Performance Modeling of Fresnel-Based CPV Systems: Effects of Deformations under Real Operation Conditions

Getting a lower energy cost has always been a challenge for concentrated photovoltaic. The FK concentrator enhances the performance (efficiency, acceptance angle and manufacturing tolerances) of the conventional CPV system based on a Fresnel primary stage and a secondary lens, while keeping its simplicity and potentially low���cost manufacturing. At the same time F���XTP (Fresnel lens+reflective prism), at the first glance has better cost potential but significantly higher sensitivity to manufacturing errors. This work presents comparison of these two approaches applied to two main technologies of Fresnel lens production (PMMA and Silicone on Glass) and effect of standard deformations that occur under real operation conditions

Estudio de la tolerancia al da��o de los materiales y sistemas de pretensado

La mayor��a de las estructuras de hormig��n pretensadas construidas en los ��ltimos 50 a��os han demostrado una excelente durabilidad cuando su construcci��n se realiza atendiendo las recomendaciones de un buen dise��o as�� como una buena ejecuci��n y puesta en obra de la estructura. Este hecho se debe en gran parte al temor que despierta el fen��meno de la corrosi��n bajo tensi��n t��pico de las armaduras de acero de alta resistencia. Menos atenci��n se ha prestado a la susceptibilidad a la corrosi��n bajo tensi��n de los anclajes de postensado, posiblemente debido a que se han reportado pocos casos de fallos catastr��ficos. El concepto de Tolerancia al Da��o y la Mec��nica de la Fractura en estructuras de Ingenier��a Civil ha empezado a incorporarse recientemente en algunas normas de dise��o y c��lculo de estructuras met��licas, sin embargo, a��n est�� lejos de ser asimilado y empleado habitualmente por los ingenieros en sus c��lculos cuando la ocasi��n lo requiere. Este desconocimiento de los aspectos relacionados con la Tolerancia al Da��o genera importantes gastos de mantenimiento y reparaci��n. En este trabajo se ha estudiado la aplicabilidad de los conceptos de la Mec��nica de la Fractura a los componentes de los sistemas de postensado empleados en ingenier��a civil, emple��ndolo para analizar la susceptibilidad de las armaduras activas frente a la corrosi��n bajo tensiones y a la p��rdida de capacidad portante de las cabezas de anclajes de postensado debido a la presencia de defectos. Con este objeto se han combinado tanto t��cnicas experimentales como num��ricas. Los defectos superficiales en los alambres de pretensado no se presentan de manera aislada si no que existe una cierta continuidad en la direcci��n axial as�� como un elevado n��mero de defectos. Por este motivo se ha optado por un enfoque estad��stico, que es m��s apropiado que el determin��stico. El empleo de modelos estad��sticos basados en la teor��a de valores extremos ha permitido caracterizar el estado superficial en alambres de 5,2 mm de di��metro. Por otro lado la susceptibilidad del alambre frente a la corrosi��n bajo tensi��n ha sido evaluada mediante la realizaci��n de una campa��a de ensayos de acuerdo con la actual normativa que ha permitido caracterizar estad��sticamente su comportamiento. A la vista de los resultados ha sido posible evaluar como los par��metros que definen el estado superficial del alambre pueden determinar la durabilidad de la armadura atendiendo a su resistencia frente a la corrosi��n bajo tensi��n, evaluada mediante los ensayos que especifica la normativa. En el caso de las cabezas de anclaje de tendones de pretensado, los defectos se presentan de manera aislada y tienen su origen en marcas, ara��azos o picaduras de corrosi��n que pueden producirse durante el proceso de fabricaci��n, transporte, manipulaci��n o puesta en obra. Dada la naturaleza de los defectos, el enfoque determin��stico es m��s apropiado que el estad��stico. La evaluaci��n de la importancia de un defecto en un elemento estructural requiere la estimaci��n de la solicitaci��n local que genera el defecto, que permite conocer si el defecto es cr��tico o si puede llegar a serlo, si es que progresa con el tiempo (por fatiga, corrosi��n, una combinaci��n de ambas, etc.). En este trabajo los defectos han sido idealizados como grietas, de manera que el an��lisis quedara del lado de la seguridad. La evaluaci��n de la solicitaci��n local del defecto ha sido calculada mediante el empleo de modelos de elementos finitos de la cabeza de anclaje que simulan las condiciones