Two-dimensional computational simulation of eccentric annular cementing displacements

We consider a two-dimensional Hele–Shaw type model fordisplacement flows occurring in the primary cementing of anoil well. The fluids are visco-plastic and may get stuck inthe annulus if a critical pressure gradient is not exceeded.The model consists of solving a nonlinear elliptic variationalinequality equation for the stream function, coupled to an equationfor interface advection, or alternatively a concentration equationfor the mass fraction of each fluid. The key difficulty is toaccurately compute yielded and unyielded zones of the wellborefluids, which we accomplish by use of an augmented Lagrangianmethod to solve the stream function equation. We validate theaccuracy of our method against analytical solutions for stablesteady-state displacements. We study the convergence of theinterface to the steady state, showing that the apparent meta-stabilityis illusory. We then explore the effects of increasing eccentricity,showing that although the interface may remain stable it becomesunsteady. Initially fully mobile flows are found, but as theeccentricity increases further the narrow side fluids fail tomove in the far field. The narrow side interface can progressslowly through the static fluids by a burrowing motion, butfor still larger eccentricities even the interface becomes staticand a narrow-side mud channel forms.     

Laser Tunable Source for the Red and Near UV Regions of the Spectrum

The spectral and lasing characteristics of a number of dyes for the red and near IR portions of the lasing spectrum in laser and lamp pumpings are investigated. Smooth tuning of a pulse-periodic lamp-pumped laser in the 660–720 nm range and generation of its second harmonic in the 330–360 nm region were obtained. As a result, the radiation range of the earlier developed tunable laser source has been extended in the red and near UV regions of the spectrum. The use of mixtures of dyes and proton-donating additives in working solutions has substantially improved the energy characteristics of this source.     

Mechanism of oxygen transfer in layered lanthanide nickelates Ln2 − x NiO4 + δ (Ln = La, Pr) and their nanocomposites with Ce0.9Gd0.1O2 − δ and Y2(Ti0.8Zr0.2)1.6Mn0.4O7 − δ solid electrolytes

The mechanism of oxygen transfer in layered nickelates having a Ruddlesden-Popper structure and their nanocomposites with Ce_0.9Gd_0.1O_{2 ? δ} (GDC) and Y₂(Ti_0.8Zr_0.2)_1.6Mn_0.4O_{7 ? δ} (YTZM) solid electrolytes having fluorite and pyrochlore structures were studied by the oxygen isotope heteroexchange method in a flow and static reactor, thermoprogrammed desorption, and semiempirical interacting bonds method. The experimental heteroexchange data were adequately described by assuming that all atoms were equivalent in exchange in the bulk of layered nickelates, which was consistent with the cooperative oxygen migration model with fast exchange between the interstitial and regular positions. Strong interaction between the domains of the nickelate phases and solid electrolytes in nanocomposites, accompanied by a redistribution of cations between the phases, hindered the cooperative oxygen migration and led to a decrease in the diffusion coefficient as the exchange rate increased.     

On the thermal oxidation of V<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>–InP heterostructures formed by the centrifugation of vanadium(V) oxide gel

The optimal mode for the application of a nanoscale layer of vanadium-pentoxide gel on the surface of indium phosphide by centrifugation is determined via spectroscopic ellipsometry and atomic-force microscopy. By oxidizing the formed V _x Oy—InP heterostructures, films are obtained with a grain structure, with the height of the relief not exceeding 70 nm. The presence of incompletely oxidized chemostimulator components (VO₂, V₂O₃) in the films and the presence of InVO₄, which binds the V₂O₅ chemostimulator and thereby blocks the regeneration cycle of V⁺⁵ ? V⁺⁴, suggest implementation of the transit mechanism of the chemostimulated oxidation of indium phosphide. The data of spectroscopic ellipsometry indicate incomplete kinetic blocking of the diffusion of indium into the films upon oxidation.     

The role of rheology of polymer solutions in predicting nanofiber formation by electrospinning

Electrospun polymer nanofibers are gaining increasing importance in tissue engineering, wound dressing and drug delivery. Here, we present a thorough rheological study of polymer solutions in the bulk and at the interface to find correlations between those properties and the electrospinnability of the solutions and the morphology of the resultant nanofibers. Our results indicate that blended solutions of chitosan or alginate with poly(ethylene oxide) (PEO) are appropriate for electrospinning when they form conductive, unstructured fluids displaying plasticity, rather than elasticity, in the bulk and at the interface. The interfacial rheological parameters are three orders of magnitude lower than those in the bulk. We demonstrate for the first time that interfacial, rather than bulk, rheological parameters show improved correlation and can be used to predict the success of the electrospinning process. Using the interfacial parameters of samples with homologous compositions, different groups of solutions can be identified that form smooth nanofibers. However, rheological parameters of the bulk and at the interface provide complimentary information. The bulk parameters are determined by polymer concentration and directly affect jet initiation, while the interfacial behaviour determines the continuation of the jet and fibre formation. We propose that interfacial parameters are indispensible tools for the design of electrospinning experiments.     

A geometric interpretation of stationary-wave type solutions of the sine-Gordon equation

Using the connection of solutions of the sine-Gordon equationz _xy =sinz with the construction of a grid of asymptotic lines on surfaces of constant negative curvature inE ³ we show that those surfaces and only those that have curvature –1 and any two asymptotic lines of a single family of which are congruent correspond to solutions of stationary-wave typez=z(x+by).Translated from Ukrainskií Geometricheskií Sbornik, No. 30, 1987, pp. 81–87.     

Evolution of the Cu/ZnO methanol synthesis catalyst during its reduction and re-oxidation

Summary Cu K EXAFS studies of the structure of Cu-Zn oxide catalyst were performed for the as prepared samples, those after its activation by hydrogen and after its subsequent re-oxidation. It was found that during the primary formation of the CuZnO solid solution, the copper ions are dissolved in the extended stacking faults of the ZnO lattice as ultra-small oxide clusters. Activation by hydrogen at 473 K leads to the reduction of most copper cations to Cu⁰with the formation of nanoparticles with the characteristic size of ca. 1.6 nm. The copper metal particles were re-oxidized to Cu²⁺at 523 K in<span lang=EN-US style='mso-ansi-language:EN-US'>ahelium flow containing 0.05 vol. % oxygen. The re-oxidized cations do not form a CuO phase. Instead, they return to the extended stacking faults of ZnO. However, this time they form stripe-like clusters of square-planar coordinated copper cations.