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At least 1,387 records · Page 77
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Mars sample collection and preservation

The intensive exploration of Mars is a major step in the systematic exploration of the solar system. Mars, earth, and Venus provide valuable contrasts in planetary evolution. Mars exploration has progressed through the stages of exploration and is now ready for a sample-return mission. About 5 kg of intelligently selected samples will be returned from Mars. A variety of samples are wanted. This requires accurate landing in areas of high interest, surface mobility and analytical capability, a variety of sampling tools, and stringent preservation and isolation measures.

Blanchard, Douglas P.↗
NASA NTRS1988

IRAS observations of an optically selected sample of interacting galaxies

IRAS observations of a large, morphologically selected sample of strongly interacting disk-type galaxies have demonstrated that galaxy-galaxy collisions can lead to enhanced infrared emission, but not in all cases. Infrared luminosities of the interacting galaxies span a large range, but are about a factor of 2 higher, on average, than those of isolated disk galaxies. The data suggest the existence of a cutoff in blue luminosity, below which no galaxies show markedly enhanced infrared emission. Only the most strongly interacting systems in the sample show extreme values of infrared excess, suggesting that deep, interpenetrating collisions are necessary to drive infrared emission to extreme levels. Comparisons with optical indicators of star formation show that infrared excess and color temperatures correlate with the level of star-formation activity in the interacting galaxies. All interacting galaxies in our sample that exhibit an infrared excess and have higher than normal color temperatures also have optical indicators of high levels of star formation. It is not necessary to invoke processes other than star formation to account for the enhanced infrared luminosity in this sample of interacting galaxies.

Bushouse, Howard A.↗
NASA NTRS1989

Electrohydrodynamic distortion of sample streams in continuous flow electrophoresis

Continuous flow electrophoresis experiments were carried out, using an electrolyte and a sample both made of aqueous solutions of phosphate buffer (with polystyrene latex added for visibility), to investigate causes of the sample spreading in this procedure. It is shown theoretically that an electric field perpendicular to a circular filament of conducting fluid surrounded by a fluid of different conductivity produces an electrohydrodynamic flow, which distorts the filament into an ellipse. Experimental results were found to be fully consistent with theretical predictions. It was found that the rate of distortion of the sample stream into a ribbon was proportional to the square of the applied voltage gradient. Furthermore, the orientation of the ribbon depends on the ratios of dielectric constant and electrical conductivity between the buffer and the sample.

Rhodes, Percy H.↗
NASA NTRS1989

Workshop on Analysis of Returned Comet Nucleus Samples

This volume contains abstracts that were accepted by the Program Committee for presentation at the workshop on the analysis of returned comet nucleus samples held in Milpitas, California, January 16 to 18, 1989. The abstracts deal with the nature of cometary ices, cryogenic handling and sampling equipment, origin and composition of samples, and spectroscopic, thermal and chemical processing methods of cometary nuclei. Laboratory simulation experimental results on dust samples are reported. Some results obtained from Halley's comet are also included. Microanalytic techniques for examining trace elements of cometary particles, synchrotron x ray fluorescence and instrument neutron activation analysis (INAA), are presented.

Source record↗
NASA NTRS1989

Candidate sample acquisition systems for the Rosetta

The Comet Nucleus Sample Return (CNSR) mission, one of the four cornerstones of the ESA scientific program, is one of the most complex space ventures within the next century, both from technological and deep space exploration point of view. In the Rosetta scenario the sample acquisition phase represents the most critical point for the global mission's success. The proposed paper illustrates the main results obtained in the context of the CNSR-SAS ongoing activity. The main areas covered are related to: (1) sample properties characterization (comet soil model, physical/chemical properties, reference material for testing); (2) concepts identification for coring, shovelling, harpooning and anchoring; (3) preferred concept (trade off among concepts, identification of the preferred configuration); and (4) proposed development activity for gaining the necessary confidence before finalizing the CNSR mission. Particular emphasis will be given to the robotic and flexibility aspects of the identified sample acquisition systems (SAS) configuration, intended as a means for the overall system performance enhancement.

Magnani, P. G.↗
NASA NTRS1990

International cooperation for Mars exploration and sample return

The National Research Council's Space Studies Board has previously recommended that the next major phase of Mars exploration for the United States involve detailed in situ investigations of the surface of Mars and the return to earth for laboratory analysis of selected Martian surface samples. More recently, the European space science community has expressed general interest in the concept of cooperative Mars exploration and sample return. The USSR has now announced plans for a program of Mars exploration incorporating international cooperation. If the opportunity becomes available to participate in Mars exploration, interest is likely to emerge on the part of a number of other countries, such as Japan and Canada. The Space Studies Board's Committee on Cooperative Mars Exploration and Sample Return was asked by the National Aeronautics and Space Administration (NASA) to examine and report on the question of how Mars sample return missions might best be structured for effective implementation by NASA along with international partners. The committee examined alternatives ranging from scientific missions in which the United States would take a substantial lead, with international participation playing only an ancillary role, to missions in which international cooperation would be a basic part of the approach, with the international partners taking on comparably large mission responsibilities. On the basis of scientific strategies developed earlier by the Space Studies Board, the committee considered the scientific and technical basis of such collaboration and the most mutually beneficial arrangements for constructing successful cooperative missions, particularly with the USSR.

