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At least 1,027 records · Page 57

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NASA NTRS1982

Multi-ion resonances in finite temperature plasma

Dispersion properties of electrostatic waves in a multi-ion plasma are examined, with an analysis that incorporates the effects of finite temperature, finite parallel wavenumber, and wave growth/damping in a systematic development of equations. Numerical solutions and analytic formulas are given for an ion plasma consisting of H(+), O(+), and S(+) for application to Jupiter's magnetosphere. It is demonstrated how observations of plasma resonance lines may be used as a diagnostic of ion composition in magnetospheric plasma. This potential use of high-sensitivity/high-resolution plasma wave instrumentation may provide information necessary to resolve issues concerning the origin of plasmas in the earth's neighborhood.

Barbosa, D. D.↗

NASA NTRS2005

Pressure Dependence of Insulator-Insulator Contact Charging

The mechanism of insulator-insulator triboelectric (contact) charging is being studied by the Electrostatics and Surface Physics Laboratory at KSC. The hypothesis that surface ion exchange is the primary mechanism is being tested experimentally. A two-phase model based on a small partial pressure of singly charged ions in an ambient ideal gas in equilibrium with a submonolayer adsorbed film will provide predictions about charging as a function Of ion mass, pressure, temperature, and surface adsorption energy. Interactions between ions will be considered in terms of coulombic and screened potential energies. This work is yielding better understanding of the triboelectrification of insulators, which is an important problem in. space exploration technology. The work is also relevant to important industrial processes such as xerography and the application of paints and coatings. Determining a better understanding of the fundamental mechanism of insulator-insulator triboelectrification will hopefully lead to better means of eliminating or at least mitigating its hazards and enhancing its useful applications.

Hogue, Michael D.↗

DOE OSTI2025

Particle-based modelling of axisymmetric tandem mirror devices

In this work, we describe the use of a 1D-2V quasi-neutral hybrid electrostatic PIC with Monte-Carlo Coulomb collisions and non-uniform magnetic field to model the parallel transport and confinement in an axisymmetric tandem mirror device. End-plugs, based on simple-mirrors, are positioned at each end of the device and fueled with neutral beams (25 and 100 keV) to produce a sloshing ion population and increase the density of the end-plugs relative to the central cell. Results show the formation of a potential difference barrier between the central cell and the end-plugs. This potential confines a large fraction of the low energy thermal ions in the central cell which would otherwise be lost in a simple mirror, demonstrating the advantage of the beam-driven tandem mirror configuration relative to simple mirrors. In addition, we explore the effect of end-plug electron temperature on the confinement time of the device and compare it with theoretical estimates. Finally, we discuss the limitations of the code in its present form and describe the next logical steps to improve its predictive capability such as a fully nonlinear Fokker–Planck collision operator, multiply nested flux surface solutions and modeling the exhaust region up to the wall.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2022

Structural evolution in Au- and Pd-based metallic glass forming liquids and the case for improved molecular dynamics force fields

The results of a combined experimental and computational investigation of the structural evolution of Au 81 Si 19 , Pd 82 Si 18 , and Pd 77 Cu 6 Si 17 metallic glass forming liquids are presented. Electrostatically levitated metallic liquids are prepared, and synchrotron x-ray scattering studies are combined with embedded atom method molecular dynamics simulations to probe the distribution of relevant structural units. Metal–metalloid based metallic glass forming systems are an extremely important class of materials with varied glass forming ability and mechanical processibility. High quality experimental x-ray scattering data are in poor agreement with the data from the molecular dynamics simulations, demonstrating the need for improved interatomic potentials. The first peak in the x-ray static structure factor in Pd 77 Cu 6 Si 17 displays evidence for a Curie–Weiss type behavior but also a peak in the effective Curie temperature. In conclusion, a proposed order parameter distinguishing glass forming ability, 1/(S(T,q 1 )−1, shows a peak in the effective Curie temperature near a crossover temperature established by the behavior of the viscosity, T A .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1978

Analytical and numerical investigation of structural response of compliant wall materials

Theoretical analysis of an electrostatically driven wall system for a compliant wall drag reduction program is reported. The electrostatic wall system is capable of producing deflections of many orders greater than the thicknesses and at small wavelengths. An intermediate large response theory was used for structural analysis. The theoretical predictions were compared to bench test results, and good agreement between the two was obtained. The effects of aerodynamic loads and perturbation electric fields on the theoretical solutions were considered. It was shown that for very small wavelengths (approximately 2mm) the aerodynamic effects can be estimated using potential theory without loss of accuracy, and the perturbation electric fields do not affect solutions as long as the deflections are less than one percent of the wavelength. Resonance effects for this type of structure were shown to be fairly small.

