OALib Journal期刊

ISSN: 2333-9721



匹配条件: “Markus GEBHARDT” ,找到相关结果约5700条。
The Spin of M87 as measured from the Rotation of its Globular Clusters
Markus Kissler-Patig,Karl Gebhardt
Physics , 1998, DOI: 10.1086/300609
Abstract: We revisit the kinematical data for 204 globular clusters in the halo of M87. Beyond 3 r_eff along the major axis of the galaxy light, these globular clusters exhibit substantial rotation (~ 300 +/- 70 km/s) that translates into an equally substantial spin (lambda ~ 0.18). The present appearance of M87 is most likely the product of a single major merger, since this event is best able to account for so sizable a spin. A rotation this large makes improbable any significant accretion of material after this merger, since that would have diluted the rotation signature. We see weak evidence for a difference between the kinematics of the metal-poor and metal-rich population, in the sense that the metal-poor globular clusters appear to dominate the rotation. If, as we suspect, the last major merger event of M87 was mainly dissipationless and did not trigger the formation of a large number of globular clusters, the kinematic difference between the two could reflect their orbital properties in the progenitor galaxies; these differences would be compatible with these progenitors having formed in dissipational mergers. However, to put strong kinematic constraints on the origin of the globular clusters themselves is difficult, given the complex history of the galaxy and its last dominant merger event.
Globular Cluster Systems I: V-I Color Distributions
Karl Gebhardt,Markus Kissler-Patig
Physics , 1999, DOI: 10.1086/301059
Abstract: We have compiled data for the globular cluster systems of 50 galaxies from the HST WFPC2 archive, of which 43 are type S0 or earlier. In this paper, we present the data set and derive the V-I color distributions. We derive the first four moments of the color distributions, as well as a measure for their non--unimodality. The number of globular clusters in each galaxy ranges from 18 (in NGC 2778) to 781 (NGC 5846). For those systems having more than 100 clusters, seven of sixteen (44%) show significant bimodality. Overall, roughly half of all the systems in our sample show hints of a bimodal color distribution. In general, the distributions of the faint galaxies are consistent with unimodality, whereas those of the brighter galaxies are not. In comparing the moments of the V-I distributions with various galaxy properties for the early-type galaxies, we find the following difference in the correlations between the field and cluster galaxy populations: the peak V-I color of the globular cluster distribution correlates well with the central velocity dispersion---and hence the Mg2 index and total luminosity---for galaxies in cluster environments; there exists no such correlation for field galaxies. This difference between cluster and field galaxies possibly reflects different formation scenarios for their globular cluster systems. Among the explanations for such a correlation, we consider either a larger age spread in the field populations or the possibility that cluster galaxies are always affected by significant accretion whereas some field galaxies could host pure ``in situ'' formed populations.
Teachers’ Attitudes Towards inclusive Education in Austria
Markus Gebhardt,Susanne Schwab,Hannelore Reicher,Barbara Ellmeier
Empirische Sonderp?dagogik , 2012,
Abstract: The study reports the results of several empirical studies on teachers’ attitudes towards the inclusion of pupils with special education needs in different academic settings. The survey’s data sets of altogether 578 primary school teachers in Austria, queried in 1998 and 2009, were reanalyzed. The chosen instrument of investigation was Reicher’s scale “Einstellung zur Integration in der Schule (EIS) [attitudes towards inclusion in school]“ (1988). Concerning reliability and factorial structure, the scale fulfills the requirements which an instrument of investigation has to achieve. With regards to content, the analysis of the data showed that teachers evaluate the inclusion of pupils with mental retardation as a greater challenge than the inclusion of pupils with physical or learning disabilities. With reference to the general attitude towards academic inclusion, there were no differences between primary school teachers and special education teachers. However, the results revealed a moderate effect of the field of work the respondents were engaged in. Teachers working in inclusive fields declare a more positive attitude towards academic inclusion than teachers in non-inclusive settings, disregarding the type of disability.
