bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effect of molecular mean‐field interaction on remanent magnetism
Authors: Takacs J. 
Published: October 2007

PurposeThe paper aims to take a critical view of the Wholfarth's assumption and the Henkel plots as the measure of molecular mean‐field interaction in magnetic materials. At the same time it seeks to formulate the effect of the molecular field interaction on the anhysteretic remanence.Design/methodology/approachBased on the recently verified Bosorth's original definition of anhysteretic state, the paper verifies Wohlfarth's conjecture. By including the molecular field interaction into the effective field expression it formulates the hysteretic and anhysteretic remanent behavior of the magnetic material.FindingsThe hysteretic and anhysteretic character of the material can be formulated up to and beyond the Barkhausen jump. The paper also points out that, the now verified, Wholfarth's conjecture is applicable to not only major hysteresis loops but also to symmetrical minor loops as well, within the same set. By doing so it removes the uncertainty surrounding its mathematical formulation.Research limitations/implicationsIn the light of these findings the conjecture's relation to multi‐phase magnetic materials has to be investigated in the future.Originality/valueThe formulation of the hyteretic and anhysteretic remanent character can provide a graphical interpretation of the materials behavior. The paper demonstrate how the Henkel plots, based on the Wholfarth's conjecture, used as an indicator of the magnitude of the molecular interaction, can be simplified to the benefit of the theoretical and practical users.
Modeling dc gain performance of 4H‐SiC BJTs
Authors: Fardi Hamid Z. 
Published: October 2007

PurposeTo model the differential dc gain, base resistance, and current voltage performance of 4H‐Silicon Carbide (SiC) bipolar junction transistors (BJT) operating at and above room temperature. Accurate modeling will result in improved process efficiency, interpretation of experimental data, and insight into device behavior.Design/methodology/approachThe PISCES two dimensional device simulation program is used to allow for modeling the behavior of 4H‐SiC BJT. The physical material parameters in PISCES such as carrier's mobility and lifetime, temperature dependent bandgap, and the density of states are modified to accurately represent 4H‐SiC. The simulation results are compared with the measured experimental data obtained by others. The comparisons made with the experimental data are for two different devices that are of interest in power electronics and RF applications.FindingsThe simulation results predict a dc current gain of about 25 for power device and a gain of about 20 for RF device in agreement with the experimental data. The comparisons confirm the accuracy of the modeling employed.Research limitations/implicationsThe simulated current‐voltage characteristics indicate that higher gain may be achieved for 4H‐SiC transistors if the leakage current is reduced.Practical implicationsThe simulation work discussed in this paper complements the current research in the design and characterization of 4H‐SiC bipolar transistors. The model presented will aid in interpreting experimental data at a wide range of temperatures.Originality/valueThis paper reports on a new model that provides insight into the device behavior and shows the trend in the dc gain performance important for the design and optimization of 4H‐SiC bipolar transistors operating at or above the room temperature.
On the analysis and control of four‐switch three‐phase inverter fed brushless motor drives
Authors: Guermazi Abdessatar , Sahbi Mariem , Masmoudi Ahmed , Elantably Ahmed 
Published: October 2007

PurposeThis paper aims at the improvement of the cost‐effectiveness of brushless DC motor (BDCM) drives integrated in electric and hybrid propulsion systems.Design/methodology/approachThe cost‐effectiveness improvement is gained through the reduction of the topology of the inverter in the armature which turns to have two legs (four switches) rather than three legs (six switches) in conventional inverters. This has been made possible thanks to the availability of the battery pack in automotive applications.FindingsIt has been found that the four‐switch three‐phase inverter (FSTPI) fed BDCM drive has almost the same performance as the six‐switch three‐phase inverter (SSTPI) fed BDCM.Research limitations/implicationsThis works should be extended by an experimental validation of the established results.Practical implicationsThe reduction of the topology of the inverter in the armature of the BDCM opens up crucial cost benefits especially in large‐scale production industries, such as the automotive one.Originality/valueThe implementation of a simple self‐control strategy in a FSTPI fed BDCM drive yields almost the same dynamic and steady state performance as those obtained by a SSTPI fed BDCM drive. An analytical assessment of the steady state features of the FSTPI‐fed BDCM drive has been confirmed by simulation.
CAD‐oriented signal and noise modeling of mm‐wave FETs: a wave approach
Authors: Abdipour Abdolali , Moradi Gholamreza 
Published: October 2007

