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Sample records for 10exp 6 cubic

  1. 39 photons/bit direct detection receiver at 810 nm, BER = 1 x 10 exp -6, 60 Mb/s QPPM

    NASA Astrophysics Data System (ADS)

    MacGregor, Andrew; Dion, Bruno; Noeldeke, Christoph; Duchmann, Olivier

    1991-06-01

    39 photons/bit direct detection receiver sensitivity is reported, at a BER of 1 x 10 exp -6, for a 2-percent extinction ratio, 810 nm, 60 Mb/s QPPM signal. The sensitivity is 68 photons/bit at a BER of 1 x 10 exp -9. These figures represent a record sensitivity for a direct detection receiver. They are achieved by a combination of a novel silicon avalanche photodiode, an optimized preamplifier and a maximum likelihood demodulator. The work was a part of Phase B Breadboarding activities for the European Space Agency (ESA) SILEX (Semiconductor Intersatellite Link EXperiment) program on Intersatellite Optical Links.

  2. Preliminary Investigation of Molybdenum Disulfide-air-mist Lubrication for Roller Bearings Operating to DN Values of 1 x 10(exp 6) and Ball Bearings Operating to Temperatures of 1000 F

    NASA Technical Reports Server (NTRS)

    Macks, E F; Nemeth, Z N; Anderson, W J

    1951-01-01

    The effectiveness of molybdenum disulfide MoS2 as a bearing lubricant was determined at high temperature and at high speeds. A 1-inch-bore ball bearing operated at temperatures to 1000 F, a speed of 1725 rpm, and a thrust load of 20 pounds when lubricated only with MoS2-air mist. A 75-millimeter-bore cageless roller bearing, provided with a MoS2-syrup coating before operation, operated at DN values to 1 x 10(exp 6) with a load of 368 pounds.

  3. Heat Transfer and Boundary-Layer Transition on a Highly Polished Hemisphere-Cone in Free Flight at Mach Numbers Up to 3.14 and Reynolds Numbers Up to 24 x 10(exp 6)

    NASA Technical Reports Server (NTRS)

    Buglia, James J.

    1961-01-01

    A highly polished hemisphere-cone having a ratio of nose radius to base radius of 0.74 and a half-angle of 14.5 was flight tested at Mach numbers up to 4.70. Temperature and pressure data were obtained at Mach numbers up to 3.14 and a free-stream Reynolds number of 24 x 10(exp 6) based on body diameter. The nose of the model had a surface roughness of 2 to 5 microinches as measured with an interferometer. The measured Stanton numbers were in good agreement with theory. Transition Reynolds numbers based on the laminar boundary-layer momentum thickness at transition ranged from 2,190 to 794. Comparison with results from previous tests of blunt shapes having a surface roughness of 20 to 40 microinches showed that the high degree of polish was instrumental in delaying the transition from laminar to turbulent flow.

  4. Measurements of Local Heat Transfer and Pressure on Six 2-Inch-Diameter Blunt Bodies at a Mach Number of 4.95 and at Reynolds Numbers Per Foot up to 81 x 10(exp 6)

    NASA Technical Reports Server (NTRS)

    Cooper, Morton; Mayo, Edward E.

    1959-01-01

    Measurements of the local heat transfer and pressure distribution have been made on six 2-inch-diameter, blunt, axially symmetric bodies in the Langley gas dynamics laboratory at a Mach number of 4.95 and at Reynolds numbers per foot up to 81 x 10(exp 6). During the investigation laminar flow was observed over a hemispherical-nosed body having a surface finish from 10 to 20 microinches at the highest test Reynolds number per foot (for this configuration) of 77.4 x 10(exp 6). Though it was repeatedly possible to measure completely laminar flow at this Reynolds number for the hemisphere, it was not possible to observe completely laminar flow on the flat-nosed body for similar conditions. The significance of this phenomenon is obscured by the observation that the effects of particle impacts on the surface in causing roughness were more pronounced on the flat-nosed body. For engineering purposes, a method developed by M. Richard Dennison while employed by Lockheed Aircraft Corporation appears to be a reasonable procedure for estimating turbulent heat transfer provided transition occurs at a forward location on the body. For rearward-transition locations, the method is much poorer for the hemispherical nose than for the flat nose. The pressures measured on the hemisphere agreed very well with those of the modified Newtonian theory, whereas the pressures on all other bodies, except on the flat-nosed body, were bracketed by modified Newtonian theory both with and without centrifugal forces. For the hemisphere, the stagnation-point velocity gradient agreed very well with Newtonian theory. The stagnation-point velocity gradient for the flat- nosed model was 0.31 of the value for the hemispherical-nosed model. If a Newtonian type of flow is assumed, the ratio 0.31 will be independent of Much number and real-gas effects.

  5. Low-Speed Longitudinal Stability and Lateral-Control Characteristics of a 0.3-Scale Model of the Republic RF-84F Airplane at a Reynolds Number of 9x10(exp 6)

    NASA Technical Reports Server (NTRS)

    Bollech, Thomas V.; Kelly, H. Neale

    1954-01-01

    An investigation was conducted in the Langley 19-foot pressure tunnel on a 0.3-scale model of the Republic RF-84F airplane to determine modifications which would eliminate the pitch-up that occurred near maximum lift during flight tests of the airplane. The effects of high-lift and stall-control devices, horizontal tail locations, external stores, and various inlets on the longitudinal characteristics of the model were investigated. For the most part, these tests were conducted at a Reynolds number of 9.0 x 10(exp 6) and a Mach number of 0.19. The results indicated that from the standpoint of stability the inlets should possess blunted side bodies. The horizontal tail located at either the highest or lowest position investigated improved the stability of the model. Three configurations were found for the model equipped with the production tail which eliminated the pitch-up through the lift range up to the maximum lift and provided a stable static margin which did not vary more than 15% of the mean aerodynamic chord through the lift range up to 85% of maximum lift. The three configurations are as follows: the production wing-fuselage-tail combination with an inlet similar to the production inlet but smaller in plan form in conjunction with either (1) a wing fence located at 65% of the win semispan or (2) an 11.7% chord leading-edge extension extending from 65.8 to 95.8% of the wing semispan and (3) the production wing-fuselage-tail combination with the production inlet and an 11.7% chord leading-edge extension extending from 70.8 to 95.8% of the wing semispan.

  6. Heat-Transfer and Pressure Measurements from a Flight Test of the Third 1/18-Scale Model of the Titan Intercontinental Ballistic Missile up to a Mach Number of 3.86 and Reynolds Number per Foot of 23.5 x 10(exp 6) and a Comparison with Heat Transfer

    NASA Technical Reports Server (NTRS)

    Graham, John B., Jr.

    1958-01-01

    Heat-transfer and pressure measurements were obtained from a flight test of a 1/18-scale model of the Titan intercontinental ballistic missile up to a Mach number of 3.86 and Reynolds number per foot of 23.5 x 10(exp 6) and are compared with the data of two previously tested 1/18-scale models. Boundary-layer transition was observed on the nose of the model. Van Driest's theory predicted heat-transfer coefficients reasonably well for the fully laminar flow but predictions made by Van Driest's theory for turbulent flow were considerably higher than the measurements when the skin was being heated. Comparison with the flight test of two similar models shows fair repeatability of the measurements for fully laminar or turbulent flow.

  7. The Influence of Low Wall Temperature on Boundary-Layer Transition and Local Heat Transfer on 2-Inch-Diameter Hemispheres at a Mach Number of 4.95 and a Reynolds Number per Foot of 73.2 x 10(exp 6)

    NASA Technical Reports Server (NTRS)

    Cooper, Morton; Mayo, Edward E.; Julius, Jerome D.

    1960-01-01

    Measurements of the location of boundary-layer transition and the local heat transfer have been made on 2-inch-diameter hemispheres in the Langley gas dynamics laboratory at a Mach number of 4.95, a Reynolds number per foot of 73.2 x 10(exp 6), and a stagnation temperature of approximately 400 F. The transient-heating thin-skin calorimeter technique was used, and the initial values of the wall-to-stream stagnation- temperature ratios were 0.16 (cold-model tests) and 0.65 (hot-model test). During two of the four cold tests, the boundary-layer flow changed from turbulent to laminar over large regions of the hemisphere as the model heated. On the basis of a detailed consideration of the magnitude of roughness possibly present during these two cold tests, it appears that this destabilizing effect of low wall temperatures (cooling) was not caused by roughness as a dominant influence. This idea of a decrease in boundary-layer stability with cooling has been previously suggested. (See, for example, NASA Memorandum 10-8-58E.) For the laminar data obtained during the early part of the hot test, the correlation of the local-heating data with laminar theory was excellent.

  8. A vacuum (10 exp -9 torr) friction apparatus for determining friction and endurance life of MoS(x) films

    NASA Technical Reports Server (NTRS)

    Miyoshi, Kazuhisa; Honecy, Frank S.; Abel, Phillip B.; Pepper, Stephen V.; Spalvins, Talivaldis; Wheeler, Donald R.

    1993-01-01

    An ultrahigh-vacuum tribometer for use in a ball-on-disk configuration was specially designed for measuring the friction and endurance life of magnetron-sputtered solid lubricating MoS(x) films deposited on sputter-cleaned 400 C stainless-steel disks, when slid against a 6-mm-diameter 440 C stainless-steel ball. The results of tests showed that the tribometer performs satisfactorily in unidirectional rotation in vacuum at a pressure of 10 exp -7 Pa, 10 exp -9 torr. Similarities are observed in the life cycle friction behavior and the coefficient of friction as a function of the number of disk revolutions, for MoS(x) films at average Hertzian contact from 0.33 to 0.69 GPa.

  9. A vacuum (10(exp -9) Torr) friction apparatus for determining friction and endurance life of MoSx films

    NASA Technical Reports Server (NTRS)

    Miyoshi, Kazuhisa; Honecy, Frank S.; Abel, Phillip B.; Pepper, Stephen V.; Spalvins, Talivaldis; Wheeler, Donald R.

    1992-01-01

    The first part of this paper describes an ultrahigh vacuum friction apparatus (tribometer). The tribometer can be used in a ball-on-disk configuration and is specifically designed to measure the friction and endurance life of solid lubricating films such as MoS(x) in vacuum at a pressure of 10 exp -7 Pa. The sliding mode is typically unidirectional at a constant rotating speed. The second part of this paper presents some representative friction and endurance life data for magnetron sputtered MoS(x) films (110 nm thick) deposited on sputter-cleaned 440 C stainless-steel disk substrates, which were slid against a 6-mm-diameter 440 C stainless-steel bearing ball. All experiments were conducted with loads of 0.49 to 3.6 N (average Hertzian contact pressure, 0.33 to 0.69 GPa), at a constant rotating speed of 120 rpm (sliding velocity ranging from 31 to 107 mm/s due to the range of wear track radii involved in the experiments), in a vacuum of 7 x 10 exp -7 Pa and at room temperature. The results indicate that there are similarities in friction behavior of MoS(x) films overs their life cycles regardless of load applied. The coefficient of friction (mu) decreases as load W increases according to mu = kW exp -1/3. The endurance life E of MoS(x) films decreases as the load W increases according to E = KW exp -1.4 for the load range. The load- (or contract-pressure-) dependent endurance life allows us to reduce the time for wear experiments and to accelerate endurance life testing of MoS(x) films. For the magnetron-sputtered MoS(x) films deposited on 440 C stainless-steel disks: the specific wear rate normalized to the load and the number of revolutions was 3 x 10 exp -8 mm exp 3/N-revolution; the specific wear rate normalized to the load and the total sliding distance was 8 x 10 exp -7 mm exp 3/N-m; and the nondimensional wear coefficient of was approximately 5 x 10 exp -6. The values are almost independent of load in the range 0.49 to 3.6 N (average Hertzian contact

  10. Laboratory Demonstration of Phase Induced Amplitude Apodization (PIAA) Coronagraph with Better than 10(exp -9) Contrast

    NASA Technical Reports Server (NTRS)

    Kern, Brian; Guyon, Olivier; Kuhnert, Andreas; Niessner, Albert; Martinache, Frantz; Balasubramanian, Kunjithapatham

    2013-01-01

    We present coronagraphic images from the Phase Induced Amplitude Apodization (PIAA) coronagraph on NASA's High Contrast Imaging Testbed (HCIT) at the Jet Propulsion Lab, showing contrasts of 5x10(exp -1) averaged from 2-4 lambda/D, in monochromatic light at 808 nm. In parallel with the coronagraph and its deformable mirror and coronagraphic wavefront control, we also demonstrate a low-order wavefront control system, giving 100 x rms suppression of introduced tip/tilt disturbances down to residual levels of 10(exp -3) lambda/D. Current limitations, as well as broadband (10% fractional bandpass) preliminary results are discussed.

  11. Cubic zero-field splitting of a 6state ion

    NASA Astrophysics Data System (ADS)

    Yu, Wan-Lun

    1989-01-01

    The zero-field splitting of a 6state ion in a cubic field has been studied in detail within the d5 configuration. It is found that the splitting arises mainly from the coupling among the excited states 4T1, 2T2, and 2E and the ground state 6A1 via the spin-orbit interaction. The splitting parameter a can be expressed approximately as F0ζ4+F1ζ5, where F0 and F1 are independent of the spin-orbit coupling constant ζ and have a property ||F0||>>||F1||. Analytical formulas of F0 and F1 are derived by a perturbation calculation with the help of the procedure suggested by Macfarlane. Based on this, a very simple expression of a is obtained semiempirically. Calculations are carried out for the splittings of Fe3+ and Mn2+ ions substituted as impurities in several octahedrally coordinated lattices and for the splitting parameter dependences on pressure for Fe3+ and Mn2+ in MgO crystals. The results are in good agreement with the values observed experimentally, indicating a successful interpretation of the crystal-field theory for the cubic zero-field splittings of 6state ions in octahedral coordinations. The power law a~R-m has been investigated on a theoretical basis. This is indicated to be able to reasonably account for the observed data for a system that has Dq or a values close to each other. In particular, a reasonable value m=12+/-2 is expected for Mn2+ ions having Dq<~B.

  12. An Instrument to Measure Elemental Energy Spectra of Cosmic Ray Nuclei Up to 10(exp 16) eV

    NASA Technical Reports Server (NTRS)

    Adams, J.; Bashindzhagyan, G.; Chilingarian, A.; Drury, L.; Egorov, N.; Golubkov,S.; Korotkova, N.; Panasyuk, M.; Podorozhnyi, D.; Procqureur, J.

    2000-01-01

    A longstanding goal of cosmic ray research is to measure the elemental energy spectra of cosmic rays up to and through the "knee" (approx. equal to 3 x 10 (exp 15) eV. It is not currently feasible to achieve this goal with an ionization calorimeter because the mass required to be deployed in Earth orbit is very large (at least 50 tonnes). An alternative method will be presented. This is based on measuring the primary particle energy by determining the angular distribution of secondaries produced in a target layer using silicon microstrip detector technology. The proposed technique can be used over a wide range of energies (10 (exp 11)- 10 (exp 16) eV) and gives an energy resolution of 60% or better. Based on this technique, a design for a new lightweight instrument with a large aperture (KLEM) will be described.

  13. Electrical characterization of 6H crystalline silicon carbide. M.S. Thesis Final Report

    NASA Technical Reports Server (NTRS)

    Lempner, Stephen E.

    1994-01-01

    Crystalline silicon carbide (SiC) substrates and epilayers, undoped as well as n- and p-doped, have been electrically characterized by performing Hall effect and resistivity measurements (van der Pauw) over the temperature range of approximately 85 K to 650 K (200 K to 500 K for p-type sample). By fitting the measured temperature dependent carrier concentration data to the single activation energy theoretical model: (1) the activation energy for the nitrogen donor ranged from 0.078 eV to 0.101 eV for a doping concentration range of 10(exp 17) cm(exp -3) to 10(exp 18) cm(exp -3) and (2) the activation energy for the aluminum acceptor was 0.252 eV for a doping concentration of 4.6 x 10(exp 18) cm(exp -3). By fitting the measured temperature dependent carrier concentration data to the double activation energy level theoretical model for the nitrogen donor: (1) the activation energy for the hexagonal site was 0.056 eV and 0.093 eV corresponding to doping concentrations of 3.33 x 10 (exp 17) cm(exp -3) and 1.6 x 10(exp 18) cm(exp -3) and (2) the activation energy for the cubic site was 0.113 and 0.126 eV corresponding to doping concentrations of 4.2 x 10(exp 17) cm(exp -3) and 5.4 x 10(exp 18) cm(exp -3).

  14. Optical anomaly in artificial cubic hieratite, K2[SiF6].

    PubMed

    Göbel, Ole F; ten Elshof, Johan E; Kaminsky, Werner; Hannss, Matthias

    2015-06-01

    Crystals of K2[SiF6] were grown in agar gel, silica gel and jelly. Crystals grown in agar gel or jelly exhibit birefringence and consist of six double refracting growth sectors, each having the shape of a tetragonal pyramid. Nevertheless, the structure of the crystals from agar gel could be refined as cubic (space group Fm3m) with a weighted R factor of 0.043. The amount of birefringence was estimated by the Senarmont compensation method and the rotating polarizer method. PMID:26027008

  15. Magnetic properties of cubic compound Ce6Ni6P17 with geometric frustrations

    NASA Astrophysics Data System (ADS)

    Takeda, N.; Izumi, K.; Ono, H.; Yodono, S.; Nakano, T.

    2012-12-01

    We report the magnetic susceptibility and the low-temperature specific heat of Ce6Ni6P17 with geometric frustrations and La6Ni6P17 as a nonmagnetic counterpart. The magnetic susceptibility of Ce6Ni6P17 decreases monotonically with decreasing temperature and the specific heat shows a broad peak around 1.4K. The evaluated magnetic entropy is about a half of Rln2 at 5.0 K. This result suggests that the frustrations persist down to very low temperatures and the residual entropy originate from frustration is present.

  16. Low temperature molten-salt synthesis of nanocrystalline cubic Sr 2SbMnO 6

    NASA Astrophysics Data System (ADS)

    Baral, Antara; Varma, K. B. R.

    2009-12-01

    Sr 2SbMnO 6 (SSM) powders were successfully synthesized at reasonably low temperatures via molten-salt synthesis (MSS) method using eutectic composition of 0.635 Li 2SO 4-0.365 Na 2SO 4 (flux). High-temperature cubic phase SSM was stabilized at room temperature by calcining the as-synthesized powders at 900 °C/10 h. The phase formation and morphology of these powders were characterized via X-ray powder diffraction and scanning electron microscopy, respectively. The SSM phase formation associated with ˜60 nm sized crystallites was also confirmed by transmission electron microscopy. The activation energy associated with the particle growth was found to be 95±5 kJ mol -1. The dielectric constant of the tetragonal phase of the ceramic (fabricated using this cubic phase powder) with and without the flux (sulphates) has been monitored as a function of frequency (100 Hz-1 MHz) at room temperature. Internal barrier layer capacitance (IBLC) model was invoked to rationalize the dielectric properties.

  17. Low temperature molten-salt synthesis of nanocrystalline cubic Sr{sub 2}SbMnO{sub 6}

    SciTech Connect

    Baral, Antara; Varma, K.B.R.

    2009-12-15

    Sr{sub 2}SbMnO{sub 6} (SSM) powders were successfully synthesized at reasonably low temperatures via molten-salt synthesis (MSS) method using eutectic composition of 0.635 Li{sub 2}SO{sub 4}-0.365 Na{sub 2}SO{sub 4} (flux). High-temperature cubic phase SSM was stabilized at room temperature by calcining the as-synthesized powders at 900 deg. C/10 h. The phase formation and morphology of these powders were characterized via X-ray powder diffraction and scanning electron microscopy, respectively. The SSM phase formation associated with {approx}60 nm sized crystallites was also confirmed by transmission electron microscopy. The activation energy associated with the particle growth was found to be 95+-5 kJ mol{sup -1}. The dielectric constant of the tetragonal phase of the ceramic (fabricated using this cubic phase powder) with and without the flux (sulphates) has been monitored as a function of frequency (100 Hz-1 MHz) at room temperature. Internal barrier layer capacitance (IBLC) model was invoked to rationalize the dielectric properties. - Graphical abstract: The as synthesized powders of Sr{sub 2}SbMnO{sub 6} calcined at 900 deg. C/10 h yielded a cubic phase ({approx}60 nm sized crystallites). Centrosymmetric tetragonal (I4/mcm) phase was obtained by increasing the calcination temperature to 1000 deg. C. Display Omitted

  18. Spectroscopy of luminous infrared galaxies at 2 microns: 1. The ultraluminous galaxies (L(sub IR) approximately greater than 10 (exp 12) solar luminosity)

    NASA Technical Reports Server (NTRS)

    Goldader, Jeffrey D.; Joseph, R. D.; Doyon, Rene; Sanders, D. B.

    1995-01-01

    We present high-quality spectra covering the K window at a resolving power of 340 for a sample of 13 ultraluminous (L(sub IR) approximately greater than 10(exp 12) solar luminosity) infrared-selected galaxies, and line fluxes for a comparison sample of 24 lower luminosity galaxies. The 2 micrometers spectra of 10 of the ultraluminous galaxies are characterized by emission and absorption features commonly associated with stars and star formation; two others have the red power-law spectra and Br gamma line widths of Seyfert 1 galaxies; the final galaxy has strong emission from hot dust. We have found no broad-line active nuclei not already known from optical observations, despite the fact that the extinction at 2 micrometers is 1/10 that at optical wavelengths; any putative Seyfert 1 nuclei must be deeply buried. Powerful continua and emission lines from H2 and Br gamma are detected in all the ultraluminous galaxies. Comparing the H2 1-0 S(1), Br gamma, and 2 micrometers and far-infrared luminosities to those of the lower luminosity galaxies yields several major results. First, the dereddened Br gamma emission, relative to the far-infrared luminosity is significantly depressed in the ultraluminous sample, when compared to the lower luminosity galaxies. Five of the ultraluminous galaxies have L(sub Br gamma)L(sub IR) ratios lower than for any of the comparison objects. Second, the H2 1-0 S(1) luminosity is also responsible, directly or indirectly, for producing the excited H2, and that the H2 apparently comes from optically thin regions in both classes of objects. Third, eight of the 13 ultraluminous systems have lower 2 micrometers/far-infrared luminosity ratios than any of the lower luminosity galaxies, and five of these are the galaxies also deficient in Br gamma. These three findings may be understood if the the H2, Br gamma, and 2 mircometers continua in the ultraluminous galaxies arise from spatially distinct regions, with the continuum and Br gamma largely

  19. Syntheses and characterization of the cubic uranium chalcogenides Rh2U6S15, Cs2Ti2U6Se15, Cs2Cr2U6Se15, and Cs2Ti2U6Te15

    NASA Astrophysics Data System (ADS)

    Ward, Matthew D.; Oh, George N.; Mesbah, Adel; Lee, Minseong; Sang Choi, Eun; Ibers, James A.

    2015-08-01

    The compounds Rh2U6S15, Cs2Ti2U6Se15, Cs2Cr2U6Se15, and Cs2Ti2U6Te15 have been synthesized at 1173 K. All crystallize in space group Oh9- Im 3 bar m of the cubic system. Rh2U6S15 has a framework structure with three-dimensional channels. The compounds Cs2Ti2U6Se15, Cs2Cr2U6Se15, and Cs2Ti2U6Te15 have structures similar to that of Rh2U6S15, but with Cs cations variably filling the channels. In all four structures the transition element is octahedrally coordinated by chalcogens and the uranium atom is in a bicapped trigonal-prismatic arrangement. The temperature dependence of the magnetic susceptibility of Cs2Cr2U6Se15 implies both Cr and U magnetic contributions. From these data the compound is not antiferromagnetic, but it could have either a ferrimagnetic or a ferromagnetic ground state.

  20. The effect of disorder in Ba{sub 2}YTaO{sub 6} on the tetragonal to cubic phase transition

    SciTech Connect

    Zhou, Qingdi; Kennedy, Brendan J.; Kimpton, Justin A.

    2011-04-15

    Synchrotron X-ray diffraction and Raman spectroscopy have been used to study the structure of the complex perovskite Ba{sub 2}YTaO{sub 6}, at temperatures down to 100 K. Where the Ta and Y cations exhibit long-range rock-salt like ordering, Ba{sub 2}YTaO{sub 6} displays a continuous phase transition from a high temperature cubic structure, described in space group Fm3-bar m, to a tetragonal, I4/m, structure near 260 K. This transition is inhibited if extensive disorder and/or vacancies are/is present in the sample. -- Graphical abstract: The tetragonal-cubic phase transition observed in the cation ordered double perovskite Ba{sub 2}YTaO{sub 6} is inhibited when these are disordered. Display Omitted Highlights: {yields} Double perovskite Ba{sub 2}YTaO{sub 6} characterised by XRD and Raman spectroscopy. {yields} Cubic-tetragonal transition in Ba{sub 2}YTaO{sub 6} studied. {yields} Impact of disorder on the structure and phase transitions established.

  1. First principles study of the structural and electronic properties of double perovskite Ba2YTaO6 in cubic and tetragonal phases

    NASA Astrophysics Data System (ADS)

    Deluque Toro, C. E.; Rodríguez M., Jairo Arbey; Landínez Téllez, D. A.; Moreno Salazar, N. O.; Roa-Rojas, J.

    2014-12-01

    The Ba2YTaO6 double perovskite presents a transition from cubic (Fm-3m) to tetragonal structure (I4/m) at high temperature. In this work, we present a detailed study of the structural and electronic properties of the double perovskite Ba2YTaO6 in space group Fm-3m and I4/m. Calculations were made with the Full-Potential Linear Augmented Plane Wave method (FP-LAPW) within the framework of the Density Functional Theory (DFT) with exchange and correlation effects in the Generalized Gradient (GGA) and Local Density (LDA) approximations. From the minimization of energy as a function of volume and the fitting of the Murnaghan equation some structural characteristics were determined as, for example, total energy, lattice parameter (a=8.50 Å in cubic phase and a=5.985 Å and c=8.576 Å in tetragonal), bulk modulus (135.6 GPa in cubic phase and 134.1 GPa in tetragonal phase) and its derivative. The study of the electronic characteristics was performed from the analysis of the electronic density of states (DOS). We find a non-metallic behavior for this with a direct band gap of approximately 3.5 eV and we found that the Ba2YTaO6 (I4/m) phase is the most stable one. © 2013 Elsevier Science.

  2. Jeff = 1/2 Mott spin-orbit insulating state close to the cubic limit in Ca4IrO6

    NASA Astrophysics Data System (ADS)

    Calder, S.; Cao, G.-X.; Okamoto, S.; Kim, J. W.; Cooper, V. R.; Gai, Z.; Sales, B. C.; Lumsden, M. D.; Mandrus, D.; Christianson, A. D.

    2014-03-01

    The Jeff = 1/2 Mott spin-orbit insulating state is manifested in systems with large cubic crystal field splitting and spin-orbit coupling that are comparable to the on-site Coulomb interaction, U. 5d transition metal oxides host parameters in this regime and recently strong evidence for this state in Sr2IrO4, and additional iridates, has been presented. All the candidates, however, have distorted octahedra, such as the elongation along the c-axis in Sr2IrO4, and consequently a non-cubic local crystal field environment. Consequently the materials form a mixed Jeff = 1/2,3/2 ground state. The lack of a material with an unmixed Jeff = 1/2 has impacted the development and testing of robust models of this novel insulating and magnetic state. We present neutron diffraction, resonant x-ray scattering and DFT calculations that not only reveal Ca4IrO6 is a new candidate Jeff = 1/2 material with long-range magnetic order, but furthermore resides close to the required cubic limit. Both our experimental and theoretical investigation indicate Ca4IrO6 is uniquely positioned to act as a canonical system to investigate of the Jeff = 1/2 state. This research was supported by the Scientific User Facilities Division and the Materials Sciences and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy.

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

    NASA Technical Reports Server (NTRS)

    Watanabe, Shuichi; Wheeler, Donald R.; Abel, Phillip B.; Street, Kenneth W.; Miyoshi, Kazuhisa; Murakawa, Masao; Miyake, Shojiro

    1998-01-01

    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.

  4. Creating Reactivity with Unstable Endmembers using Pressure and Temperature: Synthesis of Bulk Cubic Mg0.4 Fe0.6 N.

    PubMed

    Serghiou, George; Ji, Gang; Odling, Nicholas; Reichmann, Hans J; Morniroli, Jean-Paul; Boehler, Reinhard; Frost, Dan J; Wright, Jonathan P; Wunder, Bernd

    2015-12-01

    Alloy and nitride solid solutions are prominent for structural, energy and information processing applications. There are frequently however barriers to making them. We remove barriers to reactivity here using pressure with a new synthetic approach. We target pressures where the reasons for cubic endmember nitride instability can become the driving force for cubic nitride solid solution stability. Using this approach we form a novel rocksalt Mg0.4 Fe0.6 N solid solution at between 15 and 23 GPa and up to 2500 K. This is a system where, neither an alloy nor a nitride solid solution form at ambient conditions and bulk MgN and FeN endmembers do not form, either at ambient or at high pressure. The new nitride is formed, by removing endmember lattice mismatch with pressure, allowing a stabilizing redistribution of valence electrons upon heating. This approach can be employed for a range of normally unreactive systems. Mg, Fe and enhanced nitrogen presence, may also indicate a richer reaction chemistry in our planets interior. PMID:26509919

  5. Molecular dynamics simulation of radiation damage in CaCd{sub 6} quasicrystal cubic approximant up to 10 keV

    SciTech Connect

    Chen, P. H.; Avchachov, K.; Nordlund, K.; Pussi, K.

    2013-06-21

    Due to the peculiar nature of the atomic order in quasicrystals, examining phase transitions in this class of materials is of particular interest. Energetic particle irradiation can provide a way to modify the structure locally in a quasicrystal. To examine irradiation-induced phase transitions in quasicrystals on the atomic scale, we have carried out molecular dynamics simulations of collision cascades in CaCd{sub 6} quasicrystal cubic approximant with energies up to 10 keV at 0 and 300 K. The results show that the threshold energies depend surprisingly strongly on the local coordination environments. The energy dependence of stable defect formation exhibits a power-law dependence on cascade energy, and surviving defects are dominated by Cd interstitials and vacancies. Only a modest effect of temperature is observed on defect survival, while irradiation temperature increases lead to a slight increase in the average size of both vacancy clusters and interstitial clusters.

  6. Density-Functional Theory Investigation of Sr2CrOsO6 with Cubic Symmetry Using Modified Becke—Johnson Potential

    NASA Astrophysics Data System (ADS)

    Guo, San-Dong

    2014-01-01

    We investigate the electronic structures and optical dielectric functions of the high temperature phase of Sr2 CrOsO6 with cubic structure by using Tran and Blaha's modified Becke and Johnson exchange potential. In the absence of spin-orbit coupling, the total spin moment is 0μB. When spin-orbit coupling is included, the small total spin moment and an unquenched Os orbital moment appear, and the spin non-conservation gap becomes smaller. The calculated net magnetic moment is smaller than the popular generalized gradient approximation result, and the spin non-conservation gap is larger. The optical dielectric functions with spin-orbit coupling are not very different from the ones without spin-orbit coupling.

  7. Theoretical Investigation of Stabilizing Mechanism by Boron in Body-Centered Cubic Iron Through (Fe,Cr)23(C,B)6 Precipitates

    NASA Astrophysics Data System (ADS)

    Sahara, Ryoji; Matsunaga, Tetsuya; Hongo, Hiromichi; Tabuchi, Masaaki

    2016-05-01

    Small amounts of boron improve the mechanical properties in high-chromium ferritic heat-resistant steels. In this work, the stabilizing mechanism by boron in body-centered cubic iron (bcc Fe) through (Fe,Cr)23(C,B)6 precipitates was investigated by first-principles calculations. Formation energy analysis of (Fe,Cr)23(C,B)6 reveals that the compounds become more stable to elemental solids as the boron concentration increases. Furthermore, the interface energy of bcc Fe(110) || Fe23(C,B)6(111) also decreases with boron concentration in the compounds. The decreased interface energy caused by boron addition is explained by the balance between the change in the phase stability of the precipitates and the change in the misfit parameter for the bcc Fe matrix and the precipitates. These results show that boron stabilizes the microstructure of heat-resistant steels, which is important for understanding the origins of the creep strength in ferritic steels.

  8. Pressure effects on CrCl63- embedded in cubic Cs2NaMCl6 (M=Sc,Y) lattices: Study through periodic and cluster calculations

    NASA Astrophysics Data System (ADS)

    García-Lastra, J. M.; Moreno, M.; Barriuso, M. T.

    2008-04-01

    The structural, elastic, vibrational, and optical properties of cubic elpasolites Cs2NaMCl6 (M=Sc,Y) containing CrCl63- complexes have been investigated by means of both periodic and cluster calculations as a function of pressure in the framework of density functional theory. Aside from calculating the host lattice bulk modulus BH and the local modulus B1 associated with the CrCl63-, complex particular attention is paid to the pressure dependence of Huang-Rhys factors, Sa and Se (related to local a1g and eg modes), and the Stokes shift associated with the first electronic excited state T2g4 (t2g2eg) of CrCl63-. The present calculations provide a big difference between BH=231kbars and B1=676kbars derived for Cs2NaScCl6:Cr3+ at zero pressure which plays a key role for a right interpretation of pressure effects on vibration frequencies and optical parameters due to CrCl63-. The significant decrease of Huang-Rhys factors, Sa and Se, due to the pressure observed experimentally is well accounted for by the present work which supports that ∂Sa/∂P is determined by the Grüneisen constant γa of the a1g local mode (whose frequency is νa) and the dependence of 10Dq on the metal-ligand distance. At the same time, the present results point out that the Stokes shift would be little pressure dependent in the range of 0-50kbars. Accordingly the Ham effect in the T2g4 (t2g2eg) state of CrCl63- in the cubic elpasolites would also happen for a pressure up to 50kbars but the spin-orbit constant would increase with respect to that at zero pressure. From the analysis carried out in this work it is also concluded that the figures dνa/dP =0.55cm-1/kbar and dSa/dP =-7.2×10-3kbar-1 extracted from the complex emission band of Cs2NaScCl6:Cr3+ are hardly compatible. This fact underlines the usefulness of ab initio calculations for helping in the analysis of complex experimental findings. Finally, as the CrCl63- unit is found to be to a good extent elastically decoupled from the rest of

  9. A calibration of the production rate ratio P-21/P-26 by low energy secondry neutrons: Identification of Ne spallation components at the 10(exp 6) atoms/g level in terrestrial samples

    NASA Technical Reports Server (NTRS)

    Graf, TH.; Niedermann, S.; Marti, K.

    1993-01-01

    The spallation ratio (Ne-22/Ne-21)(sub c) from Si was determined as 1.243 plus or minus 0.022 in a terrestrial quartz sample. We carried out a calibration of the in-situ production rate ratio P-21/P-26 in quartz samples for which Be-10 and Al-26 production rates were previously measured. A ratio P-21/P-26 of 0.67 plus or minus 0.12 is obtained.

  10. Synthesis, Structure, Multiband Optical, and Electrical Conductive Properties of a 3D Open Cubic Framework Based on [Cu8Sn6S24](z-) Clusters.

    PubMed

    Zhang, Xian; Wang, Qiuran; Ma, Zhimin; He, Jianqiao; Wang, Zhe; Zheng, Chong; Lin, Jianhua; Huang, Fuqiang

    2015-06-01

    Two compounds with the formulas of Na4Cu32Sn12S48·4H2O and K11Cu32Sn12S48·4H2O were synthesized via flux (with thiourea as reactive flux) and hydrothermal method, respectively. The black crystals of Na4Cu32Sn12S48·4H2O and K11Cu32Sn12S48·4H2O both crystallize in the cubic space group of Fm3̅c with the cell constants a = 17.921(2) Å and a = 18.0559(6) Å, respectively. The crystal structures feature a 3D open-framework with the unique [Cu8Sn6S24](z-) (z = 13 for Na4Cu32Sn12S48·4H2O; z = 14.75 for K11Cu32Sn12S48·4H2O) clusters acting as building blocks. The [Cu8Sn6S24](z-) cluster of the Th symmetry is built up by eight [CuS3] triangles and six [SnS4] tetrahedra. The powder samples were investigated by X-ray diffraction and optical absorption measurements. Both phase-pure compounds show multiabsorption character with a main absorption edge (2.0 eV for Na4Cu32Sn12S48·4H2O and 1.9 eV for K11Cu32Sn12S48·4H2O) and an additional absorption peak (1.61 eV for Na4Cu32Sn12S48·4H2O and 1.52 eV for K11Cu32Sn12S48·4H2O), which are perfectly consistent with the first-principle calculation results. The analyses of the density of states further reveal that the two optical absorption bands in each compound are attributed to the two transitions of Cu-3d-S-3p → Sn-5s. The multiband nature of two compounds also enhances photocatalytic activity under visible light irradiation, with which the degradation of methyl blue over Na4Cu32Sn12S48·4H2O reached 100% in 3 h. The 3D open-framework features also facilitate the ionic conductivity nature of the Na4Cu32Sn12S48·4H2O compound, which achieved ∼10(-5) S/cm at room temperature. PMID:25955506

  11. Pressure effects on CrCl6(3-) embedded in cubic Cs2NaMCl6 (M=Sc,Y) lattices: study through periodic and cluster calculations.

    PubMed

    García-Lastra, J M; Moreno, M; Barriuso, M T

    2008-04-14

    The structural, elastic, vibrational, and optical properties of cubic elpasolites Cs2NaMCl6 (M=Sc,Y) containing CrCl6(3-) complexes have been investigated by means of both periodic and cluster calculations as a function of pressure in the framework of density functional theory. Aside from calculating the host lattice bulk modulus BH and the local modulus B1 associated with the CrCl6(3-), complex particular attention is paid to the pressure dependence of Huang-Rhys factors, Sa and Se (related to local a1g and eg modes), and the Stokes shift associated with the first electronic excited state 4T2g (t2g 2eg) of CrCl6(3-). The present calculations provide a big difference between BH=231 kbars and B1=676 kbars derived for Cs2NaScCl6:Cr3+ at zero pressure which plays a key role for a right interpretation of pressure effects on vibration frequencies and optical parameters due to CrCl6(3-). The significant decrease of Huang-Rhys factors, Sa and Se, due to the pressure observed experimentally is well accounted for by the present work which supports that partial differential Sa/ partial differential P is determined by the Gruneisen constant gamma a of the a1g local mode (whose frequency is nu a) and the dependence of 10Dq on the metal-ligand distance. At the same time, the present results point out that the Stokes shift would be little pressure dependent in the range of 0-50 kbars. Accordingly the Ham effect in the 4T2g (t2g 2eg) state of CrCl6(3-) in the cubic elpasolites would also happen for a pressure up to 50 kbars but the spin-orbit constant would increase with respect to that at zero pressure. From the analysis carried out in this work it is also concluded that the figures d nu a/dP=0.55 cm(-1)kbar and dSa/dP=-7.2 x 10(-3) kbar(-1) extracted from the complex emission band of Cs2NaScCl6:Cr3+ are hardly compatible. This fact underlines the usefulness of ab initio calculations for helping in the analysis of complex experimental findings. Finally, as the CrCl6(3-) unit is

  12. Evidence from x-ray and neutron powder diffraction patterns that the so-called icosahedral and decagonal quasicrystals of MnAl/sub 6/ and other alloys are twinned cubic crystals

    SciTech Connect

    Pauling, L.

    1987-06-01

    It is shown that the x-ray powder diffraction patterns of rapidly quenched MnAl/sub 6/ and Mg/sub 32/(Al,Zn)/sub 49/ and the neutron powder diffraction pattern of MnAl/sub 5/ are compatible with the proposed 820-atom primitive cubic structure. The values found for the edge of the unit cube are 23.365 A (x-ray) and 23.416 A (neutron) for MnAl/sub 6/ and 24.313 A (x-ray) for Mg/sub 32/(Al,Zn)/sub 49/.

  13. Piecewise Cubic Interpolation Package

    1982-04-23

    PCHIP (Piecewise Cubic Interpolation Package) is a set of subroutines for piecewise cubic Hermite interpolation of data. It features software to produce a monotone and "visually pleasing" interpolant to monotone data. Such an interpolant may be more reasonable than a cubic spline if the data contain both 'steep' and 'flat' sections. Interpolation of cumulative probability distribution functions is another application. In PCHIP, all piecewise cubic functions are represented in cubic Hermite form; that is, f(x)more » is determined by its values f(i) and derivatives d(i) at the breakpoints x(i), i=1(1)N. PCHIP contains three routines - PCHIM, PCHIC, and PCHSP to determine derivative values, six routines - CHFEV, PCHFE, CHFDV, PCHFD, PCHID, and PCHIA to evaluate, differentiate, or integrate the resulting cubic Hermite function, and one routine to check for monotonicity. A FORTRAN 77 version and SLATEC version of PCHIP are included.« less

  14. Synthesis, Crystal Chemistry, and Electrochemical Properties of Li(7-2x)La3Zr(2-x)Mo(x)O12 (x = 0.1-0.4): Stabilization of the Cubic Garnet Polymorph via Substitution of Zr(4+) by Mo(6+).

    PubMed

    Rettenwander, Daniel; Welzl, Andreas; Cheng, Lei; Fleig, Jürgen; Musso, Maurizio; Suard, Emmanuelle; Doeff, Marca M; Redhammer, Günther J; Amthauer, Georg

    2015-11-01

    Cubic Li7La3Zr2O12 (LLZO) garnets are exceptionally well suited to be used as solid electrolytes or protecting layers in "Beyond Li-ion Battery" concepts. Unfortunately, cubic LLZO is not stable at room temperature (RT) and has to be stabilized by supervalent dopants. In this study we demonstrate a new possibility to stabilize the cubic phase at RT via substitution of Zr(4+) by Mo(6+). A Mo(6+) content of 0.25 per formula unit (pfu) stabilizes the cubic LLZO phase, and the solubility limit is about 0.3 Mo(6+) pfu. Based on the results of neutron powder diffraction and Raman spectroscopy, Mo(6+) is located at the octahedrally coordinated 16a site of the cubic garnet structure (space group Ia-3d). Since Mo(6+) has a smaller ionic radius compared to Zr(4+) the lattice parameter a0 decreases almost linearly as a function of the Mo(6+) content. The highest bulk Li-ion conductivity is found for the 0.25 pfu composition, with a typical RT value of 3.4 × 10(-4) S cm(-1). An additional significant resistive contribution originating from the sample interior (most probably from grain boundaries) could be identified in impedance spectra. The latter strongly depends on the prehistory and increases significantly after annealing at 700 °C in ambient air. Cyclic voltammetry experiments on cells containing Mo(6+) substituted LLZO indicate that the material is stable up to 6 V. PMID:26452048

  15. A Novel Tungsten-Nickel Alloy Ohmic Contact to SiC at 900 C

    NASA Technical Reports Server (NTRS)

    Okojie, Robert S.; Evans, Laura J.; Lukco, Dorothy; Morris, Joseph P.

    2010-01-01

    A novel tungsten-nickel ohmic contact metallization on 4H-SiC and 6H-SiC capable of surviving temperatures as high as 900 C is reported. Preliminary results revealed the following: 1) ohmic contact on n-type 4H-SiC having net doping levels (Nd's) of 1.4 and 2 x 10(exp 19) per cubic centimeter, with specific contact resistances rhosNd's of 7.69 x 10(exp -4) and 5.81 x 10(exp -4) OMEGA (raised dot) square centimeters, respectively, after rapid thermal annealing (RTA), and 5.9 x 10(exp -3) and 2.51 x 10(exp -4) OMEGA (raised dot) square centimeters, respectively, after subsequent soak at 900 C for 1 h in argon, and 2) ohmic contact on n- and p-type 6H-SiC having Nd > 2 x 10(exp 19) and Na > 1 x 10(exp 20) per cubic centimeter, with rhosNd = 5 x 10(exp -5) and rhosNa = 2 X 10(exp -4) OMEGA (raised dot) square centimeter, respectively, after RTA, and rhosNd = 2.5 x 10 (exp -5) and rhosNa = 1.5 x 10(exp -4) OMEGA (raised dot) square centimeter after subsequent treatment at 900 C for 1 h in argon, respectively.

  16. Accurate monotone cubic interpolation

    NASA Technical Reports Server (NTRS)

    Huynh, Hung T.

    1991-01-01

    Monotone piecewise cubic interpolants are simple and effective. They are generally third-order accurate, except near strict local extrema where accuracy degenerates to second-order due to the monotonicity constraint. Algorithms for piecewise cubic interpolants, which preserve monotonicity as well as uniform third and fourth-order accuracy are presented. The gain of accuracy is obtained by relaxing the monotonicity constraint in a geometric framework in which the median function plays a crucial role.

  17. Design of cubic-phase optical elements using subwavelength microstructures.

    PubMed

    Mirotznik, Mark S; van der Gracht, Joseph; Pustai, David; Mathews, Scott

    2008-01-21

    We describe a design methodology for synthesizing cubic-phase optical elements using two-dimensional subwavelength microstructures. We combined a numerical and experimental approach to demonstrate that by spatially varying the geometric properties of binary subwavelength gratings it is possible to produce a diffractive element with a cubic-phase profile. A test element was designed and fabricated for operation in the LWIR, approximately lambda=10.6 microm. Experimental results verify the cubic-phase nature of the element. PMID:18542199

  18. Cubic-normal distribution

    NASA Astrophysics Data System (ADS)

    Peng, Gan Chew; Hin, Pooi Ah; Ho, C. K.

    2015-12-01

    The power-normal distribution given in Yeo and Johnson in year 2000 is a unimodal distribution with wide ranges of skewness and kurtosis. A shortcoming of the power-normal distribution is that the negative and positve parts of the underlying random variable have to be specified by two different expressions of the standard normal random variable. In this paper, we construct a new distribution, called the cubic-normal distribution, via a single polynomial expression in cubic root function. Apart from having the properties which are similar to those of the power-normal distribution, this cubic-normal distribution can be developed into a multivariate version which is more attractive from the theoretical and computational points of view.

  19. Cubic nitride templates

    DOEpatents

    Burrell, Anthony K; McCleskey, Thomas Mark; Jia, Quanxi; Mueller, Alexander H; Luo, Hongmei

    2013-04-30

    A polymer-assisted deposition process for deposition of epitaxial cubic metal nitride films and the like is presented. The process includes solutions of one or more metal precursor and soluble polymers having binding properties for the one or more metal precursor. After a coating operation, the resultant coating is heated at high temperatures under a suitable atmosphere to yield metal nitride films and the like. Such films can be used as templates for the development of high quality cubic GaN based electronic devices.

  20. Boundary-Layer Instability Measurements in a Mach-6 Quiet Tunnel

    NASA Technical Reports Server (NTRS)

    Berridge, Dennis C.; Ward, Christopher, A. C.; Luersen, Ryan P. K.; Chou, Amanda; Abney, Andrew D.; Schneider, Steven P.

    2012-01-01

    Several experiments have been performed in the Boeing/AFOSR Mach-6 Quiet Tunnel at Purdue University. A 7 degree half angle cone at 6 degree angle of attack with temperature-sensitive paint (TSP) and PCB pressure transducers was tested under quiet flow. The stationary crossflow vortices appear to break down to turbulence near the lee ray for sufficiently high Reynolds numbers. Attempts to use roughness elements to control the spacing of hot streaks on a flared cone in quiet flow did not succeed. Roughness was observed to damp the second-mode waves in areas influenced by the roughness, and wide roughness spacing allowed hot streaks to form between the roughness elements. A forward-facing cavity was used for proof-of-concept studies for a laser perturber. The lowest density at which the freestream laser perturbations could be detected was 1.07 x 10(exp -2) kilograms per cubic meter. Experiments were conducted to determine the transition characteristics of a streamwise corner flow at hypersonic velocities. Quiet flow resulted in a delayed onset of hot streak spreading. Under low Reynolds number flow hot streak spreading did not occur along the model. A new shock tube has been built at Purdue. The shock tube is designed to create weak shocks suitable for calibrating sensors, particularly PCB-132 sensors. PCB-132 measurements in another shock tube show the shock response and a linear calibration over a moderate pressure range.

  1. New tetragonal derivatives of cubic NaZn13-type structure: RNi6Si6 compounds, crystal structure and magnetic ordering (R=Y, La, Ce, Sm, Gd-Yb)

    NASA Astrophysics Data System (ADS)

    Pani, M.; Manfrinetti, P.; Provino, A.; Yuan, Fang; Mozharivskyj, Y.; Morozkin, A. V.; Knotko, A. V.; Garshev, A. V.; Yapaskurt, V. O.; Isnard, O.

    2014-02-01

    Novel RNi6Si6 compounds adopt the new CeNi6Si6-type structure for R=La-Ce (tP52, space group P4/nbm N 125-1) and new YNi6Si6-type structure for R=Y, Sm, Gd-Yb (tP52, space group P4barb2N 117) that are tetragonal derivative of NaZn13-type structure, like LaCo9Si4-type. The CeNi6Si6, GdNi6Si6, TbNi6Si6, DyNi6Si6 and HoNi6Si6 compounds are Curie-Weiss paramagnets down to ~30 K, and do not order magnetically down to 5 K. However, the inverse paramagnetic susceptibility of LaNi6Si6 does not follow Curie-Weiss law. The DyNi6Si6 shows ferromagnetic-like saturation behaviour at 5 K in applied fields of 50 kOe, giving rise to a magnetic moment value of 6.5 μB/f.u. in 50 kOe. The powder neutron diffraction study in zero applied filed indicates square modulated the c-collinear antiferromagnetic ordering of TbNi6Si6 with K=[±1/4, ±1/4, 0] wave vector below ~10 K. The CeNi6Si6, GdNi6Si6, TbNi6Si6, DyNi6Si6 and HoNi6Si6 compounds are Curie-Weiss paramagnets down to ~30 K, and do not order magnetically down to 4.2 K. The powder neutron diffraction study in zero applied filed indicates square modulated the c-collinear antiferromagnetic ordering of TbNi6Si6 with K=[±1/4, ±1/4, 0] wave vector below ~10 K.

  2. Synthesis and structures of new niobium cluster compounds with pyridinium cations: (PyrH){sub 2}[Nb{sub 6}Cl{sub 18}].EtOH (Pyr: pyridine, Et: ethyl) and the cubic modification of (PyrH){sub 2}[Nb{sub 6}Cl{sub 18}

    SciTech Connect

    Flemming, Anke; Hoppe, Alessandra

    2008-10-15

    Slow crystallization of (PyrH){sub 2}[Nb{sub 6}Cl{sub 18}] from hot ethanol solution affords triclinic (PyrH){sub 2}[Nb{sub 6}Cl{sub 18}].EtOH. Treatment of [Nb{sub 6}Cl{sub 14}(H{sub 2}O){sub 4}].4H{sub 2}O with pyridine in a methanol solution gives the second title compound, the cubic modification of (PyrH){sub 2}[Nb{sub 6}Cl{sub 18}]. Both structures were determined by single crystal X-ray diffraction, (PyrH){sub 2}[Nb{sub 6}Cl{sub 18}].EtOH: P1-bar , a=9.3475(3), b=9.3957(3), c=10.8600(3) A, {alpha}=82.582(1){sup o}, {beta}=78.608(1){sup o}, and {gamma}=78.085(1){sup o}, Z=1, R{sub 1}(F)/wR{sub 2}(F{sup 2})=0.0254/0.0573, cub.-(PyrH){sub 2}[Nb{sub 6}Cl{sub 18}]: Fd3-bar m, a=19.935(2) A, Z=8, R{sub 1}(F)/wR{sub 2}(F{sup 2})=0.0557/0.1796. The cluster compounds contain isolated, molecular [Nb{sub 6}Cl{sup i}{sub 12}Cl{sup a}{sub 6}]{sup 2-} cluster anions with an octahedron of metal atoms edge bridged by chlorido ligands with additional ones on all the six exo positions. These cluster anions are separated by the pyridinium cations and ethanol solvent molecules, respectively. For the cubic modification of (PyrH){sub 2}[Nb{sub 6}Cl{sub 18}], a structural comparison is given to the known rhombohedral modification using the group-subgroup relations as expressed by a Baernighausen tree. - Graphical abstract: The synthesis and structure of a second cubic modification of (PyrH){sub 2}[Nb{sub 6}Cl{sub 18}] and of the new (PyrH){sub 2}[Nb{sub 6}Cl{sub 18}].EtOH are reported, both of which contain isolated niobium halide cluster anions with an octahedral core of metal atoms.

  3. Influence of global and local distortion on magnetic properties of cubic La0.6Ba0.4-xCaxCoO3

    NASA Astrophysics Data System (ADS)

    Chang, Hong; Gao, Yu; Wu, Qiang; Dong, Xiaohua; Li, Yunfei; Pang, Yanbo

    2015-12-01

    The magnetic and structural study of the La0.6Ba0.4-xCaxCoO3 (x=0.0, 0.1, 0.2, 0.3, and 0.4) compounds with the lowest global or local distortion are studied. The compounds with x=0, 0.1, 0.2 and 0.3 is crystallized in the structure with the space group Pm-3m, and that with x=0.4 is Pnma. A ferromagnetic-like transition is observed and the Curie temperature, ranging from 235 K to 220 K, decreases slightly with the increasing Ca2+ content for x≤0.3, and the transition temperature is as low as 175 K with x=0.4. A hump, with the hump temperature slightly increase with the Ca2+ content, is observed in the thermal magnetization curves of all of the compounds at the ZFC state, and it is owing to the magnetic frustration because of the coexistence of the FM and the AFM interaction. Above the transition temperature, the magnetic susceptibility versus the temperature is fitted with the ferromagnetic Curie-Weiss law for the compounds with x≤0.3, and that with x=0.4 coincides with the ferrimagnetic Weiss-mean-field model. The absolute values of the exchange constants J1 in the compounds with x≤0.3 and those of J CO 3+CO 3+, J CO 3+CO4+, JCO4+CO4+ of La0.6Ca0.4CoO3 are deduced from the fitting. The results indicate that (i) the ferromagnetic exchange constants J1 increases with the Ca2+ content x≤0.3; (ii) the ferromagnetic interaction, JCo3+Co4+, plays a main role in the magnetic properties of La0.6Ca0.4CoO3; (iii) the antiferromagnetic interactions, JCo3+Co3+, JCo4+Co4+, are not negligible in the compound x=0.4. The unsaturated magnetization at 70 kOe and the high coercive field in the hysteretic magnetization curve supports the existence of the antiferromagnetic interaction, and the percentage of the antiferromagnetic domain is calculated.

  4. Zr{sub 2}Ir{sub 6}B with an eightfold superstructure of the cubic perovskite-like boride ZrIr{sub 3}B{sub 0.5}: Synthesis, crystal structure and bonding analysis

    SciTech Connect

    Hermus, Martin; Fokwa, Boniface P.T.

    2010-04-15

    Single phase powder samples and single crystals of Zr{sub 2}Ir{sub 6}B were successfully synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere. Superstructure reflections were observed both on powder and on single crystal diffraction data, leading to an eightfold superstructure of ZrIr{sub 3}B{sub x} phase. The new phase, which has a metallic luster, crystallizes in space group Fm3-barm (no. 225) with the lattice parameters a=7.9903(4) A, V=510.14(4) A{sup 3}. Its crystal structure was refined on the basis of powder as well as single crystal data. The single crystal refinement converged to R{sub 1}=0.0239 and wR{sub 2}=0.0624 for all 88 unique reflections and 6 parameters. Zr{sub 2}Ir{sub 6}B is isotypic to Ti{sub 2}Rh{sub 6}B and its structure can be described as a defect double perovskite, A{sub 2}BB'O{sub 6}, where the A site is occupied by zirconium, the B site by boron, the O site by iridium but the B' site is vacant, leading to the formation of empty and boron-filled octahedral Ir{sub 6} clusters. According to the result of tight-binding electronic structure calculations, Ir-B and Ir-Zr interactions are mainly responsible for the structural stability of the phase. According to COHP bonding analysis, the strongest bonding occurs for the Ir-B contacts, and the Ir-Ir bonding within the empty clusters is two times stronger than that in the BIr{sub 6} octahedra. - Graphical abstract: Zr{sub 2}Ir{sub 6}B crystallizes with an eightfold superstructure of the already reported simple cubic perovskite ZrIr{sub 3}B{sub x}. According to the result of tight-binding electronic structure calculations, Ir-B and Ir-Zr interactions are mainly responsible for its structural stability, and the Ir-Ir bonding within the empty Ir{sub 6} clusters is two times stronger than that in the BIr{sub 6} octahedra.

  5. The 2:3:6 quasi-periodic oscillation structure in GRS 1915+105 and cubic subharmonics in the context of relativistic discoseismology

    NASA Astrophysics Data System (ADS)

    Ortega-Rodríguez, M.; Solís-Sánchez, H.; López-Barquero, V.; Matamoros-Alvarado, B.; Venegas-Li, A.

    2014-06-01

    We propose a simple toy model to explain the 2:3:6 quasi-periodic oscillation (QPO) structure in GRS 1915+105 and, more generally, the 2:3 QPO structure in XTE J1550-564, GRO J1655-40 and H1743-322. The model exploits the onset of subharmonics in the context of discoseismology. We suggest that the observed frequencies may be the consequence of a resonance between a fundamental g mode and an unobservable p wave. The results include the prediction that, as better data become available, a QPO with a frequency of twice the higher twin frequency and a large quality factor will be observed in twin peak sources, as it might already have been observed in the especially active GRS 1915+105.

  6. A highly ordered cubic mesoporous silica/graphene nanocomposite.

    PubMed

    Lee, Chang-Wook; Roh, Kwang Chul; Kim, Kwang-Bum

    2013-10-21

    A highly ordered cubic mesoporous silica (KIT-6)/graphene nanocomposite and 2D KIT-6 nanoflakes were synthesized using a novel synthesis methodology. The non-ionic triblock copolymer, P123, played a dual role as a structure-directing agent in the formation of the cubic mesoporous structure and as a cross-linking agent between mesoporous silica and graphene. The prepared (KIT-6)/graphene nanocomposite could act as a template for the preparation of mesoporous material/graphene nanocomposites. PMID:24057016

  7. Spectroscopic characteristics of praseodymium-doped cubic double sodium-yttrium fluoride crystals Na0.4Y0.6F2.2:Pr3+. Intensities of optical transitions and luminescence kinetics

    NASA Astrophysics Data System (ADS)

    Tkachuk, A. M.; Ivanova, S. E.; Mirzaeva, A. A.; Joubert, M.-F.; Guyot, Y.

    2014-03-01

    Using the Bridgman-Stockbarger technique, we have grown a series of cubic crystals Na0.4Y0.6F2.2:Pr3+ (NYF:Pr3+) with a content of praseodymium in the range of 0.04-9 at %. We have determined the composition of crystals, evaluated their optical quality, and found the incorporation coefficient of Pr3+ ions into the Na0.4Y0.6F2.2 matrix ( K Pr ˜ 0.9). We have examined optical spectra of NaYF:Pr3+ crystals at room and low (7 K) temperatures in the range of 200-2500 nm. The low-temperature absorption spectra of NYF:Pr3+ crystals have been shown to consist of broad weakly structured bands. Based on the analysis of low-temperature absorption spectra, the structure of the Stark splitting of praseodymium levels has been represented in terms of a model of "quasi-centers," which are characterized by an inhomogeneous broadening of Stark components. From experimental absorption cross-section spectra at T = 300 K, we have calculated oscillator strengths for transitions from the ground state 3 H 4 to excited multiplets 3 H 5, 3 H 6, 3 F j ( j = 2, 3, 4), 1 G 4, 1 D 2, and (3 P j ,1 I 6) ( j = 0, 1, 2). Using the Judd-Ofelt method, we have determined intensity parameters Ω t and found that Ω2 = 0, Ω4 = 4.4 × 10-20, and Ω6 = 2.28 × 10-20 cm2. With these values, we have calculated the probabilities of radiative transitions, the branching coefficients, and the lifetimes of the radiative levels 1 D 2 and 3 P 0. The probabilities of multiphonon nonradiative transitions in NYF:Pr3+ crystals have been estimated. Using the method of kinetic spectroscopy with selective excitation, we have investigated the luminescence decay kinetics of praseodymium from the 3 P 0 and 1 D 2 levels upon their selective resonant excitation by nanosecond laser pulses. The inference has been made that Na0.4Y0.6F2.2:Pr3+ crystals are processable; admit doping by praseodymium in high concentrations; and, with respect to all their radiative characteristics, can be potentially considered as active media for

  8. Characterization of 2 MeV, 4 MeV, 6 MeV and 18 MeV buildup caps for use with a 0.6 cubic centimeter thimble ionization chamber

    SciTech Connect

    Salyer, R.L.; VanDenburg, J.W.; Prinja, A.K.; Kirby, T.; Busch, R.; Hong-Nian Jow

    1996-07-01

    The purpose of this research is to characterize existing 2 MeV, 4 MeV and 6 MeV buildup caps, and to determine if a buildup cap can be made for the 0.6 cm{sup 3} thimble ionization chamber that will accurately measure exposures in a high-energy photon radiation field. Two different radiation transport codes were used to computationally characterize existing 2 MeV, 4 MeV, and 6 MeV buildup caps for a 0.6 cm{sup 3} active volume thimble ionization chamber: ITS, The Integrated TIGER Series of Coupled Electron-Photon Monte Carlo Transport Codes; and CEPXS/ONEDANT, A One-Dimensional Coupled Electron-Photon Discrete Ordinates Code Package. These codes were also used to determine the design characteristics of a buildup cap for use in the 18 MeV photon beam produced by the 14 TW pulsed power HERMES-III electron accelerator. The maximum range of the secondary electron, the depth at which maximum dose occurs, and the point where dose and collision kerma are equal have been determined to establish the validity of electronic equilibrium. The ionization chamber with the appropriate buildup cap was then subjected to a 4 MeV and a 6 MeV bremmstrahlung radiation spectrum to determine the detector response.

  9. Theoretical and Experimental Data for a Number of NACA 6A-Series Airfoil Sections

    NASA Technical Reports Server (NTRS)

    Loftin, Laurence K., Jr.

    1946-01-01

    The NACA 6A-series airfoil sections were designed to eliminate the trailing-edge cusp which is characteristic of the NACA 6-series sections. Theoretical data are presented for NACA 6A-series basic thickness forms having the position of minimum pressure at 30-, 40-, and 50-percent chord and with thickness ratios varying from 6 percent to 15 percent. Also presented are data for a mean line designed to maintain straight sides on the cambered sections. The experimental results of a two dimensional wind tunnel investigation of the aerodynamic characteristics of five NACA 64A-series airfoil sections and two NACA 63A-series airfoil sections are presented. An analysis of these results, which were obtained at Reynolds numbers of 3 x 10(exp 6), 6 x 10(exp 6), and 9 x 10(exp 6), indicates that the section minimum drag and maximum lift characteristics of comparable NACA 6-series and 6A-series airfoil sections are essentially the same. The quarter-chord pitching-moment coefficients and angles of zero lift of NACA 6A-series airfoil sections are slightly more negative than those of corresponding NACA 6-series airfoil sections. The position of the aerodynamic center and the lift-curve slope of smooth NACA 6-series sections. The addition of standard leading-edge roughness causes the lift-curve slope of the newer sections to decrease with increasing airfoil thickness ratio.

  10. Cubic Unit Cell Construction Kit.

    ERIC Educational Resources Information Center

    Mattson, Bruce

    2000-01-01

    Presents instructions for building a simple interactive unit-cell construction kit that allows for the construction of simple, body-centered, and face-centered cubic lattices. The lit is built from inexpensive and readily available materials and can be built in any number of sizes. (WRM)

  11. Cubication of Conservative Nonlinear Oscillators

    ERIC Educational Resources Information Center

    Belendez, Augusto; Alvarez, Mariela L.; Fernandez, Elena; Pascual, Immaculada

    2009-01-01

    A cubication procedure of the nonlinear differential equation for conservative nonlinear oscillators is analysed and discussed. This scheme is based on the Chebyshev series expansion of the restoring force, and this allows us to approximate the original nonlinear differential equation by a Duffing equation in which the coefficients for the linear…

  12. New halide-centered discrete Ag(I)(8) cubic clusters containing diselenophosphate ligands, [Ag(8)(X)[Se(2)P(OR)(2)](6)](PF(6)) (X = Cl, Br; R = Et, Pr, (i)Pr): syntheses, structures, and DFT calculations.

    PubMed

    Liu, C W; Haia, Hsien-Chung; Hung, Chiu-Mine; Santra, Bidyut Kumar; Liaw, Ben-Jie; Lin, Zhenyang; Wang, Ju-Chun

    2004-07-12

    Six clusters Ag(8)(micro(8)-X)[Se(2)P(OR)(2)](6)(PF(6)) (R = Et, X = Cl, 1a, X = Br, 1b; R = Pr, X = Cl, 2a, X = Br, 2b; R = (i)Pr, X = Cl, 3a, X = Br, 3b) were isolated from the reaction of [Ag(CH(3)CN)(4)](PF(6)), NH(4)[Se(2)P(OR)(2)], and Bu(4)NX in a molar ratio of 4:3:1 in CH(2)X(2). Positive FAB mass spectra show m/z peaks at 2573.2 for 1a, 2617.3 for 1b, 2740.9 for 2a, 2786.9 for 2b, 2742.3 for 3a, and 2787.0 for 3b due to respective molecular cation, (M - PF(6))(+). (31)P NMR spectra of 1a-3b display a singlet at delta 82.3, 81.5, 82.9, 81.7, 76.3, and 75.8 ppm with a set of satellites (J(PSe) = 661, 664, 652, 652, 656, and 656 Hz, respectively). The X-ray structure (1a-2b) consists of a discrete cationic cluster in which eight silver ions are linked by six diselenophosphate ligands and a central micro(8)-Cl or micro(8)-Br ion with a noncoordinating PF(6)(-) anion. The shape of the molecule is a halide-centered distorted Ag(8) cubic cluster. The dsep ligand exhibits a tetrametallic tetraconnective (micro(2), micro(2)) coordination pattern, and each caps on a square face of the cube. Each silver atom of the cube is coordinated by three selenium atoms and the central chloride or bromide ion. Additionally, molecular orbital calculations at the B3LYP level of the density functional theory have been carried out to study the Ag-micro(8)-X (X = Cl, Br) interactions for cluster cations [Ag(8)(micro(8)-X)[Se(2)P(OR)(2)](6)](+). Calculations show very weak bonding interactions exist between micro(8)-X and Ag atoms of the cube. PMID:15236560

  13. Cubic Icosahedra? A Problem in Assigning Symmetry

    ERIC Educational Resources Information Center

    Lloyd, D. R.

    2010-01-01

    There is a standard convention that the icosahedral groups are classified separately from the cubic groups, but these two symmetry types have been conflated as "cubic" in some chemistry textbooks. In this note, the connection between cubic and icosahedral symmetries is examined, using a simple pictorial model. It is shown that octahedral and…

  14. Solving Cubic Equations by Polynomial Decomposition

    ERIC Educational Resources Information Center

    Kulkarni, Raghavendra G.

    2011-01-01

    Several mathematicians struggled to solve cubic equations, and in 1515 Scipione del Ferro reportedly solved the cubic while participating in a local mathematical contest, but did not bother to publish his method. Then it was Cardano (1539) who first published the solution to the general cubic equation in his book "The Great Art, or, The Rules of…

  15. High Cubic-Phase Purity InN on MgO (001) Using Cubic-Phase GaN as a Buffer Layer

    SciTech Connect

    Sanorpim, S.; Kuntharin, S.; Parinyataramas, J.; Yaguchi, H.; Iwahashi, Y.; Orihara, M.; Hijikata, Y.; Yoshida, S.

    2011-12-23

    High cubic-phase purity InN films were grown on MgO (001) substrates by molecular beam epitaxy with a cubic-phase GaN buffer layer. The cubic phase purity of the InN grown layers has been analyzed by high resolution X-ray diffraction, {mu}-Raman scattering and transmission electron microscopy. It is evidenced that the hexagonal-phase content in the InN overlayer much depends on hexagonal-phase content in the cubic-phase GaN buffer layer and increases with increasing the hexagonal-phase GaN content. From Raman scattering measurements, in addition, the InN layer with lowest hexagonal component (6%), only Raman characteristics of cubic TO{sub InN} and LO{sub InN} modes were observed, indicating a formation of a small amount of stacking faults, which does not affect on vibrational property.