Markus GEBHARDT,Susanne SCHWAB,Mathias KRAMMER,Klicpera Barbara GASTEIGER
Journal of Special Education and Rehabilitation , 2012,
Abstract: In Styria 77.3% of all students with special needs are educated in integrated classrooms. Currently, it is not known much either about the school performance nor the active class participation of these students. This study examined 230 fifth grade students – 43 with and 187 students without special educational needs (SEN). Moreover, it is important to acknowledge that the available data for this study represents the first wave of larger longitudinal study. The school performance of the students with SEN ranged one standard deviation below the level of the students without SEN. All students felt emotionally well integrated in the school settings, but the differences in the degree of social integration were evident. In fact, the students with SEN mentioned that they got along well with their classmates less frequently than the students without SEN.
Self-pulsing of a micro thin cathode discharge
Alexander Wollny,Markus Gebhardt,Torben Hemke,Ralf Peter Brinkmann,Thomas Mussenbrock
Physics , 2011,
Abstract: Microplasmas operated at atmospheric pressure show a number of peculiar dynamic phenomena. One of these phenomena is self-pulsing, which is characterized by intrinsic pulsing behavior of a DC driven plasma discharge. This work focuses on the numerical simulation of self-pulsing in a micro thin cathode discharge operated in atmospheric pressure argon. By means of a hybrid plasma model we show self-pulsing of the discharge in the expected MHz frequency range and described its actual origin.
Spatially resolved simulation of a radio frequency driven micro atmospheric pressure plasma jet and its effluent
Torben Hemke,Alexander Wollny,Markus Gebhardt,Ralf Peter Brinkmann,Thomas Mussenbrock
Physics , 2011, DOI: 10.1088/0022-3727/44/28/285206
Abstract: Radio frequency driven plasma jets are frequently employed as efficient plasma sources for surface modification and other processes at atmospheric pressure. The radio-frequency driven micro atmospheric pressure plasma jet ($\mu$APPJ) is a particular variant of that concept whose geometry allows direct optical access. In this work, the characteristics of the $\mu$APPJ operated with a helium-oxygen mixture and its interaction with a helium environment are studied by numerical simulation. The density and temperature of the electrons, as well as the concentration of all reactive species are studied both in the jet itself and in its effluent. It is found that the effluent is essentially free of charge carriers but contains a substantial amount of activated oxygen (O, O$_3$ and O$_2(^1\Delta)$). The simulation results are verified by comparison with experimental data.
VLT Kinematics for omega Centauri: Further Support for a Central Black Hole
Eva Noyola,Karl Gebhardt,Markus Kissler-Patig,Nora Lutzgendorf,Behrang Jalali,P. Tim de Zeeuw,Holger Baumgardt
Physics , 2010, DOI: 10.1088/2041-8205/719/1/L60
Abstract: The Galactic globular cluster omega Centauri is a prime candidate for hosting an intermediate mass black hole. Recent measurements lead to contradictory conclusions on this issue. We use VLT-FLAMES to obtain new integrated spectra for the central region of omega Centauri. We combine these data with existing measurements of the radial velocity dispersion profile taking into account a new derived center from kinematics and two different centers from the literature. The data support previous measurements performed for a smaller field of view and show a discrepancy with the results from a large proper motion data set. We see a rise in the radial velocity dispersion in the central region to 22.8+-1.2 km/s, which provides a strong sign for a central black hole. Isotropic dynamical models for omega Centauri imply black hole masses ranging from 3.0 to 5.2x10^4 solar masses depending on the center. The best-fitted mass is 4.7+-1.0x10^4 solar masses.
