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The variation of sinter strength in the sinter bed due to the mineral phase distributionJordaan, Willem Jacobus 01 July 2005 (has links)
Please read the abstract in the section 00front of this document / Dissertation (M Eng (Metallurgical Engineering))--University of Pretoria, 2006. / Materials Science and Metallurgical Engineering / unrestricted
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Solidificação transitória de ligas dos sistemas monotéticos AI-Bi, AI-Pb e AI-In / Transient solidification of alloys of the monotectic AI-Bi, AI-Pb and AI-In systemsSilva, Maria Adrina Paixão de Souza da 18 August 2018 (has links)
Orientador: Amauri Garcia / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-18T19:08:04Z (GMT). No. of bitstreams: 1
Silva_MariaAdrinaPaixaodeSouzada_D.pdf: 5780858 bytes, checksum: b602bf47a710b2fb6f161a596020054f (MD5)
Previous issue date: 2011 / Resumo: Ligas de alumínio dispersas com bismuto, chumbo e índio apresentam aplicações promissoras em componentes automotivos resistentes ao desgaste. Essas dispersões de elementos de baixa temperatura de fusão diminuem a dureza e escoam facilmente em condições de deslizamento, resultando em um comportamento tribológico favorável. Muitos estudos têm sido realizados a fim de melhor compreender as distintas morfologias obtidas pela reação monotética Algumas pesquisas assumem que a evolução do espaçamento interfásico (?) nas Iigas monotéticas ou obedece à clássica relação utilizada para eutéticos: ?2v = C, ou ainda a relação de crescimento dentrítico ?.va.Gb = C, onde v é a velocidade de solidificação e C uma constante para ambos os casos, G é o gradiente de temperatura e a e b são constantes. Tais estudos utilizaram fornos de aquecimento à resistência do tipo Bridgman para produzir a solidificação direcional de ligas monotéticas. Existe uma falta de estudos consistentes no desenvolvimento microestrutural de ligas monotéticas durante condições de fluxo de calor transitório, que são de importância primordial, uma vez que esse tipo de fluxo de calor engloba a maioria dos processes industriais e de solidificação. No presente estudo, foram realizados experimentos de solidificação unidirecional em regime não-estacionário com as Iigas hipomonotéticas Al-0,9%Pb e Al-5,5%In, com a liga monotética Al-1,2% Pb e com as Iigas hipermonotéticas Al-5,0%Bi, Al-7,0%Bi e Al- 2,1%Pb, além da análise da rnacrossegregação da liga monotética Al-3,2%Bi. Os parâmetros térmicos como velocidades de crescimento, taxas de resfriamento e gradientes térmicos foram determinados experimentalmente por curvas de resfriamento adquiridas ao longo do comprimento do lingote. A evolução microestrutural foi caracterizada por técnicas metalográficas e os espaçamentos foram correlacionados com os parâmetros térmicos de solidificação. Verificou-se que a lei de crescimento ?2v= C é válida apenas para os casos onde há ocorrência de partículas de soluto dispersas irregularmente na matriz e que esta lei não se aplicou nos casos onde foi observado uma frente monotética celular e morfologia de fibras e cordões de pérolas. Já a lei ?.va.Gb = C se mostrou aplicável em todos os casos ascendentes. O aumento do teor de soluto das ligas e o fluxo convectivo induzido provocaram mudanças nas morfologias das fases, na magnitude dos espaçamentos interfásicos e nos diâmetros das partículas / Abstract: Aluminum alloys dispersed with bismuth, lead and indium show promising applications in wearresistant automotive components. Such dispersions of low melting temperature elements decrease hardness and flow easily under sliding conditions, resulting in favorable tribological behavior. Much research has been devoted in order to better comprehend the distinct morphologies obtained by monotectic reactions. Some researches assume that the interphase spacing evolution in monotectic alloys follows the classical relationship used for eutectics: ?2v = C, or the dendritic growth relationship ?.va.Gb = C, where v is the solidification velocity and C a constant value for both cases, G is the thermal gradient and a and b are constants. Such studies have used Bridgman type het resistance furnaces to produce the directionally solidified monotectic samples. There is a lack of consistent studies on the microstructural development of monotectic alloys during transient heat flowconditions, which are of prime importance since this class of heat flow encompasses the majority of solidification industrial processes. In the present study, directional unsteady-state solidification experiments were carried out with hypomonotectic Al-0.9wt%Pb and Al-5.5wt%In, monotectic Al-1.2wt%Pb and hypermonotectic Al-5.0wt%Bi, Al-7.0wt%Bi and Al-2.1wt%Pb alloys, besides the macrosegregation analysis of the monotectic Al-3.2wt%Bi alloy. Thermal parameters such as the growth rate, cooling rate and thermal gradient were experimentally determined by cooling curves recorded along the casting length. The microstructural evolution was characterized by metallography and the spacings were correlated with the thermal parameters. It is show that the ?2v = C growth law is valid only for the cases where there is a morphology of solute particles irregularly arranged in the matrix and it is not applied on the cases where a cellular monotectic front or fibers and strings of pearls morphologies were observed. On the other hand, ?.va.Gb = C law seems to be able to characterize all the upward cases. The increase in the alloy solute content and induced convective flow affected the morphologies of the resulting phases, the magnitude of the interphase spacing and the diameters of the solute-rich particles / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica
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Three Essays on Market Depth in Futures MarketsAidov, Alexandre 02 August 2013 (has links)
Liquidity is an important market characteristic for participants in every financial market. One of the three components of liquidity is market depth. Prior literature lacks a comprehensive analysis of depth in U.S. futures markets due to past limitations on the availability of data. However, recent innovations in data collection and dissemination provide new opportunities to investigate the depth dimension of liquidity.
In this dissertation, the Chicago Mercantile Exchange (CME) Group proprietary database on depth is employed to study the dynamics of depth in the U.S. futures markets. This database allows for the analysis of depth along the entire limit order book rather than just at the first level.
The first essay examines the characteristics of depth within the context of the five-deep limit order book. Results show that a large amount of depth is present in the book beyond the best level. Furthermore, the findings show that the characteristics of five-deep depth between day and night trading vary and that depth is unequal across levels within the limit order book. The second essay examines the link between the five-deep market depth and the bid-ask spread. The results suggest an inverse relation between the spread and the depth after adjusting for control factors. The third essay explores transitory volatility in relation to depth in the limit order book. Evidence supports the relation between an increase in volatility and a subsequent decrease in market depth. Overall, the results of this dissertation are consistent with limit order traders actively managing depth along the limit order book in electronic U.S. futures markets.
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Three Essays on the Microstructure of Exchange Traded FundsMarch, Samique 05 November 2013 (has links)
Exchange traded funds (ETFs) have increased significantly in popularity since they were first introduced in 1993. However, there is still much that is unknown about ETFs in the extant literature. This dissertation attempts to fill gaps in the ETF literature by using three related essays. In these three essays, we compare ETFs to closed ended mutual funds (CEFs) by decomposing the bid-ask spread into its three components; we look at the intraday shape of ETFs and compare it to the intraday shape of equities as well as examine the co-integration factor between ETFs on the London Stock Exchange and the New York Stock Exchange; we also examine the differences between leveraged ETFs and unleveraged ETFs by analyzing the impact of liquidity and volatility. These three essays are presented in Chapters 1, 2, and 3, respectively.
Chapter one uses the Huang and Stoll (1997) model to decompose the bid-ask spread in CEFs and ETFs for two distinct periods—a normal and a volatile period. We show a higher adverse selection component for CEFs than for ETFs without regard to volatility. However, both ETFs and CEFs increased in magnitude of the adverse selection component in the period of high volatility. Chapter two uses a mix of the Werner and Kleidon (1993) and the Hupperets and Menkveld (2002) methods to get the intraday shape of ETFs and analyze co-integration between London and New York trading. We find two different shapes for New York and London ETFs. There also appears to be evidence of co-integration in the overlapping two-hour trading period but not over the entire trading day for the two locations. The third chapter discusses the new class of ETFs called leveraged ETFs. We examine the liquidity and depth differences between unleveraged and leveraged ETFs at the aggregate level and when the leveraged ETFs are classified by the leveraged multiples of -3, -2, -1, 2, and 3, both for a normal and a volatile period. We find distinct differences between leveraged and unleveraged ETFs at the aggregate level, with leveraged ETFs having larger spreads than unleveraged ETFs. Furthermore, while both leveraged and unleveraged ETFs have larger spreads in high volatility, for the leveraged ETFs the change in magnitude is significantly larger than for the unleveraged ETFs. Among the multiples, the -2 leveraged ETF is the most pronounced in its liquidity characteristics, more so in volatile times.
