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University of Twente Publications (51,738 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 6,940

1. Resonance properties of a closed rotating rectangular basin subject to space- and time-dependent wind forcing - Chen, W.; Roos, P.C.; Schuttelaars, H.M.; Hulscher, S.J.M.H.
We present an idealised process-based model to study the possibly resonant response of closed basins subject to periodic wind forcing. Two solution methods are adopted: a collocation technique (valid for arbitrary rotation) and an analytical expansion (assuming weak rotation). The spectral response, as obtained from our model, displays resonance peaks, which we explain by linking them to the spatial pattern of the wind forcing, the along-wind and cross-wind basin dimensions as well as the influence of rotation. Increasing bottom friction lowers the peaks. Finally, we illustrate how the spectral response is reflected in the time-dependent set-up due to a single...

2. Bidirectional microfluidic pumping using an array of magnetic Janus microspheres rotating around magnetic disks - Beld, W.T.E. van den; Cadena, N.L.; Bomer, J.G.; Weerd, E.L. de; Abelmann, L.; Berg, A. van den; Eijkel, J.C.T.
We demonstrate a novel, flexible and programmable method to pump liquid through microchannels in lab-on-a-chip systems without the use of an external pump. The pumping principle is based on the rotation of ferromagnetic Janus microspheres around permalloy disks, driven by an external rotating magnetic field. By placing the disks close to the edge of the microchannel, a pumping rate of at least 0.3 nL/min was measured using tracking microspheres. Geometric programming of the pumping direction is possible by positioning the magnetic disk close to the side wall. A second degree of freedom in pumping direction is offered by the rotation...

3. Scalar alignment and sustainable water governance: The case of irrigated agriculture in Turkey - Özerol, Gül; Bressers, Hans
Irrigated agriculture plays a significant role in global food security and poverty reduction. At the same time its negative impacts on water and land resources threaten environmental sustainability. With the objective of improving the understanding on the complexity of governing water resources for irrigated agriculture, this paper introduces the concept of scalar alignment, which is used to analyse governance implications of spatial and temporal scales. Using empirical data from irrigated agriculture in Turkey, implications of spatial and temporal alignment on environmental sustainability are examined. The findings indicate that both spatial and temporal alignment influence the design, implementation, monitoring and evaluation...

4. Technology assessment - Rip, Arie
Technology assessment (TA) refers to the early identification and assessment of eventual impacts of technological change and applications, as a service to policy making and decision making more generally. TA can be done by (or for) business firms, or as a medical, social, or environmental impact assessment. Its main use is in the public domain, and includes parliamentary TA. Recent developments include public participation and involvement in innovation processes (Constructive TA). Since the 1980s and 1990s, public service TA has professionalized and articulated specific methodologies for that domain. But TA is also part of broader developments such as the emergence...

5. Quantifying Cell Adhesion through Impingement of a Controlled Microjet - Visser, Claas Willem; Gielen, Marise V.; Hao, Zhenxia; Gac, Severine Le; Lohse, Detlef; Sun, Chao
The impingement of a submerged, liquid jet onto a cell-covered surface allows assessing cell attachment on surfaces in a straightforward and quantitative manner and in real time, yielding valuable information on cell adhesion. However, this approach is insufficiently characterized for reliable and routine use. In this work, we both model and measure the shear stress exerted by the jet on the impingement surface in the micrometer-domain, and subsequently correlate this to jet-induced cell detachment. The measured and numerically calculated shear stress data are in good agreement with each other, and with previously published values. Real-time monitoring of the cell detachment...

6. Mixed mode of dissolving immersed nanodroplets at a solid–water interface - Zhang, X.; Wang, J.; Bao, L.; Dietrich, E.; Veen, R.C.A. van der; Peng, S.; Friend, J.; Zandvliet, H.J.W.; Yeo, L.; Lohse, D.
The dissolution dynamics of microscopic oil droplets (less than 1 μm in height, i.e. nanodroplets) on a hydrophobilized silicon surface in water was experimentally studied. The lateral diameter was monitored using confocal microscopy, whereas the contact angle was measured by (disruptive) droplet polymerisation of the droplet. In general, we observed the droplets to dissolve in a mixed mode, i.e., neither in the constant contact angle mode nor in the constant contact radius mode. This means that both the lateral diameter and the contact angle of the nanodroplets decrease during the dissolution process. On average, the dissolution rate is faster for...

