Subalgebras of bigraded Koszul algebras

We show that diagonal subalgebras and generalized Veronese subrings of a bigraded Koszul algebra are Koszul. We give upper bounds for the regularity of sidediagonal and relative Veronese modules and apply the results to symmetric algebras and Rees rings.Comment: 13 page

East Africa: cycles of violence, and the paradox of peace

This paper contributes to explaining variation in violence in post-independence East Africa. By focussing on Tanzania and Uganda, our comparative ‘most-similar-cases’ research design ensures significant across- and within-case variation in violence against relatively similar background conditions. As a conceptual starting point the World Bank’s Collier/Hoeffler model and theory are applied to both countries. It is argued that while the model’s fit is relatively good, Collier/Hoeffler’s main theoretical proposition that civil war onset is best predicted by the existence of opportunities (or financing availability through resource extortion) for rebellion does not correspond as well with the East African context. We propose a modified rational-choice framework focusing on micro-level economic motivations for state capture, which is argued to help explain cycles of violence in Uganda until the 1980s, as well as the ‘paradox of peace’, i.e. the puzzle why East Africa has experienced sustained periods of absolute (Tanzania) and relative (Uganda nationally after 1986, Zanzibar since the 1970s) peace despite identity fragmentation. From this perspective, peace followed from successful elite strategies to co-opt opponents through a mixture of rent-sharing and non-violent authority, leading to identity-encompassing, hierarchical one-party structures able to overcome collective action problems of state capture and defence

Laboratory studies of ice-particle collisions in Saturn's dense rings

In this work, we report on microgravity studies of particle ensembles simulating ice-particle collisions in Saturn's dense main rings. We have developed an experimental method to study the energy dissipation in a many-body system consisting of approx. one hundred cm-sized glass spheres. The temporal development of the mean particle velocity, ranging from ~10 cm/s (at the beginning) to ~0.35 cm/s (after 9s of experiment duration), can be explained by a constant coefficient of restitution of 0.64. A comparison to values obtained for pure water-ice bodies shows that future cryogenic ice-collision experiments can achieve collision velocities of ~0.1 cm/s, and thus will very well simulate the conditions in Saturn's main rings.Comment: Accepted by "Proc. Powders and Grains 2009", Publisher AI

The Suborbital Particle Aggregation and Collision Experiment (SPACE): Studying the Collision Behavior of Submillimeter-Sized Dust Aggregates on the Suborbital Rocket Flight REXUS 12

The Suborbital Particle Aggregation and Collision Experiment (SPACE) is a novel approach to study the collision properties of submillimeter-sized, highly porous dust aggregates. The experiment was designed, built and carried out to increase our knowledge about the processes dominating the first phase of planet formation. During this phase, the growth of planetary precursors occurs by agglomeration of micrometer-sized dust grains into aggregates of at least millimeters to centimeters in size. However, the formation of larger bodies from the so-formed building blocks is not yet fully understood. Recent numerical models on dust growth lack a particular support by experimental studies in the size range of submillimeters, because these particles are predicted to collide at very gentle relative velocities of below 1 cm/s that can only be achieved in a reduced-gravity environment. The SPACE experiment investigates the collision behavior of an ensemble of silicate-dust aggregates inside several evacuated glass containers which are being agitated by a shaker to induce the desired collisions at chosen velocities. The dust aggregates are being observed by a high-speed camera, allowing for the determination of the collision properties of the protoplanetary dust analog material. The data obtained from the suborbital flight with the REXUS (Rocket Experiments for University Students) 12 rocket will be directly implemented into a state-of-the-art dust growth and collision model

The conceptualisation and measurement of pedagogical content knowledge and content knowledge in the COACTIV study and their impact on student learning

