bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear circuit analysis using the method of harmonic balance—a review of the art. II. Advanced concepts
Authors: Gilmore Rowan J. , Steer Michael B.
Published: July 2007

The harmonic balance method is a technique for the numerical solution of nonlinear analog circuits operating in a periodic, or quasi‐periodic, steady‐state regime. The method can be used to efficiently derive the continuous‐wave response of numerous nonlinear microwave components including amplifiers, mixers, and oscillators. Its efficiency derives from imposing a predetermined steady‐state form for the circuit response onto the nonlinear equations representing the network, and solving for the set of unknown coefficients in the response equation. Its attractiveness for nonlinear microwave applications results from its speed and ability to simply represent the dispersive, distributed elements that are common at high frequencies.

The last decade has seen the development and application of harmonic balance techniques to model analog circuits, particularly microwave circuits. The first part of this article reviewed the fundamental achievements made during this time. In this part, the extension of the method to quasi‐periodic regimes, optimization analysis, oscillator analysis, studies of various convergence strategies, and practical applications are discussed. A critical assessment of the various types of harmonic balance techniques is given. Examples of designs which have been modeled using the harmonic balance technique and built both in hybrid and MMIC form are presented.
Modern perspectives in supercomputer‐aided microwave circuit design
Authors: Rizzoli Vittorio , Lipparini Alessandro , Costanzo Alessandra , Cecchetti Claudio , Neri Andrea , Mastri Franco , Sgallari Fiorella , Frontini Valeria
Published: July 2007

The computer‐aided simulation and design of microwave integrated circuits often leads to large‐size numerical jobs, especially for modern multiple‐device MMIC subsystems such as distributed mixers and amplifiers. When this is the case, the use of large computer systems such as vector processors may become very attractive, because of the dramatic reduction of wall‐clock time and of the related improvement of cost‐to‐performance ratio. This paper discusses the application of supercomputers to the solution of a number of such advanced microwave circuit CAD problems. An overview of the performance of general‐purpose vectorized algorithms such as system solvers and Fast Fourier Transforms is first presented, in order to give a feeling of the potential of this class of machines in microwave CAD applications. Then a few typical microwave engineering problems are specifically addressed, including the statistical design (yield optimization) of linear circuits, the analysis of nonlinear circuits under multitone excitation, and the optimization of ultrabroadband nonlinear subsystems. In each case, a possible vectorization strategy is studied in depth, and the structure and performance of a specific highly vectorized algorithm are described in detail.
A comparison of CAD models for radiation from rectangular microstrip patches
Authors: Jackson David R. , Williams Jeffery T.
Published: July 2007

A comparison of radiation models for a rectangular patch antenna is made. The dominant mode electric current model and magnetic current model are each applied to the cases of a rectangular patch on an infinite substrate, and a patch on a substrate which is truncated at the edges of the patch. It is noted that exact agreement is obtained between the two models for the case of a resonant patch, for both the infinite substrate and truncated substrate cases. The effects of dielectric truncation on the radiation patterns is discussed and the electric current model is also extended to include the effects of feed‐probe radiation and radiation from higher‐order modes on the patch.
Statistical analysis of GaAs MESFET S‐parameter equivalent‐circuit models
Authors: Anholt R. , Worley R. , Neidhard R.
Published: July 2007

We compare the ability of three different equivalent‐circuit extraction methods to give ensembles of model parameters that accurately predict not only average S‐parameters but the S‐parameter statistics, i.e., the standard deviations and intercorrelations between the real and imaginary parts. Measurements were made for 400 GaAs MESFETs fabricated on a single wafer with an MBE‐grown active layer. Data is compared for different biases. We find that bimodal distributions give correlations that the equivalent‐circuit models fail to model. The possibility of using uncorrelated equivalent‐circuit values is also discussed.
Full wave solution of dielectric loaded waveguides and shielded microstrips utilizing finite difference and the conjugate gradient method
Authors: Narayanan V. , Manela M. , Lade R. K. , Sarkar T. K.
Published: July 2007

Dynamic analysis of waveguide structures containing dielectric and metal strips is presented. The analysis utilizes a finite difference frequency domain procedure to reduce the problem to a symmetric matrix eigenvalue problem. Since the matrix is also sparse, the eigenvalue problem can be solved quickly and efficiently using the conjugate gradient method resulting in considerable savings in computer storage and time. Comparison is made with the analytical solution for the loaded dielectric waveguide case. For the microstrip case, we get both waveguide modes and quasi‐TEM modes. The quasi‐TEM modes in the limit of zero frequency are checked with the static analysis which also uses finite difference. Some of the quasi‐TEM modes are spurious. This article describes their origin and discusses how to eliminate them. Numerical results are presented to illustrate the principles.
Experimental validation of electromagnetic software
Authors: Rautio James C.
Published: July 2007

While the last decade has seen an explosion in the availability of microwave software, experimental validation efforts have seen little effort. As a result, most published validation efforts are, justifiably, viewed with skepticism. Thus, when an analysis is to be validated, it must be validated again and again for, and by, each group of users, often at considerable expense. This article describes areas for improvement of validation techniques, with examples drawn from current literature. The ultimate objective in the field of experimental validation is to evaluate a test suite with such quality that multiple validations no longer need be performed by each user.
Yield sensitivity study of A1GaAs/GaAs high electron mobility transistor
Authors: Sarker Jogendra C. , Purviance John E.
Published: July 2007

A simple graphical statistical method is presented and is used to study the statistical sensitivity of the AlGaAs/GaAs High Electron Mobility Transistor (HEMT) small‐signal performances to physical model parameters, Using an analytical model and applying numerical techniques, the small‐signal performances, transconductance, gate‐to‐source capacitance, current gain cut‐off frequency, and the optimum cut‐off frequency are calculated for four different HEMTs. These are then used as the device specifications in the Monte Carlo‐based sensitivity analysis.

