Slow‐Wave Structures Utilizing Superconducting Thin‐Film Transmission Lines

Slow‐wave propagation of electromagnetic waves in transmission lines formed of thin‐film superconductors has been studied theoretically and experimentally. Previous theoretical analyses have been extended to include nonlocal theories. Strong dependence of phase velocity is found on film thickness and interfilm spacing when these become less than a few penetration depths. Velocity is also modified by coherence length, mean free path, nature of reflection of electrons at the film surfaces, and by temperature and magnetic field. Experimental measurements were made to verify the dependence on thickness, spacing, and temperature by means of a resonance technique. Agreement with theory was excellent in the case of temperature. Data taken for varying thickness and spacing verified the general trend of theoretical predictions. They indicate a nonlocal behavior with some specular reflection, but scatter of the data taken for different films prevents precise comparison of theory and experiment. Estimates of bulk penetration depths were made for indium, λ_In = 648±130 Å. For tantalum a rough estimate could be made of λTa = 580 Å. Data were consistent with the estimate of coherence length for indium of ξ_0 ≈ 3000 Å. Velocity was found to be independent of frequency in the range 50–500 MHz, while losses increased as the square. Pulse measurements indicated that delays of several microseconds and storage of several thousand pulses on a single line are feasible

Microcomputerized electric field meter diagnostic and calibration system

A computerized field meter calibration system which includes an apparatus for testing the calibration of field meters normally utilized for measuring electromagnetic field potentials is described. A reference voltage is applied to the field meter for causing signals to be produced on the output terminals thereof. A bank of relays is provided for selectively connecting output terminals of the field meter to a multiplexer by means of a digital voltmeter and an oscilloscope. A frequency-shift-keyed receiver is also connected to one of the terminals of the field meter for transmitting and converting a frequency shift keyed signal to a digital signal which is, subsequently, applied to the multiplexer

The combustion of dust suspensions

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NASTRAN solutions of problems described by simultaneous parabolic differential equations

NASTRAN solution techniques are shown for a numerical analysis of a class of coupled vector flow processes described by simultaneous parabolic differential equations. To define one physical problem type where equations of this form arise, the differential equations describing the coupled transfers of heat and mass in mechanical equilibrium with negligible mass average velocity are presented and discussed. Also shown are the equations describing seepage when both electrokinetic and hydrodynamic forces occur. Based on a variational statement of the general problem type, the concepts of scalar transfer elements and parallel element systems are introduced. It is shown that adoptation of these concepts allows the direct use of NASTRAN's existing Laplace type elements for uncoupled flow (the heat transfer elements) for treating multicomponent coupled transfer. Sample problems are included which demonstrate the application of these techniques for both steady-state and transient problems

Observations of Early Optical Afterglows

The Swift Ultra-Violet/Optical Telescope (UVOT) has performed extensive follow-up on 71 Swift Burst Alert Telescope triggered gamma-ray bursts (GRBs) in its first ten months of operations. In this paper, we discuss some of the UV and optical properties of UVOT detected afterglows such as XRF 050406, the bright GRB 050525A, the high redshift GRB 050730, the early flaring GRB 050801, and others. We also discuss some of the implications of why 75% of GRB afterglows observed by UVOT in less than one hour are "dark."Comment: 10 pages, 6 figures, to appear in the Proceedings of the 16th Annual Astrophysics Conference in Maryland "Gamma Ray Bursts in the Swift Era," Washington, DC, November 29 - December 2, 200

Causes of U.S. Bank Distress During the Depression

This paper provides the first comprehensive econometric analysis of the causes of bank distress during the Depression. We assemble bank-level data for virtually all Fed member banks, and combine those data with county-level, state-level, and national-level economic characteristics to capture cross-sectional and inter-temporal variation in the determinants of bank failure. We construct a model of bank survival duration using these fundamental determinants of bank failure as predictors, and investigate the adequacy of fundamentals for explaining bank failures during alleged episodes of nationwide or regional banking panics. We find that fundamentals explain most of the incidence of bank failure, and argue that contagion' or liquidity crises' were a relatively unimportant influence on bank failure risk prior to 1933. We construct upper-bound measures of the importance of contagion or liquidity crises. At the national level, we find that the first two banking crises identified by Friedman and Schwartz in 1930 and 1931 are not associated with positive unexplained residual failure risk, or with changes in the importance of liquidity measures for forecasting bank failures. The third banking crisis they identify is a more ambiguous case, but even if one views it as a bona fide national liquidity crisis, the size of the contagion effect could not have been very large. The last banking crisis they identify at the beginning of 1933 is associated with important, unexplained increases in bank failure risk. We also investigate the potential role of regional or local contagion and illiquidity crises for promoting bank failure and find some evidence in support of such effects, but these are of small importance in the aggregate. We also investigate the causes of bank distress measured as deposit contraction, using county-level measures of deposits of all commercial banks, and reach similar conclusions about the importance of fundamentals in determining deposit contraction.

Experimental investigation of two nonaxisymmetric wedge nozzles at free stream Mach numbers up to 1.20

Forces and pressures on two nonaxisymmetric wedge nozzles were measured in a 16 foot transonic tunnel. Tests were conducted at static conditions and at free stream Mach numbers of 0.60, 0.80, 0.90, 0.94, and 1.20. The range of nozzle pressure ratios varied with configuration and Mach number. The internal and external geometry of the nozzles and the test model are defined in detail. Nozzle performance data are presented as discharge coefficients, internal thrust ratios, thrust minus nozzle drag ratios, and ideal thrust coefficients. Extensive internal and external pressure measurements are presented