Search results

Modifications of physical and electrical properties of the vertical double‐diffused metal oxide semiconductor (VDMOS) transistor are observed on using the device under some conditions of “functional” stress. This paper presents the characterization and the 2D simulation for the pre‐ and post‐stressed device, to point out the degraded parameters due to the functional stress, and to analyze their effects on the degradation of the VDMOS static and dynamic characteristics.

The purpose of this paper is to propose a numerical method in time domain in order to solve the electric and magnetic fields radiated from lightning in the presence of the tall tower. This paper is very important in calculating lightning electromagnetic field – obtaining directly the solution in time domain with a reduced computation time and reduced space memory.

In this paper, a HYBRID method is proposed for the calculation of the electromagnetic field associated with lightning strikes to tall towers. The proposed method is a combination between a numerical integration method and the finite difference time domain (FDTD) method. The HYBRID method is an alternative approach that takes advantage of this combination to calculate, first, the radiated magnetic field; this field is obtained by the use of the Simpson method, and, second the electric field, based partially on the FDTD method.

The results of lightning electromagnetic field in the presence of a tall tower obtained by this proposed method: HYBRID method are in agreement with experimental results or simulated results (by the use of other methods: method in frequency domain). This method can be applied to solve the lightning electromagnetic field equation for far distances or close distances from lightning stroke.

This paper presents a temporal method to obtain the lightning electromagnetic field in the presence of a tall tower with reduced space memory and reduced time.

The electromagnetic field radiated from a lightning channel is the excitation for analyzing the field-to-transmission line coupling problem. The purpose of this paper is to propose a novel efficient approach to evaluate the horizontal electric field of the lightning channel expressed by the generalized Sommerfeld integral.

The asymptotic integral is extracted from the original one, which actually makes the Sommerfeld integral tail reach its convergence very quickly. To handle the sharp variance around k0, a closed-form integral, which is obtained by replacing the original kernel with an approximated function, is presented in detail. The numerical examples validated the proposed approach in the both frequency and time domain.

The approach proposed in this paper has been validated by the comparison with results in other papers. The agreement among these results reaches very well, and the approach proposed in this paper is more efficient and easy to implement, especially for the calculation of the tail integral part.

In accordance with the numerical experiments, the proposed approach can be served as a qualified candidate in terms of computational efficiency to evaluate the electromagnetic field generated by the lightning channel.

This case reflects a classic approach to entrepreneurship based on entrepreneurial resources and opportunities. It also provides a vehicle for discussing the key features of a business model. It also addresses key strategic choices such as whether to replicate a business model or not.

This case study sets out the story of an entrepreneur: Zein Rachidi. It describes his history and the key milestones in his professional development until the creation and development of his own startup “Topotrade” the first online market place for used topography equipment. It also exposes his development plan, his will to scale up his business by replicating the same business model of Topotrade in a new market, that of used biomedical equipment.

This case is written mainly with a view to its use in the context of entrepreneurship courses for undergraduate students in management, as well as for entrepreneurs who can compare Zein’s trajectory to their own. This case is designed for students also suitable for courses in basic strategy, strategy and change and disruptive business models.

Teaching Notes are available for educators only.

CSS 3: Entrepreneurship.

A fast algorithm is proposed to calculate the lightning electromagnetic field over a perfectly conducting earth surface.

The channel base current is approximated by a number of sub‐domain quadratic functions using the proposed adaptive sampling technique, and the derivative and integral of the channel base current with respect to time can be analytically expressed. With the help of these approximations, the ideal electromagnetic field of the lightning channel can be evaluated along the lightning channel with respect to the height.

The computational time can be greatly reduced using the proposed approach to evaluate the electromagnetic field of a lightning channel in the time domain.

The adaptive sampling technique is a general‐purposed approach, which can be potentially used in other applications to fit a function with the minimal number of intervals.

