Dynamics of a minimal model of interlocked positive and negative feedback loops of transcriptional regulation by cAMP-response element binding proteins.

cAMP-response element binding (CREB) proteins are involved in transcriptional regulation in a number of cellular processes (e.g., neural plasticity and circadian rhythms). The CREB family contains activators and repressors that may interact through positive and negative feedback loops. These loops can be generated by auto- and cross-regulation of expression of CREB proteins, via CRE elements in or near their genes. Experiments suggest that such feedback loops may operate in several systems (e.g., Aplysia and rat). To understand the functional implications of such feedback loops, which are interlocked via cross-regulation of transcription, a minimal model with a positive and negative loop was developed and investigated using bifurcation analysis. Bifurcation analysis revealed diverse nonlinear dynamics (e.g., bistability and oscillations). The stability of steady states or oscillations could be changed by time delays in the synthesis of the activator (CREB1) or the repressor (CREB2). Investigation of stochastic fluctuations due to small numbers of molecules of CREB1 and CREB2 revealed a bimodal distribution of CREB molecules in the bistability region. The robustness of the stable HIGH and LOW states of CREB expression to stochastic noise differs, and a critical number of molecules was required to sustain the HIGH state for days or longer. Increasing positive feedback or decreasing negative feedback also increased the lifetime of the HIGH state, and persistence of this state may correlate with long-term memory formation. A critical number of molecules was also required to sustain robust oscillations of CREB expression. If a steady state was near a deterministic Hopf bifurcation point, stochastic resonance could induce oscillations. This comparative analysis of deterministic and stochastic dynamics not only provides insights into the possible dynamics of CREB regulatory motifs, but also demonstrates a framework for understanding other regulatory processes with similar network architecture.

Developmental self-construction and -configuration of functional neocortical neuronal networks.

The prenatal development of neural circuits must provide sufficient configuration to support at least a set of core postnatal behaviors. Although knowledge of various genetic and cellular aspects of development is accumulating rapidly, there is less systematic understanding of how these various processes play together in order to construct such functional networks. Here we make some steps toward such understanding by demonstrating through detailed simulations how a competitive co-operative ('winner-take-all', WTA) network architecture can arise by development from a single precursor cell. This precursor is granted a simplified gene regulatory network that directs cell mitosis, differentiation, migration, neurite outgrowth and synaptogenesis. Once initial axonal connection patterns are established, their synaptic weights undergo homeostatic unsupervised learning that is shaped by wave-like input patterns. We demonstrate how this autonomous genetically directed developmental sequence can give rise to self-calibrated WTA networks, and compare our simulation results with biological data.

WiMAX,Technology and Market.

