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京都大学 / 新制・課程博士 / 博士(理学) / 甲第23688号 / 理博第4778号 / 新制||理||1684(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 柳瀬 陽一, 教授 川上 則雄, 教授 松田 祐司 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Arch-shaped microelectromechanical systems (MEMS) have been used as mechanical memories, micro-sensors, micro-actuators, and micro-valves. A bi-stable structure, such as an arch, is characterized by a multivalued load deflection curve. Here we study the symmetry breaking, the snap-through instability, and the pull-in instability of bi-stable arch shaped MEMS under steady and transient electric loads. We analyze transient finite electroelastodynamic deformations of perfect electrically conducting clamped-clamped beams and arches suspended over a flat rigid semi-infinite perfect conductor. The coupled nonlinear partial differential equations (PDEs) for mechanical deformations are solved numerically by the finite element method (FEM) and those for the electrical problem by the boundary element method. The coupled nonlinear PDE governing transient deformations of the arch based on the Euler-Bernoulli beam theory is solved numerically using the Galerkin method, mode shapes for a beam as basis functions, and integrated numerically with respect to time. For the static problem, the displacement control and the pseudo-arc length continuation (PALC) methods are used to obtain the bifurcation curve of arch's deflection versus the electric potential. The displacement control method fails to compute arch's asymmetric deformations that are found by the PALC method. For the dynamic problem, two distinct mechanisms of the snap-through instability are found. It is shown that critical loads and geometric parameters for instabilities of an arch with and without the consideration of mechanical inertia effects are quite different. A phase diagram between a critical load parameter and the arch height is constructed to delineate different regions of instabilities. The local water slamming refers to the impact of a part of a ship hull on stationary water for a short duration during which high local pressures occur. We simulate slamming impact of rigid and deformable hull bottom panels by using the coupled Lagrangian and Eulerian formulation in the commercial FE software LS-DYNA. The Lagrangian formulation is used to describe planestrain deformations of the wedge and the Eulerian description of motion for deformations of the water. A penalty contact algorithm couples the wedge with the water surface. Damage and delamination induced, respectively, in a fiber reinforced composite panel and a sandwich composite panel and due to hydroelastic pressure are studied. / Ph. D.

One of the most promising routes to create advanced materials is self-assembly. Self-assembly refers to the self-organisation of building blocks to form ordered structures. As the properties of the self-assembled materials will inherit the properties of the basic building blocks, it is then possible to engineer the properties of the materials by tailoring the properties of the building blocks. In order to create mesoscale materials, the self-assembly of molecular building blocks of different sizes and interactions is important. Mesoscopic materials can be obtained by using larger building blocks such as nano and colloidal particles. Colloidal particles are particularly attractive as building blocks because it is possible to design interparticle interactions by controlling both the chemistry of the particles' surface and the properties of the solvent in which the particles are immersed. The self-assembly of spherical colloidal particles has been widely reported in the literature. However, advances in experimental techniques to produce particles with different shapes and sizes have opened new opportunities to create more complex structures that cannot be formed using spherical particles. Indeed, the particles' shape and effective interactions between them dictate the spatial arrangement and micro-structure of the system, which can be engineered to produce functional materials for a wide range of applications. The driving forces determining the self-assembly of colloidal particles can be modified by the use of external influences such as geometrical confinement and electromagnetic forces. Geometrical confinement, for example, has been used to design quasi two-dimensional materials such as multi-layered structures of spheres, dimers, rods, spherical caps, and monolayers of platelets with various geometries and symmetries. In this dissertation, we present three computer simulations studies using Monte Carlo and Molecular Dynamics simulations determining the self-assembly of monolayer colloidal platelets with different shapes confined in two dimensions. These particles have been selected due to recent experiments in colloidal particles with similar shapes. All the particles' models are represented by planar polygons, and three different effects affecting their self-assembly have been analysed: (a) the curvature of the particles' vertices; (b) the curvature of the particles' edges; and finally (c) the addition of functional groups on the particles' surface. These studies aim to demonstrate that the subtle changes on the particle's shape can be used to engineer complex patterns for the fabrication of advanced materials. Monte Carlo simulations are performed to study the self-assembly of colloidal platelets with rounded corners with 4, 5, and 6-fold symmetries. Square platelets provide a rich