Identication of linear slow sausage waves in magnetic pores

The analysis of an 11-hour series of high resolution white light observations of a large pore in the sunspot group NOAA 7519, observed on 5 June 1993 with the Swedish Vacuum Solar Telescope at La Palma on Canary Islands, has been recently described by Dorotovič et al. (2002). Special attention was paid to the evolution of a filamentary region attached to the pore, to horizontal motions around the pore, and to small-scale morphological changes. One of the results, relevant to out work here, was the determination of temporal area evolution of the studied pore where the area itself showed a linear trend of decrease with time at an average rate of −0.23 Mm2h−1 during the entire observing period. Analysing the time series of the are of the pore, there is strong evidence that coupling between the solar interior and magnetic atmosphere can occur at various scales and that the referred decrease of the area may be connected with a decrease of the magnetic field strength according to the magnetic field-to-size relation. Periods of global acoustic, e.g. p-mode, driven waves are usually in the range of 5–10 minutes, and are favourite candidates for the coupling of interior oscillations with atmospheric dynamics. However, by assuming that magneto-acoustic gravity waves may be there too, and may act as drivers, the observed periodicities (frequencies) are expected to be much longer (smaller), falling well within the mMHz domain. In this work we determine typical periods of such range in the area evolution of the pore using wavelet analysis. The resulted periods are in the range of 20–70 minutes, suggesting that periodic elements of the temporal evolution of the area of this studied pore could be linked to, and considered as, observational evidence of linear low-frequency slow sausage (magneto-acoustic gravity) waves in magnetic pores. This would give us further evidence on the coupling of global solar oscillations to the overlaying magnetic atmosphere

On-line annotation editor with audio visualization

Cílem této práce je vytvořit webový editor, který vedle přepisovaného textu zobrazuje i waveform, a tím usnadňuje orientaci v audiu. Pro zobrazení waveformu byla vyvinuta knihovna, která s použitím elementu canvas ze specifikace HTML5 zobrazuje průběh signálu s možností skrolování a přibližování. Ve waveformu jsou přímo vyznačeny anotace a poloha přepisovaného textu je synchronizována s umístěním anotace v audiu. Cílem je nahradit stávající editor novým, byl proto proveden uživatelský test, který je porovnal. Čas potřebný pro naučení obsluhy aplikace a přepis krátké nahrávky se snížil o 20%. Knihovna pro zobrazení waveformu byla uvolněna pod open source licencí.The aim of this thesis is to create a web-based annotation editor, which displays the audio waveform alongside the transcribed text. A waveform viewer library was developed, which uses HTML5 canvas elements for rendering. The library allows scrolling and zooming of the waveform. Annotations are directly marked in the audio and the position of the transcribed text is synchronised with their location. The end goal is to replace an existing editor with the one being created. Therefore, a usability test was conducted to compare the two. The time needed to learn to use the application and to transcribe a short recording was reduced by 20%. The waveform viewer library was released under an open-source license.

Moving Object Detection in the Environment of Mobile Robot

Táto práca rieši problém detekcie pohybujúcich sa objektov v okolí robota. Prostredie je reprezentované dvojrozmernou okupačnou mriežkou, ktorá obsahuje aktuálne viditeľné prostredie, bez filtrovania v čase. Ako samotný detektor pohybu slúži časticový filter založený na systéme v článku Grid-based Mapping and Tracking in Dynamic Environments using a Uniform Evidential Environment Representation, ktorý uviedol Tanzmeister a kolektív. Implementácia s využitím Robotického operačného systému poskytuje možnosť pre znovupoužitie modulov, z ktorých riešenie pozostáva. Ako zdroj LiDARových dát pre experimenty bola zvolená databáza KITTI Visual Odometry, ktorá obsahuje aj pózy vozidla. Mračná bodov boli predspracované vynechaním bodov ležiacich na zemi metódou Loopy Belief Propagation. Vytvorený detektor dokáže na sekvenciách databázy rozlišovať pohybujúce sa vozidlá. Pri testoch na simulovanom prostredí sa ukázali nedostatky detekcie v prípade pohybu veľkých súvislých objektov.This work's aim is movement detection in the environment of a robot, that may move itself. A 2D occupancy grid representation is used, containing only the currently visible environment, without filtering in time. Motion detection is based on a grid-based particle filter introduced by Tanzmeister et al. in Grid-based Mapping and Tracking in Dynamic Environments using a Uniform Evidential Environment Representation. The system was implemented in the Robot Operating System, which allows for re-use of modules which the solution is composed of. The KITTI Visual Odometry dataset was chosen as a source~of LiDAR data for experiments, along with ground-truth pose information. Ground segmentation based on Loopy Belief Propagation was used to filter the point clouds. The implemeted motion detector is able to distiguish between static and dynamic vehicles in this dataset. Further tests in a simulated environment have shown some shortcomings in the detection of large continuous moving objects.

