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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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NASA NTRS1994

Permeability of membranes to amino acids and modified amino acids: mechanisms involved in translocation

The amino acid permeability of membranes is of interest because they are one of the key solutes involved in cell function. Membrane permeability coefficients (P) for amino acid classes, including neutral, polar, hydrophobic, and charged species, have been measured and compared using a variety of techniques. Decreasing lipid chain length increased permeability slightly (5-fold), while variations in pH had only minor effects on the permeability coefficients of the amino acids tested in liposomes. Increasing the membrane surface charge increased the permeability of amino acids of the opposite charge, while increasing the cholesterol content decreased membrane permeability. The permeability coefficients for most amino acids tested were surprisingly similar to those previously measured for monovalent cations such as sodium and potassium (approximately 10(-12)-10(-13) cm s-1). This observation suggests that the permeation rates for the neutral, polar and charged amino acids are controlled by bilayer fluctuations and transient defects, rather than partition coefficients and Born energy barriers. Hydrophobic amino acids were 10(2) more permeable than the hydrophilic forms, reflecting their increased partition coefficient values. External pH had dramatic effects on the permeation rates for the modified amino acid lysine methyl ester in response to transmembrane pH gradients. It was established that lysine methyl ester and other modified short peptides permeate rapidly (P = 10(-2) cm s-1) as neutral (deprotonated) molecules. It was also shown that charge distributions dramatically alter permeation rates for modified di-peptides. These results may relate to the movement of peptides through membranes during protein translocation and to the origin of cellular membrane transport on the early Earth.

Review↗

NASA NTRS1973

Lunar powder simulator under lunarlike conditions - Dielectric properties

A powered basalt simulating lunar regolith material was subjected to temperature variations similar to those found in the lunar surface during a lunation. To obtain the dielectric response under simulated lunar conditions, all measurements were made in appropriate vacuums which, in addition, allowed for an evaluation of moisture effects in the powdered sample. It is found that during approximately seven tenths of a lunation the dielectric response of a 5- to 10-cm surface layer should be fairly constant. During the remaining three tenths, it should undergo rapid changes. Changes in the dielectric properties of the surface layer should be controlled by temperature. In the subjacent layers such changes are thought to be controlled by the increasing density of the regolith.

Alvarez, R.↗

NASA NTRS1952

Free-Spinning-Tunnel Investigation of a 1/24-Scale Model of the Grumman F9F-6 Airplane TED No. NACA DE 364

An investigation of a 1/24-scale model of the Grumman F9F-6 airplane has been conducted in the Langley 20-foot free-spinning tunnel. The erect and inverted spin and recovery characteristics of the model were determined for the normal flight loading with the model in the clean condition. The effect of loading variations was investigated briefly. Spin-recovery parachute tests were also performed. The results indicate that erect spins obtained on the airplane in the clean condition will be satisfactorily terminated for all loading conditions provided full rudder reversal is accompanied by moving the ailerons and flaperons (lateral controls) to full with the spin (stick right in a right spin). Inverted spins should be satisfactorily terminated by full reversal of the rudder alone. The model tests indicate that an 11.4-foot (laid-out-flat diameter) tail parachute (drag coefficient approximately 0.73) should be effective as an emergency spin-recovery device during demonstration spins of the airplane provided the towline is attached above the horizontal stabilizer.

Klinar, Walter J.↗

NASA NTRS1980

A measurement of forward-flight effects on the noise from a JT15D-1 turbofan engine in the NASA-Ames 40- by 80-Foot Wind Tunnel

A Pratt and Whitney JT15D-1 turbofan engine was tested in two facilities at Ames Research Center: the outdoor Static Test Facility and the 40- by 80-Foot Wind Tunnel. The primary purposes of the test were to determine the effects of forward velocity on the turbofan spectra in the forward quadrant for the cruise inlet and to compare these wind-tunnel spectra with outdoor spectra to determine the possibility of simulating forward-velocity effects from purely outdoor measurements. The wind-tunnel data show a reduction in the blade-passage frequency tones of the order of 10 dB with increasing forward velocity at subsonic fan-tip speeds. No forward-velocity variation was observed at supersonic tip speeds. Comparison of in-duct spectra for the cruise inlet at forward velocity, with spectra from outdoor tests with a distortion-control inlet shows excellent agreement for the in-duct data when allowance is made for different in-duct volumes. This is also reflected in good agreement for the far-field spectra at small forward angles. The comparisons of wind-tunnel and outdoor data also indicate that at least for the JT15D-1, it may be possible to approximate the shape of the far-field spectra at large directivity angles from an outdoor measurement with the cruise inlet, providing an effective inflow control device is used.

