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University of Twente Publications (57.737 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 7.195

  1. A study on the quantities and potential use of produced water in southern Iraq

    Waisi, B.I.H.; Karim, U.F.A.; Augustijn, D.C.M.; Al-Furaiji, M.H.O.; Hulscher, S.J.M.H.
    This paper presents the results of an analysis of volumes and chemical composition of produced water (PW) accompanying oil production from five of the largest oilfields in the world situated in Basrah, Iraq. PW is potentially a valuable water resource particularly there where the ramp up of oil production puts further strains on water and the environment in an area already having severe water shortages. PW should therefore be seen as part of the country's strategic water reserves rather than as effluent. This study gives first estimates of anticipated PW volumes correlated to peak oil production and water consumption needs...

  2. Evaluation of water demand and supply in the south of Iraq

    Al-Furaiji, M.H.O.; Karim, U.F.A.; Augustijn, D.C.M.; Waisi, B.I.H.; Hulscher, S.J.M.H.
    This paper presents results from the first study that focuses on water resources availability and demand for different purposes in the four oil-rich provinces of southern Iraq. The region accounts for 23% of the surface area and 18% of the country's population, but holds 88% of its oil. A water shortage of 430 Mm3/year for 2010 is estimated for this region where irrigation accounts for 81% of the total water demand. Dhi Qar is the largest agricultural producer and water consumer while Al Basrah and Al Muthanna have the largest water shortages among the four provinces. The interrelationship of energy–water...

  3. Methods for analysing morphodynamics of tidal inlets

    Willemsen, P.W.J.M.; Hulscher, S.J.M.H.; Vermaas, T.

  4. 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...

  5. 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...

  6. 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.

  7. 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 [2]. To circumvent accurate frequency generation, uncertain IF has been proposed [4], together with envelope detection....

  8. 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...

  9. 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...

  10. 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...

  11. Convective Heat Transfer Enhancement Using Carbon Ninofibers (CNF's): Influence of Atmorphous CarbonLayer on Heat Transfer Performance

    Lefferts, L.; Meer, T.H. van der; Taha, T.J.

  12. 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...

  13. Profile: Albert van den Berg

    Berg, Albert van den

  14. 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, the nanodroplets self-organize into highly symmetric arrangements, with...

  15. 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...

  16. 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,...

  17. Charge Control And Wettability Alteration At Solid-liquid Interfaces

    Mugele, F.; Bera, B.; Cavalli, A.; Siretanu, Igor; Maestro, Armando; Duits, M.H.G.; Cohen Stuart, M.A.; Ende, H.T.M. van den; Stocker, I.; Collins, I.

  18. 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...

  19. 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...

  20. Researching the stability of CaO from different precursors under varying absorption times

    Plugge, M.; Giammaria, G.; Lefferts, L.

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