bluuebunny/crossref_metadata_2025_split huggingface dataset:
Exchange of conserved quantities, shock loci and Riemann problems
Authors: Sever Michael 
Published: August 2002

AbstractSystems of conservation laws admitting extensions, such as entropy density/flux functions, generate related systems obtained by exchanging the extension with one of the constituent equations. Often if not always, the smooth solutions of the two systems coincide, and weak solutions of one system containing only small discontinuities are approximate weak solutions of the other. The adiabatic approximation for the Euler system illustrates the utility of this procedure.Such an exchange of conserved quantities preserves hyperbolicity and genuine non‐linearity in the sense of Lax. On the other hand, the topological structure of the shock locus of a point in phase space and the solvability of Riemann problems in the large can be strongly affected. A discussion of when and how this occurs is given here.In this paper the exchange of conserved quantities is conveniently described by a simple homotopy in an extended version of the usual ‘symmetric variables’. A dynamical system in phase space is constructed, the trajectories of which describe the Hugoniot locus of a fixed point in phase space at each state of the homotopy. The appearance of critical points for this dynamical system is identified with the alteration of the topological structure of the Hugoniot locus by the exchange of conserved quantities. Copyright © 2001 John Wiley & Sons, Ltd.
Generalized factorization for N×N Daniele–Khrapkov matrix functions
Authors: Câmara M. C. , dos Santos A. F. , Manojlović N. 
Published: August 2002

AbstractA generalization to N×N of the 2×2 Daniele–Khrapkov class of matrix‐valued functions is proposed. This class retains some of the features of the 2×2 Daniele–Khrapkov class, in particular, the presence of certain square‐root functions in its definition. Functions of this class appear in the study of finite‐dimensional integrable systems. The paper concentrates on giving the main properties of the class, using them to outline a method for the study of the Wiener–Hopf factorization of the symbols of this class. This is done through examples that are completely worked out. One of these examples corresponds to a particular case of the motion of a symmetric rigid body with a fixed point (Lagrange top). Copyright © 2001 John Wiley & Sons, Ltd.
Reliable solution of an elasto–plastic torsion problem
Authors: Hlaváček Ivan 
Published: August 2002

AbstractA variational inequality with uncertain coefficients, which are given in certain bounded intervals, is considered. The inequality corresponds to a torsion problem of an elasto–plastic orthotropic bar, when employing the Haar–Kármán principle. Two maximization problems with respect to the admissible coefficients are formulated. The solvability of continuous and approximate problems is proven and a convergence analysis is presented. Copyright © 2001 John Wiley & Sons, Ltd.
A critical look at the kinematic‐wave theory for sedimentation–consolidation processes in closed vessels
Authors: Bürger R. , Kunik M. 
Published: August 2002

AbstractThe two‐phase flow of a flocculated suspension in a closed settling vessel with inclined walls is investigated within a consistent extension of the kinematic wave theory to sedimentation processes with compression. Wall boundary conditions are used to spatially derive one‐dimensional field equations for planar flows and flows which are symmetric with respect to the vertical axis. We analyse the special cases of a conical vessel and a roof‐shaped vessel. The case of a small initial time and a large time for the final consolidation state leads to explicit expressions for the flow fields, which constitute an important test of the theory. The resulting initial‐boundary value problems are well posed and can be solved numerically by a simple adaptation of one of the newly developed numerical schemes for strongly degenerate convection‐diffusion problems. However, from a physical point of view, both the analytical and numerical results reveal a deficiency of the general field equations. In particular, the strongly reduced form of the linear momentum balance turns out to be an oversimplification. Included in our discussion as a special case are the Kynch theory and the well‐known analyses of sedimentation in vessels with inclined walls within the framework of kinematic waves, which exhibit the same shortcomings. In order to formulate consistent boundary conditions for both phases in a closed vessel and in order to predict boundary layers in the presence of inclined walls, viscosity terms should be taken into account. Copyright © 2001 John Wiley & Sons, Ltd.
Non‐linear initial boundary value problems of hyperbolic–parabolic type. A general investigation of admissible couplings between systems of higher order. Part 2: abstract quasilinear theory
Authors: Ebenfeld Stefan 
Published: August 2002

