Dissertations / Theses on the topic 'Two-temperature model'

We discuss the so-called two-temperature model in linear thermoelasticity and provide a Hilbert space framework for proving well-posedness of the equations under consideration. With the abstract perspective of evolutionary equations, the two-temperature model turns out to be a coupled system of the elastic equations and an abstract ordinary differential equation (ODE). Following this line of reasoning, we propose another model which is entirely an abstract ODE.We also highlight an alternative method for a two-temperature model, which might be of independent interest.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998.
Includes bibliographical references (leaves 89-90).
Quenching is a thermal failure mechanism encountered with superconducting magnets. When a section of conductor is driven normal by an external heat input, the magnet transport cur­rent flows through a resistance, causing joule dissipation. If heat is not conducted away from the normal region faster than it is dissipated, the normal region will grow and the tempera­ture will increase indefinitely. Growth of the normal region is commonly refereed to as normal zone propagation(NZP). A reliable NZP model is necessary for designing protection systems because a quench may cause irreparable damage if a section of the winding is over-heated. This thesis develops a numerical NZP model for a three dimensional, dry-wound, BSSCO- 2223 superconducting magnet. The test magnet operates under quasi-adiabatic conditions at 20 K and above, in zero background field. It is contained in a stainless steel cryo­stat and cooled by a Daikin cryocooler. The NZP model is based on the two-dimensional transient heat diffusion equation. Quenches arc simulated by a numerical code using the finite-difference method. Agreement between voltage traces obtained in the test magnet during heater-induced quenching events and those computed by the numerical NZP model is reasonable. The model indicates that thermal contact resistance has a dominant effect on propagation in the azimuthal direction(across layers). The model is also used to simulate quenching in persistent-mode magnets similar in construction with the test magnet. Specifically studied were effects of magnet inductance, for a given set of operating current and temperature, on the maximum temperature reached in one full turn of the conductor located at the magnet outermost layer driven normal with a heater. The simulation demonstrates that there is an operating current limit for a given magnet inductance and operating temperature below which the magnet can be considered self-protecting. The simulation also demonstrates that shunted subdivision lowers the maximum temperature.
by Benjamin J. Haid.
S.M.

Water temperature directly affects biological and chemical processes of fresh water ecosystems. Elevated instream temperatures are commonplace in the Virgin River of southwestern Utah during summer due to a hot desert climate and high water demands that result in low stream flows. This is of concern since the Virgin River is home to two endangered species, the Virgin River Chub (Gila seminuda) and Woundfin (Plagopterus argentissimus). Efforts to model instream temperatures within the Virgin River have been undertaken to help mitigate elevated instream temperatures including the development of a two-zone temperature and solute (TZTS) model. This model was developed to approximate the dominant processes that influence instream temperatures and used both temperature and solute data in parameter estimation. Past model applications highlighted two concerns: (1) how to confidently estimate the high number of parameters and (2) whether Rhodamine WT (RhWT) could be used as a conservative solute tracer within the Virgin River. To begin addressing these issues, spatially representative data were collected to facilitate the physical estimation of two previously calibrated parameters: total average channel width (BTOT) and the fraction of channel width associated with dead zones (β). Methods for analyzing multispectral and thermal infrared imagery were developed to provide estimates of these parameters at different resolutions. Three different TZTS model calibration cases were then evaluated to determine how decreasing the calibrated parameters and increasing the resolution and frequency at which these parameters are estimated improved model predictions and/or decreased parameter uncertainty. While temperature predictions did not change significantly in each of the calibrations, parameter uncertainty was reduced. The concern regarding the use of RhWT resulted in a series of studies to quantify the potential losses of RhWT within this system. A batch sorption study resulted in distribution coefficient values lower than those found in literature. A photodegradation study suggested possible photolysis; however, a dual tracer study conducted within the Virgin River comparing Br- (conservative tracer) with RhWT confirmed that there was insignificant RhWT loss within this system.

For several decades the formation of different kinds of superstructures in solids has been a topical issue in condensed matter physics. The superstructures (or spatially modulated structures) may be of a different nature: magnetic patterns like spin-density waves, inhomogeneous charge distributions in charge-ordered compounds, dipolar and quadrupolar ordering in ferroelectrics or ferroelastics, regular lattice distortions and related orbital structures, stripe-like arrangements of dopants in alloys, etc. The phase diagrams of such compounds can be rather complicated involving a large number of phases with non-trivial types of ordering. Fortunately, all this wealth of seemingly unrelated phenomena can be often described by rather simple models with a due account taken of a competitive character of the most important interactions. In this thesis I will investigate the Ising model in 2-D with nearest and next-nearest neighbour interactions using several methods including exact diagonalisation of small clusters, transfer matrix technique and Monte Carlo simulation of large lattices.

Thesis advisor: Ziqiang . Wang
The transition between many-body localized states and the delocalized thermal states is an eigenstate phase transition at finite energy density outside the scope of conventional quantum statistical mechanics. We apply support vector machine (SVM) to study the phase transition between many-body localized and thermal phases in a disordered quantum Ising chain in a transverse external field. The many-body eigenstate energy E is bounded by a bandwidth W=Eₘₐₓ-Eₘᵢₙ. The transition takes place on a phase diagram spanned by the energy density ϵ=2(Eₘₐₓ-Eₘᵢₙ)/W and the disorder strength ẟJ of the spin interaction uniformly distributed within [-ẟJ, ẟJ], formally parallel to the mobility edge in Anderson localization. In our study we use the labeled probability density of eigenstate wavefunctions belonging to the deeply localized and thermal regimes at two different energy densities (ϵ's) as the training set, i.e., providing labeled data at four corners of the phase diagram. Then we employ the trained SVM to predict the whole phase diagram. The obtained phase boundary qualitatively agrees with previous work using entanglement entropy to characterize these two phases. We further analyze the decision function of the SVM to interpret its physical meaning and find that it is analogous to the inverse participation ratio in configuration space. Our findings demonstrate the ability of the SVM to capture potential quantities that may characterize the many-body localization phase transition. To further investigate the properties of the transition, we study the behavior of the entanglement entropy of a subsystem of size L_A in a system of size L > L_A near the critical regime of the many-body localization transition. The many-body eigenstates are obtained by exact diagonalization of a disordered quantum spin chain under twisted boundary conditions to reduce the finite-size effect. We present a scaling theory based on the assumption that the transition is continuous and use the subsystem size L_A/ξ as the scaling variable, where ξ is the correlation length. We show that this scaling theory provides an effective description of the critical behavior and that the entanglement entropy follows the thermal volume law at the transition point. We extract the critical exponent governing the divergence of ξ upon approaching the transition point. We again study the participation entropy in the spin-basis of the domain wall excitations and show that the transition point and the critical exponent agree with those obtained from finite size scaling of the entanglement entropy. Our findings suggest that the many-body localization transition in this model is continuous and describable as a localization transition in the many-body configuration space. Besides the many-body localization transition driven by disorder, We also study the Coulomb repulsion and temperature driving phase transitions. We apply a finite-temperature Gutzwiller projection to two-dimensional Hubbard model by constructing a "Gutzwiller-type" density matrix operator to approximate the real interacting density matrix, which provides the upper bound of free energy of the system. We firstly investigate half filled Hubbard model without magnetism and obtain the phase diagram. The transition line is of first order at finite temperature, ending at 2 second order points, which shares qualitative agreement with dynamic mean field results. We derive the analytic form of the free energy and therefor the equation of states, which benefits the understanding of the different phases. We later extend our approach to take anti-ferromagnetic order into account. We determine the Neel temperature and explore its interesting behavior when varying the Coulomb repulsion
Thesis (PhD) — Boston College, 2019
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics

Methods of solving the steady state characteristics of a node matrix equation system over a polymer electrolyte fuel cell (PEFC) were evaluated. The most suitable method, referred to as the semi-implicit method, was set up in a MATLAB program. The model covers heat transfer due to thermal diffusion throughout the layers and due to thermal advection+diffusion in the gas channels. Included mass transport processes cover only transport of water vapor and consist of the same diffusion/advection schematics as the heat transfer processes. The mass transport processes are hence Fickian diffusion throughout all the layers and diffusion+advection in the gas channels. Data regarding all the relevant properties of the layer materials were gathered to simulate these heat- and mass transfer processes.Comparing the simulated temperature profiles obtained with the model to the temperature profiles of a previous work’s model, showed that the characteristics and behavior of the temperature profile are realistic. There were however differences between the results, but due to the number of unknown parameters in the previous work’s model it was not possible to draw conclusions regarding the accuracy of the model by comparing the results.Comparing the simulated water concentration profiles of the model and measured values, showed that the model produced concentration characteristics that for the most part alignedwell with the measurement data. The part of the fuel cell where the concentration profile did not match the measured data was the cathode side gas diffusion layer (GDL). This comparison was however performed with the assumption that relative humidity corresponds to liquid water concentration, and that this liquid water concentration is in the same range as the measured data. Because of this assumption it was not possible to determine the accuracy of the model.

