Rozprawy doktorskie na temat „Two Dimensional Confined Geometry”

This thesis explores a variety of topics in two-dimensional arithmetic geometry, including the further development of I. Fesenko's adelic analysis and its relations with ramification theory, model-theoretic integration on valued fields, and Grothendieck duality on arithmetic surfaces. I. Fesenko's theories of integration and harmonic analysis for higher dimensional local fields are extended to an arbitrary valuation field F whose residue field is a local field; applications to local zeta integrals are considered. The integral is extended to F^n, where a linear change of variables formula is proved, yielding a translation-invariant integral on GL_n(F). Non-linear changes of variables and Fubini's theorem are then examined. An interesting example is presented in which imperfectness of a positive characteristic local field causes Fubini's theorem to unexpectedly fail. It is explained how the motivic integration theory of E. Hrushovski and D. Kazhdan can be modified to provide a model-theoretic approach to integration on two-dimensional local fields. The possible unification of this work with A. Abbes and T. Saito's ramification theory is explored. Relationships between Fubini's theorem, ramification theory, and Riemann-Hurwitz formulae are established in the setting of curves and surfaces over an algebraically closed field. A theory of residues for arithmetic surfaces is developed, and the reciprocity law around a point is established. The residue maps are used to explicitly construct the dualising sheaf of the surface.

Supersonic micronozzles operate in the unique viscosupersonic flow regime, characterized by large Mach numbers (M>1) and low Reynolds numbers (Re<1000). Past research has primarily focused on the design and analysis of converging-diverging de Laval nozzles; however, plug (i.e. centerbody) designs also have some promising characteristics that might make them amenable to microscale operation. In this study, the effects of plug geometry on plug micronozzle performance are examined for the Reynolds number range Re = 80-640 using 2D Navier-Stokes-based simulations. Nozzle plugs are shortened to reduce viscous losses via three techniques: one - truncation, two - the use of parabolic contours, and three - a geometric process involving scaling. Shortened nozzle are derived from a full length geometry designed for optimal isentropic performance. Expansion ratio (ε = 3.19 and 6.22) and shortened plug length (%L = 10-100%) are varied for the full Reynolds number range. The performance of plug nozzles is then compared to that of linear-walled nozzles for equal pressure ratios, Reynolds numbers, and expansion ratios. Linear-walled nozzle half-angle is optimized to to ensure plug nozzles are compared against the best-case linear-walled design. Results indicate that the full length plug nozzle delivers poor performance on the microscale, incurring excessive viscous losses. Plug performance is increased by shortening the nozzle plug, with the scaling technique providing the best performance. The benefit derived from reducing plug length depends upon the Reynolds number, with a 1-2% increase for high Reynolds numbers an up to 14% increase at the lowest Reynolds number examined. In comparison to Linear-walled nozzle, plug nozzles deliver superior performance when under-expanded, however, this trend reverses at low pressure ratios when the nozzles become over-expanded.

Since the discovery of conductance quantization within a nanostnucture, investigations have sought out causes to conductance fluctuations beyond the established plateaus. The focus of this work is to show the fundamental effects upon conductance due to longitudinal potentials and double quantum boxes when confined by hardwall boundaries. A theoretical model based upon a tight-binding recursive tureen's function methodology was modified to incorporate potential barrier variations. A qualitative evaluation, as well as, explanation of the model's results and limitations is discussed.
Department of Physics and Astronomy

This thesis presents numerical investigations of two-dimensional single-phase turbulent jets and bubbly mixing layers using Reynolds-Averaged Navier-Stokes (RANS) equations. The behavior of a turbulent jet confined in a channel depends on the Reynolds number and geometry of the channel which is given by the expansion ratio (channel width to jet thickness) and offset ratio (eccentricity of the jet entrance). Steady solutions to the RANS equations for a two-dimensional turbulent jet injected in the middle of a channel have been obtained. When no entrainment from the channel base is allowed, the flow is asymmetric for a wide range of expansion ratio at high Reynolds number. The jet attaches to one of the channel side walls. The attachment length increases linearly with the channel width for fixed value of Reynolds number. The attachment length is also found to be independent of the (turbulent) jet Reynolds number for fixed expansion ratio. By simulating half of the channel and imposing symmetry, we can construct a steady symmetric solution to the RANS equations. This implies that there are possibly two solutions to the steady RANS equations, one is symmetric but unstable, and the other solution is asymmetric (the jet attaches to one of the side walls) but stable. A symmetric solution is also obtained if entrainment from jet exit plane is permitted. Fearn et al. (Journal of Fluid Mechanics, vol. 121, 1990) studied the laminar problem, and showed that the flow asymmetry of a symmetric expansion arises at a symmetry-breaking bifurcation as the jet Reynolds number is increased from zero. In the present study the Reynolds number is high and the jet is turbulent. Therefore, a symmetry-breaking bifurcation parameter might be the level of entrainment or expansion ratio. The two-dimensional turbulent bubbly mixing layer, which is a multiphase problem, is investigated using RANS based models. Available experimental data show that the spreading rate of turbulent bubbly mixing layers is greater than that of the corresponding single phase flow. The presence of bubbles also increases the turbulence level. The global structure of the flow proved to be sensitive to the void fraction. The present RANS simulations predict this behavior, but different turbulence models give different spreading rates. There is a significant difference in turbulence kinetic energy between numerical predictions and experimental data. The models tested include k-ε, shear-stress transport (SST), and Reynolds stress transport (SSG) models. All tested turbulence models under predict the spreading rate of the bubbly mixing layer, even though they accurately predict the spreading rate for single phase flow. The best predictions are obtained by using SST model.
Master of Science

