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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

New Aspects of Data Acquisition and Reduction in Gel Permeation Chromatography

Walther, William G. 01 1900 (has links)
<p> The work of this study is divided into two parts. Part I reports on the development of a dedicated minicomputer, data acquisition, and reduction system for GPC. The hardware, software, and operating performance of the system is discussed in some detail.</p> <p> Part II, reports on an experimental study design to determine whether axial dispersion corrections are universal in the sense of being independent of polymer composition. Results for poly(vinyl-chloride), polystyrene, polybutadiene, and poly(methy-methacrylate) are discussed.</p> / Thesis / Master of Engineering (MEngr)
2

Aplicações da teoria de Bases de Gröbner para o cálculo da Cohomologia de Hochschild / Aplications of the Groebner Basis theory to the computation of the Hochschild Cohomology

Amaya, Ana Melisa Paiba 24 October 2018 (has links)
A Cohomologia de Hochschild é um invariante associado a álgebras o qual pode nos fornecer propiedades homologicas das álgebras e suas categorias de módulos. Além disso tem aplicações em Geometria Algébrica e Teoria de Representações, entre outras áreas. Para álgebras A sobre um corpo, o i-ésimo grupo de cohomologia de Hochschild HH^i(A,M) de A, com coeficientes no bimódulo M, coincide com Ext^i_{A^e}(A,M). Logo, este pode ser calculado usando uma resolução projetiva da álgebra como A-bimódulo. Diferentes autores como Dieter Happel, Claude Cibils, Edward Green, David Anick, Michael Bardzell e Andrea Solotar desenvolveram ferramentas para a construção destas resoluções em casos específicos. Um resultado recente e muito importante é apresentado por Andrea Solotar e Sergio Chohuy, onde se mostra a construção de uma resolução projetiva de bimódulos para álgebras associativas generalizando o resultado para álgebras monomiais feito por Bardzell. Nesta dissertação pretendemos introduzir ao leitor no conceito de Cohomologia de Hochschild mostrando a importância da mesma mediante resultados conhecidos para álgebras de dimensão finita. Além disso, apresentamos os conceitos e resultados do trabalho de Chohuy e Solotar mencionado acima. No decorrer deste trabalho complementamos algumas demonstrações dos resultados enunciados com o fim de propiciar uma ferramenta para o melhor entendimento dos tópicos trabalhados aqui. / The Hochschild Cohomology is an invariant attached to associative algebras which may provide us some homological aspects of the algebras and its category of modules. Moreover, it has applications to Algebraic Geometry and Representation Theory, among others areas. For algebras A over a field the Hochschild cohomology group HH^i(A,M) of A with coeficients in a bimodule M coincides with Ext^i_{A^e}(A,M). So it can be computed using a projective resolution of the algebra, as a bimodule over itself. Therefore different authors like Dieter Happel, Claude Cibils, Edward Green, David Anick, Michael Bardzell, Sergio Chohuy and Andrea Solotar developed tools for the construction of these resolutions in particular cases. A recent and very important result was introduced by Andrea Solotar and Sergio Chohuy, where they show a construction of a projective bimodule resolution for associative algebras generalizing the result for monomial algebras made by Bardzell. In this dissertation we intend to introduce the reader in the cohomology Hochschild concept, showing its importance through known results for finite dimensional algebras. Besides, we exhibit the concepts and results of Chohuy and Solotar mentioned before. During this text, we complement some demonstrations with the purpose of giving a tool for the a better understanding.
3

Aplicações da teoria de Bases de Gröbner para o cálculo da Cohomologia de Hochschild / Aplications of the Groebner Basis theory to the computation of the Hochschild Cohomology

