Near-perihelion activity of comet 67P/Churyumov–Gerasimenko. A first attempt of non-static analysis

ABSTRACT The observed rate of water production of comet 67P/Churyumov–Gerasimenko near its perihelion can be approximated by a very steep power function of the heliocentric distance. Widely used thermophysical models based on a static dust layer on top of the icy/refractory matrix are poorly consistent with these observations. We analyse published model results and demonstrate that thermophysical models with a uniform and static ice free layer do not reproduce the observed steep water production rates of 67P near perihelion. Based on transient thermal modeling we conclude that the accelerated gas activity can be explained assuming that the active area fraction near the south pole is increased. The deeper penetration of the heat wave during polar day (no sunset) can activate sublimation through thicker inert dust layers. This can also lead to removal of thicker dust layers and consequently to an expansion of the active area.

SSESSMENT OF INFLUENCE OF THE MOUNTAIN ENTERPRISE ON THE ADJACENT TERRITORY ON THE INERT DUST FACTOR

At all stages of production and processing of raw materials, the leading factor of negative impact of mountain technologies on personnel of the enterprises and the population of the next to them of residential zones is air pollution dust. Features of a natural experiment by definition of a dust pollution of the ground atmosphere by the mining enterprise close to the housing estate are considered. Regularities of dispersion and sedimentation of dust on the underplaying surface taking into account characteristics of a source of dust, values of regional and local backgrounds and also meteorological factors of the environment are presented.Regularity of scattering and deposition of dust on the underplaying surface are determined. Approximate solution of the inverse task is proposed.

EFFICACY OF NINE CROATIAN INERT DUSTS AGAINST RICE WEEVIL SITOPHILUS ORYZAE L. (COLEOPTERA: CURCULIONIDAE) ON WHEAT

Laboratory bioassay was carried out to study the insecticidal effect of 9 Croatian inert dusts against Sitophilus oryzae (L.) and to test their influence on bulk density of treated wheat. In order to compare effectiveness of Croatian inert dust samples, a standard USA diatomaceous earth (DE) Celatom® Mn 51, registered as an insecticide for stored-products protection, was used. Wheat kernels with approximately 13% moisture content were treated with inert dusts at doses 300, 400, 500 and 600 ppm and mortality of S. oryzae adults was assessed after 7 and 14 days and progeny after 49 days. The most effective Croatian inert dust samples were D-02B, D-01 and MA-4 with the LD90 values of 359.6, 447.2 and 458.7 ppm, respectively. In addition, effective dose that reduced F1 progeny in half was lower in regard to the other tested samples including the standard DE Mn 51, with the ED50 values 71.9, 54.6 and 137.6 ppm, respectively. According to the XRF analytical results, the highest amount of biogenic silica (BSi) was found in samples D-02B, D-01 and MA-4 (45.98, 35.09 and 21.28%, respectively). Paleontological data analysis confirmed diatoms species in only 5 samples of Croatian inert dusts (D-01, D-02B, PD-1, MA-4 and JU-1). All tested inert dusts affected reduction in bulk density of treated wheat at the LD90 concentrations, from 4.4 (D-02B) to 5.6 (JU-1) kg hL-1. More effective inert dusts at lower doses equally reduced bulk density as less effective inert dusts at much higher doses.

Analysis of “Finger” Flame Acceleration as a Stage of a Methane-Air-Dust Fire in a Coal Mine

To reveal the inner mechanism of gas explosion, the entire scenario of premixed flame front evolution within an accidental fire is prescribed. Specifically, “finger” flame shape, which is one of the key stages of flame evolution, is scrutinized with the situation of a methane-air explosion. A transition from a globally-spherical front to a finger-shaped one occurs when a flame starts approaching the passage walls. While this acceleration is extremely strong, it stops as soon as the flame touches the passage wall. This mechanism is Reynolds-independent; being equally relevant to micro-channels and giant tunnels. The flame speed increases by an order of magnitude during this stage. To implement dusty environments, Seshadri formulation for the planar flame [Combustion and Flame 89 (1992) 333] is employed with a non-uniform distribution of inert dust gradients, specifically, linear, parabolic and hyperbolic spatial dust distribution gradients are incorporated into the “finger” flame shape. This study systematically investigates how the noncombustible dust distributions affect fire evolution, the flame shape, and propagation velocity.