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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 1,405 records · Page 78
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Overlap Preservation Using Loosely-Coupled Boundary Conditions for Body-Fitted Structured Overset Grids

Several improvements are made to overlap preservation in the automated approach to generating overset structured meshes. A loosely-coupled boundary condition (LCBC) is introduced to maintain optimal overlap for surface meshes generated from overlapping initial curves. Extension of the LCBC scheme to three-dimensional volume meshing is also presented. Test cases include various rotary wing vehicles from NASA’s Revolutionary Vertical Lift Technology (RVLT) project, and the wing-body geometry from the NASA Juncture Flow Experiment. Results demonstrate improvements in donor stencil quality from the enhanced overlap between neighboring surface and volume meshes.

TTT↗
DOE OSTI2017

Optical variability of AGNs in the PTF/iPTF survey

We characterize the optical variability of quasars in the Palomar Transient Factory and intermediate Palomar Transient Factory (PTF/iPTF) surveys. We re-calibrate the r-band light curves for ∼28,000 luminous, broad-line active galactic nuclei from the SDSS, producing a total of ∼2.4 million photometric data points. We utilize both the structure function (SF) and power spectrum density (PSD) formalisms to search for links between the optical variability and the physical parameters of the accreting supermassive black holes that power the quasars. The excess variance (SF{sup 2}) of the quasar sample tends to zero at very short time separations, validating our re-calibration of the time-series data. We find that the the amplitude of variability at a given time-interval, or equivalently the timescale of variability to reach a certain amplitude, is most strongly correlated with luminosity with weak or no dependence on black hole mass and redshift. For a variability level of SF(τ) = 0.07 mag, the timescale has a dependency of τ∝L{sup 0.4}. This is broadly consistent with the expectation from a simple Keplerian accretion disk model, which provides τ∝L{sup 0.5}. The PSD analysis also reveals that many quasar light curves are steeper than a damped random walk. We find a correlation between the steepness of the PSD slopes, specifically the fraction of slopes steeper than 2.5, and black hole mass, although we cannot exclude the possibility that luminosity or Eddington ratio are the drivers of this effect. This effect is also seen in the SF analysis of the (i)PTF data, and in a PSD analysis of quasars in the SDSS Stripe 82.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Elastic, magnetic, and magnetoelectric properties of the CaBaCo{sub 4}O{sub 7} multiferroic

The structural, elastic, magnetic, and magnetoelectric properties of the CaBaCo{sub 4}O{sub 7} multiferroic are experimentally studied and compared with the properties of the related YBaCo{sub 4}O{sub 7} cobaltite, where Y{sup 3+} ions substitute for Ca{sup 2+} ions. Unlike the frustrated YBaCo{sub 4}O{sub 7} magnet, the softening of Young’s modulus and the hysteresis in the ΔE(T)/E{sub 0} curve of ferrimagnetic CaBaCo{sub 4}O{sub 7} in the paramagnetic region are weak, and the anomaly during the magnetic transition increases by almost an order of magnitude. This difference can point to different characters of the development of a long-range magnetic order in these two cobaltites. The distortion of the crystal structure that removes the frustrations of exchange interactions is found to correlate with the magnetic behavior of the cobaltites under study. The magnetization curves of the Ca cobaltite have two steps below 15 K, which can point to the presence of a metastable state in a high magnetic field. The study of the longitudinal and transverse magnetoelectric effects in a pulsed magnetic field demonstrates that their magnitudes are maximal near T{sub C} and change their character from linear to quadratic during passage through this temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

BECN2 interacts with ATG14 through a metastable coiled-coil to mediate autophagy: BECN2 CCD Structure and Interaction with ATG14