  16. Assessing Inquiry Learning: How Much Is a Cubic Metre?

    ERIC Educational Resources Information Center

    Fry, Kym

    2014-01-01

    In this article, Kym Fry uses the "Programme for International Student Assessment" (PISA) assessment framework to break down what her Year 6 students learned as they explored the inquiry question, "How much is a cubic metre?" First, an overview of the lessons in the unit is provided. Quality assessment opportunities are…

  17. Ferromagnetic Ground States in Face-Centered Cubic Hubbard Clusters.

    PubMed

    Souza, T X R; Macedo, C A

    2016-01-01

    In this study, the ground state energies of face-centered cubic Hubbard clusters are analyzed using the Lanczos method. Examination of the ground state energy as a function of the number of particle per site n showed an energy minimum for face-centered cubic structures. This energy minimum decreased in n with increasing coulombic interaction parameter U. We found that the ground state energy had a minimum at n = 0.6, when U = 3W, where W denotes the non-interacting energy bandwidth and the face-centered cubic structure was ferromagnetic. These results, when compared with the properties of nickel, shows strong similarity with other finite temperature analyses in the literature and supports the Hirsh's conjecture that the interatomic direct exchange interaction dominates in driving the system into a ferromagnetic phase. PMID:27583653

  18. Compensation in epitaxial cubic SiC films

    NASA Technical Reports Server (NTRS)

    Segall, B.; Alterovitz, S. A.; Haugland, E. J.; Matus, L. G.

    1986-01-01

    Hall measurements on four n-type cubic SiC films epitaxially grown by chemical vapor deposition on SiC substrates are reported. The temperature dependent carrier concentrations indicate that the samples are highly compensated. Donor ionization energies, E sub D, are less than one half the values previously reported. The values for E sub D and the donor concentration N sub D, combined with results for small bulk platelets with nitrogen donors, suggest the relation E sub D (N sub D) = E sub D(O) - alpha N sub N sup 1/3 for cubic SiC. A curve fit gives alpha is approx 2.6x10/5 meV cm and E sub D (O) approx 48 meV, which is the generally accepted value of E sub D(O) for nitrogen donors in cubic SiC.

  19. Aerothermodynamic Measurement and Prediction for Modified Orbiter at Mach 6 and 10

    NASA Technical Reports Server (NTRS)

    Micol, John R.

    1995-01-01

    Detailed heat-transfer rate distributions measured laterally over the windward surface of an orbiter-like configuration using thin-film resistance heat-transfer gauges and globally using the newly developed relative intensity, two-color thermographic phosphor technique are presented for Mach 6 and 10 in air. The angle of attack was varied from 0 to 40 deg, and the freestream Reynolds number based on the model length was varied from 4 x 10(exp 5) to 6 x 10(exp 6) at Mach 6, corresponding to laminar, transitional, and turbulent boundary layers; the Reynolds number at Mach 10 was 4 x 10(exp 5), corresponding to laminar flow. The primary objective of the present study was to provide detailed benchmark heat-transfer data for the calibration of computational fluid-dynamics codes. Predictions from a Navier-Stokes solver referred to as the Langley aerothermodynamic upwind relaxation algorithm and an approximate boundary-layer solving method known as the axisymmetric analog three-dimensional boundary layer code are compared with measurement. In general, predicted laminar heat-transfer rates are in good agreement with measurements.

  20. A highly ordered cubic mesoporous silica/graphene nanocomposite

    NASA Astrophysics Data System (ADS)

    Lee, Chang-Wook; Roh, Kwang Chul; Kim, Kwang-Bum

    2013-09-01

    A highly ordered cubic mesoporous silica (KIT-6)/graphene nanocomposite and 2D KIT-6 nanoflakes were synthesized using a novel synthesis methodology. The non-ionic triblock copolymer, P123, played a dual role as a structure-directing agent in the formation of the cubic mesoporous structure and as a cross-linking agent between mesoporous silica and graphene. The prepared (KIT-6)/graphene nanocomposite could act as a template for the preparation of mesoporous material/graphene nanocomposites.A highly ordered cubic mesoporous silica (KIT-6)/graphene nanocomposite and 2D KIT-6 nanoflakes were synthesized using a novel synthesis methodology. The non-ionic triblock copolymer, P123, played a dual role as a structure-directing agent in the formation of the cubic mesoporous structure and as a cross-linking agent between mesoporous silica and graphene. The prepared (KIT-6)/graphene nanocomposite could act as a template for the preparation of mesoporous material/graphene nanocomposites. Electronic supplementary information (ESI) available: S1: TEM images of disordered mesoporous silica/graphene nanocomposite; S2: TEM images of KIT-6/GO nanocomposite; S3: Thermogravimetric analysis of KIT-6/GO and KG-400-700; S4: SEM and TEM images of KIT-6; S5: Low angle XRD, Raman spectra, N2 adsorption isotherms, pore size distribution and photographic images of the prepared samples; S6: TEM image and N2 adsorption isotherms of mesoporous carbon/graphene nanocomposite; S7: XPS C1s spectra of the prepared samples. See DOI: 10.1039/c3nr03108j

  1. The compressibility of cubic white and orthorhombic, rhombohedral, and simple cubic black phosphorus

    SciTech Connect

    Clark, Simon M; Zaug, Joseph

    2010-03-10

    The effect of pressure on the crystal structure of white phosphorus has been studied up to 22.4 GPa. The ?alpha phase was found to transform into the alpha' phase at 0.87 +- 0.04 GPa with a volume change of 0.1 +- 0.3 cc/mol. A fit of a second order Birch- Murnaghan equation to the data gave Vo = 16.94 ? 0.08 cc/mol and Ko = 6.7 +- 0.5 GPa for the alpha phase and Vo = 16.4 +- 0.1 cc/mol and Ko = 9.1 +- 0.3 GPa for the alpha' phase. The alpha' phase was found to transform to the A17 phase of black phosphorus at 2.68 +- 0.34 GPa and then with increasing pressure to the A7 and then simple cubic phase of black phosphorus. A fit of a second order Birch-Murnaghan equation to our data combined with previous measurements gave Vo = 11.43 +- 0.05 cc/mol and Ko = 34.7 +- 0.5 GPa for the A17 phase, Vo = 9.62 +- 0.01 cc/mol and Ko = 65.0 +- 0.6 GPa for the A7 phase and , Vo = 9.23 +- 0.01 cc/mol and Ko = 72.5 +- 0.3 GPa for the simple cubic phase.

  2. Moufang loops of class 2 and cubic forms

    NASA Astrophysics Data System (ADS)

    Hsu, Tim

    2000-03-01

    We classify finite Moufang loops which are centrally nilpotent of class 2 in terms of certain cubic forms, concentrating on small Frattini Moufang loops, or SFMLs, which are Moufang loops L with a central subgroup Z of order p such that L/Z is an elementary abelian p-group. (For example, SFM 2-loops are precisely the class of code loops, in the sense of Griess.)More specifically, we first show that the nuclearly-derived subloop (normal associator subloop) of a Moufang loop of class 2 has exponent dividing 6. It follows that the subloop of elements of p-power order is associative for p > 3. Next, we show that if L is an SFML, then L/Z has the structure of a vector space with a symplectic cubic form. We then show that every symplectic cubic form is realized by some SFML and that two SFMLs are isomorphic in a manner preserving the central subgroup Z if and only if their symplectic cubic spaces are isomorphic up to scalar multiple. Consequently, we also obtain an explicit characterization of isotopy in SFM 3-loops. Finally, we extend many of our results to all finite Moufang loops of class 2.

  3. Swelling of Bicontinuous Cubic Phases in Guerbet Glycolipid: Effects of Additives.

    PubMed

    Salim, Malinda; Wan Iskandar, Wan Farah Nasuha; Patrick, Melonney; Zahid, N Idayu; Hashim, Rauzah

    2016-06-01

    Inverse bicontinuous cubic phases of lyotropic liquid crystal self-assembly have received much attention in biomedical, biosensing, and nanotechnology applications. An Ia3d bicontinuous cubic based on the gyroid G-surface can be formed by the Guerbet synthetic glucolipid 2-hexyl-decyl-β-d-glucopyranoside (β-Glc-OC6C10) in excess water. The small water channel diameter of this cubic phase could provide nanoscale constraints in encapsulation of large molecules and crystallization of membrane proteins, hence stresses the importance of water channel tuning ability. This work investigates the swelling behavior of lyotropic self-assembly of β-Glc-OC6C10 which could be controlled and modulated by different surfactants as a hydration-modulating agent. Our results demonstrate that addition of nonionic glycolipid octyl-β-d-glucopyranoside (β-Glc-OC8) at 20 and 25 mol % gives the largest attainable cubic water channel diameter of ca. 62 Å, and formation of coacervates which may be attributed to a sponge phase were seen at 20 mol % octyl-β-d-maltopyranoside (β-Mal-OC8). Swelling of the cubic water channel can also be attained in charged surfactant-doped systems dioctyl sodium sulfosuccinate (AOT) and hexadecyltrimethylammonium bromide (CTAB), of which phase transition occurred from cubic to a lamellar phase. Destabilization of the cubic phase to an inverse hexagonal phase was observed when a high amount of charged lecithin (LEC) and stearylamine (SA) was added to the lipid self-assembly. PMID:27183393

  4. Supersymmetric cubic Galileons have ghosts

    NASA Astrophysics Data System (ADS)

    Koehn, Michael; Lehners, Jean-Luc; Ovrut, Burt A.

    2013-07-01

    Galileons are higher-derivative theories of a real scalar which nevertheless admit second-order equations of motion. They have interesting applications as dark energy models and in early universe cosmology, and have been conjectured to arise as descriptions of brane dynamics in string theory. In the present paper, we study the bosonic sector of globally N=1 supersymmetric extensions of the cubic Galileon Lagrangian in detail. Supersymmetry requires that the Galileon scalar now becomes paired with a second real scalar field. We prove that the presence of this second scalar causes the equations of motion to become higher than second order, thus leading to the appearance of ghosts. We also analyze the energy scales up to which, in an effective field theory description, the ghosts can be tamed.

  5. Synthesis of carbon nanotubes over 3D cubical Co-KIT-6 and nickel decorated graphene by Hummer's method, its application as counter electrode in dye sensitive solar cell

    NASA Astrophysics Data System (ADS)

    Subramanian, Sunu; Pandurangan, Arumugam

    2016-04-01

    The challenges on carbon nanotubes and graphene are still the subject of many research works due to its unique properties. There are three main methods to synthesis carbon nanotubes in which chemical vapor deposition (CVD) method can use for large scale production. The principle of CVD is the decomposition of various hydrocarbons over transition metal supported catalyst. KIT-6 molecular sieve was used as a support to prepare cobalt catalyst for CVD method using metal impregnation method to produce cobalt loadings of 2, 4 and 6 wt%. The catalysts were characterized by XRD, FTIR &TEM. Carbon nanotubes (CNTs) synthesized on Co-KIT-6 was also characterized by XRD, TGA, SEM & Raman spectra. Graphene was synthesized by Hummers method, which is the most common method for preparing graphene oxide. Graphene oxide was prepared by oxidation of graphite using some oxidizing agents like sulphuric acid, sodium nitrate and potassium permanganate. This graphene oxide is further treated with hydrazine solution to convert it into chemically converted graphene and also decorated with nickel metal and characterized. Hummer's method is important for large scale production of graphene. Both Graphene and carbon nanotubes are used in different fields due to its unique properties. Both Graphene and carbon nanotubes are fabricated in counter electrode of Dye sensitized solar cells (DSSC). By cyclic voltammetry study, it confirms that both materials are good and efficient to replace platinum in the DSSC.

  6. Generalized Vaidya spacetime for cubic gravity

    NASA Astrophysics Data System (ADS)

    Ruan, Shan-Ming

    2016-03-01

    We present a kind of generalized Vaidya solution of a new cubic gravity in five dimensions whose field equations in spherically symmetric spacetime are always second order like the Lovelock gravity. We also study the thermodynamics of its spherically symmetric apparent horizon and get its entropy expression and generalized Misner-Sharp energy. Finally, we present the first law and second law hold in this gravity. Although all the results are analogous to those in Lovelock gravity, we in fact introduce the contribution of a new cubic term in five dimensions where the cubic Lovelock term is just zero.

  7. In-situ study of surface relief due to cubic-tetragonal martensitic transformation in Mn69.4Fe26.0Cu4.6 antiferromagnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Liu, C.; Yuan, F.; Gen, Z.; Wang, L.; Cui, Y. G.; Wan, J. F.; Zhang, J. H.; Rong, Y. H.

    2016-06-01

    Temperature-dependence surface relief during cubic↔tetragonal martensitic transformation (MT) in Mn69.4Fe26.0Cu4.6 antiferromegnetic shape memory alloy was studied by means of in-situ atomic force microscopy. The surface morphology memory effect was found and the crystallography reversibility of the transformation and its shearing characters were directly verified. Twin shearing is suggested as the main mechanism of formation of tent-type surface relief. The surface relief angle (θα|θβ)<0.5° was firstly measured and might be the smallest compared with that in other shape memory alloys. A Landau model was proposed to consider the shearing strain related with surface relief of MT varying with the coupling effect between second-order antiferromagnetic transition and first-order MT. According to this model, the Mn69.4Fe26.0Cu4.6 alloy belongs to the weak coupling system and this kind of weak coupling effect makes the main contribution to the small relief angle.

  8. Static Longitudinal and Lateral Stability Characteristics at Low Speed of 45 Degree Sweptback-midwing Models Having Wings with an Aspect Ratio of 2, 4, or 6

    NASA Technical Reports Server (NTRS)

    Thomas, David F , Jr; Wolhart, Walter D

    1957-01-01

    Results are presented of tests conducted in the Langley stability tunnel to determine the effects of various components and combinations of components on the static longitudinal and lateral stability characteristics at low speed of a series of 45 degree sweptback-midwing-airplane configurations having wings with an aspect ratio of 2, 4, or 6. The tests were made at a dynamic pressure of 24.9 pounds per square foot which corresponds to a Mach number of 0.13 and Reynolds numbers of 1.00 x 10(exp 6), 0.71 x 10 (exp 6), and 0.58 x 10 (exp 6) based on the respective wing mean aerodynamic chords. The angle-of-attack range covered was from -4 degrees to 32 degrees and the sideslip angles used for the lateral-derivative tests were 5 degrees and -5 degrees. An increasing loss in tail contribution to directional stability both with increasing wing aspect ratio and increasing angle of attack was found to be a principal cause of all the complete models becoming directionally unstable in the high angle-of-attack range.

  9. Satellite Boreal Measurements over Alaska and Canada During June-July 2004: Simultaneous Measurements of Upper Tropospheric CO, C2H6, HCN, CH3Cl, CH4, C2H2, CH2OH, HCOOH, OCS, and SF6 Mixing Ratios

    NASA Technical Reports Server (NTRS)

    Rinsland, Curtis P.; Dufour, Gaelle; Boone, Chris D.; Bernath, Peter F.; Chiou, Linda; Coheur, Pierre-Francois; Turquety, Solene; Clerbaux, Cathy

    2007-01-01

    Simultaneous ACE (Atmospheric Chemistry Experiment) upper tropospheric CO, C2H6, HCN, CH3Cl, CH4 , C2H2 , CH30H, HCOOH, and OCS measurements show plumes up to 185 ppbv (10 (exp -9) per unit volume) for CO, 1.36 ppbv for C2H6, 755 pptv (10(exp -12) per unit volume) for HCN, 1.12 ppbv for CH3C1, 1.82 ppmv, (10(exp -6) per unit volume) for CH4, 0.178 ppbv for C2H2, 3.89 ppbv for CH30H, 0.843 ppbv for HCOOH, and 0.48 ppbv for OCS in western Canada and Alaska at 50 deg N-68 deg N latitude between 29 June and 23 July 2004. Enhancement ratios and emission factors for HCOOH, CH30H, HCN, C2H6, and OCS relative to CO at 250-350 hPa are inferred from measurements of young plumes compared with lower mixing ratios assumed to represent background conditions based on a CO emission factor derived from boreal measurements. Results are generally consistent with the limited data reported for various vegetative types and emission phases measured in extratropical forests including boreal forests. The low correlation between fire product emission mixing ratios and the S176 mixing ratio is consistent with no significant SF6 emissions from the biomass fires.

  10. Topological Oxide Insulator in Cubic Perovskite Structure

    PubMed Central

    Jin, Hosub; Rhim, Sonny H.; Im, Jino; Freeman, Arthur J.

    2013-01-01

    The emergence of topologically protected conducting states with the chiral spin texture is the most prominent feature at the surface of topological insulators. On the application side, large band gap and high resistivity to distinguish surface from bulk degrees of freedom should be guaranteed for the full usage of the surface states. Here, we suggest that the oxide cubic perovskite YBiO3, more than just an oxide, defines itself as a new three-dimensional topological insulator exhibiting both a large bulk band gap and a high resistivity. Based on first-principles calculations varying the spin-orbit coupling strength, the non-trivial band topology of YBiO3 is investigated, where the spin-orbit coupling of the Bi 6p orbital plays a crucial role. Taking the exquisite synthesis techniques in oxide electronics into account, YBiO3 can also be used to provide various interface configurations hosting exotic topological phenomena combined with other quantum phases. PMID:23575973

  11. Topological Oxide Insulator in Cubic Perovskite Structure

    NASA Astrophysics Data System (ADS)

    Jin, Hosub; Rhim, Sonny H.; Im, Jino; Freeman, Arthur J.

    2013-04-01

    The emergence of topologically protected conducting states with the chiral spin texture is the most prominent feature at the surface of topological insulators. On the application side, large band gap and high resistivity to distinguish surface from bulk degrees of freedom should be guaranteed for the full usage of the surface states. Here, we suggest that the oxide cubic perovskite YBiO3, more than just an oxide, defines itself as a new three-dimensional topological insulator exhibiting both a large bulk band gap and a high resistivity. Based on first-principles calculations varying the spin-orbit coupling strength, the non-trivial band topology of YBiO3 is investigated, where the spin-orbit coupling of the Bi 6p orbital plays a crucial role. Taking the exquisite synthesis techniques in oxide electronics into account, YBiO3 can also be used to provide various interface configurations hosting exotic topological phenomena combined with other quantum phases.

  12. Electrostatic swelling of bicontinuous cubic lipid phases.

    PubMed

    Tyler, Arwen I I; Barriga, Hanna M G; Parsons, Edward S; McCarthy, Nicola L C; Ces, Oscar; Law, Robert V; Seddon, John M; Brooks, Nicholas J

    2015-04-28

    Lipid bicontinuous cubic phases have attracted enormous interest as bio-compatible scaffolds for use in a wide range of applications including membrane protein crystallisation, drug delivery and biosensing. One of the major bottlenecks that has hindered exploitation of these structures is an inability to create targeted highly swollen bicontinuous cubic structures with large and tunable pore sizes. In contrast, cubic structures found in vivo have periodicities approaching the micron scale. We have been able to engineer and control highly swollen bicontinuous cubic phases of spacegroup Im3m containing only lipids by (a) increasing the bilayer stiffness by adding cholesterol and (b) inducing electrostatic repulsion across the water channels by addition of anionic lipids to monoolein. By controlling the composition of the ternary mixtures we have been able to achieve lattice parameters up to 470 Å, which is 5 times that observed in pure monoolein and nearly twice the size of any lipidic cubic phase reported previously. These lattice parameters significantly exceed the predicted maximum swelling for bicontinuous cubic lipid structures, which suggest that thermal fluctuations should destroy such phases for lattice parameters larger than 300 Å. PMID:25790335

  13. Modified electrodes based on lipidic cubic phases.

    PubMed

    Bilewicz, Renata; Rowiński, Paweł; Rogalska, Ewa

    2005-04-01

    The lipidic cubic phase can be characterized as a curved bilayer forming a three-dimensional, crystallographical, well-ordered structure that is interwoven by aqueous channels. It provides a stable, well-organized environment in which diffusion of both water-soluble and lipid-soluble compounds can take place. Cubic phases based on monoacylglycerols form readily and attract our interest due to their ability to incorporate and stabilize proteins. Their lyotropic and thermotropic phase behaviour has been thoroughly investigated. At hydration over 20%, lipidic cubic phases Ia3d and Pn3m are formed. The latter is stable in the presence of excess water, which is important when the cubic phase is considered as an electrode-modifying material. Due to high viscosity, the cubic phases can be simply smeared over solid substrates such as electrodes and used to host enzymes and synthetic catalysts, leading to new types of catalytically active modified electrodes as shown for the determination of cholesterol, CO(2), or oxygen. The efficiency of transport of small hydrophilic molecules within the film can be determined by voltametry using two types of electrodes: a normal-size electrode working in the linear diffusion regime, and an ultramicroelectrode working under spherical diffusion conditions. This allows determining both the concentration and diffusion coefficient of the electrochemically active probe in the cubic phase. The monoolein-based cubic phase matrices are useful for immobilizing enzymes on the electrode surface (e.g., laccases from Trametes sp. and Rhus vernicifera were employed for monitoring dioxygen). The electronic contact between the electrode and the enzyme was maintained using suitable electroactive probes. PMID:15833697

  14. Synthesis and Characterization of Ru Cubic Nanocages with a Face-Centered Cubic Structure by Templating with Pd Nanocubes.

    PubMed

    Zhao, Ming; Figueroa-Cosme, Legna; Elnabawy, Ahmed O; Vara, Madeline; Yang, Xuan; Roling, Luke T; Chi, Miaofang; Mavrikakis, Manos; Xia, Younan

    2016-08-10

    Nanocages have received considerable attention in recent years for catalytic applications owing to their high utilization efficiency of atoms and well-defined facets. Here we report, for the first time, the synthesis of Ru cubic nanocages with ultrathin walls, in which the atoms are crystallized in a face-centered cubic (fcc) rather than hexagonal close-packed (hcp) structure. The key to the success of this synthesis is to ensure layer-by-layer deposition of Ru atoms on the surface of Pd cubic seeds by controlling the reaction temperature and the injection rate of a Ru(III) precursor. By selectively etching away the Pd from the Pd@Ru core-shell nanocubes, we obtain Ru nanocages with an average wall thickness of 1.1 nm or about six atomic layers. Most importantly, the Ru nanocages adopt an fcc crystal structure rather than the hcp structure observed in bulk Ru. The synthesis has been successfully applied to Pd cubic seeds with different edge lengths in the range of 6-18 nm, with smaller seeds being more favorable for the formation of Ru shells with a flat, smooth surface due to shorter distance for the surface diffusion of the Ru adatoms. Self-consistent density functional theory calculations indicate that these unique fcc-structured Ru nanocages might possess promising catalytic properties for ammonia synthesis compared to hcp Ru(0001), on the basis of strengthened binding of atomic N and substantially reduced activation energies for N2 dissociation, which is the rate-determining step for ammonia synthesis on hcp Ru catalysts. PMID:27458871

  15. Growth and characterization of low yttria-doped fully cubic stabilized zirconia-based single crystals

    NASA Astrophysics Data System (ADS)

    Berendts, Stefan; Lerch, Martin

    2013-05-01

    For the first time, fully cubic stabilized zirconia-based single crystals with large nitrogen contents and optimized anion vacancy concentrations, interesting for new electrochemical devices such as nitrogen sensors, were prepared by a two-step approach. This two-step approach combines growth of nitrogen-free zirconia single crystals via the skull melting method and their subsequent direct nitridation to form cubic nitrogen doped zirconia-based single crystals. In the initial step, zirconia crystals with various yttria contents (2, 3, 4 and 6 mol%) were prepared by the skull-melting technique. As determined by X-ray powder diffraction, tetragonal stabilized crystals were obtained, containing monoclinic segregations, when the yttria content of the grinded crystals was below 4 mol%. Subsequently, the crystals were nitrided with nitrogen gas at 1500 °C using different reaction times. Nitrogen content and crystallographic identity of the nitrided samples were investigated, revealing successful nitrogen incorporation and, hence, full cubic stabilization of the initial nitrogen-free samples also for the lowest yttria content. The degree of deviation from the cubic fluorite-type structure is discussed with respect to crystallographic parameters ('pseudo-cubic factor' etc.). The stabilization of cubic or tetragonal phases to ambient temperature is related to the anion vacancy concentration with respect to different impacts of the anion vacancies generated either by yttria or nitrogen incorporation (effective vacancy concentration [Veff]).

  16. Friction, Wear, and Evaporation Rates of Various Materials in Vacuum to 10(exp -7) mm Hg

    NASA Technical Reports Server (NTRS)

    Buckley, Donald H.; Swikert, Max; Johnson, Robert L.

    1961-01-01

    The requirements for bearings and seals to operate in the environment of space dictate a new area for lubrication research. The low ambient pressures encountered in space can be expected to influence the behavior of oil, grease, and solid-film lubricants. The property of these materials most significantly affected by low ambient pressures is the evaporation rate. Various investigators have therefore measured the evaporation rates of oils and greases in vacuum as one method of establishing their relative merit for space applications (1-3). The results of this work have given some indication as to the oils and greases with the greatest stability at reduced ambient pressures. Only limited experimental work, however, has been reported in the literature for inorganic solids and soft metals which have potential use as solid lubricant films or coatings for hard alloy substrates [e.g. Reference ( 4 )]. In general, the evaporation rates of these materials would be lower than those of oils and greases. These films might therefore be very attractive as lubricants for high vacuum service.

  17. Toward 10(exp 9) GPS geodesy: Vector baselines, Earth rotation and reference frames

    NASA Technical Reports Server (NTRS)

    Schutz, Bob E.

    1993-01-01

    The University of Texas Center for Space Research research efforts under NASA Grant No. NAG-1936 from 1 Jan. 1992 - 31 Dec. 1992 were in the following areas: GPS orbit accuracy assessments and efforts to improve the accuracy; analysis of global GPS data collected during the first three months of the IGS campaign, and analysis of regional data. A brief summary of each of the above activities is presented in the following.

  18. Towards 10(exp 9) GPS geodesy: Vector baselines, Earth rotation and reference frames

    NASA Technical Reports Server (NTRS)

    Schutz, Bob E.

    1994-01-01

    Effort during the period form January 1, 1993 to December 31, 1993 were in the following areas: GPS orbit accuracy assessments and efforts to improve the accuracy; analysis and effects of GPS receiver antenna phase center variation; analysis of global GPS data being collected for the IGS campaign; and analysis of regional (south west Pacific) campaign data. A brief summary of each of the above activities is presented.

  19. Structural forms of cubic BC2N

    SciTech Connect

    Sun, Hong; Jhi, Seung-Hoon; Roundy, David; Cohen, Marvin L.; Louie, Steven G.

    2001-03-01

    Superhard cubic boron-carbonitrides (c-BC2N) are studied with the use of the ab initio pseudopotential density functional method. The total energy, lattice constant, bulk and shear moduli, and electronic band structures as well as the electron density of states are calculated for all the possible c-BC2N structures in an eight-atom zinc-blende-structured cubic unit cell. The results obtained provide a plausible explanation for recent experimental observations as well as a possible path to synthesis of the materials.

  20. Quadratic-Like Dynamics of Cubic Polynomials

    NASA Astrophysics Data System (ADS)

    Blokh, Alexander; Oversteegen, Lex; Ptacek, Ross; Timorin, Vladlen

    2016-02-01

    A small perturbation of a quadratic polynomial f with a non-repelling fixed point gives a polynomial g with an attracting fixed point and a Jordan curve Julia set, on which g acts like angle doubling. However, there are cubic polynomials with a non-repelling fixed point, for which no perturbation results into a polynomial with Jordan curve Julia set. Motivated by the study of the closure of the Cubic Principal Hyperbolic Domain, we describe such polynomials in terms of their quadratic-like restrictions.

  1. Purely cubic action for string field theory

    NASA Technical Reports Server (NTRS)

    Horowitz, G. T.; Lykken, J.; Rohm, R.; Strominger, A.

    1986-01-01

    It is shown that Witten's (1986) open-bosonic-string field-theory action and a closed-string analog can be written as a purely cubic interaction term. The conventional form of the action arises by expansion around particular solutions of the classical equations of motion. The explicit background dependence of the conventional action via the Becchi-Rouet-Stora-Tyutin operator is eliminated in the cubic formulation. A closed-form expression is found for the full nonlinear gauge-transformation law.

  2. A monotonicity conjecture for real cubic maps

    SciTech Connect

    Dawson, S.P.; Galeeva, R.; Milnor, J.; Tresser, C.

    1993-12-01

    This will be an outline of work in progress. We study the conjecture that the topological entropy of a real cubic map depends ``monotonely`` on its parameters, in the sense that each locus of constant entropy in parameter space is a connected set. This material will be presented in more detail in a later paper.

  3. Sound velocity anisotropy in cubic crystals

    NASA Technical Reports Server (NTRS)

    Tsang, T.; Park, H. Y.

    1983-01-01

    Simple analytical expressions may be derived for sound velocities in cubic crystals by using lattice harmonics or functions which are invariant under the crystal symmetry operations. These expressions are in good agreement with the exact results for typical crystals such as metallic iron and potassium fluoride.

  4. Use of Pom Pons to Illustrate Cubic Crystal Structures.

    ERIC Educational Resources Information Center

    Cady, Susan G.

    1997-01-01

    Describes a method that uses olefin pom pons to illustrate cubic crystal structure. Facilitates hands-on examination of different packing arrangements such as hexagonal close-packed and cubic close-packed structures. (JRH)

  5. Cubic Polynomials with Rational Roots and Critical Points

    ERIC Educational Resources Information Center

    Gupta, Shiv K.; Szymanski, Waclaw

    2010-01-01

    If you want your students to graph a cubic polynomial, it is best to give them one with rational roots and critical points. In this paper, we describe completely all such cubics and explain how to generate them.

  6. Volatility and Wear Characteristics of a Variety of Liquid Lubricants for Space Applications

    NASA Technical Reports Server (NTRS)

    Nguyen, Quynhgiao N.; Jones, William R., Jr.

    2001-01-01

    The vapor pressures and near characteristics are critical properties for liquid lubricants to assure long-term reliability and performance in space applications. Vapor pressures, obtained using a Knudsen cell technique, and near properties, obtained using a vacuum four-ball apparatus, were measured for a series of unformulated liquid lubricants. These include: two multiple alkylated cyclopentanes (MACs) (X-1000 and X-2000), two linear perfluoropolyalkylethers (PFPAEs) (Z-25 and 815Z), and four silahydrocarbons (a tri-, a tetra-, and two pentas). Vapor pressures were measured at three elevated temperatures (423, 448, and 498 K) and extrapolated to room temperature 298 K. The lowest 298 K vapor pressure of 5.7 x 10(exp -14) Pa, was obtained with the PFPAE fluid (815Z) and the highest value with the low molecular weight MAC (X-1000) at 3.6 x 10(exp -7) Pa. In addition, vacuum near rates were determined for some of the lubricants. The lowest wear rates (approximately 3 x 10(exp -11) cubic mm/mm) were observed for three of the silahydrocarbons while the highest wear rate (approximately 2 x 10(exp-9) cubic mm/mm) were observed with the two PFPAE fluids (Z-25 and 815Z). The MAC (X-2000) yielded a wear rate of about 10(exp -10) cubic mm/mm. The results indicated that the silahydrocarbon class of liquid lubricants offers the better potential for space applications.

  7. Volatility and Wear Characteristics of a Variety of Liquid Lubricants for Space Applications

    NASA Technical Reports Server (NTRS)

    Nguyen, QuynhGiao N.; Jones, William R., Jr.

    2001-01-01

    The vapor pressures and wear characteristics are critical properties for liquid lubricants to assure long-term reliability and performance in space applications. Vapor pressures, obtained using a Knudsen cell technique, and wear properties, obtained using a vacuum four-ball apparatus, were measured for a series of unformulated liquid lubricants. These included two multiply alkylated cyclopentanes (MACs) (X-1000 and X2000), two linear perfluoropolyalkylethers (PFPAEs) (Z-25 and 815Z), and four silahydrocarbons (a tri, a tetra, and two pentas). Vapor pressures were measured at three elevated temperatures (423, 448, and 498 K) and extrapolated to room temperature 298 K. The lowest 298 K vapor pressure of 5.7 x 10(exp -14) Pa was obtained with the PFPAE fluid (815Z) and the highest value with the low molecular weight MAC (X-1000) at 3.6 x 10(exp -7) Pa. In addition, vacuum wear rates were determined for some of the lubricants. The lowest wear rates (approximately 3 x 10(exp -11) cubic mm/mm) were observed for three of the silahydrocarbons while the highest wear rates (approximately 2 x 10(exp -9) cubic mm/mm) were observed with the two PFPAE fluids (Z-25 and 815Z). The MAC (X-2000) yielded a wear rate of about 10(exp -10) cubic mm/mm. The results indicated that the silahydrocarbon class of liquid lubricants offers the better potential for space applications.

  8. Defect-induced hyper-Raman spectra in cubic zirconia

    SciTech Connect

    Shin, S.; Ishigame, M.

    1986-12-15

    Hyper-Raman scattering of cubic zirconia and CaF/sub 2/ is measured at room temperature. For a CaF/sub 2/ crystal, the frequencies of the TO and LO modes with T/sub 1//sub u/ symmetry are determined to be 260 and 480 cm/sup -1/, which are in good accord with the results of infrared measurements. In a fluorite-type cubic zirconia, the defect-induced hyper-Raman spectra due to the oxygen vacancies are observed. The structures of the hyper-Raman spectra are reasonably explained by the frequency distribution of hyper-Raman-active modes in the whole Brillouin zone, which is estimated from the imaginary part of the simple projections of the phonon displacement-displacement Green's functions onto a defect space consisting of an O/sub 6/ molecule. From the analysis of the mode vectors for the O/sub 6/ molecule, the attempt frequency of oxygen ions is found to correspond to the 690-cm/sup -1/ band in the observed hyper-Raman spectra with T/sub 1//sub u/ symmetry.

  9. Microstructural Evolution of Ti-6Al-4V during High Strain Rate Conditions of Metal Cutting

    NASA Technical Reports Server (NTRS)

    Dong, Lei; Schneider, Judy

    2009-01-01

    The microstructural evolution following metal cutting was investigated within the metal chips of Ti-6Al-4V. Metal cutting was used to impose a high strain rate on the order of approx.10(exp 5)/s within the primary shear zone as the metal was removed from the workpiece. The initial microstructure of the parent material (PM) was composed of a bi-modal microstructure with coarse prior grains and equiaxed primary located at the boundaries. After metal cutting, the microstructure of the metal chips showed coarsening of the equiaxed primary grains and lamellar. These metallographic findings suggest that the metal chips experienced high temperatures which remained below the transus temperature.

  10. The Preparation Conditions of Chromium Doped ZnSe and Their Effect on The Infrared Luminescence Properties

    NASA Technical Reports Server (NTRS)

    Burger, A.; Chattopadhyay, K.; Ndap, J.-O.; Ma, X.; Morgan, S. H.; Rablau, C. I.; Su, C.-H.; Feth, S.; Page, Ralph H.; Schaffers, Kathleen I.; Rose, M. Franklin

    2000-01-01

    We report the investigation by photoluminescence lifetime measurements of the near-IR emissions from a series of chromium-doped ZnSe samples, correlated to their preparation conditions. The samples were polycrystalline or single crystals prepared by post growth diffusion doping or single crystals doped during growth by the Physical Vapor Transport method. Room temperature lifetime values between 6 and 8 microseconds were measured for samples with Cr (2+) concentrations from low 10 (exp 17) to high 10 (exp 18) per cubic centimeter range. Lifetime data taken down to 78 K was found to be rather temperature independent, reconfirming previous reports indicating a quantum yield of the corresponding emission of close to 100% at room temperature. A strong decrease in the room temperature lifetime was found for chromium concentrations higher than 10 (exp 19) per cubic centimeter.

  11. The Preparation Conditions of Chromium Doped ZnSe and Their Effect on the Infrared Luminescence Properties

    NASA Technical Reports Server (NTRS)

    Burger, A.; Chattopadhyay, K.; Ndap, J.-O.; Ma, X.; Morgan, S. H.; Rablau, C. I.; Su, C. H.; Feth, S.

    2000-01-01

    We report the investigation by photoluminescence lifetime measurements of the near-IR emissions from a series of chromium-doped ZnSe samples, correlated to their preparation conditions. The samples were polycrystalline or single crystals prepared by post growth diffusion doping or single crystals doped during growth by the physical vapor transport method. Room temperature lifetime values between 6 and 8 micro seconds were measured for samples with Cr2+ from low 10(exp 17) to high 10(exp 18) / cubic cm range. Lifetime data taken down to 78 K was found to be rather temperature independent, reconfirming previous reports indicating a quantum yield of the corresponding emission of close to 100% at room temperature. A strong decrease in the room temperature lifetime was found for chromium concentrations higher than 10(exp 19) / cubic CM.

  12. Real-Tme Boron Nitride Erosion Measurements of the HiVHAc Thruster via Cavity Ring-Down Spectroscopy

    NASA Technical Reports Server (NTRS)

    Lee, Brian C.; Yalin, Azer P.; Gallimore, Alec; Huang, Wensheng; Kamhawi, Hani

    2013-01-01

    Cavity ring-down spectroscopy was used to make real-time erosion measurements from the NASA High Voltage Hall Accelerator thruster. The optical sensor uses 250 nm light to measure absorption of atomic boron in the plume of an operating Hall thruster. Theerosion rate of the High Voltage Hall Accelerator thruster was measured for discharge voltages ranging from 330 to 600 V and discharge powers ranging from 1 to 3 kW. Boron densities as high as 6.5 x 10(exp 15) per cubic meter were found within the channel. Using a very simple boronvelocity model, approximate volumetric erosion rates between 5.0 x 10(exp -12) and 8.2 x 10(exp -12) cubic meter per second were found.

  13. Thermomyces lanuginosus lipase-catalyzed hydrolysis of the lipid cubic liquid crystalline nanoparticles.

    PubMed

    Barauskas, Justas; Anderberg, Hanna; Svendsen, Allan; Nylander, Tommy

    2016-01-01

    In this study well-ordered glycerol monooleate (GMO)-based cubic liquid crystalline nanoparticles (LCNPs) have been used as substrates for Thermomyces lanuginosus lipase in order to establish the relation between the catalytic activity, measured by pH-stat titration, and the change in morphology and nanostructure determined by cryogenic transmission electron microscopy and synchrotron small angle X-ray diffraction. The initial lipase catalyzed LCNP hydrolysis rate is approximately 25% higher for large 350nm nanoparticles compared to the small 190nm particles, which is attributed to the increased number of structural defects on the particle surface. At pH 8.0 and 8.4 bicontinuous Im3m cubic LCNPs transform into "sponge"-like assemblies and disordered multilamellar onion-like structures upon exposure to lipase. At pH 6.5 and 7.5 lipolysis induced phase transitions of the inner core of the particles, following the sequence Im3m cubic → reversed hexagonal → reversed micellar Fd3m cubic → reversed micelles. These transitions to the liquid crystalline phases with higher negative curvature of the lipid/water interface were found to trigger protonation of the oleic acid produced during lipase catalyzed reaction. The increase curvature of the reversed discrete micellar cubic phase was suggested to cause an increase in the oleic acid pKa to a larger value observed by pH-stat titration. PMID:26047576

  14. Phase Transition of a Structure II Cubic Clathrate Hydrate to a Tetragonal Form.

    PubMed

    Takeya, Satoshi; Fujihisa, Hiroshi; Yamawaki, Hiroshi; Gotoh, Yoshito; Ohmura, Ryo; Alavi, Saman; Ripmeester, John A

    2016-08-01

    The crystal structure and phase transition of cubic structure II (sII) binary clathrate hydrates of methane (CH4 ) and propanol are reported from powder X-ray diffraction measurements. The deformation of host water cages at the cubic-tetragonal phase transition of 2-propanol+CH4 hydrate, but not 1-propanol+CH4 hydrate, was observed below about 110 K. It is shown that the deformation of the host water cages of 2-propanol+CH4 hydrate can be explained by the restriction of the motion of 2-propanol within the 5(12) 6(4) host water cages. This result provides a low-temperature structure due to a temperature-induced symmetry-lowering transition of clathrate hydrate. This is the first example of a cubic structure of the common clathrate hydrate families at a fixed composition. PMID:27346760

  15. Fabrication and characterization of cubic SrI2(Eu) scintillators for use in array detectors

    NASA Astrophysics Data System (ADS)

    Shimazoe, K.; Koyama, A.; Takahashi, H.; Sakuragi, S.; Yamasaki, Y.

    2016-02-01

    Strontium iodide (SrI2(Eu)) is a promising spectroscopic detector for use in both nuclear security and medical imaging owing to its excellent energy resolution and low internal background radiation. A cubic form is preferable when coupling with a silicon-based photosensor in order to build an array detector for use in applications such as Compton cameras. Here, cubic SrI2(Eu) crystals with 10 mm sides were fabricated and evaluated. The cubic SrI2(Eu) samples coupled to an avalanche photodiode exhibited an energy resolution of approximately 3.6% at 662 keV when using a shaping time of 3 μs. An increase in light output and an improvement of energy resolution were also observed at lower temperatures. The excellent energy resolution of these devices indicates that these crystals are promising potential detectors for use in Compton cameras and other imaging detectors.

  16. Wavelets based on Hermite cubic splines

    NASA Astrophysics Data System (ADS)

    Cvejnová, Daniela; Černá, Dana; Finěk, Václav

    2016-06-01

    In 2000, W. Dahmen et al. designed biorthogonal multi-wavelets adapted to the interval [0,1] on the basis of Hermite cubic splines. In recent years, several more simple constructions of wavelet bases based on Hermite cubic splines were proposed. We focus here on wavelet bases with respect to which both the mass and stiffness matrices are sparse in the sense that the number of nonzero elements in any column is bounded by a constant. Then, a matrix-vector multiplication in adaptive wavelet methods can be performed exactly with linear complexity for any second order differential equation with constant coefficients. In this contribution, we shortly review these constructions and propose a new wavelet which leads to improved Riesz constants. Wavelets have four vanishing wavelet moments.

  17. Face-Centered-Cubic Nanostructured Polymer Foams

    NASA Astrophysics Data System (ADS)

    Cui, C.; Baughman, R. H.; Liu, L. M.; Zakhidov, A. A.; Khayrullin, I. I.

    1998-03-01

    Beautifully iridescent polymer foams having Fm-3m cubic symmetry and periodicities on the scale of the wavelength of light have been synthesized by the templating of porous synthetic opals. These fabrication processes involve the filling of porous SiO2 opals (with typical cubic lattice parameters of 250 nm) with either polymers or polymer precursors, polymerization of the precursors if necessary, and removal of the fcc array of SiO2 balls to provide an all-polymer structure. The structures of these foams are similar to periodic minimal surfaces, although the Gaussian curvature can have both positive and negative values. Depending upon whether the internal surfaces of the opal are polymer filled or polymer coated, the polymer replica has either one or two sets of independent channels. We fill these channels with semiconductors, metals, or superconductors to provide electronic and optical materials with novel properties dependent on the nanoscale periodicity.

  18. Deposition Of Cubic BN On Diamond Interlayers

    NASA Technical Reports Server (NTRS)

    Ong, Tiong P.; Shing, Yuh-Han

    1994-01-01

    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.

  19. Photonic Crystal Cavities in Cubic (3C) Silicon Carbide

    NASA Astrophysics Data System (ADS)

    Radulaski, Marina; Babinec, Thomas; Buckley, Sonia; Rundquist, Armand; Provine, J.; Alassaad, Kassem; Ferro, Gabriel; Vuckovic, Jelena

    2014-03-01

    Silicon carbide (SiC) combines many of the outstanding material properties of other well-known optical and quantum optical materials, including strong optical nonlinearity, high Young's modulus, and a host of optically-active crystalline defects, in a single CMOS-compatible platform. For many applications in classical and quantum information processing, the material properties of the cubic silicon carbide polytype (3C-SiC) in particular are advantageous. We therefore present the design, fabrication, and characterization of high quality factor and small mode volume planar photonic crystal cavities in cubic 3C-SiC thin films (200 nm). We demonstrate cavity resonances across the infrared telecommunications band, with wavelengths from 1.25 - 1.6 μm. Finally, we highlight our progress developing higher Q/V nanobeam cavities, as well as extending this optical cavity platform towards integration with SiC color centers. PECASE Grant ECCS-10 25811, NSF Grant ECS-9731293, Stanford Graduate Fellowship, National Science Graduate Fellowship.

  20. Method of synthesizing cubic system boron nitride

    SciTech Connect

    Yuzu, S.; Sumiya, H.; Degawa, J.

    1987-10-13

    A method is described for synthetically growing cubic system boron nitride crystals by using boron nitride sources, solvents for dissolving the boron nitride sources, and seed crystals under conditions of ultra-high pressure and high temperature for maintaining the cubic system boron nitride stable. The method comprises the following steps: preparing a synthesizing vessel having at least two chambers, arrayed in order in the synthesizing vessel so as to be heated according to a temperature gradient; placing the solvents having different eutectic temperatures in each chamber with respect to the boron nitride sources according to the temperature gradient; placing the boron nitride source in contact with a portion of each of the solvents heated at a relatively higher temperature and placing at least a seed crystal in a portion of each of the solvents heated at a relatively lower temperature; and growing at least one cubic system boron nitride crystal in each of the solvents in the chambers by heating the synthesizing vessel for establishing the temperature gradient while maintaining conditions of ultra-high pressure and high temperature.

  1. Growth and characterization of cubic and non-cubic Ge nanocrystals

    NASA Astrophysics Data System (ADS)

    Mukherjee, S.; Pradhan, A.; Mukherjee, S.; Maitra, T.; Nayak, A.; Bhunia, S.

    2016-05-01

    Germanium nanocrystals with tetragonal (ST-12) and diamond like cubic (Ge-I) phases have been selectively grown by controlling the ionization and electrostatic potential of Ge clusters in an ion cluster beam deposition system. Predominantly tetragonal nanocrystals were obtained when grown using neutral clusters. The percentage of cubic phase increased when grown by ionizing the clusters and accelerating them towards substrates by applying electrostatic bias in the range of 1.5 -2.5 kV. Raman spectroscopic measurement showed strong peak at 275 cm-1 and 300 cm-1 for tetragonal and cubic Ge nanocrystals, respectively. TEM measurements showed crystalline lattice fringes of both type of the nanocrystals. The selected area electron diffraction patterns showed (111) and (210) as the dominating lattice planes for tetragonal nanocrystals while the cubic phases had (111), (311) and (331) as the prominent lattice planes. The optical absorption edge redshifted from 1.75 to 1.55 eV as the percentage of the cubic phases increased in the NC composition in the composite film.

  2. Novel chloride-centered discrete CuI8 cubic clusters containing diselenophosphate ligands. Syntheses and structures of [Cu8(mu8-Cl)[Se2P(OR)2](6)](PF6) (R = Et, Pr, iPr)1.

    PubMed

    Liu, C W; Hung, Chiu-Mine; Santra, Bidyut Kumar; Chen, Hsiu-Chih; Hsueh, Hsin-Hsueh; Wang, Ju-Chung

    2003-05-19

    Three clusters 1-3, Cu(8)(mu8-Cl)[Se(2)P(OR)(2)](6)(PF(6)) (R= Et, Pr, (i)Pr), were synthesized in high yield from the reaction of [Cu(CH(3)CN)(4)](PF(6)), NH(4)[Se(2)P(OR)(2)], and Bu(4)NCl in a molar ratio of 4:3:1 in diethyl ether. FAB mass spectra show m/z peaks at 2218.10 for 1, 2386.10 for 2, and 2387.34 for 3 which are due to molecular cations, [1-PF(6)]+, [2-PF(6)]+, and [3-PF(6)]+, respectively. (31)P NMR spectra of 1-3 display a singlet at delta 76.48, 76.73, and 69.32 ppm with satellites (J(PSe) = 652, 653, and 648 Hz), respectively. The (77)Se NMR spectra of 1-3 exhibit a doublet peak at -21.7, -16.42, and 2.3 ppm, respectively (J(SeP) = 652 Hz for 1, 653 Hz for 2, and 648 Hz for 3). The X-ray structure (1-3) consists of a discrete cationic cluster in which eight copper ions are linked by six diselenophosphate ligands and a central mu8-Cl ion with a noncoordinating PF(6)(-) anion. The shape of the molecule is a chloride-centered distorted Cu(8) cube in clusters 1 and 2 and a near perfect Cu(8) cube for cluster 3. The dsep ligand exhibits a tetrametallic tetraconnective (mu2, mu2)) coordination pattern, and each occupies a square face of the cube. Each copper atom of the cube is coordinated by three selenium atoms with a strong interaction with the central chloride ion. The observed Cu-Cl distances lie in the range 2.649-2.878 A. PMID:12739962

  3. Blunt body near wake flow field at Mach 6

    NASA Technical Reports Server (NTRS)

    Horvath, Thomas J.; McGinley, Catherine B.; Hannemann, Klaus

    1996-01-01

    Tests were conducted in a Mach 6 flow to examine the reattachment process of an axisymmetric free shear layer associated with the near wake of a 70 deg. half angle, spherically blunted cone with a cylindrical after body. Model angle of incidence was fixed at 0 deg. and free-stream Reynolds numbers based on body diameter ranged from 0.5 x 10(exp 6) to 4 x 10(exp 6). The sensitivity of wake shear layer transition on reattachment heating was investigated. The present perfect gas study was designed to compliment results obtained previously in facilities capable of producing real gas effects. The instrumented blunted cone model was designed primarily for testing in high enthalpy hypervelocity shock tunnels in both this country and abroad but was amenable for testing in conventional hypersonic blowdown wind tunnels as well. Surface heating rates were inferred from temperature - time histories from coaxial surface thermocouples on the model forebody and thin film resistance gages along the model base and cylindrical after body. General flow feature (bow shock, wake shear layer, and recompression shock) locations were visually identified by schlieren photography. Mean shear layer position and growth were determined from intrusive pitot pressure surveys. In addition, wake surveys with a constant temperature hot-wire anemometer were utilized to qualitatively characterize the state of the shear layer prior to reattachment. Experimental results were compared to laminar perfect gas predictions provided by a 3-D Navier Stokes code (NSHYP). Shear layer impingement on the instrumented cylindrical after body resulted in a localized heating maximum that was 21 to 29 percent of the forebody stagnation point heating. Peak heating resulting from the reattaching shear layer was found to be a factor of 2 higher than laminar predictions, which suggested a transitional shear layer. Schlieren flow visualization and fluctuating voltage time histories and spectra from the hot wire surveys

  4. Optical properties of Tb3+ doped KLaF4 in cubic and hexagonal symmetries

    NASA Astrophysics Data System (ADS)

    Ahmad, Shahzad; Das, Subrata; Nagarajan, R.; Vijaya Prakash, G.

    2013-12-01

    Tb3+ doped cubic and hexagonally ordered KLaF4 nano-sized crystals have been synthesized by solution based method with the simultaneous evaluation of their optical and magnetic properties. While higher amounts of Tb3+ (10%) can be doped in cubic KLaF4 lattice, only 3% of Tb3+ can be doped in hexagonal KLaF4 by this method. Cubic KLaF4:Tb3+ samples show a very strong green emission centered at 545 nm (5D4 → 7F5) on excitation with 337 nm laser, the intensity increases monotonically with Tb3+ content. The relative intensity of the excited state 5D3 violet emission is weaker than that of 5D4 emissions even at the low Tb3+ amounts. It is proposed that the 5D3 → 5D4 cross-relaxation may be responsible for the decrease in the 5D3 decay rate with increasing Tb3+ concentrations. The average emission decay lifetime of the green emission (545 nm; 5D4 → 7F5) of Tb3+ doped cubic KLaF4 samples are in the order of 1-3 ms. The absence of the characteristic emissions from 5D3 level in hexagonal KLaF4:Tb3+ phosphor suggests the pronounced non-radiative cross relaxation between the 5D3 to 5D4 energy levels. Further, these cubic KLaF4:Tb3+ samples show intense green upconversion emission when co-doped with moderate concentrations of sensitizer Yb3+ ions. Both cubic and hexagonal KLaF4:Tb3+ samples show paramagnetic behavior at room temperature with χg value ranging from 1.627 × 10-6 to 1.356 × 10-5 emu/g.

  5. Cherenkov and Scintillation Properties of Cubic Zirconium

    NASA Technical Reports Server (NTRS)

    Christl, M.J.; Adams, J.H.; Parnell, T.A.; Kuznetsov, E.N.

    2008-01-01

    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

  6. Craniofacial reconstruction using rational cubic ball curves.

    PubMed

    Majeed, Abdul; Mt Piah, Abd Rahni; Gobithaasan, R U; Yahya, Zainor Ridzuan

    2015-01-01

    This paper proposes the reconstruction of craniofacial fracture using rational cubic Ball curve. The idea of choosing Ball curve is based on its robustness of computing efficiency over Bezier curve. The main steps are conversion of Digital Imaging and Communications in Medicine (Dicom) images to binary images, boundary extraction and corner point detection, Ball curve fitting with genetic algorithm and final solution conversion to Dicom format. The last section illustrates a real case of craniofacial reconstruction using the proposed method which clearly indicates the applicability of this method. A Graphical User Interface (GUI) has also been developed for practical application. PMID:25880632

  7. Craniofacial Reconstruction Using Rational Cubic Ball Curves

    PubMed Central

    Majeed, Abdul; Mt Piah, Abd Rahni; Gobithaasan, R. U.; Yahya, Zainor Ridzuan

    2015-01-01

    This paper proposes the reconstruction of craniofacial fracture using rational cubic Ball curve. The idea of choosing Ball curve is based on its robustness of computing efficiency over Bezier curve. The main steps are conversion of Digital Imaging and Communications in Medicine (Dicom) images to binary images, boundary extraction and corner point detection, Ball curve fitting with genetic algorithm and final solution conversion to Dicom format. The last section illustrates a real case of craniofacial reconstruction using the proposed method which clearly indicates the applicability of this method. A Graphical User Interface (GUI) has also been developed for practical application. PMID:25880632

  8. Monte Carlo study of the hetero-polytypical growth of cubic on hexagonal silicon carbide polytypes

    NASA Astrophysics Data System (ADS)

    Camarda, Massimo

    2012-08-01

    In this article we use three dimensional kinetic Monte Carlo simulations on super-lattices to study the hetero-polytypical growth of cubic silicon carbide polytype (3C-SiC) on misoriented hexagonal (4H and 6H) substrates. We analyze the quality of the 3C-SiC film varying the polytype, the miscut angle and the initial surface morphology of the substrate. We find that the use of 6H misoriented (4°-10° off) substrates, with step bunched surfaces, can strongly improve the quality of the cubic epitaxial film whereas the 3C/4H growth is affected by the generation of dislocations, due to the incommensurable periodicity of the 3C (3) and the 4H (4) polytypes. For these reasons, a proper pre-growth treatment of 6H misoriented substrates can be the key for the growth of high quality, twin free, 3C-SiC films.

  9. Low pressure growth of cubic boron nitride films

    NASA Technical Reports Server (NTRS)

    Ong, Tiong P. (Inventor); Shing, Yuh-Han (Inventor)

    1997-01-01

    A method for forming thin films of cubic boron nitride on substrates at low pressures and temperatures. A substrate is first coated with polycrystalline diamond to provide a uniform surface upon which cubic boron nitride can be deposited by chemical vapor deposition. The cubic boron nitride film is useful as a substitute for diamond coatings for a variety of applications in which diamond is not suitable. any tetragonal or hexagonal boron nitride. The cubic boron nitride produced in accordance with the preceding example is particularly well-suited for use as a coating for ultra hard tool bits and abrasives, especially those intended to use in cutting or otherwise fabricating iron.

  10. Multiply charged monopoles in cubic dimer model

    NASA Astrophysics Data System (ADS)

    Ganesh Jaya, Sreejith; Powell, Stephen

    2015-03-01

    The classical cubic dimer model is a 3D statistical mechanical system whose degrees of freedom are dimers that occupy the edges between nearest neighbour vertices of a cubic lattice. Dimer occupancies are subject to the local constraint that every vertex is associated with exactly one dimer. In the presence of an aligning interaction, it is known that the system exhibits an unconventional continuous thermal phase transition from a symmetry broken columnar phase to a Coulomb-phase. The transition is in the NCCP1 universality class, which also describes the Neel-VBS transition in the JQ model and the S =1/2 Heisenberg model with suppression of hedgehog defects. Using Monte-Carlo simulations of a pair of defects in a background of fluctuating dimers, we calculate the scaling exponents for fugacities of monopole defects of charge Q = 2 and 3 at this critical point. Our estimates suggest that Q = 3 monopoles are relevant and could therefore drive the JQ model away from the NCCP1 critical point on a hexagonal lattice.

  11. Ti{sub 5}O{sub 5} superstructures of cubic titanium monoxide

    SciTech Connect

    Gusev, A. I.

    2013-08-15

    A cubic model is proposed for the Ti{sub 5}O{sub 5} (Ti{sub 5} Black-Small-Square O{sub 5}{open_square} {identical_to} Ti{sub 90} Black-Small-Square {sub 18}O{sub 90}{open_square}{sub 18}) superstructure of nonstoichiometric titanium monoxide Ti{sub x}O{sub z} with double imperfection. The unit cell of the cubic Ti{sub 5}O{sub 5} superstructure has the threefold lattice parameter of the unit cell of the basis disordered B1 structure of Ti{sub x}O{sub z} monoxide and belongs to space group Pm 3-bar m . The channel of the disorder-order transition, i.e., Ti{sub x}O{sub z} (space group Fm 3-bar m)-Ti{sub 5}O{sub 5} (space group Pm 3-bar m), includes 75 superstructure vectors of seven stars (k{sub 10}), (k{sub 7}), (k{sub 6(1)}), (k{sub 6(2)}), (k{sub 4(1)}), (k{sub 4(2)}), and (k{sub 1}). The distribution functions of Ti and O atoms over the sites of the cubic Ti{sub 5}O{sub 5} superstructure are calculated. A comparison of the X-ray and electron diffraction data obtained for ordered TiO{sub 1.087} monoxide with the theoretical simulation results supports the existence of the cubic Ti{sub 5}O{sub 5} superstructure. The cubic (space group Pm 3-bar m) Ti{sub 5}O{sub 5} superstructure is shown to be a high-temperature structure relative to the well-known monoclinic (space group C2/m) superstructure of the same type.

  12. Experimental Determination of the Recovery Factor and Analytical Solution of the Conical Flow Field for a 20 deg Included Angle Cone at Mach Numbers of 4.6 and 6.0 and Stagnation Temperatures to 2600 degree R

    NASA Technical Reports Server (NTRS)

    Pfyl, Frank A.; Presley, Leroy L.

    1961-01-01

    The local recovery factor was determined experimentally along the surface of a thin-walled 20 deg included angle cone for Mach numbers near 6.0 at stagnation temperatures between 1200 deg R and 2600 deg R. In addition, a similar cone configuration was tested at Mach numbers near 4.5 at stagnation temperatures of approximately 612 deg R. The local Reynolds number based on flow properties at the edge of the boundary layer ranged between 0.1 x 10(exp 4) and 3.5 x 10(exp 4) for tests at temperatures above 1200 deg R and between 6 x 10(exp 4) and 25 x 10(exp 4) for tests at temperatures near 612 deg R. The results indicated, generally, that the recovery factor can be predicted satisfactorily using the square root of the Prandtl number. No conclusion could be made as to the necessity of evaluating the Prandtl number at a reference temperature given by an empirical equation, as opposed to evaluating the Prandtl number at the wall temperature or static temperature of the gas at the cone surface. For the tests at temperatures above 1200 deg R (indicated herein as the tests conducted in the slip-flow region), two definite trends in the recovery data were observed - one of increasing recovery factor with decreasing stagnation pressure, which was associated with slip-flow effects and one of decreasing recovery factor with increasing temperature. The true cause of the latter trend could not be ascertained, but it was shown that this trend was not appreciably altered by the sources of error of the magnitude considered herein. The real-gas equations of state were used to determine accurately the local stream properties at the outer edge of the boundary layer of the cone. Included in the report, therefore, is a general solution for the conical flow of a real gas using the Beattie-Bridgeman equation of state. The largest effect of temperature was seen to be in the terms which were dependent upon the internal energy of the gas. The pressure and hence the pressure drag terms were

  13. Qualitative Assessment of the Acoustic Disturbance Environment in the NASA LaRC 20-Inch MACH 6 Wind Tunnel

    NASA Technical Reports Server (NTRS)

    Horvath, Thomas J.; Berry, Scott A.; Hamilton, H. Harris

    2001-01-01

    An experimental investigation was conducted on a 5-degree-half-angle cone with a flare in a conventional Mach 6 wind tunnel to examine the effect of facility noise on boundary layer transition. The effect of tunnel noise was inferred by comparing transition onset locations determined from the present test to that previously obtained in a Mach 6 quiet tunnel. Together, the two sets of experiments are believed to represent the first direct comparison of transition onset between a conventional and a quiet hypersonic wind tunnel using a common test model. In the present conventional hypersonic tunnel experiment, adiabatic wall temperatures were measured and heat transfer distributions were inferred on the cone flare model at zero degree angle of attack over a range of length Reynolds numbers (2 x 10(exp 6) to 10 x 10(exp 6)) which resulted in laminar and turbulent flow. Wall-to-total temperature ratio for the transient heating measurements and the adiabatic wall temperature measurements were 0.69 and 0.86, respectively. The cone flare nosetip radius was varied from 0.0001 to 0.125-inch to examine the effects of bluntness on transition onset. At comparable freestream conditions the transition onset Reynolds number obtained on the cone flare model in the conventional "noisy" tunnel was approximately 25% lower than that measured in the low disturbance tunnel.

  14. A smoothing algorithm using cubic spline functions

    NASA Technical Reports Server (NTRS)

    Smith, R. E., Jr.; Price, J. M.; Howser, L. M.

    1974-01-01

    Two algorithms are presented for smoothing arbitrary sets of data. They are the explicit variable algorithm and the parametric variable algorithm. The former would be used where large gradients are not encountered because of the smaller amount of calculation required. The latter would be used if the data being smoothed were double valued or experienced large gradients. Both algorithms use a least-squares technique to obtain a cubic spline fit to the data. The advantage of the spline fit is that the first and second derivatives are continuous. This method is best used in an interactive graphics environment so that the junction values for the spline curve can be manipulated to improve the fit.

  15. Black holes in a cubic Galileon universe

    NASA Astrophysics Data System (ADS)

    Babichev, E.; Charmousis, C.; Lehébel, A.; Moskalets, T.

    2016-09-01

    We find and study the properties of black hole solutions for a subclass of Horndeski theory including the cubic Galileon term. The theory under study has shift symmetry but not reflection symmetry for the scalar field. The Galileon is assumed to have linear time dependence characterized by a velocity parameter. We give analytic 3-dimensional solutions that are akin to the BTZ solutions but with a non-trivial scalar field that modifies the effective cosmological constant. We then study the 4-dimensional asymptotically flat and de Sitter solutions. The latter present three different branches according to their effective cosmological constant. For two of these branches, we find families of black hole solutions, parametrized by the velocity of the scalar field. These spherically symmetric solutions, obtained numerically, are different from GR solutions close to the black hole event horizon, while they have the same de-Sitter asymptotic behavior. The velocity parameter represents black hole primary hair.

  16. Note: A cubic electromagnetic harvester that convert vibration energy from all directions

    NASA Astrophysics Data System (ADS)

    Han, Mengdi; Qiu, Guolin; Liu, Wen; Meng, Bo; Zhang, Xiao-Sheng; Zhang, Haixia

    2014-07-01

    We investigate the output performance of a cubic harvester which can scavenge low-frequency vibration energy from all directions. By adjusting the size and shape of the inside magnets, higher induced voltages and output power can be achieved. The optimal magnet is found to be cubic shape with the length of 6.35 mm (25.6% volume ratio), which can generate 4.27 mV root mean square voltage and 2.45 μW average power at the frequency of 28.86 Hz and acceleration of 1.17 g. The device is also demonstrated as a self-powered tilt sensor by measuring induced voltages at different tilt angles.

  17. Ellipsometric study of cubic SiC

    NASA Technical Reports Server (NTRS)

    Alterovitz, Samuel A.; Shoemaker, Neil S.; Powell, J. A.

    1990-01-01

    Variable angle spectroscopic ellipsometry (VASE) was applied to cubic SiC. This technique gives absolute values of the refractive index (n) and the extinction coefficient (k) of a substrate and/or a thin film of unknown material. The samples were grown by chemical vapor deposition (CVD) on p-type silicon. The substrate was aligned either on the (001) axis or 1 degree of (001). Several growth temperatures and growth durations were used. The samples were divided into two groups: (1) thick films of order 10 microns grown near optimal conditions of temperature, flow, and gas ratio; and (2) thin films of order 100 A grown at various temperatures. The ellipsometric results for samples in group 1 were analyzed using a two-phase model (substrate and ambient). Results show that for wavelengths in the visible, the refractive index of these CVD samples is equal to that reported for single crystal cubic SiC, within the experimental error, which is on the order of 1 percent. However, the extinction coefficient has a relatively large value, even above the band gap. The absorption is sample dependent and has a broad peak in the visible. The results for samples in group 2 were analyzed using a three-phase model (substrate, film, and ambient). The dielectric functions of the film, deducted from the measured n and k, were further analyzed using the effective medium approximation. The results show that the films contain 30 to 40 vol. percent amorphous silicon, i.e., silicon with only short-range order.

  18. Wurtzite ZnO (001) films grown on cubic MgO (001) with bulk-like opto-electronic properties

    SciTech Connect

    Zhou Hua; Wang Huiqiong; Chen Xiaohang; Zhan Huahan; Kang Junyong; Wu Lijun; Zhu Yimei; Zhang Lihua; Kisslinger, Kim

    2011-10-03

    We report the growth of ZnO (001) wurtzite thin films with bulk-like opto-electronic properties on MgO (001) cubic substrates using plasma-assisted molecular beam epitaxy. In situ reflection high-energy electron diffraction patterns and ex situ high resolution transmission electron microscopy images indicate that the structure transition from the cubic MgO substrates to the hexagonal films involves 6 ZnO variants that have the same structure but different orientations. This work demonstrates the possibility of integrating wurtzite ZnO films and functional cubic substrates while maintaining their bulk-like properties.

  19. Rate Coefficients of C2H with C2H4, C2H6, and H2 from 150 to 359 K

    NASA Technical Reports Server (NTRS)

    Opansky, Brian J.; Leone, Stephen R.

    1996-01-01

    Rate coefficients for the reactions C2H with C2H4, C2H6, and H2 are measured over the temperature range 150-359 K using transient infrared laser absorption spectroscopy. The ethynyl radical is formed by photolysis of C2H2 with a pulsed excimer laser at 193 nm, and its transient absorption is monitored with a color center laser on the Q(sub 11)(9) line of the A(sup 2) Pi-Chi(sup 2) Sigma transition at 3593.68 cm(exp -1). Over the experimental temperature range 150-359 K the rate constants of C2H with C2H4, C2H6, and H2 can be fitted to the Arrhenius expressions k(sub C2H4) = (7.8 +/- 0.6) x 10(exp -11) exp[(134 +/- 44)/T], k(sub C2H6) = (3.5 +/- 0.3) x 10(exp -11) exp[(2.9 +/- 16)/T], and k(sub H2) = (1.2 +/- 0.3) x 10(exp -11) exp[(-998 +/- 57)]/T cm(exp 3) molecule(exp -1) sec(exp -1). The data for C2H with C2H4 and C2H6 indicate a negligible activation energy to product formation shown by the mild negative temperature dependence of both reactions. When the H2 data are plotted together with the most recent high-temperature results from 295 to 854 K, a slight curvature is observed. The H2 data can be fit to the non-Arrhenius form k(sub H2) = 9.2 x 10(exp -18) T(sup 2.17 +/- 0.50) exp[(-478 +/- 165)/T] cm(exp 3) molecules(exp -1) sec(exp -1). The curvature in the Arrhenius plot is discussed in terms of both quantum mechanical tunneling of the H atom from H2 to the C2H radical and bending mode contributions to the partition function.

  20. Experimental Investigation of Project Orion Crew Exploration Vehicle Aeroheating: LaRC 20-Inch Mach 6 Air Tunnel Test 6931

    NASA Technical Reports Server (NTRS)

    Hollis, Brian R.

