Anomalies in free flux-flow hall effect

The low-T-c layered superconductor 2H-NbSe2 shows remarkable results for free flux-flow Hall effect. At low magnetic fields, the Nozieres-Vinen result of a field-independent Hall angle appears to hold. At larger fields, a marked departure occurs leading to an extremely sharp and pronounced minimum slightly below H-c2, unaccounted for in the standard theoretical models. The results suggest the existence of collective dynamics and phase transitions (such as melting) in a clean flux line lattice.

Preparatively useful transformations of steroids and morphine alkaloids byMucor piriformis

A versatile fungus isolated in our laboratory and identified as Mucor piriformis has been shown to effect novel and preparatively useful transformations in steroids and morphine alkaloids. The organism very effectively carries out hydroxylation of various C-19 and C-21 steroids at 7 and 14-positions. Although the organism is capable of catalysing hydroxylation at 6 beta and 11 alpha-positions, these are not the major activities. The 14 alpha-hydroxylase appears to have a broad substrate specificity. However, steroids with a bulky substitution at C-17 alpha-position or without the 4-en-3-one group are not accepted as substrates by the 14 alpha-hydroxylase system. Studies have demonstrated how various C-19 and C-21 steroids can be modified to yield new structures which are either difficult to prepare by traditional methods or hitherto unknown. The organism also very efficiently and selectively carries out the N-dealkylation of thebaine and its N-variants. Interestingly, the nor-compound formed does not get further metabolized. Since thebaine is very often used as a starting material to synthesize various morphine agonists as well as antagonists, and one of the steps involved in their preparation is the N-dealkylation reaction, the microbial process could certainly offer an alternative approach.

KFVS (Kinetic Flux Vector Splitting) on moving grids for unsteady aerodynamics

Accurate numerical solutions to the problems in fluid-structure (aeroelasticity) interaction are becoming increasingly important in recent years. The methods based on FCD (Fixed Computational Domain) and ALE (Alternate Lagrangian Eulerian) to solve such problems suffer from numerical instability and loss of accuracy. They are not general and can not be extended to the flowsolvers on unstructured meshes. Also, global upwind schemes can not be used in ALE formulation thus leads to the development of flow solvers on moving grids. The KFVS method has been shown to be easily amenable on moving grids required in unsteady aerodynamics. The ability of KFMG (Kinetic Flux vector splitting on Moving Grid) Euler solver in capturing shocks, expansion waves with small and very large pressure ratios and contact discontinuities has been demonstrated.

Synthesis Based on Cyclohexadienes. 5. A New Approach to the Synthesis of a-Ring Aromatic Steroids - a Formal Total Synthesis of (+/-)-Estrone

A new strategy for the construction of A-ring aromatic steroids which resulted in the formal total synthesis of estrone is described. Thus reaction of the adduct (9), obtained from 1-methoxy-4-methylcyclohexa-1,4-diene and acrolein, with 3-(m-methoxyphenyl)propylmagnesium bromide followed by oxidation afforded the bicyclo[2.2.2]octene derivative (14). Acid-catalysed rearrangement of (14) followed by an intramolecular Michael addition resulted in the cis tetraenone (18) which was dehydrogenated with palladium chloride to the pentaenone (22). Li/NH3 reduction of (22) gave 3-methoxy-D-homoestra-1,3,5(10)-trien-16-one (31) which has been converted into the methyl ether (37) of marrianolic acid, and its methyl ester (38).

Learning the global maximum with parameterized learning automata

A feedforward network composed of units of teams of parameterized learning automata is considered as a model of a reinforcement teaming system. The internal state vector of each learning automaton is updated using an algorithm consisting of a gradient following term and a random perturbation term. It is shown that the algorithm weakly converges to a solution of the Langevin equation implying that the algorithm globally maximizes an appropriate function. The algorithm is decentralized, and the units do not have any information exchange during updating. Simulation results on common payoff games and pattern recognition problems show that reasonable rates of convergence can be obtained.

