268 research outputs found
Localized Detection of d-Serine by using an Enzymatic Amperometric Biosensor and Scanning Electrochemical Microscopy
No full textd-Serine acts as an endogenous co-agonist for N-methyl-d-aspartate receptors at synapses, making it essential for proper brain development and function. This amino acid has also been linked to several neurodegenerative diseases such as Alzheimer's disease and dementia. Nevertheless, the primary site and mechanism of d-serine release remains unclear. We recently demonstrated the use of an enzymatic amperometric biosensor for the in vivo quantification of endogenous d-serine release in Xenopus laevis tadpoles. Herein, we investigate the effect of the permselective poly(meta-phenylenediamine) electropolymerization conditions on the biosensor's response time and selectivity. Scanning electrochemical microscopy (SECM) is then used with the optimized biosensor to measure localized release of d-serine from a model system. This SECM methodology, which provides high spatial and temporal resolution, could be useful to investigate the primary site and mechanism of d-serine release in other biological samples
American Society of Biomechanics Journal of Biomechanics Award 2013: Cortical bone tissue mechanical quality and biological mechanisms possibly underlying atypical fractures
No full textThe biomechanics literature contains many well-understood mechanisms behind typical fracture types that have important roles in treatment planning. The recent association of "atypical" fractures with long-term use of drugs designed to prevent osteoporosis has renewed interest in the effects of agents on bone tissue-level quality. While this class of fracture was recognized prior to the introduction of the anti-resorptive bisphosphonate drugs and recently likened to stress fractures, the mechanism(s) that lead to atypical fractures have not been definitively identified. Thus, a causal relationship between these drugs and atypical fracture has not been established. Physicians, bioengineers and others interested in the biomechanics of bone are working to improve fracture-prevention diagnostics, and the design of treatments to avoid this serious side-effect in the future. This review examines the mechanisms behind the bone tissue damage that may produce the atypical fracture pattern observed increasingly with long-term bisphosphonate use. Our recent findings and those of others reviewed support that the mechanisms behind normal, healthy excavation and tunnel filling by bone remodeling units within cortical tissue strengthen mechanical integrity. The ability of cortical bone to resist the damage induced during cyclic loading may be altered by the reduced remodeling and increased tissue age resulting from long-term bisphosphonate treatment. Development of assessments for such potential fractures would restore confidence in pharmaceutical treatments that have the potential to spare millions in our aging population from the morbidity and death that often follow bone fracture.Peer reviewe
The resistance of cortical bone tissue to failure under cyclic loading is reduced with alendronate
No full textBisphosphonates are the most prescribed preventative treatment for osteoporosis. However, their long-term use has recently been associated with atypical fractures of cortical bone in patients who present with low-energy induced breaks of unclear pathophysiology. The effects of bisphosphonates on the mechanical properties of cortical bone have been exclusively studied under simple, monotonic, quasi-static loading. This study examined the cyclic fatigue properties of bisphosphonate-treated cortical bone at a level in which tissue damage initiates and is accumulated prior to frank fracture in low-energy situations. Physiologically relevant, dynamic, 4-point bending applied to beams (1.5 mm × 0.5 mm × 10 mm) machined from dog rib (n=12/group) demonstrated mechanical failure and micro-architectural features that were dependent on drug dose (3 groups: 0, 0.2, 1.0mg/kg/day; alendronate [ALN] for 3 years) with cortical bone tissue elastic modulus (initial cycles of loading) reduced by 21% (p<0.001) and fatigue life (number of cycles to failure) reduced in a stress-life approach by greater than 3-fold with ALN1.0 (p<0.05). While not affecting the number of osteons, ALN treatment reduced other features associated with bone remodeling, such as the size of osteons (-14%; ALN1.0: 10.5±1.8, VEH: 12.2±1.6, ×10(3) μm2; p<0.01) and the density of osteocyte lacunae (-20%; ALN1.0: 11.4±3.3, VEH: 14.3±3.6, ×10(2) #/mm2; p<0.05). Furthermore, the osteocyte lacunar density was directly proportional to initial elastic modulus when the groups were pooled (R=0.54, p<0.01). These findings suggest that the structural components normally contributing to healthy cortical bone tissue are altered by high-dose ALN treatment and contribute to reduced mechanical properties under cyclic loading conditions.NOTICE: this is the author's version of a work that was accepted for publication in Bone. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Bone, Volume 64 (July 2014) DOI: 10.1016/j.bone.2014.03.045Peer reviewe