Ana Melisa Paiba Amaya 24 October 2018 (has links)
A Cohomologia de Hochschild é um invariante associado a álgebras o qual pode nos fornecer propiedades homologicas das álgebras e suas categorias de módulos. Além disso tem aplicações em Geometria Algébrica e Teoria de Representações, entre outras áreas. Para álgebras A sobre um corpo, o i-ésimo grupo de cohomologia de Hochschild HH^i(A,M) de A, com coeficientes no bimódulo M, coincide com Ext^i_{A^e}(A,M). Logo, este pode ser calculado usando uma resolução projetiva da álgebra como A-bimódulo. Diferentes autores como Dieter Happel, Claude Cibils, Edward Green, David Anick, Michael Bardzell e Andrea Solotar desenvolveram ferramentas para a construção destas resoluções em casos específicos. Um resultado recente e muito importante é apresentado por Andrea Solotar e Sergio Chohuy, onde se mostra a construção de uma resolução projetiva de bimódulos para álgebras associativas generalizando o resultado para álgebras monomiais feito por Bardzell. Nesta dissertação pretendemos introduzir ao leitor no conceito de Cohomologia de Hochschild mostrando a importância da mesma mediante resultados conhecidos para álgebras de dimensão finita. Além disso, apresentamos os conceitos e resultados do trabalho de Chohuy e Solotar mencionado acima. No decorrer deste trabalho complementamos algumas demonstrações dos resultados enunciados com o fim de propiciar uma ferramenta para o melhor entendimento dos tópicos trabalhados aqui. / The Hochschild Cohomology is an invariant attached to associative algebras which may provide us some homological aspects of the algebras and its category of modules. Moreover, it has applications to Algebraic Geometry and Representation Theory, among others areas. For algebras A over a field the Hochschild cohomology group HH^i(A,M) of A with coeficients in a bimodule M coincides with Ext^i_{A^e}(A,M). So it can be computed using a projective resolution of the algebra, as a bimodule over itself. Therefore different authors like Dieter Happel, Claude Cibils, Edward Green, David Anick, Michael Bardzell, Sergio Chohuy and Andrea Solotar developed tools for the construction of these resolutions in particular cases. A recent and very important result was introduced by Andrea Solotar and Sergio Chohuy, where they show a construction of a projective bimodule resolution for associative algebras generalizing the result for monomial algebras made by Bardzell. In this dissertation we intend to introduce the reader in the cohomology Hochschild concept, showing its importance through known results for finite dimensional algebras. Besides, we exhibit the concepts and results of Chohuy and Solotar mentioned before. During this text, we complement some demonstrations with the purpose of giving a tool for the a better understanding.
4

Le ultime espressioni del Musteriano nell’Italia del Sud-Est. Variabilità tecnologiche e comportamenti tecno-economici in un contesto peninsulare : I casi di Grotta del Cavallo e Grotta Mario Bernardini. Nardo (Lecce) / Les dernières manifestations moustériennes dans le Sud-Ouest de l’Italie. Variabilité technologique et comportements techno-économiques en contexte péninsulaire : Etudes des cas de Grotta del Cavallo et Grotta Mario Bernardini. Nardo (Lecce)

