The effect of austenitising and tempering practice on the microstructure and mechanical properties of two martensitic stainless steels was examined with the aim of supplying heat treatment guidelines to the consumer or fabricator that, if followed, would result in a martensitic structure with minimal retained austenite, evenly dispersed carbides and a hardness of between 610 HV and 740 HV (hardness on the Vickers scale) after quenching and tempering. The steels examined during the course of this examination conform in composition to medium-carbon AISI type 420 martensitic stainless steel, except for the addition of 0.13% vanadium and 0.62% molybdenum to one of the alloys. The effect of various austenitising and tempering heat treatments was examined. Steel samples were austenitised at temperatures between 1000°C and 1200°C, followed by quenching in oil. The as-quenched microstructures were found to range from almost fully martensitic structures to martensite with up to 35% retained austenite after quenching, with varying amounts of carbide precipitates. The influence of tempering, double tempering, and sub-zero treatment was investigated. Optical and scanning electron microscopy was used to characterise the as-quenched microstructures, and X-ray diffraction analysis was employed to identify the carbide present in the as-quenched structures and to quantify the retained austenite contents. Hardness tests were performed to determine the effect of heat treatment on mechanical properties. As-quenched hardness values ranged from 700 HV to 270 HV, depending on the amount of retained austenite. Thermodynamic predictions (using the CALPHAD™ model) were used to explain these microstructures based on the solubility of the carbide particles in the matrix at various austenitising temperatures. The carbide particles were found to be mainly in the form of M7C3 at elevated temperatures, transforming to M23C6 on cooling. / Dissertation (MSc)--University of Pretoria, 2010. / Materials Science and Metallurgical Engineering / unrestricted

The motivation to use lightweight materials in the construction of the automotive structure is the resultant increased fuel efficiency. However, these materials possess certain drawbacks that make it challenging to adopt them into current automobile manufacturing processes. In this dissertation the microstructural response observed in a magnesium alloy, AZ31, and an advanced high strength steel alloy, QP1180, to uniaxial deformation is analyzed and the results are presented. In AZ31 the required slip modes are not activated at room temperature leading to its low ductility at room temperature. The resulting activity of these twins in response to uniaxial tension is analyzed and its correlations with the microstructure features is reported. Additionally, a neighborhood viscoplastic self-consistent model is developed that will allow more accurate simulation of twin response to outside deformation. Furthermore, activity of slip modes that are usually observed at high temperatures (>200°C) are also observed at lower temperatures (<125°C) and they are compared to the relative twin activity at these temperatures. It is observed that larger grains, with high schmid factors, longer grain boundaries and have misorientation with its neighboring grain greater than 27° are more favorable for twin formation and transmission in the AZ31 microstructure in response to uniaxial tension. The nature of retained austenite (RA) transformation into martensite that gives QP1180 its enhanced ductility, is not clearly understood primarily because of challenges present in characterization of these metastable RA. Further, a 2 dimensional characterization method does not provide the complete information of the RA grain. These challenges are overcome by characterization of a 3 dimensional volume element using serial sectioning and EBSD followed by reconstruction using DREAM3D. The influence of 3d morphology and orientation direction on RA transformation is studied using as-is and uniaxially deformed samples. A novel shear affinity factor is introduced as a metric to describe the ease of RA transformation under uniaxial tension. The 3d nature of the information collected allows a new classification of disk shape in addition to globular and lamellar shapes for RA. It is found that RA that are low volume laths and have low shear affinity factor transform later compared to disk shaped RA’s. Through these guidelines the preparation of a microstructure that is conducive to RA transformation under uniaxial tension is possible.

No description available.

No description available.

