bluuebunny/crossref_metadata_2025_split huggingface dataset:
The computer‐aided design of microwave matching networks
Authors: Sussman‐Fort Stephen E. 
Published: July 2007

AbstractMatching networks, as used between the consecutive stages of an amplifier to manage the transfer of power between the complex source impedance, the active devices, and the load, continue to be of importance, particularly in microwave systems. Synthesis techniques for these networks have evolved from the classical theory to novel numerical approaches that yield significant practical advantages. We review here several well‐known design methods, including the classical derivation, sloped‐approximation synthesis, and the real‐frequency technique. Also considered are enhancements and variations of these methods. Furthermore, we describe the iterated analysis approach, which appears to provide the greatest design flexibility, efficiency, and accuracy to date. Examples are given which illustrate the relative merits of some of the more modern computer‐assisted techniques. Finally, we discuss ideas for further research in the area of matching network synthesis.
Synthesis of equivalent circuits for inductive strips in homogeneous finline: W/b = 1
Authors: Knorr Jeffrey B. 
Published: July 2007

AbstractThis article describes a procedure for synthesizing equivalent circuits for inductive strips in homogeneous finline with W/b = 1. Values of strip scattering coefficients predicted by the circuit model are shown to be in excellent agreement with the scattering coefficients predicted by a spectral domain electromagnetic model.
Direct synthesis of distributed lossless networks with application to microwave amplifier design
Authors: Julien N. , Mollier J. C. 
Published: July 2007

AbstractThe Simplified Real‐Frequency Method, initiated by Carlin and Yarman in 1982, has rapidly become the most powerful one among the available numerical methods for solving singleor double‐matching problems. So far it has been applied successfully to the synthesis of multistage microwave amplifiers, but the equalizers contained inductors and capacitors only. This article describes the extension of that technique to the direct synthesis of low‐pass and high‐pass distributed matching networks. The main interest of such an extension is to avoid using equivalences between lumped and distributed elements which are not valid in a wide frequency range. In addition, technological constraints are taken into account earlier in the synthesis. Examples are given of bipolar or field‐effect transistor amplifiers which show that LIMDSYN, our in‐house software, is an efficient tool for linear microwave circuit design with distributed elements.
Analysis of discontinuities in a grounded slab waveguide by combination of finite‐element and boundary‐element methods
Authors: Hirayama Koichi , Koshiba Masanori 
Published: July 2007

AbstractA combined approach of the finite‐element and boundary‐element methods is formulated for the analysis of arbitrarily shaped discontinuities in a grounded slab waveguide. In this approach, the discontinuity region is divided into two regions. One is a finite region with arbitrary inhomogeneities; the other is a semi‐infinite and homogeneous region. The finite‐element and the boundary‐element methods are applied to the former and the latter regions, respectively, Also, analytical solutions in which both the guided and the radiation modes are taken into account are used for uniform waveguide regions connected to the discontinuity region. To show the validity and usefulness of this approach, computed results are given for several kinds of discontinuities, and some of them are compared with theoretical results previously published. © 1992 John Wiley & Sons, Inc.
An analytical FET model including overshoot and surface effects
Authors: Nevermann P. , Wolff I. 
Published: July 2007

AbstractA new approach for physical one‐dimensional FET modeling is presented, which is based on an analytical velocity overshoot approximation. As an application, an improved description of short‐channel GaAs‐MESFETs is shown. This simulation is equivalent to the use of a saturation velocity, which depends not only on gate length but also on bias. The presented approach is based on a new criterion subdividing the channel, which may also be used in simulation of other types of FETs. A comparison of the proposed model with experimental data of the DC behavior and numerical results shows the necessity of taking surface effects and substrate currents into account. © 1993 John Wiley & Sons, Inc.
Analysis of strip‐line circuit based on planar circuit model and planar circuit equations (invited review article)
Authors: Hsu Jui‐Pang 
Published: July 2007

