Near-surface stellar magneto-convection: simulations for the Sun and a metal-poor solar analog

We present 2D local box simulations of near-surface radiative magneto-convection with prescribed magnetic flux, carried out with the MHD version of the CO5BOLD code for the Sun and a solar-like star with a metal-poor chemical composition (metal abundances reduced by a factor 100, [M/H]=-2). The resulting magneto-hydrodynamical models can be used to study the influence of the metallicity on the properties of magnetized stellar atmospheres. A preliminary analysis indicates that the horizontal magnetic field component tends to be significantly stronger in the optically thin layers of metal-poor stellar atmospheres.Comment: Proc. IAU Symposium 259, Cosmic Magnetic Fields: from Planets, to Stars and Galaxies, K.G. Strassmeier, A.G. Kosovichev and J.E. Beckman, eds. (2009) p.23

New insights into pedestrian flow through bottlenecks

Capacity estimation is an important tool for the design and dimensioning of pedestrian facilities. The literature contains different procedures and specifications which show considerable differences with respect to the estimated flow values. Moreover do new experimental data indicate a stepwise growing of the capacity with the width and thus challenge the validity of the specific flow concept. To resolve these differences we have studied experimentally the unidirectional pedestrian flow through bottlenecks under laboratory conditions. The time development of quantities like individual velocities, density and individual time gaps in bottlenecks of different width is presented. The data show a linear growth of the flow with the width. The comparison of the results with experimental data of other authors indicates that the basic assumption of the capacity estimation for bottlenecks has to be revised. In contradiction with most planning guidelines our main result is, that a jam occurs even if the incoming flow does not overstep the capacity defined by the maximum of the flow according to the fundamental diagram.Comment: Traffic flow, pedestrian traffic, crowd dynamics, capacity of bottlenecks (16 pages, 8 figures); (+ 3 new figures and minor revisions

Assessing the accuracy of δ<sup>18<\sup>O<sub>sw<?sub> estimates from corals: lessons from simple Monte Carlo simulations

EGU2008-A-04391 Paired measurements of δ18O and Sr/Ca in coral aragonite are routinely used for deriving estimates of δ18Osw and, by extension, sea surface salinity variations over the past centuries. However, in practice, the accuracy (or the error) of these estimates is often difficult to assess. Here, we use simulated proxy data and Monte-Carlo simulations to investigate the accuracy of δ18Osw estimates from paired coral δ18O and Sr/Ca measurements. First, we estimate expected values of coral Sr/Ca and δ18O from instrumental or reanalysis data of sea surface temperature (SST) and sea surface salinity (SSS). We then add the typical analytical errors onto the expected Sr/Ca (δ18O) data as random numbers and compute δ18Osw+error from the noisy proxy data for a 1000 sample Monte Carlo. From this simple Monte Carlo simulation, the range of correlation coefficients between δ18Osw+error and expected δ18Osw is estimated. As expected, we find that this range mainly depends on the magnitude of the actual SSS variations at a given site, as well as on the slope of the δ18Osw-SSS relationship. A comparison with real coral-based δ18Osw reconstructions from multiple sites indicates that correlations between reconstructed δ18Osw and instrumental SSS fall within the range of correlation coefficients predicted based on our Monte-Carlo simulation. Thus, our simple simulation exercise may help to assess the feasibility of δ18Osw and salinity reconstructions from corals in different climatic settings, provided that (i) some instrumental data of δ18Osw and/or SSS is available, and (ii) the slope of the δ18Osw-SSS relationship is known

Universe acceleration and fine structure constant variation in BSBM theory

In this work we investigate the utility of using SNe Ia observations in constraining the cosmological parameters in BSBM theory where a scalar field is responsible for both fine structure constant variation and late time universe acceleration. The model is discussed in the presence of an exponential self potential for the scalar field. Stability and phase space analysis of the solutions are studied. The model is tested against observational data for Hubble parameter and quasar absorption spectra. With the best fitted model parameters, the theory predicts a good match with the experimental results and exhibits fine structure constant variation. The analysis also shows that for the equation of state parameter, recent universe acceleration and possible phantom crossing in future is forecasted.Comment: 14 pages, 10 figures, final version with minor modification accepted to be published in JCA

Computed microtomography visualization and quantification of mouse ischemic brain lesion by nonionic radio contrast agents.

AIM: To explore the possibility of brain imaging by microcomputed tomography (microCT) using x-ray contrasting methods to visualize mouse brain ischemic lesions after middle cerebral artery occlusion (MCAO). ----- METHODS: Isolated brains were immersed in ionic or nonionic radio contrast agent (RCA) for 5 days and subsequently scanned using microCT scanner. To verify whether ex-vivo microCT brain images can be used to characterize ischemic lesions, they were compared to Nissl stained serial histological sections of the same brains. To verify if brains immersed in RCA may be used afterwards for other methods, subsequent immunofluorescent labeling with anti-NeuN was performed. ----- RESULTS: Nonionic RCA showed better gray to white matter contrast in the brain, and therefore was selected for further studies. MicroCT measurement of ischemic lesion size and cerebral edema significantly correlated with the values determined by Nissl staining (ischemic lesion size: P=0.0005; cerebral edema: P=0.0002). Brain immersion in nonionic RCA did not affect subsequent immunofluorescent analysis and NeuN immunoreactivity. ----- CONCLUSION: MicroCT method was proven to be suitable for delineation of the ischemic lesion from the non-infarcted tissue, and quantification of lesion volume and cerebral edema