Дисертації з теми "Defects formation"
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Cho, S. Y. "Formation and suppression of fluorenone defects in polyfluorenes." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597627.
Повний текст джерелаDonaire, Manuel. "Formation of topological defects in gauge field theories." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613012.
Повний текст джерелаNigmatullin, Ramil. "Formation and dynamics of structural defects in ion chains." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/24567.
Повний текст джерелаThomas, Brian Gordon. "Investigation of panel crack formation in steel ingots using mathematical and physical models." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/25980.
Повний текст джерелаApplied Science, Faculty of
Mining Engineering, Keevil Institute of
Graduate
De, Weerdt Filip. "Spectroscopic studies of defects in diamond including their formation and dissociation." Thesis, King's College London (University of London), 2007. https://kclpure.kcl.ac.uk/portal/en/theses/spectroscopic-studies-of-defects-in-diamond-including-their-formation-and-dissociation(b05e7748-c1ff-4c57-9c24-ec5cb84baddf).html.
Повний текст джерелаDu, Yaojun. "The dynamics of Si small point defects and formation of Si extended structures." Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1126900310.
Повний текст джерелаTitle from first page of PDF file. Document formatted into pages; contains xix, 133 p.; also includes graphics (some col.). Includes bibliographical references (p. 126-133). Available online via OhioLINK's ETD Center
Wang, Zhihong 1972. "Modeling microdefects formation in crystalline silicon : the roles of point defects and oxygen." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/16905.
Повний текст джерелаIncludes bibliographical references (p. 225-233).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Most microelectronic devices are fabricated on single crystalline silicon substrates that are grown from the melt by the Czochralski crystal growth method. There is an ever increasing demand for control of size and density of microdefects in the silicon for control of quality and uniformity of the fabricated microelectronic devices. This thesis is aimed at developing a fundamental understanding of the mechanisms for formation of such microdefects through the development of models, theoretical analysis and large-scale simulation. Two major problems have been addressed. First, following the work of T. Sinno [150] and T. Mori [108], models have been developed for the transport, reaction and aggregation of native point defects - self-interstitials ('s) and vacancies (V's) - in crystalline silicon, so as to explain the dynamics of void formation (aggregation of V's) and stacking faults (aggregation of I's). Second, the model of point defect and cluster dynamics has been extended to include oxygen, the most common impurity in silicon, and to model oxide precipitation, an important step in silicon wafer preparation and device processing. The models of microdefect formation begin with transport equations for native point defects that include transport by diffusion and convection (crystal motion), recombination of Is and Vs, and the loss of point defects to clusters. Cluster formation is modeled by a combination of discrete rate equations for small-sized clusters (less than 100) and continuous Fokker-Planck equations for large cluster sizes. Simulation methods are developed for calculating, in time, space and cluster size, the evolution of point defect and cluster profiles, as a function of the temperature distribution in the crystal.
(cont.) Considerable effort has been devoted to analysis of the critical operating conditions that divide the crystal into V-rich and I-rich regions. As analyzed by Sinno [151], these radial regions of a CZ-grown silicon crystal are distinguished by a critical value of V/G=(V/G)crit, where V is the crystal pull rate and G is a measure of the axial temperature gradient at the melt/crystal interface. Numerical simulations identify that the evolution of microdefects at an axial slice of the crystal can be divided into three regions: (1) the region of rapid point defect dynamics near the melt-crystal interface, (2) a region of intermediate point defect concentrations where the crystal to too hot for these concentrations to become super-saturated, and (3) the nucleation and growth of point defect clusters caused by homogeneous nucleation and super-saturation. Asymptotic analysis of void formation is carried out in each of these regions and linked by point defect conservation to give predictions for a number of very important values, including (V/G)crit, the intermediate vacancy concentration, the void nucleation temperature, the total void concentration in the crystal and the average void size. These results agree remarkably well with simulations. Moreover, the asymptotic results give the foundation for creating a simple simulation tool for prediction of the dependence of these parameters on operating conditions. The framework for microdefect formation is extended to oxygen precipitation by including oxygen dynamics and precipitation ...
by Zhihong Wang.
Ph.D.
Cantin, G. M. Delphine. "An investigation of the formation of hollow bead defects in pipeline field welds /." Title page, contents and abstract only, 1997. http://web4.library.adelaide.edu.au/theses/09PH/09phc231.pdf.
Повний текст джерелаCunningham, Ross W. "Defect Formation Mechanisms in Powder-Bed Metal Additive Manufacturing." Research Showcase @ CMU, 2018. http://repository.cmu.edu/dissertations/1160.
Повний текст джерелаRyningen, Birgit. "Formation and growth of crystal defects in directionally solidified multicrystalline silicon for solar cells." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2008. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-4980.
Повний текст джерелаCoutee, Kyle L. "The Formation of Electrets by Ion Beam Induced Defects for Application in MEMS Devices." Thesis, University of Louisiana at Lafayette, 2019. http://pqdtopen.proquest.com/#viewpdf?dispub=10842266.
