Variable Mesh Size Research Articles

Three-dimensional hydrogel constructs for exposing cells to nanoparticles

In evaluating nanoparticle risks to human health, there is often a disconnect between results obtained from in vitro toxicology studies and those from in vivo activity, prompting the need for improved methods to rapidly assess the hazards of engineered nanomaterials. In vitro studies of nanoparticle toxicology often rely on high doses and short exposure periods due to the difficulty of maintaining monolayer cell cultures over extended time periods as well as the difficulty of maintaining nanoparticle dispersions within the culture environment. In this work, tissue-engineered constructs are investigated as a platform for providing doses of nanoparticles over different exposure periods to cells within a three-dimensional environment that can be tuned to mimic in vivo conditions. Uptake of quantum dots (QDs) by model neural cells was first investigated in a high-dose exposure scenario, resulting in a strong concentration-dependent uptake of carboxyl-functionalised QDs. Poly(ethylene glycol) hydrogel scaffolds with varying mesh sizes were then investigated for their ability to support cell survival and proliferation. Cells were co-encapsulated with carboxyl-functionalised poly(ethylene glycol)-coated QDs at a lower dose than is typical for monolayer cultures. Although the QDs leach from the hydrogel within 24 h, they are also incorporated by cells within the scaffold, enabling the use of these constructs in future studies of cell behaviour and function.

Surface chemistry and size influence the release of model therapeutic nanoparticles from poly(ethylene glycol) hydrogels

Nanoparticles have emerged as promising therapeutic and diagnostic tools, due to their unique physicochemical properties. The specific core and surface chemistries, as well as nanoparticle size, play critical roles in particle transport and interaction with biological tissue. Localized delivery of therapeutics from hydrogels is well established, but these systems generally release molecules with hydrodynamic radii less than ~5 nm. Here, model nanoparticles with biologically relevant surface chemistries and diameters between 10 and 35 nm are analyzed for their release from well-characterized hydrogels. Functionalized gold nanoparticles or quantum dots were encapsulated in three-dimensional poly(ethylene glycol) hydrogels with varying mesh size. Nanoparticle size, surface chemistry, and hydrogel mesh size all influenced the release of particles from the hydrogel matrix. Size influenced nanoparticle release as expected, with larger particles releasing at a slower rate. However, citrate-stabilized gold nanoparticles were not released from hydrogels. Negatively charged carboxyl or positively charged amine-functionalized quantum dots were released from hydrogels at slower rates than neutrally charged PEGylated nanoparticles of similar size. Transmission electron microscopy images of gold nanoparticles embedded within hydrogel sections demonstrated uniform particle distribution and negligible aggregation, independent of surface chemistry. The nanoparticle-hydrogel interactions observed in this work will aid in the development of localized nanoparticle delivery systems.

A comparison of the String Gradient Weighted Moving Finite Element method and a Parabolic Moving Mesh Partial Differential Equation method for solutions of partial differential equations

Abstract We compare numerical experiments from the String Gradient Weighted Moving Finite Element method and a Parabolic Moving Mesh Partial Differential Equation method, applied to three benchmark problems based on two different partial differential equations. Both methods are described in detail and we highlight some strengths and weaknesses of each method via the numerical comparisons. The two equations used in the benchmark problems are the viscous Burgers’ equation and the porous medium equation, both in one dimension. Simulations are made for the two methods for: a) a travelling wave solution for the viscous Burgers’ equation, b) the Barenblatt selfsimilar analytical solution of the porous medium equation, and c) a waiting-time solution for the porous medium equation. Simulations are carried out for varying mesh sizes, and the numerical solutions are compared by computing errors in two ways. In the case of an analytic solution being available, the errors in the numerical solutions are computed directly from the analytic solution. In the case of no availability of an analytic solution, an approximation to the error is computed using a very fine mesh numerical solution as the reference solution.

