The goal of this thesis is the optimization of task distribution in the Fitcrack system. The improvement is reached by way of increasing the accuracy of the estimation of the computational power of worker nodes, and the prevention of the creation of extremely small tasks, as well as increasing the efficiency of the transfer of the tasks to the worker nodes. In this thesis, the current state of the Fitcrack system is described, tested, and evaluated. This thesis then describes the weak points of the current implementation, proposes ways of remediating them and describes, tests and evaluates the implementation of those proposals.

Master’s thesis titled Welding of turbine rotor materials discusses evaluation of welding parameters by numerical simulation in software SYSWELD and Visual - WELD. Base material 23 CrMoNiWV 8-8 is welded by submerged arc welding technology. Used flux is F 26G and electrode is flux-cored wire TOPCORE 838 B. Material structures, hardness, values of residual stresses and distortion of weldment for this process are calculated by using the numerical analysis.

Les superalliages à base de nickel durcis par précipitation γ' et notamment l'Inconel 738 LC (IN738LC), sont des matériaux largement utilisés dans les parties chaudes de turbomoteurs d'avions et d'hélicoptères. Ces matériaux disposent d'excellentes propriétés mécaniques à haute température. Toutefois, des défauts ou des fissures peuvent apparaitre sur ces pièces, lors de leur élaboration par fonderie ou bien pendant leur durée en service, ce qui nécessite leur réparation. Cependant, les pièces constituées en IN738LC sont sujettes à de la fissuration au cours des procédés de réparation de type soudage. Il s'avère que le rechargement laser est une technique de fabrication additive prometteuse permettant de réparer des pièces abimées. Le présent travail consiste en l'étude de la réparabilité par projection de poudre de l'alliage IN738LC réputé non soudable. Cette étude comporte deux volets expérimentaux et numériques du rechargement de pièces en Inconel 738 LC au moyen du procédé CLAD. Pour cela, nous avons réalisé des essais de rechargement suivant plusieurs configurations illustrant les cas de réparations rencontrés industriellement. Deux mécanismes de fissuration distincts sont mis en évidence respectivement dans la zone affectée thermiquement du substrat et dans le dépôt. Une simulation multi-physique est également développée pour rendre compte des phénomènes thermiques, mécaniques et métallurgiques observés lors du rechargement laser. Ces simulations sont comparées à des mesures expérimentales pour validation. Enfin, ces outils de simulation sont utilisés afin de définir des critères numériques de risque de fissuration. En résumé, un préchauffage à haute température permet d'éliminer le risque de liquation et donc de fissures dans la ZAT ainsi que dans les dépôts, ce qui démontre qu'il est possible d'envisager une réparation sur cet alliage réputé non soudable. / Y' hardened nickel-based superalloys, such as Inconel 738 LC (IN738LC), are materials which are extensively used in hot sections parts of helicopter and aircraft engines. Those materials exhibit enhanced mechanical properties at high temperature. Nevertheless, cracking and several defects can occur on these parts during casting or during their service life. However, welding type repairing processes can lead to considerable cracking of IN738LC superalloy. It appears that laser cladding is a promising additive manufacturing technology which allows the repair of damaged parts. The present work main objective is aimed at investigating Inconel 738 LC repair by laser cladding. Both experimental and numerical aspects are studied for the repair of IN738LC by means of the CLAD process. Experimental laser clad deposits are produced under several configurations following industrial cases. Two distinct cracking mechanisms are identified in the heat-affected zone and within the deposit, respectively. A multi-physics simulation of laser cladding is developed in order to take into account thermal, mechanical and metallurgical phenomena. Simulation is compared to experimental measurements for validation. Finally, these numerical tools are used to define cracking risk criteria. In summary, a high preheating of the samples allows to suppress liquation and HAZ cracking, but also to obtain un-cracked deposit, which indicates that the repair of non-weldable alloys is possible.

