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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Multilayered microstructures with shape memory effects for vertical deployment

This paper presents a fabrication and characterization of multilayered microstructures with shape memory effects enabling large vertical deployment under electro-thermal actuation. Our previous research demonstrated vertical deployment of such microstructures by the effect of thermal mismatch. Development of equiatomic NiTi layers in the multilayered microstructure is investigated further for shape memory effects. Multilayered microstructures are built by sputtered NiTi layers and a lift-off process. Negative photoresist ma-N1420 enables clean lift-off of 500 nm thick NiTi layers by forming a significant undercut profile after development. The parametric study on co-sputter powers for Ti and Ni 50 Ti 50 targets suggests that 100 W RF on Ti target and 200 W DC on Ni 50 Ti 50 target can deposit Ni 49.62 Ti 50.38 layers. X-Ray Diffraction (XRD) and Atomic Force Microscopy (AFM) were used to study the crystal structures and surface topography of NiTi layers. XRD results of post-annealed Ni 49.62 Ti 50.38 layers show coexistence of austenite and martensitic phases at room temperature, suggesting that the transformation temperature of such NiTi layers should be approximate 20 °C. The surface topography of Ni 49.62 Ti 50.38 layers reveals substantial increase of surface roughness at ambient conditions after the annealing. Experimental verification of the multilayered microstructure for vertical deployment was carried out by Signatone Probe Station and Dual Scanning Electron Microscope/Focused Ion Beam (SEM/FIB) system. Finally, a vertical deployment of the two-dimensional (2D) multilayered microstructures for three-dimensional (3D) can be detected by applying a constant voltage of 0.04 V, and the expected 3D deployment displacement is enlarged from 2 μm to 10 μm by introducing the shape memory effect.

42 ENGINEERING↗
NASA NTRS1978

The occultation of Epsilon Gem by Mars as observed from Agassiz Station

Observations of the April 8, 1976, occultation of Epsilon Gem by Mars made at the Agassiz Station of the Harvard College Observatory have been analyzed to yield temperature profiles of the Martian atmosphere for number densities between 10 to the 13th and 10 to the 15th power per cu cm. Pronounced wavelike structure is evident in both immersion and emersion profiles, with a peak-to-peak variation of up to 50 K and a vertical scale of 20 km.

Liller, W.↗
NASA NTRS1985

The form of Newtonian cooling in atmospheric tidal theory

The analytical results of Zurek (1986) are applied to compare the vertical-structure equations obtained by Dickinson and Geller (1968) and Lindzen and McKenzie (1967) in solving the classical tidal equations for planetary atmospheres when Newtonian cooling (NC) is included as part of diabatic tidal forcing. The two diabatic forcings are found to be different when the basic state temperature varies with height, and it is recommended that a log-pressure NC formulation be used whenever temperature is made a function of pressure in the radiative-damping calculation. Scaling arguments are presented to show that the choice of NC formulation has significant effects only in cases where the radiative time constants are short (such as the thin CO2 atmosphere of Mars). Numerical computations for that case indicate a difference of 20 percent in amplitude and 15 deg in phase for the (probably meteorologically significant) 4.1-d wavenumber-one Rossby tidal mode.

Zurek, Richard W.↗
NASA NTRS1973

Atmospheric Aerosol and Thermal Structure in the Boundary Layer Over the Los Angeles Basin

A field study using a mobile lidar was recently conducted in the L. A. Basin, California, to (1) examine the relationship between the vertical aerosol and the thermal structure, and (2) map the vertical aerosol structure in the atmospheric boundary layer over the basin. These data are needed for use in the development of a mixing-depth submodel required for photochemical air Quality simulation models. Toward these ends, a series of lidar aerosol measurements in conjunction with balloon and aircraft temperature soundings were taken at a site in El Monte, and in a mobile mode along a 90-mile freeway loop between El Monte, Santa Monica, and Long Beach. The lidar data are presented in the form of time-height and distance-height cross sections. The results indicate that, although aerosol concentrations are frequently present above the base of the marine inversion, these are generally in stratified layers in contrast to the more uniform nature of the lower convective layer, permitting the mixing depth to be distinguished on this basis. The lidar-derived mixing depths are well correlated (within 100 m) with daytime temperature inversions. Other significant features shown by the lidar data include large Basin-wide mixing-depth variations, waves with amplitudes of 200-300 m and wavelengths of 1000-1500 m on the lower aerosol layer, and apparent aerosol "chimneys" with overrunning in the vicinity of convergence zones.

