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University of Twente Publications (61.821 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 7.375

  1. Modelling adaptive behaviour in spatial agent-­based models: coastal cities and climate change

    Filatova, T.; Horstman, E.M.; Hulscher, S.J.M.H.; Lee, J.S.; Waard, J.

  2. Modelling adaptive behaviour in spatial agent-­based models: coastal cities and climate change

    Filatova, T.; Horstman, E.M.; Hulscher, S.J.M.H.; Lee, J.S.; Waard, J.

  3. Studying the blood-brain barrier on a microfluidic chip

    Helm, M.W. van der; Broersen, K.; Meer, A.D. van der; Eijkel, J.C.T.; Berg, A. van den; Segerink, L.I.
    A realistic model of the blood-brain barrier (BBB) is valuable to perform drug screening experiments and to improve the understanding of the barrier's physiology at normal and pathological conditions. Although the conventional in vitro systems (e.g. Transwell systems) have been used for this, they lack reproducibility and have a static environment. To overcome these disadvantages so called “organs-on-chips” have been developed, which use microfluidics and (human) cells to mimic organ function. An example of the BBB chip is shown in the work of Griep et al., where human cerebral endothelial cells (hCMEC/D3) were cultured in a microfluidic device made of polydimethyl...

  4. A review of catalytic aqueous-phase reforming of oxygenated hydrocarbons derived from biorefinery water fractions

    Coronado, I.; Stekrova, M.; Reinikainen, M.; Simell, P.; Lefferts, L.; Lehtonen, J.
    Aqueous-phase reforming (APR) of oxygenated hydrocarbons is a process for the production of hydrogen and light alkanes. The reactants of APR remain in liquid phase during the reaction avoiding an energetically demanding vaporization-step compared to processes such as steam reforming (SR). Furthermore, low reaction temperatures thermodynamically favour the formation of hydrogen with low carbon monoxide content. Therefore, APR has been recently considered as a promising route to upgrade organic compounds found in biorefinery water fractions. Aqueous oxygenated hydrocarbons are reformed at low temperatures (200–250 °C) and high pressures (15–50 bar), typically with platinum- and nickel-based catalyst. In addition, metal combinations of...

  5. Pinning Stabilizes Neighboring Surface Nanobubbles against Ostwald Ripening

    Dollet, B.; Lohse, D.
    Pinning of the contact line and gas oversaturation explain the stability of single surface nanobubbles. In this article, we theoretically show that the pinning also suppresses the Ostwald ripening process between neighboring surface nanobubbles, thus explaining why in a population of neighboring surface nanobubbles different radii of curvature of the nanobubbles can be observed.

  6. Modeling of spatial lag in bed-load transport processes and its effect on dune morphology

    Duin, O.J.M. van; Hulscher, S.J.M.H.; Ribberink, J.S.; Dohmen-Janssen, C.M.
    In the present study, two bed-load transport models are introduced in an existing idealized dune model. These allow for the modeling of the spatial lag between the sediment transport rate and bed shear stress along dune surfaces. This lag is an important factor in determining transitions between bedform regimes. Results of the original dune model (using an equilibrium transport formula) are compared with (1) a new model version that directly models spatial lag with a relaxation equation and (2) a new model version including pick-up and deposition processes. Both bed-load models use mean particle step length as an important parameter,...

  7. Probleemoplossen met een computeralgebra-systeem (Maple)

    Savelsbergh, E.; Jong, T. de; Ferguson-Hessler, M.

  8. Computer game-based mathematics education: Embedded faded worked examples facilitate knowledge acquisition

    Vrugte, Judith ter; Jong, Ton de; Vandercruysse, Sylke; Wouters, Pieter; Oostendorp, Herre van; Elen, Jan
    This study addresses the added value of faded worked examples in a computer game-based learning environment. The faded worked examples were introduced to encourage active selection and processing of domain content in the game. The content of the game was proportional reasoning and participants were 12- to 15-year-old students from prevocational education. The study compared two conditions in which students worked with the environment with faded worked examples (n = 49) or without worked examples (n = 44). The students who received the faded worked examples performed better on a posttest measuring their proportional reasoning skills, and this performance was...

  9. Hamiltonian Boussinesq formulation of wave–ship interactions

    Groesen, E. van; Andonowati,
    In this paper a new approach is described for the fully nonlinear treatment of the dynamic wave–ship interaction for potential flows. A major reduction of computational complexity is obtained by describing the fluid motion in horizontal variables only, the surface elevation and the potential at the surface. In such Boussinesq type of equations, the internal fluid motion is not calculated, but modeled in a consistent approximative way. The equations for the wave–ship interaction are based on a Lagrangian variational principle, leading to the formulation of the coupled system as a Hamiltonian system. With the ship position and orientation as canonical...

