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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. Longitudinal-stability Investigation of High-lift and Stall-control Devices on a 52 Degree Sweptback Wing with and Without Fuselage and Horizontal Tail at a Reynolds Number of 6.8 x 10(exp 6).

    NASA Technical Reports Server (NTRS)

    Foster, Gerald V; Fitzpatrick, James E

    1948-01-01

    Contains low-speed longitudinal stability characteristics of a 52 degree sweptback wing of aspect ratio 2.88, taper ratio 0.625, and NACA 64 (sub 1)-112 airfoil sections normal to the 0.282-chord line, in combination with split flaps, leading-edge flaps, and upper-surface fences. Low-wing and midwing-fuselage aerodynamic characteristics are presented with and without a horizontal tail at various vertical locations. Tests were conducted at a Reynolds number of 6.8 x 10(exp 6).

  3. 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.

  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. A geodetic laser radar rangefinder with 10(exp -7) resolution

    NASA Technical Reports Server (NTRS)

    Mizushima, Y.; Takeichi, M.; Warashima, Y.; Takeshima, A.; Ogawa, I.; Ichie, K.; Schiller, N. H.

    1992-01-01

    A novel geodetic laser radar rangefinder (GLRR) unit utilizing a pair of synchronized 10-psec streak camera systems was developed for displacement measurements of the earth's plates. In order to achieve minimum computing error and assure extremely high spatial resolution, an optical pulse registration clock was developed and used to register a fiducial mark on the time scale of the system. Conventional optical rangefinders have been limited to a relative resolution of 10(exp -6) even for short distances. The system to be reported on today has the capability of measuring a 50km range with an accuracy of 4mm corresponding to a relative resolution of 10(exp -7). With a gain of greater than 3 x 10(exp 3), the system has the capability of detecting extremely weak signals on the order of photon counting. This combined with temporal gating makes daytime measurements comparable in signal-to-noise ratio to nighttime viewing. This is useful for measuring faint signals returning over a range of several tens of kilometers. The present ranging system was designed to observe the mutual displacement of geodetic plates and was employed to measure the boundary between the Philippine and Asian geodetic plates that pass beneath the Suruga Bay near Hamamatsu City, Japan. The system has been in operation for over 3 years. In addition, the system has the ability of producing and detecting optical ranging pulses of several wavelengths simultaneously, making this a complete multicolor system. The basic GLRR system consists of a frequency stabilizing crystal, optical clock, YAG laser, KDP doubling crystal, DK*P tripling crystal, two matched streak cameras (A and B), a control computer, and an output/input periscope system.

  7. 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.

  8. The study of pressure measurement techniques and devices in the range of 10(exp -1) to 10(exp -5) torr (2 millipsi to 0.2 micropsi)

    NASA Technical Reports Server (NTRS)

    Hoffman, John H.

    1990-01-01

    The atmospheric pressure range was studied in a region where conventional pressure sensing devices do not provide meaningful measurements. However, a hot filament gauge was developed and miniaturized which will measure the pressure in the 10(exp -1) to 10(exp -5) torr (2 millipsi to 0.2 micropsi) region, hence the name Micropsi gauge. Laboratory studies were made comparing the currently available devices with the newly developed miniature low power 'Micropsi' pressure sensor.

  9. 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.

  10. 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

  11. 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.

  12. Reconstruction of 10(exp 20)ev Showers in EUSO and JEM EUSO

    NASA Technical Reports Server (NTRS)

    Andreev, V.; Adams, J.; Cline, D.

    2007-01-01

    We describe the procedure to reconstruct 10(exp 20) ev showers in Extreme Universe Space Observatory (EUSO). We show the angular and energy resolution is excellent. We now apply this to the newly proposed Japanese JEM-EUSO and will present results at the meeting.

  13. The measurement of elemental abundances above 10 exp 15 eV at a lunar base

    NASA Astrophysics Data System (ADS)

    Swordy, S. P.

    1990-03-01

    At about 10 exp 15 eV the slope of the energy spectrum of cosmic rays becomes significantly steeper than at lower energies. The measurement of relative elemental abundances at these energies is expected to provide a means to resolve the origin of this feature and greatly contribute to the understanding of the sources of cosmic rays. A moon-based detector for making well-resolved elemental measurements at these energies is described using hadronic calorimetry. This detector is particularly well suited for a site on the lunar surface because there is no overlying layer of atmosphere and the large mass required can be provided by the lunar regolith.

  14. 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.

  15. 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.

  16. 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).

  17. A neutron crystallographic analysis of a cubic porcine insulin at pD 6.6

    NASA Astrophysics Data System (ADS)

    Ishikawa, Takuya; Chatake, Toshiyuki; Ohnishi, Yuki; Tanaka, Ichiro; Kurihara, Kazuo; Kuroki, Ryota; Niimura, Nobuo

    2008-04-01

    The p Ka values of ionizable amino acid side chains are tabulated in standard textbooks. However, whether a certain amino acid side chain in a protein is charged or not cannot be estimated from standard pH values measured from protein solutions. Protonation and deprotonation of various ionizable amino acid residues were observed by a neutron diffraction experiment and discussed on the basis of the charged states estimated by the p Ka values of the amino acid residues. The neutron diffraction study has been carried out at 2.7 Å resolution on cubic porcine insulin at pD 6.6 using the BIX-4 single crystal diffractometer at the JRR-3 reactor of the Japan Atomic Energy Agency. For the present work, a large single crystal of 2.7 mm 3 (=2.0 × 1.7 × 0.8 mm) was obtained by dialysis. The structure refinement was carried out using the program CNS. The resulting Rcryst is 21.6% and the Rfree is 29.1% at a resolution of 2.7 Å. In the case of His B5, both N π and N τ of an imidazole ring are protonated at pD 6.6, but at pD 9 only N π is protonated. In contrast, for His B10, both N π and N τ are protonated at pD 6.6 as well as at pD 9. The ionization states of several amino acids in porcine insulin have been obtained at pD 6.6 and they are compared with those at pD 9 obtained by neutron diffraction as well as those at pH 6.50 and 6.98 obtained by X-ray diffraction. In this manuscript, the difference between these forms will be discussed.

  18. 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.

  19. 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

  20. 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.

  1. Phosphonate-functionalized large pore 3-D cubic mesoporous (KIT-6) hybrid as highly efficient actinide extracting agent.

    PubMed

    Lebed, Pablo J; de Souza, Kellen; Bilodeau, François; Larivière, Dominic; Kleitz, Freddy

    2011-11-01

    A new type of radionuclide extraction material is reported based on phosphonate functionalities covalently anchored on the mesopore surface of 3-D cubic mesoporous silica (KIT-6). The easily prepared nanoporous hybrid shows largely superior performance in selective sorption of uranium and thorium as compared to the U/TEVA commercial resin and 2-D hexagonal SBA-15 equivalent.

  2. High pressure synthesis at 10 GPa and 1400 K using a small cubic anvil apparatus with a multi-anvil 6-6 system

    NASA Astrophysics Data System (ADS)

    Kawazoe, Takaaki; Yamada, Ikuya

    2012-09-01

    In the present study, high pressure synthesis up to 10 GPa was done using a small cubic anvil apparatus (W45×D52×H92 cm3, load capacity of 1.80 MN) with a multi-anvil 6-6 system. Its performance was demonstrated by synthesizing a ferromagnetic perovskite oxide, CaCu3Fe4O12, at pressure-temperature conditions of 10 GPa and 1400 K. The synthesized CaCu3Fe4O12 perovskite was ∼1 mm in diameter and ∼2 mm in height and its size was large enough for performing magnetic susceptibility measurements at 5-300 K using a superconducting quantum interference device magnetometer and phase identification by X-ray diffraction. The experimental system developed in the present study has many advantages when used in high pressure synthesis experiments, and the technical development of a small cubic anvil apparatus will greatly contribute to the advancement of high pressure synthesis of novel materials.

  3. Theory of the zero-field splitting of 6S(3d5)-state ions in cubic crystals

    NASA Astrophysics Data System (ADS)

    Wan-Lun, Yu; Tao, Tan

    1994-02-01

    A study is made of the zero-field splitting (ZFS) of 6S(3d5) ions in cubic crystals, based on an extended crystal-field (CF) model which assumes two constants ζte and ζtt in the description of the spin-orbit (SO) interaction. In addition to the recognized origin for the ZFS, namely, the combined effect of the CF and the SO couplings, a second source is found to arise from the SO interaction alone through a difference between ζte and ζtt caused by covalency. To understand this second effect, we have investigated the SO coupling processes which contribute to the ZFS, using the Macfarlane-Zdansky perturbation procedure. Processes in which the couplings are all between states of different configurations tm2e5-m are found to make a positive contribution proportional to ζ4te. Other processes contribute negatively through a term in ζ2teζ2tt. The ZFS is thus determined by the relative magnitudes of these two parts, and a small difference between ζte and ζtt will cause a great change in its value. Application of this new theory is successfully made to Mn2+ ions in tetrahedral II-VI compounds and in fluoroperovskites.

  4. 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.

  5. 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.

  6. Cubic Polynomials.

    ERIC Educational Resources Information Center

    Lipp, Alan

    2000-01-01

    Presents a classification of factorable cubics and shows how the associated factor graphs determine domains of disconnected branches and furnish a skeletal framework for the number and shape of the branches. Illustrates three dimensional visualization and examines level curves and spikes of surfaces. (KHR)

  7. 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

  8. 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.

  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. 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.

  11. 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

  12. Redetermination of the cubic struvite analogue Cs[Mg(OH(2))(6)](AsO(4)).

    PubMed

    Weil, Matthias

    2008-01-01

    In contrast to the previous refinement from photographic data [Ferrari et al. (1955 ▶). Gazz. Chim. Ital.84, 169-174], the present redetermination of the title compound, caesium hexa-aqua-magnesium arsenate(V), revealed the Cs atom to be on Wyckoff position 4d instead of Wyckoff position 4b of space group F3m. The structure can be derived from the halite structure. The centres of the complex [Mg(OH(2))(6)] octa-hedra and the AsO(4) tetra-hedra (both with 3m symmetry) are on the respective Na and Cl positions. The building units are connected to each other by O-H⋯O hydrogen bonds. The Cs(+) cations (3m symmetry) are located in the voids of this arrangement and exhibit a regular cubocta-hedral 12-coordination to the O atoms of the water mol-ecules. The O atom bonded to As has 2mm site symmetry (Wyckoff position 24f) and the water-mol-ecule O atom has m site symmetry (Wyckoff position 48h).

  13. Tetrahedron dynamics in the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and the cubic 1/1-approximant Zn6Sc.

    PubMed

    Euchner, H; Yamada, T; Rols, S; Ishimasa, T; Kaneko, Y; Ollivier, J; Schober, H; Mihalkovic, M; de Boissieu, M

    2013-03-20

    A comparison of periodic approximants and their quasicrystalline counterparts offers the opportunity to better understand the structure, physical properties and stabilizing mechanisms of these complex phases. We present a combined experimental and molecular dynamics study of the lattice dynamics of the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and compare it to recently published results obtained for the cubic 1/1-approximant Zn(6)Sc. Both phases, quasicrystal and approximant, are built up from large atomic clusters which contain a tetrahedral shell at the cluster centre and are packed either quasiperiodically or on a bcc lattice. Using quasielastic neutron scattering and atomic scale simulations, we show that in the quasicrystal the tetrahedra display a dynamics similar to that observed in the 1/1-approximant: the tetrahedra behave as a 'single molecule' and reorient dynamically on a timescale of the order of a few ps. The tetrahedra reorientation is accompanied by a large distortion of the surrounding cluster shells which provide a unique dynamical flexibility to the quasicrystal. However, whereas in the 1/1-approximant the tetrahedron reorientation is observed down to T(c) = 160 K, where a phase transition takes place, in the quasicrystal the tetrahedron dynamics is gradually freezing from 550 to 300 K, similarly to a glassy system.

  14. 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

  15. 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/.

  16. 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.

  17. 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

  18. 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.

  19. Cubic topological Kondo insulators.

    PubMed

    Alexandrov, Victor; Dzero, Maxim; Coleman, Piers

    2013-11-27

    Current theories of Kondo insulators employ the interaction of conduction electrons with localized Kramers doublets originating from a tetragonal crystalline environment, yet all Kondo insulators are cubic. Here we develop a theory of cubic topological Kondo insulators involving the interaction of Γ(8) spin quartets with a conduction sea. The spin quartets greatly increase the potential for strong topological insulators, entirely eliminating the weak topological phases from the diagram. We show that the relevant topological behavior in cubic Kondo insulators can only reside at the lower symmetry X or M points in the Brillouin zone, leading to three Dirac cones with heavy quasiparticles.

  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. 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.

  2. 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.

  3. 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.

  4. Influence of face-centered-cubic texturing of Co2Fe6B2 pinned layer on tunneling magnetoresistance ratio decrease in Co2Fe6B2/MgO-based p-MTJ spin valves stacked with a [Co/Pd]n-SyAF layer

    NASA Astrophysics Data System (ADS)

    Takemura, Yasutaka; Lee, Du-Yeong; Lee, Seung-Eun; Chae, Kyo-Suk; Shim, Tae-Hun; Lian, Guoda; Kim, moon; Park, Jea-Gun

    2015-05-01

    The TMR ratio of Co2Fe6B2/MgO-based p-MTJ spin valves stacked with a [Co/Pd]n-SyAF layer decreased rapidly when the ex situ magnetic annealing temperature (Tex) was increased from 275 to 325 °C, and this decrease was associated with degradation of the Co2Fe6B2 pinned layer rather than the Co2Fe6B2 free layer. At a Tex above 325 °C the amorphous Co2Fe6B2 pinned layer was transformed into a face-centered-cubic (fcc) crystalline layer textured from [Co/Pd]n-SyAF, abruptly reducing the Δ1 coherence tunneling of perpendicular-spin-torque electrons between the (100) MgO tunneling barrier and the fcc Co2Fe6B2 pinned layer.

  5. 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.

  6. 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.

  7. 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.

  8. Anisotropic cubic curvature couplings

    NASA Astrophysics Data System (ADS)

    Bailey, Quentin G.

    2016-09-01

    To complement recent work on tests of spacetime symmetry in gravity, cubic curvature couplings are studied using an effective field theory description of spacetime-symmetry breaking. The associated mass-dimension-eight coefficients for Lorentz violation studied do not result in any linearized gravity modifications and instead are revealed in the first nonlinear terms in an expansion of spacetime around a flat background. We consider effects on gravitational radiation through the energy loss of a binary system and we study two-body orbital perturbations using the post-Newtonian metric. Some effects depend on the internal structure of the source and test bodies, thereby breaking the weak equivalence principle for self-gravitating bodies. These coefficients can be measured in Solar-System tests, while binary-pulsar systems and short-range gravity tests are particularly sensitive.

  9. Polyolefin cubic silsesquioxane nanocomposites

    NASA Astrophysics Data System (ADS)

    Zheng, Lei

    This thesis focuses on the synthesis and characterization of polyolefin nanocomposites containing polyhedral oligomeric silsesquioxane (POSS) units. Two copolymerization methods were developed utilizing either ring-opening metathesis polymerization or metallocene-catalyzed reactions to incorporate cubic silsesquioxane into polyolefins. Ring-opening metathesis copolymerizations of cyclooctene and the POSS-norbornylene macromonomer have been performed using Grubbs' catalyst RuCl2(=CHPh)(PCy3)2. Random copolymers have been prepared and characterized with POSS loadings as high as 55 wt%. Diimide reduction of these copolymers affords polyethylene-POSS random copolymers. Polyethylene (PE) and isotactic polypropylene (PP) copolymers incorporating POSS have also been prepared using a metallocene/methylaluminoxane (MAO) cocatalyst system. A wide range of POSS concentrations was obtained in these polyolefin POSS copolymers under mild conditions; up to 56 wt% for PE-POSS copolymers and 73 wt% for PP-POSS copolymers were prepared. Copolymerizations of styrene and the POSS-styryl macromonomer have been performed using CpTiCl 3 in conjunction with MAO. Random copolymers of syndiotactic polystyrene and POSS copolymers have been formed and characterized. Novel nanocomposites of PE-POSS have been characterized using Wide Angle X-ray Scattering (WAXS). From both line broadening of the diffraction maxima and also the oriented diffraction in a drawn sample, we conclude that POSS forms anisotropically shaped crystallites. On the basis of this result, a novel approach to obtain nanocomposites containing inorganic nanolayers is proposed. Cubic silsesquioxane (POSS) nanoparticles are used to achieve the nanolayered "clay-like" structure through controlled self-assembly. The organic polymer, covalently connected to POSS, is intended to regulate the POSS crystallization into a two-dimensional lattice. The concept is demonstrated by random copolymers of polybutadiene and POSS. The data from

  10. Infrared cubic dielectric resonator metamaterial.

    SciTech Connect

    Sinclair, Michael B.; Brener, Igal; Peters, David William; Ginn, James Cleveland, III; Ten Eyck, Gregory A.

    2010-06-01

    Dielectric resonators are an effective means to realize isotropic, low-loss optical metamaterials. As proof of this concept, a cubic resonator is analytically designed and then tested in the long-wave infrared.

  11. 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.

  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. Effects of stacking disorder on thermal conductivity of cubic ice.

    PubMed

    Johari, G P; Andersson, Ove

    2015-08-01

    Cubic ice is said to have stacking disorder when the H2O sequences in its structure (space group Fd3̄m) are interlaced with hexagonal ice (space group P6(3)/mmc) sequences, known as stacking faults. Diffraction methods have shown that the extent of this disorder varies in samples made by different methods, thermal history, and the temperature T, but other physical properties of cubic and hexagonal ices barely differ. We had found that at 160 K, the thermal conductivity, κ, of cubic ice is ∼20% less than that of hexagonal ice, and this difference varies for cubic ice samples prepared by different methods and/or subjected to different thermal history. After reviewing the methods of forming cubic ice, we report an investigation of the effects of stacking disorder and other features by using new data, and by analyzing our previous data on the dependence of κ on T and on the pressure. We conclude that the lower κ of cubic ice and its weaker T-dependence is due mainly to stacking disorder and small crystal sizes. On in situ heating at 20-50 MPa pressure, κ increases and cubic ice irreversibly transforms more sharply to ice Ih, and at a higher T of ∼220 K, than it does in ex situ studies. Cooling and heating between 115 and 130 K at 0.1 K min(-1) rate yield the same κ value, indicating that the state of cubic ice in these conditions does not change with time and T. The increase in κ of cubic ice observed on heat-annealing before its conversion to hexagonal ice is attributed to the loss of stacking faults and other types of disorders, and to grain growth. After discussing the consequences of our findings on other properties, we suggest that detailed studies of variation of a given property of cubic ice with the fraction of stacking faults in its structure may reveal more about the effect of this disorder. A similar disorder may occur in the mono-layers of H2O adsorbed on a substrate, in bulk materials comprised of two dimensional layers, in diamond and in

  14. 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…

  15. 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)

  16. 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…

  17. 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…

  18. 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…

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

    PubMed Central

    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

  20. 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

  1. Superconductivity in cubic noncentrosymmetric PdBiSe Crystal

    NASA Astrophysics Data System (ADS)

    Joshi, B.; Thamizhavel, A.; Ramakrishnan, S.

    2015-03-01

    Mixing of spin singlet and spin triplet superconducting pairing state is expected in noncentrosymmetric superconductors (NCS) due to the inherent presence of Rashba-type antisymmetric spin-orbit coupling. Unlike low symmetry (tetragonal or monoclinic) NCS, parity is isotropicaly broken in space for cubic NCS and can additionally lead to the coexistence of magnetic and superconducting state under certain conditions. Motivated with such enriched possibility of unconventional superconducting phases in cubic NCS we are reporting successful formation of single crystalline cubic noncentrosymmetric PdBiSe with lattice parameter a = 6.4316 Å and space group P21 3 (space group no. 198) which undergoes to superconducting transition state below 1.8 K as measured by electrical transport and AC susceptibility measurements. Significant strength of Rashba-type antisymmetric spin-orbit coupling can be expected for PdBiSe due to the presence of high Z (atomic number) elements consequently making it potential candidate for unconventional superconductivity.

  2. 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

  3. Gallium substitutions as a means to stabilize alkaline-earth and rare-earth metal pnictides with the cubic Th{sub 3}P{sub 4} type: Synthesis and structure of A{sub 7}Ga{sub 2}Sb{sub 6} (A=Sr, Ba, Eu)

    SciTech Connect

    Xia Shengqing; Hullmann, Jonathan; Bobev, Svilen

    2008-08-15

    Three new compounds-Sr{sub 7.04(2)}Ga{sub 1.94(2)}Sb{sub 6}, Ba{sub 7.02(3)}Ga{sub 1.98(3)}Sb{sub 6} and Eu{sub 7.04(3)}Ga{sub 1.90(3)}Sb{sub 6}-have been synthesized from reactions of the corresponding elements using gallium as a metal flux. Their crystal structures (space group I4-bar 3d (No. 220), Z=2 with unit cell parameters: a=9.9147(9) A for the Sr-compound; a=10.3190(9) A for the Ba-compound; and a=9.7866(8) A for the Eu-compound) have been established by single-crystal X-ray diffraction. The structures are best described as Ga-stabilized derivatives of the hypothetical Sr{sub 4}Sb{sub 3}, Ba{sub 4}Sb{sub 3} and Eu{sub 4}Sb{sub 3} phases with the cubic Th{sub 3}P{sub 4} type. Such an inclusion of interstitial Ga atoms in this atomic arrangement results in the formation of isolated [Ga{sub 2}Sb{sub 6}]{sup 14-} fragments, isoelectronic and isostructural with the [Sn{sub 2}Te{sub 6}]{sup 6-} anions in the K{sub 3}SnTe{sub 3} type, and allows for the attainment of a charge-balanced electron count. In that sense, the Sr{sub 4}Sb{sub 3}, Ba{sub 4}Sb{sub 3} and Eu{sub 4}Sb{sub 3} binaries, which are expected to be electron-deficient and are currently unknown, can be 'turned' into Sr{sub 7}Ga{sub 2}Sb{sub 6}, Ba{sub 7}Ga{sub 2}Sb{sub 6} and Eu{sub 7}Ga{sub 2}Sb{sub 6}, whose structures are readily rationalized following the Zintl concept. - Graphical abstract: Three new antimonides have been structurally characterized by single-crystal X-ray diffraction. Their structures are best described as derivatives of the body-centered cubic, anti-Th{sub 3}P{sub 4} type. Unlike the one-electron-deficient A{sub 4}Sb{sub 3} phases (A=Sr, Ba, Eu), the new, A{sub 7}Ga{sub 2}Sb{sub 6} compounds are Zintl phases with closed-shell configurations for both the cations and anions.

  4. Cationic Phospholipids Forming Cubic Phases: Lipoplex Structure and Transfection Efficiency

    SciTech Connect

    Koynova, Rumiana; Wang, Li; MacDonald, Robert C.

    2008-10-29

    The transfection activity and the phase behavior of two novel cationic O-alkyl-phosphatidylcholines, 1,2-dioleoyl-sn-glycero-3-hexylphosphocholine (C6-DOPC) and 1,2-dierucoyl-sn-glycero-3-ethylphosphocholine (di22:1-EPC), have been examined with the aim of more completely understanding the mechanism of lipid-mediated DNA delivery. Both lipids form cubic phases: C6-DOPC in the entire temperature range from -10 to 90 C, while di22:1-EPC exhibits an irreversible lamellar-cubic transition between 50 and 70 C on heating. The lipoplexes formed by C6-DOPC arrange into hexagonal phase, while the lipoplexes of di22:1-EPC are lamellar. Both lipids exhibit lower transfection activity than the lamellar-forming 1,2-dioleoyl-sn-glycero-3-ethylphosphocholine (EDOPC). Thus, for the studied cationic phospholipid-DNA systems, the lipoplex phase state is a factor that does not seem to correlate with transfection activity. The parameter that exhibits better correlation with the transfection activity within the present data set is the phase state of the lipid dispersion prior to the addition of DNA. Thus, the lamellar lipid dispersion (EDOPC) produces more efficient lipoplexes than the dispersion with coexisting lamellar and cubic aggregates (diC22:1-EPC), which is even more efficient than the purely cubic dispersions (C6-DOPC; diC22:1-EPC after heating). It could be inferred from these data and from previous research that cubic phase lipid aggregates are unlikely to be beneficial to transfection. The lack of correlation between the phase state of lipoplexes and their transfection activity observed within the present data set does not mean that lipid phase state is generally unimportant for lipofection: a viewpoint now emerging from our previous studies is that the critical factor in lipid-mediated transfection is the structural evolution of lipoplexes within the cell, upon interacting and mixing with cellular lipids.