    2009-01-01

    An investigation of the aeroheating environment of the Project Orion Crew Entry Vehicle has been performed in the Langley Research Center 20-Inch Mach 6 Air Tunnel. Data were measured on a approx.3.5% scale model (0.1778-m/7-inch diameter) of the vehicle using coaxial thermocouples at free stream Reynolds numbers of 2.0 10(exp 6)/ft to 7.30 10(exp 6)/ft and computational predictions were generated for all test conditions. The primary goals of this test were to obtain convective heating data for use in assessing the accuracy of the computational technique and to validate test methodology and heating data from a test of the same wind tunnel model in the Arnold Engineering Development Center Tunnel 9. Secondary goals were to determine the extent of transitional/turbulent data which could be produced on a CEV model in this facility, either with or without boundary-layer trips, and to demonstrate continuous pitch-sweep operation in this tunnel for heat transfer testing.

  1. Cathodoluminescence study of luminescence centers in hexagonal and cubic phase GaN hetero-integrated on Si(100)

    NASA Astrophysics Data System (ADS)

    Liu, R.; Bayram, C.

    2016-07-01

    Hexagonal and cubic GaN—integrated on on-axis Si(100) substrate by metalorganic chemical vapor deposition via selective epitaxy and hexagonal-to-cubic-phase transition, respectively—are studied by temperature- and injection-intensity-dependent cathodoluminescence to explore the origins of their respective luminescence centers. In hexagonal (cubic) GaN integrated on Si, we identify at room temperature the near band edge luminescence at 3.43 eV (3.22 eV), and a defect peak at 2.21 eV (2.72 eV). At low temperature, we report additional hexagonal (cubic) GaN bound exciton transition at 3.49 eV (3.28 eV), and a donor-to-acceptor transition at 3.31 eV (3.18 eV and 2.95 eV). In cubic GaN, two defect-related acceptor energies are identified as 110 and 360 meV. For hexagonal (cubic) GaN (using Debye Temperature ( β ) of 600 K), Varshni coefficients of α = 7.37 ± 0.13 × 10 - 4 ( 6.83 ± 0.22 × 10 - 4 ) eV / K and E 0 = 3.51 ± 0.01 ( 3.31 ± 0.01 ) eV are extracted. Hexagonal and cubic GaN integrated on CMOS compatible on-axis Si(100) are shown to be promising materials for next generation devices.

  2. Effect of the introduction of oxide ion vacancies into cubic fluorite-type rare earth oxides on the NO decomposition catalysis

    SciTech Connect

    Masui, Toshiyuki; Nagai, Ryosuke; Imanaka, Nobuhito

    2014-12-15

    Cubic fluorite-type solid solutions based on Pr{sub 6}O{sub 11} and CeO{sub 2} were synthesized and oxide anion vacancies were intentionally introduced into the cubic fluorite-type lattice through the charge compensating mechanism by Mg{sup 2+} and/or Ca{sup 2+} doping into their lattices. The oxide anion vacancies bring about positive effect on NO decomposition catalysis. The reason for the increase in the catalytic activity was attributed to defect fluorite-type structures close to the C-type cubic one, because C-type cubic rare earth oxides, in which one-quarter of the oxygen atoms in the fluorite-type structure are removed, show high NO decomposition activity. In particular, the positive effect of the formation of oxide anion vacancies was significant for Pr{sub 6}O{sub 11} and its solid solutions, because the molar volume of Pr{sub 6}O{sub 11} is larger than that of CeO{sub 2}, and Pr{sub 6}O{sub 11} contains Pr{sup 3+} as well as Pr{sup 4+} and thereby a small amount of oxide anion vacancies exist inherently in the lattice. - Graphical abstract: Oxide anion vacancies intentionally introduced into the cubic fluorite-type lattice bring about positive effect on NO decomposition catalysis. - Highlights: • Cubic fluorite-type solid solutions were synthesized. • Oxide anion vacancies were intentionally introduced into the cubic fluorite-type lattice. • The oxide anion vacancies bring about positive effect on NO decomposition catalysis. • The activity was enhanced by making the structure close to the C-type cubic one.

  3. Chemical vapor deposition (CVD) of cubic silicon carbide. Patent Application

    SciTech Connect

    Addamiano, A.

    1985-07-02

    This invention relates to the growth of cubic silicon carbide crystals. More specifically, this invention relates to the growth of cubic silicon carbide by Chemical Vapor Deposition (CVD). One object of the present invention is to provide a novel method for the production of cubic SiC for high temperature electronic devices. Another object of the present invention is to provide a novel method for the production of highly pure, single crystal cubic SiC that is duplicable. Another object of the present invention is to provide a novel method for the production of large-area single-crystal wafers of cubic SiC. These and other objects of the present invention can be achieved by a method for chemical vapor deposition (CVD) of cubic Silicon Carbide (SiC) comprising the steps of etching silicon substrated having one mechanically polished face; depositing a thin buffer layer of cubic SiC formed by reaction between a heated Si substrate and a H2-C3H8 gas mixuture; and depositing SiC on the buffer layer at high temperature using H2+C3HY+SiH4 mixture.

  4. The growth of cubic silicon carbide on a compliant substrate

    NASA Technical Reports Server (NTRS)

    Mitchell, Sharanda; Soward, Ida

    1995-01-01

    Research has shown that silicon carbide grown on silicon and 6H silicon carbide has problems associated with these substrates. This is because silicon and silicon carbide has a 20% lattice mismatch and cubic silicon carbide has not been successfully achieved on 6H silicon carbide. We are investigating the growth of silicon carbide on a compliant substrate in order to grow defect free silicon carbide. This compliant substrate consists of silicon/silicon dioxide with 1200 A of single crystal silicon on the top layer. We are using this compliant substrate because there is a possibility that the silicon dioxide layer and the carbonized layer will allow the silicon lattice to shrink or expand to match the lattice of the silicon carbide. This would improve the electrical properties of the film for the use of device fabrication. When trying to grow silicon carbide, we observed amorphous film. To investigate, we examined the process step by step using RHEED. RHEED data showed that each step was amorphous. We found that just by heating the substrate in the presence of hydrogen it changed the crystal structure. When heated to 1000 C for 2 minutes, RHEED showed that there was an amorphous layer on the surface. We also heated the substrate to 900 C for 2 minutes and RHEED data showed that there was a deterioration of the single crystalline structure. We assumed that the presence of oxygen was coming from the sides of the silicon dioxide layer. Therefore, we evaporated 2500 A of silicon to all four edges of the wafer to try to enclose the oxygen. When heating the evaporated wafer to 900 C the RHEED data showed single crystalline structure however at 1000 C the RHEED data showed deterioration of the single crystalline structure. We conclude that the substrate itself is temperature dependent and that the oxygen was coming from the sides of the silicon dioxide layer. We propose to evaporate more silicon on the edges of the wafer to eliminate the escape of oxygen. this will allow

  5. Phase stability of cubic pyrochlore rare earth tantalate pinning additives in YBa2Cu3O7- superconductor

    SciTech Connect

    Wee, Sung Hun; Cantoni, Claudia; Zuev, Yuri L; Specht, Eliot D; Goyal, Amit

    2012-01-01

    Phase stability of cubic-pyrochlore-structured RE3TaO7 (RTO, where RE = rare earth elements) pinning additives in YBa2Cu3O7- (YBCO) superconductor and the pinning properties influenced by RTO addition into YBCO films were investigated. RTO completely reacts with YBCO and is converted to cubic-double-perovskite-structured Ba2RETaO6 (BRETO), a more thermodynamically stable tantalate phase within YBCO. In RTO-doped YBCO films, BRETO self-assembled nanocolumnns align along the c-axis of the film and play a major role in the improvement of flux pinning and Jc performance over wide magnetic field and angular ranges.

  6. Elevated Temperature Deformation of Fe-39.8Al and Fe-15.6Mn-39.4Al

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. Daniel

    2004-01-01

    The elevated temperature compressive properties of binary Fe-39.8 at % Al and Fe-15.6Mn-39.4Al have been measured between 1000 and 1300 K at strain rates between 10(exp 7) and 10(exp 3)/ s. Although the Mn addition to iron aluminide did not change the basic deformation characteristics, the Mn-modified alloy was slightly weaker. In the regime where deformation of FeAl occurs by a high stress exponent mechanism (n = 6), strength increases as the grain size decreases at least for diameters between approx. 200 and approx. 10 microns. Due to the limitation in the grain size-flow stress-temperature-strain rate database, the influence of further reductions of the grain size on strength is uncertain. Based on the appearance of subgrains in deformed iron aluminide, the comparison of grain diameters to expected subgrain sizes, and the grain size exponent and stress exponent calculated from deformation experiments, it is believed that grain size strengthening is the result of an artificial limitation on subgrain size as proposed by Sherby, Klundt and Miller.

  7. Radiation damage in cubic-stabilized zirconia

    SciTech Connect

    Costantini, Jean-Marc; Beuneu, Francois; Weber, William J

    2013-01-01

    Cubic yttria-stabilized zirconia (YSZ) can be used for nuclear applications as an inert matrix for actinide immobilization or transmutation. Indeed, the large amount of native oxygen vacancies leads to a high radiation tolerance of this material owing to defect recombination occurring in the atomic displacements cascades induced by fast neutron irradiation or ion implantations, as showed by Molecular dynamics (MD) simulations. Amorphization cannot be obtained in YSZ either by nuclear-collision or electronic-excitation damage, just like in urania. A kind of polygonization structure with slightly disoriented crystalline domains is obtained in both cases. In the first steps of damage, specific isolated point defects (like F+-type color centers) and point-defect clusters are produced by nuclear collisions with charged particles or neutrons. Further increase of damage leads to dislocation-loop formation, then to collapse of the dislocation network into a polygonization structure. For swift heavy ion irradiations, a similar polygonization structure is obtained above a threshold stopping power value of about 20-30 keV nm-1.

  8. Smooth cubic commensurate oxides on gallium nitride

    SciTech Connect

    Paisley, Elizabeth A.; Gaddy, Benjamin E.; LeBeau, James M.; Shelton, Christopher T.; Losego, Mark D.; Mita, Seiji; Collazo, Ramón; Sitar, Zlatko; Irving, Douglas L.; Maria, Jon-Paul; Biegalski, Michael D.; Christen, Hans M.

    2014-02-14

    Smooth, commensurate alloys of 〈111〉-oriented Mg{sub 0.52}Ca{sub 0.48}O (MCO) thin films are demonstrated on Ga-polar, c+ [0001]-oriented GaN by surfactant-assisted molecular beam epitaxy and pulsed laser deposition. These are unique examples of coherent cubic oxide|nitride interfaces with structural and morphological perfection. Metal-insulator-semiconductor capacitor structures were fabricated on n-type GaN. A comparison of leakage current density for conventional and surfactant-assisted growth reveals a nearly 100× reduction in leakage current density for the surfactant-assisted samples. HAADF-STEM images of the MCO|GaN interface show commensurate alignment of atomic planes with minimal defects due to lattice mismatch. STEM and DFT calculations show that GaN c/2 steps create incoherent boundaries in MCO over layers which manifest as two in-plane rotations and determine consequently the density of structural defects in otherwise coherent MCO. This new understanding of interfacial steps between HCP and FCC crystals identifies the steps needed to create globally defect-free heterostructures.

  9. Triangulation of cubic panorama for view synthesis.

    PubMed

    Zhang, Chunxiao; Zhao, Yan; Wu, Falin

    2011-08-01

    An unstructured triangulation approach, new to our knowledge, is proposed to apply triangular meshes for representing and rendering a scene on a cubic panorama (CP). It sophisticatedly converts a complicated three-dimensional triangulation into a simple three-step triangulation. First, a two-dimensional Delaunay triangulation is individually carried out on each face. Second, an improved polygonal triangulation is implemented in the intermediate regions of each of two faces. Third, a cobweblike triangulation is designed for the remaining intermediate regions after unfolding four faces to the top/bottom face. Since the last two steps well solve the boundary problem arising from cube edges, the triangulation with irregular-distribution feature points is implemented in a CP as a whole. The triangular meshes can be warped from multiple reference CPs onto an arbitrary viewpoint by face-to-face homography transformations. The experiments indicate that the proposed triangulation approach provides a good modeling for the scene with photorealistic rendered CPs. PMID:21833101

  10. March 20, 2012 Space Station Briefing: Cubic Satellite Deploy (Narrated)

    NASA Video Gallery

    This animation, presented by Expedition 32 Lead Flight Director Dina Contella during the March 20, 2012 ISS Program and Science Overview Briefing, shows the deploy of small cubic satellites (often ...

  11. Monotonicity preserving splines using rational Ball cubic interpolation

    NASA Astrophysics Data System (ADS)

    Zakaria, Wan Zafira Ezza Wan; Jamal, Ena; Ali, Jamaludin Md.

    2015-10-01

    In scientific application and Computer Aided Design (CAD), users usually need to generate a spline passing through a given set of data which preserves certain shape properties of the data such as positivity, monotonicity or convexity [1]. The required curves have to be a smooth shape-preserving interpolation. In this paper a rational cubic spline in Ball representation is developed to generate an interpolant that preserves monotonicity. In this paper to control the shape of the interpolant three shape parameters are introduced. The shape parameters in the description of the rational cubic interpolation are subjected to monotonicity constrained. The necessary and sufficient conditions of the rational cubic interpolation are derived and visually the proposed rational cubic interpolant gives a very pleasing result.

  12. March 20, 2012 Space Station Briefing: Cubic Satellite Deploy

    NASA Video Gallery

    This animation, presented by Expedition 32 Lead Flight Director Dina Contella during the March 20, 2012 ISS Program and Science Overview Briefing, shows the deploy of small cubic satellites (often ...

  13. Late-time attractor for the cubic nonlinear wave equation

    SciTech Connect

    Szpak, Nikodem

    2010-08-15

    We apply our recently developed scaling technique for obtaining late-time asymptotics to the cubic nonlinear wave equation and explain the appearance and approach to the two-parameter attractor found recently by Bizon and Zenginoglu.

  14. The Coulombic Lattice Potential of Ionic Compounds: The Cubic Perovskites.

    ERIC Educational Resources Information Center

    Francisco, E.; And Others

    1988-01-01

    Presents coulombic models representing the particles of a system by point charges interacting through Coulomb's law to explain coulombic lattice potential. Uses rubidium manganese trifluoride as an example of cubic perovskite structure. Discusses the effects on cluster properties. (CW)

  15. Population II Li-6 as a probe of nucleosynthesis and stellar structure and evolution

    NASA Technical Reports Server (NTRS)

    Steigman, Gary; Fields, Brian D.; Olive, Keith A.; Schramm, David N.; Walker, Terry P.

    1993-01-01

    We discuss the importance of Population II Li-6 as a diagnostic for models of primordial nucleosynthesis, cosmic-ray nucleosyntheses in the early Galaxy, and the structure and evolution of metal-poor solar-type stars. The observation of Li-6 in the subdwarf HD 84937 is shown to be consistent with the existing Population II LiBeB data within the context of a simple three-component model: (1) standard big bang nucleosynthesis, (2) Population II cosmic-ray nucleosynthesis, (3) standard (nonrotating) stellar LiBeB depletion. If this interpretation is correct, we predict a potentially detectable boron abundance for this star: about 2 x 10 exp -12. Subsequent Population II LiBeB observations, and in particular further observations of Population II Li-6, are shown to be crucial to our understanding of the primordial and early galactic creation and destruction mechanisms for light elements.

  16. Aeroheating Characteristics for a Two-Stage-To-Orbit Concept During Separation at Mach 6

    NASA Technical Reports Server (NTRS)

    Liechty, Derek S.

    2005-01-01

    An experimental study was conducted to determine the proximity aeroheating characteristics for a two-stage-to-orbit concept in close proximity in the NASA Langley 20-Inch Mach 6 Air Tunnel. A new hybrid discrete thin-film resistance gauge technique was evaluated in this study and used to measure experimental interference heating levels between the booster and the orbiter at a constant freestream Reynolds number of 8.25 x 10(exp 6)/m and a variety of separation and axial offset distances. It was found that, as the orbiter separates from the booster and the booster falls away, the windward centerline heating increased on the orbiter by as much as 13-times over the baseline, single model heating distribution, and on the booster by as much as 6-times. The aeroheating database developed can be used for computational fluid dynamic code validation.

  17. Rate Constant for the Reaction CH3 + CH3 Yields C2H6 at T = 155 K and Model Calculation of the CH3 Abundance in the Atmospheres of Saturn and Neptune

    NASA Technical Reports Server (NTRS)

    Cody, Regina J.; Romani, Paul N.; Nesbitt, Fred L.; Iannone, Mark A.; Tardy, Dwight C.; Stief, Louis J.

    2003-01-01

    The column abundances of CH3 observed by the Infrared Space Observatory (ISO) satellite on Saturn and Neptune were lower than predicted by atmospheric photochemical models, especially for Saturn. It has been suggested that the models underestimated the loss of CH3 due to poor knowledge of the rate constant k of the CH3 + CH3 self-reaction at the low temperatures and pressures of these atmospheres. Motivated by this suggestion, we undertook a combined experimental and photochemical modeling study of the CH3 + CH3 reaction and its role in determining planetary CH3 abundances. In a discharge flow-mass spectrometer system, k was measured at T = 155 K and three pressures of He. The results in units of cu cm/molecule/s are k(0.6 Torr) = 6.82 x 10(exp -11), k(1.0 Torr) = 6.98 x 10(exp -11), and k(1.5 Torr) = 6.91 x 10(exp -11). Analytical expressions for k were derived that (1) are consistent with the present laboratory data at T = 155 K, our previous data at T = 202 K and 298 K, and those of other studies in He at T = 296-298 K and (2) have some theoretical basis to provide justification for extrapolation. The derived analytical expressions were then used in atmospheric photochemical models for both Saturn and Neptune. These model results reduced the disparity with observations of Saturn, but not with observations of Neptune. However, the disparity for Neptune is much smaller. The solution to the remaining excess CH3 prediction in the models relative to the ISO observations lies, to a large extent, elsewhere in the CH3 photochemistry or transport, not in the CH3 + CH3 rate.

  18. New cubic structure compounds as actinide host phases

    NASA Astrophysics Data System (ADS)

    Stefanovsky, S. V.; Yudintsev, S. V.; Livshits, T. S.

    2010-03-01

    Various compounds with fluorite (cubic zirconia) and fluorite-derived (pyrochlore, zirconolite) structures are considered as promising actinide host phases at immobilization of actinide-bearing nuclear wastes. Recently some new cubic compounds — stannate and stannate-zirconate pyrochlores, murataite and related phases, and actinide-bearing garnet structure compounds were proposed as perspective matrices for complex actinide wastes. Zirconate pyrochlore (ideally Gd2Zr2O7) has excellent radiation resistance and high chemical durability but requires high temperatures (at least 1500 °C) to be produced by hot-pressing from sol-gel derived precursor. Partial Sn4+ substitution for Zr4+ reduces production temperature and the compounds REE2ZrSnO7 may be hot-pressed or cold pressed and sintered at ~1400 °C. Pyrochlore, A2B2O7-x (two-fold elementary fluorite unit cell), and murataite, A3B6C2O20-y (three-fold fluorite unit cell), are end-members of the polysomatic series consisting of the phases whose structures are built from alternating pyrochlore and murataite blocks (nano-sized modules) with seven- (2C/3C/2C), five- (2C/3C), eight- (3C/2C/3C) and three-fold (3C — murataite) fluorite unit cells. Actinide content in this series reduces in the row: 2C (pyrochlore) > 7C > 5C > 8C > 3C (murataite). Due to congruent melting murataite-based ceramics may be produced by melting and the firstly segregated phase at melt crystallization is that with the highest fraction of the pyrochlore modules in its structure. The melts containing up to 10 wt. % AnO2 (An = Th, U, Np, Pu) or REE/An fraction of HLW form at crystallization zoned grains composed sequentially of the 5C → 8C → 3C phases with the highest actinide concentration in the core and the lowest — in the rim of the grains. Radiation resistance of the "murataite" is comparable to titanate pyrochlores. One more promising actinide hosts are ferrites with garnet structure. The matrices containing sometime complex fluorite

  19. Consolidation of cubic and hexagonal boron nitride composites

    SciTech Connect

    Du Frane, W. L.; Cervantes, O.; Ellsworth, G. F.; Kuntz, J. D.

    2015-12-08

    When we Consolidate cubic boron nitride (cBN) it typically requires either a matrix of metal bearing materials that are undesirable for certain applications, or very high pressures within the cBN phase stability field that are prohibitive to manufacturing size and cost. We present new methodology for consolidating high stiffness cBN composites within a hexagonal boron nitride (hBN) matrix (15–25 vol%) with the aid of a binder phase (0–6 vol%) at moderate pressures (0.5–1.0 GPa) and temperatures (900–1300 °C). The composites are demonstrated to be highly tailorable with a range of compositions and resulting physical/mechanical properties. Ultrasonic measurements indicate that in some cases these composites have elastic mechanical properties that exceed those of the highest strength steel alloys. Moreover, two methods were identified to prevent phase transformation of the metastable cBN phase into hBN during consolidation: 1. removal of hydrocarbons, and 2. increased cBN particle size. Lithium tetraborate worked better as a binder than boron oxide, aiding consolidation without enhancing cBN to hBN phase transformation kinetics. These powder mixtures consolidated within error of their full theoretical mass densities at 1 GPa, and had only slightly lower densities at 0.5 GPa. This shows potential for consolidation of these composites into larger parts, in a variety of shapes, at even lower pressures using more conventional manufacturing methods, such as hot-pressing.

  20. X-33 Rev-F Turbulent Aeroheating Results From Test 6817 in NASA Langley 20-Inch Mach 6 Air Tunnel and Comparisons With Computations

    NASA Technical Reports Server (NTRS)

    Hollis, Brian R.; Horvath, Thomas J.; Berry, Scott A.

    2003-01-01

    Measurements and predictions of the X-33 turbulent aeroheating environment have been performed at Mach 6, perfect-gas air conditions. The purpose of this investigation was to compare measured turbulent aeroheating levels on smooth models, models with discrete trips, and models with arrays of bowed panels (which simulate bowed thermal protections system tiles) with each other and with predictions from two Navier-Stokes codes, LAURA and GASP. The wind tunnel testing was conducted at free stream Reynolds numbers based on length of 1.8 x 10(exp 6) to 6.1 x 10(exp 6) on 0.0132 scale X-33 models at a = 40-deg. Turbulent flow was produced by the discrete trips and by the bowed panels at ill but the lowest Reynolds number, but turbulent flow on the smooth model was produced only at the highest Reynolds number. Turbulent aeroheating levels on each of the three model types were measured using global phosphor thermography and were found to agree to within .he estimated uncertainty (plus or minus 15%) of the experiment. Computations were performed at the wind tunnel free stream conditions using both codes. Turbulent aeroheating levels predicted using the LAURA code were generally 5%-10% lower than those from GASP, although both sets of predictions fell within the experimental accuracy of the wind tunnel data.

  1. Observational Opportunities with the CUBIC Experiment on SAC-B

    NASA Astrophysics Data System (ADS)

    Nousek, J. A.; Burrows, D. N.; Moskalenko, E. I.

    1996-12-01

    The CUBIC experiment on the SAC-B satellite is now collecting data on the Diffuse X-Ray Background and bright point sources over an energy range of 0.2 - 10 keV with energy resolution ranging from 40 - 160 eV over this bandpass. CUBIC observations, several of which are discussed in other posters at this session, provide 2 - 4 high quality spectra per week. CUBIC was built as a PI-class instrument, and at present data rights are divided between Penn State (90%) and Leicester University (10%). We present the observing plan for the first six months of CUBIC operations. We are currently collaborating with several astronomers who are not on the CUBIC team but have expressed interest in one or more of these targets. We invite additional collaborations on targets which are not currently assigned to a specific observer. In order to make these data more accessible to the astronomical community, we are proposing to institute a modest Guest Investigator program. If supported by ADP funding, this would permit observing requests from outside astronomers and would place a large fraction of the CUBIC data in a public archive at the HEASARC.

  2. On the shock response of cubic metals

    NASA Astrophysics Data System (ADS)

    Bourne, N. K.; Gray, G. T.; Millett, J. C. F.

    2009-11-01

    The response of four cubic metals to shock loading is reviewed in order to understand the effects of microstructure on continuum response. Experiments are described that link defect generation and storage mechanisms at the mesoscale to observations in the bulk. Four materials were reviewed; these were fcc nickel, the ordered fcc intermetallic Ni3Al, the bcc metal tantalum, and two alloys based on the intermetallic phase TiAl; Ti-46.5Al-2Cr-2Nb and Ti-48Al-2Cr-2Nb-1B. The experiments described are in two groups: first, equation of state and shear strength measurements using Manganin stress gauges and, second, postshock microstructural examinations and measurement of changes in mechanical properties. The behaviors described are linked through the description of time dependent plasticity mechanisms to the final states achieved. Recovered targets displayed dislocation microstructures illustrating processes active during the shock-loading process. Reloading of previously shock-prestrained samples illustrated shock strengthening for the fcc metals Ni and Ni3Al while showing no such effect for bcc Ta and for the intermetallic TiAl. This difference in effective shock hardening has been related, on the one hand, to the fact that bcc metals have fewer available slip systems that can operate than fcc crystals and to the observation that the lower symmetry materials (Ta and TiAl) both possess high Peierls stress and thus have higher resistances to defect motion in the lattice under shock-loading conditions. These behaviors, compared between these four materials, illustrate the role of defect generation, transport, storage, and interaction in determining the response of materials to shock prestraining.

  3. Polyimide nanocomposites based on cubic zirconium tungstate

    NASA Astrophysics Data System (ADS)

    Ramasubramanian Sharma, Gayathri

    2009-12-01

    In this research, cubic zirconium tungstate (ZrW2O8) was used as a filler to reduce the CTE of polyimides (PI), and the effect of ZrW2O8 nanoparticles on the bulk polymer properties was studied. Polyimides are high performance polymers with exceptional thermal stability, and there is a need for PIs with low CTEs for high temperature applications. The nanofiller, cubic ZrW2O8, is well known for its isotropic negative thermal expansion (NTE) over a wide temperature range from -272.7 to 777°C. The preparation of nanocomposites involved the synthesis of ZrW 2O8 nanofiller, engineering the polymer-filler interface using linker groups and optimization of processing strategies to prepare free-standing PI nanocomposite films. A hydrothermal method was used to synthesize ZrW 2O8 nanoparticles. Polyimide-ZrW2O8 interface interaction was enhanced by covalently bonding linker moieties to the surface of ZrW2O8 nanoparticles. Specifically, ZrW 2O8 nanoparticles were functionalized with two different linker groups: (1) a short aliphatic silane, and (2) low molecular weight PI. The surface functionalization was confirmed using X-ray photoelectron spectroscopy and thermal gravimetric analysis (TGA). Reprecipitation blending was used to prepare the freestanding PI-ZrW2O8 nanocomposite films with up to 15 volume% filler loading. SEM images showed the improvements in polymer-filler wetting behavior achieved using interface engineering. SEM images indicated that there was better filler dispersion in the PI matrix using reprecipitation blending, compared to the filler dispersion achieved in the nanocomposites prepared using conventional blending technique. The structure-property relationships in PI-ZrW2O8 nanocomposites were investigated by studying the thermal degradation, glass transition, tensile and thermal expansion properties of the nanocomposites. The properties were studied as a function of filler loading and interface linker groups. Addition of ZrW2O8 nanoparticles did not

  4. Grain growth and phase stability of nanocrystalline cubic zirconia under ion irradiation

    SciTech Connect

    Zhang, Yanwen; Jiang, Weilin; Wang, Chong M.; Namavar, Fereydoon; Edmondson, Philip D.; Zhu, Zihua; Gao, Fei; Lian, Jie; Weber, William J.

    2010-11-10

    Grain growth, oxygen stoichiometry and phase stability of nanostructurally-stabilized zirconia (NSZ) in pure cubic phase are investigated under 2 MeV Au ion bombardment at 160 and 400 K to doses up to 35 displacements per atom (dpa). The NSZ films are produced by ion-beam-assisted deposition technique at room temperature with an average grain size of 7.7 nm. The grain size increases with dose, and follows a power law (n=6) to a saturation value of ~30 nm that decreases with temperature. Slower grain growth is observed under 400 K irradiations, as compared to 160 K irradiations, indicating that thermal grain growth is not activated and defect-stimulated grain growth is the dominating mechanism. While cubic phase is perfectly retained and no new phases are identified after the high-dose irradiations, reduction of oxygen in the irradiated NSZ films is detected. The ratio of O to Zr decreases from ~2.0 for the as-deposited films to ~1.65 after irradiation to ~35 dpa. Significant increase of oxygen vacancies in nanocrystalline zirconia suggests substantially enhanced oxygen diffusion under ion irradiation, a materials behavior far from equilibrium. The oxygen deficiency may be essential in stabilizing cubic phase to larger grain sizes.

  5. Chemical vapour deposition of undoped and spinel-doped cubic zirconia film using organometallic process

    NASA Astrophysics Data System (ADS)

    Takahashi, Yasutaka; Kawae, Takayuki; Nasu, Mineji

    1986-03-01

    Growth of undoped and spinel-doped ZrO 2 films on glass substrates by the vapour phase decomposition of zirconium t-butoxide (ZTB) was investigated. Undoped tetragonal and monoclinic ZrO 2 films were formed below and above 400°C, respectively. Cubic ZrO 2 films were grown when the ZrO 2 was doped with more than 5 mol% of spinel MgAl 2O 4. Magnesium aluminium isopropoxide MgAl 2 (O-i-Pr) 8 (MAI) was used as the dopant source of the spinel. The cubic films have a higher Vickers hardness than the monoclinic films by about 200-250 kg/mm 2, and are stable up to 800°C, above which they were transformed to the monoclinic phase. This is in contrast to the higher temperature stability of the spinel-doped zirconia powder with spinel content 6 mol% formed by hydrolysis of a isopropanol solution of mixed zirconium n-butoxide and MAI, where the tetragonal form of ZrO 2 was kept unchanged by annealing it up to about 1000°C. The difference is attributed to effect of surface energy control in the tetragonal powders which is absent in the cubic films produced by CVD.

  6. Grain Growth and Phase Stability of Nanocrystalline Cubic Zirconia under Ion Irradiation

    SciTech Connect

    Zhang, Yanwen; Jiang, Weilin; Wang, Chongmin; Namavar, Fereydoon; Edmondson, Philip D.; Zhu, Zihua; Gao, Fei; Lian, Jie; Weber, William J

    2010-01-01

    Grain growth, oxygen stoichiometry and phase stability of nanostructurally-stabilized cubic zirconia (NSZ) are investigated under 2 MeV Au ion bombardment at 160 and 400 K to doses up to 35 displacements per atom (dpa). The NSZ films are produced by ion-beam-assisted deposition technique at room temperature with an average grain size of 7.7 nm. The grain size increases with dose, and follows a power law (n=6) to a saturation value of ~30 nm that decreases with temperature. Slower grain growth is observed under 400 K irradiations, as compared to 160 K irradiations, indicating that the grain growth is not thermally activated and irradiation-induced grain growth is the dominating mechanism. While the cubic structure is retained and no new phases are identified after the high-dose irradiations, oxygen reduction in the irradiated NSZ films is detected. The ratio of O to Zr decreases from ~2.0 for the as-deposited films to ~1.65 after irradiation to ~35 dpa. The loss of oxygen suggests a significant increase of oxygen vacancies in nanocrystalline zirconia under ion irradiation. The oxygen deficiency may be essential in stabilizing the cubic phase to larger grain sizes.

  7. Site occupancy of interstitial deuterium atoms in face-centred cubic iron

    PubMed Central

    Machida, Akihiko; Saitoh, Hiroyuki; Sugimoto, Hidehiko; Hattori, Takanori; Sano-Furukawa, Asami; Endo, Naruki; Katayama, Yoshinori; Iizuka, Riko; Sato, Toyoto; Matsuo, Motoaki; Orimo, Shin-ichi; Aoki, Katsutoshi

    2014-01-01

    Hydrogen composition and occupation state provide basic information for understanding various properties of the metal–hydrogen system, ranging from microscopic properties such as hydrogen diffusion to macroscopic properties such as phase stability. Here the deuterization process of face-centred cubic Fe to form solid-solution face-centred cubic FeDx is investigated using in situ neutron diffraction at high temperature and pressure. In a completely deuterized specimen at 988 K and 6.3 GPa, deuterium atoms occupy octahedral and tetrahedral interstitial sites with an occupancy of 0.532(9) and 0.056(5), respectively, giving a deuterium composition x of 0.64(1). During deuterization, the metal lattice expands approximately linearly with deuterium composition at a rate of 2.21 Å3 per deuterium atom. The minor occupation of the tetrahedral site is thermally driven by the intersite movement of deuterium atoms along the ‹111› direction in the face-centred cubic metal lattice. PMID:25256789

  8. Probing new physics of cubic Higgs boson interaction via Higgs pair production at hadron colliders

    NASA Astrophysics Data System (ADS)

    He, Hong-Jian; Ren, Jing; Yao, Weiming

    2016-01-01

    Despite the discovery of a Higgs boson h (125 GeV) at the LHC run 1, its self-interaction has fully evaded direct experimental probe so far. Such self-interaction is vital for electroweak symmetry breaking, vacuum stability, and electroweak phase transition. It is a most likely place to encode new physics beyond the standard model. We parametrize such new physics by model-independent dimension-six effective operators and study their tests via Higgs pair production at hadron colliders. We analyze three major di-Higgs production channels at the parton level and compare the parameter dependence of total cross sections and kinematic distributions at the LHC (14 TeV) and p p (100 TeV) hadron collider. We further perform full simulations for the di-Higgs production channel g g →h h →b b ¯γ γ and its backgrounds at the p p (100 TeV) hadron collider. We construct four kinds of benchmark points and study the sensitivities to probing different regions of the parameter space of cubic Higgs interactions. We find that for a one-parameter analysis and with a 3 ab-1 (30 ab-1 ) integrated luminosity, the g g →h h →b b ¯γ γ channel can measure the SM cubic Higgs coupling and the derivative cubic Higgs coupling to an accuracy of about 13% (4.2%) and 5% (1.6%), respectively.

  9. Aerothermodynamic Testing of Protuberances and Penetrations on the NASA Crew Exploration Vehicle Heat Shield in the NASA Langley 20-Inch Mach 6 Air Tunnel

    NASA Technical Reports Server (NTRS)

    Liechty, Derek S.

    2008-01-01

    An experimental wind tunnel program is being conducted in support of an Agency wide effort to develop a replacement for the Space Shuttle and to support the NASA s long-term objective of returning to the moon and then on to Mars. This paper documents experimental measurements made on several scaled ceramic heat transfer models of the proposed Crew Exploration Vehicle. Global heat transfer images and heat transfer distributions obtained using phosphor thermography were used to infer interference heating on the Crew Exploration Vehicle Cycle 1 heat shield from local protuberances and penetrations for both laminar and turbulent heating conditions. Test parametrics included free stream Reynolds numbers of 1.0x10(exp 6)/ft to 7.25x10(exp 6)/ft in Mach 6 air at a fixed angle-of-attack. Single arrays of discrete boundary layer trips were used to trip the boundary layer approaching the protuberances/penetrations to a turbulent state. Also, the effects of three compression pad diameters, two radial locations of compression pad/tension tie location, compression pad geometry, and rotational position of compression pad/tension tie were examined. The experimental data highlighted in this paper are to be used to validate CFD tools that will be used to generate the flight aerothermodynamic database. Heat transfer measurements will also assist in the determination of the most appropriate engineering methods that will be used to assess local flight environments associated with protuberances/penetrations of the CEV thermal protection system.

  10. Nonlinear surface acoustic waves in cubic crystals

    NASA Astrophysics Data System (ADS)

    Kumon, Ronald Edward

    Model equations developed by Hamilton, Il'inskii, and Zabolotskaya [J. Acoust. Soc. Am. 105, 639-651 (1999)] are used to perform theoretical and numerical studies of nonlinear surface acoustic waves in a variety of nonpiezoelectric cubic crystals. The basic theory underlying the model equations is outlined, quasilinear solutions of the equations are derived, and expressions are developed for the shock formation distance and nonlinearity coefficient. A time-domain equation corresponding to the frequency-domain model equations is derived and shown to reduce to a time-domain equation introduced previously for Rayleigh waves [E. A. Zabolotskaya, J. Acoust. Soc. Am. 91, 2569-2575 (1992)]. Numerical calculations are performed to predict the evolution of initially monofrequency surface waves in the (001), (110), and (111) planes of the crystals RbCl, KCl, NaCl, CaF2, SrF2, BaF2, C (diamond), Si, Ge, Al, Ni, Cu in the moverline 3m point group, and the crystals Cs-alum, NH4- alum, and K-alum in the moverline 3 point group. The calculations are based on measured second- and third- order elastic constants taken from the literature. Nonlinearity matrix elements which describe the coupling strength of harmonic interactions are shown to provide a powerful tool for characterizing waveform distortion. Simulations in the (001) and (110) planes show that in certain directions the velocity waveform distortion may change in sign, generation of one or more harmonies may be suppressed and shock formation postponed, or energy may be transferred rapidly to the highest harmonics and shock formation enhanced. Simulations in the (111) plane show that the nonlinearity matrix elements are generally complex-valued, which may lead to asymmetric distortion and the appearance of low frequency oscillations near the peaks and shocks in the velocity waveforms. A simple transformation based on the phase of the nonlinearity matrix is shown to provide a reasonable approximation of asymmetric waveform

  11. Toward 10(exp 10) Contrast for Terrestrial Exoplanet Detection: Demonstration of Wavefront Correction in a Shaped Pupil Coronagraph

    NASA Technical Reports Server (NTRS)

    Belikov, Ruslan; Give'on, Amir; Trauger, John T.; Carr, Michael; Kasdin, Jeremy N.; Vanderbei, Robert J.; Shi, Fang; Balasubramanian, Kunjithapatham; Kuhnert, Andreas

    2006-01-01

    Experimental demonstration of wavefront control with shaped pupils. Contrast level is maintained across different wavelengths and 10% broadband light. Further improvements in contrast believed to have been possible with more time and parameter optimizations.

  12. Lattice matched crystalline substrates for cubic nitride semiconductor growth

    SciTech Connect

    Norman, Andrew G; Ptak, Aaron J; McMahon, William E

    2015-02-24

    Disclosed embodiments include methods of fabricating a semiconductor layer or device and devices fabricated thereby. The methods include, but are not limited to, providing a substrate having a cubic crystalline surface with a known lattice parameter and growing a cubic crystalline group III-nitride alloy layer on the cubic crystalline substrate by coincident site lattice matched epitaxy. The cubic crystalline group III-nitride alloy may be prepared to have a lattice parameter (a') that is related to the lattice parameter of the substrate (a). The group III-nitride alloy may be a cubic crystalline In.sub.xGa.sub.yAl.sub.1-x-yN alloy. The lattice parameter of the In.sub.xGa.sub.yAl.sub.1-x-yN or other group III-nitride alloy may be related to the substrate lattice parameter by (a')= 2(a) or (a')=(a)/ 2. The semiconductor alloy may be prepared to have a selected band gap.

  13. Evolution of cubic membranes as antioxidant defence system.

    PubMed

    Deng, Yuru; Almsherqi, Zakaria A

    2015-08-01

    Possibly the best-characterized cubic membrane transition has been observed in the mitochondrial inner membranes of free-living giant amoeba (Chaos carolinense). In this ancient organism, the cells are able to survive in extreme environments such as lack of food, thermal and osmolarity fluctuations and high levels of reactive oxygen species. Their mitochondrial inner membranes undergo rapid changes in three-dimensional organization upon food depletion, providing a valuable model to study this subcellular adaptation. Our data show that cubic membrane is enriched with unique ether phospholipids, plasmalogens carrying very long-chain polyunsaturated fatty acids. Here, we propose that these phospholipids may not only facilitate cubic membrane formation but may also provide a protective shelter to RNA. The potential interaction of cubic membrane with RNA may reduce the amount of RNA oxidation and promote more efficient protein translation. Thus, recognizing the role of cubic membranes in RNA antioxidant systems might help us to understand the adaptive mechanisms that have evolved over time in eukaryotes. PMID:26464785

  14. Evolution of cubic membranes as antioxidant defence system

    PubMed Central

    Deng, Yuru; Almsherqi, Zakaria A.

    2015-01-01

    Possibly the best-characterized cubic membrane transition has been observed in the mitochondrial inner membranes of free-living giant amoeba (Chaos carolinense). In this ancient organism, the cells are able to survive in extreme environments such as lack of food, thermal and osmolarity fluctuations and high levels of reactive oxygen species. Their mitochondrial inner membranes undergo rapid changes in three-dimensional organization upon food depletion, providing a valuable model to study this subcellular adaptation. Our data show that cubic membrane is enriched with unique ether phospholipids, plasmalogens carrying very long-chain polyunsaturated fatty acids. Here, we propose that these phospholipids may not only facilitate cubic membrane formation but may also provide a protective shelter to RNA. The potential interaction of cubic membrane with RNA may reduce the amount of RNA oxidation and promote more efficient protein translation. Thus, recognizing the role of cubic membranes in RNA antioxidant systems might help us to understand the adaptive mechanisms that have evolved over time in eukaryotes. PMID:26464785

  15. A Wind Tunnel Experiment for Trailing Edge Circulation Control on a 6 Percent 2-D Airfoil up to Transonic Mach Numbers

    NASA Technical Reports Server (NTRS)

    Alexander, Michael G.; Anders, Scott G.; Johnson, Stuart K.

    2005-01-01

    A wind tunnel test was conducted on a six percent thick slightly cambered elliptical circulation control airfoil with both upper and lower surface blowing. Parametric evaluations of jet slot heights and Coanda surface shapes were conducted at mass flow coefficients (C(sub mu)) from 0.0 to 0.12. The test data was acquired in the NASA Langley Transonic Dynamics Tunnel at Mach numbers of 0.8 and 0.3 at Reynolds numbers per foot of 1.05 x 10(exp 6) and 2.43 x 10(exp 5) respectively. For the transonic condition, (Mach = 0.8 at alpha = +3 deg), it was generally found that the smaller slot and larger Coanda surface were more effective overall than other slot/Coanda surface combinations. Generally it was found at Mach = 0.3 at alpha = 6 deg that the smaller slot and smaller Coanda surface were more effective overall than other slot/Coanda surface combinations.

  16. Consolidation of cubic and hexagonal boron nitride composites

    DOE PAGESBeta

    Du Frane, W. L.; Cervantes, O.; Ellsworth, G. F.; Kuntz, J. D.

    2015-12-08

    When we Consolidate cubic boron nitride (cBN) it typically requires either a matrix of metal bearing materials that are undesirable for certain applications, or very high pressures within the cBN phase stability field that are prohibitive to manufacturing size and cost. We present new methodology for consolidating high stiffness cBN composites within a hexagonal boron nitride (hBN) matrix (15–25 vol%) with the aid of a binder phase (0–6 vol%) at moderate pressures (0.5–1.0 GPa) and temperatures (900–1300 °C). The composites are demonstrated to be highly tailorable with a range of compositions and resulting physical/mechanical properties. Ultrasonic measurements indicate that inmore » some cases these composites have elastic mechanical properties that exceed those of the highest strength steel alloys. Moreover, two methods were identified to prevent phase transformation of the metastable cBN phase into hBN during consolidation: 1. removal of hydrocarbons, and 2. increased cBN particle size. Lithium tetraborate worked better as a binder than boron oxide, aiding consolidation without enhancing cBN to hBN phase transformation kinetics. These powder mixtures consolidated within error of their full theoretical mass densities at 1 GPa, and had only slightly lower densities at 0.5 GPa. This shows potential for consolidation of these composites into larger parts, in a variety of shapes, at even lower pressures using more conventional manufacturing methods, such as hot-pressing.« less

  17. High-temperature fiber optic cubic-zirconia pressure sensor

    NASA Astrophysics Data System (ADS)

    Peng, Wei; Pickrell, Gary R.; Wang, Anbo

    2005-12-01

    There is a critical need for pressure sensors that can operate reliably at high temperatures in many industrial segments such as in the combustion section of gas turbine engines for both transportation and power generation, coal gasifiers, coal fired boilers, etc. Optical-based sensors are particularly attractive for the measurement of a wide variety of physical and chemical parameters in high-temperature and high-pressure industrial environments due to their small size and immunity to electromagnetic interference. A fiber optic pressure sensor utilizing single-crystal cubic zirconia as the sensing element is reported. The pressure response of this sensor has been measured at temperatures up to 1000 °C. Additional experimental results show that cubic zirconia could be used for pressure sensing at temperatures over 1000 °C. This study demonstrates the feasibility of using a novel cubic-zirconia sensor for pressure measurement at high temperatures.

  18. Use of Pom Pons To Illustrate Cubic Crystal Structures

    NASA Astrophysics Data System (ADS)

    Cady, Susan G.

    1997-07-01

    In general chemistry classes, students are introduced to the ways in which atoms are arranged in cubic crystal structures. Transposing the textbook illustrations into three dimensional structures is difficult for some students. This transitions is easier if a three dimensional model is available for examination. Several 3D models are cited. A quick to assemble, inexpensive, colorful, and durable alternative to these models and styrofoam balls is the use of olefin pom pons. Different sized pom pons can be used to demonstrate how the atomic radius will vary when comparing the different types of cubic crystal unit cells. Being made of a coarse material, pom pons can be stacked to illustrate different packing arrangements such as hexagonal close-packed and cubic close-packed structures. Pom pons make great atoms.

  19. Extended temperature dependence of elastic constants in cubic crystals.

    PubMed

    Telichko, A V; Sorokin, B P

    2015-08-01

    To extend the theory of the temperature dependence of the elastic constants in cubic crystals beyond the second- and third-order elastic constants, the fourth-order elastic constants, as well as the non-linearity in the thermal expansion temperature dependence, have been taken into account. Theoretical results were represented as temperature functions of the effective elastic constants and compared with experimental data for a number of cubic crystals, such as alkali metal halides, and elements gold and silver. The relations obtained give a more accurate description of the experimental temperature dependences of second-order elastic constants for a number of cubic crystals, including deviations from linear behavior. A good agreement between theoretical estimates and experimental data has been observed. PMID:25819879

  20. Meridional Variations of C2H2 and C2H6 in Jupiter's Atmosphere from Cassini CIRS Infrared Spectra

    NASA Technical Reports Server (NTRS)

    Nixon, C. A.; Achterberg, R. K.; Conrath, B. J.; Irwin, P. G. J.; Fouchet, T.; Parrish, P. D.; Romani, P. N.; Abbas, M.; LeClair, A.; Strobel, D.

    2004-01-01

    Hydrocarbons such as acetylene (C2H2) and ethane (C2H6) are important tracers in Jupiter's atmosphere, constraining our models of the chemical and dynamical processes. However, our knowledge of the vertical and meridional variations of their abundances has remained sparse. During the flyby of the Cassini spacecraft in December 2000, the Composite Infrared Spectrometer (CIRS) instrument was used to map the spatial variation of emissions from 10-1400 cm(sup -1) (1000-7 microns). In this paper we analyze a zonally-averaged set of CIRS spectra taken at the highest (0.5 cm(sup -1)) resolution, to infer atmospheric temperatures in the stratosphere at 0.5-20 mbar via the v4 band of CH4, and in the troposphere at 150-400 mbar, via the H2 absorption at 600-800 cm(sup -1). Simultaneously, we retrieve the abundances of C2H2 and C2H6 via the v5 and vg bands respectively. Tropospheric absorption and stratospheric emission are highly anti-correlated at the CIRS resolution, introducing a non-uniqueness into the retrievals, such that vertical gradient and column abundance cannot both be found without additional constraints. Assuming profile gradients from photochemical calculations, we show that the column abundance of C2H2 decreases sharply towards the poles by a factor approximately 4, while C2H6 is unchanged in the north and increasing in the south, by a factor approximately 1.8. An explanation for the meridional trends is proposed in terms of a combination of photochemistry and dynamics. Poleward, the decreasing UV flux is predicted to decrease the abundances of C2H2 and C2H6 by factors 2.7 and 3.5 respectively at a latitude 70 deg. However, the lifetime of C2H6 in the stratosphere (5 x 10(exp 9)) is much longer than the dynamical timescale for meridional motions inferred from SL-9 debris (5 x 10(exp 8 s)), and therefore the constant or rising abundance towards high latitudes likely indicates that meridional mixing dominates over photochemical effects. For C2H2, the opposite

  1. Ultrasonic radiation from wedges of cubic profile: Experimental results.

    PubMed

    Anderson, Brian E; Remillieux, Marcel C; Le Bas, Pierre-Yves; Ulrich, T J; Pieczonka, Lukasz

    2015-12-01

    This paper presents experimental results demonstrating the increase in ultrasonic radiation obtained from a wedge of cubic profile relative to a plate of uniform thickness. The wedge of cubic profile provides high efficiency sound radiation matching layer from a mounted piezoelectric transducer into the surrounding air. Previous research on structures with indentations of power-law profile has focused on vibration mitigation using the so called "acoustic black-hole" effect, whereas here such structures are used to enhance ultrasonic radiation. The work provides experimental verification of the numerical results of Remillieux et al. (2014). PMID:26166628

  2. Cubic C8 : An Observable Allotrope of Carbon?

    PubMed

    Sharapa, Dmitry; Hirsch, Andreas; Meyer, Bernd; Clark, Timothy

    2015-07-20

    Ab initio and DFT calculations are used to investigate the structure, electronic properties, spectra and reactivity of cubic C8 , which is predicted to be aromatic according to Hirsch's rule. Although highly strained and with a small amount of diradical character, the carbon cube represents a surprisingly deep minimum and should therefore be observable as an isolated molecule. It is, however, predicted to be very reactive, both with itself and triplet oxygen. Calculated IR, Raman, and UV/Vis spectra are provided to aid identification of cubic C8 should it be synthesized. PMID:26013967

  3. Process for producing wurtzitic or cubic boron nitride

    DOEpatents

    Holt, J.B.; Kingman, D.D.; Bianchini, G.M.

    1992-04-28

    Disclosed is a process for producing wurtzitic or cubic boron nitride comprising the steps of: [A] preparing an intimate mixture of powdered boron oxide, a powdered metal selected from the group consisting of magnesium or aluminum, and a powdered metal azide; [B] igniting the mixture and bringing it to a temperature at which self-sustaining combustion occurs; [C] shocking the mixture at the end of the combustion thereof with a high pressure wave, thereby forming as a reaction product, wurtzitic or cubic boron nitride and occluded metal oxide; and, optionally [D] removing the occluded metal oxide from the reaction product. Also disclosed are reaction products made by the process described.

  4. Process for producing wurtzitic or cubic boron nitride

    DOEpatents

    Holt, J. Birch; Kingman, deceased, Donald D.; Bianchini, Gregory M.

    1992-01-01

    Disclosed is a process for producing wurtzitic or cubic boron nitride comprising the steps of: [A] preparing an intimate mixture of powdered boron oxide, a powdered metal selected from the group consisting of magnesium or aluminum, and a powdered metal azide; [B] igniting the mixture and bringing it to a temperature at which self-sustaining combustion occurs; [C] shocking the mixture at the end of the combustion thereof with a high pressure wave, thereby forming as a reaction product, wurtzitic or cubic boron nitride and occluded metal oxide; and, optionally [D] removing the occluded metal oxide from the reaction product. Also disclosed are reaction products made by the process described.

  5. The singular cubical set of a topological space

    NASA Astrophysics Data System (ADS)

    Antolini, Rosa; Wiest, Bert

    1999-01-01

    For any topological space X let C(X) be the realization of the singular cubical set of X; let * be the topological space consisting of one point. In [1] Antolini proves, as a corollary to a general theorem about cubical sets, that C(X) and X×C(*) are homotopy equivalent, provided X is a CW-complex. In this note we give a short geometric proof that for any topological space X there is a natural weak homotopy equivalence between C(X) and X×C(*).

  6. Stationary phase analysis of generalized cubic phase mask wavefront coding

    NASA Astrophysics Data System (ADS)

    Liu, Ming; Dong, Liquan; Zhao, Yuejin; Hui, Mei; Jia, Wei

    2013-07-01

    The modified generalized cubic phase mask (GCPM) has recently been applied in wavefront coding systems including infrared imaging and microscopy. In this paper, the stationary phase method is employed to analyze the GCPM characteristics. The SPA of the modulation transfer function (MTF) under misfocus aberration is derived for a wavefront coding system with a GCPM. The approximation corresponds with the Fast Fourier Transform (FFT) approach. On the basis of this approximation, we compare the characteristics of GCPM and cubic phase masks (CPM). A GCPM design approach based on stationary phase approximation is presented which helps to determine the initial parameter of phase mask, significantly decreasing the computational time required for numerical simulation.

  7. Modeling of the Dust and Gas Outflows from OH 26.5+0.6: The Superwind

    NASA Technical Reports Server (NTRS)

    Justtanont, K.; Skinner, C. J.; Tielens, A. G. G. M.; Meixner, M.; Baas, F.

    1996-01-01

    We have observed the extreme OH/IR star, OH 26.5+0.6, in the infrared dust continuum and in the sub- millimeter rotational lines of CO. Mid-infrared images reveal the compact nature of the circumstellar shell (less than 0.5 sec). A deep 9.7 microns absorption feature and an absorption at 18 microns show that the dust mass-loss rate is very high. However, the low antenna temperatures of CO J = 1-0 and 2-1 lines suggest that the outer part of the circumstellar shell is much more tenuous. In order to resolve this discrepancy, we have observed the J = 3-2 and 4-3 CO rotational transitions. We have developed a model for the circumstellar shell for OH 26.5 + 0.6 which is consistent with the infrared and submillimeter observations. The dust and gas data are well fitted by a two-shell model, consisting of a dense shell surrounded by a more tenuous shell. The former we identify with the superwind (M = 5.5 x 10(exp -4) solar mass/ yr), and the latter we identify with mass loss on the asymptotic giant branch (AGB) (M = 10(exp -6) solar mass/ yr). The transition between the two mass-loss phases is shown to be rather abrupt ((Delta)t less than 150 yr). Depending on the mass of the progenitor, this superwind phase may be the last thermal pulse (for M(sub *) less than 1.5 solar mass), or the first of a series of the superwind phases (for up to 8 solar mass), punctuated by a period of low mass-loss rates, before the star evolves off the AGB.

  8. True Triaxial Strength and Failure Modes of Cubic Rock Specimens with Unloading the Minor Principal Stress

    NASA Astrophysics Data System (ADS)

    Li, Xibing; Du, Kun; Li, Diyuan

    2015-11-01

    True triaxial tests have been carried out on granite, sandstone and cement mortar using cubic specimens with the process of unloading the minor principal stress. The strengths and failure modes of the three rock materials are studied in the processes of unloading σ 3 and loading σ 1 by the newly developed true triaxial test system under different σ 2, aiming to study the mechanical responses of the rock in underground excavation at depth. It shows that the rock strength increases with the raising of the intermediate principal stress σ 2 when σ 3 is unloaded to zero. The true triaxial strength criterion by the power-law relationship can be used to fit the testing data. The "best-fitting" material parameters A and n ( A > 1.4 and n < 1.0) are almost located in the same range as expected by Al-Ajmi and Zimmerman (Int J Rock Mech Min Sci 563 42(3):431-439, 2005). It indicates that the end effect caused by the height-to-width ratio of the cubic specimens will not significantly affect the testing results under true triaxial tests. Both the strength and failure modes of cubic rock specimens under true triaxial unloading condition are affected by the intermediate principal stress. When σ 2 increases to a critical value for the strong and hard rocks (R4, R5 and R6), the rock failure mode may change from shear to slabbing. However, for medium strong and weak rocks (R3 and R2), even with a relatively high intermediate principal stress, they tend to fail in shear after a large amount of plastic deformation. The maximum extension strain criterion Stacey (Int J Rock Mech Min Sci Geomech Abstr 651 18(6):469-474, 1981) can be used to explain the change of failure mode from shear to slabbing for strong and hard rocks under true triaxial unloading test condition.

  9. Microstructure Evolution in Cut Metal Chips of Ti-6Al-4V

    NASA Technical Reports Server (NTRS)

    Dong, L.; Schneider, J. A.

    2008-01-01

    The microstructural evolution following metal cutting was investigated within metal chips of Ti-6Al-4V. Metal cutting was used to impose a high strain rate on the order of approx.10(exp 5)/s within the primary shear zone as the metal was removed from the workpiece. The initial microstructure of the parent material (PM) was composed of a bi-modal microstructure with coarse prior beta grains and equiaxed primary alpha located at the boundaries. After metal cutting, the microstructure of the metal chips showed coarsening of the equiaxed primary alpha grains and beta lamellar. These metallographic findings suggest that the metal chips experienced high temperatures which remained below the beta transus temperature.

  10. Tangent Lines without Derivatives for Quadratic and Cubic Equations

    ERIC Educational Resources Information Center

    Carroll, William J.

    2009-01-01

    In the quadratic equation, y = ax[superscript 2] + bx + c, the equation y = bx + c is identified as the equation of the line tangent to the parabola at its y-intercept. This is extended to give a convenient method of graphing tangent lines at any point on the graph of a quadratic or a cubic equation. (Contains 5 figures.)

  11. Rheology of cubic particles suspended in a Newtonian fluid.

    PubMed

    Cwalina, Colin D; Harrison, Kelsey J; Wagner, Norman J

    2016-05-18

    Many real-world industrial processes involve non-spherical particles suspended in a fluid medium. Knowledge of the flow behavior of these suspensions is essential for optimizing their transport properties and designing processing equipment. In the present work, we explore and report on the rheology of concentrated suspensions of cubic-shaped colloidal particles under steady and dynamic shear flow. These suspensions exhibit a rich non-Newtonian rheology that includes shear thickening and normal stress differences at high shear stresses. Scalings are proposed to connect the material properties of these suspensions of cubic particle to those measured for suspensions of spherical particles. Negative first normal stress differences indicate that lubrication hydrodynamic forces dominate the stress in the shear-thickened state. Accounting for the increased lubrication hydrodynamic interactions between the flat surfaces of the cubic particles allows for a quantitative comparison of the deviatoric stress in the shear-thickened state to that of spherical particles. New semi-empirical models for the viscosity and normal stress difference coefficients are presented for the shear-thickened state. The results of this study indicate that cubic particles offer new and unique opportunities to formulate colloidal dispersions for field-responsive materials. PMID:27112791

  12. Hydrophobic Surfactant Proteins Induce a Phosphatidylethanolamine to Form Cubic Phases

    PubMed Central

    Chavarha, Mariya; Khoojinian, Hamed; Schulwitz, Leonard E.; Biswas, Samares C.; Rananavare, Shankar B.; Hall, Stephen B.

    2010-01-01

    Abstract The hydrophobic surfactant proteins SP-B and SP-C promote rapid adsorption of pulmonary surfactant to an air/water interface. Previous evidence suggests that they achieve this effect by facilitating the formation of a rate-limiting negatively curved stalk between the vesicular bilayer and the interface. To determine whether the proteins can alter the curvature of lipid leaflets, we used x-ray diffraction to investigate how the physiological mixture of these proteins affects structures formed by 1-palmitoyl-2-oleoyl phosphatidylethanolamine, which by itself undergoes the lamellar-to-inverse hexagonal phase transition at 71°C. In amounts as low as 0.03% (w:w) and at temperatures as low as 57°C, the proteins induce formation of bicontinuous inverse cubic phases. The proteins produce a dose-related shift of diffracted intensity to the cubic phases, with minimal evidence of other structures above 0.1% and 62°C, but no change in the lattice-constants of the lamellar or cubic phases. The induction of the bicontinuous cubic phases, in which the individual lipid leaflets have the same saddle-shaped curvature as the hypothetical stalk-intermediate, supports the proposed model of how the surfactant proteins promote adsorption. PMID:20409474

  13. Analytical properties of the anisotropic cubic Ising model

    SciTech Connect

    Hansel, D.; Maillard, J.M.; Oitmaa, J.; Velgakis, M.J.

    1987-07-01

    The authors combine an exact functional relation, the inversion relation, with conventional high-temperature expansions to explore the analytic properties of the anisotropic Ising model on both the square and simple cubic lattice. In particular, they investigate the nature of the singularities that occur in partially resummed expansions of the partition function and of the susceptibility.

  14. Morphosynthesis of cubic silver cages on monolithic activated carbon.

    PubMed

    Wang, Fei; Zhao, Hong; Lai, Yijian; Liu, Siyu; Zhao, Binyuan; Ning, Yuesheng; Hu, Xiaobin

    2013-11-14

    Cubic silver cages were prepared on monolithic activated carbon (MAC) pre-absorbed with Cl(-), SO4(2-), or PO4(3-) anions. Silver insoluble salts served as templates for the morphosynthesis of silver cages. The silver ions were reduced by reductive functional groups on MAC micropores through a galvanic cell reaction mechanism. PMID:24080952

  15. Integrability of Lotka-Volterra Planar Complex Cubic Systems

    NASA Astrophysics Data System (ADS)

    Dukarić, Maša; Giné, Jaume

    In this paper, we study the Lotka-Volterra complex cubic systems. We obtain necessary conditions of integrability for these systems with some restriction on the parameters. The sufficiency is proved for all conditions, except one which remains open, using different methods.

  16. A Unified Approach to Teaching Quadratic and Cubic Equations.

    ERIC Educational Resources Information Center

    Ward, A. J. B.

    2003-01-01

    Presents a simple method for teaching the algebraic solution of cubic equations via completion of the cube. Shows that this method is readily accepted by students already familiar with completion of the square as a method for quadratic equations. (Author/KHR)

  17. Natural convection of a magnetic fluid in a cubic enclosure

    NASA Astrophysics Data System (ADS)

    Kikura, H.; Sawada, T.; Tanahashi, T.

    1993-04-01

    Laminar natural convection heat transfer of a magnetic fluid in a cubic enclosure is examined experimentally. Wall-temperature distributions are visualized by thermosensitive liquid crystal sheets. The effect of the magnetic field on the transient temperature distributions, and the local and averaged Nusselt numbers are discussed.

  18. CVD Diamond, DLC, and c-BN Coatings for Solid Film Lubrication

    NASA Technical Reports Server (NTRS)

    Miyoshi, Kazuhisa; Murakawa, Masao; Watanabe, Shuichi; Takeuchi, Sadao; Miyake, Shojiro; Wu, Richard L. C.

    1998-01-01

    The main criteria for judging coating performance were coefficient of friction and wear rate, which had to be less than 0.1 and 10(exp -6) cubic MM /(N*m), respectively. Carbon- and nitrogen-ion-implanted, fine-grain, chemical-vapor-deposited (CVD) diamond and diamondlike carbon (DLC) ion beam deposited on fine-grain CVD diamond met the criteria regardless of environment (vacuum, nitrogen, and air).

  19. Origin of the Galactic Disk 6.7 kev Line Emission

    NASA Technical Reports Server (NTRS)

    Churchwell, Ed

    1997-01-01

    The goal of this program was to determine if the extended FeXXV 6.7 kev line emission might possibly be produced and confined by the hot wind-shocked bubbles to accompany UC HII regions. The main result of this study are: (1) FeXXV is detected in the W3 complex, but at a level that could only explain a small fraction of the galactic disk emission if all UC HII regions emit at about the same intensity as the W3 complex; (2) Two X-ray sources are detected in W3. W3-X 1 coincides with the radio image of this region, but W3-X2 has no radio, optical, or infrared counterpart; (3) There is no evidence for variability of W3-X1 during the period of observations (approx, 40,000 sec); (4) The X-ray spectrum of W3-X1 has no emission shortward of 1 kev, it peaks at approx. 2 kev and show significant emission out to approx. 6 kev. No individual lines are resolved. There is currently no generally accepted theory for extended hard X-ray emission in HII regions. Perhaps the most significant discovery of this program has been the detection of extended hard X-rays and the realization that some entirely new processes must be invoked to understand this; and (5)A minimum (chi)(sup 2) fit of the spectrum implies a H absorbing column of N(sub H) approx, equals to 2.1 x 10(exp 22)/ cm, a temperature of the emitting plasma of 7 x 10(exp 7) K, and a luminosity of approx. equal to 10(33)erg/s.

  20. Higher voltage plateau cubic Prussian White for Na-ion batteries

    NASA Astrophysics Data System (ADS)

    Piernas-Muñoz, María José; Castillo-Martínez, Elizabeth; Bondarchuk, Oleksandr; Armand, Michel; Rojo, Teófilo

    2016-08-01

    Cubic sodium Prussian White, Na2-xFe2(CN)6·yH2O, and potassium Prussian White, K2-xFe2(CN)6·yH2O, are prepared following a mild synthetic methodology. While cubic symmetry is confirmed by XRD and TEM, IR and XPS show characteristic features different from Prussian Blue compositions. When investigated as cathode materials in sodium ion batteries, both compounds exhibit reversible capacities above 140 mAh g-1 at 1C (ca. 80 mA g-1). While sodium Prussian White shows better high rate capability (10C/0.1C = 0.64), potassium Prussian White exhibits longer cycle stability, with up to 80% of capacity retention after 500 cycles. Interestingly, the potassium Prussian White phase also provides an increase of 0.35 V in the high voltage redox peak compared to the sodium Prussian White analogue ascribed to the preferential insertion of K+ ions instead of Na+, resulting in an increment of the gravimetric energy density. On the other hand, the insertion of Na+ seems to occur at the lower voltage plateau. This hybrid Na+ and K+ insertion in the framework of potassium Prussian White is most likely the responsible of the long cycle stability as a consequence of synergistic effects.

  1. NMR studies on polyphosphide Ce6Ni6P17

    NASA Astrophysics Data System (ADS)

    Koyama, T.; Yamada, H.; Ueda, K.; Mito, T.; Aoyama, Y.; Nakano, T.; Takeda, N.

    2016-02-01

    We report the result of 31P nuclear magnetic resonance (NMR) studies on Ce6Ni6P17. The observed NMR spectra show a Lorentzian-type and an asymmetric shapes, reflecting the local symmetry around each P site in the cubic unit cell. We have identified the observed NMR lines corresponding to three inequivalent P sites and deduced the temperature dependence of the Knight shift for each site. The Knight shifts increase with decreasing temperature down to 1.5 K, indicating a localized spin system of Ce6Ni6P17. Antiferromagnetic correlation between 4f spins is suggested from the negative sign of the Weiss-temperature.

  2. 16 CFR 500.14 - Statements of cubic measure and dry measure.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 16 Commercial Practices 1 2012-01-01 2012-01-01 false Statements of cubic measure and dry measure... UNDER SECTION 4 OF THE FAIR PACKAGING AND LABELING ACT § 500.14 Statements of cubic measure and dry measure. Statements of cubic measure and dry measure shall be expressed in terms most appropriate to...

  3. 16 CFR 500.14 - Statements of cubic measure and dry measure.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 16 Commercial Practices 1 2011-01-01 2011-01-01 false Statements of cubic measure and dry measure... UNDER SECTION 4 OF THE FAIR PACKAGING AND LABELING ACT § 500.14 Statements of cubic measure and dry measure. Statements of cubic measure and dry measure shall be expressed in terms most appropriate to...

  4. 16 CFR 500.14 - Statements of cubic measure and dry measure.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 16 Commercial Practices 1 2010-01-01 2010-01-01 false Statements of cubic measure and dry measure... UNDER SECTION 4 OF THE FAIR PACKAGING AND LABELING ACT § 500.14 Statements of cubic measure and dry measure. Statements of cubic measure and dry measure shall be expressed in terms most appropriate to...

