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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

Geology of the Terra Cimmeria-Utopia Planitia Highland Lowland Transitional Zone: Final Technical Approach and Scientific Results

The southern Utopia highland-lowland transitional zone extends from northern Terra Cimmeria to southern Utopia Planitia and contains broad, bench-like platforms with depressions, pitted cones, tholi, and lobate flows. The locally occurring geologic units and landforms contrast other transitional regions and record a spatially partitioned geologic history. We systematically delineated and described the geologic units and landforms of the southern Utopia-Cimmeria highland-lowland transitional zone for the production of a 1:1,000,000-scale geologic map (MTMs 10237, 15237, 20237, 10242, 15242, 20242, 10247, 15247, and 20247). Herein, we present technical and scientific results of this mapping project.

Skinner, J. A., Jr.↗
NASA NTRS1976

Doppler wavelength shifts of transition zone lines measured in Skylab solar spectra

Wavelengths of lines of the transition-zone ions Si IV, C IV, O IV, N V, and O V are observed to be redshifted relative to the wavelengths of chromospheric lines in XUV spectra obtained from the normal-incidence spectrograph on Skylab. The spectra cover the wavelength range from 1200 to 1565 A and were obtained with the slit positioned over chromospheric network and cell regions, on coronal holes, and above the limb. The network-area and coronal-hole spectra were obtained near the disk center. Only some of the spectra show redshifted transition-zone lines. The observed shifts are between 0.03 and 0.08 A, implying velocities of 15 km/s or less. The amount of wavelength shift does not always appear to be the same for lines of different ions. The shifts imply that descending plasma in the solar atmosphere produces more emission than ascending plasma at temperatures between approximately 70,000 and 200,000 K.

Doschek, G. A.↗
NASA NTRS1991

A review of the regional geophysics of the Arizona Transition Zone

A review of existing geophysical information and new data presented in this special section indicate that major changes in crustal properties between the Basin and Range and Colorado Plateau occur in, or directly adjacent to, the region defined as the Arizona Transition Zone. Although this region was designated on a physiographic basis, studies indicate that it is also the geophysical transition between adjoining provinces. The Transition Zone displays anomalous crustal and upper mantle seismic properties, shallow Curie isotherms, high heat flow, and steep down-to-the-plateau Bouguer gravity gradients. Seismic and gravity studies suggest that the change in crustal thickness, from thin crust in the Basin and Range to thick crust in the Colorado Plateau, may occur as a series of steps rather than a planar surface. Anomalous P wave velocities, high heat flow, shallow Curie isotherms, and results of gravity modeling suggest that the upper mantle is heterogeneous in this region. A relatively shallow asthenosphere beneath the Basin and Range and Transition Zone contrasted with a thick lithosphere beneath the Colorado Plateau would be one explanation that would satisfy these geophysical observations.

Hendricks, J. D.↗
NASA NTRS1976

Spectroscopic far ultraviolet observations of transition zone instabilities and their possible role in a pre-flare energy build-up

Highly flare-productive newly emerging active regions are characterized by numerous small low-lying loops which frequently show a chaotic pattern. Flare activity in such a region subsides as the chaotic loop structures relax and expand into a bipolar configuration. The transition zone in such an active region is highly unstable, as shown by broadened and shifted nonthermal line profiles of medium-ionized elements like Si III, Si IV, and C IV. These transition-zone instabilities, which occur as isolated events in active regions of low flare productivity, are often observed prior to flares. Transition-zone instabilities can be traced to the footpoints of active loops and seem to be accompanied by heating of the loop. The loops vary in size and show differing degrees of activity, with the brightest and most compact ones seemingly being in a pre-flare state which results in the catastrophic energy release along the loop during a flare.

Brueckner, G. E.↗
DOE OSTI2024

ARM shortwave spectrometers to study the clear-cloud transition zone and mixing processes