ATG14 binding to BECN/Beclin homologs is essential for autophagy, a critical catabolic homeostasis pathway. Here, we show that the α-helical, coiled-coil domain (CCD) of BECN2, a recently identified mammalian BECN1 paralog, forms an antiparallel, curved homodimer with seven pairs of nonideal packing interactions, while the BECN2 CCD and ATG14 CCD form a parallel, curved heterodimer stabilized by multiple, conserved polar interactions. Compared to BECN1, the BECN2 CCD forms a weaker homodimer, but binds more tightly to the ATG14 CCD. Mutation of nonideal BECN2 interface residues to more ideal pairs improves homodimer self-association and thermal stability. Unlike BECN1, all BECN2 CCD mutants bind ATG14, although more weakly than wild type. Thus, polar BECN2 CCD interface residues result in a metastable homodimer, facilitating dissociation, but enable better interactions with polar ATG14 residues stabilizing the BECN2:ATG14 heterodimer. These structure-based mechanistic differences in BECN1 and BECN2 homodimerization and heterodimerization likely dictate competitive ATG14 recruitment.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Prediction of novel phase of silicon and Si–Ge alloys

The structural, thermodynamic, elastic, anisotropic and electronic properties of P222{sub 1}-Si have been studied using first-principles calculations. The elastic constants are satisfied with mechanical stability criteria. The mechanical anisotropy is predicted by anisotropic constants Poisson's ratio, shear modulus, Young's modulus and three dimensional curved surface of Young's modulus. These results show that P222{sub 1}-Si and Si–Ge alloys are anisotropic. The sound velocities in different directions and Debye temperature for P222{sub 1}-Si and Si–Ge alloys are also predicted. Electronic structure study shows that P222{sub 1}-Si is an indirect semiconductor with band gap of 0.90 eV. In addition, the band structures of Si–Ge alloys are investigated in this paper. Finally, we also calculate the thermodynamics properties and obtained the relationships between thermal parameters and temperature. - Graphical abstract: Crystal structure and band structure of P222{sub 1}-Si. - Highlights: • A novel P222{sub 1} phase of Si and Si–Ge alloys are proposed. • The mechanical, electronic, and thermodynamic properties of P222{sub 1}-Si are calculated. • The anisotropy of mechanical properties of P222{sub 1}-Si and Si–Ge alloys are discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

A Reduced Order Model of Force Displacement Curves for the Failure of Mechanical Bolts in Tension.

Assembled mechanical systems often contain a large number of bolted connections. These bolted connections (joints) are integral aspects of the load path for structural dynamics, and, consequently, are paramount for calculating a structure's stiffness and energy dissipation prop- erties. However, analysts have not found the optimal method to model appropriately these bolted joints. The complexity of the screw geometry causes issues when generating a mesh of the model. This report will explore different approaches to model a screw-substrate connec- tion. Model parameters such as mesh continuity, node alignment, wedge angles, and thread to body element size ratios are examined. The results of this study will give analysts a better understanding of the influences of these parameters and will aide in finding the optimal method to model bolted connections.

42 ENGINEERING↗
NASA NTRS1957

Handbook of structural stability part IV : failure of plates and composite elements

Available theories on failure of flat plates are reviewed, and test data on the postbuckling behavior, effective width, and failure of flat curved plates are correlated. Test data on the crippling strength of various formed and extruded shapes are reviewed, from which a generalized method of crippling analysis is formulated. This analysis is then applied to a variety of sections and materials in common use.

Gerard, George↗
DOE OSTI2022

Impacts of Dissolved Ni 2+ on the Solid Electrolyte Interphase on a Graphite Anode

Transition metal (e.g. Ni) ions dissolved from layered-structured Ni-rich cathodes can migrate to the anode side and accelerate the failure of lithium-ion batteries. The investigations of the impact and distribution of Ni species on the solid electrolyte interphase (SEI) on the anode are crucial to understand the failure mechanism. Herein, we used time-of-flight secondary ion mass spectroscopy (TOF-SIMS) coupled with multivariate curve resolution (MCR) analysis to intuitively characterize the distribution of Ni species in the SEI. We find that the SEI on the graphite electrode using an EC-based electrolyte exhibits a multi-stratum structure. During accelerated aging of the LiNi 0.88 Co 0.08 Mn 0.04 O 2 /graphite full cell, the dissolution of Ni aggravates significantly upon cycling. A strong correlation between the dissolved-Ni and organic species in the SEI on graphite is illustrated. Here, the ion-exchange reaction between Ni 2+ and Li + ions in the SEI is demonstrated to be the main reason for the increase of SEI resistivity.

