The nature of X-ray spectral variability in Seyfert Galaxies

We use a model-independent technique to investigate the nature of the 2-15 keV X-ray spectral variability in four Seyfert galaxies and distinguish between spectral pivoting and the two-component model for spectral variability. Our analysis reveals conclusively that the softening of the X-ray continuum with increasing flux in MCG -6-30-15 and NGC 3516 is a result of summing two spectral components: a soft varying component (SVC) with spectral shape independent of flux and a constant hard component (HCC). In contrast, the spectral variability in NGC 4051 can be well described by simple pivoting of one component, together with an additional hard constant component. The spectral variability model for NGC 5506 is ambiguous, due to the smaller range of fluxes sampled by the data. We investigate the shape of the hard spectral component in MCG -6-30-15 and find that it appears similar to a pure reflection spectrum, but requires a large reflected fraction (R>3). We briefly discuss physical interpretations of the different modes of spectral variability.Comment: Accepted for publication in MNRAS letter

A brief review of long-term X-ray and optical variability in radio-quiet AGN

Long-time-scale X-ray and optical variability is a key characteristic of AGN. Here, we summarise our current understanding of the X-ray and optical continuum variability of radio-quiet AGN and the relation between the two bands. We demonstrate the strong connection between the X-ray variability properties of AGN and the variability of stellar-mass black hole candidates on much shorter time-scales, and discuss the implications of this result for the origins of the variability. The relationship between optical and X-ray variability is complex, with some AGN showing strong X-ray/optical correlations while others show no obvious correlation. We suggest a possible explanation for this variety of behaviour.Comment: 8 pages, invited contribution to the conference 'Stellar mass, Intermediate-mass and Supermassive black holes', October 28-31 2003, Kyoto, Japan (proceedings to be published in Progress of Theoretical Physics

Tax Optimization in Change of Legal Form from a Sole Entrepreneur to a Limited Company

Diplomová práce se zabývá analýzou změny právní formy podnikání z fyzické osoby na právnickou, konkrétně na společnost s ručením omezeným. Práce je zaměřená na způsob zdanění fyzických a právnických osob, na jednotlivé možnosti přechodu mezi těmito právními formami a zhodnocení záporů a kladů jednotlivých forem podnikání. Cílem práce je sdělit podnikateli výhody a nevýhody zdanění jednotlivých forem podnikání, navrhnout podnikateli změnu právní formy a seznámit ho s jednotlivými kroky, které jsou potřeba při změně právní formy udělat.This thesis analyzes the changes in the legal form of business from individuals to corporate, namely the limited liability company. The work is focused on the method of taxation of natural and legal persons, individual ability to switch between these legal forms and evaluate the pros and cons of various forms of business. The aim is to communicate the business advantages and disadvantages of different forms of taxation of business, entrepreneurs propose a change of legal form and to acquaint him with the steps that are needed to change the legal form to do.

Pulse-phase resolved spectroscopy of continuum and reflection in SAX J1808.4-3658

We perform phase-resolved spectroscopy of the accreting millisecond pulsar, SAX J1808.4-3658, during the slow-decay phase of the 2002 outburst. Simple phenomenological fits to RXTE PCA data reveal a pulsation in the iron line at the spin frequency of the neutron star. However, fitting more complex spectral models reveals a degeneracy between iron-line pulsations and changes in the underlying hotspot blackbody temperature with phase. By comparing with the variations in reflection continuum, which are much weaker than the iron line variations, we infer that the iron-line is not pulsed. The observed spectral variations can be explained by variations in blackbody temperature associated with rotational Doppler shifts at the neutron star surface. By allowing blackbody temperature to vary in this way, we also find a larger phase-shift between the pulsations in the Comptonised and blackbody components than has been seen in previous work. The phase-shift between the pulsation in the blackbody temperature and normalisation is consistent with a simple model where the Doppler shift is maximised at the limb of the neutron star, ~90 degrees prior to maximisation of the hot-spot projected area.Comment: 8 pages, 10 figures, 2 tables. Accepted by MNRA

Measuring quality of life in Duchenne muscular dystrophy : a systematic review of the content and structural validity of commonly used instruments

