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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Monte Carlo mixture model of lifetime cancer incidence risk from radiation exposure on shuttle and international space station

Estimating uncertainty in lifetime cancer risk for human exposure to space radiation is a unique challenge. Conventional risk assessment with low-linear-energy-transfer (LET)-based risk from Japanese atomic bomb survivor studies may be inappropriate for relativistic protons and nuclei in space due to track structure effects. This paper develops a Monte Carlo mixture model (MCMM) for transferring additive, National Institutes of Health multiplicative, and multiplicative excess cancer incidence risks based on Japanese atomic bomb survivor data to determine excess incidence risk for various US astronaut exposure profiles. The MCMM serves as an anchor point for future risk projection methods involving biophysical models of DNA damage from space radiation. Lifetime incidence risks of radiation-induced cancer for the MCMM based on low-LET Japanese data for nonleukemia (all cancers except leukemia) were 2.77 (90% confidence limit, 0.75-11.34) for males exposed to 1 Sv at age 45 and 2.20 (90% confidence limit, 0.59-10.12) for males exposed at age 55. For females, mixture model risks for nonleukemia exposed separately to 1 Sv at ages of 45 and 55 were 2.98 (90% confidence limit, 0.90-11.70) and 2.44 (90% confidence limit, 0.70-10.30), respectively. Risks for high-LET 200 MeV protons (LET=0.45 keV/micrometer), 1 MeV alpha-particles (LET=100 keV/micrometer), and 600 MeV iron particles (LET=180 keV/micrometer) were scored on a per particle basis by determining the particle fluence required for an average of one particle per cell nucleus of area 100 micrometer(2). Lifetime risk per proton was 2.68x10(-2)% (90% confidence limit, 0.79x10(-3)%-0. 514x10(-2)%). For alpha-particles, lifetime risk was 14.2% (90% confidence limit, 2.5%-31.2%). Conversely, lifetime risk per iron particle was 23.7% (90% confidence limit, 4.5%-53.0%). Uncertainty in the DDREF for high-LET particles may be less than that for low-LET radiation because typically there is very little dose-rate dependence. Probability density functions for high-LET radiation quality and dose-rate may be preferable to conventional risk assessment approaches. Nuclear reactions and track structure effects in tissue may not be properly estimated by existing data using in vitro models for estimating RBEs. The method used here is being extended to estimate uncertainty in spacecraft shielding effectiveness in various space radiation environments.

NASA Center LaRC↗
NASA NTRS2000

Relationship between the Fluorescence Lifetime of Chlorophyll 'a' and Primary Productivity within the Mississippi River Plume and Adjacent Shelf Region

In situ measurements of chlorophyll fluorescence intensity have been widely used to estimate phytoplankton biomass. However, because the fluorescence quantum yield of chlorophyll a in vivo can be highly variable, measurements of chlorophyll fluorescence intensity cannot be directly correlated with phytoplankton biomass and do not provide information on the physiological state of the phytoplankton under study. Conversely, lifetime-based measurements of chlorophyll fluorescence provide a framework in which photosynthetic rates of phytoplankton can be analyzed according to phytoplankton physiology. Along with the measurement of primary production and ambient nutrient concentrations within the Mississippi River plume in the northern Gulf of Mexico, phytoplankton fluorescence lifetimes were measured using a Fluorescence Lifetime Phytoplankton Analyzer (developed under a NASA Small Business Innovative Research contract to Ciencia, Inc.). Variability of fluorescence lifetimes within the plume can be used as a background from which to interpret variations in the maximum quantum yield of photochemistry. The extent to which nutrient and effluent loading in this dynamic coastal area affect the photosynthetic performance of phytoplankton will be presented as a function of phytoplankton fluorescence lifetimes.