25 ENERGY STORAGE↗
DOE OSTI2015

Using learning curves on energy-efficient technologies to estimate future energy savings and emission reduction potentials in the U.S. iron and steel industry

Increasing concerns on non-sustainable energy use and climate change spur a growing research interest in energy efficiency potentials in various critical areas such as industrial production. This paper focuses on learning curve aspects of energy efficiency measures in the U.S iron and steel sector. A number of early-stage efficient technologies (i.e., emerging or demonstration technologies) are technically feasible and have the potential to make a significant contribution to energy saving and CO 2 emissions reduction, but fall short economically to be included. However, they may also have the cost effective potential for significant cost reduction and/or performance improvement in the future under learning effects such as ‘learning-by-doing’. The investigation is carried out using ISEEM, a technology oriented, linear optimization model. We investigated how steel demand is balanced with/without the availability learning curve, compared to a Reference scenario. The retrofit (or investment in some cases) costs of energy efficient technologies decline in the scenario where learning curve is applied. The analysis also addresses market penetration of energy efficient technologies, energy saving, and CO 2 emissions in the U.S. iron and steel sector with/without learning impact. Accordingly, the study helps those who use energy models better manage the price barriers preventing unrealistic diffusion of energy-efficiency technologies, better understand the market and learning system involved, predict future achievable learning rates more accurately, and project future savings via energy-efficiency technologies with presence of learning. We conclude from our analysis that, most of the existing energy efficiency technologies that are currently used in the U.S. iron and steel sector are cost effective. Penetration levels increases through the years, even though there is no price reduction. However, demonstration technologies are not economically feasible in the U.S. iron and steel sector with the current cost structure. In contrast, some of the demonstration technologies are adapted in the mid-term and their penetration levels increase as the prices go down with learning curve. We also observe large penetration of 225kg pulverized coal injection with the presence of learning.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
NASA NTRS2018

Probabilistic Sensitivity Analyses Incorporating Surrogate Models for the Structural Response of a Representative Inflatable Space Structure

This study concentrates on results from probabilistic analysis and numerical simulation tools to identify parameter sensitivities and assess surrogate model suitability for a novel inflatable airlock concept, specifically the Non-Axisymmetric Inflatable Pressure Structure (NAIPS) under NASA's Minimalistic Advanced Softgoods Hatch (MASH) Program. The current studies extended the demonstration of probabilistic analysis tools to identify parameter sensitivities by: incorporating nonlinear material load-strain property curves and orthotropic representation of the fabric; and exploring the use of surrogate models to facilitate rapid evaluations as new information becomes available, as well as enable optimizations. The airlock model has been simplified to focus on the end dome section. Brief overviews of the finite element model and associated surrogate models are provided along with the probabilistic sensitivity analysis approaches. Responses of interest include the sensitivities of various loads in the structural elements of the NAIPS to material properties, cord lengths, inflation pressure and friction between softgoods components. The use of surrogate models was explored to facilitate rapid sensitivity evaluations as parameter ranges change. The completion of the sensitivity studies improved understanding of the dependence of load responses to several uncertain parameters and confidence in the ability to use surrogate models to represent the finite element simulations.

