An extended hydrodynamic theory for particle coarsening—I: Theory

The asymptotic hydrodynamic approach to the mathematical solution of the kinetics of particle coarsening (Ostwald ripening), first proposed by Lifshitz and Slyozov and Wagner, has been extended and generalized. The coarsening rate equations in dimensionless forms have been separated into asymptotically determinate and indeterminate parts. The generalized evaluation of the asymptotically indeterminate part allows the consideration of coarsening processes that are more complicated than those involving power law type kinetics considered in previous studies. Further, the extended theory allows the determination of particle size distribution function and averaged particle coarsening kinetics even in cases where different physical processes occur at different size regimes within the same distribution of particles.     

Strip method for steady heat-conduction problems

Summary An approximate solution of heat-conduction problems can be obtained by the strip method. The method consists of an application of the finite-difference approximation in one physical coordinate and an analytic solution in other coordinates. A simple illustrative example is given and the result is compared with that obtained by the exact solution. By application of this method, an approximate solution is given for the steady heat conduction through a rectangular parallel composite wall with different rates of heat generation.     

Randomly oscillating turbulent channel flows

The velocity response to a sinusoidally oscillating pressure gradient is obtained for turbulent flow in a two-dimensional channel. The statistical relations between a spectrum of such pressure pulsations and the resulting spectrum of velocity oscillations are then written in terms of a spectral transfer function. This function, which incorporates the dynamic solution is complicated, but is well approximated with a simple expression.

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Zusammenfassung Für turbulente Strömung in einem zweidimensionalen Kanal wird die Geschwindigkeitsverteilung, die durch einen sinusoidal oszillierenden Druckgradient verursacht ist,

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Nomenclature A, B coefficients defined by comparison of Equation (1) with the appropriate dynamical equation foru - a half width of channel, or radius of pipe - b rate of increase of withy - c defined in Equation (31) - d defined in Equation (32) - f normalized spectral density of pressure oscillations - g normalized spectral density of velocity oscillations - h turbulent viscosity parameter defined in Equation (26) - I - K _n amplitude of the individual pressure oscillations - L ₁,L ₂,L ₃,L ₄,L ₅,L ₆ functions defined by Equations (18) (19) (20) (21) (24) (25) - m defined in Equation (30) - n frequency of pressure and velocity oscillations - p pressure - p _x defined in Equation (2) - R _p autocorrelation coefficient for pressure oscillations - R _u autocorrelation coefficient for velocity oscillations - t time - u axial velocity - w variable defined after Equation (15) - x axial position coordinate - y transverse position coordinate - z variable defined after Equation (15) - eddy diffusivity for momentum - dimensionless frequency, defined in Equation (7), for laminar case - _t dimensionless frequency, defined after Equation (16), for turbulent case - function defined in Equation (13) - laminar kinematic viscosity - variable displacement in time - fluid density - spectral transfer function - variable defined after Equation (16) This study was supported in part by the R. L. Albrook Hydraulic Laboratory of the Wash. State Univ. Division of Industrial Research.     

Dielectric and NMR Studies of the superionic conductor AgI embedded in mesoporous silicate matrices

This paper reports on the results of studies of small particles of the superionic conductor AgI embedded in MCM-41 and SBA-15 molecular sieves with different sizes of pores (channels). The studies are performed by the dielectric and nuclear magnetic resonance techniques. The temperature of the superionic phase transition is shown to increase monotonically with decreasing pore size. The enthalpy of activation of the ion motion in β-AgI in restricted geometry is determined. It is shown that introduction of AgI into pores does not noticeably affect its structure.     

Carboxyboronate: A Versatile C1 Building Block

The synthesis and applications of carboxy‐MIDA‐boronate, a novel C1 building block, are described. This molecule is accessible via a ruthenium tetraoxide‐mediated cleavage of commercially available ethynyl‐MIDA‐boronate. In the course of this study, carboxy‐MIDA‐boronate was found to possess ambident reactivity towards nucleophiles. Carboxylic acid derivatization produces a broad range of previously unknown carbamoyl‐, oxycarbo‐ and thiocarboboronates. Carboxy‐MIDA‐boronate and its derivatives undergo condensations to access borylated heterocycles with boron at positions that are difficult to access using alternate methods. The resulting heterocycles participate in the Suzuki–Miyaura cross‐coupling reaction, enabling entry into diverse bis(heteroaryl) motifs. The carbon monoxide‐releasing capacity of carboxy‐MIDA‐boronate was also examined and applied in palladium‐catalyzed carbonylation.     

Synthesis and Magnetic Characteristics of Neodymium Ferrite Powders with Perovskite Structure

Russian Journal of Applied Chemistry - Nanopowders of neodymium ferrite with perovskite structure were synthesized by co-precipitation precipitation via hydrolysis of iron(III) and neodymium(III)...     

Low-field magnetoresistance of Ag-substituted perovskite-type manganites

A series of bulk polycrystalline Nd_1−xAg_xMnO₃ samples were prepared by conventional solid-state reaction processing, for x between 0.1 and 0.5. The structure, magnetism, and magnetoresistance (MR) of the samples are investigated. The X-ray diffraction patterns show that the x=0.1 sample is a single perovskite structure, while x0.167, samples consist of a ferromagnetic perovskite phase and two nonmagnetic phases, Ag and Mn₃O₄. The MR of Nd_1−xAg_xMnO₃ is enhanced by increasing the composition of Ag. Compared with the sample of x=0.1, the x=0.5 sample has a significantly larger value of low-field MR. The enhanced low-field MR is related to the spin-dependent scattering of spin-polarized electrons at the interfaces between the perovskite grains and silver granules.     

Chemical immobilization of crosslinked polymeric ionic liquids on nitinol wires produces highly robust sorbent coatings for solid-phase microextraction

Super elastic nitinol (NiTi) wires were exploited as highly robust supports for three distinct crosslinked polymeric ionic liquid (PIL)-based coatings in solid-phase microextraction (SPME). The oxidation of NiTi wires in a boiling (30% w/w) H₂O₂ solution and subsequent derivatization in vinyltrimethoxysilane (VTMS) allowed for vinyl moieties to be appended to the surface of the support. UV-initiated on-fiber copolymerization of the vinyl-substituted NiTi support with monocationic ionic liquid (IL) monomers and dicationic IL crosslinkers produced a crosslinked PIL-based network that was covalently attached to the NiTi wire. This alteration alleviated receding of the coating from the support, which was observed for an analogous crosslinked PIL applied on unmodified NiTi wires. A series of demanding extraction conditions, including extreme pH, pre-exposure to pure organic solvents, and high temperatures, were applied to investigate the versatility and robustness of the fibers. Acceptable precision of the model analytes was obtained for all fibers under these conditions. Method validation by examining the relative recovery of a homologous group of phthalate esters (PAEs) was performed in drip-brewed coffee (maintained at 60 °C) by direct immersion SPME. Acceptable recoveries were obtained for most PAEs in the part-per-billion level, even in this exceedingly harsh and complex matrix.