Ahtye, W. F.↗

NASA NTRS1981

Evaluation of pressure and thermal data from a wind tunnel test of a large-scale, powered, STOL fighter model

A STOL fighter model employing the vectored-engine-over wing concept was tested at low speeds in the NASA/Ames 40 by 80-foot wind tunnel. The model, approximately 0.75 scale of an operational fighter, was powered by two General Electric J-97 turbojet engines. Limited pressure and thermal instrumentation were provided to measure power effects (chordwise and spanwise blowing) and control-surface-deflection effects. An indepth study of the pressure and temperature data revealed many flow field features - the foremost being wing and canard leading-edge vortices. These vortices delineated regions of attached and separated flow, and their movements were often keys to an understanding of flow field changes caused by power and control-surface variations. Chordwise blowing increased wing lift and caused a modest aft shift in the center of pressure. The induced effects of chordwise blowing extended forward to the canard and significantly increased the canard lift when the surface was stalled. Spanwise blowing effectively enhanced the wing leading-edge vortex, thereby increasing lift and causing a forward shift in the center of pressure.

Howell, G. A.↗

NASA NTRS2001

DAO's Next Generation Physical-Space/Finite-Volume Data Assimilation System: Formulation and Initial Evaluation

The Physical-space/Finite-volume Data Assimilation System (fvDAS) is the next generation global atmospheric data assimilation system in development at the Data Assimilation Office at NASA's Goddard Space Flight Center. It is based on a new finite-volume general circulation model jointly developed by NASA and NCAR, and on the Physical-Space Statistical Analysis System (PSAS) developed at the DAO. In this talk we will describe the general system formulation, the adaptive quality control and general aspects of the error covariance modeling. The NASA-NCAR GCM is a completely new model which replaces the CEOs GCM used in the previous GEOS-1/2/3 Data Assimilation systems. A particular configuration of adaptive Statistical Quality Control and the Physical-space Statistical Analysis System (PSAS) are currently implemented in DAO's operational Data Assimilation System. However, the unique finite-volume formulation of the NASA-NCAR GCM, combined with the generality of the observation-space formulation of PSAS, provides for a very simple and accurate model-analysis interface. The system assimilates a variety of conventional and satellite observations. In particular, TOVS Level 1B radiances are assimilated using a 1-D variational scheme, both in clear sky and cloudy conditions. Computationally, the fvDAS runs approximately 10 times faster than the operational GEOS-Terra system. We will show that the next-generation fvDAS has much improved observation-minus-6hr forecast (O-F) statistics, as well as 5-day forecast skills. Top of the atmosphere radiation fields are in closer agreement with CERES measurements, with realistic precipitation and moisture fields. We will also show that the finite-volume formulation of the fvDAS produce assimilated fields which are more suitable for driving constituent transport models.

daSilva, A.↗

NASA NTRS1995

Uncertainty in vertically integrated liquid water content due to radar reflectivity observation error

Radar reflectivity is used to estimate meteorological quantities such as rainfall rate, liquid water content, and the related quantity, vertically integrated liquid (VIL) water content. The estimation of any of these quantities depends on several assumptions related to the characteristics of the physical processes controlling the occurrence and character of water in the atmosphere. Additionally, there are many sources of error associated with radar observations, such as those due to brighthand, hail, and drop size distribution approximations. This work addresses one error of interest, the radar reflectivity observation error; other error sources are assumed to be corrected or negligible. The result is a relationship between the uncertainty in VIL water content and radar reflectivity measurement error. An example application illustrates the estimation of VIL uncertainty from typical radar reflectivity observations and indicates that the coefficient of variation in VIL is much larger than the coefficient of variation in radar reflectivity.

