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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Quasi-Optical Millimeter-Wavelength Resonator

Quasi-optical reflection cavity serves as prototype resonator for oscillators at millimeter and submillimeter wavelengths. Exploits diffraction and reflection effects to achieve high Q. Useful mainly at wavelengths too short for conventional waveguide techniques but too long for optical techniques.

Frerking, Margaret A.↗
NASA NTRS2009

Superconducting Hot-Electron Submillimeter-Wave Detector

A superconducting hot-electron bolometer has been built and tested as a prototype of high-sensitivity, rapid-response detectors of submillimeter-wavelength radiation. There are diverse potential applications for such detectors, a few examples being submillimeter spectroscopy for scientific research; detection of leaking gases; detection of explosive, chemical, and biological weapons; and medical imaging. This detector is a superconducting-transition- edge device. Like other such devices, it includes a superconducting bridge that has a low heat capacity and is maintained at a critical temperature (T(sub c)) at the lower end of its superconducting-transition temperature range. Incident photons cause transient increases in electron temperature through the superconducting-transition range, thereby yielding measurable increases in electrical resistance. In this case, T(sub c) = 6 K, which is approximately the upper limit of the operating-temperature range of silicon-based bolometers heretofore used routinely in many laboratories. However, whereas the response speed of a typical silicon- based laboratory bolometer is characterized by a frequency of the order of a kilohertz, the response speed of the present device is much higher characterized by a frequency of the order of 100 MHz. For this or any bolometer, a useful figure of merit that one seeks to minimize is (NEP)(tau exp 1/2), where NEP denotes the noise-equivalent power (NEP) and the response time. This figure of merit depends primarily on the heat capacity and, for a given heat capacity, is approximately invariant. As a consequence of this approximate invariance, in designing a device having a given heat capacity to be more sensitive (to have lower NEP), one must accept longer response time (slower response) or, conversely, in designing it to respond faster, one must accept lower sensitivity. Hence, further, in order to increase both the speed of response and the sensitivity, one must make the device very small in order to make its heat capacity very small; this is the approach followed in developing the present device.

Karasik, Boris↗
NASA NTRS2003

High Resolution Imaging of Circumstellar Disks at Millimeter Wavelengths

We update progress on our research program to use high angular resolution imaging of thermal dust continuum emission at millimeter and submillimeter wavelengths to probe the structure of protoplanetary disks and debris disks around nearby stars. Observations at these wavelengths are advantageous because the dust emission is generally optically thin and directly proportional to mass, contrast with stellar photospheres is not problematic, and the wavelength dependence provides information on an important regime of grain sizes. We employ several facilities for state-of-the-art high resolution observations, including the Very Large Array (VLA), the Australia Telescope Compact Array (ATCA), the Plateau de Bure Interferometer (PdBI) of the Institut de RadioAstronomie Millimetrique, the Submillimeter Array (SMA) of the Smithsonian Astrophysical Observatory, and the Caltech Submillimeter Observatory (CSO). Many recent highlights of our program were presented in an invited review on High Angular Resolution Studies of Disks- the Millimetre at IAU Symposium 221, Star Formation at High Angular Resolution, in July 2003.

Wilner, David J.↗
NASA NTRS1977

Infrared continuum observations of five-minute oscillations

Infrared continuum observations of the sun at wavelengths between 10 and 30 microns show a nonisothermal response of the upper photosphere to compression waves associated with the five-minute oscillations. Observations were made with four broad-band filters with effective transmission wavelengths between 10 and 26 microns and with a 10 arcsec aperture. Further observations at submillimeter wavelengths with a 2-arcmin aperture did not resolve oscillatory fluctuations of five-minute period. Comparisons with velocity-field data of Howard (1976) suggest that the relaxation time of the photosphere exceeds (300/2 pi) seconds at the height of formation of the 26-micron continuum. The photosphere reponds to 3-mHz oscillatory motion with considerably less compression than expected for simple acoustic modes in an adiabatically responsive atmosphere, confirming the evanescent character of the five-minute oscillations.