PurposeThe purpose of this paper is to present computer‐aided simultaneous signal and noise modeling and analysis for mm‐wave field‐effect transistors (FETs) based on scattering parameters approach.Design/methodology/approachA mm‐wave FET is modeled as three active‐coupled transmission lines, and the developed wave approach is applied to this model to calculate both signal and noise performances of the device.FindingsThe measurements show a good match with the calculated data from the point of view of both signal and noise performances of the device.Originality/valueThis CAD‐oriented analysis and modeling can be easily applied to the mm‐wave simulators to improve the simultaneous signal and noise optimization, modeling and analysis of mm‐wave devices, especially for traveling wave transistors in which the distributed model seems to be more exact than the usual lumped models. Also the proposed routine compared to the admittance approach is conceptually more compatible with scattering representations of active and passive circuits. The developed algorithm has been applied successfully to mm‐wave MESFETs and HEMTs.
Epileptic seizure characterization by Lyapunov exponent of EEG signal
Authors: Osowski Stanislaw , Swiderski Bartosz , Cichocki Andrzej , Rysz Andrzej 
Published: October 2007

PurposeThe purpose of this paper is to develop the new method of estimation of the short‐term largest Lyapunov exponent of electroencephalogram (EEG) waveforms for the detection and prediction of the epileptic seizure.Design/methodology/approachThe paper proposed the modifications concerned with the way of selection of the segments of EEG waveforms taking part in estimation of Lyapunov exponent, as well as determination of the distances between two time series. The proposed method is based on Kolmogorov‐Smirnov test of similarity of two vectors. Through the application of this test more accurate and less parameterized approach to the estimation of the short‐term largest Lyapunov exponent of EEG waveforms has been obtained.FindingsThe results of performed experiments have shown that in most cases our modified method has outperformed the classical procedure, leading to more stable results, closer to the neurologist indications. The analysis of the data has proved that the change of the largest Lyapunov exponent provides a lot of information regarding the epileptic seizure. The minimum value of Lyapunov exponent indicates fairly well the seizure moment. The Tindex applied for few different electrode sites can provide good advanced prediction of the incoming epileptic seizure.Practical implicationsAfter additional experiments this method may find practical application for supporting the medical diagnosis of the epilepsy.Originality/valueThe proposed modification of the estimation of the short‐term largest Lyapunov exponent of the EEG waveforms eliminates some arbitrarily chosen parameters tuned by the user and leads to more accurate estimate. Such estimation results are better suited for the characterization of the epileptic activity.
Sensorless‐estimation of induction motors in wide speed range
Authors: Bogosyan Seta , Barut Murat , Gokasan Metin 
Published: October 2007

PurposeThe purpose of this paper is to improve performance in the estimation of velocity and flux in the sensorless control of induction motors (IMs) over a wide speed range, including low and zero speed.Design/methodology/approachTemperature and frequency dependent variations of stator (Rs) and rotor (R′r) resistances are very effective on estimation performance in sensorless control over a wide speed range. To this aim, an extended Kalman filter (EKF) is designed, which estimates the stator resistance,Rs, load torque,tL, velocity and flux. To provide robustness againstR′rvariations, the extended model is also continuously updated withR′rvalues from a look‐up table, built via EKF estimation.FindingsAs demonstrated by the experimental results, the estimated states and parameters undergo a very short transient and attain their steady‐state values accurately, with no need for signal injection due to the inherent noise introduced by EKF.Originality/valueThe value of this study is in the development of an EKF‐based scheme, which solves theRs−R′restimation problem in IM sensorless control. The successful experimental results obtained with the combined EKF and look‐up table approach also offer a solution to all EKF‐based estimation schemes which involve a high number of estimated parameters, hence, compromising estimation accuracy.
A mathematical approach for studying interconnected earthing systems inside MV networks
Authors: Campoccia Angelo , Riva Sanseverino Eleonora , Zizzo Gaetano 
Published: October 2007

PurposeThe purpose of this paper is to define a new methodology for studying interconnected earthing system inside unearthed medium voltage (MV) networks.Design/methodology/approachThe developed methodology is based on the division of the MV network into simpler sub‐systems and its resolution using a multiport approach.FindingsThe methodology has been applied to various situations giving precious information on the behaviour of the interconnected earthing systems. The comparison between the results of the simulations and measurements done on a really existing network has shown that the methodology is able to provide accurate results.Research limitations/implicationsSome factors can influence the precision of the methodology. Indeed, for a correct simulation of the system it is necessary to know several electrical and geometrical parameters, often obtainable with difficulty.Practical implicationsUtilities are quite interested in this topic. The study of interconnected earthing systems in MV networks with the purpose of identifying safe extended areas named Global Earthing Systems has important management and economic consequences.Originality/valueThe paper presents a new analysis methodology applicable to MV networks that surpasses the limits of the analysis methodology generally applied for the study of the same topic in high voltage networks.
The Crout version of ILU preconditioning applied to the fast‐multipole method for solving large‐scale electromagnetic open PEC problems
Authors: Yu Yiqiang , McCowen Andy 
Published: October 2007

PurposeThe purpose of this paper is to investigate and analyze the efficiency and stability of the implementation of the Crout version of ILU (ILUC) preconditioning on fast‐multipole method (FMM) for solving large‐scale dense complex linear systems arising from electromagnetic open perfect electrical conductor (PEC).Design/methodology/approachThe FMM is employed to reduce the computational complexity of the matrix‐vector product and the memory requirement of the impedance matrix. The numerical examples are initially solved by the quasi‐minimal residual (QMR) method with ILUC preconditioning. In order to fully investigate the performance of ILUC in connection with other iterative solvers, a case is also solved by bi‐conjugate gradient solver and conjugate gradient squared solver with ILUC preconditioning.FindingsThe solutions show that the ILUC preconditioner is stable and significantly improves the performance of the QMR solver on large ill‐conditioned open PEC problems compared to using ILU(0) and threshold‐based ILU (ILUT) preconditioners. It dramatically decreases the number of iterations required for convergence and consequently reduces the total CPU solving time with a reasonable overhead in memory.Practical implicationsThe preconditioning scheme can be applied to large ill‐conditioned open PEC problems to effectively speed up the overall electromagnetic simulation progress while maintaining the computational complexity of FMM. More complex structures including wire‐PEC junctions and microstrip arrays may be addressed in future work.Originality/valueThe performance of ILUC has been previously reported only on preconditioning sparse linear systems, in which the ILU preconditioner is constructed by the ILUC of the coefficient matrix (e.g. matrix arised from two‐dimensional finite element convection‐diffusion problem) and subsequently applied to the same sparse linear systems; so it is important to report its performance on the dense complex linear systems that arised from open PEC electromagnetic problems. In contrast, the preconditioner is constructed upon the near‐field matrix of the FMM and subsequently applied to the whole dense linear system. The comparison of its performance against the diagonal, ILU(0) and ILUT precoditioners is also presented.
Effects of moisture and freeze‐thaw cycling on the quality of rice‐hull‐PE composite
Authors: Wang W.H. , Wang Q.W. , Xiao H. , Morrell J.J. 
Published: October 2007

PurposeTo investigate the effects of moisture and freeze‐thaw cycling on the absorption and flexural properties of rice‐hull‐polyethylene (PE) composite.Design/methodology/approachVarious rice‐hull‐PE composite specimens were submerged in water at various temperatures and subjected to various freeze‐thaw cycles. Various characterisations including water absorption, bending strength and stiffness, Fourier transform infrared spectroscopy and scanning electron microscope imaging were performed.FindingsHigh temperatures accelerated the water sorption of the rice‐hull‐PE composite and increased the equilibrium moisture content. The uncoated surface was not significantly more easily permeated than the coated surface, contrary to expectations. However, more water was absorbed from the cut surface than from the original extruded surface. This was attributed to the tiny checks left on the surface by the sawing action, which indicated the importance of protecting the original surface layer from scraping or other damage. Bending strength and stiffness of the rice‐hull‐PE composite decreased significantly after the freeze‐thaw cycling treatment. The modulus of elasticity decreased more than the modulus of rupture. Compared to the effect of water immersion alone, freeze‐thaw cycling treatment slightly accelerated this decrease.Research limitations/implicationsThe results of this study were obtained from accelerated laboratory experiments. Further research could be carried out to evaluate the properties of this rice‐hull‐PE composite in practical application.Practical implicationsThe research revealed a possible degradation in quality when the rice‐hull‐PE composite is used in moist or freezing conditions. The resin layer on the extruded surface provides an important protection.Originality/valueIn China, rice‐hull powder is widely used as a reinforcing component in plastic composite. However, the durability of rice‐hull/PE composites has rarely been investigated. Results from this study will help users apply rice‐hull‐PE composites correctly and encourage the development of other agro‐fibre/polymer materials.
Synthesis of calixarene derivatives and their anticorrosive effect on steel in 1M HCl
Authors: Benabdellah M. , Souane R. , Cheriaa N. , Abidi R. , Hammouti B. , Vicens J. 
Published: October 2007

PurposeTo evaluate the effect of synthesised calixarenes as new inhibitors on the corrosion of steel in HCl media at various temperatures.Design/methodology/approachCalixarenes have been synthesised and tested as corrosion inhibitors. Gravimetric technique and potentiodynamic polarisation and impedance spectroscopy methods were used.FindingsCalixarenes exhibited a good inhibition. Their efficiency decreases slightly with temperature.Research limitations/implicationsIt was found that the inhibition efficiency increases with the concentration of inhibitors to reach 92 per cent at 10−4M.Practical implicationsThe efficiency of calixarene derivatives increases with the concentration and falls slowly with temperature to attain 84 per cent at 353 K range. Calixarenes can be used in chemical cleaning and pickling processes.Originality/valueThe originality of this work is to find an inhibitor to give protection close to 100 per cent.
The transaction‐relational continuum: conceptually elegant but empirically denied
Authors: Palmer Roger 
Published: October 2007

PurposeThis paper aims to investigate the trend and/or paradigm shift to relationship marketing as a dominant framework that has shaped the way in which relationships are understood, and also to consider how the understanding of relationships can be improved.Design/methodology/approachA case‐based study was conducted in order to examine issues concerning relationships. A series of constructs was elicited from the relationship marketing literature to be used as the basis for this study.FindingsRelationship development is explained by stages or state theory, whereby relationships develop over time or simply emerge. Confirmation is offered to the states theory, which suggests that relationships are relatively static and develop in less well‐defined ways.Research limitations/implicationsThis study is limited in scope, bounded by the context of the cases, which were limited to business‐to‐business suppliers of manufactured industrial goods.Practical implicationsManagers should be cautious of attempting to tactically change relationships as in practice this is more challenging than continuum‐based models would imply.Originality/valueContinuum models imply that the process is one of tactical implementation rather than strategic redirection. This is not confirmed by the research, which provides an alternative model to understand and manage relationships.
Interfunctional climate and a new product performance: dependence as a moderator
Authors: García Rodríguez Nuria , José Sanzo Pérez M. , Trespalacios Gutiérrez Juan A. 
Published: October 2007

PurposeThis study aims to examine the marketing/R&D relationship under different relative dependence situations. Specifically, its basic objective is to analyse if the effect that the climate between these departments exerts on new product development performance is moderated by the dependence perceived by these areas.Design/methodology/approachThe interfunctional climate was measured through six key variables of relationship marketing: cooperation, communication, trust, commitment, social satisfaction and conflict. To do this, the R&D directors of 178 Spanish innovative firms were surveyed. A sample of 345 products (177 successes and 168 failures) was been obtained.FindingsThe results derived from a multisample analysis allow the conclusion that in those situations of high dependence the creation of a satisfactory climate is specially important for the development of affective bonds, such as trust and commitment among the functional areas.Originality/valueThe novelty of the research lies in the use of the relationship marketing approach to investigate industrial intra‐functional relationships and their influence on a new product performance. Furthermore, the inclusion of dependence as a possible moderator of that influence represents an added value of the study.
How functional, psychological, and social relationship benefits influence individual and firm commitment to the relationship
Authors: Sweeney Jillian C. , Webb David A. 
Published: October 2007

PurposeThis paper aims to extend previous research investigating the effect of relationship benefits on firm outcomes by developing a model that includes the effect on individual employees in the buyer firm. The model also aims to address benefits beyond the functional in business‐to business (B2B) settings by including psychological and social benefits.Design/methodology/approachThe study is based on a survey of 275 B2B buyers in Australian manufacturing firms.FindingsThe findings reveal that functional benefits enhance firm‐level commitment to the relationship, whereas psychological and social benefits affect individual commitment to the relationship directly and firm‐level commitment indirectly, thereby emphasizing the importance of considering the individual as distinct from the firm. Given that the relationship is a process over time, and in recognition of the non‐static nature of relationship benefits, the paper also explores the changes in benefits over relationship stages, including their impact on commitment. In contrast to expectations results show that while all three types of benefits increase, there is no change in the impact of all three benefit types on commitment across relationship stages.Practical implicationsThe study recognizes that the individual in the firm also benefits from B2B relationships and offers a measure of both firm and individual relationship benefits for use in future studies. The measure may also be used as a point of discussion about relationship management.Originality/valueThe study is framed within social exchange theory and, is the first to simultaneously examine three types of relationship benefits and their interaction with both the individual and firm viewpoint. The study is also one of the first to empirically examine changes in relationships over the relationship stages.
De‐internationalisation and global strategy: the case of British Telecommunications (BT)
Authors: Turner Colin , Gardiner Paul D. 
Published: October 2007

PurposeThe paper aims to examine the process of de‐internationalisation through an analysis of British Telecommunications' (BT's) experience. There is – to date – little research upon de‐internationalisation, this paper aims to contribute to the debate through assessing how businesses with a strong domestic position would respond to a turbulent commercial environment.Design/methodology/approachThe key research issue is addressed in the paper via the use of a single case study.FindingsThe paper finds that BT, throughout the 1990s, developed an aggressive global strategy. However, by the 1990s, BT was in a process of retreat. This failure was influenced by the form and nature with which this strategy was executed, which resulted in a declining commitment to an aggressive global strategy. With the failure of the global strategy, BT reverted to a more defensive corporate strategy.Originality/valueThe paper makes a contribution through adding to an emerging debate on the form and nature of de‐internationalisation. This process is explored from the standpoint of a business that has sought to pursue an aggressive international strategy whilst sustaining a commitment to a strong domestic position. The paper highlights how de‐internationalisation is linked into the form and nature initial strategy.