Wireless communication is the transfer of information from one place to another without using wires. From the earliest times, humans have felt the need to develop techniques of remote communication. From this need arose the smoke signals, communication by sun reflection in mirrors and so on. But today the telecommunications electronic devices such as telephone, television, radio or computer. Radio and television are used for one-way communication. Telephone and computer are used for two-way communication. In wireless networks there is almost unlimited mobility, we can access the network almost anywhere or anytime. In wired networks we have the restriction of using the services in fixed area services. The demand of the wireless is increasing very fast; everybody wants broadband services anywhere anytime. WiMAX (Worldwide Interoperability for Microwave Access) is a broadband wireless technology based on IEEE 802.16-2004 and IEEE 802.16e-2005 that appears to solve this demand. WIMAX is a system that allows wireless data transmission in areas of up to 48 km of radius. It is designed as a wireless alternative to ADSL and a way to connect nodes in wireless metropolitan areas network. Unlike wireless systems that are limited in most cases, about 100 meter, providing greater coverage and more bandwidth. WIMAX promises to achieve high data transmission rates over large areas with a great amount of users. This alternative to the networks of broadband access common as DSL o Wi-Fi, can give broadband access to places quickly to rural areas and developing areas around the world. This paper is a study of WIMAX technology and market situation. First, the paper is responsible for explaining the technical aspects of WIMAX. For this gives an overview of WIMAX standards, physical layer, MAC layer and WiMAX, Technology and Market Beijing University of Post and Telecommunications 2 WIMAX network architecture. Second, the paper address the issue of market in which provides an overview of development and deployment of WIMAX to end the future development trend of WIMAX is addressed. RESUMEN: Por comunicaciones inalámbricas se entiende la transferencia de información desde un lugar a otro sin la necesidad de un soporte físico como es por ejemplo el cable. Por lo que remontándose a los principios de la existencia del ser humano, nos damos cuenta de que el ser humano siempre ha sentido la necesidad de desarrollar técnicas para lograr comunicarse a distancia con sus semejantes. De dicha necesidad, surgieron técnicas tan ancestrales como puede ser la comunicación mediante señales de humo o por reflexión de los rayos solares en espejos entre otras. La curiosidad del ser humano y la necesidad de comunicarse a distancia fue la que llevó a Alexander Graham Bell a inventar el teléfono en 1876. La aparición de un dispositivo que permitía comunicarse a distancia permitiendo escuchar la voz de aquella persona con la que se quería hablar, supuso una revolución no solo en el panorama tecnológico, si no también en el panorama social. Pues a parte de permitir comunicaciones a larga distancia, solventó el problema de la comunicación en “tiempo real”. A raíz de este invento, la tecnología en materia de comunicación ha ido avanzando significativamente, más concretamente en lo referido a las comunicaciones inalámbricas. En 1973 se realizó la primera llamada desde un terminal móvil aunque no fue hasta 1983 cuando se empezó a comercializar dicho terminal, lo que supuso un cambio de hábitos y costumbres para la sociedad. Desde la aparición del primer móvil el crecimiento del mercado ha sido exponencial, lo que ha repercutido en una demanda impensable de nuevas aplicaciones integradas en dichos dispositivos móviles que satisfagan las necesidades que día a día autogenera la sociedad. Tras conseguir realizar llamadas a larga distancia de forma inalámbrica, el siguiente paso fue la creación de los SMS (Short Message System) lo que supuso una nueva revolución además de abaratar costes al usuario a la hora de comunicarse. Pero el gran reto para la industria de las comunicaciones móviles surgió con la aparición de internet. Todo el mundo sentía la necesidad de poder