Card and Giuliano’s National Bureau of Economic Research (NBER) working paper on universal screening is discussed. This commentary provides a brief summary and critique of the article, proposes an explanation of the results in light of the author’s research on the role of nominations or screening tests in the gifted identification process, and discusses the methodological implications of this work for the field.

In this dissertation, we investigate a very interesting class of quasi-linear stochastic partial differential equations. The main purpose of this article is to prove an existence result for such type of stochastic differential equations with non-standard growth conditions. The main difficulty in the present problem is that the existence cannot be easily retrieved from the well known results under Lipschitz type of growth conditions [42]. / Dissertation (MSc)--University of Pretoria, 2010. / Mathematics and Applied Mathematics / unrestricted

Le concept de quasi-espèce, introduit par Manfred Eigen dans les années 70, décrit l'état d'équilibre d'une population subissant des forces de mutation et sélection. La plupart des modèles classiques présentant un phénomène de quasi-espèce sont déterministes et considèrent une population de taille infinie. L'objectif de cette thèse est d'étudier plusieurs modèles stochastiques, dont la taille de la population est finie, afin de montrer que le phénomène de la quasi--espèce est aussi présent dans ces modèles comme dans le modèles déterministes. Nous étudions en détail les modèles de Galton-Watson, Wright-Fisher et Moran. Nous confirmons que les trois modèles présentent un phénomène de quasi--espèce, et que la distribution de la quasi--espèce est la même pour les trois modèles, ainsi que pour le modèle original d'Eigen. De plus, nous décrivons explicitement la distribution de cette quasi--espèce pour le paysage de fitness à un pic, ainsi que pour des fonctions de fitness qui ne dépendent que de la distance de Hamming à la master sequence. / Manfred Eigen introduced the concept of quasispecies in the early 70s, in order to describe the steady--state distribution of a population subject to mutation and selection forces. Most classical models showing a quasispecies phenomenon are deterministic and deal with a population of an infinite size. The aim of this thesis is to study several stochastic and finite--population models, and to show that a quasispecies phenomenon arises in these models too. We study in detail the Galton--Watson, Wright--Fisher and Moran models. We confirm that a quasispecies phenomenon is present in the three models, and that the distribution of this quasispecies is common to all three models as well as to Eigen's original model. Moreover, we describe explicitly the distributionof the quasispecies for the sharp peak landscape, as well as for fitness functions which depend only on the Hamming distance to the master sequence.

Abstract Not Provided / Thesis / Master of Science (MSc)

Bioimpedance measurements are useful for determining a variety of biological conditions. By accounting for small impedance variations due to the arterial pulse, the effect of the blood can be studied more closely. The quasi-circulator system presented enables monitoring of pulsatile impedance changes with input frequencies above 1 MHz. The adjustable Rmatch allows for dynamic tuning of the system to increase sensitivity. By tuning Rmatch to be near the match point, the pulsatile signal in the output magnitude can be amplified, and tuning Rmatch to be at the match point causes the pulsatile signal in the output phase to be amplified. The system is tested on discrete circuit elements as well as human subjects, and results are analyzed. Pulsatile variations in the output voltage signal of up to 7 mV and 2.3° are demonstrated on human subjects. Tuning Rmatch allows for the pulsatile signal to be increased by more than 4 times.

If (X,Ƭ) is a topological space, then a quasi-uniformity U on X is compatible with Ƭ if the quasi-uniform topology, Ƭ_u = Ƭ. This paper is concerned with local properties of quasi-uniformities on a set X that are compatible with a given topology on X. Chapter II is devoted to the construction of Hausdorff completions of transitive quasi-uniform spaces that are members of the Pervin quasi-proximity class. Chapter III discusses locally complete, locally precompact, locally symmetric and locally transitive quasi-uniform spaces. Chapter IV is devoted to function spaces of quasi-uniform spaces. Chapter V and the Appendix are concerned with the topological homeomorphism groups of quasi-uniform spaces. / Ph. D.

This thesis argues that neopatrimonialism is vital to understanding the power structure of the secessionist Transnistrian Moldovan Republic (TMR), and that neopatrimonial structures have been manipulated by Soviet-era elites to sustain the unrecognized separatist state's independence. The thesis also argues that neopatrimonialism is not a stable structure and its effectiveness in retaining support for the regime has changed over time. The paper provides an empirical analysis of the TMR in order to answer two questions: "To what extent does neopatrimonialism explain the regime endurance of the Transnistrian Moldovan Republic?" and "What does the case of the Transnistrian Moldovan Republic reveal about neopatrimonialism and regime endurance over time?" The analysis examines the TMR regime's use of Soviet-era industrial and bureaucratic structures, media, party networks, and worker committees to assert and maintain control, distribute patronage, maintain support for secession, and co-opt important interest groups. The paper concludes that although neopatrimonialism is only one of several elements that support the TMR regime's endurance, the analysis of neopatrimonial systems in states with significant neopatrimonialism provides a framework for examining disparate but interwoven elements of a state's political economy. / Master of Public and International Affairs