Lindsey, C. A.↗
NASA NTRS1990

Submillimeter and millimeter observations of solar system objects

Microwave spectroscopy of solar system objects was supported. It necessarily involves millimeter and submillimeter wavelengths where rotational transitions reside. The existing national facilities are at OVRO, the 12-meter at Kitt Peak, UC array at Hat Creek, the Caltech CSO on Mauna Kea, and the 14-meter at the Univ. of Massachusetts, near Amherst. The group used all of these instruments in the last year except the Univ. of Massachusetts 14-meter. This wavelength range (0.3 to 3 mm) is about to enjoy an explosion of interest as submillimeter receivers become better and easier to use. This region of the spectrum is rich in transitions of molecules that exist in the planetary atmospheres which can be studied for temperature-pressure profiles, wind tracers, and atmospheric chemistry. The list of solar system objects that have been recently addressed with these techniques include: (1) Venus: CO studies of T-P profiles, winds, and photochemistry; SO2 detections; Continuum mapping remains to be done at 1 mm; (2) Earth H2O, CO, NO, NO2, O(18)O, etc. as a test bed for other atmospheres; (3) Mars: H2O, CO, O(18)O studies of T-P profiles, winds (fall of 1990), and photochemistry; (4) Saturn: Same as Jupiter plus submillimeter and millimeter mapping of the ring system; (5) Uranus and Neptune: Continuum thermal mapping; and (6) Titan: CO, HCN, and HC3NT-P information and photochemistry. Recent results are given.

Muhleman, Duane O.↗
NASA NTRS1990

Millipol, a millimeter/submillimeter wavelength polarimeter - Instrument, operation, and calibration

An instrument capable of measuring the polarization characteristics of weakly polarized, cold dust at millimeter and submillimeter wavelengths is presented in detail. The operation and calibration of this polarimeter at a wavelength of 1300 microns, configured for the NRAO 12-meter telescope, are discussed. Deep observations of Jupiter using this instrument revealed a main-beam instrumental polarization at, or below, the 0.2 percent level. Lunar limb observations revealed a sidelobe polarization sensitivity, in the range 0.25 percent - 1.0 percent. Further, through these efforts the nonthermal polarized flux from Jupiter at a level of about 0.04 percent of the thermal flux has been detected. Astronomical polarization measurements to 0.03 percent are possible, limited by the uncertainties in the instrumental polarization. This instrument has been primarily employed to measure and map magnetic-field directions in the very optically opaque cores of massive molecular clouds.

Clemens, Dan P.↗
NASA NTRS2002

Development of Submillimeter SIS Mixers and Broadband HEMT Amplifiers

The goal of this project is to develop and demonstrate a new generation of superconducting tunnel junction (SIS) receivers with extremely wide instantaneous (intermediate-frequency, or IF) bandwidths, of order 12 GHz. Such mixers would allow rapid submillimeter wavelength spectral line surveys to be carried out with SOFIA, and could potentially be used for future submillimeter space missions such as SAFIR. There are two major components which are being developed: (1) SIS mixers with broad (12 GHz) IF bandwidths; and (2) low-noise, broadband microwave, (6-18 GHz) amplifiers, which amplify the IF output from the SIS mixer. The work on these components is discussed in two sections

