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In this thesis, we mainly study the structure of $D_9$-brane Chan-Paton factors in Type II orientifold $O_p^{\pm}$ theories. An explicit structure is found through a thorough and systematic derivation. For this purpose, we give a complete analysis of the worldsheet parity square action for all p-q open strings (i.e, the strings starting from $D_p$-branes and ending on $D_q$-branes), which is an extension of Gimon-Polchinski's work on the parity square action for p-q strings with $p-q$ even. We also formulate the rules for computing the scattering amplitudes of open strings ending on D-branes. These are important to build phenomenological models in string theory. As an application to the mathematical aspects of string theory, we confirm the proposal that the D-brane charges in Type II orientifolds are classified by the KR-theory groups. All these results will appear in our paper\footnote{Dongfeng Gao and Kentaro Hori, Clifford Algebras and Chan-Paton Factors, to appear.}. We also show some preliminary results on the B-type D-branes in the orientifolds of linear sigma models. A typical linear sigma model has both a geometric phase and a Landau-Ginzberg phase over its K\"ahler moduli space. The B-type D-branes are described by suitable categories in a linear sigma model and its phases. The orientifold projection induces parity mappings on the various categories. By looking at the transportation of invariant branes in the moduli space, we find the relations among the parity mappings of different phases in the quintic model.

Due to the lack of feedback networks, digital class D amplifiers operating in open loop typically have inferior performance when compared to analog class D amplifiers in closed loop configuration. This thesis presents an integrated distortion suppression circuit design for digital class D amplifiers, which forms a feedback loop around the output stage. This circuit suppresses the output stage distortion and noise by equalizing the modulator effective duty ratio and the output stage effective duty ratio. The suppression circuit is integrated with the class D modulator. An integrated class D amplifier output stage is implemented separately using a 0.35μm HV-CMOS technology. Experimental results confirm that the closed loop PSRR is improved by 15dB. The THD+N value is reduced by a factor of 2 to 30. The minimum THD+N is 0.03%, which is among the state of the art class D amplifiers.

Due to the lack of feedback networks, digital class D amplifiers operating in open loop typically have inferior performance when compared to analog class D amplifiers in closed loop configuration. This thesis presents an integrated distortion suppression circuit design for digital class D amplifiers, which forms a feedback loop around the output stage. This circuit suppresses the output stage distortion and noise by equalizing the modulator effective duty ratio and the output stage effective duty ratio. The suppression circuit is integrated with the class D modulator. An integrated class D amplifier output stage is implemented separately using a 0.35μm HV-CMOS technology. Experimental results confirm that the closed loop PSRR is improved by 15dB. The THD+N value is reduced by a factor of 2 to 30. The minimum THD+N is 0.03%, which is among the state of the art class D amplifiers.

In this thesis, we mainly study the structure of $D_9$-brane Chan-Paton factors in Type II orientifold $O_p^{\pm}$ theories. An explicit structure is found through a thorough and systematic derivation. For this purpose, we give a complete analysis of the worldsheet parity square action for all p-q open strings (i.e, the strings starting from $D_p$-branes and ending on $D_q$-branes), which is an extension of Gimon-Polchinski's work on the parity square action for p-q strings with $p-q$ even. We also formulate the rules for computing the scattering amplitudes of open strings ending on D-branes. These are important to build phenomenological models in string theory. As an application to the mathematical aspects of string theory, we confirm the proposal that the D-brane charges in Type II orientifolds are classified by the KR-theory groups. All these results will appear in our paper\footnote{Dongfeng Gao and Kentaro Hori, Clifford Algebras and Chan-Paton Factors, to appear.}. We also show some preliminary results on the B-type D-branes in the orientifolds of linear sigma models. A typical linear sigma model has both a geometric phase and a Landau-Ginzberg phase over its K\"ahler moduli space. The B-type D-branes are described by suitable categories in a linear sigma model and its phases. The orientifold projection induces parity mappings on the various categories. By looking at the transportation of invariant branes in the moduli space, we find the relations among the parity mappings of different phases in the quintic model.