The objective of this research was to investigate the effects of twisted steel micro rebar (TSMR) fibers on 1) the mechanical properties of concrete used in bridge deck construction and 2) the early cracking behavior of concrete bridge decks. This research involved the evaluation of four newly constructed bridge decks through a series of laboratory and field tests. At each location, one deck was constructed using a conventional concrete mixture without TSMR, and one was constructed using the same conventional concrete mixture with an addition of 40 lb of TSMR per cubic yard of concrete. Regarding laboratory testing, the conventional and TSMR beam specimens exhibited similar average changes in height after 4 months of shrinkage testing. The electrical impedance measurements did not indicate a notable difference between specimens comprising concrete with TSMR and those comprising conventional concrete. Although no notable difference in behavior between conventional and TSMR specimens was apparent before initial cracking, the toughness of the TSMR specimens was substantially greater than that of the conventional concrete specimens. Regarding field testing, sensors installed in the bridge decks indicated that the addition of TSMR does not affect internal concrete temperature, moisture content, or electrical conductivity. The average Schmidt rebound number varied little between the TSMR decks and conventional decks; therefore, the stiffness of the TSMR concrete was very similar to that of conventional concrete. Distress surveys showed that the conventional decks exhibited notably more cracking than the TSMR decks. The TSMR fibers exhibited the ability to limit both crack density and crack width. For all of the decks, chloride concentrations increased every year as a result of the use of deicing salts on the bridge decks during winter. However, the chloride concentrations for samples collected over cracked concrete increased more rapidly than those for samples collected over non-cracked concrete. Although TSMR fibers themselves do not directly affect the rate at which chloride ions penetrated cracked or non-cracked concrete, the fibers do prevent cracking, which, in turn, limits the penetration of chloride ions into the decks. Therefore, the use of TSMR would be expected to decrease the area of a bridge deck affected by cracking and subsequent chloride-induced corrosion damage and thereby increase the service life of the bridge deck.

Previous studies have successfully used near and supercritical water (SCW) for cracking and desulfurization of heavy crude oil and bio-oil, suppressing coke formation as a low-value by-product. Some of these studies benefited from using zeolite catalysts to increase the activity and selectivity toward targeted products; however, in depth studies are required to identify the role of water on zeolite catalysis under supercritical condition. Using three common zeolites, ZSM-5, HY, and β for supercritical water cracking of dodecane at 400°C, 24±2 MPa (in a 100 ml batch reactor), we showed that ZSM-5 is the only catalyst that partially retains its crystalline structure and activity under hydrothermal conditions. Further characterization of the ZSM-5 (used under 50/50 wt% SCW/dodecane feed) revealed 95% decrease in Brønsted acid site (BAS) density and 80% decrease in microporous area after 2 h reaction time. However, compared to the runs where SCW was absent, the apparent dodecane cracking rate constant in SCW decreased only by a factor of 2.6. Examining catalytic activity of ZSM-5 degradation products and re-using ZSM-5 showed that the unexpected activity cannot be ascribed to ZSM-5 degradation products. Using a group-type model, we showed that SCW accelerated gas and suppressed coke formations. Additionally a coke gasification pathway was suggested to account for formation of CO and CO2 in the presence of SCW. Additional experiments with two different ZSM-5 particle sizes suggested that dodecane cracking reaction is diffusion-limited in the absence of SCW and reaction-limited in its presence. Zero length chromatography of calcined and hydrothermally treated ZSM-5 showed 10 times greater apparent diffusivity for un-treated catalyst. This, according to Weisz-Prater analysis, suggested a 250 times greater dodecane surface concentration in the absence of SCW. We successfully optimized the water content of feed (5-15 wt%) to decrease the destructive effects of SCW on the structure, increase the selectivity toward BTEX products and eliminate coke formation.

In the field of cybersecurity, it is often not possible to construct systems that are resistant to all attacks. For example, even a well-designed password authentication system will be vulnerable to password cracking attacks because users tend to select low-entropy passwords. In the field of cryptography, we often model attackers as powerful and malicious and say that a system is broken if any such attacker can violate the desired security properties. While this approach is useful in some settings, such a high bar is unachievable in many security applications e.g., password authentication. However, even when the system is imperfectly secure, it may be possible to deter a rational attacker who seeks to maximize their utility. In particular, if a rational adversary finds that the cost of running an attack is higher than their expected rewards, they will not run that particular attack. In this dissertation we argue in support of the following statement: Modeling adversaries as rational actors can be used to better model the security of imperfect systems and develop stronger defenses. We present several results in support of this thesis. First, we develop models for the behavior of rational adversaries in the context of password cracking and quantum key-recovery attacks. These models allow us to quantify the damage caused by password breaches, quantify the damage caused by (widespread) password length leakage, and identify imperfectly secure settings where a rational adversary is unlikely to run any attacks i.e. quantum key-recovery attacks. Second, we develop several tools to deter rational attackers by ensuring the utility-optimizing attack is either less severe or nonexistent. Specifically, we develop tools that increase the cost of offline password cracking attacks by strengthening password hashing algorithms, strategically signaling user password strength, and using dedicated Application-Specific Integrated Circuits (ASICs) to store passwords.

