Positions and sizes of X-ray solar flare sources

<p><b>Aims:</b> The positions and source sizes of X-ray sources taking into account Compton backscattering (albedo) are investigated.</p> <p><b>Methods:</b> Using a Monte Carlo simulation of X-ray photon transport including photo-electric absorption and Compton scattering, we calculate the apparent source sizes and positions of X-ray sources at the solar disk for various source sizes, spectral indices and directivities of the primary source.</p> <p><b>Results:</b> We show that the albedo effect can alter the true source positions and substantially increase the measured source sizes. The source positions are shifted by up to ~0.5” radially towards the disk centre and 5 arcsec source sizes can be two times larger even for an isotropic source (minimum albedo effect) at 1 Mm above the photosphere. The X-ray sources therefore should have minimum observed sizes, and thus their FWHM source size (2.35 times second-moment) will be as large as ~7” in the 20-50 keV range for a disk-centered point source at a height of 1 Mm (~1.4”) above the photosphere. The source size and position change is greater for flatter primary X-ray spectra, a stronger downward anisotropy, for sources closer to the solar disk centre, and between the energies of 30 and 50 keV.</p> <p><b>Conclusions:</b> Albedo should be taken into account when X-ray footpoint positions, footpoint motions or source sizes from e.g. RHESSI or Yohkoh data are interpreted, and we suggest that footpoint sources should be larger in X-rays than in either optical or EUV ranges.</p&gt

Analysis of the Competitiveness of the Small Enterprise

Diplomová práce se zabývá analýzou konkurenceschopnosti malého podniku. Práce je rozdělena na teoretickou a praktickou část. Teoretická část obsahuje vymezení základních pojmů týkající se podnikání a konkurenceschopnosti. V této části jsou také popsány jednotlivé metody pro hodnocení konkurenceschopnosti, mezi které patří PESTLE analýza, Porterův model pěti konkurenčních sil, mystery shopping, benchmarking a SWOT analýza. Praktická část zahrnuje charakteristiku firmy Marek Kaspar, na niž jsou uvedené metody aplikovány v praxi. V závěru praktické části jsou zformulovány návrhy a doporučení pro zvýšení konkurenceschopnosti firmy Marek Kaspar.This thesis deals with analysis of competitiveness of small business. The work is divided into theoretical and practical part. The theoretical part defines the basic concepts related to entrepreneurship and competitiveness. This section also describes the different methods for assessing competitiveness, which include PESTLE analysis, Porter's five forces model, mystery shopping, benchmarking and SWOT analysis. The practical part includes a characteristic of the company Marek Kaspar to which those methods are applied in practice. At the end of the practical part they are formulated proposals and recommendations to improve the competitiveness of the company Marek Kaspar.152 - Katedra podnikohospodářskávelmi dobř

Evaluation of the Selected Expenditures of the Municipal Budget of the Town Kozmice

Hlavním cílem bylo zhodnocení vybraných výdajů obce Kozmice v průběhu let 2010 až 2020. V první části je charakterizována územní samospráva, obec a obecní rozpočet. Obecní rozpočet je rozdělen na příjmy a výdaje, které se dělí podle druhu nebo odvětví. Druhové dělení člení výdaje na běžné a kapitálové a odvětvové je člení podle odvětví do šesti skupin. V další části této bakalářské práce byla část praktická která je tvořená ze dvou kapitol. V první z nich jsou charakterizovány použité metody a obec Kozmice. V druhé z nich je vybrána skupina, která tvoří běžné výdaje, které jsou hodnoceny v závislosti na vývoji v průběhu let a v závislosti na procentuálním zastoupení na běžných a celkových výdajích. Pro toto hodnocení byly vybrány tyto výdaje: neinvestiční nákupy a související výdaje, platy a podobné související výdaje, výdaje na neinvestiční transfery veřejnoprávním subjektům, výdaje na neinvestiční transfery soukromoprávním subjektům, výdaje na neinvestiční transfery obyvatelstvu, výdaje na neinvestiční transfery a související platby do zahraničí a ostatní neinvestiční výdaje. V poslední části práce je uveden závěr, ve kterém shrnuta charakteristika práce.The main goal was to evaluate selected expenditures of the municipality of Kozmice during the years 2010 to 2020. The first part characterizes the territorial self-government, the municipality and the municipal budget. The municipal budget is divided into revenues and expenditures, which are divided by type or industry. The breakdown by type divides expenditure into current and capital and sectoral into six groups. In the next part of this bachelor thesis was the practical part, which consists of two chapters. The first of them characterizes the methods used and the village Kozmice. In the second of them, a group is selected, which consists of current expenditures, which are evaluated depending on the development over the years and depending on the percentage of current and total expenditures. The following expenditure was selected for this evaluation: non-investment purchases and related expenditure, salaries and similar related expenditure, expenditure on non-investment transfers to public entities, expenditure on non-investment transfers to private entities, expenditure on non-investment transfers to the population, expenditure on non-investment transfers and related payments abroad, and other non - capital expenditure. In the last part of the work is the conclusion.153 - Katedra veřejné ekonomikyvelmi dobř