The proposed research is a collaborative effort between NASA/Goddard Space Flight Center and the Hebrew University of Jerusalem. While the NASA team focused on analyzing ground-based hyper-spectral radiance observations to understand cloud edge properties and their connection to mixing processes, the Hebrew University team tackled the problem through cloud modeling activities. By approximating the shortwave spectra in the cloud-clear transition zone as a linear combination of purely clear and purely cloudy spectra we can characterize the variations of cloud optical thickness and cloud droplet effective radius in the transition zone. When applying this method to the measurements of a ground-based shortwave spectroradiometer at the ARM’s SGP site, representing continental conditions, and MAGIC field campaign between Log Angeles, California and Honolulu, Hawaii, representing maritime scenarios, we found that cloud optical depth consistently decreases in both cases, but droplet size decreases much more substantially for the continental regime, suggesting different mixing processes for the continental and maritime conditions. The investigation and measurements of radiation clouds were coupled with a unique cloud modeling. A novel spectral bin microphysics was developed and implemented to the System of Atmospheric Modeling (SAM). In order to resolve cloud transition zones with high spatial gradients of microphysical variables a unique high resolution (10 m) was used in simulations. The model calculates droplet size distributions in each grid point. The model output was transferred to the NASA/GSFC team for utilization in radiative calculations and testing of both radiative algorithm and model representation.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1979

The energy balance and pressure in the solar transition zone for network and active region features

The electron pressure and energy balance in the solar transition zone are determined for about 125 network and active region features on the basis of high spectral and spatial resolution extreme ultraviolet spectra. Si III line intensity ratios obtained from the Naval Research Laboratory high-resolution telescope and spectrograph during a rocket flight are used as diagnostics of electron density and pressure for solar features near 3.5 x 10 to the 4th K. Observed ratios are compared with the calculated dependence of the 1301 A/1312 A and 1301 A/1296 A line intensity ratios on electron density, temperature and pressure. Electron densities ranging from 2 x 10 to the 10th/cu cm to 10 to the 12th/cu cm and active region pressures from 3 x 10 to the 15th to 10 to the 16th/cu cm K are obtained. Energy balance calculations reveal the balance of the divergence of the conductive flux and turbulent energy dissipation by radiative energy losses in a plane-parallel homogeneous transition zone (fill factor of 1), and an energy source requirement for a cylindrical zone geometry (fill factor less than 0.04).

Nicolas, K. R.↗
NASA NTRS1975

The intensities and profiles of XUV transition zone lines in a quiet sun region compared to a polar coronal hole

The intensities of XUV transition-zone lines from limb spectra of a quiet-sun region and a polar coronal hole are compared. The spectra were obtained with a slit spectrograph on Skylab and cover a region from -12 sec within the limb to 20 sec above it. The lines selected for comparison are formed at temperatures that range from 36,000 to 220,000 K. Lines of the higher-temperature ions, e.g. O v, are significantly less intense in the coronal hole, and lines of lower-temperature ions show little change. Profiles of selected optically thin transition-zone lines from the quiet-sun and coronal-hole spectra are also shown. The lines are broader than expected in ionization equilibrium, and bulk-motion velocities are deduced from the widths of the lines. There appears to be little, if any, statistically significant difference in the velocities obtained from the quiet-sun region and the coronal hole.

Feldman, U.↗
NASA NTRS2012

Fatigue Failure Modes of the Grain Size Transition Zone in a Dual Microstructure Disk

Mechanical property requirements vary with location in nickel-based superalloy disks. In order to maximize the associated mechanical properties, heat treatment methods have been developed for producing tailored grain microstructures. In this study, fatigue failure modes of a grain size transition zone in a dual microstructure disk were evaluated. A specialized heat treatment method was applied to produce varying grain microstructure in the bore to rim portions of a powder metallurgy processed nickel-based superalloy disk. The transition in grain size was concentrated in a zone of the disk web, between the bore and rim. Specimens were extracted parallel and transversely across this transition zone, and multiple fatigue tests were performed at 427 C and 704 C. Grain size distributions were characterized in the specimens, and related to operative failure initiation modes. Mean fatigue life decreased with increasing maximum grain size, going out through the transition zone. The scatter in limited tests of replicates was comparable for failures of uniform gage specimens in all transition zone locations examined.

Gabb, Timothy P.↗
NASA NTRS1988

A widespread common age resurfacing event in the highland-lowland transition zone in eastern Mars

The paper presents evidence for a widespread common-age resurfacing that affected the entire boundary transition zone between the cratered highlands and northern lowland plains in eastern Mars. This resurfacing may have been contemporaneous with other major events elsewhere on Mars. It is noted that the oldest resurfacing event at N(1) of about 86,000 was much more efficient at removing larger craters in what is today the transition zone than it was in the cratered terrain; this implies that some difference in the nature of the crust had been established prior to this resurfacing event.