Carmignani, Leonardo 15 June 2011 (has links)
Nos recherches se sont orientées vers l'étude des niveaux correspondant aux dernières phases du Moustérien de deux sites en grotte, Grotta del Cavallo et Grotta Mario Bernadini, situées sur le versant ionique des Pouilles dans la province de Lecce . Les deux sites en question ont fait l'objet de nombreuses études à partir des années 1960 (Palma Di Cesnola, 1963 ; Borzatti, 1970). Le choix de se concentrer spécifiquement sur les phases finales de cette période a été d'abord motivée par la nécessité de combler un vide de connaissance dans l'aire prise en compte concernant les aspects technologiques. L'objectif premier a été par conséquence de reconstituer les éléments liés à la production afin d'en comprendre la spécificité technologique et, dans une certaine mesure, les comportements techno-économiques. Ensuite, le choix des collections s'inscrit dans la volonté d'établir le point de départ pour évaluer à travers une confrontation entre les séries, les rapports phylogénétiques entre les dernières phases du Moustérien et les industries uluzziennes qui dans les deux sites succèdent à la séquence moustérienne. Enfin, le choix des deux sites repose sur une raison d'ordre géographique. Si les Pouilles constituent déjà un contexte particulier lié à l'isolement de l'extrême sud-est de l'Italie, la région de Salento qui est située dans sa partie méridionale se présente comme une insularité dans l'insularité. Cette position géographique singulière pourrait avoir revêtu un rôle d'isolement potentiel par rapport aux autres régions limitrophes et avoir comme conséquence laconstitution de phénomène locaux qui se sont traduit dans l'expression de caractères culturels, au sens plus large du terme, originaux. / The puzzles arising from the fragmentation of the Mousterian expressions in their late phases, as emerged fromthe archaeological evidence, have always been of interest for prehistoric research, as far as they are concerned with both cultural and biological aspects of human evolution. The cultural complexity that can be observed between 40.000 and 28.000 years ago in Europe depends onthe variety of Neanderthal economic and symbolic attitudes, in relation to both the advent of new technical expressions (Castelperronian, Uluzzian and sensu lato, transitional complexes) and to the persistente of productions that are still rooted in to the traditional variability of theMousterian groups. At the same time the appearing of techno-complexes attributed to the Upper Palaeolithic has been related by some authors to the emergence of particolar cognitive abilities, ascribed to the arrival of the anatomically modern humans (AMH) in Europe. In the last years the recognition of blades and bladelets productions in Mousterian context in France, Italy and in the Near East has mitigated this hypothetical relationship between these productionsand the spread of the AMH. This paper reports the results of the study of Mousterian lithic industries of Grotta del Cavallo and Grotta Mario Bernardini (Nardò, Lecce). The technological study shows the development of an autonomous schèma opératoire (along with other types of productions) oriented in the direction of blades and bladelets production bymeans of a volumetric exploitation. The recognition of this type of production - not recorded until now in the Salentin area - gives us the possibility to review the production systems that we can attribute at the Mousterian terminal phases of the southern Italy.
5

Prilog proučavanju mogućnosti racionalizacije tehnološkog postupka mlevenja pšenice primenom osmovaljne stolice / Study on the possibilities of the rationalization of wheat flour milling processusing the eight-roller mill

