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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
171

Many-body effect on circulating spin current in trapped Bose-Einstein condensates /

Ho, Cheuk Ting. January 2010 (has links)
Includes bibliographical references (p. 81-82).
172

Experiments with Bose-Einstein condensation in an optical box

Meyrath, Todd Philip. Raizen, Mark George, January 2005 (has links) (PDF)
Thesis (Ph. D.)--University of Texas at Austin, 2005. / Supervisor: Mark G. Raizen. Vita. Includes bibliographical references.
173

Studies on a strain-driven retro-aldol ring expansion reaction

Adams, Bruce R. January 1984 (has links)
Thesis (Ph. D.)--University of Wisconsin--Madison, 1984. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 323-333).
174

Nonlinear dynamics of Bose-Einstein condensates

Zhang, Chuanwei, January 1900 (has links) (PDF)
Thesis (Ph. D.)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.
175

Heat transfer performance during condensation inside spiralled micro-fin tubes

Bukasa, Jean-Pierre Muenja 21 November 2011 (has links)
D.Ing. / Many studies have been conducted in order to establish the respective influence of geometric parameters such as fins number, fin shape (apex angle), spiral angle, fin height, fin pitch etc. on the condensation heat transfer performance of the spiralled micro-fin tubes. However, the effect of the spiral angle could not be clearly established in those investigations, because other geometric parameters affecting the heat transfer performance such as fin height, fin thickness, apex angle were also varied. The influence of the spiral angle on the heat transfer performance during condensation inside spiralled micro-fin tubes having all other geometric parameters the same was experimentally investigated in this study. A new experimental-based predictive correlation was developed for practical design of this specific class of micro-fin tubes. Tests were conducted for condensation of R22, R134a and R407c inside a smooth and three micro-fin tubes having spiral angles of 10, 18 and 37 degrees. Experimental results indicated a heat transfer augmentation due to heat transfer area increase. As the spiral angle was increased, the heat transfer area increased causing a substantial heat transfer augmentation. Condensation inside the 10° spiralled micro-fins produced a heat transfer augmentation of about 170% for a heat transfer area increase of 1.87 when compared to condensation in ~he correspondent smooth tube while the 18° spiralled " micro-fins produced an augmentation of 180% for a heat transfer area increase of 1.94. The 37° spiralled micro-fins produced the highest enhancement of 220% for a heat transfer area increase of 2.13. Additional heat transfer augmentation was produced by: (a) the turbulence in the condensate film due to the presence of spiralled micro-fins (stronger effect at lower mass velocities and vapor qualities) and (b) the effect of surface tension forces (at higher vapor qualities). The proposed new correlation predicted the majority of experimental results of the present study within a deviation zone of ± 20 percent.
176

Dithioimidophosphinates and related systems

Birdsall, David James January 1999 (has links)
The condensation reaction of iPr2PCl with hexamethyldisilazane, HN(SiMe3)2, followed by oxidation with sulfur, selenium or hydrogen peroxide yields Pr2P(E)NHP(E'),iPr2, where E = S, Se or 0. Single crystal X-ray experiments give a hydrogen bonded chain in all cases. Analogous PhO, EtO, Et and Ph substituted compounds were synthesised via condensation reactions between R2P(S)NH2 and R'P(S)CI yielding R2P(S)NHP(S)R'2 (R =PhO, Ph; R' = iPr, Et, EtO). Further crystallographic studies revealed iPr2P(S)NHP(S)(OPh)2 and Et2P(S)NHP(S)Ph2 to be hydrogen bonded dimers and iPr2P(S)NHP(S)Ph2 and Et2P(S)NHP(S)(OPh)2 to be hydrogen bonded chains. Reacting these compounds with Zn, Cd, Pd and Pt chlorides led to the formation of tetrahedral and square planar coordination complexes. Crystallographic studies on the complexes of R2P(E)NHP(E')R'2 revealed surprising ME2P2N ring geometries, some adopting pseudo "boat" conformations and others adopting pseudo "chair" conformation. Reactions of R2P(S)NHP(S)R'2 with CuC12 yielded trimeric copper(I) complexes of the type CU3[R2P(S)NP(S)R' 2]3. The trimeric system was found to be fluxional in solution. Crystallographic studies on the complexes show the trimer to have CU3S3 core. Further reactions of R2P(S)NHP(S)R' 2 with various tellurium (H) and (IV) salts yielded complexes of the types Te[R2P(S)NP(S)R' 2]2 and Te[R2P(S)NP(S)R' 2]Cl2,C6H4.0CH3. Crystallographic studies on the complexes show the tellurium to adopt pseudo two coordinate, four coordinate (square planar) and five coordinate (square based pyramid) arrangements. Tetradentate ligands of the type R2P(S)NHP(S)Ph(CH2)3P(S)PhNHP(S)R2 (where R = Ph or OPh) were synthesised by the condensation of NH2P(S)Ph(CH2)3P(S)PhNH2 with R2P(S)CI. Preliminary coordination studies suggest the formation of ML complexes were M = Zn, Cd and Ni. Molecular modelling techniques were used to investigate the optimum size of the "spacer groups" which links the two dithioimidophosphinate ligands. Using MNDOd and DFT optimisations, and with comparison to unlinked examples, the size of the ideal group was determined with respect to each particular metal.
177

