BOOK REVIEWS

Book reviewed in this article:
Photochemische und thermische Umwandlungen einiger Colchicum-Alkaloide und ihrer Lumiverbindungen : HANS JOCHEN KUHN, OTTO-ALBRECHT NEUMÜLLER UND GÜNTHER O. SCHENCK.
Organic Photochemistry , Volume I, Edited by ORVILLE L. CHAPMAN, Edward Arnold,     

INTRAMOLECULAR FLUORESCENCE QUENCHING IN COVALENT ACRYLAMIDE-INDOLE ADDUCTS

Abstract— Indole derivatives have been prepared which have a covalently linked quencher, acrylamide. One of these adducts, N-acrylyltryptamine, has a flexible linkage and the other, N-acrylyl-1,2,3,4-tetrahydropyridoindole, has a rigid bridge between indole and the quencher. The intensity decays of these adducts were obtained using multi-frequency phase and modulation fluorometry. The fluorescence of these adducts appears to be dynamically quenched; dominant lifetimes of 64 ps and 31 ps are found for the flexible and rigid adducts. This indicates that very rapid intramolecular quenching occurs, even when the quencher and fluorophore cannot collide. Quenching in the rigid molecule probably involves electron transfer through two sigma bonds. Anisotropy decay data were also collected and rotational correlation times of 62 ps and 163 ps are reported for the flexibile and rigid adducts, respectively.     

An Algorithm for Least-Squares Circle Fitting to Data with Specified Uncertainty Ellipses

The problem considered here is that of fitting a circle to aset of measured data points specified in terms of their cartesiancoordinates. It is assumed that the data adequately representsa circle and that associated with each data point there is anuncertainty ellipse describing the measurement error. A weightednonlinear least-squares problem is formulated in order to determineunbiased estimates of the centre and radius of the circle whichbests fits the given data. The resulting problem displays structurewhich is exploited when the Gauss-Newton algorithm is used toobtain a solution. In addition to estimates of the circle parametersthe algorithm produces error ellipses for the centre of thecircle and any point on its circumference.     

An Ergodic Control Problem for Reflected Diffusion with Jump

The control of the drift of a stochastic differential equationwith jump term is considered for the long-run average cost.The convergence of the discounted problem is studied, as wellas the corresponding dynamic programming condition. This research was supported in part by U.S. Army Research Officeunder contract DAAG29-83-K-0014 and completed during a visitto INRIA.     

An existence and uniqueness theorem for the transfer of mass and heat in a rectangular cavity

The authors demonstrate an existence and uniqueness theoremfor the solutions of a system of simultaneous nonlinear partialdifferential equations which models the transfer of mass andheat in an upright rectangular cavity. To facilitate numericalsimulations, all constants which appear in the estimates aregiven explicitly in terms of the physical parameters.     

A Simultaneous Iteration Method for the Unsymmetric Eigenvalue Problem

This paper describes a method of obtaining all or a dominantsubset of the eigenvalues and corresponding left and right-handeigenvectors of unsymmetric matrices by simultaneous iteration.The method differs from Bauer's biiteration in that re-orientationof the trial vectors is achieved at each iteration by performingan "interaction analysis".     

MODELING THE EVOLUTION OF NATURAL ORGANIC MATTER IN THE ENVIRONMENT WITH AN AGENT‐BASED STOCHASTIC APPROACH

ABSTRACT. Natural organic matter (NOM) is ubiquitous in terrestrial and aquatic ecosystems, and it plays a crucial role in the evolution of soils, the transport of pollutants, and the global carbon cycle. NOM is a complex mixture of molecules and is thus heterogeneous in structure and composition. As NOM passes through an ecosystem, it is acted upon by a variety of processes, such as microbial degradation, adsorption to mineral surfaces, and photochemical reactions that can change its properties and reactivity. The evolution of NOM in space and time thus is an important research area in biology, geochemistry, ecology, soil science, and water resources. Due to its complex structural and chemical heterogeneity, new simulation approaches are needed to help better understand the evolution of NOM properties and reactivity as it passes through an ecosystem. We present a new stochastic model, which explicitly treats NOM as a large number of discrete heterogeneous molecules (“agents”) with different probabilities of transformations or reactions. The NOM, the microorganisms, and their environment are taken together as a complex system, with the NOM interactions within this system simulated using an agent‐based stochastic modeling approach. The initial users of the NOM simulations include a geographically separated group of NSF‐sponsored scientists and engineers from different research disciplines, including both academics and U.S. government scientists. A Web‐based interface serves as a prototype NOM “collaboratory” designed to promote collaboration among the various researchers and to allow them to share their data, model results, and suggested approaches or improvements across distributed sites. This Web‐based interface has been designed to allow researchers to access the simulation model remotely from a standard Web browser. The Web‐based interface thus allows researchers at distant locations to provide parameters for their simulations, to start and stop simulations, and to plot and view results, all remotely.     

Analytical second derivatives for excited electronic states using the single excitation configuration interaction method: theory and application to benzo[a]pyrene and chalcone

A compact formulation and a semi-direct implementation are described of analytical second derivatives of the single excitation configuration interaction (CIS) energy. CPU time, memory usage and disc storage all scale with the same power of system size as the ground state Hartree—Fock (HF) method, with a coefficient only 2 to 3 times larger. Thus usually analytical excited state CIS frequencies are feasible when HF frequencies are feasible. As a computational example, analytical CIS/3-21G frequencies for benzo[a]pyrene are calculated more efficiently than with finite differences. As a chemical application, analytical CIS/6-31G^* frequencies are used to investigate non-planarity in the lowest π → π excited state of transchalcone.