1,720,976 research outputs found
Design and stability analysis of single-input fuzzy logic controller
No full textIn existing fuzzy logic controllers (FLC's), input variables are mostly the error e and the change-of-error (e) over dot regardless of complexity of controlled plants. Either control input u or the change of control input Pu is commonly used as its output variable. A rule table is then constructed on a two-dimensional (2-D) space. This scheme naturally inherits from conventional proportional-derivative (PD) or proportional-integral (PI) controller. Observing that 1) rule tables of most FLC's have skew-symmetric property and 2) the absolute magnitude of the control input /u/ or /Delta u/ is proportional to the distance from its main diagonal line in the normalized input space, we derive a new variable called the signed distance, which is used as a sole fuzzy input variable in our simple FLC called single-input FLC (SFLC), The SFLC has many advantages: The total number of rules is greatly reduced compared to existing FLC's, and hence, generation and tuning of control rules are much easier. The proposed SFLC is proven to be absolutely stable using Popov criterion. Furthermore, the control performance is nearly the same as that of existing FLC's, which is revealed via computer simulations using two nonlinear plants.This work
was supported in part by the 1999 Taegu University Research Grant
Fuzzy logic-based tuning of the boundary layer thickness of the variable structure controller
No full textThe variable structure control (VSC) is a simple and powerful nonlinear controller, but it leads to a high frequency chattering on the control input. To decrease the chattering phenomenon of the VSC, a boundary layer is commonly introduced. Then its thickness requires a compromise between the steady state error and the chattering amplitude. In this paper, we propose a new VSC that tunes the boundary layer thickness using the fuzzy logic system. The tuning methods presented are two: One uses absolute error and its derivative as fuzzy input variables, which decreases the number of tuning rules as compared with using common fuzzy variables of error and change of error. The other uses only a single fuzzy variable of a distance. This variable is derived by the property of two-dimensional rule table which is composed of absolute error and its derivative. Since the second method uses a single variable for tuning the thickness, the number of tuning rules is greatly decreased. Furthermore, we obtain the good tracking performance which is almost the same as that of the first method. To ensure the control performance in both cases, we perform computer simulations using an inverted pendulum as a controlled plant
Design of a single-input fuzzy logic controller and its properties
No full textWe suggest a simple but powerful FLC (Fuzzy Logic Controller) design method using a single fuzzy input variable, which is equivalent to the pseudo sliding mode controller. Input variables of conventional FLCs are mostly the error e and the change-of-error (e) over dot regardless of the complexity of controlled plants. A rule table is then constructed in a two-dimensional input space. The output of fuzzy inference is applied to the plant as the control input u or the change of control input Delta u. This scheme came from concepts of linear PD (proportional-derivative) and PI (proportional-integral) controllers. We found that rule tables of most FLCs have skew-symmetry property, and the absolute magnitude of the control input \u\ or \Delta u\ is proportional to the distance from its main diagonal line in the normalized input space. Considering these facts, we derive a new variable called the signed distance, which is a sole fuzzy input variable in our simple FLC called single-input FLC (S-FLC). The S-FLC has many advantages: The total number of rules is greatly reduced compared to two-dimensional FLCs, and hence, generations and tuning of control rules are easy. Control performance is nearly the same as that of conventional FLCs. We also show that this S-FLC is equivalent to the pseudo SMC (sliding mode controller), and hence, the stability is guaranteed using the Lyapunov stability. The performance of S-FLC is revealed via computer simulations using a nonlinear plant. (C) 1999 Elsevier Science B.V. All rights reserved
Comparative study of CWO and ZnSe(Te) scintillation detector on the performance of X-ray imaging system
No full textRecently, much attention has been paid to ZnSe(Te) semiconductor scintillator because of its excellent scintillation characteristics. Linear-array detector modules based on the conventional CdWO4 (CWO) and new ZnSe(Te) scintillator blocks were fabricated and tested for comparison for the purpose of applying them in X-ray inspection system. From the point of view of photocurrent and of detective quantum efficiency (DQE), ZnSe(Te) showed better performance in the low-energy X-ray system and was competitive to CWO in the high-energy X-ray system when the depth of scintillator is optimized to the energy in use. The site test of these modules in a prototype container inspection system using 340 kVp X-ray showed equivalent image qualities. (C) 2004 Elsevier B.V. All rights reserved
Development of X-ray scanner using 450-kVp X-ray
No full textThe objective of this paper is to develop an X-ray scanner that consists of a 450-kVp X-ray generator, a linear detector array, an electric circuit for data acquisition, and image processing software. This work is composed of three main parts. First, Monte Carlo simulations and experiments have been performed to determine the scintillator geometry and its surface condition so that the light output from it can be maximized. According to the simulations and experiments, the CdWO4 (CWO) of 1.7 mm x 3.0 mm x 10 mm with ground surface, which is treated-with grinding material of 28-mum grain size, gives the best light yield. Secondly, a PIN photodiode for this system is fabricated and its characteristic parameters are measured to compare with those of two commercial products, one from Detection Technology and the other from Hamamatsu. From experimental results at zero bias where the system is operated, all three diodes have nearly identical leakage currents of a few pA and junction capacitances of this study. and DT are about 40 pF /mm(2) and that of Hamamatsu about 9 pF /mm(2). At 490 nm, the peak wavelength of the CWO light, the spectral responses of this work, DT, and Hamamatsu are 0.4, 0.3, and 0.2, respectively. It appears that the photodiode of this work gives excellent light sensitivity in the range of 400 to 900 nm. Thirdly, the spatial resolution of the system including our developed data acquisition system (DAS) shows 0.29 lp/mm at MTF of 10%, and this system satisfies the resolution of 4.75-mm objects that the U.S. Customs Service has suggested for cargo container inspection systems
Measurement of Neutron Spectra at the Inside and outside of the Target Room of 65 MeV Electron LINAC using an Extended Bonner Sphere
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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