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Publicações

2014

Electric vehicle models for evaluating the security of supply

Autores
Bremermann, LE; Matos, M; Pecas Lopes, JAP; Rosa, M;

Publicação
ELECTRIC POWER SYSTEMS RESEARCH

Abstract
The future large-scale deployment of electric vehicles (EV) will not only have impact on load growth, but also create opportunities for the electricity sector. Generally, the current methods for security of supply long-term evaluation do not include this new type of load. While the electric components of the generating systems are usually modelled by the Markov process, this paper presents, as its major contribution, an EV model based on the Nonhomogeneous Poisson process, which has been developed in order to better represent the motorized citizen mobility and the EV opportunity to release spinning reserve to electric systems. The simulation procedure lies in combining both Poisson and Markov processes into a sequential Monte Carlo simulation (SMCS) to measure the impact of EV when evaluating the adequacy of generating systems. This evaluation is divided into two complementary concepts: static reserve (generating capacity reserve) and operating capacity reserve. The proposed models are analyzed using a modified version of the IEEE RTS-96 including renewable sources.

2014

Handling renewable energy variability and uncertainty in power systems operation

Autores
Bessa, R; Moreira, C; Silva, B; Matos, M;

Publicação
WILEY INTERDISCIPLINARY REVIEWS-ENERGY AND ENVIRONMENT

Abstract
The concerns about global warming (greenhouse-gas emissions), scarcity of fossil fuels reserves, and primary energy independence of regions or countries have led to a dramatic increase of renewable energy sources (RES) penetration in electric power systems, mainly wind and solar power. This created new challenges associated with the variability and uncertainty of these sources. Handling these two characteristics is a key issue that includes technological, regulatory, and computational aspects. Advanced tools for handling RES maximize the resultant benefits and keep the reliability indices at the required level. Recent advances in forecasting and management algorithms provided means to manage RES. Forecasts of renewable generation for the next hours/days play a crucial role in the management tools and protocols of the system operator. These forecasts are used as input for setting reserve requirements and performing the unit commitment (UC) and economic dispatch (ED) processes. Probabilistic forecasts are being included in the management tools, enabling a move from deterministic to stochastic methods, which conduct to robust solutions. On the technological side, advances to increase mid-merit and base-load generation flexibility should be a priority. The use of storage devices to mitigate uncertainty and variability is particularly valuable for isolated power system, whereas in interconnected systems, economic criteria might be a barrier to invest in new storage facilities. The possibility of sending active and reactive control set points to RES power plants offers more flexibility. Furthermore, the emergence of the smart grid concept and the increasing share of controllable loads contribute with flexibility to increase the RES penetration levels. (C) 2013 John Wiley & Sons, Ltd.

2014

Segmentation of carotid ultrasound images

Autores
Rocha, R; Silva, J; Campilho, A;

Publicação
Multi-Modality Atherosclerosis Imaging and Diagnosis

Abstract
This chapter surveys methodologies for the segmentation of carotid ultrasound images and describes a method for the semiautomatic detection of the lumen-intima and the media-adventitia interfaces of the near and far common carotid wall. The approach is based on feature extraction, fitting of cubic splines, dynamic programming, smooth intensity thresholding surfaces, and geometric snakes. A set of 47 B-mode images of the common carotid were used to assess the performance of the method. The detection errors are similar to the ones observed in manual segmentations for 95% of the far wall interfaces and 73% of the near wall interfaces. © 2014 Springer Science+Business Media, LLC. All rights are reserved.

2014

An extended kernel density two-step floating catchment area method to analyze access to health care

Autores
Polzin, P; Borges, J; Coelho, A;

Publicação
ENVIRONMENT AND PLANNING B-PLANNING & DESIGN

Abstract
In Portugal the distribution of physicians is considered an appropriate proxy for the distribution of the actual hospital resources and additional information on hospital supply is mostly unavailable, while health care utilization data are also usually absent. A suitable method that can be used to analyze patients' access to hospital health care in countries with such characteristics is the two-step floating catchment area (2SFCA) method, since it requires only the number of physicians to represent supply and the population size to estimate demand. An improved version of the 2SFCA method is the kernel density 2SFCA (KD2SFCA) method. However, this method was not developed to analyze access to health care and it computes scores that express only the spatial access dimensions of proximity and availability. In this paper we present a new method, based on the KD2SFCA method, which improves health care access analysis and better identifies populations that are less empowered to use health care. We adapt the KD2SFCA method for the context of health care access analysis and extend it to capture additional access dimensions. We applied the extended method to the Portuguese hospital health care sector in a case study, and compared its results with those obtained with the KD2SFCA method. Our method was able to improve the identification of the less empowered populations and discovered that they represent 8.1% of the total population, instead of 4.6%, and reside in sixteen of the eighteen Portuguese districts, instead of in thirteen, as identified by the original KD2SFCA method. By improving the KD2SFCA method for the identification of the less empowered populations, our method can be a first step in an endeavor to identify opportunities to increase the health care supply or to redistribute supply resources, with the objective of increasing the access of those deprived populations.

2014

Probability Theory-Based Economic Dispatch Model for Insular Power Systems

Autores
Osorio, GJ; Lujano Rojas, JM; Matias, JCO; Catalao, JPS;

Publicação
2014 Australasian Universities Power Engineering Conference (AUPEC)

Abstract
The main problem in integration of renewable power sources to the electricity grid is the uncertainty introduced by the power forecasting process in the optimal scheduling problem, which can considerably increase the generation cost. This problem has been widely analyzed using scenario generation/reduction methodologies. However, the consideration of a reduced number of scenarios can limit the capabilities of these methodologies. As an alternative, in this manuscript the dynamic economic dispatch problem has been solved by estimating the probability density function of energy surplus, the energy not supplied and the power production considering the forecasting error and system reliability. The incorporation of the system reliability and the forecasting error as probability distribution functions can avoid the use of scenario generation and reduction processes, which are time consuming tasks. The proposed model was illustrated by analyzing a typical insular power system under different conditions of load and uncertainty, concluding that the hardware failure can introduce a relevant increment in the generation costs, due to their relationship with the value of lost load. Moreover, the scalability of the proposed model was studied by analyzing several power systems between 10 and 150 units, which have been solved in an acceptable computational time.

2014

Sentiment retrieval on web reviews using spontaneous natural speech

Autores
Pereira, JoseCosta; Luque, Jordi; Anguera, Xavier;

Publicação
IEEE International Conference on Acoustics, Speech and Signal Processing, ICASSP 2014, Florence, Italy, May 4-9, 2014

Abstract
This paper addresses the problem of document retrieval based on sentiment polarity criteria. A query based on natural spontaneous speech, expressing an opinion about a certain topic, is used to search a repository of documents containing favorable or unfavorable opinions. The goal is to retrieve documents whose opinions more closely resemble the one in the query. A semantic system based on speech transcripts is augmented with information from full-length text articles. Posterior probabilities extracted from the articles are used to regularize their transcription counterparts. This paper makes three important contributions. First, we introduce a framework for polarity analysis of sentiments that can accommodate combinations of different modalities capable of dealing with the absence of any modality. Second, we show that it is possible to improve average precision on speech transcriptions' sentiment retrieval by means of regularization. Third, we demonstrate the robustness of our approach by training regularizers on one dataset, while performing sentiment retrieval experiments, with substantial gains, on another dataset. © 2014 IEEE.

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