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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.
121

Transmission electron microscopy study of novel semiconductor heterostructures and high Tc superconductors

Xin, Yan January 1996 (has links)
No description available.
122

Investigação de problemas relacionados a mobilidade térmica de discordâncias utilizando aplicação de carga concentrada. / Investigation of problems related to the thermal mobility of dislocations using indentation.

Hummelgen, Ivo Alexandre 10 February 1987 (has links)
A mobilidade térmica de discordância foi investigada em silício puro, floating zone, livre de discordâncias, utilizando medidas de rosetas produzidas por indentação. A mobilidade das discordâncias produzidas em amostras cobertas com camada de óxido crescida termicamente foi comparada com a de superfície não coberta. Um aumento da mobilidade térmica foi encontrado em amostras cobertas. Também foram obtidas informações sobre modificações na estrutura de discordâncias em rosetas relacionadas à anisotropia na dureza. Esse efeito foi encontrado como sendo dependente da temperatura. / The thermal mobility of dislocations was investigated in intrinsic floating zone dislocation free silicon using indentation dislocation rosette (IDR) measurements. The mobility of introduced dislocations in samples covered with a thermal oxide layer was compared with that with a bare surface. An increase on dislocation thermal mobility was found in covered samples. Also information about dislocations pattern structure modifications on IDR related to hardness anisotropy was obtained. This effect was found to be temperature dependent.
123

Creep behavior of binary solid solutions of nickel with molybdenum and tungsten

Tiearney, Thomas Carson January 1978 (has links)
Thesis. 1978. Ph.D.--Massachusetts Institute of Technology. Dept. of Materials Science and Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Includes bibliographical references. / by Thomas Carson Tiearney, Jr. / Ph.D.
124

Genetic contributors to congenital joint dislocation

Bicknell, Louise Susan, n/a January 2007 (has links)
Understanding the molecular basis of Mendelian disorders featuring joint dislocation can enhance the knowledge of genetic or cellular pathways required in joint development, and provide candidate genes for studying related complex disorders, such as developmental dysplasia of the hip. Two strategies were employed in this project to investigate Mendelian contributors to congenital joint dislocation. The first strategy was to investigate in-depth a gene known to be associated with joint dislocation. Missense mutations or small in-frame deletions in FLNB, encoding filamin B, have previously been associated with a spectrum of osteochondrodysplasias. Screening a larger cohort established FLNB as the sole underlying disease gene for atelosteogenesis type I and III and also boomerang dysplasia, which was previously thought clinically to be allelic to AOI. Mutations in FLNB cause a large proportion of Larsen syndrome cases with phenotypes reminiscent of the early case series reported. Atypical or "recessive" Larsen syndrome may therefore be due to a different underlying genetic aberration. The disease-associated amino acid substitutions or in-frame deletion/insertions cluster to two main regions of the filamin B protein: the calponin homology 2 domain of the actin-binding domain, and repeats 13-17 of the rod domain. To analyse the functions of these regions, yeast two-hybrid analyses were performed. No interactors were identified with the calponin homology 2 domain, which suggests the amino acid substitutions may disrupt actin binding or the regulation thereof. A candidate interactor, centromere protein J, was identified that binds to repeats 13-15, and could suggest a model for aberrant cell division seen in growth plates of bones of individuals with atelosteogenesis types I and III and boomerang dysplasia. The second strategy used in this project was to investigate the genetic cause of a novel syndrome featuring joint dislocation. A neurocutaneous phenotype segregated in a consanguineous New Zealand family, and through a genetic mapping strategy, a significantly linked locus was identified at 10q23 (Z = 3.63), in which segregation of a common ancestral haplotype fits the linkage hypothesis of homozygosity by descent. Candidate gene analysis and subsequent screening identified a missense mutation 2350C>T in ALDH18A1, which predicts the substitution H784Y in the encoded protein [Delta]�-pyrroline-5-carboxylate synthase (P5CS). The known function of P5CS in proline and ornithine biosynthesis was not affected by the presence of H784Y in an indirect assay, and therefore the hypothesis proposed was that a novel, unknown moonlighting function of P5CS is perturbed causing the phenotype segregating in the family. As an initial exploration of functions of P5CS in the cell, yeast two-hybrid analysis was undertaken. This project examined the contribution of two genes, FLNB and ALDH18A1, to Mendelian congenital joint dislocations. How the cellular functions of the encoded proteins in the cytoskeleton, metabolism, or signal transduction, are critical for joint development is ill understood. Future investigations aimed at identifying candidate genes that confer susceptibility to developmental dysplasia of the hip should consider candidate genes that encode proteins related in function to the products of the FLNB and ALDH18A1 genes.
125

Microstructural and mechanisms of cyclic deformation of aluminum single crystals

Delos-Reyes, Michael A. 20 September 1995 (has links)
Aluminum single crystals were cyclically deformed in single-slip at small strain amplitudes at 77 K to presaturation. The observed mechanical behavior is consistent with other recent work. The dislocation substructure was analyzed in detail. The structure can be described as consisting of dense bundles or veins of dislocation dipoles, separated by lower dislocation density regions where debris is evident. This debris was determined to be principally relatively short dipole segments. Screw dislocations with the same Burgers vector span the channels. Dislocations were essentially all of the same Burgers vector. In-situ cyclic deformation experiments were successfully performed by the X-Y technique where thin foils are stressed in alternating perpendicular directions. Screw dislocations span the channel and easily move and reverse direction with shear reversal. Our experiments indicate that loops frequently expand from the dipole bundles into the channels and the edge component is absorbed by nearby bundles leaving screw segments behind. Dipole "flipping" was not observed and these edges are relatively difficult to mobilize. There is no obvious evidence for internal backstresses that assist plastic deformation on reversal of the applied shear. / Graduation date: 1996
126

