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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Enhancement of photoluminescence intensity of GaAs with cubic GaS chemical vapor deposited using a structurally designed single-source precursor

A two order-of-magnitude enhancement of photoluminescence intensity relative to untreated GaAs has been observed for GaAs surfaces coated with chemical vapor-deposited GaS. The increase in photoluminescence intensity can be viewed as an effective reduction in surface recombination velocity and/or band bending. The gallium cluster /(t-Bu)GaS/4 was used as a single-source precursor for the deposition of GaS thin films. The cubane core of the structurally characterized precursor is retained in the deposited film producing a cubic phase. Furthermore, a near-epitaxial growth is observed for the GaS passivating layer. Films were characterized by transmission electron microscopy, X-ray powder diffraction, and X-ray photoelectron and Rutherford backscattering spectroscopies.

Macinnes, Andrew N.↗
NASA NTRS1994

Deposition Of Cubic BN On Diamond Interlayers

Thin films of polycrystalline, pure, cubic boron nitride (c-BN) formed on various substrates, according to proposal, by chemical vapor deposition onto interlayers of polycrystalline diamond. Substrate materials include metals, semiconductors, and insulators. Typical substrates include metal-cutting tools: polycrystalline c-BN coats advantageous for cutting ferrous materials and for use in highly oxidizing environments-applications in which diamond coats tend to dissolve in iron or be oxidized, respectively.

Ong, Tiong P.↗
NASA NTRS1993

An extended UTD analysis for the scattering and diffraction from cubic polynomial strips

Spline and polynomial type surfaces are commonly used in high frequency modeling of complex structures such as aircraft, ships, reflectors, etc. It is therefore of interest to develop an efficient and accurate solution to describe the scattered fields from such surfaces. An extended Uniform Geometrical Theory of Diffraction (UTD) solution for the scattering and diffraction from perfectly conducting cubic polynomial strips is derived and involves the incomplete Airy integrals as canonical functions. This new solution is universal in nature and can be used to effectively describe the scattered fields from flat, strictly concave or convex, and concave convex boundaries containing edges. The classic UTD solution fails to describe the more complicated field behavior associated with higher order phase catastrophes and therefore a new set of uniform reflection and first-order edge diffraction coefficients is derived. Also, an additional diffraction coefficient associated with a zero-curvature (inflection) point is presented. Higher order effects such as double edge diffraction, creeping waves, and whispering gallery modes are not examined. The extended UTD solution is independent of the scatterer size and also provides useful physical insight into the various scattering and diffraction processes. Its accuracy is confirmed via comparison with some reference moment method results.

Constantinides, E. D.↗
NASA NTRS1994

Experimental Results of Hydrogen Slosh in a 62 Cubic Foot (1750 Liter) Tank

Extensive slosh testing with liquid and slush hydrogen was conducted in a 62 cubic foot spherical tank to characterize the thermodynamic response of the system under normal gravity conditions. Slosh frequency and amplitude, pressurant type, ramp pressure, and ullage volume were parametrically varied to assess the effect of each of these parameters on the tank pressure and fluid/wall temperatures. A total of 91 liquid hydrogen and 62 slush hydrogen slosh tests were completed. Both closed tank tests and expulsions during sloshing were performed. This report presents and discusses highlights of the liquid hydrogen closed tank results in detail and introduces some general trends for the slush hydrogen tests. Summary comparisons between liquid and slush hydrogen slosh results are also presented.

Moran, Matthew E.↗
NASA NTRS1995

Macroscopic and bulk-controlled elastic modes in an interaction of interstitial alcali metal cations within a face-centered cubic crystalline fullerine

The calculations in a majority of previous works for the fulleride (AqC-60) crystals were performed within the framework of the rigid-lattice model, neglecting the distortion relaxation of the host fullerene (C-60) crystal caused by the interstitial alkali-metal (A) cations. However, an each cation is a source of a static distortion field, and the resulting field is a superposition of such fields generated by all cations. This is a reason why the host-crystal distortions depend on the A-cations configurations, i.e. on a type of a spatial bulk distribution of interstitial cations. The given paper seeks to find a functional relation between the amplitudes of the doping-induced structure-distortion waves and of static concentration ones. A semiphenomenological model is constructed here within the scope of statistical-thermodynamic treatment and using the lattice-statistics simulation method(*). In this model the effects due to the presence of q solute A cations over available interstices (per unit cell) on the static inherent reorientation and/or displacements of the solvent molecules from the 'average-lattice' sites' as well as on the lattice parameter a of a elastically-anysotropic 'cubic' C-60 crystal are taken into account.

