368 research outputs found
Description and Optimization of Abstract Machines in a Dialect of Prolog
In order to achieve competitive performance, abstract machines for Prolog and
related languages end up being large and intricate, and incorporate
sophisticated optimizations, both at the design and at the implementation
levels. At the same time, efficiency considerations make it necessary to use
low-level languages in their implementation. This makes them laborious to code,
optimize, and, especially, maintain and extend. Writing the abstract machine
(and ancillary code) in a higher-level language can help tame this inherent
complexity. We show how the semantics of most basic components of an efficient
virtual machine for Prolog can be described using (a variant of) Prolog. These
descriptions are then compiled to C and assembled to build a complete bytecode
emulator. Thanks to the high level of the language used and its closeness to
Prolog, the abstract machine description can be manipulated using standard
Prolog compilation and optimization techniques with relative ease. We also show
how, by applying program transformations selectively, we obtain abstract
machine implementations whose performance can match and even exceed that of
state-of-the-art, highly-tuned, hand-crafted emulators.Comment: 56 pages, 46 figures, 5 tables, To appear in Theory and Practice of
Logic Programming (TPLP
Modeling and Control of Power Electronics Interfaced Load for Transmission Power Network Analysis
The penetration level of power electronics (PE) interfaced loads has been gradually increasing in recent years. It is beneficial to equip the electric load with a PE interface since it allows for more advanced control of the load performance. Furthermore, the increasing penetration of PE interfaced loads will bring both challenges and opportunities to power network resilience and reliability.
However, the lack of modeling and control design for PE interfaced load units in the transmission-level power network analysis, especially for these high-penetrated high-power-rating load applications, limits the accuracy of evaluating the dynamic performance and stability status of the power network. Additionally, the complex configuration and high bandwidth dynamic performance of the PE interfaced load computationally prohibit the model development in transient stability (TS) simulation programs.
Therefore, the dynamic PE interfaced load model can be characterized considering the following aspects: 1) Utilize the real-time experimental platform to represent the PE load dynamic performance since the power testbed can reflect the power grid operation with more robustness. 2) Adapt the simplified PE-based model to TS simulation tools, which focus on grid electromechanical transients and oscillations between 0.1 and 3 Hz.
Research of the PE interfaced load towards its modeling and control design in different simulation environments and the flexible contribution to the grid operation has been conducted. First, the variable speed drive (VSD) based motor load is studied as a typical PE interfaced load, which can actively interact with power grid operation. The model of VSD load is introduced and applied to the power emulator for the multi-converter-based hardware testbed (HTB) in the Center of Ultra-wide-area Resilient Electric Energy Transmission Network (CURENT). Second, the aggregated performance of multiple VSD load units with grid frequency support function is characterized. Third, the fast electric vehicle (EV) charging unit is studied as a typical PE interfaced load with high power consumption. The generic model of EV charger load is developed based on the detailed switching model. The accuracy of the proposed EV charger load TS model has been verified by comparing it to simulation results of the equivalent electromagnetic (EMT) model
Performance measurement and evaluation of time-shared operating systems
Time-shared, virtual memory systems
are very complex and changes in their performance may
be caused by many factors - by variations in the
workload as well as changes in system configuration.
The evaluation of these systems can thus best be
carried out by linking results obtained from a
planned programme of measurements, taken on the
system, to some model of it. Such a programme of
measurements is best carried out under conditions in
which all the parameters likely to affect the system's
performance are reproducible, and under the control of
the experimenter. In order that this be possible the
workload used must be simulated and presented to the
target system through some form of automatic
workload driver. A case study of such a methodology
is presented in which the system (in this case the
Edinburgh Multi-Access System) is monitored during a
controlled experiment (designed and analysed using
standard techniques in common use in many other branches
of experimental science) and the results so obtained
used to calibrate and validate a simple simulation
model of the system. This model is then used in
further investigation of the effect of certain system parameters upon the system performance. The
factors covered by this exercise include the effect
of varying: main memory size, process loading
algorithm and secondary memory characteristics
The role of structured induction in expert systems
A "structured induction" technique was developed and tested using a
rules- from -examples generator together with a chess -specific application
package. A drawback of past experience with computer induction, reviewed
in this thesis, has been the generation of machine -oriented rules opaque to
the user. By use of the structured approach humanly understandable rules
were synthesized from expert supplied examples. These rules correctly performed chess endgame classifications of sufficient complexity to be regarded as difficult by international master standard players. Using the "Interactive ID3" induction tools developed by the author, chess experts, with
a little programming support, were able to generate rules which solve problems considered difficult or impossible by conventional programming techniques. Structured induction and associated programming tools were
evaluated using the chess endgames Icing and Pawn vs. King (Black -tomove) and King and Pawn vs. King and Rook (White -to -move, White Pawn on
a7) as trial problems of measurable complexity.Structured solutions to both trial problems are presented, and implications of this work for the design of expert systems languages are assessed
From diversity to convergence : British computer networks and the Internet, 1970-1995
The Internet's success in the 21st century has encouraged analysts to investigate the origin of this network. Much of this literature adopts a teleological approach. Works often begin by discussing the invention of packet switching, describe the design and development of the ARPANET, and then examine how this network evolved into the Internet. Although the ARPANET was a seminal computer network, these accounts usually only briefly consider the many other diverse networks that existed. In addition, apart from momentary asides to alternative internetworking solutions, such as the Open Systems Interconnection (OSI) seven-layer reference model, this literature concentrates exclusively on the ARPANET, the Internet, and the World Wide Web. While focusing on these subjects is important and therefore justified, it can leave the reader with the impression that the world of networking started with the ARPANET and ended with the Internet. This thesis is an attempt to help correct this misconception.
