Temperature Dependence of the Dynamics of Portevin-Le Chatelier Effect in Al-2.5%Mg alloy

Tensile tests were carried out by deforming polycrystalline samples of Al-2.5%Mg alloy at four different temperatures in an intermediate strain rate regime of 2x10-4s-1 to 2x10-3s-1. The Portevin-Le Chatelier (PLC) effect was observed throughout the strain rate and temperature region. The mean cumulative stress drop magnitude and the mean reloading time exhibit an increasing trend with temperature which is attributed to the enhanced solute diffusion at higher temperature. The observed stress-time series data were analyzed using the nonlinear dynamical methods. From the analyses, we could establish the presence of deterministic chaos in the PLC effect throughout the temperature regime. The dynamics goes to higher dimension at a sufficiently high temperature of 425K but the complexity of the dynamics is not affected by the temperature.Comment: 18 pages, 8 figures; accepted in Met. Mater. Trans.

Evaluating variation in feed attributes of elite grain sorghum cultivars

Current cereal breeding programmes at commodity-oriented research centres emphasize grain yields with little consideration for fodder yield and quality. In farming systems with livestock, the use of varieties with high-grain yields but low stover yields may be rejected by farmers. This study investigated the variability in chemical characteristics and digestibility of stovers among 10 `best-bet' sorghum cultivars selected for grain yield with the view to study the merits of selecting among cultivars for feed attributes. Cluster analysis of N, ADF and NDF obtained from chemical analyses, and in sacco dry matter digestibility of stovers showed that wide intercultivar variations existed at the three-cluster solution (designated cluster groups III, IV, V). Cultivar BES, the only member of group IV, had a relatively high N content (90 g kg-1 DM), a high 48 h dry matter loss (637 g kg-1 DM) and relatively low ADF and NDF values (386 and 598 g kg -1 DM). Members of group V (KSV 8 and Gaya Early) contained the lowest N (67 g kg-1 DM), lowest digestibility coefficient (511 g kg-1 DM) and highest ADF and NDF values 466 and 665 g kg-1 DM). Values for members of group III (ICSV 111, ICSV 210, ICSV 247, ICSV 400, ICSH 89009NG and ICSH 89002NG) were intermediate. There were no significant correlations between indicators of nutritive values, grain yield and grain mass. The results suggest existence of variation in indicators of nutritive values within the cultivars to warrant consideration for selection among these for detailed nutritional studies, and that improving the nutritive values within the cultivars to warrant consideration for selection among these for detailed nutritional studies, and that improving the nutritive value in stovers through breeding may not necessarily impair grain yield and grain mass

A unified approach to approximating partial covering problems

An instance of the generalized partial cover problem consists of a ground set U and a family of subsets S ⊆ 2 U. Each element e ∈ U is associated with a profit p(e), whereas each subset S ∈ S has a cost c(S). The objective is to find a minimum cost subcollection S ′ ⊆ S such that the combined profit of the elements covered by S ′ is at least P, a specified profit bound. In the prize-collecting version of this problem, there is no strict requirement to cover any element; however, if the subsets we pick leave an element e ∈ U uncovered, we incur a penalty of π(e). The goal is to identify a subcollection S ′ ⊆ S that minimizes the cost of S ′ plus the penalties of uncovered elements. Although problem-specific connections between the partial cover and the prizecollecting variants of a given covering problem have been explored and exploited, a more general connection remained open. The main contribution of this paper is to establish a formal relationship between these two variants. As a result, we present a unified framework for approximating problems that can be formulated or interpreted as special cases of generalized partial cover. We demonstrate the applicability of our method on a diverse collection of covering problems, for some of which we obtain the first non-trivial approximability results