Based on the model, a device simulator is developed in which the gate length, the gate width, and the carrier mobility are statistically varied simultaneously about their nominal values. The yield factor histograms for each small‐signal parameter and its sensitivity to the process parameter variations are determined. In this work, we report that the current gain cut‐off frequency increases as the carrier mobility increases, but it is almost independent of the gate width. We observe that the gate‐to‐source capacitance is independent of the carrier mobility, but it is strongly dependent on the transistor dimension. All the performance yields analyzed here go down as the gate length increases.
Large‐signal modeling and simulation of GaAs‐MESFETs and HFETs
Authors: Sledzik Hardy , Wolff Ingo
Published: July 2007

A new method for the derivation of a FET‐equivalent circuit for large‐ and small‐signal applications is described. The model, which is valid at least up to 26.5 GHz, consists of 9 nonlinear intrinsic elements and 8 linear extrinsic elements. All circuit‐elements are determined from measured DC and scattering parameters without numerical optimization by an analytical method at any bias condition. The nonlinear elements are expressed by two‐dimensional spline functions of the third order. For nonlinear simulations, the harmonic‐balance technique, combined with a successive approximation method without function derivations is used. A modified harmonic‐balance technique is applied for nonlinear simulations of oscillators.
Two‐dimensional field analysis for CAD of Rotman‐type beam‐forming lenses
Authors: Sharma P. C. , Gupta K. C. , Tsai C. M. , Bruce J. D. , Presnell R.
Published: July 2007

A general procedure for design and analysis of a Rotman‐type beam‐forming lens using 2‐dimensional field analysis is proposed. Evaluation of reflection coefficients, coupling between ports, main beam direction, 3‐dB beam width and side lobe level are described. The results for a sample case are in agreement with the experimental results. The procedure developed is suitable for CAD implementation leading to optimization of Rotman lens layout configuration.
Faster computation of Z‐matrices for triangular segments in planar circuits
Authors: Lee Sung Hwan , Benalla A. , Gupta K. C.
Published: July 2007

The method of images and currently available single‐series formulation of a rectangular planar segment have been applied to speed up the computations of impedance matrix elements of 30°–60°–90° and equilateral triangular microstrip segments used in planar microwave circuits. For an equilateral triangular segment, the elements of Z‐matrix are obtained by using the results for two 30°–60°–90° triangular segments, one of which has all magnetic walls and, in the other segment, one of the magnetic walls is replaced by an electric wall. The present formulations have been verified by comparison with the previously available double series formulations.
Conductor loss on transmission lines in monolithic microwave and millimeter‐wave integrated circuits
Authors: Heinrich Wolfgang
Published: July 2007

A field‐theoretical analysis of conductor loss on planar transmission lines is presented. The full‐wave approach employed holds for arbitrary values of metallization thickness and skin depth. Its validity is checked by comparison to measurement data on coplanar waveguide (CPW). The results are discussed and compared with modeling approaches available so far. The considerations concentrate on the CPW case where, in contrast to the microstrip structures used in hybrid ICs, a significant influence of the fields inside the lossy conductors can be detected. Finally, conclusions regarding both millimeter‐wave integrated circuit design and modeling are drawn. © 1992 John Wiley & Sons, Inc.
Synthesis of Marchand baluns using multilayer microstrip structures
Authors: Goldsmith Charles L. , Kikel Anthony , Wilkens Nancy L.
Published: July 2007

New equations and nomographs are derived for the synthesis of Marchand baluns using coupled‐line structures. These equations explicitly determine the coupled‐line parameters necessary to design Marchand baluns for specific load impedances and bandwidths. Practical MIC and MMIC circuit topologies are presented for realizing the difficult coupling parameters required by these baluns. © 1992 John Wiley & Sons, Inc.
Full‐wave spectral‐domain analysis for open microstrip discontinuities of arbitrary shape including radiation and surface‐wave losses (invited paper)
Authors: Horng Tzyy‐Sheng , Alexopoulos Nicolaos G. , Wu Shih‐Chang , Yang Hung‐Yu
Published: July 2007

This article is a survey of the theoretical background for full‐wave spectral‐domain analysis of open microstrip discontinuities of arbitrary shape. The spectral‐domain dyadic Green's function, which takes into account all the physical effects, such as radiation and surface waves, is used to formulate an electric field integral equation. The method of moments is then employed to find the current distribution on the microstrips, and subsequently, the scattering parameters of the junctions. Since all field components can be expressed in terms of the dyadic Green's function and the current distribution, the losses due to both radiation and surface waves are further determined through a rigorous Poynting vector analysis. To model the discontinuities of arbitrary shape, both rectangular and triangular subdomain functions are used as the current expansion functions in the moment method procedure. In addition, the semi‐infinite traveling wave functions are applied to simulate the feeding structure and isolate individual junction effects. Several examples are demonstrated to illustrate the utility of different techniques in this analysis. Comparison of some numerical results with available experimental data shows excellent agreement. Finally, this approach is most natural for the characterization of 3‐D integrated circuits and the design of printed antennas including excitation circuit effects. © 1992 John Wiley & Sons, Inc.
A comparative study between shielded and open coplanar waveguide discontinuities
Authors: Dib N. I. , Harokopus W. P. , Ponchak G. E. , Katehi L. P. B.
Published: July 2007