AbstractStrip‐line circuits at relatively higher frequencies can be considered as two‐dimensionally extended circuits rather than one‐dimensional transmission‐line circuits. Hence, the stripline circuit can be modeled as a parallel‐plate planar circuit. In this article, the following topics are reviewed and described based on the results of many researchers: (1) how to model the strip‐line circuit to a parallel‐plate waveguide circuit, which leads to a parallel‐plate planar circuit; (2) how to analyze the strip‐line modeled parallel‐plate waveguide circuit based on planar circuit equations and conventional circuit theory where mode voltage and mode current are properly defined—especially how to construct the circuit equations after dividing the planar circuit into parallel‐plate waveguides and planar junctions, and giving the corresponding the mode characteristic impedance and mode impedance; and (3) the practical analysis of a stub‐type lowpass filter and branch‐line 3‐dB hybrid with the corresponding experimental results. The good agreement between the calculated and measured results demonstrates the validity of the present method of analysis. © 1993 John Wiley & Sons, Inc.
A practical design procedure for circularly polarized printed arrays using high frequency CAE
Authors: Naito Motoyuki , Ito Koichi , Matsuzawa Shin‐Ichiro , Takada Jun‐Ichi 
Published: July 2007

AbstractA practical design procedure for a circularly polarized printed array antenna composed of strip dipoles and slots (CP‐PASS) is presented. CP‐PASS is a kind of series‐fed array, and the equivalent circuit model of CP‐PASS is simplified to be suitable for a computer‐aided design (CAD) package. Some experimental results of a new strip element excited by a stripline and a 9‐element set CP‐PASS are also presented.
An Efficient Method to Calculate the Sommerfeld Integrals Concerning a Microstrip Antenna in Stratified Media: Extension of Discrete Complex Image Theory without the Optimization Process
Authors: Xiaowen Xu , Shizhi Li 
Published: July 2007

AbstractDiscrete complex image theory (DCIT) without the optimization process is used in the calculation of some Sommerfeld integrals (SI) involved in the problem of a microstrip antenna covered with a layer of medium. By comparison to the results of numerical integration method (NIM), it is proved that this DCIT not only has very high efficiency but also has rather satisfying accuracy so long as the proper spatial quasi‐static images (SQSI) are found. Special effort is made to the extraction of the above‐mentioned SQSI, and the analytic expressions of them are presented for the particular SI discussed here. The computation time of DCIT and that of NIM are compared to each other with microcomputer AFTI486, and the result shows that DCIT is several hundred times faster than NIM in the calculation of SI.
Endotoxemia causes a paradoxical intracellular pH recovery in exercising rat skeletal muscle
Authors: Giannesini Benoît , Izquierdo Marguerite , Dalmasso Christiane , Fur Yann Le , Cozzone Patrick J. , Verleye Marc , Guern Marie‐Emmanuelle Le , Gillardin Jean‐Marie , Bendahan David 
Published: July 2007

AbstractIn resting skeletal muscle, endotoxemia causes disturbances in energy metabolism that could potentially disturb intracellular pH (pHi) during muscular activity. We tested this hypothesis using in situ 31P‐magnetic resonance spectroscopy in contracting rat gastrocnemius muscle. Endotoxemia was induced by injecting rats intraperitoneally at t0 and t0 + 24 h with Klebsiella pneumoniae endotoxin (lipopolysaccharides at 3 mg/kg) or saline vehicle. Muscle function was investigated strictly noninvasively at t0 + 48 h through a transcutaneous electrical stimulation protocol consisting of 5.7 minutes of repeated isometric contraction at 3.3 HZ, and force production was measured with an ergometer. At rest, endotoxin treatment did not affect pHi and adenosine triphosphate concentration, but significantly reduced phosphocreatine and glycogen contents. Endotoxemia produced both a reduction of isometric force production and a marked linear recovery (0.08 ± 0.01 pH unit/min) of pHi during the second part of the stimulation period. This recovery was not due to any phenomenon of fiber inactivation linked to development of muscle fatigue, and was not associated with any change in intracellular proton buffering, net proton efflux from the cell, or proton turnovers through creatine kinase reaction and oxidative phosphorylation. This paradoxical pHi recovery in exercising rat skeletal muscle under endotoxemia is likely due to slowing of glycolytic flux following the reduction in intramuscular glycogen content. These findings may be useful in the follow‐up of septic patients and in the assessment of therapies. Muscle Nerve, 2007
Control of molecular weight in polymerization of vinyl chloride with Cp*Ti(OPh)3/MAO catalyst
Authors: Endo Kiyoshi , Nomaguchi Tsuyoshi , Tsuchiya Yoshikatsu 
Published: July 2007

