This research studies the effects of a postulated Main Steam Line Break accident in a nuclear plant on the transient loading of steam generator tubes. The problem involves complex transient two-phase flow dynamics and fluid-structural loading processes. A better understanding of this phenomenon will permit the development of improved design tools to ensure steam generator safety. This Thesis presents the results of an experimental laboratory study of the transient loading of a sectional model of steam generator tubes during a simulated two-phase blowdown. The research was carried out in a purpose designed and built experimental facility. The thermodynamic phenomena were investigated through dynamic pressures and temperatures. The transient tube loads were directly measured using dynamic load cells. The working fluid was R-134a and the tube bundle was a normal triangular array with a pitch ratio of 1.36. Preliminary testing indicated parasitic loading on the instruments and remedial actions were taken to ensure measurement accuracy. The success of the instrumentation development methodologies was validated in a series of single- phase blowdowns. Two-phase blowdown experiments were then conducted with various levels of liquid and numbers of tube rows. The results provided hitherto unknown information relating the nature of the fluid-structure interaction and flow development during a two-phase transient blowdown across a tube bundle. The pressure drop across the tube bundle established the thermal hydraulic fluid behaviour in the pressure vessel and controlled the upstream fluid discharge from the system. The flow through the bundle was choked for the majority of the transient. The transient tube loading was explained in terms of the associated fluid mechanics and the maximum load was compared with existing models obtained under steady flow conditions. An empirical model was developed that enables the prediction of the maximum tube loads once the pressure drop is known. / Thesis / Doctor of Philosophy (PhD) / The design of nuclear plant systems requires that public safety be ensured for the worst-case imaginable accident scenarios. This means that radioactive materials produced by nuclear fission must be safely contained. If the main steam pipe from a nuclear steam generator were to break, the water in the steam generator would rapidly boil off in what is called a blowdown. Such an event could produce significant loading on the heat exchanger tubes. Should the tubes rupture, radioactive materials may breach reactor containment. Thus, knowing the tube loading during this hypothetical scenario is an important input for safe design. The goal of this research is to improve our understanding of the effects of this postulated accident on the transient loading of the tubes. A laboratory study was carried out to simulate the blowdown. The experimental results provided valuable insights and guidance for the development of improved design tools.

Martin Luther’s two kingdoms has been overlooked by many as the church wrestles with what it looks like to engage with the post-Christendom political landscape. Much of this is due to the fact that a perverted version of Luther’s two kingdoms was used to justify acquiescence to the Nazi party in German. Luther’s actual two kingdoms theology calls for a critical engagement in politics that is motivated by love, operating through God’s two governments. Luther’s theology of the two kingdoms provides a way forward for political engagement after Christendom by avoiding the extremes of civic disengagement on the one hand, and a wholesale return to a Christendom synthesis on the other. / Thesis / Master of Divinity (M.Div)

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This paper presents the methods of predicting the steady-state two-phase flow (steam and water) pressure drop across the restrictions of annular geometries formed when tubes extend through circular holes in tube support plates. Two approaches are discussed and a detailed sample calculation of the one selected is presented. The major areas of discussion are the orientation of tubes-to-tube support plate holes, and the thickness of tube support plate. Finally, the conclusion gives a comparison of methods and recommendations for future investigations.

The flow patterns of an air-water mixture at atmospheric pressure were visually observed through a simulated vertical steam generator tube support plate of circular hole and trefoil designs. Flow oscillations with a period on the order of 0.4 seconds were observed in both support plates at similar mass flow rate combinations. The oscillation consisted of a period of rapid surging followed by a low flow or stagnation period on the order of 0.1 seconds. Reverse (downward) flow was also observed for part of the oscillation cycle in the trefoil support plate. The flow oscillations that exist in one tube support plate are coupled to the oscillation phase that exists in the preceding tube support plate. The operation of a steam generator in a region where this flow oscillation occurs could result in reduced to steam generator life due to increased corrosion.

Passwords are the dominant form of authentication on the web today. However,many users choose weak passwords and reuse the same password on multiple sites, thus increasing their vulnerability to having their credentials leaked or stolen. Two-factor authentication strengthens existing password authentication schemes against impersonation attacks and makes it more difficult for attackers to reuse stolen credentials on other websites. Despite the added security benefits of two-factor authentication, there are still many open questions about its usability. Many two-factor authentication systems in widespread usage today have not yet been subjected to adequate usability testing. Previous comparative studies have demonstrated significant differences in usability between various single-factor authentication systems.The main contributions of this work are as follows. First, we developed a novel user behavior model that describes four phases of interaction between a user and an authentication system. This model is designed to inform the design of future usability studies and will enable researchers and those implementing authentication systems to have a more nuanced understanding of authentication system usability. Second, we conducted a comparative usability study of some of the most common two-factor authentication systems. In contrast to previous authentication usability studies, we had participants use the system for a period of two weeks and collected both timing data and SUS metrics on the systems under test. From these studies, we make several conclusions about the state of usability and acceptance of two-factor authentication, finding that many users want more security for their sensitive online accounts and are open to using multiple forms of two-factor authentication. We also suggest that security researchers draw upon risk communication theory to better help users make informed security decisions.

Human life in Europe started to change radically in the first half of the twentieth century between two world wars. Comparing to the nineteenth-century Western musical environment, employing the early compositional technique and style of the past, mainly the Baroque and Classic period, Neo-classicism among the various movements in the twentieth century is extremely important but also controversial. With diversity of the musical style, Igor Stravinsky composed Concerto for Two Solo Pianos in 1935, which combined the compositional principles of the seventeenth and eighteenth centuries and the new musical innovations of the twentieth century. The piece reveals characteristics of Neo-classicism thoroughly. In addition to adopting four traditional forms and thematic development technique, Stravinsky replaced the orchestra part with the second piano and still kept the concertante textural treatment of a traditional concerto format. The first chapter will introduce the life and musical style of Stravinsky. In the second chapter Neo-classicism movement and how deeply Stravinsky was influence by it will be discussed. The third chapter focuses on the compositional background and formal analysis of the Concerto for Two Solo Pianos. And final part will be the conclusion of this topic.

The technique of hyper-Rayleigh scattering is employed to measure the first molecular hyperpolarizabilities£]of nonlinear optical chromophores provided by Industrial Technology Research Institute. £]0. In the thesis, the effect of the molecular structure and the solvent on the hyperpolarizabilities will be discussed further.

Thesis (Ph. D.)--Auburn University. / Abstract. Vita. Includes bibliographical references.