Cell Surface Bound Pericellular Matrix has a Spatially Varying Mesh Size

An invisible but thick polymer matrix of polysaccharides extends outward from the surface of many cell types including fibroblasts, smooth muscle cells, and chondrocytes. Grafted to the cell surface, the key backbone polymer hyaluronan is dramatically stretched outward from the surface by large bottlebrush molecules (e.g. aggrecan, versican). This extended, cell bound structure is called the pericellular matrix or cell coat. The shape and thickness of the cell coat is strongly correlated with adhesion-dependent and mechanical activities of the cell in particular proliferation and migration, for example during wound healing, embryogenesis, and cancer metastasis. Yet, much remains to be understood about the cell coat, which is invisible to both phase contrast and DIC microscopy, and which until recently was difficult to fluorescently-label without collapsing its hydrated structure. Our measurements based on optical force probe microscopy and quantitative particle exclusion assays provide some of the first quantitative mechanical and ultra-structural measurements of the cell coat. The assays reveal that cell coat structure on RCJ-P chondrocytes is not crosslinked and further that the pericellular matrix maintains a varying osmotic pressure throughout its structure which influences how objects move through the matrix. We show for the first time that the cell coat has a spatially varying mesh size perpendicular to the cell surface, ranging from approximately ∼100nm to 500nm at eight microns. The accessibility of the cell surface through the pericellular matrix both for molecules and nanoparticles as well as the cell's interaction with its surroundings will depend strongly on the cell coat configuration and its varying mesh size (e.g. adhesion to other cells and the extracellular matrix; endocytosis). These measurements provide first experimental clues for how cell coat ultrastructure and mechanics might physically regulate cell interactions with the extracellular environment.

Microclimate within litter bags of different mesh size: Implications for the ‘arthropod effect’ on litter decomposition

Litter bags are often used to determine the impact of soil animals on litter decomposition rates through the use of varied mesh sizes that exclude soil animals on the basis of body size. However, concerns have been raised regarding confounding factors that can co-vary with mesh size (e.g., microclimatic differences and leaching losses) and that might affect mass loss from litter bags independent of soil animal effects.To explore if these factors may interfere with the interpretation of studies that have used litter bags of varying mesh sizes, we quantified the effects of mesh size (50 μm, 0.4 mm and 1.0 mm aperture) on litter mass loss in the absence of soil animals. Further we measured potential microclimate (temperatures, light transmission and moisture) differences that may co-vary with mesh size. In addition, we quantified litter mass losses through litter fragmentation and leaching.Litter mass loss in the absence of soil animals did not differ between mesh sizes, suggesting that the use of the different meshes does not generate confounding factors that directly influence mass loss rates in the absence of animals.Microclimatic differences between litter bags of different mesh sizes were minimal and revealed slightly warmer (0.7 °C) temperatures and easier water entry for the fine than the coarse mesh bags, but no effect on litter evaporation rates. Light transmittance was largest for the fine mesh (79%) compared to the medium (60%) and coarse mesh (73%). The impact of UV on litter mass loss was 1% higher in the coarse mesh. Loss of fragmented litter was considerably higher from the coarse mesh (93%) than the fine mesh bags (17%).In conclusion, different mesh sizes can be used to reliably quantify the role of soil animals in litter mass loss from litter bags. The greater litter mass loss from litter bags with coarser mesh sizes is however caused by the soil animals both promoting litter decomposition and greater litter fragmentation (with the undecomposed fragments then being lost from the bags). Additional approaches are needed to determine the relative importance of these two effects of soil animals on litter mass loss from litter bags.

Using Tough2-MP on a cluster—optimization methodology and study of scalability

Evaluating the impacts of heat and gas production in a deep geological repository for radioactive waste necessitates a large number of numerical simulations. The task is best approached by running a massively parallel code such as Tough2-MP on a cluster. One key issue then becomes the optimal utilization of the computer resources. The newly developed methodology facilitates the efficient distribution of the workload on the cluster by guiding the selection of the partitioning settings for the model and the repartitioning of the computation load among the nodes and cores. Its application involves a series of numerical test routines which are performed prior to the realization of the repository simulations.The new methodology has been applied on two actual simulation cases. One is based on the Couplex-Gaz 1b exercise with variable mesh size, the other is the larger MAVL 3D model concerning the storage of intermediate-level long-lived radioactive waste. The results from testing show a good scalability of the Tough2-MP code under certain conditions.Good practices for domain partitioning and processor load repartitioning have been derived. The results may be applicable, too, for efficiency enhancements of other domain-decomposition based parallel simulation software.

