Formation of tidal starting-jet vortices through idealized barotropic inlets with finite length

This paper presents a surface particle image velocimetry study to investigate the dynamics of shallow starting-jet dipoles formed by tidal flow through inlets and their interaction with vorticity formed at the inlet channel lateral boundaries. Vortical structure in the flow field is identified using a local swirl strength criterion evaluated from the two-dimensional flow field. The starting jet dipole vortices and vortices formed as the lateral boundary layers are expelled during flow reversal are characterized by their trajectory, size, and circulation. Using these quantities, a model is developed to predict the size and strength of the expelled lateral boundary layer vortices based on the inlet velocity, channel length, and width of the lateral boundary layer. The expelled boundary layer vortices are found to disrupt the formation of the primary tidal jet dipole through two mechanisms. First, because the boundary layer vortices themselves form a dipole with each half of the starting-jet dipole, the starting-jet vortices are pulled apart and advected away from the inlet mouth early in the tidal cycle, resulting in a reduction in the spin-up time and the amount of vorticity input during starting-jet vortex formation. Second, the advection of each dipole away from the inlet disconnects each starting-jet vortex from the starting jet; hence, the vortices are not fed by fluid in the jet or energized by shear in the jet boundary layers. These influences of the lateral boundary layer on the starting-jet vortices’ formation and propagation are found to be a function of the channel length L, maximum velocity U, and tidal period T, resulting in a predictive value to characterize their trajectory, strength, and evolution.     

Herbicide safeners: uses,limitations, metabolism,and mechanisms of action

Several methods were examined to minimize crops injury caused by herbicides. Thus increase their selectivity. A selective herbicide is one that controls weeds at rates that do not injure the crop. Herbicides are selective in a particular crop within certain limits imposed by the herbicide, the plant, the application rate, the method and time of application, and environment conditions. Herbicide safeners are compounds of diverse chemical families. They are applied with herbicides to protect crops against their injury. Using chemical safeners offer practical, efficient and simple method of improving herbicide selectivity. This method has been applied successfully in cereal crops such as maize, rice and sorghum, against pre-emergence thiocarbamate and chloroacetanilide herbicides. Some reports indicate promising results for the development of safeners for post-emergence herbicides in broadleaved crops. Various hypotheses were proposed explaining mechanisms of action of herbicide safeners: interference with uptake and translocation of the herbicide, alteration in herbicide metabolism, and competition at site of action of the herbicide. Even though progress was made in the development of herbicide safeners and in understanding their mechanisms of action, more research is needed to elucidate clearly how these chemicals act and why their activity is restricted to particular crops and herbicides.     

The Economics of Household Solid Waste Generation and Disposal

We develop a household production model of waste management that explicitly incorporates many of the technical and behavioral elements germane to current regulatory and non-regulatory solid waste policy initiatives. Examination of first-order conditions shows the interaction among household preferences, these production options, and external prices and fees. A simplified simulation of our model illustrates these relationships, showing that household response elasticities can vary widely over common price ranges and that relatively large household welfare gains may be obtained by adopting curbside recycling and unit pricing programs.     

The return of the giants: ecological effects of an increasing elephant population

Northern Botswana and adjacent areas, have the world's largest population of African elephant (Loxodonta africana). However, a 100 years ago elephants were rare following excessive hunting. Simultaneously, ungulate populations were severely reduced by decease. The ecological effects of the reduction in large herbivores must have been substantial, but are little known. Today, however, ecosystem changes following the increase in elephant numbers cause considerable concern in Botswana. This was the background for the "BONIC" project, investigating the interactions between the increasing elephant population and other ecosystem components and processes. Results confirm that the ecosystem is changing following the increase in elephant and ungulate populations, and, presumably, developing towards a situation resembling that before the reduction of large herbivores. We see no ecological reasons to artificially change elephant numbers. There are, however, economic and social reasons to control elephants, and their range in northern Botswana may have to be artificially restricted.     

A computer simulation study of stochastic models to investigate the population dynamics of the screech owl (otus asio) under increased mortality

The work reported in this paper complements an earlier study in which deterministic models were used examine the effects of additional mortality imposed on a Screech Owl, Otus asio, population. Interest lay in the compensatory mechanisms that the owls might be able to adopt in their population dynamics to counteract the overall effect of the additional mortality imposed, in particular when only a part of the population is affected. Stochastic models are used here to address the same questions, and to give more detailed information about the likely behaviour of the owl population than the information an average sizes provided by the deterministic approach.     

Periodically driven circulation near the shore of a lake

Solutions are found for a linear model of the circulation near the shore of a lake that is subject to two diurnal forcing mechanisms. The first is the day/night heating/cooling induced horizontal pressure gradient. The second is an unsteady surface stress modelling a sea breeze/gully wind pattern. The two forcing mechanisms can oppose or reinforce each other depending on their relative phase. The interplay of different dynamic balances at different times and locations in the domain lead to complex circulation patterns especially during the period of flow reversal.     

Enduring decisions: Evaluating environmental impacts for sustainability planning

This paper aims to establish a framework in which potential methods for evaluating environmental impacts can be considered, with particular reference to the UK planning system. To do this a number of complementary ways of conceptualising sustainable development and making it more practical are outlined. Some basic arguments about the meaning of sustainability are reviewed; and some common misconceptions about the concept exposed. The concept of sustainability constraints is outlined and a functional distinction between quantitative and qualitative constraints is proposed. The adoption of sustainability constraints based on measures of environmental capacity is proposed. These suggest significant reductions in consumption of most environmental resources. The efficiency and sufficiency strategies that would be needed to meet the proposed quantified constraints are outlined. In conclusion, evaluation processes and indicators of sustainability, including environmental foot-printing and environmental impact assessment, are discussed, offering some pointers towards the type of measures that will be needed to help implement sustainability strategies.