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University of Twente Publications (63.542 recursos)

University of Twente Repository provides publications of UT scientific staff, in many cases full text and publicly available.

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  1. CMOS front-end techniques for in-band full-duplex radio

    Broek, Johannes Dingeman Antonius van den
    In-band full-duplex wireless communication (FD), i.e. transmission and reception at the same time at the same frequency, is an emerging research topic, driven by the increasing demand for mobile data traffic in the crowded radio spectrum. Besides promising up to twice the spectral efficiency, additional advantages are being explored. The main issue in FD is strong self-interference (SI) from the transmitter (TX) into the local receiver (RX). In typical links, over 90dB total SI-rejection is required to fully compete with half-duplex links. This rejection is achieved by combining SI-isolation and cancellation in different domains. This work shows that impairments in the...

  2. Get ready to welcome the new normal: Paying to see the doctor and expulsion of foreign workers: Tyneside-born academic Paul Benneworth, who works in the Netherlands, on what we can expect to see as Brexit unfolds

    Benneworth, Paul

  3. Eulerian method for ice crystal icing in turbofan engines

    Norde, Ellen
    The newer generations of high-bypass-ratio engines are susceptible to the ingestion of small ice crystals which may cause engine power loss or damage. The research presented in this thesis focusses on the development of a computational method for in-engine ice crystal accretion. The work has been carried out in the framework of project High Altitude Ice Crystals (HAIC), co-funded by the European Union. The developed ice accretion method is split in the numerical simulation of three distinct parts of the process: particle trajectories towards an object, particle impact on the object's surface and evolution of the ice layer on the surface....

  4. Quantitative photoacoustic integrating sphere (QPAIS) platform for absorption coefficient and Gruneisen parameter measurements: Demonstration with human blood

    Villanueva, Y.Y.; Hondebrink, E.; Petersen, W.; Steenbergen, W.
    Quantitative photoacoustic imaging in biomedicine relies on accurate measurements of relevant material properties of target absorbers. Here, we present a method for simultaneous measurements of the absorption coefficient and Grüneisen parameter of small volume of liquid scattering and absorbing media using a coupled-integrating sphere system which we refer to as quantitative photoacoustic integrating sphere (QPAIS) platform. The derived equations do not require absolute magnitudes of optical energy and pressure values, only calibration of the setup using aqueous ink dilutions is necessary. As a demonstration, measurements with blood samples from various human donors are done at room and body temperatures using...

  5. Graphene Visualizes the Ion Distribution on Air-Cleaved mica

    Bampoulis, P.; Sotthewes, K.; Siekman, M.H.; Zandvliet, H.J.W.; Poelsema, B.
    The distribution of potassium (K+) ions on air-cleaved mica is important in many interfacial phenomena such as crystal growth, self-assembly and charge transfer on mica. However, due to experimental limitations to nondestructively probe single ions and ionic domains, their exact lateral organization is yet unknown. We show, by the use of graphene as an ultra-thin protective coating and scanning probe microscopies, that single potassium ions form ordered structures that are covered by an ice layer. The K+ ions prefer to minimize the number of nearest neighbour K+ ions by forming row-like structures as well as small domains. This trend is...

  6. Porous layered double hydroxides synthesized using oxygen generated by decomposition of hydrogen peroxide

    Gonzalez Rodriguez, P.; Ruiter, M.P. de; Wijnands, T.; Elshof, J.E. ten
    Porous magnesium-aluminium layered double hydroxides (LDH) were prepared through intercalation and decomposition of hydrogen peroxide (H2O2). This process generates oxygen gas nano-bubbles that pierce holes in the layered structure of the material by local pressure build-up. The decomposition of the peroxide can be triggered by microwave radiation or chemically by reaction with iodide (I−) ions. The carbonate LDH version [Mg0.80Al0.20(OH)2](CO3)0.1∙mH2O was synthesized by microwave-assisted urea coprecipitation and further modified by iodide or H2O2 intercalation. High resolution Scanning Electron Microscopy (HR-SEM) and Brunauer-Emmet-Teller (BET) analysis were used to assess the morphology and surface area of the new porous materials. The presence...

  7. Technical Aspects and Validation of a New Biofeedback System for Measuring Lower Limb Loading in the Dynamic Situation

    Raaben, M.; Holtslag, H.R.; Augustine, R.; Merkerk, R.O. van; Koopman, H.F.J.M.; Blokhuis, T.J.
    Background: A variety of techniques for measuring lower limb loading exists, each with their own limitations. A new ambulatory biofeedback system was developed to overcome these limitations. In this study, we described the technical aspects and validated the accuracy of this system. Methods: A bench press was used to validate the system in the static situation. Ten healthy volunteers were measured by the new biofeedback system and a dual-belt instrumented treadmill to validate the system in the dynamic situation. Results: Bench press results showed that the sensor accurately measured peak loads up to 1000 N in the static situation. In...