Fišteš Aleksandar 07 September 2009 (has links)
<p>U radu je proučavana mogućnost racionalizacije tehnolo&scaron;kog postupka<br />mlevenja p&scaron;enice primenom osmovaljne stolice u fazi mlevenja griza i<br />osevaka. Na svim ispitivanim prolazi&scaron;tima mlevenja griza i osevaka, pri istom<br />razmaku između valjaka i istoj veličini otvora sejnog tkiva za odsejavanje<br />bra&scaron;na, ukupan prinos bra&scaron;na u postupku sa osmovaljnom stolicom manji je<br />nego u klasičnom postupku. Pomenuta razlika varira u zavisnosti od uzorka i<br />prolazi&scaron;ta mlevenja, ali je uvek statistički značajna. Nižim vođenjem valjaka u<br />postupku sa osmovaljnom stolicom, u poređenju sa razmacima između valjaka<br />u klasičnom postupku, u zavisnosti od uzorka i prolazi&scaron;ta mlevenja se<br />smanjuje razlika, dostiže ili prevazilazi prinos bra&scaron;na u odnosu na klasični<br />postupak. Povećanjem veličine otvora sejnog tkiva za odsejavanje bra&scaron;na<br />značajno se povećava prinos bra&scaron;na u postupku sa osmovaljnom stolicom, pri<br />čemu se pri odabiru sejnog tkiva u obzir mora uzeti i veličina svetlog otvora.<br />Odabirom odgovarajuće veličine otvora sejnog tkiva može se i prevazići<br />prinos bra&scaron;na u klasičnom postupku. Niže vođenje valjaka i/ili povećanje<br />veličine otvora sejnog tkiva za odsejavanje bra&scaron;na, pri primeni osmovaljne<br />stolice, nema za posledicu pogor&scaron;anje kvaliteta bra&scaron;na (po pitanju sadržaja<br />pepela) u odnosu na klasični postupak. Specifični utro&scaron;ak energije za<br />usitnjavanje po jedinici mase bra&scaron;na, pri istom vođenju valjaka i istoj veličini<br />otvora sejnog tkiva za odsejavanje bra&scaron;na, veći je u postupku sa osmovaljnom<br />stolicom nego u klasičnom postupku. Povećanjem izvoda bra&scaron;na u postupku sa<br />osmovaljnom stolicom, značajno se smanjuje specifični utro&scaron;ak energije za<br />usitnjavanje. Mogućnost ostvarenja bliskih efekata usitnjavanja u fazi<br />mlevenja griza i osevaka, u klasičnom i postupku sa osmovaljnom stolicom,<br />ukazuje da je za dalju racionalizaciju savremenog tehnolo&scaron;kog postupka<br />mlevenja p&scaron;enice neophodno uključivanje osmovaljne stolice.</p> / <p>Rationalization of the wheat flour milling process using the eight-roller mill in<br />the reduction system has been investigated. At the same roll gaps and same<br />sieving conditions, a lower flour yield has been obtained using an eight-roller<br />mill compared to a conventional one. The difference is statistically significant<br />regardless the passage. By decreasing the roll gap in the process with the<br />eight-roller mill, compared to the roll gap in the conventional process, it is<br />possible to decrease the difference, obtain a similar or even exceed the flour<br />release in the conventional system. Increasing the size of the screen aperture<br />for sifting flour, while percent open area of the screen also needs to be<br />observed, results in significant increase of flour yield (in some cases<br />exceeding the flour yield in the conventional system). Adjustments of the roll<br />gap and sieving conditions in the process with the eight-roller mill are not<br />followed by deterioration of flour quality. At the same roll gaps and same<br />sieving conditions, energy requirements for grinding are higher in the process<br />with the eight-roller mill compared to a conventional system. With the<br />increase of the flour release in process using the eight-roller mill, these energy<br />requirements can be significantly reduced. The possibility of achieving similar<br />milling results to those obtained in the conventional system, while the<br />investment costs and overall energy requirements are significantly lower,<br />justifies the use of the eight-roller mill in the reduction system of the wheat<br />flour milling process.</p>
6

