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At least 1,117 records · Page 62
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

An alkaline tin(II) halide compound Na{sub 3}Sn{sub 2}F{sub 6}Cl: Synthesis, structure, and characterization

A new alkali tin(II) halide compound, Na{sub 3}Sn{sub 2}F{sub 6}Cl, is synthesized by hydrothermal method. This compound crystallizes trigonally in space group of R-3c (167), and processes a zero-dimensional (0D) structure consisted of Na{sup +} cations, Cl{sup −} anions and the isolated [SnF{sub 3}]{sup -} trigonal pyramids in which the stereochemically active 5s{sup 2} lone pair electrons are attached to the Sn{sup 2+} cations. Interestingly, the [SnF{sub 3}]{sup −} trigonal pyramids are parallel arranged in the a-b plane, while oppositely arranged in line with rotation along the c- axis. Moreover, the energy bandgap, thermal stability and electronic structure of Na{sub 3}Sn{sub 2}F{sub 6}Cl are characterized and the results reveal that this compound has and indirect bandgap of 3.88 eV and is stable under 270 °C. - Graphical abstract: A zero-dimensional alkaline tin halide compound, Na{sub 3}Sn{sub 2}F{sub 6}Cl, is synthesized by hydrothermal method. Interestingly, both the anions and cations coordinating polyhedra exhibit order arranged with the [SnF{sub 3}]{sup -} trigonal pyramids rotating along the c- axis.

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

Imaging the Localized Plasmon Resonance Modes in Graphene Nanoribbons

Here, we report a nanoinfrared (IR) imaging study of the localized plasmon resonance modes of graphene nanoribbons (GNRs) using a scattering-type scanning near-field optical microscope (s-SNOM). By comparing the imaging data of GNRs that are aligned parallel and perpendicular to the in-plane component of the excitation laser field, we observed symmetric and asymmetric plasmonic interference fringes, respectively. Theoretical analysis indicates that the asymmetric fringes are formed due to the interplay between the localized surface plasmon resonance (SPR) mode excited by the GNRs and the propagative surface plasmon polariton (SPP) mode launched by the s-SNOM tip. And with rigorous simulations, we reproduce the observed fringe patterns and address quantitatively the role of the s-SNOM tip on both the SPR and SPP modes. Moreover, we have seen real-space signatures of both the dipole and higher-order SPR modes by varying the ribbon width.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Control of Polar Orientation and Lattice Strain in Epitaxial BaTiO 3 Films on Silicon

Conventional strain engineering of epitaxial ferroelectric oxide thin films is based on the selection of substrates with a suitable lattice parameter. In this work, we show that the variation of oxygen pressure during pulsed laser deposition is a flexible strain engineering method for epitaxial ferroelectric BaTiO 3 films either on perovskite substrates or on Si(001) wafers. This unconventional growth strategy permits continuous tuning of strain up to high levels (ε > 0.8%) in films greater than one hundred nanometers thick, as well as selecting the polar axis orientation to be either parallel or perpendicular to the substrate surface plane.

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

Formation of 2- and 1-methyl-1,4-dihydronaphthalene isomers via the crossed beam reactions of phenyl radicals (C 6 H 5 ) with isoprene (CH 2 C(CH 3 )CHCH 2 ) and 1,3-pentadiene (CH 2 CHCHCHCH 3 )

Crossed molecular beam reactions were exploited to elucidate the chemical dynamics of the reactions of phenyl radicals with isoprene and with 1,3-pentadiene at a collision energy of 55 ± 4 kJ mol -1 . Both reactions were found to proceed via indirect scattering dynamics and involve the formation of a van-der-Waals complex in the entrance channel. The latter isomerized via the addition of the phenyl radical to the terminal C1/C4 carbon atoms through submerged barriers forming resonantly stabilized free radicals C 11 H 13 , which then underwent cis–trans isomerization followed by ring closure. The resulting bicyclic intermediates fragmented via unimolecular decomposition though the atomic hydrogen loss via tight exit transition states located 30 kJ mol -1 above the separated reactants in overall exoergic reactions forming 2- and 1-methyl-1,4-dihydronaphthalene isomers. The hydrogen atoms are emitted almost perpendicularly to the plane of the decomposing complex and almost parallel to the total angular momentum vector (‘sideways scattering’) which is in strong analogy to the phenyl–1,3-butadiene system studied earlier. RRKM calculations confirm that 2- and 1-methyl-1,4-dihydronaphthalene are the dominating reaction products formed at levels of 97% and 80% in the reactions of the phenyl radical with isoprene and 1,3-pentadiene, respectively. This barrier-less formation of methyl-substituted, hydrogenated PAH molecules further supports our understanding of the formation of aromatic molecules in extreme environments holding temperatures as low as 10 K.

