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PtSi/Si Schottky-barrier devices detecting long-wavelength infrared (LWIR) photons demonstrated. Essential feature of one of these devices is p+ "doping spike"; layer of Si about 10 Angstrom thick, located at PtSi/Si interface, and doped with electron acceptors (boron atoms) at concentration between 5 x 10(19) and 2 x 10(20) cm(-3). Doping spikes extend cutoff wavelengths of devices to greater values than otherwise possible.
The use of synthetic aperture radar (SAR) polarimetric processing for enhancing the detection, classification, and/or identification of scene scattering features is described. This paper describes and compares the results obtained from applying the polarimetric techniques that have been developed and/or advanced by researchers at MIT Lincoln Laboratory, and basic polarimetric match filter (PMF) techniques that have been modified to treat distributed scatterers. The paper describes the individual polarimetric processing techniques and the formulation used fro their application to polarimetric imagery obtained from the NAWC P-3 SAR. In all cases, the polarimetric techniques have been applied to enhance the detection of distributed scatterers in clutter The emphasis arises from considering most complex scatterers of interest (either man made or natural) as distributed scatterers consisting of multiple scattering centers, and many modern polarimetric radar systems have the resolution performance to resolve the multiple scattering centers. Furthermore, the individual scattering centers of a distributed target can often exhibit different polarimetric scattering characteristics, and consequently do not respond favorably to polarimetric processing techniques derived for individual point scatterers. The treatment of distributed scatterers also includes concepts for tuning the polarimetric ensemble response of individual scattering centers.
A goal of this paper is to review the recent progress astrophysicists, astronomers, and physicists have made in the r-, s-, and p-processes in nucleosynthesis and to point out the problems that remain in our understanding of the formation of the heavy nuclei. Another, perhaps deeper, goal is to to seek some understanding of why there are three major processes available to nature for synthesis of heavy elements.
The investigation of the effects of inhomogeneities of the acoustic modes of the global solar oscillation spectrum has two parts, the first dealing with the prediction of wave fluxes in magnetic flux tubes due to the excitation of longitudinal (i.e. pressure) modes, and the second part, concerning the effects of radiation damping on the p-modes themselves. Part 1 of this work, in collaboration with S.S. Hasan (Indian Institute of Astro- physics, Bangalore), is complete and has resulted in a publication titled Excitation of Longitudinal Modes in Solar Magnetic Flux Tubes, By S.S. Hasan & WK. It is in press in the ASP conference series, containing the proceedings of the Cool Stars conference of 1997, R.A. Donahue and J.A. Bookbinder, editors; publication is expected in 1998. Part 2, in collaboration with Y. Zhugzhda (Izmiran, Moscow) and J. Staude (Sonnenobservatorium Einsteinturm, Potsdam) is in progress and is expected to result in a paper in the forthcoming Boston conference on Helio- and Asteroseismology in June, 1998. A fuller accounting of the work done under the grant will be given when the work started with funding from the grant is complete.
An experimental investigation has been made to determine the dynamic stability and control characteristics of a 1/6-scale flying model of the Hawker P lIP7 jet vertical-take-off-and-landing (VTOL) airplane in hovering and transition flight. The model was powered by a counter-rotating ducted fan driven by compressed-air jets at the tips of the fan blades. In hovering flight the model was controlled by jet-reaction controls which consisted of yaw and pitch jets at the extremities of the fuselage and a roll jet on each wing tip. In forward flight the model was controlled by conventional ailerons and rudder and an all-movable horizontal tail. In hovering flight the model could be flown smoothly and easily, but the roll control was considered too weak for rapid maneuvering or hovering in gusty air. Transitions from hovering to normal forward flight and back to hovering could be made smoothly and consistently and with only moderate changes in longitudinal trim. The model had a static longitudinal instability or pitch-up tendency throughout the transition range, but the rate of divergence in the pitch-up was moderate and the model could be controlled easily provided the angle of attack was not allowed to become too high. In both the transition and normal forward flight conditions the lateral motions of the model were difficult to control at high angles of attack, apparently because of low directional stability at small angles of sideslip. The longitudinal stability of the model in normal forward flight was generally satisfactory, but there was a decided pitch-up tendency for the flap-down condition at high angles of attack. In the VTOL landing approach condition, with the jets directed straight down or slightly forward, the nose-down pitch trim required was greater than in the transitions from hovering to forward flight, but the longitudinal instability was about the same. Take-offs and landings in still air could be made smoothly although there was a slight unfavorable ground effect on lift and a nose-down change in pitch trim near the ground. Short take-offs and landings could be made smoothly and consistently although the model experienced a decided nose-up change in pitching moment as it climbed out of ground effect.