  5. 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.

  6. 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

  7. 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.

  8. An optimized cubic interpolator for image resampling

    NASA Technical Reports Server (NTRS)

    Schowengerdt, R. A.; Gray, R. T.; Park, S. K.

    1984-01-01

    It is noted that the cubic resampling function is only one member of a family of functions, defined by the single parameter of the slope of the cubic function at its first zero crossing, whose other members are in some cases superior to the standard cubic. This superiority is especially noteworthy with respect to the extent of gray level overshoot induced by the resampling process at high contrast edges. It is shown that there is an optimum member of this 'parametric cubic convolution' family which minimizes the mean-squared radiometric error arising from interpolation. This interpolator requires no additional computation time over the conventional cubic one. These conclusions are supported and illustrated by resampling simulations with both a high resolution digitized aerial image and a Landsat Multispectral Scanner image.

  9. Synthesis, structure, and bonding of Sc4MgxCu15-xGa approximately 7.5 (x=0, 0.5). Two incommensurately modulated scandium substitution derivatives of cubic Mg2Cu6Ga5.

    PubMed

    Lin, Qisheng; Lidin, Sven; Corbett, John D

    2008-02-01

    The substitution of scandium for magnesium in Mg2Cu6Ga5 (Mg2Zn11-type) yields an irrational superstructure phase that includes the refined compositions, Sc4Mg0.50(2)Cu14.50(2)Ga7.61(2) and Sc4Cu14.76(2)Ga7.51(2). These crystallize in Cmmm, a=approximately 8.31 A, b=approximately 21.72 A, c=approximately 8.30 A. The structures feature Sc2 dimers, Cu6 octahedra, a 3D CuGa (Cu12Ga2) framework, and arachno gallium-centered Cu4Ga6 icosahedra that are condensed into zigzag chains. The arrangement of these building blocks exhibits a topologic relationship to Mg2Cu6Ga5. Further studies reveal that the quaternary compound exhibits incommensurate modulations along a, with q=(0.694, 0, 0). Structure refinements with superspace group Xmmm(a00)000 led to saw-tooth modulations for two fractional or mixed sites that avoid short Cu-Ga distances. Band structure analyses reveal that the Fermi surface and bonding are sensitive to the incommensurately modulated atoms. PMID:18163612

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. AuTa 5S: A Cubic Rod Packing of Condensed (Au, Ta) 13Icosahedra Interwoven with a Three-Dimensional Framework of Corner-Connected STa 6Octahedra

    NASA Astrophysics Data System (ADS)

    Harbrecht, Bernd; Wagner, Volker; Pietzonka, Clemens

    1998-08-01

    AuTa 5S was prepared from a compressed mixture of tantalum disulfide, tantalum, and gold in a sealed tantalum capsule at 1650 K within 2 days. Above 1750 K the sulfide disproportionates in the solid state. The structure of AuTa 5S ( a=1250.82(3) pm, Foverline43 m, Z=16, Pearson symbol cF112) was determined from integrated X-ray powder diffraction intensities by direct methods and subsequently refined by fitting the profiles (13 structure variables, Rwp=0.036). Three of five crystallographically distinct metal atoms have distorted icosahedral coordinations. Sulfur is trigonal antiprismatically coordinated by tantalum. The structure is composed of two mutually interpenetrating zinc blende-like frameworks consisting of corner-connected STa 6octahedra and corner-connected Au 4Ta 4and Ta 4Ta 4stellae quadrangulae. The unique structure of AuTa 5S represents a link between two major intermetallic structure families, the η-carbide-type and the Mn 23Th 6-type structures.

  15. 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.

  16. Synthesis of cubic silicon nitride

    NASA Astrophysics Data System (ADS)

    Zerr, Andreas; Miehe, Gerhard; Serghiou, George; Schwarz, Marcus; Kroke, Edwin; Riedel, Ralf; Fueß, Hartmut; Kroll, Peter; Boehler, Reinhard

    1999-07-01

    Silicon nitride (Si3N4) is used in a variety of important technological applications. The high fracture toughness, hardness and wear resistance of Si3N4-based ceramics are exploited in cutting tools and anti-friction bearings; in electronic applications, Si3N4 is used as an insulating, masking and passivating material. Two polymorphs of silicon nitride are known, both of hexagonal structure: α- and β-Si3N4. Here we report the synthesis of a third polymorph of silicon nitride, which has a cubic spinel structure. This new phase, c-Si3N4, is formed at pressures above 15GPa and temperatures exceeding 2,000K, yet persists metastably in air at ambient pressure to at least 700K. First-principles calculations of the properties of this phase suggest that the hardness of c-Si3N4 should be comparable to that of the hardest known oxide (stishovite, a high-pressure phase of SiO2), and significantly greater than the hardness of the two hexagonal polymorphs.

  17. Cubic phases and cubic phase dispersions in a phospholipid-based system.

    PubMed

    Johnsson, Markus; Barauskas, Justas; Tiberg, Fredrik

    2005-02-01

    A cubic liquid crystalline phase forming system based on the phospholipid dioleoylphosphatidylethanolamine (DOPE) which is fortified with small amounts of PEGylated (poly(ethylene) glycol) glycerol monooleate (PEG(660)-GMO) is characterized. The cubic phase formed by the DOPE/PEG(660)-GMO/water system coexists with water in the dilute part of the phase diagram and can be fragmented into colloidal size particles with retained cubic phase structure.

  18. Ultrahard nanotwinned cubic boron nitride.

    PubMed

    Tian, Yongjun; Xu, Bo; Yu, Dongli; Ma, Yanming; Wang, Yanbin; Jiang, Yingbing; Hu, Wentao; Tang, Chengchun; Gao, Yufei; Luo, Kun; Zhao, Zhisheng; Wang, Li-Min; Wen, Bin; He, Julong; Liu, Zhongyuan

    2013-01-17

    Cubic boron nitride (cBN) is a well known superhard material that has a wide range of industrial applications. Nanostructuring of cBN is an effective way to improve its hardness by virtue of the Hall-Petch effect--the tendency for hardness to increase with decreasing grain size. Polycrystalline cBN materials are often synthesized by using the martensitic transformation of a graphite-like BN precursor, in which high pressures and temperatures lead to puckering of the BN layers. Such approaches have led to synthetic polycrystalline cBN having grain sizes as small as ∼14 nm (refs 1, 2, 4, 5). Here we report the formation of cBN with a nanostructure dominated by fine twin domains of average thickness ∼3.8 nm. This nanotwinned cBN was synthesized from specially prepared BN precursor nanoparticles possessing onion-like nested structures with intrinsically puckered BN layers and numerous stacking faults. The resulting nanotwinned cBN bulk samples are optically transparent with a striking combination of physical properties: an extremely high Vickers hardness (exceeding 100 GPa, the optimal hardness of synthetic diamond), a high oxidization temperature (∼1,294 °C) and a large fracture toughness (>12 MPa m(1/2), well beyond the toughness of commercial cemented tungsten carbide, ∼10 MPa m(1/2)). We show that hardening of cBN is continuous with decreasing twin thickness down to the smallest sizes investigated, contrasting with the expected reverse Hall-Petch effect below a critical grain size or the twin thickness of ∼10-15 nm found in metals and alloys.

  19. 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.

  20. 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.

  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Superhard BC(3) in cubic diamond structure.

    PubMed

    Zhang, Miao; Liu, Hanyu; Li, Quan; Gao, Bo; Wang, Yanchao; Li, Hongdong; Chen, Changfeng; Ma, Yanming

    2015-01-01

    We solve the crystal structure of recently synthesized cubic BC(3) using an unbiased swarm structure search, which identifies a highly symmetric BC(3) phase in the cubic diamond structure (d-BC(3)) that contains a distinct B-B bonding network along the body diagonals of a large 64-atom unit cell. Simulated x-ray diffraction and Raman peaks of d-BC(3) are in excellent agreement with experimental data. Calculated stress-strain relations of d-BC(3) demonstrate its intrinsic superhard nature and reveal intriguing sequential bond-breaking modes that produce superior ductility and extended elasticity, which are unique among superhard solids. The present results establish the first boron carbide in the cubic diamond structure with remarkable properties, and these new findings also provide insights for exploring other covalent solids with complex bonding configurations.

  7. 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.

  8. 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.

  9. Diamine Functionalized Cubic Mesoporous Silica for Ibuprofen Controlled Delivery.

    PubMed

    Sivaguru, J; Selvaraj, M; Ravi, S; Park, H; Song, C W; Chun, H H; Ha, C-S

    2015-07-01

    A diamine functionalized cubic mesostructured KIT-6 (N-KIT-6) has been prepared by post-synthetic method using calcined mesoporous KIT-6 with a diamine source, i.e., N-'[3-(tri methoxysilyl)- propyl]'ethylenediamine. The KIT-6 mesoporous silica used for N-KIT-6 was synthesized under weak acidic hydrothermal method using bitemplates, viz., Pluronic P123 and 1-butanol. The synthesized mesoporous materials, KIT-6 and N-KIT-6, have been characterized by the relevant instrumental techniques such as SAXS, N2 sorption isotherm, FT-IR, SEM, TEM and TGA to prove the standard mesoporous materials with the identification of diamine groups. The characterized mesoporous materials, KIT-6 and N-KIT-6, have been extensively used in the potential application of controlled drug delivery, where ibuprofen (IBU) employed as a model drug. The rate of IBU adsorption and release was monitored by UV vis-spectrometer. On the basis of the experimental results of controlled drug delivery system, the results of IBU adsorption and releasing rate in N-KIT-6 are higher than those of KIT-6 because of the higher hydrophobic nature as well as rich basic sites on the surface of inner pore wall silica.

  10. 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.

  11. 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)

  12. Anisotropy of a cubic ferromagnet at criticality

    NASA Astrophysics Data System (ADS)

    Kudlis, A.; Sokolov, A. I.

    2016-10-01

    Critical fluctuations change the effective anisotropy of cubic ferromagnet near the Curie point. If the crystal undergoes phase transition into orthorhombic phase and the initial anisotropy is not too strong, reduced anisotropy of nonlinear susceptibility acquires at Tc the universal value δ4*=2/v* 3 (u*+v*) where u* and v* are coordinates of the cubic fixed point on the flow diagram of renormalization group equations. In the paper, the critical value of the reduced anisotropy is estimated within the pseudo-ɛ expansion approach. The six-loop pseudo-ɛ expansions for u*, v*, and δ4* are derived for the arbitrary spin dimensionality n . For cubic crystals (n =3 ) higher-order coefficients of the pseudo-ɛ expansions obtained turn out to be so small that use of simple Padé approximants yields reliable numerical results. Padé resummation of the pseudo-ɛ series for u*, v*, and δ4* leads to the estimate δ4*=0.079 ±0.006 , indicating that detection of the anisotropic critical behavior of cubic ferromagnets in physical and computer experiments is certainly possible.

  13. 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.

  14. 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

  15. 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.

  16. 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.

  17. 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

  18. Optical properties of cubic hafnia stabilized with yttria.

    PubMed

    Wood, D L; Nassau, K; Kometani, T Y; Nash, D L

    1990-02-01

    The composition, transparency, refractive index, and infrared reflectance of yttria-stabilized cubic hafnia (c-HfO(2)) single crystals were measured. The material is transparent from the ultraviolet to the mid-infrared and for 9.6-mol % Y(2)O(3), the index is slightly smaller than for comparable cubic zirconia c-ZrO(2) or for diamond, but the dispersion (n(F) - n(c) = 0.02811) is larger than that of diamond. The index vs wavelength from 0.36 microm in the ultraviolet to 5.0 microm in the infrared is represented by a three-term Sellmeier formula to 1 x 10(-4). The temperature dependence of refractive index is similar to that of c-ZrO(2). The infrared reflectance spectrum is fitted in a classical dispersion analysis with seven oscillators derived from the transverse optical phonon as well as acoustic frequencies with splittings due to lowered symmetry derived from the randomly distributed stabilizer ions.

  19. Deterministic implementation of weak quantum cubic nonlinearity

    SciTech Connect

    Marek, Petr; Filip, Radim; Furusawa, Akira

    2011-11-15

    We propose a deterministic implementation of weak cubic nonlinearity, which is a basic building block of a full-scale continuous-variable quantum computation. Our proposal relies on preparation of a specific ancillary state and transferring its nonlinear properties onto the desired target by means of deterministic Gaussian operations and feed forward. We show that, despite the imperfections arising from the deterministic nature of the operation, the weak quantum nonlinearity can be implemented and verified with the current level of technology.

  20. 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

  1. Cubic membranes: a structure-based design for DNA uptake.

    PubMed

    Almsherqi, Zakaria; Hyde, Stephen; Ramachandran, Malarmathy; Deng, Yuru

    2008-09-01

    Cubic membranes are soft three-dimensional crystals found within cell organelles in a variety of living systems, despite the aphorism of Fedorov: 'crystallization is death'. They consist of multi-bilayer lipid-protein stacks, folded onto anticlastic surfaces that resemble triply periodic minimal surfaces, forming highly swollen crystalline sponges. Although cubic membranes have been observed in numerous cell types and under different pathophysiological conditions, knowledge about the formation and potential function(s) of non-lamellar, cubic structures in biological systems is scarce. We report that mitochondria with this cubic membrane organization isolated from starved amoeba Chaos carolinense interact sufficiently with short segments of phosphorothioate oligonucleotides (PS-ODNs) to give significant ODNs uptake. ODNs condensed within the convoluted channels of cubic membrane by an unknown passive targeting mechanism. Moreover, the interaction between ODNs and cubic membrane is sufficient to retard electrophoretic mobility of the ODN component in the gel matrix. These ODN-cubic membrane complexes are readily internalized within the cytoplasm of cultured mammalian cells. Transmission electron microscopic analysis confirms ODNs uptake by cubic membranes and internalization of ODN-cubic membrane complexes into the culture cells. Cubic membranes thus may offer a new, potentially benign medium for gene transfection. PMID:18270148

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. Cubic liquid crystalline glyceryl monooleate matrices for oral delivery of enzyme.

    PubMed

    Shah, Manish H; Paradkar, Anant

    2005-04-27

    In situ cubic phase transforming system of glyceryl monooleate (GMO) has been prepared which offers protection to the metaloenzyme, seratiopeptidase (STP), in gastric environment and provides delayed and controlled release with no initial burst after oral administration. Effect of magnesium trisilicate (MTS) on floating, proteolytic activity and drug release was studied. Gelucire 43/01 was incorporated in the system to provide prolonged lag time. The drug-loaded matrices required 100 mg of MTS to overcome floatability of GMO matrix. Plain GMO matrices showed 85.3% loss of proteolytic activity in acidic medium, whereas matrices containing MTS showed retention of activity (111.6%). The hydrophobic nature of MTS induced formation of cubic phase at faster rate and the existence of cubic phase was confirmed by polarizing light microscopy. Furthermore, MTS provided alkaline microenvironment, which prevented acid-catalyzed hydrolysis and protein unfolding. The magnesium ions restored the activity of STP. The release of STP was decreased with increasing amount of MTS in the matrix. Gelucire did not affect proteolytic activity. The water uptake of matrices with gelucire was decelerated due to formation of hexagonal phase. However, the rate of STP release from these matrices was very slow due to incorporation of gelucire into lipid bilayers, which provided resistance to movement of STP. Thus, microenvironment-controlled in situ cubic phase transforming GMO matrices provided protection to STP and controlled release.

  7. 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.

  8. 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.

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

    PubMed

    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. PMID:25085194

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

    PubMed

    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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 46 CFR 160.060-6 - Construction-nonstandard vests.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Polyethylene Foam, Adult and Child § 160.060-6 Construction—nonstandard vests. (a) General. The construction... pounds. (2) Three hundred and fifty cubic inches or more for a child medium size, for children weighing from 50 to 90 pounds. (3) Two hundred and twenty-five cubic inches or more for children weighing...

  16. 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.

  17. Capturing dynamic cation hopping in cubic pyrochlores

    NASA Astrophysics Data System (ADS)

    Brooks Hinojosa, Beverly; Asthagiri, Aravind; Nino, Juan C.

    2011-08-01

    In direct contrast to recent reports, density functional theory predicts that the most stable structure of Bi2Ti2O7 pyrochlore is a cubic Fd3¯m space group by accounting for atomic displacements. The displaced Bi occupies the 96g(x,x,z) Wyckoff position with six equivalent sites, which create multiple local minima. Using nudged elastic band method, the transition states of Bi cation hopping between equivalent minima were investigated and an energy barrier between 0.11 and 0.21 eV was determined. Energy barriers associated with the motion of Bi between equivalent sites within the 96g Wyckoff position suggest the presence of dielectric relaxation in Bi2Ti2O7.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Cubic-phase-free dispersion compensation in solid-state ultrashort-pulse lasers.

    PubMed

    Lemoff, B E; Barty, C P

    1993-01-01

    We show that intracavity group-velocity dispersion compensation with the use of prisms composed of conventional optical materials can be accomplished while simultaneously eliminating the round-trip cavity cubic phase. The ability to compensate perfectly both second- and third-order dispersion exists for pulses whose central wavelengths lie within a range that depends on the prism and laser rod materials as well as on the prism angles. In the case of Ti:sapphire and Cr:LiSrAlF(6) lasers, Brewster prisms composed of readily available materials can be used to compensate for both group-velocity dispersion and cubic phase over much of the respective tuning rangers.

  5. CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: Electro-oxidation of Formic Acid on Carbon Supported Edge-Truncated Cubic Platinum Nanoparticles Catalysts

    NASA Astrophysics Data System (ADS)

    Li, She-Qiang; Fu, Xing-Qiu; Hu, Bing; Deng, Jia-Jun; Chen, Lei

    2009-11-01

    The oxidation of formic acid on edge-truncated cubic platinum nanoparticles/C catalysts is investigated. X-ray photoelectron spectroscopy analysis indicates that the surface of edge-truncated cubic platinum nanoparticles is composed of two types of coordination sites. The oxidation behavior of formic acid on edge-truncated cubic platinum nanoparticles/C is investigated using cyclic voltammetry. The apparent activation energies are found to be 54.2, 55.0, 61.8, 69.5, 71.9, 69.26, 65.28kJ/mol at 0.15, 0.3, 0.4, 0.5, 0.6, 0.65, 0.7V, respectively. A specific surface area activity of 1.76 mA·cm-2 at 0.4 V indicates that the edge-truncated cubic Platinum nanoparticles are a promising anode catalyst for direct formic acid fuel cells.

  6. 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.

  7. 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 ...

  8. Multitarget tracking with cubic energy optical neural nets.

    PubMed

    Barnard, E; Casasent, D P

    1989-02-15

    A neural net processor and its optical realization are described for a multitarget tracking application. A cubic energy function results and a new optical neural processor is required. Initial simulation data are presented.

  9. 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)

  10. 19. 1500 CUBIC FEET CAPACITY SCRAP STEEL CHARGING BOX ON ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    19. 1500 CUBIC FEET CAPACITY SCRAP STEEL CHARGING BOX ON THE CHARGING AISLE OF THE BOP SHOP LOOKING NORTHWEST. - U.S. Steel Duquesne Works, Basic Oxygen Steelmaking Plant, Along Monongahela River, Duquesne, Allegheny County, PA

  11. 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.

  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. 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

  14. Distorted asymmetric cubic nanostructure of soluble fullerene crystals in efficient polymer:fullerene solar cells.

    PubMed

    Kim, Youngkyoo; Nelson, Jenny; Zhang, Tong; Cook, Steffan; Durrant, James R; Kim, Hwajeong; Park, Jiho; Shin, Minjung; Nam, Sungho; Heeney, Martin; McCulloch, Iain; Ha, Chang-Sik; Bradley, Donal D C

    2009-09-22

    We found that 1-(3-methoxycarbonyl)propyl-1-phenyl-(6,6)C(61) (PCBM) molecules make a distorted asymmetric body-centered cubic crystal nanostructure in the bulk heterojunction films of reigoregular poly(3-hexylthiophene) and PCBM. The wider angle of distortion in the PCBM nanocrystals was approximately 96 degrees , which can be assigned to the influence of the attached side group to the fullerene ball of PCBM to bestow solubility. Atom concentration analysis showed that after thermal annealing the PCBM nanocrystals do preferentially distribute above the layer of P3HT nanocrystals inside devices.

  15. 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.

  16. 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

  17. TOPICAL REVIEW: Nonlinear photonic crystals: III. Cubic nonlinearity

    NASA Astrophysics Data System (ADS)

    Babin, Anatoli; Figotin, Alexander

    2003-10-01

    Weakly nonlinear interactions between wavepackets in a lossless periodic dielectric medium are studied based on the classical Maxwell equations with a cubic nonlinearity. We consider nonlinear processes such that: (i) the amplitude of the wave component due to the nonlinearity does not exceed the amplitude of its linear component; (ii) the spatial range of a probing wavepacket is much smaller than the dimension of the medium sample, and it is not too small compared with the dimension of the primitive cell. These nonlinear processes are naturally described in terms of the cubic interaction phase function based on the dispersion relations of the underlying linear periodic medium. It turns out that only a few quadruplets of modes have significant nonlinear interactions. They are singled out by a system of selection rules including the group velocity, frequency and phase matching conditions. It turns out that the intrinsic symmetries of the cubic interaction phase stemming from assumed inversion symmetry of the dispersion relations play a significant role in the cubic nonlinear interactions. We also study canonical forms of the cubic interaction phase leading to a complete quantitative classification of all possible significant cubic interactions. The classification is ultimately based on a universal system of indices reflecting the intensity of nonlinear interactions.

  18. 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.

  19. High sodium ion conductivity of glass-ceramic electrolytes with cubic Na3PS4

    NASA Astrophysics Data System (ADS)

    Hayashi, Akitoshi; Noi, Kousuke; Tanibata, Naoto; Nagao, Motohiro; Tatsumisago, Masahiro

    2014-07-01

    Sulfide solid electrolytes with cubic Na3PS4 phase has relatively high sodium ion conductivity of over 10-4 S cm-1 at room temperature, and all-solid-state sodium batteries Na-Sn/TiS2 with the electrolyte operated as a secondary battery at room temperature. To improve battery performance, conductivity enhancement of sulfide electrolytes is important. In this study, we have succeeded in enhancing conductivity by optimizing preparation conditions of Na3PS4 glass-ceramic electrolytes. By use of crystalline Na2S with high purity of 99.1%, cubic Na3PS4 crystals were directly precipitated by ball milling process at the composition of 75Na2S·25P2S5 (mol%). The glass-ceramic electrolyte prepared by milling for 1.5 h and consecutive heat treatment at 270 °C for 1 h showed the highest conductivity of 4.6 × 10-4 S cm-1, which is twice as high as the conductivity of the cubic Na3PS4 glass-ceramic prepared in a previous report. All-solid-state Na-Sn/NaCrO2 cells with the newly prepared electrolyte exhibited charge-discharge cycles at room temperature and kept about 60 mAh per gram of NaCrO2 for 15 cycles.

  20. 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

  1. Cubic potential models for cluster radioactivity

    NASA Astrophysics Data System (ADS)

    Shanmugam, G.

    1999-09-01

    Cluster radioactivity is a process by which nuclei equal and heavier than the a-particleis emitted spontaneously. The clusters usually emitted in this process are the a-particle, carbon, oxygen, neon, magnesium, silicon etc. When the mass of the cluster becomes comparable with the mass of the daughter, symmetric fission takes place. Thus the cluster radioactivity is an intermediate process between the well known a-decay and the spontaneous fission. In earlier years such cluster radioactivity was found mostly in actinide nuclei like radium, uranium etc. Very recently it has been predicted that such decays are possible in a new region around 114Ba. There has been an exciting experimental detection of the emission of 12C from 114Ba leading to 102Sn, which is attracting a lot of attention recently. To study the phenomenon of cluster radioactivity there are various theoretical models in vogue. The existing models generally fall under two categories: the unified fission model (UFM) and the preformed cluster model (PCM). The physics of the UFM and the PCM are completely different. The UFM considers cluster radioactivity simply as a barrier penetration phenomenon in between the fission and the a-decay without worrying about the cluster being or not being preformed in the parent nucleus. In the PCM clusters are assumed to be preborn in a parent nucleus before they could penetrate the potential barrier with a given Q-value. The basic assumption of the UFM is that heavy clusters as well as the a-particle have equal probability of being preformed. In PCM, clusters of different sizes have different probabilities of their being preformed in the parent nucleus. We have developed three fission models during the last decade using the cubic potential for the pre-scission region. The use of these models in the study of cluster radioactivity in both the actinide and barium regions will be discussed in this talk in comparison with the other existing theories.

