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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 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Quantitative investigation of compressible mixing: Staged transverse injection into Mach 2 flow

Planar measurements of the injectant mole fraction distribution and the velocity field within a supersonic mixing flowfield have been made using laser-induced iodine fluorescence. The flowfield investigated in this work is staged transverse injection of air into a Mach 2 freestream. A complete three-dimensional survey of the injectant mole fraction distribution has been generated, and a single planar velocity measurement has been completed. The measurements reveal the dramatic effect of streamwise vortices on the mixing in the near field of the injectors, as well as the rapid mixing generated by staging two fuel injectors. Analysis of the downstream decay of the maximum injectant mole fraction in this and other supersonic mixing flowfields indicates that the relative rate of injectant mixing well downstream of the injectors is independent of injection geometry, freestream Mach number, and injectant molecular weight. Mixing within this region of the flowfield is dominated by small-scale turbulence within the injectant plume. The transition of the dominant mixing mechanism, from vortex-driven mixing in the near field to small-scale turbulent mixing in the far field, was found to occur in the region about 10 diameters downstream of the injectors.

Hollo, Steven D.↗
NASA NTRS2009

A Future State for NASA Laboratories - Working in the 21st Century

The name "21 st Century Laboratory" is an emerging concept of how NASA (and the world) will conduct research in the very near future. Our approach is to carefully plan for significant technological changes in products, organization, and society. The NASA mission can be the beneficiary of these changes, provided the Agency prepares for the role of 21st Century laboratories in research and technology development and its deployment in this new age. It has been clear for some time now that the technology revolutions, technology "mega-trends" that we are in the midst of now, all have a common element centered around advanced computational modeling of small scale physics. Whether it is nano technology, bio technology or advanced computational technology, all of these megatrends are converging on science at the very small scale where it is profoundly important to consider the quantum effects at play with physics at that scale. Whether it is the bio-technology creation of "nanites" designed to mimic our immune system or the creation of nanoscale infotechnology devices, allowing an order of magnitude increase in computational capability, all involve quantum physics that serves as the heart of these revolutionary changes.

Kegelman, Jerome T.↗
NASA NTRS1994

Mixing processes within the polar night jet

Lagrangian material line simulations are performed using U.K. Meteorological Office simulated winds and temperatures to examine mixing processes in the middle- and lower-stratospheric polar night jet during the 1992 Southern Hemisphere spring and Northern Hemisphere winter. The Lagrangian simulations are undertaken to provide insight into the effects of mixing within the polar night jet on observations of the polar vortex made by instruments onboard the Upper Atmosphere Research Satellite (UARS) during these periods. A moderate to strong kinematic barrier to large-scale isentropic exchange, similar to the barrier identified in General Circulation Model (GCM) simulations, is identified during both of these periods. Characteristic timescales for mixing by large-scale isentropic motions within the polar night jet range from 20 days in the Southern Hemisphere lower stratosphere to years in the Northern Hemisphere middle stratosphere. The long mixing timescales found in the Northern Hemisphere polar night jet do not persist. Instead, the Northern Hemisphere kinematic barriers are broken down as part of the large-scale stratospheric response to a strong tropospheric blocking event. A series of Lagrangian experiments are conducted to investigate the sensitivity of the kinematic barrier to diabatic effects and to small-scale inertial gravity wave motions. Differential diabatic descent is found to have a significant impact on mixing processes within the Southern Hemisphere middle-stratospheric jet core. The interaction between small-scale displacements by idealized, inertial gravity waves and the large-scale flow is found to have a significant impact on mixing within the polar night jet in both hemispheres. These sensitivity experiments suggest that scales of motion that are unresolved in global assimilated datasets may contribute to mass exchange across the kinematic barrier to large-scale isentropic motion.

