We utilize a kinetic approach to the problem of wave propagation in dusty plasmas, taking into account the variation of the charge of the dust particles due to inelastic collisions with electrons and ions. The components of the dielectric tensor are written in terms of a finite and an infinite series, containing all effects of harmonics and Larmor radius. The formulation is quite general and valid for the whole range of frequencies above the plasma frequency of the dust particles, which are assumed motionless. The formulation is employed to the study of electrostatic waves propagating along the direction of the ambient magnetic field, in the case for which ions and electrons are described by bi-Maxwellian distributions. The results obtained in a numerical analysis corroborate previous analysis, about the important role played by the dust charge variation, particularly on the imaginary part of the dispersion relation, and about the very minor role played in the case of electrostatic waves by some additional terms appearing in the components of the dielectric tensor, which are entirely due to the occurrence of the dust charge variation.

A kinetic approach to the problem of wave propagation in dusty plasmas, which takes into account the variation of the charge of the dust particles due to inelastic collisions with electrons and ions, is utilized as a starting point for the development of a new formulation, which writes the components of the dielectric tensor in terms of a finite and an infinite series, containing all effects of harmonics and Larmor radius. The formulation is quite general and valid for the whole range of frequencies above the plasma frequency of the dust particles, which were assumed motionless. The formulation is employed to the study of electrostatic waves propagating along the direction of the ambient magnetic field, in the case for which ions and electrons are described by Maxwellian distributions. The results obtained in a numerical analysis corroborate previous analysis, about the important role played by the inelastic collisions between electrons and ions and the dust particles, particularly on the imaginary part of the dispersion relation. The numerical analysis also show that additional terms in the components of the dielectric tensor, which are entirely due these inelastic collisions, play a very minor role in the case of electrostatic waves, under the conditions considered in the present analysis.

Comunidades de peixes sofrem grande variabilidade em escala espacial e temporal em conseqüência de vários fatores abióticos e bióticos. Este estudo foi realizado na zona de arrebentação em Arraial do Cabo (22º 58'S, 42º 01'W) e testada a hipótese de que a composição e a estrutura da ictiofauna difere de acordo com a variação de maré em três praias com características morfodinâmicas distintas. De setembro/2001 a agosto/2002 foram realizados três arrastos mensais em três pontos de cada praia nos períodos de maré baixa (N = 6) e alta (N = 6), através de uma rede do tipo picaré (beach seine) com 25 m de comprimento por 2,50 m de altura e malha de 10 mm. Na Praia Grande e Prainha, o número de espécies e indivíduos foi superior em maré baixa. Já a CPUE (grama) na Praia Grande e Prainha foi superior na maré alta, indicando um movimento de muitas espécies bentívoras e piscívoras para a zona entremarés em maré cheias, devido à maior disponibilidade de alimento. A estrutura da comunidade de peixes na zona de arrebentação, Praia Grande e Prainha diferiu em função da maré com relação à biomassa de peixes capturados, superior no período de maré alta, exceto na Praia dos Anjos (maré baixa) confirmando parcialmente a hipótese inicial. Já o número de indivíduos, a riqueza e a diversidade de espécies foi superior na maré baixa, diferente do proposto, reflexo da grande abundância de indivíduos juvenis.

Natural assemblages show large variability at multiple scales in space and time as a consequence of several abiotic and biotic factors. This study was conducted in the surf zone of Arraial do Cabo (22º 58'S, 42º 01'W) and tested the hypothesis that the ichthyofauna composition and structure differ according to the tidal variation at three beaches with different morphodynamic characteristics. From September 2001 to August 2002 three monthly hauls were carried out at each beach during high (N = 6) and low tide (N = 6) with a beach seine (25 m length, 2,50 m height, 10 mm mesh). At Praia Grande and Prainha beaches, the number of species and individuals was higher during low tide. Also, CPUE (grams) at Praia Grande and Prainha was higher during high tide indicating a movement of many benthivore and piscivore species into the intertidal zone, due to the greater food availability. The fish community structure differed between Prainha and Praia Grande according to the tide in relation to fish biomass, which was higher at high tide, except for Praia dos Anjos (low tide) partially supporting the initial hypotheses. However, the number of individuals and species richness and diversity were higher during low tide, different from the proposed statement, as a reflex of juvenile individuals' abundance.

