Three-dimensional simulations of solar magneto-convection including effects of partial ionization

Over the last decades, realistic 3D radiative-MHD simulations have become the dominant theoretical tool for understanding the complex interactions between the plasma and the magnetic field on the Sun. Most of such simulations are based on approximations of magnetohydrodynamics, without directly considering the consequences of the very low degree of ionization of the solar plasma in the photosphere and bottom chromosphere. The presence of large amount of neutrals leads to a partial decoupling of the plasma and the magnetic field. As a consequence of that, a series of non-ideal effects (ambipolar diffusion, Hall effect and battery effect) arises. The ambipolar effect is the dominant one in the solar chromosphere. Here we report on the first three-dimensional realistic simulations of magneto-convection including ambipolar diffusion and battery effects. The simulations are done using the newly developed Mancha3D code. Our results reveal that ambipolar diffusion causes measurable effects on the amplitudes of waves excited by convection in the simulations, on the absorption of Poynting flux and heating and on the formation of chromospheric structures. We provide a low limit on the chromospheric temperature increase due to the ambipolar effect using the simulations with battery-excited dynamo fields.Comment: To appear in Astronomy & Astrophysic

Numerical simulations of quiet Sun magnetic fields seeded by Biermann battery

The magnetic fields of the quiet Sun cover at any time more than 90\% of its surface and their magnetic energy budget is crucial to explain the thermal structure of the solar atmosphere. One of the possible origins of these fields is due to the action of local dynamo in the upper convection zone of the Sun. Existing simulations of the local solar dynamo require an initial seed field, and sufficiently high spatial resolution, in order to achieve the amplification of the seed field to the observed values in the quiet Sun. Here we report an alternative model of seeding based on the action of the Bierman battery effect. This effect generates a magnetic field due to the local imbalances in electron pressure in the partially ionized solar plasma. We show that the battery effect self-consistently creates from zero an initial seed field of a strength of the order of micro G, and together with dynamo amplification, allows the generation of quiet Sun magnetic fields of a similar strength to those from solar observations.Comment: To appear in Astronomy & Astrophysic

Joint action of Hall and ambipolar effects in 3D magneto-convection simulations of the quiet Sun. I. Dissipation and generation of waves

The partial ionization of the solar plasma causes several nonideal effects such as the ambipolar diffusion, the Hall effect, and the Biermann battery effect. Here we report on the first three-dimensional realistic simulations of solar local dynamo where all three effects were taken into account. The simulations started with a snapshot of already saturated battery-seeded dynamo, where two new series were developed: one with solely ambipolar diffusion and another one also taking into account the Hall term in the generalized Ohm's law. The simulations were then run for about 4 hours of solar time to reach the stationary regime and improve the statistics. In parallel, a purely MHD dynamo simulation was also run for the same amount of time. The simulations are compared in a statistical way. The results show that, with the inclusion of the ambipolar diffusion, the amplitudes of the incompressible perturbations related to Alfven waves are reduced, and the Poynting flux is absorbed, with a frequency dependence. The Hall effect causes the opposite action: significant excess of incompressible perturbations is generated and an excess of the Poynting flux is observed in the chromospheric layers. The model with ambipolar diffusion shows, on average, sharper current sheets and slightly more abundant fast magneto-acoustic shocks in the chromosphere. The model with the Hall effect has higher temperatures at the lower chromosphere and stronger and more vertical magnetic field concentrations all over the chromosphere. The study of high-frequency waves reveals that significant power of incompressible perturbations is associated with areas with intense and more vertical magnetic fields and larger temperatures. We find a positive correlation between the magnitude of the ambipolar heating and the temperature increase at the same location after a characteristic time of 10^2 sec.Comment: To appear in Astronomy & Astrophysic

Сохраняем морскую историю с 1799 года (к юбилею Центральной военно-морской библиотеки)