Lyle, Karen H.↗
DOE OSTI2015

Electron percolation in realistic models of carbon nanotube networks

The influence of penetrable and curved carbon nanotubes (CNT) on the charge percolation in three-dimensional disordered CNT networks have been studied with Monte-Carlo simulations. By considering carbon nanotubes as solid objects but where the overlap between their electron cloud can be controlled, we observed that the structural characteristics of networks containing lower aspect ratio CNT are highly sensitive to the degree of penetration between crossed nanotubes. Following our efficient strategy to displace CNT to different positions to create more realistic statistical models, we conclude that the connectivity between objects increases with the hard-core/soft-shell radii ratio. In contrast, the presence of curved CNT in the random networks leads to an increasing percolation threshold and to a decreasing electrical conductivity at saturation. The waviness of CNT decreases the effective distance between the nanotube extremities, hence reducing their connectivity and degrading their electrical properties. We present the results of our simulation in terms of thickness of the CNT network from which simple structural parameters such as the volume fraction or the carbon nanotube density can be accurately evaluated with our more realistic models.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Assessing electronic structure approaches for gas-ligand interactions in metal-organic frameworks: The CO{sub 2}-benzene complex

Adsorption of gas molecules in metal-organic frameworks is governed by many factors, the most dominant of which are the interaction of the gas with open metal sites, and the interaction of the gas with the ligands. Herein, we examine the latter class of interaction in the context of CO{sub 2} binding to benzene. We begin by clarifying the geometry of the CO{sub 2}–benzene complex. We then generate a benchmark binding curve using a coupled-cluster approach with single, double, and perturbative triple excitations [CCSD(T)] at the complete basis set (CBS) limit. Against this ΔCCSD(T)/CBS standard, we evaluate a plethora of electronic structure approximations: Hartree-Fock, second-order Møller-Plesset perturbation theory (MP2) with the resolution-of-the-identity approximation, attenuated MP2, and a number of density functionals with and without different empirical and nonempirical van der Waals corrections. We find that finite-basis MP2 significantly overbinds the complex. On the other hand, even the simplest empirical correction to standard density functionals is sufficient to bring the binding energies to well within 1 kJ/mol of the benchmark, corresponding to an error of less than 10%; PBE-D in particular performs well. Methods that explicitly include nonlocal correlation kernels, such as VV10, vdW-DF2, and ωB97X-V, perform with similar accuracy for this system, as do ωB97X and M06-L.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Effect of Backbone Chemistry on the Structure of Polyurea Films Deposited by Molecular Layer Deposition

An experimental investigation into the growth of polyurea films by molecular layer deposition was performed by examining trends in the growth rate, crystallinity, and orientation of chains as a function of backbone flexibility. Growth curves obtained for films containing backbones of aliphatic and phenyl groups indicate that an increase in backbone flexibility leads to a reduction in growth rate from 4 to 1 Å/cycle. Crystallinity measurements collected using grazing incidence X-ray diffraction and Fourier transform infrared spectroscopy suggest that some chains form paracrystalline, out-of-plane stacks of polymer segments with packing distances ranging from 4.4 to 3.7 Å depending on the monomer size. Diffraction intensity is largely a function of the homogeneity of the backbone. Near-edge X-ray absorption fine structure measurements for thin and thick samples show an average chain orientation of ~25° relative to the substrate across all samples, suggesting that changes in growth rate are not caused by differences in chain angle but instead may be caused by differences in the frequency of chain terminations. In conclusion, these results suggest a model of molecular layer deposition-based chain growth in which films consist of a mixture of upward growing chains and horizontally aligned layers of paracrystalline polymer segments.

36 MATERIALS SCIENCE↗
NASA NTRS1989

Acoustic radiation from a shell with internal structures

A method is developed to compute frequency response and acoustic radiation of a complex shell. The axisymmetric geometry of the shell includes cylindrical, conical, and spherical segments stiffened by discrete rings and bulkheads. The shell is coupled to internal masses and elastic frames. Shell segments are treated by transfer matrices. Rings, bulkheads, frames, and concentrated masses are treated by impedances at junctions of segments. The shell is coupled to an external acoustic fluid treated by Green's function and curved surface elements. A major issue facing the method's treatment of the fluid would be lack of existence or uniqueness encountered in the uncoupled, external acoustic problem at characteristic wavenumbers. By using a simple spherical shell, without internal structures, this potential hindrance is shown not to arise. A fuller application of the method awaits subsequent results.

