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One of the most difficult fractional programs encountered so far is the sum-of-ratios problem. Contrary to earlier expectations it is much more removed from convex programming than other multi-ratio problems analyzed before. It really should be viewed in the context of global optimization. It proves to be essentially N P-complete in spite of its special(More)
We review some recent developments in single-ratio and generalized fractional programming. In the latter case we focus on the maximization of the smallest of several ratios. To introduce these newer results, we provide the necessary context by including some major existing results [63]. In this concise survey we consider applications, theory and algorithms.
We measured the total sputtering yield Y of amorphous water ice at 80 K for 0.35–4 keV He and Ar ions. We found that Y depends linearly on the elastic stopping cross section at low energies as predicted by the standard linear cascade theory of sputtering. As the energy increases, a quadratic dependence with the electronic stopping cross section arises due(More)
OBJECTIVE Predictions of the binding ability of antigen peptides to major histocompatibility complex (MHC) class II molecules are important in vaccine development. The variable length of each binding peptide complicates this prediction. METHODOLOGY Motivated by the search properties of the ant colony system (ACS), a method for the identification of an(More)
Previous studies have shown that the deletion of brnQ from the Corynebacterium glutamicum chromosome results in a significant reduction in l-isoleucine uptake rates, while overexpression of brnFE leads to enhanced l-isoleucine export rates. Given that net excretion rates would be an important factor for high titers of l-isoleucine accumulation, we have(More)
OBJECTIVE To study the effects of gene pta disruption on biosynthesis of L-tryptophan. METHODS The pta gene of the L-tryptophan producing strain E. coli TRTH was disrupted by Red recombination technology and a pta mutant E. coli TRTHdeltapta was constructed. Fed-batch fermentation of E. coli TRTHdeltapta was carried out in 30-Liter fermentor to(More)
We consider a global minimization problem: min{cT-c+dT 1-c E X, y G Y ^h, (X , Y) â F}, where X and Y are polytopes in Rnl and Rn2, respectively; F is a closed convex set in R"~'"~; and Gh (h = l , ,. . , m 2) is an open convex set in Rn2. We propose an alogorithm based on a combination of polyhedral outer approximation, branch-and-bound and cutting plane(More)
The following problem is considered in this paper : max x∈D { m j=1 g j (x)/h j (x)}, where g j (x) ≥ 0 and h j (x) > 0, j = 1, · · · , m are d.c. (difference of convex) functions over a convex compact set D in R n. Specifically, it is reformulated into the problem of maximizing a linear objective function over a feasible region defined by multiple reverse(More)