On Einstein four-manifolds with <Emphasis Type="Italic">S</Emphasis><Superscript>1</Superscript>-actions

We study closed Einstein 4-manifolds which admit S¹ actions of a certain type, i.e., warped products. In particular, we classify them up to isometry when the fixed point of the S¹ action satisfies certain natural geometric conditions. The proof uses the Bochner-Weitzenböck formula for 1-forms and the theory of minimal surfaces in 3-manifolds.in final form: 22 January 2003     

Multi-Item Scheduling by Benders' Decomposition

Scheduling the production of several items requires the determination of production quantities in different periods in the presence of resource constraints. Several approximate and heuristic algorithms have been proposed to solve this problem. However, no method for finding an optimal solution has as yet been developed. It is shown that the problem may be solved advantageously using Benders' decomposition. The subproblem in Benders' decomposition is shown to be a transportation problem, and some strategies for solving the master problem are indicated. The paper concludes with a sample problem demonstrating the application of the method.     

Tris(2-ethylhexyl)phosphate as an extractant for trivalent gallium, indium and thallium

A systematic study of solvent extraction behaviour of gallium(III), indium(III) and thallium(III) with tris(2-ethylhexyl)phosphate from salicylate media has been undertaken and a scheme for their separation is proposed. The optimum extraction conditions are evaluated and described. The method is applicable to the analysis of standard aluminium and aluminium alloys samples. The results obtained are reproducible and accurate.     

An extraction study of gallium, indium and thallium using TPASO as an extractant

A method is proposed for the extraction and individual separation of trivalent gallium, indium and thallium from salicylate media using triphenylarsine oxide dissolved in toluene as an extractant. The optimum extraction conditions are evaluated and described. The extracted metal ions are stripped and estimated spectrophotometrically following complexation with 4-(2-pyridylazo) resorcinol. A possible mechanism of the extraction is discussed. The method permits rapid and precise individual separation of gallium (III), indium (III) and thallium (III) and is applicable to the analysis of alloy samples.     

LC–MS Determination of Gabapentin from Human Plasma

Gabapentin is an anticonvulsant drug used for the treatment of epilepsy. It is not bound to plasma protein and is not metabolized. A high performance liquid chromatography–mass spectrometric micro method is described in this report for its determination from human plasma. Chromatography was performed on a 50 × 4.6 mm, 4 μm nitrile column and the parent ion detected in the positive ionization mode on single quadrupole analyzer (Q1MI) with atmospheric pressure ionization source. Extraction was carried out on C₁₈, 100 mg/3cc cartridge using 10 μL sample volume. The mean extraction recovery was 97% and within batch and between batch coefficients of variation were <9%. Lack of interference from endogenous substances helped in achieving a highly sensitive method without the need for monitoring fragment ions. The lowest concentration injected on column for calibration curve was 195 pg (range 0.5–64 ng). The method was applied for analysis of samples from a cross-over bio-equivalence study comparing two formulations.     

Synergetic extraction and spectrophotometric determination of iron (II) in steel

Summary A simple and rapid method is described for synergetic extraction and spectrophotometric determination of iron(II). The Fe(II)--furildioxime-pyridine complex extracted into chloroform has a characteristic pink color measurable at 570 nm. Iron is also separated from associated elements and the results of the analysis of synthetic mixtures and standard steel samples are reported.

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Zusammenfassung Eine einfache und rasche Methode zur Extraktion und Bestimmung von Eisen(II) wurde beschrieben. Der Komplex Fe(II)--Furildioxim-Pyridin wird mit Chloroform extrahiert. Seine charakteristische rosa Farbe ist bei 570 nm meßbar. Eisen läßt sich so auch von Begleitelementen trennen. Die Analysenergebnisse für synthetische Gemische und Standard-Stahlproben werden mitgeteilt.

     

Liquid-liquid extraction of tungsten(VI) with mesityl oxide application to an alloy steel

A new and simple method has been developed for the rapid extraction of tungsten(VI) with mesityl oxide. Quantitative extraction occurs from solutions 1M in hydrochloric acid and 12M in lithium chloride (as the salting-out agent) with 75% mesityl oxide in isobutyl methyl ketone. Tungsten is finally determined photometrically as the thiocyanate complex in the aqueous phase. Tungsten-(VI) can be extracted and determined satisfactorily in the presence of several elements. The method is shown to be applicable to an alloy steel.     

An efficient, rapid and regioselective nuclear bromination of aromatics and heteroaromatics with NBS using sulfonic-acid-functionalized silica as a heterogeneous recyclable catalyst

A simple, efficient and rapid method has been developed for high-yielding regioselective nuclear monobromination of aromatic and heteroaromatic compounds using NBS in the presence of sulfonic-acid-functionalized silica at room temperature. The catalyst works under heterogeneous conditions and can be recycled.