A computational study of supersonic combustion behind a wedge-shaped flameholder

In this study, large eddy simulation (LES) has been used to examine supersonic flow, mixing, self-ignition and combustion in a model scramjet combustor and has been compared against the experimental data. The LES model is based on an unstructured finite-volume discretization, using monotonicity-preserving flux reconstruction of the filtered mass, momentum, species and energy equations. Both a two-step and a seven-step hydrogen–air mechanism are used to describe the chemical reactions. Additional comparisons are made with results from a previously presented flamelet model. The subgrid flow terms are modeled using a mixed model, whereas the subgrid turbulence–chemistry interaction terms are modeled using the partially stirred reactor model. Simulations are carried out on a scramjet model experimentally studied at Deutsches Zentrum für Luft- und Raumfahrt consisting of a one-sided divergent channel with a wedge-shaped flame holder at the base of which hydrogen is injected. The LES predictions are compared with experimental data for velocity, temperature, wall pressure at different cross sections as well as schlieren images, showing good agreement for both first- and second-order statistics. In addition, the LES results are used to illustrate and explain the intrinsic flow, and mixing and combustion features of this combustor.     

Extraction of plutonium from sulphuric acid by TOA in toluene

The extraction of plutonium(VI) and plutonium(III) from sulphuric acid by TOA in toluene has been studied as a function of the acid and tri-octyl amine concentration. A comparison of the extraction properties of plutonium with those of uranium(VI) and uranium(IV) has been made. It was found that the extraction properties of plutonium(VI) are very similar to those of uranium(VI) and that TOA is a relatively poor extractant for plutonium(III). Uranium(IV) shows better extraction properties than plutonium(III). The results obtained are considered in the light of the stabilities of the complexes formed by these elements in the organic and aqueous phase. A method of separation of both elements by solvent extraction based on changing their oxidation states is suggested.     

Instability of the distribution of atomic steps on Si(111) upon submonolayer gold adsorption at high temperatures

The gold adsorption effect on the distribution of monatomic steps on the (111) silicon surface is studied in situ by ultrahigh vacuum reflection electron microscopy at temperatures of 850–1260°C. A new effect of the instability of silicon surface morphology has been detected. This effect leads to the redistribution of regular steps (RSs) to step bunches (STs) and vice versa on a surface covered with a gold submonolayer. For the crystal heated by directly passing an electric current, the behavior of the RS ? SB morphological transitions on the silicon surface is investigated as a function of the gold coverage and the direction of the heating current. Thus, isothermal annealing at 900°C is accompanied by the following transitions on the silicon surface with predeposited 0.75 monolayer gold coverage: RS (0.72) ? SB (0.42) ? RS (0.24) ? SB (0.07) RS ? (0). The numbers given in parentheses are estimated values of the critical gold coverage measured in the monolayers at which the morphological transitions are observed. A change in the direction of the electric current used to heat the crystal leads to the reversible changes RS ? SB and SB ? RS at the same values of the critical gold coverage.     

Rapid Screening and Determination of Residual Veterinary Drugs in Milk by Ultrahigh Performance Liquid Chromatography–High-Resolution Quadrupole Time-of-Flight Mass Spectrometry

A rapid screening and determination of 150 veterinary drugs of various classes in milk by UHPLC–high-resolution quadrupole time-of-flight mass spectrometry is proposed. One gram of milk was used for the analysis; the precipitation of proteins and extraction were performed with acetonitrile; the extract was analyzed without purification or preconcentration. Veterinary drugs were identified by accurate masses of analyte ions produced by electrospray ionization, their retention time, and the pattern of ion isotope distribution (mSigma). The quantitative analysis of the detected analytes was carried out by the standard addition method. The limits of detection were 0.1–0.5 ng/g; the analytical ranges were (0.1)1–500 ng/g; the duration of screening was 20–30 min; and the analysis time was 30–40 min. The relative standard deviation of the results for all analytes did not exceed 15%.     

Extended Defects in O+-Implanted Si Layers and Their Luminescence

Crystallography Reports - The structure and luminescence properties of Czochralski-grown n-Si samples implanted with oxygen ions have been comprehensively analyzed using photoluminescence and...     

Synthesis of hexasaccharide fragment of lipoarabonomannan from Mycobacteria: advantages of the benzyl-free approach

Russian Chemical Bulletin - Spacered branched hexaarabinofuranoside, which corresponds to the terminal fragment of mycobacterial lipoarabinomannan and arabinogalactan, was synthesized via three...     

Self‐Similar Solution of the Antiplane Shear Fracture Problem in a Coupled Formulation (Creep–Damage)

A growing antiplane shear crack in a damaged medium is considered. It is assumed that the crack tip neighbors a region of completely damaged material, in which all stress tensor components and the continuity parameter vanish. The stress–strained state is analyzed and the configuration of the region of completely damaged material is determined. The crack growth rate is estimated for various values of the constants included in the constitutive relations and kinetic equation.