conectarse a esa gran base de datos que es internet en cualquier parte y en cualquier momento. Las primeras conexiones a internet desde dispositivos móviles se realizaron a través de la tecnología WAP (Wireless Application Protocol) hasta la aparición de la tecnología GPRS que permitía la conexión mediante protocolo TCP/IP. A partir de estas conexiones han surgido otras tecnologías, como EDGE, HSDPA, etc., que permitían y permiten la conexión a internet desde dispositivos móviles. Hoy en día la demanda de servicios de red inalámbrica crece de forma rápida y exponencial, todo el mundo quiere servicios de banda ancha en cualquier lugar y en cualquier momento. En este documento se analiza la tecnología WiMAX ( Worldwide Interoperability for Microwave Access) que es una tecnología de banda ancha basada en el estándar IEEE 802.16 creada para brindar servicios a la demanda emergente en la banda ancha desde un punto de vista tecnológico, donde se da una visión de la parte técnica de la tecnología; y desde el punto de vista del mercado, donde se analiza el despliegue y desarrollo de la tecnología desde el punto de vista de negocio. WiMAX es una tecnología que permite la transmisión inalámbrica de datos en áreas de hasta 48Km de radio y que está diseñada como alternativa inalámbrica para ADSL y para conectar nodos de red inalámbrica en áreas metropolitanas. A diferencia de los sistemas inalámbricos existentes que están limitados en su mayoría a unos cientos de metros, WiMAX ofrece una mayor cobertura y un mayor ancho de banda que permita dar soporte a nuevas aplicaciones, además de alcanzar altas tasas de transmisión de datos en grandes áreas con una gran cantidad de usuarios. Se trata de una alternativa a las redes de acceso de banda ancha como DSL o Wi-Fi, que puede dar acceso de banda ancha a lugares tales como zonas rurales o zonas en vías de desarrollo por todo el mundo con rapidez. Existen dos tecnologías de WiMAX, WiMAX fijo (basado en el estándar IEEE 802.16d-2004) y WiMAX móvil (basado en el estándar IEEE 802.16e-2005). La tecnología fija está diseñada para comunicaciones punto a multipunto, mientras que la fija lo está para comunicaciones multipunto a multipunto. WiMAX móvil se basa en la tecnología OFDM que ofrece ventajas en términos de latencia, eficiencia en el uso del espectro y soporte avanzado para antenas. La modulación OFDM es muy robusta frente al multitrayecto, que es muy habitual en los canales de radiodifusión, frente al desvanecimiento debido a las condiciones meteorológicas y frente a las interferencias de RF. Una vez creada la tecnología WiMAX, poseedora de las características idóneas para solventar la demanda del mercado, ha de darse el siguiente paso, hay que convencer a la industria de las telecomunicaciones de que dicha tecnología realmente es la solución para que apoyen su implantación en el mercado de la banda ancha para las redes inalámbricas. Es aquí donde entra en juego el estudio del mercado que se realiza en este documento. WiMAX se enfrenta a un mercado exigente en el que a parte de tener que dar soporte a la demanda técnica, ha de ofrecer una rentabilidad económica a la industria de las comunicaciones móviles y más concretamente a las operadoras móviles que son quienes dentro del sector de las telecomunicaciones finalmente han de confiar en la tecnología para dar soporte a sus usuarios ya que estos al fin y al cabo lo único que quieren es que su dispositivo móvil satisfaga sus necesidades independientemente de la tecnología que utilicen para tener acceso a la red inalámbrica de banda ancha. Quizás el mayor problema al que se ha enfrentado WiMAX haya sido la situación económica en la que se encuentra el mundo. WiMAX a comenzado su andadura en uno de los peores momentos, pero aun así se presenta como una tecnología capaz de ayudar al mundo a salir hacia delante en estos tiempos tan duros. Finalmente se analiza uno de los debates existentes hoy en día en el sector de las comunicaciones móviles, WiMAX vs. LTE. Como se puede observar en el documento realmente una tecnología no saldrá victoriosa frente a la otra, si no que ambas tecnologías podrán coexistir y trabajar de forma conjunta.

