Thesis (Ph.D.)--University of the Witwatersrand, Faculty of Science, 2013.

在近期的研究結果中, 相分離被發現發生在具非晶結構的Pd₄₁.₂₅Ni₄₁.₂₅P₁₇.₅合金，而該合金的構成元素之間的有負值的混合焓。通過高分辨率透射電子顯微鏡的直接成像的方法，他們為Pd-Ni-P非晶系統相分離的發生提供了證據。 / 在這篇論文所論述的研究工作中，我們運用類似的技術來研究Pḍ₄₀₊₀₅{U+2093}Nị₄₀₊₀₅{U+2093}P₂₀₋{U+2093}的合金系統從 x = 0到3.5的非晶相分離。 / 實驗結果顯示，任何在空氣中冷卻到578 K再在613K退火一小時的樣品 (乙類樣本)，非晶相分離都沒有發生。然而，在613K退火一小時而沒有經過578K和613K溫度範圍的Pḍ₄₀₊₀₅{U+2093}Nị₄₀₊₀₅{U+2093}P₂₀₋{U+2093}大塊非晶金屬(丙類樣本)，卻在部分成分範圍中發生相分離。在丙類樣本中，當x>1，相分離發生；而當x≤1，相分離沒有發生。通過量度高角環形暗場影像中顯示的兩個相的平均波長，我們可得出其統計結果，而該統計結果與槓桿規則吻合。從此可見，在過冷的Pd-Ni-P熔合合金中存在著亞穩液態混溶間隙。並且這種出現在有負值混合焓的系統的亞穩液態混溶間隙，可以以短程有序的模型來解釋。 / Recently, the phase separation was found in the system of amorphous Pd₄₁.₂₅Ni₄₁.₂₅P₁₇.₅ alloys which has negative heat of mixing among the constituent elements. In their work, the directly imaging method by technique of high resolution TEM provided the evidence of phase separation in amorphous Pd-Ni-P system. / In this work, by applying the similar technique of that previous studies, the alloy systems of Pḍ₄₀₊₀₅{U+2093}Nị₄₀₊₀₅{U+2093}P₂₀₋{U+2093} for x = 0 to 3.5were studied for amorphous phase separation. / The experimental result showed that for any sample which was allowed to cool down in air to 578 K before thermal annealing (B-type), there was no amorphous phase separation. But for the Pḍ₄₀₊₀₅{U+2093}Nị₄₀₊₀₅{U+2093}P₂₀₋{U+2093} BMG that was annealed at 613K for one hour without bypassing the temperature range between 578K and 613K (C-type), phase separation occurred with x>1 but absented when x≤1. The result of average wavelength measurement of the two phases in the HAADF images of the sample with phase separation obeyed the lever rule. This result suggested that in undercooled molten Pd-Ni-P alloys, there is a metastable liquid state miscibility gap. The formation of such miscibility gap in a system with negative heat of mixing can be explained by the model of unique short range orders. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Lau, Man Tat = 過冷鈀、鎳、磷熔化物中的亞穩液態互溶間隙 / 劉文達. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references. / Abstracts also in Chinese. / Lau, Man Tat = Guo leng ba, nie, lin rong hua wu zhong de ya wen ye tai hu rong jian xi / Liu Wenda. / Abstract --- p.i / Acknowledgement --- p.iv / List of Tables --- p.vii / List of Figures --- p.viii / Chapter Chapter 1 --- : Introduction --- p.1 / Chapter 1.1 --- Amorphous metal --- p.1 / Chapter 1.2 --- Phase Separation --- p.3 / Chapter 1.3 --- Nucleation --- p.6 / Chapter 1.4 --- Spinodal Decomposition --- p.10 / Chapter 1.5 --- Objective of the project --- p.16 / Figures --- p.18 / References --- p.26 / Chapter Chapter 2 --- : Experiment --- p.27 / Chapter 2.1 --- Preparation of sample --- p.27 / Chapter 2.2 --- Differential scanning calorimetry --- p.30 / Chapter 2.3 --- Preparation of TEM sample --- p.31 / Chapter 2.4 --- Microstructural analysis --- p.33 / Figures --- p.36 / References --- p.39 / Chapter Chapter 3 --- : A metastable liquid state miscibility gap in undercooled Pd-Ni-P melts --- p.40 / Chapter 3.1 --- Introduction --- p.40 / Chapter 3.2 --- Materials and experimental --- p.41 / Chapter 3.3 --- Results --- p.44 / Chapter 3.4 --- Discussions --- p.49 / Chapter 3.5 --- Conclusions --- p.52 / Table --- p.53 / Figures --- p.54 / References --- p.75