The America Rescue Plan (ARP) transformed the Child Tax Credit (CTC) into a more generous, inclusive monthly payment from July through December 2021. However, the expansion has been terminated and the annual CTC has been reinstated. The United States is one of the few OECD countries that do not have a child allowance system and South Korea has recently adopted child allowance in 2018. This study aims to comprehensively review the existing literature and evidence on ARP-CTC in the United States and Universal Child Allowance (CA) in Korea.

The researchers completed a database search between July 1, 2022 and July 20, 2022. For the United States, the search keywords were child tax credit OR expanded child tax credit OR CTC OR child allowance. For Korea, the search keyword was child allowance. Searches were conducted using 79 databases. A total of 36 US studies and 7 Korean studies met all the inclusion criteria and proceeded to the extraction process. A narrative thematic synthesis approach was employed to identify themes in the findings. The results were organized based on the characteristics of the studies and the post-intervention outcomes.

Studies in the United States focused primarily on economic outcomes, including poverty and material hardship, reflecting the concern policymakers and researchers have about child poverty. On the other hand, Korean studies examined employment, economic well-being, psychological well-being and expenditures in a relatively balanced share. Overall, studies found that both ARP-Child Tax Credits and Universal Child Allowance reduced child poverty and improved material hardship. Also, studies in both countries suggested that both policies had positive impacts on parental psychological well-being.

To the authors knowledge, this paper is the first to comprehensively review the impact of the US ARP-CTC in comparison with the Korean child allowance. Two studies reviewed and updated the literature on US ARP-CTC as a round-up paper. Moreover, the authors conduct cross-national comparative analyses between the United States and Korea. The contexts of the child allowance system in the two nations have both similarities and differences, thereby offering a unique opportunity for a comparative study.

Solutions for the earth return mutual impedance play an important role in analyzing couplings of multi-conductor systems. Generally, the mutual impedance is approximated by Pollaczek integrals. The purpose of this paper is devising fast algorithms for calculation of this kind of improper integrals and its applications.

According to singular points, the Pollaczek integral is divided into two parts: the finite integral and the infinite integral. The finite part is computed by combining an efficient Levin method, which is implemented with a Chebyshev differential matrix. By transforming the integration path, the tail integral is calculated with help of a transformed Clenshaw–Curtis quadrature rule.

Numerical tests show that this new method is robust to high oscillation and nearly singularities. Thus, it is suitable for evaluating Pollaczek integrals. Furthermore, compared with existing method, the presented algorithm gives high-order approaches for the earth return mutual impedance between conductors over a multilayered soil with wide ranges of parameters.

An efficient truncation strategy is proposed to accelerate numerical calculation of Pollaczek integral. Compared with existing algorithms, this method is easier to be applied to computation of similar improper integrals, such as Sommerfeld integral.

This paper aims to present the approximation of lightning currents waveshapes by the multi-peaked analytically extended function (MP-AEF) for the experimentally measured channel-base currents in the artificially triggered lightning discharges. Modified transmission line model of lightning return strokes having the channel current both linearly decaying and sinusoidally changing with height (MTLSIN) is used to calculate the lightning electromagnetic field.

MP-AEF’s parameters for the artificially triggered lightning channel-base currents are calculated by using Marquardt least squares method (MLSM). Lightning electromagnetic fields are calculated based on electromagnetic theory relations, thin-wire antenna model of the vertical lightning channel and the assumption of the perfectly conducting ground. MTLSIN model as an engineering model of lightning strokes is used to obtain the electric field results as these are simultaneously measured in rocket-triggered lightning experiments together with the channel-base currents.

MP-AEF approximates multi-peaked pulse waveshapes. Some important function parameters are chosen prior to the approximation procedure, such as current peaks and the corresponding time moments of those peaks, which presents an advantage in comparison to other functions. The desired accuracy of approximation is obtained by choosing an adequate number of function terms. MLSM is used for the estimation of unknown parameters. Using MTLSIN model, the influence of the channel height and return stroke speed on the lightning electromagnetic field waveshape is analyzed in this paper.

