Institut Politècnic d’Innovació i Recerca en Sostenibilitat (INSPIRES)

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https://repositori.udl.cat/handle/10459.1/56939

INSPIRES és un centre de recerca de la Universitat de Lleida. Conforma un grup multidisciplinari que posa especial atenció a la recerca al voltant de la millor gestió energètica, l’eficiència, la usabilitat, la seguretat, la computació d’altes prestacions i la resolució i optimització de problemes, entre altres temes. Tot amb nexes comuns, girant al voltant de l’àmbit de la sostenibilitat i la tecnologia. Suposa una unió d’esforços dels diferents centres de recerca que de manera separada tractaven diferents línies i àrees, ara aquests esforços es comparteixen generant sinèrgies.[Més informació].

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Now showing 1 - 20 of 648

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The satisfiability problem in regular CNF-formulas
(Springer Verlag, 1998) Manyà Serres, Felip; Béjar Torres, Ramón; Escalada Imaz, G.
In this paper we deal with the propositional satisfiability (SAT) problem for a kind of multiple-valued clausal forms known as regular CNF-formulas and extend some known results from classical logic to this kind of formulas. We present a DavisÐPutnam-style satisfiability checking procedure for regular CNF-formulas equipped with suitable data structures and prove its completeness. Then, we describe a series of experiments for regular random 3-SAT instances. We observe that, for the regular 3-SAT problem with this procedure, there exists a threshold of the ratio of clauses to variables such that (i) the most computationally difficult instances tend to be found near the threshold, (ii) there is a sharp transition from satisfiable to unsatisfiable instances at the threshold and (iii) the value of the threshold increases as the number of truth values considered increases. Instances in the hard part provide benchmarks for the evaluation of regular satisfiability solvers.
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A Time-Domain Method for the Analysis of Thermal Impedance Response Preserving the Convolution Form
(Institute of Electrical and Electronics Engineers, 1999) Carmona, Manuel; Marco, Santiago; Palacín Roca, Jordi; Samitier, Josep
The study of the thermal behavior of complex packages as multichip modules (MCM’s) is usually carried out by measuring the so-called thermal impedance response, that is: the transient temperature after a power step. From the analysis of this signal, the thermal frequency response can be estimated, and consequently, compact thermal models may be extracted. We present a method to obtain an estimate of the time constant distribution underlying the observed transient. The method is based on an iterative deconvolution that produces an approximation to the time constant spectrum while preserving a convenient convolution form. This method is applied to the obtained thermal response of a microstructure as analyzed by finite element method as well as to the measured thermal response of a transistor array integrated circuit (IC) in a SMD package.
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Exploiting Knowledge of Temporal Behaviour in Parallel Programs for Improving Distributed Mapping
(Springer Verlag, 2000) Roig Mateu, Concepció; Ripoll, A.; Senar, M.A.; Guirado Fernández, Fernando; Luque, Emilio
In the distributed processing area, mapping and scheduling are very important issues in order to exploit the gain from parallelization. The generation of efficient static mapping techniques implies a previous modelling phase of the parallel application as a task graph, which properly reflects its temporal behaviour. In this paper we use a new model, the Temporal Task Interaction Graph (TTIG), which explicitly captures the temporal behaviour of program tasks; and we evaluate the advantages that derive from the use of the TTIG model in task allocation. Experimentation was performed in a current PVM environment, for a set of synthetic graphs which exhibit different ratios of computation/ communication cost (coarse-grain, medium-grain). The execution times when these programs were mapped using the information contained in the TTIG model, were compared with the times obtained using the two following mapping alternatives: (a) PVM default scheme and, (b) mapping strategy based on the classical model TIG (Task Interaction Graph). The results confirm that with the TTIG model, better assignments are obtained, providing improvements of up to 49% compared with the PVM assignments and up to 30% compared with TIG assignments.
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Monito: A Communication Monitoring Tool for a PVM-Linux Environment
(Springer Verlag, 2000) Solsona Tehàs, Francesc; Giné, Francesc; Lérida Monsó, Josep Lluís; Hernandez, Porfidio; Luque, Emilio
In this paper a new tool for monitoring the different queues of messages in a PVM environment is presented. The main aim of implementing this facility is to provide a means of capturing the bottlenecks and overheads of the communication system in a PVM-Linux cluster. Also, it will allow to know the communication pattern of a distributed application. Its good behaviour has been proved experimentally.