A comparative study between open and shielded coplanar waveguide (CPW) discontinuities is presented. In this study, the space domain integral equation method is used to characterize several discontinuities such as the open‐end CPW and CPW series stubs. Two different geometries of CPW series stubs (straight and bent stubs) are compared with respect to resonant frequency and radiation loss. In addition, the encountered radiation loss due to different CPW shunt stubs is evaluated experimentally. The notion offorced radiationsimulation is presented, and the results of such a simulation are compared to theactualradiation loss obtained rigorously. It is shown that such a simulation cannot give reliable results concerning radiation loss from printed circuits.
Fast FET and HEMT solvers for microwave CAD
Authors: Ladbrooke P. H. , Hill A. J. , Bridge J. P.
Published: July 2007

Methods are discussed for forecasting, in a few seconds on a personal computer with a 486 processor, equivalent circuits and S‐parameters of a GaAs FET from a physical specification. By inverting the algorithms, similarly fast simulators can be devised to fit equivalent circuits to measured S‐parameters, in the process yielding information on the FET's material and structural dimensions. The practical value of such simulators is illustrated by FETs designed and implemented to have a noise figure and associated gain at 12 GHz comparable with commercial pseudomorphic HEMTs. © 1993 John Wiley & Sons, Inc.
Nonsymmetry of Z‐matrices for planar circuits as obtained by the contour integral method
Authors: Tsai C. M. , Gupta K. C.
Published: July 2007

This article points out the possibility of obtaining nonsymmetrical Z‐matrices when the contour integral method is used for analysis of a general‐shaped, two‐dimensional planar component even when the component is passive and reciprocal. The nonsymmetry is caused by dependence of the normal derivative of the Green's function on the geometry. This nonsymmetry may be reduced by increasing the number of sections on the contour or by selecting a Green's function such that its normal derivative on the contour is zero. © 1993 John Wiley & Sons, Inc.
A moment method formulation for slot‐coupled waveguide Tee‐junction
Authors: Wang Hanyang , Sangster A. J.
Published: July 2007

A moment method analysis of an E‐plane waveguide Tee‐junction, in which the coupling element is an arbitrarily inclined slot, has been developed. Two cases are considered: namely, one in which the broad dimension of the coupled waveguide is transverse to the axis of the primary guide, and second, one in which the broad dimension of the coupled guide is axially directed. The computed results are shown to be in good agreement with network analyzer measurements on some typical cases. © 1993 John Wiley & Sons, Inc.
A new efficient CAD technique for inductive reactance coupled waveguide bandpass filters
Authors: Pramanick Protap , Bhartia Prakash
Published: July 2007

This article presents a computer‐aided synthesis technique for E‐plane and iris‐coupled waveguide bandpass filters. This technique uses fewer optimization variables than are required by the existing techniques. The designer begins with an accuratea prioriknowledge of the search direction and uses an efficient penalty function. The closed‐form expressions for waveguide discontinuities, for the initial computation of the K‐inverter values in the optimization procedure, greatly enhances the design speed. The technique has been implemented on a personal computer and has been found to be as accurate as the existing methods implemented on mainframe computers. Results are presented for several Ku and Ka‐band iris‐coupled and E‐plane filters. © 1993 John Wiley & Sons, Inc.
Analysis of waveguide directional filters by the moment method (invited article)
Authors: Seki Hajime
Published: July 2007

Analysis of a waveguide directional filter with N cavities is formulated in terms of the moment method. Electric fields on coupling apertures, being unknown, rigorously coupled integral equations, are established by using dyadic Green's functions. In this analysis, a virtual cavity technique is introduced as well as an approximate method to incorporate finite conductivity of cavity walls. Numerical results are also shown. © 1993 John Wiley & Sons, Inc.
Finite difference modeling of novel waveguiding structures for MMIC applications
Authors: Soghomonian Manook S. , Robertson Ian D.
Published: July 2007

Finite difference schemes have been utilized to model the field profiles of several novel waveguiding structures, which support a quasi‐TEM class of propagation. From the electric field values the impedance, equivalent capacitance and attenuation of the structures are calculated. This article describes modification to existing guiding structures such as a conventional coplanar waveguiding structure, by inserting longitudinal and transverse dielectric stratifications, and describes the use of finite difference scheme to obtain their characteristics. © 1993 John Wiley & Sons. Inc.
CAD of two‐port Gap‐coupled rectangular microstrip patches and linear series‐fed arrays
Authors: Benalla Abdelaziz , Gupta K. C.
Published: July 2007

A CAD approach based on the multiport network model (MNM) has been developed for the design/analysis of rectangular microstrip patches gap‐coupled to a microstrip feed line. Microstrip patches on thin substrates with and without a dielectric cover layer are considered. Results of the analysis for sample two‐port patches are compared with experimental and moment method results. The agreement validates the proposed model and the analysis procedure. Application of the MNM approach to CAD of linear series‐fed arrays of gap‐coupled rectangular microstrip patches is also discussed, © 1993 John Wiley & Sons, Inc.
Design of microstrip line‐fed patch arrays including mutual coupling
Authors: Yang Hung‐Yu David , Chen C. Harry , Castaneda Jesse A. , Wong William C.
Published: July 2007

