Coaxial Layers Research Articles

高温超伝導コイルにおける交流電圧印加時の熱気泡挙動と電気絶縁環境

This paper deals with bubble behavior in pool-cooled HTC superconducting coil, which is developed for superconducting transformers to understand the state of the insulation medium in the coil at the quenching condition and to find an effective suppression method of vicious bubble effects on electrical insulation and cryogenic cooling. The tested coil system immersed in liquid nitrogen consisted of two coaxial coil layers wound on FRP frames and a cylindrical ITO film electrode deposited on the outerside of a glass cylinder by ion sputtering, and the axis of electrode system was set vertically. The experiments show that bubbles generated thermally by a heater mounted in the superconducting wire leave from the wire discretely at lower applied voltages, but they turn bubble columns locked in cooling channels at higher applied voltages under the layer-to-layer insulation condition, i.e., boiling on the wire covered with FRP tape changes from nuclear boiling to film boiling by the application of a high electric field to the coolant. At the turn-to-turn insulation condition, bubble coagulation phenomena appear near the inner surface of the glass cylinder, and the coagulated bubbles spout through the cooling channel between coil layer and glass wall. The formation of vapor locking by an electric field can be minimized or controlled by making an inclined path crossing over the barrier between coil turns or pressurizing liquid nitrogen to a subcooled state.

Pressurizing and sub-cooling effects on electrical breakdown of LN/sub 2/ in modeled HTS coils

Pressurizing and sub-cooling of liquid nitrogen are considered to have advantageous aspects in electrical insulation and the critical current in high temperature superconducting (HTS) coils. This paper deals with experimental studies on bubble behavior and partial breakdown (PBD) characteristics in a simulated electrode system of HTS coils immersed in pressurized liquid nitrogen, following our previous reports with saturated liquid nitrogen at atmospheric pressure. The tested electrode system consists of a coaxial coil layer to a cylindrical electrode with an insulation barrier and spacers. A heater is mounted inside the coil electrode to generate boiling which appears on quenched superconducting coils. Liquid nitrogen is pressurized to 0.2 MPa under constant temperature of /spl sim/77 K. The experimental results show that the partial discharge (PD) voltage is affected markedly by the bubble behavior which depends on the applied pressure to liquid nitrogen. Pressurization suppresses bubble growth in the insulation space and increases the inception voltage of PD. The charge quantity associated with a single PD at a given applied voltage increases with the applied pressure, and deterioration of solid insulation such as spacers and barriers is accelerated compared to that at atmospheric pressure if the PBD occurred.

Analyses of axisymmetric waves in layered piezoelectric rods and their composites.

An exact treatment of the propagation of axisymmetric waves in coaxial anisotropic assembly of piezoelectric rod systems is presented. The rod system consists of an arbitrary number of coaxial layers, each possessing transversely isotropic symmetry properties. The treatment, which is based on the transfer matrix technique, is capable of deriving the dispersion relations for a variety of situations. These include the case of a single rod system that is either embedded in an infinitely extended solid or fluid host or kept free. The procedure is also adapted to derive approximate solutions for the cases of a periodic fiber distribution in a matrix material, which model unidirectional fiber-reinforced composites. The results are numerically illustrated for a widely used piezoelectric-polymer composite. It is seen that piezoelectric coupling can significantly change the morphology of the dispersive behavior of the composite.

Electron spectrum in a quantum superlattice with cylindrical symmetry

A quantum superlattice with axial symmetry, a heterostructure in which two semiconductor materials in the form of coaxial wires with a nanosize cross section are in contact with one another and form a periodic structure in the radial direction, is studied. It is shown that the electron energy spectrum consists of alternating allowed and forbidden bands. The electron dispersion law is studied for different values of the period of the potential, thicknesses of the semiconductor layers, and radius of the inner crystal of the system. It is shown that the coherent electron effective mass of the quantum superlattice is a tensor: The longitudinal component is close in value to the electron effective mass of the semiconductor material characterizing the quantum well of the superlattice and the radial component depends strongly on the period of the potential, the thicknesses of the coaxial semiconductor layers, and the core radius of the heterosystem, taking on positive or negative values in different allowed bands.

