Numerical analysis of earthing grids buried in horizontally stratified multilayer earth

This paper describes a new numerical procedure for analysing earthing grids buried in horizontally stratified multilayer earth. The procedure is very efficient and general. The total number of layers and the total number of metallically disconnected earthing grids are completely arbitrary. A single earthing grid can be positioned in several layers. The procedure is based on an integral equation formulation. Earthing grid conductors are subdivided into segments and the average potential method is used. Efficiency and generality of the computation procedure are based on the successful application of numerical approximations of two kernel functions of the integral expression for the potential distribution within a single layer which is caused by a point current source. Each kernel function of the observed layer is approximated using a linear combination of 15 exponential functions. Extension from the point source to a segment of the earthing grid conductor is done by integrating the potential contribution due to a line of point current sources along the segment axis. This computational procedure gives highly accurate results in a short execution time. © 1998 John Wiley & Sons, Ltd.     

Shape and aspect ratio analysis of anisotropic magnetic nanochains based on TEM micrographs

Due to advances in electron microscopy and to the development of novel nanoparticle structures with different morphologies and the dependence of physical properties on the nanoparticle morphology, there is a need for a more precise analysis of nanoparticle structure and morphology. That should provide a simple and unambiguous comparison of nanoparticles‘ shapes and of material properties that depend on the shape, which has been lacking thus far. Here we study nanochains consisting of silica-coated iron oxide (maghemite, γ-Fe₂O₃) nanoparticle clusters covered by an additional layer of silica (core-shell structure). We have developed an algorithm for image segmentation and a quantitative analysis of nanochain shape from real TEM images. To that end we used two distinct measures of circularity and elongation measure (the aspect ratio measure). We show that the relative position and the area of the links, as well as the links‘ shape lead to significant differences in the measured aspect ratio of the entire nanochain (substantially influence the elongation of nanochains). We have also analyzed the core-shell structures in nanochains, and computed the shell's share in the overall area of observed nanochains. A Matlab code was developed and used for the computation of the elongation measure of shapes appearing in electron microscopy images. Here we have investigated magnetic properties of synthetic nanochains, that revealed superparamagnetic behavior at room temperature (SPION) with the possibility of tuning the magnetization values (approx. from 19 to 46?emu/g). We have compared of magnetization M(H) curves of the anisotropic nanochains and of isotropic nanoparticle (nanochain links), with the conclusion that the nanochains have a higher magnetic susceptibility, which fact can be understood as a consequence of their anisotropic shapes. The nanochains may be applied in biomedicine and magnetic separation, due to their morphology and magnetic properties.     

Influence of WO3‐Doping on the Microstructure and Electrical Properties of ZnO–Bi2O3 Varistor Ceramics Sintered at 950°C

The phase evolution, microstructure, and electrical properties of WO₃‐doped ZnO–Bi₂O₃‐based varistors were investigated for different amounts x (0 ≤ x ≤ 1.60 mol%) of the dopant. When x was less than 0.40, the dissolved W⁶⁺ in the β‐Bi₂O₃ acted as a donor in the grain boundaries and reduced the electrical properties of the ZnO varistors. However, when x was 0.40 mol%, which meant an amount of WO₃ equal to that of Bi₂O₃, the electrical properties dramatically increased, which means the W⁶⁺ donor effect is removed at the grain boundaries because a new Bi₂WO₆ phase was formed in the grain‐boundary regions. The Bi₂WO₆ phase has high oxygen conductivity at high temperatures; it transfers more oxygen to the grain boundaries in order to further enhance the electrical properties. For x values higher than 0.40 (i.e., an addition of WO₃ that is greater than the content of Bi₂O₃), the electrical properties were steadily reduced in comparison to the composition with x = 0.40. This could be explained by the reduced amount of Co, Mn, and Al at the grain boundaries and in the ZnO grains as a result of their incorporation into the ZnWO₄ phase. The electrical properties of the ZnO grains and the grain boundaries were in agreement with the results of the impedance spectroscopy analysis.     

An efficient mechanism of cryptographic synchronization within selectively encrypted H.265/HEVC video stream

The challenge to which the encryption of multimedia data needs to respond is ensuring the security of data intensive video stream in an efficient way. Unlike full data encryption, selective encryption manages to achieve this by encrypting only a part of the data stream, while providing a satisfactory level of video security. This optimizes the processing time and the size of encrypted data. Regardless of the encryption technique, there is a lack of cryptographic synchronization when providing random access to the selected part of the encrypted multimedia stream. In this paper we propose a novel and efficient method of cryptographic synchronization as an extension to the H.265/HEVC crypto encoder in order to support random access in selectively encrypted video stream.     

