A Parameter Study of Classical Be Star Disk Models Constrained by Optical Interferometry

We have computed theoretical models of circumstellar disks for the classical Be stars $\kappa$ Dra, $\beta$ Psc, and $\upsilon$ Cyg. Models were constructed using a non-LTE radiative transfer code developed by \citet{sig07} which incorporates a number of improvements over previous treatments of the disk thermal structure, including a realistic chemical composition. Our models are constrained by direct comparison with long baseline optical interferometric observations of the H$\alpha$ emitting regions and by contemporaneous H$\alpha$ line profiles. Detailed comparisons of our predictions with H$\alpha$ interferometry and spectroscopy place very tight constraints on the density distributions for these circumstellar disks.Comment: 10 figures,28 pages, accepted by Ap

Effects of three-body interactions on the structure and thermodynamics of liquid krypton

Large-scale molecular dynamics simulations are performed to predict the structural and thermodynamic properties of liquid krypton using a potential energy function based on the two-body potential of Aziz and Slaman plus the triple-dipole Axilrod-Teller (AT) potential. By varying the strength of the AT potential we study the influence of three-body contribution beyond the triple-dipole dispersion. It is seen that the AT potential gives an overall good description of liquid Kr, though other contributions such as higher order three-body dispersion and exchange terms cannot be ignored.Comment: 11 pages, 3 figures, LaTeX, to appear in J. Chem. Phy

Order parameter model for unstable multilane traffic flow

We discuss a phenomenological approach to the description of unstable vehicle motion on multilane highways that explains in a simple way the observed sequence of the phase transitions "free flow -> synchronized motion -> jam" as well as the hysteresis in the transition "free flow synchronized motion". We introduce a new variable called order parameter that accounts for possible correlations in the vehicle motion at different lanes. So, it is principally due to the "many-body" effects in the car interaction, which enables us to regard it as an additional independent state variable of traffic flow. Basing on the latest experimental data (cond-mat/9905216) we assume that these correlations are due to a small group of "fast" drivers. Taking into account the general properties of the driver behavior we write the governing equation for the order parameter. In this context we analyze the instability of homogeneous traffic flow manifesting itself in both of the mentioned above phase transitions where, in addition, the transition "synchronized motion -> jam" also exhibits a similar hysteresis. Besides, the jam is characterized by the vehicle flows at different lanes being independent of one another. We specify a certain simplified model in order to study the general features of the car cluster self-formation under the phase transition "free flow synchronized motion". In particular, we show that the main local parameters of the developed cluster are determined by the state characteristics of vehicle motion only.Comment: REVTeX 3.1, 10 pages with 10 PostScript figure

New anti-perovskite-type Superconductor ZnNyNi3

We have synthesized a new superconductor ZnNyNi3 with Tc ~3 K. The crystal structure has the same anti-perovskite-type such as MgCNi3 and CdCNi3. As far as we know, this is the third superconducting material in Ni-based anti-perovskite series. For this material, superconducting parameters, lower-critical field Hc1(0), upper-critical field Hc2(0), coherence length x(0), penetration depth l(0), and Gintzburg -Landau parameter k(0) have been experimentally determined.Comment: 13 pages, 3 figures, 1 tabl

Li14Ln5[Si11N19O5]O2F2 with Ln = Ce, Nd-Representatives of a Family of Potential Lithium Ion Conductors