Повний текст джерелаA novel electret fabrication method has been explored using a 1.7 MV Pelletron accelerator. Also, a vibrating Kelvin probe was designed and constructed for the measurement of surface potentials. The electret formation method involved using proton beams of 2 MeV energy to both partially and completely penetrate dielectric samples with metallized back plates to create defect-induced surface potentials. These potentials would likely be more resilient than those of electrets fabricated by current popular methods because the effective charge would be deposited much deeper into the material. The potentials were monitored with a custom built Kelvin probe system. This method was worth exploring as there is currently a need for more resilient electrets in the design of energy efficient micro-electro-mechanical systems (MEMS). Currently, electrets cannot survive certain MEMS fabrication processes. Two types of samples were explored. The first were 150 um thick borosilicate glass slips with a sputter coated gold backing layer. The second were silicon substrates with a 300 nm thick SiO2 layer deposited on one side and a silver backing layer on the other. The results of this thesis suggest that this charging method is inferior to other methods when applied to 150 um thick borosilicate glass. The borosilicate glass electrets were inferior both with respect to effective surface charge and effective surface charge retention. The effective surface charges attained with the SiO2/Si samples were also lower than the lowest surface charges commonly achieved by other charging methods. The SiO2/Si samples irradiated at fluences of 10 11 and 1013 ions/cm2 showed decays comparable to those achieved by other methods as of this writing. This thesis is an overview of the design and construction of a Kelvin probe system, the aforementioned method, and a comparison of the results with the characteristics of electrets fabricated by other methods commonly used today.
Khalajzadeh, Vahid. "Modeling of shrinkage porosity defect formation during alloy solidification." Diss., University of Iowa, 2018. https://ir.uiowa.edu/etd/6155.
Повний текст джерелаСоловйова, Олександра Омелянівна, Александра Емельяновна Соловьева, and Oleksandra Omelianivna Soloviova. "Simulation of the Mechanism of Defect Structure Formation in Polycrystalline Indium Oxide Under Ion Irradiation." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35411.
Повний текст джерелаSilva, Línder Cândido da. "Simulações por dinâmica molecular aplicadas ao estudo de defeitos em cristais coloidais bidimensionais." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-26052014-110806/.
Повний текст джерелаColloidal suspensions of charged polystyrene microspheres provide an excellent experimental system to study many problems in condensed matter physics. Under appropriate conditions the particles in these suspensions organize themselves in a long-range-ordered crystal, the so-called colloidal crystal. In this thesis we report Molecular Dynamics simulations on point defects, vacancies and interstitials, in a 2D colloidal crystal. We have calculated the formation energy and interaction of these point defects, as well as the energy barriers between the various topological configurations that the defects may adopt while in thermal equilibrium. It is shown that the interstitials are more likely to be formed than the vacancies, and the interaction between defects (vacancy-vacancy and interstitial-interstitial) is attractive. Taken together, these results indicate that point defects may affect the melting process of a 2D colloidal crystal. With regard to the dynamics of the defects, emphasis was placed on the vacancies. The enthalpy for migration of a vacancy was calculated on the basis of exchanges between topologies. We concluded that the vacancy does not diffuse according to a single mechanism, but rather through a mixture of two processes: one is a modified Arrhenius mechanism and the other is represented by a power-law dependence on the temperature. We also calculated the relative enthalpies and entropies associated with the formation of the different topologies of vacancies, which allowed identification of the most stable topologies. We believe these results may have important bearing on experimental works involving interfaces and solid surfaces.
Höglund, Andreas. "Electronic Structure Calculations of Point Defects in Semiconductors." Doctoral thesis, Uppsala universitet, Fysiska institutionen, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7926.
Повний текст джерелаOlsson, Pär. "Modelling of Formation and Evolution of Defects and Precipitates in Fe-Cr Alloys of Reactor Relevance." Doctoral thesis, Uppsala University, Department of Neutron Research, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6014.
Повний текст джерелаFe-Cr alloys form the basis of many industrially important steels. Due to their excellent resistance to radiation induced swelling, ferritic steels are expected to be used for critical structural components in advanced nuclear systems, such as fast breeder reactors, accelerator driven systems and fusion reactors. In this thesis project, theoretical modelling of bulk properties of Fe-Cr alloys has been performed for a wide range of phenomena. Electronic structure calculations, based on density functional theory, have been used to determine equilibrium properties for different magnetic states of the alloy. Ferromagnetic alloys of low Cr concentration (<10% Cr) are anomalously stable, which is related to the variation in sign of the mixing enthalpy which was predicted for the first time in this work. This finding is in agreement with experimental evidence of long range ordering in Fe-Cr alloys with low Cr concentration, as well as the observed phase separation for compositions with higher Cr content.
The character of the interaction of point defects with solute Cr atoms in an iron matrix was investigated ab initio. It was found that due to magnetic interactions, interstitial defects are bound by Cr atoms in bulk iron. Vacancies, on the other hand, interact only weakly with Cr. These results may offer qualitative explanations to the observed concentration dependence of radiation induced swelling in Fe-Cr model alloys.
The ab initio predictions inspired an effort to develop an interatomic alloy potential capable of reproducing both the thermodynamic bulk behaviour of the alloy, such as the mixing enthalpy, and the point defect interactions, in order to perform large scale atomistic and stochastic simulations on scales out of reach for density functional theory. A two-band extension of the embedded atom method of interatomic potentials was developed in order to model ferromagnetic Fe-Cr alloys of arbitrary composition. Kinetic Monte-Carlo simulations of thermal aging, using this two-band potential, reproduce the experimentally measured formation and evolution of solute precipitation as a function of concentration for temperatures relevant to structural materials in nuclear reactors.
Olsson, Pär. "Modelling of formation and evolution of defects and precipitates in Fe-Cr alloys of reactor relevance /." Uppsala : Acta Universitatis Upsaliensis : Universitetsbiblioteket [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6014.