Peixes que vivem em águas costeiras marinhas exibem modelos de comportamento que são regulados pelos níveis de luz do ambiente. A variação nictemeral na estrutura da comunidade de peixes de zona de arrebentação foi investigada na região de Arraial do Cabo (22º58'S, 42º01'W). Desetembro/2001 a agosto/2002 foram realizadas coletas mensais, sendo efetuadas 12 arrastos utilizando cerco de praia nos períodos diurnos e noturnos na Praia dos Anjos, Praia Grande e Prainha. Diferentes padrões de distribuição da comunidade ictíca foram registrados. Na Praia dos Anjos, o número de espécies foi superior no período noturno. Já o número médio de espécies, CPUE, riqueza de Margalef e diversidade de Shannon foram, em geral, superiores no período diurno. Este padrão de comportamento foi causado pelo deslocamento noturno de algumas espécies, tais como Harengula clupeola,Trachinotus carolinus e Umbrina coroides para áreas mais profundas a procura de alimento ou para evitar predadores. Na Praia Grande e na Prainha, o número médio de espécies, CPUE e os índices de riqueza e diversidade foram, em geral, superiores no período noturno, com a dominância das espécies H. clupeola, Pomatomus saltatrix e Sardinella brasiliensis. Sugere-se que o principal fator para esta variação nictemeral seja a proteção contra predadores devido à escuridão, tornando a visualização da presa mais difícil, além da presença de bancos sazonais de macroalgas na Prainha, que pode funcionar como uma área de alimentação para peixes piscívoros devido ao encontro de uma grande quantidade de indivíduos em águas rasas especialmente à noite.

Fish living in coastal waters present behavior patterns ruled by environmental light levels. Diel variations in fish community structure were investigated at Arraial do Cabo surf zone (22º58'S, 42º01'W). From September/2001 to August/2002 monthly sampling consisted of 12 hauls of a beach seine during the day and at night at Praia dos Anjos, Praia Grande and Prainha beaches. Different temporal distribution patterns of the ichthyc community were recorded. At Praia dos Anjos, total richness was higher at night while the average number of species, CPUE, Margalef's richness and Shannon diversity were generally higher during the day. We believe that this pattern was caused by the displacement of some species such as Harengula clupeola,Trachinotus carolinus and Umbrina coroides at night to deeper areas searching for food or for predator avoidance. At Praia Grande and Prainha the average number of species, CPUE, richness and diversity indexes were generally higher at night with the dominant species H. clupeola, Pomatomus saltatrix and Sardinella brasiliensis. It is suggested that the main factor to diel variation is the protection against predators due to darkness, making visualization of the prey difficult, besides the presence of seasonal macroalgae beds at Prainha, which might function as a food area for piscivorous fishes due to the proximity of larger individuals in shallower water especially at night.

The preservation of Onsager symmetry for the effective dielectric tensor is discussed for a homogeneous plasma immersed in a inhomogeneous magnetic field, using the unperturbed orbits correct up to order kB, which is the scalelength of the field inhomogeneity. General features of the calculation of the components of the tensor are discussed and detailed calculations are developed for the zz component, which is shown to satisfy the conditions for Onsager symmetry, in agreement with previous results obtained using less precise expressions for the unperturbed orbits.

We compare and discuss several approximations to the dispersion relation for electrostatic waves in inhomogeneous plasmas, either obtained directly from Poisson's equation, or from the dielectric constant obtained using a dielectric tensor derived using the plane wave approximation, or from the dielectric constant derived using the effective dielectric tensor.

We present a detailed derivation of the effective dielectric constant to be used in the dispersion relation for electrostatic waves in the case of a plasma immersed in a inhomogeneous magnetic field, with inhomogeneity perpendicular to the direction of the magnetic field.