Application of the ellipsoid method in an interactive procedure for multicriteria linear programming

The research reported in this paper is concerned with an application of the ellipsoid algorithm in the interactive multicriteria linear programming step method (STEM) byBenayoun et al. [1971]. Due to this application we eliminate some drawbacks of the original version of STEM and, moreover, we avoid extra computations connected with sensitivity analysis in every iteration. Specifically, we use the ellipsoid algorithm to minimize the Euclidean norm in the criterion space instead of the Chebyshev norm, which ensures that every solution submitted to the decision maker is efficient. As follows from a computational experiment, in comparison with the application of the simplex method, the proposed modification of STEM shows a smaller increase of the computational effort when the number of criteria increases. However, the absolute computation time becomes worse for problems of larger size.

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Zusammenfassung In dieser Arbeit wird über eine Anwendungsmöglichkeit der Khachiyan-Shor-Algorithmus (Ellipsoid-Algorithmus) im Rahmen des STEM-Verfahrens zur interaktiven Lösung linearer Vektoroptimierungsmodelle berichtet. Auf diese Weise können einige spezifische Nachteile des STEM-Verfahrens in seiner Originalversion vermieden werden. Durch die Verwendung der Euklidischen Norm anstelle der beim STEM-Verfahren üblichen Tschebyscheff-Norm wird garantiert, daß dem Entscheidungsträger nur effiziente Lösungen vorgeschlagen werden. Die numerischen Erfahrungen zeigen, daß der Lösungsaufwand der hier vorgeschlagenen Modifikation des STEM-Verfahrens mit steigender Anzahl von Zielfunktionen weniger stark zunimmt als bei der üblichen Version. Dies gilt jedoch nicht hinsichtlich der allgemeinen Problemgröße.

     

Instrumental neutron activation analysis of large samples: A pilot experiment

A large sample INAA (LS-INAA) was conducted based on available experimental conditions. Four different materials, e.g., a quartz-sand and three wastes from an incineration plant were analyzed on sample size of 1 kg. The neutron flux spatial distribution was determined by irradiation of flux monitors in the sample. The gamma-ray apparent counting efficiency was evaluated based on the effective-solid angle concept, using linear attenuation coefficients calculated from an iteration process. The k ₀- and the modified monostandard methods were modified for the LS-INAA. To check the LS-INAA performance, a conventional small sample INAA was carried out for the quartz sand and a waste. All detected elements in the LS-INAA are presented and the discussion is conducted to explore the sources of errors in the LS-INAA. As a pilot experiment, the information from this work will be used in constructing irradiation and counting devices for the new FRM-II neutron source in Garching, Germany.     

Berechnung von mittleren Schwingungsamplituden einiger tetraedrischer Moleküle und Ionen nach der Methode der charakteristischen Schwingungen

Mean amplitudes of vibration of a series of tetrahedralXY ₄ molecules and ions (hydrides, halides, oxides and oxoanions) have been calculated using the “Method of the Characteristic Vibrations” ofA. Müller. The results indicate that this method leads to very good values for most of the investigated species, and especially in the cases of highM _X/M_Y mass ratio.     

Direct injection of plasma to determine pseudoephedrine by high performance liquid chromatography with column switching

An HPLC method has been developed for the determination of pseudoephedrine in plasma using column switching. Preparation of the sample was simple in that only 1000 microL of water was added to 200 microL of plasma before injection. A 900 microL aliquot was injected onto the precolumn. Double distilled water was used to elute and remove proteins and polar components in the sample. The components retained on the precolumn were flushed forward onto the analytical column by the mobile phase (acetonitrile-0.2 mol/L ammonium sulphate, 10:90 v/v) with automated column switching. The limit of determination of pseudoephedrine in plasma was 12 ng/mL. The relative standard deviations of intra- and inter-assay for the determination of pseudoephedrine in plasma were 1.2-9.8% over the concentration range 1020-21.8 ng/mL. The mean recovery by on-line solid phase extraction was 94.76% (RSD = 1.1%).     

Differential determination of arsenic (III) and total arsenic with L-cysteine as prereductant using a flow injection non-dispersive atomic absorption device