Повний текст джерелаRaji, Abdulrafiu Tunde. "Formation and dynamics of defects in pure and ion implanted a-titanium studied by quantum simulations." Doctoral thesis, University of Cape Town, 2010. http://hdl.handle.net/11427/11139.
Повний текст джерелаDensity-functional theory calculations have been performed to study energetics of defects formation and diffusion in pure and krypton implanted hexagonal closed-packed (h.c.p) titanium. We employed the ab initio electronic structure calculations to study the formation energies of Ti vacancies and divacancies, Kr interstitials, and the binding of Kr atoms and Ti vacancies to form defect complexes. In addition, we present results on the diffusion of vacancies, divacancies, as well as the substitutional and interstitial krypton atom in h.c.p Ti. The calculated monovacancy formation energy is 1.97eV, which is in excellent agreement with other theoretical calculations, and agrees qualitatively with published experimental results.
Tamura, Atsushi. "Achlorhydria by ezrin knockdown : defects in the formation/expansion of apical canaliculi in gastric parietal cells." Kyoto University, 2005. http://hdl.handle.net/2433/144786.
Повний текст джерелаAlmas, Ria Afifah. "Study of Grain Formation in Linseed Oil-Based Paints." Thesis, KTH, Fiber- och polymerteknologi, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-289174.
Повний текст джерелаA study of grain formation in linseed oil-based paint have been conducted. The grains were formed in linseed oil paints with either Yellow1, Yellow 2, Black, or Red as the pigments. There are two types of grain formation which has been observed from the paint samples. (a) The grains which immediately appear in the newly made paint with Yellow 1, Yellow 2, and Red paints (b) while the other type is the grain that developed as the function of storage time in Black linseed oil paint. The results clearly show the cause of the defects.
Simmonds, Scott. "Formation and avoidance of surface defects during casting and heat-treatment of single-crystal nickel-based superalloys." Thesis, University of Leicester, 2014. http://hdl.handle.net/2381/28806.
Повний текст джерелаOkumura, Hironori. "Formation Mechanism of Extended Defects in AlN Grown on SiC{0001} and Their Reduction by Initial Growth Control." 京都大学 (Kyoto University), 2012. http://hdl.handle.net/2433/157592.
Повний текст джерелаZareie, Rajani Hamid Reza. "Development of a three-dimensional multi-scale model to study the formation of solidification defects in fusion welding." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/57601.
Повний текст джерелаApplied Science, Faculty of
Engineering, School of (Okanagan)
Graduate
Repper, Elias, and Amanda Carsbring. "Defect formation in laser welded steels after use of corrosion protection coating." Thesis, KTH, Materialvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-209805.
Повний текст джерелаWaltz, Bélinda. "Le dol dans la formation des contrats : essai d'une nouvelle théorie." Thesis, Lyon 3, 2011. http://www.theses.fr/2011LYO30109.
Повний текст джерелаProfessional, or the increasing use of adhesion contracts (“take it or leave it agreements”), all are factors that can lead to the contractor’s vulnerability. The risk is, for the so-called “strong” party, to abuse its position in order to force the other party into a strongly unbalanced agreement, mainly in its own benefit. Since such a reprehensible behavior occurs during the contract formation, the weakened party should be able to find protection through the use of the defects of consent theory. However, this theory has proven inadequate to effectively protect abused contractors today. A major explanation is due to the fact that this theory remains unchanged since 1804. Based on an individualistic conception of the contract, conditions of admission of each defects of consent, such as error, abuse and fraud, are too restrictive. However, the more contractual inequalities exist, the more they will turn into abuse. Therefore, this is why such a theory should be restored in order to protect contractors. It is through the notion of “dol” (willful misrepresentation or fraudulent concealment) that we propose to do so. This choice is not a coincidence. It is justified by the fact that “dol” is a tort, even before being a defect of consent. Specifically, it is the manifestation of pre-contractual disloyalty. Its recognition as a fact altering willpower will generate two negative effects. The first is linked to the fact that “dol” appears to be a complex notion and a source of contradiction in substantive law. The second is not permitting to properly penalize the dishonesty perpetrated during the contract formation due to a too narrow scope of the “dol”, the latter being understood as an induced error. Giving it back its real nature of a civil tort defecting the contract and undermining the pre-contractual good faith, our work aims at finding a remedy to these two shortcomings
Li, Peigang. "Cold lap formation in Gas Metal Arc Welding of steel : An experimental study of micro-lack of fusion defects." Doctoral thesis, Högskolan Väst, Avd för maskinteknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-5596.
Повний текст джерелаMagnani, Dario. "Role for Gli3 in the formation of the major axonal tracts in the telencephalon." Thesis, University of Edinburgh, 2011. http://hdl.handle.net/1842/5910.
Повний текст джерелаMajidi, Seyyed Hojjat. "Modeling of air entrainment and oxide inclusion formation during pouring of metal castings." Diss., University of Iowa, 2018. https://ir.uiowa.edu/etd/6611.
Повний текст джерелаPurmová, Jindra. "Effect of the modification of the polymer-rich phase composition on the formation of structural defects in radical suspension PVC." [S.l. : [Groningen : s.n.] ; University Library Groningen] [Host], 2007. http://irs.ub.rug.nl/ppn/.
Повний текст джерелаBainbridge, Ian Frank. "The influence of molten metal surface properties on the formation of surface defects on vertical direct chill cast aluminium alloy products /." [St. Lucia, Qld.], 2005. http://adt.library.uq.edu.au/public/adt-QU20060116.141809/index.html.
