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1
Yari, Sadegh. "Heat and salt transport across the strait of Otranto." Doctoral thesis, Università degli studi di Trieste, 2009. http://hdl.handle.net/10077/3213.
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2007/2008The water transport and advected heat through the Strait of Otranto are computed applying a new methodology to the historical data set. According to the previous oceanographic studies, the Adriatic Sea annually loses heat through the air-sea interface. This heat loss should be balanced by the heat advected across the Strait of Otranto. Direct current measurements for almost one year (from December 94 through November 95), and five seasonal oceanographic campaigns are used in this study. The current data are measured at sixteen locations at different depths; near surface, intermediate depths and near bottom. The measured current data are detided and low pass filtered in order to remove tidal and inertial oscillations. A variational inverse method based on a variational principle and a finite element solver is used to reconstruct the current field across the Strait section from sparse measurements. The mean water flow across the strait consists of an inflow on the eastern side and an outflow on the western side, while there is a two layer structure in the central part. The latter has an inflow in the surface layer and an outflow in the bottom layer. The mean monthly, seasonally and yearly water transports and corresponding errors are calculated. The mean annual inflow and outflow water transport rates are estimated as 0.90±0.04 Sv and -0.94±0.31 (error) Sv and the net transport is equal to -0.04±0.32 (error) Sv. Thus, on a yearly time interval, the inflow and the outflow are practically compensated. These estimations of water transport are in agreement with previous studies. The seasonal heat flux is estimated by using the data collected during the hydrographic surveys conducted in December 1994, February, May, August and November 1995. The results show a net heat advection into the Adriatic Sea on a yearly basis. The estimated values of advected heat applying two different methods are 2.93±0.35 TW and 2.5±0.35 TW, which are equivalent to heat gain of 21.3±2.5 (error) Wm-2 and 17±2.5 Wm-2 for the whole basin which are compared to the calculated heat loss of -36±152 (std) Wm-2 over the Adriatic Sea. Salt transported salt is calculated by using salinity and current data. The average annual salt transport is estimated as an inflow of salt equal to 0.05106 Kgs-1. This is in agreement with the fact that the Adriatic Sea is a dilution basin. The average annual fresh water budget is estimated as -0.002 Sv which is equivalent to fresh water gain of 0.45 m/year for the entire Adriatic Sea.
XXI Ciclo
1972
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Cisewski, Boris. "Der Transport von Wärme, Wasser und Salz in den Arktischen Ozean = The transport of heat, mass and salt into the Arctic Ocean /." Bremerhaven : Alfred-Wegener-Institut für Polar- und Meeresforschung, 2001. http://www.gbv.de/dms/bs/toc/327039299.pdf.
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Flanders, Justin M. "Thermal Transport and Heat Exchanger Design for the Space Molten Salt Reactor Concept." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1345508695.
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Olson, Elise. "Oceanic transports of heat and salt from a global model and data." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/38560.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2006.Includes bibliographical references (leaves 49-50).
A state estimate produced by ECCO-GODAE from a global one-degree model and data spanning the years 1992-2005 is analyzed in terms of transports of volume, temperature, and freshwater. The estimate is assessed to be sufficiently close to observations to merit analysis. The methods of analysis are similar to those of Stammer et al. (2003). The longer time period allows trends to be measured with greater confidence. Time mean flow characteristics demonstrate agreement with previous estimates. The strength of the ACC (146±5Sv) is larger than in the Stammer et al. (2003) state estimate, but is within the range of other estimates. A twelve-year decreasing trend is observed in the strength of the ACC of approximately 0.88Sv/year. The Indonesian throughflow transport of 1 l±2Sv is within the expected range. There is also a decreasing twelve year trend in the strength of the ITF of 0.065Sv/year. The ITF is stronger in boreal summer than boreal winter by approximately 4Sv. A strong annual cycle is present in the transport record on most sections, but higher frequency variability is also present. Most temperature transport variability results from velocity fluctuations, except in the Southern Ocean where temperature fluctuations are more important. Recommended further work includes a more detailed analysis of variability in this state estimate.
by Elise Olson.
S.M.
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Chea, Nila. "Salt. Fat. Acid. Heat. Media." Thesis, Malmö universitet, Fakulteten för kultur och samhälle (KS), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:mau:diva-22680.
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According to Samin Nosrat’s (2017) best-selling cookbook, salt, fat, acid and heat are key to cooking good food. At the same time, the process of making food has never been more connected with media. Given how intertwined food and media are today, I also add media to the list of ingredients. Food has become a popular topic in traditional media, as well as on new digital platforms. Since there is already a large body of research on food media texts, this thesis concentrates on food media related practices in the everyday life and the convergence between traditional and digital food media. For this study, a mixed-method approach was chosen, which included a questionnaire and a subsequent in-depth interview for the participants. The qualitative analysis of the data builds on a theoretical framework which draws first and foremost on Couldry’s (2004) Practice Theory which is complemented by Foth & Hearn’s (2007) Communication Ecology Theory to organize the practices. The food media practices of the study participants illustrated how embedded media have become in everyday practices and explained the convergence between traditional and digital food media. At the same time, the results brought media power dynamics to light and demonstrated that even media, that seems innocent at first, has to be consumed with a critical eye.
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Daher, Ibrahim. "Salt transport experiments in fractured media." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/45285.
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During the sequestration of CO2 into down-hole rock formations, salt precipitation may occur due to the drying of the formation brine if the injected CO2 is dry. This can negatively affect the performance of injection wells and can even lead to well clogging, which is a serious risk for such operations. Further, the salt deposition can alter the flow of the CO2 in the formation altering the storage capacity. Therefore, it is very important to explore the effect on CCS (Carbon Capture and Storage) process of drying out and salt precipitation during CO2 injection. This study is focused on CCS in fractured aquifers, which has received less attention than their un-fractured counterparts and particularly, the flow impairment associated with salt precipitation during the injection of dry CO2. When CO2 is injected into a conductive fracture network, the brine will rapidly be displaced from the fractures near the point of injection and the subsequent mass transfer between the matrix and the fracture; orthogonal to the flow direction in the fracture, is the major target of the project. The dry-out that occurs due to the evaporation of water from the brine filled region of the matrix into the under-saturated CO2 filling the fracture can cause deposition of salt in the matrix or the fracture, locally reducing permeability. This thesis reports on an investigation of the evaporative drying kinetics and salt precipitation using a combination of gravimetric and X-ray µ-CT techniques to measure the water and brine saturation, salt precipitation and distribution of salt deposition in two rocks; a sandstone, Bentheimer and a carbonate, Ketton. Based on the experimental results for de-ionised water, two main regimes occur during the dry-out process: a capillarity driven regime which seems to be dominant for most of the dry-out process in the experiments, during which evaporation happens only at the surface of the fracture, followed by a diffusion limited regime after the liquid bridge to the surface breaks and pores near the surface become dry for the first time. In pure water, this results in an almost constant evaporation flux in the first regime followed by a mass loss that is linear when plotted against the square root of time. The experiments with brine were initially similar with an evaporative flux almost constant with time. However, a short time into the process the evaporative flux started to decrease approximately linearly with the square root of time, following the deposition of salt at the surface of the fracture. At the end of gravimetric dry-out tests, µ-CT images were obtained showing that salt was mainly precipitated at the surface of the sample; however, relatively small amount of salt was observed precipitated in the interior of the sample. The pore structure of the precipitated salt at the end of the dry-out tests maintained connectivity between the surface of the deposit and the rock matrix. Dynamic µ-CT imaging of Bentheimer during brine drying showed that during the early stage of evaporation, salt was continuously deposited at the surface of the matrix. During this stage in the evaporation of brine, advection dominates the transport of dissolved salt, indicated by a large Peclet number, and this resulted in an increased salt concentration very local to the site of evaporation. The ongoing formation of an efflorescence therefore, is evidence for the continuity of the liquid connections to the outside of the sample, despite the evaporation becoming linear against the square root of time. Unfortunately, the liquid bridges to the surface were too small to be seen directly in the µ-CT imaging. The volume of precipitated salt increased with time and this resulted in a change in the pore structure at the surface of the sample structure, consequently reducing the brine-drying rate. However, as the salt deposition and therefore the location of the evaporation continued to be at the exposed surface, vapour diffusion cannot account for the mass lost by evaporation becoming linear in the square root time as is usually stated. Some other mechanism must account for the observed behaviour and we speculate that the surface area for evaporation was reduced by the appearance of dry patched on the surface. At a very late stage of evaporation, it was observed that no further salt precipitated at the surface of the sample; and subsequently, salt precipitation progressed with time towards the interior of the sample core with small amount of salt. At this stage the liquid connection to the surface must finally have broken and a true diffusion controlled process occurred. In the limited sample size used in this study, this mechanism accounted for only a small fraction of the total salt deposited. From permeability measurements before and after the complete drying of the samples, it was demonstrated that the permeability of Bentheimer was reduced by 81 % from 2.2 D to 0.41 D by the salt deposition. However, Lattice Boltzmann simulations of single phase permeability in the segmented µ-CT images, showed a reduction by 54% from 2.27 D to 1.28 D at 6 µm scanned voxel resolution and 54% from 2.7D to 1.48D at 15um scanned voxel resolution. From these results, it can be concluded that salt precipitation during the injection of CO2 into a fractured porous medial result in a significant reduction in formation permeability, but connectivity between the matrix and the fracture is maintained.
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Venter, Jason Stephen. "Salt River multi modal transport interchange." Master's thesis, University of Cape Town, 2011. http://hdl.handle.net/11427/5580.
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Includes abstract.Includes bibliographical references.
South African cities have unique spatial design challenges which can be attributed to our historical and politically charged urban planning practices. Our cities are characterised by modernist town planning principles which have fragmented communities through spatial barriers such as highways, train lines and fences while current development perpetuates urban sprawl. Due to these circumstances many contemporary urban design policies promote densification strategies through transit orientated approaches.In my thesis project, I propose to redesign Salt River Train Station into a multi modal transport interchange. I argue that this multimodal interchange can have an urban developmental and regenerative effect that can address some of the challenges faced in our urban landscape. This design report will attempt to document the processes and explorative methods that I have incorporated during this design process.
