Buoyancy-induced, columnar vortices (dust devils) that are driven by thermal instabilities of ground-heated, stratified air in areas with sufficient insolation convert the potential energy of low-grade heat in the near-surface air layers into a vortex flow with significant kinetic energy. A variant of the naturally-occurring vortex is deliberately triggered and anchored within an azimuthal array of vertical, stator-like flow vanes that form an open-top enclosure and impart tangential momentum to the radially entrained air. The induced flow within the enclosure may be ultimately exploited for power generation by coupling the vortex to a vertical-axis turbine. The fundamental mechanisms associated with the formation, evolution, and dynamics of an anchored, buoyancy-driven columnar vortex that is formed within such an enclosure over a heated ground plane are investigated in laboratory experiments. Specific emphasis is placed on the dependence of the vortex cellular structure and vorticity production and sustainment mechanisms on the thermal resources and the magnitude and direction of the entrained flow that is regulated by the flow vanes. Manipulation of vorticity concentrations and advection are exploited in order to modify and optimize the available mechanical energy within the induced flow field and, therefore, the extractable power. Finally, anchored vortices are formed in the natural environment within a scaled field prototype of the flow enclosure using only insolation as the source of buoyancy. These field tests demonstrated formation and sustainment of energetic columnar vortices that enable potential thermomechanical link for tapping the gravitational potential energy of the unstable air layers for power generation.

There are relatively few annually resolved climate proxies in arid and semi-arid regions. Columnar cactuses are common in these regions and the stable isotopes of carbon and oxygen in durable spines record variations in rainfall, humidity and ecophysiology as they grow in series along the sides of cactuses. Despite their spines, columnar cactuses provide important ecosystem resources and services in drought prone areas, however, the impact that long-term climate variability and infrequent storms (El Niño or tropical storms) have on the ecology and ecophysiology of columnar cactus is less clear. Stable isotopes in trees and corals serve as useful proxies of climate and ecophysiological information, but for cactus we lack the most rudimentary information about the isotopic systems and their links to the environment. Here, we present an isotopic framework that begins with developing semi-empirical mechanistic models of δ¹³C, δ¹⁸O and δ²H variation in saguaro cactuses that link physical and physiological fractionation factors in stem water and spines to rainfall and humidity. We also review a novel method for determining the age of spines, an important step in developing useful chronologies of isotopic variation in spines. The mechanistic models combined with local climate records enhance our understanding of isotopic variation in daily and annually dated spine δ¹³C and δ¹⁸O records and explain the statistical association of δ¹³C and δ¹⁸O in spines with rainfall, vapor pressure deficit, and El Niño enhanced winter rains. While there are still some challenges to overcome, we expect that isotopic spine series will be used as climate proxies to answer questions regarding regional climate variability or to enhance current models of past and future climates. Likewise, ecophysiologists can use the isotopic spine series in conjunction with gas exchange or carbohydrate studies to look at reproductive or biological responses to changing environments.

No description available.

Liquid crystalline materials forming columnar mesophases are of importance for both the fundamental research and technological applications due to their supramolecular architecture allowing for one-dimensional charge transport. The potential applications of these materials include light emitting diodes, solar cells, field effect transistors and photovoltaic cells. However, to design a LC material suitable for a particular application, a fundamental understanding of the structure-property relationships is needed. In the present thesis, a variety of systems forming columnar mesophases have been explored. They include small molecular weight compounds (triphenylene, phthalocyanine derivatives and star-shaped mesogens) and polymer materials. The research was focused on the study of the influence of the molecular architecture and specific interactions such as hydrogen bonding on the supramolecular organization in the mesophase, as well as on the influence of columnar mesophase on crystal growth. The main results of the thesis are summarized below. The influence of hydrogen bonding on the structure and charge carrier mobility was investigated for a triphenylene derivative, hexaazatriphenylene, having lateral alkyl chains linked to the core via amide groups. These linking groups provide the possibility to form inter- and intra-molecular hydrogen bonds. Acting as “clamps”, the inter-molecular hydrogen bonds are found to enforce the attractive interactions between the molecules in the column. Thus, the columnar mesophase formed by this system is characterized by the smallest inter-disk distance ever found in columnar mesophases (3.18 Å). The improved intra-columnar order brings about a higher charge carrier mobility (0.02 cm2/Vs) as compared to other triphenylene derivatives without hydrogen bonds. Phthalocyanine derivatives, which are liquid crystalline at ambient temperature, could be suitable for opto-electronic applications due to their improved processibility and self-healing of structural defects. Our interest in these systems was inspired by the fact that, in spite of numerous studies performed to date, only very a few phthalocyanine derivatives were found to exhibit columnar mesophases at ambient temperature. We observed that by introducing branches in alkyl chains close to the core, we were able to render the material LC at ambient temperature. Analysis of X-ray diffraction patterns measured on oriented samples showed that these systems form hexagonal and rectangular ordered columnar mesophases. This finding is in contradiction with the general view stating that non-hexagonal mesophases can be only disordered. Since the absolute majority of applications require fabrication of films, it was very important to achieve the visualization of the organization of the phthalocyanine derivatives at the nanometer scale. AFM images on thick spin-coated films with columnar resolution are presented for the first time. They allowed the examination of columnar curvatures and breaks at the boundaries between different single crystal-like domains. The possibility of templating columnar crystal growth was studied for a star-shaped mesogen using a combination of direct- and reciprocal-space techniques. AFM images with columnar resolution showed that the crystal growth initiated in the monotropic columnar mesophase occurs almost in register with the mesomorphic template. In the final crystalline structure, the placement of the crystalline columns is controlled by the mesomorphic tracks at the scale of an individual column, i.e. at the scale of approximately 3.5 nm. The mesophase-assisted crystallization was also studied for the case of a polymer material forming columnar mesophase, poly(di-n-propylsiloxane). X-ray diffraction on oriented fibers allowed us to correct the previous indexation and solve the structure of the unit cell. The crystallization process was studied on samples crystallized in different conditions. It was found that, depending on crystallization conditions, both folded-chain and extended-chain crystals can be obtained. Thus, crystallization of the material from the mesophase results in the formation of 100-150nm thick crystals, which corresponds to a nearly extended-chain conformation. By contrast, when crystallized from a dilute solution, folded-chain crystals result. The mechanisms of chain unfolding was studied by variable temperature atomic force microscopy on PDPS single crystals. It was found that crystals rapidly thicken above the initial melting point, up to 80 nm.