L'effet thermodynamique est etudie experimentalement dans le cas d'une poche cavitante, attachee dans un venturi, se developpant dans un liquide thermosensible. Cet effet se manifeste par un refroidissement de la poche par rapport a la temperature d'entree du liquide qui est a determiner en fonction des caracteristiques cavitantes de l'ecoulement. Selon les modeles a interface, ce refroidissement est controle par le flux thermique du liquide vers la poche, lui meme fonction des parametres turbulents du liquide. Des mesures laser de vitesse et de turbulence autour de poches ont donc ete realisees. Pour le liquide thermosensible, le forane 114, la temperature de poche a ete mesuree pour connaitre le refroidissement reel ; des mesures de pression ont egalement ete faites afin de verifier l'hypothese d'equilibre thermodynamique. Les mesures laser autour de poches cavitantes en eau froide sont comparees aux mesures pres de poches ventilees afin de caracteriser la cavitation sans effet thermodynamique, puis des mesures laser pres de poches cavitantes au forane permettent de specifier l'action de l'effet thermodynamique. L'effet des parametres tels que la vitesse d'ecoulement, la longueur de poche et, dans le cas du forane, de la temperature, est etudiee. A l'eau, l'ecoulement contourne la cavite tandis qu'au forane, un debit liquide entrant dans la poche est estime. Des modeles simples permettent de calculer, a partir des mesures dans le forane, le flux cede par le liquide a la cavite, et le flux necessaire a une cavite de vapeur pure. La comparaison des flux ainsi que le debit entrant dans la cavite montrent que la poche est probablement constituee d'un melange diphasique ; dans ce cas, le flux thermique cede par le liquide intervient peu sur le refroidissement et l'effet thermodynamique est essentiellement lie au taux de vide local

Développement d'une méthode de mesure, basée sur l'émission-absorption du rayonnement thermique dans le proche infrarouge entre 1 et 5 microns, permettant de déterminer des valeurs ponctuelles sur toute l'épaisseur visée pour pouvoir établir les champs radiaux aussi bien qu'axiaux des températures et tester les modèles à deux dimensions

Modulation doped heterostructures have revolutionized the operation of field effect devices by increasing the speed of operation. One of the factors that affects the speed of operation of these devices is the mobility of the carriers, which is intrinsic to the material used. Mobility of electrons in silicon based devices has improved drastically over the years, reaching as high as 50.000cm2/Vs at 4.2K and 2600cm2/Vs at room temperature. However, the mobility of holes in p-type silicon devices still remains comparatively lesser than the electron mobility because of large effective masses and complicated valence band structure involved. Germanium is known to have the largest hole mobility of all the known semiconductors and is considered most suitable to fabricate high speed p-type devices. Moreover, it is also possible to integrate germanium and its alloy (Si1_zGex ) into the existing silicon technology. With the use of sophisticated growth techniques it has been possible to grow epitaxial layers of silicon and germanium on Si1_zGex alloy layers grown on silicon substrates. In tills thesis we investigate in detail the electrical properties of p-type germanium and n-type silicon thin films grown by these techniques. It is important to do a comparative study of transport in these two systems not only to understand the physics involved but also to study their compatibility in complementary field effect devices (cMODFET). The studies reported in this thesis lay emphasis both on the low and high field transport properties of these systems. We report experimental data for the maximum room temperature mobility of holes achieved m germanium thin films grown on Si1_zGex layers that is comparable to the mobility of electrons in silicon films. We also report experiments performed to study the high field degradation of carrier mobility due to "carrier heating" in these systems. We also report studies on the effect of lattice heating on mobility of carriers as a function of applied electric field. To understand the physics behind the observed phenomenon, we model our data based on the existing theories for low and high field transport. We report complete numerical calculations based on these theories to explain the observed qualitative difference in the transport properties of p-type germanium and ii-type silicon systems. The consistency between the experimental data and theoretical modeling reported in this work is very satisfactory.

Modulation doped heterostructures have revolutionized the operation of field effect devices by increasing the speed of operation. One of the factors that affects the speed of operation of these devices is the mobility of the carriers, which is intrinsic to the material used. Mobility of electrons in silicon based devices has improved drastically over the years, reaching as high as 50.000cm2/Vs at 4.2K and 2600cm2/Vs at room temperature. However, the mobility of holes in p-type silicon devices still remains comparatively lesser than the electron mobility because of large effective masses and complicated valence band structure involved. Germanium is known to have the largest hole mobility of all the known semiconductors and is considered most suitable to fabricate high speed p-type devices. Moreover, it is also possible to integrate germanium and its alloy (Si1_zGex ) into the existing silicon technology. With the use of sophisticated growth techniques it has been possible to grow epitaxial layers of silicon and germanium on Si1_zGex alloy layers grown on silicon substrates. In tills thesis we investigate in detail the electrical properties of p-type germanium and n-type silicon thin films grown by these techniques. It is important to do a comparative study of transport in these two systems not only to understand the physics involved but also to study their compatibility in complementary field effect devices (cMODFET). The studies reported in this thesis lay emphasis both on the low and high field transport properties of these systems. We report experimental data for the maximum room temperature mobility of holes achieved m germanium thin films grown on Si1_zGex layers that is comparable to the mobility of electrons in silicon films. We also report experiments performed to study the high field degradation of carrier mobility due to "carrier heating" in these systems. We also report studies on the effect of lattice heating on mobility of carriers as a function of applied electric field. To understand the physics behind the observed phenomenon, we model our data based on the existing theories for low and high field transport. We report complete numerical calculations based on these theories to explain the observed qualitative difference in the transport properties of p-type germanium and ii-type silicon systems. The consistency between the experimental data and theoretical modeling reported in this work is very satisfactory.

