A new connection between the opening angle and the large-scale morphology of extragalactic radio sources

In the case of an initially conical jet, we study the relation between jet collimation by the external pressure and large-scale morphology. We first consider the important length-scales in the problem, and then carry out axisymmetric hydrodynamic simulations that include, for certain parameters, all these length-scales. We find three important scales related to the collimation region: (i) where the sideways ram-pressure equals the external pressure, (ii) where the jet density equals the ambient density, and (iii) where the forward ram-pressure falls below the ambient pressure. These scales are set by the external Mach-number and opening angle of the jet. We demonstrate that the relative magnitudes of these scales determine the collimation, Mach-number, density and morphology of the large scale jet. Based on analysis of the shock structure, we reproduce successfully the morphology of Fanaroff-Riley (FR) class I and II radio sources. Within the framework of the model, an FR I radio source must have a large intrinsic opening angle. Entrainment of ambient gas might also be important. We also show that all FR I sources with radio lobes or similar features must have had an earlier FR II phase.Comment: 14 pages, 10 figures, accepted by MNRAS, same as previous versio

Graph Pattern Matching on Symmetric Multiprocessor Systems

Graph-structured data can be found in nearly every aspect of today's world, be it road networks, social networks or the internet itself. From a processing perspective, finding comprehensive patterns in graph-structured data is a core processing primitive in a variety of applications, such as fraud detection, biological engineering or social graph analytics. On the hardware side, multiprocessor systems, that consist of multiple processors in a single scale-up server, are the next important wave on top of multi-core systems. In particular, symmetric multiprocessor systems (SMP) are characterized by the fact, that each processor has the same architecture, e.g. every processor is a multi-core and all multiprocessors share a common and huge main memory space. Moreover, large SMPs will feature a non-uniform memory access (NUMA), whose impact on the design of efficient data processing concepts should not be neglected. The efficient usage of SMP systems, that still increase in size, is an interesting and ongoing research topic. Current state-of-the-art architectural design principles provide different and in parts disjunct suggestions on which data should be partitioned and or how intra-process communication should be realized. In this thesis, we propose a new synthesis of four of the most well-known principles Shared Everything, Partition Serial Execution, Data Oriented Architecture and Delegation, to create the NORAD architecture, which stands for NUMA-aware DORA with Delegation. We built our research prototype called NeMeSys on top of the NORAD architecture to fully exploit the provided hardware capacities of SMPs for graph pattern matching. Being an in-memory engine, NeMeSys allows for online data ingestion as well as online query generation and processing through a terminal based user interface. Storing a graph on a NUMA system inherently requires data partitioning to cope with the mentioned NUMA effect. Hence, we need to dissect the graph into a disjunct set of partitions, which can then be stored on the individual memory domains. This thesis analyzes the capabilites of the NORAD architecture, to perform scalable graph pattern matching on SMP systems. To increase the systems performance, we further develop, integrate and evaluate suitable optimization techniques. That is, we investigate the influence of the inherent data partitioning, the interplay of messaging with and without sufficient locality information and the actual partition placement on any NUMA socket in the system. To underline the applicability of our approach, we evaluate NeMeSys against synthetic datasets and perform an end-to-end evaluation of the whole system stack on the real world knowledge graph of Wikidata

Generation of locomotor activity in fin motoneurons of the lamprey during "fictive locomotion"

The river lamprey (Lampetra fluviatilis) possesses two different types of muscles responsible for swimming. For propulsion of the animal during undulatory movement the lateral, in the trunk of the lamprey located, myotomal musculature is responsible, that is antiphasically active. These muscles are controlled by myotomal motoneurons. For controlling of the horizontal position of the lamprey, the fin of the lamprey is used, controlled by fin motoneurons. Both types of motoneurons are located in the spinal cord. Intracellular recordings of myotomal and fin motoneurons showed during swimming that the latter ones are antiphasic activated compared to myotomal motoneurons. The main aim of this thesis was to find the answer of the question how this antiphasic activation is controlled. Therefore all experiments were performed on the �fictive swimming� animal. First it was tried to characterize fin motoneurons morphologically and electrophysiologically. Then it was resolved by current injection to the recorded fin motoneurons if they get a phasic inhibitory or excitatory drive from other neurons. Lesion experiments were used to identify whether fin motoneurons receive contralateral or ipsilateral synaptic input and whether this input was inhibitory or excitatory. It could be shown that there are at least two morphological distinct types of fin motoneurons in the spinal cord of the lamprey, both characterized by a probably specialized shape of membrane potential oscillation. After classification of the different shapes of the membrane potential oscillations of all recorded fin motoneurons using �hierarchical clustering� it could be shown that there is a third different membrane potential pattern, besides the two mentioned before. This third shape could not be allocated to the morphological fin motoneurons so far. The results show that there are at least three different patterns of membrane potential oscillations in the fin motoneurons of "Lampetra fluviatilis" and therefore this could be a hint that there are also three different types of cells located in the lamprey spinal cord. After injection of negative current to these three different types of fin motoneurons it could be shown for two types of them that they receive phasic inhibitory and excitatory input during membrane potential oscillations. The data for the third type are not enough yet to confirm this result. After sagittal and transversal lesions performed on the spinal cord of Lampetra fluviatilis showed that the shape of the membrane potential oscillation of fin motoneurons still persisted, but that the peak-to-peak amplitude was affected. It could be shown that after performing a sagittal lesion the peak-to-peak amplitude decreased significantly whereas a transversal lesion (rostral or caudal to the recorded cell) showed a significant increase of the peak-to-peak amplitude. This means that fin motoneurons receive excitatory drive from the contralateral hemisegment and that they receive inhibitory drive from ipsilateral located segments. According to all the collected results and based on known literature a possible model was developed to show which neurons, located in the spinal cord, could be involved for coordinating and controlling fin motoneurons and their antiphasic activation compared to myotomal motoneurons