A new class of scintillation detector has emerged that combines columnar scintillators and CCD/CMOS sensors for high-resolution imaging. Originally developed for single-photon gamma-ray imaging, these detectors provide better than an order-of-magnitude improvement in spatial resolution compared to conventional photomultiplier tube (PMT)-based gamma cameras; sub-100 micron detector resolutions have been achieved. This work reviews the several detector configurations developed in recent years, with a specific emphasis on a type of CCD/CMOS detector developed at the Center for Gamma-Ray Imaging, which we call BazookaSPECT, that amplifies scintillation light using an image intensifier to achieve both high spatial resolution and high event-rate capability.Ongoing research into scintillator deposition techniques has led to a new form of scintillation material where crystallites are organized into columns. Similar to optical fibers, this columnar structure helps to channels scintillation light towards an exit face while restricting lateral light spread. However, because they are not perfect optical fibers, light spreads laterally and is absorbed by an amount relating to the interaction depth. Taking advantage of this phenomenon, we discuss the use of maximum-likelihood methods to estimate the 3D position and energy of gamma-ray interactions in columnar CsI(Tl)/EMCCD-based detectors.Finally, we present new imaging applications that have arisen from BazookaSPECT. These include the the development of a gamma-ray microscope using micro-coded apertures, feasibility studies for photon-counting digital mammography and eventually X-ray CT, and FastSPECT III -- a third generation small animal stationary SPECT imager. FastSPECT III system design, fabrication methods, data acquisition system, system calibration procedure, and initial tomographic reconstructions are presented.

In the field of metal casting, solute composition inhomogeneities at the macroscale are called macrosegregation, and the transition from the elongated grains in the outer portions of a casting to the more rounded grains in the center is termed Columnar to Equiaxed Transition (CET). Simultaneous prediction of macrosegregation and CET is still an important challenge in the field. One of the open questions is the role of melt convection on the CET and the effect of the CET on macrosegregation. A three-phase macroscale model for macrosegregation and CET was developed. The model accounts for numerous phenomena such as columnar dendrite tip undercooling, undercooling behind the columnar tips, and nucleation of equiaxed grains. This three-phase model was used to develop a less complex model that consists of two phases only and disregards undercooling behind the columnar tips and nucleation of equiaxed grains. An in-house parallel computing code on the OpenFOAM platform was developed to solve the equations of these models. The models were used to perform columnar solidification simulations of a numerical benchmark problem. It was found that the predictions of these models are nearly identical. It was also found that the dendrite tip selection parameter, which appears in the constitutive relation for the dendrite tip velocity, plays a key role in these models. With a realistic value for this parameter these models account for columnar dendrite tip undercooling, but as its value is increased in the simulations, predictions of these models converge to predictions of a model that neglects undercooling. Next, the three-phase model was used to perform CET simulations in the numerical solidification benchmark problem in the presence of melt convection. It was found that accounting for stationary equiaxed grains does not change the overall macrosegregation pattern nor the form of channel segregates. Finally, for the first time in the field of solidification, we developed accurate constitutive relations for macroscale solidification models that are based on a formal mesoscale analysis on the scale of a representative elementary volume that is used in developing volume-averaged macroscale models. This upscaling enabled us to present relations that incorporate changes in the shape of grains and solute diffusion conditions around them during growth. The models and constitutive relations we developed can now be used to predict critical phenomena such as macrosegregation, channel segregates, and CET in castings.