Nous avons etudie la magnetoresistance des bronzes oxygenes de metaux de transition, le bronze violet kmo#6o#1#7 et les composes m=4, 6, 7 de la famille (po#2)#4(wo#3)#2#m. Ces composes ont des proprietes quasi-bidimensionnelles. Ils subissent des transitions de peierls a une temperature t#p. La magnetoresistance de kmo#6o#1#7 a ete mesuree a des temperatures comprises entre 1. 8 k et 300 k en champ magnetique jusqu'a 37 t. Des oscillations quantiques ont ete observees. Base sur le concept du nesting cache, nous proposons un modele de la surface de fermi dans l'etat d'onde de densite de charge. Elle serait constituee de petites poches lesquelles seraient a l'origine de la magnetoresistance elevee au-dessous de t#p. La temperature de peierls, observee par des mesures de resistivite electrique sous pression hydrostatique, augmente avec la pression. La compressibilite des parametres du reseau est anisotrope. La resistivite et la magnetoresistivite ont ete etudiees a des temperatures comprises entre 4. 2 k et 300 k en champ magnetique jusqu'a 6 t dans les composes m=4, 6, 7 de la famille (po#2)#4(wo#3)#2#m. La temperature de peierls augmente avec m. La magnetoresistivite diminue, ainsi que l'anisotropie quand m augmente. Nous discutons ce comportement en considerant le caractere de basse dimensionnalite, la densite de porteurs et la densite de defauts cristallins

2008/2009
This thesis is aimed to the study of dynamics in binary fluid mixtures by means of inelastic scattering spectroscopies. Nowadays the understanding of these dynamics is still unsatisfactory. In particular, any model is able to adequately describe collective dynamics beyond the hydrodynamic limit. In such a low momentum (k) and frequency () transfer limit, the collective dynamics is characterized by a single (adiabatic) longitudinal acoustic mode accounting for sound propagation. At frequencies above the hydrodynamics ones a transition towards a decoupled dynamic regime is expected. This is characterized by two distinct modes, namely the slow (low-) and fast (high-) sounds. The microscopic mechanisms driving such a transition, so as the related macroscopic quantities, are still unclear, even in an heuristic point of view. In this work the collective dynamics of neutral and ionic mixtures are investigated with the aim to shed light in this debated issue. He/Ne mixtures have been studied by means of Inelastic X-ray Scattering (IXS) spectroscopy. Exploiting the lack of kinematic limitations peculiar of this technique, the high frequency (>THz) dynamics has been analyzed from the mesoscopic up to the high-k range, where the dynamic response of the system can be described using the Impulse Approximation (IA). This kind of study is of particular interest for disparate mass mixtures, since inefficient kinetic energy exchanges between light and heavy particles taking place on very short time scales are expected to greatly influence the phenomenology of the aforementioned dynamic decoupling. The prototype ionic mixture, RbF, also, has been investigated by means of Inelastic Neutron Scattering (INS) spectroscopy. Ionic mixtures are particularly suited to investigate the role played by optic-like excitations (related to concentration fluctuations) in the transition from the hydrodynamics to the decoupled regime. Indeed, these kind of excitations are expected to be emphasized because of the long range Coulomb interactions. Conversely at k’s enough high, i.e. k>k* with k* dependent on the values of the electric conduction coefficient and the adiabatic sound velocity, they are expected to behave like neutral binary mixtures. The study of molten RbF has been, then, focused on the characterization of collective dynamics in the transition region, which is more difficultly accessible by IXS because of instrumental limitations. IXS data on He0.8Ne0.2 mixture have been analyzed using a generalization of the viscoelastic function, which, in our knowledge, has been applied for the first time to this purpose. This kind of data analysis permitted to extrapolate the partial dynamical structure factors related to He-He, Ne-Ne and He-Ne density fluctuations. The adiabatic and high frequency sound velocity as well as the relaxation time associated to each mixture component has been calculated from fitting parameters. The analysis of the extrapolated relaxation times permitted to define, in the probed range, two k-region depending on the behavior of such quantity. At the higher k probed the relaxation times of single components can be well described by the respective single specie collision time, indicating a complete dynamics decoupling. At lower k, conversely, the relaxation times show a deviation to respect the collisional times. The study of the same mixture in three different thermodynamic conditions, revealed a common k trend of the single component relaxation times once proper normalization, made by means of kinetic parameters, has been done. An empirical expression has then been proposed. The result can be interpreted in the framework of ‘two temperature theory’, based on the assumption that in disparate mass binary mixtures inefficient kinetic energy exchanges induce a two step process for the relaxation of density fluctuations towards the thermodynamic equilibrium. These processes are characterized by two distinct timescales: the intra-specie collision time, where each specie subsystem reaches a condition of ‘local’ equilibrium associated with a ‘local’ temperature and a characteristic time for the equilibration of the microscopic temperatures to the thermodynamic temperature trough inter-specie collisions. A further corroboration of the above picture has been found from the analysis of IXS spectra in the IA region, which allowed extrapolating the momentum distribution functions of the specie subsets. An anomalous behavior has been noticed on the He momentum distribution function, i.e. the apparent temperature associated to the momentum distribution is about 40 K higher than the macroscopic one. This striking result can be straightforwardly interpreted as a fingerprint of the peculiar ‘two temperature’ equilibration process. INS experiment on molten RbF permitted to reveal the simultaneous presence of two dispersive collective modes in the transition region. The dispersive behavior (linear with k) and the characteristic energies permitted to exclude an optic-like nature for both excitations. The performed data analysis permitted also to extrapolate the value of the electrical conduction coefficient, founding a quite low value as compared with typical values of molten salts. An estimation of k* for the studied system emphasize the possibility that at the probed k it may be isomorphous to a neutral mixture. The observed phenomenology can be thus interpreted in terms of double sound propagation phenomenon, observed in rarefied non-ionic gaseous mixtures. Finally, an alternative interpretation of these experimental results can be qualitatively provided within the frame of the generalized collective mode approach. In this case the high frequency mode is identified with the extension of the adiabatic longitudinal sound mode beyond hydrodynamic limit that, in analogy to what observed in several fluids, follows a linear dispersion with an associated sound velocity larger than the adiabatic one. The low frequency mode could instead be associated with a propagating kinetic mode related to energy fluctuations (heat waves). In conclusion, an extensive analysis of high-frequency dynamics in binary mixtures has been reported. Particular emphasis has been devoted to the study of the sound decoupling phenomenon manifesting beyond the hydrodynamic region. The experimental results indicate that such a phenomenon is manifested in both neutral and ionic disparate mass binary mixtures. It can be related to microscopic dynamics, e.g. thermalization effects related to the inefficient kinetic exchange between lighter and heavier particles.
XXI Ciclo
1978

The effect of temperature on soil behaviour has been the subject of many studies in recent years due to an increasing number of projects related to the application of high temperature to soil. One example is the construction of facilities for the disposal of hot high level nuclear waste canisters (150-200C) several hundred meters underground in the clay formations. Despite this, the effects and mechanism by which temperature affects the soil properties and behaviour are not fully known. A limited amount of reliable experimental data, technological difficulties and experimental methods employed by different researchers could have contributed to the uncertainties surrounding the soil behaviour at elevated temperature. Also several thermo-mechanical models have been developed for soil behaviour, but their validity needs to be examined by reliable experimental data. In this research, efforts have been made to improve the experimental techniques. Direct displacement measuring devices have been successfully used for the first time to measure axial and lateral displacements of clay samples during tests at various temperatures. The thermo mechanical behaviour of two reconstituted clays has been investigated by performing triaxial and permeability tests at elevated temperature. Undrained and drained triaxial tests were carried out on normally consolidated and over consolidated samples of M44 clay and Kaolin C1C under different effective stresses, and at temperatures between 22C and 100C. Permeability tests were carried out on samples of M44 clay at temperatures between 22C and 50C. The effects of temperature on permeability, volume change, pore pressure development, shear strength and stiffness, stress strain response and critical state parameters for different consolidation histories have been investigated by comparing the results at various temperatures. The results are also compared with the predictions of two models. It has been found that at elevated temperature the shear strength, friction angle and initial small strain stiffness reduce whereas permeability increases. The slope of the swelling line in the v-p� plane has been found to reduce with temperature. The slope of the isotropic normal consolidation line (INCL) and critical state line (CSL) in the v-p� plane have been observed to be independent of temperature, but both the INCL and the CSL shift downwards to lower locations as temperature increases. The deformations during drained cooling and re heating cycles have been found to be elastic and to simply reflect the expansivity of the soils solid particles. The thermal volume changes during undrained heating have been observed to be direct results of the thermal expansion of water and clay particles. The internal displacement measuring devices have been found to produce reliable data for the variation of strains at elevated temperature.

