Estimation of width and inclination of a filament sheet using He II 304 A observations by STEREO/EUVI

The STEREO mission has been providing stereoscopic view of the filament eruptions in EUV wavelengths. The most extended view during filament eruptions is seen in He II 304 \AA observations, as the filament spine appears darker and sharper. The projected filament width appears differently when viewed from different angles by STEREO satellites. Here, we present a method for estimating the width and inclination of the filament sheet using He II 304 \AA\ observations by STEREO-A and B satellites from the two viewpoints. The width of the filament sheet, when measured from its feet to its apex, gives estimate of filament height above the chromosphere.Comment: 9 pages, 2 figures, in Annales Geophysica

Dystopian Realities : Investigating the Perception of and Interaction with Surveillance Practices

This article seeks to sketch out how the field of surveillance studies has conceptualized surveillance practices, and how cultural and technological shifts have prompted scholars to re-imagine these theoretical frameworks. The article investigates the interplay of (dystopian) popular cultural representations of surveillance cultures and the perception of and attitude towards contemporary surveillance practices, as well as how individuals react to and interact with them. The article also outlines a study regarding the aforementioned issues that was conducted among a sample of 150 university students, which focused especially on each participant’s subjective ability to distinguish between fictional scenarios and real-life surveillance practices

Stress testing of real credit portfolios

Stress testing has become a crucial point on the Basel II agenda, mainly as Pillar I estimates do not explicitly take portfolio concentration into account. We start from the credit portfolio of the German pension insurer being a cross-sectional representation of the German economy and subsequently compose three bank portfolios corresponding to a small, medium and large bank. We apply univariate and multivariate stress tests both by using the Internal Rating based (IRB) model and by a model that additionally allows for variation of correlation. In a severe multivariate stress scenario based on historical data for Germany IRB capital requirements increase by more than 80% with little differences between the credit portfolios. If stress testing is additionally applied to correlation, the Value-at-Risk increases by up to 300% and portfolio differences materialize. --Credit Portfolio,Exposure concentration,Stress Testing,Basel II,Economic Capital

Stress Testing Credit Risk: Is the Czech Republic Different from Germany?

This study deals with credit risk modelling and stress testing within the context of a Merton-type one-factor model. We analyse the corporate and household sectors of the Czech Republic and Germany to find determining variables of credit risk in both countries. We find that a set of similar variables explains corporate credit risk in both countries despite substantial differences in the default rate pattern. This does not apply to households, where further research seems to be necessary. Next, we establish a framework for the stress testing of credit risk. We use a country specific stress scenario that shocks macroeconomic variables with medium severity. The test results in credit risk increasing by more than 100% in the Czech Republic and by roughly 40% in Germany. The two outcomes are not fully comparable since the shocks are calibrated according to the historical development of the time series considered and the size of the shocks for the Czech Republic was driven by the transformation period.Credit risk, credit risk modelling, stress testing.

Solar filament eruptions and their physical role in triggering Coronal Mass Ejections

Solar filament eruptions play a crucial role in triggering coronal mass ejections (CMEs). More than 80 % of eruptions lead to a CME. This correlation has been studied extensively during the past solar cycles and the last long solar minimum. The statistics made on events occurring during the rising phase of the new solar cycle 24 is in agreement with this finding. Both filaments and CMEs have been related to twisted magnetic fields. Therefore, nearly all the MHD CME models include a twisted flux tube, called a flux rope. Either the flux rope is present long before the eruption, or it is built up by reconnection of a sheared arcade from the beginning of the eruption. In order to initiate eruptions, different mechanisms have been proposed: new emergence of flux, and/or dispersion of the external magnetic field, and/or reconnection of field lines below or above the flux rope. These mechanisms reduce the downward magnetic tension and favor the rise of the flux rope. Another mechanism is the kink instability when the configuration is twisted too much. In this paper we open a forum of discussions revisiting observational and theoretical papers to understand which mechanisms trigger the eruption. We conclude that all the above quoted mechanisms could bring the flux rope to an unstable state. However, the most efficient mechanism for CMEs is the loss-of-equilibrium or torus instability, when the flux rope has reached an unstable threshold determined by a decay index of the external magnetic field.Comment: 23 pages, 13 figures, revie

Modelling dynamic portfolio risk using risk drivers of elliptical processes

The situation of a limited availability of historical data is frequently encountered in portfolio risk estimation, especially in credit risk estimation. This makes it, for example, difficult to find temporal structures with statistical significance in the data on the single asset level. By contrast, there is often a broader availability of cross-sectional data, i.e., a large number of assets in the portfolio. This paper proposes a stochastic dynamic model which takes this situation into account. The modelling framework is based on multivariate elliptical processes which model portfolio risk via sub-portfolio specific volatility indices called portfolio risk drivers. The dynamics of the risk drivers are modelled by multiplicative error models (MEM) - as introduced by Engle (2002) - or by traditional ARMA models. The model is calibrated to Moody's KMV Credit Monitor asset returns (also known as firm-value returns) given on a monthly basis for 756 listed European companies at 115 time points from 1996 to 2005. This database is used by financial institutions to assess the credit quality of firms. The proposed risk drivers capture the volatility structure of asset returns in different industry sectors. A characteristic temporal structure of the risk drivers, cyclical as well as a seasonal, is found across all industry sectors. In addition, each risk driver exhibits idiosyncratic developments. We also identify correlations between the risk drivers and selected macroeconomic variables. These findings may improve the estimation of risk measures such as the (portfolio) Value at Risk. The proposed methods are general and can be applied to any series of multivariate asset or equity returns in finance and insurance. --Portfolio risk modelling,Elliptical processes,Credit risk,multiplicative error model,volatility clustering

Displacing the Dream

Displacing the Dream: A report on Bay Area newspaper coverage of development and gentrification The YMC has spent much of this year analyzing 3 months of coverage in the San Francisco Chronicle, the Oakland Tribune, and the San Jose Mercury News. The result is this report on the dominant and missing stories in coverage of gentrification and displacement in the Bay. With contributions from anti-displacement groups in SF and Oakland and the Miami Workers Center, research support from the DataCenter, and poetry by Roopa Singh, Displacing the Dream promises to be a groundbreaking tool to support creative communications strategies for organizers in the Bay and beyond. As of 2006, Oakland and San Francisco had each lost 20-25% of their African American populations. Displacing the Dream exposes the failure of Bay Area newspapers to adequately cover the crisis of gentrification and displacement facing the Bay Area today. What did newspaper coverage of housing and development include? Whose voices were heard and whose got left out? What does it all mean