Goglia, G. L.↗

NASA NTRS1978

The Third General Scientific Assembly of the International Association of Geomagnetism and Aeronomy - Special sessions of auroral processes

Methods of timing magnetic substorms, the rapid fluctuations of aurorae, electromagnetic and electrostatic instabilities observed on the field lines of aurorae, the auroral microstructure, and the relationship of currents, electric field and particle precipitation to auroral form are discussed. Attention is given to such topics as D-perturbations as an indicator of substorm onset, the role of the magnetotail in substorms, spectral information derived from imaging data on aurorae, terrestrial kilometric radiation, and the importance of the mirror force in self-consistent models of particle fluxes, currents and potentials on auroral field lines.

Russell, C. T.↗

NASA NTRS1981

Environmental charging effects monitors for operational satellites

A set of three instruments has been developed that can provide early detection of potentially dangerous geomagnetic substorm conditions, and monitor the spacecraft response. The set consists of three instruments: (1) a 'surface voltage sensor' that measures the characteristic energy of collected electrons or ions from +100 to -20,000 volts; (2) a 'nanoammeter' or logarithmic current density sensor that measures local electron flux by measuring currents from 10 to the -9th to 10 to the -5th A; and (3) a 'transient events counter' that counts the spurious pulses from electrostatic discharges that are coupled into the spacecraft wiring harness. Performance characteristics, specifications, and application of these instruments are discussed.

Sturman, J. C.↗

NASA NTRSDate not supplied

Electrostatic Discharge Hazard in Spacesuits

Triboelectric charging with a resultant electrostatic discharge is a phenomenon with which most people are familiar, especially those living in dry climates. Spacesuits, which are elaborately designed anthropomorphic pressure vessels attempting to match the motions of the human body while providing protections from the harsh environment of space, also must contend with triboelectric charging. But for spacesuits, which operate with elevated oxygen concentrations (usually >95%) in order to enable the lowest reasonable working pressure for the human operator, additional challenges are present with potentially catastrophic results if those challenges are not met successfully. A painful spark discharge can offer as much as 15kV with an energy transfer as high as 15-20mJ. This is well above the level needed to ignite hydrocarbon vapors or fine dusts such as those in grain silos. There have been several test methods beyond the scope of this paper seeking to address the mechanistic ignition energies to ignite suit materials with a wide possible range of results due to the varied test configurations. What is not known is if the suit materials offer sufficient capability for triboelectric charge generation and discharge to generate the potential and the resultant discharge energies within the ranges needed to ignite the suit materials in this operating environment.

Colin Campbell↗

DOE OSTI2020

Application of electrodialysis pretreatment to enhance boron removal and reduce fouling during desalination by nanofiltration/reverse osmosis

we report membranes have emerged as promising technologies for treatment of non-traditional waters, but fouling and poor rejection of small, neutral solutes (e.g., boric acid) impede their further implementation for water purification. Boron rejection is increased by raising the pH to convert boric acid to borate ion, but this change often leads to calcite supersaturation. This study investigated the use of a hybrid electrodialysis-nanofiltration/reverse osmosis (ED-NF/RO) system to reduce fouling from calcite precipitation and calcium-polysaccharide sorption to NF/RO membranes. Also, the study examined the potential of the hybrid process to increase permeate flux and boron rejection during NF/RO of synthetic saline water. ED pretreatment reduced calcite oversaturation and reduced flux decline during NF/RO. Low alginate concentrations (25 mg/L) limited NF/RO fouling, but high concentrations (100 mg/L) appeared to promote calcite scaling. ED pretreatment reduced the osmotic pressure of the NF/RO feed water, enabling lower operating pressures or greater permeate water fluxes. Boron rejection during NF/RO increased with ED pretreatment, probably due to stronger electrostatic repulsion and an increase in the fraction of total boron present as B(OH)4- following ED. This hybrid ED-NF/RO system shows promise as a novel approach to enhancing the performance of current membrane systems for treating complex feed waters.