de trabajo reales de la cabeza de anclaje durante su vida ��til. A partir de estos modelos num��ricos se ha analizado la influencia en la carga de rotura del anclaje de diversos factores como la geometr��a del anclaje, las condiciones del apoyo, el material del anclaje, el tama��o del defecto su forma y su posici��n. Los resultados del an��lisis num��rico han sido contrastados satisfactoriamente mediante la realizaci��n de una campa��a experimental de modelos a escala de cabezas de anclaje de Polimetil-metacrilato en los que artificialmente se han introducido defectos de diversos tama��os y en distintas posiciones. ABSTRACT Most of the prestressed concrete structures built in the last 50 years have demonstrated an excellent durability when they are constructed in accordance with the rules of good design, detailing and execution. This is particularly true with respect to the feared stress corrosion cracking, which is typical of high strength prestressing steel wires. Less attention, however, has been paid to the stress corrosion cracking susceptibility of anchorages for steel tendons for prestressing concrete, probably due to the low number of reported failure cases. Damage tolerance and fracture mechanics concepts in civil engineering structures have recently started to be incorporated in some design and calculation rules for metallic structures, however it is still far from being assimilated and used by civil engineers in their calculations on a regular basis. This limited knowledge of the damage tolerance basis could lead to significant repair and maintenance costs. This work deals with the applicability of fracture mechanics and damage tolerance concepts to the components of prestressed systems, which are used in civil engineering. Such concepts have been applied to assess the susceptibility of the prestressing steel wires to stress corrosion cracking and the reduction of load bearing capability of anchorage devices due to the presence of defects. For this purpose a combination of experimental work and numerical techniques have been performed. Surface defects in prestressing steel wires are not shown alone, though a certain degree of continuity in the axial direction exist. A significant number of such defects is also observed. Hence a statistical approach was used, which is assumed to be more appropriate than the deterministic approach. The use of statistical methods based in extreme value theories has allowed the characterising of the surface condition of 5.2 mm-diameter wires. On the other hand the stress corrosion cracking susceptibility of the wire has been assessed by means of an experimental testing program in line with the current regulations, which has allowed statistical characterisasion of their performances against stress corrosion cracking. In the light of the test results, it has been possible to evaluate how the surface condition parameters could determine the durability of the active metal armour regarding to its resistance against stress corrosion cracking assessed by means of the current testing regulations. In the case of anchorage devices for steel tendons for prestressing concrete, the damage is presented as point defects originating from dents, scratches or corrosion pits that could be produced during the manufacturing proccess, transport, handling, assembly or use. Due to the nature of these defects, in this case the deterministic approach is more appropriate than the statistical approach. The assessment of the relevancy of defect in a structural component requires the computation of the stress intensity factors, which in turn allow the evaluation of whether the size defect is critical or could become critical with the progress of time (due to fatigue, corrosion or a combination of both effects). In this work the damage is idealised as tiny cracks, a conservative hypothesis. The stress intensity factors have been calculated by means of finite element models of the anchorage representing the real working conditions during its service life. These numeric models were used to assess the impact of some factors on the rupture load of the anchorage, such the anchorage geometry, material, support conditions, defect size, shape and its location. The results from the numerical analysis have been succesfully correlated against the results of the experimental testing program of scaled models of the anchorages in poly-methil methacrylate in which artificial damage in several sizes and locations were introduced.

