Combined compact difference method for solving the incompressible Navier–Stokes equations

This paper presents a numerical method for solving the two‐dimensional unsteady incompressible Navier–Stokes equations in a vorticity–velocity formulation. The method is applicable for simulating the nonlinear wave interaction in a two‐dimensional boundary layer flow. It is based on combined compact difference schemes of up to 12th order for discretization of the spatial derivatives on equidistant grids and a fourth‐order five‐ to six‐alternating‐stage Runge–Kutta method for temporal integration. The spatial and temporal schemes are optimized together for the first derivative in a downstream direction to achieve a better spectral resolution. In this method, the dispersion and dissipation errors have been minimized to simulate physical waves accurately. At the same time, the schemes can efficiently suppress numerical grid‐mesh oscillations. The results of test calculations on coarse grids are in good agreement with the linear stability theory and comparable with other works. The accuracy and the efficiency of the current code indicate its potential to be extended to three‐dimensional cases in which full boundary layer transition happens. Copyright © 2011 John Wiley & Sons, Ltd.     

Non-monotonic response of waxy oil gel strength to cooling rate

The oil at high temperatures in the reservoir loses heat to the surroundings and is submitted to different shear stresses while it is produced and transported. Thermal and shear histories have great influence on the rheological characteristics of waxy oils at low temperature. Wax crystals precipitate during cooling, building up a percolated matrix that entraps the oil and consequently, forms a gel-like structure. One of the main parameters that affect the crystals’ morphology and therefore the gel strength is the cooling rate. Although the oil static cooling has been widely studied in the literature, many questions are still open. The current work analyzes the influence of the cooling rate on the gel strength and on the dynamic moduli (G′ and G″) of a waxy model oil. Microscopic images of wax crystals were obtained and a hypothesis to explain the non-monotonic response of the rheological parameters as a function of the cooling rate is proposed based on the crystals’ morphology.     

Rhodium‐Catalyzed Annulation of ortho‐Alkenyl Anilides with Alkynes: Formation of Unexpected Naphthalene Adducts

o‐Alkenyl N‐triflylanilides underwent rhodium(III)‐catalyzed oxidative annulations with alkynes to produce different types of naphthylamides in a process which involves the cleavage of two C?H bonds. Remarkably, besides formal dehydrogenative (4C+2C) cycloadducts, the reaction also produces variable amounts of isomeric naphthylamides, whose formation requires a formal migration of the alkenyl moiety from the ortho to the meta position of the anilide. The annulation reaction can be efficiently carried out in the absence of external oxidants, such as Cu(OAc)₂.     

Kinetic and thermodynamic studies of aquation reactions in [RuL2(mac)]q+ complexes: [mac = 1,4,8,11-tetraazacyclotetradecane (cyclam) or 1,4,7,10-tetraazacyclododecane (cyclen); and L = Cl−, OH−, OH2]

Transition Metal Chemistry - We report here the synthesis, characterization and kinetic studies of [RuL2(mac)]n+ complexes [mac?=?1,4,8,11-tetraazacyclotetradecane (cyclam) or...     

Modeling of functionally graded piezoelectric ultrasonic transducers

The application of functionally graded material (FGM) concept to piezoelectric transducers allows the design of composite transducers without interfaces, due to the continuous change of property values. Thus, large improvements can be achieved, as reduction of stress concentration, increasing of bonding strength, and bandwidth. This work proposes to design and to model FGM piezoelectric transducers and to compare their performance with non-FGM ones. Analytical and finite element (FE) modeling of FGM piezoelectric transducers radiating a plane pressure wave in fluid medium are developed and their results are compared. The ANSYS software is used for the FE modeling. The analytical model is based on FGM-equivalent acoustic transmission-line model, which is implemented using MATLAB software. Two cases are considered: (i) the transducer emits a pressure wave in water and it is composed of a graded piezoceramic disk, and backing and matching layers made of homogeneous materials; (ii) the transducer has no backing and matching layer; in this case, no external load is simulated. Time and frequency pressure responses are obtained through a transient analysis. The material properties are graded along thickness direction. Linear and exponential gradation functions are implemented to illustrate the influence of gradation on the transducer pressure response, electrical impedance, and resonance frequencies.     

Causal groups of space-time

The present paper is concerned with a finite dimensional space, considered as a real ordered linear space, directed with respect to a partial ordering relation (causal relation) in which a given reflexion (called temporal inversion) is antiisotone and the positive cone is closed in the euclidean topology.A generalized Zeeman theorem [1] is obtained, which states that the causal group relative to the causal relation is a subgroup of the affine group ofM.     

Traces of convex domains

Diederich and Ohsawa proved that in there exists a locally hyperconvex, Stein open subset which is not hyperconvex. In this paper we generalize their results.

     

Characterization and thermal stability study of efavirenz and solid dispersion with PVPVA 64 by means of thermal analysis and pyrolysis coupled with GC/MS

Journal of Thermal Analysis and Calorimetry - The acquired immunodeficiency syndrome remains a major problem in worldwide public health and its antiretroviral treatment therapy combines at least...     

On the Existence of Tree Backbones that Realize the Chromatic Number on a Backbone Coloring

A proper k‐coloring of a graph is a function such that , for every . The chromatic number is the minimum k such that there exists a proper k‐coloring of G. Given a spanning subgraph H of G, a q‐backbone k‐coloring of is a proper k‐coloring c of such that , for every edge . The q‐backbone chromatic number is the smallest k for which there exists a q‐backbone k‐coloring of . In this work, we show that every connected graph G has a spanning tree T such that , and that this value is the best possible. As a direct consequence, we get that every connected graph G has a spanning tree T for which , if , or , otherwise. Thus, by applying the Four Color Theorem, we have that every connected nonbipartite planar graph G has a spanning tree T such that . This settles a question by Wang, Bu, Montassier, and Raspaud (J Combin Optim 23(1) (2012), 79–93), and generalizes a number of previous partial results to their question.     

On a problem of Bremermann concerning Runge domains

In this paper we give an example of a bounded Stein domain in , with smooth boundary, which is not Runge and whose intersection with every complex line is simply connected.This work was supported by Marie Curie International Reintegration Grant no. 013023 and by the Romanian Ministry of Education and Research grant 2-CEx06-11-10/25.07.06.