Optimal Design of a Fully Parallel Robot Manipulator.

Optimal design of a six degrees-of-freedom, fully parallel manipulator, called a Stewart platform is investigated. In order to optimize the mechanism, new performance measures are introduced since use of the previous methods suffer from lack of physical meaning due to dimensional inhomogeneity. To overcome the dimensional inhomogeneity problem, an Euclidean norm definition of each output space with homogeneous dimension is used to find input-output norm relation. As a result, four sets of eigenvalues are obtained which characterize translational and rotational velocity, force and torque, and position and orientation accuracy. From the four sets of eigenvalues, four determinant measures are defined, which represent the magnitude of the input-output transformation and four condition number measures are defined which are indices of uniform transformation. The invariant property of the new measures is investigated under the scaling operation. By the simplification of the design problem, the explicit equations of performance measures are derived which provide the valuable tools to analyze the parametric space of the design variables. Using the explicit formulation, singular configurations can be identified at home positions of the manipulator. It is shown that parameters satisfying the isotropic condition form the surfaces of the simple geometric entities, called the cones and cylindroids in cylindrical coordinates. These geometric entities provide the insight to figure out the behavior of the performance measures in the parametric space. Using the geometric entities, three optimum solutions are found: one for force capacity and position accuracy and one for the torque capacity and rotation accuracy and one for both aspects. It is shown that there are two isotropic surfaces corresponding to each given condition number not equal to one and in all the region bounded by the two surfaces the condition numbers are less than the given condition number. Using these facts, a minimax problem is solved for condition number measures. It is shown that the achievable minimum condition number is obtained when the geometric average of the upper and lower limit of the operating height is on the isotropic surface. The result is used to determine the adequate operating range

Parallel Manipulators

In recent years, parallel kinematics mechanisms have attracted a lot of attention from the academic and industrial communities due to potential applications not only as robot manipulators but also as machine tools. Generally, the criteria used to compare the performance of traditional serial robots and parallel robots are the workspace, the ratio between the payload and the robot mass, accuracy, and dynamic behaviour. In addition to the reduced coupling effect between joints, parallel robots bring the benefits of much higher payload-robot mass ratios, superior accuracy and greater stiffness; qualities which lead to better dynamic performance. The main drawback with parallel robots is the relatively small workspace. A great deal of research on parallel robots has been carried out worldwide, and a large number of parallel mechanism systems have been built for various applications, such as remote handling, machine tools, medical robots, simulators, micro-robots, and humanoid robots. This book opens a window to exceptional research and development work on parallel mechanisms contributed by authors from around the world. Through this window the reader can get a good view of current parallel robot research and applications

Natural Selection and Natural Processes: a philosophical examination of the processes of evolution

This thesis concerns evolution and how it is explained. The ambition here is to identify clearly the many aspects of evolution, and to evaluate past and present explanations of evolution for their coherence and validity. Historically natural selection has been taken to be the central and main explanans, with other explanations playing lesser roles. Here it will be argued that the sheer complexity and diversity within nature cannot be accounted for by any single explanatory mechanism and that a plurality of explanatory mechanisms is required. Loading natural selection with the main weight of explanation is an overburden which, far from strengthening its explanatory powers, actually renders it vacuous. A critical historical and philosophical examination of the concept of natural selection reveals that it has never received a formal scientific definition that commands universal respect. This has created a problem of demarcation between that which natural selection can legitimately be said to explain and that which it cannot. In fact, the ontology of natural selection is equivocal, giving rise to the many controversies that have plagued evolutionary biology. The disambiguation of the concept of natural selection is the principle aim of this thesis and guidelines on how this should be accomplished are provided. However, should these reforming guidelines fail to achieve a consensus then a more radical alternative is proposed. It is recommended that the selective terminology is replaced with the less anomalous and demanding principle of ‘meeting the conditions of existence’. Moreover, talk of the evolution and origins by means of natural selection is to be replaced by talk of evolution and origins by means of natural processes. Finally, drawing from a ‘Structuralist’ alternative, it will be demonstrated that biological evolution should not be divorced from general or cosmological evolution. Rather, elucidation should be drawn more deeply from the fields of physics, chemistry, mathematics and topology, without the use of selection-tinted spectacles

