d-Cube decompositions ofK n/K m

Necessary conditions onn, m andd are given for the existence of an edge-disjoint decomposition ofK _n/K _m into copies of the graph of ad-dimensional cube. Sufficiency is shown whend=3 and, in some cases, whend=2^t. We settle the problem of embedding 3-cube decompositions ofK _m into 3-cube decompositions ofK _n, wherenm.Research of P.A. and D.E.B. supported by Australian Research Council grant A49532750Research of D.E.B. supported by Australian Research Council grant ARCPDF015GResearch of S.I.E. and C.V.E. supported by Illinois State University Research Office     

On carboxylate as a leaving group at the active site of Mo nitrogenase: electrochemical reactions of some MO and W carboxylates, formation of mono-, di- and tri-hydrides and the detection of an MoH2(N2) intermediate

A carboxylate ligand can function as a leaving group at a reduced molybdenum dihydride centre and this exposes a site at which dinitrogen or other small molecules can bind ; dihydrogen loss occurs after substrate binding ; protic attack intercepts carboxylate loss affording a trihydride intermediate which can partake in a hydrogen evolution cycle : it is suggested that carboxylate loss from the reduced Mo centre of nitrogenase might similarly lead to substrate binding and thence obligatory evolution of H₂.     

Calixcrown Binding to Caesium – X-Ray Structural Determination of a 1,3-Alternate Calix[4]arenebiscrown-7 Ligand

The crystal structure of calix[4]biscrown-7, 1, (C₅₂H₆₈O₁₄), (triclinic,space group P1, Z = 2, a = 11.115 (5), b = 11.710 (5), c = 18.990 (7)Å, = 85.12 (4), = 93.11 (5), = 91.01 (5)4°,V = 2458.9 ų, Rw = 0.0737 for 4170 observed, I 3 (I),reflections) has been determined. It is suggested that the polyether loopswith a radius of ca. 2.1 Å are too shallow to efficiently complex theCs⁺ cation (radius = 1.69 Å).     

Evaluation of extraction methods for the simultaneous analysis of simple and macrocyclic trichothecenes

The article is concerned with the simultaneous determination of simple and macrocyclic trichothecenes using high-performance liquid chromatography (LC) coupled to UV and mass spectrometric (MS) detection. Emphasis is put on the liquid-liquid extraction (LLE) and solid phase extraction (SPE) procedure from plant material such as wheat, comparing SPE cartridges packed with different stationary phases based on silica and polymer sorbents. In this coherence a polymeric material on the basis of poly(glycidyl methacrylate-divinylbenzene) (GMA-DVB) is developed with special regard on synthesis procedures to enhance the extraction recovery of trichothecenes in a broad polarity range. Evaluation of extraction techniques showed that the introduced material is competitive with commercially available high quality SPE materials. Percentage recovery is 82% for polar compounds, 89% for medium polar compounds and 98% for lipophilic compounds.     

Kinetics of chlorine isotope exchange reaction between sodium chloride-36 and triphenyltin chloride in mixed solvents

Fluorine is an important trace element for life and human well-being. Food, in general, provides about 40 percent of the fluorine intake in the human body. In order to measure fluorine levels in human diet samples, Instrumental Neutron Activation Analysis (INAA) and Proton Induced Gamma-ray Emission (PIGE) analysis were used. Reactions¹⁹F(n,)²⁰F and¹⁹F(n, p)¹⁹O were employed for determination of the fluorine concentration using a reactor neutron spectrum and epithermal neutrons. Corrections were made for the sodium matrix interference caused by the²³Na(n, )²⁰F threshold reaction in the case of reactor neutron cyclic activation analysis and for the oxygen interference via¹⁸O(n, )¹⁹O reaction when using the epithermal cyclic NAA method. The fluorine content of the diet samples was also determined by PIGE analysis making use of the resonance reaction¹⁹F(p, )¹⁶O at 872 keV. Cyclic Neutron Activation Analysis (CNAA) when combined with mass fractionation was found to be the most suitable for determination of low concentration of fluorine, through the¹⁹F(n, )²⁰F reaction with a detection limit of 2.2 ppm in Bowen's Kale elemental standard.     

Novel reactions with hetaryldieneamines as activated olefins

In the presence of appropriate reagents, hetaryldieneamines were found to react with only one of their two double bonds. Reaction with aryldiazonium salts resulted in hydrazone2 while azodicarboxylic ester afforded substitution product3. In reactions with benzofuroxan and arylazides, hetaryldieneamines reacted as enamines to yield quinoxaline (4) andv-triazole derivatives (5), respectively.

