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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 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Highly uniform distribution of Pt nanoparticles on N-doped hollow carbon spheres with enhanced durability for oxygen reduction reaction

Here, carbon-supported Pt nanostructures currently exhibited great potential in polymer electrolyte membrane fuel cells. Nitrogen-doped hollow carbon spheres (NHCSs) with extra low density and high specific surface area are promising carbon support for loading Pt NPs. The doped heteroatom of nitrogen could not only contribute to the active activity for the oxygen reduction reaction (ORR), but also shows a strong interaction with Pt NPs for entrapping them from dissolution/migration. This synergetic effect/interaction resulted in the uniform dispersion and strong combination of the Pt NPs on the carbon support and thus play a significant role in hindering the degradation of the catalytic activities of Pt NPs. As expected, the as-obtained Pt/NHCSs displayed improved catalytic activity and superior durability toward ORR.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Intrinsic nonlinearities in the mechanics of hard sphere suspensions

The onset of nonlinear responses in near hard sphere suspensions is characterized as a function of oscillatory frequency and strain amplitude. At low frequencies where the viscous behavior dominates, the onset of nonlinearities is driven by increases in rate of strain. At high deformation frequency, where suspension mechanics is dominated by an elastic response, the nonlinear responses occur when deformation exceeds a characteristic strain. This strain is associated with the transient confinement of particles by nearest neighbors and its volume fraction dependence is through cage parameters derived from the high frequency elastic modulus. Furthermore, the onset of nonlinear responses takes on a universal behavior when deformation frequency is normalized by the characteristic time governing the shift from viscous to elastic behavior indicating that this transition is associated with transient particle localization and is expected to be observed for all volume fractions where pair interactions are important.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Cobalt oxide-coated N- and B-doped graphene hollow spheres as bifunctional electrocatalysts for oxygen reduction and oxygen evolution reactions

Here, a simple and scalable method has been developed for the synthesis of Co 3 O 4 -coated N- and B-doped graphene hollow spheres (Co 3 O 4 /NBGHSs). These Co 3 O 4 /NBGHSs are highly active for both oxygen reduction and evolution reactions and can exhibit higher electrocatalytic activities and better durability than commercial Pt/C and RuO 2 /C, respectively, demonstrating them to be efficient bi-functional electrocatalysts. In-depth analysis shows that the coupling between Co 3 O 4 and NBGHSs, strong interaction with adsorbed O 2 , high electric conductivity, and the specific hollow structure play important roles in imparting the higher electrocatalytic activities to the Co 3 O 4 /NBGHSs. When tested as cathode catalysts for Zn–air batteries, the Co 3 O 4 /NBGHSs exhibit better performance and higher stability than the Pt/C catalyst and other catalysts reported previously. Lastly, this strongly suggests that the Co 3 O 4 /NBGHSs could be used as efficient electrocatalysts for metal–air batteries with great potential to replace precious metal/carbon based materials.

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

Inner versus Outer Sphere Metal-Monoamide Complexation: Ramifications for Tetravalent & Hexavalent Actinide Selectivity

Extraction of tetravalent and hexavalent plutonium by straight and branched chained monoamides was studied using UV-Vis spectroscopy. It was determined that predominantly anionic, outer sphere species are, formed, in all instances instead of Pu4+ recovery by acyl branched monoamides. Distribution values calculated from UV-Vis analysis were compared to tracer level LSC measurements, and were found to agree. Distribution values of hexavalent Am were also assessed. Good distribution values were achieved with straight monoamides and bis-2-ethyl hexyl phosphoric acid.

actinide separation, amide extractant↗
DOE OSTI2018

Calculation of critical nucleation rates by the persistent embryo method: application to quasi hard sphere models

Here, we study the crystal nucleation of the Weeks–Chandler–Andersen (WCA) model, using the recently introduced persistent embryo method (PEM). The method provides detailed characterization of pre-critical, critical and post-critical nuclei, as well as nucleation rates that compare favorably with those obtained using other methods (umbrella sampling, forward flux sampling or seeding). We further map our results to a hard sphere model allowing comparison with other existing predictions. Implications for experiments are also discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Effects of strain-dependent surface stress on the adhesive contact of a rigid sphere to a compliant substrate