Proposal of ECF-Pump Using Mesh Electrodes

An Electro-Conjugate Fluid (ECF) is one of functional fluids. A strong jet flow is generated between two electrodes when a high voltage is applied to ECF through the electrodes. By the use of this strong jet flow, a pump with simple structure, no noise and no vibration can be developed. In this view point, authors had developed printed circuit board multi-layered type ECF-pump and tube type ECF-pump in order to realize a new liquid cooling system by ECF. And the performance of the liquid cooling system composed of printed circuit board multi-layered or tube type ECF-pump had been investigated. In this study, an ECF pump using two metallic meshes as electrodes is proposed. The proposed pump is fabricated, and experiments are performed to investigate the basic characteristics of the pump varying mesh size. These experimental results show that the existence of a suitable combination of metallic meshes is made clear and the proposed ECF pump has remarkable properties. In addition, the basic characteristics of this pump are investigated by carrying out experiments varying the width between two metric meshes of this pump. These experimental results show that this pump has remarkable properties when the width between two metric meshes is set at 0.1mm.

Resolution adapted finite element modeling of radio frequency interactions on conductive resonant structures in MRI

Prediction of interactions between the radiofrequency electromagnetic field in magnetic resonance scanners and electrically conductive material surrounded by tissue plays an increasing role for magnetic resonance safety. Testing of conductive implants or instruments is usually performed by standardized experimental setups and temperature measurements at distinct geometrical points, which cannot always reflect worst-case situations. A finite element method based on Matlab (The Mathworks, Natick, MA) and the finite element method program Comsol Multiphysics (Stockholm, Sweden) with a spatially highly variable mesh size solving Maxwell's full-wave equations was applied for a comprehensive simulation of the complete geometrical arrangement of typical birdcage radiofrequency coils loaded with small conductive structures in a homogenous medium. Conductive implants like rods of variable length and closed and open ring structures, partly exhibiting electromagnetic resonance behavior, were modeled and evaluated regarding the distribution of the B(1)- and E-field, induced currents and specific absorption rates. Numerical simulations corresponded well with experiments using a spin-echo sequence for visualization of marked B(1)-field inhomogeneities. Even resonance effects in conductive rods and open rings with suitable geometry were depicted accurately. The proposed method has high potential for complementation or even replacement of common experimental magnetic resonance compatibility measurements.

Environmental Quality and Fish Communities in Selected Catchments of Lake Victoria

Water quality and fish species are studied in selected catchments of Lake Victoria. The major aim of the study is to establish the relationship between the environmental quality and fish communities in the selected study sites of Lake Victoria. Physico-chemical characteristics of water in selected sites were determined on-site while nutrients and heavy metals were determined in the laboratory using standard methods. Fish samples were collected using experimental multi- filament gillnets with varying mesh sizes. Fish identification was done using external morphological characteristics and identification keys. Physico-chemical results in Thruston bay revealed rise in water column temperature and turbidity as compared to those measured by earlier studies on the lake. Dissolved oxygen (DO) ranged from 0.9 mg L -1 in Yala catchment to 11.56 mg L -1 in Thruston bay. Phosphorus (P) ranged from 9.78 � g L -1 to 120.67 � g L -1 in Thruston bay and in Yala catchment, it ranged from 185.2 � g L -1 to 1526.9 � g L -1 . The nitrate-nitrogen loading in the Geita catchment ranged from 130 to 7465 kg N between the years 2006 and 2008. The results in the inshore sites show a potential for higher photosynthetic rates than in the offshore sites implying that there is more food for the fish in the inshore sites than in the offshore sites. Results further reveal that in Thruston bay there are 13 fish species and Haplochromines dominate the fish catch in terms of numbers. Heavy metals including mercury resulting from artisanal and commercial gold mining in the Geita study site were also detected in the discharges into the lake. This paper also presents measures for the sustain- able management of the lake environment, its quality and fisheries.

Do soil organisms affect aboveground litter decomposition in the semiarid Patagonian steppe, Argentina?