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Modulation of the physico-chemical and functional properties of bread by applying surface treatmentsAltamirano Fortoul, Rossana del Carmen 11 November 2013 (has links)
El pan es un alimento de gran consumo desde la antigüedad, obtenido de
un proceso de panificación dinámico. Una de las innovaciones de mayor
éxito en panificación ha sido el pan parcialmente cocido obtenido por la
tecnología de panificación interrumpida que proporciona pan crujiente en
cualquier momento del día. La crujibilidad es el atributo más demandado
por los consumidores en el pan crujiente fresco. Desafortunadamente, la
crujibilidad es percibida por corto tiempo después del horneado y la
pérdida de ésta es uno de los atributos que causa rechazo en los
consumidores. El objetivo de esta investigación fue la modulación de las
propiedades físico-químicas y funcionales del pan mediante la aplicación
de tratamientos de superficie con el fin de comprender las características
de la corteza y el desarrollo de productos de pan con un valor agregado.
Para abordar dicho objetivo se han realizado estudios para determinar el
impacto de la adición de vapor, durante el horneado, sobre las
propiedades mecánicas de la corteza y para evaluar la influencia de estas
propiedades en los parámetros de calidad utilizando diferentes panes
comerciales. Además se han realizado estudios para modular las
propiedades de la corteza dirigidos a entender su microestructura y
modificarla mediante tratamientos enzimáticos con amiloglucosidasa o
con un recubrimiento funcional, con la finalidad de modificar la
permeabilidad de la corteza u obtener panes probióticos.
Los resultados mostraron que la cantidad de vapor utilizada durante la
cocción (100, 200 y 400 ml) modificaron las propiedades físico-químicas
y mecánicas así como la estructura de la corteza del pan. Los parámetros
de calidad permitieron la diferenciación de variedades de pan
parcialmente cocido, específicamente las propiedades mecánicas de la
corteza junto con el volumen específico, dureza y estructura de la miga.
Sin embargo, la textura de la corteza de pan fue significativamente
dependiente de las condiciones de ensayo (velocidad y sección de la
sonda). Los resultados mostraron que la velocidad más baja (0,5 mm / s)
dio información acerca de la estructura celular de la corteza relacionada
con la textura crujiente. Por otra parte, la estructura celular fue modificada por la amiloglucosidasa pulverizada sobre la superficie del
pan antes de la cocción, lo que condujo a una disminución en el
contenido de agua y actividad del agua de la corteza, lo cual se requiere
para extender crujibilidad. La aplicación de recubrimientos comestibles
con L. acidophilus microencapsulado sobre la superficie pan (disperso o
en multicapa) garantizó la supervivencia del microorganismo después
del tiempo de cocción y almacenamiento, a pesar de que estos
disminuyeron la fuerza de fractura y actividad de agua de la corteza. El
análisis de microestructura demostró la presencia de microcapsulas
dispersas en la corteza de pan. Por lo tanto, L. acidophilus incluido en
microcápsulas pueden ser incorporado en la superficie de pan a través de
recubrimientos comestibles, abriendo la posibilidad de obtener panes
funcionales. / Altamirano Fortoul, RDC. (2013). Modulation of the physico-chemical and functional properties of bread by applying surface treatments [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/33398 / TESIS
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Improving mechanical properties and microstructure development of fiber reinforced ceramic nuclear fuelSacramento Santana, Hesdras Henrique 30 April 2014 (has links)
At the present work the UO2 fuel production process was extensively studied and analyzed. The
objectives of such investigation were to understand and analyze the influence of different additives
and the variation of the production process steps on the microstructure and consequently in the
mechanical strength of the nuclear fuel pellet.
Moreover, an improvement of the qualitative characteristics of the ceramic fuel pellets was
also aimed. For this purpose UO2 pellets without additives, the so-called standard pellets, pellets
containing as additive for example AZB (Azodicarbonamid), black U3O8 (Oxidized uranium pellet
scrap - OS), green U3O8 (Oxidized uranium powder - OP), keratin fibers (a non conventional
additive) were produced.
The introduction of these additives to the UO2 powder mixture prior or after the granulation
production step and in different concentrations produced several microstructure configurations.
As it would not be possible to analyze all of them here so during the investigation pre-tests some
of them were separated to be studied in more detail.