Polynomial approximation using particle swarm optimization of lineal enhanced neural networks with no hidden layers.

This paper presents some ideas about a new neural network architecture that can be compared to a Taylor analysis when dealing with patterns. Such architecture is based on lineal activation functions with an axo-axonic architecture. A biological axo-axonic connection between two neurons is defined as the weight in a connection in given by the output of another third neuron. This idea can be implemented in the so called Enhanced Neural Networks in which two Multilayer Perceptrons are used; the first one will output the weights that the second MLP uses to computed the desired output. This kind of neural network has universal approximation properties even with lineal activation functions. There exists a clear difference between cooperative and competitive strategies. The former ones are based on the swarm colonies, in which all individuals share its knowledge about the goal in order to pass such information to other individuals to get optimum solution. The latter ones are based on genetic models, that is, individuals can die and new individuals are created combining information of alive one; or are based on molecular/celular behaviour passing information from one structure to another. A swarm-based model is applied to obtain the Neural Network, training the net with a Particle Swarm algorithm.

Implantación de un sistema de seguridad perimetral

Este proyecto está desarrollado sobre la seguridad de redes, y más concretamente en la seguridad perimetral. Para mostrar esto se hará una definición teórico-práctica de un sistema de seguridad perimetral. Para ello se ha desglosado el contenido en dos partes fundamentales, la primera incide en la base teórica relativa a la seguridad perimetral y los elementos más importantes que intervienen en ella, y la segunda parte, que es la implantación de un sistema de seguridad perimetral habitual en un entorno empresarial. En la primera parte se exponen los elementos más importantes de la seguridad perimetral, incidiendo en elementos como pueden ser cortafuegos, IDS/IPS, antivirus, proxies, radius, gestores de ancho de banda, etc. Sobre cada uno de ellos se explica su funcionamiento y posible configuración. La segunda parte y más extensa a la vez que práctica, comprende todo el diseño, implantación y gestión de un sistema de seguridad perimetral típico, es decir, el que sería de aplicación para la mayoría de las empresas actuales. En esta segunda parte se encontrarán primeramente las necesidades del cliente y situación actual en lo que a seguridad se refiere, con los cuales se diseñará la arquitectura de red. Para comenzar será necesario definir formalmente unos requisitos previos, para satisfacer estos requisitos se diseñará el mapa de red con los elementos específicos seleccionados. La elección de estos elementos se hará en base a un estudio de mercado para escoger las mejores soluciones de cada fabricante y que más se adecúen a los requisitos del cliente. Una vez ejecutada la implementación, se diseñará un plan de pruebas, realizando las pruebas de casos de uso de los diferentes elementos de seguridad para asegurar su correcto funcionamiento. El siguiente paso, una vez verificado que todos los elementos funcionan de forma correcta, será diseñar un plan de gestión de la plataforma, en el que se detallan las rutinas a seguir en cada elemento para conseguir que su funcionamiento sea óptimo y eficiente. A continuación se diseña una metodología de gestión, en las que se indican los procedimientos de actuación frente a determinadas incidencias de seguridad, como pueden ser fallos en elementos de red, detección de vulnerabilidades, detección de ataques, cambios en políticas de seguridad, etc. Finalmente se detallarán las conclusiones que se obtienen de la realización del presente proyecto. ABSTRACT. This project is based on network security, specifically on security perimeter. To show this, a theoretical and practical definition of a perimeter security system will be done. This content has been broken down into two main parts. The first part is about the theoretical basis on perimeter security and the most important elements that it involves, and the second part is the implementation of a common perimeter security system in a business environment. The first part presents the most important elements of perimeter security, focusing on elements such as firewalls, IDS / IPS, antivirus, proxies, radius, bandwidth managers, etc... The operation and possible configuration of each one will be explained. The second part is larger and more practical. It includes all the design, implementation and management of a typical perimeter security system which could be applied in most businesses nowadays. The current status as far as security is concerned, and the customer needs will be found in this second part. With this information the network architecture will be designed. In the first place, it would be necessary to define formally a prerequisite. To satisfy these requirements the network map will be designed with the specific elements selected. The selection of these elements will be based on a market research to choose the best solutions for each manufacturer and are most suited to customer requirements. After running the implementation, a test plan will be designed by testing each one of the different uses of all the security elements to ensure the correct operation. In the next phase, once the proper work of all the elements has been verified, a management plan platform will be designed. It will contain the details of the routines to follow in each item to make them work optimally and efficiently. Then, a management methodology will be designed, which provides the procedures for action against certain security issues, such as network elements failures, exploit detection, attack detection, security policy changes, etc.. Finally, the conclusions obtained from the implementation of this project will be detailed.

Entanglement distribution in optical networks

The ability to generate entangled photon pairs over a broad wavelength range opens the door to the simultaneous distribution of entanglement to multiple users in a network by using centralized sources and flexible wavelength-division multiplexing schemes. Here, we show the design of a metropolitan optical network consisting of tree-type access networks, whereby entangled photon pairs are distributed to any pair of users, independent of their location. The network is constructed employing commercial off-the-shelf components and uses the existing infrastructure, which allows for moderate deployment costs. We further develop a channel plan and a network-architecture design to provide a direct optical path between any pair of users; thus, allowing classical and one-way quantum communication, as well as entanglement distribution. This allows the simultaneous operation of multiple quantum information technologies. Finally, we present a more flexible backbone architecture that pushes away the load limitations of the original network design by extending its reach, number of users and capabilities.

Aportación de la monitorización mediante redes de sensores y técnicas no invasivas para la conservación preventiva del Patrimonio

