Knowledge Modelling in Multiagent Systems: The Case of the Management of a National Network

This paper presents the knowledge model of a distributed decision support system, that has been designed for the management of a national network in Ukraine. It shows how advanced Artificial Intelligence techniques (multiagent systems and knowledge modelling) have been applied to solve this real-world decision support problem: on the one hand its distributed nature, implied by different loci of decision-making at the network nodes, suggested to apply a multiagent solution; on the other, due to the complexity of problem-solving for local network administration, it was useful to apply knowledge modelling techniques, in order to structure the different knowledge types and reasoning processes involved. The paper sets out from a description of our particular management problem. Subsequently, our agent model is described, pointing out the local problem-solving and coordination knowledge models. Finally, the dynamics of the approach is illustrated by an example.

A modelling language for the resilience assessment of networked systems of systems

Systems of Systems (SoS) present challenging features and existing tools result often inadequate for their analysis, especially for heteregeneous networked infrastructures. Most accident scenarios in networked systems cannot be addressed by a simplistic black or white (i.e. functioning or failed) approach. Slow deviations from nominal operation conditions may cause degraded behaviours that suddenly end up into unexpected malfunctioning, with large portions of the network affected. In this paper,we present a language for modelling networked SoS. The language makes it possible to represent interdependencies of various natures, e.g. technical, organizational and human. The representation of interdependencies is based on control relationships that exchange physical quantities and related information. The language also makes it possible the identification of accident scenarios, by representing the propagation of failure events throughout the network. The results can be used for assessing the effectiveness of those mechanisms and measures that contribute to the overall resilience, both in qualitative and quantitative terms. The presented modelling methodology is general enough to be applied in combination with already existing system analysis techniques, such as risk assessment, dependability and performance evaluation

Contribution to the design of waveguide-fed compound-slot arrays by means of equivalent circuit modelling