Control-oriented modelling and diagnostics of diesel after-treatment catalysts

Mora Pérez, Javier 21 January 2019 (has links)
[ES] Esta tesis doctoral abarca el desarrollo de algoritmos orientados a mejorar el sistema de control de emisiones en motores Diesel. Para este propósito, la inclusión en el vehículo de sensores embarcados como los de temperatura, los de NOx o el de NH3 permite realizar diagnóstico a bordo de los sistemas de post-tratamiento foco de este trabajo, los cuales son el DOC y el SCR. Así pues, el objetivo es el de satisfacer las normativas de diagnóstico a bordo para mantener las emisiones por debajo del umbral permitido por la normativa a lo largo del tiempo. Los tests experimentales, incluyendo las medidas con analizador de gases, permiten tener una visión más amplia de las especies en la línea de escape. Complementariamente, se utilizan unidades nuevas y envejecidas para tener el efecto experimental del envejecimiento en los catalizadores. De esta manera, se analiza el efecto de la temperatura, el gasto de escape, las concentraciones de las especies y el envejecimiento en el DOC y en el SCR, así como la evaluación de algunas de las medidas relevantes realizadas por los sensores. Las temperaturas tienen una influencia destacada en el funcionamiento de los catalizadores, por lo que se requiere la evaluación de las medidas de los sensores de temperatura, junto con el desarrollo de modelos de transmisión de calor, para alimentar las funciones a continuación desarrolladas. En este sentido, la medida lenta del sensor aguas arriba del DOC se mejora en condiciones transitorias mediante una técnica de fusión de la información basada en un filtro de Kalman. Luego, se presenta un modelo de transmisión de calor 1D y un modelo agrupado 0D, en los cuales se evalúan las entradas aguas arriba según el uso del modelo. Por otra parte, se presenta una técnica para estimar el incremento de temperatura debido a la oxidación de los pulsos de post-inyección en el DOC. Se proponen modelos para ambos DOC y SCR para estimar el efecto del envejecimiento en las emisiones, en los cuales el factor de envejecimiento es modelado como un parámetro sintonizable que permite variar desde estados nuevos a envejecidos. Por una parte, un modelo agrupado 0D es desarrollado para el DOC con el propósito de estimar el desliz de HC y CO, el cual es validado en un WLTC para después ser usado en simulación. Por otra parte, un modelo 1D y un modelo 0D se desarrollan para el SCR, los cuales se usan a continuación para alimentar la estrategia de diagnóstico y para simulación. Finalmente, las estrategias de diagnóstico se presentan para fallo total o retirada de DOC, así como para la estimación de la eficiencia en DOC y SCR. Por una parte, la primera estrategia se divide en pasiva y activa, en la que se usan post-inyecciones en la activa para excitar el sistema y confirmar el fallo total si es el caso. A continuación, la eficiencia del DOC se estima a través de una técnica indirecta en la que la temperatura de activación se detecta y se relaciona con el incremento de emisiones a través del modelo. Por otra parte, se desarrolla un observador para estimar el estado de envejecimiento del SCR, el cual está basado en un filtro de Kalman extendido. Sin embargo, para evitar asociar baja eficiencia del catalizador debido a pobre calidad de la urea inyectada, a envejecimiento del SCR, un indicador de la calidad de la urea se ejecuta en paralelo. / [CAT] Esta tesi doctoral abasta el desenvolupament d'algoritmes orientats a millor el sistema de control d'emissions en motors Diesel. Per a este propòsit, la inclusió en el vehicle de sensor embarcats com els de temperatura, els de NOx o el d'NH3 permet realitzar el diagnòstic a bord dels sistemes de post-tractament focus d'este treball, els quals són el DOC i el SCR. Així doncs, l'objectiu és el de satisfer les normatives de diagnòstic a bord per a mantindre les emissions per baix de l'umbral permés per la normativa al llarg del temps. Els tests experimentals, incloent les mesures amb analitzador de gasos, permeten obtindre una visió més àmplia de les espècies en la línia d'escapament. Complementàriament, s'utilitzen unitats noves i envellides per tal de tindre l'efecte experimental de l'envelliment en els catalitzadors. D'aquesta manera, s'analitza l'efecte de la temperatura, la despesa d'escapament, les concentracions de les espècies i l'envelliment en el DOC i en el SCR, així com l'avaluació d'algunes mesures rellevants realitzades pels sensors. Les temperatures tenen una influència destacada en el funcionament dels catalitzadors, pel que es requerix l'avaluació de les mesures dels sensors de temperatura, junt amb el desenvolupament de models de transmissió de calor, per a alimentar les funcions a continuació desenvolupades. En este sentit, la mesura lenta del sensor a l'entrada del DOC es millora en condicions transitòries mitjançant una tècnica