bluuebunny/crossref_metadata_2025 huggingface dataset:
Direct Determination of Phosphite in Fertilizers by Flow‐Injection Amperometry
Authors: Franzini Vanessa Pezza , Fugivara Cecílio Sadao , Benedetti Assis Vicente , Ribeiro Clóvis Augusto , Cavalheiro Eder Tadeu Gomes , Neto José Anchieta Gomes
Published: July 2007

A sensor based on graphite electrode modified with palladium‐platinum‐palladium film is proposed for phosphite determination by flow‐injection amperometry. The modified electrode was prepared by a sequential cathodic deposition of Pd, Pt and Pd on a graphite electrode from 0.5% m/v PdCl2+28% m/v NH4OH and 2% m/v H2PtCl6+10% v/v H2SO4 solutions. After suitable conditioning, the electrode showed catalytic activity for phosphite oxidation when 0.15 V was applied. The proposed system handles approximately 50 samples per hour (0.01–0.05 mol L−1 Na2HPO3; R2=0.9997), consuming ca. 70 μL of sample per determination. The limit of detection and amperometric sensibility were 5×10−4 mol L−1 and 1.5 mA L mol−1, respectively. The proposed method was applied to analysis of fertilizer samples without pre‐treatment. Results are in agreement with those obtained by spectrophotometry and titrimetry at 95% confidence level and good recoveries (96–109%) of spiked samples were found. Relative standard deviation (n= 12) of a 0.01 mol L−1 Na2HPO3 sample was 2%. The useful lifetime of modified electrode was around 220 determinations. For routine purposes it means that this electrode can be continuously used for 5 hours.
Synthesis, structure, reactions, and photoelectron spectra of new mixed sulfur‐, selenium‐ or tellurium and silicon‐ or tin‐containing heterocycles
Authors: Block Eric , Glass Richard S. , Dikarev Evgeny V. , Gruhn Nadine E. , Jin Jin , Li Bo , Lorance Edward , Zakai Uzma I. , Zhang Shao‐Zhong
Published: July 2007

More than 40 new 4‐ to 12‐membered ring heterocycles containing various combinations of Group 14 elements (Si and Sn) and Group 16 elements (S, Se, and Te) have been synthesized and fully characterized. Synthesis of these small‐ring as well as medium‐ring (mesocyclic) heterocycles from α, ω‐dihalides was facilitated by the presence of gem‐dialkylsilyl and gem‐dialkylstannyl groups in the precursors. Solid‐state conformations of the new ring systems have been determined by X‐ray crystallography. Oxidation of mixed S(Se, Te)/Si eight‐membered ring mesocycles as well as 1,5‐dithia‐, 1,5‐diselena‐, and 1,5‐ditelluracyclooctane with NOPF6 gave dications, which can be characterized by NMR. On treatment with nucleophiles, mesocyclic dications or the corresponding radical cations underwent ring contraction to give five‐ or six‐membered ring heterocycles. The ionization energies of the above conformationally constrained β‐disilanyl sulfides and selenides were determined by photoelectron spectroscopy. These ionization energies reflect substantial (0.53‐‐0.75 eV) orbital destabilizations. The basis for these destabilizations was investigated by theoretical calculations, which reveal geometry‐dependent interaction between sulfur or selenium lone pair orbitals and σ‐orbitals, especially Si–Si σ‐orbitals. These results suggest facile redox chemistry for these compounds and significantly extend the concept of σ‐stabilization of electron‐deficient centers. © 2007 Wiley Periodicals, Inc. 18:509–515, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20333
Perfluoroketene dithioacetals and perfluorodithiocarboxylic acid derivatives: Versatile tools for organofluorine synthesis
Authors: Portella Charles , Muzard Murielle , Bouillon Jean‐Philippe , Brulé Cédric , Grellepois Fabienne , Shermolovich Yuriy G. , Timoshenko Vadim M. , Chernega Alexander N. , Sotoca‐Usina Enrique , Parra Margarita , Gil Salvador
Published: July 2007

Perfluoroketene dithioacetals are simple and versatile compounds that can be transformed into a large variety of trifluoromethyl derivatives, in particular aza‐ and thiaheterocycles, perhalodithiocrotonic esters, and fluorinated dithiol thiones. These unsaturated perfluorodithioesters and analogs give interesting polar cycloaddition reactions whose mechanism is strongly influenced by the fluorine substitution. This substitution plays an important role in the reactivity of saturated perfluorodithiocarboxylic acids as well. Except for the carbophilic addition of allyl Grignard reagents to perfluorocarboxamides, a domino thiophilic addition‐fluoride elimination was the main reaction process. Interestingly, a three‐step domino reaction occurs when pentafluorodithioesters are treated with allyl Grignard reagents, the third step being an effective σ[3,3] rearrangement, so that the overall reaction is a formal substitution of an allyl group for the α‐fluorine atom. 2,2‐Bis(allyl)‐3,3,3‐trifluorodithiopropanoates were prepared by performing this domino reaction twice, in a possible one‐pot procedure. © 2007 Wiley Periodicals, Inc. 18:500–508, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20346
How company and managerial characteristics influence strategic alliance adoption in the travel sector
Authors: Pansiri Jaloni
Published: July 2007