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

Coherent state quantization of quaternions

Parallel to the quantization of the complex plane, using the canonical coherent states of a right quaternionic Hilbert space, quaternion field of quaternionic quantum mechanics is quantized. Associated upper symbols, lower symbols, and related quantities are analyzed. Quaternionic version of the harmonic oscillator and Weyl-Heisenberg algebra are also obtained.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Experimental study of vorticity-strain rate interaction in turbulent partially-premixed jet flames using tomographic particle image velocimetry

In turbulent flows, the interaction between vorticity, ω, and strain rate, s, is considered a primary mechanism for the transfer of energy from large to small scales through vortex stretching. The ω-s coupling in turbulent jet flames is investigated using tomographic particle image velocimetry (TPIV). TPIV provides a direct measurement of the three-dimensional velocity field from which ω and s are determined. The effects of combustion and mean shear on the ω-s interaction are investigated in turbulent partially premixed methane/air jet flames with high and low probabilities of localized extinction as well as in a non-reacting isothermal air jet with Reynolds number of approximately 13,000. Results show that combustion causes structures of high vorticity and strain rate to agglomerate in highly correlated, elongated layers that span the height of the probe volume. In the non-reacting jet, these structures have a more varied morphology, greater fragmentation, and are not as well correlated. The enhanced spatiotemporal correlation of vorticity and strain rate in the stable flame results in stronger ω-s interaction characterized by increased enstrophy and strain-rate production rates via vortex stretching and straining, respectively. The probability of preferential local alignment between ω and the eigenvector of the intermediate principal strain rate, s 2 , which is intrinsic to the ω-s coupling in turbulent flows, is larger in the flames and increases with the flame stability. The larger mean shear in the flame imposes a preferential orientation of ω and s 2 tangential to the shear layer. The extensive and compressive principal strain rates, s 1 and s 3 , respectively, are preferentially oriented at approximately 45° with respect to the jet axis. As a result, the production rates of strain and vorticity tend to be dominated by instances in which ω is parallel to the s 1 ¯-s 2 ¯ plane and orthogonal to s 3 ¯.

42 ENGINEERING↗
DOE OSTI2016

Influence of the anions on the N-cationic benzethonium salts in the solid state and solution: Chloride, bromide, hydroxide and citrate hydrates

The crystal structures of the hydrated cationic surfactant benzethonium (Bzth) chloride, bromide, hydroxide, and citrate have been determined by X-ray diffraction analysis and compared with their structures in solution well above their critical micelle concentration. The differences in the nature of the various anions of the four Bzth-X materials lead to unique anion environments and 3-D molecular arrangements. The water molecule in the monoclinic Bzth-Cl or Bzth-Br forms is hydrogen bonded to the halides and particularly to the hydrogens of the methoxy groups of the Bzth moiety notwithstanding the weak Brønsted acidity of the methoxy hydrogens. The citrate strongly interacts with the hydrogens of the methoxy group forming an embedded anionic spherical cluster of a radius of 2.6 Å. The Bzth-OH crystallizes in a hexagonal lattice with two water molecules and reveals free water molecules forming hydrogen bonded channels through the Bzth-OH crystal along the c-axis. The distances between the cationic nitrogen and the halides are 4.04 Å and 4.20 Å, significantly longer than expected for typical van der Waals distances of 3.30 Å. The structures show weakly interacting, alternating apolar and polar layers, which run parallel to the crystallographic a-b planes or a-c planes. The Bzth-X salts were also examined in aqueous solution containing 20% (v/v) ethanol and 1.0 % (v/v) glycerol well above their critical micelle concentration by small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). The [1,1,1] planes for the Bzth Cl or Br, the [0,0,2] and [1,1,0] planes for the Bzth-citrate, the [2,-1,0] planes and the [0,0,1] planes for the Bzth-OH found in the crystalline phase were also present in the solution phase, accordingly, the preservation of these phases are a strong indication of periodicity in the solution phase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Electron transport in graphene/graphene side-contact junction by plane-wave multiple-scattering method

