The Lewis Heat Pipe Code with Application to SP-100 GES Heat Pipes

The NASA Lewis Research Center has a thermal management program supporting SP-100 goals, which includes heat pipe radiator development. As a part of the program Lewis has elected to prepare an in-house heat pipe code tailored to the needs of its SP-100 staff to supplement codes from other sources. The latter, designed to meet the needs of the originating organizations, were deemed not entirely appropriate for use at Lewis. However, a review of their features proved most beneficial in the design of the Lewis code

X-Ray Scanner for Atlas Barrel TRT Modules

X-ray scanners for gain mapping of ATLAS Barrel Transition Radiation Tracker (TRT) modules were developed at Hampton University for quality assurance purposes. Gas gain variations for each straw of the TRT modules were used to decide whether wires should be removed or restrung, and to evaluate overall module quality.Comment: Conference proceeding in the XXIV Physics in Collisions Conference (PIC04), Boston, USA, June 2004, 3 pages, LaTeX, 6 eps figures. MONP0

Conference on Automated Decision-Making and Problem Solving, the Third Day: Issues Discussed

A conference held at Langley Research Center in May of 1980 brought together university experts from the fields of Control Theory, Operations Research, and Artificial Intelligence to explore current research in automation from both the perspective of their own particular disciplines and from that of interdisciplinary considerations. Informal discussions from the final day of the those day conference are summarized

NASA Lewis steady-state heat pipe code users manual

The NASA Lewis heat pipe code was developed to predict the performance of heat pipes in the steady state. The code can be used as a design tool on a personal computer or with a suitable calling routine, as a subroutine for a mainframe radiator code. A variety of wick structures, including a user input option, can be used. Heat pipes with multiple evaporators, condensers, and adiabatic sections in series and with wick structures that differ among sections can be modeled. Several working fluids can be chosen, including potassium, sodium, and lithium, for which monomer-dimer equilibrium is considered. The code incorporates a vapor flow algorithm that treats compressibility and axially varying heat input. This code facilitates the determination of heat pipe operating temperatures and heat pipe limits that may be encountered at the specified heat input and environment temperature. Data are input to the computer through a user-interactive input subroutine. Output, such as liquid and vapor pressures and temperatures, is printed at equally spaced axial positions along the pipe as determined by the user

Self-Organized Criticality Below The Glass Transition

We obtain evidence that the dynamics of glassy systems below the glass transition is characterized by self-organized criticality. Using molecular dynamics simulations of a model glass-former we identify clusters of cooperatively jumping particles. We find string-like clusters whose size is power-law distributed not only close to T_c but for ALL temperatures below T_c, indicating self-organized criticality which we interpret as a freezing in of critical behavior.Comment: 4 pages, 3 figure

Comparing Small-Group and Individual Behavior in Lottery-Choice Experiments

Lottery-choice experiments are conducted to compare risk preferences revealed by three-person groups versus isolated individuals. A lottery-choice experiment consists of a menu of paired lottery choices structured so that the crossover point from a low-risk to a high-risk lottery can be used to infer the degree of risk aversion. A between-subjects experiment of group versus individual lottery-choice decisions reveal that there is not a significant difference in the average crossover point, but lottery choices are affected by a significant interaction between subject composition (individual or group) and lottery winning percentage. Also, a three-phased individual-group-individual sequenced experiment reveals that the count of safe lotteries chosen by groups is, on average, significantly greater than the mean of the individual members. Finally, making a phase-two group decision has a significant impact on subsequent phase-three individual decisions relative to the initial phase-one (individual) decisions.lab experiments, risk preferences, group decisions

Comparing Small-Group and Individual Behavior in Lottery-Choice Experiments

Lottery-choice experiments are conducted to compare risk preferences revealed by three-person groups versus isolated individuals. A lottery-choice experiment consists of a menu of paired lottery choices structured so that the crossover point from a low-risk to a high-risk lottery can be used to infer the degree of risk aversion. A between-subjects experiment of group versus individual lottery-choice decisions reveal that there is not a significant difference in the average crossover point, but lottery choices are affected by a significant interaction between subject composition (individual or group) and lottery winning percentage. Also, a three-phased individual-group-individual sequenced experiment reveals that the count of safe lotteries chosen by groups is, on average, significantly greater than the mean of the individual members. Finally, making a phase-two group decision has a significant impact on subsequent phase-three individual decisions relative to the initial phase-one (individual) decisions.lab experiments, risk preferences, group decisions

Differentiation between polaron-pair and triplet-exciton polaron spin-dependent mechanisms in organic light-emitting diodes by coherent spin beating

Pulsed electrically detected magnetic resonance offers a unique avenue to distinguish between polaron-pair (PP) and triplet-exciton polaron (TEP) spin-dependent recombination, which control the conductivity and magnetoresistivity of organic semiconductors. Which of these two fundamental processes dominates depends on carrier balance: by injecting surplus electrons we show that both processes simultaneously impact the device conductivity. The two mechanisms are distinguished by the presence of a half-field resonance, indicative of TEP interactions, and transient spin beating, the signature of PPs. Coherent spin Rabi flopping in the half-field (triplet) channel is observed, demonstrating that the triplet exciton has an ensemble phase coherence time of at least 60 ns, offering insight into the effect of carrier correlations on spin dephasing

Image Ellipticity from Atmospheric Aberrations

We investigate the ellipticity of the point-spread function (PSF) produced by imaging an unresolved source with a telescope, subject to the effects of atmospheric turbulence. It is important to quantify these effects in order to understand the errors in shape measurements of astronomical objects, such as those used to study weak gravitational lensing of field galaxies. The PSF modeling involves either a Fourier transform of the phase information in the pupil plane or a ray-tracing approach, which has the advantage of requiring fewer computations than the Fourier transform. Using a standard method, involving the Gaussian weighted second moments of intensity, we then calculate the ellipticity of the PSF patterns. We find significant ellipticity for the instantaneous patterns (up to more than 10%). Longer exposures, which we approximate by combining multiple (N) images from uncorrelated atmospheric realizations, yield progressively lower ellipticity (as 1 / sqrt(N)). We also verify that the measured ellipticity does not depend on the sampling interval in the pupil plane using the Fourier method. However, we find that the results using the ray-tracing technique do depend on the pupil sampling interval, representing a gradual breakdown of the geometric approximation at high spatial frequencies. Therefore, ray tracing is generally not an accurate method of modeling PSF ellipticity induced by atmospheric turbulence unless some additional procedure is implemented to correctly account for the effects of high spatial frequency aberrations. The Fourier method, however, can be used directly to accurately model PSF ellipticity, which can give insights into errors in the statistics of field galaxy shapes used in studies of weak gravitational lensing.Comment: 9 pages, 5 color figures (some reduced in size). Accepted for publication in the Astrophysical Journa