  2. Effects of stacking disorder on thermal conductivity of cubic ice

    NASA Astrophysics Data System (ADS)

    Johari, G. P.; Andersson, Ove

    2015-08-01

    Cubic ice is said to have stacking disorder when the H2O sequences in its structure (space group F d 3 ¯ m ) are interlaced with hexagonal ice (space group P63/mmc) sequences, known as stacking faults. Diffraction methods have shown that the extent of this disorder varies in samples made by different methods, thermal history, and the temperature T, but other physical properties of cubic and hexagonal ices barely differ. We had found that at 160 K, the thermal conductivity, κ, of cubic ice is ˜20% less than that of hexagonal ice, and this difference varies for cubic ice samples prepared by different methods and/or subjected to different thermal history. After reviewing the methods of forming cubic ice, we report an investigation of the effects of stacking disorder and other features by using new data, and by analyzing our previous data on the dependence of κ on T and on the pressure. We conclude that the lower κ of cubic ice and its weaker T-dependence is due mainly to stacking disorder and small crystal sizes. On in situ heating at 20-50 MPa pressure, κ increases and cubic ice irreversibly transforms more sharply to ice Ih, and at a higher T of ˜220 K, than it does in ex situ studies. Cooling and heating between 115 and 130 K at 0.1 K min-1 rate yield the same κ value, indicating that the state of cubic ice in these conditions does not change with time and T. The increase in κ of cubic ice observed on heat-annealing before its conversion to hexagonal ice is attributed to the loss of stacking faults and other types of disorders, and to grain growth. After discussing the consequences of our findings on other properties, we suggest that detailed studies of variation of a given property of cubic ice with the fraction of stacking faults in its structure may reveal more about the effect of this disorder. A similar disorder may occur in the mono-layers of H2O adsorbed on a substrate, in bulk materials comprised of two dimensional layers, in diamond and in

  3. 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.

  4. 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).

  5. 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

  6. Lattice matched crystalline substrates for cubic nitride semiconductor growth

    DOEpatents

    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.

  7. Cubic titanium dioxide photoanode for dye-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Chae, Jinho; Kang, Misook

    Following from the recently evolved concept of significantly improving the photovoltaic efficiency in dye-sensitized solar cells (DSSCs) by reducing the loss of electrons on the spherical surface of titanium dioxide, this study examines the synthesis of cubic TiO 2 with a special morphology to overcome this electron loss and investigates its application to DSSCs. Cubic TiO 2 is synthesized by an advanced rapid hydrothermal method, with the addition of an amine species additive. Transmission electron microscopy (TEM) images confirm the cubic shape of the TiO 2 particles with a diameter less than 5-10 nm. Using N719 dye under illumination with 100 mW cm -2 simulated sunlight, the application of cubic TiO 2 to DSSCs affords an energy conversion efficiency of approximately 9.77% (4.0-μm thick TiO 2 film), which is considerably enhanced compared with that achieved using a commercial, spherical TiO 2. Electrostatic force microscopy (EFM) and impedance analyses reveal that the electrons are transferred more rapidly to the surface of a cubic TiO 2 film than on a spherical TiO 2 film.

  8. 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.

  9. 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.

  10. Closure of the cubic tensor polynomial failure surface

    NASA Technical Reports Server (NTRS)

    Jiang, Zhiqing; Tennyson, R. C.

    1989-01-01

    An analytical method has been developed to ensure closure of the cubic form of the tensor polynomial strength criterion. The intrinsic complexity of the cubic function is such that special conditions must be met to close the failure surface in three-dimensional stress space. These requirements are derived in terms of non-intersecting conditions for asymptotes and an asymptotic plane. To demonstrate the validity of this approach, closed failure surfaces were derived for two graphite/epoxy material systems (3M SP288-T300 and IM7 8551-7). The agreement of test data with this model clearly shows that it is possible to use a higher order cubic failure theory with confidence.

  11. Boron suboxide: As hard as cubic boron nitride

    NASA Astrophysics Data System (ADS)

    He, Duanwei; Zhao, Yusheng; Daemen, L.; Qian, J.; Shen, T. D.; Zerda, T. W.

    2002-07-01

    The Vickers hardness of boron suboxide single crystals was measured using a diamond indentation method. Under a loading force of 0.98 N, our test gave an average Vickers hardness of 45 GPa. The average fracture toughness was measured as 4.5 MPa m1/2. We also measured the hardness of the cubic boron nitride and sapphire single crystals for comparison. The average measured hardness for boron suboxide was found to be very close to that of cubic boron nitride under the same loading force. Our results suggest that the boron suboxide could be a new superhard material for industrial applications, surpassed in hardness only by diamond and cubic boron nitride.

  12. Consolidation of cubic and hexagonal boron nitride composites

    DOE PAGES

    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

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. Board-foot and cubic-foot volume tables for Alaska-cedar in southeast Alaska. Forest Service research note

    SciTech Connect

    DeMars, D.J.

    1996-03-01

    Four tables give cubic-foot and board-foot volume estimates for Alaska-cedar given breast-height diameter outside bark (DBHOB) and either total tree height or number of logs to a 6-inch top. The values for DBHOB and total tree height (or number of logs in the tree) that are in the tables have been limited to the ranges these variables had in the sample data.

  19. Board-foot and cubic-foot volume tables for western redcedar in southeast Alaska. Forest Service research note

    SciTech Connect

    DeMars, D.J.

    1996-02-01

    Four tables give cubic-foot and board-foot volume estimates for western redcedar given breast height diameter outside bark (DBHOB) and either total tree height or number of logs to a 6-inch top. The values for DBHOB and total tree height (or number of logs in the tree) that are in the tables have been limited to the ranges these variables had in the sample data.

  20. 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.

  1. 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)

  2. 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

  3. Cubic spline approximation techniques for parameter estimation in distributed systems

    NASA Technical Reports Server (NTRS)

    Banks, H. T.; Crowley, J. M.; Kunisch, K.

    1983-01-01

    Approximation schemes employing cubic splines in the context of a linear semigroup framework are developed for both parabolic and hyperbolic second-order partial differential equation parameter estimation problems. Convergence results are established for problems with linear and nonlinear systems, and a summary of numerical experiments with the techniques proposed is given.

  4. 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.)

  5. 46 CFR 160.035-9 - Cubic capacity of lifeboats.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... its cubic capacity. (1) Length (L). The length is the distance in feet from the inside of the plating... square stern, the after terminus is the inside of the transom. (2) Breadth (B). The breadth is the...) Depth (D). The depth is the distance in feet amidships inside the plating from the top of the keel...

  6. 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.

  7. Dynamic mirror-symmetry breaking in bicontinuous cubic phases.

    PubMed

    Dressel, Christian; Liu, Feng; Prehm, Marko; Zeng, Xiangbing; Ungar, Goran; Tschierske, Carsten

    2014-11-24

    Chiral segregation of enantiomers or chiral conformers of achiral molecules during self-assembly in well-ordered crystalline superstructures has fascinated chemists since Pasteur. Here we report spontaneous mirror-symmetry breaking in cubic phases formed by achiral multichain-terminated diphenyl-2,2'-bithiophenes. It was found that stochastic symmetry breaking is a general phenomenon observed in bicontinuous cubic liquid crystal phases of achiral rod-like compounds. In all compounds studied the Im3̄m cubic phase is always chiral, while the Ia3̄d phase is achiral. These intriguing observations are explained by propagation of homochiral helical twist across the entire networks through helix matching at network junctions. In the Ia3̄d phase the opposing chiralities of the two networks cancel, but not so in the three-networks Im3̄m phase. The high twist in the Im3̄m phase explains its previously unrecognized chirality, as well as the origin of this complex structure and the transitions between the different cubic phases.

  8. Preparation of cubic boron nitride films by RF bias sputtering

    SciTech Connect

    Tsuda, Osamu; Yamada, Yukiko; Tatebayashi, Yoshinao

    1995-07-01

    Cubic boron nitride (cBN) films were successfully prepared by the phase-regulated rf bias sputtering with the aid of magnetic field. The effects of the substrate bias voltage (V{sub s}), the working gas pressure (p) and the deposition time were investigated systematically. Cubic phase was formed in the filmed deposited with V{sub s} above the threshold which depended on p. Even at p = 0.4 mTorr, cBN films were grown with V{sub s} above 100 V. The prepared cBN films had a double-layered structure which consists of an initially deposited layer of sp{sup 2} phase and a layer of cubic phase subsequently grown. The maximum growth rate of the cubic layer was estimated to be approximately 1 nm/s. Stress measurements of the cBN films were also carried out, revealing that the cBN films had compressive stress of a few GPa.

  9. On a Cubically Convergent Iterative Method for Matrix Sign

    PubMed Central

    Sharifi, M.; Karimi Vanani, S.; Khaksar Haghani, F.; Arab, M.; Shateyi, S.

    2015-01-01

    We propose an iterative method for finding matrix sign function. It is shown that the scheme has global behavior with cubical rate of convergence. Examples are included to show the applicability and efficiency of the proposed scheme and its reciprocal. PMID:25954769

  10. Synthesis of nanowires and nanoparticles of cubic aluminium nitride

    NASA Astrophysics Data System (ADS)

    Balasubramanian, C.; Godbole, V. P.; Rohatgi, V. K.; Das, A. K.; Bhoraskar, S. V.

    2004-03-01

    Nanostructures of cubic aluminium nitride were synthesized by DC arc-plasma-induced melting of aluminium in a nitrogen-argon ambient. The material flux ejected from the molten aluminium surface was found to react with nitrogen under highly non-equilibrium conditions and subsequently condense on a water-cooled surface to yield a mixture of nanowires and nanoparticles of crystalline cubic aluminium nitride. Both x-ray diffraction and electron diffraction measurements revealed that the as-synthesized nitrides adopted the cubic phase. Fourier transform infrared spectroscopy was used to understand the bonding configuration. Microstructural features of the synthesized material were best studied by transmission electron microscopy. From these analyses cubic aluminium nitride was found to be the dominating phase for both nanowires and nanoparticles synthesized at low currents. The typical particle size distribution was found to range over 15-80 nm, whereas the wires varied from 30 to 100 nm in diameter and 500 to 700 nm in length, depending upon the process parameters such as arc current and the nitrogen pressure. The reaction products inside the plasma zone were also obtained theoretically by minimization of free energy and the favourable zone temperature necessary for the formation of aluminium nitride was found to be {\\sim } 6000 K. Results are discussed in view of the highly non-equilibrium conditions that prevail during the arc-plasma synthesis.

  11. Dynamic Mirror-Symmetry Breaking in Bicontinuous Cubic Phases**

    PubMed Central

    Dressel, Christian; Liu, Feng; Prehm, Marko; Zeng, Xiangbing; Ungar, Goran; Tschierske, Carsten

    2014-01-01

    Chiral segregation of enantiomers or chiral conformers of achiral molecules during self-assembly in well-ordered crystalline superstructures has fascinated chemists since Pasteur. Here we report spontaneous mirror-symmetry breaking in cubic phases formed by achiral multichain-terminated diphenyl-2,2′-bithiophenes. It was found that stochastic symmetry breaking is a general phenomenon observed in bicontinuous cubic liquid crystal phases of achiral rod-like compounds. In all compounds studied the ${{\\it Im}\\bar 3m}$ cubic phase is always chiral, while the ${Ia\\bar 3d}$ phase is achiral. These intriguing observations are explained by propagation of homochiral helical twist across the entire networks through helix matching at network junctions. In the ${Ia\\bar 3d}$ phase the opposing chiralities of the two networks cancel, but not so in the three-networks ${{\\it Im}\\bar 3m}$ phase. The high twist in the ${{\\it Im}\\bar 3m}$ phase explains its previously unrecognized chirality, as well as the origin of this complex structure and the transitions between the different cubic phases. PMID:25257551

  12. 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.

  13. 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.

  14. 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.

  15. 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...

  16. 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...

  17. 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.

  18. The Norwegian Healthier Goats program--modeling lactation curves using a multilevel cubic spline regression model.

    PubMed

    Nagel-Alne, G E; Krontveit, R; Bohlin, J; Valle, P S; Skjerve, E; Sølverød, L S

    2014-07-01

    In 2001, the Norwegian Goat Health Service initiated the Healthier Goats program (HG), with the aim of eradicating caprine arthritis encephalitis, caseous lymphadenitis, and Johne's disease (caprine paratuberculosis) in Norwegian goat herds. The aim of the present study was to explore how control and eradication of the above-mentioned diseases by enrolling in HG affected milk yield by comparison with herds not enrolled in HG. Lactation curves were modeled using a multilevel cubic spline regression model where farm, goat, and lactation were included as random effect parameters. The data material contained 135,446 registrations of daily milk yield from 28,829 lactations in 43 herds. The multilevel cubic spline regression model was applied to 4 categories of data: enrolled early, control early, enrolled late, and control late. For enrolled herds, the early and late notations refer to the situation before and after enrolling in HG; for nonenrolled herds (controls), they refer to development over time, independent of HG. Total milk yield increased in the enrolled herds after eradication: the total milk yields in the fourth lactation were 634.2 and 873.3 kg in enrolled early and enrolled late herds, respectively, and 613.2 and 701.4 kg in the control early and control late herds, respectively. Day of peak yield differed between enrolled and control herds. The day of peak yield came on d 6 of lactation for the control early category for parities 2, 3, and 4, indicating an inability of the goats to further increase their milk yield from the initial level. For enrolled herds, on the other hand, peak yield came between d 49 and 56, indicating a gradual increase in milk yield after kidding. Our results indicate that enrollment in the HG disease eradication program improved the milk yield of dairy goats considerably, and that the multilevel cubic spline regression was a suitable model for exploring effects of disease control and eradication on milk yield.

  19. 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.

  20. 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.

  1. 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.

  2. Low temperature synthesis of pure cubic ZrO2 nanopowder: structural and luminescence studies.

    PubMed

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

    2014-03-25

    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.

  3. 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.

  4. Low temperature synthesis of pure cubic ZrO2 nanopowder: structural and luminescence studies.

    PubMed

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

    2014-03-25

    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. PMID:24317256

  5. 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.

  6. Negative thermal expansion materials related to cubic zirconium tungstate

    NASA Astrophysics Data System (ADS)

    Lind, Cora

    2001-12-01

    A non-hydrolytic sol-gel method for the preparation of ZrW2O 8 was developed. A new trigonal polymorph was discovered, which is structurally related to trigonal ZrMO2O8 and MnRe2O 8 as evidenced by powder x-ray diffraction and EXAFS studies. Seeding of the starting mixtures with cubic ZrW2O8 promoted crystallization of the cubic phase instead of trigonal material. Dehydration of ZrW2O7(OH)2·2H 2O gave cubic ZrW2O8 at 650°C, and a modification of this route led to the discovery of the new NTE materials cubic ZrMo 2O8 and HfMo2O8. These compounds crystallize in the same temperature range as the more stable trigonal AMo2O 8 polymorphs. To facilitate preparation of phase pure cubic molybdates, the influence of precursor chemistry on the crystallization behavior was investigated. The synthesis was extended to the solid solution system ZrxHf 1-xMoyW2-yO8 (0 ≤ x ≤ 1, 0 ≤ y ≤ 2). All compounds showed negative thermal expansion between 77 and 573 K. High-pressure in situ diffraction experiments were conducted on several AM2O8 polymorphs. With the exception of monoclinic ZrMo2O8, all materials underwent at least one pressure induced phase transition. Quasi-hydrostatic experiments on cubic AMo 2O8 led to a reversible transition to a new high-pressure structure, while low-pressure amorphization was observed under non-hydrostatic conditions. Isothermal kinetic studies of the cubic to trigonal transformation for ZrMo2O8 were carried out on four samples. Apparent activation energies of 170--290 kJ/mol were obtained using an Avrami model in combination with an Arrhenius analysis. This corresponds to 5% conversion levels after one year at temperatures between 220 and 315°C. Ex situ studies showed that the conversion at lower temperatures was considerably slower than what would be expected from extrapolation of the kinetic data. Drop solution calorimetry was carried out on several polymorphs of ZrMo 2O8, HfMo2O8 and ZrW2O 8. Only monoclinic ZrMo2O8 was enthalpically

  7. Nonlinear optical imaging of defects in cubic silicon carbide epilayers.

    PubMed

    Hristu, Radu; Stanciu, Stefan G; Tranca, Denis E; Matei, Alecs; Stanciu, George A

    2014-06-11

    Silicon carbide is one of the most promising materials for power electronic devices capable of operating at extreme conditions. The widespread application of silicon carbide power devices is however limited by the presence of structural defects in silicon carbide epilayers. Our experiment demonstrates that optical second harmonic generation imaging represents a viable solution for characterizing structural defects such as stacking faults, dislocations and double positioning boundaries in cubic silicon carbide layers. X-ray diffraction and optical second harmonic rotational anisotropy were used to confirm the growth of the cubic polytype, atomic force microscopy was used to support the identification of silicon carbide defects based on their distinct shape, while second harmonic generation microscopy revealed the detailed structure of the defects. Our results show that this fast and noninvasive investigation method can identify defects which appear during the crystal growth and can be used to certify areas within the silicon carbide epilayer that have optimal quality.

  8. 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.

  9. Structural and magnetic transitions in cubic Mn3Ga.

    PubMed

    Kharel, P; Huh, Y; Al-Aqtash, N; Shah, V R; Sabirianov, R F; Skomski, R; Sellmyer, D J

    2014-03-26

    The structural, magnetic and electron-transport properties of cubic Mn3Ga have been investigated. The alloys prepared by arc melting and melt-spinning show an antiferromagnetic spin order at room temperature but undergo coupled structural and magnetic phase transitions at 600 and 800 K. First-principles calculations show that the observed magnetic properties are consistent with that of a cubic Mn3Ga crystallizing in the disordered Cu3Au-type structure. The samples exhibit metallic electron transport with a resistance minimum near 30 K, followed by a logarithmic upturn below the minimum. The observed anomaly in the low-temperature resistivity has been discussed as a consequence of electron scattering at the low-lying excitations of the structurally disordered Mn3Ga lattice.

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

    PubMed

    Weierstall, Uwe; James, Daniel; Wang, Chong; White, Thomas A; Wang, Dingjie; Liu, Wei; Spence, John C H; Bruce Doak, R; 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; Marvin Seibert, M; 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.

  12. Multinomial Combinatorial Group Representations of the Octahedral and Cubic Symmetries

    SciTech Connect

    Balasubramanian, K

    2003-12-22

    We consider the full multinomial combinatorics of all irreducible representations of the octahedral (cubic) symmetry as a function of partitions for vertex, face and edge colorings. Full combinatorial tables for all irreducible representations and all multinomial partitions are constructed. These enumerations constitute multinomial expansions of character-based cycle index polynomials, and grow in combinatorial complexity as a function of edge or vertex coloring partitions.

  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. Infinite Simple 3d Cubic Network of Identical Capacitors

    NASA Astrophysics Data System (ADS)

    Asad, Jihad H.

    2013-06-01

    In this paper, the effective capacitance between the origin (0, 0, 0) and any other lattice site (l1, l2, l3), in an infinite simple cubic (SC) network consisting of identical capacitors each of capacitance C, has been expressed rationally in terms of the known value go and π. The asymptotic behavior is also investigated, and some numerical values for the effective capacitance are presented.

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

    PubMed

    Weierstall, Uwe; James, Daniel; Wang, Chong; White, Thomas A; Wang, Dingjie; Liu, Wei; Spence, John C H; Bruce Doak, R; 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; Marvin Seibert, M; 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

  16. Field-effect transistors based on cubic indium nitride

    PubMed Central

    Oseki, Masaaki; Okubo, Kana; Kobayashi, Atsushi; Ohta, Jitsuo; Fujioka, Hiroshi

    2014-01-01

    Although the demand for high-speed telecommunications has increased in recent years, the performance of transistors fabricated with traditional semiconductors such as silicon, gallium arsenide, and gallium nitride have reached their physical performance limits. Therefore, new materials with high carrier velocities should be sought for the fabrication of next-generation, ultra-high-speed transistors. Indium nitride (InN) has attracted much attention for this purpose because of its high electron drift velocity under a high electric field. Thick InN films have been applied to the fabrication of field-effect transistors (FETs), but the performance of the thick InN transistors was discouraging, with no clear linear-saturation output characteristics and poor on/off current ratios. Here, we report the epitaxial deposition of ultrathin cubic InN on insulating oxide yttria-stabilized zirconia substrates and the first demonstration of ultrathin-InN-based FETs. The devices exhibit high on/off ratios and low off-current densities because of the high quality top and bottom interfaces between the ultrathin cubic InN and oxide insulators. This first demonstration of FETs using a ultrathin cubic indium nitride semiconductor will thus pave the way for the development of next-generation high-speed electronics. PMID:24492240

  17. Field-effect transistors based on cubic indium nitride.

    PubMed

    Oseki, Masaaki; Okubo, Kana; Kobayashi, Atsushi; Ohta, Jitsuo; Fujioka, Hiroshi

    2014-02-04

    Although the demand for high-speed telecommunications has increased in recent years, the performance of transistors fabricated with traditional semiconductors such as silicon, gallium arsenide, and gallium nitride have reached their physical performance limits. Therefore, new materials with high carrier velocities should be sought for the fabrication of next-generation, ultra-high-speed transistors. Indium nitride (InN) has attracted much attention for this purpose because of its high electron drift velocity under a high electric field. Thick InN films have been applied to the fabrication of field-effect transistors (FETs), but the performance of the thick InN transistors was discouraging, with no clear linear-saturation output characteristics and poor on/off current ratios. Here, we report the epitaxial deposition of ultrathin cubic InN on insulating oxide yttria-stabilized zirconia substrates and the first demonstration of ultrathin-InN-based FETs. The devices exhibit high on/off ratios and low off-current densities because of the high quality top and bottom interfaces between the ultrathin cubic InN and oxide insulators. This first demonstration of FETs using a ultrathin cubic indium nitride semiconductor will thus pave the way for the development of next-generation high-speed electronics.

  18. Cubic and hexagonal liquid crystals as drug delivery systems.

    PubMed

    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

  19. 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

  20. 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.

  1. 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

  2. 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.

  3. 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

  4. Cubic phase nanoparticles for sustained release of ibuprofen: formulation, characterization, and enhanced bioavailability study

    PubMed Central

    Dian, Linghui; Yang, Zhiwen; Li, Feng; Wang, Zhouhua; Pan, Xin; Peng, Xinsheng; Huang, Xintian; Guo, Zhefei; Quan, Guilan; Shi, Xuan; Chen, Bao; Li, Ge; Wu, Chuanbin

    2013-01-01

    In order to improve the oral bioavailability of ibuprofen, ibuprofen-loaded cubic nanoparticles were prepared as a delivery system for aqueous formulations. The cubic inner structure was verified by cryogenic transmission electron microscopy. With an encapsulation efficiency greater than 85%, the ibuprofen-loaded cubic nanoparticles had a narrow size distribution around a mean size of 238 nm. Differential scanning calorimetry and X-ray diffraction determined that ibuprofen was in an amorphous and molecular form within the lipid matrix. The in vitro release of ibuprofen from cubic nanoparticles was greater than 80% at 24 hours, showing sustained characteristics. The pharmacokinetic study in beagle dogs showed improved absorption of ibuprofen from cubic nanoparticles compared to that of pure ibuprofen, with evidence of a longer half-life and a relative oral bioavailability of 222% (P < 0.05). The ibuprofen-loaded cubic nanoparticles provide a promising carrier candidate with an efficient drug delivery for therapeutic treatment. PMID:23468008

  5. 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

  6. 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.

  7. 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.

  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. Higher excited states of acceptors in cubic semiconductors

    NASA Astrophysics Data System (ADS)

    Said, M.; Kanehisa, M. A.; Balkanski, M.