Johnson, Warren B.↗
DOE OSTI2025

Design of a High-Assay Low-Enriched Uranium Tri-Structural Isotropic Critical Experiment for Advanced Reactor Validation

High-assay low-enriched uranium (HALEU) fuel is a key component of many small modular reactor designs. Critical experiments are an important way to understand the neutronic performance of systems by obtaining nuclear data validations through measurements. Data reduce uncertainty and risk by showing that systems respond as predicted to changes such as temperature, subsequently advancing the overall technology readiness level of the materials within. Numerous critical experiments have been performed at the National Criticality Experiments Research Center (NCERC) operated by Los Alamos National Laboratory at the Nevada National Security Site since it became operational in 2011. However, the first experiment with HALEU fuel did not occur until 2024. Through extensive engineering, the experiment described in this paper was successfully designed and executed for the Comet vertical lift assembly at NCERC to perform measurements with HALEU tri-structural isotropic fuel that will assist in validation of nuclear data and computational modeling of small modular reactors for years to come.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Observation of a super-tetrahedral cluster of acetonitrile-solvated dodecaborate dianion via dihydrogen bonding

We launched a combined negative ion photoelectron spectroscopy and multiscale theoretical investigation on the geometric and electronic structures of a series of acetonitrile-solvated dodecaborate clusters, i.e., B 12 H 12 2- ·nCH 3 CN (n = 1–4). The electron binding energies of B 12 H 12 2- ·nCH 3 CN are observed to increase with cluster size, suggesting their enhanced electronic stability. B3LYP-D3(BJ)/ma-def2-TZVP geometry optimizations indicate each acetonitrile molecule binds to B 12 H 12 2- via a threefold dihydrogen bond (DHB) B3–H3 ⋮⋮⋮ H3C–CN unit, in which three adjacent nucleophilic H atoms in B 12 H 12 2- interact with the three methyl hydrogens of acetonitrile. The structural evolution from n = 1 to 4 can be rationalized by the surface charge redistributions through the restrained electrostatic potential analysis. Notably, a super-tetrahedral cluster of B 12 H 12 2- solvated by four acetonitrile molecules with 12 DHBs is observed. The post-Hartree–Fock domain-based local pair natural orbital- coupled cluster singles, doubles, and perturbative triples [DLPNO-CCSD(T)] calculated vertical detachment energies agree well with the experimental measurements, confirming the identified isomers as the most stable ones. Furthermore, the nature and strength of the intermolecular interactions between B 12 H 12 2- and CH 3 CN are revealed by the quantum theory of atoms-in-molecules and the energy decomposition analysis. Ab initio molecular dynamics simulations are conducted at various temperatures to reveal the great kinetic and thermodynamic stabilities of the selected B 12 H 12 2- ·CH 3 CN cluster. The binding motif in B 12 H 12 2- ·CH 3 CN is largely retained for the whole halogenated series B 12 X 12 2- ·CH 3 CN (X = F–I). This study provides a molecular-level understanding of structural evolution for acetonitrile-solvated dodecaborate clusters and a fresh view by examining acetonitrile as a real hydrogen bond (HB) donor to form strong HB interactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2013

Rain Characteristics and Large-Scale Environments of Precipitation Objects with Extreme Rain Volumes from TRMM Observations

