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At least 73 records · Page 4

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NASA NTRS1975

Quantization and symmetry in periodic coverage patterns with applications to earth observation

The general orbit-coverage problem in a simplified physical model is investigated by application of numerical approaches derived from basic number theory. A system of basic and general properties is defined by which idealized periodic coverage patterns may be characterized, classified, and delineated. The principal common features of these coverage patterns are their longitudinal quantization, determined by the revolution number R, and their overall symmetry.

King, J. C.↗

NASA NTRS1984

Origin of the coverage-dependent vibrational shift for O on Ni(100)

The p(2 x 2) and c(2 x 2) coverages of O on Ni(100) are studied with a cluster model. The p(2 x 2) coverge is modeled by the addition of a single O at a fourfold site. The c(2 x 2) is modeled by the explicit inclusion of four additional O atoms. Consistent with electron-energy-loss spectroscopy results, the O-Ni vibration is 85/cm lower for the c(2 x 2) cluster than for the p(2 x 2). The height of O above the surface is 11 pm smaller for the c(2 x 2) coverage. The nature of the O-to-Ni bonding is similar for both coverages.

Bauschlicher, C. W., Jr.↗

NASA NTRS1985

Origin of the difference of the coverage-dependent vibrational shift for S on Ni(100) and O on Ni(100)

The p(2 x 2) and c(2 x 2) coverages of S on Ni(100) are studied with a cluster model. Consistent with a recent lattice-dynamics study, the chemical contribution (rigid Ni lattice) to the coverage-dependent shift of the S vibrational energy is of opposite sign to that for O. Analysis of the cluster wave functions suggests that S becomes less negatively charged with coverage, while O becomes more ionic; however, this effect is small.

Bauschlicher, C. W., Jr.↗

NASA NTRS1986

Low-altitude coverage of ST radars

Clear air ST (stratosphere troposphere) radars are now widely used for atmospheric research and wind profiling. Most attention to date has been directed toward extending the altitude coverage as high as possible. It is also desirable to extend the coverage as low as possible. Any improvement in the low altitude coverage of existing wind profiling radars would be useful. The approximate lower limits of some existing ST radars are listed and what set these limits are briefly examined.

Ecklund, W. L.↗

NASA NTRS2012

Global Coverage from Ad-Hoc Constellations in Rideshare Orbits

A promising area of small satellite development is in providing higher temporal resolution than larger satellites. Traditional constellations have required specific orbits and dedicated launch vehicles. In this paper we discuss an alternative architecture in which the individual elements of the constellation are launched as rideshare opportunities. We compare the coverage of such an ad-hoc constellation with more traditional constellations. Coverage analysis is based on actual historical data from rideshare opportunities. Our analysis includes ground coverage and temporal revisits for Polar, Tropics, Temperate, and Global regions, comparing ad-hoc and Walker constellation.

small satellite development↗

NASA NTRS2013

Planning Coverage Campaigns for Mission Design and Analysis: CLASP for DESDynl

Mission design and analysis presents challenges in that almost all variables are in constant flux, yet the goal is to achieve an acceptable level of performance against a concept of operations, which might also be in flux. To increase responsiveness, automated planning tools are used that allow for the continual modification of spacecraft, ground system, staffing, and concept of operations, while returning metrics that are important to mission evaluation, such as area covered, peak memory usage, and peak data throughput. This approach was applied to the DESDynl mission design using the CLASP planning system, but since this adaptation, many techniques have changed under the hood for CLASP, and the DESDynl mission concept has undergone drastic changes. The software produces mission evaluation products, such as memory highwater marks, coverage percentages, given a mission design in the form of coverage targets, concept of operations, spacecraft parameters, and orbital parameters. It tries to overcome the lack of fidelity and timeliness of mission requirements coverage analysis during mission design. Previous techniques primarily use Excel in ad hoc fashion to approximate key factors in mission performance, often falling victim to overgeneralizations necessary in such an adaptation. The new program allows designers to faithfully represent their mission designs quickly, and get more accurate results just as quickly.

