Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “LEADING ABSTRACT”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,675 records · Page 93
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Accelerated Deterministic Phonon Transport With Consistent Material Temperature and Intensities

Abstract We present a method for deterministically solving the frequency and temperature dependent phonon radiative transport (PRT) equation in the single-mode relaxation time (SMRT) approximation in the self-adjoint angular flux (SAAF) form. To handle the nonlinear coupling between the phonon intensities and the material temperature, we apply a linearization approach that is similar to one in thermal radiative transport. This procedure leads to the PRT equation with pseudo-scattering. The method presented includes acceleration of both the inner pseudo-scattering source iterations and outer temperature iteration with a gray diffusion synthetic acceleration (DSA) and Anderson acceleration, respectively. We use the finite-element method to discretize the PRT equation in space and the method of discrete ordinates (SN) for angular discretization. The proposed method is verified by a gray method of manufactured solutions problem and demonstrated on a problem using temperature and direction dependent multigroup data from lithium aluminate (LiAlO2). The iterative performance of the acceleration method in each test is then compared to the unaccelerated method.

Engineering↗
DOE OSTI2022

A Reanalysis of Public Galactic Bulge Gravitational Microlensing Events from OGLE-III and -IV

Abstract Modern surveys of gravitational microlensing events have progressed to detecting thousands per year, and surveys are capable of probing Galactic structure, stellar evolution, lens populations, black hole physics, and the nature of dark matter. One of the key avenues for doing this is the microlensing Einstein radius crossing time (t E) distribution. However, systematics in individual light curves as well as oversimplistic modeling can lead to biased results. To address this, we developed a model to simultaneously handle the microlensing parallax due to Earth's motion, systematic instrumental effects, and unlensed stellar variability with a Gaussian process model. We used light curves for nearly 10,000 OGLE-III and -IV Milky Way bulge microlensing events and fit each with our model. We also developed a forward model approach to infer the t E distribution by forward modeling from the data rather than using point estimates from individual events. We find that modeling the variability in the baseline removes a source of significant bias in individual events, and the previous analyses overestimated the number of t E > 100 day events due to their oversimplistic model ignoring parallax effects. We use our fits to identify the hundreds filling a regime in the microlensing parameter space that are 50% pure of black holes. Finally, we have released the largest-ever catalog of Markov Chain Monte Carlo parameter estimates for microlensing events.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1991

Parallel computation of manipulator inverse dynamics

In this article, parallel computation of manipulator inverse dynamics is investigated. A hierarchical graph-based mapping approach is devised to analyze the inherent parallelism in the Newton-Euler formulation at several computational levels, and to derive the features of an abstract architecture for exploitation of parallelism. At each level, a parallel algorithm represents the application of a parallel model of computation that transforms the computation into a graph whose structure defines the features of an abstract architecture, i.e., number of processors, communication structure, etc. Data-flow analysis is employed to derive the time lower bound in the computation as well as the sequencing of the abstract architecture. The features of the target architecture are defined by optimization of the abstract architecture to exploit maximum parallelism while minimizing architectural complexity. An architecture is designed and implemented that is capable of efficient exploitation of parallelism at several computational levels. The computation time of the Newton-Euler formulation for a 6-degree-of-freedom (dof) general manipulator is measured as 187 microsec. The increase in computation time for each additional dof is 23 microsec, which leads to a computation time of less than 500 microsec, even for a 12-dof redundant arm.

