Showing papers by "Applied Science Private University published in 1989"

Magnetoresistance of c-axis-oriented epitaxial YBa2Cu3O7-x films above Tc.

Abstract: Magnetoresistance in high-quality single-crystal films of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{x}}$ studied in a temperature range ${T}_{c}$\ensuremath{\lesssim}T\ensuremath{\lesssim}210 K is presented for magnetic field configurations both parallel and perpendicular to the conducting ab plane. The data are analyzed in terms of recent theories of superconducting fluctuations considering both orbital and Zeeman effects in Aslamazov-Larkin and Maki-Thompson terms. From the analysis, the phase-breaking time of carriers is determined to be ${\ensuremath{\tau}}_{\ensuremath{\rho}}$=(1\ifmmode\pm\else\textpm\fi{}0.1)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}13}$ sec at 100 K with a T dependence of 1/${\ensuremath{\tau}}_{\ensuremath{\rho}}$\ensuremath{\propto}${T}^{1\mathrm{\ensuremath{-}}2}$. ${\ensuremath{\xi}}_{c}$(0)=1.5\ifmmode\pm\else\textpm\fi{}0.5 A\r{} and ${\ensuremath{\xi}}_{\mathrm{ab}}$(0) =11.5\ifmmode\pm\else\textpm\fi{}0.5 A\r{} are also derived for the inter- and intralayer coherence lengths.

Advanced techniques for automatic finite element meshing from solid models

Abstract: A systematic analysis and evaluation of algorithms for automatic meshing from solid models is attempted. Focusing on algorithms that can be integrated into existing solid-modelling-based CAD systems, only three families of algorithms have been included: element extraction, domain triangulation, and recursive spatial decomposition. Algorithms in these families are particularly important because first, they tend to satisfy more closely the conditions for genuine automatic operations, second, they have been shown to be applicable to 3D (solid) domains, and third, they are well documented. A short discussion of expert systems dealing with finite element mesh generation concludes this paper.

Twisting of the Human Back in Forward Flexion

Abstract: This paper addresses the role of torsion in the production of spinal injury and in particular the possibility of injury resulting from torsion combined with flexion. The back movement of 16 normal male subjects was measured using a non-invasive, three-dimensional measurement system for assessing spinal mobility, the opto-electronic CODA-3 scanner. Measurements were made of the ability to twist the back while standing upright and in two flexed postures. Rotational ability was shown, in general, to be increased in a flexed posture, presumed to be due to an opening of the lumbar zygapophysial joints. This suggests that twisting in a flexed posture could be a mechanism for intervertebral disc injury.

Appraisal of ground vibration from civil engineering construction

Abstract: Amplitude and style of ground vibration from two types of pile driving — vibrodriver (periodic) and drophammer (transient) — are considered for the analysis of deformation in a portal frame structure. It is argued that the three-dimensional character of the vibration should be determined in the form of a resultant vector and this requires the measurement of vibration in three directions at right angles together with information on the sense of the motion along each orthogonal axis of vibration. Such resultant vector data during the period of vibration are best processed and presented in the style of a suite of hemispherical projections that comprise upper and lower hemisphere forms, respectively embodying components of upward and downward vibrational motion. It is shown that analysis for the dynamic stability of a simple block foundation is assisted by reference to the hemispherical projection representation and by the use of ground surface acceleration data.

Critical Field Anisotropy in “2K-Superconducting State” of Organic Superconductor β-(BEDT-TTF)2I3

Abstract: The anisotropy of the upper critical field H c2 has been measured at ambient pressure on a layered organic superconductor β-(BEDT-TTF) 2 I 3 both in the states before and after annealing at 109 K for 120 hours. By annealing, the critical temperature T c increases from 1.4 to 2.08 K, while the H c2⊥plane increases and the anisotropy, H c2//plane / H c2⊥plane , decreases. The angular dependences of H c2 for both states are explained in terms of the effective mass model. It is clarified that the enhanced T c which is ascribed to the annealing-induced configurational orderings of ethylene groups is closely related to the enhanced effective mass in the basal plane.

The effect of aluminium on the electrical and mechanical properties of BaTiO3 ceramics as a function of sintering temperature

Abstract: The effect of aluminium additions on the mechanical behaviour of BaTiO3 positive temperature coefficient of resistance ceramics sintered in air at temperatures ranging between 1220 and 1400° C has been investigated. Tensile strength has been measured indirectly by the diametral compression of lapped discs using concave loading anvils. Values of ∼ 85 and ∼ 110 MPa for samples fired near their optimum sintering temperature were determined for two batches of material, the latter of which contained additions of Al2O3 (0.55 mol%). Strength did not vary systematically with grain size and appeared to be controlled by near surface defects. The size of these cavities, which were generally crescent shaped, was consistent with the material having a bulk fracture toughness of ∼1.3 MPam1/2. The higher mechanical strength of samples which contained Al2O3 additions was attributed to the enhanced “healing up” of these cavities by the liquid phase giving a smaller inherent critical defect size rather than by increasing the bulk toughness of the ceramic.

Some Remarks on Critical Phenomena of Fluid Metals

Abstract: Critical phenomena of fluid metals are studied by observing the potential range of effective ion-ion interaction in their liquid phases. This is done by two different methods. First, the Fourier transform of March's potential with a cutoff is calculated. Secondly, by means of quantum mechanical perturbation theory, the effective potential is derived and discussed within the lowest order approximation for the electronic dielectric function. Both methods yield the result that the effective potential is of short-range from a viewpoint of critical phenomena. On the basis of ion-ion interaction obtained by the second method, a scaling form for the critical temperature is derived and examined by the use of existent experimental data.

Topologically independent state estimation: part 1 — theory and conclusions

Abstract: The paper develops a novel method for the estimation of the voltage magnitudes and phase angles at the nodes of an interconnected electric power system. The proposed algorithm decomposes the state estimation problem into four sets of linear equations. The first set of linear equations defines the estimates of the active power flows throughout the system in terms of the power flow measurements, the power flow losses in the transmission lines and Kirchoff's first law, similarly the second set defines the reactive power flows through the system. The third set defines the square of the estimates of the voltage magnitudes at all the nodes in the system in terms of the voltage magnitude measurements and the voltage drops across the transmission lines and the fourth set defines the estimates of the phase angles in a similar way to those of the voltage magnitude except that an addtional equation is required which defines the reference phase angle. The solution of the four sets of linear equations is achieved by sparse linear programming. The proposed algorithm is able to operate at the busbar level and it treats the bus couplers in a similar fashion to the transmission lines, however they are deemed to have zero impedance. This feature combined with the excellent bad data rejection property of linear programming methods results in a robust state estimation algorithm which is also able to identify and correct switch status measurement errors.