AbstractPolymerization of vinyl chloride (VC) with titanium complexes containing Ti‐OPh bond in combination with methylaluminoxane (MAO) catalysts was investigated. Among the titanium complexes examined, Cp*Ti(OPh)3/MAO catalyst (Cp*; pentamethylcyclopentadienyl, Ph; C6H5) gave the highest activity for the polymerization of VC, but the polymerization rate was slow. From the kinetic study on the polymerization of VC with Cp*Ti(OPh)3/MAO catalyst, the relationship between the Mn of the polymer and the polymer yields gave a straight line, and the line passed through the origin. The Mw/Mn values of the polymer gradually decrease as a function of polymer yields, but the Mw/Mn values were somewhat broad. This may be explained by a slow initiation in the polymerization of VC with Cp*Ti(OPh)3/MAO catalyst. The results obtained in this study demonstrate that the molecular weight control of the polymers is possible in the polymerization of VC with the Cp*Ti(OPh)3/MAO catalyst. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3872–3876, 2007
Synthesis of AB‐type block copolymers containing benzoxazole and anthracene groups by ATRP and fluorescent property
Authors: Lu Jian‐Mei , Xu Qing‐Feng , Yuan Xin , Xia Xue‐Wei , Wang Li‐Hua 
Published: July 2007

AbstractTwo functional monomers, methacrylic acid 4‐(2‐benzoxazol)‐benzyl ester (MABE) containing the benzoxazole group and 4‐(2‐(9‐anthryl))‐vinyl‐styrene (AVS) containing the anthracene group were synthesized by rational design. The MABE was polymerized via atom transfer radical polymerization (ATRP) using ethyl 2‐bromoisobutyrate (EBIB) as initiator in CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) catalyst system; block copolymers poly(MABE‐b‐AVS) was obtained, which was conducted by using poly(MABE) as macro‐initiator, AVS as the second monomer, and CuBr/PMDETA as catalyst. The constitute of two monomers in block copolymers poly(MABE‐b‐AVS) by ATRP could be adjusted, that is the constitute of the benzoxazole group and the anthracene group could be controlled in AB‐type block copolymers. Moreover, the fluorescent properties of homopolymers poly(MABE) and block copolymers poly(MABE‐b‐AVS) were discussed herein. With the excitation at λex = 330 nm, the fluorescent emission spectrum of poly(MABE) solution showed emission at 375 nm corresponding to the benzoxazole‐based part; with the same excitation, the fluorescent emission spectrum of poly(MABE‐b‐AVS) solution showed a broad peek at 330–600 nm when the monomer AVS to the total monomers mole ratio was 0.31, and the fluorescent emission spectrum of poly(MABE‐b‐AVS) in film state only showed one peak at 525 nm corresponding to the anthracene‐based unit that indicated a complete energy transfer from the benzoxazole group to the anthracene group. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3894–3901, 2007
Synthesis and morphology of Fe3O4/polystyrene/poly(isopropylacrylamide‐co‐methyl acrylate acid) magnetic composite latex – 2,2′‐azobis (2‐methylpropionamidine) dihydrochloride as initiator
Authors: Lee Chia‐Fen , Chou Yu‐Hui , Chiu Wen‐Yen 
Published: July 2007

AbstractIn this work, Fe3O4/polystyrene/poly(N‐isopropylacryl amide‐co‐methylacrylate acid) (Fe3O4/PS/P(NIPAAM‐co‐MAA)) magnetic composite latex was synthesized by the method of two stage emulsion polymerization. In this reaction system, 2,2′‐azobis(2‐methyl propionamidine) dihydrochloride (AIBA) was used as initiator to initiate the first stage reaction and second stage reaction. The Fe3O4 particles were prepared by a traditional coprecipitation method. Fe3O4 particles were surface treated by either PAA oligomer or lauric acid to form the stable ferrofluid. The first stage for the synthesis of magnetic composite latex was to synthesize PS in the presence of ferrofluid by soapless emulsion polymerization to form the Fe3O4/PS composite latex particles. Following the first stage of reaction, the second stage of polymerization was carried out by the method of soapless emulsion polymerization with NIPAAM and MAA as monomers and Fe3O4/PS latex as seeds. The magnetic composite particles, Fe3O4/PS/P(NIPAAM‐co‐MAA), were thus obtained. The mechanism of the first stage reaction and second stage reaction were investigated. Moreover, the effects of PAA and lauric acid on the reaction kinetics, morphology, and particle size distribution were studied. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3912–3921, 2007
Exploring pathways to reduce the distribution of active sites in the Ziegler–Natta polymerization of propylene
Authors: Ribour David , Bollack‐Benoit Valérie , Monteil Vincent , Spitz Roger 
Published: July 2007

