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Rae, Kevin Julian. "A modified Supercell Composite Parameter for supercell thunderstorms over the Gauteng Province, South Africa." Diss., University of Pretoria, 2014. http://hdl.handle.net/2263/45918.
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South Africa is a country prone to frequent outbreaks of thunderstorms which are often of a severe nature. Supercell thunderstorms are a particular class of thunderstorm which are typically long-lived and are associated with severe thunderstorm phenomena in as many as 9 out of 10 instances. In particular, the southern African moist Highveld climatological region is known to experience one of the highest rates of occurrences of thunderstorms and lightning within southern Africa and indeed the world. The domain for this Highveld-based study chiefly encompassed the industrialised metropolis of the Gauteng province. The population and infrastructure of this province are vulnerable to a variety of adverse effects relating to severe thunderstorms, comprising one or more of strong damaging winds, large hail, urban flooding or even tornadoes of varying intensity. In this study a sample of 15 supercell (SUP) proximity soundings of upper air data for Irene, Gauteng was compared against a large, independant sample of 510 Irene proximity soundings for austral summers during the period 2007 to 2011, representing non-supercell (NON-SUP) thunderstorm days. Hypothesis testing as well as box and whisker representations of the SUP versus NON-SUP samples were applied to various thunderstorm parameters to determine which SUP parameters exhibit the greatest statistical departure from their NON-SUP counterparts. Selected quartiles of SUP parameters so identified were further utilised to formulate a Modified Supercell Composite Parameter (MSCP) tuned to Gauteng supercells. MSCP as well as formulations of the Supercell Composite Parameter (SCP) were subsequently applied to five case-study events where some of the events were associated with observed supercells and some not.
The results strongly indicated that, in a short-term forecast context, MSCP has useful discriminatory ability to provide quantitative predictive guidance as to the relative likelihood of the development of supercell thunderstorms in the Gauteng area. Prior to this research, neither the SCP nor the MSCP were in operational use in South Africa. To the best of the author’s knowledge this work is the first of its kind in southern Africa, especially with consideration to the unique high-altitude Highveld domain of the Gauteng province. In the light of the research results presented herein, it is proposed that MSCP be jointly implemented on point-based (upper air sounding analysis) platforms as well as that of gridpoint-based (deterministic NWP) platforms for short-term predictions of supercell-type thunderstorm conditions in Gauteng province.Dissertation (MSc)--University of Pretoria, 2014.
tm2015
Geography, Geoinformatics and Meteorology
MSc
Unrestricted
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Santos, Jorge Ruben. "Numerical study of a tornado-like vortex in a supercell storm." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=115876.
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Recent observations and numerical simulations have significantly improved our understanding of tornadic storms. However, our knowledge of tornado-genesis remains rudimentary. Necessary atmospheric conditions favoring the formation of tornadoes in supercell storms are known, but sufficient conditions remain elusive. The underlying reason is that the processes involved in environment-storm and storm-tornado interactions are not fully understood, as numerical models in the past lacked sufficient resolution to resolve these interactions satisfactorily. In this thesis, an attempt is made to fill this gap by performing a multi-grid high resolution simulation of a supercell storm spawning a tornado-like vortex. Four grids, with grid sizes of 600 m, 200 m, 70 m, and 30 m, are used to allow explicit simulation of storm-tornado interactions. Diagnostic analysis of the modeling results allows an investigation of the origin of rotation at both the storm scale and the tornado scale.The simulation results showed that the origin of vertical rotation at storm scale during the early stage of storm development is due to tilting of the horizontal vorticity in the environment. This so called mesocyclone then further strengthens by the mechanism of stretching and Dynamic Pipe Effect and descends downwards. During the time of mesocyclone intensification, incipient surface vertical vortices form along the outflow boundary created by the rear flank downdraft due to the process of horizontal shear instability.
One of the surface vortices experiences an initial exponential growth in its vorticity by interacting with the descending mesocyclone and merging with multiple smaller satellite vortices. The tornado-like vortex (TLV) which forms has a maximum horizontal wind of 103 m s-1 and a minimum central pressure of 927 hPa. Vorticity budgets of the mesocyclone and the TLV are computed to assess quantitatively the importance of various processes for rotation.
Sensitivity experiments were also performed to determine the effect of varying the environmental conditions on the mesocyclone and surface vorticity. It was found that as the low-level vertical shear of the environmental wind increases, the mesocyclone intensifies and favors the intensification of near surface vorticity. The presence of drier layers in the upper and middle troposphere eventually produces a weaker mesocyclone and weaker outflow boundaries. On the other hand, inclusion of the ice phase processes produces a stronger mesocyclone and more intense outflow boundaries to enhance the intensification of near surface vorticity.
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Thornhill, Kenneth L. II. "An investigation of the environment surrounding supercell thunderstorms using wind profiler data." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/26958.
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Hasa and Petrit J. "Nowcasting Hail Size for Non-Supercell Thunderstorms in the Northeastern U. S." Thesis, Monterey, California. Naval Postgraduate School, 2012. http://hdl.handle.net/10945/6805.
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Hail size prediction is a difficult task for meteorologists. The most recent method used by the United States Air Force after thunderstorm initiation involves identifying the amount of storm-top divergence and correlating that value to the height of the freezing level. However, this method was based on a study that looked at both supercell and multicell thunderstorms alike. This paper attempts to build off this previous study, although solely looking at non-supercell thunderstorms based on the hypothesis that due to dynamic differences between the storm types, common indicators found in both are not indicative that hail of similar size will be produced.
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Dahdah, Jean. "Etude théorique et expérimentale de cavités photoniques en niobate de lithium : appliquation à la détection de gaz." Besançon, 2010. http://www.theses.fr/2010BESA2045.
