bluuebunny/crossref_metadata_2025 huggingface dataset:
Multi‐Scale Analysis of Mechanical Properties of Amorphous Polymer Systems
Authors: Meijer Han E. H. , Govaert Leon E.
Published: February 2003

Use of proper constitutive equations for the intrinsic behavior of glassy polymers (including yield, strain softening and hardening) allows nowadays for analyzing the mechanical response of homogeneous and heterogeneous polymer systems in great detail. Analyses are performed on both the periodic RVE, representative volume element, level and, via a MLFEM, multi‐level finite element method, also on the macroscopic level of e.g. a notched, scratched tensile test bar. Introduction of a failure criterion, in this case the critical tri‐axial stress that initiates crazing, allows for the prediction of brittle‐to‐tough transitions, both as a function of temperature as well as of the absolute critical local material thickness. The analyses give clear suggestions towards possible directions to optimize the microstructure in heterogeneous polymer systems in order to obtain the ultimate toughness of polymers.

Ductile deformation of mechanically rejuvenated polystyrene.

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Ductile deformation of mechanically rejuvenated polystyrene.
Nanocomposites of Hairy‐Rod Macromolecules: Concepts, Constructs, and Materials
Authors: Wegner Gerhard
Published: February 2003

The rational construction of nanocomposites based on so‐called hairy‐rod macromolecules (HRM) is the objective of this review covering 15 years of extensive research at the Max Planck Institute for Polymer Research. HRM are described as shape‐persistent objects, which are processed into ultrathin films by the Langmuir–Blodgett protocol. Transfer of monolayers initially formed on the water surface to solid substrates is understood as a two‐dimensional analogue of an extrusion process giving rise to molecular orientation phenomena. The scope of HRM concerning chemical composition and molecular architecture is reviewed, and examples of how to obtain complex constructs having device functions are given. Recent work on hairy‐rod polyelectrolytes based on poly(p‐phenylene sulfonates)s is summarized as well, and their ability to form hierarchical superstructures in aqueous solution is presented.

Assembly process of multilayers of hairy‐rod macromolecules by the LB technique.

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Assembly process of multilayers of hairy‐rod macromolecules by the LB technique.
90 Years of Polymer Latexes and Heterophase Polymerization: More vital than ever
Authors: Antonietti Markus , Tauer Klaus
Published: February 2003

An attempt is made to give an overview on the historical and possible future development of heterophase polymerization techniques in liquid continuous media to prepare polymer dispersions. Polymer latexes play an essential role in our daily life as they are present visibly or hidden in a variety of products such cosmetics, detergents, newspapers, or paints and lacquers. More than 10 million tons of polymers are produced by heterophase polymerization techniques worldwide yearly. The majority of heterophase polymerizations is carried out in water as continuous phase and hence, they are belong to green chemistry with increasing importance due to environmental reasons. The compartmentalization of the reaction volume into domains of colloidal size (between a few nm3 and μm3) is the characteristic feature and relates both to the problems and the potential promises of this class of polymers. Special emphasis is placed with regard to the development of new heterophase polymerization techniques, the adoption of new polymerization mechanism to the particular conditions of heterophase polymerization, the synthesis of block copolymers and nanoparticulate hybride structures, the development of new stabilizers and polymerization aids, and the usage of specialty latexes as model systems to learn more about complex matter.

Colloidal crystal made of monodisperse polystyrene latexes.

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Colloidal crystal made of monodisperse polystyrene latexes.
Biomacromolecules and Bio‐Related Macromolecules
Authors: Kobayashi Shiro , Uyama Hiroshi
Published: February 2003

The present article briefly reviews research developments in the area of biomacromolecules and bio‐related macromolecules, whose research papers have been published for several decades preferably in the Macromolecular Journals. The area covers the important classes of macromolecules, polysaccharides (cellulose, amylose, chitin, etc.), polyesters (poly(lactic acid), poly(hydroxyalkanoate)s, etc.), and phenolic polymers (lignin, urushi, etc.). These polymers and their derivatives are very important for scientific interests as well as for industrial applications. Their synthesis, structure, reactions, and properties are mainly mentioned, and important topics of the target polymers are selected and mostly chronologically reviewed.

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Catalytic Polymerization and Post Polymerization Catalysis Fifty Years After the Discovery of Ziegler's Catalysts
Authors: Mülhaupt Rolf
Published: February 2003

