62 research outputs found
Modelado, implementación, optimización y generación de estadísticas de desempeño en una BDOO
El presente trabajo, muestra los resultados obtenidos en el proyecto de investigación de cátedra realizado en la Sede Rafaela de la Universidad Católica de Santiago del Estero en un lapso de catorce meses iniciados en mayo del 2011, el cual aborda la problemática de la optimización en el diseño de una Base de Datos Orientada a Objetos (BDOO), garantizando bloqueos eficientes, concurrencia y acceso multiusuario.
Se realizó el diseño e implementación de una BDOO del material bibliográfico existente en la UCSE DAR, explotando los beneficios que estas proponen.
Al trabajar con gran cantidad de datos, es fundamental buscar en la Base de Datos tan eficazmente como sea posible. Para esto se probaron dos productos de BDOO lo que nos permitió realizar un análisis comparativo de la respuesta de estas, tiempos, bloqueos, flexibilidad, desempeño, etc.
A partir de las Bases de Datos generada, se realizaron diferentes optimizaciones sobre estas de manera tal que podamos comprobar y comparar el comportamiento ante consultas sobre muchos objetos, sobre objetos complejos, sin indexar e indexados.
Luego, todos los casos de prueba y mediciones de desempeño realizados, nos permitieron generar conclusiones acerca de las particularidades y similitudes en ambos Sistemas de Administración de Bases de Datos.Red de Universidades con Carreras en Informática (RedUNCI
Metal-insulator transition in a 2D electron gas: Equivalence of two approaches for determining the critical point
The critical electron density for the metal-insulator transition in a
two-dimensional electron gas can be determined by two distinct methods: (i) a
sign change of the temperature derivative of the resistance, and (ii) vanishing
activation energy and vanishing nonlinearity of current-voltage characteristics
as extrapolated from the insulating side. We find that in zero magnetic field
(but not in the presence of a parallel magnetic field), both methods give
equivalent results, adding support to the existence of a true zero-field
metal-insulator transition.Comment: As publishe
The key role of smooth impurity potential in formation of hole spectrum for p-Ge/Ge_{1-x}Si_x heterostructures in the quantum Hall regime
We have measured the temperature (0.1 <= T <= 15 K) and magnetic field (0 <=
B <= 12 T) dependences of longitudinal and Hall resistivities for the
p-Ge_0.93Si_0.07/Ge multilayers with different Ge layer widths 10 <= d_w <= 38
nm and hole densities p_s = (1-5)10^11 cm^-2. Two models for the long-range
random impurity potential (the model with randomly distributed charged centers
located outside the conducting layer and the model of the system with a spacer)
are used for evaluation of the impurity potential fluctuation characteristics:
the random potential amplitude, nonlinear screening length in vicinity of
integer filling factors nu = 1 and nu = 2 and the background density of state
(DOS). The described models are suitable for explanation of the unusually high
value of DOS at nu = 1 and nu = 2, in contrast to the short-range impurity
potential models. For half-integer filling factors the linear temperature
dependence of the effective QHE plateau-to-plateau transition width nu_0(T) is
observed in contrast to scaling behavior for systems with short-range disorder.
The finite T -> 0 width of QHE transitions may be due to an effective low
temperature screening of smooth random potential owing to Coulomb repulsion of
electrons.Comment: Accepted for publication in Nanotechnolog
Effect of screening of the Coulomb interaction on the conductivity in the quantum Hall regime
We study variable range hopping in the quantum Hall effect regime in the
presence of a metallic gate parallel to the plane of a two-dimensional electron
gas. Screening of the Coulomb interaction by the gate causes the partial
``filling'' of the Coulomb gap in the density of localized states. At low
enough temperatures this leads to a substantial enhancement and a new
temperature behavior of the hopping conductivity. As a result, the diagonal
conductivity peaks become much wider. The power law dependence of the width of
the peaks on the temperature changes: the corresponding exponent turns out to
be twice as small as that for gateless structures. The width dependences on the
current in non-ohmic regime and on the frequency for the absorption of the
electromagnetic waves experience a similar modification. The experimental
observation of the crossovers predicted may demonstrate the important role of
the Coulomb interaction in the integer quantum Hall regime.Comment: 14 pages + 3 figures by request preprint TPI-MINN-93/58-
Weak anisotropy and disorder dependence of the in-plane magnetoresistance in high mobility (100) Si-inversion layers
We report studies of the magnetoresistance (MR) in a two-dimensional electron
system in (100) Si-inversion layers, for perpendicular and parallel
orientations of the current with respect to the magnetic field in the 2D-plane.
The magnetoresistance is almost isotropic; this result does not support the
suggestion of the orbital origin of the MR in Si-inversion layer. In the
hopping regime, however, the MR contains a weak anisotropic component that is
non-monotonic in magnetic field. We found that the field, at which the MR
saturates, for different samples varies by a factor of two, being lower or
higher than the field of complete spin polarization of free carriers.
Therefore, the saturation of the MR can not be identified with the spin
polarization of free carriers.Comment: 4 pages, 4 figures; New data adde
Determinación de la contaminación gaseosa en el Aeropuerto Internacional de Ezeiza
El presente trabajo tiene como objetivo presentar los resultados sobre el análisis de los gases contaminantes resultantes de la operación de los motores de las aeronaves durante las fases de aproximación, aterrizaje, tiempo en plataforma, rodaje y despegue. También cuantificar los gases contaminantes emitidos por los vehículos de asistencia que operan dentro del aeropuerto.