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Reed, D. J. "Suspended sediment transport in salt marsh creeks." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355891.
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Drake, Arly Marie. "EFFECT OF PLANT GROWTH REGULATORS ON CREEPING BENTGRASS GROWTH AND HEALTH DURING HEAT, SALT, AND COMBINED HEAT AND SALT STRESS." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1546450732510932.
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Legault, Stephane. "Heat transport in quasicrystals." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0021/NQ55355.pdf.
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Legault, Stéphane. "Heat transport in quasicrystals." Thesis, McGill University, 1999. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=36034.
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In this thesis, we performed a detailed study of the thermal conductivity in a wide range of quasicrystals. Three systems were studied: AlPdMn, AlCuFe and AlPdRe, and the samples were in both single and polycrystalline form. A further variable was added by introducing a controlled level of defects.At low temperatures (below 20K), the thermal conductivity is defect limited, being controlled by boundary scattering, two level systems, stacking faults and dislocations. At high temperatures (above 20K), we find the thermal conductivity is limited by intrinsic properties of the quasicrystalline structure and phonon-phonon scattering.
From fitting the thermal conductivity to a detailed model we are able to predict the maximum thermal conductivity of a perfect quasicrystal.
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Allsopp, Adrian J. "The effects of dietary sodium intake on heat acclimation and thermoregulation during heat exposure." Thesis, University of Southampton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241791.
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Clark, Rowan Elizabeth. "Structural studies of salt hydrates for heat-storage applications." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31333.
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Salt hydrates have the potential to be used in heat storage as both phase-change materials (PCMs) and thermochemical materials (TCMs). These materials offer advantages over traditional heat storage methods due to their high energy densities. However, both domestic and industrial applications require thousands of thermal cycles and there are often many issues that need to be overcome before these materials can be used reliably for heat storage. One of the major issues with using salt hydrates as PCMs is incongruency - the formation of anhydrous phases during melting. In this research, the mechanisms of the action of polymers to prevent incongruency in sodium acetate trihydrate have been investigated. A new polymorph of anhydrous sodium acetate, Form IV, was obtained in the presence of the polymer. This polymorph crystallises as long, blade-shaped crystals, thereby increasing the surface area to volume ratio. Indexing of the crystal faces revealed that every face had Na+ or the oxygen atoms of the acetate ion near or on the surface, as opposed to hydrophobic methyl groups found on the faces of the anhydrous salt grown without polymer. These two factors are believed to significantly increase the dissolution kinetics. This technique has the potential to be used for screening polymers to reformulate other salt hydrates that display incongruent behaviour. Eutectic compositions of NaCl and KCl with strontium hydroxide octahydrate were investigated as a potential means to prevent the incongruency of this PCM. However, degradation was observed with thermal cycling. Variable temperature PXRD studies discovered a new Sr(OH)2 hydrate when heating above 75 °C - Sr(OH)2. ⅓H2O. The recrystallisation of the octahydrate from the new phase was slow with incomplete conversion, explaining the degradation with continuous cycling. The effect of addition of NaCl and KCl to congruent barium hydroxide octahydrate was also investigated. On heating, a phase transition was observed, but the samples remained solid. Variable temperature PXRD investigations discovered that this was due to the formation of the salt hydrate, Ba(OH)Cl.2H2O. This hydrate melted at 110 °C, showing its potential as a high temperature PCM. The dehydration pathways of magnesium sulfate heptahydrate were investigated. In-situ PXRD studies showed that changing the heating rate changed the intermediates present during the dehydration. The fast dehydration rate saw both the known phases of trihydrate and 2.5 hydrate form as the dehydration product of the tetrahydrate. These both then dehydrated to the known dihydrate. This differed when the slower heating rate was used, as the trihydrate was the only product of dehydration from the tetrahydrate. The trihydrate then proceeded to dehydrate to a new phase. This was found to be a new polymorph of the dihydrate, β-MgSO4.2H2O. Dehydration of MgSO4.7H2O with 50 mol% NaCl was also performed. Loeweite, Na12Mg7(SO4)13.15H2O, a dication sulfate hydrate, was formed as the major intermediate. This mixture showed advantages over the pure MgSO4.7H2O as dehydration to the monohydrate took less time and occurred at a lower temperature. There were also three fewer intermediate phases before dehydration to the monohydrate. Suspension and encapsulation materials were used in order to overcome the major issue of agglomeration with magnesium sulfate. Liquid water was ruled out as a viable hydration medium. Apparatus was developed to test humidity cycling, which allowed the effects of dehydration time and temperature to be investigated, as well testing a range of different formulations.
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Shukla, Nitin. "Heat Transport across Dissimilar Materials." Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/27820.
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All interfaces offer resistance to heat transport. As the size of a device or structure approaches nanometer lengthscales, the contribution of the interface thermal resistance often becomes comparable to the intrinsic thermal resistance offered by the device or structure itself. In many microelectronic devices, heat has to transfer across a metal-nonmetal interface, and a better understanding about the origins of this interface thermal conductance (inverse of the interface thermal resistance) is critical in improving the performance of these devices. In this dissertation, heat transport across different metal-nonmetal interfaces are investigated with the primary goal of gaining qualitative and quantitative insight into the heat transport mechanisms across such interfaces. A time-domain thermoreflectance (TDTR) system is used to measure the thermal properties at the nanoscale. TDTR is an optical pump-probe technique, and it is capable of measuring thermal conductivity, k, and interface thermal conductance, G, simultaneously.
The first study examines k and G for amorphous and crystalline Zr47Cu31Al13Ni9 metallic alloys that are in contact with poly-crystalline Y2O3. The motivation behind this study is to determine the relative importance of energy coupling mechanisms such as electron-phonon or phonon-phonon coupling across the interface by changing the material structure (from amorphous to crystalline), but not the composition. From the TDTR measurements k=4.5 W m-1 K-1 for the amorphous metallic glass of Zr47Cu31Al13Ni9, and k=5.0 W m-1 K-1 for the crystalline Zr47Cu31Al13Ni9. TDTR also gives G=23 MW m-2 K-1 for the metallic glass/Y2O3 interface and G=26 MW m-2 K-1 for the interface between the crystalline Zr47Cu31Al13Ni9 and Y2O3. The thermal conductivity of the poly-crystalline Y2O3 layer is found to be k=5.0 W m-1 K-1. Despite the small difference between k and G for the two alloys, the results are repeatable and they indicate that the structure of the alloy plays a role in the electron-phonon coupling and interface conductance.
The second experimental study examines the effect of nickel nanoparticle size on the thermal transport in multilayer nanocomposites. These nanocomposites consist of five alternating layers of nickel nanoparticles and yttria stabilized zirconia (YSZ) spacer layers that are grown with pulsed laser deposition. Using TDTR, thermal conductivities of k=1.8, 2.4, 2.3, and 3.0 W m-1 K-1 are found for nanocomposites with nickel nanoparticle diameters of 7, 21, 24, and 38 nm, respectively, and k=2.5 W m-1 K-1 for a single 80 nm thick layer of YSZ. The results indicate that the overall thermal conductivity of these nanocomposites is strongly influenced by the Ni nanoparticle size and the interface thermal conductance between the Ni particles and the YSZ matrix. An effective medium theory is used to estimate the lower limits for the interface thermal conductance between the nickel nanoparticles and the YSZ matrix (G>170 MW m-2 K-1), and the nickel nanoparticle thermal conductivity.Ph. D.
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Hawkins, Kirstie. "Salt tolerance and chloride transport in three beet subspecies." Thesis, University of York, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270062.
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Skosana, Petrus Jabu. "Wall Heat Transfer Coefficient in a Molten Salt Bubble Column." Diss., University of Pretoria, 2014. http://hdl.handle.net/2263/46246.
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The Council for Scientific and Industrial Research (CSIR) is developing a novel process to
produce titanium metal at a lower cost than the current Kroll process used commercially. The
technology initiated by the CSIR will benefit South Africa in achieving the long-term goal of
establishing a competitive titanium metal industry.
A bubble column reactor is one of the suitable reactors that were considered for the
production of titanium metal. This reactor will be operated with a molten salt medium. Bubble
columns are widely used in various fields of process engineering, such as oxidation,
hydrogenation, fermentation, Fischer–Tropsch synthesis and waste water treatment. The
advantages of these reactors over other multiphase reactors are simple construction, good
mass and heat transfer, absence of moving parts and low operating costs.
High heat transfer is important in reactors when high thermal duties are required. An
appropriate measurement of the heat transfer coefficient is of primary importance for
designing reactors that are highly exothermic or endothermic.
An experimental test facility to measure wall heat transfer coefficients was constructed and
operated. The experimental setup was operated with tap water, heat transfer oil 32 and
lithium chloride–potassium chloride (LiCl–KCl) eutectic by bubbling argon gas through the
liquids. The column was operated at a temperature of 40 oC for the water experiments, at 75,
103 and 170 oC for the heat transfer oil experiments, and at 450 oC for the molten salt
experiments. All the experiments were run at superficial gas velocities in the range of 0.006
to 0.05 m/s. Three heating tapes, each connected to a corresponding variable AC voltage
controller, were used to heat the column media. Heat transfer coefficients were determined by inducing a known heat flux through the column
wall and measuring the temperature difference between the wall and the reactor contents. In
order to balance the system, heat was removed by cooling water flowing through a copper
tube on the inside of the column. Temperature differences between the column wall and the
liquid were measured at five axial locations.
A mechanistic model for estimating the kinematic turbulent viscosity and dispersion
coefficient was developed from a mechanism of momentum exchange between large
circulation cells. By analogy between heat and momentum transfer, these circulation cells
also transfer heat from the wall to the liquid.