During the 1950's the discoveries of Ziegler's organometallic catalyst systems and Natta's stereoselective olefin polymerization set the stage for extraordinary progress in polymer science and technology. Today advanced catalyst systems are available for catalytic carbon carbon bond formation by means of polyinsertion, metathesis, coupling reactions, and controlled radical polymerization. Modern catalytic olefin polymerization processes and polyolefins are environmentally friendly and meet the demands of a sustainable development. The architectures of homo‐ and copolymers based upon olefin, cycloolefin, diene, styrene and arene feed stocks are tailored as a function of single site catalysts' ligand frameworks. Polymer properties are varied over a very wide range, e.g., liquid/solid, rigid/soft, crystalline/amorphous/rubbery, permeable/impermeable, opaque/transparent, moldable/thermosetting, insulating/conducting. Advanced polymerization reaction engineering, copolymerization processes, reactor granule and reactor blend technologies, tailor‐made single site catalysts, catalyst blends and tandem catalysis improve property profiles, stability, morphology, and melt processing. Tuned cycloolefin polymers are new functional materials for electronic applications. Catalytic chain transfer (CCT) and atom transfer polymerization (ATRP) produce a variety of new functional polymers, reactive oligomers, and block copolymers. Aqueous polyolefin emulsions are obtained when catalytic olefin polymerization is performed in nanodroplets of catalyst miniemulsions. The scope of catalytic polymerization and post polymerization catalysis is progressing well beyond the frontiers of commodity polyolefin manufacturing. Advanced catalytic processes produce polar polymers such as polyethers, polyketones, polyesters, polycarbonates, polyamides, polyaramids, and polyimides. The new phosgene free polycarbonate syntheses are based upon the palladium catalyzed oxidative carbonylation. This overview highlights history, recent progress and modern trends in catalytic polymerization and catalytic polymer modification illustrated by selected examples.

Ziegler's glass reactor for performing his Mülheim low pressure ethylene polymerization. The reactor is on display at the Max Planck Institut für Kohlenforschung in Mülheim (this picture was made available by courtesy of G. Fink).

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Ziegler's glass reactor for performing his Mülheim low pressure ethylene polymerization. The reactor is on display at the Max Planck Institut für Kohlenforschung in Mülheim (this picture was made available by courtesy of G. Fink).
Dendronized Polymers: Recent Progress in Synthesis
Authors: Zhang Afang , Shu Lijin , Bo Zhishan , Schlüter A. Dieter
Published: February 2003

This article divides the synthetic routes leading to dendronized polymers into two main categories (attach‐to and macromonomer) and compares their respective advantages and disadvantages. It gives a comprehensive overview on the kind of structures presently available and also spans the bridge between both polymers and molecular objects, decorated with only a few dendrons, and the structurally related, but less well defined polymers with hyperbranched side chains.

A coiled polymer backbone's stretching through the attachment of increasingly sterically demanding dendrons: a) no dendrons; b) dendrons of the first generation; c) second generation; d) third generation.

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A coiled polymer backbone's stretching through the attachment of increasingly sterically demanding dendrons: a) no dendrons; b) dendrons of the first generation; c) second generation; d) third generation.
T‐probe proximity‐fed short‐circuited patch antenna
Authors: Guo Yong‐Xin , Luk Kwai‐Man , Lee Kai‐Fong
Published: February 2003

A broadband T‐probe proximity‐fed short‐circuited quarter‐wavelength rectangular patch antenna is proposed as one possible candidate for mobile communication applications. Using a foam layer of thickness ∼0.09λ0 as a supported substrate, an impedance bandwidth of 59% and a gain of over 4.5 dBi have been obtained. The far‐field patterns are stable across the passband. Experimental and computed results based on the finite‐difference time‐domain (FDTD) method are provided. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 1–2, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10805
A low‐cost surface‐mount monopole antenna for GSM/DCS operation
Authors: Lee Gwo‐Yun , Chen Hong‐Twu , Wong Kin‐Lu
Published: February 2003

By folding a metallic strip onto a foam base, a low‐cost surface‐mount monopole antenna suitable for GSM/DCS dual‐band operation is presented. The antenna has a compact size of 33 × 7.5 × 7.5 mm3 and requires no isolation distance to the system ground plane when surface‐mounted to the system circuit board of a communication device. Experimental results of a constructed prototype covering the operating bandwidths of the GSM (890–960 MHz) and DCS (1710–1880 MHz) systems are presented. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 2–4, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10806
Wave propagation, refraction, and focusing phenomena in Lorentzian double‐negative materials: A theoretical and numerical study
Authors: Kärkkäinen M. K. , Maslovski S. I.
Published: February 2003

Electromagnetic effects in double‐negative (DNG) materials are considered from the theoretical and numerical points of view. Special attention is given to the causality aspects. The refracton of a cylindrical wave excited by a line source placed above a plane DNG slab and the wave propagation through the slab are studied. The DNG material response is modelled by the resonant constitutive parameters of the Lorentzian form. A novel technique for discretization of the constitutive equations is proposed. The negative refraction and slab focusing phenomena are clearly seen from the simulations. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 4–7, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10807
Development of a higher‐order ADI‐FDTD method
Authors: Wang Zhu , Chen Ji , Chen Yinchao
Published: February 2003

In this paper, a higher‐order alternative‐direction‐implicit (ADI) finite‐difference time‐domain (FDTD) method is presented. The dispersion analysis is performed and the results are compared with those derived from the regular ADI‐FDTD method. Based on the dispersion analysis, a guideline for choosing an appropriate time step in the ADI‐FDTD implementation is also developed. Both numerical simulation and dispersion analysis demonstrate the advantage of this higher order ADI‐FDTD method for improving accuracy. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 8–12, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10808
A linear approximation of the coupling coefficient in the WDM coupler
Authors: Chen Ye , Joines William T.
Published: February 2003

