164 research outputs found
Self-compensation in phosphorus-doped CdTe
We investigate the self-compensation mechanism in phosphorus-doped CdTe. The
formation energies, charge transition levels, and defects states of several
P-related point defects susceptible to cause self-compensation are addressed by
first-principles calculations. Moreover, we assess the in uence of the
spin-orbit coupling and supercell-size effects on the stability of AX centers
donors, which are believed to be responsible for most of the self-compensation.
We report an improved result for the lowest-energy configuration of the P
interstitial (P) and find that the self-compensation mechanism is
not due to the formation of AX centers. Under Te-rich growth conditions,
(P) exhibits a formation energy lower than the substitutional
acceptor (P) when the Fermi level is near the valence band, acting
as compensating donor. While, for Cd-rich growth conditions, our results
suggest that p-type doping is limited by the formation of
(P-V) complexes.Comment: 5 page
UNA APROXIMACIÓN NO LINEAL A LA RELACIÓN INFLACIÓN– CRECIMIENTO ECONÓMICO: UN ESTUDIO PARA AMÉRICA LATINA
Existe un amplio consenso del efecto adverso de altas tasas de inflación sobre el crecimiento económico, no obstante, no existe pleno acuerdo en cuanto al efecto de tasas de inflación moderadas. Este trabajo re- examina la relación entre la inflación y el crecimiento en una muestra de nueve paÃses de América Latina utilizando nuevas técnicas econométricas apropiadas para la evaluación e inferencia de relaciones no lineales. Los resultados de la investigación confirman la existencia de una relación no lineal entre ambas variables encontrando que tasas de inflación superiores a 17% ocasionan una contracción en la tasa de crecimiento del producto, pero tienen un efecto positivo cuando no superan este nivel. Sin embargo, el amplio intervalo de confianza encontrado para el punto de quiebre sugiere cautela al momento de hacer recomendaciones de polÃtica económica. Tasas de inflación mayores al 9%, dependiendo el paÃs, podrÃan tener efectos adversos sobre el crecimiento. Cabe destacar que, de manera contraria a trabajos anteriores, los resultados encontrados se mantienen robustos ante la eliminación de observaciones extremas.Inflación, crecimiento, América Latina, datos de panel
XOR gate response in a mesoscopic ring with embedded quantum dots
We address XOR gate response in a mesoscopic ring threaded by a magnetic flux
. The ring, composed of identical quantum dots, is symmetrically attached
to two semi-infinite one-dimensional metallic electrodes and two gate voltages,
viz, and , are applied, respectively, in each arm of the ring which
are treated as the two inputs of the XOR gate. The calculations are based on
the tight-binding model and the Green's function method, which numerically
compute the conductance-energy and current-voltage characteristics as functions
of the ring-electrodes coupling strengths, magnetic flux and gate voltages.
Quite interestingly it is observed that, for (,
the elementary flux-quantum) a high output current (1) (in the logical sense)
appears if one, and only one, of the inputs to the gate is high (1), while if
both inputs are low (0) or both are high (1), a low output current (0) appears.
It clearly demonstrates the XOR behavior and this aspect may be utilized in
designing the electronic logic gate.Comment: 7 pages, 5 figure
NOR gate response in a double quantum ring: An exact result
NOR gate response in a double quantum ring, where each ring is threaded by a
magnetic flux , is investigated. The double quantum ring is sandwiched
symmetrically between two semi-infinite one-dimensional metallic electrodes and
two gate voltages, namely, and , are applied, respectively, in lower
arms of the two rings those are treated as the two inputs of the NOR gate. A
simple tight-binding model is used to describe the system and all the
calculations are done through the Green's function formalism. Here we exactly
calculate the conductance-energy and current-voltage characteristics as
functions of the ring-to-electrode coupling strengths, magnetic flux and gate
voltages. Our numerical study predicts that, for a typical value of the
magnetic flux (, the elementary flux-quantum), a
high output current (1) (in the logical sense) appears if both the inputs to
the gate are low (0), while if one or both are high (1), a low output current
(0) results. It clearly demonstrates the NOR gate behavior and this aspect may
be utilized in designing an electronic logic gate.Comment: 8 pages, 5 figure
Electron transport in a double quantum ring: Evidence of an AND gate
We explore AND gate response in a double quantum ring where each ring is
threaded by a magnetic flux . The double quantum ring is attached
symmetrically to two semi-infinite one-dimensional metallic electrodes and two
