A virtual backbone based approach for cooperative caching in mobile ad hoc networks

Cache look up is an integral part of cooperative caching in ad hoc networks. In this paper, we discuss a cooperative caching architecture with a distributed cache look up protocol which relies on a virtual backbone for locating and accessing data within a cooperate cache. Our proposal consists of two phases: (i) formation of a virtual backbone and (ii) the cache look up phase. The nodes in a Connected Dominating Set (CDS) form the virtual backbone. The cache look up protocol makes use of the nodes in the virtual backbone for effective data dissemination and discovery. The idea in this scheme is to reduce the number of nodes involved in cache look up process, by constructing a CDS that contains a small number of nodes, still having full coverage of the network. We evaluated the effect of various parameter settings on the performance metrics such as message overhead, cache hit ratio and average query delay. Compared to the previous schemes the proposed scheme not only reduces message overhead, but also improves the cache hit ratio and reduces the average delay

FEM based Virtual Prototyping and Design of Third Harmonic Excitation System for Low Voltage Brushless Alternators

Salient pole brushless alternators coupled to IC engines are extensively used as stand-by power supply units for meeting in- dustrial power demands. Design of such generators demands high power to weight ratio, high e ciency and low cost per KVA out- put. Moreover, the performance characteristics of such machines like voltage regulation and short circuit ratio (SCR) are critical when these machines are put into parallel operation and alterna- tors for critical applications like defence and aerospace demand very low harmonic content in the output voltage. While designing such alternators, accurate prediction of machine characteristics, including total harmonic distortion (THD) is essential to mini- mize development cost and time. Total harmonic distortion in the output voltage of alternators should be as low as possible especially when powering very sophis- ticated and critical applications. The output voltage waveform of a practical AC generator is replica of the space distribution of the ux density in the air gap and several factors such as shape of the rotor pole face, core saturation, slotting and style of coil disposition make the realization of a sinusoidal air gap ux wave impossible. These ux harmonics introduce undesirable e ects on the alternator performance like high neutral current due to triplen harmonics, voltage distortion, noise, vibration, excessive heating and also extra losses resulting in poor e ciency, which in turn necessitate de-rating of the machine especially when connected to non-linear loads. As an important control unit of brushless alternator, the excitation system and its dynamic performance has a direct impact on alternator's stability and reliability. The thesis explores design and implementation of an excitation i system utilizing third harmonic ux in the air gap of brushless al- ternators, using an additional auxiliary winding, wound for 1=3rd pole pitch, embedded into the stator slots and electrically iso- lated from the main winding. In the third harmonic excitation system, the combined e ect of two auxiliary windings, one with 2=3rd pitch and another third harmonic winding with 1=3rd pitch, are used to ensure good voltage regulation without an electronic automatic voltage regulator (AVR) and also reduces the total harmonic content in the output voltage, cost e ectively. The design of the third harmonic winding by analytic methods demands accurate calculation of third harmonic ux density in the air gap of the machine. However, precise estimation of the amplitude of third harmonic ux in the air gap of a machine by conventional design procedures is di cult due to complex geome- try of the machine and non-linear characteristics of the magnetic materials. As such, prediction of the eld parameters by conven- tional design methods is unreliable and hence virtual prototyping of the machine is done to enable accurate design of the third har- monic excitation system. In the design and development cycle of electrical machines, it is recognized that the use of analytical and experimental methods followed by expensive and in exible prototyping is time consum- ing and no longer cost e ective. Due to advancements in com- putational capabilities over recent years, nite element method (FEM) based virtual prototyping has become an attractive al- ternative to well established semi-analytical and empirical design methods as well as to the still popular trial and error approach followed by the costly and time consuming prototyping. Hence, by virtually prototyping the alternator using FEM, the important performance characteristics of the machine are predicted. Design of third harmonic excitation system is done with the help of results obtained from virtual prototype of the machine. Third harmonic excitation (THE) system is implemented in a 45 KVA ii experimental machine and experiments are conducted to validate the simulation results. Simulation and experimental results show that by utilizing third harmonic ux in the air gap of the ma- chine for excitation purposes during loaded conditions, triplen harmonic content in the output phase voltage is signi cantly re- duced. The prototype machine with third harmonic excitation system designed and developed based on FEM analysis proved to be economical due to its simplicity and has the added advan- tage of reduced harmonics in the output phase voltage.