Surface litter decomposition in arid and semiarid ecosystems is often faster than predicted by climatic parameters such as annual precipitation or evapotranspiration, or based on standard indices of litter quality such as lignin or nitrogen concentrations. Abiotic photodegradation has been demonstrated to be an important factor controlling aboveground litter decomposition in aridland ecosystems, but soil fauna, particularly macrofauna such as termites and ants, have also been identified as key players affecting litter mass loss in warm deserts. Our objective was to quantify the importance of soil organisms on surface litter decomposition in the Patagonian steppe in the absence of photodegradative effects, to establish the relative importance of soil organisms on rates of mass loss and nitrogen release. We estimated the relative contribution of soil fauna and microbes to litter decomposition of a dominant grass using litterboxes with variable mesh sizes that excluded groups of soil fauna based on size class (10, 2, and 0.01 mm), which were placed beneath shrub canopies. We also employed chemical repellents (naphthalene and fungicide). The exclusion of macro- and mesofauna had no effect on litter mass loss over 3 years (P = 0.36), as litter decomposition was similar in all soil fauna exclusions and naphthalene-treated litter. In contrast, reduction of fungal activity significantly inhibited litter decomposition (P < 0.001). Although soil fauna have been mentioned as a key control of litter decomposition in warm deserts, biogeographic legacies and temperature limitation may constrain the importance of these organisms in temperate aridlands, particularly in the southern hemisphere.

A surface remeshing approach

AbstractA method is presented to remesh three‐dimensional discrete data surfaces. The originality of the method resides in mimicking heavily the classical adva10ncing front method for quality while always relying on a valid mesh for robustness. Therefore, local operations are applied in a first step to obtain a mesh of appropriate length scale compared to the specified size, and an original procedure has been developed for refinement that automatically degenerates to a surface mesh optimization if the size map has been respected. A valid mesh is then always available during the remeshing procedure.A new background grid is proposed that relies on a Cartesian mesh for the size distribution. Interpolation is performed very quickly and the size distribution is smoothed out to provide a slowly varying mesh size distribution.Various numerical results are presented to illustrate the efficiency but mainly the quality and robustness of the method. Copyright © 2010 John Wiley &amp; Sons, Ltd.

On the parallelization of unsteady BEM problems with variable mesh size

This paper presents code acceleration strategies for a boundary element method (BEM) simulation of an unsteady free-surface problem with a variable mesh size. The evolution of the film and droplet field emanating from a classical swirl injector/nozzle is used as a test case for the methodology. The unsteady free-surface problem (dynamic grid problem) presents challenges for load balancing the inversion of a matrix that is changing size with time. Since inversion of the matrix of linear equation coefficients represents the dominant computational cost for large problems, the parallelization of the second-order BEM code is implemented using a portable computation library, ScaLAPACK. A different processor grid topology using ScaLAPACK has been implemented and compared to the recommendation of ScaLAPACK guide. Implementation of ScaLAPACK in the solver routine of BEM has been successful and a significant simulation time reduction is demonstrated on an Opteron Dual Processor high-performance computing cluster employing two processors per node.

Plant litter quality influences the contribution of soil fauna to litter decomposition in humid tropical forests, southwestern China

The aim of this field experiment was to quantify the contribution of soil fauna to plant litter decomposition in three forest sites differing in C/N ratio under natural conditions in Xishuangbanna, southwestern China. We conducted a survey of soil fauna communities, the forest floor litter and investigated mass loss of mixed tree species leaf litter for two years in a tropical secondary forest, an evergreen broad-leaf forest and a tropical rain forest. Exclusion treatments of different sized soil fauna from the leaf litter by using varying mesh size litter bags (2 mm and 0.15 mm) were also performed. Mass loss and C and N concentrations in litter bag leaf materials were determined at monthly intervals. We found that: (1) the three forests differed in floor litter biomass and nutrient contents but not in soil fauna richness and abundance; (2) litter mass loss and decomposition rate were slower when soil macrofauna and most of mesofauna were excluded; and (3) greatest soil fauna contribution to plant litter decomposition occurred in the rain forest, where leaf litter C/N ratio was also highest (41.5% contribution: 54.8 C/N ratio), in comparison to 8.69% in the broad-leaf forest and 19.52% in the secondary forest, both with low leaf litter C/N ratios (<32). Our results suggested that, soil fauna played a more pronounced role in the decomposition of mixed leaf litter in tropical rain forest, and significantly bigger effects from fauna were ascribed to the enhancement of N concentration and decrease of C concentration of the initially high C/N ratio litter in this forest site.