A linear approximation of the coupling coefficient for the wavelength division multiplexing (WDM) coupler is presented. Our aim is to better understand and to simplify the design of couplers used in optical communications. The theoretical calculation and the derivation of the linear coupling coefficient were obtained based on coupled mode theory and a simplified equation pertaining to rectangular and circular waveguide couplers. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 12–15, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10809
A simple fiber‐Bragg‐grating sensor system based on a linear‐cavity fiber laser
Authors: Peng Peng‐Chun , Tseng Hong‐Yih , Chi Sien
Published: February 2003

A simple fiber‐Bragg‐grating (FBG) sensor system based on a linear‐cavity fiber laser is proposed and experimentally demonstrated. The lasing wavelength shift resulting from the temperature variation on this sensing element is discriminated by two FBGs. These two FBGs, acting as wavelength discriminators, are used to increase the real‐time measurement range for monitoring the temperature variation. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 15–17, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10810
Direction‐of‐arrival estimation for ultra‐wideband EM pulses with an interferometry
Authors: Morimoto T. , Hirata A. , Kawasaki Z. , Shiozawa T.
Published: February 2003

In this paper, we present an interferometry for the direction‐of‐arrival estimation of ultra‐wideband electromagnetic waves. The interaction between the antennas composing the interferometer is calculated by using the finite‐difference time‐domain (FDTD) method, and taken into account in the analysis. We propose a new signal processing scheme for wideband pulses, and demonstrate its effectiveness using a typical wideband pulse. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 17–18, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10811
Investigation of printed reflectarrays as permanent scatterers in SAR interferometry
Authors: Venneri Francesca , Costanzo Sandra , Di Massa Giuseppe , Angiulli Giovanni
Published: February 2003

The use of printed reflectarrays as permanent scatterers in SAR interferometry is investigated. The required feature of a backscattered field in a fixed direction of incidence is obtained as in the usually employed corner‐reflectors, with a more stable and flat structure. A 10‐GHz prototype has been successfully designed and tested. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 18–20, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10812
Extension of forward‐backward method with a DFT‐based acceleration algorithm for efficient analysis of radiation/scattering from large finite‐printed dipole arrays
Authors: Çivi Özlem Aydın
Published: February 2003

A discrete‐Fourier‐transform (DFT) based forward‐backward (FB) algorithm has been developed for the fast and accurate analysis of electrically large freestanding dipole arrays [1]. In this paper, an extension of the FB method (FBM) with a DFT‐based acceleration approach is presented to provide a relatively efficient analysis of EM radiation/scattering from an electrically large, planar, periodic, finite dipole array printed on a grounded dielectric substrate. Computational complexity of this new approach is O(Ntot), where Ntot is the number of unknowns. Numerical results are presented to validate the efficiency and accuracy of the method. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 20–26, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10813
A distributed network model of SOI MOSFET for microwave frequency applications
Authors: Kapoor Nirupama , Haldar Subhasis , Gupta Mridula , Gupta R. S.
Published: February 2003

In this paper, a small signal model of SOI MOSFET operating in the inversion region is developed, taking into account the distributed nature of the gate structure. Because the width of the device is large compared to its length, it is essential to consider it as a transmission line. The y and s parameters have been evaluated to obtain various gains, which otherwise cannot be predicted using lumped analysis. This model is useful in predicting the device's high‐frequency performance. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 26–31, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10814
A wideband rectangular microstrip antenna using an asymmetric T‐shaped feed
Authors: Lethakumary B. , Menon Sreedevi K. , Aanandan C. K. , Mohanan P.
Published: February 2003

An electromagnetically coupled T‐shaped microstrip feed used to enhance the impedance bandwidth of a rectangular microstrip antenna is reported. The proposed antenna offers a 2:1 VSWR bandwidth of ∼36% with an increase in gain of 0.8 dB. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 31–32, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10815
Pulse wave propagating in coplanar waveguides (CPWS) on LTCC substrates
Authors: Yin W. Y. , Guo B. , Dong X. T.
Published: February 2003

The propagation of pulse waves in coplanar waveguides (CPWs) is investigated, and these CPWs are assumed to be fabricated on a single‐layer low‐temperature co‐fired ceramic (LTCC) substrate. The input pulse wave can be a Gaussian pulse or a sinusoidally modulated Gaussian pulse. Based on the standard Galerkin's method in the spectral domain, combined with fast Fourier transform (FFT), the pulse waveform and delay in CPWs are demonstrated and compared for LTCCs with different permittivities. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 32–34, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10816
A tunable‐output wavelength converter based on a self‐seeded Fabry‐Perot laser diode with a chirped fiber grating
Authors: Lee Kwang‐Hyun , Cho Yong‐Sang , Kim Sangin , Choi Woo‐Young
Published: February 2003