There were some challenges when operating the bubble column with molten salt due to
leakages on the welds and aggressive corrosion of the column. The experimental results
were obtained when operating the column with water and heat transfer oil. It was found that
the heat transfer coefficient increases with superficial gas velocity. The values of the heat
transfer coefficient for the argon–water system were higher than those for the argon–heat
transfer oil system. The heat transfer coefficients were also found to increase with an
increase in temperature. Gas holdup increased with the superficial gas velocity. It was found
that the estimated axial dispersion coefficients are within the range of those reported in the
literature and the ratios of dispersion coefficients are in agreement with those in the
literature. The estimated kinematic turbulent viscosities were comparable with those in the
literature.Dissertation (MEng)--University of Pretoria, 2014.
tm2015
Chemical Engineering
MEng
Unrestricted
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Raud, Ralf. "Optimized salt selection for solar thermal latent heat energy storage." Thesis, Queensland University of Technology, 2018. https://eprints.qut.edu.au/116429/1/Ralf_Raud_Thesis.pdf.
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This thesis contributes to the state of the art of Concentrating Solar Thermal by rigorously examining the selection process for the thermal storage medium. An optimized process is developed and then applied to the local constraints to optimize the technoeconomic performance of the storage media for the ongoing Australian Solar Thermal Research Initiative.
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Beardo, Ricol Albert. "Generalized Hydrodynamic Heat Transport in Semiconductors." Doctoral thesis, Universitat Autònoma de Barcelona, 2021. http://hdl.handle.net/10803/673590.
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La tesis presenta una descripció unificadora d'una varietat d'experiments de transport tèrmic a la micro i nano escala en semiconductors com el silici o el germani. S'utilitza un model de transport de calor hidrodinàmic per predir la resposta no difusiva de sistemes complexes en situacions de rellevància tecnològica, com el procés de refredament d'un component electrònic alliberant calor cap a un substrat semiconductor. El model no utilitza paràmetres d'ajust en funció de la geometria, sinó que utilitza paràmetres calculats des de primers principis. Els efectes de mida petita o alta freqüència es capturen a través de condicions de contorn específiques i, per tant, el model és una eina útil pel disseny de dispositiu micro electrònics. Degut a que la descripció hidrodinàmics pel silici no és el mètode convencional, en aquesta tesis es posa especial èmfasis en determinar l'aplicabilitat del model en múltiples experiments de manera unificadora. Com a resultat, s'identifiquen fenòmens no difusius com la propagació del segon so en camps tèrmics fluctuants en germani o múltiples temps de relaxació en l'evolució tèrmica d'escalfadors nano estructurats en silici. A més, la descripció hidrodinàmica es compara amb altres models moderns per descriure els mateixos experiments, i es proporciona un resum de les eines teòriques necessàries (la termodinàmica de no equilibri i la teoria cinètica). Utilitzant les evidències experimentals que s'aporten, es conclou que el model hidrodinàmic té capacitat predictiva de la resposta tèrmica de materials com el silici a la nano escala dins d'un cert rang d'aplicabilitat.Ésta tesis presenta una descripción unificadora de una variedad de experimentos de transporte térmico a la micro y nano escala en semiconductores como el silicio o el germanio. Se utilitza un modelo de transporte de calor hidrodinámico para predecir la respuesta no difusiva de sistemas complejos en situacions de relevancia tecnológica, como el proceso de enfriamento de un componente electrónico liberando calor hacia un sustrato semiconductor. El modelo no utilitza parámetros de ajuste en función de la geometría, sinó que utiliza parámetros calculados des de primeros principios. Los efectos de tamaño reducido o alta frecuencia se capturan a través de condiciones de contorno específicas y, por tanto, el modelo es una herramienta útil para el diseño de dispositivos micro electrónicos. Dado que la descripción hidrodinámica para el silicio no es el método convencional, en ésta tesis se presta especial atención a determinar la aplicabilidad del modelo en múltiples experimentos de forma unificadora. Como resultado, se identifican fenómenos no difusivos como la propagación de segundo sonido en campos térmicos fluctuantes en germanio, o múltiples tiempos de relajación en la evolución térmica de calentadores nano estructurados en silicio. Además, la descripción hidrodinámica se compara con otros modelos modernos para describir los mismos experimentos, y se proporciona un resumen de las herramientas teóricas necesarias (la termodinámica de no equilibrio y la teoria cinética). Utilizando las evidencias experimentales que se aportan, se concluye que el modelo hidrodinámico tiene capacidad predictiva de la respuesta térmica de materiales como el silicio a la nano escala dentro de un cierto rango de aplicabilidad.
This thesis presents a unifying description of a variety of experiments on micro- and nano-scale heat transport in semiconductors like silicon or germanium. A hydrodynamic-like heat transport model is used to predict the non-diffusive thermal response of complex systems in technologically relevant situations, like the process of energy release from nanostructured heat sources towards a semiconductor substrate. The model does not use geometry-dependent or fitted parameters, but use intrinsic material properties that can be calculated from first principles. Small-size and high-frequency effects are captured through the use of specific boundary conditions, thus resulting in a practical tool for complex microelectronic device design. Since hydrodynamic modeling is not the state-of-the-art approach to describe standard semiconductors like silicon, special care is devoted to quantitatively determine the applicability of the model, and multiple experiments using different techniques are considered and studied in a unifying way. As a result, previously unreported non-Fourier phenomena in materials like silicon or germanium is identified and demonstrated (e.g. second sound in rapidly varying thermal fields or multiple decay times characterizing the evolution of nano-structured heaters). Furthermore, the hydrodynamic description is compared with alternative modern frameworks describing size and frequency effects in semiconductor heat transport, and a summarized overview of the theoretical background, namely non-equilibrium thermodynamics and kinetic theory, is presented. In light of the extensive experimental evidence provided, this thesis demonstrate the predictive capability of hydrodynamic-like thermal transport modeling in semiconductors within a certain range of applicability that is well beyond the diffusive regime.
Universitat Autònoma de Barcelona. Programa de Doctorat en Física
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Niemi, Daniel, and Joel Hambraeus. "Heat Transport in Inhomogeneous Harmonic Chains." Thesis, KTH, Skolan för teknikvetenskap (SCI), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-275699.
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It is still to this day a challenge for theoretical physicists to derive Fourier’s law from microscopic models. Motivated by this, we study in this thesis the thermal conduction properties of harmonic chains. A semi-analytical method and simulation are used to find that on average the conduction through harmonic chains resembles Fourier like conduction when impurities of the form k_i=kw_i and 1/m_i=1/m*w_i are introduced, where k_i and m_i are the spring constants and masses of the chain and w_i are weights drawn from a random distribution. A few of these distributions are studied in detail, with similar results.Also the classical field theory limit of this model is studied. It is shown by analytical means that heat is transported diffusively in this model when impurities are introduced, whereas the transport is completely ballistic in the absence of impurities.
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Visarraga, Darrin Bernardo. "Heat transport models with distributed microstructure." Access restricted to users with UT Austin EID, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3036605.
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Sharma, Mukta. "Parallel Heat Transport in Magnetized Plasma." DigitalCommons@USU, 2013. https://digitalcommons.usu.edu/etd/1470.
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A code that solves the coupled electron drift kinetic and temperature equations has been written to study the effects of collisionality and particle trapping on temperature equilibration along magnetic field lines. A Chapman-Enskog-like approach is adopted with the time-dependent distribution function written as the sum of a dynamic Maxwellian and a kinetic distortion expanded in Legendre polynomials. The drift kinetic equation is solved on a discrete grid in normalized speed, and an FFT algorithm is used to treat the onedimensional spatial domain along the magnetic field. The dependence of the steady-state temperature on collisionality and magnetic well depths is discussed in detail. As collisionality decreases (increasing background temperature), temperature variations decrease. As magnetic well depth increases (at fixed collisionality), temperature variations along the field line increase.
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Lippy, Matthew Stephen. "Development of a Minichannel Compact Primary Heat Exchanger for a Molten Salt Reactor." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/32603.
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The first Molten Salt Reactor (MSR) was designed and tested at Oak Ridge National Laboratory (ORNL) in the 1960â s, but recent technological advancements now allow for new components, such as heat exchangers, to be created for the next generation of MSRâ s and molten salt-cooled reactors. The primary (fuel salt-to-secondary salt) heat exchanger (PHX) design is shown here to make dramatic improvements over traditional shell-and-tube heat exchangers when changed to a compact heat exchanger design. While this paper focuses on the application of compact heat exchangers on a Molten Salt Reactor, many of the analyses and results are similarly applicable to other fluid-to-fluid heat xchangers.
The heat exchanger design in this study seeks to find a middle-ground between shell- and-tube designs and new ultra-efficient, ultra-compact designs. Complex channel geometries and microscale dimensions in modern compact heat exchangers do not allow routine maintenance to be performed by standard procedures, so extended surfaces will be omitted and hydraulic diameters will be kept in the minichannel regime (minimum channel dimension between 200 μm and 3 mm) to allow for high-frequency eddy current inspection methods to be developed. High aspect ratio rectangular channel cross-sections are used. Various plant layouts of smaller heat exchanger banks in a â modularâ design are introduced.
FLUENT was used within ANSYS Workbench to find optimized heat transfer and hydrodynamic performance. With similar boundary conditions to ORNLâ s Molten Salt Breeder Reactorâ s shell-and-tube design, the compact heat exchanger interest in this thesis will lessen volume requirements, lower fuel salt volume, and decrease material usage.Master of Science
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Saleh, Livia [Verfasser]. "Chloride transport and salt tolerance mechanisms in plants / Livia Saleh." Kiel : Universitätsbibliothek Kiel, 2011. http://d-nb.info/1036243052/34.
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Konukcu, Fatih. "Upward transport of water and salt from shallow saline watertables." Thesis, University of Newcastle Upon Tyne, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360265.
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Bowen, Melissa Marie. "Mechanisms and variability of salt transport in partially-stratified estuaries." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1912/2130.
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Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), February 2000."February 2000."
Includes bibliographical references (leaves 163-171).
