Non-uniform Configuration Research Articles

Effect of oil quality and field configuration on steep-front breakdown strength of processed pressboard

The surface and puncture strength of flat processed pressboard samples have been measured under application of steep fronted short duration pulses in uniform and nonuniform field configurations. With the latter configuration the strengths have also been measured with new, field aged and reclaimed mineral oil. Tests have also been conducted to simulate retrofilling of transformers in the field with reclaimed oil. It is shown that with the exception of tests conducted with new mineral oil, a similar strength is obtained under all of the above conditions; with new oil higher strengths are obtained.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Transverse beam combiner for ILSE

Previous heavy-ion fusion driver system studies suggest that transverse beam combining significantly reduces driver cost. In a combiner, several beams are brought together to a common transport channel which accommodates the increased line charge density. Combining intense beams increases the transverse emittance mainly due to the heating of the beam by space charge forces as the non-uniform original beam configuration becomes more uniform. The combiner itself introduces additional aberrations, which are small for the present design. Those aberrations are due to the reduced available space for the focusing electrodes and reduced clearance from the beamlets to the surrounding electrodes, thereby generating field aberrations and larger image forces. These aberrations can also lead to particle loss. We have studied a particular design of the proposed induction linac system experiment (ILSE) combiner which is a first-order achromat that tolerates a rather large fractional head-to-tail momentum tilt of ± 10%. Using a 2D particle-in-cell code we have found that ≈7% of particles are lost in the combiner. The emittance growth after the combiner is large enough so that the emittance growth due to combiner aberrations is unimportant. The scaled projection to a driver shows the growth is small enough to be tolerated. At present, methods of improving combiner design to reduce particle loss and to minimize emittance growth are being studied.

Simulations of the magnetization reversal of clustered Co-Cr particles

Micromagnetic simulations of the magnetization reversal of clusters of 9 and 25 magnetostatically coupled Co-Cr particles are presented. The magnetostatic interaction between neighbouring particles facilitates reversal. The non-uniform magnetization configuration plays an important role in this effect.

Analysis of the evanescent field coupling between a fiber and a planar waveguide using the explicit finite difference method with a nonuniform mesh

We investigate an optical waveguide system consisting of an unclad fiber core suspended at a constant distance parallel to the surface of a planar waveguide. The coupling and propagation of light in the combined system is studied using the three-dimensional explicit finite difference beam propagation method with a nonuniform mesh configuration. The power loss in the fiber and the field distribution in the waveguide are studied as a function of various parameters, such as index changes, index profile, and propagation distance, for the combined system.

Effects of Footing Location on Bridge Pier Scour

A laboratory study was conducted to investigate the effects of footing location on the depth of scour. None of the existing pier‐scour equations have provisions for accounting for nonuniform pier configurations; rather they have a single characteristic pier dimension. This study was aimed at evaluating various techniques for characterizing the effective dimensions for a pier/footing combination when both are exposed to the flow field. The following three techniques were considered in the analysis: (f) Use of the footing width as the characteristic dimension when the footing occupies more than 10% of the flow depth; otherwise, use of the pier width (10% depth switch); (2) use of a weighted pier width (weighted width technique); and (3) use of the dominant pier/footing component by making two computations with appropriate flow parameters and selecting the larger value (dominant component technique). The first technique was the Federal Highway Administration (FHWA) recommended procedure prior to this study, ...

Some aspects of array signal processing

The paper presents an overview of some important aspects of array signal processing in the context of narrowband applications. Inverse methods for solving the array signal processing problem are reviewed. Two case studies are presented, to illustrate the various issues discussed here. The first case study presents a comparison of various array signal processing algorithms; computer simulated data are used to conduct this study. The second study relates to the angle-of-arrival estimation problem in a low-angle tracking radar environment; the results presented for this case study are based on experimental data obtained by means of a sophisticated 32-element array system. Different kinds of nonuniformly spaced linear arrays are also reviewed, with particular attention given to minimum redundancy and nonredundant arrays. The tradeoffs; namely, array span and sampling gain that decide the choice of one non-uniform configuration over another, are discussed. To aid in this study, the well known Cramér-Rao lower bound (CRLB) and the newly developed Weiss-Weinstein lower bound (WWLB) are computed for the simple and yet informative case of a single source under different conditions. A novel method for the adaptive (online) control of the measurement space (and therefore the amount of information available for parameter estimation) is described. This method incorporates use of the CRLB as a component in online adjustment of the system. The paper also includes real-time processing considerations, and a review of calibration array techniques.

