Dissertations / Theses on the topic 'Powdered analysis'

An investigation into the potential of time-wavelength resolved luminescence spectroscopy for the analysis of inorganic powders was performed. A time-wavelength resolved luminescence spectrometer consisting of an excimer laser, scanning monochromator, and gated integrator was constructed. The spectrometer had wavelength coverage from 265 nm to 800 nm, it was capable of measuring lifetimes between 100 ns and 500 ms. Sample excitation was done at 193 nm and 248 nm. A luminescence system model of first order decay in the time domain and a Gaussian function for the emission band was assumed. The time-wavelength resolved luminescence spectrum was described by the parameters: lifetime, peak maxima, peak halfwidth, and intensity factor. Parameter estimation was done with an algorithm employing a linear algebra construct and simplex optimization. The algorithm's performance on highly overlapped spectra was evaluated. For two component mixtures having a 1 % RSD noise level, overlaps greater than 0.3 halfwidths in the spectral domain and lifetime ratios greater than 1:1.3 were resolved with all parameter estimates having an error of less than ±2%. The luminescence spectra of CaMo0₄, SrMo0₄, BaMo0₄, ZnMoO₄, CdMo0₄, PbMoO₄, CaWO₄, SrW0₄, BaWO₄, ZnWO₄, CdW0₄ and PbWO₄ consisted of broad featureless bands showing simple exponential decay. Mixed crystals of Ca(MOxW₁-x)O₄ and Sr(MOxW₁-x)0₄ were examined. Tungstate emission was quenched by molybdate, the molybdate emission dominated when x was greater than 0.15. The tungstate lifetime was found to be proportional to molybdate concentration. The luminescence spectra of CaZrO₃, SrZr O₃, BaZr O₃ CaHfO₃ SrHfO₃, BaHfO₃, CaO, SrO, and BaO as pure compounds and doped with T1, Pb, Sb, and Bi were studied. The pure zirconates and hafnates showed short lived (<100 ns) luminescence with 248 not excitation; no readily discernible luminescence was observed with 193 nm excitation. Doped compounds tended to show luminescence characteristic of the dopant ion.<br>Science, Faculty of<br>Chemistry, Department of<br>Graduate

Dry powder inhalers (DPIs) are widely used for the therapy of respiratory and pulmonary diseases. In this study, a coupled discrete element method and computational fluid dynamics (DEM-CFD) is employed to investigate the micromechanics of carrier-based DPIs. The effects of van der Waals forces and electrostatic forces on the mixing process, and the influences of air flow and particle-wall impact on the dispersion process are examined. For the mixing of carrier and active pharmaceutical ingredient (API) particles in a vibrating container, it is found that vibration conditions affect the mixing performance. While there is an optimal mixing condition to maximise the number of API particles attaching to the carrier (i.e. contact number) for van der Waals cases, the contact number decreases with increasing vibration velocity amplitude and frequency for electrostatic force cases. It is also revealed that van der Waals forces (short range) and electrostatic forces (long range) result in different mixing behaviours. For the air flow induced and impact induced dispersion, it is found that the dispersion performance improves with increasing air velocity, impact velocity and impact angle, and reduces with increasing work of adhesion. The dispersion performance can be approximated using the cumulative Weibull distribution function governed by the ratio of air drag force to adhesive force or the ratio of impact energy to adhesion energy.

This thesis presents the development of the experimental techniques required to study microstructure in powder samples at high pressure through the use of 2-d data. A description is given of the upgrade and installation of new experimental apparatus constructed to permit routine investigation of microstructure in samples under pressure. The experimental techniques have been applied to the modelling of preferred orientation in powders at high pressure. A demonstration of the qualitative information about preferred orientation in powders available from a 2-d detector is given. Details are presented of a quantitative model applied to image-plate data based on preferred orientation corrections commonly used in Rietvald refinement programs. It is shown that this quantitative model is not completely adequate for describing the extremely strong preferred orientation often found in powder samples at high-pressure and a new more general model based on a commonly used model of texture used by the texture analysis community is presented and shown to work well. The structural pressure dependence of the cinnabar phase of HgS is presented. Strong preferred orientation can be induced in HgS at high pressure, it is shown that, by using the preferred orientation modelling techniques presented in this thesis, it has been possible to de-correlate the effect of preferred orientation from the refined structural parameters.

The aim of this master thesis project was to statistically correlate various powder characteristics to the quality of additively manufactured parts. An additional goal of this project was to find a potential second source supplier of powder for GKN Aerospace Sweden in Trollhättan. Five Inconel® alloy 718 powders from four individual powder suppliers have been analyzed in this project regarding powder characteristics such as: morphology, porosity, size distribution, flowability and bulk properties. One powder out of the five, Powder C, is currently used in production at GKN and functions as a reference. The five powders were additively manufactured by the process of laser metal deposition according to a pre-programmed model utilized at GKN Aerospace Sweden in Trollhättan. Five plates were produced per powder and each cut to obtain three area sections to analyze, giving a total of fifteen area sections per powder. The quality of deposited parts was assessed by means of their porosity content, powder efficiency, geometry and microstructure. The final step was to statistically evaluate the results through the analysis methods of Analysis of Variance (ANOVA) and simple linear regression with the software Minitab. The method of ANOVA found a statistical significant difference between the five powders regarding their experimental results. This made it possible to compare the five powders against each other. Statistical correlations by simple linear regression analysis were found between various powder characteristics and quality of deposited part. This led to the conclusion that GKN should consider additions to current powder material specification by powder characteristics such as: particle morphology, powder porosity and flowability measurements by a rheometer. One powder was found to have the potential of becoming a second source supplier to GKN, namely Powder A. Powder A had overall good powder properties such as smooth and spherical particles, high particle density at 99,94% and good flowability. The deposited parts with Powder A also showed the lowest amount of pores compared to Powder C, a total of 78 in all five plates, and sufficient powder efficiency at 81,6%.

