Angular momentum transport in convectively unstable shear flows

Angular momentum transport owing to hydrodynamic turbulent convection is studied using local three dimensional numerical simulations employing the shearing box approximation. We determine the turbulent viscosity from non-rotating runs over a range of values of the shear parameter and use a simple analytical model in order to extract the non-diffusive contribution (Lambda-effect) to the stress in runs where rotation is included. Our results suggest that the turbulent viscosity is of the order of the mixing length estimate and weakly affected by rotation. The Lambda-effect is non-zero and a factor of 2-4 smaller than the turbulent viscosity in the slow rotation regime. We demonstrate that for Keplerian shear, the angular momentum transport can change sign and be outward when the rotation period is greater than the turnover time, i.e. when the Coriolis number is below unity. This result seems to be relatively independent of the value of the Rayleigh number.Comment: 10 pages, 12 figures, published version. Version with higher resolution figures can be found at http://www.helsinki.fi/~kapyla/publ.htm

From Frequency to Sequence: How Quantitative Methods Can Inform Qualitative Analysis of Digital Media Discourse

This paper aims at showing how quantitative corpus linguistic analysis can inform qualitative analysis of digital media discourse with respect to the mediality of language in use. Using the example of protest discourse in Twitter, in the field of anti-Islamic ‘Pegida’ demonstrations, a three-step method of collecting, reducing and interpreting salient data is proposed. Each step is aligned with opera-tive medial features of the microblog: hashtags, retweets and @-interactions. The exemplary analysis reveals the importance of discussions of attendance numbers in protest discourse and the asymmetry between administrative (i.e. the police) and non-administrative discourse agents. Furthermore, it exemplifies how frequency analysis and sequence analysis can be combined for research in media linguistics

Monitoring coastal sea level using reflected GNSS signals

A continuous monitoring of coastal sea level changes is important for human society since it is predicted that up to 332 million people in coastal and low-lying areas will be directly affected by flooding from sea level rise by the end of the 21st century. The traditional way to observe sea level is using tide gauges that give measurements relative to the Earth’s crust. However, in order to improve the understanding of the sea level change processes it is necessary to separate the measurements into land surface height changes and sea surface height changes. These measurements should then be relative to a global reference frame. This can be done with satellite techniques, and thus a GNSS-based tide gauge is proposed. The GNSS-based tide gauge makes use of both GNSS signals that are directly received and GNSS signals that are reflected from the sea surface. An experimental installation at the Onsala Space Observatory (OSO) shows that the reflected GNSS signals have only about 3 dB less signal-to-noise-ratio than the directly received GNSS signals. Furthermore, a comparison of local sea level observations from the GNSS-based tide gauge with two stilling well gauges, located approximately 18 km and 33 km away from OSO, gives a pairwise root-mean-square agreement on the order of 4 cm. This indicates that the GNSS-based tide gauge gives valuable results for sea level monitoring

Sea Level Monitoring Using a GNSS-Based Tide Gauge

A continuous monitoring of sea level changes is important for human society since more than 50% of the world's population live within 60 km of the coast. Sea level is traditionally observed with tide gauges that give measurements relative to the Earth's crust. To improve the understanding of sea level changes it is necessary to perform measurements with respect to the Earth's center of gravity. This can be done with satellite techniques, and thus a GNSS-based tide gauge is proposed that makes use of both GNSS-signals that are directly received and that are reflected on the sea surface. A test installation at the Onsala Space Observatory shows that the reflected GNSS-signals have only about 3 dB less signal-to-noise-ratio than the directly received GNSS-signals. A comparison of relative sea level observations from the GNSS-based tide gauge to traditional tide gauges gives an RMS-agreement on the order of 4 cm

Optical Underwater Communication: The Potential of Using Converted Green LEDs in Coastal Waters

Compared to the open ocean where blue light-emitting diodes (LEDs) perform well for data communications, in coastal and harbor environments optical transmission becomes worse and the color of lowest attenuation shifts to green. Another problem concerns the “green–yellow gap” of LEDs, as the quantum efficiency of current commercially available green LEDs is poor. Since energy consumption is an important factor, particularly for battery-powered systems, using blue LEDs is a tradeoff. Recently, phosphor-converted green LEDs, which are pumped by highly efficient blue LEDs, have been introduced to the market, and this type of LED promises better performance. This paper compares the use of blue, green, and converted green LEDs for applications in optical underwater communication systems in coastal waters. Theoretical aspects of the overall LED-water-detector channel are presented. A method for determining individual system coefficients is developed, and the impact on the communication system performance is explained. Practical approaches are introduced, complemented by measurements in the Baltic Sea

High-rate local sea level monitoring with a GNSS-based tide gauge

We present first results from the analysis of high-rate observations with a GNSS-based tide gauge at the Onsala Space Observatory. The goal is to determine local sea level with high temporal resolution. The GNSS-based tide gauge makes use of right-hand circular polarized GNSS signals that are directly received and left-hand circular polarized GNSS signals that are reflected from the sea surface. An experimental setup of the GNSS-based tide gauge was operated in the spring of 2010 and data were recorded with a sampling rate of 20 Hz. We analyzed data decimated to 1 Hz using different temporal resolution between 5 and 240 seconds, and the resulting time series of local sea level were compared to each other and to results from two stilling well gauges. The comparison with the data from the stilling well gauges shows a common trend. The comparison of the results from analyses with different temporal resolution show consistent results. There is also an indication that the GNSS-based tide gauge might be able to give information on the sea surface state

Aristokraten und Poeten

Dieses Buch handelt von der Mentalität der Menschen, die im 12. und frühen 13. Jahrhundert im tolosanischen Okzitanien lebten. Dazu untersucht der Autor ihre sozialen Praktiken, insbesondere diejenigen der kulturellen Produktion und Konsumtion. Von grundsätzlichem Wert hierfür ist die Dechiffrierung des sprachlichen Verhaltens der tolosanischen Oberschicht, wozu J. Rüdiger vor allem die "Reden" der Trobadors analysiert und kontextualisiert. Neben der okzitanischen und mediterranen Überlieferung zieht er auch die nordische Skaldendichtung vergleichend heran. Das hier entwickelte Konzept der "Grammatik der Mentalität" eröffnet eine neue Sicht auf den nordwestlichen Mittelmeerraum und ermöglicht ein besseres Verständnis der Ereignisse des Albigenserkrieges (1209-1229). Das Werk stellt eines der bislang ganz wenigen geglückten deutschen Zeugnisse einer "histoire totale" im Sinne der Annales-Schule dar: die Rekonstruktion einer räumlich begrenzten Kultur von europäischem Rang