Further numerical methods for the Falkner-Skan equations: Shooting and continuation techniques

We consider in this paper the numerical solution of the Falkner-Skan differential equation, modelling under some similarity assumptions the boundary layer equation. We look for the extremal solution of this third order differential equation. The methods we use are basically the Newton method with a shooting process, which is coupled with a continuation method: they allow us to follow the solution arcs which contain regular and turning point solutions.     

First observation of an iron porphyrin in heavy crude oil

Studying one of the iron richest crudes from Orinoco river region, an iron porphyrin was clearly identified for the first time in a heavy oil; its structure is DPEP type and the iron state is divalent (FeII) with low spin.     

Photoactive Cryptands. Crystal Structure of the Sodium Cryptate of the Tris(phenanthroline) Macrobicyclic Ligand

The crystal structure of the complex [phen · phen · phen] · NaBr · 2 CHCl₃ of the macrobicyclic ligand 1 has been determined. The complex is of cryptate type, the Na⁺ cation being contained in the molecular cavity of 1 and coordinated to all eight N-atoms. The ligand has a propeller shape and interconverts in solution between the two enantiomeric helical forms.     

Wide-line H NMR: a new application for the study of Brönsted acidity strength of solids with HY zeolite as example

The fitting of 4 K ¹H wide-line NMR spectra of Brönsted-acidic solid samples loaded with known amounts of water allows the determination of the concentration of the following species: H₃O⁺, H₂O…HO; and of the remaining initial species: OH and H₂O.     

Crystal Structures of the Lithium Cryptates of Two Macrobicyclic Ligands Containing Pyridine,Bipyridine, and Biisoquinoline Units

The crystal structures of the LiBr complexes of two macrobicyclic ligands, [py.py.bpy] 1 and [py.biqi.biqi] 2 , have been determined. They confirm the cryptate nature of these species. In 3 , the Li⁺ cation is bound in the shallow cavity of a ligand of flattened shape, whereas in 4 , it is buried inside the macrobicycle and surrounded by its three bridges.     

Analysis of pesticide residues in lettuce by large volume-difficult matrix introduction-gas chromatography-time of flight-mass spectrometry (LV-DMI-GC-TOF-MS)

A multi-residue method is described that eliminates the need for a clean-up step and thus allows the rapid determination of pesticides in crude extracts of lettuce. Samples were extracted with a mixture of ethyl acetate, Na2SO4 and NaHCO3 and the crude extracts analysed directly using large volume-difficult matrix introduction (LV-DMI) in combination with gas chromatography-time of flight-mass spectrometry (GC-TOF-MS). The LV-DMI procedure described was evaluated for the analysis of dimethoate, pyrimethanil, chlorothalonil, vinclozolin, furalaxyl and oxadixyl. Satisfactory response was obtained at the lowest calibrated level (LCL) of 0.0025 microg ml(-1), with good linearity over the range 0.0025-0.5 microg ml(-1) (0.005-1.0 mg kg(-1) equivalent). Average recoveries between 73 and 118% were obtained at the 0.01-0.5 mg kg(-1) levels with RSD values < or = 13%.