Non-Newtonian flow past a sphere in a long cylindrical tube

Consideration is given to the problem of a sphere falling along the axis of a vertical cylindrical tube containing a viscoelastic fluid. Numerical predictions of the flow are obtained using a well established finite element Galerkin mixed formulation. The effect of elasticity on the streamline pattern, the drag and the stress field are discussed.     

The effect of thermal annealing on luminescence centres in Ge-silica fibres

The radioluminescence spectrum of Ge-silica fibres doped with Nd is found to change by the effect of pre-irradiation and thermal annealing. Originally the spectrum consists of a gaussian band centred near 3.1 eV (400 nm). Following the irradiation and heating an additional asymmetric band appears near 2.4 eV (520 nm). On top of this band there is a line spectrum, which can be ascribed to internal transitions of the Nd³⁺. On the basis of the spectroscopic data and previous results of thermoluminescence measurements, a model is suggested for the luminescence and the effect of the thermal annealing. The blue and green bands are ascribed to an O₂ ^– molecular ion and a hole centre near the Nd³⁺ ion, respectively.

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Zusammenfassung Das Radiolumineszenzspektrum von mit Nd versetzten Ge-Siliziumoxidfasern ändert sich durch den Einfluß von vorheriger Bestrahlung und thermischem Tempern. Ursprünglich besteht das Spektrum aus einer Gaußschen Bande mit dem Mittelpunkt bei etwa 3.1 eV (400 nm). Nach Bestrahlung und Erhitzen zeigt sich in der Nähe von 2.4 eV (520 nm) eine zusätzliche, asymmetrische Bande. An der Spitze dieser Bande befindet sich ein Linienspektrum, was internen Übergängen von Nd³⁺ zugeschrieben werden kann. Auf der Grundlage der spektroskopischen Angaben und vorangehender Resultate aus Thermolumineszenzuntersuchungen wurde für die Lumineszenz und den Einfluß des thermischen Temperas ein Modell entwickelt. Blaue bzw. grüne Banden werden O₂ ^– Molekülionen bzw. Leerstellenzentren in der Nähe von Nd³⁺-Ionen zugeschrieben.

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Dedicated to Professor Dr. H. J. Seifert on the occasion of his 60^th birthday     

A complex T-matrix derivation of a resonance amplitude

A resonant transition amplitude, valid to arbitrary order, is derived through the use of a complex energy T-matrix. A feature of this amplitude is its generality and simplicity making it useful for widespread applications in resonance theory.     

Correlations in alpha-alpha scattering and semi-classical optical models

We show the equivalence of semi-classical solutions to optical model coupled-channel equations derived from Watson's form of the nucleus-nucleus multiple-scattering series to the Glauber multiple-scattering series. A second-order solution to the semi-classical coupled-channel elastic amplitude is shown to be nearly equivalent to a second-order optical-phase-shift approximation to the Glauber amplitude if the densities of all nuclear excited states are approximated by the ground-state density. Using the Jastrow method to model the two-body density we find an average excited-state density to be of negligible importance in the double-scattering region of alpha-alpha scattering.     

Vibrational spectra of 1-butanol

Infrared and Raman spectra were obtained for 1-butanol that showed the presence of trans and gauche conformers in the liquid, vapor, and amorphous solid, but only the trans conformer is present in the annealed solid.     

The biosynthetic gene cluster for a monocyclic beta-lactam antibiotic, nocardicin A

The monocyclic beta-lactam antibiotic nocardicin A is related structurally and biologically to the bicyclic beta-lactams comprised of penicillins/cephalosporins, clavams, and carbapenems. Biosynthetic gene clusters are known for each of the latter, but not for monocyclic beta-lactams. A previously cloned gene encoding an enzyme specific to the biosynthetic pathway was used to isolate the nocardicin A cluster from Nocardia uniformis. Sequence analysis revealed the presence of 14 open reading frames involved in antibiotic production, resistance, and export. Among these are a two-protein nonribosomal peptide synthetase system, p-hydroxyphenylglycine biosynthetic genes, an S-adenosylmethionine-dependent 3-amino-3-carboxypropyl transferase (Nat), and a cytochrome P450. Gene disruption mutants of Nat, as well as an activation domain of the NRPS system, led to loss of nocardicin A formation. Several enzymes involved in antibiotic biosynthesis were heterologously overproduced, and biochemical characterization confirmed their proposed activities.     

Purine nucleosides XVII. The synthesis and conformation of 6-amino-9-β-D-ribopyranosylpurine and related derivatives prepared via the fusion procedure

The preparation of 2, 6-dichloro-9-(2′,3′,4′-tri-O-acetyl-β-D-ribopyranosyl)purine (I) has been accomplished utilizing the acid catalyzed fusion procedure. The displacement of the 6-chloro group, or the 2- and 6-chloro group has been studied. Several new 6-substituted-9-(β-D-ribopyranosyl)purines have been prepared by catalytic dehalogenation of the corresponding 2-chloropurine nucleosides. The conformation and configuration of these D-ribopyranosylpurines has been assigned with the assistance of proton magnetic resonance studies.     

Hydrolysis kinetics of photo-excited 6-methoxyquinoline in aqueous ethanol

The kinetics of hydrolysis in the lowest excited single state of 6-methoxyquinoline in aqueous solutions can be evaluated from the pH-dependence of its fluorescence spectrum. In ethanol/water solutions, the rate constant for hydrolysis decreases exponentially with increasing mole fraction of ethanol and hydrolysis is completely inhibited at a mole fraction of ethanol greater than about 0.2. The slope of a plot of the logarithm of the hydrolysis rate constant against the mole fraction of ethanol was found to correlate well with the ratio of the diffusion volume of excited 6-methoxyquinoline to the molecular volume of ethanol. This also appears to explain why the linear plot of the logarithm of the hydrolysis rate constant against the logarithm of the water activity has a slope of 31, suggesting that 30 molecules of water, beside the one that is split in hydrolysis, participate in the reaction.