The expanding role of electronic nose instrumentation, as a quality-monitoring tool for food-packaging materials, is examined and reviewed. The food industry is interested in determining the applicability of using an electronic nose for odor analysis of retained printing solvent levels in packaging. Three electronic nose systems were optimized for this application and their performance assessed. These include the FOX 3000, the Cyranose 320, and the QMB6. Response surface methodology was used to generate 2nd order models of sensor response as a function of system and experimental parameters for the three electronic nose systems. Forty-seven of 50 sensor models generated were found to be significant at an a-level of 0.05. Optimum settings, that allowed adequate signals to be obtained for the full range of examined retained solvents levels, were selected for the remaining work using these models. Performance analyses of these systems, which use three leading sensor technologies, showed that the conducting polymer sensor technology demonstrated the most discriminatory power. All three technologies proved able to discriminate among different levels of retained solvents. Each complete electronic nose system was also able to discriminate between assorted packaging having either conforming or non-conforming levels of retained solvents. Each system correctly identified 100% of unknown samples. Sensor technology had a greater effect on performance than the number of sensors used. Based on discriminatory power and practical features, the FOX 3000 and the Cyranose 320 were superior. The results indicate that electronic nose instrumentation can be used as a complimentary discriminatory tool in quality control. / Master of Science

This thesis contains descriptions of works I have made over the last two years. These descriptions have been applied to support themes of melancholia, restraint, and indeterminacy, which serve as prevalent strains connecting recent work. A few stories are also shared in the way pieces come about through thinking and making.

Grade retention is an educational practice that requires students to repeat the grade level they have just completed (Jimerson, 2001). In the United States, an estimated 15% to 19% of students are retained each year (Holmes, 2006). Previous research on grade retention is comprised of quantitative studies describing students who have been retained as having higher suspension rates, coming from a low socio-economic status, and having an increased chance of dropping out of school (Christle, Jolivette, & Nelson, 2007; Janosz, et al., 1997; Jimerson & Ferguson, 2007; Jimerson et al., 2002; Suh & Suh 2007). While these studies provide a wealth of information about grade retention, they do not describe how adolescents reacted when they were retained and how they experienced retention in their lives. In this qualitative study, eight students and one of their parents were interviewed about their experiences and reactions with retention. The dominant themes identified from student and parent interviews suggest that adolescent students and their parents believed that adolescent students reacted negatively to retention, experienced changes in their lives, experienced a loss of self-esteem, felt left behind by peers, felt older than peers, felt that retention added another year of school to their education, and that adolescent students’ school performance improved following retention. Implications for school counselors are provided.

