Probabilistic error bounds on constraint violation for empirical-analytical Lagrangian models of motion

Nonlinear Dynamics - In contrast to many systems studied in the field of classical mechanics, models of animal motion are often distinguished in that they are both highly uncertain and evolve in a...     

Secondary metabolites produced by fungi derived from a microbial mat encountered in an iron-rich natural spring

A collection of fungal isolates was obtained from a complex microbial mat, which occupied an iron-rich freshwater spring that feeds into Clear Creek, Golden, Colorado, USA. Two of the fungal isolates, a Glomeromycete (possibly Entrophospora sp.) and a Dothideomycete (possibly Phaeosphaeria sp.), were investigated for bioactive secondary metabolites. In total, six new compounds consisting of clearanols A-E (5, 6, 10-12) and disulochrin (7) were purified and their structures were determined. Disulochrin exhibited modest antibacterial activity against methicillin-resistant Staphylococcus aureus, whereas clearanol C showed weak inhibitory activity against Candida albicans biofilm formation.     

Radiolysis of Aqueous Solutions of Benzoate Ion: A Radiation Chemistry Experiment for Undergraduates

This investigation describes the chemical effects of ionizing radiation on dilute aqueous solutions of benzoate ion. We have composed an experimental procedure that allows undergraduate chemistry students to identify and to quantitatively determine the amount of the products that are produced. The student investigators determine the absorbed dose that a sample receives when exposed to a ⁶⁰Co source, irradiate dilute aqueous solutions of benzoate ion, and analyze the resulting mixture of hydroxybenzoate ions using high-performance liquid chromatography. The radiolysis of dilute solutions of benzoate ion results in the formation of a mixture of ortho-, meta-, and para-hydroxybenzoate ions that are readily separated on a C₁₈ -Bondapak column. By the use of appropriate calibration curves, the yield (G values) of each of the isomers may be determined and compared.This paper was presented at the 15th Biennial Conference on Chemical Education, Waterloo, Ontario, Canada, August 1998 by N. Zevos and at the 26th Northeast Regional Meeting of the American Chemical Society by Evon Powell.     

The crystal structure of 3-R Nb1.06S2

The X-ray single crystal structure of 3-R Nb_1.06S₂ has been determined. The material crystallizes in the space group R_3m with a = 3.3285(4) and c = 17.910(4) Å when indexed on a hexagonal lattice. The structure was refined by full matrix least squares procedures to a final residual of R = 0.026 based on 79 observed (I > 3σ_I) reflections. The sulfurs form closest-packed layers with the majority of the metal in sheets of trigonal prismatic sites. A small portion of niobium was found to occupy octahedral sites, between the van der Waals gaps of the sulfur lattice. Niobium in the van der Waals region is trigonally distorted from octahedral symmetry, with niobium-sulfur distances of 2.234(8) and 2.577(11) Å, because of repulsion from niobium in adjacent trigonal prismatic layers.