We report a new all‐optical wavelength conversion scheme based on a self‐seeded Fabry–Perot laser diode with a chirped fiber grating as the external cavity. This converter can convert the wavelength of input optical signals into 14 discrete wavelengths with external RF modulation. We successfully demonstrate all‐optical wavelength conversion at 10 Mbps. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 35–36, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10817
On radiation from canonical source configurations embedded in structurally chiral materials
Authors: Lakhtakia Akhlesh
Published: February 2003

Radiation due to six canonical configurations for the source current density embedded in a structurally chiral medium is analyzed theoretically. The radiation spectrum is highly dependent on whether its source is co‐chiral or cross‐chiral, and is localized either in or on the edges of the Bragg regime. The obtained conclusions hold for both chiral liquid crystals and chiral sculptured thin films doped with fluorescent dyes, etc. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 37–40, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10818
The generalized Foster theorem and network‐Q
Authors: Liang Changhong , Su Tao
Published: February 2003

This paper proves the generalized Foster theorem, which can be applied to any lossy situation, while the original Foster theorem [1] only applied to reactive termination. Furthermore, the formula of Q with network parameters is described. One example, the quality factor Q of a pass‐through resonant cavity, is given here. It is clearly seen that the slope of the reactance function may be negative in a lossy situation. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 40–45, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10819
Design of long‐period gratings: Necessity of a three‐layer fiber geometry for cladding mode characteristics
Authors: Singh Rashmi , Kumar Harish , Sharma Enakshi Khular
Published: February 2003

In this paper, we show that a complete three‐layer analysis is necessary to characterise the cladding modes in order to obtain grating period, resonances, and coupling length in the design of long‐period gratings (LPGs), and that the simplified two‐layer fiber geometry used by many authors leads to incorrect designs. This is illustrated by design calculations corresponding to actual applications of long‐period gratings as sensors and gain equalisation filters for EDFA. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 45–49, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10820
High performance RF integrated passive devices on thick oxide substrate using Cu‐BCB process
Authors: Jeong Inho , Kim Ki‐Joong , Kong Tong‐Ook , Kim Jun‐Seok , Choi Hyung‐Kyu , Nam Choong‐Mo , Kim Dong‐Wook , Kwon Young‐Se
Published: February 2003

In this paper, we develop a low‐cost manufacturing technology for RF substrate and a high‐performance process technology for integrated passive devices by electrochemically forming thick oxide on Si wafer and processing Cu thick metal and BCB. Several integrated passive devices such as LPF, BPF, and balun are fabricated using this technology and they show good RF performance in spite of their small chip size. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 49–52, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10821
Non‐linear modeling of 0.18‐μM CMOS using neural network
Authors: Alam M. S. , Armstrong G. A. , Toner B. , Fusco V. F.
Published: February 2003

This paper describes an artificial‐neural‐network (ANN) based non‐linear modeling of deep‐submicron CMOS for RF applications. The neural network model is concise when compared to the conventional modeling approach based on empirical equations and can demonstrate comparable accuracy. The non‐linear voltage dependence of drain current, transconductance, and inter electrode capacitance can be characterized by a 3‐layered neural network, whose inputs are the gate‐to‐source bias voltage Vgs and drain‐to‐source bias Vds. The corresponding “well‐trained” neutral network has been found to be in excellent agreement with all intrinsic parameters and the drain current with measured data exhibits good extrapolation characteristics. This model has been implemented in an Agilent ADS simulation environment and tested on a 0.18‐μm CMOS technology operating at 2.4 GHz. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 53–56, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10822
Combination of genetic algorithm (GA) and fast fourier transform (FFT) for synthesis of arrays
Authors: Wang L. L. , Fang D. G. , Sheng W. X.
Published: February 2003

A novel method based on a combination of genetic algorithm (GA) and fast Fourier transform (FFT) is developed to synthesize antenna arrays. Compared with the synthesis method using GA in an angle domain, it can calculate more quickly while maintaining the same precision. Simulation results show this method is applicable. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 56–59, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10823
A circular microstrip‐fed single‐layer single‐slot antenna for multi‐band mobile communications
Authors: Jang Yong‐Woong
Published: February 2003

In this paper, we study a circular microstripline‐fed single‐layer single‐slot antenna. In this case, a modified circular microstrip feedline leads to good impedance matching in a wide dual band. The 10‐dB return loss impedance bandwidth is 50.8% for cellular (0.824–0.96 GHz) and GSM (0.86–0.88 GHz) operations, and is 37.1% for DCS (1.71–1.88 GHz), PCS (1.85–1.99 GHz), and IMT‐2000 (1.90–2.20 GHz) operations. We obtain the result for the return loss of exhibited multi‐band characteristics. The peak antenna gain is 4.61 dBi and 3.80 dBi for the lower (cellular and GSM) and upper (DCS, PCS, and IMT‐2000) bands, respectively. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 59–62, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10824
A two‐layer compact electromagnetic bandgap (EBG) structure and its applications in microstrip filter design
Authors: Yang Ning , Chen Zhi Ning , Wang Yun Yi , Chia M. Y. W.
Published: February 2003