AbstractChemical treatments of classical supported Ziegler–Natta precatalysts were conducted by using additional bulky ligands to attempt to narrow and homogenize the active sites distribution in propylene polymerization. Additions of monodentate ligands such as bis(trimethylsilyl)amide, cyclopentadienyl derivates or triphenylsilanol were seen to slow down the polymerization without modifying the distribute properties of polypropylenes. In the case of multidentate ligands (porphines or biquinolines), in addition to the poisoning of active sites, an extraction of titanium from the catalyst surface is observed. A decrease of both melting point and isotacticity (II%) of polymers using these compounds suggest that the most isospecific titanium sites are first extracted from the MgCl2‐surface. The narrowing of the molecular weight distribution confirms that the highly isospecific sites are the most active sites, producing the higher molecular weight polymers. Moreover, this study shows that the distributed properties of polymers are due to the chemical diversity of the active sites with various steric and electronic environments at the catalyst surface and not to mass transfer limitations. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3941–3948, 2007
Quantum diffusion of hydrogen in the B.C.C. transition metals
Authors: Rogan J. , Lagos M. 
Published: July 2007

AbstractThe auxiliary function governing the temperature dependence of the small‐polaron diffusion coefficient D(T) is calculated with improved accuracy for impurities occupying tetrahedral and octahedral interstitial sites in tantalum, niobium, and vanadium. This function depends only on the host crystal and determines the shape of the curve D versus T. The nature of the diffusing species enters as just a scale factor and displacement of the Arrhenius plot of D(T). The calculation considers the real vibrational modes of the host crystals and employ state‐of‐the‐art integration techniques over the Brillouin zone to give highly reliable and accurate results. Tables of use in the interpretation of further experiments are given. As an example of application, the diffusion data of hydrogen in tantalum, available for temperatures in the range 15 K < T < 500 K, are analyzed on the basis of the quantum theory of diffusion and a two‐states model.
A comparison of force constants, mechanical and thermal properties in Hg1−xCdxTe and Hg1−xZnxTe mixed crystals
Authors: Bagot D. , Granger R. , Rolland S. 
Published: July 2007

AbstractInteratomic force constants are deduced from a fit of infrared reflectivity data of HgCdTe (MCT) and HgZnTe (MZT) mixed crystals using a basic unit model for the description of vibrational modes of low wave vector. This allows, for the first time, a direct comparison of bond strengths between MCT and MZT. The obtained results are consistent with a slight decrease in bond strength when Cd is substituted for Hg in MCT and an increase when Zn replaces Hg in MZT. These results are visualized through the bulk modulus variations with composition in both mixed crystals and are compared to known results on their thermal properties.
Electronic structure calculation of Mg, Si, P, S, and Cl impurities in aluminium
Authors: Thiagarajan M. , Iyakutti K. , Palaniyandi E. 
Published: July 2007

AbstractA fully self‐consistent calculation using the multiple scattering Xα method is used to study the electronic structure, the relation between charge transfer and electronegativity, the bonding characteristics, and the alloying of Mg with Al. The present investigation indicates that the charge transfer from the host Al atoms to the central impurity atom increases with the increase of electronegativity of impurity atoms. It is found that the bonding is metallic for AlMg and for the other impurities considered it gradually becomes ionic. The alloying of Mg with Al is more favourable than with other impurities. The results are compared with the available experimental and theoretical data.
High‐field magnetoconductivity of double‐quantum‐well systems
Authors: Kleinert P. , Bryskin V. V. 
Published: July 2007

AbstractThe high‐field magnetoconductivity of double‐quantum‐well structures is treated on the basis of a microscopic one‐particle model which includes broadening effects due to disorder, finite temperatures, and a phenomenological inclusion of inelastic scattering processes. The theoretical results are consistent with the experimentally observed suppression of quantum Hall states at odd integer filling factors.
Quantum Beats of Recoil‐Free γ‐Radiation in the Direct and Bragg Diffracted Beam
Authors: Kuhn D. , Jex H. , Kienle A. 
Published: July 2007

AbstractThe interaction of recoil‐free γ‐radiation of a 57Co Mössbauer source with a piezo electrically excited X‐cut quartz crystal is investigated. The experiments are performed in the direct beam and in the diffracted beam of the (1120) Bragg reflection. In both geometries we applied time‐resolved correlation experiments to analyze the γ‐quantum beats due to phonon energy transfers. A consistent theoretical explanation of the quantum beats is proposed.
Surface Plasmons Modified by External Light
Authors: Gerlach E. 
Published: July 2007

