Complete determination of the orbital parameters of a system with N+1 bodies using a simple Fourier analysis of the data

Here we show how to determine the orbital parameters of a system composed of a star and N companions (that can be planets, brown-dwarfs or other stars), using a simple Fourier analysis of the radial velocity data of the star. This method supposes that all objects in the system follow keplerian orbits around the star and gives better results for a large number of observational points. The orbital parameters may present some errors, but they are an excellent starting point for the traditional minimization methods such as the Levenberg-Marquardt algorithms.Comment: 4 page

Tidal Evolution of Exoplanets

Tidal effects arise from differential and inelastic deformation of a planet by a perturbing body. The continuous action of tides modify the rotation of the planet together with its orbit until an equilibrium situation is reached. It is often believed that synchronous motion is the most probable outcome of the tidal evolution process, since synchronous rotation is observed for the majority of the satellites in the Solar System. However, in the 19th century, Schiaparelli also assumed synchronous motion for the rotations of Mercury and Venus, and was later shown to be wrong. Rather, for planets in eccentric orbits synchronous rotation is very unlikely. The rotation period and axial tilt of exoplanets is still unknown, but a large number of planets have been detected close to the parent star and should have evolved to a final equilibrium situation. Therefore, based on the Solar System well studied cases, we can make some predictions for exoplanets. Here we describe in detail the main tidal effects that modify the secular evolution of the spin and the orbit of a planet. We then apply our knowledge acquired from Solar System situations to exoplanet cases. In particular, we will focus on two classes of planets, "Hot-Jupiters" (fluid) and "Super-Earths" (rocky with atmosphere).Comment: 30 pages, 19 figures. Chapter in Exoplanets, ed. S. Seager, to be published by University of Arizona Pres

Spin-orbit coupling and chaotic rotation for coorbital bodies in quasi-circular orbits

Coorbital bodies are observed around the Sun sharing their orbits with the planets, but also in some pairs of satellites around Saturn. The existence of coorbital planets around other stars has also been proposed. For close-in planets and satellites, the rotation slowly evolves due to dissipative tidal effects until some kind of equilibrium is reached. When the orbits are nearly circular, the rotation period is believed to always end synchronous with the orbital period. Here we demonstrate that for coorbital bodies in quasi-circular orbits, stable non-synchronous rotation is possible for a wide range of mass ratios and body shapes. We show the existence of an entirely new family of spin-orbit resonances at the frequencies $n\pm k\nu/2$, where $n$ is the orbital mean motion, $\nu$ the orbital libration frequency, and $k$ an integer. In addition, when the natural rotational libration frequency due to the axial asymmetry, $\sigma$, has the same magnitude as $\nu$, the rotation becomes chaotic. Saturn coorbital satellites are synchronous since $\nu\ll\sigma$, but coorbital exoplanets may present non-synchronous or chaotic rotation. Our results prove that the spin dynamics of a body cannot be dissociated from its orbital environment. We further anticipate that a similar mechanism may affect the rotation of bodies in any mean-motion resonance.Comment: 6 pages. Astrophysical Journal (2013) 6p

Non-renormalization for planar Wess-Zumino model

Using a non-perturbative functional method, where the quantum fluctuations are gradually set up,it is shown that the interaction of a N=1 Wess-Zumino model in 2+1 dimensions does not get renormalized. This result is valid in the framework of the gradient expansion and aims at compensating the lack of non-renormalization theorems

An alternative approach to dynamical mass generation in QED3

Some quantum properties of QED3 are studied with the help of an exact evolution equation of the effective action with the bare fermion mass. The resulting effective theory and the occurrence of a dynamical mass are discussed in the framework of the gradient expansion

Deformation and tidal evolution of close-in planets and satellites using a Maxwell viscoelastic rheology