The purpose of this paper is to examine the role of company and executive characteristics in strategic alliance formation in the tourism sector of travel. A survey of Australian travel sector businesses was carried out and the results indicate a high level of interaction through alliances between various sectors of the Australian tourism industry. Top managers' characteristics (experience, ownership and risk‐taking attitude) were found to be influential in taking strategic decisions of whether to form alliances or not. These characteristics do not play an important role in determining the number of alliances an organisation has and their geographical location, as much as company characteristics do. The findings of this paper imply that company characteristics are important in determining alliance formation. Managers should thoroughly consider these characteristics when deciding not only to form alliances, but also the types of alliances that could help their organisations to be more competitive, given limited resources. Copyright © 2007 John Wiley & Sons, Ltd.
Evaluation of the cognitive image of a country/destination by the media during the coverage of mega‐events: the case of UEFA EURO 2004TM in Portugal
Authors: Custódio Maria João Ferreira , Gouveia Pedro M. D. C. B.
Published: July 2007

By reporting a study undertaken during the final stages of the European Football Championships—UEFA (Union of European Football Associations) EURO 2004TM, this paper aims to evaluate the cognitive image of a country/destination by the media during the coverage of mega‐events, which may in turn contribute to the field of tourism promotion and planning. By applying various statistical methods, it is possible not only to assess and identify the aspects which have contributed the most to the opinion‐forming of autonomous agents, but also to present empirical evidence of the influence of the organisation of this event on the image formation of the destination as a whole. Copyright © 2007 John Wiley & Sons, Ltd.
Kinetic study of oxidation of N‐(α‐methylbenzylidene) anilines by dimethyldioxirane
Authors: Nose Žiga , Kovač Franci
Published: July 2007

A kinetic study of the oxidation of substituted N‐(α‐methylbenzylidene) anilines by dimethyldioxirane was investigated using a UV/VIS spectrophotometer. Oxaziridines and nitrones were formed as intermediates, and in the excess of dimethyldioxirane corresponding carbonyl compounds, nitrosobenzene or nitrobenzene, were formed quantitatively. The kinetic data were used in the equation for the formation of oxaziridines and nitrones as an intermediate and further oxidation to the corresponding acetophenones and nitrosobenzene. Hammett ρ values were determined for compounds p‐substituted on the aromatic ring attached to the carbon atom of the imino group, and it was found that these substituents have very little effect on the oxidation reaction. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 492–497, 2007
Effects of wildfire, salvage logging and slash treatments on soil degradation
Authors: Fernández C. , Vega J. A. , Fonturbel T. , Pérez‐Gorostiaga P. , Jiménez E. , Madrigal J.
Published: July 2007

The effect of wildfire and the subsequent harvesting on soil degradation was evaluated in a burned Pinus pinaster stand in Galicia (NW Spain). During the first year following a fire of moderate intensity, burned trees were not harvested and soil erosion losses, measured by sediment collection at the bottom of bordered plots, were very low. An apparently limited impact of fire on soil and reduced rainfall erosivity for this period could be responsible for that result.

Salvage logging took place 13 months after fire. Three post‐fire alternatives were compared: no harvesting (standing burned trees), harvesting + windrowed slash and harvesting + slash chopping. Soil losses were even lower during the 14 months after these treatments than for the previous pre‐harvesting period. Again, low mineral soil exposition and rainfall erosivity seemed to contribute to that result.

Changes in soil bulk density and soil shear strength after clearcutting and slash manipulation were small and not enough to trigger sediment yield significantly.

Harvesting and logging operations apparently increased soil inhomogeneities. This degree of variability was more adequately assessed by using micro‐plot fences instead of plot fences. The percentage of soil disturbed by machinery was the variable most related with the observed minor soil losses after harvesting, at micro‐plot level. This study indicated that the combined effect of wildfire and clearcutting caused only an acceleration of soil erosion when significant exposition of mineral soil occurred after these perturbations. However, these results must be taken with caution because rain erosivity during the study was low. To delay post‐fire clearcutting until several months after the fire could reduce the impact of this forestry operation on burned soils, taking advantage of the natural mulch created by scorched leaves fall, although other issues must be taken into account. Copyright © 2007 John Wiley & Sons, Ltd.
Are they always offering the lowest price? An empirical analysis of the persistence of price dispersion in a low inflation environment
Authors: Bahadir‐Lust Sebnem , Loy Jens‐Peter , Weiss Christoph R.
Published: July 2007

We study the existence of price distributions and the intra‐distribution dynamics for 10 food products across 131 retail stores in Germany for a time period of 43 weeks. Based upon Varian's (1980) model of sales, we aim at investigating whether the position of stores within the cross‐sectional price distribution is persistent or changes over time (mixed‐strategy equilibrium). Our results suggest a substantial degree of price dispersion even after controlling for unobserved store heterogeneity. Despite some intra‐distribution dynamics, we find evidence for a persistence of stores in the cross‐sectional price distribution over time. Copyright © 2007 John Wiley & Sons, Ltd.
The reflection coefficient of a flared microstrip line radiating in an infinite parallel‐plate waveguide
Authors: Cruz J. L. , Gimeno B. , Navarro E. A. , Such V.
Published: July 2007

In this article the reflection coefficient of a tapered microstrip line radiating in an infinite parallel‐plate conducting waveguide is calculated. The reflection coefficient at the feed line is evaluated by using the aperture admittance of the horn and the scattering matrix of the continuous taper. The theoretical behavior of the aperture admittance is shown and the reflection coefficient of a microstrip horn radiating in the parallel‐plate region of a bootlace lens is measured in order to verify the model. © 1993 John Wiley & sons, Inc.
A new hybrid method of calibration for polarimetric radar cross‐section measurements
Authors: Desclos L.
Published: July 2007

