Effects of unsymmetrical voltage sags on industrial adjustable speed drives

This paper researches unsymmetrical voltage sag influence on torque ripple in scalar controlled (V/Hz), rotor field oriented (RFO) and direct torque controlled (DTC) drives. Electric drives performance degradation during voltage sag mainly depends on the used control algorithm. Industrial drives with all three types control methods are experimentally tested. Experiments with digital observer's application confirm the proposed solution.

Analysis of risk factors for perifocal oedema after endovascular embolization of unruptured intracranial arterial aneurysms

© 2015 Snezana Lukic et al., published by De Gruyter Open. Background. Endovascular embolization is a treatment of choice for the management of unruptured intracranial aneurysms, but sometimes is complicated with perianeurysmal oedema. The aim of our study was to establish incidence and outcomes of perianeurysmal oedema after endovascular coiling of unruptured intracranial aneurysms, and to reveal possible risk factors for development of this potentially serious complication. Methods. In total 119 adult patients with endovascular embolization of unruptured intracranial aneurysm (performed at Department for Interventional Neuroradiology, Clinical Center, Kragujevac, Serbia) were included in our study. The embolizations were made by electrolite-detachable platinum coils: pure platinum, hydrophilic and combination of platinum and hydrophilic coils. Primary outcome variable was perianeurysmal oedema visualized by magnetic resonance imaging (MRI) 7, 30 and 90 days after the embolization. Results. The perianurysmal oedema appeared in 47.6% of patients treated with hydrophilic coils, in 21.6% of patients treated with platinum coils, and in 53.8% of those treated with mixed type of the coils. The multivariate logistic regression showed that variables associated with occurrence of perianeurysmal oedema are volume of the aneurysm, hypertension, diabetes and smoking habit. Hypertension is the most important independent predictor of the perianeurysmal oedema, followed by smoking and diabetes. Conclusions. The results of our study suggest that older patients with larger unruptured intracranial aneurysms, who suffer from diabetes mellitus and hypertension, and have the smoking habit, are under much higher risk of having perianeurysmal oedema after endovascular coiling

Positrons in gas filled traps and their transport in molecular gases

In this paper we give a review of two recent developments in positron transport, calculation of transport coefficients for a relatively complete set of collision cross sections for water vapour and for application of they Monte Carlo technique to model gas filled subexcitation positron traps such as Penning Malmberg Surko (Surko) trap. Calculated transport coefficients, very much like those for argon and other molecular gases show several new kinetic phenomena. The most important is the negative differential conductivity (NDC) for the bulk drift velocity when the flux drift velocity shows no sign of NDC. These results in water vapour are similar to the results in argon or hydrogen. The same technique that has been used for positron (and previously electron) transport may be applied to model development of particles in a Surko trap. We have provided calculation of the ensemble of positrons in the trap from an initial beam like distribution to the fully thermalised distribution. This model, however, does not include plasma effects (interaction between charged particles) and may be applied for lower positron densities

Loss of heterozygosity of PTEN in patients with non-small cell lung cancer treated and not treated with neoadjuvant chemotherapy

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Loss of heterozygosity of PTEN in patients with non-small cell lung cancer treated and not treated with neoadjuvant chemotherapy

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On diffusion of positrons in electric and magnetic fields in molecular gases

Diagonal elements of the diffusion tensor for positron swarms in molecular gases under the influence of electric and magnetic fields are investigated using a Monte Carlo simulation technique and multi-term theory for solving the Boltzmann equation. The focus was on the synergetic effects of non-conservative collisions and magnetic fields on\ud the diffusion of positrons. It is found that different diagonal elements of the diffusion tensor show different sensitivities to the strength of magnetic field and on the presence of non-conservative collisions

Effect of silver modification on structure and catalytic performance of Ni-Mg/diatomite catalysts for edible oil hydrogenation

Silver modified Mg-Ni/diatomite materials with ratios of SiO2/Ni = 1.07 and Mg/Ni = 0.1, differing in Ag content (Ag/Ni = 0.025 and 0.1) were prepared by the precipitation-deposition method. The effects of silver presence and content on the structure, morphology, texture and H2-adsorption capacity of the obtained precursors were studied by X-ray diffraction, scanning electron microscopy, Hg-porosimetry and H2-chemisorption techniques. The catalytic performance of the corresponding catalysts in the soybean oil hydrogenation was investigated. The increase of the silver loading resulted in the development of macroporosity and increase in the total sample porosity. The decrease of both H2-adsorption capacity and hydrogenation activity are related to the metallic silver covering and blocking effects on the Ni2+ species, thus hampering the access of hydrogen. The decrease of hydrogenation activity and favorable limiting of cis-trans isomerization on the silver modified catalyst are explained by Horiuti-Polanyi mechanism based on the assumption that hydrogenation and isomerization proceed at the same active metallic nickel sites via half-hydrogenated intermediates. It was shown that the adjustment of the catalyst composition by changing the content of silver modifier offers the possibility to control the total amount of solid fat content, stearic acid and detrimental trans fatty acids in the hydrogenated derivatives. The catalyst with higher silver content is proposed as a promising candidate for selective edible oil hydrogenation catalyst

Transport coefficients for positron swarms in molecular gases

[Extract] Transport of positrons in various environments is interesting from many points of view [1]. They are standing behind the origin of astrophysical sources of annihilation radiation; they play a crucial role in production and detection of cold anti-hydrogen and also in the production of positronium (Ps). Recent investigations of positrons have triggered a whole new interesting research area – ionized gases with positrons that may be analyzed using similar techniques albeit for their short lifetime and even the antimatter plasmas. In addition, positrons have been already used for characterization of materials. However, perhaps the most important applications of positrons from the viewpoint of transport studies are the positron buffer-gas traps, such as the Surko trap, and also the use of positrons in the medical diagnostics of positron emission\ud tomography (PET) and possible cancer treatments. Thanks to the recent advances in experimental measurements of high-resolution, low-energy inelastic positron scattering cross sections [2], the determination of positron transport coefficients over a wide range of energies has become possible. These measurements confirm that Ps formation, a non-conservative process unique to positrons, has a much larger cross section than annihilation and the analogous loss process for electrons- the dissociative attachment. This fact, coupled with a very strong energy dependence\ud for Ps formation, is expected to lead to kinetic effects [3]