Recent experiments have reported that the surface stress of soft elastic solids can increase rapidly with surface strain. For example, when a small hard sphere in adhesive contact with a soft silicone gel is slowly retracted from its rest position, it was found that the retraction force versus displacement relation cannot be explained either by the Johnson–Kendall–Roberts (JKR) theory or a recent indentation theory based on an isotropic surface stress that is independent of surface strain. In this paper, we address this problem using a finite element method to simulate the retraction process. Our numerical model does not have the restrictions of the aforementioned theories; that is, it can handle large nonlinear elastic deformation as well as a surface-strain-dependent surface stress. Our simulation is in good agreement with experimental force versus displacement data with no fitting parameters. Therefore, our results lend further support to the claim that significant strain-dependent surface stresses can occur in simple soft elastic gels. However, significant challenges remain in the reconciliation of theory and experiments, particularly regarding the geometry of the contact and substrate deformation.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Designing nanoparticle interfaces for inner-sphere catalysis

Interfaces are an intrinsic component of nanoparticle catalysts and play a critical role in directing their function. Our understanding of the complexity of the nanoparticle interface and how to manipulate it at the molecular level has advanced significantly in recent years. Given this, attention is shifting towards the creation of designer nanoparticle interfaces that impact the activity and direct the mechanisms of inner-sphere catalytic reactions. In this perspective, we seek to highlight and contextualize these efforts. First, methods to alter nanoparticle surfaces are presented, including annealing and plasma treating, as well as more mild chemical treatments, including ligand exchange, etching, and addition (via covalent functionalization). Then interfacial chemistry developed to alter catalytic activity, selectivity, and reaction environment will be highlighted. Finally, we look forward to the challenges that remain to be overcome for realizing the true potential of colloidal nanoparticle catalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Design of a multi-functional gel polymer electrolyte with a 3D compact stacked polymer micro-sphere matrix for high-performance lithium metal batteries

We report lithium metal batteries (LMBs) are considered as promising high energy density batteries. However, they still suffer from poor cyclability due to the instability of solid electrolyte interphases (SEIs) and Li dendrite issues. Herein, a novel 3D densely packed multifunctional crosslinked gel polymer electrolyte (PHGPE) has been synthesized by in situ copolymerization of pentaerythritol tetraacrylate and 2-hydroxyethyl acrylate in a liquid electrolyte via a thermal initiation method. Due to intermolecular hydrogen bonding in the frameworks, the PHGPE exhibits a 3D compact-stacked and crosslinked micro-sphere structure, which benefits the construction of homogeneous Li + flux, enabling uniform Li plating/stripping and formation of robust SEIs onto the lithium electrode. Benefiting from the above advantages, symmetric Li cells in the PHGPE deliver excellent cyclabilities of 6000 h at a current density of 1 mA cm -2 (1 mA h cm -2 ) and 7700 h at 0.5 mA cm -2 (2 mA h cm -2 ). Moreover, the PHGPE has such a wide electrochemical window that it is compatible with both high-voltage LiNi 0.8 Co 0.1 Mn 0.1 O 2 and sulfur cathodes to realize long cycle life. Additionally, a LiFePO 4 based pouch size LMB also presents promising performance. Therefore, this study of the PHGPE has opened a new avenue for high-performance LMBs with excellent versatility and practicality.

