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University of Twente Publications (47,064 recursos)
University of Twente Repository provides publications of UT scientific staff, in many cases full text and publicly available.

Group = KEUR

Mostrando recursos 1 - 20 de 6,698

1. Bed load and suspended load contributions to migrating sand dunes in equilibrium - Naqshband, S.; Ribberink, J.S.; Hurther, D.; Hulscher, S.J.M.H.
Dunes dominate the bed of sand rivers and are of central importance in predicting flow roughness and water levels. The present study has focused on the details of flow and sediment dynamics along migrating sand dunes in equilibrium. Using a recently developed acoustic system (Acoustic Concentration and Velocity Profiler), new insights are obtained in the behavior of the bed and the suspended load transport along mobile dunes. Our data have illustrated that, due to the presence of a dense sediment layer close to the bed and migrating secondary bedforms over the stoss side of the dune toward the dune crest,...

2. The role of suspended load transport in the occurrence of tidal sand waves - Borsje, B.W.; Kranenburg, W.M.; Roos, P.C.; Matthieu, J.; Hulscher, S.J.M.H.
Tidal sand waves are dynamic bed patterns which are formed by the complex interaction between hydrodynamics, sediment transport, and geomorphology. Field data from the southern North Sea reveal that sand waves are absent where suspended load transport is the dominant transport mode. In order to understand the mechanisms responsible for the absence of sand waves, we study the influence of suspended load transport on the formation of tidal sand waves with a numerical process-based geomorphological model (Delft3D). Model simulations are presented in which the vertical eddy viscosity and sediment diffusivity are both spatially and temporally variable (k-ε turbulence model). First,...

3. Using both free surface effect and sediment transport mode parameters in defining the morphology of river dunes and their evolution to upper stage plane beds, doi: 10.1061/(ASCE)HY.1943-7900.0000873 - Naqshband, S.; Ribberink, J.S.; Hulscher, S.J.M.H.
Dunes are common bed forms in sand bed rivers and are of central interest in water management purposes. Due to flow separation and associated energy dissipation, dunes form the main source of hydraulic roughness. A large number of dune dimension data sets was compiled and analyzed in this study—414 experiments from flumes and the field—showing a significantly different evolution of dune height and length in flows with low Froude numbers (negligible free surface effects) and flows with high Froude numbers (large free surface effects). For high Froude numbers (0.32–0.84 ), relative dune heights are observed to grow only in the...

4. A Shift Toward Building with Nature in the Dredging and Port Development Industries: Managerial Implications for Projects in or Near Natura 2000 Areas - Vikolainen, Vera; Bressers, Hans; Lulofs, Kris
Building with Nature is a new approach to designing water infrastructure, one that seeks to realize socioeconomic project goals in harmony with the environment. The Dutch dredging industry is promoting its application in the Netherlands, but similar concepts are emerging internationally. The Working with Nature concept has been developed under the auspices of the World Association for Waterborne Transport Infrastructure, Engineering with Nature by the US Army Corps of Engineers, and Flanders Bays 2100 by a group of Belgian dredging companies and international consultants. The research discussed in this article focuses on the feasibility of implementing the Building with Nature...

5. Formation and erosion of biogeomorphological structures: A model study on the tube-building polychaete Lanice conchilega - Borsje, B.W.; Bouma, T.J.; Rabaut, M.; Herman, P.M.J.; Hulscher, S.J.M.H.
We study how organism traits and population densities of ecosystem engineering species, in combination with environmental factors, affect the formation and erosion rates of biogeomorphological structures, and focus on the widely distributed marine tube-building polychaete Lanice conchilega, which lives in patches that form mounds up to 80 cm high in soft-bottom sediments. We modeled the tube-building worms as thin solid piles that affect drag and turbulence, and thereby the local sediment dynamics and thus mound dynamics. Hydrodynamic model predictions showed good agreement with flume experiments for flow-velocity adaptations both within and in front of a patch of tube-building worms. The...

