Die Baumkronenspinnen (Araneae) des Leipziger Auwaldes

The canopy spiders of the floodplain forest in Leipzig have become a focus of ecological studies in recent years. In 2006 we sampled 30 tree canopies in the ‘Burgaue’ nature reserve with pyrethrum knock-down fogging, recording 502 adult spiders belonging to 48 species and 11 families. Based on these data and the results of a previous fogging study, the studied spider community was dominated by forest and forest-edge species with a preference for the shrub and canopy strata as well as by spiders of the web spider feeding guild. The community structure was typical for arboreal spider communities from northern temperate forests but very different from communities in the tropics. Species richness and evenness were similar to the old growth near-primary Białowieża Forest in Poland. The checklist of 96 canopy spider species of the floodplain forest of Leipzig includes 54 additions to the spider fauna of Leipzig and vicinity by recent canopy studies and eight first canopy records for Leipzig from our field work. The theridiid Dipoena torva (Thorell, 1875) was recorded for the first time in Saxony. The floodplain forest of Leipzig sustains a large and species-rich arboreal spider community and is thus a valuable habitat for a large proportion of endangered species (12%).Die Spinnen der Baumkronen des Leipziger Auwaldes wurden in den vergangenen Jahren ein Schwerpunkt ökologischer Forschung. Im Jahr 2006 untersuchten wir 30 Baumkronen im Naturschutzgebiet „Burgaue“ mithilfe der Insektizid-Baumkronenbenebelung und erhielten dabei 502 adulte Spinnen aus 48 Arten und 11 Familien. Basierend auf diesen Daten und Ergebnissen einer früheren Benebelungsstudie fanden wir, dass die untersuchte Spinnengemeinschaft von Wald- und Waldrandarten mit Präferenz für die Strauch- und Kronenschicht dominiert war. Auf Gildenniveau dominierten die Netzspinnen. Die Gemeinschaftsstruktur war typisch für eine arboreale Spinnengemeinschaft der nördlichen temperaten Wälder aber sehr verschieden von Gemeinschaften in den Tropen. Artenvielfalt und Evenness waren ähnlich dem Urwald von Białowieża in Polen. Aufgrund der Baumkronenforschungen in Leipzig beinhaltet die Baumkronen-Checkliste der 96 Spinnenarten des Leipziger Auwaldes 54 Erstnachweise für Leipzig und Umgebung. Acht Arten wurden erstmals durch unsere neuen Feldarbeiten in Leipzig nachgewiesen, die Kugelspinne Dipoena torva (Thorell, 1875) dabei erstmals in Sachsen. Der Leipziger Auwald beherbergt eine große und artenreiche arboreale Spinnengemeinschaft und ist ein wertvolles Habitat für einen großen Anteil gefährdeter Arten (12 %)

Assisted Vacuum Decay by Time Dependent Electric Fields

We consider the vacuum decay by electron-positron pair production in spatially homogeneous, time dependent electric fields by means of quantum kinetic equations. Our focus is on the impact of various pulse shapes as envelopes of oscillating fields and the assistance effects in multi-scale fields, which are also seen in photons accompanying the creation and motion of pairs.Comment: 9 pages, 7 figure

Surface Plasmons and Topological Insulators

We study surface plasmons localized on interfaces between topologically trivial and topologically non-trivial time reversal invariant materials in three dimensions. For the interface between a metal and a topological insulator the magnetic polarization of the surface plasmon is rotated out of the plane of the interface; this effect should be experimentally observable by exciting the surface plasmon with polarized light. More interestingly, we argue that the same effect also is realized on the interface between vacuum and a doped topological insulator with non-vanishing bulk carrier density.Comment: 6 pages, 1 figure; v2: typo in eq. (27) correcte

Technological Uncertainty and Cost-effectiveness of CO2 Emission Trading Schemes

This paper studies implications of uncertainty about the arrival date of a competitive CO2 backstop technology for the design of cost-effective CO2 emission trading schemes. For this purpose, we develop a dynamic general equilibrium model that captures empirical links between CO2 emissions associated with energy use, the rate and direction of technical change and the economy. We specify CO2 capture and storage (CCS) as the backstop technology whose competitiveness is anticipated or not. We find that the discounted welfare loss associated with the environmental target is lower if CCS is not anticipated and that CO2 shadow prices are then relatively high in the years before CCS is competitive. By not simply postponing the implementation of an emission reduction strategy until CCS is competitive, one relies more on economy-wide technical change and its welfare-enhancing technology externalities, thus allowing for a higher steady state. -- Dieses Papier untersucht die Implikationen von Unsicherheit bezüglich der Verfügbarkeit einer kompetitiven Technologie zur Kohlenstoffabscheidung und ?speicherung auf die Ausgestaltung kosteneffektiver CO2 Emissionshandelssysteme. Zu diesem Zweck wird ein dynamisches rechenbares allgemeines Gleichgewichtsmodell entwickelt, welches den empirischen Zusammenhang zwischen CO2 Emissionen, Rate und Richtung des technischen Wandels und wirtschaftlichen Aktivitäten berücksichtigt. Kohlenstoffabscheidung und ?speicherung wird als sogenannte Backstop-Technologie modelliert, deren Wirtschaftlichkeit antizipiert wird oder eben nicht. Die Simulationsergebnisse zeigen, dass die diskontierten Wohlfahrtsverluste der Klimapolitik niedriger sind, wenn die Technologie zur Kohlenstoffabscheidung und ?speicherung nicht antizipiert wird. In diesem Fall sind die Preise für CO2 Emissionszertifikate vor der unerwarteten Einführung der Backstop-Technologie relativ hoch. Es wird nicht einfach auf die Wirtschaftlichkeit der Kohlenstoffabscheidung und ? speicherung gewartet. Vielmehr wird ohne die Berücksichtigung von Kohlenstoffabscheidung und ? speicherung ein strikterer Politikpfad zur Erreichung der klimapolitischen Ziele implementiert, der die Internalisierung von technologischen Externalitäten und somit ein höheres Wohlfahrtsniveau ermöglicht. Die Umweltpolitik sollte gegeben der großen technologischen Unsicherheiten vorsichtig sein, Vermeidungsanstrengungen zu verschieben und auf eine Wunderwaffe zu Lösung des Klimaproblems im Energiesektor zu warten.CO2 capture and storage,computable general equilibrium modeling,directed technical change,emission trading,technological uncertainty