25 ENERGY STORAGE↗
DOE OSTI2012

SPHERES, Juelich's high-flux neutron backscattering spectrometer at FRM II

SPHERES is a third-generation neutron backscattering spectrometer, located at the 20 MW German neutron source FRM II and operated by the Juelich Centre for Neutron Science. It offers an energy resolution (fwhm) better than 0.65 {mu}eV, a dynamic range of {+-} 31 {mu}eV, and a signal-to-noise ratio of up to 1750:1.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Equations of motion solved by the Cremmer-Scherk configuration on even-dimensional spheres

Equations of motion of low-energy effective theories of quantum electrodynamics include infinitely many interaction terms, which make them difficult to solve. The self-duality property has facilitated research on the solutions to these equations. In this paper, equations of motion of systems of non-Abelian gauge fields on even-dimensional spheres are considered. It is demonstrated that the Cremmer-Scherk configuration, which satisfies certain generalized self-duality equations, becomes the classical solution for the class of systems that are given by arbitrary functions of class C{sup 1} of 2m+ 1 quantities. For instance, Lagrangians consisting of multi-trace terms are included in this class. This result is likely to generate several new and interesting directions of research, including the classification of actions with respect to the stability condition against the Cremmer-Scherk configuration.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Simulation-guided optimization of small-angle analyzer geometry in the neutron backscattering spectrometer SPHERES

The resolution of neutron backscattering spectrometers deteriorates at small scattering angles where analyzers deviate from exact backscattering. By reducing the azimuth angle range of the analyzers, the resolution can be improved with little loss of peak intensity. Measurements at the spectrometer SPHERES are in excellent agreement with simulations, which proves the dominance of geometric effects.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Numerical method for computing Maass cusp forms on triply punctured two-sphere

A quantum mechanical system on a punctured surface modeled on hyperbolic space has always been an important subject of research in mathematics and physics. This corresponding quantum system is governed by the Schrödinger equation whose solutions are the Maass waveforms. Spectral studies on these Maass waveforms are known to contain both continuous and discrete eigenvalues. The discrete eigenfunctions are usually called the Maass Cusp Forms (MCF) where their discrete eigenvalues are not known analytically. We introduce a numerical method based on Hejhal and Then algorithm using GridMathematica for computing MCF on a punctured surface with three cusps namely the triply punctured two-sphere. We also report on a pullback algorithm for the punctured surface and a point locater algorithm to facilitate the complete pullback which are essential parts of the main algorithm.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2014

Elastically Cooperative Activated Hopping Theory of Relaxation in Viscous Liquids. I. General Formulation and Application to Hard Sphere Fluids.

We generalize the force-level nonlinear Langevin equation theory of single particle hopping to includecollective effects associated with long range elastic distortion of the liquid. The activated alpharelaxation event is of a mixed spatial character, involving two distinct, but inter-related, local and collectivebarriers. There are no divergences at volume fractions below jamming or temperatures abovezero Kelvin. The ideas are first developed and implemented analytically and numerically in the contextof hard sphere fluids. In an intermediate volume fraction crossover regime, the local cage processis dominant in a manner consistent with an apparent Arrhenius behavior. The super-Arrhenius collectivebarrier is more strongly dependent on volume fraction, dominates the highly viscous regime,and is well described by a nonsingular law below jamming. The increase of the collective barrieris determined by the amplitude of thermal density fluctuations, dynamic shear modulus or transientlocalization length, and a growing microscopic jump length. Alpha relaxation time calculations arein good agreement with recent experiments and simulations on dense fluids and suspensions of hardspheres. Comparisons of the theory with elastic models and entropy crisis ideas are explored. Thepresent work provides a foundation for constructing a quasi-universal, fit-parameter-free theory forrelaxation in thermal molecular liquids over 14 orders of magnitude in time.

Mirigian, Stephen↗
DOE OSTI2014

Realization of polarization evolution on higher-order Poincaré sphere with metasurface

We present a simple and convenient method to yield cylindrical vector (CV) beams and realize its polarization evolution on higher-order Poincaré sphere based on inhomogeneous birefringent metasurface. By means of local polarization transformation of the metasurface, it is possible to convert a light beam with homogeneous elliptical polarization into a vector beam with any desired polarization distribution. The Stokes parameters of the output light are measured to verify our scheme, which show well agreement with the theoretical prediction. Our method may provide a convenient way to generate CV beams, which is expected to have potential applications in encoding information and quantum computation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