Hall, Callie↗
NASA NTRS2005

The Effect of 17-4 PH Stainless Steel on the Lifetime of a Pennzane(Trademark) Lubricated Microwave Limb Sounder Antenna Actuator Assembly Ball Screw for the AURA Spacecraft

During ground based life testing of a Microwave Limb Sounder (MLS) Antenna Actuator Assembly (AAA) ball-screw assembly, lubricant darkening and loss were noted when approximately 10 percent of required lifetime was completed. The MLS-AAA ball screw and nut are made from 17-4 PH steel, the nut has 440C stainless steel balls, and the assembly is lubricated with a Pennzane formulation containing a three weight percent lead naphthenate additive. Life tests were done in dry nitrogen at 50 C. To investigate the MLS-AAA life test anomaly, Spiral Orbit Tribometer (SOT) accelerated tests were performed. SOT results indicated greatly reduced relative lifetimes of Pennzane formulations in contact with 17-4 PH steel compared to 440C stainless steel. Also, dry nitrogen tests yielded longer relative lifetimes than comparable ultrahigh vacuum tests. Generally, oxidized Pennzane formulations yielded shorter lifetimes than non-oxidized lubricant. This study emphasizes surface chemistry effects on the lubricated lifetime of moving mechanical assemblies.

Jones, William R., Jr.↗
NASA NTRS2008

Deriving Lifetime Maps in the Time/Frequency Domain of Coherent Structures in the Turbulent Boundary Layer

The lifetimes of coherent structures are derived from data correlated over a 3 sensor array sampling streamwise sidewall pressure at high Reynolds number (> 10(exp 8)). The data were acquired at subsonic, transonic and supersonic speeds aboard a Tupolev Tu-144. The lifetimes are computed from a variant of the correlation length termed the lifelength. Characteristic lifelengths are estimated by fitting a Gaussian distribution to the sensors cross spectra and are shown to compare favorably with Efimtsov s prediction of correlation space scales. Lifelength distributions are computed in the time/frequency domain using an interval correlation technique on the continuous wavelet transform of the original time data. The median values of the lifelength distributions are found to be very close to the frequency averaged result. The interval correlation technique is shown to allow the retrieval and inspection of the original time data of each event in the lifelength distributions, thus providing a means to locate and study the nature of the coherent structure in the turbulent boundary layer. The lifelength data are converted to lifetimes using the convection velocity. The lifetime of events in the time/frequency domain are displayed in Lifetime Maps. The primary purpose of the paper is to validate these new analysis techniques so that they can be used with confidence to further characterize the behavior of coherent structures in the turbulent boundary layer.

Palumbo, Dan↗
NASA NTRS2004

Phytoplankton-Fluorescence-Lifetime Vertical Profiler

A battery-operated optoelectronic instrument is designed to be lowered into the ocean to measure the intensity and lifetime of fluorescence of chlorophyll A in marine phytoplankton as a function of depth from 0 to 300 m. Fluorescence lifetimes are especially useful as robust measures of photosynthetic productivity of phytoplankton and of physical and chemical mechanisms that affect photosynthesis. The knowledge of photosynthesis in phytoplankton gained by use of this and related instruments is expected to contribute to understanding of global processes that control the time-varying fluxes of carbon and associated biogenic elements in the ocean. The concentration of chlorophyll in the ocean presents a major detection challenge because in order to obtain accurate values of photosynthetic parameters, the intensity of light used to excite fluorescence must be kept very low so as not to disturb the photosynthetic system. Several innovations in fluorometric instrumentation were made in order to make it possible to reach the required low detection limit. These innovations include a highly efficient optical assembly with an integrated flow-through sample interface, and a high-gain, low-noise electronic detection subsystem. The instrument also incorporates means for self-calibration during operation, and electronic hardware and software for control, acquisition and analysis of data, and communications. The electronic circuitry is highly miniaturized and designed to minimize power demand. The instrument is housed in a package that can withstand the water pressure at the maximum depth of 300 m. A light-emitting diode excites fluorescence in the sample flow cell, which is placed at one focal point of an ellipsoidal reflector. A photomultiplier tube is placed at the other focal point. This optical arrangement enables highly efficient collection of fluorescence emitted over all polar directions. Fluorescence lifetime is measured indirectly, by use of a technique based on the same principle as the one described in "Fluorometer for Analysis of Photosynthesis in Phytoplankton" (SSC-00110), NASA Tech Briefs, Vol. 24, No. 1 (November 2000), page 79. The excitation is modulated at a frequency of 70 MHz, and the phase shift between the excitation light and the emitted fluorescence is measured by a detection method in which the 70 MHz signal is down-converted to a 400 Hz signal. The fluorescence lifetime can be computed from the known relationship among the fluorescence lifetime, phase shift, and modulation frequency

