Constrained Variational Calculus for Higher Order Classical Field Theories

We develop an intrinsic geometrical setting for higher order constrained field theories. As a main tool we use an appropriate generalization of the classical Skinner-Rusk formalism. Some examples of application are studied, in particular, applications to the geometrical description of optimal control theory for partial differential equations.Comment: 25 pages; 4 diagram

Epic Black: Poetics in Protest in the Time of Black Lives Matter

This dissertation examines certain book-length poetic works released between 2014 to 2016, corresponding to the rise of the Black Lives Matter movement formed in the wake of the killing of Trayvon Martin in 2013. I argue that these works emerge from the same political and poetic urgency that demanded a movement like BLM. Using Beyoncé’s Lemonade (2016) as an entrance, I focus on a genre/strategy that Farah Jasmine Griffin calls Epic Black, a poetics that uses the hypervisibility of Black bodies, the inescapable place that Black expression has in popular American culture, and the scale and scope of the Western epic as a liberatory artistic strategy. Epic Black uses the cultural weight of institutions against those institutions, subverting or re-appropriating the dominant systems that would seek to appropriate Blackness.Popular culture is a political battleground like any other, and the most contested zones are the places where Whiteness encounters the limits of its power in the encounter with the Black body. This place, where the dominant language encounters its limit, I call noirporia. It marks the borderland or frontiers of Whiteness, where it is most open to the possibilities of fugitivity or marronage. Each of the Epic Black works I discuss claim territory out of this contested ground, taking up space in the cultural imaginary through the medium of the poetry book as cultural object, which has dimensions both physical and discursive. After discussing Lemonade as one of the most visible examples of Epic Blackness, I turn to Claudia Rankine’s Citizen, winner of the 2015 National Book Critics Circle Award in Poetry and nominee in both poetry and criticism; Tyehimba Jess’s Olio, winner of the 2017 Pulitzer Prize for Poetry; and Robin Coste Lewis’s Voyage of the Sable Venus, winner of the 2015 National Book Award. Each of these book-length works is a performance of Epic Black: hypervisible as a cultural object, capacious in breadth and scope, and self-conscious in formal difficulty. I conclude with a brief look at Alexis Pauline Gumbs’s M Archive: After the End of the World as a new phase of Epic Black, suggesting that epic strategies must change with the centers of cultural power

Formulación para incorporar conceptos de riesgo en el diseño estructural y su aplicación a un edificio de concreto reforzado para hospital en una zona de alto peligro sísmico

Las pérdidas humanas y económicas causadas por terremotos en zonas altamente sísmicas, se deben principalmente al hecho de que estos eventos son impredecibles en intensidad y tiempo de ocurrencia entre otras características. Los criterios de diseño sísmico de estructuras que se usan en la actualidad se basan en un coeficiente de diseño que considera parcial y subjetivamente los daños potenciales y las consecuencias que podrían ocurrir si se presentara el evento sísmico. En el presente trabajo se propone introducir conceptos de confiabilidad, riesgo y costo esperado en el ciclo de vida para mejorar los procedimientos de diseño sísmico identificando, entre otros aspectos, el coeficiente sísmico óptimo necesario para minimizar los costos en el largo plazo

Nonholonomic constraints in classical field theories

A multisymplectic setting for classical field theories subjected to non-holonomic constraints is presented. The infinite dimensional setting in the space of Cauchy data is also given.Comment: 14 pages; 1 figur