de fusió de la informació basada en un filtre de Kalman. Després, es presenta un model de transmissió de calor 1D i un model agrupat 0D, en els quals s'avaluen les entrades a l'entrada segons l'ús del model. Per altra banda, es presenta una tècnica per a estimar l'increment de temperatura degut a l'oxidació dels polsos de post-injecció en el DOC. Es proposen models per a DOC i SCR per a estimar l'efecte de l'envelliment en les emissions, en els quals es modela el factor d'envelliment com un paràmetre sintonitzable, que permet variar des d'estats nous a envellits. Per altra banda, un model agrupat 0D _es desenvolupat per al DOC amb el propòsit d'estimar la relliscada de HC i CO, el qual és validat en un WLTC per a després ser usat en simulació. Per altra banda, un model 1D i un model 0D es desenvolupen per al SCR, els quals s'usen a continuació per a alimentar l'estratègia de diagnòstic i per a simulació. Finalment, les estratègies de diagnòstic es presenten per a la fallada total o retirada del DOC, així com per a l'estimació de l'eficiència en DOC i SCR. Per altra banda, la primera estratègia es divideix en passiva i activa, en la que s'utilitzen post-injeccions en la activa per a excitar el sistema i confirmar la fallada total si es dona el cas. A continuació, l'eficiència del DOC s'estima a través d'una tècnica indirecta en la que la temperatura d'activació es detecta i es relaciona amb l'increment d'emissions a través del model. Per altra banda, es desenvolupa un observador per a estimar l'estat d'envelliment del SCR, el qual està basat en un filtre de Kalman extés. No obstant això, per a evitar associar baixa eficiència degut a pobre qualitat de l'urea injectada a l'envelliment del SCR, un indicador de la qualitat de l'urea s'executa en paral·lel. / [EN] This dissertation covers the development of algorithms oriented to improve the emission control system of Diesel engines. For this purpose, the inclusion of on-board sensors like temperature, NOx and NH3 sensors allows performing on-board diagnostics to the after-treatment systems focus of this work, which are the DOC and the SCR system. Then, the target is to meet on-board diagnostics regulations in order to keep emissions below a regulation threshold over time. Experimental tests, including gas analyzer measurements, allow having a wider view of the species in the exhaust line. Complementary, new and aged units are used in order to have the experimental effect of ageing on the catalysts. Then, the effect of temperature, exhaust mass flow, species concentrations and ageing is analyzed for DOC and SCR, in combination with the assessment of some relevant sensors measurements. As a result, the characteristics, opportunities and limitations extracted from experimental data are used as the basis for the development of models and diagnostics techniques. The assessment of temperature sensors measurements, along with the development of heat transfer models is required to feed temperature dependent functions. In this sense, the slow measurement of the DOC upstream temperature sensor is improved in transient conditions by means of a data fusion technique, based on a fast model and a Kalman filter. Then, a 1D and a 0D lumped heat transfer models are presented, in which the upstream inputs are assessed in relation to its use. On the other hand, a technique to estimate the temperature increase due to post-injection pulses oxidation is also presented. Both DOC and SCR models are proposed in order to estimate the effect of ageing on emissions, in which an ageing factor is modelled as a tunable parameter that allows varying from new to aged states. On the one hand, a 0D lumped model is developed for DOC in order to estimate the HC and CO species slip, which is validated in a WLTC and is then used for simulation. On the other hand, a 1D and a 0D models are developed for SCR, which are then used to feed the diagnostics strategy and for simulation. Finally, diagnostics strategies are presented for total failure or removal of DOC, as well as for efficiency estimation of DOC and SCR. On the one hand, the former strategy is separated into passive and active diagnostics, in which post-injections are used in active diagnostics in order to excite the system and confirm a total failure, in case. Then, the DOC efficiency estimation is done by means of an indirect technique in which the light-off temperature is detected and an emissions increase is related by means of the DOC ageing model. On the other hand, an observer to estimate the SCR ageing state is developed, which is based on an extended Kalman filter. However, in order to avoid associating low SCR efficiency to ageing, an indicator of the injected urea quality is developed to run in parallel. / Mora Pérez, J. (2018). Control-oriented modelling and diagnostics of diesel after-treatment catalysts [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/115937 / TESIS
7

