaron concentraciones de 20, 30, 40 y 50% de aluminio con tiempos de molienda de 12, 24, 36 y 48 horas. Todas las aleaciones presentan fase BCC. Todos los espectros Mössbauer tienen la característica de un sistema ferromagnético y desordenado. Cuando la concentración aumenta se nota una tendencia al comportamiento paramagnético.
TRANSICIONES DE FASE INCONMENSURABLE – CONMENSURABLE EN EL CRISTAL DE Rb2CoCl4 UTILIZANDO LA T&Eacut
Propiedades similares a las de las perovskitas exhiben algunas sales de la familia A2BX4. En el presente trabajo las propiedades en consideración son la inconmensurabilidad y el efecto Janh Teller en el cristal de Rb2CoCl4, Este cristal es un miembro defectuoso de la familia de las perovskitas cuya formula ideal es ABX3, a este grupo pertenecen los superconductores de alta temperatura, por lo que una conexión entre las características es lógicamente posible. Se encontró que este cristal pasa por una serie de transiciones inconmensurable – conmensurable y el acoplamiento entre niveles energéticos y electrónicos, detectadas de manera fácil por la técnica de calorimetría diferencial (DSC).
ÓPTICA
MATERIA CONDENSADA
PROPIEDADES MAGNÉTICAS Y ESTRUCTURALES DE ALEACIONES Fe1-x Alx PRODUCIDAS POR ALEAMIENTO MEC&
En este trabajo reportamos las propiedades magnéticas y estructurales obtenidas por espectroscopia Mössbauer y difracción de rayos X, de aleaciones de hierro aluminio producido por aleamiento mecánico. Se estudiaron concentraciones de 20, 30, 40 y 50% de aluminio con tiempos de molienda de 12, 24, 36 y 48 horas. Todas las aleaciones presentan fase BCC. Todos los espectros Mössbauer tienen la característica de un sistema ferromagnético y desordenado. Cuando la concentración aumenta se nota una tendencia al comportamiento paramagnético.
TRANSICIONES DE FASE INCONMENSURABLE &#8211; CONMENSURABLE EN EL CRISTAL DE Rb2CoCl4 UTILIZANDO
Propiedades similares a las de las perovskitas exhiben algunas sales de la familia A2BX4 . En el presente trabajo las propiedades en consideración son la inconmensurabilidad y el efecto Janh Teller en el cristal de Rb2CoCl4, Este cristal es un miembro defectuoso de la familia de las perovskitas cuya formula ideal es ABX3, a este grupo pertenecen los superconductores de alta temperatura, por lo que una conexión entre las características es lógicamente posible. Se encontró que este cristal pasa por una serie de transiciones inconmensurable &#8211; conmensurable y el acoplamiento entre niveles energéticos y electrónicos, detectadas de manera fácil por la técnica de calorimetría diferencial (DSC). La técnica que se utilizó para el crecimiento del cristal de Rb2CoCl4 fue el método de Bridgman modificado.
METAL - INSULATOR TRANSITION STUDIES BY PHOTOLUMINESCENCE ON Sn-DOPED GaAs EPITAXIAL LAYERS.
Se le hizo fotoluminiscencia a una muestra de GaAs crecida por Epitaxia en Fase Líquida y dopada con Sn con concentraciones alrededor de 1x 1017 cm-3, muy cercana a la transición metal- aislador. Se varió la temperatura desde 12 hasta 300 K y la potencia de excitación se cambió en tres ordenes de magnitud. Los espectros mostraron que las transiciones del excitón libre y los excitones ligados se mezclan en una sola banda, mientras que las transiciones libre a ligado y donador-aceptor igualmente forman una sola banda. Se estudian en este trabajo las intensidades, posiciones y anchos de cada banda. Se comparan los resultados de los espectros de PL para las muestras dopadas con concentraciones de impureza menores y mayores para que ocurra la transición metal-aislador para demostrar que esta transición no ocurre abruptamente.
DETERMINACION DE LA ENERGIA DE IONIZACION DEL DONADOR Sn EN AlXGa1-XAs Y SU DEPENDENCIA CON LA FRACC
Para determinar la energía de ionización del donador Sn se analizaron las transiciones donador-banda de valencia de espectros de fotoluminiscencia de muestras epitaxiales de AlxGa1-xAs. Los espectros se tomaron a muestras dopadas con Sn en concentración de 1x1017 cm-3 , a temperatura de 11 K y con fracciones molares del Al en el rango 0<x<0.5. Se utilizó como modelo de análisis el de Eagle modificado con la densidad de estados de Kane y la temperatura del portador caliente con las cuales se pueden obtener mejores ajustes de las curvas espectrales y se pueden reproducir con mayor exactitud parámetros como la brecha de energía y el nivel de Fermi. De esa manera el modelo sólo tiene dos parámetros de ajuste y uno de ellos es la energía de ionización de la impureza.
ESTUDIO DEL CAMPO ELÉCTRICO INTRÍNSECO DE UNA PELÍCULA SEMICONDUCTORA GaAs:Ge A
En este trabajo se analiza la dependencia del campo eléctrico intrínseco F, las energías de transición E0 y Ex, y el parámetro de ensanchamiento G, con la temperatura, para una película epitaxial de GaAs:Ge con concentraciones de 5x1016 cm-3. La muestra estudiada fueron almacenadas por varios años en condiciones ambientales normales. La técnica experimental usada fue la fotorreflectancia a baja temperatura, omándose espectros antes y después de realizar un decapado por ataque químico. Se encontró que los parámetros de ajuste G y F se encuentran fuertemente influenciados por el ataque químico. Estos comportamientos se asocian a defectos superficiales introducidos durante el envejecimiento, los cuales fueron reducidos después del decapado.