This thesis analyses the evolution of British computer networks and the Internet between the years 1970 and 1995. After an introduction in Chapter 1, the thesis analyses several networks. In Chapters 2 and 3, the focus is on academic networks, especially JANET and SuperJANET. Attention moves to videotex networks in Chapter 4, specifically Prestel, and in Chapter 5, the dissertation examines electronic mail networks such as Telecom Gold and Cable & Wireless Easylink. Chapter 6 considers online services, including CompuServe, American Online, and the Microsoft Network, and the thesis ends with a conclusion in Chapter 7. All of the networks discussed used protocols that were incompatible with each other which limited the utility of the networks for their users. Although it was possible that OSI or another solution could have solved this problem, the Internet's protocols achieved this objective. This thesis shows how the networks converged around TCP/IP
μGIM - Microgrid intelligent management system based on a multi-agent approach and the active participation of end-users
[ES] Los sistemas de potencia y energía están cambiando su paradigma tradicional, de sistemas centralizados a sistemas descentralizados. La aparición de redes inteligentes permite la integración de recursos energéticos descentralizados y promueve la gestión inclusiva que involucra a los usuarios finales, impulsada por la gestión del lado de la demanda, la energía transactiva y la respuesta a la demanda. Garantizar la escalabilidad y la estabilidad del servicio proporcionado por la red, en este nuevo paradigma de redes inteligentes, es más difícil porque no hay una única sala de operaciones centralizada donde se tomen todas las decisiones. Para implementar con éxito redes inteligentes, es necesario combinar esfuerzos entre la ingeniería eléctrica y la ingeniería informática. La ingeniería eléctrica debe garantizar el correcto funcionamiento físico de las redes inteligentes y de sus componentes, estableciendo las bases para un adecuado monitoreo, control, gestión, y métodos de operación. La ingeniería informática desempeña un papel importante al proporcionar los modelos y herramientas computacionales adecuados para administrar y operar la red inteligente y sus partes constituyentes, representando adecuadamente a todos los diferentes actores involucrados. Estos modelos deben considerar los objetivos individuales y comunes de los actores que proporcionan las bases para garantizar interacciones competitivas y cooperativas capaces de satisfacer a los actores individuales, así como cumplir con los requisitos comunes con respecto a la sostenibilidad técnica, ambiental y económica del Sistema.
La naturaleza distribuida de las redes inteligentes permite, incentiva y beneficia enormemente la participación activa de los usuarios finales, desde actores grandes hasta actores más pequeños, como los consumidores residenciales. Uno de los principales problemas en la planificación y operación de redes eléctricas es la variación de la demanda de energía, que a menudo se duplica más que durante las horas pico en comparación con la demanda fuera de pico. Tradicionalmente, esta variación dio como resultado la construcción de plantas de generación de energía y grandes inversiones en líneas de red y subestaciones. El uso masivo de fuentes de energía renovables implica mayor volatilidad en lo relativo a la generación, lo que hace que sea más difícil equilibrar el consumo y la generación. La participación de los actores de la red inteligente, habilitada por la energía transactiva y la respuesta a la demanda, puede proporcionar flexibilidad en desde el punto de vista de la demanda, facilitando la operación del sistema y haciendo frente a la creciente participación de las energías renovables.
En el ámbito de las redes inteligentes, es posible construir y operar redes más pequeñas, llamadas microrredes. Esas son redes geográficamente limitadas con gestión y operación local. Pueden verse como áreas geográficas restringidas para las cuales la red eléctrica generalmente opera físicamente conectada a la red principal, pero también puede operar en modo isla, lo que proporciona independencia de la red principal.
Esta investigación de doctorado, realizada bajo el Programa de Doctorado en Ingeniería Informática de la Universidad de Salamanca, aborda el estudio y el análisis de la gestión de microrredes, considerando la participación activa de los usuarios finales y la gestión energética de lascarga eléctrica y los recursos energéticos de los usuarios finales. En este trabajo de investigación se ha analizado el uso de conceptos de ingeniería informática, particularmente del campo de la inteligencia artificial, para apoyar la gestión de las microrredes, proponiendo un sistema de gestión inteligente de microrredes (μGIM) basado en un enfoque de múltiples agentes y en la participación activa de usuarios. Esta solución se compone de tres sistemas que combinan hardware y software: el emulador de virtual a realidad (V2R), el enchufe inteligente de conciencia ambiental de Internet de las cosas (EnAPlug), y la computadora de placa única para energía basada en el agente (S4E) para permitir la gestión del lado de la demanda y la energía transactiva. Estos sistemas fueron concebidos, desarrollados y probados para permitir la validación de metodologías de gestión de microrredes, es decir, para la participación de los usuarios finales y para la optimización inteligente de los recursos.
Este documento presenta todos los principales modelos y resultados obtenidos durante esta investigación de doctorado, con respecto a análisis de vanguardia, concepción de sistemas, desarrollo de sistemas, resultados de experimentación y descubrimientos principales. Los sistemas se han evaluado en escenarios reales, desde laboratorios hasta sitios piloto. En total, se han publicado veinte artículos científicos, de los cuales nueve se han hecho en revistas especializadas. Esta investigación de doctorado realizó contribuciones a dos proyectos H2020 (DOMINOES y DREAM-GO), dos proyectos ITEA (M2MGrids y SPEAR), tres proyectos portugueses (SIMOCE, NetEffiCity y AVIGAE) y un proyecto con financiación en cascada H2020 (Eco-Rural -IoT)
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