Observing the Solar Chromosphere

This review is split into two parts: one on chromospheric line formation in answer to the frequent question "where is my line formed", and one presenting state-of-the-art imagery of the chromosphere. In the first part I specifically treat the formation of the Na D lines, Ca II H & K, and Halpha. In the second I show DOT, IBIS, VAULT, and TRACE images as evidence that the chromosphere consists of fibrils of intrinsically different types. The straight-up ones are hottest. The slanted ones are filled by shocks and likely possess thin transition sheaths to coronal plasma. The ones hovering horizontally over "clapotispheric" cell interiors outline magnetic canopies and are buffeted by shocks, most violently in the quietest regions. In the absence of integral-field ultraviolet spectrometry, H$\alpha$ remains the principal chromosphere diagnostic. The required fast-cadence profile-sampling imaging is an important quest for new telescope technology.Comment: in press,"Physics of Chromospheric Plasmas" (Coimbra), ASP 368, 27 (2007

Temporal Variations in Fibril Orientation

We measure variations in orientation of fourteen dynamic fibrils as a function of time in a small isolated plage and nearby network using a 10-min time sequence of H-alpha filtergrams obtained by the Dutch Open Telescope. We found motions with average angular velocities of the order of 1 deg/min suggesting systematic turning from one limit position to another, particularly apparent in the case of fibrils with lifetimes of a few minutes. Shorter fibrils tend to turn faster than longer ones, which we interpret as due to vortex flows in the underlying granulation that twist magnetic fields.Comment: In press,"Physics of Chromospheric Plasmas" (Coimbra), ASP 368, 115 (2007

Aperture Increase Options for the Dutch Open Telescope

This paper is an invitation to the international community to participate in the usage and a substantial upgrade of the Dutch Open Telescope on La Palma (DOT, \url{http://dot.astro.uu.nl}). We first give a brief overview of the approach, design, and current science capabilities of the DOT. The DOT database (\url{http://dotdb.phys.uu.nl/DOT}) now contains many tomographic image sequences with 0.2-0.3 arcsec resolution and up to multi-hour duration. You are welcome to pull them over for analysis. The main part of this contribution outlines DOT upgrade designs implementing larger aperture. The motivation for aperture increase is the recognition that optical solar physics needs the substantially larger telescope apertures that became useful with the advent of adaptive optics and viable through the DOT's open principle, both for photospheric polarimetry at high resolution and high sensitivity and for chromospheric fine-structure diagnosis at high cadence and full spectral sampling. Realization of an upgrade requires external partnership(s). This report about DOT upgrade options therefore serves also as initial documentation for potential partners.Comment: in press,"Physics of Chromospheric Plasmas" (Coimbra), ASP 368, 573 (2007

Photospheric observations of surface and body modes in solar magnetic pores

Over the past number of years, great strides have been made in identifying the various low-order magnetohydrodynamic wave modes observable in a number of magnetic structures found within the solar atmosphere. However, one aspect of these modes that has remained elusive, until now, is their designation as either surface or body modes. This property has significant implications for how these modes transfer energy from the waveguide to the surrounding plasma. Here, for the first time to our knowledge, we present conclusive, direct evidence of these wave characteristics in numerous pores that were observed to support sausage modes. As well as outlining methods to detect these modes in observations, we make estimates of the energies associated with each mode. We find surface modes more frequently in the data, as well as that surface modes appear to carry more energy than those displaying signatures of body modes. We find frequencies in the range of ~2–12 mHz, with body modes as high as 11 mHz, but we do not find surface modes above 10 mHz. It is expected that the techniques we have applied will help researchers search for surface and body signatures in other modes and in differing structures from those presented here

Photospheric logarithmic velocity spirals as MHD wave generation mechanisms

High-resolution observations of the solar photosphere have identified a wide variety of spiralling motions in the solar plasma. These spirals vary in properties, but are observed to be abundant at the solar surface. In this work, these spirals are studied for their potential as magnetohydrodynamic (MHD) wave generation mechanisms. The inter-granular lanes, where these spirals are commonly observed, are also regions where the magnetic field strength is higher than average. This combination of magnetic field and spiralling plasma is a recipe for the generation of Alfvén waves and other MHD waves. This work employs numerical simulations of a self-similar magnetic flux tube embedded in a realistic, gravitationally stratified, solar atmosphere to study the effects of a single magnetic flux tube perturbed by a logarithmic velocity spiral driver. The expansion factor of the logarithmic spiral driver is varied and multiple simulations are run for a range of values of the expansion factor centred around observational constraints. The simulations are analysed using ‘flux surfaces’ constructed from the magnetic field lines so that the vectors perpendicular, parallel and azimuthal to the local magnetic field vector can be calculated. The results of this analysis show that the Alfvén wave is the dominant wave for lower values of the expansion factor, whereas for the higher values the parallel component is dominant. This transition occurs within the range of the observational constraints, meaning that spiral drivers, as observed in the solar photosphere, have the potential to generate a variety of MHD wave modes

Standing sausage waves in photospheric magnetic waveguides

By focusing on the oscillations of the cross-sectional area and the intensity of magnetic waveguides located in the lower solar atmosphere, we aim to detect and identify magnetohydrodynamic (MHD) sausage waves. Capturing several series of high-resolution images of pores and sunspots and employing wavelet analysis in conjunction with empirical mode decomposition (EMD) makes the MHD wave analysis possible. For this paper, two sunspots and one pore (with a light bridge) were chosen as representative examples of MHD waveguides in the lower solar atmosphere. The sunspots and pore display a range of periods from 4 to 65 minutes. The sunspots support longer periods than the pore - generally enabling a doubling or quadrupling of the maximum pore oscillatory period. All of these structures display area oscillations indicative of MHD sausage modes and in-phase behaviour between the area and intensity, presenting mounting evidence for the presence of the slow sausage mode within these waveguides. The presence of fast and slow MHD sausage waves has been detected in three different magnetic waveguides in the lower solar photosphere. Furthermore, these oscillations are potentially standing harmonics supported in the waveguides which are sandwiched vertically between the temperature minimum in the lower solar atmosphere and the transition region. Standing harmonic oscillations, by means of solar magneto-seismology, may allow insight into the sub-resolution structure of photospheric MHD waveguides