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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Uncertainty relations as Hilbert space geometry

Precision measurements involve the accurate determination of parameters through repeated measurements of identically prepared experimental setups. For many parameters there is a 'natural' choice for the quantum observable which is expected to give optimal information; and from this observable one can construct an Heinsenberg uncertainty principle (HUP) bound on the precision attainable for the parameter. However, the classical statistics of multiple sampling directly gives us tools to construct bounds for the precision available for the parameters of interest (even when no obvious natural quantum observable exists, such as for phase, or time); it is found that these direct bounds are more restrictive than those of the HUP. The implication is that the natural quantum observables typically do not encode the optimal information (even for observables such as position, and momentum); we show how this can be understood simply in terms of the Hilbert space geometry. Another striking feature of these bounds to parameter uncertainty is that for a large enough number of repetitions of the measurements all V quantum states are 'minimum uncertainty' states - not just Gaussian wave-packets. Thus, these bounds tell us what precision is achievable as well as merely what is allowed.

Braunstein, Samuel L.↗
NASA NTRS1992

Study of natural convection and interface shape in directional solidification of succinonitrile

Flow visualization experiments in a Bridgman furnace at zero growth velocity have been performed. The experiments were intended to investigate if the photochromic dye activation method could be used in a crystal growth study. The results from this work have confirmed that with a carefully designed experimental setup, the photochromic-dye method permits qualitative and quantitative evaluation of the flow field near the interface in crystal growth experiments. For the horizontal orientation of a 6 mm x 6 mm ampoule and an axial temperature gradient of 26.5 C/cm, velocity profiles have been obtained accurately at various positions near the interface. The maximum velocity of 1.29 mm/sec was measured in the central vertical plane and the flow was symmetrical about that plane. A flow inversion point was also noted, above which the flow was towards the interface and below it, away from the interface. The results obtained are useful for validating 3-dimensional numerical models and establishing a link between the macroscopic processing conditions and the formation of crystalline defects.

Kawaji, M.↗
NASA NTRS1995

The effect of gravity on the combustion synthesis of Ni-Al and Ni3Al-TiB2 composites from elements

Previous studies on the combustion synthesis of advanced materials indicate that combustion and structure formation mechanisms involve several stages including melting of reactants and products, spreading of the melt, droplet coalescence, diffusion and convection, buoyancy of solid particles, and densification of the liquid product. Most of these processes are affected by gravity. Conducting the combustion synthesis under microgravity conditions is expected to help elucidate the reaction mechanisms. Two systems were examined. The first involves Ni/AI cladded particles, which is an ideal system to examine the individual particle and liquid flow before combustion occurs. For comparison, elemental Ni and Al powders with the same stoichiometry as that of the cladded particles were also used in some experiments. The second system was the Ni3AITiB2 composite in which the Ni3AI (-delta H(sub f) = 153.1 kJ/mol) phase melts during reaction enabling us to examine settling of the liquid phase. The amount of liquid phase was controlled by varying the TiB2 (-delta H(sub f) = 323.8 kJ/mol) content which generates the additional heat. The overall reactions for the two systems can be expressed as follows. System 1: 4Ni + 2AI yields Ni3AI + NiA and System 2: 3Ni + Al + x (Ti + 2B) yields Ni3Al + x(TiB2). For the first system, pellets were pressed directly from the cladded particles, at green densities about 77 +/- 3% of theoretical value. For the second, the pellets were prepared by mixing the elemental reactant powders in the required stoichiometry by ball-milling and then pressing uniaxially at green densities about 70 +/- 3 percent of theoretical. The pellets were cylindrical in shape, 10 mm in diameter and length typically 20-30 mm. The pellet samples were reacted in UHP Argon (1 atm) using the experimental setup and procedure described previously. After reaction, the samples were sectioned axially in order to conduct the microstructural analysis in the longitudinal direction. The phase composition of the reacted product was determined by X-ray diffraction (XRD) and the microstructure was analyzed using scanning electron microscopy (SEM) along with energy dispersive X-ray spectrometry (EDX).

Varma, Arvind↗
NASA NTRS1995

Evaluation of wireless data communications at KSC

This project is motivated by the need for temporary or emergency provisioning of LAN service at KSC. The main goal of the project was to evaluate existing wireless bridge equipment in the KSC environment. Wireless bridge equipment can be used to make a wireless connection between two remotely located LAN segments. This report describes the experimental setup used to evaluate the equipment, including antenna connections, workstation connections, bridge software and workstation software The rangefinder program on the bridge was used to gather data about how the RF propagation environment at KSC affects the performance of the wireless bridge. Data was gathered for indoor as well as outdoor propagation. The report concludes with recommendations on how to take into account the particular terrain and building structures at KSC to design future applications of wireless bridges.