Arquitectura de informaci��n para medicion de rendimiento en entornos e-manufacturing

La implantaci��n de las tecnolog��as Internet ha permitido la extensi��n del uso de estrategias e-manufacturing y el desarrollo de herramientas para la recopilaci��n, transformaci��n y sincronizaci��n de datos de fabricaci��n v��a web. En este ��mbito, un ��rea de potencial desarrollo es la extensi��n del virtual manufacturing a los procesos de Performance Management (PM), ��rea cr��tica para la toma de decisiones y ejecuci��n de acciones de mejora en fabricaci��n. Este trabajo doctoral propone un Arquitectura de Informaci��n para el desarrollo de herramientas virtuales en el ��mbito PM. Su aplicaci��n permite asegurar la interoperabilidad necesaria en los procesos de tratamiento de informaci��n de toma de decisi��n. Est�� formado por tres sub-sistemas: un modelo conceptual, un modelo de objetos y un marco Web compuesto de una plataforma de informaci��n y una arquitectura de servicios Web (WS). El modelo conceptual y el modelo de objetos se basa en el desarrollo de toda la informaci��n que se necesita para definir y obtener los diferentes indicadores de medida que requieren los procesos PM. La plataforma de informaci��n hace uso de las tecnolog��as XML y B2MML para estructurar un nuevo conjunto de esquemas de mensajes de intercambio de medici��n de rendimiento (PMXML). Esta plataforma de informaci��n se complementa con una arquitectura de servicios web que hace uso de estos esquemas para integrar los procesos de codificaci��n, decodificaci��n, traducci��n y evaluaci��n de los performance key indicators (KPI). Estos servicios realizan todas las transacciones que permiten transformar los datos origen en informaci��n inteligente usable en los procesos de toma de decisi��n. Un caso pr��ctico de intercambio de datos en procesos de medici��n del ��rea de mantenimiento de equipos es mostrado para verificar la utilidad de la arquitectura. ABSTRAC The implementation of Internet technologies has led to e-Manufacturing technologies becoming more widely used and to the development of tools for compiling, transforming and synchronizing manufacturing data through the Web. In this context, a potential area for development is the extension of virtual manufacturing to Performance Measurement (PM) processes, a critical area for decision-making and implementing improvement actions in manufacturing. This thesis proposes a Information Architecture to integrate decision support systems in e-manufacturing. Specifically, the proposed architecture offers a homogeneous PM information exchange model that can be applied trough decision support in emanufacturing environment. Its application improves the necessary interoperability in decision-making data processing tasks. It comprises three sub-systems: a data model, a object model and Web Framework which is composed by a PM information platform and PM-Web services architecture. . The data model and the object model are based on developing all the information required to define and acquire the different indicators required by PM processes. The PM information platform uses XML and B2MML technologies to structure a new set of performance measurement exchange message schemas (PM-XML). This PM information platform is complemented by a PM-Web Services architecture that uses these schemas to integrate the coding, decoding, translation and assessment processes of the key performance indicators (KPIs). These services perform all the transactions that enable the source data to be transformed into smart data that can be used in the decision-making processes. A practical example of data exchange for measurement processes in the area of equipment maintenance is shown to demonstrate the utility of the architecture.

Improving the efficiency of nondeterministic indepemndent and-parallel systems

We present the design and implementation of the and-parallel component of ACE. ACE is a computational model for the full Prolog language that simultaneously exploits both or-parallelism and independent and-parallelism. A high performance implementation of the ACE model has been realized and its performance reported in this paper. We discuss how some of the standard problems which appear when implementing and-parallel systems are solved in ACE. We then propose a number of optimizations aimed at reducing the overheads and the increased memory consumption which occur in such systems when using previously proposed solutions. Finally, we present results from an implementation of ACE which includes the optimizations proposed. The results show that ACE exploits and-parallelism with high efficiency and high speedups. Furthermore, they also show that the proposed optimizations, which are applicable to many other and-parallel systems, significantly decrease memory consumption and increase speedups and absolute performance both in forwards execution and during backtracking.

Experiments in abstract interpretation-based code certification for pervasive systems

Proof carrying code (PCC) is a general is originally a roof in ��rst-order logic of certain vermethodology for certifying that the execution of an un- ification onditions and the checking process involves trusted mobile code is safe. The baste idea is that the ensuring that the certif��cate is indeed a valid ��rst-order code supplier attaches a certif��cate to the mobile code proof. which the consumer checks in order to ensure that the The main practical dif��culty of PCC techniques is in code is indeed safe. The potential benefit is that the generating safety certi��eates which at the same time: i) consumer's task is reduced from the level of proving to allow expressing interesting safety properties, ii) can be the level of checking. Recently, the abstract interpre- generated automatically and, iii) are easy and efficient tation techniques developed, in logic programming have to check. In [1], the abstract interpretation techniques been proposed as a basis for PCC. This extended ab- [5] developed in logic programming1 are proposed as stract reports on experiments which illustrate several is- a basis for PCC. They offer a number of advantages sues involved in abstract interpretation-based certifica- for dealing with the aforementioned issues. In particution. First, we describe the implementation of our sys- lar, the xpressiveness of existing abstract domains will tem in the context of CiaoPP: the preprocessor of the be implicitly available in abstract interpretation-based Ciao multi-paradigm programming system. Then, by code certification to de��ne a wide range of safety propermeans of some experiments, we show how code certifi- ties. Furthermore, the approach inherits the automation cati��n is aided in the implementation of the framework. and inference power of the abstract interpretation en- Finally, we discuss the application of our method within gines used in (Constraint) Logic Programming, (C)LP. the ��rea, of pervasive systems

A generic persistence model for CLP systems (and two useful implementations)

This paper describes a model of persistence in (C)LP languages and two different and practically very useful ways to implement this model in current systems. The fundamental idea is that persistence is a characteristic of certain dynamic predicates (Le., those which encapsulate state). The main effect of declaring a predicate persistent is that the dynamic changes made to such predicates persist from one execution to the next one. After proposing a syntax for declaring persistent predicates, a simple, file-based implementation of the concept is presented and some examples shown. An additional implementation is presented which stores persistent predicates in an external dat��base. The abstraction of the concept of persistence from its implementation allows developing applications which can store their persistent predicates alternatively in files or databases with only a few simple changes to a declaration stating the location and modality used for persistent storage. The paper presents the model, the implementation approach in both the cases of using files and relational databases, a number of optimizations of the process (using information obtained from static global analysis and goal clustering), and performance results from an implementation of these ideas.