The article describes the history of the Naval Library beginning with the Ordinance of Emperor Paul I of 25 November, 1799 till the present day. The article contains the story of Library Directors - the outstanding people of their time, employees, saving the library during the siege of Leningrad, as well as gives an outlook for the near future. The first part of the article describes the difficulties the new library had to overcome in the beginning of its glorious historical path. The second part covers the activities of the great Directors - seafarers, such as I. Kruzenshtern, F. Wrangell - Admirals, toured round the world, and many others, successfully managed the library in the nineteenth century. The third part focuses on the difficulties that befell the library in the twentieth century: Revolution, the Civil War and the Great Patriotic War. We are still grateful to E. Kazais, A. Maimistov, B. Nikolsky for their hard work, that allowed to save the collections. The final part of the article gives an overview on the current state of library and the prospects for the near future.Рассматриваются исторические сведения о зарождении и становлении Центральной военно-морской библиотеки с указа Императора Павла I от 25 ноября 1799 г. по сегодняшний день. Статья содержит рассказ о директорах - выдающихся людях своего времени, о сотрудниках, спасавших библиотеку в годы блокады Ленинграда и о перспективах на ближайшее время. В первой части повествуется о том, как зарождалась библиотека, какие трудности ей пришлось преодолеть в самом начале своего славного пути. Во второй части освещается деятельность великих директоров-моряков, таких как И.Ф. Крузенштерн, Ф.П. Врангель - адмиралов-кругосветчиков, и многих других, успешно руководивших библиотекой в XIX веке. Третья часть посвящена трудностям, постигшим библиотеку в ХХ в.: революция, Гражданская и Великая Отечественная войны. Людям, сумевшим спасти фонды: Э.М. Казаис, А.Р. Маймистову, Б.С. Никольскому мы до сих пор благодарны за их самоотверженный труд. Заключительная часть дает представление о современном состоянии библиотеки, а также о перспективах развития на ближайшее время

Opacity for realistic 3D MHD simulations of cool stellar atmospheres

Context. Realistic 3D time-dependent simulations of stellar near-surface convection employ the opacity binning method for efficient and accurate computation of the radiative energy exchange. The method provides several orders of magnitude of speed-up, but its implementation includes a number of free parameters. Aims. Our aim is to evaluate the accuracy of the opacity binning method as a function of the choice of these free parameters. Methods. The monochromatic opacities computed with the SYNSPEC code are used to construct opacity distribution function (ODF) that is then verified through detailed comparison with the results of the ATLAS code. The opacity binning method is implemented with the SYNSPEC opacities for four representative cool main-sequence stellar spectral types (F3V, G2V, K0V, and M2V). Results. The ODFs from SYNSPEC and ATLAS show consistent results for the opacity and bolometric radiative energy exchange rate Q in case of the F, G, and K -- type stars. Significant differences, coming mainly from the molecular line lists, are found for the M -- type star. It is possible to optimise a small number of bins to reduce the deviation of the results coming from the opacity grouping with respect to the ODF for the F, G, and K -- type stars. In the case of the M -- type star, the inclusion of splitting in wavelength is needed in the grouping to get similar results, with a subsequent increase in computing time. In the limit of a large number of bins, the deviation for all the binning configurations tested saturates and the results do not converge to the ODF solution. Due to this saturation, the Q rate cannot be improved by increasing the number of bins to more than about 20 bins. The more effective strategy is to select the optimal location of fewer bins.Comment: 26 pages, 29 figures. Accepted for publication in section 15 (Numerical methods and codes) of Astronomy and Astrophysic

In vitro mutagenicity assessment of fried meat-based food from mass catering companies

The current article aimed to evaluate the in vitro mutagenicity of ten fried meat-based food extracts obtained from different catering companies from Navarra (Spain). A miniaturized 6-well version of the Ames test in Salmonella typhimurium TA98, and the in vitro micronucleus test (OECD TG 487) in TK6 cells were performed. None of the ten extracts of fried meat-based food induced gene mutations in S. typhimurium TA98 with or without metabolic activation, but five induced chromosomal aberrations after 24 h treatment of TK6 without metabolic activation. More studies are needed to check the biological relevance of these in vitro studies