Gejji, Raghvendra R.↗
NASA NTRS1996

Two-Photon Entanglement and EPR Experiments Using Type-2 Spontaneous Parametric Down Conversion

Simultaneous entanglement in spin and space-time of a two-photon quantum state generated in type-2 spontaneous parametric down-conversion is demonstrated by the observation of quantum interference with 98% visibility in a simple beam-splitter (Hanburry Brown-Twiss) anticorrelation experiment. The nonlocal cancellation of two-photon probability amplitudes as a result of this double entanglement allows us to demonstrate two different types of Bell's inequality violations in one experimental setup.

Sergienko, A. V.↗
NASA NTRS1996

Stereo viewing 3-component, planar PIV utilizing fuzzy inference

An all electronic 3-D Digital Particle Image Velocimetry (DPIV) system has been developed for use in high velocity (supersonic) flows. Two high resolution CCD cameras mounted in a stereo viewing configuration are used to determine the out-of-plane velocity component from the difference of the in-plane velocity measurements. Double exposure image frames are acquired and Fuzzy inference techniques are used to maximize the validity of the velocity estimates obtained from the auto-correlation analysis. The CCD cameras are tilted relative to their respective lens axes to satisfy Scheimpflug's condition. Tilting the camera film plane ensures that the entire image plane is in focus. Perspective distortion still results, but can be corrected by proper calibration of the optical system. A calibration fixture is used to determine the experimental setup parameters and to assess the accuracy to which the z-plane displacements can be estimated. The details of the calibration fixture and procedure are discussed in the text. A pair of pulsed Nd:YAG lasers operating at 532 nm are used to illuminate the seeded flow from a convergent nozzle operated in an underexpanded condition. The light sheet was oriented perpendicular to the nozzle flow, yielding planar cross-sections of the 3-component velocity field at several axial stations. The key features of the supersonic jet are readily observed in the cross-plane vector plots.

Wernet, Mark P.↗
NASA NTRS1995

Fabrication of Fabry-Perot Interferometer Sensors and Characterization of their Performances for Aircraft Inspection

This work provides the information for fabricating Fabry-Perot Interferometer sensors and their performances. The Fabry-Perot Interferometer sensors developed here will be used for the detection of flaws in aircraft structures. The sequel also contains discussion of the experimental setups for the Ultrasonic technique and the Fabry-Perot Interferometer.

Pendergrass, LeRuth Q.↗
NASA NTRS1995

Performance of Low-Power Pulsed Arcjets

The Electric Propulsion Laboratory at UIUC has in place all the capability and diagnostics required for performance testing of low power pulsed and DC arcjets. The UIUC thrust stand is operating with excellent accuracy and sensitivity at very low thrust levels. An important aspect of the experimental setup is the use of a PID controller to maintain a constant thruster position, which reduces hysterisis effects. Electrical noise from the arcjet induces some noise into the thrust signal, but this does not affect the measurement.

Burton, Rodney L.↗
NASA NTRS1997

Calibration of Direct Velocimetry Using Hot Wire Anemometry

We studied the functionality of the IFA300 Hot Wire Anemometry system and its feasibility for the calibration of Direct Estimator Velocimetry (DEV) using Laser Induced Florescence (LIF). The experimental setup consisted of a single-wire hot wire probe measuring one component of velocity, the anemometry computational hardware and software, an HP oscilloscope, and a table fan to produce a simple flow with fluctuations. Measurements were taken at several points in the stream wise and transverse directions in the flow and various parameters recorded such as mean velocities temperature, turbulence intensities, skewness coefficients and flatness coefficients. The IFA300 software also allowed us to perform statistical manipulations such as spectrum analysis on velocities samples and correlation. Utilization of data files, also produced by the anemometry software, and post analysis were performed to produce graphical representations of turbulent intensity versus probe position and a flow field velocity profile. We concluded that the IFA300 Hot Wire Anemometry system is a reliable and functional method for calibration of DEV using LIF. Our future intentions are to set up a test chamber such that both velocity measurement techniques can be applied simultaneously, thus the calibration.

