SPH modelling of turbulent open channel flow over and within natural gravel beds with rough interfacial boundaries

Smoothed Particle Hydrodynamics (SPH) is brought to a level that can be applied to simulate turbulent open channel flows over and within natural porous gravel beds. For this, improvements have been made with regards to i) turbulence modelling, ii) open boundaries (inflow and outflow), and iii) treatment of the rough interface boundary between the porous bed and the overlying free-flow. Flow through the porous bed is simulated macroscopically, and the coefficients of the drag closure model are carefully determined at different layers of the flow; the effect of turbulence is taken into account using a three-layer mixing-length model; and a porous inflow boundary at the inlet as well as an imaginary pressure wall at the outlet are introduced to obtain the required steady and uniform flow conditions. The developed model is then used to simulate eight test cases with two bed conditions, each with four flow conditions. Through the velocity analysis, a nearly S-shaped distribution is observed within the roughness layer for the present test cases. The comparison of the results of the velocity and shear stress with a set of experimental data reveals that the SPH model with the present drag and turbulence closure models as well as the proposed inflow/outflow boundary techniques is capable of simulating complex turbulent channel flows over highly sheared natural porous beds

Demarcating circulation regimes of synchronously rotating terrestrial planets within the habitable zone

We investigate the atmospheric dynamics of terrestrial planets in synchronous rotation within the habitable zone of low-mass stars using the Community Atmosphere Model (CAM). The surface temperature contrast between day and night hemispheres decreases with an increase in incident stellar flux, which is opposite the trend seen on gas giants. We define three dynamical regimes in terms of the equatorial Rossby deformation radius and the Rhines length. The slow rotation regime has a mean zonal circulation that spans from day to night side, with both the Rossby deformation radius and the Rhines length exceeding planetary radius, which occurs for planets around stars with effective temperatures of 3300 K to 4500 K (rotation period > 20 days). Rapid rotators have a mean zonal circulation that partially spans a hemisphere and with banded cloud formation beneath the substellar point, with the Rossby deformation radius is less than planetary radius, which occurs for planets orbiting stars with effective temperatures of less than 3000 K (rotation period < 5 days). In between is the Rhines rotation regime, which retains a thermally-direct circulation from day to night side but also features midlatitude turbulence-driven zonal jets. Rhines rotators occur for planets around stars in the range of 3000 K to 3300 K (rotation period ∼ 5 to 20 days), where the Rhines length is greater than planetary radius but the Rossby deformation radius is less than planetary radius. The dynamical state can be observationally inferred from comparing the morphology of the thermal emission phase curves of synchronously rotating planets

Exoplanet phase curves: observations and theory

Phase curves are the best technique to probe the three dimensional structure of exoplanets' atmospheres. In this chapter we first review current exoplanets phase curve observations and the particular challenges they face. We then describe the different physical mechanisms shaping the atmospheric phase curves of highly irradiated tidally locked exoplanets. Finally, we discuss the potential for future missions to further advance our understanding of these new worlds.Comment: Fig.5 has been updated. Table 1 and corresponding figures have been updated with new values for WASP-103b and WASP-18b. Contains a table sumarizing phase curve observation

Bethe-Salpeter equation and a nonperturbative quark-gluon vertex

A Ward-Takahashi identity preserving Bethe-Salpeter kernel can always be calculated explicitly from a dressed-quark-gluon vertex whose diagrammatic content is enumerable. We illustrate that fact using a vertex obtained via the complete resummation of dressed-gluon ladders. While this vertex is planar, the vertex-consistent kernel is nonplanar and that is true for any dressed vertex. In an exemplifying model the rainbow-ladder truncation of the gap and Bethe-Salpeter equations yields many results; e.g., pi- and rho-meson masses, that are changed little by including higher-order corrections. Repulsion generated by nonplanar diagrams in the vertex-consistent Bethe-Salpeter kernel for quark-quark scattering is sufficient to guarantee that diquark bound states do not exist.Comment: 16 pages, 12 figures, REVTEX

A rocky planet transiting a nearby low-mass star

M-dwarf stars -- hydrogen-burning stars that are smaller than 60 per cent of the size of the Sun -- are the most common class of star in our Galaxy and outnumber Sun-like stars by a ratio of 12:1. Recent results have shown that M dwarfs host Earth-sized planets in great numbers: the average number of M-dwarf planets that are between 0.5 to 1.5 times the size of Earth is at least 1.4 per star. The nearest such planets known to transit their star are 39 parsecs away, too distant for detailed follow-up observations to measure the planetary masses or to study their atmospheres. Here we report observations of GJ 1132b, a planet with a size of 1.2 Earth radii that is transiting a small star 12 parsecs away. Our Doppler mass measurement of GJ 1132b yields a density consistent with an Earth-like bulk composition, similar to the compositions of the six known exoplanets with masses less than six times that of the Earth and precisely measured densities. Receiving 19 times more stellar radiation than the Earth, the planet is too hot to be habitable but is cool enough to support a substantial atmosphere, one that has probably been considerably depleted of hydrogen. Because the host star is nearby and only 21 per cent the radius of the Sun, existing and upcoming telescopes will be able to observe the composition and dynamics of the planetary atmosphere.Comment: Published in Nature on 12 November 2015, available at http://dx.doi.org/10.1038/nature15762. This is the authors' version of the manuscrip

Determinants of the Use of a Diabetes Risk-Screening Test

A study was designed to investigate why people do or do not make use of a diabetes risk test developed to facilitate the timely diagnosis of diabetes. Data were collected using a web-based questionnaire, which was based on the Health Belief Model, the Theory of Planned Behavior, and the Threatening Medical Situations Inventory. People who had and had not used the risk test were recruited to complete the survey. The sample consisted of 205 respondents: 44% who had used the test and 56% who had not. The hypothesized relationships between the dependent variable (diabetes risk test use) and the determinants used in this study were tested using logistic regression analysis. Only two significant predictors of diabetes risk test use were found: gender and barriers. More women than men use the test. Furthermore, people who experience more barriers will be less inclined to use the test. The contribution of diabetes screening tests fully depends on people’s willingness to use them. To optimize the usage of such test, it is especially important to address the barriers as perceived by the public. Two types of barriers must be addressed: practical barriers (time to take the test, fear of complexity of the test), and consequential barriers (fear of the disease and treatment, uncertainties about where to go in the case of an increased risk of diabetes)