The variability of salt transport determines the variation of the length of the salinity intrusion and the large-scale density gradient in an estuary. This thesis contains three studies that address salt transport and the salt balance. The variation of salt transport with the depth, the along-channel salinity gradient, and the amplitude of the tidal velocity is investigated with analytic and numerical models. The results indicate that salt transport increases dramatically during stratified periods when vertical mixing is weak. Analysis of salt transport from observations in the Hudson Estuary show that stratified periods with elevated estuarine salt transport occur in five-day intervals once a month during apogean neap tides. Oscillatory salt transport, which is hypothesized to be primarily caused by lateral exchange and mixing of salt, appears to play a more minor role in the salt balance of the estuary. The salt balance of the estuary adjusts very little to the spring-neap modulation of salt transport but adjusts rapidly to pulses of freshwater flow. A simple model is used to investigate the process and time scales of adjustment of the salt balance by connecting variations of salt transport to the variations of freshwater flow and vertical mixing. The results show the length of the salinity intrusion adjust via advection to rapid and large increases in freshwater flow. The salinity intrusion adjusts more rapidly to the spring-neap cycle of tidal mixing the higher the freshwater flow.
by Melissa Marie Bowen.
Ph.D.
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Splith, Tobias, Christian Chmelik, Frank Stallmach, Stefan K. Henninger, Gerrit Füldner, Panagiotis D. Kolokathis, Evangelia Pantatosaki, and George K. Papadopoulos. "Adsorptive heat transformation with SAPO-34." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-198701.
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Fan, Jing, and 范菁. "Heat transport in nanofluids and biological tissues." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B47752853.
Full textAbstract:
The present work contains two parts: nanofluids and bioheat transport, both involving
multiscales and sharing some common features. The former centers on addressing the
three key issues of nanofluids research: (i) what is the macroscale manifestation of
microscale physics, (ii) how to optimize microscale physics for the optimal system
performance, and (iii) how to effectively manipulate at microscale. The latter
develops an analytical theory of bioheat transport that includes: (i) identification and
contrast of the two approaches for developing macroscale bioheat models: the
mixture-theory (scaling-down) and porous-media (scaling-up) approaches, (ii)
rigorous development of first-principle bioheat model with the porous-media
approach, (iii) solution-structure theorems of dual-phase-lagging (DPL) bioheat
equations, (iv) practical case studies of bioheat transport in skin tissues and during
magnetic hyperthermia, and (v) rich effects of interfacial convective heat transfer,
blood velocity, blood perfusion and metabolic reaction on blood and tissue macroscale
temperature fields.
Nanofluids, fluid suspensions of nanostructures, find applications in various
fields due to their unique thermal, electronic, magnetic, wetting and optical properties
that can be obtained via engineering nanostructures. The present numerical simulation
of structure-property correlation for fourteen types of two/three-dimensional
nanofluids signifies the importance of nanostructure’s morphology in determining
nanofluids’ thermal conductivity. The success of developing high-conductive
nanofluids thus depends very much on our understanding and manipulation of the
morphology. Nanofluids with conductivity of upper Hashin-Shtrikman bounds can be
obtained by manipulating structures into an interconnected configuration that
disperses the base fluid and thus significantly enhancing the particle-fluid interfacial
energy transport. The numerical simulation also identifies the particle’s radius of
gyration and non-dimensional particle-fluid interfacial area as two characteristic
parameters for the effect of particles’ geometrical structures on the effective thermal
conductivity. Predictive models are developed as well for the thermal conductivity of
typical nanofluids.
A constructal approach is developed to find the constructal microscopic physics
of nanofluids for the optimal system performance. The approach is applied to design
nanofluids with any branching level of tree-shaped microstructures for cooling a
circular disc with uniform heat generation and central heat sink. The constructal
configuration and system thermal resistance have some elegant universal features for
both cases of specified aspect ratio of the periphery sectors and given the total number
of slabs in the periphery sectors.
The numerical simulation on the bubble formation in T-junction microchannels
shows: (i) the mixing enhancement inside liquid slugs between microfluidic bubbles,
(ii) the preference of T-junctions with small channel width ratio for either producing
smaller microfluidic bubbles at a faster speed or enhancing mixing within the liquid
phase, and (iii) the existence of a critical value of nondimensional gas pressure for
bubble generation. Such a precise understanding of two-phase flow in microchannels
is necessary and useful for delivering the promise of microfluidic technology in
producing high-quality and microstructure-controllable nanofluids.
Both blood and tissue macroscale temperatures satisfy the DPL bioheat equation
with an elegant solution structure. Effectiveness and features of the developed
solution structure theorems are demonstrated via examining bioheat transport in skin
tissues and during magnetic hyperthermia.published_or_final_version
Mechanical Engineering
Doctoral
Doctor of Philosophy
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Jayne, Steven Robert. "Dynamics of global ocean heat transport variability." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/69203.
Full textAbstract:
Thesis (Sc. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and Woods Hole Oceanographic Institution), 1999.Includes bibliographical references (p. 161-169).
A state-of-the-art, high-resolution ocean general circulation model is used to estimate the time-dependent global ocean heat transport and investigate its dynamics. The north-south heat transport is the prime manifestation of the ocean's role in global climate, but understanding of its variability has been fragmentary owing to uncertainties in observational analyses, limitations in models, and the lack of a convincing mechanism. These issues are addressed in this thesis. Technical problems associated with the forcing and sampling of the model, and the impact of high-frequency motions are discussed. Numerical schemes are suggested to remove the inertial energy to prevent aliasing when the model fields are stored for later analysis. Globally, the cross-equatorial, seasonal heat transport fluctuations are close to +4.5 x 1015 watts, the same amplitude as the seasonal, cross-equatorial atmospheric energy transport. The variability is concentrated within 200 of the equator and dominated by the annual cycle. The majority of it is due to wind-induced current fluctuations in which the time-varying wind drives Ekman layer mass transports that are compensated by depth-independent return flows. The temperature difference between the mass transports gives rise to the time-dependent heat transport. The rectified eddy heat transport is calculated from the model. It is weak in the central gyres, and strong in the western boundary currents, the Antarctic Circumpolar Current, and the equatorial region. It is largely confined to the upper 1000 meters of the ocean. The rotational component of the eddy heat transport is strong in the oceanic jets, while the divergent component is strongest in the equatorial region and Antarctic Circumpolar Current. The method of estimating the eddy heat transport from an eddy diffusivity derived from mixing length arguments and altimetry data, and the climatological temperature field, is tested and shown not to reproduce the model's directly evaluated eddy heat transport. Possible reasons for the discrepancy are explored.
by Steven Robert Jayne.
Sc.D.
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Witharana, S. "Thermal transport in nanofluids : boiling heat transfer." Thesis, University of Leeds, 2011. http://etheses.whiterose.ac.uk/1648/.
Full textAbstract:
This thesis is constructed around the topic of thermal transport in nanofluids, with special emphasis of boiling heat transfer. Nanofluids boiling, as it is popularly known, have been researched nearly for two decades. While some controversies surrounding the boiling mechanisms had been sorted out, others still remained. The aim of this thesis is to address the remaining concerns. For the best treatment of the research problem, the experimental work was divided into three segments. Time-resolved small angle x-ray scattering studies of nanofluids were focused to examine the nanoparticle aggregation in liquid media. These were conducted at two national synchrotron facilities located at Daresbury Laboratory and Diamond Light source in Oxford, UK. In-situ experiments were conducted with static and convective nanofluidic samples. Types of nanofluids and the experimental conditions were chosen to cover a broad range of practical applications. Water based nanofluids of spherical particles of aluminium oxide (Al2O3) and titanium dioxide (TiO2) and acicular particles of aluminium oxide (Al2O3) were exposed to 1Ă wavelength x-ray beam for varying duration of times at a frame rate of 10miliseconds. Data analysis was conducted using the Dream and SAXS Utilities software. Signs of change in particle size were discovered with the near-IEP nanofluids. For further clarification of these SAXS observations, microscopic and photography studies were conducted in the laboratory. SEM studies were supported by optical microscopy. It helped to estimate the aggregate sizes and porosity within aggregates. The settling rates were determined by still photography, which were subsequently compared with the prediction of Stoke’s settling theory. At the end of data and image analysis, it was discovered that the x-ray beam had successfully predicted the settling rates of nanoparticle aggregates. Although SAXS has long been used to analyse particulate systems, for the best of the knowledge of this author, this is the first time its capability as a tool to estimate particle settling rates in nanofluids has been showcased. Furthermore, by fine tuning the present methodology, it seems possible to determine the nanoparticle aggregation rates in a nanofluid. Saturated pool boiling of nanofluids was experimentally investigated under the atmospheric pressure. A boiling test rig was designed and constructed for this purpose in the Leeds University. Water based and water-ethylene glycol (WEG) based nanofluids were examined for boiling heat transfer on flat copper substrates. The substrates were resistively heated from the bottom, providing surface heat fluxes up to 189kW/m2. Boiling heat transfer coefficients were calculated using the measured temperature differences between substrate and the boiling liquid at each surface heat flux. All nanofluids in general displayed deterioration in boiling heat transfer. Moreover all substrates were found fouled with nanoparticles after boiling. SEM observation on fouled substrates revealed the presence of structures consisting of sub-micron size cavities and pores, which are possibly interconnected by sub-surface network of channels. By measuring their surface roughness, it was further understood that the degree of change of roughness due to boiling depended upon its initial roughness, the particle concentration in the nanofluid, as well as the shape of nanoparticles. This study also points to an interval of roughnesses that gives optimum boiling heat transfer performance. Further experiments are recommended to focus on this aspect. Also to avoid in future is the bubble nucleation in the periphery of the copper substrates that became a major obstacle to visualise bubbles in the middle. The need to explore the bubble nucleation phenomena on at sub-micron size cavities was inspired by the presence of such cavities on nanofouled substrates. Moreover in literature sometimes the inconsistencies on the degree of enhancement or deterioration were attributed to hitherto-unknown boiling phenomena at these length scales. Two key challenges were to create very small cavities on a smooth substrate and to conduct phenomenally clean boiling experiments on them. In principle there should not be a foreign particle inside the boiler which is larger than the cavity mouth. The biggest challenge however was to find a technique to measure the temperature of the liquid layer on top of the cavities. The infrared thermometry facility at the Nuclear Science and Engineering Department of the Massachusetts Institute of Technology (MIT) was used as a part of research collaboration. Tiny cavities were machined on ultra smooth silicon substrate using the focus ion beam (FIB) technology at the University of Leeds and at Harvard Centre for Nanoscale Systems. The mouth diameters of conical cavities were ranging from 0.6µm to 4.5µm. A boiling test rig was simultaneously developed at MIT. Heating to the liquid was provided by a halogen spot heater. The cleanliness of the test rig was successfully proved by reaching the heterogeneous nucleation superheat of liquid methanol on a silicon wafer. Water and a water based dilute SiO2 nanofluid were boiled in this novel test rig. Temperature profiles of bubble evolution were captured using the IR thermometry. Also the superheated liquid layer temperatures were measured. It was found that the measured values were in good agreement with Young-Laplace theory. Moreover the SiO2 0.01wt%-water nanofluid in most cases demonstrated boiling heat transfer enhancement up to 40% above water. With this work, for the first time the classical Young-Laplace theory was proved for sub-micron cavities. It further removed the suspicion that there might be a different phenomenon governing the bubble nucleation on nanofouled substrates.
