Shared WiFi-Communities – User Generated Infrastructure am Beispiel von FON

Shared WiFi-Communities emerge when users share their private Wireless Fidelity with others and in return get free internet access via community members’ internet connection. Supply of wireless capacity and demand for WLAN usually are coordinated by a central authority therewith users can find specific hosts within the community. Initial players that conduct commercial WiFi-Communities established their position in the market. The international market leader with 170,000 hotspots worldwide is FON. The commercial success of shared WiFi-communities (e.g. FON) depends on the adoption of a special router or modifications of the existing WLAN-infrastructure. More importantly it is essential that users permanently offer broadband capacity to the community. Only then net effects can durably generate enhanced usage benefits. A survey of 268 German FON users reveals that the community shows a high level of cohesion. Users barely vary from the default setting concerning shared bandwidth of the router. Additionally most interviewees offer their WLAN 24 hours a day. Despite the possibility of earning money with the wireless capacity most users do not offer bandwidth with a purely economic ambition. Although the market potential of shared WiFi communities appears tremendous legal obstructions and technical restraints exacerbate penetration.     

Thermodynamic measurements of submilligram bulk samples using a membrane-based "calorimeter on a chip"

Calorimetry offers a direct measurement of thermodynamic properties of materials, including information on the energetics of phase transitions. Many materials can only be prepared in thin film or small crystal (submilligram) form, negating the use of traditional bulk techniques. The use of micromachined, membrane-based calorimeters for submilligram bulk samples is detailed here. Numerical simulations of the heat flow for this use have been performed. These simulations describe the limits to which this calorimetric technique can be applied to the realm of small crystals (1-1000 microg). Experimental results confirm the feasibility of this application over a temperature range from 2 to 300 K. Limits on sample thermal conductivity as it relates to the application of the lumped and distributed tau 2 models are explored. For a typical sample size, the simulations yield 2.5% absolute accuracy for the heat capacity of a sample with thermal conductivity as low as 2 x 10(-5) W/cm K at 20 K, assuming a strong thermal link to the device. Silver paint is used to attach (both thermally and physically) the small samples; its heat capacity and reproducibility are discussed. Measurements taken of a submilligram single crystal of cobalt oxide (CoO) compare favorably to the results of a bulk calorimetric technique on a larger sample.     

Ein Steuerverfahren für dreistufige Umrichter am Drehstromnetz

Übersicht Ein neues Raumzeigersteuerschema für dreistufige am Dreiphasennetz arbeitende Pulsumrichter wird vorgestellt. Es basiert auf einem Steuerverfahren für dreiphasige, zweistufige Motorwechselrichter. Die Erweiterung auf dreistufige Pulsumrichter und die dazugehörige Steuertabelle werden gezeigt. Dieses Verfahren erreicht eine symmetrische Spannungsaufteilung auf der Gleichspannungsseite auch bei unsymmetrischer Belastung des Zwischenkreises. Messungen an einem Versuchaaufbau werden gezeigt.

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A control scheme for three-phase, three-level lineside converters

Contents A novel control scheme for three-phase three-level lineside converters operating in the -frame is proposed. It is based on a principle proposed for and approved with three-phase two-level motor inverters. The adaption for three-level inverters is explained and the look-up tables for the switching states are presented. The control scheme is also able of self-balancing the potential of the center-tap of the DC capacitors in case of asymmetric loads. The scheme is realized with an IGBT-converter and measurements are shown.

     

Dynamique des lasers à fibre dopée à I’erbium

The dynamics of the erbium doped fiber laser is analysed both experimentally and theoretically. This laser operates spontaneously in self-pulsing, in sinusoidal or in CW regime. Experiments have allowed to determine the control parameters : the cavity losses, the pumping rate and the ion pairs concentration. An antiphase dynamics is observed when the laser operates simultaneously at 1.55 µn and 1.536 µm. The self-pulsing behavior is attributed to a fast energy transfer which occurs between two neighboring ions (pair induced quenching). A simple model considering the active medium as a mixture of isolated ions and ions pairs is developped and leads to a good qualitative agreement with the experimental results.     

Licence de brevet et partage du risque: Résultats de simulation

Annals of Telecommunications - Le partage du risque est une des raisons les plus souvent avancées pour expliquer les clauses financières des contrats de licence. Pour autant, aucune...     

The effects of boundary conditions on the basal glide of ice crystals in compression

Creep experiments were conducted on ice crystals in compression to investigate the effects of boundary conditions on a single-slip system deformed in plane strain. Friction at the platens of the deformation apparatus introduces a bending moment which causes a variation in the amount of lattice rotation across the specimen. This is shown to occur in mechanically constrained crystals observed through plane polarized light. Relieving the constraints and minimizing friction at the ice-platen contact leads to the widening of the sample near the specimen-platen interface and the production of tails symmetrically disposed about the longitudinal axis of the deformed crystals. This is interpreted to originate from a bending moment in the opposite sense from that obtained in the constrained crystals, resulting from a progressive increase in slip displacement towards the platens where the segments of the slip plane become shorter. When the crystal ends were constrained but allowed to move sideways, a simple shear regime was established in which lattice slip was concentrated in the centre of the crystal.     

Modelling and condition-based control of a flexible and hybrid disassembly system with manual and autonomous workstations using reinforcement learning

Journal of Intelligent Manufacturing - Remanufacturing includes disassembly and reassembly of used products to save natural resources and reduce emissions. While assembly is widely understood in...     

Vademecum‐based GFEM (V‐GFEM): optimal enrichment for transient problems

This paper proposes a generalized finite element method based on the use of parametric solutions as enrichment functions. These parametric solutions are precomputed off‐line and stored in memory in the form of a computational vademecum so that they can be used on‐line with negligible cost. This renders a more efficient computational method than traditional finite element methods at performing simulations of processes. One key issue of the proposed method is the efficient computation of the parametric enrichments. These are computed and efficiently stored in memory by employing proper generalized decompositions. Although the presented method can be broadly applied, it is particularly well suited in manufacturing processes involving localized physics that depend on many parameters, such as welding. After introducing the vademecum‐generalized finite element method formulation, we present some numerical examples related to the simulation of thermal models encountered in welding processes. Copyright © 2016 John Wiley & Sons, Ltd.