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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

A comparison of parametric decay of oblique Langmuir wave in high and low density magneto-plasmas

The parametric decay instability of an obliquely propagating Langmuir wave into the low-frequency electromagnetic shear Alfven wave and the Left-Handed Circularly Polarized wave has been investigated in an electron-ion plasma, immersed in a uniform external magnetic field. Quantum magneto-hydrodynamic model has been used to find the linear and non-linear response of a high density quantum magneto-plasma. Going to the classical limit (ℏ→0) retrieves the results for low density classical plasma. Nonlinear dispersion relations and growth rates are derived with analytically and numerically. It is observed that growth rate in the high density degenerate magneto-plasma increases exponentially, while in the low density classical case it increases logarithmically.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Synthesis and characterization of nanostructured zinc oxide layers for sensor applications

Fractal structures and arrays of nanowires based on zinc oxide are fabricated by two different methods, sol-gel dip-coating and chemical bath deposition combined with sol-gel synthesis. The gas-sensitive properties of the structures are analyzed. It is found that the greatest sensitivity to reducing ethanol vapor is exhibited by the structure with a lower layer in the form of an array of zinc-oxide nanowires modified by four immersions in a copper nitrate solution.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Unavoidable multilevel biaxial symmetry breaking in chiral hybrid liquid crystals

Chiral nematic or cholesteric liquid crystals (LCs) are fluid mesophases with long-ranged orientational order featuring a quasilayered periodicity imparted by a helical director configuration but lacking long-range positional order. Doping molecular cholesteric LCs with strongly anisotropic uniaxial colloidal particles adds another level of complexity because of the interplay between weak surface-anchoring boundary conditions and bulk-based elastic distortions near the particle-LC interface. Using cylindrical colloidal disks and rods with different geometric shapes and surface conditions, we demonstrate that these colloidal inclusions generically exhibit biaxial orientational probability distributions which may impart anomalously strong local biaxiality onto the hybrid cholesteric LC structure. Unlike nonchiral hybrid molecular-colloidal LCs, where biaxial order emerges only at critical colloid volume fractions exceeding some uniaxial-biaxial transition value, the orientational probability of the colloidal inclusions immersed in chiral nematic hosts is unambiguously biaxial even at infinite dilution. We demonstrate that the colloids induce local biaxial perturbations within the molecular orientational order of the LC host medium which strongly enhances the weak but native biaxial order of chiral nematic LC induced by the chiral symmetry breaking of the director field. With the help of analytical modeling and computer simulations based on the Landau–de Gennes free energy of the host LC around the colloids, we rationalize the observed multilevel biaxial order and conclude that it is not only unavoidable but also strongly enhanced compared to both achiral hybrid LCs and purely molecular cholesteric LCs.

biaxial liquid crystals↗
DOE OSTI2025

Field Testing of Safeguards Technologies in the Hot Fuel Examination Facility

Recent developments in nuclear fuel reprocessing techniques have yielded more efficient processes and fuel cycle options that strengthen the nuclear industry and production of clean energy. One such area of interest is pyroprocessing of used oxide fuel. However, with these advances in the back end of the nuclear fuel cycle, advances in safeguards instrumentation, measurements, and approaches are needed to ensure special nuclear material (SNM) is accounted for according to regulatory requirements. As a high-level overview of a nominal pyroprocessing approach, used oxide fuel from commercial light water reactors (LWR) is mechanically removed from the metallic cladding. Then the fuel is crushed and randomized representative samples are taken and sent to an analytical lab for analysis. The analytical results of the feed material are used for input accountancy into the rest of the process. The crushed oxide fuel is then moved to the oxide reduction (OR) furnace where it is reduced from an oxide to metallic form. The OR product is distilled to remove salt and then moved to an electrorefiner (ER), where it is immersed in a eutectic mixture of lithium chloride potassium chloride (LiCl-KCl) that typically ranges between 450-550 ?. Within the ER, the usable uranium is electrochemically transported through the molten salt from the anode to the cathode, and then subsequently removed as a relatively pure U product.. A simplified model of pyroprocessing techniques with added emphasis on the safeguards can be seen below in Fig. 1

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2011

Amplifying single impurities immersed in a gas of ultracold atoms

We present a method for amplifying a single or scattered impurities immersed in a background gas of ultracold atoms so that they can be optically imaged and spatially resolved. Our approach relies on a Raman transfer between two stable atomic hyperfine states that is conditioned on the presence of an impurity atom. The amplification is based on the strong interaction among atoms excited to Rydberg states. We perform a detailed analytical study of the performance of the proposed scheme with particular emphasis on the influence of inevitable many-body effects.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2013