6. The challenge of addressing Grand Challenges: a think piece on how innovation can be driven towards the "Grand Challenges" as defined under the prospective European Union Framework Programme Horizon 2020 - Kuhlmann, Stefan; Rip, Arie

7. Understanding river dune splitting through flume experiments and analysis of a dune evolution model - Warmink, J.J.; Dohmen-Janssen, C.M.; Lansink, J.; Naqshband, S.; Duin, O.J.M. van; Paarlberg, A.J.; Termes, A.P.P.; Hulscher, S.J.M.H.
Forecasts of water level during river floods require accurate predictions of the evolution of river dune dimensions, because the hydraulic roughness of the main channel is largely determined by the bed morphology. River dune dimensions are controlled by processes like merging and splitting of dunes. Particularly the process of dune splitting is still poorly understood and – as a result – not yet included in operational dune evolution models. In the current paper, the process of dune splitting is investigated by carrying out laboratory experiments and by means of a sensitivity analysis using a numerical dune evolution model. In the...

8. Situative Prävention von Cybercrime: ein chancenreicher Bekämpfungsansatz - Hartel, P.H.

9. Situative Prävention von Cybercrime: ein chancenreicher Bekämpfungsansatz - Hartel, P.H.

10. Stub resonators for online monitoring early stages of corrosion - Hoog, N.A.; Mayer, M.J.J.; Miedema, H.; Wagterveld, R.M.; Snaakes, M.; Tuinstra, J.; Olthuis, W.; Berg, A. van den
Here we demonstrate the proof-of-principle of a new type of sensor to assess effects due to corrosion of metal surfaces. The method can be applied to all situations where metals are exposed to a corrosive (fluidic) environment, including, for instance, the interior of pipes and tubes. The sensing device is based on the operating principle of a quarter wave length open-ended stub resonator. In the absence of corrosion, inner and outer conductors of the resonator are separated by a single dielectric, i.e., a fluid. Oxidation of the metal surface of inner and/or outer conductor changes the properties of the dielectric...

11. Modeling and simulations of the amplitude–frequency response of transmission line type resonators filled with lossy dielectric fluids - Mayer, M.J.J.; Miedema, H.; Olthuis, W.; Leferink, F.B.J.; Berg, A. van den
Stub resonators can be used to assess the dielectric properties of fluids. The resonance frequencies, determined from the amplitude versus frequency (AF) response of such resonators, are mainly determined by the permittivity of the fluid while damping arises from dielectric losses. Even though this methodology has been extensively reported in the literature, without almost any exception these studies refer to (near) ideal behavior regarding for example, geometry and negligibly low conductivity of the fluid studied. Online stub resonator-based sensors (i.e., flow-through) in use for industrial applications, however, quite often suffer from high dielectric losses, non-ideal material choice of the conductors...

12. De inhoud van het beleid - Bressers, J.T.A.; Klok, P.J.

13. Imaging of the ejection process of nanosecond laser-induced forward transfer of gold - Pohl, R.; Visser, C.W.; Römer, G.R.B.E.; Sun, C.; Huis in 't Veld, A.J.; Lohse, D.
Laser-induced forward transfer is a direct-write process suitable for high precision 3D printing of several materials. However, the driving forces related to the ejection mechanism of the donor ma-terial are still under debate. So far, most of the experimental studies of nanosecond LIFT, are based on post process analysis of either the donor layer and/or the deposits, which were transferred to the receiving substrate. To gain further insights into the ejection dynamics, this article presents results of a series of imaging experiments of the release process of nanosecond LIFT of a 200 nm thick gold donor layer. Images were obtained...

