Exchange interaction effects in inter-Landau level Auger scattering in a two-dimensional electron gas

We consider the influence of spin effects on the inter-Landau level electron-electron scattering rate in a two-dimensional electron gas. Because of exchange spin splitting, the Landau levels are not equidistant. This leads to the suppression of Auger processes and a nonlinear dependence of the lifetime on the concentration of excited electrons even at very low excitation levels. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 8, 574–579 (25 April 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Evaluation of the Effect of the Furazane Fragment on the NH Acidity of 4- and 5-Picrylaminobenzofurazanes in DMF and DMSO

The products of the reactions of picryl chloride with isomeric aminobenzofurazanes in DMF and DMSO were studied by means of nonaquoeus potentiometric titration. The effect of the position of the furazane fragment in 4- and 5-picrylaminobenzofurazanes on the NH acidity is considered. The electron-acceptor properties of the furazane fragment were evaluated via inclusion of the resulting data into the pK _a-σ correlation for 2,4,6-trinitrodiphenylamines. On this basis, conventional Hammett σ constants were calculated for the furazane fragment located in the immediate vicinity of the N-H center and one position distant from it.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 6, 2005, pp. 988–990.(-10V)Original Russian Text Copyright © 2005 by Levinson, Akimova, Ermolaeva, Khairutdinov, Evgen’ev.     

Adaptive computation of articulatory parameters from the speech signal

An unconstrained optimization technique is used to find the values of parameters, of a combination of an articulatory and a vocal tract model, that minimize the difference between model spectra and natural speech spectra. The articulatory model is anatomically realistic and the vocal tract model is a "lossy" Webster equation for which a method of solution is given. For English vowels in the steady state, anatomically reasonable articulatory configurations whose corresponding spectra match those of human speech to within 2 dB have been computed in fewer than ten iterations. Results are also given which demonstrate a limited ability of the system to track the articulatory dynamics of voiced speech.     

Direct measurements of electric fields in weak OH···π hydrogen bonds

Hydrogen bonds and aromatic interactions are of widespread importance in chemistry, biology, and materials science. Electrostatics play a fundamental role in these interactions, but the magnitude of the electric fields that support them has not been quantified experimentally. Phenol forms a weak hydrogen bond complex with the π-cloud of benzene, and we used this as a model system to study the role of electric fields in weak OH···π hydrogen bonds. The effects of complex formation on the vibrational frequency of the phenol OH or OD stretches were measured in a series of benzene-based aromatic solvents. Large shifts are observed and these can be converted into electric fields via the measured vibrational Stark effect. A comparison of the measured fields with quantum chemical calculations demonstrates that calculations performed in the gas phase are surprisingly effective at capturing the electrostatics observed in solution. The results provide quantitative measurements of the magnitude of electric fields and electrostatic binding energies in these interactions and suggest that electrostatics dominate them. The combination of vibrational Stark effect (VSE) measurements of electric fields and high-level quantum chemistry calculations is a general strategy for quantifying and characterizing the origins of intermolecular interactions.