Molecular Beam Epitaxial Growth of III-V Semiconductor Nanostructures on Silicon Substrates

The main focus and concerns of this PhD thesis is the growth of III-V semiconductor nanostructures (Quantum dots (QDs) and quantum dashes) on silicon substrates using molecular beam epitaxy (MBE) technique. The investigation of influence of the major growth parameters on their basic properties (density, geometry, composition, size etc.) and the systematic characterization of their structural and optical properties are the core of the research work. The monolithic integration of III-V optoelectronic devices with silicon electronic circuits could bring enormous prospect for the existing semiconductor technology. Our challenging approach is to combine the superior passive optical properties of silicon with the superior optical emission properties of III-V material by reducing the amount of III-V materials to the very limit of the active region. Different heteroepitaxial integration approaches have been investigated to overcome the materials issues between III-V and Si. However, this include the self-assembled growth of InAs and InGaAs QDs in silicon and GaAx matrices directly on flat silicon substrate, sitecontrolled growth of (GaAs/In0,15Ga0,85As/GaAs) QDs on pre-patterned Si substrate and the direct growth of GaP on Si using migration enhanced epitaxy (MEE) and MBE growth modes. An efficient ex-situ-buffered HF (BHF) and in-situ surface cleaning sequence based on atomic hydrogen (AH) cleaning at 500 °C combined with thermal oxide desorption within a temperature range of 700-900 °C has been established. The removal of oxide desorption was confirmed by semicircular streaky reflection high energy electron diffraction (RHEED) patterns indicating a 2D smooth surface construction prior to the MBE growth. The evolution of size, density and shape of the QDs are ex-situ characterized by atomic-force microscopy (AFM) and transmission electron microscopy (TEM). The InAs QDs density is strongly increased from 108 to 1011 cm-2 at V/III ratios in the range of 15-35 (beam equivalent pressure values). InAs QD formations are not observed at temperatures of 500 °C and above. Growth experiments on (111) substrates show orientation dependent QD formation behaviour. A significant shape and size transition with elongated InAs quantum dots and dashes has been observed on (111) orientation and at higher Indium-growth rate of 0.3 ML/s. The 2D strain mapping derived from high-resolution TEM of InAs QDs embedded in silicon matrix confirmed semi-coherent and fully relaxed QDs embedded in defectfree silicon matrix. The strain relaxation is released by dislocation loops exclusively localized along the InAs/Si interfaces and partial dislocations with stacking faults inside the InAs clusters. The site controlled growth of GaAs/In0,15Ga0,85As/GaAs nanostructures has been demonstrated for the first time with 1 μm spacing and very low nominal deposition thicknesses, directly on pre-patterned Si without the use of SiO2 mask. Thin planar GaP layer was successfully grown through migration enhanced epitaxy (MEE) to initiate a planar GaP wetting layer at the polar/non-polar interface, which work as a virtual GaP substrate, for the GaP-MBE subsequently growth on the GaP-MEE layer with total thickness of 50 nm. The best root mean square (RMS) roughness value was as good as 1.3 nm. However, these results are highly encouraging for the realization of III-V optical devices on silicon for potential applications.

Interface issues in the ESCHER visual database editor

Presentation at the 1997 Dagstuhl Seminar "Evaluation of Multimedia Information Retrieval", Norbert Fuhr, Keith van Rijsbergen, Alan F. Smeaton (eds.), Dagstuhl Seminar Report 175, 14.04. - 18.04.97 (9716). - Abstract: This presentation will introduce ESCHER, a database editor which supports visualization in non-standard applications in engineering, science, tourism and the entertainment industry. It was originally based on the extended nested relational data model and is currently extended to include object-relational properties like inheritance, object types, integrity constraints and methods. It serves as a research platform into areas such as multimedia and visual information systems, QBE-like queries, computer-supported concurrent work (CSCW) and novel storage techniques. In its role as a Visual Information System, a database editor must support browsing and navigation. ESCHER provides this access to data by means of so called fingers. They generalize the cursor paradigm in graphical and text editors. On the graphical display, a finger is reflected by a colored area which corresponds to the object a finger is currently pointing at. In a table more than one finger may point to objects, one of which is the active finger and is used for navigating through the table. The talk will mostly concentrate on giving examples for this type of navigation and will discuss some of the architectural needs for fast object traversal and display. ESCHER is available as public domain software from our ftp site in Kassel. The portable C source can be easily compiled for any machine running UNIX and OSF/Motif, in particular our working environments IBM RS/6000 and Intel-based LINUX systems. A porting to Tcl/Tk is under way.

Pi: A Parallel Architecture Interface for Multi-Model Execution

This thesis defines Pi, a parallel architecture interface that separates model and machine issues, allowing them to be addressed independently. This provides greater flexibility for both the model and machine builder. Pi addresses a set of common parallel model requirements including low latency communication, fast task switching, low cost synchronization, efficient storage management, the ability to exploit locality, and efficient support for sequential code. Since Pi provides generic parallel operations, it can efficiently support many parallel programming models including hybrids of existing models. Pi also forms a basis of comparison for architectural components.