The effect of temperature on soil behaviour has been the subject of many studies in recent years due to an increasing number of projects related to the application of high temperature to soil. One example is the construction of facilities for the disposal of hot high level nuclear waste canisters (150-200C) several hundred meters underground in the clay formations. Despite this, the effects and mechanism by which temperature affects the soil properties and behaviour are not fully known. A limited amount of reliable experimental data, technological difficulties and experimental methods employed by different researchers could have contributed to the uncertainties surrounding the soil behaviour at elevated temperature. Also several thermo-mechanical models have been developed for soil behaviour, but their validity needs to be examined by reliable experimental data. In this research, efforts have been made to improve the experimental techniques. Direct displacement measuring devices have been successfully used for the first time to measure axial and lateral displacements of clay samples during tests at various temperatures. The thermo mechanical behaviour of two reconstituted clays has been investigated by performing triaxial and permeability tests at elevated temperature. Undrained and drained triaxial tests were carried out on normally consolidated and over consolidated samples of M44 clay and Kaolin C1C under different effective stresses, and at temperatures between 22C and 100C. Permeability tests were carried out on samples of M44 clay at temperatures between 22C and 50C. The effects of temperature on permeability, volume change, pore pressure development, shear strength and stiffness, stress strain response and critical state parameters for different consolidation histories have been investigated by comparing the results at various temperatures. The results are also compared with the predictions of two models. It has been found that at elevated temperature the shear strength, friction angle and initial small strain stiffness reduce whereas permeability increases. The slope of the swelling line in the v-p� plane has been found to reduce with temperature. The slope of the isotropic normal consolidation line (INCL) and critical state line (CSL) in the v-p� plane have been observed to be independent of temperature, but both the INCL and the CSL shift downwards to lower locations as temperature increases. The deformations during drained cooling and re heating cycles have been found to be elastic and to simply reflect the expansivity of the soils solid particles. The thermal volume changes during undrained heating have been observed to be direct results of the thermal expansion of water and clay particles. The internal displacement measuring devices have been found to produce reliable data for the variation of strains at elevated temperature.

A new oceanic climatology to calculate ocean heat content (OHC) was developed for application year-round in the Atlantic Ocean basin. The Systematically Merged Atlantic Regional Temperature and Salinity (SMARTS) Climatology blends temperature and salinity fields from the World Ocean Atlas 2001 (WOA) and Generalized Digital Environmental Model v.3.0 (GDEM) at 1/4° resolution. This higher resolution climatology better resolves features in the Gulf of Mexico (GOM), including the Loop Current and eddy structures, than the previous coarser 1/2° products. Daily mean isotherm depths of the 20° C (D20) and 26° C (D26) (and their mean ratio), reduced gravity (e.g., 2-layer model), mixed layer depth (MLD), and OHC were estimated from the blended climatology. Using SMARTS with satellite-derived surface height anomaly and SST fields, daily values of D20, D26, MLD, and OHC were calculated from 1998 to 2010 using a two-layer model approach. Airborne and ship-deployed eXpendable BathyThermographs (XBT), long-term moorings, and Argo profiling floats provided the in-situ data to blend and assess the SMARTS Climatology. A clear, direct relationship emerged from the detailed analysis between satellite-derived and in-situ measurements of isotherm depths and OHC. This new climatological approach created a more accurate estimation of isotherm depths and OHC from satellite radar altimetry measurements, which can be used in hurricane intensity forecasts from the Statistical Hurricane Intensity Prediction Scheme (SHIPS). The Mainelli (2000) technique of calculating OHC was reexamined to most accurately project sea surface height anomalies (SSHA) into changes in depths of D20, D26, and MLD. SSHA surface features were tracked to determine realistic drift velocities ingested into the objective analysis algorithm. The former OHC algorithm assumed a climatological MLD, however observations show large temporal variability of MLD. Using a SSHA-dependent MLD for the OHC estimation improves the two-layer model by 5%. Upper ocean thermal structure estimations improved by 25% using the SMARTS Climatology as compared to that of Mainelli (2000).

Die Untersuchung von Klimaszenarien ergab, dass die Grundwasserneubildung in Nordostdeutschland abnehmen könnte. Um Süßgewässer zu erhalten müssen neue Strategien entwickelt werden. Im Gebiet des Lietzengrabens wird Klarwasser eingeleitet, um Feuchtgebiete und Seen zu erhalten. Diese Strategie wurde durch eine Szenarioanalyse erarbeitet, die sich auf das hydrologische iterative Modell ArcEGMO-ASM stützte. In dieser Arbeit wurde das voll integrierte Modell HydroGeoSphere genutzt, um den Fluss von Wasser an der Oberfläche und im Untergrund zu simulieren. Basierend auf dieser Simulation wurden Fließpfade und Aufenthaltszeiten abgeschätzt. Die Ergebnisse beider Modelle wurden analysiert und verglichen. Mit beiden Modellen war es möglich, die Abfluss- und Grundwasserdynamiken im Einzugsgebiet zu reproduzieren. Bei der Anwendung von HydroGeoSphere fehlten Möglichkeiten zur Berücksichtigung von z.B. Schneefall und Wehren, welche in ArcEGMO-ASM vorhanden sind. Die Kalibrierung des Modells lieferte Parameterwerte, die eine Reproduktion der Dynamiken erlaubten. Allerdings könnte HydroGeoSphere nur eingeschränkt nutzbar sein, da die Werte teils unrealistisch waren. HydroGeoSphere ermöglichte aber die Abschätzung von unterirdischen Fließpfaden und Aufenthaltszeiten. Weiter wurde der Austritt von Grundwasser in einen Bachabschnitt durch Messungen bestimmt und mit Simulationsergebnissen verglichen. Keines der Modelle war geeignet, die räumlichen Muster auf dieser Skala zu reproduzieren. Die simulierten Exfiltrationsraten wichen von den beobachteten ab. Der Vergleich von ArcEGMO-ASM und HydroGeoSphere zeigte die Vorteile und Grenzen der Modelle auf. Der Einsatz von HydroGeoSphere bei Untersuchungen von Bewirtschaftungsstrategien macht sich noch nicht bezahlt, vergleicht man den Aufwand mit den Vorteilen. Da HydroGeoSphere weiterentwickelt wird und die Rechenkapazitäten zunehmen, könnte das Modell in der nahen Zukunft in der Praxis nutzbar sein.
Analysis of climatic scenarios for North-East Germany showed that groundwater recharge could decline. In order to sustain freshwaters, new strategies must be developed. At the Lietzengraben catchment treated wastewater is discharged to sustain wetlands and lakes in the catchment. This management strategy was developed previously by scenario analysis, performed by the hydrological iterative model ArcEGMO-ASM. In this work, the fully integrated model HydroGeoSphere was used to simulate the surface and subsurface water flow in the catchment. Based on the simulation results, flow paths and residence times were estimated. The results of the simulations by both models were investigated and compared. It was possible to reproduce the catchment dynamics regarding discharge and groundwater heads reasonably well with both models. The application of HydroGeoSphere was limited due to the inability of the model to represent features like snowfall and weirs, which are represented in ArcEGMO-ASM. The calibrated parameter values enabled the model to reproduce the catchment dynamics reasonably well. HydroGeoSphere may be limited in its use since the obtained values are partially unrealistic. HydroGeoSphere allowed the approximation of subsurface flow paths and residence times. The exfiltration of groundwater to a stream reach was estimated by measurements and compared to simulation results. Both models were not able to reproduce the spatial patterns on a sub-reach scale and the calculated exfiltration rates did not match the observed rates. The comparison of ArcEGMO-ASM and HydroGeoSphere showed the advantages and limitations of both models. Comparing the overall additional effort to the benefits, however, the application of HydroGeoSphere to investigations regarding management strategies or scenario analyses may not pay off. Since HydroGeoSphere is under steady development and computational resources improve, the use of HydroGeoSphere may be applicable in the near future.