Cabe destacar que el estudio efectuado se encuentra estrechamente relacionado con la iniciativa propuesta por las principales entidades y autoridades aeronáuticas sobre el desarrollo de aeropuertos ecológicamente sustentables (denominados como “Green Airports”), y a su vez, con los valores máximos de contaminantes permitidos por la Organización Mundial de la Salud (OMS).
Dichos análisis fueron realizados mediante software computacionales específicos. Se plantearon distintos escenarios operativos del aeropuerto, para luego proceder a su simulación. De esta manera, se obtienen las curvas de concentración de contaminantes permitiendo analizar el aporte contaminante dentro del predio aeroportuario y su entorno.
(Párrafo extraído del texto a modo de resumen)Facultad de Ingenierí
Determinación de la contaminación acústica en el entorno del Aeropuerto Internacional de Ezeiza
A través del presente trabajo se buscó obtener una noción preliminar de la situación actual del aeropuerto en lo referente a contaminación acústica. Este estudio se enfocó en el marco de los Green airports (aeropuertos verdes), iniciativa llevada a cabo por las principales autoridades del ámbito aeronáutico para el desarrollo de aeropuertos ecológicamente sustentables.
Dichos análisis fueron realizados mediante software especializado, tales como el INM 7.0 (Integrated Noise Model de la FAA) y el Custic 3.2. La Metodología consistió en plantear distintos escenarios operativos del aeropuerto, para luego simularlos. Con esta información se pudieron construir las respectivas huellas de ruido.
Este documento se centra sobre tres pilares fundamentales que hacen a la actividad de los aeropuertos; las operaciones de los vehículos de asistencia a las aeronaves o GSE (Ground Support Equipment) que circulan por la plataforma comercial, las operaciones de rodaje de las aeronaves (Taxing) y las operaciones de aproximación y despegue.Facultad de Ingenierí
Electron-Electron Interactions and the Hall-Insulator
Using the Kubo formula, we show explicitly that a non-interacting electron
system can not behave like a Hall-insulator, {\it ie.,} a DC resistivity matrix
and finite in the zero temperature
limit, as has been observed recently in experiment. For a strongly interacting
electron system in a magnetic field, we illustrate, by constructing a specific
form of correlations between mobile and localized electrons, that the Hall
resistivity can approximately equal to its classical value. A Hall-insulator is
realized in this model when the density of mobile electrons becomes vanishingly
small. It is shown that in non-interacting electron systems, the
zero-temperature frequency-dependent conductacnce generally does not give the
DC conductance.Comment: 11 pages, RevTeX3.
Sliding motion of a two-dimensional Wigner crystal in a strong magnetic field
We study the sliding state of a two-dimensional Wigner crystal in a strong
magnetic field and a random impurity potential. Using a high-velocity
perturbation theory, we compute the nonlinear conductivity, various correlation
functions, and the interference effects arising in combined AC + DC electric
effects, including the Shapiro anomaly and the linear response to an AC field.
Disorder is found to induce mainly transverse distortions in the sliding state
of the lattice. The Hall resistivity retains its classical value. We find that,
within the large velocity perturbation theory, free carriers which affect the
longitudinal phonon modes of the Wigner crystal do not change the form of the
nonlinear conductivity. We compare the present sliding Wigner crystal in a
strong magnetic field to the conventional sliding charge-density wave systems.
Our result for the nonlinear conductivity agrees well with the
characteristics measured in some experiments at low temperatures or large
depinning fields, for the insulating phases near filling factor = 1/5. We
summarize the available experimental data, and point out the differences among
them.Comment: appeared in RPB vol. 50, 4600 (1994); LaTex file; 3 figures available
from [email protected]
Variational quantum Monte Carlo study of two-dimensional Wigner crystals: exchange, correlation, and magnetic field effects
The two-dimensional Wigner crystals are studied with the variational quantum
Monte Carlo method. The close relationship between the ground-state
wavefunction and the collective excitations in the system is illustrated, and
used to guide the construction of the ground-state wavefunction of the strongly
correlated solid. Exchange, correlation, and magnetic field effects all give
rise to distinct physical phenomena. In the absence of any external magnetic
field, interesting spin-orderings are observed in the ground-state of the
electron crystal in various two-dimensional lattices. In particular,
two-dimensional bipartite lattices are shown not to lead necessarily to an
antiferromagnetic ground-state. In the quantum Hall effect regime, a strong
magnetic field introduces new energy and length scales. The magnetic field
quenches the kinetic energy and poses constraints on how the electrons may
correlate with each other. Care is taken to ensure the appropriate
translational properties of the wavefunction when the system is in a uniform
magnetic field. We have examined the exchange, intra-Landau-level correlation
as well as Landau-level-mixing effects with various variational wavefunctions.
We also determine their dependences on the experimental parameters such as the
carrier effective mass at a modulation-doped semiconductor heterojunction. Our
results, when combined with some recent calculations for the energy of the
fractional quantum Hall liquid including Landau-level-mixing, show
quantitatively that in going from -doping to -doping in
heterojunction systems, the crossover filling factor from the fractional
quantum Hall liquid to the Wigner crystal changes from filling factor to . This lends strong support to the claim that theComment: LaTex file, 14 figures available from [email protected]
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