alginate↗

DOE OSTI2022

Advanced Modes of Electrostatic and Kelvin Probe Force Microscopy for Energy Applications

Since their invention over three decades ago, electrostatic and Kelvin probe force microscopies (EFM and KPFM) have become primary tools for the characterization of electrical phenomena on the nanometer scale, with multiple applications for ferroelectrics, photovoltaics, batteries, and fuel cells among a myriad of other energy-related materials. Meanwhile, the techniques have undergone remarkable advances in terms of resolution, sensitivity, and informational content (e.g., dynamic information). In this chapter, we review the operational principles behind classical EFM/KPFM, including the various excitation/detection schemes, while also highlighting potential cross-talk and instrumental issues. Beyond classical approaches, we will describe more recent advances involving open loop detection, multifrequency/multidimensional excitation, and time-resolved methods. Finally, potential pathways for the further development of EFM/KPFM at the solid-liquid interface are discussed.

Checa, Marti↗

NASA NTRS2002

Dust Mitigation for Mars Solar Arrays

Settling of atmospheric dust onto the surface of the solar array is potentially a lifetime-limiting factor for a power system on any Mars mission. For long-term operation of arrays on Mars, it will be necessary to develop techniques to remove deposited dust. Dust is expected to adhere to the array by Van der Waals adhesive forces. These forces are quite strong at the dust particle sizes expected. Dust removal methods must overcome this force. Removal methods can be categorized briefly into four categories: natural, mechanical, electromechanical, and electrostatic. The environment of Mars is expected to be an ideal one for use of electrostatic dust-removal techniques.

Landis, Geoffrey A.↗

DOE OSTI2023

Molecular Dynamics Simulation Study of the Protonation State Dependence of Glutamic Acid Transport through a Cyclic Peptide Nanotube

The effect of the protonation state of glutamic acid on its translocation through cyclic peptide nanotubes (CPNs) was assessed by using molecular dynamics (MD) simulations. Anionic (GLU–), neutral zwitterionic (GLU0), and cationic (GLU+) forms of glutamic acid were selected as three different protonation states for an analysis of energetics and diffusivity for acid transport across a cyclic decapeptide nanotube. Based on the solubility-diffusion model, permeability coefficients for the three protonation states of the acid were calculated and compared with experimental results for CPN-mediated glutamate transport through CPNs. Potential of mean force (PMF) calculations reveal that, due to the cation-selective nature of the lumen of CPNs, GLU–, so-called glutamate, shows significantly high free energy barriers, while GLU+ displays deep energy wells and GLU0 has mild free energy barriers and wells inside the CPN. The considerable energy barriers for GLU– inside CPNs are mainly attributed to unfavorable interactions with DMPC bilayers and CPNs and are reduced by favorable interactions with channel water molecules through attractive electrostatic interactions and hydrogen bonding. Unlike the distinct PMF curves, position-dependent diffusion coefficient profiles exhibit comparable frictional behaviors regardless of the charge status of three protonation states due to similar confined environments imposed by the lumen of the CPN. The calculated permeability coefficients for the three protonation states clearly demonstrate that glutamic acid has a strong protonation state dependence for its transport through CPNs, as determined by the energetics rather than the diffusivity of the protonation state. In addition, the permeability coefficients also imply that GLU– is unlikely to pass through a CPN due to the high energy barriers inside the CPN, which is in disagreement with experimental measurements, where a considerable amount of glutamate permeating through the CPN was detected. To resolve the discrepancy between this work and the experimental observations, several possibilities are proposed, including a large concentration gradient of glutamate between the inside and outside of lipid vesicles and bilayers in the experiments, the glutamate activity difference between our MD simulations and experiments, an overestimation of energy barriers due to the artifacts imposed in MD simulations, and/or finally a transformation of the protonation state from GLU– to GLU0 to reduce the energy barriers. Altogether, our study demonstrates that the protonation state of glutamic acid has a strong effect on the transport of the acid and suggests a possible protonation state change for glutamate permeating through CPNs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1991

