8-channel optical demultiplexer realized as SiO2/Siflat-field spectrograph

The operation of a flat-field spectrograph in silica on silicon (SiO₂/Si) for 2-nm channel spacing is demonstrated. Crosstalk attenuations of >20 dB and significantly reduced fiber-to-fiber insertion losses of 5 dB could be obtained     

Ultra-fast vapour-liquid-solid synthesis of Si nanowires using ion-beam implanted gallium as catalyst

The feasibility of gallium as a catalyst for vapour-liquid-solid (VLS) nanowire (NW) growth deriving from an implantation process in silicon by a focused ion beam (FIB) is investigated. Si(100) substrates are subjected to FIB implantation of gallium ions with various ion fluence rates. NW growth is performed in a hot wall chemical vapour deposition (CVD) reactor at temperatures between 400 and 500?°C with 2% SiH(4)/He as precursor gas. This process results in ultra-fast growth of (112)- and (110)-oriented Si-NWs with a length of several tens of micrometres. Further investigation by transmission electron microscopy indicates the presence of a NW core-shell structure: while the NW core yields crystalline structuring, the shell consists entirely of amorphous material.     

Intermetallische Werkstoffe für Anwendungen in Automobil- und Flugzeugtriebwerken

Zusammenfassung  Die Entwicklung von innovativen Hochtemperaturwerkstoffen spielt eine Schlüsselrolle in Anwendungsbereichen, wo Werkstoffe extremen Anforderungen ausgesetzt sind. Solche Anwendungsbereiche sind unter anderem die Luftfahrt- und die Automobilindustrie. Neue Konstruktionswerkstoffe für hohe Anwendungstemperaturen müssen "fester, steifer und leichter" sein, damit sie den st?ndig steigenden Anforderungen, wie sie z. B. in der n?chsten Generation von Flugzeugtriebwerken und Verbrennungsmotoren auftreten, gerecht werden. Diese Flugzeugtriebwerke und Verbrennungsmotoren werden deutlich gesenkten Treibstoffverbrauch sowie stark verringerte Schadstoffemissionen aufweisen. Intermetallische Titanaluminide besitzen attraktive Eigenschaften, wie hoher Schmelzpunkt, geringe Dichte, hohen spezifischen Elastizit?tsmodul, gutes Oxidationsverhalten sowie hohe spezifische Zug- und Kriechfestigkeit im Temperaturbereich von 600 bis 800 °C, die diese Anforderungen erfüllen. Aus diesen Gründen besitzen sie das Potenzial, in manchen Anwendungsbereichen die doppelt so schweren Nickellegierungen zu verdr?ngen.

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Intermetallic Materials for Automotive and Aero-engine Applications

Summary  Development of advanced high-temperature materials is the key to technological advancement in engineering areas where materials have to meet extreme requirements. Examples for such areas are the aerospace and the automotive industries. New structural materials have to be "stronger, stiffer and lighter" to withstand the extremely demanding conditions in the next generation of aircraft and automotive engines. These aero-engines and internal combustion engines will exhibit reduced fuel consumption as well as a significantly decreased emission of pollutants. Intermetallic titanium aluminides possess numerous attractive properties which meet these demands. These properties include high melting point, low density, high specific elastic modulus, good oxidation resistance, and high specific tensile and creep strength up to application temperatures of 600 to 800 °C. Thus, titanium aluminides have the potential to replace heavy nickel based superalloys.

     