Com o objetivo de avaliar a influência do puerpério e da retenção dos anexos fetais no proteinograma de fêmeas bovinas da raça Holandesa, foram colhidas 291 amostras de sangue de vacas nos primeiros 90 dias após o parto. Para estudo do puerpério fisiológico, foram colhidas amostras de sangue de 162 fêmeas bovinas clinicamente sadias, divididas em 9 grupos experimentais, 0 -| 1º dia; 1º -| 2º dia; 2º -| 4º dia; 4º -| 6º dia; 6º -| 8º dia; 8º -| 15º dia; 15º -| 30º dia; 30º -| 60º dia; e, 60º -| 90º dia pós-parto. Para avaliar a influência da retenção dos anexos fetais, foram colhidas 129 amostras de soro sanguíneo de vacas da raça Holandesa que retiveram os anexos fetais, divididas em 8 grupos experimentais, 1º -| 2º dia; 2º -| 4º dia; 4º -| 6º dia; 6º -| 8º dia; 8º -| 15º dia; 15º -| 30º dia; 30º -| 60º dia; e, 60º -| 90º dia pós-parto. Os teores séricos de proteínas totais foram determinados pela técnica de Biureto e o fracionamento das proteínas foi realizado por eletroforese em fita de acetato de celulose e eletroforese em gel de poliacrilamida contendo dodecil sulfato de sódio (SDS-PAGE). Os resultados permitem concluir que ocorreu um aumento significativo das proteínas de fase aguda tanto nos animais com puerpério fisiológico quanto nos animais com retenção dos anexos fetais. As proteínas haptoglobina, ceruloplasmina e glicoproteína ácida responderam ao estímulo do parto e à contaminação bacteriana pós-parto nos animais com puerpério fisiológico; e nos animais com retenção dos anexos fetais, responderam de forma significativa ao estímulo da contaminação bacteriana pós-parto e da retenção dos anexos fetais prolongando o tempo de resposta das proteínas. A glicoproteína ácida representou mais evidentemente o quadro de inflamação aguda induzida pela retenção dos anexos fetais. Nos animais com retenção dos anexos fetais, a proteína albumina comportou-se como proteína de fase aguda negativa, provavelmente pela interferência de vários fatores, como distúrbios hepáticos ou metabólicos; desvio de sua síntese hepática para a produção de outras proteínas; e inflamação, infecção e absorção de toxinas bacterianas. A técnica de eletroforese em gel de poliacrilamida contendo dodecil sulfato de sódio (SDS-PAGE) a 10%, com tampão de aplicação com agente redutor, não é indicada para o estudo do comportamento das proteínas albumina e imunoglobulinas. Pela técnica de eletroforese em fita de acetato de celulose demonstrou-se que o puerpério não alterou de forma significativa a concentração de albumina, mas alterou significativamente as frações alfa, beta e gamaglobulinas. / The aim of this study was to evaluate the influence of the puerperal period and retained fetal membranes on the proteinogram of Holstein cows. Two hundred ninety one blood samples were collected from cows through ninety days postpartum. In order to study the physiologic puerperium, blood samples from one hundred two clinically animals, divided in 9 experimental groups, following the chronogram, 0 -| 1º day; 1º -| 2º day; 2º -| 4º day; 4º -| 6º day; 6º -| 8º day; 8º -| 15º day; 15º -| 30º day; 30º -| 60º day; and, 60º -| 90º day postpartum were analyzed. To evaluate the fetal membranes retention influence, one hundred twenty nine blood samples from Holstein cows with this clinical condition, in moments1º -| 2º day; 2º -| 4º day; 4º -| 6º day; 6º -| 8º day; 8º -| 15º day; 15º -| 30º day; 30º -| 60º day; and, 60º -| 90º day postpartum were also analyzed and divided in 8 experimental groups. Total proteins concentration was determined by the Biuret method and protein electrophoresis were performed in acetate cellulose and in sodium dodecyl sulfate polyacrilamide gel (SDS-PAGE). The results showed a significant elevation in acute phase proteins in both conditions, physiologic puerperium and retained fetal membranes. Haptoglobin, ceruloplasmin and acid glycoprotein were increased in the partum stimuli and postpartum bacterial contamination in animals with physiologic puerperium. In the retained fetal membranes animals, those proteins significantly responded to the pos-partum bacterial contamination stimulli and retained fetal membranes, rising the proteins response time. The acid glycoprotein concentration evidenciated an acute inflammation induced by retained fetal membranes. In the animals with this condition, albumin behaved as negative acute phase protein, probably by several factors like hepatic or metabolic disturbance, deviation of the hepatic synthesis secondary to other proteins production, and bacterial toxins absortion, inflammation and infection. Sodium dodecyl sulfate poliacrilamide 10% gel (SDS-PAGE) electrophoresis with reducing sample aplication buffer, is not indicated for albumin and immunoglobulins behavior study. Acetate cellulose electrophoresis showed that physiologic puerperium did not influencied albumin concentration, but significantly did with alfa, beta and gammaglobulins.

