Les bases de données présentent des problèmes de passage à l’échelle. Ceci est principalement dû à la compétition pour les ressources et au coût du contrôle de la concurrence. Une alternative consiste à centraliser les écritures afin d’éviter les conflits. Cependant, cette solution ne présente des performances satisfaisantes que pour les applications effectuant majoritairement des lectures. Une autre solution est d’affaiblir les propriétés transactionnelles mais cela complexifie le travail des développeurs d’applications. Notre solution, Gargamel, répartie les transactions effectuant des écritures sur différentes répliques de la base de données tout en gardant de fortes propriétés transactionnelles. Toutes les répliques de la base de donnée s’exécutent séquentiellement, à plein débit; la synchronisation entre les répliques reste minime. Les évaluations effectuées avec notre prototype montrent que Gargamel permet d’améliorer le temps de réponse et la charge d’un ordre de grandeur quand la compétition est forte (systèmes très chargés avec ressources limitées) et que dans les autres cas le ralentissement est négligeable. / Databases often scale poorly in distributed configurations, due to the cost of concurrency control and to resource contention. The alternative of centralizing writes works well only for read-intensive workloads, whereas weakening transactional properties is problematic for application developers. Our solution spreads non-conflicting update transactions to different replicas, but still provides strong transactional guarantees. In effect, Gargamel partitions the database dynamically according to the update workload. Each database replica runs sequentially, at full bandwidth; mutual synchronisation between replicas remains minimal. Our prototype show that Gargamel improves both response time and load by an order of magnitude when contention is high (highly loaded system with bounded resources), and that otherwise slow-down is negligible.

[pt] Na área de dados interligados, usuários frequentemente utilizam ferramentas de descoberta de links para materializar links sameAs entre diferentes base de dados. No entanto, pode ser difícil especificar as regras de ligação nas ferramentas, se as bases de dados tiverem modelos complexos. Uma possível solução para esse problema seria estimular os administradores das base de dados a publicarem visões simples, que funcionem como catálogos de recursos. Uma vez que os links estão materializados, um segundo problema que surge é como manter esses links atualizados quando as bases de dados são atualizadas. Para ajudar a resolver o segundo problema, este trabalho apresenta um framework para a manutenção de visões e links materializados, utilizando uma estratégia incremental. A ideia principal da estratégia é recomputar apenas os links dos recursos que foram atualizadas e que fazem parte da visão. Esse trabalho também apresenta um experimento para comparar a performance da estratégia incremental com a recomputação total das visões e dos links materializados. / [en] In the Linked Data field, data publishers frequently materialize sameAs links between two different datasets using link discovery tools. However, it may be difficult to specify linking conditions, if the datasets have complex models. A possible solution lies in stimulating dataset administrators to publish simple predefined views to work as resource catalogues. A second problem is related to maintaining materialized sameAs linksets, when the source datasets are updated. To help solve this second problem, this work presents a framework for maintaining views and linksets using an incremental strategy. The key idea is to re-compute only the set of updated resources that are part of the view. This work also describes an experiment to compare the performance of the incremental strategy with the full re-computation of views and linksets.

This study investigates the possibilities of using mesh networking in underground mines. It is of utmost importance to investigate the safety and ethical aspects of implementing new systems in mines, namely mesh networking. Simulations and calculations have been made to analyze and arrive at findings of update intervals for a potential mesh network. Semi-structured interviews have been conducted with responsible staff at underground mine sites, and this study has followed a qualitative approach. Theoretical concepts such as Locatilization infrastructures in underground mines and Personal security and work environment laws in underground mines have been analyzed and discussed in relation to empirical results using thematic analysis. Due to the importance of safety aspects of emergency notifications and real time location tracking, our findings show that mesh networks may not be a viable replacement for a fully connected network in a mine network infrastructure. However, mesh networks or hybrid networks may be a more viable way to improve safety for certain mines that do not have an existing network infrastructure, or as a temporary extension to a fully connected network infrastructure.

The Internet of Things (IoT) is a concept where sensors combined with microcontrollers enhance our everyday life. In the year 2050, there will be around 30 billion connected IoT systems, for developing this large amount of systems and maintaining them there will be a need to use over-the-air updates (OTA). With the increasing growth of IoT systems, there will also rise more OTA update solutions as tools for maintaining and enhancing IoT systems. In this bachelor's degree project, evaluations and comparisons of different OTA update techniques supporting microcontrollers of the type ESP32 are done by using controlled experiments. This study focuses on testing the update procedure with experiments that test OTA update deployment time and update rollback functionality.

