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University of Twente Publications (63.031 recursos)

University of Twente Repository provides publications of UT scientific staff, in many cases full text and publicly available.

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Mostrando recursos 1 - 20 de 27.179

  1. Differentiaalvergelijkingen begrijpen

    Zwarteveen, J.A.; Verhoef, N.C.; Hendrikse, H.P.; Pieters, J.M.
    Een domein van het nieuwe vak wiskunde D van het vwo is het domein Dynamische systemen, waarin het concept differentiaalvergelijkingen een prominente plaats inneemt. Dit concept speelt in technische universitaire studierichtingen een centrale rol, maar wordt door de studenten als moeilijk ervaren. Omdat een van de doelen van het vak wiskunde D voor het vwo een adequate voorbereiding op technische universitaire vervolgopleidingen is, is een optimale didactiek voor dit concept wenselijk. Voor zo’n didactiek is inzicht in hoe leerlingen het concept differentiaalvergelijkingen begrijpen nodig. Om dit inzicht te verkrijgen wordt een onderzoeksinstrument ontwikkeld om leerprocessen te kunnen beschrijven. In dit...

  2. Differentiaalvergelijkingen begrijpen: het effect van het opstellen van een differentiaalvergelijking op het begrijpen van het concept

    Zwarteveen-Roosebrand, Joke; Verhoef, Nellie; Hendrikse, H.P.; Pieters, J.M.
    Het vak wiskunde D op het vwo is bedoeld als voorbereiding op een technische universitaire studie. Bij dit vak wordt het concept differentiaalvergelijkingen (DVn) - in het technische hoger onderwijs een belangrijk onderwerp - behandeld. Onderzoek heeft aangetoond dat het voor begrijpen van dit concept noodzakelijk is eerst het opstellen ervan te behandelen (Chaachoua & Saglan, 2006). In de schoolboeken wordt hieraan echter weinig aandacht besteed. In dit onderzoek zijn voor een didactiek van het concept DV aanwijzingen ontworpen waarin het opstellen van een DV een belangrijk element is. De effectiviteit van deze aanwijzingen is vervolgens onderzocht. De onderzoeksvraag hieraan...

  3. Veranderingen in het eindexamenprogramma?

    Zwarteveen, Joke; Verhoef, Nellie
    De commissie Toekomst Wiskunde Onderwijs (cTWO) kwam in januari 2013 met het voorstel ‘Denken & doen, wiskunde op havo en vwo per 2015’. Wat is er veranderd? Joke Zwarteveen, docent wiskunde op een Vavo (Voortgezet algemeen volwassenenonderwijs), gaat op zoek, vakdidacticus Nellie Verhoef kijkt mee.

  4. Tako-Tsubo Cardiomyopathy Triggered by Paroxysmal Supraventricular Tachycardia in an Octogenarian

    Hartmann, M.; Houwelingen, G.K. van; Lambregts, H.P.C.M.; Verhorst, P.M.J.; Birgelen, C. von
    An 82-year-old emotionally stressed woman was admitted with palpitations and chest pain. Her blood pressure was 95/60 mmHg and heart rate 150 beats/min. The electrocardiogram (ECG) showed a regular small QRS-complex tachycardia (Fig. 1a). Serum levels of creatinine (220 μmol/l) and troponin I (0.12 μg/l) were elevated. Intravenous adenosine (6 mg bolus) terminated the tachycardia. After conversion, the ECG showed sinus rhythm with slow precordial R-wave progression (Fig. 1b). The blood pressure returned to normal, and her chest discomfort disappeared. Transthoracic echocardiography showed akinesia/dyskinesia of the mid-apical left ventricular segments, hyperkinesia of the basal segments, and moderately depressed systolic function...

  5. Acute left ventricular failure in a patient with hydroxychloroquine-induced cardiomyopathy

    Hartmann, M.; Meek, I.L.; Houwelingen, G.K. van; Lambregts, H.P.C.M.; Toes, G.J.; Wal, A.C. van der; Birgelen, C. von
    We present the case of a 75-year-old woman with a medical history of rheumatoid arthritis treated with hydroxychloroquine, who was admitted with acute left-sided heart failure due to a hydroxychloroquine-induced cardiomyopathy as supported by endomyocardial biopsy

  6. Droplets Formation and Merging in Two-Phase Flow Microfluidics

    Gu, Hao; Duits, Michel H.G.; Mugele, Frieder
    Two-phase flow microfluidics is emerging as a popular technology for a wide range of applications involving high throughput such as encapsulation, chemical synthesis and biochemical assays. Within this platform, the formation and merging of droplets inside an immiscible carrier fluid are two key procedures: (i) the emulsification step should lead to a very well controlled drop size (distribution); and (ii) the use of droplet as micro-reactors requires a reliable merging. A novel trend within this field is the use of additional active means of control besides the commonly used hydrodynamic manipulation. Electric fields are especially suitable for this, due to...

