Este trabalho apresenta uma metodologia experimental para investigar a relação entre taxas de desgaste abrasivo e dureza. Investigam-se os regimes moderado e severo de desgaste abrasivo em função da razão entre a dureza do abrasivo (HA) e a dureza do material desgastado (H). Foram realizados ensaios pino contra lixa, utilizando vidro como abrasivo em dois tamanhos, grana #80 e grana #240, e pinos com 3 mm de diâmetro sob força de 20 N. Os materiais ensaiados foram os aços AISI 1006 e AISI 52100, este último em diferentes condições metalúrgicas, e um ferro fundido branco de alto cromo, de composição eutética e matriz perlítica. Três tipos de resposta do sistema tribológico foram utilizadas para avaliar os regimes de desgaste: perda de massa, coeficiente de atrito e força de penetração do abrasivo. Determinaram-se as perdas de massa ao longo dos ensaios; o coeficiente de atrito medido por meio de célula de carga e a força de penetração com o uso de ensaios instrumentados de dureza estimando-se a profundidade máxima de penetração com base no parâmetro Rz. A partir das medidas de dureza, foi utilizado um parâmetro para incorporar os efeitos do comportamento elasto-plástico dos materiais, que considera a morfologia de impressão de dureza. Com este parâmetro, foi possível obter uma dureza denominada \"verdadeira\", que incorpora os efeitos de formação de bordas ou retração dos materiais. Verificou-se que os valores de resistência ao desgaste relativa não dependem do tamanho do abrasivo, mas que os valores de coeficiente de atrito dependem, sob regime severo de desgaste. Por sua vez, no regime moderado, os valores de coeficiente de atrito são independentes do tamanho do abrasivo. / This work presents an experimental methodology to investigate the relationship between abrasive wear rates and hardness. The mild and severe abrasive wear regimes are investigated in relation to the abrasive hardness-to-worn material hardness ratio (HA/H). Pin-against-paper tests were performed, using glass as abrasive material in two grain sizes, grit #80 and grit #240, and 3-mm diameter pins under 20 N of applied load. The tested materials were AISI 1006 e AISI 52100 steels, the last one in different metallurgical conditions, and a high-chromium white cast iron, with eutetic composition and pearlitic matrix. Three kinds of tribological system responses were used to evaluate the wear regimes: mass loss, friction coefficient and load of penetration of abrasive. Mass losses were determined along testing time; friction coefficient was determined by means of load cell and the load of penetration using instrumented hardness test, selecting the maximum depth penetration based on the Rz roughness parameter. From hardness measurements, a parameter was used to incorporate the elastic-plastic behavior of materials, which consider the indentation hardness morphology. Using this parameter, it was possible to obtain a kind of hardness called \"true\", which incorporate the pilling-up and sinking-in effects. It has been demonstrated that the relative abrasive resistance is not dependent of the abrasive particle size, but the friction coefficient values change, under severe wear regime. On the other hand, under mild regime, the friction coefficient values are independent of the abrasive particle size.