L’étude du déplacement par le courant électrique des parois de domaine magnétique a généré beaucoup d’intérêt depuis l’observation de leurs importantes vitesses de déplacement dans des multicouches ayant une asymétrie d’inversion verticale (SIA). Cet intérêt se justifie par leur fort potentiel pour de nouvelles applications à basse consommation d’énergie en mémoire cache ou mémoires centrale. L’inversion de symétrie (SIA) induit deux mécanismes dont l’action conjointe permet de déplacer efficacement les parois de domaines. Il s’agit d’une contribution énergétique chirale, appelée l’interaction Dzyaloshinskii-Moriya (DMI), et des couples de spin-orbite (SOT). Ce modèle reste incomplet vu qu’il n’explique pas plusieurs résultats expérimentaux. De plus, une contribution dissipative chirale appelée l’amortissement anisotrope, également induite par la SIA, a été proposée récemment et dont le rôle, sous courant, n’as pas encore été étudié.Le but de ce travail a été d’amener une connaissance détaillée des différentes interactions en jeu dans la dynamique des parois de domaine. Pour cela, j’ai étudié la propagation de parois sous courant dans une géométrie non colinéaire. Cette étude a été réalisée dans des systèmes ayant des SIA différentes (Pt/Co/Pt et Pt/Co/AlOx). Dans cette géométrie, j’ai observé l’asymétrie du déplacement qui illustre la compétition entre les contributions chirales d’énergie et d’amortissement dans des multicouches à faible SIA. Quant aux multicouches à forte SIA, l’asymétrie ne peut être expliquée par l’action conjointe de DMI et SOT même dans le régime à forte mobilité. Une des conséquences de ce type de déplacement est de contribuer à la déviation des bulles de skyrmion en mouvement. Nous avons appelé cet effet l’effet Hall extrinsèque des skyrmions.En mettant en évidence de nouveaux effets induits par SIA, les résultats de cette thèse contribuent à une meilleur compréhension des mécanismes intervenant dans les déplacements des parois et des skyrmions sous courant dans les multicouches magnétiques
The study of the current-induced magnetic domain walls motion has attracted a lot of interest since the report of their large velocities of motion in thin layers with structural inversion asymmetry (SIA). This interest comes from their high potential for low power consumption functionalities in cache and main memories applications. The SIA induces two mechanisms whose combined action allows to drive efficiently the domain walls. The two mechanisms are the chiral energy term, called the Dzyaloshinskii-Moriya interaction (DMI), and the spin-orbit torques (SOT). This model is still incomplete since it does not explain several experimental results. In addition, a chiral dissipation term called the chiral damping, also induced by SIA, has recently been proposed. However, its effect on current-induced domain wall motion has not been studied.The objective of this work was to bring a more detailed understanding of the interactions involved in the domain wall motion. To that end, I have studied the domain wall motion in a non-collinear geometry with respect to the current, in materials with different SIA (Pt/Co/Pt and Pt/Co/AlOx). This motion has been found to be asymmetric. It illustrates the interplay between chiral energy and chiral dissipation in current-induced domain wall motion in weak SIA materials. In large SIA materials, the DMI and SOT model, even in the flow regime of motion, cannot explain this asymmetry. I have also evidenced that the asymmetric non-collinear domain wall motion induces a well-defined deflection of the skyrmion bubbles. This is the first observation of the extrinsic skyrmion Hall effect.The results of this thesis contribute to the understanding of the physical mechanisms behind domain wall and skyrmion motion in ultrathin layers by evidencing supplementary effects from SIA

Convective heat transfer in a steady developing laminar flow in domains of complex geometry is investigated numerically using the finite difference method and orthogonal boundary-fitted coordinates. A Fortran code was developed and validated. The following cases involving complex flow domains were examined in detail; (1) The flow and heat transfer characteristics of Newtonian and power-law fluids in a two-dimensional duct fitted with transverse fins of triangular, semi-circular, and rectangular sections. The calculated velocity distribution is compared with experimental measurements made with a laser-Doppler anemometer. (2) The flow and heat transfer in a two-dimensional 90$ sp circ$ bend formed between two corrugated walls with variable corrugation angles. The results are compared with those obtained for a plain bend and a straight corrugated duct. (3) The flow and heat transfer under a submerged, confined slot jet impinging on planar, wavy, and semi-circular target surfaces. The containment surface was either perpendicular to the jet axis or inclined at a different angle to it.
The Nusselt number and friction factor dependence on the appropriately defined Reynolds number and domain geometry was examined; a number of correlations based on extensive numerical experiments are proposed for design calculations. The physical domains chosen in this study have potential applications in heat transfer augmentation and novel compact heat exchanger designs.

This thesis is a study of the effects of distributed roughness elements on a two-dimensional turbulent boundary layer. Measurements were taken on a total of ten rough wall configurations: four involving Gaussian spikes, and six with circular cylindrical posts. Rough wall flows are particularly suited to study with Laser Doppler Velocimetry (LDV) due to the fact that measurements are required near a solid surface, as well has in highly turbulent fluid. The LDV system used in this study is a fine resolution (~50 micron), three-component, fiber optic system. All mean velocities, Reynolds stresses, and triple products are measured. This study is unique in the range and variety of roughness cases for which data was taken.

The data show that the flow over a rough wall is characterized by high levels of turbulence near the roughness element peaks at the interface between low-speed, near-wall fluid and the higher speed fluid above. Behind an element, high-momentum fluid sweeps toward the wall, and there is a small region of ejection of low-momentum fluid. Cylindrical elements typically have larger magnitudes of turbulent stresses at their peaks compared to Gaussian elements. Trends in mean velocity profile parameters such as displacement height, roughness effect, and wake parameter are examined with respect to roughness element geometry and spacing.
Master of Science

In this study, the pre-failure behavior of a jointed rock block is modeled by an incrementally linear elastic anisotropic constitutive model (using an orthotropic model in 2D). In order to estimate the parameters in the constitutive model, a new technique was used in this dissertation. A 2D joint geometry generation code was used to generate finite size actual joint networks in 2D rock blocks. A 2D distinct element code (UDEC) was chosen as the stress analysis tool in this study. Fictitious joints were introduced into the rock blocks which contain finite size actual joints to discretize the problem domain into polygons. A number of stress analyses of rock blocks which contain only persistent joints were performed to estimate representative values for mechanical properties of fictitious joints to simulate the intact rock behavior. Finally, the rock blocks having different deterministic actual joint configurations with fictitious joints were subjected to 2D stress analysis under various stress paths using UDEC. Results of these stress analyses were used to estimate the deformational and strength properties of these rock blocks. Influence of joint geometry parameters on the mechanical properties of jointed rock blocks were found to be very significant. Plots are given to show how mechanical properties of rock blocks vary with joint intensity and joint size/block size for different joint orientations. These plots can also be used to estimate REV (Representative Elementary Volume) size and REV properties for rock masses. It is important to note that these REV property values depend on the chosen constitutive models for intact rock and joints. The concept of fracture tensor is reviewed at the 2D level. Relationships between the mechanical properties of jointed rock blocks and the fracture tensor parameters (its first invariant and components) are established. These relationships can be used to estimate the parameters of the chosen constitutive model for the rock block. This constitutive model has captured both scale dependent and anisotropic behaviors of rock masses. The possibility of obtaining the equivalent continuum properties (REV properties) of jointed rock blocks is explored by using the aforementioned relationships. (Abstract shortened by UMI.)

