A Computational Model for High Current Density Arc Plasmas

A computational model for high current density arc plasmas is developed. Under the assumption of thermodynamic equilibrium the arc plasma is described as a compressible laminar fluid based on the magnetohydrodynamic (MHD) equations and the transport and thermodynamic properties of air. The arc plasma is studied in time and space on macroscopic values such as the temperature and the pressure. The simulation results are discussed and future research work is identified addressing the scientific domain of high current density arc plasmas

Examining the Performance of Islamic and Conventional Stock Indices: A Comparative Analysis

Islamic indices encompass different fundamental principles to those held by conventional ones, which directs attention onto comparative financial performance. This paper offers a comprehensive performance comparison between Islamic indices and conventional indices, based on four main markets: worldwide, the US, Europe, and Asia-Pacific for the period of 2007 and 2017 through financial ratio comparison and also the CAPM-EGARCH model. The main finding shows that Islamic indices yield higher average returns and lower risks during the 2007-2009 and 2013-2017 periods for all four markets, compared with respective conventional markets. During 2009-2013 period, the comparison proves inconclusive, since Islamic indices demonstrate better performance in European and Asia-Pacific markets, while conventional indices operate at an enhanced level within other markets. Overall, Islamic indices outperformed conventional indices during the global financial crisis period (2007-2009) and the latter post-crisis phase (2013-2017), especially in the European and Asia-Pacific markets

Investigating of the Recovery Behaviour of a Small Switching Gap after Current Interuption

The recovery behaviour of switching arcs in a small gap was investigated experimentally. Therefore a simple mechanical model switch without an arcing chamber was designed. For the investigation the current carring contacts are separated. After various arcing times, the current is interrupted by an electronic switch. At a fixed contact distance, the switching gap was tested with variable voltages to investigate the dielectric strength. Based on these results the recovery behaviour was studied using the Weibull distribution function

Influence of the synergy of neutron and gamma radiation and functional aging on the efficiency of a hybrid protection circuit

Due to the shortcomings of commercial filters and non-linear components for overvoltage protection in the conditions of synergy of neutron and gamma radiation and functional aging, the behavior of the hybrid protection circuit under the same conditions was examined. In order for the experimental procedure to correspond as closely as possible to the real situation, the load of the hybrid circuit was not adjusted by impedance. The standard model of the hybrid protection circuit recommended in accordance with IEC 1.3 is simulated using the software package PSPICE. To that end, it is necessary to create a varistor with appropriate elements. The equivalent inductance parameters were found to be stable in relation to the experimental conditions. It was also established that due to the synergy of neutron and gamma radiation and functional aging, there is a change in the steepness of the varistor characteristic and the tangent of the loss angle in the capacitors. The overall effect of neutron and gamma radiation and functional aging was tested on the hybrid circuit and on individual components. The experiments were performed under well-controlled laboratory conditions, and the combined measurement uncertainty of the experimental procedure did not exceed 5%

J. A. Comenius: su impulso renovador y su pervivencia en la enseñanza / aprendizaje de lenguas

En este trabajo se lleva a cabo un acercamiento a algunas de las aportaciones básicas del humanista J. A. Comenius al campo de la didáctica de lenguas, en especial al de las segundas lenguas, y se pone de manifiesto la vigencia de algunos de sus planteamientos, sobre todo los referidos al uso de imágenes, en las propuestas pedagógicas actuales. This article approaches some of the basic contributions of the humanist Comenius to the field of language teaching, specially to the one of second languages.It also shows the validity of some of his expositions, mainly the ones referred to the use of images, in the present pedagogical proposals

Vortex ratchet reversal at fractional matching fields in kagom\'e-like array with symmetric pinning centers

Arrays of Ni nanodots embedded in Nb superconducting films have been fabricated by sputtering and electron beam lithography techniques. The arrays are periodic triangular lattices of circular Ni dots arranged in a kagom\'e-like pattern with broken reflection symmetry. Relevant behaviors are found in the vortex lattice dynamics : i) At values lower than the first integer matching field, several fractional matching fields are present when the vortex lattice moves parallel or perpendicular to the reflection symmetry axis of the array showing a clear anisotropic character in the magnetoresistance curves, ii) injecting an ac current perpendicular to the reflection symmetry axis of the array yields an unidirectional motion of the vortex lattice (ratchet effect) as a result of the interaction between the whole vortex lattice and the asymmetric lattice of dots, iii) increasing the input current amplitudes the ratchet effect changes polarity independently of matching field values. These experimental results can be explained taking into account the vortex lattice density.Comment: 9 pages, 4 figures, 1 tabl

