From embedded sensors to sensorial materials—The road to function scale integration

Ubiquitous computing is about to become part of our everyday lives by integrating hundreds of “invisible” to us computing devices in our environment, so that they can unobtrusively and constantly assist us. This will imply more and smaller “invisible” sensors, homogeneously distributed and at the same time densely packed in host materials, responding to various stimuli and immediately delivering information. In order to reach this aim, the embedded sensors should be integrated within the host material, heading towards sensorial materials. The first step is to omit all parts that are not needed for the sensorial task and to find new solutions for a gentle integration. This is what we call function scale integration. The paper discusses sensor embedding in the human hand as an example of integration in nature, new technological applications and main challenges associated with this approach.     

Developing Web literacy in collaborative inquiry activities

Although many children are technically skilled in using the Web, their competences to use it in a critical and meaningful way are usually less well developed. In this article, we report on a multiple case study focusing on the possibilities and limitations of collaborative inquiry activities as an appropriate context to acquire Web literacy skills in primary education. Four 5th grade school teachers and their students worked with collaborative inquiry activities on the subject of ‘healthy food’. The project was aimed at both the development of Web literacy skills and content knowledge building. Data from a variety of sources were collected: videotaped and written lesson observations, interviews with teachers and students, teacher diaries, student questionnaires, and student assignments. The teachers appeared to be able to carry out the program to varying degrees. Contextual factors that influenced the realization of the project’s goals and results were the adequacy of the research questions formulated by students, students’ inquiry skills, and the teachers’ teaching styles. Students’ learning results show that it is possible to teach Web literacy skills in the context of collaborative inquiry activities. All classes show knowledge gain with regard to the subject healthy food and all classes but one show knowledge gain with regard to Web literacy skills. Although many students show adequate use of particular Web searching, reading and evaluating skills after the project, inconsistency, impulsiveness and impatience are also typical of their Web behaviour. In the context of collaborative inquiry activities teachers are challenged to deal with the paradox that they want their students to be active knowledge builders with help of the Web, whereas the Web seems to invite students to be more or less passive searchers.     

Efficient randomised broadcasting in random regular networks with applications in peer-to-peer systems

We consider broadcasting in random d-regular graphs by using a simple modification of the random phone call model introduced by Karp et al. (Proceedings of the FOCS ’00, 2000). In the phone call model, in every time step, each node calls a randomly chosen neighbour to establish a communication channel to this node. The communication channels can then be used bi-directionally to transmit messages. We show that, if we allow every node to choose four distinct neighbours instead of one, then the average number of message transmissions per node required to broadcast a message efficiently decreases exponentially. Formally, we present an algorithm that has time complexity \(O(\log n)\) and uses \(O(n\log \log n)\) transmissions per message. In contrast, we show for the standard model that every distributed algorithm in a restricted address-oblivious model that broadcasts a message in time \(O(\log n)\) requires \(\Omega (n \log n{/} \log d)\) message transmissions. Our algorithm efficiently handles limited communication failures, only requires rough estimates of the number of nodes, and is robust against limited changes in the size of the network. Our results have applications in peer-to-peer networks and replicated databases.     

Flood Risk Management in Flanders: Past Developments and Future Challenges

This paper presents the state of the art of flood risk management in Flanders, a low-lying region in the northern part of Belgium which is vulnerable to flooding. Possible flood hazard sources are not only the many rivers which pass through the Flemish inland, but also the North Sea, which is sensitive to the predicted sea level rise and which can affect large parts of the Flemish coastal area. Due to the expected increase in flood risks in the 21st century, the Flemish government has changed its flood management strategy from a flood control approach to a risk-based approach. Instead of focusing on protection against a certain water level, the objective now is to assure protection against the consequences of a flood, while considering its probability. In the first part, attention is given to the reasoning and functioning of the risk-based approach. Recent improvements to the approach are discussed, as well as the GIS-implementation of the entire model. The functioning of the approach is subsequently demonstrated in two case studies. The second part of the paper discusses future challenges for the flood risk management in Flanders. The driving force behind these challenges is the European Directive on the assessment and management of flood risks, which entered into force in 2007. The Flemish implementation of the directive is discussed and situated in the European landscape. Finally, attention is given to the communication of flood risks to the general public, since the “availability” of flood risk management plans is among the requirements of the EU Floods Directive.     