MP-AEF may be used for approximation of various multi-peaked waveshapes. It has no errors in the points of maxima which is important for the lightning protection systems design. MTLSIN model may be validated by using simultaneously measured lightning electromagnetic fields at various distances from the channel and for channel heights estimated in the experiments. It is also possible to approximate measured current derivatives by MP-AEF and use them for further computation.

MTLSIN model is proposed in this paper for the evaluation of lightning electromagnetic fields induced by artificially triggered lightning discharges. The procedure is based on the approximation of lightning channel-base currents by the multi-peaked analytically extended function previously proposed by the authors. This function may be used not only for representing lightning currents but also for other waveshapes as current derivatives, electric and magnetic fields and their derivatives, which are all important for the lightning protection design. MTLSIN gives lightning electromagnetic fields results which are in better agreement with measured fields than those obtained by other models from literature.

The lightning phenomenon is one of the main threats in photovoltaic (PV) applications. Suitable protection systems avoid major damages from direct strikes but also nearby strikes may induce overvoltage transients in the module itself and in the power conditioning circuitry, which can permanently damage the system. The effects on the PV system sensibly depend on the converter topology and on the adopted power switch. In the present study, a comparative analysis of the transient response due to a nearby lightning strike (LS) is carried out for three PV systems, each equipped with a different converter, namely, boost, buck and buck–boost, based on either silicon carbide metal oxide semiconductor field effect transistors (SiC MOSFET) or insulated gate bipolar transistors controlled power switch devices, allowing in this way an analysis at different switching frequencies. The purpose of this paper is to present the results of the numerical analysis to help the design of suited protection systems.

Using a recently introduced three-dimensional semi-analytical method to simulate the electromagnetic transients caused in PV modules by nearby LSs, we investigate numerically the effect of a LS on the electronic circuits connecting the module to the alternate current (AC) power systems. This study adopts numerical simulations because experimental analyses are not easy to perform and does not grant a sufficient coverage of all statistically relevant aspects. The approach was validated in a previous paper against available experimental data.

It is found that the load voltage is not severely interested by the strike effects, thanks to the low pass filters present at the converter output, whereas a relatively high overvoltage develops between the negative pin of the inner circuitry and the “ground” voltage reference. The overcurrent present in the active switches is hardly comparable because of the different topologies and working frequencies; however, the highest overcurrent is observed in the buck converter topology, with SiC MOSFET technology, although it shows the fastest decay.

This research proposes, to the best of the authors’ knowledge, a comprehensive comparison of the indirect lighting strike effects on the converter connected to PV panels. A proper design of the lightning and surge protection system should take into account such aspects to reduce the risk of induced overvoltage and overcurrent transients.

The main purpose of the study is to examine the willingness of Moroccan small- and medium-sized enterprises (SMEs) to adopt profit and loss sharing (PLS) method of finance and the factors that may influence their decision.

The research model is based on the decomposed theory of planned behaviour (DTPB). A total of 340 questionnaires were randomly distributed to SMEs’ owner-managers, out of which 177 were collected and only 153 were valid for analysis. Factor analysis and partial least squares regression were subsequently applied.

The results showed that cost, loss of control, constrained access to conventional debt, financial suitability, stage of development as well as religious beliefs have a significant impact on the SMEs’ attitude towards PLS modes. Likewise, normative belief was also found to have a significant influence on subjective norm, by particular reference to the family, financial external consultants and internal managers, as the main referent groups. In addition, finally, attitude and perceived behavioural control were found to have a significant impact on the intention to adopt PLS financing by Moroccan SMEs.

The sample is not representative; hence, the findings cannot be generalized to all Moroccan SMEs. Furthermore, the variables and dimensions used are not exhaustive. With regard to implications, the study confirms the applicability of the DTPB to SME financing questions. Moreover, this study provides great indications to the practitioners, investors, policy makers and regulators on the perception of the Moroccan entrepreneurs, which should be taken into consideration to establish the necessary strategies to attract them.

This paper verifies the applicability of the DTPB in another area, that is, adoption of PLS instruments and contributes to explain the entrepreneurs’ perceptions towards theses modes of financing.