Dynamics of small-scale convective motions

Previous studies have discovered a population of small granules with diameters less than 800 km showing differing physical properties. High resolution simulations and observations of the solar granulation, in combination with automated segmentation and tracking algorithms, allow us to study the evolution of the structural and physical properties of these granules and surrounding vortex motions with high temporal and spatial accuracy. We focus on the dynamics of granules (lifetime, fragmentation, size, position, intensity, vertical velocity) over time and the influence of strong vortex motions. Of special interest are the dynamics of small granules compared to regular-sized granules. We developed a temporal tracking algorithm based on our developed segmentation algorithm for solar granulation. This was applied to radiation hydrodynamics simulations and high resolution observations of the quiet Sun by SUNRISE/IMaX. The dynamics of small granules differ in regard to their diameter, intensity and depth evolution compared to regular granules. The tracked granules in the simulation and observations reveal similar dynamics (lifetime, evolution of size, vertical velocity and intensity). The fragmentation analysis shows that the majority of granules in simulations do not fragment, while the opposite was found in observations. Strong vortex motions were detected at the location of small granules. Regions of strong vertical vorticity show high intensities and downflow velocities, and live up to several minutes. The analysis of granules separated according to their diameter in different groups reveals strongly differing behaviors. The largest discrepancies can be found within the groups of small, medium-sized and large granules and have to be analyzed independently. The predominant location of vortex motions on and close to small granules indicates a strong influence on the dynamics of granules

Pulse propagation in decorated granular chains: An analytical approach

We study pulse propagation in one-dimensional chains of spherical granules decorated with small grains placed between large granules. The effect of the small granules can be captured by replacing the decorated chains by undecorated chains of large granules of appropriately renormalized mass and effective interaction between the large granules. This allows us to obtain simple analytic expressions for the pulse propagation properties using a generalization of the binary collision approximation introduced in our earlier work [Phys. Rev. E in print (2009); Phys. Rev. E {\bf 69}, 037601 (2004)]Comment: 10 pages and 12 figure

Pulse Dynamics in a Chain of Granules With Friction

We study the dynamics of a pulse in a chain of granules with friction. We present theories for chains of cylindrical granules (Hertz potential with exponent $n=2$) and of granules with other geometries ($n>2$). Our results are supported via numerical simulations for cylindrical and for spherical granules ($n=5/2$).Comment: Submitted to PR

Effects of flux application and melting parameters in investment casting of pure aluminium by in-situ melting technique

Investment cast aluminium suffers porosity defect attributed to the complex combination of various factors including melt quality, casting process parameter and pouring technique. Even though, melt treatment and controlled of the process parameter have promising result, however turbulence developed during pouring of molten aluminium increasing the formation of porosity as a result of the entrainment of the surface oxide (Al2O3) film known as bifilm. Currently, turbulence free filling system was applied in casting process using tilt casting, bottom filling integrated with low pressure and also in-situ casting or in-situ melting techniques to address the porosity problem. However, in-situ melting technique has not been studied to reduce the porosity of the investment cast aluminium due to the oxidation of the granular aluminium occurs during heating hinders the complete melting of the granules. This research develops a procedure for investment casting of aluminium granules of 99.4% purity by in-situ melting technique. The aluminium granules were filled in ceramic moulds and heated at four different temperatures of 700, 750, 800 and 850oC for 30 and 60 min in a high temperature muffle furnace in ambient. As the heating temperature and duration were increased, the aluminium granules incompletely melt and produced a casting, however the granules agglomerate and replicate the shape of the ceramic mould. The aluminium granules oxidised during heating, encapsulated by a layer of complex oxides composed of stable [α-Al2O3], metastable [γ-Al2O3] and hydroxides. The thickness of the oxide layer formed on the surface of the air-heated granules increased as the heating temperature and duration were increased. The aluminium granules then were heated at the temperature of 850oC for 30 min in argon environment at the flow rate of argon gas 0.5, 2.5 and 5 l/min to reduce the oxidation of the aluminium granules. The thickness of the oxide layer formed on the argon-heated granule (5 l/min) was reduced by 60%, but failed to produce a casting. NaCl-KCl flux was applied, which was mixed and sprinkled on the aluminium granules at the Al:Flux ratio of 1:0.2, 1:0.25 and 1:0.33 and heated at the temperature of 850oC for 30 min to break the oxide layer that encapsulate the granules during heating. At the Al:Flux ratio of 1:0.33, 99% of the aluminium granules were successfully melted and produced a casting. The granules began melting at the temperature range 657.2 to 658.4oC and completely melted in 16 min with final melting temperature between 660.1 and 660.6oC. The average porosity level of the casting was 1.22%, which is lower than the investment cast aluminium produced by current pouring technique (2.48%). The low porosity level was attributed to micro-intergranular porosity present in the casting due to volume shrinkage. Investment casting of aluminium granules by in-situ melting technique with application of NaCl-KCl flux at the Al:Flux ratio of 1:0.33 mixed and sprinkled on the granules heated at the temperature of 850oC for 30 min producing low porosity aluminium casting