Speciation of arsenic in environmental samples gains increasingly importance, as the toxic effects of arsenic are related to its oxidation state. A method was developed for the determination of trace amounts of arsenic (III) and total arsenic by flow injection hydride generation coupled with an in-house made non-dispersive AAS device. The total arsenic is determined after prereduction of arsenic (V) to arsenic (III) with L-cysteine in a low concentration of hydrochloric, acetic or nitric acid. The conditions for the prereduction, hydride generation and atomization were systematically investigated. A quartz tube temperature of 800 degrees C was found to be optimum in view of peak shape and baseline stability. Pb(II), Ni(II), Fe(III), Cu(II), Ag(I), Al(III), Ga(II), Se(IV), Bi(III) were checked for interfering with the 2 microg/L As(V) signal. A serious signal depression was only observed for Se(IV) and Bi(III) at a 150-fold excess. With the above system, arsenic was determined at a sampling frequency of about 1/min with a detection limit (3sigma) of 0.01 microg/L using a 0.5 mL sample. The reagent blank was 0.001+/-0.0003 absorbance units and the standard deviation of 10 measurements of the 2 microg/l As signal was found to be 1.2%. Results obtained for standard reference materials and water samples are in good agreement with the certified values and those obtained by ICP-MS     

Simultaneous determination of neodymium, erbium and holmium in rare earth mixtures with 2-phenyltrifluoroacetone and octylphenol poly(ethyleneglycol) ether by third-derivative spectrophotometry

The complexes of the rare earth metals with 2-phenyltrifluoroacetone in the presence of TX-100 are reported. The characteristic absorbances of neodymium, holmium and erbium complexes can be increased by factors of 8.5, 31 and 15 respectively, compared to those of the cholrides. The third-derivative spectra have been used to eliminate the interference of cerium, and the sensitivities are increased again by factors of 7.4, 5.5 and 6.5. A method for the direct determination of neodymium, erbium and holmium in rare earth mixtures is proposed.     

Beiträge zur Chemie des Sulfamids, 1. Mitt.: Zur Konstitution des Disilber-sulfamids

According to spectroscopic (IR, broadline proton NMR) and chemical (alkylation) investigations of disilver sulphamide the following molecular structure is assumed: $$\begin{gathered} O \hfill \\ || \hfill \\ H_2 N\_\_S\_\_NAg| \hfill \\ OAg \hfill \\ \end{gathered}$$ From the IR and NMR data deduction concerning the nature of the chemical bonds in this compound is possible. The instability of the still unknown mono-and trisilver sulphamide is discussed with regard to the structure of disilver sulphamide.     

Improved flask-combustion method for phosphorus in petroleum products

Summary An electrical assembly for the oxygen-flask combustion of lubricants and similar petroleum products is described. The pyrolysis is performed in two consecutive steps. After the ignition and burning of the sample (sorbed on sodium carbonate) the combustion is completed by further heating. The sample weight should not exceed 140 mg. In this way the sensitivity of phosphorus determination of the tentative IP standard procedure is enhanced from 0.01 to 0.001% phosphorus if the volume of solution for the final spectrophotometric measurement is reduced.

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Zusammenfassung Ein elektrisches Gerät für die Verbrennung von Schmierölen und ähnlichen Erdölprodukten im Schöniger-Kolben wurde beschrieben. Die Pyrolyse erfolgt in zwei aufeinander folgenden Schritten. Nach der Entflammung der an Natriumcarbonat adsorbierten Probe und nach Erlöschen der Flamme erfolgt die vollständige Verbrennung von Einwaagen, die 140 mg nicht überschreiten. So konnte die Empfindlichkeit der Phosphorbestimmung nach der tentativen IP-Standardmethode von 0,01% auf 0,001% Phosphor gesteigert werden, wenn man die spektrophotometrische Messung mit vermindertem Lösungsvolumen durchführt.

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Herrn Professor Dr. H. Lieb zum 90. Geburtstag gewidmet.     

Isotherme und thermisch stimulierte Depolarisation in Polyäthylen

Zusammenfassung An verschiedenen Modifikationen eines Polyäthylens niederer Dichte wurden thermisch stimulierte Ströme (TSC) und isotherme Depolarisationsströme gemessen. Die thermisch stimulierten Ströme zeigen Maxima im Bereich der ß- und -Relaxationen der molekularen Beweglichkeit des Materials und weitgehende Übereinstimmung mit mechanischen und dielektrischen Verlustfaktormessungen. Die Zeitabhängigkeit isothermer Depolarisationsströme folgt im untersuchten Temperaturbereich 80 bis 320 K einem Potenzgesetzjt ^–n mitn ¨ 1. Die gesamten Depolarisationserscheinungen sind auf die Relaxation in die Polyäthylenkette eingebauter Dipole zurückzuführen und die Ergebnisse können mit Hilfe des Fröhlich-Modells der Dipolorientierung durch ein kontinuierliches Relaxationszeitspektrum beschrieben werden. Die Messung thermisch stimulierter Ströme erweist sich als einfaches Hilfsmittel das Spektrum der molekularen Beweglichkeit abzutasten.Die diesem Vortrag zugrunde liegenden Arbeiten werden mit Mitteln des Bundesministers für Forschung und Technologie im Rahmen des Technologieprogramms gefördert. Die Verantwortung für den Inhalt liegt jedoch allein bei den Autoren.