    1986-02-01

    For the first time, higher excited states of shallow acceptors up to the 3s and 4s states are calculated based on the Balderschi and Lipari theory including the cubic correction. The eigenvalues and eigenvectors of the effective mass Hamiltonian for shallow acceptor states were obtained by the finite element method. The resultant sparse matrix is diagonalized by a newly developed Saad's method based on Arnoldi's algorithm. Comparison with experimental spectra on ZnTe:Li and ZnTe:P gives best valence band parameters for ZnTe; μ = 0.60 and δ = 0.12.

  10. A cubic extended interior penalty function for structural optimization

    NASA Technical Reports Server (NTRS)

    Prasad, B.; Haftka, R. T.

    1979-01-01

    This paper describes an optimization procedure for the minimum weight design of complex structures. The procedure is based on a new cubic extended interior penalty function (CEIPF) used with the sequence of unconstrained minimization technique (SUMT) and Newton's method. The Hessian matrix of the penalty function is approximated using only constraints and their derivatives. The CEIPF is designed to minimize the error in the approximation of the Hessian matrix, and as a result the number of structural analyses required is small and independent of the number of design variables. Three example problems are reported. The number of structural analyses is reduced by as much as 50 per cent below previously reported results.

  11. 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.

  12. 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

  13. Submicron cubic boron nitride as hard as diamond

    NASA Astrophysics Data System (ADS)

    Liu, Guoduan; Kou, Zili; Yan, Xiaozhi; Lei, Li; Peng, Fang; Wang, Qiming; Wang, Kaixue; Wang, Pei; Li, Liang; Li, Yong; Li, Wentao; Wang, Yonghua; Bi, Yan; Leng, Yang; He, Duanwei

    2015-03-01

    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.

  14. 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.

  15. 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.

  16. 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

  17. 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.

  18. 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

  19. 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

  20. 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.

  1. 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

  2. Non-hamiltonian 3-connected cubic planar graphs with only two types of faces besides 4-gons

    NASA Astrophysics Data System (ADS)

    Ong, Siew-Hui; Abidin, Nornadia Zainal

    2015-10-01

    Let G(p,q,r) denote the class of all 3-connected cubic planar graphs whose faces are of only three types, namely p-gon, q-gon and r-gon. Here, we show that there exist non-hamiltonian members for the following classes of graphs: (i) G(3,4,r) for r ≥ 7, (ii) G(4,5,r) for r ≥ 8, (iii) G(4,q,r) for q ∈ {7,9,11} and r ≥ 6 and (iv) G(4,q,q + 5) and G(4,q,q + 2,q + 5) for q ≥ 5.

  3. Microstructural characterization of random packings of cubic particles

    PubMed Central

    Malmir, Hessam; Sahimi, Muhammad; Tabar, M. Reza Rahimi

    2016-01-01

    Understanding the properties of random packings of solid objects is of critical importance to a wide variety of fundamental scientific and practical problems. The great majority of the previous works focused, however, on packings of spherical and sphere-like particles. We report the first detailed simulation and characterization of packings of non-overlapping cubic particles. Such packings arise in a variety of problems, ranging from biological materials, to colloids and fabrication of porous scaffolds using salt powders. In addition, packing of cubic salt crystals arise in various problems involving preservation of pavements, paintings, and historical monuments, mineral-fluid interactions, CO2 sequestration in rock, and intrusion of groundwater aquifers by saline water. Not much is known, however, about the structure and statistical descriptors of such packings. We have developed a version of the random sequential addition algorithm to generate such packings, and have computed a variety of microstructural descriptors, including the radial distribution function, two-point probability function, orientational correlation function, specific surface, and mean chord length, and have studied the effect of finite system size and porosity on such characteristics. The results indicate the existence of both spatial and orientational long-range order in the packing, which is more distinctive for higher packing densities. The maximum packing fraction is about 0.57. PMID:27725736

  4. Partially Blended Constrained Rational Cubic Trigonometric Fractal Interpolation Surfaces

    NASA Astrophysics Data System (ADS)

    Chand, A. K. B.; Tyada, K. R.

    2016-08-01

    Fractal interpolation is an advance technique for visualization of scientific shaped data. In this paper, we present a new family of partially blended rational cubic trigonometric fractal interpolation surfaces (RCTFISs) with a combination of blending functions and univariate rational trigonometric fractal interpolation functions (FIFs) along the grid lines of the interpolation domain. The developed FIFs use rational trigonometric functions pi,j(θ) qi,j(θ), where pi,j(θ) and qi,j(θ) are cubic trigonometric polynomials with four shape parameters. The convergence analysis of partially blended RCTFIS with the original surface data generating function is discussed. We derive sufficient data-dependent conditions on the scaling factors and shape parameters such that the fractal grid line functions lie above the grid lines of a plane Π, and consequently the proposed partially blended RCTFIS lies above the plane Π. Positivity preserving partially blended RCTFIS is a special case of the constrained partially blended RCTFIS. Numerical examples are provided to support the proposed theoretical results.

  5. 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

  6. Cubic titanium trialuminide thermal spray coatings—A review

    NASA Astrophysics Data System (ADS)

    Dewald, D.; Austin, M.; Laitila, E.; Mikkola, D.

    2001-03-01

    The recently discovered Cr-stabilized cubic titanium trialuminides of the form (Al,Cr)3Ti exhibit excellent oxidation resistance up to 1200 °C and have formed the basis for development of a new family of protective coatings. These intermetallic compounds can be fabricated into powders and thermal spray coatings much the same as traditional metal alloys. Cubic trialuminide coatings have physical properties that are compatible with a variety of common engineering materials, including alloys based on Ti, TiAl, Fe, Ni, and Al. Typically, the coatings will impart sufficient protection to permit an increase in the service temperature of a substrate alloy by 150 °C, or more. The purpose here is to summarize the development of these new thermal spray coatings, including properties and microstructures, as well as performance of the coating on various substrates. A brief comparison is made between the deposition processes used to date, which include low-pressure plasma spray (LPPS), air plasma spray (APS), and high-velocity oxy-fuel (HVOF) deposition. Recent successes in modifying the coatings to a composite form by incorporating a very fine dispersion of nanoscale carbide particles are also discussed.

  7. Microstructural characterization of random packings of cubic particles

    NASA Astrophysics Data System (ADS)

    Malmir, Hessam; Sahimi, Muhammad; Tabar, M. Reza Rahimi

    2016-10-01

    Understanding the properties of random packings of solid objects is of critical importance to a wide variety of fundamental scientific and practical problems. The great majority of the previous works focused, however, on packings of spherical and sphere-like particles. We report the first detailed simulation and characterization of packings of non-overlapping cubic particles. Such packings arise in a variety of problems, ranging from biological materials, to colloids and fabrication of porous scaffolds using salt powders. In addition, packing of cubic salt crystals arise in various problems involving preservation of pavements, paintings, and historical monuments, mineral-fluid interactions, CO2 sequestration in rock, and intrusion of groundwater aquifers by saline water. Not much is known, however, about the structure and statistical descriptors of such packings. We have developed a version of the random sequential addition algorithm to generate such packings, and have computed a variety of microstructural descriptors, including the radial distribution function, two-point probability function, orientational correlation function, specific surface, and mean chord length, and have studied the effect of finite system size and porosity on such characteristics. The results indicate the existence of both spatial and orientational long-range order in the packing, which is more distinctive for higher packing densities. The maximum packing fraction is about 0.57.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. 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

  14. Using a CAS in the Mathematics Classroom: Two Examples for Exploring Cubic Curves.

    ERIC Educational Resources Information Center

    Leinbach, Carl

    2001-01-01

    Illustrates two ways of exploring the properties of cubic polynomials. The first exploration uses a Computer Algebra System (CAS) to help students understand an important part of mathematical history, the discovery of an algorithm to find the roots of a cubic equation. The second exploration states some conditions required for a curve and finds a…

  15. 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

    2014-03-07

    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.

  16. 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…

  17. 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

  18. Re-sintered boron-rich polycrystalline cubic boron nitride and method for making same

    SciTech Connect

    Lavens, T.R.; Corrigan, F.R.; Shott, R.L.; Bovenkerk, H.P.

    1987-06-16

    A method is described for making re-sintered polycrystalline cubic boron nitride (CBN) which comprises: (a) placing sintered substantially catalyst-free boron-rich polycrystalline cubic boron nitride particles in a high pressure/high temperature apparatus, the particles being substantially free of sintering inhibiting impurities; (b) subjecting the boron-rich cubic boron nitride particles to a pressure and a temperature adequate to re-sinter the particles, the temperature being below the CBN reconversion temperature; (c) maintaining the temperature and pressure for a time sufficient to re-sinter the boron-rich cubic boron nitride particles in the apparatus, and (d) recovering the re-sintered polycrystalline cubic boron nitride from the apparatus.

  19. Traveling kinks in cubic nonlinear Ginzburg-Landau equations.

    PubMed

    Rosu, H C; Cornejo-Pérez, O; Ojeda-May, P

    2012-03-01

    Nonlinear cubic Euler-Lagrange equations of motion in the traveling variable are usually derived from Ginzburg-Landau free energy functionals frequently encountered in several fields of physics. Many authors considered in the past damped versions of such equations, with the damping term added by hand simulating the friction due to the environment. It is known that even in this damped case kink solutions can exist. By means of a factorization method, we provide analytic formulas for several possible kink solutions of such equations of motion in the undriven and constant field driven cases, including the recently introduced Riccati parameter kinks, which were not considered previously in such a context. The latter parameter controls the delay of the switching stage of the kinks. The delay is caused by antikink components that are introduced in the structure of the solution through this parameter. PMID:22587214

  20. 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.

  1. 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

  2. Bistable dark solitons of a cubic-quintic Helmholtz equation

    SciTech Connect

    Christian, J. M.; McDonald, G. S.; Chamorro-Posada, P.

    2010-05-15

    We provide a report on exact analytical bistable dark spatial solitons of a nonlinear Helmholtz equation with a cubic-quintic refractive-index model. Our analysis begins with an investigation of the modulational instability characteristics of Helmholtz plane waves. We then derive a dark soliton by mapping the desired asymptotic form onto a uniform background field and obtain a more general solution by deploying rotational invariance laws in the laboratory frame. The geometry of the new soliton is explored in detail, and a range of new physical predictions is uncovered. Particular attention is paid to the unified phenomena of arbitrary-angle off-axis propagation and nondegenerate bistability. Crucially, the corresponding solution of paraxial theory emerges in a simultaneous multiple limit. We conclude with a set of computer simulations that examine the role of Helmholtz dark solitons as robust attractors.

  3. 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.

  4. 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.

  5. Topologically correct cortical segmentation using Khalimsky's cubic complex framework

    NASA Astrophysics Data System (ADS)

    Cardoso, Manuel J.; Clarkson, Matthew J.; Modat, Marc; Talbot, Hugues; Couprie, Michel; Ourselin, Sébastien

    2011-03-01

    Automatic segmentation of the cerebral cortex from magnetic resonance brain images is a valuable tool for neuroscience research. Due to the presence of noise, intensity non-uniformity, partial volume effects, the limited resolution of MRI and the highly convoluted shape of the cerebral cortex, segmenting the brain in a robust, accurate and topologically correct way still poses a challenge. In this paper we describe a topologically correct Expectation Maximisation based Maximum a Posteriori segmentation algorithm formulated within the Khalimsky cubic complex framework, where both the solution of the EM algorithm and the information derived from a geodesic distance function are used to locally modify the weighting of a Markov Random Field and drive the topology correction operations. Experiments performed on 20 Brainweb datasets show that the proposed method obtains a topologically correct segmentation without significant loss in accuracy when compared to two well established techniques.

  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. Quantum-Carnot engine for particle confined to cubic potential

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    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.

  8. 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.

  9. 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.

  10. Electron field emission from nanostructured cubic boron nitride islands

    SciTech Connect

    Teii, Kungen; Matsumoto, Seiichiro; Robertson, John

    2008-01-07

    Nanocrystal-assembled cubic boron nitride (cBN) islands are formed by using low-energy ({approx}20 eV) ion irradiation in an inductively coupled fluorine-containing plasma. The temporal evolution of surface morphology and roughness reveals three-dimensional island growth for initial sp{sup 2}-bonded BN and subsequent cBN, accompanied by a high frequency of renucleation. The formation of cBN islands enhances the field emission and reduces the turn-on field down to around 9 V/{mu}m due to an increase in the island-related field. The results demonstrate the high potential of cBN for field emitters, comparable to other wide band gap semiconductors.

  11. Crystallographic texture in cubic boron nitride thin films

    SciTech Connect

    Medlin, D.L.; Friedmann, T.A.; Mirkarimi, P.B.; Cardinale, G.F.; McCarty, K.F.

    1996-04-01

    We examine the crystallographic texture exhibited by cubic boron nitride (cBN) in thin films grown by ion-assisted deposition. Our analysis indicates that the cBN is preferentially oriented such that individual crystallites have at least one [111] direction lying in the plane of the film but are otherwise randomly oriented about (1) the substrate normal and (2) the in-plane cBN [111] axis. This preferential orientation is consistent with an alignment between the cBN {l_brace}111{r_brace} planes and the basal planes of the layer of highly oriented graphitic boron nitride that forms in the initial stages of film growth. {copyright}{ital 1996 American Institute of Physics.}

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

    DOE PAGES

    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. A cubic spline approximation for problems in fluid mechanics

    NASA Technical Reports Server (NTRS)

    Rubin, S. G.; Graves, R. A., Jr.

    1975-01-01

    A cubic spline approximation is presented which is suited for many fluid-mechanics problems. This procedure provides a high degree of accuracy, even with a nonuniform mesh, and leads to an accurate treatment of derivative boundary conditions. The truncation errors and stability limitations of several implicit and explicit integration schemes are presented. For two-dimensional flows, a spline-alternating-direction-implicit method is evaluated. The spline procedure is assessed, and results are presented for the one-dimensional nonlinear Burgers' equation, as well as the two-dimensional diffusion equation and the vorticity-stream function system describing the viscous flow in a driven cavity. Comparisons are made with analytic solutions for the first two problems and with finite-difference calculations for the cavity flow.

  14. 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.

  15. 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.

  16. Structure and energetics of nanotwins in cubic boron nitrides

    NASA Astrophysics Data System (ADS)

    Zheng, Shijian; Zhang, Ruifeng; Huang, Rong; Taniguchi, Takashi; Ma, Xiuliang; Ikuhara, Yuichi; Beyerlein, Irene J.

    2016-08-01

    Recently, nanotwinned cubic boron nitrides (NT c-BN) have demonstrated extraordinary leaps in hardness. However, an understanding of the underlying mechanisms that enable nanotwins to give orders of magnitude increases in material hardness is still lacking. Here, using transmission electron microscopy, we report that the defect density of twin boundaries depends on nanotwin thickness, becoming defect-free, and hence more stable, as it decreases below 5 nm. Using ab initio density functional theory calculations, we reveal that the Shockley partials, which may dominate plastic deformation in c-BNs, show a high energetic barrier. We also report that the c-BN twin boundary has an asymmetrically charged electronic structure that would resist migration of the twin boundary under stress. These results provide important insight into possible nanotwin hardening mechanisms in c-BN, as well as how to design these nanostructured materials to reach their full potential in hardness and strength.

  17. Adaptive Predistortion Using Cubic Spline Nonlinearity Based Hammerstein Modeling

    NASA Astrophysics Data System (ADS)

    Wu, Xiaofang; Shi, Jianghong

    In this paper, a new Hammerstein predistorter modeling for power amplifier (PA) linearization is proposed. The key feature of the model is that the cubic splines, instead of conventional high-order polynomials, are utilized as the static nonlinearities due to the fact that the splines are able to represent hard nonlinearities accurately and circumvent the numerical instability problem simultaneously. Furthermore, according to the amplifier's AM/AM and AM/PM characteristics, real-valued cubic spline functions are utilized to compensate the nonlinear distortion of the amplifier and the following finite impulse response (FIR) filters are utilized to eliminate the memory effects of the amplifier. In addition, the identification algorithm of the Hammerstein predistorter is discussed. The predistorter is implemented on the indirect learning architecture, and the separable nonlinear least squares (SNLS) Levenberg-Marquardt algorithm is adopted for the sake that the separation method reduces the dimension of the nonlinear search space and thus greatly simplifies the identification procedure. However, the convergence performance of the iterative SNLS algorithm is sensitive to the initial estimation. Therefore an effective normalization strategy is presented to solve this problem. Simulation experiments were carried out on a single-carrier WCDMA signal. Results show that compared to the conventional polynomial predistorters, the proposed Hammerstein predistorter has a higher linearization performance when the PA is near saturation and has a comparable linearization performance when the PA is mildly nonlinear. Furthermore, the proposed predistorter is numerically more stable in all input back-off cases. The results also demonstrate the validity of the convergence scheme.

  18. 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.

  19. 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.

  20. Growth of carbon-doped base GaAs/AlGaAs HBT by gas-source MBE using TEG, TEA, TMG, AsH3, and Si2H6

    NASA Astrophysics Data System (ADS)

    Ando, Hideyasu; Fujii, Toshio; Sandhu, Adarsh; Takahashi, Tsuyoshi; Ishikawa, Hideaki; Okamoto, Naoya; Yokoyama, Naoki

    1992-05-01

    High-performance carbon-doped-base GaAs/AlGaAs heterobipolar transistors (HBTs) were grown by gas-source MBE using only gaseous sources including dopant sources. The AlGaAs emitter layer was doped with Si from uncracked SI2H6 and the base layer was doped with carbon from TMG. From SIMS analysis it was confirmed that a well-defined emitter-base junction with sharp carbon profile was obtained. The base-current ideality factor from the Gummel plot was 1.47, and the emitter-base junction ideality factor was 1.12. A high dc current gain of 53 was obtained at a current density of 4 x 10 exp 4 A/sq cm. The device characteristics of our carbon-doped HBTs were found to be stable under current stress.

  1. 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.

  2. 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.

  3. Doping of MBE grown cubic GaN on 3C-SiC (001) by CBr{sub 4}

    SciTech Connect

    Zado, A.; Tschumak, E.; Lischka, K.; As, D. J.; Gerlach, J. W.

    2010-11-01

    We report on carbon doping of cubic GaN by CBr{sub 4} using plasma-assisted molecular beam epitaxy on 3C-SiC (001) substrates. The samples consist of a 70 nm thick GaN buffer followed by a 550 nm thick GaN:C layer. Carbon doping is realized with a home-made carbon tetrabromide sublimation source. The CBr{sub 4} beam equivalent pressure was established by a needle valve and was varied between 2x10{sup -9} mbar and 6x10{sup -6} mbar. The growth was controlled by in-situ reflection high energy electron diffraction. The incorporated carbon concentration is obtained from secondary ion mass spectroscopy. Capacitance voltage characteristics were measured using metal-insulator-semiconductor structures. Capacitance voltage measurements on nominally undoped cubic GaN showed n-type conductivity with N{sub D}-N{sub A} = 1x10{sup 17} cm{sup -3}. With increasing CBr{sub 4} flux the conductivity type changes to p-type and for the highest CBr{sub 4} flux N{sub A}-N{sub D} = 4{center_dot}5x10{sup 18} cm{sup -3} was obtained.

  4. 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.

  5. 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…

  6. 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.

  7. 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.

  8. 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...

  9. 46 CFR 160.052-6 - Construction-nonstandard vests.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Plastic Foam, Adult and Child § 160.052-6 Construction—nonstandard vests. (a) General. The construction... child, medium size; (3) Two hundred and twenty-five cubic inches or more for a child, small size. (c... must be made with adjustments to: (1) Fit a range of wearers for the type designed; and (2)...

  10. 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.

  11. 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.

  12. 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

  13. 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

  14. 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.

  15. 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

  16. 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.

  17. Superconducting properties of the noncentrosymmetric superconductor Re6Hf

    NASA Astrophysics Data System (ADS)

    Singh, D.; Hillier, A. D.; Thamizhavel, A.; Singh, R. P.

    2016-08-01

    We report synthesis and detailed characterization of the noncentrosymmetric superconductor Re6Hf using powder x-ray diffraction (XRD), magnetization, transport, and thermodynamic measurements. XRD confirmed the noncentrosymmetric, α -Mn cubic structure in Re6Hf with the cubic cell parameter a =9.6850 (3 ) Å. Resistivity, DC, and AC magnetization measurements confirmed the type-II superconductivity in Re6Hf with the transition temperature Tconset˜5.96 K, having the lower critical field Hc 1(0 ) 5.6 mT and upper critical field Hc 2(0 ) 12.2 T. The electronic specific heat data fits well with the single-gap BCS model. The Sommerfeld coefficient (γ ) also shows linear relation with the magnetic field. All above results suggest s -wave superconductivity in Re6Hf .

  18. 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.

  19. 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.

  20. A three-dimensional finite element model of human atrial anatomy: New methods for cubic Hermite meshes with extraordinary vertices

    PubMed Central

    Gonzales, Matthew J.; Sturgeon, Gregory; Krishnamurthy, Adarsh; Hake, Johan; Jonas, René; Stark, Paul; Rappel, Wouter-Jan; Narayan, Sanjiv M.; Zhang, Yongjie; Segars, W. Paul; McCulloch, Andrew D.

    2013-01-01

    High-order cubic Hermite finite elements have been valuable in modeling cardiac geometry, fiber orientations, biomechanics, and electrophysiology, but their use in solving three-dimensional problems has been limited to ventricular models with simple topologies. Here, we utilized a subdivision surface scheme and derived a generalization of the “local-to-global” derivative mapping scheme of cubic Hermite finite elements to construct bicubic and tricubic Hermite models of the human atria with extraordinary vertices from computed tomography images of a patient with atrial fibrillation. To an accuracy of 0.6 millimeters, we were able to capture the left atrial geometry with only 142 bicubic Hermite finite elements, and the right atrial geometry with only 90. The left and right atrial bicubic Hermite meshes were G1 continuous everywhere except in the one-neighborhood of extraordinary vertices, where the mean dot products of normals at adjacent elements were 0.928 and 0.925. We also constructed two biatrial tricubic Hermite models and defined fiber orientation fields in agreement with diagrammatic data from the literature using only 42 angle parameters. The meshes all have good quality metrics, uniform element sizes, and elements with aspect ratios near unity, and are shared with the public. These new methods will allow for more compact and efficient patient-specific models of human atrial and whole heart physiology. PMID:23602918

  1. 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.

  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. Internal structure of hexagonal skyrmion lattices in cubic helimagnets

    NASA Astrophysics Data System (ADS)

    McGrouther, D.; Lamb, R. J.; Krajnak, M.; McFadzean, S.; McVitie, S.; Stamps, R. L.; Leonov, A. O.; Bogdanov, A. N.; Togawa, Y.

    2016-09-01

    We report the most precise observations to date concerning the spin structure of magnetic skyrmions in a nanowedge specimen of cubic B20 structured FeGe. Enabled by our development of advanced differential phase contrast (DPC) imaging (in a scanning transmission electron microscope (STEM)) we have obtained high spatial resolution quantitative measurements of skyrmion internal spin profile. For hexagonal skyrmion lattice cells, stabilised by an out-plane applied magnetic field, mapping of the in-plane component of magnetic induction has revealed precise spin profiles and that the internal structure possesses intrinsic six-fold symmetry. With increasing field strength, the diameter of skyrmion cores was measured to decrease and accompanied by a nonlinear variation of the lattice periodicity. Variations in structure for individual skyrmions across an area of the lattice were also studied utilising a new increased sensitivity DPC detection scheme and a variety of symmetry lowering distortions were observed. To provide insight into fundamental energetics we have constructed a phenomenological model, with which our experimental observations of spin profiles and field induced core diameter variation are in good agreement with predicted structure in the middle of the nanowedge crystal. In the vicinity of the crystal surfaces, our model predicts the existence of in-plane twisting distortions which our current experimental observations were not sensitive to. As an alternative to the requirement for as yet unidentified sources of magnetic anisotropy, we demonstrate that surface states could provide the energetic stabilisation needed for predomination over the conical magnetic phase.

  4. 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

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

    NASA Astrophysics Data System (ADS)

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

    1997-07-01

    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 μm 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.

  6. Hardness analysis of cubic metal mononitrides from first principles

    NASA Astrophysics Data System (ADS)

    Fulcher, B. D.; Cui, X. Y.; Delley, B.; Stampfl, C.

