Pressboard, a high density cellulose-based material used for insulation in high voltage power transformers, exhibits stress relaxation during compressive loading. Investigating the micro-mechanical mechanisms responsible for the relaxation can lead to modifications of the production process to control the behaviour of the material. This investigation can be done using Synchrotron X-ray micro Computed Tomography which provides sufficient temporal and spatial resolutions to capture the stress relaxation process. In the present thesis, a compression rig for in-situ mechanical loading during X-ray micro Computed Tomography was designed and constructed. Local tomography scans with sub-micrometre resolution were obtained at the TOMCAT beamline at the Swiss Light Source, Paul Scherrer Institut, Switzerland. Several fibre segmentation techniques are analysed, together with Optical Flow and Digital Volume Correlation (DVC), methods used for estimating displacement, strain and velocity vector fields. Suitability of the tested methods is evaluated, and it is found that segmentation of individual fibres in a cellulose material of such a high density is probably not possible using currently available segmentation techniques. The movements during relaxation are measurable at the used resolution, and can be estimated using Optical Flow. Further work into correction of image shift due to rig movement between scans, as well as image artefact reduction should allow for measurement and comparisons of displacement during relaxation as well as DVC-computed strain measurements during compression, recreating earlier results.

Les récents développements en programmation semi-définie positive et en optimisation globale ont montré que les échanges entre les communautés de la théorie de la commande et de l'optimisation sont souvent à l'origine d'avancées significatives dans l'une ou l'autre des communautés. Originellement défini en théorie de la commande robuste, le formalisme lié aux inégalités matricielles linéaires a rapidement permis de développer le champ original de recherche en théorie de l'optimisation connu sous le terme de programmation semi-définie positive. En retour, les nombreux progrès théoriques (théorie de la dualité, méthodes de barrière...) et numériques (méthodes de points intérieurs, optimisation non différentiable...) ont fourni un support rigoureux à la majeure partie des développements algorithmiques produit en théorie de la commande robuste. Pour tous les formalismes actuellement utilisés en analyse et synthèse robustes allant de la théorie du mu (analyse et synthèse) au cadre de travail défini par les contraintes intégrales quadratiques, en passant par la théorie de la séparation des graphes, il est nécessaire de disposer d'une théorie de l'optimisation adéquate ainsi que des outils numériques efficaces associés. Au delà des liens habituels unissant les deux communautés, il nous a semblé qu'une relation plus subtile les liait. Outre le fait que les notions de performance et de robustesse conduisent naturellement à celle d'optimisation, les recherches entreprises et les résultats obtenus en théorie de la commande montrent souvent une parenté étroite avec le corpus issu de la théorie de l'optimisation. Une formalisation possible de ce lien organique entre les deux champs scientifiques est constituée par la théorie de Lyapunov. Nous nous attachons donc à illustrer les différents aspects que peut recouvrir la relation entre optimisation et théorie de la commande robuste. L'accent est particulièrement placé sur la théorie de Lyapunov, même si celle-ci n'en épuise pas t outes les facettes. Ainsi, après avoir présenté le contexte général de l'analyse et de la synthèse robustes et les problèmes d'optimisation particuliers qui leur sont liés, nous montrons comment de nombreux résultats obtenus dans le cadre de la théorie de Lyapunov peuvent être interprétés en terme de relaxations.

The HIV-1 transactivator of transcription (Tat) is a protein essential for both viral gene expression and virus replication. Tat is an RNA-binding protein that, in cooperation with host cell factors cyclin T1 and cyclin-dependent kinase 9, regulates transcription at the level of elongation. Tat also interacts with numerous other intracellular and extracellular proteins, and is implicated in a number of pathogenic processes. The Tat protein is encoded by two exons and is 101 residues in length. The first exon encodes a 72-residue molecule that activates transcription with the same proficiency as the full-length protein. The physico-chemical properties of Tat make it a particularly challenging target for structural studies: Tat contains seven cysteine residues, six of which are essential for transactivation, and is highly susceptible to oxidative cross-linking and aggregation. In addition, a basic segment (residues 48-57) gives the protein a high net positive charge of +12 at pH 7, endowing it with a high affinity for anionic polymers and surfaces. In order to study the structure of Tat, both alone and in complex with partner molecules, we have developed a system for the bacterial expression and purification of polyhistidine-tagged and isotopically enriched (in 15N and 15N /13C) recombinant HIV-1 Tat1-72 (BH10 isolate) that yields large amounts of protein. These preparations have facilitated the assignment of 95% of the non-proline backbone resonances using heteronuclear 3-dimensional nuclear magnetic resonance (NMR) spectroscopy. Analysis by mass spectrometry and NMR demonstrate that the cysteine-rich Tat protein is unambiguously reduced and monomeric in aqueous solution at pH 4. NMR chemical shifts and coupling constants suggest that it exists in a disordered conformation. Line broadening and multiple peaks in the cysteine-rich and core regions suggest that transient folding occurs in two of the five sequence domains. NMR relaxation parameters were measured and analysed by spectral density and model-free approaches both confirming the lack of structure throughout the length of the molecule. The absence of a fixed conformation and the observation of fast dynamics are consistent with the ability of the Tat protein to interact with a wide variety of proteins and nucleic acid lending further support to the concept that Tat exists as an intrinsically disordered protein.

