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At least 1,171 records · Page 65
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Evaluation of Radiography for TRISO Buffer Layer Density Measurement

Tristructural isotropic (TRISO) fuel particles consist of a central uranium-bearing kernel and a series of coating layers designed to retain fission products and to ensure fuel performance. Several parameters such as thickness and density must be measured for these coating layers to show that they conform with fuel specifications. Current methods for measuring the density of pyrolytic carbon and silicon carbide layers (liquid gradient density column) and the buffer layer (mercury porosimetry) generate Resource Conservation and Recovery Act (RCRA) radiological-mixed waste. In addition, measurement of buffer and inner pyrolytic carbon layer densities require hot sampling or interrupted coating runs and the mercury porosimetry method used for buffer density measurement only measures the mean buffer density, not the interparticle distribution. A new approach has been evaluated to measure the density of coating layers in TRISO particles based on the dependence of x-ray attenuation in radiographs on material density. This method does not generate RCRA mixed waste, measures density on a particle-by-particle basis, and in principle is capable of measuring the density of all coating layers in a single process. Initial results using thinned TRISO particle sections to evaluate radiography measurement of density as a quality control characterization method are reported herein. In this work, the primary focus is on measurement of the density of the buffer layer; however, with appropriate calibration the method should be applicable to other coating layers. Improvements to the initial method and a full demonstration of the method on the remaining coating layers may be pursued as a future effort.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Similarity of the turbulent kinetic energy dissipation rate distribution in the upper mixed layer of the tropical Indian Ocean

Turbulence within the upper ocean mixed layer plays a key role in various physical, biological, and chemical processes. Between September and November 2011, a dataset of 570 vertical profiles of the turbulent kinetic energy (TKE) dissipation rate, as well as conventional hydrological and meteorological data, were collected in the upper layer of the tropical Indian Ocean. These data were used to statistically analyze the vertical distribution of the TKE dissipation rate in the mixed layer. The arithmetic-mean method made the statistical TKE dissipation rate profile more scattered than the median and geometric-mean methods. The statistical TKE dissipation rate were respectively scaled by the surface buoyancy flux and the TKE dissipation rate at the mixed-layer base. It was found that the TKE dissipation rate scaled by that at the mixed-layer base exhibited better similarity characteristics than that scaled by the surface buoyancy flux, whether the stability parameter D/|L MO | was greater or less than 10, indicating that the TKE dissipation rate at the mixed-layer base is a better characteristic scaling parameter for reflecting the intrinsic structure of the TKE dissipation rate in the mixed layer, where D and L MO are respectively the mixed-layer thickness and the Monin-Obukhov length scale. The parameterization of the TKE dissipation rate at the mixed-layer base on the shear-driven dissipation rate and the surface buoyancy flux was further explored. It was found that the TKE dissipation rate at the mixed-layer base could be well fitted by a linear combination of three terms: the wind-shear-driven dissipation rate, the surface buoyancy flux, and a simple nonlinear coupling term of these two.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1988

Provenance of the K/T boundary layers

An array of chemical, physical and isotopic evidence indicates that an impact into oceanic crust terminated the Cretaceous Period. Approximately 1500 cu km of debris, dispersed by the impact fireball, fell out globally in marine and nonmarine environments producing a 2 to 4 mm thick layer (fireball layer). In North American locales, the fireball layer overlies a 15 to 25 mm thick layer of similar but distinct composition. This 15 to 25 mm layer (ejecta layer) may represent approximately 1000 cu km of lower energy ejecta from a nearby impact site. Isotopic and chemical evidence supports a mantle provenance for the bulk of the layers. The extraordinary REE pattern of the boundary clays was modelled as a mixture of oceanic crust, mantle, and approximately 10 percent continental material. The results are presented. If the siderophiles of the ejecta layer were derived solely from the mantle, a test may be available to see if the siderophile element anomaly of the fireball layer had an extraterrestrial origin. Radiogenic Os-187 is depleted in the mantle relative to an undifferentiated chondritic source. Os-187/Os-186 ratios of 1.049 and 1.108 were calculated for the ejecta and fireball layers, respectively.

