The mechanical waveform of the basilar membrane. IV. Tone and noise stimuli

Analysis of mechanical cochlear responses to wide bands of random noise clarifies many effects of cochlear nonlinearity. The previous paper [de Boer and Nuttall, J. Acoust. Soc. Am. 107, 1497-1507 (2000)] illustrates how closely results of computations in a nonlinear cochlear model agree with responses from physiological experiments. In the present paper results for tone stimuli are reported. It was found that the measured frequency response for pure tones differs little from the frequency response associated with a noise signal. For strong stimuli, well into the nonlinear region, tones have to be presented at a specific level with respect to the noise for this to be true. In this report the nonlinear cochlear model originally developed for noise analysis was modified to accommodate pure tones. For this purpose the efficiency with which outer hair cells modify the basilar-membrane response was made into a function of cochlear location based on local excitation. For each experiment, the modified model is able to account for the experimental findings, within 1 or 2 dB. Therefore, the model explains why the type of filtering that tones undergo in the cochlea is essentially the same as that for noise signals (provided the tones are presented at the appropriate level).     

Ruthenium alkylidenes: modulation of a new class of catalysts for controlled radical polymerization of vinyl monomers

Air-stable and readily available ruthenium benzylidene complexes of the general type [RuCl2(=CHPh)(L)(L')] (L, L' = PCy3 and/or N-heterocyclic carbene) constitute a new class of catalyst precursors for atom-transfer radical polymerization (ATRP) of methyl methacrylate and styrene, and provide an unprecedented example for the involvement of ruthenium alkylidenes in radical reactions. They promote the polymerization of various monomers with good to excellent yields, and in a controlled way with methyl methacrylate and styrene. Variations of their basic structural motif provide insights into the essential parameters responsible for catalytic activity. The ligands L (PCy3 and/or N-heterocyclic carbene) turned out to play a particularly important role in determining the rate of the polymerizations. A similarly pronounced influence is exerted by the substituents on the N-heterocyclic carbene. Our results indicate that the catalysts decompose quickly under ATRP conditions, and polymerizations are mediated by both [RuCl2(=CHPh)(L)(L')] complexes and ruthenium species bereft of the benzylidene moiety, through a pathway in which both tricyclohexylphosphane and/or N-heterocyclic carbene ligands remain bound to the metal center. Polymerization of n-butyl acrylate and vinyl acetate is not controlled and most probably takes place through a redox-initiated free-radical process.     

A method for bioconjugation of carbohydrates using Diels-Alder cycloaddition

Diels-Alder-type cycloaddition of an electronically matched pair of saccharide-linked conjugated dienes and a dienophile-equipped protein gives neoglycoproteins at ambient temperature in pure water with a reaction half-life of approximately 2 h. Uncoupled saccharides can be recovered by diafiltration with complete conservation of the diene moiety, thus allowing their repeated use. The procedure described is the first for creating a carbon-carbon covalent bond in the bioconjugation step between a saccharide and a protein.     

Development of an HPLC-NMR method for the determination of PAHs in soil samples - a comparison with conventional methods

A hyphenated HPLC-(1)H NMR method for the identification and quantification of PAHs in soil samples has been developed and applied to a PAH reference sample provided by the Federal Institute for Materials Research and Testing (BAM, Berlin, Germany). The results were compared with those obtained by HPLC-DAD, HPLC-F, and GC-MS analyses of the same sample.     

Chelation of Na+ cations in nonaqueous solvents. Structural requirements and methodological considerations

Intrinsic formation constants for complexes of Na⁺ ions with a series of polyamines have been determined from²³Na NMR measurements in binary mixtures of tetrahydrofuran (THF) and amines. The results show in a totally unambiguous manner a regular decrease in the magnitude of the chelate effect with the number of atoms intervening between the nitrogen ligators. The key assumption, tetracoordination of the cation, is critically examined, and experimental evidence is adduced in its support.     

Analyse synthetischer Flugturbinen?le durch Gas-Chromatographie-Massenspektrometrie

Zusammenfassung Ein handelsübliches synthetisches Flugturbinenöl auf Basis von Fettsäuretriestern des Trimethylolpropans und Fettsäurehexaestern des Dipentaerythrits wurde mittels GC-MS untersucht. Die Bildung der für die Analytik beider Polyolester wichtigen Ionen bei der elektronenstoßinduzierten Fragmentierung wird diskutiert. Die komplexen Estergemische konnten gas-chromatographisch nach der Molmasse der Esterkomponenten getrennt werden. Die Auftrennung isomerer Trimethylolpropanester gelang nicht. Ihre Identifizierung war aber massenspektrometrisch möglich.Die Struktur der als Nebenkomponenten vorliegenden Fettsäurehexaester des Dipentaerythrits konnte ebenfalls massenspektrometrisch geklärt werden. Die Bestimmung der quantitativen Fettsäurezusammensetzung des Trimethylolpropanester und Dipentaerythritesteranteils nach säulenchromatographischer Trennung und Berechnung der möglichen Esterkomponenten erlaubten eine detaillierte Charakterisierung dieses komplexen Systems.

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Analysis of synthetic aviation turbine oils by gas chromatography-mass spectrometry.Part II. trimethylolpropane ester/dipentaerythritol ester oils

Summary A commercial synthetic aviation turbine oil based on fatty acid triesters of trimethylolpropane and hexaesters of dipentaerythritol was investigated by gems. The formation of specific ions by electron impact induced fragmentation which are important for the analysis of these oils is discussed. The complex ester mixtures can be separated by gas chromatography according to molecular size of the ester components. The separation of isomeric trimethylolpropane esters is not successful.The identification of these components is possible by mass spectrometry. The structure of the minor components present, fatty acid hexaesters of dipentaerythritol, was also determined by mass spectrometry. The determination of quantitative fatty acid composition of the trimethylolpropane ester and dipentaerythritol ester components after separation by column chromatography and calculation of the possible ester components allowed a detailed characterisation of the complex ester system present.