La presente tesis doctoral presenta una serie de estudios en el campo del patrimonio basados en metodologías de monitorización mediante redes de sensores y técnicas no invasivas con el objetivo de realizar nuevas aportaciones a la conservación preventiva mediante el seguimiento de los daños de deterioro o la prevención de los mismos. Las metodologías de monitorización mediante el despliegue de redes tridimensionales basadas en data loggers abordan estudios microclimáticos, de confort y energéticos a corto plazo, donde se establecen conclusiones relativas a la eficiencia energética de tres sistemas de calefacción muy utilizados en iglesias de la región centro de la Península Ibérica, abordando aspectos de afección de los mismos en el confort de los ocupantes o en el deterioro de los elementos patrimoniales o constructivos. Se desplegaron además distintas plataformas de redes de sensores inalámbricas procediendo a analizar en esta tesis cuál es la que presenta mejores resultados en el ámbito del patrimonio con el objetivo de una monitorización a largo plazo y considerando aspectos de comunicaciones, consumo y configuración de las redes. Una vez conocida la plataforma que presenta mejores resultados comparativos se muestra una metodología de estudio de la calidad de las comunicaciones en múltiples escenarios de patrimonio cultural y natural con la misma, que servirá para establecer una serie de aspectos a considerar en el despliegue de redes de sensores inalámbricas en futuros escenarios a monitorizar. Al igual que ocurre con las redes de sensores basadas en data loggers, las tareas de monitorización desarrolladas en esta tesis mediante el despliegue de las distintas plataformas inalámbricas ha permitido la detección de numerosos fenómenos de deterioro que son descritos a lo largo de la investigación y cuyo seguimiento supone una aportación a la prevención de daños en los distintos escenarios. Asimismo en el desarrollo de la tesis se realiza una aportación para la conservación preventiva mediante la monitorización con distintas técnicas no invasivas como la termografía infrarroja, las medidas de humedad superficial mediante protimeter, las técnicas de prospección de resistividad eléctrica de alta resolución o la prospección georradar. De este modo se desarrollan distintas aportaciones y conclusiones acerca de las ventajas y/o limitaciones de uso de las mismas analizando la idoneidad de aplicar cada una de ellas en distintas fases de análisis o con distintas capacidades de detección o caracterización de los daños. El estudio de imbricación de dichas técnicas ha sido desarrollado en un escenario real que presenta graves daños por humedad, habiendo sido posible la caracterización del origen de los mismos. ABSTRACT This doctoral dissertation discusses field research conducted to monitor heritage assets with sensor networks and other non-invasive techniques. The aim pursued was to contribute to conservation by tracking or preventing decay-induced damage. Monitoring methodologies based on three-dimensional data logger networks were used in short-term micro-climatic, comfort and energy studies to draw conclusions about the energy efficiency of three heating systems widely used in central Iberian churches. The impact of these systems on occupant comfort and decay of heritage or built elements was also explored. Different wireless sensor platforms were deployed and analysed to determine which delivered the best results in the context of long-term heritage monitoring from the standpoints of communications, energy demand and network architecture. A methodology was subsequently designed to study communication quality in a number of cultural and natural heritage scenarios and help establish the considerations to be borne in mind when deploying wireless sensor networks for heritage monitoring in future. As in data logger-based sensor networks, the monitoring conducted in this research with wireless platforms identified many instances of decay, described hereunder. Tracking those situations will help prevent damage in the respective scenarios. The research also contributes to preventive conservation based on non-invasive monitoring using techniques such as infrared thermography, protimeter-based surface damp measurements, high resolution electrical resistivity surveys and georadar analysis. The conclusions drawn address the advantages and drawbacks of each technique and its suitability for the various phases of analysis and capacity to detect or characterise damage. This dissertation also describes the intermeshed usage of these techniques that led to the identification of the origin of severe damp-induced damage in a real scenario.

