239 research outputs found
Bullying Roles in Changing Contexts: The Stability of Victim and Bully Roles from Primary to Secondary School
The present study was conducted to predict bullying roles over a six years time period and across contexts differing in the degree of peer hierarchies. Out of two representative data sets from primary (N = 1525) and secondary school (N = 2958), 282 children (156 boys; 126 girls) were followed up longitudinally. Self reports on bullying experiences and peer reports about social status were assessed by a structured individual interview (in primary school) and by questionnaire given classwise (in secondary school). Risk analyses showed, that only a bully role in primary school yields a risk to be sustained in secondary school. However, victims in primary school classes with a more pronounced degree of hierarchical structuring proved stable in their role while the victim role was unstable from primary school classes with low hierarchical structuring. This interaction did not apply to bully role stability. Differential characteristics of the victim and the bully role in primary school and secondary school settings are discussed.Die vorliegende Untersuchung wurde durchgefĂŒhrt, um Bullyingrollen ĂŒber einen Zeitraum von sechs Jahren und Kontexte, die sich im AusmaĂ der sozialen Strukturierung unterschieden, vorherzusagen. Auf der Grundlage von zwei reprĂ€sentativen DatensĂ€tzen aus der Grundschule (n= 1525) und der weiterfĂŒhrenden Schule (N= 2958) wurden dazu die Daten von 282 Kinder (156 Jungen, 126 MĂ€dchen) lĂ€ngsschnittlich analysiert. Die Selbstberichte ĂŒber Bullyingerfahrungen und MitschĂŒlerberichte ĂŒber den sozialen Status der Kinder wurden in der Grundschule durch ein strukturiertes Interview und in der weiterfĂŒhrenden Schule durch klassenweise Fragebogenerhebung erfasst. Riskikoanalysen zeigen, dass nur die TĂ€terrolle in der Grundschule einen Risikofaktor fĂŒr eine TĂ€terrolle in der weiterfĂŒhrenden Schule darstellt. Eine Opferrolle war hingegen nur dann stabil, wenn die Opfer in Grundschulklassen mit schon ausgeprĂ€gten Dominanzstrukturen viktimisiert wurden, wĂ€hrend aus Grundschulklassen mit geringer hierarchischer Strukturierung keine stabile Opferrolle vorhersagbar war. Dieses Interaktionmuster gilt nicht fĂŒr die StabilitĂ€t der TĂ€terrollen. Differentielle Charakteristika der Opferrolle und der TĂ€terrolle in der Grundschule und der weiterfĂŒhrenden Schule werden diskutiert
Controlling hole spin dynamics in twoâdimensional hole systems at low temperatures
With the recent discovery of very long hole spin decoherence times in GaAs/AlGaAs heterostructures of more than 70 ns
in two-dimensional hole systems, using the hole spin as a viable alternative to electron spins in spintronic applications seems
possible. Furthermore, as the hyperfine interaction with the nuclear spins is likely to be the limiting factor for electron spin
lifetimes in zero dimensions, holes with their suppressed Fermi contact hyperfine interaction due to their p-like nature should
be able to show even longer lifetimes than electrons. For spintronic applications, electric-field control of hole spin dynamics
is desirable.
Here, we report on time-resolved Kerr rotation and resonant spin amplification measurements on a two-dimensional hole
system in a p-doped GaAs/AlGaAs heterostructure. Via a semitransparent gate, we tune the charge density within the sample.
We are able to observe a change in the hole g factor, as well as in the hole spin dephasing time at high magnetic fields
Resonant spin amplification of hole spin dynamics in twoâdimensional hole systems: experiment and simulation
Spins in semiconductor structures may allow for the realization of scalable quantum bit arrays, an essential
component for quantum computation schemes. Specifically, hole spins may be more suited for this purpose than electron
spins, due to their strongly reduced interaction with lattice nuclei, which limits spin coherence for electrons in quantum dots.
