39 research outputs found
Classical Exact Algorithms for the Capacitated Vehicle Routing Problem
No full textIn this chapter we present an overview of the early exact methods used for the solution of the Capacitated Vehicle Routing Problem (CVRP). The CVRP is an extension of the well-known Traveling Salesman Problem (TSP), calling for the determination of a Hamiltonian circuit with minimum cost visiting exactly once a given set of points. Therefore, the foundation of many exact approaches for the CVRP were derived from the extensive and successful work done for the exact solution of the TSP. However, even if tremendous progress has been made with respect to the first algorithms, such as the tree search method by Christofides and Eilon [17], the CVRP is still far from being satisfactorily solved. Our analysis encompasses more than three decades of research and examines the main families of approaches, from direct tree search methods based on Branch-and-Bound to column generation and Branch-and-Cut algorithms presented around the year 2000. The wide variety and richness of methods proposed in these early decades of CVRP history is witnessed by the good number of survey works that analyzed the relevant literature. Following the first comprehensive work of Laporte and Nobert [39], several review papers were devoted to the analysis of exact algorithms for the VRP as those of Laporte [36], Toth and Vigo [52, 53], Bramel and Simchi-Levi [15], Naddef and Rinaldi [47], Cordeau et al. [20], and Baldacci, Toth, and Vigo [10,11]. More recent Branch-and-Cut-and-Price algorithms, which have successfully combined and enhanced those described in the following, will be covered in detail in Chapter 3
Selenomethionine reduces visual deficits due to developmental methylmercury exposures
No full textPublished in final edited form as:
Physiol Behav. 2008 Jan 28; 93(1-2): 250–260.Developmental exposures to methylmercury (MeHg) have life-long behavioral effects. Many micronutrients, including selenium, are involved in cellular defenses against oxidative stress and may reduce the severity of MeHg-induced deficits. Zebrafish embryos (<4 hours post fertilization, hpf) were exposed to combinations of 0.0-0.30 μM MeHg and/or selenomethionine (SeMet) until 24 hpf then placed in clean medium. Fish were tested as adults under low light conditions (~60 μW/m2) for visual responses to a rotating black bar. Dose-dependent responses to MeHg exposure were evident (ANOVA, P<0.001) as evidenced by reduced responsiveness, whereas SeMet did not induce deficits except at 0.3 μM,. Ratios of SeMet:MeHg of 1:1 or 1:3 resulted in responses that were indistinguishable from controls (ANOVA, P<0.001). No gross histopathologies were observed (H&E stain) in the retina or optic tectum at any MeHg concentration. Whole-cell, voltage-gated, depolarization-elicited outward K+ currents of bipolar cells in intact retina of slices adult zebrafish were recorded and outward K+ current amplitude was larger in bipolar cells of MeHg-treated fish. This was due to the intense response of cells expressing the delayed rectifying IK current; cells expressing the transient IA current displayed a slight trend for smaller amplitude among MeHg-treated fish. Developmental co-exposure to SeMet reduced but did not eliminate the increase in the MeHg-induced IK response, however, IA responses increased significantly over MeHg-treated fish to match control levels. Electrophysiological deficits parallel behavioral patterns in MeHg-treated fish, i.e., initial reactions to the rotating bar were followed by periods of inactivity and then a resumption of responses
Vitamin B6 and selenium supplementation induce contrasting effects in the transsulfuration pathway of juvenile rainbow trout (Oncorhynchus mykiss) with interactive effects in stressed fish
No full textThis study aimed to investigate the interactive effects between selenium and vitamin B6 supplementation in the transsulfuration pathway and glutathione metabolism of juvenile rainbow trout (Oncorhynchus mykiss) and in response to oxidative stress. Four plant protein-based diets (48% crude protein and 23% total lipid) naturally low in selenium and vitamin B6 were designed: CTL, without any selenium or vitamin B6 supplementation; SEL, supplemented with 4 mg selenium per kg diet supplied as selenomethionine (SeMet); PYR, supplemented with 50 mg pyridoxine hydrochloride (PN.HCL) per kg diet and SEPY, co-supplemented with SeMet and PN.HCL. Groups of 50 juvenile rainbow trout (28 ± 3 g) were randomly distributed in a flow-through system in triplicate tanks per treatment and fed on one of the experimental diets two times per day for twelve weeks. In addition, 15 fish per tank were exposed to