Los arrays de ranuras son sistemas de antennas conocidos desde los a��os 40, principalmente destinados a formar parte de sistemas r��dar de nav��os de combate y grandes estaciones terrenas donde el tama��o y el peso no eran altamente restrictivos. Con el paso de los a��os y debido sobre todo a importantes avances en materiales y m��todos de fabricaci��n, el rango de aplicaciones de este tipo de sistemas radiantes creci�� en gran medida. Desde nuevas tecnolog��as biom��dicas, sistemas anticolisi��n en autom��viles y navegaci��n en aviones, enlaces de comunicaciones de alta tasa binaria y corta distancia e incluso sistemas embarcados en sat��lites para la transmisi��n de se��al de televisi��n. Dentro de esta familia de antennas, existen dos grupos que destacan por ser los m��s utilizados: las antennas de placas paralelas con las ranuras distribuidas de forma circular o espiral y las agrupaciones de arrays lineales construidos sobre guia de onda. Continuando con las tareas de investigaci��n desarrolladas durante los ��ltimos a��os en el Instituto de Tecnolog��a de Tokyo y en el Grupo de Radiaci��n de la Universidad Polit��cnica de Madrid, la totalidad de esta tesis se centra en este ��ltimo grupo, aunque como se ver�� se separa en gran medida de las t��cnicas de dise��o y metodolog��as convencionales. Los arrays de ranuras rectas y paralelas al eje de la gu��a rectangular que las alimenta son, sin ninguna duda, los modelos m��s empleados debido a la fiabilidad que presentan a altas frecuencias, su capacidad para gestionar grandes cantidades de potencia y la sencillez de su dise��o y fabricaci��n. Sin embargo, tambi��n presentan desventajas como estrecho ancho de banda en p��rdidas de retorno y r��pida degradaci��n del diagrama de radiaci��n con la frecuencia. ��stas son debidas a la naturaleza resonante de sus elementos radiantes: al perder la resonancia, el sistema global se desajusta y sus prestaciones degeneran. En arrays bidimensionales de slots rectos, el campo el��ctrico queda polarizado sobre el plano transversal a las ranuras, correspondi��ndose con el plano de altos l��bulos secundarios. Esta tesis tiene como objetivo el desarrollo de un m��todo sistem��tico de dise��o de arrays de ranuras inclinadas y desplazadas del centro (en lo sucesivo ���ranuras compuestas���), definido en 1971 como uno de los desaf��os a superar dentro del mundo del dise��o de antennas. La t��cnica empleada se basa en el M��todo de los Momentos, la Teor��a de Circuitos y la Teor��a de Conexi��n Aleatoria de Matrices de Dispersi��n. Al tratarse de un m��todo circuital, la primera parte de la tesis se corresponde con el estudio de la aplicabilidad de las redes equivalentes fundamentales, su capacidad para recrear fen��menos f��sicos de la ranura, las limitaciones y ventajas que presentan para caracterizar las diferentes configuraciones de slot compuesto. Se profundiza en las diferencias entre las redes en T y en ! y se condiciona la selecci��n de una u otra dependiendo del tipo de elemento radiante. Una vez seleccionado el tipo de red a emplear en el dise��o del sistema, se ha desarrollado un algoritmo de cascadeo progresivo desde el puerto alimentador hacia el cortocircuito que termina el modelo. Este algoritmo es independiente del n��mero de elementos, la frecuencia central de funcionamiento, del ��ngulo de inclinaci��n de las ranuras y de la red equivalente seleccionada (en T o en !). Se basa en definir el dise��o del array como un Problema de Satisfacci��n de Condiciones (en ingl��s, Constraint Satisfaction Problem) que se resuelve por un m��todo de B��squeda en Retroceso (Backtracking algorithm). Como resultado devuelve un circuito equivalente del array completo adaptado a su entrada y cuyos elementos consumen una potencia acorde a una distribuci��n de amplitud dada para el array. En toda agrupaci��n de antennas, el acoplo mutuo entre elementos a trav��s del campo radiado representa uno de los principales problemas para el ingeniero y sus efectos perjudican a las prestaciones globales del sistema, tanto en adaptaci��n como en capacidad de radiaci��n. El empleo de circuito equivalente se descart�� por la dificultad que supon��a la caracterizaci��n de estos efectos y su inclusi��n en la etapa de dise��o. En esta tesis doctoral el acoplo tambi��n se ha modelado como una red equivalente cuyos elementos son transformadores ideales y admitancias, conectada al conjunto de redes equivalentes que representa el array. Al comparar los resultados estimados en t��rminos de p��rdidas de retorno y radiaci��n con aquellos obtenidos a partir de programas comerciales populares como CST Microwave Studio se confirma la validez del m��todo aqu�� propuesto, el primer m��todo de dise��o sistem��tico de arrays de ranuras compuestos alimentados por gu��a de onda rectangular. Al tratarse de ranuras no resonantes, el ancho de banda en p��rdidas de retorno es mucho mas amplio que el que presentan arrays de slots rectos. Para arrays bidimensionales, el ��ngulo de inclinaci��n puede ajustarse de manera que el campo quede polarizado en los planos de bajos l��bulos secundarios. Adem��s de simulaciones se han dise��ado, construido y medido dos prototipos centrados en la frecuencia de 12GHz, de seis y diez elementos. Las medidas de p��rdidas de retorno y diagrama de radiaci��n revelan excelentes resultados, certificando la bondad del m��todo genuino Method of Moments - Forward Matching Procedure desarrollado a lo largo de esta t��sis. Abstract The slot antenna arrays are well known systems from the decade of 40s, mainly intended to be part of radar systems of large warships and terrestrial stations where size and weight were not highly restrictive. Over the years, mainly due to significant advances in materials and manufacturing methods, the range of applications of this type of radiating systems grew significantly. From new biomedical technologies, collision avoidance systems in cars and aircraft navigation, short communication links with high bit transfer rate and even embedded systems in satellites for television broadcast. Within this family of antennas, two groups stand out as being the most frequent in the literature: parallel plate antennas with slots placed in a circular or spiral distribution and clusters of waveguide linear arrays. To continue the vast research work carried out during the last decades in the Tokyo Institute of Technology and in the Radiation Group at the Universidad Polit��cnica de Madrid, this thesis focuses on the latter group, although it represents a technique that drastically breaks with traditional design methodologies. The arrays of slots straight and parallel to the axis of the feeding rectangular waveguide are without a doubt the most used models because of the reliability that they present at high frequencies, its ability to handle large amounts of power and their simplicity of design and manufacturing. However, there also exist disadvantages as narrow bandwidth in return loss and rapid degradation of the radiation pattern with frequency. These are due to the resonant nature of radiating elements: away from the resonance status, the overall system performance and radiation pattern diminish. For two-dimensional arrays of straight slots, the electric field is polarized transverse to the radiators, corresponding to the plane of high side-lobe level. This thesis aims to develop a systematic method of designing arrays of angled and displaced slots (hereinafter "compound slots"), defined in 1971 as one of the challenges to overcome in the world of antenna design. The used technique is based on the Method of Moments, Circuit Theory and the Theory of Scattering Matrices Connection. Being a circuitry-based method, the first part of this dissertation corresponds to the study of the applicability of the basic equivalent networks, their ability to recreate the slot physical phenomena, their limitations and advantages presented to characterize different compound slot configurations. It delves into the differences of T and ! and determines the selection of the most suitable one depending on the type of radiating element. Once the type of network to be used in the system design is selected, a progressive algorithm called Forward Matching Procedure has been developed to connect the proper equivalent networks from the feeder port to shorted ending. This algorithm is independent of the number of elements, the central operating frequency, the angle of inclination of the slots and selected equivalent network (T or ! networks). It is based on the definition of the array design as a Constraint Satisfaction Problem, solved by means of a Backtracking Algorithm. As a result, the method returns an equivalent circuit of the whole array which is matched at its input port and whose elements consume a power according to a given amplitude distribution for the array. In any group of antennas, the mutual coupling between elements through the radiated field represents one of the biggest problems that the engineer faces and its effects are detrimental to the overall performance of the system, both in radiation capabilities and return loss. The employment of an equivalent circuit for the array design was discarded by some authors because of the difficulty involved in the characterization of the coupling effects and their inclusion in the design stage. In this thesis the coupling has also been modeled as an equivalent network whose elements are ideal transformers and admittances connected to the set of equivalent networks that represent the antennas of the array. By comparing the estimated results in terms of return loss and radiation with those obtained from popular commercial software as CST Microwave Studio, the validity of the proposed method is fully confirmed, representing the first method of systematic design of compound-slot arrays fed by rectangular waveguide. Since these slots do not work under the resonant status, the bandwidth in return loss is much wider than the longitudinal-slot arrays. For the case of two-dimensional arrays, the angle of inclination can be adjusted so that the field is polarized at the low side-lobe level plane. Besides the performed full-wave simulations two prototypes of six and ten elements for the X-band have been designed, built and measured, revealing excellent results and agreement with the expected results. These facts certify that the genuine technique Method of Moments - Matching Forward Procedure developed along this thesis is valid and trustable.

