Modelling methane migration in soil

Based on Bear-Bachmat porous medium model, the governing equations for the migration of gases through soil from a buried source are presented. A finite element solution system for the equations is developed. The resulting model is capable of incorporating medium anistropy and inhomogeneity in an axisymmetric configuration. The model has facilities for including time-varying fluid properties and boundary conditions. Convergence of the solution is examined. Potential applications for the modelling of gas migration from waste burial sites and the evaluation of control mechanisms are discussed.     

Fabrication of an ion-selective electrode for determination of propylhexedrine

Electrodes of both conventional and micro-sizes were based on the use of propylhexedrine-reineckate as the ion-exchanger in a plastic membrane. The electrodes exhibited Nernstian response towards propylhexedrine (PX) over the concentration range 10^–6–10^–2 M and had life spans of up to 2 days continuous work. The working pH range was 2.3–8. Investigation of diverseions reveals good selectivity for propylhexedrine over several inorganic cations, amines, aminoacids, sugars and some pharmaceutical compounds. The electrode was applied for determination of the drug in urine with 99.1% recovery and 0.15–0.31% relative standard deviation.     

Electromagnetic field representation in the source region

Representation of electromagnetic fields in the source region in inhomogeneous anisotropic media is developed in terms of Hertz vectors. Differential equations satisfied by these vectors as functions of stream potentials of the sources are obtained. Conditions for representation in terms of uncoupled transverse electric and magnetic modes satisfying second-order differential equations are derived.     

Synthesis of a carbon-14 analogue of aryl N-alkoxycarbamates and its application for synthesis of unsymmetrical N,N′-urea derivatives

Aryl N-alkoxycarbamates labeled with carbon-14 have been synthesized from aryl nitrile-[cyano-¹⁴C] as part of a 2-step sequence. The resulted carbamates were treated with amines, generating [carbonyl-¹⁴C]-Ureas in high yield and purity.     

Catalytic Kinetic Determination of Trace Amounts of Palladium with Photometric Detection

 A new, simple photometric method for the determination of palladium was described. Palladium was determined photometrically at 600 nm and pH = 5.4 based on its heterogeneous catalytic effect on the reduction of thionine (TN) with hypophosphite (HP) using a probe-type photometer system (variable time method). The influence of reaction variables was discussed. The calibration curve was found linear in the range 0.11–5.55 μg/ml (at 30 °C) and the detection limit was 0.06 μg/ml. The relative standard deviation of the developed method was 1.6% (for 10 replicate determinations of 2.22 μg/ml Pd(II)). The effect of interference from other metal ions and anions was studied. The proposed method was successfully applied to catalysts, Pd–C, Al–Si–Pd (new and used). Received March 1, 2001 Revision August 10, 2001     

Convenient and Regiospecific Method for Synthesis of 4,5-Diaryl-1-methyl-2-(methylthio)-1H-imidazole

A convenient, high-yielding, regiospecific synthesis of 1H-imidazole-2-thiones ring has been developed. In addition, a series of 4,5-diaryl-1-methyl-2-(methylthio)-1H-imidazoles 8 were synthesized and characterized. The structure of regioisomers was confirmed through nuclear Overhauser effect spectroscopy and NMR spectroscopy.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

A matricial extension of the Helson-Szegö theorem and its application in multivariate prediction

It is shown that the positivity of the angle between the past and future of a multivariate stationary process is sufficient for the existence of a mean-convergent autoregressive series representation of its linear predictor. A large class of multivariate processes whose past and future are at positive angle is characterized, thus providing a matricial extension of the Helson-Szegö theorem.     

Interaction of an intermediate structure of Bacillus subtilis α-amylase with alkyl-substituted sepharose 4B

An intermediate form of alpha-amylase from Bacillus subtilis was prepared following a previously reported procedure. Stabilization of this protein structure by various additives and its interaction with alkyl-substituted Sepharose 4B (Sepharose-lipid), used to mimic the role of the alkyl chains of the phospholipid bilayer, were investigated. Exposure of hydrophobic clusters in the protein structure on denaturation was indicated by a greater affinity of the intermediate form for interaction with the alkyl chains on the matrix, as compared with the original native structure. Near- and far-ultraviolet circular dichroism studies supported loss of tertiary structure with retention of secondary structure, as expected from molten globular intermediate forms. Based on the results presented, we suggest that interaction of a protein in its native and nonnative forms with an alkyl-substituted matrix may provide useful information regarding its capacity for insertion into and translocation across the biologic membrane.     

Reaction of N1,N2-diarylacetamidines with (2,4,7-trinitro-9H-fluoren-9-ylidene)propanedinitriles

Novel spiro[fluorene-9,4′-(1′,2′,3′,4′-tetrahydropyridine)]-5′-carbonitriles 6a-c have been obtained from the reaction of N¹,N²-diarylacetamidines 1a-c with (2,4,7-trinitro-9H-fluoren-9-ylidene)propanedinitrile ( 2 ) in ethyl acetate solutions at ambient temperature for 6a,b or under reflux for 6c , respectively.     

Acetylacetone-formaldehyde reagent for the spectrophotometric determination of some sulfa drugs in pure and dosage forms

A new simple and sensitive spectrophotometric procedure for the determination of sulfacetamide sodium (I), sulfadiazine (II), sulfadimidine (III) and sulfathiazole (IV) is based on the reaction of the drug with acetylacetone-formaldehyde reagent to give a yellow product having _max at 400 nm. Optimization of the reaction conditions has been investigated. A linear correlation was obtained between absorbance at _max and the concentration. The Beer's law limits of I, II, III and IV are 4–80, 4–72, 4–60 and 4–80 g/ml, respectively. For more accurate results, Ringbom optimum concentration ranges were evaluated to be 6–76, 8–66, 6–56 and 8–75 g/ml for I, II, III and IV, respectively. The molar absorptivities and Sandell sensitivities for all sulfa drugs under consideration were evaluated. Relative standard deviations of 0.98, 1.07, 0.86 and 0.79% were obtained for I, II, III and IV, respectively. The method has been compared to the official method and found to be simple, accurate (t-test) and reproducible (F-test). The developed procedures were applied for bulk sulfa drugs and some of their dosage forms without interferences from additive and common prescribed drugs.