Die richtige Vorstellung vom elektrischen Strom

Die für elektrische Stromkreise verbreitete Wasserkreisanalogie wird mit deren Anschaulichkeit erklärt. Respektive Ursache und Wirkung entsprechen Ladung, Spannung und Stromstärke im elektrischen System hier Volumen, Druckdifferenz und Volumenstrom. Den drei elementaren Baugliedern Widerstand, Kondensator und Spule stehen lediglich Rohrleitung und Behälter gegenüber. Ein analoges Element zur Spule, welche Energie im magnetischen Feld speichert, fehlt. Mit bewegten Ladungen verbundene magnetische Felder bleiben unberücksichtigt. Die Analogie Kondensator-Wasserbehälter ist zumindest hinsichtlich der Kräfte zwischen den Platten fragwürdig, da auch elektrische Felder im Modell nicht berücksichtigt werden. Überhaupt kann eine Wasserkreisanalogie auf dem Fundament von positiven und negativen Ladungen nicht aufsetzen. Der Wasserkreisanalogie wird eine multimediale "Bottom up" Strategie ausgehend von beiden Ladungssorten und ihren Feldern gegenübergestellt. Die Kontaktierung geladener Kondensatorplatten mit unterschiedlichen Materialien leitet zu Widerstand und Strömungsfeld über. Dem sich entladenden Kondensator wird die Batterie gegenübergestellt, die permanent Ladungen nachliefert. Zur nachhaltigen Illustration der zugrundeliegenden Physik dienen Animationen, Videos und interaktive Experimente. Fehlinterpretationen aus der Wasserkreisanalogie können vermieden werden: Den Rotor eines Elektromotors z. B. treibt der elektrische Strom nicht wie strömendes Wasser ein Laufrad an, sondern über sein Feld

Spatial patterns of microsclerotia from Verticillium dahliae Kleb. in soils of Bavarian maple stands

In den vergangenen Jahren wurden durch die Bayerische Landesanstalt für Wald und Forstwirtschaft vermehrt Stammnekrosen an Ahornbäumen, die durch den bodenbürtigen Erreger Verticillium dahliae Kleb. verursacht werden, diagnostiziert. In dem hier vorgestellten Projekt wurden in fünf Ahornbeständen entlang eines jeweils 100 m langen Transektes Bodenproben auf Mikrosklerotien hin und Stammschäden an dem Bestand untersucht. Ziel war es zu prüfen, ob der Erreger durch infiziertes Pflanzgut in die Bestände gebracht worden ist. Die Ergebnisse konnten diesen Zusammenhang nicht bestätigen. Die Verteilung der Mikrosklerotien im Boden wies keinen erkennbaren Zusammenhang mit den geschädigten Ahornbäumen auf. Die Ergebnisse deuten viel mehr darauf hin, dass sich der Erreger unabhängig von gesunden und kranken Ahornen in den Beständen etabliert hat. Jahrringzählungen anhand von geschädigten Bäumen deuten darauf hin, dass der Schaden unmittelbar nach der extremen Trockenheit im Jahr 2003 eingetreten ist. Somit wird ein Zusammenhang zwischen extremen Witterungsereignissen und der Erkrankung vermutet.    During the last years, the Bavarian State Institute of Forestry received increasing numbers of announcements that dealt with necrosis on stems of maple trees caused by the soilborne fungus Verticillium dahliae Kleb. In this study, five forest areas were investigated along transects up to 100 m by soil sampling and mapping of diseased trees to find out if the pathogen had been introduced by infested maple seedlings. Our results yielded no evidence for this assumption. The spatial distribution of microsclerotia concentrations in the soil did not correlate with spatial patterns of diseased trees. This indicates that Verticillium was established on the sample plots independently from healthy or infested maple trees. Counting of year rings of infested maple trees revealed that the trees had developed their necrosis immediately after the drought in the year 2003. Hence, a connection between these extreme climate conditions and disease incidence cannot be excluded.   &nbsp

Radiative Corrections to the Decay τ→πντ\tau\to\pi\nu_\tau

We have calculated the radiative corrections to the decay $\tau\to \pi(K) \nu_\tau$, taking to account internal bremsstrahlung and structure dependent radiation in the radiative decay and point meson, hadronic structure dependent and short distance contributions in the virtual corrections. We display the spectra of the photon energy and of the pion-photon invariant mass in the decay $\tau\to\pi\nu_\tau\gamma$ and compare with the PHOTOS Monte-Carlo. Our result for the radiative correction to the ratio $\Gamma(\tau\to\pi\nu_\tau(\gamma))/ \Gamma(\pi\to\mu\nu_\mu(\gamma))$ is $\delta R_{\tau/\pi} = \left(0.16 \pm 0.14 \right) \%$ and for the ratio $\Gamma(\tau\to K\nu_\tau(\gamma))/ \Gamma(K\to\mu\nu_\mu(\gamma))$, we obtain $\delta R_{\tau/K } = \left(0.90 \pm 0.22 \right) \%$.Comment: 12 pages, Latex, using: epsfig, subfigure, rotating. 9 figures not included, complete Postscript file (including the figures) available via e-mail on request. Invited talk at the Third Workshop on Tau Lepton Physics (Montreux, September 94), presented by Markus Finkemeie

