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At least 811 records · Page 45

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NASA NTRS1981

Catalytic autothermal reforming increases fuel cell flexibility

Experimental results are presented for the autothermal reforming (ATR) of n-hexane, n-tetradecane, benzene and benzene solutions of naphthalene. The tests were run at atmospheric pressure and at moderately high reactant preheat temperatures in the 800-900 K range. Carbon formation lines were determined for paraffinic and aromatic liquids. Profiles were determined for axial bed temperature and composition. Space velocity efforts were assessed, and the locations and types of carbon were recorded. Significant reactive differences between hydrocarbons were identified. Carbon formation characteristics were hydrocarbon specific. The differing behavior of paraffinic and aromatic fuels with respect to their carbon formation may be important in explaining the narrow range of carbon-free operating conditions found in the ATR of number two fuel oil.

Flytzani-Stephanopoulos, M.↗

NASA NTRS1995

Retrieval of water vapor mixing ratios from a laser-based sensor

Langley Research Center has developed a novel external path sensor which monitors water vapor along an optical path between an airplane window and reflective material on the plane's engine. An infrared tunable diode laser is wavelength modulated across a water vapor absorption line at a frequency f. The 2f and DC signals are measured by a detector mounted adjacent to the laser. The 2f/DC ratio depends on the amount of wavelength modulation, the water vapor absorption line being observed, and the temperature, pressure, and water vapor content of the atmosphere. The present work concerns efforts to quantify the contributions of these factors and to derive a method for extracting the water vapor mixing ratio from the measurements. A 3 m cell was fabricated in order to perform laboratory tests of the sensor. Measurements of 2f/DC were made for a series of pressures and modulation amplitudes. During my 1994 faculty fellowship, a computer program was created which allowed 2f/DC to be calculated for any combination of the variables which effect it. This code was used to generate 2f/DC values for the conditions measured in the laboratory. The experimental and theoretical values agreed to within a few percent. As a result, the laser modulation amplitude can now be set in the field by comparing the response of the instrument to the calculated response as a function of modulation amplitude. Once the validity of the computer code was established, it was used to investigate possible candidate absorption lines. 2f/DC values were calculated for pressures, temperatures, and water vapor mixing ratios expected to be encountered in future missions. The results have been incorporated into a database which will be used to select the best line for a particular mission. The database will also be used to select a retrieval technique. For examples under some circumstances there is little temperature dependence in 2f/DC so temperature can be neglected. In other cases, there is a dependence with temperature for a particular pressure, requiring a more complicated retrieval algorithm. Future experimental work is necessary to test agreement with the theoretical values over a range of temperatures and mixing ratios. Additionally, retrieval algorithms for forthcoming missions must be incorporated into the software package which controls the instrument.

Tucker, George F.↗

NASA NTRS1974

Studies of K line filtergrams

The paper describes the material obtained on a Lyot filter for K at the Big Bear Solar Observatory. This material is compared with simultaneous H-alpha observations. K-line filtergrams are used to interpret K-line double reversal. The structure of the general chromosphere is discussed. It is found that the absorption of the cool clouds of the chromosphere, covering about one third of the area inside the cells, oscillating rapidly, and having a vertical extent around 3000 km, is not clearly seen in K3. In active regions K is close to H-alpha. Here all plagettes and plages are bounded by systems of strongly inclined bright and dark fibrils. Umbral flashes are found to be less visible in H-alpha, except that the running penumbral waves are bright in K and dark in H-alpha.

Zirin, H.↗

NASA NTRS1983

Non-noble metal based metallization systems

The results of efforts to produce a nonsilver metallization system for silicon photovoltaic cells are given. The system uses a metallization system based on molybdenum, tin, and titanium hydride. The initial work in this system was done using the MIDFILM process. The MIDFILM process attains a line resolution comparable to photoresist methods with a process related to screen printing. The surface to be processed is first coated with a thin layer of photopolymer material. Upon exposure to ultraviolet light through a suitable mask, the polymer in the non-pattern area crosslinks and becomes hard. The unexposed pattern areas remain tacky. The conductor material is then applied in the form of a dry mixture of metal which adheres to the tacky pattern area. The assemblage is then fired to ash the photopolymer and sinter the conductor powder.

Garcia, A., III↗

NASA NTRS1989

Infrared line intensity measurements in the v = 0-1 band of the ClO radical

Integrated line intensity measurements in the ClO-radical fundamental vibrational v = 0-1 band were carried out using a high-resolution Fourier transform spectrometer coupled to a long-path-length absorption cell. The results of a series of measurements designed to minimize systematic errors, yielded a value of the fundamental IR band intensity of the ClO-radical equal to 9.68 + or - 1.45/sq cm per atm at 296 K. This result is consistent with all the earlier published results, with the exception of measurements reported by Kostiuk et al. (1986) and Lang et al. (1988).