This paper presents a compact electromagnetic bandgap (EBG) structure and its applications in microstrip bandstop filter designs in the S band. The proposed EBG cell is constructed in a two‐layer dielectric substrate, which saves the lateral sizes due to a multi‐layer topology. A lumped‐LC equivalent circuit is extracted from EM simulation. By adjusting the patch dimensions and positions of the shorting pins, the center frequency and equivalent L, C parameters can meet design requirements. Based on the proposed structure and its equivalent circuit, a wideband 3‐pole notch filter is designed. The simulation and measurement show its promising applications in microwave and RF systems. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 62–64, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10825
Correct analysis of Gires–Tournois absorbing interferometer by the method of single expression
Authors: Baghdasaryan Hovik V. , Knyazyan Tamara M. , Berberyan Suren S. , Mankulov Albert A.
Published: February 2003

A unidirectional reflective Gires–Tournois interferometer consisting of a highly reflective metallic mirror, an absorbing semitransparent metallic layer, and a dielectric layer between them, is correctly analyzed using the method of single expression (MSE). The interferometer's spectral characteristics versus the distance between the mirrors for different values of semitransparent metallic layer thickness are obtained. Optimal parameters of the interferometer for maximal reflection and maximal absorption of light are defined. Electric‐field and power‐flow density distributions within the whole structure of the interferometer for maximal reflection and absorption are obtained. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 64–67, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10826
A broadband self‐biased monolithic frequency doubler for X‐band application
Authors: Giannini F. , Limiti E. , Serino A.
Published: February 2003

A broadband monolithic single‐ended active frequency doubler fed by a single positive DC power supply is presented. The effects of the self‐bias approach on the doubler performances are investigated and a design method is proposed. Measured performances demonstrate the competitiveness of the proposed circuit with respect to more traditional doublers. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 67–69, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10827
A theoretical analysis of the propagation characteristics of an annular circular waveguide with a helical winding as the inner cladding
Authors: Kumar N. , Srivastava S. K. , Ojha S. P.
Published: February 2003

In this paper, we present a fairly rigorous analysis of a helically inner‐cladded annular step‐index waveguide. Using the sheath‐helix boundary conditions on the inner core‐cladding boundary and simple step‐index boundary conditions on the outer core‐cladding boundary, the modal characteristic equation of the waveguide is derived by taking a vector approach and dispersion curves are drawn. We observe the effect of the pitch angle of the helical windings on the modal dispersion characteristics of the proposed waveguide. The main feature of the waveguide is the occurrence of negative dispersion and band gap. This property may be attributed to the periodicity of the inner helical cladding. The width of the forbidden region increases with the pitch angle and thereafter at the pitch angle ≈90° the region is not found. It is also observed that the lowest cutoff value for the usual curves slightly decreases with the increase in the pitch angle. Thus the pitch angle acts as the controlling factor for the negative dispersion and photonic band gap. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 69–74, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10828
Design of a double‐looped monopole array antenna for a DSRC system roadside base station
Authors: Kim Yongjin , Song Choongho , Koo Inmo , Choi Hyungjin , Lee Sangseol
Published: February 2003

The antenna system for a dedicated short‐range communication (DSRC) system must have pattern characteristics that satisfy the system's specifications. Also, the antenna system needs to have good space efficiency for mounting on a roadside base station. The proposed antenna has the traveling‐wave structure of a double‐looped monopole array. The Wilkinson power divider is used for the in‐phase feeding of the array. The designed antenna system's performance is suitable for the DSRC system. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 74–77, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10829
The boundary contour method for piezoelectric media with linear boundary elements
Authors: Wang Qing , Wang Guoqing , Liu Zhengxing , Ding Haojiang
Published: February 2003

This paper presents a development of the boundary contour method (BCM) for piezoelectric media. First, the divergence‐free property of the integrand of the piezoelectric boundary element is proved. Secondly, the boundary contour method formulation is derived and potential functions are obtained by introducing linear shape functions and Green's functions (Computer Methods in Applied Mechanics and Engineering 1998; 158: 65) for piezoelectric media. The BCM is applied to the problem of piezoelectric media. Finally, numerical solutions for illustrative examples are compared with exact ones and those of the conventional boundary element method (BEM). The numerical results of the BCM coincide very well with the exact solution, and the feasibility and efficiency of the method are verified. Copyright © 2003 John Wiley & Sons, Ltd.
Implicit solid, flow and flow–solid finite element approaches in blade forging simulation
Authors: Soltani B. , Mattiasson K. , Samuelsson A.
Published: February 2003

A comparative theoretical and numerical study of the flow (rigid‐plastic) and solid (elasto‐plastic, in rate form) simulation approaches applied to the isothermal blade forging process for closing and opening of the dies is presented. In the rigid‐plastic approach the solution is followed by an elasto‐plastic solution in unloading (opening of the dies). The deformation of the billet, effective plastic strains and stresses were compared between the two solutions in the closing of the dies and when the dies were opened. Furthermore, the flow–solid approach was used in simulating the process and then the results, including the time–load and time–volume curves, were compared with previous results. The cost was lower and the efficiency was superior in the suggested flow–solid approach. Copyright © 2003 John Wiley & Sons, Ltd.
A methodology for the generation of low‐cost higher‐order methods for linear dynamics
Authors: Mancuso M. , Ubertini F.
Published: February 2003