This study adopts a "precipitation object" approach by using 14 years of Tropical Rainfall Measuring Mission (TRMM) Precipitation Feature (PF) and National Centers for Environmental Prediction (NCEP) reanalysis data to study rainfall structure and environmental factors associated with extreme heavy rain events. Characteristics of instantaneous extreme volumetric PFs are examined and compared to those of intermediate and small systems. It is found that instantaneous PFs exhibit a much wider scale range compared to the daily gridded precipitation accumulation range. The top 1% of the rainiest PFs contribute over 55% of total rainfall and have 2 orders of rain volume magnitude greater than those of the median PFs. We find a threshold near the top 10% beyond which the PFs grow exponentially into larger, deeper, and colder rain systems. NCEP reanalyses show that midlevel relative humidity and total precipitable water increase steadily with increasingly larger PFs, along with a rapid increase of 500 hPa upward vertical velocity beyond the top 10%. This provides the necessary moisture convergence to amplify and sustain the extreme events. The rapid increase in vertical motion is associated with the release of convective available potential energy (CAPE) in mature systems, as is evident in the increase in CAPE of PFs up to 10% and the subsequent dropoff. The study illustrates distinct stages in the development of an extreme rainfall event including: (1) a systematic buildup in large-scale temperature and moisture, (2) a rapid change in rain structure, (3) explosive growth of the PF size, and (4) a release of CAPE before the demise of the event.

TRMM↗
NASA NTRS1974

Measurement of atmospheric turbulence strength at high altitude with balloon-borne temperature sensors

A technique to measure a vertical profile of the optical strength of turbulence employs the measurement of a root mean square temperature difference between two microthermal probes carried aloft as part of a balloon payload. Microthermal fluctuations provide a measure for the density fluctuations of turbulence. Examination of recorded profiles of refractive-index structure coefficients reveals a turbulence structure which is organized into multiple, thin groupings of strong turbulence separated by relatively quiescent intervals of variable length.

Bufton, J. L.↗
NASA NTRS1976

Tropical waves and the quasi-biennial oscillation in the lower stratosphere

By means of spectrum analysis of 11 years of lower stratospheric daily winds and temperatures at Balboa, Ascension and Canton-Singapore, evidence is presented supporting the existence of two principal wave modes with periods of about 11-17 days (Kelvin waves) and about 4-5 days (mixed Rossby-gravity waves). The structure of the two wave modes, as well as the vertical eddy momentum flux by the waves, is shown to be related to the quasi-biennial cycle, although for the mixed Rossby-gravity waves this is obvious only at Ascension. In addition, the Coriolis term, suggested as a source of vertical easterly momentum flux for the mixed Rossby-gravity waves, is investigated and found to be of the same magnitude as the vertical eddy flux term. Finally, we have examined the mean meridional motion and the meridional eddy momentum flux for its possible association with the quasi- biennial variation.

Miller, A. J.↗
NASA NTRS1991

Hourly observations of the jet stream - Wind shear, Richardson number and pilot reports of turbulence

Results are presented of observations of the jet stream made on the basis of over 400 hr of wind and temperature data taken during two prolonged jet stream passages above western and central Pennsylvania during mid-November 1986 and mid-January 1987. Wind profilers are found to be far better suited for the detailed examination of jet stream structure than are weather balloons. The combination of good vertical resolution with not previously obtained temporal resolution reveals structural details not seen before. Development of probability forecasts of turbulence based on wind profiler-derived shear values appears possible. A good correlation between pilot reports and turbulence and wind shear is found.

Syrett, William J.↗
NASA NTRS1993

Coupled ice-ocean variability in the Greenland Sea

A major surface feature of the Greenland Sea during winter is the frequent eastward extension of sea ice south of 75 deg N and an associated embayment to the north. These features are nominally connected with the East Greenland Current, and both the promontory) and the embayment are readily apparent on climatic ice charts. However, there are significant changes in these features on time-scales as short as a few days. Using a combination of satellite microwave images (SSM/I) of ice cover, meteorological data and in situ velocity, temperature and salinity records, we relate the ice distribution and its changes to the developing structure and circulation of the upper ocean during winter 1988-1989. Our measurements illustrate the preconditioning that leads to convective overturn, which in turn brings warmer water to the surface and results in the rapid disappearance of ice. In particular, the surface was cooled to the freezing point by early December and the salinity then increased through ice formation (about 0.016 m/d) and brine rejection. Once the vertical density gradient was sufficiently eroded, a period of high heat flux (greater than 300 W/sq m) in late January provided enough buoyancy loss to convectively mix the upper water column to at least 200 m. We estimate vertical velocities at about 3 cm/s downward during the initial sinking. The deepening of the thermocline raised surface temperatures by over 1 C resulting in nearly 1.5 x 105 km of ice-melt within two days. Average rates of ice retreat are about 2 km/d southwestward, generally consistent with a wind-driven flow. Comparison of hydrographic surveys from before and after the overturning indicate the fresh water was advected out of the area, possibly to the south and east of our moorings.

