As the rapid evolution in semiconductor technology, transistors’ feature size has reached to 22nm and below, which brings great impact to analog and mixed-signal circuits. As the significant bridge connecting the analog world and digital system, data converter suffers from nonlinearity resulting from mismatch among its unit components. The smaller transistors are, the larger relative mismatch among them becomes. However, using larger transistors leads to more area cost and power consumption. Therefore, researchers have been working hard on how to alleviate the mismatch issue. In recent years, Dynamic Element Matching (DEM) becomes a popular approach that can significantly improve linearity, especially Spurious-free Dynamic Range (SFDR), of a data converter system. The basic idea of DEM is to shuffle the usage pattern of unit elements so that the mismatch error is no longer correlated to the input signal. Thus, DAC’s linearity will be improved. Generally, DEM Nyquist-rate DAC does mismatch scrambling, which smooths distortions resulting from mismatch into white noise. DEM Delta-Sigma DAC does mismatch shaping, which pushes distortions away from the signal band, typically lower frequencies. In this thesis, we focused on mismatch-shaping Delta-Sigma DACs. Two of those various algorithms are implemented logically and physically. With placement and routing information, we got more accurate result on the speed and power dissipation. The comparison shows the tradeoff among number of quantization levels, mismatch-shaping order, and hardware complexity. / text

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The sigma-delta modulator is a popular signal amplitude quantization error (or noise) shaper used in oversampling analogue-to-digital and digital-to-analogue converter systems. The shaping of the noise frequency spectrum is performed by feeding back the quantization errors through a time delay element filter and feedback loop in the circuit, and by the addition of a possible stochastic dither signal at the quantizer. The aim in audio systems is to limit audible noise and distortions in the reconverted analogue signal. The formulation of the sigma-delta modulator as a discrete dynamical system provides a useful framework for the mathematical analysis of such a complex nonlinear system, as well as a unifying basis from which to consider other systems, from pseudorandom number generators to stochastic resonance processes, that yield equivalent formulations. The study of chaos and other complementary aspects of internal dynamical behaviour in previous research has left important issues unresolved. Advancement of this study is naturally facilitated by the dynamical systems approach. In this thesis, the general order feedback/feedforward sigma-delta modulator with multi-bit quantizer (no overload) and general input, is modelled and studied mathematically as a dynamical system. This study employs pertinent topological methods and relationships, which follow centrally from the symmetry of the circle map interpretation of the error state space dynamcis. The main approach taken is to reduce the nonlinear system into local or special case linear systems. Systems of sufficient structure are shown to often possess structured random, or random-like behaviour. An adaptation of Devaney's definition of chaos is applied to the model, and an extensive investigation of the conditions under which the associated chaos conditions hold or do not hold is carried out. This seeks, in part, to address the unresolved research issues. Chaos is shown to hold if all zeros of the noise transfer function lie outside the unit circle of radius two, provided the input is either periodic or persistently random (mod delta). When the filter satisfies a certain continuity condition, the conditions for chaos are extended, and more clear cut classifications emerge. Other specific chaos classifications are established. A study of the statistical properties of the error in dithered quantizers and sigma-delta modulators is pursued using the same state space model. A general treatment of the steady state error probability distribution is introduced, and results for predicting uniform steady state errors under various conditions are found. The uniformity results are applied to RPDF dithered systems to give conditions for a steady state error variance of delta squared over six. Numerical simulations support predictions of the analysis for the first-order case with constant input. An analysis of conditions on the model to obtain bounded internal stability or instability is conducted. The overall investigation of this thesis provides a theoretical approach upon which to orient future work, and initial steps of inquiry that can be advanced more extensively in the future.

With recent advances in CCD technology, it has become possible to detect low-amplitude variability in stars. Thus, the number of low-amplitude variables has increased at an exceptional rate over the past decade. Many of these low-amplitude variables are pulsating stars such as Delta Scuti or Gamma Doradus stars, whose periods are on the orders of hours and days, respectively. One particular place where these variables are being found is in close binary systems. A close binary system has two components separated on the order of tens of solar radii and whose periods are on the order of days. Eclipsing binary systems occur when the orbital plane of the system is aligned such that the stars eclipse each other with respect to Earth’s line of sight. Soydugan et al. (2006) presented a paper in which a small number of eclipsing systems with a Delta Scuti-type pulsating component were analyzed. The group derived an observational relationship between the pulsation and orbital periods, thus indicating a physical phenomenon. The proposed project herein will seek to further determine whether there is a statistically significant relationship between the pulsation period and orbital parameters of close binary systems with a Delta Scuti-type pulsating component by searching for such pulsations in close binary systems using the method of high-precision CCD photometry. / Stellar dynamics -- Observations -- [Delta] Scuti stars in close binary systems. / Department of Physics and Astronomy