Influence de la microstructure et du mode de sollicitation sur l'irréversibilité du glissement des dislocations lors d'une sollicitation mécanique cyclique

Kachit, Mahmoud Buffière, Jean-Yves. Maire, Eric. January 2004 (has links)
Thèse doctorat : Matériaux : INSA LYON : 2004. / Titre provenant de l'écran-titre. Bibliogr. p. 170-176.
127

Etude par simulations à l' échelle atomique de la formation de boucles de dislocation à partir d' irrégularités de surface d' un métal contraint

Hirel, Pierre Pizzagalli, Laurent. Brochard, Sandrine. January 2008 (has links) (PDF)
Reproduction de : Thèse de doctorat : Milieux denses, matériaux et composants : Poitiers : 2008. / Titre provenant de l'écran-titre. Bibliogr. 82 réf.
128

Nucleation and cross-slip of partial dislocations in FCC metals

Liu, Gang January 2009 (has links)
Thesis (Ph. D.)--University of California, Riverside, 2009. / Includes abstract. Available via ProQuest Digital Dissertations. Title from first page of PDF file (viewed March 20, 2010). Includes bibliographical references. Also issued in print.
129

An investigation of efficient room temperature luminescence from silicon which contains dislocations

Stowe, David John January 2006 (has links)
This thesis presents an investigation of the phenomenon of efficient, room temperature luminescence from dislocation-engineered (DE) silicon. Previous work had demonstrated that the introduction of near-surface dislocation loops to a silicon substrate by boron ion implantation and high temperature annealing produced efficient electroluminescence at room temperature. However, the mechanism by which high efficiency luminescence is produced was not understood. A wide matrix of specimens containing dislocations was fabricated by a variety of methods, including ion implantation, and their luminescence efficiencies were correlated to their physical properties. Transmission electron microscopy was used to characterise the defect structures created by ion implantation. In the majority of specimens a band of dislocation loops in close proximity to the surface was observed. The dislocation loops were shown to be consistent with a mixture of Frank and perfect dislocation loops, the relative proportions of which were dependent upon processing conditions. The thermal evolution of the dislocation loop size distribution was investigated. For the first time, a size distribution displaying a double peak was observed. The size distribution was shown to be consistent with the Gaussian distribution of two defect populations of different mean diameter. The thermal evolution of the size distribution was investigated in silicon implanted samples. A flux of self-interstitials from Frank dislocation loops to perfect dislocation loops was deduced. The evolution of the dislocation loop sizes was found to be consistent with Ostwald ripening. Cathodoluminescence (CL) was used to investigate the luminescent properties of silicon at room temperature for the first time. A new CL system was installed for this work, initially the CL system was characterised and a routine to ensure a high degree of reproducibility was formed. The luminescence mechanism of DE-silicon was shown to be the same as in unprocessed silicon wafers; TO phonon-assisted recombination. The mechanism of enhanced luminescence from DE-silicon was unambiguously shown to be due to the gettering of electrically active impurities from the specimen bulk. A reduction in the bulk transition metal impurity concentration of up to 35 times was inferred. In samples which were implanted with boron the degree of gettering was found to show a logarithmic dependence on the dislocation density. Using a crosssectional mapping technique, implanted samples were shown to contain a lower concentration of transition metal impurities throughout the entire wafer in comparison to as-received, unprocessed specimens. Furthermore, the impurity concentration was found to be lowest in close proximity to the band of dislocation loops. The dislocation loops were found to act as non-radiative recombination centres and their strength was strongly influenced by the local carrier concentration. The high doping levels of samples implanted with boron were found to minimise the non-radiative recombination action of the dislocations. Low temperature annealing was used to improve the luminescence efficiency of DE-silicon further.
130

An SEM EBIC study of the electronic properties of dislocations in silicon

Wilshaw, P. R. January 1984 (has links)
Individual, well structurally characterised dislocations present in n-type silicon have been studied using the electron beam induced current (EBIC) mode of an SEM.</p>An EBIC system has been designed and constructed which includes i) phase sensitive detection, ii) computerised control of the experimental equipment and data capture and iii) a variable temperature SEM specimen stage. With this system measurements have been made of the EBIC contrast of individual segments of deformation induced dislocations produced by two stage compressive deformation at 850°C and 420°C. An experimental and theoretical analysis of EBIC signal generation in the Schottky barrier specimens used in this work is presented. This shows that the EBIC contrast measurements made may be directly correlated to the dislocation recombination strength. Contrast measurements have been made at temperatures in the range 120K to 370K and for electron beam currents from 6 x 10<sup>-12</sup>A to 2 x 10<sup>-9</sup>A. Several new effects have been observed. Minority carrier diffusion length measurements have also been performed in silicon containing dislocations. These show that the value obtained may depend upon experimental parameters used in a hitherto undetected manner. A new theory describing recombination of carriers at charged dislocations has been developed and this has been extended to provide a description of the variation of the EBIC contrast of dislocations with temperature, electron beam current and also the transient response of the EBIC contrast. Comparison of the theoretical predictions with the results gained experimentally shows full agreement for low temperatures or large beam currents. At high temperatures and small beam currents the theory shows the EBIC contrast will behave differently depending on the density of dislocation states present. Interpretation of the experimental results in terms of this theory allows some new insight to be gained for recombination at dislocations, and values for some of the parameters controlling recombination have been obtained.

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