Burkholder, James B.↗

NASA NTRS1990

Clutter filter design considerations for Airborne Doppler radar detection of windshear

The problem of clutter rejection when processing down-looking Doppler radar returns from a low altitude airborne platform is a paramount problem. With radar as a remote sensor for detecting and predicting windshear in the vicinity of an urban airport, dynamic range requirements can exceed 50 dB because of high clutter to signal ratios. This presentation describes signal processing considerations in the presence of distributed and/or discrete clutter interference. Previous analyses have considered conventional range cell processing of radar returns from a rigidly mounted radar platform using either the Fourier or the pulse-pair method to estimate average windspeed and windspeed variation within a cell. Clutter rejection has been based largely upon analyzing a particular environment in the vicinity of the radar and employing a variety of techniques to reduce interference effects including notch filtering, Fourier domain line editing, and use of clutter maps. For the airborne environment the clutter characteristics may be somewhat different. Conventional clutter rejection methods may have to be changed and new methods will probably be required to provide useful signal to noise ratios. Various considerations are described. A major thrust has been to evaluate the effect of clutter rejection filtering upon the ability to derive useful information from the post-filter radar data. This analysis software is briefly described. Finally, some ideas for future analysis are considered including the use of adaptive filtering for clutter rejection and the estimation of windspeed spatial gradient directly from radar returns as a means of reducing the effects of clutter on the determination of a windshear hazard.

Baxa, Ernest G., Jr.↗

NASA NTRS2007

Performance of a Herriott Cell, Designed for Variable Temperatures between 296 and 20 K

We designed, fabricated and tested a multipath Herriott cell (or off-axis spherical mirror interferometer) to achieve low temperature absorption measurements. The cell is fabricated entirely from copper and the 15 cm radius of curvature copper mirrors have gold coated reflective surfaces. The cell was tested at temperatures between 296 and 30 K with a folded absorption path length of 5.37 m utilizing a lead salt tunable diode laser. Short term temperature stability (1 h) of the Herriott cell is better than 0.005 K under normal operating conditions with a temperature uniformity better than 0.01 K (not measurable). The cell was tested by performing collisional cooling experiments on 13C16O2 in helium at temperatures between 70 and 20 K and by performing more traditional pressure broadening and shift measurements on molecular infrared absorption lines at temperatures between 300 and about 80 K on 13C16O2 methane.

Mondelain, Didier↗

NASA NTRS2015

Summer 2015 Internship Abstract

Green fluorescent protein (GFP) visually shows the expression of proteins by fluorescing when exposed to certain wavelengths of light. The GFP in this experiment was used to identify cells actively releasing viruses. The experiment focused on the effect of microgravity on the GFP expression of Akata B-cells infected with Epstein Barr Virus (EBV). Two flasks were prepared with 30 million cells each and two bioreactors were prepared with 50 million cells each. All four cultures were incubated for 16 days and fed every four days. Cellometer readings were taken on the feeding days to find cell size, viability, and GFP expression. In addition, the cells were treated with Propodium monoazide (PMA) and run through real time PCR to determine viral load on the feeding days. On the International Space Station air samples are taken to analyze the bacterial and fungal organisms in the air. The Sartorius Portable Airport is being investigated for potential use on the ISS to analyze for viral content in the air. Multiple samples were taken around Johnson Space Center building 37 and in Clear Lake Pediatric Clinic. The filter used was the gelatin membrane filter and the DNA was extracted directly from the filter. The DNA was then run through real time PCR for Varicella Zoster Virus (VZV) and EBV as well as GAPDH to test for the presence of DNA. The results so far have shown low DNA yield and no positive results for VZV or EBV. Further inquiry involves accurately replicating an atmosphere with high viral load from saliva as would be found on the ISS to run the air sampler in. Another line of research is stress hormones that may be correlated to the reactivation of latent viruses. The stress hormones from saliva samples are analyzed rather than blood samples. The quantity found in saliva shows the quantity of the hormones actually attached to cells and causing a reaction, whereas in the blood the quantity of hormones is the total amount released to cause a reaction. The particular hormones tested for were cortisol, alpha-amylase, and DHEA. The DHEA was very high in the two control samples tested. Regularly, samples came into the lab from local clinics to be tested for various viruses. Saliva, blood, body scrapes, and tears were received from the clinics and then run for VZV, EBV, and Human Simplex Virus 1 (HSV-1) with the results then reported back to the clinician. Blood, saliva, and urine from astronauts were also tested for viruses and logged. In addition, several cell cultures were brought up and grown, including adherent Human Lung Fibroblast (HFL) cells infected with VZV, and Akata B-cells infected with EBV.