Titanium and its alloys have been widely used in oral implantology due to their mechanical properties, corrosion resistance and biocompatibility. However, under in vivo conditions the implants are subjected to the tribocorrosion phenomenon, which consists in the degradation mechanisms due to the combined effect of wear and corrosion. This process contributes to limiting the life span of the implant and may generate clinical problems in patients as metallic ions are released. Another cause of dental implant failure may be the loosening of the implant as metal does not promote osseointegration. The powder-metallurgy process is a promising alternative to the traditional casting fabrication process of titanium alloys for bone implants design, as the porous structure would allow the bone to grow into the pores. This would result in a better fixation of the metal implant without the need of sandblasting /acid etching the surface. The present Doctoral thesis aims at describing the corrosion and tribocorrosion behavior of titanium alloys and their degradation mechanisms when processed by powder metallurgy, as a possible alternative to standard casting for dental implant application. For this, model Ti6Al4V titanium alloy and possible substitute Ti6Al7Nb alloy, where Vanadium has been replaced by Niobium in order to avoid cytotoxicity of the resulting biomaterial, have been studied. Electrochemical and tribo-electrochemical characterization of the biomaterials have been carried out under different physico-chemical conditions with biological relevance (in artificial saliva (AS) with different fluoride content, pH and oxidising conditions) which noticeably influences the degradation mechanisms of the studied materials. A new tribocorrosion technique that allows measuring the galvanic potential and current between the wear track (anode) and the passive material (cathode) through Zero-Resistance Ammetry (ZRA) has been also used to elucidate tribocorrosion mechanisms of the model Ti6Al4V cast alloy in AS. The ZRA technique for tribocorrosion allowed predicting the real depassivated area and therefore, the deviation of the wear mechanisms from Archard wear law at Open Circuit Potential (OCP). All alloys show passivity in artificial saliva although active dissolution occurs in presence of high fluoride concentration (1000 ppm) and acidic conditions, pH 3. The degradation mechanism of sintered alloys is mainly governed by the mechanical wear in AS and only determined by the active dissolution when fluorides are added to acidified artificial saliva (pH 3). Wear was found to be governed by the prevailing oxidizing condition (simulated by changes in the electrode potential). Ti6Al4V alloy processed by powder metallurgy showed a similar tribocorrosion resistance when compared to commercially available cast alloy suggesting that powder metallurgy is a promising fabrication process for implant applications. The influence of the alloying elements, Al and Nb, on the corrosion and tribocorrosion behavior of different titanium alloys, Ti6Al7Nb, Ti7Nb and Ti6Al has been studied and in all cases, the corrosion resistance is improved when compared to pure titanium. Wear damage was found to be critically affected by the ductility of the material, thus by the alloying element. Ti6Al7Nb showed a better corrosion resistance and similar tribocorrosion behaviour when compared to Ti6Al4V. The results of this thesis have shown that Ti6Al7Nb obtained by Powder metallurgy is a promising biomedical alloy for oral implants. Wear damage of sintered Ti alloys depends on the electrochemical potential and their tribocorrosion behaviour is critically affected by a high content of fluoride found in common daily dental health care products.<br>El titanio y sus aleaciones han sido utilizados en implantología oral debido a sus propiedades mecánicas, resistencia a la corrosión y biocompatibilidad. Sin embargo, bajo condiciones in vivo los implantes están sometidos al fenómeno de tribocorrosión, que consiste en mecanismos de degradación debido al efecto combinado de desgaste y corrosión. Este proceso disminuye la vida útil del implante y genera problemas clínicos a medida que se liberan iones metálicos. La pérdida de fijación del implante es otra causa de fracaso del implante, por falta de osteointegración. El proceso de pulvimetalurgia es una alternativa prometedora al proceso tradicional de fabricación (colada, forja) de aleaciones de titanio para el diseño de implantes óseos, ya que la estructura porosa permitiría que el hueso crezca dentro de los poros, dando lugar a una mejor fijación del implante. La presente tesis doctoral pretende describir el comportamiento frente a la corrosión y tribocorrosión de las aleaciones de titanio y sus mecanismos de degradación cuando se procesan mediante pulvimetalurgia, como una posible alternativa a la colada estándar para la aplicación de implantes dentales. Se ha estudiado el modelo de aleación de titanio Ti6Al4V y posible sustitución por la aleación Ti6Al7Nb, donde el Vanadio ha sido sustituido por Niobio para evitar la citotoxicidad del biomaterial. La caracterización electroquímica y tribo-electroquímica de los biomateriales se ha llevado a cabo en diferentes condiciones físico-químicas con relevancia biológica (en saliva artificial (AS) con fluoruro, pH y condiciones oxidantes) que influye notablemente en los mecanismos de degradación de los materiales estudiados. También se ha utilizado una nueva técnica de tribocorrosión que permite medir el potencial galvánico y la corriente entre la pista de desgaste (ánodo) y el material pasivo (cátodo) a través de la ametría de resistencia cero (Zero-Resistence Ammetry, ZRA) para elucidar los mecanismos de tribocorrosión de la aleación de forja Ti6Al4V en AS. La técnica ZRA para tribocorrosión permitió predecir el área real despasivada y, por tanto, la desviación de los mecanismos de desgaste de la ley de desgaste de Archard en OCP. Las aleaciones muestran pasividad en AS, aunque la disolución activa se produce en presencia de alta concentración de fluoruro (1000 ppm) y condiciones ácidas, pH 3. El mecanismo de degradación de las aleaciones sinterizadas se rige principalmente por el desgaste mecánico en AS y sólo determinado por la disolución activa cuando se añaden fluoruros a la saliva artificial acidificada (pH3). Se encontró que el desgaste se rige por la condición oxidante predominante (simulada por cambios en el potencial de electrodo). La aleación Ti6Al4V procesada por pulvimetalurgia mostró una resistencia similar a la tribocorrosión cuando se comparó con la aleación forjada comercial disponible, lo que sugiere que la pulimetalurgia es un prometedor proceso de fabricación para aplicaciones de implantes. Se ha estudiado la influencia de los elementos aleantes Al y Nb sobre el comportamiento de corrosión y tribocorrosión de diferentes aleaciones de titanio Ti6Al7Nb, Ti7Nb y Ti6Al y en todos los casos la resistencia a la corrosión se mejora en comparación con el titanio puro. El daño de desgaste está afectado críticamente por la ductilidad del material, por lo tanto, por el elemento de aleación. La aleación Ti6Al7Nb mostró una mejor resistencia a la corrosión y un comportamiento similar de tribocorrosión en comparación con la aleación Ti6Al4V. Los resultados de esta tesis han demostrado que el Ti6Al7Nb obtenido por pulvimetalurgia es una prometedora aleación biomédica para implantes orales. El deterioro del desgaste de las aleaciones de Ti sinterizadas depende del potencial electroquímico y su comportamiento a tribocorrosión se ve afectado de manera crítica por un alto contenido de ion flúor<br>El titani i els seus aliatges s'han utilitzat en l'implantologia oral degut a les seves propietats mecàniques, resistència a la corrosió i biocompatibilitat. No obstant això, en condicions in vivo els implants són sotmesos al fenomen de tribocorrosió, que consisteix en els mecanismes de degradació causats per l'efecte combinat de desgast i corrosió. Aquest procés contribueix a limitar la vida útil de l'implant i pot generar problemes clínics com l'alliberament d'ions metàl¿lics. Una altra causa de fracàs de l'implant dental pot ser la pèrdua de fixació de l'implant, ja que el metall no promou l'osteointegració. El procés de pulvimetal¿lúrgia és una alternativa prometedora al procés tradicional de fabricació (colada i forja) d'aliatges de titani per al disseny d'implants ossis, ja que l'estructura porosa permetria que l'os creixca dins dels porus. Això donaria lloc a una millor fixació de l'implant metàl¿lic. La present tesi doctoral pretén descriure el comportament enfront de la corrosió i tribocorrosió dels aliatges de titani i els seus mecanismes de degradació quan es processen mitjançant pulverimetal¿lúrgia, com una possible alternativa a la fabricació estàndard per forja per a l'aplicació d'implants dentals. Per a això, s'ha estudiat el model d'aliatge de titani Ti6Al4V i possible substitució per l'aliatge Ti6Al7Nb, on el vanadi ha estat substituït per niobi per evitar la citotoxicitat del biomaterial resultant. La caracterització electroquímica i tribo-electroquímica dels biomaterials s'ha dut a terme en diferents condicions fisicoquímiques amb rellevància biològica (en saliva artificial (AS) amb fluorur, pH i condicions oxidants) que influix notablement en els mecanismes de degradació dels materials estudiats. També s'ha utilitzat una nova tècnica de tribocorrosió que permet mesurar el potencial galvànic i el corrent entre la pista de desgast (ànode) i el material passiu (càtode) a través de la ametria de resistència zero (Zero-Resistence Ammetry, ZRA) per elucidar els mecanismes de tribocorrosió de l'aliatge de forja Ti6Al4V en AS. La tècnica ZRA per tribocorrosió va permetre predir l'àrea real despassivada i, per tant, la desviació dels mecanismes de desgast de la llei de desgast de Archard en OCP. Tots els aliatges mostren passivitat en la saliva artificial, tot i que la dissolució activa es produix en presència d'alta concentració de fluorur (1000 ppm) i condicions àcides, pH 3. El mecanisme de degradació dels aliatges sinteritzats es regix principalment pel desgast mecànic en AS i només determinat per la dissolució activa quan s'afegixen fluorurs a la saliva artificial acidificada (pH 3). Es va trobar que el desgast es regix per la condició oxidant predominant (simulada per canvis en el potencial d'elèctrode). L'aliatge Ti6Al4V processada per pulverimetal¿lúrgia va mostrar una resistència similar a la tribocorrosió quan es va comparar amb l'aliatge forjada comercial disponible, el que suggerix que la pulverimetal¿lúrgia és un prometedor procés de fabricació per a aplicacions d'implants. S'ha estudiat la influència dels elements d'aliatge Al i Nb sobre el comportament de corrosió i tribocorrosió de diferents aliatges de titani Ti6Al7Nb, Ti7Nb i Ti6Al i en tots els casos la resistència a la corrosió es millora en comparació amb el titani pur. Es va trobar que el dany de desgast està afectat críticament per la ductilitat del material, per tant, per l'element d'aliatge. L'aliatge Ti6Al7Nb va mostrar una millor resistència a la corrosió i un comportament similar de tribocorrosió en comparació amb l'aliatge Ti6Al4V. Els resultats d'aquesta tesi han demostrat que el Ti6Al7Nb obtingut per pulverimetal¿lúrgia és un prometedor aliatge biomèdic per a implants orals. El deteriorament del desgast dels aliatges de Ti sinteritzats depèn del potencial electroquímic i el seu comportament a tribocorrosió es veu afectat de manera crí<br>Licausi, M. (2017). Analysis of tribocorrosion behavior of biomedical powder metallurgy titanium alloys [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/90448<br>TESIS