Electron transport in graphene is along the sheet but junction devices are often made by stacking different sheets together in a “side-contact” geometry which causes the current to flow perpendicular to the sheets within the device. Such geometry presents a challenge to first-principles transport methods. We solve this problem by implementing a plane-wave-based multiple-scattering theory for electron transport. In this study, this implementation improves the computational efficiency over the existing plane-wave transport code, scales better for parallelization over large number of nodes, and does not require the current direction to be along a lattice axis. As a first application, we calculate the tunneling current through a side-contact graphene junction formed by two separate graphene sheets with the edges overlapping each other. We find that transport properties of this junction depend strongly on the AA or AB stacking within the overlapping region as well as the vacuum gap between two graphene sheets. Finally, such transport behaviors are explained in terms of carbon orbital orientation, hybridization, and delocalization as the geometry is varied.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Crack Front Segmentation and Facet Coarsening in Mixed-Mode Fracture

A planar crack generically segments into an array of “daughter cracks” shaped as tilted facets when loaded with both a tensile stress normal to the crack plane (mode I) and a shear stress parallel to the crack front (mode III). We investigate facet propagation and coarsening using in situ microscopy observations of fracture surfaces at different stages of quasistatic mixed-mode crack propagation and phase-field simulations. The results demonstrate that the bifurcation from propagating a planar to segmented crack front is strongly subcritical, reconciling previous theoretical predictions of linear stability analysis with experimental observations. As a result, they further show that facet coarsening is a self-similar process driven by a spatial period-doubling instability of facet arrays.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

TU-H-CAMPUS-IeP3-02: Neurovascular 4D Parametric Imaging Using Co-Registration of Biplane DSA Sequences with 3D Vascular Geometry Obtained From Cone Beam CT

Purpose: To create 4D parametric images using biplane Digital Subtraction Angiography (DSA) sequences co-registered with the 3D vascular geometry obtained from Cone Beam-CT (CBCT). Methods: We investigated a method to derive multiple 4D Parametric Imaging (PI) maps using only one CBCT acquisition. During this procedure a 3D-DSA geometry is stored and used subsequently for all 4D images. Each time a biplane DSA is acquired, we calculate 2D parametric maps of Bolus Arrival Time (BAT), Mean Transit Time (MTT) and Time to Peak (TTP). Arterial segments which are nearly parallel with one of the biplane imaging planes in the 2D parametric maps are co-registered with the 3D geometry. The values in the remaining vascular network are found using spline interpolation since the points chosen for co-registration on the vasculature are discrete and remaining regions need to be interpolated. To evaluate the method we used a patient CT volume data set for 3D printing a neurovascular phantom containing a complete Circle of Willis. We connected the phantom to a flow loop with a peristaltic pump, simulating physiological flow conditions. Contrast media was injected with an automatic injector at 10 ml/sec. Images were acquired with a Toshiba Infinix C-arm and 4D parametric image maps of the vasculature were calculated. Results: 4D BAT, MTT, and TTP parametric image maps of the Circle of Willis were derived. We generated color-coded 3D geometries which avoided artifacts due to vessel overlap or foreshortening in the projection direction. Conclusion: The software was tested successfully and multiple 4D parametric images were obtained from biplane DSA sequences without the need to acquire additional 3D-DSA runs. This can benefit the patient by reducing the contrast media and the radiation dose normally associated with these procedures. Partial support from NIH Grant R01-EB002873 and Toshiba Medical Systems Corp.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Conversion acoustic resonances in orthorhombic crystals

A classification of acoustic-beam reflection resonances in orthorhombic crystals under conditions where a proximity to conversion is implemented in the vicinity of total internal reflection is proposed. In this case, the energy from the incident pump beam falls almost entirely into a narrow intense reflected beam propagating at a small angle with respect to the surface. The crystal boundary is parallel to one of the elastic symmetry planes, and the excited beam propagates near one of axes 2 in this plane. Depending on the relations between the elastic moduli and the chosen propagation geometry, 18 types of resonances may occur, but no more than three in each crystal. The developed theory combines an approximate analytical description and accurate computer analysis. The relations between the elastic moduli providing minimum energy loss over the parasite reflected wave are determined. Some crystals with resonant excitation very close to conversion are revealed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1985