La cryptographie sur les réseaux est l’une des approches les plus compétitives pour protéger la confidentialité, dans les applications actuelles et l’ère post-quantique. Le problème central qui sert de fondement de complexité de la cryptographie sur réseaux est Learning with Errors (LWE). Il consiste à résoudre un système d’équations bruité, linéaire et surdéterminé. Ce problème est au moins aussi difficile que les problèmes standards portant sur les réseaux, tels que le décodage à distance bornée (BDD pour Bounded Distance Decoding) et le problème du vecteur le plus court unique (uSVP pour unique Shortest Vector Problem). Tous ces problèmes sont conjecturés difficiles à résoudre, même avec un ordinateur quantique de grande échelle. En particulier, le meilleur algorithme connu pour résoudre ces problèmes, BKZ, est très coûteux. Dans cette thèse, nous étudions les relations de difficulté entre BDD et uSVP, la difficulté quantique de LWE et les performances pratiques de l’algorithme BKZ. Tout d’abord, nous donnons une relation de difficulté plus étroite entre BDD et uSVP. Plus précisément, nous améliorons la réduction de BDD à uSVP d’un facteur √2, comparément à celle de Lyubashevsky et Micciancio. Ensuite, Nous apportons un nouvel élément à la conjecture que LWE est quantiquement difficile. Concrètement, nous considérons une version relâchée de la version quantique du problème du coset dièdral et montrons une équivalence computationnelle entre LWE et ce problème. Enfin, nous proposons un nouveau simulateur pour BKZ. Dans ce dernier travail, nous proposons le premier simulateur probabiliste pour BKZ, qui permet de prévoir le comportement pratique de BKZ très précisément. / Lattice-based cryptography is one of the most competitive candidates for protecting privacy, both in current applications and post quantum period. The central problem that serves as the hardness foundation of lattice-based cryptography is called the Learning with Errors (LWE). It asks to solve a noisy equation system, which is linear and over-determined modulo q. Normally, we call LWE problem as an average-case problem as all the coefficients in the equation system are randomly chosen modulo q. The LWE problem is conjectured to be hard even wtih a large scale quantum computer. It is at least as hard as standard problems defined in the lattices, such as Bounded Distance Decoding (BDD) and unique Shortest Vector Problem (uSVP). Finally, the best known algorithm for solving these problems is BKZ, which is very expensive. In this thesis, we study the quantum hardness of LWE, the hardness relations between the underlying problems BDD and uSVP, and the practical performance of the BKZ algorithm. First, we give a strong evidence of quantum hardness of LWE. Concretely, we consider a relaxed version of the quantum version of dihedral coset problem and show an computational equivalence between LWE and this problem. Second, we tighten the hardness relation between BDD and uSVP. More precisely, We improve the reduction from BDD to uSVP by a factor √2, compared to the one by Lyubashevsky and Micciancio. Third, we propose a more precise simulator for BKZ. In the last work, we propose the first probabilistic simulotor for BKZ, which can pridict the practical behavior of BKZ very precisely.

As the semiconductor technology moves further into scaled down device structures, modern day complexities in the fabrication processes become more prevalent. This thesis focuses on the issues associated with mechaincal and adhesion failure in low dielectric constant (low-k) thin films. In this thesis the four point bend test and nanoscratch test method was used for evaluating adhesion of boro-phosphate-silicate glass (BPSG) and tetraethylorthosilicate (TEOS) low-k thin films to silicon subtrates. Nanoindation tests were also performed on the low-k films to evaluate material properties such as hardness and elastic modulus. The sample preparation and testing set up for the four point bend test and nanoscratch test were observed to be greatly disparate. Nanoscratch and nanoindentation sample preparation and sample testing were able to be carried out much quicker than in four point bending. It was observed that nanoscratch testing holds an immense potential for reducing the time needed to evaluate thin film adhesion then in FPB testing. Nanoindentation performed on the BPSG and TEOS dielectric thin films showed uniform mechinacal properties throughout the surface of the films. The adhesion energy for BPSG and TEOS using FPB testing ranged from 29.5390 J/m² - 3.0379 J/m². While the adhesion energy for BPSG and TEOS using nanoscratch testing ranged from 0.0012 J/m² - 0.0028 J/m². It was observed that the difference in adhesion energy for FPB and nanoscratch testing was due to differing failures modes.

No description available.

