Random walk model for dual cascades in wave turbulence.

Dual cascades in turbulent systems with two conserved quadratic quantities famously arise in both two-dimensional hydrodynamic turbulence and also in wave turbulence based on four-wave interactions. Examples for the latter include surface waves and nonlinear Schrödinger equations with cubic nonlinearity. However, numerical simulations in forced-dissipative equilibrium of two-dimensional turbulence and of a one-dimensional wave system reveal that the physical nature of their cascades is starkly different. This is demonstrated by comparing their spectra in a finite inertial range and by comparing the temporal fluctuations of their spectral fluxes. In particular, the flux fluctuations are much larger in the wave case and frequently lead to instantaneous flux values that have the opposite sign of the mean flux, a phenomenon that is completely absent in the hydrodynamic case. A simple random walk model for the dual cascade in wave turbulence is then formulated that is very successful in explaining these effects. In particular, the model is able to replicate the detailed shape of the observed turbulent spectrum in a finite inertial range, and it also offers a ready explanation for the large flux fluctuations. It is also shown that a nonlinear diffusion model for the wave system cannot explain the observed spectral shapes. Overall, this suggests that in wave turbulence the systematic spectral fluxes observed in a dual cascade do not require an irreversible dynamical mechanism, rather, they arise as the inevitable outcome of blind chance.

How Does the Amount and Composition of PM Deposited on Platanus acerifolia Leaves Change Across Different Cities in Europe?

Particulate matter (PM) deposited on Platanus acerifolia tree leaves has been sampled in the urban areas of 28 European cities, over 20 countries, with the aim of testing leaf deposited particles as indicator of atmospheric PM concentration and composition. Leaves have been collected close to streets characterized by heavy traffic and within urban parks. Leaf surface density, dimensions, and elemental composition of leaf deposited particles have been compared with leaf magnetic content, and discussed in connection with air quality data. The PM quantity and size were mainly dependent on the regional background concentration of particles, while the percentage of iron-based particles emerged as a clear marker of traffic-related pollution in most of the sites. This indicates that Platanus acerifolia is highly suitable to be used in atmospheric PM monitoring studies and that morphological and elemental characteristics of leaf deposited particles, joined with the leaf magnetic content, may successfully allow urban PM source apportionment.

Transition from geostrophic turbulence to inertia-gravity waves in the atmospheric energy spectrum.

Midlatitude fluctuations of the atmospheric winds on scales of thousands of kilometers, the most energetic of such fluctuations, are strongly constrained by the Earth's rotation and the atmosphere's stratification. As a result of these constraints, the flow is quasi-2D and energy is trapped at large scales­nonlinear turbulent interactions transfer energy to larger scales, but not to smaller scales. Aircraft observations of wind and temperature near the tropopause indicate that fluctuations at horizontal scales smaller than about 500 km are more energetic than expected from these quasi-2D dynamics. We present an analysis of the observations that indicates that these smaller-scale motions are due to approximately linear inertia-gravity waves, contrary to recent claims that these scales are strongly turbulent. Specifically, the aircraft velocity and temperature measurements are separated into two components: one due to the quasi-2D dynamics and one due to linear inertia-gravity waves. Quasi-2D dynamics dominate at scales larger than 500 km; inertia-gravity waves dominate at scales smaller than 500 km.

Yersinia enterocolitica adhesin A induces production of interleukin-8 in epithelial cells.

The major invasive factor of Yersinia enterocolitica, the invasin (Inv) protein, induces proinflammatory host cell responses, including interleukin-8 (IL-8) secretion from human epithelial cells, by engagement of beta1 integrins. The Inv-triggered beta1 integrin signaling involves the small GTPase Rac; the activation of MAP kinases, such as p38, MEK1, and JNK; and the activation of the transcription factor NF-kappaB. In the present study, we demonstrate that Y. enterocolitica YadA, which is a major adhesin of Y. enterocolitica with pleiotropic virulence effects, induces IL-8 secretion in epithelial cells. The abilities of YadA and Inv to promote adhesion to and invasion of HeLa cells and to induce IL-8 production by the cells were investigated by expression of YadA and Inv in Escherichia coli. While YadA mediates efficacious adhesion to HeLa cells, it mediates marginal invasion compared with Inv. Both YadA and Inv trigger comparable levels of IL-8 production. Conformational changes of the YadA head domain by mutation of NSVAIG-S motifs, which abolish collagen binding, also abolish adhesion of Yersinia to HeLa cells and YadA-mediated IL-8 secretion. Furthermore, experiments in which blocking antibodies against beta1 integrins were used demonstrate that beta1 integrins are crucial for YadA-mediated IL-8 secretion. Inhibitor studies demonstrate the involvement of small GTPases and MAP kinases, such as p38, MEK1, and JNK, indicating that beta1 integrin-dependent signaling mediated by Inv or YadA involves similar signaling pathways. These data present YadA, in addition to Inv, YopB, and Yersinia lipopolysaccharide, as a further inducer of proinflammatory molecules by which Y. enterocolitica might promote inflammatory tissue reactions.

Interaction of Yersinia enterocolitica with epithelial cells: invasin beyond invasion.

The chromosomally encoded inv gene product is an outer membrane protein that is functionally expressed in the enteropathogenic Yersinia species Yersinia enterocolitica and Yersinia pseudotuberculosis. Invasin protein is a high-affinity ligand for beta1 integrins and especially important in the early phase of intestinal infection for efficient translocation through the M cells located in the follicle-associated epithelium overlying the Peyer's patches. In addition to bacterial internalization, Yersinia invasin mediates proinflammatory epithelial cell reactions. Epithelial cells exhibit immunological functions including production of cytokines thereby signaling to the immune system the presence of invasive or pathogenic bacteria. Several other enteropathogenic bacteria also induce cytokine production in epithelial cells. However, the signaling pathways by which this reaction is accomplished differ for various pathogens. Binding of invasin-expressing Yersinia to beta1 integrin receptors of epithelial cells induces activation of a signal cascade involving Rac1, MAP kinases, activation of the transcription factor NF-kappaB, and the subsequent production of chemotactic cytokines. The Yersinia invasin-triggered inflammatory epithelial cell reaction may lead to the recruitment of phagocytes followed by tissue disruption which may be part of the strategy of the pathogen to promote its dissemination in the host tissue.