Ingeniero Civil Matemático / En esta memoria se estudian dos problemas semilineales elípticos clásicos en la literatura: el problema de la curvatura Gaussiana prescrita en dimensión 2, y el problema de Lin-Ni-Takagi con exponente crítico en dimensión 3. En ambos se encuentran soluciones con reviente cuando el valor de un parámetro involucrado se aproxima a cierto valor crítico. En el primer capítulo se estudia el siguiente problema: Dada una función escalar $\kappa(x)$, suficientemente regular, definida en una variedad Riemanniana compacta $(M,g)$ de dimensión 2, se desea saber si $\kappa$ puede corresponder a la curvatura Gaussiana de $M$ para una métrica $g_1$, que es adicionalmente conforme a la métrica inicial $g$, es decir, $g_1=e^ug$ para alguna función escalar $u$ en $M$. Sea $f$ una función regular en $M$ tal que \equ{f\geq 0,\quad f\not\equiv 0, \quad \min_M f=0.} Sean $p_1,\ldots,p_n$ una colección de puntos cualesquiera en los que $f(p_i)=0$ y $D^2f(p_i)$ es no singular. Se demuestra que para todo $\la>0$ suficientemente pequeño, existe una familia de metricas conformes de tipo burbuja $g_\la=e^{u_\la}g$ tal que su curvatura Gaussiana está dada por la función que cambia de signo $K_{g_\la}=-f+\la^2$. Más aún, la familia $u_\la$ satisface \equ{u_\la(p_j)=-4\log \la -2 \log \left(\frac{1}{\sqrt2}\log \frac{1}{\la}\right)+O(1), \quad \la^2e^{u_\la}\rightharpoonup 8\pi\sum_{i=1}^n\delta_{p_i},} donde $\delta_p$ corresponde a la masa de Dirac en el punto $p$. En el segundo capítulo se considera el problema \equ{-\Delta u+\la u-u^5=0,\quad u>0 \quad \mbox{in }\Omega,\quad \ddn{u}=0\quad \mbox{on }\partial\Omega,} donde $\Omega\subset \R^3$ es un dominio acotado con frontera regular $\partial\Omega$, $\la>0$ and $\nu$ denota la normal unitaria exterior a $\partial\Omega$. Se demuestra que cuando $\la$ se apoxima por arriba a cierto valor explícitamente caracterizado en términos de funciones de Green, una familia de soluciones con reviente en un cierto punto interior del dominio existe.

Student Number : 9900131F - MSc (Eng) dissertation - School of Mechanical Engineering - Faculty of Engineering / Recent high-resolution numerical studies of weak shock reflections have shown that a complex flow structure exists behind the triple point which consists of multiple shocks, expansion fans and triple points. This region had not been detected earlier in experimental observations or numerical studies of weak shock reflections due to the small size of this region. New components were designed and built to modify an existing large-scale shock tube in order to obtain experimental observations to validate the numerical results. The shock tube produced a large, expanding cylindrical incident wave which was reflected off a 15° corner on the roof of the section to produce a weak shock Mach reflection with a large Mach stem in the test section. The shock tube was equipped with PCB high-speed pressure transducers and digital scope for data acquisition, and a schlieren optical system to visualise the region behind the triple point. The tests were conducted over a range of incident wave Mach numbers (M12 = 1.060-1.094) and produced Mach stems of between 694 mm and 850 mm in length. The schlieren photographs clearly show an expansion fan centered on the triple point in all the successful tests conducted. In some of the more resolved images, a shocklet can be seen terminating the expansion fan, and in others a second expansion fan and/or shocklet can be seen. A ‘von Neumann reflection’ was not visualised experimentally, and hence it has been proposed that the four-wave reflection found in these tests be named a ‘Guderley reflection’. The experimental validation of Hunter & Tesdall’s (2002) work resolves the ‘von Neumann Paradox’.