A physical model for a quality control concept in injection molding

In this work, a model is presented, which is the basis of a quality control concept for the injection molding process. Contrary to statistical methods, this model uses physical dependencies of two quality parameters on four influencing parameters. The influences of holding pressure, holding time, melt temperature, and mold temperature on part mass and dimensions are described based on the fundamental material behavior such as pvT‐data or energy equation. Furthermore, the influence of viscosity changes is indirectly taken into account using the injection work. Assuming only small deviations of the influencing parameters around an optimized operating point, the four parameters are treated as being independent from each other. With this assumption, a product ansatz was chosen with different functions for each influencing factor. Applying basic algebra, the starting equation was transformed into a form that describes either the change in part mass or characteristic part dimensions as a function of the influencing factors. The final equation for the part mass contains six model parameters, whereas nine model parameters are necessary for the equation for the part length. To obtain those model parameters some systematic experiments are required. Once the parameters are known, the model is able to calculate the change of the target values when the influencing factors vary around the operating point. The model was tested experimentally with focus on dimensions using a plastic cover made of an acrylonitrile butadiene styrene (ABS) grade. For the investigated part geometry and material grade, the process behavior was described well by the model. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Locating illicit connections in storm water sewers using fiber-optic distributed temperature sensing

A newly developed technique using distributed temperature sensing (DTS) has been developed to find illicit household sewage connections to storm water systems in the Netherlands. DTS allows for the accurate measurement of temperature along a fiber-optic cable, with high spatial (2 m) and temporal (30 s) resolution. We inserted a fiber-optic cable of 1300 m in two storm water drains. At certain locations, significant temperature differences with an intermittent character were measured, indicating inflow of water that was not storm water. In all cases, we found that foul water from households or companies entered the storm water system through an illicit sewage connection. The method of using temperature differences for illicit connection detection in storm water networks is discussed. The technique of using fiber-optic cables for distributed temperature sensing is explained in detail. The DTS method is a reliable, inexpensive and practically feasible method to detect illicit connections to storm water systems, which does not require access to private property.     

Multi-Agent Radio Resource Allocation

This paper presents a spatially distributed and dynamic billing, pricing and allocation mechanism for which a user terminal requires Cognitive Radio abilities. That is, the Cognitive Radio abilities will be applied to the economical environment. The radio resource goods are allocated to the users by a multi-unit sealed-bid auction. Intelligent entities like the bidding strategy have to represent operator’s and users’ behavior and to make decisions for them in order to fulfill the preferences and QoS. The main functionalities, used to execute the dynamic auction sequence and located in the MAC are described, assuming the entities possess Cognitive Radio abilities.

Adaptive Resource Management Platform for Reconfigurable Networks

Users’ expectations towards technology, in terms of quality, service availability and accessibility are ever increasing. Aligned with this, the wireless world is rapidly moving towards the next generation of systems, featuring cooperating and reconfiguring capabilities for coexisting (and upcoming) Radio Access Technologies (RATs), so that to improve connectivity and reduce costs. In this respect, conventional planning and management techniques ought to be replaced by advanced schemes that consider multidimensional characteristics, increased complexity and high speeds. To this effect, means are needed capable to support scalability and to cater for advanced service features, provided to users at high rates and cost-effectively. This article provides a scheme to optimize resource management in future systems, by describing a platform that accommodates engineering mechanisms that deal with dynamic, demand driven planning and managing of spectrum and radio resources in reconfigurable networks. To do so, it first discusses the fundamentals and the approach followed in the proposed architecture and then investigates the basic functional modules. The architecture is validated through a set of use-cases that exemplify the operational applicability and efficiency in a wide range of communication scenarios.

Effect of Sintering on the Thermoelectric Transport Properties of Bulk Nanostructured Bi0.5Sb1.5Te3 Pellets Prepared by Chemical Synthesis

Considerable research effort has gone into improving the performance of traditional thermoelectric materials such as Bi_2?x Sb _x Te₃ through a variety of nanostructuring approaches. Bottom-up, chemical approaches have the potential to produce very small nanoparticles (?100?nm) with narrow size distribution and controlled shape. For this study, nanocrystalline powder of Bi_0.5Sb_1.5Te₃ was synthesized using a ligand-assisted chemical method, and consolidated into pellets with cold pressing followed by sintering in Ar atmosphere. The thermoelectric transport properties were measured from 7?K to 300?K as a function of sintering temperature. Sintering is found to increase ZT and to move the maximum in ZT to lower temperatures due to a reduction in the free charge concentration. Hall mobility studies indicate that sintering increases the electron mean free path more than it increases the phonon mean free path up to sintering temperature of 598?K. A maximum ZT of 0.42 was measured at temperature of 275?K.