Knight, Russell L.↗

NASA NTRS2017

Full-Coverage High-Resolution Daily PM(sub 2.5) Estimation using MAIAC AOD in the Yangtze River Delta of China

Satellite aerosol optical depth (AOD) has been used to assess population exposure to fine particulate matter (PM (sub 2.5)). The emerging high-resolution satellite aerosol product, Multi-Angle Implementation of Atmospheric Correction(MAIAC), provides a valuable opportunity to characterize local-scale PM(sub 2.5) at 1-km resolution. However, non-random missing AOD due to cloud snow cover or high surface reflectance makes this task challenging. Previous studies filled the data gap by spatially interpolating neighboring PM(sub 2.5) measurements or predictions. This strategy ignored the effect of cloud cover on aerosol loadings and has been shown to exhibit poor performance when monitoring stations are sparse or when there is seasonal large-scale missngness. Using the Yangtze River Delta of China as an example, we present a Multiple Imputation (MI) method that combines the MAIAC high-resolution satellite retrievals with chemical transport model (CTM) simulations to fill missing AOD. A two-stage statistical model driven by gap-filled AOD, meteorology and land use information was then fitted to estimate daily ground PM(sub 2.5) concentrations in 2013 and 2014 at 1 km resolution with complete coverage in space and time. The daily MI models have an average R(exp 2) of 0.77, with an inter-quartile range of 0.71 to 0.82 across days. The overall Ml model 10-fold cross-validation R(exp 2) (root mean square error) were 0.81 (25 gm(exp 3)) and 0.73 (18 gm(exp 3)) for year 2013 and 2014, respectively. Predictions with only observational AOD or only imputed AOD showed similar accuracy.Comparing with previous gap-filling methods, our MI method presented in this study performed bette rwith higher coverage, higher accuracy, and the ability to fill missing PM(sub 2.5) predictions without ground PM(sub 2.5) measurements. This method can provide reliable PM(sub 2.5)predictions with complete coverage that can reduce biasin exposure assessment in air pollution and health studies.

PM2.5↗

NASA NTRS1997

Constellation Coverage Analysis

The design of satellite constellations require an understanding of the dynamic global coverage provided by the constellations. We have developed a fast and simple algorithm for detemining the global constellation coverage dynamically using image processing techniques. This approach provides a fast, powerful and simple method for the anysis of global constellation coverage.

Satellite↗

NASA NTRS2024

Determination of Percent Area Coverage of Lunar Simulant on a Surface and Observations of Fairy Castle Structures

With NASA’s goal of returning humans to the Moon, it has become increasingly important to understand the impact of lunar regolith on spacecraft systems. The ability to measure the level of dust coverage on a surface is essential. Developing an accurate technique to determine percent area coverage is challenging due to the unique and complex layering of the dust particles on the surface, creating what is called fairy castle structures that form complex towers, bridges, and buttresses using the smallest of dust particles as building blocks. For this study, these structures have been simulated using a unique dust distributor device and imaged with a scanning electron microscope. The results show the dusted surface’s complex topology, thus demonstrating the difficulty with determining the percent area of dust coverage. Implications for dust buildup on spacecraft can include issues for heat transfer, making continuation of this research critical to support future human exploration of the Moon.

Emma J Quick↗

DOE OSTI2025

Complete coverage fouling model for constant flux crossflow ultrafiltration and experimental validation

A complete coverage model is proposed to describe fouling in constant flux crossflow ultrafiltration. Constant flux crossflow fouling experiments were conducted using dilute latex bead suspensions and commercial poly(ether sulfone) flat sheet ultrafiltration membranes to investigate the influence of operating conditions on evolution of transmembrane pressure (ΔP, TMP) with time. Changes in permeate flux or crossflow rate had little influence on the normalized TMP profile at high latex bead concentration (i.e., above 25 ppm) because the membrane surface was covered with latex beads. At low concentration (i.e., below 25 ppm), increases in permeate flux or foulant concentration increased normalized ΔP. However, this increase in normalized ΔP with permeate flux or foulant concentration diminishes when the permeate flux/concentration is high enough to overwhelm particle removal due to crossflow. Furthermore, these results are in good agreement with the new complete coverage model which describes the influence of operating parameters on fouling better than the previous model.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Portable Distortion Free Large Solid Angle Coverage Detector