Effect of Aging in the Perception of Health-Related Quality of Life in End-Stage Renal Disease Patients under Online-Hemodiafiltration

This work aimed to evaluate how aging could influence patients' perception of health quality of life (HRQOL), as well as, the effect of aging on dialysis adequacy and in hematological, iron status, inflammatory and nutritional markers. In this transversal study were enrolled 305 ESRD patients under online-hemodiafiltration (OL-HDF) (59.67% males; 64.9 ± 14.3 years old). Data about comorbidities, hematological data, iron status, dialysis adequacy, nutritional and inflammatory markers were collected from patient's records. Moreover, HRQOL score, by using the Kidney Disease Quality of Life-Short Form (KDQOL-SF), was assessed. Analyzing the results according to quartiles of age, significant differences were found for some parameters evaluated by the KDQOL-SF instrument, namely for work status, physical functioning and role-physical, which decreased with increasing age. We also found a higher proportion of diabetic patients, a decrease in creatinine, iron, albumin serum levels, transferrin saturation and nPCR, with increasing age. Moreover, significant negative correlations were found between age and mean cell hemoglobin concentration, iron, transferrin saturation, albumin, nPCR, work status, physical functioning and role-physical. In conclusion, our results showed that aging is associated with a decreased work status, physical functioning and role-physical, with a decreased dialysis adequacy, iron availability and nutritional status, and with an increased proportion of diabetic patients and of patients using central venous catheter, as the vascular access. The knowledge of these changes associated with aging, which have impact in the quality of life of the patients, could be useful in their management

Directed motion of domain walls in biaxial ferromagnets under the influence of periodic external magnetic fields

Directed motion of domain walls (DWs) in a classical biaxial ferromagnet placed under the influence of periodic unbiased external magnetic fields is investigated. Using the symmetry approach developed in this article the necessary conditions for the directed DW motion are found. This motion turns out to be possible if the magnetic field is applied along the most easy axis. The symmetry approach prohibits the directed DW motion if the magnetic field is applied along any of the hard axes. With the help of the soliton perturbation theory and numerical simulations, the average DW velocity as a function of different system parameters such as damping constant, amplitude, and frequency of the external field, is computed.Comment: Added references, corrected typos, extended introductio

Enhancement of synchronized vortex lattice motion in hybrid magnetic/amorphous superconducting nanostructures

Superconducting a-Mo_(3)Si and Nb films have been grown on arrays of Ni nanodots. We have studied the vortex lattice dynamics close to critical temperatures. Different vortex lattice configurations are obtained with the same array unit cell. These different vortex lattices occur at matching conditions between the vortex lattice and the array unit cell. The interplay between the random intrinsic pinning of the superconducting films and the periodic pinning of the array govern the vortex lattice configurations. Different vortex lattice configurations and enhancement of synchronized vortex lattice motion are obtained by increasing the periodic pinning strength and decreasing the random pinning strength

Geological engineering problems associated with tunnel construction in karst rockmasses: The case of Gavarres tunnel (Spain)

A representative example of the problems associatedwith the excavation and support of tunnels in karst ground is presented. It is a peculiar case in terms of heterogeneity and spatial distribution of zones of poor geotechnical quality, requiring the need to define, preferably in the study phases, adequate site investigation, suitable design procedures, efficient construction techniques and appropriate ground treatment. The difficulties associatedwith the instability of the karstified ground, and the presence of cavities, wholly or partially filled with soils of low cohesion, are discussed via retrospective analysis. The solutions adopted to solve the problems encountered during the tunnel construction enabled a systematic approach, useful for newconstruction projects in limestone terrains of medium to high karstification.Alija, S.; Torrijo Echarri, FJ.; Quinta Ferreira, M. (2013). Geological engineering problems associated with tunnel construction in karst rockmasses: The case of Gavarres tunnel (Spain). Engineering Geology. 157:103-111. doi:10.1016/j.enggeo.2013.02.010S10311115