Promising half-metallic ferromagnetism in double perovskites Ba2VTO6 (T=Nb and Mo): Ab-initio LMTO-ASA investigations

The electronic and magnetic properties of new ordered vanadium-based double perovskite oxides Ba₂VTO₆ (T=Nb and Mo) have been investigated using the ab-initio linear muffin-tin orbitals method with the atomic-sphere approximation (LMTO-ASA). The calculations performed by using the local spin-density approximation with on-site Coulomb interaction (LSDA+U) style. The self-consistent band structure calculations predict half-metallic ferromagnetic (HM-FM) ground states with total spin magnetic moments of 2.1021 μ_B and 3.0633 μ_B per formula unit cell for Ba₂VNbO₆ and Ba₂VMoO₆, respectively. HM-FM nature in two compounds organizes from the ddpπ-superexchange interactions 3d-t_2g²–O (2p)–4d-t_2gⁿ (n=0 or 1), conformity with Zener–Goodenough–Kanamori rules.     

Solar Fuels: Visible‐Light‐Driven Generation of Dihydrogen at p‐Type Silicon Electrocatalysed by Molybdenum Hydrides

We show that a robust molybdenum hydride system can sustain photoelectrocatalysis of a hydrogen evolution reaction at boron‐doped, hydrogen‐terminated, p‐type silicon. The photovoltage for the system is about 600–650 mV and the current densities, which can be sustained at the photocathode in non‐catalytic and catalytic regimes, are similar to those at a photoinert vitreous carbon electrode. The kinetics of electrocatalysed hydrogen evolution at the photocathode are also very similar to those measured at vitreous carbon—evidently visible light does not significantly perturb the catalytic mechanism. Importantly, we show that the doped (1–10 Ω cm) p‐type Si can function perfectly well in the dark as an ohmic conductor and this has allowed direct comparison of the cyclic voltammetric behaviour of the response of the system under dark and illuminated conditions at the same electrode. The p‐type Si we have employed optimally harvests light energy in the 600–700 nm region and with 37 mW cm^?2 illumination in this range; the light to electrochemical energy conversion is estimated to be 2.8 %. The current yield of hydrogen under broad tungsten halide lamp illumination at 90 mW cm^?2 is (91±5) % with a corresponding chemical yield of (98±5) %.     

Stokes flow between eccentric rotating spheres with slip regime

The steady axisymmetric flow problem of a viscous fluid contained between two eccentric spheres that rotate about an axis joining their centers with different angular velocities is considered. A linear slip of Basset-type boundary condition at both surfaces of the spherical particle and the container is used. Under the Stokesian assumption, a general solution is constructed from the superposition of basic solutions in the spherical coordinate systems based on the inner solid particle and the spherical container. The boundary conditions on the particle’s surface and spherical container are satisfied by a collocation technique. Numerical results for the coupling coefficient acting on the particle are obtained with good convergence for various values of the ratio of particle-to-container radii, the relative distance between the centers of the particle and container, the slip coefficients and the relative angular velocity. In the limiting cases, the numerical values of the coupling coefficient for the solid sphere in concentric position with the container and when the particle is near the inner surface of the container are obtained, and the results are in good agreement with the available values in the literature. The variation of the coupling coefficient with respect the parameters considered are tabulated and displayed graphically.     

On the response of MEMS resonators under generic electrostatic loadings: experiments and applications

Nonlinear Dynamics - We present an investigation of the dynamic behavior of an electrostatically actuated clamped–clamped microbeam, under the simultaneous excitation of primary and...     

Slip at the surface of a sphere translating perpendicular to a plane wall in micropolar fluid

The Stokes axisymmetrical flow caused by a sphere translating in a micropolar fluid perpendicular to a plane wall at an arbitrary position from the wall is presented using a combined analytical-numerical method. A linear slip, Basset type, boundary condition on the surface of the sphere has been used. To solve the Stokes equations for the fluid velocity field and the microrotation vector, a general solution is constructed from fundamental solutions in both cylindrical, and spherical coordinate systems. Boundary conditions are satisfied first at the plane wall by the Fourier transforms and then on the sphere surface by the collocation method. The drag acting on the sphere is evaluated with good convergence. Numerical results for the hydrodynamic drag force and wall effect with respect to the micropolarity, slip parameters and the separation distance parameter between the sphere and the wall are presented both in tabular and graphical forms. Comparisons are made between the classical fluid and micropolar fluid.      