Impact of Weather Conditions and Farming Systems on Size Distribution of Starch Granules and Flour Yield of Winter Wheat

The size distribution of wheat-grain starch granules has an impact on the yield of finne flour. The aim of the study was to compare the impact of conventional (mineral fertilizers, pesticides) and organic farming treatments (cover crops, composted cattle manure) on (i) the size distribution of starch granules, (ii) the level of the first break whole and fine flour yield. The grain samples of winter wheat cv Fredis were taken from a long-term field crop rotation experiment established in 2008 at the Estonian University of Life Sciences in Tartu County (58°22′ N, 26°40′ E) on Stagnic Luvisol soil. The weather conditions during the grain filling period of winter wheat had a strong impact (p < 0.001) on the grain starch granule size distribution. The proportion of starch granules with a smaller diameter (C-type granules) was higher in years with a longer grain filling period. The size distribution of starch granules was not influenced by farming system. The increased proportion of C-type granules increased the fine flour yield significantly. Fertilisation with organic manure and twice with mineral nitrogen increased significantly the mean diameter value of different starch granules

Vigorous convection in a sunspot granular light bridge

Light bridges are the most prominent manifestation of convection in sunspots. The brightest representatives are granular light bridges composed of features that appear to be similar to granules. An in-depth study of the convective motions, temperature stratification, and magnetic field vector in and around light bridge granules is presented with the aim of identifying similarities and differences to typical quiet-Sun granules. Spectropolarimetric data from the Hinode Solar Optical Telescope were analyzed using a spatially coupled inversion technique to retrieve the stratified atmospheric parameters of light bridge and quiet-Sun granules. Central hot upflows surrounded by cooler fast downflows reaching 10 km/s clearly establish the convective nature of the light bridge granules. The inner part of these granules in the near surface layers is field free and is covered by a cusp-like magnetic field configuration. We observe hints of field reversals at the location of the fast downflows. The quiet-Sun granules in the vicinity of the sunspot are covered by a low-lying canopy field extending radially outward from the spot. The similarities between quiet-Sun and light bridge granules point to the deep anchoring of granular light bridges in the underlying convection zone. The fast, supersonic downflows are most likely a result of a combination of invigorated convection in the light bridge granule due to radiative cooling into the neighboring umbra and the fact that we sample deeper layers, since the downflows are immediately adjacent to the slanted walls of the Wilson depression.Comment: 10 pages, 11 figure

Synaptobrevin cleavage by the tetanus toxin light chain is linked to the inhibition of exocytosis in chromaffin cells

Exocytosis of secretory granules by adrenal chromaffin cells is blocked by the tetanus toxin light chain in a zinc specific manner. Here we show that cellular synaptobrevin is almost completely degraded by the tetanus toxin light chain within 15 min. We used highly purified adrenal secretory granules to show that synaptobrevin, which can be cleaved by the tetanus toxin light chain, is localized in the vesicular membrane. Proteolysis of synaptobrevin in cells and in secretory granules is reversibly inhibited by the zinc chelating agent dipicolinic acid. Moreover, cleavage of synaptobrevin present in secretory granules by the tetanus toxin light chain is blocked by the zinc peptidase inhibitor captopril and by synaptobrevin derived peptides. Our data indicate that the tetanus toxin light chain acts as a zinc dependent protease that cleaves synaptobrevin of secretory granules, an essential component of the exocytosis machinery in adrenal chromaffin cells