Aggradation and Degradation of Alluvial-Channel Beds

The objectives of the present investigation were the determination of the characteristic parameters of morphological processes in alluvial channels. Special attention was directed toward the aggradation process due to total sediment-load augmentation and degradation due to either sediment-discharge diminution or base-level lowering. Linear and nonlinear parabolic formulations based on validated mathematical expressions of the equations governing one-dimensional flows over movable beds were developed. The classical linear, parabolic model was revisited as well. Analytical solutions for the characteristic parameters of aggradation and degradation processes in alluvial channels of semi-infinite and finite length subjected to both time dependent and time independent boundary conditions were obtained. The analytical solutions developed can be used in conjunction with almost any of the sediment-transport-rate and friction-factor predictors available. The validity and limitations of the linear and nonlinear parabolic models and their corresponding solutions were assessed by means of comparison with flume data. The ranges of application for both linear and nonlinear models were established. As a result of its more rigorous formulation, the nonlinear parabolic model, which constitutes the principal contribution of this study, was found to be particularly useful and accurate for a wide range of practical applications. The good prediction capabilities of the nonlinear model can be enhanced through the use of available laboratory and/or field data, which enable an easy and effective calibration of the model. Easy-to-follow application, calibration, and extrapolation procedures are outlined. Experiments on the evolution of the bed forms during aggradation due to a sudden increase in total sediment discharge were performed. Analyses of the experimental data led to a better understanding of the phenomena involved, to an explanation of the experimental findings of the present and similar investigations, and to justification of some of the main assumptions introduced in the development of mathematical models for unsteady nonuniform flows over deformable beds

Dental education in Colombia.

This article describes Colombia's development of formal dentistry, its dental school system, curriculum, and dental licensure, and current issues in oral health care. In 1969, there were only 4 dental schools in Colombia; at this writing there are 21. Five dental schools are public and the other 16 are private. Nearly all classes are conducted in Spanish. Undergraduate pre-dental coursework is not a prerequisite for dental school in Colombia. To obtain licensure, Colombian dental students must complete 5 years of study in dental school, earn a diploma, and work for the government for 1 year. There are approximately 41,400 dentists in Colombia, and the number is increasing quickly. However, the unemployment rate among dentists is very high, even though graduation from dental school is extremely difficult. Although the 1,100:1 ratio of citizens to dentists is considered satisfactory, access to dental care is limited due to the high rate of poverty

Population dynamics and secondary production of Euzonus furciferus Ehlers (Polychaeta, Opheliidae) in an exposed sandy beach of Southern Brazil Dinâmica populacional e produção secundaria de Euzonus furciferus Ehlers (Polychaeta, Opheliidae) numa praia exposta do sul do Brasil

The distribution, population dynamics and secondary production of the polychaete Euzonus furciferus was studied in Atami Beach (Southern Brazil), from February 1992 to March 1993. Euzonus furciferus Ehlers, 1897 is the only deposit feeder species of the upper intertidal region. The organisms were present in the sandy beach all over the year, concentrated in a narrow band, and reaching maximal densities of 3,029 individuals m-2. Peaks of abundance occurred in September 1992, with a mean of 681.8 individuals m-2. Recruitment occurred in winter, with a peak in July. Mean annual biomass was estimated in 0.218 gAFDW m-2, with a total annual production of 0.466 gAFDW m-2 y-1, giving a P/B ratio of 2.13 y-1. Similar values were found for a filter-feeder polychaete inhabiting the same beach, suggesting that general food disposability of each particular environment is more important for production than the trophic strategic employed by those organisms exploring this environment.<br>A dinâmica populacional e a produção secundária do poliqueta Euzonus furciferus foi estudada em uma praia arenosa exposta do sul do Brasil. O estudo foi realizado na praia de Atami, de fevereiro de 1992 a março de 1993. Euzonus furciferus Ehlers, 1897 é a única espécie comedora de depósito da região superior do intermareal. Os organismos foram encontrados na praia ao longo de todo o ano, concentrados em uma estreita faixa, e alcançando densidades máximas de 3.029 indivíduos.m-2. Picos de abundância ocorreram em setembro de 1992, com uma média de 681,8 indivíduos.m-2. O recrutamento ocorreu no inverno, com um pico em julho. A biomassa média anual foi estimada em 0,218 gPSLC m-2, com uma produção anual total de 0,466 gPSLC m-2ano-1, e com uma razão P/B de 2,13 ano-1. Valores similares foram encontrados para um poliqueta filtrador existentes na mesma praia, sugerindo que a disponibilidade geral de alimento para cada ambiente particular é mais importante para a produção do que a estratégia trófica empregada pelos organismos que exploram este ambiente