Fijany, Amir↗
NASA NTRS2021

Accessible Telemetry Streams using a Zero Trust Architecture for the Flight Operations Directorate

As a result of information technology based work becoming increasingly distributed, unique challenges have been presented within the realm of defined network perimeters, namely with respect to secure access to resources. Historically, and from a simplistic abstract perspective, the common approach has been to adopt the, so-called, moat model whereby a physical network perimeter (or interconnected perimeters) is defined to encapsulate resources behind a boundary protected by a firewall. Users are provisioned access through a virtual private network (VPN) and may be further constrained to resources through specific firewall allow and disallow rulesets. Virtual Private Networks and firewall rulesets lead to common problems, particularly at scale and, as a result, perimeter-less architectures provided over the public internet are increasingly becoming prevalent, particularly with its more popular implementation, the Zero Trust Architecture. We present a proposed implementation of the Zero Trust Architecture with a particular concrete example utilizing a de-perimeterized network that requires authentication and authorization for each action between nodes and does not operate within an implicit trust boundary. It should be noted that this paper is not an attempt at providing comprehensive resolutions for the specific problem space with respect to perimeter based security and is more directed at providing information with regard to our proposed implementation of a Zero Trust Architecture for the Flight Operations Directorate. We direct the reader to our Introduction and Background section for more details on specific documentation and where it can be located as it relates to de-perimeterization and Zero Trust.

Paul Shoemaker↗
DOE OSTI2014

Anisotropic lattice thermal expansion of PbFeBO{sub 4}: A study by X-ray and neutron diffraction, Raman spectroscopy and DFT calculations

Highlights: • Mullite-type PbFeBO{sub 4} shows uni-axial negative coefficient of thermal expansion. • Anisotropic thermal expansion of the metric parameters was modeled using modified Grüneisen approximation. • The model includes harmonic, quasi-harmonic and intrinsic anharmonic contributions to the internal energy. • DFT calculation, temperature- and pressure-dependent Raman spectra help understand the phonon decay and associated anharmonicity. - Abstract: The lattice thermal expansion of mullite-type PbFeBO{sub 4} is presented in this study. The thermal expansion coefficients of the metric parameters were obtained from composite data collected from temperature-dependent neutron and X-ray powder diffraction between 10 K and 700 K. The volume thermal expansion was modeled using extended Grüneisen first-order approximation to the zero-pressure equation of state. The additive frame of the model includes harmonic, quasi-harmonic and intrinsic anharmonic potentials to describe the change of the internal energy as a function of temperature. The unit-cell volume at zero-pressure and 0 K was optimized during the DFT simulations. Harmonic frequencies of the optical Raman modes at the Γ-point of the Brillouin zone at 0 K were also calculated by DFT, which help to assign and crosscheck the experimental frequencies. The low-temperature Raman spectra showed significant anomaly in the antiferromagnetic regions, leading to softening or hardening of some phonons. Selected modes were analyzed using a modified Klemens model. The shift of the frequencies and the broadening of the line-widths helped to understand the anharmonic vibrational behaviors of the PbO{sub 4}, FeO{sub 6} and BO{sub 3} polyhedra as a function of temperature.

36 MATERIALS SCIENCE↗
NASA NTRSDate not supplied

Effects of Porous Gap Fillers on Leading-Edge Slat Noise of 30P30N. Part II: PIV Measurements

The leading edge slat of a high-lift system is one of the main contributors to the airframe noise during approach conditions. This paper, the second of two parts, continues our previous studies on the slat gap filler as a passive noise control device on the two-dimensional, 30P30N multielement airfoil. Whereas the earlier study was focused on the effects of an impermeable gap filler that completely blocks the flow through the gap, this follow-on assessment is devoted to permeable slat gap fillers that allow limited amounts of flow to pass through the gap. Part I of this two-part abstract described the aerodynamic and acoustic effects of the permeable gap fillers, as inferred from both the measurements of static and unsteady surface pressures and the microphone array data for the radiated noise. To understand the physical mechanism responsible for the noise reduction documented in Part I, as well as for the accompanying aerodynamic penalty due to the porous gap fillers, Particle Image Velocimetry (PIV) is used in this paper to measure the flow details in the slat-cove region of the 30P30N model. A single angle of attack (𝛼 = 5.5◦) and a chord based Reynolds number of 1.71𝑒6 are selected as the test conditions. The PIV results show that the slat flow features are significantly altered with the presence of the porous gap filler, resulting in a more stable slat-cove shear layer and, thus, reduced velocity fluctuations with a successive decrease in the permeability. The porous gap filler with the lowest permeability acts similar to the solid gap filler. However, flow separation is observed on the upper side of the porous interface, which leads to an aerodynamic performance penalty via a reduction in lift on the main wing.