AbstractIt is shown that the (non‐retarded) surface plasmon spectrum is modified by external light. This effect should be observable, if k∥︁v/Ω is not too small (k∥︁ wave vector of the surface plasmon parallel to the surface, v drift velocity of the carriers, Ω frequency of the external light). Semiconductors are expected to be good candidates, but also metals for small Ω.
Combined Monte‐Carlo Functional Integral Approach to Rare‐Earth Transition Metal Compounds RT2
Authors: de Oliveira N. A. , Gomes A. A. 
Published: July 2007

AbstractThe functional integral formalism, combined with a Monte‐Carlo calculation for the magnetization of rare‐earth spins, is used to describe the magnetic properties of RT2 compounds. The results of the numerical solution of the coupled self‐consistent equations, involving both itinerant d electrons and localized f spins, are presented and discussed.
Re‐Entrant Ferromagnetism in a Two‐Dimensional Spin‐3/2 Ising Model with Random Nearest‐Neighbour Interactions
Authors: Atri A. El , Saber M. 
Published: July 2007

AbstractThe existence of a re‐entrant ferromagnetic phase seems to be a general characteristic of systems with frustration and disorder even when no spin‐glass phase exists. Using an effective field theory based on the use of a probability distribution that correctly accounts for the single site kinematic relations, a two‐dimensional nearest‐neighbour random interaction spin‐3/2 Ising model is studied in which the interactions are indepcndent random variables distributed according to the following law: P (Jij ) = p δ(Jij − J ) + ( 1 − p) δ (Jij − αJ), where J > 0. In a certain range of negative values of α, re‐entrant phase diagrams are found and the threshold p* at which the critical temperature goes to zero depends on α.
LO‐Phonon Instability in Semiconductors in the Presence of Two Laser Fields Plus DC Strong Magnetic Field
Authors: Fonseca A. L. A. , Nunes O. A. C. 
Published: July 2007

AbstractPhonon scattering by electrons in a bulk semiconductor in two laser fields in the additional presence of a strong (quantizing) magnetic field is discussed. A kinetic equation for the LO‐phonon population is derived, from which the damping rate is calculated. It is found that longitudinal optical lattice waves may be amplified over a relatively narrow range of plasmon wave numbers in the direction perpendicular to the magnetic field direction. Furthermore, the joint action of the three external fields results in a very large amplification rate, in contrast to the zero magnetic field case.
Pressure Dependence of Positron Annihilation in Si
Authors: Benkabou F. , Dufour J. P. , Soudini B. , Amrane N. , Khelifa B. , Aourag H. 
Published: July 2007

AbstractThe pressure dependence of the electron‐positron and the electron‐electron momentum densities in silicon are studied. The observations that the electron‐positron momentum density increases more rapidly with pressure than the electron‐electron momentum density alone is explained in terms of increased positron penetration into the ion cores. The computational technique used here is based on the independent‐particle model (IPM) coupled with the use of the electron pseudo‐wave functions.
EPR Spectroscopy of Thulium Impurities in ZnS Crystals
Authors: Müller St. , Dziesiaty J. 
Published: July 2007

AbstractEPR spectroscopy is applied to Tm impurities in ZnS crystals containing Ag, Li, and La codopants. After optical irradiation, Tm2+ resonances are observed and make it possible to separate different interstitial sites occupied by Tm2+, cubic sites without local charge compensation and axially distorted ones with [111]w and [001] symmetry due to charge compensation by neighboured defects. Additionally a light‐insensitive signal could be ascribed to Tm3+ ions, occupying substitutional (Zn)sites, compensated by a negatively charged defect in 〈110〉 directions. From the photoionization spectrum the Tm2+ state is located in the upper half of the band gap.
Solitary Magnon Localization and Two‐Magnon Bound State in Antiferromagnet RbFeCl3
Authors: Liu Wu‐Ming , Zhou Ben‐Lian 
Published: July 2007

AbstractIntroducing the Holstein‐Primakoff transformation, the coherent‐state ansatz, and the time‐dependent variation principle, two partial differential equations of motion from the Hamiltonian are obtained. Employing the method of multiple scales, these equations are reduced to envelope function equations and the amplitude function satisfying a nonlinear Schrödinger equation is found. Using the inverse scattering transformation, single, two, and N solition solutions and the gap soliton are obtained and the solitary excitations in the antiferromagnet RbFeCl3 are investigated.