Tools and strategies for engaging the supervisor in technology-supported work-based learning : evaluation research - Bianco, Manuela; Collis, Betty
This study reports the results of the formative evaluations of two computer-supported tools and the associated strategies for their use. Tools and strategies embedded in web-based courses can increase a supervisor’s involvement in helping employees transfer learning onto the workplace. Issues relating to characteristics of the tools and strategies as well as factors influencing their likelihood of use are identified via summaries of the two evaluation studies.
Thermal-wave balancing flow sensor with low-drift power feedback - Dijkstra, M.; Lammerink, T.S.J.; Pjetri, O.; Boer, M.J. de; Berenschot, J.W.; Wiegerink, R.J.; Elwenspoek, M.C.
A control system using a low-drift power-feedback signal was implemented applying thermal waves, giving a sensor output independent of resistance drift and thermo-electric offset voltages on interface wires. Kelvin-contact sensing and power control is used on heater resistors, thereby inhibiting the influence of heater resistance drift. The thermal waves are detected with a sensing resistor using a lock-in amplifier and are mutually cancelled by a thermal-wave balancing controller. Offset due to thermal gradient across the chip and resistor drift are eliminated by the lock-in amplifier and power controller, and therefore do not influence the sensor output signal. A microchannel thermal-wave...
Thermal flow-sensor drift reduction by thermopile voltage cancellation via power feedback control - Dijkstra, Marcel; Lammerink, Theo S.J.; Boer, Meint J. de; Berenschot, Erwin J.W.; Wiegerink, Remco J.; Elwenspoek, Miko
The research question that is addressed in this paper relates to the performance limitations of thermal flow sensors due to miniaturization. Sensor elements in current microflow sensors are mostly made by metal thin films. The problem is that thin-films reproduce poorly and that practically all material properties are subject to drift. This drift and poor reproducibility translates directly into the accuracy of thermal microflow sensors. This paper presents a thermal flow sensor consisting of freely suspended silicon-rich silicon-nitride microchannels with
an integrated Al/poly-Si++ thermopile in combination with up
and downstream Al heater resistors. The drift-free zero offset of a thermopile at uniform...
Microfabricated solid-state ion-selective electrode probe for measuring potassium in the living rodent brain: Compatibility with DC-EEG recordings to study spreading depression - Odijk, M.; Wouden, E.J. van der; Olthuis, W.; Ferrari, M.D.; Tolner, E.A.; Maagdenberg, A.M.J.M. van den; Berg, A. van den
There is considerable need in neuroscience research to reliably measure concentrations of extracellular ions in the living brain as the dynamics of ion levels increasingly is considered to play a key role in the pathophysiology of many brain disorders. Unfortunately, most probes currently used for direct measurement of extracellular ion concentrations in living brain tissue in experimental animals have considerable limitations. They are custom-made glass capillary ion-selective microelectrodes that are fragile, timeconsuming to prepare, and can practically only be used to measure at one depth and one location in the brain. We here present the design and fabrication of a...
Improved precision using internal standards in disposable point-of-care capillary electrophoresis devices - Bidulock, A.C.E.; Berg, A. van den; Eijkel, J.C.T.
This paper presents a systematic investigation of the viability of using internal standards to correct for chip-to-chip imprecision in disposable microchip capillary electrophoresis (μCE) devices. The effects of two internal standards (CsCl and LiCl) on the reproducibility of Na quantification were explored using in-house fabricated microchips. Five concentrations of NaCl were analyzed consecutively over five days, resulting in a dataset of 900 electropherograms with which to draw reliable conclusions from. We find internal standards can strongly improve the precision of disposable devices.
Embedded wave generation for dispersive surface wave models - She Liam, L.; Adytia, D.; Groesen, E. van
This paper generalizes previous research on embedded wave generation in Boussinesq-type of equations for multi-directional surface water waves; the generation takes place by adding a suitable source term to the equations. Accurate generation is important to prevent influx errors in simulated waves downstream. For numerical implementations it may be a useful alternative to boundary influx methods since it is relatively easy to implement and will account accurately for the dispersive properties of the model. The source functions are unique only when the spatial and temporal constituents satisfy the dispersion relation of the model; this ambiguity can be used to choose...