periodic hyperoxia stress for one week prior to sampling. Therefore, the dissolved oxygen levels in the tanks were increased from 8 mg/l to 13 mg/l during 8 h per day. Dietary SeMet supplementation increased feed intake (1.44 ± 0.03 vs. 1.49 ± 0.02), but without any significant differences in final body weight (180 ± 3 vs 184 ± 3 g) between groups. SeMet supplementation was associated with increased liver and muscle S-adenosylhomocysteine levels. There was a general decrease of transsulfuration metabolites by SeMet supplementation in muscle tissue. On the other hand, PN.HCL supplementation increased the gene expression of the first step transsulfuration pathway enzyme, cbs, in liver tissue with similarly higher levels of transsulfuration metabolite homocysteine and total glutathione. Fish subjected to periodic hyperoxia showed lower reduced glutathione levels in liver tissue, which indicates modifications to the cellular redox system of fish in response to the stress. In stressed fish, interactive effects of SeMet and PN.HCL supplementation were detected on transsulfuration metabolites in both liver and muscle tissue. The results show that SeMet and PN.HCL supplementation can induce contrasting effects in the transsulfuration system of fish. The significant interactions in stressed fish between SeMet and PN.HCL supplementation indicate that both nutrients are required to maintain glutathione homeostasis under challenging environmental conditions
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Effect of dietary methionine on selenomethionine metabolism and utilization for selenoproteins
No full textThe effects of dietary methionine (Met) on the utilization of selenium (Se) from stored tissue Se and dietary selenomethionine (SeMet) for glutathione peroxidase (GSH-Px) synthesis were studied in male rats. Plasma, liver and muscle Se significantly increased when rats were fed 0.5 mg Se/kg diet as SeMet in a Met-deficient diet for 21 d, whereas tissue GSH-Px activities decreased 43-50% during the SeMet supplementation period, suggesting that Se is deposited as SeMet in general body proteins. By calculation, a significant lower percentage of Se was associated with GSH-Px in Met-deficient as compared to Met-supplemented rats. Dietary Met supplementation increased the incorporation of 75Se from 75SeMet into specific rat selenoproteins in addition to liver GSH-Px. Overall, these results suggest that intact SeMet is preferentially incorporated non-specifically into general body proteins in Met-deficient rats, whereas with supplemental Met, more SeMet is degraded and the released Se used for specific selenoprotein synthesis. (Abstract shortened with permission of author.
Selenium uptake, translocation, subcellular distribution and speciation in winter wheat in response to phosphorus application combined with three types of selenium fertilizer
No full text© 2023, The Author(s). cc-byBackground: Selenium (Se) deficiency causes a series of health disorders in humans, and Se concentrations in the edible parts of crops can be improved by altering exogenous Se species. However, the uptake, transport, subcellular distribution and metabolism of selenite, selenate and SeMet (selenomethionine) under the influence of phosphorus (P) has not been well characterized. Results: The results showed that increasing the P application rate enhanced photosynthesis and then increased the dry matter weight of shoots with selenite and SeMet treatment, and an appropriate amount of P combined with selenite treatment increased the dry matter weight of roots by enhancing root growth. With selenite treatment, increasing the P application rate significantly decreased the concentration and accumulation of Se in roots and shoots. P1 decreased the Se migration coefficient, which could be attributed to the inhibited distribution of Se in the root cell wall, but increased distribution of Se in the root soluble fraction, as well as the promoted proportion of SeMet and MeSeCys (Se-methyl-selenocysteine) in roots. With selenate treatment, P0.1 and P1 significantly increased the Se concentration and distribution in shoots and the Se migration coefficient, which could be attributed to the enhanced proportion of Se (IV) in roots but decreased proportion of SeMet in roots. With SeMet treatment, increasing the P application rate significantly decreased the Se concentration in shoots and roots but increased the proportion of SeCys2 (selenocystine) in roots. Conclusion: Compared with selenate or SeMet treatment, treatment with an appropriate amount of P combined with selenite could promote plant growth, reduce Se uptake, alter Se subcellular distribution and speciation, and affect Se bioavailability in wheat