Levy, Eugene H.↗
NASA NTRS1989

The dependence of the soft X ray spectral slope with radio property, luminosity, and redshift, for a large sample of AGN from the Einstein IPC data base

The dependence of the soft X-ray spectral slope on radio, optical and X-ray properties, and on redshift are reported for a large sample of Active Galactic Nuclei (AGN). The sample includes 317 optically and radio-selected AGN from a preliminary version of the Einstein Imaging Proportional Counter (IPC) quasar and AGN data base. The main results are: the difference in X-ray slope between radio-loud and radio-quiet AGN were confirmed for an independent and much larger sample of sources; a difference in X-ray slope between flat and steep radio spectrum AGN is observed only in high luminosity sub-sample; in flat radio spectrum AGNs there is an indication for a dependence of the X-ray spectral index on X-ray luminosity redshift and alpha sub 0x.

Brunner, H.↗
NASA NTRS1990

On the determination of iridium in diverse geological samples employing HPGe-coincidence/NaI(Tl)-anticoincidence spectrometry

This paper reports the Ir content of a variety of geological samples determined by the high-purity Ge-coincidence/NaI(Tl)-anticoincidence gamma-ray spectrometry (henceforth referred to as coincidence/anticoincidence technique) and by the conventional INAA. The advantages of this technique are: (1) the Ir content of the samples is obtained (ppm to a fraction of ppb ranges) not only by the 468.1 keV peak as in the conventional INAA but also by the 784.6 keV and 920.9 keV sum peaks, which gives more confidence in the values obtained; and (2) it is well suited for the samples with high Compton background for which it is difficult to measure the Ir content by the conventional INAA technique. The practical sensitivity of this technique depends on the sample matrix. Under present experimental conditions, it varied from 0.1 ng for Mn nodules and 0.004 ng for Libyan Desert Glass. Iridium values obtained on small (about 1 microg) olivine grains demonstrate the potential application of this new technique to microsamples. The principle and methodology of this new technique as well as its advantages and disadvantages over the conventional INAA are discussed.

Murali, A. V.↗
NASA NTRS1991

Ellipsometric study of metal samples

Exposed and unexposed (shielded) portions of the surfaces of six different metal samples (Al, Cu, Ni, Ta, W, and Zr) that had been mounted on LDEF were studied by variable angle spectroscopic ellipsometry. The change in the optical constants of the metals caused by exposure to the space environment was measured. The measured optical constants reflect changes in the morphology and stoichiometry of a surface layer to a depth of this order of magnitude. For all the samples examined in this manner the exposed and unexposed portions exhibited dramatically different optical properties. In order to determine whether the observed changes were caused by the impact of oxygen atoms encountered in flight an experiment was set up in which samples identical to the original metal samples are exposed to a low-energy oxygen plasma in a microwave discharge chamber. Results of this experiment are reported, as well as an analysis of the observed data in terms of surface layers of different composition.

Franzen, W.↗
NASA NTRS1991

Study of activation of metal samples from LDEF-1 and Spacelab-2

The activation of metal samples and other material orbited onboard the Long Duration Exposure Facility (LDEF) and Spacelab-2 were studied. Measurements of the radioactivities of spacecraft materials were made, and corrections for self-absorption and efficiency were calculated. Activation cross sections for specific metal samples were updated while cross sections for other materials were tabulated from the scientific literature. Activation cross sections for 200 MeV neutrons were experimentally determined. Linear absorption coefficients, half lives, branching ratios and other pertinent technical data needed for LDEF sample analyses were tabulated. The status of the sample counting at low background facilities at national laboratories is reported.

Laird, C. E.↗
NASA NTRS1990

Continuous monitoring of a changing sample by multiplex gas chromatography

Results are presented from a study in which a continuously changed gaseous sample was monitored by multiplex gas chromatography (MGC), using the exponential dilution (ED) technique of Ritter and Adams (1976) to change the composition and concentration of a gaseous mixture in such a way as to imitate changes in the atmospheric gases sampled by a descending aircraft. A calibration of the MGC system was performed with four different rates of sample dilution, and the errors resulting from various degrees of change in the sample concentration were determined.