The isotypic layered oxonitridosilicates Li14Ln5[Si11N19O5]O2F2 (Ln = Ce, Nd) have been synthesized using Li as fluxing agent and crystallize in the orthorhombic space group Pmmn (Z = 2, Li14Ce5[Si11N19O5]O2F2: a = 17.178(3), b = 7.6500(15), c = 10.116(2) Å, R1 = 0.0409, wR2 = 0.0896; Li14Nd5 Si11N19O5]O2F2: a = 17.126(2), b = 7.6155 15), c = 10.123(2) Å, R1 = 0.0419, wR2 = 0.0929). The silicate layers consist of dreier and sechser rings interconnected via common corners, yielding an unprecedented silicate substructure. A topostructural analysis indicates possible 1D ion migration pathways between five crystallographic independent Li positions. The specific Li-ionic conductivity and its temperature dependence were determined by impedance spectroscopy as well as DC polarization/depolarization measurements. The ionic conductivity is on the order of 5 × 10−5 S/cm at 300°C, while the activation energy is 0.69 eV. Further adjustments of the defect chemistry (e.g., through doping)can make these compounds interesting candidates for novel oxonitridosilicate based ion conductors

CHARA Array K'-band Measurements of the Angular Dimensions of Be Star Disks

We present the first K'-band, long-baseline interferometric observations of the northern Be stars gamma Cas, phi Per, zeta Tau, and kappa Dra. The measurements were made with multiple telescope pairs of the CHARA Array interferometer, and in every case the observations indicate that the circumstellar disks of the targets are resolved. We fit the interferometric visibilities with predictions from a simple disk model that assumes an isothermal gas in Keplerian rotation. We derive fits of the four model parameters (disk base density, radial density exponent, disk normal inclination, and position angle) for each of the targets. The resulting densities are in broad agreement with prior studies of the IR excess flux and the resulting orientations generally agree with those from interferometric H-alpha and continuum polarimetric observations. We find that the angular size of the K' disk emission is smaller than that determined for the H-alpha emission, and we argue that the difference is the result of a larger H-alpha opacity and the relatively larger neutral hydrogen fraction with increasing disk radius. All the targets are known binaries with faint companions, and we find that companions appear to influence the interferometric visibilities in the cases of phi Per and kappa Dra. We also present contemporaneous observations of the H-alpha, H-gamma, and Br-gamma emission lines. Synthetic model profiles of these lines that are based on the same disk inclination and radial density exponent as derived from the CHARA Array observations match the observed emission line strength if the disk base density is reduced by approximately 1.7 dex.Comment: ApJ in press (2007 Jan 1), 55 pages, 14 figure

Copernicus Marine Service Ocean State Report

This is the final version. Available from Taylor & Francis via the DOI in this record

Challenges for Sustained Observing and Forecasting Systems in the Mediterranean Sea

The Mediterranean community represented in this paper is the result of more than 30 years of EU and nationally funded coordination, which has led to key contributions in science concepts and operational initiatives. Together with the establishment of operational services, the community has coordinated with universities, research centers, research infrastructures and private companies to implement advanced multi-platform and integrated observing and forecasting systems that facilitate the advancement of operational services, scientific achievements and mission-oriented innovation. Thus, the community can respond to societal challenges and stakeholders needs, developing a variety of fit-for-purpose services such as the Copernicus Marine Service. The combination of state-of-the-art observations and forecasting provides new opportunities for downstream services in response to the needs of the heavily populated Mediterranean coastal areas and to climate change. The challenge over the next decade is to sustain ocean observations within the research community, to monitor the variability at small scales, e.g., the mesoscale/submesoscale, to resolve the sub-basin/seasonal and inter-annual variability in the circulation, and thus establish the decadal variability, understand and correct the model-associated biases and to enhance model-data integration and ensemble forecasting for uncertainty estimation. Better knowledge and understanding of the level of Mediterranean variability will enable a subsequent evaluation of the impacts and mitigation of the effect of human activities and climate change on the biodiversity and the ecosystem, which will support environmental assessments and decisions. Further challenges include extending the science-based added-value products into societal relevant downstream services and engaging with communities to build initiatives that will contribute to the 2030 Agenda and more specifically to SDG14 and the UN's Decade of Ocean Science for sustainable development, by this contributing to bridge the science-policy gap. The Mediterranean observing and forecasting capacity was built on the basis of community best practices in monitoring and modeling, and can serve as a basis for the development of an integrated global ocean observing system