Seeing spin dynamics in atomic gases

The dynamics of internal spin, electronic orbital, and nuclear motion states of atoms and molecules have preoccupied the atomic and molecular physics community for decades. Increasingly, such dynamics are being examined within many-body systems composed of atomic and molecular gases. Our findings sometimes bear close relation to phenomena observed in condensed-matter systems, while on other occasions they represent truly new areas of investigation. I discuss several examples of spin dynamics that occur within spinor Bose-Einstein gases, highlighting the advantages of spin-sensitive imaging for understanding and utilizing such dynamics.Comment: Chapter in upcoming Review Volume entitled "From Atomic to Mesoscale: The Role of Quantum Coherence in Systems of Various Complexities" from World Scientifi

Building a Socio-technical Perspective of Community Resilience with a Semiotic Approach

Situated in the diversity and adversity of real-life contexts facing crisis situations, this research aims at boosting the resilience process within communities supported by digital and social technology. In this paper, eight community leaders in different parts of the world are invited to express their issues and wishes regarding the support of technology to face social challenges. Methods and artefacts based on the Organisational Semiotics (OS) and the Socially-Aware computing have been applied to analyse and consolidate this data. By providing both a systemic view of the problem and also leading to the identification of requirements, the analysis evidences some benefits of the OS-based approach to consolidate perspectives from different real-life scenarios towards building a socio-technical solution

Making, probing and understanding Bose-Einstein condensates

Contribution to the proceedings of the 1998 Enrico Fermi summer school on Bose-Einstein condensation in Varenna, Italy.Comment: Long review paper with ~90 pages, ~20 figures. 2 GIF figures in separate files (4/5/99 fixed figure

Witnessing the Web: The Rhetoric of American E-Vangelism and Persuasion Online

From the distribution of religious tracts at Ellis Island and Billy Sunday’s radio messages to televised recordings of the Billy Graham Crusade and Pat Robertson’s 700 Club, American evangelicals have long made a practice of utilizing mass media to spread the Gospel. Most recently, these Christian evangelists have gone online. As a contribution to scholarship in religious rhetoric and media studies, this dissertation offers evangelistic websites as a case study into the ways persuasion is carried out on the Internet. Through an analysis of digital texts—including several evangelical home pages, a chat room, discussion forums, and a virtual church—I investigate how conversion is encouraged via web design and virtual community as well as how the Internet medium impacts the theology and rhetorical strategies of web evangelists. I argue for “persuasive architecture” and “persuasive communities”—web design on the fundamental level of interface layout and tightly-controlled restrictions on discourse and community membership—as key components of this strategy. In addition, I argue that evangelical ideology has been influenced by the web medium and that a “digital reformation” is taking place in the church, one centered on a move away from the Prosperity Gospel of televangelism to a Gospel focused on God as divine problem-solver and salvation as an uncomplicated, individualized, and instantaneously-rewarding experience, mimicking Web 2.0 users’ desire for quick, timely, and effective answers to all queries. This study simultaneously illuminates the structural and fundamental levels of design through which the web persuades as well as how—as rhetoricians from Plato’s King Thamus to Marshall McLuhan have recognized—media inevitably shapes the message and culture of its users

Generating Schr\"{o}dinger-cat states in momentum and internal-state space from Bose-Einstein condensates with repulsive interactions

Resonant Raman coupling between internal levels induced by continuous illumination of non-collinear laser beams can create double-well momentum-space potentials for multi-level ``periodically-dressed'' atoms. We develop an approximate many-body formalism for a weakly interacting, trapped periodically-dressed Bose gas which illustrates how a tunable exchange interaction yields correlated many-body ground states. In contrast to the case of a position-space double well, the ground state of stable periodically-dressed Bose gases with repulsive interactions tends toward a Schr\"{o}dinger cat state in the regime where interactions dominate the momentum-space tunnelling induced by the external trapping potential. The dependence of the momentum-space tunnelling and exchange interaction on experimental parameters is derived. We discuss how real-time control of experimental parameters can be used to create Schr\"{o}dinger cat states either between momentum or internal states, and how these states could be dynamically controlled towards highly sensitive interferometry and frequency metrology.Comment: 7 pages, 3 figures. Submitted to PR

AN EXPERIMENTAL INVESTIGATION OF HIGH-SPEED AIR-BREATHING VEHICLE PERFORMANCE METRICS

High-speed air-breathing vehicles are one of the main hypersonic vehicles currently being developed. There is a current push by major world powers to develop these vehicles and one of the major limiting factors is engine design. The high-speed air-breathing vehicles necessitate an engine that can perform at higher speeds and higher temperatures, such as a scramjet. This engine is broken into three main parts: the inlet, isolator, and combustor. One of the primary concerns for these vehicles is engine unstart, which is when there is no longer supersonic flow through the engine and the engine can no longer perform. This is typically considered a worst-case scenario for these vehicles and is equated with vehicle loss. This study is broken into two main experiments looking at the inlet and isolator sections of the scramjet flow path. These experiments were done with computational counterparts as the need for complementary studies has been well documented in the literature. Specifically for scramjets, the flight Mach number, Reynolds number, and enthalpy are very difficult to match in ground testing. Thus, there is a distinct need for computational studies to support ground testing in vehicle development. The inlet study uses a crossing shock-wave/boundary-layer interaction as a canonical representation of an inlet, specifically at an off-design-condition with a large shock-wave/boundary layer created in the inlet flow. Then, vortex generators were employed to determine the effect of passive flow control on such an interaction. They were shown to delay separation but cause in increase in flow distortion. The isolator study used a dynamic cylinder model to create a shock train in the wind tunnel test section. This accurately modeled a shock train in an isolator section of a scramjet flow path. Unstart was then created by moving the shock train with the dynamic cylinder which changed the backpressure ratio. Additionally, the asymmetrical nature of the shock train was investigated in the experimental data after the asymmetry was noted in the computations. The experimental data conferred well with the computational data as a strong asymmetrical trend was shown