Virtual Radio Engine

Software Defined Radio (SDR) hardware platforms use parallel architectures. Current concepts of developing applications (such as WLAN) for these platforms are complex, because developers describe an application with hardware-specifics that are relevant to parallelism such as mapping and scheduling. To reduce this complexity, we have developed a new programming approach for SDR applications, called Virtual Radio Engine (VRE). VRE defines a language for describing applications, and a tool chain that consists of a compiler kernel and other tools (such as a code generator) to generate executables. The thesis presents this concept, as well as describes the language and the compiler kernel that have been developed by the author. The language is hardware-independent, i.e., developers describe tasks and dependencies between them. The compiler kernel performs automatic parallelization, i.e., it is capable of transforming a hardware-independent program into a hardware-specific program by solving hardware-specifics, in particular mapping, scheduling and synchronizations. Thus, VRE simplifies programming tasks as developers do not solve hardware-specifics manually.

Plataforma Virtual y Redes del Profesorado de Bibliotecas Escolares.

Monográfico con el título: 'Leer para aprender'. Resumen basado en el de la publicación

Aula virtual de matemáticas.

Se aborda el uso de internet como herramienta en el proceso enseñanza aprendizaje en la asignatura de matemáticas en el centro de Enseñanza Secundaria Carlinda de Málaga. Los objetivos son: 1. Identificar las posibilidades reales de acceso de nuestros alumnos a las nuevas tecnologías incluyendo tanto la infraestructura de que disponen como su formación; 2. Estudio en profundidad de los recursos existentes actualmente en internet aplicables a la docencia en las asignaturas de matemáticas en niveles educativos no universitarios; 3. Crear un portal web que sirva de punto de encuentro de los alumnos en el aula virtual de matemáticas complemento de la tradicional clase presencial de matemáticas; 4. Iniciar al alumnado en el uso de las herramientas de comunicación vía internet como instrumento para el aprendizaje de las matemáticas de forma cooperativa; 5. Elaboración de materiales didácticos que permitan a los alumnos realizar prácticas con el ordenador. Uso de los programas de cálculo simbólico que permitan manipular los objetos matemáticos como medio para descubrir el conocimiento; 6. Utilización de los materiales didácticos para la integración de alumnos y alumnas con minusvalía; 7. Elaboración de tutoriales que incluyen test de autoevaluación para propiciar una ecuación autodidacta que permita llevar a cabo el proceso de enseñanza aprendizaje a distintos ritmos; 8. Propiciar la labor investigadora del alumnado, incluyendo en la web enlaces de interés que cautiven la curiosidad del alumno; 9. Propiciar un encuentro con la matemática aplicada, que destaque su carácter interdisciplinar. El proceso consta de tres fases: en la primera se realizó una encuesta al alumnado sobre las posibilidades reales de acceso a internet, su formación y su uso. Paralelamente se ha rastreado en internet para buscar otras experiencias parecidas que incluyesen la creación de páginas webs de contenidos matemáticos de nivel medio; en la segunda fase se han creado algunos materiales de trabajo para la inclusión en las webs. Básicamente hay dos tipos de actividades: guías para la utilización de programas de ordenador de cálculo simbólico y test de autoevaluación de modo de tutorial; la tercera fase ha consistido en el diseño y la creación de la web que integra las actividades realizadas en las fases anteriores con una serie de herramientas de comunicación. Los resultados concretos obtenidos han sido las actividades realizadas en el marco del proyecto: 1. Realización de una encuesta sobre las posibilidades reales de acceso a internet, su formación y su uso; 2. Relación de referencias de otras experiencias parecidas que incluyesen la creación de páginas webs de contenidos matemáticos de nivel medio; 3. Creación de materiales de trabajo para la inclusión en la webs: guías para la utilización de programas de ordenador de cálculo simbólico y test de autoevaluación a modo de tutorial; 4. Creación de la web que integra los materiales de trabajo junto a una serie de utilidades y herramientas de comunicación.

Enseñanza virtual para el alumnado adulto.

Uso de recursos telemáticos en la Formación de Personas Adultas.