  5. Synchrotron X-ray powder diffraction and convergent beam electron diffraction studies on the cubic phase of MgV{sub 2}O{sub 4} spinel

    SciTech Connect

    Niitaka, Seiji; Lee, Soyeon; Oshima, Yoshifumi; Kato, Kenichi; Hashizume, Daisuke; Takata, Masaki; Takagi, Hidenori

    2014-07-01

    The A V{sub 2}O{sub 4} (A=Mg{sup 2+}, Zn{sup 2+}, Cd{sup 2+}) spinels are three-dimensional spin-1 frustrated systems with orbital degree of freedom, which have been known to possess intriguing orbital states causing releases of spin frustration at low temperatures. We have performed synchrotron X-ray and convergent beam electron diffraction measurements for one of these vanadates, MgV{sub 2}O{sub 4} in order to clarify its crystal structure in the high temperature cubic phase, which is regarded as an important starting point for understanding the details of the low temperature phase. We have successfully observed that the [001] zone axis convergent beam electron diffraction pattern exhibits 4mm symmetry, suggesting the space group of Fd3{sup ¯}m in the cubic MgV{sub 2}O{sub 4}. It has also been demonstrated that the crystal structure of the cubic MgV{sub 2}O{sub 4} contains VO{sub 6} octahedra elongated along the threefold rotation axis. Based on our results, we discuss the orbital states of MgV{sub 2}O{sub 4} as well as the other spinel vanadates. - Graphical abstract: Precise geometry of the VO{sub 6} octahedra in the cubic phase of MgV{sub 2}O{sub 4} spinel determined with the synchrotron powder XRD data. - Highlights: • We examined the crystal structure of the cubic phase of MgV{sub 2}O{sub 4} spinel. • We prepared the single crystal and powdered sample of MgV{sub 2}O{sub 4} with high quality. • The result of the CBED measurement agrees with the space group of Fd3{sup ¯}m in the phase. • The cubic phase has VO{sub 6} octahedra elongated along the threefold rotation axis.

  6. Cesium hafnium chloride: A high light yield, non-hygroscopic cubic crystal scintillator for gamma spectroscopy

    SciTech Connect

    Burger, Arnold; Rowe, Emmanuel; Groza, Michael; Morales Figueroa, Kristle; Cherepy, Nerine J.; Beck, Patrick R.; Hunter, Steven; Payne, Stephen A.

    2015-10-05

    We report on the scintillation properties of Cs{sub 2}HfCl{sub 6} (cesium hafnium chloride or CHC) as an example of a little-known class of non-hygroscopic compounds having the generic cubic crystal structure of K{sub 2}PtCl{sub 6}. The crystals are easily growable from the melt using the Bridgman method with minimal precursor treatments or purification. CHC scintillation is centered at 400 nm, with a principal decay time of 4.37 μs and a light yield of up to 54 000 photons/MeV when measured using a silicon CCD photodetector. The light yield is the highest ever reported for an undoped crystal, and CHC also exhibits excellent light yield nonproportionality. These desirable properties allowed us to build and test CHC gamma-ray spectrometers providing energy resolution of 3.3% at 662 keV.

  7. Anharmonic phonon decay in cubic GaN

    NASA Astrophysics Data System (ADS)

    Cuscó, R.; Domènech-Amador, N.; Novikov, S.; Foxon, C. T.; Artús, L.

    2015-08-01

    We present a Raman-scattering study of optical phonons in zinc-blende (cubic) GaN for temperatures ranging from 80 to 750 K. The experiments were performed on high-quality, cubic GaN films grown by molecular-beam epitaxy on GaAs (001) substrates. The observed temperature dependence of the optical phonon frequencies and linewidths is analyzed in the framework of anharmonic decay theory, and possible decay channels are discussed in the light of density-functional-theory calculations. The longitudinal-optical (LO) mode relaxation is found to occur via asymmetric decay into acoustic phonons, with an appreciable contribution of higher-order processes. The transverse-optical mode linewidth shows a weak temperature dependence and its frequency downshift is primarily determined by the lattice thermal expansion. The LO phonon lifetime is derived from the observed Raman linewidth and an excellent agreement with previous theoretical predictions is found.

  8. Alpha decay self-damage in cubic and monoclinic zirconolite

    SciTech Connect

    Clinard, F.W. Jr.; Land, C.C.; Peterson, D.E.; Rohr, D.L.; Roof, R.B.

    1981-01-01

    Samples of primarily-monoclinic /sup 238/Pu-doped zirconolite were stored at ambient temperature to allow accumulation of alpha decay self-damage to a dose of 1 x 10/sup 24/ ..cap alpha../m/sup 3/ (equivalent to a SYNROC age of approx. 10/sup 3/y). Bulk swelling reached 2.3 vol% with no tendency toward saturation, a damage response similar to that observed for cubic Pu-doped zirconolite. X-ray volumetric swelling at 4 x 10/sup 24/ ..cap alpha../m/sup 3/ was 1 vol%, considerably less than that for the cubic material. Changes in cell dimensions differed significantly from those reported by others for a monoclinic natural mineral. Extensive microcracking was observed, and is attributed at least partially to swelling differences between the matrix and minor phases.

  9. Experimental Impacts into Chondritic Targets. Part 1; Disruption of an L6 Chondrite by Multiple Impacts

    NASA Technical Reports Server (NTRS)

    Cintala, Mark J.; Horz, Friedrich

    2007-01-01

    A fragment of an L6 chondrite (ALH 85017,13) with an initial mass (M(sub 0)) of 464.1 g was the target in a series of experimental impacts in which the largest remaining fragment (M(sub R)) after each shot was impacted by a 3.18-mm ceramic sphere at a nominal speed of 2 km/s. This continued until the mass of the largest remaining piece was less than half the mass of the target presented to that shot (M(sub S)). Two chunks of Bushveldt gabbro with similar initial masses were also impacted under the same conditions until M(sub R) was less than half M(sub 0). The two gabbro targets required a total of 1.51x10(exp 7) and 1.75x10(exp 7) erg/g to attain 0.27 and 0.33 M(sub R)/M(sub 0), respectively; the chondrite, however, was considerably tougher, reaching 0.40 and 0.21 M(sub R)/M(sub 0) only after receiving 2.37x10(exp 7) and 3.10x10(exp 7) erg g-1, respectively. The combined ejecta and spallation products from the gabbro impacts were coarser than those from the chondrite and in sufficient quantities that the new surface areas exceeded those from the meteorite until the fifth shot in the chondrite series, which was the number of impacts required to disrupt each gabbro target (i.e., MR/M0 = 0.5). Unlike the behavior shown in previous regolith-evolution series, neither gabbro target produced an enhancement in the size fraction reflecting the mean size of the crystals composing the rock (about 3 mm), an effect possibly related to the width of the shock pulse. The original chondrite was so fine-grained and fractured, and the variance in its grain-size distribution so large, that effects related to grain-size were relegated to the <63- m fraction. Impacts into ALH 85017 produced abundant, fine-grained debris, but otherwise the slopes of its size distributions were comparable to those from other experiments involving natural and fabricated terrestrial targets. The characteristic slopes of the chondrite's size distributions, however, were notably more constant over the entire

  10. Anodic etching of p-type cubic silicon carbide

    NASA Technical Reports Server (NTRS)

    Harris, G. L.; Fekade, K.; Wongchotigul, K.

    1992-01-01

    p-Type cubic silicon carbide was anodically etched using an electrolyte of HF:HCl:H2O. The etching depth was determined versus time with a fixed current density of 96.4 mA/sq cm. It was found that the etching was very smooth and very uniform. An etch rate of 22.7 nm/s was obtained in a 1:1:50 HF:HCl:H2O electrolyte.

  11. Higher-order numerical solutions using cubic splines

    NASA Technical Reports Server (NTRS)

    Rubin, S. G.; Khosla, P. K.

    1976-01-01

    A cubic spline collocation procedure was developed for the numerical solution of partial differential equations. This spline procedure is reformulated so that the accuracy of the second-derivative approximation is improved and parallels that previously obtained for lower derivative terms. The final result is a numerical procedure having overall third-order accuracy of a nonuniform mesh. Solutions using both spline procedures, as well as three-point finite difference methods, are presented for several model problems.

  12. Large scale structures and the cubic galileon model

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Sourav; Dialektopoulos, Konstantinos F.; Tomaras, Theodore N.

    2016-05-01

    The maximum size of a bound cosmic structure is computed perturbatively as a function of its mass in the framework of the cubic galileon, proposed recently to model the dark energy of our Universe. Comparison of our results with observations constrains the matter-galileon coupling of the model to 0.033lesssim α lesssim 0.17, thus improving previous bounds based solely on solar system physics.

  13. Lipidic cubic phase injector facilitates membrane protein serial femtosecond crystallography

    PubMed Central

    Weierstall, Uwe; James, Daniel; Wang, Chong; White, Thomas A.; Wang, Dingjie; Liu, Wei; Spence, John C.H.; Doak, R. Bruce; Nelson, Garrett; Fromme, Petra; Fromme, Raimund; Grotjohann, Ingo; Kupitz, Christopher; Zatsepin, Nadia A.; Liu, Haiguang; Basu, Shibom; Wacker, Daniel; Han, Gye Won; Katritch, Vsevolod; Boutet, Sébastien; Messerschmidt, Marc; Williams, Garth J.; Koglin, Jason E.; Seibert, M. Marvin; Klinker, Markus; Gati, Cornelius; Shoeman, Robert L.; Barty, Anton; Chapman, Henry N.; Kirian, Richard A.; Beyerlein, Kenneth R.; Stevens, Raymond C.; Li, Dianfan; Shah, Syed T.A.; Howe, Nicole; Caffrey, Martin; Cherezov, Vadim

    2014-01-01

    Lipidic cubic phase (LCP) crystallization has proven successful for high-resolution structure determination of challenging membrane proteins. Here we present a technique for extruding gel-like LCP with embedded membrane protein microcrystals, providing a continuously-renewed source of material for serial femtosecond crystallography. Data collected from sub-10 μm-sized crystals produced with less than 0.5 mg of purified protein yield structural insights regarding cyclopamine binding to the Smoothened receptor. PMID:24525480

  14. The Number of Real Roots of a Cubic Equation

    ERIC Educational Resources Information Center

    Kavinoky, Richard; Thoo, John B.

    2008-01-01

    To find the number of distinct real roots of the cubic equation (1) x[caret]3 + bx[caret]2 + cx + d = 0, we could attempt to solve the equation. Fortunately, it is easy to tell the number of distinct real roots of (1) without having to solve the equation. The key is the discriminant. The discriminant of (1) appears in Cardan's (or Cardano's) cubic…

  15. Study on the electrochemical properties of cubic ordered mesoporous carbon for supercapacitors

    NASA Astrophysics Data System (ADS)

    Lang, Jun-Wei; Yan, Xing-Bin; Yuan, Xiao-Yan; Yang, Jie; Xue, Qun-Ji

    Highly ordered, three-dimensional (3D) cubic mesoporous carbon CMK-8 is prepared by a facile nanocasting approach using cubic mesoporous silica KIT-6 as starting template. Afterwards, in order to increase the active sites of surface electrochemical reactions and promote the wettability in aqueous electrolyte, a chemical surface modification is carried out on the CMK-8 by nitric acid treatment. Two electrodes are prepared from the CMK-8 and the acid-modified CMK-8 (H-CMK-8) and used as the active materials for supercapacitors. The unique 3D mesoporous network combined with high specific surface area makes the nano-channel surfaces of the CMK-8 carbon favorable for charging the electric double-layer, resulting in that the CMK-8 and the H-CMK-8 electrodes both show well supercapacitive properties. Furthermore, the specific capacitance of the CMK-8 can be further improved by acid treatment, so that the H-CMK-8 exhibits the largest specific capacitance of 246 F g -1 at a current density of 0.625 A g -1 in 2 M KOH electrolyte. Also, the two carbon electrodes both exhibit good cycling stability and lifetime. Therefore, based on the above investigations, such CMK-8 carbon, especially H-CMK-8 carbon can be a potential candidate for supercapacitors.

  16. Lattice dynamics and vibrational spectra of the orthorhombic, tetragonal, and cubic phases of methylammonium lead iodide

    NASA Astrophysics Data System (ADS)

    Brivio, Federico; Frost, Jarvist M.; Skelton, Jonathan M.; Jackson, Adam J.; Weber, Oliver J.; Weller, Mark T.; Goñi, Alejandro R.; Leguy, Aurélien M. A.; Barnes, Piers R. F.; Walsh, Aron

    2015-10-01

    The hybrid halide perovskite CH3NH3PbI3 exhibits a complex structural behavior, with successive transitions between orthorhombic, tetragonal, and cubic polymorphs around 165 and 327 K. Herein we report first-principles lattice dynamics (phonon spectrum) for each phase of CH3NH3PbI3 . The equilibrium structures compare well to solutions of temperature-dependent powder neutron diffraction. By following the normal modes, we calculate infrared and Raman intensities of the vibrations, and compare them to the measurement of a single crystal where the Raman laser is controlled to avoid degradation of the sample. Despite a clear separation in energy between low-frequency modes associated with the inorganic (PbI3-)n network and high-frequency modes of the organic CH3NH3+ cation, significant coupling between them is found, which emphasizes the interplay between molecular orientation and the corner-sharing octahedral networks in the structural transformations. Soft modes are found at the boundary of the Brillouin zone of the cubic phase, consistent with displacive instabilities and anharmonicity involving tilting of the PbI6 octahedra around room temperature.

  17. Low temperature synthesis of pure cubic ZrO2 nanopowder: Structural and luminescence studies

    NASA Astrophysics Data System (ADS)

    Prakashbabu, D.; Hari Krishna, R.; Nagabhushana, B. M.; Nagabhushana, H.; Shivakumara, C.; Chakradar, R. P. S.; Ramalingam, H. B.; Sharma, S. C.; Chandramohan, R.

    2014-03-01

    Pure cubic zirconia (ZrO2) nanopowder is prepared for the first time by simple low temperature solution combustion method without calcination. The product is characterized by Powder X-ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier Transform Infra Red spectroscopy (FTIR) and Ultraviolet-Visible spectroscopy (UV-Vis). The PXRD showed the formation of pure stable cubic ZrO2 nanopowders with average crystallite size ranging from 6 to 12 nm. The lattice parameters were calculated from Rietveld refinement method. SEM micrograph shows fluffy, mesoporous, agglomerated particles with large number of voids. TEM micrograph shows honey comb like arrangement of particles with particle size ∼10 nm. The PL emission spectrum excited at 210 nm and 240 nm consists of intense bands centered at ∼365 and ∼390 nm. Both the samples show shoulder peak at ∼420 nm, along with four weak emission bands at ∼484, ∼528, ∼614 and ∼726 nm. TL studies were carried out pre-irradiating samples with γ-rays ranging from 1 to 5 KGy at room temperature. A well resolved glow peak at 377 °C is recorded which can be ascribed to deep traps. With increase in γ radiation there is linear increase in TL intensity which shows the possible use of ZrO2 as dosimetric material.

  18. Ab-Initio Computations of Electronic and Related Properties of cubic Lithium Selenide (Li2Se)

    NASA Astrophysics Data System (ADS)

    Goita, Abdoulaye; Nwigboji, Ifeanyi H.; Malozovsky, Yuriy; Bagayoko, Diola

    We present theoretical predictions, from ab-initio, self-consistent calculations, of electronic and related properties of cubic lithium selenide (Li2Se). We employed a local density approximation (LDA) potential and the linear combination of atomic orbitals (LCAO). We performed the computations following the Bagayoko, Zhao, and Williams (BZW) method, as enhanced by Ekuma and Franklin (BZW-EF). Our results include electronic energies, total and partial densities of states, effective masses, and the bulk modulus. The theoretical equilibrium lattice constant is 5.882 Å. We found cubic Li2Se to have a direct band gap of 4.363 eV (prediction), at Γ. This gap is 4.065 eV for a room temperature lattice constant of 6.017 Å. The calculated bulk modulus is 31.377 GPa. Acknowledgments: This work was funded in part by the National Science Foundation (NSF) and the Louisiana Board of Regents, through LASiGMA [Award Nos. EPS- 1003897, NSF (2010-15)-RII-SUBR] and NSF HRD-1002541, the US Department of Energy - National, Nuclear Security Administration (NNSA) (Award No. DE- NA0002630), LaSPACE, and LONI-SUBR.

  19. High critical current densities reproducibly observed for hot-isostatic-pressed PbMo6S8 wires with Mo barriers

    NASA Astrophysics Data System (ADS)

    Yamasaki, H.; Umeda, M.; Kosaka, S.

    1992-08-01

    Fabrication process, critical current densities (Jc), and microstructure of the superconducting PbMo6S8 wires with Mo barriers have been investigated. Reducing the volume fraction of the Mo barrier and using electron-beam-melted Mo with less deformation resistance than that of conventional powder-metallurgy-processed Mo, facilitate the densification of PbMo6S8 and Jc improvement by the hot-isostatic-pressing (HIP) treatments. It was possible to obtain reproducibly HIP-treated PbMo6S8 wires with homogeneously high Jc not less than 10 exp 8 A/sq m at 22 T and 4.2 K, which is promising for the production of future high field (greater than 20 T) superconducting magnets.

  20. Viscoelastic Response of the Titanium Alloy Ti-6-4: Experimental Identification of Time- and Rate-Dependent Reversible and Irreversible Deformation Regions

    NASA Technical Reports Server (NTRS)

    Lerch, Bradley A.; Arnold, Steven M.

    2014-01-01

    In support of an effort on damage prognosis, the viscoelastic behavior of Ti-6Al-4V (Ti-6-4) was investigated. This report documents the experimental characterization of this titanium alloy. Various uniaxial tests were conducted to low load levels over the temperature range of 20 to 538 C to define tensile, creep, and relaxation behavior. A range of strain rates (6x10(exp -7) to 0.001/s) were used to document rate effects. All tests were designed to include an unloading portion, followed by a hold time at temperature to allow recovery to occur either at zero stress or strain. The titanium alloy was found to exhibit viscoelastic behavior below the "yield" point and over the entire range of temperatures (although at lower temperatures the magnitude is extremely small). These experimental data will be used for future characterization of a viscoelastic model.

  1. Cubic and Hexagonal Liquid Crystals as Drug Delivery Systems

    PubMed Central

    Chen, Yulin; Ma, Ping; Gui, Shuangying

    2014-01-01

    Lipids have been widely used as main constituents in various drug delivery systems, such as liposomes, solid lipid nanoparticles, nanostructured lipid carriers, and lipid-based lyotropic liquid crystals. Among them, lipid-based lyotropic liquid crystals have highly ordered, thermodynamically stable internal nanostructure, thereby offering the potential as a sustained drug release matrix. The intricate nanostructures of the cubic phase and hexagonal phase have been shown to provide diffusion controlled release of active pharmaceutical ingredients with a wide range of molecular weights and polarities. In addition, the biodegradable and biocompatible nature of lipids demonstrates the minimum toxicity and thus they are used for various routes of administration. Therefore, the research on lipid-based lyotropic liquid crystalline phases has attracted a lot of attention in recent years. This review will provide an overview of the lipids used to prepare cubic phase and hexagonal phase at physiological temperature, as well as the influencing factors on the phase transition of liquid crystals. In particular, the most current research progresses on cubic and hexagonal phases as drug delivery systems will be discussed. PMID:24995330

  2. High-Field Fast-Risetime Pulse Failures in 4H- and 6H-SiC pn Junction Diodes

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Fazi, Christian

    1996-01-01

    We report the observation of anomalous reverse breakdown behavior in moderately doped (2-3 x 10(exp 17 cm(exp -3)) small-area micropipe-free 4H- and 6H-SiC pn junction diodes. When measured with a curve tracer, the diodes consistently exhibited very low reverse leakage currents and sharp repeatable breakdown knees in the range of 140-150 V. However, when subjected to single-shot reverse bias pulses (200 ns pulsewidth, 1 ns risetime), the diodes failed catastrophically at pulse voltages of less than 100 V. We propose a possible mechanism for this anomalous reduction in pulsed breakdown voltage relative to dc breakdown voltage. This instability must be removed so that SiC high-field devices can operate with the same high reliability as silicon power devices.

  3. Co2(nu2)-o Quenching Rate Coefficient Derived from Coincidental SABER-TIMED and Fort Collins Lidar Observations of the Mesosphere and Lower Thermosphere

    NASA Technical Reports Server (NTRS)

    Feofilov, A. G.; Kutepov, A. A.; She, C.-Y.; Smith, A. K.; Pesnell, W. D.; Goldberg, R. A.

    2012-01-01

    Among the processes governing the energy balance in the mesosphere and lower thermosphere (MLT), the quenching of CO2(nu2) vibrational levels by collisions with O atoms plays an important role. However, there is a factor of 3-4 discrepancy between the laboratory measurements of the CO2-O quenching rate coefficient, k(sub VT),and its value estimated from the atmospheric observations. In this study, we retrieve k(sub VT) in the altitude region85-105 km from the coincident SABER/TIMED and Fort Collins sodium lidar observations by minimizing the difference between measured and simulated broadband limb 15 micron radiation. The averaged k(sub VT) value obtained in this work is 6.5 +/- 1.5 X 10(exp -12) cubic cm/s that is close to other estimates of this coefficient from the atmospheric observations.However, the retrieved k(sub VT) also shows altitude dependence and varies from 5.5 1 +/-1 10(exp -12) cubic cm/s at 90 km to 7.9 +/- 1.2 10(exp -12) cubic cm/s at 105 km. Obtained results demonstrate the deficiency in current non-LTE modeling of the atmospheric 15 micron radiation, based on the application of the CO2-O quenching and excitation rates, which are linked by the detailed balance relation. We discuss the possible model improvements, among them accounting for the interaction of the non-thermal oxygen atoms with CO2 molecules.

  4. Large-scale cubic InN nanocrystals by a combined solution- and vapor-phase method under silica confinement.

    PubMed

    Chen, Zhuo; Li, Yanan; Cao, Chuanbao; Zhao, Songrui; Fathololoumi, Saeed; Mi, Zetian; Xu, Xingyan

    2012-01-18

    Large-scale cubic InN nanocrystals were synthesized by a combined solution- and vapor-phase method under silica confinement. Nearly monodisperse cubic InN nanocrystals with uniform spherical shape were dispersed stably in various organic solvents after removal of the silica shells. The average size of InN nanocrystals is 5.7 ± 0.6 nm. Powder X-ray diffraction results indicate that the InN nanocrystals are of high crystallinity with a cubic phase. X-ray photoelectron spectroscopy and energy-dispersive spectroscopy confirm that the nanocrystals are composed of In and N elements. The InN nanocrystals exhibit infrared photoluminescence at room temperature, with a peak energy of ~0.62 eV, which is smaller than that of high-quality wurtzite InN (~0.65-0.7 eV) and is in agreement with theoretical calculations. The small emission peak energy of InN nanocrystals, as compared to other low-cost solution or vapor methods, reveals the superior crystalline quality of our samples, with low or negligible defect density. This work will significantly promote InN-based applications in IR optoelectronic device and biology. PMID:22224725

  5. Improvement of critical current density in thallium-based (Tl,Bi)Sr(1.6)Ba(0.4)Ca2Cu3O(x) superconductors

    NASA Technical Reports Server (NTRS)

    Ren, Z. F.; Wang, C. A.; Wang, J. H.; Miller, D. J.; Goretta, K. C.

    1995-01-01

    Epitaxial (Tl,Bi)Sr(1.6)Ba(0.4)Ca2Cu3O(x) ((Tl,Bi)-1223) thin films on (100) single crystal LaAlO3 substrates were synthesized by a two-step procedure. Phase development, microstructure, and relationships between film and substrate were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Resistance versus temperature, zero-field-cooled and field cooled magnetization, and transport critical current density (J(sub c)) were measured. The zero-resistance temperature was 105-111 K. J(sub c) at 77 K and zero field was greater than 2 x 10(exp 6) A/sq cm. The films exhibited good flux pinning properties.

  6. Homogeneous nanocrystalline cubic silicon carbide films prepared by inductively coupled plasma chemical vapor deposition.

    PubMed

    Cheng, Qijin; Xu, S; Long, Jidong; Huang, Shiyong; Guo, Jun

    2007-11-21

    Silicon carbide films with different carbon concentrations x(C) have been synthesized by inductively coupled plasma chemical vapor deposition from a SiH(4)/CH(4)/H(2) gas mixture at a low substrate temperature of 500 °C. The characteristics of the films were studied by x-ray photoelectron spectroscopy, x-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared absorption spectroscopy, and Raman spectroscopy. Our experimental results show that, at x(C) = 49 at.%, the film is made up of homogeneous nanocrystalline cubic silicon carbide without any phase of silicon, graphite, or diamond crystallites/clusters. The average size of SiC crystallites is approximately 6 nm. At a lower value of x(C), polycrystalline silicon and amorphous silicon carbide coexist in the films. At a higher value of x(C), amorphous carbon and silicon carbide coexist in the films. PMID:21730481

  7. Magma generation on Mars - Amounts, rates, and comparisons with earth, moon, and Venus

    NASA Technical Reports Server (NTRS)

    Greeley, Ronald; Schneid, Byron D.

    1991-01-01

    Total extrusive and intrusive magma generated on Mars over the last approximately 3.8 billion years is estimated at 654 x 10 exp 6 cubic kilometers, or 0.17 cubic kilometers per year, substantially less than rates for earth (26 to 34 cu/km yr) and Venus (less than 20 cu/km yr) but much more than for the moon (0.025 cu/km yr). When scaled to earth's mass the Martian rate is much smaller than that for earth or Venus and slightly smaller than for the moon.

  8. Cubic to tetragonal crystal lattice reconstruction during ordering or decomposition

    SciTech Connect

    Cheong, Byung-kl

    1992-09-01

    This thesis studied thermodynamic stability and morphology of product phases in diffusional phase transformations involving cubic-to-tetragonal crystal lattice reconstructions. Two different kinds of diffusional transformations were examined: L1{sub 0} ordering (fcc to fct lattice change) and decomposition of off-stoichiometric B2 ordering alloys accompanying bcc to fcc Bain transformation. In the first case, Fe-45 at.% Pd alloys were studied by TEM; in the second, the Bain strain relaxation during decomposition of hyper-eutectoid Cu-9.04 wt% Be alloy was studied. CuAu and InMg were also studied.

  9. Preparation of superhydrophobic nanodiamond and cubic boron nitride films

    SciTech Connect

    Zhou, Y. B.; Liu, W. M.; Wang, P. F.; Yang, Y.; Ye, Q.; He, B.; Pan, X. J.; Zhang, W. J.; Bello, I.; Lee, S. T.; Zou, Y. S.

    2010-09-27

    Superhydrophobic surfaces were achieved on the hardest and the second hardest materials, diamond and cubic boron nitride (cBN) films. Various surface nanostructures of nanocrystalline diamond (ND) and cBN films were constructed by carrying out bias-assisted reactive ion etching in hydrogen/argon plasmas; and it is shown that surface nanostructuring may enhance dramatically the hydrophobicity of ND and cBN films. Together with surface fluorination, superhydrophobic ND and cBN surfaces with a contact angle greater than 150 deg. and a sliding angle smaller than 10 deg. were demonstrated. The origin of hydrophobicity enhancement is discussed based on the Cassie model.

  10. A topological coordinate system for the diamond cubic grid.

    PubMed

    Čomić, Lidija; Nagy, Benedek

    2016-09-01

    Topological coordinate systems are used to address all cells of abstract cell complexes. In this paper, a topological coordinate system for cells in the diamond cubic grid is presented and some of its properties are detailed. Four dependent coordinates are used to address the voxels (triakis truncated tetrahedra), their faces (hexagons and triangles), their edges and the points at their corners. Boundary and co-boundary relations, as well as adjacency relations between the cells, can easily be captured by the coordinate values. Thus, this coordinate system is apt for implementation in various applications, such as visualizations, morphological and topological operations and shape analysis. PMID:27580205

  11. Positron beam investigations of natural cubic and coated diamonds

    NASA Astrophysics Data System (ADS)

    Shiryaev, A. A.; van Veen, A.; Schut, H.; Kruseman, A. C.; Zakharchenko, O. D.

    2000-06-01

    Positron beam and 2D-ACAR investigation of cubic and coated diamonds are reported. In type IIA diamonds, positrons are mostly trapped in vacancies in the carbon lattice; in type Ia diamonds, two main defect-related annihilation sites are nitrogen-vacancy complexes (H2, H3) and the vicinity of split interstitial atoms. No correlation between principal nitrogen defects and annihilation rate was found. PAS data indicate the presence of a significant amount of vacancies in all studied diamonds, which increases the rate of nitrogen aggregation. It is shown that pressurised fluid inclusions may serve as a positron trap, giving rise to the long component in the lifetime spectra.

  12. Thermal expansion of rock-salt cubic AlN

    NASA Astrophysics Data System (ADS)

    Bartosik, M.; Todt, M.; Holec, D.; Todt, J.; Zhou, L.; Riedl, H.; Böhm, H. J.; Rammerstorfer, F. G.; Mayrhofer, P. H.

    2015-08-01

    We combine continuum mechanics modeling and wafer curvature experiments to characterize the thermal expansion coefficient of AlN in its metastable cubic rock-salt (B1) structure. The latter was stabilized as nm thin layers by coherency strains in CrN/AlN epitaxial multilayers deposited on Si (100) substrates using reactive magnetron sputtering. The extraction of the B1-AlN thermal expansion coefficient, from experimentally recorded temperature dependent wafer curvature data, is formulated as an inverse problem using continuum mechanics modeling. The results are cross-validated by density functional theory calculations.

  13. Pseudorecurrence and chaos of cubic-quintic nonlinear Schroedinger equation

    SciTech Connect

    Zhou, C.; Lai, C.H.

    1996-12-01

    Recurrence, pseudorecurrence, and chaotic solutions for a continuum Hamiltonian system in which there exist spatial patterns of solitary wave structures are investigated using the nonlinear Schrodinger equation (NSE) with cubic and quintic terms. The theoretical analyses indicate that there may exist Birkhoff`s recurrence for the arbitrary parameter values. The numerical experiments show that there may be Fermi-Pasta-Ulam (FPU) recurrence, pseudorecurrence, and chaos when different initial conditions are chosen. The fact that the system energy is effectively shared by finite Fourier modes suggests that it may be possible to describe the continuum system in terms of some effective degrees of freedom.

  14. Temperature dependent cubic and hexagonal close packing in micellar structures.

    PubMed

    Wolff, Nicole; Gerth, Stefan; Gutfreund, Philipp; Wolff, Max

    2014-11-14

    The interfacial structure and phase diagram of a micellar solution formed by the three block copolymer (EO20-PO70-EO20) also known as P123 solved in deuterated water close to a solid boundary is investigated with respect to temperature. We find a hysteretic behavior of the d-spacing of the micellar crystal and a spontaneous change in the lateral correlation length going hand in hand with a structural reorganization between cubic and hexagonal. The phase transitions may be initiated by a change in the shape of the micelles from spherical to elongated together with a minimization of the polymer water interface. PMID:25212786

  15. Inhomogeneous atomic Bose-Fermi mixtures in cubic lattices.

    PubMed

    Cramer, M; Eisert, J; Illuminati, F

    2004-11-01

    We determine the ground state properties of inhomogeneous mixtures of bosons and fermions in cubic lattices and parabolic confining potentials. For finite hopping we determine the domain boundaries between Mott-insulator plateaux and hopping-dominated regions for lattices of arbitrary dimension within mean-field and perturbation theory. The results are compared with a new numerical method that is based on a Gutzwiller variational approach for the bosons and an exact treatment for the fermions. The findings can be applied as a guideline for future experiments with trapped atomic Bose-Fermi mixtures in optical lattices. PMID:15600816

  16. Theoretical studies of native defects in cubic boron nitride

    SciTech Connect

    Piquini, P.; Mota, R.; Schmidt, T.M.; Fazzio, A.

    1997-08-01

    We have studied the electronic and structural properties of native defects in cubic boron nitride (nitrogen vacancy, boron antisite, and oxygen substitutional) using all-electron first-principles total-energy calculations. We find that all defects introduce a deep state above the middle-energy gap. These defects present a C{sub 3v}-local symmetry. In the case of nitrogen vacancy the possibility of the F-center formation is discussed. {copyright} {ital 1997} {ital The American Physical Society}

  17. Emission properties of body-centered cubic elemental metal photocathodes

    SciTech Connect

    Li, Tuo; Rickman, Benjamin L. Schroeder, W. Andreas

    2015-04-07

    A first principles analysis of photoemission is developed to explain the lower than expected rms transverse electron momentum measured using the solenoid scan technique for the body-centered cubic Group Vb (V, Nb, and Ta) and Group VIb (Cr, Mo, and W) metallic photocathodes. The density functional theory based analysis elucidates the fundamental role that the electronic band structure (and its dispersion) plays in determining the emission properties of solid-state photocathodes and includes evaluation of work function anisotropy using a thin-slab method.

  18. An optochemically organized nonlinear waveguide lattice with primitive cubic symmetry.

    PubMed

    Ponte, Matthew R; Welch, Robert; Saravanamuttu, Kalaichelvi

    2013-02-25

    We describe the first example of a primitive cubic lattice assembled spontaneously from three mutually orthogonal and intersecting arrays of cylindrical, multimode waveguides. The lattice is generated in a single, room-temperature step with separate (mutually incoherent) incandescent light bulbs. To demonstrate its potential as a nonlinear photonic lattice, we generated a self-trapped lattice beam of incoherent white light. These two findings open entirely new experimental opportunities to study the behavior of spatially and temporally incoherent, polychromatic lattice solitons in 3-D Bravais lattices. PMID:23481954

  19. Local environment of silicon in cubic boron nitride

    SciTech Connect

    Murata, Hidenobu Taniguchi, Takashi; Hishita, Shunichi; Yamamoto, Tomoyuki; Oba, Fumiyasu; Tanaka, Isao

    2013-12-21

    Si-doped cubic boron nitride (c-BN) is synthesized at high pressure and high temperature, and the local environment of Si is investigated using X-ray absorption near edge structure (XANES) and first-principles calculations. Si-K XANES indicates that Si in c-BN is surrounded by four nitrogen atoms. According to first-principles calculations, the model for substitutional Si at the B site well reproduces experimental Si-K XANES, and it is energetically more favorable than substitutional Si at the N site. Both the present experimental and theoretical results indicate that Si in c-BN prefers the B site to the N site.

  20. Magnetic interactions in cubic-, hexagonal- and trigonal-barium iron oxide fluoride, BaFeO2F

    NASA Astrophysics Data System (ADS)

    Clemens, Oliver; Marco, José F.; Thomas, Michael F.; Forder, Susan D.; Zhang, Hongbin; Cartenet, Simon; Monze, Anais; Bingham, Paul A.; Slater, Peter R.; Berry, Frank J.

    2016-09-01

    57Fe Mössbauer spectra have been recorded from the hexagonal (6H)- and trigonal (15R)- modifications of BaFeO2F and are compared with those previously recorded from the cubic form of BaFeO2F. The spectra, recorded over a temperature range from 15 to 650 K show that all of the iron in all the compounds is in the Fe3+ state. Spectra from the 6H- and 15R-modifications were successfully fitted with components that were related to the Fe(1) and Fe(2) structural sites in the 6H variant and to the Fe(1), Fe(2) and Fe(3) structural sites in the 15R form. The magnetic ordering temperatures were determined as 597  ±  3 K for 6H-BaFeO2F and 636  ±  3 K for 15R-BaFeO2F. These values are surprisingly close to the value of 645  ±  5 K determined for the cubic form. The magnetic interactions in the three forms are compared with a view to explaining this similarity of magnetic ordering temperature.

  1. Magnetic interactions in cubic-, hexagonal- and trigonal-barium iron oxide fluoride, BaFeO2F.

    PubMed

    Clemens, Oliver; Marco, José F; Thomas, Michael F; Forder, Susan D; Zhang, Hongbin; Cartenet, Simon; Monze, Anais; Bingham, Paul A; Slater, Peter R; Berry, Frank J

    2016-09-01

    (57)Fe Mössbauer spectra have been recorded from the hexagonal (6H)- and trigonal (15R)- modifications of BaFeO2F and are compared with those previously recorded from the cubic form of BaFeO2F. The spectra, recorded over a temperature range from 15 to 650 K show that all of the iron in all the compounds is in the Fe(3+) state. Spectra from the 6H- and 15R-modifications were successfully fitted with components that were related to the Fe(1) and Fe(2) structural sites in the 6H variant and to the Fe(1), Fe(2) and Fe(3) structural sites in the 15R form. The magnetic ordering temperatures were determined as 597  ±  3 K for 6H-BaFeO2F and 636  ±  3 K for 15R-BaFeO2F. These values are surprisingly close to the value of 645  ±  5 K determined for the cubic form. The magnetic interactions in the three forms are compared with a view to explaining this similarity of magnetic ordering temperature. PMID:27355806

  2. Vacancy-dependent stability of cubic and wurtzite Ti1−xAlxN

    PubMed Central

    Euchner, H.; Mayrhofer, P.H.

    2015-01-01

    While it is well-known that supersaturated cubic-structured Ti1−xAlxN can be prepared by physical vapor deposition, the impact of point defects on formation process and cubic to wurtzite transition is largely unexplored. Irrespective of point defects, ab initio calculations correctly predict the Al concentration of the cubic to wurtzite transition. By means of density functional theory we show that vacancies on metal and/or non-metal sites only slightly affect the cubic to wurtzite transition region, whereas they clearly affect the physical properties. PMID:26412921

  3. Proton Ordering of Cubic Ice Ic: Spectroscopy and Computer Simulations

    PubMed Central

    2014-01-01

    Several proton-disordered crystalline ice structures are known to proton order at sufficiently low temperatures, provided that the right preparation procedure is used. For cubic ice, ice Ic, however, no proton ordering has been observed so far. Here, we subject ice Ic to an experimental protocol similar to that used to proton order hexagonal ice. In situ FT-IR spectroscopy carried out during this procedure reveals that the librational band of the spectrum narrows and acquires a structure that is observed neither in proton-disordered ice Ic nor in ice XI, the proton-ordered variant of hexagonal ice. On the basis of vibrational spectra computed for ice Ic and four of its proton-ordered variants using classical molecular dynamics and ab initio simulations, we conclude that the features of our experimental spectra are due to partial proton ordering, providing the first evidence of proton ordering in cubic ice. We further find that the proton-ordered structure with the lowest energy is ferroelectric, while the structure with the second lowest energy is weakly ferroelectric. Both structures fit the experimental spectral similarly well such that no unique assignment of proton order is possible based on our results. PMID:24883169

  4. Elastic interaction of point defects in cubic and hexagonal crystals

    NASA Astrophysics Data System (ADS)

    Kukushkin, S. A.; Osipov, A. V.; Telyatnik, R. S.

    2016-05-01

    The elastic interaction of two point defects in cubic and hexagonal structures has been considered. On the basis of the exact expression for the tensor Green's function of the elastic field obtained by the Lifschitz-Rozentsveig for a hexagonal medium, an exact formula for the interaction energy of two point defects has been obtained. The solution is represented as a function of the angle of their relative position on the example of semiconductors such as III-nitrides and α-SiC. For the cubic medium, the solution is found on the basis of the Lifschitz-Rozentsveig Green's tensors corrected by Ostapchuk, in the weak-anisotropy approximation. It is proven that the calculation of the interaction energy by the original Lifschitz-Rozentsveig Green's tensor leads to the opposite sign of the energy. On the example of the silicon crystal, the approximate solution is compared with the numerical solution, which is represented as an approximation by a series of spherical harmonics. The range of applicability of the continual approach is estimated by the quantum mechanical calculation of the lattice Green's function.

  5. Observation of Body-Centered Cubic Gold Nanocluster.

    PubMed

    Liu, Chao; Li, Tao; Li, Gao; Nobusada, Katsuyuki; Zeng, Chenjie; Pang, Guangsheng; Rosi, Nathaniel L; Jin, Rongchao

    2015-08-17

    The structure of nanoparticles plays a critical role in dictating their material properties. Gold is well known to adopt face-centered cubic (fcc) structure. Herein we report the first observation of a body-centered cubic (bcc) gold nanocluster composed of 38 gold atoms protected by 20 adamantanethiolate ligands and two sulfido atoms ([Au38S2(SR)20], where R=C10H15) as revealed by single-crystal X-ray crystallography. This bcc structure is in striking contrast with the fcc structure of bulk gold and conventional Au nanoparticles, as well as the bi-icosahedral structure of [Au38(SCH2CH2Ph)24]. The bcc nanocluster has a distinct HOMO-LUMO gap of ca. 1.5 eV, much larger than the gap (0.9 eV) of the bi-icosahedral [Au38(SCH2CH2Ph)24]. The unique structure of the bcc gold nanocluster may be promising in catalytic applications. PMID:26136241

  6. Nano-Engineered Cubic Zirconia for Orthopaedic Implant Applications

    NASA Astrophysics Data System (ADS)

    Namavar, F.; Rubinstein, A.; Sabirianov, R.; Thiele, G.; Sharp, J.; Pokharel, U.; Namavar, R.; Garvin, K.

    2012-02-01

    Osseointegration failure of the prosthesis prevents long-term stability, which contributes to pain, implant loosening, and infection that usually necessitates revision surgery. Cell attachment and spreading in vitro is generally mediated by adhesive proteins such as fibronectin and vitronectin. We designed and produced pure cubic zirconia (ZrO2) ceramic coatings by ion beam assisted deposition (IBAD) with nanostructures comparable to the size of proteins. Our ceramic coatings exhibit high hardness and a zero contact angle with serum. In contrast to Hydroxyapatite (HA), nano-engineered zirconia films possess excellent adhesion to all orthopaedic materials. Adhesion and proliferation experiments were performed with a bona fide mesenchymal stromal cells cell line (OMA-AD). Our experimental results indicated that nano-engineered cubic zirconia is superior in supporting growth, adhesion, and proliferation. We performed a comparative analysis of adsorption energies of the FN fragment using quantum mechanical calculations and Monte Carlo simulation on both types of surfaces: smooth and nanostructured. We have found that the initial FN fragment adsorbs significantly stronger on the nanostructured surface than on the smooth surface.

  7. Reversible Nanoparticle Cubic Lattices in Blue Phase Liquid Crystals.

    PubMed

    Gharbi, Mohamed Amine; Manet, Sabine; Lhermitte, Julien; Brown, Sarah; Milette, Jonathan; Toader, Violeta; Sutton, Mark; Reven, Linda

    2016-03-22

    Blue phases (BPs), a distinct class of liquid crystals (LCs) with 3D periodic ordering of double twist cylinders involving orthogonal helical director twists, have been theoretically studied as potential templates for tunable colloidal crystals. Here, we report the spontaneous formation of thermally reversible, cubic crystal nanoparticle (NP) assemblies in BPs. Gold NPs, functionalized to be highly miscible in cyanobiphenyl-based LCs, were dispersed in BP mixtures and characterized by polarized optical microscopy and synchrotron small-angle X-ray scattering (SAXS). The NPs assemble by selectively migrating to periodic strong trapping sites in the BP disclination lines. The NP lattice, remarkably robust given the small particle size (4.5 nm diameter), is commensurate with that of the BP matrix. At the BP I to BP II phase transition, the NP lattice reversibly switches between two different cubic structures. The simultaneous presence of two different symmetries in a single material presents an interesting opportunity to develop novel dynamic optical materials. PMID:26900753

  8. Debinding Process of Fe-6Ni-4Cu Compact Fabricated by Metal Injection Molding

    NASA Astrophysics Data System (ADS)

    Wang, Jenn-Shing; Lin, Shih-Pin; Hon, Min-Hsiung; Wang, Moo-Chin

    2000-02-01

    The debinding process in the case of metal injection molding for fabrication of the Fe-6Ni-4Cu compact and variables such as temperature and time has been studied. The debinding process of multiple organic binders in the Fe-6Ni-4Cu compact was investigated by thermal gravimetric analysis (TGA) weight loss and mercury porosimetry analysis. The weight loss of wax and SA dramatically increases from below 10 wt% to 76.0 wt% and 86.0 wt% after immersion in 35°C and 40°C n-hexane for 6 h, respectively. The interdiffusion coefficients of the binder and solvent are 9.763× 10-7 cm2/s and 1.295× 10-6 cm2/s, respectively. The temperature dependent interdiffusion coefficient for the Fe-6Ni-4Cu compact can be expressed as Dx=4.534× 10\\exp({-}5437.2/T). The distribution of pore size is about 0.1-1.9 μm for the Fe-6Ni-4Cu compact.

  9. Temperature-dependent EXAFS study of the local structure and lattice dynamics in cubic Y2O3.

    PubMed

    Jonane, Inga; Lazdins, Karlis; Timoshenko, Janis; Kuzmin, Alexei; Purans, Juris; Vladimirov, Pavel; Gräning, Tim; Hoffmann, Jan

    2016-03-01

    The local structure and lattice dynamics in cubic Y2O3 were studied at the Y K-edge by X-ray absorption spectroscopy in the temperature range from 300 to 1273 K. The temperature dependence of the extended X-ray absorption fine structure was successfully interpreted using classical molecular dynamics and a novel reverse Monte Carlo method, coupled with the evolutionary algorithm. The obtained results allowed the temperature dependence of the yttria atomic structure to be followed up to ∼6 Å and to validate two force-field models. PMID:26917139

  10. Microscopic insight into properties and electronic instabilities of impurities in cubic and lower symmetry insulators: the influence of pressure.

    PubMed

    Moreno, M; Barriuso, M T; Aramburu, J A; García-Fernández, P; García-Lastra, J M

    2006-05-01

    This article reviews the microscopic origin of properties due to transition-metal (TM) impurities, M, in insulator materials. Particular attention is paid to the influence of pressure upon impurity properties. Basic concepts such as the electronic localization in an MX(N) complex, the electrostatic potential, V(R), arising from the rest of the lattice ions or the elastic coupling of the complex to the host lattice are initially exposed. The dependence of optical and magnetic parameters on the impurity-ligand distance, R, in cubic lattices is discussed in a first step. Emphasis is put on the actual origin of the R dependence of 10Dq. Examples revealing that laws for strict cubic symmetry cannot in general be transferred to lower symmetries are later given. This relevant fact is shown to come from allowed hybridizations like nd-(n+1)s as well as the influence of V(R). As a salient feature the different colour in ruby and emerald is stressed to arise from distinct V(R) potentials in Al(2)O(3) and Be(3)Si(6)Al(2)O(18). The last part of this review deals with electronic instabilities. The phenomena associated with the Jahn-Teller (JT) effect in cubic lattices, the origin of the energy barrier among equivalent minima and the existence of coherent tunnelling in systems like MgO:Cu(2+) are discussed. An increase of elastic coupling is pointed out to favour a transition from an elongated to a compressed equilibrium conformation. Interestingly the equilibrium geometry of JT ions in non-cubic lattices is shown to be controlled by mechanisms different to those in cubic systems, V(R) playing again a key role. The relevance of first principles calculations for clarifying the subtle mechanisms behind off-centre instabilities is also pointed out. Examples concern monovalent and divalent TM impurities in lattices with the CaF(2) structure. The instability due to the transition from the ground to an excited state is finally considered. For complexes with significant elastic coupling

  11. Lattice vibrations and structural instability in caesium near the cubic-to-tetragonal transition

    NASA Astrophysics Data System (ADS)

    Kong, Y.; Jepsen, O.

    2000-10-01

    Under pressure, caesium undergoes a transition from a high-pressure fcc (face-centred cubic) phase (Cs-II) to a collapsed fcc phase (Cs-III) near 4.2 GPa. At 4.4 GPa there follows a transition to the tetragonal Cs-IV phase. In order to investigate the lattice vibrations in the fcc phase and seek a possible dynamical instability of the lattice, the phonon spectra of fcc Cs at volumes near the III-to-IV transition are calculated using Savrasov's density functional linear-response LMTO (linear muffin-tin orbital) method. Compared with quasiharmonic model calculations including non-central interatomic forces up to second neighbours, at the volume V/V0 = 0.44 (V0 is the experimental volume of bcc Cs (bcc≡body-centred cubic) with a0 = 6.048 Å), the linear-response calculations show soft intermediate-wavelength T[1ξξ0] phonons. Similar softening is also observed for short-wavelength L[ξξξ] and L[00ξ] phonons and intermediate-wavelength L[ξξξ] phonons. The Born-von Kármán analysis of the dispersion curves indicates that the interplanar force constants exhibit oscillating behaviours against plane spacing n and the large softening of intermediate-wavelength T[1ξξ0] phonons results from a negative (110) interplanar force constant Φn = 2. The calculated frequencies for high-symmetry K and W and longitudinal X and L phonons decrease with volume compression. In particular, the frequencies of the T[1ξξ0] phonons with ξ around 1/3 become imaginary and the fcc structure becomes dynamically unstable for volumes below 0.41V0. It is suggested that superstructures corresponding to the q&\

  12. An Unusual Coronal Mass Ejection: First Solar Wind Electron, Proton, Alpha Monitor (SWEPAM) Results from the Advanced Composition Explorer. Appendix 6

    NASA Technical Reports Server (NTRS)

    McComas, D. J.; Bame, S. J.; Barker, P. L.; Delapp, D. M.; Gosling, J. T.; Skoug, R. M.; Tokar, R. L.; Riley, P.; Feldman, W. C.; Santiago, E.

    2001-01-01

    This paper reports the first scientific results from the Solar Wind Electron Proton Alpha Monitor (SWEPAM) instrument on board the Advanced Composition Explorer (ACE) spacecraft. We analyzed a coronal mass ejection (CME) observed in the solar wind using data from early February, 1998. This event displayed several of the common signatures of CMEs, such as counterstreaming halo electrons and depressed ion and electron temperatures, as well as some unusual features. During a portion of the CME traversal, SWEPAM measured a very large helium to proton abundance ratio. Other heavy ions, with a set of ionization states consistent with normal (1 to 2x10(exp 6) K) coronal temperatures, were proportionately enhanced at this time. These observations suggest a source for at least some of the CME material, where heavy ions are initially concentrated relative to hydrogen and then accelerated up into the solar wind, independent of their mass and first ionization potential.

  13. Infrared Measurements of Atmospheric Ethane (C2H6) From Aircraft and Ground-Based Solar Absorption Spectra in the 3000/ cm Region

    NASA Technical Reports Server (NTRS)

    Coffey, M. T.; Mankin, W. G.; Goldman, A.; Rinsland, C. P.; Harvey, G. A.; Devi, V. Malathy; Stokes, G. M.

    1985-01-01

    A number or prominent Q-branches or the upsilon(sub 7) band or C2H6 have been identified near 3000/ cm in aircraft and ground-based infrared solar absorption spectra. The aircraft spectra provide the column amount above 12 km at various altitudes. The column amount is strongly correlated with tropopause height and can be described by a constant mixing ratio of 0.46 ppbv in the upper troposphere and a mixing ratio scale height of 3.9 km above the tropopause. The, ground-based spectra yield a column of 9.0 x 10(exp 15) molecules/sq cm above 2.1 km; combining these results implies a tropospheric mixing ratio of approximately 0.63 ppbv.

  14. Effect of Phospholipids and a Transmembrane Peptide on the Stability of the Cubic Phase of Monoolein: Implication for Protein Crystalization from a Cubic Phase

    PubMed Central

    Chupin, V.; Killian, J. A.; de Kruijff, B.

    2003-01-01

    The cubic phase of monoolein has successfully been used for crystallization of a number of membrane proteins. However, the mechanism of protein crystallization in the cubic phase is still unknown. It was hypothesized, that crystallization occurs at locally formed patches of bilayers. To get insight into the stability of the cubic phase, we investigated the effect of different phospholipids and a model transmembrane peptide on the lipid organization in mixed monoolein systems. Deuterium-labeled 1-oleoyl-rac-[2H5]-glycerol was used as a selective probe for 2H NMR. The phase behavior of the phospholipids was followed by 31P NMR. Upon incorporation of phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, or phosphatidic acid, the cubic phase of monoolein transformed into the Lα or HII phase depending on the phase preference of the phospholipid and its concentration. The ability of phospholipids to destabilize the cubic phase was found to be dependent on the phospholipid packing properties. Electrostatic repulsion facilitated the cubic-to-Lα transition. Incorporation of the transmembrane peptide KALP31 induced formation of the Lα phase with tightly packed lipid molecules. In all cases when phase separation occurs, monoolein and phospholipid participate in both phases. The implications of these findings for protein crystallization are discussed. PMID:12668446

  15. Extending a Property of Cubic Polynomials to Higher-Degree Polynomials

    ERIC Educational Resources Information Center

    Miller, David A.; Moseley, James

    2012-01-01

    In this paper, the authors examine a property that holds for all cubic polynomials given two zeros. This property is discovered after reviewing a variety of ways to determine the equation of a cubic polynomial given specific conditions through algebra and calculus. At the end of the article, they will connect the property to a very famous method…

  16. Deformation-induced structural transition in body-centred cubic molybdenum

    PubMed Central

    Wang, S. J.; Wang, H.; Du, K.; Zhang, W.; Sui, M. L.; Mao, S. X.

    2014-01-01

    Molybdenum is a refractory metal that is stable in a body-centred cubic structure at all temperatures before melting. Plastic deformation via structural transitions has never been reported for pure molybdenum, while transformation coupled with plasticity is well known for many alloys and ceramics. Here we demonstrate a structural transformation accompanied by shear deformation from an original <001>-oriented body-centred cubic structure to a <110>-oriented face-centred cubic lattice, captured at crack tips during the straining of molybdenum inside a transmission electron microscope at room temperature. The face-centred cubic domains then revert into <111>-oriented body-centred cubic domains, equivalent to a lattice rotation of 54.7°, and ~15.4% tensile strain is reached. The face-centred cubic structure appears to be a well-defined metastable state, as evidenced by scanning transmission electron microscopy and nanodiffraction, the Nishiyama–Wassermann and Kurdjumov–Sachs relationships between the face-centred cubic and body-centred cubic structures and molecular dynamics simulations. Our findings reveal a deformation mechanism for elemental metals under high-stress deformation conditions. PMID:24603655

  17. The Normals to a Parabola and the Real Roots of a Cubic

    ERIC Educational Resources Information Center

    Bains, Majinder S.; Thoo, J. B.

    2007-01-01

    The geometric problem of finding the number of normals to the parabola y = x[squared] through a given point is equivalent to the algebraic problem of finding the number of distinct real roots of a cubic equation. Apollonius solved the former problem, and Cardano gave a solution to the latter. The two problems are bridged by Neil's (semi-cubical)…

  18. Some Curious Properties and Loci Problems Associated with Cubics and Other Polynomials

    ERIC Educational Resources Information Center

    de Alwis, Amal

    2012-01-01

    The article begins with a well-known property regarding tangent lines to a cubic polynomial that has distinct, real zeros. We were then able to generalize this property to any polynomial with distinct, real zeros. We also considered a certain family of cubics with two fixed zeros and one variable zero, and explored the loci of centroids of…

  19. Deformation-induced structural transition in body-centred cubic molybdenum.

    PubMed

    Wang, S J; Wang, H; Du, K; Zhang, W; Sui, M L; Mao, S X

    2014-01-01

    Molybdenum is a refractory metal that is stable in a body-centred cubic structure at all temperatures before melting. Plastic deformation via structural transitions has never been reported for pure molybdenum, while transformation coupled with plasticity is well known for many alloys and ceramics. Here we demonstrate a structural transformation accompanied by shear deformation from an original <001>-oriented body-centred cubic structure to a <110>-oriented face-centred cubic lattice, captured at crack tips during the straining of molybdenum inside a transmission electron microscope at room temperature. The face-centred cubic domains then revert into <111>-oriented body-centred cubic domains, equivalent to a lattice rotation of 54.7°, and ~15.4% tensile strain is reached. The face-centred cubic structure appears to be a well-defined metastable state, as evidenced by scanning transmission electron microscopy and nanodiffraction, the Nishiyama-Wassermann and Kurdjumov-Sachs relationships between the face-centred cubic and body-centred cubic structures and molecular dynamics simulations. Our findings reveal a deformation mechanism for elemental metals under high-stress deformation conditions. PMID:24603655

  20. Relations between Roots and Coefficients of Cubic Equations with One Root Negative the Reciprocal of Another

    ERIC Educational Resources Information Center

    Asiru, M. A.

    2007-01-01

    Under predetermined conditions on the roots and coefficients, necessary and sufficient conditions relating the coefficients of a given cubic equation x[cubed] + ax[squared] + bx + c = 0 can be established so that the roots possess desired properties. In this note, the condition for one root of a cubic equation to be "the negative reciprocal of…

  1. Effects of Nonlocality in Cubic Superconductor V3Si

    NASA Astrophysics Data System (ADS)

    Yethiraj, M.; Christen, D. K.; Paul, D. McK.; Dewhurst, C.; Cubitt, R.

    2004-03-01

    Non-locality in superconductors is an important effect which produces an anisotropic distribution of current flow around the core of a flux-line in the mixed state of a type II superconductor. Such anistropic interactions produce varying forces between the fluxlines as a function of their seperation and hence changes in the symmetry of the flux line lattice (FLL) with field. V3Si has a cubic crystal symmetry and the material shows no evidence of any structure in the energy gap, making this an ideal model system for studies of the influence of "non-locality" on the FLL. We report on the structural changes of the FLL in this clean system with changes in applied field and temperature with particular emphasis on the region near HC2, where this effect weakens. We compare these results with what happens in other systems where nodal structure can also lead to changes in morphology for the FLL.

  2. Ferrimagnetic behaviors in a double-wall cubic metal nanotube

    NASA Astrophysics Data System (ADS)

    Liang, Ji-Yan; Zou, Cheng-Long; Jiang, Wei; Li, Xiao-Xi

    2015-05-01

    A double-wall cubic metal nanotube consists of the ferromagnetic spin-1 inner shell and spin-3/2 surface shell. It is of the ferrimagnetic exchange coupling between two shells. Considering the single-ion anisotropy and transverse field exist together, the magnetization, the initial susceptibility, the internal energy and the specific heat have been investigated by using the effective-field theory with correlations. Some interesting phenomena have been found in the thermal variations of the system. Magnetization appears two or three compensation points in certain parameters. It is an unconventional ferrimagnetic behavior in the nanotube. The shapes of total magnetization and the initial susceptibility are great influenced by the surface exchange coupling, surface single-ion anisotropy and surface transverse field. Some results of nanotube may have potential applications in different research fields, such as electronics, optics, mechanics, and even biomedicine and molecular devices.

  3. Quantum-Carnot engine for particle confined to cubic potential

    SciTech Connect

    Sutantyo, Trengginas Eka P. Belfaqih, Idrus H. Prayitno, T. B.

    2015-09-30

    Carnot cycle consists of isothermal and adiabatic processes which are reversible. Using analogy in quantum mechanics, these processes can be well explained by replacing variables in classical process with a quantum system. Quantum system which is shown in this paper is a particle that moves under the influence of a cubic potential which is restricted only to the state of the two energy levels. At the end, the efficiency of the system is shown as a function of the width ratio between the initial conditions and the farthest wall while expanding. Furthermore, the system efficiency will be considered 1D and 2D cases. The providing efficiencies are different due to the influence of the degeneration of energy and the degrees of freedom of the system.

  4. Submicron cubic boron nitride as hard as diamond

    SciTech Connect

    Liu, Guoduan; Kou, Zili E-mail: yanxz@hpstar.ac.cn; Lei, Li; Peng, Fang; Wang, Qiming; Wang, Kaixue; Wang, Pei; Li, Liang; Li, Yong; Wang, Yonghua; Yan, Xiaozhi E-mail: yanxz@hpstar.ac.cn; Li, Wentao; Bi, Yan; Leng, Yang; He, Duanwei

    2015-03-23

    Here, we report the sintering of aggregated submicron cubic boron nitride (sm-cBN) at a pressure of 8 GPa. The sintered cBN compacts exhibit hardness values comparable to that of single crystal diamond, fracture toughness about 5-fold that of cBN single crystal, in combination with a high oxidization temperature. Thus, another way has been demonstrated to improve the mechanical properties of cBN besides reducing the grain size to nano scale. In contrast to other ultrahard compacts with similar hardness, the sm-cBN aggregates are better placed for potential industrial application, as their relative low pressure manufacturing perhaps be easier and cheaper.

  5. Cubic derivative interactions and asymptotic dynamics of the galileon vacuum

    NASA Astrophysics Data System (ADS)

    De Arcia, Roberto; Gonzalez, Tame; Leon, Genly; Nucamendi, Ulises; Quiros, Israel

    2016-06-01

    In this paper we apply the tools of the dynamical systems theory in order to uncover the whole asymptotic structure of the vacuum interactions of a galileon model with a cubic derivative interaction term. It is shown that, contrary to what occurs in the presence of background matter, the galileon interactions of vacuum appreciably modify the late-time cosmic dynamics. In particular, a local late-time attractor representing phantom behavior arises which is inevitably associated with a big rip singularity. It seems that the gravitational interactions of the background matter with the galileon screen the effects of the gravitational self-interactions of the galileon, thus erasing any potential modification of the late-time dynamics by the galileon vacuum processes. Unlike other galileon models inspired in the DGP scenario, self-accelerating solutions do not arise in this model.

  6. A cubic autocatalytic reaction in a continuous stirred tank reactor

    SciTech Connect

    Yakubu, Aisha Aliyu; Yatim, Yazariah Mohd

    2015-10-22

    In the present study, the dynamics of the cubic autocatalytic reaction model in a continuous stirred tank reactor with linear autocatalyst decay is studied. This model describes the behavior of two chemicals (reactant and autocatalyst) flowing into the tank reactor. The behavior of the model is studied analytically and numerically. The steady state solutions are obtained for two cases, i.e. with the presence of an autocatalyst and its absence in the inflow. In the case with an autocatalyst, the model has a stable steady state. While in the case without an autocatalyst, the model exhibits three steady states, where one of the steady state is stable, the second is a saddle point while the last is spiral node. The last steady state losses stability through Hopf bifurcation and the location is determined. The physical interpretations of the results are also presented.

  7. G2 cubic transition between two circles with shape control

    NASA Astrophysics Data System (ADS)

    Habib, Zulfiqar; Sakai, Manabu

    2009-01-01

    This paper describes a method for joining two circles with an S-shaped or with a broken back C-shaped transition curve, composed of at most two spiral segments. In highway and railway route design or car-like robot path planning, it is often desirable to have such a transition. It is shown that a single cubic curve can be used for blending or for a transition curve preserving G2 continuity with local shape control parameter and more flexible constraints. Provision of the shape parameter and flexibility provide freedom to modify the shape in a stable manner which is an advantage over previous work by Meek, Walton, Sakai and Habib.

  8. Lipidic cubic phase serial millisecond crystallography using synchrotron radiation

    PubMed Central

    Nogly, Przemyslaw; James, Daniel; Wang, Dingjie; White, Thomas A.; Zatsepin, Nadia; Shilova, Anastasya; Nelson, Garrett; Liu, Haiguang; Johansson, Linda; Heymann, Michael; Jaeger, Kathrin; Metz, Markus; Wickstrand, Cecilia; Wu, Wenting; Båth, Petra; Berntsen, Peter; Oberthuer, Dominik; Panneels, Valerie; Cherezov, Vadim; Chapman, Henry; Schertler, Gebhard; Neutze, Richard; Spence, John; Moraes, Isabel; Burghammer, Manfred; Standfuss, Joerg; Weierstall, Uwe

    2015-01-01

    Lipidic cubic phases (LCPs) have emerged as successful matrixes for the crystallization of membrane proteins. Moreover, the viscous LCP also provides a highly effective delivery medium for serial femtosecond crystallography (SFX) at X-ray free-electron lasers (XFELs). Here, the adaptation of this technology to perform serial millisecond crystallography (SMX) at more widely available synchrotron microfocus beamlines is described. Compared with conventional microcrystallography, LCP-SMX eliminates the need for difficult handling of individual crystals and allows for data collection at room temperature. The technology is demonstrated by solving a structure of the light-driven proton-pump bacteriorhodopsin (bR) at a resolution of 2.4 Å. The room-temperature structure of bR is very similar to previous cryogenic structures but shows small yet distinct differences in the retinal ligand and proton-transfer pathway. PMID:25866654

  9. Surface Brillouin scattering of cubic boron nitride films

    NASA Astrophysics Data System (ADS)

    Zinin, P.; Manghnani, M. H.; Zhang, X.; Feldermann, H.; Ronning, C.; Hofsäss, H.

    2002-04-01

    Surface Brillouin scattering has been used to determine the elastic properties of thin hard submicron cubic boron nitride (cBN) films grown on silicon by mass selected ion beam deposition. The elastic properties of the films have been determined by fitting experimental data to theoretical dispersion curves. A Green's function method was used to predict Brillouin scattering spectra of the acoustic excitation at the free surface. Our results demonstrate that the effect of the thin hexagonal boron nitride interlayer located between cBN film and the Si substrate on the velocity of the surface acoustic wave does not exceed 2% for a thin (16 nm) film and is negligible for cBN films thicker than 100 nm. The elastic properties of the cBN films are not softer than those of bulk cBN.

  10. New cubic phase of lithium nitride to 200 GPa

    SciTech Connect

    Lazicki, A; Maddox, B; Evans, W; Yoo, C S; McMahan, A K; Pickett, W E; Scalettar, R T; Hu, M Y; Chow, P

    2005-07-19

    We present a new cubic ({gamma}) Li{sub 3}N phase discovered above 40({+-}5) GPa. Structure and electronic bands are examined at high pressure with synchrotron x-ray diffraction and inelastic x-ray scattering in a diamond anvil cell, and also with first-principles calculations. We observe a dramatic band-gap widening and volume collapse at the phase transition. {gamma}-Li{sub 3}N remains extremely stable and ionic to 200 GPa, with predicted metallization near 8 TPa. The high structural stability, wide band-gap and simple electronic structure of {gamma}-Li{sub 3}N are analogous to that of such lower valence closed-shell solids as NaCl, MgO and Ne, meriting its use as a low-Z internal pressure standard.

  11. Nonuniversal weak antilocalization effect in cubic topological Kondo insulators

    NASA Astrophysics Data System (ADS)

    Dzero, Maxim; Vavilov, Maxim G.; Kechedzhi, Kostyantyn; Galitski, Victor M.

    2015-10-01

    We study the quantum correction to conductivity on the surface of cubic topological Kondo insulators with multiple Dirac bands. We consider the model of time-reversal invariant disorder which induces the scattering of the electrons within the Dirac bands as well as between the bands. When only intraband scattering is present we find three long-range diffusion modes leading to weak antilocalization correction to conductivity which remains independent of the microscopic details such as Fermi velocities and relaxation times. Interband scattering gaps out two diffusion modes leaving only one long-range mode. We find that depending on the value of the phase coherence time, either three or only one long-range diffusion modes contribute to weak localization correction rendering the quantum correction to conductivity nonuniversal. We provide an interpretation for the results of the recent transport experiments on samarium hexaboride where weak antilocalization has been observed.

  12. Serial femtosecond crystallography of soluble proteins in lipidic cubic phase

    DOE PAGESBeta

    Fromme, Raimund; Ishchenko, Andrii; Metz, Markus; Chowdhury, Shatabdi Roy; Basu, Shibom; Boutet, Sébastien; Fromme, Petra; White, Thomas A.; Barty, Anton; Spence, John C. H.; et al

    2015-08-04

    Serial femtosecond crystallography (SFX) at X-ray free-electron lasers (XFELs) enables high-resolution protein structure determination using micrometre-sized crystals at room temperature with minimal effects from radiation damage. SFX requires a steady supply of microcrystals intersecting the XFEL beam at random orientations. An LCP–SFX method has recently been introduced in which microcrystals of membrane proteins are grown and delivered for SFX data collection inside a gel-like membrane-mimetic matrix, known as lipidic cubic phase (LCP), using a special LCP microextrusion injector. Here, it is shown enabling a dramatic reduction in the amount of crystallized protein required for data collection compared with crystals deliveredmore » by liquid injectors. High-quality LCP–SFX data sets were collected for two soluble proteins, lysozyme and phycocyanin, using less than 0.1 mg of each protein.« less

  13. Serial femtosecond crystallography of soluble proteins in lipidic cubic phase

    SciTech Connect

    Fromme, Raimund; Ishchenko, Andrii; Metz, Markus; Chowdhury, Shatabdi Roy; Basu, Shibom; Boutet, Sébastien; Fromme, Petra; White, Thomas A.; Barty, Anton; Spence, John C. H.; Weierstall, Uwe; Liu, Wei; Cherezov, Vadim

    2015-08-04

    Serial femtosecond crystallography (SFX) at X-ray free-electron lasers (XFELs) enables high-resolution protein structure determination using micrometre-sized crystals at room temperature with minimal effects from radiation damage. SFX requires a steady supply of microcrystals intersecting the XFEL beam at random orientations. An LCP–SFX method has recently been introduced in which microcrystals of membrane proteins are grown and delivered for SFX data collection inside a gel-like membrane-mimetic matrix, known as lipidic cubic phase (LCP), using a special LCP microextrusion injector. Here, it is shown enabling a dramatic reduction in the amount of crystallized protein required for data collection compared with crystals delivered by liquid injectors. High-quality LCP–SFX data sets were collected for two soluble proteins, lysozyme and phycocyanin, using less than 0.1 mg of each protein.

