An apparatus has been designed and constructed that will allow determination of the mechanical behavior of polymer specimens subject to applied tensile and compressive loading, while the sample is simultaneously subject to a hydrostatic pressure environment. The moduli of high-density polyethylene and polypropylene determined from compressive tests show a significant increase with pressure. Tensile nominal stress-strain curves have been obtained at various pressures up to 100 000 psi. These show that the yield stress also increases significantly with increasing pressure for both materials. The nature of yielding and fracture is found to be quite different for the two polymers studied. Polyethylene tends to deform more by shear, and the necked region at high pressures reduces to a fine point before separation. In polypropylene, fracture occurs by plastic tearing across the cross section. An attempt is made to account for the experimental results by use of yield criteria that includes a hydrostatic pressure component. Consideration is also given to the effect of finite deformation theory on the increase in modulus of elasticity under a high pressure environment. The specific nature of the effects produced by the high pressure is found to depend strongly on the molecular structure of the polymer.

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Environmentally sound greenhouse production requires that: demand for market products is understood; greenhouse design addresses the climate circumstances; input resources are available and consumed efficiently, and; there must be a reasonable balance of production products to the environmental impacts from system. Engineering greenhouse production systems to meet these requirements must include: a cost-effective and structurally sound facility; various subsystems controlled to interact harmoniously together; and educated and experienced system operators. The major components of the environmentally sound greenhouse are: Superstructure and glazing (for a specific location and climate conditions); Climate control subsystems (ventilation, heating, cooling, CO 2 control, pest protection, energy conservation, shading/lighting); Monitoring and control (for system operations data; decisionsupport systems; and, operations control procedures); Automation systems (for quality control, and effective resource utilization); and Crop nutrient delivery system (for control of plant root zone environment). Effective greenhouse engineering design, operations and management, must incorporate input from academic, private and public sectors of society. Therefore this team of researchers, educators, industry/ business, and experienced crop production operators has cooperated to include a current real-world applications perspective to the presentation. Greenhouse production systems are described that not only include the fundamentals for success, but also the combination of subsystems , at appropriate technological levels to meet the design requirements and restrictions for success. The collaborators on this presentation have capabilities and experiences of successful greenhouse production systems from around the world that range from simple, low-input systems to highly complex production systems. Our goal is to emphasize the current basics of greenhouse design, and to support the symposium about greenhouse production systems for people.