L'apolipoprotéine D (apoD) est une glycoprotéine sécrétée dont l'expression est modulée dans une multitude de situations incluant les cancers de différents tissus, les désordres métaboliques et les maladies neurodégénératives. Bien que la liste des conditions présentant une augmentation de l'apoD s'allonge chaque jour, les facteurs provoquant le déclenchement de son expression, de même que la fonction de celle-ci, restent inconnus. Les travaux présentés dans cette thèse ont permis de jeter un peu de lumière sur ces deux aspects. Dans un premier temps, ces travaux ont permis de déterminer que l'apoD est une protéine de stress spécifique et que son expression est déclenchée par des stress ayant une forte composante oxydante ou inflammatoire. Cependant, alors que l'expression de l'apoD en réponse au stress oxydatif est associée à un arrêt de croissance, en condition inflammatoire, elle est accompagnée d'une stimulation de la prolifération. De plus, ces stress modifient non seulement le niveau d'expression, mais aussi la localisation intracellulaire de l'apoD. L'apoD, qui est normalement sécrétée, est réinternalisée et s'accumule dans le cytoplasme et le noyau. L'entrée de l'apoD dans la cellule influence, de plus, la prolifération cellulaire. Ces travaux ont ensuite permis de mieux cerner le rôle de cette modulation de l'apoD en situations de stress chez l'animal. Pour cela, nous avons soumis des souris surexprimant l'apoD humaine dans leur système nerveux ou n'exprimant pas l'apoD à des conditions neurodégénératives. Nous avons ainsi établi que l'apoD serait impliquée dans les mécanismes régulant la protection contre diverses atteintes neurodégénératives, incluant le stress oxydatif et l'inflammation, favorisant donc la survie suite à ces atteintes. Ainsi, l'apoD joue un rôle dans la fonction neuronale basale tel que déterminé grâce à des tests comportementaux. De plus, l'apoD limite la peroxydation lipidique lors de l'exposition au paraquat, un générateur de stress oxydatif. De façon similaire, l'apoD contrôle la production de cytokines et de phospholipase A2, réduit l'infiltration de cellules T et induit l'activation gliale en réponse à l'infection par le coronavirus humain OC43, un modèle d'inflammation aiguë. Par ailleurs, la surexpression de l'apoD humaine chez la souris favorise l'accumulation de lipides dans le foie et les muscles, favorisant ainsi le développement de la résistance à l'insuline accompagnant souvent le vieillissement physiologique. Cette accumulation de lipides a été associée à une stimulation de gènes impliqués dans la synthèse d'acides gras. Les travaux présentés dans cette thèse contribuent donc à établir l'apoD comme un facteur bénéfique favorisant la survie suite à une atteinte cellulaire. Ils suggèrent aussi l'importance de contrôler les niveaux physiologiques de l'apoD afin de maintenir l'homéostasie métabolique. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Apolipoprotéine D, Arrêt de croissance, Inflammation, Lipocaline, Résistance à l'insuline, Stress oxydatif.

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We studied the local single-particle tunneling characteristics [as observed with scanning tunnel microscopy (STM)] for N D and S D tunneling, where N is a normal metal, S is a s-wave superconductor, and D is a d-wave superconductor with a {100} | {110} grain boundary. The tunneling Hamiltonian method was used. The self-consistent order parameter is first determined using the quasiclassical Green'sfunction method, and then the tunneling characteristics at various distances from the interface, reectivity of the interface, and temperature are studied. For N D tunneling, a zero-bias conductance peak (ZBCP) occurs near the interface with diminishing magnitude away from it. For S D tunneling, the ZBCP splits to exhibit the gap of the s-wave low-Tc superconducting tunneling tip and there is a range of negative conductance just outside the peaks when the tunneling point is near the grain boundary. The results are compared with those obtained by using a constant order parameter in each grain.

The main goal of string phenomenology is to find a convincing connection be- tween realistic particle physics and string theory. An extended object called D-brane in string theory is shown as a very powerful tool to resolve phenomenology problems. D-branes, D standing for Dirichlet boundary conditions, naturally appear in the T- dual space along one of the toroidally compactified dimensions in non-perturbative Type I theory. A D-brane forms an U(1) gauge group and the group structure can be enriched by Chan-Paton indices with multiple coincided D-branes and orientifold ac- tions. Oribfolds define fixed points of the compactified space and break the theory to N = 1 supersymmetry, and the extended orientifold from world-sheet parity projects the brane image to help cancel the anomalies. Strings at the intersections of two D-branes (Type IIA) form massless chiral fermions as bi-fundamental representations of the gauge groups of the intersecting branes. With these properties, we construct Grand Unification Theory (GUT) and standard-like models by intersecting D-brane configuration on T6/(Z2 × Z2) orientifold. Also, supergravity and geometrical fluxes are introduced to stabilize the moduli. In this dissertation, first a brief review of the D-brane theory is discussed, then the complete construction of D-brane configuration on T6/(Z2 × Z2) is presented, and finally some realistic Trinification, Pati-Salam, SU(5) and flipped SU(5) models are constructed and discussed. We present the models both in D-brane wrapping numbers and the corresponding particle spectra.