Thesis. 1976. Ph.D.--Massachusetts Institute of Technology. Dept of Physics. / Microfiche copy available in Archives and Science. / Includes bibliographical references. / Ph.D.

Differential scanning calorimetry (DSC) melting analysis was performed on 27 short double stranded DNA duplexes containing 15 to 25 base pairs and short single stranded overhangs from one to 10 bases, on both ends. Molecules have two 5' dangling ends or one 5' and one 3' dangling end. For these molecules the duplex region was incrementally reduced from 25 to 15 base pairs with increased length of the dangling ends from one to 10 bases. A third set of molecules contained 21 base pair duplexes with a four base dangling end on either the 5' or 3' end. Blunt ended duplexes from 15 to 25 base pairs were also examined and served as control duplexes. DSC melting curves were measured in solution containing 85 mM, 300 mM or 1.0 M Na+. From these measurements, thermodynamic parameters for 5' and 3' dangling ends as a function of end length were evaluated. Results showed the 5' ends were slightly stabilizing, and this stability was essentially constant with end length, while the 3' ends were generally destabilizing with increasing length of the end. This finding of lower stability for the 3' ends is consistent with results of published studies that have found 5' dangling ends to be more than or equally as stabilizing as 3' dangling ends. Our finding that 3' dangling ends are actually destabilizing for duplex DNA contrasts with published results. The 3' ends also display a stronger dependence on the [Na+]. In the lower Na+ environment the 3' ends are more destabilizing than at the higher salt environments. Analysis of the thermodynamic parameters of the dangling-ended duplexes as a function [Na+] indicated the 3' dangling end molecules behave differently compared to 5' dangling ended and blunt ended duplexes. The net counterion release per phosphate upon melting the molecules having one 5' and one 3' end was approximately 15% smaller as a function of end length compared to the duplex having two 5' ends. Further analysis of the DSC evaluated thermodynamic transition parameter, ΔHcal, and its relationship to the measured transition temperatures of the DNA molecules, provided an estimate on the excess heat capacity differences, ΔCp, between duplex and melted single strands for the dangling-ended molecules. The analysis revealed the molecules with one 5' and one 3' dangling end had very different ΔCp values compared to the blunt-ended molecule; while the molecules with two 5' ends have ΔCp that are essentially the same as the blunt-ended duplex. These observations are interpreted as differences in the interactions with Na+, solvent and the terminal base pairs of the duplex for the 5' versus 3' dangling ends.

