Photonic crystals emerged at the end of the last decade as a new frame to control the interaction between radiation and matter. The potential advances that such structures could report in photonics technology has lead to an increasing research focused on the implementation of photonic crystals possessing full photonic band gaps, hindering the fact that more simple structures, possessing band gaps in selected directions of space, may also provide strong control of the electromagnetic radiation leading to the observation of many new interesting phenomena. In fact, the scope of this control is not limited to a linear interaction and can be extended to nonlinear interactions of any order.
In this work we present a study of the second order nonlinear interaction from nonlinear organic molecules placed within two different types of photonic crystals. First, we will discuss the enhancement and inhibition of the radiation at the second-harmonic frequency of a sheet of dipoles embedded in a 1D photonic crystal. The experimentally observed reflected second-harmonic intensity as a function of the angle of incidence shows sharp resonances corresponding to the excitation of the SH field in a local mode within the forbidden band in the structure, which position depends on the size of the defect, and additional resonance at the high angular band edge, which position is independent of the size of the defect. Comparison among these results and the SH intensity reflected by the same monolayer in free space (which presents a bell shaped radiation pattern as a function of the angle of incidence), shows an enhancement of the radiation at the resonances, and strong inhibition of the radiation at other angles within the gap. Theoretical simulation of the experiment shows a good agreement with the experimental results.
A detailed analysis of the enhancement and inhibition phenomena occurring in these structures shows a clear dependence of the resulting intensity with the position of the monolayer within the defect and with the dipole orientation. The change in phase difference between the oscillating dipoles and the field at the SH frequency at the monolayer as it is moved within the defect is found to play a determining role in the final energy transfer to the second-harmonic field. The resulting enhancement and inhibition of the radiation may be studied in terms of a nonsymmetric contribution of the different components of the field to the energy transfer process.
The second configuration studied in the present work consider the experimental demonstration of second-harmonic generation in a 3-dimensional macroscopically centrosymmetric lattice formed by spherical particles of optical dimensions. In such photonic crystals, the local breaking of the inversion symmetry at the surface of each sphere, allows for the existence of a nonvanishing second order interaction. The growth of the SH radiation is provided by the phase-matching mechanism caused by the bending of the photon dispersion curve near the Bragg reflection bands of this photonic crystal. Experimental evidence of this phase-matching mechanism, inherent of such crystals, is reported in this work. By measuring the SH intensity radiated from several crystals with different concentrations, we obtained the angular dependence of this type of emission and confirmed the surface character of the nonlinear interaction. A simplified theoretical model shows very good agreement with the experimental results. It is important to notice that in this mechanism of SHG, the nonlinearity of the molecule is independent of the phase-matching mechanism, that is inherent to the periodicity of the crystal.
In conclusion, the results obtained show a clear influence of the photonic crystals in the radiated SH intensity, resulting in enhancement and inhibition of the dipoles radiation.
Los grandes deslizamientos volcánicos son uno de los procesos geológicos más devastadores y pueden representar un importante peligro para la población de las zonas volcánicas. Este tipo de deslizamientos puede sobrepasar volúmenes de decenas o incluso centenares de kilómetros cúbicos. En Tenerife, siete grandes deslizamientos han afectado durante los últimos ~6 millones de años la morfología subaérea y submarina de la isla. En este estudio se ha realizado un extenso análisis de los eventos que han formado el valle de "La Orotava" en la parte Norte de Tenerife. El estudio incluye una investigación de campo, ensayos de laboratorio y análisis de estabilidad. En el laboratorio, las propiedades mecánicas de un suelo residual han sido investigadas mediante cortes directos y ensayos triaxiales. Durante el análisis de estabilidad, los resultados de los ensayos de laboratorio han sido incorporados a diferentes tipos de modelos de estabilidad. Finalmente, las condiciones mecánicas de los modelos dos y tres dimensionales han sido estudiados mediante el método de equilibrio límite y métodos de elementos finitos. Los resultados de los análisis revelan que la estabilidad de las laderas volcánicas puede ser reducida debido a diversos factores, como geológicos, morfológicos, climáticos y volcánicos. Los suelos residuales - bastante comunes en Tenerife - pueden haber actuado como superficie de rotura a causa de su débil comportamiento mecánico. Por otra parte, los estrechos y profundos barrancos han definido los límites laterales de los deslizamientos. Además de ello, los acantilados, el clima húmedo y especialmente la constante intrusión de diques, han llevado la ladera a condiciones de estabilidad críticas. Finalmente, una aceleración sísmica causada por un seísmo fuerte y cercano provocó muy probablemente el deslizamiento catastrófico. En Tenerife, se ha observado una relación temporal entre los colapsos de caldera y los grandes deslizamientos, lo que permite suponer que los fuertes terremotos asociados a los colapsos de caldera hayan provocado los deslizamientos.