AbstractThis is the second part of an article that is devoted to the theory of non‐linear initial boundary value problems. We consider coupled systems where each system is of higher order and of hyperbolic or parabolic type.Our goal is to characterize systematically all admissible couplings between systems of higher order and different type.By an admissible coupling we mean a condition that guarantees the existence, uniqueness and regularity of solutions to the respective initial boundary value problem.In part 1, we develop the underlying theory of linear hyperbolic and parabolic initial boundary value problems. Testing the PDEs with suitable functions we obtain a priori estimates for the respective solutions. In particular, we make use of the regularity theory for linear elliptic boundary value problems that was previously developed by the author. In part 2 at hand, we prove the local in time existence, uniqueness and regularity of solutions to the quasilinear initial boundary value problem (3.4) using the so‐called energy method. In the above sense the regularity assumptions (A6) and (A7) about the coefficients and right‐hand sides define the admissible couplings. In part 3, we extend the results of part 2 to non‐linear initial boundary value problems. In particular, the assumptions about the respective parameters correspond to the previous regularity assumptions and hence define the admissible couplings now. Moreover, we exploit the assumptions about the respective parameters for the case of two coupled systems. Copyright © 2002 John Wiley & Sons, Ltd.
An optimal shape design formulation for inhomogeneous dam problems
Authors: Chakib Abdelkrim , Ghemires Touria , Nachaoui Abdeljalil 
Published: August 2002

AbstractIn this paper, the flow problem of incompressible liquid through an inhomogeneous porous medium (say dam), with permeability allowing parametrization of the free boundary by a graph of continuous unidimensional function, is considered. We propose a new formulation on an optimal shape design problem. We show the existence of a solution of the optimal shape design problem. The finite element method is used to obtain numerical results which show the efficiency of the proposed approach. Copyright © 2002 John Wiley & Sons, Ltd.
Volterra series analysis of MMIC active baluns in HEMT technology
Authors: Reina‐Tosina Javier , Crespo Carlos , Alonso José I. , Pérez Félix 
Published: August 2002

AbstractIn this paper, two active‐balun structures based in a differential pair are proposed for the LO and output port of a double‐balanced mixer. A Volterra series approach based on an appropriate nonlinear model for active devices is followed to analyze the baluns, and closed‐form expressions are obtained for the evaluation of the gain and IMD. Criteria for the selection of design parameters are proposed. Results have been compared with alternative nonlinear circuit analysis methods, showing a good correspondence. An MMIC was implemented with HEMTs, demonstrating a good performance up to 10 GHz with a low LO level and power consumption. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 31: 272–277, 2001.
Frequency tuning of a dual‐band dual‐feed PIFA antenna for future mobile communications
Authors: Karmakar Nemai C. , Heng Lee Chin , Teong Chew Boon 
Published: August 2002

AbstractA dual‐band dual‐feed planar inverted‐F antenna (PIFA) is tuned with its physical parameters. It is demonstrated that the corner truncation of the patch is less sensitive to the resonant frequency than the patch lengths, but the corner truncation has no adverse effect on the radiation characteristics of the PIFA. This new technique yields quicker convergence of design frequency than the conventional patch length only tuning. Both theoretical and measured results of the input return loss and radiation patterns are presented. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 31: 345–349, 2001.
Admittance parameter and unilateral power‐gain evaluation of GaN MESFET for microwave circuit applications
Authors: Singh Adarsh , Bose Srikanta , Gupta Mridula , Gupta R. S. 
Published: August 2002