slat noise↗
DOE OSTI2016

Compendium of photovoltaic degradation rates

Abstract Published data on photovoltaic (PV) degradation measurements were aggregated and re‐examined. The subject has seen an increased interest in recent years resulting in more than 11 000 degradation rates in almost 200 studies from 40 different countries. As studies have grown in number and size, we found an impact from sampling bias attributable to size and accuracy. Because of the correlational nature of this study we examined the data in several ways to minimize this bias. We found median degradation for x‐Si technologies in the 0.5–0.6%/year range with the mean in the 0.8–0.9%/year range. Hetero‐interface technology (HIT) and microcrystalline silicon (µc‐Si) technologies, although not as plentiful, exhibit degradation around 1%/year and resemble thin‐film products more closely than x‐Si. Several studies showing low degradation for copper indium gallium selenide (CIGS) have emerged. Higher degradation for cadmium telluride (CdTe) has been reported, but these findings could reflect a convolution of less accurate studies and longer stabilization periods for some products. Significant deviations for beginning‐of‐life measurements with respect to nameplate rating have been documented over the last 35 years. Therefore, degradation rates that use nameplate rating as reference may be significantly impacted. Studies that used nameplate rating as reference but used solar simulators showed less variation than similar studies using outdoor measurements, even when accounting for different climates. This could be associated with confounding effects of measurement uncertainty and soiling that take place outdoors. Hotter climates and mounting configurations that lead to sustained higher temperatures may lead to higher degradation in some, but not all, products. Wear‐out non‐linearities for the worst performing modules have been documented in a few select studies that took multiple measurements of an ensemble of modules during the lifetime of the system. However, the majority of these modules exhibit a fairly linear decline. Modeling these non‐linearities, whether they occur at the beginning‐of‐life or end‐of‐life in the PV life cycle, has an important impact on the levelized cost of energy. Copyright © 2016 John Wiley & Sons, Ltd.

Jordan, Dirk C.↗
DOE OSTI2018

Work Function Modification via Combined Charge-Based Through-Space Interaction and Surface Interaction

Work function modification of electrodes is an important factor to achieve high performance in organic electronics. However, a clear explanation of the origin of work function modification has remained elusive. Here, it is investigated how the work function of electrodes is affected by the charge-based through-space interaction with the well-known surface interaction. The studies reveal that the formation of a surface dipole leads to a work function shift, even when the work function modifying layer and substrate are separated. A work function shift is also demonstrated by electrophoretic deposition of ionic polyelectrolytes while the same polyelectrolytes do not cause any work function shift when they are spin cast. More noteworthy is that a neutral (nonionic) polymer which has no specific surface-interacting functional groups can induce work function shift of its substrate by a charge-based through-space interaction when deposited by electrospraying. These results provide a more comprehensive understanding of work function modification and motivate the design and selection of a wide range of effective work function modifying layers for organic electronics.

36 MATERIALS SCIENCE↗
DOE OSTI2016

CO 2 Hydrogenation over Oxide‐Supported PtCo Catalysts: The Role of the Oxide Support in Determining the Product Selectivity

Abstract By simply changing the oxide support, the selectivity of a metal–oxide catalysts can be tuned. For the CO 2 hydrogenation over PtCo bimetallic catalysts supported on different reducible oxides (CeO 2 , ZrO 2 , and TiO 2 ), replacing a TiO 2 support by CeO 2 or ZrO 2 selectively strengthens the binding of C,O‐bound and O‐bound species at the PtCo–oxide interface, leading to a different product selectivity. These results reveal mechanistic insights into how the catalytic performance of metal–oxide catalysts can be fine‐tuned.

