Scale Factor Self-Dual Cosmological Models

We implement a conformal time scale factor duality for Friedmann-Robertson-Walker cosmological models, which is consistent with the weak energy condition. The requirement for self-duality determines the equations of state for a broad class of barotropic fluids. We study the example of a universe filled with two interacting fluids, presenting an accelerated and a decelerated period, with manifest UV/IR duality. The associated self-dual scalar field interaction turns out to coincide with the "radiation-like" modified Chaplygin gas models. We present an equivalent realization of them as gauged K\"ahler sigma models (minimally coupled to gravity) with very specific and interrelated K\"ahler- and super-potentials. Their applications in the description of hilltop inflation and also as quintessence models for the late universe are discussed.Comment: v3, improved and extended version to be published in JHEP; new results added to sect.2; 4 figures; 17pg

Analysis and Control of Cable-Stayed Bridges Subject to Seismic Action

Cable-stayed bridges are key points in transport networks and at present one of the most challenging structures for the civil engineering community. The integrity of these bridges should be guaranteed even under extremely large earthquakes. This paper begins with a discussion of the advantages of a new non-linear static “Pushover” procedure that includes the three-dimensional contribution of the governing vibration modes. The efficacy and the accuracy of the proposed Pushover in the non-linear seismic analysis of bridges with significant coupling between the towers, deck and cable system is verified. In the second part of this paper, the seismic responses of several cable-stayed bridges have been studied, verifying the influence of the tower shape, cable arrangement and the main span length on the structural behaviour under strong ground motions. Severe damage is identified at critical tower sections by means of extensive non-linear dynamic analyses. Finally, retrofit solutions with viscous dampers (VDs) and yielding metallic dampers (MDs) connecting the deck and the tower in the transverse direction are explored. The proposed connection with dampers effectively prevents yielding of the reinforcement and cracking in the tower legs

Spatial and temporal distribution of North Atlantic tropical cyclones

The aim of this work is to provide a classification of tropical cyclones (TC) according to their location, month of genesis and their lifecycles and to study the role of African Easterly Waves (AEWs) in North Atlantic cyclogenesis. Between 1980 and 2004, 269 tropical cyclones (TCs) were formed over the North Atlantic, 77% of which occurred during the August-October period and 95% of major hurricanes (TCs in which the maximum sustained wind was greater or equal to 50 m/s) were generated in the same period. The high activity of the August-October period was due to the favourable thermodynamic and dynamic conditions that simultaneously exist over the main development region (MDR). A classification of TCs according to their months of genesis and lifecycles showed that TCs generated before August and after October have no preferential latitude and longitude of genesis. TCs generated at the East of 60°W and over the southern part of the MDR have long lifecycles. Major hurricanes have long lifecycles and are generally initiated over the southern part of the MDR and East of 60°W. The spatial representation of the cyclogenesis area shows that cyclones are generated along two main axes; one is situated around 12.5°N (southern axis) and the second around 27.5°N (northern axis). 56% (44%) of TCs are generated over the southern axis (northern axis). 92% of TCs initiated along the southern axis originate from African Easterly Waves. While 64% of those generated over the northern axis are linked to mid-latitude baroclinic systems and upper level cold lows. This study contributes to a better understanding of North Atlantic cyclogenesis characteristics as well as the role of AEWs

Fundamental mode estimation for modern cable-stayed bridges considering the tower flexibility

The design of cable-stayed bridges is typically governed by the dynamic response. This work provides designers with essential information about the fundamental vibration modes, proposing analytical expressions based on the mechanical and geometrical properties of the structure. Different bridge geometries are usually considered in the early design stages until the optimum solution is defined. In these design stages, the analytical formulation is advantageous, because finite-element models are not required and modifying the bridge characteristics is straightforward. The influence of the tower flexibility is included in this study, unlike in previous attempts on mode estimation. The dimensions and proportions of the canonical models proposed in the analytical study stem from the previous compilation of the dimensions of a large number of constructed cable-stayed bridges. Five tower shapes, central or lateral cable-system layouts and box- or U-shaped deck sections, have been considered. The vibration properties of more than 1,000 cable-stayed bridges with main spans ranging from 200 to 800 m long were extracted within an extensive parametric analysis. The Vaschy-Buckingham theorem of dimensional analysis was applied to the numerical results to propose the formulation for period estimation. Finally, the formulas were validated with the vibration properties of 17 real cable-stayed bridges constructed in different countries. The importance of the tower flexibility is verified, and the errors observed are typically below 15%, significantly improving the estimations obtained by previous research works. © 2014 American Society of Civil Engineers

Desempenho agronômico de sorgo sacarino no agreste alagoano em função da densidade e espaçamento de plantio.

A cana-de-açúcar é colhida em Alagoas, em geral, entre os meses de setembro a março. No restante do ano ocorre a entressafra com a paralisação da moagem. Uma alternativa para aumentar a produção de bioenergia do Estado seria o prolongamento da safra com o uso de culturas com potencial para a produção de etanol durante o período de entressafra e uma das alternativas que poderiam ser utilizadas é o sorgo sacarino. O objetivo do trabalho foi avaliar a influência de diferentes espaçamentos e densidades de plantio de sorgo sacarino cultivado em usinas sucroalcooleiras na região Agreste do Estado de Alagoas. Foram avaliados três espaçamentos entre linhas (0,5m, 0,7m e 0,9m) e cinco densidades de plantio (100, 120, 140, 160 e 180 mil plantas.ha-1) no delineamento em parcela subdividida com três repetições. As densidades de plantio não afetaram as características avaliadas. O espaçamento 0,5m proporcionou maior produtividade de massa verde total, massa verde e seca de colmo e produtividade de panículas quando comparado ao espaçamento de 0,9m e maior produtividade de massa verde total em relação ao espaçamento 0,7m

Structural behaviour and design criteria of under-deck cable-stayed bridges subjected to seismic action

SUMMARY: Under-deck cable-stayed bridges are very effective structural systems for which the strong contribution of the stay cables under live loading allows for the design of very slender decks for persistent and transient loading scenarios. Their behaviour when subjected to seismic excitation is investigated herein and a set of design criteria are presented that relate to the type and arrangement of bearings, the number and configuration of struts, and the transverse distribution of stay cables. The nonlinear behaviour of these bridges when subject to both near-field and far-field accelerograms has been thoroughly investigated through the use of incremental dynamic analyses. An intensity measure that reflects the pertinent contributions to response when several vibration modes are activated was proposed and is shown to be effective for the analysis of this structural type. The under-deck cable-stay system contributes in a very positive manner to reducing the response when the bridges are subject to very strong seismic excitation. For such scenarios, the reduction in the stiffness of the deck because of crack formation, when prestressed concrete decks are used, mobilises the cable system and enhances the overall performance of the system. Sets of natural accelerograms that are compliant with the prescriptions of Eurocode 8 were also applied to propose a set of design criteria for this bridge type in areas prone to earthquakes. Particular attention is given to outlining the optimal strategies for the deployment of bearings