  10. Hydrophobic Ice Confined between Graphene and MoS2

    Bampoulis, P.; Teernstra, V.J.; Lohse, D.; Zandvliet, H.J.W.; Poelsema, B.
    The structure and nature of water confined between hydrophobic molybdenum disulfide (MoS2) and graphene (Gr) are investigated at room temperature by means of atomic force microscopy. We find the formation of two-dimensional (2D) crystalline ice layers. In contrast to the hexagonal ice “bilayers” of bulk ice, these 2D crystalline ice phases consist of two planar hexagonal layers. Additional water condensation leads to either lateral expansion of the ice layers or to the formation of three-dimensional water droplets on top or at the edges of the two-layer ice, indicating that water does not wet these planar ice films. The results presented...

  11. Deformation and orientation statistics of neutrally buoyant sub-Kolmogorov ellipsoidal droplets in turbulent Taylor–Couette flow

    Spandan, Vamsi; Lohse, Detlef; Verzicco, Roberto
    The influence of the underlying flow topology on the shape and size of sub-Kolmogorov droplets dispersed in a turbulent flow is of considerable interest in many industrial and scientific applications. In this work we study the deformation and orientation statistics of sub-Kolmogorov droplets dispersed into a turbulent Taylor–Couette flow. Along with direct numerical simulations (DNS) of the carrier phase and Lagrangian tracking of the dispersed droplets, we solve a phenomenological equation proposed by Maffettone and Minale (J. Non-Newtonian Fluid Mech., vol. 78, 1998, pp. 227–241) to track the shape evolution and orientation of approximately 10 5 ellipsoidal droplets. By varying...

  12. ATR-IR spectroscopic cell for in situ studies at solid-liquid interface at elevated temperatures and pressures

    Koichumanova, Kamila; Visan, Aura; Geerdink, Bert; Lammertink, Rob G.H.; Mojet, Barbara L.; Seshan, K.; Lefferts, Leon
    An in situ ATR-IR spectroscopic cell suitable for studies at solid-liquid interface is described including the design and experimental details in continuous flow mode at elevated temperatures (230 °C) and pressures (30 bar). The design parameters considered include the cell geometry, the procedure to immobilize the catalyst on a cylindrical internal reflection element (IRE), as well as shape and material of choice for the IRE, optics configuration and temperature/pressure control. The hydrodynamics and concentration profiles in the cell were assessed via numerical simulations using incompressible Navier-Stokes equation and convection-diffusion model showing significant deviation from ideal plug flow. Experimental response times...

  13. Piping erosion safety assessment of flood defences founded over sewer pipes

    Aguilar Lopez, J.P.; Warmink, J.J.; Schielen, R.M.J.; Hulscher, S.J.M.H.
    Piping erosion is one of the major causes of failure of flood defences. The occurrence of this failure mechanism is difficult to predict and it can be triggered during a flood event. The inclusion of hard structures under flood defences will change the probability of occurrence of this erosion process. The present study aimed at understanding the effect of an embedded sewer pipe under the flood defence foundation in its safety assessment for piping erosion failure. This was done by setting a probabilistic analysis framework based on emulation of finite element models of porous media flow and the fictitious permeability...

  14. Gradient capacitance for solid particle position detection in electrolyte

    Solsona, Miguel; Olthuis, Wouter; Berg, Albert van den
    The conductivity of an electrolyte is a property that depends on the mobility of charged species inside a solution. Electrolyte conductivity measurements is a technique used for the study of the electrical properties of solutions and solids inside the electrolyte. Impedance measurements enable the possibility of measuring the electrical properties of the system, however, the result is solid position dependent due to fringing effects of the electric field lines. In this study, we demonstrate the principle of a new method able to determine the position of the solid in electrolyte between two parallel electrodes. The technique consists of a gradient...

  15. Studying the blood-brain barrier on a microfluidic chip

    Helm, Marinke W. van der; Broersen, K.; Meer, Andries D. van der; Eijkel, Jan C.T.; Berg, Albert van den; Segerink, Loes I.
    A realistic model of the blood-brain barrier (BBB) is valuable to perform drug screening experiments and to improve the understanding of the barrier's physiology at normal and pathological conditions. Although the conventional in vitro systems (e.g. Transwell systems) have been used for this, they lack reproducibility and have a static environment. To overcome these disadvantages so called “organs-on-chips” have been developed, which use microfluidics and (human) cells to mimic organ function. An example of the BBB chip is shown in the work of Griep et al., where human cerebral endothelial cells (hCMEC/D3) were cultured in a microfluidic device made of polydimethyl...