Повний текст джерелаAdler, Jeanette. "Film Formation and Surface Tension Studies of Powder Coatings." Thesis, KTH, Fibre and Polymer Technology, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3935.
Повний текст джерелаIn industrial use of paint systems a swift processing is crucial. Another very important issue is to improve the quality of the final coating. This report investigates the film formation process of powder coatings, specially the spreading of individual powder particles. The obtained results can be used to understand and control the film formation process. In this way the desired levelling can be achieved and thus the desired gloss or other surface characteristics that may be required. This means that the method could be used when evaluating different polymer and additive combinations that could be used to change film formation behaviour or curing time for powder coating systems to suit various substrates. It makes it possible to avoid and minimize different surface defects as orange peel or cratering in the powder coated film.
We used a reflection optical microscope to better understand the film formation process and especially the spreading of a powder melt on surfaces with various surface energies. The obtained data were: the particle diameter, the area, area ratio and the contact angle of the powder particle as a function of time and temperature. This information can be used to derive the surface tension of any powder melt.
In this report we evaluate the dependencies of temperature, heat rate and surface energy for powder coatings on different substrates. The method provides information that can be used to optimize the film formation of a specific powder coating/substrate combination. This method can be used to evaluate the powder spreading and levelling on different substrates from a surface tension point of view.
We found, as expected, that the powder flows out on a hydrophilic surface and is inhibited by a hydrophobic. The increase of the area ratio on a hydrophilic surface was about five times as the initial area coverage and on a hydrophobic surface only two times the initial area coverage. The contact angle between the melted powder particle on the different surface types could be calculated. The melt surface tension could be calculated since three substrates surfaces with various surface energies were used. The melt surface tension was found to be about 18.5 mN/m.
Sammanfattning
Vid industriell användning av ett färgsystem är det viktigt med en snabb och smidig målningsprocess. En viktig del är att förbättra kvaliteten på den färdiga ytan. Denna rapport undersöker filmbildningsprocessen för pulverfärg, närmare bestämt spridningen av individuella pulverpartiklar. Resultaten från utvärderingen av denna metod kan användas för att bättre förstå och få kontroll över filmbildningsprocessen. Med denna undersökningsmetod kan den önskade utslätningen uppnås och därmed den önskade glansen eller annan yteffekt som kan vara önskvärd.
Metoden kan användas för att utvärdera olika polymer- och additivkombinationer som kan användas för att ändra filmbildningens uppförande eller bestämma härdningstiden för en pulverfärg att passa ett visst substrat. Metoden gör det möjligt att förhindra och minska olika ytdefekter såsom apelsinskals- eller kratereffekter i pulverfärgens yta.
Ett optiskt reflectionsmikroskop användes för att bättre kunna förstå filmbildningsprocessen och särskilt spridningen av smält pulver på substrat med olika ytenergier. De mätdata vi fick var partikeldiameter, area, areaförändring och kontaktvinkeln för pulverpartiklar som funktion av tid och temperatur. Ur denna information kunde pulversmältans ytenergier härledas.
I denna rapport utvärderas pulvrets beroende av temperatur, uppvärmning och ytenergi på olika substrat. Denna metod ger information som kan användas för att optimera filmbildningen av en specifik kombination av pulverfärg och substrat. Denna metod kan också användas för att utvärdera pulverspridning och utjämning av färgfilmen på olika substrat med avseende på ytenergierna.
Som förväntat flyter pulvret ut på hydrofila ytor och utflytningen ändras på en hydrofob yta. På en hydrofil yta sprider sig partikeln till fem gånger den ursprungliga arean över substratet och motsvarande två gånger för en hydrofob yta. Kontaktvinkeln mellan en smält pulverpartikel på olika sorters substrat från utförda mätningar beräknas utifrån utförda mätningar. Kontaktvinklar mellan pulver och olika substrat kan användas för att beräkna smältans ytspänning. Smältans ytspänning kan beräknas då experiment gjorts på tre sorters ytor med olika kända ytenergier. Smältans ytspänning var 18,5 mN/m.
Slutsatsen är att det går att observera och utvärdera resultaten av utsmältningsförloppet för pulverfärg med denna metod.
Doutt, Daniel R. "THE ROLE OF NATIVE POINT DEFECTS AND SURFACE CHEMICAL REACTIONS IN THE FORMATION OF SCHOTTKY BARRIERS AND HIGH N-TYPE DOPING IN ZINC OXIDE." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1366199639.
Повний текст джерелаHe, Chenwei. "Experimental study of the interaction of vacancy defects with Y, O and Ti solutes to better understand their roles in the nanoparticles formation in ODS steels." Thesis, Orléans, 2014. http://www.theses.fr/2014ORLE2057/document.