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Implementing Explicit and Implicit Coscheduling in a PVM Environment
(Springer Verlag, 2000) Solsona Tehàs, Francesc; Giné, Francesc; Hernandez, Porfidio; Luque, Emilio
Our efforts are directed towards the understanding of the coscheduling mechanism in a NOW system when a parallel job is executed with local workloads, balancing parallel efficiency against the local interactive response. Explicit and implicit coscheduling techniques in a PVM-Linux NOW (or cluster) has been implemented. Their performance and overheads executing local tasks and representative distributed benchmarks have been analyzed and compared.
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MemTo: A Memory Monitoring Tool for a Linux Cluster
(Springer Verlag, 2001) Giné, Francesc; Solsona Tehàs, Francesc; Navarro, Xavi; Hernandez, Porfidio; Luque, Emilio
Studies dealing with tuning, performance debugging and diagnosis in cluster environments largely benefit from in-depth knowledge of memory system information. In this paper a tool (called MemTo) for monitoring the behavior of the memory system through a Linux cluster is presented. MemTo has been designed to have as low intrusiveness as possible while keeping a high detail of monitoring data. The good behavior and usefulness of this tool are proved experimentally.
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Suboptimal Filtering and Nonlinear Time Scale Transformation for the Analysis of Multiexponential Decays
(IEEE, 2001) Palacín Roca, Jordi; Marco, Santiago; Samitier, Josep
Multiexponential decays may contain time-constants differing in several orders of magnitudes. In such cases, uniform sampling results in very long records featuring a high degree of oversampling at the final part of the transient. Here, we analyze a nonlinear time scale transformation to reduce the total number of samples with minimum signal distortion, achieving an important reduction of the computational cost of subsequent analyses. We propose a time-varying filter whose length is optimized for minimum mean square error.
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Extending the Reach of SAT with Many-Valued Logics
(Elsevier, 2001) Béjar Torres, Ramón; Cabiscol i Teixidó, Alba; Fernàndez Camon, César; Manyà Serres, Felip; Gomes, Carla
We present Regular-SAT, an extension of Boolean Satisfiability based on a class of many-valued CNFform ulas. Regular-SAT shares many properties with Boolean SAT, which allows us to generalize some of the best known SAT results and apply them to Regular-SAT. In addition, Regular-SAT has a number of advantages over Boolean SAT. Most importantly, it produces more compact encodings that capture problem structure more naturally. Furthermore, its simplicity allows us to develop Regular-SAT solvers that are competitive with SAT and CSP procedures. We present a detailed performance analysis of Regular-SAT on several benchmark domains. These results show a clear computational advantage of using a Regular- SAT approach over a pure Boolean SAT or CSP approach, at least on the domains under consideration. We therefore believe that an approach based on Regular-SAT provides a compelling intermediate approach between SAT and CSPs, bringing together some of the best features of each paradigm.
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Efficient Mapping for Message-Passing Applications Using the TTIG Model: A Case Study in Image Processing
(Springer Verlag, 2001) Roig Mateu, Concepció; Ripoll, A.; Borrás, Javier; Luque, Emilio
In this paper we describe the development and performance of an image processing application with functional parallelism within the PVM framework. The temporal behaviour of the application is statically modelled with the new task graph model TTIG (Temporal Task Interaction Graph), that enhances classical models by capturing percentages of concurrency between adjacent tasks. We show how this information can be used in the mapping phase in order to obtain better assignments of tasks to processors. The effectiveness of the TTIG in allocation for the application under study is established through experimentation on a cluster of PCs.
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Predictive Coscheduling Implementation in a non-dedicated Linux Cluster
(Springer Verlag, 2001) Solsona Tehàs, Francesc; Giné, Francesc; Hernandez, Porfidio; Luque, Emilio
Our research is focussed on keeping both local and parallel jobs together in a non-dedicated cluster or NOW (Network Of Workstations) and efficiently scheduling them by means of coscheduling mechanisms. A real implementation of a predictive coscheduling technique in a Linux cluster is presented in this article and its performance analyzed and compared with other coscheduling algorithms in the literature.
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Improved Multiexponential Transcient Spectroscopy By Iterative Deconvolution
(Institute of Electrical and Electronics Engineers, 2001) Marco, Santiago; Palacín Roca, Jordi; Samitier, Josep
The analysis of multiexponential decays is challenging because of their complex nature. When analyzing these signals, not only the parameters, but also the orders of the models, have to be estimated. Here, we present an improved spectroscopic technique specially suited for this purpose. The proposed algorithm combines an iterative linear filter with an iterative deconvolution method. A thorough analysis of the noise effect is presented. The performance is tested with synthetic and experimental data.