In this thesis, I numerically simulate the flow past a 180 degree sharp bend. The main objective of this research is to characterize the influences of the bend geometry on the flow regimes when Reynolds number (Re) is varied. Reynolds number and the opening ratio () (the definition of is defined in section 4.1.1) of the bend are the control parameters which are varied to perform the parametric study. For the first part of our research, I focus on the flow past a twodimensional 180 sharp bend. An extensive parametric study on the transitions of the flow regimes by varying the values of Re and is performed. The values of Re and are in the ranges of (0...2500] and [0.1...10], respectively. As Reynolds number is increased, I find a laminar flow, then a flow with a first recirculation attached the inside boundary, then a flow with a second recirculation attached to the top boundary. The onset of the unsteadiness occurs through instability of the main stream and the vortex shedding starts from the inside boundary. For < 0.3, the flow is characterised by the dynamics of the jet flow near the very narrow turning part. For 0.3, the flow exhibits strong similarities with the flow behind an obstacle placed in a channel. For the second part of our work, I focus on the flow past a threedimensional 180 sharp bend. Simulations with periodic conditions are performed for selected Re and in order to determine the validity of the 2D assumptions. The results show that two-dimensional dynamics can predict the features of three-dimensional flow in steady flow regimes, even for unsteady flow regimes to some extent. Simulations on the more realistic situations of a three-dimensional bend with walls are carried out as well. The results show that flow is symmetric to the center of the bend at low Re along spanwise direction. As Re increases, the influences of Dean flow on the mainstream flow are obvious. Near-wall quasi-symmetric shedding is presented in unsteady flow regimes as well. The unsteadiness is first originated from the shear layer between the first recirculation and the Dean flow region.

Cette thèse est consacrée à la description de la physique à une particule ainsi qu'à celle de fluides quantiques bosoniques dans des systèmes topologiques. Les deux premiers chapitres sont introductifs. Dans le premier, nous introduisons des éléments de théorie des bandes et les quantités géométriques et topologiques associées : tenseur métrique quantique, courbure de Berry, nombre de Chern. Nous discutons différents modèles et réalisations expérimentales donnant lieu à des effets topologiques. Dans le second chapitre, nous introduisons les condensats de Bose-Einstein ainsi que les excitons-polaritons de cavité.La première partie des résultats originaux discute des phénomènes topologiques à une particule dans des réseaux en nid d'abeilles. Cela permet de comparer deux modèles théoriques qui mènent à l'effet Hall quantique anormal pour les électrons et les photons dû à la présence d'un couplage spin-orbite et d'un champ Zeeman. Nous étudions aussi l'effet Hall quantique de vallée photonique à l'interface entre deux réseaux de cavités avec potentiels alternés opposés.Dans une seconde partie, nous discutons de nouveaux effets qui émergent due à la présence d'un fluide quantique interagissant décrit par l’équation de Gross-Pitaevskii dans ces systèmes. Premièrement, il est montré que les interactions spin anisotropes donnent lieu à des transitions topologiques gouvernées par la densité de particules pour les excitations élémentaires d’un condensat spineur d’exciton-polaritons.Ensuite, nous montrons que les tourbillons quantifiés d'un condensat scalaire dans un système avec effet Hall quantique de vallée, manifestent une propagation chirale le long de l'interface contrairement aux paquets d'ondes linéaires. La direction de propagation de ces derniers est donnée par leur sens de rotation donnant lieu à un transport de pseudospin de vallée protégé topologiquement, analogue à l’effet Hall quantique de spin.Enfin, revenant aux effets géométriques linéaires, nous nous sommes concentrés sur l’effet Hall anormal. Dans ce contexte, nous présentons une correction non-adiabatique aux équations semi-classiques décrivant le mouvement d’un paquet d’ondes qui s’exprime en termes du tenseur géométrique quantique. Nous proposons un protocole expérimental pour mesurer cette quantité dans des systèmes photonique radiatifs
This thesis is dedicated to the description of both single-particle and bosonic quantum fluid Physics in topological systems. After introductory chapters on these subjects, I first discuss single-particle topological phenomena in honeycomb lattices. This allows to compare two theoretical models leading to quantum anomalous Hall effect for electrons and photons and to discuss the photonic quantum valley Hall effect at the interface between opposite staggered cavity lattices.In a second part, I present some phenomena which emerge due to the interplay of the linear topological effects with the presence of interacting bosonic quantum fluid described by mean-field Gross-Pitaevskii equation. First, I show that the spin-anisotropic interactions lead to density-driven topological transitions for elementary excitations of a condensate loaded in the polariton quantum anomalous Hall model (thermal equilibrium and out-of-equilibrium quasi-resonant excitation configurations). Then, I show that the vortex excitations of a scalar condensate in a quantum valley Hall system, contrary to linear wavepackets, can exhibit a robust chiral propagation along the interface, with direction given by their winding in real space, leading to an analog of quantum spin Hall effect for these non-linear excitations. Finally, coming back to linear geometrical effects, I will focus on the anomalous Hall effect exhibited by an accelerated wavepacket in a two-band system. In this context, I present a non-adiabatic correction to the known semiclassical equations of motion which can be expressed in terms of the quantum geometric tensor elements. We also propose a protocol to directly measure the tensor components in radiative photonic systems