Large volcanic landslides are one of the most hazardous of geological processes. They have occurred about once every 25 years during the last 500 years, and are a serious risk for the population due to their great volume and mobility. In spite of their destructive potential there are few comprehensive studies analysing large landslides on volcano flanks, and the mechanisms of such mass movements are not yet resolved. Within the last few years, several hypotheses concerning the potential causes of volcanic landslides have been proposed including processes such as dike intrusion, volcanic spreading, hydrothermal alteration, seismic shocks and caldera collapse events. Tenerife exhibits three large subaerial valleys originated by giant flank failures with ages ranging from Upper Pliocene to Middle Pleistocene. The northern submarine flank of the island is characterised by a voluminous apron of landslide debris. The La Orotava valley has been selected for analysis due to the amount of available data concerning its structure and evolution, and has been used as a test site to validate new assumptions that could be applied to other volcanic areas. The site investigation has revealed that the present morphology of the La Orotava valley was formed by two different failures: one in the western sector and the other in the eastern sector. The mechanical stability of the preslide volcano flank was strongly reduced by geologic, morphologic, climatic and volcanological factors which play a fundamental role in the initiation of the landslides. Widespread residual soils (paleosols) might have acted as potential slip surfaces, while deep erosive canyons probably evolved into the lateral limits of the failures. A high coastal cliff and a humid climate have also contributed to the critical stability conditions. The location of the landslide amphitheatre is perpendicular to the active Dorsal rift zone and adjacent to the Las Cañadas caldera, both important influences on the stability of the volcano slopes. On Tenerife, the relationship between large volcanic landslides and vertical caldera collapses is supported by a temporal coincidence of at least two failures with caldera collapse events. The mechanical behaviour of a residual soil sampled in the La Orotava valley has been analysed. Red coloured residual soils are generally located at the top of phonolitic pyroclastic deposits and are proposed as potential slip surfaces due to their very weak behaviour and their flat, homogeneous characteristics. They represent the only planar surface within the succession making up the volcano slopes. Their weak mechanical behaviour is characterised by volumetric collapse during shearing, a substantial reduction of shear strength for high normal stresses, and a significant increase of pore water pressure during undrained loading. The last feature is fundamental to the stability of volcano flanks since it strongly reduces the soil strength. Earthquakes, common processes in active volcanic areas, and saturated conditions can generate high excess pore pressures indicating the importance of regional climate and seismicity. The stability analysis has considered three different mechanisms: 1) ground acceleration due to seismicity - including both tectonic earthquakes and volcano-tectonic seismic shocks produced by caldera collapse; 2) horizontal stress due to dike intrusion, and; 3) vertical shear stress due to caldera collapse. The results indicate that ground acceleration principally decreases the mechanical stability of volcano flanks, enabling failure. Horizontal stresses due to dike intrusion can also influence slope stability, but preferably act as a preparing factor destabilising the slope, and not as a final triggering mechanism. The 3D numerical simulations show the significant effect of deeply incised canyons creating high shear stress at their base. Applying the results to the La Orotava events, the following scenario is assumed: First, deep narrow canyons, weak residual soils, humid climate, coastal cliff and persistent dike intrusion have significantly reduced the mechanical stability of the volcano slope and determined the limits of the failing mass. Then, seismicity generated by the caldera collapse episode at the end of the Guajara cycle at ~0.56 Ma triggered the catastrophic landslides. The results of the mobility analysis show the important influence of water on the runout distances of landslides. Subaqueous drag forces reduce the velocity, while hydroplaning effects strongly increase the runout distance. For Tenerife, the model indicates that a sliding mass can advance great distances, tens of kilometres away from the island, at water depths exceeding 3000 m, as can be observed in the bathymetric data.
