Empfehlungen zum Gebrauch einheitlicher Halbwertzeiten einiger wichtiger Radionuklide

The present work represents the results of angular distribution measurements performed for promt gamma-rays in the range of 1.1 … 1.2. MeV due to the ²³³U(n, f) and ²³⁹Pu(n,f) reactions. The measurements yielded anisotropy values found to be consistent with values previously measured and using the same technique at different gamma energy bands. Such consistency, also found to exist between anisotropy values previously measured for the ²³⁵U(n,f) reaction, is a strong evidence about the energy independence of the anisotropy and indicates that the gamma spectra (at 180° and 90° to the fission direction) are essentially the same. The average values of the fragment angular momentum were calculated according to Strutinsky and Nix-Swiatecki theories. It was found that the values of the average angular momentum calculated for ²³⁴U, ²³⁶U and ²⁴⁰Pu according to Strutinsky,s formula (at different gamma energy bands) are consistent and yield average values which are in good agreement with those obtained from direct measurements.     

Ein tragbares Kontrollgerät fÜr α-Oberflächenkontaminationen

Es wird ein volltransistorisiertes, tragbares Gerät zur Bestimmung von a-Oberflächenkontaminationen beschrieben, welches mit 7 Proportionahählrohren VA-Z-520 arbeitet. Ein mechanisches Zählwerk dient zur Verbesserung der Anzeige bei kleinen Aktivitätswerten, bei gröβeren erfolgt diese durch ein Ratemeter. Die laut Strahlenschutzverordnung zulässigen α-Oberflächenkontaminationen können mit diesem Gerät kontrolliert werden. Die Kalibrierung wurde mit Hilfe eines ²³⁹Pu-Standardflächenpräparates ausgeführt. Das Gerät ist auβerdem für β-γ-Messungen geeignet. Hierzu wird lediglich der Zählrohrteil der Sonde gegen den β-γ-Kopf mit 7 Stück VA-Z-310 ausgetauscht.     

Isotopengeochemisches Kompartimentmodell des Stickstoffkreislaufs

Es wird ein Modell des globalen Kreislaufs des Stickstoffs und seiner Isotope beschrieben, das die folgenden geochemischen Reservoire berücksichtigt: Stickstoff in Magmatiten, Stickstoff in Metamorphiten, Stickstoff in Sedimentiten und Stickstoff der Atmosphäre. Das Modell berücksichtigt den Stickstoffaustausch zwischen Magmatiten und dem Oberen Mantel, den Übergang des Stickstoffs aus Magmatiten und Metamorphiten in die Atmosphäre und den Stickstoffaustausch zwischen Sedimentiten und der Atmosphäre und andere geochemische Prozesse.

Auf der Grundlage aller gegenwärtig zugänglichen δ¹⁵N-Werte magmatischer, metamorpher und sedimentärer Gesteine und plausibler Annahmen über die Isotopieeffekte, die bei der Bildung dieser Stickstoffflüsse wirken, werden – unter Benutzung des mathematischen Formalismus der Kompartimenttheorie – quantitative Aussagen abgeleitet über das Ausmaß des Stickstoffaustausches zwischen der Erdkruste und dem Oberen Mantel und über andere Stickstoffflüsse, die den globalen Stickstoffkreislauf charakterisieren.     

Characterising ontogenetic niche shifts in Nile crocodile using stable isotope (δ13C, δ15N) analyses of scute keratin

Nile crocodiles undergo a three to five order of magnitude increase in body size during their lifespan. This shift coincides with a change in resource and habitat use which influences the strength, type and symmetry of interactions with other species. Identifying size-specific crocodile groups displaying similar traits is important for conservation planning. Here, we illustrate how stable carbon (δ¹³ C) and nitrogen (δ¹⁵ N) isotope analysis of scute keratin, together with breakpoint modelling analysis can be used to characterise ontogenetic niche shifts. Using a sample set of 238 crocodiles from the Okavango Delta, Botswana (35–463 cm total length), we found prominent size-related changes in the scute keratin δ¹³ C and δ¹⁵ N profiles close to 40 and 119 cm snout-vent length. The first shift corroborated the findings of a traditional stomach-content study conducted on the same population at the same time, and the second conformed to known crocodile ecology. This approach can be used as a first approximation to identify size-specific groups within crocodile populations, and these can then be investigated further using isotopic or other methods.     

Theoretische Aspekte der Untersuchung des Stickstoffmetabolismus mit 15N beim Menschen II. Probleme der Auswertung und Interpretation klinischer Untersuchungen

Klinische Untersuchungen zum menschlichen Stickstoffmetabolismus, die unter Verwendung des stabilen Stickstoffisotops ¹⁵N durchgeführt wurden, werden mit Hilfe eines 3-Compartmentmodells ausgewertet und interpretiert. Möglichkeiten zur Erweiterung dieses Modells werden diskutiert, und durch Computerstudien wird die Aussagekraft der aus Modellen gewonnenen Resultate überprüft.     

Stability analysis of a multi-phase car-following model

This paper presents a numerical stability analysis of a multi-phase car-following model under mild to severe disturbances. The results show that local stability was always conformed. An asymptotically unstable region was found for traffic in congested states. One of the previously calibrated boundary conditions for close-following situations was found to be in conflict with the stable condition required by the car-following model, which had attributed to speed oscillations during transition of the traffic from a non-congested to a congested state. Suggestions were made to the choice of model parameter values to meet the stability conditions and ways to improve the model.     

Unified scaling law in the coherent noise model

The waiting time distribution between successive events and the unified scaling law is studied using the coherent noise model. It is shown that, although this model generates uncorrelated event sizes and does not exhibit criticality, it still provides the unified scaling law. We argue the role of characteristic kink observed in the unified scaling law and the meaning of the parameter C$C$ used to fix the peak of the kink to unity. Our results indicate that the parameter C$C$ is indeed a physical quantity localizing the end of the linear tendency in the scaling law, which corresponds to the completion of the dominance of correlated events in time.     

Clustering of financial time series

This paper addresses the topic of classifying financial time series in a fuzzy framework proposing two fuzzy clustering models both based on GARCH models. In general clustering of financial time series, due to their peculiar features, needs the definition of suitable distance measures. At this aim, the first fuzzy clustering model exploits the autoregressive representation of GARCH models and employs, in the framework of a partitioning around medoids algorithm, the classical autoregressive metric. The second fuzzy clustering model, also based on partitioning around medoids algorithm, uses the Caiado distance, a Mahalanobis-like distance, based on estimated GARCH parameters and covariances that takes into account the information about the volatility structure of time series. In order to illustrate the merits of the proposed fuzzy approaches an application to the problem of classifying 29 time series of Euro exchange rates against international currencies is presented and discussed, also comparing the fuzzy models with their crisp version.     

Empirical scaling laws and the aggregation of non-stationary data

Widely cited evidence for scaling (self-similarity) of the returns of stocks and other securities is inconsistent with virtually all currently-used models for price movements. In particular, state-of-the-art models provide for ubiquitous, irregular, and oftentimes high-frequency fluctuations in volatility (“stochastic volatility”), both intraday and across the days, weeks, and years over which data is aggregated in demonstrations of self-similarity of returns. Stochastic volatility renders these models, which are based on variants and generalizations of random walks, incompatible with self-similarity. We show here that empirical evidence for self-similarity does not actually contradict the analytic lack of self-similarity in these models. The resolution of the mismatch between models and data can be traced to a statistical consequence of aggregating large amounts of non-stationary data.