The Markoff-Automaton - a New Algorithm for Simulating the Time--Evolution of Large Stochastic Dynamic Systems

We describe a new algorithm for simulating complex Markoff-processes. We have used a reaction-cell method in order to simulate arbitrary reactions. It can be used for any kind of RDS on arbitrary topologies, including fractal dimensions or configurations not being related to any spatial geometry. The events within a single cell are managed by an event handler which has been implemented independently of the system studied. The method is exact on the Markoff level including the correct treatment of finite numbers of molecules. To demonstrate its properties, we apply it on a very simple reaction-diffusion-systems (RDS). The chemical equations A+A -> inert and A+B -> inert in 1 to 4 dimensions serve as models for systems whose dynamics on an intermediate time scale are governed by fluctuations. We compare our results to the analytic approach by the scaling ansatz. The simulations confirm the exponents of the A+B system within statistical errors, including the logarithmic corrections in the dimension d=2. The method is capable to simulate the crossover from the reaction to diffusion limited regime, which is defined by a crossover time depending on the system size.Comment: 29 Pages, uuencoded, compressed Dvi file, 89kB. pictures included as uuencoded, compressed tar file, 32 Kb full postscript version (191KB) available at http://summa.physik.hu-berlin.de:80/papers/ThomasFricke/rdcompphys.ps.

Homodyne detection for laser-interferometric gravitational wave detectors

Gravitational waves are ripples of space-time predicted by Einstein\u27s theory of General Relativity. The Laser Interferometer Gravitational-wave Observatory (LIGO), part of a global network of gravitational wave detectors, seeks to detect these waves and study their sources. The LIGO detectors were upgraded in 2008 with the dual goals of increasing the sensitivity (and likelihood of detection) and proving techniques for Advanced LIGO, a major upgrade currently underway. As part of this upgrade, the signal extraction technique was changed from a heterodyne scheme to a form of homodyne detection called DC readout. The DC readout system includes a new optical filter cavity, the output mode cleaner, which removes unwanted optical fields at the interferometer output port. This work describes the implementation and characterization of the new DC readout system and output mode cleaner, including the achieved sensitivity, noise couplings, and servo control systems

Raumbezogene und multivariate Analyse der Einflussgrößen auf den Weißkleeanteil eines Dauergrünlandstandortes

The relationship between white clover (Trifolium repens), site conditions, species composition and forage quality has been analysed by conducting a factor analysis (incl. varimax rotation) based on data sets sampled along a 50 m grid on a 20 ha permanent grassland site in Central Germany with heterogeneous site conditions, sown in 1998. Three factors which are related to the appearance of white clover has been interpreted, showing a positive relationship of white clover to (A) Lolium perenne on heavy and productive soils, (B) Poa pratensis and Festuca rubra on heavy and stony soils at slopes and ridges and (C) Lolium perenne and weeds on wet soils along the field border, often characterised by sward damage. The white clover factor loadings sometimes are not very strong, depending on complex interactions and a distinct site heterogeneity. Further analysis is in progress

Abschätzung von Bestandeseigenschaften in Leguminosengras-Gemengen mit nichtdestruktiven Methoden

To describe spatial heterogeneity of crop properties, non-destructive methods can be helpful in capturing whole field data sets. This paper shows examples of different sensor methods that have been evaluated to measure biomass and legume content in legume-grass mixtures. Biomass has been estimated using vegetation indices (NDVI, SR, EVI and REIP) calculated from spectral reflectance measurements in greenhouse experiments. The index REIP has been used to identify species composition as well. Furthermore, biomass values can be derived from ultra sonic measurements of sward heights. To quantify legume contents in short term leys, which is important for forage quality and nitrogen flows, image analysis tools have been used in different experi-ments with good results. These examples indicate a hopeful perspective to estimate biomass and species composition. However, the structural and functional complexity of legume-grass mixtures requires adapted methods to specific crop characteristics like e.g. predefinition of legume species

Entwicklung einer bildanalytischen Methode zur Abschätzung des Leguminosenanteils in Futterbaugemengen