El imaginario de la ciudad que sobra del plano

La ciudad, como extensión lógico-racional del cuerpo, pero también como depositaria de sus excesos e impulsos, existe inserida en un determinado contexto histórico-social que configura el imaginario colectivo. Pensar el imaginario colectivo implica considerar, además de la histórica relación de la ciudad con la configuración biológica del cuerpo, como funciona la imaginación de la psique. El reconocimiento de la importancia del deseo en el proceso de pensamiento ha sugerido el principio de la inscripción corporal, mediante el cual se asume un vínculo profundo entre lo biológico y lo psíquico humano. Esta valoración de un pensamiento integrador de lo pulsional, de lo racional e de lo histórico, permite considerar dos aspectos que participan en la construcción de la ciudad: lo funcional y lo poiético. La lógica moderna, anclada a la concepción fragmentaria del cuerpo ? sumatorio de órganos ? estuvo en la base de la división del trabajo que generó el sistema capitalista. Sabiendo que la conciencia del propio cuerpo determina la relación con otros cuerpos y con el espacio, es reconocible una conexión entre la producción industrial y la vida urbana moderna, que ha degenerado en una ciudad abstracta ? resultado de una fragmentación espacial del todo en partes disociadas. La superposición del orden funcional de la máquina a la ciudad alimenta, así, una dualidad entre las ideas de cuerpo acabado - ciudad proyectada, heredadas de una lógica eminentemente racional y las ideas de cuerpo inacabable - ciudad circunstancial. La ciudad se halla en ese equilibrio inestable, entre el proyecto y el imprevisto, entre la coherencia de los lugares acabados y la incongruencia de los lugares casuales. La condición de apertura de los espacios que sobran del plano permite examinar las huellas del pasado y proporciona una mirada prospectiva sobre lo que la ciudad podría ser, sugiriendo una arqueología dual de regresión al pasado para intuir una proyección futura.

Association Patterns in Saproxylic Insect Networks in Three Iberian Mediterranean Woodlands and Their Resistance to Microhabitat Loss

The assessment of the relationship between species diversity, species interactions and environmental characteristics is indispensable for understanding network architecture and ecological distribution in complex networks. Saproxylic insect communities inhabiting tree hollow microhabitats within Mediterranean woodlands are highly dependent on woodland configuration and on microhabitat supply they harbor, so can be studied under the network analysis perspective. We assessed the differences in interacting patterns according to woodland site, and analysed the importance of functional species in modelling network architecture. We then evaluated their implications for saproxylic assemblages’ persistence, through simulations of three possible scenarios of loss of tree hollow microhabitat. Tree hollow-saproxylic insect networks per woodland site presented a significant nested pattern. Those woodlands with higher complexity of tree individuals and tree hollow microhabitats also housed higher species/interactions diversity and complexity of saproxylic networks, and exhibited a higher degree of nestedness, suggesting that a higher woodland complexity positively influences saproxylic diversity and interaction complexity, thus determining higher degree of nestedness. Moreover, the number of insects acting as key interconnectors (nodes falling into the core region, using core/periphery tests) was similar among woodland sites, but the species identity varied on each. Such differences in insect core composition among woodland sites suggest the functional role they depict at woodland scale. Tree hollows acting as core corresponded with large tree hollows near the ground and simultaneously housing various breeding microsites, whereas core insects were species mediating relevant ecological interactions within saproxylic communities, e.g. predation, competitive or facilitation interactions. Differences in network patterns and tree hollow characteristics among woodland sites clearly defined different sensitivity to microhabitat loss, and higher saproxylic diversity and woodland complexity showed positive relation with robustness. These results highlight that woodland complexity goes hand in hand with biotic and ecological complexity of saproxylic networks, and together exhibited positive effects on network robustness.

Morphological classification of microtidal sand and gravel beaches

A new classification of microtidal sand and gravel beaches with very different morphologies is presented below. In 557 studied transects, 14 variables were used. Among the variables to be emphasized is the depth of the Posidonia oceanica. The classification was performed for 9 types of beaches: Type 1: Sand and gravel beaches, Type 2: Sand and gravel separated beaches, Type 3: Gravel and sand beaches, Type 4: Gravel and sand separated beaches, Type 5: Pure gravel beaches, Type 6: Open sand beaches, Type 7: Supported sand beaches, Type 8: Bisupported sand beaches and Type 9: Enclosed beaches. For the classification, several tools were used: discriminant analysis, neural networks and Support Vector Machines (SVM), the results were then compared. As there is no theory for deciding which is the most convenient neural network architecture to deal with a particular data set, an experimental study was performed with different numbers of neuron in the hidden layer. Finally, an architecture with 30 neurons was chosen. Different kernels were employed for SVM (Linear, Polynomial, Radial basis function and Sigmoid). The results obtained for the discriminant analysis were not as good as those obtained for the other two methods (ANN and SVM) which showed similar success.