Hildebrand, A. R.↗
NASA NTRS1983

Comparison Between Navier-Stokes and Thin-Layer Computations for Separated Supersonic Flow

In the numerical simulation of high Reynolds-number flow, one can frequently supply only enough grid points to resolve the viscous terms in a thin layer. As a consequence, a body-or stream-aligned coordinate system is frequently used and viscous terms in this direction are discarded. It is argued that these terms cannot be resolved and computational efficiency is gained by their neglect. Dropping the streamwise viscous terms in this manner has been termed the thin-layer approximation. The thin-layer concept is an old one, and similar viscous terms are dropped, for example, in parabolized Navier-Stokes schemes. However, such schemes also make additional assumptions so that the equations can be marched in space, and such a restriction is not usually imposed on a thin-layer model. The thin-layer approximation can be justified in much the same way as the boundary-layer approximation; it requires, therefore, a body-or stream-aligned coordinate and a high Reynolds number. Unlike the boundary-layer approximation, the same equations are used throughout, so there is no matching problem. Furthermore, the normal momentum equation is not simplified and the convection terms are not one-sided differenced for marching. Consequently, the thin-layer equations are numerically well behaved at separation and require no special treatment there. Nevertheless, the thin-layer approximation receives criticism. It has been suggested that the approximation is invalid at separation and, more recently, that it is inadequate for unsteady transonic flow. Although previous comparisons between the thin-layer and Navier-Stokes equations have been made, these comparisons have not been adequately documented.

Degani, David↗
NASA NTRS2003

Comparison of Methods for Determining Boundary Layer Edge Conditions for Transition Correlations

Data previously obtained for the X-33 in the NASA Langley Research Center 20-Inch Mach 6 Air Tunnel have been reanalyzed to compare methods for determining boundary layer edge conditions for use in transition correlations. The experimental results were previously obtained utilizing the phosphor thermography technique to monitor the status of the boundary layer downstream of discrete roughness elements via global heat transfer images of the X-33 windward surface. A boundary layer transition correlation was previously developed for this data set using boundary layer edge conditions calculated using an inviscid/integral boundary layer approach. An algorithm was written in the present study to extract boundary layer edge quantities from higher fidelity viscous computational fluid dynamic solutions to develop transition correlations that account for viscous effects on vehicles of arbitrary complexity. The boundary layer transition correlation developed for the X-33 from the viscous solutions are compared to the previous boundary layer transition correlations. It is shown that the boundary layer edge conditions calculated using an inviscid/integral boundary layer approach are significantly different than those extracted from viscous computational fluid dynamic solutions. The present results demonstrate the differences obtained in correlating transition data using different computational methods.

Liechty, Derek S.↗
NASA NTRS2002

Discovery of coesite and shocked quartz associated with the upper Eocene cpx spherule layer

At least two major impact ejecta layers have been discovered in upper Eocene strata. The upper layer is the North American microtektite layer. lt consists tektite fragments, microtektites, and shocked mineral grains (e.g., quartz and feldspar with multiple sets of PDFs, coesite and reidite (a high-pressure polymorph of zircon)). The slightly older layer contains clinopyroxene-bearing (cpx) spherules and microtektites associated with an Ir anomaly. The North American tektite layer may be derived from the Chesapeake Bay impact structure, and the cpx spherule layer may from the Popigai impact crater. A cpx spherule layer associated with a positive Ir anomaly was recently found at ODP Site 709, western Indian Ocean. A large sample (Hole 709C, core 31, section 4, 145-150 cm), originally used for a study of interstitial water by shipboard scientists, was acquired for the purpose of recovering a large number of spherules for various petrographic and geochemical studies. A split of the sample (50.35 g) was disaggregated and wet-sieved. More than 17,000 cpx spherules and several hundred microtektites (larger than 125 microns) were recovered from the sample. Rare white opaque grains were observed in the 125-250 micron size fraction after removal of the carbonate component using dilute HCI. Seven of the white opaque grains were X-rayed using a Gandolfi camera and six were found to be coesite (probably mixed with lechatelierite). Eighty translucent colorless grains from the 63-125 micron size fraction were studied with a petrographic microscope. Four of the grains exhibit one to two sets of planar deformation features (PDFs). The only other possible known occurrence of shocked minerals associated with the cpx spherule layer is at Massignano, Italy, where pancake-shaped clay spherules (thought to be diagenetically altered cpx spherules are associated with a positive Ir anomaly and Ni- rich spinel crystals. Shocked quartz grains with multiple sets of PDFs also occur at this site. Until now, unmelted impact ejecta have not been found associated with the cpx spherules at any of the other 20 sites around the world and this is the first time that coesite has been found associated with the cpx spherule layer. The discovery of coesite and shocked quartz associated with the cpx spherules at Site 709 in Indian Ocean is further evidence for the impact origin of the cpx spherule layer. We hope that future discovery of other unmelted minerals from this sample may provide materials to establish constraints on the provenance of this late Eocene ejecta.