An ongoing question is the extent to which teachers' professional knowledge has an impacton their teaching and, in particular, on their students' achievement. The COACTIV1 studysurveyed and tested the mathematics teachers of the classes sampled for PISA 2003/04 inGermany. The study’s key components were newly developed tests of teachers’ pedagogicalcontent knowledge and content knowledge. This article gives a report of theconceptualisation and operationalisation of both domains of knowledge and describes theconstruction of the COACTIV tests. Findings from the tests show that there are differenceswith respect to both knowledge domains regarding teachers’ school types, but thatpedagogical content knowledge and content knowledge astoundingly both do not depend onteaching experience. Furthermore we show that the two domains of knowledge correlatepositively with constructivist teachers’ subjective beliefs, on the one hand, and with somecrucial aspects of their instruction, on the other hand. Finally, we show that pedagogicalcontent knowledge – but not pure content knowledge per se – significantly contributes tostudents’ learning gains

East Africa: cycles of violence, and the paradox of peace

This paper contributes to explaining variation in violence in post-independence East Africa. By focussing on Tanzania and Uganda, our comparative 'most-similar-cases' research design ensures significant across- and within-case variation in violence against relatively similar background conditions. As a conceptual starting point the World Bank's Collier/Hoeffler model and theory are applied to both countries. It is argued that while the model's fit is relatively good, Collier/Hoeffler's main theoretical proposition that civil war onset is best predicted by the existence of opportunities (or financing availability through resource extortion) for rebellion does not correspond as well with the East African context. We propose a modified rational-choice framework focusing on micro-level economic motivations for state capture, which is argued to help explain cycles of violence in Uganda until the 1980s, as well as the 'paradox of peace', i.e. the puzzle why East Africa has experienced sustained periods of absolute (Tanzania) and relative (Uganda nationally after 1986, Zanzibar since the 1970s) peace despite identity fragmentation. From this perspective, peace followed from successful elite strategies to co-opt opponents through a mixture of rent-sharing and non-violent authority, leading to identity-encompassing, hierarchical one-party structures able to overcome collective action problems of state capture and defence

Immunogenetic studies of Guillain - Barré syndrome and chronic inflammatory demyelinating polyradiculoneuropathy

Guillain-Barre syndrome (GBS) is an acute inflammatory neuropathy that is frequently triggered by an infectious illness. It is thought to be autoimmune in origin, but differs from other autoimmune diseases in being of male predominance and not showing a HLA-association. Chronic inflammatory demyelinating polyradiculoneuropathy is a chronic inflammatory neuropathy, which shares some pathological features with GBS. We investigated the clinical features of GBS in an Australian cohort of subjects by performing a retrospective chart review. We obtained subjects from several public hospitals and private neurologists in Queensland and New South Wales. We found 335 patients, for 228 of whom electrophysiological data was available. Of these acute inflammatory demyelinating polyradiculoneuropathy (AIDP) with 168 cases was the most common form, whilst axonal and focal forms were rarer. We identified upper respiratory tract infections, occurring predominantly in winter months, as the most frequently named triggering factor for GBS. The illness severity in our cohort was similar to that in earlier Australian studies. Also, we identified a cohort of 78 subjects fulfilling diagnostic criteria for CIDP from similar sources. We investigated a possible underlying genetic susceptibility to develop GBS or CIDP by contacting members of this cohort and collecting their DNA. We embarked on both a candidate gene approach to investigate the killer immunoglobulin-like receptors (KIRs) and their HLA ligands, as well as performing a genome-wide association study (GWAS) of the subjects with GBS as a hypothesis-free method. For the KIR/HLA system, whilst no significant differences were detected in the frequency of KIR genes, HLA-C2 and HLA-B Bw4-T were more frequent in subjects with GBS than controls (

On Koszul Algebras

Eine standard graduierte Algebra über einem Körper heißt Koszul, falls der Restklassenkörper als graduierter Modul über der Algebra eine lineare Auflösung besitzt. In dieser Arbeit werden verschiedene Klassen von Koszul Algebren untersucht. Dazu zählen initial Koszul (initially Koszul)Algebren, die eine bestimmte Koszul Filtrierung erlauben. Es wird die Klasse der basis-sortierbaren (base-sortable) Matroide eingeführt, deren Basisringe Koszul sind. Es wird gezeigt, dass sich die Koszul Eigenschaft auf Diagonalen bigraduierter Koszul Algebren überträgt. Anwendungen bei symmetrischen Algebren und Rees-Ringen werden dargestellt