The Genetic Basis of Strokes in Pediatric Populations and Insight into New Therapeutic Options

Strokes within pediatric populations are considered to be the 10th leading cause of death in the United States of America, with over half of such events occurring in children younger than one year of life. The multifactorial etiopathology that has an influence on stroke development and occurrence signify the importance of the timely recognition of both modifiable and non-modifiable factors for adequate diagnostic and treatment approaches. The early recognition of a stroke and stroke risk in children has the potential to advance the application of neuroprotective, thrombolytic, and antithrombotic interventions and rehabilitation strategies to the earliest possible timepoints after the onset of a stroke, improving the outcomes and quality of life for affected children and their families. The recent development of molecular genetic methods has greatly facilitated the analysis and diagnosis of single-gene disorders. In this review, the most significant single gene disorders associated with pediatric stroke are presented, along with specific therapeutic options whenever they exist. Besides monogenic disorders that may present with stroke as a first symptom, genetic polymorphisms may contribute to the risk of pediatric and perinatal stroke. The most frequently studied genetic risk factors are several common polymorphisms in genes associated with thrombophilia; these genes code for proteins that are part of the coagulation cascade, fibrolysis, homocystein metabolism, lipid metabolism, or platelets. Single polymorphism frequencies may not be sufficient to completely explain the stroke causality and an analysis of several genotype combinations is a more promising approach. The recent steps forward in our understanding of the disorders underlying strokes has given us a next generation of therapeutics and therapeutic targets by which to improve stroke survival, protect or rebuild neuronal connections in the brain, and enhance neural function. Advances in DNA sequencing and the development of new tools to correct human gene mutations have brought genetic analysis and gene therapy into the focus of investigations for new therapeutic options for stroke patients.     

On the tungsten carbide synthesis for PEM fuel cell application – Problems,challenges and advantages

Fuel cell application of tungsten carbide is revisited starting with four different tungsten carbide precursors used for high temperature synthesis. It was shown that the final products greatly depend on the nature of the precursor. Using tungsten peroxide/2-propanol derived precursor almost pure WC was obtained which was subjected to further electrochemical investigation. It was shown that it is necessary to decorate WC with Pt nanoparticles in order to obtain satisfactory fuel cell performance, but catalytic activity of Pt/WC anode catalyst is not expected to overcome the activity of Pt/C. It is argued that new synthetic routes for the preparation of WC should be directed towards obtaining highly dispersed WC, that is, WC with high external surface area available for Pt deposition, rather than high specific surface area WC with large contribution of micropores having no importance when it comes to the use of WC as a catalyst support. The true benefit of the use of WC as catalyst support is found in increased CO tolerance/CO oxidation activity of WC-supported Pt catalysts. Qualitative mechanistic view on increased CO oxidation activity of Pt/WC is offered.     

Electrochemical properties of nanostructured Li1.2V3O8 in aqueous LiNO3 solution

The amorphous hydrated precursor of Li_1.2V₃O₈ was synthesized by soft chemistry method, and then heat-treated in air at several temperatures within the range 200–400 °C. The heat-treatment changed its morphological, structural and charging/discharging performance. The product obtained upon the treatment at 300 °C, consisting of uniform, rod-shaped particles, 100–150 nm in diameter and 300–800 nm in length, displayed the best electrochemical performance in aqueous LiNO₃ solution. Its initial discharge capacity amounted to 136.8 mAh g⁻¹ at a rate of C/5, which upon 50 charging/discharging cycles decreased for only 12%.     

Electrochemical polymerization of 2-methyl-1-naphthylamine

Summary 2-methyl-1-naphthylamine has been electropolymerized from the acidic aqueous solutions by three different synthetic routes. The polymerization products, deposited at a platinum working electrode as very adherent films, were characterized by cyclic voltammetry (CV), infrared spectroscopy (IR) and gel permeation chromatography (GPC). In a strongly acidic medium, the products display redox properties, in a form of two well-defined redox pairs with the formal potentials at 0.19 V and 0.47 V vs. SCE. IR-spectroscopy indicated that the polymerization occurs via the –NH₂ groups, by different coupling ways: N-C(4), N-C(5) and N-C(7), as well as that CIO ₄ ^- ions incorporate themselves into the product of electropolymerization. GPC of the polymerization products evidenced oligomeric chains with molar masses up to 1600 g/mol as main species.