Liu, S.↗
NASA NTRS2006

Assessment of Bulk Absorber Properties for Multi-Layer Perforates in Porous Honeycomb Liners

CONTINUING progress in materials technology provides potential for improved acoustic liners for attenuating broadband fan noise emissions from aircraft engine nacelles. Conventional liners (local-reacting perforate-over-honeycomb structures) provide significant narrow-band attenuation, but limited attenuation over wide bandwidths. Two approaches for increasing attenuation bandwidth are to (1) replace the honeycomb structure with bulk material, or (2) cascade multiple layers of perforate/honeycomb structures. Usage of the first approach is limited because of mechanical and maintenance reasons, while multi-layer liners are limited to about three layers because of their additional mechanical complexity, depth and weight. The current research concerns a novel approach reported by the University of Cincinnati, in which a single-layer conventional liner is converted into an extended-reaction, broadband absorber by making the honeycomb core structure porous. This modified single-layer liner requires no increase in depth and weight, and minimal increase in mechanical complexity. Langley has initiated research to identify potential benefits of liner structures with porous cell walls. This research has two complementary goals: (1) develop and validate experimental techniques for treating multi-layer perforates (representative of the internal cells of a liner with porous cell walls) as 1-D bulk materials, and (2) develop analytical approaches to validate this bulk material assumption. If successful, the resultant model can then be used to design optimized porous honeycomb liners. The feasibility of treating an N-layer perforate system (N porous plates separated by uniform air gaps) as a one-dimensional bulk absorber is assessed using the Two-Thickness Method (TTM), which is commonly used to educe bulk material intrinsic acoustic parameters. Tests are conducted with discrete tone and random noise sources, over an SPL range sufficient to determine the nonlinearity of the test specimens, for test specimens consisting of 5, 10 and 15% porous plates. Measured impedances for two liner thicknesses (e.g., 12 and 24 layers) are used as input to the TTM to determine the characteristic impedance and propagation constant that characterize these liners as bulk absorbers. These parameters are then used to calculate the predicted impedance of liners with different thicknesses (e.g., 36 layers), and a comparison of predicted and measured impedances for these other thicknesses is used to determine the efficacy of this approach. Finally, an independent method is used to educe the propagation constant for a single representative sample, and excellent comparison between the results for this method and those for the TTM provides increased confidence in the results achieved with the TTM. In general, the results demonstrate these multi-layer perforates can be acceptably treated as bulk absorbers.

Jones, Michael G.↗
NASA NTRS2006

Widespread Layers in Arabia Terra: Implications for Martian Geologic History

Layered rocks in Arabia Terra have been the focus of several recent papers. Studies have focused on the layers found in crater basins located in the southwest portion of the region. However, Mars Orbiter Camera (MOC) images have identified layered deposits across the region. Terrestrial layered rocks are usually sedimentary, and often deposited in water. Thus extensive layered sequences in Arabia Terra may indicate locations of past, major depositional basins on Mars. Other mechanisms can also create layered rocks, or the appearance of layered rocks, including volcanism (both lava flows and ash falls), wind-blown deposits, and wave-cut terraces at shorelines. By identifying where in the region layers occur, and classifying the layers according to morphology and albedo, past depositional environments may be identified. Arabia Terra is characterized by heavily cratered Noachian plains, as well as a rise from -4000 m in the northwest to 4000 m in the southeast (Mars Orbital Laser Altimeter [MOLA] datum). This slope may have provided a constraint on sediment deposition and thus layer formation. While most of the region is Noachian in age, a significant percentage of the area is identified as Hesperian. Although the history of the Arabia Terra initially seems to be straightforward cratered plains with several younger units atop them analysis of high-resolution imagery may reveal a more complex history.

