Stochastic excitation and Hadamard correlation spectroscopy with bandwidth extension in RF FT-EPR

The application of correlation spectroscopy employing stochastic excitation and the Hadamard transform to time-domain Fourier transform electron paramagnetic resonance (FT-EPR) spectroscopy in the radiofrequency (RF) band is described. An existing, time-domain FT-EPR spectrometer system with a Larmor frequency (L(f)) of 300 MHz was used to develop this technique by incorporating a pseudo-random pulse sequence generator to output the maximum length binary sequence (MLBS, 10- and 11-bit). Software developed to control the EPR system setup, acquire the signals, and post process the data, is outlined. The software incorporates the Hadamard transform algorithm to perform the required cross-correlation of the acquired signal and the MLBS after stochastic excitation. To accommodate the EPR signals, bandwidth extension was accomplished by sampling at a rate many times faster than the RF pulse repetition rate, and subsequent digital signal processing of the data. The results of these experiments showed that there was a decrease in the total acquisition time, and an improved free induction decay (FID) signal-to-noise (S/N) ratio compared to the conventional coherent averaging approach. These techniques have the potential to reduce the RF pulse power to the levels used in continuous wave (CW) EPR while retaining the advantage of time-domain EPR methods. These methods have the potential to facilitate the progression to in vivo FT-EPR imaging of larger volumes.     

Synthesis,spectral and redox properties of metal complexes of macrocyclic tetraaza chiral Schiff bases

New transition metal(II) coordination compounds of tetraaza macrocyclic chiral Schiff bases, derived from 2-hydroxybenzylideneacetylacetone or 4-hydroxybenzylideneacetylacetone and (1R, 2R)-(–)-1,2-diaminocyclohexane, have been prepared and characterised spectroscopically and electrochemically. E.p.r. spectral data for the Cu^II complexes reveal a strong metal-to-ligand -interaction in their square-planar configuration and the broadening of the g component is due to the strain created by 1R and 2R groups in the cyclohexane rings. The cyclic voltammetric (c.v.) data of the copper complexes show an unusual oxidation state of Cu^III, while Co^II complexes show a reversible Co^II/Co^III redox peak along with an additional peak in the negative potential region characteristic of reversibly bound oxygen. The c.v. results reveal that both Cu^II and Co^II complexes bind axially with added bases. The spectroscopic results reveal that copper, cobalt and nickel complexes are in square-planar geometry, whereas manganese is in octahedral geometry.     

Das Titsgebäude von Siegeischen Modulgruppen vom Geschlecht 2

Zusammenfassung  We describe the Tits buildings of the Siegel modular groups and fort squarefree. These give the configuration of boundary components in the moduli spaces of abelian surfaces with polarization of type (1,t) and polarization of type (1,t) with canonical level structure. We also do the same calculation for the Siegel modular groups forp,q prime,p odd, corresponding to moduli of abelian surfaces with polarization of type (1,p) and full level-q structure. Colour pictures are available at: http ://www.bath.ac.uk/~masgks/Buildings Dieser Artikel beruht im wesentlichen auf der Hannoverschen Diplomarbeit des ersten Autors, die unter Begleitung von Prof. K. Hulek zustande gekommen ist. Die Verfasser danken dem DAAD und dem British Council für finanzielle Unterstützung im Rahmen des ARC-Projekts 313-ARC-XIII-99/45.     

The allylic alcohol function in alkyltin (IV)-mediated carbocyclization. Regiospecific octalin and hydrindene synthesis.

The employment of the allylic alcohol function in the initiation of tetraalkylstannane-mediated carbocyclization and the application of this methodology to the regiospecific synthesis of Δ^1,2-octalins and Δ^4,5-hydrindene ring systems is described.     

Large eddy simulation of swirling particle-laden flow in a model axisymmetric combustor

This paper focuses on the application of the large eddy simulation (LES) technique to a swirling particle-laden flow in a model combustion chamber. A series of calculations have been performed and compared directly with detailed experimental measurements. The computational domain identically matches the laboratory configuration, which effectively isolates effects related to dilute particle dispersion and momentum coupling. Results highlight the predictive capabilities of LES when implemented with the appropriate numerics, grid resolution (as dictated by the class of models employed) and well-defined boundary conditions. The case study provides a clearer understanding of the effectiveness and feasibility of current state-of-the-art models and a quantitative understanding of relevant modeling issues by analyzing the characteristic parameters and scales of importance. The novel feature of the results presented is that they establish a baseline level of confidence in our ability to simulate complex flows at conditions representative of those typically observed in gas-turbine (and similar) combustors.     

Ruthenium(III) complexes with tetradentate Schiff bases containing triphenylphosphine or triphenylarsine

Ruthenium(III) complexes of Schiff bases derived from the condensation of salicylaldehyde or o-vanillin with diamines have been prepared and characterised. The complexes are of the type [RuX(EPh₃)(L)] [X=Cl or Br; E=P or As; L=bis(salicylaldehyde)tetramethylenediimine, bis(salicylaldehyde)o-phenylenediimine, bis(o-vanillin)ethylenediimine, bis(o-vanillin)propylenediimine, bis(o-vanillin)tetramethylenediimine or bis(o-vanillin)o-phenylenediimine]. The Schiff bases behave as dibasic tetradentate ligands.     

A new approach to standard monomial theory for classical groups

We describe a procedure for constructing monomial bases for finite dimensional irreducible representations of complex semisimple Lie algebras. A basis is calledmonomial if each of its elements is the result of applying to a (fixed) highest weight vector a monomial in the Chevalley basis elementsY , a simple root, in the opposite Borel subalgebra. As an immediate application we obtain a new proof of the main theorem of standard monomial theory for classical groups.     

Polyaromatic ether-ketone-sulfones containing 1,3-butadiene units

The acid chloride of 1,4-bis-p-carboxyphenyl-1,3-butadiene (XI) and isophthaloyl chloride (XIV) were polymerized with 4,4′-diphenoxy-diphenyl sulfone (XII) and diphenyl ether (XIII) in a Friedel-Crafts type of polymerization. The polymers obtained, which contained 5–20 mole % of butadiene units, were insoluble in all solvents. The polyamides prepared from the acid chloride of 1,4-bis-p-carboxyphenyl-1,3-butadiene (XI) and aromatic diamines were also insoluble in all solvents.     

Evidence for the synchronous cleavage of C—C and C—H bonds bis(2,2′-bipyridyl)copper(II) permanganate oxidation of cobalt(III) bound and unbound α-hydroxy acids

The kinetics of bis(2,2-bipyridyl)copper(II) permanganate oxidation of Co^III bound and unbound -hydroxy acids such as mandelic, lactic and glycolic acids have been studied in aqueous MeCO₂H. The reaction exhibits second order kinetics: first order in each reactant. The formation of Co^II, PhCHO and CO₂ to the extent of 24% [Co^III]_initial indicate C—bonds;H cleavage occurring to the extent of 24% and ca. 76% yield of the phenylglyoxylato-pentaamminecobalt(III) complex indicate C—H cleavage occurring to the extent of 76%.