The main problem in polarimetric measurement is to retrieve all the properties (phase and magnitude) of the scattering matrix of the studied object. In most cases the proposed techniques [1–3] are very complicated and are not adaptable to intensive applications, as in the industrial domain. The development of an original technique is proposed here. The technique is very efficient and simple to use. It is based on a modification of an existing technique developed in Reference [1]. The main advantages are the facility of placement of the targets and the fact that there is no need to know the distances between the calibration targets and the emission reception system. © 1993 John Wiley & sons, Inc.
Polarimetric analysis of an anechoic chamber in a time domain
Authors: Desclos L. , Pouliguen P.
Published: July 2007

In an anechoic chamber, radar cross‐section (RCS) or antenna measurements intensify the need of knowing perfectly the electromagnetic (em) behavior of the locale of treatment. So it is very important to characterize the noise in the anechoic chamber. This can be done by locating and recognizing the elements which cause the perturbation. In this article a new technique using a combination of polarimetric and time domain analyses is presented. © 1993 John Wiley & sons, Inc.
Plots with matching circles for optimizing the performance of a low‐noise amplifier
Authors: Bor Sheau‐Shong , Liu Ji‐Chyun , Lu Po‐Chiang , Chang Chung‐Chi
Published: July 2007

Plots for optimizing the performance of LNA are presented here. From the study of the interaction between the input/output stability and the conjugate‐match conditions, four modified stability circles which are designated as matching circles are analytically developed for the input/ouptut networks. The available matching area is specified by using the modified determinations of the stability criteria. © 1993 John Wiley & sons, Inc.
Application of a banded matrix iterative approach to monte carlo simulations of scattering of waves by a random rough surface: TM case
Authors: Tsang Leung , Chan Chi H. , Sangani Haresh
Published: July 2007

A banded matrix iterative approach is applied to study scattering of a TM incident wave from a perfectly conducting one‐dimensional random rough surface. It is much faster than the full matrix inversion approach. When compared to the Kirchoff iterative approach, it is of comparable CPU time, is more accurate, and works for cases when the Kirchoff iteration fails. © 1993 John Wiley & sons, Inc.
Nepal—an algorithm for solving the volume integral equation
Authors: Chew Weng Cho , Lu Cai‐Cheng
Published: July 2007

A new algorithm is proposed to solve the volume integral equation whereby the scatterer is first divided into N subscatterers. Smaller problems are nested within larger problems using the Huygens equivalence principle. The resultant algorithm has reduced computational complexity whose CPU time is proportional to N1.5. © 1993 John Wiley & sons, Inc.
Polarization‐encoded optical shadow casting: Edge detection using roberts operator
Authors: Alam M. S. , Iftekharuddin K. M. , Karim M. A.
Published: July 2007

Roberts‐operator‐based edge detection is implemented using polarization‐encoded optical shadow casting. The proposed technique yields better results than the previously reported shadow‐casting edge detectors. © 1993 John Wiley & sons, Inc.
Evolution of nonlinear guided waves along a bent planar waveguide
Authors: Chang Wen‐Ching , Liu Shuh‐Fang , Wang Way‐Seen
Published: July 2007

Optical field propagation in a nonlinear bent slab waveguide with a Kerr‐like nonlinear cladding medium is presented. With increasing input power, the self‐focusing effect significantly disturbs the original waveguide configuration, and a nonstationary evolution behavior is found. It is shown that the onset and the direction of soliton emission are sensitive to the guiding capability of the initial waveguide. In particular, a novel result is observed when the waveguide supports more than one mode. © 1993 John Wiley & sons, Inc.
Combined effect of harmonic distortion and pulse dispersion in optical fiber transmission
Authors: Fraile‐Pelaez F. Javier , Gil‐Vazquez Fernando
Published: July 2007

We study the transmission of Gaussian pulses by subcarrier modulation of the laser power and obtain an analytical expression of the detected photocurrent. This result provides insight into the effects of the fiber dispersion on the transmission of AM‐modulated subcarriers. © 1993 John Wiley & sons, Inc.
Symmetrical coplanar waveguide with finite ground plane
Authors: Cai M. , Kooi P. S. , Leong M. S. , Yeo T. S.
Published: July 2007

A symmetrical coplanar waveguide with finite ground plane (SCPW) has been analyzed. The symmetrical configuration is obtained by simply placing a dielectric substrate above a conventional finite ground plane coplanar waveguide (FCPW). The conformal mapping method is used to calculate the quasistatic effective permittivity ϵeff and characteristic impedance Z0. The SCPW has a larger ϵeff and a smaller Z0, compared with the conventional FCPW. This configuration should be useful for the design of balanced mixer circuits and for applications to the design of balanced feed lines in printed antennas. © 1993 John Wiley & sons, Inc.
Effect of a dielectric overlay on a linearly tapered slot antenna excited by a coplanar waveguide
Authors: Simons Rainee N. , Lee Richard Q. , Perl Thomas D. , Silvestro John
Published: July 2007

A linearly tapered slot antenna (LTSA) with a dielectric overlay was experimentally investigated. The presence of dielectric overlay alters the guide wavelength of the LTSA, and thus the radiation characteristics of the antenna. Results indicate that dielectric overlay could be used to reduce the physical length and to improve the radiation characteristics of the LTSA. © 1993 John Wiley & sons, Inc.
An equivalent circuit model for multielectrode lasers: Potential devices for millimeter‐wave applications
Authors: Elkadi H. , Vilcot J. P. , Decoster D.
Published: July 2007