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Vertebrates, annelids, and arthropods have evolved to form their body plans via segmentation. The question is whether this process stems from a common, segmented ancestor or if segmentation in these three phyla evolved from a series of independent events. To determine which of these theories is true, we look to determining whether these phyla share any pathways in the development of their segments. The Notch signaling pathway is a well-known pathway that vertebrates utilize for segmentation. Without it, somitogenesis does not occur properly as the segmentation oscillator is not functioning. Drosophila does not use this pathway for segmentation, but several other arthropods have recently been found to utilize it in the formation and maintenance of their segments (17-24). There has been debate as to whether Tribolium castaneum also uses the Notch pathway during segmentation as previous knockdowns of the Notch and Delta genes have led to a loss of segments and appendages/mouthparts (25-27). To determine this pathway’s involvement in Tribolium segmentation, I knocked down the Delta gene via eRNAi and attempted to determine Notch and Delta expression patterns via in situ hybridization. My results were inconclusive for determining the role of the Notch signaling pathway in segmentation. In the Delta dsRNA embryos, a loss of the labial segment, head and mouthpart defects, a loss of leg formation, and midline defects were seen. Future experiments need to be performed to determine whether an overexpression of mesoderm, ectoderm, or both is the cause of the defective ventral midline and whether this could lead to a loss of segments later in development. Overall, I can conclude that the Notch signaling pathway plays a role in mouthpart/leg development, the labial segment, and what I believe to be lateral inhibition between mesoderm and ectoderm determination.

Dans le Supergroupe Ouest-Congolais du bassin du Niari-Nyanga (Afrique centrale), les marqueurs des Glaciations Globales Sturtienne et Marinoenne sont représentés par les formations des «Diamictite inférieure» et «Diamictite supérieure».Ce travail de thèse présente une étude à haute résolution du Cap Carbonate associé à la Diamictite supérieure (6 coupes dans le bassin et 2 coupes dans la zone externe de la Chaîne du Mayombe). Les études pétrographiques révèlent la préservation des structures sédimentaires primaires et permettent de définir six microfaciès (MF0 à MF5) caractéristiques des paléoenvironnements de types inter- à supratidaux ou subtidaux. Dans le Cap Carbonate étudié, les indices de Kübler montrent une évolution croissante depuis la diagenèse profonde dans le bassin jusqu'à l'épimétamorphisme dans la zone externe de la Chaîne du Mayombe. Le signal isotopique ([delta]13C et [delta]18O) des Cap Carbonate échantillonnés est généralement reproductible dans le synclinal comme dans la chaîne, avec les valeurs du [delta]13C montrant une excursion négative variant de -2.6 [pour mille] à -5.6 [pour mille]. Les valeurs de d18O oscillent entre -6 [pour mille] et -12 [pour mille]. Par ailleurs, la confrontation des données minéralogiques, chimiques et isotopiques indique une influence négligeable des transformations post-sédimentaires sur la signature isotopique du Cap Carbonate indiquant la préservation des valeurs du [delta]13C de l'océan néoprotérozoïque. Enfin, l'ensemble des données de cette thèse et les résultats préliminaires des « Projets GLANEC» replacés dans un contexte régional permettent de définir le Membre SCIa du synclinal du Niari-Nyanga comme un Cap Carbonate lié à la Glaciation Marinoenne. / Within West-Congolian Supergroup of Niari-Nyanga Basin (Central Africa), the markers of Sturtian and Marinoan Global Glaciations are documented by the so-called «Lower Diamictite» and «Upper Diamictite». This work is based on 6 and 2 lithological sections from the basin and the external zone of the Mayombe fold belt. It corresponds to a high-resolution study of the Cap Carbonate lying unconformably on the Upper Diamictite. Petrographic analyses show preservation of primary sedimentary structures and lead to define six microfacies (MF0 to MF5). These microfacies caracterize paleoenvironments such as inter- to supratidal or subtidal types. Kübler index values of the studied Cap Carbonate display an increasing evolution from East to West, ie from a deep diagenesis in the basin to an epimetamorphism in the Mayombe external zone. Stable isotope signature ([delta]13C, [delta]18O) of the various components of this Cap Carbonate is reproducible throughout the basin as in the Mayombe external zone, with [delta]13C values displaying a negative excursion, decreasing from -2.6 ? to -5.6 ?. [delta]18O values of these components vary between -6 ? and -12 ?. Moreover, comparison between mineralogic, chemical and isotopic data indicates that post-sedimentary transformations had a very negligible influence on the isotopic signature of the Cap Carbonate, indicating preservation of d13C values of the Neoproterozoic ocean. Finally, when they are compared with other regional studies, all data of the present work and the preliminary results of the GLANEC Projects lead to the conclusion that the SCIa Member of the Niari-Nyanga Basin must be considered as a Cap Carbonate related to the Marinoan Global Glaciation.

