A test method for analog circuits : using sensitivity analysis and the singular value decomposition

XVII+C.3hlm.;24c

Time-resolved spectroscopy of the pulsating CV GW Lib

We present time-resolved optical spectroscopy of the dwarf nova GW Librae during its rare 2007 April superoutburst and compare these with quiescent epochs. The data provide the first opportunity to track the evolution of the principal spectral features. In the early stages of the outburst, the optically thick disc dominates the optical and the line components show clear orbital radial velocity excursions. In the course of several weeks, optically thin regions become more prominent as strong emission lines replace the broad disc absorption. Post-outburst spectroscopy covering the I band illustrates the advantages of Ca II relative to the commonly used Balmer lines when attempting to constrain binary parameters. Due to the lower ionization energy combined with smaller thermal and shear broadening of these lines, a sharp emission component is seen to be moving in between the accretion disc peaks in the Ca II line. No such component is visible in the Balmer lines. We interpret this as an emission component originating on the hitherto unseen mass donor star. This emission component has a mean velocity of similar to -15 +/- 5 km s(-1) which is associated with the systemic velocity., and a velocity semi-amplitude of K-em = 82.2 +/- 4.9 km s(-1). Doppler tomography reveals an asymmetric accretion disc, with the S-wave mapping to a sharp spot in the tomogram with a velocity consistent to what is obtained with line profile fitting. A centre of symmetry analysis of the disc component suggests a very small value for the WD orbital velocity K-1 as is also inferred from double Gaussian fits to the spectral lines. While our conservative dynamical limits place a hard upper limit on the binary mass ratio of q < 0.23, we favour a significantly lower value near q similar to 0.06. Pulsation modelling suggests a white dwarf mass similar to 1 M-circle dot. This, paired with a low-mass donor, near the empirical sequence of an evolved cataclysmic variable close to the period bounce, appears to be consistent with all the observational constraints to date

Exploring new emission line diagnostics for accreting compact objects

Theory predicts that a large fraction of CVs should have passed through the minimum period. The Sloan Digital Sky Survey (sdss) sample is finally unearthing these systems in large numbers. But due to their faint donor stars, the orbital period is often the only measurable system parameter for most CVs. The indirect measurable of the superhump period, and hence superhump excess, could potentially provide an indication of the mass ratio of the systems via the empirical relation between the two observables. While this relation is potentially very useful for the determination of mass ratios, the large scatter in the calibrators, especially at the low mass ratio end, prohibits a direct conversion between easy to measure light curve variability and the much sought after mass ratio. To place a short period CV firmly on the evolutionary track (e.g pre- or post bounce systems), more direct methods to determine the mass ratio are required, as well as a better calibration and validation of the relation between the superhump excess and mass ratio. We can achieve this, by constraining the mass ratios of short period CVs using dynamical constraints on the radial velocities of the binary components. The radial velocity of the WD (K1) is only occasionally directly measurable as the WD features are typically swamped by the strong disc features. As the disc is centred on the WD, measuring the disc radial velocity can give an indication of the WD radial velocity, but these measures tend to be biased by hotspots and other asymmetries in the disc. Measuring the radial velocity of the donor star (K2) is less straightforward and normally performed by either measuring the radial velocity of the donor absorption lines for earlier type donor stars, or via emission lines associated with the donor star, if irradiated by the disc and WD. The first method fails in short period CVs as the faint features from the late type donors in these systems are concealed in the accretion and WD dominated optical spectrum, even at very low mass loss rates. The second method comes with tight timing constraints as the irradiated donor is generally only visible on top of the double peaked disc emission shortly after outburst and data needs to be obtained via target of opportunity programs. In this thesis, we present a spectroscopic survey of short periods CVs and explore new techniques in addition to the traditional methods for the determination of the radial velocity components. We combine these new methods with the exploitation of the more `exotic' Ca ii triplet lines in the I-band in addition to the commonly used Balmer lines. We will show that, while it suffers from some of the same systematics as the Balmer lines, we can measure K1 better in Ca ii than in Balmer, especially when exploiting Doppler maps for these measures. More importantly for many systems, donor emission is visible in the Ca ii lines, which provides us with measures for the radial velocity amplitude of this feature (Kem). These, combined with K-correction models, yield a good measure of K2. We find that the determination of Kem is easy in Doppler maps, and that the K-correction, via irradiation methods, is fairly solid. We use these values to dynamically constrain the mass ratios for 13 CVs, including several eclipsing systems to test the validity of our method. The survey includes well known systems such as GW Lib, WZ Sge, OY Car and IP Peg