A Rotor Flux Estimation During Zero and Active Vector Periods Using Current Error Space Vector From a Hysteresis Controller for a Sensorless Vector Control of IM Drive

This paper proposes a sensorless vector control scheme for general-purpose induction motor drives using the current error space phasor-based hysteresis controller. In this paper, a new technique for sensorless operation is developed to estimate rotor voltage and hence rotor flux position using the stator current error during zero-voltage space vectors. It gives a comparable performance with the vector control drive using sensors especially at a very low speed of operation (less than 1 Hz). Since no voltage sensing is made, the dead-time effect and loss of accuracy in voltage sensing at low speed are avoided here, with the inherent advantages of the current error space phasor-based hysteresis controller. However, appropriate device on-state drops are compensated to achieve a steady-state operation up to less than 1 Hz. Moreover, using a parabolic boundary for current error, the switching frequency of the inverter can be maintained constant for the entire operating speed range. Simple sigma L-s estimation is proposed, and the parameter sensitivity of the control scheme to changes in stator resistance, R-s is also investigated in this paper. Extensive experimental results are shown at speeds less than 1 Hz to verify the proposed concept. The same control scheme is further extended from less than 1 Hz to rated 50 Hz six-step operation of the inverter. Here, the magnetic saturation is ignored in the control scheme.

Optical studies of SN 2009jf: a Type Ib supernova with an extremely slow decline and aspherical signature

Optical UBVRI photometry and medium-resolution spectroscopy of the Type Ib supernova SN 2009jf, during the period from similar to -15 to +250 d, with respect to the B maximum are reported. The light curves are broad, with an extremely slow decline. The early post-maximum decline rate in the V band is similar to SN 2008D; however, the late-phase decline rate is slower than other Type Ib supernovae studied. With an absolute magnitude of M-V = -17.96 +/- 0.19 at peak, SN 2009jf is a normally bright supernova. The peak bolometric luminosity and the energy deposition rate via the 56Ni -> 56Co chain indicate that similar to 0.17+0.03(-0.03) M-circle dot of 56Ni was ejected during the explosion. The He i 5876 A line is clearly identified in the first spectrum of day similar to -15, at a velocity of similar to 16 000 km s-1. The O i] 6300-6364 A line seen in the nebular spectrum has a multipeaked and asymmetric emission profile, with the blue peak being stronger. The estimated flux in this line implies that greater than or similar to 1.34 M-circle dot oxygen was ejected. The slow evolution of the light curves of SN 2009jf indicates the presence of a massive ejecta. The high expansion velocity in the early phase and broader emission lines during the nebular phase suggest it to be an explosion with a large kinetic energy. A simple qualitative estimate leads to the ejecta mass of M-ej = 4-9 M-circle dot and kinetic energy E-K = 3-8 x 1051 erg. The ejected mass estimate is indicative of an initial main-sequence mass of greater than or similar to 20-25 M-circle dot.

Influence of growth below and above T-c on the morphology and domain structure in flux-grown KTP crystals

KTP crystals have been grown below and above the ferroelectric transition temperature by flux method employing both spontaneous and top-seeded solution growth techniques. A slight morphological difference has been observed in these crystals when grown below and above the T-c. Ferroelectric domains are studied in these crystals by selective domain etching. It is seen that the ferroelectric domains in crystals grown spontaneously below T, show a complicated structure. A systematic investigation of the factors influencing domain structure has been carried out. Stress to some extent has been shown to affect the domain structure. Finally, a convenient way of converting the multidomain crystals into monodomain ones is described.

Traveling waves in a drifting flux lattice

Starting from the time-dependent Ginzburg-Landau equations for a type II superconductor, we derive the equations of motion for the displacement field of a moving vortex lattice ignoring pinning and inertia. We show that it is linearly stable and, surprisingly, that it supports wavelike long-wavelength excitations arising not from inertia or elasticity but from the strain-dependent mobility of the moving lattice. It should be possible to image these waves, whose speeds are a few mu m/s, using fast scanning tunneling microscopy.