Os objetivos foram avaliar os efeitos da aplicação de vitamina E pré-parto sobre a incidência de retenção de placenta e desempenho reprodutivo de vacas leiteiras. Entre maio de 2012 e abril de 2013, 890 animais, sendo 390 Holandesas (132 nulíparas e 258 vacas) e 500 mestiças Holandês x Gir (199 nulíparas e 301 vacas) foram envolvidas no estudo em três fazendas. Vacas e novilhas pré-parto foram alojadas em áreas de pastagem com piquetes rotacionados entre outubro e março e receberam 2 kg/d de concentrado, contendo fubá de milho, farelo de soja, minerais e vitaminas. De abril a setembro, as fêmeas pré-parto receberam dieta total composta de silagem de milho, fubá de milho, farelo de soja, minerais e vitaminas. Durante o período pré-parto, as fêmeas receberam 280 (Fazenda 1), 390 (Fazenda 2) e 480 (Fazenda 3) UI de vitamina E por dia via dieta. Em cada fazenda, os animais foram aleatorizados a não receberam tratamento algum (Controle), ou receberem aplicações semanais de 1.000 UI de vitamina E via intramuscular, aos 258 ± 3, 265 ± 3 e 272 ± 3 d de gestação (VitE). Amostras de sangue foram colhidas de um subgrupo de 141 fêmeas imediatamente antes de serem aleatorizadas para determinar a concentração sérica de ?-tocoferol. Amostras de sangue também foram analisadas para determinar as concentrações de cortisol e ácidos graxos não esterificados (AGNEs). As análises estatísticas foram feitas através dos procedimentos GLIMMIX, MIXED, PHREG E LIFETEST do SAS. Variáveis binárias foram analisadas por regressão logística, variáveis contínuas foram analisadas por ANOVA e variáveis relacionadas a tempo a um evento foram avaliadas através de curva de sobrevivência. O ?-tocoferol sérico não diferiu entre grupos Controle e VitE, com concentração média de 2,97 ± 0,10 ?g/mL. 53,2% das fêmeas apresentaram concentração inadequada de ?-tocoferol sérico baseado em 3 ?g/mL como ponto de corte. A probabilidade das vacas terem retenção de placenta diminuiu à medida em que a concentração sérica de ?-tocoferol aumentou (P = 0,01). A produção de leite foi igual nos grupos Controle e VitE. Aplicação de vitamina E pré-parto reduziu a incidência de natimortos, retenção de placenta e mortalidade até os 200 DEL. O grupo VitE apresentou tendência (P = 0,08) de aumento na taxa de concepção à primeira IA (36,7 vs 30,1%) pela menor perda embrionária/fetal entre 30 e 60 d de gestação (12,5 vs 20,5%). Apesar de similar taxa de inseminação entre os grupos, suplementação com vitamina E pré-parto acarretou em 22% de aumento na taxa de prenhez em relação ao grupo Controle. As fêmeas no grupo VitE tiveram menores concentrações de cortisol e AGNEs ao redor do parto. Em resumo, quando as vacas e novilhas foram alimentadas com quantidades limitadas de vitamina E, 28 a 48% das recomendações do NRC para vacas no pré-parto, a suplementação com vitamina E injetável melhorou a saúde e o desempenho reprodutivo das mesmas. / Objectives were to evaluate the effects of injectable vitamin E supplementation during the last 3 weeks prepartum on the incidence of retained fetal membranes (RFM) and reproductive performance of dairy cows. Eight-hundred and ninety dairy cows and heifers, being 390 Holsteins (132 nuliparous and 258 parous) and 500 crossbred Holstein x Gyr (199 nuliparous and 301 parous) from three dairy farms were assigned to the study from May 2012 to April 2013. In all three farms, prepartum females were housed in pastures, and from October to March, cows had access to pasture and were managed under grazing and received 2 kg/d of a mixture of finely ground corn, soybean meal, and minerals and vitamins. From April to September, prepartum animals received a TMR composed of corn silage, finely ground corn, soybean meal, and minerals and vitamins. During the prepartum period, animals received 280 (Farm 1), 390 (Farm 2), and 480 (Farm 3) IU of vitamin E/d. Within each farm, cows and heifers were randomly assigned to remain as untreated controls or to receive three i.m. injections of 1,000 IU each of DL-?-tocopherol administered at 258 ± 3, 265 ± 3, and 272 ± 3 d of gestation (VitE). Blood was sampled from a subset of 141 animals immediately before enrollment to determine the _-tocopherol status. Blood was also analyzed for concentrations of cortisol and nonesterified fatty acids (NEFA). Statistical analysis was performed with SAS software using the GLIMMIX, MIXED, PHREG and LIFETEST procedures. The concentration of ?-tocopherol in serum of females did not differ between treatments and averaged 2.97 ± 0.10 ?g/mL. A total of 53.2% of the animals had inadequate concentration of serum ?-tocopherol based on the 3.0 ?g/mL cut-off for adequacy. The probability of cows to have RFM decreased as the concentration of ?-tocopherol in serum increased (P = 0,01). Milk production did not differ between Control and VitE cows. Treatment with injectable ?-tocopherol improved postpartum health by reducing the incidence of stillbirths, RFM, and death by 200 d postpartum. Cows receiving VitE tended (P = 0,08) to have improved pregnancy per insemination (P/AI) at first AI (36.7 vs. 30.1%) because of less pregnancy loss between 30 and 60 d of gestation (12.5 vs. 20.5%). Despite similar insemination rate, cows receiving VitE had 22% greater pregnancy rate than control cows, which was attributed to the improved P/AI and reduced pregnancy loss in all inseminations during the first 200 d in milk. Females in VitE had reduced concentrations of cortisol and NEFA around calving. In summary, when cows and heifers were fed limited amounts of supplemental vitamin E, 28 to 48% of the recommendations for prepartum dry cows, supplementation with injectable ?-tocopherol improved postpartum health and reproduction.