Background. Three-dimensional echocardiography (3DE) enables a comprehensive, accurate and reproducible quantification of cardiac chamber size and function without any geometric assumption about their shape. Superior accuracy and reproducibility of 3DE over stabdard two-dimensional (2DE) approach for cardiac chamber volume measurements in comparison to cardiac magnetic resonance (CMR) has been well documented in a number of studies. Both the European Association of Cardiovascular Imaging and the American Society of Echocardiography recommend 3DE, rather than 2DE, for routine clinical assessment of cardiac chamber volumes. However, both Societes also acknowledge that the application of 3DE into routine clinical practice has been hindered by the limited availability of reference values, and particularly the lack of gender- and anthropometric-based analysis. Therefore, identification of reference values for cardiac chamber size, geometry and function has become a prerequisite for the routine clinical application of quantitative 3DE. Research Project Single-centre, prospective, observational cohort study aimed to: (i). comprehensively analyze the four cardiac chamber geometry and function using state-of-the-art 3DE equipment in a large cohort of healthy volunteers; (ii). assess the effects of age, body size and gender on these parameters; and (iii). compare the values measured using 3DE with those obtained by conventional echocardiography in the same subjects and with other cohorts of healthy subjects from published 3DE studies. Methods. 263 healthy volunteers (43±14 years, range 18-75; 58% women) whose data sets have been acquired from October 2011 to July 2013 using a commercially available 3D echo scanner (Vivid E9, GE Vingmed, Horten, NO) equipped with 4V matrix array probe. Data sets were analyzed with different commercially available (EchoPac BT 12, GEVingmed Horten, NO; 4D RV function, TomTec Imaging system, Unterschleissheim, D ) and prototype (EchoPac BT 13, GEVingmed Horten, NO; 4D LA Tomtec Imaging systems, Unterschleissheim, D) analysis softwares. The study was approved by the University of Padua Ethics Committee (protocol # 2380 P approved on 06/10/2011) and signed informed consent has been obtained in all volunteers before the screening for eligibility in the study. Results Study #1: Analysis of left ventricular (LV) size, geometry and function. In 226 consecutive healthy volunteers (125 women, aged 18-76 years), we performed a comprehensive 3DE analysis of LV parameters and compared them with values obtained by conventional echocardiography. Upper reference values (mean+2 standard deviatons) for 3D LV end-diastolic (EDV) and end-systolic (ESV) volumes were 85 ml/m2 and 34 ml/m2 in men, and 72 ml/m2 and 28 ml/m2 in women, respectively. Indexing LV volumes by body surface area did not eliminate gender differences. Lower reference values (mean-2 standard deviations) for ejection fraction (EF) were 54% in men and 57% in women, while for stroke volume (SV) were 25 ml/m2 and 24 ml/m2, respectively. Upper reference values for LV mass were 97 g/m2 in men and 90 g/m2 in women, while for end-diastolic sphericity index were 0.49 and 0.48, respectively. Significant age-dependency of LV parameters was identified and reported across age groups. 3DE LV volumes were larger, EF was similar, SV and mass were significantly smaller in comparison with the corresponding values obtained by conventional echocardiography. Study #2: Analysis of right ventricular (RV) size and function. RV volumes, SV and EF were measured by 3DE in 540 healthy adult volunteers, prospectively enrolled, evenly distributed across age and gender. The relation of age, gender and body size parameters with RV volumes and EF were investigated using bivariate and multiple linear regressions. Analysis was feasible in 507 (94%) subjects (260 women, age 45±16 years, range 18-90). Age, gender, height and weight significantly influenced RV volumes and EF. Gender effect was significant (p<0.01), with RV volumes larger and EF smaller in men than in women. Older age was associated with smaller volumes (EDV, -5 ml/decade; ESV, -3 ml/decade; SV, -2 ml/decade), and higher EF (+1%/decade). Inclusion of body size parameters in the statistical models resulted in improved overall explained variance for volumes (EDV, R2=0.43; ESV, R2=0.35; SV, R2=0.30), while EF was unaffected. Ratiometric and allometric indexing for age, gender and body size resulted in no significant residual correlation between RV geometry measures and height or weight. Study #3: Analysis left atrial size and function. 244 healthy volunteers (43±14 years, range 18-75; 58% women) underwent 3DE and 2DE to measure maximal (Vmax), minimal (Vmin) and preA (VpreA) LA volumes to calculate total, passive and active LA emptying volumes (TotEV, PassEV, ActEV) and fractions (TotEmptFr, PassEmptFr, ActEemptFr). Feasibility of 3DE and 2DE LA volumes was 91% and 96% (p=0.59 ). 3DE LA volumes were larger than 2DE ones (Vmax: 48±11 ml vs. 43±11 ml; Vmin: 18±5 vs. 14±6, respectively, p<0.001). LA TotEmptFr (61±6% vs. 68±9%) and ActEmptFr (30±7% vs. 47±10%) were lower by 3DE than 2DE (p<0.001), whereas PassEmptFr (44±10% vs. 41±11%) was higher by 3DE than 2DE (p= 0.002). 3DE LA volumes indexed by body surface area were similar in both genders and increased with ageing (p=0.002). Study #4: Analysis of right atrial (RA) size and function. 200 healthy volunteers (43±15 years; 44% men) underwent 2DE and 3DE to measure maximal (Vmax), minimal (Vmin) and preA (VpreA) volumes to derive total (TotEV), passive (PassEV) and true (TrueEV) emptying volumes and emptying fractions (TotEmptFr, PassEmptFr, TrueEmptFr). 3DE volumes (Vmax, 52±15 ml vs 41±14 ml, p<0.0001), EVs (TotSV, 33±10 ml vs. 24±9 ml, p<0.0001) and EmptFrs (TotEmptFr, 63±9% vs. 58±9%, p<0.0001) were larger than 2DE ones. Indexed 3D RA volumes were significantly larger in men than in women. Aging was associated with a significant decrease in passive RA function (PassEV, r= -0.26; PassEmptFr, r= -0.38; all p<0.0001) and an increase in active RA function (TrueEV, r= 0.25; p<0.0001; and TrueEmptFr, r= 0.15; p= 0.035) in order to maintain TotEV (r= -0.14, p= 0.05). Conclusions The present research project provides a comprehensive quantitative analysis of the four cardiac chamber geometry and function using 3DE in a relatively large cohort of Caucasian healthy volunteers with a wide age range. The main results can be summarized as follows: (i). Cardiac chamber quantification with 3DE is feasible and reproducible; (ii) Reference values for cardiac chamber size and function by 3DE were found to be significantly different from those obtained with conventional echocardiography, highlighting the importance of applying method-specific reference values for a reliable identification of remodeling and/or dysfunction of cardiac chambers; (iii). Cardiac chamber parameters measured by 3DE showed excellent reproducibility, and were more robust than 2DE indices at repeated measurements; (iii). Most parameters describing cardiac chamber size should be defined according to age and gender, since indexing them only for BSA does not account for all the physiologic variations in geometry and function. Availability of reference values and age- and gender-specific cut-off values should facilitate the implementation of 3DE to identify cardiac chamber remodelling and dysfunction in both clinical routine and research.
