Spherical Particle in Nematic Liquid Crystal Under an External Field: The Saturn Ring Regime

We consider a nematic liquid crystal occupying the exterior region in \({\mathbb {R}}^3\) outside of a spherical particle, with radial strong anchoring. Within the context of the Landau-de Gennes theory, we study minimizers subject to an external field, modeled by an additional term which favors nematic alignment parallel to the field. When the external field is high enough, we obtain a scaling law for the energy. The energy scale corresponds to minimizers concentrating their energy in a boundary layer around the particle, with quadrupolar symmetry. This suggests the presence of a Saturn ring defect around the particle, rather than a dipolar director field typical of a point defect.     

Ueber die Sj?qvist'sche Methode zur Bestimmung der freien Salzs?ure im Magensaft

Ohne Zusammenfassung     

Gas-chromatographic determination of traces of <Emphasis Type="Italic">O</Emphasis>-isopropyl methylphosphonofluoridate (sarin) in soils using its diastereomers

A procedure was developed for determining traces of O-isopropyl methylphosphonofluoridate (sarin) in soils at a level of 2 × 10⁻⁴ mg/kg. The procedure is based on solvent extraction with a hexane-benzene mixture, the preconcentration of the extract to a small volume, the synthesis of dialkyl esters using secondary alcohol aluminates, and gas-chromatographic separation on an HP-1 column with a flame ionization detector. The determination error does not exceed 29%; the time of analysis is 1 h.     

Plasma-induced deposition of thin films of aluminum oxide

Plasma-induced deposition of wear-protecting A1₂O₃ films has been investigated for two different gas mixtures, one of which is ususally used in thermal CVD. It is shown that, contrary to thermal CVO, the properties of thin films deposited from an AlCl₃/O₂/Ar mixture are superior to those prepared from AICl₃/CO₂/H₂. High Vickers hardness of 1800-2500 and a low chlorine content of 0.7 at. % have been obtained in films deposited from an AICl₃/O₂/Ar mixture at a substrate temperature of 500°C.     

CAPA--Computer Aided Pesticide Analysis. Computer program for the automated evaluation of chromatographic data for residue analysis of foods

Pesticide residue analysis in food by means of gas chromatography with columns of different polarity and several selective detectors provides the analyst with a great number of chromatographic data. The introduction of personal computer based chromatographic data systems into research laboratories increased the efficiency of information management and organization; user designed software packages now have direct access to the stored data. The computer program CAPA (Computer Aided Pesticide Analysis) was developed for the interpretation and evaluation of chromatographic results. The program is written in TURBO PASCAL 3.0 and consists of several subprograms. In the main database all pesticides are filed in a multidimensional structure. The various subprograms have access to this catalog of retention and response data. Using the subprogram INTERPRET, which is the core of CAPA, the analyst is provided with all information necessary to interpret a gas chromatogram: identification of calibrated pesticides and estimation of their concentration. Automated screening analyses can be evaluated with the subprogram AUTOINTERPRET, an automated of INTERPRET that uses all relevant information stored in the data base. A report is produced containing the pesticides found in the sample and proposals how to confirm them best with the equipment and methods available. Finally the analyst has to make the decision about the probable presence and quantity of the indicated pesticides and to project the next confirmatory step by using INTERPRET.     

Asymptotic partition of energy in linear generalized thermoelasticity

Summary The asymptotic partition of energy is investigated within the context of linear theory of thermoelasticity proposed by Green and Lindsay in [1]. The asymptotic equipartition occurs between the Cesàro means of the kinetic and strain energies.

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Résumé On étudie la partition asymptotique de l'énergie dans la théorie linéaire de la thermoélasticité proposée par Green et Lindsay [1]. L'équipartition asymptotique a lieu entre les moyens Cesàro des énergies cinétiques et de déformation.

     

Pesticide residue analysis in food with CGC — study of long-term stability by the use of different injection techniques

An experiment was designed to study the long-term stability of analyses of pesticide residues in a complex food matrix using three different injection techniques. A spinach sample was spiked with five sulfur-containing pesticides of varying volatility and thermolability: azinphos-ethyl, dimethoate, methiocarb, ethiofencarb, and tri-allate. Tri-allate was selected as internal standard because of its thermal stability and its good chromatographic properties. Flame photometric detection resulted in chromatograms not subject to interference by peaks of compounds of the matrix. Starting with a clean and freshly, silanized injector an additional deactivation was found to occur on the first injection of a food sample resulting in an increased peak area for all pesticides in relation to tri-allate. Highest long-term stability was found with PTV injection. Best results for thermolabile carbamates were obtained using on-column injection. However, they were prone to faster deterioration.     

Pesticide residue analysis in foodstuffs applying capillary gas chromatography with atomic emission detection State-of-the-art use of modified multimethod S19 of the Deutsche Forschungsgemeinschaft and automated large-volume injection with programmed-temperature vaporization and solvent venting

Atomic emission detection (AED) provides high element-specific detection of all compounds amenable to gas chromatography (GC). The heteroatoms nitrogen, chlorine, phosphorus, sulfur, bromine and fluorine, which are important elements in pesticide residue analysis, are of major interest. A main drawback of AED is its lower sensitivity with respect to other selective detection methods used in pesticide residue analysis such as electron-capture and nitrogen-phosphorus detection. This holds true especially for the important nitrogen trace. For this reason, more sensitive detection can be achieved by injection of larger volumes or higher concentrations of sample extracts, because matrix compounds were usually registered only in the carbon, hydrogen and oxygen traces. This paper focuses on recent developments from the authors' laboratory in order to demonstrate the feasibility of screening analyses with the identification of pesticide residues down to the 0.01 ppm concentration level in plant foodstuffs. This has been achieved by means of automated large volume injection with programmed-temperature vaporization and solvent venting as well as careful optimization of make-up and reactant gases with AED. Clean up follows the principle of multimethod S19 of the Deutsche Forschungsgemeinschaft in a reduced procedure. After elimination of lipids and waxes by gel permeation chromatography, extracts from 10 g of the food samples were concentrated to 200 μl, of which 12.5 μl were introduced into the GC-AED system. Two analyses were usually performed with the element traces of sulfur, phosphorus, nitrogen and carbon in the first run and chlorine and bromine in the second run. Fluorine and oxygen were not detected in any screening analyses. The method has proved to be of great value especially with “problem foodstuffs”. The limits of detection were determined for 385 pesticides and are presented together with their retention data.