University of Bremen

About: University of Bremen is a education organization based out in Bremen, Germany. It is known for research contribution in the topics: Population & Glacial period. The organization has 14563 authors who have published 37279 publications receiving 970381 citations. The organization is also known as: Universität Bremen.

amoA-based consensus phylogeny of ammonia-oxidizing archaea and deep sequencing of amoA genes from soils of four different geographic regions.

Abstract: Ammonia-oxidizing archaea (AOA) play an important role in nitrification and many studies exploit their amoA genes as marker for their diversity and abundance. We present an archaeal amoA consensus phylogeny based on all publicly available sequences (status June 2010) and provide evidence for the diversification of AOA into four previously recognized clusters and one newly identified major cluster. These clusters, for which we suggest a new nomenclature, harboured 83 AOA species-level OTU (using an inferred species threshold of 85% amoA identity). 454 pyrosequencing of amoA amplicons from 16 soils sampled in Austria, Costa Rica, Greenland and Namibia revealed that only 2% of retrieved sequences had no database representative on the species-level and represented 30–37 additional species-level OTUs. With the exception of an acidic soil from which mostly amoA amplicons of the Nitrosotalea cluster were retrieved, all soils were dominated by amoA amplicons from the Nitrososphaera cluster (also called group I.1b), indicating that the previously reported AOA from the Nitrosopumilus cluster (also called group I.1a) are absent or represent minor populations in soils. AOA richness estimates on the species level ranged from 8–83 co-existing AOAs per soil. Presence/absence of amoA OTUs (97% identity level) correlated with geographic location, indicating that besides contemporary environmental conditions also dispersal limitation across different continents and/or historical environmental conditions might influence AOA biogeography in soils.

Physical, verbal, and relational forms of bullying among German students: Age trends, gender differences, and correlates

Abstract: A revised version of the Bully/Victim Questionnaire [Olweus, 1991] was given to 2,086 fifth-tenth grader students from schools in two German federal states. The results were analysed in terms of frequencies of self-reports of different forms of bullying (physical, verbal, relational/indirect; for bullies and for victims), gender and grade differences. Overall, 12.1% of the students reported bullying others and 11.1% reported being bullied (victimisation). We classified 2.3% of the students as bully/victims due to their self-report. Significantly more boys reported bullying others, regardless of bullying form, and significantly more boys than girls were classified as bully/victims. Although there was no gender difference for victimisation at all, boys reported significantly more often than girls being bullied physically. Besides, self-reports of pure and overlapping forms of bullying behaviour (relational, verbal, physical) were analysed. With regard to age trends, students from middle grades reported the highest rates of bullying. Self-reported rates of victimisation were higher for younger students, regardless of form of victimisation. Furthermore, class size was not linked to reports of bullying and victimisation. Results from logistic regression analyses emphasised that the variables "gender" and "grade" add significantly to the prediction of self-reported bullying; "grade" and variables measuring impaired psychosocial "well-being" of students at school (e.g., feeling of not being popular, negative attitude towards breaks) add significantly to the prediction of self-reported victimisation. The results are discussed against the background of other study findings, accentuating the significance of gender- and age-specific forms of bullying/victimisation. Language: en

Deep glacial troughs and stabilizing ridges unveiled beneath the margins of the Antarctic ice sheet

Abstract: The Antarctic ice sheet has been losing mass over past decades through the accelerated flow of its glaciers, conditioned by ocean temperature and bed topography. Glaciers retreating along retrograde slopes (that is, the bed elevation drops in the inland direction) are potentially unstable, while subglacial ridges slow down the glacial retreat. Despite major advances in the mapping of subglacial bed topography, significant sectors of Antarctica remain poorly resolved and critical spatial details are missing. Here we present a novel, high-resolution and physically based description of Antarctic bed topography using mass conservation. Our results reveal previously unknown basal features with major implications for glacier response to climate change. For example, glaciers flowing across the Transantarctic Mountains are protected by broad, stabilizing ridges. Conversely, in the marine basin of Wilkes Land, East Antarctica, we find retrograde slopes along Ninnis and Denman glaciers, with stabilizing slopes beneath Moscow University, Totten and Lambert glacier system, despite corrections in bed elevation of up to 1 km for the latter. This transformative description of bed topography redefines the high- and lower-risk sectors for rapid sea level rise from Antarctica; it will also significantly impact model projections of sea level rise from Antarctica in the coming centuries.