Premessa. L’ecocardiografia tridimensionale (3DE) permette una completa, accurata e riproducibile valutazione quantitativa delle dimensioni e della funzione delle camere cardiache prescindendo da qualsiasi assunzione geometrica sulla loro forma. Numerosi studi di confronto con la risonanza magnetica nucleare (RMN) hanno dimostrato la maggiore accuratezza e riproducibilità della misura dei volumi delle camere cardiache con 3DE rispetto alla ecocardiografia bidimensionale convenzionale (2DE). Sia la European Association of Cardiovascular Imaging che l’American Society of Echocardiography raccomandano la 3DE, piuttosto che la 2DE, per la misura dei volumi delle camere cardiache. Tuttavia, entrambe le Società riconoscono anche il fatto che l’applicazione del 3DE nella routine clinica è stata penalizzata dalla mancanza di valori di riferimento e, in particolare, dalla mancanza di valori di riferimento specifici per i due sessi e normalizzati per i dati antropometrici. Pertanto, l’identificazione di valori di riferimento per le dimensioni, la geometria e la funzione delle camera cardiache è diventato un prerequisito per l’applicazione clinica routinaria della 3DE quantitativa. Il progetto di ricerca. Abbiamo pianificato uno studio osservazionale, di coorte, prospettico, monocentrico con l’obiettivo di: (i). Analizzare in maniera comprensiva la geometria e la funzione delle 4 camere cardiache in un ampia cohorte di volontari sani utilizzando ecografi allo stato dell’arte; (ii). Valutare gli effetti dell’età, delle dimensioni corporee e del sesso su questi parametri; e (iii). Confrontare le misure così ottenute con quelle calcolate con ecocardiografia convenzionale nello stesso soggetto ed con quelle 3DE pubblicate in altre coorti di soggetti sani. Metodi. 263 volontari sani (43±14 anni, range 18-75; 58% donne) i cui data set sono stati acquisiti tra Ottobre 2011 e Luglio 2013 utilizzando un ecografo 3DE disponibile in commercio (Vivid E9, GE Vingmed, Horten, NO) equipaggiato con una sonda a matrice 4V. I data set così acquisiti sono stati elaborate a posteriori utilizzando sia software di analisi disponibili in commercio (EchoPac BT 12, GEVingmed Horten, NO; 4D RV function, TomTec Imaging system, Unterschleissheim, D ) che softwares prototipali (EchoPac BT 13, GEVingmed Horten, NO; 4D LA Tomtec Imaging systems, Unterschleissheim, D). Il progetto di ricerca è stato approvato dal comitato etico dell’Università di Padova (protocollo # 2380 P approvato il 06/10/2011) e tutti i soggetti arruolati hanno fornito un consenso scritto prima della valutazione clinica per l’eligibilità allo studio. Risultati Studio #1: Analisi delle dimensioni, della geometria e della funzione del ventricolo sinistro (VS). Abbiamo eseguito un’analisi completa dei parametric 3DE del VS e li abbiamo confrontati con gli analoghi parametrii ottenuti con ecocardiografia convenzionale in 226 volontari sani consecutivi (125 donne, età compresa tra 18-76 anni). I limiti superiori dei valori di riferimento (media+2DS) per i volumi telediastolico e telesistolico del VS sono risultati 85 ml/m2 e 34 ml/m2 nei maschi, and 72 ml/m2 and 28 ml/m2 nelle femmine, rispettivamente. L’indicizzazione dei volume del VS per la superficie corporea non ha eliminato la differenza tra maschi e femmine. I limiti inferiori dei valori di riferimento (media-2Ds) per la frazione d’eiezione sono risultati 54% nei maschi e 57% nelle femmine, mentre per la gittata sistolica sono risultati 25 ml/m2 e 24 ml/m2, rispettivamente. I limiti superiori dei valori di riferimento per la massa ventricolare sinistra sono risultati 97 g/m2 nei maschi and 90 g/m2 nelle femmine, mentre quelli per la sfericità diastolica sono risultati 0.49 e 0.48, rispettivamente. Abbiamo inoltre identificato e descritto (differenziando i valori di riferimento per gruppi di età) una significativa variazione dei parametri del VS con l’età. Con il 3DE, i volumi erano più grandi, la frazione d’eiezione era simile, la gittata sistolica e la massa del VS erano più piccole degli analoghi parametri calcolati con ecocardiografia convenzionale Studio #2: Analisi delle dimensioni e della funzione del ventricolo destro (VD). I volumi del VD (tele-diastolico, VTD; tele-sistolico, VTS), la gitatta sistolica (GS) e la frazione d’eiezione (FE) del VD sono stati misurati con 3DE in 540 volontari sani adulti, arruolati in maniera prospettica, e distribuiti equamente relativamente alle classi di età ed al sesso. Le relazioni di questi parametri con l’età, il sesso e le dimensioni corporee dei soggetti arruolati sono state analizzate utilizzando regression lineari bi- e multi-variate. L’analisi dei data set venne effettuata con successo in 507 (94%) soggetti (260 donne, età 45±16 anni, età compresa tra 18 e 90 anni). Età, sesso, peso corporeo ed altezza hanno dimostrato influenze significative sui volume e sulla FE del VD. L’effetto del sesso era altrettanto significativo (p<0.01), I volumi del VD erano più piccoli e la FE era più alta nelle donne rispetto aglii uomini. L’incremento dell’età era associate a volumi VD più piccoli (VTD, -5 ml/decade; VTS, -3 ml/decade; SV, -2 ml/decade), e ad FE più alta (+1%/decade). L’inclusione delle dimensioni corporee nei modelli statistici aumentò significativamente la spiegazione della varianza dei volumi (VTD, R2=0.43; VTS, R2=0.35; SV, R2=0.30), mentre non aveva alcun effetto sulla FE. Sia l’utilizzo di modelli ratiometrici che allometrici per indicizzare per età sesso, e dimensioni corporee determine l’eliminazione di ulteriori residue correlazioni dei parametri del VD con l’altezza e il peso dei soggetti studiati. Studio #3: Analisi delle dimensioni e della funzione dell’atrio sinistro (AS). Abbiamo sottoposto 244 volontari sani (43±14 anni, età compresa tra 18-75; 58% donne) a 3DE e 2DE per misurare i volumi massimo (Vmax), minimo (Vmin) e preA (VpreA) dell’AS per poter calcolare i volumi di svuotamente dell’AS totale, passivo ed attivo (TotEV, PassEV, ActEV) e le relative frazioni di svuotamento (TotEmptFr, PassEmptFr, ActEemptFr). La fattibilità dei volume dell’AS con 3DE e con 2DE fu 91% e 96% (p=0.59 ). I volumi dell’AS misurati con 3DE erano più grandi di quelli calcolati con 2DE (Vmax: 48±11 ml vs. 43±11 ml; Vmin: 18±5 vs. 14±6, rispettivamente, p<0.001). La TotEmptFr (61±6% vs. 68±9%) e la ActEmptFr (30±7% vs. 47±10%) erano più basse al 3DE che al 2DE (p<0.001), mentre la PassEmptFr (44±10% vs. 41±11%) era maggiore con 3DE che con 2DE (p= 0.002). I volume dell’AS al 3DE indicizzati per la superficie corporea erano simili nei maschi e nelle femmine ed aumentavano progressivamente con l’età (p=0.002). Studio #4: Analisi delle dimensioni e della funzione dell’atrio destro (AD). Abbiamo sottoposto 200 volontari sani (43±15 anni; 44% maschi) a 2DE e 3DE per misurare I volume dell’AD massimo (Vmax), minimo (Vmin) e preA (VpreA) per calcolare volume di svuotamento totale (TotEV), passivo (PassEV) and attivo (TrueEV) and le rispettive frazioni di svuotamento (TotEmptFr, PassEmptFr, TrueEmptFr). Al 3DE i volumi (Vmax, 52±15 ml vs 41±14 ml, p<0.0001), i volumi di svuotamento (TotEV, 33±10 ml vs. 24±9 ml, p<0.0001) e laTotEmptFr, 63±9% vs. 58±9%, p<0.0001) dell’AD erano significativamente maggiori che al 2DE. I volumi 3D dell’AD indicizzati per la superficie corporea erano significativamente più grandi nei maschi che nelle femmine. L’invecchiamento fisiologico era associato ad una significativa riduzione della funzione passiva dell’AD (PassEV, r= -0.26; PassEmptFr, r= -0.38; all p<0.0001) e ad un significativo aumento della funzione attiva (TrueEV, r= 0.25; p<0.0001; and TrueEmptFr, r= 0.15; p= 0.035) per poter mantenere costante il volume di svuotamento (TotEV, r= -0.14, p= 0.05). Conclusioni Questo progetto di ricerca fornisce un’analisi quantitative completa della geometria e della funzione delle quattro camere cardiache utilizzando 3DE in un gruppo relativamente ampio di volontari sani di razza caucasica con un relativamente ampio range di età. I risultati principali possono essere riassunti in: (i). L’analisi quantitativa della geometria e della funzione delle camere cardiache con 3DE è fattibile e riproducibile; (ii) I valori di riferimento per le dimensioni delle camere cardiache misurati con 3DE sono significativamente più grandi di quelli calcolati con 2DE, sottolineando ancora una volta l’importanza di applicare valori di riferimento metodica-specifici per identificare il rimodellamento o la disfunzione delle camere cardiache in maniera affidabile; (iii). I parametri di geometria e funzione delle camere cardiache misurati con 3DE hanno mostrato una buona riproducibilità e si sono dimostrati più robusti di quelli calcolati con 2DE all’analisi test/re-test; (iv). La maggior parte dei parametri che descrivono le dimensioni delle camere cardiache dovrebbero essere definiti in base all’età ed al sesso poiché la semplice indicizzazione per la superficie corporea non riesce a tener conto di tutte le loro variazioni fisiologiche. La disponibilità degli intervalli di riferimento e dei limiti superiori ed inferiori di normalità specifici per classi di età e per sesso dovrebbe facilitare l’implementazione del 3DE per identificare il rimodellamento e la disfunzione delle camere cardiache sia nella routine clinica che a scopo di ricerca.