ISEE-1 and 2 observations of field-aligned currents in the distant midnight magnetosphere

Magnetic field measurements obtained in the nightside magnetosphere by the co-orbiting ISEE-1 and 2 spacecraft have been examined for signatures of field-aligned currents (FAC). Such currents are found on the boundary of the plasma sheet both when the plasma sheet is expanding and when it is thinning. Evidence is often found for the existence of waves on the plasma sheet boundary, leading to multiple crossings of the FAC sheet. At times the boundary layer FAC sheet orientation is nearly parallel to the X-Z GSM plane, suggesting 'protrusions' of plasma sheet into the lobes. The boundary layer current polarity is, as expected, into the ionosphere in the midnight to dawn local time sector, and outward near dusk. Current sheet thicknesses and velocities are essentially independent of plasma sheet expansion or thinning, having typical values of 1500 km and 20-40 km/s respectively. Characteristic boundary layer current densities are about 10 nanoamps per square meter.

Elphic, R. C.↗
NASA NTRS1987

Rays versus modes - Pictorial display of energy flow in an open-ended waveguide

The problem of a plane wave impinging on a semiinfinite parallel-plate waveguide is investigated. It is demonstrated that, for waveguide separation large compared to the wavelength, the fields inside the waveguide obey a single ray optics description. The beam behavior persists for more than 1000 lambda into a 50 lambda waveguide. For a small 3 lambda waveguide, the beam picture begins to blur approximately 5 lambda into the guide.

Ling, Hao↗
NASA NTRS1988

Direct emissivity measurements on liquids and corrections to multi-color pyrometers

Optical pyrometry provides a means for non-contact temperature measurements whose accuracy depends on the accuracy with which specimen emittance is known. Two methods for obtaining the required emittance data are discussed in which the emittance is determined from measurements of the wavelength or polarization dependence of light emitted by the specimen. The spectral technique, multi-color pyrometry, yields apparent values for specimen emittance and temperature from emitted intensity measurements at two or more wavelengths. Emittance corrections cannot be eliminated by increasing the number of spectral intensity measurements required by an n-color pyrometer. Even if this were possible, the accuracy of temperature measurements by n-color pyrometry decreases with n such that pyrometers that require four intensity measurements would be impractical. In contrast, emittance values and corrections for one-color pyrometers can be accurately measured by the polarized light technique. The polarized light technique involves measurement of the degree of polarization for light emitted at an angle of 45 deg to the specimen normal. The reflectivities (r) for light polarized parallel (p) and normal (n) to the plane of emission are related by r(p) = r(n) squared. This leads to a simple relation between the intensity ratio for light emitted in the two polarized states and the emittance, i.e., e(n) = 2 - I(p)/I(n). The true specimen temperature is also obtained if absolute intensities are measured. Delvelopment of the polarized light technique in combination with one-color optical pyrometry is recommended to achieve accurate non-contact temperature measurements on liquids.

Nordine, Paul C.↗
NASA NTRS2003

Engineered Carbon Nanotube Materials for High-Q Nanomechanical Resonators

This document represents a presentation offered by the Jet Propulsion Laboratory, with assistance from researchers from Brown University and Northrop Grumman. The presentation took place in Seoul, Korea in July 2003 and attempted to demonstrate the fabrication approach regarding the development of high quality factor (high-Q) mechanical oscillators (in the forms of a tunable nanotube resonator and a nanotube array radio frequency [RF] filter) aimed at signal processing and based on carbon nanotubes. The presentation also addressed parallel efforts to develop both in-plane single nanotube resonators as well as vertical array power devices.

chemical vapor depositions↗
NASA NTRS1995

Transparent magnetic state in single crystal Nd(1.85)Ce(0.15)CuO(4-y) superconductors