CARACTERIZAÇÃO DE UMA PESCARIA DE PEQUENA ESCALA EM UMA ÁREA DE IMPORTÂNCIA ECOLÓGICA PARA ELASMOBRÂNQUIOS, NO RECREIO DOS BANDEIRANTES, RIO DE JANEIRO

A pesca de pequena escala sustenta milhões de pessoas em todo o mundo e opera principalmente na zonacosteira. Esta região é utilizada por muitas espécies de Elasmobrânquios como área de alimentação, reprodução, parto e/ou crescimento. A APREBAN é um grupo de pescadores urbanos de pequena escala que atua na costa do Rio de Janeiro (RJ), principalmente em torno da isóbata de 30 m, empregando redes-de-espera de dimensões e malhas variáveis. Durante dois anos de acompanhamento dos desembarques, registrou-se 1.617 Elasmobrânquios de 27 espécies, incluindo nove ameaçadas de extinção. Diversos estágios de maturação foram observados incluindo neonatos e fêmeas grávidas ou pós-parto de oito espécies, além de Squatina spp. Esta região mostrou-se uma área de importância ecológica para Elasmobrânquios, com especial destaque para Rhizoprionodon spp. Sphyrna spp., Squatina spp., Rhinobatos horkeliie Carcharhinus spp. Recomenda-se um monitoramento mais abrangente da costa do Estado do Rio de Janeiro a fim de melhor caracterizar o usodos habitats costeiros pelos Elasmobrânquios e as formas de interação com a pesca de pequena escala.

Recyclable Polymer-Supported Organolanthanide Hydroamination Catalysts. Immobilization and Activation via Dynamic Transamination

A series of divinylbenzene cross-linked, amino-functionalized polystyrene resins such as aminomethylated polystyrenes of varying mesh size, piperazinomethyl polystyrene, 1,12-diaminododecanetrityl resin, 1,7-diaminoheptanetrityl resin, 1,2-diaminoethanetrityl resin, 1,4-bis-(aminomethyl)benzenetrityl resin, N-(2-aminoethyl)aminomethyl polystyrene, cis-1,2-diaminocyclohexanetrityl resin, and trans-1,2-diaminocyclohexanetrityl resin are used as supports for the intramolecular hydroamination/cyclization precatalysts Cp‘2SmCH(SiMe3)2, Cp‘2LaCH(SiMe3)2 (Cp‘ = η5-Me5C5), and CGCSmN(SiMe3)2 (CGC = Me2Si[(η5-Me4C5)(tBuN)]). It is shown that these catalyst precursors can be immobilized on the polymer supports via transaminative protonolysis to give the corresponding bound precatalysts, which, in the presence of aminoalkene substrates, are transaminatively released for efficient homogeneous intramolecular hydroamination/cyclization processes. Upon substrate consumption, the catalysts are readsorbed on the supports. In many cases, these catalysts exhibit activities comparable to the homogeneous precursors and are recoverable/recyclable with only minor to moderate loss of activity, depending on the particular resin amino substituents.

Application of the finite volume method to the radial conduction model of the CATHENA code

The CATHENA code uses the finite element method (FEM) for the one-dimensional heat conduction model, which determines the temperature distribution from the fuel center to the cladding in the radial direction. However, it is shown that the finite element solutions in the heat source region such as a fuel pellet are converged to exact solutions with an increasing number of the mesh elements. Since the finite volume method (FVM) ensures local and global energy conservation due to an integral conservation over each control volume, the FVM is applied to the CATHENA wall conduction model to avoid the mesh size effect on the fuel temperature prediction. The accuracy and validity of the finite volume model in the CATHENA code are tested against two cases, a steady state and a transient heat conduction case, for which exact solutions are available. The constant temperature on the boundary surface and a uniform internal heat generation rate are assumed for the steady state problem. In the transient heat conduction problem, a cylinder is initially at a uniform temperature and suddenly its boundary surface is subjected to convection with a constant heat transfer coefficient into an ambient at a constant temperature. The steady state solutions by the FVM model are found to give almost the same results as the analytical solutions and consistent results with varying mesh sizes, while the original CATHENA with FEM over-predicts the center temperature with larger mesh sizes. The new model also closely follows the analytic solutions of the dimensionless transient heat conduction equation for a long cylinder.