The problem of constituting and substantiating media pedagogy

Dieser Beitrag verortet Medienpädagogik im Feld der Wissenschaften. Es wird die Frage diskutiert, inwieweit ein eigenständiger Zugang der Medienpädagogik zu ihren Forschungsanliegen als grundlegend für die Konstitution einer wissenschaftlichen Disziplin gilt bzw. geltend gemacht werden kann. Dazu werden, erstens, allgemeine Konstitutionsmöglichkeiten einer Disziplin schematisch aufgezeigt und ihre je unterschiedlichen Begründungszusammenhänge für wissenschaftliche Disziplinen diskutiert, um – zweitens bestehende Konstitutionsformen und Begründungszusammenhänge der Medienpädagogik einzuordnen, zu hinterfragen und dem Problem des Gemeinsamen und Spezifischen einer «Medienpädagogik» nachzugehen. Drittens, wird eine gemeinsame und spezifische Grundlegung im Verhältnis von Medien und Pädagogik geltend gemacht, die als Beitrag zu einer disziplinären Auffassung von Medienpädagogik gelten kann.This article situates Media Pedagogy in the field of science and humanities. We scrutinise, if or in how far Media Pedagogy can be constituted as its own discipline. Therefore, we discuss in general criteria for the constitution of academic disciplines that may include specific research objectives, styles of reasoning, and certain scientific practices. We conclude that disciplines can be constituted through shared approaches that unite academic practises and through specific criteria that distinguish academic practises from other disciplinary practices. Based on these two distinctive processes, we show how research object, methodology, and policy alone cannot sufficiently function as the common and the specific of Media Pedagogy. We layout, thirdly, that and how the relation between media and pedagogy is a common and specific starting point of Media Pedagogy as an academic discipline, and constitute media pedagogy through this relation

Graduate Recital:Kent Alexander Krause, Euphonium

Kemp Recital Hall Saturday Evening March 31, 2007 7:00p.m

Discovery of an X-ray cavity near the radio lobes of Cygnus A indicating previous AGN activity

Cygnus A harbours the nearest powerful radio jet of an Fanaroff-Riley (FR) class II radio galaxy in a galaxy cluster where the interaction of the jet with the intracluster medium (ICM) can be studied in detail. We use a large set of Chandra archival data, VLA and new LOFAR observations to shed new light on the interaction of the jets with the ICM. We identify an X-ray cavity in the distribution of the X-ray emitting plasma in the region south of the Cyg A nucleus which has lower pressure than the surrounding medium. The LOFAR and VLA radio observations show that the cavity is filled with synchrotron emitting plasma. The spectral age and the buoyancy time of the cavity indicates an age at least as large as the current Cyg A jets and not much larger than twice this time. We suggest that this cavity was created in a previous active phase of Cyg A when the energy output of the Active Galactic Nucleus (AGN) was about two orders of magnitude less than today.Comment: Letter submitted on 4 May 2012 to A&A, 4 pages, 4 figure

Measurements of the Cosmological Evolution of Magnetic Fields with the Square Kilometre Array

We investigate the potential of the Square Kilometre Array (SKA) for measuring the magnetic fields in clusters of galaxies via Faraday rotation of background polarised sources. [...] We find that about 10 per cent of the sky is covered by a significant extragalactic Faraday screen. Most of it has rotation measures between 10 and 100 rad/m/m. We argue that the cluster centres should have up to about 5000 rad/m/m. We show that the proposed mid frequency aperture array of the SKA as well as the lowest band of the SKA dish array are well suited to make measurements for most of these rotation measure values, typically requiring a signal-to-noise of ten. We calculate the spacing of sources forming a grid for the purpose of measuring foreground rotation measures: it reaches a spacing of 36 arcsec for a 100 hour SKA observation per field. We also calculate the statistics for background RM measurements in clusters of galaxies. We find that a first phase of the SKA would allow us to take stacking experiments out to high redshifts (>1), and provide improved magnetic field structure measurements for individual nearby clusters. The full SKA aperture array would be able to make very detailed magnetic field structure measurements of clusters with more than 100 background sources per cluster up to a redshift of 0.5 and more than 1000 background sources per cluster for nearby clusters, and could for reasonable assumptions about future measurements of electron densities in high redshift clusters constrain the power law index for the magnetic field evolution to better than dm=0.4, if the magnetic field in clusters should follow B ~ (1+z)^m.Comment: 12 pages, 10 figures, 3 tables, accepted by MNRAS, minor correction to eq (5