ADAM: A Decentralized Parallel Computer Architecture Featuring Fast Thread and Data Migration and a Uniform Hardware Abstraction

The furious pace of Moore's Law is driving computer architecture into a realm where the the speed of light is the dominant factor in system latencies. The number of clock cycles to span a chip are increasing, while the number of bits that can be accessed within a clock cycle is decreasing. Hence, it is becoming more difficult to hide latency. One alternative solution is to reduce latency by migrating threads and data, but the overhead of existing implementations has previously made migration an unserviceable solution so far. I present an architecture, implementation, and mechanisms that reduces the overhead of migration to the point where migration is a viable supplement to other latency hiding mechanisms, such as multithreading. The architecture is abstract, and presents programmers with a simple, uniform fine-grained multithreaded parallel programming model with implicit memory management. In other words, the spatial nature and implementation details (such as the number of processors) of a parallel machine are entirely hidden from the programmer. Compiler writers are encouraged to devise programming languages for the machine that guide a programmer to express their ideas in terms of objects, since objects exhibit an inherent physical locality of data and code. The machine implementation can then leverage this locality to automatically distribute data and threads across the physical machine by using a set of high performance migration mechanisms. An implementation of this architecture could migrate a null thread in 66 cycles -- over a factor of 1000 improvement over previous work. Performance also scales well; the time required to move a typical thread is only 4 to 5 times that of a null thread. Data migration performance is similar, and scales linearly with data block size. Since the performance of the migration mechanism is on par with that of an L2 cache, the implementation simulated in my work has no data caches and relies instead on multithreading and the migration mechanism to hide and reduce access latencies.

An Immersed Interface Method for the Incompressible Navier-Stokes Equations in Irregular Domains

We present an immersed interface method for the incompressible Navier Stokes equations capable of handling rigid immersed boundaries. The immersed boundary is represented by a set of Lagrangian control points. In order to guarantee that the no-slip condition on the boundary is satisfied, singular forces are applied on the fluid at the immersed boundary. The forces are related to the jumps in pressure and the jumps in the derivatives of both pressure and velocity, and are interpolated using cubic splines. The strength of singular forces is determined by solving a small system of equations at each time step. The Navier-Stokes equations are discretized on a staggered Cartesian grid by a second order accurate projection method for pressure and velocity.

Lecture 15 - Interface this

A quick word about abstract How a class interfaces Making Pets The Deadly Diamond of Death Interfaces (not interfaces)

Initial Assessment of Colombian-Canadian Migration

The results presented in this paper are aim at examining and comparing the migratory events occurred betwixt two countries which have different social and economic conditions. The information developed along this text is, therefore, an initial assessment on migration between Canada and Colombia. The author used hermeneutics as a main methodological tool for conducting this study.This paper concludes that, although there are a range of motivations behind the decision to leaving one’s home country, the pursuit for better economic conditions is the dominant factor.

A Grey Area of Rights and Knowledge: Displacement in Colombia, South-South Migration and Health Equity

Globalization and liberalization of the economies have produced among others drastic effects on the human mobility, generating confusion, enhancing discrimination and a lack of respect to the rights of several migrant collectives. In this article we analyse several challenges for the study of these phenomena, based on the case of the neglected health rights of Colombian women, who have been forced to displace by the country's internal conflict, and are thus pushed to cross the border to Ecuador. The article identifies several knowledge gaps that could allow and advance a better understanding of these critical subjects. The paper - a think piece -is based upon a general review of documents and studies on the relation between migration and health. The supporting theory on the research comes from international organisations such as the WHO and IOM, NGOs, grass-roots organisations and academic research. This paper shows the need for focusing on the reality of supra states which globalization has generated, and t e urgency of securing the access to essential health preconditions to migrant populations. These issues can no longer be neglected and should be included on agendas at international level, widening the approach of programs to the displaced/immigrant population by taking into account the need to ensure the essential health preconditions (equity), prevention, and protection. Further, it is clear that women and children require a better protection with enhanced prevention and responding measures to sexual abuse, stigmatisation, violence and the respect of their rights.

Diseño de una interface entre un programa de cálculo simbólico y un programa CAD : aplicación al caso de modelado geométrico y modelado de caras.

El objetivo de este trabajo es el diseño de una interface entre un programa de cálculo simbólico y uno de CAD y su aplicación al caso de modelado geométrico y modelado de caras. El libro, se divide en tres capítulos: curvas en 2D, curvas en 3D y superficies. Dado que existen programas de cálculo simbólico que representan sus curvas, resultará favorable captar el fichero de puntos producido por dicho programa y, con los tratamientos convenientes, transformarlo en una lista susceptible de ser leída desde un programa CAD, los puntos trasvasados serán los vértices de una polilínea que posteriormente adaptada representará la curva en cuestión. Y, siguiendo un proceso análogo, también será posible obtener el fichero de puntos de una superficie. Para desarrollar esta aplicación, se ha elegido como programa de cálculo simbólico Maple V2, y como programa CAD, AUTOCAD V12.

