Role of Self-Interaction Effects in the Geometry Optimization of Small Metal Clusters

By combining the Self-Interaction Correction (SIC) with pseudopotential perturbation theory, the role of self-interaction errors inherent to the Local Density Approximation (LDA) to Density Functional Theory is estimated in the determination of ground state and low energy isomeric structures of small metallic clusters. Its application to neutral sodium clusters with 8 and 20 atoms shows that the SIC provides sizeable effects in Na_8, leading to a different ordering of the low lying isomeric states compared with ab-initio LDA predictions, whereas for Na_20, the SIC effects are less pronounced, such that a quantitative agreement is achieved between the present method and ab-initio LDA calculations.Comment: RevTeX, 4 pages, 1 figure available from [email protected]

Ein risikobasiertes Verfahren zur Sicherheitsbeurteilung von Bahnübergängen

Ausgehend von der Feststellung, dass in Deutschland bislang kein quantitatives Verfahren zur Beurteilung der Sicherheit von Bahnübergängen existiert, wurde in der vorliegenden Arbeit ein Vorschlag für ein solches Verfahren entwickelt. Das zugrunde liegende Risikomodell ermöglicht es, aus den Parametern eines einzelnen Bahnübergangs die individuellen Risiken unterschiedlicher Gruppen von Straßenverkehrsteilnehmern sowie das kollektive Risiko des Bahnübergangs abzuschätzen. Zur Bewertung dieser Risiken wurden Vorschläge für Akzeptanzkriterien hergeleitet. Ein weiterer Teil der Untersuchung beschäftigte sich mit der Ermittlung und Bewertung risikoreduzierender Maßnahmen. Das Verfahren entstand auf Basis umfangreicher Literaturstudien, qualifizierter Schätzungen und ergänzender empirischer Untersuchungen. Der Neuigkeitswert des Modells – auch vor dem Hintergrund der aus dem Ausland bekannten Ansätze – besteht in der differenzierten Betrachtung nicht nur des einzelnen Bahnübergangs, sondern auch der einzelnen Verkehrsarten und insbesondere der einzelnen zum Bahnübergang hin- und vom Bahnübergang wegführenden Verkehrsströme. Dadurch wird der Erkenntnis Rechnung getragen, dass sich die spezifischen Eigenschaften der Straßenverkehrsteilnehmer sowie der von ihnen genutzten Zu- und Abflusswege auf die Sicherheit auswirken können. Aus den erzielten Erkenntnissen wurden Empfehlungen zur Weiterentwicklung der Regelwerke abgeleitet. Hierzu gehört die Forderung nach einer stärkeren Risikoorientierung der Gestaltungsregeln, die insbesondere die aufgezeigten Einflussfaktoren berücksichtigen müssen.:Abbildungsverzeichnis 6 Tabellenverzeichnis 8 Formelzeichenverzeichnis 9 1 Einleitung 11 1.1 Ausgangssituation 11 1.2 Zielstellung 13 1.3 Abgrenzung 13 1.4 Vorgehen 14 2 Forschungsstand 16 2.1 Risikomodelle 16 2.1.1 Deutschland 16 2.1.2 Europäisches Ausland 21 2.1.3 Nordamerika 26 2.1.4 Asien und Australien 29 2.1.5 Schlussfolgerungen 32 2.2 Verhaltensmodelle 35 2.2.1 Anlagen 35 2.2.2 Abläufe 36 2.2.3 Fehler 38 2.2.4 Schlussfolgerungen 41 2.3 Risikoschwerpunkte 42 2.3.1 Verkehrsarten 43 2.3.2 Unfallsituationen 44 2.3.3 Unfallursachen 45 2.3.4 Schlussfolgerungen 47 3 Systemdefinition 49 3.1 Bahnübergangsanlagen 49 3.2 Straßenverkehrsteilnehmer 52 4 Risikoanalyse 55 4.1 Grundlagen 55 4.2 Entscheidungsbereich 60 4.2.1 Aussetzung 60 4.2.2 Gefährdung 72 4.2.3 Unabwendbarkeit 96 4.2.4 Schadensausmaß 103 4.3 Räumungsbereich 113 4.3.1 Aussetzung 113 4.3.2 Gefährdung 114 4.3.3 Unabwendbarkeit 116 4.3.4 Schadensausmaß 118 4.4 Zusammenfassung 119 5 Risikobewertung 120 5.1 Grundlagen 120 5.2 Methoden 120 5.3 Anwendung 123 5.3.1 Individuelles Risiko 123 5.3.2 Kollektives Risiko 124 5.4 Zusammenfassung 125 6 Risikobeherrschung 127 6.1 Grundlagen 127 6.2 Entscheidungsbereich 128 6.2.1 Aussetzung 128 6.2.2 Gefährdung 129 6.2.3 Unabwendbarkeit 134 6.2.4 Schadensausmaß 134 6.3 Räumungsbereich 135 6.3.1 Aussetzung 135 6.3.2 Gefährdung 135 6.3.3 Unabwendbarkeit 136 6.3.4 Schadensausmaß 136 6.4 Zusammenfassung 137 7 Gesamtverfahren 138 7.1 Ablauf 138 7.2 Plausibilitätsprüfung 139 7.3 Sensitivitätsanalyse 143 7.3.1 Ausgangsszenarien 143 7.3.2 Schienenfahrzeuglänge 144 7.3.3 Schienenfahrzeuggeschwindigkeit 145 7.3.4 Schienenverkehrsstärke 146 7.3.5 Vorsperrzeit 147 7.3.6. Straßenverkehrsstärke 148 7.3.7 Kreuzungswinkel 150 7.3.8 Straßengeschwindigkeiten 151 7.3.9 Sicherungsart 152 7.3.10 Gefährdungsfaktoren 153 7.3.11 Sichtverhältnisse I 154 7.3.12 Sichtverhältnisse II 155 7.3.13 Räumungsprobleme 156 7.3.14 Schlussfolgerungen 157 7.4 Anwendungsbeispiele 158 7.4.1 Beispiel 1 158 7.4.2 Beispiel 2 162 7.4.3 Beispiel 3 165 8 Empfehlungen 170 8.1 Überblick 170 8.2 EBO 171 8.3 DB-Richtlinie 815 173 8.4 BÜV-NE 174 8.5 StVO 175 8.6 VwV-StVO 176 9 Zusammenfassung und Ausblick 177 9.1 Zusammenfassung 177 9.2 Ausblick 180 Quellenverzeichnis 184 Glossar 199 Anhang 20

