Nonlinear Time-Domain Structure/Aerodynamics Coupling in Systems with Concentrated Structural Nonlinearities

This paper details a practical approach for predicting the aeroelastic response (structure/aerodynamics coupling) of flexible pod/missile-type configurations with freeplay/hysteresis concentrated structural nonlinearities. The nonlinear aeroelastic response of systems in the presence of these nonlinearities has been previously studied by different authors; this paper compiles methodologies and related airworthiness regulations. The aeroelastic equations of the pod/missile configuration are formulated in state-space form and time-domain integrated with Fortran/Matlab codes developed ad hoc for dealing with freeplay/hysteresis nonlinearities. Results show that structural nonlinearities change the classical aeroelastic behaviour with appearence of non-damped motion (LCOs and chaotic motion)

Evaluación de los mecanismos de acción biológica de Trichoderma

Este trabajo describe los mecanismos de control biológico que se expresan en Trichoderma, además mediante la aplicación de los marcadores ITS y Tef1α se realiza la caracterización taxonómica de 10 cepas de Trichoderma aisladas en la región hortícola de Tenango y a través de pruebas de confrontación dual se determina su capacidad antagónica contra diferentes patógenos fúngicos de la papaEl presente trabajo demostró que en la Peñuela localidad del Municipio de Zinacantepec, Estado de México, en los últimos años, el cultivo de la papa (Solanum tuberosum) se ha visto afectado por la presencia de agentes patógenos principalmente hongos como P. infestans, F. avenaceum, Alternaria sp y Rhizoctonia sp. causantes de enfermedades que degradan la calidad del tubérculo tales como Tizón temprano, Damping off, Tizón tardío y Rizoctoniasis respectivamente. La caracterización morfológica ayudó a ubicar taxonómicamente a nivel de género a los cuatro hongos patógenos. Pero, para el caso de Fusarium fue necesaria la caracterización molecular lo cual permitió comprobar que F. avenaceum es una especie patógena para el cultivo de papa en esta zona de estudio. Ya que esta especie es reportada como patógena de cultivos de gramíneas como la avena, sin embargo, se encontró que rompió las barreras agroecológicas y ahora daña a este tubérculo. También con herramientas moleculares utilizando los marcadores ITS y Tef1α se ubicaron taxonómicamente a diez cepas nativas de Trichoderma; 6 cepas como T. asperellum (TL2, TL4, TX7, TX8, TT6,TF8) y 4 cepas como Hipocrea lixii (TL5,TL6,TF10 TJ6), el teleomorfo de T. harzianum. Como estrategia ecológica y con la finalidad de conocer el potencial de biocontrol de estas cepas de Trichoderma se realizaron pruebas de antagonismo mediante cultivos duales enfrentando a los patógenos que afectan el cultivo de papa Alternaria sp., Rhizoctonia sp. P. infestans y Fusarium avenaceum. Los resultados registraron diferencias significativas en el porcentaje de biocontrol de las cepas de Trichoderma sobre los patógenos. Donde la cepa TX8 (T. asperellum) registró los porcentajes más altos de inhibición sobre, F. avenaceum, Alternaria sp y P. infestas con 100%, 100% y 98.12%, respectivamente Para el caso de Rhizoctonia sp., H. lixii presentó los porcentajes de inhibición más altos 65% y 51% para las cepas TF10 y TL5 respectivamente. La cepa TL4 (T. asperellum) hacia los cuatro patógenos mostró el valor más bajo de antagonismo. La respuesta antagónica de la cepas nativas de Trichoderma desencadeno mecanismos de acción biológica, donde el más frecuente fue la competencia hacia Alternaria sp. y Rhizoctonia sp. y P. infestans mientras que para F. avenaceum la antibiosis fue el mecanismo que favoreció el antagonismo. Sin embargo, también el micoparasitismo en algunos casos se presentó junto con la competencia hacia P. infestans y Rhizoctonia sp.CONACyT UAEMEX COMECy

Aeroelastic characteristics of slender wing/bodies with freeplay non-linearities

This article presents a time domain approach to the flutter analysis of a missile-type wing/body configuration with concentrated structural non-linearities. The missile wing is considered fully movable and its rotation angle contains the structural freeplay-type non-linearity. Although a general formulation for flexible configurations is developed, only two rigid degrees of freedom are taken into account for the results: pitching of the whole wing/body configuration and wing rotation angle around its hinge. An unsteady aerodynamic model based on the slender-body approach is used to calculate aerodynamic generalized forces. Limit-cycle oscillations and chaotic motion below the flutter speed are observed in this study