No description available.

La presente investigación buscara la dosificación optima de microfibra para controlar la retracción plástica comparando microfibras sintéticas de polipropileno FIBRA ULTRAFINA de la marca CHEMA y microfibra sintética acrílica DRYMIX RC4020 de la marca SUDAMERICANA DE FIBRAS, considerando las dosificaciones que recomiendan los proveedores por cada metro cubico de concreto. Se realizarán ensayos de laboratorio en 17 mezclas para luego medir la retracción plástica en cada una de ellas utilizando los paneles normados por el ASTM C1579-13, midiendo también las demás propiedades que serán comparadas con el desempeño de un concreto convencional. El resultado de esta investigación será el valor de dosificación óptima con la que se logre disminuir la retracción plástica sin afectar otras propiedades del concreto, tales como resistencia a la compresión, tracción, flexión y trabajabilidad. De igual manera se realizará un análisis económico de acuerdo con las dosificaciones realizadas de las fibras anteriormente mencionadas. / The present investigation will search the optimal dosage from microfiber to control the plastic shrinkage comparing the polypropylene synthetic microfiber Fibra Ultrafina by the brand CHEMA and the acrylic synthetic microfiber Drymix RC4020 by the brand SUDAMERICANA DE FIBRAS, considering the dosages per cubic meter that the providers recommend. It will perform laboratory tests in 17 mixes by then measure the plastic shrinkage in each of them using the standardized panels by the ASTM C1579-13, also will measure the other properties that will be compared with the performance from a conventional concrete. The investigation result will be the optimal dosage valor that can reduce the plastic shrinkage without affecting the other concrete properties like the compressive strength, tensile strength, flexural strength and slump. Likewise, it will perform an economic analysis according the fiber dosages aforementioned. / Tesis

Certain varieties of snap bean, Phaseolus vulgaris L. , seeds are very susceptible to cracks that develop naturally across the cotyledons during pre-harvest, storage, or germination. This phenomenon is commonly known as cotyledonal cracking and may cause serious yield reductions on plants developing from affected seeds. Cotyledonal cracking susceptibility of six white and six colored seeded varieties of snap beans were compared. Considerable differences were found in cracking susceptibility, but there was little or no relationship between seed coat color and cracking susceptibility. An experiment was conducted to determine if a metabolic stress of the plant during the time of pod set could be involved in cotyledonal cracking. Blossoms were tagged on individual plants beginning with the day of first blossom, and tagging was continued for 21 days as blossoms emerged . Individual pods were harvested at maturity and maintained under controlled conditions throughout a simulated weathering treatment to follow. Seeds of each pod were classified according to the amount of cotyledonal cracking sustained. It was concluded that if a stress were involved, it apparently affected the seed several days after pod initiation and that an increase in cotyledonal cracking was negatively correlated to an increase in the number of pods set during one day. Simulated weathering tests were made of seeds remaining in the pod and seeds from the same varieties that were shelled. The results indicated that the pod provides about equal cotyledonal cracking protection for all varieties tested. Apparently the pod is not an important cause of cracking resistance in certain varieties of snap beans. Seed coat permeability was measured and compared for the 12 varieties . A technique was employed by which the bean seed coat served as a semipermeable membrane between a distilled water and a sucrose solution. Sucrose dilution was measured refractometrically and the rate of water penetration calculated. There was little relationship between seed coat permeability and cracking susceptibility among the varieties. The rate of imbibition and drying for seeds of six varieties having varying degrees of cracking susceptibility was tested. Imbibition and drying conditions were closely controlled and weight changes were recorded at regular intervals during imbibition and drying. Results indicated that some of the varieties expressing the most rapid moisture changes were also the most resistant to cracking. It was concluded that the rate of change of seed moisture was not the primary factor controlling cotyledonal cracking susceptibility. Rate of imbibition was tested for two susceptible and two resistant varieties. When the pre-imbibition seed moisture was above 10 percent, a ll varieties imbibed water freely. When pre-imbibition moisture was below 10 percent, several seeds of resistant varieties became slowly permeable while nearly all seeds of the susceptible varieties imbibed freely. This suggested the possibility that a hard seed tendency of the resistant varieties may be one source of protection against cotyledonal cracking. Preliminary data suggested that the seed coats of susceptible varieties remain permeable even at moisture levels below 10 percent, while many seed coats of the resistant varieties become rather impermeable at low moisture levels. Microscopic examination of cotyledonal cracks from four different varieties indicated that the splitting occurred across cotyledonal cell walls more rapidly than between cell walls. This suggested that a weakness of the intercellular middle lamella is not responsible for cotyledonal cracking susceptibility. Further microscopic examination and comparison of the cotyledonal cell structure of two susceptible and two resistant varieties failed to show any structural differences between varieties that could account for differences in cotyledonal cracking susceptibility.