A pot experiment in a greenhouse was conducted to follow the question how to esti-mate dominance of legumes in legume/grass swards by image analysis. Pure swards and binary legume/grass mixtures of red clover, white clover, lucerne and perennial ryegrass were sown in two week intervals and harvested together 35, 49 or 63 days after sowing to have different old swards. Digital photos of all variants were taken one day before harvesting. Sward composition was detected by fractionating biomass in grass, legumes and unsown species as reference. Eight images of the oldest swards were selected for determining an optimal image analysis procedure with Optimas®. This image analysis procedure was used for all variants of all ages. The estimated dominances of legumes were compared to the references. Using image analysis for estimating the dominance of legumes we could detect first good results. Red and white clover both pure and mixtures show a closer relationship with the reference than lucerne and grass. Legumes identification in pure grass swards with image analysis can be caused by weeds with rounded leaves (Stel-laria media) and visible ground. The dominance of lucerne determined by image analysis was lower then the measured dry matter yield (%). The younger the swards the more inexactly are the calculations because the visible ground increases. Next intended steps are verifying a relationship for swards of different ages and checking further procedures of image analysis

Strategien zur standortspezifischen Grünlandansaat - Retrospektive Analyse von Selektionskriterien

Um Hinweise für eine verbesserte Standortanpassung und damit effizientere Gestaltung von Grünlandansaaten zu erreichen, wurde eine 20 ha große Grünlandfläche mit sehr heterogenen Standorteigenschaften 5 Jahre nach Ansaat untersucht. Im Jahr 2003 erfolgte die Erhebung des Arteninventars und zahlreicher Standortfaktoren an 300 Messpunkten. Zusammen mit bereits vorliegenden Daten erfolgte eine statistische und räumliche Analyse, inwieweit das Vorkommen der angesäten Arten mit der Ausprägung bestimmter Lebensbedingungen in Beziehung steht. Kontinuierliche Beziehungen zwischen einzelnen oder mehreren Standortfaktoren und der Zusammensetzung der Grünlandvegetation bzw. des Auftretens einzelner Arten konnten nicht oder in nur sehr schwacher Form ermittelt werden. Vielmehr wurden eher strikte Grenzen von Standorteigenschaften wie z.B. Nährstoffgehalten ermittelt, jenseits derer sich eine Art in ihrem Vorkommen deutlich unterscheiden ließ. So traten der Rotschwingel (Festuca rubra) und die Wiesenrispe (Poa pratensis) in feuchten bis sehr feuchten und in tonigen beschatteten Bereichen sowie auf einem ausgedehnten Nordhang nicht oder nur in sehr geringen Anteilen auf. Die betroffenen Flächen umfassten beim Rotschwingel ca. 6 ha und bei der Wiesenrispe ca. 4 ha. Dieses Ergebnis führt zu der Frage, ob auf diesen Teilflächen in einer Ansaatmischung auf die genannten Arten hätte verzichtet werden können. Die erzielten Ergebnisse bestätigen die Hypothese, dass eine standortangepasste teilflächenspezifisch durchgeführte Ansaat sinnvoll ist und auch zu einer Ersparnis von Saatgut und damit Kosten führen kann. Für die Entwicklung von teilflächenspezifischen Ansaatempfehlungen sind aber noch zahlreiche Untersuchungen auf anderen Standorten unter verschiedensten Bewirtschaftungssystemen notwendig. Vorerst bleibt daher die Strategie, den Mischungsempfehlungen der Landesinstutionen zu folgen und vor allem eine angepasste Pflege, Nutzung und Düngung durchzuführen, um eine produktive und stabile Grünlandnarbe zu erhalten. Individuelle Anpassungen der Saatstärke einzelner Arten sind in einem begrenzten Rahmen möglich. Hierzu wurden eine Zusammenstellung der Standardmischungen in Deutschland sowie Hinweise zur Ansaatgestaltung mit der Möglichkeit einer einfachen teilflächenspezifischen Anpassung erstellt

“From sweet potatoes to God Almighty”: Roy Rappaport on being a hedgehog

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71618/1/ae.2007.34.3.581.pd