Reconstruction of Atlantic herring (Clupea harengus) recruitment in the North Sea for the past 455 years based on the δ13C from annual shell increments of the ocean quahog (Arctica islandica)

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this recordnderstanding the recruitment variability of the Atlantic herring North Sea stock remains a key objective of stock assessment and management. Although many efforts have been undertaken linking climatic and stock dynamic factors to herring recruitment, no major attempt has been made to estimate recruitment levels before the 20th century. Here, we present a novel annually resolved, absolutely dated herring recruitment reconstruction, derived from stable carbon isotope geochemistry (δ13C), from ocean quahog shells from the Fladen Ground (northern North Sea). Our age model is based on a growth increment chronology obtained from fourteen shells. Ten of these were micromilled at annual resolution for δ13C analysis. Our results indicate that the anthropogenically driven relative depletion of 13C, the oceanic Suess effect (oSE), became evident in the northern North Sea in the 1850s. We calculated a regression line between the oSE‐detrended δ13C results (δ13CṠ) and diatom abundance in the North Sea, the regression being mediated by the effect of phytoplankton on the δ13C of the ambient dissolved inorganic carbon. We used this regression to build an equation mediated by a nutritional link to reconstruct herring recruitment using δ13CṠ. The reconstruction suggests that there were five extended episodes of low‐recruitment levels before the 20th century. These results are supported by measured recruitment estimates and historical fish catch and export documentation. This work demonstrates that molluscan sclerochronological records can contribute to the investigation of ecological baselines and ecosystem functioning impacted by anthropogenic activity with implications for conservation and stock management.Natural Environment Research Council (NERC)FP7 People: Marie‐Curie Action