A generic persistence model for CLP systems

This paper describes a model of persistence in (C)LP languages and two different and practically very useful ways to implement this model in current systems. The fundamental idea is that persistence is a characteristic of certain dynamic predicates (i.e., those which encapsulate state). The main effect of declaring a predicate persistent is that the dynamic changes made to such predicates persist from one execution to the next one. After proposing a syntax for declaring persistent predicates, a simple, file-based implementation of the concept is presented and some examples shown. An additional implementation is presented which stores persistent predicates in an external database. The abstraction of the concept of persistence from its implementation allows developing applications which can store their persistent predicates alternatively in files or databases with only a few simple changes to a declaration stating the location and modality used for persistent storage. The paper presents the model, the implementation approach in both the cases of using files and relational databases, a number of optimizations of the process (using information obtained from static global analysis and goal clustering), and performance results from an implementation of these ideas.

Using attributed variables in the implementation of concurrent and parallel logic programming systems

Incorporating the possibility of attaching attributes to variables in a logic programming system has been shown to allow the addition of general constraint solving capabilities to it. This approach is very attractive in that by adding a few primitives any logic programming system can be turned into a generic constraint logic programming system in which constraint solving can be user de��ned, and at source level - an extreme example of the "glass box" approach. In this paper we propose a different and novel use for the concept of attributed variables: developing a generic parallel/concurrent (constraint) logic programming system, using the same "glass box" flavor. We arg��e that a system which implements attributed variables and a few additional primitives can be easily customized at source level to implement many of the languages and execution models of parallelism and concurrency currently proposed, in both shared memory and distributed systems. We illustrate this through examples and report on an implementation of our ideas.

ACE: And/or-parallel copying-based execution of logic programs

In this paper we present a novel execution model for parallel implementation of logic programs which is capable of exploiting both independent and-parallelism and or-parallelism in an efficient way. This model extends the stack copying approach, which has been successfully applied in the Muse system to implement or-parallelism, by integrating it with proven techniques used to support independent and-parallelism. We show how all solutions to non-deterministic andparallel goals are found without repetitions. This is done through recomputation as in Prolog (and in various and-parallel systems, like &-Prolog and DDAS), i.e., solutions of and-parallel goals are not shared. We propose a scheme for the efficient management of the address space in a way that is compatible with the apparently incompatible requirements of both and- and or-parallelism. We also show how the full Prolog language, with all its extra-logical features, can be supported in our and-or parallel system so that its sequential semantics is preserved. The resulting system retains the advantages of both purely or-parallel systems as well as purely and-parallel systems. The stack copying scheme together with our proposed memory management scheme can also be used to implement models that combine dependent and-parallelism and or-parallelism, such as Andorra and Prometheus.

Relating goal scheduling, precedence, and memory management in and-parallel execution of logic programs

The interactions among three important issues involved in the implementation of logic programs in parallel (goal scheduling, precedence, and memory management) are discussed. A simplified, parallel memory management model and an efficient, load-balancing goal scheduling strategy are presented. It is shown how, for systems which support "don't know" non-determinism, special care has to be taken during goal scheduling if the space recovery characteristics of sequential systems are to be preserved. A solution based on selecting only "newer" goals for execution is described, and an algorithm is proposed for efficiently maintaining and determining precedence relationships and variable ages across parallel goals. It is argued that the proposed schemes and algorithms make it possible to extend the storage performance of sequential systems to parallel execution without the considerable overhead previously associated with it. The results are applicable to a wide class of parallel and coroutining systems, and they represent an efficient alternative to "all heap" or "spaghetti stack" allocation models.