Fernandez, Salvador M.↗
NASA NTRS2013

Preindustrial to Present-Day Changes in Tropospheric Hydroxyl Radical and Methane Lifetime from the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP)

We have analysed time-slice simulations from 17 global models, participating in the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP), to explore changes in present-day (2000) hydroxyl radical (OH) concentration and methane (CH4) lifetime relative to preindustrial times (1850) and to 1980. A comparison of modeled and observation-derived methane and methyl chloroform lifetimes suggests that the present-day global multi-model mean OH concentration is overestimated by 5 to 10% but is within the range of uncertainties. The models consistently simulate higher OH concentrations in the Northern Hemisphere (NH) compared with the Southern Hemisphere (SH) for the present-day (2000; inter-hemispheric ratios of 1.13 to 1.42), in contrast to observation-based approaches which generally indicate higher OH in the SH although uncertainties are large. Evaluation of simulated carbon monoxide (CO) concentrations, the primary sink for OH, against ground-based and satellite observations suggests low biases in the NH that may contribute to the high north–south OH asymmetry in the models. The models vary widely in their regional distribution of present-day OH concentrations (up to 34%). Despite large regional changes, the multi-model global mean (mass-weighted) OH concentration changes little over the past 150 yr, due to concurrent increases in factors that enhance OH (humidity, tropospheric ozone, nitrogen oxide (NOx) emissions, and UV radiation due to decreases in stratospheric ozone), compensated by increases in OH sinks (methane abundance, carbon monoxide and non-methane volatile organic carbon (NMVOC) emissions). The large inter-model diversity in the sign and magnitude of preindustrial to present-day OH changes (ranging from a decrease of 12.7% to an increase of 14.6%) indicate that uncertainty remains in our understanding of the long-term trends in OH and methane lifetime. We show that this diversity is largely explained by the different ratio of the change in global mean tropospheric CO and NOx burdens (Delta CO/Delta NOx, approximately represents changes in OH sinks versus changes in OH sources) in the models, pointing to a need for better constraints on natural precursor emissions and on the chemical mechanisms in the current generation of chemistry-climate models. For the 1980 to 2000 period, we find that climate warming and a slight increase in mean OH (3.5 +/- 2.2%) leads to a 4.3 +/- 1.9% decrease in the methane lifetime. Analysing sensitivity simulations performed by 10 models, we find that preindustrial to present-day climate change decreased the methane lifetime by about four months, representing a negative feedback on the climate system. Further, we analysed attribution experiments performed by a subset of models relative to 2000 conditions with only one precursor at a time set to 1860 levels. We find that global mean OH increased by 46.4 +/- 12.2% in response to preindustrial to present-day anthropogenic NOx emission increases, and decreased by 17.3 +/-2.3%, 7.6 +/- 1.5%, and 3.1 +/- 3.0% due to methane burden, and anthropogenic CO, and NMVOC emissions increases, respectively.

nitrogen oxides↗
NASA NTRS2018

Lifetimes of Multiply Alkylated Cyclopentane Oil in Contact with Various Metals, Evaluated with Vacuum Spiral Orbit Tribometer

