<div>New approaches in topology optimization and manufacturing techniques are generating multi-scale, physically realized mechanical components from advanced materials. Current optimization formulations do not consider the dependence of strength on feature size. By failing to account for the mechanical models of this behavior, sub-optimal structures are generated.</div><div><br></div><div>A currently available academic density-based topology optimization code is extended to incorporate strength constraints. A continuum theory of failure novel to the optimization field is implemented to account for both general yielding and fracture dominated failure. The fracture limit is then formulated in terms of well-established models of brittle and quasi-brittle size dependence. Additional models of size dependence based on assumed flaw sizes are considered using the theory of linear elastic fracture mechanics. To unify the optimized topology and the empirical geometric-scaling models used, a novel geometric measure of local size is proposed. This measure interprets the evolving density field using a consistent domain of support and maintains consistency with gradient-based methods of optimization. The geometric measure is evaluated using test-problems which consider a minimum compliance objective under geometric constraints.</div><div><br></div><div>The resulting optimized structures are presented for the geometric and size-dependent strength constrained formulations. The geometrically constrained results illustrate the flexibility and robustness of the proposed local size measure. The various models of size-dependent strength illustrate the impact and necessity of considering physical models of material within the topology optimization formulation. Results which exhibit clear "micro-structural" features and scale transitioning architectures are presented for limited multi-scale optimization studies.</div><div><br></div><div>An attempt at physical validation considering a single model of quasi-brittle material failure is made. Existing approaches for generating 3D volumetric meshes from image data are leveraged to yield CAD interpretations of optimized structures. Structures are then printed using a 3D printing PolyJet process with a previously established size-dependent material. Structures are destructively evaluated under displacement controlled load testing. The resulting tests indicate that the stress states in the structure fail to induce the expected size-dependent material characteristics. Furthermore, the testing results indicate the difficulty in properly accounting for boundary conditions in the topology optimization approach.</div>

Studying dynamics of magnetization relaxation in excited magnetic materials is important both for understanding the rates and pathways of magnetization relaxation and for the potential use in spin-based electronics and data storage devices in the future. Previous studies have demonstrated that the size of nanocrystals is an important factor for energy relaxation in quantum dots and metal nanoparticles. Since magnetization relaxation is one of energy relaxation pathways, the size of nanocrystals may be also an important factor for magnetization relaxation in nanoscale magnetic materials. The goal of this study is to have a better understanding of magnetization relaxation in nanoscale magnetic materials. In particular, we focused on the correlation between the nanocrystal size and the rates of spin-lattice relaxation (SLR), a magnetization relaxation pathway, in magnetic nanocrystals. The size-dependent magnetization relaxation rate after optically induced demagnetization in colloidal Fe3O4 nanocrystals was measured by using time-resolved Faraday rotation (FR). Fe3O4 nanocrystals were chosen as the model system to study the correlation between the size of nanocrystals and the rates of SLR due to the wellestablished synthetic procedure of making nanocrystals with various sizes and narrow size dispersion. Faster SLR rates were observed in smaller Fe3O4 nanocrystals. The results suggested the surface of nanocrystals have higher efficiency of SLR than the interior region by using a simple model to analyze the SLR rates of Fe3O4 nanocrystals with various sizes. Higher efficiency of SLR at the surface may be due to the stronger spin-orbit coupling at the surface relative to the interior region. In addition to magnetization dynamics studies, the effect of oxidation on static FR in iron oxide nanocrystals (between Fe3O4 and y-Fe2O3) was studied. The results indicated FR signal is linearly correlated to the strength of optical transition between Fe2 and Fe3 in Fe3O4 for a given size of nanocrystals.

The costal populations of perch (Perca fluviatilis) in some parts of the Baltic Sea have been in decline for about two decades. Recruitment failure in the early larval stages has been put forward as a possible cause and the decline has also been suggested to coincide with increases in three-pined stickleback (Gasterosteus aculeatus) densities. The aim of this study was to study the effects of growth and survival of newly hatched perch larvae in the presence of the three-pined stickleback, and if possible determine the main mechanism behind any negative effects the perch may suffer under such conditions. Using large scale experimental ponds as a controlled habitat, an experiment was conducted where perch larvae were being exposed to sticklebacks under four different stages of their development. Results showed that the three- spine stickleback can have a strong negative effect on the survival of young perch. This effect was strongest in the earliest stage of perch development and decreased as they grew bigger. The zooplankton densities didn't differ between the controls and stickleback treatments, suggesting that the young perch didn't suffer from food limitation. Instead predation was identified as the main mechanism behind the high mortality. The results of this study highlight the potential danger of the observed patterns of decreasing predator populations in conjunction with increasing populations of smaller prey species in the Baltic Sea.