Several experimental studies have been reported as evidence of Josephson coupling between the superconducting layers in the highly anisotropic oxide such as the Bi2Sr2CaCu2O8 and Tl2Ba2CuO6 systems. These include the large penetration depth of 100 mu m measured, ac and dc Josephson effects. Recently two critical temperatures corresponding to Josephson coupling in between the layers and the Berezinskii-Kosterlitz-Thouless transition in the ab-plane have been directly observed in the transport measurements. If the field is applied parallel to the superconducting layers, the magnetic excitation is not the conventional Abrikosov vortices, but the Josephson vortices which extend lambda(sub ab) in the c-axis direction and lambda(sub J) = gamma s in the plane (s is the interlayer distance, gamma is the anisotropy constant). Because of the weak screening effect associated with the Josephson vortices, there have been predictions of magnetic transparent states at magnetic field above a characteristic field H(sub J), a behavior distinctively different from that of the type-II superconductors. In this paper, we report an experimental result which illustrates a transition from the Meissner state to the magnetic transparent state in single crystal of Nd(1.85)Ce(0.15)CuO(4-y). Magnetization has been measured as a function of temperature and field in the magnetic field parallel or close to ab-plane geometry. For a fixed magnetic field, the magnetization shows a two-step transition in M(T); for a fixed temperature, the magnetization shows an abrupt change to almost zero value above a characteristic field H(sub J), an indication of magnetic transparent state. The data of magnetization as a function of field clearly deviates from the behavior predicted by the Abrikosov theory for type-II superconductors. Instead, the data fit well into the picture of Josephson decoupling between the CuO2 layers.

Zuo, F.↗
DOE OSTI2014

SU-E-T-118: Dose Verification for Accuboost Applicators Using TLD, Ion Chamber and Gafchromic Film Measurements

Purpose: To verify dose delivered with HDR Accuboost applicators using TLD, ion chamber and Gafchromic film measurements and to examine applicator leakage. Methods: A microSelectron HDR unit was used to deliver a dose of 50cGy to the mid-plane of a 62mm thick solid water phantom using dwell times from Monte Carlo pre-calculated nomograms for a 60mm, 70mm Round and 60mm Skin-Dose Optimized (SDO) applicators respectively. GafChromic EBT3+ film was embedded in the phantom midplane horizontally to measure dose distribution. Absolute dose was also measured with TLDs and an ADCL calibrated parallel-plate ion chamber placed in the film plane at field center for each applicator. The film was calibrated using 6MV x-ray beam. TLDs were calibrated in a Cs-137 source at UW-Madison calibration laboratory. Radiation leakage through the tungsten alloy shell was measured with a film wrapped around outside surface of a 60mm Round applicator. Results: Measured maximum doses at field center are consistently lower than predicated by 5.8% for TLD, 8.8% for ion chamber, and 2.6% for EBT3+ film on average, with measurement uncertainties of 2.2%, 0.3%, and 2.9% for TLD, chamber, film respectively. The total standard uncertainties for ion chamber and Gafchromic film measurement are 4.9% and 4.6% respectively[1]. The area defined by the applicator aperture was covered by 80% of maximum dose for 62mm compression thickness. When 100cGy is delivered to mid-plane with a 60mm Round applicator, surface dose ranges from 60cGy to a maximum of 145cGy, which occurs at source entrance to the applicator. Conclusion: Measured doses by all three techniques are consistently lower than predicted in our measurements. For a compression thickness of 62 mm, the field size defined by the applicator is only covered by 80% of prescribed dose. Radiation leakage of up to 145cGy was found at the source entrance of applicators.

07 ISOTOPE AND RADIATION SOURCES↗
NASA NTRS1991

The improved robustness of multigrid elliptic solvers based on multiple semicoarsened grids

Multigrid convergence rates degenerate on problems with stretched grids or anisotropic operators, unless one uses line or plane relaxation. For 3-D problems, only plane relaxation suffices, in general. While line and plane relaxation algorithms are efficient on sequential machines, they are quite awkward and inefficient on parallel machines. A new multigrid algorithm is presented based on the use of multiple coarse grids, that eliminates the need for line or plane relaxation in anisotropic problems. This algorithm was developed and the standard multigrid theory was extended to establish rapid convergence for this class of algorithms. The new algorithm uses only point relaxation, allowing easy and efficient parallel implementation, yet achieves robustness and convergence rates comparable to line and plane relaxation multigrid algorithms. The algorithm described is a variant of Mulder's multigrid algorithm for hyperbolic problems. The latter uses multiple coarse grids to achieve robustness, but is unsuitable for elliptic problems, since its V-cycle convergence rate goes to one as the number of levels increases. The new algorithm combines the contributions from the multiple coarse grid via a local switch, based on the strength of the discrete operator in each coordinate direction.

Naik, Naomi H.↗