Radiative Corrections to πl2\pi_{l2} and Kl2K_{l2} Decays

We reexamine radiative corrections to $\pi_{l2}$ and $K_{l2}$ decays. We perform a matching calculation, including vector and axial vector resonances as explicit degrees of freedom in the long distance part. By considering the dependence on the matching scale and on the hadronic parameters, and by comparing with model independent estimates, we scrutinize the model dependence of the results. For the pseudoscalar meson decay constants, we extract the values f_pi = (92.1 \pm 0.3) MeV and f_K = (112.4 \pm 0.9) MeV. For the ratios R_pi and R_K of the electronic and muonic decay modes, we predict R_pi = (1.2354 \pm 0.0002) 10^{-4} and R_K = (2.472 \pm 0.001) 10^{-5}.Comment: 8 pages, Latex, uses epsfig. Revised version: Major changes in the presentaion, but no changes in the results. To appear in Phys. Lett.

The Clinical and Socio-Economic Relevance of Increased IPMN Detection Rates and Management Choices

Background: Increased usage of computed tomography and magnetic resonance imaging has led to a large increase in identified pancreatic cysts of up to 25% in population-based studies. The clinical and economic relevance of identifying so many cystic lesions has not been established. Compared to other organs such as liver or kidney, dysontogenetic pancreatic cysts are rare. Pancreatic cysts comprise a variety of benign, premalignant or malignant lesions; however, precise diagnosis before resection has an accuracy of only 80%. The focus of recent research was the malignant potential of intraductal papillary mucinous neoplasms (IPMN) with the aim of establishing clinical pathways addressing risk of malignancy, age and comorbidity, treatment-related morbidity and mortality as well as cost-effectiveness of treatment and surveillance. The focus of this review is to analyze the clinical and socio-economic relevance as well as the cost-benefit relation for IPMNs. Methods: For analysis, the following MESH terms were used to identify original articles, reviews, and guidelines in PubMed: (‘intraductal papillary mucinous neoplasm' OR ‘pancreatic cysts') and (incidence OR relevance OR socio-economic OR economic OR cost-effectiveness OR cost-benefit). The retrieved publications were reviewed with a focus on clinical and socio-economic relevance in relation to the increasing incidence of IPMN. Results: Addressing the increasing prevalence of pancreatic cystic lesions, recent consensus guidelines suggested criteria for risk stratification according to ‘worrisome features' and ‘high-risk stigmata'. Recent prospective cohort studies evaluated whether these can be applied in clinical practice. Evaluation of three different clinical scenarios with regard to costs and quality-adjusted life years suggested a better effectiveness of surveillance after initial risk stratification by endoscopic ultrasound-guided fine-needle aspiration with cyst fluid analysis compared with immediate resection or follow-up without further intervention. Of interest, the ‘immediate surgery' strategy was lowest for cost-effectiveness. Conclusions: The increasing incidence of identified pancreatic cysts requires an improved strategy for non-invasive risk stratification based on advanced imaging strategies. In light of a malignancy risk of 2% for branch-duct IPMN, the socio-economic necessity of a balance between surveillance and resection has to be agreed on

Virtual Testing of Geometrically Imperfect Additively Manufactured Lattice Structures

Additively manufactured lattice structures increase the lightweight potential of components for technical applications. When modelling the mechanical behaviour of those lattice structures, imperfections within the structures need to be considered. In this contribution we investigate the effect of process induced pores of varying size and location inside the lattice structure during pressure tests using a 2D minimal model in two configurations. It shows that the location of pores with respect to the configuration of the model has a strong influence on whether the imperfection decreases the mechanical performance

TatS: a novel in vitro tattooed human skin model for improved pigment toxicology research

Reports of tattoo-associated risks boosted the interest in tattoo pigment toxicity over the last decades. Nonetheless, the influence of tattoo pigments on skin homeostasis remains largely unknown. In vitro systems are not available to investigate the interactions between pigments and skin. Here, we established TatS, a reconstructed human full-thickness skin model with tattoo pigments incorporated into the dermis. We mixed the most frequently used tattoo pigments carbon black (0.02 mg/ml) and titanium dioxide (TiO2, 0.4 mg/ml) as well as the organic diazo compound Pigment Orange 13 (0.2 mg/ml) into the dermis. Tissue viability, morphology as well as cytokine release were used to characterize TatS. Effects of tattoo pigments were compared to monolayer cultures of human fibroblasts. The tissue architecture of TatS was comparable to native human skin. The epidermal layer was fully differentiated and the keratinocytes expressed occludin, filaggrin and e-cadherin. Staining of collagen IV confirmed the formation of the basement membrane. Tenascin C was expressed in the dermal layer of fibroblasts. Although transmission electron microscopy revealed the uptake of the tattoo pigments into fibroblasts, neither viability nor cytokine secretion was altered in TatS. In contrast, TiO2 significantly decreased cell viability and increased interleukin-8 release in fibroblast monolayers. In conclusion, TatS emulates healed tattooed human skin and underlines the advantages of 3D systems over traditional 2D cell culture in tattoo pigment research. TatS is the first skin model that enables to test the effects of pigments in the dermis upon tattooing