The dependence of the lifetimes of small quantities of a Multiply Alkylated Cyclopentane (MAC) lubricant oil, Pennzane (Registered Trademark) 2001A (Nye Lubricants, Inc.), in rolling and sliding contact with different metals was evaluated with a vacuum spiral orbit tribometer. The metals were the bearing alloys 52100 steel, 440C steel, 17-4 PH steel and Nitinol 60 and the elements chromium, vanadium and titanium. The lifetimes of the lubricant oil on different metals fell into distinct groups with 52100 greater than 440C approx. Nitinol 60 greater than 17-4 PH for the order of the lifetimes of the steels and chromium greater than vanadium greater than titanium for the order of the lifetimes for the elements. The limited life of the small quantities of oil is assumed to be due to its consumption by the tribochemical reaction of the oil with the different metal bearing materials. The lifetimes are then inversely related to the reaction rates of the oil molecules with the various metals: the longest life of 52100 steel having the lowest reaction rate and the shortest life of titanium having the highest reaction rate. Mechanisms for the tribochemical reactions are discussed.

lubrication↗
NASA NTRS2021

On the effects of the ocean on atmospheric CFC-11 lifetimes and emissions

The ocean is a reservoir for CFC-11, a major ozone-depleting chemical. Anthropogenic production of CFC-11 dramatically decreased in the 1990s under the Montreal Protocol, which stipulated a global phase out of production by 2010. However, studies raise questions about current overall emission levels and indicate unexpected increases of CFC-11 emissions of about 10 Gg/yr after 2013 (based upon measured atmospheric concentrations and an assumed atmospheric lifetime). These findings heighten the need to understand processes that could affect the CFC-11 lifetime, including ocean fluxes. We evaluate how ocean uptake and release through 2300 affects CFC-11 lifetimes, emission estimates, and the long-term return of CFC-11 from the ocean reservoir. We show that ocean uptake yields a shorter total lifetime and larger inferred emission of atmospheric CFC-11 from 1930 to 2075 compared to estimates using only atmospheric processes. Ocean flux changes over time result in small but not completely negligible effects on the calculated unexpected emissions change (decreasing it by 0.4 ± 0.3 Gg/yr). Moreover, it is expected that the ocean will eventually become a source of CFC-11, increasing its total lifetime thereafter. Ocean outgassing should produce detectable increases in global atmospheric CFC-11 abundances by the mid-2100s, with emission of around 0.5 Gg/yr; this should not be confused with illicit production at that time. An illustrative model projection suggests that climate change is expected to make the ocean a weaker reservoir for CFC-11, advancing the detectable change in the global atmospheric mixing ratio by about 5 yr.

Anthropogenic production of CFC-11↗
NASA NTRSDate not supplied

Implementation of the Lifetime Method in Unsteady Pressure Sensitive Paint Measurements

At NASA Ames Research Center, unsteady pressure-sensitive paint (uPSP) measurements are obtained using the ‘intensity method’ which measures paint luminescence in response to a continuous, constant excitation. These measurements are obtained using high-speed cameras and are processed into fluctuating components of pressure. However, the nature of the intensity method also requires a separate steady state (time mean) pressure measurement to be obtained. This steady state measurement has typically been obtained using a separate set of PSP equipment that uses the ‘lifetime method’, which uses pulsed excitation to measure paint decay lifetime. If the lifetime method were implemented in the high-speed uPSP system, both the fluctuating and mean components of pressure could be obtained with a single system. This would greatly streamline setup, operations, and processing. In this paper, we describe work performed at the Fluid Mechanics Laboratory at NASA Ames to implement the lifetime method in our uPSP system. The uPSP acquisition system uses Phantom v2512 high-speed cameras, and it was initially uncertain if results of adequate quality could be obtained - their high framerate comes at the cost of several undesirable characteristics, which are explored in this paper. It was also uncertain if illumination using LED lamps, rather than a stronger source such as lasers, would be adequate. The data acquisition and data processing are discussed and the results analyzed. It was found that satisfactory lifetime method results can indeed be obtained using these high-speed cameras and LED lamps. This will allow the uPSP system to be greatly simplified and will have a large operational impact on how uPSP data is acquired in future wind tunnel tests.