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Ronetti, Flavio. "Charge and heat transport in topological systems." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0541/document.
Full textAbstract:
Dans cette thèse, j'adresse le sujet fascinant et attirant du transport de charge électrique et de chaleur dans les systèmes Hall quantiques, qui sont parmi l'exemple le plus célèbre des phases topologiques de la matière, en présence de potentiels électriques dépendantes du temps. L'effet Hall se produit dans des systèmes électroniques bidimensionnels dans la limite de forts champs magnétiques perpendiculaires. Le cachet de systèmes de Hall quantiques est l'apparition d'états de bord métalliques unidimensionnels sur les frontières du système.La longueur de cohérence assurée par la protection topologique garantit d’avoir accès à la nature ondulatoire des électrons. Ces propriétés ont inspiré un nouveau domaine de la recherche, connu comme la l'optique quantique électronique. Une source d’électrons individuels peut être réalisée en s'appliquant à un système de Hall quantique impulsions Lorentzian. En considérant l'application d'un train périodique d'impulsions Lorentzian à un système Hall quantique, j'examine la densité de charge d'un état composé par beaucoup de levitons dans le régime de Hall quantique fractionnaire, constatant ainsi qu'il est réarrangé dans une configuration réguliere de sommets et des vallées. Alors, j'analyse les propriétés de transport de chaleur des levitons dans les systèmes Hall quantiques, qui représente un nouveau point de vue sur l'optique quantique électronique, étendant et généralisant les résultats obtenus dans le transport de chargeIn this thesis, I address the intriguing and appealing topic of charge and heat transport in quantum Hall systems, which are among the most famous example of topological phases of matter, in presence of external time-dependent voltages. Quantum Hall effect occurs in two-dimensional electron systems in the limit of strong perpendicular magnetic fields. The hallmark of quantum Hall systems is the emergence of one-dimensional metallic edge states on the boundary. Along these edge states particles propagate with a definite direction. The coherence length ensured by topological protection guarantees to access wave-like nature of electrons. This properties inspired a new field of research, known as electron quantum optic. Single-electron source can be realized by applying to a quantum Hall system a periodic train of Lorentzian-shaped pulses.Plateaus of the Hall resistance appear also at fractional values of the resistance quantum. The physical explanation of fractional quantum Hall effect cannot neglect the correlation between electrons and this phase of matter is inherently strongly-correlated. By considering the application of a periodic train of Lorentzian pulses to a quantum Hall system, I investigate the charge density of a state composed by many levitons in the fractional quantum Hall regime, thus finding that it is re-arranged into a regular pattern of peaks and valleys, reminiscent of Wigner crystallization in strongly-interacting electronic systems. Then, I analyze heat transport properties of levitons in quantum Hall systems, which represent a new point of view on electron quantum optics, extending and generalizing the results obtained in the charge domain
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RONETTI, FLAVIO. "Charge and heat transport in topological systems." Doctoral thesis, Università degli studi di Genova, 2018. http://hdl.handle.net/11567/933059.
Full textAbstract:
In this thesis, I address the intriguing and appealing topic of charge and heat transport in quantum Hall systems, which are among the most famous example of topological phases of matter, in presence of external time-dependent voltages. The interest of condensed matter community towards topological systems has been considerably raised in recent years. For instance, it is worth to recall the Nobel prize for physics 2016 awarded to Professors Thouless, Kosterlitz and Haldane for their contribution to the study of topological states of matter.
These states are exotic phases of matter, whose properties are described in terms of quantities that do not depend on the details of a system, are very robust against defects and perturbations. The research field of topological systems takes place due to the interplay between condensed matter physics and mathematics. As a matter of fact, many concepts have been borrowed from the mathematical branch of topology in order to classify these novel states of matter.
Quantum Hall effect was discovered almost forty years ago and still attracts a lot of attention from the theoretical and experimental point of view. This remarkable physical phenomenon occurs in two-dimensional electron systems in the limit of strong perpendicular magnetic fields. In quantum Hall systems, the transverse resistance, which is commonly defined Hall resistance, is very precisely quantized in terms of the resistance quantum. When this quantization occurs for integer values, this phenomenology is termed integer quantum Hall effect. It can be understood in a satysfying way by resorting to a non-interacting quantum mechanical description. The hallmark of quantum Hall systems is the emergence of one-dimensional metallic edge states on the boundaries of the system. Along these edge states particles propagate with a definite direction. As a result, they are topologically protected against backscattering.
The coherence length ensured by topological protection guarantees to access the wave-like nature of electrons. Intriguingly, this investigation can be pushed to its fundamental limit by exploring quantum transport at the single-electron level. This idea embodies the core of a new field of research, known as electron quantum optics Single-electron source can be realized by applying to a quantum Hall system a periodic train of Lorentzian-shaped pulses, carrying an integer number of particles per period, thus emitting into the edge states minimal single-electron excitations, then termed levitons.
Plateaus of the Hall resistance appear also at fractional values of the resistance quantum. Contrarily to the integer case, the physical explanation of fractional quantum Hall effect cannot neglect the correlation between electrons and this phase of matter is inherently strongly-correlated. Intriguingly, elementary excitations of fractional quantum Hall systems are quasi-particle with fractional charge and statistics. Remarkably, one-dimensional conducting edge states arise also in the fractional quantum Hall effect and their excitations inherit the charge and statistical properties of the one in the bulk.
By considering the application of a periodic train of Lorentzian pulses to a quantum Hall system, I focus on the transport properties of levitons propagating along integer and fractional edge states. I investigate the charge density of a state composed by many levitons in the fractional quantum Hall regime, thus finding that it is re-arranged into a regular pattern of peaks and valleys, reminiscent of Wigner crystallization in strongly-interacting electronic systems. Then, I analyze heat transport properties of levitons in quantum Hall systems, which represent a new point of view on electron quantum optics, extending and generalizing the results obtained in the charge domain.
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DiGuilio, Ralph Michael. "The thermal conductivity of molten salts and concentrated aqueous salt solutions." Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/11847.
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Goff, Kenneth Michael. "The transport of cadmium through molten salts." Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/13409.
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Elphick, Carmen Heather. "Na'+ transport and Ca'2'+ signalling in higher plant salt tolerance." Thesis, University of York, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341845.
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Tedder, Newton William. "Dissolved Road Salt Transport in Urban and Rural Watersheds in Massachusetts." Thesis, Boston College, 2009. http://hdl.handle.net/2345/984.
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Thesis advisor: Rudolph HonThesis advisor: Yvette Kuiper
Chloride-based deicers (NaCl, CaCl2, MgCl2), also referred to as road salt, are the most common substances used in maintaining safe roadway surfaces during the winter months. Upon application, road salt reacts with the accumulated snow or ice to form brine equilibrium solutions along the liquidus line in the salt-water system. Dissolved salts dissociate, leading to increased concentrations of the respective ions in nearby soils, surface water, and groundwater. Of the ions present in road salt, chloride has the advantage of tracking all chloride deicers at the same time and since chloride ions are conservative tracers in soils it stays unaffected by ionic exchange interferences. This study explores the mechanisms of chloride return flows by investigating chloride dissolved loads, chloride concentrations in stream waters, seasonal patterns, and changes over the course of four years in two separate watersheds in Massachusetts with differing degrees of urbanization. The chloride tracking technique used in this study is based on calibrated chloride concentrations obtained from specific conductance signals recorded every 15 minutes by automatic recording systems at two locations, one in rural central Massachusetts and the other in urban eastern Massachusetts. These systems are maintained by the USGS, which also provide the simultaneously recorded stream flow datasets. The dissolved chloride load carried by each river is calculated for each single 15-minute interval by multiplying water volume with the corresponding chloride concentration, resulting in a total of over 34,000 data points per annum per site. Hydrograph separation techniques were used to separate dissolved load transported by each river into two separate flow components, event flow resulting from precipitation events, and baseflow resulting from groundwater discharge. Well defined hydrograph baseflow supported periods yield consistent chloride concentrations independent of the season at either urban or rural study sites. Comparison of direct runoff dissolved chloride loads with the total annual dissolved loads suggests that only a small fraction of the deicers actually removed during the overland runoff events and that a minimum of 60% of the total load discharged each year in both urban and rural systems is transported by groundwater. From groundwater recharge by brines rural watersheds are currently retaining as much as 95% of the total chloride applied to roadways each year while urban and suburban watersheds may only retain 75% of the total chloride applied to roadways each year. The increased retention of chloride in rural areas is likely due to the decreased amount of chloride transported during winter seasons as event flow compared to urban watersheds
Thesis (MS) — Boston College, 2009
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Geology and Geophysics
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Persson, Kajsa. "High temperature corrosion on heat exchanger material exposed to alkali salt deposits." Thesis, Umeå universitet, Institutionen för tillämpad fysik och elektronik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-104121.