Roach, A. T.↗
NASA NTRS1980

Vertical structure of the atmosphere of Venus from Pioneer Venus orbiter radio occultations

Between December 1978 and February 1979 the Pioneer Venus orbiter spacecraft returned some 140 S band and X band radio occultation measurements of the Venus atmosphere. Results from 13 measurements, covering diverse latitudes from near equatorial to polar, are presented in this paper in the form of vertical profiles of temperature. The temperature profiles show a pronounced inversion at the tropopause for latitudes higher than about 50 deg, with the deepest inversions occurring between the latitudes of 60 deg and 70 deg, the latitudes at which the cold collar cloud feature was observed by the Pioneer Venus Vortex instrument. A comparison of the temperature profiles derived from radio occultation measurements with the stratospheric infrared temperature soundings of the Vortex instrument and the in situ measurements of tropospheric temperature and pressure by the North, Sounder, and Day probes indicates excellent agreement.

Kliore, A. J.↗
DOE OSTI2020

Summertime Post-Cold-Frontal Marine Stratocumulus Transition Processes over the Eastern North Atlantic

Abstract Marine boundary layer (MBL) cloud morphology associated with two summertime cold fronts over the eastern North Atlantic (ENA) is investigated using high-resolution simulations from the Weather Research and Forecasting (WRF) Model and observations from the Atmospheric Radiation Measurement (ARM) ENA Climate Research Facility. Lagrangian trajectories are used to study the evolution of post-cold-frontal MBL clouds from solid stratocumulus to broken cumulus. Clouds within specified domains in the vicinity of transitions are classified according to their degree of decoupling, and cloud-base and cloud-top breakup processes are evaluated. The Lagrangian derivative of the surface latent heat flux is found to be strongly correlated with that of the cloud fraction at cloud base in the simulations. Cloud-top entrainment instability (CTEI) is shown to operate only in the decoupled MBL. A new indicator of inversion strength at cloud top that employs the vertical gradients of equivalent potential temperature and saturation equivalent potential temperature, which can be computed directly from soundings, is proposed as an alternative to CTEI. Overall, results suggest that the deepening–warming hypothesis suggested by Bretherton and Wyant explains many of the characteristics of the summertime postfrontal MBL evolution of cloud structure over the ENA, thereby widening the phase space over which the hypothesis may be applied. A subset of the deepening–warming hypothesis involving warming initially dominating over moistening is proposed. It is postulated that changes in climate change–induced modifications in cold-frontal structure over the ENA may be accompanied by coincident changes in the location and timing of MBL cloud transitions in the post-cold-frontal environment.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1990

Theoretical and experimental studies of baroclinic processes

The geophysical fluid flow simulation code, GEOSIM, is being used to study the phenomenon of vacillation in the baroclinic annulus. Having verified that the code predicts vacillation for the same points as the experiments, the work is aiming toward explaining the mechanics of vacillation and pointing out some of the sensitivities of the results to the numerical method. Researchers are finding that there is a structural change associated with amplitude vacillation, where the structural changes are in the vertical. The results disagree with the premise of Lindzen et al, that the vacillation is due to constructive and destructive interference of neutral modes with different phase speeds. The researchers are continuing to study the Spacelab 3 Geophysical Fluid Flow Cell (GFFC) results with horizontal temperature gradients and heating from below. GEOSIM has been used to compute a wide range of cases, and these are being compared with the observations. The computations and observations compare well, and the model is being used to extend the results beyond cases studied in the experiments and to study the mechanics and predictability of the flows. The study of fully nonlinear baroclinic instability using the GFFC apparatus is proceeding with the numerical code. While the first instability that occurs is of planetary scale, secondary instabilities consisting of small-scale, penetrative convection occurs where cold fluid flows over a warm surface. The simultaneous modeling of the planetary scale and the convective scale is possible because of the nonhydrostatic formulation of the model. Some of these results have been animated on the Stardent computer, which shows the explosive nature of the small-scale convection.