Повний текст джерелаThe severe operating conditions of the future nuclear reactor, Generation-IV, -high temperature and high irradiation damage-, require the adapted materials development. Oxide-dispersion strengthened (ODS) alloy is one of the most potential candidates expected to be used for fuel cladding material because of their outstanding swelling and creep properties. Their excellent properties are induced by the fine dispersion of oxide nanoparticles (Y, O, Ti), obtained by mechanical alloying of steel and oxide powders and which has to be better mastered. But the atomic scale clustering mechanism of these nanoparticles is not yet cleared. In this context, the present thesis using positron annihilation spectroscopy (PAS) and secondary ion mass spectrometry (SIMS) sheds light on the interaction of vacancy defects with Y, O and Ti solutes to better understand their roles in the nanoparticles formation. The He irradiations have been performed to reveal the vacancy defects properties and Y, Ti, O implantations realized to study the Y, Ti, O-vacancy interactions in bcc Fe matrix. In all cases, the defects depth distribution shows a lower size of vacancy defects in the region where the concentration of the incident ions Y, Ti and O is the highest. This effect of the ions on the damage formation is more pronounced for respectively O, Y and Ti. It is explained by the formation of V-X (X=O, Y, Ti) complexes which reduce the mobility and agglomeration probability of the vacancy defects. The annealing of the Y and O implanted samples reveals that some O-vacancy complexes are mobile at room temperature and Y doesn’t diffuse up to 550°C whilst Y-vacancy complexes remain as it is expected from theory. A model of the first steps of the ODS nanoparticles nucleation is proposed by using the results obtained in this thesis
Pentecoste, Lucile. "Etude de la formation de défauts lacunaires dans un cristal de tungstène par accumulation d’hélium." Thesis, Orléans, 2015. http://www.theses.fr/2015ORLE2040/document.
Повний текст джерелаTungsten will be exposed to severe plasma conditions such as high temperature and high particle bombardment as a target of the divertor in the nuclear fusion reactor ITER. High fluxes of light ions will impact its surface and can generate defects in the crystal. This study means to observe the first steps of the vacancy-type defects formation in the tungsten crystal subject to low ion flux of low kinetic energy in order to understand the influence of the accumulation of helium, one of the nuclear reaction products. For the experiments, an ICP-RF plasma source was developed and characterized to perform helium implantations under perfectly controlled conditions. Helium implantations were performed under various conditions of fluence, energy and substrate temperature on polycrystalline tungsten samples. Positron annihilation spectroscopy was used to characterize vacancy-type defects, nuclear reaction analysis to quantify implanted helium and thermal desorption spectrometry to characterize the interactions of helium in the crystal. Results show that, for a kinetic energy of 320 eV and at room temperature, a saturation of the helium implanted quantity is reached for a limit incident fluence and that large vacancy defects starts to form. Study of the kinetic energy and the surface temperature influences show the importance of the depth distribution and the mobility of the helium in the crystal on the size and the diversity of the generated defects. Implantations are performed by molecular dynamic simulations. Results obtained by the numerical approach are compared to experimental ones in order to get a better understanding of the atomic scale mechanisms
Jabur, Roberto de Oliveira. "Avaliação clínica, histológica e histomorfométrica do reparo de defeitos ósseos criados em mandíbula de cães preenchidos com Biovidro 45S5 ou Biosilicato® após a colocação de implantes osseointegráveis." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/58/58136/tde-23012009-170150/.
Повний текст джерелаThe aim of the present study was to investigate the amount of bone formation on Ti implants in sites with intra-bony defects filled with different bone substitutes. Mandibular premolars and first molars were extracted from 5 dogs, and after 12 weeks 3 implants were bilaterally placed in sites with intra-bony defects and each implantation site randomly received the following treatment: Biosilicate®, Bioglass® 45S5, aoutologous bone or no treatment. At 18 weeks after implantation, the hemi-mandibles containing the implants were removed and processed for morphological and histomorphometric analysis. Data were submitted to Kruskal-Wallis and Fishers test. The histological sections of the 4 experimental groups exhibited mature bone tissue in contact with implants, but not related with bioactive glasses or autologous bone used. The percentage of bone-implant contact, mineralized bone matrix between implant threads, and mineralized bone matrix within mirror area in the treated or non-treated sites were not statistically different among the 4 experimental groups. These results indicates that the presence of the bone substitutes evaluated here did not interfere with bone formation on Ti implants in sites with intra-bony defects. In addition, tissue response to Biosilicate® was similar to that of Bioglass® 45S5 and autologous bone.
Presley, Michael. "The Formation of Amorphous and Crystalline Damage in Metallic and Semiconducting Materials under Gallium Ion Irradiation." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1469056293.
Повний текст джерелаCooper, James. "Contrôle de la Formation de vacuoles dans les cristaux d'hexogène (RDX)." Thesis, Normandie, 2020. http://www.theses.fr/2020NORMR005.
Повний текст джерелаBy using antisolvent addition, it was possible to obtain symmetrical, ordered and periodic inclusions within RDX crystals. Antisolvent-induced inclusions were found off-centre in RDX, suggesting a growth-linked process to their genesis. The sizes of these inclusions were modified by changing the antisolvent addition method. These size modifications were most likely down to changes in solvent/antisolvent hydrodynamics influencing nucleation rates and subsequent growth rates. By changing the solvent and/or antisolvent, it was possible to modify the inclusion pattern within RDX crystals. This was linked to a change in crystal habitus. Inclusions were found parallel to only certain faces in every solvent/antisolvent combination. These faces were not always the largest, nor were they the fastest-growing. Results suggest that whilst large crystal faces do indeed ease the process of inclusion formation, sufficiently high growth rates of these faces are also required. The formation of inclusions may therefore be the product of solute-supply deficits to the centre of larger faces, amplified by increased solute demand required for high growth rates of these same faces. This perfect combination of adequate face sizes and growth speeds only seems to occur once during the growth process of RDX when an antisolvent is added as an initiator of crystallisation. Eight batches of RDX containing various numbers and sizes of inclusions were produced using antisolvent addition. Gap-testing was employed in order to establish a relationship between increasing inclusion sizes/numbers and increased sensitivities. Low-pressure and sustained shocks were used to determine RDX batch sensitivities. This regime has been previously demonstrated to highlight the importance of intragranular defects such as inclusions on energetic material sensitivities. Whilst the compositions of fluid inclusions in these batches remain unclear, they do not seem to have a profound influence on shock sensitivities. However, it has been demonstrated that doping RDX inclusions with an Infra-Red sensitive solid is possible. This doping has the potential to add extra hot spots within RDX inclusions upon remote activation although this remains untested. The control of inclusion sizes and numbers may not only be useful in the field of energetic materials but also for the pharmaceutical industry. Whilst fluid inclusions may be seen as a nuisance by many, they may also prove to be very useful in the encapsulation of desired compounds
Oliveira, Tarsila Marília de. "Estudo das propriedades estruturais, eletrônicas e ópticas do tetraborato de magnésio (MgB4O7) e do defeito antissítio em compostos Bi12MO20 (M=Ge,Si,Ti) utilizando cálculos de primeiros princípios." Universidade Federal de Sergipe, 2017. https://ri.ufs.br/handle/riufs/5273.
