The City Trip Planner: An expert system for tourists

Over the last few years, advanced digital applications have become available to tourists. Some of these offer the possibility of creating personalised routes. This paper introduces a tourist expert system, called the City Trip Planner, that allows planning routes for five cities in Belgium. It is implemented as a web application that takes into account the interests and trip constraints of the user and matches these to a database of locations in order to predict personal interests. A fast and effective planning algorithm provides an on-the-fly suggestion of a personal trip for a requested number of days, taking into account opening hours of attractions and time for a (lunch) break. The expert system is discussed in detail. Usage statistics and user feedback demonstrate that it is highly appreciated by tourists.     

A pseudo-spectral method with volume penalisation for magnetohydrodynamic turbulence in confined domains

We present a Fourier pseudo-spectral method for solving the resistive magnetohydrodynamic equations of incompressible flow in confined domains. A volume penalisation method allows to take into account boundary conditions and the geometry of the domain. A code validation is presented for the z-pinch test case. Numerical simulations of decaying MHD turbulence in two space dimensions show spontaneous spin-up of the flow in non-axisymmetric geometries, which is reflected by the generation of angular momentum. First results of decaying MHD turbulence in a cylinder illustrate the potential of the new method for three-dimensional simulations.     

Combining vegetation indices, constrained ordination and fuzzy classification for mapping semi-natural vegetation units from hyperspectral imagery

Vegetation mapping of plant communities at fine spatial scales is increasingly supported by remote sensing technology. However, combining ecological ground truth information and remote sensing datasets for mapping approaches is complicated by the complexity of ecological datasets. In this study, we present a new approach that uses high spatial resolution hyperspectral datasets to map vegetation units of a semiarid rangeland in Central Namibia. Field vegetation surveys provide the input to the workflow presented in this study. The collected data were classified by hierarchical cluster analysis into seven vegetation units that reflect different ecological states occurring in the study area. Spectral indices covering vegetation and soil characteristics were calculated from hyperspectral remote sensing imagery and used as environmental variables in a constrained ordination by applying redundancy analysis (RDA). The resulting statistical relationships between vegetation data and spectral indices were transferred into images of ordination axes, which were subsequently used in a supervised fuzzy c-means classification approach relying on a k-NN distance metric. Membership images for each vegetation unit as well as a confusion image of the classification result allowed a sound ecological interpretation of the resulting hard classification map. Classification results were validated with two independent reference datasets. For an internal and external validation dataset, overall accuracy reached 98% and 64% with kappa values of 0.98 and 0.53, respectively. Critical steps during the mapping workflow were highlighted and compared with similar mapping approaches.     

The effects of discovery learning and expository instruction on the acquisition of definitional and intuitive knowledge

Abstract Types of learning with a strong emphasis on the responsibility of the learner (such as discovery learning) are gaining popularity over traditional forms of (expository) instruction. Discovery learning distinguishes itself by the central role of learning processes such as hypothesis generation (induction), experiment design, and data interpretation. Expository instruction pays more attention to directly ‘exposing’ definitions and equations to learners. In the current study, students worked with either a simulation (discovery learning) or a hypertext learning environment (expository instruction) with the same domain content. Each of the environments contained a large number of assignments. The study followed a pre‐test, post‐test design. To measure the knowledge acquired a definitional knowledge test, an intuitive knowledge test (where both correctness and speed of answering are aspects that are measured) and a test in which relations needed to be explained were administered. It was predicted that the hypertext group would outperform the simulation group on the definitional knowledge test and it was expected that the simulation group would perform better on the intuitive knowledge test. Results showed that both the interaction with the simulation and with the hypertext resulted in substantial learning gains. It was found that the hypertext group performed better on the definitional knowledge test. On the intuitive knowledge test the hypertext scored better than the simulation group on the correctness of the items but not on the time needed to answer items. On the explanation test there was no difference between the two groups. An analysis of interaction processes as recorded in the logfiles indicates that the differences between both environments in their actual usage were less distinctive than expected. In the simulation group many students followed the assignments given and did not engage in self‐guided discovery. Since the assignments were rather directive, this resulted in ‘discovery behaviour’ that focused on generating outcomes; outcomes that were also, and more directly presented in the hypertext environment. For research and practice, this implies that simulations are to be considered only when clear benefits of discovery are expected, and only with complex domains, sufficient learning time and freedom for students in the assignments to engage in discovery.     