Thesis (M.S.)--University of Missouri-Columbia, 2005.<br>The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (July 14, 2006) Includes bibliographical references.

In order to produce crack free metal powder compacts, the critical region of failure should be detected, so that the particular region can be strengthened during the compaction process. The finite element method, through the use of an appropriate constitutive model of the powder medium, has recently been used as an efficient design tool. The accuracy of this method highly depends on the faithfulness of the constitutive model and the quality of the material parameter set. Furthermore, in order for the simulation results to be reliable, they should be experimentally validated on real parts featuring density variations. Hence, the main concerns are the development of a standard calibration procedure for the cap material model as well as the development of a reliable technique for the experimental validation of the powder compaction simulation results. A FC-0208 automotive main bearing cap was compacted to investigate the microstructure changes at different locations within the parts. Measurements of the pore volume fraction, pore size, pore nearest neighbor, pore aspect ratio, and grain size were performed after compaction and sintering for the MBC. A finite element model for the compaction and monotonic performance of the bearing cap was developed to study the density distribution and the performance of the bearing cap during monotonic loading respectively. The image analysis methodology and monotonic load testing was created to measure density in the main bearing cap and to predict the critical location of failure respectively, and to validate the finite element model results. A comparison between the experiment and model for determining the performance of the bearing cap was carried out such that the model predicts the damage state during loading of the bearing cap.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, September 2005.<br>"August 2005."<br>Includes bibliographical references.<br>A Multi-Scale Analysis methodology was developed and carried out for gaining fundamental understanding of the pharmaceutical powder blending process. Through experiment, analysis and computer simulations, microscopic particle properties were successfully linked to their macroscopic process performance. This work established this micro-to-macro approach as a valid way to study unit operations in the pharmaceutical manufacturing of solid dosage forms. The pharmaceutical materials investigated were anhydrous caffeine, lactose monohydrate and micro- crystalline cellulose (MCC). At the macroscopic level, blending experiments were conducted in mini-scale lab blenders using the Light-Induced Fluorescence (LIF) technique. Effects of operating parameters on blending kinetics were systematically evaluated. It was found that the time required to reach a homogeneous mixture (thg) increased with blender fill volume (FV) and decreased with blender rotation rate (RPM). It was also found that MCC, as an excipient, always took longer time to mix with caffeine than lactose. At the microscopic level, force interactions - cohesion/adhesion and friction - were measured directly at the single particle level with Atomic Force Microscopy (AFM).<br>(cont.) It was found that cohesion/adhesion and friction fell into lognormal distributions. Based on AFM force maps, these distributions were attributed to the particle surface morphology. Chemically modified AFM cantilever tips were used to probe the hygroscopicity on the particle surfaces. In addition, the cohesive/adhesive forces were found to be size- dependent and thus, were converted to JKR surface energies to eliminate this dependence. Amongst the materials tested, MCC showed the strongest cohesive/adhesive and friction interactions. The AFM-measured microscopic force interactions were used to explain the blending kinetics profiles observed in the blending experiments. The longer blending time (thg) required by MCC was linked to its strong cohesive nature. In addition to these multi-scale relations, the AFM force interactions were used in Discrete Element Method (DEM) models for simulating blending processes. A two-dimensional model was used to simulate blending in a circular blender. With respect to the effect of operating parameters on blending kinetics, the simulations showed that thg increased as FV increased, RPM decreased, or when MCC as opposed to lactose was chosen as the excipient.<br>(cont.) These trends were identical to experimental observation. A three dimensional DEM code was developed. Blending in a V-shaped blender was simulated and results were consistent with experiments, namely the flow behavior correlated well with the differences in cohesion/adhesion and friction intensities of the excipients. Through a fundamental understanding at a microscopic level, one can identify opportunities for process improvement. In this way, Multi-Scale Analysis will facilitate the ability of pharmaceutical companies in pursuing the desired quality-by-design state in manufacturing.<br>Samuel SH Ngai.<br>Ph.D.