Pierce, R. Bradley↗
NASA NTRS1982

Infrared observations of the Saturnian system from Voyager 2

During the passage of Voyager 2 through the Saturn system, infrared spectral and radiometric data were obtained for Saturn, Titan, Enceladus, Tethys, Iapetus, and the rings. Combined Voyager 1 and Voyager 2 observations of temperatures in the upper troposphere of Saturn indicate a seasonal asymmetry between the northern and southern hemispheres, with superposed small-scale meridional gradients. Comparison of high spatial resolution data from the two hemispheres poleward of 60 deg latitude suggests an approximate symmetry in the small-scale structure, consistent with the extension of a symmetric system of zonal jets into the polar regions. Longitudinal variations of 1 to 2 K are observed. Disk-averaged infrared spectra of Titan show little change over the 9-month interval between Voyager encounters. By combining Voyager 2 temperature measurements with ground-based geometric albedo determinations, phase integrals of 0.91 plus or minus 0.13 and 0.89 plus or minus 0.09 were derived for Tethys and Enceladus, respectively. The subsolar point temperature of dark material on Iapetus must exceed 110 K. Temperatures (and infrared optical depths) for the A and C rings and for the Cassini division are 69 plus or minus 1 K (0.40 plus or minus 0.05), 85 plus or minus 1 K (0.10 plus or minus 0.03), and 85 plus or minus 2 K (0.07 plus or minus 0.04), respectively.

Hanel, R.↗
NASA NTRS2008

Radiation from Relativistic Jets

Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., gamma-ray bursts (GRBs), active galactic nuclei (AGNs), and Galactic microquasar systems usually have power-law emission spectra. Recent PIC simulations of relativistic electron-ion (electron-positron) jets injected into a stationary medium show that particle acceleration occurs within the downstream jet. In the presence of relativistic jets, instabilities such as the Buneman instability, other two-streaming instability, and the Weibel (filamentation) instability create collisionless shocks, which are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The 'jitter' radiation from deflected electrons in small-scale magnetic fields has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation, a case of diffusive synchrotron radiation, may be important to understand the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.

Nishikawa, K.-I.↗
NASA NTRS2005

Biology-Inspired Distributed Consensus in Massively-Deployed Sensor Networks

Promises of ubiquitous control of the physical environment by large-scale wireless sensor networks open avenues for new applications that are expected to redefine the way we live and work. Most of recent research has concentrated on developing techniques for performing relatively simple tasks in small-scale sensor networks assuming some form of centralized control. The main contribution of this work is to propose a new way of looking at large-scale sensor networks, motivated by lessons learned from the way biological ecosystems are organized. Indeed, we believe that techniques used in small-scale sensor networks are not likely to scale to large networks; that such large-scale networks must be viewed as an ecosystem in which the sensors/effectors are organisms whose autonomous actions, based on local information, combine in a communal way to produce global results. As an example of a useful function, we demonstrate that fully distributed consensus can be attained in a scalable fashion in massively deployed sensor networks where individual motes operate based on local information, making local decisions that are aggregated across the network to achieve globally-meaningful effects.

Jones, Kennie H.↗
NASA NTRS2012

Global Scale Attribution of Anthropogenic and Natural Dust Sources and their Emission Rates Based on MODIS Deep Blue Aerosol Products

Our understanding of the global dust cycle is limited by a dearth of information about dust sources, especially small-scale features which could account for a large fraction of global emissions. Here we present a global-scale high-resolution (0.1 deg) mapping of sources based on Moderate Resolution Imaging Spectroradiometer (MODIS) Deep Blue estimates of dust optical depth in conjunction with other data sets including land use. We ascribe dust sources to natural and anthropogenic (primarily agricultural) origins, calculate their respective contributions to emissions, and extensively compare these products against literature. Natural dust sources globally account for 75% of emissions; anthropogenic sources account for 25%. North Africa accounts for 55% of global dust emissions with only 8% being anthropogenic, mostly from the Sahel. Elsewhere, anthropogenic dust emissions can be much higher (75% in Australia). Hydrologic dust sources (e.g., ephemeral water bodies) account for 31% worldwide; 15% of them are natural while 85% are anthropogenic. Globally, 20% of emissions are from vegetated surfaces, primarily desert shrublands and agricultural lands. Since anthropogenic dust sources are associated with land use and ephemeral water bodies, both in turn linked to the hydrological cycle, their emissions are affected by climate variability. Such changes in dust emissions can impact climate, air quality, and human health. Improved dust emission estimates will require a better mapping of threshold wind velocities, vegetation dynamics, and surface conditions (soil moisture and land use) especially in the sensitive regions identified here, as well as improved ability to address small-scale convective processes producing dust via cold pool (haboob) events frequent in monsoon regimes.

