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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 181 records · Page 10
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NASA NTRS1988

Analog MOS integrated circuits

The goal was to design single-chip lowpass filters with constant group delay in the pass band and 60 dB minimum attenuation in the stop band. The desired 3 dB frequencies are (in Hertz) 2.5, 5, 10, 20, 40, 80, 160, and 320. A filter class that satisfies the constant delay (linear phase) requirement while providing quite a narrow transition band is the Bessel-Chebyshev filters. It was found that the 7th order Bessel-Chebyshev response satisfied the requirement of the filter.

Temes, Gabor C.↗
NASA NTRS1988

Helioseismology from the South Pole: Comparison of 1987 and 1981 Results

Full disk images with 10 arc sec pixels and filtered to a 7 A pass band centered on the Ca II K line were obtained from the geographic South Pole in 1981 and 1987. In 1981, 50hr of essentially uninterrupted data were obtained. In 1987, three such runs were obtained over a period of 325 hours for a duty cycle of 47 percent. The 1987 observations are characterized by a much lower level of solar activity than 1981, a much improved CCD camera, considerably better image stability and a varying amount of instrumental scatter. The 1987 data have a substantially better signal-to-noise ratio than the 1981 data so that oscillations with degrees from 0 to 150 and frequencies from 2 to 7 mHz are well observed. The observations were reduced to spectra in l, m, and v. A comparison of p-mode frequencies measured in 1981 and 1987, and coefficients of Legendre polynomial expansions of frequency shifts caused by solar rotation are presented. The time behavior of systematic frequency shifts which depend upon m but which do not arise from rotation is described.

Jefferies, S. M.↗
NASA NTRS1989

New observations of a large concentration of ClO in the springtime lower stratosphere over Antarctica and its implications for ozone-depleting chemistry

New measurements of stratospheric chlorine monoxide (ClO) were made at McMurdo Station, Antarctica, during the austral spring of 1987. Rotational emission line spectroscopy, employing a ground-based detector, was used to determine mixing ratio profiles over the range about 17-45 km. A spectral band pass double that was used for similar measurements in 1986 allowed an improvement to be made in the definition of the anomalous low-altitude stratospheric ClO layer associated with springtime ozone depletion. A peak mixing ratio of 1.6 + or - 0.4 parts per billion by volume (ppbv) (95 percent confidence level) was found at 19.5 + or - 1 km at midday during the period September 20-24, 1987. The observed peak mixing ratio and diurnal behavior are discussed in relation to chemical depletion theories. Calculations indicate that the large observed ClO concentration provides an efficient closure for a catalytic Cl cycle through the ClO dimer mechanism, yielding good agreement with various observed features of O3 depletion.

De Zafra, R. L.↗
NASA NTRS1990

Frequency-Tracking-Error Detector

Frequency-tracking-error detector compares average period of output signal from band-pass tracking filter with average period of signal of frequency 100 f(sub 0) that controls center frequency f(sub 0) of tracking filter. Measures difference between f(sub 0) and frequency of one of periodic components in output of bearing sensor. Bearing sensor is accelerometer, strain gauge, or deflectometer mounted on bearing housing. Detector part of system of electronic equipment used to measure vibrations in bearings in rotating machinery.

Randall, Richard L.↗
NASA NTRS1990

Coplanar waveguide discontinuities for P-I-N diode switches and filter applications

A full wave space domain integral equation (SDIE) analysis of coplanar waveguide (CPW) two port discontinuities is presented. An experimental setup to measure the S-parameters of such discontinuities is described. Experimental and theoretical results for CPW realizations of pass-band and stop-band filters are presented. The S-parameters of such structures are plotted in the frequency range 5 to 25 GHz.

Dib, N. I.↗
NASA NTRS1989

Calibration of the Berkeley EUV Airglow Rocket Spectrometer

The Berkeley Extreme-ultraviolet Airglow Rocket Spectrometer (BEARS), a multiinstrument sounding rocket payload, made comprehensive measurements of the earth's dayglow. The primary instruments consisted of two near-normal Rowland mount spectrometers: one channel to measure several atomic oxygen features at high spectral resolution (about 1.5 A) in the band passes 980-1040 and 1300-1360 A, and the other to measure EUV dayglow and the solar EUV simultaneously in a much broader bandpass (250-1150 A) at moderate resolution (about 10 A). The payload also included a hydrogen Lyman-alpha photometer to monitor the solar irradiance and goecoronal emissions. The instrument was calibrated at the EUV calibration facility at the University of California at Berkeley, and was subsequently launched successfully on September 30, 1988 aboard a four-stage experimental sounding rocket, Black Brant XII flight 12.041 WT. The calibration procedure and resulting data are presented.

Cotton, Daniel M.↗
NASA NTRS1991

Scanning X-Ray Or Extreme-Ultraviolet Monochromator

Wavelength of peak transmission of proposed high-throughput, narrow-band-pass x-ray or extreme-ultraviolet monochromator continuously adjustable. Essential filtering and reflecting components designed according to principles described in "Compact X-Ray and Extreme-Ultraviolet Monochromator" (MFS-28499). However, angle of incidence varied to change wavelength of Bragg reflection.