Preparation et caracterisation par rmn a haute resolution d'alpha -omega -dihydroxy polyesters insatures modeles par rmn bidimensionnelle: mise en evidence de 3 types de branchements: cours, longs, cycliques. Preparation de polyesters lineaires par synthese en solution ou a partir de diacetates, reactions non adaptables industriellement sans modification des procedes; mise au point d'une technique de dosage de la reaction de saturation des produits industriels et etude des parametres influant sur cette reaction

Etude des proprietes electriques et structurales de deux series de composes a coordinat dmit : composes a etat d'oxydation fractionnaire (m(dmit)::(2))c::(x) et composes donneur-accepteur d(m(dmit)::(2))::(y) (avec m = zn,ni,pt,pd; c = nbu**(+)::(4) et asph**(+)::(4); d = ttf, tmttf, ttmttf, bedt-ttf et tmtsf; n dans (m(dmit)::(2))**(n-) etant egal a 2,1,x,0). Mise en evidence de la nature 2d des composes de la premiere serie et quasi 3d de ceux de la deuxieme; relations structure-conductivite. Mise en evicence de la supraconduction dans le cas du complexe ttf(ni(dmit)::(2))::(2), avec une temperature de transition de 1,62 k sous 7 kbar

[ES] Esta tesis doctoral presenta un estudio de compresores scroll con inyección de vapor (SCVI) para bombas de calor que operan en climas fríos o para aplicaciones de calentamiento de agua a alta temperatura. Para ello, se comparó experimentalmente un SCVI con un compresor de dos etapas de pistones (TSRC) trabajando con R-407C en condiciones extremas. La comparación se realizó en términos de eficiencias del compresor, capacidad, COP y rendimientos estacionales tanto para el modo calefacción como para el modo refrigeración. Los resultados proporcionan una idea general sobre el rango de aplicación de los compresores estudiados y sobre las diferencias en los rendimientos de los compresores. Sin embargo, se identificaron varias limitaciones en la caracterización de los compresores y en el análisis del ciclo. Esto motivó a profundizar en el estudio del ciclo de compresión de dos etapas y sus componentes. El siguiente paso fue realizar un análisis teórico de los ciclos de compresión de dos etapas para aplicaciones de calefacción, en donde se identificó a la presión intermedia y a la relación de inyección como los parámetros del sistema más influyentes sobre el COP. La presión intermedia se optimizó para dos configuraciones de inyección (tanque de separación y economizador) utilizando varios refrigerantes. Basándose en los resultados de la optimización, se propuso una correlación que permite obtener la presión intermedia óptima del ciclo, considerando la influencia del subenfriamiento a la salida del condensador. Además, se analizó la influencia del diseño de los componentes del sistema sobre el COP del ciclo. Posteriormente, el estudio se profundizó a nivel de componentes. El factor más crítico en el sistema es el rendimiento del compresor. Por lo tanto, el siguiente paso fue evaluar la influencia de varios sistemas de compresión con inyección de vapor sobre el COP. Se tomaron en cuenta tres tecnologías de compresores, un SCVI, un TSRC y un compresor scroll de dos etapas (TSSC). Estas tecnologías de compresores fueron caracterizadas y modeladas para estudiar su rendimiento. Para ello, se propuso una nueva metodología para caracterizar compresores scroll con inyección de vapor. Esta metodología permite evaluar el rendimiento del compresor independientemente del mecanismo de inyección que se utiliza en el ciclo. Se identificó una correlación lineal entre la relación de inyección de refrigerante y la relación de compresión intermedia. Esta correlación se utiliza para determinar el flujo másico de inyección en función de la presión intermedia. Posteriormente, se propuso un modelo semi-empírico de compresores scroll y una metodología para extender dicho modelo para compresores scroll con inyección de vapor. Los modelos fueron ajustados y validados usando datos experimentales de cuatro compresores scroll trabajando con R-290 y un SCVI trabajando con R-407C. Finalmente, se comparó un SCVI con dos compresores de dos etapas, un TSSC y un TSRC, trabajando en condiciones extremas. Se optimizó la relación de volúmenes de los compresores de dos etapas. Los resultados muestran que, en las condiciones nominales de funcionamiento (Te=-15 °C, Tc=50 °C), la relación de volúmenes óptima del TSSC es 0.58, y del TSRC es 0.57. El TSSC consigue un COP 6% mayor que el SCVI y un COP 11.7% mayor que el TSRC. Bajo un amplio rango de condiciones de operación, el SCVI presenta una mejor eficiencia y COP para relaciones de presión inferiores a 5. Para relaciones de presión más altas, el TSSC presenta mejor rendimiento y consigue una temperatura de descarga más baja. Se concluye que el SCVI es una solución fácil de implementar, desde el punto de vista del mecanizado, y que permite extender el mapa de trabajo de los compresores de una etapa. Sin embargo, los resultados muestran que la compresión en dos etapas consigue mejorar en mayor medida el COP del ciclo y la capacidad, con una mayor redu
[CA] Aquesta tesi doctoral presenta un estudi de compressors scroll amb injecció de vapor (SCVI) per a bombes de calor que operen en climes freds o per a aplicacions d'escalfament d'aigua a alta temperatura. Per a això, es va comparar experimentalment un SCVI amb un compressor de dues etapes de pistons (TSRC) treballant amb R-407C en condicions extremes. La comparació es va realitzar en termes d'eficiències del compressor, capacitat, COP i rendiments estacionals tant per al mode calefacció com per al mode refrigeració. Els resultats proporcionen una idea general sobre el rang d'aplicació dels compressors estudiats i sobre les diferències en els rendiments dels compressors. No obstant això, es van identificar diverses limitacions en la caracterització dels compressors i en l'anàlisi del cicle. Això va motivar a aprofundir en l'estudi del cicle de compressió de dues etapes i els seus components. El següent pas va ser realitzar una anàlisi teòrica dels cicles de compressió de dues etapes per a aplicacions de calefacció, on es va identificar la pressió intermèdia i la relació d'injecció com els paràmetres del sistema més influents sobre el COP. La pressió intermèdia es va optimitzar per a dues configuracions d'injecció (tanc de separació i economitzador) utilitzant diversos refrigerants. Basant-se en els resultats de l'optimització, es va proposar una correlació que permet obtindre la pressió intermèdia òptima del cicle, considerant la influència del subrefredament a l'eixida del condensador. A més, es va analitzar la influència del disseny dels components del sistema sobre el COP del cicle. Posteriorment, l'estudi es va aprofundir a nivell de components. El factor més crític en el sistema és el rendiment del compressor. Per tant, el següent pas va ser avaluar la influència de diversos sistemes de compressió amb injecció de vapor sobre el COP. Es van prendre en compte tres tecnologies de compressors, un SCVI, un TSRC i un compressor scroll de dues etapes (TSSC). Aquestes tecnologies de compressors van ser caracteritzades i modelades per a estudiar el seu rendiment. Per a això, es va proposar una nova metodologia per a caracteritzar compressors scroll amb injecció de vapor. Aquesta metodologia permet avaluar el rendiment del compressor independentment del mecanisme d'injecció que s'utilitza en el cicle. Es va identificar una correlació lineal entre la relació d'injecció de refrigerant i la relació de compressió intermèdia. Aquesta correlació s'utilitza per a determinar el flux màssic d'injecció en funció de la pressió intermèdia. Posteriorment, es va proposar un model semi-empíric de compressors scroll i una metodologia per a estendre aquest model per a compressors scroll amb injecció de vapor. Els models van ser ajustats i validats utilitzant dades experimentals de quatre compressors scroll treballant amb R-290 i un SCVI treballant amb R-407C. Finalment, es va comparar un SCVI amb dos compressors de dues etapes, un TSSC i un TSRC, treballant en condicions extremes. Es va optimitzar la relació de volums dels compressors de dues etapes. Els resultats mostren que, en les condicions nominals de funcionament (Te=-15 °C, Tc=50 °C), la relació de volums òptima del TSSC és 0.58, i del TSRC és 0.57. El TSSC aconsegueix un COP 6% major que el SCVI i un COP 11.7% major que el TSRC. Sota un ampli rang de condicions d'operació, el SCVI presenta una millor eficiència i COP per a relacions de pressió inferiors a 5. Per a relacions de pressió més altes, el TSSC presenta millor rendiment i aconsegueix una temperatura de descàrrega més baixa. Es conclou que el SCVI és una solució fàcil d'implementar, des del punt de vista del mecanitzat, i que permet estendre el mapa de treball dels compressors d'una etapa. No obstant això, els resultats mostren que la compressió en dues etapes aconsegueix millorar en major mesura el COP del cicle i la capacitat, amb una major reducció de la
[EN] This Ph.D. thesis presents a study of scroll compressors with vapor-injection (SCVI) for heat pumps operating in cold climates or in high-temperature water heating applications. To do so, firstly, an SCVI was experimentally compared with a two-stage reciprocating compressor (TSRC) working with R-407C under extreme conditions. The comparison was made in terms of compressor efficiencies, capacity, COP, and seasonal COP, both for heating and cooling modes. The results give a general idea about the application range of the studied compressors and the differences in the compressors' performance. Nevertheless, several restrictions in the compressors' characterization and the cycle analysis were identified. This motivated us to deepen in the study of the two-stage compression cycle and its components. The next step was performing a theoretical analysis of two-stage compression cycles for heating applications, where the intermediate pressure and the injection ratio were identified as the most influential system parameters on the COP. The intermediate pressure was optimized for two vapor-injection configurations (flash tank and economizer) using several refrigerants. Based on the optimization results, a correlation was proposed that allows obtaining the optimal intermediate pressure of the cycle, considering the influence of the subcooling at the condenser outlet. In addition, a theoretical analysis of the influence of the design of the system components on the COP of the cycle was performed. Once the thermodynamic analysis of the two-stage cycle was carried out, the study was deepened at the component level. The most critical factor in the system is the compressor performance. Hence, the next step was evaluating the influence of several compression systems with vapor-injection on the COP. Three compressor technologies were taken into account, an SCVI, a TSRC and a two-stage scroll compressor (TSSC). These compressor technologies were characterized and modeled in order to study their performance. To do so, a new methodology to characterize SCVI was proposed. This methodology allows evaluating the compressor performance independently of the injection mechanism used in the cycle. A linear correlation was identified between the refrigerant injection ratio and the intermediate compression ratio. This correlation is used to determine the injection mass flow as a function of the intermediate pressure. Then, a semi-empirical model of scroll compressors and a methodology to extend the model for scroll compressors with vapor-injection was proposed. The models were adjusted and validated using experimental data from four scroll compressors working with R-290 and an SCVI compressor working with R-407C. Finally, an SCVI was compared with two two-stage compressors, a TSSC, and a TSRC, working in extreme conditions. The displacement ratio of the two-stage compressors was optimized. Results show that, at the nominal operating conditions (Te=-15 °C, Tc=50 °C), the optimal displacement ratio of the TSSC is 0.58, and of the TSRC is 0.57. The TSSC achieves 6% larger COP than the SCVI and 11.7% larger COP than the TSRC. Under a wide range of operating conditions, the SCVI presents a better efficiency and COP for pressure ratios below 5. For higher-pressure ratios, the TSSC presents better performance and achieves lower discharge temperature. It is concluded that the SCVI is an easy solution to implement from the point of view of machining, which allows extending the working map of the single-stage compressors. However, the results show that the two-stage compression technology gets further improve the COP of the cycle and the capacity, with a greater reduction of the discharge temperature operating under extreme conditions.
I thank the financial support provided by the Secretaría de Educación Superior, Ciencia, Tecnología e Innovación (SENESCYT) of Ecuador, through the international scholarship program for postgraduate studies “Convocatoria Abierta 2013 Segunda Fase, Grant No 2015-AR37665”.
Tello Oquendo, FM. (2019). Study of scroll compressors with vapor-injection for heat pumps operating in cold climates or in high-temperature water heating applications [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/120473
TESIS

