Engineering topics

Buhl, D.

Publications and source records attributed to Buhl, D..

At least 19 records

NASA NTRS2009

High Spectral Resolution Infrared Studies of Titan: Winds, Temperature and Composition

Results from the most recent analyses of resolved ethane Line emission profiles from the stratosphere of Titan, measured before (2003) [1, 2], near the time of (2005) [3, 4], and after (2008) Huygens descent, will be presented. Wind velocity, temperature and ethane abundance are retrieved from 11.7 micron measurements at spectral resolving, powers > 1000000 using the NASA Goddard Space Flight Center Heterodyne Instrument for Planetary Wind And Composition (HIPWAC) interfaced with the 8.2 meter Subaru telescope of the National Astronomical Observatory of Japan. Retrieved wind velocities (approx.190 m/s at 230 km) from Doppler shifts of measured emission lines are compared to previous infrared heterodyne studies and compared to results front either direct wired measurements - Huygens Doppler Wind Experiment [5], Doppler shifts of reflected visible radiation [6], and mm-wave investigations [7]. Comparison to indirect wind retrievals from stellar occultation [8] observations and Cassini CIRS thermal maps [9] is also made, An empirical altitude-dependent wired model will be presented. The narrow ethane emission lines are analyzed to retrieve the ethane mole fraction and an attempt is made to evaluate the altitude distribution of ethane in the stratosphere for thermal profiles derived from measurements from Cassini and Huygens. Resultant ethane altitude distributions will be discussed and comparison to results front earlier HIPWAC and other remote sensing measurements and from contemporaneous Cassini/Huygens investigations [10, 11] will be made. Preliminary comparison suggests temporal or spatial variability in the line emission and retrieved ethane abundance in Titan's stratosphere:. Possible detection of minor hydrocarbon constituents and evidence of possible probing of Titan's mesosphere and of mesospheric wind shear will be discussed.

Kostiuk, T.↗

NASA NTRS1999

Jovian Northern Ethane Aurora and the Solar Cycle

Thermal infrared auroral spectra from Jupiter's North polar region have been collected from 1979 to 1998 in a continuing study of long-term variability in the northern thermal IR aurora, using C2H6 emission lines near 12 microns as a probe. Data from Voyager I and 2 IRIS measurements and ground based spectral measurements were analyzed using the same model atmosphere to provide a consistent relative comparison. A retrieved equivalent mole fraction was used to compare the observed integrated emission. Short term (days), medium term (months) and long term (years) variability in the ethane emission was observed. The variability Of C2H6 emission intensities was compared to Jupiter's seasonal cycle and the solar activity cycle. A positive correlation appears to exist, with significantly greater emission and short term variability during solar maxima. Observations on 60 N latitude during increased solar activity in 1979, 1989, and most recently in 1998 show up to 5 times brighter integrated line emission of C2H6 near the north polar "hot spot" (150-210 latitude) than from the north quiescent region. Significantly lower enhancement was observed during periods of lower solar activity in 1982, 1983, 1993, and 1995. Possible sources and mechanisms for the enhancement and variability will be discussed.

Kostiuk,T.↗

NASA NTRS1999

Temporal Behavior of Ammonia and Temperature in the Jovian Stratosphere following the SL9 Impacts

We will present new results in the study of temporal changes in ammonia (NH3) abundance, altitude distribution, and temperature in the stratosphere of Jupiter after the Comet Shoemaker-Levy 9 impact in 1994. Data obtained by Betz et al. (1994) using infrared heterodyne spectroscopy were analyzed using a newly developed beam integration radiative transfer code. The spectra are from six different impact regions and were acquired from hours to three weeks following the impact. The data consist of single NH3 stratospheric emission line profiles near 10 microns measured at a resolving power of approximately 10(exp 7). The true line profiles and the new radiative transfer program permitted the simultaneous retrieval of information on both the NH3 abundance and thermal structure as well as to set constraints on the altitude distribution of stratospheric ammonia. Retrieved column densities varied from approximately 10(exp 18) to 10(exp 16) over the three week period. Over the same time period the altitude of the emitting region varied from levels above the few mbar pressure region to below the 50 mbar pressure regions. Stratospheric temperatures hours after impact were approximately 220 K and about 8 days after impact returned to the quiescent levels (approximately 170-180 K). Results from this self-consistent set of measurements will be presented, compared to those from other measurements, and compared to theoretical retrievals from photochemical models for NH3 in the Jovian stratosphere.