  7. A microfluidic platform for on-demand formation and merging of microdroplets using electric control

    Gu, Hao; Murade, Chandrashekhar U.; Duits, Michael H.G.; Mugele, Frieder
    We discuss a microfluidic system in which (programmable) local electric fields originating from embedded and protected electrodes are used to control the formation and merging of droplets in a microchannel. The creation of droplets-on-demand (DOD) is implemented using the principle of electrowetting. Combined with hydrodynamic control, the droplet size and formation frequency can be varied independently. Using two synchronized DOD injectors, merging-on-demand (MOD) is achieved via electrocoalescence. The efficiency of MOD is 98% based on hundreds of observations. These two functionalities can be activated independently.

  8. Supporting inquiry and modelling with interactive drawings

    Joolingen, Wouter van
    Creating models is at the heart of any scientific endeavor and therefore should have a place in science curricula. However, creating computer-based models faces resistance in early science education because of the difficulty to create the formal representations required by computational systems. In this keynote I will present SimSketch, an approach to integrate the creation of drawing into the process of inquiry and modeling. In SimSketch, drawings are used by learners to represent their ideas about phenomena they investigate. Assisted by the learner, SimSketch converts these drawings to computational models, that generate animations that behave according to the learner’s specification....

  9. SimSketch & GearSketch: Sketch-based modelling for early science education

    Joolingen, Wouter van; Bollen, Lars; Leenaars, Frank
    In this interactive demo, we will present two modelling and drawing applications - SimSketch & GearSketch, which exemplarily demonstrate our approaches to sketch-based learning and modelling in early (science) education. Since drawings and sketches denote are very basic and fundamental way of sharing ideas, of externalising and disambiguating mental models and conceptual understanding, they constitute a convenient tool in learning. Even more, creating and understanding drawings is a skill which is trained and used in very early education, and since drawings are free of syntactical constraints, they can be used in numerous domains and school subjects. Today, modern technology (tablet...

  10. Thinking with drawings - Sketch-based modelling in early science education

    Bollen, Lars; Joolingen, Wouter van
    Self-constructed external representations can positively affect the course and type of reasoning for various reasons, e.g. by proving a ground for (self-) explanations, by helping to disambiguate learners’ mental models of phenomena or by reducing working memory load. Especially in early education, drawings and sketches can be beneficial, since they make use of known and established techniques and do not impose a formal syntax or modelling language. By making use of computer-supported, pen-based input devices, applying sketches in educational contexts can be brought to a higher level, e.g. by supporting the learner with awareness information and feedback, by enabling collaborative...

  11. Vimentin levels and Serine 71 phosphorylation in the control of cell-matrix adhesions, migration speed, and shape of transformed human fibroblasts

    Terriac, E.; Coceano, G.; Mavajian, Z.; Hageman, T.A.G.; Christ, A.F.; Testa, I.; Lautenschläger, F.; Gad, A.K.B.
    Metastasizing tumor cells show increased expression of the intermediate filament (IF) protein vimentin, which has been used to diagnose invasive tumors for decades. Recent observations indicate that vimentin is not only a passive marker for carcinoma, but may also induce tumor cell invasion. To clarify how vimentin IFs control cell adhesions and migration, we analyzed the nanoscale (30–50 nm) spatial organization of vimentin IFs and cell-matrix adhesions in metastatic fibroblast cells, using three-color stimulated emission depletion (STED) microscopy. We also studied whether wild-type and phospho-deficient or -mimicking mutants of vimentin changed the size and lifetime of focal adhesions (FAs), cell...

  12. Future aesthetics of technology; context specific theories from design and philosophy of technology

    Eggink, Wouter; Snippert, Jeroen
    Since Postmodernism, presenting universal guidelines for aesthetics is highly suspect. However, aesthetics can play a significant role in the acceptance of technology and its success in society, so this paper argues for the generating of specific aesthetic guidelines, based on a general perspective. The goal of the research was to find a method of generating guidelines for the design of a technology to improve the diffusion of that technology in society. Aesthetic theories were generated by comparison of factors with historic precedents (the automobile, the television and the personal computer) The theories were then tested for the design of a...

  13. Severe regurgitation due to perforation of the mitral–aortic intervalvular fibrosa 3 years after aortic valve replacement

    Gorselen, Edwin van; Nihoyannopoulos, Petros; Verhorst, Patrick M.J.; Birgelen, Clemens von; Prendergast, Bernard; Bellamy, Michael
    We report the case of a 91-year-old man with severe symptomatic mitral regurgitation (MR), referred for assessment of percutaneous edge-to-edge repair 3 years after bioprosthetic aortic valve replacement (AVR). Detailed transthoracic, trans-oesophageal (TEE), and three-dimensional (3D) echocardiography showed a perforation in the subaortic curtain leading to severe regurgitation from the left ventricular outflow tract to the left atrium, which was undiagnosed on previous two-dimensional echocardiography. This regurgitation might be iatrogenic in origin after AVR in the absence of previous known endocarditis. This case highlights the utility and added value of 3D TEE in identifying the mechanism of MR.