Hydrogen Balmer line formation in solar flares affected by return currents

Aims. We investigate the effect of the electric return currents in solar flares on the profiles of hydrogen Balmer lines. We consider the monoenergetic approximation for the primary beam and runaway model of the neutralizing return current. Methods. Propagation of the 10 keV electron beam from a coronal reconnection site is considered for the semiempirical chromosphere model F1. We estimate the local number density of return current using two approximations for beam energy fluxes between $4\times 10^{11}$ and $1\times 10^{12} {\rm erg cm^{-2} s^{-1}}$. Inelastic collisions of beam and return-current electrons with hydrogen are included according to their energy distributions, and the hydrogen Balmer line intensities are computed using an NLTE radiative transfer approach. Results. In comparison to traditional NLTE models of solar flares that neglect the return-current effects, we found a significant increase emission in the Balmer line cores due to nonthermal excitation by return current. Contrary to the model without return current, the line shapes are sensitive to a beam flux. It is the result of variation in the return-current energy that is close to the hydrogen excitation thresholds and the density of return-current electrons.Comment: 4 pages, 3 figures, 1 table, accepted for publication in Astronomy and Astrophysics Letter

Non-thermal recombination - a neglected source of flare hard X-rays and fast electron diagnostic

Context. Flare Hard X-Rays (HXRs) from non-thermal electrons are commonly treated as solely bremsstrahlung (f-f), recombination (f-b) being neglected. This assumption is shown to be substantially in error, especially in hot sources, mainly due to recombination onto Fe ions. Aims. We analyse the effects on HXR spectra and electron diagnostics by including non-thermal recombination onto heavy elements in our model. Methods. Using Kramers hydrogenic cross sections with effective Z, we calculate f-f and f-b spectra for power-law electron spectra, in both thin and thick target limits, and for Maxwellians, with summation over all important ions. Results. We find that non-thermal electron recombination, especially onto Fe, must, in general, be included together with f-f, for reliable spectral interpretation, when the HXR source is hot. f-b contribution is greatest when the electron spectral index is large, and any low energy cut-off small. f-b spectra recombination edges mean a cut-off in F(E) appears as a HXR feature at Photon energy = Ec + Vz, offering an Ec diagnostic. Including f-b lowers, greatly in some cases, the F(E) needed for prescribed HXR fluxes and, even when small, seriously distorts F(E) as inferred by inversion or forward fitting based on f-f alone. Conclusions. f-b recombination from non-thermal electrons can be an important contributor to HXR spectra and should be included in spectral analyses, especially for hot sources. Accurate results will require use of better cross sections than ours and consideration of source ionisation structure.Comment: 13 pages, 2 tables, 9 figures, Accepted for publication in A&

