ALBERT

Description: Radio frequency identification (RFID) is a technology enabling a contactless exchange of data. Thistechnology features the possibility to wirelessly transfer power to the transponder (opponent). HF-RFID is used in mobile devices like smart phones and shows potential for applications like payment,identification, etc. Unfortunately, the needed functionality increases the battery drain of the device. Asa countermeasure, power-management techniques are implemented. However, these techniques com-monly do not consider the whole system, which also consists of the communication to the transpon-der, to prevent wasting energy. One cross-system technique of reducing the wasted energy is magneticfield strength scaling, which regulates the power transfer to the transponder. This article shows threeinvestigations made, regarding field strength scaling to prevent this wastage of energy. The resultsof one investigation, how to use field strength scaling at card detection phase in form of the PTF-Determinator method, is described in detail. This method determines the Power Transfer Function(PTF) during run-time and scales the provided power accordingly to save energy. As a case study thePTF-Determinator is integrated in an application to read digital business cards. The resulting powerconsumption and timing has been evaluated by simulation and measurement of a development plat-form for mobile phones. Furthermore, the impact of field strength scaling to the energy consumptionof a state of the art NFC-enhanced smart phone has been analyzed. The results of the case study showsthat up to 26% less transmission energy (energy drain of NFC) is needed, if field strength scaling isapplied (proofen by measurement). According to this result a smart phone's battery drain (energydrain of the whole system) can be decreased by up to 13% by using field strength scaling for this casestudy.

Description: We present a comprehensive analysis of four south föhn events observed during the Penetration and Interruption of Alpine Foehn (PIANO) field campaign in the Inn Valley, Austria, in the vicinity of Innsbruck. The goal is to detect and quantify processes of cold-air pool (CAP) erosion by föhn as well as processes of föhn breakdown. Despite differences in föhn breakthrough and strength, the four cases exhibit similarities in CAP evolution: initially, the CAP experienced strongest warming in the centre of Innsbruck, where the föhn jet from the Wipp Valley interacted with the CAP in the Inn Valley. The resulting shear-flow instability at the föhn–CAP interface caused turbulent CAP erosion and, together with vertical warm-air advection, led to CAP depression over the city centre. This depression drove pre-föhn westerlies near the surface that caused cold-air advection inside the CAP west of the city centre and warm-air advection in the east. Ultimately, the latter contributed to stronger CAP erosion in the east than in the west. This stronger heating also explains the preferential initial föhn breakthrough at the valley floor east of Innsbruck. In two of the cases, subsequent westward propagation of the föhn–CAP boundary across the city accompanied by northerly (deflected) föhn winds led to a complete föhn breakthrough. Föhn breakdown occurred either by a backflow of the CAP remnant or by a cold-frontal passage. This study emphasizes the importance of both turbulence and advection in the CAP heat budget and reveal their large spatio–temporal variability.