Search results

The purpose of this paper is to investigate the extension of Delaunay refinement algorithms to work directly with a curved geometry in arbitrary dimensional spaces, which is also able to refine geometry pieces of different dimensions altogether.

The extension of Delaunay refinement is based on ideas of the Bowyer‐Watson algorithm and Ruppert algorithm.

The attempt to extend the fundamental ideas of Delaunay refinement to cope with curved geometries led to an algorithm whose performance in practice, regarding speed and mesh quality, is comparable to classical Delaunay refinement for flat geometries. Unfortunately, there are only theoretical guarantees that the refinement itself works under some conditions. No theoretical mesh quality bounds are provided.

A mesh refinement algorithm that deals with curved geometries is a key feature for adaptive mesh generators, so that points are inserted properly in the curved pieces instead of in linear approximations of them. For instance, it is well known that sharp edges are singular points of finite element formulations. This singularity fulfills in practice as mesh is refined around them. Those corners can be rounded up to avoid singularities. Furthermore, with this kind of tool, for instance, a user could start to mesh a disc from a single triangle representing it. Points would be efficiently inserted in the circle as needed during refinement.

This paper introduces the concept of manifold complex and also an extension of Delaunay refinement algorithm to deal with curved geometries.

The paper aims to present a new methodology for hybrid genetic algorithms (GA) in the solution of electromagnetic optimization problems.

This methodology can be seen as a local search operator which uses local quadratic approximations for each objective and constraint function in the problem. In the local search phase, these approximations define an associated local search problem that is efficiently solved using a formulation based on linear matrix inequalities.

The paper illustrates the proposed methodology comparing the performance of the hybrid GA against the basic GA in two analytical problems and in the well‐known TEAM benchmark Problem 22. For the analytical problems, 30 independent runs for each algorithm were considered whereas for Problem 22, ten independent runs for each algorithm were taken.

For the analytical problems, the hybrid GA enhanced both the convergence speed, in terms of the number of function evaluations, and the accuracy of the final result. For Problem 22, the hybrid GA was able to reach a better solution, with a better value of the standard deviation with less CPU time.

The paper could be useful both for device designers and researchers involved optimization in computational electromagnetics.

The hybrid GA proposed enhanced the convergence speed, in terms of the number of function evaluations, representing a faster and robust algorithm for practical optimization problems.

This paper aims to present a SPICE model to represent antennas in receiving mode. The model can be used to evaluate the performance of the antenna when it is coupled to several different nonlinear electric circuits. The proposed methodology is particularly suitable for rectenna applications, as it allows the analysis of different configurations for a rectenna more efficiently than using full-wave analysis simulators coupled directly to each rectifier circuit.

The model presented uses reciprocity theory to calculate the ideal voltage source of the Thevenin-equivalent circuit for an antenna. Vector fitting is then used to approximate the model to rational functions that can be converted to Resistor, Inductor and Capacitor circuits. Additional components are added to the circuit to prevent numerical instability.

Two rectennas are used to illustrate the performance of the proposed model, one based on a 2.45-GHz rectangular patch antenna and another based on a planar spiral antenna. The second antenna has impedance with positive and negative real parts along the frequency range, which could lead to numerical instabilities. The proposed method is shown to be stable while working with these negative resistance values, which may appear during circuit parameterization.

The equivalent SPICE circuit model for the antenna makes it easy to simulate nonlinear circuits connected to the antenna and perform transient analyses. The computational cost of antenna analysis is reduced, being more computationally efficient than methods that involve full-wave simulation. This characteristic makes it an interesting approach for working with rectennas, or any application where the time constant of the circuit is much longer than the period of the incident wave.

For most antenna applications, the numerical stability of the circuit can be achieved using passive enforcement. However, depending on the phase response of the antenna, the impedance that represents its far-field characteristic may present a negative real part, in which case, passive enforcement will fail. In this paper, the problem of numerical instability is solved by introducing an offset resistance and a current-controlled voltage source to the model.