NOISE FROM SUPERSONIC COAXIAL JETS, PART 2: NORMAL VELOCITY PROFILE

Instability waves have been established as noise generators in supersonic jets. Recent analysis of these slowly diverging jets has shown that these instability waves radiate noise to the far field when the waves have components with phase velocities that are supersonic relative to the ambient speed of sound. This instability wave noise generation model has been applied to supersonic jets with a single shear layer and is now applied to supersonic coaxial jets with two initial shear layers. In this paper the case of coaxial jets with normal velocity profiles is considered, where the inner jet stream velocity is higher than the outer jet stream velocity. To provide mean flow profiles at all axial locations, a numerical scheme is used to calculate the mean flow properties. Calculations are made for the stability characteristics in the coaxial jet shear layers and the noise radiated from the instability waves for different operating conditions with the same total thrust, mass flow and exit area as a single reference jet. The effects of changes in the velocity ratio, the density ratios and the area ratio are each considered independently.

NOISE FROM SUPERSONIC COAXIAL JETS, PART 3: INVERTED VELOCITY PROFILE

The instability wave noise generation model is used to study the instability waves in the two shear layers of an inverted velocity profile, supersonic, coaxial jet and the noise radiated from the dominant wave. The inverted velocity profile jet has a high speed outer stream surrounding a low speed inner stream and the outer shear layer is always larger than the inner shear layer. The jet mean flows are calculated numerically. The operating conditions are chosen to exemplify the effect of the coaxial jet outer shear layer initial spreading rates. Calculations are made for the stability characteristics in the coaxial jet shear layers and the noise radiated from the instability waves for different operating conditions with the same total thrust, mass flow and exit area as a single reference jet. Results for inverted velocity profile jets indicate that relative maximum instability wave amplitudes and far field peak noise levels can be reduced from that of the reference jet by having higher spreading rates for the outer shear layer, low velocity ratios and outer streams hotter than the inner stream.

Mathematical model of the dynamics of porous elastoplastic media saturated with liquid upon electric discharge in warer

A system of equations was devised describing in bound statement the processes in the channel of an electric discharge, a liquid, and elastoplastic solids with finite dimensions, including porous media saturated with liquid. An algorithm for solving the obtained system of equations was worked out, and it was tested. Investigated was the dynamics of a porous medium saturated with liquid that consisted of a number of coaxial cylindrical layers with different physicomechanical characteristics and was subjected to a pulsed load.

General study of axisymmetric waves in layered anisotropic fibers and their composites

A unified general treatment of the propagation of longitudinal waves in coaxial anisotropic assembly of fiber systems is presented. The fiber system consists of an arbitrary number of coaxial layers, each possessing transversely isotropic symmetry properties, that are either perfectly attached at their interfaces or bonded via imperfect interface zones. The single fiber system is either embedded in an infinitely extended solid or fluid host or kept free. As a natural extension of the single fiber case, uniformly distributed fiber systems in a matrix material, which model unidirectional fiber-reinforced composites, are also studied. All solutions are derived in the form of dispersion relations using the transfer matrix technique. Imperfect interface zones are modeled by degenerate transfer matrices reflecting jumps in the field variables of the neighboring layers. The results are numerically illustrated for a wide range of applications.

Field analysis of a tape helix with embedded bio-media for microwave hyperthermia.

A general field theory has been developed for the EM wave propagation on a tape helix with embedded bone, muscle, fat and skin co-axial biological layers in a multilayered dielectric environment. The electric and magnetic fields in every biological/dielectric layer is formulated in terms of complex modified Bessel functions and complex exponentials, i.e. in terms of complex radial and axial propagation constants for the azimuthally symmetric and higher order spatial harmonics. A complete dispersion relation is derived by substituting the field expressions into as many boundary conditions as there are unknown constants. The dispersion relation is numerically solved for the complex axial propagation constant and hence for the phase velocity and depth of penetration for n = 0 and 1 modes propagating along three dielectric loaded tape helices of different dimensions at several spot frequencies within the range of 300 MHz to 3.00 GHz. The results for variations in normalized phase velocity and depth of penetration with frequency for these modes separately and for the combined mode are presented. The patterns of specific absorption rate (SAR) across the cross-section of the dielectric loaded helices are also computed and presented. The variations with frequency, and cross-sectional dimension of the helix of the normalized phase velocity, axial depth and SAR across the cross-section of each of the helices are discussed for the modes considered. The theoretical results for the propagation constant obtained by using a tape helix model for the azimuthally symmetric mode propagating along a wire helix loaded with a phantom muscle sample of known dielectric constant are compared with experimental results and with those obtained theoretically employing a sheath helix model at 2.45 and 2.55 GHz. The use of a helix for human limb hyperthermia is also discussed.