Patrons moleculars de Legionella

Les torres de refrigeració estan implicades en la majoria de brots comunitaris de legionel·losi. En aquest treball es va estudiar la variabilitat genotípica dels patrons moleculars de Legionella pneumophila en 34 torres de refrigeració. La gran diversitat genotípica de Legionella observada en les torres de refrigeració ajuda a la investigació en els brots de legionel·losi

Influence of a liquid on the natural frequencies of almost circular plates

In this work, the influence of the surrounding fluid on the dynamic characteristics of almost circular plates is investigated. First the natural frequencies and normal modes for the plates in vacuum are calculated by a perturbation procedure. The method is applied for the case of elliptical plates with a low value of eccentricity. The results are compared with other available methods for this type of plates with good agreement. Next, the effect of the fluid is considered. The normal modes of the plate in vacuum are used as a base to express the vibration mode of the coupled plate-fluid system. By applying the Hankel transformation the nondimensional added virtual mass 2 increment (NAVMI) are calculated for elliptical plates. Results of the NAVMI factors and the effect of the fluid on the natural frequencies are given and it is shown that when the eccentricity of the plate is reduced to zero (circular plate) the known results of the natural frequencies for circular plates surrounded by liquid are recovered

Induced Damping on Vibrating Circular Plates Submerged in still Fluid

When a structure vibrates immersed in a fluid it is known that the dynamic properties of the system are modified. The surrounding fluid will, in general, contribute to the inertia, the rigidity and the damping coefficient of the coupled fluid-structure system. For light structures, like spacecraft antennas, even when the fluid is air the contribution to the dynamic properties can be important. For not so light structures the ratio of the equivalent fluid/structure mass and rigidity can be very small and the fluid contribution could be neglected. For the ratio of equivalent fluid/structure damping both terms are of the same order and therefore the fluid contribution must be studied. The working life of the spacecraft structure would be on space and so without any surrounding fluid. The response of a spacecraft structure on its operational life would be attenuated by the structural damping alone but when the structure is dynamically tested on the earth the dynamic modal test is performed with the fluid surrounding it. The results thus are contaminated by the effects of the fluid. If the damping added by the fluid is of the same order as the structural damping the response of the structure in space can be quite different to the response predicted on earth. It is therefore desirable to have a method able to determine the amount of damping induced by the fluid and that should be subtracted of the total damping measured on the modal vibration test. In this work, a method for the determination of the effect of the surrounding fluid on the dynamic characteristics of a circular plate has been developed. The plate is assumed to vibrate harmonically with the vacuum modes and the generalized forces matrix due to the fluid is thus computed. For a compressible fluid this matrix is formed by complex numbers including terms of inertia, rigidity and damping. The matrix due to the fluid loading is determined by a boundary element method (BEM). The BEM used is of circular rings on the plate surface so the number of elements to obtain an accurate result is very low. The natural frequencies of the system are computed by an iteration procedure one by one and also the damping fluid contribution. Comparisons of the present method with various experimental data and other theories show the efficiency and accuracy of the method for any support condition of the plate

La sociedad estadunidense hoy: valores fundacionales y seguridad

This article underlines the importance of the meaning of nationalism and patriotism in the United States as ideologies and key socio-political values in its historical development. Contrasting different interpretations of these terms, it underlines the differences, specific attributes and the impact that the events of 9/11 have had on their traditional meanings. Alluding to society's mistrust caused by the enforcement of new laws for combating terrorism (the Homeland Security Act and the USA Patriot Act), the article shows the currency of Gertrude Himmel's hypothesis that in the United States there are currently two diverging political cultures: one traditionalist and the other secular. It also looks critically at the fact that the Bush administration has attempted to impose a single way forward in the construction of the universal right to security.Este trabajo subraya la importancia del significado del nacionalismo y el patriotismo en Estados Unidos como ideologías y valores sociopolíticos claves de su de­venir histórico. Contrastando diversas interpretaciones de dichos términos, des­taca las diferencias, atributos particulares y el impacto que los sucesos del 11 de septiembre de 2001 han tenido sobre sus acepciones tradicionales. Aludiendo a la desconfianza social, provocada por la aplicación de nuevas leyes para combatir el terrorismo –Ley de Seguridad Nacional (Homeland Security Act) y Ley Patriótica (USA Patriot Act)–, este artículo ejemplifica la vigencia de la tesis de Gertrude Himmel, quien sostiene que en dicho país se perfilan actualmente dos culturas políticas divergentes: una tradicionalista y otra secular. El texto asimismo aborda de manera crítica el hecho de que la administración de Bush haya pretendido imponer una única salida hacia la construcción del derecho universal a la seguridad