aerosols↗
NASA NTRS1992

Global deformation on the surface of Venus

Large-scale mapping of tectonic structures on Venus shows that there is an organized global distribution to deformation. The structures we emphasize are linear compressive mountain belts, extensional rafted zones, and the small-scale but widely distributed wrinkle ridges. Ninety percent of the area of the planet's compressive mountain belts are concentrated in the northern hemisphere whereas the southern hemisphere is dominated by extension and small-scale compression. We propose that this striking concentration of fold belts in the northern hemisphere, along with the globe-encircling equatorial rift system, represents a global organization to deformation on Venus.

Bilotti, Frank↗
NASA NTRS1995

Description of and preliminary tests results for the Joint Damping Experiment (JDX)

An effort is currently underway to develop an experiment titled joint Damping E_periment (JDX) to fly on the Space Shuttle as Get Away Special Payload G-726. This project is funded by NASA's IN-Space Technology Experiments Program and is scheduled to fly in July 1995 on STS-69. JDX will measure the influence of gravity on the structural damping of a three bay truss having clearance fit pinned joints. Structural damping is an important parameter in the dynamics of space structures. Future space structures will require more precise knowledge of structural damping than is currently available. The mission objectives are to develop a small-scale shuttle flight experiment that allows researchers to: (1) characterize the influence of gravity and joint gaps on structural damping and dynamic behavior of a small-scale truss model, and (2) evaluate the applicability of low-g aircraft test results for predicting on-orbit behavior. Completing the above objectives will allow a better understanding and/or prediction of structural damping occurring in a pin jointed truss. Predicting damping in joints is quite difficult. One of the important variables influencing joint damping is gravity. Previous work has shown that gravity loads can influence damping in a pin jointed truss structure. Flying this experiment as a GAS payload will allow testing in a microgravity environment. The on-orbit data (in micro-gravity) will be compared with ground test results. These data will be used to help develop improved models to predict damping due to pinned joints. Ground and low-g aircraft testing of this experiment has been completed. This paper describes the experiment and presents results of both ground and low-g aircraft tests which demonstrate that damping of the truss is dramatically influenced by gravity.

Bingham, Jeffrey G.↗
NASA NTRS1973

Theoretical studies of tone noise from a fan rotor

An analytical study was made of some possible rotor alone noise sources of dipole, quadrapole and monopole characters which generate discrete tone noise. Particular emphasis is given to the tone noise caused by fan inlet flow distortion and turbulence. Analytical models are developed to allow prediction of absolute levels. Experimental data measured on a small scale fan is presented which indicates inlet turbulence interaction with a fan rotor can be a source of tone noise. Predicted and measured tone noise for the small scale rotor are shown to be in reasonable agreement.

Rao, G. V. R.↗
NASA NTRS1977

Triaxial digital fluxgate magnetometer for NASA applications explorer mission: Results of tests of critical elements

Tests performed to prove the critical elements of the triaxial digital fluxgate magnetometer design were described. A method for improving the linearity of the analog to digital converter portion of the instrument was studied in detail. A sawtooth waveform was added to the signal being measured before the A/D conversion, and averaging the digital readings over one cycle of the sawtooth. It was intended to reduce bit error nonlinearities present in the A/D converter which could be expected to be as much as 16 gamma if not reduced. No such nonlinearities were detected in the output of the instrument which included the feature designed to reduce these nonlinearities. However, a small scale nonlinearity of plus or minus 2 gamma with a 64 gamma repetition rate was observed in the unit tested. A design improvement intended to eliminate this small scale nonlinearity was examined.