This work presents a methodology which generates efficient higher‐order methods for linear dynamics by improving the accuracy properties of Nørsett methods towards those of Padé methods. The methodology is based on a simple and low‐cost iterative procedure which is used to implement a set of higher‐order methods with controllable dissipation. A sequence of improved solutions is obtained which correspond to algorithms offering an effective compromise between the efficiency of Nørsett methods and the accuracy of Padé methods. Moreover, a direct control over high‐frequency dissipation is possible by means of an algorithmic parameter. Numerical tests are reported which confirm that this set of algorithms is really attractive for linear dynamic analysis. Copyright © 2003 John Wiley & Sons, Ltd.
Level set calculations of the evolution of boundaries on a dynamically adaptive grid
Authors: Sochnikov Vassili , Efrima Shlomo
Published: February 2003

We present a general algorithm for the study of the evolution of interfaces in growth processes based on the level set method, using the narrow band and the fast marching approximations, applied on a dynamically adaptive grid. A novel construction of a dynamical adaptive grid is presented. One important feature is that we establish a controllable finite‐width region of the highest resolution straddling the physically important boundary. This high‐resolution stripe provides a better description of the important physical variables. An efficient and robust coupling of a hierarchical space description structure with the state‐of‐the‐art level set method is established. Copyright © 2003 John Wiley & Sons, Ltd.
Boundary knot method for 2D and 3D Helmholtz and convection–diffusion problems under complicated geometry
Authors: Hon Y. C. , Chen W.
Published: February 2003

The boundary knot method (BKM) of very recent origin is an inherently meshless, integration‐free, boundary‐type, radial basis function collocation technique for the numerical discretization of general partial differential equation systems. Unlike the method of fundamental solutions, the use of non‐singular general solution in the BKM avoids the unnecessary requirement of constructing a controversial artificial boundary outside the physical domain. The purpose of this paper is to extend the BKM to solve 2D Helmholtz and convection–diffusion problems under rather complicated irregular geometry. The method is also first applied to 3D problems. Numerical experiments validate that the BKM can produce highly accurate solutions using a relatively small number of knots. For inhomogeneous cases, some inner knots are found necessary to guarantee accuracy and stability. The stability and convergence of the BKM are numerically illustrated and the completeness issue is also discussed. Copyright © 2003 John Wiley & Sons, Ltd.
Data structure and algorithms for fast automatic differentiation
Authors: Tsukanov I. , Hall M.
Published: February 2003

In this paper we discuss the data structure and algorithms for the direct application of generalized Leibnitz rules to the numerical computation of partial derivatives in forward mode. The proposed data structure provides constant time access to the partial derivatives, which accelerates the automatic differentiation computations. The interaction among elements of the data structure is explained by several numerical examples. The paper contains analysis of the developed data structure and algorithms. Copyright © 2003 John Wiley & Sons, Ltd.
An efficient artificial compressibility (AC) scheme based on the characteristic based split (CBS) method for incompressible flows
Authors: Nithiarasu P.
Published: February 2003

In this paper, an artificial compressibility scheme using the finite element method is introduced. 2002 Zienkiewicz Silver Medal and Prize winning paper. The multi‐purpose CBS scheme is implemented in its fully explicit form to solve incompressible fluid dynamics problems. It is important to note that the scheme developed here includes split and velocity correction. The proposed method takes advantage of good features from both velocity correction and standard artificial compressibility schemes. Unlike many other artificial compressibility schemes, the proposed one works on a variety of grids and gives results for a wide range of Reynold's numbers. The paper presents some bench mark two‐ and three‐dimensional steady and unsteady incompressible flow solutions obtained from the proposed scheme. Copyright © 2003 John Wiley & Sons, Ltd.
Influence of a zwitterionic surfactant on the chromogenic behavior of a dye‐containing aqueous PVA–polyether gel network
Authors: Kriwanek J. , Lötzsch D. , Vetter R. , Seeboth A.
Published: February 2003

The effect of the addition of a zwitterionic sulfobetaine to a dye‐containing polymer gel composed of two polymers – poly(vinyl alcohol) (PVA) and polyether – was investigated. With increasing sulfobetaine content a remarkable reduction of the UV‐vis‐absorption intensity of the longest wavelength absorption band of Phenol Red in the aqueous polymer network was observed, even for sulfobetaine concentrations below its critical micelle concentration (cmc). It can be assumed that this effect is based on the formation of ionic complexes between dye molecules and either single sulfobetaine molecules or aggregates of sulfobetaine. Furthermore, thermotropic behavior occurs in the investigated polymer gel system even at a polyether concentration as low as 0.8 wt%. Copyright © 2003 John Wiley & Sons, Ltd.
Structure–property relationships for film‐forming copoly(amide imide)s
Authors: Privalko Valery P. , Mudrak Claudia V. , Privalko Eleonora G. , Usenko Andriy A. , Pissis Policarpos
Published: February 2003