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Power generation through decentralized small scale CHP would facilitate the use of biomass as an energy source, with the externally fired gas turbine (EFGT) being a promising technology due to its high electrical efficiency. In an EFGT hot flue gases are heat-exchanged with an air cycle, driving the turbine. The operation requires higher flue gas temperatures than other technologies, for example steam turbines, to achieve optimal performance. The operating conditions subjects the high temperature heat exchanger (HT-HE) to both physical and chemical stress, with the corrosion related issues yet to be solved. Problems concerning deposit formation and corrosion, on for example super heaters and heat exchangers, when firing biomass are important issues even in commercially available technologies, where the choice of fuel and fuel additives together with component design and choice of material plays important roles in order to minimize the problems. The significantly higher temperatures of the heat transferring surfaces for an EFGT entails combustion deposit related problems less studied. The evaluation of turbine control, deposit formation and corrosion as well as design of the HT-HE and system integration will enable the development of the EFGT technology for applications with small- and medium-size biomass combustion. In this work four potential HT-HE alloys of various grades have been evaluated with respect to corrosion resistance, when exposed to alkali salts and salt mixtures in the KCl-K2CO3-K2SO4 system. The exposures were done in a tube furnace during 24 h for each experiment at four temperature levels between 700–1000oC. Morphological and elemental analysis of the alloy surface and corrosion layers was performed with SEM-EDS. The presence of KCl in the salt caused the most severe corrosion attacks while the corrosion attacks of the pure sulfate and carbonate were more modest. Significant differences between the four materials were observed. X20 experienced severe corrosion, with corrosion scale formation in most cases. The KCl-containing salts caused 253MA to form corrosion scales at all temperatures, while the corrosion resistance to other salts was fairly good. Inconel 600 had the second best overall corrosion resistance. However, it should be pointed out that in some cases the alloy was surpassed by 253MA. Kanthal showed the best overall performance, with limited corrosion scale formation and surprisingly high corrosion resistance to the KCl-containing ternary salt mixture at 900°C and 1000°C.
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Al-Saleh, N. "A salt gradient solar pond for heat collection and long term storage." Thesis, University of Sussex, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375133.
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A salt gradient solar pond offers an economical means of both collecting summer solar heat, and storing it in water over periods of a few months for use in winter space heating. The vertical gradient of salt density prevents convection in the pond and makes it self-insulating against heat losses. The solar pond project at the university of Sussex aimed to study the design, construction, filling, and operation of a salt gradient solar pond, and to develop inexpensive instrumentation for the harsh environment of hot salt water solution, for monitoring behaviour and performance. A new method of heat extraction, from both the insulation and storage layers of the pond, was tested, and a computer program was developed to model pond behaviour under non-steady techniques. Construction, filling, and operation of indoor and state conditions, using finite difference outdoor pilot solar ponds is described and a simple means of maintaining salt density gradient, as well as work on achieving good pond transparency over the two-year period of operation of the pond. To improve the efficiency of the pond successful experiments were carried out to extract heat from both the convecting storage layer and the non-convecting insulation layer of the pond. This permits interception and extraction of heat flow in the non-convecting layer which would otherwise be lost to the surface. Laboratory and outdoor exper iments were car ried out to test whether this causes unwanted convective mixing and increased upward diffusion of salt in the non-convective zone of the pond. Heat transfer coefficients were measured with the heat exchanger placed in the non-convecting insulation layer. Both steady-state and finite difference model calculations are presented to indicate the improvements in operating efficiency and temperatures that are achievable with the new method of heat extraction. Theoretical results from the finite difference model are in good agreement with observed performance.
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Alm, David Michael. "Comparison and interaction of heat and salt stress in cultured tobacco cells." Virtual Press, 1986. http://liblink.bsu.edu/uhtbin/catkey/445616.
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Cultured tobacco cells (Nicotiana tabacum L., cv Wisconsin-38) were subjected to temporary sub-lethal heat and salt shock treatments to determine the effects of these treatments on various physiological parameters after subsequent lethal heat or salt stresses. Tobacco cells developed a tolerance to a non-permissive temperature stress (54C for 14 min) when pretreated with heat shock of 38C for 2h but not when pretreated at 42C for 2h. Cells pretreated at 38 (2h) exhibited less than 30% normal growth when the 54C stress came immediately after the 38C treatment. Tolerance to the 54C stress developed with increased interval between shock and stress with cells exhibiting 95% normal regrowth when the 54C stress was administered 8h after the 38C shock. The developement of heat tolerance was inhibited if heat shock was done in the presence of a non-injuring level of EGTA (.0.5mM). Cells treated with EGTA during heat shock grew normally at 23C but not after a 54C heat stress. EDTA (0.5mM) had little effect on the acquisition of tolerance to heat stress.Wisconsin-38 cells developed a tolerance to a non-permissive salt stress (2% NaCl for 16h) when pretreated at a lower salt level (1.2% NaCl) for 3h. Cells heat shocked at 38C exhibited increased tolerance of the lethal salt stress up to 8h. Conversely, cells heat shocked at 42C exhibited immediate tolerance to lethal salt stress and this tolerance decayed over eight hours. The heat shock-induced acquisition of salt tolerance was inhibited by both EGTA and EDTA.Proteins synthesized during heat and salt stress treatments were labeled with [35S]-methionine and/or [3H]-leucine and separated using Sodium dodecylsulfate polyacrylamide gel electrophoresis. Fluorographic analysis of the gels indicate that a number of proteins are produced in response to heat shock. Similar analysis of proteins from salt shocked cells indicates that no salt shock proteins are produced in response to a brief low-level sodium chloride shock.
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French, Jonathan Rupert. "Hydrodynamics and sedimentation in a macro-tidal salt marsh, Norfolk, England." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235907.
Full textAbstract:
This thesis integrates existing work on surface accretion rates with more recent advances in the understanding of creek hydrodynamics. Concepts drawn from various disciplines are formulated into a revised framework within which marsh sedimentation may be better understood. Channel flux studies that treat the marsh as a 'black box' contribute little to our understanding of marsh functioning, whatever the accuracy of their execution. Marshes are better conceptualised as complex bio-sedimentary systems, characterised not only by an intimate relationship with adjacent tidal waters, but also by numerous internal pathways along which transport of water and materials may take place. Data relating to surface sediments, surface sedimentation, channel and over-marsh hydrodynamics, and suspended sediment composition and settling behaviour have been obtained within a relatively mature back-barrier marsh, 54 ha in area, at Scolt Head Island, on the north Norfolk coast. Tidal range averages 3.2m at neaps and 6.4m at springs. The annual sediment input to the marsh surface is estimated at 675 tonnes, equivalent to a mean accretion rate of approximately 0.26 cm/year. The broad pattern in sedimentation reflects surface topography via its control over inundation frequency. Locally, however, proximity to the creek system as an intermediate sediment source determines the rate and nature of sedimentation. The formation of composite particles via the action of flocculation and organic binding agents determines the depositional behaviour of fine cohesive sediment introduced to the marsh. Particle fall velocities are thereby enhanced, with settling from over-marsh tidal flows being a continuous process and not confined to slack water. Reworking of newly deposited material by deposit feeding gastropods appears to be intense over much of the marsh, and may be an explanation for the paucity of sedimentary structures. The marsh surface acts as a topographic threshold separating markedly different spring and neap creek flow regimes. Morphological development of the creeks is effectively confined to ebb-dominated spring tides, when export of sand occurs. Though the creeks act as effective conduits for material transport, a large proportion of the total spring tidal prism may be exchanged directly over the marsh edge. These results may be viewed in the context of present concern over rising sea levels linked to human-induced global warming. Scenarios for future sea-level change vary widely, though most estimates put the present rate of eustatic rise at approximately 1-2 mm/year. Subsidence along this coast is around 1mm/year. Thus many marshes exist in delicate equilibrium with present relative sea level. A numerical model incorporating quasi-continuous deposition, annual tide data, and eustatic and crustal movements successfully simulates historic marsh sedimentation along the north Norfolk coast and provides an insight into the possible effects of future eustatic changes.
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Hlubek, Nikolai. "Magnetic heat transport in one-dimensional quantum antiferromagnets." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-70187.
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Fundamental conservation laws predict a dissipationless transport behavior in one-dimensional S=1/2 spin chains. This truly ballistic heat transport suggests anomalously large life times and mean free paths of the elementary excitations of the spin chain, spinons. Despite this rigorous prediction, in any real system, the transport is dissipative, due to the interaction of spinons with defects and phonons. Nevertheless, a promising large magnetic thermal conductivity \\kappa_{mag} has been observed in a few copper-oxide systems. Characteristic for these cuprate systems is a large exchange interaction J along the spin chain. However, due to the limited number and knowledge of the systems showing a large \\kappa_{mag}, it has been difficult, to identify overarching trends. The goal of this thesis therefore is twofold. First, to test new compounds for the appearance of magnetic heat transport and second, to broaden the understanding of the known compounds by studying the influence of various kinds of impurities.
In particular, three families of materials are studied. First, the thermal conductivity \\kappa(T) of the compounds TiOBr and TiOCl is investigated. Below room temperature the compounds undergo two phase transitions T_{c2} and T_{c1}. Above T_{c2} the compounds contain S=1/2 spin chains with J_{Cl}=676 K and J_{Br}=375 K respectively, formed by direct orbital overlap of the Ti-atoms. Below T_{c1} the chains dimerize to form a non-magnetic ground state. The thermal conductivity exhibits pronounced anomalies at T_{c2} and T_{c1} confirming the transitions being of second and first order respectively. Surprisingly, \\kappa(T) appears to be dominated by phonon heat conduction, since no indications of a significant magnetic contribution is found. This is in contrast to the expectation of a spin chain system. In this context possible scenarios to understand the unusual behavior of the thermal conductivity are discussed.