French, Mark N.↗

DOE OSTI2024

Challenges of COVID-19 Case Forecasting in the US, 2020–2021

During the COVID-19 pandemic, forecasting COVID-19 trends to support planning and response was a priority for scientists and decision makers alike. In the United States, COVID-19 forecasting was coordinated by a large group of universities, companies, and government entities led by the Centers for Disease Control and Prevention and the US COVID-19 Forecast Hub ( https://covid19forecasthub.org ). We evaluated approximately 9.7 million forecasts of weekly state-level COVID-19 cases for predictions 1–4 weeks into the future submitted by 24 teams from August 2020 to December 2021. We assessed coverage of central prediction intervals and weighted interval scores (WIS), adjusting for missing forecasts relative to a baseline forecast, and used a Gaussian generalized estimating equation (GEE) model to evaluate differences in skill across epidemic phases that were defined by the effective reproduction number. Overall, we found high variation in skill across individual models, with ensemble-based forecasts outperforming other approaches. Forecast skill relative to the baseline was generally higher for larger jurisdictions (e.g., states compared to counties). Over time, forecasts generally performed worst in periods of rapid changes in reported cases (either in increasing or decreasing epidemic phases) with 95% prediction interval coverage dropping below 50% during the growth phases of the winter 2020, Delta, and Omicron waves. Ideally, case forecasts could serve as a leading indicator of changes in transmission dynamics. However, while most COVID-19 case forecasts outperformed a naïve baseline model, even the most accurate case forecasts were unreliable in key phases. Further research could improve forecasts of leading indicators, like COVID-19 cases, by leveraging additional real-time data, addressing performance across phases, improving the characterization of forecast confidence, and ensuring that forecasts were coherent across spatial scales. In the meantime, it is critical for forecast users to appreciate current limitations and use a broad set of indicators to inform pandemic-related decision making.

59 BASIC BIOLOGICAL SCIENCES↗

NASA NTRS1998

Performance of the Spacecraft Propulsion Research Facility During Altitude Firing Tests of the Delta 3 Upper Stage

The Spacecraft Propulsion Research Facility at the NASA Lewis Research Center's Plum Brook Station was reactivated in order to conduct flight simulation ground tests of the Delta 3 cryogenic upper stage. The tests were a cooperative effort between The Boeing Company, Pratt and Whitney, and NASA. They included demonstration of tanking and detanking of liquid hydrogen, liquid oxygen and helium pressurant gas as well as 12 engine firings simulating first, second, and third burns at altitude conditions. A key to the success of these tests was the performance of the primary facility systems and their interfaces with the vehicle. These systems included the structural support of the vehicle, propellant supplies, data acquisition, facility control systems, and the altitude exhaust system. While the facility connections to the vehicle umbilical panel simulated the performance of the launch pad systems, additional purge and electrical connections were also required which were unique to ground testing of the vehicle. The altitude exhaust system permitted an approximate simulation of the boost-phase pressure profile by rapidly pumping the test chamber from 13 psia to 0.5 psia as well as maintaining altitude conditions during extended steady-state firings. The performance of the steam driven ejector exhaust system has been correlated with variations in cooling water temperature during these tests. This correlation and comparisons to limited data available from Centaur tests conducted in the facility from 1969-1971 provided insight into optimizing the operation of the exhaust system for future tests. Overall, the facility proved to be robust and flexible for vehicle space simulation engine firings and enabled all test objectives to be successfully completed within the planned schedule.