The applicability of recurrent neural networks for biological sequence analysis

Selection of machine learning techniques requires a certain sensitivity to the requirements of the problem. In particular, the problem can be made more tractable by deliberately using algorithms that are biased toward solutions of the requisite kind. In this paper, we argue that recurrent neural networks have a natural bias toward a problem domain of which biological sequence analysis tasks are a subset. We use experiments with synthetic data to illustrate this bias. We then demonstrate that this bias can be exploitable using a data set of protein sequences containing several classes of subcellular localization targeting peptides. The results show that, compared with feed forward, recurrent neural networks will generally perform better on sequence analysis tasks. Furthermore, as the patterns within the sequence become more ambiguous, the choice of specific recurrent architecture becomes more critical.

Methods for conflict resolution in policy-based management systems

While developments in distributed object computing environments, such as the Common Object Request Broker Architecture (CORBA) [17] and the Telecommunication Intelligent Network Architecture (TINA) [16], have enabled interoperability between domains in large open distributed systems, managing the resources within such systems has become an increasingly complex task. This challenge has been considered for several years within the distributed systems management research community and policy-based management has recently emerged as a promising solution. Large evolving enterprises present a significant challenge for policy-based management partly due to the requirement to support both mutual transparency and individual autonomy between domains [2], but also because the fluidity and complexity of interactions occurring within such environments requires an ability to cope with the coexistence of multiple, potentially inconsistent policies. This paper discusses the need of providing both dynamic (run-time) and static (compile-time) conflict detection and resolution for policies in such systems and builds on our earlier conflict detection work [7, 8] to introduce the methods for conflict resolution in large open distributed systems.