This paper investigates alternative scheduling for game objects in a game engine by using priority based algorithms and comparing different priority assigning methods. Research concerning commercial game engines, game loops, concurrency and scheduling was performed. Three different scheduling algorithms were created and tested using a varying amount of game objects between two different testing scenarios. The results showed that using priority based scheduling gave a slight increase in average frames  per second (FPS) as well as boosting logical update performance of prioritized objects, however overall performance was decreased. The reason this decrease in performance occurred could have been due to the way the scheduler was implemented, and despite the decrease in performance using a priority based scheduling system was considered feasible within certain game engines. / Denna uppsats undersöker alternativa sätt för schemaläggning av spelobjekt i en spelmotor genom att använda prioriteringsbaserade algoritmer och jämföra olika tilldelningssätt för prioritetsmetoder. Forskning gällande kommersiella spelmotorer, ''game loops'', parallellisering och schemaläggning utfördes. Tre olika schemaläggningsalgoritmer skapades och testades med ett varierande antal spelobjekt i två olika testscenarion. Resultaten visade att användning av prioritetsbaserad schemaläggning gav en lätt ökning av det genomsnittliga antalet bilder per sekund (FPS) och gav bättre logikuppdateringsprestanda för prioriterade objekt. Den totala prestandan minskade dock. Anledningen till att denna minskning i prestanda skedde kan bero på hur schemaläggaren implementerades, men trots denna prestandaminskning ansågs schemaläggningssystemet vara möjlig inom vissa spelmotorer.

As the automotive industry becomes increasingly reliant on digital systems it is of utmost importance that these systems are secure. Secure systems are of interest both for the general public as well as manufactures. This Master’s thesis evaluates potential cybersecurity solutions for a proposed damper system prototype developed by Öhlins Racing AB. A systematic literature study was performed to identify known vulnerabilities of similar systems as well as potential cybersecurity solutions. A threat model was constructed using vehicleLang, the Meta Attack Language, and securiCAD. The model was created utilizing preexisting assets from vehicleLang and a newly implemented Bluetooth asset. The result from the systematic literature study was used to validate preexisting attack steps and also to create the Bluetooth asset. To validate the model, experts in the field of automotive security and/or threat modeling were asked to assess the model. Using Cochran’s Equation, a target of eight expert evaluations were decided. Unfortunately, only seven evaluations were obtained, equivalent to an increase in the error margin from 25% to 26.6%. However, of the seven expert evaluations obtained none indicated the existence of critical flaws within the model. The model was therefore considered a good reflection of the damper system and its security aspects. Critical defenses included the utilization of cryptography, mutual authentication, and on-the-fly decryption. These defenses were shown to prevent unauthorized modifications of firmware and protect Öhlins intellectual property in form of source code. While it was not possible to defend against all attacks the identified defenses would increase the safety and security of the system, benefiting not only Öhlins but also overall road users. / Allt eftersom fordonsindustrins beroende av digitala system ökar är det av yttersta vikt att dessa system är säkra. Säkra system är av intresse för både allmänheten likväl som för systemtillverkarna. Denna masteruppsats evaluerar potentiella cybersäkerhetslösningar för en föreslagen stötdämparprototyp utvecklad av Öhlins Racing AB. En systematisk litteraturöversikt skapades med syfte att identifiera kända sårbarheter av liknande system och potentiella cybersäkerhetslösningar. En hotmodell skapades med hjälp av vehicleLang, the Meta Attack Language, och securiCAD. Hotmodellen skapades med existerande komponenter från vehicleLang och en nyskapad Bluetooth komponent. Resultaten från den systematiska litteraturöversikten användes för att validera existerande komponenter från vehicleLang och för implementationen av Bluetooth komponenten. För att evaluera modellen bads experter inom fordonssäkerhet och/eller hotmodellering utvärdera modellen. Genom Cochran’s ekvation beslutades att åtta expert utvärderingar skull införskaffas. Tyvärr erhölls enbart sju utvärderingar, vilket motsvarar en ökning av felmarginalen från 25% till 25.6%. Av de sju experter som utvärderade modellen identifierades dock inga kritiska brister. Kritiska säkerhetslösningar inkluderade användandet av: kryptografi, ömsesidig autentisering, och on-the-fly decryption. Dessa försvar anses kunna skydda mot obehörig modifiering av programvara, samt skydda Öhlins intellektuella egendom i form av källkod. Trots att det inte var möjligt att förhindra alla attacker skulle de identifierade försvaren öka systemets säkerhet, vilket är fördelaktigt inte bara för Öhlins utan även trafikanter i allmänhet.

No description available.