Thesis (Ph.D.)--University of Missouri-Columbia, 2005.<br>The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (November 15, 2006) Vita. Includes bibliographical references.

<p>There are today strong incentives for an increased understanding of material properties and manufacturing processes to facilitate the development of new technologies in the pharmaceutical industry. The purpose of this thesis was to suggest methods requiring a low sample amount for characterization of technical properties of powders.</p><p>Compression analysis was used to evaluate the formulation relevance of some compression equations. Using the mechanics of single granules to estimate powder functionality was part of this work. It was concluded that the formability of granular solids and the plasticity of single granules could be determined with compression analysis by using the Kawakita model for single components and binary mixtures of ductile granules.</p><p>Further on, the fragmentation propensity of solid particles could be estimated from compression analysis by using the Shapiro equation, enabling indicators of both the fragmentation and the deformation propensity of particles to be derived in one single compression test.</p><p>The interpretations of the compression parameters were only valid if the influence of particle rearrangement was negligible for the overall compression profile. An index indicating the extent of particle rearrangement was developed and a classification system of powders into groups dependent on the incidence of particle rearrangement was suggested as tools to enable rational interpretations of compression parameters.</p><p>The application of compression analysis was demonstrated by investigating the relevance of the mechanics of granular solids for their tableting abilities. The plasticity of single gran-ules was suggested to influence both the rate of compactibility and the mode of deformation, and consequently the maximal tablet strength. The degree of granule bed deformation was shown to be a potential in line process indicator to describe the tableting forming ability.</p><p>This thesis contributes to a scheme, suitable in formulation work and process control, to describe manufacturability of powders for an enhanced tablet formulation technology.</p>

Powdery mildew, caused by Blumeria graminis (DC.) E.O. Speer f. sp. tritici E'm. Marchal (syn. Erysiphe graminis f. sp. tritici), is one of the major diseases of wheat (Triticum aestivum L.) worldwide. The use of cultivars with resistance to powdery mildew is an efficient, economical and environmentally safe way to control powdery mildew. Race-specific resistance has been extensively used in breeding programs; however, it is ephemeral. Adult plant resistance (APR) to powdery mildew is more durable as demonstrated by the cultivar Massey, which has maintained its APR to powdery mildew since its release in 1981. To develop an efficient breeding strategy, it is essential to understand the genetic basis of APR. The objectives of this study were to identify molecular markers associated with APR to powdery mildew in common wheat Massey and to verify their association using recombinant inbred (RI) lines. A cross was made between the powdery mildew susceptible cultivar Becker and Massey. One hundred and eighty F2:3 lines were rated for disease severity under natural pressure of powdery mildew in field. Using both restriction fragment length polymorphism (RFLP) and microsatellite markers, three quantitative trait loci (QTL), designated as QPm.vt-1B, QPm.vt-2A and QPm.vt-2B, were identified in the Becker x Massey F2:3 generation. These loci are located on chromosomes 1B, 2A and 2B, respectively, and explained 17%, 29% and 11% of the total variation among F2:3 lines for powdery mildew resistance, respectively. Cumulatively, the three QTLs explained 50% of the phenotypic variation among F2:3 lines in a multi-QTL model. The three QTLs associated with APR to powdery mildew were derived from Massey and displayed additive gene action. QPm.vt-2B also fits a recessive model for APR to powdery mildew. In the second part of this study, 97 RI lines were developed from the Becker x Massey cross. The RI lines were evaluated for APR to powdery mildew under natural disease pressure for three years. Both single marker analysis and interval mapping confirmed the presence of the three QTLs identified in the F2:3 generation. The three QTLs, QPm.vt-1B, QPm.vt-2A and QPm.vt-2B, accounted for 15%, 26% and 15% of the variation of mean powdery mildew severity of the RI lines over three years. In a multi-QTL model, the three QTLs explained 44% of the phenotypic variation of the RI lines. The RI lines were grouped according to the genotype of the three QTLs, represented by markers GWM304a, KSUD22 and PSP3100, respectively. The RI lines with Massey alleles at all three loci had a mean disease severity of 3.4%, whereas the RI lines with Becker alleles at all three loci had a mean disease severity of 22.3%. These severity values are similar to those of the corresponding parents. The molecular markers identified and verified as to their association with APR to powdery mildew in Massey have the potential for use in marker-assisted selection for resistance to powdery mildew and in pyramiding powdery mildew resistance genes, as well as facilitating a better understanding of the molecular basis of APR to powdery mildew.<br>Ph. D.

Barley is one of the most important crop species in Turkey and powdery mildew is one of the most common pathogen decreasing yield in barley. For this problem, agricultural biologists apply breeding technologies in order to select and propagate resistant barley cultivars. However, this is not a permanent solution since pathogens evolve rapidly to overcome plant resistance mechanisms. On the other hand, molecular plant pathologists are trying to understand basic mechanisms underlying plant-pathogen interactions by using molecular tools in order to develop long term solutions for preventing yield loss. In this thesis, miR159 mediated regulation of barley GAMyb transcription factor is studied. According to microRNA microarray results regarding to infection with powdery mildew pathogen Blumeria graminis f.spp hordei (Bgh) at different time points, miR159 expression level showed significant differences. Bioinformatics analysis revealed that miRNA159 targets GAMyb gene in barley. In order to investigate this relationsh&amp<br>#8223<br>p, both miRNA and miRNA target were cloned into GFP containing expression vectors through Gateway cloning and resulting vectors were transformed into Nicotiana benthamiana through Agrobacterium mediated gene transfer. Observations based on GFP expression showed that miRNA159 targets and decreases the expression of GAMyb in vivo. v To conclude, this study can be evaluated as a distinctive study for two aspects<br>(i) it is the first study assessing a &ldquo<br>putative&rdquo<br>barley miRNA function biologically and (ii) developed a practical and effective functional assay for miRNA studies in plants.

