Robust global exponential stabilization on the n-dimensional sphere with applications to trajectory tracking for quadrotors

In this paper, we design a hybrid controller that globally exponentially stabilizes a system evolving on the n-dimensional sphere, denoted by Sn. This hybrid controller is induced by a “synergistic” collection of potential functions on Sn. We propose a particular construction of this class of functions that generates flows along geodesics of the sphere, providing convergence to the desired reference with minimal path length. We show that the proposed strategy is suitable to the exponential stabilization of a quadrotor vehicle

Hybrid Control for Robust and Global Tracking on Smooth Manifolds

In this paper, we present a hybrid control strategy that allows for global asymptotic tracking of reference trajectories evolving on smooth manifolds, with nominal robustness. Two different versions of the hybrid controller are presented: One which allows for discontinuities of the plant input and a second one that removes the discontinuities via dynamic extension. By taking an exosystem approach, we provide a general construction of a hybrid controller that guarantees global asymptotic stability of the zero tracking error set. The proposed construction relies on the existence of proper indicators and a transport map-like function for the given manifold. We provide a construction of these functions for the case where each chart in a smooth atlas for the manifold maps its domain onto the Euclidean space. We also provide conditions for exponential convergence to the zero tracking error set. To illustrate these properties, the proposed controller is exercised on three different compact manifolds-the two-dimensional sphere, the unit-quaternion group, and the special orthogonal group of order three- A nd further applied to the problems of obstacle avoidance in the plane and global synchronization on the circle

An optimized strategy to measure protein stability highlights differences between cold and hot unfolded states

Macromolecular crowding ought to stabilize folded forms of proteins, through an excluded volume effect. This explanation has been questioned and observed effects attributed to weak interactions with other cell components. Here we show conclusively that protein stability is affected by volume exclusion and that the effect is more pronounced when the crowder's size is closer to that of the protein under study. Accurate evaluation of the volume exclusion effect is made possible by the choice of yeast frataxin, a protein that undergoes cold denaturation above zero degrees, because the unfolded form at low temperature is more expanded than the corresponding one at high temperature. To achieve optimum sensitivity to changes in stability we introduce an empirical parameter derived from the stability curve. The large effect of PEG 20 on cold denaturation can be explained by a change in water activity, according to Privalov's interpretation of cold denaturation

Shapley Decomposition by Components of a Welfare Aggregate

We present an exercise to account for changes in an indicator into components of a welfare aggregate. The decomposition presented in this paper focus on the distribution of the welfare variable rather than a decomposable indicator. Thus, it is a statistical exercise in which we assume that we can in fact modify one factor at a time and keep everything else constant. This paper contributes to the existing literature by applying the concept of a Shapley decomposition to deal with the path dependence that arises from changing one element at a time. Although, the interpretation changes, the proposed decomposition is applicable to both the case of panel data as well as repeated cross section and allows accounting the contribution of each component to change in any given indicator

Shapley Decomposition by Components of a Welfare Aggregate

We present an exercise to account for changes in an indicator into components of a welfare aggregate. The decomposition presented in this paper focus on the distribution of the welfare variable rather than a decomposable indicator. Thus, it is a statistical exercise in which we assume that we can in fact modify one factor at a time and keep everything else constant. This paper contributes to the existing literature by applying the concept of a Shapley decomposition to deal with the path dependence that arises from changing one element at a time. Although, the interpretation changes, the proposed decomposition is applicable to both the case of panel data as well as repeated cross section and allows accounting the contribution of each component to change in any given indicator

Introdução à nanotecnologia.

BREVE HISTÓRICO SOBRE A NANOTECNOLOGIA E NANOCIÊNCIA A possibilidade de se manipular e controlar coisas ?muito pequenas? foi vislumbrada há mais de seis décadas pelo físico norte-americano Richard Feynman (ganhador do prêmio Nobel de Física em 1985), em sua seminal palestra ministrada durante o encontro da Sociedade Americana de Física em Pasadena, Estados Unidos. Nessa palestra, Feynman conjecturou que não haveria limites físicos para, por exemplo, se escrever na cabeça de um alfinete, sugerindo que ?havia muito espaço lá embaixo?.1 Apesar da manipulação da matéria na escala atômica ou nanométrica já existir, sua comprovação experimental esbarrava na necessidade do desenvolvimento de técnicas avançadas de microscopia que permitissem a visualização e a manipulação de átomos e moléculas e seus arranjos. Em 1974 o professor Norio Taniguchi associou o conceito "nano" à tecnologia, época em que já havia se tornado possível a obtenção de materiais na escala nanométrica, devido principalmente à evolução dos microscópios eletrônicos.2 De fato, um dos feitos mais importantes para o desenvolvimento da nanociência foi a invenção, em 1981, do microscópio de tunelamento por varredura (STM, do inglês scanning tunneling microscope) pelos cientistas Gerd Binning e Heinrich Rohrer na IBM de Zurich, Suíça. A descoberta permitiu o imageamento bidimensional de superfícies condutoras com resolução atômica, e ambos os pesquisadores foram agraciados com o prêmio Nobel de Física em 1986 pela importante descoberta.1 Alguns anos depois, Binning e colaboradores desenvolveram o microscópio de força atômica (AFM, do inglês atomic force microscope), que não demandava utilização de corrente elétrica no imageamento e possibilitava varrer qualquer tipo de superfície, fosse ela condutora elétrica ou não.3 Desde então, muito se tem avançado no desenvolvimento de técnicas e tecnologias empregadas na formação e caracterização de diversos tipos de nanoestruturas, bem como em investigações sobre muitas de suas interessantes propriedades e potenciais aplicações, em áreas diversas como eletroeletrônica, medicina, agricultura e pecuária e meio ambiente. Nesse contexto, dois termos são conhecidos e vêm sendo cada vez mais difundidos em nosso cotidiano: a nanociência e a nanotecnologia. Enquanto a nanociência diz respeito ao estudo e conhecimento dos fenômenos que envolvem a manipulação, seja no desenho, controle e modificação dos materiais nas diferentes escalas (atômica, molecular e macromolecular), estando relacionada às diversas áreas do conhecimento (engenharia, física, química, biologia, eletrônica, computação, medicina), a nanotecnologia diz respeito à produção, caracterização e aplicação dos nanomateriais nas mais diferentes áreas.4,5 Sendo assim, nanociência e nanotecnologia objetivam a compreensão, o controle e aplicação da matéria na escala nanométric

Electronic Tongue Based on Nanostructured Hybrid Films of Gold Nanoparticles and Phthalocyanines for Milk Analysis

The use of gold nanoparticles combined with other organic and inorganic materials for designing nanostructured films has demonstrated their versatility for various applications, including optoelectronic devices and chemical sensors. In this study, we reported the synthesis and characterization of gold nanoparticles stabilized with poly(allylamine hydrochloride) (Au@PAH NPs), as well as the capability of this material to form multilayer Layer-by-Layer (LbL) nanostructured films with metal tetrasulfonated phthalocyanines (MTsPc). Film growth was monitored by UV-Vis absorption spectroscopy, atomic force microscopy (AFM), and Fourier transform infrared spectroscopy (FTIR). Once LbL films have been applied as active layers in chemical sensors, Au@PAH/MTsPc and PAH/MTsPc LbL films were used in an electronic tongue system for milk analysis regarding fat content. The capacitance data were treated using Principal Component Analysis (PCA), revealing the role played by the gold nanoparticles on the LbL films electrical properties, enabling this kind of system to be used for analyzing complex matrices such as milk without any prior pretreatment