Performance analysis of single-symbol maximum likelihood decodable linear STBCs

Performance of space-time block codes can be improved using the coordinate interleaving of the input symbols from rotated M-ary phase shift keying (MPSK) and M-ary quadrature amplitude modulation (MQAM) constellations. This paper is on the performance analysis of coordinate-interleaved space-time codes, which are a subset of single-symbol maximum likelihood decodable linear space-time block codes, for wireless multiple antenna terminals. The analytical and simulation results show that full diversity is achievable. Using the equivalent single-input single-output model, simple expressions for the average bit error rates are derived over flat uncorrelated Rayleigh fading channels. Optimum rotation angles are found by finding the minimum of the average bit error rate curves.

Modified kinetic flux vector splitting (m-KFVS) method for compressible flows

To resolve many flow features accurately, like accurate capture of suction peak in subsonic flows and crisp shocks in flows with discontinuities, to minimise the loss in stagnation pressure in isentropic flows or even flow separation in viscous flows require an accurate and low dissipative numerical scheme. The first order kinetic flux vector splitting (KFVS) method has been found to be very robust but suffers from the problem of having much more numerical diffusion than required, resulting in inaccurate computation of the above flow features. However, numerical dissipation can be reduced by refining the grid or by using higher order kinetic schemes. In flows with strong shock waves, the higher order schemes require limiters, which reduce the local order of accuracy to first order, resulting in degradation of flow features in many cases. Further, these schemes require more points in the stencil and hence consume more computational time and memory. In this paper, we present a low dissipative modified KFVS (m-KFVS) method which leads to improved splitting of inviscid fluxes. The m-KFVS method captures the above flow features more accurately compared to first order KFVS and the results are comparable to second order accurate KFVS method, by still using the first order stencil. (C) 2011 Elsevier Ltd. All rights reserved.

Thermal instability in a three-dimensional rigid container with prescribed heat flux at lower boundary

The Bénard–Marangoni convection is studied in a three-dimensional container with thermally insulated lateral walls and prescribed heat flux at lower boundary. The upper surface of the incompressible, viscous fluid is assumed to be flat with temperature dependent surface tension. A Galerkin–Tau method with odd and even trial functions satisfying all the essential boundary conditions except the natural boundary conditions at the free surface has been used to solve the problem. The critical Marangoni and Rayleigh numbers are determined for the onset of steady convection as a function of aspect ratios x0 and y0 for the cases of Bénard–Marangoni, pure Marangoni and pure Bénard convections. It is observed that critical parameters are decreasing with an increase in aspect ratios. The flow structures corresponding to the values of the critical parameters are presented in all the cases. It is observed that the critical parameters are higher for case with heat flux prescribed than those corresponding to the case with prescribed temperature. The critical Marangoni number for pure Marangoni convection is higher than critical Rayleigh number corresponding to pure Bénard convection for a given aspect ratio whereas the reverse was observed for two-dimensional infinite layer.

Reduction of oxygen impurity at GaN/beta-Si(3)N(4)/Si interface via SiO(2) to Ga(2)O conversion by exposing of Si surface under Ga flux

The removal of native oxide from Si (1 1 1) surfaces was investigated by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectra (SIMS) depth profiles. Two different oxide removal methods, performed under ultrahigh-vacuum (UHV) conditions, were carried out and compared. The first cleaning method is thermal desorption of oxide at 900 degrees C. The second method is the deposition of metallic gallium followed by redesorption. A significant decrease in oxygen was achieved by thermal desorption at 900 degrees C under UHV conditions. By applying a subsequent Ga deposition/redesorption, a further reduction in oxygen could be achieved. We examine the merits of an alternative oxide desorption method via conversion of the stable SiO(2) surface oxide into a volatile Ca(2)O oxide by a supply of Ga metals. Furthermore, ultra thin films of pure silicon nitride buffer layer were grown on a Si (1 1 1) surface by exposing the surface to radio-frequency (RF) nitrogen plasma followed by GaN growth. The SIMS depth profile shows that the oxygen impurity can be reduced at GaN/beta-Si(3)N(4)/Si interfaces by applying a subsequent Ga deposition/redesorption. (C) 2011 Elsevier B.V. All rights reserved.