Towards Next Generation Sequential and Parallel SAT Solvers / Hin zur nächsten Generation Sequentieller und Paralleler SAT-Solver

Manthey, Norbert 08 January 2015 (has links) (PDF)
This thesis focuses on improving the SAT solving technology. The improvements focus on two major subjects: sequential SAT solving and parallel SAT solving. To better understand sequential SAT algorithms, the abstract reduction system Generic CDCL is introduced. With Generic CDCL, the soundness of solving techniques can be modeled. Next, the conflict driven clause learning algorithm is extended with the three techniques local look-ahead, local probing and all UIP learning that allow more global reasoning during search. These techniques improve the performance of the sequential SAT solver Riss. Then, the formula simplification techniques bounded variable addition, covered literal elimination and an advanced cardinality constraint extraction are introduced. By using these techniques, the reasoning of the overall SAT solving tool chain becomes stronger than plain resolution. When using these three techniques in the formula simplification tool Coprocessor before using Riss to solve a formula, the performance can be improved further. Due to the increasing number of cores in CPUs, the scalable parallel SAT solving approach iterative partitioning has been implemented in Pcasso for the multi-core architecture. Related work on parallel SAT solving has been studied to extract main ideas that can improve Pcasso. Besides parallel formula simplification with bounded variable elimination, the major extension is the extended clause sharing level based clause tagging, which builds the basis for conflict driven node killing. The latter allows to better identify unsatisfiable search space partitions. Another improvement is to combine scattering and look-ahead as a superior search space partitioning function. In combination with Coprocessor, the introduced extensions increase the performance of the parallel solver Pcasso. The implemented system turns out to be scalable for the multi-core architecture. Hence iterative partitioning is interesting for future parallel SAT solvers. The implemented solvers participated in international SAT competitions. In 2013 and 2014 Pcasso showed a good performance. Riss in combination with Copro- cessor won several first, second and third prices, including two Kurt-Gödel-Medals. Hence, the introduced algorithms improved modern SAT solving technology.
8

Reduktionssysteme zur Berechnung einer Auflösung der orthogonalen freien Quantengruppen A<sub>o</sub>(n) / Reduction systems for computing a resolution of the free orthogonal quantum groups A<sub>o</sub>(n)

Härtel, Johannes 04 July 2008 (has links)
No description available.
9

Towards Next Generation Sequential and Parallel SAT Solvers

Manthey, Norbert 01 December 2014 (has links)
This thesis focuses on improving the SAT solving technology. The improvements focus on two major subjects: sequential SAT solving and parallel SAT solving. To better understand sequential SAT algorithms, the abstract reduction system Generic CDCL is introduced. With Generic CDCL, the soundness of solving techniques can be modeled. Next, the conflict driven clause learning algorithm is extended with the three techniques local look-ahead, local probing and all UIP learning that allow more global reasoning during search. These techniques improve the performance of the sequential SAT solver Riss. Then, the formula simplification techniques bounded variable addition, covered literal elimination and an advanced cardinality constraint extraction are introduced. By using these techniques, the reasoning of the overall SAT solving tool chain becomes stronger than plain resolution. When using these three techniques in the formula simplification tool Coprocessor before using Riss to solve a formula, the performance can be improved further. Due to the increasing number of cores in CPUs, the scalable parallel SAT solving approach iterative partitioning has been implemented in Pcasso for the multi-core architecture. Related work on parallel SAT solving has been studied to extract main ideas that can improve Pcasso. Besides parallel formula simplification with bounded variable elimination, the major extension is the extended clause sharing level based clause tagging, which builds the basis for conflict driven node killing. The latter allows to better identify unsatisfiable search space partitions. Another improvement is to combine scattering and look-ahead as a superior search space partitioning function. In combination with Coprocessor, the introduced extensions increase the performance of the parallel solver Pcasso. The implemented system turns out to be scalable for the multi-core architecture. Hence iterative partitioning is interesting for future parallel SAT solvers. The implemented solvers participated in international SAT competitions. In 2013 and 2014 Pcasso showed a good performance. Riss in combination with Copro- cessor won several first, second and third prices, including two Kurt-Gödel-Medals. Hence, the introduced algorithms improved modern SAT solving technology.

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