Duchenne muscular dystrophy (DMD) is an inherited X-linked neuromuscular disorder. A number of questionnaires are available to assess quality of life in DMD, but there are concerns about their validity. This systematic review aimed to appraise critically the content and structural validity of quality of life instruments for DMD. Five databases (EMBASE, MEDLINE, CINAHL, PsycINFO, and Cochrane Library) were searched, with supplementary searches in Google Scholar. We included articles with evidence on the content and/or structural validity of quality of life instruments in DMD, and/or instrument development. Evidence was evaluated against the Consensus-based Standards for the selection of health Measurement INstruments (COSMIN) criteria. Fifty five articles featured a questionnaire assessing quality of life in DMD. Forty instruments were extracted and 26 underwent assessment. Forty-one articles contained evidence on content or structural validity (including 37 development papers). Most instruments demonstrated low quality evidence and unsatisfactory or inconsistent validity in DMD, with the majority not featuring direct validation studies in this population. Only KIDSCREEN received an adequate rating for instrument design and a satisfactory result for content validity based on its development, yet, like the majority of PROMs, the measure has not been directly validated for use in DMD. Further research is needed on the validity of quality of life instruments in DMD, including content and structural validity studies in this population

A multi-country test of brief reappraisal interventions on emotions during the COVID-19 pandemic.

The COVID-19 pandemic has increased negative emotions and decreased positive emotions globally. Left unchecked, these emotional changes might have a wide array of adverse impacts. To reduce negative emotions and increase positive emotions, we tested the effectiveness of reappraisal, an emotion-regulation strategy that modifies how one thinks about a situation. Participants from 87 countries and regions (n = 21,644) were randomly assigned to one of two brief reappraisal interventions (reconstrual or repurposing) or one of two control conditions (active or passive). Results revealed that both reappraisal interventions (vesus both control conditions) consistently reduced negative emotions and increased positive emotions across different measures. Reconstrual and repurposing interventions had similar effects. Importantly, planned exploratory analyses indicated that reappraisal interventions did not reduce intentions to practice preventive health behaviours. The findings demonstrate the viability of creating scalable, low-cost interventions for use around the world

Timing studies of Seyfert galaxies with the Rossi X-ray timing explorer

Previous studies of the X-ray variability power spectra of active galactic nuclei (AGN) on time-scales of hours to days revealed striking similarities to the timing properties of black hole X-ray binary systems (XRBs) on much shorter time-scales (&lt; 1 s). The unique capabilities of the Rossi X-ray Timing Explorer (RXTE) mission allow us to sample AGN lightcurves over a far greater range of time-scales than before, enabling us to compare the broadband power spectrum of AGN with that of XRBs. Here we present the results of an RXTE program to monitor 4 Seyfert galaxies (NGC 4051, MCG-6-30-15, NGC 5506 and NGC 5548) to measure their power spectra from 10-8 Hz to 10-2 Hz.We use RXTE long-look observations to show that the power spectra of our sample are intrinsically non-stationary, in that their RMS variability scales with local mean flux. We show that this relation also applies to the black hole XRB Cygnus X-1 and the accreting millisecond pulsar SAX J1808.4-3658 and is highly linear, implying that it is intrinsic to the red-noise variability process which dominates the X-ray lightcurves of accreting compact objects. The scaling of RMS variability with flux occurs on all measured time-scales, posing problems for models where lightcurves are made from small building blocks, such as conventional shot-noise models. We suggest that the lightcurves are built from the top down, out of large flaring events which break up into self-similar structure on smaller scales.Discrete sampling of lightcurves causes distortion in the observed power spectrum due to red-noise leak and aliaising effects. We develop a Monte Carlo technique, based on the 'response method' of Done et al. (1992), to robustly estimate the shape of the underlying broadband power spectrum. We apply this technique to our data, and data obtained from a separate program to monitor the Seyfert galaxy NGC 3516. We find that the broad-band power spectra of MCG-6-30-15, NGC 5506 and NGC 3516 flatten significantly at low frequencies, and that this flattening can be well fitted by a high-frequency break mode analogous to the shape of the high-frequency power spectrum of Cygnus X-1.</p