Electrostatic phenomena are pervasive in powder handling processes. In this study, contact electrification and electrostatic interactions during powder handling processes are explored using the discrete element method coupled with computational fluid dynamics (DEM-CFD), in which contact electrification and electrostatic interaction models are developed and implemented. The effects of particle shape on contact electrification are also investigated, for which multi-sphere methods are adapted and implemented into the DEM-CFD. The electrostatic and dynamic behaviours in various powder handling processes are analyzed, which include contact electrification of spherical particles during fluidization; electrostatic interactions during deposition of mono-charged and bi-charged particles; contact electrification and electrostatic interactions of spherical particles during fluidization; contact electrification of elongated particles in a vibrating container and particles of arbitrary shapes in a rotating drum. It is found that charge accumulation and distribution of particles are caused by contact electrification and dispersion of mono-charged particles and agglomeration of bi-charged particles are induced by electrostatic interactions. The combined effects of contact electrification and electrostatic interactions can alter the dynamic behaviours of particles and the performance of powder handling processes. Non-uniform charge distributions can be induced on particles of irregular shapes and the charge accumulation is also affected by particle shapes.

Bibliography: leaves 60-61.<br>During the commercial compaction of metal powder in a punch-die setup and the subsequent sintering of the compacted preform, the large confining pressures, friction and heat that arise determine the properties of the final component. An important application of the modelling of metal powder compaction is the determination of the properties of the compacted preform as these affect the properties of the final sintered component. An uneven density distribution in the compacted preform, for example, can cause cracking in the component during the sintering stage. The mechanical behaviour of the metal powder during compaction largely determines the properties of the compacted preform. To date the consolidation of metal powders has been conveniently represented using constitutive theories based on elastic-plastic material models. Most of the work has concentrated on the use of quadratic yield surfaces but experimentation has shown that this type of yield surface does not always correctly represent metal powder behaviour (Brown, 1994 ). This thesis details the development of a new constitutive model for the finite element analysis of metal powder compaction based on extensive experimental testing done by Watson(1993) on aluminium powder. Watson found that a cap yield surface, often used in soil plasticity, best fitted the experimental data obtained from the aluminium powder. A model similar to that proposed by Watson was implemented in this thesis in an attempt to show that a cap yield surface is more accurate for modelling the compaction of aluminium powder and other powders than a quadratic yield surface. The new constitutive model combines a Drucker-Prager or shear yield surface and a density evolving cap or consolidation yield surface to model powder compaction and differs from other cap models as the shear yield surface also evolves with density. A combination of an associative flow rule on the consolidation yield surface and a von Mises flow rule on the shear yield surface made for easier numerical implementation of the model. The model was implemented in ABAQUS as a FORTRAN 77 User-Material Subroutine using an Euler Backward integration scheme.

Laser Melting (LM) is an Additive Layer Manufacturing (ALM) process used to produce three-dimensional parts from metal powders by fusing the material in a layerby- layer manner controlled by a CAD model. During LM, rapid temperature cycles and steep temperature gradients occur in the scanned layers. Temperature gradients induce thermal stresses which remain in the part upon completion of the process (i.e. residual stresses). These residual stresses can be detrimental to the functionality and structural integrity of the built parts. The work presented in this thesis developed a finite element model for the purpose of investigating the development of the thermal and residual stresses in the laser melting of metal powders. ANSYS Mechanical software was utilised in performing coupled thermal-structural field analyses. The temperature history was predicted by modelling the interaction of the moving laser heat source with the metal powders and base platform. An innovative ‘element birth and death’ technique was employed to simulate the addition of layers with time. Temperature dependent material properties and strain hardening effects were also considered. The temperature field results were then used for the structural field analysis to predict the residual stresses and displacements. Experiments involving laser melting Ti-6Al-4V powder on a steel platform were performed. Surface topography analyses using a laser scanning confocal microscope were carried out to validate the numerically predicted displacements against surface measurements. The results showed that the material strain hardening model had a direct effect on the accuracy of the predicted displacement results. Using the numerical model, parametric studies were carried out to investigate the effects of a number of process variables on the magnitude of the residual stresses in the built layers. The studies showed that: (i) the average residual stresses increased with the number of melted powder layers, (ii) increasing the chamber temperature to 300°C halved the longitudinal stresses. At 300°C, compressive stresses appeared on the Ti64 surface layer, (iii) reducing the raster length from 1 mm to 0.5 mm reduced the average longitudinal stress in the top layer by 51 MPa (0.04σy), (iv) reducing the laser scan speed from 1200 mm/s to 800 mm/s increased the longitudinal stress by 57 MPa (0.05σy) but reduced the transverse stress by 46 MPa (0.04σy).

COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR<br>UNIVERSIDADE FEDERAL DA BAHIA<br>A análise de sistemas de medição consiste do exame da adequação do sistema quanto ao operador, ao instrumento e a outras fontes de variação, bem como da comparação da variância do erro de medição com a variância natural do processo. Nesse aspecto, esta pesquisa teve por objetivo a análise das incertezas da quantificação de fase pelo método de Rietveld em análise de pó. Os efeitos de vários fatores na quantificação de fase foram avaliados utilizando técnicas estatísticas de planejamento experimental e de análise multivariada, com a utilização de materiais de alto nível de rastreabilidade na realização dos experimentos, no Laboratório de difração de raios X do Departamento de Ciências de Materiais e Metalurgia da PUC-Rio. Através da determinação do construto de variação do processo, constatou-se que a quantificação das fases analisadas sofre influência das condições de medição de forma diferenciada de material para material, impossibilitando a obtenção de uma fórmula geral para cálculo dos erros de quantificação, embora os erros possam ser determinados por uma análise de repetitividade e reprodutibilidade apropriadamente conduzida.<br>The analysis of measurement systems is done by the examination of the adequacy of the system according to the operator, the instrument and other sources of variability, as well as by the comparison of the measurement error variance with the natural process variance. This research consisted in the evaluation of the uncertainties of phase quantification in powder analysis by the Rietveld method. The evaluation of the effects of several factors on the phase quantification was performed using statistical techniques of design of experiments and of multivariate analysis, with the use of materials of high level of traceability for the conduction of the experiments, in the Laboratory of X-ray Diffraction of the Pontifícia Universidade Católica do Rio de Janeiro. Through the determination of the variational structure of the process it was verified that the analyzed phases suffer influence of the measurement conditions in a differentiated way, which prevents the obtention of a general formula for calculation of the quantification error, although the errors can be determined by a repeatability and reproducibility analysis properly conducted.

