Experiments in Solving Mixed Integer Programming Problems on a Small Array of Transputers

The time-consuming process of solving large-scale Mixed Integer Programming problems using the branch-and-bound technique can be speeded up by introducing a degree of parallelism into the basic algorithm. This paper describes the development and implementation of a parallel branch-and-bound algorithm created by adapting a commercial MIP solver. Inherent in the design of this software are certain ad hoc methods, the use of which are necessary in the effective solution of real problems. The extent to which these ad hoc methods can successfully be transferred to a parallel environment, in this case an array of at most nine transputers, is discussed. Computational results on a variety of real integer programming problems are reported.     

Effect of film thickness on the electro-reduction of molecular oxygen on electropolymerized cobalt tetra-aminophthalocyanine films

We studied the electrocatalytic activity of cobalt tetra-aminophthalocyanine (CoTAPc) for the reduction of molecular oxygen (O₂) on adsorbed monomeric and on electropolymerized films of different thicknesses on glassy carbon (GC) electrode. The polymeric films, denoted poly-CoTAPc, were first characterized by electrochemical impedance spectroscopy and it appears that the types of phenomena revealed to be occurring depend less on the film thickness in basic than in acid media. For O₂ reduction, the results showed that poly-CoTAPc is more active than the monomeric CoTAPc adsorbed on GC. Indeed, rotating ring-disk electrode data showed that polymeric CoTAPc promotes the four-electron reduction of O₂ to water in parallel to a two-electron reduction to give peroxide. On monomeric and thin films of poly-CoTAPc, a two-electron reduction mechanism predominates. In basic media the activity increases very slightly with thickness, whereas in acid media this increase is more pronounced. This parallels the observed behavior revealed by electrochemical impedance spectroscopy.     

Sorption of uranium by non-living water hyacinth roots

Summary Many studies have shown that water hyacinth (Eichhornia crassipes) roots can be used to accumulate high concentrations of organic as well as inorganic pollutants. They are currently used to remediate aquatic environments and aqueous solutions. In the present study, sorption of uranium from aqueous solutions by using dried roots of water hyacinth has been investigated. The sorption of uranium was examined as a function of initial concentration, pH, weight of roots and contact time. Five different concentrations 20, 40, 60, 80, and 100 μg ^. ml^-1 were used. Sorption proves to be very rapid and depend on pH, weight of roots and concentration of uranium. Maximum sorption capacity of water hyacinth roots was 64,000 U⁶⁺ μg/g. The sorption of uranium by water hyacinth roots follows a Langmuir isotherm.     

Dérivés de la dihydro-2,4 triazole-1,2,4 thione-3 et de l'amino-2 thiadiazole-1,3,4 à partir de nouvelles thiosemicarbazones d'esters

A new general synthesis of 4,5-disubstituted 2,4-dihydro-1,2,4-triazole-3-thiones is proposed. These heterocycles are obtained by the action of primary amines, arylhydrazines or aroylhydrazines on the thiosemicarbazones of eaters. These last compounds are prepared by action of chlorhydrates of iminoethers on thiosemicarbazide in dimethylformamide. These thiosemicarbazones react also with strong acids, acid anhydrides and chlorides; by thermolysis and they give 2-amino-1,3,4-thiadiazole derivatives. Also, two derivatives of 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazole have been prepared.     

Nitric oxide photorelease from ruthenium salen complexes in aqueous and organic solutions

The complexes [Ru(salen)(NO)Cl] and [Ru(salen)(NO)(H(2)O)](+) were shown to release the nitrosyl ligand as nitric oxide upon exposure to visible light in organic and aqueous solutions respectively, by means of UV-visible, EPR, and FTIR spectroscopies. The former was prepared by a new synthetic route and had its structure determined by single-crystal X-ray diffraction. A crystal of the dichloromethane solvate is orthorhombic, space group Fdd2 (No. 43) and formula C(16)H(14)ClN(3)O(3)Ru.CH(2)Cl(2), with Z = 16 and cell parameters a = 25.489(4), b = 33.435(4), and c = 9.3716(9) A. The electronic absorption spectra of the complexes were calculated using the INDO/S method. The water-soluble complex is a potential drug for antitumoral phototreatment.     

