Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 173-177).

Th.--Sci. phys.--Toulouse--I.N.P., 1985. N°: 100.

Th. Univ.--Chimie physique--Paris 6, 1989. / Résumé en anglais. Notes bibliogr.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 182-184).

Th. doct.-ing.--Phys. des mater.--Nancy--I.N.P.L., 1980.

Crystallization is an increasingly important process in a variety of applications from drug development to single crystal X-ray diffraction structure determination. However, while there is a good deal of research into prediction of molecular crystal structure, the factors that cause a molecule to be crystallizable have so far remained poorly understood. The aim of this project was to answer the seemingly straightforward question: can we predict how easily a molecule will crystallize? The Cambridge Structural Database contains almost a million examples of materials from the scientific literature that have crystallized. Models for the prediction of crystallization propensity of organic molecular materials were developed by training machine learning algorithms on carefully curated sets of molecules which are either observed or not observed to crystallize, extracted from a database of commercially available molecules. The models were validated computationally and experimentally, while feature extraction methods and high resolution powder diffraction studies were used to understand the molecular and structural features that determine the ease of crystallization. This led to the development of a new molecular descriptor which encodes information about the conformational flexibility of a molecule. The best models gave error rates of less than 5% for both cross-validation data and previously-unseen test data, demonstrating that crystallization propensity can be predicted with a high degree of accuracy. Molecular size, flexibility and nitrogen atom environments were found to be the most influential factors in determining the ease of crystallization, while microstructural features determined by powder diffraction showed almost no correlation with the model predictions. Further predictions on co-crystals show scope for extending the methodology to other relevant applications.

abstract: Many species e.g. sea urchin form amorphous calcium carbonate (ACC) precursor phases that subsequently transform into crystalline CaCO3. It is certainly possible that the biogenic ACC might have more than 10 wt% Mg and ∼ 3 wt% of water. The structure of ACC and the mechanisms by which it transforms to crystalline phase are still poorly understood. In this dissertation our goal is to determine an atomic structure model that is consistent with diffraction and IR measurements of ACC. For this purpose a calcite supercell with 24 formula units, containing 120 atoms, was constructed. Various configurations with substitution of Ca by 6 Mg ions (6 wt.%) and insertion of 3-5 H2O molecules (2.25-3.75 wt.%) in the interstitial positions of the supercell, were relaxed using a robust density function code VASP. The most noticeable effects were the tilts of CO3 groups and the distortion of Ca sub-lattice, especially in the hydrated case. The distributions of Ca-Ca nearest neighbor distance and CO3 tilts were extracted from various configurations. The same methods were also applied to aragonite. Sampling from the calculated distortion distributions, we built models for amorphous calcite/aragonite of size ∼ 1700 nm3 based on a multi-scale modeling scheme. We used these models to generate diffraction patterns and profiles with our diffraction code. We found that the induced distortions were not enough to generate a diffraction profile typical of an amorphous material. We then studied the diffraction profiles from several nano-crystallites as recent studies suggest that ACC might be a random array of nanocryatallites. It was found that the generated diffraction profile from a nano-crystallite of size ∼ 2 nm3 is similar to that from the ACC. / Dissertation/Thesis / Ph.D. Physics 2012

Doctor of Philosophy / Department of Grain Science and Industry / Yong Cheng Shi / Wheat bran is a by-product of the wheat flour milling industry. The number of food products containing wheat bran is on the rise because it is a well-recognized good source of dietary fiber. Currently, bran is a low-value commodity used mostly in animal feed, but it has the potential for more extensive applications. To understand the functional and nutritional properties of wheat bran and better use wheat bran in food, it is critical to understand the physical structure of wheat bran. For the first time, solid-state ¹³C cross-polarization magic-angle spinning nuclear magnetic resonance (¹³C CP/MAS NMR), X-ray diffraction (XRD), and small angle X-ray scattering (SAXS) were used to study the physical structure of wheat bran and its dissected layers. The XRD and Solid-State ¹³C CP/MAS NMR both confirmed the presence of crystalline cellulose in untreated bran, enzymatically treated bran, and dissected bran layers. Destarched and deproteinized wheat bran (DSDPB) was treated with a mixture of either 7 or 9% sodium hydroxide and 12% urea solvent and structure of the extracted polymers was investigated. Three and 6 cycle dissolution schemes, were examined involving the repeated cooling of the solvent bran mixture to -12.6 °C and then agitating it at 25 °C. When 7% NaOH/12% urea (6 cycle) was applied to DSDPB, 84.1% of the material was solubilized including 89.8% of the arabinoxylans (AX). This procedure recovered more wheat bran AX for characterization than any previous study using alkaline dissolution. Wheat bran was enzymatically and hydrothermally treated to maximize the soluble fraction. Unlike previous research, the starch and protein were kept and not removed before endoxylanase treatment. The retained protein and glucose polymers (starch, β-glucan, cellulose) could provide functional benefits in addition to the arabinoxylan and could make the process more economical. Wheat bran hydrolyzed with thermostable α-amylase, protease, and xylanase was the recommended treatment. The combined solubles had a viscosity of 23 cP (10% w/w solids) and ranged in estimated molecular weight from ~600 to 20,000. The percentage of untreated wheat bran AX that was solubilized was 50% and the percentage of AX in the solubles was 23%.

The aim of this project is to fabricate highly efficient grating couplers in thin-film silicon-on-insulator (SOI) wafers, which have a silicon (Si) thickness of the order of 1 mum. These thin-film waveguides allow the development of higher speed Si optical modulators, sensors and vertical surface coupling for Si light emitting diodes (LEDs), Hence, SOI rectangular and blazed grating couplers were fabricated where the buried oxide layer in SOI was designed as a reflective layer. The former gratings were fabricated by electron beam lithography followed by reactive ion etching, while the latter gratings were fabricated by angled argon ion beam etching. Both types of grating were designed at the diffraction order of -1, for a wavelength of 1.3 mum. The fabricated rectangular gratings have grating heights of 0.14, 0.23, 0.30 and 0.44 mum and a pitch of 0.40 mum whereas the sawtooth blazed gratings have a grating depth of 0.08 mum and a period of 0.38 mum To our knowledge, no Si blazed gratings with a pitch of less than 500 nm have been fabricated before. The SOI rectangular grating couplers yield a maximum output efficiency of 71 +/- 5 % towards the superstrate, while the blazed grating couplers produce an output efficiency of 84 +/- 5 % towards the substrate. These experimental output efficiencies are the highest yet reported in SOI for each grating profile, respectively. In addition, an optical loss of 0.15 +/- 0.05 dB/cm of Unibond SOI was measured for the first time. Furthermore, the experimental output efficiencies of the grating couplers with various grating heights were found to be consistent with perturbation theory. Thus, our aim of designing and fabricating an highly efficient thin film SOI waveguide grating coupler has been achieved. These grating couplers may enhance the applications of integrated optics in Si, and may allow the development of devices such as those mentioned above.

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