No description available.

The HIV-1 transactivator of transcription (Tat) is a protein essential for both viral gene expression and virus replication. Tat is an RNA-binding protein that, in cooperation with host cell factors cyclin T1 and cyclin-dependent kinase 9, regulates transcription at the level of elongation. Tat also interacts with numerous other intracellular and extracellular proteins, and is implicated in a number of pathogenic processes. The Tat protein is encoded by two exons and is 101 residues in length. The first exon encodes a 72-residue molecule that activates transcription with the same proficiency as the full-length protein. The physico-chemical properties of Tat make it a particularly challenging target for structural studies: Tat contains seven cysteine residues, six of which are essential for transactivation, and is highly susceptible to oxidative cross-linking and aggregation. In addition, a basic segment (residues 48-57) gives the protein a high net positive charge of +12 at pH 7, endowing it with a high affinity for anionic polymers and surfaces. In order to study the structure of Tat, both alone and in complex with partner molecules, we have developed a system for the bacterial expression and purification of polyhistidine-tagged and isotopically enriched (in 15N and 15N /13C) recombinant HIV-1 Tat1-72 (BH10 isolate) that yields large amounts of protein. These preparations have facilitated the assignment of 95% of the non-proline backbone resonances using heteronuclear 3-dimensional nuclear magnetic resonance (NMR) spectroscopy. Analysis by mass spectrometry and NMR demonstrate that the cysteine-rich Tat protein is unambiguously reduced and monomeric in aqueous solution at pH 4. NMR chemical shifts and coupling constants suggest that it exists in a disordered conformation. Line broadening and multiple peaks in the cysteine-rich and core regions suggest that transient folding occurs in two of the five sequence domains. NMR relaxation parameters were measured and analysed by spectral density and model-free approaches both confirming the lack of structure throughout the length of the molecule. The absence of a fixed conformation and the observation of fast dynamics are consistent with the ability of the Tat protein to interact with a wide variety of proteins and nucleic acid lending further support to the concept that Tat exists as an intrinsically disordered protein.

In this thesis, we consider joint beamforming, power, and channel allocation in a multi-user and multi-channel underlay cognitive radio network (CRN). In this system, beamforming is implemented at each SU-TX to minimize the co-channel interference. The formulated joint optimization problem is a non-convex, mixed integer nonlinear programming (MINLP) problem. We propose a solution which consists of two stages. At first, given a channel allocation, a feasible solutions for power and beamforming vectors are derived by converting the problem into a convex form with an introduced optimal auxiliary variable and semidefinite relaxation (SDR) approach. Next, two explicit searching algorithms, i.e., genetic algorithm (GA) and simulated annealing (SA)-based algorithm are proposed to determine optimal channel allocations. Simulation results show that beamforming, power and channel allocation with SA (BPCA-SA) algorithm achieves a close optimal sum-rate with a lower computational complexity compared with beamforming, power and channel allocation with GA (BPCA-GA) algorithm. Furthermore, our proposed allocation scheme shows significant improvement than zero-forcing beamforming (ZFBF).

On-line nuclear orientation at low temperature has become an important technique for the study of nuclei far from stability, through measurements of nuclear moments and other quantities of spectroscopic interest. The theory of low temperature nuclear orientation and its application to the study of nuclear structure are reviewed. Of particular importance to the on-line measurement, in which a wide range of short-lived nuclei are available for study, is the question of how fast these nuclei can be cooled to the lattice temperature, and thus oriented. To address this, the theory of nuclear spin-lattice relaxation, relevant to the online technique, is outlined. In particular, quantitative methods to deal with cases in which the spin-lattice relaxation time is comparable with the isotope half-life have been developed and applied. One of the major current interests in nuclear structure physics is to investigate how the neutron-proton interaction influences the structure of nuclei that are transitional, between well established regions of spherical and deformed nuclei. In such nuclei, intruder excitations, which signal the onset of deformation, are observed low in energy. Using the Daresbury on-line isotope separator, an extensive study of the decay of ¹¹⁸I to ¹¹⁸Te has been performed using nuclear orientation techniques, combined with γ - γ and conversion electron spectroscopy measurements. Interpretation of the results obtained for ¹¹⁸Te within the framework of IBM-2, gives strong evidence for the existence of such an ,em>intruder configuration in this nucleus. On-line experiments have also been performed in which a range of neutrondeficient Cs nuclei has been oriented for the first time. In these measurements the hyperfine field of CsFe has been determined as (+)40.8(7) T, and also the Korringa constant for the system ¹²¹Cs^mFe has been measured (using a new technique) to be C_k = 0.059(l6)sK. These results have been applied to the case of ¹¹⁸Cs^m, for which the magnetic moment has been measured to be 5.4(1.1)nm. This large value clearly indicates the presence of the [404]9/2 orbital, which provides further evidence for the existence of intruder states in this region.

