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

Studying Cosmic Evolution with the XMM-Newton Distant Cluster Project

Investigating X-ray luminous galaxy clusters at high redshift (z>~1) provides a challenging but fundamental constraint on evolutionary studies of the largest virialized structures in the Universe, the baryonic matter component in form of the hot intracluster medium (ICM), their galaxy populations, and the effects of the mysterious Dark Energy. The main aim of this thesis work is to establish the observational foundation for the XMM-Newton Distant Cluster Project (XDCP). This new generation serendipitous X-ray survey is focused on the most distant galaxy clusters at z>1, based on the selection of extended X-ray sources, their identification as clusters and redshift estimation via two-band imaging, and their final spectroscopic confirmation. As a first step, I have analyzed 80 deg^2 (469 fields) of deep XMM-Newton archival X-ray data with a new pipeline processing system and selected almost 1000 extended sources as galaxy cluster candidates, 75% of which could be identified as clusters or groups at z<~0.6 using available optical data. This left about 250 candidates with typical 0.5-2.0keV X-ray fluxes of ~10^{-14} erg/s/cm^2 in need of confirmation as distant cluster sources. Therefore, I have adopted a new strategy to efficiently establish the nature of these extended X-ray sources and estimate their redshifts, based on medium deep Z- and H-band photometry and the observed Z-H `red-sequence' color of early-type cluster galaxies. To fully exploit this technique, I have designed a new near-infrared data reduction code, which was applied to the data collected for 25% of the 250 distant cluster candidates in two imaging campaigns at the 3.5m telescope at the Calar Alto Observatory. As a first main result, more than 20 X-ray luminous clusters were discovered to lie at a photometric redshift of z>~0.9. Furthermore, the new Z-H red sequence method has allowed a cluster sample study over an unprecedented redshift baseline of 0.2<~z<~1.5. From a comparison of the observed color evolution of the cluster red-sequence galaxies with model predictions, I could constrain the formation epoch of the bulk of their stellar populations as z_f=4.2+-1.1. This confirms the well-established old age of the stellar populations of early-type galaxies in clusters. The preliminary investigation of the H-band luminosity evolution of 63 brightest cluster galaxies (BCGs) over the same redshift range provides for the first time direct observational indications that the most massive cluster galaxies in the local Universe have doubled their stellar mass since z~1.5. My tentative finding that nearby BCGs have old, passively evolving stellar populations and were assembled in the last 9Gyr is in qualitative agreement with predictions from the latest numerical simulations based on the standard cold dark matter scenario of galaxy formation and evolution via hierarchical merging. The confirmation and refinement of these preliminary results will contribute to the development of a consistent picture of the cosmic evolution of galaxy populations and the large-scale structure