A multiple-objective linear programming model for the citrus rootstock selection problem in Florida

Citrus is one of Florida's key agricultural crops, with annual production accounting for over 70% of all U.S. production. During the 1970s and 1980s, citrus blight, tristeza and freezes caused citrus rootstock selection to become a critical issue in Florida, and it remains so today. This paper describes a multiple-objective linear programming model that we have developed for solving the citrus roostock selection problem in Florida. The model has four objective functions. These functions, together with the constraints of the model, capture the main factors that Florida citrus growers use in choosing portfolios of rootstocks for planting in their groves. We tested the usefulness of this model by solving an experimental application for the Fort Pierce area with the interactive STEM algorithm. From our research we conclude that, when properly solved with the aid of STEM, the multiple-objective linear programming model has the potential to serve Florida citrus growers as a useful decision aid in formulating rootstock selection plans. © 1997 John Wiley & Sons, Ltd.     

SPECIESISM AND MORAL STATUS

Abstract: Many people believe that all human life is of equal value. Most of them also believe that all human beings have a moral status superior to that of nonhuman animals. But how are these beliefs to be defended? The mere difference of species cannot in itself determine moral status. The most obvious candidate for regarding human beings as having a higher moral status than animals is the superior cognitive capacity of humans. People with profound mental retardation pose a problem for this set of beliefs, because their cognitive capacities are not superior to those of many animals. I argue that we should drop the belief in the equal value of human life, replacing it with a graduated view that applies to animals as well as to humans.     

Psychological functions of urban busdrivers exposed to exhaust gases: A cross sectional study of urban busdrivers in Denmark

Busdrivers are assumed to be exposed to air pollutants in the exhaust gases from other vehicles via the defroster system of the buses. A cross sectional study using questionnaires and psychological tests was conducted on 171 urban busdrivers from the three largest cities in Denmark (Copenhagen, Aarhus, and Odense). A group of 47 commuter train drivers, assumed to be exposed to air pollutants no more than the average citizen, was studied as referents. The air of the busdrivers' breathing zone was analysed for its content of toxic agents. The hygienic effect in the winter season was found to be 0.63 and in the summer season 0.36. The year mean hygienic effect was found to be 0.42. Neurastenic complaints such as difficulties of concentration, verbal retrieval, and tiredness were significantly more frequent among the busdrivers, particularly in the Copenhagen group. On psychological tests of verbal and spatial learning, retrieval and memory, psychomotor functions, visual perception, and vigilance, the Copenhagen busdrivers compared to the reference group only showed significant dysfunctions of verbal learning and long-term memory. The bus-drivers from the two smaller cities did not differ significantly from the reference group. It is suggested that the subjective complaints are due to psychosocial stressors in the busdrivers' condition of work, whereas the few differences in psychological test results may indicate a subclinical effect caused by the presence of neurotoxic agents in the busdrivers' working environment.