Rank of stably dissipative graphs

For the class of stably dissipative Lotka–Volterra systems we prove that the rank of its defining matrix, which is the dimension of the associated invariant foliation, is completely determined by the system’s graph.     

Metaheuristics for the linear ordering problem with cumulative costs

The linear ordering problem with cumulative costs (LOPCC) is a variant of the well-known linear ordering problem, in which a cumulative propagation makes the objective function highly non-linear. The LOPCC has been recently introduced in the context of mobile-phone telecommunications. In this paper we propose two metaheuristic methods for this NP-hard problem. The first one is based on the GRASP methodology, while the second one implements an Iterated Greedy-Strategic Oscillation procedure. We also propose a post-processing based on Path Relinking to obtain improved outcomes. We compare our methods with the state-of-the-art procedures on a set of 218 previously reported instances. The comparison favors the Iterated Greedy - Strategic Oscillation with the Path Relinking post-processing, which is able to identify 87 new best objective function values.     

Variable neighborhood search with ejection chains for the antibandwidth problem

In this paper, we address the optimization problem arising in some practical applications in which we want to maximize the minimum difference between the labels of adjacent elements. For example, in the context of location models, the elements can represent sensitive facilities or chemicals and their labels locations, and the objective is to locate (label) them in a way that avoids placing some of them too close together (since it can be risky). This optimization problem is referred to as the antibandwidth maximization problem (AMP) and, modeled in terms of graphs, consists of labeling the vertices with different integers or labels such that the minimum difference between the labels of adjacent vertices is maximized. This optimization problem is the dual of the well-known bandwidth problem and it is also known as the separation problem or directly as the dual bandwidth problem. In this paper, we first review the previous methods for the AMP and then propose a heuristic algorithm based on the variable neighborhood search methodology to obtain high quality solutions. One of our neighborhoods implements ejection chains which have been successfully applied in the context of tabu search. Our extensive experimentation with 236 previously reported instances shows that the proposed procedure outperforms existing methods in terms of solution quality.     

Powder Pattern Hyperfine Spectroscopy of Shallow- Donor Muonium Centres

The hyperfine spectroscopy of muonium in II–VI semiconductors is reviewed, suggesting that whereas hydrogen is a deep-level defect in ZnS, ZnSe and ZnTe, it constitutes a shallow donor in ZnO, CdS, CdSe and CdTe. Shallow and deep states coexist in CdTe. Using new data for ZnO, it is shown that the principal values of the muonium hyperfine tensor may be obtained with equal facility from measurements in longitudinal or in transverse magnetic field, and from samples that are polycrystalline powders or single crystals. Spin density on the central muon in the shallow states correlates with the electron binding energy or donor depth. This revised version was published online in September 2006 with corrections to the Cover Date.     

A finite element solution of an added mass formulation for coupled fluid-solid vibrations

Summary. A finite element method to approximate the vibration modes of a structure in contact with an incompressible fluid is analyzed in this paper. The effect of the fluid is taken into account by means of an added mass formulation, which is one of the most usual procedures in engineering practice. Gravity waves on the free surface of the liquid are also considered in the model. Piecewise linear continuous elements are used to discretize the solid displacements, the variables to compute the added mass terms and the vertical displacement of the free surface, yielding a non conforming method for the spectral coupled problem. Error estimates are settled for approximate eigenfunctions and eigenfrequencies. Implementation issues are discussed and numerical experiments are reported. In particular the method is compared with other numerical scheme, based on a pure displacement formulation, which has been recently analyzed. Received August 31, 1998 / Published online July 12, 2000     

Asymmetric Diels–Alder cycloadditions of d-erythrose 1,3-butadienes to achiral t-butyl 2H-azirine 3-carboxylate

Two d-erythrose 1,3-butadienes were reacted with electrophilic achiral t-butyl 2H-azirine 3-carboxylate giving cycloadducts with good yields and moderate selectivity. The isomers could be separated to give the major (R)-isomers at C-2 in approximately 50% yield in both cases. Alternatively LACASA-DA methodology was applied to one of the reactions leading to homochiral (R)- and (S)-products by changing the chiral nature of an extra chiral BINOL inductor used.     

Unexpected reactivity of trifluoromethylated olefins with indole: a mechanistic investigation

Several trifluoromethylated compounds were reacted with indole sodium salt, leading to monofluorinated compounds. The unexpected products formation was rationalized by DFT calculations.     

Evaluation of low-dose irradiation on microbiological quality of white carrots and string beans

The minimally processed food provided the consumer with a product quality, safety and practicality. However, minimal processing of food does not reduce pathogenic population of microorganisms to safe levels. Ionizing radiation used in low doses is effective to maintain the quality of food, reducing the microbiological load but rather compromising the nutritional values and sensory property. The association of minimal processing with irradiation could improve the quality and safety of product. The purpose of this study was to evaluate the effectiveness of low-doses of ionizing radiation on the reduction of microorganisms in minimally processed foods. The results show that the ionizing radiation of minimally processed vegetables could decontaminate them without several changes in its properties.