Wrocław University of Technology

About: Wrocław University of Technology is a education organization based out in Wrocław, Poland. It is known for research contribution in the topics: Laser & Computer science. The organization has 13115 authors who have published 31279 publications receiving 338694 citations.

Power system harmonics estimation using linear least squares method and SVD

Abstract: The paper examines singular value decomposition (SVD) for the estimation of harmonics in signals in the presence of high noise. The proposed approach results in a linear least squares method. The methods developed for locating the frequencies as closely spaced sinusoidal signals are appropriate tools for the investigation of power system signals containing harmonics and interharmonics differing significantly in their multiplicity. The SVD approach is a numerical algorithm to calculate the linear least squares solution. The methods can also be applied for frequency estimation of heavy distorted periodical signals. To investigate the methods several experiments have been performed using simulated signals and the waveforms of a frequency converter current. For comparison, similar experiments have been repeated using the FFT with the same number of samples and sampling period. The comparison has proved the superiority of SVD for signals buried in the noise. However, the SVD computation is much more complex than FFT and requires more extensive mathematical manipulations.

Silicon anisotropic etching in alkaline solutions IV The effect of organic and inorganic agents on silicon anisotropic etching process

Abstract: Silicon anisotropic etching process in organic and inorganic solutions has been studied. Experimental results on silicon etching in KOH and TMAH solutions with and without IPA addition have been presented. Etching rate curves versus solution concentration were plotted for different crystallographic planes with special emphasis on high-indexed ones. A comparison of our own experimental results with the results of other authors, concerning silicon anisotropic etching process in hydroxides of other metals from the first group of periodic table, revealed that their ions and molecules contained in the solution play an important role in the process and influence its anisotropy. The observations led us to some general conclusions regarding physical and chemical phenomena associated with the silicon anisotropic etching. We have suggested that the lowering of etching rates is connected with adsorption of cations and organic additions on some crystallographic planes.

Polypyrrole/iron oxide/reduced graphene oxide ternary composite as a binderless electrode material with high cyclic stability for supercapacitors

Abstract: Herein, we present a facile two-step synthesis of polypyrrole/Fe 2 O 3 /reduced graphene oxide (PFG) ternary composite. It includes the preparation of the binary Fe 2 O 3 /reduced graphene oxide (FG) composite under hydrothermal conditions, followed by oxidative polymerization of pyrrole on the FG composite surface. X-ray diffraction measurements revealed the presence of the α-Fe 2 O 3 phase in both composites. The electrochemical measurements performed using the composite electrodes in a 1 M Na 2 SO 4 solution revealed that the binder-free PFG electrode exhibits a high specific capacitance of 140 F g −1 with an excellent capacitance retention of 93% after 5000 cycles at 1 A g −1 which can be attributed to the synergistic effect between polypyrrole and FG composite.