Effect of base dissipation on the granular flow down an inclined plane

The effect of base dissipation on the granular flow down an inclined plane is examined by altering the coefficient of restitution between the moving and base particles in discrete element (DE) simulations. The interaction laws between two moving particles are kept fixed, and the coefficient of restitution (damping constant in the DE simulations) between the base and moving particles are altered to reduce dissipation, and inject energy from the base. The energy injection does result in an increase in the strain rate by up to an order of magnitude, and the temperature by up to two orders of magnitude at the base. However, the volume fraction, strain rate and temperature profiles in the bulk (above about 15 particle diameters from the base) are altered very little by the energy injection at the base. We also examine the variation of h(stop), the minimum height at the cessation of flow, with energy injection from the base. It is found that at a fixed angle of inclination, h(stop) decreases as the energy dissipation at the base decreases.

Transition due to base roughness in a dense granular flow down an inclined plane

Particle simulations based on the discrete element method are used to examine the effect of base roughness on the granular flow down an inclined plane. The base is composed of a random configuration of fixed particles, and the base roughness is decreased by decreasing the ratio of diameters of the base and moving particles. A discontinuous transition from a disordered to an ordered flow state is observed when the ratio of diameters of base and moving particles is decreased below a critical value. The ordered flowing state consists of hexagonally close packed layers of particles sliding over each other. The ordered state is denser (higher volume fraction) and has a lower coordination number than the disordered state, and there are discontinuous changes in both the volume fraction and the coordination number at transition. The Bagnold law, which states that the stress is proportional to the square of the strain rate, is valid in both states. However, the Bagnold coefficients in the ordered flowing state are lower, by more than two orders of magnitude, in comparison to those of the disordered state. The critical ratio of base and moving particle diameters is independent of the angle of inclination, and varies very little when the height of the flowing layer is doubled from about 35 to about 70 particle diameters. While flow in the disordered state ceases when the angle of inclination decreases below 20 degrees, there is flow in the ordered state at lower angles of inclination upto 14 degrees. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.4710543]

Current transport in nonpolar a-plane InN/GaN eterostructures Schottky junction

The temperature dependent current transport properties of nonpolar a-plane (11 2 0) InN/GaN heterostructure Schottky junction were investigated. The barrier height ( b) and ideally factor (η) estimated from the thermionic emission (TE) model were found to be temperature dependent in nature. The conventional Richardson plot of the ln(I s/T 2) versus 1/kT has two regions: the first region (150-300 K) and the second region (350-500 K). The values of Richardson constant (A +) obtained from this plot are found to be lower than the theoretical value of n-type GaN. The variation in the barrier heights was explained by a double Gaussian distribution with mean barrier height values ( b ) of 1.17 and 0.69 eV with standard deviation (� s) of 0.17 and 0.098 V, respectively. The modified Richardson plot in the temperature range 350-500 K gives the Richardson constant which is close to the theoretical value of n-type GaN. Hence, the current mechanism is explained by TE by assuming the Gaussian distribution of barrier height. At low temperature 150-300 K, the absence of temperature dependent tunneling parameters indicates the tunneling assisted current transport mechanism. © 2012 American Institute of Physics.

PIV study on the dimple mid-plane of a narrow rectangular channel with dimples applied to one wall

This paper presents an investigation of the fluid flow in the fully developed portion of a rectangular channel (Aspect Ratio of 2) with dimples applied to one wall at channel Reynolds numbers of 20,000, 30,000, and 40,000. The dimples are applied in a staggered-row, racetrack configuration. Results for three different dimple geometries are presented: a large dimple, small dimple, and double dimple. Heat transfer and aerodynamic results from preceding works are presented in Nusselt number and friction factor augmentation plots as determined experimentally. Using particle image velocimetry, the region near the dimple feature is studied in detail in the location of the entrainment and ejection of vortical packets into and out of the dimple; the downstream wake region behind each dimple is also studied to examine the effects of the local flow phenomenon that result in improved heat transfer in the areas of the channel wall not occupied by a feature. The focus of the paper is to examine the secondary flows in these dimpled channels in order to support the previously presented heat transfer trends. The flow visualization is also intended to improve the understanding of the flow disturbances in a dimpled channel; a better understanding of these effects would lead the development of more effective channel cooling designs. Copyright © 2011 by ASME.

Nucleation-Growth Mode of Cubic-Tetragonal Transition with Coexistence of Phases over a Wide Temperature Interval in the High Temperature Ferroelectric Systems PbTiO3-BiMeO3:Me = Sc , and Zn1/2Ti1/2

Temperature dependent X-ray powder diffraction and dielectric studies have been carried out on tetragonal compositions of (1-x) PbTiO 3(x) BiMeO 3; Me similar to Sc and Zn 1/2 Ti 1/2. The cubic and the tetragonal phases coexist over more than 100 degrees C for 0.70 PbTiO 30.3 Bi ( Zn 1/2 Ti 1/2) O 3 and 0.66 PbTiO 30.34 BiScO 3. The wide temperature range of phase coexistence is shown to be an intrinsic feature of the system, and is attributed to the increase in the degree of the covalent character of the ( Pb +Bi ) O bond with increasing concentration of Bi at the Pb -site. The d-values of the {111} planes of the coexisting phases are nearly identical, suggesting this plane to be the invariant plane for the martensitic type cubic-tetragonal transformation occurring in these systems.