AbstractThe admittance parameters and unilateral power gain of a nonself‐aligned GaN MESFET incorporating the parasitic elements along with gate‐length modulation are evaluated analytically in the present model. The cutoff frequency of the maximum available gain and the maximum frequency of oscillation are also determined in the model. For a GaN MESFET (4 μm×100 μm), the maximum frequency of oscillation is obtained to be about 2 GHz at zero gate bias. Using the present model, a unilateral power gain of 18 dB is predicted for the device. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 31: 387–393, 2001.
Linear transmitter for a frequency‐hopping system using an adaptive predistortion linearizer
Authors: Kang Kyeongwon , Lee Sangseol 
Published: August 2002

AbstractWe have designed a linear power amplifier for a VHF frequency‐hopping (FH) transmitter using an adaptive predistortion linearizer. We employed an analog polynomial linearizer as a predistorter. In the predistortion linearizer, the recursive least squares (RLS) algorithm is employed for the optimization process to minimize the errors between the predistorter and postdistorter output signals. The experimental results of the FH transmitter demonstrate that the spectral spreading is reduced by 10 dB. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 31: 457–460, 2001.
Finite elements and evolution programs for the CAD of broadband rectangular‐waveguideH‐plane matched loads
Authors: Monge F. J. , Esteban J. , Zapata J. 
Published: August 2002

AbstractA full‐wave CAD tool has been implemented for the design ofH‐plane rectangular‐waveguide passive circuits. The software is based on the finite‐element method and evolution programs. The tool has been employed for the design of a load, optimized for both miniaturization and robustness with respect to fabrication tolerances. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 31: 491–494, 2001.
Global modeling approach for prematched multifinger FET
Authors: Cetiner B. A. , Coccioli R. , Housmand B. , De Flaviis Franco , Itoh T. 
Published: August 2002

AbstractA scalable lumped‐element equivalent circuit of a prematched, multifinger FET cell is proposed. The model is derived using a global modeling approach that exploits both circuit and full‐wave analysis, accounting for phase delay along gate and drain manifolds. The availability of such a model is useful to perform fast performance analysis and optimization of the prematching network. © 2002 John Wiley & Sons, Inc. Microwave Opt Technol Lett 32: 174–178, 2002.
Propagation characteristics of a plane wave in an unbounded nonlocal omega medium
Authors: Laforgia Michela , Toscano Alessandro , Vegni Lucio 
Published: August 2002

AbstractIn this paper, we derive the main propagation characteristics and the polarization properties of plane waves propagating inside a nonlocal bianisotropic medium. An original condition of circular polarizability is also derived and studied. The nonlocal omega medium can, in principle, be thought of as a spreading of a large number of nonlocal omega elements in an otherwise simple isotropic dielectric host medium. A nonlocal omega element is an electrically conducting microstructure having its stem parallel to the electric field at a given point, and its loop axis parallel to the magnetic field at another point that is somewhat displaced from the first along the direction of the wave propagation. © 2002 John Wiley & Sons, Inc. Microwave Opt Technol Lett 32: 183–186, 2002.
A new approach to standard Schwarz–Christoffel formula calculations
Authors: Costamagna Eugenio 
Published: August 2002

AbstractA new approach to the computation of the Schwarz–Christoffel formula is presented, which was suggested by previous experience with various algorithms. It exploits the similarity between actual and image polygon geometries to implement singularity cancellations in a simple, yet effective way. Some results are presented for significant mapping examples, and they are briefly discussed. © 2002 John Wiley & Sons, Inc. Microwave Opt Technol Lett 32: 196–199, 2002.
Microstrip line on ground plane with closely spaced perforations—fringe fields and formulas by synthetic asymptote
Authors: Chow Y. L. , Wan K. L. , Sarkar T. K. , Kolundzija B. 
Published: August 2002

AbstractAccurate CAD formulas of a microstrip line on a ground plane with periodic perforations, closely spaced and at quasistatic frequencies, are derived (error <5%) for applications in multilayer circuits such as an LTCC package. By a novel technique of a synthetic asymptote, the formula has just one arbitrary constant and two separate fringe‐field terms, from the strip and from the perforation. The separation gives clear physical insights into the effects of fringe fields on both the capacitance and inductance. One insight is that the effective dielectric constant may be made to rise above the actual dielectric constant of the substrate with perforation. © 2002 John Wiley & Sons, Inc. Microwave Opt Technol Lett 32: 201–204, 2002.
A new characteristic impedance perturbation method for finding attenuation constants
Authors: Changhong Liang , Long Li 
Published: August 2002