Static and dynamic behaviors of multielectrode lasers are, for the first time, studied using an equivalent circuit model. The model is based on the monomode rate equations and the Fermi integral. The potential controlled absorption in the active‐region quantum wells and its saturation are included as well as the different carrier recombination mechanisms. The model predicts a higher resonance amplitude and a ‐ 20‐dB/decade slope above resonance instead of the commonly known ‐40‐dB/decade slope for direct current modulation and consequently higher cutoff frequencies are to be expected for such structures. We also discuss briefly the impedance level of such structures as well as the different phenomena to be taken into account for a more precise representation. © 1993 John Wiley & sons, Inc.
Full guided mode expansion method and optimized sine method for analyzing optical waveguides
Authors: Wang Ye Heng
Published: July 2007

This article shows that the full guided mode expansion method and its limit, the optimized sine method, provide simple, fast, and accurate calculations of the propagation constant, even near the cutoff frequency. Use of a smaller scale matrix results in good agreement with previous works. © 1993 John Wiley & sons, Inc.
Optimal design of long‐haul optical soliton communication systems with lumped amplifiers
Authors: Ye Xiongyan Tang Peida
Published: July 2007

A method of designing an optical soliton communication system with lumped amplifiers is presented in this article. The design requirements and the design procedure are discussed. An exact bit‐error‐rate expression of the system is derived. Some design examples of the optimal systems are given. © 1993 John Wiley & sons, Inc.
A theoretical and experimental study of microshield circuits
Authors: Dib Nihad I. , Drayton Rhonda F. , Katehi Linda P. B.
Published: July 2007

A theoretical and experimental study of a new type of monolithic planar transmission line is presented. This line can operate without the need for via holes or the use of air bridges for ground equalization. Furthermore, it has shown the tendency to radiate less than the conventional coplanar waveguide (CPW) and can provide a wide range of impedances due to the many available parameters for design. The space‐domain integral equation method is used to analyze several discontinuities of the proposed line. In order to validate the theory, measurements are performed on scaled models of a specific discontinuity. The experimental and theoretical results are in good agreement. In addition, it is demonstrated that the proposed line discontinuities radiate considerably less than the corresponding coplanar waveguide ones. © 1993 John Wiley & sons, Inc.
The fresnel prism as polarization interferometer
Authors: Echarri Rodolfo
Published: July 2007

Here we show that a Fresnel prism can be used as a polarization interferometer. A linearly polarized beam, which is incident in this interferometer, is split into two circularly polarized beams, one right and another left, which generate the interference pattern. Interposing a solution of common sugar in the incident beam, the former pattern is shifted because of the circular birefringence of the sugar. Measuring the displacement of the interference pattern, we determine the phase difference between both circular polarizations introduced by the solution. Moreover, we compare this result with that obtained by measuring the rotation power, concluding that they are in good agreement. © 1993 John Wiley & Sons, Inc.
Efficient analysis of a dielectric post in a rectangular waveguide based on the two‐dimensional FD‐TD method
Authors: And Zhang Feng , Junmei Fu
Published: July 2007

A modified two‐dimensional FD‐TD method is used for the analysis of an H‐plane waveguide loaded with a dielectric post of arbitrary shape, size, number, and location, and the dielectric post resonances and the application of measurement of permittivity constant are discussed. The numerical results are in good agreement with data available in the literature, and the versatility of this approach is given. © 1993 John Wiley & Sons, Inc.
Analysis of uncovered two‐layer three‐coupled microstrip lines on anisotropic substrates
Authors: And Chulhun Seo , Lee Choong Woong
Published: July 2007

General expressions of the variational method are obtained for the quusistatic analysis of uncovered two‐layer three‐coupled microstrip lines. The frequency‐dependent parameter is obtained by employing the extended spectral domain in the full‐wave analysis. Accurate numerical results are presented for the line capacitances to the various widths of the first layer of two‐layer three‐coupled microstrip lines on anisotropic substrates. The propagation constants and the characteristic impedances are obtained for various frequencies. © 1993 John Wiley & Sons, Inc.
A hybrid gauss‐newton‐simulated annealing optimizer for extraction of mesfet equivalent circuit elements
Authors: Leong M. S. , Kooi P. S. , Yeo T. S. , Ooi B. L.
Published: July 2007

A new optimizer is presented for the extraction of the small‐signal equivalent circuit elements (X) of a CaAs FET from its measured scattering (S) parameters. The approach is a combination of the damped Gauss‐Newton method, for the least‐squares fitting of the S parameters, and the random search generalized simulated annealing (GSA). Novel features of the proposed approach include (i) an improved Kondoh step‐by‐step optimization of the objective functions grouped according to their sensitivity to variation of key equivalent circuit parameters (X), and (ii) exploitation of the advantages derived from a transformation of the objective functions from scattering parameters to impedance parameters. © 1993 John Wiley & Sons, Inc.
Plane‐wave propagation in a uniaxial chiro‐omega medium
Authors: Lindell Ismo V. , Tretyakov Sergei A. , Viitanen Ari J.
Published: July 2007

Plane‐wave propagation is considered in a medium which is a generalization of the uniaxial chiral and the uniaxial omega medium, both of which have shown properties useful for the design of electromagnetic devices. The medium is reciprocal and it can be easily realized by mixing certain metal wire elements in a host material. The resulting bianisotropic medium is isotropic in directions perpendicular to an axis in space. Wave‐number expressions are derived and numerical examples considered. © 1993 John Wiley & Sons, Inc.
Performance of MMIC components at cryogenic temperatures
Authors: Bhandari Anil , Butler Donald P. , Agarwal Krishna K.
Published: July 2007