Optical and structural stability of blue SrO:Eu{sup 2+} phosphor

Chemical stability of 6-coodinated SrO is a fundamental problem when this is used for various applications. In this study, optical and chemical stabilities of 8-coordinated SrO:Eu{sup 2+} phosphor were investigated. SrO:Eu{sup 2+} phosphor was synthesized from thermal treatment of SrO:Eu powder located on a single crystalline MgO at 1500° C under reduction atmosphere. Obtained 8-coordinated SrO:Eu{sup 2+} phosphor exhibit strong blue luminescence and chemical stability in distilled water for 3 days. Our findings prove that obtained 8-coordinated SrO:Eu{sup 2+} possesses relative optical and chemical stabilities in water. - Graphical abstract: Obtained 8-coordinated SrO:Eu{sup 2+} phosphor exhibit strong blue luminescence in distilled water. Highlights: • We investigated optical and chemical stabilities of 8-coordinated SrO:Eu{sup 2+} phosphor in water. • Obtained 8-coordinated SrO:Eu{sup 2+} phosphor exhibit strong blue luminescence and chemical stability in distilled water for 3 days. • We found that the 8-coodrodinated SrO crystal structure changed to SrCO{sub 3} crystal structure after the 5 days immersion. • The obtained SrO:Eu{sup 2+} phosphor possesses high chemical stability under water, compared with commercial (6-coordinated) SrO.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Platinum-based electrocatalysts synthesized by depositing contiguous adlayers on carbon nanostructures

High-surface-area carbon nanostructures coated with a smooth and conformal submonolayer-to-multilayer thin metal films and their method of manufacture are described. The preferred manufacturing process involves the initial oxidation of the carbon nanostructures followed by immersion in a solution with the desired pH to create negative surface dipoles. The nanostructures are subsequently immersed in an alkaline solution containing non-noble metal ions which adsorb at surface reaction sites. The metal ions are then reduced via chemical or electrical means and the nanostructures are exposed to a solution containing a salt of one or more noble metals which replace adsorbed non-noble surface metal atoms by galvanic displacement. Subsequent film growth may be performed via the initial quasi-underpotential deposition of a non-noble metal followed by immersion in a solution comprising a more noble metal. The resulting coated nanostructures may be used, for example, as high-performance electrodes in supercapacitors, batteries, or other electric storage devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

The role of material flexibility on the drying transition of water between hydrophobic objects: A thermodynamic analysis

Liquid water confined between hydrophobic objects of sufficient size becomes metastable with respect to its vapor at separations smaller than a critical drying distance. Macroscopic thermodynamic arguments predicting this distance have been restricted to the limit of perfectly rigid confining materials. However, no material is perfectly rigid and it is of interest to account for this fact in the thermodynamic analysis. We present a theory that combines the current macroscopic theory with the thermodynamics of elasticity to derive an expression for the critical drying distance for liquids confined between flexible materials. The resulting expression is the sum of the well-known drying distance for perfectly rigid confining materials and a new term that accounts for flexibility. Thermodynamic arguments show that this new term is necessarily positive, meaning that flexibility increases the critical drying distance. To study the expected magnitude and scaling behavior of the flexible term, we consider the specific case of water and present an example of drying between thin square elastic plates that are simply supported along two opposite edges and free at the remaining two. We find that the flexible term can be the same order of magnitude or greater than the rigid solution for materials of biological interest at ambient conditions. In addition, we find that when the rigid solution scales with the characteristic size of the immersed objects, the flexible term is independent of size and vice versa. Thus, the scaling behavior of the overall drying distance will depend on the relative weights of the rigid and flexible contributions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1993

Ionospheric plasma flow about a system of electrically biased flat plates

The steady state interaction of two electrically biased parallel plates immersed in a flowing plasma characteristic of low earth orbit is studied numerically. Fluid equations are developed to describe the motion of the cold positively charged plasma ions, and are solved using finite-differences in two dimensions on a Cartesian grid. The behavior of the plasma electrons is assumed to be described by the Maxwell-Boltzmann distribution. Results are compared to an analytical and a particle simulation technique for a simplified flow geometry consisting of a single semi-infinite negatively biased plate. Comparison of the extent of the electrical disturbance into the flowing plasma and the magnitude of the current collected by the plate is very good. The interaction of two equally biased parallel plates is studied as a function of applied potential. The separation distance at which the current collected by either plate decreases by five and twenty percent is determined as a function of applied potential. The percent decreases were based on a non-interacting case. The decrease in overall current is caused by a decrease in ionic density in the region between the plates. As the separation between the plates decreases, the plates collect the ions at a faster rate than they are supplied to the middle region by the oncoming plasma flow. The docking of spacecraft in orbit is simulated by moving two plates of unequal potential toward one another in a quasi-static manner. One plate is held at a large negative potential while the other floats electrically in the resulting potential field. It is found that the floating plate does not charge continuously negative as it approaches the other more negatively biased plate. Instead, it charges more and then less negative as ionic current decreases and then increases respectively upon approach. When the two plates come into contact, it is expected that the electrically floating plate will charge rapidly negative to a potential near that of the other plate.