Thin films of copoly(amide imide)s (coPAIs) from dichloro‐dianhydride of trimellitimide‐N‐acetic acid and mixtures of diphenylmethane diamine (DPA) and cardo 9,9′‐bis‐phenylfluorene diamine (CDA) cast from solutions in dimethylacetamide (DMAA) were characterized by wide‐angle and small‐angle X‐ray scattering (WAXS and SAXS), dynamic mechanical thermal analysis (DMTA) (temperature interval: 293–703 K, frequency range: 1–100 Hz), and thermogravimetric analysis (TGA) (nitrogen flux, temperature interval: 303–973 K). The mean interchain spacings (WAXS) smoothly increased with the CDA/DPA molar ratio from 0.55 nm for CDA/DPA = 0/1 up to 0.60 nm for CDA/DPA = 1/0. The smooth patterns of the SAXS curves for all coPAIs were explained by the smearing‐out of electron density differences between densely‐packed and loosely‐packed microregions of coPAIs due to the wide dispersion of their sizes. The step‐like patterns of the TGA traces in the temperature intervals below and above 600 K were associated with successive weight losses due to the evaporation of residual water and of DMAA, and to the thermal degradation of diamine and dianhydride chain fragments, respectively. As could be inferred from the TGA data, the loosely‐packed regions comprise about 25–35% of the total volume of studied coPAIs. The mechanical relaxations observed in all coPAIs at Tβ < Tα′ < Tα (DMA) were attributed to the onset of non‐cooperative segment motion in loosely‐packed regions, of cooperative segment motion in loosely‐packed regions, and of cooperative segment motion in densely‐packed regions, respectively. At constant frequency, the sub‐glass relaxations were roughly composition‐independent, while chain‐stiffening effect was assumed to be responsible for the smooth increase of Tα′ and Tα, as well as of the corresponding apparent activation energies with the CDA/DPA ratio. Copyright © 2003 John Wiley & Sons, Ltd.
Protein adsorption and platelet adhesion of polysulfone membrane immobilized with chitosan and heparin conjugate
Authors: Yang M.‐C. , Lin W.‐C.
Published: February 2003

Polysulfone (PSF) membranes were treated with ozone to introduce peroxides, and then grafted with either acrylic acid or chitosan, followed by the immobilization of heparin. The effect of spacer arm on blood compatibility was investigated using three chitosans of different molecular weight [1170 (water soluble), 160 000, and 400 000] and similar degrees of deacetylation (75%). The hydrophilicity was evaluated by measuring the contact angle of water. Blood compatibility was evaluated using the activated partial thromboplastin time (APTT) as well as the adhesion of platelets. The protein affinity was determined by the absorption of human serum albumin (HSA) and human plasma fibrinogen (HPF). The results show that by the coupling of chitosan, the amount of heparin immobilized can be increased by four times. Water contact angle (from 78 ° to 41 °) decreased with the increase of the amount of heparin immobilized, showing increased wettability. The heparinized PSF membrane showed longer APTT and decreasing platelet adhesion, compared to that of unmodified PSF membrane. The adsorption of HSA and HPF were reduced to 17 and 6%, respectively. This suggests that longer spacer binding to heparin can increase the opportunity of anti‐coagulation on contacting blood. These results demonstrated that the hydrophilicity and blood compatibility of PSF membrane could be improved by chitosan and heparin conjugate. Copyright © 2003 John Wiley & Sons, Ltd.
The preparation and characterization of novel cocylic(arylene disulfide) oligomers
Authors: Chen K. , Du X. S. , Meng Y. Z. , Tjong S. C. , Zhang Y. M. , Hay A. S.
Published: February 2003

A series of homo‐ and cocyclic(arylene disulfide) oligomers were synthesized under high dilution conditions by the catalytic oxidation of arylenedithiols with oxygen in the presence of a copper‐amine catalyst in DMAc. The aryl groups contained moieties such as sulfone, ether, and ketone. The free radical ring‐opening polymerization of these cyclic(arylene disulfide) oligomers led to the formation of linear poly(thio arylene)s. The homo‐ and cocyclic(arylene disulfide) oligomers were characterized by gradient high pressure liquid chromatography (HPLC), get permeation chromatography (GPC), 1H‐NMR, and differential scanning calorimetry (DSC) methods. These cocyclic(arylene disulfide) oligomers except those containing sulfone moiety had lower melt flow temperature as low as 140 °C and therefore could readily undergo free radical ring‐opening polymerization under mild conditions. The glass transition temperatures of these cocyclics ranged from 72.3 to 190.0 °C, while the glass transition temperatures of the polydisulfides derived from these cocyclics ranged from 78.4 to 194.5 °C. In this article, a new method of preparing arylene dithiols 4,4′‐oxybis(benzenethiol) and diphenylmethane‐4,4′‐dithiol is reported. Copyright © 2003 John Wiley & Sons, Ltd.
Pyridinium chlorochromate oxidation route to polyaniline
Authors: Palaniappan S. , Amarnath C. A.
Published: February 2003