Less is not more: a small-scale study of corrective feedback

This study deals with one specific aspect of classroom interaction through an additional language: corrective feedback. By drawing on research and theories from bilingual, immersion and international contexts the study attempts to chart the grey area between corrective feedback and scaffolding, and to distil results that might be relevant across all contexts. As such, this study examines how subject teachers in an international setting correct language mistakes when interacting with students in the classroom, which types of corrective feedback are used in response to different types of errors, and which language goals can be deduced from the types of corrective feedback used. In order to find the answers to these questions, several lessons given by two international school teachers were observed, transcribed and analysed. The results show that the subject teachers focused mainly on meaning and mostly used recasts, but also used two as yet uncharted types of corrective feedback (‘confirmative’ feedback and corrective feedback in response to non-verbal language) in order to negotiate both meaning and form.Een colloquium over universitair taalvaardigheidsonderwijs Universiteit Leiden, 2 december 2016,the complete issue can be found at http://hdl.handle.net/1887/57204Wetensch. publicati

Evaluating Key Factors Influencing ERTMS Risk Assessment:A Reference Model

The European Railway Traffic Management system (ERTMS) aims to replace the various national train command and control systems in Europe, and will serve to improve cross-border interoperability, with the final aim of improving the competitiveness of the rail sector. As an additional effect, it is argued that implementation of ERTMS will improve safety. To provide insight into safety developments within the European railway system, this study evaluates ERTMS at both the national and international levels. For this purpose, international data from European ERTMS implementations is combined using data obtained from interviews with ERTMS stakeholders and safety experts from the Netherlands. Effects of the safety case regime, interoperability, deregulation and dynamic specifications on the European railway system have been researched. We present our findings into a reference model that describes the existing situation and shows what key factors are most suitable to improve the situation. The challenges are to improve resilience, to generate more awareness of interrelationships between hazards and risks, but even more: comprehending the safety architecture and creating cross-discipline understanding

Two new ultracool benchmark systems from WISE+2MASS

We have used the Two-Micron All-Sky Survey and the Wide-field Infrared Survey Explorer to look for ultracool dwarfs that are part of multiple systems containing main-sequence stars. We cross-matched L dwarf candidates from the surveys with Hipparcos and Gliese stars, finding two new systems. The first system, G255-34AB, is an L2 dwarf companion to a K8 star, at a distance of 36 pc. We estimate its bolometric luminosity as log L/L-circle dot = -3.78 +/- 0.045 and T-eff = 2080 +/- 260 K. The second system, GJ499ABC, is a triple, with an L5 dwarf as a companion to a binary with an M4 and K5 star. These two new systems bring the number of L dwarf plus main-sequence star multiple systems to 24, which we discuss. We consider the binary fraction for L dwarfs and main-sequence stars, and further assess possible unresolved multiplicity within the full companion sample. This analysis shows that some of the L dwarfs in this sample might actually be unresolved binaries themselves, since their M-J appears to be brighter than the expected for their spectral types.Peer reviewe

A Radial Velocity Study of CTCV J1300-3052

We present time-resolved spectroscopy of the eclipsing, short period cataclysmic variable CTCV J1300-3052. Using absorption features from the secondary star, we determine the radial velocity semi-amplitude of the secondary star to be K2 = 378 \pm 6 km/s, and its projected rotational velocity to be v sin i = 125 \pm 7 km/s. Using these parameters and Monte Carlo techniques, we obtain masses of M1 = 0.79 \pm 0.05 MSun for the white dwarf primary and M2 = 0.198 \pm 0.029 MSun for the M-type secondary star. These parameters are found to be in excellent agreement with previous mass determinations found via photometric fitting techniques, supporting the accuracy and validity of photometric mass determinations in short period CVs.Comment: Accepted for publication in MNRAS (24th January 2012). 10 pages, 9 figures (black and white