Frey, Herbert↗
NASA NTRS2021

Precipitable Water Vapor Variation in the Clear-Cloud Transition Zone From the ARM Shortwave Spectrometer

A new technique to retrieve precipitable water vapor (PWV)amount in the clear-cloud transition zone using ground-based zenith spectral radiance is developed. The method uses zenith radiances at the water vapor band at 720 nm and adjacent non-absorbing band at 750 nm.Radiative transfer calculations show that the relative difference in zenith radiance between the two bands depends on PWV and the variations in cloud optical depth introduce a small change in the relative difference which is independent of PWV amount. This allows us to retrieve PWV variations in the cloud-clear transition zone for clouds over dark ocean surface. We applied this method to a Cu cloud case with zenith radiance observations by the Shortwave Array Spectroradiometer-Zenith (SASZe) during the Marine ARM GPCI Investigation of Clouds (MAGIC) field campaign. We found that there is about 10% change in PWV amount from known-cloudy region to known-clear sky in cloud edges.

Atmosphere↗
NASA NTRS1982

Observations of solar flare transition zone plasmas from the Solar Maximum Mission

The spatial and temporal evolution of the Si IV and O IV intensity, density and mass motions in preflare and flare transition zone plasmas are studied for the case of the April 8, 1980 flare. It is found that: (1) the UV flare observed in the Si IV and O IV lines is unambiguously identified as occurring in a low-lying, preexisting transition zone loop which spanned the magnetic neutral line separating a larger leader spot and a newly emerged, isolated spot of opposite polarity; (2) at the onset of the flare, the easternmost footpoint, which was anchored in an isolated spot region of high longitudinal magnetic field gradient, showed sudden, impulsive brightening with large intensity increases; and (3) the release flare energy was transported by way of large-scale connecting field lines to other parts of the active region, producing the hot plasma and H-alpha kernels observed near the trailing spot.

Cheng, C.-C.↗
NASA NTRS2009

Physical Interpretation of the Spectral Radiative Signature in the Transition Zone Between Cloud-Free and Cloudy Regions

One-second-resolution zenith radiance measurements from the Atmospheric Radiation Measurement program's new shortwave spectrometer (SWS) provide a unique opportunity to analyze the transition zone between cloudy and cloud-free air, which has considerable bearing on the aerosol indirect effect. In the transition zone, we find a remarkable linear relationship between the sum and difference of radiances at 870 and 1640 nm wavelengths. The intercept of the relationship is determined primarily by aerosol properties, and the slope by cloud properties. We then show that this linearity can be predicted from simple theoretical considerations and furthermore that it supports the hypothesis of inhomogeneous mixing, whereby optical depth increases as a cloud is approached but the effective drop size remains unchanged.

Chiu, J. C.↗
NASA NTRS1974

The effect of droplets in the air-sea transition zone on the sea brightness temperature

A model is presented which shows that, for a fully developed sea driven by the wind with speeds above 5 m/sec the air in the transition zone immediately above the air-sea interface is mixed with sea water droplets from bursting air bubbles. The absorptive droplet concentration in the zone is assumed to have a profile tapering off from the interface to zero at a certain height. The dielectric constant of the absorptive inhomogeneous droplet profile is thus both a function of the wind speed and the height above the interface. Both the inhomogeneity effect and the absorption-emission effect of the droplet concentration have been considered. Theoretical calculations show that the presence of the absorptive inhomogeneous droplet transition zone significantly increases the sea brightness temperature as wind speed rises. Combined effects of both the droplet areas and the foam areas on sea surface have also been considered.

Tang, C. C. H.↗
DOE OSTI2026

An Integrated Computational Materials Engineering (ICME) Approach to Design Nonlinear Transition Zones Between Dissimilar Metals

Current approaches to designing graded transition joints (GTJs) between dissimilar metals often rely on linear changes in both composition profiles and thickness of each sublayer. This increases fabrication cost and may not be optimal with respect to residual stress or the formation of undesirable phases. Here, in this study, GTJs between P91 ferritic/martensitic steel and 347H austenitic stainless steel were designed using Integrated Computational Materials Engineering (ICME) principles with nonlinear composition and length profiles. Guided by inputs from classical mechanics and CALPHAD predictions of carbon chemical potential, a novel transition zone consisting of five discrete compositions was proposed, with the thickness of each sublayer varying according to a brachistochrone-inspired distribution. In addition to carbon potential gradients, CALPHAD was used to predict coefficients of thermal expansion, which were incorporated into finite element models to evaluate stress evolution. The proposed nonlinear design resulted in a smoother carbon potential gradient, lower carbon depletion at the P91 interface, and a comparable residual stress under long-term thermal exposure, compared to a conventional linear design using ten sublayers with equal thickness. This work introduces a brachistochrone-inspired distribution for GTJ design, offering a general framework for optimizing graded interfaces between dissimilar metals.