Miller, Tim↗
NASA NTRS1992

The abundance and distribution of water vapor in the Jovian troposphere as inferred from Voyager IRIS observations

The Voyager IRIS spectra of the Jovian North Equatorial Belt (NEB) hot spots are reanalyzed using a radiative transfer model which includes the full effects of anisotropic multiple scattering by clouds. The atmospheric model includes the three thermochemically predicted cloud layers, NH3, NH4SH, and H2O. Spectrally dependent cloud extinction is modeled using Mie theory and the refractive indices of NH3 ice, NH4SH ice, water, and H2O ice. The upper tropospheric temperature profile, gas abundances, height-dependent parahydrogen profile, and vertical distribution of NH3 cloud opacity are retrieved from an analysis of the far-infrared (180-1200/cm) IRIS observations. With these properties constrained, the 5-micron (1800-2300/cm) observations are analyzed to determine the atmospheric and cloud structure of the deeper atmosphere (P of greater than 1.5 bars). The results show that the abundance of water is at least 1.5 times solar with 2 times solar (0.00276 mixing ratio relative to H2) providing the best-fit to the Voyager IRIS hot spot observations.

Carlson, Barbara E.↗
NASA NTRS1974

Jovian atmosphere - Structure and composition between the turbopause and the mesopause

The occultation of the star Beta Scorpii by Jupiter was observed at high time resolution in three wavelength channels. The results imply a temperature of 220 K at an altitude in the Jovian atmosphere corresponding to 100 trillion molecules per cubic centimeter, and temperature fluctuations of 2 to 10 K over vertical scales of 2 to 10 kilometers. They suggest that the vertical eddy diffusion coefficient near the turbopause has a lower limit of 700,000 square centimeters per second, and that the turbopause lies above the altitude where the density is 50 trillion molecules per cubic centimeter. Below the turbopause, the ratio of hydrogen to helium is consistent with cosmic abundances.

Sagan, C.↗
NASA NTRS1978

Possible effects of solar UV variations on ozone and climate

A one-dimensional photochemical model was used to estimate the consequences of 27-day, 11-year, 22-year, and several-hundred-year variations of ultraviolet solar radiation on the concentration of ozone and nitrogen dioxide, and a one-dimensional radiative-convective equilibrium model was used to assess the joint effect of the radiation and concentration variations on the global temperature structure. For the several-hundred-year variations, the ozone column density increases by about 17.5% from minimum to maximum solar UV flux. For the 11-year period the ozone column density fluctuates by only about 7%, the lack of a full response being due to the time required for vertical motions to redistribute ozone from the altitudes of maximum production to those of maximum steady-state value. The 22-year period shows a full response, which the density varies by less than a percent for the 27-day period. Climatic consequences of these results are briefly discussed.

Pollack, J. B.↗
NASA NTRS2002

Investigations of Control Surface Seals for Re-entry Vehicles

Re-entry vehicles generally require control surfaces (e.g., rudders, body flaps) to steer them during flight. Control surface seals are installed along hinge lines and where control surface edges move close to the vehicle body. These seals must operate at high temperatures and limit heat transfer to underlying structures to prevent them from overheating and causing possible loss of vehicle structural integrity. This paper presents results for thermal analyses and mechanical testing conducted on the baseline rudder/fin seal design for the X-38 re-entry vehicle. Exposure of the seals in a compressed state at the predicted peak seal temperature of 1900 F resulted in loss of seal resiliency. The vertical Inconel rudder/fin rub surface was re-designed to account for this loss of resiliency. Room temperature compression tests revealed that seal unit loads and contact pressures were below limits set to protect Shuttle thermal tiles on the horizontal sealing surface. The seals survived an ambient temperature 1000 cycle scrub test over sanded Shuttle tiles and were able to disengage and re-engage the tile edges during testing. Arc jet tests confirmed the need for seals in the rudder/fin gap location because a single seal caused a large temperature drop (delta T = 1710 F) in the gap.

Dunlap, Patrick H., Jr.↗