O processo de tratamento térmico à baixa temperatura é um dos métodos mais promissores para melhorar o desempenho dos materiais. O tratamento criogênico promove a transformação de austenita retida do aço em martensita, o que é atribuída para melhorar a dureza e resistência ao desgaste. Neste trabalho foram analisados os efeitos dos diferentes ciclos de tratamentos térmicos, comparando-se à tempera convencional (têmpera 1050°C + revenido simples e duplo a 200/530°C) respeito à adição do tratamento criogênico, (têmpera 1050°C + criogenia a -125°C + revenido simples e duplo a 200/530°C) com e sem tempo de espera de 24 horas, com a finalidade de avaliar a estabilização térmica da austenita retida no aço em relação a quantidade presente na microestrutura e consequentemente na influencia nas propriedades mecânicas do aço ferramenta para trabalho a frio AISI D2. As análises foram conduzidas através de testes de dureza, impacto, microscopia óptica, microscopia eletrônica de varredura e difração de raios-X. Os resultados encontrados foram uma variação pouco significativa na dureza entre 57 e 58 HRC. Foi evidenciada a baixa tenacidade ao impacto do aço AISI D2, independente das rotas dos ciclos de tratamento térmico, resultado da alta percentagem de carbonetos dispostos na microestrutura. A resistência ao impacto no aço em estudo após o tratamento criogênico, esses resultados foram relacionados à microestrutura do material. / The heat treatment process at low temperature is one of the most promising methods to improve the performance of materials. The cryogenic treatment promotes the transformation of retained austenite from the steel into martensite, which is attributed to improved hardness and wear resistance. In this work the effects of the different cycles of thermal treatments were analyzed, comparing to conventional tempering (tempering 1050°C + single and double annealing at 200/530°C) with respect to the addition of the cryogenic treatment (tempera 1050°C + cryogenics to - 125°C + single and double tempering at 200/530°C) with and without waiting time of 24 hours, in order to evaluate the thermal stabilization of the austenite retained in the steel in relation to the amount present in the microstructure and consequently in the influence on the mechanical properties of cold working tool steel AISI D2. The analyzes were conducted through tests of hardness, impact, optical microscopy, scanning electron microscopy and X-ray diffraction. The results found were a minor variation in hardness between 57 and 58 HRC. It was evidenced the low impact toughness of the AISI D2 steel, independent of the thermal treatment cycle routes, as a result of the high percentage of carbides disposed in the microstructure. The impact resistance in the steel studied after the cryogenic treatment, these results was related to the microstructure of the material.