Topology of vortex creation in the cylinder wake

We analyze the topology of the two-dimensional flow around a circular cylinder at moderate Reynolds numbers in the regime where the vortex wake is created. A normal form for the stream function close to the cylinder is presented and used to predict the streamline pattern both in the steady and the periodic regime, where two different vortex shedding scenarios are identified. The theoretical predictions are verified numerically. For the vorticity, a very different topology occurs with infinite nested sequences of iso-curves moving downstream. General equations of motion for critical points are derived.     

Trimethylsilylcyanation of heterocyclic imines catalysed by Lewis acids

The addition of Me₃SiCN to Schiff bases 1a–8a, synthesized by the reaction of furan and thiophene aldehydes with 3‐ and 4‐aminobenzotrifluorides, has been studied in the presence of various Lewis acids. A series of the corresponding trifluoromethyl derivatives of heterocyclic α‐aminonitriles 1–8 was synthesized in 38–80% isolated yields. It was found that 4A molecular sieves (MS) accelerate the addition and increase the yields of the products. The investigated catalysts are ranked by their activity in the following order: AlBr₃ + 4AMS > AlBr₃ > AlCl₃ > Ti[O(iPr)]₄. A single crystal of N‐(5‐methyl‐2‐thienylcyanomethyl)‐3‐trifluoromethylaniline was obtained and studied by X‐ray diffraction. The results showed that it was the crystal of the (R) isomer of this compound. Copyright © 2000 John Wiley & Sons, Ltd.     

Stratifications on the Ran Space

We describe a partial order on finite simplicial complexes. This partial order provides a poset stratification of the product of the Ran space of a metric space and the nonnegative real numbers, through the ?ech simplicial complex. We show that paths in this product space respecting its stratification induce simplicial maps between the endpoints of the path.

     

DTC ultrafilters on groups

Semigroup Forum - We say that an ultrafilter on an infinite group G is DTC if it determines the topological centre of the semigroup $$\beta G$$ . If G has a subgroup of finite index in which...     

Modular approach to functional hyaluronic acid hydrogels using orthogonal chemical reactions

A modular approach for the synthesis of hyaluronic acid hydrogels using orthogonal chemoselective reactions for subsequent enzymatic decomposition to nanoparticles is described.     

A review on the thermal stability of calcium apatites

High temperature processing is essential for the preparation of apatites for biomaterials, lighting, waste removal and other applications. This requires a good understanding of the thermal stability and transitions upon heating. The most widely used is hydroxyapatite (HAp), but increasing interest is being directed to fluorapatite (FAp) and chlorapatite (ClAp). The structural modifications for substitutions are discussed to understand the temperature processing range for the different apatites. This is based on a review of the literature from the past few decades, together with recent research results. Apatite thermal stability is mainly determined by the stoichiometry (Ca/P ratio and structural substitutions) and the gas composition during heating. Thermal stability is lowered the most by a substitution of calcium and phosphate, leading to loss in phase stability at temperatures less than 900?°C. The anions in the hexagonal axis, OH in HAp, F in FAp and Cl in ClAp are the last to leave upon heating, and prevention of the loss of these groups ensures high temperature stability. The information discussed here will assist in understanding the changes of apatites during heating in calcination, sintering, hydrothermal processing, plasma spraying, flame pyrolysis, and other high-temperature processes.