Superresolution algorithms for spatial extended scattering centers

Scattering centers model (SCM) is usually considered for modeling target backscattered signal in high-resolution radar. In this case the impulse response of each scattering center is represented by a time-delayed Dirac pulse. Some of most popular superresolution imagery techniques, such as MUSIC or ESPRIT, are well-matched to this model. Under this hypothesis, they outperform Fourier-based techniques in terms of both spatial and dynamic resolutions. However, the behavior of real-world targets is often very different from that of the SCM. Indeed, their reflectivity function is not confined just to several perfectly localized scattering centers, but it can be rather approximated by a set of scattering regions having different spatial extent. SCM becomes then inappropriate and the superresolution methods may provide unexpected results. Furthermore, the amplitude information is difficult to interpret in this case. In this paper we propose an extension of two superresolution methods, MUSIC and ESPRIT, to cope with extended scattering centers (ESC). According to this model, the impulse response of an ESC is not a Dirac pulse, but a window of finite support. Besides the position, the size (spatial extent) of this window is also recovered. This additional information about the target structure can be used for increasing ATR (automatic target recognition) accuracy and robustness.     

High impedance fault arcing on sandy soil in 15 kV distributionfeeders: contributions to the evaluation of the low frequency spectrum

The measured values of current harmonics at a staged high-impedance ground fault on sandy soil are presented. The measured low-frequency spectrum is compared with current harmonics recorded continuously for one week at the substation. This comparison was carried out to determine to what extent 120 Hz and 180 Hz components can be used to help detect a high-impedance fault. The field measurements are supported by a simple theoretical model and laboratory measurements. It is concluded that, for the studied feeder, detection of high-impedance arcing faults may be possible by monitoring of the second-harmonic current     

Polymer-Derived SiOC/ZrO2 Ceramic Nanocomposites with Excellent High-Temperature Stability

Polymer-derived SiOC/ZrO₂ ceramic nanocomposites have been prepared using two synthetic approaches. A commercially available polymethylsilsesquioxane (MK Belsil PMS) was filled with nanocrystalline zirconia particles in the first approach. The second method involved the addition of zirconium tetra( n -propoxide), Zr(OⁿPr)₄, as zirconia precursor to polysilsesquioxane. The prepared materials have been subsequently cross-linked and pyrolyzed at 1100°C in argon atmosphere to provide SiOC/ZrO₂ ceramics. The obtained SiOC/ZrO₂ materials were characterized by means of X-ray diffraction, elemental analysis, Raman spectroscopy as well as transmission electron microscopy. Furthermore, annealing experiments at temperatures from 1300° to 1600°C have been performed. The annealing experiments revealed that the incorporation of ZrO₂ into the SiOC matrix remarkably increases the thermal stability of the composites with respect to crystallization and decomposition at temperatures exceeding 1300°C. The results obtained within this study emphasize the enormous potential of polymer-derived SiOC/ZrO₂ composites for high-temperature applications.     

Phase separation of a hafnium alkoxide-modified polysilazane upon polymer-to-ceramic transformation—A case study

The polymer-to-ceramic transformation of a hafnium alkoxide-modified polysilazane was investigated via thermogravimetric analysis coupled with in situ mass spectrometry (TG/MS), nuclear magnetic resonance (MAS NMR) and transmission electron microscopy (TEM). The results indicate that the structural evolution of the polysilazane upon ceramization is strongly affected by the modification with hafnium alkoxide. Thus, the content of carbon in the ceramic backbone was relatively low, whereas a large amount of SiN₄ sites and a segregated carbon phase was present in the sample. Furthermore, this study revealed the formation of a SiHfCNO amorphous single phase ceramic via pyrolysis of the polymer at 700 °C, whereas at higher pyrolysis temperatures precipitation of hafnia was observed, leading to an amorphous hafnia/silicon carbonitride ceramic nanocomposite. The precipitation of hafnia was shown to not rely on decomposition processes, but to be a result of rearrangement reactions occurring within the ceramic material.     

Evaluation of single-point measurements method for harmonicpollution cost allocation

This paper reports on the reliability of single-point measurements for harmonic pollution cost allocation. Simulated results give the correlation between the cost and four physical electrical quantities that can be measured at the end-user bus: harmonic active power; harmonic apparent power; total harmonic current squared; and nonfundamental apparent power squared. The nonfundamental apparent power squared produced the best correlation, with errors less than 5%     

Topics in the Theory of Random Noise. Vol. 1. General Theory of Random Processes. Non-Linear Transformations of Signals and Noise

Residuals from fit are often examined in regression analysis. A test suggested by Ellenberg [5] and Prescott [7] for the largest residual being an outlier is implemented through table development. Tables of critical valltes for tests at levels (α ≤ 0.10, 00.5, and 0.01 are included.     

Ink-Jet Printing of Binders for Ceramic Components

Layered manufacturing methods for fabricating ceramic components can involve selective deposition of binder using ink-jet printing. Selection of a proper binder plays a critical role in fabricating parts with good surface finish, dimensional accuracy, and high resolution. Several polymeric solution-phase binders were investigated in terms of their physical properties, printing performance, and binder-powder bed interaction. It was observed that the molecular weight should be <15 000 for the binder to be penetrated into dense powder compacts. Binder infiltration kinetics and printed line width were also significantly influenced by powder-bed characteristics, such as surface roughness and pore size, as well as the physical properties of the binder, such as viscosity and surface tension.