Charge control experiments on a CH-53E helicopter in a dusty environment

Charge control tests were carried out on a ground based, Marine Corps helicopter to determine if control of the electric fields acting on the engine exhaust gases could be used to reduce the electrification of the helicopter when it operated in a dusty atmosphere. The test aircraft was flown to a dusty, unpaved area and was then isolated electrically from the earth. When the helicopter engines were operated at ground idle with the rotor locked, the isolated aircraft charged positively, as had been observed previously. However, when the rotor brake was released and the turning rotor created a downdraft that raised dust clouds, the aircraft always became charged more positively, to potentials ranging form +30 to +45 kV. The dust clouds raised by the rotor downwash invariably carried negative space charges with concentrations of up to -100 nC/cu m and caused surface electric fields with strengths of up to 10 kV/m immediately down wind of the aircraft. The natural charging of the helicopter operating in these dust clouds was successfully opposed by control of the electric fields acting on the hot, electrically conductive exhaust gases. The control was achieved by placing electrostatic shield around the exhausts.

Moore, C. B.↗

NASA NTRS2016

Stair-Step Particle Flux Spectra on the Lunar Surface: Evidence for Nonmonotonic Potentials?

We present examples of unusual "stair‐step" differential flux spectra observed by the Apollo 14 Suprathermal Ion Detector Experiment on the lunar dayside surface in Earth's magnetotail. These spectra exhibit a relatively constant differential flux below some cutoff energy and then drop off precipitously, by about an order of magnitude or more, at higher energies. We propose that these spectra result from photoions accelerated on the lunar dayside by nonmonotonic potentials (i.e.,potentials that do not decay to zero monotonically) and present a model for the expected differential flux. The energy of the cutoff and the magnitude of the differential flux are related to the properties of the local space environment and are consistent with the observed flux spectra. If this interpretation is correct, these surface‐based ion observations provide a unique perspective that both complements and enhances the conclusions obtained by remote‐sensing orbiter observations on the Moon's exospheric and electrostatic properties.

Stair-step↗

DOE OSTI2021

From classical thermodynamics to phase-field method

Phase-field method is a density-based computational method at the mesoscale for modeling and predicting the temporal microstructure and property evolution during materials processes. The focus of this article is on connecting the most common phase-field equations to the very basic first and second laws of classical thermodynamics through rudimentary irreversible thermodynamics. It briefly discusses the relations of the continuum phase-field equations to their counter parts at the microscopic and atomic levels. It attempts to clarify the contributions of long-range elastic, electrostatic, and magnetic interactions to domain structure evolution during structural, ferroelectric, and ferromagnetic phase transformations by separating order parameter changes due to the presence of quasi-static fields and those arising from phase transformations. A few examples are presented to demonstrate the possibility of employing the phase-field method to provide guidance to designing materials for optimum properties or discovering novel mesoscale phenomena or new materials functionalities. Here, the article ends with a brief perspective on a number of potential future directions on the development and applications of phase-field method beyond its traditional applications to structural alloys.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Investigating Electron Conductivity Regimes in the Bacterial Cytochrome Wire OmcS