Kostiuk, Ttheodor↗

NASA NTRS1995

Tape casting and partial melting of Bi-2212 thick films

To produce Bi-2212 thick films with high critical current densities tape casting and partial melting is a promising fabrication method. Bi-2212 powder and organic additives were mixed into a slurry and tape casted onto glass by the doctor blade tape casting process. The films were cut from the green tape and partially molten on Ag foils during heat treatment. We obtained almost single-phase and well-textured films over the whole thickness of 20 microns. The orientation of the (a,b)-plane of the grains was parallel to the substrate with a misalignment of less than 6 deg. At 77 K/0T a critical current density of 15, 000 A/sq cm was reached in films of the dimension 1 cm x 2 cm x 20 microns (1 micron V/cm criterion, resistively measured). At 4 K/0T the highest value was 350,000 A/sq cm (1 nV/cm criterion, magnetically measured).

Buhl, D.↗

NASA NTRS1995

The role of silver in the processing and properties of Bi-2212

The influence of the silver content and the oxygen partial pressure on the solidus temperature and the weight loss during melting of Bi2Sr2Ca1Cu2O(x) has been examined by means of DTA and TGA. By decreasing the oxygen partial pressure the solidus is lowered (e.g. del T = 59 C by decreasing pO2 from 1 atm to 0.001 atm) and the weight loss is increased. The addition of silver causes two effects: (1) the solidus is further decreased (e.g. 2 wt% Ag lower T (solidus) by up to 25 C, depending on the oxygen partial pressure); and (2) the weight loss during melting is reduced. Thick films (10-20 micron in thickness) with 0 and 5 wt% silver and bulk samples with) and 2.7 wt% silver were melt processed in flowing oxygen on a silver substrate in the DTA, allowing the observation of the melting process and a good temperature control. The critical current densities are vigorously dependent on the maximum processing temperature. The highest j(sub c) in thick films (8000 A/sq cm at 77 K, O T) was reached by melting 7 C above the solidus temperature. The silver addition shows no significant effect on the processing parameters or the superconducting properties. The highest j(sub c) for bulk samples (1 mm in thickness) was obtained by partial melting at 900 C or 880 C, depending on the silver content of the powder (0 or 2.7 wt%). The j(sub c) of the samples is slightly enhanced from 1800 A/sq cm (at 77 K, O T) to 2000 A/sq cm by the silver addition. To be able to reach at least 80% of the maximum critical current density, the temperature has to be controlled in a window of 5 C for thick films and 17 C for bulk samples.

Lang, TH.↗

NASA NTRS1992

Sudbury project (University of Muenster-Ontario Geological Survey): Summary of results - an updated impact model

In 1984 the Ontario Geological Survey initiated a research project on the Sudbury structure (SS) in cooperation with the University of Muenster. The project included field mapping (1984-1989) and petrographic, chemical, and isotope analyses of the major stratigraphic units of the SS. Four diploma theses and four doctoral theses were performed during the project (1984-1992). Specific results of the various investigations are reported. Selected areas of the SS were mapped and sampled: Footwall rocks; Footwall breccia and parts of the sublayer and lower section of the Sudbury Igneous Complex (SIC); Onaping Formation and the upper section of the SIC; and Sudbury breccia and adjacent Footwall rocks along extended profiles up to 55 km from the SIC. All these stratigraphic units of the SS were studied in substantial detail by previous workers. The most important characteristic of the previous research is that it was based either on a volcanic model or on a mixed volcanic-impact model for the origin of the SS. The present project was clearly directed toward a test of the impact origin of the SS without invoking an endogenic component. In general, our results confirm the most widely accepted stratigraphic division of the SS. However, our interpretation of some of the major stratigraphic units is different from most views expressed. The stratigraphy of the SS and its new interpretation is given as a basis for discussion.

Avermann, M.↗

NASA NTRS1992

Sudbury project (University of Muenster-Ontario Geological Survey): Sr-Nd in heterolithic breccias and gabbroic dikes

