The polar cluster like behavior in Ti substituted BaZrO3 ceramics

In this paper we report the evolution of the polar cluster like behavior with the incorporation of Ti⁴⁺ ion in BaZrO₃ Ceramics. Dielectric behavior of BaZr_xTi_(1−x)O₃ (x = 1.00, 0.95, 0.90, 0.85) ceramics is studied in the temperature range from 300 to 30 K. Polar cluster like behavior becomes more prominent with the increase in content of Ti⁴⁺ ion. The dielectric relaxation is analyzed by Vogel–Fulcher relation and Arrhenius law. Frequency dependence of dielectric constant and low loss tangent of these materials can be useful for the potential applications at low temperature.     

Cyclic fatigue of long and short cracks in alumina

The cyclic fatigue behaviour of long and microstructurally short cracks in a 10 μm grain-size alumina has been investigated. This material was found to be stress sensitive, a modest drop in applied stress resulting in a considerable lifetime enhancement. The growth of long cracks was studied using the circular compact tension geometry and was found to follow a Paris law behaviour. The crack path was entirely intergranular in this material with long fatigue crack growth governed by the degradation of crack-wake bridging. Short-crack growth was investigated using indented discs in a biaxial flexure geometry. Short cracks were observed to grow at lower values of applied ΔK than long cracks, increasing with crack length as bridging of the crack wake increased. The fatigue crack growth of AD90 alumina was also investigated by in situ testing within the specimen chamber of an SEM. The long-crack behaviour was found to be similar to the 10 μm grain-size alumina and other data reported in the literature. However, the crack path followed a mixture of transgranular and intergranular fracture and discontinuous in nature with frequent arrests. The crack-advancement mechanisms in these two alumina materials are different and affect the short-crack behaviour. However, in both cases the long-crack behaviour is dominated by crack-wake effects. This revised version was published online in November 2006 with corrections to the Cover Date.     

Analysis of the “Wavelet Tree Quantization” watermarking strategy and a modified robust scheme

Here we study a recently proposed watermarking scheme based on the paper “Wavelet Tree Quantization” (WTQ) by Wang and Lin (IEEE Trans Image Process 13(2):154–165, 2004). In given scheme, wavelet coefficients corresponding to the same spatial locations are grouped together. Two such groups, selected at random, constitute a supertree. Some of these supertrees are quantized to embed the watermark information in the image. In the process of cryptanalysis we first identify the groups which are quantized during the watermark insertion process. Then we select the non-quantized groups and quantize them too, to remove the watermark. Experimental results show that the watermark is completely removed by this attack. The cryptanalysis falls under the cipher text only jamming attack which requires only a single watermarked copy. Further, we suitably modify the WTQ scheme to make it robust against such cryptanalytic attacks.This is an extended and revised version of the paper Cryptanalysis of “Wavelet Tree Quantization” Watermarking Scheme presented at the International Workshop on Distributed Computing, IWDC 2004, Kolkata, 27–30 December 2004, Lecture Notes in Computer Science, vol. 3326, pp. 219–230. Springer, Berlin Heidelberg New York (2004). Section 4 of this paper introduces a modified scheme which is an addition over the conference version. Part of this work has been done while the author T. K. Das was visiting Indian Statistical Institute, Kolkata during 2004.     

Monte Carlo calculation of velocity-field characteristics in II-VI compound semiconductors

The velocity field characteristics of II–VI compound semiconductors at 77K have been obtained by the Monte Carlo simulation technique. The results agree with the available experimental data and with those obtained by solving the Boltzmann Transport Equation analytically. The simulation technique is described in detail and various aspects regarding the convergence of the simulation are discussed. The carrier distribution function has also been obtained from the simulation. The effects of the various simulation parameters, as well as those of the ionized impurity concentration, on the mobility values for the different semiconductors are discussed and results are presented.     

Generation of solar spicules and subsequent atmospheric heating

Science China Technological Sciences -     

Assessment of Strength by Young's Modulus and Porosity: A Critical Evaluation

Literature data on strength, porosity, and Young's modulus at room temperature of reaction-bonded silicon nitride, sintered silicon nitride, and hot-pressed silicon nitride have been fitted into available and proposed strength-porosity relationships. In general, the Lewis method of iterative least-squares fitting in these relationships has been found to be better than conventional linearized least-squares fitting. Further a semiempirically proposed strength–Young's modulus relationship has been found to predict strength more precisely than the conventional strength-porosity relationship.     

The stochastic aeroelastic response analysis of helicopter rotors using deep and shallow machine learning

Neural Computing and Applications - This paper addresses the influence of manufacturing variability of a helicopter rotor blade on its aeroelastic responses. An aeroelastic analysis using finite...     

Experimental investigations and comparison of various MPPT techniques for photovoltaic system

This paper deals with Matlab/Simulink and experimental investigations of various maximum power point tracking (MPPT) techniques namely incremental conductance (Inc), perturb and observation (P&O), constant voltage control (CVC) method, and introduction of a novel reference power (Pref) method for extracting the maximum power from the solar photovoltaic (PV) system. The complete system model along with these MPPT methods are developed in Matlab/Simulink and simulation results are obtained during sudden increase in irradiation of 1000 W/m², and verified experimentally. These MPPT methods are also implemented on Inverse-Sepic converter, which claims to extract maximum power from the PV system. Various experimental observations are taken to access the performance of these MPPT techniques such as settling time of the full load current under sudden exposure of irradiation level of 1000 W/m², performance during step increase in irradiation level (from 500 W/m² to 1000 W/m²) and vice versa. Extensive results are taken to compare these methods. The proposed Pref method is found to have lowest settling time to stabilize the load current as 520 ms, whereas, Inc method takes 1.24 s. Further, the efficiency of Inverse-Sepic converter with Pref method achieves the highest efficiency of 95.26%, whereas, it extracts lowest efficiency on same input as 90.77% with P&O method. The overall performance of the proposed Pref method is found to be superior as compared to other discussed MPPT methods as verified by experimental results.     

Exploitation of Social Media for Emergency Relief and Preparedness: Recent Research and Trends

Online Social Media, such as Twitter, Facebook and WhatsApp, are important sources of real-time information related to emergency events, including both natural calamities, man-made disasters, epidemics, and so on. There has been lot of recent work on designing information systems that would be useful for aiding post-disaster relief operations, as well as for pre-disaster preparedness. A special issue on “Exploitation of Social Media for Emergency Relief and Preparedness” was conducted for the journal Information Systems Frontiers. The objective of this special issue was to present a platform for dissemination of the empirical results of various technologies for extracting vital and actionable information from social media content in disaster situations. The papers included in this issue are expected to be the stepping stones for future explorations and technical innovations towards technologies meant for utilizing various online and offline information sources for enhancing pre-disaster preparedness and post-disaster relief operations.