Neutron single crystal diffractometers require large solid angle coverage for optimum performance. This can be achieved by tiling flat detectors in a cylindrical or spherical geometry, but results in large gaps in detector coverage and parallax distortion. The detector edges exhibit degraded resolution, distortion, and gamma rejection. Since the detector edge regions are a significant fraction of the detector active area, they must be removed from the experimental data set, requiring extra beam time to collect enough analysis data. A spherical detector with a continuous surface would effectively address this issue while eliminating most boundary ‘dead’ areas. Here we report on the development of a novel hemispherical shaped neutron detector using seamlessly tiled readout modules to form the desired shape. The heart of the detector is a specially developed curved neutron scintillator coupled to high resolution silicon photomultiplier (SiPM) Anger cameras via custom made fiber optic tapers (FOTs). The detector has been assembled and initial tests have been conducted at the High Flux Isotope Reactor (HFIR) beamlines at Oak Ridge National Laboratory (ORNL). Here, in this work, we describe details of the scintillator design, fabrication and characterization, evaluation of individual detector modules, the details of the detector design implementation, and evaluation of the assembled detector at ORNL beamlines.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2025

First-Principles-Based Study of the Decomposition of Phenol and Hydroquinone on Pt(111) Combined with Quantitative Information from XPS Spectra to Address the Impact of Coverage and Number of Hydroxyl Functional Groups

A combined first-principles-based and experimental X-ray photoelectron spectroscopy approach was used to investigate the thermal decomposition of two model biofuel compounds, phenol and hydroquinone, on Pt(111) at both low and high coverages. The DFT-based approach yields adsorption geometries and energies, activation barriers and core-level binding energy shifts for C 1s and O 1s. Increasing the coverage in the theoretical model leads to slight shifts in core-level binding energies─toward higher values for C 1s and lower values for O 1s. It also alters the energy profiles of the decomposition reaction pathway, resulting in weaker adsorption energies and changes in both reaction and activation barriers. At low temperatures, we observe a multilayer for phenol and hydroquinone upon adsorption, with desorption occurring at 200 and 270 K, respectively. Following desorption of the multilayer, decomposition proceeds via initial O–H bond scission, followed by two parallel pathways involving either C–H or C–C bond scission, whereby in the case of phenol C–H bond scission occurs first. Here, we further provide characteristic core level binding energies by theoretical calculations that are subsequently used in experimental analyses, establishing a reference database for key spectra of phenolic functionalities applicable to a range of catalytic reactions.

09 BIOMASS FUELS↗

DOE OSTI2024

Nanobubble Formation and Coverage during High Current Density Alkaline Water Electrolysis

Gas bubbles are a necessary byproduct of water electrolysis whereby hydrogen and oxygen are produced from water. These attached gases reduce the electrode’s active area, which necessitates a deep understanding of the bubble life cycle starting from nanobubbles. Synchronized with the electrochemistry, the time evolution of the surface nanobubble size and coverage is resolved using grazing incidence small-angle X-ray scattering (GISAXS) and correlated with optical microscopy and theoretical calculations to show that a significant portion of the surface is covered in nanobubbles after larger micron-sized bubbles are observed. Further, these nanobubbles increase in number and decrease in size, toward 2 nm diameter, with the charge passed. The trend in size and number is consistent with an increase in supersaturation, which reduces the nascent bubble size. Altogether, this study suggests a significant portion of the surface contains nanobubbles and that strategies to reduce the dissolved hydrogen would be effective at reducing the nanobubble surface coverage.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Anolyte Buffering and CO Coverage Effects in the Electrochemical Reduction of CO at Cu Electrocatalysts