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Les travaux de thèses reposent sur l'étude et le développement des structurez photoniques sur niobate de lithium pour des applications capteurs de gaz. L'originalité du travail est d'étudier l'effet de l'absorption des couches de porphyrines spécifiques à la détection du benzène et déposées sur le cristal photonique sur la réponse spectrale de ce dernier. En premier lieu, une étude théorique par des méthodes numériques, maîtrisées a laboratoire d'optique (FDTD, PWE), étaient nécessaires pour étudier l'effet de la présence de certains gaz sur la réponse spectrale des cristaux photoniques. Nous avons montré qu'avec la structure choisie, une variation de la transmission de de 23 % est obtenue lorsque le système est exposé à 50ppm de benzène. La sensibilité de la structure au benzène est estimée à 2,3ppm. En second lieu, nous avons étudié des réalisations en salle blanche des structures photoniques. En utilisant la méthode de gravure directe par faisceau d'ions focalisé (FIB), on a réalisé plusieurs cavités photoniques sur des guides d'ondes optiques fabriqués en collaboration avec Photoline Technologies. Un banc de caractérisation automatisé (interface GPI) en réflexion et en transmission est monté pour vérifier les prédictions théoriques. En plus, les études théoriques et expérimentales en champ proche optique ont été réalisées pour mettre en évidence la résonance des cavités gravées sur niobate de lithium. Ainsi ces études expérimentales sont les premières sur ce type de matériauxIn this thesis we show photonic crystal cavities can be exploited for sensing application, provided that theyare filled with a sensitive absorbent layer. A Lorentz dispersion model implementedin a 2D-FDTD code shoxw that the abbsorption of the layer can be exploited for enhancing the sensitivity of the sensor. We found that a variation of the refractive index of 10-7 leads to a variation of the transmittivity of 23% at the resonnance peak. Also, we will report the first study and realization of two types of tithium niobate photonic cavities (LiNbO3 PhCs). The choice of the LiNbO3 substrate is motived by its capability of combiningpiezoelectric, electro-optical, acousto-optical, non-linear optical properties, which offers the perspective of controlling the operating point of of photonic devices such as sensors. The cavities wre fabricated by focused ion beam (FIB) milling, on annealed proton exchange (APE) sttrip waveguide. Numerical analysis with plane wave expansion method (PWE) has been realized to define the lattice parameters of the studied structures. This study was followed by finite difference time domain (FDTD) simulations to extractthe transmission and reflexion spectra of the cavities. Experimental setup was mounted to characterize the PhCs cavities, wherethe incident light consists of a supercontiuum powerful white source. In addition, experimental near field measurements (SNOM) show the presence of resonnance mode at the defect region of the cavity
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Davenport, Robert T. "Potential vorticity analysis of low level thunderstorm dynamics in an idealized supercell simulation." Thesis, Monterey, Calif. : Naval Postgraduate School, 2009. http://edocs.nps.edu/npspubs/scholarly/theses/2009/Mar/09Mar%5FDavenport.pdf.
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Thesis (M.S. in Meteorology)--Naval Postgraduate School, March 2009.Thesis Advisor(s): Nuss, Wendell A. "March 2009." Description based on title screen as viewed on April 23, 2009. Author(s) subject terms: Potential Vorticity, Severe Weather, Supercell, Weather Research and Forecasting Model, Advanced WRF. Includes bibliographical references (p. 43-47). Also available in print.
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Weygandt, Stephen Scott. "The retreival of initial forecast fields from single Doppler observations of a supercell thunderstorm /." Full-text version available from OU Domain via ProQuest Digital Dissertations, 1998.
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Maharjan, Nikesh. "Electronic band engineering of Transition metal dichalcogenides: First Principles Calculation." OpenSIUC, 2015. https://opensiuc.lib.siu.edu/theses/1661.
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Based on first principles Density Functional Theory calculations, we have investigated for possible paths for engineering electronic band structure of Transition Metal Dichalco- genides (TMDs). We have considered two approaches which have shown to be promising for engineering electronic bands of TMDs: substitutional chemical doping and heterostruc- turing. All the calculations are done using first principles Density Functional Theory as it is implemented in Quantum Espresso package. Two possible substitutional doping meth- ods for MoS2 are considered in our calculations; cation doping where Mo is substituted by metal atoms and anion doping where Nitrogen and halogen group atoms take the posi- tion of S-sites. We observe the n-type characteristics for halogen group doping and p-type characteristics for Nitrogen group doping at S site. Similarly, we observe these bipolar characteristics when substituted by the transition metal elements (4d elements in the peri- odic table) at Mo site. Our results on doping monolayer MoS2 are in agreement with those results obtained by Dolui et al. for similar systems. Our work is extended to explore the effect of substitutional doping in bilayer MoS2. We observe the promising bipolar char- acteristics on doping while the magnitude of the band gap decreases upon the controlled S-site doping with F and As. In the second part, we considered two types of heterostructuring; Van der Waals heterostructures, and lateral heterostructures. In Van der Waals heterostructures, a direct band gap is observed with a physical separation of charges into two layers from orbital isosurface plots. We present a brief overview of the folding of energy bands in supercell approach. Using heterogeneous supercell approach, we studied the electronic properties of a mixed system of MoS2 -WS2 . The separation of the charges into the two sections shows that our MoS2 -WS2 in-plane heterostructure shows a potential for a pn junction. These systematic studies of the doped and heterostructures of TMDs can be useful for device applications.
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White, Trevor Stewart. "Dual-Doppler Derived Vorticity as a Predictor of Hail Size in Severe Thunderstorms." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/74927.
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One of the primary missions of the National Weather Service (NWS) is to use a network of more than 150 NEXRAD radar installations to monitor weather for threats to life and property. Large hail produced by severe thunderstorms is a major focus of this mission. An algorithm known as the Maximum Estimated Size of Hail (MESH) algorithm is in operational use to diagnose the presence and size of hail. This study aims to use dual-Doppler observations as well as the MESH algorithm to test the idea that storms that rotate produce larger hail. Previous studies have used polarimetric radar products to detect the presence of large hail and dual-Doppler methods have been used to study embryonic hail, but no research has tested the theory of hail and rotating storms with observational evidence. A set of 59 case studies was gathered; each included a hail report submitted by a trained weather spotter or NWS employee and complete radar observations through the depth of a storm from two radars. The radar observations were resampled to a three-dimensional Cartesian grid and a dual-Doppler analysis was run on each case study. A strong correlation (stronger even than the MESH algorithm) was found between measured vorticity and hail size, lending credence to the idea that rotating storms do indeed have a higher ceiling for hail production. However, no correlation was found between MESH error and rotation. Further research will be required to evaluate whether or not this relationship can be used to augment the MESH algorithm so as to improve its skill.Master of Science
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Prociv, Kathryn A. "Terrain and Landcover Effects of the Southern Appalachian Mountains on the Low-Level Rotational Wind Fields of Supercell Thunderstorms." Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/32463.
