Hitting all Maximal Independent Sets of a Bipartite Graph

We prove that given a bipartite graph G with vertex set V and an integer k, deciding whether there exists a subset of V of size k hitting all maximal independent sets of G is complete for the class Sigma_2^P.Comment: v3: minor chang

Structural analysis, magnetic and transport properties of the (Ru1-xCox)Sr2GdCu2O8 system

The effects of Co substitution on structural and superconducting properties of RuSr2GdCu2O8 compound have been studied. Rietveld refinements of the X-ray diffraction patterns indicate that the cobalt ion progressively replaces ruthenium sites. This replacement induces significant changes on the crystal structure and on the magnetic and superconducting properties. The effects Co substitution on the superconducting behaviour, and more particulary on the changes induce by the hole doping mechanism, were investigated in (Ru1-xCox)Sr2GdCu2O8 by a "bond valence sum" analysis with Co content from x= 0.0 to x = 0.2. The weak ferromagnetic transition at Tm= 138.2 K is shifted to lower temperature, and suppressed at higher Co content. From the crystallographic point of view the Ru-O(1)-Cu bond angle, associated to the rotation of the RuO6 octahedra, around the c-axis remain essetially constant when Ru is substituted by Co. Furthermore, increasing Co content has the effect to increase the weak ferromagnetic moment, which may be interpreted as the main responsible for breaking the delicate balance between magnetic and superconducting ordering.Comment: 21 pages, 8 figure

Tissue eosinophilia induced by recombinant human interleukin-5 in the hamster cheek pouch membrane

Interleukin-5 (IL-5) is a cytokine that preferentially effects the development and function of eosinophils, and is considered important in the pathophysiology of allergic inflammation. In this study, we evaluated the ability of recombinant human IL-5 (rHu IL-5) to promote tissue eosinophilia and the importance of this eosinophilia to pathological alterations in vascular function. Repetitive subcutaneous administration for 18 days of rHu IL-5 resulted in a 7-fold increase in the number of eosinophils found in the ipsilateral hamster cheek pouch membrane. The contralateral cheek pouch membrane and peritoneum of these animals showed lesser but significant elevations in the number of eosinophils. In contrast, denatured rHu IL-5 did not elevate eosinophils in these tissues. Through the use of intravital microscopy and fluorometric analysis, rHu IL-5 treated hamster cheek pouch membranes were evaluated for alterations in microvascular permeability, using plasma clearance of FITC-dextran 150 as an index. Despite promoting a prominent tissue eosinophilia, the repetitive subcutaneous injections of rHu IL-5 did not alter the clearance of FITC-dextran 150. Topical application of rHu IL-5 to the cheek pouch, also, had no effect on the clearance of FITC-dextran 150. Immunofluorescence observations using an antibody to the granule protein, eosinophil peroxidase, indicated that the recruited cells had not degranulated. Our results support the importance of IL-5 in the recruitment of tissue eosinophils, but further stimulation is probably required to cause degranulation of these cells and the ensuing tissue damage

Role of twin boundaries on the vortex dynamics in YBa2_2Cu3_3O7_7

By means of a novel technique of rotating the applied current we have directly measured the influence of twin boundaries on the vortex motion in a YBa$_2$Cu$_3$O$_7$ single crystal. The results indicate that the effect of twin planes on the vortex dynamics starts to develop below a certain temperature, being responsible for an anisotropic viscosity in the vortex liquid state and a guided motion in the solid state.Comment: 4 pages, 4 figure

The apparent roughness of a sand surface blown by wind from an analytical model of saltation

We present an analytical model of aeolian sand transport. The model quantifies the momentum transfer from the wind to the transported sand by providing expressions for the thickness of the saltation layer and the apparent surface roughness. These expressions are derived from basic physical principles and a small number of assumptions. The model further predicts the sand transport rate (mass flux) and the impact threshold (the smallest value of the wind shear velocity at which saltation can be sustained). We show that, in contrast to previous studies, the present model's predictions are in very good agreement with a range of experiments, as well as with numerical simulations of aeolian saltation. Because of its physical basis, we anticipate that our model will find application in studies of aeolian sand transport on both Earth and Mars