Pellets with AZB added after the granulation presented larger grains and larger pores than
those with AZB added before granulation, also porosity free grains and a granulate structure
instead of a homogeneous one. Pellets with OS present fine porosity distributed all over the pellet
matrix with some porosity clusters whereas pellets containing OP show in its matrix porosity
agglomerated in form of hooks. As for the grain size, a more uniform grain size distribution can
be observed in pellets OS than in pellets with OP.
The variations in the amount of keratin fibers added, sintering dwell time and green density
resulted indeed in different microstructures. Nevertheless, some common characteristics among
them were observed such as the presence of elongated pores, porosity clusters and larger grains
located at the pellets borders while the smaller ones were concentrated more in the central part
of the pellet. This distribution of grains was identified as bi-modal structure.
The mentioned microstructure aspects certainly influence on the mechanical properties of the
fuel pellet. However, the sintering parameters, the green and final pellet density and the pellet
dimensions also have an influence on the mechanical characteristics of the pellets. For studying
the influence of all these parameters on the pellet mechanical properties four testing procedures were utilized the so-called squirrel-cage where the mechanical resistance of the not sintered pellets
against mechanical shocks was tested, the diametrical compression test (Brazilian Test) where
the strength of sintered and not sintered pellets was studied, the Vickers indentation technique
and the creep test where the pellet plasticity respectively at room and at elevated temperatures
was analyzed.
The squirrel-cage results showed that the pellets with keratin fibers were much more mechanically
resistant than those pellets without it, which means that the keratin fibers acted, prior
sintering, as a powder binder increasing the cohesion among the powder granules proportionating
the green pellets higher mechanical resistance against impacts.
The Brazilian test evaluated the influence of the pellet length to the pellet diameter (L/D
ratio), the influence of different additives mixed to the UO2 powder and the different pellet
production processes. The L/D influence analysis showed that if one fixes the pellet diameter
and increase the pellet length the Weibull modulus (here a measure of the pellet lot reliability)
will also increase. By comparing pellets with OS, OP and 0.3% keratin fibers it was observed
that pellets with OS presented the highest volume of pores smaller than 10 mm while pellets with
OP and keratin presented the highest volume of pores larger than 20 mm. It seems that this
relevant characteristic favored to the highest Weibull strength value for pellets with OS.
In the indentation test standard pellets, pellets with OS and pellets with keratin fibers were
tested. The results showed that the calculated hardness for the standard pellets is slightly lower
when compared to the values obtained by the pellets with keratin fibers. Also the pellets containing
OS when compared to the keratin fibers pellets have in most of the cases a lower hardness. The
calculated fracture toughness and fracture surface energy values show also a better mechanical
behavior for the keratin fibre pellets than in the standard pellets.
Standard pellets, pellets with 30%OP, which had the smallest grain size, pellets with keratin
fibers, having the bi-modal structure and pellets with chromium oxide, which had the largest
grain size, were tested in the creep furnace. The results showed that all pellets with additives
presented a better creep behavior than the standard pellets. Among the pellets prepared with
additives the comparison clearly showed that under lower stresses pellets with smaller grains have
a better creep rate. By increasing the applied stresses we observe an improvement of the creep
rate of the pellets with chromium oxide and keratin fibre even slightly overcoming the pellets
with 30%OP at the highest applied stress. / Sacramento Santana, HH. (2014). Improving mechanical properties and microstructure development of fiber reinforced ceramic nuclear fuel [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/37199 / TESIS
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Two Essays on Ownership and Market CharacteristicsChen, Honghui 07 August 1999 (has links)
Theoretical models suggest that ownership structure may be an important determinant of securities' market characteristics. For example, the presence of informed traders leads to greater bid-ask spreads (Copeland and Galai (1983), and Glosten and Milgrom (1985)), and strategic trading of informed and discretionary liquidity traders leads to intertemporal variation in both trading volume and trading costs (Admati and Pfleiderer (1988), and Foster and Viswanathan (1990)). However, the empirical studies on the effect of ownership structure on market characteristics are limited. Prior studies focus on either one type of market characteristics or one type of owners, and usually do not address the potential endogeneity problem between market characteristics and ownership structure. This dissertation extends existing literature with two essays on ownership and market characteristics.