Die nichtlineare Wechselwirkung der Quasi Zwei-Tage-Welle (QZTW) mit anderen planetaren Wellen führt zu wesentlichen Amplitudenmodulationen der Zwei-Tage Welle und zu einer Reihe auftretender sekundärer Wellen. die Ergebnisse der verschiedenen Experimte zur Wechselwirkung der Quasi Zwei-Tage Welle mit jeweils der 10-Tage Welle, der 16-Tage Welle und der 5-Tage Welle zeigen, dass die Amplitude der QZTW unter der Wechselwirkung mit der der 16-Tage Welle und der 10-Tage Welle um bis zu 20 % reduziert wird. Die stationäre planetare Welle mit der zonalen Wellenzahl 1 (SPW1) scheint die wichtigste Rolle bei den nichtlinearen Wechselwirkungen mit der QZTW zu spielen, da die daraus entstehenden sekundären Wellen mit den Wellenzahlen 2 und 4 dieselbe Periode wie die QZTW haben. Die Überlagerung der Quasi Zwei-Tage Welle und ihrer sekundären Wellen verstärkt die Amplitude um bis zu 60 %. / The non-linear interaction of the quasi two-day wave (QTDW) with other planetary waves leads to remarkable amplitude modulations of the QTDW and to arising secondary waves. Results of several numerical experiments considering the behaviour of the QTDW in connection with the 16-, 10-, and 5-day wave have shown that the amplitude of the QTDW reduces under interaction with the 16DW and 10DW. The stationary planetary wave with zonal wave number 1 (SPW1) seems to play the most important role, because resulting secondary waves exhibit the same period as the QTDW. The superposition of these waves leads to an enhancement of the QTDW-amplitude up to 60 %. This means, that a strong amplification of the QTDW measured by RADAR instruments can be due to interaction between the QTDW and a strong SPW1.

Estudamos a evolução temporal de perturbações escalares na vizinhança de uma estrela com densidade uniforme que colapsa em um buraco negro. O trabalho começa com um estudo básico de gravitação e modos quasi-normais. O objetivo principal é resolver a equação de Klein-Gordon sem massa para a perturbação escalar, cuja solução depende de métodos numéricos. Com este objetivo, tratamos os aspectos teóricos de buracos negros e estrelas a partir da solução prevista pela Relatividade Geral para um buraco negro, estrelas com densidade uniforme e estrelas em colapso. Estudamos também uma maneira de reduzirmos a Equação de Klein-Gordon para uma forma conveniente de ser integrada, assim como os métodos numéricos necessários para resolver essa equação. Encontramos soluções para os modos variando a massa M, o raio inicial R e o rótulo do momento angular l. Essas soluções são irregulares em muitas situações, mas em geral elas são crescentes, de acordo com o comportamente observado de explosões de Supernovas. / This work is a study on the time evolution of scalar perturbations around a star collapsing to a black hole. It starts with a basic study of gravitation and quasi-normal modes. The aim is to derive the solution of the massless Klein-Gordon equation, that depends on numerical methods. Aiming at this goal, we studied theoretical aspects of stars, black holes and gravitational collapse. The methods include coordinate substitutions to modify the Klein-Gordon equation to a simple form. We also studied numerical methods for partial differential equations. Solutions of the quasi-normal modes were found with different values of M, R and l. The solutions are irregular in several situations, but some of them display increasing modes, that could be explained by the explosive behavior of Supernovas.

O presente trabalho trata do estudo, projeto, desenvolvimento, construção e medida de lentes discretas planares (DLAs). Estes dispositivos atuam como sistemas irradiantes, especialmente com características multi-feixes. A construção destas lentes utiliza tecnologias compatíveis com a fabricação de circuitos impressos, com alguns detalhes que são característicos da área de antenas e circuitos planares. O estudo aborda as equações de projeto e considerações gerais relativas ao atendimento de especificações técnicas preliminares. Foram desenvolvidas duas lentes discretas, uma na frequência de 8GHz (banda X) e outra na frequência de 40GHz (banda Ka- faixa de ondas milimétricas). São apresentados os resultados de medidas destas duas lentes, que comprovam a possibilidade de uso em aplicações multi-feixes, bem como seu efeito de foco, análogo ao observado em lentes óticas comuns. / The object of this work is the study, design, development, fabrication and measurement of discrete lens arrays (DLAs). These devices act as radiant systems, especially with multi-beam characteristics. Their construction follows the same procedures and techniques normally found in printed circuit fabrication, with some further details that are pertinent to the antenna and planar circuit field. This study contains the design equations and general remarks as to fulfill preliminary technical specifications. Two real designs were developed, one in the X-band (8GHz) and another in the millimeter range, Ka band (40GHz). Their respective measurement results are presented, which proved their possible application in multi-beam systems, as well as their focusing effect, which is analogous to that observed in common optical lenses.