by Lo Chui-sim. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references (leaves 91-93). / Abstract --- p.i / Introcution --- p.1 / Chapter 1 --- Preliminaries --- p.3 / Chapter 1.1 --- Preliminaries on von-Neumann algebra --- p.3 / Chapter 1.2 --- Modular theory --- p.6 / Chapter 2 --- Abstract Lp Spaces --- p.10 / Chapter 2.1 --- "Preliminaries on dual action, dual weights and extended positive part" --- p.10 / Chapter 2.2 --- Abstract LP spaces associated with von-Neumann algebras --- p.20 / Chapter 2.3 --- "LP(M) is a Banach space for p E [1, ∞ ]" --- p.25 / Chapter 2.4 --- Independence of the choice of ψ --- p.32 / Chapter 3 --- Spatial Lp Spaces --- p.34 / Chapter 3.1 --- Definition and elementary properties of spatial derivative --- p.35 / Chapter 3.2 --- Modular properties of spatial derivatives --- p.47 / Chapter 3.3 --- Spatial Lp spaces --- p.51 / Chapter 4 --- LP Spaces constructed by using complex interpolation method --- p.60 / Chapter 4.1 --- The complex interpolation space --- p.60 / Chapter 4.2 --- LP space with respect to a faithful normal state --- p.71 / Chapter 4.3 --- LP spaces with respect to a normal faithful semifinite weight . . --- p.78 / Chapter 4.4 --- Equivalence to spatial LP spaces --- p.87 / Bibliography --- p.91

Tse, Wang Hung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 75-77). / Abstract also in Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- On bounded interval with n jumps in inhibitor diffusivity --- p.3 / Chapter 2.1 --- Introduction --- p.3 / Chapter 2.2 --- Preliminaries --- p.5 / Chapter 2.3 --- Review of previous results in the two segment case: interior spike and spike near the jump discontinuity of the diffusion coefficient --- p.7 / Chapter 2.4 --- The construction and analysis of spiky steady-state solutions --- p.9 / Chapter 2.5 --- Stability Analysis --- p.10 / Chapter 2.6 --- Spikes near the jump discontinuity xb of the inhibitor diffusivity --- p.11 / Chapter 2.7 --- Stability Analysis II: Small Eigenvalues of the Spike near the Jump --- p.16 / Chapter 2.8 --- Existence of interior spikes for N segments --- p.20 / Chapter 2.9 --- Existence of a spike near a jump for N segments --- p.24 / Chapter 2.10 --- Appendix: The Green´ةs function for three segments --- p.25 / Chapter 3 --- On a compact Riemann surface without boundary --- p.30 / Chapter 3.1 --- Introduction --- p.30 / Chapter 3.2 --- Some Preliminaries --- p.35 / Chapter 3.3 --- Existence --- p.43 / Chapter 3.4 --- Refinement of Approximate Solution --- p.50 / Chapter 3.5 --- Stability --- p.52 / Chapter 3.6 --- Appendix I: Expansion of the Laplace-Beltrami Operator --- p.67 / Chapter 3.7 --- Appendix II: Some Technical Calculations --- p.73

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The purpose of this thesis is to provide an exposition of the \textit{modular theory} of von Neumann algebras. The motivation of the theory is to classify and describe von Neumann algebras which do not admit a trace, and in particular, type III factors. We replace traces with weights, and for a von Neumann algebra $\mathcal{M}$ which admits a weight $\phi$, we show the existence of an automorphic action $\sigma^\phi:\mathbb{R}\rightarrow\text{Aut}(\mathcal{M})$. After showing the existence of these actions we can discuss the crossed product construction, which will then allow us to study the structure of the algebra.

For smooth bounded pseudoconvex domains in Cn, we provide geometric conditions on (the points of infinite type in) the boundary which imply compactness of the ∂-Neumann operator. This is an extension of a theorem of Straube for smooth bounded pseudoconvex domains in C2.

An outcome is ambiguous if it is an incomplete description of the probability distribution over consequences. An `incomplete description' is identified with the set of probabilities that satisfy the incomplete description. A choice problem is uncertain if the decision maker is choosing between distributions, and is ambiguous if the decision maker is choosing between sets of probabilities. The von Neumann/Morgenstern approach to uncertain choice problems uses a continuous linear function on probabilities. This paper develops the theory of ambiguous choice problems as a continuous, linear functions on closed convex sets of probabilities. This delivers: a framework encompassing most of the extant ambiguity averse preferences; a complete separation of attitudes towards risk and attitudes toward ambiguity; and generalizations of rst and second order stochastic dominance rankings to ambiguous decision problem. Quasi-concave preferences on sets that satisfy a restricted betweenness property capture variational preferences. / text

The purpose of this thesis is to provide an exposition of the \textit{modular theory} of von Neumann algebras. The motivation of the theory is to classify and describe von Neumann algebras which do not admit a trace, and in particular, type III factors. We replace traces with weights, and for a von Neumann algebra $\mathcal{M}$ which admits a weight $\phi$, we show the existence of an automorphic action $\sigma^\phi:\mathbb{R}\rightarrow\text{Aut}(\mathcal{M})$. After showing the existence of these actions we can discuss the crossed product construction, which will then allow us to study the structure of the algebra.