AbstractA new characteristic impedance perturbation method for finding the attenuation constant α of transmission lines is presented, which not only clarifies some unclear concepts and applied limitations of the Wheeler incremental inductance rule, but which also can be extended to the TM mode transmission line in some cases. © 2002 John Wiley & Sons, Inc. Microwave Opt Technol Lett 32: 243–245, 2002.
Experimental investigations of microwave absorber with FSS embedded in carbon fiber composite
Authors: Sha Yanan , Jose K. A. , Neo C. P. , Varadan Vijay K. 
Published: August 2002

AbstractIn this paper, we present the experimental results of microwave absorbers with a frequency‐selective surface (FSS) embedded in an impedance‐graded carbon fiber (CF) composite. Samples with different FSS patterns embedded in CF composites are fabricated, and experiments are carried out to find the effects of embedded FSSs. It is found that both the FSS pattern and its location in the composite are critical for the reflection property of the sample. The results are compared with the theoretical predictions using the microgenetic algorithm (MGA), and are in good agreement. © 2002 John Wiley & Sons, Inc. Microwave Opt Technol Lett 32: 245–249, 2002.
Broadband T and shunt‐stub‐shaped microstrip‐fed slot antenna backed by a ground plane
Authors: Jang Yong‐Woong 
Published: August 2002

AbstractIn this letter, we experimentally study a T and a shunt‐stub‐shaped microstrip‐fed slot antenna backed by a ground plane. The proposed antenna has a frequency bandwidth of approximately 54% forS11≤−10 dB, centered around 2.5 GHz, with relatively good pattern characteristics. © 2002 John Wiley & Sons, Inc. Microwave Opt Technol Lett 32: 278–280, 2002.
A technique for the fast raster‐scanned motion of a small window for millimeter‐wave image acquisition
Authors: Soto José , Dávila J. A. 
Published: August 2002

AbstractHere, we propose a technique that utilizes a Nipkow disk and an integrating sphere for the fast acquisition of millimeter‐wave images. This technique has the potential for quietly achieving video frame rates. A demonstration of the principle is made in the optical region. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 32: 440–442, 2002.
Null‐forming synthesis for cylindrical patch arrays
Authors: Niemand P. , Joubert J. , Odendaal J. W. 
Published: August 2002

AbstractA synthesis method is modified to synthesize patterns with multiple nulls in an otherwise omnidirectional pattern for cylindrical microstrip patch arrays. The directive radiation pattern of a cylindrical microstrip patch is incorporated into the synthesis procedure. The effect of the number of array elements and interelement spacing is investigated. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 32: 442–446, 2002.
Fiber‐optic microdisplacement sensor based on diffraction grating
Authors: Das K. K. , Alam M. S. 
Published: August 2002

AbstractA new multimode‐fiber‐based microdisplacement sensor using a diffraction grating component is proposed. An analytical model is presented for the proposed technique. The performance of the proposed technique is verified via computer simulation and experimentation. The experimental results agree quite well with the theoretical model. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 32: 446–449, 2002.
Broadband property and time‐domain application of general transmission‐line equations on microstrip low‐pass filter
Authors: Zhong Xiaolong , Liu Yaowu , Mei Kenneth K. 
Published: August 2002

AbstractGeneral transmission‐line equations based on the theory of differential equations [1] were introduced in [2] and [3]. The equations' dispersion characteristic of a microstrip low‐pass filter is studied. The parameters L, C, α, and β of general transmission‐line equations are found to be almost invariant to frequency in the passband of the microstrip low‐pass filter. By restoring current and voltage distributions with the use of equations in both frequency and time domains, the broadband property of these equations on the microstrip low‐pass filter is evident. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 33: 123–126, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10250
Microstrip‐fed cavity‐backed slot antennas
Authors: Li Quan , Shen Zhongxiang , Teo Peng Thian 
Published: August 2002