Crystal Cartography: Mapping Nanostructure with Scanning Electron Diffraction

Nanostructure describes the network of defective and distorted atomic structure existing on the nanoscale within materials. This nanostructure bridges the gap between idealised crys- talline structure and real materials, playing a deterministic role in tailoring physico-chemical properties, as well as providing a basis for mechanistic understanding of complex processes such as mechanical deformation and phase transformation. Characterising nanostructure, to develop understanding of materials, requires experimental techniques capable of probing the structure with spatial resolution on the order of nanometres and across regions of interest up to micrometres. Recent developments in electron microscopy, enabling the acquisition of numerous diffraction patterns in a spatially resolved manner, combined with modern computational power, provides a route to meet this need as developed in this work. Scanning electron diffraction (SED) involves the acquisition of a two-dimensional elec- tron diffraction pattern at each probe position in a two-dimensional scan of a specimen. An information rich 4-dimensional (4D-SED) dataset is obtained that can be analysed extensively post-facto using a wide-range of computational methods. The acquisition of such 4D-SED data from the specimen at numerous orientations may also enable the reconstruction of nanostructure in three-dimensions via tomographic methods. In this work, methods for the acquisition and analysis of 4D-SED data are developed and applied to reveal nanostructure in two and three-dimensions. These methods are applied to various prototypical characterisation challenges in materials science, particularly: strain mapping in two and three dimensions, revealing inter-phase crystallographic relationships, mapping grains in two-dimensional materials, and probing nanostructure in polyethylene

First-principles modeling of thermoelectric materials

Thermoelektrische Materialien sind für umweltfreundliche Stromerzeugung von Interesse. Die Motivation der Dissertation ist es, thermoelektrische Eigenschaften auf einem fundamentalen Niveaus zu beschreiben und zu verstehen. Grundzustandseigenschaften wurden im Rahmen der Dichtefunktionaltheorie berechnet und die thermoelektrischen Eigenschaften mit Hilfe der Boltzmannschen Transportheorie. Zwei Klassen von thermoelektrischen Materialien, Skutterudite und Clathrate, wurden erforscht. Schwingungseigenschaften von einigen Ge-basierten Skutteruditen wurden untersucht, um Rasselmoden zu verstehen, die für die thermische Leitfähigkeit des Gitters wichtig sind. Die Resultate für einige Ge-basierte Skutterudite ergaben einen niedrigen Seebeckwert, der um zwei Größenordnungen verbessert werden könnte, wenn man geeignete Substituierungen des Ge durch Sb macht. Weiters wurden thermoelektrische Eigenschaften von einigen Ge-basierten Clathraten erfolgreich untersucht. Die Lorenzzahl, die wichtig für die thermische Leitfähigkeit ist, wurde für ein Clathrat bestimmt, wobei sich eine starke Abhängigkeit von Temperatur und Zusammensetzung zeigte. Die Resultate beweisen die Stärke einer Materialwissenschaft, die von den tiefsten Grundlagen ausgeht.Thermoelectric materials provide potential applications for an environment friendly power generation. The thesis aimed at an understanding of thermoelectric properties of selected materials at a fundamental level. Ground state properties were calculated within the density functional theory and thermoelectric properties were derived within Boltzmann's transport theory. Two classes of thermoelectric materials, namely skutterudites and clathrates, were investigated. Vibrational properties of some Ge-based skutterudites were studied for an understanding of rattling modes, which are of importance for the lattice thermal conductivity. The results for some Ge-based skutterudites revealed rather low Seebeck coefficients, which may be improved by two orders of magnitude by appropriate replacements of Ge by Sb. Furthermore, thermoelectric properties of some Ge-based clathrates are successfully studied. The Lorenz number for the electronic thermal conductivity is determined, which strongly varies as a function of temperature and composition. The results manifest the capabilities of a first-principles computational materials design