We have measured the cryogenic performance of off‐the‐shelf GaAs MMIC amplifier and mixer‐converter modules from different foundries, with room‐temperature designs, without finding significant degradation in performance to 77 K. Therefore, existing MMIC modules would be suitable for hybrid microwave systems with high‐Tc superconducting transmission line filters, representing a cost savings. © 1993 John Wiley & Sons, Inc.
Mode energy transfer along a circular open chirowaveguide
Authors: Cory H. , Gov S.
Published: July 2007

Mode energy transfer along a circular open chirowaveguide is analyzed. It is shown that the TE0 and the TM0 are the only unperturbed modes that undergo coupling processes and that if the guide is exclusively excited with the TE01 mode, or the TM01, or both, only these modes are dominant. The energy variation along the guide is then almost periodic and the distance at which the energy transfer is largest is of the order of the radius, making this device attractive as a TE → TM mode converter, especially when a cylindrical geometry is required in a specific circuit design. © 1993 John Wiley & Sons, Inc.
On the TM101 mode of a hemispherical dielectric resonator antenna
Authors: Leung K. W. , Luk K. M. , Lai K. Y. A. , Lin D.
Published: July 2007

A hemispherical dielectric resonator antenna axisymmetrically fed by a coaxial probe is investigated both theoretically and experimentally. The input impedance of the lowest‐order TM mode (the TM101 mode) is evaluated by using the variational formula and the result agrees well with measured data. The effects of the probe length and dielectric constant on the input impedance are studied. Finally, the theoretical radiation pattern is compared with that of a bare mono‐pole of a quarter‐wavelength in height. © 1993 John Wiley & Sons, Inc.
A new rectenna circuit using a bow‐tie antenna for the conversion of microwave power to dc power
Authors: And Michael Tran , Nguyen Cam
Published: July 2007

A new rectenna circuit is described. The rectenna circuit uses a bow‐tie antenna integrated with a diode. The newly developed bow‐tie rectenna has a high conversion efficiency, is broadband, is not sensitive to the angle of the incident field, has a good match to its circuit, and behaves as a low‐pass filter for dc output. A microwave‐to‐dc conversion efficiency of 79% has been achieved at 2.45 GHz. © 1993 John Wiley & Sons, Inc.
The effects of strain on the microwave performance of SiGe HBTs
Authors: Rosenfeld D. , Alterovitz S. A.
Published: July 2007

The results of a theoretical study of the effects of the strain on the cutoff frequencies of SiGe HBTs are presented. The influence of the strain on the base resistance and transit time, and through them on high‐frequency performance, was taken into account. The positive role played by the strain is demonstrated. © 1993 John Wiley & Sons, Inc.
Cross‐polarization characteristics of a probe‐fed spherical‐circular microstrip patch antenna
Authors: Chen Hong‐Twu , Wong Kin‐Lu
Published: July 2007

The cross‐polarization characteristics of a spherical‐circular microstrip patch antenna excited at TM11 mode by a probe are investigated theoretically. The theoretical treatment is based on a rigorous Green's‐function formulation in the spectral domain. Numerical calculations are performed by using Galerkin's moment method. Numerical results of the cross‐polarization characteristics for different curvature radii of the spherical microstrip antenna are presented and analyzed. It is found that a smaller curvature radius of the spherical microstrip antenna can reduce the cross‐polarized radiation of the circular patch antenna at TM11 mode, and the cross‐polarization level increases with decreasing curvature radius. © 1993 John Wiley & Sons, Inc.
High‐temperature superconductor/III‐V hybrid microwave circuits (invited paper)
Authors: Shen Z‐Y. , Wilker C. , Pang P. S. W. , Carter C. F. , Nguyen V. X. , Laubacher D. B.
Published: July 2007

The electrical parameters of III‐V semiconductor devices were measured at cryogenic temperatures. These data were used for the accurate design of high‐temperature superconductor (HTS)III‐V hybrid microwave circuits. A number of such hybrid circuits, including amplifiers, oscillators, balanced mixers, and a dual channel receiver front end were designed and fabricated. Some of the test data for these circuits are presented. © 1993 John Wiley & Sons, Inc.
Performance of two‐pole bandpass filters photodefined on double‐sided Y‐Ba‐Cu‐O AND Tl‐Ba‐Ca‐Cu‐O thin films
Authors: Miranda F. A. , Toncich S. S. , Bhasin K. B.
Published: July 2007

The performance of 7.3‐GHz two‐pole bandpass filters (5% bandwidth) fabricated on double‐sided Y‐Ba‐Cu‐O and Tl‐Ba‐Ca‐Cu‐O thin films deposited on LaAlO3is discussed. At 77 K, the Tl‐Ba‐Ca‐Cu‐O and Y‐Ba‐Cu‐O superconducting filters exhibited minimum passband insertion losses of 0.3 and 1.2 dB, respectively. An insertion loss of 3.4 dB was measured for an all‐gold filter at 77 K. © 1993 John Wiley & Sons, Inc.
Impact of kinetic inductance effect on high‐Tc
Authors: Kain A. Z. , Pond J. M. , Fetterman H. R. , Jackson C. M.
Published: July 2007