    2012-05-01

    Density functional theory calculations are performed to evaluate the hardness of various cubic metal nitrides: rocksalt TiN, VN, ZrN, NbN, AlN, and SiN; zincblende AlN and BN; and diamond C for comparison. The isotropic elastic stiffness constants cij, bulk modulus K, shear modulus G, Young's modulus E, and isotropic Poisson's ratio ν¯ are calculated. From simulated uniaxial stress-strain curves, ideal strength values σmax in the [100], [110], and [111] directions are also evaluated for all systems. In particular, rocksalt AlN is found to possess both high elastic moduli and ideal strength. These quantities are then compared for correlations with existing experimental Vicker's hardness data. The bulk modulus is found to be a poor indicator of hardness, while E, G, 1/ν¯, and σmax all exhibit stronger correlations. With a view to circumvent the need to run computationally expensive relaxation steps, different methodologies for approximating uniaxial stress-strain curves are introduced. Utilizing the anisotropic Poisson's ratio to approximate the relaxed transverse lattice parameters at a given axial strain is a good approximation to stress-strain curves, and the ideal strengths obtained in this way exhibit strong correlations to experimental Vicker's hardness values.

  7. 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.

  8. 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

  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. 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

  11. 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.

  12. 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.

  13. Cubic scaling G W : Towards fast quasiparticle calculations

    NASA Astrophysics Data System (ADS)

    Liu, Peitao; Kaltak, Merzuk; Klimeš, Jiří; Kresse, Georg

    2016-10-01

    Within the framework of the full potential projector-augmented wave methodology, we present a promising low-scaling G W implementation. It allows for quasiparticle calculations with a scaling that is cubic in the system size and linear in the number of k points used to sample the Brillouin zone. This is achieved by calculating the polarizability and self-energy in the real-space and imaginary-time domains. The transformation from the imaginary time to the frequency domain is done by an efficient discrete Fourier transformation with only a few nonuniform grid points. Fast Fourier transformations are used to go from real space to reciprocal space and vice versa. The analytic continuation from the imaginary to the real frequency axis is performed by exploiting Thiele's reciprocal difference approach. Finally, the method is applied successfully to predict the quasiparticle energies and spectral functions of typical semiconductors (Si, GaAs, SiC, and ZnO), insulators (C, BN, MgO, and LiF), and metals (Cu and SrVO3). The results are compared with conventional G W calculations. Good agreement is achieved, highlighting the strength of the present method.

  14. 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.

  15. Diamond deposition on polycrystalline films of cubic boron nitride

    SciTech Connect

    Friedmann, T.A.; Bernardez, L.J.; McCarty, K.F.; Klaus, E.J.; Ottesen, D.K.; Johnsen, H.A.; Clift, W.M. )

    1993-09-06

    We have grown diamond films on films of cubic boron nitride (cBN). The cBN films were grown on Si(100) substrates using ion-assisted pulsed laser deposition. Fourier transform infrared (FTIR) spectroscopy indicated that the BN films contained [similar to]75% [ital sp][sup 3]-bonded cBN. The as-grown cBN films were inserted with no surface pretreatment (e.g., abrading or scratching) into a conventional hot filament diamond reactor. [ital In] [ital situ] Raman spectroscopy was used to confirm diamond synthesis during growth. The nucleation density of the diamond films was estimated at 1[times]10[sup 9]/cm[sup 2], equivalent to or higher than the best values for scratched silicon substrates. In addition, we found that the cBN films were etched in the diamond reactor; a film thickness [approx gt]1500 A was required to prevent total film loss before diamond nucleation occurred. The presence of cBN under the diamond was established using FTIR spectroscopy and Auger electron spectroscopy.

  16. Theory for plasticity of face-centered cubic metals

    PubMed Central

    Jo, Minho; Koo, Yang Mo; Lee, Byeong-Joo; Johansson, Börje; Vitos, Levente; Kwon, Se Kyun

    2014-01-01

    The activation of plastic deformation mechanisms determines the mechanical behavior of crystalline materials. However, the complexity of plastic deformation and the lack of a unified theory of plasticity have seriously limited the exploration of the full capacity of metals. Current efforts to design high-strength structural materials in terms of stacking fault energy have not significantly reduced the laborious trial and error works on basic deformation properties. To remedy this situation, here we put forward a comprehensive and transparent theory for plastic deformation of face-centered cubic metals. This is based on a microscopic analysis that, without ambiguity, reveals the various deformation phenomena and elucidates the physical fundaments of the currently used phenomenological correlations. We identify an easily accessible single parameter derived from the intrinsic energy barriers, which fully specifies the potential diversity of metals. Based entirely on this parameter, a simple deformation mode diagram is shown to delineate a series of convenient design criteria, which clarifies a wide area of material functionality by texture control. PMID:24753563

  17. 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.

  18. 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

  19. 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

  20. Vortex dynamics in cubic-quintic Bose-Einstein condensates

    NASA Astrophysics Data System (ADS)

    Mithun, T.; Porsezian, K.; Dey, Bishwajyoti

    2013-07-01

    We study vortex dynamics in a trapped Bose-Einstein condensate with tunable two- and three-body interactions. The dynamics is governed by two-dimensional cubic-quintic Gross-Pitaevskii equation. A time-dependent variational method has been used to obtain critical rotational frequency and surface mode frequency analytically and are compared with numerical simulation results. An imaginary time propagation method and Crank-Nicolson scheme for discretization have been used for numerical simulation. The numerically calculated average value of the angular momentum per particle shows very clearly its dynamical relation with the time development of the vortex formation. The rotational frequency dependence of the variation of average value of the angular momentum per particle with time shows that vortices form much faster in time for higher rotational frequency. Similarly, the vortex forms much faster in time with an increase of the strength of the repulsive three-body interaction. The simulation of the vortex lattice formation in the condensate shows that the presence of the three-body interactions does not alter the vortex lattice pattern but it helps in the shape deformations of the condensate thereby leading to vortex lattice formation. Likewise, the three-body interactions enable the vortex lattice formation in Bose-Einstein condensates even with attractive two-body interactions and in purely quintic BEC.

  1. Three-dimensional microstructural characterization of porous cubic zirconia.

    PubMed

    Bobrowski, Piotr; Pędzich, Zbigniew; Faryna, Marek

    2015-11-01

    A set of cubic zirconia samples were investigated using 3-dimensional electron backscatter diffraction (3D EBSD) to analyze the grain structure, grain boundary networks and pore morphology. 3D EBSD is a variation of conventional EBSD, whereby a focused ion beam (FIB) is used in a dual beam scanning electron microscope (SEM) i.e. FIB-SEM to mill away material and to create 'serial sections' through the material being analyzed. Each new surface revealed is subject to an EBSD scan, which continues sequentially until a desired volume of material has been removed. In this manner, many consecutive 2D EBSD scans can be rendered in 3D to gain a greater insight of microstructural features and parameters. The three samples were examined in order to determine the effect of differences in the manufacturing process used for each. For each sample, a volume of ca. 15,000 μm(3) was studied. The analysis of several microstructure parameters revealed a strong dependence on manufacturing conditions. Subsequently, the results of 3D EBSD analysis were compared to conventional 2D EBSD. Significant differences between the values of microstructure parameters determined by 2D and 3D EBSD were observed.

  2. 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).

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

    PubMed

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

    2014-07-17

    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.

  4. 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

  5. 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.

  6. Reduction in burst release of PLGA microparticles by incorporation into cubic phase-forming systems.

    PubMed

    Ahmed, Abid Riaz; Dashevsky, Andrei; Bodmeier, Roland

    2008-11-01

    A high initial burst release of an phosphorothioate oligonucleotide drug from poly(lactide-co-glycolide) (PLGA) microparticles prepared by the w/o/w solvent extraction/evaporation was reduced by incorporating the microparticles into the following glycerol monooleate (GMO) formulations: 1) pure molten GMO, 2) preformed cubic phase (GMO+water) or 3) low viscosity in situ cubic phase-forming formulations (GMO+water+cosolvent). The in situ cubic phase-forming formulations had a low viscosity in contrast to the first two formulations resulting in good dispersability of the microparticles and good syringability/injectability. Upon contact with an aqueous phase, a highly viscous cubic phase formed immediately entrapping the microparticles. A low initial burst and a continuous extended release over several weeks was obtained with all investigated formulations. The drug release profile could be well controlled by the cosolvent composition with the in situ systems.

  7. 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.

  8. Structure of the body-centered cubic phase of lipid systems

    PubMed Central

    Saludjian, Pedro; Reiss-Husson, Françoise

    1980-01-01

    A new model is proposed for the structure of the body-centered cubic phase of lipid systems. Infinite rods of polar groups (and water) are arranged with axes parallel to the four cubic [unk]1 1 1[unk] directions. The hydrocarbon chains fill the space between the rods to form a continuous matrix. With this unified topology, the model explains satisfactorily the x-ray diffraction patterns of strontium soaps, lecithin, galactolipids, potassium soaps, and hexadecyltrimethylammonium bromide and explains the transition between cubic/HII phases. The paradoxical thermal effects on the lipid cubic phase, in particular the decrease of unit cell dimensions with increasing temperature, can be explained with the proposed model by mechanisms similar to those used for the monodimensional and bidimensional (mesomorphic) phases. Images PMID:16592934

  9. 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)

  10. Effect of Percolation on the Cubic Susceptibility of Metal Nanoparticle Composites

    NASA Technical Reports Server (NTRS)

    Smith, David D.; Bender, Matthew W.; Boyd, Robert W.

    1998-01-01

    Generalized two-dimensional and three-dimensional Maxwell Garnett and Bruggeman geometries reveal that a sign reversal in the cubic susceptibility occurs for metal nanoparticle composites near the percolation threshold.

  11. Discovery of a 6.4 keV Emission Line in a Burst from SGR 1900+14

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod E.; Ibrahim, Alaa I.

    2000-01-01

    We present evidence of a 6.4 key emission line during a burst from the soft gamma repeater SGR 1900+14. The Rossi X-Ray Timing Explorer (RXTE) monitored this source extensively during its outburst in the summer of 1998. A strong burst observed on 1998 August 29 revealed a number of unique properties. The burst exhibits a precursor and is followed by a long (approx. 10(exp 3) s) tail modulated at the 5.16 s stellar rotation period. The precursor has a duration of approx. equals 0.85 s and shows both significant spectral evolution as well as an emission feature centered near 6.4 keV during the first 0.3 s of the event, when the X-ray spectrum was hardest. The continuum during the burst is well fit with an optically thin thermal bremsstrahlung spectrum with the temperature ranging from approx. equals 40 to 10 keV. The line is strong, with an equivalent width of approx. 400 eV, and is consistent with Fe K(alpha) fluorescence from relatively coot material. If the rest-frame energy is indeed 6.4 keV, then the lack of an observed redshift indicates that the source is at least approx. 80 km above the neutron star surface. We discuss the implications of the line detection in the context of models for SGRs.

  12. A numerical study of the laminar incompressible flow over a 6:1 prolate spheroid at 10 deg incidence

    NASA Astrophysics Data System (ADS)

    Rosenfeld, Moshe; Wolfshtein, Micha; Israeli, Moshe

    1992-07-01

    The steady incompressible laminar flowfield over a 6:1 prolate spheroid at 10 deg incidence and a Reynolds number of 1.6 x 10 exp 6 is investigated numerically by solving a reduced set of the Navier-Stokes equations. The present study moves one step beyond the boundary-layer approximation by relaxing the requirement of an imposed pressure field to permit the calculation of both attached and longitudinal vortical flowfields. The results shed light on the flow properties over slender bodies at intermediate incidence. The longitudinal vortex is found to be weak relative to vortex-dominated flows. Nevertheless, it has pronounced effects on the flow near the surface and on global features of the flowfield. A displacement velocity which describes the effect of the vortical flow on the outer inviscid flow is defined. The line on the spheroid where the displacement velocity vanishes closely follows the projection of the vortex centerline on the surface of the spheroid. It is demonstrated numerically that the convergence of the skin friction lines is not a unique criterion for identifying a vortex flow.

  13. 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.

  14. 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

  15. 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.

  16. 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.

  17. Strain dependent electron spin dynamics in bulk cubic GaN

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    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.

  18. Stability of the face-centered-cubic phase of heavy rare gas solids

    SciTech Connect

    Ree, F.H.; Choi, Yumi

    1993-07-01

    Our recent perturbation theory is applied to show that heavy rare gases solidify into a face-centered-cubic phase over a large temperature range near the melting lines. We have investigated the static, harmonic, and anharmonic contributions to the excess Helmholtz free energy and the stability to the face-centered-cubic phase. The observed stability is due to thermal contributions in the Helmholtz free energy.

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

    PubMed

    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. PMID:24329232

  20. 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.

  1. Inverse cubic liquid-crystalline phases of phospholipids and related lyotropic systems

    NASA Astrophysics Data System (ADS)

    Seddon, J. M.; Bartle, E. A.; Mingins, J.

    1990-12-01

    The authors have previously found that saturated phospholipids such as phosphatidyl-ethanolamines can, in certain cases, adopt as many as three different inverse bicontinuous cubic phases in water, of probable space groups Ia3d (No 230), Im3m (No 229) and Pn3m (No 224). They found that these cubic phases could be induced to appear by reducing the chain length or by increasing the hydrophilicity of the headgroup of the phospholipid molecule. All of these cubic phases are located in the phase diagrams between the lamellar and the inverse hexagonal (HII) phases. They now report the observation of a novel inverse face-centred cubic phase, of probable space group Fd3m (No 227), in two different systems of hydrated binary lipid mixtures. One of these systems consists of mixtures of phosphatidylcholine with diacylglycerol; the other is an acid-soap mixture of an unsaturated fatty acid with its alkali salt. This Fd3m cubic phase in both systems occurs between the inverse hexagonal (HII) phase and the inverse micellar solution (L2), with increasing concentration of the lipid component with the less strongly hydrophilic headgroup. They surmise that the average mean curvature of the polar/nonpolar interface in this Fd3m cubic phase is more negative than that of the neighbouring HII phase; this is quite different from the inverse bicontinuous cubic phases, where it has a value intermediate between those of the lamellar and HII phases. They conclude that the structure of this Fd3m cubic phase most probably consists solely of closed inverse micellar aggregates.

  2. 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.

  3. Black hole solutions in Horava-Lifshitz gravity with cubic terms

    SciTech Connect

    Koutsoumbas, George; Pasipoularides, Pavlos

    2010-08-15

    We study four-dimensional nonprojectable Horava-Lifshitz type gravity, in the case of an action with terms cubic in curvature. For special choices of the free parameters of the model, we obtain two new analytic black hole solutions which exhibit the standard Schwarzschild asymptotic behavior in the large-distance limit. The effect of cubic terms in the short-range behavior of the black hole solutions is discussed.

  4. 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.

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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

  10. Large-scale-circulation dynamics of turbulent Rayleigh-Benard convection in a cubic container

    NASA Astrophysics Data System (ADS)

    Bai, Kunlun; Ji, Dandan; Brown, Eric

    2014-11-01

    We present measurements of the large-scale-circulation (LSC) in turbulent Rayleigh-Benard convection in a cubic container. The experiments cover the Rayleigh number ranging from 0 . 5 ×109 to 3 ×109 at Prandtl number 6.4. Using three rows of thermistors at different height of the container, the large-scale-circulation (LSC) can then be identified. It is found that the LSC prefers to lock at the corners of the container, and switches between them stochastically. The strength of LSC keeps as a constant during the switching which suggests those switching correspond to fluctuation driven crossings of a potential barrier in θ due to the side wall geometry as predicted by Brown and Ahlers (Phys. Fluids, 2008). The switching frequency is found to decrease as Ra increases. The measured LSC orientation and its switching will be compared to the model which predicts the effects of container geometry on large-scale coherent structure dynamics for arbitrary geometry.

  11. Log-cubic method for generation of soil particle size distribution curve.

    PubMed

    Shang, Songhao

    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.

  12. 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.

  13. Further evidence for closed, nonspherical aggregates in the cubic I1 phase of lysolecithin and water

    PubMed Central

    Lindblom, Göran; Johansson, Lennart B.-Å.; Wikander, Göran; Eriksson, Per-Olof; Arvidson, Gösta

    1992-01-01

    Measurements of time-resolved fluorescence quenching have been performed in the binary lauroyllysophosphatidylcholine (LaLPC)/water system. The aggregation numbers, N, are determined for the micellar solution phase (Nmicelle ≈ 80) and the cubic liquid crystalline I1 phase (Ncub ≈ 90) at 298-303 K. When a quencher is present, the fluorescence decays for the hexagonal phase of the LaLPC/water system and for the bicontinuous cubic phase of monooleoylglycerol/water system are nonexponential, as expected for phase structures having long-range continuous apolar regions. Nuclear magnetic resonance (NMR) measurements of the lipid translational diffusion conclusively show that the cubic I1 phase consists of closed micelles. NMR spectra of 31P obtained at 202.4 MHz of this cubic phase exhibit a characteristic line shape, which is compatible with a phase structure containing short nonspherical micelles. A comparison between electron spin resonance (ESR) spin-label spectra recorded for a micellar solution and the cubic phases of the LaLPC and monooleoylglycerol systems are also shown to support a structure of closed micelles in the cubic I1 phase of the lysolecithin system. PMID:19431845

  14. 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

  15. 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

  16. Interactions of Lipidic Cubic Phase Nanoparticles with Lipid Membranes.

    PubMed

    Jabłonowska, Elżbieta; Nazaruk, Ewa; Matyszewska, Dorota; Speziale, Chiara; Mezzenga, Raffaele; Landau, Ehud M; Bilewicz, Renata

    2016-09-20

    The interactions of liquid-crystalline monoolein (GMO) cubic phase nanoparticles with various model lipid membranes spread at the air-solution interface by the Langmuir technique were investigated. Cubosomes have attracted attention as potential biocompatible drug delivery systems, and thus understanding their mode of interaction with membranes is of special interest. Cubosomes spreading at the air-water interface as well as interactions with a monolayer of 1, 2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) compressed to different surface pressures were studied by monitoring surface pressure-time dependencies at constant area. Progressive incorporation of the nanoparticles was shown to lead to mixed monolayer formation. The concentration of cubosomes influenced the mechanism of incorporation, as well as the fluidity and permeability of the resulting lipid membranes. Brewster angle microscopy images reflected the dependence of the monolayer structure on the cubosomes presence in the subphase. A parameter Csat was introduced to indicate the point of saturation of the lipid membrane with the cubosomal material. This parameter was found to depend on the surface pressure showing that the cubosomes disintegrate in prolonged contact with the membrane, filling available voids in the lipid membrane. At highest surface pressures when the layer is most compact, the penetration of cubosomal material is not possible and only some exchange with the membrane lipid becomes the route of including GMO into the layer. Finally, comparative studies of the interactions between lipids with various headgroup charges with cubosomes suggest that at high surface pressure an exchange of lipid component between the monolayer and the cubosome in its intact form may occur. PMID:27550742

  17. 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.

  18. Interactions of Lipidic Cubic Phase Nanoparticles with Lipid Membranes.

    PubMed

    Jabłonowska, Elżbieta; Nazaruk, Ewa; Matyszewska, Dorota; Speziale, Chiara; Mezzenga, Raffaele; Landau, Ehud M; Bilewicz, Renata

    2016-09-20

    The interactions of liquid-crystalline monoolein (GMO) cubic phase nanoparticles with various model lipid membranes spread at the air-solution interface by the Langmuir technique were investigated. Cubosomes have attracted attention as potential biocompatible drug delivery systems, and thus understanding their mode of interaction with membranes is of special interest. Cubosomes spreading at the air-water interface as well as interactions with a monolayer of 1, 2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) compressed to different surface pressures were studied by monitoring surface pressure-time dependencies at constant area. Progressive incorporation of the nanoparticles was shown to lead to mixed monolayer formation. The concentration of cubosomes influenced the mechanism of incorporation, as well as the fluidity and permeability of the resulting lipid membranes. Brewster angle microscopy images reflected the dependence of the monolayer structure on the cubosomes presence in the subphase. A parameter Csat was introduced to indicate the point of saturation of the lipid membrane with the cubosomal material. This parameter was found to depend on the surface pressure showing that the cubosomes disintegrate in prolonged contact with the membrane, filling available voids in the lipid membrane. At highest surface pressures when the layer is most compact, the penetration of cubosomal material is not possible and only some exchange with the membrane lipid becomes the route of including GMO into the layer. Finally, comparative studies of the interactions between lipids with various headgroup charges with cubosomes suggest that at high surface pressure an exchange of lipid component between the monolayer and the cubosome in its intact form may occur.

  19. 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.

  20. 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.

  1. X-ray photoelectron spectroscopy study of cubic boron nitride single crystals grown under high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Hou, Lixin; Chen, Zhanguo; Liu, Xiuhuan; Gao, Yanjun; Jia, Gang

    2012-02-01

    The defects, impurities and their bonding states of unintentionally doped cubic boron nitride (cBN) single crystals were investigated by X-ray photoelectron spectroscopy (XPS). The results indicate that nitrogen vacancy (VN) is the main native defect of the cBN crystals since the atomic ratio of B:N is always larger than 1 before Ar ion sputtering. After sputter cleaning, around 6 at% carbon, which probably comes from the growth chamber, remains in the samples as the main impurity. Carbon can substitute nitrogen lattice site and form the bonding states of Csbnd Bsbnd N or Csbnd B, which can be verified by the XPS spectra of C1s, B1s and N1s. The C impurity (acceptor) and N vacancy (donor) can compose the donor-acceptor complex to affect the electrical and optical properties of cBN crystals.

  2. Transport properties of cubic crystalline Ge2Sb2Te5: a potential low-temperature thermoelectric material.

    DOE PAGES

    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

  3. 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

  4. Composition design for Laves phase-related body-centered cubic V solid solution alloys with large hydrogen storage capacities

    NASA Astrophysics Data System (ADS)

    Wang, H. B.; Wang, Q.; Dong, C.; Yuan, L.; Xu, F.; Sun, L. X.

    2008-03-01

    This paper analyzes the characteristics of alloy compositions with large hydrogen storage capacities in Laves phase-related body-centered cubic (bcc) solid solution alloy systems using the cluster line approach. Since a dense-packed icosahedral cluster A6B7 characterizes the local structure of AB2 Laves phases, in an A-B-C ternary system, such as Ti-Cr (Mn, Fe)-V, where A-B forms AB2 Laves phases while A-C and B-C tend to form solid solutions, a cluster line A6B7-C is constructed by linking A6B7 to C. The alloy compositions with large hydrogen storage capacities are generally located near this line and are approximately expressed with the cluster-plus-glue-atom model. The cluster line alloys (Ti6Cr7)100-xVx (x = 2.5-70 at.%) exhibit different structures and hence different hydrogen storage capacities with increasing V content. The alloys (Ti6Cr7)95V5 and Ti30Cr40V30 with bcc solid solution structure satisfy the cluster-plus-glue-atom model.

  5. Synthesis of Cubic Alpha-Alumina Using a Blocking Reagent of Tetraethyl Ammonium Hydroxide.

    PubMed

    Kim, Hyun Soo; Park, No-Kuk; Lee, Tae Jin; Kang, Misook

    2015-02-01

    This study was an attempt to obtain a stable and reproducible cubic primary alumina by a hydrothermal method using various aluminum precursors, AIP, AlO(OH), and Al(OH)3. Tetraethyl ammonium hydroxide was introduced as a blocking reagent to control the shape of alumina. The synthesized primary alumina powders from Al precursors showed a boehmite structure after hydrothermal treatment at 200 °C for 1 h. The primary alumina powders synthesized using the precursors of AIP and AlO(OH) had irregular shapes, however the cubic-shape of approximately 300 nm was observed in the primary alumina powder synthesized using Al(OH)3 precursor. The cubic primary alumina samples were transformed to different solid phases like gamma-, delta-, theta-, and alpha-phases according to the calcined temperatures. The theta-phase alumina formed at 1100 °C continually kept the cubic shape, but the shape was collapsed at 1200 °C. However the cubic alpha-alumina alpha-alumina was stably remained by thermal treatment at 1100 °C under the fierce oxygen atmosphere. PMID:26353660

  6. Dislocation mechanism for transformation between cubic ice Ic and hexagonal ice Ih

    NASA Astrophysics Data System (ADS)

    Hondoh, T.