Mcleod, M. G.↗
NASA NTRS2019

CMB-HD: An Ultra-Deep, High-Resolution Millimeter-Wave Survey Over Half the Sky

A millimeter-wave survey over half the sky, that spans frequencies in the range of 30 to 350 GHz, and that is both an order of magnitude deeper and of higher-resolution than currently funded surveys would yield an enormous gain in understanding of both fundamental physics and astrophysics. By providing such a deep, high-resolution millimeter-wave survey (about 0.5 Karcmin noise and 15 arcsecond resolution at 150 GHz), CMB-HD will enable major advances.It will allow 1.) the use of gravitational lensing of the primordial microwave background to map the distribution of matter on small scales (k 10 hMpc1), which probes dark matter particle properties. It will also allow 2.) measurements of the thermal and kinetic Sunyaev-Zel'dovich effects on small scales to map the gas density and gas pressure profiles of halos over a wide field,which probes galaxy evolution and cluster astrophysics. In addition, CMB-HD would allow us to cross critical thresholds in fundamental physics: 3.) ruling out or detecting any new, light (< 0:1 eV), thermal particles, which could potentially be the dark matter, and 4.) testing a wide class of multi-field models that could explain an epoch of inflation in the early Universe. Such a survey would also 5.) monitor the transient sky by mapping the full observing region every few days,which opens a new window on gamma-ray bursts, novae, fast radio bursts, and variable active galactic nuclei. Moreover, CMB-HD would 6.) provide a census of planets, dwarf planets, andasteroids in the outer Solar System, and 7.) enable the detection of exo-Oort clouds around othersolar systems, shedding light on planet formation. The combination of CMB-HD with contemporaryground and space-based experiments will also provide powerful synergies. CMB-HD willdeliver this survey in 5 years of observing 20,000 square degrees, using two new 30-meter-classoff-axis cross-Dragone telescopes to be located at Cerro Toco in the Atacama Desert. The telescopeswill field about 2.4 million detectors (600,000 pixels) in total. The CMB-HD survey willbe made publicly available, with usability and accessibility a priority.

Sehgal, Neelima↗
NASA NTRS1990

A new twist to the solar cycle

Recent numerical simulations of magnetic buoyancy instabilities suggest a new mechanism for the variation with the solar cycle in the scale and structure of surface magnetic flux. The nonlinear evolution of a predominantly toroidal field is found to depend crucially on the distribution of the weaker poloidal ingredient. For certain field configurations large, helical magnetic fragments are produced; for others the escaping field is small-scale and untwisted. We propose that the observed structural variations in flux may be accounted for by small changes in the twist of a deep-seated field. The large fragments will appear at the surface as active regions, which dominate at solar maximum, while the small-scale field will emerge as ephemeral regions which constitute practically all of the flux at solar minimum.

Cattaneo, Fausto↗
NASA NTRS2010

The Evolution of the Spectrum of Velocity Fluctuations in the Solar Wind

Recent work has shown that at 1AU from the Sun the power spectrum of the solar wind magnetic field has the -5/3 spectral slope expected for Kolmogorov turbulence, but that the velocity has closer to a -3/2 spectrum. This paper traces the changes in solar wind velocity spectra from 0.3 to 5 AU using data from the Helios and Ulysses spacecraft to show that this is a transient stage in the evolution. The spectrum of the velocity is found to be flatter than that of the magnetic field for the higher frequencies examined for all cases until the slopes become equal (at -5/3) well past 1 AU when the wind is relatively nonAlfvenic. In some respects, in particular in the evolution of the frequency at which the spectrum changes from flatter at larger scales to a traditionally turbulent spectrum at smaller scales, the velocity field evolves more rapidly that the magnetic, and this is associated with the dominance of the magnetic energy over the kinetic at "inertial range" scales. The Alfvenicity of the fluctuations, not the speed of the flow, is shown to control the rate of the spectral evolution. This study shows that, for the solar wind ., the idea of a simple "inertial range" with uniform spectral properties is not realistic, and new phenomenologies will be needed to capture the true situation. In addition a flattening of the velocity spectrum persists at times for small scales, which may provide a clue to the nature of the small-scale interactions.