A finalidade principal deste trabalho é o da obtenção de soluções numéricas de movimento de carga espacial livre em que as grandezas pertinentes dependem de mais de uma coordenada espacial (casos não unidimensionais). Mais especificamente, os problemas estudados versam sobre casos em que um eletródio plano a um dado potencial emite carga não uniformemente ao longo de sua extensão e procura-se obter a deformação das linhas de campo daí resultantes, no espaço até um outro eletródio aterrado disposto paralelamente ao primeiro. Um método baseado em soluções tentativas bem como um outro global usando a \"transformação hodográfica\" recentemente formulada por Budd e Wheeler são apresentados. E também realizado um estudo breve sobre a validade da muito empregada \"suposição de Deutsch\"
The aim of the present work is to obtain numerical solutions of free space charge motion in cases in which the pertinent quantites depend on more than one space coordinate (non uni-dimensional cases). More specifically, the problems under concern here are those in which a plane electrode, at a constant potential, emit charge in a non-uniform way along them and the resultant deformation of the field lines, in the space between it and another plane grounded electrode parallelly disposed, is looked for. A method based on guessed solutions and also a global one using the hodographic transformation recently developed by Budd and Wheeler are presented. A brief study of the validity of the often employed \"Deutsch assumption\" is also carried out

Les propriétés géométriques des phénomènes critiques ont généré un intérêt croissant en physique théorique ainsi qu'en mathématiques au cours des trente dernières années. Les systèmes de percolation sont l'exemple par excellence de tels phénomènes géométriques, où la transition de phase est caractérisée par le comportement de degrés de liberté non-locaux, les amas de percolation. Au point critique, ces amas sont des exemples d'objets aléatoires dont la mesure est invariante conforme, c'est à dire invariante sous tout changement d'échelle local. Nous ne savons en général pas caractériser complètement ces amas, ni même pour le modèle le plus simple de la percolation pure. En deux dimensions, la présence de la symétrie conforme a des conséquences particulièrement importantes. Dans cette thèse nous examinons les implications de cette symétrie sur les propriétés universelles des systèmes critiques bidimensionnels, en utilisant une approche dite de bootstrap conforme. La première partie détaille les implications générales de l'invariance conforme, en examinant ses conséquences sur les fonctions de corrélation. Sont considérés en particulier les effets induits par une topologie de tore, ce qui est appliqué dans la deuxième partie de la thèse à l'étude de modèle statistiques particuliers. Nous discutons également les propriétés analytiques des fonctions de corrélation et présentons des résultats sur des questions techniques liées à l'implémentation de méthodes numériques de bootsrap conforme en deux dimensions. La seconde partie est dédiée à l'étude de deux familles particulières de modèles critiques de percolation avec des corrélations de longue portée : le modèle d'amas aléatoires de Potts à Ǫ états, et un modèle de percolation de surfaces aléatoires. Nous explorons les propriétés percolatoires de ces modèles en étudiant les propriétés de connectivité des amas, c'est à dire les probabilités que des points appartiennent au même amas. Nous avons réalisé que les connectivités sur le tore représentent des observables très intéressantes. En les décrivant comme fonction de corrélation de champs quantiques dans une théorie des champs conforme, nous obtenons de nouveaux résultats sur les classes d'universalité de ces modèles
The geometric properties of critical phenomena have generated an increasing interest in theoretical physics and mathematics over the last thirty years. Percolation-type systems are a paradigm of such geometric phenomena, their phase transition being characterised by the behaviour of non-local degrees of freedom: the percolation clusters. At criticality, such clusters are examples of random objects with a conformally invariant measure, namely invariant under all local rescalings. Even in the simplest percolation model --pure percolation, we do not know how to fully characterise these clusters. In two dimensions, the presence of conformal symmetry has especially important implications. In this thesis we investigate the consequences of this symmetry on the universal properties of two-dimensional critical statistical models, by using a conformal bootstrap approach. The first part details the general implications of conformal invariance, by examining its consequences on correlation functions. Are addressed in particular the effects induced by the torus topology, applied in the second part to the study of specific statistical models. We also examine the analytic properties of correlation functions and present results on technical questions related to the implementation of numerical conformal bootstrap methods in two dimensions. The second part is devoted to the study of two specific families of critical long-range correlated percolation models: the random cluster Q-state Potts model and the percolation of random surfaces. We investigate the percolative properties of these models by studying the clusters connectivity properties, namely the probability that points belong to the same cluster. We find that the connectivities on a torus represent particularly interesting observables. By describing them as correlation functions of quantum fields in a conformal field theory, we obtain new results on the universality classes of these models

Thesis (M.S. in Computer Science)--Naval Postgraduate School, September 2007.
Thesis Advisor(s): Kölsch, Mathias ; Squire, Kevin. "September 2007." Description based on title screen as viewed on October 24, 2007. Includes bibliographical references (p. 169-171). Also available in print.