The mismatch between desired and actual hours of work per week is common among the employed in many countries and has important effects on the adequate functioning of labour markets. The purpose of this paper is to investigate the likelihood of being underemployed, matched or overemployed in terms of hours worked for workers without and with disabilities in Germany by using longitudinal data.

Data are taken from the German Socio-Economic Panel (1985-2013) for a large sample of salaried workers aged 16-64. The authors have used a “Random-effects ordered probit model” to estimate the impact of being disabled on the likelihood of suffering any type of working time mismatch. Additionally, the authors have estimated a “Tobit Random-effects model” on the number of hours of underemployment and overemployment.

Females with disabilities are more likely to be overemployed than females without disabilities. In addition, only females with disabilities experience a lower number of hours of underemployment than females without disabilities. As for overemployment, both males and females with disabilities are more likely to report a higher number of hours of overemployment as compared to their non-disabled counterparts.

This paper therefore shows the importance of combating and reducing the hours of overemployment for all workers in general and for males and females with disabilities in particular. A large longitudinal data set has been used in the paper and it is the first attempt to estimate the determinants of being underemployed, matched and overemployed for workers without and with disabilities.

University–industry projects provide special challenges in understanding and expressing the values required of project management (PM) in delivering stakeholder benefits. This paper presents a framework for understanding, identifying and managing the values of PM in major university–industry R&D projects.

The value framework identifies for each of the key stakeholders, the key PM values that may require to be managed and are largely derived from research literature. Empirical research then explores, prioritises and selects key PM values that need to be managed for a specific project. A large case study is used involving one university and one industry collaborating on a multi-million Euro initiative over six years. Empirical research was conducted by researchers who observed at close quarters, the challenges and successes of managing the competing values of key stakeholders.

The value framework takes a stakeholders' perspective by identifying the respective PM values for each of six stakeholders: university–industry consortium, university, industry, R&D external entities, funding entity and society.

The research was performed using only one case study which limits the generalisability of its findings; however, the findings are presented as a decision support aid for project consortia in developing values for their own collaboration.

Guidance and decision support are provided to multi-stakeholder research consortia when selecting values that need to be managed for achieving tangible and intangible project benefits.

The paper demonstrates a proposed framework for designing and managing the value of PM in large multi-stakeholder university–industry R&D projects.

The paper aims to focus on the memory-polynomial model (MPM) as special case of Volterra series, implemented in hardware. The behavior of the MPM is fully proved through a comparison with AM-AM and AM-PM measured data. The results show that this simulation technique is able to prove the effectiveness of the MPM implementation as behavioural model for high power radiofrequency amplifiers. The system is able to compensate perturbations caused by modern communication systems.

The implementation uses Matlab-Simulink, and its digital signal processing (DSP) builder. The first stage allows developing the model in Matlab using the DSP builder blockset through the signal compiler block. Then, the design is downloaded to the DSP board.

The paper demonstrates a proper behavior of the MPM as a truncation of the Volterra series, with respect to different inputs. This is a key point, because the series truncations allow first to implement this model in real time and second to obtain a correct precision, for instance when modeling amplification of digital signals in high frequency.

The global system approach permits to easily develop, simulate, and validate a wireless system. The efficiency of a complete connected solution based on Agilent Technologies tools, combining simulations and measurements under true operating conditions, seems to be clearly demonstrated.

The purpose of this paper is to study the nonlinear impact of quality dimensions of third-party logistics (3PL) services on customer satisfaction and loyalty.

By interviewing 167 small-size companies, and using penalty and reward contrast analysis, the paper explores the nonlinear impact of seven dimensions of 3PL services (safety, fault’s recovery, reliability, speed, flexibility, communication, and friendliness) on customer satisfaction and loyalty.

