arXiv subjects

J. M. Rodriguez

Publications and source records attributed to J. M. Rodriguez.

6 recordsLinked to original sources

arXiv2020

On the hyperbolicity constant of circular-arc graphs

Gromov hyperbolicity is an interesting geometric property, and so it is natural to study it in the context of geometric graphs. It measures the tree-likeness of a graph from a metric viewpoint. In particular, we are interested in circular-arc graphs, which is an important class of geometric intersection graphs. In this paper we give sharp bounds for the hyperbolicity constant of (finite and infinite) circular-arc graphs. Moreover, we obtain bounds for the hyperbolicity constant of the complement and line of any circular-arc graph. In order to do that, we obtain new results about regular, chordal and line graphs which are interesting by themselves.

math.CO↗

arXiv2016

New inequalities involving the Geometric-Arithmetic index

Let $G=(V,E)$ be a simple connected graph and $d_i$ be the degree of its $i$th vertex. In a recent paper [J. Math. Chem. 46 (2009) 1369-1376] the first geometric-arithmetic index of a graph $G$ was defined as $$GA_1=\sum_{ij\in E}\frac{2 \sqrt{d_i d_j}}{d_i + d_j}.$$ This graph invariant is useful for chemical proposes. The main use of $GA_1$ is for designing so-called quantitative structure-activity relations and quantitative structure-property relations. In this paper we obtain new inequalities involving the geometric-arithmetic index $GA_1$ and characterize the graphs which make the inequalities tight. In particular, we improve some known results, generalize other, and we relate $GA_1$ to other well-known topological indices.

math.CO↗

arXiv2012

Muckenhoupt inequality with three measures and applications to Sobolev orthogonal polynomials

We generalize the classical Muckenhoupt inequality with two measures to three under appropriate conditions. As a consequence, we prove a simple characterization of the undedness of the multiplication operator and thus of the boundedness of the zeros and the asymptotic behavior of the Sobolev orthogonal polynomials, for a large class of measures which includes the most usual examples in the literature.

math.FA↗

arXiv2011

Determination of $ππ$ scattering lengths from measurement of $π^+π^-$ atom lifetime

The DIRAC experiment at CERN has achieved a sizeable production of $π^+π^-$ atoms and has significantly improved the precision on its lifetime determination. From a sample of 21227 atomic pairs, a 4% measurement of the S-wave $ππ$ scattering length difference $|a_0-a_2| = (.0.2533^{+0.0080}_{-0.0078}|_\mathrm{stat}.{}^{+0.0078}_{-0.0073}|_\mathrm{syst})M_{π^+}^{-1}$ has been attained, providing an important test of Chiral Perturbation Theory.

hep-ex↗

arXiv2005

All electromagnetic form factors

The electromagnetic form factors of spin-1/2 particles are known, but due to historical reasons only half of them are found in many textbooks. Given the importance of the general result, its model independence, its connection to discrete symmetries and their violations we made an effort to derive and present the general result based only on the knowledge of Dirac equation. We discuss the phenomenology connected directly with the form factors, and spin precession in external fields including time reversal violating terms. We apply the formalism to spin-flip synchrotron radiation and suggest pedagogical projects.

physics.ed-ph↗

arXiv1999

The Micro Wire Detector

We present the performance of a new proportional gas detector. Its geometry consists of a cathode plane with 70x70 micron apertures, crossed by 25 micron anode strips to which it is attached by 50 micron kapton spacers. In the region where the avalanche takes place, the anode strips are suspended in the gas mixture like in a standard wire chamber. This detector exhibits high rate capability and large gains, introducing very little material.

hep-ex↗