  14. High-order numerical solutions using cubic splines

    NASA Technical Reports Server (NTRS)

    Rubin, S. G.; Khosla, P. K.

    1975-01-01

    The cubic spline collocation procedure for the numerical solution of partial differential equations was reformulated so that the accuracy of the second-derivative approximation is improved and parallels that previously obtained for lower derivative terms. The final result is a numerical procedure having overall third-order accuracy for a nonuniform mesh and overall fourth-order accuracy for a uniform mesh. Application of the technique was made to the Burger's equation, to the flow around a linear corner, to the potential flow over a circular cylinder, and to boundary layer problems. The results confirmed the higher-order accuracy of the spline method and suggest that accurate solutions for more practical flow problems can be obtained with relatively coarse nonuniform meshes.

  15. Elastic constants of cubic and wurtzite boron nitrides

    NASA Astrophysics Data System (ADS)

    Nagakubo, A.; Ogi, H.; Sumiya, H.; Kusakabe, K.; Hirao, M.

    2013-06-01

    We synthesized pure polycrystalline cubic boron nitride (cBN) and wurtzite boron nitride (wBN) by the direct conversion method from hexagonal boron nitride, and measured their longitudinal-wave elastic constants CL between 20 and 300 K using picosecond ultrasound spectroscopy. Their room-temperature values are 945 ± 3 GPa and 930 ± 18 GPa for cBN and wBN, respectively. The shear modulus G of cBN was also determined by combining resonance ultrasound spectroscopy and micromechanics calculation as G = 410 GPa. We performed ab-initio calculations and confirmed that the generalized gradient approximation potential fails to yield correct elastic constants, which indicated the necessity of a hybrid-functional method.

  16. On the Properties of Cubic Metric for OFDM Signals

    NASA Astrophysics Data System (ADS)

    Kim, Kee-Hoon; No, Jong-Seon; Shin, Dong-Joon

    2016-01-01

    As a metric for amplitude fluctuation of orthogonal frequency division multiplexing (OFDM) signal, cubic metric (CM) has received an increasing attention because it is more closely related to the distortion induced by nonlinear devices than the well-known peak-to-average power ratio (PAPR). In this paper, the properties of CM of OFDM signal is investigated. First, asymptotic distribution of CM is derived. Second, it is verified that 1.7 times oversampling rate is good enough to capture the CM of continuous OFDM signals in terms of mean square error, which is also practically meaningful because the fast Fourier transform size is typically 1.7 times larger than the nominal bandwidth in the long-term evolution (LTE) of cellular communication systems.

  17. Electrical transport in three-dimensional cubic Skyrmion crystal

    NASA Astrophysics Data System (ADS)

    Zhang, Xiao-Xiao; Nagaosa, Naoto

    2015-03-01

    Two-dimensional magnetic Skyrmions have been well confirmed via various experimental techniques in the bulk or on epitaxial thin films. Besides, a topologically nontrivial three-dimensional cubic Skyrmion crystal in the bulk, which is essentially a hedgehog-antihedgehog pair texture predicted theoretically, has also been tentatively observed. Equipped with a sophisticated spectral analysis program, we adopt Matsubara Green's function technique to study electrical transport, especially diagonal conductivity, in such system. We consider conduction electrons interacting with spinwaves via the strong Hund's rule coupling, wherein fluctuation of monopolar emergent electromagnetic field exits within adiabatic approximation. We describe in detail the influence of temperature and Skyrmion number on both dc and ac conductivities. Possible deviation from Fermi liquid behavior will also be discussed.

  18. Nonlinear structure formation in the cubic Galileon gravity model

    SciTech Connect

    Barreira, Alexandre; Li, Baojiu; Hellwing, Wojciech A.; Baugh, Carlton M.; Pascoli, Silvia E-mail: baojiu.li@durham.ac.uk E-mail: c.m.baugh@durham.ac.uk

    2013-10-01

    We model the linear and nonlinear growth of large scale structure in the Cubic Galileon gravity model, by running a suite of N-body cosmological simulations using the ECOSMOG code. Our simulations include the Vainshtein screening effect, which reconciles the Cubic Galileon model with local tests of gravity. In the linear regime, the amplitude of the matter power spectrum increases by ∼ 20% with respect to the standard ΛCDM model today. The modified expansion rate accounts for ∼ 15% of this enhancement, while the fifth force is responsible for only ∼ 5%. This is because the effective unscreened gravitational strength deviates from standard gravity only at late times, even though it can be twice as large today. In the nonlinear regime (k∼>0.1h Mpc{sup −1}), the fifth force leads to only a modest increase (∼<8%) in the clustering power on all scales due to the very efficient operation of the Vainshtein mechanism. Such a strong effect is typically not seen in other models with the same screening mechanism. The screening also results in the fifth force increasing the number density of halos by less than 10%, on all mass scales. Our results show that the screening does not ruin the validity of linear theory on large scales which anticipates very strong constraints from galaxy clustering data. We also show that, whilst the model gives an excellent match to CMB data on small angular scales (l∼>50), the predicted integrated Sachs-Wolfe effect is in tension with Planck/WMAP results.

  19. Cosmological evolution with the cubic order field derivative coupling

    NASA Astrophysics Data System (ADS)

    Minamitsuji, Masato

    2016-03-01

    We investigate cosmological evolution in the scalar-tensor theory with the field derivative coupling to the double-dual of the Riemann tensor (the cubic-type theory). The theory can be seen as the straightforward extension of the scalar-tensor with the quadratic order field derivative coupling to the Einstein tensor (the quadratic-type theory). Both the field derivative couplings to the Einstein tensor and the double-dual of the Riemann tensor have been argued in terms of the successful realization of the self-tuning of the cosmological constant within the Horndeski theory. Assuming the constant potential given by the sum of the cosmological constant and the quantum vacuum energy, the shift symmetry for the scalar field and no matter fields, in the spatially-flat Friedmann-Lemaître-Robertson-Walker spacetime, we can reduce the set of the field equations to the first-order ordinary nonlinear differential equation for the Hubble parameter, showing the existence of the self-tuned and runaway de Sitter solutions, in addition to the standard de Sitter solutions in general relativity and the finite Hubble singularities which can be reached within the finite time. We then argue the possible cosmological evolution in terms of the values of the effective cosmological constant, the kinetic coupling constants and the initial Hubble parameter. Although the behavior of the universe around each of the de Sitter solutions as well as the finite time singularities is very similar in both theories, we find that the crucial difference appears in terms of no bounce or turnaround behavior across the vanishing Hubble parameter as well as no limitation for the range of the Hubble parameter in the cubic-type theory.

  20. Measurements of Nucleation-Mode Particle Size Distributions in Aircraft Plumes during SULFUR 6

    NASA Technical Reports Server (NTRS)

    Brock, Charles A.; Bradford, Deborah G.

    1999-01-01

    This report summarizes the participation of the University of Denver in an airborne measurement program, SULFUR 6, which was undertaken in late September and early October of 1998 by the Deutsches Zentrum fur Luft und Raumfahrt (DLR). Scientific findings from two papers that have been published or accepted and from one manuscript that is in preparation are presented. The SULFUR 6 experiment was designed to investigate the emissions from subsonic aircraft to constrain calculations of possible atmospheric chemical and climatic effects. The University of Denver effort contributed toward the following SULFUR 6 goals: (1) To investigate the relationship between fuel sulfur content (FSC--mass of sulfur per mass of fuel) and particle number and mass emission index (El--quantity emitted per kg of fuel burned); (2) To provide upper and lower limits for the mass conversion efficiency (nu) of fuel sulfur to gaseous and particulate sulfuric acid; (3) To constrain models of volatile particle nucleation and growth by measuring the particle size distribution between 3 and 100 nm at aircraft plume ages ranging from 10(exp -1) to 10(exp 3) s; (4) To determine microphysical and optical properties and bulk chemical composition of soot particles in aircraft exhaust; and (5) To investigate the differences in particle properties between aircraft plumes in contrail and non-contrail situations. The experiment focused on emissions from the ATTAS research aircraft (a well characterized, but older technology turbojet) and from an in-service Boeing 737-300 aircraft provided by Lufthansa, with modem, high-bypass turbofan engines. Measurements were made from the DLR Dassault Falcon 900 aircraft, a modified business jet. The Atmospheric Effects of Aviation Program (AEAP) provided funding to operate an instrument, the nucleation-mode aerosol size spectrometer (N-MASS), during the SULFUR 6 campaign and to analyze the data. The N-MASS was developed at the University of Denver with the support of

  1. Observations of the CO J=6-5 transition in starburst galaxies

    NASA Technical Reports Server (NTRS)

    Harris, A. I.; Hills, R. E.; Stutzki, J.; Graf, U. U.; Russell, A. P. G.; Tacconi, L. J.; Genzel, R.

    1993-01-01

    Over the past several years, short-submillimeter observations of carbon monoxide's (CO) mid-J rotational levels have revealed the presence of a large amount of excited molecular gas in luminous giant molecular clouds in our Galaxy. Submillimeter lines are specific probes of excited material: collisional excitation of the level energy of 116 K above ground, and 6-5 transition's critical density is approximately 10(exp 6) cm(exp -3) in optically thin gas. Radiative trapping effects reduce the excitation requirements to some extent, but detection of the CO J=6-5 line is nearly indisputable proof of the existence of gas that is both warm and dense. The excitation conditions also imply that cool (T less than 20 K) molecular clouds within the beam neither emit nor absorb in the short-submillimeter lines; in our Galaxy, clouds with active massive star formation emit the strongest short-submillimeter CO rotational lines. We used these properties to explore the distribution of excited molecular material and physical conditions within the star formation regions of several classical starburst nuclei: NGC253, M82, and IC342. We have used the 6-5 transition as a thermometer of warm molecular gas in starburst nuclei, unambiguously finding that the nuclear molecular gas in starburst galaxies is substantially warmer than in typical disk clouds.

  2. Friction surfaced Stellite6 coatings

    SciTech Connect

    Rao, K. Prasad; Damodaram, R.; Rafi, H. Khalid; Ram, G.D. Janaki; Reddy, G. Madhusudhan; Nagalakshmi, R.

    2012-08-15

    Solid state Stellite6 coatings were deposited on steel substrate by friction surfacing and compared with Stellite6 cast rod and coatings deposited by gas tungsten arc and plasma transferred arc welding processes. Friction surfaced coatings exhibited finer and uniformly distributed carbides and were characterized by the absence of solidification structure and compositional homogeneity compared to cast rod, gas tungsten arc and plasma transferred coatings. Friction surfaced coating showed relatively higher hardness. X-ray diffraction of samples showed only face centered cubic Co peaks while cold worked coating showed hexagonally close packed Co also. - Highlights: Black-Right-Pointing-Pointer Stellite6 used as coating material for friction surfacing. Black-Right-Pointing-Pointer Friction surfaced (FS) coatings compared with casting, GTA and PTA processes. Black-Right-Pointing-Pointer Finer and uniformly distributed carbides in friction surfaced coatings. Black-Right-Pointing-Pointer Absence of melting results compositional homogeneity in FS Stellite6 coatings.

  3. Anisotropy in twinned terfenol-D crystals

    NASA Astrophysics Data System (ADS)

    Lord, D. G.; Harvey, D.

    1994-11-01

    The highly magnetostrictive cubic compound Terfenol-D (Tb0.3Dy0.7Fe2) solidifies via a (211) dendritic growth front when growth by a free-standing zone technique. The resulting material is usually composed of dendritic plates often containing crystallographic twins, the predominant plate and twin plane being the (1-11) orthogonal to the (-2-11) growth plane. Results of room temperature magnetic torque analysis from (011) disk specimens, having differing twin densities, are presented which yield both the magnetic anisotropy constants, K(sub 1) = -1.6 x 10(exp 5) J/cu m and K(sub 2) = -0.16 x 10(exp 5) J/cu m, and the relative parent/twin volume. Magnetic susceptibility data both parallel and transverse to the applied field are presented which, in conjunction with the anisotropy results, emphasize the importance of twin density on magnetoelastic response for typical application geometries.

  4. Experimental and numerical study of turbulent natural convection in an open cubic cavity

    NASA Astrophysics Data System (ADS)

    Maytorena, V. M.; Piña-Ortiz, A.; Hinojosa, J. F.

    2015-09-01

    Study of natural convection in an open cubic cavity with side length of 1 m is presented. The experimental setup was built with the air as the heat transfer fluid. The vertical wall opposite to the aperture is subjected to uniform heat flux condition with the four different heat flux values in the range 55-333 W/m2, whereas the remaining walls were kept thermally insulated. The temperature at discrete locations inside the cavity was obtained which followed evaluation of heat transfer coefficient and Rayleigh number. The thermal and flow analysis in 3-D was based on the standard k-ɛ turbulence model and implemented using CFD software Fluent 6.3. The spatial distribution for temperature, velocity and turbulent viscosity are determined and analyzed in the perspective of experimental observations. The experimentally determined ranges of Rayleigh number, Nusselt number and heat transfer coefficient are 1.66 × 1011-7.1 × 1011, 185.94-243.31 and 4.88-6.83 W/m2 K, respectively. The observed maximum difference between the experimental and numerical values for heat transfer coefficient and Nusselt number are 10.8 and 14 % respectively.

  5. BV analysis of tachyon fluctuation around multi-brane solutions in cubic string field theory

    NASA Astrophysics Data System (ADS)

    Hata, Hiroyuki

    2016-05-01

    We study whether the tachyon mode exists as a physical fluctuation on the 2-brane solution and on the tachyon vacuum solution in cubic open string field theory. Our analysis is based on the Batalin-Vilkovisky formalism. We first construct a set of six string states which corresponds to the set of fields and anti-fields containing the tachyon field. Whether the tachyon field can exist as a physical fluctuation is determined by the 6 × 6 matrix defining the anti-bracket in the present sector. If the matrix is degenerate/non-degenerate, the tachyon field is physical/unphysical. Calculations for the pure-gauge type solutions in the framework of the KBc algebra and using the K ɛ -regularization lead to the expected results. Namely, the matrix for the anti-bracket is degenerate/non-degenerate in the case of the 2-brane/tachyon-vacuum solution. Our analysis is not complete, in particular, in that we have not identified the four-fold degeneracy of tachyon fluctuation on the 2-brane solution, and moreover that the present six states do not satisfy the hermiticity condition.

  6. The compressibility of cubic white, orthorhombic black and rhombohedral black phosphorus

    SciTech Connect

    Clark, S; Zaug, J M

    2009-06-05

    The effect of pressure on the crystal structure of white phosphorus has been studied up to 22.4 GPa. The {alpha} phase was found to transform into the {alpha}' phase at 0.87 {+-} 0.04 GPa with a volume change of 0.1 {+-} 0.3 cc/mol. A fit of a second order Birch-Murghanan equation to the data gave Vo = 16.94 {+-} 0.08 cc/mol and K{sub o} = 6.7 {+-} 0.5 GPa for the {alpha} phase and Vo = 16.4 {+-} 0.1 cc/mol and K{sub o} = 9.1 {+-} 0.3 GPa for the {alpha}' phase. The {alpha}' phase was found to transform to the A17 phase of black phosphorus at 2.68 {+-} 0.34 GPa and then with increasing pressure to the A7 and then simple cubic phase of black phosphorus. A fit of a second order Birch-Murnaghan equation to our orthorhombic and rhombohedral black phosphorus data gave Vo = 11.43 {+-} 0.02 cc/mol and K{sub o} = 34.7 {+-} 0.5 GPa for the A17 phase and Vo = 9.62 {+-} 0.01 cc/mol and K{sub o} = 65.0 {+-} 0.6 GPa for the A7 phase.

  7. Universal magnetic behavior the electron-doped SrMnO3 cubic perovskite

    NASA Astrophysics Data System (ADS)

    Kolesnik, S.; Dabrowski, B.; Chmaissem, O.

    2009-03-01

    SrMnO3 is the end member of a widely explored family of colossal magnetoresistive manganites RxSr1-xMnO3 (R=rare earth elements). Low-level R^3+ substitutions change the antiferromagnetic order from G-type in cubic SrMnO3 to C-type in tetragonal RxSr1-xMnO3 through first-order resistive and structural transitions. From the magnetization, transport, and neutron diffraction experiments we observe that a similar change can be induced by B-site substitutions in SrMn1-xMxO3 (M=Ru^5+,Mo^6+) both generating Mn^3+ in the Mn^4+ matrix. For both A-site and B-site substitutions, the N'eel temperature is dependent on the Mn^3+ concentration in a universal way. These observations reveal that the magnetic and electronic properties of low-level substituted SrMnO3 are controlled by the band filling throughout the increasing role of local distortions of Mn^3+O6 octahedra changing from randomly diluted to cooperative character of the entire lattice. Work at NIU was supported by the NSF (DMR-0706610) and at ANL by the U.S. DOE under contract No. DE-AC02-06CH11357.

  8. Use of the Primitive Unit Cell in Understanding Subtle Features of the Cubic Closest-Packed Structure

    ERIC Educational Resources Information Center

    Hawkins, John A.; Rittenhouse, Jeffrey L.; Soper, Linda M.; Rittenhouse, Robert C.

    2008-01-01

    One of the most important crystal structures adopted by metals is characterized by the "abcabc"...stacking of close-packed layers. This structure is commonly referred to in textbooks as the cubic close-packed (ccp) or face-centered cubic (fcc) structure, since the entire lattice can be generated by replication of a face-centered cubic unit cell…

  9. Superconducting and structural properties of {delta}-MoC{sub 0.681} cubic molybdenum carbide phase

    SciTech Connect

    Sathish, C.I.; Guo, Yanfeng; Wang, Xia; Tsujimoto, Yoshihiro; Li, Jun; Zhang, Shoubao; Matsushita, Yoshitaka; Shi, Youguo; Tian, Huanfang; Yang, Huaixin; Li, Jianqi; Yamaura, Kazunari

    2012-12-15

    The superconducting and lattice properties of {delta}-MoC{sub 0.681} were studied by electromagnetic measurements, synchrotron X-ray diffraction, neutron diffraction, and electron diffraction. The superconducting properties (T{sub c}=12 K) of {delta}-MoC{sub 0.681} were well characterized by a weak coupling model. The carbon vacancies present in the host cubic structure were found to be robust, although the material was synthesized from stoichiometric carbon and Mo powder under a high-pressure of 6 GPa. A thermodynamically-stable structure with ordered vacancies did not account for the robust features of {delta}-MoC{sub 0.681} since the vacancies are unlikely to be ordered in long range in the host structure. A model based on inherent phonon instability theoretically predicted for a stoichiometric MoC phase might be responsible for the robust features of {delta}-MoC{sub 0.681}. - Graphical Abstract: The cubic molybdenum carbide shows an excellent superconductivity with robust carbon vacancies. Inherent phonon instability theoretically predicted for a stoichiometric MoC phase might be responsible for the vacancies rather than a thermodynamically-stable structure with vacancies ordering. Highlights: Black-Right-Pointing-Pointer The 12 K superconductivity is well characterized by a weakly coupling model. Black-Right-Pointing-Pointer Carbon vacancies are robust and disordered in the cubic host structure. Black-Right-Pointing-Pointer Inherent phonon instability might be responsible for the robust carbon vacancies in {delta}-MoC{sub 0.681}.

  10. Surface charges and optical characteristic of colloidal cubic SiC nanocrystals

    PubMed Central

    2011-01-01

    Colloidal cubic silicon carbide (SiC) nanocrystals with an average diameter of 4.4 nm have been fabricated by anisotropic wet chemical etching of microsized cubic SiC powder. Fourier transform infrared spectra show that these cubic SiC nanocrystals contain carboxylic acid, SiH, CH, and CHx groups. UV/Vis absorption and photoluminescence (PL) spectroscopy clearly indicate that water and ethanol colloidal suspensions of the as-fabricated colloidal samples exhibit strong and above band gap blue and blue-green emissions. The cubic SiC nanocrystals show different surface charges in water and ethanol solutions due to the interaction of water molecules with polar Si-terminated surfaces of cubic SiC nanocrystals. The results explain the distinctive optical characteristics of colloidal cubic SiC nanocrystals in water and ethanol, and reveal that quantum confinement and surface charges play a great role in determining the optical characteristics of colloidal cubic SiC nanocrystals. PMID:21762496

  11. Synthesis and crystal structure of cubic Ca16Si17N34.

    PubMed

    Hick, Sandra M; Miller, Mattheu I; Kaner, Richard B; Blair, Richard G

    2012-12-01

    Since the late 1960s, the exact structure of cubic calcium silicon nitride has been a source of debate. This paper offers evidence that the cubic phase CaSiN(2) described in the literature is actually Ca(16)Si(17)N(34). Presented here is a method for synthesizing single crystals of cubic-calcium silicon nitride from calcium nitride and elemental silicon under flowing nitrogen at 1500 °C. The colorless millimeter-sized crystals of Ca(16)Si(17)N(34) with a refractive index (n(25)) = 1.590 were found to be cubic (a = 14.8882 Å) and belong to the space group F43m (216). The synthesis of bulk, powdered cubic-Ca(16)Si(17)N(34) from calcium cyanamide and silicon is also discussed. Ca(16)Si(17)N(34) is a relatively air-stable refractory ceramic. In contrast to the orthorhombic phase of CaSiN(2), in which Ca(2+) sits in octahedral sites, this cubic phase has Ca(2+) in cubic sites that makes it an interesting host for new phosphors and gives rise to unique crystal field splitting. PMID:23157279

  12. Identification of silver cubic structures during ultrasonication of chitosan AgNO3 solution.

    PubMed

    Raghavendra, Gownolla Malegowd; Jung, Jeyoung; Kim, Dowan; Varaprasad, Kokkarachedu; Seo, Jongchul

    2016-11-01

    During ultrasonication of chitosan AgNO3 solution (10mM), silver cubic structures were identified along with other dispersed silver nanoparticles. Temperature influenced the formation of the cubic structures. Formation of the silver cubic structures occurred via initial formation of 'four petal flower-like' structures that underwent transformation to the "cubic morphology" in the latter stages. Aging of the reaction mixture led to formation of complete dendrites. These dendrites comprised a large quantity of silver nanoparticles. Upon repetition of the experiment with starch instead of chitosan, the identified silver cubic structures were completely absent, indicating that formation of the 'silver cubic structures' is dependent on the polysaccharide used. It is believed that the structural features of chitosan facilitate the formation of 'silver cubic structures' under ultrasonic conditions. The phenomena occurring during the experiments were evaluated via scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), ultraviolet-visible (UV-vis) spectra, transmission electron microscopy (TEM), and selected area electron diffraction (SAED) analysis. PMID:27516304

  13. Surface charges and optical characteristic of colloidal cubic SiC nanocrystals

    NASA Astrophysics Data System (ADS)

    Li, Yong; Chen, Changxin; Li, Jiang-Tao; Yang, Yun; Lin, Zhi-Ming

    2011-07-01

    Colloidal cubic silicon carbide (SiC) nanocrystals with an average diameter of 4.4 nm have been fabricated by anisotropic wet chemical etching of microsized cubic SiC powder. Fourier transform infrared spectra show that these cubic SiC nanocrystals contain carboxylic acid, SiH, CH, and CHx groups. UV/Vis absorption and photoluminescence (PL) spectroscopy clearly indicate that water and ethanol colloidal suspensions of the as-fabricated colloidal samples exhibit strong and above band gap blue and blue-green emissions. The cubic SiC nanocrystals show different surface charges in water and ethanol solutions due to the interaction of water molecules with polar Si-terminated surfaces of cubic SiC nanocrystals. The results explain the distinctive optical characteristics of colloidal cubic SiC nanocrystals in water and ethanol, and reveal that quantum confinement and surface charges play a great role in determining the optical characteristics of colloidal cubic SiC nanocrystals.

  14. Interaction between a percolation network and a cubic cavity

    NASA Astrophysics Data System (ADS)

    Mourzenko, Valeri; Adler, Pierre; Thovert, Jean Francois; Sangaré, Daouda

    2015-04-01

    The intersection between a percolating network of fractures modeled as polygons and a cubic cavity is important for the safe storage of wastes in a fractured medium. The cavities where the wastes are stored should not intersect the percolating network of fractures which may exist, or these cavities should not enable a fracture network to percolate. The fractures are hexagons inscribed in a circle of radius R which are uniformly distributed in space and isotropically oriented. Nfr is the number of fractures generated in a finite unit cell Omega of size L^3. The fracture density is conveniently represented by the dimensionless density rho ' which is the average number of intersections per fracture with the other fractures [1]. In addition, a cubic cavity C formed by six squares inscribed in a circle of radius Rs is randomly located in Omega. N spatially periodic networks are generated. Generally, N is equal to 500. Among these N networks, Np percolate and the cavity intersects one or more fractures in Nrc realizations; no fracture-cavity intersection occurs in Nnrc realizations. Moreover, when the network alone does not percolate (which occurs in Nnp realisations), the set composed by the hexagons and the cavity percolates Nnpc times. These quantities and the corresponding probabilities were systematically calculated as functions of L' = L/R , R' s = R_s/R and rho'. An important quantity is the conditional probability Pic that the percolating cluster intersects the cavity when it exists. It could be extrapolated to an infinite cell size L'. This conditional probability is an increasing function of rho' and of R' _s. The probability Pi that an object X intersects the fracture network with the density rho is given by the expression Pi=1-exp(- rho V) where V is the excluded volume for the object X and a fracture. This quantity is obtained for a cube. This prediction is in good agreement with the conditional probability Pic for large rho' or small R_s. However, Pi and

  15. An efficient algorithm for computing the roots of general quadratic, cubic and quartic equations

    NASA Astrophysics Data System (ADS)

    Mahmood, Munir; Hammad, Sali; Mahmood, Ibtihal

    2014-10-01

    While the solution to deriving the roots of the general quadratic equation is adequately covered in a typical classroom environment, the same is not true for the general cubic and quartic equations. To the best of our knowledge, we do not see the roots of the general cubic or quartic equation discussed in any typical algebra textbook at the undergraduate level. In this paper, we propose an efficient algorithm in order to calculate the roots of the general quadratic, cubic and quartic equations. Examples are given to demonstrate the usefulness of this proposed algorithm.

  16. Noise-to-signal transition of a Brownian particle in the cubic potential: I. general theory

    NASA Astrophysics Data System (ADS)

    Filip, Radim; Zemánek, Pavel

    2016-06-01

    The noise-to-signal transitions are very interesting processes in physics, as they might transform environmental noise to useful mechanical effects. We theoretically analyze stochastic noise-to-signal transition of overdamped Brownian motion of a particle in the cubic potential. The particle reaches thermal equilibrium with its environment in the quadratic potential which is suddenly swapped to the cubic potential. We predict a simultaneous increase of both the displacement and signal-to-noise ratio in the cubic potential for the position linearly powered by the temperature of the particle environment. The short-time analysis and numerical simulations fully confirm different dynamical regimes of this noise-to-signal transition.

  17. Chiral Surface Twists and Skyrmion Stability in Nanolayers of Cubic Helimagnets

    NASA Astrophysics Data System (ADS)

    Leonov, A. O.; Togawa, Y.; Monchesky, T. L.; Bogdanov, A. N.; Kishine, J.; Kousaka, Y.; Miyagawa, M.; Koyama, T.; Akimitsu, J.; Koyama, Ts.; Harada, K.; Mori, S.; McGrouther, D.; Lamb, R.; Krajnak, M.; McVitie, S.; Stamps, R. L.; Inoue, K.

    2016-08-01

    Theoretical analysis and Lorentz transmission electron microscopy (LTEM) investigations in an FeGe wedge demonstrate that chiral twists arising near the surfaces of noncentrosymmetric ferromagnets [Meynell et al., Phys. Rev. B 90, 014406 (2014)] provide a stabilization mechanism for magnetic Skyrmion lattices and helicoids in cubic helimagnet nanolayers. The magnetic phase diagram obtained for freestanding cubic helimagnet nanolayers shows that magnetization processes differ fundamentally from those in bulk cubic helimagnets and are characterized by the first-order transitions between modulated phases. LTEM investigations exhibit a series of hysteretic transformation processes among the modulated phases, which results in the formation of the multidomain patterns.

  18. Evidence of reaction rate influencing cubic and hexagonal phase formation process in CdS nanocrystals

    NASA Astrophysics Data System (ADS)

    Deka, Kuldeep; Kalita, M. P. C.

    2016-05-01

    CdS nanocrystals are synthesized by co-precipitation method using 2-mercaptoethanol (ME) as capping agent. Cubic, hexagonal and their mixture are obtained by varying the ME concentration. Lower (higher) ME concentration results in cubic (hexagonal) phase. The crystallite sizes are in the range 3-7 nm. Increase in ME concentration lead to lower reaction rate between Cd2+ and S2- of the precursors, and slower reaction rate is found to favor hexagonal phase formation over the cubic one in CdS nanocrystals. Role of reaction rate in the phase formation process provides a way to synthesize CdS nanocrystals in desired crystal phase.

  19. Chiral Surface Twists and Skyrmion Stability in Nanolayers of Cubic Helimagnets.

    PubMed

    Leonov, A O; Togawa, Y; Monchesky, T L; Bogdanov, A N; Kishine, J; Kousaka, Y; Miyagawa, M; Koyama, T; Akimitsu, J; Koyama, Ts; Harada, K; Mori, S; McGrouther, D; Lamb, R; Krajnak, M; McVitie, S; Stamps, R L; Inoue, K

    2016-08-19

    Theoretical analysis and Lorentz transmission electron microscopy (LTEM) investigations in an FeGe wedge demonstrate that chiral twists arising near the surfaces of noncentrosymmetric ferromagnets [Meynell et al., Phys. Rev. B 90, 014406 (2014)] provide a stabilization mechanism for magnetic Skyrmion lattices and helicoids in cubic helimagnet nanolayers. The magnetic phase diagram obtained for freestanding cubic helimagnet nanolayers shows that magnetization processes differ fundamentally from those in bulk cubic helimagnets and are characterized by the first-order transitions between modulated phases. LTEM investigations exhibit a series of hysteretic transformation processes among the modulated phases, which results in the formation of the multidomain patterns. PMID:27588877

  20. Voyager observations of O(+6) and other minor ions in the solar wind

    NASA Technical Reports Server (NTRS)

    Villanueva, Louis; Mcnutt, Ralph L., Jr.; Lazarus, Alan J.; Steinberg, John T.

    1994-01-01

    The plasma science (PLS) experiments on the Voyager 1 and 2 spacecraft began making measurements of the solar wind shortly after the two launches in the fall of 1977. In reviewing the data obtained prior to the Jupiter encounters in 1979, we have found that the large dynamic range of the PLS instrument generally allows a clean separation of signatures of minor ions (about 2.5% of the time) during a single instrument scan in energy per charge. The minor ions, most notably O(+6), are well separated from the protons and alpha particles during times when the solar wind Mach number (ratio of streaming speed to thermal speed) is greater than approximately 15. During the Earth to Jupiter cruise we find that the average ratio of alpha particle number density to that of oxygen is 66 +/- 7 (Voyager 1) and 71 +/- 17 (Voyager 2). These values are consistent with the value 75 +/- 20 inferred from the Ion Composition Instrument on ISEE 3 during the period spanning 1978 and 1982. We have inferred an average coronal temperature of (1.7 +/- 0.1) x 10(exp 6) K based on the ratio of O(+7) to O(+6) number densities. Our observations cover a period of increasing solar activity. During this time we have found that the alpha particle to proton number density ratio is increasing with the solar cycle, the oxygen to proton ratio increases, and the alpha particle to oxygen ratio remains relatively constant in time.

  1. Low-temperature formation of cubic β-PbF2: precursor-based synthesis and first-principles phase stability study.

    PubMed

    Erk, Christoph; Hammerschmidt, Lukas; Andrae, Dirk; Paulus, Beate; Schlecht, Sabine

    2011-04-01

    A precursor-based approach to the cubic β-phase of PbF(2) was developed and allowed the preparation of this high-temperature phase well below the temperature for transition from the orthorhombic α- to the cubic β-phase. The formation of β-PbF(2) from the molecular precursors Pb[Se(C(6)H(2)(CF(3))(3))](2) and Pb(C(6)H(2)(CF(3))(3))(2) is facilitated by the presence of several short PbF contacts in these molecules. The cubic form of PbF(2) was obtained as macroscopic crystals as well as nanoparticulate powder. Its formation at relatively low temperature suggested a theoretical re-investigation of the phase stabilities of the two polymorphs. The theoretical results from the Kohn-Sham density functional theory indicate that the energy content for the β-phase is slightly lower than the one for the α-phase, by 0.5-1.7 kJ mol(-1) depending on the density functional used (zero-point vibrational energy correction included). PMID:21336413

  2. Twinning of cubic diamond explains reported nanodiamond polymorphs

    NASA Astrophysics Data System (ADS)

    Németh, Péter; Garvie, Laurence A. J.; Buseck, Peter R.

    2015-12-01

    The unusual physical properties and formation conditions attributed to h-, i-, m-, and n-nanodiamond polymorphs has resulted in their receiving much attention in the materials and planetary science literature. Their identification is based on diffraction features that are absent in ordinary cubic (c-) diamond (space group: Fd-3m). We show, using ultra-high-resolution transmission electron microscope (HRTEM) images of natural and synthetic nanodiamonds, that the diffraction features attributed to the reported polymorphs are consistent with c-diamond containing abundant defects. Combinations of {113} reflection and <011> rotation twins produce HRTEM images and d-spacings that match those attributed to h-, i-, and m-diamond. The diagnostic features of n-diamond in TEM images can arise from thickness effects of c-diamonds. Our data and interpretations strongly suggest that the reported nanodiamond polymorphs are in fact twinned c-diamond. We also report a new type of twin (<11> rotational), which can give rise to grains with dodecagonal symmetry. Our results show that twins are widespread in diamond nanocrystals. A high density of twins could strongly influence their applications.

  3. Twinning of cubic diamond explains reported nanodiamond polymorphs.

    PubMed

    Németh, Péter; Garvie, Laurence A J; Buseck, Peter R

    2015-01-01

    The unusual physical properties and formation conditions attributed to h-, i-, m-, and n-nanodiamond polymorphs has resulted in their receiving much attention in the materials and planetary science literature. Their identification is based on diffraction features that are absent in ordinary cubic (c-) diamond (space group: Fd-3m). We show, using ultra-high-resolution transmission electron microscope (HRTEM) images of natural and synthetic nanodiamonds, that the diffraction features attributed to the reported polymorphs are consistent with c-diamond containing abundant defects. Combinations of {113} reflection and <011> rotation twins produce HRTEM images and d-spacings that match those attributed to h-, i-, and m-diamond. The diagnostic features of n-diamond in TEM images can arise from thickness effects of c-diamonds. Our data and interpretations strongly suggest that the reported nanodiamond polymorphs are in fact twinned c-diamond. We also report a new type of twin (<121> rotational), which can give rise to grains with dodecagonal symmetry. Our results show that twins are widespread in diamond nanocrystals. A high density of twins could strongly influence their applications. PMID:26671288

  4. Liquid water in the domain of cubic crystalline ice Ic

    NASA Technical Reports Server (NTRS)

    Jenniskens, P.; Banham, S. F.; Blake, D. F.; McCoustra, M. R.

    1997-01-01

    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.

  5. Serial femtosecond crystallography of soluble proteins in lipidic cubic phase

    SciTech Connect

    Fromme, Raimund; Ishchenko, Andrii; Metz, Markus; Chowdhury, Shatabdi Roy; Basu, Shibom; Boutet, Sébastien; Fromme, Petra; White, Thomas A.; Barty, Anton; Spence, John C. H.; Weierstall, Uwe; Liu, Wei; Cherezov, Vadim

    2015-08-04

    Serial femtosecond crystallography (SFX) at X-ray free-electron lasers (XFELs) enables high-resolution protein structure determination using micrometre-sized crystals at room temperature with minimal effects from radiation damage. SFX requires a steady supply of microcrystals intersecting the XFEL beam at random orientations. An LCP–SFX method has recently been introduced in which microcrystals of membrane proteins are grown and delivered for SFX data collection inside a gel-like membrane-mimetic matrix, known as lipidic cubic phase (LCP), using a special LCP microextrusion injector. Here, it is demonstrated that LCP can also be used as a suitable carrier medium for microcrystals of soluble proteins, enabling a dramatic reduction in the amount of crystallized protein required for data collection compared with crystals delivered by liquid injectors. High-quality LCP–SFX data sets were collected for two soluble proteins, lysozyme and phycocyanin, using less than 0.1 mg of each protein.

  6. Femtosecond crystallography of membrane proteins in the lipidic cubic phase

    PubMed Central

    Liu, Wei; Wacker, Daniel; Wang, Chong; Abola, Enrique; Cherezov, Vadim

    2014-01-01

    Despite recent technological advances in heterologous expression, stabilization and crystallization of membrane proteins (MPs), their structural studies remain difficult and require new transformative approaches. During the past two years, crystallization in lipidic cubic phase (LCP) has started gaining a widespread acceptance, owing to the spectacular success in high-resolution structure determination of G protein-coupled receptors (GPCRs) and to the introduction of commercial instrumentation, tools and protocols. The recent appearance of X-ray free-electron lasers (XFELs) has enabled structure determination from substantially smaller crystals than previously possible with minimal effects of radiation damage, offering new exciting opportunities in structural biology. The unique properties of LCP material have been exploited to develop special protocols and devices that have established a new method of serial femtosecond crystallography of MPs in LCP (LCP-SFX). In this method, microcrystals are generated in LCP and streamed continuously inside the same media across the intersection with a pulsed XFEL beam at a flow rate that can be adjusted to minimize sample consumption. Pioneering studies that yielded the first room temperature GPCR structures, using a few hundred micrograms of purified protein, validate the LCP-SFX approach and make it attractive for structure determination of difficult-to-crystallize MPs and their complexes with interacting partners. Together with the potential of femtosecond data acquisition to interrogate unstable intermediate functional states of MPs, LCP-SFX holds promise to advance our understanding of this biomedically important class of proteins. PMID:24914147

  7. Random walks on cubic lattices with bond disorder

    SciTech Connect

    Ernst, M.H.; van Velthoven, P.F.J.

    1986-12-01

    The authors consider diffusive systems with static disorder, such as Lorentz gases, lattice percolation, ants in a labyrinth, termite problems, random resistor networks, etc. In the case of diluted randomness the authors can apply the methods of kinetic theory to obtain systematic expansions of dc and ac transport properties in powers of the impurity concentration c. The method is applied to a hopping model on a d-dimensional cubic lattice having two types of bonds with conductivity sigma and sigma/sub 0/ = 1, with concentrations c and 1-c, respectively. For the square lattice the authors explicitly calculate the diffusion coefficient D(c,sigma) as a function of c, to O(c/sup 2/) terms included for different ratios of the bond conductivity sigma. The probability of return at long times is given by P/sub 0/(t) approx. (4..pi..D(c,sigma)t)/sup -d/2/, which is determined by the diffusion coefficient of the disordered system.

  8. Twinning of cubic diamond explains reported nanodiamond polymorphs

    PubMed Central

    Németh, Péter; Garvie, Laurence A. J.; Buseck, Peter R.

    2015-01-01

    The unusual physical properties and formation conditions attributed to h-, i-, m-, and n-nanodiamond polymorphs has resulted in their receiving much attention in the materials and planetary science literature. Their identification is based on diffraction features that are absent in ordinary cubic (c-) diamond (space group: Fd-3m). We show, using ultra-high-resolution transmission electron microscope (HRTEM) images of natural and synthetic nanodiamonds, that the diffraction features attributed to the reported polymorphs are consistent with c-diamond containing abundant defects. Combinations of {113} reflection and <011> rotation twins produce HRTEM images and d-spacings that match those attributed to h-, i-, and m-diamond. The diagnostic features of n-diamond in TEM images can arise from thickness effects of c-diamonds. Our data and interpretations strongly suggest that the reported nanodiamond polymorphs are in fact twinned c-diamond. We also report a new type of twin (<11> rotational), which can give rise to grains with dodecagonal symmetry. Our results show that twins are widespread in diamond nanocrystals. A high density of twins could strongly influence their applications. PMID:26671288

  9. Mechanical properties for irradiated face-centred cubic nanocrystalline metals

    PubMed Central

    Xiao, X. Z.; Song, D. K.; Chu, H. J.; Xue, J. M.; Duan, H. L.

    2015-01-01

    In this paper, a self-consistent plasticity theory is proposed to model the mechanical behaviours of irradiated face-centred cubic nanocrystalline metals. At the grain level, a tensorial crystal model with both irradiation and grain size effects is applied for the grain interior (GI), whereas both grain boundary (GB) sliding with irradiation effect and GB diffusion are considered in modelling the behaviours of GBs. The elastic-viscoplastic self-consistent method with considering grain size distribution is developed to transit the microscopic behaviour of individual grains to the macroscopic properties of nanocrystals (NCs). The proposed theory is applied to model the mechanical properties of irradiated NC copper, and the feasibility and efficiency have been validated by comparing with experimental data. Numerical results show that: (i) irradiation-induced defects can lead to irradiation hardening in the GIs, but the hardening effect decreases with the grain size due to the increasing absorption of defects by GBs. Meanwhile, the absorbed defects would make the GBs softer than the unirradiated case. (ii) There exists a critical grain size for irradiated NC metals, which separates the grain size into the irradiation hardening dominant region (above the critical size) and irradiation softening dominant region (below the critical size). (iii) The distribution of grain size has a significant influence on the mechanical behaviours of both irradiated and unirradiated NCs. The proposed model can offer a valid theoretical foundation to study the irradiation effect on NC materials. PMID:27547091

  10. Photoluminescence and electronic transitions in cubic silicon nitride

    PubMed Central

    Museur, Luc; Zerr, Andreas; Kanaev, Andrei

    2016-01-01

    A spectroscopic study of cubic silicon nitride (γ-Si3N4) at cryogenic temperatures of 8 K in the near IR - VUV range of spectra with synchrotron radiation excitation provided the first experimental evidence of direct electronic transitions in this material. The observed photoluminescence (PL) bands were assigned to excitons and excited and centers formed after the electron capture by neutral structural defects. The excitons are weakly quenched on neutral and strongly on charged defects. The fundamental band-gap energy of 5.05 ± 0.05 eV and strong free exciton binding energy ~0.65 eV were determined. The latter value suggests a high efficiency of the electric power transformation in light in defect-free crystals. Combined with a very high hardness and exceptional thermal stability in air, our results indicate that γ-Si3N4 has a potential for fabrication of robust and efficient photonic emitters. PMID:26725937

  11. Serial femtosecond crystallography of soluble proteins in lipidic cubic phase

    PubMed Central

    Fromme, Raimund; Ishchenko, Andrii; Metz, Markus; Chowdhury, Shatabdi Roy; Basu, Shibom; Boutet, Sébastien; Fromme, Petra; White, Thomas A.; Barty, Anton; Spence, John C. H.; Weierstall, Uwe; Liu, Wei; Cherezov, Vadim

    2015-01-01

    Serial femtosecond crystallography (SFX) at X-ray free-electron lasers (XFELs) enables high-resolution protein structure determination using micrometre-sized crystals at room temperature with minimal effects from radiation damage. SFX requires a steady supply of microcrystals intersecting the XFEL beam at random orientations. An LCP–SFX method has recently been introduced in which microcrystals of membrane proteins are grown and delivered for SFX data collection inside a gel-like membrane-mimetic matrix, known as lipidic cubic phase (LCP), using a special LCP microextrusion injector. Here, it is demonstrated that LCP can also be used as a suitable carrier medium for microcrystals of soluble proteins, enabling a dramatic reduction in the amount of crystallized protein required for data collection compared with crystals delivered by liquid injectors. High-quality LCP–SFX data sets were collected for two soluble proteins, lysozyme and phycocyanin, using less than 0.1 mg of each protein. PMID:26306196

  12. Electron affinity of cubic boron nitride terminated with vanadium oxide

    NASA Astrophysics Data System (ADS)

    Yang, Yu; Sun, Tianyin; Shammas, Joseph; Kaur, Manpuneet; Hao, Mei; Nemanich, Robert J.

    2015-10-01

    A thermally stable negative electron affinity (NEA) for a cubic boron nitride (c-BN) surface with vanadium-oxide-termination is achieved, and its electronic structure was analyzed with in-situ photoelectron spectroscopy. The c-BN films were prepared by electron cyclotron resonance plasma-enhanced chemical vapor deposition employing BF3 and N2 as precursors. Vanadium layers of ˜0.1 and 0.5 nm thickness were deposited on the c-BN surface in an electron beam deposition system. Oxidation of the metal layer was achieved by an oxygen plasma treatment. After 650 °C thermal annealing, the vanadium oxide on the c-BN surface was determined to be VO2, and the surfaces were found to be thermally stable, exhibiting an NEA. In comparison, the oxygen-terminated c-BN surface, where B2O3 was detected, showed a positive electron affinity of ˜1.2 eV. The B2O3 evidently acts as a negatively charged layer introducing a surface dipole directed into the c-BN. Through the interaction of VO2 with the B2O3 layer, a B-O-V layer structure would contribute a dipole between the O and V layers with the positive side facing vacuum. The lower enthalpy of formation for B2O3 is favorable for the formation of the B-O-V layer structure, which provides a thermally stable surface dipole and an NEA surface.

  13. Taylor line swimming in microchannels and cubic lattices of obstacles.

    PubMed

    Münch, Jan L; Alizadehrad, Davod; Babu, Sujin B; Stark, Holger

    2016-09-21

    Microorganisms naturally move in microstructured fluids. Using the simulation method of multi-particle collision dynamics, we study in two dimensions an undulatory Taylor line swimming in a microchannel and in a cubic lattice of obstacles, which represent simple forms of a microstructured environment. In the microchannel the Taylor line swims at an acute angle along a channel wall with a clearly enhanced swimming speed due to hydrodynamic interactions with the bounding wall. While in a dilute obstacle lattice swimming speed is also enhanced, a dense obstacle lattice gives rise to geometric swimming. This new type of swimming is characterized by a drastically increased swimming speed. Since the Taylor line has to fit into the free space of the obstacle lattice, the swimming speed is close to the phase velocity of the bending wave traveling along the Taylor line. While adjusting its swimming motion within the lattice, the Taylor line chooses a specific swimming direction, which we classify by a lattice vector. When plotting the swimming velocity versus the magnitude of the lattice vector, all our data collapse on a single master curve. Finally, we also report more complex trajectories within the obstacle lattice. PMID:27510576

  14. An analytic reconstruction method for PET based on cubic splines

    NASA Astrophysics Data System (ADS)

    Kastis, George A.; Kyriakopoulou, Dimitra; Fokas, Athanasios S.

    2014-03-01

    PET imaging is an important nuclear medicine modality that measures in vivo distribution of imaging agents labeled with positron-emitting radionuclides. Image reconstruction is an essential component in tomographic medical imaging. In this study, we present the mathematical formulation and an improved numerical implementation of an analytic, 2D, reconstruction method called SRT, Spline Reconstruction Technique. This technique is based on the numerical evaluation of the Hilbert transform of the sinogram via an approximation in terms of 'custom made' cubic splines. It also imposes sinogram thresholding which restricts reconstruction only within object pixels. Furthermore, by utilizing certain symmetries it achieves a reconstruction time similar to that of FBP. We have implemented SRT in the software library called STIR and have evaluated this method using simulated PET data. We present reconstructed images from several phantoms. Sinograms have been generated at various Poison noise levels and 20 realizations of noise have been created at each level. In addition to visual comparisons of the reconstructed images, the contrast has been determined as a function of noise level. Further analysis includes the creation of line profiles when necessary, to determine resolution. Numerical simulations suggest that the SRT algorithm produces fast and accurate reconstructions at realistic noise levels. The contrast is over 95% in all phantoms examined and is independent of noise level.

  15. Fast RPA and GW calculations: cubic system size scaling

    NASA Astrophysics Data System (ADS)

    Kresse, Georg

    The random phase approximation (RPA) to the correlation energy and the related GW approximation are among the most promising methods to obtain accurate correlation energy differences and QP energies from diagrammatic perturbation theory at reasonable computational cost. The calculations are, however, usually one to two orders of magnitude more demanding than conventional density functional theory calculations. Here, we show that a cubic system size scaling can be readily obtained reducing the computation time by one to two orders of magnitude for large systems. Furthermore, the scaling with respect to the number of k points used to sample the Brillouin zone can be reduced to linear order. In combination, this allows accurate and very well-converged single-point RPA and GW calculations, with a time complexity that is roughly on par or better than for self-consistent Hartree-Fock and hybrid-functional calculations. Furthermore, the talk discusses the relation between the RPA correlation energy and the GW approximation: the self-energy is the derivative of the RPA correlation energy with respect to the Green's function. The calculated self-energy can be used to compute QP-energies in the GW approximation, any first derivative of the total energy, as well as corrections to the correlation energy from the changes of the charge density when switching from DFT to a many-body body description (GW singles energy contribution).

  16. Serial femtosecond crystallography of soluble proteins in lipidic cubic phase.

    PubMed

    Fromme, Raimund; Ishchenko, Andrii; Metz, Markus; Chowdhury, Shatabdi Roy; Basu, Shibom; Boutet, Sébastien; Fromme, Petra; White, Thomas A; Barty, Anton; Spence, John C H; Weierstall, Uwe; Liu, Wei; Cherezov, Vadim

    2015-09-01

    Serial femtosecond crystallography (SFX) at X-ray free-electron lasers (XFELs) enables high-resolution protein structure determination using micrometre-sized crystals at room temperature with minimal effects from radiation damage. SFX requires a steady supply of microcrystals intersecting the XFEL beam at random orientations. An LCP-SFX method has recently been introduced in which microcrystals of membrane proteins are grown and delivered for SFX data collection inside a gel-like membrane-mimetic matrix, known as lipidic cubic phase (LCP), using a special LCP microextrusion injector. Here, it is demonstrated that LCP can also be used as a suitable carrier medium for microcrystals of soluble proteins, enabling a dramatic reduction in the amount of crystallized protein required for data collection compared with crystals delivered by liquid injectors. High-quality LCP-SFX data sets were collected for two soluble proteins, lysozyme and phycocyanin, using less than 0.1 mg of each protein. PMID:26306196

  17. The deformation texture of rolled ribbons of copper-based alloys as a condition of producing a sharp cubic texture upon recrystallization

    NASA Astrophysics Data System (ADS)

    Gervas'eva, I. V.; Rodionov, D. P.; Khlebnikova, Yu. V.

    2015-07-01

    It has been shown that a specific quantitative relationship of main textural components after cold deformation (by rolling to 98.6-99%) of copper alloys determines the possibility of producing a sharp cubic texture in the ribbons after subsequent recrystallization annealing. The binary alloys of copper with nickel (up to 40 at %) and of copper with additions of iron and chromium correspond to this criterion. It has been found that the optimum deformation texture can be created in some ternary copper-nickel alloys with addition of Cr, Fe or Mn. It has been shown that the analysis of the component composition of deformation textures using the orientation distribution function can yield more precise predictions than the stacking fault energy values, as well as make it possible to obtain a cubic texture upon subsequent recrystallization.

  18. Stabilization of cubic lithium-stuffed garnets of the type “Li7La3Zr2O12” by addition of gallium

    NASA Astrophysics Data System (ADS)

    El Shinawi, Hany; Janek, Jürgen

    2013-03-01

    Cubic lithium-stuffed garnets of the type Li7La3Zr2O12 have been successfully stabilized by incorporation of gallium. The materials have been prepared by a sol-gel procedure with final calcination at 1085 °C for 6 h. Under the applied synthesis conditions, 0.3 mole of gallium ions (per mole of Li7La3Zr2O12) were sufficient to fully stabilize the cubic garnet-type phase. Increasing the fraction of gallium led to significant improvement of sinterability and lithium ion conductivity. Excess gallium ions, in the form of LiGaO2, act as a sintering aid and reside exclusively at the grain boundaries. The gallium-modified garnets showed conductivities up to 5.4 × 10-4 S cm-1 at 20 °C, and activation energies in the range 0.32-0.37 eV.

  19. HST eclipse mapping of dwarf nova OY Carinae in quiescence: An 'Fe II curtain' with Mach approx. = 6 velocity dispersion veils the white dwarf

    NASA Technical Reports Server (NTRS)

    Horne, Keith; Marsh, T. R.; Cheng, F. H.; Hubeny, Ivan; Lanz, Theirry

    1994-01-01

    Hubble Space Telescope (HST) observations of the eclipsing dwarf nova OY Car in its quiescent state are used to isolate the ultraviolet spectrum (1150-2500 A at 9.2 A Full Width at Half Maximum (FWHM) resolution) of the white dwarf, the accretion disk, and the bright spot. The white dwarf spectrum has a Stark-broadened photospheric L(alpha) absorption, but is veiled by a forest of blended Fe II features that we attribute to absorption by intervening disk material. A fit gives T(sub w) approx. = 16.5 x 10(exp 3) K for the white dwarf with a solar-abundance, log g = 8 model atmosphere, and T approx. = 10(exp 4) K, n(sub e) approx. = 10(exp 13)/cu cm, N(sub H) approx. = 10(exp 22) sq cm, and velocity dispersion delta V approx. = 60 km/s for the veil of homogeneous solar-abundance local thermodynamic equilibrium (LTE) gas. The veil parameters probably measure characteristic physical conditions in the quiescent accretion disk or its chromosphere. The large velocity dispersion is essential for a good fit; it lowers (chi square)/778 from 22 to 4. Keplerian shear can produce the velocity dispersion if the veiling gas is located at R approx. = 5 R(sub W) with (delta R)/R approx. = 0.3, but this model leaves an unobscured view to the upper hemisphere of the white dwarf, incompatible with absorptions that are up to 80% deep. The veiling gas may be in the upper atmosphere of the disk near its outer rim, but we then require supersonic (Mach approx. = 6) but sub-Keplerian (delta V/V(sub Kep) approx. = 0.07) velocity disturbances in this region to produce both the observed radial velocity dispersion and vertical motions sufficient to elevate the gas to z/R = cos i = 0.12. Such motions might be driven by the gas stream, since it may take several Kepler periods to reestablish the disk's vertical hydrostatic equilibrium. The temperature and column density of the gas we see as Fe II absorption in the ultraviolet are similar to what is required to produce the strong Balmer jump and

  20. Synthesis of nano-scale fast ion conducting cubic Li7La3Zr2O12

    NASA Astrophysics Data System (ADS)

    Sakamoto, Jeff; Rangasamy, Ezhiylmurugan; Kim, Hyunjoung; Kim, Yunsung; Wolfenstine, Jeff

    2013-10-01

    A solution-based process was investigated for synthesizing cubic Li7La3Zr2O12 (LLZO), which is known to exhibit the unprecedented combination of fast ionic conductivity, and stability in air and against Li. Sol-gel chemistry was developed to prepare solid metal-oxide networks consisting of 10 nm cross-links that formed the cubic LLZO phase at 600 ° C. Sol-gel LLZO powders were sintered into 96% dense pellets using an induction hot press that applied pressure while heating. After sintering, the average LLZO grain size was 260 nm, which is 13 times smaller compared to LLZO prepared using a solid-state technique. The total ionic conductivity was 0.4 mS cm-1 at 298 K, which is the same as solid-state synthesized LLZO. Interestingly, despite the same room temperature conductivity, the sol-gel LLZO total activation energy is 0.41 eV, which 1.6 times higher than that observed in solid-state LLZO (0.26 eV). We believe the nano-scale grain boundaries give rise to unique transport phenomena that are more sensitive to temperature when compared to the conventional solid-state LLZO.

  1. Synthesis of nano-scale fast ion conducting cubic Li7La3Zr2O12.

    PubMed

    Sakamoto, Jeff; Rangasamy, Ezhiylmurugan; Kim, Hyunjoung; Kim, Yunsung; Wolfenstine, Jeff

    2013-10-25

    A solution-based process was investigated for synthesizing cubic Li7La3Zr2O12 (LLZO), which is known to exhibit the unprecedented combination of fast ionic conductivity, and stability in air and against Li. Sol-gel chemistry was developed to prepare solid metal-oxide networks consisting of 10 nm cross-links that formed the cubic LLZO phase at 600 ° C. Sol-gel LLZO powders were sintered into 96% dense pellets using an induction hot press that applied pressure while heating. After sintering, the average LLZO grain size was 260 nm, which is 13 times smaller compared to LLZO prepared using a solid-state technique. The total ionic conductivity was 0.4 mS cm(-1) at 298 K, which is the same as solid-state synthesized LLZO. Interestingly, despite the same room temperature conductivity, the sol-gel LLZO total activation energy is 0.41 eV, which 1.6 times higher than that observed in solid-state LLZO (0.26 eV). We believe the nano-scale grain boundaries give rise to unique transport phenomena that are more sensitive to temperature when compared to the conventional solid-state LLZO. PMID:24067448

  2. Compositionally-tuned epitaxial cubic MgxZn1-xO on Si(100) for deep ultraviolet photodetectors

    NASA Astrophysics Data System (ADS)

    Yang, W.; Hullavarad, S. S.; Nagaraj, B.; Takeuchi, I.; Sharma, R. P.; Venkatesan, T.; Vispute, R. D.; Shen, H.

    2003-05-01

    We report on the epitaxial growth of wide-band-gap cubic-phase MgxZn1-xO thin films on Si(100) by pulsed-laser deposition and fabrication of oxide-semiconductor-based ultraviolet photodetectors. The challenges of large lattice and thermal expansion mismatch between Si and MgxZn1-xO have been overcome by using a thin SrTiO3 buffer layer. The heteroepitaxy of cubic-phase MgxZn1-xO on Si was established with epitaxial relationship of MgxZn1-xO(100)//SrTiO3(100)//Si(100) and MgxZn1-xO[100]//SrTiO3[100]//Si[110]. The minimum yield of the Rutherford backscattering ion channeling in MgxZn1-xO layer was only 4%, indicating good crystalline quality of the film. Smooth surface morphology with rms roughness of 0.6 nm was observed using atomic force microscopy. Photodetectors fabricated on Mg0.68Zn0.32O/SrTiO3/Si show peak photoresponse at 225 nm, which is in the deep UV region.

  3. Crystal structures of orthorhombic, hexagonal, and cubic compounds of the Sm{sub (x)}Yb{sub (2−x)}TiO{sub 5} series

    SciTech Connect

    Aughterson, Robert D.; Lumpkin, Gregory R.; Reyes, Massey de los; Sharma, Neeraj; Ling, Christopher D.; Gault, Baptiste; Smith, Katherine L.; Avdeev, Maxim; Cairney, Julie M.

    2014-05-01

    A series of single phase compounds with nominal stoichiometry Sm{sub (x)}Yb{sub (2−x)}TiO{sub 5} (x=2, 1.4, 1, 0.6, and 0) have been successfully fabricated to generate a range of crystal structures covering the most common polymorphs previously discovered in the Ln{sub 2}TiO{sub 5} series (Ln=lanthanides and yttrium). Four of the five samples have not been previously fabricated in bulk, single phase form so their crystal structures are refined and detailed using powder synchrotron and single crystal x-ray diffraction, neutron diffraction and transmission electron microscopy. Based on the phase information from diffraction data, there are four crystal structure types in this series; orthorhombic Pnma, hexagonal P6{sub 3}/mmc, cubic (pyrochlore-like) Fd-3m and cubic (fluorite-like) Fm-3m. The cubic materials show modulated structures with variation between long and short range ordering and the variety of diffraction techniques were used to describe these complex crystal structure types. - Graphical abstract: A high resolution image of the compound Sm{sub 0.6}Yb{sub 1.4}TiO{sub 5} showing contrast from lattice fringes and the corresponding fast Fourier transform (FFT) of the HREM image with pyrochlore related diffraction spots marked “P” and fluorite marked “F”. The crystal is oriented down the [1 1 0] zone axis based on the Fd-3m structure. The ideal crystal structure (no vacancies) of the cubic, pyrochlore-like (Sm{sub 0.6}Yb{sub 1.4}TiO{sub 5}). - Highlights: • First fabrication of bulk single-phase material with stoichiometry Sm{sub 2}TiO{sub 5}. • Systematic study of crystal structure types within Ln{sub 2}TiO{sub 5} series (Ln=lanthanides). • A novel technique using IFFT of HREM images to study cubic structures.

  4. Blocking temperature of interacting magnetic nanoparticles with uniaxial and cubic anisotropies from Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Russier, V.

    2016-07-01

    The low temperature behavior of densely packed interacting spherical single domain nanoparticles (MNP) is investigated by Monte Carlo simulations in the framework of an effective one spin model. The particles are distributed through a hard sphere like distribution with periodic boundary conditions and interact through the dipole dipole interaction (DDI) with an anisotropy energy including both cubic and uniaxial symmetry components. The cubic component is shown to play a sizable role on the value of the blocking temperature Tb only when the MNP easy axes are parallel to the cubic easy direction ([111] direction for a negative cubic anisotropy constant). The nature of the collective low temperature state, either ferromagnetic or spin glass like, is found to depend on the ratio of the anisotropy to the dipolar energies characterizing partly the disorder in the system.

  5. An Easily Constructed Model of a Coordination Polyhedron that Represents the Cubic Closest-Packed Structure.

    ERIC Educational Resources Information Center

    Yamana, Shukichi

    1987-01-01

    Illustrates the 18 steps to the development of a model of a coordination polyhedron that represents the cubic closest-packed structure. Uses a sealed, empty envelope in developing the model in teaching about stereochemistry. (TW)

  6. Cubic PdNP-based air-breathing cathodes integrated in glucose hybrid biofuel cells

    NASA Astrophysics Data System (ADS)

    Faggion Junior, D.; Haddad, R.; Giroud, F.; Holzinger, M.; Maduro de Campos, C. E.; Acuña, J. J. S.; Domingos, J. B.; Cosnier, S.

    2016-05-01

    Cubic Pd nanoparticles (PdNPs) were synthesized using ascorbic acid as a reducing agent and were evaluated for the catalytic oxygen reduction reaction. PdNPs were confined with multiwalled carbon nanotube (MWCNT) dispersions to form black suspensions and these inks were dropcast onto glassy carbon electrodes. Different nanoparticle sizes were synthesized and investigated upon oxygen reduction capacities (onset potential and electrocatalytic current densities) under O2 saturated conditions at varying pH values. Strong evidence of O2 diffusion limitation was demonstrated. In order to overcome oxygen concentration and diffusion limitations in solution, we used a gas diffusion layer to create a PdNP-based air-breathing cathode, which delivered -1.5 mA cm-2 at 0.0 V with an onset potential of 0.4 V. This air-breathing cathode was combined with a specially designed phenanthrolinequinone/glucose dehydrogenase-based anode to form a complete glucose/O2 hybrid bio-fuel cell providing an open circuit voltage of 0.554 V and delivering a maximal power output of 184 +/- 21 μW cm-2 at 0.19 V and pH 7.0.Cubic Pd nanoparticles (PdNPs) were synthesized using ascorbic acid as a reducing agent and were evaluated for the catalytic oxygen reduction reaction. PdNPs were confined with multiwalled carbon nanotube (MWCNT) dispersions to form black suspensions and these inks were dropcast onto glassy carbon electrodes. Different nanoparticle sizes were synthesized and investigated upon oxygen reduction capacities (onset potential and electrocatalytic current densities) under O2 saturated conditions at varying pH values. Strong evidence of O2 diffusion limitation was demonstrated. In order to overcome oxygen concentration and diffusion limitations in solution, we used a gas diffusion layer to create a PdNP-based air-breathing cathode, which delivered -1.5 mA cm-2 at 0.0 V with an onset potential of 0.4 V. This air-breathing cathode was combined with a specially designed phenanthrolinequinone

  7. Preparation of cubic boron nitride thin film by the helicon wave plasma enhanced chemical vapor deposition

    SciTech Connect

    Kim, S.; Kim, I.; Kim, K.

    1996-12-01

    Cubic boron nitride ({ital c}-BN) film was deposited on Si(100) substrate using the chemical vapor deposition process assisted by high density plasma of Helicon wave with Borazine (B{sub 3}N{sub 3}H{sub 6}) precursor. It was found that the bombardment of ions with high flux and energy onto the film was necessarily required for synthesizing a {ital c}-BN film. Increasing a negative rf bias on the substrate increased the formation fraction of {ital c}-BN in the film. A nearly pure {ital c}-BN phase was synthesized at the conditions of plasma density in the reactor and rf substrate bias, above 10{sup 11} cm{sup {minus}3} and {minus}350 V, respectively. The phase identification of BN film was carried out by the transmission electron microscopy as well as Fourier transformed infrared spectroscopy. The infrared spectra for {ital c}-BN film synthesized at the rf bias of {minus}350 V appeared at 1093 cm{sup {minus}1} with a strong single peak, which is close to a value for the characteristic vibration mode of bulk {ital c}-BN (1065 cm{sup {minus}1}). The {ital c}-BN in the film was also confirmed and found to be a fine poly-crystalline with the grain sizes ranging from 200 to 400 A. {copyright} {ital 1996 American Institute of Physics.}

  8. Transdermal baicalin delivery using diethylene glycol monoethyl ether-mediated cubic phase gel.

    PubMed

    Zhang, Yongtai; Zhang, Kai; Guo, Teng; Li, Yuan; Zhu, Chunyun; Feng, Nianping

    2015-02-01

    This study investigated the transdermal permeability of baicalin, a hydrophobic and readily hydrolyzed drug, delivered by glyceryl monooleate (GMO)-based cubic phase gel (CPG) mediated with Transcotol(®) P (TP, diethylene glycol monoethyl ether). A range of CPGs was produced by varying GMO, water, and TP levels. Examination of their physicochemical properties revealed that the optically isotropic CPG showed higher viscosity than lamellar phase gels (LPG), and the baicalin cargo increased CPG viscosity. The GMO:TP ratio and water content also altered viscosity. CPG-mediated delivery increased baicalin's skin permeation, with 76.65- to 200.24-fold higher (p<0.05) transdermal flux than that of a Carbopol(®)-based hydrogel (HDG), and 6.72- to 17.55-fold (p<0.05) higher than that of LPG, with the same water content. Rat in vivo microdialysis showed that CPG produced sustained baicalin release, with superior pharmacokinetic parameters to those of HDG. Furthermore, cutaneous drug absorption was more efficient on rat abdominal skin, compared to that in the chest or scapular region. Effective fusion between the CPG lipid matrix and the stratum corneum may explain this enhancement of transdermal permeation. CPG containing TP therefore, achieved excellent transdermal drug delivery and good baicalin stability, indicating that this system represents a promising transdermal delivery vehicle. PMID:25543112

  9. Growth of cubic SiC single crystals by the physical vapor transport technique

    NASA Astrophysics Data System (ADS)

    Semmelroth, K.; Krieger, M.; Pensl, G.; Nagasawa, H.; Püsche, R.; Hundhausen, M.; Ley, L.; Nerding, M.; Strunk, H. P.

    2007-10-01

    Suitable process parameters for the growth of cubic 3C-SiC single crystals via the seeded physical vapor transport (PVT) technique, also known as the modified Lely method, have been determined. Free-standing, 200 μm thick 3C-SiC epilayers with (0 0 1)- or (0 0 1¯)-face grown on undulant Si (0 0 1) as well as 3C-SiC platelets with [1 1 1]- or [1¯ 1¯ 1¯]-orientation grown by thermal decomposition of methyl trichlorosilane in hydrogen were employed as seed crystals. The source material consisted of stoichiometric SiC; in addition, a separate Si source was deposited in the furnace at a temperature of about 1500 °C. The temperature of the seed crystals was kept at about 1900 °C. Stable growth of 3C-SiC bulk material of high crystalline quality was reached on 3C-SiC seed crystals with (0 0 1)-face providing a low density of planar defects and at near-thermal-equilibrium conditions resulting in a reduction of internal stress and as a consequence in avoiding the generation of new extended crystal defects. The growth rate achieved under these conditions was approximately 0.05 mm/h. The nitrogen donor concentration in the grown 3C-SiC crystals was determined to be equal to (2-6)×10 18 cm -3.