A computer‐aided design algorithm is developed to facilitate the design of E‐plane series‐fed patch arrays. A rigorous moment method is used to compute the impedance of and the currents on each patch element in the array. Mutual coupling between adjacent patch elements is included in the computation. Experimental validation of the algorithm is reported. The effects of fabrication tolerance, material parameter variations, and mutual coupling on the array performance are highlighted.
Moment method analysis of linearly tapered slot antennas
Authors: Köksal Adnan , Kauffman J. Frank
Published: July 2007

An accurate Method of Moments (MoM) model is developed and implemented for the analysis of the linearly tapered slot antenna (LTSA). The model employs an unequal size reactangular sectioning for conducting parts of the antenna. Piecewise sinusoidal basis functions are used for the expansion of conductor current. The effect of the dielectric is incorporated in the model by using equivalent volume polarization current density and solving the equivalent problem in free space. The feed section of the antenna including the micro‐stripline is handled rigorously in the MoM model by including slotline short‐circuit and microstripline currents among the unknowns. Comparison with measurements is made to demonstrate the validity of the model for both the air case and the dielectric case. Numerical results for the effect of the dielectric permittivity are presented.
Synthesis and performance of an active microstrip antenna
Authors: Fusco Vincent F. , Drew Stephen , McDowall D. Stewart
Published: July 2007

This article discusses the application of a synthesis method for, and the subsequent experimental characterization, of an active microstrip patch antenna. The active antenna incorporates a GaAs MESFET on the patch periphery and the circuit acts as a self‐oscillating radiating element. The MESFET and the antenna are mounted on the same side of the circuit, thereby preserving the conformal nature of the structure. The synthesis approach described is based on the method of harmonic balance and allows optimal FET terminations to be selected for a predefined, added power at a specified frequency of operation. Application of a time domain simulator is illustrated in order to demonstrate start‐up performance and limit cycle formation in the presence and absence of a frequency entrainment signal. The issue of stability of the active element is also addressed using a modified device/load line method. Theoretical and experimental results are presented for the external quality factor, locking power/phase variation, and power and frequency pushing characteristics of the active antenna. Finally, the effect on oscillator behavior of the mutual coupling between the microstrip patch and the active antenna distributed embedding elements is discussed.
Nuclear localization of valosin‐containing protein in normal muscle and muscle affected by inclusion‐body myositis
Authors: Greenberg Steven A. , Watts Giles D. , Kimonis Virginia E. , Amato Anthony A. , Pinkus Jack L.
Published: July 2007

Inclusion‐body myopathy with Paget's disease and frontotemporal dementia (IBMPFD) is a disease of muscle, bone, and brain that results from mutations in the gene encoding valosin‐containing protein (VCP). The mechanism of disease resulting from VCP mutations is unknown. Previous studies of VCP localization in normal human muscle samples have found a capillary and perinuclear distribution, but not a nuclear localization. Here we demonstrate that VCP is present in both myonuclei and endothelial cell nuclei in normal human muscle tissue. The immunodetection of VCP varies with acetone or paraformaldehyde fixation. Within the nucleus, VCP associates with the nucleolar protein fibrillarin and Werner syndrome protein (Wrnp) in normal and IBMPFD muscle. In patients with inclusion‐body myositis (IBM), normal nuclear localization is present and some rimmed vacuoles are lined with VCP. These findings suggest that impairment in the nuclear function of VCP might contribute to the muscle pathology occurring in IBMPFD. Muscle Nerve, 2007
Mechanisms of fatigue differ after low‐ and high‐force fatiguing contractions in men and women
Authors: Yoon Tejin , Schlinder Delap Bonnie , Griffith Erin E. , Hunter Sandra K.
Published: July 2007

The magnitude of failure in voluntary drive after fatiguing contractions of different intensities in men and women is not known. The purpose of this study was to compare the time to task failure and voluntary activation of men and women for a sustained isometric contraction performed at a low and high intensity with the elbow flexor muscles. Nine men and nine women sustained an isometric contraction at 20% and 80% of maximal voluntary contraction (MVC) force until task failure during separate sessions. The men had a shorter time to failure than women for the 20% but not the 80% MVC task. Voluntary activation was reduced to similar levels for the men and women at the end of the fatiguing contractions but was reduced less after the 80% MVC task than the 20% MVC contraction. Twitch amplitude was reduced similarly at task failure for both sexes and to similar levels at termination of the 20% and 80% MVC tasks. The rate of change in mean arterial pressure was the main predictor of time to failure for the low‐force sustained contraction. These results suggest that women experienced greater muscle perfusion, less peripheral fatigue, and a longer time to task failure than men during the low‐force fatiguing contraction. However, the low‐force task induced greater central fatigue than the high‐force contraction for both men and women. Thus, low‐force, long‐duration fatiguing contractions can be used in rehabilitation to induce significant fatigue within the central nervous system and potentially greater neural adaptations in men and women. Muscle Nerve, 2007
Quality of life in Swedish workers exposed to hand–arm vibration
Authors: Cederlund Ragnhild , Iwarsson Susanne , Lundborg Göran
Published: July 2007