Venechuk, Elizabeth M.↗
NASA NTRS2009

nBn Infrared Detector Containing Graded Absorption Layer

It has been proposed to modify the basic structure of an nBn infrared photodetector so that a plain electron-donor- type (n-type) semiconductor contact layer would be replaced by a graded n-type III V alloy semiconductor layer (i.e., ternary or quarternary) with appropriate doping gradient. The abbreviation nBn refers to one aspect of the unmodified basic device structure: There is an electron-barrier ("B" ) layer between two n-type ("n" ) layers, as shown in the upper part of the figure. One of the n-type layers is the aforementioned photon-absorption layer; the other n-type layer, denoted the contact layer, collects the photocurrent. The basic unmodified device structure utilizes minority-charge-carrier conduction, such that, for reasons too complex to explain within the space available for this article, the dark current at a given temperature can be orders of magnitude lower (and, consequently, signal-to-noise ratios can be greater) than in infrared detectors of other types. Thus, to obtain a given level of performance, less cooling (and, consequently, less cooling equipment and less cooling power) is needed. [In principle, one could obtain the same advantages by means of a structure that would be called pBp because it would include a barrier layer between two electron-acceptor- type (p-type) layers.] The proposed modifications could make it practical to utilize nBn photodetectors in conjunction with readily available, compact thermoelectric coolers in diverse infrared- imaging applications that could include planetary exploration, industrial quality control, monitoring pollution, firefighting, law enforcement, and medical diagnosis.

Gunapala, Sarath D.↗
NASA NTRS2003

CLARAty Functional-Layer Software

Functional-layer software for the Coupled Layer Architecture for Robotics Autonomy (CLARAty) is being developed. [CLARAty was described in Coupled-Layer Architecture for Advanced Software for Robots (NPO-21218), NASA Tech Briefs, Vol. 26, No. 12 (December 2002), page 48. To recapitulate: CLARAty was proposed to improve the modularity of robotic software while tightening the coupling between planning/execution and control subsystems. Whereas prior robotic software architectures have typically contained three levels, the CLARAty architecture contains two layers: a decision layer and a functional layer.] Just as an operating system provides abstraction from computational hardware, the CLARAty functional-layer software provides for abstraction for the different robotic systems. The functional-layer software establishes interrelated, object-oriented hierarchies that contain active and passive objects that represent the different levels of system abstrations and components. The functional-layer software is decomposed into a set of reusable core components and a set of extended components that adapt the reusable set to specific hardware implementations. The reusable components (a) provide behavior and interface definitions and implementations of basic functionality, (b) provide local executive capabilities, (c) manage local resources, and (d) support state and resource queries by the decision layer. Software for robotic systems can be built by use of these components.

Nesnas, Issa↗
DOE OSTI2015

Membranes having aligned 1-D nanoparticles in a matrix layer for improved fluid separation

Membranes for fluid separation are disclosed. These membranes have a matrix layer sandwiched between an active layer and a porous support layer. The matrix layer includes 1-D nanoparticles that are vertically aligned in a porous polymer matrix, and which substantially extend through the matrix layer. The active layer provides species-specific transport, while the support layer provides mechanical support. A matrix layer of this type has favorable surface morphology for forming the active layer. Furthermore, the pores that form in the matrix layer tend to be smaller and more evenly distributed as a result of the presence of aligned 1-D nanoparticles. Improved performance of separation membranes of this type is attributed to these effects.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Conductive polymer layers to limit transfer of fuel reactants to catalysts of fuel cells to reduce reactant crossover

An apparatus of an aspect includes a fuel cell catalyst layer. The fuel cell catalyst layer is operable to catalyze a reaction involving a fuel reactant. A fuel cell gas diffusion layer is coupled with the fuel cell catalyst layer. The fuel cell gas diffusion layer includes a porous electrically conductive material. The porous electrically conductive material is operable to allow the fuel reactant to transfer through the fuel cell gas diffusion layer to reach the fuel cell catalyst layer. The porous electrically conductive material is also operable to conduct electrons associated with the reaction through the fuel cell gas diffusion layer. An electrically conductive polymer material is coupled with the fuel cell gas diffusion layer. The electrically conductive polymer material is operable to limit transfer of the fuel reactant to the fuel cell catalyst layer.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Oxide layers and methods of making the same

The present application discloses devices that include a perovskite layer, a first layer that includes an oxide, and an interface layer, where the interface layer is positioned between the first layer and the perovskite layer, the interface layer is in physical contact with both the first layer and the perovskite layer, and the interface layer consists essentially of the oxide.

Schulz, Philip↗
DOE OSTI2023

Nanostructured devices having perovskite nanocrystal layer for photodetection, optical memory, and neuromorphic functionality

The present disclosure relates to a device that includes a perovskite nanocrystal (NC) layer, a charge separating layer, an insulating layer, a gate electrode, a cathode, and an anode, where the charge separating layer is positioned between the perovskite NC layer and the insulating layer, the insulating layer is positioned between the charge separating layer and the gate electrode, and the cathode and the anode both electrically contact the charge separating layer and the insulating layer. In some embodiments of the present disclosure, the device may be configured to operate as at least one of a photodetector, an optical switching device, and/or a neuromorphic switching device.