Statement of the problem. The insertion and polymerization of the first resin composite layer in the proximal cavity of class II restorations require attention to achieve cervical sealing as well as good physical properties and clinical longevity. Objective. To evaluate the polymerization efficiency of four resin composites (Filtek Z250XT- 3M ESPE, Filtek One Bulk-Fill-3M ESPE, Filtek Bulk-Fill Flow-3M ESPE and Opus Bulk Fill- FGM) in the cervical region of class II restorations. Material and methods. Sixteen groups (n = 12) were prepared by inserting 2mm increments of the resin composites in a bipartite matrix and being cured with a lightsource of 1000mW/cm2 in continuous mode during 20 or 40 seconds directly on the material (M group) or through a slot preparation (S group) in typodont teeth and all were stored at 37 +/- 1°C, for 24 hours. The Knoop microhardness was evaluated with 25-g-load and 5-s dwell time. Data were analysed with three-way Anova and Tukeys HSD ( = 5%). Results. The results of relative hardness did not show significant difference for the M groups, regardless of the time and type of resin. All the resins had a relative hardness higher than 0.80. In contrast, for S groups, Z250 20s (0.39+0.08) and Bulk FGM 20s (0.47+0.04) showed significant lowest ratios. Bulk Flow 20s (0.70+0.12) and 40s (0.72+0.09), One Bulk 20s (0.65+0.05) and 40s (0.71+0.06) presented no statistical difference with group Z250 40s (0.63+0.05). Conclusion. It would beneficial to increase the time of photoactivation for resins Z250XT and Bulk FGM, differently for Bulk Flow and One Bulk in class 2 proximal slot restorations to ensure adequate hardening. / Problematização. A inserção e polimerização do primeiro incremento de resina composta na caixa proximal de restaurações classe II deve ser efetuada com atenção para garantir um bom selamento cervical, bem como alcançar boas propriedades físicas e longevidade clínica. Objetivo. Avaliar a eficiência da polimerização de quatro resinas compostas (Filtek Z250XT- 3M ESPE, Filtek One Bulk-Fill-3M ESPE, Filtek Bulk-Fill Flow-3M ESPE e Opus Bulk Fill- FGM) na parede cervical de restaurações classe II. Material e métodos. Dezesseis grupos (n=12) foram preparados através da inserção de incrementos de 2mm das resinas em uma matriz bipartida, sendo fotoativados com uma fonte de luz de 1000mW/cm2 em modo contínuo durante 20 e 40 segundos diretamente no material (M) ou através do preparo slot (S) em um dente artificial e armazenados em estufa a 37 +/- 1ºC, por 24 horas. A microdureza Knoop foi avaliada com carga de 25gramas e tempo de permanência de 5segundos. Todos os grupos foram submetidos aos testes estatísticos e avaliados pela análise de variância com três fatores (Anova) e pelo teste de Tukey HSD ( = 5%). Resultados. Os resultados de dureza relativa não apresentaram diferença significante para os grupos M, independente do tempo e tipo de resina. Todas as resinas apresentaram dureza relativa superior a 0.80. Por outro lado, para os grupos S, Z250 20s (0.39+0.08) e Bulk FGM 20s (0.47+0.04) apresentaram valores significativamente menores. Bulk Flow 20s (0.70+0.12) e 40s (0.72+0.09), One Bulk 20s (0.65+0.05) e 40s (0.71+0.06) não apresentaram diferença estatística com o grupo Z250 40s (0.63+0.05). Conclusão. Seria benéfico aumentar o tempo de fotoativação para as resinas Z250XT e Bulk FGM, ao contrário das resinas Bulk Flow e One Bulk em restaurações de classe 2 com preparo slot para melhorar a dureza.

