Photophoretic Structuring of Circumstellar Dust Disks

We study dust accumulation by photophoresis in optically thin gas disks. Using formulae of the photophoretic force that are applicable for the free molecular regime and for the slip-flow regime, we calculate dust accumulation distances as a function of the particle size. It is found that photophoresis pushes particles (smaller than 10 cm) outward. For a Sun-like star, these particles are transported to 0.1-100 AU, depending on the particle size, and forms an inner disk. Radiation pressure pushes out small particles (< 1 mm) further and forms an extended outer disk. Consequently, an inner hole opens inside ~0.1 AU. The radius of the inner hole is determined by the condition that the mean free path of the gas molecules equals the maximum size of the particles that photophoresis effectively works on (100 micron - 10 cm, depending on the dust property). The dust disk structure formed by photophoresis can be distinguished from the structure of gas-free dust disk models, because the particle sizes of the outer disks are larger, and the inner hole radius depends on the gas density.Comment: 15 pages, 9 figures, Accepted by ApJ; corrected a typo in the author nam

Influence of primary particle density in the morphology of agglomerates

Agglomeration processes occur in many different realms of science such as colloid and aerosol formation or formation of bacterial colonies. We study the influence of primary particle density in agglomerate structure using diffusion-controlled Monte Carlo simulations with realistic space scales through different regimes (DLA and DLCA). The equivalence of Monte Carlo time steps to real time scales is given by Hirsch's hydrodynamical theory of Brownian motion. Agglomerate behavior at different time stages of the simulations suggests that three indices (fractal exponent, coordination number and eccentricity index) characterize agglomerate geometry. Using these indices, we have found that the initial density of primary particles greatly influences the final structure of the agglomerate as observed in recent experimental works.Comment: 11 pages, 13 figures, PRE, to appea

Radiometric force in dusty plasmas

A radiofrequency glow discharge plasma, which is polluted with a certain number of dusty grains, is studied. In addition to various dusty plasma phenomena, several specific colloidal effects should be considered. We focus on radiometric forces, which are caused by inhomogeneous temperature distribution. Aside from thermophoresis, the role of temperature distribution in dusty plasmas is an open question. It is shown that inhomogeneous heating of the grain by ion flows results in a new photophoresis like force, which is specific for dusty discharges. This radiometric force can be observable under conditions of recent microgravity experiments.Comment: 4 pages, amsmat

Higher soil respiration under mowing than under grazing explained by biomass differences

Different management practices may change the rate of soil respiration, thus affecting the carbon balance of grasslands. Therefore, we investigated the effect of grazing and mowing on soil respiration along with its driving variables (soil water content, soil temperature, above and below ground biomass, vegetation indices and soil carbon) in adjacent treatments (grazed and mowed) at a semi-arid grassland in Hungary (2011-2013). The average soil respiration over three years was higher in the mown (6.03±4.07 µmol CO2 m-2 s-1) than in the grazed treatment (5.29±3.50 µmol CO2 m-2 s-1). While soil water content and soil temperature did not differ between treatments, mowing resulted in 20 % higher soil respiration than grazing, possibly due to 17% higher average above ground biomass in the mowed than in the grazed treatment. Inclusions of vegetation index VIGreen in the soil respiration model in addition to abiotic drivers improved the explained Rs variance by 16% in the mowed and by 5% in the grazed site, respectively. VIGreen alone proved to be a simple and fast indicator of soil respiration (r2=0.31 at grazed, r2=0.44 at mowed site). We conclude that soil respiration is responsive to the combined effect soil water content, soil temperature, biomass and soil carbon content as affected by the management (grazing vs. mowing) practice