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Immersion corrosion tests on metal-salt hydrate pairs used for latent heat storage in the 32 to 36 8C temperature range
(Wiley, 2001) Cabeza, Luisa F.; Illa i Alibés, Josep; Roca Enrich, Joan; Badia Pascual, Ferran; Mehling, Harald; Hiebler, Stefan; Ziegler, F.
During the last decades, energy storage has become more and more important. It is required in order to utilize alternative energy sources, which often are available at times when energy is not needed. The main applications of PCMs (Phase Change Materials) in thermal energy storage are when space restrictions limit larger thermal storage units. But widespread use of latent heat stores has not been realized till today due to two main problems: the low heat flux, and the insufficient long term stability of the storage materials and containers. In the present work, we studied this second problem selecting different common metals (aluminum, brass, copper, steel, and stainless steel) and testing their corrosion resistance in contact with salt hydrates that are used as PCMs (zinc nitrate hexahydrate, sodium hydrogen phosphate dodecahydrate, calcium chloride hexahydrate). The method used was the immersion corrosion test. The tests here presented and evaluated were short term. As a consequence of the results from the experiments several pairs can be ruled out. The combinations of zinc nitrate hexahydrate with stainless steel, sodium hydrogen phosphate dodecahydrate with brass, copper and stainless steel, and calcium chloride hexahydrate with brass and copper shared no significant corrosion in the short term and should be studied further.
Open Access
A Fully Scalable and Distributed Architecture for Video-on-Demand
(Springer Verlag, 2001) Cores Prado, Fernando; Ripoll, A.; Luque, Emilio
In spite of the attractiveness of Video-on-demand (VoD) services, their implantation to the present has not been as widespread as could have been desired due to centralized VoD systems have a limited streaming capacity and its grown is costly. One level proxy-based systems have been proposed to increase the system capacity but their scalability are still limited by the main network bandwidth. Our investigation are focussed on designing a flexible LVoD (large-scale Video-on-Demand) system capable of easy scaling with limited costs, which can adapt its size to the needs of the system. To achieve a scalable LVoD system, it is essential that the communications system bandwidth is able to grow in keeping with system growth (with a reasonable cost and limited loss of efficiency). To get these requirements we have proposed a hierarchical tree topology based on the use of independent local networks with proxies. To allow the system’s grow, the functionality of the proxy has been modified in such a way that it works at the same time as cache for the most watched movies, and as a mirror for the remaining movies. The evaluation of these systems has been done using an analytical model. The results shows that this architecture guarantees unlimited and low-cost growth for LVoD systems, the VoD system capacity can easily be adapted to any number of users and the system is fault-tolerant.
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Implementing and Analysing an Effective Explicit Coscheduling Algorithm on a NOW
(Springer Verlag, 2001) Solsona Tehàs, Francesc; Giné, Francesc; Molina, Fermín; Hernandez, Porfidio; Luque, Emilio
Networks of workstations (NOWs) have become important and cost-effective parallel platforms for scientific computations. In practice, a NOW system is heterogeneous and non-dedicated. These two unique factors make scheduling policies on multiprocessor/multicomputer systems unsuitable for NOWs, but the coscheduling principle is still an important basis for parallel process scheduling in these environments. The main idea of this technique is to schedule the set of tasks composing a parallel application at the same time, to increase their communication performance. In this article we present an explicit coscheduling algorithm implemented in a Linux NOW, of PVM distributed tasks, based on Real Time priority assignment. The main goal of the algorithm is to execute efficiently distributed applications without excessively damaging the response time of local tasks. Extensive performance analysis as well as studies of the parameters and overheads involved in the implementation demonstrated the applicability of the proposed algorithm.
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Coscheduling under Memory Constraints in a NOW
(Springer Verlag, 2001) Giné, Francesc; Solsona Tehàs, Francesc; Hernández Budé, Porfidio; Luque, Emilio
Networks of Workstations (NOW) have become important and cost-effective parallel platforms for scientific computations. In practice, a NOW system is heterogeneous and non-dedicated. These two unique factors make scheduling policies on multiprocessor/multicomputer systems unsuitable for NOWs. However, the coscheduling principle is still an important basis for parallel process scheduling in these environments. We propose a new coscheduling algorithm for reducing the number of page faults across a non-dedicated cluster by increasing the execution priority of parallel tasks with lower page fault rate. Our method is based on knowledge of events obtained during execution, as communication activity and memory size of every task. The performance of our proposal has been analyzed and compared with other coscheduling implementations by means of simulation.