Second, two related materials, the single chain Sr_{2}CuO_{3} and the double chain SrCuO_{2} are investigated. In high purity samples huge magnetic heat conductivities and concomitantly, extremely large spinon mean free paths of >0.5 µm for Sr_{2}CuO_{3} and >1 µm for SrCuO_{2} are observed. This demonstrates that \\kappa_{mag} is only limited by extrinsic scattering processes, which is a clear signature of ballistic transport in the underlying spin model. Additionally, various subtle modifications of the spin chain are studied. Due to the large mean free path a pristine picture of the intrinsic incidents is expected. In particular, a chemical pressure is applied to the spin chain by doping SrCuO_{2} with Ca. This has a surprisingly strong effect on \\kappa_{mag}. Furthermore, the influence of magnetic Ni and non-magnetic Mg doping is studied for SrCuO_{2}. While Ni-doping has a large impact on the magnetic thermal conductivity, Mg-doping shows no influence. In order to clarify this surprising behavior, \\kappa_{mag} is compared to measurements of the single chain compound Sr_{2}CuO_{3}.
Third, the magnetic thermal conductivity of the spin chain material CaCu_{2}O_{3} doped with non-magnetic Zn impurities is studied. \\kappa_{mag} of the pure compound is linear up to room temperature, which is indicative of a T-independent scattering rate of the magnetic excitations. Both, magnitude and T-dependence of \\kappa_{mag} exhibit a very unusual doping dependence. At moderate Zn-doping the linear temperature dependence of \\kappa_{mag} is preserved and the absolute value of \\kappa_{mag} increases. A slight suppression of \\kappa_{mag} occurs only at high Zn doping, where, surprisingly, the T-dependence of \\kappa_{mag} changes from linearity to one with a higher power of T . In order to clarify this surprising behavior, the results are compared to a detailed study of the g-tensor of the impurities in the material by means of ESR experiments, which reveal a change of the impurity type with increasing Zn-content.
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Jeong, Taehee. "Spin-dependent heat transport and thermal boundary resistance." Research Showcase @ CMU, 2011. http://repository.cmu.edu/dissertations/66.
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Spin-dependent heat transport is a new research area and can create many future applications. The Giant Magnetoresistance (GMR) effect, which was discovered in 1988, is significant change in electric resistance due to spin-dependent electron scattering. The GMR effect has greatly impacted on techniques of data storage and magnetic sensors. For example, the areal density of hard disk drive was increased 100 times using the GMR effect. Likewise, spin-dependent heat transport, which is also called the Giant Magnetothermal Resistance (GMTR) effect, is expected to create a wealth of new applications, for example nanoscale heat or temperature detectors and spin thermoelectrics. In addition, the technique developed for this study will help with heat management in micro/nano electronics including data storage devices and heat/energy assisted magnetic recording.
In this thesis, thermal conductivity change depending on the magnetic configurations has been studied. In order to make different magnetic configurations, we developed a spin valve structure, which has high MR ratio and low saturation field. The high MR ratio was achieved using Co/Cu multilayer and 21Å or 34Å thick Cu layer. The low saturation field was obtained by implementing different coercivities of the successive ferromagnetic layers. For this purpose, Co/Cu/Cu tri-layered structure was used with the thicknesses of the Co layers; 15 Å and 30 Å. For the thermal conductivity measurement, a three-omega method was employed with a thermally isolated microscale rod. We fabricated the microscale rod using optical lithography and MEMS process. Then the rod was wire-bonded to a chip-carrier for further electrical measurement. For the thermal conductivity measurement, we built the three-omega measurement system using two lock-in amplifiers and two differential amplifiers. A custom-made electromagnet was added to the system to investigate the impact of magnetic field.
We observed titanic thermal conductivity change depending on the magnetic configurations of the Co/Cu/Co multilayer. The thermal conductivity change was closely correlated with that of the electric conductivity in terms of the spin orientation, but the thermal conductivity was much more sensitive than that of the electric conductivity. The relative thermal conductivity change was 50% meanwhile that of electric resistivity change was 8.0%. The difference between the two ratios suggests that the scattering mechanism for charge and heat transport in the Co/Cu/Co multilayer is different. The Lorentz number in Weidemann-Franz law is also spin-dependent. The application of this significant thermal conductivity change is remained for future work.
Thermal boundary resistance between metal and dielectrics was also studied in this thesis. The thermal boundary resistance becomes critical for heat transport in a nanoscale because the thermal boundary resistance can potentially determine overall heat transport in thin film structures. A transient thermoreflectance (TTR) technique can be used for measuring the thermal conductivity of thin films in cross-sectional direction. In this study, a pump-probe scheme was employed for the TTR technique. We built an optical pump-probe system by using a nanosecond pulse laser for pumping and a continuous-wave laser for probing. A short-time heating event occured at the surface of a sample by shining a laser pulse on the surface. Then the time-resolved thermoreflectance signals were detected using a photodetector and an oscilloscope. The increased temperature decreases slowly and its thermal decay depends on the thermal properties of a sample. Since the reflectivity is linearly proportional to the temperature, the time-resolved thermoreflectance signals have the information of the thermal properties of a sample. In order to extract the thermal properties of a sample, a thermal analysis was performed by fitting the experimental data with thermal models. We developed 2-layered and 3-layered thermal models using the analogies between thermal conduction and electric conduction and a transmission-line concept.
We used two sets of sample structures: Au/SiNx/Si substrate and Au/CoFe/SiNx/Si substrate with various thickness of SiNx layer. Using the pump-probe system, we measured the time-resolved thermoreflectance signals for each sample. Then, the thermal conductivity and thermal boundary resistance were obtained by fitting the experimental data with the thermal models. The thermal conductivity of SiNx films was measured to be 2.0 W/mK for both structures. In the case of the thermal boundary resistance, it was 0.81´10-8 m2K/W at the Au/SiNx interface and 0.54´10-8 m2K/W at the CoFe/SiNx interface, respectively. The difference of the thermal boundary resistance between Au/SiNx and CoFe/SiNx might be came from the different phonon dispersion of Au and CoFe. The thermal conductivity did not depend on the thickness of SiNx films in the thickness range of 50-200nm. However, the thermal boundary resistance at metal/SiNx interfaces will impact overall thermal conduction when the thickness of SiNx thin films is in a nanometer order. For example, apparent thermal conductivity of SiNx film becomes half of the intrinsic thermal conductivity when the thickness decreases to 16nm. Therefore, it is advised that the thermal boundary resistance between metal and dielectrics should be counted in nano-scale electronic devices.
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Sulistyo, Hary. "Axial and radial heat transport in packed beds." Thesis, University of Salford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293824.
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Raju, Mandhapati P. "HEAT AND MASS TRANSPORT INSIDE A CANDLE WICK." Case Western Reserve University School of Graduate Studies / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=case1157564736.
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Hamed, Myriam. "Electron heat transport in tokamak H-mode pedestals." Electronic Thesis or Diss., Aix-Marseille, 2019. http://theses.univ-amu.fr.lama.univ-amu.fr/191128_HAMED_534gjvrc761ijwn176jbu525de_TH.pdf.
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Dans les plasmas en mode H, la modélisation de la dynamique du piédestal est une question importante pour prédire les profils de température et de densité dans le bord et le cœur des tokamaks. Le modèle EPED , basé sur la stabilité de modes Magnetohydrodynamiques, est le plus souvent utilisé pour caractériser la région du piédestal. Ce modèle EPED ne prend pas en compte les microinstabilités pouvant se développer dans la région du piédestal. Ainsi, la prédiction des caractéristiques du piédestal est toujours une question ouverte. De plus, certaines analyses récentes des plasmas JET suggèrent qu’une autre classe d’instabilités, appelée modes de microdéchirement, peut être responsable du transport de chaleur des électrons et jouer ainsi un certain rôle dans la détermination des caractéristiques du piédestal. Les modes de microdéchirement appartiennent à une classe d’instabilités où une modification de la topologie des lignes de champ magnétique. Cela conduit à la formation d’îlots magnétiques qui peuvent augmenter le transport de chaleur électronique. La stabilité des MTMs a été théoriquement étudiée dans le passé, montrant qu’une couche de courant est stable en l’absence de collisions. En revanche, des simulations gyrocinétiques récentes ont révélé que les MTMs étaient instables, même à faible collisionalité. Le but de cette thèse est d'améliorer la compréhension de la stabilité des modes de microdéchirement en comparant une théorie analytique avec des simulations gyrocinétique. Plus précisément, différents mécanismes physiques (dérive magnétique..) ont été ajouté progressivement au modèle dans le but de réconcilier les résultats numériques avec la théorie analytiqueIn H-mode plasmas, the modeling of the pedestal dynamics is an important issue to predict temperature and density profiles in the tokamak edge and therefore in the core. The EPED model, based on the stability of large scales MagnetoHydroDynamic (MHD) modes, is most commonly used to characterize the pedestal region. The EPED model has been successful until now. However, EPED model does not take into account small scales instabilities linked the the sharp pressure gradient and the pedestal characteristics prediction in terms of width and height is still open. Moreover, some recent analysis of JET plasmas suggest that another class of instabilities, called microtearing modes, may be responsible for electron heat transport in the pedestal, and thereby play some role in determining the pedestal characteristics. Microtearing modes belong to a class of instabilities where a modification of the magnetic field line topology is induced at the ion Larmor radius scale. This leads to the formation of magnetic islands, which can enhance the electron heat transport. The stability of MTMs has been theoretically studied in the past showing that a slab current sheet is stable in the absence of collisions. In contrast, recent gyrokinetic simulations in toroidal geometry found unstable MTMs, even at low collisionality. The purpose of our work is to improve the MTM stability understanding by comparing new analytical theory to linear gyrokinetic simulations. More precisely, physical mechanisms (magnetic drift, electric potential) are progressively included in the analytical description to recover the numerical simulations results and to "reconcile" numerical MTM investigations with theory
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Fleming, Laura Elizabeth. "The Influence of heat transport on Arctic amplification." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122324.
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Thesis: S.M., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2019Cataloged from PDF version of thesis.
Includes bibliographical references (pages 53-58).