Meyer, Michael L.↗

NASA NTRS2011

Thermal Structure of Titan's Troposphere and Middle Atmosphere

The thermal structure of Titan's atmosphere is reviewed, with particular emphasis on recent Cassini-Huygens results. Titan's has a similar troposphere-stratosphere-mesosphere pattern like Earth, but with a much more extended atmosphere, because of the weaker gravity, and also much lower temperatures, because of its greater distance from the sun. Titan's atmosphere exhibits an unusually large range in radiative relaxation times. In the troposphere, these are long compared to seasonal time scales, but in the stratosphere they are much shorter than a season. An exception is near the winter pole, where the stratospheric relaxation times at 100-170 km become comparable to the seasonal time scale; at the warm stratopause, they are comparable to a Titan day. Hence, seasonal behavior in the troposphere should be muted, but significant in the stratosphere. This is reflected in the small meridional contrast observed in temperatures in the troposphere and the large stratospheric contrasts noted above. A surprising feature of the vertical profiles of temperature is the abrupt transition between these regimes in at high northern latitudes in winter, where the temperatures in the lower stratosphere exhibit a sudden drop with increasing altitude. This could be a radiative effect, not associated with spatial variations in gaseous opacity, but rather from an optically thick condensate at thermal-infrared wavelengths. A curious aspect of Titan's middle atmosphere is that the axis of symmetry of the temperature field is tilted by several degrees relative to the rotational axis of the moon itself. Whether this is driven by solar heating or gravitational perturbations is not known. Titan's surface exhibits weak contrasts in temperature, approximately 3 K in the winter hemisphere. At low latitudes, there is evidence of a weak nocturnal boundary layer on the morning terminator, which is not radiatively controlled, but can be explained in terms of vertical mixing with a small eddy viscosity.

Flasar, F. M.↗

NASA NTRS1996

Lunar Base Heat Pump

The objective of this project was to investigate the feasibility of constructing a heat pump suitable for use as a heat rejection device in applications such as a lunar base. In this situation, direct heat rejection through the use of radiators is not possible at a temperature suitable for lde support systems. Initial analysis of a heat pump of this type called for a temperature lift of approximately 378 deg. K, which is considerably higher than is commonly called for in HVAC and refrigeration applications where heat pumps are most often employed. Also because of the variation of the rejection temperature (from 100 to 381 deg. K), extreme flexibility in the configuration and operation of the heat pump is required. A three-stage compression cycle using a refrigerant such as CFC-11 or HCFC-123 was formulated with operation possible with one, two or three stages of compression. Also, to meet the redundancy requirements, compression was divided up over multiple compressors in each stage. A control scheme was devised that allowed these multiple compressors to be operated as required so that the heat pump could perform with variable heat loads and rejection conditions. A prototype heat pump was designed and constructed to investigate the key elements of the high-lift heat pump concept. Control software was written and implemented in the prototype to allow fully automatic operation. The heat pump was capable of operation over a wide range of rejection temperatures and cooling loads, while maintaining cooling water temperature well within the required specification of 40 deg. C +/- 1.7 deg. C. This performance was verified through testing.

Walker, D.↗

NASA NTRS1997

Kinematic principles of primate rotational vestibulo-ocular reflex. II. Gravity-dependent modulation of primary eye position

The kinematic constraints of three-dimensional eye positions were investigated in rhesus monkeys during passive head and body rotations relative to gravity. We studied fast and slow phase components of the vestibulo-ocular reflex (VOR) elicited by constant-velocity yaw rotations and sinusoidal oscillations about an earth-horizontal axis. We found that the spatial orientation of both fast and slow phase eye positions could be described locally by a planar surface with torsional variation of <2.0 +/- 0.4 degrees (displacement planes) that systematically rotated and/or shifted relative to Listing's plane. In supine/prone positions, displacement planes pitched forward/backward; in left/right ear-down positions, displacement planes were parallel shifted along the positive/negative torsional axis. Dynamically changing primary eye positions were computed from displacement planes. Torsional and vertical components of primary eye position modulated as a sinusoidal function of head orientation in space. The torsional component was maximal in ear-down positions and approximately zero in supine/prone orientations. The opposite was observed for the vertical component. Modulation of the horizontal component of primary eye position exhibited a more complex dependence. In contrast to the torsional component, which was relatively independent of rotational speed, modulation of the vertical and horizontal components of primary position depended strongly on the speed of head rotation (i.e., on the frequency of oscillation of the gravity vector component): the faster the head rotated relative to gravity, the larger was the modulation. Corresponding results were obtained when a model based on a sinusoidal dependence of instantaneous displacement planes (and primary eye position) on head orientation relative to gravity was fitted to VOR fast phase positions. When VOR fast phase positions were expressed relative to primary eye position estimated from the model fits, they were confined approximately to a single plane with a small torsional standard deviation ( approximately 1.4-2.6 degrees). This reduced torsional variation was in contrast to the large torsional spread (well >10-15 degrees ) of fast phase positions when expressed relative to Listing's plane. We conclude that primary eye position depends dynamically on head orientation relative to space rather than being fixed to the head. It defines a gravity-dependent coordinate system relative to which the torsional variability of eye positions is minimized even when the head is moved passively and vestibulo-ocular reflexes are evoked. In this general sense, Listing's law is preserved with respect to an otolith-controlled reference system that is defined dynamically by gravity.