Tatarenko, Valentine A.↗
NASA NTRS1993

A UGO/EUTD Solution for the Scattering and Diffraction from Cubic Polynomial Strips

A uniform geometrical optics (UGO) and an extended uniform geometrical theory of diffraction (EUTD) solution is developed for the scattering and diffraction from perfectly conducting cubic polynomial strips. The new solution overcomes the difficulties of the classic GO/UTD solution near caustics and composite shadow boundaries. The approach for constructing the UGO/EUTD solution is based on a spatial domain physical optics (PO) radiation integral representation for the scattered field which is then reduced using a uniform asymptotic procedure. New uniform reflection, zero-curvature diffraction, and edge diffraction coefficients are derived and involve the ordinary and incomplete Airy integrals as canonical functions. Higher order effects such as double edge diffraction, edge-excited creeping waves, and whispering gallery modes are not examined in this work. The UGO/EUTD solution is very efficient and provides useful physical insight into the various scattering and diffraction processes. It is also universal in nature and can be used to effectively describe the scattered fields from flat, strictly concave or convex, and concave-convex boundaries containing edges. Its accuracy is confirmed via comparison with some reference moment method (MM) results.

Constantinides, Evagoras D.↗
NASA NTRS1998

Surface Chemistry, Microstructure, and Tribological Properties of Cubic Boron Nitride Films

This report deals with the surface chemistry, microstructure, bonding state, morphology, and friction and wear properties of cubic boron nitride (c-BN) films that were synthesized by magnetically enhanced plasma ion plating. Several analytical techniques - x-ray photoelectron spectroscopy, transmission electron microscopy and electron diffraction, Fourier transform infrared spectroscopy, atomic force microscopy, and surface profilometry - were used to characterize the films. Sliding friction experiments using a ball-on-disk configuration were conducted for the c-BN films in sliding contact with 440C stainless-steel balls at room temperature in ultrahigh vacuum (pressure, 10(exp -6), in ambient air, and under water lubrication. Results indicate that the boron-to-nitrogen ratio on the surface of the as-deposited c-BN film is greater than 1 and that not all the boron is present as boron nitride but a small percentage is present as an oxide. Both in air and under water lubrication, the c-BN film in sliding contact with steel showed a low wear rate, whereas a high wear rate was observed in vacuum. In air and under water lubrication, c-BN exhibited wear resistance superior to that of amorphous boron nitride, titanium nitride, and titanium carbide.

Watanabe, Shuichi↗
NASA NTRS1997

Single Crystal Fibers of Yttria-Stabilized Cubic Zirconia with Ternary Oxide Additions

Single crystal fibers of yttria (Y2O3)-stabilized cubic zirconia, (ZrO2) with ternary oxide additions were grown using the laser float zone fiber processing technique. Ternary additions to the ZrO2-Y2O3 binary system were studied aimed at increasing strength while maintaining the high coefficient of thermal expansion of the binary system. Statistical methods aided in identifying the most promising ternary oxide candidate (Ta2O5, Sc2O3, and HfO2) and optimum composition. The yttria, range investigated was 14 to 24 mol % and the ternary oxide component ranged from 1 to 5 mol %. Hafnium oxide was the most promising ternary oxide component based on 816 C tensile strength results and ease of fabrication. The optimum composition for development was 81 ZrO2-14 Y203-5 HfO2 based upon the same elevated temperature strength tests. Preliminary results indicate process improvements could improve the fiber performance. We also investigated the effect of crystal orientation on strength.

Ritzert, F. J.↗
NASA NTRS2003

Cubic Calorimeter for High-Energy Electrons in Ultra-Long Ballooning

The concept and optimization study of a balloon-borne instrument to study high-energy (from 100 GeV to 5 TeV) cosmic ray electrons will be presented. This energy range of electrons is very interesting for the study of cosmic ray propagation and the search for the nearby sources of high-energy electrons. The instrument is based on a cubic design that allows the detection from all sides. Proton rejection is provided by stringent track analysis, which allows defining when an electron shower is exhausted while the hadron shower continues development. The collecting power of a nominal balloon-borne instrument using this concept will be over 2 square meters sr. This will provide approximately 3,000 electron events above 500 GeV for 3-month long ULDB flight. This instrument will also be capable of detecting sharp features in the high energy gamma-ray spectrum such as gamma-ray lines originating from the dark matter annihilation.

Moiseev, Alexander A.↗
NASA NTRS2002

A Cubic Radial Basis Function in the MLPG Method for Beam Problems

A non-compactly supported cubic radial basis function implementation of the MLPG method for beam problems is presented. The evaluation of the derivatives of the shape functions obtained from the radial basis function interpolation is much simpler than the evaluation of the moving least squares shape function derivatives. The radial basis MLPG yields results as accurate or better than those obtained by the conventional MLPG method for problems with discontinuous and other complex loading conditions.