  8. Tuning of large piezoelectric response in nanosheet-buffered lead zirconate titanate films on glass substrates

    Chopra, A.; Bayraktar, M.; Nijland, M.; Elshof, J.E. ten; Bijkerk, F.; Rijnders, A.J.H.M.
    Renewed interest has been witnessed in utilizing the piezoelectric response of PbZr0.52Ti0.48O3 (PZT) films on glass substrates for applications such as adaptive optics. Accordingly, new methodologies are being explored to grow well-oriented PZT thin films to harvest a large piezoelectric response. However, thin film piezoelectric response is significantly reduced compared to intrinsic response due to substrate induced clamping, even when films are well-oriented. Here, a novel method is presented to grow preferentially (100)-oriented PZT films on glass substrates by utilizing crystalline nanosheets as seed layers. Furthermore, increasing the repetition frequency up to 20 Hz during pulsed laser deposition helps to tune...

  9. Photoacoustic reflection artifact reduction using photoacoustic-guided focused ultrasound: comparison between plane-wave and element-by-element synthetic backpropagation approach

    Kuniyil Ajith Singh, M.; Jaeger, M.; Frenz, M.; Steenbergen, W.
    Reflection artifacts caused by acoustic inhomogeneities constitute a major problem in epi-mode biomedical photoacoustic imaging. Photoacoustic transients from the skin and superficial optical absorbers traverse into the tissue and reflect off echogenic structures to generate reflection artifacts. These artifacts cause difficulties in the interpretation of images and reduce contrast and imaging depth. We recently developed a method called PAFUSion (photoacoustic-guided focused ultrasound) to circumvent the problem of reflection artifacts in photoacoustic imaging. We already demonstrated that the photoacoustic signals can be backpropagated using synthetic aperture pulse-echo data for identifying and reducing reflection artifacts in vivo. In this work, we propose...

  10. In Vitro Testing of Femoral Impaction Grafting With Porous Titanium Particles: A Pilot Study

    Aquarius, Rene; Walschot, Luc; Buma, Pieter; Schreurs, Berend Willem; Verdonschot, Nico
    The disadvantages of allografts to restore femoral bone defects during revision hip surgery have led to the search for alternative materials. We investigated the feasibility of using porous titanium particles and posed the following questions: (1) Is it possible to create a high-quality femoral graft of porous titanium particles in terms of graft thickness, cement thickness, and cement penetration? (2) Does this titanium particle graft layer provide initial stability when a femoral cemented stem is implanted in it? (3) What sizes of particles are released from the porous titanium particles during impaction and subsequent cyclic loading of the reconstruction? We...

  11. Reproducibility of volumetric intravascular ultrasound radiofrequency-based analysis of coronary plaque composition in vivo

    Hartmann, Marc; Mattern, Eline S.; Huisman, Jennifer; Houwelingen, Gert K. van; Man, Frits H.A.F. de; Stoel, Martin G.; Danse, Peter W.; Louwerenburg, Hans W.; Birgelen, Clemens von

  12. Hoe worden we gezond oud? Een leidraad voor heren met een zittend leven. Door Vopiscus Fortunatus Plemp: ingeleid, vertaald en van aantekeningen voorzien

    Kerkhoff, A.H.M.

  13. Interleukin-6 is elevated in synovial fluid of patients with focal cartilage defects and stimulates cartilage matrix production in an in vitro regeneration model

    Tsuchida, Anika I.; Beekhuizen, Michiel; Rutgers, Marijn; Osch, Gerjo J.V.M. van; Bekkers, Joris E.J.; Bot, Arjan G.J.; Geurts, Bernd; Dhert, Wouter J.A.; Saris, Daniël B.F.; Creemers, Laura B.
    Introduction This study aimed to determine whether, as in osteoarthritis, increased levels of interleukin-6 (IL-6) are present in the synovial fluid of patients with symptomatic cartilage defects and whether this IL-6 affects cartilage regeneration as well as the cartilage in the degenerated knee. Methods IL-6 concentrations were determined by ELISA in synovial fluid and in conditioned media of chondrocytes regenerating cartilage. Chondrocytes were obtained from donors with symptomatic cartilage defects, healthy and osteoarthritic donors. The effect of IL-6 on cartilage regeneration and on metabolism of the resident cartilage in the knee was studied by both inhibition of endogenous IL-6 and addition of IL-6,...

