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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.

The effects of subcortical lesions on memory

Au, May-lan, Alma January 1987 (has links)
published_or_final_version / abstract / toc / Clinical Psychology / Master / Master of Social Sciences

Microbially Induced and Disrupted Memory Phenomena during Gas-Hydrate Occurrences in Seafloor Sediments

Xiong, Shangmin 08 August 2009 (has links)
Sediments collected from various cores in Mississippi Canyon 118 were tested to evaluate the abilities to promote natural gas hydrate formation. Memory effects for hydrate formation of sediments with in-situ seawater were of a major concern. The possible mechanisms of memory effects were combined to give an overall hypothesis on the bioproducts-mineral-microorganism system. Unique permanent memory effects in the sediment were found. Temperatures from 50 to 65°C dissipated all memory effects by disrupting microbial cell wall material. Bacillus subtilis is known to produce several types of biosurfactants, including surfactin. The catalytic effect of purified surfactin from B. subtilis on hydrate formation was studied in the presence of smectite clays. The interlayer spacings of clay minerals measured by X-ray powder diffraction indicated that hydrate formation and surfactin adsorption on the smectite clays have impacts on their structures. Laboratory gas mixture sequestering was also conducted by hydrate formation to study the various factors that may affect the separation of its hydrateorming gases. The effects of agitation, temperature, initial pressure and thermal conductors were explored.

The constitutive modeling of shape memory alloys /

Liang, Chen, January 1990 (has links)
Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 186-197). Also available via the Internet.

Memory improvement with the metabolic enhancer methylene blue

Wrubel, Kathryn Marigrace 28 August 2008 (has links)
Not available / text

Memory Effect Analysis and Power Combining Design of Power Amplifiers

Huang, Pin-Chiang 12 July 2010 (has links)
This thesis consists of two parts. Part one presents a design of class-AB power amplifier in 0.15£gm pHEMT process, and establishes a nonlinear model with memory effects for the power amplifier using Volterra series. To observe the memory effects, two-tone continuous wave signals have been applied to the model to predict the phase variation between IM3H and IM3L as a function of tone spacing. In the meanwhile, a time-domain measurement technique for the third-order intermodulation responses using a digital storage oscilloscope has been developed to verify the modeled predictions on IM3H and IM3L. Comparison between modeled and measured results shows good agreement. Part two of this thesis is to study the CMOS power-combining techniques. At first, the pros and cons between series and parallel combining transformers are discussed. Then, a design of class-E power amplifier using a pair of parallel combining transformers for power combining is presented. Both simulated and measured results show that the presented Class-E power amplifier has a high power-added efficiency.

Degradation of Ni-Ti alloy in cyclic loading

Lim, Tzi-shing Jesse 12 1900 (has links)
No description available.

Evaluation par nanoindentation des propriétés mécaniques locales d’alliages de titane superélastiques et à mémoire de forme / Evaluation by nanoindentation of the local mechanical properties in superelastic and shape memory titanium alloys