  14. The Spatial Structure of Bubble Pinch-Off

    Fontelos, M.A.; Snoeijer, J.H.; Eggers, J.
    We have previously found [J. Eggers, M. A. Fontelos, D. Leppinen, and J. H. Snoeijer, Phys. Rev. Lett., 98 (2007), 094502] that the pinch-off of a gas bubble in an inviscid environment is controlled by scaling exponents which are slowly varying in time. To leading order, these results did not require the spatial profile of the interface near break-up. Here we refine our previous analysis by computing the entire shape of the neck. The neck shape is characterized by similarity functions that are also slowly varying on a logarithmic scale. We compare these results to experiments and find agreement within...

  15. Correlation of Process Parameters with Mechanical Properties of Laser Sintered PA12 Parts

    Hofland, Eva C.; Baran, Ismet; Wismeijer, Dagmar A.
    Selective laser sintering (SLS) is an additive manufacturing technique that enables the production of customized, complex products. SLS has proven itself a viable prototyping tool and production method for noncritical products. The industry has picked up on the potential of SLS, which raised the question whether it is possible to produce functional products with reproducible mechanical properties for application in critical sectors. Properties of SLS parts highly depend on the applied process settings. Hence, present work examined the influence of key process parameters (preheating temperature, laser power, scan spacing, scan speed, layer thickness, and part build orientation) on the properties...

  16. Distributed Cognition, Mimic, Representation and Decision Making: Hybrid Interaction Environments in Support of Collaborative Design Processes

    Wendrich, Robert E.
    On-going [re]search and experimentation has lead to further development of our Hybrid Design Tools to support individual or collaborative design and engineering interaction. The Loosely Fitted Design Synthesizer (LFDS) we present here is a synthetic design environment based on interaction with mixed-reality. The user-centered (human-in-the-loop) approach in conjunction with computational assistance affords intuition, creativity, stimulates interaction and triggers ambiguity in iterations. The user has real-time control through the use of a special interface and allows intuit decisions in choice-architecture. The real-time high definition video captures convey a time-line and iterative listing of these instances whereas the interface allows synthesizing the...

  17. Exploring Tacit and Tangible Interaction Design: Towards an Intuitive Design Tool

    Wendrich, Robert E.; Houten, Fred J.A.M. van

  18. RSFF: Hybrid Design Tool

    Wendrich, Robert E.
    This paper is aiming at the identification of essential voids in the support of design processes offered by commonly available methods and tools. Some remarkable results were obtained during design sessions with novices and experts by engaging them in tangible experiments that were designed to trigger and enhance their skills, tacit knowing and creativity that enable them to represent their ideas and concepts in an intuitive way. We explored the differences in designer’s behavior during use of "analogue" and digital representation tools. We will explain our laboratory experiments, test results, educational embedding and creative opportunities that emerge from hybrid design tools....

  19. Electrochemical sensing using micro- and nanostructured poly(ferrocenylsilane)s

    Folkertsma-Hendriks, Laura
    In this thesis, we look for ways to use the polymer poly(ferrocenylsilane) in sensor applications. Drying a mix of PFS-Vinylimidazole with polyacrylic acid (PAA) results in a partially phase-separated layer. We have visualised this using electron microscopy (SEM) and X-ray scattering (SAXS). When the dried layer is exposed to ammonia, a porous membrane is formed. The size of the pores in the membrane can be influenced by oxidation and reduction of the PFS. We investigated fully oxidised and fully reduced membranes using electron microscopy (SEM) and X-rays (SAXS). Furthermore, we developed an electrochemical cell which allows us to carry out...

  20. Bridging the Design Gap: Towards an Intuitive Design Tool

    Wendrich, R.E.; Tragter, H.; Kokkeler, F.G.M.; Houten, F.J.A.M. van
    A main task of industrial designers is the shaping and transformations of ideas or fuzzy notions into abstract or materialized equivalents. These sketches, models or other representations can be described as the sum of form and shape aspects, aesthetics, intuitive qualities as well as technical and sustainable functionalities. The designer must understand the elements involved in this synthesis of form giving and design. Successful designers compose these characteristics carefully and join them together to form and shape artefacts into a harmonious and balanced whole, while simultaneously manoeuvring within implicit and explicit mechanical and functional aspects. With the emergence of 3D computational...

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