In this work, for the first time, pyridinium chlorochromate is used as an oxidizing agent inorder to oxidize aniline to polyaniline salts via an aqueous polymerization pathway in the presence of protic acids such as sulfuric, nitric, hydrochloric and phosphoric acid. The polymer samples were characterized by infrared, electronic absorption spectral, elemental analysis, conductivity, density and water absorption measurements. The results of the polyaniline salts prepared by pyridinium chlorochromate as an oxidizing agent were compared with that of the polyaniline salt prepared by ammonium persulfate. Generally, aniline is oxidized using ammonium persulfate as an oxidizing agent, which is unstable. In this work, pyridinium chlorochromate is used to oxidize aniline to polyaniline salt and the polymerization reaction could be completed in 30 min. Copyright © 2003 John Wiley & Sons, Ltd.
Synergistic mechanical behaviour and improved processability of poly(ether imide) by blending with poly(trimethylene terephthalate)
Authors: Ramiro J. , Eguiazábal J. I. , Nazábal J.
Published: February 2003

Fully miscible poly(ether imide) (PEI)/poly(trimethylene terephthalate) (PTT) blends were obtained by melt mixing in an extruder followed by injection moulding. The viscosity of PEI, represented by the pressure at the extruder output, almost halved upon the addition of only 10% PTT, allowing the use of PEI in applications where either complex parts or thin sections must be moulded. The modulus of elasticity showed a synergistic behaviour which was absolute (modulus higher than that of any of the two components) in the blend with 10% PTT. This was attributed mainly to the decrease in specific volume upon blending. The additional absolute synergism in the yield stress of PEI‐rich blends and their ductile nature depict a set of properties that make these new materials attractive in a number of new applications. Copyright ­© 2003 John Wiley & Sons, Ltd.
Mechanical, thermal and morphological behavior of bismaleimide modified polyurethane‐epoxy IPN matrices
Authors: Mahesh K. P. O. , Alagar M. , Ananda Kumar S.
Published: February 2003

An intercrosslinked network of bismaleimide modified polyurethane‐epoxy systems were prepared from the bismaleimide having ester linkages, polyurethane modified epoxy and cured in the presence of 4,4′‐diaminodiphenylmethane. Infrared spectral analysis was used to confirm the grafting of polyurethane into the epoxy skeleton. The prepared matrices were characterized by mechanical, thermal and morphological studies. The results obtained from the mechanical and thermal studies reveal that the incorporation of polyurethane into the epoxy skeleton increases the mechanical strength and decreases the glass transition temperature, thermal stability and heat distortion temperature. Whereas, the incorporation of bismaleimide having ester linkages into polyurethane modified epoxy systems increases the thermal stability, tensile and flexural properties and decreases the impact strength, glass transition temperature and heat distortion temperature. Surface morphology of polyurethane modified epoxy and bismaleimide modified polyurethane‐epoxy systems were studied using scanning electron microscopy. Copyright © 2003 John Wiley & Sons, Ltd.
Enhanced thermal properties and flame retardancy from a thermosetting blend of a phosphorus‐containing bismaleimide and epoxy resins
Authors: Jeng Ru‐Jong , Lo Geng‐Sheng , Chen Chih‐Ping , Liu Ying‐Ling , Hsiue Ging‐Ho , Su Wen‐Chiung
Published: February 2003

Epoxy resins modified by an organosoluble phosphorus‐containing bismaleimide (3,3′‐bis(maleimidophenyl) ­phenylphosphine oxide; BMPPPO) were prepared by simultaneously curing epoxy/diaminodiphenylmethane (DDM), and BMPPPO. The resulted epoxy resins were found to exhibit glass transition temperatures as high as 212 °C, thermal stability at temperatures over 350 °C, and excellent flame retardancy with Limited oxygen index (LOI) values around 40. Incorporation of BMPPPO into epoxy resins via the thermosetting blend was demonstrated to be an effective way to enhance the thermal properties and flame retardancy simultaneously. Copyright © 2003 John Wiley & Sons, Ltd.
Improvement of gas meter performance using polymer materials
Authors: Kobayashi Hayao , Takamoto Masaki
Published: February 2003

The measuring elements of both dry‐ and wet‐type gas meters are composed of a diaphragm and rotary drum. In this article an explanation on the principle of measuring and the structure of the gas meter for each of these two types was discussed. Such applications were made as follows: synthetic rubber was used for the measuring diaphragm, engineering plastic was employed instead of metal for the measuring drum, and poly(butylene terephthalate) (PBT) was used for the casing, respectively. As a result, an improvement in the gas resistance performance and productivity, which led to a lighter weight, more compactness and a lower cost of productions was achieved. Also the influence of the solubility of the measured gas to the plastic on the measured valve was discussed. Copyright © 2003 John Wiley & Sons, Ltd.