The results confirm the existence of the dimensions’ nonlinear impact on customer satisfaction. It also shows that some quality dimensions have a direct and nonlinear impact on loyalty. The dimension “friendliness” has a direct impact on loyalty if the company has a below market average performance, which may lead customers to switch service providers. “Flexibility on collection and delivery” has a direct impact if the company has a higher performance, contributing to customers’ intention to continue using the service. Another finding is that, if the company delivers good service recovery after the customer found faults in the service, and if customers trust the company service, they say they intend to continue to work with the company.

The present research focused only on small companies in one country (Brazil). Further studies should be carried out to explore different countries, with different realities, and different size of companies.

3PL companies should not only deal with customers’ satisfaction, but also with other quality aspects that directly affect customer intention to continue doing business with the 3PL service provider. These are friendliness, flexibility regarding time and frequency of collection and delivery and faults’ recovery.

The present research confirms that the personal relationship is a crucial aspect to be managed in order to keep customers in the long term. In addition, as opposed to most research looking for the antecedents of satisfaction and loyalty of 3PL customers, the present research shows that there is a direct nonlinear impact of the dimensions’ performance on customers’ loyalty, what should be taken in consideration by 3PL managers. It also shows how penalty-reward contrast analysis may reveal nonlinear antecedents that could be used for better understandings companies’ success in the long term.

The purpose of this paper is to explore current questions about metaphor, experience and aesthetic awareness that persist through the variations of critical approaches and projective research in architectural theory and practice.

Further considerations focus on the advanced technological possibilities which re‐invest the relations between principles of cybernetics and architecture.

The current between art and architecture is more than ever manifested in fields related to the computer sciences and its conceptual background: cybernetic sciences.

The paper re‐thinks the aesthetic value of architecture and architectural experience in this time of digital productivity.

Identifying if aid flows have contributed to economic growth or growth divergence between a sample of Asian and African countries is the purpose of this paper. Using data over the period of 1980–2015, the paper attempts to establish whether aid, in any of its forms, has played a role in economic growth in these countries.

A comprehensive literature analysis over the past 70 years sets the scene for the paper. A panel data fixed-effects model is applied for each sample (Africa and Asia) between 1980 and 2015. Both theoretical predictions and empirical studies are used to derive the independent variables selected for modelling.

The findings strongly suggest that aid flows in both the Asian and African samples have no relation at all to either long-run growth paths or growth divergence. However, there is a suggestion in the case of the Africa sample that governance decline may well be the primary source of growth divergence.

This result cannot be generalised because it only focuses on six countries but as demonstrated in the paper, other possible samples (from both regions) actually make no difference to the results. It could also be argued (given the comprehensive literature analysis presented here) that it is not essential to have a theoretical relationship between aid and growth because aid is given to different countries with very different characteristics, needs, governance and policy environments.

Donor countries must play a more supervisory role to ensure aid flows are directed to the right channels in recipient countries. Aid should be given to countries which have a certain degree of macroeconomic stability and “good” policy to ensure effectiveness. They also need to pay attention to the sectoral distribution of aid as do recipient countries to better allocate aid flows to productive sectors that contribute to both short- and long-term growth.

These are not given much emphasis in this paper.

Most aid–growth studies are based on a large number of countries from different regions with different characteristics or on a single country case. This paper compares between two samples of countries sharing the same characteristics to overcome the heterogeneity problem. This paper is based on a more protracted time series from 1980 to 2015 to capture more accurately the impact of foreign aid on economic growth.

Six sigma has been considered a business strategy that employs a well‐structured continuous improvement methodology to tackle process variability and drive out waste from the business processes using statistical tools and techniques. This paper first examines the differences and similarities of six‐sigma improvement methodology compared with the DFSS approach. This work illustrates the use of analytical hierarchy process (AHP), a multiple criteria decision‐making technique, for the evaluation of six‐sigma projects in order to determine when the six‐sigma approach becomes a priority over DFSS. The use of AHP to determine the transition from six sigma to design for six sigma represents a major challenge to many researchers today, as very little has been done on this subject.