Here, we present resonant spin amplification (RSA) measurements, performed on a p-modulation doped GaAs-based quantum
well at temperatures below 500 mK. The RSA traces have a peculiar, butterfly-like shape, which stems from the initialization
of a resident hole spin polarization by optical orientation. The combined dynamics of the optically oriented electron and hole
spins are well-described by a rate equation model, and by comparison of experiment and model, hole spin dephasing times of
more than 70 ns are extracted from the measured data
Late Viséan pelagic chondrichthyans from northern Europe
The relatively rich assemblages of shark teeth from pelagic limestone (Mississippian, late VisĂ©an, late Asbianâmiddle
Brigantian) of three northern European regions: the Rhenish Mountains (Westenfeld Quarry, Germany), the Holy Cross
Mountains (Todowa Grz
Ä
ba at the edge of OstrĂłwka Quarry, Poland), and Derbyshire (Cawdor Quarry, Matlock, England,
UK) display certain similarities, with the absolute predominance of the teeth of Falcatidae (small Symmoriiformes)
and
the constant presence of
Thrinacodus
spp. The largest and most diverse assemblage from Todowa Grz
Ä
ba contains at
least three species of a falcatid
Denaea
, a xenacanthimorph
Bransonella nebraskensis
, a newly described phoebodontid
Thrinacodus dziki
sp. nov., a few ctenacanthiform and euselachian teeth, and two abraded euchondrocephalan dental
elements. Anachronistidae, common in the most of late Viséan pelagic faunas, are absent from Todowa Grz
Ä
ba and
Westenfeld. The material under study differs from the shallow-water chondrichthyan fauna, hitherto described from
the Mississippian carbonate platform facies, by its taxonomic content (particularly almost total absence of Euchondro-
cephali), generally lower diversity, and higher frequency of small teet
Exceptions to the temperatureâsize rule: no Lilliput Effect in end-Permian ostracods (Crustacea) from Aras Valley (northwest Iran)
The body size of marine ectotherms is often negatively correlated with ambient water temperature, as seen in many clades during the hyperthermal crisis of the end-Permian mass extinction (c. 252âMa). However, in the case of ostracods, size changes during ancient hyperthermal events are rarely quantified. In this study, we evaluate the body size changes of ostracods in the Aras Valley section (northwest Iran) in response to the drastic warming during the end-Permian mass extinction at three taxonomic levels: class, order, species. At the assemblage level, the warming triggers a complete species turnover in the Aras Valley section, with larger, newly emerging species dominating the immediate post-extinction assemblage for a short time. Individual ostracod species and instars do not show dwarfing or a change in body size as an adaptation to the temperature stress during the end-Permian crisis. This may indicate that the ostracods in the Aras Valley section might have been exceptions to the temperatureâsize rule (TSR), using an adaptation mechanism that does not involve a decrease in body size. This adaptation might be similar to the accelerated development despite constant instar body sizes that can be observed in some recent experimental studies of ostracod responses to thermal stress
Taphonomy and palaeoecology of the green Devonian gypidulid brachiopods from the Aferdou El Mrakib, eastern Anti-Atlas, Morocco
On Aferdou El Mrakib, a large reef mound in the MaĂŻder region (Anti-Atlas, Morocco), thick-shelled gypidulids of two genera are locally very abundant. Like Stringocephalus in the shallow water limestone formations in Germany, these Moroccan brachiopods of the genera Devonogypa and Ivdelinia often display greenish shells. By analysing these shells by EDX, it turned out that the colour was possibly caused by impurities of Fe2+-ions. The concentration varies, indicating that the colour is less dependent on the concentration than on shell thickness, because only the thickest parts of the shells appear green and thin-shelled forms never display the green colour. There is also some indication that the Fe content increases towards deeper shell layers (further away from the surface). In addition, we examined the quality and spatial distribution of sublethal injuries in over 200 specimens of Devonogypa and Ivdelinia. Shape, spatial distribution on the shells, and abundance of the sublethal injuries support the hypotheses that (1) the injuries had several causes, (2) some of these were inflicted by predators, probably cephalopods, and (3) many fractures and deformations might have been caused by the brachiopod shells hitting each other in dense populations in agitated water. The existence of dense clusters, built by the association of members of both genera or of only one taxon, is corroborated by the patchy occurrence of these brachiopod
Depositional setting of the Devonian/Carboniferous biohermal Bolâshaya Nadota Carbonate Complex, Subpolar Urals
Multi-stage development of carbonate buildups has been recognised in the Bolâshaya Nadota Carbonate Complex, in
the vicinity of the town of Inta (Subpolar Urals). The growth of typical stromatoporoid-coral bioherms, characteristic
of the Middle-Late Devonian stage, was terminated by the appearance of the shallow water oolitic facies, most probably
at the beginning of the Famennian. During the Viséan stage the carbonate platform was reconstructed, but algalbrachiopod-
coral bioherms were characterized by relatively small dimensions and an interfingering with organodetrital-
oolitic facies. Sporadically, the inter-mound facies is represented by goniatite-bivalve coquinas with two new goniatite
species: Goniatites olysya sp.nov. and Lusitanoceras kusinae sp.nov.
The persistence of biohermal sedimentation in the Bolâshaya Nadota area is most probably caused by the specific position
of the region on the boundary of two sedimentary-structural units: Lemva and Elets Zones, which corresponded to
a basinal and a tectonically-active elevated part of a platform margin respectively.
The overall biotic composition of the Carboniferous bioherms from Bolâshaya Nadota, situated in the northern periphery
of Laurussia, falls generally within the diversity spectrum of Lower Carboniferous mounds described from the
southern margin of the continent
Gradual warming prior to the endâPermian mass extinction
The biggest known mass extinction in the history of animal life occurred at the PermianâTriassic boundary and has often been linked to global warming. Previous studies have suggested that a geologically rapid (<40âkyr) temperature increase of more than 10°C occurred simultaneously with the main extinction pulse. This hypothesis is challenged by geochemical and palaeontological data indicating profound environmental perturbations and a temperature rise prior to the main extinction. Using secondary ion mass spectrometry (SIMS), we measured oxygen isotope ratios from Changhsingian (late Permian) ostracods of northâwestern Iran. Our data show that ambient seawater temperature began to rise at least 300âkyr prior to the main extinction event. Gradual warming by approximately 12°C was probably responsible for initial environmental degradation that eventually culminated in the global endâPermian mass extinction
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