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Polarization Direction (polarization + direction)
Selected AbstractsA geometrically and materially non-linear piezoelectric three-dimensional-beam finite element formulation including warping effectsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2008A. Butz Abstract This paper is concerned with a three-dimensional piezoelectric beam formulation and its finite element implementation. The developed model considers geometrically and materially non-linear effects. An eccentric beam formulation is derived based on the Timoshenko kinematics. The kinematic assumptions are extended by three additional warping functions of the cross section. These functions follow from torsion and piezoelectrically induced shear deformations. The presented beam formulation incorporates large displacements and finite rotations and allows the investigation of stability problems. The finite element model has two nodes with nine mechanical and five electrical degrees of freedom. It provides an accurate approximation of the electric potential, which is assumed to be linear in the direction of the beam axis and quadratic within the cross section. The mechanical degrees of freedom are three displacements, three rotations and three scaling factors for the warping functions. The latter are computed in a preprocess by solving a two-dimensional in-plane equilibrium condition with the finite element method. The gained warping patterns are considered within the integration through the cross section of the beam formulation. With respect to material non-linearities, which arise in ferroelectric materials, the scalar Preisach model is embedded in the formulation. This model is a mathematical model for the general description of hysteresis phenomena. Its application to piezoelectric materials leads to a phenomenological model for ferroelectric hysteresis effects. Here, the polarization direction is assumed to be constant, which leads to unidirectional constitutive equations. Some examples demonstrate the capability of the proposed model. Copyright © 2008 John Wiley & Sons, Ltd. [source] Double Hysteresis Loop and Aging Effect in K0.5Na0.5NbO3,K5.4Cu1.3Ta10O9 Lead-Free CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2009Dunmin Lin In this work, the double-loop-like characteristics of K0.5Na0.5NbO3+x mol% K5.4Cu1.3Ta10O9 ceramic and its relationships with the transition temperature, aging, and switching have been investigated. Our results reveal that the phase transition temperature is an important parameter determining the aging requirement for the ceramics to exhibit the double-loop-like characteristics. For a ceramic with a high transition temperature, e.g. the ceramic with x=0.75 (tetragonal,orthorhombic phase temperature ,206°C), the vacancies can migrate during the crystal transformation and settle in a distribution with the same symmetry as the crystal after the transformation. As a result, defect dipoles along the polarization direction are formed and provide restoring forces to reverse the switched polarizations, and thus producing a double polarization hysteresis (P,E) loop. On the other hand, aging is required for a ceramic with a low transition temperature, e.g. aging at 80°C for 30 days is required for the ceramic with x=1.5 (transition temperature ,175°C). Our results also reveal that the defect dipoles can be switched under a slow-switching electric field (<1 Hz) or at high temperatures (>100°C), thus leading to an opening of the double P,E loop. [source] Demonstration of high lateral resolution in laser confocal microscopy using annular and radially polarized lightMICROSCOPY RESEARCH AND TECHNIQUE, Issue 6 2009Jeongyong Kim Abstract The authors present the experimental result of improved lateral resolution in laser confocal microscopy (LCM) by using annular and radially polarized light as the input illumination of an existing LCM. The authors examined the lateral resolution of the LCM by imaging a single fluorescent bead and measuring the lateral width of the single bead profile appearing in the optical image. Compared to no aperture and linearly polarized light, the central peak of the single bead profile narrowed by ,40%, being as small as 122 nm in full width at half maximum using 405 nm laser excitation in a reflection imaging. In addition, the authors showed that radial polarization helps to preserve the circular shape of the single bead profile whereas linearly polarized light tends to induce an elongation along the polarization direction. Microsc. Res. Tech., 2009. © 2009 Wiley-Liss, Inc. [source] RF characteristics of spaceborne antenna mesh reflecting surfaces: Application of periodic method of momentsMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 4 2005Amane Miura Abstract This paper describes a numerical-analysis methodology for RF characterization of various mesh reflecting surfaces used as the reflector surface of spaceborne antennas. Two mesh reflecting surfaces, which demonstrate different polarization characteristics, are studied. Because the mesh reflecting surface has a periodic weaving structure, periodic MoM with RWG basis and testing functions is applied, which allows only one periodic cell of mesh surface to be simulated. The analysis of transmission and reflection losses indicated that Single Satin mesh was much better than Single Atlas mesh, in terms of independence of transmission or reflection loss on polarization. This is because Single Satin mesh model has denser strips than the Single Atlas mesh model. Therefore, for any polarization direction, there is always at least one strip with its axis along or nearly along the incident electric field. The methodology and results presented in this paper are useful for accurate performance prediction of mesh reflector antennas. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 365,370, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21171 [source] Lead-free piezoelectric (Na0.5Bi0.5)0.94TiO3,Ba0.06TiO3 nanofiber by electrospinningPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 9 2009Y. Q. Chen Abstract Lead-free (Na0.5Bi0.5)0.94TiO3,Ba0.06TiO3 (NBT-BT6) nanofibers were synthesized by the sol,gel process and electrospinning, and a butterfly-shaped piezoelectric response was measured by scanning force microscopy. NBT-BT6 nanofibers with perovskite phase were formed, after being cleaned at 700 °C for 1 hour, and the diameters are in the range of 150 nm to 300 nm. The average value of the effective piezoelectric coefficient d33 is 102 pm/V. The high piezoelectricity may be attributed to the easiness for the electric field to tilt the polar vector of the domain and to the increase of the possible spontaneous polarization direction. There is a potential for the application of NBT-BT6 nanofibers in nanoscale piezoelectric devices. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Complete correlation, detection loophole and Bell's theoremFORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 1 2005A. Shafiee Two new formulations of Bell's theorem are given here. First, we consider a definite set of two entangled photons with only two polarization directions, for which Bell's locality assumption is violated for the case of perfect correlation. Then, using a different approach, we prove an efficient Bell-type inequality which is violated by some quantum mechanical predictions, independent of the efficiency factors. [source] Shear wave splitting changes associated with the 2001 volcanic eruption on Mt EtnaGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2006Francesca Bianco SUMMARY The time delays and polarizations of shear wave splitting above small earthquakes show variations before the 2001 July 17,August 9 2001 flank eruption on Mt Etna, Sicily. Normalized time delays, measured by singular value decomposition, show a systematic increase starting several days before the onset of the eruption. On several occasions before the eruption, the polarization directions of the shear waves at Station MNT, closest to the eruption, show 90°-flips where the faster and slower split shear waves exchange polarizations. The last 90°-flip being 5 days before the onset of the eruption. The time delays also exhibit a sudden decrease shortly before the start of the eruption suggesting the possible occurrence of a ,relaxation' phenomena, due to crack coalescence. This behaviour has many similarities to that observed before a number of earthquakes elsewhere. [source] The Geysers geothermal field: results from shear-wave splitting analysis in a fractured reservoirGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2005Maya Elkibbi SUMMARY Clear shear-wave splitting (SWS) is observed in 1757 high signal-to-noise ratio microearthquake seismograms recorded by two high density seismic arrays in the NW and the SE Geysers geothermal fields in California. The Geysers reservoir rocks within the study area are largely composed of lithic, low-grade metamorphism, well-fractured metagraywackes which commonly lack schistosity, warranting the general assumption that shear-wave splitting here is induced solely by stress-aligned fracturing in an otherwise isotropic medium. The high quality of observed shear-wave splitting parameters (fast shear-wave polarization directions and time delays) and the generally good data spatial coverage provide an unprecedented opportunity to demonstrate the applicability and limitations of the shear-wave splitting approach to successfully detect fracture systems in the shallow crust based on SWS field observations from a geothermal reservoir. Results from borehole stations in the NW Geysers indicate that polarization orientations range between N and N60E; while in the SE Geysers, ground surface stations show polarization directions that are generally N5E, N35E-to-N60E, N75E-to-N85E, and N20W-to-N55W. Crack orientations obtained from observed polarization orientations are in good agreement with independent field evidence, such as cracks in geological core data, tracer tests, locally mapped fractures, and the regional tectonic setting. Time delays range typically between 8 and 40 ms km,1, indicating crack densities well within the norm of fractured reservoirs. The sizeable collection of high resolution shear-wave splitting parameters shows evidence of prevalent vertical to nearly vertical fracture patterns in The Geysers field. At some locations, however, strong variations of SWS parameters with ray azimuth and incident angle within the shear-wave window of seismic stations indicate the presence of more complex fracture patterns in the subsurface. [source] Polarized Raman microspectroscopy on intact human hairJOURNAL OF BIOPHOTONICS, Issue 5 2008K. R. Ackermann Abstract Polarization-resolved Raman microspectroscopy with near-infrared laser excitation was applied to intact human hair in order to non-invasively investigate the conformation and orientation of the polypeptide chains. By varying the orientation of the hair shaft relative to the polarization directions of the laser/analyzer, a set of four polarized Raman spectra is obtained; this allows to simultaneously determine both the secondary structure of hair proteins and the orientation of the polypeptide strands relative to the axis of the hair shaft. For the amide I band, results from a quantitative analysis of the polarized Raman spectra are compared with theoretically expected values for fibers with uniaxial symmetry. Based on the polarization behavior of the amide I band and further vibrational bands, a partial ordering of ,-helical polypeptide strands parallel to the hair shaft can be concluded. We suggest that this microspectroscopic approach may be used for human hair diagnostics by detecting structural or orientational alterations of keratins. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||