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That tornadoes cannot occur in mountains due to disruptive influences of the complex terrain is a common misperception. Multiple tornadoes occur each year in mountainous environments, including the Appalachian Mountains. Copious research examines the influences of complex terrain on large severe weather systems such as multicell convective systems and squall lines, but research is lacking investigating this same relationship for smaller-scale severe weather phenomena like supercells and tornadoes. This study examines how complex terrain may have influenced the rotational low-level wind fields of fourteen supercell thunderstorms in the Appalachians. The terrain variables include elevation, land cover, slope, and aspect. Using GIS mapping techniques, the individual storm tracks were overlaid onto elevation, land cover, slope, and aspect layers; points along the storm tracks were measured to correlate storm intensities with the underlying terrain. Hypotheses predict that lower elevations, areas of shallower slopes, agricultural land covers, and terrain features with a southeasterly orientation represent terrain variables that would enhance low-level rotation in the lower levels. Results indicate that elevation has a significant impact on storm rotational intensity, especially in mountainous regions. Lower and flatter elevations augment storm rotational intensity, and higher elevations decrease storm rotational intensity. Additionally, northern and western facing slopes exhibited a negative relationship to storm intensity. A qualitative examination revealed vorticity stretching to be evident in eight of the fourteen storms; with vorticity stretching evident on both southeasterly and northwesterly slopes. Future research on appropriate scale for storm-terrain interactions could reveal even stronger relationships between topography and supercell thunderstorms.Master of Science
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Faidley, Galen William. "The Virtual Storm an exploratory virtual environment of a supercell tornadic thunderstorm for meteorological education /." [Ames, Iowa : Iowa State University], 2006.
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McKinney, Christopher Michael. "Total lightning observations of severe convection over North Texas." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2874.
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Foster, James A. "A Comparison of Mobile Radar-Inferred Rain-Drop Size Estimates between Tornadic and Non-Tornadic Supercell Hook Echoes." Ohio University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou157832340334202.
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Beveridge, Susan Lynn. "Quantifying the Relationship Between Southern-end Supercells and Tornado Production." Ohio University Honors Tutorial College / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors1556127178521766.
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Schuster, Doug E. "Soil Moisture Effects on Supercellular Convective Initiation and Atmospheric Moisture in the Midwestern United States." Ohio University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1462232761.
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Soussi, Sofiane. "Quelques Modélisations Mathématiques en Optique." Phd thesis, Ecole Polytechnique X, 2004. http://tel.archives-ouvertes.fr/tel-00008756.
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La première partie de la thèse est consacrée à l'étude de la diffraction d'ondes électromagnétiques par des objets bornés recouverts de couches minces de diélectriques non linéaires. Un développement asymptotique de l'onde fondamentale et de la seconde harmonique est donné en utilisant des techniques d'équations intégrales.Dans la deuxième partie de la thèse, on s'intéressé à la méthode dite de la (\em supercell) qui est utilisée par les physiciens afin de donner une approximation des modes introduits par un défaut à support compact dans un cristal photonique. On étudie la convergence de cette méthode donnant un sens à la convergence du spectre de l'opérateur approché. La convergence exponentielle des valeurs propres dues au défaut est démontrée.
La troisième partie de la thèse est consacrée à l'étude de la propagation d'ondes électromagnétiques dans les fibres optiques photoniques. On dérive une modélisation mathématique de ces fibres dont l'enveloppe est constituée d'un cristal photonique bidimensionnel invariant selon l'axe de la fibre. Les modes guidés par la fibre sont caractérisés comme étant les valeurs propres d'opérateurs intégraux.
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Aiena, Christine N. "The Influence of the Wichita Mountain Range on Convection Initiation of Tornado and Large Hail Producing Supercells in Central Oklahoma." Ohio University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou153374861711777.
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Marten, Tobias. "Ab-initio study of disorder broadening of core photoemission spectra in random metallic alloys." Thesis, Linköping University, The Department of Physics, Chemistry and Biology, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-2580.
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Ab-initio results of the core-level shift and the distribution about the average for the 3d5/2 electrons of Ag, Pd and 2p3/2 of Cu are presented for the face-centered-cubic AgPd and CuPd random alloys. The complete screening model, which includes both initial and final states effects in the same scheme, has been used in the investigations.
The alloys have been modeled with a supercell containing 256 atoms. Density-functional theory calculations are carried out using the locally self consistent Green's function approach.
Results from the calculations clearly shows that the core-level shift distributions characteristic is Gaussian, but the components reveals a substantial difference in the FWHM (Full-Width at Half-Maximum). Comparison between the experimental and the calculated broadening shows a remarkable agreement.
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Harman, Christopher Peter Dereck. "Very strong and supercool electroweak phase transitions." Thesis, University of Sussex, 2017. http://sro.sussex.ac.uk/id/eprint/70363/.
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The aim of this work is to determine whether any zero temperature features of the scalar potential strongly influence the finite temperature properties of the electroweak phase transition. In particular, we address whether one can get an arbitrarily strong phase transition from zero temperature effects. We investigate a variety of models of varying complexity. For the models we look into, we successfully determine that the vacuum energy difference at zero temperature has a direct influence on the critical temperature. This leads to arbitrarily strong phase transitions, subject to the caveat that sliding behaviour does not occur. What we call sliding behaviour is the scenario in which the broken vacuum destabilises under thermal corrections before reaching the critical temperature. The parameter subspace in which sliding behaviour does occur often leads to significantly weakened phase transitions. For a more detailed investigation of the phase transition one must look at the thermal decay of the false vacuum. Choosing a non-supersymmetric real singlet extension to the Standard Model, called the xSM, we detail by example how one can systematically investigate some non-trivial phase transition properties. The specific model we adopt is the Z2xSM which has a Z2 discrete symmetry imposed on the singlet as well as the Higgs field. We focus on the non-sliding parameter subspace, which has a minimal zero temperature parameter space of only three free parameters. For this setup, the depth of the potential at zero temperature has a one-to-one mapping with the strength of the phase transition at critical temperature so we can trivially choose the strength. This allows for a systematic approach to investigating very strong phase transitions and their connection to the amount of supercooling, latent heat, bubble nucleation rate, and a hydrodynamical friction parameter. We also trace out the parameter region in which runaway bubbles are expected and discuss the implications for gravitational wave production.
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Pinto, Marcelo Fett. "Características estruturais, fitossociológicas e produtividade de um campo sobre basalto supercial." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2011. http://hdl.handle.net/10183/37500.
