High-temperature optically activated GaAs power switching for aircraft digital electronic control

Gallium arsenide high-temperature devices were fabricated and assembled into an optically activated pulse-width-modulated power control for a torque motor typical of the kinds used in jet engine actuators. A bipolar heterojunction phototransistor with gallium aluminum arsenide emitter/window, a gallium arsenide junction field-effect power transistor and a gallium arsenide transient protection diode were designed and fabricated. A high-temperature fiber optic/phototransistor coupling scheme was implemented. The devices assembled into the demonstrator were successfully tested at 250 C, proving the feasibility of actuator-located switching of control power using optical signals transmitted by fibers. Assessments of the efficiency and technical merits were made for extension of this high-temperature technology to local conversion of optical power to electrical power and its control at levels useful for driving actuators. Optical power sources included in the comparisons were an infrared light-emitting diode, an injection laser diode, tungsten-halogen lamps and arc lamps. Optical-to-electrical power conversion was limited to photovoltaics located at the actuator. Impedance matching of the photovoltaic array to the load was considered over the full temperature range, -55 C to 260 C. Loss of photovoltaic efficiency at higher temperatures was taken into account. Serious losses in efficiency are: (1) in the optical source and the cooling which they may require in the assumed 125 C ambient, (2) in the decreased conversion efficiency of the gallium arsenide photovoltaic at 260 C, and (3) in impedance matching. Practical systems require improvements in these areas

Observation of emission from chaotic lasing modes in deformed microspheres: displacement by the stable orbit modes

By combining detailed imaging measurements at different tilt angles with simulations of ray emission from prolate deformed lasing micro-droplets, we conclude that the probability density for the lasing modes in a three-dimensional dielectric microcavity must reside in the chaotic region of the ray phase space. In particular, maximum emission from such chaotic lasing modes is not from tangent rays emerging from the highest curvature part of the rim. The laser emission is observed and calculated to be non-tangent and displaced from the highest curvature due to the presence of stable orbits. In this Letter we present the first experimental evidence for this phenomenon of ``dynamical eclipsing''.Comment: 4 figure

Eigenvector Expansion and Petermann Factor for Ohmically Damped Oscillators

Correlation functions $C(t) \sim$ in ohmically damped systems such as coupled harmonic oscillators or optical resonators can be expressed as a single sum over modes $j$ (which are not power-orthogonal), with each term multiplied by the Petermann factor (PF) $C_j$, leading to "excess noise" when $|C_j| > 1$. It is shown that $|C_j| > 1$ is common rather than exceptional, that $|C_j|$ can be large even for weak damping, and that the PF appears in other processes as well: for example, a time-independent perturbation \sim\ep leads to a frequency shift \sim \ep C_j. The coalescence of $J$ ($>1$) eigenvectors gives rise to a critical point, which exhibits "giant excess noise" ($C_j \to \infty$). At critical points, the divergent parts of $J$ contributions to $C(t)$ cancel, while time-independent perturbations lead to non-analytic shifts \sim \ep^{1/J}.Comment: REVTeX4, 14 pages, 4 figures. v2: final, 20 single-col. pages, 2 figures. Streamlined with emphasis on physics over formalism; rewrote Section V E so that it refers to time-dependent (instead of non-equilibrium) effect

Chaotic Waveguide-Based Resonators for Microlasers

We propose the construction of highly directional emission microlasers using two-dimensional high-index semiconductor waveguides as {\it open} resonators. The prototype waveguide is formed by two collinear leads connected to a cavity of certain shape. The proposed lasing mechanism requires that the shape of the cavity yield mixed chaotic ray dynamics so as to have the appropiate (phase space) resonance islands. These islands allow, via Heisenberg's uncertainty principle, the appearance of quasi bound states (QBS) which, in turn, propitiate the lasing mechanism. The energy values of the QBS are found through the solution of the Helmholtz equation. We use classical ray dynamics to predict the direction and intensity of the lasing produced by such open resonators for typical values of the index of refraction.Comment: 5 pages, 5 figure

Pragmatism and a “Catholic” Philosophical Anthropology

Catholic identity is often discussed in relation to institutions such as schools and hospitals. Catholic identity can also be investigated in relationship to various disciplines, including philosophy, anthropology, and psychology. This article builds a bridge to neoscholastic thought in articulating a philosophical anthropology which strives to maintain a Catholic identity and focus. The work of Charles Taylor, a leading Catholic philosopher, is presented in an effort to place the existential problem of personal agency within a Catholic framework

Ideology, Political Power, And Economic Development In Alabama, 1990-2000

US states have many policy options to promote short-term and long-term development of local economies and workforces. During the 1990s and 2000s, Alabama voters rejected a number of policy proposals designed with long -term, balanced development in mind, maintaining by default their state's capital-subsidy framework for economic growth. These outcomes were surprising; many observers expected the bills to pass because they were progressive and had strong business support. Using a power framework and methodology developed by Gaventa (1980) and others, this mixedmethods study explores the way power was used to shape two vote outcomes. Through consideration of the historical, structural, and cultural makeup of the state, and mindful of theories about -the end of Southern exceptionalism[DOUBLE VERTICAL LINE] (Shafer & Johnston, 2006), the study develops hypotheses about the continued role of regressive institutions in shaping Alabamians' ideas about development. Content analysis of public debate suggests that -jobs and development[DOUBLE VERTICAL LINE] arguments for the proposals were less resonant with voters than expected. Subsequent regression analysis of countylevel voting confirms that race still plays an important role in predicting voters' response to progressive development policies. This research is important because it focuses on the causes and durability of spatial inequality at the subnational level, a scale that has been neglected by social science but is a key site for public policy interventions (Lobao, Hooks, & Tickameyer, 2008). It also provides a lens for the iii study of economically -uneven[DOUBLE VERTICAL LINE] regions negotiating post-industrial change and a new knowledge-based global economy. i

Jean-Luc Marion

https://dsc.duq.edu/phen-intro-videos/1011/thumbnail.jp