Modelling of chloride transport in non-saturated concrete : from microscale to macroscale

Corrosion of steel bars embedded in concrete has a great influence on structural performance and durability of reinforced concrete. Chloride penetration is considered to be a primary cause of concrete deterioration in a vast majority of structures. Therefore, modelling of chloride penetration into concrete has become an area of great interest. The present work focuses on modelling of chloride transport in concrete. The differential macroscopic equations which govern the problem were derived from the equations at the microscopic scale by comparing the porous network with a single equivalent pore whose properties are the same as the average properties of the real porous network. The resulting transport model, which accounts for diffusion, migration, advection, chloride binding and chloride precipitation, consists of three coupled differential equations. The first equation models the transport of chloride ions, while the other two model the flow of the pore water and the heat transfer. In order to calibrate the model, the material parameters to determine experimentally were identified. The differential equations were solved by means of the finite element method. The classical Galerkin method was employed for the pore solution flow and the heat transfer equations, while the streamline upwind Petrov Galerkin method was adopted for the transport equation in order to avoid spatial instabilities for advection dominated problems. The finite element codes are implemented in Matlab�� . To retrieve a good understanding of the influence of each variable and parameter, a detailed sensitivity analysis of the model was carried out. In order to determine the diffusive and hygroscopic properties of the studied concretes, as well as their chloride binding capacity, an experimental analysis was performed. The model was successfully compared with experimental data obtained from an offshore oil platform located in Brazil. Moreover, apart from the main objectives, numerous results were obtained throughout this work. For instance, several diffusion coefficients and the relation between them are discussed. It is shown how the electric field set up between the ionic species depends on the gradient of the species��� concentrations. Furthermore, the capillary hysteresis effects are illustrated by a proposed model, which leads to the determination of several microstructure properties, such as the pore size distribution and the tortuosity-connectivity of the porous network. El fen��meno de corrosi��n del acero de refuerzo embebido en el hormig��n ha tenido gran influencia en estructuras de hormig��n armado, tanto en su funcionalidad estructural como en aspectos de durabilidad. La penetraci��n de cloruros en el interior del hormig��n esta considerada como el factor principal en el deterioro de la gran mayor��a de estructuras. Por lo tanto, la modelizaci��n num��rica de dicho fen��meno ha generado gran inter��s. El presente trabajo de investigaci��n se centra en la modelizaci��n del transporte de cloruros en el interior del hormig��n. Las ecuaciones diferenciales que gobiernan los fen��menos a nivel macrosc��pico se deducen de ecuaciones planteadas a nivel microsc��pico. Esto se obtiene comparando la red porosa con un poro equivalente, el cual mantiene las mismas propiedades de la red porosa real. El modelo est�� constituido por tres ecuaciones diferenciales acopladas que consideran el transporte de cloruros, el flujo de la soluci��n de poro y la transferencia de calor. Con estas ecuaciones se tienen en cuenta los fen��menos de difusi��n, migraci��n, advecci��n, combinaci��n y precipitaci��n de cloruros. El an��lisis llevado a cabo en este trabajo ha definido los par��metros necesarios para calibrar el modelo. De acuerdo con ellas, se seleccionaron los ensayos experimentales a realizar. Las ecuaciones diferenciales se resolvieron mediante el m��todo de elementos finitos. El m��todo cl��sico de Galerkin se emple�� para solucionar las ecuaciones de flujo de la soluci��n de poro y de la transferencia de calor, mientras que el m��todo streamline upwind Petrov-Galerkin se utiliz�� para resolver la ecuaci��n de transporte de cloruros con la finalidad de evitar inestabilidades espaciales en problemas con advecci��n dominante. El c��digo de elementos finitos est�� implementado en Matlab�� . Con el objetivo de facilitar la comprensi��n del grado de influencia de cada variable y par��metro, se realiz�� un an��lisis de sensibilidad detallado del modelo. Se llev�� a cabo una campa��a experimental sobre los hormigones estudiados, con el objeto de obtener sus propiedades difusivas, qu��micas e higrosc��picas. El modelo se contrast�� con datos experimentales obtenidos en una plataforma petrolera localizada en Brasil. Las simulaciones num��ricas corroboraron los datos experimentales. Adem��s, durante el desarrollo de la investigaci��n se obtuvieron resultados paralelos a los planteados inicialmente. Por ejemplo, el an��lisis de diferentes coeficientes de difusi��n y la relaci��n entre ellos. As�� como tambi��n se observ�� que el campo el��ctrico establecido entre las especies i��nicas disueltas en la soluci��n de poro depende del gradiente de concentraci��n de las mismas. Los efectos de hist��resis capilar son expresados por el modelo propuesto, el cual conduce a la determinaci��n de una serie de propiedades microsc��picas, tales como la distribuci��n del tama��o de poro, adem��s de la tortuosidad y conectividad de la red porosa.