14. High-resolution imaging of ejection dynamics in laser-induced forward transfer - Pohl, R.; Visser, C.W.; Römer, G.R.B.E.; Sun, C.; Huis in 't Veld, A.J.; Lohse, D.
Laser-induced Forward Transfer (LIFT) is a 3D direct-write method suitable for precision printing of various materials. As the ejection mechanism of picosecond LIFT has not been visualized in detail, the governing physics are not fully understood yet. Therefore, this article presents an experimental imaging study on the ejection process of gold-based LIFT. The LIFT experiments were performed using a 6.7 picosecond Yb:YAG laser source equipped with a SHG. The beam was focused onto a 200 nm thick gold donor layer. The high magnification images were obtained using bright field illumination by a 6 ns pulsed Nd:YAG laser source and a...

15. An Open FOAM-based electro-hydrodynamical model - Roghair, I.; Ende, H.T.M. van den; Mugele, F.G.

16. Design and analysis of a high-efficiencyv high-voltage class-D power output stage - Ma, Haifeng; Zee, Ronan van der; Nauta, Bram
The analysis and design of a highly-efficient 80 V class-D power stage design in a 0.14 μm SOI-based BCD process is described. It features immunity to the on-chip supply bounce, realized by internally regulated floating supplies, variable driving strength for the gate driver, and an efficient 2-step level shifter design. Fast switching transition and low switching loss are achieved with 94% peak efficiency for the complete class-D power stage in the realized chip.

17. Coaxial stub resonator for online monitoring early stages of corrosion - Hoog, Natalia A.; Mayer, Mateo J.J.; Miedema, Henk; Olthuis, Wouter; Berg, Albert van den
Here we demonstrate the proof-of-principle of a new type of flow-through sensor to assess the corrosion rate of metal surfaces. The method can be applied to all situations where metals are exposed to a corrosive (fluidic) environment, including, for instance, the interior of pipes and tubes. Our sensing device is based on the operating principle of a quarter wave length open-ended coaxial stub resonator. The method described here can be applied for on-line monitoring corrosion.

18. Surface-enhanced Raman Spectroscopy of self-assembled monolayer conformation and spatial uniformity on silver surfaces - Wiedemair, Justyna; Le Thi Ngoc, Loan; Berg, Albert van den; Carlen, Edwin T.
We apply well-characterized silver nanowire grating (Ag-NWG) plasmonic surfaces as a Raman surface spectroscopy tool, which is based on surface-enhanced Raman scattering (SERS), to study the surface conformation characteristics of amine terminated alkanethiol self-assembled monolayers (SAMs). The surface conformation has implications for amine group availability, which is important when SAMs are used as linking layers for the binding of secondary molecules. Two different alkanethiols with different alkane chain lengths, namely 2-aminoethanethiol (cysteamine, CEA) and 11-aminoundecanethiol (AUT), are investigated. It is shown that both alkanethiols bind to Ag surfaces forming corresponding Ag-thiolates, however surface conformations, which are related to the ordering...

19. A novel side electrode configuration integrated in fused silica microsystems for synchronous optical and electrical spectroscopy - Sukas, Sertan; Schreuder, Erik; Wagenaar, Bjorn de; Swennenhuis, Joost; Berg, Albert van den; Terstappen, Leon; Le Gac, Séverine
We present a novel electrode configuration consisting of coplanar side electrode pairs integrated at the half height of the microchannels for the creation of a homogeneous electric field distribution as well as for synchronous optical and electrical measurements. For the integration of such electrodes in fused silica microsystems, a dedicated microfabrication method was utilized, whereby an intermediate bonding layer was applied to lower the temperature for fusion bonding to avoid thereby metal degradation and subsequently to preserve the electrode structures. Finally, we demonstrate the applicability of our devices with integrated electrodes for single cell electrical lysis and simultaneous fluorescence and...

20. Quantum oscillations and subband properties of the two-dimensional electron gas at the LaAlO3/SrTiO3 interface - McCollam, A.; Wenderich, S.; Kruize, M.K.; Guduru, V.K.; Molegraaf, H.J.A.; Huijben, M.; Koster, G.J.; Blank, D.H.A.; Rijnders, A.J.H.M.; Brinkman, A.; Hilgenkamp, H.; Zeitler, U.; Maan, J.C.

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