Skin effect in a high-T c flux-flow superconducting wire

As a candidate for a low ac-loss bulk power transmission cable, a high-Tc superconducting wire in a flux-flow state, which is called a flux-flow superconductor here, is theoretically studied. The electrodynamics of such a wire in a self-excited ac field is formulated, where the governing equation is nonlinear because of the magnetic field dependence of the flux-flow resistivity. The current distribution inside the wire and the ac loss are numerically calculated to investigate the influence of the skin effect in such a nonlinear system. The ac loss is enhanced by the skin effect, and it is found that the amount of this enhancement can be scaled by a nondimensional parameter which depends not only on the frequency and the radius of the wire but also on the peak current. As a means to reduce the ac loss in the presence of the skin effect, it is shown to be effective to divide the wire into many coaxial layers and to set the current distribution between the layers artificially. It is also shown that, if an optimized current distribution is settled between the layers, the ac loss can be reduced to a smaller value than that for a nondivided wire neglecting the skin effect.

Disclinations in Heterogeneous Small Particles

AbstractElastic effects in elastically inhomogeneous pentagonal small particles are analyzed. Two continual elastic models are applied and considered in detail: a wedge Frank disclination in an infinite elastic cylinder consisting of two coaxial layers of different phases and a Marks‐Yoffe disclination in an elastic sphere consisting of two concentrical layers of different phases. The corresponding boundary problems are solved. It is shown on the basis of these solutions that the disclination–interface elastic interaction stimulates interface migration and hence may either promote or retard phase transformation processes. Disclination elastic fields may initiate dislocation generation at the interface and cause a point‐defect diffusion flux resulting in an inhomogeneous distribution of impurities in the particle.

Solitons in a ring superlattice

We consider the propagation of electromagnetic solitons in a ring superlattice formed by the successive deposition of coaxial ring-shaped layers lying in parallel planes. In contrast to a rectilinear (infinite) superlattice, in which either one soliton (a single solution) or an infinite number of solitons (fluxon solution), any finite number of equidistant solitons is possible in a ring superlattice. We calculate the constant component of the electric field along the axis of the superlattice and the density of the current of electron drag by solitons (“solitonelectric current”).

Calculations of potential distributions produced by implanted electrodes in a man model by finite elements

The finite-element (FE) method is used to analyze and determine the potential distribution produced by implanted stimulating electrodes used in conjunction with an implanted defibrillator. These electrodes are used to deliver an energy shock to halt ventricular fibrillation during fatal arrhythmias in human beings. The FE solution was obtained by solving the Laplace equation using a Galerkin procedure. An infinite cylindrical model having three coaxial layers of tissue with two electrodes was used to show preliminary results of the FE model. An analytical procedure was developed and used to validate the FE results. The overall objective of this study is to develop a computer model for the study of defibrillation fields. This model can be used to estimate the potential distribution and potential gradients on the heart for various electrode sizes and configurations for a given shock strength. The most promising variation of these defibrillation-electrode configurations can be chosen for experimental testing in laboratory animals and possibly in human beings. >

The design and the construction of the scintillating fiber detector for the UA2 experiment

The scintillating fiber detector (SFD) is a key part of the upgraded UA2 experiment. It includes 60000 scintillating fibers 1 mm in diameter and 2 m long, arranged in 24 coaxial layers fitting in a cylindrical space from 760 to 880 mm in diameter around pp intersection. The fiber layers are arranged in eight stereo triplets. Each one contains one fiber set parallel to the axis and two others inclined at an angle of +or-20 degrees on the average. The SFD has two separate functions: The inside layers give a precise localization of the particles; the outside layers initiate the electromagnetic showers by conversion in a lead sheet 1.5-radiation-lengths thick. Each fiber is optically tested; when not rejected, its scintillating efficiency and attenuation length are recorded. The position of every fiber is measured and recorded, and each fiber is individually read out.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High-resolution electron microscopic study of the structure of filamentary carbon on iron and nickel catalysts