Kattel, Shyam↗
DOE OSTI2022

A Metal‐Organic Framework (MOF)‐Based Multifunctional Cargo Vehicle for Reactive‐Gas Delivery and Catalysis

Abstract The efficient delivery of reactive and toxic gaseous reagents to organic reactions was studied using metal‐organic frameworks (MOFs). The simultaneous cargo vehicle and catalytic capabilities of several MOFs were probed for the first time using the examples of aromatization, aminocarbonylation, and carbonylative Suzuki–Miyaura coupling reactions. These reactions highlight that MOFs can serve a dual role as a gas cargo vehicle and a catalyst, leading to product formation with yields similar to reactions employing pure gases. Furthermore, the MOFs can be recycled without sacrificing product yield, while simultaneously maintaining crystallinity. The reported findings were supported crystallographically and spectroscopically (e.g., diffuse reflectance infrared Fourier transform spectroscopy), foreshadowing a pathway for the development of multifunctional MOF‐based reagent‐catalyst cargo vessels for reactive gas reagents as an attractive alternative to the use of toxic pure gases or gas generators.

Kittikhunnatham, Preecha↗
DOE OSTI2013

The Hydrological Impact of Geoengineering in the Geoengineering Model Intercomparison Project (GeoMIP)

Abstract: The hydrologic impact of enhancing Earth’s albedo due to solar radiation management (SRM) is investigated using simulations from 12 models contributing to the Geoengineering Model Intercomparison Project (GeoMIP). An artificial experiment is investigated, where global mean temperature is preserved at pre-industrial conditions, while atmospheric carbon dioxide concentrations are quadrupled. The associated reduction of downwelling surface solar radiation in a high CO2 environment leads to a reduction of global evaporation of 10% and 4% and precipitation of 6.1% and 6.3% over land and ocean, respectively. An initial reduction of latent heat flux at the surface is largely driven by reduced evapotranspiration over land with instantly increasing CO2 concentrations in both experiments. A warming surface associated with the transient adjustment in the 4xCO2 experiment further generates an increase of global precipitation, with considerable regional changes, such as a significant precipitation reduction of 7% for the North American summer monsoon. Reduced global precipitation persists in the geoengineered experiment where temperatures are stabilized, with considerable regional rainfall deficits. Precipitation reductions that are consistent in sign across models are identified in the geoengineered experiment over monsoonal land regions of East Asia (6%), North America (7%), South America (6%) and South Africa (5%). In contrast to the 4xCO2 experiment, where the frequency of months with heavy precipitation intensity is increased by over 50%, it is reduced by up to 20% in the geoengineering scenario . The reduction in heavy precipitation is more pronounced over land than over the ocean, and accompanies a stronger reduction in evaporation over land. For northern mid-latitudes, maximum precipitation reduction over land ranges from 1 to 16% for individual models. For 45-65°N, the frequency of median to high intensity precipitation in summer is strongly reduced. These changes in precipitation in both total amount and frequency of extremes, point to a considerable weakening of the hydrological cycle in a geoengineered world.

Earth's albedo↗
DOE OSTI2018

Improving Automation Transparency: Addressing Some of Machine Learning’s Unique Challenges

Abstract. A variety of factors can affect one’s reliance on an automated aid. Some of these factors include one’s per-ception of the system’s trustworthiness, such as perceived reliability of the system or one’s ability to understand the system’s underlying reasoning. A mismatch between the operator’s perception and the true capabilities and charac-teristics of the system can lead to inappropriate reliance on the tool. This improper use of the system can manifest as either underutilization of the technology or complacency resulting from over-trusting the system. Increasing an au-tomated tool’s transparency is one approach that enables the operator to more appropriately rely on the technology. Transparent automated systems provide additional infor-mation that allows the user to see the system’s intent and understand its underlying processes and capabilities. Sev-eral researchers have developed frameworks to support the design of more transparent automation. However, these frameworks may not fully consider the particular challeng-es to transparency design introduced by automation that leverages machine learning. Like all automation, these systems can benefit from transparency. However, artificial intelligence poses new challenges that must be considered when designing for transparency. Unique considerations must be made in terms of the type, and amount or level of transparency information conveyed to the user.

