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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.
21

Biosynthesis and characterisation of polyhydroxyalkanoate based natural-synthetic hybrid copolymers.

Sanguanchaipaiwong, Vorapat, Biotechnology & Biomolecular Sciences, Faculty of Science, UNSW January 2006 (has links)
Natural-synthetic hydrid biomaterials have been isolated from the growth of Alcaligenes latus and Pseudomonas oleovorans in the presence of diethylene glycol (DEG). A. latus could cometabolise DEG with 10 g/L glucose, while DEG was consumed by P. oleovorans with 20 mM sodium octanoate or octanoic acid. The presence of DEG in bioprocessing systems for the production of short chain length (scl-) and medium chain length (mcl-) PHAs consequently lowered cell viability and PHA yield. Cell morphology was slightly changed, but the PHA inclusion bodies apparently were not. DEG affected the composition of the mclPHA which was confirmed to be polyhydroxyoctanoate (PHO) with a significant increase in the C8 component. Gas chromatography-mass spectrometry (GC-MS) was used to quantitatively monitor DEG in the system and revealed its cellular adsorption. Intracellularly, the DEG significantly decreased the molar weight of the mclPHA and sclPHA. P1PH NMR, 2-D COSY and HSQC spectra confirmed that the polymer samples consisted of PHA chains terminated by DEG. Similar to the cultivation of P. oleovorans with DEG, the presence of PEG200 and PEG400 also had an effect on cell growth, PHO yield and cell viability. Furthermore, a hybrid copolymer of PHO-PEG200 was synthesised. The synthesis of these natural-synthetic hybrid copolymers could lead the way for a wide variety of PHA-PEG copolymers with a range of bioactive properties. All thermal properties of PHB were higher than those of PHB-DEG. This may be due to a combination of lower PHB molecular weight and termination of the chains by DEG, i.e. ???DEGylation???. However, PHB-DEG was more elastomeric when compared to PHB, showing properties similar to its copolymer with 20 mol% 3-hydroxyvalerate. Contact angles revealed that the PHB-DEG film was slightly more hydrophilic than PHB. Despite the large difference in their respective proportions, the comparatively small DEG component exerted an influence on chain confirmation, such that solvent casting under humid conditions apparently induced self-assembly and formed a disordered microporous film. DEGylation of PHO also had noticeable effects on the physiochemical properties of the biopolymer. A major decrease in molecular weight, together with the termination of hydrophobic PHO chains with hydrophilic end-groups resulted in changes to its thermal properties when compared to PHO. In comparison to PHO, solvent cast films of PHO-DEG were apparently less flexible, but more hydrophilic.
22

Thermal characterization technique for thin dielectric films

Indermuehle, Scott W. 14 April 1998 (has links)
A phase sensitive measurement technique that permits the simultaneous determination of two independent thermal properties of thin dielectric films is presented. Applying the technique results in a film's thermal diffusivity and effusivity, from which the thermal conductivity and specific heat can be calculated. The technique involves measuring a specimen's front surface temperature response to a periodic heating signal. The heating signal is produced by passing current through a thin layer of nichrome that is deposited on the specimen's surface, and the temperature response is measured with a HgCdTe infrared detector operating at 77 K. The signal that is produced by the infrared detector is first conditioned, and then sent to a lock-in amplifier. The lock-in is used to extract the phase shift present between the temperature and heating signal through a frequency range of 500 Hz-20 kHz. The corresponding phase data is fit to an analytical model using thermal diffusivity and effusivity as fitting parameters. The method has been applied effectively to 1.72 ��m films of Si0��� that have been thermally grown on a silicon substrate. Thermal properties have been obtained through a temperature range of 25��C-300��C. One unanticipated outcome stemming from analysis of the experimental data is the ability to extract both the thermal conductivity and specific heat of a thin film from phase information alone, with no need for signal magnitude. This improves the overall utility of the measurement process and provides a 'clean', direct path with fewer assumptions between data and final results. The thermal properties determined so far with this method are consistent with past work on Si0��� films. / Graduation date: 1998
23

