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Wyświetlanie 1-8 z 8
Tytuł:
Document Clustering : Concepts, Metrics and Algorithms
Autorzy:
Tarczynski, T.
Powiązania:
https://bibliotekanauki.pl/articles/226231.pdf
Data publikacji:
2011
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
document clustering
text mining
k-means
hierarchical clustersting
vector space model
Opis:
Document clustering, which is also refered to as text clustering, is a technique of unsupervised document organisation. Text clustering is used to group documents into subsets that consist of texts that are similar to each orher. These subsets are called clusters. Document clustering algorithms are widely used in web searching engines to produce results relevant to a query. An example of practical use of those techniques are Yahoo! hierarchies of documents [1]. Another application of document clustering is browsing which is defined as searching session without well specific goal. The browsing techniques heavily relies on document clustering. In this article we examine the most important concepts related to document clustering. Besides the algorithms we present comprehensive discussion about representation of documents, calculation of similarity between documents and evaluation of clusters quality.
Źródło:
International Journal of Electronics and Telecommunications; 2011, 57, 3; 271-277
2300-1933
Pojawia się w:
International Journal of Electronics and Telecommunications
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Crude Oil Price and Speculative Activity: A Cointegration Analysis
Autorzy:
Socha, Robert
Wdowiński, Piotr
Powiązania:
https://bibliotekanauki.pl/articles/2076245.pdf
Data publikacji:
2018
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
crude oil price
speculation
futures
cointegration
vector error correction model
Opis:
The aim of the study is to discuss the relationship of the crude oil price, speculative activity and fundamental factors. An empirical study was conducted with a VEC model. Two cointegrating vectors were identified. The first vector represents the speculative activity. We argue that the number of short noncommercial positions increases with the crude oil stock and price, decreases with the higher number of long non-commercial positions. A positive trend of crude oil prices may be a signal for traders outside the industry to invest in the oil market, especially as access to information could be limited for them. The second vector represents the crude oil price under the fundamental approach. The results support the hypothesis that the crude oil price is dependent on futures trading. The higher is a number of commercial long positions, the greater is the pressure on crude oil price to increase.
Źródło:
Central European Journal of Economic Modelling and Econometrics; 2018, 3; 263-304
2080-0886
2080-119X
Pojawia się w:
Central European Journal of Economic Modelling and Econometrics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A Long-Run Relationship between Daily Prices on Two Markets: The Bayesian VAR(2)–MSF-SBEKK Model
Autorzy:
Osiewalski, Krzysztof
Osiewalski, Jacek
Powiązania:
https://bibliotekanauki.pl/articles/483271.pdf
Data publikacji:
2013
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
Bayesian econometrics
vector error correction model
hybrid MGARCH-MSV processes
financial markets
commodity markets
Opis:
We develop a fully Bayesian framework for analysis and comparison of two competing approaches to modelling daily prices on different markets. The first approach, prevailing in financial econometrics, amounts to assuming that logarithms of prices behave like a multivariate random walk; this approach describes logarithmic returns most often by the VAR(1) model with MGARCH (or sometimes MSV) disturbances. In the second approach, considered here, it is assumed that daily price levels are linked together and, thus, the error correction term is added to the usual VAR(1)–MGARCH or VAR(1)–MSV model for logarithmic returns, leading to a reduced rank VAR(2) specification for logarithms of prices. The model proposed in the paper uses a hybrid MSVMGARCH structure for VAR(2) disturbances. In order to keep cointegration modelling as simple as possible, we restrict to the case of two prices representing two different markets. The aim of the paper is to show how to check if a long-run relationship between daily prices exists and whether taking it into account influences our inference on volatility and short-run relations between returns on different markets. In the empirical example the daily values of the S&P500 index and the WTI oil price in the period 19.12.2005 – 30.09.2011 are jointly modelled. It is shown that, although the logarithms of the values of S&P500 and WTI oil price seem to be cointegrated, neglecting the error correction term leads to practically the same conclusions on volatility and conditional correlation as keeping it in the model.
Źródło:
Central European Journal of Economic Modelling and Econometrics; 2013, 5, 1; 65-83
2080-0886
2080-119X
Pojawia się w:
Central European Journal of Economic Modelling and Econometrics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Model predictive direct power control of energy storage quasi-Z-source grid-connected inverter
Autorzy:
Tang, Min'an
Yang, Shangmei
Zhang, Kaiyue
Wang, Qianqian
Liu, Chenggang
Dong, Xuewang
Powiązania:
https://bibliotekanauki.pl/articles/2042769.pdf
Data publikacji:
2022
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
quasi Z-Source
inverter
energy storage
power control
model predictive
space vector
Opis:
In order to overcome the shortcoming of large switching losses caused by variable switching frequency appears in the conventional finite control set model predictive control (FCS-MPC) algorithm, a model predictive direct power control (MP-DPC) for an energy storage quasi-Z-source inverter (ES-qZSI) is proposed. Firstly, the power prediction model of the ES-qZSI is established based on the instantaneous power theory. Then the average voltage vector in the coordinate system is optimized by the power cost function. Finally, the average voltage vector is used as the modulation signal, and the corresponding switching signal with fixed frequency is generated by the shoot-through segment space vector pulse width modulation (SVPWM) technology. The simulation results show that the ES-qZSI realizes six shoot-through actions per control cycle and achieves the constant frequency control of the system, which verifies the correctness of the proposed control strategy.