Herr, Joel L.↗
DOE OSTI2019

Amino-functionalized graphene quantum dots (aGQDs)-embedded thin film nanocomposites for solvent resistant nanofiltration (SRNF) membranes based on covalence interactions

Solvent resistant nanofiltration (SRNF) membranes are highly demanded in processing organic solutions especially those contain large molecules with molecular weight between 200 to 2000 Da, yet they have some drawbacks such as relatively poor solvent resistance and low solvent permeance. The current work presented an innovative class of amino-functionalized graphene quantum dots (aGQDs) embedded thin film nanocomposites (TFN) for SRNF membranes which were prepared via interfacial polymerization (IP) and subsequent steps (chemical imidization, crosslinking, and solvent activation). The prepared membranes enabled covalent interactions not only between the IP skin layer and the substrate, but also between the IP layer and the embedded aGQDs. The ethanol permeance and surface porosity increased by 44% and 69%, respectively, with the embedment of aGQDs under the optimal conditions, while the Rhodamine B (RDB, 479 Da) rejection maintained essentially stable above 99%. Furthermore, our novel membranes exhibited excellent long-term stability, with a rejection of over 99% for Rose Bengal (RB, 1017 Da) during the continuous filtration of 100 mg L -1 RB/N,N-dimethyl formamide (DMF) solution at room temperature for more than 768 h. They also exhibited good organic solvent resistance and high-temperature tolerance in both DMF and NMP solvents, with a RDB rejection of over 99% and an ethanol permeance of about 38 L m -2 h -1 MPa -1 after being immersed in DMF at 80 °C for 248 h, and a RDB rejection of over 99% and an ethanol permeance of about 41 L m -2 h -1 MPa -1 after being immersed in NMP at 80 °C for 232 h. The results demonstrated that the aGQDs-embedded TFN OSN membrane has vast potential in SRNF applications.

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

Self-Supporting, Hydrophobic, Ionic Liquid-Based Reference Electrodes Prepared by Polymerization-Induced Microphase Separation

Interfaces of ionic liquids and aqueous solutions exhibit stable electrical potentials over a wide range of aqueous electrolyte concentrations. This makes ionic liquids suitable as bridge materials that separate in electroanalytical measurements the reference electrode from samples with low and/or unknown ionic strengths. However, methods for the preparation of ionic liquid-based reference electrodes have not been explored widely. We have designed a convenient and reliable synthesis of ionic liquid-based reference electrodes by polymerization-induced microphase separation. This technique allows for a facile, single-pot synthesis of ready-to-use reference electrodes that incorporate ion conducting nanochannels filled with either 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide or 1-dodecyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide as ionic liquid, supported by a mechanically robust cross-linked polystyrene phase. This synthesis procedure allows for the straightforward design of various reference electrode geometries. These reference electrodes exhibit a low resistance as well as good reference potential stability and reproducibility when immersed into aqueous solutions varying from deionized, purified water to 100 mM KCl, while requiring no correction for liquid junction potentials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1972

A flight evaluation of methods for predicting vortex wake effects on trailing aircraft

The results of four current analytical methods for predicting wing vortex strength and decay rate are compared with the results of a flight investigation of the wake characteristics of several large jet transport aircraft. An empirical expression defining the strength and decay rate of wake vortices is developed that best represents most of the flight-test data. However, the expression is not applicable to small aircraft that would be immersed in the vortex wake of large aircraft.

Robinson, G. H.↗
NASA NTRS1993

On the origin of planetary spins

We examine the rate of accretion of mass and spin angular momentum by a spherical solid body ('planet') immersed in a differentially rotating disk of particles ('planetesimals'). If the planet travels on a circular orbit, the accretion process is described by two dimensionless parameters r and s, which measure the ratio of the planet's radius to its Hill radius and the ratio of the rms radial velocity of the planetesimals to the shear across the Hill radius, respectively. Using a combination of analytic arguments and numerical simulations, we derive the mass and angular momentum accretion rates and their scaling with r and s. By introducing an additional parameter, the effective mass of the planetesimals relative to the planet, we can derive the obliquities and spins arising from the stochastic nature of the accretion process. Our results are consistent with those of previous calculations by Lissauer and Kary (1991) wherever there is overlap in parameter space. In particular, we conclude that ordered accretion from a uniform or slowly varying disk of small bodies cannot result in rotation as rapid as that of earth or Mars for any value of the disk velocity dispersion s. The spin rates of these planets are most naturally explained as arising from one or a few 'giant' impacts by planetesimals.

