A Hamiltonian Krylov-Schur-type method based on the symplectic Lanczos process

We discuss a Krylov-Schur like restarting technique applied within the symplectic Lanczos algorithm for the Hamiltonian eigenvalue problem. This allows to easily implement a purging and locking strategy in order to improve the convergence properties of the symplectic Lanczos algorithm. The Krylov-Schur-like restarting is based on the SR algorithm. Some ingredients of the latter need to be adapted to the structure of the symplectic Lanczos recursion. We demonstrate the efficiency of the new method for several Hamiltonian eigenproblems

AGN triggering in the infall regions of distant X-ray luminous galaxy clusters at 0.9 < z <~ 1.6

Observational constraints on the average radial distribution profile of AGN in distant galaxy clusters can provide important clues on the triggering mechanisms of AGN activity in dense environments and are essential for a completeness evaluation of cluster selection techniques in the X-ray and mm-wavebands. The aim of this work is a statistical study with XMM-Newton of the presence and distribution of X-ray AGN in the large-scale structure environments of 22 X-ray luminous galaxy clusters in the redshift range 0.9 < z \lesssim 1.6 compiled by the XMM-Newton Distant Cluster Project (XDCP). To this end, the X-ray point source lists from detections in the soft-band (0.35-2.4 keV) and full-band (0.3-7.5 keV) were stacked in cluster-centric coordinates and compared to average background number counts extracted from three independent control fields in the same observations. A significant full-band (soft-band) excess of \sim78 (67) X-ray point sources is found in the cluster fields within an angular distance of 8' (4Mpc) at a statistical confidence level of 4.0 sigma (4.2 sigma), corresponding to an average number of detected excess AGN per cluster environment of 3.5\pm0.9 (3.0\pm0.7). The data point towards a rising radial profile in the cluster region (r<1Mpc) of predominantly low-luminosity AGN with an average detected excess of about one point source per system, with a tentative preferred occurrence along the main cluster elongation axis. A second statistically significant overdensity of brighter soft-band detected AGN is found at cluster-centric distances of 4'-6' (2-3Mpc), corresponding to about three times the average cluster radius R200 of the systems. If confirmed, these results would support the idea of two different physical triggering mechanisms of X-ray AGN activity in dependence of the radially changing large-scale structure environment of the distant clusters.Comment: 18 pages, 7 color figures, accepted for publication in Advances in Astronomy for the special issue 'Seeking for the Leading Actor on the Cosmic Stage: Galaxies versus Supermassive Black Holes

An investigation of the role of background music in IVWs for learning

Empirical evidence is needed to corroborate the intuitions of gamers and game developers in understanding the benefits of Immersive Virtual Worlds (IVWs) as a learning environment and the role that music plays within these environments. We report an investigation to determine if background music of the genre typically found in computer‐based role‐playing games has an effect on learning in a computer‐animated history lesson about the Macquarie Lighthouse within an IVW. In Experiment 1, music stimuli were created from four different computer game soundtracks. Seventy‐two undergraduate students watched the presentation and completed a survey including biographical details, questions on the historical material presented and questions relating to their perceived level of immersion. While the tempo and pitch of the music was unrelated to learning, music conditions resulted in a higher number of accurately remembered facts than the no music condition. One soundtrack showed a statistically significant improvement in memorisation of facts over other music conditions. Also an interaction between the levels of perceived immersion and ability to accurately remember facts was observed. Experiment 2, involving 48 undergraduate students, further investigated the effect of music, sense of immersion and how different display systems affect memory for facts

On the mechanism of irradiation enhanced exchange bias

By means of layer resolved ion irradiation the mechanisms involved in the irradiation driven modifications of the exchange bias effect in NiFe/FeMn bilayers have been investigated. It is shown that not only the locations of the defects but also the magnetic coupling between both layers during the irradiation process is of crucial importance. This requires an extension of current models accounting for defects in exchange bias systems.Comment: 3 pages, 3 figures, revised version, added results from further structural characterization by TEM, submitted to Europhysics Letter

