Papers by Keyword: Polarisation

Abstract: An analytical expression for the spectrum of stochastic spatially and temporally partially coherent electromagnetic Gaussian Schell-model pulsed (GSMP) beams is derived, and used to study the spectral changes of electromagnetic GSMP beams in free space. The influence of polarization on the on-axis relative spectral shift is emphasized. It is shown that the on-axis relative spectral shift increases with increasing the degree of polarization of source P0 for the case of δxx≠δyy, i.e. the spatial coherence length δxx of x component of the electric field at the source is not equal to that of y component. For δxx=δyy or δxx→∞ and δyy→∞, the on-axis relative spectral shift is independent of P0.

Abstract: Electrodeposited hard chromium (EHC) coatings have been widely used for improving wear characteristics of engineering tools and components. In the electrodeposition processes, in general solutions containing hexavalent chromium have been used. Hexavalent chromium is classified as a carcinogen compound, which causes health risks if used in production, and environmental problems due to the toxic character of the wastes [1]. In the present study plasma sprayed coatings (aluminum oxide, Co-28Mo-8Cr-2Si, tungsten carbide, chrome carbide) and electrolytic hard chrome coatings corrosion resistances have been compared through electrochemical polarization tests and immersion test in 0.1 N HCl aqueous solution.

Abstract: The demands of nano-measurement and nano-positioning now in research and industries become the challenge for heterodyne interferometer because its nonlinearity often limits the effective resolution. This paper introduces new developed method for compensation of the nonlinearity in heterodyne interferometer and explains what accuracy can be reached with demonstrations figured by the test results. On the basis of theoretical analyses and experimental investigations it shows which exactness can be expected.

Abstract: The value of dielectric constant of paraffin wax doped with different concentrations of lamp black carbon decreases with the increase in the concentration of lamp black carbon in it. It is a case of loss of dielectric property and gain in conducting property and the specimen behaves as a random binary mixture of conductors and insulators, more specifically, a random network of resistors and capacitors. Anderson Bridge is used to investigate the magnetic permeability and susceptibility of different media inside a solenoid. The resistive property of manganin wire is studied using Kelvin double Bridge.

Abstract: Barium titanate (BaTiO3) ceramics with various grain sizes from 0.7 to 13 μm on average were prepared by a conventional sintering method, a two-step sintering method and a rate controlled two-step sintering method. The permittivity of the ceramics was increased with decreasing grain size to 1.1 μm on average. However, the permittivity of the ceramics was decreased when the grain size was below 1 μm. The field emission scanning electron microscope (FE-SEM) observations revealed that the 90º domain width decreased with decreasing the grain size. By ultrawide range dielectric spectra from kHz to THz range of the BaTiO3 ceramics, the domain contribution to the permittivity was investigated. For the BaTiO3 ceramics with grain sizes over 1 μm, the dipole polarizability and the ionic polarizability were enhanced by high domain-wall density. In contrast, for the BaTiO3 ceramics with grain sizes below 1 μm, these polarizabilities were weakened.

Abstract: As any linear antennas can be considered to be comprised of a large number of dipole antenna, therefore the study of dipole antenna characteristics has a very important significance to the application of the general linear antennas. In this paper, Firstly, the radiation field of the dipole antenna is analyzed, and then the radiation field mathematic model of a specific structural antenna is established. The antenna is composed of two orthogonal half-wavelength dipoles, and the current phase of one dipole is advanced the other by 90°. According to the polarization theory of electromagnetic wave, the polarization of this antenna is discussed. The antenna pattern mathematical formula is deduced in horizontal and perpendicular plane, and the antenna pattern is given in graphics. Finally, a new method is introduced that the directivity of horizontal polarization component can be enhanced by increasing the number of antenna elements in the vertical plane, the simulation result show that this method not only enhance the energy of horizontal direction, but also restrain the radiation of other direction.

Abstract: A comparative study of the corrosion behavior of the copper-nickel-tin alloy in a nutrient–rich simulated seawater-based nutrient-rich medium in the presence and the absence of the marine bacteria was carried out by electrochemical experiments, microscopic methods. Comparing to the corresponding control samples, the electrochemical data demonstrated that the presence of the bacteria accelerated the corrosion of the alloy. Scanning electron microscopy (SEM) images revealed the occurrence of micro-pitting and intergranular corrosion underneath the biofilm on the alloy surface.

Abstract: Density functional theory plane-wave pseudopotential with the general gradient approximation (GGA) was used to investigate electronic structural properties and the bulk spontaneous polarization (Ps) of PbZr0.4Ti0.6O3. It is found that there are strong hybridizations between Ti 3d states or Zr 4d states and O 2p states, which can reduce short-range repulsion in atoms and enhance the stability of the ferroelectric phase of PbZr0.4Ti0.6O3. Compared with cubic ideal structure, the calculated internal electronic structural data indicate that the slightly distorted O6 octahedrons around the central Ti and Zr atoms change to the Ti-O5 and Zr-O5 pyramid in the optimized structure, respectively. The major contribution to the spontaneous polarization along [001] comes from the stronger interaction along the c axis between the Ti and O rather than the Zr and O ions. The Pb atom’s relative displacement of oxygen octahedral implies that the Pb-O bonding interaction is also a key factor impacting the ferroelectricity of PbZr0.4Ti0.6O3. A theoretical spontaneous polarization of 0.78 C/m2 was computed in the tetragonal PbZr0.4Ti0.6O3 along [001] direction, consistent with the single crystal experimental data.

Abstract: The three dimensional (3D) coupling model is set up for analyzing the energy reflection and absorption on the kerf using ray tracing method after the laser beam cutting nonmetallic materials with high absorptance through multiple reflections. The laser beam characterized by focused gauss beam and fresnel absorption on the kerf are taken into account. The influences of the polarization on the absorbed intensity both in the front and the two walls are also discussed. Results indicate the differences of absorptive intensity among the three polarized lights are relatively small compared to metal. Thus, the polarization has little effects on the kerf of nonmetallic materials with high absorptance. The experimental results also agree well with the theoretical analysis.

Abstract: With the aim of evaluating corrosion inhibition for various inhibitors, a new qualitative method for corrosion inhibition effect test for magnesium and magnesium alloys was developed. The change of polarization current density of AZ61 magnesium alloy in electrochemical polarization experiments in alkali aqueous solution with 5mmol/L sodium dodecylsulphate(SDS), phytic acid(PA), ethylenediamine tetraacetic acid(EDTA), p-nitro-benzene-azo-resorcinol(PNBAR), acidum tannicum(AT) or stearic acid(SA) were tested. The SEM-EDS techniques and deposition experiment method were used for further confirmation of the corrosion inhibition. The results showed that those organic compounds which could form the inhibitor-magnesium precipitation in aqueous solution could be used as corrosion inhibitors for magnesium alloys to inhibit the increase of polarization current density as well as the dissolution and oxidation of magnesium alloys effectively.