Sensitivity analysis is a technique for determining derivatives of system responses with respect to design parameters. Among many methods available for sensitivity analysis, automatic differentiation has been proven through many applications in fluid dynamics and structural mechanics to be an accurate and easy method for obtaining derivatives. Nevertheless, the method can be computational expensive and can require a high memory space. This project will apply an automatic differentiation tool, ADIFOR, to a p-version finite element code to obtain first- and second- order then-nal derivatives, respectively. The focus of the study is on the implementation process and the performance of the ADIFOR-enhanced codes for sensitivity analysis in terms of memory requirement, computational efficiency, and accuracy.
Given the high density (approx. 10(exp 4)/sq cm) of elementary screw dislocations (Burgers vector = 1c with no hollow core) in commercial SiC wafers and epilayers, all appreciable current (greater than 1 A) SiC power devices will likely contain elementary screw dislocations for the foreseeable future. It is therefore important to ascertain the electrical impact of these defects, particularly in high-field vertical power device topologies where SiC is expected to enable large performance improvements in solid-state high-power systems. This paper compares the DC-measured reverse-breakdown characteristics of low-voltage (less than 250 V) small-area (less than 5 x 10(exp -4)/sq cm) 4H-SiC p(+)n diodes with and without elementary screw dislocations. Compared to screw dislocation-free devices, diodes containing elementary screw dislocations exhibited higher pre-breakdown reverse leakage currents, softer reverse breakdown I-V knees, and highly localized microplasmic breakdown current filaments. The observed localized 4H-SiC breakdown parallels microplasmic breakdowns observed in silicon and other semiconductors, in which space-charge effects limit current conduction through the local microplasma as reverse bias is increased.
Antiproton production in heavy ion collisions reflects subtle interplay between initial production and absorption by nucleons. Because the AGS energies (10--20 A(center-dot)GeV/c) are close to the antiproton production threshold, antiproton may be sensitive to cooperative processes such as QGP and hadronic multi-step processes. On the other hand, antiproton has been proposed as a probe of baryon density due to large N(anti N) annihilation cross sections. Cascade models predict the maximum baryon density reaches about 10 times the normal nucleus density in central Au+Au collisions, where the strong antiproton absorption is expected. In this paper, the authors show systematic studies of antiproton production from p+A to Au+Au collisions.
This paper outlines the dynamic reverse-breakdown characteristics of low-voltage (<250 V) small-area <5 x 10(exp -4) sq cm 4H-SiC p(sup +)n diodes subjected to nonadiabatic breakdown-bias pulsewidths ranging from 0.1 to 20 microseconds. 4H-SiC diodes with and without elementary screw dislocations exhibited positive temperature coefficient of breakdown voltage and high junction failure power densities approximately five times larger than the average failure power density of reliable silicon pn rectifiers. This result indicates that highly reliable low-voltage SiC rectifiers may be attainable despite the presence of elementary screw dislocations. However, the impact of elementary screw dislocations on other more useful 4H-SiC power device structures, such as high-voltage (>1 kV) pn junction and Schottky rectifiers, and bipolar gain devices (thyristors, IGBT's, etc.) remains to be investigated.
Given the high density (approx. 10(exp 4)/sq cm) of elementary screw dislocations (Burgers vector = lc with no hollow core) in commercial SiC wafers and epilayers, all appreciable current (greater than 1 A) SiC power devices will likely contain elementary screw dislocations for the foreseeable future. It is therefore important to ascertain the electrical impact of these defects, particularly in high-field vertical power device topologies where SiC is expected to enable large performance improvements in solid-state high-power systems. This paper compares the DC-measured reverse-breakdown characteristics of low-voltage (less than 250 V) small-area (less than 5 x 10(exp -4) sq cm) 4H-SiC p(+)n diodes with and without elementary screw dislocations. Compared to screw dislocation-free devices, diodes containing elementary screw dislocations exhibited higher pre-breakdown reverse leakage currents, softer reverse breakdown I-V knees, and highly localized microplasmic breakdown current filaments. The observed localized 4H-SiC breakdown parallels microplasmic breakdowns observed in silicon and other semiconductors, in which space-charge effects limit current conduction through the local microplasma as reverse bias is increased.
