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The purpose of this research is to identify the configurations of several mechanism classes which result in bistable behavior. Bistable mechanisms have use in many applications, such as switches, clasps, closures, hinges, and so on. A powerful method for the design of such mechanisms would allow the realization of working designs much more easily than has been possible in the past. A method for the design of bistable mechanisms is especially needed for micro-electro-mechanical systems (MEMS) because fabrication and material constraints often prevent the use of simple, well-known bistable mechanism configurations. In addition, this knowledge allows designers to take advantage of the many benefits of compliant echanisms, especially their ability to store and release energy in their moving segments. Therefore, an analysis of a variety of mechanism classes has been performed to determine the configurations of compliant segments or rigid-body springs in a mechanism which result in bistable behavior. The analysis revealed a relationship between the placement of compliant segments and the stability characteristics of the mechanism which allows either analysis or synthesis of bistable mechanisms to be performed very easily. Using this knowledge, a method of type synthesis for bistable mechanisms has been developed which allows bistable mechanisms to be easily synthesized. Several design examples have been presented which demonstrate the method. The theory has also been applied to the design of several bistable micromechanisms. In the process of searching for usable designs for micro-bistable mechanisms, a mechanism class was defined, known as "Young" mechanisms, which represent a feasible and useful way of achieving micro-mechanism motion similar to that of any four-bar mechanism. Based on this class, several bistable micro-mechanisms were designed and fabricated. Testing demonstrated the ability of the mechanisms to snap between the two stable states. In addition, the mechanisms showed a high degree of repeatability in their stable positions.

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To the reader <p> Since I worked on two separate projects towards my doctorate thesis, the arrangement of my thesis is rather unusual. The reader will find that my thesis is divided into four parts. Part 1 is dedicated to a very general introduction about the basic knowledge needed to guide you, the reader, through the rest of the thesis. Within this part, different sections focus on different fundamental aspects of Biophysics related to my work. In Part 2, I discuss my studies of the distribution and dynamics of the nuclear protein Ran in live interphase HeLa cells. This part contains a background section specific to this project, the materials and methods used for this study, experimental results, a discussion of our findings, and it ends with conclusions. Part 3 is dedicated to the study of the dynamical mechanisms responsible for the establishment of the Bed protein concentration gradient along the anterior-posterior axis in live Drosophila melanogaster embryos. Again, a specific background section is included in this part, followed by the materials and methods used to perform this research, results, discussions and finally I will summarize my results to conclude this work. The last part, part 4, is rather short and contains the summary of the overall results of my work on both nuclear proteins with some emphasis on the similarities and differences in their dynamical behavior.</p> / Thesis / Doctor of Philosophy (PhD)

The main aim of this dissertation is to relate measurable and hopefully controllable features of a material's microstructure to its observed failure modes to provide a basis for designing better materials. The understanding of creep in materials used at high temperatures is of prime engineering importance. Single crystal Ni-based superalloys used in turbine aerofoils of jet engines are exposed to long dwell times at very high temperatures. In contrast to current theories, creep tests on Ni-based superalloy specimens have shown size dependent creep response termed as the thickness debit effect. To investigate the mechanism of the thickness debit effect, isothermal creep tests were performed on uncoated Ni-based single crystal superalloy sheet specimens with two thicknesses and under two test conditions: a low temperature high stress condition and a high temperature low stress condition. At the high temperature, surface oxidation induced microstructural changes near the free surface forming a layered microstructure. Finite element calculations showed that this layered microstructure gave rise to local changes in the stress state. The specimens also contained nonuniform distribution of initial voids formed during the solidification and homogenization processes. The experiments showed that porosity evolution could play a significant role in the thickness debit effect. This motivated a basic mechanics study of porosity evolution in single crystals subjected to creep for a range of stress states. The study was performed using three-dimensional finite deformation finite element analysis of unit cells containing a single initially spherical void in a single crystal matrix. The materials are characterized by a rate-dependent crystal plasticity constitutive relation accounting for both primary and secondary creep. The effect of initial void spacing and creep exponent was also explored. Based on the experimental observations and results of finite element calculations a quantitative mechanistic model is proposed that can account for both bulk and surface damage effects and assess their relative roles in the observed thickness debit effect. Another set of calculations aim at relating the crack growth resistance and fracture surface morphology to material microstructure for ductile structural metals. The process that governs the ductile fracture of structural materials at room temperature is one of nucleation, growth and coalescence of micron scale voids, and involves large plastic deformations. Experimental studies have shown that fracture surfaces in a wide variety of materials and under a wide variety of loading conditions have remarkable scaling properties. For thirty years, the hope to relate the statistical characterization of fracture surfaces to a measure of a material's crack growth resistance has remained unfulfilled. Only recently has the capability been developed to calculate sufficient amounts of three dimensional ductile crack growth in heterogeneous microstructures to obtain a statistical characterization of the predicted fracture surfaces. This development has enabled the exploration of the relation of both fracture toughness and fracture surface statistics to material properties and microstructure when the fracture mechanism is one of void nucleation, growth and coalescence. The relation of both toughness and the statistical properties of fracture surfaces in calculations of heterogeneous microstructures to various microstructural features is discussed and a remarkable correlation between fracture surface roughness and fracture toughness is shown for the first time.

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Yes / Concrete structures in sewer systems, marine engineering, underground engineering and other humid environments are easily subjected to microbial attachment, colonization and, eventually, deterioration. With careful selection and treatment, some additives including inorganic and organic antimicrobial agents were found to be able to endow concrete with excellent antimicrobial performance. This paper reviews various types of antimicrobial concrete fabricated with different types of antimicrobial agents. The classification and methods of applying antimicrobial agents into concrete are briefly introduced. The antimicrobial and mechanical properties as well as mass/weight loss of concrete incorporating antimicrobial agents are summarised. Applications reported in this field are presented and future research opportunities and challenges of antimicrobial concrete are also discussed in this review. / National Science Foundation of China (51908103 and 51978127), China Postdoctoral Science Foundation (2019M651116)