Electrolytic CO reduction was investigated at copper electrocatalysts in zero-gap membrane electrode assemblies as a function of buffering agents and cofeeding with CO 2 or Ar. Results show an acetate Faradaic efficiency (FE) of 90% at 300 mA cm −2 using pure CO feeds and phosphate-buffered anolyte near pH 8. When using CO feeds with more alkaline anolytes, the hydrogen evolution reaction becomes the dominant reduction reaction, independent of the buffer. Product distributions of cofeeding experiments with CO and CO 2 show that increasing CO 2 cofeeding results in increased selectivity toward ethylene (42% FE) in near-neutral KHCO 3 anolytes or ethanol (40% FE) in alkaline KOH anolytes. Evaluation of several commercial anion exchange membranes shows similar selectivity trends, suggesting product selectivity is dominated by the local pH and surface coverage of CO. Based on these results, we propose pH buffering and CO coverage behaviors that facilitate high selectivities to acetate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

Code Coverage Reporter

The code-coverage-reporter is a JavaScript GitHub Action that may be called from within GitHub workflows. Its role is to parse a code coverage report file in the LCOV format and translate the contents into a summary that gets added to individual Pull Requests. It is fully reusable and repository-agnostic.

Curley, Jacob [Fermilab]↗

NASA NTRS1972

Tracking coverage of the Radio Astronomy Explorer-B

Launch and arrival parameters for the Radio Astronomy Explorer-B mission were revised to provide better tracking station coverage of the transfer trajectory. It is shown that changing the launch azimuth and flight time is sufficient to provide postinjection tracking by Tananarive and Carnarvon, and redundant lunar orbit insertion coverage by command stations. These changes can be made with no significant influence on the other parameters and without sacrificing many launch opportunities. All acceptable launch opportunties during the RAE-B launch period are tabulated together with pertinent launch and arrival parameters.

Swartwood, H., Jr.↗

NASA NTRS1971

Coverage by land, sea, and airplane surveys, 1900-1967.

The worldwide coverage of the earth by land, sea, and aircraft magnetic surveys since the beginning of the 20th century is shown on three world maps for surface surveys spanning the periods of 1900-1930, 1930-1955, and 1955-1967, respectively, on a fourth map for ship-towed magnetometer surveys performed after 1956, and on a fifth map for 1953-1966 airborne survey data. The technique used, involving a position plotting of each measurement with a microfilm plotter, results in the appearance of heavily surveyed regions as completely darkened areas. The coverage includes measurements at about 100,000 land stations, airborne measurements at over 90,000 points, and marine measurements at over 25,000 points. The marine measurements cover over 1,000,000 km of trackline.

Fabiano, E.↗

NASA NTRS1976

Full-coverage film cooling heat transfer study: Summary of data for normal-hole injection and 30 deg slant-hole injection

Heat transfer to a full coverage film cooled turbulent boundary layer over a flat surface was studied. The surface consisted of a discrete hole test section containing 11 rows of holes spaced 5 diameters apart in a staggered array and an instrumented recovery region. Ten diameter spacing was also studied by plugging appropriate holes. Two test sections were used, one having holes normal to the surface and the other having holes angled 30 deg to the surface in the downstream direction. Stanton number data were obtained both in the full coverage region and in the downstream recovery region for a range of blowing ratios, or mass flux ratios, from 0 to 1.3. Initial conditions at the upstream edge of the blowing region were varied from 500 to 5000 for momentum thickness Reynolds number and from 100 to 1800 for enthalpy thickness Reynolds number. The range of Reynolds numbers based on hole diameter and mainstream velocity was 6000 to 22000. Initial boundary layer thicknesses range from 0.5 to 2.0 hole diameters. Air was used as the working fluid. The data were taken for the secondary injection temperature equal to the wall temperature and also equal to the mainstream temperature. Superposition was then used to obtain Stanton number as a continuous function of the injectant temperature. The heat transfer coefficient was defined on the basis of a mainstream-to-wall temperature difference. This definition permits direct comparison of performance between film cooling and transpiration cooling.

Crawford, M. E.↗