Asistencia virtual para alumnado que por razones de enfermedad no puede asistir al centro educativo.

Garantizar la continuidad del proceso educativo del alumnado de enseñanza obligatoria que por razones de enfermedad no puede asistir físicamente al centro educativo ordinario. Incluir a este alumnado virtualmente en el aula con sus compañeros minimizando el aislamiento y consecuencias que son propias de esta situación.

Comunidad Virtual Educativa Pablo García Baena.

Este proyecto pretende proporcionar los conocimientos y práctica necesarios para utilizar las TICs como recurso educativo y medio de comunicación, tanto por el profesorado como por el alumnado. Asimismo pretende desarrollar las competencias textuales necesarias para evitar la manipulación sutil que a través de la diversidad de códigos y textos que ofrecen estas tecnologías suele producirse, sobre todo en la infancia y la adolescencia. Por otro lado pretende implicar a madres y padres realizando una formación específica para ellos y solicitando su colaboración en las actividades previstas, como el portal virtual.

Aula virtual de inglés : desarrollo de la expresión escrita mediante la integración de las TIC.

Mejorar la producción escrita de los alumnos de ESO y Bachillerato a través de un cambio en la metodología, creando materiales que incorporen las TIC como instrumento didáctico.

Museo virtual.

Contiene información sobre artistas, sobre museos, enlaces web, recomendaciones bibliográficas, aplicaciones didácticas y detalles técnicos.

Virtual Model Control of a Biped Walking Robot

The transformation from high level task specification to low level motion control is a fundamental issue in sensorimotor control in animals and robots. This thesis develops a control scheme called virtual model control which addresses this issue. Virtual model control is a motion control language which uses simulations of imagined mechanical components to create forces, which are applied through joint torques, thereby creating the illusion that the components are connected to the robot. Due to the intuitive nature of this technique, designing a virtual model controller requires the same skills as designing the mechanism itself. A high level control system can be cascaded with the low level virtual model controller to modulate the parameters of the virtual mechanisms. Discrete commands from the high level controller would then result in fluid motion. An extension of Gardner's Partitioned Actuator Set Control method is developed. This method allows for the specification of constraints on the generalized forces which each serial path of a parallel mechanism can apply. Virtual model control has been applied to a bipedal walking robot. A simple algorithm utilizing a simple set of virtual components has successfully compelled the robot to walk eight consecutive steps.

Virtual Model Control of a Hexapod Walking Robot

Since robots are typically designed with an individual actuator at each joint, the control of these systems is often difficult and non-intuitive. This thesis explains a more intuitive control scheme called Virtual Model Control. This thesis also demonstrates the simplicity and ease of this control method by using it to control a simulated walking hexapod. Virtual Model Control uses imagined mechanical components to create virtual forces, which are applied through the joint torques of real actuators. This method produces a straightforward means of controlling joint torques to produce a desired robot behavior. Due to the intuitive nature of this control scheme, the design of a virtual model controller is similar to the design of a controller with basic mechanical components. The ease of this control scheme facilitates the use of a high level control system which can be used above the low level virtual model controllers to modulate the parameters of the imaginary mechanical components. In order to apply Virtual Model Control to parallel mechanisms, a solution to the force distribution problem is required. This thesis uses an extension of Gardner`s Partitioned Force Control method which allows for the specification of constrained degrees of freedom. This virtual model control technique was applied to a simulated hexapod robot. Although the hexapod is a highly non-linear, parallel mechanism, the virtual models allowed text-book control solutions to be used while the robot was walking. Using a simple linear control law, the robot walked while simultaneously balancing a pendulum and tracking an object.

A Virtual Machine for a Type-omega Denotational Proof Language

In this thesis, I designed and implemented a virtual machine (VM) for a monomorphic variant of Athena, a type-omega denotational proof language (DPL). This machine attempts to maintain the minimum state required to evaluate Athena phrases. This thesis also includes the design and implementation of a compiler for monomorphic Athena that compiles to the VM. Finally, it includes details on my implementation of a read-eval-print loop that glues together the VM core and the compiler to provide a full, user-accessible interface to monomorphic Athena. The Athena VM provides the same basis for DPLs that the SECD machine does for pure, functional programming and the Warren Abstract Machine does for Prolog.