Smith, Courtney↗

NASA NTRS2013

Spectroscopic Determination of Trace Contaminants in High-Purity Oxygen

Oxygen used for extravehicular activities (EVAs) must be free of contaminants because a difference in a few tenths of a percent of argon or nitrogen content can mean significant reduction in available EVA time. These inert gases build up in the extravehicular mobility unit because they are not metabolized or scrubbed from the atmosphere. A prototype optical emission technique capable of detecting argon and nitrogen below 0.1% in oxygen has been developed. This instrument uses a glow discharge in reduced-pressure gas to produce atomic emission from the species present. Because the atomic emission lines from oxygen, nitrogen, and argon are discrete, and in many cases well-separated, trace amounts of argon and nitrogen can be detected in the ultraviolet and visible spectrum. This is a straightforward, direct measurement of the target contaminants, and may lend itself to a device capable of on-orbit verification of oxygen purity. A glow discharge is a plasma formed in a low-pressure (1 to 10 Torr) gas cell between two electrodes. Depending on the configuration, voltages ranging from 200 V and above are required to sustain the discharge. In the discharge region, the gas is ionized and a certain population is in the excited state. Light is produced by the transitions from the excited states formed in the plasma to the ground state. The spectrum consists of discrete, narrow emission lines for the atomic species, and broader peaks that may appear as a manifold for molecular species such as O2 and N2, the wavelengths and intensities of which are a characteristic of each atom. The oxygen emission is dominated by two peaks at 777 and 844 nm.

Hornung, Steven↗

NASA NTRS1981

Two-photon excitation of nitric oxide fluorescence as a temperature indicator in unsteady gasdynamic processes

A laser-induced fluorescence technique based on the pulsed two-photon excitation of NO is presented which is especially suited for the measurement of fluctuating temperatures in cold turbulent flows. The technique uses the fluorescence from the UV gamma bands of NO produced by two-photon excitation of NO (A 2 Sigma +, nu-prime = 0 - X 2 Pi, nu-double prime = 0) to obtain a rotational temperature. An analysis is presented of relevant aspects of the two-photon absorption process including microphysical processes, spectral intensities as a function of transition and laser spectral widths, line-shape integrals, the nonequilibrium response of the medium to a laser pulse, fluorescence energies, signal to noise ratio, and focusing effects. An analysis of absolute two-photon absorptivity measured in a nonflowing cell is then presented and used to predict signal to noise ratios greater than 50 for supersonic flows at temperatures below 300 K.

Mckenzie, R. L.↗

NASA NTRS1983

Improved 02/H2 Gas Mixture Sensor

Monitor of mixture concentrations uses catalyzed and uncatalyzed temperature probe. Sensor includes Pt-catalyzed temperature probe mounted in line with similar uncatalyzed temperature probe. Use of common temperature probes and standard, flareless, high-pressure tubefittings resulted in design conductive to installation in almost any system. Suitable for use in regenerative fuel cells, life-support systems, and other closed systems.

Moulthrop, L. C.↗

NASA NTRS1997

A new look at the quiet sun network in the upper atmosphere during a minimum of activity cycle

The preliminary results obtained with the solar extreme ultraviolet spectrometer, onboard the Solar and Heliospheric Observatory (SOHO), are reported on. The solar ultraviolet measurement of emitted radiation (SUMER) instrument established a long time series of the network evolution in following the solar rotation. The maps of the network evolution were obtained in lines spanning from 10(sup 4) K to 6 x 10(sup 6) K. Line profiles were also recorded with a sampling of 1 x 0.76 sq arcsec over the entire field. The progress analysis of this set of data is underlined and the velocity distribution in the cell network is considered.

Lemaire, P.↗

NASA NTRS1996

Spectral line discriminator for passive detection of fluorescence

A method and apparatus for detecting fluorescence from sunlit plants is based on spectral line discrimination using the A-band and B-band absorption of atmospheric oxygen. Light from a plant including scattered sunlight and the fluorescence from chlorophyll is passed through a chopper into a cell containing low-pressure, high-purity oxygen. A-band or B-band wavelengths present in the light are absorbed by the oxygen in the cell. When the chopper is closed, the absorbed light is remitted as fluorescence into a detector. The intensity of the fluorescence from the oxygen is proportional to the intensity of fluorescence from the plant.

