University of Twente Publications
University of Twente Repository provides publications of UT scientific staff, in many cases full text and publicly available.
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Microfluidic organ-on-chip technology for blood-brain barrier research - Helm, Marinke W. van der; Meer, Andries D. van der; Eijkel, Jan C.T.; Berg, Albert van den; Segerink, Loes I.
Organs-on-chips are a new class of microengineered laboratory models that combine several of the advantages of current in vivo and in vitro models. In this review, we summarize the advances that have been made in the development of organ-on-chip models of the blood-brain barrier (BBBs-on-chips) and the challenges that are still ahead. The BBB is formed by specialized e3ndothelial cells and separates blood from brain tissue. It protects the brain from harmful compounds from the blood and provides homeostasis for optimal neuronal function. Studying BBB function and dysfunction is important for drug development and biomedical research. Microfluidic BBBs-on-chips enable real-time...
Towards low power N-Path filters for flexible RF-Channel selection - Klumperink, Eric A.M.; Soer, Michiel C.M.; Struiksma, Remko E.; Vliet, Frank E. van; Nauta, Bram
N-path filters can offer high-linearity high-Q channel selection filtering at a flexibly programmable RF center frequency, which is highly wanted for Software Defined Radio. Relying on capacitors and MOSFET switches, driven by digital non-overlapping clocks, N-path filters fit well to CMOS and benefit from Moore’s law. The basis of this filtering is the linear periodically time variant (LPTV) behaviour of a switch-R-C series circuit, which realizes frequency translated filtering, where a baseband filter characteristic is shifted around the switching frequency. This paper reviews the basic concept of N-path filters and recent developments, with special attention to possibilities to reduce power...
RF Self-Interference reduction techniques for compact full duplex radios - Deballie, B.; Broek, D.J. van den; Lavin, C.; Liempd, B.; Klumperink, E.A.M.; Palacios, C.; Craninckx, J.; Nauta, B.
This paper describes three RF self-interference reduction techniques for full-duplex wireless links, which specifically target integration in compact radios. Concretely, a self-interference cancelling front-end, a dual-polarized antenna, and an electrical balance duplexer are proposed. Each technique offers specific benefits in terms of implementation density, selfinterference rejection, bandwidth and flexibility. Depending on their characteristics, they can be adopted in different next generation full-duplex applications and standards. All concepts are prototyped, and achieve at least 45dB of self-interference reduction over more than 10MHz bandwidth. Index Terms—Full-duplex wireless, self-interference, polarized antenna, electrical balance duplexer, analog cancellation.
An Ultra-Low-Power receiver using transmitted-reference and shifted limiters for in-band interference resilience - Ye, Dawei; Zee, Ronan van der; Nauta, Bram
The coexistence of more and more wireless standards in the ISM bands increases the design difficulty of interference-robust receivers (RX), especially for Wireless Sensor Nodes because of their Ultra-Low-Power (ULP) budget. Superheterodyne receivers [1-3] are difficult to design for low power due to the challenges of generating a clean oscillator signal with low power. The phase noise of the LO leads to reciprocal mixing, and non-linearities and limited low-Q RF filtering make them vulnerable to in-band interferers, even when external passive components are used . To circumvent accurate frequency generation, uncertain IF has been proposed , together with envelope detection....
Relationship between the Ca/P ratio of hydroxyapatite thin films and the spatial energy distribution of the ablation laser in pulsed laser deposition - Nishikawa, H.; Hasegawa, T; Miyake, A.; Tashiro, Y.; Hashimoto, Y.; Blank, D.H.A.; Rijnders, A.J.H.M.
Variation of the Ca/P ratio in hydroxyapatite (Ca10(PO4)6(OH)2) thin films was studied in relation to the spot size of the ablation laser for two different spatial energy distributions in pulsed laser deposition. One energy distribution is the defocus method with a raw distribution and the other is the projection method without the weak portion at the edges of the ablation laser spot. A Ca/P ratio closer to that of stoichiometry was obtained with the larger spot sizes for both methods, and with the projection method compared to the defocus method. It is considered that a more uniform spatial energy distribution...