Повний текст джерелаThis work represents a theoretical study, based on density functional theory (DFT), on structural, electronic and optical properties of magnesium tetraborate (MBO, MgB 4 O 7 ) compound and of antisite Bi M O 4 defect in Bi 12 MO 20 (BMO, M=Ge, Si, Ti) compounds. All calculations have been realized by linear augmented plane wave (LAPW) method implemented in Wien2k computer code. The relaxation of atomic positions and lattice parameters has been performed using LDA (MBO) and PBE-GGA (BMO) exchange- correlation (XC) functional. Electronic structure, optical properties and chemical bonds were investigated using the semi-local XC potential of Tran and Blaha (TB-mBJ), which significantly improved the band gap description and optical properties of studied systems. The thesis is divided in two parts. The first refers to study of magnesium tetraborate in pure form. Electronic structure calculations predicted a 9.58 eV band gap value, quite close to the value determined in the similar compounds. The electronic structure around the band gap is found to be dominated by the O 2p-states and 2p-states of the boron ion with trigonal coordination with neighbouring O‘s. Optical properties were analysed in terms of complex dielectric tensor which imaginary part is directly proportional to the optical absorption spectra. The latter is found to exhibit two prominent peaks. The lower energy peak originates from electron transitions within the trigonal B−O 3 structural group. Refractive index, reflectivity, extinction coefficient and energy loss were analysed in ultraviolet range (up to 40 eV) and all calculated optical properties are found to be anisotropic. The second part presents a theoretical study upon the antisite defect Bi M O 4 in sillenites compounds, which consists of wrong occupation of the M site by the Bi ion. Calculations were performed firstly for the pure compounds. The crystal structure has been computatio- nally optimized and the band gaps found to be 3.39 eV, 3.35 eV and 3.37 eV for the BGO, BSO and BTO respectively. These values are in very good agreement with experimental data. Defects were investigated in q=-1,0,1 charge states. Electronic structure calculations demonstrated that the antisite defect introduces an energy band inside the gap formed by O 2p- and 6s- states of Bi M ion. This band occupation is directly related to the defect charge state. The neutral defect presents a semi populated band, the positively defect adonor band and the negatively defect an acceptor band. The Bader analysis confirmed that the electron added or removed from the host system is always localised in the area of the defect. The analysis of the defect formation energies demonstrated that the neutral defect is energetically favourable, and thus dominates the lowest thermal state of the sillenites (also called colour state). On the other hand, the charged defects are predominant in the so-called transparent thermal state of the sillenites. From the results, it was possible to associate the presence of the antisite defect with important properties observed in the BMO crystals, such as: (1) explanation of the charge mobility required to produce the photorefractive effect; (2) reversible transitions between the thermal states and (3) photocromic effect in sillenites.
