Water quality was monitored at the upper course of the Rio das Velhas, a major tributary of the São Francisco basin located in the state of Minas Gerais, over an extension of 108 km from its source up to the limits with the Sabara district. Monitoring was done at 37 different sites over a period of 2 years (2003-2004) for 39 parameters. Multivariate statistical techniques were applied to interpret the large water-quality data set and to establish an optimal long-term monitoring network. Cluster analysis separated the sampling sites into groups of similarity, and also indicated the stations investigated for correlation and recommended to be removed from the monitoring network. Principal component analysis identified four components, which are responsible for the data structure explaining 80% of the total variance of the data. The principal parameters are characterized as due to mining activities and domestic sewage. Significant data reduction was achieved.

Este artigo apresenta um modelo em duas dimensões para o espalhamento de I2 pela superfície de líquidos poliméricos: poliéterperfluorado (PFPE), polidimentilsiloxano (PDMS) e esqualano. A função energia potencial adotada para descrever a interação do gás com a superfície líquida formulada é do tipo LEPS. Cada molécula diatômica I2 e o potencial I-superfície são representados como uma função de Morse, com parâmetros ajustados de dados experimentais do espalhamento sobre as referidas superfícies. A superfície líquida foi modelada como um oscilador harmônico bidimensional. Os resultados obtidos com este modelo simplificado da superfície reproduzem, satisfatoriamente, os dados experimentais da dinâmica do espalhamento, em que os processos de espalhamento inelástico e captura e desorção são caraterizados. A temperatura vibracional da molécula de I2 espalhada foi determinada em concordância com os resultados experimentais.

This paper presents two dimension classical trajectory calculations for the scattering of an I2 molecule in the liquid polymeric surfaces of perfluorinatedpolyether (PFPE), polydimethyl-siloxane (PDMS) and squalane. The potential function describing the interaction of the gas molecule with the liquid surface is formulated as a modified LEPS potential. Each diatomic I2 molecule and the I-surface potential are represented as a Morse function, with parameters adjusted from experimental data of scattering experiments. The surface was modeled as a typical effective mass with two harmonic vibrational degrees of freedom. This dynamics of the scattering process is in good agreement with experimental dynamical data. The experimentally observed inelastic scattering (IS) and the trapping and desorption (TD) processes were characterized and the determined I2 vibrational temperatures showed good agreement with experimental values.

In this work we present a theoretical model to investigate the scattering of Xe and Ne by a liquid squalane surface. The liquid surface is modeled as a grid of harmonic oscillators with frequencies adjusted to experimental vibration as frequencies of the liquid squalane and the atom-surface interaction potential is modeled by a Lennard-Jones function. The three dimensional description of the dynamics of the process which occurs at the gas-liquid interface is obtained by the classical trajectory method. The general characteristics of the dynamics of the scattering process are in good agreement with experimental data.