The first essay broadly examines the effect of ownership structure (inside ownership, institutional ownership, and individual ownership) on market characteristics such as order flow, price impact of trade, quoted spread and quoted depth. For each market characteristic examined, I establish an empirical model based on existing theories and empirical evidence. My results indicate that stocks with greater inside ownership have lower order flow, greater price impact of trade, greater quoted spread and lower quoted depth, while stocks with greater active institutional ownership and greater individual shareholders have greater order flow, smaller price impact of trade, lower spread and greater depth. These results may have implications for corporate governance. For example, while agency theory suggests managerial ownership may align interests of managers and shareholders, this essay finds that this comes with a liquidity cost. Further, my results suggest there are liquidity benefits of individual and institutional ownership. If as suggested by Amihud and Mendelson (1989), investors require a higher rate of return for illiquid stocks, firms can target their shares to specific types of investors (for example, active institutions and individuals) to improve liquidity, and reduce their cost of capital.
The second essay is a specific application of the first essay and examines the effect of institutional ownership on price discovery around earnings announcements. I select earnings announcements as the event for my analysis because there are three well-documented regularities about earnings announcements. First, market participants anticipate the forthcoming earnings announcements. Second, the announcements of earnings news are usually accompanied by abnormal price changes and abnormal volume. Third, there is evidence that stock price continues to move in the direction of earnings surprise after the announcements of earnings news. Since results from the first essay suggest that institutional investors affect market characteristics such as price impact of trade and quoted spread, I expect that institutional participation would also affect the price discovery process around earnings announcements. My results indicate that institutional ownership is associated with greater anticipation of earnings news. Further, stocks with greater institutional ownership have a greater price response to announcements of earnings news. Finally, institutional investors have no significant effect on post-announcement drift. The results of the second essay suggest that institutional investors contribute to the price discovery process. / Ph. D.
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Impact of Gray Cast Iron Microstructure on Brake Pad StictionTang, Jiaming 01 September 2021 (has links)
This research study talks about the possible influence of gray cast iron microstructure on the corrosion properties of the brake rotor and the effect of stiction. Three Gray cast iron rotors with fully pearlitic microstructure and below 5% volume content of ferrite were studied in this research to understand their microstructural influence over corrosion. The selected gray cast iron rotors were friction tested against a 2009 Original Equipment Manufacturer (OEM) Ford F150 brake pad using scaled-down SAE J2522 standard test. Tested samples were later subjected to GMW16696 standard test, to identify the breakaway forces indirectly defining the corrosion resistance of the friction material used. The results show that the degree of corrosion and breakaway forces observed are greatly influenced by the graphite content quantified from quantitative analysis techniques adopted. Rotor with higher graphite content observed higher breakaway force and higher oxygen content compared to the other two studied rotors. Higher graphite content is considered to provide more cathodes, it accelerates the corrosion of the iron element in the rotor. There is no reliable correlation between the pearlite and ferrite of the gray cast iron rotor stiction force. The poor correlation between stiction force and microstructure also shows that the size of stiction force is not determined by a single factor.
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Effect of Microstructural Parameters on Mechanical Properties and Fracture in α+β Titanium Alloy / α+β型チタン合金の機械的性質と破壊に及ぼす微視組織の影響Yi, Jangho 24 September 2019 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22066号 / 工博第4647号 / 新制||工||1725(附属図書館) / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 辻 伸泰, 教授 安田 秀幸, 教授 宇田 哲也 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM
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Studium nových slitin na bázi Mg s řízenou mikrostrukturou a texturou / Study of novel magnesium alloys with controlled microstructure and textureDrozdenko, Daria January 2016 (has links)
Title: Study of novel magnesium alloys with controlled microstructure and texture Author: Daria Drozdenko Department / Institute: Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University in Prague Supervisor of the doctoral thesis: Ing. Patrik Dobroň, Ph.D., Department of Physics of Materials. Abstract: The work elucidates the role of dislocation slip and twinning during plastic deformation in selected magnesium (Mg) alloys with controlled microstructure and texture. The acoustic emission (AE) technique was concurrently applied during deformation to determine the activity of particular deformation mechanisms. A detailed insight into microstructure was provided by electron microscopy. In order to obtain a comprehensive set of AE data for particular deformation mechanisms, Mg single crystals with various crystallographic orientations were channel-die and uniaxially compressed. The obtained results were applied on deformation mechanisms in polycrystalline textured Mg alloys. Particularly, the twinning - detwinning processes, in the sense of twin boundary mobility, during one cycle loading (pre-compression followed by tension) were described. Clear correlations between changes in the AE response and the inflection points on the deformation curve were found. An analysis of twin...
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