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Capturing Structure with Satisfiability
(Springer Verlag, 2001) Béjar Torres, Ramón; Cabiscol i Teixidó, Alba; Fernàndez Camon, César; Manyà Serres, Felip; Gomes, Carla
We present Regular-SAT, an extension of Boolean Satisfiability basedon a class of many-valuedCNF formulas. Regular-SAT shares many properties with Boolean SAT, which allows us to generalize some of the best known SAT results and apply them to Regular-SAT. In addition, Regular-SAT has a number of advantages over Boolean SAT. Most importantly, it produces more compact encodings that capture problem structure more naturally. Furthermore, its simplicity allows us to develop Regular-SAT solvers that are competitive with SAT andCSP procedures. We present a detailed performance analysis of Regular-SAT on several benchmark domains. These results show a clear computational advantage of using a Regular-SAT approach over a pure Boolean SAT or CSP approach, at least on the domains under consideration. We therefore believe that an approach basedon Regular-SAT provides a compelling intermediate approach between SAT and CSPs, bringing together some of the best features of each paradigm.
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Towards an Automated Deduction System for First-Order Possibilistic Logic Programming with Fuzzy Constants
(Wiley, 2002) Alsinet, Teresa; Godo i Lacasa, Lluís
In this article, we present a first-order logic programming language for fuzzy reasoning under possibilistic uncertainty and poorly known information. Formulas are represented by a pair (ϕ, α), in which ϕ is a first-order Horn clause or a query with fuzzy constants and regular predicates, and α ∈ [0, 1] is a lower bound on the belief on ϕ in terms of necessity measures. Since fuzzy constants can occur in the logic component of formulas, the truth value of formulas is many-valued instead of Boolean. Moreover, since we have to reason about the possibilistic uncertainty of formulas with fuzzy constants, belief states are modeled by normalized possibility distributions on a set of many-valued interpretations. In this framework, (1) we define a syntax and a semantics of the underlying logic; (2) we give a sound modus ponens-style calculus by derivation based on a semantic unification pattern of fuzzy constants; (3) we develop a directional fuzzy unification algorithm based on the distinction between general and specific object constants; and (4) we describe a backward first-order proof procedure oriented to queries that is based on the calculus of the language and the computation of the unification degree between fuzzy constants in terms of a necessity measure for fuzzy events.
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Minimal and Redundant SAT Encodings for the All-Interval-Series Problem
(Springer Verlag, 2002) Alsinet, Teresa; Béjar Torres, Ramón; Cabiscol i Teixidó, Alba; Fernàndez Camon, César; Manyà Serres, Felip
The SAT encodings defined so far for the all-interval-series (ais) problem are very hard for local search but rather easy for systematic algorithms. We define different SAT encodings for the ais problem and provide experimental evidence that this problem can be efficiently solved with local search methods if one chooses a suitable SAT encoding.
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Adjusting Time Slices to Apply Coscheduling Techniques in a non-dedicated NOW
(Springer Verlag, 2002) Giné, Francesc; Solsona Tehàs, Francesc; Hernandez, Porfidio; Luque, Emilio
Our research is focussed on keeping both local and parallel jobs together in a time-sharing NOW and efficiently scheduling them by means of coscheduling mechanisms. In such systems, the proper length of the time slice still remains an open question. In this paper, an algorithm is presented to adjust the length of the quantum dynamically to the necessity of the distributed tasks while keeping good response time for interactive processes. It is implemented and evaluated in a Linux cluster.
Open Access
La resolución de problemas entre iguales: incidencia de la mediación del ordenador en los procesos de interacción y en el aprendizaje
(Fundación Infancia y Aprendizaje, 2002) Pifarré Turmo, Manoli; Sanuy Burgués, Jaume
En el presente trabajo se analiza la incidencia de la mediación del ordenador en la resolución de problemas y en los procesos de interacción entre parejas de alumnos de la Enseñanza Secundaria Obligatoria. Para ello, se diseña e implementa una propuesta de enseñanza-aprendizaje que guía el proceso de resolución de problemas e incide en los procesos de interacción entre iguales. Esta propuesta se realiza en dos modalidades o contextos de aprendizaje distintos: un contexto utiliza la mediación del ordenador y el otro contexto no. El análisis de los resultados obtenidos en nuestro trabajo muestra la incidencia positiva de la mediación de la hoja de cálculo en el proceso de aprendizaje de los alumnos y en los procesos de interacción que presentan las distintas parejas durante la resolución de un problema. Los alumnos que han resuelto los problemas con la hoja de cálculo obtienen resultados estadísticamente superiores a los obtenidos por los alumnos que no han utilizado esta herramienta informática y presentan, principalmente, una interacción compartida.

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