Hoover, Richard↗
NASA NTRS1990

Reappraisal of solid selective emitters

New rare earth oxide emitters show greater efficiency than previous emitters. As a result, based on a simple model the efficiency of these emitters was calculated. Results indicate that the emission band of the selective emitter must be at relatively low energy (less than or equal to .52 eV) to obtain maximum efficiency at moderate emitter temperatures (less than or equal to 1500 K). Thus low bandgap energy PV materials are required to obtain an efficient thermophotovoltaic (TPV) system. Of the 4 specific rare earths (Nd, Ho, Er, Yb) studied Ho has the largest efficiency at moderate temperatures (72 percent at 1500 K). A comparison was made between a selective emitter TPV system and a TPV system that uses a thermal emitter plus a band pass filter to make the thermal emitter behave like a selective emitter. Results of the comparison indicate that only for very optimistic filter and thermal emitter properties will the filter TPV system have a greater efficiency than the selective emitter system.

Chubb, Donald L.↗
NASA NTRS1990

Reappraisal of solid selective emitters

New rare earth oxide emitters show greater efficiency than previous emitters. As a result, based on a simple model the efficiency of these emitters was calculated. Results indicate that the emission band of the selective emitter must be at relatively low energy (less than or equal to .52 eV) to obtain maximum efficiency at moderate emitter temperatures (less than or equal to 1500 K). Thus, low bandgap energy PV materials are required to obtain an efficient thermophotovoltaic (TPV) system. Of the 4 specific rare earths (Nd, Ho, Er, Yb) studied, Ho has the largest efficiency at moderate temperatures (72 percent at 1500 K). A comparison was made between a selective emitter TPV system and a TPV system that uses a thermal emitter plus a band pass filter to make the thermal emitter behave like a selective emitter. Results of the comparison indicate that only for very optimistic filter and thermal emitter properties will the filter TPV system have a greater efficiency than the selective emitter system.

Chubb, Donald L.↗
NASA NTRS1992

Channelized-Coplanar-Waveguide PIN-Diode Switches

Three positive/intrinsic/negative (PIN-diode) reflective CPW (coplanar waveguide) switches demonstrated. First includes series-mounted diode to bridge gap in center strip conductor of CPW. Second includes pair of diodes to short center strip conductor to ground planes. Third includes diode to switch between band-pass filter and notch filter. Isolation exceeds 20 dB, while insertion loss is less than 1 dB.

Ponchak, G. E.↗
NASA NTRS1992

Enhanced Eddy-Current Detection Of Weld Flaws

Mixing of impedances measured at different frequencies reduces noise and helps reveal flaws. In new method, one excites eddy-current probe simultaneously at two different frequencies; usually, one of which integral multiple of other. Resistive and reactive components of impedance of eddy-current probe measured at two frequencies, mixed in computer, and displayed in real time on video terminal of computer. Mixing of measurements obtained at two different frequencies often "cleans up" displayed signal in situations in which band-pass filtering alone cannot: mixing removes most noise, and displayed signal resolves flaws well.

Van Wyk, Lisa M.↗
NASA NTRS1991

The SOHO space satellite - UV instrumentation

The UV and EUV instruments designed for the ESA/NASA Solar and Heliospheric Observatory (SOHO) are described, and their characteristics are presented. The SOHO instruments include the SUMER telescope for measuring line profiles and images in the wavelength range 500-1600 A, with a 1.5-arcsec resolution; the Coronal Diagnostics Spectrometer for measuring line ratios and images in the range 170-800 A, with a 2 arcsec resolution; a EUV imaging telescope for producing narrow band pass images in the spectral lines at 171 A, 195 A, 195 A, 284 A, and 304 A, with a 3-arcsec resolution; a UV coronagraph spectrometer for measuring line profiles and images of EUV lines from about 500 A to about 1200 A, with a several arcsec rosolution; and the SWAN, a lens with hydrogen absorption cell for measuring Ly-alpha profiles in the far corona and heliosphere.

Poland, Arthur I.↗
NASA NTRS1993

Acoustical Detection Of Leakage In A Combustor

Abnormal combustion excites characteristic standing wave. Acoustical leak-detection system gives early warning of failure, enabling operating personnel to stop combustion process and repair spray bar before leak grows large enough to cause damage. Applicable to engines, gas turbines, furnaces, and other machines in which acoustic emissions at known frequencies signify onset of damage. Bearings in rotating machines monitored for emergence of characteristic frequencies shown in previous tests associated with incipient failure. Also possible to monitor for signs of trouble at multiple frequencies by feeding output of transducer simultaneously to multiple band-pass filters and associated circuitry, including separate trigger circuit set to appropriate level for each frequency.

Puster, Richard L.↗
NASA NTRS1993

Multiresponse Imaging For Improved Resolution

Images restored with resolution finer than sampling lattice. Multiresponse imaging overcomes sampling-passband constraint and critically constrained only by optical response and sensitivity of image-gathering device. Process consists of multiresponse image gathering and Wiener-matrix restoration. Image-gathering process acquires sequence of images, each with different optical response so within-pass-band and aliased signal components weighted differently. Wiener-matrix filter, in turn, unscrambles within-passband and aliased frequency components of undersampled signal and restores them up to cutoff frequency of optical response.