Nesse trabalho foi realizado um estudo te´orico, baseado na Teoria do Funcional da Densidade (DFT), das propriedades estruturais, eletrˆonicas e ´opticas do tetraborato de magn´esio (MgB 4 O 7 ) e um estudo do defeito tipo antiss´ıtio Bi M O 4 em cristais do estruturas silenitas Bi 12 MO 20 (BMO, onde M=Ge, Si e Ti). As otimiza¸c˜oes das posi¸c˜oes atˆomicas e parˆametros de rede foram realizadas para todos os sistemas utilizando o funcional LDA e GGA-PBE para o MgB 4 O 7 e BMO’s, respecti- vamente. As estruturas eletrˆonicas e propriedades ´opticas do sistemas estudados foram calculadas utilizando o m´etodo LAPW implementado no c´odigo computacional WIEN2k. Os efeitos de correla¸c˜ao e troca, das estruturas eletrˆonicas e ´opticas, foram simulados pelo recentemente desenvolvido potencial TB-mBJ, que foi mostrado ser adequado para tratamento de sistemas que possuem gap. Essa tese foi dividida em duas partes. A primeira parte refere-se ao estudo do tetraborato de magn´esio puro. Os c´alculos da estrutura eletrˆonica resultaram em um valor do gap de 9,58 eV, bem pr´oximo ao esperado (comparando a compostos similares). O topo da banda de valˆencia ´e dominado por estados 2p dos oxigˆenios, enquanto o fundo da banda de condu¸c˜ao consiste predominantemente de estados 2p do boro de coordena¸c˜ao trigonal com os oxigˆenios vizinhos (BO 3 ). As caracter´ısticas propriedades ´opticas foram calculadas a partir do tensor diel´etrico complexo, cuja parte imagin´aria ´e diretamente proporcional ao espectro de absor¸c˜ao ´optica verificou-se que a borda de absor¸c˜ao ´optica ´e originada por poss´ıveis transi¸c˜oes eletrˆonicas entre os ´ıons que formam a estrutura trigonal BO 3 . O espectro de absor¸c˜ao tamb´em indicou um car´ater anisotr´opico para o composto. O ´ındice de refra¸c˜ao, coeficiente de extin¸c˜ao, refletividade e a perda de energia de el´etrons foram calculados na regi˜ao ultravioleta at´e 40 eV. A segunda parte refere-se ao estudo do defeito tipo antiss´ıtio em silenitas. Os cristais foram estudados nas formas puras e com a presen¸ca de um ´atomo de Bi ocupando o s´ıtio do ´atomo M (Bi M O 4 ). Os defeitos foram investigados nos estados de carga q=−1, 0, +1. Os band gaps dos BMO’s puros foram determinados com os valores de 3,39 eV para BGO, 3,35 eV para BSO e 3,37 eV para o BTO. Atrav´es das an´alises das densidades de estados eletrˆonicos foi confirmado que o defeito antiss´ıtio introduz uma banda de energia situada dentro do intervalo de energias proibidas,bandgap, formada por estados 2p dos oxigˆenios e 6s do defeito Bi M . A popula¸c˜ao eletrˆonica dessa banda est´a diretamente relacionada ao estado de carga. O defeito neutro (Bi 0 M ) introduz uma banda semi populada, o defeito carregado negativamente (Bi −1 M ) uma banda doadora e o defeito carregado positivamente (Bi +1 M ) uma banda aceitadora. A an´alise das liga¸c˜oes qu´ımicas confirmou que a adi¸c˜ao (ou retirada) de um el´etron do sistema sempre ocorre na banda associada ao defeito. A an´alise da energia de forma¸c˜ao de defeito constatou que o defeito neutro ´e o energeticamente favor´avel, dominando assim o estado de menor energia (tamb´em chamado de estado colorido). A partir dos resultados, tamb´em foi poss´ıvel associar a presen¸ca do defeito antiss´ıtio como geradora de importantes propriedades observadas nos cristais BMO’s, tais como: a mobilidade de carga que ocasiona o efeito fotorrefrativo; a compreens˜ao das transi¸c˜oes revers´ıveis entre estados t´ermicos e o efeito fotocrˆomico.
Wells, George Henry. "Growth and defect formation in graphene." Thesis, Durham University, 2016. http://etheses.dur.ac.uk/11616/.
Повний текст джерелаMiah, Farid. "Numerical and experimental analysis of CFRP machining process in orthogonal cutting." Thesis, Toulouse 3, 2020. http://www.theses.fr/2020TOU30005.
Повний текст джерелаThe composite materials, including CFRP (Carbon Fiber Reinforced Polymer), are increasingly used in aeronautics and automotives which is currently raising many complications in the machining processes. As those materials are made with multiple phases, they are accountable for poor machining quality and undesired defects. This thesis seeks to better understand the fundamental physical technique involved in chip formation mechanism in orthogonal cutting of CFRP machining by combined numerical and experimental studies. Then, the analysis focuses to how certain cutting parameters, e.g., cutting depth, affect to the cutting efforts, surface quality, interply delaminations, inner crack generation and to generated chip shape and size. Moreover, an experimental observation has been made to find out the minimum cuttable depth below which the material does not get cut smoothly over the whole surface. This research work has been finished by a preliminary study on cutting tool wear mechanism
Traoré, Boubacar. "Etude des cellules mémoires résistives RRAM à base de HfO2 par caractérisation électrique et simulations atomistiques." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAT037/document.
Повний текст джерелаAmong non-volatile memory technologies, NAND Flash represents a significant portion in the IC market and has benefitted from the traditional scaling of semiconductor industry allowing its high density integration. However, this scaling seems to be problematic beyond the 22 nm node. In an effort to go beyond this scaling limitation, alternative memory solutions are proposed among which Resistive RAM (RRAM) stands out as a serious candidate for NAND Flash replacement. Hence, in this PhD thesis we try to respond to many open questions about RRAM devices based on hafnium oxide (HfO2), in particular, by addressing the lack of detailed physical comprehension about their operation and reliability. The impact of scaling, the role of electrodes, the process of defects formation and diffusion are investigated. The impact of alloying/doping HfO2 with other materials for improved RRAM performance is also studied. Finally, our study attempts to provide some answers on the conductive filament formation, its stability and possible composition
Gillman, Edward. "Topological defect formation in quantum phase transitions." Thesis, Imperial College London, 2018. http://hdl.handle.net/10044/1/62633.
Повний текст джерелаLightfoot, James S. "Mechanisms of defect formation in carbon fibre composites." Thesis, University of Bristol, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619140.
Повний текст джерелаAsplet, William. "Etude des interactions entre les défauts lacunaires et les solutés Y,O, Ti pour mieux comprendre leur rôle dans la formation des nanoparticules d'oxydes dans les aciers ODS." Thesis, Orléans, 2018. http://www.theses.fr/2018ORLE2056/document.