Local re-acceleration and a modified thick target model of solar flare electrons

The collisional thick target model (CTTM) of solar hard X-ray (HXR) bursts has become an almost 'Standard Model' of flare impulsive phase energy transport and radiation. However, it faces various problems in the light of recent data, particularly the high electron beam density and anisotropy it involves.} {We consider how photon yield per electron can be increased, and hence fast electron beam intensity requirements reduced, by local re-acceleration of fast electrons throughout the HXR source itself, after injection.} {We show parametrically that, if net re-acceleration rates due to e.g. waves or local current sheet electric (${\cal E}$) fields are a significant fraction of collisional loss rates, electron lifetimes, and hence the net radiative HXR output per electron can be substantially increased over the CTTM values. In this local re-acceleration thick target model (LRTTM) fast electron number requirements and anisotropy are thus reduced. One specific possible scenario involving such re-acceleration is discussed, viz, a current sheet cascade (CSC) in a randomly stressed magnetic loop.} {Combined MHD and test particle simulations show that local ${\cal E}$ fields in CSCs can efficiently accelerate electrons in the corona and and re-accelerate them after injection into the chromosphere. In this HXR source scenario, rapid synchronisation and variability of impulsive footpoint emissions can still occur since primary electron acceleration is in the high Alfv\'{e}n speed corona with fast re-acceleration in chromospheric CSCs. It is also consistent with the energy-dependent time-of-flight delays in HXR features.Comment: 8 pages, 2 figure

Hydrogen Hα\alpha line polarization in solar flares. Theoretical investigation of atomic polarization by proton beams considering self-consistent NLTE polarized radiative transfer

Context. We present a theoretical review of the effect of impact polarization of a hydrogen H$\alpha$ line due to an expected proton beam bombardment in solar flares. Aims. Several observations indicate the presence of the linear polarization of the hydrogen H$\alpha$ line observed near the solar limb above 5% and preferentially in the radial direction. We theoretically review the problem of deceleration of the beam originating in the coronal reconnection site due to its interaction with the chromospheric plasma, and describe the formalism of the density matrix used in our description of the atomic processes and the treatment of collisional rates. Methods. We solve the self-consistent NLTE radiation transfer problem for the particular semiempirical chromosphere models for both intensity and linear polarization components of the radiation field. Results. In contrast to recent calculations, our results show that the energy distribution of the proton beam at H$\alpha$ formation levels and depolarizing collisions by background electrons and protons cause a significant reduction of the effect below 0.1%. The radiation transfer solution shows that tangential resonance-scattering polarization dominates over the impact polarization effect in all considered models. Conclusions. In the models studied, proton beams are unlikely to be a satisfying explanation for the observed linear polarization of the H$\alpha$ line.Comment: 11 pages, 11 figures, accepted for publication in A&

Thermalisation of self-interacting solar flare fast electrons

Most theoretical descriptions of the production of solar flare bremsstrahlung radiation assume the collision of dilute accelerated particles with a cold, dense target plasma, neglecting interactions of the fast particles with each other. This is inadequate for situations where collisions with this background plasma are not completely dominant, as may be the case in, for example, low-density coronal sources. We aim to formulate a model of a self-interacting, entirely fast electron population in the absence of a dense background plasma, to investigate its implications for observed bremsstrahlung spectra and the flare energy budget. We derive approximate expressions for the time-dependent distribution function of the fast electrons using a Fokker-Planck approach. We use these expressions to generate synthetic bremsstrahlung X-ray spectra as would be seen from a corresponding coronal source. We find that our model qualitatively reproduces the observed behaviour of some flares. As the flare progresses, the model's initial power-law spectrum is joined by a lower energy, thermal component. The power-law component diminishes, and the growing thermal component proceeds to dominate the total emission over timescales consistent with flare observations. The power-law exhibits progressive spectral hardening, as is seen in some flare coronal sources. We also find that our model requires a factor of 7 - 10 fewer accelerated electrons than the cold, thick target model to generate an equivalent hard X-ray flux. This model forms the basis of a treatment of self-interactions among flare fast electrons, a process which affords a more efficient means to produce bremsstrahlung photons and so may reduce the efficiency requirements placed on the particle acceleration mechanism. It also provides a useful description of the thermalisation of fast electrons in coronal sources.Comment: 9 pages, 7 figures, accepted for Astronomy & Astrophysics; this version clarifies arguments around Eqs. (11) and (20

Principy ekonomického řízení RVT

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Ověření Oswaldovy hypotézy pro okresy České republiky

The main aim of the thesis is to decide whether the share of home ownership has any effect on the unemployment rate for districts of the Czech Republic and whether Oswald hypothesis is valid. There are issues concerning Oswald hypothesis in the Bibliography, especially labour market and residential market. The chapter Methodology describes econometric analysis, which was used for the needs of the practical part. The results of this thesis are discussed and compared with foreign works