京都大学 / 新制・課程博士 / 博士(エネルギー科学) / 甲第24001号 / エネ博第437号 / 新制||エネ||82(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)准教授 高井 茂臣, 教授 萩原 理加, 教授 佐川 尚 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

The primary objective of the studies described in this thesis was to improve the cryopreservation success of koala spermatozoa for the purpose of establishing a genome resource bank for this species. A defining feature of the studies in this thesis was the implementation of an organelle-specific approach to better understand the causes of koala sperm cryo-injury. The functional attributes of spermatozoa, such as mitochondrial function, plasma membrane fluidity, membrane lipid asymmetry and DNA integrity were assessed as an indication of cryo-injury. Sperm mitochondrial function and plasma membrane integrity were examined by cryomicroscopy using the fluorescent probes JC-1 and propidium iodide (PI) respectively in a dual staining technique. Cooling and re-warming koala spermatozoa were more detrimental to mitochondrial function than to plasma membrane integrity. Mitochondrial membrane potential (MMP) was suppressed by freezing and thawing treatments; after thawing, MMP declined significantly during rewarming (from 5ºC to 35ºC). The distribution of GM1 ganglioside was examined using fluorescent-labelled cholera toxin B. No significant redistribution of GM1 was observed after chilling or cryotreatment. The externalisation of phosphatidylserine (PS) was examined using fluorescent-labelled annexin V. There was no significant increase in translocation of PS after chilling or cryopreservation. These observations imply that cryotreatment had little effect on plasma membrane lipid asymmetry. Koala spermatozoa were incubated in a range of anisotonic media to investigate whether nuclear swelling was caused by osmotic flux during the cryopreservation process. Although the most hypotonic solution tested (64 mOsm/kg) induced the highest incidence of nuclear relaxation (mean ± SEM; 12 ± 3%), this was not as severe as that previously documented following cryopreservation. Chromatin relaxation is a phenomenon observed in koala spermatozoa, where the sperm nucleus expands due to the result of structural changes in the natural conformation of the sperm DNA/protamine complex. DNA fragmentation was not a primary cause of cryopreservation-induced sperm chromatin relaxation, although in situ nick translation of putative DNA breaks indicated that these increased as the sperm head became progressively more relaxed. Using a Sperm Chromatin Dispersion test (SCDt) specifically developed and validated for koala spermatozoa, a continuum of nuclear morphotypes was observed, ranging from no apparent DNA fragmentation to spermatozoa with highly dispersed and degraded chromatin. A double comet assay was also developed to investigate DNA fragmentation in the koala spermatozoa. Conducted under neutral followed by alkaline conditions, this assay was able to differentiate between single- (SSB) and double-stranded (DSB) DNA damage in an effort to refine the interpretation of DNA damage in mature koala spermatozoa; the majority of the koala spermatozoa had nuclei with DNA abasic-like residues. The ubiquity of these residues suggested that constitutive alkali-labile sites are part of the structural configuration of the koala sperm nucleus. Spermatozoa with “true” DNA fragmentation exhibited a continuum of comet morphologies, ranging from a more severe form of alkaline-susceptible DNA, to nuclei that exhibited both SSB and DSB. Swelling of koala sperm chromatin following cryopreservation has largely been attributed to the absence of inter-molecular disulphide cross-linkages in the marsupial sperm nucleus. Fish spermatozoa also lack disulphide bonds within their chromatin, but nevertheless, have been successfully cryopreserved. To examine the hypothesis that the cryoprotectants used for fish sperm cryopreservation will confer a similar degree of protection on koala spermatozoa, various concentrations of five cryoprotectants (dimethyl sulphoxide, methanol, propylene glycol, ethylene glycol and dimethylacetamide) were evaluated. Each treatment was compared against an established koala sperm cryopreservation protocol that uses 14% glycerol. Dimethylacetamide at a concentration of 12.5% (v/v) was found to be comparable to glycerol in the successful cryopreservation of koala spermatozoa although high inter-male variability was observed. However, when the new protocol was subsequently validated for a larger population of captive koalas (n = 22), glycerol emerged the better cryoprotectant with respect to all sperm viability parameters assessed except for that of the incidence of chromatin relaxation, which was not affected by the cryoprotectant. Significant difference was also observed in the post-thaw survival of spermatozoa from different animals, which was independent of pre-freeze semen quality. Based on post-thaw semen viability parameters, the koalas could be divided into two distinct groups, where one group had significantly higher sperm viability compared to the other group, regardless of cryoprotectant used. Positive correlation between motility and MMP was observed before and after cryopreservation. However, cryopreservation significantly reduced the dependency between these variables (P < 0.001), suggesting that cryopreservation reduced the dependency between mitochondrial function and motility.

Thesis (Ph. D.)--University of Virginia, 2007. / Includes bibliographical references. Also available online through Digital Dissertations.