Zmuidzinas, Jonas↗
NASA NTRS2011

The Relationship Between Solar Radio and Hard X-Ray Emission

This review discusses the complementary relationship between radio and hard Xray observations of the Sun using primarily results from the era of the Reuven Ramaty High Energy Solar Spectroscopic Imager satellite. A primary focus of joint radio and hard X-ray studies of solar flares uses observations of nonthermal gyrosynchrotron emission at radio wavelengths and bremsstrahlung hard X-rays to study the properties of electrons accelerated in the main flare site, since it is well established that these two emissions show very similar temporal behavior. A quantitative prescription is given for comparing the electron energy distributions derived separately from the two wavelength ranges: this is an important application with the potential for measuring the magnetic field strength in the flaring region, and reveals significant differences between the electrons in different energy ranges. Examples of the use of simultaneous data from the two wavelength ranges to derive physical conditions are then discussed, including the case of microflares, and the comparison of images at radio and hard X-ray wavelengths is presented. There have been puzzling results obtained from observations of solar flares at millimeter and submillimeter wavelengths, and the comparison of these results with corresponding hard X-ray data is presented. Finally, the review discusses the association of hard X-ray releases with radio emission at decimeter and meter wavelengths, which is dominated by plasma emission (at lower frequencies) and electron cyclotron maser emission (at higher frequencies), both coherent emission mechanisms that require small numbers of energetic electrons. These comparisons show broad general associations but detailed correspondence remains more elusive.

White, S. M.↗
NASA NTRS1972

Atmospheric absorption measurements in the region of 1 mm wavelength.

A Froome-type plasma-metal-junction device (1962) was used in high-resolution radiation transmission measurements in the atmosphere at wavelengths from 0.5 to 3.0 mm. The experimental and theoretical results for water vapor absorption lines in two submillimeter wavelength windows were compared, showing that this technique provided a much higher wavelength accuracy than more conventional optical-type spectroscopy.

Emery, R.↗
NASA NTRS1991

The microwave limb sounder (MLS) experiments for UARS and EOS

Microwave limb sounding can provide important measurements for understanding global change and processes in earth's stratosphere, mesosphere, and lower thermosphere. An experiment for this purpose operating at millimeter wavelengths is now ready for launch on the NASA Upper Atmosphere Research Satellite (UARS). An enhanced experiment at submillimeter wavelengths is also being studied for the future NASA Earth Observing System (EOS).

Waters, Joe W.↗
NASA NTRS2015

The Evolution of Volatile Production in Comet C-2009 P1(Garradd) During its 2011-2012 Apparition

We report observations at millimeter and submillimeter wavelengths of comet C/2009 P1 (Garradd) from 2011 December 28 to 2012 April 24, using the Arizona Radio Observatory submillimeter telescope (SMT) and the James Clerk Maxwell Telescope (JCMT). Garradd is a dynamically young long-period comet from the Oort Cloud, with a periodicity of 127,000 years, that reached perihelion on 2011 December 23 (at Heliocentric distance (Rh) = 1.55 Astronomical Units and delta = 20.1 Astronomical Units ) and made its closest approach to the Earth on 2012 March 05 (at Heliocentric distance (Rh) = 1.84 Astronomical Units and delta = 1.26 Astronomical Units). We obtained gas production rates, and molecular abundances relative to water for HCN, ortho-H2CO, CS, CO and CH3OH. A rotational temperature, T (sub rot) approximately equal to 50 degrees Kelvin, was determined by observing multiple methanol lines with the JCMT. By averaging the abundance ratio relative to water from the SMT and the JCMT we derive: CO: 7.03 plus or minus 1.84 percent, HCN: 0.04 plus or minus 0.01 percent, ortho H2CO: 0.14 plus or minus 0.03 percent as a parent molecule (and 0.28 plus or minus 0.06 percent as an extended source), CS: 0.03 plus or minus 0.01 percent and CH3OH: 3.11 for a range from plus 1:86 to minus 0.51 percent. We concluded that Garradd is normal in CH3OH, depleted in HCN, ortho-H2CO and CS and slightly enriched in CO with respect to typically observed cometary mixing ratios. We also studied the temporal evolution of HCN and CO and find that the production of HCN has a trend similar to water (but with short-term variation), with a decrease after perihelion, while that of CO shows contrary behavior: remaining constant or increasing after perihelion.

Comets: individual↗