Non-existence of an invariant measure for a homogeneous ellipsoid rolling on the plane

It is known that the reduced equations for an axially symmetric homogeneous ellipsoid that rolls without slipping on the plane possess a smooth invariant measure. We show that such an invariant measure does not exist in the case when all of the semi-axes of the ellipsoid have different length.Comment: v2: Minor changes after journal review. This text uses the theory developed in arXiv:1304.1788 for the specific example of a homogeneous ellipsoid rolling on the plan

Unimodularity and preservation of volumes in nonholonomic mechanics

The equations of motion of a mechanical system subjected to nonholonomic linear constraints can be formulated in terms of a linear almost Poisson structure in a vector bundle. We study the existence of invariant measures for the system in terms of the unimodularity of this structure. In the presence of symmetries, our approach allows us to give necessary and sufficient conditions for the existence of an invariant volume, that unify and improve results existing in the literature. We present an algorithm to study the existence of a smooth invariant volume for nonholonomic mechanical systems with symmetry and we apply it to several concrete mechanical examples.Comment: 37 pages, 3 figures; v3 includes several changes to v2 that were done in accordance to the referee suggestion

The inhomogeneous Suslov problem

We consider the Suslov problem of nonholonomic rigid body motion with inhomogeneous constraints. We show that if the direction along which the Suslov constraint is enforced is perpendicular to a principal axis of inertia of the body, then the reduced equations are integrable and, in the generic case, possess a smooth invariant measure. Interestingly, in this generic case, the first integral that permits integration is transcendental and the density of the invariant measure depends on the angular velocities. We also study the Painlev\'e property of the solutions.Comment: 10 pages, 5 figure

Antifungal effect and reduction of Ulmus minor symptoms to Ophiostoma novo-ulmi by carvacrol and salicylic acid

There are still no effective means to control Dutch elm disease (DED), caused by the vascular fungi Ophiostoma ulmi and O. novo-ulmi. Plant phenolics may provide a new strategy for DED control, given their known antifungal activity against pathogens and their involvement in plant defence mechanisms. The in vitro antifungal activity of salicylic acid, carvacrol, thymol, phenol, o-cresol, m-cresol, p-cresol, and 2,5-xylenol against the DED pathogens was tested. Also, the protective effect of watering Ulmus minor seedlings with these compounds was tested against O. novo-ulmi. Salicylic acid, carvacrol, and thymol showed the strongest antifungal in vitro activity, while carvacrol and salicylic acid provided the strongest in vivo protection against O. novo-ulmi (63 and 46% reduction of leaf wilting symptoms with respect to controls, respectively). The effect of the treatments on tree phenology was low, and a significant negative relation was observed between the number of days to bud burst and the leaf wilting symptoms after inoculation, probably determined by genetic differences among the elm tree progenies used. The treatments with salicylic acid, carvacrol and thymol induced the highest shift in phenolic metabolite profile with respect to control trees. The protective effect of carvacrol and salicylic acid is discussed in terms of their combined activity as antifungal compounds and as inductors of tree defence responses

Multi-objective optimization of the geometry of a double wishbone suspension system

The vehicle suspension system optimal design problem is multi-objective, has a hierarchical multi-level structure and presents couplings with the rest of the vehicle design. Moreover, many of the vehicle performances are dependent of the suspension system, specifically on its geometry. For this reason, it is desirable to develop a strategy in which the geometry of the suspension system is automatically generated with optimal characteristics. For this type of problems, the Analytical Target Cascading (ATC) brings a powerful optimization strategy that permits the management of a complex optimal design problem in a partitioned manner. This work proposes a new approach for the automatic optimal geometry generation of the suspension system of the vehicle, the development of the optimization problem in order to use the ATC optimization strategy and a case study in which a full-scale functional prototype is designed with the use of the developed tools

Unveiling quantum entanglement degradation near a Schwarzschild black hole

We analyze the entanglement degradation provoked by the Hawking effect in a bipartite system Alice-Rob when Rob is in the proximities of a Schwarzschild black hole while Alice is free falling into it. We will obtain the limit in which the tools imported from the Unruh entanglement degradation phenomenon can be used properly, keeping control on the approximation. As a result, we will be able to determine the degree of entanglement as a function of the distance of Rob to the event horizon, the mass of the black hole, and the frequency of Rob's entangled modes. By means of this analysis we will show that all the interesting phenomena occur in the vicinity of the event horizon and that the presence of event horizons do not effectively degrade the entanglement when Rob is far off the black hole. The universality of the phenomenon is presented: There are not fundamental differences for different masses when working in the natural unit system adapted to each black hole. We also discuss some aspects of the localization of Alice and Rob states. All this study is done without using the single mode approximation.Comment: 16 pages, 10 figures, revtex4. Added Journal referenc

Desarrollo de la competencia lectora en secundaria

En México, los alumnos de telesecundaria obtienen los puntajes más bajos en competencia lectora. Este trabajo presenta los resultados de una investigación que tuvo como objetivo determinar la eficacia de un programa de comprensión lectora implementado en telesecundarias de una región marginada. El diseño fue experimental, con 16 grupos de octavo grado como grupo experimental y siete como control. Los resultados muestran que el grupo de control obtuvo los mismos puntajes antes y después de la intervención, mientras que el grupo experimental presentó una mejoría en la segunda evaluación, por lo que se considera que el programa fue eficaz.ITESO, A.C