Electrical conductivity cell and method for fabricating the same

A flask having a threaded neck and a cap adapted for threaded engagement on the neck are used. A laminated disc between the cap and the neck forms a gas tight seal and the cap has a central opening that exposes a medial region of the disc. Piercing the disc through the opening are two electrodes, the inner ends of which contact the sample within the flask and the outer ends of which can be connected to test equipment. Cylindric glass tubes are fitted over the external portion of the electrodes to provide physical support and silicone rubber or a similar material serves to retain the glass cylinders in place and form a gas tight seal between the cylinders and the electrodes. Shrinkable tubing is shrunk over the glass tubes to afford further mechanical support and sealing. A final relatively large diameter shrinkable tube is shrunk over both electrodes and their associated glass cylinders. The support and sealing means for the electrodes is confined to a limited portion of the medial region of the disc so that the remainder of such region can be punctured by a hollow needle to introduce a test sample within the flask

Litter and ground dwelling spiders of mixed mesophytic forest in southeast Louisiana

During Pleistocene glaciation much of the southeastern United States was covered with mixed mesophytic hardwood forest. These forests are composed predominantly of magnolia, holly, and beech with a mixture of other tree species, such as oak and hickory, and a distinct understory. Remnants of mixed mesophytic hardwood forests occur in the southern United States and are important refugia for disjunct and habitat-restricted species. In Louisiana, the mixed mesophytic forest habitat is found mostly in West Feliciana Parish, particularly in the area around St. Francisville. I chose two sites to conduct a study of spider diversity in litter habitats of disturbed and mature forests. Comparing spider species found these two habitats was necessary to understand the effects of disturbance on species richness and abundance. Berlese sampling was used to collect 10-kg samples of forest litter twice monthly from both sites. Collections were made from October 1998 to October 1999. I collected 1725 adult specimens representing 89 species in 14 families. At the mature forest site (Tunica Hills WMA) I collected 909 adult specimens, 58 species in 12 families. At the disturbed forest site (Feliciana Preserve) I collected 816 adult specimens, 73 species in 12 families. Species accumulation and richness estimators indicated the likelihood that additional species were present but not collected during the sampling period. The disturbed site had significantly greater species diversity and more uncommon species, perhaps because of a wider variety of microhabitats and presence of tourist and colonizer species. The mature forest site was less diverse, perhaps as a result of more stable and homogeneous habitat. Multiple disjunct species with northern affinities were found during the course of this study. Twelve species previously unreported for the state were discovered bringing the total to 225 spider species that are known to occur in Louisiana

Collective skill formation regimes in times of Covid-19: a governance-focused analysis of the German dual training system

Context: Covid-19 poses major challenges for vocational education and training (VET), as VET—in contrast to general education—is closely linked to the economic system and cannot escape the impact of current economic restrictions. Additionally, strict infection control regulations, as well as temporary school and company closures, inhibit the teaching of practical skills at the workplace. Rapid action by the responsible actors is essential to ensure that VET can take place even under these difficult conditions. It can be assumed that both the complex decision-making processes and the multiplicity of actors involved in collective training systems complicate or delay the reaction to this exogenous shock. Using the example of the German dual training system, this explorative article aims to examine the ability of collective training systems to deal with the challenges posed by the pandemic. Methods: Based on a document analysis, various publications (e.g., press releases, reports) by central actors of the German dual system were reviewed, which provided information about the provision of training activities as well as the measures taken or required to counteract the pandemic-related consequences for dual apprenticeships. This corpus of literature was expanded by scientific studies and publications from national or international institutions related to VET. Following a governance-analytical and actor-centred perspective, the documents were analysed with regard to the indications they provide about the realised coordination of action between the actors, the realised processes and outcomes, as well as the levels affected within the VET system. Findings: The way of dealing with the crisis demonstrates that the German dual system is influenced by the actions of various actors at multiple levels. Actors who are involved in the decision-making processes share common interests, resulting in a strategically bound cooperation among them. However, influence or power from bottom-up seems to be rather limited, as not all of the actors considered in this study are included in essential governance processes. Despite the comprehensive reactions to the pandemic, problems and optimisation needs are also apparent, e.g. with regard to vocational orientation or the support of vocational schools. Conclusion: Despite its complexity, the dual system as a collective training model is capable of acting and adapting to face the challenges posed by the pandemic. This may also be due to the historically entrenched corporatist structures within the dual system: Even in times of crisis, the trust in this historically evolved institutional framework leads to a high degree of accountability and cooperation among the decisive actors. (DIPF/Orig.