Źródło:
Archives of Electrical Engineering; 2022, 71, 1; 21-35
1427-4221
2300-2506
Pojawia się w:
Archives of Electrical Engineering
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Predictive-SVM control method dedicated to an AC/DC converter with an LCL grid filter
Autorzy:
Dmitruk, K.
Powiązania:
https://bibliotekanauki.pl/articles/200760.pdf
Data publikacji:
2020
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
three-phase voltage converter
model predictive control
space vector modulation
infinite control set
Opis:
This paper presents simulation and laboratory test results of an implementation of an infinite control set model predictive control into a three-phase AC/DC converter. The connection between the converter and electric grid is made through an LCL filter, which is characterized by a better reduction of grid current distortions and smaller (cheaper) components in comparison to an L-type filter. On the other hand, this type of filter can cause strong resonance at specific current harmonics, which is efficiently suppressed by the control strategy focusing on the strict control input filter capacitors voltage vector. The presented method links the benefits of using linear control methods based on a space vector modulator and the nonlinear ones, which result in excellent control performance in a steady state as well as in a transient state.
Źródło:
Bulletin of the Polish Academy of Sciences. Technical Sciences; 2020, 68, 5; 1049-1056
0239-7528
Pojawia się w:
Bulletin of the Polish Academy of Sciences. Technical Sciences
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Prediction of protein subcellular localization using support vector machine with the choice of proper kernel
Autorzy:
Hasan, M.A.M.
Ahmad, S.
Molla, M.K.I.
Powiązania:
https://bibliotekanauki.pl/articles/81150.pdf
Data publikacji:
2017
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
subcellular localization
protein
prediction
support vector machine
model selection
kernel
radial base function
Źródło:
BioTechnologia. Journal of Biotechnology Computational Biology and Bionanotechnology; 2017, 98, 2
0860-7796
Pojawia się w:
BioTechnologia. Journal of Biotechnology Computational Biology and Bionanotechnology
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Traffic fatalities prediction based on support vector machine
Autorzy:
Li, T.
Yang, Y.
Wang, Y.
Chen, C.
Yao, J.
Powiązania:
https://bibliotekanauki.pl/articles/223743.pdf
Data publikacji:
2016
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
traffic accident
support vector machine
SVM
particle swarm optimization (PSO)
PSO
prediction model
optimal parameters
wypadek drogowy
Particle Swarm Optimization
model prognostyczny
optymalne parametry
Opis:
To effectively predict traffic fatalities and promote the friendly development of transportation, a prediction model of traffic fatalities is established based on support vector machine (SVM). As the prediction accuracy of SVM largely depends on the selection of parameters, Particle Swarm Optimization (PSO) is introduced to find the optimal parameters. In this paper, small sample and nonlinear data are used to predict fatalities of traffic accident. Traffic accident statistics data of China from 1981 to 2012 are chosen as experimental data. The input variables for predicting accident are highway mileage, vehicle number and population size while the output variables are traffic fatality. To verify the validity of the proposed prediction method, the back-propagation neural network (BPNN) prediction model and SVM prediction model are also used to predict the traffic fatalities. The results show that compared with BPNN prediction model and SVM model, the prediction model of traffic fatalities based on PSO-SVM has higher prediction precision and smaller errors. The model can be more effective to forecast the traffic fatalities. And the method using particle swarm optimization algorithm for parameter optimization of SVM is feasible and effective. In addition, this method avoids overcomes the problem of “over learning” in neural network training progress.
Źródło:
Archives of Transport; 2016, 39, 3; 21-30
0866-9546
2300-8830
Pojawia się w:
Archives of Transport
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A computationally low burden MPTC of induction machine without prediction loop and weighting factor
Autorzy:
Kiani, Babak
Powiązania:
https://bibliotekanauki.pl/articles/2173663.pdf
Data publikacji:
2022
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
MPTC
model predictive torque control
induction motor
duty ratio
voltage vector
lookup table
weighting factor
modelowa predykcyjna kontrola momentu obrotowego
silnik indukcyjny
współczynnik wypełnienia impulsu
wektor napięcia
tabela przeglądowa
współczynnik ważenia
Opis:
This paper presents a novel method to overcome problems of finite set-model-based predictive torque control (MPTC) which has received a lot of attention in the last two decades. Tuning the weighting factor, evaluating a large number of switching states in the loop of the predictive control, and determining the duty cycle are three major challenges of the regular techniques. Torque and flux responses of deadbeat control have been developed to overcome these problems. In our method, firstly, the prediction stage is performed just once. Then, both the weighted cost function and its evaluation are replaced with only simple relationships. The relationships reduce torque ripple and THD of stator current compromisingly. In the next step, the length of the virtual vector is used to determine the duty cycle of the optimum voltage vector without any additional computations. The duty ratio does not focus on any relation or criteria minimizing torque or flux ripple. As a result, torque and flux ripples are reduced equally. The proposed duty cycle is calculated by using a predicted virtual voltage vector. Hence, no new computation is needed to determine the proposed duty cycle. Simulation and experimental results confirm both the steady and dynamic performance of the proposed method in all speed ranges.
Źródło:
Bulletin of the Polish Academy of Sciences. Technical Sciences; 2022, 70, 4; art. no. e142050
0239-7528
Pojawia się w:
Bulletin of the Polish Academy of Sciences. Technical Sciences
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-8 z 8

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