Sudden Trust Collapse in Networked Societies

Trust is a collective, self-fulfilling phenomenon that suggests analogies with phase transitions. We introduce a stylized model for the build-up and collapse of trust in networks, which generically displays a first order transition. The basic assumption of our model is that whereas trust begets trust, panic also begets panic, in the sense that a small decrease in trust may be amplified and ultimately lead to a sudden and catastrophic drop of trust. We show, using both numerical simulations and mean-field analytic arguments, that there are extended regions of the parameter space where two equilibrium states coexist: a well-connected network where confidence is high, and a poorly connected network where confidence is low. In these coexistence regions, spontaneous jumps from the well-connected state to the poorly connected state can occur, corresponding to a sudden collapse of trust that is not caused by any major external catastrophe. In large systems, spontaneous crises are replaced by history dependence: whether the system is found in one state or in the other essentially depends on initial conditions. Finally, we document a new phase, in which agents are connected yet distrustful.Comment: 15 pages, 10 figure

Definition of a New Level One Test Case Measurements of Equilibrium Radiation from an Inductively Coupled Plasma in the Near-UV to Near-IR Spectral Region for a Titan-Type N2-CH4 Mixture. Preliminary Results

A test case, using a similar methodology and experimental set-up than previous test case TC5-Level 1 is presented in this paper. An inductively coupled plasma torch, working at atmospheric pressure, is used to create N2-CH4 Titan-like plasma (98%N2 - 2%CH4). The operating frequency and power are 64 MHz and 3 kW respectively. This kind of apparatus allows obtaining plasma in chemical and quasi-thermal equilibrium The spectral measurements cover the [300-800] nm range and are performed inside the induction coil. Each interesting spectrum is calibrated and compared to the line-by-line spectral code SPARTAN used for the simulation of the radiative emission of entry-type plasma. Finally, a discussion is proposed about the nucleation phenomenon which is occurred in the ICP torch with the N2-CH4 plasma. Preliminary studies show the synthesis of nanostructured carbon on the quartz tube.Comment: Radiation of High Temperature Gases in Atmospheric Entry, Heraklion : Greece (2008

On numerical simulation of cavitating flows under thermal regime

International audienceIn this work, we investigate closure laws for the description of interfacial mass transfer in cavitating flowsunder thermal regime. In a first part, we show that, if bubble resident time in the low pressure area of theflow is larger than the inertial/thermal regime transition time, bubble expansion are no longer monitoredby Rayleigh equation, but by heat transfer in the liquid phase at bubbles surfaces. The modelling of inter-facial heat transfer depends thus on a Nusselt number that is a function of the Jakob number and of thebubble thermal Péclet number. This original approach has the advantage to include the kinetic of phasechange in the description of cavitating flow and thus to link interfacial heat flux to interfacial mass fluxduring vapour production. The behaviour of such a model is evaluated for the case of inviscid cavitatingflow in expansion tubes for water and refrigerant R114 using a four equations mixture model. Comparedwith inertial regime (Rayleigh equation), results obtained considering thermal regime seem to predictlower local gas volume fraction maxima as well as lower gradients of velocity and gas volume fraction.It is observed that global vapour production is closely monitored by volumetric interfacial area (bubblesize and gas volume fraction) and mainly by the Jakob number variations. It is found that, in contrast withphase change occurring in common boiling flow, Jakob number variation is influenced by phasic temper-ature difference but also by density ratio variation with pressure and temperature

ELODIE metallicity-biased search for transiting Hot Jupiters II. A very hot Jupiter transiting the bright K star HD189733

Among the 160 known exoplanets, mainly detected in large radial-velocity surveys, only 8 have a characterization of their actual mass and radius thanks to the two complementary methods of detection: radial velocities and photometric transit. We started in March 2004 an exoplanet-search programme biased toward high-metallicity stars which are more frequently host extra-solar planets. This survey aims to detect close-in giant planets, which are most likely to transit their host star. For this programme, high-precision radial velocities are measured with the ELODIE fiber-fed spectrograph on the 1.93-m telescope, and high-precision photometry is obtained with the CCD Camera on the 1.20-m telescope, both at the Haute-Provence Observatory. We report here the discovery of a new transiting hot Jupiter orbiting the star HD189733. The planetary nature of this object is confirmed by the observation of both the spectroscopic and photometric transits. The exoplanet HD189733b, with an orbital period of 2.219 days, has one of the shortest orbital periods detected by radial velocities, and presents the largest photometric depth in the light curve (~ 3%) observed to date. We estimate for the planet a mass of 1.15 +- 0.04 Mjup and a radius of 1.26 +- 0.03 RJup. Considering that HD189733 has the same visual magnitude as the well known exoplanet host star HD209458, further ground-based and space-based follow-up observations are very promising and will permit a characterization of the atmosphere and exosphere of this giant exoplanet.Comment: 5 pages, submitted to Astronomy & Astrophysic