Flexible and cost effective reconfigurable UHF RFID antenna system
No full textIn this paper a reconfigurable matching network for achieving frequency agility of an electrically small UHF RFID patch antenna is proposed. In order to allow switching under high power transmission a state-of-the-art SP3T CMOS switch is employed for selecting specific components and thus achieving a proper matching in the EU and US frequency bands. Moreover, in the proposed design, only one switch is used instead of four needed in standard aperture tuning approaches. An optimized design of a RFID microstrip antenna has been simulated, showing good performance and high degree of flexibility of this technique, which for its low cost and high integration rate, can become an alternative to aperture tuning for frequency agility purposes
<i>(Invited)</i> Detection of D-serine using an enzymatic amperometric biosensor and its localized detection using scanning electrochemical microscopy
No full textD-Serine acts as an endogenous co-agonist for N-methyl-D-aspartate receptors at synapses, making it essential for proper brain development and function. This amino acid has also been linked to several neurodegenerative diseases such as Alzheimer's disease and dementia. Nevertheless, the primary site and mechanism of D-serine release remains unclear. We recently demonstrated the use of an enzymatic amperometric biosensor for the in vivo quantification of endogenous D-serine release in Xenopus laevis tadpoles. We also investigate the effect of the permselective polymer layer thickness on the biosensor's response time and selectivity. Finally, scanning electrochemical microscopy (SECM) is then used with the optimized biosensor to measure localized release of D-serine from a model system. This SECM methodology, which provides high spatial and temporal resolution, could be useful to investigate the primary site and mechanism of D-serine release in other biological samples
Multi-sensor chip for the investigation of different types of metal oxides for the detection of H2O2 in the ppm range.
No full textIn this work, a multi-sensor chip for the investigation of the sensing properties of different types of metal oxides towards hydrogen peroxide in the ppm range is presented. The fabrication process and physical characterization of the multi-sensor chip are described. Pure SnO2 and WO3 as well as Pd- and Pt-doped SnO2 films are characterized in terms of their sensitivity to H2O2. The sensing films have been prepared by drop-coating of water-dispensed nano-powders. A physical characterization, including scanning electron microscopy and X-ray diffraction analysis of the deposited metal-oxide films, was done. From the measurements in hydrogen peroxide atmosphere, it could be shown, that all of the tested metal oxide films are suitable for the detection of H2O2 in the ppm range. The highest sensitivity and reproducibility was achieved using Pt-doped SnO2. Calibration plot of a SnO2, WO3, Pt-, and Pd-doped SnO2 gas sensor for H2O2 concentrations in the ppm range. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.status: Publishe
The role of collective motion in examples of coarsening and self-assembly
No full textThe simplest prescription for building a patterned structure from its constituents is to add particles, one at a time, to an appropriate template. However, self-organizing molecular and colloidal systems in nature can evolve in much more hierarchical ways. Specifically, constituents (or clusters of constituents) may aggregate to form clusters (or clusters of clusters) that serve as building blocks for later stages of assembly. Here we evaluate the character and consequences of such collective motion in a set of prototypical assembly processes. We do so using computer simulations in which a system's capacity for hierarchical dynamics can be controlled systematically. By explicitly allowing or suppressing collective motion, we quantify its effects. We find that coarsening within a two dimensional attractive lattice gas (and an analogous off-lattice model in three dimensions) is naturally dominated by collective motion over a broad range of temperatures and densities. Under such circumstances, cluster mobility inhibits the development of uniform coexisting phases, especially when macroscopic segregation is strongly favored by thermodynamics. By contrast, the assembly of model viral capsids is not frustrated but is instead facilitated by collective moves, which promote the orderly binding of intermediates consisting of several monomers
