In the literature of graph recognition algorithms, two of the most extensively covered graphs are interval graphs and permutation graphs [6, 2]. One way of generalizing both interval graphs and permutation graphs is the intersection graph of a collection of trapezoids with corner points lying on two parallel lines. Such a graph is called the trapezoid graph [3, 4]; Ma and Spinrad [8] show that ...

Tolerance graphs have been extensively studied since their introduction, due to their interesting structure and their numerous applications, as they generalize both interval and permutation graphs in a natural way. It has been conjectured by Golumbic, Monma, and Trotter in 1984 that the intersection of tolerance and cocomparability graphs coincides with bounded tolerance graphs. Since cocompara...

gibbs and martin build on durkheim’s view that the degree of social integration is inversely related to the rate of suicide. according to gibbs and martin, which is expressed in terms of five axioms, the rate of suicide is a function of the degree of status integration in a society. this theory has been extensively subjected to experimental studies, which have supported its axioms. most of thes...

Tunisia’s unemployment rate has been among the highest in the world for almost two decades. This article claims that such a high rate reflects measurement problems rather than labor market inefficiency. After discussing the reasons why unemployment rates may not be comparable across countries and reviewing the tools that are available to analyze unemployment in a specific country, the article p...

The focus of my research is extremal graph theory and random combinatorial structures. I have also worked in a variety of other areas, including intersecting hypergraphs, the theory of positional games and Ramsey theory. Combinatorics, and particularly graph theory, has a wide variety of applications. My own research in the edit distance of graphs has applications in biology and computer scienc...

animals that breed in ground holes can be exposed to higher doses of radiation from natural radioactive isotopes, including radon and its daughters, present in soil air. one of such species is the sand martin riparia riparia. examination of natural burrows in sand mines revealed radon levels of 2.82-1320 bq/m3 in the examined soil horizon where martins dug their burrows. it was shown that adult...

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Bill Martin studied biology at Texas A&M and the University of Hannover. He did his PhD at the Max-Planck Institute for Breeding Research in Cologne under the generous supervision of Heinz Saedler, who discovered the transposons known as IS elements. After fi nishing his PhD in 1988, he did his postdoctoral work on chloroplastcytosol isoenzymes, endosymbiosis, and gene transfer at the Universit...

Martin Nowak is Head of the Program in Theoretical Biology at the Institute for Advanced Study in Princeton. He will move to Harvard University later this year. Nowak’s work initiated the field of virus dynamics — the mathematical description of how viruses spread within infected individuals. This led to a quantitative understanding of HIV infection (see ‘Virus dynamics’, by Martin Nowak and Ro...