Roberts, D. Aaron↗
NASA NTRS2019

Magnetic Flux Cancelation as the Buildup and Trigger Mechanism for CME-Producing Eruptions in Two Small Active Regions

We follow two small, magnetically isolated CME (Coronal Mass Ejection)-producing solar active regions (ARs) from the time of their emergence until several days later, when their core regions erupt to produce the CMEs. In both cases, magnetograms show: (a) following an initial period where the poles of the emerging regions separate from each other, the poles then reverse direction and start to retract inward; (b) during the retraction period, flux cancelation occurs along the main neutral line of the regions, (c) this cancelation builds the sheared core field/flux rope that eventually erupts to make the CME. In the two cases, respectively 30 percent and 50 percent of the maximum flux of the region cancels prior to the eruption. Recent studies indicate that solar coronal jets frequently result from small-scale filaments eruptions (Sterling et al. 2015), with those “minifilament” eruptions also being built up and triggered by cancelation of magnetic flux (Panesar et al. 2016). Together, the small-AR eruptions here and the coronal jet results suggest that isolated bipolar regions tend to erupt when some threshold fraction, perhaps in the range of 50 percent, of the region’s maximum flux has canceled. Our observed erupting filaments/flux ropes form at sites of flux cancelation, in agreement with previous observations. Thus, the recent finding that minifilaments that erupt to form jets also form via flux cancelation is further evidence that minifilaments are small-scale versions of the long-studied full-sized filaments. (Details are in Sterling et al. 2018, ApJ, 864, 68.) Supported by NASA's Heliophysics Guest Investigators (HGI) Program and the MSFC (Marshall Space Flight Center)/Hinode project.

Sterling, Alphonse C.↗
NASA NTRS1977

Mars surface properties observed by earth-based radar at 70-, 12.5-, and 3.8-cm wavelengths

In the present paper, the results are summarized of a study aimed at determining the small-scale surface properties of Mars (for the Viking project) from a thorough review of all available Martian radar data for the 1973 opposition. Analysis of the quasi-specular echo component showed changes in apparent reflectivity of at least 5 to 1. If attributed entirely to variations in surface material, these correspond to dielectric constants between 1.6 and 4.0. Values of rms surface slope on 1- to 100-m scales range from as low as 0.5 degrees in tablelands near Valles Marineris to more than 3.0 degrees in certain other areas. There is a weak correlation between the small-scale surface characteristics inferred from radar and those inferred from Mariner 9 images and other remote-sensing data sets.

Simpson, R. A.↗
NASA NTRS1979

Gravitational field models for study of Earth mantle dynamics

The tectonic forces or stresses due to the small scale mantle flow under the South American plate are detected and determined by utilizing the harmonics of the geopotential field model. The high degree harmonics are assumed to describe the small scale mantle convection patterns. The input data used in the derivation of this model is made up of 840,000 optical, electronic, and laser observations and 1,656 5 deg x 5 deg mean free air anomalies. Although there remain some statistically questionable aspects of the high degree harmonics, it seems appropriate now to explore their implications for the tectonic forces or stress field under the crust.

Source record↗
NASA NTRS1987

Northwest Airlines flight experiments

An experiment was conducted in which real-time Total Ozone Mapping Spectrometer (TOMS) data was compared with Northwest Airlines upper air charts. It was demonstrated that the regions of steep gradient in total ozone corresponded with fronts in the upper troposphere, specifically breaks in the tropopause associated with jet streams. Other small scale structures in the ozone could be related to minor trough and ridge lines. This suggests that the relation between total ozone and tropopause height might apply even on relatively small scales, and an analysis produced high correlation coefficients provided that the air mass origin was considered. In a second test, cabin ozone mixing at 37,000 ft. varied from less than 100 ppb (300 DU total ozone) to greater than 300 ppb in a trough (400 DU total ozone). A third analysis showed that clear air turbulence was located where upper air fronts were in rapid motion as suggested by comparison of the 1200 UT synoptic charts and the ozone map taken about six hours later.

Krueger, Arlin J.↗