DEM simulations of the frictional and frictionless polydisperse packings of spheres under uniaxial compression

The uniaxial compression of polydisperse assemblies of spherical frictional and frictionless particles is modeled with the discrete element method (DEM). The normal particle size distribution with standard deviation of particle mean diameter in the range from 0% to 80% was applied. The series of numerical tests have been conducted to study the micromechanical and macromechanical properties of packings of spheres. The micro-scale analyses included distribution of contact forces and average coordination number, whereas macromechanical study included the elasticity, stress transmission and angle of internal friction in the assemblies. The linear increase in solid fraction was observed for standard deviation of particle mean diameter increasing up to 50% in assemblies of both, frictional and frictionless spheres under pressure of 100kPa. Further increase in particle size heterogeneity decreased solid fraction in systems. The increase in coefficient of interparticle friction resulted in decrease in solid fraction by above 10% in the whole range of variability of SD value due to the different space-filling properties of frictional particles. The stiffness of samples increased with compressive loads increasing, however no clear effect of particle size polydispersity on the effective elastic modulus of mixtures was found in frictional sphere packings. The effective elastic modulus increased with SD value increasing up to 50% in sample composed of smooth particles that decreased for higher SD values. Discrete element method predicted decrease in pressure ratio with standard deviation of particle mean diameter increasing up to 50%. Further increase in particle size polydispersity increased value of the parameter. Increase in coefficient of interparticle friction to 0.4 resulted in about 40% decrease in pressure ratio in sphere packings

A Revised Effective Temperature Scale for the Kepler Input Catalog

We present a catalog of revised effective temperatures for stars observed in long-cadence mode in the Kepler Input Catalog (KIC). We use SDSS griz filters tied to the fundamental temperature scale. Polynomials for griz color-temperature relations are presented, along with correction terms for surface gravity effects, metallicity, and statistical corrections for binary companions or blending. We compare our temperature scale to the published infrared flux method (IRFM) scale for VJKs in both open clusters and the Kepler fields. We find good agreement overall, with some deviations between (J - Ks)-based temperatures from the IRFM and both SDSS filter and other diagnostic IRFM color-temperature relationships above 6000 K. For field dwarfs we find a mean shift towards hotter temperatures relative to the KIC, of order 215 K, in the regime where the IRFM scale is well-defined (4000 K to 6500 K). This change is of comparable magnitude in both color systems and in spectroscopy for stars with Teff below 6000 K. Systematic differences between temperature estimators appear for hotter stars, and we define corrections to put the SDSS temperatures on the IRFM scale for them. When the theoretical dependence on gravity is accounted for we find a similar temperature scale offset between the fundamental and KIC scales for giants. We demonstrate that statistical corrections to color-based temperatures from binaries are significant. Typical errors, mostly from uncertainties in extinction, are of order 100 K. Implications for other applications of the KIC are discussed.Comment: Corrected for sign flip errors in the gravity corrections. Erratum to this paper is attached in Appendix. Full version of revised Table 7 can be found at http://home.ewha.ac.kr/~deokkeun/kic/sdssteff_v2.dat.g

Airflow Resistance of Wheat Bedding as Influenced by the Filling Method

A study was conducted to estimate the degree of variability of the airflow resistance in wheat caused by the filling method, compaction of the sample, and airflow direction. Two types of grain chambers were used: a cylindrical column 0.95 m high and 0.196 m in diameter, and a cubical box of 0.35 m side. All factors examined were found to influence considerably the airflow resistance. Gravitational axial filling of the grain column from three heights (0.0, 0.95 and 1.8 m) resulted in the pressure drops of 1.0, 1.3, and 1.5 kPa at the airflow velocity of 0.3 m/s. Consolidation of axially filled samples by vibration resulted in a maximum 2.2 times increase in airflow resistance. The tests with cubical sample showed that in axially filled samples the pressure drop in vertical direction was maximum 1.5 times higher than in horizontal directions. In the case of asymmetrically filled samples, the pressure drop at the airflow velocity of 0.3 m/s in vertical direction Z was found to be 1.3 of that in horizontal direction X and 1.95 times higher than with horizontal direction Y, perpendicular to X. Variations in airflow resistance in values comparable to that found in the present project may be expected in practice