New degrees of freedom in resonant tunneling heterostructure devices

Lateral degrees of freedom in resonant tunneling heterostructure devices are investigated in a model which omits the usual assumption that the electric field and current density are laterally uniform. Relaxation of spatially nonuniform configurations of field and current into the usual uniform configurations is examined. For certain device parameters and operating conditions, stable nonuniform configurations are found in addition to the conventional uniform configurations. An eigenvalue criterion for stability is established. The possibility of nonuniform configurations with spatially localized oscillation is also discussed.

Analysis of Z-invariant and Z-variant semiconductor rib waveguides by explicit finite difference beam propagation method with nonuniform mesh configuration

An efficient and simple explicit finite difference beam propagation method (EFD-BPM) incorporating nonuniform mesh is described. The criteria for stability are developed, and it is shown that this algorithm is power conserving when the stability criteria are met. EFD-BPM is applied to the analysis of single and coupled semiconductor rib waveguides and its accuracy is confirmed by comparing the results with the reported results. Nonuniform mesh is found to improve the efficiency of the method significantly for the analysis of weakly guiding waveguide structures. Several coupled rib waveguide structures with curved input and output branching sections are analyzed using both three-dimensional EFD-BPM and two-dimensional finite difference BPM combined with effective index approximation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Numerical study of RF discharge caused by secondary electron emission

A numerical method is presented for studying an RF discharge caused by secondary electron emission from the electrode, i.e. the multipactoring discharge. Using this method, the precise thresholds of the electron multiplication are obtained systematically. Also, this method can be extended to a nonuniform configuration of the electrode and the applied field. For example, the simulation results are compared with typical experimental results in the previous work. Good agreement is obtained for parallel electrodes. Furthermore, an intermediate (subharmonics) mode is found between the usual resonant modes. In the case of the coaxial electrodes, the agreement was obtained when the reflection of low-energy electrons on the surface of the electrode was assumed.

A numerical analysis of submicrometer InP-transferred electron devices

A numerical technique combining the Boltzmann transport equation and a cathode mobility model has been used to simulate the nonuniform field configurations and the static and dynamic transport behavior of submicrometer InP-transferred electron devices (TEDs). Significant interrelated controlling features for the 70-230-GHz operation of these devices have been analyzed. They determine the manifestation of the current instabilities in the following ways: (1) the length has a significant effect on the velocity-field characteristics for submicrometer TEDs, and thus on the oscillation threshold as well as the upper-frequency limit for transit-time oscillations; and (2) the cathode mobility (boundary condition), doping density, and bias acting together have a dominant effect on the threshold and cutoff of the current instability. The numerical results can be used to determine the optimum efficiency and frequency of actual devices. >

Breakdown of a coaxial diode transverse to the magnetic field

It is noted that the modern development of pulsed power generators with fast energy storage systems in the range of several megajoules makes it necessary to find conditions for charge particle beam formation with the same energy characteristics. Presently, the highest parameters of electron beams (E/sub 0/=140 kJ) are obtained in coaxial diodes, with magnetic insulation. However, even in these experiments the energy transport efficiency from a storage system into the beam was only approximately 20%. One of the main reasons for low efficiency is the breakdown in the diode transverse to the magnetic field. A breakdown centrifugal instability model is described and compared with experiments. It is shown that, in order to raise the electron-beam energy in coaxial diodes it is necessary to suppress the centrifugal instability in the plasma created on the inner diode electrode. For inner cathode diodes it is advisable to use a nonuniform magnetic field configuration with the field strength increasing rapidly enough in the direction from cathode to anode. The large radius diode with uniform magnetic field also seems to be promising for this purpose. >

Enhancement of membrane transport of ions by spatially nonuniform electric fields

The influence of spatially nonuniform electric fields on the transport of ions through ion-selective membranes is investigated both experimentally and theoretically. The flux of ions is determined indirectly by following the change of pH with time. The uniformity of the field is varied with a Pt wire electrode configuration by changing the relative positions of the anode and cathode. Higher fluxes are found for the nonuniform configuration than for the uniform configuration. These results were previously predicted in a theoretical investigation which revealed the importance of nonlinearity in the transport laws. The experimental observations are found to be consistent with theoretical calculations based on the Goldman flux equation.