An abstract machine for restricted and-parallel execution of logic programs

Although the sequential execution speed of logic programs has been greatly improved by the concepts introduced in the Warren Abstract Machine (WAM), parallel execution represents the only way to increase this speed beyond the natural limits of sequential systems. However, most proposed parallel logic programming execution models lack the performance optimizations and storage efficiency of sequential systems. This paper presents a parallel abstract machine which is an extension of the WAM and is thus capable of supporting ANDParallelism without giving up the optimizations present in sequential implementations. A suitable instruction set, which can be used as a target by a variety of logic programming languages, is also included. Special instructions are provided to support a generalized version of "Restricted AND-Parallelism" (RAP), a technique which reduces the overhead traditionally associated with the run-time management of variable binding conflicts to a series of simple run-time checks, which select one out of a series of compiled execution graphs.

A program transformation for continuation call-based tabled execution

The advantages of tabled evaluation regarding program termination and reduction of complexity are well known ���as are the significant implementation, portability, and maintenance efforts that some proposals (especially those based on suspensi��n) require. This implementation effort is reduced by program transformation-based continuation cali techniques, at some e��rciency cost. However, the traditional formulation of this proposal by Ramesh and Cheng limits the interleaving of tabled and non-tabled predicates and thus cannot be used as-is for arbitrary programs. In this paper we present a complete translation for the continuation cali technique which, using the runtime support needed for the traditional proposal, solves these problems and makes it possible to execute arbitrary tabled programs. We present performance results which show that CCall offers a useful tradeoff that can be competitive with state-of-the-art implementations.

Towards high-level execution primitives for and-parallelism: preliminary results

Most implementations of parallel logic programming rely on complex low-level machinery which is arguably difflcult to implement and modify. We explore an alternative approach aimed at taming that complexity by raising core parts of the implementation to the source language level for the particular case of and-parallelism. Therefore, we handle a signiflcant portion of the parallel implementation mechanism at the Prolog level with the help of a comparatively small number of concurrency-related primitives which take care of lower-level tasks such as locking, thread management, stack set management, etc. The approach does not eliminate altogether modiflcations to the abstract machine, but it does greatly simplify them and it also facilitates experimenting with different alternatives. We show how this approach allows implementing both restricted and unrestricted (i.e., non fork-join) parallelism. Preliminary experiments show that the amount of performance sacriflced is reasonable, although granularity control is required in some cases. Also, we observe that the availability of unrestricted parallelism contributes to better observed speedups.

Abstract interpretation-based code certification for pervasive systems: Preliminary experiments

Proof carrying code is a general methodology for certifying that the execution of an untrusted mobile code is safe, according to a predefined safety policy. The basic idea is that the code supplier attaches a certif��cate (or proof) to the mobile code which, then, the consumer checks in order to ensure that the code is indeed safe. The potential benefit is that the consumer's task is reduced from the level of proving to the level of checking, a much simpler task. Recently, the abstract interpretation techniques developed in logic programming have been proposed as a basis for proof carrying code [1]. To this end, the certif��cate is generated from an abstract interpretation-based proof of safety. Intuitively, the verification condition is extracted from a set of assertions guaranteeing safety and the answer table generated during the analysis. Given this information, it is relatively simple and fast to verify that the code does meet this proof and so its execution is safe. This extended abstract reports on experiments which illustrate several issues involved in abstract interpretation-based code certification. First, we describe the implementation of our system in the context of CiaoPP: the preprocessor of the Ciao multi-paradigm (constraint) logic programming system. Then, by means of some experiments, we show how code certification is aided in the implementation of the framework. Finally, we discuss the application of our method within the ��rea of pervasive systems which may lack the necessary computing resources to verify safety on their own. We herein illustrate the relevance of the information inferred by existing cost analysis to control resource usage in this context. Moreover, since the (rather complex) analysis phase is replaced by a simpler, efficient checking process at the code consumer side, we believe that our abstract interpretation-based approach to proof-carrying code becomes practically applicable to this kind of systems.

WWW Programming using computational logic systems (and the PiLLoW/Ciao library)

We discuss from a practical point of view a number of issues involved in writing Internet and WWW applications using LP/CLP systems. We describe Pd_l_oW, a public-domain Internet and WWW programming library for LP/CLP systems which we arg��e significantly simplifies the process of writing such applications. Pd_l_oW provides facilities for generating HTML structured documents, producing HTML forms, writing form handlers, accessing and parsing WWW documents, and accessing code posted at HTTP addresses. We also describe the architecture of some application classes, using a high-level model of client-server interaction, active modules. We then propose an architecture for automatic LP/CLP code downloading for local execution, using generic browsers. Finally, we also provide an overview of related work on the topic. The PiLLoW library has been developed in the context of the &- Prolog and CIAO systems, but it has been adapted to a number of popular LP/CLP systems, supporting most of its functionality.