Les proprietes de transport (magnetoconductivite, effet hall, ondes de densite de charge, ondes de densite de spin, transitions supraconductrices) des oxydes metalliques et supraconducteurs quasi-bidimensionnels sont etudiees a basse temperature

Pour les projets de tunnels profonds; la prévision des températures naturelles au rocher est essentielle pour le choix des méthodes de perforation, de ventilation et de refroidissement. Une méthode numérique de prévision des températures a été développée à cet effet, à partir d'un logiciel 2D d'éléments finis. Les températures sont calculées dans un plan vertical du massif, à partir de l'équation fondamentale de la chaleur en conduction pure. La modélisation nécessite la connaissance de cinq paramètres de base que sont: le profil topographique, les températures de surface, la structure géologique, la conductivité anisotrope des roches et le flux géothermique profond. Une méthode de correction du profil topographique permet de prendre en compte la troisième dimension. Différents tests sont effectués sur un profil de montagne idéalisé, pour évaluer le poids des différents paramètres dans la modélisation. Le modèle est appliqué ensuite au massif comprenant le tunnel Maurienne-Ambin, dans le cadre du projet de ligne à grande vitesse entre Lyon et Turin. Une sonde de mesure des températures a été mise au point et utilisée dans les sondages de reconnaissance pour ce projet de tunnel profond (55km sous un recouvrement maximal de 2500m). Les forages nous permettent de déterminer la structure géologique, les valeurs de conductivité des roches et le flux géothermique de la région en appliquant la "méthode des intervalles". La température maximale calculée le long du tunnel est de 48,5°C. La confrontation entre les mesures de température dans les forages et la modélisation permet de valider les résultats, sauf dans les premières centaines de mètres du massif, où les circulations d'eau, qui ne sont pas prises en compte par notre modèle, modifient la distribution des températures.

The ion implantation process is a very precise, controllable, and reproducible method used to enhance material properties of finished components such as ball bearings. Essentially, the target material is bombarded by accelerated ions to form a thin alloyed layer in the substrate. As the ions deposit their kinetic energy in the target it begins to heat up. To prevent thermal distortion in the finished pieces the ion implantation is performed at dose levels (dependent on the ion fluence and time duration of implantation) to insure that the target pieces stay at relatively low temperatures. Consequently, the low temperature requirement for many applications limits the economic, and probably, the physical success of ion implantation. The purpose of this study was to show the applicability of using a two-dimensional computer code developed to model plasma disruptions and subsequent energy deposition on a fusion reactor first wall to calculate surface and bulk temperature information during ion implantation. In turn the code may assist researchers pursuing development of adequate cooling for target materials in an attempt to overcome the low temperature constraint. All data supported the hypotheses that the two-dimensional code previously developed for fusion reactor applications was adequate to model the ion implantation process.
Graduation date: 1992

碩士
國立臺灣科技大學
電機工程系
104
In this study, a novel forecasting method for the temperature is proposed. The proposed method combines a learning idea into the two-factor fuzzy time series model proposed in the literature [1]. The considered factors for temperature prediction are two factors, the values of temperature and the cloud density. The idea is that when more historical data are used, the accuracy of forecasting model may increase. It is assumed that the weather temperatures similar to past temperature histories. After the fuzzy time series for prediction was proposed, based on it, many researchers proposed different models used in many various fields. The important ingredients of fuzzy time series forecasting model are definition and partition of the universe of discourse, definition of fuzzy sets, establishment of fuzzy logical relationship and defuzzification. The proposed model combine the fuzzy time series with the method of classification of Logistic Regression (LR). The method of LR is to extract fuzzy logical relationships from historical data and can be regarded as a learning mechanism. From this study, it can be found that the method of LR can get more accuracy and stability than LVQ and another method in [1].