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Neue Reaktionen mit Hetaryldienaminen als aktivierte Olefine

Zusammenfassung Mit entsprechenden Reagenzien traten Hetaryldienamine nur mit einer der zwei Doppelbindungen in Reaktion. Die Umsetzung mit Aryldiazoniumsalzen führte zum Hydrazon2, währen Azodicarbonsäureester das Substitutionsprodukt3 ergab. In Reaktionen mit Benzofuroxan und mit Arylaziden reagierten die Dienamine1 als Enamine und es entstanden Chinoxalin-(4) bzw. Triazolderivate (5).

     

Composition and stability constants of iron- and copper-oxytetracycline chelates

Summary The composition and stability constants of iron and copper oxytetracycline chelates are determined by spectrophotometric and pH-metric methods. The stepwise stability constants are log ₁ 9.79, log ₂ 7.08, log ₃ 5.92 and log ₁ 7.28 and log ₂ 5.29 for iron and copper chelates, respectively. The thermodynamic parameters of these reactions and the site of chelation in oxytetracycline are also investigated. The reaction of iron(III) has been used for the spectrophotometric determination of oxytetracycline in some pharmaceutical preparations. Results with a coefficient of variation in the range of 1.6% and a mean recovery of 98.6% are obtained.

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Zusammensetzung und Stabilitätskonstanten der Eisen- und Kupferkomplexe mit Oxytetracyklin

Zusammenfassung Spektrophotometrische Methoden und pH-Messung ermöglichten die Bestimmung der im Titel angeführten Größen. Die Stabilitätskonstanten für die Eisen- bzw. Kupfer-Chelate sind: log/gb₁ 9,79; log ₂ 7,08; log ₃ 5,92; bzw. log ₁ 7,28; log ₂ 5,59. Die thermodynamischen Parameter dieser Reaktionen und die Art der Chelatbildung des Oxytetracyklin-Moleküls wurden ebenfalls untersucht. Die Reaktion mit Eisen(III) wurde für die Bestimmung von Oxytetracyklin verwendet. Ergebnisse mit einem Variationskoeffizienten 1,6% und einer mittleren Wiederfindungsrate von 98,6% wurden erzielt.

     

A tutorial on using genetic algorithms for the design of network topology

The design of network topology is an important part of network design, since network topology is directly associated with network operational behavior, capacity, reliability, and cost. This paper is a tutorial paper concerned with illustrating how the optimization capabilities of genetic algorithms can be used to design suitable network topologies considering basic topology problems. Simple genetic algorithms have been developed for the topology problem of mesh networks, considering single node and single link failure tolerance. The algorithms are based on criteria of two important measures: minimizing the length of communication links; and minimizing traffic flow through these links for given traffic loads. The first measure contributes to minimizing the cost of cabling, while the second measure contributes to minimizing the cost of link capacity. The work provides a useful approach and tools to network students and professionals concerned with the topology design of backbone networks. The developed software is made available on the Internet. Copyright © 2006 John Wiley & Sons, Ltd.     

Determination of cinnarizine in pharmaceutical preparations by spectrophotometry, atomic absorption spectrometry and potentiometry

New methods are developed for the determination of cinnarizine in various dosage forms. They are based on the reaction of cinnarizinium cation with cobalt tetrathiocyanate anion, whereby a sparingly soluble blue 21 drug: reagent ion-pair complex is quantitatively formed. The complex is (a) extracted with nitrobenzene and spectrophotometrically measured at 622 nm; (b) extracted with nitrobenzene and nebulized in an air-acetylene flame for atomic absorption spectrometric monitoring of cobalt at 242.5 nm; and (c) dispersed in a PVC membrane plasticized with 2-nitrophenyloctyl ether and used as a sensor for direct potentiometric determination of the drug. Optimum reaction conditions and performances of the three analytical techniques are evaluated and compared. At the 25 mg level of cinnarizine, the three methods give results with equal accuracy and precision. The average recovery is 98–99% of the nominal and the mean standard deviation is 0.7%. No significant interferences are caused by drug excipients and diluents.     

Shell model yrast states in the many-particle nucleus 72 157 Hf85

In-beam- andn-measurements have for the first time identified excited states in the ₇₂ ¹⁵⁷ Hf₈₅ nucleus and have established its yrast levels up to 6.5 MeV and I=(51/2). The results of parameter-free 11-particle recoupling calculations in the framework of the shell model for the configurationsh ₁₁ ^2/8 f ₇ ^2/3 andh ₁₁ ^2/8 f ₇ ^2/2 h_9/2 are in excellent agreement with the observed levels up to 39/2 at 4.758 MeV. A weakly populated 52 ns 29/2⁺ yrast isomer at 2.876 MeV is assigned as the three-neutron configurationf_7/2h_9/2i_13/2.