Повний текст джерелаThis PhD thesis is dedicated to the study of interaction between vacancies and Y, Ti,O solutes for a better understanding of formation of oxide nanoparticles in ODS steel (Oxide Dispersion Strengthened). These ODS steels are considered as structural material for the next generation of fission and fusion nuclear reactors. Their good properties are induced by the fine dispersion of low size oxide nanoparticles. However, obtaining this distribution is not mastered and atomic scale clustering is not yet defined. Furthermore, it was shown by theoretical models that the presence of vacancy during mechanical alloying could affect the formation of these nanoparticles. This study follows upon on a previous study made by C.He, and bring new results, new interpretation and conclusions. Some implantations with Y, Ti, O ions with several energy have been made in order to simulate the mechanical alloying step used for ODS steel fabrication. Theses irradiations have induced defects and solutes into the iron matrix. Then we characterized samples using positron annihilation spectroscopy (PAS) and secondary ion mass spectrometry (SIMS). The nature of defects was studied according to nature of the implanted ion and the annealing temperature by PAS and correlated to depth profiles of solutes obtained by SIMS. Annihilation characteristics of some defects still unknown were able to be determined thanks to positron lifetime measurements. SIMS analysis showed that titanium doesn’t migrate for annealing experiments between 100°C and 450°C and that oxygen show a complex behavior of migration and trapping dependent on the microstructure of the material. PAS results show that ionic implantations produce vacancy clusters, dislocations and solutes-vacancies complex. Their proportion changes as a function of depth and nature of these irradiations. Vacancy clusters and dislocations are detected deeper than the implantation peak with a higher fraction for the dislocations indicating that the defects were able to migrate during implantations. The fraction of vacancy-solutes complexes is the highest in the ion stopping zone and is in a good agreement with the theoretical binding energy of vacancies-solutes complex. The nature and the distribution of the defects evolve according to the annealing temperature. Vacancy clusters disappear between RT and 300°C while the dislocations are eliminated from 400°C. Oxide phases are detected for annealing at 500 and 550°C in relation with the oxygen contamination during these annealings. Some defects which the nature is not yet identified were highlighted for annealing between 300 and 400°C for Y, O and Y+O irradiations
Lu, Haichang. "Electronic structure, defect formation and passivation of 2D materials." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/284926.
Повний текст джерелаCacciuto, Angelo. "Statistical mechanics of self-avoiding crystalline membranes and topological defect formation." Related electronic resource: Current Research at SU : database of SU dissertations, recent titles available full text, 2002. http://wwwlib.umi.com/cr/syr/main.
Повний текст джерелаGrandfield, John F. "Hot tear defect formation during horizontal direct chill casting of magnesium /." St. Lucia, Qld, 2001. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe16285.pdf.
Повний текст джерелаPascoe, Katie Clare, and n/a. "Heritable and early life growth factors affect arterial elastic tissue defect formation." University of Otago. Dunedin School of Medicine, 2006. http://adt.otago.ac.nz./public/adt-NZDU20070306.160709.
Повний текст джерелаWiegel, Michaela E. K. (Michaela Emilie Kurt) 1973. "Gravitational effects on defect formation in melt grown photorefractive materials : bismuth silicate." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/29626.
Повний текст джерелаIncludes bibliographical references (leaves 206-213).
Photorefractivity is the modulation of index of refraction due to nonuniform illumination, and numerous applications have been demonstrated utilizing this nonlinear optical property. However, commercial production is seriously impeded by the inability to produce bulk material with the homogeneity of opto-electronic properties that is required for device applications. Bismuth Silicate, Bi12SiO20, (BSO) is a photorefractive material with outstanding properties including a fast response time and high sensitivity is studied. Its photorefractivity is due to a native defect whose exact nature and origin have not been unambiguously determined. Motivation for current research arose from unexplained optical variations observed in BSO that implicate convective interference as playing a role in native defect formation. Microgravity growth experiments are proposed in order to establish a controlled, convection-free environment to study the origin and nature of the critical native defect. This work aims at resolving critical aspects of performing quantitative microgravity growth experiments that include the interaction of BSO melts with its confinement material; development and characterization of a vertical Bridgman-Stockbarger growth system with a quantifiable, reproducible, and controllable thermal environment; and Bridgman-Stockbarger growth experiments. A comparative analysis of crystals was done in order to establish the relationship between variations in opto-electronic properties as a function of changes in growth conditions. Wetting experiments revealed the sessile drop method to be inappropriate for the BSO-platinum system due to grain boundary pinning. No fundamental difference between the wetting behavior in a terrestrial and a low gravity environment was observed.
(cont.) Results from the comparative analysis indicate a lower defect concentration in Bridgman-Stockbarger material as compared to Czochralski material. The ambient atmosphere during processing and high temperature annealing was found affect material response, including removal of the photochromic response and decrease of carrier lifetime. The lack of the critical defect in hydrothermal BSO, and its existence in all melt grown material indicates that the melt plays a fundamental role in its formation. Clustering in the melt is implicated in the literature from nonlinear melt properties. It is therefore hypothesized that these clusters in the melt act as precursors for native defect formation and subject to gravitationally induced convection. The support of the National Aeronautics and Space Administration is gratefully acknowledged.
by Michaela E.K. Wiegel.
Ph.D.
Gromov, V. E., V. V. Sizov, S. V. Vorobyov, and S. V. Konovalov. "Nanosize Carbides Formation and Fatigue Life Increase of Stainless Steel by Electron Beam Treatment." Thesis, Сумський державний університет, 2012. http://essuir.sumdu.edu.ua/handle/123456789/34807.
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