Observations on the intestinal helminth parasites of cichlids in the upper reaches of River Orogodo, a freshwater body in Delta State, Southern Nigeria

The prevalence and intensity of intestinal helminth parasites of five predominant cichlids; Hemichromis fasciatus, Chromidotilapia guentheri, Tilapia mariae, Tilapia zilli and Tilapia aurea of the upper reaches of River Orogodo in Delta State, Southern Nigeria were examined. The water body was randomly sampled using a variety of fishing gear which included funnel entrance traps, cast nets of varying mesh sizes and baited hook long lines. Of a total of 183 fishes investigated, 111 (60.66%) were infected. The increasing order of relative prevalence was Chromidotilapia quentheri (21.62%), Tilapia mariae (63.64%), Tilapia aurea (70.97%), Tilapia zilli (71.79%) and Hemichromis faciatus (74.42%). The intestinal helminth parasites recovered were Acanthophalans (Acanthogyrus sp and Octospiniferoides sp), Nematodes (Camallanus sp and Cucullanus sp) and Cestodes (Wenyonia sp). Tilapia mariae had the highest parasite intensity (425) while Chromidotilapia quentheri had the least (65). Although, the sex predilection skewed towards females (64.77%) as against males (56.84%) significant difference was not observed (P>0.05). Viable preventive measures against fish parasitism in Nigerian freshwater bodies are highly recommended.Keywords: helminth, cichlids, freshwater, Nigeria Tropical Freshwater Biology 2003/2004 Vol. 12/13: 131-136

A probability density function Eulerian Monte Carlo field method for large eddy simulations: Application to a turbulent piloted methane/air diffusion flame (Sandia D)

The Eulerian stochastic field method is applied to the solution of the modeled evolution equation for the subgrid joint probability density function (JPDF) of the reacting scalars in a large eddy simulation (LES) of a piloted methane/air diffusion flame (Sandia Flame D). A simple model for subgrid scale (SGS) stresses and fluxes and a global four-step mechanism for combustion are combined in the formulation. Test cases with varying mesh sizes and numbers of stochastic fields were completed. The differences in the results obtained with the two grids were very small and this indicates that the mesh resolution was sufficient. However, incorporation of the JPDF, via the stochastic field solution method, improved the quality of predictions significantly, particularly those quantities related to reaction, such as temperature. Eight stochastic fields were shown to be enough to characterize the influence of SGS fluctuations on filtered species formation rate to reasonable accuracy and at moderate computational cost. With the exceptions of H 2 and CO, good agreement between measured and computed mean and RMS profiles of velocity, composition, and temperature was achieved. The discrepancies in H 2 and CO concentrations are attributable to limitations in the global chemistry mechanism used in the LES. Overall the results serve to highlight the potential of the Eulerian stochastic field method in LES.

Patient-Specific Modeling Based on the X-ray CT Images(New Meshing Algorithm Considering Bony Shape and Density)

This study deals with a patient-specific modeling method that generates a finite element model based on the X-ray CT images. The basic idea of our modeling method is to express an objective shape with small tetrahedral elements. This paper proposes a new meshing algorithm that controls element size according to shape or density information extracted from the CT images. For the automated modeling, we introduce “form factor” that indicates degree of complexity of the objective shape. The factor at a remarking point is easily obtained by a simple calculation using a local inspection region around the point. The new method produces a finite element model with variable mesh size. To validate the method, we discuss following three issues : proper volume of the inspection region for precise modeling, accuracy verification of stress analysis, and required working time for modeling and analysis. The computational results by the proposed method shows good analytical precision with a smaller FE model.

Diet and feeding of fish from Grande River, located below the Volta Grande Reservoir, MG-SP

We compare the classic model of feeding of tropical fish by means of six bimonthly samplings using gillnets of varying mesh sizes that were inspected every twelve hours throughout a forty-eight hour period. The stomachs of the fish caught were classified in three categories according to quantity of food found. The amount of fat in the visceral cavity with respect to the energetic reserve deposition was also studied. The relative frequencies of the different categories of stomach repletion and fat deposition were examined for patterns of feeding seasonality. The stomachs considered full were examined to record diet composition. To assess the relative importance of the different food resources, we applied Feeding Importance Degree (FID), which is a useful index when difficulties exist in determining a common basis for volume, number, or weight of a given food item in different species, a common problem when dealing with fish species having different feeding habits. The fish species whose stomach contents were analyzed using the FID index were Serrasalmus spilopleura (Characidae), L. prolixa (Loricaridae), Schizodon nasutus (Anostomidae), and Pimelodus maculatus (Pimelodidae). Our findings indicate some contrasting elements, in dietary composition in relation to the classic model for tropical rivers. These factors include the importance of aquatic macrophytes, the lack of piscivorous species, and a lesser presence of allochthonous vegetation in the diet of the species studied.