GPS water level measurements for Indonesia's Tsunami Early Warning System

On Boxing Day 2004, a severe tsunami was generated by a strong earthquake in Northern Sumatra causing a large number of casualties. At this time, neither an offshore buoy network was in place to measure tsunami waves, nor a system to disseminate tsunami warnings to local governmental entities. Since then, buoys have been developed by Indonesia and Germany, complemented by NOAA's Deep-ocean Assessment and Reporting of Tsunamis (DART) buoys, and have been moored offshore Sumatra and Java. The suite of sensors for offshore tsunami detection in Indonesia has been advanced by adding GPS technology for water level measurements. <br><br> The usage of GPS buoys in tsunami warning systems is a relatively new approach. The concept of the German Indonesian Tsunami Early Warning System (GITEWS) (Rudloff et al., 2009) combines GPS technology and ocean bottom pressure (OBP) measurements. Especially for near-field installations where the seismic noise may deteriorate the OBP data, GPS-derived sea level heights provide additional information. <br><br> The GPS buoy technology is precise enough to detect medium to large tsunamis of amplitudes larger than 10 cm. The analysis presented here suggests that for about 68% of the time, tsunamis larger than 5 cm may be detectable

Life history, environment and extinction of the scallop Carolinapecten eboreus (Conrad) in the Plio-Pleistocene of the U.S. eastern seaboard.

Plio-Pleistocene mass extinction of marine bivalves on the U.S. eastern seaboard has been attributed to declines in temperature and primary production. We investigate the relationship of growth rate in the scallop Carolinapecten eboreus to variation in these parameters to determine which contributed to its extinction. We use ontogenetic profiles of shell d18O to estimate growth rate and seasonal temperature, microgrowth-increment data to validate d18O-based figures for growth rate, and shell d13C to supplement assemblage evidence of production. Postlarval growth started in the spring/summer in individuals from the Middle Atlantic Coastal Plain but in the autumn/winter in some from the Gulf Coastal Plain. Growth rate typically declined with age and was usually higher in summer than winter. Many individuals died in winter but the largest forms typically died in spring, possibly on spawning for the first time. No individuals lived longer than two years and some grew exceedingly fast overall, up to 60% more rapidly than any other scallop species (, 145.7 mm in a year). Faster growth was generally achieved by secreting more rather than larger microgrowth increments. Some very fast-growing individuals lived in settings of high production and low temperature. No individuals grew slowly under high production whereas most if not all grew slowly under ‘average’ production and low temperature. In that the rapid growth evidently enabled by high production would have afforded protection from predators, Plio-Pleistocene decline in production was probably contributory to the extinction of C. eboreus. However, the negative impact of low temperature on growth under ‘average’ production suggests that temperature decline played some part.British Geological Survey (BUFI S157), NERC Isotope Goscience Facilities (IP-1351-1112), University of Derby (Research-Inspired Curriculum Fund

Time-dependent screening of a positive charge distribution in metals: Excitons on an ultra-short time scale

Experiments determining the lifetime of excited electrons in crystalline copper reveal states which cannot be interpreted as Bloch states [S. Ogawa {\it et al.}, Phys. Rev. B {\bf 55}, 10869 (1997)]. In this article we propose a model which explains these states as transient excitonic states in metals. The physical background of transient excitons is the finite time a system needs to react to an external perturbation, in other words, the time which is needed to build up a polarization cloud. This process can be probed with modern ultra-short laser pulses. We calculate the time-dependent density-response function within the jellium model and for real Cu. From this knowledge it is possible within linear response theory to calculate the time needed to screen a positive charge distribution and -- on top of this -- to determine excitonic binding energies. Our results lead to the interpretation of the experimentally detected states as transient excitonic states.Comment: 24 pages, 9 figures, to appear in Phys. Rev. B, Nov. 15, 2000, issue 2

Anti-predation strategy, growth rate and extinction amongst Pliocene scallops of the US eastern seaboard

