Comparative study of different scattering geometries for the proposed Indian X-ray polarization measurement experiment using Geant4

Polarization measurements in X-rays can provide unique opportunity to study the behavior of matter and radiation under extreme magnetic fields and extreme gravitational fields. Unfortunately, over past two decades, when X-ray astronomy witnessed multiple order of magnitude improvement in temporal, spatial and spectral sensitivities, there is no (or very little) progress in the field of polarization measurements of astrophysical X-rays. Recently, a proposal has been submitted to ISRO for a dedicated small satellite based experiment to carry out X-ray polarization measurement, which aims to provide the first X-ray polarization measurements since 1976. This experiment will be based on the well known principle of polarization measurement by Thomson scattering and employs the baseline design of a central low Z scatterer surrounded by X-ray detectors to measure the angular intensity distribution of the scattered X-rays. The sensitivity of such experiment is determined by the collecting area, scattering and detection efficiency, X-ray detector background, and the modulation factor. Therefore, it is necessary to carefully select the scattering geometry which can provide the highest modulation factor and thus highest sensitivity within the specified experimental constraints. The effective way to determine optimum scattering geometry is by studying various possible scattering geometries by means of Monte Carlo simulations. Here we present results of our detailed comparative study based on Geant4 simulations of five different scattering geometries which can be considered within the weight and size constraints of the proposed small satellite based X-ray polarization measurement experiment.Comment: 14 pages, 6 figures, accepted for publication in "Nuclear Inst. and Methods in Physics Research, A

Polarization of synchrotron emission from relativistic reconfinement shocks

We study the polarization properties of relativistic reconfinement shocks with chaotic magnetic fields. Using our hydrodynamical model of their structure, we calculate synthetic polarization maps, longitudinal polarization profiles and discuss the spatially averaged polarization degree as a function of jet half-opening angle Theta_j, jet Lorentz factor Gamma_j and observer inclination angle to the jet axis theta_{obs}. We find, that for theta_{obs} <= Theta_j the wave electric vectors are parallel in the vicinity of the structure ends and perpendicular in between, while for theta_{obs} > Theta_j the polarization can only be perpendicular. The spatially averaged polarization degree does not exceed 30%. Parallel average polarization, with polarization degrees lower than 10%, have been found for theta_{obs} < Theta_j under the condition Gamma_j * Theta_j > 1. As earlier works predicted the parallel polarization from relativistic conical shocks, we explain our results by discussing conical shocks with divergent upstream flow.Comment: 8 pages, 10 figures, accepted for publication in MNRA

Image processing using Android device

Tato diplomová práce se zabývá zpracováním obrazu v platformě Android, respektive vývojem mobilní aplikace, která je schopná provádět detekci a rozpoznávání obličejů v reálné scéně. V rámci projektu byla provedená rešerše současně existujících metod detekce obličejů, byly prozkoumány a porovnány standardní prostředky platformy Android pro detekci tváří (FaceDetector a FaceDetectionListener) a také knihovny JJIL, OpenIMAJ, OpenCV. Pro rozpoznání obličejů byla použita knihovna OpenCV a vyzkoušeny tři algoritmy identifikace: FisherFaces, EigenFaces a Local Binary Patterns Histograms. Na základě porovnání nejúspěšnější metody byly uplatněny ve vyvinuté aplikaci.This master’s Thesis focuses on image processing on Android platform and development of an application, that is able to do face detection and recognition in real scene. Thesis gives highlight of modern algorithms of face detection. It first examines and compares the standard features of Android platform (FaceDetector a FaceDetectionListener) and JJIL, OpenIMAJ, OpenCV libraries experiment, and presents the results. For purposes of face recognition was selected OpenCV library. Three different algorithms of identification were tested: FisherFaces, EigenFaces a Local Binary Patterns Histograms. Based on performance comparison best methods were implemented in developed application.

Active Galactic Nuclei Jets and Multiple Oblique Shock Acceleration: Starved Spectra

Shocks in jets and hot spots of Active Galactic Nuclei (AGN) are one prominent class of possible sources of very high energy cosmic ray particles (above 10^18eV). Extrapolating their spectrum to their plausible injection energy from some shock, implies an enormous hidden energy for a spectrum of index ~-2. Some analyzes suggest the particles' injection spectrum at source to be as steep as -2.4 to -2.7, making the problem much worse, by a factor of order 10^6. Nevertheless, it seems implausible that more than at the very best 1/3 of the jet energy, goes into the required flux of energetic particles thus, one would need to allow for the possibility that there is an energy problem, which we would like to address in this work. Sequences of consecutive oblique shock features, or conical shocks, have been theorized and eventually observed in many AGN jets. Based on that, we use by analogy the 'Comptonisation' effect and we propose a scenario of a single injection of particles which are accelerated consecutively by several oblique shocks along the axis of an AGN jet. We use detailed test-particle approximation Monte Carlo simulations in order to calculate particle spectra by acceleration at such a shock pattern while monitoring the efficiency of acceleration, calculating differential spectra. We find that the first shock of a sequence of oblique shocks, establishes a low energy power-law spectrum with ~E^-2.7. The consecutive shocks push the spectrum up in energy, rendering flatter distributions with steep cut-offs and characteristic depletion at low energies, an effect which could explain the puzzling apparent extra source power as well as the flat or inverted spectra from distant flaring sources.Comment: 14 pages, submitted to A&

Image processing using Android device

Tato diplomová práce se zabývá zpracováním obrazu v platformě Android, respektive vývojem mobilní aplikace, která je schopná provádět detekci a rozpoznávání obličejů v reálné scéně. V rámci projektu byla provedená rešerše současně existujících metod detekce obličejů, byly prozkoumány a porovnány standardní prostředky platformy Android pro detekci tváří (FaceDetector a FaceDetectionListener) a také knihovny JJIL, OpenIMAJ, OpenCV. Pro rozpoznání obličejů byla použita knihovna OpenCV a vyzkoušeny tři algoritmy identifikace: FisherFaces, EigenFaces a Local Binary Patterns Histograms. Na základě porovnání nejúspěšnější metody byly uplatněny ve vyvinuté aplikaci.This master’s Thesis focuses on image processing on Android platform and development of an application, that is able to do face detection and recognition in real scene. Thesis gives highlight of modern algorithms of face detection. It first examines and compares the standard features of Android platform (FaceDetector a FaceDetectionListener) and JJIL, OpenIMAJ, OpenCV libraries experiment, and presents the results. For purposes of face recognition was selected OpenCV library. Three different algorithms of identification were tested: FisherFaces, EigenFaces a Local Binary Patterns Histograms. Based on performance comparison best methods were implemented in developed application.