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Vrije Universiteit Amsterdam
Country: Netherlands
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608 Projects, page 1 of 122
  • Funder: EC Project Code: 328695
    Partners: VU
  • Open Access mandate for Publications
    Funder: EC Project Code: 695677
    Overall Budget: 2,497,660 EURFunder Contribution: 2,497,660 EUR
    Partners: VU

    A key component of the Standard Model is Quantum Electrodynamics (QED). QED explains e.g. the anomalous magnetic moment of the electron and small energy shifts in the energy structure of atoms and molecules due to vacuum fluctuations. After decades of precision measurements, especially laser spectroscopy in atomic hydrogen, QED is considered the most successful and best-tested theory in physics. However, in 2010 precision spectroscopy in muonic-hydrogen (where the electron is replaced with a muon) has lead to discrepancies in energy level structure that cannot be accounted for. If QED is considered correct, then one way of interpreting the results is that the size of the proton is different in normal (electronic) hydrogen by as much as 4% (a 7 sigma effect) compared to muonic hydrogen. Despite great theoretical and experimental efforts, this 'proton size puzzle' is still unsolved. I propose to perform precision spectroscopy in the extreme ultraviolet near 30 nm in the helium+ ion, to establish an exciting new platform for QED tests and thereby shed light on the proton-size puzzle. The advantages of helium ions over hydrogen atoms are that they can be trapped (observed longer), QED effects are more than an order of magnitude larger, and the nuclear size of the alpha particle is better known than the proton. Moreover, the CREMA collaboration has recently measured the 2S-2P transition in muonic He+ (both 3He and 4He isotopes) at the Paul Scherrer Institute. Evaluation of the measurements is ongoing, but could lead to an 8 fold (or more) improved alpha-particle radius, so that it is no longer limiting QED theory in normal He+. I will use several ground-breaking methods such as Ramsey-comb spectroscopy in the extreme ultraviolet to measure the 1S-2S transition in trapped normal electronic He+, with (sub) kHz spectroscopic accuracy. This will provide a unique and timely opportunity for a direct comparison of QED in electronic and muonic systems at an unprecedented level.

  • Open Access mandate for Publications and Research data
    Funder: EC Project Code: 101053880
    Overall Budget: 2,493,580 EURFunder Contribution: 2,493,580 EUR
    Partners: VU

    Tipping points or phase transitions separate stable states in psycho-social systems. Examples are quitting smoking, radicalization, and dropping-out of school. Two knowledge gaps prevent our ability to predict and control these tipping points. First, we miss explanatory mathematical models of such non-linear processes. Second, we ignore the multilevel character of psycho-social transitions. I contend that important changes in many psycho-social systems are cascading transitions, where individual transitions trigger or are triggered by social transitions. The cascade of radicalization of individuals in the context of political polarization in societies is an example of such a multilevel process. Being able to predict and control cascading transitions in psycho-social systems would be a major scientific breakthrough. As an expert of complex systems research in the behavioural and social sciences, with an extensive track record in studying single level psychological transition processes (e.g., in perception, sleep, disorders, cognition, and attitudes), my key objective is to develop a novel and broadly applicable methodology to study multilevel cascading transitions in psycho-social systems. This methodology comprises theory construction in the form of mathematical modelling and innovative empirical analyses. I will do so by studying three important examples: a) opinion change from individuals to populations and back, b) learning, where progression and drop-out are embedded in collective processes, c) addiction, where transitions to addiction or abstinence within individuals are part of cascading epidemiological changes of substance use in populations. Beyond its immediate utility in these three cases, I envisage this novel, highly interdisciplinary project to stimulate future scientific research on cascading transitions in other disciplines, such as climate research, and to have significant impact on practices in conflict management, healthcare, and education.

  • Open Access mandate for Publications and Research data
    Funder: EC Project Code: 788363
    Overall Budget: 2,499,580 EURFunder Contribution: 2,499,580 EUR
    Partners: VU

    Sensory cilia are organelles extending like antennas from many eukaryotic cells, with crucial functions in sensing and signalling. Cilia consist of an axoneme built of microtubules, enveloped by a specialized membrane. Ciliary development and maintenance depend critically on a specific, microtubule-based intracellular transport mechanism, intraflagellar transport (IFT). In my laboratory, we study the chemosensory cilia of C. elegans, which sense water-soluble molecules in the animal’s environment for chemotaxis. Over the past years, we have developed a unique set of quantitative, single-molecule fluorescence microscopy tools that allow us to visualize and quantify IFT dynamics with unprecedented detail in living animals. So far, our focus has been on the cooperation of the motor proteins driving IFT. The overall objective of my current proposal is to zoom out and shed light on the connection between ciliary structure, chemosensory function and IFT, from a systems perspective. Recent work has indicated that axoneme length is controlled by IFT. Preliminary results from my laboratory show that axoneme length changes dynamically in response to perturbations of IFT or cilia. Furthermore, we have shown that IFT is substantially affected upon exposure of animals to known repellent solutions. The four major aims in my proposal are to: • determine how directional changes in IFT are regulated and are affected by external disturbances, • understand the dynamics of the axonemal microtubules and how IFT affects these dynamics and vice versa, • study how sensory ciliary function affects IFT and ciliary structure, • further develop our (single-molecule) fluorescence microscopy toolbox by improving instrumentation and using better fluorescent probes and sensors. These experiments will place my lab in a unique position to push forward our understanding of the relationship between structure, function and dynamics of transport of this fascinating and fundamental organelle.

  • Open Access mandate for Publications and Research data
    Funder: EC Project Code: 883724
    Overall Budget: 175,572 EURFunder Contribution: 175,572 EUR
    Partners: VU

    Mathematics is a human activity, and as for all human activities ethical considerations arise. However, so far the ethics of mathematics has remained an under-explored topic both among philosophers and mathematicians. Because mathematics is a collective epistemic endeavour injustices in its social structure, such as biased refereeing practices, impact its epistemic output. These injustices have not yet received sustained critical reflection, even though they are both socially relevant, since they impact the careers and hence lives of mathematicians, and epistemologically relevant, because they shape publicly available mathematical knowledge. VaViM will study the virtues and vices that manifest in such injustices and develop an interventionist philosophy which supports concrete recommendations, such as policy advice. VaViM expands the theoretical frameworks provided by the virtue-theoretic literature to a study of cases of injustices in mathematical practices. This empirically informed philosophy will provide detailed investigations of how virtues (e.g. charity) and vices (e.g. egotism) manifest in mathematical knowledge-making. This will reveal points of connection between the ethics and epistemology of mathematical practices and open up a discursive field for philosophers and mathematicians to engage with the ethics of mathematics. As a European centre of excellence in socially relevant philosophy the VU Amsterdam is the perfect host for VaViM. The shared philosophical interest in the sciences ensures the two-way transfer of knowledge between VaViM and its host and provides ample opportunity for collaboration. The VU’s expertise with public philosophy and its research networks provide excellent means for dissemination for VaViM’s findings on the societal challenges mathematicians are facing in Europe in a changing world. Through VaViM I will enrich the European Research Area as a pioneer of a socially and epistemologically relevant philosophy of mathematics.