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Poucos estudos descrevem adequadamente as características e capacidade produtiva dos ecossistemas campestres do Bioma Pampa associadas a Neossolos Litólicos derivados de basalto. Esse estudo foi desenvolvido sobre um campo natural no município de Santana do Livramento, região da Campanha do RS e objetivou descrever a diversidade florística e estrutural dessa fisionomia campestre e compreender sua dinâmica produtiva associada ao desempenho animal. O levantamento florístico identificou 232 espécies pertencentes a 40 famílias botânicas, com predominância de Poaceae e Asteraceae. Os Índices de Diversidade de Shannon-Wiener e de Equidade de Pielou foram de 3,00 e 0,874, respectivamente. O percentual de solo descoberto e de afloramentos rochosos representou 19,3% da área. A análise multivariada indicou a existência de apenas dois diferentes padrões de vegetação, com alto grau de agregação interna, os quais determinam a variabilidade estrutural do pasto. Um padrão é caracterizado pela presença de espécies de porte mais alto em locais de solos mais profundos e outro padrão com espécies de menor altura e menor massa de forragem associado aos solos mais rasos. O desenvolvimento de novilhas Hereford entre os 15 e 25 meses de idade apenas a campo (Tratamento 1) ou com a utilização estratégica de suplementação proteico ou proteico-energética (Tratamento 2), bem como das características produtivas do pasto, foram avaliados num delineamento de blocos casualizados, com três repetições. Utilizou-se pastoreio contínuo com carga variável para manter uma oferta média de forragem superior a 13% do peso vivo/dia. Os diferentes padrões de fisionomia identificados “a priori” como aberto, fechado, macio e indecorum se caracterizaram por massas de forragem médias de 547, 1552, 3053 e 829 kg/ha de matéria seca, altura média de 3,3, 8,6, 16,5 e 5,5 cm e ocuparam 32, 52, 12 e 4% da área, respectivamente. As taxas de acúmulo de matéria seca do pasto foram de 27; 14; 3 e 17 kg/ha/dia para o verão, outono, inverno e primavera, respectivamente. Bons ganhos médios diários foram obtidos no outono e primavera, mas no inverno o desempenho foi afetado negativamente pela alta percentagem de material morto na forragem. O desempenho médio não diferiu entre os tratamentos, e as novilhas chegaram aos dois anos com um escore de condição corporal de 3,2 e peso médio de 337 kg, permitindo atingir 100% de prenhez.Few studies had adequately described the characteristics and productive capacity of natural grasslands associated to shallow basaltic soils in Pampa Biome. This study was carried out on natural pasture at Santana do Livramento municipality, in the Campanha region of Rio Grande do Sul, Brazil aiming to describe their floristic and structural diversity and to understand the productivity dynamics associated with animal performance. 232 vegetal species from 40 botanical families were identified in the floristic survey, with predominance of Poaceae and Asteraceae. The Shannon-Wiener Diversity and Equability Pielou Indexes were 3,00 and 0,874, respectively. Bare soil and rock outcrop represents 19,3% of surface area. Multivariate analysis revealed only two different pattern of vegetation, both with high degree of internal aggregation, determining the structural variability of the pasture. One characterized by the presence of tall species and associated with deep soils and the other in the shallow soils and presence of prostrated species. The evaluation of agronomic characteristics of the pasture and the effect of mineral supplementation or not on the development of Hereford heifers during the period between 14 and 25 month of age were tested in a completely randomized block design with three replicates. Continuous grazing with variable stocking rate was used in order to maintain minimal forage allowance of 13% of live weight/day. Different physiognomic patterns identified "a priori" as "open", "closed", "soft" and "indecorum", were characterized respectively by dry matter mass of 547, 1552, 3053 e 829 kg/ha and 3,3, 8,6, 16,5 e 5,5 cm of average high and occupied 32, 52, 12 and 4% of the entire grassland surface. Independent of the vegetation patterns measured accumulation forage rates were 27, 14, 3 and 17 kg/ha of dry matter, in summer, autumn, winter and spring, respectively. Good live weight daily gains were obtained during autumn and spring but the high percentage of dead material in the forage on offer during winter affected negatively the animal performance in this season. Average animal performance was not affected by supplementation treatment and all heifers reached two years age whit a body score condition of 3,2 and 337 kg of average weight that allow to attain 100% of pregnancy.
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Santor, Marcelo Silva. "INFLUÊNCIA DE MATERIAIS DE PROTEÇÃO SUPERCIAL NA RESISTIVIDADE ELÉTRICA E ABSORÇÃO CAPILAR DO CONCRETO." Universidade Federal de Santa Maria, 2011. http://repositorio.ufsm.br/handle/1/7762.
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Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorThe durability of concrete structures is the result of protective action of concrete over the rebar. When the passivation of steel ceases to exist the structure becomes vulnerable to the phenomenon of corrosion, which spread after start is largely controlled by the electrical resistivity of concrete. Another important factor in the durability of concrete structures is the absorption, which is one of the properties governing the transport of ions inside the concrete. This study aimed to evaluate the electrical resistivity and capillary absorption of concrete that have undergone surface treatment: a monolithic polymeric mortar applied in a layer of 4mm, and a pore blocker with a single coat and a pore blocker with a double coat. The concrete surface subjected to treatment were made with three types of cement,CP IV-32, CP II-F 32 and CP V and levels of compressive strength of 15MPa, 20MPa and 25MPa. The electrical resistivity was measured by the method of four electrodes and capillary absorption by the method NBR 9779. Treatment with the pore blocker with a double coat was more effective in reducing capillary absorption than a pore blocker with a single coat for the three types of cement, but the best results were obtained using the polymer mortar. In this work the pozzolanic effect present on cement CP IV became more clear in the result of electrical resistivity for all treatment studied. The different behavior of the electrical resistivity of concrete with cement CP IV in relation to others, CPII F and CP V, is justified by changes in the microstructure of the paste, pore refinement and composition of pore solution. In addition to this, when compared to concrete made with CP V, the lower relations/binder of CP IV to obtain the compressive strengh levels investigated, fck = 15 Mpa , 20Mpa and 25Mpa. Even the reference concrete without surface treatment showed values of resistivity well above the actual reference compounds with CP II-F and CP V and also subjected to surface treatment.
A durabilidade das estruturas de concreto armado é resultado da ação protetora do concreto sobre a armadura. Quando a passivação do aço deixa de existir a estrutura torna-se vulnerável ao fenômeno da corrosão, cuja propagação, após iniciada é essencialmente controlada pela resistividade elétrica do concreto. Outro fator importante na durabilidade das estruturas do concreto é a absorção capilar, a qual é uma das propriedades que regem o transporte de íons no interior do concreto. O presente estudo teve por objetivo avaliar a resistividade elétrica e a absorção capilar em concretos que foram submetidos a tratamento superficial: uma argamassa polimérica monocomponente aplicada em camada de 4mm, e um produto obturador dos poros aplicado em uma e duas demãos. Os concretos submetidos ao tratamento superficial foram produzidos com três tipos de cimento, CP IV 32, CP II F 32 e CP V, e para os níveis de resistência à compressão de 15MPa, 20MPa e 25MPa. A resistividade elétrica foi medida pelo método dos quatros eletrodos e a absorção capilar segundo o método NBR 9779. O tratamento com o produto obturador dos poros em dupla demão mostrou-se mais efetivo na redução da absorção capilar do que o tratamento com uma demão para os três tipos de cimento, contudo, os melhores resultados foram obtidos com o uso da argamassa polimérica. Neste trabalho o efeito pozolânico presente no cimento CP IV ficou claro nos resultados de resistividade elétrica para todos os tratamentos estudados. Este comportamento diferenciado do CP IV em relação aos demais, CP II F e CP V, se justifica pelas alterações na microestrutura da pasta, refinamento dos poros e composição da solução dos poros. Acresce a isto, quando comparado aos concretos produzidos com CP V, as menores relações a/agl do CP IV para obtenção dos níveis de resistência à compressão investigados. Mesmo o concreto de referência sem tratamento superficial apresentou valores de resistividade elétrica muito superiores aos concretos de referência compostos com CP II F e CP V e também submetidos a tratamento superficial.