Holland, Michael L.↗
NASA NTRS1997

High-Resolution Temperature-Dependent Photoabsorption Cross Section Measurements of S2, with Application to HST UV Spectra of SL9/Jupiter

The Hubble Space Telescope (HST) UV spectra of Jupiter after the collision of Comet SL9 show predominantly molecular features of S2, CS2, NH3, and H2S in the 1800-3200 A region. The HST observations were made under various phases of impact conditions which gave temperatures higher than 1000 K. It is thus clear that temperature-dependent laboratory cross section data are required in order to determine the molecular abundances in Jupiter's atmosphere after the impact of Comet Shoemaker-Levy 9. The required high-resolution temperature dependent S2 absorption cross sections have not been directly measured in the laboratory. To provide the required data for modelers our objective is to accurately measure the high-resolution (FWHM = 0.003 A) and medium resolution (FWHM - 0.08 A) temperature dependent S2 in the 2450-3200 A region. Using the experimental setup we have obtained absorbtion spectra of S2 under various temperature conditions.

Wu, C. Y. Robert↗
NASA NTRS1960

Centrifuge Study of Pilot Tolerance to Acceleration and the Effects of Acceleration on Pilot Performance

A research program the general objective of which was to measure the effects of various sustained accelerations on the control performance of pilots, was carried out on the Aviation Medical Acceleration Laboratory centrifuge, U.S. Naval Air Development Center, Johnsville, PA. The experimental setup consisted of a flight simulator with the centrifuge in the control loop. The pilot performed his control tasks while being subjected to acceleration fields such as might be encountered by a forward-facing pilot flying an atmosphere entry vehicle. The study was divided into three phases. In one phase of the program, the pilots were subjected to a variety of sustained linear acceleration forces while controlling vehicles with several different sets of longitudinal dynamics. Here, a randomly moving target was displayed to the pilot on a cathode-ray tube. For each combination of acceleration field and vehicle dynamics, pilot tracking accuracy was measured and pilot opinion of the stability and control characteristics was recorded. Thus, information was obtained on the combined effects of complexity of control task and magnitude and direction of acceleration forces on pilot performance. These tests showed that the pilot's tracking performance deteriorated markedly at accelerations greater than about 4g when controlling a lightly damped vehicle. The tentative conclusion was also reached that regardless of the airframe dynamics involved, the pilot feels that in order to have the same level of control over the vehicle, an increase in the vehicle dynamic stability was required with increases in the magnitudes of the acceleration impressed upon the pilot. In another phase, boundaries of human tolerance of acceleration were established for acceleration fields such as might be encountered by a pilot flying an orbital vehicle. A special pilot restraint system was developed to increase human tolerance to longitudinal decelerations. The results of the tests showed that human tolerance of longitudinal deceleration forces was considerably improved through use of the special restraint system.

Creer, Brent Y.↗
NASA NTRS1998

Performance Analysis of the HTTP Protocol on Geostationary Satellite Links

Various issues associated with HTTP protocol on geostationary satellite links are presented in viewgraph form. Specific topics include: 1) Network reference points; 2) The HTTP 1.0 and 1.1 mechanisms; 3) Experimental setup; 4) TCP and HTTP configuration; 5) Modelling slow start and 6) Results and future work.

Krus, Hans↗
NASA NTRS1998

Ultrasonic Nondestructive Evaluation Techniques Applied to the Quantitative Characterization of Textile Composite Materials

An overall goal of this research has been to enhance our understanding of the scientific principles necessary to develop advanced ultrasonic nondestructive techniques for the quantitative characterization of advanced composite structures. To this end, we have investigated a thin woven composite (5-harness biaxial weave). We have studied the effects that variations of the physical parameters of the experimental setup can have on the ultrasonic determination of the material properties for this thin composite. In particular, we have considered the variation of the nominal center frequency and the f-number of the transmitting transducer which in turn address issues such as focusing and beam spread of ultrasonic fields. This study has employed a planar, two-dimensional, receiving pseudo-array that has permitted investigation of the diffraction patterns of ultrasonic fields. Distortion of the ultrasonic field due to the spatial anisotropy of the thin composite has prompted investigation of the phenomenon of phase cancellation at the face of a finite-aperture, piezoelectric receiver. We have performed phase-sensitive and phase-insensitive analyses to provide a measure of the amount of phase cancellation at the face of a finite-aperture, piezoelectric receiver. The pursuit of robust measurements of received energy (i.e., those not susceptible to phase cancellation at the face of a finite-aperture, piezoelectric receiver) supports the development of robust techniques to determine material properties from measure ultrasonic parameters.