Condensation of steam in a packed column in direct contact with immiscible liquids

Rai, Virendra Chandra January 1966 (has links)
A packed condenser and the auxiliary equipment were designed, built and tested for the condensation of steam in direct contact with Aroclor 1242 and 1248, which are commercial heat transfer agents and are immiscible with water. The co-current flow of steam and liquid, through a four inch inside diameter column packed with three-eighth inch ceramic Raschig rings, was studied. The packing heights used in the condensation of steam were estimated from the liquid temperature profile in the column. The heights of the transfer units for condensation and the average volumetric overall heat transfer coefficients were calculated. The height of the transfer unit for condensation was found to be affected largely by the mean viscosity and the flow rate of the liquid. Two empirical equations have been developed to describe the results of this study. HCU = F ( μ ) (n) where n = 1. 10 for Aroclor 1242 and n = 1. 16 for Aroclor 1248 is mean viscosity of the Aroclor in centipoise. For Aroclor 1242, F= 0.0535 + 8.90 x l0⁻⁶ L when L ≤ 2290 and F =-0. 0737 + 6. 44 x 10⁻⁵ L when L > 2290. For Aroclor 1248, F = 0. 02765 + 1. 244 x 10⁻⁵ L. L is superficial mass velocity of the Aroclor in lb /hr. ft² / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate
178

The reductive condensation of 2,5-disubstituted pyrroles

White, James David January 1961 (has links)
The problem initially presented was the structural elucidation of a compound obtained when 2,5-dimethylpyrrole was subjected to conditions of acidic reduction. Previous workers had assigned a molecular formula C₁₂H₁₇N to this product and a partial structure had been put forward based on the indolenine system. In the course of this work it was found that the compound obtained by these earlier workers was the result of a reductive self-condensation of 2,5-dimethylpyrrole, and Its structure was conclusively established as 1,3,4,7-tetramethylisoindoline. The methods used in the structural elucidation of this product included elemental analysis of its derivatives, measurement of its basicity and equivalent weight, infrared and ultraviolet spectroscopic evidence, oxidative degradation, and its proton magnetic resonance spectrum. Two related isoindolines were prepared by different routes. 2,4,7-trimethylisoindoline was synthesised by methods analogous to those already known, and the ultraviolet spectrum of its methiodide, when compared with that of the methiodide from 1,3,4,7-tetramethylisoindoline, reinforced the structural assignment of the latter. 1,3-diphenyl-4,7-dimethylisoindoline was obtained by the reductive condensation of acetonylacetone with 2,5-diphenylpyrrole (which did not undergo self-condensation). The favourable result of this reaction suggested that a similar condensation may have occurred to give the 1,3,4,7-tetramethylisoindoline and also admitted the possibility of a general synthesis of substituted isoindolines by this route. An attempt was made to resolve the mechanism of the 2,5-dimethylpyrrole condensation, for which either a Diels-Alder reaction or a ring-opening process may be postulated. The failure of the dimethylpyrrole to show dienic character, even in the presence of very strong dienophiles, together with positive evidence for ring-opening and ketone-pyrrole condensation argued forcibly for the latter mechanism. / Science, Faculty of / Chemistry, Department of / Graduate
179