    2015-11-01

    Cubic ice Ic is metastable, yet can form by the freezing of supercooled water, vapour deposition at low temperatures and by depressurizing high-pressure forms of ice. Its structure differs from that of common hexagonal ice Ih in the order its molecular layers are stacked. This stacking order, however, typically has considerable disorder; that is, not purely cubic, but alternating in hexagonal and cubic layers. In time, stacking-disordered ice gradually decreases in cubicity (fraction having cubic structure), transforming to hexagonal ice. But, how does this disorder originate and how does it transform to hexagonal ice? Here we use numerical data on dislocations in hexagonal ice Ih to show that (1) stacking-disordered ice (or Ic) can be viewed as fine-grained polycrystalline ice with a high density of extended dislocations, each a widely extended stacking fault bounded by partial dislocations, and (2) the transformation from ice Ic to Ih is caused by the reaction and motion of these partial dislocations. Moreover, the stacking disorder may be in either a higher stored energy state consisting of a sub-boundary network arrangement of partial dislocations bounding stacking faults, or a lower stored energy state consisting of a grain structure with a high density of stacking faults, but without bounding partial dislocations. Each state transforms to Ih differently, with a duration to fully transform that strongly depends on temperature and crystal grain size. The results are consistent with the observed transformation rates, transformation temperatures and wide range in heat of transformation.

  7. The formation of cubic ice under conditions relevant to Earth's atmosphere.

    PubMed

    Murray, Benjamin J; Knopf, Daniel A; Bertram, Allan K

    2005-03-10

    An important mechanism for ice cloud formation in the Earth's atmosphere is homogeneous nucleation of ice in aqueous droplets, and this process is generally assumed to produce hexagonal ice. However, there are some reports that the metastable crystalline phase of ice, cubic ice, may form in the Earth's atmosphere. Here we present laboratory experiments demonstrating that cubic ice forms when micrometre-sized droplets of pure water and aqueous solutions freeze homogeneously at cooling rates approaching those found in the atmosphere. We find that the formation of cubic ice is dominant when droplets freeze at temperatures below 190 K, which is in the temperature range relevant for polar stratospheric clouds and clouds in the tropical tropopause region. These results, together with heat transfer calculations, suggest that cubic ice will form in the Earth's atmosphere. If there were a significant fraction of cubic ice in some cold clouds this could increase their water vapour pressure, and modify their microphysics and ice particle size distributions. Under specific conditions this may lead to enhanced dehydration of the tropopause region. PMID:15758996

  8. The formation of cubic ice under conditions relevant to Earth's atmosphere.

    PubMed

    Murray, Benjamin J; Knopf, Daniel A; Bertram, Allan K

    2005-03-10

    An important mechanism for ice cloud formation in the Earth's atmosphere is homogeneous nucleation of ice in aqueous droplets, and this process is generally assumed to produce hexagonal ice. However, there are some reports that the metastable crystalline phase of ice, cubic ice, may form in the Earth's atmosphere. Here we present laboratory experiments demonstrating that cubic ice forms when micrometre-sized droplets of pure water and aqueous solutions freeze homogeneously at cooling rates approaching those found in the atmosphere. We find that the formation of cubic ice is dominant when droplets freeze at temperatures below 190 K, which is in the temperature range relevant for polar stratospheric clouds and clouds in the tropical tropopause region. These results, together with heat transfer calculations, suggest that cubic ice will form in the Earth's atmosphere. If there were a significant fraction of cubic ice in some cold clouds this could increase their water vapour pressure, and modify their microphysics and ice particle size distributions. Under specific conditions this may lead to enhanced dehydration of the tropopause region.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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

  15. 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.

  16. Phase diagram for a cubic-Q interacting boson model Hamiltonian: Signs of triaxiality

    SciTech Connect

    Fortunato, L.; Alonso, C. E.; Arias, J. M.; Garcia-Ramos, J. E.; Vitturi, A.

    2011-07-15

    An extension of the Interacting Boson Model that includes the cubic (QxQxQ){sup (0)} term is proposed. The potential energy surface for the cubic quadrupole interaction is explicitly calculated within the coherent state formalism using the complete ({chi}-dependent) expression for the quadrupole operator. The Q-cubic term is found to depend on the asymmetry deformation parameter {gamma} as a linear combination of cos(3{gamma}) and cos{sup 2}(3{gamma}) terms, thereby allowing for triaxiality. The phase diagram of the model in the large N limit is explored: The orders of the phase transition surfaces that define the phase diagram are described, and the possible nuclear equilibrium shapes are established. It is found that for this particular Hamiltonian, contrary to expectations, there is only a very tiny region of triaxiality, and that the transition from prolate to oblate shapes is so fast that, in most cases, the onset of triaxiality might go unnoticed.

  17. 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

  18. Testing a generalized cubic Galileon gravity model with the Coma Cluster

    SciTech Connect

    Terukina, Ayumu; Yamamoto, Kazuhiro; Okabe, Nobuhiro; Matsushita, Kyoko; Sasaki, Toru E-mail: kazuhiro@hiroshima-u.ac.jp E-mail: matusita@rs.kagu.tus.ac.jp

    2015-10-01

    We obtain a constraint on the parameters of a generalized cubic Galileon gravity model exhibiting the Vainshtein mechanism by using multi-wavelength observations of the Coma Cluster. The generalized cubic Galileon model is characterized by three parameters of the turning scale associated with the Vainshtein mechanism, and the amplitude of modifying a gravitational potential and a lensing potential. X-ray and Sunyaev-Zel'dovich (SZ) observations of the intra-cluster medium are sensitive to the gravitational potential, while the weak-lensing (WL) measurement is specified by the lensing potential. A joint fit of a complementary multi-wavelength dataset of X-ray, SZ and WL measurements enables us to simultaneously constrain these three parameters of the generalized cubic Galileon model for the first time. We also find a degeneracy between the cluster mass parameters and the gravitational modification parameters, which is influential in the limit of the weak screening of the fifth force.

  19. 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.

  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. Direct visualization of dispersed lipid bicontinuous cubic phases by cryo-electron tomography.

    PubMed

    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

  2. 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.

  3. Effect of pressure on itinerant magnetism and spin disorder in cubic FeGe.

    PubMed

    Pulikkotil, J J; Auluck, S; Rout, P K; Budhani, R C

    2012-03-01

    The results of ab initio calculations of the pressure dependence of Fe magnetism in cubic FeGe are presented. We find that when the pressure-volume scale is set by means of generalized gradient approximation total energies and magnetism is described by means of the local density approximation, the critical pressure at which the magnetic phase transition occurs is estimated at ≈18 GPa, which is in good agreement with experiments. Using the disordered local moment method we find a localized to itinerant model cross-over of Fe magnetism in cubic FeGe, as a function of volume. Moreover, our calculations also suggest subtle signatures of longitudinal spin fluctuations in cubic FeGe, and that the stiffness parameter softens with increasing pressure. We associate the retention of metallicity in FeGe under pressure with the spin-disorder scattering. The effect of spin-orbit coupling on the electronic structure is also discussed.

  4. Tunnel magnetoresistance effect using perpendicularly magnetized tetragonal and cubic Mn-Co-Ga Heusler alloy electrode

    NASA Astrophysics Data System (ADS)

    Kubota, T.; Mizukami, S.; Ma, Q. L.; Naganuma, H.; Oogane, M.; Ando, Y.; Miyazaki, T.

    2014-05-01

    Epitaxially grown tetragonal and cubic Mn-Co-Ga thin films were fabricated onto single crystalline Cr (001) under a layer. High perpendicular magnetic anisotropy is achieved in the tetragonal Mn2.3Co0.4Ga1.3 film, and a small, unexpected perpendicular magnetic anisotropy was induced in the cubic Mn1.8Co1.2Ga1.0 film as well. The tunnel magnetoresistance (TMR) effect of the Mn-Co-Ga/MgO/CoFeB magnetic tunnel junctions (MTJs) were investigated. TMR ratios of 5% and 11% were observed at room temperature for the MTJs using tetragonal Mn2.3Co0.4Ga1.3 and cubic Mn1.8Co1.2Ga1.0 electrodes, respectively. The composition dependence is discussed briefly.

  5. 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.

  6. Direct visualization of dispersed lipid bicontinuous cubic phases by cryo-electron tomography

    NASA Astrophysics Data System (ADS)

    Demurtas, Davide; Guichard, Paul; Martiel, Isabelle; Mezzenga, Raffaele; Hébert, Cécile; Sagalowicz, Laurent

    2015-11-01

    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.

  7. The n-component cubic model and flows: Subgraph break-collapse method

    NASA Astrophysics Data System (ADS)

    de Magalhães, A. C. N.; Essam, J. W.

    1990-03-01

    We specialize to the n-component cubic model the subgraph break-collapse method which we recently developed for the Z(λ) model. The cubic model has less symmetry than the Potts model, for which the method was originally developed, but nevertheless it is still possible to reduce considerably the computational complexity of the general Z(λ) model. Our recursive algorithm is similar, for n=2, to the break-collapse method for the Z(4) model proposed by Mariz and co-workers. It allows the exact calculation for the partition function and correlation functions for n-component cubic clusters, with n as a variable, without the need to examine all of the spin configurations. An important application is therefore in real-space renormalization-group calculations.

  8. Synthesis of Cubic Boron Nitride Nanoparticles from Boron Oxide, Melamine and NH3 by Non-Transferred Ar-N2 Thermal Plasma.

    PubMed

    Ko, Eun Ha; Kim, Tae-Hee; Choi, Sooseok; Park, Dong-Wha

    2015-11-01

    Cubic boron nitride (c-BN) which is has extremely high hardness and thermal conductivity comparable to the diamond was synthesized in nanoparticle form by using non-transferred thermal plasma. The input power of arc plasma was fixed at 13.5 kW and the operating pressure was also fixed at atmospheric pressure. Boron oxide (B2O3) and melamine (C3H6N6) were used as raw materials for the sources of boron and nitrogen. Ammonia gas (NH3) was additionally injected to plasma jet as reactive gas providing additional nitrogen. Decomposed B2O3 and C3H6N6 enhance reactivity for synthesizing c-BN with exothermic reactions between carbon, hydrogen and oxygen. Products were collected from the inner wall of reactor. In X-ray diffraction and scanning electron microscope measurements, the collected powder was confirmed as c-BN nanoparticles which have crystalline size smaller than 150 nm.

  9. 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.

  10. 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

  11. Distinguishing bicontinuous lipid cubic phases from isotropic membrane morphologies using (31)P solid-state NMR spectroscopy.

    PubMed

    Yang, Yu; Yao, Hongwei; Hong, Mei

    2015-04-16

    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 line shapes, bicontinuous lipid cubic phases are more difficult to discern, since the static NMR spectra of cubic-phase lipids consist of an isotropic (31)P or (2)H 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 (31)P chemical shift line shapes of oriented cubic-phase membranes in the limit of slow lateral diffusion. We then show that (31)P T2 relaxation times differ significantly between isotropic micelles and cubic-phase membranes: the latter exhibit 2 orders of magnitude shorter T2 relaxation times. These differences are explained by the different time scales of lipid lateral diffusion on the cubic-phase surface versus the time scales 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 (31)P 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

  12. 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

  13. 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.

  14. Anharmonic Nuclear Motion and the Relative Stability of Hexagonal and Cubic ice

    NASA Astrophysics Data System (ADS)

    Engel, Edgar A.; Monserrat, Bartomeu; Needs, Richard J.

    2015-04-01

    We use extensive first-principles quantum mechanical calculations to show that, although the static lattice and harmonic vibrational energies are almost identical, the anharmonic vibrational energy of hexagonal ice is significantly lower than that of cubic ice. This difference in anharmonicity is crucial, stabilizing hexagonal ice compared with cubic ice by at least 1.4 meV /H2O , in agreement with experimental estimates. The difference in anharmonicity arises predominantly from molecular O-H bond-stretching vibrational modes and is related to the different stacking of atomic layers.

  15. 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.

  16. A compressed primal-dual method for generating bivariate cubic L1 splines

    NASA Astrophysics Data System (ADS)

    Wang, Yong; Fang, Shu-Cherng; Lavery, John E.

    2007-04-01

    In this paper, we develop a compressed version of the primal-dual interior point method for generating bivariate cubic L1 splines. Discretization of the underlying optimization model, which is a nonsmooth convex programming problem, leads to an overdetermined linear system that can be handled by interior point methods. Taking advantage of the special matrix structure of the cubic L1 spline problem, we design a compressed primal-dual interior point algorithm. Computational experiments indicate that this compressed primal-dual method is robust and is much faster than the ordinary (uncompressed) primal-dual interior point algorithm.

  17. 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.

  18. 3D imaging in CUBIC-cleared mouse heart tissue: going deeper

    PubMed Central

    Nehrhoff, Imke; Bocancea, Diana; Vaquero, Javier; Vaquero, Juan José; Ripoll, Jorge; Desco, Manuel; Gómez-Gaviro, María Victoria

    2016-01-01

    The ability to acquire high resolution 3D images of the heart enables to study heart diseases more in detail. In this work, the CUBIC (clear, unobstructed brain imaging cocktails and computational analysis) clearing protocol was optimized for thick mouse heart sections to enhance the penetration depth of the confocal microscope lasers into the tissue. In addition, the optimized CUBIC clearing of the heart enhances antibody penetration into the tissue by a factor of five. The present protocol enables deep 3D high-quality image acquisition in the heart allowing a much more accurate assessment of the cellular and structural changes that underlie heart diseases. PMID:27699132

  19. 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)

  20. 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.

  1. Spinor-helicity three-point amplitudes from local cubic interactions

    NASA Astrophysics Data System (ADS)

    Conde, Eduardo; Joung, Euihun; Mkrtchyan, Karapet

    2016-08-01

    We make an explicit link between the cubic interactions of off-shell fields and the on-shell three-point amplitudes in four dimensions. Both the cubic interactions and the on-shell three-point amplitudes had been independently classified in the literature, but their relation has not been made explicit. The aim of this note is to provide such a relation and discuss similarities and differences of their constructions. For the completeness of our analysis, we also derive the covariant form of all parity-odd massless vertices.

  2. Secure optical generalized filter bank multi-carrier system based on cubic constellation masked method.

    PubMed

    Zhang, Lijia; Liu, Bo; Xin, Xiangjun

    2015-06-15

    A secure optical generalized filter bank multi-carrier (GFBMC) system with carrier-less amplitude-phase (CAP) modulation is proposed in this Letter. The security is realized through cubic constellation-masked method. Large key space and more flexibility masking can be obtained by cubic constellation masking aligning with the filter bank. An experiment of 18 Gb/s encrypted GFBMC/CAP system with 25-km single-mode fiber transmission is performed to demonstrate the feasibility of the proposed method.

  3. 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

  4. 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.

  5. 3D imaging in CUBIC-cleared mouse heart tissue: going deeper

    PubMed Central

    Nehrhoff, Imke; Bocancea, Diana; Vaquero, Javier; Vaquero, Juan José; Ripoll, Jorge; Desco, Manuel; Gómez-Gaviro, María Victoria

    2016-01-01

    The ability to acquire high resolution 3D images of the heart enables to study heart diseases more in detail. In this work, the CUBIC (clear, unobstructed brain imaging cocktails and computational analysis) clearing protocol was optimized for thick mouse heart sections to enhance the penetration depth of the confocal microscope lasers into the tissue. In addition, the optimized CUBIC clearing of the heart enhances antibody penetration into the tissue by a factor of five. The present protocol enables deep 3D high-quality image acquisition in the heart allowing a much more accurate assessment of the cellular and structural changes that underlie heart diseases.

  6. 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.

  7. 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).

  8. 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.

  9. 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.

  10. Release kinetics of acyclovir from a suspension of acyclovir incorporated in a cubic phase delivery system.

    PubMed

    Helledi, L S; Schubert, L

    2001-11-01

    Acyclovir is a widely used agent in the treatment of herpes virus infections of the skin, but owing to its poor physicochemical properties in terms of bioavailability and suboptimal formulations, the treatment is far from optimal. The liquid crystalline cubic phase system has been reported to act as a bioadhesive drug delivery system. In the present study, acyclovir was suspended in a cubic phase of glycerol monooleate (GMO) and water 65%:35% w/w, and the phase behavior and release kinetics were examined. X-ray diffraction and differential scanning calorimetry (DSC) measurements demonstrated that the cubic phase containing 1%-10% (w/w) acyclovir retains its phase condition in the temperature range investigated (20 degrees C-70 degrees C). Acyclovir can be incorporated in high amounts (approximately 40% w/w) without causing phase transition, as is shown in polarized light. This is probably because of its low solubility (approximately 0.11% w/w) in the cubic phase. The release characteristics of acyclovir incorporated as a suspension (1%-5% w/w) into a cubic phase were investigated using Franz diffusion cells. Acyclovir was quantified by high-performance liquid chromatography (HPLC). The drug was readily released from the system, and the release increased with the initial drug load concentration. About 25%-50% was released after 24 h. The release is dependent on the square root of time, and the kinetics can be described by the Higuchi theory. The rate-limiting step in the release process is most likely diffusion. The suggested theory is further supported by identical release data obtained for micronized and nonmicronized acyclovir. The fluxes for 1% and 5% w/w were 380 and 900 microg/h(1/2), respectively. Comparison of the release rates of acyclovir delivered from a cubic phase and from the commercial product, Zovir cream, showed the rate to be six times faster from the cubic phase. The results indicate that the cubic phase is a promising drug delivery system for

  11. 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.

  12. Spt6

    PubMed Central

    Kato, Hiroaki; Okazaki, Kosuke; Urano, Takeshi

    2013-01-01

    As posttranslational modifications of histones H3 and H4 determine the state of chromatin in cis, these histones should remain attached to template DNA during transcription in order to maintain the state of chromatin. RNA polymerase II itself can transcribe the nucleosome template without changing nucleosome positioning. However, it was uncertain whether Spt6, a highly conserved polymerase-associated histone chaperone, prevents “preexisting” histone molecules from being dissociated from template DNA during transcription. We recently showed that Spt6 prevents transcription-coupled loss of posttranslationally modified histone H3. Taking previous studies into account, we would like to propose here that Spt6 has two fundamentally distinct functions in the regulation of histone modification: one is to act as a platform for histone modifiers and the other is to act as a molecular liaison between histone molecules and template DNA to prevent cotranscriptional dissociation of preexisting histones in order to maintain locus-specific modifications. PMID:24107707

  13. 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.

  14. Deconvoluting the Effect of the Hydrophobic and Hydrophilic Domains of an Amphiphilic Integral Membrane Protein in Lipid Bicontinuous Cubic Mesophases.

    PubMed

    van 't Hag, Leonie; Shen, Hsin-Hui; Lu, Jingxiong; Hawley, Adrian M; Gras, Sally L; Drummond, Calum J; Conn, Charlotte E

    2015-11-10

    Lipidic bicontinuous cubic mesophases with encapsulated amphiphilic proteins are widely used in a range of biological and biomedical applications, including in meso crystallization, as drug delivery vehicles for therapeutic proteins, and as biosensors and biofuel cells. However, the effect of amphiphilic protein encapsulation on the cubic phase nanostructure is not well-understood. In this study, we illustrate the effect of incorporating the bacterial amphiphilic membrane protein Ag43, and its individual hydrophobic β(43) and hydrophilic α(43) domains, in bicontinuous cubic mesophases. For the monoolein, monoalmitolein, and phytantriol cubic phases with and without 8% w/w cholesterol, the effect of the full length amphiphilic protein Ag43 on the cubic phase nanostructure was more significant than the sum of the individual hydrophobic β(43) and hydrophilic α(43) domains. Several factors were found to potentially influence the impact of the hydrophobic β(43) domain on the cubic phase internal nanostructure. These include the size of the hydrophobic β(43) domain relative to the thickness of the lipid bilayer, as well as its charge and diameter. The size of the hydrophilic α(43) domain relative to the water channel radius of the cubic mesophase was also found to be important. The secondary structure of the Ag43 proteins was affected by the hydrophobic thickness and physicochemical properties of the lipid bilayer and the water channel diameter of the cubic phase. Such structural changes may be small but could potentially affect membrane protein function.

  15. 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.

  16. The near-Surface Region of Cubic Boron Nitride Single Crystal from the Li3N-hBN System

    NASA Astrophysics Data System (ADS)

    Guo, Xiao-Fei; Xu, Bin; Wen, Zhen-Xing; Fan, Xiao-Hong; Tian, Bin

    2014-04-01

    Cubic boron nitride single crystals are synthesized with lithium nitride as a catalyst under high pressure and high temperature. The main phases in the near-surface region, which around the single crystal are determined as a mixture of hexagonal boron nitride (hBN), cubic boron nitride (cBN) and lithium boron nitride (Li3BN2). High resolution transmission electron microscopy examinations show that there exist lots of nanometer-sized cubic boron nitride nuclei in this region. The interface phase structures of cubic boron nitride crystal and its near-surface region are investigated by means of transmission electron microscopy. The growth mechanism of cubic boron nitride crystal is analyzed briefly. It is supposed that Li3BN2 impels the direct conversion of hBN to cBN as a real catalyst, and cBN is homogeneously nucleated in the molten state under high pressure and high temperature.

  17. Phonon softening induced cubic-to-tetragonal phase transition in ReO3

    NASA Astrophysics Data System (ADS)

    Liu, Yaming; Zhang, Niu; Jia, Yu; Sun, Qiang; Chao, Mingju

    2015-10-01

    Within density functional theory, the structural, electronic and lattice dynamical properties of ReO3 in cubic Pm-3m and tetragonal P4/mbm phases are studied by using quasiharmonic approximation. The enthalpy-pressure curves show that a phase transition may take place at 5.0 kbar and the nonexistence of imaginary frequency in phonon dispersions demonstrates the two phases are dynamically stable under proper conditions. With the increase of pressure, an obvious softening of M3 mode at M point appears in cubic phase, and a cubic-to-tetragonal phase transition is accompanied with the presence of negative frequency in M3 mode at 5.0 kbar. In detail, one type of O atoms displaced from x = 0.2500 to x = 0.2401, which corresponds to the softening of M3 mode, are responsible for the phase transition. Our theoretical results show that ReO3 can exist in the tetragonal P4/mbm phase, and a cubic-to-tetragonal phase transition will appear at around 5.0 kbar.

  18. 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

  19. Nano- and microsized cubic gel particles from cyclodextrin metal-organic frameworks.

    PubMed

    Furukawa, Yuki; Ishiwata, Takumi; Sugikawa, Kouta; Kokado, Kenta; Sada, Kazuki

    2012-10-15

    Sweet cube o' mine: Bottom-up control of gel particles has been regarded as a great challenge. By employing internal cross-linking of cyclodextrin metal-organic frameworks, cubic sugar gels were formed with sharp edges that reflect the shape of the crystals. This enabled the fabrication of shape- and size-controlled polymer gels from porous crystals (see picture).

  20. 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

  1. Vibrational renormalisation of the electronic band gap in hexagonal and cubic ice

    NASA Astrophysics Data System (ADS)

    Engel, Edgar A.; Monserrat, Bartomeu; Needs, Richard J.

    2015-12-01

    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.

  2. CENTER CONDITIONS AND CYCLICITY FOR A FAMILY OF CUBIC SYSTEMS: COMPUTER ALGEBRA APPROACH

    PubMed Central

    Ferčec, Brigita; Mahdi, Adam

    2013-01-01

    Using methods of computational algebra we obtain an upper bound for the cyclicity of a family of cubic systems. We overcame the problem of nonradicality of the associated Bautin ideal by moving from the ring of polynomials to a coordinate ring. Finally, we determine the number of limit cycles bifurcating from each component of the center variety. PMID:24223469

  3. 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

    2016-04-25

    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.

  4. Nature of the cubic to tetragonal phase transition in methylammonium lead iodide perovskite

    NASA Astrophysics Data System (ADS)

    Saidi, Wissam A.; Choi, Joshua J.

    2016-10-01

    Hybrid organic-inorganic perovskites, as well as the perovskites in general, are known for their phase complexity evidenced by the stabilization of different polymorphs, and thus an understanding of their regions of stability and transitions can be important for their photovoltaic and optoelectronic technologies. Here we use a multiscale approach based on first-principles calculations with van der Waals corrections and classical force-field molecular dynamics to determine the finite-temperature properties of the tetragonal and cubic phases of CH3NH3PbI3. Temperature effects are implicitly included using the quasi-harmonic approximation that can describe anharmonic behavior due to thermal expansion through the dependence of the harmonic frequencies on structural parameters. Our finite-temperature free-energy surfaces predict the lattice and elastic moduli evolution with temperature, and show in particular that the calculated lattice parameters of the cubic and tetragonal phases are to within 1% of experimental values. Further, our results show that the phonons are the major contributing factor for stabilizing the cubic phase at high temperatures mainly due to the low-energy phonon modes that are associated with the inorganic lattice. On the other hand, the configurational entropy due to CH3NH3+ rotational degrees of freedom is slightly more favored in the cubic phase and amounts to less than 0.2% of the T = 0 K free-energy difference between the two phases.