NASA Discipline Neuroscience↗

NASA NTRS2008

Space Technology 5 Observations of Auroral Field-Aligned Currents

During its three month long technology validation mission, Space Technology 5 (ST-5) returned high quality multi-point measurements of the near-Earth magnetic field. Its three micro-satellites were launched into a 300 x 4500 km, dawn - dusk, sun synchronous orbit (inclination = 105.60) orbit with a period of 138 min by a Pegasus launch vehicle on March 22, 2006. The spacecraft were maintained in a "pearls on a sting" constellation with controlled spacings ranging from just over 5000 km down to under 50 km. The individual micro-satellites were 48 cm tall octagons with diameters of 50 cm. They were spin-stabilized at approximately 20 rpm at deployment and slowly spun-down to about 15 rpm by the end of the mission. Each spacecraft carried a miniature tri-axial fluxgate magnetometer (MAG) provided by the University of California at Los Angeles mounted at the end of a ultra-low mass 72 cm boom. These data allow, for the first time, the separation of temporal and spatial variations in field-aligned current (FAC) perturbations measured in low-Earth orbit on time scales of 10 sec to 10 min. The constellation measurements are used to directly determine field-aligned current sheet motion, thickness. and current density. Two multi-point methods for the inference of FAC current density that have not previously been possible in low-Earth orbit are demonstrated: 1) the -standard method." based upon s/c velocity, but corrected for FAC current sheet motion. and 2) the "gradiometer method" which uses simultaneous magnetic field measurements at two points with known separation. Future studies will apply these methods to the entire ST-5 data sct and expand to include horizontal ionospheric currents. ULF waves and geomagnetic field gradient analyses.

Slavin, James↗

NASA NTRS1983

A study on the spectral models for waves in finite water depth

From an extension of the Wallops Spectrum (Huang et al., 1981) for the deep water waves, spectral models for waves in finite water depths are developed. Stokes wave expansions are found to offer a good approximation for intermediate water depth. The spectral function in this case is controlled by three parameters: the significant slope, the nondimensional depth, and the peak frequency. It is pointed out that solitary and cnoidal wave models must be used for the shallow water waves. The controlling parameters now reduce to the Urell number and the peak frequency. Even though the resulting spectral models place special emphasis on the energy-containing range of the spectrum, they are not limited to this range and they are not limited to any particular sea state. They are seen as offering a possible explanation of the variations in the special slope observed by previous investigators.

Huang, N. E.↗

NASA NTRS1985

Static internal performance of a single-engine onaxisymmetric-nozzle vaned-thrust-reverser design with thrust modulation capabilities

An investigation has been conducted at wind-off conditions in the stati-test facility of the Langley 16-Foot Transonic Tunnel. The tests were conducted on a single-engine reverser configuration with partial and full reverse-thrust modulation capabilities. The reverser design had four ports with equal areas. These ports were angled outboard 30 deg from the vertical impart of a splay angle to the reverse exhaust flow. This splaying of reverser flow was intended to prevent impingement of exhaust flow on empennage surfaces and to help avoid inlet reingestion of exhaust gas when the reverser is integrated into an actual airplane configuration. External vane boxes were located directly over each of the four ports to provide variation of reverser efflux angle from 140 deg to 26 deg (measured forward from the horizontal reference axis). The reverser model was tested with both a butterfly-type inner door and an internal slider door to provide area control for each individual port. In addition, main nozzle throat area and vector angle were varied to examine various methods of modulating thrust levels. Other model variables included vane box configuration (four or six vanes per box), orientation of external vane boxes with respect to internal port walls (splay angle shims), and vane box sideplates. Nozzle pressure ratio was varied from 2.0 approximately 7.0.