For wood products such as flooring and worktop, only one surface is normally exposed in their use, and the mechanical properties like hardness and wearing resistance of that surface is then important. Since mechanical properties are strongly related to the density, surface densification, i.e. transverse compression of the wood cells beneath the surface of a piece of wood with the aim to increase the density of that region, may be a method for improving hardness and wearing resistance when low-density species are used for such products. The set-recovery, i.e. the moisture-induced swelling of the densified wood cells back to their original shape, is the main obstacle in the use of densified wood products. Although there are several methods reported in literature, such as post heat-treatment, that can almost eliminate the set-recovery, but such methods are either time consuming or difficult to implement into an industrial continuous process which may do densification competitive to techniques or materials that can achieve at least the same hardness.     In the present study, furfuryl alcohol was used as pre-treatment to fix the set-recovery of surface-densified Scots pine sapwood. The main effect and interactive influence of four process parameter (impregnation time, press temperature, press time and compression ratio) on set-recovery and Brinell hardness after two wet-dry cycles were studied by a two-level full factorial design of experiments. The characterizing variables of the density profile after the surface densification and set-recovery test were carried out as a supplementary tool to learn the mechanism of this two-step modification process. According to the result, the surface densified wood with furfuryl alcohol pre-treatment can retain their dimension and keep hardness at a very high level after two wet-dry cycles. The set-recovery and hardens after two wet-dry cycles were about 20 % and 30 N/mm2, respectively. The Pearson correlation analysis shows that the correlation coefficients between set-recovery with impregnation time, press temperature, press temperature, compression ratio were -0.35, -0.52, -0.37, and 0.16, respectively. That means that for the specimens with furfuryl alcohol pre-treatment, the higher press temperature can reduce the set-recovery significantly. The longer press time and impregnation time can also reduce the set-recovery in some extent, but the influence was  low. As expected, the hardness improvement was retained with low set-recovery. The lowest set-recovery value was 14% with the corresponding hardness of 41 N/mm2 was achieved by specimens processed with 120 minutes of impregnation, 10% compression ratio, 210℃ pressing temperature, and 15 minutes of pressing time. With 20 minutes of impregnation time, 10% compression ratio, 210℃ pressing temperature, and 5 minutes of pressing time, the sample still owns twofold hardness after the set-recovery test.

<p> In the work of this doctoral dissertation a new resonator sensor technique, first presented in 1989, has been further developed and evaluated with focus on technical characteristics and applications within the medical field.</p><p> In a first part a catheter-type tactile sensor using the resonator sensor technique was evaluated in a silicone model and applied to human prostate in vitro. The main finding was that different histological compositions of prostate tissue correlated with the frequency shift, .fS, of the resonator sensor and that the common property was the hardness of the tissue. The results indicated that hardness of the prostate tissue, and maybe hardness of human tissue in general, can be expressed according to a cone penetration standard (DIN ISO 2137) and that the hardness can be measured with this tactile sensor system. The tissue hardness application for the resonator sensor technique has to be further developed and evaluated in a larger study. The study also produced results that has led to the basic understanding of the resonator sensor system. One important result was that .fS of the sensor system was related to the contact area between sensor and sample. This indicated that the resonance sensor could be used for contact area measurement.</p><p> In a second part, containing three studies, the area-sensing capability from the first study was utilised in the development and evaluation of the applanation resonator sensor (ARS) for measurement of intraocular pressure (IOP). For the purpose of evaluating IOP-tonometers, an in vitro pig-eye model was developed, and it was shown that a saline column connected to the vitreous chamber could be used successfully to induce variations in IOP.</p><p> A ARS sensor with a flat contact surface was applied onto the cornea with constant force and .fS was measured. A mathematical model based on the Imbert-Fick law and the assumption that .fS was linearly related to contact area was proposed and verified with a convincing result. IOP measured with the ARS correlated well (r=0.92, n=360) with the IOP elicited by a saline column.</p><p> The ARS in a constant-force arrangement was evaluated on healthy human subjects in vivo. The results verified the sensor principle but revealed a nonnegligible source of error in off-centre positioning between the sensor and cornea. The sensor probe was redesigned and evaluated in the in vitro model. The new probe, with a spherical contact surface against the eye reduced the sensitivity to off-centre positioning. It was also shown that a .fS normalisation procedure could reduce the between-eye differences.</p><p> The ARS method for IOP measurement was further developed using combined continuous force and area measurement during the dynamic phase when the sensor initially contacts the cornea. A force sensor was included with the resonator sensor in one probe. Evaluation was performed with the in vitro pig-eye model. The hypothesis was that the IOP could be deduced from the differential change of force and area during that phase. The study showed good accuracy and good reproducibility with a correlation of r=0.994 (n=414) between measured pressure in the vitreous chamber and IOP according to the ARS. Measurement time was short, 77 ms after initial contact. Problems with inter-eye differences and low resolution at high pressures were reduced. The ARS method is the first to combine simultaneous, continuous sampling of both parameters included in the applanation principle. Consequently, there is a potential for reducing errors in the clinical IOP tonometry. </p>