Submitted by Reginaldo Soares de Freitas (reginaldo.freitas@ufv.br) on 2017-06-20T17:30:34Z No. of bitstreams: 1 texto completo.pdf: 1425926 bytes, checksum: ee624a74ef4a36d197d9316ae8fe4072 (MD5)<br>Made available in DSpace on 2017-06-20T17:30:34Z (GMT). No. of bitstreams: 1 texto completo.pdf: 1425926 bytes, checksum: ee624a74ef4a36d197d9316ae8fe4072 (MD5) Previous issue date: 2016-08-25<br>Conselho Nacional de Desenvolvimento Científico e Tecnológico<br>Oídio do eucalipto é uma importante doença que ocorre principalmente em casas de vegetação e minijardins clonais protegidos de eucalipto (Eucalyptus spp.) no Brasil. O fungo infecta folhas jovens e brotações. Sobre o tecido afetado, observam-se colônias superficiais isoladas ou agrupadas do fungo de coloração branca, que podem atingir toda superfície foliar e induzir malformação dos órgãos afetados e resultar em redução do crescimento e da produção de brotos para estaquia. Devido ao aumento da incidência e importância dessa doença nos últimos anos e também à falta de pesquisas relacionadas a esse patossistema, esse estudo objetivou: i) determinar a etiologia do oídio do eucalipto por meio do sequenciamento da região ITS e 28S do rDNA e de análises morfológicas de isolados de oídio coletados em diferentes regiões geográficas do Brasil; e ii) analisar o transcriptoma do patógeno durante a infecção em Eucalyptus urophylla gerado pelo sequenciamento do transcriptoma (RNA-Seq) e montagem de novo. Baseado nos resultados de análises filogenéticas e caracterização morfológica, todos os 42 isolados coletados foram identificados como Podosphaera pannosa, também conhecido como agente etiológico do oídio das roseiras. Inoculações cruzadas com isolados de P. pannosa de roseira e eucalipto demonstraram que P. pannosa pode infectar ambas as espécies. O sequenciamento do transcriptoma de P. pannosa pela plataforma Illumina resultou em 12.107 transcritos. Entre os 10 transcritos mais abundantes, encontram-se os genes codificadores de enzimas envolvidas no estabelecimento e crescimento do fungo. A predição do secretoma do fungo resultou em 217 proteínas, das quais 14 foram consideradas como candidatas a efetores. Além disso, 242 pares de primers foram desenhados a partir das sequências do transcriptoma com potencial para amplificar regiões microssatélites (Simple Sequence Repeats - SSR) de P. pannosa. Os resultados gerados neste trabalho demonstram que apenas a espécie P. pannosa causa doença no eucalipto. Além disso, fornece informações úteis para novos avanços nos estudos sobre a doença por oferecer uma base para a melhor compreensão sobre o patossistema P. pannosa- eucalipto.<br>Eucalypt powdery mildew is an important disease that occurs mainly in greenhouses and protected clonal hedges of eucalypt (Eucalyptus spp.) in Brazil. The fungal pathogen infects new leaves and shoots. White superficial colonies isolated or grouped that grow over the affected plant tissue are observed, which can subsequently spread to all leaf surface, causing leaf malformation and reduction on growth and production of shoots for mini-cutting. Because this disease has increased in incidence and importance in recent years, and research on this pathosystem is largely lacking, the objectives of this study were to i) determine the etiology of the disease through ITS and 28S rDNA sequencing and morphological analyses of powdery mildew pathogens isolates collected in different regions in Brazil; and ii) analyze the transcriptome of the powdery mildew pathogen during infection on Eucalyptus urophylla generated by RNA sequencing (RNA-Seq) and de novo assembly. Based on the results of phylogenetic analyses and morphological characteristics, all 42 pathogen isolates collected were identified as Podosphaera pannosa, also known to cause rose powdery mildew. Cross inoculations with pathogen isolates from rose (Rosa spp.) and eucalypt demonstrated that P. pannosa can infect both host species. The transcriptome sequencing by Illumina platform resulted in 12,107 transcripts. Among the 10 most abundant transcripts included genes encoding enzymes involved in fungal establishment and growth. The secretome prediction resulted in 217 proteins, of which 14 were considered as candidate effectors. In addition, 242 primer pairs were designed from the transcriptome sequences with potential to amplify P. pannosa microsatellites (Simple Sequence Repeats – SSR) regions. The results demonstrate that P. pannosa is the only causal agent found for eucalypt powdery mildew. In addition, this study provides technological advances in the study of this disease that will provide a basis for a better understanding of the P. pannosa- eucalypt pathosystem.

Hydroxyapatite (HAP) coatings are used in orthopaedic surgery for bone regeneration. Current methods of phase quantification of HAP coatings suffer from drawbacks. A novel methodology of quantitative phase analysis of HAP coatings has been devised and validated. This method, based on whole pattern fitting with a fundamental parameters approach, incorporates amorphous calcium phosphate (ACP) and apatite phases into structural refinements. A comparison of the structural and chemical properties of plasma sprayed (PS) and novel electrodeposited (ED) HAP coatings has been conducted. ED coatings contained less ACP and more preferred orientation than the PS coatings, although the stoichiometry was similar. In vitro investigations of PS and ED coatings in simulated body fluid and foetal calf serum revealed that both are bioactive. A carbonated apatite layer produced on the ED coatings was -0.7μm thick with a stoichiometry and chemical constituents similar to that of natural bone apatite. PS coatings produced a nanocrystalline carbonated apatite layer (-4μm). For the first time it has been possible to model crystalline HAP and nanocrystalline apatite as independent phases and obtain accurate lattice parameters for each. A positive linear correlation has been made between microstrain and the solubility of HAP and carbonated apatites. Dissolution studies have shown that the behaviour of HAP and carbonated apatite is dominated by crystallite size at low undersaturation and by crystallite size and microstrain at high undersaturation for crystallites between -30OA- 1000A. Metastable equilibrium occurred for crystallites <_400A at low undersaturation. Carbonate content did not affect the solubility or dissolution behaviour. A novel technology for coating polymeric tape with HAP for potential use in anterior cruciate ligament reconstruction has been devised. Mechanical tests have demonstrated that no adverse properties are induced by the coating technology. Cell culture studies have shown that the HAP layer is capable of enhanced attachment, proliferation and differentiation of osteoblast cells compared to uncoated tape.