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Müller, Knut [Verfasser]. "Transmission electron microscopy of InxGa1-xNyAs1-y nanostructures using ab-initio structure factors for strain-relaxed supercells / Knut Müller." Berlin : mbv, Mensch-und-Buch-Verl, 2011. http://d-nb.info/1012725987/34.
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Oliveira, Flávio Pereira de. "Modelagem do escoamento supercial e da erosão hídrica em bacia rural em Arvorezinha, RS, utilizando o WEPP." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2010. http://hdl.handle.net/10183/26997.
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Os modelos de predição da erosão hídrica do solo são utilizados para melhor compreender os processos erosivos, analisar o desempenho de práticas de manejo e avaliar os riscos e os benefícios de diferentes usos do solo. Para tanto, antes de serem utilizados para uma dada condição edafoclimática, devem ser avaliados e, ou, calibrados, principalmente quando se trata de condições diferentes daquelas para as quais o modelo foi desenvolvido. Dentre os inúmeros modelos existentes, o modelo de base física WEPP é um dos mais relevantes na predição da erosão hídrica, pois incorpora os conhecimentos da mecânica de erosão que tem sido gerado nos últimos anos. Este trabalho foi realizado com objetivo de avaliar o desempenho do modelo WEPP em duas vertentes geomorfologicamente distintas localizadas na bacia hidrográfica da comunidade de Cândido Brum, município de Arvorezinha, na região das encostas basálticas do Estado do Rio Grande do Sul. O modelo foi utilizado sem calibração onde os parâmetros de entrada (erodibilidade do solo em entressulcos e em sulcos, tensão crítica de cisalhamento do solo, condutividade hidráulica saturada) foram obtidos experimentalmente e estimados por equações da rotina interna do modelo. Para fins de avaliação dos valores sedimentológicos simulados esses foram comparados com valores de erosão estimados com a utilização do método de redistribuição do “fallout” 137Césio e com valores hidrossedimentológicos medidos no exutório da bacia que contem as vertentes utilizadas na simulação. Os resultados mostraram que as diferenças entre os valores sedimentológicos simulados pelo modelo e os medidos foram menores quando os parâmetros de entrada foram obtidos experimentalmente ao invés daqueles estimados por equações da rotina interna do modelo. Os valores de coeficientes de escoamento simulados pelo modelo com dados do componente solo obtidos sob condição experimental de campo, nas duas vertentes estudadas, se assemelharam em relação aos valores observados por meio de monitoramento da bacia. Já os resultados da distribuição espacial dos processos desagregação e deposição simulada pelo WEPP e comparados com resultados da atividade do 137Cs mostraram alguma discrepância em relação à desagregação e uma tendência similar relacionado à deposição de sedimentos. O modelo WEPP apresenta boas condições para ser aplicado nas condições edafoclimáticas da região sul do Brasil, especialmente quando seus principais parâmetros são determinados nas condições locais.Erosion models have been used to better understand erosive processes, analyze soil conservation practices, and evaluate the risks and benefits of different soil uses. However, before a model can be used for a given soil and climactic situation, it must be validated and/or calibrated, especially if it is to be used in conditions other than those for which it was developed. Among the many erosion prediction models which exist, the WEPP model is one of the most relevant because it incorporates the current understanding of erosion mechanics. This study seeks to evaluate the WEPP model in two hillslopes with different shapes (concave and convex) in a catchment on the basalt scarp of Rio Grande do Sul, in southern Brazil. The model was run without calibration with starting parameters (rill and interrill erodibility, critical shear stress, saturated hydraulic conductivity) determined experimentally and through the model’s standard equations. To evaluate the simulated hydrologic and sedimentologic values, these were compared with erosion values measured using the 137cesium “fallout” method and also with hydrosedimentologic measures from the outflow of the experimental watershed. Results show that differences between the simulated and measured values were smaller when initial parameters were obtained experimentally rather than estimated by the model’s standard equations. The overland flow coefficients simulated by the model in the two hillslopes studied were similar to those observed through monitoring, especially when the initial soil parameters were experimentally determined. The spatial distribution of detachment and deposition processes simulated by WEPP and those obtained via the cesium method show some discrepancies for detachment and a similar trend for deposition. The WEPP model has a good condition to be applied at southern conditions of Brazil since its major components being experimentally evaluated at local conditions.
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Höijertz, Erik. "Supercoiled Actuators with Liquid Metal Joule Heating : novel miniaturized actuators for pneumatic control of reconfigurable wearables." Thesis, Uppsala universitet, Mikrosystemteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-426008.
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Garments serve a number of purposes, from protection and physiological comfort to social and cultural expressions. With the recent developments of active textiles, sensors and actuators with shapes and sizes similar to textiles, the real multifunctional garments have been realized. The functions of such garments can be regulating heat by changing the spacing between the strands of yarn, giving massage or assisting lifting movement by expanding and contracting one or more actuators. This project is a part of a main project targeting on reconfigurable hybrid wearables. The main started from studying possible actuators that could have textile-like properties, where pneumatic actuators were chosen. A model of different forces, strains and braiding angles of a pneumatic actuator sometimes called a McKibben muscle was made. It should be noted that such garments with pneumatic actuators to be functional and applicable each segment needed an external pump. For local actuation, miniaturized servo valves were needed. Hence, study on super coiled actuators (SCAs) was initiated to investigate their potential of controlling the valves for constricting the flow when needed. In this project different SCAs were developed and their performances were recorded. To assist with heating of the SCAs Galinstan and Gallium were used as electric resistors to provide for Joule heating. A contraction of over 19% and an efficiency of 0.29% were achieved but could most likely be improved by optimizing the fabrication and testing process.
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Sauger, Emmanuel. "Contribution à l'étude de la transformation tribologique superficielle en fretting." Ecully, Ecole centrale de Lyon, 1997. http://bibli.ec-lyon.fr/exl-doc/TH_T1717_esauger.pdf.