ANÁLISIS MÖSSBAUER DE LA TRANSFORMACIÓN HEMATITA A MAGNETITA BAJO TRATAMIENTO T&E
Se presenta un estudio de la cinética de transformación hematita (a-Fe2O3) a magnetita (Fe3O4) mediante un método alternativo que consiste en un tratamiento térmico bajo atmósfera de hidrógeno (20%) y nitrógeno (80 ), a una temperatura de 375°C. Se estudia la evolución de las fases como función del tiempo de tratamiento térmico, desde 0 hasta 25 minutos cada 2.5 minutos mediante las técnicas de espectroscopía Mössbauer y difracción de rayos X.
THE INFLUENCE OF CRISTALLINE ELECTRIC FIELD AND OTHER MAGNETIC INTERACTIONS ON RNiBC COMPOUNDS (R =
The quaternary intermetallic compounds (RC)Ni2B2, has been studied by several techniques because the members of this family show exotic superconductivity and magnetic properties. This compounds, belong to the quaternary family of compounds (RC)m(NiB)n with m = 1, 2 and n = 2. In spite, compounds (RC)2 Ni2B2 was not very intensively studied although they show a similarities in their structural features. The magnetic ordering temperatures TM, as obtained from AC susceptibility measurements, do not show a simple linear scaling with the de Gennes factor as it was observed for the RNi2B2C series.
SÍNTESIS, CARACTERIZACIÓN TÉRMICA Y ELÉCTRICA DE POLÍMEROS ELECTR
Se prepararon combinaciones de complejos poliméricos basados en poli (óxido de etileno), como matriz sólida y la sal metálica sulfato de cobre (CuSO4). Se realizaron estudios de impedancia como función de la temperatura, los termogramas de calorimetría diferencial de barrido muestran una primera anomalía térmica atribuible a la formación de complejo alrededor de 33 oC, una segunda anomalía alrededor de 67 oC correspondiente a la del polímero y una tercer anomalía térmica alrededor de 80 oC debida a la liberación de agua.
ESTADOS CUANTICOS EN UN PUNTO CONFINADO MAGNETICAMENTE.
En este trabajo estudiamos un sistema en el cual un portador (electrón o hueco) o un excitón está confinado por un campo magnético inhomogéneo. Calculamos numéricamente las energías de confinamiento y las correspondientes funciones de ondas para algunos estados del electrón, el hueco y el excitón como sistemas independientes en el punto cuántico. Usamos un perfil de campo inhomogéneo tipo antipunto mag nético.
ESPECTRO DE ABSORCION DE UN EXCITON EN UN PUNTO CUANTICO EN PRESENCIA DE UN CAMPO MAGNETICO
Presentamos resultados concernientes al calculo del espectro de absorcion de un exciton en un punto cuantico autoesamblado en presencia de un campo magnetico uniforme. El hamiltoniano del exciton se soluciona por medio del metodo de la diagonalizacion numerica.
DELOCALIZED ELECTRONIC STATES IN 1D SUPERLATTICES.
Models of one-dimensional systems with short-range correlated disorder have predicted the existence of an energy region where the states are delocalized. This is in contrast to the earlier belief that all the eigenstates are localized in 1D disordered systems. We study the statistical proper- ties of the spectrum of unite superlattice formed from short chains with correlated disorder (repulsive binary alloy).
MEDICIONES DE TERMOPOTENCIA EN PELÍCULAS DELGADAS DE OXIDO DE INDIO.
Se elaboraron películas conductoras y transparentes de óxido de indio por pulverización catódica d.c. en atmósfera reactiva de Ar y O2. Se caracterizan eléctricamente a través de mediciones de termopotencia. Adicionalmente se determinó la densidad de portadores y el mecanismo de dispersión dominante con base en mediciones del coeficiente termoeléctrico en dependencia de la temperatura, los resultados mostraron que los portadores son principalmente dispersados por impurezas neutras.
CUANTIZACIÓN DEL FLUJO MAGNÉTICO EN SUPERCONDUCTORES NO SIMPLEMENTE CONEXOS.
Presentamos desde el punto de vista de la teoría BCS la cuantización del flujo magnético en una región no simplemente conexa. Usualmente, en los textos se muestra esta propiedad del flujo magnético mediante la teoría de Ginzburg-Landau o a través de aproximaciones semiclásicas; nos proponemos en parte mostrar cómo desde la teoría microscópica surge la cuantización del flujo lo que es de utilidad en cursos avanzados de estado sólido o de superconductividad. Para tal fin consideramos un cilindro hueco y encontramos la función de onda del estado base y el hamiltoniano en forma explícita para este sistema. Adicionalmente, ampliamos el contenido del teorema de Byers y Yang al calcular el flujo magnético en el cilindro superconductor hueco.
ELECTRICIDAD Y ELECTRODINAMICA.
Histéresis
Un trabajo sobre el ciclo de histéresis en varios núcleos de hierro dulce.
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