La predicción precisa de los efectos producidos por el acoplamiento fluido estructura para cuerpos parcial o totalmente sumergidos, incluyendo superficies libres, es un problema de gran relevancia en la ingeniería naval así como en muchos otros campos del diseño de estructuras sometidas a la acción de fluidos. Las dificultades que se encuentran en la resolución de los problemas de interacción fluido estructura se deben principalmente a las siguientes causas:
1. La dificultad de resolver numéricamente las ecuaciones de la dinámica de un fluido incompresible que, en general, si descartamos el caso más simple del modelo del flujo potencial, tienen un importante carácter no lineal.
2. Los obstáculos que se presentan al resolver la ecuación de la superficie libre, que constriñen el movimiento de las partículas a una superficie fluida de posición a priori desconocida.
3. Las dificultades asociadas a la resolución del problema del movimiento de un cuerpo sumergido debido a las fuerzas de interacción, minimizando la deformación de los elementos de la malla y reduciendo, de esta manera, la necesidad del remallado.
En la presente tesis se presenta un método estabilizado basado en el método de los elementos finitos que pretende solventar cada uno de los problemas anteriores. La metodología se basa en la modificación de las ecuaciones diferenciales de la dinámica de fluidos que gobiernan el flujo viscoso incompresible y el movimiento de la superficie libre, mediante la aplicación del método de cálculo finitesimal (FIC) propuesto en este trabajo. En el presente caso las ecuaciones modificadas son resueltas usando un esquema de pasos fraccionados semi-implícito y el método de los elementos finitos (FEM). El movimiento del cuerpo sumergido en el fluido debido a las fuerzas de interacción se calcula resolviendo un problema estructural dinámico, para el cual las fuerzas del fluido son las condiciones iniciales. Se incluye, además, un algoritmo para el movimiento de la malla debido a la deformación del dominio de cálculo. Este método minimiza la distorsión de la malla debida al movimiento del sólido rígido y al cambio de posición de la superficie libre. Este algoritmo se basa en la solución iterativa por el método de elementos finitos de un problema lineal, donde la malla de cálculo se considera un sólido elástico sometido a la deformación prescrita por el cambio en el dominio de cálculo. Las características de elasticidad del sólido, y en concreto su rigidez, se aplican de manera que los elementos que más se deforman tienen una rigidez mayor. Por último se presentan varios ejemplos de interés industrial, aplicación de la metodología propuesta en diferentes campos de la ingeniería naval.
In the context of the global human/earth issues (population, poverty, imbalances, environment problematic, global warming, water scarcity, economical globalization, etc.) with the others the Carrying Capacity issue is emerging. It is a "driver" which is not always simply related with sustainable development concepts. It is therefore enormously important to give adequate answers to the majority of the global dilemmas.
The definition of carrying capacity is not easy because it is controversial. So the first chapter of this study is to adopt a clearer position in reference to the meaning, the borders, the key aspects, etc., of our approach to this issue. Basically, our approach is, first, from the sustainable development point of view and, second, a local approach in a global view. Finally and concretely, we indicate what aspects, in which place, how do we study carrying capacity? The answer to these questions will be: the agricultural (land and water) reality in a very specific region of East Sub Saharan Africa.
So the next step of the work is to specify and delimit our chosen region and, obviously, to study it in detail. Chapter 2, and some parts of Chapter 8, are the results of this.
The kind of methodological approach to global human/earth issues is, clearly, the most characteristic point of our work. We follow a scientific approach developed by Dr. Mihajlo Mesarovic over forty years ago in the mathematical systems analysis field and "finished" in multilevel integrated assessment with reasoning support tools for policy analysis. We study in depth and analyze this methodology in Chapter 3.
