PATH-DEPENDENCE WITHOUT INCREASING RETURNS TO SCALE AND NETWORK EXTERNALITIES

Research Methods/ Statistical Methods,

The riparian flora of the upper part of the river Weser (Germany)

The riparian flora of the upper part of the river Weser, about 200 km long, was recorded between Münden and Minden. 42 representative sections each in a distance of 5 km to each other were mapped. For recording the stock of species as completely as possible further parts of the river banks were investigated by spot-checks. Altogether 236 vascular plant species were found. For 196 of these species the frequency distribution is pointed out. The plant communities of the river banks are described by sociological releves. Despite the relatively high similarity of the investigated sections, manifested by 32 high frequent species, the data allow to divide this part of the river Weser into 3 sectors by floristical aspects. For each sector the frequency of the river bank species are stated. By reasons of the high salt content of this part of the river Weser 20 species which are at least weakly salt tolerating are to be found, predominantly in the upper sector. Obviously the more salt tolerating taxa are receding, caused by the decreasing salt content. In a whole 36 neophytes were found on the river banks of this part of the Weser, the spreading of which occurred in general in this Century. Most frequent species are Bidens frondosa, Atriplex sagittata, and Impatiens glandulifera. In the recent past Atriplex oblongifolia and Xanthium albinum are disseminating. The spreading of the neophytes is discussed as well as the decrease of genuine species. The present paper is part of a larger designed investigation of the flora riverbanks of the Weser System. The dynamics of the flora along the upper part of the Weser can be followed on quantitative basis in future by the help of 42 sample areas. This underlies a long-term monitoring

The riparian flora of the Oker river system

Flora and vegetation of riverbanks are examined by us europewide with emphasis to the Weser and Elbe river. The riparian flora of the Oker and its major tributaries as a part of the Weser system were investigated most intensively by a standardized method. Species richness and most frequent species of different rivers just as different reaches of the Oker are compared with each other. Special attention was paid to spread and establishment of alien plant

Nonequilibrium stabilization of charge states in double quantum dots

We analyze the decoherence of charge states in double quantum dots due to cotunneling. The system is treated using the Bloch-Redfield generalized master equation for the Schrieffer-Wolff transformed Hamiltonian. We show that the decoherence, characterized through a relaxation $\tau_{r}$ and a dephasing time $\tau_{\phi}$, can be controlled through the external voltage and that the optimum point, where these times are maximum, is not necessarily in equilibrium. We outline the mechanism of this nonequilibrium-induced enhancement of lifetime and coherence. We discuss the relevance of our results for recent charge qubit experiments.Comment: 5 pages, 5 figure

Nonlinear cotunneling through an artificial molecule

We study electron transport through a system of two lateral quantum dots coupled in series. We consider the case of weak coupling to the leads and a bias point in the Coulomb blockade. After a generalized Schrieffer-Wolf transformation, cotunneling through this system is described using methods from lowest-order perturbation theory. We study the system for arbitrary bias voltages below the Coulomb energy. We observe a rich, non-monotonic behavior of the stationary current depending on the internal degrees of freedom. In particular, it turns out that at fixed transport voltage, the current through the system is largest at weak-to-intermediate inter-dot coupling.Comment: 4 pages, 5 figure

A Rapid Crosstalk of Human γδ T Cells and Monocytes Drives the Acute Inflammation in Bacterial Infections

Vγ9/Vδ2 T cells are a minor subset of T cells in human blood and differ from other T cells by their immediate responsiveness to microbes. We previously demonstrated that the primary target for Vγ9/Vδ2 T cells is (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMB-PP), an essential metabolite produced by a large range of pathogens. Here we wished to study the consequence of this unique responsiveness in microbial infection. The majority of peripheral Vγ9/Vδ2 T cells shares migration properties with circulating monocytes, which explains the presence of these two distinct blood cell types in the inflammatory infiltrate at sites of infection and suggests that they synergize in anti-microbial immune responses. Our present findings demonstrate a rapid and HMB-PP-dependent crosstalk between Vγ9/Vδ2 T cells and autologous monocytes that results in the immediate production of inflammatory mediators including the cytokines interleukin (IL)-6, interferon (IFN)-γ, tumor necrosis factor (TNF)-α, and oncostatin M (OSM); the chemokines CCL2, CXCL8, and CXCL10; and TNF-related apoptosis-inducing ligand (TRAIL). Moreover, under these co-culture conditions monocytes differentiate within 18 hours into inflammatory dendritic cells (DCs) with antigen-presenting functions. Addition of further microbial stimuli (lipopolysaccharide, peptidoglycan) induces CCR7 and enables these inflammatory DCs to trigger the generation of CD4+ effector αβ T cells expressing IFN-γ and/or IL-17. Importantly, our in vitro model replicates the responsiveness to microbes of effluent cells from peritoneal dialysis (PD) patients and translates directly to episodes of acute PD-associated bacterial peritonitis, where Vγ9/Vδ2 T cell numbers and soluble inflammatory mediators are elevated in patients infected with HMB-PP-producing pathogens. Collectively, these findings suggest a direct link between invading pathogens, microbe-responsive γδ T cells, and monocytes in the inflammatory infiltrate, which plays a crucial role in the early response and the generation of microbe-specific immunity