碩士
國立清華大學
物理學系
89
In general, the Ising model is a well-known model of ferromagnetism. Ising solve the model in one-dimension in 1925 eraly.But until in 1944 ,the partition function of the rectangular-lattice Ising model in two-demension with nearest-neighbor interaction in the absence of external magnetic field was derived by Onsager. The spontaneous magnetization of the model was first obtained by Osanger but he never publish his derivation. C.N. Yang was first to publish a detailed derivation of the spontaneous magnetization on the square lattice and the critical exponentβis 0.125 in 1952 .And then Yang suggests that C.H. Chang generalize the above calculation to the rectangular lattice and the result coincide with before .Therefore Chang noted that the exponentβ=0.125 does not change with varying the ratio of the vertical and the horizontal interactions.Maybe according to the same result , he speculate about all two-dimensional Ising models have the same critical exponents naturally. This is the interesting direction of study people are striving toward .However after a long time research, statistical physicists find regular plan lattices enable to exist exact solution ,but two-dimensional Ising model with non-planer lattice or in the external field is unsolved exactly. The low-temperature series expansions for the square lattice Ising model where the nearest-neighbor interaction is the same as the next-nearest-neighbor(cross-interacting) was first studied by Dalton and Wood in1969. They derived the low temperature series expansions of the spontaneous magnetization up to the 17th order .Their result is that 0.122<β<0.134, Lee and Lin extended the series to 24th order and found that 0.124<β<0.131 in1996. Because the generalized square(checkerboard) lattice with next-nearest neighbor interactions in the external magnetic field and this model can not be solved exactly, so we use a powerful method of low-temperature expansions to study the critical behavior of the Ising model .This method applies to any kind of Ising models, we imposed this method to calculate the models without exact solution, because the method of series expansion yields accurate estimate of the critical temperature and exponent. So we consider two dimensional Ising model with checkerboard(non-planer)lattice in the external magnetic field and want to check the valueβof this system is still remain certainly. I think this more general case is conducive to verify the value of universality in existence. The low-temperature series expansions for checkerboard lattice was studied by Shyu and Lin in 1997. He derived the low-temperature series expansions of spontaneous magnetization up to the 13th order and use the Pade approximation to estimate the critical exponent, he concluded that 0.126<β<0.151. In this thesis ,the main purpose of my research improves the order up to 19th and the universality hypothesis is further convinced .

Two-particle excitations, such as spin and charge excitations, play a key role in high-Tc cuprate superconductors (HTSC). Due to the antiferromagnetism of the parent compound the magnetic excitations are supposed to be directly related to the mechanism of superconductivity. In particular, the so-called resonance mode is a promising candidate for the pairing glue, a bosonic excitation mediating the electronic pairing. In addition, its interactions with itinerant electrons may be responsible for some of the observed properties of HTSC. Hence, getting to the bottom of the resonance mode is crucial for a deeper understanding of the cuprate materials . To analyze the corresponding two-particle correlation functions we develop in the present thesis a new, non-perturbative and parameter-free technique for T=0 which is based on the Variational Cluster Approach (VCA, an embedded cluster method for one-particle Green's functions). Guided by the spirit of the VCA we extract an effective electron-hole vertex from an isolated cluster and use a fully renormalized bubble susceptibility chi0 including the VCA one-particle propagators.Within our new approach, the magnetic excitations of HTSC are shown to be reproduced for the Hubbard model within the relevant strong-coupling regime. Exceptionally, the famous resonance mode occurring in the underdoped regime within the superconductivity-induced gap of spin-flip electron-hole excitations is obtained. Its intensity and hourglass dispersion are in good overall agreement with experiments. Furthermore, characteristic features such as the position in energy of the resonance mode and the difference of the imaginary part of the susceptibility in the superconducting and the normal states are in accord with Inelastic Neutron Scattering (INS) experiments. For the first time, a strongly-correlated parameter-free calculation revealed these salient magnetic properties supporting the S=1 magnetic exciton scenario for the resonance mode. Besides the INS data on magnetic properties further important new insights were gained recently via ARPES (Angle-Resolved Photoemission-Spectroscopy) and Raman experiments which disclosed a quite different doping dependence of the antinodal compared to the near-nodal gap. This thesis provides an approach to the Raman response similar to the magnetic case for inspecting this gap dichotomy. In agreement with experiments and one-particle data obtained in the VCA, we recover the antinodal gap decreasing and the near-nodal gap increasing as a function of doping. Hence, our results prove the Hubbard model to account for these salient gap features. In summary, we develop a two-particle cluster approach which is appropriate for the strongly-correlated regime and contains no free parameter. Our results obtained with this new approach combined with the phase diagram and the one-particle excitations obtained in the VCA strongly constitute a Hubbard model description of HTSC cuprate materials
Zwei-Teilchen Anregungen, darunter Spin und Ladungs Anregungen, sind von besonderer Bedeutung in Hoch-Tc Kuprat Supraleitern (HTSL). Aufgrund der antiferromagnetischen Phase bei niedrigen Dotierungen werden magnetische Anregungen direkt mit dem Mechanismus der Supraleitung in Verbindung gebracht. Gerade die sogenannte Resonanzmode ist ein vielversprechender Kandidat für den pairing glue, eine bosonische Anregung, welche die Paarung von Elektronen induziert. Weiterhin wird deren Wechselwirkung mit itineranten Elektronen verantwortlich gemacht für einige der beobachteten Eigenschaften der HTSL. Für ein tieferes Verständnis der Kuprate ist es daher unerlässlich, der Resonanzmode auf den Grund zu gehen. Um die entsprechenden Zwei-Teilchen Korrelationsfunktionen zu analysieren, entwickeln wir auf Basis des Variational Cluster Approach (VCA, eine Cluster Methode, um Ein-Teilchen Green Funktionen zu berechnen) in der vorliegenden Dissertation eine neue, nicht-perturbative und parameterfreie Technik für T=0. Im Sinne der VCA berechnen wir einen effektiven Elektron-Loch Vertex auf einem einzelnen Cluster und verwenden eine vollkommen renormierte Bubble Suszeptibilität chi0, welche die VCA Ein-Teilchen-Propagatoren beinhaltet. Mit Hilfe unserer neuen Technik können wir die magnetischen Anregungen der HTSL im Rahmen des Hubbard Modells in der stark korrellierten Phase reproduzieren. Als herausragendes Ergebnis erhalten wir die berühmte Resonanzmode im underdotierten Bereich innerhalb des von der Supraleitung induzierten Gaps der Spin-Flip Elektron-Loch Anregungen. Deren Intensität und Sanduhren-förmige Dispersion zeigen eine sehr gute Übereinstimmung mit den Experimenten. Weiterhin sind charakteristische Eigenschaften, wie die Energie der Resonanzmode oder die Differenz des Imaginärteils der Suszeptibilität in der supraleitenden und normalen Phase im Einklang mit Inelastischen Neutronenstreu (INS) Experimenten. Zum ersten Mal bringt eine stark-korrellierte und parameterfreie theoretische Rechnung diese besonderen magnetischen Eigenschaften hervor und bekräftigt damit die Erklärung der Resonanzmode als S=1 magnetisches Exziton. Neben den INS Resultaten zu magnetischen Eigenschaften wurden kürzlich weitere wichtige neue Erkenntnisse mittels ARPES (Winkelaufgelöste Photoemissionen Spektroskopie) und Raman Experimenten erhalten. Beide legten eine deutlich unterschiedliche Dotierungsabhängigkeit des anti-nodalen Gaps verglichen mit dem Gap nahe des nodalen Punktes offen. Im Rahmen dieser Dissertation wird eine der magnetischen Berechnung ähnliche Technik für den Raman Response benutzt, um dieses unterschiedliche Verhalten des Gaps zu untersuchen. Übereinstimmend mit den Experimenten und Ein-Teilchen Ergebnissen aus VCA Rechnungen bekommen wir ein Abfallen des anti-nodalen Gaps und Ansteigen des Gaps nahe dem nodalen Punkt als Funktion der Dotierung. Folglich zeigen unsere Ergebnisse, dass das Hubbard Modell diese besonderen Eigenschaften des Gaps beinhaltet. Zusammenfassend entwickeln wir eine Zwei-Teilchen Cluster Technik, welche für stark korrellierte Systeme geeignet ist und keine freien Parameter enthält. Unsere Ergebnisse mit dieser neuen Technik in Verbindung mit dem Phasendiagramm und Ein-Teilchen Anregungen der VCA Rechnungen bekräftigen mit Nachdruck eine Beschreibung der HTSL Kuprate auf Basis des Hubbard Modells

