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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Cluster evolution and microwave source counts

We present the modeled counts for the expected Sunyaev-Zel'dovich microwave sources associated with clusters of galaxies, predicted for experiments with arcminute-scale spatial resolution, assuming self-similar cluster evolution, for different spectra of the primordial density fluctuations and values of the cosmological density parameter Omega. Our simulations show that the source counts should be a powerful test of the evolution of very high redshift clusters. Experiments with 1 - 2 min spatial resolution, with moderate sensitivity but covering a large area of the sky, would be most effective for studying the SZ source population. Recent arcminute-scale radio experiments, the Owens Valley Radio Observatory (OVRO) RING experiment and VLA deep imaging, achieved sensitivity and sky coverage close to that needed for the detection of negative sources associated with very distant clusters. From the absence of cluster detections in these experiments, we rule out, with 90% confidence, models with Omega less than 0.3 and n = +1 as predicting too many bright sources; or there is no hot gas in clusters more distant than z(sub max) = 5 in such models. If the single negative source detected in the RING experiment is a distant cluster, the Omega = 1, n = -2 model also may be ruled out as it predicts too few sources. The new generation of telescopes, including the new SUZIE and Ryle instruments, will soon be able to detect distant clusters. The cluster population in the past has been modeled by scaling the observed present-day sample of X-ray clusters back to high redshifts, an approach which makes the best use of the observed cluster gas parameters, and makes the simulations robust to the assumed evolution at very early epochs. Although the pure self-similar model may be incompatible with the variety of observed evolutionary effects, we show that reasonable modifications to the intracluster gas history in that model, proposed to reconcile the self-similar evolution of cluster mass and the observed evolution of their X-ray luminosity, do not considerably change our microwave predictions made using the pure self-similar model. That is, the results of our simulations are applicable to the wide class of evolutionary models in which the cluster gas mass times gas temperature evolves as the dark mass times cluster virial temperature.

Markevitch, M.↗
NASA NTRS1981

S-Band Shallow Bulk Acoustic Wave (SBAW) microwave source

Techniques necessary to fabricate a high performance S-band microwave single source using state-of-the-art shallow bulk acoustic wave (SBAW) were explored. The bulk wave structures of the AlN/Al 2O3 were investigated for both the R plane and basal plane of sapphire. A 1.072 GHz SBAW delay line and oscillators were developed. A method of selecting and setting oscillator output frequency by selecting substrate orientation angle was also established.

Source record↗
NASA NTRS2011

Organic Chemistry of Southern Sources: Microwave Spectroscopy of Cha-MMS1 and IRAS 15194-5115

We report new spectra of molecule-rich sources in the southern hemisphere obtained using the 22-meter Mopra telescope. Spectra and maps are presented of organic molecules detected between 30 and 50 GHz in the young Class 0 protostar Chamaeleon MMS-1. The large abundances of polyynes, cyanopolyynes and methanol may be indicative of a warm carbon chemistry in the dense gas surrounding this protostar. Spectra are also presented from a 78-96 GHz scan of the carbon-rich AGB star IRAS 15194-5115, including new detections of HC5N, CCS and C13CH.

Cordiner, Martin↗
NASA NTRS1983

S-band SBAW microwave source, phase 2

Results of aging experiments on 1.072 GHz SBAW oscillators are discussed as well as the design, fabrication and test of 2.143 GHz SBAW delay lines. Two design approaches were implemented. The third harmonic transducer on 36 deg rotated Y cut quartz proved to be the most useful design, whereas the fifth harmonic transducer on - 50 5 deg rotated Y cut quartz suffered from high insertion loss and poor sidelobe rejection. The construction and characterization of the 2 GHz SBAW oscillator are described. Phase noise, frequency dependence on temperature, and 6-month aging were measured. Some SAW and SBAW oscillators were compared as were both the 1 and 2 GHz oscillators. The 2 GHz SBAW oscillator showed significant improvement in phase noise and temperature stability over the 2 GHz SAW oscillator developed in previous NASA programs. A technique to produce SBAW delay lines of different frequencies from a single mask is examined. The delay lines were incorporated into oscillator circuits to demonstrate the ability to select the frequency output of the SBAW oscillator.

Source record↗
NASA NTRS1984

Center-to-limb variation of a sunspot-associated microwave source

Observations of the simple bipolar active region McMath 16862, obtained with the Westerbork Synthesis Radio Telescope at 6.16 cm over six consecutive days, indicate two bright sources associated with the region's two main spots, as well as some weaker emission that may be associated with loop structures. Application of a novel analytical method has allowed the mapping of the vertical as well as the horizontal component of the sunspot magnetic field at specific locations in the low corona. While the vertical component decreases away from the source's center, the horizontal component has both a radial and an azimuthal part. These results are interpreted in terms of a force-free magnetic field model, as well as in terms of a dipole whose axis is inclined to the vertical.