Characterization of the surface charge distribution on kaolinite particles using high resolution atomic force microscopy - Kumar, N.; Zhao, C.; Klaassen, A.H.; Ende, H.T.M. van den; Mugele, F.; Siretanu, Igor
Most solid surfaces, in particular clay minerals and rock surfaces, acquire a surface charge upon exposure to an aqueous environment due to adsorption and/or desorption of ionic species. Macroscopic techniques such as titration and electrokinetic measurements are commonly used to determine the surface charge and ζζ-potential of these surfaces. However, because of the macroscopic averaging character these techniques cannot do justice to the role of local heterogeneities on the surfaces. In this work, we use dynamic atomic force microscopy (AFM) to determine the distribution of surface charge on the two (gibbsite-like and silica-like) basal planes of kaolinite nanoparticles immersed in...
Losing the roadmap: Renewable energy paralysis in Spain and its implications for the EU low carbon economy - Martínez Alonso, Patricia; Hewitt, Richard; Diaz Pacheco, Jaime; Bermejo, Lara Roman; Hernández Jiménez, Verónica; Guillen, Jara Vicente.; Bressers, Hans; Boer, Cheryl de
After many years at the forefront of renewable energy (RE) implementation both in Europe and worldwide, Spain experienced a sudden transformation in 2012 to its RE development model in which national government backing and financial incentives for renewables were removed, throwing the RE sector into a paralysis which continues to the present day. This is in marked contrast to the case of the other major European RE leader, Germany, where it has been argued that RE implementation has produced a “regime shift” that has transformed the energy generation model to a new resilient pathway. In this paper, key differences between...
Reversible Phase Transfer of (CdSe/ZnS) Quantum Dots between Organic and Aqueous Solutions - Dorokhin, Denis; Tomczak, Nikodem; Han, Mingyong; Reinhoudt, David N.; Velders, Aldrik H.; Vancso, G. Julius
Ttrioctylphosphine oxide (TOPO) stabilized CdSe/ZnS quantum dots (QD) were modified with 6-ferrocenyl-1-hexanethiol (FcHT) or 11-ferrocenyl-1-undecanethiol (FcUT) via ligand exchange. The presence of ferrocenyl thiol ligands on the surface of the QDs was proven by diffusion ordered NMR spectroscopy. Upon replacement of the initial TOPO ligand with ferrocene derivatives the emission of the QDs decreased. Phase transfer of ferrocene-modified QDs from organic solvents into water was achieved by complexation reactions with β-cyclodextrin (β-CD). The QDs coated with ferrocene thiols are soluble in nonpolar solvents and are transferred into the aqueous phase upon formation of host−guest complexes between the ferrocene units and...
Spontaneous Pattern Formation of Surface Nanodroplets from Competitive Growth - Peng, S.; Lohse, D.; Zhang, X.
Nanoscale droplets on a substrate are of great interest because of their
relevance for droplet-based technologies for light manipulation, lab-on-chip devices,
miniaturized reactors, encapsulation, and many others. In this work, we establish a basic
principle for symmetrical arrangements of surface nanodroplets during their growth out of
oversaturated solution established through solvent exchange, which takes place under
simple and controlled flow conditions. In our model system, nanodroplets nucleate at the
rim of spherical cap microstructures on a substrate, due to a pulse of oversaturation supplied
by a solvent exchange process. We find that, while growing at the rim of the microcap, the
nanodroplets self-organize into highly symmetric arrangements, with...
Spontaneous Pattern Formation of Surface Nanodroplets from Competitive Growth - Peng, Shuhua; Lohse, Detlef; Zhang, Xuehua
Nanoscale droplets on a substrate are of great interest because of their relevance for droplet-based technologies for light manipulation, lab-on-chip devices, miniaturized reactors, encapsulation, and many others. In this work, we establish a basic principle for symmetrical arrangements of surface nanodroplets during their growth out of oversaturated solution established through solvent exchange, which takes place under simple and controlled flow conditions. In our model system, nanodroplets nucleate at the rim of spherical cap microstructures on a substrate, due to a pulse of oversaturation supplied by a solvent exchange process. We find that, while growing at the rim of the microcap,...