The objective of the present study was to analyse whether differences existed among workers exposed to hand–arm vibration (HAV) with regard to quality of life (QoL) issues. One hundred and eight male workers from a heavy manufacturing plant, with and without HAV symptoms, and workers referred to a hand surgery department with severe HAV symptoms participated in the study. The participants attended a clinical interview, were given a physical examination of the hands and administered the Göteborg Quality of Life instrument and the Evaluation of Daily Activity Questionnaire (EDAQ). Results indicated that workers referred to a hand surgery department with more severe HAV symptoms described a lower quality of life, defined here as lower subjective well‐being, more symptoms of ill‐health and difficulties with activities of daily living (ADL), than workers with no HAV symptoms. Workers from a heavy manufacturing plant with HAV symptoms experienced more difficulties with ADL, especially while working outdoors in cold weather, than workers with no HAV symptoms. Limitations of the present study include the use of a subjective scale to describe HAV symptoms. Further research is recommended on a larger sample of workers at risk for HAV symptoms to develop preventative ergonomic strategies. Copyright © 2007 John Wiley & Sons, Ltd.
Biomimetic modification of chitosan with covalently grafted lactose and blended heparin for improvement of in vitro cellular interaction
Authors: Tan Huaping , Lao Lihong , Wu Jindan , Gong Yihong , Gao Changyou
Published: July 2007

Lactose‐ and heparin‐modified chitosan films were prepared and their physical and biological properties were compared with chitosan, chitosan‐g‐heparin, and chitosan‐g‐lactose films. Atomic force microscopy (AFM) measurement showed that all these films in the dry state were rather flat with a roughness smaller than 20 nm. While the chitosan‐g‐lactose/heparin and chitosan‐g‐lactose films have the highest swelling and weight loss ratios, the chitosan and chitosan‐g‐heparin films have the lowest. The chitosan‐g‐lactose/heparin film showed stronger ability to induce chondrocyte attachment, proliferation, viability, and glycosaminoglycan (GAG) secretion than that of the chitosan, chitosan‐g‐heparin, and chitosan‐g‐lactose films. Chondrocyte aggregates and nodules were observed on the chitosan‐g‐lactose/heparin and chitosan‐g‐lactose films, which still preserved viable metabolic ability. These results show that the lactose‐modified and heparin‐incorporated chitosan film can enhance the cell–biomaterial interaction synchronously. The resulting chitosan‐g‐lactose/heparin material is more bioactive that might be applicable as promising scaffold for chondrogenesis. Copyright © 2007 John Wiley & Sons, Ltd.
Effect of pH on the drug release rate from a new polymer–drug conjugate system
Authors: Kenawy El‐Refaie , Abdel‐Hay Fouad , El‐Newehy Mohamed , Ottenbrite Raphael M
Published: July 2007

The corresponding N‐hydroximide and N‐methyl‐N‐hydroximide of poly[ethylene‐alt‐(maleic anhydride)] (weight average molecular weight (Mw) of 100–500 g mol−1) were prepared as a new oral drug delivery system. Syntheses of N‐hydroximide and N‐methylhydroxamic acid of poly[ethylene‐alt‐(maleic anhydride)] were carried out by chemical modification of polymer with hydroxylamine and N‐methylhydroxylamine, respectively, to give water‐soluble polymers. These activated polymers were immobilized with ketoprofen in the presence of dicyclohexylcarbodiimide to give the corresponding water‐insoluble ketoprofen conjugates. All products were characterized by elemental analysis as well as Fourier transform infrared and 1H NMR spectra. In vitro release of ketoprofen was studied by measuring UV absorption at λmax = 260 nm as a function of time. This study demonstrated the potential use of N‐hydroximide and N‐methyl‐N‐hydroxamic acid of poly[ethylene‐alt‐(maleic anhydride)] as a drug delivery system. Controlled release was studied at different pH values and at different temperatures. At physiological temperature, the amount of drug released increased with increasing pH. The copolymer‐drug adducts released the drug very slowly at the low pH found in the stomach thus protecting the drug from the action of high acid conditions and resident digestive enzymes. These N‐hydroxamic acid polymer‐drug conjugates were found to be potentially useful in the delivery of macromolecular drugs to targeted sites in the lower gastrointestinal tract and the colon area. Copyright © 2007 Society of Chemical Industry
Synthesis and properties of hyperbranched polyurethanes, hyperbranched polyurethane copolymers with and without ether and ester groups using blocked isocyanate monomers
Authors: Vanjinathan Mahalingam , Shanavas A. , Raghavan A. , Nasar A. Sultan
Published: July 2007