Miller, James G.↗
NASA NTRS1999

A Study of Flame Propagation on Water-Mist Laden Gas Mixtures in Microgravity

The use of water mists (very fine water sprays) for fire suppression is currently receiving increased attention as a replacement technology for halogen-based chemical agents-such as Halon 1301 (CF3Br)--the manufacturing of which has been banned by the Montreal Protocol due to their high ozone depletion potential. Water mist technology has been found effective for a wide range of applications such as Class B pool fires, shipboard machinery, aircraft cabins, computers, and electronic equipment. There are five distinct mechanisms by which water droplets may interact with a flame. First, the high enthalpy of vaporization of water (2450 kJ/kg) leads to heat removal from the flame front as the liquid droplets turn to steam. Second, as water vaporizes its volume increases approximately three orders of magnitude, which leads to the dilution of the oxygen and vaporized fuel required to maintain the flame. The third effect is the recombination of H-atoms and other radicals on the droplet surface. A fourth effect of water mists in fires is the retardation of surface propagation rates due to the wetting of walls and surfaces. The last potential impact of fine water mists affects the radiative propagation of the fire by forming an optically thick barrier to infrared radiation which prevents ignition of the unburned regions. Unfortunately, little fundamental information exists on the interaction of a flame with a water mist. To date, there is no widely accepted interpretation of the critical concentration of droplets required to suppress a flame or of the fundamental mechanisms involved in flame extinguishment by water mists. One of the main obstacles to obtaining such understanding is the difficulty of providing a simple, well-defined experimental setup for the flame front/water mist interaction. Some of the difficulty stems from the problem of generating, distributing and maintaining a homogeneous concentration of droplets throughout a chamber while gravity depletes the concentration and alters the droplet size by coalescence and agglomeration mechanisms. Experiments conducted in the absence of gravity provide an ideal environment to study the interaction of water mists and flames by eliminating these distorting effects. In addition, microgravity eliminates the complex flow patterns induced between the flame front and the water droplets. The long duration and quality of microgravity in space flights provide the required conditions to perform the setup and monitoring of flame suppression experiments. Consequently, a series of experiments have been identified to be performed on the Combustion Module (CM-2) in the Space Shuttle. These consist of measuring the extinguishing capability of a water mist on a premixed flame propagating along a tube. These experiments should provide the necessary data to obtain further understanding of the water mist suppression phenomena that can be later used to design and manufacture appropriate fire suppression systems. In preparation for the orbital flights, experiments have been conducted on low-gravity ground facilities to obtain the preliminary data necessary to define the scientific objectives and technical issues of the spacecraft experiments.

Abbud-Madrid, A.↗
NASA NTRS1999

Interference of Backscatter from Two Droplets in a Focused Continuous Wave CO2 Doppler Lidar Beam

Interference due to the superposition of backscatter, beta, from two micron-sized droplets using a NASA/MSFC cw (continuous wave) CO2 Doppler lidar at 9.1 micrometer wavelength was detected for the first time. The resultant single beta signal from both droplets contained an interference structure with a well-defined periodicity which was accurately measured and compared with cw lidar theory. The agreement between measurements and theory is excellent, indicating that the interference arises because the droplets are moving at different speeds and, therefore, the relative droplet separation is not constant. This gives the superimposed beta signal from both droplets in the lidar beam moving in and out of constructive and destructive interference with a well-defined periodic structure. A measurement of a time-resolved signal pulse with an oscilloscope of the combined from two approx. 14.12 micrometers in diameter silicone oil droplets responding to the Gaussian lidar beam intensity at the lidar beam focus is shown. Full details of this laboratory experimental setup, particle generation method, measurement technique, and the cw lidar can be found elsewhere. The stream of silicone oil droplets resided at a Doppler-shift center frequency of f (sub D) approx. (3.4 plus or minus 0.2) MHz, giving droplet speed v approx.(21.9 plus or minus 1.3) ms (exp. -1). Also shown on a separate channel is the corresponding signature using an amplitude demodulator circuit designed to detect the amplitude envelope of f(sub D) within the pulse profile. beta from simultaneous droplet events show a complete cyclic interference structure of maximum and minimum. The average period T of the complete cycle of interference is 13.02 plus or minus.39 microseconds. Toward the right edge of the profile, the interference disappears because one of the droplets is leaving the lidar beam while the other one remains in the beam, thus, giving beta for a single droplet.