From convection rolls to finger convection in double-diffusive turbulence - Yang, Yantao; Verzicco, Roberto; Lohse, Detlef
Double-diffusive convection (DDC), which is the buoyancy-driven flow with fluid density depending on two scalar components, is ubiquitous in many natural and engineering environments. Of great interests are scalars’ transfer rate and flow structures. Here we systematically investigate DDC flow between two horizontal plates, driven by an unstable salinity gradient and stabilized by a temperature gradient. Counterintuitively, when increasing the stabilizing temperature gradient, the salinity flux first increases, even though the velocity monotonically decreases, before it finally breaks down to the purely diffusive value. The enhanced salinity transport is traced back to a transition in the overall flow pattern, namely...
Modeling river dune development and dune transition to upper stage plane bed - Naqshband, S.; Duin, O.J.M. van; Ribberink, J.S.; Hulscher, S.J.M.H.
Large asymmetric bedforms known as dunes commonly dominate the bed of sand rivers. Due to the turbulence generation over their stoss and lee sides, dunes are of central importance in predicting hydraulic roughness and water levels. During floods in steep alluvial rivers, dunes are observed to grow rapidly as flow strength increases, undergoing an unstable transition regime, after which they are washed out in what is called upper stage plane bed. This transition of dunes to upper stage plane bed is associated with high transport of bed sediment in suspension and large decrease in bedform roughness. In the present study,...
Gravitational Effect on the Formation of Surface Nanodroplets - Yu, Haitao; Lu, Ziyang; Lohse, Detlef; Zhang, Xuehua
Nanoscale droplets at a solid–liquid interface are of high relevance for many fundamental phenomena and applied processes. The solvent exchange process is a simple approach to produce, e.g., oil nanodroplets over a large surface area on a substrate, by exchange oil-saturated ethanol by oil-saturated water, which has a lower oil solubility than ethanol. In this process, the size of the nanodroplets is closely related to the flow conditions. To achieve control of the droplet size, it is essential to fully understand the nucleation and growth of nanodroplets under different flow conditions. In this work, we investigate the gravitational effect on...
Sensitivity of Interferometric Cross-Polarization Microscopy for Nanoparticle Detection in the Near-Infrared - Miles, B.T.; Robinson, E.C.; Dijk, E.M.H.P. van; Lindsay, I.D.; Hulst, N.F. van; Gersen, H.
We address the sensitivity of Interferometric Cross-Polarization Microscopy by comparing scattering and absorption by spherical 10 nm nanoparticles through a combination of modeling and experiment. We show that orthogonality of light in the two polarization branches of Cross-Polarization Microscopy ensures that only light that has interacted with a nanoparticle is interferometrically enhanced. As a result background-free shot noise-limited detection is achieved for sub-μW optical powers at the sample. Our modeling in particular shows that in the near-infrared regime, above the plasmon resonance frequency of spherical nanoparticles, the cross-polarization approach is several orders of magnitude more sensitive than conventional extinction based...
Effects of the computational domain size on DNS of Taylor-Couette turbulence with stationary outer cylinder - Ostilla Monico, Rodolfo; Verzicco, Roberto; Lohse, Detlef
In search for the cheapest but still reliable numerical simulation, a systematic study on the effect of the computational domain (“box”) size on direct numerical simulations of Taylor-Couette flow was performed. Four boxes with varying azimuthal and axial extents were used. The radius ratio between the inner cylinder and the outer cylinder was fixed to η = ri/ro = 0.909. The outer cylinder was kept stationary, while the inner rotated at a Reynolds number Rei = 105. Profiles of mean and fluctuation velocities are compared, as well as autocorrelations and velocity spectra. The smallest box is found to accurately reproduce...
Water induced blister formation in a thin film polymer - Berkelaar, R.P.; Bampoulis, P.; Dietrich, E.; Jansen, H.P.; Zhang, Xuehua; Kooij, E.S.; Lohse, D.; Zandvliet, H.J.W.
A failure mechanism of thin film polymers immersed in water is presented: the formation of blisters. The growth of blisters is counterintuitive as the substrates were noncorroding and the polymer does not swell in water. We identify osmosis as the driving force behind the blister formation. The dynamics of the blister formation is studied experimentally as well as theoretically, and a quantitative model describing the blister growth is developed, which accurately describes the temporal evolution of the blisters.