Starting from 3,5‐diamino benzoic acid, 2‐hydroxy propyl[3,5‐bis{(benzoxycarbonyl)imino}]benzyl ether, an AB2‐type blocked isocyanate monomer with flexible ether group, and 2‐hydroxy propyl[3,5‐bis{(benzoxycarbonyl)imino}]benzoate, an AB2‐type blocked isocyanate monomer with ester group, were synthesized for the first time. Using the same starting compound, 3,5‐bis{(benzoxycarbonyl)imino}benzylalcohol, an AB2‐type blocked isocyanate monomer, was synthesized through a highly efficient short‐cut route. Step‐growth polymerization of these monomers at individually optimized experimental conditions results in the formation of hyperbranched polyurethanes with and without ether and ester groups. Copolymerizations of these monomers with functionally similar AB monomers were also carried out. The molecular weights of the polymers were determined using GPC and the values (Mw) were found to vary from 1.5 × 104 to 1.2 × 106. While hyperbranched polyurethanes having no ether or ester group were found to be thermally stable up to 217 °C, hyperbranched poly(ether–urethane)s and poly(ester–urethane)s were found to be thermally stable up to 245 and 300 °C, respectively. Glass transition temperature (Tg) of polyurethane was reduced significantly when introducing ether groups into the polymer chain, whereas Tg was not observed even up to 250 °C in the case of poly(ester–urethane). Hyperbranched polyurethanes derived from all the three different AB2 monomers were soluble in highly polar solvents and the copolymers showed improved solubility. Polyethylene glycol monomethyl ether of molecular weight 550 and decanol were used as end‐capping groups, which were seen to affect the thermal, solution, and solubility properties of polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3877–3893, 2007
Electrosyntheses of high‐quality polyphenanthrene in the electrolyte of boron trifluoride diethyl etherate containing trifluoroacetic acid
Authors: Nie Guangming , Han Xuejun , Zhang Shusheng , Wei Qingli
Published: July 2007

A novel inherently conducting polymer, high‐quality polyphenanthrene (PPh) films were synthesized electrochemically by direct anodic oxidation of phenanthrene (Ph) in boron trifluoride diethyl etherate (BFEE) containing a certain amount of trifluoroacetic acid (TFA). The oxidation potential of Ph in this medium was measured to be only 0.63 V versus SCE, which was greatly lower than that determined in acetonitrile + 0.1 mol L−1 Bu4NBF4 (1.55 V vs. SCE). The electrolytes of BFEE containing TFA enable facile anodic oxidation of Ph monomer; however, similar oxidation using acetonitrile never produces such a polymeric material. PPh films obtained from this medium showed good redox activity and stability even in concentrated sulfuric acid. Dedoped PPh films were partly soluble in polar solvent such as CH2Cl2, acetone, tetrahydrofuran, and dimethyl sulfoxide. Fluorescent spectral studies indicate that PPh is a good blue‐light emitter. The structure and morphology of the polymer were studied by UV–vis spectroscopy, FTIR spectroscopy, 1H NMR spectroscopy, and scanning electron microscopy, respectively. The results of quantum chemistry calculations of Ph monomer and the spectroscopies of dedoped PPh indicated the polymerization mainly occurred at C(9) and C(10) positions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3929–3940, 2007
Effects of hydrogen in ethylene polymerization and oligomerization with magnesium chloride‐supported bis(imino)pyridyl iron catalysts
Authors: Huang Rubin , Koning Cor E. , Chadwick John C.
Published: July 2007

The effects of hydrogen in ethylene polymerization and oligomerization with different bis(imino)pyridyl iron(II) complexes immobilized on supports of type MgCl2/AlEtn(OEt)3–n have been investigated. Hydrogen has a significant activating effect on polymerization catalysts containing relatively bulky bis(imino)pyridyl ligands, but this is not the case in ethylene oligomerization with a catalyst containing relatively little steric bulk in the ligand. It was found that the presence of hydrogen in the latter system led to decreased activity and an overall increase rather than a decrease in product molecular weight, indicating deactivation of active species producing low molecular weight polymer and oligomer. Decreased formation of vinyl‐terminated oligomers in the presence of hydrogen can therefore contribute to the activating effect of hydrogen in ethylene polymerization with immobilized iron catalysts, if it is assumed that hydrogen activation is related to chain transfer after a 2,1‐insertion of a vinyl‐terminated oligomer into the growing polymer chain. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4054–4061, 2007
Impact Fragmentation of Metal Nanoparticle Agglomerates
Authors: Seipenbusch Martin , Toneva Petya , Peukert Wolfgang , Weber Alfred P.
Published: July 2007

Deagglomeration experiments were performed with agglomerates of nanoparticles of Ni and Pt. The fragmentation was induced by high velocity impaction of the agglomerates in a single‐stage low pressure impactor and the fragmentation patterns were evaluated by TEM analysis. Weibull statistics are employed for a quantitative description of the fragmentation behavior. This study shows that for well‐defined interparticle contacts, the impact fragmentation technique combined with the evaluation according to Weibull statistics, allows the recovery of the expected size dependencies. For Pt and Ag, the adhesion force particle size dependency was dominated by van der Waals forces. In contrast, the adhesion force between Ni particles in the size range from 12–28 nm revealed a much stronger increase with particle size. This phenomenon may be attributed to permanent magnetic dipole moments which are also reflected in the chain‐like shape of the agglomerates. For nanoparticle agglomerates with less well‐defined contacts, such as those in industrial environments, the method provides a promising application to reveal the bond strength and cohesiveness of nanoparticle powders.
Improving the Robustness of Particle Size Analysis by Multivariate Statistical Process Control
Authors: Mattila Marko , Saloheimo Kari , Koskinen Kari
Published: July 2007

The robustness of online particle size analysis in wet processes is improved by applying data based modeling methods to the control of the sample preparation and measurement sequence of the particle size analyzer. The aim is to find a more accurate and reliable method of determining the end of the particle size integration period using multivariate statistical process control (MSPC).