High‐Q transmission high‐Tcsuperconducting coplanar waveguide resonators have been employed to make accurate measurements of the temperature dependence of the penetration depth via the change in phase velocity. Resonators made from several different film thicknesses are well described using a zero temperature penetration depth and a T‐squared temperature dependence using a full‐wave spectral‐domain model of the coplanar waveguide transmission line. © 1993 John Wiley & Sons, Inc.
Effects of cylindrical curvature on radiation from a microstrip antenna with a thick cover layer
Authors: Hoorfar Ahmad , Gupta K. C. , Chang D. C.
Published: July 2007

The fundamental radiation characteristics of a microstrip antenna on a cylindrical substrate with a thick cover layer is investigated by using a magnetic line source model. Numerical results for the radiation pattern and conductance are presented. It is found that certain combinations of curvature radius and cover‐layer thickness could result in significant distortions in the pattern. Lossy dielectric material may be used to reduce these undesired effects. © 1993 John Wiley & Sons, Inc.
On the radiation sensibility of a microstrip transmission line
Authors: And Renato Cicchetti , Pirone Carmine
Published: July 2007

A transmission‐line model excited by distributed generators is used to analyze the voltage and current induced by an external electromagnetic field in a microstrip transmission line. The influence of the electrical and geometrical parameters of the planar structure on the line's response to external transient electromagnetic fields has been analyzed. Design guidelines to reduce the disturbance induced are considered and the optimum choice for the substrate's parameters are discussed. © 1993 John Wiley & Sons, Inc.
On the subzone phase correction of fresnel zone plate antennas
Authors: Guo Y. J. , Barton S. K.
Published: July 2007

Subzone phase correction is a practical technique to produce high‐efficiency Fresnel zone plate antennas. In this article a strict theory underlying the technique is presented. A closed‐form expression of the focal field for the subzone phase correcting Fresnel zone plate (FZP) illuminated by a plane wave is given first. The subzone division and the corresponding phase correction are then optimized to produce the maximum focal field intensity. To overcome the difficulty of placing many subzone phase shifters in the narrow outer full‐wave zones, an aperiodic subzone phase correction technique is proposed.
Wideband equivalent circuit model of nonsymmetrical microstrip double step discontinuities
Authors: Bartolucci Giancarlo , Giannini Franco , Limiti Ernesto
Published: July 2007

A simple lumped‐element equivalent circuit for a double nonsymmetrical microstrip step discontinuity has been derived using a planar approach. The model has been verified by comparison with experimental data.
Field‐theory analysis of cross‐iris coupling in circular waveguide resonators
Authors: Zapata J. , Garcia J. , Valor L. , Garai J. M.
Published: July 2007

Dual‐mode circular waveguide filters employ cross‐iris couplings usually designed by small‐aperture approximations. This Letter presents a full‐wave method, which is able to rigorously analyze irises of any shape, thickness, and size, based on a mixed finite‐element method (FEM) and a mode‐matching technique. The accuracy of the method has been tested by comparing measured and computed data.
Optical‐fiber PPM soliton systems: Implications of the gordon‐haus effect
Authors: Cryan R. A. , Phillips A. J. , Senior J. M.
Published: July 2007

The fundamental limit in transmission distance, associated with the Gordon‐Haus timing jitter, is evaluated for an optical‐fiber pulse position modulation (PPM) soliton system. We demonstrate that soliton PPM is more susceptible to this type of timing jitter and that the maximum span length is limited to 65% of that of an equivalent soliton PCM system. © 1994 John Wiley & Sons, Inc.
A new set of orthogonal polynomial functions for waveguide analysis
Authors: Wang B. K. , Lam K. Y. , Leong M. S. , Kool P. S.
Published: July 2007

This article presents a new numerical procedure involving the use of orthogonal polynomials in a Rayleigh‐Ritz procedure to investigate the wave propagation characteristics of uniform hollow conducting waveguides of polygonal cross section. As examples of the applicability of the new functions, the TM modes in metallic waveguides of rectangular and triangular cross sections have been studied. © 1994 John Wiley & Sons, Inc.
InP‐based lasers on Si substrates with microcleaved mirrors
Authors: Sugo M. , Mori H. , Itoh Y. , Tachikawa M. , Sakai Y.
Published: July 2007

An InP‐based multiple quantum‐well laser diode on a Si substrate with microcleaved mirrors exhibits cw operation at room temperature. Microcleaved mirrors can be fabricated without having to cleave a Si substrate. The laser emits at a 1.54‐μm wavelength and exhibits stable operation even after more than 1000 hours. © 1994 John Wiley & Sons, Inc.
Strained GaInAsP/InP multiple‐quantum‐well lasers for wideband analog and high‐speed digital fiber‐optic networks
Authors: Fukushima T. , Matsumoto N. , Nakayama H. , Ikegami Y. , Namegaya T. , Kasukawa A. , Shibata M.
Published: July 2007

Compressively strained 1.3‐μm GaInAsP/InP multiple‐quantum‐well (MQW) lasers suitable for wide‐band analog and high‐speed digital transmissions were fabricated. With the ridge waveguide structure and an optimum well number, a large bandwidth of 11 GHz was achieved. The short‐cavity buried‐heterostructure lasers showed low threshold current (2 to 3 mA) and small turn‐on delay time (<200 ps) at biasless 30‐mA pulse current. © 1994 John Wiley & Sons, Inc.
On the application of Kirchhoff's approximation to scattering from discontinuities in large waveguide ducts
Authors: Ling Hao , Kim Hyeongdong
Published: July 2007