Fizanne, Cécile 07 November 2014 (has links)
Le titane, comme ses alliages, présente des caractéristiques remarquables qui peuvent être modulées du fait des nombreuses microstructures qu’il est possible d’obtenir. Grâce à cette grande variété, le titane et ses alliages possèdent un grand nombre de propriétés. Parmi les plus intéressantes, on peut citer leur résistance à la corrosion, leur biocompatibilité, mais aussi leurs excellentes propriétés mécaniques (résistance, ductilité, ténacité, fluage…). Pour toutes ces raisons, l’attrait pour les alliages de titane n’a cessé de croître dans de nombreux secteurs. En effet ils sont maintenant largement utilisés dans les industries aéronautique et chimique, mais aussi l’architecture, le naval, l’industrie automobile, le sport ou encore la médecine. La nanoindentation est utilisée couramment de nos jours pour déterminer les propriétés mécaniques locales des matériaux. Elle permet notamment de caractériser des alliages métalliques possédant une microstructure polycrystalline. La taille de l’indenteur en nanoindentation étant faible (de quelques micromètres à quelques dizaines de micromètres), cette technique est idéale pour caractériser les propriétés mécaniques de surface des différents grains d’un matériau. Elle permet notamment de mesurer simultanément la dureté et le module d’élasticité. Si les essais de nanoindentation sont associés à un banc motorisé X-Y, une matrice étendue d’indents peut être réalisée avec un pas de quelques micromètres. Grâce à cette technique et dans le cadre de ce travail de thèse, nous avons réalisé dans un premier temps des cartographies de dureté et de module d’élasticité (HIPF et EIPF). Dans un second temps, nous avons évalué des propriétés non-conventionnelles d’alliages de titane, telles que l’effet mémoire de forme et la superélasticité. Dans la première partie de l’étude, la nanoindentation a été corrélée à l’EBSD (diffraction des électrons rétro-diffusés) afin d’identifier la relation entre l’orientation cristallographique d’un grain et ses propriétés mécaniques. L’étude a été menée sur les alliages de composition Ti-30Nb et Ti-27Nb (%at) de structure cubique centrée (phase ), et sur le titane de pureté commerciale T40, de structure hexagonale compacte (phase ). Dans la seconde partie de l’étude, la nanoindentation a été utilisée pour mesurer l’effet mémoire de forme (SM) et la superélasticité (SE) de différents alliages de titane à travers une large gamme de profondeur d’indentation. La mesure de ces propriétés non-conventionnelles a été réalisée à partir de l’étude des courbes charge-déplacement obtenues pour chaque essai d’indentation. L’amplitude de l’effet SE et SM a été caractérisée par des ratios de hauteur et de travail déterminés par l’étude des courbes de nanoindentation ainsi que des profils AFM réalisés au microscope à force atomique. / Titanium and titanium alloys presents remarkable characteristics which can be modulated due to the many different microstructures that is possible to obtain. Thanks to this huge variety, titanium and its alloys can exhibit many properties. Among the most interesting, there may be mentioned their corrosion resistance, biocompatibility, but also their excellent mechanical properties (strength, ductility, toughness, creep…). For all these reasons, interest for of titanium alloys has been growing in many areas. Indeed they are now widely used in the aerospace and chemical industries, but also in architecture, naval, automotive, sports or medicine. Nanoindentation is commonly used nowadays to determine local mechanical properties of materials. For example, this technique allows the characterization of metallic alloys having a polycrystalline microstructure. The size of the indenter in nanoindentation being small (few microns to few tens microns), and consequently this technique is ideal for characterizing the surface mechanical properties of different grains of a material. It allows simultaneous measurement of the hardness and the elastic modulus. If nanoindentation tests are associated with a XY motorized test bed, a wide array of indents can be achieved with a step of few micrometers. Thanks to this technique and as part of this thesis, we have realized at first hardness and elastic modulus mapping (HIPF and EIPF). In a second time, we have evaluated unconventional properties of titanium alloys, such as shape memory effect and superelasticity. In the first part of the study, nanoindentation was correlated with EBSD (Electron backscattered diffraction) to identify the relationship between the crystallographic orientation of a grain and its mechanical properties. The study was conducted on the Ti-30Nb and Ti-27Nb (at.%) alloy compositions having a bodycentered cubic structure ( phase), and the commercially pure titanium (CP-Ti) having a hexagonal close packed structure ( phase). In the second part of the study, nanoindentation was used to measure the shape memory effect (SM) and the superelasticity (SE) of various titanium alloys through a range of indentation depth. The measurement of these unconventional properties was performed from the study of load-displacement curves for each indentation test. The magnitude of the SE and SM effect was characterized by depth and work ratios determined from the study of nanoindentation curves and AFM profiles.

The constitutive modeling of shape memory alloys

Liang, Chen 23 August 2007 (has links)
This dissertation presents a one-dimensional thermomechanical constitutive model for shape memory alloys based on basic concepts of thermodynamics and phase transformation kinetics. Compared with other developed constitutive relations, this thermomechanical constitutive relation not only reflects the physical essence of shape memory alloys, i.e., the martensitic phase transformation involved, but also provides an easy-to-use design tool for engineers. It can predict and describe the behavior of SMA quantitatively. A multi-dimensional constitutive relation for shape memory alloys is further developed based on the one-dimensional model. It can be used to study the mechanical behavior including shape memory effect of complex SMA structures that have never been analytically studied, and provide quantitative analysis for many diverse applications of shape memory alloys. A general design method for shape memory alloy actuators has also been developed based on the developed constitutive relation and transient thermal considerations. The design methodology provides a quantitative approach to determine the design parameters of shape memory alloy force actuators, including both bias spring SMA force actuators and differential SMA force actuators. / Ph. D.

An experimental investigation of the behavior of Nitinol

Dye, Tracy Earl 07 October 2005 (has links)
Shape memory alloys (SMA) have the unique ability to recover large strains and generate large recovery stresses via a repeatable martensitic transformation. Stress-strain and shape memory effect characteristics are needed in order to develop SMA force actuator design methods. Moreover, constitutive models able to quantitatively predict these characteristics and thus be useful as engineering design tools are also needed. An experimental apparatus designed to characterize the mechanical behavior of SMA was built and utilized. The apparatus is used specifically to gather stress-strain and shape memory effect characteristics from nitinol wire whereby mechanical properties associated with the material are determined. Phenomena such as the R-phase and stress induced martensite serration are investigated. A one-dimensional constitutive model is presented that quantitatively predicts stress-strain and shape memory effect behavior and was developed with the intention of being an engineering design tool for SMA force actuators. Experimental stress-strain and shape memory effect results are compared against that predicted by the model with the intention of verifying the model. The model displays the ability to predict stress-strain behavior that is in good quantitative agreement with experiment. The model also displays the ability to predict hysteric shape memory effect behavior for free, controlled, and restrained recovery cases of selected prestrains that is in good quantitative agreement with experiment. The model is unable to predict shape memory effect behavior such as the R-phase. Demonstrating the ability to experimentally investigate a constitutive model will hopefully inspire further combined experimental and theoretical SMA research. / Master of Science

Multi-functional SMA hybrid composite materials and their applications /

Paine, Jeffrey Steven Nelson, January 1994 (has links)
Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references. Also available via the Internet.

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