High-pressure synchrotron x-ray diffraction study of RMnO3 (R=Eu, Gd, Tb and Dy) upto 50 GPa

We have carried out synchrotron based high-pressure x-ray diffraction study of orthorhombic EuMnO3, GdMnO3, TbMnO3 and DyMnO3 up to 54.4, 41.6, 47.0 and 50.2 GPa, respectively. The diffraction peaks of all the four manganites shift monotonically to higher diffraction angles and the crystals retain the orthorhombic structure till the highest pressure. We have fitted the observed volume versus pressure data with the Birch-Murnaghan equation of state and determined the bulk modulus to be 185 +/- 6 GPa, 190 +/- 16 GPa, 188 +/- 9 GPa and 192 +/- 8 GPa for EuMnO3, GdMnO3, TbMnO3 and DyMnO3, respectively. The bulk modulus of EuMnO3 is comparable to other manganites, in contrast to theoretical predictions.

Angular amplification by a diffraction grating for chiro-optical measurements

The angles at which a light beam gets diffracted by a grating depend strongly on the direction of incidence for diffraction angles close to a right angle. Accordingly, it is possible to amplify small beam deflections by placing a grating at an optimal orientation to the light path. We use this principle to amplify small beam deviations arising out of a light beam refracting at the interface of an optically active medium, and demonstrate a new technique of enhancing the limit of detection of chiro-optical measurements. (C) 2012 Optical Society of America

Severe diffraction anisotropy, rotational pseudosymmetry and twinning complicate the refinement of a pentameric coiled-coil structure of NSP4 of rotavirus

The crystal structure of the region spanning residues 95-146 of the rotavirus nonstructural protein NSP4 from the asymptomatic human strain ST3 was determined at a resolution of 2.5 angstrom. Severe diffraction anisotropy, rotational pseudo-symmetry and twinning complicated the refinement of this structure. A systematic explanation confirming the crystal pathologies and describing how the structure was successfully refined is given in this report.

Ex Situ X-ray Diffraction, X-ray Absorption Near Edge Structure, Electron Spin Resonance, and Transmission Electron Microscopy Study of the Hydrothermal Crystallization of Vanadium Oxide Nanotubes: An Insight into the Mechanism of Formation

The nucleation and growth of vanadium oxide nanotubes (VOx-NT) have been followed by a combination of numerous ex situ techniques. long the hydrothermal process. Intermediate solid phases extracted at different reaction times have been characterized by powder X-ray diffraction, scanning and transmission electron microscopy, electron spin resonance, and V-K edge :X-ray absorption near-edge structure spectroscopy. The supernatant vanadate solutions extracted during the hydrothermal treatment have been studied by liquid V-51 NMR and flame. spectroscopy. For short durations of the hydrothermal synthesis, the initial V2O5-surfactant intercalate. is progressively transformed into VOx-NT whose crystallization starts to be detected after a hydrothermal treatment of 24 h. Upon heating from 24 h to 7 days, VOx-NT are obtained in larger amount and with an improved crystallinity. The detection of soluble amines and cyclic metavanadate V4O12](4-) in the supernatant solution along the hydrothermal process suggests that VOx-NT result from a dissolution precipitation mechanism. Metavanadate species V4O12](4-) could behave as molecular precursors in the polymerization reactions leading to VOx-NT.

Perturbative expansion of the QCD Adler function improved by renormalization-group summation and analytic continuation in the Borel plane

We examine the large-order behavior of a recently proposed renormalization-group-improved expansion of the Adler function in perturbative QCD, which sums in an analytically closed form the leading logarithms accessible from renormalization-group invariance. The expansion is first written as an effective series in powers of the one-loop coupling, and its leading singularities in the Borel plane are shown to be identical to those of the standard ``contour-improved'' expansion. Applying the technique of conformal mappings for the analytic continuation in the Borel plane, we define a class of improved expansions, which implement both the renormalization-group invariance and the knowledge about the large-order behavior of the series. Detailed numerical studies of specific models for the Adler function indicate that the new expansions have remarkable convergence properties up to high orders. Using these expansions for the determination of the strong coupling from the hadronic width of the tau lepton we obtain, with a conservative estimate of the uncertainty due to the nonperturbative corrections, alpha(s)(M-tau(2)) = 0.3189(-0.0151)(+0.0173), which translates to alpha(s)(M-Z(2)) = 0.1184(-0.0018)(+0.0021). DOI: 10.1103/PhysRevD.87.014008

Air oxygenation chemistry of 4-TBC catalyzed by chloro bridged dinuclear copper(II) complexes of pyrazole based tridentate ligands: synthesis, structure, magnetic and computational studies