[pt] A otimização online de portfólios é um problema de engenharia financeira que consiste na escolha sequencial de alocação de capital entre um conjunto de ativos, com o objetivo de maximizar o retorno acumulado no longo prazo. Com o avanço dos estudos de modelos de machine learning, diversos algorítmos estão sendo utilizados para resolver esse problema. Uma série de algoritmos seguem a metodologia Follow-the-winner (FTW) , onde o peso de ações com boa performance é aumentado baseado na hipótese de que a tendência de alta será mantida; outros seguem a metodologia inversa Follow-the-loser (FTL), em que ações com má performance tem seu peso aumentado apostando em uma reversão dos preços. Algoritmos estado-da-arte do tipo FTW possuem garantia teórica de se aproximar da performance da melhor ação escolhida de antemão, entretanto, algoritmos do tipo FTL tem performance superior observada empiricamente. Nosso trabalho busca explorar a ideia de aprender quando utilizar cada uma das duas categorias. Os mecanismos utilizados são algoritmos de online learning com flexibilidade para assumir ambos comportamentos. Foi realizado um estudo da literatura sobre indicadores de memória em séries financeiras e sua possível utilização de forma explícita para escolha entre FTL e FTW. Posteriormente, propomos um método de se realizar o aprendizado entre essas duas categorias de forma online e de forma dinâmica para utilização em algoritmos de online learning. Em nossos experimentos, o método proposto supera o benchmark estabelecido UCRP com excesso de retorno de 36.76 por cento. / [en] Online portfolio selection is a financial engineering problem which aims to sequentially allocate capital among a set of assets in order to maximize long-term return. With the recent advances in the field of machine learning, several models have been proposed to address this problem. Some algorithms approach the problem with a Follow-the-winner (FTW) methodology, which increases the weights of more successful stocks based on their historical performance. Contrarily, a second approach, Follow-theloser (FTW), increases the weights of less successful stocks, betting on the reversal of their prices. Some state-of-the-art FTW type algorithms have the guarantee to asymptotically approach the same performance as the best stock chosen in hindsight, while FTL algorithms have empirical evidence of overperforming the previous. Our goal is to explore the idea of learning when to use each of those two algorithm categories. We do this by using online learning algorithms that are capable of switching between the described regimes. We review the literature for existing measures of time series memory and predictability, and explicitly use this information for chosing between FTW and FTL. Later, we propose a method for choosing between this two types of algorithms in an online and dynamic manner for usage together with online learning algorithms. The method outperforms the chosen benchmark UCRP in our experiments with 36.76 percent excess returns.

