Experimental and numerical investigation of fracture in double-edge notched steel plates

Double-edge notched (DENT) steel plates were pulled until complete fracture and several experimental observations were made (using profilometry and scanning electron microscopy). The essential work of fracture (EWF) model was found to be well verified. Numerical simulations—up to the maximum load only—of some experiments were performed using the finite element method (FEM), and incorporating geometric and material non-linearities (large deformation elasto-plasticity). Some experimental measurements were compared with the corresponding numerical computations and excellent agreement was found.     

Carotene Degradation and Isomerization during Thermal Processing: A Review on the Kinetic Aspects

Kinetic models are important tools for process design and optimization to balance desired and undesired reactions taking place in complex food systems during food processing and preservation. This review covers the state of the art on kinetic models available to describe heat-induced conversion of carotenoids, in particular lycopene and β-carotene. First, relevant properties of these carotenoids are discussed. Second, some general aspects of kinetic modeling are introduced, including both empirical single-response modeling and mechanism-based multi-response modeling. The merits of multi-response modeling to simultaneously describe carotene degradation and isomerization are demonstrated. The future challenge in this research field lies in the extension of the current multi-response models to better approach the real reaction pathway and in the integration of kinetic models with mass transfer models in case of reaction in multi-phase food systems.     

Content Management Systems: Enriched learning opportunities for all?

This article examines the popular claim of Content Management Systems (CMSs) that providing a rich toolset and leaving the use under learner control is beneficial to learning. By means of a literature review, the current contribution examines whether all students are capable of using CMS tools so that their learning is enhanced. In contrast to what is assumed, the study conceptualizes tool use as a complex self-regulation strategy that cannot be taken for granted. Specifically, the article reviews empirical studies in relation to three topics: (a) personal agency in tool use, (b) performance effects of tool use and (c) influencing tool use variables. Findings reveal that not every student profited from the CMS learning opportunities; in multiple studies students differed in their tool use, and these differences had significant performance effects. Hence, these findings suggest that the pedagogical claim CMSs make is problematic. Besides this accumulated corpus of knowledge, the review revealed serious limitations in the retrieved studies which could hamper our findings. As a consequence, the review establishes a need for further research into students’ CMS tool use from an instructional design perspective. In addition to the theoretical framework, several directions for future research are given.     

Students’ tool-use within a web enhanced course: Explanatory mechanisms of students’ tool-use pattern

The popularity of content management systems (CMSs) in today’s higher education is driven by the assumption that providing a rich toolset and leaving the use of this toolset under learner control will stimulate self-regulated and deeper learning. Current evidence on students’ tool-use within CMS supported courses however tackles this assumption and indicates that CMSs may empower students’ learning only under particular learner-related conditions. The current study addresses this concern and investigates how students’ tool-use within a CMS supported course can be explained in terms of (a) students’ conceptions on the tool functionalities, (b) self-efficacy beliefs for self-regulated learning and (c) goal orientation. Data were collected within a first year undergraduate course ‘Learning and Instruction’. Students’ (n = 182) tool-use within the course was logged throughout the course episode and the influencing variables were measured through questionnaires. K-means cluster analyses revealed four clusters that reflected differences in students’ tool-choice and tool-use throughout the course. Multinominal regression analyses revealed that these tool-use differences could be explained in terms of students’ goal orientation. The study provides thus perspectives in order to capture students’ academic motivation through unobtrusive, behavioral, measures. Furthermore, questions are raised regarding the parallel between students’ tool-use pattern and study strategy use.     

An FFT-based signal identification approach for obtaining the propagation constants of the leaky modes in layered media

We propose to find the propagation constants of modes in layered media by means of signal identification methods. To this effect we employ Cauchy's theorem, conformal mapping and Fast Fourier Transform (FFT) techniques to generate relevant Hankel moments, afterwards to be processed with selected signal identification algorithms. The method, terminated by a few Newton steps, provides a batch of highly accurate roots in appropriate disks or half-disks.     

Modifying the feature-selective validation method to validate noisy data sets

Objective validation and ranking of measurements and simulations may be done by methods such as feature selective validation (FSV). FSV is used to compare two EMC-measurement results. Owing to the noisy nature of these type of data, the FSV results are corrupted. The reasons are discussed and solutions are proposed to make FSV feasible in a broader area of applications. The final solution is a combination of denoising the data and changing the weight of the data to be in accordance with our visual interpretation.     

Study of the bias of the MTC estimate by noise analysis due to the presence of feedback

This paper discusses the bias of the non-parametric Moderator Temperature Coefficient (MTC) estimate due to the presence of feedback. Up to now the non-parametric estimation of the Frequency Response Function (FRF) is the most commonly used method to estimate the MTC by noise analysis. This estimation method is proportional to the Cross Power Spectral Density between the total neutron flux variation and total temperature variation divided by the auto power spectral density of the total temperature variation. The estimation method is very popular since feedback is considered to be negligible in the frequency band of interest. Unfortunately this is not the case in practice. Measurements at a Nuclear Power Plant in Belgium will be used to confirm that this feedback cannot be neglected. In case of feedback the chosen estimator always results in a biased estimate when there are external neutron flux variations present. It will be seen that the ratio between the external neutron flux and external temperature variation in combination with the amplitude of the feedback determines the bias. The theoretical analysis of the bias is based on a simplified scheme of the MTC measurement setup. A simulation in MATLAB is used to confirm the theoretical results. In order to avoid a biased estimate due to the feedback we will advise to measure the external temperature variation and to use another non-parametric estimator.     

Integral equation for the fields inside a dielectric cylinder immersed in an incidentE-wave

The scattering of a time-harmonicE-wave by a dielectric cylinder is solved by a single integral equation. Two alternatives are investigated to derive such a single integral equation. Interest is focused on the fields inside the dielectric. In this case the integral equation has only the incident electric field as its source term.     

Generalized Poisson-Neumann polygonal basis functions for the electromagnetic simulation of complex planar structures

Rooftop functions are commonly used for the discretization of planar currents in electromagnetic (EM) simulators. We describe the generalization of the rectangular and triangular rooftop functions to arbitrary polygonally shaped subdomains. It is shown that these generalized basis functions are solutions to a pertinent Neumann-Poisson problem, and we derive the integral equations satisfied by these basis functions. The new generalized polygonal functions allow for a more efficient meshing of complex geometrical structures in terms of polygonally shaped cells. They naturally model the current flow in the polygonal cells, satisfy the current continuity relation, and significantly enhance the EM simulation performance for complex geometrical structures. The increased simulation performance is demonstrated for a complex radio-frequency board interconnection layout and a spiral inductor on a silicon substrate.