Transparency, Machine Learning, Automation↗
DOE OSTI2019

On the role of joint probability distributions of incompatible observables in Bell and Kochen–Specker Theorems

Highlights: •Bell and Kochen–Specker theorems rule out local or noncontextual realist models. •Still, they assume a joint probability distribution for incompatible observables. •Those joint probability distributions do not exist in quantum mechanics. •Realist models without joint distributions for incompatible observables are given. •A reformulation of Bell and Kochen–Specker arguments is provided to rule them out. -- Abstract: We analyze the validity of Bell and Kochen–Specker theorems under local (or noncontextual) realism but avoiding an assumption of the existence of a joint probability distribution for incompatible observables. We formulate a realist model which complies with this requirement. This is obtained by employing divergent sequences that nevertheless have marginals which are convergent. We find that under standard reasonable assumptions this possibility does not lead to a loophole of those theorems, by deriving a short of CHSH inequality valid for any finite size ensemble. Moreover, we analyze a Hardy’s paradox setting where noncontextual realism imposes the existence of joint probabilities for incompatible observables.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Mutational definition of binding requirements of an hnRNP-like protein in Arabidopsis using fluorescence correlation spectroscopy

Highlights: • We use FCS to investigate binding site requirements for the hnRNP-like protein AtGRP7. • We identify three nucleotides critical for AtGRP7 binding to its own intron. • Mutation of the conserved R{sup 49} abolishes binding altogether. • The paralogue AtGRP8 binds to an overlapping motif with different sequence requirement. • The glycine-rich stretch of a plant hnRNP-like protein contributes to binding. - Abstract: Arabidopsis thaliana glycine-rich RNA binding protein 7 (AtGRP7) is part of a negative feedback loop through which it regulates alternative splicing and steady-state abundance of its pre-mRNA. Here we use fluorescence correlation spectroscopy to investigate the requirements for AtGRP7 binding to its intron using fluorescently-labelled synthetic oligonucleotides. By systematically introducing point mutations we identify three nucleotides that lead to an increased K{sub d} value when mutated and thus are critical for AtGRP7 binding. Simultaneous mutation of all three residues abrogates binding. The paralogue AtGRP8 binds to an overlapping motif but with a different sequence preference, in line with overlapping but not identical functions of this protein pair. Truncation of the glycine-rich domain reduces the binding affinity of AtGRP7, showing for the first time that the glycine-rich stretch of a plant hnRNP-like protein contributes to binding. Mutation of the conserved R{sup 49} that is crucial for AtGRP7 function in pathogen defence and splicing abolishes binding.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2013

Lifting the geometric frustration through a monoclinic distortion in “114” YBaFe{sub 4}O{sub 7.0}: Magnetism and transport