El tema principal de esta tesis es el desarrollo de técnicas de actualización de precondicionadores para resolver sistemas lineales de gran tamaño y dispersos Ax=b mediante el uso de métodos iterativos de Krylov. Se consideran dos tipos interesantes de problemas. En el primero se estudia la solución iterativa de sistemas lineales no singulares y antisimétricos, donde la matriz de coeficientes A tiene parte antisimétrica de rango bajo o puede aproximarse bien con una matriz antisimétrica de rango bajo. Sistemas como este surgen de la discretización de PDEs con ciertas condiciones de frontera de Neumann, la discretización de ecuaciones integrales y métodos de puntos interiores, por ejemplo, el problema de Bratu y la ecuación integral de Love. El segundo tipo de sistemas lineales considerados son problemas de mínimos cuadrados (LS) que se resuelven considerando la solución del sistema equivalente de ecuaciones normales. Concretamente, consideramos la solución de problemas LS modificados y de rango incompleto. Por problema LS modificado se entiende que el conjunto de ecuaciones lineales se actualiza con alguna información nueva, se agrega una nueva variable o, por el contrario, se elimina alguna información o variable del conjunto. En los problemas LS de rango deficiente, la matriz de coeficientes no tiene rango completo, lo que dificulta el cálculo de una factorización incompleta de las ecuaciones normales. Los problemas LS surgen en muchas aplicaciones a gran escala de la ciencia y la ingeniería como, por ejemplo, redes neuronales, programación lineal, sismología de exploración o procesamiento de imágenes. Los precondicionadores directos para métodos iterativos usados habitualmente son las factorizaciones incompletas LU, o de Cholesky cuando la matriz es simétrica definida positiva. La principal contribución de esta tesis es el desarrollo de técnicas de actualización de precondicionadores. Básicamente, el método consiste en el cálculo de una descomposición incompleta para un sistema lineal aumentado equivalente, que se utiliza como precondicionador para el problema original. El estudio teórico y los resultados numéricos presentados en esta tesis muestran el rendimiento de la técnica de precondicionamiento propuesta y su competitividad en comparación con otros métodos disponibles en la literatura para calcular precondicionadores para los problemas estudiados. / The main topic of this thesis is updating preconditioners for solving large sparse linear systems Ax=b by using Krylov iterative methods. Two interesting types of problems are considered. In the first one is studied the iterative solution of non-singular, non-symmetric linear systems where the coefficient matrix A has a skew-symmetric part of low-rank or can be well approximated with a skew-symmetric low-rank matrix. Systems like this arise from the discretization of PDEs with certain Neumann boundary conditions, the discretization of integral equations as well as path following methods, for example, the Bratu problem and the Love's integral equation. The second type of linear systems considered are least squares (LS) problems that are solved by considering the solution of the equivalent normal equations system. More precisely, we consider the solution of modified and rank deficient LS problems. By modified LS problem, it is understood that the set of linear relations is updated with some new information, a new variable is added or, contrarily, some information or variable is removed from the set. Rank deficient LS problems are characterized by a coefficient matrix that has not full rank, which makes difficult the computation of an incomplete factorization of the normal equations. LS problems arise in many large-scale applications of the science and engineering as for instance neural networks, linear programming, exploration seismology or image processing. Usually, incomplete LU or incomplete Cholesky factorization are used as preconditioners for iterative methods. The main contribution of this thesis is the development of a technique for updating preconditioners by bordering. It consists in the computation of an approximate decomposition for an equivalent augmented linear system, that is used as preconditioner for the original problem. The theoretical study and the results of the numerical experiments presented in this thesis show the performance of the preconditioner technique proposed and its competitiveness compared with other methods available in the literature for computing preconditioners for the problems studied. / El tema principal d'esta tesi és actualitzar precondicionadors per a resoldre sistemes lineals grans i buits Ax=b per mitjà de l'ús de mètodes iteratius de Krylov. Es consideren dos tipus interessants de problemes. En el primer s'estudia la solució iterativa de sistemes lineals no singulars i antisimètrics, on la matriu de coeficients A té una part antisimètrica de baix rang, o bé pot aproximar-se amb una matriu antisimètrica de baix rang. Sistemes com este sorgixen de la discretització de PDEs amb certes condicions de frontera de Neumann, la discretització d'equacions integrals i mètodes de punts interiors, per exemple, el problema de Bratu i l'equació integral de Love. El segon tipus de sistemes lineals considerats, són problemes de mínims quadrats (LS) que es resolen considerant la solució del sistema equivalent d'equacions normals. Concretament, considerem la solució de problemes de LS modificats i de rang incomplet. Per problema LS modificat, s'entén que el conjunt d'equacions lineals s'actualitza amb alguna informació nova, s'agrega una nova variable o, al contrari, s'elimina alguna informació o variable del conjunt. En els problemes LS de rang deficient, la matriu de coeficients no té rang complet, la qual cosa dificultata el calcul d'una factorització incompleta de les equacions normals. Els problemes LS sorgixen en moltes aplicacions a gran escala de la ciència i l'enginyeria com, per exemple, xarxes neuronals, programació lineal, sismologia d'exploració o processament d'imatges. Els precondicionadors directes per a mètodes iteratius utilitzats més a sovint són les factoritzacions incompletes tipus ILU, o la factorització incompleta de Cholesky quan la matriu és simètrica definida positiva. La principal contribució d'esta tesi és el desenvolupament de tècniques d'actualització de precondicionadors. Bàsicament, el mètode consistix en el càlcul d'una descomposició incompleta per a un sistema lineal augmentat equivalent, que s'utilitza com a precondicionador pel problema original. L'estudi teòric i els resultats numèrics presentats en esta tesi mostren el rendiment de la tècnica de precondicionament proposta i la seua competitivitat en comparació amb altres mètodes disponibles en la literatura per a calcular precondicionadors per als problemes considerats. / Guerrero Flores, DJ. (2018). On Updating Preconditioners for the Iterative Solution of Linear Systems [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/104923

There is a need for a fuel-optimal required time of arrival (RTA) mode for aircraft flight management systems capable of enabling controlled time of arrival functionality in the presence of wind speed forecast uncertainty. A computationally tractable two-stage stochastic algorithm utilizing a data-driven, location-specific forecast uncertainty model to generate forecast uncertainty scenarios is proposed as a solution. Three years of Aircraft Communications Addressing and Reporting Systems (ACARS) wind speed reports are used in conjunction with corresponding wind speed forecasts from the Rapid Update Cycle (RUC) forecast product to construct an inhomogeneous Markov model quantifying forecast uncertainty characteristics along specific route through the national airspace system. The forecast uncertainty modeling methodology addresses previously unanswered questions regarding the regional uncertainty characteristics of the RUC model, and realizations of the model demonstrate a clear tendency of the RUC product to be positively biased along routes following the normal contours of the jet stream. A two-stage stochastic algorithm is then developed to calculate the fuel optimal stage one cruise speed given a required time of arrival at a destination waypoint and wind forecast uncertainty scenarios generated using the inhomogeneous Markov model. The algorithm utilizes a quadratic approximation of aircraft fuel flow rate as a function of cruising Mach number to quickly search for the fuel-minimum stage one cruise speed while keeping computational footprint small and ensuring RTA adherence. Compared to standard approaches to the problem utilizing large scale linear programming approximations, the algorithm performs significantly better from a computational complexity standpoint, providing solutions in fractional power time while maintaining computational tractability in on-board systems.