ESTIMACIÓN DEL IMPACTO DEL TIEMPO DE CORROSIÓN EN LA EVOLUCIÓN DEL RIESGO DE ESTRUCTURAS DE CONCRETO REFORZADO

En las últimas tres décadas, se ha observado un incremento en agrietamientos y delaminaciones en elementos de estructuras de concreto reforzado, relacionados con la corrosión del acero de refuerzo, bajo la acción de los efectos ambientales, que ha provocado el deterioro prematuro de muchas de ellas a nivel mundial. Esto implica que, además del diseño por resistencia, se consideren aspectos de durabilidad que ayuden a prevenir este deterioro, tal que, la probabilidad de tener un comportamiento satisfactorio de la estructura durante su vida útil, sea aceptable. Con lo anterior, adquiere relevancia evaluar el riesgo que presentan este tipo de estructuras sujetas a corrosión en el tiempo y, en función de ello, adoptar las medidas preventivas que permitan garantizar su durabilidad. Para tratar esta situación, en el presente trabajo se estudia la relación entre el tiempo de corrosión del acero y la evolución de riesgo de una estructura de concreto reforzado, mediante el desarrollo de un modelo para estimar la variación del índice de confiabilidad durante el tiempo de inicio y propagación de la corrosión del acero, a partir de la modificación de un modelo de deterioro existente. Con el modelo propuesto en este trabajo, se obtuvo un perfil de confiabilidad de una estructura de concreto reforzado sujeta a daño por corrosión (caso de un puente vehicular), mediante la estimación cuantitativa del agrietamiento del recubrimiento de concreto y su evolución en el tiempo en varios de sus elementos estructurales dañados por corrosión. A partir de ello, se determinó la disminución del diámetro de las barras de acero de cada uno de los elementos, su correspondiente pérdida del área de su sección transversal y la disminución de la capacidad de carga, con el consiguiente aumento y reducción de su probabilidad de falla e índice de confiabilidad, respectivamente. Con el desarrollo del ejemplo y los resultados obtenidos, se observó que los elementos dañados por corrosión, presentaron cambios de rigidez y una reducción en su momento de fluencia nominal, durante el periodo de propagación de la corrosión, lo que provocó una disminución en su índice de confiabilidad a valores menores de 2 para acciones sísmicas, además de presentar una reducción de la vida útil de 15%, para la condición más crítica de falla (falla simultanea de dos elementos estructurales). Así, se probó la hipótesis del trabajo, referente a que una estructura de concreto reforzado sujeta a corrosión en el tiempo, presenta cambios en la rigidez de sus elementos estructurales y reduce su capacidad para resistir cargas, disminuyendo su índice de confiabilidad a valores menores de 2 para acciones sísmicas, acortando en un 20% o más su vida útil, aunque para el caso estudiado la reducción fue del 15% únicamente. Finalmente, se realizó una comparación de los resultados del perfil obtenido con el modelo desarrollado, y los de un perfil de confiabilidad utilizando un modelo de durabilidad existente, para la estructura estudiada, obteniendo resultados similares, del tiempo de inicio de la corrosión, del tiempo de propagación de la corrosión y del tiempo para el cual la estructura supera su estado límite último, para la condición más crítica de falla.Over the last three decades an increase in cracks and spalling of concrete in elements of reinforced concrete structures has been observed. These damages are related to the corrosion of reinforcing steel under the action of environmental effects, which have normally caused worldwide premature deterioration of structures. This implies that, apart from strength, durability should be considered to prevent this deterioration, such that the probability of satisfactory performance of the structure during its lifetime is acceptable. Consequently, it becomes relevant to assess the risk posed by this type of structures subject to corrosion over time and, accordingly, adopt preventive measures to ensure their durability. To address this situation, this piece of research deals with the relationship between the steel corrosion time and the evolution of risk for a reinforced concrete structure, by developing a model to estimate the reliability index variation during both the initiation time and the corrosion propagation process, by means of the modification of an existing deterioration model. With the proposed model, the reliability index of the reinforced concrete structure subject to corrosion damage (considering the case of a vehicular bridge) was obtained. To do so, it was required to carry out the quantitative estimation of the cracking of concrete cover and its evolution over time, analyzing several of its structural elements damaged by corrosion. Following on from this, the reduction on diameter of the steel bars of each of the elements was determined, along with the corresponding loss of its cross-sectional area and the load decrease, thus increasing the likelihood of failure and reducing the reliability index. With the example developed and the results obtained, it was observed that the corrosion damaged elements showed reductions not only in stiffness but also in its nominal yield moment, during the propagation of corrosion. This led to reductions on the structure reliability index (achieving values lower than 2 for seismic action), and in its lifetime of 15%, for the most critical failure (presented simultaneously in two structural elements). Thus, the working hypothesis has been proven, showing that a reinforced concrete structure subject to corrosion over its lifetime, has changes in its structural rigidity and reduces their ability to withstand loads, reducing its reliability index to values lower than 2 for seismic actions, and shortening by 20% or more of its lifetime (although for the studied case the reduction was only 15%). Finally, a comparison was made of the results obtained with the developed model, and the reliability index estimated by using a durability existing model for the studied structure. The results were similar in terms of the corrosion initiation time, the corrosion propagation time, and the time for which the structure exceeds its ultimate limit state, for the most critical failure

Compositional study of asteroids in the Erigone collisional family using visible spectroscopy at the 10.4 m GTC

Two primitive near Earth asteroids, (101955) Bennu and (162173) Ryugu, will be visited by a spacecraft with the aim of returning samples back to Earth. Since these objects are believed to originate in the inner main belt primitive collisional families (Erigone, Polana, Clarissa, and Sulamitis) or in the background of asteroids outside these families, the characterization of these primitive populations will enhance the scientific return of the missions. The main goal of this work is to shed light on the composition of the Erigone collisional family by means of visible spectroscopy. Asteroid (163) Erigone has been classified as a primitive object, and we expect the members of this family to be consistent with the spectral type of the parent body. We have obtained visible spectra (0.5 to 0.9 microns) for 101 members of the Erigone family, using the OSIRIS instrument at the 10.4 m Gran Telescopio Canarias. We found that 87 percent of the objects have typically primitive visible spectra consistent with that of (163) Erigone. In addition, we found that a significant fraction of these objects (approximately 50 percent) present evidence of aqueous alteration