On Musical Self-Similarity : Intersemiosis as Synecdoche and Analogy

Self-similarity, a concept borrowed from mathematics, is gradually becoming a keyword in musicology. Although a polysemic term, self-similarity often refers to the multi-scalar feature repetition in a set of relationships, and it is commonly valued as an indication for musical ‘coherence’ and ‘consistency’. In this study, Gabriel Pareyon presents a theory of musical meaning formation in the context of intersemiosis, that is, the translation of meaning from one cognitive domain to another cognitive domain (e.g. from mathematics to music, or to speech or graphic forms). From this perspective, the degree of coherence of a musical system relies on a synecdochic intersemiosis: a system of related signs within other comparable and correlated systems. The author analyzes the modalities of such correlations, exploring their general and particular traits, and their operational bounds. Accordingly, the notion of analogy is used as a rich concept through its two definitions quoted by the Classical literature—proportion and paradigm, enormously valuable in establishing measurement, likeness and affinity criteria. At the same time, original arguments by Benoît B. Mandelbrot (1924–2010) are revised, alongside a systematic critique of the literature on the subject. In fact, connecting Charles S. Peirce’s ‘synechism’ with Mandelbrot’s ‘fractality’ is one of the main developments of the present study

Spectroscopic Studies on Semiconducting Interfaces with Giant Spin Splitting

The application of an external magnetic field can lift the spin degeneracy of electronic states through its interaction with the electronic magnetic moment. A closely-related phenomenon is the Rashba-Bychkov (RB) effect where symmetry breaking at surfaces or interfaces gives rise to an electric field which is in turn seen as an effective magnetic field in the electrons' rest frame. The resulting k-dependent energy splitting of spin-polarized electronic states has been observed on various metal surfaces but the effect is much larger in artificially-grown surface alloys; such as the BiAg2 grown at the surface of Ag(111). The spin splitting magnitude observed in these systems might be very useful in spintronics applications since it could decrease the spin precession time in a spin transistor and distinguish between the extrinsic and intrinsic spin Hall effects. Nevertheless, their metallic character poses serious obstacles in the exploitation of the RB effect due to the presence of spin-degenerate electronic states at the Fermi level which would dominate transport experiments. We have used angle-resolved photoelectron spectroscopy (ARPES) to explore the RB effects on various artificially grown structures, formed on semiconducting substrates. The interplay of quantum confinement and giant RB splitting on a trilayer Si(111)-Ag-BiAg2 system reveals the formation of a complex spin-dependent structure, which can be externally tuned by varying the Ag layer thickness. This provides a means to tailor the electronic structure and spin polarization near the Fermi level, with potential applications on Si-compatible spintronic devices. Moreover, we have discovered a giant spin splitting in a true semiconducting system, namely the Si(111)-Bi trimer phase. The size of the RB parameters is comparable to those of metallic surface alloys. Using theoretical models we have identified the peculiar band topology as the origin of the giant spin splitting on the Bi/Si(111) system. All our findings are supported by relativistic first-principles calculations. Finally, a chapter of this thesis manuscript is devoted to the description of phenomeno-logical theoretical simulation, which can capture the experimental results related to the RB effect on low-dimensional systems. A parallel experimental project is discussed in a separate chapter. It has been focused on the band topology of the novel p(2 × 2) reconstruction of the Pt(111)-Ag-Bi trilayer. We investigated the symmetry properties of the interface states by varying the amount of Ag. ARPES results present the electronic signature of a strain-related structural transition

Laser Systems for Applications

This book addresses topics related to various laser systems intended for the applications in science and various industries. Some of them are very recent achievements in laser physics (e.g. laser pulse cleaning), while others face their renaissance in industrial applications (e.g. CO2 lasers). This book has been divided into four different sections: (1) Laser and terahertz sources, (2) Laser beam manipulation, (3) Intense pulse propagation phenomena, and (4) Metrology. The book addresses such topics like: Q-switching, mode-locking, various laser systems, terahertz source driven by lasers, micro-lasers, fiber lasers, pulse and beam shaping techniques, pulse contrast metrology, and improvement techniques. This book is a great starting point for newcomers to laser physics