Kebabian, Paul L.↗

NASA NTRS1993

Migration of Co in nickel oxide/hydroxide of a nickel electrode in a Ni/H2 cell

Cobalt redistribution in nickel active material has been reported. This redistribution was suspected to be related to capacity fading. The objective of this work is to establish a relationship between cobalt redistribution and capacity fading. Microscopic cobalt distribution in nickel active material was studied using three EDX techniques: line scan, point-by-point analysis, and dot maps. Results from this study are presented.

Lim, Hong S.↗

NASA NTRS1976

The pressure and energy balance of the cool corona over sunspots

The 22 largest sunspots observed with the Skylab SO55 spectrometer are studied for a relation between their EUV radiation and their umbral size or magnetic classification. The ultimate goal is to determine why the coronal plasma is so cool over a sunspot and how this cool plasma manages to support itself against gravity. Based on the time behavior of the EUV emission, a steady-state model is developed for the pressure and energy balance of the cool coronal-plasma loops over the spots. Analysis of the temperature structure in a typical loop indicates that the loop is exceedingly well insulated from the outside corona, that its energy balance is determined purely by internal heating and cooling processes, and that a heat input of about 0.0001 erg/cu cm per sec is required along the full length of the loop. It is proposed that: (1) coronal material flows steadily across the field lines at the tops of the loops and falls downward along both sides under gravity; (2) the corona is heated by mechanical-energy transport across the very thin transition region immediately over network-cell interiors; and (3) strong magnetic fields tend to inhibit mechanical-energy dissipation in the corona.

Foukal, P. V.↗

NASA NTRS1993

Intensities and broadening coefficients for the Q branch of the 4nu-2 - nu-1 + nu-2 (471.511/cm) band of CO2

Absolute intensities for the Q-branch of the 4nu-2 - nu-1 + nu-1/2 (20,003-11,101) band in CO2 were measured for the first time. Measurements were performed for lines Q10 to Q28, at temperatures ranging from 385 to 426 K, for pressures from 3 to 40 torr, using our long wavelength tunable diode laser spectrometer. The combination of tunable diode lasers, a White cell, and a blocked impurity band detector made it possible to obtain signal to noise ratios greater than 1000 in the 471/cm spectral region, with about 3 x 10 exp -4/cm spectral resolution. The band strength was found to be 8.6(2) x 10 exp -25 cm/molec at 296 K, and the Hermann-Wallis factor was determined. Comparison with the values listed in the HITRAN 92 data base are presented. Self-, N2- and O2-broadening coefficients were also measured.

Sirota, J. M.↗

NASA NTRS2004

Russian Activities in Space Photovoltaic Power Modules with Concentrators

Space concentrator modules with point-and line-focus Fresnel lenses and with reflective parabolic troughs have been developed recently at Ioffe Physico-Technical Institute. PV receivers for these modules are based: on the single junction LPE and MOCVD AlGaAs/GaAs solar cells characterized by AM0 efficiencies of 23.5 - 24% at 20 - 50 suns and 24 - 24.75 at 50 - 200 suns; on the mechanically stacked tandem AlGaAs/GaAs-GaSb cells with efficiency of 27 - 28 at 20 - 100 suns. MOCVD AlGaAs/GaAs cells with internal Bragg reflector have shown a higher radiation resistance as compared to a traditional structure. Monolithic two-terminal tandems AlGaAs (top)-GaAs (bottom) for space application and GaSb (top) - InGaAsSb (bottom) for TRV application are under development as well.

Andreev, Vyacheslav M.↗

NASA NTRS1989

Amplified spontaneous emission measurement of a line-narrowed, tunable, Ti:Al2O3 amplifier using rubidium absorption

Amplified spontaneous emission, ASE, generated by a Ti:Al2O3 laser amplifier has been measured as a function of pump energy, and thus gain, using the atomic absorption of rubidium, Rb, gas at 0.780 micron. By tuning the Ti:Al2O3 laser, the Rb cell could selectively absorb the narrow spectral bandwidth laser radiation while transmitting the wide spectral bandwidth ASE. Transmission of laser amplifier pulses through a Rb absorption cell, measured at various temperatures, thus allows the measurement of the weak ASE in the vicinity of the strong laser pulse. A model for the transmission of Rb as a function of temperature and wavelength has been developed. The measured transmissions are in good agreement with the transmission model predictions.

Barnes, James C.↗