Charge Control And Wettability Alteration At Solid-liquid Interfaces - Mugele, F.; Sîretanu, I.; Kumar, N.; Bera, B.; Wang, L.; Maestro, M.A.; collins, I
Most solid surfaces acquire a finite surface charge upon exposure to aqueous environments due to desorption and/or adsorption of ionic species. The resulting electrostatic forces play a crucial role in many fields of science, including colloidal stability, self-assembly, wetting, and biophysics as well as technology. Enhanced oil recovery is an example of a large scale industrial process that hinges in many respects on these phenomena.
In this paper, we present a series of experiments illustrating fundamental aspects of low salinity water flooding in well-defined model systems. We show how pH and ion content of the water phase as well as the...
Dynamic trapping of sliding drops on wetting defects - Cavalli, A.; Musterd, M.; Mannetje, D.J.C.M. 't; Ende, H.T.M. van den; Mugele, F.
for the DFD14 Meeting of
The American Physical Society
Dynamic trapping of sliding drops on wetting defects ANDREA
CAVALLI, University of Twente, MICHIEL MUSTERD, TU Delft, DIETER ’T
MANNETJE, DIRK VAN DEN ENDE, FRIEDER MUGELE, University of Twente
—We present a numerical analysis of the dynamic interaction of a sessile sliding drop
with a wetting defect. Our three-dimensional model, developed with OpenFOAM,
allows us to describe inertial and viscous effects, as well as the internal degrees of
freedom of the droplet. We observe that the ability of a drop to deform and stretch
enhances the strength and range of the wetting defect, in comparison to a simplified
Repeated bouncing of drops on wetting and non-wetting surfaces mediated by a persisting thin air film - Ruiter, Jolet de; Lagraauw, R.; Ende, H.T.M. van den; Mugele, F.
for the DFD14 Meeting of
The American Physical Society
Repeated bouncing of drops on wetting and non-wetting sur-
faces mediated by a persisting thin air lm JOLET DE RUITER, RUDY
LAGRAAUW, DIRK VAN DEN ENDE, FRIEDER MUGELE, MESA+ Institute
for Nanotechnology, University of Twente — Liquid drops impinging onto solid surfaces
undergo a variety of impact scenarios such as splashing, sticking, and bouncing,
depending on impact conditions and substrate properties. Bouncing requires efficient
conversion of initial kinetic energy into surface energy and back into kinetic
energy. This process is believed to be limited to non-wetting, in particular superhydrophobic
surfaces, for which viscous dissipation during drop-substrate contact
is minimal. Here, we...
Hard and soft colloids at fluid interfaces: Adsorption, interactions, assembly & rheology - Deshmukh, O.S.; Ende, H.T.M. van den; Mugele, F.; Duits, M.H.G.
Soft microgel particles inherently possess qualities of both polymers as well as particles. We review the similarities and differences between soft microgel particles and stiff colloids at fluid–fluid interfaces. We compare two fundamental aspects of particle-laden interfaces namely the adsorption kinetics and the interactions between adsorbed particles. Although it is well established that the transport of both hard particles and microgels to the interface is driven by diffusion, the analysis of the adsorption kinetics needs reconsideration and a proper equation of state relating the surface pressure to the adsorbed mass should be used. We review the theoretical and experimental investigations...
The bifurcation diagram of drops in a sphere/plane geometry: influence of contact angle hysteresis - Ruiter, Riëlle de; Gorcum, M. van; Semprebon, C.; Duits, M.H.G.; Brinkmann, M.; Mugele, F.
We study liquid drops that are present in a generic geometry, namely the gap in between a sphere and a plane. For the ideal system without contact angle hysteresis, the drop position is solely dependent on the contact angle, drop volume, and sphere/ plane separation distance. Performing a geometric analysis and Surface Evolver calculations, a continuous and fully reversible transition between axisymmetric non-spherical shapes and non-axisymmetric spherical shapes is predicted. We also study these transitions experimentally, varying the contact angle using electrowetting. Then, pinning forces drastically alter the pitchfork bifurcation as the unstable branch gets stabilized, and introduce a history-dependence...