Correlating low energy impact damage with changes in modal parameters: a preliminary study on composite beams

This paper is an experimental study of the effects of multi-site damage on the vibration response of a composite beam damaged by low energy impact. The variation of the modal parameters with different levels of impact energy and density of impact is studied. Specimens are impacted symmetrically in order to induce a global rate of damage. A damage detection tool Damage Index is introduced in order to verify the estimation of damping ratios. Design of Experiments is used to establish the sensitivity of both energy of impact and density of damage. The DOE analysis results (using natural frequency only) indicate that impact energy for 2nd, 3rd and 4th bending modes is the most significant factor contributing to the changes in the modal parameters for this kind of symmetrical dynamic test

Emergence of communities on a coevolutive model of wealth interchange

We present a model in which we investigate the structure and evolution of a random network that connects agents capable of exchanging wealth. Economic interactions between neighbors can occur only if the difference between their wealth is less than a threshold value that defines the width of the economic classes. If the interchange of wealth cannot be done, agents are reconnected with another randomly selected agent, allowing the network to evolve in time. On each interaction there is a probability of favoring the poorer agent, simulating the action of the government. We measure the Gini index, having real world values attached to reality. Besides the network structure showed a very close connection with the economic dynamic of the system.Comment: 5 pages, 7 figure

Discrete Variational Optimal Control

This paper develops numerical methods for optimal control of mechanical systems in the Lagrangian setting. It extends the theory of discrete mechanics to enable the solutions of optimal control problems through the discretization of variational principles. The key point is to solve the optimal control problem as a variational integrator of a specially constructed higher-dimensional system. The developed framework applies to systems on tangent bundles, Lie groups, underactuated and nonholonomic systems with symmetries, and can approximate either smooth or discontinuous control inputs. The resulting methods inherit the preservation properties of variational integrators and result in numerically robust and easily implementable algorithms. Several theoretical and a practical examples, e.g. the control of an underwater vehicle, will illustrate the application of the proposed approach.Comment: 30 pages, 6 figure

Influence of maturity stage on nutritive value of typha for ruminants

The study evaluated the influence of maturity on the nutritive value and fermentation parameters of Typha. Typha samples were collected at two different stages of growth, as indicated by the height of the plants: either 0.5 m (Low Typha; LT, age 3-6months) or 1.5 m (High Typha; HT, age 9-12 months). Samples were analyzed for chemical composition, and incubated in vitro with ruminal fluid from sheep to determine the main fermentation parameters. As maturity advanced, the dry matter, fiber and lignin content (25.30%, 70.40%, 47.30% and 10.58%) in the Typha increased, whereas the content of ashes and protein (12.18% and 12.24%) decreases. The changes in chemical composition caused a significant reduction in both the in vitro ruminal degradability after 96 h of incubation (38.6 and 22.9% for LT and HT, respectively) and the production of volatile fatty acids after 24 h of incubation (6.08 and 5.87 mmol/g dry matter incubated), indicating that the nutritive value of the Typha declines with advancing maturity. The results indicate that Typha plants for ruminant feeding should be preferably harvested at early growth stages

Importancia, toxicogénesis y agresividad de especies pertenecientes a Gibberella fujikuroi en maíz en el Noroeste Argentino = Importance, Fumonisin production and aggressiveness of Gibberella fujikuroi complex recovered from maize in northwestern Argentina

