A D.C. Algorithm via Convex Analysis Approach for Solving a Location Problem Involving Sets

We study a location problem that involves a weighted sum of distances to closed convex sets. As several of the weights might be negative, traditional solution methods of convex optimization are not applicable. After obtaining some existence theorems, we introduce a simple, but effective, algorithm for solving the problem. Our method is based on the Pham Dinh - Le Thi algorithm for d.c. programming and a generalized version of the Weiszfeld algorithm, which works well for convex location problems

Evaluation of agro-industrial by-products as protein sources for duck production in the Mekong Delta of Vietnam

This thesis is based on four studies to determine the nutritive value and ileal and total tract amino acid digestibility of agro-industrial by-products, and the effects of inclusion of these by-products in diets on the biological performance of growing crossbred Muscovy and common ducks in the Mekong Delta, Vietnam. The results show that brewery waste (BW) was characterised by high protein content,good balance of essential amino acids, but high crude fibre content. The best growth performance was observed when 50% of the concentrate was replaced by BW for both Muscovy and common ducks. The crossbred Muscovies had better performance and gave higher economic benefit than the local Muscovies, and common ducks gave the lowest profit. BW could be offered either in mixed or separate feeding systems without any effects on performance and carcass yield (Paper I and II). Soya waste (SW) and ensiled shrimp waste (ESW) are good protein sources, but low in dry matter (DM) and methionine content (SW) and high in chitin content (ESW). The best performance in terms of growth rate and carcass quality was found with replacement of up to 60% of soybean meal by SW, and only 20% of fish meal by ESW, which gave the lowest feed costs (Paper III). The inclusion of ESW in diets for adult crossbred common ducks resulted in a linear decrease of the apparent total tract digestibility of dry matter, organic matter, ether extract, N free extract and N retention with increasing levels of ESW. The digestibility of individual amino acids followed a similar pattern to the nutrient digestibility. The apparent total tract digestibility of most individual amino acids was higher than the apparent ileal value (Paper IV). It can be concluded that from nutritive and economic apects the three agro-industrial byproducts evaluated have proven to be acceptable feed ingredients in duck diets. Replacement up to levels of 20% (ESW), 50% (BW) and 60% (SW) of fish meal, concentrate and soybean meal, respectively, in diets for growing crossbred ducks can be recommended under the conditions of the Mekong Delta