Nouveaux specimens du genre Leclercqia Banks, H.P., Bonamo, P.M. et Grierson, J.D., 1972, du Givetien ( ? ) Du Queensland (Australie)

Axis fragments with « protolepidodendroid » surface pattern from the Middle Devonian (Givetian ?) of the Burdekin Basin (Queensland, Australia)are assigned, following their preparation to the genus Leclercqia,BANKS, H. P., BONAMO, P. M. et GRIERSON, J . D., 1972, formerly restricted to North America

Trigonometric real form of the spin RS model of Krichever and Zabrodin

We investigate the trigonometric real form of the spin Ruijsenaars-Schneider system introduced, at the level of equations of motion, by Krichever and Zabrodin in 1995. This pioneering work and all earlier studies of the Hamiltonian interpretation of the system were performed in complex holomorphic settings; understanding the real forms is a non-trivial problem. We explain that the trigonometric real form emerges from Hamiltonian reduction of an obviously integrable 'free' system carried by a spin extension of the Heisenberg double of the ${\rm U}(n)$ Poisson-Lie group. The Poisson structure on the unreduced real phase space ${\rm GL}(n,\mathbb{C}) \times \mathbb{C}^{nd}$ is the direct product of that of the Heisenberg double and $d\geq 2$ copies of a ${\rm U}(n)$ covariant Poisson structure on $\mathbb{C}^n \simeq \mathbb{R}^{2n}$ found by Zakrzewski, also in 1995. We reduce by fixing a group valued moment map to a multiple of the identity, and analyze the resulting reduced system in detail. In particular, we derive on the reduced phase space the Hamiltonian structure of the trigonometric spin Ruijsenaars-Schneider system and we prove its degenerate integrability.Comment: 52 pages, 1 figure. v2: typos removed, final versio

Multiplicative quiver varieties and generalised Ruijsenaars–Schneider models

We study some classical integrable systems naturally associated with multiplicative quiver varieties for the (extended) cyclic quiver with m vertices. The phase space of our integrable systems is obtained by quasi-Hamiltonian reduction from the space of representations of the quiver. Three families of Poisson-commuting functions are constructed and written explicitly in suitable Darboux coordinates. The case m = 1 corresponds to the tadpole quiver and the Ruijsenaars–Schneider system and its variants, while for m > 1 we obtain new integrable systems that generalise the Ruijsenaars–Schneider system. These systems and their quantum versions also appeared recently in the context of supersymmetric gauge theory and cyclotomic DAHAs (Braverman et al. [32,34,35] and Kodera and Nakajima [36]), as well as in the context of the Macdonald theory (Chalykh and Etingof, 2013)

Automatic Item Text Generation in Educational Assessment

We present an automatic text generation system (ATG) developed for the generation of natural language text for automatically produced test items. This ATG has been developed to work with an automatic item generation system for analytical reasoning items for use in tests with high-stakes outcomes (such as college admissions decisions). As such, the development and implementation of this ATG is couched in the context and goals of automated item generation for educational assessment

L∞L_\infty-Algebras, the BV Formalism, and Classical Fields

We summarise some of our recent works on $L_\infty$-algebras and quasi-groups with regard to higher principal bundles and their applications in twistor theory and gauge theory. In particular, after a lightning review of $L_\infty$-algebras, we discuss their Maurer-Cartan theory and explain that any classical field theory admitting an action can be reformulated in this context with the help of the Batalin-Vilkovisky formalism. As examples, we explore higher Chern-Simons theory and Yang-Mills theory. We also explain how these ideas can be combined with those of twistor theory to formulate maximally superconformal gauge theories in four and six dimensions by means of $L_\infty$-quasi-isomorphisms, and we propose a twistor space action.Comment: 19 pages, Contribution to Proceedings of LMS/EPSRC Durham Symposium Higher Structures in M-Theory, August 201