  16. Spermometer: electrical characterization of single boar sperm motility

    Wagenaar, Bjorn de; Geijs, Daan J.; Boer, Hans de; Bomer, Johan G.; Olthuis, Wouter; Berg, Albert van den; Segerink, Loes I.
    Objective: To study single sperm boar motility using electrical impedance measurements in a microfluidic system. Design: Comparison of the optical data and electrical impedance data. Setting: Research laboratory at a university. Animal(s): Boar semen sample were used. Intervention(s): A microfluidic system is developed that is able to spatially confine single boar sperm cells and allows noninvasive analysis of their motility on the single cell level. Using this system, the single sperm motility was affected by changing the temperature or adding chemical stimuli (caffeine). The retrieved electrical impedance and video data were processed using Matlab. Main Outcome Measure(s): The sperm beat frequency and amplitude determined from the...

  17. Enzymatic crosslinking of polymer conjugates is superior over ionic or UV crosslinking for the on-chip production of cell-laden microgels

    Henke, Sieger; Leijten, Jeroen; Kemna, Evelien; Neubauer, Martin; Fery, Andreas; Berg, Albert van den; Karperien, Marcel
    Cell-laden micrometer-sized hydrogels (microgels) hold great promise for improving high throughput ex- vivo drug screening and engineering biomimetic tissues. Microfluidics is a powerful tool to produce microgels. However, only a limited amount of biomaterials have been reported to be compatible with on-chip microgel formation. Moreover, these biomaterials are often associated with mechanical instability, cytotoxicity, and cellular senescence. To resolve this challenge, dextran-tyramine has been explored as a novel biomaterial for on-chip microgel formation. In particular, dextran-tyramine is compared with two commonly used biomaterials, namely, polyethylene-glycol diacrylate (PEGDA) and alginate, which crosslink through enzymatic reaction, UV polymerization, and ionic interaction, respectively....

  18. Potentiometric measurement with a Kelvin probe: Contactless measurement of chloride ions in aqueous electrolyte

    Abbas, Y.; Zhu, X.; Boer, H.L. de; Tanvir, N.B.; Olthuis, W.; Berg, A. van den
    For the first time the chloride ion concentration in electrolyte is measured using a Kelvin probe. A silver-silver chloride (Ag/AgCl) electrode, which is a chloride ion selective electrode, is used as a sample plate in the electrolyte and the Kelvin probe is used as a reference plate that is vibrating above the electrolyte. The open-circuit potential (OCP) of the Ag/AgCl electrode is a function of the Cl- concentration. The contact potential difference (CPD), measured by the Kelvin probe, gives the OCP of the Ag/AgCl electrode. The measurement does not require any contact between the reference plate and the electrolyte. This...

  19. Ballistic energy conversion: physical modeling and optical characterization

    Xie, Yanbo; Bos, Diederik; Meulen, Mark-Jan van der; Versluis, Michel; Berg, Albert van den; Eijkel, Jan C.T.
    The growing demand for renewable energy stimulates the exploration of new materials and methods for clean energy, a process which is boosted by nanoscience and emerging nanotechnologies. Recently a high efficiency and high power density energy conversion mechanism was demonstrated through the use of jetted charged microdroplets, which fully relies on the net charges stored in the electrical double layer within a hundred nanometers of the water/gas interface, and then delivered at a metal target for converting kinetic energy to electrical energy. The method is fundamentally different from the traditional electrokinetic conversion and electrostatic generators, termed as ballistic energy conversion....

  20. Spatial control of direct chemical vapor deposition of graphene on silicon dioxide by directional copper dewetting

    Beld, Wesley T.E. van den; Berg, Albert van den; Eijkel, Jan C.T.
    In this paper we present a method for the spatial control of direct graphene synthesis onto silicon dioxide by controlled dewetting. The dewetting process is controlled through a combination of using a grooved substrate and conducting copper deposition at an angle. The substrate is then treated using a typical graphene chemical vapor deposition synthesis process at an elevated temperature during which directional dewetting of the copper into the grooves occurs while graphene is deposited at the mesas in between the grooves. The dewetting process and the synthesized graphene layer are characterized. The method is a non-manual, controllable and wafer-scale process,...

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