ICRF fundamental minority heating in inhomogeneous tokamak plasmas

A theoretical model for the investigation of the ICRF fundamental minority plasma heating scheme in tokamak configurations is developed. The wave differential operator is obtained by including in a selfconsistent manner the effects of strong wave damping, linear mode conversion and a one-dimensional non-uniform equilibrium configuration. It is found that the use of a self-consistent equilibrium distribution function yields important modifications of the ICRF wave differential operator applicable to this heating regime. In particular, the paper presents a set of new terms which are resonant at the fundamental cyclotron frequency and which ensure the self-adjointness of the resulting wave operator in the limit k‖ → 0. A numerical scheme is developed with which solutions for the ICRF electromagnetic field and the corresponding power deposition and energy flux profiles can be obtained. An extensive parametric study is carried out for a range of wave and plasma parameters illustrative of current and proposed JET operating regimes. The results are considerably different from those obtained using a WKB fast wave model. In particular, the ‘full wave’ model presented in this paper yields a percentage for the wave power absorbed by the ionic species which is much larger than the one predicted by the WKB theory. The model presented also shows that the majority species can absorb a much higher proportion of the incident wave power than previously reported. Finally, the results obtained for JET indicate that in the case of low magnetic field incidence a sizeable percentage of the launched wave energy can be reflected on the fast wave branch for values of k‖ ≤ 6 m−1 and that at higher plasma temperatures electron heating becomes appreciable.

Stability and causality in dissipative relativistic fluids

The standard theory of relativistic dissipative fluid mechanics developed by Eckart contains several undesirable features: thermal and viscous fluctuations propagate acausally; there exist generic short wavelength secular instabilities; and there is not a well posed initial value problem for rotating fluids. In this paper we examine whether the generalization of Eckart's theory developed by Israel has succeeded in eliminating these features. We first generalize Israel's theory to include the possibility of nonuniform equilibrium configurations. This generalization allows us to describe equilibrium configurations which may be rotating and self-gravitating such as neutron stars. We then evaluate the stability conditions for these fluids and compute the characteristic velocities at which perturbations propagate. Our main result is that if these fluids are stable, then the characteristic velocities are subluminal and the perturbations propagate via hyperbolic equations. Thus Israel's theory is causal for all stable fluids. In addition, there is no generic instability, and the initial value problem is well posed. In our opinion, for these reasons, Israel's theory should replace Eckart's as the standard theory of relativistic dissipative fluid mechanics.

Stability and causality in dissipative relativistic fluids: William A. Hiscock. Center for Relativity, Department of Physics, The University of Texas, Austin, Texas 78712: Lee Lindblom. Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637 and Institute of Theoretical Physics, Department of Physics, Stanford University, Stanford, California 94305

The standard theory of relativistic dissipative fluid mechanics developed by Eckart contains several undesirable features: thermal and viscous fluctuations propagate acausally; there exist generic short wavelength secular instabilities; and there is not a well posed initial value problem for rotating fluids. In this paper we examine whether the generalization of Eckart's theory developed by Israel has succeeded in eliminating these features. We first generalize Israel's theory to include the possibility of nonuniform equilibrium configurations. This generalization allows us to describe equilibrium configurations which may be rotating and self-gravitating such as neutron stars. We then evaluate the stability conditions for these fluids and compute the characteristic velocities at which perturbations propagate. Our main result is that if these fluids are stable, then the characteristic velocities are subluminal and the perturbations propagate via hyperbolic equations. Thus Israel's theory is causal for all stable fluids. In addition, there is no generic instability, and the initial value problem is well posed. In our opinion, for these reasons, Israel's theory should replace Eckart's as the standard theory of relativistic dissipative fluid mechanics.

