The prospects for U.S. beef products in the advent of a North American Free Trade Agreement were examined using a system-wide approach to import allocation. Results indicate that increases in the standard of living in Mexico and Canada would stimulate increased importation of processed and unprocessed beef products. Bulk beef product in both countries had expenditure elasticities greater than one, while semi-processed and highly processed beef products had expenditure elasticities of less than one.

AlN single crystals were grown on AlN/SiC seeds by sublimation of AlN powder in TaC crucibles in a nitrogen atmosphere. The seeds were produced by metallorganic chemical vapor deposition (MOCVD) of AlN on SiC crystals. The influence of growth temperature, growth time and source-to-seed distance on the crystallinity and the crystal growth rate were investigated. Crystals were grown in an RF heated sublimation reactor at growth temperatures ranging from 1800-2000°C, at a pressure of 600 Torr, nitrogen flow-rate of 100 sccm and source-to-seed distances of 10 and 35 mm. At 1870°C and a source-to-seed distance of 35 mm, isolated crystals were observed with few instances of coalescence. At 1930°C, a source-to-seed distance of 10 mm and longer growth times (~30 hrs), crystal coalescence was achieved. Above 1930°C, the decomposition of SiC was evidently affecting the growth morphology and resulted in growth of polycrystalline AlN. After an initial nucleation period, the observed growth rates (10-30 µm/hr) were in close agreement with predictions of a growth model that assumed gas-phase diffusion controlled growth. Optical and electron microscope observations revealed step-flow growth, while X-ray diffraction results showed the single crystal nature of the grown material. Single crystalline AlN was grown over surface areas of 200-300 mm2 and was transparent and essentially colorless.

Data from pigs between 12 and 120 kg live weight were used to develop a relationship between the capacity for food bulk and live weight. High bulk foods, intended to limit growth, were offered for 21 days to pigs of 12, 36 (600 g sugar-beet pulp per kg (SBP60)) and 108 (800 g sugar-beet pulp per kg (SBP80)) kg live weight. Control pigs were given a low bulk food C at all weights. After 21 days the pigs were slaughtered and measurements made on the gastro-intestinal tract (GIT). In two additional treatment groups SBP60 was offered from a weight of either 36 kg or 72 kg before SBP80 was offered at 108 kg. Daily live-weight gain, after allowing for the effects of a change of gut fill, was less at all weights on the high bulk foods than on C. At all weights the high bulk foods caused a significant increase in the weights of the stomach, large intestine, caecum and gut fill. Effects on the weight of the small intestine were small. Previous nutrition had no significant effect on the adapted performance, or on the size of the GIT, of pigs given SBP80 at 108 kg but pre-feeding SBP60 significantly increased initial consumption of SBP80. Constrained intake was not directly proportional to live weight beyond 40 kg. The absolute capacity for bulk (Cap, kg water-holding capacity per day) was related to live weight (W, kg) by the quadratic function Cap = (0·192.W) - (0·000299.W2). The value of Cap is predicted to reach a maximum when W = 321 kg. The combined weights of the large intestine and caecum (WLIC) changed with W in ways that were similar to the way in which Cap changed. In addition the ratio of Cap to WLIC was close to constant. The combined weight of the large intestine and the caecum may determine the capacity for food bulk in pigs.

We present recent results on bulk GaN crystallization. The best quality GaN crystals grown from the solution at high N2 pressure without an intentional seeding are single crystalline platelets of stable morphology reaching dimensions up to 10 mm. The fastest growth direction for such crystals is [1 0 0], perpendicular to the GaN c-axis. The maximum stable growth rate perpendicular to crystal c-axis is determined from the experiment and used for an estimate of the effective supersaturation for the {10 0} face assuming two dimensional layer growth. The heat of GaN disssolution, determined from experimental solubility data, is used for the estimation of the edge energy of 2-D nuclei on the growing {10 0} face. Bulk crystal growth seeded by a single hexagonal needle with well developed {10 0} faces is also reported. The crystallization mechanisms and morphological stability in seeded growth of GaN are discussed on the basis of experimental results. The physical properties of the GaN crystals and homoepitaxial layers grown on them are briefly reviewed.