Discotic liquid crystals (DLCs), which consist of disc-like molecules, are known to be able to form nematic and columnar mesophases through self-assembly. Because of the high electric charge mobility in one-dimension, DLCs are found to have uses in making electronic and photonic devices, such as organic light emitting diode, photovoltaic and molecular wires. In order to achieve better performance of these applications, it is essential to obtain the desired alignment of the DLCs. The purpose of this study is to investigate the stacking of disk-like molecules and to control their alignment. The materials used in the present studies are HDBP-8 and LC10. In this thesis, we will show that the stack of disk-like molecules is strongly influenced by temperature. We will also discuss how the molecules stacking is influenced by surface free energy. The disk-like molecules tend to stack with face-on when the surface free energy of the substrates is high. On a surface with lower surface free energy, molecules tend to stack with edge-up. In the latter part of the research, substrates are specially treated to have different surface free energies, and molecular stack on these substrates is observed.

The polyglutamate which grafts with flexible alkyl side-chain by ester exchange reaction is like rod-hairy molecule. The numbers of methylene group of side-chain and the graft-density affect the molecular packing of poly(gama-alkyl-L-glutamate)s. To be sure the correct chemical structure of poly(gama-alkyl-L-glutamate)s by Fourier transform infrared spectrometer (FTIR), and find out the graft-density of each sample by proton nuclear resonance spectrometer (1H-NMR). Phase behavior of poly(gama-alkyl-L-glutamate)s were studied via differential scanning calorimetry (DSC) and variable temperature x-ray diffraction (XRD).We combine the results from C. C. Hsu(24). When the side-chain length is long enough (m>10), side-chains will crystallize into a 3D hexagonal lattice. The results of DSC and XRD analyses show that the side-chain crystalline phase will melt at Tm1, where as a liquid crystalline (LC) phase transition exists at Tm2. Poly(gama-alkyl-L-glutamate)s with shorter side-chain (m<8) tend to form 2D hexagonal LC structure. On the other hand, longer side-chains (m>10) tend to give lamellar structure. The critical number of methylene group of side-chain between hexagonal and lamellar structure is between 8 and 10.

京都大学 / 新制・課程博士 / 博士(医学) / 甲第23374号 / 医博第4743号 / 新制||医||1051(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 藤田 恭之, 教授 椛島 健治, 教授 斎藤 通紀 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

The results from this study, on a few commercial and model metastable beta titanium alloys, indicate that the growth restriction factor (GRF) model fails to interpret the grain growth behavior in the additively manufactured alloys. In lieu of this, an approach based on the classical nucleation theory of solidification incorporating the freezing range has been proposed for the first time to rationalize the experimental observations. Beta titanium alloys with a larger solidification range (liquidus minus solidus temperature) exhibited a more equiaxed grain morphology, while those with smaller solidification ranges exhibited columnar grains. Subsequently, the printability of two candidate beta titanium alloys containing eutectoid elements (Fe) that are prone to beta fleck in conventional casting, i.e., Ti-1Al-8V-5Fe (wt%) or Ti-185, and Ti-10V-2Fe-3Al (wt%) or Ti-10-2-3, is further investigated via two different AM processing routes. These alloys are used for high-strength applications in the aerospace industry, such as landing gears and fasteners. The Laser Engineered Net Shaping and Selective Laser Melting (the two AM techniques) results show that locally higher solidification rates in AM can prevent the problem of beta fleck and potentially produce β-titanium alloys with significantly enhanced mechanical properties over conventionally cast/forged counterparts. Further, the detailed investigation of microstructure-mechanical property relationships indicates that the precipitation or formation of non-equilibrium secondary phases like α or ω in these commercial systems can be advantageous to the mechanical properties. The influence of process parameters on the evolution of such secondary phases within the β matrix grains has also been rationalized using a FEM-based multi-physics thermo-kinetic model that predicts the multiple heating-cooling cycles experienced by the layers during the LENS deposition. Overall, the results indicate that Ti-1-8-5 and Ti-10-2-3 are promising β-Ti alloys for AM processing. Further, the results also demonstrate the ability to tune the microstructure (secondary phase precipitation and grain size) via changes in the process parameters to achieve desirable mechanical properties, obviating the need for any secondary post-processing. The understanding obtained through this work can be coupled with the concept of β-phase stability prediction, via parameters like bond order (Bo), the energy level of metal d-orbital (Md), Mo equivalency, etc., to design novel beta titanium alloys with the desired microstructures tailored via AM for structural applications.