Recreational fishing: Its expansion, its economic value and aquaculture's role in sustaining it

Economic growth usually leads to a substantial increase in the demand for recreational fishing, and China is likely to follow this trend. Factors influencing this expansion in demand are identified. Recreational fishing is of major economic importance in higher income countries and indicators of its economic significance are given. Growing demand for recreational fishing results in intensified involvement of recreational fishers in conflicts about resource use. With increasing demand for recreational fishing, recreational fishers face growing competition with one another for limited fish stocks and with commercial fishers. Their concerns for environmental threats to fish stocks also intensify. Furthermore, some strategies of recreational fishers are increasingly criticised by conservationists. Governments, therefore, are put under pressure to adopt policies to address these conflicts. Some of the policy measures adopted to help sustain the fisheries and reduce conflict are outlined. These include limits on the catch and exclusive zones for recreational fishing. However, wild stocks of fish are likely to remain under mounting harvesting and other pressures. Therefore, we need to consider the role that aquaculture can play in overcoming these problems. The possible ways in which aquaculture can do this are outlined and discussed.

Three-point boundary value problems for second-order, ordinary, differential equations

We establish existence results for solutions to three-point boundary value problems for nonlinear, second-order, ordinary differential equations with nonlinear boundary conditions. (C) 2001 Elsevier Science Ltd. All rights reserved.

Topological methods for some boundary value problems

We establish existence of solutions for a finite difference approximation to y = f(x, y, y ') on [0, 1], subject to nonlinear two-point Sturm-Liouville boundary conditions of the form g(i)(y(i),y ' (i)) = 0, i = 0, 1, assuming S satisfies one-sided growth bounds with respect to y '. (C) 2001 Elsevier Science Ltd. All rights reserved.

Electron beam current loss at the high-vacuum-high-pressure boundary in the environmental scanning electron microscope

A significant loss in electron probe current can occur before the electron beam enters the specimen chamber of an environmental scanning electron microscope (ESEM). This loss results from electron scattering in a gaseous jet formed inside and downstream (above) the pressure-limiting aperture (PLA), which separates the high-pressure and high-vacuum regions of the microscope. The electron beam loss above the PLA has been calculated for three different ESEMs, each with a different PLA geometry: an ElectroScan E3, a Philips XL30 ESEM, and a prototype instrument. The mass thickness of gas above the PLA in each case has been determined by Monte Carlo simulation of the gas density variation in the gas jet. It has been found that the PLA configurations used in the commercial instruments produce considerable loss in the electron probe current that dramatically degrades their performance at high chamber pressure and low accelerating voltage. These detrimental effects are minimized in the prototype instrument, which has an optimized thin-foil PLA design.