  10. Preparation of cubic niobium pyrophosphate containing Nb(IV) and topatactic extraction of phosphorus atoms

    SciTech Connect

    Fukuoka, Hiroshi; Imoto, Hideo; Saito, Taro

    1995-10-01

    A reduced phase of niobium pyrophosphate containing Nb{sup 4+} has been prepared from the reaction of Nb{sup 6}Cl{sub 14}{center_dot}8H{sub 2}O and phosphoric acid. The X-ray powder diffraction and electron diffraction studies have shown that the compound belongs to the Pa3 space group and has the ZrP{sub 2}O{sub 7} structure with a cubic superstructure (a{prime} = 3a{sub 0}). Magnetic susceptibility was measured for two samples, and the mean oxidation numbers of niobium in them are deduced to by + 4.66 and +4.88. The cell constants of these samples are a = 8.0830(4) and 8.0705(2) {angstrom}, respectively. As the mean oxidation number of niobium increases, the color of the compound varies from brown to gray. When the compound is heated in oxygen, it changes into the known white niobium pyrophosphate, in which all niobium is in the +5 oxidation state. Rietveld refinements indicate that niobium pyrophosphates have defects in the phosphorus sites. The topotactic extraction of the phosphorus atoms in the reaction with oxygen was confirmed by the analysis of phosphorus oxide generated during the reaction.

  11. Cubic zirconia as a species permeable coating for zinc diffusion in gallium arsenide

    SciTech Connect

    Bisberg, J.E.; Dabkowski, F.P.; Chin, A.K.

    1988-10-31

    Diffusion of zinc into GaAs through an yttria-stabilized cubic zirconia (YSZ) passivation layer has been demonstrated with an open-tube diffusion method. Pure zinc or GaAs/Zn/sub 2/As/sub 3/ sources produced high quality planar p-n junctions. The YSZ layer protects the GaAs surface from excessive loss of arsenic, yet is permeable to zinc, allowing its diffusion into the semiconductor. The YSZ films, deposited by electron beam evaporation, were typically 2000 A thick. Zinc diffusion coefficients (D/sub T/) at 650 /sup 0/C in the YSZ passivated GaAs ranged from 3.6 x 10/sup -10/ cm/sup 2//min for the GaAs/Zn/sub 2/As/sub 3/ source to 1.9 x 10/sup -9/ cm/sup 2//min for the pure zinc source. Doping concentrations for both YSZ passivated and uncapped samples were approximately 5 x 10/sup 19/ cm/sup -3/.

  12. The effect of voids on the hardening of body-centered cubic Fe

    NASA Astrophysics Data System (ADS)

    Nakai, Ryosuke; Yabuuchi, Kiyohiro; Nogami, Shuhei; Hasegawa, Akira

    2016-04-01

    The mechanical properties of metals are affected by various types of defects. Hardening is usually described through the interaction between dislocations and obstacles, in the so-called line tension theory. The strength factor in the line tension theory represents the resistance of a defect against the dislocation motion. In order to understand hardening from the viewpoint of the microstructure, an accurate determination of the strength factor of different types of defects is essential. In the present study, the strength factor of voids in body-centered cubic (BCC) Fe was investigated by two different approaches: one based on the Orowan equation to link the measured hardness with the average size and density of voids, and the other involving direct observation of the interaction between dislocations and voids by transmission electron microscope (TEM). The strength factor of voids induced by ion irradiation estimated by the Orowan equation was 0.6, whereas the strength factor estimated by the direct TEM approach was 0.8. The difference in the strength factors measured by the two approaches is due to the positional relationship between dislocations and voids: the central region of a void is stronger than the tip. Moreover, the gliding plane and the direction of dislocation may also affect the strength factor of voids. This study determined the strength factor of voids in BCC Fe accurately, and suggested that the contribution of voids to the irradiation hardening is larger than that of dislocation loops and Cu-rich precipitates.

  13. Photocurrent generation in carbon nanotube/cubic-phase HfO2 nanoparticle hybrid nanocomposites

    PubMed Central

    Galeckas, Augustinas; Salumaa, Martin; Ducroquet, Frédérique; Rauwel, Erwan

    2016-01-01

    Summary A hybrid material consisting of nonfunctionalized multiwall carbon nanotubes (MWCNTs) and cubic-phase HfO2 nanoparticles (NPs) with an average diameter of 2.6 nm has been synthesized. Free standing HfO2 NPs present unusual optical properties and a strong photoluminescence emission in the visible region, originating from surface defects. Transmission electron microscopy studies show that these NPs decorate the MWCNTs on topological defect sites. The electronic structure of the C K-edge in the nanocomposites was probed by electron energy loss spectroscopy, highlighting the key role of the MWCNT growth defects in anchoring HfO2 NPs. A combined optical emission and absorption spectroscopy approach illustrated that, in contrast to HfO2 NPs, the metallic MWCNTs do not emit light but instead expose their discrete electronic structure in the absorption spectra. The hybrid material manifests characteristic absorption features with a gradual merger of the MWCNT π-plasmon resonance band with the intrinsic defect band and fundamental edge of HfO2. The photoluminescence of the nanocomposites indicates features attributed to combined effects of charge desaturation of HfO2 surface states and charge transfer to the MWCNTs with an overall reduction of radiative recombination. Finally, photocurrent generation under UV–vis illumination suggests that a HfO2 NP/MWCNT hybrid system can be used as a flexible nanodevice for light harvesting applications. PMID:27547626

  14. Photocurrent generation in carbon nanotube/cubic-phase HfO2 nanoparticle hybrid nanocomposites.

    PubMed

    Rauwel, Protima; Galeckas, Augustinas; Salumaa, Martin; Ducroquet, Frédérique; Rauwel, Erwan

    2016-01-01

    A hybrid material consisting of nonfunctionalized multiwall carbon nanotubes (MWCNTs) and cubic-phase HfO2 nanoparticles (NPs) with an average diameter of 2.6 nm has been synthesized. Free standing HfO2 NPs present unusual optical properties and a strong photoluminescence emission in the visible region, originating from surface defects. Transmission electron microscopy studies show that these NPs decorate the MWCNTs on topological defect sites. The electronic structure of the C K-edge in the nanocomposites was probed by electron energy loss spectroscopy, highlighting the key role of the MWCNT growth defects in anchoring HfO2 NPs. A combined optical emission and absorption spectroscopy approach illustrated that, in contrast to HfO2 NPs, the metallic MWCNTs do not emit light but instead expose their discrete electronic structure in the absorption spectra. The hybrid material manifests characteristic absorption features with a gradual merger of the MWCNT π-plasmon resonance band with the intrinsic defect band and fundamental edge of HfO2. The photoluminescence of the nanocomposites indicates features attributed to combined effects of charge desaturation of HfO2 surface states and charge transfer to the MWCNTs with an overall reduction of radiative recombination. Finally, photocurrent generation under UV-vis illumination suggests that a HfO2 NP/MWCNT hybrid system can be used as a flexible nanodevice for light harvesting applications. PMID:27547626

  15. Electronic band structure and optical properties of the cubic, Sc, Y and La hydride systems

    SciTech Connect

    Peterman, D.J.

    1980-01-01

    Electronic band structure calculations are used to interpret the optical spectra of the cubic Sc, Y and La hydride systems. Self-consistent band calculations of ScH/sub 2/ and YH/sub 2/ were carried out. The respective joint densities of states are computed and compared to the dielectric functions determined from the optical measurements. Additional calculations were performed in which the Fermi level or band gap energies are rigidly shifted by a small energy increment. These calculations are then used to simulate the derivative structure in thermomodulation spectra and relate the origin of experimental interband features to the calculated energy bands. While good systematic agreement is obtained for several spectral features, the origin of low-energy interband transitions in YH/sub 2/ cannot be explained by these calculated bands. A lattice-size-dependent premature occupation of octahedral sites by hydrogen atoms in the fcc metal lattice is suggested to account for this discrepancy. Various non-self-consistent calculations are used to examine the effect of such a premature occupation. Measurements of the optical absorptivity of LaH/sub x/ with 1.6 < x < 2.9 are presented which, as expected, indicate a more premature occupation of the octahedral sites in the larger LaH/sub 2/ lattice. These experimental results also suggest that, in contrast to recent calculations, LaH/sub 3/ is a small-band-gap semiconductor.

  16. Ising-like phase transition of an n-component Eulerian face-cubic model

    NASA Astrophysics Data System (ADS)

    Ding, Chengxiang; Guo, Wenan; Deng, Youjin

    2013-11-01

    By means of Monte Carlo simulations and a finite-size scaling analysis, we find a critical line of an n-component Eulerian face-cubic model on the square lattice and the simple cubic lattice in the region v>1, where v is the bond weight. The phase transition belongs to the Ising universality class independent of n. The critical properties of the phase transition can also be captured by the percolation of the complement of the Eulerian graph.

  17. Bistability and instability of dark-antidark solitons in the cubic-quintic nonlinear Schroedinger equation

    SciTech Connect

    Crosta, M.; Fratalocchi, A.; Trillo, S.

    2011-12-15

    We characterize the full family of soliton solutions sitting over a background plane wave and ruled by the cubic-quintic nonlinear Schroedinger equation in the regime where a quintic focusing term represents a saturation of the cubic defocusing nonlinearity. We discuss the existence and properties of solitons in terms of catastrophe theory and fully characterize bistability and instabilities of the dark-antidark pairs, revealing mechanisms of decay of antidark solitons into dispersive shock waves.

  18. Macromolecule loading into spherical, elliptical, star-like and cubic calcium carbonate carriers.

    PubMed

    Parakhonskiy, Bogdan V; Yashchenok, Alexey M; Donatan, Senem; Volodkin, Dmitry V; Tessarolo, Francesco; Antolini, Renzo; Möhwald, Helmuth; Skirtach, Andre G

    2014-09-15

    We fabricated calcium carbonate particles with spherical, elliptical, star-like and cubical morphologies by varying relative salt concentrations and adding ethylene glycol as a solvent to slow down the rate of particle formation. The loading capacity of particles of different isotropic (spherical and cubical) and anisotropic (elliptical and star-like) geometries is investigated, and the surface area of such carriers is analysed. Potential applications of such drug delivery carriers are highlighted. PMID:25044943

  19. Epitaxial Growth of Cubic Crystalline Semiconductor Alloys on Basal Plane of Trigonal or Hexagonal Crystal

    NASA Technical Reports Server (NTRS)

    Park, Yeonjoon (Inventor); Choi, Sang H. (Inventor); King, Glen C. (Inventor)

    2011-01-01

    Hetero-epitaxial semiconductor materials comprising cubic crystalline semiconductor alloys grown on the basal plane of trigonal and hexagonal substrates, in which misfit dislocations are reduced by approximate lattice matching of the cubic crystal structure to underlying trigonal or hexagonal substrate structure, enabling the development of alloyed semiconductor layers of greater thickness, resulting in a new class of semiconductor materials and corresponding devices, including improved hetero-bipolar and high-electron mobility transistors, and high-mobility thermoelectric devices.

  20. Linear and cubic response to the initial eccentricity in heavy-ion collisions

    NASA Astrophysics Data System (ADS)

    Noronha-Hostler, Jacquelyn; Yan, Li; Gardim, Fernando G.; Ollitrault, Jean-Yves

    2016-01-01

    We study the relation between elliptic flow, v2, and the initial eccentricity, ɛ2, in heavy-ion collisions, using hydrodynamic simulations. Significant deviations from linear eccentricity scaling are seen in more peripheral collisions. We identify the mechanism responsible for these deviations as a cubic response, which we argue is a generic property of the hydrodynamic response to the initial density profile. The cubic response increases elliptic flow fluctuations, thereby improving agreement of initial condition models with experimental data.

  1. Strain dependent electron spin dynamics in bulk cubic GaN

    SciTech Connect

    Schaefer, A.; Buß, J. H.; Hägele, D.; Rudolph, J.; Schupp, T.; Zado, A.; As, D. J.

    2015-03-07

    The electron spin dynamics under variable uniaxial strain is investigated in bulk cubic GaN by time-resolved magneto-optical Kerr-rotation spectroscopy. Spin relaxation is found to be approximately independent of the applied strain, in complete agreement with estimates for Dyakonov-Perel spin relaxation. Our findings clearly exclude strain-induced relaxation as an effective mechanism for spin relaxation in cubic GaN.

  2. 26 CFR 50.6 - Ascertainment of quantity mined.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... EXCISE TAXES (CONTINUED) REGULATIONS RELATING TO THE TAX IMPOSED WITH RESPECT TO CERTAIN HYDRAULIC MINING § 50.6 Ascertainment of quantity mined. Each person engaged in hydraulic mining operations within the... hydraulic mining operations are conducted for the purpose of determining the cubic yardage mined from...

  3. 26 CFR 50.6 - Ascertainment of quantity mined.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... EXCISE TAXES (CONTINUED) REGULATIONS RELATING TO THE TAX IMPOSED WITH RESPECT TO CERTAIN HYDRAULIC MINING § 50.6 Ascertainment of quantity mined. Each person engaged in hydraulic mining operations within the... hydraulic mining operations are conducted for the purpose of determining the cubic yardage mined from...

  4. 26 CFR 50.6 - Ascertainment of quantity mined.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... EXCISE TAXES (CONTINUED) REGULATIONS RELATING TO THE TAX IMPOSED WITH RESPECT TO CERTAIN HYDRAULIC MINING § 50.6 Ascertainment of quantity mined. Each person engaged in hydraulic mining operations within the... hydraulic mining operations are conducted for the purpose of determining the cubic yardage mined from...

  5. 26 CFR 50.6 - Ascertainment of quantity mined.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... EXCISE TAXES (CONTINUED) REGULATIONS RELATING TO THE TAX IMPOSED WITH RESPECT TO CERTAIN HYDRAULIC MINING § 50.6 Ascertainment of quantity mined. Each person engaged in hydraulic mining operations within the... hydraulic mining operations are conducted for the purpose of determining the cubic yardage mined from...

  6. 26 CFR 50.6 - Ascertainment of quantity mined.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... EXCISE TAXES (CONTINUED) REGULATIONS RELATING TO THE TAX IMPOSED WITH RESPECT TO CERTAIN HYDRAULIC MINING § 50.6 Ascertainment of quantity mined. Each person engaged in hydraulic mining operations within the... hydraulic mining operations are conducted for the purpose of determining the cubic yardage mined from...

  7. Optimization, characterization and evaluation of chitosan-tailored cubic nanoparticles of clotrimazole.

    PubMed

    Verma, Purnima; Ahuja, Munish

    2015-02-01

    The present study deals with improvement of the mucoadhesive properties of monoolein based cubic nanoparticles by incorporating chitosan. Chitosan-tailored cubic nanoparticles were prepared by thin film hydration followed by ultrasonication employing clotrimazole as model drug. The effect of Pluronic F127 fraction and concentration of chitosan on particle size and % mucin binding of the formulations was studied using 2-factor, 3-level, central composite experimental design. The concentration of chitosan was found to influence particle size and % mucin binding of cubic nanoparticles while Pluronic F127 fraction influenced only the % mucin binding. Studies indicated 8.33(%w/w) fraction of Pluronic F127 and 0.17 (%w/v) concentration of chitosan as optimum concentration. Finally, the optimized batch was characterized by polarized light microscopy, small-angle X-ray scattering (SAXS) and transmission electron microscopy. The results unveiled incorporation of chitosan did not disrupt the inner cubic structure of nanoparticles. Peak indexing of SAXS data revealed the coexistence of P-type and D-type cubic phases in nanoparticles. Further, comparative evaluation studies showed significantly higher anti-fungal activity of clotrimazole-loaded chitosan-tailored cubic nanoparticles than conventional suspension of clotrimazole against Candida albicans. PMID:25463320

  8. Design and performance of tapered cubic anvil used for achieving higher pressure and larger sample cell.

    PubMed

    Han, Qi-Gang; Yang, Wen-Ke; Zhu, Pin-Wen; Ban, Qing-Chu; Yan, Ni; Zhang, Qiang

    2013-07-01

    In order to increase the maximum cell pressure of the cubic high pressure apparatus, we have developed a new structure of tungsten carbide cubic anvil (tapered cubic anvil), based on the principle of massive support and lateral support. Our results indicated that the tapered cubic anvil has some advantages. First, tapered cubic anvil can push the transfer rate of pressure well into the range above 36.37% compare to the conventional anvil. Second, the rate of failure crack decreases about 11.20% after the modification of the conventional anvil. Third, the limit of static high-pressure in the sample cell can be extended to 13 GPa, which can increase the maximum cell pressure about 73.3% than that of the conventional anvil. Fourth, the volume of sample cell compressed by tapered cubic anvils can be achieved to 14.13 mm(3) (3 mm diameter × 2 mm long), which is three and six orders of magnitude larger than that of double-stage apparatus and diamond anvil cell, respectively. This work represents a relatively simple method for achieving higher pressures and larger sample cell. PMID:23902079

  9. High reflected cubic cavity as long path absorption cell for infrared gas sensing

    NASA Astrophysics Data System (ADS)

    Yu, Jia; Gao, Qiang; Zhang, Zhiguo

    2014-10-01

    One direct and efficient method to improve the sensitivity of infrared gas sensors is to increase the optical path length of gas cells according to Beer-Lambert Law. In this paper, cubic shaped cavities with high reflected inner coating as novel long path absorption cells for infrared gas sensing were developed. The effective optical path length (EOPL) for a single cubic cavity and tandem cubic cavities were investigated based on Tunable Diode Laser Absorption Spectroscopy (TDLAS) measuring oxygen P11 line at 763 nm. The law of EOPL of a diffuse cubic cavity in relation with the reflectivity of the coating, the port fraction and side length of the cavity was obtained. Experimental results manifested an increase of EOPL for tandem diffuse cubic cavities as the decrease of port fraction of the connecting aperture f', and the EOPL equaled to the sum of that of two single cubic cavities at f'<0.01. The EOPL spectra at infrared wavelength range for different inner coatings including high diffuse coatings and high reflected metallic thin film coatings were deduced.

  10. Log-Cubic Method for Generation of Soil Particle Size Distribution Curve

    PubMed Central

    2013-01-01

    Particle size distribution (PSD) is a fundamental physical property of soils. Traditionally, the PSD curve was generated by hand from limited data of particle size analysis, which is subjective and may lead to significant uncertainty in the freehand PSD curve and graphically estimated cumulative particle percentages. To overcome these problems, a log-cubic method was proposed for the generation of PSD curve based on a monotone piecewise cubic interpolation method. The log-cubic method and commonly used log-linear and log-spline methods were evaluated by the leave-one-out cross-validation method for 394 soil samples extracted from UNSODA database. Mean error and root mean square error of the cross-validation show that the log-cubic method outperforms two other methods. What is more important, PSD curve generated by the log-cubic method meets essential requirements of a PSD curve, that is, passing through all measured data and being both smooth and monotone. The proposed log-cubic method provides an objective and reliable way to generate a PSD curve from limited soil particle analysis data. This method and the generated PSD curve can be used in the conversion of different soil texture schemes, assessment of grading pattern, and estimation of soil hydraulic parameters and erodibility factor. PMID:23766698

  11. High resolution 1H NMR of a lipid cubic phase using a solution NMR probe

    NASA Astrophysics Data System (ADS)

    Boyle-Roden, E.; Hoefer, N.; Dey, K. K.; Grandinetti, P. J.; Caffrey, M.

    2007-11-01

    The cubic mesophase formed by monoacylglycerols and water is an important medium for the in meso crystallogenesis of membrane proteins. To investigate molecular level lipid and additive interactions within the cubic phase, a method was developed for improving the resolution of 1H NMR spectra when using a conventional solution state NMR probe. Using this approach we obtained well-resolved J-coupling multiplets in the one-dimensional NMR spectrum of the cubic-Ia3d phase prepared with hydrated monoolein. A high resolution t-ROESY two-dimensional 1H NMR spectrum of the cubic-Ia3d phase is also reported. Using this new methodology, we have investigated the interaction of two additive molecules, L-tryptophan and ruthenium-tris(2,2-bipyridyl) dichloride (rubipy), with the cubic mesophase. Based on the measured chemical shift differences when changing from an aqueous solution to the cubic phase, we conclude that L-tryptophan experiences specific interactions with the bilayer interface, whereas rubipy remains in the aqueous channels and does not associate with the lipid bilayer.

  12. Temperature and pressure tuneable swollen bicontinuous cubic phases approaching nature's length scales.

    PubMed

    Barriga, H M G; Tyler, A I I; McCarthy, N L C; Parsons, E S; Ces, O; Law, R V; Seddon, J M; Brooks, N J

    2015-01-21

    Bicontinuous cubic structures offer enormous potential in applications ranging from protein crystallisation to drug delivery systems and have been observed in cellular membrane structures. One of the current bottlenecks in understanding and exploiting these structures is that cubic scaffolds produced in vitro are considerably smaller in size than those observed in biological systems, differing by almost an order of magnitude in some cases. We have addressed this technological bottleneck and developed a methodology capable of manufacturing highly swollen bicontinuous cubic membranes with length scales approaching those seen in vivo. Crucially, these cubic systems do not require the presence of proteins. We have generated highly swollen Im3m symmetry bicontinuous cubic phases with lattice parameters of up to 480 Å, composed of ternary mixtures of monoolein, cholesterol and negatively charged lipid (DOPS or DOPG) and we have been able to tune their lattice parameters. The swollen cubic phases are highly sensitive to both temperature and pressure; these structural changes are likely to be controlled by a fine balance between lipid headgroup repulsions and lateral pressure in the hydrocarbon chain region. PMID:25430049

  13. Preparation of films of a highly aligned lipid cubic phase.

    PubMed

    Squires, Adam M; Hallett, James E; Beddoes, Charlotte M; Plivelic, Tomás S; Seddon, Annela M

    2013-02-12

    We demonstrate a method by which we can produce an oriented film of an inverse bicontinuous cubic phase (Q(II)(D)) formed by the lipid monoolein (MO). By starting with the lipid as a disordered precursor (the L(3) phase) in the presence of butanediol, we can obtain a film of the Q(II)(D) phase showing a high degree of in-plane orientation by controlled dilution of the sample under shear within a linear flow cell. We demonstrate that the direction of orientation of the film is different from that found in the oriented bulk material that we have reported previously; therefore, we can now reproducibly form Q(II)(D) samples oriented with either the [110] or the [100] axis aligned in the flow direction depending on the method of preparation. The deposition of MO as a film, via a moving fluid-air interface that leaves a coating of MO in the L(3) phase on the capillary wall, leads to a sample in the [110] orientation. This contrasts with the bulk material that we have previously demonstrated to be oriented in the [100] direction, arising from flow producing an oriented bulk slug of material within the capillary tube. The bulk sample contains significant amounts of residual butanediol, which can be estimated from the lattice parameter of the Q(II)(D) phase obtained. The sample orientation and lattice parameters are determined from synchrotron small-angle X-ray scattering patterns and confirmed by simulations. This has potential applications in the production of template materials and the growth of protein crystals for crystallography as well as deepening our understanding of the mechanisms underlying the behavior of lyotropic liquid-crystal phases. PMID:23347289

  14. Electron affinity of cubic boron nitride terminated with vanadium oxide

    SciTech Connect

    Yang, Yu; Sun, Tianyin; Shammas, Joseph; Hao, Mei; Nemanich, Robert J.; Kaur, Manpuneet

    2015-10-28

    A thermally stable negative electron affinity (NEA) for a cubic boron nitride (c-BN) surface with vanadium-oxide-termination is achieved, and its electronic structure was analyzed with in-situ photoelectron spectroscopy. The c-BN films were prepared by electron cyclotron resonance plasma-enhanced chemical vapor deposition employing BF{sub 3} and N{sub 2} as precursors. Vanadium layers of ∼0.1 and 0.5 nm thickness were deposited on the c-BN surface in an electron beam deposition system. Oxidation of the metal layer was achieved by an oxygen plasma treatment. After 650 °C thermal annealing, the vanadium oxide on the c-BN surface was determined to be VO{sub 2}, and the surfaces were found to be thermally stable, exhibiting an NEA. In comparison, the oxygen-terminated c-BN surface, where B{sub 2}O{sub 3} was detected, showed a positive electron affinity of ∼1.2 eV. The B{sub 2}O{sub 3} evidently acts as a negatively charged layer introducing a surface dipole directed into the c-BN. Through the interaction of VO{sub 2} with the B{sub 2}O{sub 3} layer, a B-O-V layer structure would contribute a dipole between the O and V layers with the positive side facing vacuum. The lower enthalpy of formation for B{sub 2}O{sub 3} is favorable for the formation of the B-O-V layer structure, which provides a thermally stable surface dipole and an NEA surface.

  15. Study of nonlinear waves described by the cubic Schroedinger equation

    SciTech Connect

    Walstead, A.E.

    1980-03-12

    The cubic Schroedinger equation (CSE) is ubiquitous as a model equation for the long-time evolution of finite-amplitude near-monochromatic dispersive waves. It incorporates the effects of the radiation field pressure on the constitutive properties of the supporting medium in a self-consistent manner. The properties of the uniformly transiating periodic wave solutions of the one-dimensional CSE are studied here. These (so-called cnoidal) waves are characterized by the values of four parameters. Whitham's averaged variational principle is used to derive a system of quasilinear evolution equations (the modulational equations) for the values of these parameters when they are slowly varying in space and time. Explicit expressions for the characteristic velocities of the modulational equations are obtained for the full set of cnoidal waves. Riemann invariants are obtained for several limits for the stable case, and growth rates are obtained for several limits, including the solitary wave chain, for the unstable case. The results for several nontrivial limiting cases agree with those obtained by independent methods by others. The dynamics of the CSE generalized to two spatial dimensions are studied for the unstable case. A large class of similarity solutions with cylindrical symmetry are obtained systematically using infinitesimal transformation group techniques. The methods are adapted to obtain the symmetries of the action functional of the CSE and to deduce nine integral invariants. A numerical study of the self-similar solutions reveals that they are modulationally unstable and that singularities dominate the dynamics of the CSE in two dimensions. The CSE is derived using perturbation theory for a specific problem in plasma physics: the evolution of the envelope of a near-monochromatic electromagnetic wave in a cold magnetized plasma. 13 figures, 2 tables.

  16. Effects of Fin Leading Edge Sweep on Shock-Shock Interaction at Mach 6

    NASA Technical Reports Server (NTRS)

    Berry, Scott A.; Nowak, Robert J.

    1996-01-01

    The effects of fin leading edge sweep on peak heating rates due to shock-shock interaction have been experimentally examined in the Langley 20-Inch Mach 6 Tunnel. The shock interaction was produced by the intersection of a planar incident shock (16.8 deg shock angle relative to the freestream, generated by a 9 deg wedge) with the bow shock formed around a O.5-inch diameter cylindrical leading edge fin. Heating distributions along the leading edge stagnation line have been obtained using densely spaced thin film resistive-type sensors. Schlieren images were obtained to illustrate the very complex shock-shock interactions. The fin leading edge sweep angle was varied from 15-degrees swept back to 45-degrees swept forward for a freestream unit Reynolds number of 2 x 10(exp 6)/ft. Two models were utilized during the study, one with 0.025-inch spacing between gage centers, and the other 0.015-inch spacing. Gage spatial resolution on the order of 0.015-in appeared to accurately capture the narrow spike in heating. Peak heating due to shock interaction was maximized when the fin was swept forward 15 deg and 25 deg, both promoting augmentations about 7 times the baseline value. The schlieren images for these cases revealed Type 4 and Type 3 interactions, respectively.

  17. The National Aeronautics and Space Administration's Gilmore Load Cell Machine: Load Cell Calibrations to 2.22 x 10(exp 7) Newtons

    NASA Technical Reports Server (NTRS)

    Haynes, Michael W.

    2000-01-01

    Designed in 1964 and erected in 1966, the mission of the Gilmore Load Cell Machine was to provide highly accurate calibrations for large capacity load cells in support of NASA's Apollo Program. Still in use today, the Gilmore Machine is a national treasure with no equal.

  18. Initial Results from a Search for Lunar Radio Emission from Interactions of >= 10(exp 19) eV Neutrinos and Cosmic Rays

    NASA Technical Reports Server (NTRS)

    Gorham, P. W.; Liewer, K. M.; Naudet, C. J.

    2000-01-01

    Using the NASA Goldstone 70m antenna DSS 14 both singly and in coincidence with the 34 m antenna DSS 13 (21.7 km to the southeast), we have acquired approximately 12 hrs of livetime in a search for predicted pulsed radio emission from extremely-high energy cascades induced by neutrinos or cosmic rays in the lunar regolith. In about 4 hrs of single antenna observations, we reduced our sensitivity to impulsive terrestrial interference to a negligible level by use of a veto afforded by the unique capability of DSS 14. In the 8 hrs of dual-antenna observations, terrestrial interference is eliminated as a background. In both observing modes the thermal noise floor limits the sensitivity. We detected no events above statistical background. We report here initial limits based on these data which begin to constrain several predictions of the flux of EHE neutrinos.

  19. Variable-temperature single-crystal X-ray diffraction study of tetragonal and cubic perovskite-type barium titanate phases.

    PubMed

    Nakatani, Tomotaka; Yoshiasa, Akira; Nakatsuka, Akihiko; Hiratoko, Tatsuya; Mashimo, Tsutomu; Okube, Maki; Sasaki, Satoshi

    2016-02-01

    A variable-temperature single-crystal X-ray diffraction study of a synthetic BaTiO3 perovskite has been performed over the temperature range 298-778 K. A transition from a tetragonal (P4mm) to a cubic (Pm \\overline 3 m) phase has been revealed near 413 K. In the non-centrosymmetric P4mm symmetry group, both Ti and O atoms are displaced along the c-axis in opposite directions with regard to the Ba position fixed at the origin, so that Ti(4+) and Ba(2+) cations occupy off-center positions in the TiO6 and BaO12 polyhedra, respectively. Smooth temperature-dependent changes of the atomic coordinates become discontinuous with the phase transition. Our observations imply that the cations remain off-center even in the high-temperature cubic phase. The temperature dependence of the mean-square displacements of Ti in the cubic phase includes a significant static component which means that Ti atoms are statistically distributed in the off-center positions. PMID:26830807

  20. ATMOS/ATLAS 1 measurements of sulfur hexafluoride (SF6) in the lower stratosphere and upper troposphere

    NASA Technical Reports Server (NTRS)

    Rinsland, C. P.; Gunson, M. R.; Abrams, M. C.; Lowes, L. L.; Zander, R.; Mahieu, E.

    1993-01-01

    Vertical profiles of sulfur hexafluoride (SF6) in the lower stratosphere and upper troposphere have been retrieved from 0.01/cm resolution infrared solar occultation spectra recorded by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer during the ATLAS (Atmospheric Laboratory for Applications and Science) 1 shuttle mission of March 24 to April 2, 1992. Based on measurements of the unresolved absorption by the SF6 mu(sub 3) band Q branch at 947.9/cm, average SF6 volume mixing ratios and 1-sigma uncertainties of 3.20 +/- 0.54 parts per trillion by volume (pptv; 10(exp -12) ppv) at 200 mbar (approximately 11.8 km) declining to 2.86 +/- 0.29 pptv at 100 mbar (approximately 16.2 km) and 1.95 +/- 0.50 pptv at 30 mbar (approximately 23.9 km) have been retrieved. The profiles show no obvious dependence with latitude over the range of the measurements (eight occultations spanning 28 deg S to 54 deg S). Assuming an exponential growth model and applying a correction for the interhemispheric concentration difference, an average SF6 rate of increase of 8.7 +/- 2.2% per year, 2 sigma, between 12 and 18 km has been derived by fitting the present measurements, ATMOS measurements from the April-May 1985 Spacelab 3 mission, and balloon-borne IR measurements obtained in March 1981 and June 1988.

  1. Transport properties of cubic crystalline Ge2Sb2Te5: A potential low-temperature thermoelectric material

    NASA Astrophysics Data System (ADS)

    Sun, Jifeng; Mukhopadhyay, Saikat; Subedi, Alaska; Siegrist, Theo; Singh, David J.

    2015-03-01

    Ge2Sb2Te5 (GST) has been widely used as a popular phase change material. In this study, we show that it exhibits high Seebeck coefficients 200-300 μV/K in its cubic crystalline phase (c-GST) at remarkably high p-type doping levels of ˜1 × 1019-6 × 1019 cm-3 at room temperature. More importantly, at low temperature (T = 200 K), the Seebeck coefficient was found to exceed 200 μV/K for a doping range of 1 × 1019-3.5 × 1019 cm-3. Given that the lattice thermal conductivity in this phase has already been measured to be extremely low (˜0.7 W/m-K at 300 K) [K. S. Siegert et al., Rep. Prog. Phys. 78, 013001 (2015)], our results suggest the possibility of using c-GST as a low-temperature thermoelectric material.

  2. Stem cubic-foot volume tables for tree species in the Delta area. Forest Service research paper

    SciTech Connect

    Clark, A.; Souter, R.A.

    1996-03-01

    Steamwood cubic-foot volume inside bark tables are presented for 13 species and 6 species groups based on equations used to estimate timber sale volumes on national forests in the Delta Area. Tables are based on form class measurement data for 990 trees sampled in the Delta Area and taper data collected across the South. A series of tables is presented for each species based on diameter at breast height (d.b.h.) in combination with total height and height to a 4-inch diameter outside bark (d.o.b.) top. Volume tables are also presented based on diameter outside of the bark (d.o.b.) in combination with height with to a 9-inch d.o.b. top.

  3. Transport properties of cubic crystalline Ge2Sb2Te5: a potential low-temperature thermoelectric material.

    DOE PAGESBeta

    Sun, Jifeng; Mukhopadhyay, Saikat; Subedi, Alaska; Siegrist, Theo; Singh, David J.

    2015-03-26

    Ge2Sb2Te5 (GST) has been widely used as a popular phase change material. In this study, we show that it exhibits high Seebeck coe cients 200 - 300 μV/K in its cubic crystalline phase (c-GST) at remarkably high p-type doping levels of 1 1019 - 6 1019 cm-3 at room temperature. More importantly, at low temperature (T = 200 K), the Seebeck coe cient was found to exceed 200 μV/K for a doping range 1 1019 - 3.5 1019 cm-3. Given that the lattice thermal conductivity in this phase has already been measured to be extremely low ( 0.7 W/m-K atmore » 300 K), our results suggest the possibility of using c-GST as a low-temperature thermoelectric material.« less

  4. Star Formation in Hi Tails: HCG 92, HCG 100 and 6 Interacting Systems

    NASA Technical Reports Server (NTRS)

    deMello, D. F.; Urrutia-Viscarra, F.; MendesdeOliveira, C.; Torres-Flores, S.; Carrasco, E. R.; Cypriano, E.

    2012-01-01

    We present new Gemini spectra of 14 new objects found within the HI tails of Hickson Compact Groups 92 and 100. Nine of them are GALEX Far-UV (FUV) and Near-UV (NUV) sources. The spectra confirm that these objects are members of the compact groups and have metallicities close to solar, with an average value of 12+log(O/H)approx.8.5. They have average FUV luminosities 7 x 10(exp 40) erg/s, very young ages (< 100 Myr) and two of them resemble tidal dwarf galaxies (TDGs) candidates. We suggest that they were created within gas clouds that were ejected during galaxy-galaxy interactions into the intergalactic medium, which would explain the high metallicities of the objects, inherited from the parent galaxies from which the gas originated. We conduct a search for similar objects in 6 interacting systems with extended HI tails, NGC 2623, NGC 3079, NGC 3359, NGC 3627, NGC 3718, NGC 4656. We found 35 UV sources with ages < 100 Myr, however most of them are on average less luminous/massive than the UV sources found around HCG 92 and 100. We speculate that this might be an environmental effect and that compact groups of galaxies are more favorable to TDG formation than other interacting systems.

  5. Flow mechanism of Forchheimer's cubic equation in high-velocity radial gas flow through porous media

    SciTech Connect

    Ezeudembah, A.S.; Dranchuk, P.M.

    1982-01-01

    Formal derivation of Forchheimer's cubic equation is made by considering the kinetic energy equation of mean flow and dimensional relations for one-dimensional, linear, incompressible fluid flow. By the addition of the cubic term, this equation is regarded as a modified Forchheimer's quadratic equation which accounts for the flow rates obtained beyond the laminar flow condition. The cubic equation spans a wide range of flow rates and regimes. For suitable use in gas flow studies, this equation has been adapted, modified, and corrected for the gas slippage effect. The physical basis of the cubic term has been established by using boundary layer theory to explain the high-velocity, high-pressure flow behavior through a porous path. Gamma, the main parameter in the cubic term, is related directly to a characteristic, dimensionless shape factor which is significant at higher flow rates. It is inversely related to viscosity, but has no dependence on the gas slippage coefficient in the higher flow regime. 25 references.

  6. Stability of a cubic fixed point in three dimensions: Critical exponents for generic N

    NASA Astrophysics Data System (ADS)

    Varnashev, K. B.

    2000-06-01

    The detailed analysis of the global structure of the renormalization-group (RG) flow diagram for a model with isotropic and cubic interactions is carried out in the framework of the massive field theory directly in three dimensions (3D) within an assumption of isotropic exchange. Perturbative expansions for RG functions are calculated for arbitrary N up to four-loop order and resummed by means of the generalized Padé-Borel-Leroy technique. Coordinates and stability matrix eigenvalues for the cubic fixed point are found under the optimal value of the transformation parameter. Critical dimensionality of the model is proved to be equal to Nc=2.89+/-0.02 that agrees well with the estimate obtained on the basis of the five-loop ɛ expansion [H. Kleinert and V. Schulte-Frohlinde, Phys. Lett. B 342, 284 (1995)] resummed by the above method. As a consequence, the cubic fixed point should be stable in 3D for N>=3, and the critical exponents controlling phase transitions in three-dimensional magnets should belong to the cubic universality class. The critical behavior of the random Ising model being the nontrivial particular case of the cubic model when N=0 is also investigated. For all physical quantities of interest the most accurate numerical estimates with their error bounds are obtained. The results achieved in the work are discussed along with the predictions given by other theoretical approaches and experimental data.

  7. Effect of a solid insulator on the spark yield of S2F10 in SF6(*)

    NASA Astrophysics Data System (ADS)

    Sauers, I.; Mahajan, S. M.; Cacheiro, R. A.

    Because of its toxicity S2F10 production in SF6 discharges has been the focus of intensive study in recent years. In previous work we have examined the yield of S 2F10 for corona, spark and arc discharges and, in sparks, the effects of water and oxygen have been studied systematically. Here we report the influence of an insulating solid spacer on the production of S2F10 in SF6 when subjected to spark discharges in the energy range 1.6-43 J/spark at a gas pressure of 1 atm. Analyses of the sparked gases were performed using a cryogenic enrichment gas chromatography technique with a sensitivity of less than 10 ppb (parts-per-billion) or 1 in 10(exp 8). With this sensitivity S2F10 can be detected after one or just a few spark(s), minimizing secondary effects of gas contamination, electrode erosion and insulator damage that can influence S2F10 production and make quantitative yield determinations difficult to establish. For these studies Teflon was used as the spacer sandwiched between two stainless steel electrodes. Energy measurements were made after recording the voltage and current waveforms. The amount of S2F10 produced per unit energy deposited into the discharge was found to be greater in the presence of the spacer than for a purely gas gap. Factors which influence S2F10 stability such as surfaces and water will also b e discussed.

  8. Structural and magnetic behavior of the cubic oxyfluoride SrFeO{sub 2}F studied by neutron diffraction

    SciTech Connect

    Thompson, Corey M.; Blakely, Colin K.; Flacau, Roxana; Greedan, John E.; Poltavets, Viktor V.

    2014-11-15

    The oxyfluoride SrFeO{sub 2}F has been prepared via a low temperature route involving the infinite-layer SrFeO{sub 2} and XeF{sub 2}. SrFeO{sub 2}F crystallizes in the cubic space group Pm-3m with disordered oxygen and fluorine atoms on the anion site. Recent reports demonstrated that SrFeO{sub 2}F is antiferromagnetic at room temperature and the zero field cooled and field cooled curves diverge at ∼150 K and ∼60 K, suggesting that the material has a spin glassy magnetic state at low temperatures. In this article, variable-temperature neutron diffraction (4–723 K) was performed to clarify the magnetic behavior observed in this material. Neutron powder diffraction measurements confirmed the antiferromagnetic (AFM) ordering of the system at room temperature. Below 710(1) K, the magnetic structure is a G-type AFM structure characterized by a propagation vector k=(1/2 , 1/2 , 1/2 ). The ordered moments on Fe{sup 3+} are 4.35(6)µ{sub B} at 4 K and 4.04(5)µ{sub B} at 290 K. Our results indicate that the cubic structure is retained all the way to base temperature (4 K) in contrast to PbFeO{sub 2}F. These results are compared with those of Pb and Ba analogs which exhibit very similar magnetic behavior. Furthermore, the observation of magnetic reflections at 4 K in the diffraction pattern shows the absence of the previously proposed spin glassy behavior at low temperatures. Previous proposals to explain the ZFC/FC divergences are examined. - Graphical abstract: Variable temperature powder neutron diffraction was employed to follow the evolution of the long range antiferromagnetic state in SrFeO{sub 2}F. - Highlights: • SrFeO{sub 2}F prepared via low temperature route involving SrFeO{sub 2} and XeF{sub 2}. • The cubic structure, Pm-3m, is retained at low temperatures, 4 K. • The magnetic structure is G-type AFM with T{sub N}=710 K and Fe{sup 3+} moment of 4.35µ{sub B}. • A small volume, bulk decoupled, spin glassy domain/cluster mechanism is proposed.

  9. Hexagonal graphite to cubic diamond transition from equilibrium lines and barrier calculations

    NASA Astrophysics Data System (ADS)

    Qiu, Shen Li

    2014-07-01

    Phase equilibrium lines of hexagonal graphite (hg) and cubic diamond (cd) phases of carbon as well as a saddle-point equilibrium line between the two phase equilibrium lines are studied by first-principles total-energy calculations. The Gibbs free energies ( G) of the three equilibrium lines determine the transition pressure p t = 70 kbar (0.070 Mbar) from hg phase to cd phase and the barrier height at p t of ΔG = 178 mRy/atom that stabilizes the two phases against a phase transition. The cd phase becomes unstable at V = 13.6 au3/atom ( p = 26 Mbar) where the curvature at the equilibrium point of the energy curve (denoted E V ( c/ a) curve) goes to zero. The hg and cd phase equilibrium lines cross at V = 14.5 au3/atom where the regular hg phase (with one minimum in each E V ( c/ a) curve) ends and the irregular hg phase (with two minima in each E V ( c/ a) curve) develops. The feature of "two phase equilibrium lines cross" was not observed in our previous work [S.L. Qiu, P.M. Marcus, J. Phys.: Condens. Matter 24, 225501 (2012); S.L. Qiu, P.M. Marcus, Eur. Phys. J. B 86, 425 (2013)] where the two interacting crystal phases have a common unit cell with different c/ a ratios. This work demonstrates that the saddle-point equilibrium line along with the two phase equilibrium lines are all needed for a complete description of crystal phases and their transitions under pressure.

  10. Hexagonal graphite to cubic diamond transition from equilibrium lines and barrier calculations

    NASA Astrophysics Data System (ADS)

    Li Qiu, Shen

    2014-07-01

    Phase equilibrium lines of hexagonal graphite (hg) and cubic diamond (cd) phases of carbon as well as a saddle-point equilibrium line between the two phase equilibrium lines are studied by first-principles total-energy calculations. The Gibbs free energies (G) of the three equilibrium lines determine the transition pressure pt = 70 kbar (0.070 Mbar) from hg phase to cd phase and the barrier height at pt of ΔG = 178 mRy/atom that stabilizes the two phases against a phase transition. The cd phase becomes unstable at V = 13.6 au3/atom (p = 26 Mbar) where the curvature at the equilibrium point of the energy curve (denoted EV(c/a) curve) goes to zero. The hg and cd phase equilibrium lines cross at V = 14.5 au3/atom where the regular hg phase (with one minimum in each EV(c/a) curve) ends and the irregular hg phase (with two minima in each EV(c/a) curve) develops. The feature of "two phase equilibrium lines cross" was not observed in our previous work [S.L. Qiu, P.M. Marcus, J. Phys.: Condens. Matter 24, 225501 (2012); S.L. Qiu, P.M. Marcus, Eur. Phys. J. B 86, 425 (2013)] where the two interacting crystal phases have a common unit cell with different c/a ratios. This work demonstrates that the saddle-point equilibrium line along with the two phase equilibrium lines are all needed for a complete description of crystal phases and their transitions under pressure.

  11. Thermo and photoluminescence properties of Eu3+ activated hexagonal, monoclinic and cubic gadolinium oxide nanorods

    NASA Astrophysics Data System (ADS)

    Dhananjaya, N.; Nagabhushana, H.; Nagabhushana, B. M.; Rudraswamy, B.; Shivakumara, C.; Ramesh, K. P.; Chakradhar, R. P. S.

    2011-04-01

    Different phases of Eu3+ activated gadolinium oxide (Gd (OH)3, GdOOH and Gd2O3) nanorods have been prepared by the hydrothermal method with and without cityl trimethyl ammonium bromide (CTAB) surfactant. Cubic Gd2O3:Eu (8 mol%) red phosphor has been prepared by the dehydration of corresponding hydroxide Gd(OH)3:Eu after calcinations at 350 and 600 °C for 3 h, respectively. When Eu3+ ions were introduced into Gd(OH)3, lattice sites which replace the original Gd3+ ions, a strong red emission centered at 613 nm has been observed upon UV illumination, due to the intrinsic Eu3+ transition between 5D0 and 7F configurations. Thermoluminescence glow curves of Gd (OH)3: Eu and Gd2O3:Eu phosphors have been recorded by irradiating with gamma source (60CO) in the dose range 10-60 Gy at a heating rate of 6.7 °C sec-1. Well resolved glow peaks in the range 42-45, 67-76, 95-103 and 102-125 °C were observed. When γ-irradiation dose increased to 40 Gy, the glow peaks were reduced and with increase in γ-dose (50 and 60 Gy) results the shift in first two glow peak temperatures at about 20 °C and a new shouldered peak at 86 °C was observed. It is observed that there is a shift in glow peak temperatures and variation in intensity, which is mainly attributed to different phases of gadolinium oxide. The trapping parameters namely activation energy (E), order of kinetics (b) and frequency factor were calculated using peak shape and the results are discussed.

  12. Vibrational effects on surface energies and band gaps in hexagonal and cubic ice

    NASA Astrophysics Data System (ADS)

    Engel, Edgar A.; Monserrat, Bartomeu; Needs, Richard J.

    2016-07-01

    Surface energies of hexagonal and cubic water ice are calculated using first-principles quantum mechanical methods, including an accurate description of anharmonic nuclear vibrations. We consider two proton-orderings of the hexagonal and cubic ice basal surfaces and three proton-orderings of hexagonal ice prism surfaces, finding that vibrations reduce the surface energies by more than 10%. We compare our vibrational densities of states to recent sum frequency generation absorption measurements and identify surface proton-orderings of experimental ice samples and the origins of characteristic absorption peaks. We also calculate zero point quantum vibrational corrections to the surface electronic band gaps, which range from -1.2 eV for the cubic ice basal surface up to -1.4 eV for the hexagonal ice prism surface. The vibrational corrections to the surface band gaps are up to 12% smaller than for bulk ice.

  13. Direct visualization of dispersed lipid bicontinuous cubic phases by cryo-electron tomography

    PubMed Central

    Demurtas, Davide; Guichard, Paul; Martiel, Isabelle; Mezzenga, Raffaele; Hébert, Cécile; Sagalowicz, Laurent

    2015-01-01

    Bulk and dispersed cubic liquid crystalline phases (cubosomes), present in the body and in living cell membranes, are believed to play an essential role in biological phenomena. Moreover, their biocompatibility is attractive for nutrient or drug delivery system applications. Here the three-dimensional organization of dispersed cubic lipid self-assembled phases is fully revealed by cryo-electron tomography and compared with simulated structures. It is demonstrated that the interior is constituted of a perfect bicontinuous cubic phase, while the outside shows interlamellar attachments, which represent a transition state between the liquid crystalline interior phase and the outside vesicular structure. Therefore, compositional gradients within cubosomes are inferred, with a lipid bilayer separating at least one water channel set from the external aqueous phase. This is crucial to understand and enhance controlled release of target molecules and calls for a revision of postulated transport mechanisms from cubosomes to the aqueous phase. PMID:26573367

  14. Cubic GaS: A Surface Passivator For GaAs

    NASA Technical Reports Server (NTRS)

    Hepp, Aloysius F.; Barron, Andrew R.; Power, Michael B.; Jenkins, Phillip P.; Macinnes, Andrew N.

    1994-01-01

    Thin films of cubic form of gallium sulfide (GaS) formed on surfaces of gallium arsenide (GaAs) substrates via metal/organic chemical vapor deposition (MOCVD). Deposited cubic GaS, crystalline lattice matched to substrate GaAs, neutralizes electrically active defects on surfaces of both n-doped and p-doped GaAs. Enabling important GaAs-based semiconducting materials to serve as substrates for metal/insulator/semiconductor (MIS) capacitors. Cubic GaS enables fabrication of ZnSe-based blue lasers and light-emitting diodes. Because GaS is optically transparent, deposited to form window layers for such optoelectronic devices as light-emitting diodes, solar optical cells, and semiconductor lasers. Its transparency makes it useful as interconnection material in optoelectronic integrated circuits. Also useful in peeled-film technology because selectively etched from GaAs.

  15. Acoustic band gaps of three-dimensional periodic polymer cellular solids with cubic symmetry

    NASA Astrophysics Data System (ADS)

    Chen, Yanyu; Yao, Haimin; Wang, Lifeng

    2013-07-01

    The band structure and sound attenuation of the triply periodic co-continuous composite materials with simple cubic lattice, body-centered cubic lattice, and face-centered cubic lattice consisting of PMMA and air are investigated using finite element method. Complete band gaps are found in these structures and the width of band gaps is depending on volume fraction. It is shown that the width of band gaps along different directions in the first irreducible Brillouin zone enlarges as the volume fraction increases from 0.2 to 0.7. The largest complete band gap widths of the three types of co-continuous structures are 0.29, 0.54, and 0.55, respectively. As the complete band gaps appear in audible range of frequencies, these triply periodic co-continuous composite materials can be utilized to control noise.

  16. Orientation dependence of the dislocation microstructure in compressed body-centered cubic molybdenum

    SciTech Connect

    Wang, S.; Wang, M.P.; Chen, C.; Xiao, Z.; Jia, Y.L.; Li, Z.; Wang, Z.X.

    2014-05-01

    The orientation dependence of the deformation microstructure has been investigated in commercial pure molybdenum. After deformation, the dislocation boundaries of compressed molybdenum can be classified, similar to that in face-centered cubic metals, into three types: dislocation cells (Type 2), and extended planar boundaries parallel to (Type 1) or not parallel to (Type 3) a (110) trace. However, it shows a reciprocal relationship between face-centered cubic metals and body-centered cubic metals on the orientation dependence of the deformation microstructure. The higher the strain, the finer the microstructure is and the smaller the inclination angle between extended planar boundaries and the compression axis is. - Highlights: • A reciprocal relationship between FCC metals and BCC metals is confirmed. • The dislocation boundaries can be classified into three types in compressed Mo. • The dislocation characteristic of different dislocation boundaries is different.

  17. Hydrolysis of lanthanide dicarbides: Rates of reaction of cubic and tetragonal solid solutions with water

    SciTech Connect

    McColm, I.J. )

    1993-05-01

    Two series of solid solutions, Ho[sub 1[minus]x]La[sub x]C[sub 2] and Nd[sub 1[minus]x]LaC[sub 2], have been made and their X-ray unit cell parameters measured. The Ho[sub 1[minus]x]La[sub x]C[sub 2] series contains two tetragonal phases and a cubic solid solution series which has enabled the reaction rate constants for the water hydrolysis reaction of a cubic dicarbide phase to be determined for the first time. By comparing the linear rate constants and the activation energies across the two series the nature of bonding in general and the structure of the cubic phase are elucidated. A comparison with microhardness data is made and the change in M-C[sub 2] bonding as a function of composition is considered. 10 refs., 9 figs., 3 tabs.

  18. On the approximation of finding A(nother) Hamiltonian cycle in cubic Hamiltonian graphs

    NASA Astrophysics Data System (ADS)

    Bazgan, Cristina; Santha, Miklos; Tuza, Zsolt

    It is a simple fact that cubic Hamiltonian graphs have at least two Hamiltonian cycles. Finding such a cycle is NP-hard in general, and no polynomial time algorithm is known for the problem of fording a second Hamiltonian cycle when one such cycle is given as part of the input. We investigate the complexity of approximating this problem where by a feasible solution we mean a(nother) cycle in the graph. First we prove a negative result showing that the LONGEST PATH problem is not constant approximable in cubic Hamiltonian graphs unless P = NP. No such negative result was previously known for this problem in Hamiltonian graphs. In strong opposition with this result we show that there is a polynomial time approximation scheme for fording another cycle in cubic Hamiltonian graphs if a Hamiltonian cycle is given in the input.

  19. Excavated Cubic Platinum-Tin Alloy Nanocrystals Constructed from Ultrathin Nanosheets with Enhanced Electrocatalytic Activity.

    PubMed

    Chen, Qiaoli; Yang, Yanan; Cao, Zhenming; Kuang, Qin; Du, Guifen; Jiang, Yaqi; Xie, Zhaoxiong; Zheng, Lansun

    2016-07-25

    Excavated polyhedral noble-metal materials that were built by the orderly assembly of ultrathin nanosheets have both large surface areas and well-defined facets, and therefore could be promising candidates for diverse important applications. In this work, excavated cubic Pt-Sn alloy nanocrystals (NCs) with {110} facets were constructed from twelve nanosheets by a simple co-reduction method with the assistance of the surface regulator polyvinylpyrrolidone. The specific surface area of the excavated cubic Pt-Sn NCs is comparable to that of commercial Pt black despite their larger particle size. The excavated cubic Pt-Sn NCs exhibited superior electrocatalytic activity in terms of both the specific area current density and the mass current density towards methanol oxidation. PMID:27325395

  20. All bulk and boundary unitary cubic curvature theories in three dimensions

    SciTech Connect

    Guellue, Ibrahim; Sisman, Tahsin Cagri; Tekin, Bayram

    2011-01-15

    We construct all the bulk and boundary unitary cubic curvature parity invariant gravity theories in three dimensions in (anti)-de Sitter spaces. For bulk unitarity, our construction is based on the principle that the free theory of the cubic curvature theory reduces to one of the three known unitary theories which are the cosmological Einstein-Hilbert theory, the quadratic theory of the scalar curvature, or the new massive gravity (NMG). Bulk and boundary unitarity in NMG is in conflict; therefore, cubic theories that are unitary both in the bulk and on the boundary have free theories that reduce to the other two alternatives. We also study the unitarity of the Born-Infeld extensions of NMG to all orders in curvature.

  1. The curvature elastic-energy function of the lipid-water cubic mesophase

    NASA Astrophysics Data System (ADS)

    Chung, Hesson; Caffrey, Martin

    1994-03-01

    CELL and lipid membranes are able to bend, as manifested during membrane fusion and the formation of non-lamellar lyotropic mesopbases in water. But there is an energy cost to bending of lipid layers, called the curvature elastic energy. Although the functional form of this energy is known1, a complete quantitative knowledge of the curvature elastic energy, which is central to predicting the relative stability of the large number of phases that lipid membranes can adopt, has been lacking. Here we use X-ray synchrotron diffraction measurements of the variation of lattice parameter with pressure and temperature for the periodic Ia3d (Q230) cubic phase of hydrated monoolein to calculate the complete curvature elastic-energy function for the lipid cubic mesophase. This allows us to predict the stabilities of different cubic and lamellar phases for this system as a function of composition.

  2. Relationship Between LIBS Ablation and Pit Volume for Geologic Samples: Applications for the In Situ Absolute Geochronology

    NASA Technical Reports Server (NTRS)

    Devismes, Damien; Cohen, Barbara; Miller, J.-S.; Gillot, P.-Y.; Lefevre, J.-C.; Boukari, C.

    2014-01-01

    These first results demonstrate that LIBS spectra can be an interesting tool to estimate the ablated volume. When the ablated volume is bigger than 9.10(exp 6) cubic micrometers, this method has less than 10% of uncertainties. Far enough to be directly implemented in the KArLE experiment protocol. Nevertheless, depending on the samples and their mean grain size, the difficulty to have homogeneous spectra will increase with the ablated volume. Several K-Ar dating studies based on this approach will be implemented. After that, the results will be shown and discussed.

  3. Mixed structural face-centered cubic and body-centered cubic orders in near stoichiometric Fe2MnGa alloys

    NASA Astrophysics Data System (ADS)

    Kudryavtsev, Y. V.; Perekos, A. E.; Uvarov, N. V.; Kolchiba, M. R.; Synoradzki, K.; Dubowik, J.

    2016-05-01

    Magnetic and transport properties of near stoichiometric metastable FexMnyGaz alloys (46 ≤ x ≤ 52, 17 ≤ y ≤ 25, 26 ≤ z ≤ 30) with face-centered cubic (FCC), body-centered cubic (BCC), and two-phase (FCC + BCC) structures are investigated. The experimental results are analyzed in terms of first-principles calculations of stoichiometric Fe2MnGa alloy with the L21, L12, and the tetragonally distorted L21 structural orderings. It is shown that the pure BCC and FCC phases have distinct magnetic and transport properties. Two-phase Fe2MnGa alloys have magnetic and transport properties typical of the mixed BCC and FCC phases. Among the investigated alloys, Fe46Mn24Ga30 has a martensitic transformation accompanied with significant changes of its magnetic and transport properties.

  4. Structural insights into the cubic-hexagonal phase transition kinetics of monoolein modulated by sucrose solutions

    PubMed Central

    Reese, Caleb W.; Strango, Zachariah I.; Dell, Zachary R.; Tristram-Nagle, Stephanie; Harper, Paul E.

    2015-01-01

    Using DSC (differential scanning calorimetry), we measure the kinetics of the cubic-HII phase transition of monoolein in bulk sucrose solutions. We find that the transition temperature is dramatically lowered, with each 1 mol/kg of sucrose concentration dropping the transition by 20 °C. The kinetics of this transition also slow greatly with increasing sucrose concentration. For low sucrose concentrations, the kinetics are asymmetric, with the cooling (HII-cubic) transition taking twice as long as the heating (cubic-HII) transition. This asymmetry in transition times is reduced for higher sucrose concentrations. The cooling transition (cubic-HII) exhibits Avrami exponents in the range of 2 to 2.5 and the heating transition shows Avrami exponents ranging from 1 to 3. A classical Avrami interpretation would be that these processes occur via a one or two dimensional pathway with variable nucleation rates. A non-classical perspective would suggest that these exponents reflect the time dependence of pore formation (cooling) and destruction (heating). New density measurements of monoolein show that the currently accepted value is about 5% too low; this has substantial implications for electron density modeling. Structural calculations indicate that the head group area and lipid length in the cubic-HII transition shrink by about 12 % and 4 % respectively; this reduction is practically the same as that seen in a lipid with a very different molecular structure (rac-di-12:0 β-GlcDAG) that makes the same transition. Thermodynamic considerations suggest there is a hydration shell about one water molecule thick in front of the lipid head groups in both the cubic and HII phases. PMID:25758637

  5. Modeling of crossbred cattle growth, comparison between cubic and piecewise random regression models.

    PubMed

    Mirzaei, H R; Pitchford, W S; Verbyla, A P

    2011-01-01

    Two analyses, cubic and piecewise random regression, were conducted to model growth of crossbred cattle from birth to about two years of age, investigating the ability of a piecewise procedure to fit growth traits without the complications of the cubic model. During a four-year period (1994-1997) of the Australian "Southern Crossbreeding Project", mature Hereford cows (N = 581) were mated to 97 sires of Angus, Belgian Blue, Hereford, Jersey, Limousin, South Devon, and Wagyu breeds, resulting in 1141 steers and heifers born over four years. Data included 13 (for steers) and eight (for heifers) live body weight measurements, made approximately every 50 days from birth until slaughter. The mixed model included fixed effects of sex, sire breed, age (linear, quadratic and cubic), and their interactions between sex and sire breed with age. Random effects were sire, dam, management (birth location, year, post-weaning groups), and permanent environmental effects and for each of these when possible, their interactions with linear, quadratic and cubic growth. In both models, body weights of all breeds increased over pre-weaning period, held fairly steady (slightly flattening) over the dry season then increased again towards the end of the feedlot period. The number of estimated parameters for the cubic model was 22 while for the piecewise model it was 32. It was concluded that the piecewise model was very similar to the cubic model in the fit to the data; with the piecewise model being marginally better. The piecewise model seems to fit the data better at the end of the growth period. PMID:21968730

  6. Cubic Phases in Phosphatidylcholine-Cholesterol Mixtures: Cholesterol as Membrane 'Fusogen'

    SciTech Connect

    Tenchov, Boris G.; MacDonald, Robert C.; Siegel, David P.

    2010-01-18

    X-ray diffraction reveals that mixtures of some unsaturated phosphatidylcholines (PCs) with cholesterol (Chol) readily form inverted bicontinuous cubic phases that are stable under physiological conditions. This effect was studied in most detail for dioleoyl PC/Chol mixtures with molar ratios of 1:1 and 3:7. Facile formation of Im3m and Pn3m phases with lattice constants of 30-50nm and 25-30nm, respectively, took place in phosphate-buffered saline, in sucrose solution, and in water near the temperature of the L{alpha}HII transition of the mixtures, as well as during cooling of the HII phase. Once formed, the cubic phases displayed an ability to supercool and replace the initial L{sub {alpha}} phase over a broad range of physiological temperatures. Conversion into stable cubic phases was also observed for mixtures of Chol with dilinoleoyl PC but not for mixtures with palmitoyl-linoleoyl PC or palmitoyl-oleoyl PC, for which only transient cubic traces were recorded at elevated temperatures. A saturated, branched-chain PC, diphytanoyl PC, also displayed a cubic phase in mixture with Chol. Unlike the PEs, the membrane PCs are intrinsically nonfusogenic lipids: in excess water they only form lamellar phases and not any of the inverted phases on their own. Thus, the finding that Chol induces cubic phases in mixtures with unsaturated PCs may have important implications for its role in fusion. In ternary mixtures, saturated PCs and sphingomyelin are known to separate into liquid-ordered domains along with Chol. Our results thus suggest that unsaturated PCs, which are excluded from these domains, could form fusogenic domains with Chol. Such a dual role of Chol may explain the seemingly paradoxical ability of cell membranes to simultaneously form rigid, low-curvature raft-like patches while still being able to undergo facile membrane fusion.

  7. A Suzaku X-ray Observation of One Orbit of the Supergiant Fast X-ray Transient IGR J16479-4514

    NASA Technical Reports Server (NTRS)

    Sidoli, L.; Esposito, P.; Sguera, V.; Bodaghee, A.; Tomsick, J. A.; Pottschmidt, K.; Rodriguez, J.; Ramano, P.; Wilms, J.

    2013-01-01

    We report on a 250 ks long X-ray observation of the supergiant fast X-ray transient (SFXT) IGR J16479-4514 performed with Suzaku in 2012 February. During this observation, about 80% of the short orbital period (P(sub orb) approximates 3.32 days) was covered as continuously as possible for the first time. The source light curve displays variability of more than two orders of magnitude, starting with a very low emission state (10(exp -13) erg / sq cm/s; 1-10 keV) lasting the first 46 ks, consistent with being due to the X-ray eclipse by the supergiant companion. The transition to the uneclipsed X-ray emission is energy dependent. Outside the eclipse, the source spends most of the time at a level of 6-7X10)(exp-12) erg/sq. cm/s) punctuated by two structured faint flares with a duration of about 10 and 15 ks, respectively, reaching a peak flux of 3-4X10(exp -11) erg/sq. cm./S, separated by about 0.2 in orbital phase. Remarkably, the first faint flare occurs at a similar orbital phase of the bright flares previously observed in the system. This indicates the presence of a phase-locked large scale structure in the supergiant wind, driving a higher accretion rate onto the compact object. The average X-ray spectrum is hard and highly absorbed, with a column density, NH, of 10*exp 23)/sq cm, clearly in excess of the interstellar absorption. There is no evidence for variability of the absorbing column density, except that during the eclipse, where a less absorbed X-ray spectrum is observed. A narrow Fe K-alpha emission line at 6.4 keV is viewed along the whole orbit, with an intensity which correlates with the continuum emission above 7 keV. The scattered component visible during the X-ray eclipse allowed us to directly probe the wind density at the orbital separation, resulting in rho(sub w)=7X10(exp -14) g/cubic cm. Assuming a spherical geometry for the supergiant wind, the derived wind density translates into a ratio M(sub w)/v(sub infinity) = 7X10(exp -17) Solar M

  8. TOPICAL REVIEW: Microscopic insight into properties and electronic instabilities of impurities in cubic and lower symmetry insulators: the influence of pressure

    NASA Astrophysics Data System (ADS)

    Moreno, M.; Barriuso, M. T.; Aramburu, J. A.; García-Fernández, P.; García-Lastra, J. M.

    2006-05-01

    This article reviews the microscopic origin of properties due to transition-metal (TM) impurities, M, in insulator materials. Particular attention is paid to the influence of pressure upon impurity properties. Basic concepts such as the electronic localization in an MXN complex, the electrostatic potential, VR, arising from the rest of the lattice ions or the elastic coupling of the complex to the host lattice are initially exposed. The dependence of optical and magnetic parameters on the impurity-ligand distance, R, in cubic lattices is discussed in a first step. Emphasis is put on the actual origin of the R dependence of 10Dq. Examples revealing that laws for strict cubic symmetry cannot in general be transferred to lower symmetries are later given. This relevant fact is shown to come from allowed hybridizations like nd-(n+1)s as well as the influence of VR. As a salient feature the different colour in ruby and emerald is stressed to arise from distinct VR potentials in Al2O3 and Be3Si6Al2O18. The last part of this review deals with electronic instabilities. The phenomena associated with the Jahn-Teller (JT) effect in cubic lattices, the origin of the energy barrier among equivalent minima and the existence of coherent tunnelling in systems like MgO:Cu2+ are discussed. An increase of elastic coupling is pointed out to favour a transition from an elongated to a compressed equilibrium conformation. Interestingly the equilibrium geometry of JT ions in non-cubic lattices is shown to be controlled by mechanisms different to those in cubic systems, VR playing again a key role. The relevance of first principles calculations for clarifying the subtle mechanisms behind off-centre instabilities is also pointed out. Examples concern monovalent and divalent TM impurities in lattices with the CaF2 structure. The instability due to the transition from the ground to an excited state is finally considered. For complexes with significant elastic coupling vibrational frequencies

  9. Optical properties of GaAs 2D hexagonal and cubic photonic crystal

    SciTech Connect

    Arab, F. Assali, A.; Grain, R.; Kanouni, F.

    2015-03-30

    In this paper we present our theoretical study of 2D hexagonal and cubic rods GaAs in air, with plan wave expansion (PWE) and finite difference time domain (FDTD) by using BandSOLVE and FullWAVE of Rsoft photonic CAD package. In order to investigate the effect of symmetry and radius, we performed calculations of the band structures for both TM and TE polarization, contour and electromagnetic propagation and transmission spectra. Our calculations show that the hexagonal structure gives a largest band gaps compare to cubic one for a same filling factor.

  10. Preconditioning cubic spline collocation method by FEM and FDM for elliptic equations

    SciTech Connect

    Kim, Sang Dong

    1996-12-31

    In this talk we discuss the finite element and finite difference technique for the cubic spline collocation method. For this purpose, we consider the uniformly elliptic operator A defined by Au := -{Delta}u + a{sub 1}u{sub x} + a{sub 2}u{sub y} + a{sub 0}u in {Omega} (the unit square) with Dirichlet or Neumann boundary conditions and its discretization based on Hermite cubic spline spaces and collocation at the Gauss points. Using an interpolatory basis with support on the Gauss points one obtains the matrix A{sub N} (h = 1/N).

  11. In vitro drug release mechanism and drug loading studies of cubic phase gels.

    PubMed

    Lara, Marilisa G; Bentley, M Vitória L B; Collett, John H

    2005-04-11

    Glyceryl monooleate/water cubic phase systems were investigated as drug delivery systems, using salicylic acid as a model drug. The liquid crystalline phases formed by the glyceryl monooleate (GMO)/water systems were characterized by polarizing microscopy. In vitro drug release studies were performed and the influences of initial water content, swelling and drug loading on the drug release properties were evaluated. Water uptake followed second-order swelling kinetics. In vitro release profiles showed Fickian diffusion control and were independent on the initial water content and drug loading, suggesting GMO cubic phase gels suitability for use as drug delivery system. PMID:15778062

  12. The quantization of the radii of coordination spheres cubic crystals and cluster systems

    NASA Astrophysics Data System (ADS)

    Melnikov, G.; Emelyanov, S.; Ignatenko, N.; Ignatenko, G.

