V. Chv atal proved that no minimal imperfect graph has a small transversal, that is, a set of vertices of cardinality at most + ! 1 which meets every !-clique and every -stable set. In this paper we prove that a slight generalization of this notion of small transversal leads to a conjecture which is as strong as Berge's Strong Perfect Graph Conjecture for a very large class of graphs, although ...

In order to prove the Strong Perfect Graph Conjecture, the existence of a ”simple” property P holding for any minimal non-quasi-parity Berge graph G would really reduce the difficulty of the problem. We prove here that this property cannot be of type ”G is F-free”, where F is any fixed family of Berge graphs.

Our proof (with Robertson and Thomas) of the strong perfect graph conjecture ran to 179 pages of dense matter; and the most impenetrable part was the final 55 pages, on what we called “wheel systems”. In this paper we give a replacement for those 55 pages, much easier and shorter, using “even pairs”. This is based on an approach of Maffray and Trotignon.

We introduce M -tensors. This concept extends the concept ofM -matrices. We denote Z-tensors as the tensors with nonpositive off-diagonal entries. We show that M -tensors must be Ztensors and the maximal diagonal entry must be nonnegative. The diagonal elements of a symmetric M -tensor must be nonnegative. A symmetric M -tensor is copositive. Based on the spectral theory of nonnegative tensors,...

We consider discrete time Heath–Jarrow–Morton type interest rate models, where the interest rate curves are driven by a geometric spatial autoregression field. Strong consistency and asymptotic normality of the maximum likelihood estimators of the parameters are proved for stable no-arbitrage models containing a general stochastic discounting factor, where explicit form of the ML estimators is ...

In reliability or medical studies, we may only observe each ongoing renewal process for a certain period of time. When the underlying distribution F is arithmetic, Vardi (Ann. Statist. 10 (1982b), 772-785) developed the RT algorithm for nonparametric estimation. In this paper we extend the study to the nonarithmetic case and show that the choice of an arbitrary constant in the RT algorithm can ...

We consider the question of strong cosmic censorship in spatially compact, spatially locally homogeneous vacuum models. We show in particular that strong cosmic censorship holds in Bianchi IX vacuum space–times with spherical spatial topology.

Forty-six strains derived from American and French natural populations of Drosophila melanogaster were tested for the presence and activity of hobo elements by using Southern blotting and a gonadal dysgenesis assay. The oldest available strains exhibited weak detectable hybridization to the hobo-element probe and revealed neither hobo-activity potential nor hobo-repression potential. In contras...

At least 16 nutrient elements are required by plants for growth and survival, but the factors affecting element concentration and their temporal evolution are poorly understood. The objective was to investigate i) element concentration pattern in winter wheat as affected by crop developmental stage and weather, and ii) whether, in the short term, element stoichiometry reflects the type of prece...

Introduction: Various iodine isotopes are undergoing radioactive decay except Iodine-127 (I-127. Iodine I-131 is unsealed radioactive material used in nuclear medicine for both diagnostic and therapeutic procedures in Royal Hospital since 2006. In radiotoxic classification, I-131 is in group 2 element. I-131 is highly reactive element due to its volatilization nature. Currently...