Direct high-resolution electron microscopy was employed to study the structure of filamentary carbon in carbon-containing iron, nickel and Ni/Al 2O 3 catalysts. Metal particles initiate the growth of filaments with hollow channels. The filaments are composed of coaxial (002) layers of graphite which are slightly out of parallel to the filament axis. Graphite is in contact with the metal surface through both (002) basal and side planes. In a series of cases there are thin graphite partitions within a hollow channel. Filamentary carbon formed on highly dispersed nickel particles (2–4 nm in size) on Ni/Al 2O 3 catalysts has a strongly disordered structure. The mechanism of the growth of filamentary carbon is discussed in detail.

Anisotropic Layered Absorbers on Cylindrical Structures

ABSTRACT A curved structure consisting of an imperfectly conducting circular cylinder coated by any number of coaxial thin anisotropic layers separated by isotroplc regions of different materials is considered. Each thin anisotroplc layer is represented by a sheet with an anisotropic Jump Impedance. Thus, the structure is a generalization to the anisotropic case of Jaumann absorbers on curved surfaces. For a normally incident and obliquely polarized plane wave, the scattered field is determined via a chain-matrix algorithm. An optimization procedure is developed to minimize the radar cross section over an assigned frequency band by varying the geometric and electromagnetic parameters of the structure. Numerical results based on this design procedure are presented and discussed.

Propagation on a Sheath Helix in a Coaxially Layered Lossy Dielectric Medium (Short Paper)

Radial and axial dependence of the azimuthally symmetric fields in each coaxial layer may be expressed in terms of modified Bessel functions and complex exponentials, respectively.

Three Dimensional Electro-magnetic Field Diffusion in Multilayer Cylindrical Structures

The problem of the magnetic field diffusion through cylindrical structures is considered. An analytic solution is given for the problem of diffusion, through any number of resistive coaxial layers, of the three components of a quite general input vector magnetic field assigned on a boundary cylindrical surface. The limitations on the class of input functions (or more generally distributions) are the existence of the double space Fourier transform and the time Laplace transform; this makes the solution suitable for studying the transient-state behaviour in cylindrical structures of finite or infinite length.

Increased cable ampacity using multiple coaxial conductors and inductive compensation

Temperature buildup due to resistive losses in the conductor may limit the current capacity (ampacity) of a cable. One method for increasing cable capacity is to reduce joulean heating by using two or more coaxial conductors in a single cable to carry the desired current. To distribute the current among several concentric layers, inductive compensation in the form of internal transpositions or series connected reactors is required. Due to the geometrical arrangement of the conductors, additional eddy losses are induced by an alternating magnetic field acting on the outer layers of the conductor. A general result is obtained for the ac resistance of a multiple conductor cable, incorporating the proximity effect of the adjacent conductors. It is shown that resistive losses in the cable can be minimized by correctly choosing the thickness (radial build) of each layer. To illustrate the mathematical results, a simple example comprising two coaxial layers of conductor is presented. The example shows that lower losses (in comparison with a single layer cable of the same radius) can be obtained by using two coaxial layers in conjunction with inductive compensation. The results of this analysis should be applicable to gas-insulated (SF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> ) conductors which must carry large continuous currents.

Cytoplasmic streaming inParamecium

Certain species ofParamecium demonstrate rotational cytoplasmic streaming, in which most cytoplasmic particles and organelles flow along permanent route, in a constant direction. By means of novel methods of immobilization, observation and recording, some dynamic properties of cytoplasmic streaming have been described. It was found that the velocity profiles of coaxial layers of cytoplasm have a (parabolic) paraboidal shape and the mean output of cytoplasm flow in different examined zones of streaming is constant. As the consequence of randomly distributed elementary propulsion units within the cytoplasm, particles, which serve as markers of movement, exhibit movements of a saltatory nature; this form of movement is seen inParamecium streaming only in cases of error due to polarization of the saltating particles. Interaction of actin filaments and myosin is likely to occur under specific conditions in microcompartments of cytoplasm where local solations are generated eventually leading to contractions which might propagate on gelated neighbouring areas. Places of elementary contractions are scattered. Therefore the motile effect appears as streaming. Rotational cytoplasmic streaming inParamecium may serve as a convenient model for the study of the dynamics and function of cytoplasmic motility.