1,769 research outputs found
Variational Principle for Mixed Classical-Quantum Systems
An extended variational principle providing the equations of motion for a
system consisting of interacting classical, quasiclassical and quantum
components is presented, and applied to the model of bilinear coupling. The
relevant dynamical variables are expressed in the form of a quantum state
vector which includes the action of the classical subsystem in its phase
factor. It is shown that the statistical ensemble of Brownian state vectors for
a quantum particle in a classical thermal environment can be described by a
density matrix evolving according to a nonlinear quantum Fokker-Planck
equation. Exact solutions of this equation are obtained for a two-level system
in the limit of high temperatures, considering both stationary and
nonstationary initial states. A treatment of the common time shared by the
quantum system and its classical environment, as a collective variable rather
than as a parameter, is presented in the Appendix.Comment: 16 pages, LaTex; added Figure 2 and Figure
Imaging 3D seismic velocity along the seismogenic zone of Algarve region (southern Portugal)
The present seismic tomographic study is focused around Algarve region, in South of Portugal. To locate the seismic events and find the local velocity structure of epicentral area, the P and S arrival times at 38 stations are used. The data used in this study were obtained during the Algarve campaign which worked from January/2006 to July/2007. The preliminary estimate of origin times and hypocentral coordinates are determined by the Hy- poinverse program. Linearized inversion procedure was applied to comprise the following two steps: 1) finding the minimum 1D velocity model using Velest and 2) simultaneous relocation of hypocenters and determination of local velocity structure. The velocity model we have reached is a 10 layer model which gave the lowest RMS, after several runnings of eight different velocity models that we used “a priori”. The model parameterization assumes a continuous velocity field between 4.5 km/s and 7.0 km/s until 30 km depth. The earth structure is represented in 3D by velocity at discrete points, and velocity at any intervening point is determined by linear interpolation among the surrounding eight grid points. A preliminary analysis of the resolution capabilities of the dataset, based on the Derivative Weight Sum (DWS) distribution, shows that the velocity structure is better resolved in the West part of the region between the surface to15 km. The resulting tomographic image has a prominent low-velocity anomaly that shows a maximum decrease in P-wave velocity in the first 12 kms in the studied region. We also identified the occurrence of local seismic events of reduced magnitude not catalogued, in the neighbourhood of Almodôvar (low Alentejo). The spatial distribution of epicentres defines a NE-SW direction that coincides with the strike of the mapped geological faults of the region and issued from photo-interpretation. Is still expectable to refine the seismicity of the region of Almodôvar and establish more rigorously its role in the seismotectonic picture of the region. This work is expected to produce a more detailed knowledge of the structure of the crust over the region of Algarve, being able to identify seismogenic zones, potentially generators of significant seismic events and also the identification of zones of active faults
Measurement induced quantum-classical transition
A model of an electrical point contact coupled to a mechanical system
(oscillator) is studied to simulate the dephasing effect of measurement on a
quantum system. The problem is solved at zero temperature under conditions of
strong non-equilibrium in the measurement apparatus. For linear coupling
between the oscillator and tunneling electrons, it is found that the oscillator
dynamics becomes damped, with the effective temperature determined by the
voltage drop across the junction. It is demonstrated that both the quantum
heating and the quantum damping of the oscillator manifest themselves in the
current-voltage characteristic of the point contact.Comment: in RevTex, 1 figure, corrected notatio
GestĂŁo da Sala de Aula: Perspetiva Psicoeducacional
A informação que aparece sistematizada neste capĂtulo tem como finalidade
o estudo da gestĂŁo da sala de aula pelos professores, apresentando perspetivas
teĂłricas e investigações empĂricas que permitam a sua compreensĂŁo e promoção,
à luz de contributos situados, sobretudo, no âmbito da Psicologia da Educação.