L’auto-cicatrisation des fissures des matériaux cimentaires présente un intérêt important pour améliorer leur durabilité (propriétés de transfert par exemple). L’impact du laitier de haut-fourneau sur ce phénomène a été peu étudié bien qu’il ait été observé sur des ouvrages du Génie Civil. Dans cette étude, la cinétique et l’amplitude de l’auto-cicatrisation ont été suivies par des essais non destructifs : la tomographie aux rayons X et la perméabilité à l’air, pour une fissuration créée à 7 jours et à 28 jours. Les résultats montrent que le laitier de haut-fourneau possède un potentiel d’auto-cicatrisation intéressant pouvant dépasser les résultats obtenus pour les formulations de référence sans laitier. Ce bon potentiel dépend des caractéristiques physicochimiques des matériaux brutes et du potentiel d’hydratation de la formulation au cours du temps. De plus pour suivre l’auto-cicatrisation, un nouvel essai a été mis en place afin de fissurer les éprouvettes de mortier par retrait gêné et d’étudier l’auto-cicatrisation d’une fissure naturelle. Cet essai s’est avéré efficace sur la formulation de référence. Une caractérisation des produits de cicatrisation par MEB-EDS témoigne de la formation de nouveaux produits dans les fissures et de l’impact important des conditions de stockage sur le type de produits formés: des C-S-H pour un stockage sous eau et des carbonates de calcium pour un stockage en chambre humide (CO2 + eau). Les résultats de migration aux chlorures de nano-indentation montrent que ces produits de cicatrisation possèdent de bonnes propriétés de durabilité et des propriétés mécaniques à l’échelle microscopique intéressantes (pour le carbonate de calcium). Enfin, une modélisation du phénomène d’auto-cicatrisation est proposée au moyen du code de calcul de géochimie PHREEQC. L’étude a révélé le potentiel intéressant de PHREEQC pour modéliser l’auto-cicatrisation et en faire un outil de prédiction du phénomène. / Self-healing of cementitious materials presents great interest to improve the durability of concrete structure (transfer properties for example). The impact of blast-furnace slag on this phenomenon is not yet clear even if the self-healing of concrete with blast-furnace slag was observed in building sites. To understand the blast-furnace slag influence, non-destructive methods were used to follow self-healing: X-ray tomography and gas permeability test. All specimens were cracked at 7 days and 28 days. The results show that the blast furnace slag has an interesting self-healing potential that can exceed the reference formulation results. This good potential depends on the physico-chemical characteristics of the raw materials and the hydration potential of the formulation over time. In addition to follow the self-healing, a new trial was set up to crack mortar specimens by restrained shrinkage and study the self-healing of a natural crack. In addition to follow the self-healing, a new trial was set up to crack mortar specimens by restrained shrinkage and study the self-healing of a natural crack. This test has proven effective over the reference formulation.The SEM with EDS analysis showed the formation of new products in the crack and the impact of storage conditions on these products : C-S-H for specimens stored in water and calcium carbonate for specimens stored in a damp chamber (CO2 + water). Migration chlorures and nano-indentation tests results showed that self-healing products had interesting durability properties and micro-mechanical properties (for calcium carbonate). Finally, self-healing modelling is proposed by means of geochemistry PHREEQC calculation code. The study revealed interesting potential PHREEQC to model self- healing phenomenon and make it a of predictive tool.