The studied approach is tested on analyzers installed at two mineral processing plant sites and validated using two validation tests. Research shows that the proposed method works with two very different slurry types. The main advantage of the adapted approach is that there are no adjustable parameters that have to be set by the user.
Inhibition of SULT2B1b expression alters effects of 3β‐hydroxysteroids on cell proliferation and steroid hormone receptor expression in human LNCaP prostate cancer cells
Authors: He Dongning , Falany Charles N.
Published: July 2007

BACKGROUND

Sulfation is an important steroid inactivation in human tissues. Sulfotransferase (SULT) 2B1b selectively conjugates 3β‐hydroxysteroids and is expressed in epithelial cells of normal and cancerous prostate tissues. Dehydroepiandrosterone (DHEA) and Δ5‐androstenediol (Δ5‐Adiol) sulfation prevents their conversion to more potent androgens and estrogens in tissues although both compounds may also be biologically active.

METHODS

SULT2B1b expression and activity were inhibited >85% in human LNCaP prostate adenocarcinoma cells using short interference RNA (siRNA). The effects of treating control and SULT2B1b‐deficient LNCaP cells with DHEA, Δ5‐Adiol, and 5α‐androstane‐3β‐17β‐diol (Anstane‐diol) on cellular proliferation, estrogen receptors (ERs), androgen receptor (AR), and prostate specific antigen protein levels were examined.

RESULTS

Physiological concentrations of DHEA and Δ5‐Adiol increased proliferation of control cells and the proliferative effects were significantly increased in SULT2B1b‐siRNA cells. DHEA, but not Δ5‐Adiol increased AR levels at concentrations ≥1,000 nM in SULT2B1b‐siRNA cells but not in control LNCaP cells. ER‐α levels were not affected with any of the compounds tested. Physiological concentrations of DHEA and Δ5‐A‐diol decreased ER‐β levels in control cells and had significantly greater effects in SULT2B1b‐siRNA cells. In contrast, Anstane‐diol had no effect on AR or ER‐α levels but induced more elevation of ER‐β levels in SULT2B1b‐siRNA cells at concentrations ≥1,000 nM.

CONCLUSIONS

SULT2B1b is involved in regulating prostate cell responsiveness to DHEA and Δ5‐Adiol. Inhibition of SULT2B1b increased cell proliferation and ER‐β repression after treatment with physiological levels of DHEA and Δ5‐Adiol indicating that SULT2B1b has an inhibitory effect on DHEA and Δ5‐Adiol activity. Prostate 67: 1318–1329, 2007. © 2007 Wiley‐Liss, Inc.
Development of an androgen‐deprivation induced and androgen suppressed human prostate cancer cell line
Authors: Lee Soo Ok , Dutt Smitha S. , Nadiminty Nagalakshmi , Pinder Elaine , Liao Hongtao , Gao Allen C.
Published: July 2007

BACKGROUND

Emergence of recurrent cells during androgen‐deprivation therapy and intermittent androgen suppression therapy suggest that a subset of prostate cancer cells survive and proliferate in the androgen deprivation condition. Some of the recurrent cells that emerge during the androgen‐deprivation therapy and intermittent androgen suppression therapy could be suppressed by replacement of androgen. In an attempt to recapitulate the clinical phenomenon, we developed an androgen‐deprivation induced and androgen suppressed human prostate cancer cell line.

METHODS

LNCS, an androgen‐deprivation induced and androgen suppressed human prostate cancer cell line, was generated from an androgen‐sensitive LNCaP cells cultured in PRMI‐1640 media containing charcoal‐stripped FBS for a prolong period for more than a year. The responsiveness to androgen in vitro and in vivo was examined. The characteristics of this subline including activation of signaling pathways were investigated.

RESULTS

LNCS, an androgen‐deprivation induced and androgen suppressed human prostate cancer cell line, was developed. LNCS cells express considerably lower levels of androgen receptor than LNCaP cells and grow vigorously in androgen deprived condition in vitro, and develop tumors in castrated male mice in vivo. Addition of androgen inhibits cell growth in vitro and tumor growth in vivo. LNCS cells are more resistant to etoposide, a typical apoptotic inducing agent. Although AR signaling is less active in LNCS cells, Stat3 is constitutively activated. Down regulation of Stat3 activation inhibits LNCS cell growth in vitro.

CONCLUSIONS

We have developed an androgen‐deprivation induced and androgen suppressed human prostate cancer cell line. This cell line is a valuable tool to study molecular mechanisms of the progression of androgen refractory prostate cancer and intermittent androgen suppression therapy. Prostate 67: 1293–1300, 2007. © 2007 Wiley‐Liss, Inc.
Change of expression levels of alpha1‐adrenoceptor subtypes by administration of alpha1d‐adrenoceptor‐subtype‐selective antagonist naftopidil in benign prostate hyperplasia patients
Authors: Kojima Yoshiyuki , Sasaki Shoichi , Shinoura Hitomi , Hayase Masa , Kubota Yasue , Hayashi Yutaro , Tsujimoto Gozoh , Kohri Kenjiro
Published: July 2007

BACKGROUND

We examined whether the change of alpha1‐adrenoceptor (α1‐AR) subtype expression levels in the prostate occurred by administration of the α1d‐AR‐subtype‐selective antagonist naftopidil to benign prostate hyperplasia (BPH) patients, and discussed the possible alternation of its effectiveness by the chronic administration of α1‐AR antagonists.

METHODS

Fifteen patients with untreated BPH aged 58–76 (mean age, 68.2 ± 7.4 years) underwent prostate biopsy from the transition zone before and after 50 mg naftopidil administration daily for 12 weeks. Taqman quantitative reverse transcription polymerase chain reaction was performed using these biopsy specimens to estimate the expression level of each α1‐AR subtype. Comparison was made of the expression level of α1‐AR subtypes before and after naftopidil administration. We also examined the correlation between the change of α1‐AR subtype expression levels and the short‐term efficacy of naftopidil.