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En frottement sec, la formation des débris s'effectue généralement à partir d'une structure particulière appelée Transformation Tribologique Superficielle (TTS). De ce fait, toute modélisation de révolution du contact passe nécessairement par la compréhension de la formation et de la destruction de cette TTS. Dans cette étude, en utilisant le fretting comme sollicitation tribologique, nous nous sommes attachés aux mécanismes de formation. Nous avons abordé ce problème complexe qu'est la TTS au travers d'approches mécaniques simples, physicochimiques et analytiques, utilisant des techniques allant de l'observation métallographique à la microscopie électronique en transmission. Les travaux effectués au laboratoire ont montré que la TTS se forme très rapidement: - sa dureté est élevée (de 700 a 1000 Hvo. 025 pour des matériaux aussi différents que des alliages d'aluminium ou des aciers), - sa composition chimique est identique à celle de l'alliage avant frottement, - la TTS est formée de nanograins (20 a 60 nm) orientés aléatoirement et ayant la structure de la phase stable à température ambiante de l'alliage testé. Nous avons analysé deux modèles de formation. Le premier considère la TTS comme le résultat d'un phénomène de "Mechanical Alloying". Le second, proposé par le laboratoire, met en cause une recristallisation due aux fortes déformations plastiques. Par des analyses tres fines en perte d'energie (EELS), effectuées en microscopie électronique en transmission, nous avons montré que le premier modèle était peu probable. Quelles que soient les conditions de sollicitation étudiées (glissement partiel ou total, conditions d'élasticité ou de plasticité macroscopiques), la TTS se forme dès qu'il y a déplacement relatif entre les deux surfaces. De plus, par une approche énergétique du frottement, basée sur des considérations mécaniques simples, nous avons mis en évidence que la TTS se formait rapidement et en quantité importante à partir d'un seuil d'énergie.
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Mendelson, Neil, Patrick Shipman, Darshan Roy, Liling Chen, and John Thwaites. "The dynamic behavior of bacterial macrofibers growing with one end prevented from rotating: variation in shaft rotation along the fiber's length, and supercoil movement on a solid surface toward the constrained end." BioMed Central, 2003. http://hdl.handle.net/10150/610048.
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BACKGROUND:Bacterial macrofibers twist as they grow, writhe, supercoil and wind up into plectonemic structures (helical forms the individual filaments of which cannot be taken apart without unwinding) that eventually carry loops at both of their ends. Terminal loops rotate about the axis of a fiber's shaft in contrary directions at increasing rate as the shaft elongates. Theory suggests that rotation rates should vary linearly along the length of a fiber ranging from maxima at the loop ends to zero at an intermediate point. Blocking rotation at one end of a fiber should lead to a single gradient: zero at the blocked end to maximum at the free end. We tested this conclusion by measuring directly the rotation at various distances along fiber length from the blocked end. The movement of supercoils over a solid surface was also measured in tethered macrofibers.RESULTS:Macrofibers that hung down from a floating wire inserted through a terminal loop grew vertically and produced small plectonemic structures by supercoiling along their length. Using these as markers for shaft rotation we observed a uniform gradient of initial rotation rates with slopes of 25.6degrees/min. mm. and 36.2degrees/min. mm. in two different fibers. Measurements of the distal tip rotation in a third fiber as a function of length showed increases proportional to increases in length with constant of proportionality 79.2 rad/mm. Another fiber tethered to the floor grew horizontally with a length-doubling time of 74 min, made contact periodically with the floor and supercoiled repeatedly. The supercoils moved over the floor toward the tether at approximately 0.06 mm/min, 4 times faster than the fiber growth rate. Over a period of 800 minutes the fiber grew to 23 mm in length and was entirely retracted back to the tether by a process involving 29 supercoils.CONCLUSIONS:The rate at which growing bacterial macrofibers rotated about the axis of the fiber shaft measured at various locations along fibers in structures prevented from rotating at one end reveal that the rate varied linearly from zero at the blocked end to maximum at the distal end. The increasing number of twisting cells in growing fibers caused the distal end to continuously rotate faster. When the free end was intermittently prevented from rotating a torque developed which was relieved by supercoiling. On a solid surface the supercoils moved toward the end permanently blocked from rotating as a result of supercoil rolling over the surface and the formation of new supercoils that reduced fiber length between the initial supercoil and the wire tether. All of the motions are ramifications of cell growth with twist and the highly ordered multicellular state of macrofibers.
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Selvam, Sangeetha. "Molecular Population Dynamics of DNA Tetraplexes using Magneto-Optical Tweezers." Kent State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=kent1516742116760289.
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Santos, Elisa Caroline da Silva. "Efeito dos métodos de vitrificação, OPS e SSV, com adição de bloqueador sintético de gelo, sobre a viabilidade de oócitos de camundongos e bovinos." Universidade Federal de Pelotas, 2008. http://guaiaca.ufpel.edu.br/handle/123456789/1256.
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Previous issue date: 2008-05-09Oocyte vitrification is a valuable tool for preservation of genetic material. This study compared the effects of vitrification in OPS and SSV, with addition of SupercoolTM X- 1000 (copolymer), on the viability of mature murine oocytes and immature bovine oocytes. Oocytes were vitrified in OPS and SSV, with addition of 0.1%, 1.0% copolymer and without copolymer, besides a control group with no vitrification. Murine oocytes were evaluated for membrane viability, in the first experiment, and for cleavage rate, in the second experiment. Results were superior with the concentration of 0.1% copolymer, for both methods, in the first experiment. In the second experiment, the SSV method without copolymer presented lower cleavage rate (9.2%) than the control group (26.6%). In the third experiment, bovine oocytes were vitrified and evaluated for maturation and membrane viability, but the results were numerically inferior than those for the control group, for both methods. Those results indicate that both vitrification methods can be used with inclusion of 0.1% of copolymer, for mature murine oocytes, considering membrane viability, but the SSV method without copolymer should not be used due to its low cleavage rate. However, the procedures tested in this study are not recommended for cryopreservation of bovine oocytes.