phase behaviour that ranges between disorder-order and order-order phase transitions. Suprisingly, the disk-like shape of pentagons and hexagons prevents the total crystallisation of these systems, even at a high pressure state. A hysteresis gap is observed by the analysis of compression and expansion runs for the case of square platelets and the thermodynamic method known as direct coexistence method is used to be accurately determined the point of the order-order transition. Further, unexpected results are obtained by performing Molecular Dynamics simulations in systems with platelets with 3, 4, 5, and 6-fold symmetries when all the sides of each polygon are curved. Macroscopic chiral symmetry breaking is observed for platelets with 4 and 6-fold symmetries, and for the first time a rule is promoted to explain when these chiral structures can be formed driven only by packing effects. This unique rule is verified also for platelets with the same curved sides as previously when functional chains tethered to either vertices or sides. Indeed, square platelets with curved sides confined in two dimensions can form chiral structures at medium densities when flexible chains tethered to either vertices or sides. Triangular platelets with curved sides can form chiral structures only when the chains are tethered to the corners, since the chains experience an one-hand rotation to sterically protect one side. When the chains are symmetrically tethered to the sides, local chiral symmetry breaking is observed as both left-hand and right-hand sides on each vertex are sterically protected allowing the same probability for rotation either in clockwise or anticlockwise direction.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / O objetivo deste trabalho à aplicar o modelo de bumblebee, um modelo de quebra de simetria espontÃnea de Lorentz gerada por um quadri-vetor de valor esperado de vÃcuo nÃo-nulo, a um espaÃo de vÃcuo. Apresentamos resultados para quebra de simetria de Lorentz radial/temporal em um espaÃo de Schwarzschild. AlÃm disso, à verificada uma incompatibilidade entre a hipÃtese de o universo ser homogÃneo quando nÃo hà presenÃa de matÃria massiva ordinÃria e a imposiÃÃo de um campo de bumblebee paralelamente transportado na direÃÃo radial. / The objective of this work is apply bumblebee model, a spontaneously Lorentz symmetry breaking model due to a non-vanishing vacuum expectation value vector field, to a vacuum space. Results are presented for a radial/temporal Lorentz symmetry breaking in a Schwarzschild space. Also, it is verified an incompatibility between the hypothese of the universe to be homogenous in the absence of massive ordinary matter and the imposition of a parallelly transported bumblebee field in radial direction.

No presente trabalho estudamos duas variações do problema de empacotamento de itens retangulares idênticos, permitindo rotações de 90 graus, em um poliedro. Uma variação consiste em encontrar a maior quantidade de itens retangulares idênticos que podem ser empacotados em um poliedro. A outra consiste em encontrar o poliedro de um determinado tipo com menor área para empacotar uma quantidade fixa de itens retangulares idênticos. Desenvolvemos restrições de eliminação de simetrias para estes problemas, o que tornou a resolução dos mesmos mais eficiente, por métodos do tipo branch-&-bound. Estudamos também o problema de corte no qual há uma determinada demanda (de itens) a ser cortada e um conjunto de objetos disponíveis. Desejamos satisfazer a demanda minimizando o custo dos objetos utilizados e, dentre as diferentes possibilidades de se fazer isso, desejamos aquela que maximize as sobras aproveitáveis. De forma geral, sobras aproveitáveis podem ser entendidas como regiões retangulares de um objeto que possuem altura e largura iguais ou superiores a de um item de referência e representam sobras do processo de corte que podem se tornar objetos e serem reaproveitadas em um novo procedimento de corte. Apresentamos modelos de otimização em dois níveis para duas variações do problema de corte com sobras aproveitáveis a saber: o problema de corte de itens retangulares em dois estágios e o problema de corte de itens retangulares não guilhotinado. Como formas de resolver os modelos propostos, apresentamos reformulações destes modelos de programação em dois níveis em modelos de programação inteira mista. Lidamos também com uma variação do problema de corte com sobras aproveitáveis considerando a minimização da quantidade de sobras. Aplicamos restrições de eliminação de simetrias aos modelos desenvolvidos para o problema de corte de itens retangulares com sobras aproveitáveis, a fim de resolver instâncias maiores, e desenvolvemos uma estratégia de solução alternativa para os modelos. Os modelos desenvolvidos foram implementados computacionalmente e fomos capazes de resolver instâncias pequenas dos problemas em questão. / In this work we study two variations of the packing problem where identical rectangular items must be packed into a polyhedron. One of the variations consists in finding the largest amount of rectangular items that can fit in a polyhedron. The other one consists in finding a minimal area polyhedron of a certain type that packs a set of rectangular identical items. We present some symmetry-breaking constraints that reduce the computational effort in solving those problems through a branch-&-bound method. We also studied the cutting stock problem where there are some items to be cut from a set of rectangular objects and we need to satisfy