RESULTS

Naftopidil administration for 12 weeks down‐regulated the expression of α1a‐AR and α1b‐AR mRNA and up‐regulated the expression of α1d‐AR mRNA without a change in the total α1‐AR mRNA expression level. There was no correlation between the change of α1‐AR subtype expression levels and the short‐term efficacy of naftopidil for BPH patients.

CONCLUSION

The change of α1d‐AR expression level may be regarded as a compensatory adaptation to chronic α1d‐AR antagonist naftopidil administration. This may mean that long‐term use of the same α1‐AR antagonist for BPH patients induces therapeutic tolerance. Prostate 67: 1285–1292, 2007. © 2007 Wiley‐Liss, Inc.
Current optimum management of dyspepsia and ulcers
Authors: Anderson Simon , Wilkinson Mark
Published: July 2007

Several protocols and management guide lines for dyspepsia have been produced in recent years. This Drug review outlines the current recommendations on the investiga tion and treatment of dyspepsia, GORD and peptic ulceration, followed by sources of further information and the Datafile. Copyright © 2007 Wiley Interface Ltd
Drug treatment of childhood mental health disorders
Authors: Hindley Peter
Published: July 2007

Our series Prescribing in children gives practical advice for successful man agement of childhood prob lems in general practice. Here, the author describes the management of attention deficit/hyperactivity disorder, autism spectrum disorders and early‐onset psychoses. Copyright © 2007 Wiley Interface Ltd
Parameters of band structure in surface layers of zero‐gap semiconductors (CdHg)Te
Authors: Yafyasov A. , Bogevolnov V. , Perepelkin A.
Published: July 2007

The field‐effect method in electrolytes is used for finding the band structure parameters in surface layers of zero‐gap semiconductors (ZGS) (CdHg)Te. It is found that the conduction band both in surface layers and in the volume of ZGS (CdHg)Te obeys the ultrarelativistic dispersion relation. The electron effective mass in surface layers of ZGS (CdHg)Te is close to the electron effective mass in the volume of ZGS (CdHg)Te. It is stated that the heavy‐hole valence band both in surface layers and in the volume of ZGS (CdHg)Te has a non‐parabolic dispersion relation, and that the heavy‐hole effective mass is less than 0.5m0 and depends on the composition of (CdHg)Te. It is found that the position of the Fermi level in ZGS (CdHg)Te is described in the model of zero‐gap semiconductors with fluctuating potential. The “step” structure in the dependences of the differential capacitance of the space‐charge layer in ZGS (CdHg)Te on temperature at fixed values of the surface potential is observed experimentally for the first time.
The properties of surface polarons in polar crystals
Authors: Xiao Jing‐Lin , Xing Tong‐Hai , Sun Bao‐Quan , Xiao Wei
Published: July 2007

Some properties of a surface polaron in polar crystals are studied. The effective Hamiltonian of the surface polaron is derived using a perturbation method. If we consider the interaction between phonons of different wave vectors in the recoil process, the influence on the effective Hamiltonian, effective potential, and effective mass are discussed. Numerical calculations for GaAs, ZnS, and AgBr crystals, as examples, are performed.
Temperature dependence of the excitonic transitions in GaAsGaAlAs superlattices under a weak electric field
Authors: Depeyrot J. , Tronc P. , Umdenstock E. , Palmier J. F. , Etienne B.
Published: July 2007

The temperature variations (between 9 and 80 K) of the ratio ϱ = I−1/I0 of the intensities of the −1 and 0 peaks of the Wannier‐Stark ladder in a GaAsGa0.65Al0.35 As superlattice under an electric field are interpreted. The model is based on the thermal equilibrium between the two populations of excitons. The filling rate of every excitonic levels is given by the Maxwell‐Boltzmann distribution function. A discrepancy appears at low temperatures (T < 50 K); the excitons are trapped into the direct state rather than in the crossed one, showing that the equilibrium statistics are not respected.
On the theory of shallow acceptor states in real semiconductors
Authors: Zubkova S. M. , Filin V. G. , Smelyanskaya E. V. , Tolpygo K. B.
Published: July 2007

Shallow acceptor states in crystals with diamond and sphalerite type structures are investigated by analytical and numerical methods, proposed by the authors for an exciton problem previously. The complicated valence band structure and the chemical nature of the impurity are taken into account. The obtained results for B and Al in Ge, Si, Zn Te, SiC, and GaAs are in good agreement with available experimental data and theoretical calculations of other works.
Antiferromagnetic interaction between two easy‐plane ferromagnetic heisenberg chains
Authors: Diaz V. , Gutiérrez G. , Ferrer R.
Published: July 2007

Nonlinear magnetic excitations in the Heisenberg magnetic system CsNiF3, when an antiferromagnetic interchain interaction is present between two neighboring easy‐plane ferromagnetic chains, are studied. Using a two‐lattice model and defining coherent states on each site for the two chains the discrete coupled equation for the averages of the spin components are given. In the easy‐plane limit it is found that three kinds of static magnetic excitations can exist, depending on the value of the antiferromagnetic interchain exchange interaction J2. The inclusion of this antiferromagnetic interchain interaction makes the problem of the nonlinear magnetic excitations appear in a new light.