Hydroxyapatite (HAP) coatings are used in orthopaedic surgery for bone regeneration. Current methods of phase quantification of HAP coatings suffer from drawbacks. A novel methodology of quantitative phase analysis of HAP coatings has been devised and validated. This method, based on whole pattern fitting with a fundamental parameters approach, incorporates amorphous calcium phosphate (ACP) and apatite phases into structural refinements. A comparison of the structural and chemical properties of plasma sprayed (PS) and novel electrodeposited (ED) HAP coatings has been conducted. ED coatings contained less ACP and more preferred orientation than the PS coatings, although the stoichiometry was similar. In vitro investigations of PS and ED coatings in simulated body fluid and foetal calf serum revealed that both are bioactive. A carbonated apatite layer produced on the ED coatings was -0.7μm thick with a stoichiometry and chemical constituents similar to that of natural bone apatite. PS coatings produced a nanocrystalline carbonated apatite layer (-4μm). For the first time it has been possible to model crystalline HAP and nanocrystalline apatite as independent phases and obtain accurate lattice parameters for each. A positive linear correlation has been made between microstrain and the solubility of HAP and carbonated apatites. Dissolution studies have shown that the behaviour of HAP and carbonated apatite is dominated by crystallite size at low undersaturation and by crystallite size and microstrain at high undersaturation for crystallites between -30OA- 1000A. Metastable equilibrium occurred for crystallites <_400A at low undersaturation. Carbonate content did not affect the solubility or dissolution behaviour. A novel technology for coating polymeric tape with HAP for potential use in anterior cruciate ligament reconstruction has been devised. Mechanical tests have demonstrated that no adverse properties are induced by the coating technology. Cell culture studies have shown that the HAP layer is capable of enhanced attachment, proliferation and differentiation of osteoblast cells compared to uncoated tape.

The quest for developing high performance materials, originally responsible for the birth and growth of the composites industry, is now responsible for the drive to produce composites which outperform those used today. A great deal of this interest lies in the use of thermoplastic polymers as the composite matrix. Thermoplastics offer the potential of improved mechanical performance, greater solvent resistance, better impact tolerance, as well as cost saving processing attributes such as infinite shelf life, the ability to be recycled, short processing time and repairability. Unfortunately, these advantages come at the expense of a very high melt viscosity which makes the prepregging process, where the fiber and polymer are combined, very difficult. To overcome this and associated difficulties a detailed analysis of thermoplastic matrix composite processing is developed. The primary area of focus involves the development of an electrostatic dry polymer powder prepregging facility. This unit is capable of the production of high quality towpreg from thermoplastic polymers and reinforcing fibers. Two approaches, statistical and stochastic, were employed to model the process of polymer deposition on the fibers in the prepregging process. These models are used to optimize the production of towpreg. A modification of the prepregging facility allows for the production of towpreg from very small (15 g) samples of polymer. This is extremely useful for analysis and performance verification of state of the art polymer systems.<br>Ph. D.

Direct powder rolling (DPR) is thought to be a more cost-effective, more direct route to producing flat product of near final thickness. It is a particularly attractive route for titanium given that the existing wrought method of melting titanium sponge to ingot followed by rolling to slab to plate and finally to thin gauge product is an energy and capital-intensive process. There are several studies that have investigated the operational parameters of DPR, but there has been little assessment of the realization of DPR as a fully operational process producing a commercially viable product. The commercial viability of DPR is a particularly pertinent question for South Africa given the investment, by the Council for Scientific and Industrial Research and the Department of Science and Technology, in the development of an innovative powder manufacturing technology, as well as complementary powder metallurgy methods. A commercial viability assessment of DPR was structured around three analyses: 1.) whether a supply-side market exists to support a commercial enterprise, 2.) how the performance of DPR product compares to the performance of product produced via the conventional wrought route, and 3.) what range of potential product applications could be suitable for DPR product. A systematic review of published research was conducted by extracting and consolidating performance and process data, and a market analysis was conducted by sourcing price points from powder suppliers and wrought product suppliers. The performance of DPR product, in terms of elongation and ultimate tensile strength, was found to be comparable to the typical properties of ASTM grade 3 and 4 wrought product, which contain higher oxygen and are the least ductile of the commercially pure titanium grades. Due to the particulate nature of the starting stock and titanium’s affinity for oxygen, oxidation was found to be the single greatest problem in powder metallurgy. The upper and lower bounds of the oxygen range were identified, and the consolidation of data showed that an oxygen content of less than 0.2 wt% is not commonly achieved for non-hydride derived product. The possibility of producing a weldable product via DPR was found to be low, due to the unacceptable degree of chlorine content, which is typically greater than 0.02 wt% in low-cost (non-melt) commercially available powders, as well as the fact that weldability has not been reliably demonstrated for powder metallurgy product made from these powders. The existing powder market was also found to be inadequately geared towards supporting a commercial enterprise due to the small size of the market and the lack of availability of low-cost quality powders. The comparison of powder prices to wrought product prices showed that the potential for commercial viability is likely to exist only for thin gauge strip of less than 1mm thickness, as this is where cost savings can be attained through direct route processing. Based on the DPR product profile identified, the range of potential product applications was found to be greatly limited. The inability to reliably meet the typical properties of the “workhorse”, grade 2, excludes the largest proportion of applications for which pure titanium in strip form is used (heat exchangers and tubing). Furthermore, the lack of evidence of adequate weldability further restricts the usage of DPR product to applications where welding is not a critical requirement. For these reasons, it was concluded that DPR is not a commercially viable process.

