Semi-fragile spatial watermarking based on local binary pattern operators

Local binary pattern (LBP) operators, which measure the local contrast within a pixel's neighborhood, have been successfully applied to texture analysis, visual inspection, and image retrieval. In the paper, we present a novel semi-fragile spatial watermarking method based on LBP operators by using the local pixel contrast for the embedding and extraction of watermarks. We also propose a general framework for multi-level image watermarking. Experimental results show that the proposed watermarking methods are robust against commonly-used image processing operations, such as additive noise, luminance change, contrast adjustment, color balance, and JPEG compression. At the same time, they achieve good invisibility, fragility, and image tamper detection and localization with less computational cost.     

Fast turn-on characteristics of tungsten-based dispenser cathodes. II

In the Proceedings of the 1982 Tri-Service Cathode Workshop, the authors described studies of the reactivations of tungsten-based dispenser cathodes following poisonings of the kind expected during shelf storage of a microwave tube [Appl. Surface Sci. 16 (1983) 73]. Further work on the problems of reactivation following such poisoning is described here. In addition to coated (“M”) and uncoated tungsten matrix cathodes, the tungsten-iridium mixed metal matrix (“MM”) cathode has been studied. In general reproducible results have been obtained from different examples of the same type of “M” and uncoated cathodes. However, although some “MM” cathodes have exhibited good reactivation characteristics, a large variation has been observed between different examples of “MM” cathodes. The composition of the impregnant in the dispenser cathodes has been found to be an important factor in determining the reactivation rate of a cathode. As the barium oxide concentration in the impregnant increases, the cathode will recover faster from a poisoning exposure. Studies of the poisoning caused by combinations of different gases suggest that poisoning will occur if there is a sufficient exposure of a poisoning agent, regardless of the total exposure. The exposures necessary to poison a cathode are so small, that poisoning of the cathode appears probable during shelf storage of a microwave tube. The reactivation results have been summarised in terms of the times and temperatures required to achieve both a given current density and a given degree of reactivation from a poisoned cathode. The studies also indicate that the limiting step during the reactivation process involves the dispensing of fresh material to the cathode surface rather than the desorption or conversion of a poisoned surface layer.     

Electron energy loss and secondary emission mechanisms in BaO

Electron Loss Spectroscopy (ELS), X-ray Photoemission (XPS), Secondary Emission Energy Distribution, and Secondary Electron yield data have been obtained on both evaporated films and sprayed-on coatings of BaO. Using the ELS correlated with the XPS data, bulk and surface plasmon losses as well as excitonic and interband transition electron loss mechanisms have been identified. It was found that at low primary beam energies (<100 eV), structure in the secondary emission energy distribution could be correlated with a conduction band energy structure. This structure was consistent with the model used to explain the loss transitions. The structure in the energy distribution curves shows little, if any, correlation with plasmon decay mechanisms and other two-step electron emission processes. On the contrary, for the case of BaO (at least at low primary energies), the energy distribution data and structure in the secondary yield vs. primary beam energy data indicate that most secondaries are produced by direct excitation of secondaries by the primary electrons.     

Angle-independent plasmonic infrared band-stop reflective filter based on the Ag/SiO₂/Ag T-shaped array

A plasmonic infrared (IR) filter assisted by localized surface plasmon polaritons (LSPPs) in a Ag/SiO?/Ag T-shaped array was theoretically and experimentally investigated. By using a Fourier transform infrared (FTIR) spectrometer, an angle-independent LSPP resonant mode caused by a Fabry-Pérot resonance in the structure was observed in agreement with the prediction from the rigorous coupled-wave analysis (RCWA) simulation. The resonant wavelength of the mode can also be controlled by modifying the geometry of the T-shaped structure. Such LSPP property can be used as an IR reflection-type band-stop filter with a single spectral bandwidth and an ultrahigh immunity to incident angles.