Explaining the work-hardening behavior of crystalline materials and the size dependent plasticity has been a long lasting problem. Plastic deformation mainly arises from the collective motion of dislocations. Although individual dislocation processes are well studied, the study of the overall effects of these processes was challenging before the emergence of computer modeling. Of the computer simulation techniques, discrete dislocation dynamics (DDD) is the most suitable method to model thin films at the micron scale and below. This method allows us to study the quantitative effects of certain mechanisms. / Engineering and Applied Sciences

Gap dynamics theory proposes that forest canopy gaps provide the high light levels needed for regeneration. Little attention has been given to more gradual alternatives; however, recent studies have demonstrated declines in within-crown leaf area index with tree size in temperate forest trees. Our project builds on this previous research by assessing the prevalence of this age-related crown thinning phenomenon. We quantified crown openness for 18 dominant tree species in temperate and tropical forests (n = 1786 trees). Separate pooled groupings of tropical and temperate species showed significantly positive relationships between openness and DBH (p<0.001). Of the 9 sampled species showing positive relationships, significance (p< 0.05) was detected in 3 out of 10 tropical species and 1 out of 8 temperate species. Two temperate species showed significantly reduced canopy openness with size. These trends highlight the role that very large trees play in influencing light availability for understorey regeneration.

Gap dynamics theory proposes that forest canopy gaps provide the high light levels needed for regeneration. Little attention has been given to more gradual alternatives; however, recent studies have demonstrated declines in within-crown leaf area index with tree size in temperate forest trees. Our project builds on this previous research by assessing the prevalence of this age-related crown thinning phenomenon. We quantified crown openness for 18 dominant tree species in temperate and tropical forests (n = 1786 trees). Separate pooled groupings of tropical and temperate species showed significantly positive relationships between openness and DBH (p<0.001). Of the 9 sampled species showing positive relationships, significance (p< 0.05) was detected in 3 out of 10 tropical species and 1 out of 8 temperate species. Two temperate species showed significantly reduced canopy openness with size. These trends highlight the role that very large trees play in influencing light availability for understorey regeneration.

abstract: Palladium metal in its various forms has been heavily studied for many catalytic, hydrogen storage and sensing applications and as an electrocatalyst in fuel cells. A short review on various applications of palladium and the mechanism of Pd nanoparticles synthesis will be discussed in chapter 1. Size dependent properties of various metal nanoparticles and a thermodynamic theory proposed by Plieth to predict size dependent redox properties of metal nanoparticles will also be discussed in chapter 1. To evaluate size dependent stability of metal nanoparticles using electrochemical techniques in aqueous media, a synthetic route was designed to produce water soluble Pd nanoparticles. Also, a purification technique was developed to obtain monodisperse metal nanoparticles to study size dependent stability using electrochemical methods. Chapter 2 will describe in detail the synthesis, characterization and size dependent anodic dissolution studies of water soluble palladium nanoparticles. The cost associated with using expensive metal catalysts can further decreased by using the underpotential deposition (UPD) technique, in which one metal is electrodeposited in monolayer or submonolayer form on a different metal substrate. Electrochemically, this process can be detected by the presence of a deposition peak positive to the bulk deposition potential in a cyclic voltammetry (CV) experiment. The difference between the bulk deposition potential and underpotential deposition peak (i.e. the UPD shift), which is a measure of the energetics of the monolayer deposition step, depends on the work function difference between the metal pairs. Chapter 3 will explore how metal nanoparticles of different sizes will change the energetics of the UPD phenomenon, using the UPD of Cu on palladium nanoparticles as an example. It will be shown that the UPD shift depends on the size of the nanoparticle substrate in a way that is understandable based on the Plieth model. High electrocatalytic activity of palladium towards ethanol oxidation in an alkaline medium makes it an ideal candidate for the anode electrocatalyst in direct ethanol based fuel cells (DEFCs). Chapter 4 will explore the poisoning of the catalytic activity of palladium in the presence of halide impurities, often used in synthesis of palladium nanoparticles as precursors or shape directing agents. / Dissertation/Thesis / Doctoral Dissertation Chemistry 2016