Otimização de rotas num sistema de Bike-Sharing usando sinais fisiológicos

Com o passar dos anos, o bike-sharing tem merecido uma crescente atenção, devido às iniciativas para aumentar o uso de bicicletas em detrimento dos transportes motorizados. O objetivo desta mudança visa minimizar o uso dos transportes urbanos que libertam gases poluentes causando problemas ambientais e congestionamento de tráfego. Tendo em vista a alternativa aos transportes urbanos e veículos motorizados, com objetivo de adotar um estilo de vida verde e saudável, várias cidades em todo o planeta tentam proporcionar esse estilo de vida aos seus cidadãos, construindo sistemas os bike-sharing e pondo à disposição parques de estacionamento com bicicletas.Neste documento, pretende-se mencionar a criação de um sistema que com a medição de parâmetros físicos, através de sensores fisiológicos e dispositivos Wearable, pode dar a perceber quais as rotas mais otimizadas para um utilizador e de que forma a utilização dos sistema de bike-sharing se pode articular com os restantes transportes públicos da cidade. No final da dissertação, espera-se como resultado uma aplicação Android, denominada SmartBikeEmotion, que pretende permitir aos utilizadores usufruir do que os sistemas de bike-sharing proporcionam, com o acréscimo da adaptação dos circuitos à sua condição física, auxiliando na sua movimentação pela cidade. Esta aplicação será integrada com o projeto BikeEmotion, um projeto de bike-sharing, desenvolvido em consórcio pela Ubiwhere, Ponto.C, Micro I/O, e Universidade de Aveiro.Over the years, the bike-sharing has received a widespread attention due to initiatives to increase the use of bicycles instead of motorized transports. The objective of this change is to minimize the use of urban transport that release greenhouse gases which causes environmental problems and traffic congestion. Take in account the alternative to urban transport and motor vehicles, in order to adopt a green and healthy lifestyle, many cities around the world attempts to provide this lifestyle to its citizens, building bike-sharing systems and making available parking spaces for bicycles.In this paper, we intended to show the creation of a system which with the measurement of physical parameters, through physiological sensors and Wearable devices, may advise about the more optimized routes for the users and how the bike-sharing system can be linked with other public transports. In the end of this thesis, we expect an Android application, called SmartBikeEmotion, which aims to allow the users take advantages of the bike-sharing system, with the strength of the circuits adaption to the user's physical condition, assisting them in the cycling through the city. This application will be integrated with BikeEmotion project, a bike-sharing project, developed in partnership by Ubiwhere, Ponto.C, Micro I / O, and University of Aveiro

Analyses spectroscopiques d'un plasma CO2-N2 (97%-3%), de type atmosphère martienne, par torche ICP

Une torche à plasma à couplage inductif, fonctionnant à la pression atmosphérique, est utilisée pour créer un plasma à partir d'un mélange CO2-N2 reproduisant une atmosphère martienne (97%-3%). La fréquence ainsi que la puissance de fonctionnement de la torche ICP sont respectivement 64 Mhz et 3 kW. Ce type d'outil analytique permet d'obtenir un plasma relativement proche de l'équilibre thermodynamique. La caractérisation du plasma consistera dans un premier temps à déterminer la composition chimique; un code de calcul basé sur la minimisation de l'énergie libre de Gibbs est utilisé. Dans un second temps, les profils de températures seront données à travers les applications de l'inversion d'Abel des systèmes moléculaires considérés. Les mesures spectroscopiques couvrent le domaine [250-800] nm et sont réalisés à l'intérieur des spires inductives. Chaque spectre est ainsi comparé au code SESAM (Simulation de l'Emission Spectrale de l'Atmosphère de Mars)

Workspace and Singularity analysis of a Delta like family robot

Workspace and joint space analysis are essential steps in describing the task and designing the control loop of the robot, respectively. This paper presents the descriptive analysis of a family of delta-like parallel robots by using algebraic tools to induce an estimation about the complexity in representing the singularities in the workspace and the joint space. A Gr{\"o}bner based elimination is used to compute the singularities of the manipulator and a Cylindrical Algebraic Decomposition algorithm is used to study the workspace and the joint space. From these algebraic objects, we propose some certified three dimensional plotting describing the the shape of workspace and of the joint space which will help the engineers or researchers to decide the most suited configuration of the manipulator they should use for a given task. Also, the different parameters associated with the complexity of the serial and parallel singularities are tabulated, which further enhance the selection of the different configuration of the manipulator by comparing the complexity of the singularity equations.Comment: 4th IFTOMM International Symposium on Robotics and Mechatronics, Jun 2015, Poitiers, France. 201

Cenários para investigação como ferramenta de avaliação: uma discussão

Neste artigo, apresenta-se uma discussão no campo teórico sobre a possibilidade da utilização dos cenários para investigação como ferramenta de avaliação. Nesse sentido, são contrastadas formas de se conceber o ensino e a avaliação em matemática. Procura-se enfatizar a relação do modelo ora hegemônico de avaliação com o ensino tradicional de matemática, bem como a proposta dos cenários para investigação com uma concepção mais formativa de avaliação dentro de um ensino mais preocupado com uma formação crítica dos indivíduos. Assim, tal estratégia é percebida como um modelo de avaliação que se distancia da medida do desempenho, classificação e seleção dos alunos, onde o erro é fonte de punição e não de reflexão ou investigação por parte do professor. Espera-se que essa discussão possa fomentar espaços de reflexão sobre as práticas de ensino e sobre as práticas avaliativas de professores de Matemática