  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. 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.

  7. On the spectral-spatial instability of a light wave in a medium with cubic nonlinearity

    SciTech Connect

    Afanas'ev, Anatolii A; Volkov, V M

    2003-11-30

    Based on the analysis of frequency-nondegenerate four-photon parametric scattering, the spectral-angular dependences of the increments of perturbing modes are obtained in the field of an intense light wave propagating in a medium with cubic nonlinearity. (nonlinear optical phenomena)

  8. 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

  9. Effect of chemically active media on the structure and properties of cubic boron nitride

    SciTech Connect

    Bogatyreva, G.P.; Maevsky, V.M.; Zusmanov, E.R.; Roitsin, A.V.

    1997-10-01

    Properties of cubic boron nitride (cBN) powders from 2 to 200 mm particle size have been studied before and after chemical treatment. Impurity compositions of the bulk and surface, density, magnetic, electrophysical, physicochemical, and radio-spectroscopic characteristics are considered. Structural changes in samples and the origin of the observed effects are discussed.

  10. 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.

  11. 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.

  12. CENTER CONDITIONS AND CYCLICITY FOR A FAMILY OF CUBIC SYSTEMS: COMPUTER ALGEBRA APPROACH.

    PubMed

    Ferčec, Brigita; Mahdi, Adam

    2013-01-01

    Using methods of computational algebra we obtain an upper bound for the cyclicity of a family of cubic systems. We overcame the problem of nonradicality of the associated Bautin ideal by moving from the ring of polynomials to a coordinate ring. Finally, we determine the number of limit cycles bifurcating from each component of the center variety.

  13. The three dimensionality of cell membranes: lamellar to cubic membrane transition as investigated by electron microscopy.

    PubMed

    Chong, Ketpin; Deng, Yuru

    2012-01-01

    Biological membranes are generally perceived as phospholipid bilayer structures that delineate in a lamellar form the cell surface and intracellular organelles. However, much more complex and highly convoluted membrane organizations are ubiquitously present in many cell types under certain types of stress, states of disease, or in the course of viral infections. Their occurrence under pathological conditions make such three-dimensionally (3D) folded and highly ordered membranes attractive biomarkers. They have also stimulated great biomedical interest in understanding the molecular basis of their formation. Currently, the analysis of such membrane arrangements, which include tubulo-reticular structures (TRS) or cubic membranes of various subtypes, is restricted to electron microscopic methods, including tomography. Preservation of membrane structures during sample preparation is the key to understand their true 3D nature. This chapter discusses methods for appropriate sample preparations to successfully examine and analyze well-preserved highly ordered membranes by electron microscopy. Processing methods and analysis conditions for green algae (Zygnema sp.) and amoeba (Chaos carolinense), mammalian cells in culture and primary tissue cells are described. We also discuss methods to identify cubic membranes by transmission electron microscopy (TEM) with the aid of a direct template matching method and by computer simulation. A 3D analysis of cubic cell membrane topology by electron tomography is described as well as scanning electron microscopy (SEM) to investigate surface contours of isolated mitochondria with cubic membrane arrangement.

  14. 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…

  15. 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.

  16. Critical temperature of noninteracting bosonic gases in cubic optical lattices at arbitrary integer fillings

    NASA Astrophysics Data System (ADS)

    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.

  17. Infinite face-centered-cubic network of identical resistors: Application to lattice Green's function

    NASA Astrophysics Data System (ADS)

    Asad, J. H.; Diab, A. A.; Hijjawi, R. S.; Khalifeh, J. M.

    2013-01-01

    The equivalent resistance between the origin and any other lattice site, in an infinite face-centered-cubic network consisting of identical resistors, has been expressed rationally in terms of the known value f_o(3;0,0,0) and π . The asymptotic behavior is investigated, and some calculated values for the equivalent resistance are presented.

  18. 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.

  19. Radio Detections During Two State Transitions of the Intermediate-Mass Black Hole HLX-1

    NASA Technical Reports Server (NTRS)

    Webb, Natalie; Cseh, David; Lenc, Emil; Godet, Olivier; Barret, Didier; Corbel, Stephane; Farrell, Sean; Fender, Robert; Gehrels, Neil; Heywood, Ian

    2012-01-01

    Relativistic jets are streams of plasma moving at appreciable fractions of the speed of light. They have been observed from stellar-mass black holes (approx. 3 to 20 solar masses) as well as supermassive black holes (approx.. 10(exp 6) to 10(exp 9) Solar Mass) found in the centers of most galaxies. Jets should also be produced by intermediate-mass black holes (approx. 10(exp 2) to 10(exp 5) Solar Mass), although evidence for this third class of black hole has, until recently, been weak. We report the detection of transient radio emission at the location of the intermediate-mass black hole candidate ESO 243-49 HLX-1, which is consistent with a discrete jet ejection event. These observations also allow us to refine the mass estimate of the black hole to be between approx. 9 × 10(exp 3) Solar Mass and approx. 9 × 10(exp 4) Solar Mass.

  20. 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.

  1. A generalized spherical harmonic deconvolution to obtain texture of cubic materials from ultrasonic wave speed

    NASA Astrophysics Data System (ADS)

    Lan, Bo; Lowe, Michael J. S.; Dunne, Fionn P. E.

    2015-10-01

    In this paper, the spherical harmonic convolution approach for HCP materials (Lan et al., 2015) is extended into a generalised form for the principal purpose of bulk texture determination in cubic polycrystals from ultrasonic wave speed measurements. It is demonstrated that the wave speed function of a general single crystal convolves with the polycrystal Orientation Distribution Function (ODF) to make the resultant polycrystal wave speed function such that when the three functions are expressed in harmonic expansions, the coefficients of any one function may be determined from the coefficients of the other two. All three Euler angles are taken into account in the description of the ODF such that the theorem applies for all general crystal systems. The forward problem of predicting polycrystal wave speed with knowledge of single crystal properties and the ODF is solved for all general cases, with validation carried out on cubic textures showing strong sensitivity to texture and excellent quantitative accuracy in predicted wave speed amplitudes. Importantly, it is also revealed by the theorem that the cubic structure is one of only two crystal systems (the other being HCP) whose orientation distributions can be inversely determined from polycrystal wave velocities by virtue of their respective crystal symmetries. Proof of principle is then established by recovering the ODFs of representative cubic textures solely from the wave velocities generated from a computational model using these texture inputs, and excellent accuracies are achieved in the recovered ODF coefficients as well as the resultant pole figures. Hence the methodology is argued to provide a powerful technique for wave propagation studies and bulk texture measurement in cubic polycrystals and beyond.

  2. 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

  3. On structural transitions in a discontinuous micellar cubic phase loaded with sodium diclofenac.

    PubMed

    Efrat, R; Aserin, A; Garti, N

    2008-05-01

    An intermediate mesophase of lyotropic liquid crystalline structure from the ternary mixtures of glycerol monooleate, water, and ethanol was recently characterized in our lab. This mesophase, termed Q(L), consists of discrete discontinuous micelles arranged in a cubic array. The Q(L) phase can solubilize very significant loads of water-insoluble anti-inflamatory drug sodium diclofenac (Na-DFC). Close examination of the internal structures of the lyotropic liquid structure upon increasing the solubilization loads reveals the existence of three structural transitions controlled by the Na-DFC levels. Up to 0.4 wt% Na-DFC, the Q(L) structure remains intact with some influence on the hydration of the headgroups and on the intermicellar forces. However, at 0.8 to 1.2 wt% Na-DFC, the discontinuous micellar cubic phase is transformed into a more condensed mesophase of a bicontinuous cubic phase. At > or =1.2 wt% Na-DFC, the cubic phase is converted into a lamellar phase (L(alpha)). Within 5.5 to 7.3 wt% Na-DFC the mesophase is progressively transformed into a less ordered lamellar structure. At 12 wt% Na-DFC crystals tend to precipitate out. At low Na-DFC concentrations the drug behaves like a lyotropic or kosmotropic salt and can salt-out the surfactant from its water layer, but at higher levels it behaves like a hydrotropic, chaotropic salt and can salt-in the surfactant. The Na-DFC location and position within the interface as well as its polarization and partial ionization are strongly affected by its solubilization contents and the structure that it is inducing. In the cubic phase the drug is located less close to the hydration layer while once transition occurs it is exposed more to the water layer and the surfactant headgroups.

  4. Spray dried glyceryl monooleate-magnesium trisilicate dry powder as cubic phase precursor.

    PubMed

    Shah, Manish H; Biradar, Shailesh V; Paradkar, Anant R

    2006-10-12

    Glyceryl monooleate (GMO) is a polar amphiphilic lipid, which forms different sequential lyotropic liquid crystals upon hydration. GMO has been utilized for various delivery systems and routes of administrations. Owing to sticky and waxy nature of GMO, preparation of oral solid dosage form utilizing GMO is still a challenge for pharmaceutical researchers. Therefore, the objective of the present work was to fabricate dry powder precursors using GMO, which upon hydration in situ forms cubic phase and can be wisely used for fabrication of oral solid dosage forms. In addition to this, dry powder precursor was evaluated for drug loading, in vitro release behavior and in vivo performance of model drug diclofenac sodium (DiNa). The dry powder precursor was obtained by spray-drying GMO with DiNa using magnesium trisilicate (MTS) as adsorbent. The percent drug entrapment of various batches of powder precursor was in the range of 84-93% indicating high content uniformity. SEM and image analysis showed that as the amount of MTS in powder precursor was increased, the particle size decreased. Furthermore, the viscosity of powder precursor was function of amount of MTS. The rate of water uptake of powder precursor was higher due to uniform layer of GMO on the MTS surface, which led to faster transformation of lamellar phase into cubic phase. The polarizing light microscopy confirmed that cubic phase was formed upon hydration of powder precursor. The drug released from powder precursor was initially governed by the cubic phase formed and in later stage it depends upon dynamic swelling behavior of hexagonally packed cylindrical aggregates. The drug loaded powder precursor was found to have more effective and prolonged anti-inflammatory and analgesic activity as compared to pure drug. Thus the dry powder precursor of cubic phase was prepared in which drug release was entirely governed by the mesophases formed.

  5. A Comparison of Pressure Measurements Between a Full-Scale and a 1/6-Scale F/A-18 Twin Tail During Buffet

    NASA Technical Reports Server (NTRS)

    Moses, Robert W.; Pendleton, Ed

    1996-01-01

    In 1993, tail buffet tests were performed on a full-scale, production model F/A-18 in the 80 x 120-foot Wind Tunnel at NASA Ames Research Center. Steady and unsteady pressures were recorded on both sides of the starboard vertical tail for an angle-of-attack range of 20 to 40 degrees and at a sideslip range of -1 6 to 16 degrees at freestream velocities up to 100 knots (Mach 0.15, Reynolds number 1.23 x 10(exp 7). The aircraft was equipped with removable leading edge extension (LEX) fences that are used in flight to reduce tail buffet loads. In 1995, tail buffet tests were performed on a 1/6-scale F-18 A/B model in the Transonic Dynamics Tunnel (TDT) at NASA Langley Research Center. Steady and unsteady pressures were recorded on both sides of both vertical tails for an angle-of-attack range of 7 to 37 degrees at freestream velocities up to 65 knots (Mach 0.10). Comparisons of steady and unsteady pressures and root bending moments are presented for these wind-tunnel models for selected test cases. Representative pressure and root bending moment power spectra are also discussed, as are selected pressure cross-spectral densities.

  6. 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

  7. Performance of Soviet and US hydrogen masers

    NASA Technical Reports Server (NTRS)

    Uljanov, Adolph A.; Demidov, Nikolai A.; Mattison, Edward M.; Vessot, Robert F. C.; Allan, David W.; Winkler, Gernot M. R.

    1990-01-01

    The frequencies of Soviet- and U.S.-built hydrogen masers located at the Smithsonian Astrophysical Observatory and at the United States Naval Observatory (USNO) were compared with each other and, via Global Positioning System (GPS) common-view measurements, with three primary frequency-reference scales. The best masers were found to have fractional frequency stabilities as low as 6 times 10(exp -16) for averaging times of approximately 10(exp 4) s. Members of the USNO maser ensemble provided frequency prediction better than 1 times 10(exp 14) for periods up to a few weeks. The frequency residuals of these masers, after removal of frequency drift and rate of change of drift, had stabilities of a few parts in 10(exp -15), with serveral masers achieving residual stabilities well below 1 times 10(exp -15) for intervals from 10(exp 5)s to 2 times 10(exp 6)s. The fractional frequency drifts of the 13 masers studied, relative to the primary reference standards, ranged from -0.2 times 10(exp -15)/day to +9.6 times 10(exp -15)/day.

  8. 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

  9. Cubic Mesoporous Silica Material as a Highly Efficient Solid Phase Extraction Sorbent for Bisphenol A, Tert-Nonylphenol from Water.

    PubMed

    Jin, Zhongxiu; Xu, Yuanyuan; Lin, Shilei; Sheng, Jie

    2016-06-01

    Endocrine disrupting chemicals (EDCs), including bisphenol A (BPA), tert-nonylphenol (t-NP) in aqueous solutions, were extracted by cubic mesoporous silica material (MCM-48) and determined by high performance liquid chromatography--fluorometric detection simultaneously. The effect of eluent solvent and its volume, the pH of sample solution and the sample volume on the extraction recovery of MCM-48 composite for EDCs was investigated by the batch techniques. Comparative studies showed that MCM-48 was superior to C18 for the extraction of the more polar analyte bisphenol A and and at least as effective as C18 for the extraction of tert-nonylphenol. The results showed that the excellent recovery towards BPA (87.4%-95.6%) and t-NP (83.6%-96.3%) was achieved by using this method. The good linearity was obtained for BPA and t-NP (R2 > 0.993) at a range from 5 to 1000 μg L(-1). Under the optimum conditions, the detection limits of this method were 96 and 150 ng L(-1) for BPA and t-NP in water sample, based on a signal-to-noise ratio (S/N) of 3, respectively. This method has been also successfully applied for the determination of other EDCs in natural environmental water samples. PMID:27427640

  10. 46 CFR 160.055-6 - Construction-nonstandard, life preservers.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Plastic Foam, Adult and Child, for Merchant Vessels § 160.055-6 Construction—nonstandard, life preservers... cubic inches or more for a child size. (c) Arrangement of buoyant materials. The buoyant material in...) Adjusted to fit a range of wearers for the type designed; and (3) Donned in a time comparable to that of...

  11. HST Observations of Star Formation in Interacting Galaxies: NGC 4194, the "Medusa"

    NASA Technical Reports Server (NTRS)

    Weistrop, D.; Eggers, D.; Nelson, C. H.; Kaiser, M. E.

    2001-01-01

    Ultraviolet and visible imaging of the blue compact galaxy NGC4194 was obtained to survey the star-forming knots in the center of this galaxy. Photometry and image analysis were performed on these regions. Comparison with evolutionary tracks indicates many of the knots are reddened with a typical E(B-V)approx.0.3. The knot ages range from 10(exp 6-10(exp 8)years. Some of the knots may have masses 3-5x10(exp 5) solar mass. The FUV fluxes correspond to the flux from 60-3.8x10(exp 3) O5V stars.

  12. Tables of model atmospheres of bursting neutron stars

    NASA Technical Reports Server (NTRS)

    Madej, Jerzy

    1991-01-01

    This paper presents tables of plane-parallel neutron star model atmospheres in radiative and hydrostatic equilibrium, with effective temperatures of 8 x 10 exp 6, 1.257 x 10 exp 7, 2 x 10 exp 7, and 3 x 10 exp 7 K, and surface gravities of 15.0 and less (cgs units). The equations of model atmospheres on which the tables are based fully account for nonisotropies of the radiation field and effects of noncoherent Compton scattering of thermal X-rays by free electrons. Both the effective temperatures and gravities listed above are measured on the neutron star surface.

  13. 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.

  14. 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

  15. 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

  16. 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.

  17. 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

  18. 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

  19. 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

  20. 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

  1. 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.

  2. 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

  3. Experimental Surface Pressure Data Obtained on 65 deg Delta Wing Across Reynolds Number and Mach Number Ranges. Vol. 3: Medium-radius leading edge

    NASA Technical Reports Server (NTRS)

    Chu, Julio; Luckring, James M.

    1996-01-01

    An experimental wind tunnel test of a 65 deg delta wing model with interchangeable leading edges was conducted in the Langley National Transonic Facility (NTF). The objective was to investigate the effects of Reynolds and Mach numbers on slender-wing leading-edge vortex flows with four values of wing leading-edge bluntness. Experimentally obtained pressure data are presented without analysis in tabulated and graphical formats across a Reynolds number range of 6 x 10(exp 6) to 120 x 10(exp 6) at a Mach number of 0.85 and across a Mach number range of 0.4 to 0.9 at Reynolds numbers of 6 x 10(exp 6), 60 x 10(exp 6), and 120 x 10(exp 6). Normal-force and pitching-moment coefficient plots for these Reynolds number and Mach number ranges are also presented.

  4. 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.

  5. 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.

  6. Elastic collision and molecule formation of spatiotemporal light bullets in a cubic-quintic nonlinear medium

    NASA Astrophysics Data System (ADS)

    Adhikari, S. K.

    2016-09-01

    We consider the statics and dynamics of a stable, mobile three-dimensional (3D) spatiotemporal light bullet in a cubic-quintic nonlinear medium with a focusing cubic nonlinearity above a critical value and any defocusing quintic nonlinearity. The 3D light bullet can propagate with a constant velocity in any direction. Stability of the light bullet under a small perturbation is established numerically. We consider frontal collision between two light bullets with different relative velocities. At large velocities the collision is elastic with the bullets emerge after collision with practically no distortion. At small velocities two bullets coalesce to form a bullet molecule. At a small range of intermediate velocities the localized bullets could form a single entity which expands indefinitely, leading to a destruction of the bullets after collision. The present study is based on an analytic Lagrange variational approximation and a full numerical solution of the 3D nonlinear Schrödinger equation.

  7. An empirical analysis of the quantitative effect of data when fitting quadratic and cubic polynomials

    NASA Technical Reports Server (NTRS)

    Canavos, G. C.

    1974-01-01

    A study is made of the extent to which the size of the sample affects the accuracy of a quadratic or a cubic polynomial approximation of an experimentally observed quantity, and the trend with regard to improvement in the accuracy of the approximation as a function of sample size is established. The task is made possible through a simulated analysis carried out by the Monte Carlo method in which data are simulated by using several transcendental or algebraic functions as models. Contaminated data of varying amounts are fitted to either quadratic or cubic polynomials, and the behavior of the mean-squared error of the residual variance is determined as a function of sample size. Results indicate that the effect of the size of the sample is significant only for relatively small sizes and diminishes drastically for moderate and large amounts of experimental data.

  8. 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.

  9. Performance evaluation of a micro ultrasonic motor using a one-cubic-millimeter stator.

    PubMed

    Mashimo, Tomoaki

    2015-10-01

    A piezoelectric ultrasonic motor has two significant advantages, high energy density and simple structure, and these advantages can help in the miniaturization of the motor. We build a prototype micro ultrasonic motor using a stator with a volume of approximately 1 cubic millimeter. To evaluate its representative performance values (torque, angular velocity, and energy efficiency), we built an experimental setup and operated the prototype motor by varying experimental conditions, such as the preload between the stator and rotor and the amplitude of voltages applied to motor. The performance values obtained at the millimeter to sub-millimeter scale are discussed analytically using the macro scale models of ultrasonic motors. Experimentally, the prototype motor has generated a torque of more than 10 μNm with a 1-cubic-millimeter stator. The motor described herein is now the smallest micro ultrasonic motor with a practical torque, although its efficiency is still low.

  10. 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.

  11. 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

    2014-11-20

    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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Bottom-up engineering of the surface roughness of nanostructured cubic zirconia to control cell adhesion.

    PubMed

    Singh, A V; Ferri, M; Tamplenizza, M; Borghi, F; Divitini, G; Ducati, C; Lenardi, C; Piazzoni, C; Merlini, M; Podestà, A; Milani, P

    2012-11-30

    Nanostructured cubic zirconia is a strategic material for biomedical applications since it combines superior structural and optical properties with a nanoscale morphology able to control cell adhesion and proliferation. We produced nanostructured cubic zirconia thin films at room temperature by supersonic cluster beam deposition of nanoparticles produced in the gas phase. Precise control of film roughness at the nanoscale is obtained by operating in a ballistic deposition regime. This allows one to study the influence of nanoroughness on cell adhesion, while keeping the surface chemistry constant. We evaluated cell adhesion on nanostructured zirconia with an osteoblast-like cell line using confocal laser scanning microscopy for detailed morphological and cytoskeleton studies. We demonstrated that the organization of cytoskeleton and focal adhesion formation can be controlled by varying the evolution of surface nanoroughness.

  17. 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.

  18. 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

  19. Control of grain growth using intergranular silicate phases in cubic yttria stabilized zirconia

    SciTech Connect

    Sharif, A.A.; Imamura, P.H.; Mecartney, M.L.; Mitchell, T.E.

    1998-07-01

    Grain growth kinetics for 8 mol% yttria stabilized cubic zirconia (8Y-CSZ) were investigated. Optimal process parameters required to achieve a small grain size and full density for cubic 8Y-CSZ included a rapid heating rate (100 C/min) and hot isostatic pressing. Grain growth rates could also be controlled by the deliberate addition of 1 wt% of intergranular phases of borosilicate, barium silicate, and lithium aluminum silicate glasses. Lithium aluminum silicate, the intergranular phase with the highest solubility for yttria and zirconia, enhanced grain growth compared to control samples without grain boundary phases. The borosilicate intergranular phase, with the lowest solubility for yttria and zirconia, was the most effective in suppressing grain growth. Activation energies for grain growth were in the range of 400 kJ/mol, and the grain growth exponent ranged from 2 for lithium aluminum silicate containing samples, to 3 for pure samples, to 4 for barium silicate and borosilicate containing samples.

  20. Surprising stability of neutral interstitial hydrogen in diamond and cubic BN

    DOE PAGES

    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

  1. 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.

  2. 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}

  3. 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.

  4. Curie temperatures of cubic (Ga, Mn)N diluted magnetic semiconductors from the RKKY spin model.

    PubMed

    Zhu, Li-Fang; Liu, Bang-Gui

    2009-11-01

    We explore how much the RKKY spin interaction can contribute to the high-temperature ferromagnetism in cubic (Ga, Mn)N diluted magnetic semiconductors. The usual coupling constant is used and effective carriers are considered independent of doped magnetic atoms, as is shown experimentally. Our Monte Carlo simulated results show that maximal Curie temperature is reached at the optimal carrier concentration for a given Mn concentration, equaling 373 K for 5% Mn and 703 K for 8% Mn. Because such a Monte Carlo method does not overestimate transition temperatures, these calculations indicate that the RKKY spin interaction alone can yield high-enough Curie temperatures in cubic (Ga, Mn)N under optimized conditions.

  5. Reference models for thermospheric NO

    NASA Technical Reports Server (NTRS)

    Barth, C. A.

    1989-01-01

    Nitric oxide has been measured with an ultraviolet spectrometer on the polar-orbiting satellite Solar Mesosphere Explorer (SME) for the period January 1982 to August 1986. The nitric oxide database contains densities at all latitudes sorted into 5 degree bins and at altitudes between 100 and 140 km sorted into 3.3 km-bins. The largest densities occur at latitudes in the auroral zones where the density varies as a function of geomagnetic activity. Variations of a factor of 10 occur between times of intense activity and quiet times. At low latitudes, the nitric oxide density at 110 km varies from a mean value of 3 times 10(exp 7) molecules per cubic cm in January 1982 to a mean value of 4 times 10(exp 6) molecules per cubic cm during solar minimum conditions in 1986. In addition, the low-latitude nitric oxide density varies plus or minus 50 percent with a period of 27 days during times of high solar activity.

