Thesis (doctoral)--Friedrich-Wilhelms-Universität zu Berlin, 1928. / "Sonderabdruck aus: Zeitschrift für angewandte Mathematik und Mechanik, Band 8, 1928, Seite 18 bis 44"--P. [1]. Vita. Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Madison, 1957. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf 59).

No description available.

No description available.

Fatigue life prediction following overloads is required in such applications as, aerospace, automobile, and pressure vessels industries for damage tolerant design. Modelling of life prediction in fatigue is complicated by a host of variables which includes loading history. The characteristic features which result as a posteriori evidence of the loading history include overload plasticity zone, crack closure with a special trend with respect to crack length, spike-dip in fatigue crack growth rate and retardation in fatigue growth. This research focuses on life prediction of components subjected to variable magnitude single overloads, in a cyclic loading situation. This thesis introduces the plasticity range interaction, and closure effects for variable magnitude single overload problems. A simple model is presented which captures these characteristic features following overloads. A detailed study on the crack-tip plasticity is conducted to identify the dimensions of the plasticity zone. A new approach is presented which is useful in obtaining suppression factor for fatigue growth retardation. This factor is required in fatigue crack growth models to account for retardation effect following overloads. The model for fatigue crack growth is tested for constant amplitude loads. A detailed study is presented on fatigue crack closure based constant amplitude calculations. Two different approaches to fatigue growth calculations are presented. An assessment of the errors that occur in assumed-crack extension method is also presented. Several examples have shown a good agreement between experimental and theoretical results. The study is extended to variable magnitude single overload problem for determination of fatigue growth calculations. Two different approaches have been adopted, one based on plasticity range interaction, and the other on closure. It has been shown that the two approaches are equivalent. There is an excellent agreement between predictions and theory for fatigue life calculations and fatigue growth rate. This research directly contributes to life prediction under single overloads without reliance on data fitting. It has tremendous potential for fatigue life prediction under programmed block loads, multiple overloads and finally for random loads, which can be investigated in further studies. / Graduate

Synaptic plasticity plays a key role in processes of learning and memory. Long-term potentiation (LTP) is a relatively stable enhancement of synaptic transmission following specific patterns of electrical stimulation. Some types of learning (e.g. motor learning, fear conditioning) result in LTP-like changes at synapses. However, no studies have examined LTP-like plasticity in the visual cortex as a result of visual discrimination learning. A visual discrimination task was used to examine changes in LTP in the primary visual cortex (V1) of adult rats. Rats were placed in a Y-shaped water maze and required to swim to one choice arm containing a hidden platform. Distinct visual cues indicated the presence (CS+) and absence (CS-) of the platform. Rats learned to reliably discriminate the visual cues to successfully navigate the maze. Control rats received the same procedure, but the visual cues did not have a predictive relation with the platform. Following training, trained, control, and task-naïve rats were anesthetized and visual evoked potentials (VEPs) in V1 were recorded in response to CS+, CS-, and novel stimuli. Results indicate that, in both task-naïve and control animals, all visual stimuli elicit VEPs of similar (p > 0.05) amplitude. In contrast, trained animals show significantly larger amplitude VEPs to stimuli encountered during training relative to novel stimuli, regardless of whether stimuli act as CS+ or CS-. In addition, trained animals show 71% and controls 47% potentiation (p < .05) that was induced by electrical (theta-burst) stimulation of the lateral geniculate nucleus (LGN) indicating greater plasticity of thalamocortical synapses following training. There were no differences between controls and task-naïve animals. This facilitation of LTP was shown to allow past visual experience to influence the efficiency of encoding novel visual features. These experiments demonstrate that visual discrimination learning might involve stimulus-selective facilitation of neuronal responses at early stages of visual processing (LGN, V1). The effect requires that stimuli carry some significance to the animal, while exposure to stimuli with no significance does not result in the same level of neuronal enhancement. Further, visual experience alters the plasticity properties of V1 (metaplasticity) by facilitating LTP along thalamocortical sensory fibers. / Thesis (Master, Psychology) -- Queen's University, 2008-09-25 12:28:27.468

No description available.

Thesis (Ph.D.)--University of California, Berkeley, 1963. / "UC-28 Metals, Ceramics, and Materials" -t.p. Includes bibliographical references (p. 32-34).

Thesis (M.S.)--University of Wisconsin--Madison, 1963. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf 76).

Single crystals of the CsCl type intermetallic compound β’AuZn were prepared and tested in tension over a wide range of temperatures, strain rates and orientations for three compositions, Au-rich (51.0 at.% Au), stoichiometric and Zn-rich (51.0 at. % Zn). Slip surfaces are generally non-crystallographic planes in the zone of the slip direction [001], and are temperature, strain rate and orientation sensitive. A model based on thermally activated sessile-glissile transformations of screw dislocations has been proposed to explain non-crystallographic slip. Multi-stage work-hardening is observed over the temperature range 0.2 ⪝T/T𝘮⪝ O.35. In stage I the work-hardening rate is low[(formula omitted) /lOOO to (formula omitted)/5000] but rises sharply during stage II [Q₁₁ ~ (formula omitted)/5OO]. Stage III is characterized by a rapidly decreasing hardening rate coincident with the onset of profuse large-scale cross-slip. Surface slip line studies revealed that the end of easy glide is coincident with the onset of localized slip on non-crystallographic planes in the [100] zone. Thin foil electron microscopy was carried out on critically chosen crystallographic sections from annealed and deformed crystals. At the beginning of stage I clusters of edge dislocation dipoles were revealed, forming walls perpendicular to the glide plane. The dislocation density of the walls increases during easy glide. During testing at intermediate temperatures ( ~ .3 to .4 T𝘮 ) serrated yielding was detected in non-stoichiometric crystals and was attributed to dislocation-solute atom interactions. Under special testing conditions (77°K or near < OOl> orientations) slip occurs in <111> directions. The associated work-hardening rates are very high and ductility is low. Thermal activation studies were made to determine the dislocation mechanism responsible for the temperature sensitivity of yield in stoichiometric crystals below 〜220°K. Activation volume measurements are consistent with both the Peierls-Nabarro and cross-slip mechanisms below 〜150°K. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate