bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of demand on stock prices: new evidence from S&P 500 weight adjustments
Authors: Hrazdil Karel
Published: August 2009

Purpose

Many papers have argued that there are long‐run downward‐sloping demand curves (LRDDC) for stocks. The purpose of this paper is to analyze this hypothesis using a new, unique, and ostensibly information‐free event: the re‐weighting of the Standard & Poor (S&P) 500 index from market based to free‐float based, which involves a significant shift in supply that, under the LRDDC, should result in significant and permanent price movements.

Design/methodology/approach

Event study methodology is used to examine abnormal returns and trading activity around the free‐float weight implementation dates for S&P 500 firms with various investable weight factors.

Findings

As a result of S&P 500 index re‐weighting, affected stocks experience statistically significant excess returns of −1.54 percent during the event week. This return is reversed during the following 30 days as trading volume returns to normal levels. These results are contrary to previous studies that analyze ostensibly informational events and/or different exchanges.

Research limitations/implications

Results of this study indicate that arbitrage appears to be effective in eliminating a long‐term mispricing, which challenges the validity of the LRDDC hypothesis.

Originality/value

This study contributes to the body of literature on the S&P 500 index firms by providing supporting evidence for the price‐pressure hypothesis.
Maturity policies of CEO severance contracts and forced internal turnover
Authors: van Dalsem Shane
Published: August 2009

Purpose

The purpose of this paper is to investigate the effect of executive severance contract maturity policies on the likelihood of forced turnover and the length of tenure for CEOs who are forced from their positions.

Design/methodology/approach

The paper utilizes logistic and accelerated failure time models to test the hypothesis that severance contracts decrease information asymmetries resulting in an increased likelihood of forced turnover and a shortened tenure for those CEOs who are forced out.

Findings

The results provide evidence that fixed‐term severance contracts increase the likelihood of forced tenure and decrease the length of tenure for CEOs who experience a forced turnover during the period, while time‐independent contracts do not.

Research limitations/implications

The limitation is the possibility that an omitted variable jointly determines the likelihood of the presence of a severance contract and the effect on forced turnover. Future research should investigate other possibilities beyond the CEO coming from outside of the firm.

Practical implications

The findings confirm that the maturity policies of severance contracts affect forced turnover. The results suggest that there may be a benefit in designing severance contracts to expire to encourage more efficient turnover of underperforming CEOs.

Originality/value

This paper contributes to the empirical corporate finance and accounting literature by differentiating between forced and unforced turnover when analyzing the effects of severance contracts and demonstrating that the time dimension of severance contracts may provide the desired result of encouraging the identification of CEO‐firm mismatches.
In government we trust: rise and fall of Canadian business income trust conversions
Authors: Kryzanowski Lawrence , Lu Ying
Published: August 2009

Purpose

The purpose of this paper is to assess the market impact of announcements that publicly traded limited liability firms would convert to business income trusts, and to test the robustness of the tax motive as the primary determinant of any conversion announcement effects by estimating the market impact of the announcement by the Canadian Federal Government that the corporate income of Canadian income trusts would be taxed at the trust level.

Design/methodology/approach

Event‐study methodology (including various tests of robustness) is used to examine the market impacts of the initial conversion announcement and the announcement that the corporate income of Canadian income trusts would be taxed at the trust level. Cross‐sectional regressions are used to identify the determinants of the market effect associated with income trust conversion announcements.

Findings

The paper finds that the market‐ and risk‐adjusted abnormal returns (ARs) are positive and very significant on the announcement dates and not significant on the conversion effective dates. The price discovery process is not as smooth for the Canadian government's announcement after the market close on Halloween day 2006, that it would tax income trusts at the trust level. While the ARs are negative and very significant on the first and second trading days after the announcement, much of the second day ARs are reversed in the subsequent two days. Furthermore, negative and significant ARs precede the government announcement. The market impact of trust conversion announcements is primarily related to the tax savings associated with such conversions and more weakly related to potential agency problems associated with free cash flows.

Research limitations/implications

The research indicates the importance of any taxation changes associated with changes in organization form on firm value. It also identifies the potential for informational leakage associated with government decisions.

Originality/value

The paper highlights the importance of taxes and tax changes and organization form changes on firm valuation.
Publicly traded homebuilders’ and insiders’ trading: a new perspective
Authors: Ghosh Sudip , Abdou Khaled
Published: August 2009

Purpose

The purpose of this paper is to examine the insiders’ activities (buy/sell) during the recent meltdown of the homebuilders’ industry.

Design/methodology/approach

This study applies a regression model to analyze the relationship between the insiders’ net sales and variables that could be affecting the trading decisions controlling for other market variables.

Findings

The results show that CEOs of homebuilding companies had net positive selling activities and enjoyed massive gains by timing the market correctly. The insiders’ massive selling period was followed by significant declines in share prices of homebuilding companies. More specifically, CEOs (but not all top executives) acted as contrarian investors and sold when the share prices hit a record high, coupled by optimistic analysts’ recommendations, which were later seen as incorrect by the market. Also, CEOs sold at a time when EPS was at its highest level.

Research limitations/implications

The current work can not disprove the “argument of diversification” cited by insiders as the reason for their stock sell off, mainly because it is not possible to obtain data about the CEOs’ personal portfolios.

Practical implications

This paper implies that CEOs were able to time the market by forecasting the trend in their industry.

Originality/value

The paper investigates the period between January 2004 and August 2007 which is characterized by mass selling by CEOs in the whole industry of home building companies and not only a specific entity.
Determining US workers' training: history and constructivist paradigm
Authors: Altman Brian A.
Published: August 2009

Purpose

The aim of this paper is to review two accounts of the history of workplace learning and training in the USA that emphasize issues of power and control in the determination of what training occurs, and place these issues at the center of their analyses.

Design/methodology/approach

The two texts are reviewed and a constructivist paradigm is considered to address issues raised in the texts.

Findings

It is suggested that a constructivist view by managers and workers can foster a positive approach to determining what training workers receive, allowing for worker training that meets the needs of managers as well as workers.

Research limitations/implications

While these two works were the only ones identified through a literature search that focuses on the history of who determined worker training in the USA, and they prove insightful on this topic, this paper is limited in that these works are now respectively approximately one and three decades old.

Practical implications

Implementation of a constructivist view of determining training for workers can meet the needs of managers as well as workers, avoiding a zero‐sum game view.

Originality/value

By reviewing these two texts, and considering a constructivist paradigm in addressing issues raised by the authors, a vision of a constructivist approach to determining training is presented, with advantages to workers and managers.
Building a bridge of understanding
Authors: Brown T.C. , McCracken Martin
Published: August 2009

Purpose

The purpose of this paper is to look at the issues concerning barriers that managers face in relation to participation in training and transfer of training, which have become increasingly important to HRD scholars and practitioners. To date, these areas have largely been examined independently. This paper aims to argue that there is an increasing need to understand and explore these two areas in unison.

Design/methodology/approach

Although this paper is primarily conceptual in nature, in order to investigate a model derived from relevant literature, survey data from 137 Canadian employees, mostly from the broader public sector, was examined. These respondents completed a short transfer of training questionnaire three months after a one‐day managerial training programme. In this study, open‐ended questions investigating training barriers are analysed.

Findings

The exploratory examination of information from participants of a managerial training programme suggests that the model which links literature on participation in training and transfer of training warrants additional examination. Most significantly, there was substantial overlap between the participation and transfer barriers with the most common barriers being linked to “lack of time” and “unsupportive culture”.

Research limitations/implications

The main limitation of this paper is the relatively small sample size with regard to data concerning barriers to transfer. However, the authors feel that a key implication is that a “bridge of understanding” is created concerning the numerous factors that impact participation in training, transfer of training and the relationships between them. Hence, HRD practitioners and scholars can now use this model to begin to understand how they might improve the overall quality of training programmes and to further explore the relationship between transfer and participation.

Originality/value

The conceptual model developed further integrates the respective literatures pertaining to management training participation and transfer of learning in the workplace. The proposed model shows how barriers to participation can become barriers to transfer and how barriers to transfer from one programme may become barriers to participation to subsequent learning activities.
The evaluation of HRD: a critical study with applications
Authors: Tomé Eduardo
Published: August 2009

Purpose

The purpose of this paper is to analyze critically the most important methods that are used in the evaluation of human resource development (HRD).

Design/methodology/approach

The approach is to ask two questions: What are the methods available to define the impact of HRD in the economy? How can we evaluate the evaluations that have been made?

Findings

There are two main perspectives to evaluate any program, by results (counting occurrences) and by impacts (calculating the differences the investment made in the society). The first type of method does not find the impact of the program, the second type does.

Research limitations/implications

The analysis is limited by existing studies on HRD. The implications are that the conditions that underline the existence of HRD programs define the type of evaluation that is used.

Originality/value

The results of this paper put the evaluation problem in a new perspective. It explains the difference between methodologies (results and impacts) and scientific fields used (public administration, social policy, HRD, KM, IC, microeconomics, HR economics) by the type of person responsible: public administrator, private manager, HRD expert, knowledge manager, IC expert, microeconomist. The differences between the applications of those methodologies based on the type of funding – private, public, external – are also explained.
Intercultural training: six measures assessing training needs
Authors: Graf Andrea , Mertesacker Marion
Published: August 2009

Purpose

The purpose of this paper is to develop recommendations for measures assessing intercultural training needs for international human resource management. Based on scientific as well as application‐oriented criteria the aim is to select six measures assessing general intercultural competencies and with the help of behaviour ratings in interactive intercultural exercises to evaluate the psychometric quality and practicability of the questionnaires for training purposes.

Design/methodology/approach

Psychometric quality including prognostic power of ICSI, FLCS, NVCCS, ISAS, TIHK, and SIB was tested by correlating subjects' questionnaires results with observations of their actual behaviour in intercultural exercises.

Findings

Satisfying psychometric quality and prognostic validity of almost all measures was found. Especially TIHK, ICSI, and FLCS score well for assessing training needs whereas the results for SIB were problematic.

Research limitations/implications

The study observed student participants of the same culture. Replication studies should examine large samples of different cultural backgrounds and manager populations.

Practical implications

Human resource managers may benefit from gaining knowledge about which measures to use for identifying employee's weaknesses in intercultural competence in order to create tailor‐made training interventions.

Originality/value

The study is the first providing information about the psychometric quality, including predictive power, of six measures, that assess intercultural skills to detect intercultural training needs.
The emotional impact of leaders' behaviours
Authors: Fowlie Julie , Wood Matthew
Published: August 2009

Purpose

The purpose of this article is to analyse MBA students' actual experiences of both good and bad leadership and the resulting emotional responses; to determine which emotionally intelligent competencies, if any, have greater importance in times of change.

Design/methodology/approach

The paper follows a deductive approach: moving from the general to the particular based within the phenomenological paradigm, extending Goleman's inductive research into emotional intelligence competencies. Goleman's framework was adopted because his research was based upon competency models from both private and public organisations, which matches the MBA students' experiences.

Findings

The findings suggest that bad leadership equates to a lack of self‐management and relationship management competencies; however good leadership is not the exact opposite. If a person has developed self‐management competencies it does not follow that he/she will be considered a good leader. Leaders should aim to have a clear focus on their followers; in other words, highly developed relationship management competencies. It also appears that face‐to‐face communication is relevant.

Research limitations/implications

The research adopted a qualitative approach, with a small sample, which limits the generalisability of the findings. Also, the interpretation of the responses was based on the researchers' knowledge of Goleman's model, which could be considered to be subjective.

Practical implications

This research could be used to support HRD professionals in the design of both selection and developmental programmes for managers, including competency descriptions, introduction of testing and developmental activities.

Originality/value

The paper discusses the role of emotions in management and adds to the evidence that the competencies within the relationship management quadrant could be used as selection and developmental criteria.
Aberration coefficients in the optics of accelerator tubes
Authors: Trowbridge C.W. , Emson C.R.I. , Hyder H.R.McK.
Published: August 2009

Purpose

The purpose of this paper is to investigate the use of the finite element (FE) method in calculating accurate field gradients to achieve good estimates of aberration coefficients in accelerator tubes.

Design/methodology/approach

Gradient fields up to third order are calculated using FE calculations with higher order basis functions. A commercial code with the ability to use high order basis functions was embedded within the MathCad system which provides a convenient interface for evaluating the aberration coefficients. Analytic and realistic models are used to test the methodology.

Findings

It is shown that the ability to use higher order FEs achieves sufficient accuracy and smoothness to allow the third order aberration coefficients to be determined with confidence.

Originality/value

The results demonstrate the importance of using higher order basis FEs in determining optical properties of accelerator tubes and other particle optical devices.
Asymptotic Fourier decomposition of tooth forces in terms of convolved air gap field harmonics for noise diagnosis of electrical machines
Authors: van der Giet M. , Rothe R. , Hameyer K.
Published: August 2009

Purpose

The electromagnetic excited audible noise of electrical machines can be mostly attributed to radial forces on stator tooth‐heads. The methodology proposed in this paper uses numerical field simulation to obtain the magnetic air gap field of electrical machines and an analytical‐based post‐processing approach to reveal the relationship between air gap field harmonics and the resulting force wave.

Design/methodology/approach

The simulated air gap field is sampled in space and time and a two‐dimensional Fourier transform is performed. The convolution of the Fourier transformed air gap field by itself represents a multiplication in space time domain. During the convolution process, all relevant combinations of field waves are stored and displayed using space vectors.

Findings

The effectiveness of the proposed approach is shown on an example machine. Particular examples of individual force waves demonstrate how the approach can be used for practical application in analysis of noise and vibration problems in electrical machines. The proposed method is compared to the result of a Maxwell stress tensor calculation. It shows that the deviation is small enough to justify the approach for analysis purposes.

Originality/value

The combination of analytically understood force waves and the use of numerical simulation by means of air gap field convolution has not been proposed before.
Physical modeling and numerical computation of magnetostriction
Authors: Kaltenbacher M. , Meiler M. , Ertl M.
Published: August 2009

Purpose

Magnetostrictive alloys are widely used in actuator and sensor applications. The purpose of this paper is to developed a realistic physical model and a numerical computational scheme for their precise computation.

Design/methodology/approach

The main step in the physical modeling is the decomposition of the mechanical strain and the magnetic induction into a reversible and an irreversible part. For the efficient solution of the arising coupled nonlinear partial differential equations the authors apply the finite element method.

Findings

It can be demonstrated, that the hysteresis operators can be fitted by appropriate measurements. Therewith, the developed physical model and numerical simulation scheme is applicable for the design of magnetostrictive actuators and sensors.

Originality/value

The decomposition of the mechanical strain and the magnetic induction into a reversible and an irreversible part. The reversible part is described by the linear magnetostrictive constitutive equations, where the entries of the coupling tensor depend on the magnetization. The irreversible part of the magnetic induction is modeled by a Preisach hysteresis operator, and the irreversible part of the mechanical strain by a polynomial function depending on the magnetization.
New operators for multi‐objective clonal selection algorithms
Authors: de S. Batista Lucas , Ramírez Jaime A. , Guimarães Frederico G.
Published: August 2009

Purpose

The purpose of this paper is to present a new multi‐objective clonal selection algorithm (MCSA) for the solution of electromagnetic optimization problems.

Design/methodology/approach

The method performs the somatic hypermutation step using different probability distributions, balancing the local search in the algorithm. Furthermore, it includes a receptor editing operator that implicitly realizes a dynamic search over the landscape.

Findings

In order to illustrate the efficiency of MCSA, its performance is compared with the nondominated sorting genetic algorithm II (NSGA‐II) in some analytical problems and in the well‐known TEAM benchmark Problem 22. Three performance evaluation techniques are used in the comparison, and the effect of each operator of the MCSA in its accomplishment is estimated.

Research limitations/implications

In the analytical problems, the MCSA enhanced both the extension and uniformity in its solutions, providing better Pareto‐optimal sets than the NSGA‐II. In the Problem 22, the MCSA also outperformed the NSGA‐II. The MCSA was not dominated by the NSGA‐II in the three variables case and clearly presented a better convergence speed in the eight variables problem.

Practical implications

This paper could be useful for researchers who deal with multi‐objective optimization problems involving high‐computational cost.

Originality/value

The new operators incorporated in the MCSA improved both the extension, uniformity and the convergence speed of the solutions, in terms of the number of function evaluations, representing a robust tool for real‐world optimization problems.
Characterization of a 3D defect using the expected improvement algorithm
Authors: Bilicz Sándor , Vazquez Emmanuel , Lambert Marc , Gyimóthy Szabolcs , Pávó József
Published: August 2009

Purpose

The purpose of this paper is to provide a new methodology for the characterization of a defect by eddy‐current testing (ECT). The defect is embedded in a conductive non‐magnetic plate and the measured data are the impedance variation of an air‐cored probe coil scanning above the top of the plate.

Design/methodology/approach

The inverse problem of defect characterization is solved by an iterative global optimization process. The strategy of the iterations is the kriging‐based expected improvement (EI) global optimization algorithm. The forward problem is solved numerically, using a volume integral approach.

Findings

The proposed method seems to be efficient in the light of the presented numerical results. Further investigation and comparison to other methods are still needed.

Originality/value

This is believed to be the first time when the EI algorithm has been used to solve an inverse problem related to the ECT.
Real‐time reconstruction of endocardial potential maps in non‐contact cardiac mapping
Authors: Badics Zsolt , Harlev Doron
Published: August 2009

Purpose

The purpose of this paper is to describe a numerical inversion technology developed to reconstruct endocardial electric potential maps on the internal surface of heart chambers utilizing intracavitary multi‐electrode catheter measurements. The objective is to perform the reconstruction real time with high accuracy, thereby allowing the incorporation of the technology into medical imaging systems.

Design/methodology/approach

Electrode potential points from several beats are merged in order to maximize the information extracted from the catheter measurements. To solve the ill‐posed inverse problem fast, numerically stable solution algorithms based on generalized Tikhonov regularization and bidiagonalization are developed. The latter algorithm also provides an efficient framework for choosing the regularization parameter optimally.

Findings

Results of three examples are presented to thoroughly illustrate the performance of the algorithm: one with synthetic data generated in a computational electromagnetics (virtual lab) environment, thereby allowing exact error analysis; another with measured data from a phantom‐bench human heart model where the effect of measurement errors can be investigated in a controlled environment; and a third example that illustrates how the algorithm performs when the catheter data are collected in vivo in a swine heart.

Practical implications

The speed and accuracy in the three examples successfully prove that the inversion technology can be a key component of medical imaging systems.

Originality/value

While some elements of these computational models and techniques presented have been used for decades, the authors achieve speed and accuracy that have not been reported before by combining multi‐beat catheter measurements, the generalized Tikhonov regularization technique, a bidiagonalization algorithm and other top‐notch linear algebra techniques.
Logarithmic parameter reconstruction in electrical tomography
Authors: Steiner Gerald , Watzenig Daniel
Published: August 2009

Purpose

The purpose of this paper is to investigate the achievable improvement in reconstruction accuracy in electrical tomography through the incorporation of physical bound constraints as prior knowledge in the inverse problem solution.

Design/methodology/approach

The structure of the nonlinear least squares inverse problem formulation and the importance of prior knowledge are addressed. Several different methods for the incorporation of bound constraints are discussed. The methods are compared by means of reconstructions from simulated and measured data and the computational demands.

Findings

The inclusion of bound constraints on the material values in the inverse problem solution results in a considerable improvement of the reconstructions. The occurrence of artefacts and blurring can be reduced. Among the investigated constraint handling methods, the logarithmic parameter reconstruction approach can be implemented with minimal additional computational effort.

Research limitations/implications

The study is performed with discrete two‐phase material distributions as occurring in industrial problems. A further step would be the extension to multiple phases.

Originality/value

The logarithmic transform method is a novel approach for the incorporation of bound constraints in tomography. It outperforms other constraint handling approaches and may be of interest for electrical tomography systems in various applications.
Adaptive monotonicity method for permittivity imaging
Authors: Wallinger C. , Watzenig D. , Steiner G. , Brandstätter B.
Published: August 2009

Purpose

The purpose of this paper is to demonstrate improvement of the accuracy of electrical tomography reconstruction by incorporation of a priori knowledge into the inverse problem solution.

Design/methodology/approach

The fusion of two different inversion algorithms capable of real‐time operation is discussed, namely a non‐iterative monotonicity‐based approach, determining the a priori knowledge and an iterative Gauss‐Newton (GN)‐based reconstruction algorithm. Furthermore, the method is compared with the unmodified algorithms themselves by means of reconstructions from simulated inclusions at different noise levels.

Findings

The accuracy of the inverse problem reconstructions, especially at the boundary regions of the unknown inclusions, benefit from the investigations of incorporating a priori knowledge about material values and can be considerable improved. The monotonicity method itself, which has low complexity, provides remarkable reconstruction results in electrical tomography.

Research limitations/implications

The paper is applied to simulated discrete two‐phase scenarios, e.g. gas/oil mixtures. In a further step the method would be tested with measured data. Moreover, investigations have to be carried out in order to make the monotonicity‐based reconstruction principle more robust against disturbing artifacts.

Originality/value

The fusion of the non‐iterative monotonicity‐based method with the GN‐based algorithm demonstrates a novel approach of improving the reconstruction accuracy in electrical tomography.
Dimensional reduction of field problems in a differential‐forms framework
Authors: Kurz S. , Auchmann B. , Flemisch B.
Published: August 2009

Purpose

The purpose of this paper is to present a geometric approach to the problem of dimensional reduction. To derive (3 + 1) D formulations of 4D field problems in the relativistic theory of electromagnetism, as well as 2D formulations of 3D field problems with continuous symmetries.

Design/methodology/approach

The framework of differential‐form calculus on manifolds is used. The formalism can thus be applied in arbitrary dimension, and with Minkowskian or Euclidean metrics alike.

Findings

The splitting of operators leads to dimensionally reduced versions of Maxwell's equations and constitutive laws. In the metric‐incompatible case, the decomposition of the Hodge operator yields additional terms that can be treated like a magnetization and polarization of empty space. With this concept, the authors are able to solve Schiff's paradox without use of coordinates.

Practical implications

The present formalism can be used to generate concise formulations of complex field problems. The differential‐form formulation can be readily translated into the language of discrete fields and operators, and is thus amenable to numerical field calculation.

Originality/value

The approach is an evolution of recent work, striving for a generalization of different approaches, and deliberately avoiding a mix of paradigms.
Periodic boundary conditions in element free Galerkin method
Authors: Coppoli E.H.R. , Mesquita R.C. , Silva R.S.
Published: August 2009

Purpose

The purpose of this paper is to introduce a new methodology to implement periodic and anti‐periodic boundary conditions in the element free Galerkin method (EFGM).

Design/methodology/approach

This paper makes use of the interpolating moving least squares (IMLS) in the EFGM to implement periodic and anti‐periodic boundary conditions. This fact allows imposing periodic and anti‐periodic boundary conditions in a way similar to the one used by the finite element method.

Findings

EFGM generally uses the moving least squares to obtain its shape functions. So, these functions do not possess the Kronecker delta property. As a consequence, the imposition of essential, as well as periodic and anti‐periodic boundary conditions needs other techniques to do it. When EFGM makes use of IMLS the shape functions satisfy the Kronecker delta property. As consequence the periodic boundary conditions implementation can be done in a direct way, similar to the FEM.

Originality/value

IMLS provides a new way of periodic boundary conditions implementation in EFGM. This kind of implementation provides an easy and direct way in comparison to usual existing methods. With this technique EFGM can now easily take advantage of electrical machines symmetry.
Augmented reality in teaching of electrodynamics
Authors: Buchau André , Rucker Wolfgang M. , Wössner Uwe , Becker Martin
Published: August 2009

Purpose

The purpose of this paper is to present an application of augmented reality (AR) in the context of teaching of electrodynamics. The AR visualization technique is applied to electromagnetic fields. Carrying out of numerical simulations as well as preparation of the AR display is shown. Presented examples demonstrate an application of this technique in teaching of electrodynamics.

Design/methodology/approach

The 3D electromagnetic fields are computed with the finite element method (FEM) and visualized with an AR display.

Findings

AR is a vivid method for visualization of electromagnetic fields. Students as well as experts can easily connect the characteristics of the fields with the physical object.

Research limitations/implications

The focus of the presented work has been on an application of AR in a lecture room. Then, easy handling of a presentation among with low‐hardware requirements is important.

Practical implications

The presented approach is based on low‐hardware requirements. Hence, a presentation of electromagnetic fields with AR in a lecture room can be easily done. AR helps students to understand electromagnetic field theory.

Originality/value

Well‐known methods like FEM and AR have been combined to develop a visualization technique for electromagnetic fields, which can be easily applied in a lecture room.
Modelling eddy currents in thin shields
Authors: Hantila Florea I. , Ciric Ioan R. , Moraru Augustin , Maricaru Mihai
Published: August 2009

Purpose

The purpose of this paper is to present a simplified rigorous mathematical formulation of the problem of electric currents induced in thin shields with holes yielding more efficient numerical computations with respect to available methods.

Design/methodology/approach

A surface integral equation satisfied by the current density was constructed, which is, subsequently, represented at any point by linear combinations of novel vector basis functions only associated with the interior nodes of the discretization mesh, such that the current continuity is everywhere insured. The existence of the holes in the shield is taken into account by associating only one surface vector function with each hole. A method of moments is then applied to compute the scalar coefficients of the vector functions employed.

Findings

It was found that the induced current distribution for shields with holes having the complexity of real world structures can be determined with a satisfactory accuracy utilizing a moderate size processor notebook in a time of the order of minutes.

Originality/value

The originality of the proposed method consists in using specialized surface vector functions only associated with individual interior nodes of the shield, its multiply connected structure being efficiently accounted for by introducing one unknown for each hole, instead of unknowns for every node along the hole contours. The method presented is straightforward and highly efficient for mathematical analysis of thin shields with holes, and of other physical fields in the presence of multiply connected surface structures.
Magnetic model refinement via a perturbation finite element method – from 1D to 3D
Authors: Dular Patrick , Sabariego Ruth V. , Krähenbühl Laurent
Published: August 2009

Purpose

The purpose of this paper is to develop a sub‐domain perturbation technique for refining magnetic circuit models with finite element (FE) models of different dimensions.

Design/methodology/approach

A simplified problem considering ideal flux tubes is first solved, as either a 1D magnetic circuit or a simplified FE problem. Its solution is then corrected via FE perturbation problems considering the actual flux tube geometry and the exterior regions, that allow first 2D and then 3D leakage fluxes. Each of these sub‐problems requires an appropriate proper volume mesh, with no need of interconnection. The solutions are transferred from one problem to the other through projections of source fields between meshes.

Findings

The developed perturbation FE method allows to split magnetic circuit analyses into subproblems of lower complexity with regard to meshing operations and computational aspects. A natural progression from simple to more elaborate models, from 1D to 3D geometries, is thus possible, while quantifying the gain given by each model refinement and justifying its utility.

Originality/value

Approximate problems with ideal flux tubes are accurately corrected when accounting for leakage fluxes via surface sources of perturbations. The constraints involved in the subproblems are carefully defined in the resulting FE formulations, respecting their inherent strong and weak nature. As a result, an efficient and accurate computation of local fields and global quantities, i.e. flux, MMF, reluctance, is obtained. The method is naturally adapted to parameterized analyses on geometrical and material data.
Modelling earthing systems and cables with moment methods
Authors: Jacqmaer Pieter , Driesen Johan , Geuzaine Christophe
Published: August 2009

Purpose

The purpose of this paper is to present a method to model earthing systems subjected to lightning strikes with a one‐dimensional moment method. This paper was conducted because an accurate method to model earthing systems subjected to lightning strikes, was deemed necessary. To name a few examples of relevant situations: supply stations of railway systems, from which also critical signalling infrastructure is fed, earthing systems of cellular phone basestations, located in the vicinity of high‐antenna towers, prone to lightning strikes, and gas and oil pipelines. There exist already methods to solve this problem, based on circuit theory, but the electromagnetic method of this work is based directly on Maxwell's equations and therefore more accurate.

Design/methodology/approach

The earthing electrodes and meshes are represented as wire scatterers. First, the method is outlined for scatterers in a single medium. Next, the method is extended to model to presence of the soil‐air interface layer. An approximate technique, known as the modified image theory, is used to account for the vicinity of the soil. Finally, a second extension is given so that cables without metal sheets which are in the vicinity of the earthing systems, can be included in the model. Thereafter, it is described how the method can be used to calculate the effects of lightning strikes on earthing structures, and finally a validation of the method is presented.

Findings

The method is validated by applying it to simple situations which can also analytically be calculated, and by applying it to earthing structures for which the transient voltage was measured or calculated with circuit methods. A good agreement is seen. However, the method is computationally very expensive.

Research limitations/implications

In order to account for the influence of the air‐ground interface, an approximate method was used: the modified image method, and not the exact Sommerfeld theory. This was done because of its simplicity and in order to speed up the calculation process. Furthermore, cables can be included in the model, but they must be of simple structure: a cylindrical core, surrounded by an insulating cladding.

Originality/value

A few authors have already described this method to simulate lightning strikes on earthing systems. However, in this paper, a new and easy model for underground cables in the vicinity of earthing systems is presented.
A coupled electro‐chemical model of a direct methanol fuel cell for portable electronic devices
Authors: Alotto Piergiorgio , Guarnieri Massimo , Moro Federico
Published: August 2009

Purpose

The purpose of this paper is to optimize the performance of direct methanol fuel cells for portable applications by combining a non‐linear, fully coupled circuit model and a stochastic optimization procedure.

Design/methodology/approach

A novel non‐linear equivalent circuit that accounts for electrochemical reactions and charge generation inside catalyst layers, electronic and protonic conduction, methanol crossover through the membrane, mass transport of reactants inside diffusion layers is presented. The discharge dynamic of the fuel cell, depending on the initial methanol concentration and on the load profile, is modelled by using the mass conservation equation. The equivalent circuit is interfaced to a stochastic optimization procedure in order to maximize the battery duration while minimizing fuel crossover.

Findings

In the proposed circuit scheme, unlike semi‐empirical models, lumped circuit parameters are derived directly from mass transport and electric equations in order to fully describe the dynamic performance of the fuel cell. Physical and geometrical parameters are optimized in order to improve the system runtime. It is shown that a combined use of fuel cells and lithium batteries can improve the runtime of portable electronic devices compared to traditional supply systems based on lithium batteries only.

Research limitations/implications

The one‐dimensional model of the micro fuel cell does not take into account possible transverse mass and electric charge flows in the fuel cell layers; most of the geometric and physics model parameters cannot be estimated from direct in situ or ex situ measurements.

Practical implications

Direct methanol fuel cells are nowadays a promising technology for replacing or complementing lithium batteries due to their high energy density. Most limiting features of direct methanol fuel cells are the fuel crossover and its slow oxidation kinetics. By using the proposed approach, fuel cell parameters can be optimized in order to enhance the discharge runtime and to reduce the methanol crossover.

Originality/value

The equivalent circuit model with optimized lumped non‐linear parameters can be used when designing power management units for portable electronic devices.
Tolerance and multiobjective optimization in electromagnetic devices
Authors: Ray Subhasis , Lowther David
Published: August 2009

Purpose

The purpose of this paper is to develop a novel multi‐objective optimization algorithm which takes into account the uncertainty in design parameters by using a reduced resolution for their representation, thus implementing a simple form of robustness. Additionally, the number of function evaluations should be minimized.

Design/methodology/approach

The proposed approach is based on an elitist evolutionary algorithm coupled with a reduction in the number of significant figures used to represent design parameters. In effect, this becomes a filter in the optimization process and allows the system to avoid extremely sharp optima within the search space. By reducing the resolution of the search and maintaining a full archive of previous solutions, the number of evaluations of the objective functions, each of which may require an expensive numerical solution, is reduced.

Findings

The algorithm was tested both on an algebraic test function and on two TEAM Workshop Problems (22 and 25). The results demonstrated that it is stable; can emerge from deceptive fronts; and find optimal solutions which match those previously published at a relatively low‐computational cost.

Originality/value

The originality of this paper lies in the concept of using a low‐resolution representation of the design parameters. This results in a finite size search space and increases the speed of the algorithm while avoiding non‐manufacturable solutions.
Extraction of DC busbar parasitics in PWM inverters
Authors: Çay Zarife , Henze Olaf , Weiland Thomas
Published: August 2009

Purpose

The purpose of this paper is to present and apply a parasitic extraction approach for the calculation of DC busbar inductances.

Design/methodology/approach

A computational approach based on the finite integration technique and computed magnetic energy is developed to extract parasitic inductances. The finite integration analysis is conducted via the magnetoquasistatic solver of CST EM Studio® capturing the 3D geometrical effects of the design, as well as the skin and proximity effects.

Findings

The method is applied successfully to evaluate the leakage inductances of two printed circuit boards structures; a backplane sample for the verification purpose and a real DC bus employed in a three‐phase pulse width modulation inverter.

Research limitations/implications

The paper demonstrates that the method calculates the loop inductances accurately. It does not, however, verify the used technique to split loop inductances into partial inductances.

Practical implications

The extraction method is easy‐to‐use and able to handle complex geometries within acceptable computation time and accuracy.

Originality/value

The paper introduces a way to compute the parasitic inductances from the results of a numerical electromagnetic field solver.
Plane elliptic or toroidal multipole expansions for static fields
Authors: Schnizer P. , Schnizer B. , Akishin P. , Fischer E.
Published: August 2009

Purpose

The purpose of this paper is to present new basis functions suitable to parameterize two‐dimensional static potentials or (magnetic) fields and to show their application in practical cases.

Design/methodology/approach

Regular multipole solutions of the potential equation in plane elliptic coordinates are found by separation. The resulting set of functions is reduced to complete subsets suitable for expanding regular potentials or irrotational source‐free fields. Approximate regular plane solutions of the potential equation in local toroidal coordinates are computed by R‐separation and power series expansions in the inverse aspect ratio. The harmonic signals induced in a coil rotating in such a toroidal multipole field are computed from the induction law by similar expansions.

Findings

The elliptic expansions are useful in a larger area than circular multipole expansions and give better fits. The toroidal expansions permit one to estimate the effect of the curvature of magnets on the field and give better adapted expansions. However, while the scalar multipoles for the potential are orthogonal the vector fields derived for the two‐dimensional field are not.

Research limitations/implications

Derivations presuppose analytical fields.

Practical implications

Field data obtained from numeric field calculations or measurements do not represent exactly analytic fields. Application of the expansion requires care and checks.

Originality/value

The paper presents novel approaches for parameterizing longitudinally uniform cylindrical or toroidally uniform potentials and fields.
Comparison between continuous and discrete frequency domain solution methods for structural steady state calculations with the finite element method
Authors: Rainer O. Bíró S. , Stermecki A.
Published: August 2009

Purpose

Different solution methods, using finite element method in continuous and discrete frequency domain, are compared with each other in order to find the most appropriate method for the estimation of steady state vibrations in linear structural and mechanical problems. The purpose of this paper is to describe the procedures.

Design/methodology/approach

The continuous and some relevant discrete frequency domain solution methods are compared by an analytical investigation as well as by the numerical examination of a simple model. Finally, results for a more relevant example using finite elements are presented.

Findings

It is shown that the steady state computation using the continuous frequency domain system description delivers the exact solution for a given system.

Originality/value

Based on the presented results, the use of continuous frequency domain system description is recommendable in most cases.
Discontinuous Galerkin formulation for eddy‐current problems
Authors: Außerhofer S. , Bíró O. , Preis K.
Published: August 2009

Purpose

The purpose of this paper is to describe a method for solving eddy current problems. Discontinuous basis functions are applied to conducting regions in eddy‐current problems. This results in a block‐diagonal mass matrix allowing explicit time stepping without having to solve large algebraic systems.

Design/methodology/approach

The effect of the basis functions in the conducting region is limited to the respective finite element. This yields to a block‐diagonal mass matrix, whereas each block in this matrix belongs to one finite element. In the nonconducting region, traditional finite elements are used which leads to well‐conditioned system matrices. For the two regions, different time steps are used.

Findings

To avoid instability, a term which penalizes the tangential jump of the magnetic vector potential A has to be added. A value for weighting this term is suggested and tested on a simple two dimensional example.

Originality/value

The proposed method leads to a potentially fast method for solving eddy‐current problems.