El-Raheb, M.↗
DOE OSTI2016

H-terminated diamond field effect transistor with ferroelectric gate insulator

An H-terminated diamond field-effect-transistor (FET) with a ferroelectric vinylidene fluoride (VDF)-trifluoroethylene (TrFE) copolymer gate insulator was fabricated. The VDF-TrFE film was deposited on the H-terminated diamond by the spin-coating method and low-temperature annealing was performed to suppress processing damage to the H-terminated diamond surface channel layer. The fabricated FET structure showed the typical properties of depletion-type p-channel FET and showed clear saturation of the drain current with a maximum value of 50 mA/mm. The drain current versus gate voltage curves of the proposed FET showed clockwise hysteresis loops due to the ferroelectricity of the VDF-TrFE gate insulator, and the memory window width was 19 V, when the gate voltage was swept from 20 to −20 V. The maximum on/off current ratio and the linear mobility were 10{sup 8} and 398 cm{sup 2}/V s, respectively. In addition, we modulated the drain current of the fabricated FET structure via the remnant polarization of the VDF-TrFE gate and obtained an on/off current ratio of 10{sup 3} without applying a DC gate voltage.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Comparative Study of Nano- and Bulk La{sub 0.5}Sr{sub 0.5}Ti{sub 0.5}Co{sub 0.5}O{sub 3} Perovskite: Structural, Magnetic, and Transport Properties

In this paper, we report a detailed study of the structural, magnetic, and electrical transport properties of nano- and bulk La{sub 0.5}Sr{sub 0.5}Ti{sub 0.5}Co{sub 0.5}O{sub 3} perovskite with the aim to study the effect of size reduction on resistivity and the antiferromagnetic spin order that is seen in the bulk samples of the cobaltites. Both the phases crystallize with orthorhombic structure in the Pbnm space group. Size reduction causes an increase in both the lattice parameters and unit cell volume. The M–H curve of nanosample shows appearance of hysteresis and gives a clear evidence of the formation of ferromagnetic (FM) moments while almost no RT-FM behavior was found for bulk sample. The resistivity of the nanocrystalline sample has been found to be much lower than that of the bulk sample in the entire temperature range of investigation which could be due to the formation of ferromagnetic moments in the nanocrystallites.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Dosimetry of an In-Line Kilovoltage Imaging System and Implementation in Treatment Planning

Purpose: To present the beam properties of the Siemens 70-kV and 121-kV linear accelerator-mounted imaging modalities and commissioning of the 121-kV beam in the Philips Pinnacle treatment planning system (TPS); measurements in an Alderson phantom were performed for verification of the model and to estimate the cone-beam CT (CBCT) imaging dose in the head and neck, thorax, and pelvis. Methods and Materials: The beam profiles and depth–dose curve were measured in an acrylic phantom using thermoluminescent dosimeters and a soft x-ray ionization chamber. Measurements were imported into the TPS, modeled, and verified by phantom measurements. Results: Modeling of the profiles and the depth–dose curve can be achieved with good quality. Comparison with the measurements in the Alderson phantom is generally good; only very close to bony structures is the dose underestimated by the TPS. For a 200° arc CBCT of the head and neck, a maximum dose of 7 mGy is measured; the thorax and pelvis 360° CBCTs give doses of 4-10 mGy and 7-15 mGy, respectively. Conclusions: Dosimetric characteristics of the Siemens kVision imaging modalities are presented and modeled in the Pinnacle TPS. Thermoluminescent dosimeter measurements in the Alderson phantom agree well with the calculated TPS dose, validating the model and providing an estimate of the imaging dose for different protocols.

62 RADIOLOGY AND NUCLEAR MEDICINE↗