Cette thèse est axée sur la coopération entre l'analyse d'images et la géométrie algorithmique sur la base des diagrammes de Voronoi et de Delaunay. Le propos de l'analyse d'images est la description du contenu d'une image, en vue de son interprétation et d'une prise de décision. La géométrie algorithmique quant à elle consiste à trouver des algorithmes efficaces en vue de résoudre des problèmes a caractère géométrique. Nous nous intéresserons ici au problème de représentation des images par des partitionnements plus ou moins complexes, adaptes ou non au contenu informatif des images. Parmi ces partitionnements, nous développerons plus particulièrement celui en régions de Voronoi. Nous aborderons ensuite le problème du codage de formes tridimensionnelles par leur squelette qui est lié aux diagramme de Voronoi généralisé 3D. Nous montrerons enfin comment utiliser les partitionnements en région de Voronoi dans un contexte pyramidal contrôlé par un réseau de Hopfield en vue de la segmentation, et dans un contexte markovien en vue de trouver un partitionnement répondant a une certaine optimalité

Two dimensional magnetic recording (TDMR) achieves high areal densities by reducing the size of a bit comparable to the size of the magnetic grains resulting in two dimensional (2D) inter symbol interference (ISI) and very high media noise. Therefore, it is critical to handle the media noise along with the 2D ISI detection. In this paper, we tune the generalized belief propagation (GBP) algorithm to handle the media noise seen in TDMR. We also provide an intuition into the nature of hard decisions provided by the GBP algorithm. The performance of the GBP algorithm is evaluated over a Voronoi based TDMR channel model where the soft outputs from the GBP algorithm are used by a belief propagation (BP) algorithm to decode low-density parity check (LDPC) codes.

Beaucoup de programmes de visualisation, de planification de trajectoire, etc. , utilisent intensivement des calculs de visibilité. Si ces calculs de visibilité ne constituent qu'une petite partie de ces programmes, ils sont en revanche responsables d'une grande partie du temps d'exécution de ces programmes: leur efficacité est donc cruciale. Les algorithmes traditionnels de calculs de visibilité ont deux défauts: ils effectuent - inutilement - des calculs sur des objets non visibles et refont tous ces calculs à chaque nouvelle requête, même si les changements avec la requête précédente sont minimes. Pour remédier à ces inconvénients dans le cadre de scènes polygonales bidimensionnelles, nous nous servons d'une structure de données - le complexe de visibilité - qui code toutes les relations de visibilité entre objets d'une scène. Après avoir montré comment construire de façon optimale le complexe de visibilité, nous montrons comment il permet d'utiliser la cohérence spatiale de la scène dans les calculs de polygones de visibilité. Nous montrons aussi comment il permet d'utiliser la cohérence temporelle dans le maintien d'une vue autour d'un point se déplaçant dans la scène. Nous étudions ces algorithmes non seulement d'un point de vue théorique mais aussi d'un point de vue pratique. Nous avons programmé ces algorithmes et effectué des comparaisons expérimentales entre algorithmes. Nous nous sommes aussi intéressés aux problèmes de dégénérescences et d'imprécisions des calculs numériques qui se posent dès que les programmes sont exécutés sur des données «réelles»

La méthode de radiosité, méthode de simulation globale de l'éclairage, est très utilisée pour la visualisation de scènes d'intérieur statiques. Malgré les différentes améliorations apportées jusqu'à présent, son coût reste conditionné par le calcul des facteurs de forme qui modélisent l'interaction lumineuse entre deux surfaces. Ce calcul constitue l'étape la plus coûteuse de la méthode de radiosité, compte tenu des calculs de visibilité qu'il implique. D'autre part, il semble primordial d'utiliser un maillage qui suive les discontinuités (c'est à dire les limites d'ombre et de pénombre), pour obtenir une solution de radiosité de bonne qualité. Or cette méthode est très coûteuse car elle nécessite de nombreux calculs géométriques. De plus les méthodes proposées jusqu'à présent pour des environnements dits dynamiques (environnements où la géométrie, les propriétés des matériaux, etc., peuvent changer) effectuent toujours trop de recalculs. Le problème reste d'arriver à identifier précisément et efficacement quels facteurs de forme doivent vraiment être recalculés. Nous avons considéré le cas 2D qui permet une meilleure compréhension et une analyse plus approfondie, ne serait-ce que grâce à l'existence de solutions analytiques. Nous nous sommes intéressés au complexe de visibilité (introduit récemment en géométrie algorithmique) qui code les relations de visibilité entre les objets dans le plan. Nous présentons dans cette thèse son utilisation dans le cadre de la radiosité, pour les environnements statiques, puis pour les environnements dynamiques. Nous montrons que le complexe permet d'effectuer le calcul des facteurs de forme de manière efficace et analytique, et de construire le maillage de discontinuité de façon simple. De plus, seuls les facteurs de forme entre deux éléments mutuellement visibles de la scène sont calculés. Enfin, dans le cas dynamique, le complexe permet d'identifier et de mettre à jour uniquement les facteurs de forme strictement nécessaires lorsqu'un objet se déplace.

碩士
國立台北師範學院
數理教育研究所
90
Abstract Study on Fifth & Sixth Graders’ Understanding to Two-Dimensional Geometry Concepts The purpose of this study is to explore the recognition of fifth and sixth graders on their levels of understanding in two-dimensional geometry. The researcher has selected two schools from two cities in Taiwan, Taipei and Taipei Hsien. A total of 283 samples were randomly collected from four classes by giving written exams. Interview materials were then prepared by analyzing the test results along with suggestions provided by the experts. Next, interviews were given to a selected group of students. Based on test scores, the selected sixteen interviewees were separated into high and low performance levels, which included half female and half male students. There are four categories in the interview questions: 1. Draw and Identify Geometric Shapes. 2. Determine Similarities Between Geometric Shapes 3. Category Recognition Activities 4. Recognize Mysterious Geometric Shapes The main conclusions evaluated from these results are as follows: 1. Based on students’ use of mathematical terms to describe each geometric shape, most students from fifth and sixth grades have evolved from visual recognition to analytical level. 2. The ranking of the scores from the written exam for basic characteristics of rectangles is (highest to lowest): “all four angles are right angles”, “all four sides are equal”, “the opposite sides are parallel”, and “the opposite angles are equal”. For basic characteristics of triangles, most students score higher on “equal sides” than “equal angles”. 3. The lower level students would choose to hand draw circles and use tools to draw other shapes. However, they seemed to select only one tool at a time to draw selected shapes. Furthermore, they only noticed single characteristics of each shape during drawing. On the other hand, higher level students would follow characteristics of each shape and use more than one tool to draw. 4. When categorizing various shapes, most fifth and sixth graders would use “right angle” as a feature to distinguish differences between different types of triangles and rectangles. 5. While identifying shapes, the students get confused when “shape positioning”, “shape altering”, and “prototype” were used as factors to distract their ability to distinguish. 6. Students’ inconsistency in understanding geometric shapes can be categorized between shape naming, characteristics determination, and visual recognition. Key Words: Fifth and Sixth Grades, Geometric Shapes, Concept, Consistency, and Drawing

Thesis (Ph.D.)--State University of New York at Buffalo, 2006.
Title from PDF title page (viewed on Oct. 03, 2006) Available through UMI ProQuest Digital Dissertations. Thesis adviser: Gasparini, Francis M.