Generating feature spaces for linear algorithms with regularized sparse kernel slow feature analysis

Without non-linear basis functions many problems can not be solved by linear algorithms. This article proposes a method to automatically construct such basis functions with slow feature analysis (SFA). Non-linear optimization of this unsupervised learning method generates an orthogonal basis on the unknown latent space for a given time series. In contrast to methods like PCA, SFA is thus well suited for techniques that make direct use of the latent space. Real-world time series can be complex, and current SFA algorithms are either not powerful enough or tend to over-fit. We make use of the kernel trick in combination with sparsification to develop a kernelized SFA algorithm which provides a powerful function class for large data sets. Sparsity is achieved by a novel matching pursuit approach that can be applied to other tasks as well. For small data sets, however, the kernel SFA approach leads to over-fitting and numerical instabilities. To enforce a stable solution, we introduce regularization to the SFA objective. We hypothesize that our algorithm generates a feature space that resembles a Fourier basis in the unknown space of latent variables underlying a given real-world time series. We evaluate this hypothesis at the example of a vowel classification task in comparison to sparse kernel PCA. Our results show excellent classification accuracy and demonstrate the superiority of kernel SFA over kernel PCA in encoding latent variables.     

Performance limits of electron holography

Transmission electron microscopy is wave optics. The object exit wave contains the full object information. However, in the usual intensity images, recorded either in real space or in Fourier space, the phases are missing. In many applications at medium and at high resolution, electron holography has shown its unique ability of solving the “missing phase problem” and utilizing the recovered phase for complete interpretation of the object structure. The question is “What are the performance limits?” with respect to field of view, lateral resolution and signal resolution. In this article, the performance limits are derived and discussed.     

Evaluation of non-linear strain paths using Generalized Forming Limit Concept and a modification of the Time Dependent Evaluation Method

The prediction of formability is one of the most important tasks in sheet metal forming process simulation. The common criterion for ductile fracture in industrial applications is the Forming Limit Diagram (FLD). This is only applicable for linear strain paths. However, in most industrial simulation cases non-linear strain paths occur. To resolve this problem, a phenomenological approach is introduced, the so-called Generalized Forming Limit Concept (GFLC). The GFLC enables prediction of localized necking on arbitrary non-linear strain paths. Another possibility is the use of the Time Dependent Evaluation Method (TDEM) within the simulation as a failure criteria. During the Numisheet Benchmark 1 (2014) a two-stage forming process was performed with three typical sheet materials (AA5182, DP600 and TRIP 780) and three different blank shapes. The task was to determinate the point in time and space of local instability. Therefore the strain path for the point of maximum local thinning is evaluated. To predict the start of local necking the Generalized Forming Limit Concept (GFLC), the Time Dependent Evaluation Method (TDEM) and the modified TDEM were applied. The results of the simulation are compared with the results of the Benchmark experiment.     

Using enterprise architecture analysis and interview data to estimate service response time

Insights into service response time is important for service-oriented architectures and service management. However, directly measuring the service response time is not always feasible or can be very costly. This paper extends an analytical modeling method which uses enterprise architecture modeling to support the analysis. The extensions consist of (i) a formalization using the Hybrid Probabilistic Relational Model formalism, (ii) an implementation in an analysis tool for enterprise architecture and (iii) a data collection approach using expert assessments collected via interviews and questionnaires. The accuracy and cost effectiveness of the method was tested empirically by comparing it with direct performance measurements of five services of a geographical information system at a Swedish utility company. The tests indicate that the proposed method can be a viable option for rapid service response time estimates when a moderate accuracy within 15% is sufficient.     

A Multiphase Pore Scale Network Model of Gas Exchange in Apple Fruit

A multiphase pore scale network model was developed to describe mass transfer in apple fruit. The 3D microscale geometry of the tissue was reconstructed from synchrotron radiation tomography images. Individual cells and pores were identified using a watershed segmentation procedure on a Euclidean distance map of the tissue microstructure. Further morphological characteristics of each individual pore, including its volume, connections to the neighbors and the connected area between the pore and its neighbors, were determined. The tissue was represented by a network of nodes (simplified individual pores and cells) that were interconnected by tubes. The transport of the respiratory gases O₂ and CO₂ between two nodes was modelled using diffusion laws and irreversible thermodynamics, while respiration was taken into account in the individual cellular nodes. A numerical procedure was applied to simulate the gas transport within the discrete network and to compute the local diffusivities of the links in the network. The predicted overall gas diffusivities compared well to experimental data and results computed from a microscale continuum model, thereby validating the pore scale network model. This approach is a computationally attractive alternative to a continuum multiphase approach for modelling gas transport in fruit.     

Connecting geodesics on smooth surfaces

In this paper, we present a novel method for computing multiple geodesic connections between two arbitrary points on a smooth surface. Our method is based on a homotopy approach that is able to capture the ambiguity of geodesic connections in the presence of positive Gaussian curvature that generates focal curves. Contrary to previous approaches, we exploit focal curves to gain theoretical insights on the number of connecting geodesics and a practical algorithm for collecting these. We consider our method as a contribution to the contemporary debate regarding the calculation of distances in general situations, applying continuous concepts of classical differential geometry which are not immediately transferable in purely discrete settings.