    2016-02-01

    The article deals with the creation of an algorithm for calculating the radii of coordination spheres and coordination numbers cubic crystal structure and cluster systems in liquids. Solution has important theoretical value since it allows us to calculate the amount of coordination in the interparticle interaction potentials, to predict the processes of growth of the crystal structures and processes of self-organization of particles in the cluster system. One option accounting geometrical and quantum factors is the use of the Fibonacci series to construct a consistent number of focal areas for cubic crystals and cluster formation in the liquid.

  13. Disorder-induced cubic phase in Fe2-based Heusler alloys

    NASA Astrophysics Data System (ADS)

    Kiss, Janos; Chadov, Stanislav; Fecher, Gerhard H.; Felser, Claudia

    2013-06-01

    Based on the first-principles electronic structure calculations, we analyze the chemical and magnetic mechanisms stabilizing the cubic phase in Fe2-based Heusler materials, which were predicted to be tetragonal when being chemically ordered. In agreement with recent experimental data, we found that these compounds crystallize within the so-called “inverted” cubic Heusler structure perturbed by a certain portion of the intrinsic chemical disorder. Understanding of these mechanisms is a necessary step to guide the successful future synthesis of the stable Fe2-based tetragonal phases, which are promising candidates for the rare-earth-free permanent magnets.

  14. Cubic boron nitride: A new prospective material for ultracold neutron application

    NASA Astrophysics Data System (ADS)

    Sobolev, Yu.; Lauer, Th.; Borisov, Yu.; Daum, M.; du Fresne, N.; Göltl, L.; Hampel, G.; Heil, W.; Knecht, A.; Keunecke, M.; Kratz, J. V.; Lang, T.; Meister, M.; Plonka-Spehr, Ch.; Pokotilovski, Yu.; Reichert, P.; Schmidt, U.; Krist, Th.; Wiehl, N.; Zenner, J.

    2010-03-01

    At the ultracold neutron (UCN) source of the TRIGA research reactor in Mainz, we have measured for the first time the material optical wall-potential of cubic boron nitride. The measurements were performed with a time-of-flight (TOF) spectrometer. The samples investigated had a wall-potential of (305±15) neV. This value is in good agreement with the result extracted from neutron reflectometry data and theoretical expectations. Because of its high critical velocity for UCN and its good dielectric characteristics, cubic boron nitride coatings (isotopically enriched) will be useful for a number of applications in UCN experiments.

  15. Experimental evidence of the theoretical spatial frequency response of cubic phase mask wavefront coding imaging systems.

    PubMed

    Somayaji, Manjunath; Bhakta, Vikrant R; Christensen, Marc P

    2012-01-16

    The optical transfer function of a cubic phase mask wavefront coding imaging system is experimentally measured across the entire range of defocus values encompassing the system's functional limits. The results are compared against mathematical expressions describing the spatial frequency response of these computational imagers. Experimental data shows that the observed modulation and phase transfer functions, available spatial frequency bandwidth and design range of this imaging system strongly agree with previously published mathematical analyses. An imaging system characterization application is also presented wherein it is shown that the phase transfer function is more robust than the modulation transfer function in estimating the strength of the cubic phase mask. PMID:22274533

  16. Dynamics of Structural Transformations between Lamellar and Inverse Bicontinuous Cubic Lyotropic Phases

    SciTech Connect

    Conn, Charlotte E.; Ces, Oscar; Mulet, Xavier; Seddon, John M.; Templer, Richard H.; Finet, Stephanie; Winter, Roland

    2006-03-17

    The liquid crystalline lamellar (L{sub {alpha}}) to double-diamond inverse bicontinuous cubic (Q{sub II}{sup D}) phase transition for the amphiphile monoelaidin in excess water exhibits a remarkable sequence of structural transformations for pressure or temperature jumps. Our data imply that the transition dynamics depends on a coupling between changes in molecular shape and the geometrical and topological constraints of domain size. We propose a qualitative model for this coupling based on theories of membrane fusion via stalks and existing knowledge of the structure and energetics of bicontinuous cubic phases.

  17. Application of the cubic polynomial strength criterion to the failure analysis of composite materials

    NASA Technical Reports Server (NTRS)

    Tennyson, R. C.; Nanyaro, A. P.; Wharram, G. E.

    1980-01-01

    A comparative failure analysis is presented based on the application of quadratic and cubic forms of the tensor polynomial lamina strength criterion to various composite structural configurations in a plane stress state. Failure loads have been predicted for off-angle laminates under simple loading conditions and for symmetric-balanced laminates subject to varying degrees of biaxial tension, including configurations subject to multimode failures. Some experimental data are also provided to support these calculations. From these results, the necessity of employing a cubic strength criterion to accurately predict the failure of composite laminae is demonstrated.

  18. Cubic and Quartic Higgs Couplings of Higgs Potentials and CP Phases

    NASA Astrophysics Data System (ADS)

    Song, You; Yan, Qi-Shu; Zhao, Xiao-Ran

    2016-06-01

    We derive cubic and quartic couplings of the Higgs singlet extension of the SM and the two Higgs doublet model. We also examine the number of CP violated couplings in a model with n Higgs doublet model and a model with ns Higgs singlets and nd Higgs doublets. We conclude that in order to reconstruct the Higgs potential with multi Higgs fields at the LHC and future colliders, to detect the cubic/quartic couplings is necessary. Supported by the Natural Science Foundation of China under Grant Nos. 11175251 and 11575005

  19. Temperature dependence of the electron Landé g-factor in cubic GaN

    NASA Astrophysics Data System (ADS)

    Buß, J. H.; Schupp, T.; As, D. J.; Hägele, D.; Rudolph, J.

    2015-12-01

    The temperature dependence of the electron Landé g-factor in bulk cubic GaN is investigated over an extremely broad temperature range from 15 K up to 500 K by time-resolved Kerr-rotation spectroscopy. The g-factor is found to be approximately constant over the full investigated temperature range. Calculations by k .p -theory predict a negligible temperature dependence g(T) in complete agreement with the experiment as a consequence of the large band-gap and small spin orbit splitting in cubic GaN.

  20. Higher Spin Interactions from Conformal Field Theory: The Complete Cubic Couplings

    NASA Astrophysics Data System (ADS)

    Sleight, Charlotte; Taronna, Massimo

    2016-05-01

    In this Letter we provide a complete holographic reconstruction of the cubic couplings in the minimal bosonic higher spin theory in (d +1 )-dimensional anti- de Sitter space. For this purpose, we also determine the operator-product expansion coefficients of all single-trace conserved currents in the d -dimensional free scalar O (N ) vector model, and we compute the tree-level three-point Witten diagram amplitudes for a generic cubic interaction of higher spin gauge fields in the metriclike formulation.

  1. Higher Spin Interactions from Conformal Field Theory: The Complete Cubic Couplings.

    PubMed

    Sleight, Charlotte; Taronna, Massimo

    2016-05-01

    In this Letter we provide a complete holographic reconstruction of the cubic couplings in the minimal bosonic higher spin theory in (d+1)-dimensional anti- de Sitter space. For this purpose, we also determine the operator-product expansion coefficients of all single-trace conserved currents in the d-dimensional free scalar O(N) vector model, and we compute the tree-level three-point Witten diagram amplitudes for a generic cubic interaction of higher spin gauge fields in the metriclike formulation. PMID:27203314

  2. Guiding and confinement of light induced by optical vortex solitons in a cubic-quintic medium.

    PubMed

    Reyna, Albert S; de Araújo, Cid B

    2016-01-01

    The observation of confinement and guiding of light induced by an optical vortex soliton (OVS) in a cubic-quintic (defocusing-focusing) medium is reported. The waveguide effect induced by the bright region of the vortex beam, is mainly due to the defocusing nonlinearity that allows the guiding of a probe beam propagating inside of the OVS dark region. The experimental results are corroborated by numerical simulations based on the cubic-quintic nonlinear Schrödinger equation, showing excellent agreement. PMID:26696191

  3. Influence of cubic nonlinearity on compensation of thermally induced polarisation distortions in Faraday isolators

    SciTech Connect

    Kuzmina, M S; Khazanov, E A

    2013-10-31

    The problem on laser radiation propagation in a birefringent medium is solved with the allowance made for thermally induced linear birefringence under the conditions of cubic nonlinearity. It is shown that at high average and peak radiation powers the degree of isolation in a Faraday isolator noticeably reduces due to the cubic nonlinearity: by more than an order of magnitude when the B-integral is equal to unity. This effect is substantial for pulses with the energy of 0.2 – 3 J, duration of 10 ps to 4 ns and pulse repetition rate of 0.2 – 40 kHz. (components of laser devices)

  4. Distinguishing Bicontinuous Lipid Cubic Phases from Isotropic Membrane Morphologies Using 31P Solid-State NMR Spectroscopy

    PubMed Central

    Yang, Yu; Yao, Hongwei

    2015-01-01

    Nonlamellar lipid membranes are frequently induced by proteins that fuse, bend, and cut membranes. Understanding the mechanism of action of these proteins requires the elucidation of the membrane morphologies that they induce. While hexagonal phases and lamellar phases are readily identified by their characteristic solid-state NMR lineshapes, bicontinuous lipid cubic phases are more difficult to discern, since the static NMR spectra of cubic-phase lipids consist of an isotropic 31P or 2H peak, indistinguishable from the spectra of isotropic membrane morphologies such as micelles and small vesicles. To date, small-angle X-ray scattering is the only method to identify bicontinuous lipid cubic phases. To explore unique NMR signatures of lipid cubic phases, we first describe the orientation distribution of lipid molecules in cubic phases and simulate the static 31P chemical shift lineshapes of oriented cubic-phase membranes in the limit of slow lateral diffusion. We then show that 31P T2 relaxation times differ significantly between isotropic micelles and cubic-phase membranes: the latter exhibit two-orders-of magnitude shorter T2 relaxation times. These differences are explained by the different timescales of lipid lateral diffusion on the cubic-phase surface versus the timescales of micelle tumbling. Using this relaxation NMR approach, we investigated a DOPE membrane containing the transmembrane domain (TMD) of a viral fusion protein. The static 31P spectrum of DOPE shows an isotropic peak, whose T2 relaxation times correspond to that of a cubic phase. Thus, the viral fusion protein TMD induces negative Gaussian curvature, which is an intrinsic characteristic of cubic phases, to the DOPE membrane. This curvature induction has important implications to the mechanism of virus-cell fusion. This study establishes a simple NMR diagnostic probe of lipid cubic phases, which is expected to be useful for studying many protein-induced membrane remodeling phenomena in biology

  5. Voltage gating by molecular subunits of Na+ and K+ ion channels: higher-dimensional cubic kinetics, rate constants, and temperature

    PubMed Central

    2015-01-01

    The structural similarity between the primary molecules of voltage-gated Na and K channels (alpha subunits) and activation gating in the Hodgkin-Huxley model is brought into full agreement by increasing the model's sodium kinetics to fourth order (m3 → m4). Both structures then virtually imply activation gating by four independent subprocesses acting in parallel. The kinetics coalesce in four-dimensional (4D) cubic diagrams (16 states, 32 reversible transitions) that show the structure to be highly failure resistant against significant partial loss of gating function. Rate constants, as fitted in phase plot data of retinal ganglion cell excitation, reflect the molecular nature of the gating transitions. Additional dimensions (6D cubic diagrams) accommodate kinetically coupled sodium inactivation and gating processes associated with beta subunits. The gating transitions of coupled sodium inactivation appear to be thermodynamically irreversible; response to dielectric surface charges (capacitive displacement) provides a potential energy source for those transitions and yields highly energy-efficient excitation. A comparison of temperature responses of the squid giant axon (apparently Arrhenius) and mammalian channel gating yields kinetic Q10 = 2.2 for alpha unit gating, whose transitions are rate-limiting at mammalian temperatures; beta unit kinetic Q10 = 14 reproduces the observed non-Arrhenius deviation of mammalian gating at low temperatures; the Q10 of sodium inactivation gating matches the rate-limiting component of activation gating at all temperatures. The model kinetics reproduce the physiologically large frequency range for repetitive firing in ganglion cells and the physiologically observed strong temperature dependence of recovery from inactivation. PMID:25867741

  6. Voltage gating by molecular subunits of Na+ and K+ ion channels: higher-dimensional cubic kinetics, rate constants, and temperature.

    PubMed

    Fohlmeister, Jürgen F

    2015-06-01

    The structural similarity between the primary molecules of voltage-gated Na and K channels (alpha subunits) and activation gating in the Hodgkin-Huxley model is brought into full agreement by increasing the model's sodium kinetics to fourth order (m(3) → m(4)). Both structures then virtually imply activation gating by four independent subprocesses acting in parallel. The kinetics coalesce in four-dimensional (4D) cubic diagrams (16 states, 32 reversible transitions) that show the structure to be highly failure resistant against significant partial loss of gating function. Rate constants, as fitted in phase plot data of retinal ganglion cell excitation, reflect the molecular nature of the gating transitions. Additional dimensions (6D cubic diagrams) accommodate kinetically coupled sodium inactivation and gating processes associated with beta subunits. The gating transitions of coupled sodium inactivation appear to be thermodynamically irreversible; response to dielectric surface charges (capacitive displacement) provides a potential energy source for those transitions and yields highly energy-efficient excitation. A comparison of temperature responses of the squid giant axon (apparently Arrhenius) and mammalian channel gating yields kinetic Q10 = 2.2 for alpha unit gating, whose transitions are rate-limiting at mammalian temperatures; beta unit kinetic Q10 = 14 reproduces the observed non-Arrhenius deviation of mammalian gating at low temperatures; the Q10 of sodium inactivation gating matches the rate-limiting component of activation gating at all temperatures. The model kinetics reproduce the physiologically large frequency range for repetitive firing in ganglion cells and the physiologically observed strong temperature dependence of recovery from inactivation. PMID:25867741

  7. Sonic Boom Computations for a Mach 1.6 Cruise Low Boom Configuration and Comparisons with Wind Tunnel Data

    NASA Technical Reports Server (NTRS)

    Elmiligui, Alaa A.; Cliff, Susan E.; Wilcox, Floyd; Nemec, Marian; Bangert, Linda; Aftosmis, Michael J.; Parlette, Edward

    2011-01-01

    Accurate analysis of sonic boom pressure signatures using computational fluid dynamics techniques remains quite challenging. Although CFD shows accurate predictions of flow around complex configurations, generating grids that can resolve the sonic boom signature far away from the body is a challenge. The test case chosen for this study corresponds to an experimental wind-tunnel test that was conducted to measure the sonic boom pressure signature of a low boom configuration designed by Gulfstream Aerospace Corporation. Two widely used NASA codes, USM3D and AERO, are examined for their ability to accurately capture sonic boom signature. Numerical simulations are conducted for a free-stream Mach number of 1.6, angle of attack of 0.3 and Reynolds number of 3.85x10(exp 6) based on model reference length. Flow around the low boom configuration in free air and inside the Langley Unitary plan wind tunnel are computed. Results from the numerical simulations are compared with wind tunnel data. The effects of viscous and turbulence modeling along with tunnel walls on the computed sonic boom signature are presented and discussed.

  8. Stability of a general mixed additive-cubic functional equation in non-Archimedean fuzzy normed spaces

    SciTech Connect

    Xu Tianzhou; Rassias, John Michael; Xu Wanxin

    2010-09-15

    We establish some stability results concerning the general mixed additive-cubic functional equation in non-Archimedean fuzzy normed spaces. In addition, we establish some results of approximately general mixed additive-cubic mappings in non-Archimedean fuzzy normed spaces. The results improve and extend some recent results.

  9. Alkyl-bis(imidazolium) salts: a new amphiphile platform that forms thermotropic and non-aqueous lyotropic bicontinuous cubic phases

    SciTech Connect

    Robertson, LA; Schenkel, MR; Wiesenauer, BR; Gin, DL

    2013-01-01

    New ionic amphiphiles with a hexyl-bridged bis(imidazolium) headgroup; Br-, BF4-, or Tf2N- anions; and a long n-alkyl tail can form thermotropic bicontinuous cubic liquid crystal phases in neat form and/or lyotropic bicontinuous cubic phases with several non-aqueous solvents or water.

  10. 1,2-Dichlorohexafluoro-Cyclobutane (1,2-c-C4F6Cl2, R-316c) a Potent Ozone Depleting Substance and Greenhouse Gas: Atmospheric Loss Processes, Lifetimes, and Ozone Depletion and Global Warming Potentials for the (E) and (Z) stereoisomers

    NASA Technical Reports Server (NTRS)

    Papadimitriou, Vassileios C.; McGillen, Max R.; Smith, Shona C.; Jubb, Aaron M.; Portmann, Robert W.; Hall, Bradley D.; Fleming, Eric L.; Jackman, Charles H.; Burkholder, James B.

    2013-01-01

    The atmospheric processing of (E)- and (Z)-1,2-dichlorohexafluorocyclobutane (1,2-c-C4F6Cl2, R-316c) was examined in this work as the ozone depleting (ODP) and global warming (GWP) potentials of this proposed replacement compound are presently unknown. The predominant atmospheric loss processes and infrared absorption spectra of the R-316c isomers were measured to provide a basis to evaluate their atmospheric lifetimes and, thus, ODPs and GWPs. UV absorption spectra were measured between 184.95 to 230 nm at temperatures between 214 and 296 K and a parametrization for use in atmospheric modeling is presented. The Cl atom quantum yield in the 193 nm photolysis of R- 316c was measured to be 1.90 +/- 0.27. Hexafluorocyclobutene (c-C4F6) was determined to be a photolysis co-product with molar yields of 0.7 and 1.0 (+/-10%) for (E)- and (Z)-R-316c, respectively. The 296 K total rate coefficient for the O(1D) + R-316c reaction, i.e., O(1D) loss, was measured to be (1.56 +/- 0.11) × 10(exp -10)cu cm/ molecule/s and the reactive rate coefficient, i.e., R-316c loss, was measured to be (1.36 +/- 0.20) × 10(exp -10)cu cm/molecule/s corresponding to a approx. 88% reactive yield. Rate coefficient upper-limits for the OH and O3 reaction with R-316c were determined to be <2.3 × 10(exp -17) and <2.0 × 10(exp -22)cu cm/molecule/s, respectively, at 296 K. The quoted uncertainty limits are 2(sigma) and include estimated systematic errors. Local and global annually averaged lifetimes for the (E)- and (Z)-R-316c isomers were calculated using a 2-D atmospheric model to be 74.6 +/- 3 and 114.1 +/-10 years, respectively, where the estimated uncertainties are due solely to the uncertainty in the UV absorption spectra. Stratospheric photolysis is the predominant atmospheric loss process for both isomers with the O(1D) reaction making a minor, approx. 2% for the (E) isomer and 7% for the (Z) isomer, contribution to the total atmospheric loss. Ozone depletion potentials for (E)- and (Z

  11. High-temperature powder synchrotron diffraction studies of synthetic cryolite Na 3AlF 6

    NASA Astrophysics Data System (ADS)

    Zhou, Qingdi; Kennedy, Brendan J.

    2004-03-01

    A high-resolution synchrotron diffraction study of the structures of a synthetic sample of cryolite Na 3AlF 6 from room temperature to 800°C is reported. At room temperature Na 3AlF 6 is monoclinic and the structure is described in space group P2 1/n. Heating the sample to 560°C results in only minor changes to the structure. A first-order transition from this monoclinic structure to a high-temperature cubic structure is observed near 567°C. The cubic Fm 3¯m structure is characterized by disorder of the fluoride atoms.

  12. Bare and boron-doped cubic silicon carbide nanowires for electrochemical detection of nitrite sensitively

    PubMed Central

    Yang, Tao; Zhang, Liqin; Hou, Xinmei; Chen, Junhong; Chou, Kuo-Chih

    2016-01-01

    Fabrication of eletrochemical sensors based on wide bandgap compound semiconductors has attracted increasing interest in recent years. Here we report for the first time electrochemical nitrite sensors based on cubic silicon carbide (SiC) nanowires (NWs) with smooth surface and boron-doped cubic SiC NWs with fin-like structure. Multiple techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS) were used to characterize SiC and boron-doped SiC NWs. As for the electrochemical behavior of both SiC NWs electrode, the cyclic voltammetric results show that both SiC electrodes exhibit wide potential window and excellent electrocatalytic activity toward nitrite oxidation. Differential pulse voltammetry (DPV) determination reveals that there exists a good linear relationship between the oxidation peak current and the concentration in the range of 50–15000 μmoL L−1 (cubic SiC NWs) and 5–8000 μmoL L−1 (B-doped cubic SiC NWs) with the detection limitation of 5 and 0.5 μmoL L−1 respectively. Compared with previously reported results, both as-prepared nitrite sensors exhibit wider linear response range with comparable high sensitivity, high stability and reproducibility. PMID:27109361

  13. Cubic-quintic long-range interactions with double well potentials

    NASA Astrophysics Data System (ADS)

    Tsilifis, Panagiotis A.; Kevrekidis, Panayotis G.; Rothos, Vassilis M.

    2014-01-01

    In the present work, we examine the combined effects of cubic and quintic terms of the long-range type in the dynamics of a double well potential. Employing a two-mode approximation, we systematically develop two cubic-quintic ordinary differential equations and assess the contributions of the long-range interactions in each of the relevant prefactors, gauging how to simplify the ensuing dynamical system. Finally, we obtain a reduced canonical description for the conjugate variables of relative population imbalance and relative phase between the two wells and proceed to a dynamical systems analysis of the resulting pair of ordinary differential equations. While in the case of cubic and quintic interactions of the same kind (e.g. both attractive or both repulsive), only a symmetry-breaking bifurcation can be identified, a remarkable effect that emerges e.g. in the setting of repulsive cubic but attractive quintic interactions is a ‘symmetry-restoring’ bifurcation. Namely, in addition to the supercritical pitchfork that leads to a spontaneous symmetry breaking of the antisymmetric state, there is a subcritical pitchfork that eventually reunites the asymmetric daughter branch with the antisymmetric parent one. The relevant bifurcations, the stability of the branches and their dynamical implications are examined both in the reduced (ODE) and in the full (PDE) setting. The model is argued to be of physical relevance, especially so in the context of optical thermal media.

  14. Cross-polarized wave generation by effective cubic nonlinear optical interaction.

    PubMed

    Petrov, G I; Albert, O; Etchepare, J; Saltiel, S M

    2001-03-15

    A new cubic nonlinear optical effect in which a linearly polarized wave propagating in a single quadratic medium is converted into a wave that is cross polarized to the input wave is observed in BBO crystal. The effect is explained by cascading of two different second-order processes: second-harmonic generation and difference frequency mixing. PMID:18040322

  15. A Comparison of Low Performing Students' Achievements in Factoring Cubic Polynomials Using Three Different Strategies

    ERIC Educational Resources Information Center

    Ogbonnaya, Ugorji I.; Mogari, David L.; Machisi, Eric

    2013-01-01

    In this study, repeated measures design was employed to compare low performing students' achievements in factoring cubic polynomials using three strategies. Twenty-five low-performing Grade 12 students from a secondary school in Limpopo province took part in the study. Data was collected using achievement test and was analysed using repeated…

  16. Bare and boron-doped cubic silicon carbide nanowires for electrochemical detection of nitrite sensitively.

    PubMed

    Yang, Tao; Zhang, Liqin; Hou, Xinmei; Chen, Junhong; Chou, Kuo-Chih

    2016-01-01

    Fabrication of eletrochemical sensors based on wide bandgap compound semiconductors has attracted increasing interest in recent years. Here we report for the first time electrochemical nitrite sensors based on cubic silicon carbide (SiC) nanowires (NWs) with smooth surface and boron-doped cubic SiC NWs with fin-like structure. Multiple techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS) were used to characterize SiC and boron-doped SiC NWs. As for the electrochemical behavior of both SiC NWs electrode, the cyclic voltammetric results show that both SiC electrodes exhibit wide potential window and excellent electrocatalytic activity toward nitrite oxidation. Differential pulse voltammetry (DPV) determination reveals that there exists a good linear relationship between the oxidation peak current and the concentration in the range of 50-15000 μmoL L(-1) (cubic SiC NWs) and 5-8000 μmoL L(-1) (B-doped cubic SiC NWs) with the detection limitation of 5 and 0.5 μmoL L(-1) respectively. Compared with previously reported results, both as-prepared nitrite sensors exhibit wider linear response range with comparable high sensitivity, high stability and reproducibility. PMID:27109361

  17. Bare and boron-doped cubic silicon carbide nanowires for electrochemical detection of nitrite sensitively

    NASA Astrophysics Data System (ADS)

    Yang, Tao; Zhang, Liqin; Hou, Xinmei; Chen, Junhong; Chou, Kuo-Chih

    2016-04-01

    Fabrication of eletrochemical sensors based on wide bandgap compound semiconductors has attracted increasing interest in recent years. Here we report for the first time electrochemical nitrite sensors based on cubic silicon carbide (SiC) nanowires (NWs) with smooth surface and boron-doped cubic SiC NWs with fin-like structure. Multiple techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS) were used to characterize SiC and boron-doped SiC NWs. As for the electrochemical behavior of both SiC NWs electrode, the cyclic voltammetric results show that both SiC electrodes exhibit wide potential window and excellent electrocatalytic activity toward nitrite oxidation. Differential pulse voltammetry (DPV) determination reveals that there exists a good linear relationship between the oxidation peak current and the concentration in the range of 50–15000 μmoL L‑1 (cubic SiC NWs) and 5–8000 μmoL L‑1 (B-doped cubic SiC NWs) with the detection limitation of 5 and 0.5 μmoL L‑1 respectively. Compared with previously reported results, both as-prepared nitrite sensors exhibit wider linear response range with comparable high sensitivity, high stability and reproducibility.

  18. USE OF CUBIC SPLINES FOR ESTIMATING LACTATION CURVES OF HOLSTEIN COWS TREATED WITH BOVINE SOMATOTROPIN

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Cubic splines can be used to model fixed and random effects of lactation curves. A total of 64,138 test-day observations for first lactation Holstein cows recorded as treated with bovine somatotropin (bST) and 138,008 test-day observations for untreated cows were obtained from Dairy Records Manageme...

  19. 16 CFR 500.14 - Statements of cubic measure and dry measure.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    .... 500.14 Section 500.14 Commercial Practices FEDERAL TRADE COMMISSION RULES, REGULATIONS, STATEMENT OF GENERAL POLICY OR INTERPRETATION AND EXEMPTIONS UNDER THE FAIR PACKAGING AND LABELING ACT REGULATIONS UNDER SECTION 4 OF THE FAIR PACKAGING AND LABELING ACT § 500.14 Statements of cubic measure and...

  20. 16 CFR 500.14 - Statements of cubic measure and dry measure.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    .... 500.14 Section 500.14 Commercial Practices FEDERAL TRADE COMMISSION RULES, REGULATIONS, STATEMENT OF GENERAL POLICY OR INTERPRETATION AND EXEMPTIONS UNDER THE FAIR PACKAGING AND LABELING ACT REGULATIONS UNDER SECTION 4 OF THE FAIR PACKAGING AND LABELING ACT § 500.14 Statements of cubic measure and...

  1. Non-Cubic Power-law Scaling of Density in Metallic Glasses (Invited)

    NASA Astrophysics Data System (ADS)

    Zeng, Q. C.; Kono, Y.; Lin, Y.; Zeng, Z.; Wang, J.; Sinogeikin, S. V.; Park, C.; Meng, Y.; Yang, W.; Mao, W. L.

    2013-12-01

    Understanding structure-property relationships and dimensionality plays a central role in materials science. A cubic power law relationship between the average interatomic distance and the global density is commonly expected in 'disordered' glasses and has been extensively employed in various measurements. However, this relationship has never been rigorously verified which challenges our understanding of glass materials. Here, by using high pressure as a tuning tool, we rigorously demonstrated that the density of metallic glass (MG) varies with the 2.5 power of its fundamental atomic-level length scale (the inverse of the principal diffraction peak position, 1/q1). This falls between the 3-dimensional density and 1-dimensional length instead of the expected cubic power-law relationship. We further demonstrated the 2.5 power-law is universally valid for MGs of different compositions, as well as the same MG at different pressures. This study includes high quality data from multiple techniques which provides compelling evidence of the non-cubic power-law scaling in MGs. It has important implications not only in the practical measurements of density, or any measurement involving a change in length scale under various environments by correcting the extensively employed cubic power-law, but also in understanding the real atomic packing in glasses by providing a critical new constraint on a structure-property relationship.

  2. Stabilization of high-order solutions of the cubic nonlinear Schroedinger equation

    SciTech Connect

    Alexandrescu, Adrian; Montesinos, Gaspar D.; Perez-Garcia, Victor M.

    2007-04-15

    In this paper we consider the stabilization of nonfundamental unstable stationary solutions of the cubic nonlinear Schroedinger equation. Specifically, we study the stabilization of radially symmetric solutions with nodes and asymmetric complex stationary solutions. For the first ones, we find partial stabilization similar to that recently found for vortex solutions while for the later ones stabilization does not seem possible.

  3. Formation of a Cubic Iron-Sulfur Alloy at Megabar Pressures and its Equation of State

    NASA Astrophysics Data System (ADS)

    Seagle, C. T.; Heinz, D. L.; Campbell, A. J.; Miller, N. A.; Prakapenka, V. B.

    2008-12-01

    The details of binary iron-light element systems at pressures and temperatures relevant to the core can be used to constrain core composition and temperature. The addition of light elements to iron is known to affect the stability field of iron polymorphs. In this study, an iron plus 10 wt. percent sulfur sample was compressed and laser heated at 145 GPa in a diamond anvil cell at the GSECARS beamline of the APS. Phases present in the sample were monitored with x-ray diffraction. At this pressure, hcp-Fe was found to coexist with Fe3S. However, at 158 GPa, upon laser heating a new cubic phase formed at the expense of hcp-Fe until all hcp-Fe was consumed and a single cubic phase was left, apparently indicating solid solution behavior. The strongest x-ray diffraction lines closely resemble the x-ray diffraction pattern of bcc-Fe, however several additional weak lines rule out a structure as simple as bcc. The sample was slowly decompressed in order to measure the pressure-volume relationship. The unit cell volume of the metastable cubic phase began to expand rapidly below 100 GPa during decompression, and was completely amorphous below 80 GPa. Solid solution behavior would suggest that sulfur could be an important component of Earth's inner core; the implications of this, and the possible structure of the cubic phase in relation to the known iron polymorphs, will be discussed.

  4. Shape-controlled synthesis of cubic-like selenium nanoparticles via the self-assembly method.

    PubMed

    Luesakul, Urarika; Komenek, Seamkwan; Puthong, Songchan; Muangsin, Nongnuj

    2016-11-20

    The ability to control the morphology of nanoparticles by molecular design and synthesis is gaining increasing attention for achieving improved unique properties. In this work, we designed the chemical structure of a stabilizer for controlling the shape of selenium nanoparticles (SeNPs) via a self-assembly process. When folic acid-gallic acid-N,N,N-trimethyl chitosan (FA-GA-TMC) was used as a stabilizer, SeNPs were observed to self-organize into cubic-like structures with an average size of approximately 300nm. In contrast to the product obtained when unmodified chitosan was used as a stabilizer, this method resulted in spherical shape with an average size of approximately 200nm. The data suggested that the cubic-like SeNPs were controlled by a combination of electrostatic interaction, π-π stacking and hydrogen bonding between neighboring particles. Furthermore, the cubic-like SeNPs exhibited good anticancer efficacy and cellular uptake against breast cancer cells while exhibiting low toxicity against normal cells. These data demonstrates a simple approach for the shape-controlled synthesis of cubic-like SeNPs for biological applications via the self-assembly method. PMID:27561515

  5. Vibrational renormalisation of the electronic band gap in hexagonal and cubic ice

    SciTech Connect

    Engel, Edgar A. Needs, Richard J.; Monserrat, Bartomeu

    2015-12-28

    Electron-phonon coupling in hexagonal and cubic water ice is studied using first-principles quantum mechanical methods. We consider 29 distinct hexagonal and cubic ice proton-orderings with up to 192 molecules in the simulation cell to account for proton-disorder. We find quantum zero-point vibrational corrections to the minimum electronic band gaps ranging from −1.5 to −1.7 eV, which leads to improved agreement between calculated and experimental band gaps. Anharmonic nuclear vibrations play a negligible role in determining the gaps. Deuterated ice has a smaller band-gap correction at zero-temperature of −1.2 to −1.4 eV. Vibrations reduce the differences between the electronic band gaps of different proton-orderings from around 0.17 eV to less than 0.05 eV, so that the electronic band gaps of hexagonal and cubic ice are almost independent of the proton-ordering when quantum nuclear vibrations are taken into account. The comparatively small reduction in the band gap over the temperature range 0 − 240 K of around 0.1 eV does not depend on the proton ordering, or whether the ice is protiated or deuterated, or hexagonal, or cubic. We explain this in terms of the atomistic origin of the strong electron-phonon coupling in ice.

  6. Identification of optical transitions in cubic and hexagonal GaN by spatially resolved cathodoluminescence

    NASA Astrophysics Data System (ADS)

    Menniger, J.; Jahn, U.; Brandt, O.; Yang, H.; Ploog, K.

    1996-01-01

    The hexagonal and cubic phases of GaN are characterized by spatially resolved cathodoluminescence (CL) spectra from micrometer-size single crystals with either hexagonal or cubic habits grown by plasma-assisted molecular-beam epitaxy. At 5 K, distinct narrow excitonic lines are found at 3.472 and 3.272 eV for the hexagonal and cubic phase, yielding energy gaps of 3.500 and 3.300 eV, respectively. Detailed temperature- and intensity-dependent CL measurements on cubic GaN crystals enable us to clearly identify the exciton (free: 3.272 eV, bound: 3.263 eV) and the donor-acceptor pair (3.150 eV) transition. Moreover, we determine the donor-band and acceptor-band transition energy for this phase. In addition, phonon replicas of the exciton line and of the donor-acceptor pair transition are observed at 3.185 and 3.064 eV, respectively.

  7. Localized Pd Overgrowth on Cubic Pt Nanocrystals for Enhanced Electrocatalytic Oxidation of Formic Acid

    SciTech Connect

    Lee, H.; Habas, S.E.; Somorjai, G.A.; Yang, P.

    2008-03-20

    Binary Pt/Pd nanoparticles were synthesized by localized overgrowth of Pd on cubic Pt seeds for the investigation of electrocatalytic formic acid oxidation. The binary particles exhibited much less self-poisoning and a lower activation energy relative to Pt nanocubes, consistent with the single crystal study.

  8. On Schrödinger systems with cubic dissipative nonlinearities of derivative type

    NASA Astrophysics Data System (ADS)

    Li, Chunhua; Sunagawa, Hideaki

    2016-05-01

    Consider the initial value problem for systems of cubic derivative nonlinear Schrödinger equations in one space dimension with the masses satisfying a suitable resonance relation. We give structural conditions on the nonlinearity under which the small data solution gains an additional logarithmic decay as t\\to +∞ compared with the corresponding free evolution.

  9. Critical temperature of noninteracting bosonic gases in cubic optical lattices at arbitrary integer fillings.

    PubMed

    Rakhimov, Abdulla; Askerzade, Iman N

    2014-09-01

    We have shown that the critical temperature of a Bose-Einstein condensate to a normal phase transition of noninteracting bosons in cubic optical lattices has a linear dependence on the filling factor, especially at large densities. The condensed fraction exhibits a linear power law dependence on temperature in contrast to the case of ideal homogeneous Bose gases. PMID:25314412

  10. Stability of a new cubic monoxide of Thorium under pressure

    PubMed Central

    Sun, Weiwei; Luo, Wei; Ahuja, Rajeev

    2015-01-01

    Density functional theory has been applied to elucidate the stability of thorium monoxide (ThO). It is found out that the pressure can stabilize the rocksalt phase of ThO, and the transition pressure is estimated between 14 and 22 GPa. The stability of ThO can be attributed due to the gradually filling 5f orbitals at the expense of 7s and 6d electrons in Th metal. For ThO, the pressure induces stronger Th-O bond reflected by the newly established 6d-2p hybridization which is the dominant cause of its stability. The phonon dispersion curves of the rocksalt phase show the positive frequencies which indicates its dynamical stability. Our successful prediction of the stabilization of the metallic ThO has proposed a route to synthesize novel actinide monoxides. PMID:26337015

  11. Organic Chemistry of Low-Mass Star-Forming Cores. I. 7 mm Spectroscopy of Chamaeleon MMSl

    NASA Technical Reports Server (NTRS)

    Cordiner, Martn A.; Charnley, Steven B.; Wirtstroem, Eva S.; Smith, Robert G.

    2012-01-01

    Observations are presented of emission lines from organic molecules at frequencies 32-50 GHz in the vicinity of Chamaeleon MMS1. This chemically rich dense cloud core harbors an extremely young, very low luminosity protostellar object and is a candidate first hydrostatic core. Column densities are derived and emission maps are presented for species including polyynes, cyanopolyynes, sulphuretted carbon chains, and methanol. The polyyne emission peak lies about 5000 AU from the protostar, whereas methanol peaks about 15,000 AU away. Averaged over the telescope beam, the molecular hydrogen number density is calculated to be 10(exp 6) / cubic cm and the gas kinetic temperature is in the range 5-7 K. The abundances of long carbon chains are very large and are indicative of a nonequilibrium carbon chemistry; C6H and HC7N column densities are 5.9(sup +2.9) (sub -1.3) x 10(exp 11) /cubic cm and 3.3 (sup +8.0)(sub -1.5) x 10(exp 12)/sq cm, respectively, which are similar to the values found in the most carbon-chain-rich protostars and prestellar cores known, and are unusually large for star-forming gas. Column density upper limits were obtained for the carbon chain anions C4H(-) and C6H(-), with anion-to-neutral ratios [C4H(-)]/[C4H] < 0.02% and [C6H(-l)]/[C6H] < 10%, consistent with previous observations in interstellar clouds and low-mass protostars. Deuterated HC,3 and c-C3H2 were detected. The [DC3N]/[HC,N] ratio of approximately 4% is consistent with the value typically found in cold interstellar gas.

  12. A parametric experimental investigation of a scramjet nozzle at Mach 6 with Freon and argon or air used for exhaust simulation

    NASA Technical Reports Server (NTRS)

    Cubbage, James M.; Monta, William J.

    1991-01-01

    A parametric experimental investigation of a scramjet nozzle was conducted with a gas mixture used to simulate the scramjet engine exhaust flow at a free-stream Reynolds number of approximately 6.5 x 10(exp 6) per foot. External nozzle surface angles of 16, 20, and 24 deg were tested with a fixed-length ramp and for cowl internal surface angles of 6 and 12 deg. Pressure data on the external nozzle surface were obtained for mixtures of Freon and argon gases with a ratio of specific heats of about 1.23, which matches that of a scramjet exhaust. Forces and moments were determined by integration of the pressure data. Two nozzle configurations were also tested with air used to simulate the exhaust flow. On the external nozzle surface, lift and thrust forces for air exhaust simulation were approximately half of those for Freon-argon exhaust simulation and the pitching moment was approximately a third. These differences were primarily due to the difference in the ratios of specific heats between the two exhaust simulation gases. A 20 deg external surface angle produced the greatest thrust for a 6 deg cowl internal surface angle. A flow fence significantly increased lift and thrust forces over those for the nozzle without a flow fence.

  13. M8L12 cubic cages with all facial Δ or facial Λ configuration: effects of surface anions on the occupancy of the cage and anion exchange.

    PubMed

    Yang, Jing; Chang, Xiao-Yong; Sham, Kiu-Chor; Yiu, Shek-Man; Kwong, Hoi-Lun; Che, Chi-Ming

    2016-05-21

    M8L12 cubic cages (M = Mn(II), Zn(II) or Cd(II)), with all eight metal ions having all facial Δ or facial Λ configurations and having an encapsulated anion, were prepared by the self-assembly of m-xylene-bridged imidazolyl-imine ligands and MX2 (X = PF6(-), SbF6(-), TfO(-)) salts; the encapsulated anion exchange with different anions (SbF6(-), Tf2N(-), NO3(-), TsO(-)) was studied and the results with NO3(-) and TsO(-) indicate that anions on the cage surfaces affect the encapsulated anion exchange and the occupancy of the cage. PMID:27064122

  14. Turbulent Aeroheating Testing of Mars Science Laboratory Entry Vehicle

    NASA Technical Reports Server (NTRS)

    Hollis, Brian R.; Collier, Arnold S.

    2008-01-01

    An experimental investigation of turbulent aeroheating on the Mars Science Laboratory entry vehicle heat shield has been conducted in the Arnold Engineering Development Center Hypervelocity Wind Tunnel No. 9. Testing was performed on a 6-in. (0.1524 m) diameter MSL model in pure N2 gas in the tunnel's Mach 8 and Mach 10 nozzles at free stream Reynolds numbers of 4.1 x 10(exp 6)/ft to 49 x 10(exp 6)/ft (1.3 x 10(exp 7)/m to 19 x 10(exp 6/ft) and 1.2 x 10(exp 6)/ft to 19 x 10(exp 6)/ft (0.39 x 10(exp 7)/m to 62 x 10(exp 7)/m), respectively. These conditions were sufficient to span the regime of boundary-layer flow from completely laminar to fully-developed turbulent flow over the entire forebody. A supporting aeroheating test was also conducted in the Langley Research Center 20-Inch Mach 6 Air Tunnel at free stream Reynolds number of 1 x 10(exp 6)/ft to 7 x 10(exp 6)/ft (0.36 x 10(exp 7)/m to 2.2 x 10(exp 7)/m) in order to help corroborate the Tunnel 9 results. A complementary computational fluid dynamics study was conducted in parallel to the wind tunnel testing. Laminar and turbulent predictions were generated for the wind tunnel test conditions and comparisons were performed with the data for the purpose of helping to define uncertainty margins on predictions for aeroheating environments during entry into the Martian atmosphere. Data from both wind tunnel tests and comparisons with the predictions are presented herein. It was concluded from these comparisons that for perfect-gas conditions, the computational tools could predict fully-laminar or fully-turbulent heating conditions to within 12% or better of the experimental data.

  15. Self-Assembled Cubic Liquid Crystalline Nanoparticles for Transdermal Delivery of Paeonol

    PubMed Central

    Li, Jian-Chun; Zhu, Na; Zhu, Jin-Xiu; Zhang, Wen-Jing; Zhang, Hong-Min; Wang, Qing-Qing; Wu, Xiao-Xiang; Wang, Xiu; Zhang, Jin; Hao, Ji-Fu

    2015-01-01

    Background The aim of this study was to optimize the preparation method for self-assembled glyceryl monoolein-based cubosomes containing paeonol and to characterize the properties of this transdermal delivery system to improve the drug penetration ability in the skin. Material/Methods In this study, the cubic liquid crystalline nanoparticles loaded with paeonol were prepared by fragmentation of glyceryl monoolein (GMO)/poloxamer 407 bulk cubic gel by high-pressure homogenization. We evaluated the Zeta potential of these promising skin-targeting drug-delivery systems using the Malvern Zeta sizer examination, and various microscopies and differential scanning calorimetry were also used for property investigation. Stimulating studies were evaluated based on the skin irritation reaction score standard and the skin stimulus intensity evaluation standard for paeonol cubosomes when compared with commercial paeonol ointment. In vitro tests were performed on excised rat skins in an improved Franz diffusion apparatus. The amount of paeonol over time in the in vitro penetration and retention experiments both was determined quantitatively by HPLC. Results Stimulating studies were compared with the commercial ointment which indicated that the paeonol cubic liquid crystalline nanoparticles could reduce the irritation in the skin stimulating test. Thus, based on the attractive characteristics of the cubic crystal system of paeonol, we will further exploit the cosmetic features in the future studies. Conclusions The transdermal delivery system of paeonol with low-irritation based on the self-assembled cubic liquid crystalline nanoparticles prepared in this study might be a promising system of good tropical preparation for skin application. PMID:26517086

  16. Structural insights into the cubic-hexagonal phase transition kinetics of monoolein modulated by sucrose solutions.

    PubMed

    Reese, Caleb W; Strango, Zachariah I; Dell, Zachary R; Tristram-Nagle, Stephanie; Harper, Paul E

    2015-04-14

    Using DSC (differential scanning calorimetry), we measure the kinetics of the cubic-HII phase transition of monoolein in bulk sucrose solutions. We find that the transition temperature is dramatically lowered, with each 1 mol kg(-1) of sucrose concentration dropping the transition by 20 °C. The kinetics of this transition also slow greatly with increasing sucrose concentration. For low sucrose concentrations, the kinetics are asymmetric, with the cooling (HII-cubic) transition taking twice as long as the heating (cubic-HII) transition. This asymmetry in transition times is reduced for higher sucrose concentrations. The cooling transition exhibits Avrami exponents in the range of 2 to 2.5 and the heating transition shows Avrami exponents ranging from 1 to 3. A classical Avrami interpretation would be that these processes occur via a one or two dimensional pathway with variable nucleation rates. A non-classical perspective would suggest that these exponents reflect the time dependence of pore formation (cooling) and destruction (heating). New density measurements of monoolein show that the currently accepted value is about 5% too low; this has substantial implications for electron density modeling. Structural calculations indicate that the head group area and lipid length in the cubic-HII transition shrink by about 12% and 4% respectively; this reduction is practically the same as that seen in a lipid with a very different molecular structure (rac-di-12:0 β-GlcDAG) that makes the same transition. Thermodynamic considerations suggest there is a hydration shell about one water molecule thick in front of the lipid head groups in both the cubic and HII phases. PMID:25758637

  17. Cubic ice and large humidity with respect to ice in cold cirrus clouds

    NASA Astrophysics Data System (ADS)

    Bogdan, A.; Loerting, T.

    2009-04-01

    Recently several studies have reported about the possible formation of cubic ice in upper-tropospheric cirrus ice clouds and its role in the observed elevated relative humidity with respect to hexagonal ice, RHi, within the clouds. Since cubic ice is metastable with respect to stable hexagonal ice, its vapour pressure is higher. A key issue in determining the ratio of vapour pressures of cubic ice Pc and hexagonal ice Ph is the enthalpy of transformation from cubic to hexagonal ice Hc→h. By dividing the two integrated forms of the Clausius-Clapeyron equation for cubic ice and hexagonal ice, one obtains the relationship (1): ln Pc-- ln P*c-=--(Hc→h--) Ph P*h R 1T-- 1T* (1) from which the importance of Hc→h is evident. In many literature studies the approximation (2) is used: ln Pc-= Hc-→h. Ph RT (2) Using this approximated form one can predict the ratio of vapour pressures by measuring Hc→h. Unfortunately, the measurement of Hc→h is difficult. First, the enthalpy difference is very small, and the transition takes place over a broad temperature range, e.g., between 230 K and 260 K in some of our calorimetry experiments. Second, cubic ice (by contrast to hexagonal ice) can not be produced as a pure crystal. It always contains hexagonal stacking faults, which are evidenced by the (111)-hexagonal Bragg peak in the powder diffractogram. If the number of hexagonal stacking faults in cubic ice is high, then one could even consider this material as hexagonal ice with cubic stacking faults. Using the largest literature value of the change of enthalpy of transformation from cubic to hexagonal ice, Hc→h ? 160 J/mol, Murphy and Koop (2005) calculated that Pc would be ~10% higher than that of hexagonal ice Phat 180 K - 190 K, which agrees with the measurements obtained later by Shilling et al. (2006). Based on this result Shilling et al. concluded that "the formation of cubic ice at T < 202 K may significantly contribute to the persistent in

  18. Phenomenological theory of phase transitions in epitaxial BaxSr1-xTiO3 thin films on (111)-oriented cubic substrates

    NASA Astrophysics Data System (ADS)

    Shirokov, V. B.; Shakhovoy, R. A.; Razumnaya, A. G.; Yuzyuk, Yu. I.

    2015-07-01

    A phenomenological thermodynamic theory of BaxSr1-xTiO3 (BST-x) thin films epitaxially grown on (111)-oriented cubic substrates is developed using the Landau-Devonshire approach. The group-theoretical analysis of the low-symmetry phases was performed taking into account two order parameters: the polarization related to ionic shifts in polar zone-center F1u mode and the out-of-phase rotation of TiO6 octahedra corresponding to the R25 zone-boundary mode in the parent cubic phase P m 3 ¯ m . The eight-order thermodynamic potential for BST-x solid solutions was developed and analyzed. We constructed the "concentration-misfit strain" phase diagram for BST-x thin films at room temperature and found that polar rhombohedral R3m phase with the polarization normal to the substrate is stable for x > 0.72 and negative misfit strains, while ferroelectric monoclinic C2 and Cm phases with in-plane polarization are stable for much smaller x and positive or slightly negative misfit strains. We constructed the "temperature-misfit strain" phase diagrams for several concentrations (x = 1, 0.8, 0.6, 0.4, and 0.2). Systematic changes of the phase transition lines between the paraelectric and ferroelectric phases are discussed. The phase diagrams are useful for practical applications in thin-film engineering.

  19. Turbulent Aeroheating Testing of Mars Science Laboratory Entry Vehicle in Perfect-Gas Nitrogen

    NASA Technical Reports Server (NTRS)

    Hollis, Brian R.; Collier, Arnold S.

    2007-01-01

    An experimental investigation of turbulent aeroheating on the Mars Science Laboratory entry vehicle heat shield has been conducted in the Arnold Engineering Development Center Hypervelocity Wind Tunnel No. 9. Testing was performed on a 6-in. (0.1524 m) diameter MSL model in pure N2 gas in the tunnel s Mach 8 and Mach 10 nozzles at free stream Reynolds numbers of 4.1x10(exp 6)/ft to 49x10(exp 6)/ft (1.3x10(exp 7)/m to 16x10(exp 7)/m) and 1.2x10(exp 6)/ft to 19x10(exp 6)/ft (0.39x10(exp 7)/m to 62x10(exp 7)/m), respectively. These conditions were sufficient to span the regime of boundary-layer flow from completely laminar to fully-developed turbulent flow over the entire forebody. A supporting aeroheating test was also conducted in the Langley Research Center 20-Inch Mach 6 Air Tunnel at free stream Reynolds number of 1x10(exp 6)/ft to 7x10(exp 6)/ft (0.36x10(exp 7)/m to 2.2x10(exp 7)/m) in order to help corroborate the Tunnel 9 results. A complementary computational fluid dynamics study was conducted in parallel to the wind tunnel testing. Laminar and turbulent predictions were generated for all wind tunnel test conditions and comparisons were performed with the data for the purpose of helping to define uncertainty margins on predictions for aeroheating environments during entry into the Martian atmosphere. Data from both wind tunnel tests and comparisons with the predictions are presented herein. It was concluded from these comparisons that for perfect-gas conditions, the computational tools could predict fully-laminar or fully-turbulent heating conditions to within 10% of the experimental data

  20. Synthesis, structure, and superconductivity in the new-structure-type compound: SrPt6P2.

    PubMed

    Lv, Bing; Jawdat, BenMaan I; Wu, Zheng; Sorolla, Maurice; Gooch, Melissa; Zhao, Kui; Deng, Liangzi; Xue, Yu-Yi; Lorenz, Bernd; Guloy, Arnold M; Chu, Ching-Wu

    2015-02-01

    A metal-rich ternary phosphide, SrPt(6)P(2), with a unique structure type was synthesized at high temperatures. Its crystal structure was determined by single-crystal X-ray diffraction [cubic space group Pa3̅; Z = 4; a = 8.474(2) Å, and V = 608.51(2) Å(3)]. The structure features a unique three-dimensional anionic (Pt(6)P(2))(2-) network of vertex-shared Pt(6)P trigonal prisms. The Sr atoms occupy a 12-coordinate (Pt) cage site and form a cubic close-packed (face-centered-cubic) arrangement, and the P atoms formally occupy tetrahedral interstices. The metallic compound becomes superconducting at 0.6 K, as evidenced by magnetic and resistivity measurements. PMID:25525885

  1. Controllable Phase Transformation and Mid-infrared Emission from Er3+-Doped Hexagonal-/Cubic-NaYF4 Nanocrystals

    PubMed Central

    Yang, Dandan; Chen, Dongdan; He, Huilin; Pan, Qiwen; Xiao, Quanlan; Qiu, Jianrong; Dong, Guoping

    2016-01-01

    The morphology of hexagonal phase NaYF4:Er3+ nanorods synthesized by hydrothermal method changed greatly after a continuing calcination, along with a phase transformation to cubic phase. Photoluminescence (PL) spectra indicated that mid-infrared (MIR) emission was obtained in both hexagonal and cubic phase NaYF4:Er3+ nanocrystals for the first time. And the MIR emission of NaYF4:Er3+ nanocrystals enhanced remarkably at higher calcination temperature. To prevent uncontrollable morphology from phase transformation, the cubic phase NaYF4:Er3+ nanospheres with an average size of ~100 nm were prepared via a co-precipitation method directly. In contrast, the results showed better morphology and size of cubic phase NaYF4:Er3+ nanocrystals have realized when calcined at different temperatures. And PL spectra demonstrated a more intense MIR emission in the cubic phase NaYF4:Er3+ nanocrystals with an increasing temperature. Besides, the MIR emission peak of Er3+ ions had an obvious splitting in cubic phase NaYF4. Therefore, cubic phase NaYF4:Er3+ nanospheres with more excellent MIR luminescent properties seems to provide a new material for nanocrystal-glass composites, which is expected to open a broad new field for the realization of MIR lasers gain medium. PMID:27453150

  2. Controllable Phase Transformation and Mid-infrared Emission from Er(3+)-Doped Hexagonal-/Cubic-NaYF4 Nanocrystals.

    PubMed

    Yang, Dandan; Chen, Dongdan; He, Huilin; Pan, Qiwen; Xiao, Quanlan; Qiu, Jianrong; Dong, Guoping

    2016-01-01

    The morphology of hexagonal phase NaYF4:Er(3+) nanorods synthesized by hydrothermal method changed greatly after a continuing calcination, along with a phase transformation to cubic phase. Photoluminescence (PL) spectra indicated that mid-infrared (MIR) emission was obtained in both hexagonal and cubic phase NaYF4:Er(3+) nanocrystals for the first time. And the MIR emission of NaYF4:Er(3+) nanocrystals enhanced remarkably at higher calcination temperature. To prevent uncontrollable morphology from phase transformation, the cubic phase NaYF4:Er(3+) nanospheres with an average size of ~100 nm were prepared via a co-precipitation method directly. In contrast, the results showed better morphology and size of cubic phase NaYF4:Er(3+) nanocrystals have realized when calcined at different temperatures. And PL spectra demonstrated a more intense MIR emission in the cubic phase NaYF4:Er(3+) nanocrystals with an increasing temperature. Besides, the MIR emission peak of Er(3+) ions had an obvious splitting in cubic phase NaYF4. Therefore, cubic phase NaYF4:Er(3+) nanospheres with more excellent MIR luminescent properties seems to provide a new material for nanocrystal-glass composites, which is expected to open a broad new field for the realization of MIR lasers gain medium. PMID:27453150

  3. Controllable Phase Transformation and Mid-infrared Emission from Er3+-Doped Hexagonal-/Cubic-NaYF4 Nanocrystals

    NASA Astrophysics Data System (ADS)

    Yang, Dandan; Chen, Dongdan; He, Huilin; Pan, Qiwen; Xiao, Quanlan; Qiu, Jianrong; Dong, Guoping

    2016-07-01

    The morphology of hexagonal phase NaYF4:Er3+ nanorods synthesized by hydrothermal method changed greatly after a continuing calcination, along with a phase transformation to cubic phase. Photoluminescence (PL) spectra indicated that mid-infrared (MIR) emission was obtained in both hexagonal and cubic phase NaYF4:Er3+ nanocrystals for the first time. And the MIR emission of NaYF4:Er3+ nanocrystals enhanced remarkably at higher calcination temperature. To prevent uncontrollable morphology from phase transformation, the cubic phase NaYF4:Er3+ nanospheres with an average size of ~100 nm were prepared via a co-precipitation method directly. In contrast, the results showed better morphology and size of cubic phase NaYF4:Er3+ nanocrystals have realized when calcined at different temperatures. And PL spectra demonstrated a more intense MIR emission in the cubic phase NaYF4:Er3+ nanocrystals with an increasing temperature. Besides, the MIR emission peak of Er3+ ions had an obvious splitting in cubic phase NaYF4. Therefore, cubic phase NaYF4:Er3+ nanospheres with more excellent MIR luminescent properties seems to provide a new material for nanocrystal-glass composites, which is expected to open a broad new field for the realization of MIR lasers gain medium.

  4. Three-dimensional kinetic Monte Carlo simulations of cubic transition metal nitride thin film growth

    NASA Astrophysics Data System (ADS)

    Nita, F.; Mastail, C.; Abadias, G.

    2016-02-01

    A three-dimensional kinetic Monte Carlo (KMC) model has been developed and used to simulate the microstructure and growth morphology of cubic transition metal nitride (TMN) thin films deposited by reactive magnetron sputtering. Results are presented for the case of stoichiometric TiN, chosen as a representative TMN prototype. The model is based on a NaCl-type rigid lattice and includes deposition and diffusion events for both N and Ti species. It is capable of reproducing voids and overhangs, as well as surface faceting. Simulations were carried out assuming a uniform flux of incoming particles approaching the surface at normal incidence. The ballistic deposition model is parametrized with an interaction parameter r0 that mimics the capture distance at which incoming particles may stick on the surface, equivalently to a surface trapping mechanism. Two diffusion models are implemented, based on the different ways to compute the site-dependent activation energy for hopping atoms. The influence of temperature (300-500 K), deposition flux (0.1-100 monolayers/s), and interaction parameter r0 (1.5-6.0 Å) on the obtained growth morphology are presented. Microstructures ranging from highly porous, [001]-oriented straight columns with smooth top surface to rough columns emerging with different crystallographic facets are reproduced, depending on kinetic restrictions, deposited energy (seemingly captured by r0), and shadowing effect. The development of facets is a direct consequence of the diffusion model which includes an intrinsic (minimum energy-based) diffusion anisotropy, although no crystallographic diffusion anisotropy was explicitly taken into account at this stage. The time-dependent morphological evolution is analyzed quantitatively to extract the growth exponent β and roughness exponent α , as indicators of kinetic roughening behavior. For dense TiN films, values of α ≈0.7 and β =0.24 are obtained in good agreement with existing experimental data. At this

  5. Activation Energy of the Low-pH-Induced Lamellar to Bicontinuous Cubic Phase Transition in Dioleoylphosphatidylserine/Monoolein.

    PubMed

    Oka, Toshihiko; Saiki, Takahiro; Alam, Jahangir Md; Yamazaki, Masahito

    2016-02-01

    Electrostatic interaction is an important factor for phase transitions between lamellar liquid-crystalline (Lα) and inverse bicontinuous cubic (QII) phases. We investigated the effect of temperature on the low-pH-induced Lα to double-diamond cubic (QII(D)) phase transition in dioleoylphosphatidylserine (DOPS)/monoolein (MO) using time-resolved small-angle X-ray scattering with a stopped-flow apparatus. Under all conditions of temperature and pH, the Lα phase was directly transformed into an intermediate inverse hexagonal (HII) phase, and subsequently the HII phase slowly converted to the QII(D) phase. We obtained the rate constants of the initial step (i.e., the Lα to HII phase transition) and of the second step (i.e., the HII to QII(D) phase transition) using the non-negative matrix factorization method. The rate constant of the initial step increased with temperature. By analyzing this result, we obtained the values of its apparent activation energy, Ea (Lα → HII), which did not change with temperature but increased with an increase in pH. In contrast, the rate constant of the second step decreased with temperature at pH 2.6, although it increased with temperature at pH 2.7 and 2.8. These results indicate that the value of Ea (HII → QII(D)) at pH 2.6 increased with temperature, but the values of Ea (HII → QII(D)) at pH 2.7 and 2.8 were constant with temperature. The values of Ea (HII → QII(D)) were smaller than those of Ea (Lα → HII) at the same pH. We analyzed these results using a modified quantitative theory on the activation energy of phase transitions of lipid membranes proposed initially by Squires et al. (Squires, A. M.; Conn, C. E.; Seddon, J. M.; Templer, R. H. Soft Matter 2009, 5, 4773). On the basis of these results, we discuss the mechanism of this phase transition. PMID:26766583

  6. Electron paramagnetic resonance and spinlattice relaxation of Cu2+ ions in ZnSeO4·6H2O

    NASA Astrophysics Data System (ADS)

    Al'-Sufi, A. R.; Bulka, G. R.; Vinokurov, V. M.; Kurkin, I. N.; Nizamutdinov, N. M.; Salikhov, I. Kh.

    1993-06-01

    In this paper, we present detailed studies of the EPR spectra of Cu2+ ions in single crystals of ZnSeO4·6H2O. We describe the spectrum with a rhombic spin Hamiltonian with the following parameters: gz=2.427; gy=2.095; gx=2.097; A{z/65}=138.4·10-4 cm-1; A{x/65}=22.3·10-4 cm-1. We studied spin-lattice relaxation in the temperature range 4 300 K at the frequency v≈9.3 GHz. The measured spin-lattice relaxation rate for the orientation H∥L4 is described well at T<5 K by a linear dependence, while at T>5 K it is described by the sum of three exponentials: T_1^{ - 1} = 0.27T + 3.3 \\cdot 10^{text{s}} exp left( {{ - 69.5}/T} right) + 2.6 \\cdot 10^7 exp left( {{ - 140}/T} right) + 1.36 \\cdot 10^{10} exp left( {{ - 735.6}/T} right){text{ sec}}^{{text{ - 1}}} .We discuss possible reasons for the exponential dependence of T{1/-1} for the Raman process.

  7. Photocatalytic water splitting for hydrogen generation on cubic, orthorhombic, and tetragonal KNbO3 microcubes

    NASA Astrophysics Data System (ADS)

    Zhang, Tingting; Zhao, Kun; Yu, Jiaguo; Jin, Jian; Qi, Yang; Li, Huiquan; Hou, Xinjuan; Liu, Gang

    2013-08-01

    Potassium niobate (KNbO3) microcubes with orthorhombic and tetragonal phases were hydrothermally prepared and characterized by powder X-ray diffraction, nitrogen adsorption-desorption, micro-Raman spectroscopy, Fourier transform infrared spectroscopy, diffuse reflectance UV-visible spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The photoreactivity of the as-prepared KNbO3 samples was evaluated regarding the hydrogen evolution from aqueous methanol under UV, and the results were compared with that of cubic KNbO3 microcubes. The photocatalytic reactivity was shown to be phase-dependent, following the order cubic > orthorhombic > tetragonal. Insight into the phase-dependent photocatalytic properties was gained by first-principles density functional calculations. The best photocatalytic performance of cubic KNbO3 is ascribed to it having the highest symmetry in the bulk structure and associated unique electronic structure. Further, the surface electronic structure plays a key role leading to the discrepancy in photoreactivity between orthorhombic and tetragonal KNbO3. The results from this study are potentially applicable to a range of perovskite-type mixed metal oxides useful in water splitting as well as other areas of heterogeneous photocatalysis.Potassium niobate (KNbO3) microcubes with orthorhombic and tetragonal phases were hydrothermally prepared and characterized by powder X-ray diffraction, nitrogen adsorption-desorption, micro-Raman spectroscopy, Fourier transform infrared spectroscopy, diffuse reflectance UV-visible spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The photoreactivity of the as-prepared KNbO3 samples was evaluated regarding the hydrogen evolution from aqueous methanol under UV, and the results were compared with that of cubic KNbO3 microcubes. The photocatalytic reactivity was

  8. Aligned platinum nanowire networks from surface-oriented lipid cubic phase templates

    NASA Astrophysics Data System (ADS)

    Richardson, S. J.; Burton, M. R.; Staniec, P. A.; Nandhakumar, I. S.; Terrill, N. J.; Elliott, J. M.; Squires, A. M.

    2016-01-01

    Mesoporous metal structures featuring a bicontinuous cubic morphology have a wide range of potential applications and novel opto-electronic properties, often orientation-dependent. We describe the production of nanostructured metal films 1-2 microns thick featuring 3D-periodic `single diamond' morphology that show high out-of-plane alignment, with the (111) plane oriented parallel to the substrate. These are produced by electrodeposition of platinum through a lipid cubic phase (QII) template. Further investigation into the mechanism for the orientation revealed the surprising result that the QII template, which is tens of microns thick, is polydomain with no overall orientation. When thicker platinum films are grown, they also show increased orientational disorder. These results suggest that polydomain QII samples display a region of uniaxial orientation at the lipid/substrate interface up to approximately 2.8 +/- 0.3 μm away from the solid surface. Our approach gives previously unavailable information on the arrangement of cubic phases at solid interfaces, which is important for many applications of QII phases. Most significantly, we have produced a previously unreported class of oriented nanomaterial, with potential applications including metamaterials and lithographic masks.Mesoporous metal structures featuring a bicontinuous cubic morphology have a wide range of potential applications and novel opto-electronic properties, often orientation-dependent. We describe the production of nanostructured metal films 1-2 microns thick featuring 3D-periodic `single diamond' morphology that show high out-of-plane alignment, with the (111) plane oriented parallel to the substrate. These are produced by electrodeposition of platinum through a lipid cubic phase (QII) template. Further investigation into the mechanism for the orientation revealed the surprising result that the QII template, which is tens of microns thick, is polydomain with no overall orientation. When thicker

  9. Diffusivity in Alumina Scales Grown on Al-MAX Phases

    NASA Technical Reports Server (NTRS)

    Smialek, James L.

    2014-01-01

    Ti3AlC2, Ti2AlC, and Cr2AlC are oxidation resistant MAX phase compounds distinguished by the formation of protective Al2O3 scales with well controlled kinetics. A modified Wagner treatment was used to obtain interfacial grain boundary diffusivity, deltaD(sub gb,O,int.), from scale growth rates and corresponding grain size. It is based on the p(O2)(exp -1/6) dependency of the double charged oxygen vacancy and oxygen diffusivity, coupled with the effective diffusion constant for short circuit grain boundary paths. Data from the literature for MAX phases was analyzed accordingly, and deltaD(sub gb,O,int.) was found to nearly coincide with the Arrhenius line developed for Zr-doped FeCrAl, where: deltaD(sub gb,O,int.) = 1.8x10(exp -10) exp(-375 kJ/RT) cubic meters/s. Furthermore, this oxidation relation suggests the more general format applicable to bulk samples under ambient conditions: deltaD(sub gb,O) = 7.567x10(exp -8) exp(-544 kJ/RT) p(O2)(exp -1/6) cubic meters/[s x Pa(exp -1/6)]. Data from many other FeCrAl(X) studies were similarly assessed to show general agreement with the relation for deltaD(sub gb,O,int.). This analysis reinforces the view that protective alumina scales grow by similar mechanisms for these Al-MAX phases and oxidation resistant FeCrAl alloys.

  10. Possible significance of cubic water-ice, H2O-Ic, in the atmospheric water cycle of Mars

    NASA Technical Reports Server (NTRS)

    Gooding, James L.

    1988-01-01

    The possible formation and potential significance of the cubic ice polymorph on Mars is discussed. When water-ice crystallizes on Earth, the ambient conditions of temperature and pressure result in the formation of the hexagonal ice polymorph; however, on Mars, the much lower termperature and pressures may permit the crystallization of the cubic polymorph. Cubic ice has two properties of possible importance on Mars: it is an excellant nucleator of other volatiles (such as CO2), and it undergoes an exothermic transition to hexagonal ice at temperatures above 170 K. These properties may have significant implications for both martian cloud formation and the development of the seasonal polar caps.

  11. Third-Order Doppler Parameter Estimation of Bistatic Forward-Looking SAR Based on Modified Cubic Phase Function

    NASA Astrophysics Data System (ADS)

    Li, Wenchao; Yang, Jianyu; Huang, Yulin; Kong, Lingjiang

    For Doppler parameter estimation of forward-looking SAR, the third-order Doppler parameter can not be neglected. In this paper, the azimuth signal of the transmitter fixed bistatic forward-looking SAR is modeled as a cubic polynomial phase signal (CPPS) and multiple time-overlapped CPPSs, and the modified cubic phase function is presented to estimate the third-order Doppler parameter. By combining the cubic phase function (CPF) with Radon transform, the method can give an accurate estimation of the third-order Doppler parameter. Simulations validate the effectiveness of the algorithm.