Thesis advisor: Marc A. T. Muskavitch / Notch signaling is an evolutionarily conserved developmental pathway regulated by two classes of transmembrane proteins: the Notch receptors and the Delta/Serrate/LAG-2 (DSL) ligands. Notch and DSL ligands mediate cell-cell communication that results in a downstream signaling cascade that affects many aspects of metazoan development. Additional regulatory mechanisms that affect Notch signaling are being discovered continuously, and recent findings highlight the importance of endocytosis, ubiquitylation and subcellular trafficking as essential requirements for proper signaling. In order to obtain further insights into the regulation of Notch signaling, I took a two-fold approach, combining genetic and molecular techniques in <italic>Drosophila</italic>. First, I took part in a large-scale transposon-based screen in the developing <italic>Drosophila</italic> eye to identify additional genes involved in the pathway. We screened 10,447 transposon lines from the Exelixis collection for modifiers of cell fate alterations caused by overexpression of Delta, and we identified 170 distinct modifier lines that may affect up to 274 genes. I further analyzed a previously uncharacterized gene, which we have named <italic>Amun</italic>, and showed that it localizes to the nucleus and contains a putative DNA glycosylase domain. Further analyses of Amun reveal that altered levels of Amun function interfere with cell fate specification during eye and sensory organ development. Second, to investigate structural requirements for ubiquitylation of Delta, I analyzed four individual lysine residues in the Delta intracellular domain, and assessed their necessity for Delta signaling activity. I find that a conserved residue, DeltaK742, is essential for Notch signaling in the <italic>Drosophila</italic> imaginal wing disc and is apparently required for ubiquitylation of Delta by the E3 ubiquitin ligase, Mind bomb1 (one of two E3 ubiquitin ligases required for Delta signaling activity). Taken together, the findings from this thesis research contribute to the advancement of our understanding of different aspects of Notch signaling and Notch-mediated development. / Thesis (PhD) — Boston College, 2009. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Biology.

Na primeira parte do trabalho estudamos a equação de Schrödinger logarítmica com um delta potencial; $V(x)=-\\gamma \\,\\delta(x)$, onde $\\delta$ é a distribuição de Dirac na origem e o parâmetro real $\\gamma$ descreve a intensidade do potencial. Estabelecemos a existência e unicidade das soluções do problema de Cauchy associado em um espaço de funções adequado. No caso do potencial atrativo ($\\gamma>0$), calculamos de forma explícita o seu único ground state e mostramos a sua estabilidade orbital.\\\\ A segunda parte trata detalhadamente da equação de Schrödinger logarítmica com um delta derivada potencial; $V(x)=-\\gamma\\, \\delta^{\\prime}(x)$. A boa colocação global para o problema de Cauchy é verificada em um espaço de funções adequado. No caso do potencial atrativo ($\\gamma>0$), o conjunto dos ground states é completamente determinado. Mais precisamente: se $0<\\gamma\\leq2$, então há um único ground state e é uma função ímpar; se $\\gamma>2$, então existem dois ground states não-simétricos. Em adição, provamos que cada ground state é orbitalmente estável através de uma abordagem variacional. Finalmente, usando a teoria de extensão de operadores simétricos, também mostramos um resultado de instabilidade para $\\gamma>2$. / The first part of this thesis deals with the logarithmic Schrödinger equation with a delta potential; $V(x)=-\\gamma \\,\\delta(x)$, where $\\delta$ is the Dirac distribution at the origin and the real parameter $\\gamma$ is interpreted as the strength of the potential. We establish the existence and uniqueness of the solutions of the associated Cauchy problem in a suitable functional framework. In the attractive potential case ($\\gamma>0$), we explicitly compute the unique ground state and we show their orbital stability .\\\\ The second part deals with the case of the logarithmic Schrödinger equation with a delta prime potential; $V(x)=-\\gamma\\, \\delta^{\\prime}(x)$. Global well-posedness is verified for the Cauchy problem in a suitable functional space. In the attractive potential case ($\\gamma>0$), the set of the ground state is completely determined. More precisely: if $0<\\gamma\\leq2$, then there is a single ground state and it is an odd function; if $\\gamma>2$, then there exist two non-symmetric ground states. Moreover, we show that every ground state is orbitally stable via a variational approach. Finally, by applying the theory of extensions of symetric operators, we also prove a result of instability for $\\gamma>2$.