Editorial

This special issue of the Journal of the Operational Research Society is dedicated to papers on the related subjects of knowledge management and intellectual capital. These subjects continue to generate considerable interest amongst both practitioners and academics. This issue demonstrates that operational researchers have many contributions to offer to the area, especially by bringing multi-disciplinary, integrated and holistic perspectives. The papers included are both theoretical as well as practical, and include a number of case studies showing how knowledge management has been implemented in practice that may assist other organisations in their search for a better means of managing what is now recognised as a core organisational activity. It has been accepted by a growing number of organisations that the precise handling of information and knowledge is a significant factor in facilitating their success but that there is a challenge in how to implement a strategy and processes for this handling. It is here, in the particular area of knowledge process handling that we can see the contributions of operational researchers most clearly as is illustrated in the papers included in this journal edition. The issue comprises nine papers, contributed by authors based in eight different countries on five continents. Lind and Seigerroth describe an approach that they call team-based reconstruction, intended to help articulate knowledge in a particular organisational. context. They illustrate the use of this approach with three case studies, two in manufacturing and one in public sector health care. Different ways of carrying out reconstruction are analysed, and the benefits of team-based reconstruction are established. Edwards and Kidd, and Connell, Powell and Klein both concentrate on knowledge transfer. Edwards and Kidd discuss the issues involved in transferring knowledge across frontières (borders) of various kinds, from those borders within organisations to those between countries. They present two examples, one in distribution and the other in manufacturing. They conclude that trust and culture both play an important part in facilitating such transfers, that IT should be kept in a supporting role in knowledge management projects, and that a staged approach to this IT support may be the most effective. Connell, Powell and Klein consider the oft-quoted distinction between explicit and tacit knowledge, and argue that such a distinction is sometimes unhelpful. They suggest that knowledge should rather be regarded as a holistic systemic property. The consequences of this for knowledge transfer are examined, with a particular emphasis on what this might mean for the practice of OR Their view of OR in the context of knowledge management very much echoes Lind and Seigerroth's focus on knowledge for human action. This is an interesting convergence of views given that, broadly speaking, one set of authors comes from within the OR community, and the other from outside it. Hafeez and Abdelmeguid present the nearest to a 'hard' OR contribution of the papers in this special issue. In their paper they construct and use system dynamics models to investigate alternative ways in which an organisation might close a knowledge gap or skills gap. The methods they use have the potential to be generalised to any other quantifiable aspects of intellectual capital. The contribution by Revilla, Sarkis and Modrego is also at the 'hard' end of the spectrum. They evaluate the performance of public–private research collaborations in Spain, using an approach based on data envelopment analysis. They found that larger organisations tended to perform relatively better than smaller ones, even though the approach used takes into account scale effects. Perhaps more interesting was that many factors that might have been thought relevant, such as the organisation's existing knowledge base or how widely applicable the results of the project would be, had no significant effect on the performance. It may be that how well the partnership between the collaborators works (not a factor it was possible to take into account in this study) is more important than most other factors. Mak and Ramaprasad introduce the concept of a knowledge supply network. This builds on existing ideas of supply chain management, but also integrates the design chain and the marketing chain, to address all the intellectual property connected with the network as a whole. The authors regard the knowledge supply network as the natural focus for considering knowledge management issues. They propose seven criteria for evaluating knowledge supply network architecture, and illustrate their argument with an example from the electronics industry—integrated circuit design and fabrication. In the paper by Hasan and Crawford, their interest lies in the holistic approach to knowledge management. They demonstrate their argument—that there is no simple IT solution for organisational knowledge management efforts—through two case study investigations. These case studies, in Australian universities, are investigated through cultural historical activity theory, which focuses the study on the activities that are carried out by people in support of their interpretations of their role, the opportunities available and the organisation's purpose. Human activities, it is argued, are mediated by the available tools, including IT and IS and in this particular context, KMS. It is this argument that places the available technology into the knowledge activity process and permits the future design of KMS to be improved through the lessons learnt by studying these knowledge activity systems in practice. Wijnhoven concentrates on knowledge management at the operational level of the organisation. He is concerned with studying the transformation of certain inputs to outputs—the operations function—and the consequent realisation of organisational goals via the management of these operations. He argues that the inputs and outputs of this process in the context of knowledge management are different types of knowledge and names the operation method the knowledge logistics. The method of transformation he calls learning. This theoretical paper discusses the operational management of four types of knowledge objects—explicit understanding; information; skills; and norms and values; and shows how through the proposed framework learning can transfer these objects to clients in a logistical process without a major transformation in content. Millie Kwan continues this theme with a paper about process-oriented knowledge management. In her case study she discusses an implementation of knowledge management where the knowledge is centred around an organisational process and the mission, rationale and objectives of the process define the scope of the project. In her case they are concerned with the effective use of real estate (property and buildings) within a Fortune 100 company. In order to manage the knowledge about this property and the process by which the best 'deal' for internal customers and the overall company was reached, a KMS was devised. She argues that process knowledge is a source of core competence and thus needs to be strategically managed. Finally, you may also wish to read a related paper originally submitted for this Special Issue, 'Customer knowledge management' by Garcia-Murillo and Annabi, which was published in the August 2002 issue of the Journal of the Operational Research Society, 53(8), 875–884.

A constructive learning algorithm based on back-propagation

There are been a resurgence of interest in the neural networks field in recent years, provoked in part by the discovery of the properties of multi-layer networks. This interest has in turn raised questions about the possibility of making neural network behaviour more adaptive by automating some of the processes involved. Prior to these particular questions, the process of determining the parameters and network architecture required to solve a given problem had been a time consuming activity. A number of researchers have attempted to address these issues by automating these processes, concentrating in particular on the dynamic selection of an appropriate network architecture.The work presented here specifically explores the area of automatic architecture selection; it focuses upon the design and implementation of a dynamic algorithm based on the Back-Propagation learning algorithm. The algorithm constructs a single hidden layer as the learning process proceeds using individual pattern error as the basis of unit insertion. This algorithm is applied to several problems of differing type and complexity and is found to produce near minimal architectures that are shown to have a high level of generalisation ability.

On bandwidth request mechanism with piggyback in fixed IEEE 802.16 networks

This paper investigates the random channel access mechanism specified in the IEEE 802.16 standard for the uplink traffic in a Point-to-MultiPoint (PMP) network architecture. An analytical model is proposed to study the impacts of the channel access parameters, bandwidth configuration and piggyback policy on the performance. The impacts of physical burst profile and non-saturated network traffic are also taken into account in the model. Simulations validate the proposed analytical model. It is observed that the bandwidth utilization can be improved if the bandwidth for random channel access can be properly configured according to the channel access parameters, piggyback policy and network traffic.