One major objective of our Sudbury project was to define origin and age of the huge breccia units below and above the Sudbury Igneous Complex (SIC). The heterolithic Footwall Breccia (FB) represents a part of the uplifted crater floor. It contains subrounded fragments up to several meters in size and lithic fragments with shock features (greater than 10 GPa) embedded into a fine- to medium-grained matrix. Epsilon(sub Nd)-epsilon(sub Sr) relationships point to almost exclusively parautochthonous precursor lithologies. The different textures of the matrix reflect the metamorphic history of the breccia layer; thermal annealing by the overlying hot impact melt sheet (SIC) at temperatures greater than 1000 C resulted in melting of the fine crushed material, followed by an episode of metasomatic K-feldspar growth and, finally, formation of low-grade minerals such as actinolite and chlorite. Isotope relationships in the Onaping breccias (Gray and Green Member) are much more complex. All attempts to date the breccia formation failed: Zircons are entirely derived from country rocks and lack the pronounced Pb loss caused by the heat of the slowly cooling impact melt sheet (SIC). Rb-Sr techniques using either lithic fragments of different shock stages or the thin slab method, set time limits for the apparently pervasive alkali mobility in these suevitic breccias. The data array and the intercept in the plots point to a major Rb-Sr fractionation around 1.54 Ga ago. This model age is in the same range as the age obtained for the metasomatic matrix of the FB. Rb-Sr dating of a shock event in impact-related breccias seems to be possible only if their matrix had suffered total melting by the hot melt sheet (FB) or if they contain a high fraction of impact melt (suevitic Onaping breccias), whereas the degree of shock metamorphism in rock or lithic fragments plays a minor role. In the Sudbury case, however, the impact melt in the seuvitic breccias is devitrified and recrystallized, which changed Rb/Sr ratios quite drastically. Therefore, the Onaping breccias give only age limits for alteration and low-grade metamorphism. The Sm-Nd system was not reset during the Sudbury event; clasts as well as the matrix in the FB and in the Onaping breccias show preimpact 'Archean' Nd isotope signatures.

Buhl, D.↗

NASA NTRS1992

Sudbury project (University of Muenster-Ontario Geological Survey): Isotope systematics support the impact origin

Within the framework of the Sudbury project a considerable number of Sr-Nd isotope analyses were carried out on petrographically well-defined samples of different breccia units. Together with isotope data from the literature these data are reviewed under the aspect of a self-consistent impact model. The crucial point of this model is that the Sudbury Igneous Complex (SIC) is interpreted as a differentiated impact melt sheet without any need for an endogenic 'magmatic' component such as 'impact-triggered' magmatism or 'partial' impact melting of the crust and mixing with a mantle-derived magma.

Deutsch, A.↗

NASA NTRS1986

Monitoring observations of selected SiO maser sources at 7 mm wavelength - 1977-1979

High-spectral-resolution SiO maser observations at 7 mm wavelength were made for 13 circumstellar objects and Ori A over a 34 month interval from January 1977 to November 1979. These data precede and adjoin the SiO monitoring data taken at 3 and 7 mm wavelengths by Lane (1982) and at 3 mm wavelengths by Nyman and Olofsson (1985) and thus provide an important link in the record of the temporal behavior of SiO masers over a period of several years. The time-averaged center of the weak SiO maser emission pedestal gives the stellar radial velocity. This reinforces the idea that the SiO maser emission pedestal is representative of the true structure of a stellar SiO maser, while the more visible and stronger, narrow SiO emission spikes represent chance coherences along the velocity range of the pedestal. Similarities between the SiO maser velocity patterns of VY CMa and Ori A may suggest similarities in their evolutionary stages.

Snyder, L. E.↗

NASA NTRS1984

Molecular astronomy at submillimeter wavelengths

It is pointed out that the region of the spectrum from 300 to 3000 GHz (100 to 1000 microns), which is referred to as the submillimeter, is one of the least explored areas in the electromagnetic spectrum. The reasons for this situation are related to a lack of adequate instrumentation for detecting the radiation and an almost complete absorption of the radiation by the earth's atmosphere. The vast majority of the rotational transitions of molecules occur in the millimeter and submillimeter wavelength region of the spectrum. The strength of the lines increases at higher frequencies until a condition is reached in which the energy levels are no longer populated. The study of molecular clouds at submillimeter wavelengths promises to provide new important results. Attention is given to the design of suitable submillimeter receivers, problems of atmospheric transmission, and galactic molecular lines.

Buhl, D.↗

NASA NTRS1983

An extensive galactic search for conformer II glycine

The most extensive galactic search reported to date for conformer II glycine, a higher energy form of the simplest amino acid has been conducted. The search utilized four glycine transitions at centimeter wavelengths and 21 at millimeter wavelengths to observe 18 galactic molecular sources and one comet. No conformer II glycine lines were detected, and measurements of representative sources were used to compute upper limits on total column densities. Several unidentified lines were detected and are reported here with some suggested possible identifications.

Snyder, L. E.↗

NASA NTRS1982

Infrared heterodyne spectroscopy

Infrared heterodyne spectroscopy is an extremely useful tool for Doppler-limited studies of atomic and molecular lines in diverse astrophysical regions. The current state of the art is reviewed, and the analysis of CO2 lines in the atmosphere of Mars is outlined. Doppler-limited observations have enabled the discovery of natural laser emission in the mesosphere of Mars and the discovery of failure of local thermodynamic equilibrium near the surface of Mars.

