Pravidelné semináře pořádáme jednou měsíčně (říjen–červen, zpravidla první pondělí v měsíci) od 13 hod v seminární místnosti pracoviště Ondřejov. (archiv seminářů)
Dále pořádáme menší semináře jednotlivých oddělení:
Semináře slunečního oddělení
Každé úterý v 12:45 (září–červen, s výjimkou úterků po celoústavním semináři) v zasedací místnosti slunečního oddělení pracoviště Ondřejov.
01/11/2011, 13:00MERGING OF PLASMOIDS AND FRAGMENTATION DURING SOLAR FLARE RECONNECTION AND THEIR X-RAY AND RADIO SIGNATURESAbstract: Using a 2.5-D electromagnetic particle-in-cell model with free boundary conditions, merging of plasmoids was modelled. We recognized the plasmoids which mutually interacted and finally merged into one large plasmoid. Between interacting plasmoids further plasmoids and current sheets on smaller spatial scales were formed in agreement with the fragmentation found in MHD simulations. During interactions (merging - coalescences) of the plasmoids the electrons were very efficiently accelerated and heated. We found that after a series of such merging processes the electrons in some regions reached the energies relevant for the emission in the hard X-ray range. Considering these energetic electrons and assuming the plasma density 10^9-10^10 cm^(-3) and the source volume as in the December 31, 2007 flare, we computed the X-ray spectra as produced by the bremsstrahlung emission process. Comparing these spectra with observations, we propose that these processes can explain the observed above-the-loop-top hard X-ray sources. Furthermore, we show that the process of a fragmentation between two merging plasmoids can generate the narrowband dm-spikes.
Zářivě-(magneto)hydrodynamické semináře
Zpravidla 1x za 14 dní ve čtvrtek od 11 hod (říjen–červen) v zasedací místnosti slunečního oddělení pracoviště Ondřejov.
03/11/2011, 11:00Astronomical Institute, OndrejovParallelised Thomas algorithm for solution of TDM systems: Foundations and applications to implicit numerical schemes for integration of PDEs.Abstract: Chaotic nature of various microphysical processes leads to the blurring of edges and high gradients in continuous dynamic systems. These effects are reflected by the presence of parabolic (i.e. Laplace-like) terms in the PDEs governing the large-scale evolution of the studied system. The diffusion, heat conduction or resistivity are well known distinct examples of the above mentioned processes. Parabolic PDEs are, on the other hand, very restrictive what concerns the maximum time-step size that can be used for their numerical integration using explicit numerical schemes (see the CFL condition). In particular, this restriction becomes almost prohibitive in the high-resolution simulations as the time-step decreases quadratically with increasing resolution. The obvious way out is the use of the (semi)implicit numerical schemes. These frequently lead to the large tridiagonal-matrix (TDM) systems of linear algebraic equations. A standard and fast algorithm for solution of the TDM systems is that by Thomas. For its sequential nature it seems hard to make it parallelized, in particular for calculations in distributed-memory environments (MPI at computer clusters). Nevertheless, solution of this problem exists. In the talk an implementation based on the matrix Woodbury formula will be presented. After detailed explanation of the idea in behind the performance (scaling with CPU number) will be demonstrated. Finally, the Parallel Linear Algebra Manipulation Package (P-LAMPa) library developed in C++, which implements this (and other useful LA algorithms) will be briefly described.
Semináře oddělení GPS
Zpravidla v knihovně pracoviště Praha–Spořilov v různé dny.
29. 11. 2011, 10:00Astronomical Institute, Academy of Sciences, PragueThe Galactic center regionAbstract: High angular resolution radio interferometry at high frequencies enables us to study in great detail the emission mechanisms of the central region of our Galaxy, which harbours the supermassive black hole source Sagittarius A*. This talk will focus on recent results from our observations with two radio interferometer arrays, the Combined Array for Research in Millimeter-wave Astronomy (CARMA) and Australia Telescope Compact Array (ATCA), and the infrared Very Large Telescope (VLT). I will also present results from the flare modelling of Sgr A* based on multi-wavelength observing campaigns, along with high-resolution maps and a spectral index analysis of the extended emission of the central region (the "mini-spiral") at 3 and 1.3 mm, and compare them to maps in near-infrared Br-gamma (2.16 micron) and mid-indfrared (8.6 micron) wavelengths. I will discuss physical properties of gas and dust that can be deduced from these measurements, such as spectral index, emission measure, density, mass, and extinction.(Takes place at: Institute of Theoretical Physics, Praha-Troja)