Gallium arsenide-based microcoolers and self-cooled laser structure

Zhang, Jizhi 01 January 2003 (has links)
Two types of GaAs-based microcoolers have been demonstrated for the first time. One has a 2 μm thermal barrier made from a 100-period Al0.10 Ga0.90As - Al0.20Ga0.80As superlattice. Another has a thermal barrier made from a 5.2 μm Al0.10Ga 0.90As layer. Microcoolers of these two types with a size of 60 μm x 60 μm show maximum cooling temperatures around 0.8°C and 2°C at heatsink temperatures of 25°C and 100°C respectively. The microcoolers have potential to provide in situ cooling for semiconductor devices. As an application of in situ cooling, a unipolar self-cooled laser structure is proposed and has been fabricated. The structure integrates a graded-index (GRIN) separate confining heterostructure (SCH) strained-layer InGaAs quantum well (QW) laser unit and a single-layer AlGaAs cooler using an Esaki tunnel junction as a connector. In this scheme, cooling exists on two sides of the tunnel junction. Broad-area lasers of this structure with a cavity length of 500 μm have an average threshold current density around 212 A/cm 2. A preliminary method is proposed to evaluate the cooling effect of the integrated cooler. With this method, cooling can be estimated from the movement of the spectrum of the laser, excited by pulsed current, as the pulse width varies. Using this method, potential 2∼4°C temperature reduction as a result of the integrated cooler is found in the active layer of the self-cooled laser. Some technological platforms have been built-up to support the investigations on the microcoolers and self-cooled laser structure. Firstly, some primary MOCVD technologies such as controlling compositions, fabricating high quality interfaces, and doping have been developed for the MOCVD system itself and the compound semiconductor group. Secondly, annealing parameters—temperature and time—have been optimized for making ohmic contacts in a homemade carbon-stripe furnace. Thirdly, the SiH4 flow rate for doping the n-side of GaAs tunnel junction has been optimized to obtain a tunnel junction with low zero-bias tunnel resistance. A low zero-bias specific tunnel resistance of 9.59 × 10−5 Ω·cm2 has been achieved, which is the best reported result for the tunnel junction grown at normal growth temperatures. Theoretical evaluation and experimental results indicate that tunneling of the tunnel junction with the n-side doped with optimal SiH4 flow rate is mainly defect-assisted. Finally, a nominal-980-nm In0.2Ga0.8As GRIN-SCH strained-layer QW laser has been grown, fabricated, and characterized.
180

Multiple quantum-well intersubband devices for photodetectors and emitters

Lutz, Charles Richard 01 January 1997 (has links)
Intersubband transitions in both lattice-matched GaAs/AlGaAs and pseudomorphically strained GaAs/InGaAs/AlGaAs multi-quantum well structures are investigated. Absorption and emission devices were grown by atmospheric organometallic vapor phase epitaxy (OMVPE) and characterized using electroluminescence (EL) and Fourier transform (FT) spectroscopes. Several GaAs/AlGaAs quantum well infrared photodetectors infrared photodetectors (QWIPs) were fabricated and their performance evaluated. The dark currents and responsivities were measured and are found to be comparable to devices grown by advanced molecular beam epitaxial (MBE) methods. Significant improvements in the absorption characteristics were obtained by adopting a localized delta-doping profile in the absorption QWs as opposed to homogeneously doped structures. The measured absorption strength increased significantly in samples which were delta doped with silicon to sheet carrier densities of approximately $1\times10\sp{12}$ cm$\sp{-2}$. The transition linewidths decreased from 40 meV in the uniformly doped sample to 20 meV in the delta-doped devices. In addition, designs for intersubband emitters based on multiple quantum well structures are investigated. The electrical and optical properties of these devices are characterized. While no intersubband emission was observed from these device some possibilities for future designs are discussed. Electrons injected into the excited subbands of SQW structures via a resonant tunneling mechanism was also investigated. The optical properties of light emitted from electron-hole recombination in the QW, characterized by electroluminescence spectroscopy, is correlated with the device electrical characteristics. At 77$\sp\circ$ K both the I-V and the light attributes show strong nonlinear differential behavior similar to NDR effects in resonant tunneling diodes. Semiconductor laser diodes fabricated using these materials exhibit a single mode lasing spectrum and an output power characteristic which is abruptly extinguished as the field-induced resonant injection condition is exceeded.

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