AbstractTwo types of cavity‐backed slot (CBS) antennas fed by a microstrip line and operating at 5.8 GHz are described in this letter. One is a broadband linearly polarized CBS antenna, which can provide 34% bandwidth for a 10‐dB return loss. The other is a circularly polarized dual T‐shape CBS, which has 4% bandwidth for a 3‐dB axial ratio and a 15% bandwidth for a 10‐dB return loss. The simulated and measured results of both antennas are in good agreement. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 33: 229–233, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10283
Analysis and design of cylindrical MICs with the use of a unified nonuniform cylindrical FDTD algorithm
Authors: Shen Guoqiang , Zhou Guoxiang , Chen Yinchao 
Published: August 2002

AbstractIn this Letter a unified nonuniform cylindrical finite‐difference–time‐domain (NU‐CFDTD) algorithm is utilized for the analysis and design of cylindrical millimeter‐wave integrated circuits (CMICs). It is shown that the algorithm is efficient in coding and flexible in treating various materials and discontinuities without adding computational resources compared with the traditional FDTD method. A visual mesh generator, CylinMesh, is developed to generate nonuniform meshes and input parameter files for practical cylindrical MIC analysis and design. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 33: 256–262, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10291
Evaluation of polarization diversity schemes using dipole antennas
Authors: Kar Mohua , Wahid Parveen 
Published: August 2002

AbstractThis Letter presents analytical comparisons of properties such as output signal‐to‐interference‐plus‐noise‐ratios (SINR), correlation coefficients (ρe) and mean effective gains (MEG) for a H/V cross‐dipole scheme and a ± 45° slant dipole scheme. These polarization schemes, combined with space diversity, provide good results useful for wireless communications applications. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 33: 277–284, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10296
Characterization of the radio wave propagation over mixed land–sea paths with the use of the forward‐backward method
Authors: López Jesús Alberto , Pino Marcos Rodríguez , Obelleiro Fernando 
Published: August 2002

AbstractThe objective of this Letter is to study the propagation over a nonhomogeneous surface composed of land and sea. To tackle this study, an integral‐equation (IE) formulation plus impedance boundary conditions (IBCs) are used. In order to solve the problem raised, an efficient algorithm based on the method of moments (MoM) is employed. Numerical results show that the field strength over a mixed‐path terrain, beyond the coastline, is larger or smaller than the one over a homogeneous surface, depending on the receiver height. Besides the reception height, the effect is characterized by other parameters, such as the transmitter antenna height, the surface geometry, the frequency, and the electrical properties of the soil. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 33: 287–292, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10298
Practical double‐channel variable polarization system with short switching time
Authors: Che Wenquan , Sha Kan , Yung Edward K. N. , Wen Junding 
Published: August 2002

AbstractThe design consideration of a double‐channel variable polarization system is investigated in this Letter, and the important components in the system are introduced. In addition, the experimental results of several components and indexes of the system are presented: the polarization switching time of the double‐channel variable polarization system is 3 μs; the peak and average power capability are 14 kW and 80 W, respectively; the polarization isolation is 20 dB; the ellipticity is 1 dB. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 33: 292–294, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10299
Highly decoupled planar dipoles in an air waveguide backed by a perfect‐magnetic‐conductor plate above the earth
Authors: Je Do‐Heung , Ra Jung‐Woong 
Published: August 2002

AbstractTwo planar dipoles inside an air waveguide backed by a perfect‐magnetic‐conducting (PMC) plane are suggested as a highly isolating transmitting‐and‐receiving subsurface continuous‐wave‐radar antenna. Its coupling mechanism is shown to be the contributions of the evanescent lateral wave and the leaky wave. A design finding the optimum frequency and its bandwidth yielding the minimum mutual coupling less than −60 dB is shown. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 33: 303–306, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10302