Thermal stability of surface treated zirconium

Hayes, Troy A. 14 June 1996 (has links)
Zirconium press plates have been developed for the production of melamine coated particle board, using shot-peening to achieve the desired plate (and therefore coated particle board) surface texture. Service temperatures of the press plates approach 200��C. This study examined the microstructural effects of extended exposure of shot-peened zirconium to temperatures of 200��C and 300��C. Softening of the surface may reduce wear resistance and possibly the surface morphology of the plate, affecting the usability of the plates. It was discovered that the shot-peened surface of the plates experienced a loss in hardness from approximately 230 VHN (DPH) to about 220 VHN after 560 hrs at 200��C. The same drop in hardness was experienced after only 5.5 hrs at 300��C. This decrease in hardness was determined from hardness profiles before and after heat treating the zirconium to various times from 0.5 hours to 4458 hrs and 2790 hrs at 200��C and 300��C respectively. The decrease in hardness is believed to be a result of static recovery, the annihilation of point and/or line defects and/or alignment of dislocations into relatively low misorientation substantially relatively close to the shot-peened surface (about 35 ��m), and decreased more modestly over the next 100 ��m until virtually no drop was experienced further than approximately 150 ��m from the surface. The shot-peening hardens the surface region which extends about 150 ��m from the surface. Thus, the level of recovery appears to depend on the stored energy associated with cold work, or ambient temperature deformation. This increases from about 2-3% cold work (equivalent percent cold reduction from rolling) in the bulk of the specimens to near 99% at the surface resulting from shot-peening. The dislocation structure of the shot-peened zirconium was examined in the as-peened as well as the annealed conditions using transmission electron microscopy. / Graduation date: 1997
24

Cast keepers for dental magnets: effects of laboratory procedures

陳鴻釗, Chan, Hung-chiu, Kingsley. January 2005 (has links)
published_or_final_version / Dentistry / Master / Master of Dental Surgery
25

Modeling temperature sensitivity and heat evolution of concrete

Poole, Jonathan Larkin, 1977- 28 August 2008 (has links)
The hydration of cement in concrete is exothermic, which means it gives off heat. In large elements, the heat caused by hydration can dissipate at the surface, but is trapped in the interior, resulting in potentially large thermal gradients. The thermal expansion of concrete is greater at higher temperatures, so if the temperature differential between the surface and the interior becomes too great, the interior will expand more than the exterior. When the thermal stress from this mis-matched expansion exceeds the tensile strength of the material, the concrete will crack. This phenomenon is referred to as thermal cracking. Accurate characterization of the progress of hydration of a concrete mixture is necessary to predict temperature gradients, maximum concrete temperature, thermal stresses, and relevant mechanical properties of concrete that will influence the thermal cracking risk of concrete. Calorimetry is the most direct test method to quantify the heat evolution from a concrete mixture. There is currently no model, based solely on calorimetry, which completely describes the effects of mixture proportions, cement and SCM chemistry, and chemical admixture dosages on the temperature sensitivity and adiabatic temperature rise of concrete. The objective of this study is to develop a comprehensive model to describe these effects. First, the temperature sensitivity of the hydration reaction (described with activation energy, E[subscript a]) is needed to accurately predict the behavior of concrete under a variety of temperature conditions. A multivariate regression model is from isothermal calorimetry testing to describe the effects of water-cementitious materials ratio, cement chemistry, supplementary cementing materials, and chemical admixtures on the E[subscript a] of portland cement pastes. Next, a multivariate regression model is developed from semiadiabatic calorimetry testing that predicts the temperature development of concrete mixtures based on mixture proportions, cement and SCM chemistry, and chemical admixture dosages. The results of the models are validated using data from literature. The final model provides a useful tool to assess the temperature development of concrete mixtures, and thereby reduce the thermal cracking risk of the concrete structure.
26

HELIUM POSITIONAL BEHAVIOR IN METAL MATRICES UNDER TEMPERATURE GRADIENTS

Rodriguez Perazza, Manuel Francisco, 1943- January 1972 (has links)
No description available.
27

Effect of internal thermal mass on building thermal performance

Yam, Chi-wai., 任志偉. January 2003 (has links)
published_or_final_version / abstract / toc / Mechanical Engineering / Master / Master of Philosophy
28

THERMAL CONDUCTIVITY OF P,P' AZOXYANISOLE

Longley-Cook, Mark Timothy, 1943- January 1972 (has links)
No description available.
29

Simulation of microsegregation during binary alloy solidification

Kim, J. H. 08 1900 (has links)
No description available.
30

Synthesis, characterization and properties of diacetylene functionalized polyimides

Karangu, Njeri T. 12 1900 (has links)
No description available.

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