7. Pinning and gas oversaturation imply stable single surface nanobubbles - Lohse, Detlef; Zhang, Xuehua
Surface nanobubbles are experimentally known to survive for days at hydrophobic surfaces immersed in gas-oversaturated water. This is different from bulk nanobubbles, which are pressed out by the Laplace pressure against any gas oversaturation and dissolve in submilliseconds, as derived by Epstein and Plesset [J. Chem. Phys. 18, 1505 (1950)]. Pinning of the contact line has been speculated to be the reason for the stability of the surface nanobubbles. Building on an exact result by Popov [Phys. Rev. E 71, 036313 (2005)] on coffee stain evaporation, here we confirm this speculation by an exact calculation for single surface nanobubbles. It...

8. Salinity transfer in bounded double diffusive convection - Yang, Yantao; Poel, Erwin van der; Ostilla Monico, Rodolfo; Sun, Chao; Verzicco, Roberto; Grossmann, Siegfried; Lohse, Detlef
The double diffusive convection between two parallel plates is numerically studied for a series of parameters. The flow is driven by the salinity difference and stabilised by the thermal field. Our simulations are directly compared with experiments by Hage & Tilgner (Phys. Fluids, vol. 22, 2010, 076603) for several sets of parameters and reasonable agreement is found. This, in particular, holds for the salinity flux and its dependence on the salinity Rayleigh number. Salt fingers are present in all simulations and extend through the entire height. The thermal Rayleigh number seems to have a minor influence on the salinity flux...

9. Vertical natural convection: application of the unifying theory of thermal convection - Ng, C.S.; Ooi, A.; Lohse, D.; Chung, D.
Results from direct numerical simulations of vertical natural convection at Rayleigh numbers 1.0×10 5 –1.0×10 9 and Prandtl number 0.709 support a generalised applicability of the Grossmann–Lohse (GL) theory, which was originally developed for horizontal natural (Rayleigh–Bénard) convection. In accordance with the GL theory, it is shown that the boundary-layer thicknesses of the velocity and temperature fields in vertical natural convection obey laminar-like Prandtl–Blasius–Pohlhausen scaling. Specifically, the normalised mean boundary-layer thicknesses scale with the −1/2 -power of a wind-based Reynolds number, where the ‘wind’ of the GL theory is interpreted as the maximum mean velocity. Away from the walls, the...

10. An improved modeling and analysis technique for peak current-mode control-based boost converters - Amir, Saifullah; Zee, Ronan van der; Nauta, Bram
A modeling approach is presented that calculates an accurate open-loop transfer characteristic for a boost converter that employ peak current-mode control (PCMC). Many techniques exist for modeling a PCMC-based boost converter; however, all these techniques focus on purely resistive loads and are not always accurate for a purely capacitive load. In this paper, a new modeling technique is presented, which is simple and gives accurate results for both capacitive and resistive loads. Furthermore, the useful expressions for dc gain and pole locations of a boost converter operating in continuous-conduction mode with PCMC are derived and compare well to simulations and...

11. Helmholtz solver with transparent influx boundary conditions and nonuniform exterior - Stoffer, R.; Sopaheluwakan, A.; Hammer, M.; Groesen, E. van

12. Drop Shaping by Laser-Pulse Impact - Klein, A.L.; Bouwhuis, W.; Visser, C.W.; Lhuissier, H.E.; Sun, C.; Snoeijer, J.H.; Villermaux, E.; Lohse, D.; Gelderblom, H.
We show how the deposition of laser energy induces propulsion and strong deformation of an absorbing liquid body. Combining high speed with stroboscopic imaging, we observe that a millimeter-sized dyed water drop hit by a millijoule nanosecond laser pulse propels forward at several meters per second and deforms until it eventually fragments. The drop motion results from the recoil momentum imparted at the drop surface by water vaporization. We measure the propulsion speed and the time-deformation law of the drop, complemented by boundary-integral simulations. The drop propulsion and shaping are explained in terms of the laser-pulse energy, the drop size,...