Placopecten, Chesapecten and Carolinapecten are scallop (pectinid bivalve) genera occurring in the Pliocene of the US eastern seaboard. The first, present in the area today, is a smooth, streamlined form, adept at escaping predators by swimming (‘flight’ strategy). The other two, which are extinct, are plicate (‘ribbed’) forms. Plication facilitates a ‘resistance’ strategy towards predators which is benefited by large size and high shell thickness - maximally so if these states are achieved early in life. Oxygen isotope profiles show that early ontogenetic extensional growth in Pliocene Placopecten was at the same moderate rate as in modern Placopecten. By contrast, in Chesapecten it was as fast as in the fastest-growing modern scallop (c. 80 mm/annum), and accompanied by development of an unusually thick shell, while in Carolinapecten it was substantially faster still (<150 mm/annum). Rapid growth in Chesapecten and Carolinapecten was probably enabled by high primary productivity, for which there is evidence from sediment composition and the associated biota. The extinction of Chesapecten and Carolinapecten, and the survival of Placopecten, can be attributed to a decline in primary productivity which prevented a maximally effective ‘resistance’ strategy towards predators but had no deleterious impact on a ‘flight’ strategy.British Geological Survey (BUFI S157

The use of seasonally resolved temperature data to identify the cause of marine climate change

On the continental shelf of the eastern USA, seasonal variation in water temperature is much lower south of Cape Hatteras than it is to the north as a result of the influence of warm currents, which raise winter temperature. High temperatures north of Cape Hatteras during the Pliocene have been attributed to greater northward penetration of warm currents in the absence of a feature analogous to Cape Hatteras. However, oxygen isotope thermometry using serial ontogenetic samples from scallops reveals a high seasonal temperature range at some horizons, suggesting that overall warming was the consequence of general climate change, with the absence of a ‘Cape Hatteras’ feature allowing greater southward penetration of cold currents, resulting in low winter temperatures at a southerly latitude. Evidence from other taxa indicates that at times seasonal variation in water temperature was quite low and that there was greater northward penetration of warm currents. This may relate to increases in vigour of the Gulf Stream. The study shows how seasonally resolved temperature data can assist identification of the driving forces of marine climate change.British Geological Survey (BUFI S157

Isotopic temperatures from the early and mid-pliocene of the US Middle Atlantic coastal plain, and their implications for the cause of regional marine climate change

Mean seasonal extreme temperatures on the seafloor calculated from the shell δ18O of the scallop Placopecten clintonius from the basal part of the early Pliocene Sunken Meadow Member (Yorktown Formation) in Virginia are very similar to those from the same horizon at the latitude of Cape Hatteras in North Carolina (~210 km to the south). The lowest and highest temperatures calculated from each shell (using δ18Oseawater = +0.7‰) give mean values for winter and summer of 8.4 ± 1.1 °C (± 1σ) and 18.2 ± 0.6 °C in Virginia, and 8.6 ± 0.4 °C and 16.5 ± 1.1 °C in North Carolina (respective median temperatures: 13.3 °C and 12.6 °C). Patterns of ontogenetic variation in δ18O, δ13C and microgrowth increment size indicate summer water-column stratification in both areas, with summer surface temperatures perhaps 6 °C higher than on the seafloor. The low winter paleotemperatures in both areas are most simply explained by the greater southward penetration of cool northern waters in the absence of a feature equivalent to Cape Hatteras. The same current configuration but a warmer general climate can account for the high benthic seasonal range (over 15.0 °C in some cases) but warmer median temperatures (15.7-21.3 °C) derived from existing δ18O data from scallops of the higher Yorktown Formation (using δ18Oseawater = +0.7‰ for the upper Sunken Meadow Member and δ18Oseawater = +1.1‰ for the mid-Pliocene Rushmere, Morgarts Beach and Moore House members). Existing δ18O data from the infaunal bivalve Mercenaria of the Rushmere Member yields a similarly high median temperature (21.6 °C) but a low seasonal range (9.2 °C), pointing to the periodic influence of warm currents, possibly at times when the Gulf Stream was exceptionally vigorous.British Geological Survey (BUFI S157 Studentship); UoD Research-Inspired Curriculum Fun