碩士
國立成功大學
太空與電漿科學研究所
104
For an efficient etching by plasma, in generating trench geometries, anisotropy is an important factor. For the ions to perpendicularly bombard the semiconductor surface, stationary plasma sheaths need to be formed to accelerate the ions. However, not many journal publications have reported on the stability of a plasma in a multi-dimensional trench geometry. A Particle-in-Cell model is built solely from the beginning in Fortran 95 to investigate basic plasma interaction between two electrode plates including ions and electrons. A secondary electron emission (SEE) effect in one-dimensional PIC model is incorporated. Then, our PIC model is extend to a two-dimensional trench geometry. The plasma behavior in the vicinity of the trench geometry is investigated by varying its size. In this study, radio frequency (RF) electric potential is employed in the system as in capacitively coupled plasma (CCP) process widely used in the plasma etching process. Furthermore, the influence of charging up by ions’ bombardment, which results in a positive potential on the trench bottom, is also examined.

碩士
國立清華大學
核子工程與科學研究所
102
Abstract A 2-D multi-group nodal diffusion code is developed. The code is formulated based on Nodal Green’s Function Method together with coarse mesh finite difference method (CMFD), which is coupling with nodal averaged fluxes as unknowns. The code is applicable in either rectangle geometry or hexagonal geometry with arbitrary prompt neutron groups. For hexagonal geometry, singular terms arise from the transverse integration procedure. Wagner’s approximation is applied, which omits these terms and then, following Fitzpatrick and Ougouag, we compensate for the omitted terms through rigorous nodal balance equations. There are two different coupling methods used in this code development. One is traditionally 1-D coupling, which is achieved by spatial sweeping through a set of 1-D equation systems. Another is full-scale coupling, which is achieved by using multi-dimensional nodal balance equation to couple all the spatial nodes. Therefore, a “sweep-free” algorithm is formed. Transient calculations routine is further developed for rectangle geometry and slab geometry. Backward difference method was used to approximate the time derivative terms in space-time kinetic equations. Several benchmark problems have been performed. All the results agree well with results of other codes in the literatures.

abstract: This dissertation aims to study and understand relevant issues related to the electronic, spin and valley transport in two-dimensional Dirac systems for different given physical settings. In summary, four key findings are achieved. First, studying persistent currents in confined chaotic Dirac fermion systems with a ring geometry and an applied Aharonov-Bohm flux, unusual whispering-gallery modes with edge-dependent currents and spin polarization are identified. They can survive for highly asymmetric rings that host fully developed classical chaos. By sustaining robust persistent currents, these modes can be utilized to form a robust relativistic quantum two-level system. Second, the quantized topological edge states in confined massive Dirac fermion systems exhibiting a remarkable reverse Stark effect in response to an applied electric field, and an electrically or optically controllable spin switching behavior are uncovered. Third, novel wave scattering and transport in Dirac-like pseudospin-1 systems are reported. (a), for small scatterer size, a surprising revival resonant scattering with a peculiar boundary trapping by forming unusual vortices is uncovered. Intriguingly, it can persist in arbitrarily weak scatterer strength regime, which underlies a superscattering behavior beyond the conventional scenario. (b), for larger size, a perfect caustic phenomenon arises as a manifestation of the super-Klein tunneling effect. (c), in the far-field, an unexpected isotropic transport emerges at low energies. Fourth, a geometric valley Hall effect (gVHE) originated from fractional singular Berry flux is revealed. It is shown that gVHE possesses a nonlinear dependence on the Berry flux with asymmetrical resonance features and can be considerably enhanced by electrically controllable resonant valley skew scattering. With the gVHE, efficient valley filtering can arise and these phenomena are robust against thermal fluctuations and disorder averaging.
Dissertation/Thesis
Doctoral Dissertation Electrical Engineering 2017

碩士
國立中央大學
電機工程研究所碩士在職專班
99
This　research　studied　five　different　designs　of　electrode-pair　geometry　for　impedimetric　biosensing　applications.　These　included　interdigitated,　rectangular,　circular,　triangular,　and　dish　electrode　pairs.　ADS　(Advanced　Design　System)　software　was　utilized　to　simulate　these　different　electrode-pair　designs　on　their　impedance,　capacitance,　and　electric　intensity.　The　simulated　capacitances　of　these　five　electrode-pair　geometries　of　commensurate　dimensions　were　1.600　×　10－14　F,　1.086　×　10－14　F,　6.513　×　10－15　F,　6.576　×　10－15　F,　9.924　×　10－15　F,　respectively.　One　of　the　simulations　showed　that　the　electric　intensity　in　the　area-of-interest　in　the　interdigitated　electrode　pair　was　quasi-uniform.　A　sensor　of　this　geometry　will　be　insensitive　to　the　movement　of　the　measured　object.　An　impedance　change　of　merely　0.19%　was　caused　by　changing　location　of　the　measured　object.　The　electric　intensity　in　the　area-of-interest　in　the　triangular　electrode　pair　was　non-uniform.　A　sensor　of　this　geometry　will　be　able　to　sense　the　movement　of　the　measured　object.　An　impedance　change　of　up　to　4.54%　was　caused　by　changing　the　location　of　the　measured　object.　Among　the　five　electrode-pair　types,　the　interdigitated　one　had　the　highest　sensitivity.　Adding　measured　substance　caused　60.43%　impedance　change　from　the　status　with　background　solution　only.　The　results　of　this　study　will　be　useful　for　guiding　the　electrode-pair　geometry　design　of　 impedimetric　biosensors.

Exciton dynamics in semiconductor nanostructures are dominated by the effects of many-body physics. The application of coherent spectroscopic tools, such as two-dimensional Fourier transform spectroscopy (2dFTS), to the study of these systems can reveal signatures of these effects, and in combination with sophisticated theoretical modeling, can lead to more complete understanding of the behaviour of these systems. 2dFTS has previously been applied to the study of GaAs quantum well samples. In this thesis, we outline a precis of the technique before describing our own experiments using 2dFTS in a partially collinear geometry. This geometry has previously been used to study chemical systems, but we believe these experiments to be the first such performed on semiconductor samples. We extend this technique to a reflection mode 2dFTS experiment, which we believe to be the first such measurement. In order to extend the techniques of coherent spectroscopy to structured systems, we construct an experimental apparatus that permits us to control the beam geometry used to perform four-wave mixing reflection measurements. To isolate extremely weak signals from intense background fields, we extend a conventional lock-in detection scheme to one that treats the optical fields exciting the sample on an unequal footing. To the best of our knowledge, these measurements represent a novel spectroscopic tool that has not previously been described.
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