Internal energy content of n-butylbenzene, bromobenzene, iodobenzene and aniline molecular ions generated by two-photon ionization at 266 nm. A photodissociation study

A technique to investigate photodissociation kinetics on a nanosecond time scale has been devised for molecular ions generated by multiphoton ionization (MPI) using mass-analyzed ion kinetic energy spectrometry. The branching ratio or rate constant has been determined for the photodissociation of the n-butylbenzene, bromobenzene, iodobenzene, and aniline molecular ions generated by MPI at 266 nm. The ion internal energies have been estimated by comparing the measured kinetic data with the previous energy dependence data. The analysis has shown that only those molecular ions generated by two-photon ionization contribute to the photodissociation signals. Around half of the available energy has been found to remain as molecular ion internal energy in the two-photon ionization process. Copyright 1999 John Wiley & Sons, Ltd.     

Total synthesis of mycocyclosin

The first total synthesis of mycocyclosin, a diketopiperazine natural product isolated from M. tuberculosis, is described. While direct oxidative coupling of tyrosine phenolic groups was unsuccessful, construction of the highly strained bicyclic framework was successfully accomplished through an intramolecular Miyaura-Suzuki cross-coupling to generate the biaryl linkage.     

The role of nitric oxide in cancer improved methods for measurement of nitrite and nitrate by high-performance ion chromatography

The short lifetime of nitric oxide (NO) in vivo impedes its quantitation directly; however, the determination of nitrite and nitrate ions as the end-products of NO oxidation has proven a more practical approach. High-performance ion chromatographic analysis of nitrite in biological fluids is hampered by the large amount of chloride ion (up to 100mmol/l) which results in insufficient peak resolution when utilizing conductimetric detection. Analysis of both anions in small sample volumes is also constrained by the need to minimise sample handling to avoid contamination by environmental nitrate. We report a means to remove Cl⁻ ions from small sample volumes using Ag⁺ resin which facilitates quantitation of either nitrite and nitrate anions in biological samples, using silica or polymer based ion-exchange resins with conductimetric or electrochemical and spectrophotometric detection. Including a reversed-phase guard column before the anion-exchange guard and analytical column also greatly extends column lifetime.     

EXPLORING THE PROPERTIES OF QUASI-OPTION VALUE IN THE CONTEXT OF GLOBAL WARMING

This paper demonstrates the principles of sequential choice. A numerical simulation model based on the theoretical framework is utilized to illustrate the economics of climate change. The model is used to relate the value of information and quasi-option value in situations where protective measures are nonbinary.     

The Atlas project-a new pulsed power facility for high energydensity physics experiments

Atlas is a facility being designed at Los Alamos National Laboratory (LANL) to perform high-energy-density experiments in support of weapon physics and basic research programs. It is designed to be an international user facility, providing experimental opportunities to researchers from national laboratories and academic institutions. For hydrodynamic experiments, it will be capable of achieving a pressure exceeding 30 Mbar in a several cubic centimeter volume. With the development of a suitable opening switch, it will be capable of producing more than 3 MJ of soft X-rays. The capacitor bank design consists of a 36 MJ array of 240 kV Marx modules. The system is designed to deliver a peak current of 45-50 MA with a 4-5-μs rise time. The Marx modules are designed to be reconfigured to a 480-kV configuration for opening switch development. The capacitor bank is resistively damped to limit fault currents and capacitor voltage reversal. An experimental program for testing and certifying prototype components is currently under way. The capacitor bank design contains 300 closing switches. These switches are a modified version of a railgap switch originally designed for the DNA-ACE machines. Because of the large number of switches in the system, individual switch prefire rates must be less than 10^-4 to protect the expensive target assemblies. Experiments are under way to determine if the switch-prefire probability can be reduced with rapid capacitor charging