Directed Energy Deposition↗
NASA NTRS1975

Limb-brightening curves of XUV transition zone lines in the quiet sun and in a polar coronal hole observed from Skylab

Solar limb-brightening curves are discussed for XUV spectral lines formed in the upper chromosphere and transition zone of a quiet region and a polar coronal hole. The spectra were recorded with a slit spectrograph on Skylab. The lines considered are emitted from ions formed within the temperature range from 10,000 to 220,000 K. The limb-brightening curves cover a region from -4 sec within the limb to +20 sec above it. The data from 0 sec to +20 sec are compared with predictions based on both homogeneous and inhomogeneous models of the transition zone. The limb-brightening curve of the O I line at 1355.6 A indicates that O I is formed in spicules. The limb brightening of the He II line at 1640.4 A is consistent with a temperature of formation between about 40,000 and 90,000 K for He II.

Doschek, G. A.↗
NASA NTRS1982

Mass motions in the solar chromosphere and transition zone

A comparison is made between H-alpha and C IV observations of Active Region 2717 on October 9, 1980. On the basis of this comparison, it is found that upward velocities are present above sunspots in the chromosphere-corona transition zone (20 km/s). The downward velocities are found to be well correlated in both lines. Doppler-shift ratios between C IV and H-alpha levels (approximately 10) are seen to be much smaller than expected from density ratio estimates. The comparison is seen as suggesting that flow lines are probably far from vertical in the transition zone. It is pointed out, however, that this depends on model densities that may not be correct. A simple method for comparing matter flows is presented. The best fit between H-alpha and C IV levels is obtained when C IV Doppler shifts are multiplied by the line intensity to the power 0.5 (approximately) in order to make allowance for density fluctuations.

Mein, P.↗
DOE OSTI2024

Centriole and transition zone structures in photoreceptor cilia revealed by cryo-electron tomography

Primary cilia mediate sensory signaling in multiple organisms and cell types but have structures adapted for specific roles. Structural defects in them lead to devastating diseases known as ciliopathies in humans. Key to their functions are structures at their base: the basal body, the transition zone, the “Y-shaped links,” and the “ciliary necklace.” We have used cryo-electron tomography with subtomogram averaging and conventional transmission electron microscopy to elucidate the structures associated with the basal region of the “connecting cilia” of rod outer segments in mouse retina. The longitudinal variations in microtubule (MT) structures and the lumenal scaffold complexes connecting them have been determined, as well as membrane-associated transition zone structures: Y-shaped links connecting MT to the membrane, and ciliary beads connected to them that protrude from the cell surface and form a necklace-like structure. These results represent a clearer structural scaffold onto which molecules identified by genetics, proteomics, and superresolution fluorescence can be placed in our emerging model of photoreceptor sensory cilia.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS2005

Relative Ages of the Highlands, Lowlands, and Transition Zone Along a Portion of the Mars Crustal Dichotomy from Densities of Visible and Buried Impact Craters

Understanding the fundamental age relationships of the different parts of the Mars Crustal Dichotomy is essential to fully understanding the events that shaped the early history and formation of the surface of Mars. A dominant question is what are the true relative ages of the Northern Lowlands and the Southern Highlands? Using MOLA data from the Mars Global Surveyor and Viking visual images, a dataset of both buried and visible crater diameters was created over a nine million sq km study area of a section of the dichotomy boundary stretching from Arabia Terra to Utopia Planitia. Cumulative frequency plots on a log-log scale were used to determine the relative ages for the Highlands, the Lowlands, and the Transition Zone, separately for the visible, the buried and the combined total (visible+ buried) populations. We find the overall Highland crater population in this area is slightly older than the Lowlands, consistent with previous global studies, but the Lowlands and Transition Zone are also very old and formed at roughly the same time. It appears that the formation of the Lowlands in this region formed contemporaneously with a large-scale resurfacing event in the Highlands, perhaps caused by the process responsible for the Lowland formation.

DeSoto, G. E.↗