Multiscale velocity correlations in turbulence and Burgers turbulence: Fusion rules, Markov processes in scale, and multifractal predictions

We compare different approaches towards an effective description of multi-scale velocity field correlations in turbulence. Predictions made by the operator product expansion, the so-called fusion rules, are placed in juxtaposition to an approach that interprets the turbulent energy cascade in terms of a Markov process of velocity increments in scale. We explicitly show that the fusion rules are a direct consequence of the Markov property provided that the structure functions exhibit scaling in the inertial range. Furthermore, the limit case of joint velocity gradient and velocity increment statistics is discussed and put into the context of the notion of dissipative anomaly. We generalize a prediction made by the multifractal (MF) approach derived in [Phys. Rev. Lett. 80, 3244 (1998)] to correlations among inertial range velocity increment and velocity gradients of any order. We show that for the case of squared velocity gradients such a relation can be derived from "first principles" in the case of Burgers equation. Our results are benchmarked by intensive direct numerical simulations of Burgers turbulence.Comment: 18 pages, 6 figure

Advanced Protocols for Peer-to-Peer Data Transmission in Wireless Gigabit Networks

This thesis tackles problems on IEEE 802.11 MAC layer, network layer and application layer, to further push the performance of wireless P2P applications in a holistic way. It contributes to the better understanding and utilization of two major IEEE 802.11 MAC features, frame aggregation and block acknowledgement, to the design and implementation of opportunistic networks on off-the-shelf hardware and proposes a document exchange protocol, including document recommendation. First, this thesis contributes a measurement study of the A-MPDU frame aggregation behavior of IEEE 802.11n in a real-world, multi-hop, indoor mesh testbed. Furthermore, this thesis presents MPDU payload adaptation (MPA) to utilize A-MPDU subframes to increase the overall throughput under bad channel conditions. MPA adapts the size of MAC protocol data units to channel conditions, to increase the throughput and lower the delay in error-prone channels. The results suggest that under erroneous conditions throughput can be maximized by limiting the MPDU size. As second major contribution, this thesis introduces Neighborhood-aware OPPortunistic networking on Smartphones (NOPPoS). NOPPoS creates an opportunistic, pocket-switched network using current generation, off-the-shelf mobile devices. As main novel feature, NOPPoS is highly responsive to node mobility due to periodic, low-energy scans of its environment, using Bluetooth Low Energy advertisements. The last major contribution is the Neighborhood Document Sharing (NDS) protocol. NDS enables users to discover and retrieve arbitrary documents shared by other users in their proximity, i.e. in the communication range of their IEEE 802.11 interface. However, IEEE 802.11 connections are only used on-demand during file transfers and indexing of files in the proximity of the user. Simulations show that NDS interconnects over 90 \% of all devices in communication range. Finally, NDS is extended by the content recommendation system User Preference-based Probability Spreading (UPPS), a graph-based approach. It integrates user-item scoring into a graph-based tag-aware item recommender system. UPPS utilizes novel formulas for affinity and similarity scoring, taking into account user-item preference in the mass diffusion of the recommender system. The presented results show that UPPS is a significant improvement to previous approaches

Modelling the CAP Reform at the Regional Level with ProLand

The reform of the European Common Agricultural Policy (CAP) will fundamentally affect the decision behaviour of land users. So far transfer payments were coupled to specific forms of land use. The reform encourages land users to make decisions concerning production based solely on market aspects. The effects of the CAP reform on the Lahn Dill region in Germany are simulated with the spatially explicit land use model ProLand. The results show that land use decisions will be based stronger on site specific natural conditions than was the case in the Agenda 2000 scenario. The transfer payment volume directed into the region increases considerably.modelling, decision support, land use, spatially explicit, Agricultural and Food Policy, Q01,

Poseidon-Reise Nr. 55 [POS55] - Fahrtleiterbericht

1. 24.02.-05.03.1980 (Fahrtleiter: Dr. Theilen) 2. 05.03.-13.03.1980 (Fahrtleiter: Dr. Rumohr) 1. Allgemeines Die Reise in das Skagerrak vom 24.02. bis 05.03.1980 enthält die nachstehend aufgeführten Teilprogramme: a) Die Erfassung oberflächennaher Schichtstrukturen unter dem Meeresboden südlich des Oslo-Fjords sowie im zentralen und westlichen Teil des Skagerraks mit flachseismischen Verfahren. b) Bestimmung der Dämpfung seismischer Wellen und der seismischen Geschwindigkeiten aus Weitwinkelmessungen mit einem 400 Meter langen Streamer. Diese Messungen sollten auf besonderen Profilabschnitten erfolgen, die nach den kontinuierlichen reflexionsseismischen Messungen ausgewählt wurden. c) Magnetische Messungen zur Erfassung magnetischer Anomalien des kristallinen Untergrundes. d) Entnahme von Bodenproben zur Bestimmung der Feinschichtung des Meeresbodens. e) Untersuchungen mit der Multisonde zur Aufnahme der hydrographischen Situation und der Untersuchung der partikulären Substanzen. Gleichzeitig soll die räumliche und zeitliche Varianz der hydrographischen Situation erfaßt werden