13. A self-interference cancelling receiver for in-band full-duplex wireless with low distortion under cancellation of strong TX leakage - Broek, J.D.A. van den; Klumperink, E.A.M.; Nauta, B.
In-band full-duplex (FD) wireless communication, i.e. simultaneous transmission and reception at the same frequency, in the same channel, promises up to 2x spectral efficiency, along with advantages in higher network layers [1]. the main challenge is dealing with strong in-band leakage from the transmitter to the receiver (i.e. self-interference (SI)), as TX powers are typically >100dB stronger than the weakest signal to be received, necessitating TX-RX isolation and SI cancellation. Performing this SI-cancellation solely in the digital domain, if at all possible, would require extremely clean (low-EVM) transmission and a huge dynamic range in the RX and ADC, which is...

14. A forward-body-bias tuned 450MHz Gm-C 3rd-order low-pass filter in 28nm UTBB FD-SOI with >1dBVp IIP3 over a 0.7-to-1V supply - Lechevallier, Joeri; Struiksma, Remko; Sherry, Hani; Cathelin, Andreia; Klumperink, Eric; Nauta, Bram
Due to the absence of internal nodes, inverter-based Gm-C filters [1,2] allow achieving bandwidths beyond what is possible with opamp-RC techniques. The class-AB behavior of the inverter, together with the high transconductance for a given quiescent current, results in a high dynamic range for a given power consumption when optimally biased [3]. The major disadvantage of traditional inverter-based Gm-C filters is that they are tuned with the supply voltage, VDD, and hence require a finely controllable supply. Voltage regulators used to accomplish this require a voltage headroom (including margin for tuning) and degrade total power efficiency by tens of percent....

15. Compact cascadable gm-C all-pass true time delay cell with reduced delay variation over frequency - Garakoui, Seyed Kasra; Klumperink, Eric A.M.; Nauta, Bram; Vliet, Frank E. van
At low-GHz frequencies, analog time-delay cells realized by LC delay lines or transmission lines are unpractical in CMOS, due to their large size. As an alternative, delays can be approximated by all-pass filters exploiting transconductors and capacitors (g m -C filters). This paper presents an easily cascadable compact g m -C all-pass filter cell for 1-2.5 GHz. Compared to previous g m -RC and g m -C filter cells, it achieves at least 5x larger frequency range for the same relative delay variation, while keeping gain variation within 1 dB. This paper derives design equations for the transfer function and...

16. In situ ellipsometry studies on swelling of thin polymer films: A review - Ogieglo, W.; Wormeester, H.; Eichhorn, K.-J.; Wessling, M.; Benes, N.E.
The properties of a thin polymer film can be significantly affected by the presence of a penetrant. This can have potential implications for many technological applications, suchas protective and functional coatings, sensors, microelectronics, surface modification andmembrane separations. In situ ellipsometry is a powerful technique for the characteriza-tion of a film in contact with a penetrant. The main advantages of ellipsometry includethe very high precision and accuracy of this technique, combined with the fact that it isnon-intrusive. Recent advances in the speed and automation of the technique have furtherexpanded its application.This article provides an overview of the research that has been...

17. An interleaved full nyquist high-speed DAC technique - Olieman, Erik; Annema, Anne-Johan; Nauta, Bram
A 9 bit 11 GS/s DAC is presented that achieves an SFDR of more than 50 dB across Nyquist and IM3 below 50 dBc across Nyquist. The DAC uses a two-times interleaved architecture to suppress spurs that typically limit DAC performance. Despite requiring two current-steering DACs for the interleaved architecture, the relative low demands on performance of these sub-DACs imply that they can be implemented in an area and power efficient way. Together with a quad-switching architecture to decrease demands on the power supply and bias generation and employing the multiplexer switches in triode, the total core area is only...

18. Anticipating the dynamics of converging technologies - Doorn, Maurits; Rip, Arie

19. Introduction - Rip, Arie; Doorn, Maurits

20. Microneedles coupled to a microanalysis chip for lithium measurement in blood - Berg, Albert van den; Vrouwe, Elwin

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