Jarzembski, Maurice A.↗
NASA NTRS1997

Cabauw Experimental Results from the Project for Intercomparison of Land-Surface Parameterization Schemes

In the Project for Intercomparison of Land-Surface Parameterization Schemes phase 2a experiment, meteorological data for the year 1987 from Cabauw, the Netherlands, were used as inputs to 23 land-surface flux schemes designed for use in climate and weather models. Schemes were evaluated by comparing their outputs with long-term measurements of surface sensible heat fluxes into the atmosphere and the ground, and of upward longwave radiation and total net radiative fluxes, and also comparing them with latent heat fluxes derived from a surface energy balance. Tuning of schemes by use of the observed flux data was not permitted. On an annual basis, the predicted surface radiative temperature exhibits a range of 2 K across schemes, consistent with the range of about 10 W/m in predicted surface net radiation. Most modeled values of monthly net radiation differ from the observations by less than the estimated maximum monthly observational error (+/- 10 W/sq m). However, modeled radiative surface temperature appears to have a systematic positive bias in most schemes; this might be explained by an error in assumed emissivity and by models' neglect of canopy thermal heterogeneity. Annual means of sensible and latent heat fluxes, into which net radiation is partitioned, have ranges across schemes of 30 W/sq m and 25 W/sq m, respectively. Annual totals of evapotranspiration and runoff, into which the precipitation is partitioned, both have ranges of 315 mm. These ranges in annual heat and water fluxes were approximately halved upon exclusion of the three schemes that have no stomatal resistance under non-water-stressed conditions. Many schemes tend to underestimate latent heat flux and overestimate sensible heat flux in summer, with a reverse tendency in winter. For six schemes, root-mean-square deviations of predictions from monthly observations are less than the estimated upper bounds on observation errors (5 W/m for sensible beat flux and 10 W/m for latent heat flux). Actual runoff at the site is believed to be dominated by vertical drainage to ground water, but several schemes produced significant amounts of runoff as overland flow or interflow. There is a range across schemes of 184 mm (40% of total pore volume) in the simulated annual mean root-zone soil moisture. Unfortunately, no measurements of soil moisture were available for model evaluation. A theoretical analysis suggested that differences in boundary conditions used in various schemes are not sufficient to explain the large variance in soil moisture. However, many of the extreme values of soil moisture could be explained in terms of the particulars of experimental setup or excessive evapotranspiration.

Chen, Tian Hong↗
NASA NTRS2000

Mechanisms for the Crystallization of ZBLAN

A number of research teams have observed that glass forming melts that are solidified in low-g exhibit enhanced glass formation. This project will examine one of these glasses, the heavy metal fluoride glass ZBLAN. A four year ground based research program has been approved to examine the crystallization of ZBLAN glasses with the purpose of testing a theory for the crystallization of ZBLAN glass. The theory could explain the general observations of enhanced glass formation of other glasses melted and solidified in low-g. Fluid flow in 1-g results from buoyancy forces and surface tension driven convection. This fluid flow can introduce shear in undercooled liquids in 1-g. In low-g it is known that fluid flows are greatly reduced so that the shear rate in fluids in low-g are extremely low. It is believed that fluids may have some weak structure in the absence of flow. Even very small shear rates could cause this structure to collapse in response to the shear. A general result would be shear thinning of the fluid. The hypothesis of this research is that: Shear thinning in undercooled liquids increases the rate of nucleation and crystallization of glass forming melts. Shear of the melt can be reduced in low-g enhancing undercooling and glass formation. Samples will be melted and quenched in 1-g under quiescent conditions at a number of controlled cooling rates to determine times and temperatures of crystallization and heated at controlled heating rates to determine kinetic crystallization parameters. Experiments will also be performed on the materials while under controlled vibration conditions and compared with the quiescent experiments in order to evaluate the effect of shear in the liquid on crystallization kinetics. After the experimental parameters are well known, experiments will be repeated under low-g (and 2-g) conditions on the KC-135 aircraft during low-g parabolic maneuvers. The results will determine the effects of shear on crystallization. Our experimental setups will be designed with low-g experiments in mind and will be tested as breadboard low-g experiments. It is very likely that the thermal analysis instrumentation can be adapted to be run in the microgravity glovebox facilities. Critical space experiments may result to test the theory at longer low-g time experiments in space.

Ethridge, Edwin C.↗