A simple Kirchhoff‐based approximation is presented to account for the mode conversion at discontinuities such as bends and steps in open‐ended waveguide ducts. Comparisons with other more numerically exact approaches and with experimental results for a variety of two‐ and three‐dimensional inlet duct configurations show that this approximation is surprisingly accurate when the transverse dimension of the duct is above 5 wavelengths. This approximation reduces the computational burden of predicting the scattering from large inlet ducts. © 1994 John Wiley & Sons, Inc.
Pupil symmetries for identical axial response
Authors: Escalera Juan C. , Campos Juan , Yzuel Maria J.
Published: July 2007

In this article we establish a symmetry condition for nonuniform pupils with different transmission functions to produce the same response along the axis. Besides, these pupils can produce different effects in the transverse response like apodization or hyperresolution. We also show the relation that different annular pupils have to satisfy in order to produce identical axial behavior. Some results of annular color filters that fulfill this condition are given. © 1994 John Wiley & Sons, Inc.
Analysis of a two‐octave polarization rotator using the method of equivalent boundary conditions
Authors: Pereyaslavets Michael L. , Kastner Raphael
Published: July 2007

A rapid analysis of a two‐octave, 45° polarization rotator is achieved by the approximate method of equivalent boundary conditions (EBC). Results achieved by this approximation and the conjugate gradient‐FFT (CG‐FFT) appear to be closely matched, with differences well within measurement error. Computation speed is significantly improved when compared with purely numerical techniques. © 1994 John Wiley & Sons, Inc.
On the interpolation of numerically defined surfaces in collimated‐beam dual reflector antennas
Authors: Bergmann J. R. , Hasselmann F. J. V. , Costa L. P. N. , Telxeira F. L. , Rego C. G.
Published: July 2007

Geometrical‐optics syntheses of shaped reflector antennas yield numerically defined surfaces that must be interpolated for subsequent evaluation of the radiation field and its check against design specifications. The implementation of three global interpolating functions is explored in connection with a typical dual‐shaped offset reflector antenna designed to produce a collimated beam with high efjkiency and low side‐lobe envelope. © 1994 John Wiley & Sons, Inc.
Combining SDA and fdtd methods for the modeling of planar applicators used in microwave hyperthermia
Authors: Duhamel F. , Dubois L. , Chive M. , Pribetich J.
Published: July 2007

An improved bidimensional finite‐difference time‐domain (2D FDTD) method has been achieved in order to compute all electromagnetic fields in heterogeneous media when planar microstripmicroslot applicators are used for microwave hyperthermia. This method consists of combining 2D FDTD and classical spectral domain approach (SDA). Good agreements are exhibited with classical SDA, thus allowing the study of inhomogeneous media. © 1994 John Wiley & Sons, Inc.
A new design approach for a high‐transimpedance and low‐noise optoelectronic integrated lightwave receiver with 24‐GHz bandwidth
Authors: John Eugene , Das Mukunda B.
Published: July 2007

This article illustrates how the bandwidth of a high‐transimpedance optoelectronic integrated circuit amplifier, involving a metal‐semiconductor‐metal (MSM) photodiode and heterojunction bipolar transistors (HBTs), can be improved by incorporating the concept of emitter RC‐network shunt peaking often used in common‐emitter voltage amplifiers. In the IC amplifier considered, the bandwidth has been shown to increase, with shunt peaking from 17.2 to 24 GHz, with no change of the equivalent input noise current (=2.3 pA/√Hz), arising mainly due to the input transistor's base current and the feedback resistor. © 1994 John Wiley & Sons, Inc.
An efficient approach for the evaluation of the double integrals in the analysis of printed circuit antennas
Authors: Cai M. , Kooi P. S. , Leong M. S.
Published: July 2007

A numerical approach for the evaluation of the double integrals that arise in the analysis of printed circuit antennas is developed. In this method, the integration variables in the integrals are transferred to the polar coordinate system (λ, θ). The approach focuses on the fact that the oscillating frequency of the integrand in the azimuth direction θ is nearly proportional to the radius A. An adaptive scheme to increase sampling points in the θ direction is therefore introduced. Numerical results show that the sampling points can be reduced by 50%. © 1994 John Wiley & Sons, Inc.
Automatic generation of the solution path of a parametrized nonlinear circuit in the presence of turning points
Authors: Rizzoli Vittorio , Costanzo Alessandra , Neri Andrea
Published: July 2007

The generation of the solution path of a parametrized nonlinear circuit represents the key step of a computer‐aided stability analysis. When this process is carried out by the Newton‐iteration‐based harmonic‐balance technique coupled with a continuation method, numerical ill conditioning occurs in the vicinity of the turning points due to the singularity of the Jacobian matrix. The Letter introduces a novel switching‐parameter algorithm allowing the turning points to be automatically detected without loss of numerical efficiency. In the neighborhood of the turning point the roles of the parameter and of one of the steady‐state harmonics are interchanged, so that the latter becomes the independent quantity. In this way the singularity is removed, and the analysis at the turning point can be performed with the same accuracy and efficiency as at any ordinary point. The switching criterion is based on the condition number of the conventional Jacobian. © 1994 John Wiley & Sons, Inc.
Automated finite‐element solution of nonlinear optical waveguide problems in two dimensions
Authors: Cvetkovic Srfoa R. , Zhao An Ping , Punjani Minaz
Published: July 2007

