On the importance function in splitting simulation

The splitting method is a simulation technique for the estimation of very small probabilities. In this technique, the sample paths are split into multiple copies, at various stages in the simulation. Of vital importance to the efficiency of the method is the Importance Function (IF). This function governs the placement of the thresholds or surfaces at which the paths are split. We derive a characterisation of the optimal IF and show that for multi-dimensional models the natural choice for the IF is usually not optimal. We also show how nearly optimal splitting surfaces can be derived or simulated using reverse time analysis. Our numerical experiments illustrate that by using the optimal IF, one can obtain a significant improvement in simulation efficiency.

Hydrodynamic origin of diffusion in nanopores

We study the transport of a subcritical Lennard-Jones fluid in a cylindrical nanopore, using a combination of equilibrium and nonequilibrium as well as dual control volume grand canonical molecular dynamics methods. We show that all three techniques yield the same value of the transport coefficient for diffusely reflecting pore walls, even in the presence of viscous transport. We also demonstrate that the classical Knudsen mechanism is not manifested, and that a combination of viscous flow and momentum exchange at the pore wall governs the transport over a wide range of densities.

Estados de Direito Constitucionais Governativos Europeus

“Nem sempre quem tem mais votos governa. Conheça alguns casos na Europa" § "Not everyone who has the most votes governs. Meet some cases in Europe "

A tributação das sociedades gestoras de participações sociais em Portugal (regime comparativo com o RETGS)

Mestrado em Fiscalidade

Coordinated transportation of a large object by a team of three robots

Dynamical systems theory in this work is used as a theoretical language and tool to design a distributed control architecture for a team of three robots that must transport a large object and simultaneously avoid collisions with either static or dynamic obstacles. The robots have no prior knowledge of the environment. The dynamics of behavior is defined over a state space of behavior variables, heading direction and path velocity. Task constraints are modeled as attractors (i.e. asymptotic stable states) of the behavioral dynamics. For each robot, these attractors are combined into a vector field that governs the behavior. By design the parameters are tuned so that the behavioral variables are always very close to the corresponding attractors. Thus the behavior of each robot is controlled by a time series of asymptotical stable states. Computer simulations support the validity of the dynamical model architecture.

Coordinated transportation of a large object by a team of two robots

In this paper dynamical systems theory is used as a theoretical language and tool to design a distributed control architecture for a team of two robots that must transport a large object and simultaneously avoid collisions with obstacles (either static or dynamic). This work extends the previous work with two robots (see [1] and [5]). However here we demonstrate that it’s possible to simplify the architecture presented in [1] and [5] and reach an equally stable global behavior. The robots have no prior knowledge of the environment. The dynamics of behavior is defined over a state space of behavior variables, heading direction and path velocity. Task constrains are modeled as attractors (i.e. asymptotic stable states) of a behavioral dynamics. For each robot, these attractors are combined into a vector field that governs the behavior. By design the parameters are tuned so that the behavioral variables are always very close to the corresponding attractors. Thus the behavior of each robot is controlled by a time series of asymptotic stable states. Computer simulations support the validity of the dynamical model architecture.

Using attractor dynamics to generate decentralized motion control of two mobile robots transporting a long object in coordination

Dynamical systems theory is used here as a theoretical language and tool to design a distributed control architecture for a team of two mobile robots that must transport a long object and simultaneously avoid obstacles. In this approach the level of modeling is at the level of behaviors. A “dynamics” of behavior is defined over a state space of behavioral variables (heading direction and path velocity). The environment is also modeled in these terms by representing task constraints as attractors (i.e. asymptotically stable states) or reppelers (i.e. unstable states) of behavioral dynamics. For each robot attractors and repellers are combined into a vector field that governs the behavior. The resulting dynamical systems that generate the behavior of the robots may be nonlinear. By design the systems are tuned so that the behavioral variables are always very close to one attractor. Thus the behavior of each robot is controled by a time series of asymptotically stable states. Computer simulations support the validity of our dynamic model architectures.

Carbon key-properties for microcystin adsorption in drinking water treatment: structure or surface chemistry?

Dissertação para Obtenção de Grau de Mestre em Engenharia Química e Bioquímica

Storage of water molecules into biomimetic heterostructures: the role of roughness