<p>In the maximum solution equation problem a collection of equations are given over some algebraic structure. The objective is to find an assignment to the variables in the equations such that all equations are satisfied and the sum of the variables is maximised. We give tight approximability results for the maximum solution equation problem when the equations are given over finite abelian groups. We also prove that the weighted and unweighted versions of this problem have asymptotically equal approximability thresholds.</p><p>Furthermore, we show that the problem is equally hard to solve as the general problem even if each equation is restricted to contain at most three variables and solvable in polynomial time if the equations are restricted to contain at most two variables each. All of our results also hold for the generalised version of maximum solution equation where the elements of the group are mapped arbitrarily to non-negative integers in the objective function.</p>

<p>This thesis presents exact means to solve a family of NP-hard problems. Starting with the well-studied Exact Satisfiability problem (XSAT) parents, siblings and daughters are derived and studied, each with interesting practical and theoretical properties. While developing exact algorithms to solve the problems, we gain new insights into their structure and mutual similarities and differences.</p><p>Given a Boolean formula in CNF, the XSAT problem asks for an assignment to the variables such that each clause contains exactly one true literal. For this problem we present an <em>O</em>(1.1730ⁿ) time algorithm, where n is the number of variables. XSAT is a special case of the General Exact Satisfiability problem which asks for an assignment such that in each clause exactly i literals be true. For this problem we present an algorithm which runs in <em>O</em>(2^(1-<em>ε</em>⁾<em>n</em>) time, with 0 < <em>ε</em> < 1 for every fixed <em>i</em>; for <em>i</em>=2, 3 and 4 we have running times in <em>O</em>(1.4511ⁿ), <em>O</em>(1.6214ⁿ) and <em>O</em>(1.6848ⁿ) respectively.</p><p>For the counting problems we present an O(1.2190ⁿ) time algorithm which counts the number of models for an XSAT instance. We also present algorithms for #2SAT<em>w</em><em> </em>and #3SAT<em>w</em><em>,</em> two well studied Boolean problems. The algorithms have running times in O(1.2561ⁿ) and <em>O</em>(1.6737ⁿ) respectively.</p><p>Finally we study optimisation problems: As a variant of the Maximum Exact Satisfiability problem, consider the problem of finding an assignment exactly satisfying a maximum number of clauses while the rest are left with no true literal. This problem is reducible to #2SAT<em>w</em> without the addition of new variables and thus is solvable in time <em>O</em>(1.2561ⁿ). Another interesting optimisation problem is to find two XSAT models which differ in as many variables as possible. This problem is shown to be solvable in O(1.8348ⁿ) time.</p>

This thesis includes two parts. The first part reviews the history and fundamentals of surface science and tribology. The second part presents the major research outcomes and contributions. This research explores the aspects of friction, wear, and surface modification for tribological augmentation of surfaces. An effort has been made to study these aspects through gaining insights by fundamental studies leading to specific practical applications in railroads. The basic idea was to surface engineer metals for enhanced surface properties. A micro- and nano- scale experimental approach has been used to achieve these objectives. Novel principles of nano technology are incorporated into the experiments. Friction has the potential to generate sufficient energy to cause surface reactions through high flash temperatures at the interface of two materials moving in relative motion. This allows surface modifications which can be tailored to be tribologically beneficial through a controlled process. The present work developed a novel methodology to generate a functional tribofilm that has combined properties of high hardness and high wear resistance. A novel methodology was implemented to distinguish sliding/rolling contact modes during experiments. Using this method, a super hard high-performance functional tribofilm with “regenerative” properties was formed. The main instrument used in this research for laboratory experiments is a tribometer, using which friction, wear and phase transformation characteristics of railroad tribo-pairs have been experimentally studied. A variety of material characterization techniques have been used to study these characteristics at both micro and nano scale. Various characterization tools used include profilometer, scanning electron microscope, transmission electron microscope, atomic force microscope, X-ray diffractometer, nanoindenter, and X-ray photon spectroscope. The regenerative tribofilms promise exciting applications in areas like gas turbines, automotive industry, compressors, and heavy industrial equipment. The outcome of this technology will be an economical and more productive utilization of resources, and a higher end performance.