A vitrificação de oócitos é uma metodologia valiosa para a conservação de material genético. Este trabalho comparou o efeito dos métodos de vitrificação OPS e SSV, com adição de copolímero SupercoolTM X-1000 (copolímero), sobre a viabilidade de oócitos maturos murinos e oócitos bovinos imaturos. Os oócitos foram vitrificados em OPS e SSV, ambos com as concentrações de copolímero: 0%, 0,1% e 1% e o controle não foi vitrificado. No primeiro experimento, os oócitos maturos murinos vitrificados foram avaliados quanto à viabilidade de membrana e no segundo experimento, quanto à clivagem. A concentração 0,1% de copolímero foi superior (P>0.05) em ambos os métodos no primeiro experimento. No segundo experimento, o tratamento SSV 0% apresentou resultado inferior (P<0.05) (9,2%) ao controle (26,6%). No terceiro experimento, oócitos bovinos imaturos foram vitrificados e avaliados quanto à taxa de maturação e viabilidade de membrana. Aparentemente, segundo observações numéricas, os resultados de todos os tratamentos parecem ser inferiores ao controle. Os resultados desta pesquisa indicam que ambos os métodos podem ser utilizados com a concentração 0,1% de copolímero, na vitrificação de oócitos murinos maturos. No entanto, a vitrificação, seguindo os protocolos utilizados nesta pesquisa, não é indicada para a criopreservação de oócitos bovinos imaturos.
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Santini, Davide. "Struttura nuvolosa del temporale." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amslaurea.unibo.it/5916/.
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La tesi descrive in modo analitico la formazione del temporale e i suoi stadi di vita, i tipi di temporale suddivisi in base alla struttura e le nubi accessorie, particolari formazioni nuvolose che appartengono al temporale e alla sua evoluzione.
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Wilt, Brett Alan. "Supercell index prediction of supercells and tornadoes with model output diagnostics /." 1994. http://catalog.hathitrust.org/api/volumes/oclc/32966175.html.
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Thesis (M.S.)--University of Wisconsin--Madison, 1994.Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 105-110).
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Kirby, Shaun K. "Three-dimensional supercell simulation of novel semiconductor nanostructures." Thesis, 1994. https://thesis.library.caltech.edu/7659/1/Kirby_sk_1994.pdf.
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In this thesis we investigate atomic scale imperfections and fluctuations in the quantum transport properties of novel semiconductor nanostructures. For this purpose, we have developed a numerically efficient supercell model of quantum transport capable of representing potential variations in three dimensions. This flexibility allows us to examine new quantum device structures made possible through state-of-the-art semiconductor fabrication techniques such as molecular beam epitaxy and nanolithography. These structures, with characteristic dimensions on the order of a few nanometers, hold promise for much smaller, faster and more efficient devices than those in present operation, yet they are highly sensitive to structural and compositional variations such as defect impurities, interface roughness and alloy disorder. If these quantum structures are to serve as components of reliable, mass-produced devices, these issues must be addressed.
In Chapter 1 we discuss some of the important issues in resonant tunneling devices and mention some of thier applications. In Chapters 2 and 3, we describe our supercell model of quantum transport and an efficient numerical implementation. In the remaining chapters, we present applications.
In Chapter 4, we examine transport in single and double barrier tunneling structures with neutral impurities. We find that an isolated attractive impurity in a single barrier can produce a transmission resonance whose position and strength are sensitive to the location of the impurity within the barrier. Multiple impurities can lead to a complex resonance structure that fluctuates widely with impurity configuration. In addition, impurity resonances can give rise to negative differential resistance. In Chapter 5, we study interface roughness and alloy disorder in double barrier structures. We find that interface roughness and alloy disorder can shift and broaden the n = 1 transmission resonance and give rise to new resonance peaks, especially in the presence of clusters comparable in size to the electron deBroglie wavelength. In Chapter 6 we examine the effects of interface roughness and impurities on transmission in a quantum dot electron waveguide. We find that variation in the configuration and stoichiometry of the interface roughness leads to substantial fluctuations in the transmission properties. These fluctuations are reduced by an attractive impurity placed near the center of the dot.
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Frame, Jeffrey W. Markowski Paul M. "The dynamical influences of cloud shading on simulated supercell thunderstorms." 2008. http://etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-3362/index.html.
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Zi-Gui, Huang. "ANALYSIS OF WAVE PROPAGATION IN PHONONIC CRYSTALS USING THE PLANE-WAVE EXPANSION AND SUPERCELL TECHNIQUES." 2005. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-2507200508584000.
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Huang, Zi-Gui, and 黃自貴. "ANALYSIS OF WAVE PROPAGATION IN PHONONIC CRYSTALS USING THE PLANE-WAVE EXPANSION AND SUPERCELL TECHNIQUES." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/66023573996608715677.
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博士國立臺灣大學
應用力學研究所
93
Successful application of photonic crystals has led to a rapid growing interest in the analogous acoustic effects in periodic elastic structures called phononic crystals recently. The phenomenon of frequency band gap in the phononic crystal can be applied to the designs of filters for surface and bulk acoustic waves. The repetitive structures made up of different elastic materials can prevent elastic/acoustic waves from passing by at some specific angles or certain frequency bands. The analysis is carried out within the framework of the theorems in solid-state physics and wave equation of motion in inhomogeneous elastic media. The methods employed in studying the wave motion in phononic crystals are based on the plane-wave expansion method and supercell technique. The formulations for elastic/acoustic wave propagation in phononic crystals are consisted of the materials with general anisotropy. The frequency band-gap features and wave propagation of surface and bulk acoustic waves in the two-dimensional phononic crystals with either square or hexagonal lattices are investigated. The concept of tunable frequency band gaps of the surface and bulk modes in the two-dimensional phononic crystals is introduced by changing the filling fraction, rotating square rods, hollow cylinders, and sectional phononic crystals. On the other hand, the supercell technique is adopted to calculate the defect modes and extended modes in phononic crystals. The technique is also used to analyze the propagating modes and couplings of waveguides in phononic crystals with acoustic channels. It is worth noting that through a suitable design by using the plane-wave expansion and supercell techniques, the acoustic filters, mirrors, resonators, and waveguides are the possible applications in the two-dimensional phononic crystals.
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Laflin, Jennifer M. "A targeted modeling study of the interaction between a supercell and a preexisting airmass boundary." 2010. http://digitalcommons.unl.edu/geoscidiss/6.
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Thesis (M.S.)--University of Nebraska-Lincoln, 2010.Title from title screen (site viewed April 22, 2010). PDF text: i, 80 p. : ill. (chiefly col.) Publication: Dissertations & Theses in Geosciences. Includes bibliographical references.
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Johnson, Daniel Eric. "A study of the 2 August 1981 CCOPE supercell storm using the Wisconsin Dynamical/Microphysical Model." 1991. http://catalog.hathitrust.org/api/volumes/oclc/24350658.html.
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Thesis (M.S.)--University of Wisconsin--Madison, 1991.Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 154-157).
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"Full-band Schrödinger Poisson Solver for DG UTB SOI MOSFET." Master's thesis, 2016. http://hdl.handle.net/2286/R.I.40796.
