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We report preliminary results from a series of numerical simulations of the reduced magnetohydrodynamic equations used to describe the dynamics of magnetic loops in active regions of the solar corona. A stationary velocity field is applied at the photospheric boundaries to imitate the driving action of granule motions. A turbulent stationary regime is reached, characterized by a broadband power spectrum Ek approximately k-3&solm0;2 and heating rate levels compatible with the energy requirements of active region loops. A dimensional analysis of the equations indicates that their solutions are determined by two dimensionless parameters: the Reynolds number and the ratio between the Alfvén time and the photospheric turnover time. From a series of simulations for different values of this ratio, we determine how the heating rate scales with the physical parameters of the problem, which might be useful for an observational test of this model. 相似文献
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The scenario of magnetohydrodynamic turbulence in connection with coronal active regions has been actively investigated in recent years. According to this viewpoint, a turbulent regime is driven by footpoint motions and the incoming energy is efficiently transferred to small scales due to a direct energy cascade. The development of fine scales to enhance the dissipation of either waves or DC currents is therefore a natural outcome of turbulent models. Numerical integrations of the reduced magnetohydrodynamic equations are performed to simulate the dynamics of coronal loops driven at their bases by footpoint motions. These simulations show that a stationary turbulent regime is reached after a few photospheric times, displaying a broadband power spectrum and a dissipation rate consistent with the energy loss rates of the plasma confined in these loops. Also, the functional dependence of the stationary heating rate with the physical parameters of the problem is obtained, which might be useful for an observational test of this theoretical framework. 相似文献
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The Vistula (Wisla) river, the biggest river in Poland, is 1038 km long and has a drainage area of 168 689 km2. The river is strongly polluted by wastewaters. Big industrial plants are situated mainly in the upper part of the river, where it is slow‐flowing. This paper presents the results of the analysis of bottom sediment samples gathered from different locations along the Vistula river, from Kraków to Gdansk. The study was conducted in 2005. The following parameters were determined: chloroorganic pesticides, polychlorinated biphenyls (PCBs), chlorophenols, polycyclic aromatic hydrocarbons (PAHs), total organic carbon (TOC). The sum of chloroorganic pesticides was in the range of 2.0 to 77.5 ng/g d.w. (dry wet) with the highest values in the upper part of the river. p,p′‐DDT was found in the highest concentration. The sum of PCBs was in the range of 0.9 to 64.2 ng/g d.w. The sum of chlorophenols varied from 0.48 to 14.3 ng/g d.w. 2,4‐Dichlorophenol and pentachlorophenol occurred in the highest concentration. The sum of PAHs was in the range of 1552 to 7832 ng/g d.w. Phenantren was found in the highest concentration and antracen in the lowest. TOC values varied from 4.3 to 43.9 g/kg d.w. The concentrations of pesticides and PCBs were the highest in the upper part of the river and decreased along the course of the river, but the other determined compounds did not show this trend. However, the highest values occurred always in the upper part of the river. 相似文献
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