The anaerobic bacterium Geobacter sulfurreducens produces extracellular, electronically conductive cytochrome polymer wires that are conductive over micron length scales. Structure models from cryo-electron microscopy data show OmcS wires form a linear chain of hemes along the protein wire axis, which is proposed as the structural basis supporting their electronic properties. However, the mechanism by which this heme arrangement supports long-range electronic conduction remains unknown. Structure models from cryo-electron microscopy data show these wires form a linear chain of hemes along the protein wire axis, which is proposed as the structural basis supporting their electronic properties. Existing computational models using static heme redox potentials and coupling energies fail to explain experimental observations, predicting conductances 10,000 to 100,000 times lower than measured values. Here, we investigate how dynamic disorder affects site energies, interheme coupling, and long-range electronic conductivity within these cytochrome wires. We introduce an approach to extract charge carrier site information directly from Kohn–Sham density functional theory, without employing projector schemes, and show that site and coupling energies are highly sensitive to changes in interheme geometry and the surrounding electrostatic environment. Unlike models that incorporate dynamic disorder as a thermally averaged quantity, our quantum charge carrier model incorporates proxies for dynamic disorder through decoherence corrections, yielding predicted diffusion coefficient closer to what is expected from experiment and comparable with other organic-based electronic materials. Based on these simulations, we propose that the instantaneous fluctuations of the local electrostatic environment can transiently lift energy degeneracies and delocalize charge carriers. Furthermore, these studies reveal how incorporating dynamic fluctuations associated with the environment resolves the discrepancy between theory and experiment in microbial cytochrome wires and highlight design principles for bioinspired, heme-based conductive materials.

Bioinorganic chemistry↗

NASA NTRS2017

Understanding Breaks in Flare X-Ray Spectra: Evaluation of a Cospatial Collisional Return-Current Model

Hard X-ray (HXR) spectral breaks are explained in terms of a one-dimensional model with a cospatial return current. We study 19 flares observed by the Ramaty High Energy Solar Spectroscopic Imager with strong spectral breaks at energies around a few deka-keV, which cannot be explained by isotropic albedo or non-uniform ionization alone. We identify these breaks at the HXR peak time, but we obtain 8 s cadence spectra of the entire impulsive phase. Electrons with an initially power-law distribution and a sharp low-energy cutoff lose energy through return-current losses until they reach the thick target, where they lose their remaining energy through collisions. Our main results are as follows. (1) The return-current collisional thick-target model provides acceptable fits for spectra with strong breaks. (2) Limits on the plasma resistivity are derived from the fitted potential drop and deduced electron-beam flux density, assuming the return current is a drift current in the ambient plasma. These resistivities are typically 2-3 orders of magnitude higher than the Spitzer resistivity at the fitted temperature, and provide a test for the adequacy of classical resistivity and the stability of the return current. (3) Using the upper limit of the low-energy cutoff, the return current is always stable to the generation of ion-acoustic and electrostatic ion-cyclotron instabilities when the electron temperature is nine times lower than the ion temperature. (4) In most cases, the return current is most likely primarily carried by runaway electrons from the tail of the thermal distribution rather than by the bulk drifting thermal electrons. For these cases, anomalous resistivity is not required.

Alaoui, Meriem↗

DOE OSTI2020

Structure of an ancestral mammalian family 1B1 cytochrome P450 with increased thermostability

Mammalian cytochrome P450 enzymes often metabolize many pharmaceuticals and other xenobiotics, a feature that is valuable in a biotechnology setting. However, extant P450 enzymes are typically relatively unstable, with T 50 values of ~30–40 °C. Reconstructed ancestral cytochrome P450 enzymes tend to have variable substrate selectivity compared with related extant forms, but they also have higher thermostability and therefore may be excellent tools for commercial biosynthesis of important intermediates, final drug molecules, or drug metabolites. In this work, the mammalian ancestor of the cytochrome P450 1B subfamily was characterized structurally and functionally, revealing differences from the extant human CYP1B1 in ligand binding, metabolism, and potential molecular contributors to its thermostability. Whereas extant human CYP1B1 has one molecule of α-naphthoflavone in a closed active site, we observed that subtle amino acid substitutions outside the active site in the ancestor CYP1B enzyme yielded an open active site with four ligand copies. A structure of the ancestor with 17β-estradiol revealed only one molecule in the active site, which still had the same open conformation. Detailed comparisons between the extant and ancestor forms revealed increases in electrostatic and aromatic interactions between distinct secondary structure elements in the ancestral forms that may contribute to their thermostability. To the best of our knowledge, this represents the first structural evaluation of a reconstructed ancestral cytochrome P450, revealing key features that appear to contribute to its thermostability.

16beta-estradiol↗