The development of devices based on heterostructured thin films of biomolecules conveys a huge contribution on biomedical field. However, to achieve high efficiency of these devices, the storage of water molecules into these heterostructures, in order to maintain the biological molecules hydrated, is mandatory. Such hydrated environment may be achieved with lipids molecules which have the ability to rearrange spontaneously into vesicles creating a stable barrier between two aqueous compartments. Yet it is necessary to find conditions that lead to the immobilization of whole vesicles on the heterostructures. In this work, the conditions that govern the deposition of open and closed liposomes of 1.2-dipalmitoyl-sn-Glycero-3-[Phospho-rac-(1-glycerol)] (sodium Salt) (DPPG) onto polyelectrolytes cushions prepared by the layer-by-layer (LbL) method were analyzed. Electronic transitions of DPPG molecules as well as absorption coefficients were obtained by vacuum ultraviolet spectroscopy, while the elemental composition of the heterostructures was characterized by x-ray photoelectron spectroscopy (XPS). The presence of water molecules in the films was inferred by XPS and infrared spectroscopy. Quartz crystal microbalance (QCM) data analysis allowed to conclude that, in certain cases, the DPPG adsorbed amount is dependent of the bilayers number already adsorbed. Moreover, the adsorption kinetics curves of both adsorbed amount and surface roughness allowed to determine the kinetics parameters that are related with adsorption processes namely, electrostatic forces, liposomes diffusion and lipids re-organization on surface. Scaling exponents attained from atomic force microscopy images statistical analysis demonstrate that DPPG vesicles adsorption mechanism is ruled by the diffusion Villain model confirming that adsorption is governed by electrostatic forces. The power spectral density treatment enabled a thorough description of the accessible surface of the samples as well as of its inner structural properties. These outcomes proved that surface roughness influences the adsorption of DPPG liposomes onto surfaces covered by a polyelectrolyte layer. Thus, low roughness was shown to induce liposome rupture creating a lipid bilayer while high roughness allows the adsorption of whole liposomes. In addition, the fraction of open liposomes calculated from the normalized maximum adsorbed amounts decreases with the cushion roughness increase, allowing us to conclude that the surface roughness is a crucial variable that governs the adsorption of open or whole liposomes. This conclusion is fundamental for the development of well-designed sensors based on functional biomolecules incorporated in liposomes. Indeed, LbL films composed of polyelectrolytes and liposomes with and without melanin encapsulated were successfully applied to sensors of olive oil.

Dynamic behavior of sylvatic yellow fever in Brazil (1954-2008)

INTRODUCTION: Sylvatic yellow fever (SYF) is enzootic in Brazil, causing periodic outbreaks in humans living near forest borders or in rural areas. In this study, the cycling patterns of this arbovirosis were analyzed. METHODS: Spectral Fourier analysis was used to capture the periodicity patterns of SYF in time series. RESULTS: SYF outbreaks have not increased in frequency, only in the number of cases. There are two dominant cycles in SYF outbreaks, a seven year cycle for the central-western region and a 14 year cycle for the northern region. Most of the variance was concentrated in the central-western region and dominated the entire endemic region. CONCLUSIONS: The seven year cycle is predominant in the endemic region of the disease due the greater contribution of variance in the central-western region; however, it was possible identify a 14 cycle that governs SYF outbreaks in the northern region. No periodicities were identified for the remaining geographical regions.

Controlo da qualidade de betões

Dissertação de mestrado em Construção e Reabilitação Sustentáveis

L’Europe des partis: paradoxes, contradictions et antinomies

L’autor constata la presència de clivelles europeus conseqüència d’apostes que només la Unió Europea pot tractar ja que s’escapen de l’acció dels governs europeus. De les dos clivelles descobertes per Hix i Lord en el Parlament europeu, la que oposa els partidaris de la "Europa liberal" amb els de l’"Europa social" és avui determinant per dues raons, doctrinal la primera i empírica la segona, que l’autor desenvolupa en aquest treball.

Les coalicions polítiques a Catalunya. El cas del govern catalanista i d’esquerres

El fenomen coalicional ha anat guanyant centralitat arreu a mesura que s’ha assumit que els governs d’aquest signe no tenen per què ser febles i inestables. A Catalunya, que en aquest capítol se situa dins la més absoluta normalitat europea, aquest tipus d’aliances han esdevingut moneda corrent. Manejant l’utillatge propi de les teories multidimensionals, el present treball identifica els factors que han influït en la formació del denominat govern catalanista i d’esquerres (2003-2006), examinant la intervenció de les regles del joc del marc institucional, factors exògens com els media o els agents socials i econòmics, a més d’analitzar els processos de formació (negociació, document programàtic, protocols d’actuació), a més d’avaluar les conseqüències per als partits i el sistema polític en general.

Conceptos y contexto. En torno al desarrollo de la comparación en ciencia política

El autor, profesor titular emérito de Ciencia Política de la Universidad de Heidelberg, revisa el desarrollo de la ciencia política contemporánea en el área del gobierno comparado y debate sus métodos y alcances de investigación. Diferenciando entre los enfoques empírico-estadístico e histórico-empírico, precisa esta distinción en lo relativo al tratamiento de los conceptos y del contexto en ambas escuelas comparativas. Advierte sobre la necesidad de invertir mucha dedicación al trabajo conceptual y de respetar seriamente el contexto para no caer en la tentación del reduccionismo y la simplificación que él observa en los estudios empírico-estadísticos, a menudo autoreferenciales y sin mayor relevancia práctica. Se compromete, desde una perspectiva histórico-empírica, con propuestas relevantes para la praxis y adecuadas al contexto. A modo de epílogo, Claudia Zilla, asistente de investigación para América Latina en la Fundación Ciencia y Política (Agencia de Consultoría del Gobierno Alemán), destaca en su contribución las raíces weberianas del enfoque histórico-empírico.