Design parameters of four-terminal distributed thin film integrated band-reject filter

The paper presents for the first time some new results in the form of design curves associated with one band-reject (br) filter configurations of four-terminal uniform and non-uniform R-C-KR microstructures. The circuit is found to have a notch behaviour in uniform configuration and band-rejection filter characteristics in non-uniform configuration. The band-reject filter requirements are shown to be achieved by a suitable combination of parameters of the microsystem structure.

Rossby Normal Modes in Nonuniform Background Configurations. Part II. Equinox and Solstice Conditions

Abstract The existence of planetary normal modes in the presence of realistic mean fields is examined. For sufficiently large wavenumber m, or meridional index n, the response of the Rossby modes is diffused beyond identification. This is primarily a result of the Doppler shifting of mean winds and supersedes the increasing role of dissipation. Several initial modes for the first few wavenumbers should be both realizable and identifiable in typical conditions. “At least” the first three modes of wavenumber 1, the first two of wavenumber 2, and the first of wavenumber 3 should occur with periods isolated to within 12.5% of median values. The mode structures for the first four modes of wavenumbers 1, 2 and 3 are insensitive to the mean fields in the lowest two scale heights. In addition, the response of each of these is readily discernable in both equinox and solstice conditions. The modes' horizontal character is notably robust. Although the solutions typically exhibit regions where they are affected by th...

Nonuniform spin configurations in a uniaxial antiferromagnet

The low-energy spin configurations of a simple, uniaxial antiferromagnet have been determined for applied fields both above and below the critical field for the spin-flop transition. The stability of the states has been examined. It is shown that the uniform antiparallel state becomes unstable well below the critical field. The lowest-energy nonuniform configuration is described in detail for all relevant applied-field regions. Higher-energy states are also described and examined for stability. It is shown that some higher-energy states containing both anitiparallel and spin-flopped regions are locally stable.

Single-domain grain size limits for metallic iron

Theoretical examination of possible nonuniform spin configurations in metallic iron indicates that circular spin (CS) is the lowest-energy nonuniform arrangement. The upper grain size limit (d0) to single-domain (SD) behavior is thus defined by the SD to CS transition. Superparamagnetic (SP) behavior marks the lower grain size limit to the stable SD range, and the SP to SD threshold size (ds) can be determined by Néel's relaxation theory. Calculations of d0 and ds for spherical metallic iron particles at 290°K indicate that d0 ( = 173 Å) < ds ( =260 Å), and no stable SD range exists. A stable SD range does exist for prolate ellipsoids of elongation q > 1.1 but remains very constricted. For a prolate ellipsoid of q = 1.67, a stable SD range occurs between the SP critical length LS = 150 Å and d0 = 360 Å. Both d0 and ds increase with temperature, but the stable SD range decreases. The size and shape criteria for the stable SD behavior of metallic iron help to explain (1) the low SD content of lunar samples, (2) the widespread occurrence of SP behavior and viscous magnetization in lunar soils and low metamorphic grade breccias, (3) the changes in the magnetic properties of breccias during annealing, and (4) the increased SD content of shocked breccias. The narrow grain size limits for SD behavior also suggest that magnetostatic interaction between metal grains in the solar nebula is not a viable mechanism for iron-silicate fractionation.

The Boltzmann-Vlasov Equation in Or hogonal Curvilinear Coodinate System and its Application in Non-Uniform Magnetic Field

We have, derived the simple form of Boltzmann-Vlasov equation in the orthogonal curvilinear coodinate system by use of the curvature and the tortion of the coodinate axes, tried to introduce a term of the effect of non-uniform magnetic field configuration and formulated it also in a simple magnetic mirror field configuration. Moreover we have dirived a few of momentum equations from the Boltzmann-Vlasov. equation derived above. it is shown that the derived momentum equations become to well-known fluid equations of plasma if fluid approximation is satisfied. In application, we have examined the axial distribution function of collision-free plasma particles in a idealized magnetic mirror field configuration by moo of the Boltzmann-Vlsov equation in nor-uniform magnetic field.