On Spherically Symmetric Minimally Coupled Brane Worlds

For a static, spherically symmetric brane in the framework of the RS2 concept, we study the conditions under which the 4D tensor E _v, arising from the 5D Weyl tensor, vanishes on the brane. Gravity on the brane is then decoupled from the bulk geometry, it is the so-called minimally coupled brane world (MCBW). Assuming E _v =0 in the whole bulk, we try to solve the 5D Einstein equations G _AB + _5gAB =0 and obtain an overdetermined set of equations for functions of the radial coordinate. Some special solutions are found, among which are the well-known black string solution with the Schwarzschild metric on the brane and its generalizations with Schwarzschild–(A)dS on-brane metrics. It is concluded that a MCBW can be embedded, in general, in a bulk where E_v is not identically zero but only vanishes on the brane. We also present some previous results on the general properties of scalar fields on the brane and give an example of a wormhole supported by a scalar field in a MCBW.     

Design of coke-free methane dry reforming catalysts by molecular tuning of nitrogen-rich combustion precursors

The valorization of methane and carbon dioxide is a promising solution for mitigating global warming. The dry reforming of methane (DRM) is capable of concomitant conversion of these greenhouse gases into starting materials for production of synthetic fuels, promoting a carbon neutral avenue for fuel production. The development of efficient, stable, and economic catalysts presents a challenge owing to the comparatively rapid deactivation of DRM catalysts under reaction conditions. Here, Ni/La₂O₃ DRM catalysts are prepared by combustion synthesis of Ni and La complexes of nitrogen-rich precursors. We expound the relationship between structures of the combustion precursors, the thermochemistry of their combustion, the structures of the resultant Ni/La₂O₃ catalysts, and their performance under DRM conditions. We show that the best catalyst is derived from energetic precursor which has the sharpest exotherm and rapidly releases the largest amounts of nitrogen gas. These properties give rise to the crystallization of the Ni/La₂O₃ catalyst with high Ni dispersion and strong metal-support interactions. This work can act as starting point to expand the link between the chemistry of combustion precursors and the resulting catalyst properties, eventually realizing the rational design of high-performance catalysts prepared by combustion synthesis through tailoring the chemistry and structure of the nitrogen-rich precursors.     

Effect of longitudinal riblets on axisymmetric body drag

The results of comparative gravimetric measurements of the total drag on an axisymmetric body with a smooth and ribbed cylindrical surface are described. The experiments were carried out in a closed wind tunnel at initial tunnel circuit pressures equal to 0.5 and 1 absolute atmosphere with artificially generated model boundary layer turbulence. The free-stream Mach number was varied on the range from 0.15 to 0.85, the Reynolds number Re, calculated from the model length, on the range 4·10⁶–30·10⁶, and the angle of attack on the range from 0 to 12°. The maximum total drag advantage obtained with the ribbed model was 8%. A significant fraction of the drag reduction achieved may be associated with the effect of the ribbing on the drag created by the smooth tail of the body.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.2, pp. 174–178, March–April, 1992.     

Synthesis,hypolipidemic and antifungal activity of tetrahydroberberrubine sulfonates

The paper describes the synthesis of new tetrahydroberberrubine derivatives containing polyfl uorophenyl- or alkylsulfonate groups at the O(9) position as well as those containing or not containing a bromine atom at the C(12) position. In a model of acute Triton-induced hyperlipidemia, tetrahydroberberrubine 9-O-(heptafluoro-4’-toluene)sulfonate was shown to reduce the cholesterol level by 23.5%, which is comparable with the eff ect of Simvastatin. At a concentration of 32 μg mL^?1, tetrahydroberberrubine 9-O-pentafluorobenzenesulfonate inhibits the growth of the fungus Cryptococcus neoformans by 81.3±3.5%.

     

Model for Thermal Oxidation of Silicon

Technical Physics - Nanometer-thick silicon oxide films are needed for miniaturization and increase in the working rate of electronic devices. Interpretation of the initial stages of silicon...     

Highly-ordered layered organo-mineral materials prepared via reactions of n-alkylphosphonic acids with apatite

This work describes a novel class of layered organo-mineral materials manufactured via a single-step solution-phase reaction of n-alkylphosphonic acids (CnH(2n+1)P(O)(OH)2) with calcium hydroxyapatite mineral (CaHAP). TEM, SAXS, WAXS, FTIR, and Vapor Phase Adsorption data suggest that these alkyl-CaHAP materials present a surface-modified CaHAP matrix coated with ordered layers of calcium alkylphosphonates that are strongly adhered to the surface. Interlayer spacing increases from 1.47 (C3-CaHAP) to 4.77 nm (C18-CaHAP). According to FTIR, ordering of alkyl chains improves with the alkyl chain length. The organic loads in these alkyl-CaHAP can be controlled over a wide range (up to approximately 60%) by varying alkyl chain and the concentration of alkylphosphonic acids in the solution.     

Experimental determination of features of sound propagation in a shallow pond with an ice layer

An experiment on sound propagation in a shallow natural pond covered with an ice layer is described. The results from processing the experimental data are presented. It is found that the sound propagates along the ice-covered water layer and at the pond’s bottom. The corresponding velocities are determined.     

Study of a one-dimensional model,accounting for cell division,of regulation of the renewing zone size in a biological tissue

We describe the modeling of the dynamics of renewing zone structure in biological tissues in the formalism of parameterized L-systems on an example of the shoot apical meristem. Under study is the influence of the ratio of the characteristic times of the cell cycle and diffusion of morphogens on the stability of some spatially distributed molecular-genetic control system. We show that cell division is a perturbing factor for the system regulating the renewing zone structure. Some conditions are found for the loss of stability of the regulation.