gate voltages, namely, and , are applied, respectively, in the lower
arms of the two rings which are treated as two inputs of the AND gate. The
system is described in the tight-binding framework and the calculations are
done using the Green's function formalism. Here we numerically compute the
conductance-energy and current-voltage characteristics as functions of the
ring-to-electrode coupling strengths, magnetic flux and gate voltages. Our
study suggests that, for a typical value of the magnetic flux
(, the elementary flux-quantum) a high output current (1) (in the
logical sense) appears only if both the two inputs to the gate are high (1),
while if neither or only one input to the gate is high (1), a low output
current (0) results. It clearly demonstrates the AND gate behavior and this
aspect may be utilized in designing an electronic logic gate.Comment: 8 pages, 5 figure
Propuesta de extracción automática de candidatos a término del dominio médico procesando información lingüÃstica. Descripción y evaluación de resultados
The description of a method for automatic extraction of term candidates from the medical field by applying linguistic information is presented. Lexicography, morphological and syntactic rules were used. First, the detection was performed by applying a standard dictionary that assigned the tag ‘MED’ (‘MEDICAL’) to the words that could be considered terms. Morphological and syntactic rules were used to try to deduce the part of speech of the words that were not considered in the dictionary (WNCD). Afterwards, nominal phrases that included WNCD and MED were gathered to extract them as term candidates of the field. Smorph, Post Smorph Module (MPS) – both working in groups – and Xfst were the software used. Smorph performs the morphological analysis of character strings and MPS works on local grammar. Xfst is a finite state tool that works on character strings assigning previously stated categories to allow the automatic analysis of expressions. This method was tested on a section of the corpus of clinical cases collected by Burdiles (CCCM - 2009) containing 217,258 words. The results showed 92.58% of precision, 95.02% of recall and 93.78% of F-measure.Se presenta la descripción de un método de extracción automática de candidatos a términos del área médica a partir del procesamiento de información lingüÃstica. Para ello, se trabajó con reglas en el nivel léxico, morfológico y sintáctico. En primer lugar, se realizó la detección aplicando un diccionario estándar, el cual asignó a las palabras consideradas términos, la etiqueta MED (MÉDICO). Luego, para las palabras que no estaban contempladas en el diccionario (PNCD), se dedujeron las categorÃas gramaticales apelando a reglas morfológicas y sintácticas. Posteriormente, se procedió a la conformación de sintagmas nominales que involucraban PNCD y MED, para extraerlos como candidatos a términos del dominio. Se utilizaron los softwares Smorph y Módulo Post Smorph (MPS), que trabajan en bloque, y Xfst. Smoprh realiza el análisis morfológico y MPS trabaja sobre gramáticas locales. Xfst, por su parte, es una herramienta de estados finitos que opera sobre cadenas de caracteres, a las que asigna categorÃas previamente declaradas. El método se probó en una parte del corpus de casos clÃnicos compilado por Burdiles (2012), que contenÃa 217258 palabras, y los resultados arrojaron una precisión de 92,58%, una cobertura de 95,02% y una medida f de 93,78%
Estudio comparativo entre contenidos enseñados a través de dos estrategias metodológicas en alumnos de NM1 del instituto Andrés Bello de Talca.
75 p.El presente trabajo es un estudio comparativo que pretende determinar la estrategia de enseñanza en FÃsica más pertinente para lograr un aprendizaje significativo en alumnos de primero medio (NM1) respecto a la unidad de la Luz en el Instituto Andrés Bello de la ciudad de Talca. Para realizar la investigación se trabajó con dos grupos curso, en uno de ellos se dictaron clases teóricas-expositivas, llamado grupo control y en el grupo experimental en las mismas clases se presentaron experimentos demostrativos
relacionados con los temas tratados, en este caso correspondió a fenómenos luminosos.
Para medir los aprendizajes de ambos grupos, a los alumnos se les aplicó sendas pruebas sobre la unidad de Luz, la cual abarcaba los conceptos de: reflexión, refracción, espejos, lentes, traz ado de rayos en espejos y lentes. Se tuvo cuidado de no hacer preguntas sobre los experimentos demostrativos en sà ya que el grupo control se habrÃa visto impedido de responderlas. Se realizó un análisis estadÃstico para comparar los resultados obtenidos, tanto por concepto como global en la unidad. Se encontraron diferencias
significativas entre ambos grupos, favoreciendo ampliamente en todos los conceptos tratados al grupo experimenta
- …