Mumma, M. J.↗

NASA NTRS1982

Tunable diode-laser heterodyne spectrometer for remote observations near 8 microns

A diode-laser-based, ultrahigh resolution IR heterodyne spectrometer for laboratory and field use has been developed for operation between 7.5 and 8.5 microns. The local oscillator is a PbSe tunable diode laser kept continuously at operating temperatures of 12-60 K using a closed-cycle cooler. The laser output frequency is controlled and stabilized using a high-precision diode current supply, constant temperature controller, and a shock isolator mounted between the refrigerator cold tip and the diode mount. The system largely employs reflecting optics to minimize losses from internal reflection and absorption and to eliminate chromatic effects. Spectral analysis of the diode-laser output between 0 and 1 GHz reveals excess noise at many diode current settings, which limits the IR spectral regions over which useful heterodyne operation can be achieved. Observations have been made of atmospheric N2O, O3, and CH4 between 1170 and 1200/cm, using both a single-frequency swept IF channel and a 64-channel RF spectral line receiver with a total IF coverage of 1600 MHz.

Glenar, D.↗

NASA NTRS1982

Tunable diode laser heterodyne spectrometer for remote observations near 8 microns

Infrared heterodyne spectroscopy is a passive technique employing coherent optical detection for the study of spectral features in remote sources. It employs optical components such as mirrors and lenses normally associated with incoherent optics, but because of it's coherent nature, it offers the advantages of ultrahigh spectral resolving power, high frequency precision, and diffraction limited field-of-view. Attention is given to the development of an ultrahigh resolution diode laser heterodyne spectrometer for observational and laboratory use. The instrument is designed for operation in the spectral range from 7.5 to 8.5 microns. A PbSe tuneable diode laser (TDL) is employed as local oscillator. A closed-cycle cooler is employed to keep the oscillator at operating temperatures in the range from 12 to 60 K. Attention is given to factors determining the TDL heterodyne sensitivity, the spectrometer design, and a survey of 8 micron observations, SiO could be detected in the sunspot spectrum.

Glenar, D. A.↗

NASA NTRS1982

The excitation and distribution of CO (J = 6-5) emission in the Orion Nebula

Observations of the 691-GHz (J = 6-5) transition of CO in the BN/KL region of Orion obtained in February 1981, at the IR Telescope Facility at Mauna Kea are reported. The system employs a heterodyne receiver with an overall noise temperature of 3900 K DSB at 432 microns, 64 5-MHz IF-filter-bank channels, and a chopping secondary with 120-arcsec excursion, and has 35-arcsec resolution. Sample data are presented graphically and analyzed using a rate equation and a kinetic model. A 35 x 45-arcsec core with hot broad plateau emission (antenna temperature 180 + or - 36 K) surrounded by an area of strong narrow-line 120-K emission is found. It is suggested that the plateau emission originates in a wide thin sheet after a shock wave, with H2 density at least 10 to the 6th/cu cm and gas kinetic temperature greater than 500 K.

Buhl, D.↗

NASA NTRS1981

Bulk and integrated acousto-optic spectrometers for radio astronomy

The development of sensitive heterodyne receivers (front end) in the centimeter and millimeter range, and the construction of sensitive RF spectrometers (back end) enable the spectral lines of interstellar molecules to be detected and identified. A technique was developed which combines acoustic bending of a collimated coherent light beam by a Bragg cell followed by detection by a sensitive array of photodetectors (thus forming an RF acousto-optic spectrometer (AOS). An AOS has wide bandwidth, large number of channels, and high resolution, and is compact, lightweight, and energy efficient. The thrust of receiver development is towards high frequency heterodyne systems, particularly in the millimeter, submillimeter, far infrared, and 10 micron spectral ranges.

Chin, G.↗

NASA NTRS1981

Discovery of natural gain amplification in the 10-micrometer carbon dioxide laser bands on Mars - A natural laser

Fully resolved intensity profiles of various lines in the carbon dioxide band at 10.4 micrometers have been measured on Mars with an infrared heterodyne spectrometer. Analysis of the line shapes shows that the Mars atmosphere exhibits positive gain in these lines. The detection of natural optical gain amplification enables identification of these lines as a definite natural laser.

Mumma, M. J.↗

NASA NTRS1981

Submillimeter heterodyne detection of interstellar carbon monoxide at 434 micrometers

Laser heterodyne observations of submillimeter emissions from carbon monoxide in the Orion molecular cloud are reported. High frequency and spatial resolution observations were made at the NASA Infrared Telescope Facility on Mauna Kea by the use of an optically pumped laser local oscillator and quasi-optical Schottky diode mixer for heterodyne detection of the J = 6 - 5 rotational transition of CO at 434 microns. Spectral analysis of the 434-micron emission indicates that the emitting gas is optically thin and is at a temperature above 180 K. Results thus demonstrate the potential contributions of ground-based high-resolution submillimeter astronomy to the study of active regions in interstellar molecular clouds.

Fetterman, H. R.↗