New developments of conductometric measurements in analytical biochemistry

A recently described conductometric device with precise temperature regulation is used. For determination of cholinesterase activities, different substrates were studied; with regard to the enzyme activities present in serum or in whole blood, butyrylcholine was selected for the serum assay and propionylcholine for whole blood assay. Ethanol was determined by using alcohol and aldehyde dehydrogenases with measurement of the conductance changes, mainly from the appearance of acetate ions. In the kinetic method, the relationship between the rate of conductance variation and ethanol concentration was linear in the range 0–0.2 mM.     

A SiCl4-ZnCl2 induced general, mild and efficient one-pot, three-component synthesis of β-amido ketone libraries

A general, mild and efficient protocol for the synthesis of β-amido ketone libraries was achieved utilizing tetrachlorosilane and zinc chloride in dichloromethane at ambient temperature via a one-pot, three-component condensation of various aldehydes, ketones and nitriles.     

Spectrophotometric determination of some steroid sex-hormones

Summary A detailed spectrophotometric study of the reaction of estrogens and androgens with 98% sulphuric acid at 20° C and of the effect of various dilutions with water on the nature of the spectra is presented. Dilution of the androgens-acid and estrogens-acid solutions with water to 40% and 80% v/v acid, respectively, increases the absorption intensity 3 to 11 times. The optimum conditions for determination of down to 2g/ml of estrone, estradiol, ethinylestradiol, testosterone, and rostanalone and progesterone are reported. The results show a relative standard deviation of +-1.5 %.

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Spektralphotometrische Bestimmung einiger Steroid-Sexualhormone

Zusammenfassung Die Reaktion der Östrogene und Androgene mit 98%iger Schwefelsäure bei 20° C und der Einfluß von Verdünnungen. mit Wasser auf die Art der Spektren wurden eingehend untersucht. Verdünnungen auf einen Säuregehalt von 40% und 80% bewirken eine 3–11fache Zunahme der Absorption. Die optimalen Bedingungen zur Bestimmung von >2g/ml Östron, Östradiol, Äthinylöstradiol, Testosteron, Androstanalon und Progesteron wurden ausgearbeitet. Die relative Standardabweichung beträgt+-1,5%.

     

Electron-transfer chemistry of the iron-molybdenum cofactor of nitrogenase: delocalized and localized reduced states of FeMoco which allow binding of carbon monoxide to iron and molybdenum

The electron-transfer chemistry of the isolated iron-molybdenum cofactor of nitrogenase (FeMoco) has been studied by electrochemical and spectroelectrochemical methods. Two interconverting forms of the cofactor arise from a redox-linked ligand isomerism at the terminal iron atom; this is attributed to rotamerism of an anionic N-methyl formamide ligand bound at this site. FeMoco in its EPR-silent oxidised state is shown to undergo three successive one-electron transfer steps. We argue that the first and second redox processes are associated with electron-transfer delocalised over the iron-sulfur core of the cofactor, whilst the third irreversible process is localised on molybdenum. This is strongly reinforced by spectroelectrochemical studies under (12)CO and (13)CO which reveal two independent carbon monoxide binding sites that are specifically associated with the second (iron core) and third (molybdenum) electron-transfer processes and which give rise to terminal nu((12)CO) bands at 1885 and 1920 cm(-1) respectively. Moreover, in parallel with earlier studies on the enzyme system, it is shown that at low CO concentration, carbon monoxide binds to the cofactor in bridging modes, with nu(CO) bands at 1835 and 1808 cm(-1) that are interconverted by single-electron transfer. Importantly we show that the contentious overall 2e difference in the assignment of the metal oxidation levels in the resting state of the enzyme-bound cofactor, arising from analysis of (57)Fe ENDOR and M?ssbauer data, can be resolved in the light of the electron-transfer chemistry of the isolated cofactor described herein.