The balassa-samuelson hypothesis and elderly migration

We present an Overlapping Generations Model with two final goods: tradable goods are produced with a standard Cobb-Douglas production function and non-tradable goods are produced with linear production function where the only factor is labor. We maintain the fundamental assumption of factor mobility between sectors so model is consistent with the Balassa-Samuelson hypothesis. Given the general equilibrium structure of our model we can examine the effect of the saving rate on migration and non-tradable relative prices. Under this setting, we find that the elderly have incentives to migrate from economies where productivity is high to economies with low productivity because of the lower cost of living. In more general terms the elderly migration is likely to go from rich to poor countries. We also find that, for poor countries, the elderly migration has a positive effect in wages and capital accumulation.

Activitats de matemàtiques del grup Interface. 'Actividades de matemáticas del grupo Interface'.

Nueve paquetes de actividades para Windows para ciclo superior de Primaria. Se trabajan medidas de capacidad y longitud y masa, fracciones, enteros y porcentajes entre otros contenidos. Las actividades se basan en ejercicios visuales y problemas. Permite instalar el programa o hacer una copia en un disquete.

Orientaçoes para o design da interface de software educativo multimédia. 'Orientaciones para el diseño de un interfaz de software educativo multimedia'.

Conocer qué desafíos se fijan los creadores de software educativo multimedia, qué tipo de comunicación debemos establecer entre el usuario y el ordenador para que sus exploraciones desemboquen en situaciones de aprendizaje y cómo favorecer la realización de software adecuado a la naturaleza del proceso educativo en las cuales las características de accesibilidad, transparencia, atractivo, claridad de objetivos educativos y la realización de actividades, contribuyen a una mayor interactividad del hombre con la máquina. Se utilizó la investigación por compilación, con compilación documental, por entrevista y por encuesta, y la investigación documental, utilizando fuentes primarias y secundarias de información para esbozar la evolución, tendencias y orientaciones de diseño de interfaces. La investigación empírica se divide en dos estudios, el primero abordó la cuestión del nivel de conocimientos y la utilización del software educativo por parte de los maestros de Educación infantil y profesores de primaria y, el segundo, tenía como objetivo confeccionar una lista de orientaciones para el diseño de interfaces, a partir de aspectos estudiados en el marco teórico, y a partir de los cuales se diseñó una tabla de evaluación de interfaces de software educativo multimedia. El estudio se llevó a cabo con maestros y profesores de primaria que asistían al curso complementario de formación en la Escuela Superior de Educación de Fafe durante los años 1999-2000, 2000-2001, 2001-2002. Se elaboró una tabla de evaluación de interfaces destinado a los realizadores de software educativo que sirve para controlar la calidad del interfaz. Los docentes a pesar de conocer algún que otro software educativo disponible en el mercado, su uso en el contexto educativo es poco frecuente. Los profesores que estuvieron ligados a proyectos con prácticas en ordenador o que realizaron acciones de formación en Nuevas Tecnologías conocen y recurren más al software educativo.

Second lives and newer islands : language, culture and identity through migration literature. 'Second lives and newer islands : lengua, cultura e identidad a trav??s de la literatura de migraci??n'

Resumen en espa??ol

Configuración de la interfaz discurso-gramática en el lenguaje del profesor de preescolar en el aula ILE : presentación de una red sistémica como herramienta para un análisis sistemático de las funciones reguladoras. Modelling the discourse-grammar interface of ELF pre-school teacher talk (native and non-native) : proposal of a system network enabling the systematic analysis of regulatory functions.

Esta investigación pretende alcanzar dos objetivos. Cubrir el vacío existente en los estudios de las funciones comunicativas del habla de profesores, en este caso de inglés como Lengua Extranjera (ILE) destinado a nivel preescolar, y configurar una interfaz discurso-gramática de las funciones reguladoras del lenguaje.. En primer lugar, para lograr un análisis discursivo-semántico, en este trabajo se diseña la Red Sistémica de Funciones Reguladoras, RSFR, una herramienta que resume las diferentes opciones discursivo-semánticas de los contextos de las funciones reguladoras. A continuación, se analizan los datos en el estrato léxico-gramatical para facilitar conclusiones sobre la relación función-realización formal. Por último se exponen las similitudes y diferencias en la producción lingüística de las funciones reguladoras entre profesores nativos y no nativos.. Las aportaciones más destacadas de esta investigación son cuatro: hacer posible un estudio sistemático del significado mediante el diseño de una herramienta; la propuesta de una taxonomía de funciones reguladoras; el análisis de la dependencia entre las funciones reguladoras, y sus realizaciones lingüísticas; y las diferencias encontradas en la comparación del discurso del profesor nativo y no-nativo..