In this paper we present a new approach to tidal theory. Assuming a Maxwell viscoelastic rheology, we compute the instantaneous deformation of celestial bodies using a differential equation for the gravity field coefficients. This method allows large eccentricities and it is not limited to quasi-periodic perturbations. It can take into account an extended class of perturbations, including chaotic motions and transient events. We apply our model to some already detected eccentric hot Jupiters and super-Earths in planar configurations. We show that when the relaxation time of the deformation is larger than the orbital period, spin-orbit equilibria arise naturally at half-integers of the mean motion, even for gaseous planets. In the case of super-Earths, these equilibria can be maintained for very low values of eccentricity. Our method can also be used to study planets with complex internal structures and other rheologies.Comment: 16 pages, 13 figures, 2 table

Experimental Study of the Performance of a Low Consumption Electric Car Prototype

In this dissertation all steps to characterize the performance of an electric prototype road vehicle of high energy-efficiency are portrayed. The AERO@Ubi team from the University of Beira Interior, Covilhã, developed a vehicle that competed in the 2014 and 2015 editions of the Shell Eco-Marathon®, which took place in Rotterdam. The team presented a prototype that stands out for its innovative methods of movement and design. Among these innovations is a distinguished aerodynamic body, that differs from the conventional form of water drop, and instead uses a turning that consists in tilting the prototype with only one wheel at the front and employs radial tires as well as ceramic bearings. The prototype was subjected to several tests in order to characterize the aerodynamic drag coefficient, the rolling friction coefficient and the lift coefficient in order to quantify the losses related to friction and aerodynamic drags.These tests, which will be described in detail in Chapter 3 can be divided into three stages: a preliminary stage, which included topographic measurements of corridors and respective launch ramps at the Faculty of Engineering of the University of Beira Interior as well as of roads with different slopes at Tortosendo Industrial Park were carried out; an initial stage, where the car components were tested separately , without or with minimal influence from other components or weather conditions; a final stage, where the prototype was tested, as a whole, through downhill roads in order to verify different terminal velocities down different slopes. The results are analyzed and compared with results obtained in other studies. In the initial stage the results were encouraging as the prototype revealed a rolling friction coefficient value of 0.002 leading to a foreseen total of 2 N of rolling friction force for a 1000 N of the prototype with the pilot weight. In the final stage of testing, the results increase significantly to 9 N and this may suggest an unidentified feature of the prototype. The prototype obtained a result of 331 km/kWh, reaching the 19th place for prototypes with electric battery in the Shell Eco-Marathon® Europe.Nesta dissertação são descritas todas as medidas para a caracterização do desempenho de um veículo terrestre protótipo elétrico de alta eficiência energética. A equipa AERO@Ubi da Universidade da Beira Interior, Covilhã, desenvolveu um veículo que competiu nas edições 2014 e 2015 da Shell Eco-Marathon®, que teve lugar em Roterdão. A equipa apresentou-se com um protótipo que se destaca em diversos métodos inovadores de movimento e design. Entre estas inovações estão presentes um corpo aerodinâmico distinto, que difere da forma convencional de gota de água, a utilização de um método de viragem que consiste na inclinação do protótipo com apenas uma roda na frente e o uso de pneus radiais bem como rolamentos de cerâmica. O protótipo foi submetido a vários testes de forma a caracterizar o coeficiente de arrasto aerodinâmico e o coeficiente de atrito de rolamento a fim de quantificar as perdas relacionadas a atritos. Estes testes serão descritos em pormenor no capítulo 3 e podem ser divididos em três fases: a fase preliminar, que incluiu medições topográficas de corredores e respetivas rampas de lançamento na Faculdade de Engenharia da Universidade da Beira Interior, bem como estradas com diferentes inclinações no Parque Industrial do Tortosendo; uma fase inicial, em que os componentes do carro foram testados separadamente, sem ou com mínima influência de outros componentes ou condições meteorológicas; uma fase final, em que o protótipo foi testado como um todo, através de descidas de estradas, a fim de verificar as diferentes velocidades terminais atingidas para diferentes inclinações de estradas. Os resultados são analisados e comparados com os resultados obtidos noutros estudos. Na fase inicial, os resultados foram encorajadores com o protótipo atingindo um valor de coeficiente de atrito de rolamento de 0,002 levando a um total previsto de 2 N de força de atrito de rolamento para 1000 N de peso do protótipo com piloto. Na fase final do teste, as perdas aumentaram significativamente para os 9 N o que indica uma característica não identificada do protótipo. O protótipo obteve um resultado de 331 km/kW.h, alcançando o 19º lugar para protótipos com propulsão a bateria elétrica na Shell Eco-Marathon® Europa