On the Limitations of the Color Dipole Picture

We discuss two aspects of the color dipole picture of high energy photon-proton scattering. First we present bounds on various ratios of deep inelastic structure functions resulting from the dipole picture that, together with the measured data, can be used to restrict the kinematical range of its applicability. The second issue that we address is the choice of energy variable in the dipole-proton cross section.Comment: 6 pages; talk presented by C.E. at 12th International Conference on Elastic and Diffractive Scattering (EDS07), DESY Hamburg, May 200

Energy Biased Technical Change: A CGE Analysis

This paper studies energy bias in technical change. For this purpose, we develop a computable general equilibrium model that builds on endogenous growth models. The model explicitly captures links between energy, the rate and direction of technical change, and the economy. We derive the equilibrium determinants of biased technical change and show the importance of feedback in technical change, substitution possibilities between final goods, and general-equilibrium effects for the equilibrium bias. If the feedback effect is strong, or the substitution elasticity large, or both, our model tends to a corner solution in which only technologies are developed that are appropriate for production of non-energy intensive goods.Computable general-equilibrium models, Endogenous technical change, Energy, Environment

Directed Technical Change and Climate Policy

This paper studies the cost effectiveness of climate policy if there are technology externalities. For this purpose, we develop a forward-looking CGE model that captures empirical links between CO2 emissions associated with energy use, directed technical change and the economy. We find the cost-effective climate policy to include a combination of R&D subsidies and CO2 emission constraints, although R&D subsidies raise the shadow value of the CO2 constraint (i.e. CO2 price) because of a strong rebound effect from stimulating innovation. Furthermore, we find that CO2 constraints differentiated toward CO2-intensive sectors are more cost effective than constraints that generate uniform CO2 prices among sectors. Differentiated CO2 prices, through technical change and concomitant technology externalities, encourage growth in the non-CO2 intensive sectors and discourage growth in CO2-intensive sectors. Thus, it is cost effective to let the latter bear relatively more of the abatement burden. This result is robust to whether emission constraints, R&D subsidies or combinations of both are used to reduce CO2 emissions.Directed Technical Change, Climate Policy, Computable General Equilibrium Model, R&D

Present Status of Organic Fruit Growing in Europe

Organic fruit growing in Europe has experienced remarkable growth rates since the mid 1990's. Southern states, especially Italy, Spain and France have the largest land area with organic fruit, are also growing olives, citrus and chestnuts. Mainly increasing interest of supermarket chains is responsible for this buoyancy, but also the availability of better plant protection products e.g. granulosis virus and mating disruption against codling moth, and Neem oil against Rosy Apple Aphid. State subsidies varying from 600 to more than 1600 Euro /ha/y in the EU-countries (15) are less decisive for the conversion of top fruit production. Market share of organic table fruit is only 1 to 2 %, reaching 4 to 5 % in Switzerland. For Switzerland, we estimate a market potential of around 12 to 15 %, which is already achieved with organic vegetables. In order to reach that percentage, better solutions for several key problems have to be found, e.g. control of scab, fire blight, sooty blotch, brown rot, weed management, fertilisation and crop load regulation. Also the assortment of organically produced “modern-standard” varieties is not satisfactory, in particular with stone fruit. The economics of organic fruit growing is comparatively healthy, however, it depends on receiving a one third higher farm gate price for the product. In Switzerland the benefit of organic orchards is 16 % higher compared to integrated fruit production; but labour hours exceed those of IFP by 7%, due to blossom thinning by hand, manual weed control and mice control. Supermarkets have a tendency to just “substitute” conventional with organic fruit if requiring organic fruit from disease susceptible varieties with no cosmetic blemishes. This can/does feed back to the growers resulting in “substitutional” production with disease and pest sensitive orchards managed with intensive “organic” spray and fertilisation programs. This certainly does not correspond with either the original concept of organic farming or with expectations of organic consumers. Thus, still a lot of development - also on the marketing side - has to be undertaken