  6. Stationary Plasma Thruster Plume Characteristics

    NASA Technical Reports Server (NTRS)

    Myers, Roger M.; Manzella, David H.

    1994-01-01

    Stationary Plasma Thrusters (SPT's) are being investigated for application to a variety of near-term missions. This paper presents the results of a preliminary study of the thruster plume characteristics which are needed to assess spacecraft integration requirements. Langmuir probes, planar probes, Faraday cups, and a retarding potential analyzer were used to measure plume properties. For the design operating voltage of 300 V the centerline electron density was found to decrease from approximately 1.8 x 10 exp 17 cubic meters at a distance of 0.3 m to 1.8 X 10 exp 14 cubic meters at a distance of 4 m from the thruster. The electron temperature over the same region was between 1.7 and 3.5 eV. Ion current density measurements showed that the plume was sharply peaked, dropping by a factor of 2.6 within 22 degrees of centerline. The ion energy 4 m from the thruster and 15 degrees off-centerline was approximately 270 V. The thruster cathode flow rate and facility pressure were found to strongly affect the plume properties. In addition to the plume measurements, the data from the various probe types were used to assess the impact of probe design criteria

  7. A YBCO RF-squid variable temperature susceptometer and its applications

    NASA Technical Reports Server (NTRS)

    Zhou, Luwei; Qiu, Jinwu; Zhang, Xianfeng; Tang, Zhimin; Cai, Yimin; Qian, Yongjia

    1991-01-01

    The Superconducting QUantum Interference Device (SQUID) susceptibility using a high-temperature radio-frequency (rf) SQUID and a normal metal pick-up coil is employed in testing weak magnetization of the sample. The magnetic moment resolution of the device is 1 x 10(exp -6) emu, and that of the susceptibility is 5 x 10(exp -6) emu/cu cm.

  8. Anomalous Variability in Antarctic Sea Ice Extents During the 1960s With the Use of Nimbus Data

    NASA Technical Reports Server (NTRS)

    Gallaher, David W.; Campbell, G. Garrett; Meier, Walter N.

    2013-01-01

    The Nimbus I, II, and III satellites provide a new opportunity for climate studies in the 1960s. The rescue of the visible and infrared imager data resulted in the utilization of the early Nimbus data to determine sea ice extent. A qualitative analysis of the early NASA Nimbus missions has revealed Antarctic sea ice extents that are significant larger and smaller than the historic 1979-2012 passive microwave record. The September 1964 ice mean area is 19.7x10(exp 6) sq. km +/- 0.3x10(exp 6) sq. km. This is more the 250,000 sq. km greater than the 19.44x10(exp 6) sq. km seen in the new 2012 historic maximum. However, in August 1966 the maximum sea ice extent fell to 15.9x10(exp 6) sq. km +/- 0.3x10(exp 6) sq. km. This is more than 1.5x10(exp 6) sq. km below the passive microwave record of 17.5x10(exp 6) sq. km set in September of 1986. This variation between 1964 and 1966 represents a change of maximum sea ice of over 3x10(exp 6) sq. km in just two years. These inter-annual variations while large, are small when compared to the Antarctic seasonal cycle.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Cubic spline reflectance estimates using the Viking lander camera multispectral data

    NASA Technical Reports Server (NTRS)

    Park, S. K.; Huck, F. O.

    1976-01-01

    A technique was formulated for constructing spectral reflectance estimates from multispectral data obtained with the Viking lander cameras. The output of each channel was expressed as a linear function of the unknown spectral reflectance producing a set of linear equations which were used to determine the coefficients in a representation of the spectral reflectance estimate as a natural cubic spline. The technique was used to produce spectral reflectance estimates for a variety of actual and hypothetical spectral reflectances.

  14. Geometrical Solution of Some Cubic Equations with Non-Real Roots

    ERIC Educational Resources Information Center

    Pathak, H. K.; Grewal, A. S.

    2002-01-01

    A general cubic equation ax[cubed] + bx[squared] + cx + d = 0 where a , b , c , d [is a member of R], a [not equal to] 0 has three roots with two possibilities--either all three roots are real or one root is real and the remaining two roots are imaginary. Dealing with the second possibility this paper attempts to give the geometrical locations of…

  15. Spatial anisotropy of xenon-defect configurations in cubic single crytals

    NASA Astrophysics Data System (ADS)

    Claes, J.; Namavar, F.; Rots, M.

    1982-03-01

    Ion-implanted tungsten and copper single crystals are investigated by the perturbed angular correlation technique, using an allowed β- γ cascade in 133Xe decay. The spatial distribution function describing the orientation of the quadrupole hyperfine interaction does not show up the cubic symmetry of the lattice in the case of xenon-induced radiation damage. This conclusion is interpreted in terms of xenon-vacancy loop interaction.

  16. 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

  17. 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.

  18. Stabilization of insulin against agitation-induced aggregation by the GMO cubic phase gel.

    PubMed

    Sadhale, Y; Shah, J C

    1999-11-25

    The main objective of the study was to evaluate if the liquid crystalline cubic phase gel of glyceryl monooleate (GMO) protects insulin from agitation induced aggregation. The aggregation of Humulin(R), Regular Iletin I(R) and Regular Iletin II(R), in cubic phase GMO gels at 30 U/g of gel was compared with that in PBS at 100 oscillations/min at 37 degrees C using optical density at 600 nm. The effect of agitation on the secondary structure of insulin in solution and in the gels was determined with circular dichroism (CD) spectroscopy, and the time course of aggregation was also followed by HPLC. A sigmoidal increase in optical density of solution with time indicated formation of increasing amounts of insoluble insulin aggregates. However, in the gels, optical density values stayed at, or around, the initial optical density value, comparable with that of a blank gel suggesting that insulin had not aggregated in the gel. CD spectroscopy of the soluble insulin showed a total loss of native conformation upon aggregation of insulin in solution. In contrast, CD spectra of insulin in the gel were unaltered suggesting protection from aggregation during agitation. Furthermore, agitation of insulin in gels for a duration as long as 2 months at 37 degrees C, had very little adverse effect on the native conformation of insulin, as indicated by the lack of a significant change in its CD spectrum. Therefore, the cubic phase gel was indeed able to protect insulin from agitation-induced aggregation and subsequent precipitation. Although the majority of insulin in solution appeared to have aggregated and precipitated after 8 days by UV and CD spectroscopy, RP-HPLC results indicated the presence of some soluble aggregates of insulin. In summary, the liquid crystalline cubic phase gel of GMO protects peptides, like insulin, from agitation-induced aggregation.

  19. Glyceryl monooleate cubic phase gel as chemical stability enhancer of cefazolin and cefuroxime.

    PubMed

    Sadhale, Y; Shah, J C

    1998-11-01

    The primary objective of this study was to determine the ability of the glyceryl monooleate (GMO) cubic phase gel to protect drugs from chemical instability reactions such as hydrolysis and oxidation. Stability was assessed on cefazolin incorporated in cubic phase gel and in solution at two different concentrations (200 and 50 micrograms/g), at 22, 37, and 50 degrees C. Degradation profiles, plotting percent cefazolin remaining on a logarithmic scale versus time, were constructed and the degradation rate constants calculated from the slopes. At both concentrations, degradation of cefazolin was found to be slower in the cubic phase gel than in solution at 22 and 37 degrees C, but not at 50 degrees C. The degradation rate constants were 3- to 18-fold lower in the gel than in solution at low concentration of cefazolin. At 22 and 37 degrees C, the kinetics of degradation at high concentration of cefazolin was not first-order but showed a lag phase followed by an exponential loss of cefazolin, typical of oxidation. The potential oxidation of the thioether moiety of cefazolin was confirmed by its 18-fold higher stability in the presence of ethylenediaminetetraacetic acid (EDTA) and nitrogen in solution. Cefuroxime, a cephalosporin which degrades solely via beta-lactam hydrolysis, degraded twice as fast in solution as it did in the gel. The enhanced stability of cefazolin and cefuroxime in the GMO cubic phase gel shows its potential as a chemical stability enhancer and this is the first report to demonstrate oxidation, in addition to beta-lactam hydrolysis, as a mechanism for degradation of cefazolin.

  20. Robust synthesis of gold cubic nanoframes through a combination of galvanic replacement, gold deposition, and silver dealloying.

    PubMed

    Wan, Dehui; Xia, Xiaohu; Wang, Yucai; Xia, Younan

    2013-09-23

    A facile, robust approach to the synthesis of Au cubic nanoframes is described. The synthesis involves three major steps: 1) preparation of Au-Ag alloyed nanocages using a galvanic replacement reaction between Ag nanocubes and HAuCl4 ; 2) deposition of thin layers of pure Au onto the surfaces of the nanocages by reducing HAuCl4 with ascorbic acid, and; 3) formation of Au cubic nanoframes through a dealloying process with HAuCl4 . The key to the formation of Au cubic nanoframes is to coat the surfaces of the Au-Ag nanocages with sufficiently thick layers of Au before they are dealloyed. The Au layer could prevent the skeleton of a nanocage from being fragmented during the dealloying step. The as-prepared Au cubic nanoframes exhibit tunable localized surface plasmon resonance peaks in the near-infrared region, but with much lower Ag content as compared with the initial Au-Ag nanocages.

  1. Concentric Archimedean polyhedra: Mn(III)12Mn(II)9 aggregates linked into a cubic network.

    PubMed

    Nayak, Sanjit; Lan, Yanhua; Clérac, Rodolphe; Anson, Christopher E; Powell, Annie K

    2008-11-30

    A Mn(III)(12)Mn(II)(9) aggregate has a structure built up of concentric polyhedra with these units linked into a cubic network to give a remarkably pleasing structure isotypic with iron pyrites. PMID:19009052

  2. Luminescence enhancement in nanocrystalline Eu2O3 nanorods - Microwave hydrothermal crystallization and thermal degradation of cubic phase

    NASA Astrophysics Data System (ADS)

    Kaszewski, Jarosław; Witkowski, Bartłomiej S.; Wachnicki, Łukasz; Przybylińska, Hanka; Kozankiewicz, Bolesław; Mijowska, Ewa; Godlewski, Marek

    2016-09-01

    Thermally induced crystallization of cubic Eu2O3 obtained with the microwave hydrothermal method has been investigated. The starting material crystallized in the form of needle-shaped agglomerates of nanocrystalline hexagonal Eu(OH)3. Thermal treatment up to 800 °C induced the crystallization of cubic Eu2O3, after further calcination at 1200 °C in the air a monoclinic phase appeared. The phase transformation caused abnormal reduction of Eu3+ ions, related to the oxygen vacancy creation during sintering of the oxide crystallites. The crystallization process of cubic Eu2O3 occurred within the agglomerates without change of their shapes. The cubic form exhibited bright emission of Eu3+ related luminescence with intensity increasing with the size of crystallites.

  3. Critical effect of cubic phase on aging in 3mol% yttria-stabilized zirconia ceramics for hip replacement prosthesis.

    PubMed

    Chevalier, Jérôme; Deville, Sylvain; Münch, Etienne; Jullian, Romain; Lair, Frédéric

    2004-11-01

    The isothermal tetragonal-to-monoclinic transformation of 3Y-TZP ceramics sintered at two different temperatures (1450 degrees C and 1550 degrees C) and duration (2 and 5h) is investigated at 134 degrees C in steam. Particular attention is paid to the presence of a cubic phase and its effect on isothermal aging. Sintering at 1550 degrees C can result in a significant amount of large cubic grains in the specimens, that have a detrimental impact on aging resistance, especially for the first stage of the aging process. Cubic grains appear to be enriched in yttrium, which in turn leads to a depletion of yttrium in the neighboring tetragonal grains. These grains will act as nucleation sites for tetragonal-to-monoclinic transformation. Even for specimens sintered at lower temperature, i.e. 1450 degrees C, the presence of a cubic phase is expected from the phase diagram, leading to a significant effect on aging sensitivity.

  4. Pulsed field gradient MAS-NMR studies of the mobility of carboplatin in cubic liquid-crystalline phases

    NASA Astrophysics Data System (ADS)

    Pampel, André; Michel, Dieter; Reszka, Regina

    2002-05-01

    A drug delivery system with cubic liquid-crystalline phase structure (cubic phase) containing the anti-cancer drug Carboplatin is studied. It is demonstrated that the combination of pulsed field gradient (PFG) NMR and MAS-NMR is a useful tool to study the biophysical properties of a cubic phase. The linewidth in 1H-NMR spectra is narrowed by MAS, which can be exploited to perform PFG diffusion NMR experiments under high-resolution conditions. Measurement of self-diffusion coefficients of all components of the cubic phase becomes possible. The influence of polyethylene glycol chains on the drug mobility is discussed. It is shown that polyethylene glycol chains interact with Carboplatin.

  5. Growth of Sobolev Norms in the Cubic Nonlinear Schrödinger Equation with a Convolution Potential

    NASA Astrophysics Data System (ADS)

    Guardia, Marcel

    2014-07-01

    Fix s > 1. Colliander et al. proved in (Invent Math 181:39-113, 2010) the existence of solutions of the cubic defocusing nonlinear Schrödinger equation in the two torus whose s-Sobolev norm undergoes arbitrarily large growth as time evolves. In this paper we generalize their result to the cubic defocusing nonlinear Schrödinger equation with a convolution potential. Moreover, we show that the speed of growth is the same as the one obtained for the cubic defocusing nonlinear Schrödinger equation in Guardia and Kaloshin (Growth of Sobolev norms in the cubic defocusing Nonlinear Schrödinger Equation. To appear in the Journal of the European Mathematical Society, 2012).

  6. 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.

  7. 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.

  8. 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

  9. Wiener index on rows of unit cells of the face-centred cubic lattice.

    PubMed

    Mujahed, Hamzeh; Nagy, Benedek

    2016-03-01

    The Wiener index of a connected graph, known as the `sum of distances', is the first topological index used in chemistry to sum the distances between all unordered pairs of vertices of a graph. The Wiener index, sometimes called the Wiener number, is one of the indices associated with a molecular graph that correlates physical and chemical properties of the molecule, and has been studied for various kinds of graphs. In this paper, the graphs of lines of unit cells of the face-centred cubic lattice are investigated. This lattice is one of the simplest, the most symmetric and the most usual, cubic crystal lattices. Its graphs contain face centres of the unit cells and other vertices, called cube vertices. Closed formulae are obtained to calculate the sum of shortest distances between pairs of cube vertices, between cube vertices and face centres and between pairs of face centres. Based on these formulae, their sum, the Wiener index of a face-centred cubic lattice with unit cells connected in a row graph, is computed.

  10. Formation of hexagonal and cubic ice during low-temperature growth.

    PubMed

    Thürmer, Konrad; Nie, Shu

    2013-07-16

    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.

  11. First-principles investigation of cubic BaRuO3: A Hund's metal

    NASA Astrophysics Data System (ADS)

    Dasari, Nagamalleswararao; Yamijala, S. R. K. C. Sharma; Jain, Manish; Dasgupta, T. Saha; Moreno, Juana; Jarrell, Mark; Vidhyadhiraja, N. S.

    2016-08-01

    A first-principles investigation of cubic BaRuO3, by combining density functional theory with dynamical mean-field theory and a hybridization expansion continuous time quantum Monte Carlo solver, has been carried out. Nonmagnetic calculations with appropriately chosen on-site Coulomb repulsion U and Hund's exchange J for single-particle dynamics and static susceptibility show that cubic BaRuO3 is in a spin-frozen state at temperatures above the ferromagnetic transition point. A strong redshift with increasing J of the peak in the real frequency dynamical susceptibility indicates a dramatic suppression of the Fermi liquid coherence scale as compared to the bare parameters in cubic BaRuO3. The self-energy also shows clear deviation from Fermi liquid behavior that manifests in the single-particle spectrum. Such a clean separation of energy scales in this system provides scope for an incoherent spin-frozen (SF) phase that extends over a wide temperature range, to manifest in non-Fermi liquid behavior and to be the precursor for the magnetically ordered ground state.

  12. Identification of Clathrate Hydrates, Hexagonal Ice, Cubic Ice, and Liquid Water in Simulations: the CHILL+ Algorithm.

    PubMed

    Nguyen, Andrew H; Molinero, Valeria

    2015-07-23

    Clathrate hydrates and ice I are the most abundant crystals of water. The study of their nucleation, growth, and decomposition using molecular simulations requires an accurate and efficient algorithm that distinguishes water molecules that belong to each of these crystals and the liquid phase. Existing algorithms identify ice or clathrates, but not both. This poses a challenge for cases in which ice and hydrate coexist, such as in the synthesis of clathrates from ice and the formation of ice from clathrates during self-preservation of methane hydrates. Here we present an efficient algorithm for the identification of clathrate hydrates, hexagonal ice, cubic ice, and liquid water in molecular simulations. CHILL+ uses the number of staggered and eclipsed water-water bonds to identify water molecules in cubic ice, hexagonal ice, and clathrate hydrate. CHILL+ is an extension of CHILL (Moore et al. Phys. Chem. Chem. Phys. 2010, 12, 4124-4134), which identifies hexagonal and cubic ice but not clathrates. In addition to the identification of hydrates, CHILL+ significantly improves the detection of hexagonal ice up to its melting point. We validate the use of CHILL+ for the identification of stacking faults in ice and the nucleation and growth of clathrate hydrates. To our knowledge, this is the first algorithm that allows for the simultaneous identification of ice and clathrate hydrates, and it does so in a way that is competitive with respect to existing methods used to identify any of these crystals. PMID:25389702

  13. 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.

  14. 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

  15. 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.

  16. Wiener index on rows of unit cells of the face-centred cubic lattice.

    PubMed

    Mujahed, Hamzeh; Nagy, Benedek

    2016-03-01

    The Wiener index of a connected graph, known as the `sum of distances', is the first topological index used in chemistry to sum the distances between all unordered pairs of vertices of a graph. The Wiener index, sometimes called the Wiener number, is one of the indices associated with a molecular graph that correlates physical and chemical properties of the molecule, and has been studied for various kinds of graphs. In this paper, the graphs of lines of unit cells of the face-centred cubic lattice are investigated. This lattice is one of the simplest, the most symmetric and the most usual, cubic crystal lattices. Its graphs contain face centres of the unit cells and other vertices, called cube vertices. Closed formulae are obtained to calculate the sum of shortest distances between pairs of cube vertices, between cube vertices and face centres and between pairs of face centres. Based on these formulae, their sum, the Wiener index of a face-centred cubic lattice with unit cells connected in a row graph, is computed. PMID:26919376

  17. Synthesis and characterization of cubic mesoporous bridged polysilsesquioxane for removing organic pollutants from water.

    PubMed

    Lin, Derong; Zhao, Qing; Hu, Lijiang; Xing, Baoshan

    2014-05-01

    Hexane, octane, phenyl, and biphenyl-bridged bis(triethoxysilyl) precursors were used in synthesizing cubic mesoporous bridged polysilsesquioxane (BPS) copolymers. Structural characterization was carried out by FTIR, small angle XRD, Brunauer-Emmett-Teller-N2 sorption, (1)H NMR, and TEM. We successfully synthesized both "rigid" and "soft" 3D cubic mesoporous BPS with high surface area and pore volume, as attested by the comprehensive characterization data. Adsorption of pyrene, phenanthrene, nitrobenzene, and 2,4-dichlorophenol on BPS was greatly affected by adsorbate properties, i.e., Kow, solvation properties and molecular size. Hydrophobic interaction dominantly controlled organic pollutants' sorption on BPS. Other interactions, e.g., π-π and H-bond interactions, also have effects on sorption as indicated by Kow normalized sorption isotherms. Rigid aromatic BPS (phenyl and biphenyl) showed a higher sorption capacity than soft aliphatic BPS (hexane and octane). A conceptual model was proposed to further explain the phenomena. This study suggests a promising application of cubic mesoporous BPS in wastewater treatment.

  18. Curcumin-Loaded Lipid Cubic Liquid Crystalline Nanoparticles: Preparation, Optimization, Physicochemical Properties and Oral Absorption.

    PubMed

    He, Xiuli; Li, Qinghua; Liu, Xiuju; Wu, Guangsheng; Zhai, Guangxi

    2015-08-01

    In order to improve the oral absorption of curcumin, curcumin-loaded lipid cubic liquid crystalline nanoparticles were prepared and evaluated in vitro and in vivo. The hot and high-pressure homogenization method was used to prepare the nanoparticles. The formulation and process were optimized by uniform design with drug loading and entrapment efficiency as index, and physicochemical properties were also investigated. Spherical nanoparticles were observed under transmission electron microscope (TEM), with average particle size of 176.1 nm, zeta potential of -25.19 mV, average drug loading of (1.5 ± 0.2)% and entrapment efficiency of (95 ± 1.8)%. The in vitro release of curcumin from the nanoparticle formulation showed a sustained property, while the pharmacokinetics results after oral administration of curcumin loaded lipid cubic liquid crystalline nanoparticles in rat showed that the oral absorption of curcumin fitted one-compartment model and relative bioavailability was 395.56% when compared to crude curcumin. It can be concluded from these results that the lipid cubic liquid crystalline nanoparticles, as carriers, can markedly improve the oral absorption of curcumin.

  19. Insights into photoluminescence property and photocatalytic activity of cubic and rhombohedral ZnIn{sub 2}S{sub 4}

    SciTech Connect

    Shen Shaohua; Guo Penghui; Zhao Liang; Du Yuanchang; Guo Liejin

    2011-08-15

    Cubic and rhombohedral ZnIn{sub 2}S{sub 4} were synthesized by thermal sulfidation of Zn-In mixed oxide precursor in H{sub 2}S atmosphere at different temperatures. Cubic ZnIn{sub 2}S{sub 4} was obtained when Zn-In mixed oxide precursor was sulfurized at 400 deg. C. With sulfidation temperature increasing from 400 to 800 deg. C, the crystal phase of ZnIn{sub 2}S{sub 4} gradually turned from cubic to rhombohedral, which was demonstrated by different analysis techniques such as XRD, Raman, SEM, etc. UV-vis absorption spectra indicated that cubic ZnIn{sub 2}S{sub 4} displayed better light absorption property than rhombohedral ZnIn{sub 2}S{sub 4}, with band gaps calculated to be 2.0 and 2.5 eV, respectively. However, under visible light irradiation, rhombohedral ZnIn{sub 2}S{sub 4} photocatalyzed H{sub 2} evolution from aqueous sodium sulfite/sulfide solution efficiently, whereas cubic ZnIn{sub 2}S{sub 4} was not active for this reaction. The photoluminescence property revealed the different dynamics of photogenerated carriers, which made a predominant contribution to the increasing photocatalytic performances of ZnIn{sub 2}S{sub 4} with crystal phase turning from cubic to rhombohedral. - Graphical Abstract: Rhombohedral ZnIn{sub 2}S{sub 4} showed a superior photocatalytic activity for H{sub 2} evolution than cubic ZnIn{sub 2}S{sub 4}, which was proved to be related with their different dynamics of photogenerated carriers. Highlights: > Cubic and rhombohedral ZnIn{sub 2}S{sub 4} were synthesized by thermal sulfidation. > Rhombohedral ZnIn{sub 2}S{sub 4} could photocatalyze H{sub 2} evolution efficiently. > The dynamics of photogenerated carriers affected the photocatalytic activity.

  20. Surface Transfer Doping of Cubic Boron Nitride Films by MoO3 and Tetrafluoro-tetracyanoquinodimethane (F4-TCNQ).

    PubMed

    He, Bin; Ng, Tsz-Wai; Lo, Ming-Fai; Lee, Chun-Sing; Zhang, Wenjun

    2015-05-13

    Cubic boron nitride (cBN) has strong potential for the applications in high-temperature and high-power electronics and deep ultraviolet devices due to its outstanding combined physical and chemical properties. P-type surface transfer doping of heteroepitaxial cBN films was achieved by employing MoO3 and tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) as the surface dopants. The surface conductivities of hydrogenated cBN films increased by 3-6 orders after the deposition of surface dopants. The photoemission spectroscopy (PES) measurements revealed the variation of electronic structures at the interface regions, which suggested that the electron transfer from cBN films to the surface dopants induced hole accumulation at the cBN surface and the increase of surface conductivity. Based on the PES results, the energy level diagrams at MoO3/cBN and F4-TCNQ/cBN interfaces were determined. The achievement provided a potential approach for fabricating cBN-based electronic devices, especially on micrometer and nanometer scales. PMID:25915092