  14. Cytokine profiles in the joint depend on pathology, but are different between synovial fluid, cartilage tissue and cultured chondrocytes

    Tsuchida, A.I.; Beekhuizen, M.; Hart, M.C. 't; Radstake, T.R.D.J.; Dhert, W.J.A.; Saris, D.B.F.; Osch, G.J.V.M. van; Creemers, L.B.
    Introduction This study aimed to evaluate whether profiles of several soluble mediators in synovial fluid and cartilage tissue are pathology-dependent and how their production is related to in vitro tissue formation by chondrocytes from diseased and healthy tissue. Methods Samples were obtained from donors without joint pathology (n = 39), with focal defects (n = 65) and osteoarthritis (n = 61). A multiplex bead assay (Luminex) was performed measuring up to 21 cytokines: Interleukin (IL)-1α, IL-1β, IL-1RA, IL-4, IL-6, IL-6Rα, IL-7, IL-8, IL-10, IL-13, tumor necrosis factor (TNF)α, Interferon (IFN)γ, oncostatin M (OSM), leukemia inhibitory factor (LIF), adiponectin, leptin, monocyte chemotactic factor (MCP)1,...

  15. Editorial Special Issue: Neuronus

    Lubbe, Rob H.J. van der; Kuniecki, Michal
    This special issue of the 12th volume of Advances in Cognitive Psychology is devoted to the Neuronus conference that took place in Kraków in 2015. In this editorial letter, we will focus on a selection of the materials and some follow-up research that was presented during this conference. We will also briefly introduce the conference contributions that successfully passed an external reviewing process.

  16. Finite Element Analysis of Meniscal Anatomical 3D Scaffolds: Implications for Tissue Engineering

    Moroni, L.; Lambers, F.M.; Wilson, W.; Donkelaar, C.C. van; Wijn, J.R. de; Huiskes, R.; Blitterswijk, C.A. van
    Solid Free-Form Fabrication (SFF) technologies allow the fabrication of anatomical 3D scaffolds from computer tomography (CT) or magnetic resonance imaging (MRI) patients’ dataset. These structures can be designed and fabricated with a variable, interconnected and accessible porous network, resulting in modulable mechanical properties, permeability, and architecture that can be tailored to mimic a specific tissue to replace or regenerate. In this study, we evaluated whether anatomical meniscal 3D scaffolds with matching mechanical properties and architecture are beneficial for meniscus replacement as compared to meniscectomy. After acquiring CT and MRI of porcine menisci, 3D fiber-deposited (3DF) scaffolds were fabricated with different...

  17. Bone regeneration: molecular and cellular interactions with calcium phosphate ceramics

    Barrere, Florence; Blitterswijk, Clemens A. van; Groot, Klaas de
    Calcium phosphate bioceramics are widely used in orthopedic and dental applications and porous scaffolds made of them are serious candidates in the field of bone tissue engineering. They have superior properties for the stimulation of bone formation and bone bonding, both related to the specific interactions of their surface with the extracellular fluids and cells, ie, ionic exchanges, superficial molecular rearrangement and cellular activity.

  18. STM visualisation of counterions and the effect of charges on self-assembled monolayers of macrocycles

    Kudernac, Tibor; Shabelina, Natalia; Mamdouh, Wael; Höger, Sigurd; De Feyter, Steven
    Despite their importance in self-assembly processes, the influence of charged counterions on the geometry of self-assembled organic monolayers and their direct localisation within the monolayers has been given little attention. Recently, various examples of self-assembled monolayers composed of charged molecules on surfaces have been reported, but no effort has been made to prove the presence of counterions within the monolayer. Here we show that visualisation and exact localisation of counterions within self-assembled monolayers can be achieved with scanning tunnelling microscopy (STM). The presence of charges on the studied shape-persistent macrocycles is shown to have a profound effect on the self-assembly...

  19. Meta matters in interactive storytelling and serious gaming (a play on worlds)

    Linssen, Johannes Maria
    In this dissertation, I investigate the use of storytelling techniques in the domains of interactive storytelling and serious gaming. The field of interactive storytelling attempts to create and analyse systems that allow users to influence the plots of stories. Serious games provide experiences not solely for entertainment; in this dissertation, I investigate serious games with educational purposes. In both domains, I inspect how both human users and virtual agents (artificial, autonomous entities) can perceive stories. My main thesis is that the meta matters when interacting with interactive storytelling systems and serious games. All stories and games take place in virtual worlds...

  20. Frictional and bone ingrowth properties of engineered surface topographies produced by electron beam technology

    Biemond, J. Elizabeth; Aquarius, Rene; Verdonschot, Nico; Buma, Pieter
    Background Electron beam melting (E-beam) is a new technology to produce 3-dimensional surface topographies for cementless orthopedic implants. Methods The friction coefficients of two newly developed E-beam produced surface topographies were in vitro compared with sandblasted E-beam and titanium plasma sprayed controls. Bone ingrowth (direct bone–implant contact) was determined by implanting the samples in the femoral condyles of 6 goats for a period of 6 weeks. Results Friction coefficients of the new structures were comparable to the titanium plasma sprayed control. The direct bone–implant contact was 23.9 and 24.5% for the new surface structures. Bone–implant contact of the sandblasted and titanium plasma sprayed control was...

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