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第19198号 / 農博第2137号 / 新制||農||1034(附属図書館) / 学位論文||H27||N4944(農学部図書室) / 32190 / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 北山 兼弘, 教授 北島 宣, 教授 神﨑 護 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

Materials with length scales in the nanometer regime demonstrate properties that are remarkably different from analogous bulk matter. As a result, researchers are striving to catalog the changes in properties that occur with decreasing size, and more importantly, understand the reason behind novel nanomaterial properties. By learning the true nature of nanomaterials, scientists and engineers can design better materials for a variety of applications. Inert gas-phase condensation synthesis of metal oxide nanoparticles was used to develop materials to explore the optical and chemical properties of metal oxide nanoparticles. One potential application for nanomaterials is use in optical applications. The possibility of interparticle energy transfer was investigated for lanthanide-doped yttrium oxide nanoparticles using laser spectroscopy. Experimental evidence collected with this study indicates that interparticle, lanthanide-mediated energy transfer may have been observed. In addition, lanthanide-doped gadolinium oxide nanoparticles were synthesized and investigated with optical spectroscopy to identify the best potential candidates for bioanalytical applications of this material. The influence of particle annealing and dopant concentration were also studied. Nanoparticle film structure was investigated with scanning electron microscopy. Two different film structures composed of oxide nanoparticles were found to grow under different synthesis conditions. The film structure was found to be determined by the degree of particle aggregation in the gas phase during synthesis. Aggregation of the particles was found to be controlled by a combination of gas pressure and properties. Chemical properties of metal oxide nanoparticles also are very important. Reflection-absorption Infrared Spectroscopy and vacuum surface analytical techniques were used to explore the chemistry of the chemical warfare agent dimethyl methylphosphonate (DMMP) on yttrium oxide as well as other metal oxide nanoparticles. DMMP was found to dissociate at room temperature on several types of metal oxide nanoparticles. Hydroxyl groups were found to be critical for the adsorption of DMMP onto the particles. Finally, the reactivity of the nanoparticles was found to increase with decreasing particle size. This was attributed to a relative increase in the number of high-energy surface defects for the smaller particles. / Ph. D.

Monoecy, the production of distinct male and female flowers on the same plant, is an important, though little studied, sexual strategy in the rainforest understory. This study of a monoecious plant discovered a cue to induce flowering, explored the interplay of gender constraint vs. plasticity in a natural population, and tested possible causes of gender in two laboratory experiments. An experiment in the lab found that reduced photoperiod for three weeks is an unambiguous cue for flowering. The remarkably long inductive period is followed by a long and variable period of floral initiation. This results in only partial synchronization of flowering among plants in a patch, which enhances mating opportunities in this protandrous plant. Inflorescence architecture is highly constrained, and ideally produces a phenotypic gender (proportion female) of about 0.5. However, in the forest at Las Cruces, Costa Rica, most plants were less female than predicted, mostly through abortion of female buds. Plants showed gender plasticity between and within years. Large plants produced more flowers and were more female in gender, and less variable in gender, than small plants. Reproduction was poorly correlated with environmental resource availability, measured as canopy openness, soil moisture, pH, and soil phosphorus, ammonium and nitrate. Phenotypic selection analysis on seed production suggests an optimal gender of 50-60% female, yet plasticity to be less female than this optimum, and in particular to express only male function, has been maintained. In a factorial experiment in the lab, high light or high nitrogen caused plants to produce more flowers and to be proportionally more female, and larger in weight, than low light or nitrogen. The effects of light and nitrogen on reproduction, plant size, and leaf greenness suggest an energy based determination of gender. Gender may be mostly influenced by plant size, but sometimes also opportunistically by environment. Inoculation with mycorrhizas caused plants to be less female in gender, and smaller in weight, than plants that were not inoculated. This suggests a net cost of mycorrhizas under experimental conditions, and supports the emerging view of the mycorrhizal symbiosis as not necessarily mutualistic under all circumstances.