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Zagreb, Croatia

Medimorec D.,HEP Group | Tomsic T.,University of Zagreb
Renewable Energy | Year: 2015

Development of a wind farm project includes a lot of interconnected steps and one of the most important ones is the proper energy yield assessment. Wind energy yield assessment is typically based on wind measurements on a measurement mast that are later used in one of the wind flow software models. In cases where there are multiple wind measurements on the potential wind farm site, a question arises on how to optimally use all the available data. This paper shows a method of using such data through the application of the portfolio theory, a well-established theory in economics and frequently used in other scientific disciplines. The method shown is very flexible in terms of input data and software models, and the results of its application show that it is possible to increase accuracy and reduce uncertainty of energy yield assessment. The key result of the method is the possibility to achieve better quality of input data for the energy yield assessment without spending additional resources. The method opens up a wide space for further research and improvements, all with the objective of achieving better results of energy yield assessment and finally, better prepared wind project. © 2014 Elsevier Ltd. Source


Soldo B.,HEP Group
Applied Energy | Year: 2012

Publishing papers in the area of forecasting natural gas consumption has begun in the middle of last century and led to a tremendous surge in research activities in the past decade. This paper presents a state-of-the-art survey of forecasting natural gas consumption. Purpose of this paper is to provide analysis and synthesis of published research in this area from beginning to the end of 2010, insights on applied area, used data, models and tools to achieve usable results, in order to be helpful base for future researchers. © 2011 Elsevier Ltd. Source


Meessen P.,HEP Group | Ortin T.,Institute Fisica Teorica UAM CSIC | Perz J.,Institute Fisica Teorica UAM CSIC | Shahbazi C.S.,Institute Fisica Teorica UAM CSIC
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2012

We rewrite the Ferrara-Gibbons-Kallosh (FGK) black-hole effective action of N= 2, d= 4, 5 supergravities coupled to vector multiplets, replacing the metric warp factor and the physical scalars with real variables that transform in the same way as the charges under duality transformations, which simplifies the equations of motion. For a given model, the form of the solution in these variables is the same for all spherically symmetric black holes, regardless of supersymmetry or extremality. © 2012 Elsevier B.V. Source


Ceperic E.,HEP Group | Ceperic V.,University of Zagreb | Ceperic V.,Catholic University of Leuven | Baric A.,University of Zagreb
IEEE Transactions on Power Systems | Year: 2013

This paper presents a generic strategy for short-term load forecasting (STLF) based on the support vector regression machines (SVR). Two important improvements to the SVR based load forecasting method are introduced, i.e., procedure for generation of model inputs and subsequent model input selection using feature selection algorithms. One of the objectives of the proposed strategy is to reduce the operator interaction in themodel-building procedure. The proposed use of feature selection algorithms for automatic model input selection and the use of the particle swarm global optimization based technique for the optimization of SVR hyper-parameters reduces the operator interaction. To confirm the effectiveness of the proposed modeling strategy, the model has been trained and tested on two publicly available and well-known load forecasting data sets and compared to the state-of-the-art STLF algorithms yielding improved accuracy. © 2013 IEEE. Source


Meessen P.,HEP Group | Ortin T.,Institute Fisica Teorica UAM
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2012

We study the generalization of the Ansatz of Galli et al. (2011) [1] for non-extremal black holes of N=2, d=4 supergravities for a simple model of N=2, d=5 supergravity with a vector multiplet whose moduli space has two branches. We use the formalism of Ferrara, Gibbons and Kallosh (1997) [2], which we generalize to any dimension d. We find that the equations of motion of the model studied can be completely integrated without the use of our Anstaz (which is, nevertheless, recovered in the integration). The family of solutions found (common to both branches) is characterized by five independent parameters: the mass M, the electric charges q0, q1, the asymptotic value of the scalar at infinity Φ ∞ and the scalar charge Σ. The solutions have a singular horizon whenever Σ differs from a specific expression Σ 0(M,q 0,q 1,Φ ∞) (i.e. when there is primary scalar hair Σ-Σ 0≠0). The family of regular black holes interpolates between its two extremal limits. The supersymmetry properties of the extremal solutions depend on the choice of branch: one is always supersymmetric and the other non-supersymmetric in one branch and the reverse in the other one. © 2011 Elsevier B.V. Source

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