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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Shear Thickening and Jamming of Dense Suspensions: The "Roll" of Friction.

Particle-based simulations of discontinuous shear thickening (DST) and shear jamming (SJ) suspensions are used to study the role of stress-activated constraints, with an emphasis on resistance to gearlike rolling. Rolling friction decreases the volume fraction required for DST and SJ, in quantitative agreement with real-life suspensions with adhesive surface chemistries and "rough" particle shapes. It sets a distinct structure of the frictional force network compared to only sliding friction, and from a dynamical perspective leads to an increase in the velocity correlation length, in part responsible for the increased viscosity. The physics of rolling friction is thus a key element in achieving a comprehensive understanding of strongly shear-thickening materials.

Singh, Abhinendra↗
DOE OSTI2025

Emergence of Intermediate Range Order in Jammed Packings

We perform a structural analysis of large scale jammed packings of monodisperse, frictionless and frictional spheres to elucidate structural signatures of the static structure factor in the low-to-intermediate wave number region. We employ discrete element method simulations containing up to 8×10^{7} particles, in which the particle friction coefficient(s), including sliding, rolling, and twisting interactions, are varied. At intermediate wave number values, corresponding to length scales that lie between that of the nearest neighbor primary peak and the system size, we find the emergence of a prepeak-a signature of intermediate range order-that grows with increasing friction. We correlate the emergence of this peak to real space fluctuations in the local particle coordination number, which exhibits a grainy fluctuating field throughout the packing process that is retained in the final, mechanically stable state. While the formation of the prepeak shows varying degrees of robustness to packing protocol changes, our results suggest that preparation history may be used to construct packings with variable large length scale structural properties.

Monti, Joseph M↗
DOE OSTI2018

Guiding kinetic trajectories between jammed and unjammed states in 2D colloidal nanocrystal-polymer assemblies with zwitterionic ligands

Mesostructured matter composed of colloidal nanocrystals in solidified architectures abounds with broadly tunable catalytic, magnetic, optoelectronic, and energy storing properties. Less common are liquid-like assemblies of colloidal nanocrystals in a condensed phase, which may have different energy transduction behaviors owing to their dynamic character. Limiting investigations into dynamic colloidal nanocrystal architectures is the lack of schemes to control or redirect the tendency of the system to solidify. We show how to solidify and subsequently reconfigure colloidal nanocrystal assemblies dimensionally confined to a liquid-liquid interface. Our success in this regard hinged on the development of competitive chemistries anchoring or releasing the nanocrystals to or from the interface. With these chemistries, it was possible to control the kinetic trajectory between quasi–two-dimensional jammed (solid-like) and unjammed (liquid-like) states. In future schemes, it may be possible to leverage this control to direct the formation or destruction of explicit physical pathways for energy carriers to migrate in the system in response to an external field.

36 MATERIALS SCIENCE↗
NASA NTRS1981

Coherent detection of frequency-hopped quadrature modulations in the presence of jamming. I - QPSK and QASK modulations

This paper examines the performance of coherent QPSK and QASK systems combined with FH or FH/PN spread spectrum techniques in the presence of partial-band multitone or noise jamming. The worst-case jammer and worst-case performance are determined as functions of the signal-to-background noise ratio (SNR) and signal-to-jammer power ratio (SJR). Asymptotic results for high SNR are shown to have a linear dependence between the jammer's optimal power allocation and the system error probability performance.

Simon, M. K.↗
NASA NTRS1981

Coherent detection of frequency-hopped quadrature modulations in the presence of jamming. II - QPR Class I modulation

This paper considers the performance of quadrature partial response (QPR) in the presence of jamming. Although a QPR system employs a single sample detector in its receiver, while quadrature amplitude shift keying (or quadrature phase shift keying) requires a matched-filter type of receiver, it is shown that the coherent detection performances of the two in the presence of the intentional jammer have definite similarities.

Simon, M. K.↗
NASA NTRS1985

Stepped-Pin Clevis Resists Jamming

Pin modification allows pyrotechnic release devices to operate more smoothly. New clevis pin has stepped diameters to prevent bending as it exits yoke. In contrast, conventional unstepped clevis pin bends and jams as it is withdrawn. Stepped pin design suitable for explosive and possible hammer driven pin sullers.

Killgrove, T. O.↗
NASA NTRS1985

Performance of a normalized energy metric without jammer state information for an FH/MFSK system in worst case partial band jamming

For a frequency-hopped noncoherent MFSK communication system without jammer state information (JSI) in a worst case partial band jamming environment, it is well known that the use of a conventional unquantized metric results in very poor performance. In this paper, a 'normalized' unquantized energy metric is suggested for such a system. It is shown that with this metric, one can save 2-3 dB in required signal energy over the system with hard decision metric without JSI for the same desired performance. When this very robust metric is compared to the conventional unquantized energy metric with JSI, the loss in required signal energy is shown to be small. Thus, the use of this normalized metric provides performance comparable to systems for which JSI is known. Cutoff rate and bit error rate with dual-k coding are used for the performance measures.

Lee, P. J.↗
DOE OSTI2018

Stabilizing liquid drops of arbitrary shape by the interfacial jamming of nanoparticles

A stabilized assembly including a first liquid phase of non-spherical droplets in a second liquid phase, wherein the second liquid phase is immiscible with the first phase, and nanoparticle surfactants assembled at an interface of the non-spherical droplets and the second phase is disclosed. The nanoparticle surfactants include nanoparticles and end-functionalized polymers that can interact through ligand type interactions, and the first phase is stabilized by a disordered, jammed layer of nanoparticle surfactants. A method of preparing a stabilized assembly is also disclosed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Protocol-dependent frictional granular jamming simulations: cyclical, compression, and expansion

Granular matter takes many paths to pack in natural and industrial processes. The path influences the packing microstructure, particularly for frictional grains. We perform discrete element modeling simulations of different paths to construct packings of frictional spheres. Specifically, we explore four stress-controlled protocols implementing packing expansions and compressions in various combinations thereof. We characterize the eventual packed states through their dependence of the packing fraction and coordination number on packing pressure, identifying non-monotonicities with pressure that correlate with the fraction of frictional contacts. These stress-controlled, bulk-like particle simulations access very low-pressure packings, namely, the marginally stable limit, and demonstrate the strong protocol dependence of frictional granular matter.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Correlation of plastic events with local structure in jammed packings across spatial dimensions

Significance Mean-field theories, exact in the limit of infinite spatial dimensions, succeed in describing many features of glasses and amorphous solids in low dimensions, leading to considerable effort to understand how behavior evolves with dimension. Until now, all evidence has supported a picture in which “localized physics,” responsible for deviations from mean-field behavior in low dimensions, fades away with rising dimension. Our work shows that rearrangements, in which particles change relative positions leading to fluid-like response, reveal a different picture of dimensional cross-over. We find that rearrangements, which are localized in two- and three-dimensional systems and correlated with local structure, remain just as correlated with local structure up to five dimensions, suggesting that local structure is important even in high dimensions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