Personality characteristics, preferences for rewards, and the propensity to choose an auditing job

Mestrado Bolonha em Contabilidade, Fiscalidade e Finanças EmpresariaisA presente dissertação explora as relações teóricas entre características de personalidade, preferências por diferentes tipos de recompensas e a propensão para a escolha de um emprego em auditoria. Especificamente, consideramos como características de personalidade - motivação, locus de controlo (interno e externo) e autoeficácia – e como tipos de recompensas - financeiras, extrínsecas, de suporte e intrínsecas. Para testar empiricamente o modelo, foram recolhidos dados com base numa técnica de amostragem em bola-de-neve, que incidiu sobre alunos da área de gestão e afins. Aplicámos, posteriormente, o Modelo de Equações Estruturais dos Mínimos Quadrados Parciais (PLS-SEM), usando o Smart PLS 3.0, para analisar os dados. Os nossos resultados mostram que a motivação extrínseca está positivamente associada com preferências por recompensas financeiras e extrínsecas, enquanto a motivação intrínseca está positivamente associada às preferências por recompensas de suporte e intrínsecas. Também descobrimos que o locus de controlo externo está positivamente associado a uma preferência por recompensas extrínsecas, e o locus de controlo interno relaciona-se positivamente com preferências por todas as recompensas, à exceção das financeiras. Adicionalmente, a autoeficácia tem uma associação positiva com preferências por recompensas financeiras, extrínsecas e intrínsecas. Finalmente, identificamos uma associação positiva entre preferência por recompensas extrínsecas e a propensão para escolher um emprego em auditoria. O nosso estudo tem contribuições teóricas e práticas. Em relação às teóricas, somos - para aquele que é o nosso melhor conhecimento - os primeiros a avaliar preferências por diferentes tipos de recompensas considerando múltiplas características de personalidade e um conjunto completo de incentivos. Na dimensão prática, o nosso estudo fornece novos conhecimentos que podem ser usados pelas firmas de auditoria para definir estratégias de recrutamento mais persuasivas baseadas no perfil dos indivíduos, o que pode ajudar estas empresas a atrair e reter potenciais auditores.This dissertation explores theoretical relationships among personality characteristics, preferences for different types of rewards and the propensity to choose a job in auditing. Specifically, we consider as personality characteristics - motivation, locus of control (internal and external), and self-efficacy – and as types of rewards - financial, extrinsic, support and intrinsic. In order to empirically test our proposed conceptual model, we collected data through a snowball sampling technique targeted at management-related higher education students. We applied Partial Least Squares Structural Equation Modeling (PLS-SEM) using Smart PLS 3.0 to analyse the data. Our findings show that extrinsic motivation is positively associated with preferences for financial and extrinsic rewards, whereas intrinsic motivation is positively associated with preferences for support and intrinsic rewards. We also find that external locus of control is positively associated with a preference for extrinsic rewards, and internal locus of control relates positively to preferences for all types of rewards, except financial rewards. Additionally, self-efficacy has a positive association with preferences for financial, extrinsic, and intrinsic rewards. Finally, we find a positive association between preferences for extrinsic rewards and the propensity to choose a job in auditing. Our study provides both theoretical and practical contributions. Regarding theoretical contributions, we are - to the best of our knowledge - the first to assess preferences for different types of rewards considering multiple personality characteristics and a full range of incentives. For practitioners, our study provides insights that can be used by auditing firms to develop more persuasive recruitment strategies based on one’s profile, which can help these companies to attract and retain auditor candidates.info:eu-repo/semantics/publishedVersio