碩士
國立交通大學
電子物理學系
82
In this thesis we try to use vHs model to explain some physical properties of high temperature superconductor. First we study the chemical potential difference between normal state and superconducting state. It shows that the difference can be as large as 1meV. Compared with Fermi energy, 1meV is small and we can neglect its influence on gap and Tc. Nevertheless we notice that 1meV can be experimentally observed. We find that the tendency of the result of this model is the same as that of experiment. Second we use a phenomenological method to study the tunneling conductance. We assume the tunneling probability is proportional to the group velocity of electron and add a rectifying term. The conductance will display double peaks and asymmetry. And then the double peaks broaden to a broader peak. Hense it is difficult to point out the real value of energy gap. This may be the reason why the value 2gap/KTc of many experiments are scattered and why it does not conform to traditional BCS result.

The phase behaviour of shape-anisotropic particles is an emerging field of research that gives rise to various liquid crystal phases. In this thesis, we explore various equilibrium and non-equilibrium properties of shape-anisotropic particles by modelling them as soft repulsive spherocylinders (SRSs) and soft helical rods. In the first part, we introduce the two-temperature model to study the phase behaviour of scalar active SRS and soft helical rods. Most realisations of activity are vectorial in nature due to the force of self-propulsion. Recent studies have shown that many physical and biological processes, like phase separation in colloidal systems, chromatin organisation in the nucleus, are operated by the unequal sharing of energy by the constituents of the system. Such systems are classified as scalar active systems. In the simplest case, these systems can be modelled by connecting half the particles with a thermostat of higher temperature (labelled ‘hot’/‘active’) while maintaining temperature of the rest constant (labelled ‘cold’/‘passive’) at a lower value. The relative temperature difference between the two constituents of the system is a measure of activity. This model is known as two-temperature model that has been found to capture many essential properties of scalar activity. Starting from a homogeneous isotropic phase at a definite temperature, we show that this model leads to phase separation into hot and cold regions and induces liquid-crystal ordering of the cold particles while hot particles remain in the isotropic phase. In particular, we find that activity drives the cold particles through a phase transition to a more ordered state and the hot particles to a state of less order compared to the initial equilibrium state. Hence, the phase boundary of the isotropic-nematic transition shifts towards lower densities for cold particles and higher densities for the hot particles with respect to its equilibrium location. Remarkably, we find liquid crystalline phases for the aspect ratios [length(L)/diameter(D)] as low as L/D = 2, 3 which do not satisfy the minimum shape-anisotropy criteria that Onsager’s theory demands in equilibrium. Similar model we have employed in a system of soft helical particles of various intrinsic chiralities and found different liquid crystal ordering in these cases as well. The following nonequilibrium features emerge from our study: an enhancement of the temperature of half of the particles gives rise to LC ordering in the remaining half of the particles at any density. The hot and cold domains should not be viewed as bulk equilibrium phases with non-equilibrium behaviour only at the interfaces. By calculating the stress anisotropy and heat current, we find that the non-equilibrium behaviour is not restricted to the hot-cold interfaces but pervades the system as a whole, driving various ordering transitions in the cold zone. Thus, our study unravels various aspects of non-equilibrium scalar active rods in the framework of the two-temperature model. In the second part, we discuss the Two-phase thermodynamic (2PT) model for computing entropy, free energy, and other thermodynamic properties of various liquid crystal phases in equilibrium. In the 2PT method, the density of state (DoS) of the LC phases is decomposed into vibrational (solid) and diffusive (gas) components. The thermodynamic quantities are then calculated using harmonic oscillator approximations for the solid component, hard sphere approximations for the gas component, and the rigid rotor approximation for the rotational mode. In the 2PT method, the entropy of a definite state point is calculated from a single MD trajectory, which makes it advantageous for systems for which the analytical form of the equation of state is unknown (such as SRS). Our method can be used to calculate entropy and other thermodynamic quantities of different liquid crystal phases formed by the SRS system.
Inspire fellowship

L’ablation de cibles d’Al nanocristallines (taille moyenne des cristallites d = 3,1 et 6,2 nm) par impulsions laser ultrabrèves (200 fs) a été étudiée par l’entremise de si- mulations combinant la dynamique moléculaire et le modèle à deux températures (two- temperature model, TTM) pour des fluences absorbées allant de 100 à 1300 J/m2. Nos simulations emploient un potentiel d’interaction de type EAM et les propriétés électro- niques des cibles en lien avec le TTM sont représentées par un modèle réaliste possédant une forme distincte dans le solide monocristallin, le solide nanocristallin et le liquide. Nous avons considéré l’effet de la taille moyenne des cristallites de même que celui de la porosité et nous avons procédé à une comparaison directe avec des cibles mono- cristallines. Nous avons pu montrer que le seuil d’ablation des métaux nanocristallins est significativement plus bas, se situant à 400 J/m2 plutôt qu’à 600 J/m2 dans le cas des cibles monocristallines, l’écart étant principalement dû à l’onde mécanique plus im- portante présente lors de l’ablation. Leur seuil de spallation de la face arrière est aussi significativement plus bas de par la résistance à la tension plus faible (5,40 GPa contre 7,24 GPa) des cibles nanocristallines. Il est aussi apparu que les contraintes résiduelles accompagnant généralement l’ablation laser sont absentes lors de l’ablation de cibles d’aluminium nanocristallines puisque la croissance cristalline leur permet d’abaisser leur volume spécifique. Nos résultats indiquent aussi que le seuil de fusion des cibles nano- cristallines est réduit de façon marquée dans ces cibles ce qui s’explique par la plus faible énergie de cohésion inhérente à ces matériaux. Nos simulations permettent de montrer que les propriétés structurelles et électroniques propres aux métaux nanocristallins ont toutes deux un impact important sur l’ablation.
The ablation of nanocrystalline (mean crystallite size d = 3.1 and 6.2 nm) Al tar- gets by ultrashort (200 fs) laser pulses was studied using hybrid simulations combining molecular-dynamics and the two-temperature model (TTM) for a range of absorbed flu- ence of 100 to 1300 J/m2. Our simulations employ an EAM interatomic potential and the TTM-related electronic properties are modelled using three distinct functions to rep- resent the monocrystalline solid, the nanocrystalline solid, and the liquid in an accurate way. Comparison between targets displaying two mean grain sizes, porous targets, and monocrystalline targets are reported. This study showed a significantly reduced abla- tion threshold of 400 J/m2 instead of the 600 J/m2 obtained for the single crystals, the discrepancy being mainly accounted for by an increase in the magnitude of the pressure wave generated during ablation. The spallation threshold of the back side of the target is also reduced owing to a lower tensile strength (5.40 GPa against 7.24 GPa). This work also allowed to discover that residual stress generally associated with laser ablation is totally absent in nanocrystalline samples as crystal growth provides a mechanism for volume reduction near the melting temperature. Furthermore, our results demonstrate that the melting threshold shows an important decrease and the melting depth an im- portant increase in the nanocrystalline samples which can be explained by their lower cohesion energy. Our simulations shed light on the fact that a realistic modelling of both structural and electronic properties of the nanocrystalline target is important to produce a reliable representation of laser ablation.