Four dinuclear bis(mu-Cl) bridged copper(II) complexes, Cu-2(mu-Cl)(2)(L-X)(2)](ClO4)(2) (L-X = N,N-bis(3,5-dimethylpyrazole-1-yl)-methyl]benzylamine with X = H(1), OMe(2), Me(3) and Cl(4)), have been synthesized and characterized by the single crystal X-ray diffraction method. In these complexes, each copper(II) center is penta-coordinated with square-pyramidal geometry. In addition to the tridentate L-X ligand, a chloride ion occupies the last position of the square plane. This chloride ion is also bonded to the neighboring Cu(II) site in its axial position forming an SP-I dinuclear Cu(II) unit that exhibits small intramolecular ferromagnetic interactions and supported by DFT calculations. The complexes 1-3 exhibit methylmonooxygenase (pMMO) behaviour and oxidise 4-tert-butylcatechol (4-TBCH2) with molecular oxygen in MeOH or MeCN to 4-tert-butyl-benzoquinone (4-TBQ), 5-methoxy-4-tert-butyl-benzoquinone (5-MeO-4-TBQ) as the major products along with 6,6'-Bu-t-biphenyl-3,4,3',4'-tetraol and others as minor products. These are further confirmed by ESI- and FAB-mass analyses. A tentative catalytic cycle has been framed based on the mass spectral analysis of the products and DFT calculations on individual intermediates that are energetically feasible.

Molecular beam epitaxial growth of (11-22) GaN on m-plane sapphire

The structural and optical properties of semipolar (1 1 -2 2) GaN grown on m-plane (1 0 -1 0) sapphire substrates by molecular beam epitaxy were investigated. An in-plane orientation relationship was found to be 1 -1 0 0] GaN parallel to 1 2-1 0] sapphire and -1 -1 2 3] GaN parallel to 0 0 0 1] sapphire for semipolar GaN on m-plane sapphire substrates. The near band emission (NBE) was found at 3.432 eV, which is slightly blue shifted compared to the bulk GaN. The Raman E-2 (high) peak position observed at 569.1 cm(-1), which indicates that film is compressively strained. Schottky barrier height (phi(b)) and the ideality factor (eta) for the Au/semipolar GaN Schottky diode found to be 0.55 eV and 2.11, respectively obtained from the TE model.

Analysis of multi-conductor coupled microstrip lines with an aperture in the ground plane for the design of a broadband filter

Closed-form expressions for the propagation characteristics of coupled microstrip lines with a symmetrical aperture in the ground plane are derived. Expressions for the regular microstrip coupled lines have been modified using physical insights to incorporate the effect of the aperture. The accuracy of these expressions has been verified by full-wave simulations and compared with conformal mapping analysis. These expressions are accurate within 5% for a substrate whose thickness varies from 0.2 to 1.6mm and permittivity in the range of 210. Designing a broadband filter based on planar multi-conductor coupled lines with aperture in the ground plane is demonstrated in this paper using the proposed expressions for its practical use.

Anisotropic low field magnetoimpedance in (001) oriented La0.7Sr0.3MnO3 thin films

We report the evidence for the anisotropic magnetoimpedance behavior in (001) oriented La0.7Sr0.3MnO3 (LSMO) thin films, in low frequency-low magnetic field regime. (001) oriented LSMO thin films were deposited using pulsed laser deposition and characterized with X-ray diffraction and temperature dependent magnetization studies. In the in-plain configuration, an ac magnetoresistance (MRac) of similar to -0.5% was observed at 1000 Oe, at 100 Hz frequency in these films. The MRac was found to decrease with increase in frequency. We observe increases in MRac at low frequency, indicating major contribution for change of permeability from domain wall motion. At higher frequencies, it decreases due to decrease in transverse permeability, resulting from dampening of domain wall motion. Out-of-plane configuration showed MRac similar to 5.5% at 1000 Oe, at 100 Hz frequency. The MRac turned from positive to negative with increase in frequency in out-of-plane configuration. These changes are attributed to the change in permeability of the film with the frequency and applied magnetic field.

Deposition and characterization of pure and Cd doped SnO2 thin films by the nebulizer spray pyrolysis (NSP) technique

Pure and cadmium doped tin oxide thin films were deposited on glass substrates from aqueous solution of cadmium acetate, tin (IV) chloride and sodium hydroxide by the nebulizer spray pyrolysis (NSP) technique. X-ray diffraction reveals that all films have tetragonal crystalline structure with preferential orientation along (200) plane. On application of the Scherrer formula, it is found that the maximum size of grains is 67 nm. Scanning electron microscopy shows that the grains are of rod and spherical in shape. Energy dispersive X-ray analysis reveals the average ratio of the atomic percentage of pure and Cd doped SnO2 films. The electrical resistivity is found to be 10(2) Omega cm at higher temperature (170 degrees C) and 10(3) Omega cm at lower temperature (30 degrees C). Optical band gap energy was determined from transmittance and absorbance data obtained from UV-vis spectra. Optical studies reveal that the band gap energy decreases from 3.90 eV to 3.52 eV due to the addition of Cd as dopant with different concentrations.