Search results for "Distortion"
showing 10 items of 309 documents
Graphical THD minimization procedure for single phase five-level converters
2017
This paper proposes two graphycal procedure to mitigate h harmonics and to minimize the total harmonic distortion (THD), respectively. The paper considers a five-level inverter and fundamental frequency modulation: it computes the two switching angles able to reduce low order harmonics and able to minimize the THD. Simulation results are obtained and, in order to validate the proposed procedure, an experimental prototype is built and experimental results are carried out. The comparison between simulation and experimental results confirms the accuracy of the proposed graphycal procedure. It is shown that the switching angles to mitigate the third-fifth and the third-fifth-seventh harmonics e…
Harmonic sources detection in power systems via nonactive power measurements according to IEEE Std. 1459–2010: Theoretical approach and ex…
2010
In this paper an enhanced decision-making strategy is presented for the detection of harmonic sources in power systems able to detect also which is the prevailing nature of the disturbance (nonlinearity or unbalance). It makes use of some simple indices, which are evaluated by means of the measurements of some nonactive power quantities, proposed by the authors and derived from the approach of the IEEE Std. 1459–2010. The decision-making rules for the proposed strategy are presented and discussed by means of simulation and experimental tests. The results obtained are presented, showing the effectiveness of the proposed strategy for the detection of the dominant harmonic source upstream or d…
Effect of cobalt doping on the local structure and dynamics of multiferroic MnWO4and Mn0.7Co0.3WO4
2013
The local atomic structure and dynamics in multiferroic MnWO4 and Mn0.7Co0.3WO4 have been studied by X-ray absorption spectroscopy at the Co(Mn) K-edge and W L3-edge. The analysis of the first coordination shell of metal ions using single-shell Gaussian approximation and regularization-like method allowed us to determine a distortion of Mn(Co)O6 and WO6 octahedra. It was found that the local environment of Co2+ ions in Mn0.7Co0.3WO4 is close to that in CoWO4, whereas the presence of cobalt ions reduces the distortion of MnO6 octahedra in comparison with pure MnWO4.
Optical absorption and Raman spectroscopy of CuWO4
2010
Th e electronic absorption and Raman spectra of CuWO4 are studied as a function of pressure in the 0 - 20 GPa range. The below-gap absorption bands at 1.15, 1.38 and 1.56 eV correspond to Cu 2+ d-transitions split by the Jahn-Teller distortion of CuO6 (Req = 1.98 A; Rax = 2.39 A; Qθ = 0.47 A). Pressure induces a strong reduction of the JT distortion up to 10 GPa. Above this pressure we observe, by optical absorption and Raman spectroscopy, a first-order phase transition at 11 GPa with phase coexistence in the 10-12 GPa range, as it is confirmed by Raman spectroscopy. The absorption spectra suggest that two different Cu 2+ sites are formed in the high pressure phase, each having rather diffe…
The role of perceptual contrast non-linearities in image transform quantization
2000
Abstract The conventional quantizer design based on average error minimization over a training set does not guarantee a good subjective behavior on individual images even if perceptual metrics are used. In this work a novel criterion for transform coder design is analyzed in depth. Its aim is to bound the perceptual distortion in each individual quantization according to a non-linear model of early human vision. A common comparison framework is presented to describe the qualitative behavior of the optimal quantizers under the proposed criterion and the conventional rate-distortion based criterion. Several underlying metrics, with and without perceptual non-linearities, are used with both cr…
HDR image generation from LDR image with highlight removal
2015
The emergency of High Dynamic Range (HDR) display device impels the study of generating HDR image from Low Dynamic Range (LDR) image. Most existing generation methods apply complicated handing to highlight areas in image, which perplexes the algorithm and introduces the probability of generating artifacts. In this paper, we investigate a separated scheme: instead of sophisticated treatment to the highlight areas during expanding, the processing to the highlight areas is separated from the dynamic range expansion, which facilitates the framework and reduces the artifacts. The image quality metric shows that the separated scheme reveals more details with little artifacts compared to the algor…
A feedback view of behavioural distortions from perceived public service gaps at ‘street‐level’ policy implementation: The case of unintended outcome…
2020
This paper discusses the limitations and risks associated with the use of output-oriented measures to assess public school performance. In particular, it questions the capability of the performance measures set by external institutions, with respect to schools, to support sustainable educational outcomes. To this end, the ‘street-level bureaucracy’ theory is used in the paper as a basis to analyse the behavioural distortions generated by perceived public service gaps at school level policy implementation. Such unintended behavioural effects are often a major cause of disappointing outcomes when test-based accountability systems are adopted. In the second part of the paper, an insight model …
Mappings of exponentially integrable distortion: Decay of the Jacobian
2018
We establish an integrability result on the reciprocal of the Jacobian determinant for a mapping of exponentially integrable distortion and thus answer a question raised by S. Hencl and P. Koskela.
Generalized Dimension Distortion under Mappings of Sub-Exponentially Integrable Distortion
2010
We prove a dimension distortion estimate for mappings of sub-exponentially integrable distortion in Euclidean spaces, which is essentially sharp in the plane.
Mappings of Finite Distortion:¶Discreteness and Openness
2001
We establish a sharp integrability condition on the partial derivatives of a mapping with L p -integrable distortion for some p>n− 1 to guarantee discreteness and openness. We also show that a mapping with exponentially integrable distortion and integrable Jacobian determinant is either constant or both discrete and open. We give an example demonstrating the preciseness of our criterion.