A baseband wireless spectrum hypervisor for multiplexing concurrent OFDM signals

The next generation of wireless and mobile networks will have to handle a significant increase in traffic load compared to the current ones. This situation calls for novel ways to increase the spectral efficiency. Therefore, in this paper, we propose a wireless spectrum hypervisor architecture that abstracts a radio frequency (RF) front-end into a configurable number of virtual RF front ends. The proposed architecture has the ability to enable flexible spectrum access in existing wireless and mobile networks, which is a challenging task due to the limited spectrum programmability, i.e., the capability a system has to change the spectral properties of a given signal to fit an arbitrary frequency allocation. The proposed architecture is a non-intrusive and highly optimized wireless hypervisor that multiplexes the signals of several different and concurrent multi-carrier-based radio access technologies with numerologies that are multiple integers of one another, which are also referred in our work as radio access technologies with correlated numerology. For example, the proposed architecture can multiplex the signals of several Wi-Fi access points, several LTE base stations, several WiMAX base stations, etc. As it able to multiplex the signals of radio access technologies with correlated numerology, it can, for instance, multiplex the signals of LTE, 5G-NR and NB-IoT base stations. It abstracts a radio frequency front-end into a configurable number of virtual RF front ends, making it possible for such different technologies to share the same RF front-end and consequently reduce the costs and increasing the spectral efficiency by employing densification, once several networks share the same infrastructure or by dynamically accessing free chunks of spectrum. Therefore, the main goal of the proposed approach is to improve spectral efficiency by efficiently using vacant gaps in congested spectrum bandwidths or adopting network densification through infrastructure sharing. We demonstrate mathematically how our proposed approach works and present several simulation results proving its functionality and efficiency. Additionally, we designed and implemented an open-source and free proof of concept prototype of the proposed architecture, which can be used by researchers and developers to run experiments or extend the concept to other applications. We present several experimental results used to validate the proposed prototype. We demonstrate that the prototype can easily handle up to 12 concurrent physical layers

Detection and fine-grained classification of cyberbullying events

In the current era of online interactions, both positive and negative experiences are abundant on the Web. As in real life, negative experiences can have a serious impact on youngsters. Recent studies have reported cybervictimization rates among teenagers that vary between 20% and 40%. In this paper, we focus on cyberbullying as a particular form of cybervictimization and explore its automatic detection and fine-grained classification. Data containing cyberbullying was collected from the social networking site Ask.fm. We developed and applied a new scheme for cyberbullying annotation, which describes the presence and severity of cyberbullying, a post author's role (harasser, victim or bystander) and a number of fine-grained categories related to cyberbullying, such as insults and threats. We present experimental results on the automatic detection of cyberbullying and explore the feasibility of detecting the more fine-grained cyberbullying categories in online posts. For the first task, an F-score of 55.39% is obtained. We observe that the detection of the fine-grained categories (e.g. threats) is more challenging, presumably due to data sparsity, and because they are often expressed in a subtle and implicit way

Antiquities of the rainforest: evolution of mycoheterotrophic angiosperms growing on Glomeromycota

Dit proefschrift behandelt de evolutie en biogeografie van een bijzondere groep plantensoorten die leven in associatie met schimmels. Deze planten zijn mycoheterotroof; ze hebben hun fotosynthese capaciteit verloren en verkrijgen hun koolstofverbindingen van de schimmels. Ik bestudeerde de enigmatische plantenfamilies Triuridaceae, Corsiaceae en het genus Epirixanthes (Polygalaceae). Een eerste hoofdstuk beschrijft de voorheen onduidelijke verwantschappen en de biogeografie van de Triuridaceae. De resultaten suggereren dat dit een zeer oude groep is, die in het Krijt is ontstaan in Afrika of Zuid-Amerika. In het tweede hoofdstuk concludeerde ik dat de Corsiaceae een oorsprong hebben in het oercontinent Gondwana en dat ze sterk verwant zijn aan de Campynemataceae in de orde van de lelies. Mijn studie van Epirixanthes toonde aan dat dit voorheen onderbestudeerde genus zeer gespecialiseerd is in vergelijking met haar zustergroep, het fotosynthetiserende genus Salomonia. In het laatste hoofdstuk bediscussieer ik de biogeografische geschiedenis van alle mycoheterotrofe bloemplanten. De resultaten wijzen uit dat deze planten in tropische regenwouden zijn ontstaan, waarbij de Zuidoost Aziatische vertegenwoordigers jonger zouden zijn dan de andere groepen. Doordat deze bijzondere planten veelal in bedreigde gebieden voorkomen, zijn ze hoogstwaarschijnlijk erg kwetsbaar.Alberta Mennega Stichting Schure-Beijerinck-Popping Fonds (nu KNAW Fonds Ecologie)Plant science

De Theatro Motivarum, Motivation: In Search of Essentials. Research on a Theoretical Model of the Process of Motivation and on Critical Determinants of Interference

In using a fundamentally different approach to theory formation, a new Model of Motivation is presented and tested through empirical research in various studies. Motivation is assumed to evolve around an objective and to proceed in twenty-four consecutive ‘stages’ that can be organized according to eight distinct groups or 'phases'. In covering current literature, the Model appears to provide a comprehensive conceptual framework for classification of current theories on human motivation. In empirical research, a first confirmation is found for constructs, based on the Model, that appear to capture the process of motivation. In making a distinction between the process of motivation and a so-called ‘process of interference’ aimed at addressing motivation, further confirmation is obtained for critical determinants of interference, including conditions, competencies and instruments, that appear to play an essential role in management of motivation. In an overview of implications, so-called ‘mechanisms of coping’ and ‘mechanisms of collective coping’ are introduced and observed on their potential impact on societyFdR – Publicaties niet-programma gebonde