Blackburn, Jeffrey Lee↗
DOE OSTI2023

Method for forming a temperature sensing layer within a thermal barrier coating

A thermal barrier coated component, such as a turbine blade formed from a superalloy substrate, includes a thermal barrier coating applied onto the substrate. A metallic bond coat layer is on the substrate and includes rare-earth luminescent dopants. A ceramic top coat layer is on the bond coat layer. A temperature sensing thermally grown oxide (TGO) layer is formed at the interface of the bond coat layer and ceramic top coat layer. The temperature sensing TGO layer includes grown rare-earth luminescent ions migrated from the metallic bond coat layer in an amount sufficient to enable luminescence sensing of the TGO layer for real-time phosphor thermometry temperature measurements at the TGO layer.

Fouliard, Quentin↗
DOE OSTI2023

Bipolar transistor structure with collector on polycrystalline isolation layer and methods to form same

Embodiments of the disclosure provide a bipolar transistor structure with a collector on a polycrystalline isolation layer. A polycrystalline isolation layer may be on a substrate, and a collector layer may be on the polycrystalline isolation layer. The collector layer has a first doping type and includes a polycrystalline semiconductor. A base layer is on the collector layer and has a second doping type opposite the first doping type. An emitter layer is on the base layer and has the first doping type. A material composition of the doped collector region is different from a material composition of the base layer.

Holt, Judson R.↗
DOE OSTI2016

Active layer hydrology in an arctic tundra ecosystem: quantifying water sources and cycling using water stable isotopes

Climate change and thawing permafrost in the Arctic will significantly alter landscape hydro-geomorphology and the distribution of soil moisture, which will have cascading effects on climate feedbacks (CO 2 and CH 4 ) and plant and microbial communities. Fundamental processes critical to predicting active layer hydrology are not well understood. This study applied water stable isotope techniques (δ 2 H and δ 18 O) to infer sources and mixing of active layer waters in a polygonal tundra landscape in Barrow, Alaska (USA), in August and September of 2012. Results suggested that winter precipitation did not contribute substantially to surface waters or subsurface active layer pore waters measured in August and September. Summer rain was the main source of water to the active layer, with seasonal ice melt contributing to deeper pore waters later in the season. Surface water evaporation was evident in August from a characteristic isotopic fractionation slope (δ 2 H vs δ 18 O). Freeze-out isotopic fractionation effects in frozen active layer samples and textural permafrost were indistinguishable from evaporation fractionation, emphasizing the importance of considering the most likely processes in water isotope studies, in systems where both evaporation and freeze-out occur in close proximity. The fractionation observed in frozen active layer ice was not observed in liquid active layer pore waters. Such a discrepancy between frozen and liquid active layer samples suggests mixing of meltwater, likely due to slow melting of seasonal ice. In conclusion, this research provides insight into fundamental processes relating to sources and mixing of active layer waters, which should be considered in process-based fine-scale and intermediate-scale hydrologic models.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

A Study of Intermittent Turbulence in Stable Arctic Boundary Layers

Abstract Polar boundary layers are difficult to model due to the existence of intermittent turbulence within stable layers. Here we present a case study evaluation of coherent structures in a stable boundary layer observed during a series of flights with an uncrewed aircraft system (DataHawk2) on 19 October 2016 at Oliktok Point, Alaska as part of the ERASMUS (Evaluation of Routine Atmospheric Sounding Measurements using Unmanned Systems) field campaign. During a sequence of five flights over a nine-hour period, 57 profiles of atmospheric properties (0–400 m a.g.l) were collected. Turbulence was identified using derived Richardson Number, temperature structure function parameter, and turbulence kinetic energy dissipation. Throughout all flights on this strongly stable day, intermittent turbulence was observed. These turbulent layers showed well-mixed potential temperature profiles embedded within otherwise stable potential temperature profiles; often resulting in a characteristic staircase pattern. Turbulent layers ranged from 1 to 30 m deep, with most individual layers being 1–2 m deep. Vertical propagation velocities of layers in the lower atmosphere were on the order of a few cm s −1 , typical of non-convective environments. In different regions of the profile, turbulence was driven by a different balance of buoyancy and shear forces, with turbulence in the near surface environment driven by strong shear forces overcoming strong resistance to buoyancy, while turbulence in elevated layers characterized by weaker shear forces overcoming weaker resistance to buoyancy. We discuss the potential of such datasets for improving subgrid parameterizations of small-scale turbulence embedded within stable boundary layers.

54 ENVIRONMENTAL SCIENCES↗