HUMIC MACROMOLECULES IN NATURAL WATERS

Abstract

Humic substances are the major organic constituents of soils and sediments. They also occur in small concentrations in natural surface waters and groundwaters. They form through the breakdown of plant and animal tissues by chemical and biological processes that tend to produce complex chemical structures that are more stable than the original material from which they were derived. One of the more important characteristics of humic substances is their ability to form water-soluble and water-insoluble complexes with metal ions and hydrous oxides and to interact with clay minerals and various organic compounds such as alkanes, fatty acids, and toxic organic substances such as pesticides.     

Observation of J/psi-->3gamma

We report the first observation of the decay J/psi-->3gamma. The signal has a statistical significance of 6sigma and corresponds to a branching fraction of B(J/psi-->3gamma)=(1.2+/-0.3+/-0.2)x10;{-5}, in which the errors are statistical and systematic, respectively. The measurement uses psi(2S)-->pi;{+}pi;{-}J/psi events acquired with the CLEO-c detector operating at the CESR e;{+}e;{-} collider.     

Weighted percolation on directed networks

We present and numerically test an analysis of the percolation transition for general node removal strategies valid for locally treelike directed networks. On the basis of heuristic arguments we predict that, if the probability of removing node i is p(i), the network disintegrates if p(i) is such that the largest eigenvalue of the matrix with entries A(ij)(1-p(i)) is less than 1, where A is the adjacency matrix of the network. The knowledge or applicability of a Markov network model is not required by our theory, thus making it applicable to situations not covered by previous works.     

Applications of the study of end-groups. A new approach to the determination of transfer constants

A summary is given of established procedures depending on analyses of polymers for initiator fragments incorporated as end-groups; attention is paid to determinations of kinetic chain lengths and rates of initiation in polymerizations and also of the relative importances of combination and disproportionation during termination. Recent developments allow determination of transfer constants from information on the average number of initiator fragments in a molecule of a polymer, even in some cases where the transfer is degradative. Their applications are discussed for various transfer agents including iodoform and derivatives of propene from which allylic radicals could be produced. There is consideration of the possibilities of applying analyses for initiator fragments to study of transfer initiator, transfer to polymer and primary radical transfer.