The Arctic surface air temperature has warmed nearly twice as much as the global mean since the mid-20th century. Arctic sea ice has also been declining rapidly in recent decades. There is still discussion about how much of this Arctic amplification is caused by local factors, such as changes in surface albedo, versus remote factors, such as changes in heat transport from the midlatitudes. This thesis focuses mainly on the role of poleward heat transport on Arctic amplification. Most of the previous studies on this topic have defined ocean heat transport as the zonally averaged ocean heat transport at 65°N or 70°N, which ignores the physical pathways of heat into the Arctic and may include recirculation of heat in the North Atlantic. In this thesis, we define the ocean heat transport as the heat transport across five sections surrounding the Arctic, to create a closed domain in the Arctic.
Previous studies on Arctic amplification have used either a single model run or have compared results from a multi-model ensemble. While the multi-model ensemble approach may potentially average out biases in individual models, the ensemble spread confounds the model differences and the internal climate variability. In this thesis, we investigate the Arctic amplification in the Community Earth System Model version 1 (CESMi) Large Ensemble. The CESMI Large Ensemble includes 40 members that use the same model and external forcing, but different initializations. This simulates different climate trajectories that can occur in a given atmosphere-ocean-land-cryosphere system. We find that CESMI Large Ensemble projects a large increase towards the end of the 21st century in ocean heat transport into the Arctic, and that the increase in ocean heat transport is significantly correlated with Arctic amplification.
The main contributor to the increase in ocean heat transport is the increase across the Barents Sea Opening. The increase in Barents Sea Opening ocean heat transport is highly correlated with the decrease in sea ice in the Barents-Kara Sea region. We propose that this is because the increase in ocean heat transport melts the ice at the sea ice margin, which results in increased surface heat flux from the ocean and further local feedback through decreased surface albedo and increased cloud coverage. We also find that while the changes in atmosphere heat transport into the Arctic circle at 66.5 N are on the same order as the changes in ocean heat transport, they are not correlated with Arctic amplification.
by Laura Elizabeth Fleming.
S.M.
S.M. Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution)
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BAIOCCHI, BENEDETTA. "UNDERSTANDING AND PREDICTING ION HEAT TRANSPORT IN TOKAMAKS." Doctoral thesis, Università degli Studi di Milano, 2012. http://hdl.handle.net/2434/170629.
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One of the most attractive options to satisfy the continuously growing world energy demand is controlled thermonuclear fusion. The scientific and technological work for achieving it has been significantly boosted after the recent decision to build the international tokamak ITER (International Thermonuclear Experimental Reactor). Amongst the physical problems still open, understanding and controlling heat transport is of primary importance for the optimization of the operational scenarios of ITER. Given the complexity of plasma transport processes, a full theoretical understanding of the experimental observations and validated numerical models for the simulation of a complete tokamak discharge are not yet available. Work in this field is therefore actively ongoing, with a view to increasing integration between theoretical developments, experimental results and numerical predictions. This is the context in which the present thesis work takes place. It has long been known that the high measured levels of heat transport in tokamaks are due to turbulent phenomena, in particular the so-called drift waves. The ion heat transport, on which is focused this thesis, is carried by ion temperature gradient (ITG) modes, that are destabilized when a threshold value of the inverse ion temperature gradient length (1/LTi=|∇Ti/Ti|) is exceeded. Above threshold, the ion heat flux is a strongly increasing function of 1/LTi, which prevents the Ti profiles from departing significantly from threshold, a property known as profile stiffness. The main target of ion heat transport studies is to find ways to suppress or mitigate ITG modes, namely by increasing the threshold or reducing the stiffness level, in order to be able to achieve high core Ti values without having to rely on too high edge Ti values, which would raise plasma-wall interaction issues. Sophisticated ion heat transport experiments carried out at the JET tokamak have recently indicated that a strong reduction of ion stiffness takes place in presence of low magnetic shear and high toroidal rotation. This mechanism has been proposed as the key ingredient to explain the improved core ion confinement observed in Hybrid scenarios or Advanced Tokamak (AT) scenarios with Internal Transport Barriers, two regimes that are considered for ITER operations beyond the standard inductive H-mode regime.
This thesis work starts from the above mentioned JET results and from the already developed theoretical models and existing numerical codes, and includes four main items of work, with the purpose of integrating experimental analysis and theory-based numerical modelling of JET experiments, in order to reach predictive capabilities for the future tokamak FAST, a device proposed by the Italian Fusion Association as a possible ITER satellite. First, new experiments have been carried out in JET and analyzed in detail, in order to assess if the cause for ion stiffness reduction is the rotation value or the rotational shear. The data analysis has given as result that it is the absolute value of the rotational shear the key factor for ion stiffness mitigation. This gives the indication for ITER that the necessary condition for reducing the ion stiffness and access improved core confinement regimes is to induce some rotational shear, which may be easier than achieving high absolute values of rotation.
Second, a numerical study has been carried out in JET and ITER plasmas to quantify the impact of ion threshold and stiffness on global confinement and fusion power compared to the effect of edge Ti value. This work has the aim of evaluating if threshold and particularly stiffness are indeed two useful control tools for scenario performance optimization. The variation of global confinement has been found quantitatively significant for changes of the ion stiffness, and comparable with the ones due to changes of ion threshold and Ti pedestal height, when they are varied in an experimentally realistic range. In ITER, the calculated fusion power, which is what really matters for a fusion device, is as much affected by variations of ion stiffness as by changes of ion threshold and Ti pedestal height. This work gives the indication that all the three investigated parameters influence comparably the core performances in present and future machines. In particular the quantitative level of ion stiffness, which is a parameter not much considered until now, and assumed or predicted very high in most existing models, can be a useful knob to act upon in order to optimize the scenario performance and must be taken into account for an accurate predictive modelling of future machines.
Third, a prediction work for the foreseen scenarios of FAST has been carried out, using a mixture of first-principle models and experiment driven considerations. The results obtained in the two previous steps have led to the conviction that predictive modelling of future devices cannot neglect including toroidal rotation profiles and their effects on transport, which is not common practice in tokamak simulation work. Both H-modes and fully non-inductive AT scenarios have been simulated, predicting profiles of current, ion and electron temperature, density and toroidal rotation. Various heating options have been explored. The simulations have provided a set of FAST scenarios in which fast particle and burning plasma studies can be performed, reaching values of thermal and fast particle energy contents well in line with the needs for exciting meso-scale fluctuations with the same characteristics of those expected in reactor relevant conditions.
Fourth, linear gyro-kinetic simulations have been carried out to check the validity of simplified threshold formulae used in simulations in the high toroidal field and high density FAST plasmas. Very good agreement was found between the analytical threshold approximation and the GKW simulations with adiabatic electrons, whilst the threshold with kinetic electrons is slightly lower. The discrepancy is anyway small enough to justify the use of the threshold analytic approximation for FAST simulations, taking into account the other sources of uncertainty linked to various other modelling approximations and to empirical extrapolations from experimental data of existing machines.
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Yao, Xiaobo. "Characterization of fire induced flow transport along ceilings using salt-water modeling." College Park, Md. : University of Maryland, 2006. http://hdl.handle.net/1903/3491.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2006.Thesis research directed by: Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Ramsay, Scott Wilson. "Studies on an Arabidopsis MYB transcription factor involved in heat and salt tolerance." Thesis, University of Glasgow, 2014. http://theses.gla.ac.uk/8117/.
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Heat stress has a significant impact on the productivity and yield of crops grown in the hot, arid zones of the world. There is mounting evidence that what has classically been termed ‘drought stress’ may in some cases be caused not by water stress per se, but rather by the uncontrolled elevation in leaf temperature that occurs when a plant loses its capacity for transpirational cooling. A previous screen of activation-tagged Arabidopsis thaliana seeds for novel halotolerant mutants implicated elevated levels of the transcription factor MYB64 in mediating improved survival on high salt growth medium, and subsequent transcript profiling of this activation-tagged halotolerant line (HT5) revealed the upregulation of several members of the heat shock protein family. Based on these preliminary findings, expression of two of the small heat shock proteins reported to be among the most highly upregulated in the HT5 line was investigated under various stress conditions in wild type Arabidopsis. Transcript and protein levels were measured in response to heat; their subcellular localisation was observed; and the phenotype of various knockout mutants was recorded. These studies have contributed to an understanding of how these might function in relation to one another and to the rest of the heat shock protein family. This thesis also reports on the investigations of a transgenic line created to constitutively overexpress the MYB64 transcription factor. Transcript profiling produced a list of ‘upregulated’ sequences, of which a significant proportion were previously shown to play key roles in abiotic (and, to an extent, biotic) stress responses. The robustness of these responses in the transgenic lines was investigated by qPCR under heat stress, and the phenotype of the plants was characterised in response to various stress regimes. The findings implicate MYB64 in the regulation of a wide range of stress responses, and as plants are unlikely to encounter stress factors individually outside of the controlled conditions of a laboratory, these findings highlight the importance of considering such stresses in concert rather than isolation.
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Green, Andrew J. "Heat Transfer from Optically Excited Gold Nanostructures into Water, Sugar, and Salt Solutions." Ohio University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1376498592.
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Benjamin, Daniel. "Thermal transport and photo-induced charge transport in graphene." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42746.
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The electronic material graphene has attracted much attention for its unique physical properties such as, linear band structure, high electron mobility, and room temperature ballistic conduction. The possibilities for device applications utilizing graphene show great variety, from transistors for computing to chemical sensors. Yet, there are still several basic physical properties such as thermal conductivity that need to be determined accurately.
This work examines the thermal properties of graphene grown by the chemical vapor deposition technique. The thermoelectric power of graphene is studied in ambient and vacuum environments and is shown to be highly sensitive to surface charge doping. Exploiting this effect, we study the change in thermoelectric power due to introduction of gaseous species. The temperature dependent thermal conductivity of graphene is measured using a comparison method. We show that the major contribution to the thermal conductivity is the scattering of in-plane phonons.
Graphene also shows promise as an optoelectronic material. We probe the Landau level structure of graphene in high magnetic fields using a differential photoconductivity technique. Using this method we observed the lifting of spin and valley degeneracies of the lowest Landau level in graphene.