Comparing league formats with respect to match importance in Belgian football

Recently, most clubs in the highest Belgian football division have become convinced that the format of their league should be changed. Moreover, the TV station that broadcasts the league is pleading for a more attractive competition. However, the clubs have not been able to agree on a new league format, mainly because they have conflicting interests. In this paper, we compare the current league format, and three other formats that have been considered by the Royal Belgian Football Association. We simulate the course of each of these league formats, based on historical match results. We assume that the attractiveness of a format is determined by the importance of its games; our importance measure for a game is based on the number of teams for which this game can be decisive to reach a given goal. Furthermore, we provide an overview of how each league format aligns with the expectations and interests of each type of club

Técnica microquirúrgica de anastomosis vascular sin sutura en el trasplante experimental de órganos

Las anastomosis vasculares para e! trasplante de órganos en pequeños animales se realizan habitualmente por sutura manual ya sea continua o discontinua, aunque en los últimos años se ha difundido una técnica sin sutura consistente en la utilización de «cuffs». En e! presente trabajo se describe la técnica de! cuff que nuestro equipo utilizó para la realización de las anastomosis vasculares en e! trasplante experimental de órganos. El cuff consta de un tubo o cuerpo, que se prolonga por una pestaña, y su tamaño es diferente según el calibre del vaso que se pretende anastornosar. Entre las ventajas que ofrece su utilización respecto de la sutura manual, destacan su sencillo aprendizaje, bajo coste y el reducido tiempo en que se realizan las anastomosis, que siempre son estancas. Se concluye que esta técnica constituye una alternativa a las ya clásicas técnicas de sutura manual y no aumenta al porcentaje de complicaciones, permitiendo además supervivencias a largo plazo en los modelos experimentales que fueron estudiados.Vascular anastornoses in organ transplants of small anirnals are usually performed with a manual suture using interrupted or continuous stitcbes, although over the last few years a suturefree technique has been deueloped consisting of the use of cuffs. In this paper, the cuff technique which our team used to perform vascular anastomoses in experimental organ transplants, is described. The cuff is made up oi a tube or body wich has a prolongation or up, tbe size varying according to the calibre of the blood vessel to be anastomosed. The advantages of this method in cornparison with manual sutures, is the ease with which the tecbnique is learnt, its low cost, and the speed with which the anastomoses are carried out, all of which are watertight. In conclusion, this technique constitutes an alternative to the classical manual suture techniques without increasing the percentage of cornplications, and allowing long-term suruiual rates in the experimental models studied

Vortex Plastic Motion in Twinned Superconductors

We present simulations, without electrodynamical assumptions, of $B(x,y,H(t)), M(H(t))$, and $J_c(H(t))$, in hard superconductors, for a variety of twin-boundary pinning potential parameters, and for a range of values of the density and strength of the pinning sites. We numerically solve the overdamped equations of motion of up to 10^4 flux-gradient-driven vortices which can be temporarily trapped at $\sim 10^6$ pinning centers. These simulations relate macroscopic measurements (e.g., M(H), ``flame'' shaped $B(x,y)$ profiles) with the underlying microscopic pinning landscape and the plastic dynamics of individual vortices

Leibniz Seminorms and Best Approximation from C*-subalgebras

We show that if B is a C*-subalgebra of a C*-algebra A such that B contains a bounded approximate identity for A, and if L is the pull-back to A of the quotient norm on A/B, then L is strongly Leibniz. In connection with this situation we study certain aspects of best approximation of elements of a unital C*-algebra by elements of a unital C*-subalgebra.Comment: 24 pages. Intended for the proceedings of the conference "Operator Algebras and Related Topics". v2: added a corollary to the main theorem, plus several minor improvements v3: much simplified proof of a key lemma, corollary to main theorem added v4: Many minor improvements. Section numbers increased by

Fermi-level alignment at metal-carbon nanotube interfaces: application to scanning tunneling spectroscopy

At any metal-carbon nanotube interface there is charge transfer and the induced interfacial field determines the position of the carbon nanotube band structure relative to the metal Fermi-level. In the case of a single-wall carbon nanotube (SWNT) supported on a gold substrate, we show that the charge transfers induce a local electrostatic potential perturbation which gives rise to the observed Fermi-level shift in scanning tunneling spectroscopy (STS) measurements. We also discuss the relevance of this study to recent experiments on carbon nanotube transistors and argue that the Fermi-level alignment will be different for carbon nanotube transistors with low resistance and high resistance contacts.Comment: 4 pages, 3 ps figures, minor corrections, accepted by Phys. Rev. Let