Pressure Sensitive Paint↗
NASA NTRSDate not supplied

Implementation of the Lifetime Method in uPSP Measurements

At NASA Ames Research Center, unsteady pressure-sensitive paint (uPSP) measurements are obtained using the ‘intensity method’ which measures paint luminescence in response to a continuous, constant excitation. These measurements are obtained using high-speed cameras and are processed into fluctuating components of pressure. However, the nature of the intensity method also requires a separate steady state (time mean) pressure measurement to be obtained. This steady state measurement has typically been obtained using a separate set of PSP equipment that uses the ‘lifetime method’, which uses pulsed excitation to measure paint decay lifetime. If the lifetime method were implemented in the high-speed uPSP system, both the fluctuating and mean components of pressure could be obtained with a single system. This would greatly streamline setup, operations, and processing. In this paper, we describe work performed at the Fluid Mechanics Laboratory at NASA Ames to implement the lifetime method in our uPSP system. The uPSP acquisition system uses Phantom v2512 high-speed cameras, and it was initially uncertain if results of adequate quality could be obtained - their high framerate comes at the cost of several undesirable characteristics, which are explored in this paper. It was also uncertain if illumination using LED lamps, rather than a stronger source such as lasers, would be adequate. The data acquisition and data processing are discussed and the results analyzed. It was found that satisfactory lifetime method results can indeed be obtained using these high-speed cameras and LED lamps. This will allow the uPSP system to be greatly simplified and will have a large operational impact on how uPSP data is acquired in future wind tunnel tests.

Pressure Sensitive Paint↗
NASA NTRS1974

Laser measurements of the radiative lifetime of the B state of CN

A turnable dye laser was used to measure the radiative lifetime of the individual rotational levels of the B2 Sigma (+) state of CN. The radiative lifetime of the unperturbed rotational levels is 65.6 plus or minus 1.0 nsec. A longer radiative lifetime of 72 plus or minus 1 nsec is observed for the Kaon prime = 4 level of the B state. The measured values of the perturbed and unperturbed levels support the longer lifetimes for the A2 meson pion state of CN. The quenching cross section of the B2 Sigma state of CN is 41 plus or minus 20 Angstroms squared and is independent of the rotational energy of the B state.

Jackson, W. M.↗
NASA NTRS1975

Lifetimes for OH and OD electronic states with resonance transitions in the region between 1700 and 1950 A

The upper states of the OH and OD bands in the region between 1700 and 1950 A have been studied with a phase-shift radiative lifetime apparatus. Lifetimes varying from 1.8 to 2.9 ns have been found. Lifetimes for OH and OD are essentially the same, indicating that the upper states are likely to be depopulated via purely radiative processes under the present experimental conditions. Lifetimes have also been obtained for the C(2)Sigma(+) - A(2)Sigma(+) transition in OH and OD. These results are consistent with the preliminary analysis of Pryce (private communication) that the bands between 1700 and 1950 A in OH are partly due to the C(2)Sigma(+) - X(2)Pi sub i transition.

Smith, W. H.↗
NASA NTRS1978

Characterization of nonideal silicon in terms of lifetime and diffusion length

Experimental methods have been evaluated for the determination of lifetime and diffusion length in silicon intentionally doped with potentially lifetime-degrading impurities which may be present in low-cost silicon intended for use in terrestrial flat-plate arrays. Results obtained with these methods have been compared for mutual consistency. The effects of a number of impurities on bulk lifetime were determined from steady-state photoconductivity, and solar cells fabricated from this material were characterized in terms of diffusion length using a penetrating light technique. Comparison was made with results obtained by others using photoconductivity decay. General agreement was found in terms of the hierachy of impurities to which the lifetime is sensitive. The utility of the steady-state photoconductivity method is established even in the presence of considerable trapping.