From a first or high level point of view of a hierarchy of models in our methodology, we study the population and, for the moment in this level, the carrying capacity reality, which is a dynamic system in reality, of our case study region. We have created the corresponding model and then, we have used a reference study from FAO/IIASA/UN [B.3.7] that, according to our bibliography searches and the role that it is continuing to play in the international studies of this issue in developing countries, is a "key reference". We find all of this in chapters 5 (population) and 6 (carrying capacity). In fact one of the goals of this work as a whole is to involve, extend, and indeed test the results of the mentioned report using our methodology.
Always from the hierarchical point of view we affront, finally, the second level representation of our issue. It is the most creative part of our study. We decide, after a deep analysis of the background, that we can succeed in developing a new agricultural model involving land and water aspects.
Because water is another controversial driving factor of the global human/earth issues, we focus on it in chapter 7. We add some personal special approach according to our methodology and "philosophy".
Chapter 8 is the highlight and plays, at the same time, an integrated role of the whole study and, in particular, the second level approach from the point of view of the hierarchy of the models. It allows us to make many final conclusions in several directions. About the methodology itself: extremely powerful with the interrelated combination of the different models levels approach. About the key report cited: only needs to be revised in its high input/output forecasting. The success and new possibilities in order to study the carrying capacity issue, for future policy "vision" analysis, that we now have from the point of view of agricultural reality. Finally, a dramatic foresight and call to the international decision- makers about the situation in our Case Study Region (essentially, the more stressful sub-region of East Sub-Saharan Africa).
0.4.2. OBJECTIVES AND CONTRIBUTIONS
Assessment of carrying capacity is essential in the search for the condition of sustainable development. While sustainability has a global dimension focus, for carrying capacity assessment has to be on geographic areas within which the needs of population have to be satisfied consistent with the physiologically determined time constraints. Specifically, food had to be secured for the population on location and in time where the need exists. Large geographic areas cannot be sustained by food imported from distant locations on the globe. In short, some degree of food self-sufficiency is a prerequisite for sustainability. The research reported here started by identifying eastern Sub-Sahara Africa as the most vulnerable geographic region in the sense of carrying capacity.
The objective of the research was to approach the question of carrying capacity in a practical integrated manner ("problematique"); i.e., in the context of real constraints imposed by environmental life support resources, rather than to "reduce" the problem to the considerations of the theoretical extreme capacity that have no chance of being achieved in reality.
On the first level, a model is developed focusing on the most dominant relationship between population evolution and carrying capacity as a dynamic, time varying system. Broad based data available in international sources are used. Results of FAO research, which is recognized as being the most authoritative, is used to parameterize the model for all countries in the region as well as for the region itself. The concept of an index of carrying capacity potential is developed to assess the results of the simulation using three levels of technology inputs of agricultural production, identified by the FAO.
A second level model is developed in which actual physical constraints -land, yields, water and irrigation- are explicitly taken into account. Assessment of carrying capacity supported by actual data is then conducted using the same carrying capacity potential index as the first level. Consistency of the results on the two levels has been demonstrated. This conclusion -not to be expected a priori- has justified the application of the multilevel, from the hierarchical of the models point of view, approach. As such it presents a contribution to the methodology beyond the carrying capacity problem per se.
So, in summary, the main contributions of the thesis are threefold:
a) Contribution to the complex systems analysis methodology based on the multilevel modeling hierarchy approach, that uses the notions of a dominant relationship rather than more detailed approximation, in order to construct models on different levels of the modeling hierarchy. Consistency of the results on two levels-not expected a priori-open the ways for application of the approach to other problem domains (global warming, water scarcity, etc.).
b) Development of an agricultural (land and water) model to study carrying capacity for any country, region, on the globe. The developed models and the reasoning approach in scenario analysis can be applied to other agricultural carrying capacity problems such as, i.e., for Afghanistan, Bangladesh, etc.
c) Concrete results about targets and policies for the region in the East Sub-Saharan Africa in order to improve their food self-security.
Pizza, A. 1949/1999 CINQUANTIANNI DAL PIANO AN-CASA. CITTÀ, ARCHITETTURA, EDILIZIA PUBBLICA: DALLA RICOSTRUZIONE ALLA CITTÀ CONTEMPORANEA Fecha de presentación: 1999-12-16 Presentación de trabajo en congreso