Dones, Luke↗
DOE OSTI2013

Low temperature synthesis of {tau}-zirconium hydrogenophosphate [{tau}-Zr(HPO{sub 4}){sub 2}] and a new sodic form obtained by ion exchange

A new method for the synthesis of 3-D {tau}-zirconium hydrogenophosphate (TZP) was developed using solid-state reactions at low temperature and atmospheric pressure in a nitrogen atmosphere in a two-hour reaction time. The characterization of the compound was performed using X-ray diffraction, infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, differential scanning calorimetric, thermochemical analysis and X-ray photoelectron spectroscopy. A sodic form of the compound obtained by the immersion of TZP in a sodium hydroxide solution was characterized using the same techniques along with neutron activation analysis. The XPS spectra confirm the binding energy value for sodium-oxygen, and the XRD diffraction reveals the formation of a new sodium compound. - Graphical abstract: DRX, XPS and MEB of {tau}-zirconium hydrogenophosphate and its sodic form on the surface of TZP. Highlights: Black-Right-Pointing-Pointer New method for the syntheses of 3-D {tau}-zirconium hydrogenophosphate (TZP). Black-Right-Pointing-Pointer A sodic form of the TZP was obtained by the immersion of TZP in a sodium hydroxide. Black-Right-Pointing-Pointer The sodium compound is only formed on the TZP surface.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Spin effect on parametric decay of oblique Langmuir wave in degenerate magneto-plasmas

The electron spin −1/2 effects on the parametric decay instability of oblique Langmuir wave into low-frequency electromagnetic shear Alfven wave and Left-Handed Circularly Polarized wave (LHCP) has been investigated in detail, in an electron-ion quantum plasma immersed in the uniform external magnetic field. Incorporating the quantum effects due to electron spin, Fermi pressure and Bohm potential term, the quantum magneto-hydrodynamic (QMHD) model has been used to investigate the linear and nonlinear response of the plasma species for three-wave coupling interaction in a quantum magneto-plasmas. Nonlinear dispersion relations and growth rate of the problem have been derived analytically. It has been shown that the spin of electrons has considerable effect on the growth rate of parametric instability problem even when the external magnetic field B{sub 0} is below the quantum critical magnetic field strength B{sub Q}=4.4138×10{sup 13}G.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Cross-linked poly(methyl vinyl ether-co-maleic acid)/poly(ethylene glycol)/nanocellulosics foams via directional freezing

Aligned micro- and nanoporous materials have gained tremendous interest since they demonstrate great potential in organic electronics, absorbents, biomedicine and tissue engineering. Herein, cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs) cross-linked with poly(methyl vinyl ether-co-maleic acid) (PMVEMA) and poly(ethylene glycol) (PEG) foams were prepared by both the directional and un-directional freezing techniques. Aligned three-dimensional porous structures were indicated for the directional frozen foams after lyophilization via scanning electron microscope (SEM). As a result, these highly organized structures exhibited enhanced mechanical performance properties. Particularly, for the 25% CNF foams, the compression modulus increased 60% compared with the un-directional frozen samples. These nanocellulosics-based foams could absorb up to 10-fold water of their initial weight with excellent water stability when immersed in water for more than 48 h. Overall, this study describes a novel process combining cross-linking and directional freezing which successfully fabricates naturally derived foams with anisotropic structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Simulation of confined magnetohydrodynamic flows with Dirichlet boundary conditions using a pseudo-spectral method with volume penalization

A volume penalization approach to simulate magnetohydrodynamic (MHD) flows in confined domains is presented. Here the incompressible visco-resistive MHD equations are solved using parallel pseudo-spectral solvers in Cartesian geometries. The volume penalization technique is an immersed boundary method which is characterized by a high flexibility for the geometry of the considered flow. In the present case, it allows to use other than periodic boundary conditions in a Fourier pseudo-spectral approach. The numerical method is validated and its convergence is assessed for two- and three-dimensional hydrodynamic (HD) and MHD flows, by comparing the numerical results with results from literature and analytical solutions. The test cases considered are two-dimensional Taylor–Couette flow, the z-pinch configuration, three dimensional Orszag–Tang flow, Ohmic-decay in a periodic cylinder, three-dimensional Taylor–Couette flow with and without axial magnetic field and three-dimensional Hartmann-instabilities in a cylinder with an imposed helical magnetic field. Finally, we present a magnetohydrodynamic flow simulation in toroidal geometry with non-symmetric cross section and imposing a helical magnetic field to illustrate the potential of the method.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Plasma sheath and presheath development near a partially reflective surface

This work addresses one-dimensional evolution of a collisionless plasma next to a solid surface that is immersed into the plasma instantaneously. In particular, we consider how the self-similar rarefaction wave establishes dynamically and how the electron reflection from the surface modifies the structure of the rarefaction wave and the Debye sheath. Here, we demonstrate that a sufficiently strong reflection eliminates the Debye sheath and changes the wall potential and the plasma flow parameters significantly. The paper presents numerical results that illustrate the developed analytical theory.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