Valentin, Jose R.↗
NASA NTRS1992

Sparsely Sampled Phase-Insensitive Ultrasonic Transducer Arrays

Three methods of interpretation of outputs from sparsely sampled two-dimensional array of receiving ultrasonic transducers used in transmission experiments investigated. Methods are: description of sampled beam in terms of first few spatial moments of sampled distribution of energy; use of signal-dependent cutoff to limit extent of effective receiver aperture; and use of spatial interpolation to increase apparent density of sampling during computation. Methods reduce errors in computations of shapes of ultrasonic beams.

Patrick H. Johnston↗
NASA NTRS1992

Analysis of particulate contamination on tape lift samples from the VETA optical surfaces

Particulate contamination analysis was carried out on samples taken from the Verification Engineering Test Article (VETA) x-ray detection system. A total of eighteen tape lift samples were taken from the VETA optical surfaces. Initially, the samples were tested using a scanning electron microscope. Additionally, particle composition was determined by energy dispersive x-ray spectrometry. Results are presented in terms of particle loading per sample.

Germani, Mark S.↗
NASA NTRS1992

Xylan - A potential contaminant for lunar samples and Antarctic meteorites

The possibility that lunar samples have been contaminated by the proprietary lubricant paint known as Xylan, which has been applied to screw threads in dry-N sample processing cabinets at NASA JSC, is considered. From a sample analysis using sealed-tube and stepped combustion, it is argued that the unexpectedly high concentration of organic materials found in EET A79001 is not due to Xylan contamination. It is considered unlikely that previous C and N analyses of lunar samples have been affected by the introduction of Xylan.

Wright, I. P.↗
NASA NTRS1991

Optimal sampling theory and population modelling - Application to determination of the influence of the microgravity environment on drug distribution and elimination

The optimal sampling theory is evaluated in applications to studies related to the distribution and elimination of several drugs (including ceftazidime, piperacillin, and ciprofloxacin), using the SAMPLE module of the ADAPT II package of programs developed by D'Argenio and Schumitzky (1979, 1988) and comparing the pharmacokinetic parameter values with results obtained by traditional ten-sample design. The impact of the use of optimal sampling was demonstrated in conjunction with NONMEM (Sheiner et al., 1977) approach, in which the population is taken as the unit of analysis, allowing even fragmentary patient data sets to contribute to population parameter estimates. It is shown that this technique is applicable in both the single-dose and the multiple-dose environments. The ability to study real patients made it possible to show that there was a bimodal distribution in ciprofloxacin nonrenal clearance.

Drusano, George L.↗
NASA NTRS1993

Mineralogy of three slightly palagonitized basaltic tephra samples from the summit of Mauna Kea, Hawaii

The paper characterizes the mineralogy and spectral properties of three slightly palagonitized basaltic tephra samples collected near the summit of Mauna Kea in order to contribute to the basis for inferring mineralogy and processes for Martian surface materials. The mineralogy of size fractions of these samples is examined by diffuse reflectance and FIR spectroscopy, optical microscopy, X-ray diffraction, Moessbauer spectroscopy, magnetic analysis, EMPA, TEM, and SEM. For the 20-1000 micron size fraction, sample HWMK11 (red) is essentially completely oxidized and has a hematite (Ti-hematite) pigment dispersed throughout the silicate matrix. Sample HWMK12 (black) has the lowest proportion of ferric-bearing phases and is thus least weathered. For HWMK11, the amount of hematite is essentially constant, and mica is present only in the coarse clay-sized fraction; smectites are low in structural Fe.

Golden, D. C.↗
NASA NTRS1993

A proof of the Woodward-Lawson sampling method for a finite linear array

An extension of the continuous aperture Woodward-Lawson sampling theorem has been developed for a finite linear array of equidistant identical elements with arbitrary excitations. It is shown that by sampling the array factor at a finite number of specified points in the far field, the exact array factor over all space can be efficiently reconstructed in closed form. The specified sample points lie in real space and hence are measurable provided that the interelement spacing is greater than approximately one half of a wavelength. This paper provides insight as to why the length parameter used in the sampling formulas for discrete arrays is larger than the physical span of the lattice points in contrast with the continuous aperture case where the length parameter is precisely the physical aperture length.

Somers, Gary A.↗
NASA NTRS1993

Spatial structure, sampling design and scale in remotely-sensed imagery of a California savanna woodland

This article describes research related to sampling techniques for establishing linear relations between land surface parameters and remotely-sensed data. Predictive relations are estimated between percentage tree cover in a savanna environment and a normalized difference vegetation index (NDVI) derived from the Thematic Mapper sensor. Spatial autocorrelation in original measurements and regression residuals is examined using semi-variogram analysis at several spatial resolutions. Sampling schemes are then tested to examine the effects of autocorrelation on predictive linear models in cases of small sample sizes. Regression models between image and ground data are affected by the spatial resolution of analysis. Reducing the influence of spatial autocorrelation by enforcing minimum distances between samples may also improve empirical models which relate ground parameters to satellite data.

Mcgwire, K.↗