Evaluation of the gn-->pi-p differential cross sections in the Delta-isobar region

Differential cross sections for the process gn-->pi-p have been extracted from MAMI-B measurements of gd-->pi-pp, accounting for final-state interaction effects, using a diagrammatic technique taking into account the NN and piN final-state interaction amplitudes. Results are compared to previous measurements of the inverse process, pi-p--> ng, and recent multipole analyses.Comment: 6 pages, 4 figures. v2: Further clarifications and minor changes. A new figure inserte

The Rarita--Schwinger field: renormalization and phenomenology

We discuss renormalization of propagator of interacting Rarita--Schwinger field. Spin-3/2 contribution after renormalization takes usual resonance form. For non-leading spin-1/2 terms we found procedure, which guarantees absence of poles in energy plane. The obtained renormalized propagator has one free parameter and is a straight generalization of the famous free propagator of Moldauer and Case. Application of this propagator for production of $\Delta^{++}(1232)$ in \pi^{+}\particle{p}\to \pi^{+}\particle{p} leads to good description of total cross-section and to reasonable agreement with results of partial wave analysis.Comment: 19 pages, 3 figures, revtex4; misprints, min editorial change

Isospin Splitting in the Baryon Octet and Decuplet

Baryon mass splittings are analyzed in terms of a simple model with general pairwise interactions. At present, the $\Delta$ masses are poorly known from experiments. Improvement of these data would provide an opportunity to make a significant test of our understanding of electromagnetic and quark-mass contributions to hadronic masses. The problem of determining resonance masses from scattering and production data is discussed.Comment: 9 pages, LATEX inc. 2 LATEX "pictures", CMU-HEP91-24-R9

Basic properties of nonsmooth Hormander's vector fields and Poincare's inequality

We consider a family of vector fields defined in some bounded domain of R^p, and we assume that they satisfy Hormander's rank condition of some step r, and that their coefficients have r-1 continuous derivatives. We extend to this nonsmooth context some results which are well-known for smooth Hormander's vector fields, namely: some basic properties of the distance induced by the vector fields, the doubling condition, Chow's connectivity theorem, and, under the stronger assumption that the coefficients belong to C^{r-1,1}, Poincare's inequality. By known results, these facts also imply a Sobolev embedding. All these tools allow to draw some consequences about second order differential operators modeled on these nonsmooth Hormander's vector fields.Comment: 60 pages, LaTeX; Section 6 added and Section 7 (6 in the previous version) changed. Some references adde

Deformations of N=2 super-conformal algebra and supersymmetric two-component Camassa-Holm equation

This paper is concerned with a link between central extensions of N=2 superconformal algebra and a supersymmetric two-component generalization of the Camassa--Holm equation. Deformations of superconformal algebra give rise to two compatible bracket structures. One of the bracket structures is derived from the central extension and admits a momentum operator which agrees with the Sobolev norm of a coadjoint orbit element. The momentum operator induces via Lenard relations a chain of conserved hamiltonians of the resulting supersymmetric Camassa-Holm hierarchy.Comment: Latex, 21 pages, version to appear in J. Phys.

Quantum deformations of associative algebras and integrable systems

Quantum deformations of the structure constants for a class of associative noncommutative algebras are studied. It is shown that these deformations are governed by the quantum central systems which has a geometrical meaning of vanishing Riemann curvature tensor for Christoffel symbols identified with the structure constants. A subclass of isoassociative quantum deformations is described by the oriented associativity equation and, in particular, by the WDVV equation. It is demonstrated that a wider class of weakly (non)associative quantum deformations is connected with the integrable soliton equations too. In particular, such deformations for the three-dimensional and infinite-dimensional algebras are described by the Boussinesq equation and KP hierarchy, respectively.Comment: Numeration of the formulas is correcte

Método para la evaluación de un microcontrolador de núcleo abierto

La etapa de verifi cación desempeña un papel fundamental en el diseñoe implementación de microcontroladores. Con el fi n de realizar una verificación acertada del diseño, son utilizadas algunas técnicas de verificación funcional tales como: pruebas defi nidas por el diseñador paraverifi car el desempeño ante casos extremos, la simulación a través detestbenches, y la ejecución de aplicaciones extensas. El proyecto propuestoen este trabajo tiene como objetivo desarrollar e implementarun método para la evaluación de un microcontrolador de núcleo abierto,con la realización de pruebas directamente sobre el hardware. Esteenfoque presenta como ventajas, un proceso mucho más rápido queotros métodos que emplean simulaciones y menos requerimiento dememoria para las pruebas. Un Ethernet IP Core ha sido integrado alproyecto, con el fi n de hacer que el método sea independiente del sistemaoperativo, de la arquitectura de microprocesador y de la herramientade diseño

Reduction of bihamiltonian systems and separation of variables: an example from the Boussinesq hierarchy

We discuss the Boussinesq system with $t_5$ stationary, within a general framework for the analysis of stationary flows of n-Gel'fand-Dickey hierarchies. We show how a careful use of its bihamiltonian structure can be used to provide a set of separation coordinates for the corresponding Hamilton--Jacobi equations.Comment: 20 pages, LaTeX2e, report to NEEDS in Leeds (1998), to be published in Theor. Math. Phy

MSH3 protein expression and nodal status in MLH1-deficient colorectal cancers.

View the MathML source: Colorectal tumors manifesting high-frequency microsatellite instability (MSI-H) develop genetically as a consequence of mutations in genes harboring repetitive DNA sequences. The activin type 2 receptor (ACVR2), possessing 2 polyadenine coding sequences, was identified as a mutational target, but it is not clear if expression is abrogated. Here, we analyzed MSI-H colorectal cancers for ACVR2 mutation and expression to assess if biallelic inactivation occurs. View the MathML source: All 54 MSI-H colon cancers and 20 random microsatellite stable (MSS) tumors from a population-based cohort of 503 patients were analyzed for mutations in 2 A8 tracts (exon 3 and 10) of ACVR2 and the A10 tract of transforming growth factor \u3b2 receptor 2 (TGFBR2). Additionally, we sequenced exon 10 of ACVR2 in select cancers. ACVR2 expression was determined by immunohistochemistry using an antibody targeting an epitope beyond the predicted truncated protein. View the MathML source: Forty-five of 54 MSI-H cancers (83%) showed mutation (A8 to A7) in the polyadenine tract of exon 10 compared with no MSS tumors. Of tumors with mutant ACVR2, 62% lacked protein expression but all MSS and MSI-H tumors with wild-type ACVR2 expressed protein. We found no evidence of loss of heterozygosity at the ACVR2 locus in MSS tumors. Comparatively, 69% of MSI-H cancers had frameshift mutation in TGFBR2. View the MathML source:ACVR2 mutations are highly frequent in MSI-H colon cancers and in most cases cause loss of ACVR2 expression, indicating biallelic inactivation of the gene. Loss of activin signaling through mutation of ACVR2, similar to observations with TGFBR2, may be important in the genesis of MSI-H colorectal cancer