Depois de uma primeira parte a incidir na teoria, apresenta-se uma segunda parte
dedicada à investigação e uma terceira parte de aplicação prática. Na primeira
parte, as competĂŞncias de gestĂŁo da sala de aula sĂŁo consideradas na sua multi-
dimensionalidade, gestĂŁo de conteĂşdos, gestĂŁo de comportamentos e gestĂŁo de
conflitos. CompetĂŞncias comunicacionais na gestĂŁo da sala de aula sĂŁo descritas
no âmbito do Modelo Comunicacional Eclético (MCE), dado que este modelo
fornece conceitos, procedimentos e estratégias que, pela sua abrangência e facilidade de aplicação, agilizam a compreensão dos processos que caraterizam as
interações na sala de aula. Competências de organização dos espaços e dos tempos aparecem também contempladas, no âmbito da teorização apresentada. Na
segunda parte, descreve-se um conjunto de investigações acerca da gestão da sala
de aula, diferenciadas em estudos de caraterização e de avaliação, estudos sobre
a gestão da sala de aula como variável independente, e estudos sobre a gestão da
sala de aula como variável dependente. Na terceira parte, incluem-se propostas
de atividades mais práticas e, ainda, sugestões de leitura de aprofundamento do
tema gestão da sala de aula, bem como indicações de recursos online
Mass – Radius Relationship in Extrasolar Planets
The increasing number of Extrasolar planets observed in the last years makes important to define, as soon as possible, a mass – radius relationship, and so, we adjusted an planetary constitution independent experimental equation. Using the latest database of Extrasolar planets, a bi-logarithmic graphic was plotted that represents the mass - radius relationship where we adjusted a polynomial equation, which better suited the sample of Extrasolar planets at current time
Quantum fluctuations in thin superconducting wires of finite length
In one dimensional wires, fluctuations destroy superconducting long-range
order and stiffness at finite temperatures; in an infinite wire, quasi-long
range order and stiffness survive at zero temperature if the wire's
dimensionless admittance is large, . We analyze the
disappearance of this superconductor-insulator quantum phase transition in a
finite wire and its resurrection due to the wire's coupling to its environment
characterized through the dimensionless conductance . Integrating over phase
slips, we determine the flow of couplings and establish the -- phase
diagram.Comment: 4 pages, 2 figure
Non-Markoffian effects of a simple nonlinear bath
We analyze a model of a nonlinear bath consisting of a single two-level
system coupled to a linear bath (a classical noise force in the limit
considered here). This allows us to study the effects of a nonlinear,
non-Markoffian bath in a particularly simple situation. We analyze the effects
of this bath onto the dynamics of a spin by calculating the decay of the
equilibrium correlator of the spin's z-component. The exact results are
compared with those obtained using three commonly used approximations: a
Markoffian master equation for the spin dynamics, a weak-coupling
approximation, and the substitution of a linear bath for the original nonlinear
bath.Comment: 7 pages, 6 figure
Wireless Sensor Networks for Building Robotic Paths - A Survey of Problems and Restrictions
The conjugation of small nodes with sensing, communication and processing capabilities allows for the
creation of wireless sensor networks (WSNs). These networks can be deployed to measure a very wide
range of environmental phenomena and send data from remote locations back to users. They offer new and
exciting possibilities for applications and research. This paper presents the background of WSNs by firstly
exploring the different fields applications, with examples for each of these fields, then the challenges faced
by these networks in areas such as energy-efficiency, node localization, node deployment, limited storage
and routing. It aims at explaining each issue and giving solutions that have been proposed in the research
literature. Finally, the paper proposes a practical scenario of deploying a WSN by autonomous robot path
construction. The requirements for such a scenario and the open issues that can be tackled by it are
exposed, namely the issues of associated with measuring RSSI, the degree of autonomy of the robot and
connectivity restoration.The authors would like to acknowledge the
company Inspiring Sci, Lda for the interest and
valuable contribution to the successful development
of this work.info:eu-repo/semantics/publishedVersio
From optical tracking to tactical performance via Voronoi diagrams: Team formation and players’ roles constrain interpersonal linkages in high-level football
Football performance behaviour relies on the individual and collective perceptual attunement to the opportunities for action (affordances) available in a given competitive environment. Such perception–action coupling is constrained by players’ spatial dominance. Aiming to understand the influence of team formation and players’ roles in their dynamic interaction (interpersonal linkages), Voronoi diagrams were used to assess the differences in players’ spatial dominance resulting from their interactions according to ball-possession status in high-performance football. Notational (i.e., team formation, players’ role, and ball-possession status) and positional data (from optical sensors) from ten matches of the men’s French main football league were analysed. Voronoi diagrams were computed from players’ positional data for both teams. Probability density functions of the players’ Voronoi cell areas were then computed and compared, using the Kolmogorov–Smirnov test, for the different variables (i.e., team formation, player role, and ball-possession status) and their classes. For these variables, the players’ Voronoi cell areas presented statistical differences, which were sensitive to team formation classes (i.e., defenders, midfielders, and forwards) and relative pitch location (interior or exterior in the effective play space). Differences were also found between players with similar roles when in different team formations. Our results showed that team formation and players’ roles constrain their interpersonal linkages, resulting in different spatial dominance patterns. Using positional data captured by optical sensors, Voronoi diagrams can be computed into compound variables, which are meaningful for understanding the match and thus offer information to the design representative training tasks.info:eu-repo/semantics/publishedVersio
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