the demand of items to be cut minimizing the cost of the used objects and, among the different ways of doing this, we want that which maximize the usable leftovers. Loosely speaking,usable leftovers can be understood as rectangular regions in an object that has the width and the height greater than or equal to the ones of a reference item. These leftovers can be seen as leftovers from a cutting process that will become items in a new cutting process. We present bilevel programming models to two variations of this problem with usable leftovers: the two-stage cutting stock problem of rectangular items and the non-guillotine cutting stock problem of rectangular items. In order to solve the proposed models we present also MIP reformulations of these bilevel programming problem models. We also developed some symmetry breaking constraints in order to accelerate the solving process of those models. The developed models were computationally programmed and we were able to solve small instances of the proposed problems

Precision measurements of superallowed Fermi β-decay allow for stringent tests of the magnitude of isospin-symmetry-breaking effects in nuclei, the validity of the conserved vector current hypothesis, and the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) quark-mixing matrix. A high-precision measurement of the branching ratio for the superallowed β+ decay of 74Rb has been performed at the Isotope Separator and ACcelerator (ISAC) facility at TRIUMF. The 8π spectrometer, an array of 20 HPGe detectors, was used to detect γ-rays emitted following the Gamow-Teller and non-analogue Fermi β-decays of 74Rb. PACES, an array of 5 Si(Li) detectors, was used to detect emitted conversion electrons, while half of SCEPTAR, a close-packed array of 10 plastic scintillators, was used to detect emitted β particles. In this experiment, 23 excited states were identified in 74Kr which were populated following the β-decay of 74Rb. A total of 58 γ-rays were identified following the 8.241(4)x108 detected β-particles. An observed non-superallowed branching ratio of 0.396(7)% was determined from the intensity of the identified γ-rays, while the unobserved non-superallowed intensity was calculated to be 0.05(5)%, leading to a superallowed branching ratio of 99.55(5)%. The superallowed branching ratio is now the most precise experimental quantity in the determination of the superallowed ft-value of 74Rb. Combining the half-life and Q-value with the superallowed branching ratio measured in this work leads to a superallowed ft-value of 3082.6(66) s. Finally, comparisons between the superallowed ft-value, the world average Ft-value, and the non-analogue Fermi branching ratio are made to provide future guidance in the refinement of the theoretical models required to describe the crucial isospin-symmetry-breaking term in superallowed β-decay.

As part of an ongoing program to study fundamental symmetries in nuclear physics, a thorough investigation into shell-model isospin-symmetry-breaking (ISB) calculation theory has been conducted using direct reactions to observe detailed nuclear-structure information. The work presented in this Thesis focuses on the 62Ga superallowed beta-decay system, and consists of two primary experiments; 1) A 64Zn(d,t)63Zn single-neutron transfer reaction, aimed at observing spectroscopic strengths to help guide calculation model-space truncations for the beta-decay wave function radial-overlap component of ISB, and 2) A two-neutron 64Zn(p,t)62Zn transfer to search for excited 0+ states in the daughter nucleus of 62Ga. The experiments were performed at the Maier-Leibnitz-Laboratory, on the joint campuses of the Ludwig-Maximilians Universitat and the Technische Universitat Munchen, in Garching, Germany. In total, 162 states in 63Zn were populated from the 64Zn(d,t) reaction, up to an excitation energy of 4.8 MeV, including the observation of 125 new levels, and unique spin/parity assignments for 92 states. As a result, this work provides the most complete picture for low-spin states in 63Zn to date. A comparison of the extracted S values to the predicted shell-model spectroscopic factors shows an overall over-prediction of strength for the 2p3/2 orbital, and a large disagreement for the 1f7/2 orbital above ~3.5 MeV. No significant 1g9/2 strength was observed, leading to the conclusion that the importance of the 1g9/2 orbital for ISB is small. Additionally, 67 states were observed in 62Zn using the two-neutron pickup mechanism, including the observation of five 0+ states. More than 99% of the total 0+ (p,t) cross-section is observed in the ground-state reaction channel, implying a nearly maximal overlap of the wave functions with the two-nucleon transfer operator. The dominance of the ground-state-to-ground-state (p,t) cross section is strikingly similar to the dominance of the superallowed Fermi beta-decay between isobaric-analogue 0+ states. This suggests that the population of excited 0+ states in the (p,t) reaction may reflect the population in the Fermi decay process, and can be used to guide future experimental and theoretical work. Further discussion of these results as they relate to the ISB correction calculations, and the implications for future theoretical work are presented in this Thesis. / This work was supported in part by the Natural Sciences and Engineering Research Council of Canada, the Ontario Ministry of Economic Development and Innovation, the DFG Cluster of Excellence `Origin and Structure of the Universe', and NSF grant PHY-1068217.