An efficient synthesis of acetylide/trimetal/acetylide molecular wires

Efficient syntheses are reported for incorporating trimetal units of the type M(3)(dpa)(4)(2+) (M = Cr, Co, Ni, and dpa = 2,2'-dipyridylamide) into polyalkynyl assemblies to give the prototypical bis-phenylacetylide complexes M(3)(dpa)(4)(CCPh)(2). Reactions of M(3)(dpa)(4)Cl(2) with LiCCPh have led only to mixtures of products which cocrystallize forming materials of the composition M(3)(dpa)(4)(CCPh)(x)()Cl(2)(-)(x)(). Here we report that acetonitrile complexes [M(3)(dpa)(4)(NCCH(3))(2)](PF(6))(2) react cleanly with LiCCPh in MeCN to afford the desired target molecules in 40-60% yield and in excellent purity. Isolation of the mixed ligand complex [Co(3)(dpa)(4)(NCCH(3))(CCPh)]PF(6) has been accomplished, which suggests that these reactions are stepwise and that it will be possible to synthesize mixed acetylide complexes (i.e., M(3)(dpa)(4)(CCR)(CCR')) via this method.     

Stabilization of γ‘ phase in Bi<Subscript>4</Subscript>V<Subscript>2-x</Subscript>Fe<Subscript>x</Subscript><Superscript>II</Superscript>O<Subscript>11-1.5x</Subscript> series

Summary This work reports the room-temperature stabilization of the Bi₄V_2-xFe_x^IIO_11-1.5x γ ‘ phase, a promising ionic conductive material that finds application in solid oxide fuel cell and oxygen sensor devices. The Fe(II) cation proved to be a better stabilizer than Fe(III), which was previously used, since a lower substitution degree of V⁵⁺ is needed for the former. Powder X-ray diffraction, Fourier-transform infrared spectroscopy and differential scanning calorimetry were used in these experiments.     

Development of a quality control method for the characterization of oligonucleotides by capillary zone electrophoresis-electrospray ionization-quadrupole time of flight-mass spectrometry

A capillary zone electrophoresis-negative electrospray ionization-quadrupole time of flight-mass spectrometric method was developed for the characterization of oligonucleotides after synthesis, using model compounds. The major difficulty is the adduction of metal cations to the polyanionic backbone of the oligonucleotide sample, resulting in complex spectra and decreased sensitivity. Several approaches were investigated to circumvent this problem. Separation was performed in an ammonium carbonate buffer. During separation, the interfering metal ions were exchanged for ammonium ions, which are less tightly bound to the oligonucleotide when ionized. The influence of the addition of piperidine and imidazole or trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA) to the running buffer for further reduction of cation adduction was investigated. Addition of CDTA to the buffer system resulted in a deconvoluted spectrum with very little adducts. On-line sample stacking proved vital to preconcentrate the samples. The pH and the concentration of the ammonium carbonate buffer as well as the electrophoresis voltage were optimized to achieve the best signal response for the oligonucleotides and a maximum reduction of the cation adducts as well as a short analysis time. Finally, the sheath liquid composition was examined for further improvement of the signal. The developed method was used to analyze different oligonucleotides (5000-9200 Da) in light of its use as a final quality control method for oligonucleotides in terms of purity and sequence homogeneity of the synthesized products. In all cases, very little adducts were observed in the deconvoluted spectra, and the relative errors of the measured molecular masses ranged from 3 to 35 ppm.     

Trennung,Identifizierung und Bestimmung von Bactericiden auf der Basis von halogenierten Aromaten mittels Gas-Chromatographie

The separation of a mixture of 22 bactericides has been achieved by gas chromatography on columns with silicone rubber W-982 as stationary phase with temperatures between 100° and 300°C. The unchanged compounds as well as their silylation products have been used. The latter are more conveniently used especially for the quantitative determination. To be able to calculate the retention indices after Kovats gas chromatography has been performed isothermally at 180°C for the more volatile compounds and at 250°C for all other bactericides.The retention indices obtained under these conditions are tabulated together with the limits of detection.