6,412 research outputs found
Ionospheric E-region Irregularities Produced by Non-linear Coupling of Unstable Plasma Waves
Ionospheric E region irregularities produced by nonlinear coupling of unstable plasma wave
Cation-pi interactions in aromatics of biological and medicinal interest: Electrostatic potential surfaces as a useful qualitative guide
The cation-pi interaction is an important, general force for molecular recognition in biological receptors. Through the sidechains of aromatic amino acids, novel binding sites for cationic ligands such as acetylcholine can be constructed. We report here a number of calculations on prototypical cation-pi systems, emphasizing structures of relevance to biological receptors and prototypical heterocycles of the type often of importance in medicinal chemistry. Trends in the data can be rationalized using a relatively simple model that emphasizes the electrostatic component of the cation-pi interaction. In particular, plots of the electrostatic potential surfaces of the relevant aromatics provide useful guidelines for predicting cation-pi interactions in new systems
A Stereochemical Test of a Proposed Structural Feature of the Nicotinic Acetylcholine Receptor
Understanding the gating mechanism of the nicotinic acetylcholine receptor (nAChR) and similar channels constitutes a significant challenge in chemical neurobiology. In the present work, we use a stereochemical probe to evaluate a proposed pin-into-hydrophobic socket mechanism for the αVal46 side chain of the nAChR. Utilizing nonsense suppression methodology we incorporated isoleucine (Ile), O-methyl threonine (Omt) and threonine (Thr) as well as their side chain epimers (the allo counterparts). Surprisingly, our results indicate that only the pro-S methyl group of the αVal46 side chain is sensitive to changes in hydrophobicity, consistent with the precise geometrical requirements of the pin-into-socket mechanism
WR146 - observing the OB-type companion
We present new radio and optical observations of the colliding-wind system
WR146 aimed at understanding the nature of the companion to the Wolf-Rayet star
and the collision of their winds. The radio observations reveal emission from
three components: the WR stellar wind, the non-thermal wind-wind interaction
region and, for the first time, the stellar wind of the OB companion. This
provides the unique possibility of determining the mass-loss rate and terminal
wind velocity ratios of the two winds, independent of distance. Respectively,
these ratios are determined to be 0.20+/-0.06 and 0.56+/-0.17 for the
OB-companion star relative to the WR star. A new optical spectrum indicates
that the system is more luminous than had been believed previously. We deduce
that the ``companion'' cannot be a single, low luminosity O8 star as previously
suggested, but is either a high luminosity O8 star, or possibly an O8+WC binary
system.Comment: 9 pages, 5 figures,
ftp://fto.drao.nrc.ca/pub/smd/wr146/accepted.ps.gz To be published in Monthly
Notices of the Royal Astronomical Societ
Accountability Without Causality: Tort Litigation Reaches Fairy Tale Levels
This article is adapted from a lecture delivered on September 18, 1991, at the Columbus School of Law, The Catholic University of America, as part of the Brendan Brown Lecture Series. The Lecture Series honors Dr. Brendan Brown, the sixth dean of the Columbus School of Law (1942-54)
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