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This thesis examines the underlying physics that gives rise to the Hawking and Unruh effects. The Rindler coordinate system is constructed from a physical argument that shows how an observer would actually go about building such a coordinate system out of scaffolding and clocks. Quantum theory is discussed in detail with particular relevance to quantum entanglement as this is an important issue relating to information loss in black holes. The thesis demonstrates the general impossibility of utilising quantum entanglement to transmit information faster than light. Bell's theorem is also reviewed from the perspective of anti-correlated spin-half particles. This theorem shows the impossibility of describing nature by a local hidden variable theory, and hence emphasises the importance of the topic of information loss in black holes as a bridge between general relativity and quantum theory. The Unruh effect is a purely quantum field theoretic effect that displays considerable mathematical similarities to the Hawking effect. The effects are nevertheless quite dissimilar in some respects and this thesis examines some of these differences. The other aim of the thesis is to discuss the possible loss of information in a black hole. The Hawking effect raises the possibility that a black hole may evaporate and potentially disappear completely. This raises a significant problem related to how the information that entered the black hole may escape, if at all. If information cannot escape the black hole then this implies a violation of one of the principles of quantum mechanics: a pure quantum state cannot undergo unitary evolution to become a thermal distribution of radiation but this is what the Hawking effect essentially predicts. These two conclusions are new and are important contributions to the understanding of the coupling between gravity and quantum theory. The thesis also looks at a number of subsidiary topics to do with the underlying physics of these effects along the way, always with an emphasis on the physical. In particular, the method for quantizing a field is developed in a physical manner by examining the continuum limit of a quantized discretely modelled string. Two other topics within the thesis that are of interest are a demonstration of the coordinate independence of the Euler-Lagrange equations and a heuristic method of 'deriving' the Lorentz transformation equations that is presented in an appendix. These two presentations are new and have not appeared elsewhere to my knowledge. / Doctor of Philosophy (PhD) (Science)

Quantum mechanics (QM) calculations, coupled with statistical mechanics (SM), provide a means to obtain thermophysical properties from first principles. Because of the limitations in modern computational resources, many of these properties are obtained for isolated molecules. Despite this limitation, QM is still very useful for thermophysical property generation in an ideal gas reference state where the molecules are isolated. In this thesis, a combination of quantum mechanics and statistical mechanics calculations is used to generate entropies of aromatic compounds in the ideal gas reference state. This information is necessary for practical calculations such as the determination of the free energy of a reaction involving these compounds and the equilibrium distribution between isomers. The QM and SM calculation procedure is used to generate entropies of simple aromatic compounds—benzene, toluene, p-xylene, m-xylene and o-xylene— in the ideal gas state from 250 K to 540 K. Having accurate experimental frequencies and entropies for these compounds from literature, we systematically examine how the choice of the QM level of theory impacts the agreement between theory and experiment. The calculated entropies fall within 0.5% of experimentally determined values for these compounds. We acknowledge that given the state of the art of computational quantum mechanics today, all levels of theory require an empirical scaling factor for vibrational frequencies. This empirical scaling factor largely eliminates the advantage in accuracy of more sophisticated levels of theory. Thus we see that our “purely computational” estimates of the entropy still have a fundamental connection to experiment through this single empirical scaling factor.

Graduation date: 1991

Sustainable development in chemical engineering offers technical, industrially relevant solutions to environmental and economic issues. This work focuses on three specific issues; improving solvent selection and reducing costly experimentation, improving catalyst recovery while reducing reaction time, and producing commercial viable biofuels by cost effective pretreatments and valuable side product extractions. Novel solvent systems are a sustainable solution because they provide the ability to replace costly solvents with cheap, benign, and recyclable systems. Specifically, this work investigated the use of one novel solvent system, Gas Expanded Liquids (GXL).When a solvent is exposed to a gas in which it is miscible at modest pressures and temperatures, the liquid solvent becomes expanded, providing a unique tunable and reversible solvent with properties that can be much different then that of the solvent itself. If you apply this gas to a mixture of two liquids of a solid dissolved in a liquid phase, it can often provide a miscibility switch, aiding in separation, crystallization, and recovery of products or catalysts. In this work several different applications for organic solvents expanded with carbon dioxide were studied including miscibility switches for catalyst recycle, pretreatment of biomass for improved bio-ethanol production, and extraction of valuable chemicals from lignin waste in the pulp and paper industry. Solid solubility models to improve solvent selection and predict unique solvent mixtures during crystallization were also studied. The results reported here show promise for the use of GXL novel solvent systems and solid solubility models in many sustainable applications.

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