Participatory modelling to support decision making in water management under uncertainty: Two comparative case studies in the Guadiana river basin, Spain.

A participatory modelling process has been conducted in two areas of the Guadiana river (the upper and the middle sub-basins), in Spain, with the aim of providing support for decision making in the water management field. The area has a semi-arid climate where irrigated agriculture plays a key role in the economic development of the region and accounts for around 90% of water use. Following the guidelines of the European Water Framework Directive, we promote stakeholder involvement in water management with the aim to achieve an improved understanding of the water system and to encourage the exchange of knowledge and views between stakeholders in order to help building a shared vision of the system. At the same time, the resulting models, which integrate the different sectors and views, provide some insight of the impacts that different management options and possible future scenarios could have. The methodology is based on a Bayesian network combined with an economic model and, in the middle Guadiana sub-basin, with a crop model. The resulting integrated modelling framework is used to simulate possible water policy, market and climate scenarios to find out the impacts of those scenarios on farm income and on the environment. At the end of the modelling process, an evaluation questionnaire was filled by participants in both sub-basins. Results show that this type of processes are found very helpful by stakeholders to improve the system understanding, to understand each others views and to reduce conflict when it exists. In addition, they found the model an extremely useful tool to support management. The graphical interface, the quantitative output and the explicit representation of uncertainty helped stakeholders to better understand the implications of the scenario tested. Finally, the combination of different types of models was also found very useful, as it allowed exploring in detail specific aspects of the water management problems.

Global research alliance modelling platform (GRAMP): an open web platform for modelling greenhouse gas emissions from agro-ecosystems

Carbon (C) and nitrogen (N) process-based models are important tools for estimating and reporting greenhouse gas emissions and changes in soil C stocks. There is a need for continuous evaluation, development and adaptation of these models to improve scientific understanding, national inventories and assessment of mitigation options across the world. To date, much of the information needed to describe different processes like transpiration, photosynthesis, plant growth and maintenance, above and below ground carbon dynamics, decomposition and nitrogen mineralization. In ecosystem models remains inaccessible to the wider community, being stored within model computer source code, or held internally by modelling teams. Here we describe the Global Research Alliance Modelling Platform (GRAMP), a web-based modelling platform to link researchers with appropriate datasets, models and training material. It will provide access to model source code and an interactive platform for researchers to form a consensus on existing methods, and to synthesize new ideas, which will help to advance progress in this area. The platform will eventually support a variety of models, but to trial the platform and test the architecture and functionality, it was piloted with variants of the DNDC model. The intention is to form a worldwide collaborative network (a virtual laboratory) via an interactive website with access to models and best practice guidelines; appropriate datasets for testing, calibrating and evaluating models; on-line tutorials and links to modelling and data provider research groups, and their associated publications. A graphical user interface has been designed to view the model development tree and access all of the above functions.