Se estudió la composición, patogenicidad y toxicogénesis de aislamientos pertenecientes al complejo Gibberella fujikuroi en una de las regiones productoras de maíz de la región Noroeste de Argentina. Los resultados evidencian que el género Fusarium Sección Liseola está conformado por tres especies. La especie dominante fue la población tipo A (F. verticillioides), representada por un 53% seguida de la población tipo D (F. proliferatum) representando un 29 %. Y por último la población E (F. subglutinans) en un 18 %. Se detectó variabilidad entre aislamientos respecto a su agresividad hacia tres híbridos de maíz, con niveles de resistencia variable, sin que se haya observado un importante efecto de interacción híbrido× aislamiento. La producción de fumonisinas en los aislamientos de F. verticillioides varió de 4000 a 7457 ppb. Los correspondiente a la población de apareamiento tipo E (F. subglutinans) produjeron muy bajos niveles de fumonisinas variando de 0,1 a 0,54 a mg/kg (ppb). La información lograda en el presente trabajo representa un primer paso, para la región en estudio, hacia el conocimiento del patosistema Fusarium-maíz, a fin de determinar la importancia de esta enfermedad, y plantear las bases que conduzcan a delinear estrategias de manejo, dentro del marco de una agricultura sustentable.Mating population, in vitro fumonisin production and aggressiveness of maize isolates belonging to the Gibberella fujikuroi complex were assessed in corn producing area of northwestern Argentina. Mating population A (F. verticillioides) was the most prevalent species (53%) coexisting with some isolates belonging to MAT-D (F. proliferatum) 29% and MAT-E (F. subglutinans) 18%. Fumonisin production varied from 4000 to 7457 ųg/kg (ppb) for MAT-A and from 0,1 - 0,54 a ųg/kg for MATE. The isolates belonging to MAT-D produced undetectable levels. All isolates caused more disease severity to the most susceptible hybrid in comparison to that of the two moderately resistant hybrids regardless of the fungal species, in most environments, but with no effect for the interaction hybrid x isolate. Results indicate that these three Fusarium spp. coexist in the region, with low environmental specialization to cause ear rots, with potential to contaminate the grain with fumonisins and that, broad resistance mechanisms effective across prevalent local fungal species might exist. The information obtained in the present work represents a first step for the region under study and it will help to determine the importance of this disease, and to delineate management strategies within the framework of sustainable agriculture.EEA PergaminoFil: Díaz, C.G. Universidad Nacional Tucumán. Facultad de Agronomía y Zootecnia; ArgentinaFil: Heredia, A.M. Universidad Nacional Tucumán. Facultad de Agronomía y Zootecnia; ArgentinaFil: Iglesias, Juliana. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Pergamino; ArgentinaFil: Presello, Daniel Alberto. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Pergamino; ArgentinaFil: Lori, Gladys Albina. Universidad Nacional de La Plata. Facultad de Ciencias Agrarias y Forestales. Centro de Investigaciones de Fitopatología; Argentin

Discrete Nonholonomic Lagrangian Systems on Lie Groupoids

This paper studies the construction of geometric integrators for nonholonomic systems. We derive the nonholonomic discrete Euler-Lagrange equations in a setting which permits to deduce geometric integrators for continuous nonholonomic systems (reduced or not). The formalism is given in terms of Lie groupoids, specifying a discrete Lagrangian and a constraint submanifold on it. Additionally, it is necessary to fix a vector subbundle of the Lie algebroid associated to the Lie groupoid. We also discuss the existence of nonholonomic evolution operators in terms of the discrete nonholonomic Legendre transformations and in terms of adequate decompositions of the prolongation of the Lie groupoid. The characterization of the reversibility of the evolution operator and the discrete nonholonomic momentum equation are also considered. Finally, we illustrate with several classical examples the wide range of application of the theory (the discrete nonholonomic constrained particle, the Suslov system, the Chaplygin sleigh, the Veselova system, the rolling ball on a rotating table and the two wheeled planar mobile robot).Comment: 45 page

A Generalization of Chaplygin's Reducibility Theorem

In this paper we study Chaplygin's Reducibility Theorem and extend its applicability to nonholonomic systems with symmetry described by the Hamilton-Poincare-d'Alembert equations in arbitrary degrees of freedom. As special cases we extract the extension of the Theorem to nonholonomic Chaplygin systems with nonabelian symmetry groups as well as Euler-Poincare-Suslov systems in arbitrary degrees of freedom. In the latter case, we also extend the Hamiltonization Theorem to nonholonomic systems which do not possess an invariant measure. Lastly, we extend previous work on conditionally variational systems using the results above. We illustrate the results through various examples of well-known nonholonomic systems.Comment: 27 pages, 3 figures, submitted to Reg. and Chaotic Dy

Stellar evolution and modelling stars

In this chapter I give an overall description of the structure and evolution of stars of different masses, and review the main ingredients included in state-of-the-art calculations aiming at reproducing observational features. I give particular emphasis to processes where large uncertainties still exist as they have strong impact on stellar properties derived from large compilations of tracks and isochrones, and are therefore of fundamental importance in many fields of astrophysics.Comment: Lecture presented at the IVth Azores International Advanced School in Space Sciences on "Asteroseismology and Exoplanets: Listening to the Stars and Searching for New Worlds" (arXiv:1709.00645), which took place in Horta, Azores Islands, Portugal in July 201

Ginzburg-Landau functional for nearly antiferromagnetic perfect and disordered Kondo lattices

Interplay between Kondo effect and trends to antiferromagnetic and spin glass ordering in perfect and disordered bipartite Kondo lattices is considered. Ginzburg-Landau equation is derived from the microscopic effective action written in three mode representation (Kondo screening, antiferromagnetic correlations and spin liquid correlations). The problem of local constraint is resolved by means of Popov-Fedotov representation for localized spin operators. It is shown that the Kondo screening enhances the trend to a spin liquid crossover and suppresses antiferromagnetic ordering in perfect Kondo lattices and spin glass ordering in doped Kondo lattices. The modified Doniach's diagram is constructed, and possibilities of going beyond the mean field approximation are discussed.Comment: 18 pages, RevTeX, 7 EPS figures include