Raju, I. S.↗
NASA NTRS1997

Liquid water in the domain of cubic crystalline ice Ic

Vapor-deposited amorphous water ice when warmed above the glass transition temperature (120-140 K), is a viscous liquid which exhibits a viscosity vs temperature relationship different from that of liquid water at room temperature. New studies of thin water ice films now demonstrate that viscous liquid water persists in the temperature range 140-210 K. where it coexists with cubic crystalline ice. The liquid character of amorphous water above the glass transition is demonstrated by (1) changes in the morphology of water ice films on a nonwetting surface observed in transmission electron microscopy (TEM) at around 175 K during slow warming, (2) changes in the binding energy of water molecules measured in temperature programmed desorption (TPD) studies, and (3) changes in the shape of the 3.07 micrometers absorption band observed in grazing angle reflection-absorption infrared spectroscopy (RAIRS) during annealing at high temperature. whereby the decreased roughness of the water surface is thought to cause changes in the selection rules for the excitation of O-H stretch vibrations. Because it is present over such a wide range of temperatures, we propose that this form of liquid water is a common material in nature. where it is expected to exist in the subsurface layers of comets and on the surfaces of some planets and satellites.

NASA Center ARC↗
NASA NTRS2004

Error and Symmetry Analysis of Misner's Algorithm for Spherical Harmonic Decomposition on a Cubic Grid

In an earlier paper, Misner (2004, Class. Quant. Grav., 21, S243) presented a novel algorithm for computing the spherical harmonic components of data represented on a cubic grid. I extend Misner s original analysis by making detailed error estimates of the numerical errors accrued by the algorithm, by using symmetry arguments to suggest a more efficient implementation scheme, and by explaining how the algorithm can be applied efficiently on data with explicit reflection symmetries.

Fiske, David R.↗
NASA NTRS2008

Cherenkov and Scintillation Properties of Cubic Zirconium

Cubic zirconium (CZ) is a high index of refraction (n =2.17) material that we have investigated for Cherenkov counter applications. Laboratory and proton accelerator tests of an 18cc sample of CZ show that the expected fast Cherenkov response is accompanied by a longer scintillation component that can be separated by pulse shaping. This presents the possibility of novel particle spectrometers which exploits both properties of CZ. Other high index materials being examined for Cherenkov applications will be discussed. Results from laboratory tests and an accelerator exposure will be presented and a potential application in solar energetic particle instruments will be discussed

Christl, M.J.↗
NASA NTRS2017

Rhombohedral Super Hetero Epitaxy of Cubic SiGe on Trigonal c-plane Sapphire

New rhombohedral super-hetero-epitaxy technology was developed at NASA. This epitaxy technology enables the growth of unprecedented cubic-trigonal hybrid single crystal structures with lattice match on sapphire (Al2O3) substrates, hence with little strain and very few defects at the interface.

Choi, Sang H.↗
DOE OSTI2021

Determination of impurities in cubic boron nitride (cBN) by inductively coupled plasma mass spectrometry (ICPMS)

The phase stability of cBN is critically dependent on the content and amount of impurities present. While studies have shown qualitatively that the addition of certain impurities can either increase or decrease the cBN-hBN phase transition temperature, studies have yet to show this effect quantitatively. This is because analytical methods to characterize minor and trace impurities in cBN are currently lacking. To this end, we present flux fusion methods capable of fully digesting cBN samples for ICPMS analyses. The materials used in this study are commercially available cBN powders in three different sizes. Two types of fluxes (LiOH and NaOH·H 2 O) are utilized so that both Li and Na impurities can be determined. To ensure the accuracy of Si measurements, a column chromatography method has been developed to purify Si from flux materials in order to increase the amount of dissolved sample sent to the ICP. Detection limits have been determined using procedural blanks and are found to be below 20 μg/g for all 58 elements analyzed except for Si, for which the detection limit is 312 μg/g. Nonetheless, all cBN powders studied are found to have high Si impurity levels that are above detection limit. This study provides a much-needed analytical protocol to enable comprehensive screening of impurities in cBN.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Stellarator coil design using cubic splines for improved access on the outboard side

In recent years many efforts have been undertaken to simplify coil designs for stellarators due to the difficulties in fabricating non-planar coils. Additionally, the FOCUS code removes the need for a winding surface and represents the coils as arbitrary curves in 3D. In the following work, the implementation of a spline representation for the coils in FOCUS is described, along with the implementation of a new engineering constraint to design coils with a straighter outer section. The new capabilities of the code are shown as an example on HSX, NCSX, and a prototype quasi-axisymmetric reactor-sized stellarator. The flexibility granted by splines along with the new constraint will allow for stellarator coil designs with improved accessibility and simplified maintenance.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