Leavitt, L. D.↗

NASA NTRS1950

Stall Characteristics Obtained from Flight 10 of Northrop X-4 No. 2 Airplane (USAF No. 46-677)

NACA instrumentation has been installed ii the X-J4 airplanes to obtain stability and control data during the acceptance tests conducted by the Northrop Aircraft Corporation. This report presents data obtained on the stalling characteristics of the airplane in the clean and gear- down configurations. The center of gravity was located at approximately 18 percent of the mean aerodynamic chord during the tests. The results indicated that the airplane was not completely stalled when stall was gradually approached during nominally U accelerated flight but that it was completely stalled during a more abruptly approached stall in accelerated flight. The stall in accelerated flight was relatively mild, and this was attributed to the nature of the variation of lift with angle of attack for the 001-614 airfoil section, the plan form of the wing, and to the fact that the initial sideslip at the stall produced (as shown by wind-tunnel tests of a model of the airplane) a more symmetrical stall pattern.

Sadoff, Melvin↗

NASA NTRS2004

Induction and quantification of gammma-H2AX foci following cx- and gamma-irradiaton

Following DNA damage the histone H2AX becomes phosphorylated and can be visualised by immunofluorescence as an indicator of DSBs in individual cells. Using a wild type hamster cell line (V79-4) exposed to either a-particles or to Co-60 gamma-rays to induce DNA DSBs at different doses (20-200OmGy), the dose dependent induction of gamma-H2AX foci were scored both manually (by eye) and using image analysis. A linearly dependence on dose was found for both radiations. The number of DSBs determined by image analysis after a post-irradiation period of 30 minutes at 37 C, is 16.6 foci/cell/Gy for alpha-irradiation and 12.2 foci/cell/Gy for gamma-irradiation; the latter being 3-4 times the levels observed by eye and comparable to gamma-radiation-induced levels of prompt DSBs more recently reported using pulse field gel electrophoresis (approx. 16 DSBs/Gy). The average size of the gamma-H2AX foci induced by alpha-irradiation (0.30 square micrometers) is approximately 1.5 times larger than those induced by gamma-irradiation (0.19 square micrometers). The timescale of induction and removal of DSBs up to 24 hours post-irradiation, was investigated with gamma-H2AX foci levels found to remain significantly higher than controls for 4 or 6 hours in gamma-irradiated samples or alpha irradiated samples, respectively. These results demonstrate that not only gamma radiation but also alpha-radiation induce phosphorylation of the H2AX histone in response to DSBs even at low doses (20mGy for gamma-rays, 1 track/cell on average for alpha-particles) and the variation in size and dephosphorylation of the induced foci is dependent on radiation quality (LET).

Leatherbarrow, E. L.↗

NASA NTRS1993

The Fe/Mn constraint on precursors of basaltic achondrites

Most achondritic meteorites have Fe/Mn ratios that are lower than those of carbonaceous chondrites and of course are lower than the solar system abundance ratio of these elements. Models of the origin of achondritic assemblages must, therefore, account for these ratios. Fe/Mn ratios are suggested to be distinctive for samples from each achondrite parent body and for the Earth and Moon, but the correspondence between the Fe/Mn systematics of achondrites and chondritic precursors is unclear. Most models of achondrite genesis involve magmatic differentiation of chondritic precursors. The Fe/Mn difference between achondrites and chondrites is particularly significant since Fe and Mn are geochemically similar elements with similar partitioning behavior in familiar magmatic systems and are generally coupled during crystal-liquid fractionation. In contrast, however, Mn is more volatile than Fe in a nebular setting. Variation of Fe/Mn ratios based on the relative volatility of these elements in the early nebula provides a constraint for models by which the basaltic achondrites (with Fe/Mn ratios approximately = 25-50) are derived from mixtures of nebular components that were enriched in volatile components such as Mn. However, such volatile enriched components have not been identified in chondrites. When the abundance in achondrites of elements of similar volatility is examined, anomalies appear. For example, Na is massively depleted in basaltic achondrites when compared to Mn. These anomalies might be explained using current models but the alternative hypothesis, that Fe/Mn ratio is controlled not by nebular volatility constraints, but by planetary differentiation should be explored.

Delaney, Jeremy S.↗