Alissandrakis, C. E.↗
NASA NTRS1985

Simultaneous observations of hard X-ray and microwave burst sources in a limb flare

Observations of a flare which occurred just behind the west solar limb on 1981 August 3 are reported. A hard X-ray source (20-30 keV) and a microwave source at 5 GHz were observed simultaneously using the Very Large Array and the hard X-ray telescope aboard the Hinotori spacecraft. Both sources were located in the corona, apparently near the tops of two independent coronal arcades or loops. The source may be composed of many thin filaments unresolved by the VLA observations.

Takakura, T.↗
NASA NTRS1984

Recent work on a microwave ion source

The performance of a microwave (2.45 GHz) plasma-disk ion source using a cylindrical microwave cavity is described. The operating characteristics in argon and xenon gases with 50-200 W of input power and gas flow rates from 10-80 sccm are presented. In particular, extracted beam current versus accelerating voltage, and specific energy vs. mass utilization efficiency and extracted beam current are presented. Double Langmuir probe measurements indicate that electron densities in excess of 10 to the 12th per cu cm can be readily achieved in the microwave generated plasma.

Asmussen, J.↗
NASA NTRS1981

Fundamental design problems and properties of microwave plasma/ion sources

Design problems and procedures associated with microwave plasma sources are applied to cylindrical plasmas inside coaxial and cylindrical cavities. The experimental performance of these cavities is presented. Measurements of electron density and electron temperature for several inert gases, and different tube diameters and pressures are presented and compared with microwave and positive column discharge theories. Results show that plasmas with electron densities in excess of 10 to the 12th/cu cm are easily produced from microwave S band energy. The potential for these sources for ion engines is evaluated.

Root, J.↗
NASA NTRS2005

Optical Techniques for Low Noise Microwave Frequency Sources

Optical techniques and mathematical models are described for low noise microwave frequency sources. The contents include: 1) Why Optical Techniques; 2) Wavemixing: Advantages and Disadvantages; 3) Wavemixing with Feedback: The OEO; 4) Feedback in both loops: COEO; and 5) State of the Art and Future Prospects.

microwave oscillators↗
NASA NTRS1994

Transient microwave brightenings in solar active regions: Comparison between VLA and Yohkoh observations

We report observations of transient microwave (2 cm) brightenings and their relationship with brightenings in soft X-rays. The peak flux of the microwave brightenings observed by the Very Large Array (VLA) is smaller than the previously reported fluxes by two orders of magnitude. The microwave sources were highly polarized (up to 100%) and were situated on the periphery of a sunspot umbra. Among the many transients observed in X-rays by Yohkoh, two were observed simultaneously in microwaves. The microwave sources were found to be closer to the umbra of the sunspot than were the X-ray loops. It seems that the microwave sources are located at the footpoints of the looplike X-ray transients. Using the combined VLA, Yohkoh, and Mees data set, we determine the physical parameters of the loop in which the brightenings occur. We find that an increase in emission measure accompanied by small-scale heating can account for the X-ray brightening. The microwave emission can be interpreted as thermal gyroresonance or nonthermal gyrosynchrotron processes during the X-ray brightening. The magnetic field in the microwave-source region is found to be 1200-1800 G. The observations also provide evidence for temperature gradient in the coronal loops.

Gopalswamy, N.↗
NASA NTRS1988

Polarization of microwave noise source radiation in the 30 GHz to 300 GHz range

Radiation spectra have been obtained in order to calculate the frequency bandwidth and polarization of three microwave noise sources. Results were obtained in the 1-10-mm wavelength region using a lamellar grating Fourier transform spectrometer and a helium-cooled bolometer detector. A secondary transmission region was found to have an input current as well as a polarization dependence, despite the directional output of the waveguide antenna.

Poutous, M. K.↗
NASA NTRS1980

Water vapor as an error source in microwave geodetic systems: Background and survey of calibration techniques

Water vapor as an error source in radio interferometry systems is briefly examined. At microwave frequencies, the delay imposed by tropospheric water vapor becomes a limiting error source for high accuracy geodetic systems. The mapping of tropospheric induced errors into 'solved-for' parameters depends upon baseline length and observing strategy. Simulation analysis (and experience) indicates that in some cases, errors in estimating tropospheric delay can be magnified in their effect on baseline components. The various techniques by which tropospheric water can be estimated or measured are surveyed with particular consideration to their possible use as a calibration technique in support to very long baseline interferometry experiments. The method of remote sensing using a microwave radiometer seems to be the most effective way to provide an accurate estimate of water vapor delay.

Claflin, E. S.↗