Nachführbare Antennen für die mobile Satellitenkommunikation auf Basis des Multimode-Monopuls-Prinzips
No full textDie hier präsentierte Arbeit beschäftigt sich mit dem Entwurf und der Realisierung von nachführbaren Antennen für die mobile Satellitenkommunikation auf Basis von Reflektorantennen. Dieser Antennentyp spielt eine zentrale Rolle für Bodenstationsantennen, die hohe Datenraten auch während der Fahrt des Trägerfahrzeugs zur Verfügung stellen sollen. Ausgehend von der Vorstellung bestehender Systeme und den Anforderungen an mobile Satellitenantennen werden Konstruktionsgrundlagen für die Dimensionierung von Cassegrain-Antennen beschrieben. Für die Nachführung dieses Antennentyps stehen verschiedene technische Prinzipien zur Verfügung, bei denen in dieser Arbeit besonderer Fokus auf Monopuls-Technologien besteht. Dieses Prinzip ermöglicht die Schätzung der Fehlausrichtung einer Antenne in Bezug zur Richtung, aus der das Empfangssignal kommt, für einen begrenzten räumlichen Ausschnitt aus dem Richtdiagramm der Antenne. Die hiermit generierten Richtungsinformationen werden für einen Regelkreis zur mechanischen Nachführung der Antenne verwendet. Basierend auf den vorgestellten Konzepten wird ein Demonstrator für eine Außeneinheit eines mobilen Satellitenterminals beschrieben. Dieser Demonstrator besteht aus einem individuell angefertigten mechanischen Antennenpositionierer und einer 60 cm Ka-Band Cassegrain-Antenne, welche mit einem neu entworfenen TM01-Multimode-Monopuls-Speisesystem bestehend aus einem Hohlleiter-Modenkoppler versehen ist. Die Entwicklung der Speisekette wird über eine erste Variante für reinen Empfangsbetrieb bis hin zu einer vollständigen Dual-Band-Version für Sende- und Empfangsfunktion dargestellt. Hierbei wird auf die numerische Simulation der Strukturen sowie auf die messtechnische Charakterisierung nach der Fertigung eingegangen. Darüber hinaus wird die Generierung des Fehlervektors, der für die Nachführung der Antenne benötigt wird, beschrieben. Zusätzlich zum Hohlleiter-basierten Koppler wird in dieser Arbeit ein neuartiger Modenkoppler für TM01-Multimode-Monopuls vorgestellt, bei dem Übergänge von gedruckten Koplanarleitungen zu Hohlleitern eingesetzt werden. Diese Methode ermöglicht die Integration des Kopplers zusammen mit dem Sendeempfänger in derselben Technologie, wodurch ein sehr kompakter, leichter und kostengünstiger Aufbau der Speisekette möglich wird.The presented thesis discusses the design and realisation of tracking-antennas for mobile satellite communications based on reflector antennas. This type of antenna plays an important role for earth station antennas used for high data rate communications while the carrier vehicle is moving. Starting from the introduction of existing systems and the requirements of mobile satellite antennas, design fundamentals for the construction of Cassegrain antennas are described. For the tracking of this type of antenna various technical principles are available of which in this work a deeper focus lies on monopulse technologies. This principle allows the estimation of the misalignment of an antenna with respect to the direction from which the signal is received for a limited spatial segment of the radiation pattern of the antenna. This direction information is used for a control loop for mechanical tracking of the antenna.
Based on the presented concepts a demonstrator for an outdoor unit of a mobile satellite antenna terminal is described. The demonstrator consists of a custom-made mechanical antenna positioner and a 60 cm Ka-band Cassegrain antenna, which is equipped with an individually designed TM01 multimode monopulse feed system consisting of a waveguide mode coupler. The development of the feed chain started with a receive-only coupler and went to a full dual-band version for transmitting and receiving function. The numerical simulation of the structures and the metrological characterization after fabrication are described in detail. Moreover, the generation of the error vector, which is required for the tracking of the antenna, is described.