An efficient and automated finite‐element package (named WAVEGIDE), which is implemented within the PDE/ProtranTM problem‐solving environment, is extended here to the analysis of two‐dimensional nonlinear optical waveguiding structures. With WAVEGIDE, through an interactive question‐and‐answer session, which requires modest knowledge of programming and minimal effort for the input of waveguide parameters, the problem can be defined using high‐level PDE/ProtranTM commands. To illustrate the ease of use, flexibility, and accuracy of the developed package, numerical results for the first quasi‐TE power‐dependent mode in a buried nonlinear waveguide was presented. The program is available in the public domain. © 1994 John Wiley & Sons, Inc.
The effect of sample rate on propagation measurements
Authors: Stutzman Warren L. , Will Remaklus P.
Published: July 2007

This article presents results from a study on the effect of data sampling rate for earth‐space propagation experiments. Data taken from the Olympus 30‐GHz satellite beacon signal at Blacksburg, VA were sampled at 10 Hz in real time and then postprocessed to obtain effective sampling rates down to 0.1 Hz. Both event and statistical data are presented. © 1994 John Wiley & Sons, Inc.
A ray‐propagation fast multipole algorithm
Authors: Wagner Robert L. , Chew Weng Cho
Published: July 2007

A new technique is presented for accelerating the fast multipole method, allowing rapid solution of surface integral equations for wave‐scattering problems. A nonnested, ray‐propagation approach is used to compute a matrix‐vector multiply in O(N4/3) operations, where N is the number of unknowns in the discretized integral equation. © 1994 John Wiley & Sons, Inc.
Signal propagation in the presence of side‐band instability in long fiber links
Authors: Matera F. , Mecozzi A. , Romagnoli M. , Settembre M.
Published: July 2007

We study signal propagation in the presence of the side‐band instability process that is due to the periodic power variation due to the lumped amplifiers. We show that such side bands, which were previously observed for soliton signals, are a general process that show up also for conventional signals. © 1994 John Wiley & Sons, Inc.
Orthogonal‐polarization reflective star couplers
Authors: Barnard C. W. , Chrostowski J. , Kavehrad M.
Published: July 2007

New reflective optical fiber star couplers are proposed. The star broadcasts to all receiwers without excess loss by rotating the polarization of the transmitted light by 90°. The couplers use an orthogonal‐polarization variable reflector that can act as either a full or half reflector. Published by John Wiley & Sons, Inc. © 1994 John Wiley & Sons, Inc.
A novel uniplanar microstrip to slot‐line transition
Authors: Ho Thinh Q. , Hart Stephen M.
Published: July 2007

A novel approach for designing a uniplanar microstrip to slot‐line transition for MIC/MMIC and antenna applications is described. A slot‐line radial stub is utilized to create resonance conditions at the junction of the two transmission lines so that maximum intermodal power transfer occurs. Excellent insertion loss and impedance match is obtained over a 30% bandwidth. © 1994 John Wiley & Sons, Inc.
Matched loads simulation using ghost basis functions for moment‐method analysis: Applications to microwave planar circuits
Authors: Delabie C. , Delplanque Y. , Pribetich P. , Kennis P.
Published: July 2007

A clever way to simulate numerical matched loads is presented and applied in the mathematical framework of the moment method. This approach presents a lot of advantages with regard to other numerical matched load simulations, and could be used whateier the shape of the planar circuit without the help of the characteristic impedance concept. Results show that very good efficiency is obtained for the reflection coefficient of such matched loads. Typical results are exhibited for S‐parameter determination of multipart microstrip circuits. © 1994 John Wiley & Sons, Inc.
Multireference detection using iterative joint transform operation with composite filtering
Authors: Yu Francis T. S. , Cheng Feng
Published: July 2007

In this article we shall introduce an interative joint transform operation for multireference detection utilizing composite intensity compensation filtering. This technique essentially uses the normalized correlation peak intensity values as the iterative feedback into the input and Fourier planes to update the weight coefficients for the reference patterns and the composite intensity compensation filter. As shown in the simulated results, this technique can detect highly similar objects which cannot normally be differentiated with the conventional joint transform correlator. The effect due to noise is also investigated, in which we have shown that the technique improves the performance of the joint transform correlation. © 1994 John Wiley & Sons, Inc.
A perturbative approach to the scattering from a perfectly conducting wedge with a crack or gap in one of its faces
Authors: Pelosi G. , Manara G. , Monorchio A. , Coccioli R.
Published: July 2007

A perturbative solution is described for determining the field scattered by a perfectly conducting wedge with a crack or gap in one of its faces. The wedge is illuminated by a plane wave perpendicularly incident on its edge. The gap aperture is modeled by an equivalent surface impedance strip. Numerical results are presented to demonstrate the applicability of this perturbative technique. © 1994 John Wiley & Sons, Inc.
Characterization of dissipative losses in microwave circuits
Authors: Livernois Thomas G.
Published: July 2007

The analytical expression for the fractional power dissipated by a microwave circuit is derived in terms of the scattering parameters. Consideration is given to both complex and real port reference impedances. Theoretical values of fractional dissipated power, computed using a full‐wave analysis technique, are compared to experimentally obtained data. © 1994 John Wiley & Sons, Inc.
Correction factors for fresnel knife‐edge diffraction based on uniform theory of diffraction results
Authors: Legendre J. F. , Chassay G.
Published: July 2007

In this article shortcomings of the Fresnel knife‐edge theory are discussed and simple analytical correction factors are obtained with the help of UTD single‐wedge results. This new formulation is especially helpful in radio links where great diffraction effects are a concern. © 1994 John Wiley & Sons, Inc.