Influence of bed elevation discordance on flow patterns and head losses in an open-channel confluence

Confluences play a major role in the dynamics of networks of natural and man-made open channels, and field measurements on river confluences reveal that discordance in bed elevation is common. Studies of schematized confluences with a step at the interface between the tributary and the main channel bed reveal that bed elevation discordance is an important additional control for the confluence hydrodynamics. This study aimed to improve understanding of the influence of bed elevation discordance on the flow patterns and head losses in a right-angled confluence of an open channel with rectangular cross-sections. A large eddy simulation (LES)-based numerical model was set up and validated with experiments by others. Four configurations with different bed discordance ratios were investigated. The results confirm that, with increasing bed elevation discordance, the tributary streamlines at the confluence interface deviate less from the geometrical confluence angle, the extent of the recirculation zone (RZ) gets smaller, the ratio of the water depth upstream to that downstream of the confluence decreases, and the water level depression reduces. The bed elevation discordance also leads to the development of a large-scale structure in the lee of the step. Despite the appearance of the large-scale structure, the reduced extent of the RZ and associated changes in flow deflection/contraction reduce total head losses experienced by the main channel with an increase of the bed discordance ratio. It turns out that bed elevation discordance converts the lateral momentum from the tributary to streamwise momentum in the main channel more efficiently. (C) 2019 Hohai University. Production and hosting by Elsevier B.V

Tracking ability of global emerging markets exchange traded funds

Classificação JEL: C50 – General; G11 – Portfolio Choice, Investment DecisionsEste estudo tem como objectivo analisar a tracking ability dos ETF dos mercados emergentes em replicar 3 dos mais conhecidos e procurados benchmarks a nível mundial: MSCI EM Broad, MSCI EM Asia e MSCI Latin America. Para estudar essa capacidade foi utilizada uma amostra de 20 ETF comercializados e domiciliados na Europa por 5 das maiores entidades mundiais. Adicionalmente foram tidas em conta 4 formas de cálculo do tracking error, sendo que nesta dissertação se teve um cuidado especial com a volatilidade, uma vez que foram utilizados modelos assimétricos GARCH para ajustamento da volatilidade dos retornos. Os resultados mostram que os ETF dos mercados emergentes apresentam valores substancialmente elevados para o tracking error, e não replicam totalmente os seus benchmarks. Destes, os que seguem o índice MSCI EM Broad são os que evidenciam maiores dificuldades no tracking. Relativamente aos betas e aos alfas, todos os fundos apresentam valores muito próximos do beta objectivo e alfas não estatisticamente significativos. Por outro lado, os ETF dos mercados desenvolvidos ainda são os que apresentam melhores resultados em termos de replicação. No que diz respeito ao ajustamento da volatilidade os nossos resultados demonstraram que em 86% dos casos as conclusões sobre o tracking error são as mesmas se considerarmos retornos ajustados à volatilidade e retornos não ajustados. Conclui-se então que, apesar da generalidade dos ETF dos mercados emergentes ainda não estarem totalmente maduros, estes representam oportunidades fantásticas de lucros, por vezes muito superiores às dos mercados maduros. Por isso, é altura de olhar para novos horizontes. É altura de olhar para os mercados emergentes.This study examines the tracking ability of global emerging markets ETF to replicate 3 of the best known and most popular benchmarks worldwide: MSCI EM Broad, MSCI EM Asia and MSCI Latin America. To study this ability we used a sample of 20 ETF traded and domiciled in Europe by 5 of the largest global management companies. Additionally were taken into account 4 ways to calculate the tracking error, and in this dissertation we took a special care with the volatility, since were used asymmetric GARCH models to adjust the volatility of returns. The results show that global emerging markets ETF present substantially high values for tracking error and that they do not fully replicate their benchmarks. From these funds we find that the ones that mimic MSCI EM Broad seem to be the worst into track their benchmark. Additionally, all funds present values for beta close to the objective beta and, in most of cases, not statistically alphas. Regarding volatility adjustment, our results show that in 86% of the cases the results that we reach about tracking error are the same if we consider volatility adjustment returns or unadjusted volatility returns. We conclude that, despite the majority of emerging market ETF is not yet fully mature, these represent fantastic opportunities for profit, sometimes much higher than those of mature markets. It is time to look to new horizons. It is time to look to emerging markets

Pointwise convergence, maximal functions and regularity issues in harmonic analysis

This cumulative thesis is dedicated to the study of different maximal operators related to pointwise convergence in Fourier Analysis and is divided in three main parts. The first part is dedicated to regularity results for maximal functions. The Hardy–Littlewood maximal function is an essential tool in establishing pointwise convergence in harmonic analysis, and recently more importance has been given to its regularity properties. We make progress in the question of estimating the variation of the maximal function in one dimension, and explore different perspectives of the regularizing properties of fractional maximal functions. The second part is aimed at maximal versions of classical Fourier restriction theorems. Although the restriction operator has been considered for the past 40 years, it was not until very recently that it was asked whether it can be defined pointwise almost everywhere. We answer this question affirmatively in the two-dimensional case, make progress on the Tomas-Stein exponent case and discuss stronger assertions about Lebesgue points of the Fourier transform. The third part of this thesis deals with the interplay between Carleson operators and the Hilbert transform along the parabola. An interesting recent conjecture states that the maximally modulated Hilbert transform along the parabola must be bounded in L^2(R^2 ). We make partial progress in this question, considering a class of functions essentially constant in directions orthogonal to any fixed line in R^2. The thesis consists of seven chapters, where Chapters 1 to 6 contain each a scientific article. In Chapter 0 we develop the historical framework and discuss the motivation for our results, connecting them to the main subject of pointwise convergence and giving a summary of the techniques used. In Chapter 1 we prove a sharp variation bound for a class of maximal functions interpolating the centered and uncentered maximal functions in one dimension. We also prove a sharp variation bound for Lipschitz truncated uncentered maximal functions. We provide counterexamples showing that our techniques are also sharp. In Chapter 2 we connect the framework of derivative estimates for fractional maximal functions to Fourier analysis tools. In particular, we prove sharp regularity bounds for certain classes of smooth fractional maximal functions, as well as regularizing bounds for the fractional spherical maximal function. In Chapter 3 we investigate the regularizing properties of the local fractional maximal function on domains, extending the previous known results to the sharp range in case the domain is smooth enough. In Chapter 4 we bridge the gap in the recently started line of research of maximal restriction estimates. In particular, we prove that H^1 −almost every point in the unit circle is a Lebesgue point of the Fourier transform of an L^p function, 1 ≤ p In Chapter 5 we extend the results in the previous chapter to L^r −norm and spherical Lebesgue points of Fourier transforms of L^p functions. We also devise counterexamples to show sharpness of some of our results and impose restrictions to when the strong maximal function can satisfy full-range maximal restriction estimates. In Chapter 6 we consider a family of one-dimensional maximally modulated operators arising from the parabolic Carleson operator. We prove uniform bounds in the slope of the line, settling the degenerate case of the conjecture where the Fourier support of the function under consideration collapses into a line