In addition to the waveguide-based coupler in this work, a novel mode coupler for TM01 multimode monopulse is presented. This coupler employs transitions from printed coplanar waveguides to circular waveguides. This method facilitates the integration of the coupler together with the transceiver using the same technology, thereby providing the potential for a very compact, lightweight, and cost-effective construction of the feed chain
Messkonzepte für Funksysteme bei Mobilfunk-basierter Fahrzeugkommunikation
No full textDie vorliegende Arbeit beschäftigt sich in interdisziplinärer Weise mit Fragestellungen und anhand von over-the-air Tests mit Lösungsansätzen zur Antennenmesstechnik und Funkkanalemulation sowie mit Testverfahren bei LTE-basierter Mobilkommunikation im Kontext vernetzter Automobile. Die Herausforderung besteht darin, dass der Speisepunkt der Antennen aufgrund des Einbauzustandes im Fahrzeug sowie der fortschreitenden Integration von Antennen und Empfängern nur schwer oder gar nicht zugänglich ist. Durch Nutzung modulierter Kommunikationssignale gelingt es, direkt und ohne komplexe Algorithmen dreidimensionale Gewinn- und Phaseninformation von Fahrzeugantennen im Einbauzustand aus einfachen Leistungsmessungen zu ermitteln. Kenntnis des Phasendiagramms der Antennen ist insbesondere bei der Übertragung mit mehreren Antennen essenziell und wird außerdem für die Bestimmung der Position von Antennen anhand ihres Phasenzentrums benötigt. Nach der Charakterisierung der Strahlungseigenschaften der Antennen werden diese als Teil einer Funkumgebung betrachtet und in der Funkkanalnachbildung berücksichtigt. Für die Bestimmung der Leistungsfähigkeit von Fahrzeugantennen durch die Emulation drahtloser Ausbreitungskanäle wurden im Rahmen dieser Arbeit mittels programmierbarer Funkmodule Alternativen zu etablierten Kanalemulatoren sowie die Zahl und Anordnung von Beleuchtungsantennen für die Nachbildung räumlicher Eigenschaften erforscht. Im Bereich realer und virtueller Fahrtests mit vernetzten Automobilen bestehen die Ergebnisse dieser Arbeit aus einem Messkonzept für virtuelle Fahrtests mit dem Ziel der Nachbildung relevanter Ausbreitungseffekte aus realen Fahrtests. Als relevantes Testszenario wurden die Grenzbereiche zwischen Mobilfunkzellen, bzw. die Nachbarbasisstation als größter Störeinfluss, identifiziert. Anhand gezielter Regelung von Nutz- und Störsignalpegeln im virtuellen Test kann das Verhalten des Testgeräts an den kritischen Stellen in Nähe der Zellränder mit Schwankungen < 5 % nachgebildet werden. Dieses Konzept ermöglicht einen einfachen Test, ohne notwendigerweise detaillierte Kenntnis des Funkkanals haben zu müssen, indem der Fokus auf der Nachbildung von für die Übertragung kritischen Szenarien anstelle der Nachbildung eines spezifischen Funkkanals liegt.This thesis deals in an interdisciplinary manner with questions and, on the basis of over-the-air tests, with solution approaches for antenna measurement techniques and radio channel emulation as well as with test procedures for LTE-based mobile communication in the context of connected automobiles. The challenge is that the feed point of the antennas is difficult or impossible to access due to the installed state of the antenna in the vehicle and the progressive integration of antennas and receivers. By using modulated communication signals, it is possible to determine three-dimensional gain and phase information of vehicular antennas in the installed state directly and without complex algorithms from simple power measurements. Knowledge of the phase diagram of the antennas is particularly essential for transmission and reception with multiple antennas and is also required for determining the position of antennas based on their phase center. After characterizing the radiation properties of the antennas, they are considered as part of a radio environment and taken into account in the radio channel emulation. In order to determine the performance of vehicular antennas by emulating wireless propagation channels, alternatives to established channel emulators as well as the number and arrangement of illumination antennas for simulating spatial characteristics were investigated as part of this work using programmable radio modules. In the area of real and virtual driving tests with connected cars, the results of this work consist of a measurement concept for virtual drive tests with the aim of simulating relevant propagation effects from real driving tests. The edges between mobile radio cells, and the neighboring base stations as interferers were identified as the most relevant test scenario. The behavior of the test device at the critical points near the cell edges can be simulated with fluctuations < 5 % by means of targeted control of useful and interference signal levels in the virtual test. This concept enables a simple test without necessarily having detailed knowledge of the radio channel by focusing on simulating critical transmission scenarios instead of simulating a specific radio channel
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