The possibility to lift the geometric frustration in the “114” stoichiomeric tetragonal oxide YBaFe{sub 4}O{sub 7.0} by decreasing the temperature has been investigated using neutron and synchrotron powder diffraction techniques. Besides the structural transition from tetragonal to monoclinic symmetry that appears at T{sub S}=180 K, a magnetic transition is observed below T{sub N}=95 K. The latter corresponds to a lifting of the 3D geometric frustration toward an antiferromagnetic long range ordering, never observed to date in a cubic based “114’” oxide. The magnetic structure, characterized by the propagation vector k{sub 1}=(0,0,½), shows that one iron Fe2 exhibits a larger magnetic moment than the three others, suggesting a possible charge ordering according to the formula YBaFe{sup 3+}Fe{sub 3}{sup 2+}O{sub 7.0}. The magnetic M(T) and χ′(T) curves, in agreement with neutron data, confirm the structural and magnetic transitions and evidence the coexistence of residual magnetic frustration. Moreover, the transport measurements show a resistive transition from a thermally activated conduction mechanism to a variable range hopping mechanism at T{sub S}=180 K, with a significant increase of the dependence of the resistivity vs. temperature. Mössbauer spectroscopy clearly evidences a change in the electronic configuration of the iron framework at the structural transition as well as coexistence of several oxidation states. The role of barium underbonding in these transitions is discussed. - Graphical abstract: Atomic displacements at the tetragonal-monoclinic transition in YBaFe{sub 4}O{sub 7}. Display Omitted - Highlights: • The structural and magnetic phase transitions of YBaFe{sub 4}O{sub 7} were studied below room temperature. • The tetragonal to monoclinic transition, characterized by NPD and SXRD, was studied using mode crystallography approach. • Monoclinic distortion allows the lifting of the geometrical frustration on the iron sublattice, leading to AF order at T=95 K.

36 MATERIALS SCIENCE↗
DOE OSTI2018

N-doped CMK-3 anchored with SnS{sub 2} nanosheets as anode of lithium ion batteries with superior cyclic performance and enhanced reversible capacity

Highlights: • composites prepared by a facile hot bath method at low temperature display a high initial capacity and maintain excellent reversible capacity. - Abstract: The composites of N-doped ordered mesoporous carbon (N-CMK-3) anchored with tin disulfide (SnS{sub 2}) nanosheets (NSs) have been synthesized via a maneuverable hot bath method at low temperature. The as-synthesized SnS{sub 2}@N-CMK-3 composites exhibit a hierarchical structure with two dimensional (2D) SnS{sub 2} nanosheets uniformly grown on N-CMK-3, leading to a large specific area (126.7 m{sup 2} g{sup −1}) with mesoscale porosity. As anode material for lithium ion batteries (LIBs), SnS{sub 2}@N-CMK-3 composite exhibits a high initial capacity of 1438.9 mA h g{sup −1} (200 mA g{sup −1}). Moreover, the electrochemical performance remained at 618.9 mA h g{sup −1} after 200 cycles, which are significantly higher than that of the pristine SnS{sub 2}. The outstanding electrochemical properties might be due to the 2D nanosheet-morphology feature of SnS{sub 2} and the addition of N-CMK-3 that could availably inhibit the agglomeration of active substances and raise the conductivity of the composite electrode.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Hybrid polymer films based ZnS nanocomposites and its optical and morphological properties: Monitoring the role of the binding-site interaction

Highlights: • ZnS NPs were formed with adequate quantum confinement, leading to a blue shift. • The hybrid polymer films exhibited different optical behavior, which was attributed to the greater size of NPs. • The emission bands for the hybrid polymer films exhibited slight blue-shifts. • A slightly quenched emission band was observed after varying the length of the hydrophilic block. • AFM images also show changes in morphology, which may be attributed mainly to the hydrophilic domain. - Abstract: A series of hybrid polymer films were prepared using self-assembly block copolymers as nanoreactor of ZnS nanoparticles (NPs). The self-assembled poly(acrylic acid)-block-poly(N-phenylmaleimide) was prepared by Atom-Transfer Radical Polymerization (ATRP) in different block composition. Subsequently the fluorescent NPs were synthesized into the polymer matrices in order to modify its optical and thermal properties and to analyze its effect on the morphology properties (roughness and porosity). As results, significant effects on the properties of the hybrid materials were obtained under different percentages of the NPs. These materials exhibited blue- or red-shift emission bands depending on the length of hydrophilic domain. Additionally, a quenched emission band is seen, which may also be attributed primarily to the composition of the hydrophilic domain and to the greater percentage of ZnS NPs. The hybrid polymer films showed effects on the porosity and roughness of the surfaces, which was analyzed by AFM and SEM microscopic techniques.

77 NANOSCIENCE AND NANOTECHNOLOGY↗