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Homogeneous Structure (homogeneous + structure)

Distribution by Scientific Domains

Engineering	37%
Polymers and Materials Science	25%

Selected Abstracts

Capacity analysis for underlaying CDMA microcell/macrocell systems

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 4 2001
Jen-Kung Chung
Abstract The CDMA system can provide more capacity than the conventional AMPS system and the hierarchical layer of cells is required for system design in the future. However, the problem is whether the same RF channels used in a CDMA underlaying macrocell/microcell structure also obtain high capacity as in the homogeneous structure. This paper investigates the interference of uplink and downlink from both the microcell and macrocell in a hierarchical structure. Downlink power control is also considered. The results show that the capacity of microcell in a hierarchical structure is 23 per cent less than in homogeneous cells. The capacity of macrocell in a hierarchical structure decreases dramatically in proportion to the number of microcells. The capacities of the microcell and macrocell are limited in downlink, and uplink, respectively. In addition, more efforts for microcell should be made, such as more power is transmitted by microcell basestation if the same RF channel is used in a hierarchical structure. The results suggest that different RF channels are used in a two-tier cellular environment. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Model order reduction of linear and nonlinear 3D thermal finite-element description of microwave devices for circuit analysis

INTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 5 2005
Raphaël Sommet
Abstract Electrothermal models of power devices are necessary for the accurate analysis of their performances. For this reason, this article deals with a methodology to obtain an electrothermal model based on a reduced model of a 3D thermal finite-element (FE) description for its thermal part and on pulsed electrical measurements for its electrical part. The reduced thermal model is based on the Ritz vector approach, which ensures a steady-state solution in every case. An equivalent SPICE subcircuit implementation for circuit simulation is proposed and discussed. An extension of the method to a nonlinear reduced model based on the Kirchoff transformation is also proposed. The complete models have been successfully implemented in circuit simulators for several HBT or PHEMT device structures. Many results concerning devices and circuits are presented, including simulation of both the static and dynamic collector-current collapse in HBTs due to the thermal phenomenon. Moreover, the results in terms of the circuit for an X-band high-power amplifier are also presented. As for the nonlinear approach, results concerning an homogeneous structure is given. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005. [source]

Preparation and characterization of interpenetration polymer network films based on poly(vinyl alcohol) and poly(acrylic acid) for drug delivery

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008
Yu-Mei Yue
Abstract A series of full interpenetrating polymer network (full-IPN) films of poly(acrylic acid) (PAA)/poly (vinyl alcohol) (PVA) were prepared by radical solution polymerization and sequential IPN technology. Attenuated total reflectance-Fourier transform infrared spectroscopy, swelling properties, mechanical properties, morphology, and glass transition temperature of the films were investigated. FTIR spectra analysis showed that new interaction hydrogen bonds between PVA and PAA were formed. Swelling property of the films in distilled water and different pH buffer solution was studied. Swelling ratio increased with increasing PAA content of IPN films in all media, and swelling ratio decreased with increasing PVA crosslink degree. Tensile strength and elongation at break related not only to the constitution of IPNs but also to the swelling ratio of IPNs. Mechanical property of glutaraldehyde (0.5%) for poly(vinyl alcohol) crosslinking was better than that of glutaraldehyde (1.0%). DSC of the IPN films showed only a single glass transition temperature (Tg) for each sample, and Tg data showed a linear relationship with network composition. Morphology was observed a homogeneous structure, indicating the good compatibility and miscibility between PAA and PVA. Potential application of the IPN films in controlled drug delivery was also examined using crystal violet as a model drug. The release rate of the drug was higher at 37°C than 25°C for all IPNs and also increased slightly with decreasing of poly(acrylic acid) content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Characteristics of anodic coatings oxidized to different voltage on AZ91D Mg alloy by micro-arc oxidization technique

MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 2 2005
Y. Wang
Abstract With increasing applied voltage, three types of anodic coatings, passive film, micro-spark ceramic coating and spark ceramic coating were made by micro-arc oxidization (MAO) technique on AZ91D magnesium alloy in alkali-silicate solution. The structure, composition characteristics and the electrochemical properties of coatings were also studied with SEM, XRD and EIS (electrochemical impedance spectroscopy) technique, respectively. It is found that the electrochemical properties are closely related to the structure and composition characteristics of the anodic coatings. At the same time, the characteristics of the three types of anodic coatings differ significantly, among them, the micro-spark ceramic coating, prepared in the voltage range of 170~220V exhibits compact, homogeneous structure and highest corrosion-resistance. [source]

Finiteness of U -rank implies simplicity in homogeneous structures

MLQ- MATHEMATICAL LOGIC QUARTERLY, Issue 6 2003
Tapani Hyttinen
Abstract A (large) superstable homogeneous structure is said to be simple if every complete type over any set A has a free extension over any B , A. In this paper we give a characterization for this property in terms of U -rank. As a corollary we get that if the structure has finite U -rank, then it is simple. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Non-Asymptotic Modelling of Medium Thickness Plates with Plane Periodic Structure

PROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2008
Eugeniusz BaronArticle first published online: 26 FEB 200
The main aim of this contribution are presented a certain selected problems (aspects) of non,asymptotic modelling of medium thickness (or Reissner,type) rectangular plates with a plane periodic in,homogeneous structure. In course of non,asymptotic modeling, by using tolerance averaging technique (TAT), apart from the known separation for biperiodic and uniperiodic plates, it is necessary to introduce extra partitions. The four non,asymptotic models of plates with plane periodic structure can be led out independently (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Single dopant diffusion in semiconductor technology

MATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 2 2004
A. Glitzky
Abstract The paper deals with the analysis of pair diffusion models in semiconductor technology. The underlying model contains reaction-drift-diffusion equations for the mobile point defects and dopant-defect pairs as well as reaction equations for immobile dopants which are coupled with a non-linear Poisson equation for the chemical potential of the electrons. For homogeneous structures we present an existence and uniqueness result for strong solutions. Starting with energy estimates we derive further a priori estimates such that fixed point arguments due to Leray,Schauder guarantee the solvability of the model equations. Copyright © 2004 John Wiley & Sons, Ltd. [source]