Symmetry and symmetry-breaking have, in the last one hundred and fifty years, become incorporated as central explanatory concepts within the natural sciences and mathematics. An abbreviated review of the incorporation of symmetry within the disciplines of mathematics, physics, philosophy and biology, provides a frame within which to develop of a model of mind. This thesis combines the framework provided by symmetry and symmetry-breaking with a structural understanding of self-referential dynamics in examining the implied Kantian model of mind. It considers that Kant’s assumption of a transcendental self unnecessarily isolates consciousness from being understood as a product of complex natural processes. Kant’s structural model of mind is examined and reformulated in terms of a more fundamental form and process. The space required for any non-reductionist model of mind is proposed as being generated through an enfolding of dimensionality in the occurrence of categorical level symmetry breaking during evolutionary development. The temporally extended function is accounted for in terms of self-referential structural dynamics operating within the primary temporal asymmetry. The model of mind proposed is created through application of naturalistic explanations incorporating symmetry and has attributes that may prove of interest to non-reductionists. The phenomenological geometry established provides a framework to understand the experiential phenomenon of qualia while conforming to the requirements of a natural explanation. Information is conceived as being transmitted inwaveforms propagated across spaces of enfolded dimensionalities through structural framesdemarcating nested spaces and condensing in the synthesis of unity in the object of attention,or image, and returning to distribute, the now reformulated, information outward acrosscontextual frames and spaces. This simplified dynamic is considered to operate at all levels of natural phenomena and involves the reintroduction of Bohm’s concepts of implicate and explicate order. The result is a model of mind employing a minimum structural form and self-referential dynamics that has potential for integration across the discipline theoretic frames of the natural sciences while retaining, for the domain of conscious phenomena, an independent causal significance in terms of a temporal structuralism.

The study of the muon decay process μ+ → e+νeν ̄μ is a powerful constraint on the behaviour of the weak interaction, without contamination of the other, stronger, fundamental interactions. The spectrum measured from the momentum and angles of the decay positrons is parametrized using a set of four decay parameters. The purpose of the TWIST experiment is to measure these decay parameters to an unprecedented precision; an order of magnitude improvement in the uncertainties over measurements completed before the TWIST experiment. Measurements of the muon decay parameters constrain the values of a series of 19 weak coupling constants. In the standard model, V-A weak interaction, 18 of these constants are 0, while the remaining constant describes interactions between left handed particles, gV_LL= 1.The decay parameter ρ quantifies the behaviour of the spectrum with respect to momentum. According to the standard model the value of this parameter is 3/4. TWIST measured a value of ρ = 0.74991±0.00009(stat)±0.00028(sys). The measurement is limited by its systematic uncertainty, so a large focus of the experiment was on the determination and control of these uncertainties. The systematic uncertainties are derived from uncertainties in the detector construction and uncertainties in the biases generated by differences between the data and a matching Monte Carlo. Muon decay also limits the possibility of family symmetry breaking interactions. TWIST can be used to search for the possibility of muons decaying into a positron and a single unidentified neutral particle μ+ → e+X0 that does not otherwise interact with normal matter. The large momentum and angle acceptance of the TWIST spectrometer allows for searches of two body decays for masses of the X0 boson mX0 ∈ [0,80] MeV/c, with a variety of behaviours with respect to the angle of the positron track. Upper limits on massive and mass-less X0 decays are set with a 90% confidence level separately at parts per million for massive decays and parts in 10000 for mass-less decays.