  12. The three-cubic method: An optional online robot joint trajectory generator under velocity, acceleration, and wandering constraints

    SciTech Connect

    Tondu, B.; Bazaz, S.A.

    1999-09-01

    An original method called the three-cubic method is proposed to generate online robot joint trajectories interpolating given position points with associated velocities. The method is based on an acceleration profile composed of three cubic polynomial segments, which ensure a zero acceleration at each intermediate point. Velocity and acceleration continuity is obtained, and this three-cubics combination allows the analytical solution to the minimum time trajectory problem under maximum velocity and acceleration constraints. Possible wandering is detected and can be overcome. Furthermore, the analytical solution to the minimum time trajectory problem leads to an online trajectory computation.

  13. Systematic and controllable negative, zero, and positive thermal expansion in cubic Zr(1-x)Sn(x)Mo2O8.

    PubMed

    Tallentire, Sarah E; Child, Felicity; Fall, Ian; Vella-Zarb, Liana; Evans, Ivana Radosavljević; Tucker, Matthew G; Keen, David A; Wilson, Claire; Evans, John S O

    2013-08-28

    We describe the synthesis and characterization of a family of materials, Zr1-xSnxMo2O8 (0 < x < 1), whose isotropic thermal expansion coefficient can be systematically varied from negative to zero to positive values. These materials allow tunable expansion in a single phase as opposed to using a composite system. Linear thermal expansion coefficients, αl, ranging from -7.9(2) × 10(-6) to +5.9(2) × 10(-6) K(-1) (12-500 K) can be achieved across the series; contraction and expansion limits are of the same order of magnitude as the expansion of typical ceramics. We also report the various structures and thermal expansion of "cubic" SnMo2O8, and we use time- and temperature-dependent diffraction studies to describe a series of phase transitions between different ordered and disordered states of this material. PMID:23895493

  14. Melting and Sintering of a Body-Centered Cubic Superlattice of PbSe Nanocrystals Followed by Small Angle X-ray Scattering

    PubMed Central

    Goodfellow, Brian W.; Patel, Reken N.; Panthani, Matthew G.; Smilgies, Detlef-M.; Korgel, Brian A.

    2011-01-01

    The structural evolution of a body-centered cubic (bcc) superlattice of 6.6 nm diameter organic ligand-coated PbSe nanocrystals was studied in situ by small angle X-ray scattering (SAXS) as it was heated in air from room temperature to 350°C. As it was heated above room temperature, the superlattice contracted slightly, but maintained bcc structure up to 110°C. Once the temperature rose above 110°C, the superlattice began to disorder, by first losing long-range translational order and then local positional order. At temperatures exceeding 168°C, the nanocrystals sintered and oxidized, transforming into PbSeO3 nanorods. PMID:21566701

  15. Struktur und Bindung in Übergangsmetall-Fluoriden MIIMeIVF6. Neutronenbeugungs-Strukturuntersuchungen an CaSnF6, FeZrF6, und CrZrF6

    NASA Astrophysics Data System (ADS)

    Mayer, H. W.; Reinen, D.; Heger, G.

    1983-11-01

    Compounds MIIMe IVF 6 requently undergo phase transitions from the cubic ordered ReO 3 to the trigonal LiSbF 6 structure when lowering the temperature. In case of a strongly Jahn-Teller unstable cation in the MII position additional phases may occur. Results of powder neutron-diffraction studies on CaSnF 6, FeZrF 6, and CrZrF 6 at different temperatures are reported. The high-temperature phases have the space group Fm3 m; the F - ligands are either statistically displaced from the MIIMe IV directions or undergo a strong thermal motion perpendicular to these directions ( ∢M II FMe IV: 165-180°). The thermal ellipsoids of the CrF bonds are strongly indicative of a dynamical Jahn-Teller effect in addition. In the low-temperature phases of CaSnF 6 and FeZrF 6 (space group R overline3) the ∢M II FMe IV is more distinctly bent (⋍155-160°). CrZrF 6 undergoes two reversible phase transitions, which are determined to occur at 415 ± 5 K (cubic → tetragonal, dynamic to static Jahn-Teller distortion of CrF 6 octahedra and 150 ± 10 K (tetragonal → (pseudo)monoclinic).

  16. Single-photon emission from cubic GaN quantum dots

    SciTech Connect

    Kako, Satoshi; Holmes, Mark; Sergent, Sylvain; Bürger, Matthias; As, Donat J.; Arakawa, Yasuhiko

    2014-01-06

    We report the demonstration of single-photon emission from cubic GaN/AlN quantum dots grown by molecular beam epitaxy. We have observed spectrally clean and isolated emission peaks from these quantum dots. Clear single-photon emission was detected by analyzing one such peak at 4 K. The estimated g{sup (2)}[0] value is 0.25, which becomes 0.05 when corrected for background and detector dark counts. We have also observed the single-photon nature of the emission up to 100 K (g{sup (2)}[0] = 0.47). These results indicate that cubic GaN quantum dots are possible candidates for high-temperature operating UV single-photon sources with the possibility of integration into photonic nanostructures.

  17. Cubic Zig-Zag Enrichment of the Classical Kirchhoff Kinematics for Laminated and Sandwich Plates

    NASA Technical Reports Server (NTRS)

    Nemeth, Michael P.

    2012-01-01

    A detailed anaylsis and examples are presented that show how to enrich the kinematics of classical Kirchhoff plate theory by appending them with a set of continuous piecewise-cubic functions. This analysis is used to obtain functions that contain the effects of laminate heterogeneity and asymmetry on the variations of the inplane displacements and transverse shearing stresses, for use with a {3, 0} plate theory in which these distributions are specified apriori. The functions used for the enrichment are based on the improved zig-zag plate theory presented recently by Tessler, Di Scuva, and Gherlone. With the approach presented herein, the inplane displacements are represented by a set of continuous piecewise-cubic functions, and the transverse shearing stresses and strains are represented by a set of piecewise-quadratic functions that are discontinuous at the ply interfaces.

  18. Low energy radiation stability of nano-crystalline cubic Zirconia films

    NASA Astrophysics Data System (ADS)

    Kalita, Parswajit; Ghosh, Santanu; Avasthi, Devesh K.

    2016-07-01

    The radiation stability of nano-crystalline cubic Zirconia films was investigated under 41 keV He ion irradiation. These ions were chosen to simulate alpha particles (produced during fission events) because of the similar electronic energy loss in Zirconia. The ZrO2 films, with an average grain size of 8 nm, were grown on Si (1 0 0) substrates by electron beam assisted thermal evaporation. Although the cubic structure was retained upon irradiation, a slight reduction in crystallinity in the irradiated films was detected as compared to the as-deposited film. No bulk amorphization was however observed for any of the fluences and hence these films are radiation tolerant to alpha particles.

  19. Spin excitations in cubic maghemite nanoparticles studied by time-of-flight neutron spectroscopy

    NASA Astrophysics Data System (ADS)

    Disch, S.; Hermann, R. P.; Wetterskog, E.; Podlesnyak, A. A.; An, K.; Hyeon, T.; Salazar-Alvarez, G.; Bergström, L.; Brückel, Th.

    2014-02-01

    We have determined the field dependence of collective magnetic excitations in iron oxide nanoparticles of cubic shape with 8.42(2) nm edge length and a narrow log normal size distribution of 8.2(2)% using time-of-flight neutron spectroscopy. The energy dependence of the uniform precession modes was investigated up to 5 T applied field and yields a Landé factor g =2.05(2) as expected for maghemite (γ-Fe2O3) nanoparticles. A large effective anisotropy field of BA ,eff=0.45(16) T was determined, in excellent agreement with macroscopic measurements. This anisotropy is attributed to enhanced shape anisotropy in these monodisperse cubic nanoparticles. The combination of our results with macroscopic magnetization information provides a consistent view of the energy scales of superparamagnetic relaxation and collective magnetic excitations in magnetic nanoparticles.

  20. Magnetic properties of cubic FeCo nanoparticles with anisotropic long chain structure

    NASA Astrophysics Data System (ADS)

    Liu, Jinming; Wu, Kai; Wang, Jian-Ping

    2016-05-01

    Cubic FeCo alloy nanoparticles (NPs) with body-centered cubic (bcc) phase were prepared using sputter based gas-condensation method. When the NPs formed long chain assemblies, the magnetic properties were quite different from that of well-dispersed NPs. Most of the well-dispersed NPs were superparamagnetic at room temperature while the long chain NP assemblies were ferromagnetic with coercivities around 765 Oe, which displayed quite different magnetic properties. The ferromagnetism of long chain NPs was from the exchange coupling between NPs, which eventually led to the transition from superparamagnetism (SPM) to superferromagetism (SFM). Zero-field-cooled (ZFC) and field-cooled (FC) curves were obtained and long chain NP assemblies displayed ferromagnetism at the temperature ranging from 10 K to 400 K. Time-dependent remanent magnetic moment curves also indicated that the long chain structure had better thermal stability due to the strong exchange coupling.

  1. pH-responsive lyotropic liquid crystals for the preparation of pure cubic zirconia nanoparticles

    NASA Astrophysics Data System (ADS)

    He, Wei Yan; Liu, Jin Rong; He, Zhang; Cao, Zhen Zhu; Li, Cai Hong; Gao, Yan Fang

    2016-07-01

    We present a lyotropic liquid crystal system consisting of SDS/Triton X-100/water at 25 °C. This system is respond to pH variations with a phase switch. When pH is altered from alkaline (pH 13) to acidic (pH 2) conditions, phase change occurs from a bicontinuous hexagonal phase to a partially hexagonal phase until it disappears. The hexagonal phase under alkaline conditions is stable. Thus, this system is an ideal candidate for the preparation of pure cubic ZrO2 nanoparticles. XRD results confirm that the as-synthesized powder is composed of pure cubic ZrO2. These nanoparticles also exhibit a thermal stability of up to 800 °C. The size and morphological characteristics of the nanoparticles are greatly affected by ZrOCl2 concentration. The mechanism of zirconia nanoparticle synthesis in a lyotropic hexagonal phase was proposed.

  2. Lyotropic Liquid Crystalline Cubic Phases as Versatile Host Matrices for Membrane-Bound Enzymes.

    PubMed

    Sun, Wenjie; Vallooran, Jijo J; Fong, Wye-Khay; Mezzenga, Raffaele

    2016-04-21

    Lyotropic liquid crystalline cubic mesophases can function as host matrices for enzymes because of their biomimetic structural characteristics, optical transparency, and capability to coexist with water. This study demonstrates that the in meso immobilized membrane-bound enzyme d-fructose dehydrogenase (FDH) preserves its full activity, follows ideal Michaelis-Menten kinetics, and shows improved stability compared to its behavior in solution. Even after 5 days, the immobilized FDH retained its full activity in meso, whereas a model hydrophilic enzyme, horseradish peroxidase, maintained only 21% of its original activity. We reason that the lipidic bilayers in the three-dimensional structures of cubic mesophases provide an ideal environment for the reconstitution of a membrane-bound enzyme. The preserved activity, long-term stability, and reusability demonstrate that these hybrid nanomaterials are ideal matrices for biosensing and biocatalytic fuel cell applications. PMID:27050734

  3. Analytic cubic and quartic force fields using density-functional theory

    SciTech Connect

    Ringholm, Magnus; Gao, Bin; Thorvaldsen, Andreas J.; Ruud, Kenneth; Jonsson, Dan; Bast, Radovan; Ekström, Ulf; Helgaker, Trygve

    2014-01-21

    We present the first analytic implementation of cubic and quartic force constants at the level of Kohn–Sham density-functional theory. The implementation is based on an open-ended formalism for the evaluation of energy derivatives in an atomic-orbital basis. The implementation relies on the availability of open-ended codes for evaluation of one- and two-electron integrals differentiated with respect to nuclear displacements as well as automatic differentiation of the exchange–correlation kernels. We use generalized second-order vibrational perturbation theory to calculate the fundamental frequencies of methane, ethane, benzene, and aniline, comparing B3LYP, BLYP, and Hartree–Fock results. The Hartree–Fock anharmonic corrections agree well with the B3LYP corrections when calculated at the B3LYP geometry and from B3LYP normal coordinates, suggesting that the inclusion of electron correlation is not essential for the reliable calculation of cubic and quartic force constants.

  4. Breakup of shearless invariant tori in cubic and quartic nontwist maps

    NASA Astrophysics Data System (ADS)

    Wurm, A.; Fuchss Portela, K.

    2012-05-01

    The effect of symmetry on invariant torus breakup in nontwist maps is investigated. In particular, the breakup of shearless invariant tori with winding number ω=(√{5}-1)/2 (inverse golden mean) and ω=√{2}-1 (an inverse silver mean) is studied numerically using Greene's residue criterion in a cubic and a quartic nontwist map. The details of the breakup are compared to those previously obtained for the standard nontwist map, which has the same particular spatial symmetry as the quartic map. The cubic map lacks this symmetry. The results show that if the symmetry exists, the details of the breakup are the same as in the standard nontwist map. If the symmetry does not exist, the breakup is shown to be different.

  5. Lonsdaleite is faulted and twinned cubic diamond and does not exist as a discrete material.

    PubMed

    Németh, Péter; Garvie, Laurence A J; Aoki, Toshihiro; Dubrovinskaia, Natalia; Dubrovinsky, Leonid; Buseck, Peter R

    2014-01-01

    Lonsdaleite, also called hexagonal diamond, has been widely used as a marker of asteroidal impacts. It is thought to play a central role during the graphite-to-diamond transformation, and calculations suggest that it possesses mechanical properties superior to diamond. However, despite extensive efforts, lonsdaleite has never been produced or described as a separate, pure material. Here we show that defects in cubic diamond provide an explanation for the characteristic d-spacings and reflections reported for lonsdaleite. Ultrahigh-resolution electron microscope images demonstrate that samples displaying features attributed to lonsdaleite consist of cubic diamond dominated by extensive {113} twins and {111} stacking faults. These defects give rise to nanometre-scale structural complexity. Our findings question the existence of lonsdaleite and point to the need for re-evaluating the interpretations of many lonsdaleite-related fundamental and applied studies. PMID:25410324

  6. Growth of cubic boron nitride on diamond particles by microwave plasma enhanced chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Saitoh, H.; Yarbrough, W. A.

    1991-06-01

    The nucleation and growth of cubic boron nitride (c-BN) onto diamond powder using solid NaBH4 in low pressure gas mixtures of NH3 and H2 by microwave plasma enhanced chemical vapor deposition has been studied. Boron nitride was deposited on submicron diamond seed crystals scattered on (100) silicon single crystal wafers and evidence was found for the formation of the cubic phase. Diamond powder surfaces appear to preferentially nucleate c-BN. In addition, it was found that the ratio of c-BN to turbostratic structure boron nitride (t-BN) deposited increases with decreasing NH3 concentration in H2. It is suggested that this may be due to an increased etching rate for t-BN by atomic hydrogen whose partial pressure may vary with NH3 concentration.

  7. Analytic cubic and quartic force fields using density-functional theory.

    PubMed

    Ringholm, Magnus; Jonsson, Dan; Bast, Radovan; Gao, Bin; Thorvaldsen, Andreas J; Ekström, Ulf; Helgaker, Trygve; Ruud, Kenneth

    2014-01-21

    We present the first analytic implementation of cubic and quartic force constants at the level of Kohn-Sham density-functional theory. The implementation is based on an open-ended formalism for the evaluation of energy derivatives in an atomic-orbital basis. The implementation relies on the availability of open-ended codes for evaluation of one- and two-electron integrals differentiated with respect to nuclear displacements as well as automatic differentiation of the exchange-correlation kernels. We use generalized second-order vibrational perturbation theory to calculate the fundamental frequencies of methane, ethane, benzene, and aniline, comparing B3LYP, BLYP, and Hartree-Fock results. The Hartree-Fock anharmonic corrections agree well with the B3LYP corrections when calculated at the B3LYP geometry and from B3LYP normal coordinates, suggesting that the inclusion of electron correlation is not essential for the reliable calculation of cubic and quartic force constants. PMID:25669359

  8. Self-trapped elliptical super-Gaussian beam in cubic-quintic media

    NASA Astrophysics Data System (ADS)

    Jana, Soumendu; Singh, Ajitpal; Porsezian, K.; Mithun, T.

    2014-12-01

    We find self-trapped propagation of elliptical super-Gaussian beam in cubic-quintic nonlinear media. The soliton beam preserves its shape and size during propagation in Kerr media. Both defocusing and focusing quintic nonlinearities are considered. In a cubic (focusing)-quintic (defocusing) media breather like beam propagation with intriguing beam width oscillation is observed. The influence of beam ellipticity, super-Gaussian nature and quintic nonlinearity on self-trapping has been studied. A formula for critical power for self-focusing has been derived and it readily agrees with the results obtained by variational method. In Kerr and focusing quintic media beam collapse occurs quicker for higher order super-Gaussian beam. The critical power of self-focusing in defocusing (focusing) quintic medium prominently increases (decreases) with increasing strength of quintic nonlinearity. This variation rate is greater for higher order super Gaussian beam. A beam with greater ellipticity requires larger power for self-trapping.

  9. Lonsdaleite is faulted and twinned cubic diamond and does not exist as a discrete material

    NASA Astrophysics Data System (ADS)

    Németh, Péter; Garvie, Laurence A. J.; Aoki, Toshihiro; Dubrovinskaia, Natalia; Dubrovinsky, Leonid; Buseck, Peter R.

    2014-11-01

    Lonsdaleite, also called hexagonal diamond, has been widely used as a marker of asteroidal impacts. It is thought to play a central role during the graphite-to-diamond transformation, and calculations suggest that it possesses mechanical properties superior to diamond. However, despite extensive efforts, lonsdaleite has never been produced or described as a separate, pure material. Here we show that defects in cubic diamond provide an explanation for the characteristic d-spacings and reflections reported for lonsdaleite. Ultrahigh-resolution electron microscope images demonstrate that samples displaying features attributed to lonsdaleite consist of cubic diamond dominated by extensive {113} twins and {111} stacking faults. These defects give rise to nanometre-scale structural complexity. Our findings question the existence of lonsdaleite and point to the need for re-evaluating the interpretations of many lonsdaleite-related fundamental and applied studies.

  10. Renaturing Membrane Proteins in the Lipid Cubic Phase, a Nanoporous Membrane Mimetic

    PubMed Central

    Li, Dianfan; Caffrey, Martin

    2014-01-01

    Membrane proteins play vital roles in the life of the cell and are important therapeutic targets. Producing them in large quantities, pure and fully functional is a major challenge. Many promising projects end when intractable aggregates or precipitates form. Here we show how such unfolded aggregates can be solubilized and the solution mixed with lipid to spontaneously self-assemble a bicontinuous cubic mesophase into the bilayer of which the protein, in a confined, chaperonin-like environment, reconstitutes with 100% efficiency. The test protein, diacylglycerol kinase, reconstituted in the bilayer of the mesophase, was then crystallized in situ by the in meso or lipid cubic phase method providing an X-ray structure to a resolution of 2.55 Å. This highly efficient, inexpensive, simple and rapid approach should find application wherever properly folded, membrane reconstituted and functional proteins are required where the starting material is a denatured aggregate. PMID:25055873

  11. Surprising stability of neutral interstitial hydrogen in diamond and cubic BN

    NASA Astrophysics Data System (ADS)

    Lyons, J. L.; Van de Walle, C. G.

    2016-02-01

    In virtually all semiconductors and insulators, hydrogen interstitials ({{\\text{H}}i} ) act as negative-U centers, implying that hydrogen is never stable in the neutral charge state. Using hybrid density functional calculations, we find a different behavior for {{\\text{H}}i} in diamond and cubic BN. In diamond, {{\\text{H}}i} is a very strong positive-U center, and the \\text{H}i0 charge state is stable over a Fermi-level range of more than 2 eV. In cubic BN, a III-V compound similar to diamond, we also find positive-U behavior, though over a much smaller Fermi-level range. These results highlight the unique behavior of {{\\text{H}}i} in these covalent wide-band-gap semiconductors.

  12. Surprising stability of neutral interstitial hydrogen in diamond and cubic BN

    DOE PAGESBeta

    Lyons, J. L.; Van de Walle, C. G.

    2016-01-21

    We report that in virtually all semiconductors and insulators, hydrogen interstitials (Hi) act as negative-U centers, implying that hydrogen is never stable in the neutral charge state. Using hybrid density functional calculations, we find a different behavior for Hi in diamond and cubic BN. In diamond, Hi is a very strong positive-U center, and the H0icharge state is stable over a Fermi-level range of more than 2 eV. In cubic BN, a III-V compound similar to diamond, we also find positive-U behavior, though over a much smaller Fermi-level range. Finally, these results highlight the unique behavior of Hi in thesemore » covalent wide-band-gap semiconductors.« less

  13. Roughening and Preroughening of Diamond-Cubic {l_brace}111{r_brace} Surfaces

    SciTech Connect

    Woodraska, D.L.; Jaszczak, J.A.

    1997-01-01

    A solid-on-solid model for {l_brace}111{r_brace} surfaces of diamond-cubic materials that correctly takes into account the diamond-cubic crystal structure has been developed for Monte Carlo simulation. In addition to a roughening transition at temperature T{sub R}, a distinct preroughening transition at T{sub PR}{approx}0.43T{sub R} is indicated by divergences in the surface specific heat and order-parameter susceptibility. Preroughening appears to arise naturally in our nearest-neighbor bond model from the entropic freedom available in the nontrivial crystal structure. Preroughening is shown to dramatically lower the nucleation barrier for growth and etching at low driving forces. {copyright} {ital 1997} {ital The American Physical Society}

  14. Green cubic GaInN/GaN light-emitting diode on microstructured silicon (100)

    SciTech Connect

    Stark, Christoph J. M.; Detchprohm, Theeradetch; Wetzel, Christian; Lee, S. C.; Brueck, S. R. J.; Jiang, Y.-B.

    2013-12-02

    GaInN/GaN light-emitting diodes free of piezoelectric polarization were prepared on standard electronic-grade Si(100) substrates. Micro-stripes of GaN and GaInN/GaN quantum wells in the cubic crystal structure were grown on intersecting (111) planes of microscale V-grooved Si in metal-organic vapor phase epitaxy, covering over 50% of the wafer surface area. Crystal phases were identified in electron back-scattering diffraction. A cross-sectional analysis reveals a cubic structure virtually free of line defects. Electroluminescence over 20 to 100 μA is found fixed at 487 nm (peak), 516 nm (dominant). Such structures therefore should allow higher efficiency, wavelength-stable light emitters throughout the visible spectrum.

  15. Depletion-driven crystallization of cubic colloids sedimented on a surface.

    PubMed

    Hatch, Harold W; Krekelberg, William P; Hudson, Steven D; Shen, Vincent K

    2016-05-21

    Cubic colloids, sedimented on a surface and immersed in a solution of depletant molecules, were modeled with a family of shapes which smoothly varies from squares to circles. Using Wang-Landau simulations with expanded ensembles, we observe the formation of rhombic lattices, square lattices, hexagonal lattices, and a fluid phase. This systematic investigation includes locating transitions between all combinations of the three lattice structures upon changing the shape and transitions between the fluid and crystal upon changing the depletant concentration. The rhombic lattice deforms smoothly between square-like and hexagonal-like angles, depending on both the shape and the depletant concentration. Our results on the effect of the depletant concentration, depletant size, and colloid shape to influence the stability of the fluid and the lattice structures may help guide experimental studies with recently synthesized cubic colloids. PMID:27208969

  16. Numerical solution of fractional differential equations using cubic B-spline wavelet collocation method

    NASA Astrophysics Data System (ADS)

    Li, Xinxiu

    2012-10-01

    Physical processes with memory and hereditary properties can be best described by fractional differential equations due to the memory effect of fractional derivatives. For that reason reliable and efficient techniques for the solution of fractional differential equations are needed. Our aim is to generalize the wavelet collocation method to fractional differential equations using cubic B-spline wavelet. Analytical expressions of fractional derivatives in Caputo sense for cubic B-spline functions are presented. The main characteristic of the approach is that it converts such problems into a system of algebraic equations which is suitable for computer programming. It not only simplifies the problem but also speeds up the computation. Numerical results demonstrate the validity and applicability of the method to solve fractional differential equation.

  17. Cubic and hexagonal GaN nanoparticles synthesized at low temperature

    NASA Astrophysics Data System (ADS)

    Qaeed, M. A.; Ibrahim, K.; Saron, K. M. A.; Salhin, A.

    2013-12-01

    This study involves a simple and low cost chemical method for the synthesis of Gallium Nitride (GaN) nanoparticles at low temperature. Structural and optical characterizations were carried out using various techniques in order to investigate the properties of the nanoparticles. The Field-Emission Scanning Electron Microscope (FESEM) images showed that the nanoparticles consist of cubic and hexagonal shapes, indicating crystallized structural quality of the GaN nanoparticles. The average size of the nanoparticles was found to be 51 nm. The X-ray Diffraction (XRD) and Raman analysis further confirmed the hexagonal and cubic phases of GaN nanoparticles. The room temperature photoluminescence deduced h-GaN energy gaps of 2.95, 3.12 and 3.13 eV.

  18. Traveling waves for conservation laws with cubic nonlinearity and BBM type dispersion

    NASA Astrophysics Data System (ADS)

    Shearer, Michael; Spayd, Kimberly R.; Swanson, Ellen R.

    2015-10-01

    Scalar conservation laws with non-convex fluxes have shock wave solutions that violate the Lax entropy condition. In this paper, such solutions are selected by showing that some of them have corresponding traveling waves for the equation supplemented with dissipative and dispersive higher-order terms. For a cubic flux, traveling waves can be calculated explicitly for linear dissipative and dispersive terms. Information about their existence can be used to solve the Riemann problem, in which we find solutions for some data that are different from the classical Lax-Oleinik construction. We consider dispersive terms of a BBM type and show that the calculation of traveling waves is somewhat more intricate than for a KdV-type dispersion. The explicit calculation is based upon the calculation of parabolic invariant manifolds for the associated ODE describing traveling waves. The results extend to the p-system of one-dimensional elasticity with a cubic stress-strain law.

  19. Interplay between lattice dynamics and the low-pressure phase of simple cubic polonium

    NASA Astrophysics Data System (ADS)

    Zaoui, A.; Belabbes, A.; Ahuja, R.; Ferhat, M.

    2011-04-01

    Low-pressure structural properties of simple cubic polonium are explored through first-principles density-functional theory based relativistic total energy calculations using pseudopotentials and plane-wave basis set, as well as linear-response theory. We have found that Po undergoes structural phase transition at low pressure near 2 GPa, where the element transforms from simple cubic to a mixture of two trigonal phases namely, hR1 (α=86°) and hR2 (α=97.9°) structures. The lattice dynamics calculations provide strong support for the observed phase transition, and show the dynamical stability (instability) of the hR2 (hR1) phase.

  20. Current-voltage characteristics of seven-helix proteins from a cubic array of amino acids

    NASA Astrophysics Data System (ADS)

    Alfinito, Eleonora; Reggiani, Lino

    2016-06-01

    The electrical properties of a set of seven-helix transmembrane proteins, whose space arrangement [three-dimensional (3D) structure] is known, are investigated by using regular arrays of the amino acids. These structures, specifically cubes, have topological features similar to those shown by the chosen proteins. The theoretical results show a good agreement between the predicted current-voltage characteristics obtained from a cubic array and those obtained from a detailed 3D structure. The agreement is confirmed by available experiments on bacteriorhodopsin. Furthermore, all the analyzed proteins are found to share the same critical behavior of the voltage-dependent conductance and of its variance. In particular, the cubic arrangement evidences a short plateau of the excess conductance and its variance at high voltages. The results of the present investigation show the possibility to predict the I -V characteristics of a multiple-protein sample even in the absence of detailed knowledge of the proteins' 3D structure.

  1. Theoretical study for the cubic spin-Hamiltonian parameters of 3d ions

    NASA Astrophysics Data System (ADS)

    Lei, Y.

    2009-08-01

    In this paper, the whole microscopic energy matrix elements of 3d3 and 3d7 within the molecular orbit scheme are obtained. Both the electrostatic parameters, the spin-orbit interaction of the central metal ion and the ligands, the crystal-field potential and the Tress correction, and the spin-spin interaction are considered. By means of the perturbation method, the cubic spin-Hamiltonian parameters g and u are investigated. Results show that the contribution to g due to the spin-spin interaction is negligible. However, the contribution to u due to the spin-spin interaction cannot be neglected. As some illustrations, the 3d7 energy matrix is used to study the cubic electronic paramagnetic resonance experiments of Co in ZnS and ZnSe crystals. The theoretical results agree well with the experimental findings.

  2. On splitting methods for Schroedinger-Poisson and cubic nonlinear Schroedinger equations

    NASA Astrophysics Data System (ADS)

    Lubich, Christian

    2008-12-01

    We give an error analysis of Strang-type splitting integrators for nonlinear Schroedinger equations. For Schroedinger-Poisson equations with an H^4 -regular solution, a first-order error bound in the H^1 norm is shown and used to derive a second-order error bound in the L_2 norm. For the cubic Schroedinger equation with an H^4 -regular solution, first-order convergence in the H^2 norm is used to obtain second-order convergence in the L_2 norm. Basic tools in the error analysis are Lie-commutator bounds for estimating the local error and H^m -conditional stability for error propagation, where mD1 for the Schroedinger-Poisson system and mD2 for the cubic Schroedinger equation.

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

    NASA Technical Reports Server (NTRS)

    Raju, I. S.; Phillips, D. R.

    2002-01-01

    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.

  4. Phase Separation on Bicontinuous Cubic Membranes: Symmetry Breaking, Reentrant, and Domain Faceting

    NASA Astrophysics Data System (ADS)

    Paillusson, Fabien; Pennington, Matthew R.; Kusumaatmaja, Halim

    2016-07-01

    We study the phase separation of binary lipid mixtures that form bicontinuous cubic phases. The competition between the nonuniform Gaussian membrane curvature and line tension leads to a very rich phase diagram, where we observe symmetry breaking of the membrane morphologies and reentrant phenomena due to the formation of bridges between segregated domains. Upon increasing the line tension contribution, we also find faceting of lipid domains that we explain using a simple argument based on the symmetry of the underlying surface and topology.

  5. Lattice distortions and oxygen vacancies produced in Au+ irradiated nano-crystalline cubic zirconia

    SciTech Connect

    Edmondson, Philip D; Weber, William J; Namavar, Fereydoon; Zhang, Yanwen

    2011-01-01

    The structural impact of oxygen vacancies in nanocrystalline cubic zirconia is investigated. A non-equilibrium number of oxygen vacancies in introduced to the lattice by ion irradiation. The lattice is observed to be initially compressed, undergoes a relaxation at 0.7 displacements per atom (dpa), and experiences a contraction before reaching a temperature dependent steady state value at above 7 dpa. The level of lattice distortion is related to the charge state of the accumulating oxygen vacancies.

  6. Transformation of a cubic precipitate to a butterfly shape due to localized instabilities

    SciTech Connect

    Colin, J.; Grilhe, J.; Junqua, N.

    1998-02-13

    Localized surface instabilities have been used to explain the transformation to a butterfly shape of a cubic precipitate submitted to epitaxial stress. An energy variation calculation shows that each of the precipitate-matrix interfaces can develop by diffusion of a Mexican hat shaped instability to minimize the stored elastic energy. Using classical results of stress induced diffusion, the most probable dimension of the resulting fluctuations has been determined. A typical butterfly configuration can be obtained with characteristic dimensions.

  7. Oxidation of Membrane Curvature-Regulating Phosphatidylethanolamine Lipid Results in Formation of Bilayer and Cubic Structures.

    PubMed

    Sankhagowit, Shalene; Lee, Ernest Y; Wong, Gerard C L; Malmstadt, Noah

    2016-03-15

    Oxidation is associated with conditions related to chronic inflammations and aging. Cubic structures have been observed in the smooth endoplasmic reticulum and mitochondrial membranes of cells under oxidative stress (e.g., tumor cells and virus-infected cells). It has been previously suspected that oxidation can result in the rearrangement of lipids from a fluid lamellar phase to a cubic structure in organelles containing membranes enriched with amphiphiles that have nonzero intrinsic curvature, such as phosphatidylethanolamine (PE) and cardiolipin. This study focuses on the oxidation of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), a lipid that natively forms an inverted hexagonal phase at physiological conditions. The oxidized samples contain an approximately 3:2 molar ratio of nonoxidized to oxidized DOPE. Optical microscopy images collected during the hydration of this mixture from a dried film suggest that the system evolves into a coexistence of a stable fluid lamellar phase and transient square lattice structures with unit cell sizes of 500-600 nm. Small-angle X-ray scattering of the same lipid mixture yielded a body-centered Im3m cubic phase with the lattice parameter of 14.04 nm. On average, the effective packing parameter of the oxidized DOPE species was estimated to be 0.657 ± 0.069 (standard deviation). This suggests that the oxidation of PE leads to a group of species with inverted molecular intrinsic curvature. Oxidation can create amphiphilic subpopulations that potently impact the integrity of the membrane, since negative Gaussian curvature intrinsic to cubic phases can enable membrane destabilization processes. PMID:26866900

  8. Metal-oxide-semiconductor characteristics of chemical vapor deposited cubic-SiC

    NASA Astrophysics Data System (ADS)

    Shibahara, K.; Nishino, S.; Matsunami, H.

    1984-11-01

    Thermal oxidation of chemical vapor deposited (CVD) cubic-SiC and fabrication of MOS diodes using a thermal oxide film were carried out. The thermal oxide was found to be SiO2 by Auger electron spectroscopic analysis. Capacitance-voltage curves of MOS diodes measured under the dark condition showed deep depletion characteristics. Inversion characteristics were observed under the illuminated condition for the first time.

  9. The cubic period-distance relation for the Kate reversible pendulum

    NASA Astrophysics Data System (ADS)

    Rossi, Michele; Zaninetti, Lorenzo

    2005-12-01

    We describe the correct cubic relation between the mass configuration of a Kater reversible pendulum and its period of oscillation. From an analysis of its solutions we conclude that there could be as many as three distinct mass configurations for which the periods of small oscillations about the two pivots of the pendulum have the same value. We also discuss a real compound Kater pendulum that realizes this property.

  10. G-factors of hole bound states in spherically symmetric potentials in cubic semiconductors

    NASA Astrophysics Data System (ADS)

    Miserev, Dmitry; Sushkov, Oleg

    2016-03-01

    Holes in cubic semiconductors have effective spin 3/2 and very strong spin orbit interaction. Due to these factors properties of hole bound states are highly unusual. We consider a single hole bound by a spherically symmetric potential, this can be an acceptor or a spherically symmetric quantum dot. Linear response to an external magnetic field is characterized by the bound state Lande g-factor. We calculate analytically g-factors of all bound states.

  11. Detergents Destabilize the Cubic Phase of Monoolein: Implications for Membrane Protein Crystallization

    PubMed Central

    Misquitta, Y.; Caffrey, M.

    2003-01-01

    The in meso method for membrane protein crystallization uses a lipidic cubic phase as the hosting medium. The cubic phase provides a lipid bilayer into which the protein presumably reconstitutes and from which protein crystals nucleate and grow. The solutions used to spontaneously form the protein-enriched cubic phase often contain significant amounts of detergents that were employed initially to purify and to solubilize the membrane protein. By virtue of their surface activity, detergents have the potential to impact on the phase properties of the in meso system and, by extension, the outcome of the crystallization process. The purpose of this study was to quantify the effects that a popular series of nonionic detergents, the n-alkyl-β-d-glucopyranosides, have on the phase behavior of hydrated monoolein, the lipid upon which the in meso method is based. Phase identity and phase microstructure were characterized by small-angle x-ray diffraction on samples prepared to mimic in meso crystallization conditions. Measurements were made in the 0–40°C range. Samples prepared in the cooling direction allow for the expression of metastability, a feature of liquid crystalline phases that might be exploited in low-temperature crystallization. The results show that the cubic phase is relatively insensitive to small amounts of alkyl glucosides. However, at higher levels the detergents trigger a transition to the lamellar phase in a temperature- and salt concentration-dependent manner. These effects have important implications for in meso crystallization. A diffraction-based method for assaying detergents is presented. PMID:14581209

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

    NASA Technical Reports Server (NTRS)

    Fiske, David R.

    2004-01-01

    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.

  13. Strong phonon anomalies and Fermi surface nesting of simple cubic Polonium

    NASA Astrophysics Data System (ADS)

    Belabbes, A.; Zaoui, A.; Ferhat, M.

    2010-12-01

    The unknown lattice dynamics of simple cubic Polonium is calculated using first-principles density-functional perturbation theory with pseudopotentials and a plane-wave basis set. We notice several phonon anomalies, in particular along major symmetry directions namely M-R, R-Γ, Γ-M, M-X, and X-Γ. The analysis of the Fermi surface strongly suggests that the observed phonon anomalies are Kohn anomalies arising from strong Fermi surface nesting.

  14. Resistance calculation of the face-centered cubic lattice: Theory and experiment

    NASA Astrophysics Data System (ADS)

    Owaidat, M. Q.

    2013-12-01

    The effective resistance between two arbitrary lattice points in an infinite, face-centered cubic lattice network of identical resistors is calculated using the lattice Green's function method. Theoretical results have been verified experimentally by constructing actual finite networks of resistors. This problem could be useful in undergraduate courses (e.g., advanced mathematical methods course) and would provide a good example for introducing the concept of Green's function.

  15. Reconstruction of craniofacial image using rational cubic Ball interpolant and soft computing technique

    NASA Astrophysics Data System (ADS)

    Majeed, Abdul; Piah, Abd Rahni Mt

    2015-10-01

    Spline has been used extensively in engineering design and modelling for representation, analysis and manufacturing purposes. This paper presents an application of spline methods in bio-medical modelling. We reconstruct craniofacial fractured skull bone images using rational cubic Ball interpolant with two free parameters. The free parameters are optimized with the help of genetic algorithm. Our emphasis is placed on the accuracy and smoothness of the reconstructed images.

  16. Surface acoustic wave velocity and elastic constants of cubic GaN

    NASA Astrophysics Data System (ADS)

    Jiménez Riobóo, Rafael J.; Cuscó, Ramon; Prieto, Carlos; Kopittke, Caroline; Novikov, Sergei V.; Artús, Luis

    2016-06-01

    We present high-resolution surface Brillouin scattering measurements on cubic GaN layers grown on GaAs substrate. By using a suitable scattering geometry, scattering by surface acoustic waves is recorded for different azimuthal angles, and the surface acoustic wave velocities are determined. A comparison of experimental results with numerical simulations of the azimuthal dependence of the surface wave velocity shows good agreement and allows a consistent set of elastic constants for c-GaN to be determined.

  17. Negative thermal expansion in cubic ZrW2O8: Role of phonons in the entire Brillouin zone from ab initio calculations

    NASA Astrophysics Data System (ADS)

    Gupta, M. K.; Mittal, R.; Chaplot, S. L.

    2013-07-01

    We report the ab initio density functional theory calculation of phonons in the cubic phase of ZrW2O8 in the entire Brillouin zone and identify specific anharmonic phonons that are responsible for large negative thermal expansion (NTE) in terms of the translation, rotation, and distortion of WO4 and ZrO6. We have used density functional calculations to interpret the experimental phonon spectra as a function of pressure and temperature as reported in literature. We discover that the phonons showing anharmonicity with temperature are not necessarily the same as those showing anharmonicity with pressure although both are of similar frequencies. Only the latter phonons are associated with NTE. Therefore, the cubic and/or quadratic anharmonicity of phonons is not relevant to NTE but just the volume dependence of frequencies. The calculations are able to reproduce the observed anomalous trends, namely, the softening of the low-frequency peak at about 4 meV in the phonon spectra with pressure and its hardening with temperature, whereas, both changes involve a compression of the lattice.

  18. Understanding ferromagnetism and optical absorption in 3d transition metal-doped cubic ZrO{sub 2} with the modified Becke-Johnson exchange-correlation functional

    SciTech Connect

    Boujnah, M.; Zaari, H.; El Kenz, A.; Labrim, H.; Benyoussef, A.; Mounkachi, O.

    2014-03-28

    The electronic structure, magnetic, and optical properties in cubic crystalline phase of Zr{sub 1−x}TM{sub x}O{sub 2} (TM = V, Mn, Fe, and Co) at x = 6.25% are studied using density functional theory with the Generalized Gradient Approximation and the modified Becke-Johnson of the exchange-correlation energy and potential. In our calculations, the zirconia is a p-type semiconductor and has a large band gap. We evaluated the possibility of long-range magnetic order for transition metal ions substituting Zr. Our results show that ferromagnetism is the ground state in V, Mn, and Fe-doped ZrO{sub 2} and have a high value of energy in Mn-doped ZrO{sub 2}. However, in Co-doped ZrO{sub 2}, antiferromagnetic ordering is more stable than the ferromagnetic one. The exchange interaction mechanism has been discussed to explain the responsible of this stability. Moreover, it has been found that the V, Mn, and Fe transition metals provide half-metallic properties considered to be the leading cause, responsible for ferromagnetism. Furthermore, the optical absorption spectra in the TM -doped cubic ZrO{sub 2} are investigated.

  19. Stoichiometry dependent phase transition in Mn-Co-Ga-based thin films: From cubic in-plane, soft magnetized to tetragonal perpendicular, hard magnetized

    SciTech Connect

    Ouardi, Siham; Fecher, Gerhard H.; Stinshoff, Rolf; Felser, Claudia; Kubota, Takahide; Mizukami, Shigemi; Miyazaki, Terunobu; Ikenaga, Eiji

    2012-12-10

    Epitaxial thin films of Mn{sub 3-x}Co{sub x}Ga were grown on MgO by magnetron co-sputtering with different Co content. Dependent on the Co content tetragonal or cubic structures are obtained. The composition dependence of saturation magnetization M{sub S} and uniaxial magnetic anisotropy K{sub u} in the epitaxial films were investigated. A high magnetic anisotropy K{sub u} of 1.2 MJ m{sup -3} was achieved for the Mn{sub 2.6}Co{sub 0.3}Ga{sub 1.1} film with low magnetic moment of 0.84 {mu}{sub B}. The valence band spectra of the films were investigated mainly by hard x-ray photoelectron spectroscopy. The evidence of sharp states in the cubic case, which are smeared out in the tetragonal case, proof the existence of a van Hove singularity that causes a band Jahn-Teller effect accompanied by a tetragonal distortion. These differences are in well agreement to the ab-initio calculations of the electronic structure.

  20. Synthesis of zirconia sol stabilized by trivalent cations (yttrium and neodymium or americium): a precursor for Am-bearing cubic stabilized zirconia.

    PubMed

    Lemonnier, Stephane; Grandjean, Stephane; Robisson, Anne-Charlotte; Jolivet, Jean-Pierre

    2010-03-01

    Recent concepts for nuclear fuel and targets for transmuting long-lived radionuclides (minor actinides) and for the development of innovative Gen-IV nuclear fuel cycles imply fabricating host phases for actinide or mixed actinide compounds. Cubic stabilized zirconia (Zr, Y, Am)O(2-x) is one of the mixed phases tested in transmutation experiments. Wet chemical routes as an alternative to the powder metallurgy are being investigated to obtain the required phases while minimizing the handling of contaminating radioactive powder. Hydrolysis of zirconium, neodymium (a typical surrogate for americium) and yttrium in aqueous media in the presence of acetylacetone was firstly investigated. Progressive hydrolysis of zirconium acetylacetonate and sorption of trivalent cations and acacH on the zirconia particles led to a stable dispersion of nanoparticles (5-7 nm) in the 6-7 pH range. This sol gels with time or with temperature. The application to americium-containing solutions was then successfully tested: a stable sol was synthesized, characterized and used to prepare cubic stabilized zirconia (Zr, Y, Am)O(2-x). PMID:20162199

  1. A processor-time-minimal systolic array for cubical mesh algorithms

    SciTech Connect

    Cappello, P. . Dept. of Computer Science)

    1992-01-01

    Using a directed acyclic graph (dag) model of algorithms, the paper focuses on time-minimal multiprocessor schedules that use as few processors as possible. Such a processor-time-minimal scheduling of an algorithm's dag first is illustrated using a triangular shaped 2-D directed mesh (representing, for example, an algorithm for solving a triangular system of linear equations). Then, algorithms represented by an n {times} n {times} n directed mesh are investigated. This cubical directed mesh is fundamental; it represents the standard algorithm for computing matrix product as well as many other algorithms. Completion of the cubical mesh requires 3n - 2 steps. It is shown that the number of processing elements needed to achieve this time bound is at least (3n{sup 2/4}). A systolic array for the cubical directed mesh is then presented. It completes the mesh using the minimum number of steps and exactly (3n{sup 2/4}) processing elements: it is processor-time-minimal. The systolic array's topology is that of a hexagonally shaped, cylindrically- connected, 2-D directed mesh.

  2. Structure and Luminescence Properties of Eu3+-Doped Cubic Mesoporous Silica Thin Films

    PubMed Central

    2010-01-01

    Eu3+ ions-doped cubic mesoporous silica thin films with a thickness of about 205 nm were prepared on silicon and glass substrates using triblock copolymer as a structure-directing agent using sol–gel spin-coating and calcination processes. X-ray diffraction and transmission electron microscopy analysis show that the mesoporous silica thin films have a highly ordered body-centered cubic mesoporous structure. High Eu3+ ion loading and high temperature calcination do not destroy the ordered cubic mesoporous structure of the mesoporous silica thin films. Photoluminescence spectra show two characteristic emission peaks corresponding to the transitions of5D0-7F1 and 5D0-7F2 of Eu3+ ions located in low symmetry sites in mesoporous silica thin films. With the Eu/Si molar ratio increasing to 3.41%, the luminescence intensity of the Eu3+ ions-doped mesoporous silica thin films increases linearly with increasing Eu3+ concentration. PMID:20672132

  3. Properties of interfaces between cubic and hexagonal polytypes of silicon carbide

    NASA Astrophysics Data System (ADS)

    Raffy, C.; Furthmüller, J.; Bechstedt, F.

    2002-12-01

    We present ab initio calculations of the properties of two types of interface between the cubic and hexagonal (wurtzite) polytypes of silicon carbide. The results are derived from density-functional calculations within the local-density approximation and the pseudopotential-plane-wave approach. We first study the interface along the (111) plane (corresponding to (0001) in the hexagonal representation) perpendicular to the stacking axis of the bilayers. Then we consider the interface along the (115) plane, which was already identified experimentally as a grain boundary in silicon and germanium. The (115) interfaces are especially interesting, since they may contribute to a quantum wire consisting of an inclusion of cubic SiC in hexagonal SiC. They are made up of five-and seven-membered atom rings and are free of dangling bonds. The cubic and hexagonal grains are tilted with respect to one another by an angle of 38.94°. In both cases of interfaces, the electronic properties are discussed. Whereas the (111) interface induces practically no states in the bulk fundamental gaps, the particular structure of the (115) interface generates a lot of states, resulting in a metallic behaviour.

  4. CUBIC: a three-dimensional colored projection of Consort 30 generated trivariate flow cytometric data.

    PubMed

    Greimers, R; Rongy, A M; Schaaf-Lafontaine, N; Boniver, J

    1991-01-01

    The CUBIC program displays three-dimensional colored dot plots of flow cytometric trivariate data collected by unmodified commercial instruments (FACScan flow cytometer, FACS 440 cell sorter). Assuming a bimodal distribution of the fluorescence intensity of the cells, the eight theoretical subpopulations involved in a three-color fluorescence histogram are clearly localized in the 3-D space by colored dots that are clustered near each corner of a cubic frame. Rotation, tilting, and zoom functions are available. Table look-up is not needed. CUBIC was illustrated by two experiments: 1) three-color immunofluorescence of antigens on human lymphocytes using monoclonal antibodies conjugated either to fluorescein (FITC), to R-phycoerythrin (PE), or to biotin revealed by a streptavidin coupled to a PE-Texas red tandem conjugate (TC); 2) two-color immunofluorescence of CD4 and CD8 antigens on thymocytes of healthy or preleukemic mice correlated to the DNA content quantified by 7-amino-actinomycin D (7-AAD). The three fluorescences were excited by a single argon-ion laser emitting at 488 nm. PMID:1764980

  5. Pronounced negative thermal expansion from a simple structure : Cubic ScF{sub 3}.

    SciTech Connect

    Greve, B. K.; Martin, K. L.; Lee, P. L.; Chupas, P. J.; Chapman, K. W.; Wilkinson, A. P.; X-Ray Science Division; Georgia Inst. of Tech.

    2010-10-19

    Scandium trifluoride maintains a cubic ReO{sub 3} type structure down to at least 10 K, although the pressure at which its cubic to rhombohedral phase transition occurs drops from >0.5 GPa at {approx}300 K to 0.1-0.2 GPa at 50 K. At low temperatures it shows strong negative thermal expansion (NTE) (60-110 K, {alpha}{sub l} {approx} -14 ppm K{sup -1}). On heating, its coefficient of thermal expansion (CTE) smoothly increases, leading to a room temperature CTE that is similar to that of ZrW{sub 2}O{sub 8} and positive thermal expansion above {approx}1100 K. While the cubic ReO{sub 3} structure type is often used as a simple illustration of how negative thermal expansion can arise from the thermally induced rocking of rigid structural units, ScF{sub 3} is the first material with this structure to provide a clear experimental illustration of this mechanism for NTE.

  6. Local structures surrounding Zr in nanostructurally stabilized cubic zirconia: Structural origin of phase stability

    SciTech Connect

    Soo, Y. L.; Chen, P. J.; Huang, S. H.; Shiu, T. J.; Tsai, T. Y.; Chow, Y. H.; Lin, Y. C.; Weng, S. C.; Chang, S. L.; Wang, G.; Cheung, C. L.; Sabirianov, R. F.; Mei, W. N.; Namavar, F.; Haider, H.; Garvin, K. L.; Lee, J. F.; Lee, H. Y.; Chu, P. P.

    2008-12-01

    Local environment surrounding Zr atoms in the thin films of nanocrystalline zirconia (ZrO{sub 2}) has been investigated by using the extended x-ray absorption fine structure (EXAFS) technique. These films prepared by the ion beam assisted deposition exhibit long-range structural order of cubic phase and high hardness at room temperature without chemical stabilizers. The local structure around Zr probed by EXAFS indicates a cubic Zr sublattice with O atoms located on the nearest tetragonal sites with respect to the Zr central atoms, as well as highly disordered locations. Similar Zr local structure was also found in a ZrO{sub 2} nanocrystal sample prepared by a sol-gel method. Variations in local structures due to thermal annealing were observed and analyzed. Most importantly, our x-ray results provide direct experimental evidence for the existence of oxygen vacancies arising from local disorder and distortion of the oxygen sublattice in nanocrystalline ZrO{sub 2}. These oxygen vacancies are regarded as the essential stabilizing factor for the nanostructurally stabilized cubic zirconia.

  7. Ammonium fluoride-activated synthesis of cubic δ-TaN nanoparticles at low temperatures

    PubMed Central

    2013-01-01

    Cubic delta-tantalum nitride (δ-TaN) nanoparticles were selectively prepared using a K2TaF7 + (5 + k) NaN3 + kNH4F reactive mixture (k being the number of moles of NH4F) via a combustion process under a nitrogen pressure of 2.0 MPa. The combustion temperature, when plotted as a function of the number of moles of NH4F used, was in the range of 850°C to 1,170°C. X-ray diffraction patterns revealed the formation of cubic δ-TaN nanoparticles at 850°C to 950°C when NH4F is used in an amount of 2.0 mol (or greater) in the combustion experiment. Phase pure cubic δ-TaN synthesized at k = 4 exhibited a specific surface area of 30.59 m2/g and grain size of 5 to 10 nm, as estimated from the transmission electron microscopy micrograph. The role of NH4F in the formation process of δ-TaN is discussed with regard to a hypothetical reaction mechanism. PMID:23497396

  8. Influence of electrostatic interactions on the release of charged molecules from lipid cubic phases.

    PubMed

    Negrini, Renata; Sánchez-Ferrer, Antoni; Mezzenga, Raffaele

    2014-04-22

    The release of positive, negative, and neutral hydrophilic drugs from pH responsive bicontinuous cubic phases was investigated under varying conditions of electrostatic interactions. A weak acid, linoleic acid (LA), or a weak base, pyridinylmethyl linoleate (PML), were added to the neutral monolinolein (ML) in order to form lyotropic liquid-crystalline (LLC) phases, which are negatively charged at neutral pH and positively charged at acidic pH. Release studies at low ionic strength (I = 20 mM) and at different pH values (3 and 7) revealed that electrostatic attraction between a positive drug, proflavine (PF), and the negatively charged LLC at pH = 7 or between a negative drug, antraquinone 2-sulfonic acid sodium salt (AQ2S), and the positively charged LLC at pH = 3 did delay the release behavior, while electrostatic repulsion affects the transport properties only to some extent. Release profiles of a neutral drug, caffeine, were not affected by the surface charge type and density in the cubic LLCs. Moreover, the influence of ionic strength was also considered up to 150 mM, corresponding to a Debye length smaller than the LLC water channels radius, which showed that efficient screening of electrostatic attractions occurring within the LLC water domains results in an increased release rate. Four transport models were applied to fit the release data, providing an exhaustive, quantitative insight on the role of electrostatic interactions in transport properties from pH responsive bicontinuous cubic phases. PMID:24673189

  9. Observations of ionospheric ELF and VLF wave generation by excitation of the thermal cubic nonlinearity.

    PubMed

    Moore, R C; Fujimaru, S; Kotovsky, D A; Gołkowski, M

    2013-12-01

    Extremely-low-frequency (ELF, 3-3000 Hz) and very-low-frequency (VLF, 3-30 kHz) waves generated by the excitation of the thermal cubic nonlinearity are observed for the first time at the High-Frequency Active Auroral Research Program high-frequency transmitter in Gakona, Alaska. The observed ELF and VLF field amplitudes are the strongest generated by any high frequency (HF, 3-30 MHz) heating facility using this mechanism to date. This manner of ELF and VLF generation is independent of naturally forming currents, such as the auroral electrojet current system. Time-of-arrival analysis applied to experimental observations shows that the thermal cubic ELF and VLF source region is located within the collisional D-region ionosphere. Observations are compared with the predictions of a theoretical HF heating model using perturbation theory. For the experiments performed, two X-mode HF waves were transmitted at frequencies ω1 and ω2, with |ω2-2ω1| being in the ELF and VLF frequency range. In contrast with previous work, we determine that the ELF and VLF source is dominantly produced by the interaction between collision frequency oscillations at frequency ω2-ω1 and the polarization current density associated with the lower frequency HF wave at frequency ω1. This specific interaction has been neglected in past cubic thermal nonlinearity work, and it plays a major role in the generation of ELF and VLF waves. PMID:24476285

  10. In situ synthesis of mesoporous CdS nanoparticles in ternary cubic phase lyotropic liquid crystal

    NASA Astrophysics Data System (ADS)

    Huang, N. M.; Kan, C. S.; Radiman, S.

    An in situ technique for the synthesis of CdS nanoparticles in a ternary lyotropic cubic phase liquid crystal has been carried out. The extremely viscous cubic phase liquid-crystal system consists of poly(oxyethylene)10 nonyl phenol ether as non-ionic surfactant, octane as oil phase and an aqueous phase containing reactant ions (Cd2+ and S2-). Thioacetamide (TAA) has been utilized as a source for slow release of sulfur in the in situ synthesis of CdS. Rheological results show that CdS nanoparticle growth did not disrupt the structure of the cubic phase liquid-crystal system. This indicates that homogenous synthesis of CdS in the liquid crystal had been achieved. The final products were characterized using X-ray photoelectron spectroscopy, thermal gravimetric analysis, transmission electron microscopy and UV-visible spectroscopy. It was found that the CdS nanoparticles formed have a mesoporous structure with a size dependent on the TAA decomposition aging time.

  11. Synthesis and Properties of La2O3-Doped 8 mol% Yttria-Stabilized Cubic Zirconia

    NASA Astrophysics Data System (ADS)

    Aktas, Bulent; Tekeli, Suleyman; Salman, Serdar

    2014-01-01

    In this study, 8 mol% yttria-stabilized cubic zirconia (8YSZ) powder as a matrix material and 0-15 wt.% La2O3 powder as an additive were used to determine the effect of La2O3 addition and its amount on the phase stability, microstructure, sintering, and mechanical properties of 8YSZ. Colloidal processing was used to mix the powders uniformly and to obtain a homogenous microstructure. XRD results showed the existence of only a cubic crystal structure for 1 and 5 wt.% La2O3 addition amounts. However, La2Zr2O7 with a hexagonal and cubic crystal structure was observed in 8YSZ specimens doped with 10 and 15 wt.% La2O3. Further, up to 5 wt.% La2O3 was completely dissolved in the crystal structure of the specimens; however, above 5 wt.%, La2O3 reacted with 8YSZ at high temperatures and formed pyrochloric La2Zr2O7. Grain size measurements revealed that the grain size of 8YSZ increased up to 1 wt.% La2O3 addition, and then decreased beyond this amount. The hardness and fracture toughness of 8YSZ decreased and increased, respectively, with the increasing La2O3 amount.

  12. Geometrical aspects of the frustration in the cubic phases of lyotropic liquid crystals.

    PubMed Central

    Anderson, D M; Gruner, S M; Leibler, S

    1988-01-01

    Bicontinuous cubic phases, composed of bilayers arranged in the geometries of periodic minimal surfaces, are found in a variety of different lipid/water systems. It has been suggested recently that these cubic structures arrive as the result of competition between two free-energy terms: the curvature energy of each monolayer and the stretching energy of the lipid chains. This scenario, closely analogous to the one that explains the origin of the hexagonal phases, is investigated here by means of simple geometrical calculations. It is first assumed that the lipid bilayer is of constant thickness and the distribution of the (local) mean curvature of the phospholipid-water interfaces is calculated. Then, assuming the mean curvature of these interfaces is constant, the distribution of the bilayer's thickness is calculated. Both calculations quantify the fact that the two energy terms are frustrated and cannot be satisfied simultaneously. However, the amount of the frustration can be smaller for the cubic phase than for the lamellar and hexagonal structures. Therefore, this phase can appear in the phase diagram between the other two, as observed in many recent experiments. PMID:3399497

  13. Cubical Shape Enhances the Interaction of Layer-by-Layer Polymeric Particles with Breast Cancer Cells.

    PubMed

    Alexander, Jenolyn F; Kozlovskaya, Veronika; Chen, Jun; Kuncewicz, Thomas; Kharlampieva, Eugenia; Godin, Biana

    2015-12-01

    Blood-borne objects display a nonspherical shape with in-flow dimensions much larger than the vascular endothelial fenestrations, yet, at the diseased state, are able to traverse through these fenestrations owing to their elasticity. The role of physical parameters including shape and elasticity in the behavior of objects found in the tumor microenvironment needs to be understood to ultimately enhance chemotherapy and minimize its side effects. In this study, sphere- and cube-shaped biocompatible elastic microparticles (EM) made via layer-by-layer assembly of hydrogen-bonded tannic acid/poly(N-vinylpyrrolidone) (TA/PVPON) as hollow polymer shells and their rigid core-shell precursors (RM) are explored. In contrast to rigid five-bilayer (TA/PVPON) core shells, hollow elastic shells are unrecognized by J774A.1 macrophages, yet interact with endothelial and breast cancer cells. Internalization of cubical shells is fivefold more efficient by HMVEC (human microvascular endothelial cells) and sixfold and 2.5-fold more efficient by MDA-MB-231 and by SUM159 (breast cancer cells), respectively, compared to spherical shells. The interaction of cubical (TA/PVPON)5 shells with endothelial cells is similar under 10 s(-1) (characteristic of tumor vasculature) and 100 s(-1) shear rate (normal vasculature) while it is decreased at 100 s(-1) shear rate for the spherical shells. Our data suggest that cubical geometry promotes interaction of particles with breast cancer cells, while elasticity prevents engulfment by phagocytic cells in the tumor microenvironment. PMID:26424126

  14. Higher-order elasticity of cubic metals in the embedded-atom method

    NASA Astrophysics Data System (ADS)

    Chantasiriwan, Somchart; Milstein, Frederick

    1996-06-01

    The higher-order elasticity of cubic metals in the framework of the embedded-atom method (EAM) is investigated. Proper groupings of the second- and third-order elastic moduli are shown to yield expressions that depend solely on either the electron density function or the pair potential and which therefore facilitate the construction of EAM models. This formulation also makes evident some important restrictions on the EAM functions and lattice summations. In order for the EAM to model the anharmonic properties accurately, (a) at least the third-nearest-neighbor interactions must be included in the expressions for the cohesive energies of both the body-centered-cubic and face-centered-cubic metals and (b) an electron density function of an inverse power form, as has been employed previously, generally is not valid. Specific EAM models are constructed for a diverse selection of metals (i.e., aluminum, copper, sodium, and molybdenum). These models identically reproduce the respective second- and third-order elastic moduli, as well as the binding energy, atomic volume, unrelaxed vacancy formation energy, and Rose's universal equation of state. They also provide reasonable phonon frequency spectra and structural energy differences

  15. Particle linear theory on a self-gravitating perturbed cubic Bravais lattice

    SciTech Connect

    Marcos, B.

    2008-08-15

    Discreteness effects are a source of uncontrolled systematic errors of N-body simulations, which are used to compute the evolution of a self-gravitating fluid. We have already developed the so-called ''particle linear theory''(PLT), which describes the evolution of the position of self-gravitating particles located on a perturbed simple cubic lattice. It is the discrete analogue of the well-known (Lagrangian) linear theory of a self-gravitating fluid. Comparing both theories permits us to quantify precisely discreteness effects in the linear regime. It is useful to develop the PLT also for other perturbed lattices because they represent different discretizations of the same continuous system. In this paper we detail how to implement the PLT for perturbed cubic Bravais lattices (simple, body, and face-centered) in a cubic simulation box. As an application, we will study the discreteness effects--in the linear regime--of N-body simulations for which initial conditions have been set up using these different lattices.

  16. Structure and optical properties of cubic gallium oxynitride synthesized by solvothermal route

    SciTech Connect

    Oberländer, Andreas; Kinski, Isabel; Zhu, Wenliang; Pezzotti, Giuseppe; Michaelis, Alexander

    2013-04-15

    Cubic gallium oxynitride was synthesized using a solvothermal processing route. Crystal structure, chemical composition, optical properties and the influence of heat treatment in either reactive or inert atmospheres have been investigated. Despite a strongly distorted lattice revealed using X-ray diffraction, the Raman active modes of a cubic gallium oxynitride structure could be observed. With diffusive reflectance UV–Vis spectroscopy a band gap at around 4.8 eV has been observed. Additionally, cathodoluminescence spectroscopy exhibited observable luminescence caused by defect-related transitions within the optical gap. Cathodoluminescence and photoluminescence spectra collected after heat treatments showed significant changes in the defect structure. In particular, for annealing in ammonia the main spectral modifications were related to the substitution of oxygen by nitrogen on anion sites. - Graphical abstract: CL spectra of gallium oxynitride: As-prepared and heat-treated at temperatures of 500 °C in different atmospheres. Highlights: ► Raman spectrum of cubic gallium oxynitride. ► Experimental determination of optical band gap. ► Shift of band gap energy due to heat treatment. ► Nitrogen incorporation leads to deep level acceptor states. ► Red shifted luminescence spectrum.

  17. Investigation of grain-boundary geometry and pores morphology in dense and porous cubic zirconia polycrystals

    SciTech Connect

    Bobrowski, Piotr; Faryna, Marek; Pędzich, Zbigniew

    2014-09-15

    Highlights: • Cubic zirconia sinters were investigated in three dimensions using dual-beam FEGSEM. • The 3D-EBSD technique was successfully applied to non-conductive ceramics. • New sample preparation approach to automated 3D-EBSD was proposed. • Grain boundary microstructures were reconstructed from inverse pole figure maps. • Pore microstructures were reconstructed from image quality maps. - Abstract: Three-dimensional electron backscatter diffraction technique was used for the visualization of grain boundary geometry and pore morphology in cubic zirconia. A set of four samples sintered under different conditions was investigated. Specimens which were characterized by energy dispersive spectroscopy and X-ray diffraction were entirely composed of cubic phase. Investigations of boundaries and pore structures were carried out in a dual-beam scanning electron microscope. For each sample, a volume of 1000 μm{sup 3} was investigated. The analysis of grain boundary networks reconstructed from inverse pole figure maps revealed a strong dependence between grain boundary density and sample preparation parameters. Sintering also affects the size and distribution of pores. The total number of grains analyzed varied from 17 to 357 and the calculated volume of cavities from 0.01% to 21%. This paper shows the application of three-dimensional crystallographic orientation analysis to characterize the microstructure of yttria stabilized zirconia ceramics.

  18. Grain growth and phase stability of nanocrystalline cubic zirconia under ion irradiation

    SciTech Connect

    Zhang Yanwen; Jiang Weilin; Wang Chongmin; Edmondson, Philip D.; Zhu Zihua; Gao Fei; Namavar, Fereydoon; Lian Jie; Weber, William J.

    2010-11-01

    Grain growth, oxygen stoichiometry, and phase stability of nanostructurally stabilized cubic zirconia (NSZ) are investigated under 2 MeV Au-ion bombardment at 160 and 400 K to doses up to 35 displacements per atom (dpa). The NSZ films are produced by ion-beam-assisted deposition technique at room temperature with an average grain size of 7.7 nm. The grain size increases with irradiation dose to {approx}30 nm at {approx}35 dpa. Slower grain growth is observed under 400 K irradiations, as compared to 160 K irradiations, indicating that the grain growth is not thermally activated and irradiation-induced grain growth is the dominating mechanism. While the cubic structure is retained and no new phases are identified after the high-dose irradiations, oxygen reduction in the irradiated NSZ films is detected. The ratio of O to Zr decreases from {approx}2.0 for the as-deposited films to {approx}1.65 after irradiation to {approx}35 dpa. The loss of oxygen suggests a significant increase in oxygen vacancies in nanocrystalline zirconia under ion irradiation. The oxygen deficiency may be essential in stabilizing the cubic phase to larger grain sizes.

  19. Formation of hexagonal and cubic ice during low-temperature growth

    PubMed Central

    Thürmer, Konrad; Nie, Shu

    2013-01-01

    From our daily life we are familiar with hexagonal ice, but at very low temperature ice can exist in a different structure––that of cubic ice. Seeking to unravel the enigmatic relationship between these two low-pressure phases, we examined their formation on a Pt(111) substrate at low temperatures with scanning tunneling microscopy and atomic force microscopy. After completion of the one-molecule-thick wetting layer, 3D clusters of hexagonal ice grow via layer nucleation. The coalescence of these clusters creates a rich scenario of domain-boundary and screw-dislocation formation. We discovered that during subsequent growth, domain boundaries are replaced by growth spirals around screw dislocations, and that the nature of these spirals determines whether ice adopts the cubic or the hexagonal structure. Initially, most of these spirals are single, i.e., they host a screw dislocation with a Burgers vector connecting neighboring molecular planes, and produce cubic ice. Films thicker than ∼20 nm, however, are dominated by double spirals. Their abundance is surprising because they require a Burgers vector spanning two molecular-layer spacings, distorting the crystal lattice to a larger extent. We propose that these double spirals grow at the expense of the initially more common single spirals for an energetic reason: they produce hexagonal ice. PMID:23818592

  20. Investigation of the validity of radiosity for sound-field prediction in cubic rooms

    NASA Astrophysics Data System (ADS)

    Nosal, Eva-Marie; Hodgson, Murray; Ashdown, Ian

    2004-12-01

    This paper explores acoustical (or time-dependent) radiosity using predictions made in four cubic enclosures. The methods and algorithms used are those presented in a previous paper by the same authors [Nosal, Hodgson, and Ashdown, J. Acoust. Soc. Am. 116(2), 970-980 (2004)]. First, the algorithm, methods, and conditions for convergence are investigated by comparison of numerous predictions for the four cubic enclosures. Here, variables and parameters used in the predictions are varied to explore the effect of absorption distribution, the necessary conditions for convergence of the numerical solution to the analytical solution, form-factor prediction methods, and the computational requirements. The predictions are also used to investigate the effect of absorption distribution on sound fields in cubic enclosures with diffusely reflecting boundaries. Acoustical radiosity is then compared to predictions made in the four enclosures by a ray-tracing model that can account for diffuse reflection. Comparisons are made of echograms, room-acoustical parameters, and discretized echograms. .