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2015.<br>Made available in DSpace on 2016-12-13T03:03:04Z (GMT). No. of bitstreams: 1 340514.pdf: 4063742 bytes, checksum: 6a2f911982008b177bc31b52c459c372 (MD5) Previous issue date: 2015<br>Abstract: The quality of the Laser Metal Deposition process depends on several factors and components. One of them and also one of the most important is the powder jet. Regular monitoring of the different variables involved on the powder jet need to be performed in order to assure the demanded high stability and quality standards of the produced coating layers. This monitoring is done through process monitoring techniques, where the powder jet is illuminated from the side, by a laser line, and recorded by a coaxially aligned camera through the powder feed nozzle. Symmetry, geometry and position of different levels of the powder jet can be analyzed through relevant algorithms. They also provide calculations of the particle density distribution the recorded images. The spatial particle density distribution of the powder jet can be calculated by superimposing individual levels along the jet. The measurement and monitoring principle was successfully tested with various nozzles and powder properties, making it possible to fully characterize a powder jet.<br><br>A qualidade do processo de deposição de metais a laser depende de diversos fatores e componentes. Um dos componentes mais importantes é o fluxo de pó metálico. É necessário o monitoramento contínuo das diferentes variáveis e parâmetros que influenciam no fluxo de pó para se garantir os altos padrões de qualidade e estabilidade requeridos nas peças produzidas. Este monitoramento é realizado através de técnicas de controle de processos, onde o fluxo de pó metálico é iluminado lateralmente, por um laser de iluminação em formato de linha, e gravado por uma câmera coaxial ao bocal alimentador de pó. Simetria, geometria e posição de diferentes níveis do fluxo de pó podem ser analisados através de algoritmos relevantes. Tais algoritmos tornam possíveis também cálculos da distribuição das partículas no fluxo, através da sobreposição de imagens de todos os frames gravados no vídeo em cada nível do fluxo de pó. O processo de medição e análise foi testado com sucesso em diferentes bocais alimentadores de pó e com diferentes materiais e parâmetros do fluxo, tornando possível sua caracterização e qualificação.

The first study focuses on the development of a laser based method for the elemental analysis of solid milk powder. Milk powder samples originating from five different countries were analyzed to determine any geographic differences. A LA-ICP-MS method was developed and compared to k0-INAA for several milk samples as well as a reference sample. Precision of 10% RSD or better and a bias of 10% was achieved for both techniques for most elements with LA-ICP-MS producing lower limits of detection (~ 1 ppm) for Sr. The comparison of LA-ICP-MS to k0-INAA showed overlap of the 95% confidence intervals for all comparison samples. The data for 68 authentic milk powder samples representing 5 different countries (Argentina, Russia, Singapore, Slovenia, and the United States) was collected and used as a preliminary database. Principle component analysis (PCA) shows different groupings for the United States, Argentina, Singapore, and Slovenia. However the large number and geographic distribution of samples from Russia were not able to be distinguished from the samples from the United States and Slovenia. The second study focuses on the use of trace element databases for the objective interpretation of forensic glass evidence. Ten laboratories conducting analysis of glass participated in three inter-laboratory exercises. The aims of these exercises were to evaluate the use of a standard method for the analysis and comparison of glass evidence and to investigate different statistical approaches for interpreting results. Elemental analysis was performed on 420 vehicle windshield samples collected from 210 different vehicles representing manufacturing dates between 2004-2017 and 26 vehicle manufacturers. Using a variation of a previously reported comparison criterion for comparing samples to a database, the false exclusion rate and false inclusion rate for the new vehicle database were calculated to be 1.9% and 0.1 % respectively. This criterion was used to calculate the frequency of an elemental profile for the case scenarios distributed as part of the inter-laboratory exercises. Similarities were observed between labs that calibrated their data the same way, thus showing it is possible for labs to use a central database.

Made available in DSpace on 2014-10-09T12:48:48Z (GMT). No. of bitstreams: 0<br>Made available in DSpace on 2014-10-09T13:59:47Z (GMT). No. of bitstreams: 1 09623.pdf: 10580829 bytes, checksum: 0030255b59926321efcd78e25d95462d (MD5)<br>Tese (Doutoramento)<br>IPEN/T<br>Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

A method has been developed to produce grain sizes as low as 5µm in β-CuAlNi alloys and the effect of grain size on mechanical and strain-memory properties was studied. The thermomechanical treatment procedure involved two. sequential warm working and recrystallization steps at 600° C and 800° C respectively on eutectoid alloys. Three different eutectoid alloys, two with Ms temperature of around 0°C and one with Ms = 220° C were used for the present studies. Even at fine grain sizes, the specimens produced were of single β- phase type without any second phases. Two-stage characteristic stress-strain curves were obtained for most of the specimens in both the strain memory and pseudoelastic states. It was found that the ultimate tensile strength and strain to failure increased with decreasing grain size according to a Hall-Petch relationship down to a grain size of 5µm with the exception of one alloy. Fracture strengths of 1,200 MPa and fracture strains of 10% could be obtained. It was found that the major recovery mode, whether pseudoelastic or strain memory, did not have any significant effect on the total recovery obtained. Recovery properties were not affected significantly by decreasing grain size. Approximately 86% recovery could be obtained for an initial applied strain of 5% at a grain size of around 10µm. Grain refinement increased the fatigue life considerably, possibly due to high ultimate fracture strength and ductile fracture mode. Fatigue life of 275,000 cycles could be obtained for an applied stress of 330 MPa and a steady state strain of 0.6%. Most of the fractures are due to intergranular-type brittle fracture. At fine grain sizes, transgranular-type brittle fracture and microvoid coalescence-type ductile fracture dominated the fracture mode. Oxygen segregation at grain boundaries is the possible explanation for the different mechanical properties shown by different alloys in the present work by being a major factor in causing intergranular-type fracture.<br>Applied Science, Faculty of<br>Materials Engineering, Department of<br>Graduate

碩士<br>大葉大學<br>生物資源學系碩士班<br>101<br>Kefir is a fermented milk product by kefir grain. Kefir has been certidied with antibacteria, antifungal, antivirus, anti-allergy, anti-inflammatory, and blood pressure-lowering activities. The kefir powder was subjected to genotoxicity analysis. In this study, Ames test, mouse lymphoma tk assay, chromosome aberrations assay, cytokinesis-block micronucleus assay, and mice peripheral blood micronucleus assay were performed in accordance with OECD guidelines for the testing of Chemicals. These results reveal that the kefir powder was not genotoxic in five independent assays.

碩士<br>國立臺灣大學<br>化學工程學研究所<br>88<br>This paper principally discuss how the surface hydroxyls removed by HDMS treatment or not influece the ZrO2 powders.For the powders without HDMS treatment the content of t-ZrO2 was found to decrease with increasing calcination time and temperature. Nevertheless, for the powders with removing surface hydroxyls by HDMS treatment, either pure or with yttrium-doping, only the t-ZrO2 was produced throughout the entire calcination temperature from 300 to 1100 oC and the average crystallite size of t-ZrO2 was merely 6.5nm after calcination up to 900 oC. In addition, the specific surface area of powders with HDMS treatment was larger than those without HDMS treatment. These make it possible to test the reversibility by, after the cold work, carrying out thermal treatment at sufficiently high temperatures while maintaining the crystallite not exceeding the "critical size".