Othmer, S.↗
NASA NTRS1979

Residence lifetimes of 1.79- to 2.15-MeV protons in the equatorial region of the Jovian magnetosphere

The magnitude of the strong flow of 1.79-2.15 MeV protons away from the Jovian magnetic equator is used to estimate the residence lifetimes of these protons in the equatorial source region. The lifetime is approximately 1.2 x 10 to the 5th/(R - 5.8)-squared sec, where R is distance in Jovian radii from Jupiter's center to the equatorial region of interest. At Europa and Ganymede (but not at Io) this lifetime is 1-2 orders of magnitude shorter than sweepup lifetimes by the moons. The fluxes of these protons, integrated over the observed range from 6 to 40 Jovian radii, amount to 3 x 10 to the 23rd particles per second, per degree of longitude and carry away about 9 x 10 to the 17th ergs per second per degree.

Northrop, T. G.↗
NASA NTRS1981

Analysis of the photo voltage decay /PVD/ method for measuring minority carrier lifetimes in P-N junction solar cells

The photo voltage decay (PVD) method for the measurement of minority carrier lifetimes in P-N junction solar cells with cell thickness comparable to or even less than the minority carrier diffusion length is examined. The method involves the generation of free carriers in the quasi-neutral bulk material by flashes of light and the monitoring of the subsequent decay of the induced open-circuit voltages as the carriers recombine, which is dependent on minority carrier recombination lifetime. It is shown that the voltage versus time curve for an ordinary solar cell (N(+)-P junction) is proportional to the inverse minority carrier lifetime plus a factor expressing the ratio of diffusion length to cell thickness. In the case of an ideal back-surface-field cell (N(+)-P-P(+) junction) however, the slope is directly proportional to the inverse minority carrier lifetime. It is noted that since most BSF cells are not ideal, possessing a sizable back surface recombination velocity, the PVD measurements must be treated with caution and supplemented with other nonstationary methods.

Von Roos, O.↗
NASA NTRS1983

On the method of positron lifetime measurement

A fast-slow coincidence system was constructed for the measurement of positron lifetimes in material. The time resolution of this system was 270 ps for the (60)Co gamma rays. Positron lifetime spectra for 14 kinds of alkali halides were measured with this system. Two lifetime components and their intensities were derived from analyses of the lifetime spectra.

Nishiyama, F.↗
NASA NTRS1984

Lifetimes in Si CVD-epitaxial and other layers determined by spectral LBIC

In an effort to evaluate the minority carrier lifetimes in CVD-epitaxially grown layers in their dependence on the CVD process variables, the absolute spectral LBIC method was found to be the only available method capable of yielding both lifetime and surface recombination velocity in layers, independent of the resistivity of this layer or that of the substrate, as long as they are separated by a pn-junction. With this method, it was not only possible to determine the minority carrier lifetimes in as-grown epi-layers, but to observe their changes through the device fabrication processes. In addition, it was possible for the first time to determine the lifetimes in the alloy-regrowth p(+) layers of base high/low junction structures.

Wolf, M.↗
NASA NTRS1988

Index grating lifetime in photorefractive GaAs

The index grating lifetime in liquid encapsulated Czochralski-grown undoped semi-insulating GaAs was measured using a beam coupling technique. The largest lifetime measure was about 8 s under a read beam intensity of 0.7 mW/sq cm with the grating periodicity being 0.63 microns. The measured value decreases to milliseconds as the read beam intensity and the grating periodicity increase to about 10 mW/sq cm and 4 microns, respectively. This range of grating lifetime in this material is adequate for its use in real-time spatial light modulators, reconfigurable beam steering devices, and dynamic memory elements, for optical computing. In addition, the results suggest that the lifetime is sensitive to residual imperfections in the crystal.

Cheng, Li-Jen↗