Absolute rate data for the Cl(2)P(J) + CH4 yields HCl + CH3 reaction have been obtained from 218 to 298 K by using the discharge-flow resonance fluorescence technique at I Torr total pressure. The result at 298 K is (10.1 +/- 0.6) x 10(exp -14) cu cm/molecule/s. The temperature dependence in Arrhenius form is (6.5 +/- 0.9 ) x 10(exp -12) exp[(-1235 +/- 34 )/T]. The errors given are one standard deviation; overall experimental error is estimated at +/- 15%. Because of the relatively large disagreement among earlier measurements at low temperatures, the results were examined for possible effects of non-Boltzmann spin distribution and vibrational excitation of CH4, secondary chemistry of CH3 radicals, and impurities in the CH4 source. There was no significant change in the observed rate constant when an efficient spin quencher, CF4, was added and estimates indicate that vibrational partitioning in CH4 should be at the ambient reactor temperature before the start of the reaction. The results were also independent of the source of Cl atoms (microwave discharge or thermal decomposition of Cl2) and whether CH4 was purified in-situ. However, the observed rate constant did depend on initial Cl atom concentrations and to a lesser extent on CH4 concentrations. Numerical simulations were used to assess the importance of secondary chemistry over a range of reactant concentrations
Live footage of a preflight interview with Soyuz Commander Yuri P. Gidzenko is seen. The interview addresses many different questions including why Gidzenko became interested in the space program, the events that led to his interest, the transition from being a military pilot to being selected as a Russian cosmonaut. Other interesting information that this one-on-one interview discusses are the main goals of the first Expedition Crew, their scheduled docking with the International Space Station (ISS), making the ISS ready for human inhabitance, and all the specifics that will make his living arrangements difficult. Gidzenko mentions his responsibilities during the much-anticipated two-day flight to the ISS on the Soyuz spacecraft, as well as the possibility of his space-walk. Gidzenko also discusses the crew's first tasks upon entrance including other scheduled tasks for the first week, docking from cargo ships, and spacecraft delivering equipment or performing Extra Vehicular Activities (EVA). He explains his opinion of the implications of having human beings in space.
This project involved the design and construction of a new instrument for airborne measurement of DMS and SO2. The instrument is intended for use on field missions to study the global atmospheric sulfur cycle. The ultimate scientific goal is to provide insight into the mechanisms of atmospheric transport and transformations impacting both natural and anthropogenic sulfur emissions. This report summarizes the progress made to date and the goals for future work on the project. The PI's for this project have recently relocated from the University of Miami to the University of California, Irvine, and a request has been made to transfer remaining funds to UCI. All equipment associated with this project has been transferred to UCI. The instrument design goal was to develop an instrument roughly one quarter the size and weight of currently available airborne instrumentation used for DMS and S02 measurements. Another goal was full automation, to allow unattended operation for the duration of a P-3 or DC-8 flight. The original performance design specifications for the instrument are given.
This project involved the installation of a downsized multichannel mass spectrometer instrument on the NASA P-3B aircraft and its subsequent use on the PEM-Tropics B mission. The new instrument performed well, measuring a number of difficult-to-measure compounds and providing much new photochemical and sulfur data as well as possibly uncovering a new nighttime DMSO source. The details of this effort are discussed.
This paper describes the procedures and algorithms for the laboratory calibration and the field data retrieval of the NASA Langley / Ames Diode Laser Hygrometer as implemented during the NASA Trace-P mission during February to April 2000. The calibration is based on a NIST traceable dewpoint hygrometer using relatively high humidity and short pathlength. Two water lines of widely different strengths are used to increase the dynamic range of the instrument in the course of a flight. The laboratory results are incorporated into a numerical model of the second harmonic spectrum for each of the two spectral window regions using spectroscopic parameters from the HITRAN database and other sources, allowing water vapor retrieval at upper tropospheric and lower stratospheric temperatures and humidity levels. The data retrieval algorithm is simple, numerically stable, and accurate. A comparison with other water vapor instruments on board the NASA DC-8 and ER-2 aircraft is presented.
The effect of 40 keV electron irradiation on a-Si:H p-i-n single-junction solar cells was investigated using measured and simulated dark J-V characteristics. EPRI-AMPS and PC-1D simulators were explored for use in the studies. The EPRI-AMPS simulator was employed and simulator parameters selected to produce agreement with measured J-V characteristics. Three current mechanisms were evident in the measured dark J-V characteristics after electron irradiation, namely, injection, shunting and a term of the form CV(sup m). Using a single discrete defect state level at the center of the band gap, good agreement was achieved between measured and simulated J-V characteristics in the forward-bias voltage region where the dark current density was dominated by injection. The current mechanism of the form CV(sup m) was removed by annealing for two hours at 140 C. Subsequent irradiation restored the CV(sup m) current mechanism and it was removed by a second anneal. Some evidence of the CV(sup m) term is present in device simulations with a higher level of discrete density of states located at the center of the bandgap.
A method for eliminating spurious solution in the k dot p Hamiltonian has been proposed. Introduction of additional off-diagonal alpha k(exp 2) term converts spurious solution with large real wave vector to evanescent solution with large imaginary wave vector. This modification keeps the same effective masses at Gamma point and introduces negligible deviation from original nonparabolicity. A set of unphysical fast oscillation eigenfunctions in confined states of heterostructures are removed.
This report contains the flight-test results of the lateral and directional-stability and control phase (including tests with wing-tip tanks) of a general flying-qualities investigation of the Lockheed P-80A airplane (Army No. 44-85099). These tests were conducted at indicated airspeeds up to 494 miles per hour (0.691 Mach number) at low altitude and up to 378 miles per hour (0.816 Mach number) at high altitude. These tests showed that the flying qualities of the airplane were for the most part in accordance with the requirements of the Army Air Forces Stability and Control Specifications. The only major deficiency noted was the negative lateral stability with the wing-tip tanks installed.