A re-evaluation of the central velocity-dispersion profile in NGC 6388
Nora Lützgendorf,Karl Gebhardt,Holger Baumgardt,Eva Noyola,Nadine Neumayer,Markus Kissler-Patig,Tim de Zeeuw
Physics , 2015, DOI: 10.1051/0004-6361/201425524
Abstract: Recently, two independent groups found very different results when measuring the central velocity dispersion of the galactic globular cluster NGC 6388 with different methods. While L\"utzgendorf et al. (2011) found a rising profile and a high central velocity dispersion (23.3 km/s), measurements obtained by Lanzoni et al. (2013) showed a value 40% lower. The value of the central velocity dispersion has a serious impact on the mass and possible presence of an intermediate-mass black hole at the center of NGC 6388. We use a photometric catalog of NGC 6388 to create a simulated SINFONI and ARGUS dataset. The construction of the IFU data cube is done with different observing conditions reproducing the conditions reported for the original observations as closely as possible. In addition, we produce an N-body realization of a 10^6 M_SUN stellar cluster with the same photometric properties as NGC 6388 to account for unresolved stars. We find that the individual radial velocities, i.e. the measurements from the simulated SINFONI data, are systematically biased towards lower velocity dispersions. The reason is that due to the wings in the point spread function the velocities get biased towards the mean cluster velocity. This study shows that even with AO supported observations, individual radial velocities in crowded fields are likely to be biased. The ARGUS observations do not show this kind of bias but were found to have larger uncertainties than previously obtained. We find a bias towards higher velocity dispersions in the ARGUS pointing when fixing the extreme velocities of the three brightest stars but find those variations are within the determined uncertainties. We rerun Jeans models and fit the kinematic profile with the new uncertainties. This yields a BH mass of M_BH = (2.8 +- 0.4) x 10^4 M_SUN and M/L ratio M/L = (1.6 +- 0.1) M_SUN/L_SUN, consistent with our previous results.
Inszenierung und Verortung von Identit t in der computervermittelten Kommunikation. Rahmenanalytische überlegungen am Beispiel des Online-Chat
Julian Gebhardt
[email protected] , 2001,
Abstract: Inszenierung und Verortung von Identit t in der computervermittelten Kommunikation. Rahmenanalytische überlegungen am Beispiel des Online-Chat. Auf der Grundlage einer explorativen Studie über das Online-Chatten“ und bezugnehmend auf die Goffmansche Rahmen-Analyse“ werden im vorliegenden Beitrag einige der Strategien herausgearbeitet, mit denen die Teilnehmer eines Online-Chats“ versuchen – trotz der medialen Restriktionen – soziale Interaktionsprozesse herzustellen und zu bew ltigen. Am Beispiel des Umgangs der NutzerInnen mit dem Problem der Pr sentation und Verortung von Identit t im Chat l sst sich zeigen, wie sich die Teilnehmer im Zuge aktiver Aneignungsprozesse neue interaktionsrelevante Orientierungsm glichkeiten und Kontextinformationen konstruieren, um kommunikative Beziehungen auch in einem auf den Computerbildschirm beschr nkten gemeinsamen Wahrnehmungsraum koordinieren zu k nnen. Hierfür müssen sich die Teilnehmer sowohl spezifische (selbst-)darstellerische F higkeiten aneignen, als auch Kompetenzen dahingehend ausbilden, den Interaktionspartner anhand der im Chat verfügbaren Verortungsmerkmale einzusch tzen und einzuordnen.
Influence of Black Holes on Stellar Orbits
Karl Gebhardt
Physics , 2003,
Abstract: We review the current state of dynamical modeling for galaxies in terms of being able to measure both the central black hole mass and stellar orbital structure. Both of these must be known adequately to measure either property. The current set of dynamical models do provide accurate estimates of the black hole mass and the stellar orbital distribution. Generally, these models are able to measure the black hole mass to about 20%--30% accuracy given present observations, and the stellar orbital structure to about 20% accuracy in the radial to tangential dispersions. The stellar orbital structure of the stars near the galaxy center show strong tangential velocity anisotropy for most galaxies studied. Theoretical models that best match this trend are black hole binary/merger models. There is also a strong correlation between black hole mass and the contribution of radial motion at large radii. This correlation may be an important aspect of galaxy evolution.

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