Fales, Carl L., Jr.↗
NASA NTRS1993

Planetary circulations in the presence of transient and self-induced heating

The research program focuses on large-scale circulations and their interaction with the global convective pattern. An 11-year record of global cloud imagery and contemporaneous fields of motion and temperature have been used to investigate organized convection and coherent variability of the tropical circulation operating on intraseasonal time scales. This study provides a detailed portrait of tropical variability associated with the so-called Madden-Julian Oscillation (MJO). It reveals the nature, geographical distribution, and seasonality of discrete convective signal, which is a measure of feedback between the circulation and the convective pattern. That discrete spectral behavior has been evaluated in light of natural variability of the ITCZ associated with climatological convection. A composite signature of the MJO, based on cross-covariance statistics of cloud cover, motion, and temperature, has been constructed to characterize the lifecycle of the disturbance in terms of these properties. The composite behavior has also been used to investigate the influence the MJO exerts on the zonal-mean circulation and the involvement of the MJO in transfers of momentum between the atmosphere and the solid Earth. The aforementioned observational studies have led to the production of two animations. One reveals the convective signal in band-pass filtered OLR and compares it to climatological convection. The other is a 3-dimensional visualization of the composite lifecycle of the MJO. With a clear picture of the MJO in hand, feedback between the circulation and the convective pattern can be diagnosed meaningfully in numerical simulations. This process is being explored in calculations with the linearized primitive equations on the sphere in the presence of realistic stability and shear. The numerical framework represents climatological convection as a space-time stochastic process and wave-induced convection in terms of the vertically-integrated moisture flux convergence. In these calculations, frictional convergence near the equator emerges as a key to feedback between the circulation and the convective pattern. At low latitudes, nearly geostrophic balance in the boundary layer gives way to frictional balance. This shifts the wave-induced convection into phase with the temperature anomaly and allows the attending heating to feed back positively onto the circulation. The calculations successfully reproduce the salient features of the MJO. They are being used to understand the growth and decay phases of the composite lifecycle and the conditions that favor amplification of the MJO.

Salby, Murry L.↗
NASA NTRS1993

Using x ray images to detect substructure in a sample of 40 Abell clusters

Using a method for constraining the dynamical state of a galaxy cluster by examining the moments of its x-ray surface brightness distribution, we determine the statistics of cluster substructure for a sample of 40 Abell clusters. Using x-ray observations from the Einstein Observatory Imaging Proportional Counter (IPC), we measure the first moment M1(r), the ellipsoidal orientation angle theta2(r), and the axial ratio eta(r) at several different radii in the cluster. We determine the effects of systematics such as x-ray point source emission, telescope vignetting, Poisson noise, and characteristics of the IPC by measuring the same parameters on an ensemble of simulated cluster images. Due to the small band-pass of the IPC, the ICM emissivity is nearly independent of temperature so the intensity at each point in the IPC images is simply proportional to the emission measure calculated along the line of sight through the cluster (e.g. Fabricant et al. 1980). Therefore, barring a change superposition of two x-ray emitting clusters, a significant variation in the image centroid M1(r) as a function of radius indicates that the center of mass of the intra-cluster medium (ICM) varies with radius. We argue that such a configuration (essentially an m = 1 component in the ICM density distribution) is a non-equilibrium component; it results from an off-center subclump or a recent merger in the ICM.

Mohr, J. J.↗
NASA NTRS1991

Coplanar waveguide microwave filter of YBa2Cu3O7

Thin film low-pass microwave filters have been made with laser-ablated YBa2Cu3O(7-delta) (YBCO) deposited on LaAlO3 substrates, using a coplanar waveguide structure. The coplanar waveguide sections had dimensions suited for integrated circuits. Measured losses in liquid nitrogen were superior to the loss in a similar thin-film copper filter throughout the 0 to 9.5 GHz pass-band. A simple transmission-line model is adequate for filter design using YBCO films with repeatable characteristics. The measured filters demonstrate the performance of fully patterned YBCO after sealing in space-qualifiable hermetic packages. Five packaged filters of this design were delivered to the Naval Research Laboratory as candidates for space flight in the High Temperature Superconductivity Space Experiment.

Chew, Wilbert↗
NASA NTRS1992

Millimeter-wave imaging radiometer for cloud, precipitation and atmospheric water vapor studies

A millimeter-wave imaging radiometer (MIR) developed by NASA Goddard Space Flight Center is described. The MIR is a nine-channel total power radiometer developed for atmospheric research. Three dual-pass band channels are centered about the strongly opaque 183-GHz water vapor absorption line; the frequencies are 183 +/- 1, +/- 3, and +/- 7 GHz. Another channel is located on the wing of this band at 150 GHz. These four channels have varying degrees of opacity from which the water vapor profile can be inferred. The design and salient characteristics of this instrument are discussed, together with its expected benefits.

Racette, P. E.↗