1,741 research outputs found
Current differential line protection using a pattern recognition method
This paper presents a new approach to a numerical current differential protection for the transmission lines. The current differential algorithm uses a pattern recognition method. First the acquired current signals are transformed into “dqo” components by applying the Park transformation. The transformed currents will originate typical patterns according the fault type. Using a pattern recognition algorithm the different faulty conditions are identified. Several tests under different fault conditions were performed. The obtained results allow verifying the effectiveness of the proposed approach
Number of spanning clusters at the high-dimensional percolation thresholds
A scaling theory is used to derive the dependence of the average number
of spanning clusters at threshold on the lattice size L. This number should
become independent of L for dimensions d<6, and vary as log L at d=6. The
predictions for d>6 depend on the boundary conditions, and the results there
may vary between L^{d-6} and L^0. While simulations in six dimensions are
consistent with this prediction (after including corrections of order loglog
L), in five dimensions the average number of spanning clusters still increases
as log L even up to L = 201. However, the histogram P(k) of the spanning
cluster multiplicity does scale as a function of kX(L), with X(L)=1+const/L,
indicating that for sufficiently large L the average will approach a finite
value: a fit of the 5D multiplicity data with a constant plus a simple linear
correction to scaling reproduces the data very well. Numerical simulations for
d>6 and for d=4 are also presented.Comment: 8 pages, 11 figures. Final version to appear on Physical Review
Soft triaxial roto-vibrational motion in the vicinity of
A solution of the Bohr collective hamiltonian for the soft,
soft triaxial rotor with is presented making use
of a harmonic potential in and Coulomb-like and Kratzer-like
potentials in . It is shown that, while the angular part in the
present case gives rise to a straightforward extension of the rigid triaxial
rotor energy in which an additive harmonic term appears, the inclusion of the
part results instead in a non-trivial expression for the spectrum. The
negative anharmonicities of the energy levels with respect to a simple rigid
model are in qualitative agreement with general trends in the experimental
data.Comment: 4 pages, 2 figures, accepted in Phys.Rev.
Outflow Dynamics in Modeling Oligopoly Markets: The Case of the Mobile Telecommunications Market in Poland
In this paper we introduce two models of opinion dynamics in oligopoly
markets and apply them to a situation, where a new entrant challenges two
incumbents of the same size. The models differ in the way the two forces
influencing consumer choice -- (local) social interactions and (global)
advertising -- interact. We study the general behavior of the models using the
Mean Field Approach and Monte Carlo simulations and calibrate the models to
data from the Polish telecommunications market. For one of the models
criticality is observed -- below a certain critical level of advertising the
market approaches a lock-in situation, where one market leader dominates the
market and all other brands disappear. Interestingly, for both models the best
fits to real data are obtained for conformity level . This
agrees very well with the conformity level found by Solomon Asch in his famous
social experiment
A current differential line protection using a synchronous reference frame approach
This paper presents a new approach for a current differential protection of the transmission lines. This approach is based on the Park transformation or ABC-dqo transformation. Using the ABC-dqo transformation the three phase quantities are transformed into a synchronous rotating reference frame. In this way, the line currents of the three phase system are measured and transformed into three dc components. So, immunity to problems such as sampling misalignment and time delay of the communication channel will be improved.
Several test results are presented in order to show the effectiveness of the proposed approach
Multiresolution community detection for megascale networks by information-based replica correlations
We use a Potts model community detection algorithm to accurately and
quantitatively evaluate the hierarchical or multiresolution structure of a
graph. Our multiresolution algorithm calculates correlations among multiple
copies ("replicas") of the same graph over a range of resolutions. Significant
multiresolution structures are identified by strongly correlated replicas. The
average normalized mutual information, the variation of information, and other
measures in principle give a quantitative estimate of the "best" resolutions
and indicate the relative strength of the structures in the graph. Because the
method is based on information comparisons, it can in principle be used with
any community detection model that can examine multiple resolutions. Our
approach may be extended to other optimization problems. As a local measure,
our Potts model avoids the "resolution limit" that affects other popular
models. With this model, our community detection algorithm has an accuracy that
ranks among the best of currently available methods. Using it, we can examine
graphs over 40 million nodes and more than one billion edges. We further report
that the multiresolution variant of our algorithm can solve systems of at least
200000 nodes and 10 million edges on a single processor with exceptionally high
accuracy. For typical cases, we find a super-linear scaling, O(L^{1.3}) for
community detection and O(L^{1.3} log N) for the multiresolution algorithm
where L is the number of edges and N is the number of nodes in the system.Comment: 19 pages, 14 figures, published version with minor change
Integração arquitetónica de sombreamento solar otimizado
Os sistemas de sombreamento ajudam não só no equilíbrio energético do edifício como também desenvolvem um papel fundamental na fachada. O presente artigo aborda uma revisão dos conceitos de uma arquitetura sustentável através de sistemas de sombreamento de forma a dar uma melhor resposta no que toca à problemática atual relacionada com temas como a crise energética e o aquecimento global. Apresenta a importância de um sistema que proteja o edifício de ganhos solares excessivos e que, consequentemente, diminua o consumo de energia proveniente de fontes não renováveis. Para concretizar este estudo foi necessário a utilização de uma ferramenta de cálculo OIKONET/ISCTE-IUL, que disponibiliza a informação do valor dos ângulos solares e das dimensões dos elementos horizontais de sombreamento consoante a época que se deseja sombrear, a latitude e a altura do vão. Este estudo apresenta e analisa o modo como estes são fundamentais num edifício na procura de uma arquitetura sustentável e esclarece o seu desempenho. É também apresentado um sistema de sombreamento num Centro de Investigação Marítima, onde se pretende encontrar um equilíbrio luz/sombra e pensar a estética que este pode dar ao edifício tendo a conta a sua localização e clima local.info:eu-repo/semantics/publishedVersio
Sustainable management methods: performance assessment in large companies
The general objective of this study is to contribute to the understanding of the performance evaluation methods used by large companies. As specific objectives we have the following: to identify the methods used and the importance attributed to them; to analyse their implementation process and the level of success given to it. The data collection method used was a survey to the financial managers of the largest companies in Portugal, which resulted in thirty-five valid responses. The main contributions of this study were the associations found between the following variables: the method used and the level of importance assigned to it; the person in charge of implementing the method and training provided to employees; the method used and the degree of success attributed to its implementation; the degree of resistance to change and the degree of success in implementing the performance evaluation method.info:eu-repo/semantics/acceptedVersio
Transmission lines protection based on the current eigenvalues differential concept
This work presents a new approach for a current differential protection of the transmission lines. The proposed approach is based on the Clarke-Concordia transformation and principal component analysis. First the acquired current signals are transformed into “αβo” components by applying the Clarke-Concordia transformation. This allows obtaining typical patterns. To identify these patterns a principal component analysis is performed. Several tests under different fault conditions were performed. The obtained results allow
verifying the effectiveness of the proposed approach
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