Anisotropy studies around the galactic centre at EeV energies with the Auger Observatory

Data from the Pierre Auger Observatory are analyzed to search for anisotropies near the direction of the Galactic Centre at EeV energies. The exposure of the surface array in this part of the sky is already significantly larger than that of the fore-runner experiments. Our results do not support previous findings of localized excesses in the AGASA and SUGAR data. We set an upper bound on a point-like flux of cosmic rays arriving from the Galactic Centre which excludes several scenarios predicting sources of EeV neutrons from Sagittarius $A$. Also the events detected simultaneously by the surface and fluorescence detectors (the `hybrid' data set), which have better pointing accuracy but are less numerous than those of the surface array alone, do not show any significant localized excess from this direction.Comment: Matches published versio

Flame acceleration and DDT in gas explosions

A qualitative description of flame acceleration (FA) process is presented, which shows a complexity of the processes that can follow a weak ignition in a combustible mixture. Considering the exclusive role of the confinement and obstructions, the main focus is made on the processes of FA and DDT typical for areas with strong confinement and heavy obstructions. Main characteristic combustion regimes are described as well as possible routes for development of FA processes. A framework of ideas and criteria that can be used to evaluate initial and boundary conditions under which FA and DDT may be possible is presented. Limitations and uncertainties of these criteria are discussed

NITRATE REDUCTASE ACTIVITY DURING HEAT SHOCK IN WINTER WHEAT

Nitrates are the basic source of nitrogen for the majority of plants. Absorption and transformation of nitrates in plants are determined by external conditions and, first of all, temperature and light intensity. The influence of the temperature increasing till +40 0С on activity of nitrate reductase was studied. It is shown, that the rise of temperature was accompanied by sharp decrease of activity nitrate reductase in leaves of winter wheat, what, apparently, occurred for the account deactivations of enzyme and due to its dissociation

Run-up distances to supersonic flames in obstacle-laden tubes

The problem of the minimum run-up distance for the flame acceleration to supersonic combustion regimes in tubes with obstacles is studied both experimentally and numerically. Experiments were made in an explosion tube equipped with orifice plate obstacles. The tube was of 12-m long with internal tube diameter of 0.35 m. Blockage ratios (BR) of the orifice plates were 0.3, 0.45, 0.6 and 0.75. Hydrogen mixtures were used in the tests. The process of the flame acceleration in a geometry, which is similar to the experimental one, was studied numerically in a series of 3D gasdynamic simulations. It was found both in the tests and in the simulations that characteristic distance of the flame acceleration decreases with the increase of the blockage ratio and with the increase of the mixture reactivity (burning rate). A simple analytical model is proposed, which describes the evolution of the flame shape in the channel with obstacles. The dimensionless flame acceleration distance is determined in the model, which accounts for BR, laminar burning rate, and sound speed in combustion products

Flame acceleration in a tube with variable cross-section

An experimental study is presented on the effect of tube cross-section variations on flame acceleration. A geometry where flames propagated from a tube with large diameter to another tube with smaller diameter was studied. Experiments were performed in an explosion tube combined of two parts, which were equal in length and different in diameters (174 and 520 mm id). Tests were made with lean hydrogen-air mixtures. The mixtures were chosen to be near the critical composition of 10.5% H$_2$ in air for fast flames in tubes with constant cross-section. Critical mixture compositions for development of fast flames were determined in the tests. It was found that compared to cases with a constant tube diameter, the critical mixture composition for strong flame acceleration was shifted towards less energetic mixtures in our case. It was shown that this shift is due to an effective compression and heating of the reactants ahead of the flame in the geometry studied. This effect appeared to be in a good qualitative and quantitative agreement with the critical values of mixture expansion ratio for strong flame acceleration determined in our earlier studies for hydrogen mixtures