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abstract: Moore's law has been the most important driving force for the tremendous progress of semiconductor industry. With time the transistors which form the fundamental building block of any integrated circuit have been shrinking in size leading to smaller and faster electronic devices.As the devices scale down thermal effects and the short channel effects become the important deciding factors in determining transistor architecture.SOI (Silicon on Insulator) devices have been excellent alternative to planar MOSFET for ultimate CMOS scaling since they mitigate short channel effects. Hence as a part of thesis we tried to study the benefits of the SOI technology especially for lower technology nodes when the channel thickness reduces down to sub 10nm regime. This work tries to explore the effects of structural confinement due to reduced channel thickness on the electrostatic behavior of DG SOI MOSFET. DG SOI MOSFET form the Qfinfet which is an alternative to existing Finfet structure. Qfinfet was proposed and patented by the Finscale Inc for sub 10nm technology nodes.
As part of MS Thesis we developed electrostatic simulator for DG SOI devices by implementing the self consistent full band Schrodinger Poisson solver. We used the Empirical Pseudopotential method in conjunction with supercell approach to solve the Schrodinger Equation. EPM was chosen because it has few empirical parameters which give us good accuracy for experimental results. Also EPM is computationally less expensive as compared to the atomistic methods like DFT(Density functional theory) and NEGF (Non-equilibrium Green's function). In our workwe considered two crystallographic orientations of Si,namely [100] and [110].Dissertation/Thesis
Masters Thesis Electrical Engineering 2016
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Kim, Jiseok. "Band structure calculations of strained semiconductors using empirical pseudopotential theory." 2011. https://scholarworks.umass.edu/dissertations/AAI3445166.
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Electronic band structure of various crystal orientations of relaxed and strained bulk, 1D and 2D confined semiconductors are investigated using nonlocal empirical pseudopotential method with spin-orbit interaction. For the bulk semiconductors, local and nonlocal pseudopotential parameters are obtained by fitting transport-relevant quantities, such as band gap, effective masses and deformation potentials, to available experimental data. A cubic-spline interpolation is used to extend local form factors to arbitrary q and the resulting transferable local pseudopotential V(q) with correct work function is used to investigate the 1D and 2D confined systems with supercell method. Quantum confinement, uniaxial and biaxial strain and crystal orientation effects of the band structure are investigated. Regarding the transport relavant quantities, we have found that the largest ballistic electron conductance occurs for compressively-strained large-diameter [001] wires while the smallest transport electron effective mass is found for larger-diameter [110] wires under tensile stress.
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"Theoretical investigations of cobalt/platinum alloys and supercells." Tulane University, 2003.
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In this work I have studied a number of technologically important magnetic materials using density functional theory. Two ab-initio methods have been employed to investigate several ferromagnetic materials, the Vienna ab-initio Simulation Package and the layer Korringa-Kohn-Rostoker Method. The systems studied include two series of L10 alloys, and Co3Pt (both form natural superlattices) as well as artificially grown Co1Pt5 superlattices. Experimental difficulties associated with the growth of L10 alloys is discussed, along with theoretical calculations of the magnetic properties as a function of content. Another candidate for perpendicular data storage, the orthorhombic derivative Pmm2 phase of Co 3Pt, has also proven difficult to grow as it appears to be metastable. The possibility of phase stabilization has been explored using first principles methods. In a collaborative effort to improve micromagnetics simulations, the way in which local magnetic properties are affected near grain boundaries of Co1Pt5 supercells has been examined. Results of these first principles calculations have been used as input parameters in micromagnetics simulations. Both the first principles calculations and specifics of the micromagnetic simulations are discussed, in addition to calculations of Cr buffer layers acting to magnetically decouple grains. Conclusions are drawn as to the achievement of the stated research goalsacase@tulane.edu
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Niu, Ze. "Atomistic modelling of semiconductor supercells using the empirical pseudopotential method." Thesis, 2019. https://hdl.handle.net/2144/38658.
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Semiconductor superlattices and alloys based on III-V semiconductors have important applications in the design of optoelectronic devices in particular photodetectors. Understanding the electronic properties of such system is critical to be able to properly design and optimize the performance of such devices. Atomistic modelling is the most suitable approach to understand the microscopic properties of these systems.
While density functional theory (DFT) is the approach of choice for many studies, it cannot be applied to systems comprised of a large number of atoms. The goal of this thesis is to explore the possibility of applying the empirical pseudopotential method associate with hybrid pseudopotential method to compute the electronic structure and optical properties of Ga_xAl_1-xAs alloy. The proposed work will address first the derivation of portable continuous screened atomic pseudopotentials for the constituent atoms. These will be validated using calculation on small systems. Subsequently, the atomic pseudopotential will be used to study Ga_xAl_1-xAs alloy with different microstructure.
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YANG, ZHI-HAN, and 楊智涵. "Dynamic Wetting of Droplet Surface on Supercool Effect." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/829aw3.
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碩士國立聯合大學
機械工程學系碩士班
106
The purpose of this research is to investigate the effect of dynamic wetting on the hydrophobic and hydrophilic surfaces while the surface temperature was heated from room temperature to the supercooled temperature. The surface tends to absorb water strongly when surface reaches supercooled. However, the hydrophobicity has been proven to have ice-resistant and water-resistant properties. Therefore, these two effects of hydrophobic (non-wetting) surface and supercooled (cold) surface are repellent. However, the hydrophilic (wetting) surface can help the Supercool effect, and these two effects are attracting. The experimental observation shows that droplet impacted on the surfaces with the change of the contact diameter of the droplet spreading and the droplet bounced on the non-wetting surface. The aim of this study focus on the supercool effect with different surface wettabilities. The supercool surfaces with different wetting conditions were tested, with the control variables of temperature level and impact velocity (Weber numbers). At the hydrophilic surface, the results show that the lower temperature had the larger maximum contact diameter of droplets spreading. At the case of wetting surface with the lower Weber number, the maximum contact diameter at -16 °C are 1.5 times larger than at room temperature. The supercool effect helps the droplet spread on hydrophilic surface. However, on the case of non-wetting surface, the difference in droplet contact diameter between -20 °C and 25 °C is small. Because the droplets after impacting will bounce on the super-hydrophobic surface. The dynamic of droplets impacting are totally different on these two cases. Through the energy balance, the potential energy could transfer to the kinematic energy of spreading and bounce after the droplets impacting. This study will finally discuss the energy distribution on the cold effect and wettability effect during the dynamic wetting of the droplets.
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Hunger, Karen [Verfasser]. "Kälteschockantwort von Bacillus subtilis : supercoil-regulierte Kälteschockproteine und die kälteinduzierten DEAD-box RNA-Helikasen CshA und CshB / von Karen Hunger." 2006. http://d-nb.info/982577303/34.
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