A Session Layer Concept for Overlay Networks

Current day mobility solutions are characterized by a number of essential restrictions that prevent them from being successful in an overlay network environment. This paper proposes 4 properties that mobility solutions must have to address these restrictions: application cooperation, higher layer mobility awareness, general applicability and protocol heterogeneity. Subsequently, a mobility solution that realizes all these properties is described. The solution introduces a session layer in the protocol stack that consists of two subsystems: the connection abstraction system and the address management system. Other mobility solutions found in the literature, session layer and others, typically only realize a subset of the four properties. Tom Mahieu holds a Bachelor's and Master's degree in computer sciences that he obtained at the Catholic University of Leuven. After obtaining his Master's degree in 1997, he was admitted into the Distrinet research group at the Department of Computer Science of the Catholic University of Leuven in Belgium as a research and teaching assistant, where he is current working on flexible component architectures for protocol stacks under the supervision of Prof. Pierre Verbaeten and Prof. Wouter Joosen. His Ph.D. dissertation deals with protocol stack support for applications that operate in dynamically changing network environments, such as mobile and wireless networks. Pierre Verbaeten is the head of the DistriNet research group. His main research interest is on system support and software engineering support for distributed systems. Under his supervision, DistriNet has grown to a group of 40 researchers (both Ph.D. students and postdocs) and 6 professors. He is responsible for teaching courses on computer architecture, computer networks and distributed systems. Wouter Joosen received a Ph.D. degree at the K.U. Leuven in 1996. His main research interests are in the areas of software architecture for distributed systems, aspect-oriented and component-based development, middleware, software security and embedded systems. Over the last 10 years, Wouter Joosen has been researching software development technologies (processes, architectures, notations and prototypes) that enable the construction and management of distributed applications that need support for a number of non-functional requirements, including security, real-time aspects, reliability and load balancing.     

Infrastructural Support for Enforcing and Managing Distributed Application-Level Policies

State-of-the-art security mechanisms are often enforced in isolation from each other, which limits the kinds of policies that can be enforced in distributed and heterogeneous settings. More specifically, it is hard to enforce application-level policies that affect, or use information from multiple distributed components. This paper proposes the concept of a Security Service Bus (SSB), which is a dedicated communication channel between the applications and the different security mechanisms. The SSB treats the security mechanisms as reusable, stand-alone security services that can be bound to the applications and it allows the enforcement of advanced policies by providing uniform access to application-level information. This leads to a security infrastructure that is more flexible and more manageable and that can enforce more expressive policies.     

An effective coherence measure to determine topical consistency in user-generated content

When searching for blogs on a specific topic, information seekers prefer blogs that place a central focus on that topic over blogs whose mention of the topic is diffuse or incidental. In order to present users with better blog feed search results, we developed a measure of topical consistency that is able to capture whether or not a blog is topically focused. The measure, called the coherence score, is inspired by the genetics literature and captures the tightness of the clustering structure of a data set relative to a background collection. In a set of experiments on synthetic data, the coherence score is shown to provide a faithful reflection of topic clustering structure. The properties that make the coherence score more appropriate than lexical cohesion, a common measure of topical structure, are discussed. Retrieval experiments show that integrating the coherence score as a prior in a language modeling-based approach to blog feed search improves retrieval effectiveness. The coherence score must, however, be used judiciously in order to avoid boosting the ranking of irrelevant but topically focused blogs. To this end, we experiment with a series of weighting schemes that adjust the contribution of the coherence score according to the relevance of a blog to the user query. An appropriate weighting scheme is able to improve retrieval performance. Finally, we show that the coherence score can be reliably estimated with a sample exceeding 20 posts in size. Consistent with this finding, experiments show that the best retrieval performance is achieved if coherence scores are used when a blog contains more than 20 posts.     

Converter-connected distributed generation units with integrated harmonic voltage damping and harmonic current compensation function

The steadily growing share of converter-connected distributed generators, combined with a large amount of nonlinear and unbalanced loads connected to the electric power system, has led to a degraded power quality. Both harmonic voltage and harmonic current distortion may cause many unfavourable effects on the power system. However, the converter-connected distributed generators can be redesigned to have a positive effect on the distortion of the grid voltage. Two different approaches can be discerned. At the one hand, distributed generation units can be controlled to synthesize a resistive load for harmonic voltage components. This approach is called harmonic voltage damping. At the other hand, if the polluting current of an adjacent nonlinear load is measured and added to the control loop, the converter-connected distributed generator is able to compensate all harmonic current components of the nonlinear load. This approach is referred to as harmonic current compensation. In this paper, a control strategy for a converter-connected distributed generator is extended with a harmonic voltage damping function and a harmonic current compensation function. Experimental tests show that the voltage distortion of the grid voltage can be significantly improved.