Earliest land plants created modern levels of atmospheric oxygen

The progressive oxygenation of the Earth’s atmosphere was pivotal to the evolution of life, but the puzzle of when and how atmospheric oxygen (O2) first approached modern levels (~21%) remains unresolved. Redox proxy data indicate the deep oceans were oxygenated during 435-392 Ma, and the appearance of fossil charcoal indicates O2>15-17% by 420-400 Ma. However, existing models have failed to predict oxygenation at this time. Here we show that the earliest plants, which colonized the land surface from ~470 Ma onwards, were responsible for this mid- Paleozoic oxygenation event, through greatly increasing global organic carbon burial – the net long-term source of O2. We use a trait-based ecophysiological model to predict that cryptogamic vegetation cover could have achieved ~30% of today’s global terrestrial net primary productivity by~445 Ma. Data from modern bryophytes suggests this plentiful early plant material had a much higher molar C:P ratio (~2000) than marine biomass (~100), such that a given weathering flux of phosphorus could support more organic carbon burial. Furthermore, recent experiments suggest that early plants selectively increased the flux of phosphorus (relative to alkalinity) weathered from rocks. Combining these effects in a model of long-term biogeochemical cycling, we reproduce a sustained +2‰ increase in the carbonate carbon isotope (δ13C) record by ~445 Ma, and predict a corresponding rise in O2 to present levels by 420-400 Ma, consistent with geochemical data. This oxygen rise represents a permanent shift in regulatory regime to one where fire-mediated negative feedbacks on organic carbon burial stabilise high O2 levels

On the Hamiltonian formulation of the trigonometric spin Ruijsenaars-Schneider system

We suggest a Hamiltonian formulation for the spin Ruijsenaars–Schneider system in the trigonometric case. Within this interpretation, the phase space is obtained by a quasi-Hamiltonian reduction performed on (the cotangent bundle to) a representation space of a framed Jordan quiver. For arbitrary quivers, analogous varieties were introduced by Crawley-Boevey and Shaw, and their interpretation as quasi-Hamiltonian quotients was given by Van den Bergh. Using Van den Bergh’s formalism, we construct commuting Hamiltonian functions on the phase space and identify one of the flows with the spin Ruijsenaars–Schneider system. We then calculate all the Poisson brackets between local coordinates, thus answering an old question of Arutyunov and Frolov. We also construct a complete set of commuting Hamiltonians and integrate all the flows explicitly

Estinnophyton gracile gen. et sp. nov., a new name for specimens previously determined Protolepidodendron wahnbachense Kräusel & Weyland, from the Siegenian of Belgium

Estinnophyton gracile gen. et sp. nov. is established for plant remains from the Lower Siegenian of Estinnes-au-Mont (Belgium) which have been long confused with Protolepidodendron wahnbachense Kräusel & Weyland 1932, from the Siegenian of the Wahnbachtal (Germany). The distinctive features of the new genus are discussed as well as its possible relationship with Lycophytes and Sphenophyllales.Estinnophyton gracile gen. et sp. nov. est fondé pour désigner des restes végétaux du Siegenien Inférieur d'Estinnes-au-Mont (Belgique) qui furent longtemps confondus avec Protolepidodendron wahnbachense Kräusel & Weyland 1932, du Siegenien de la Wahnbachtal (Allemagne). Les caractères distinctifs du nouveau genre sont discutés ainsi que ses affinités éventuelles avec les Lycophytes et les Sphénophyllales.Fairon-Demaret M. Estinnophyton gracile gen. et sp. nov., a new name for specimens previously determined Protolepidodendron wahnbachense Kräusel & Weyland, from the Siegenian of Belgium. In: Bulletin de la Classe des sciences, tome 64, 1978. pp. 597-610

À propos de certains spécimens de Drepanophycus gaspianus (Dawson) Stockmans, F., 1939, du Dévonien inférieur de Belgique

Some specimens amongst those described by F. Crépin in 1875 and the same year, by A. Gilkinet (1875) are included in, or excluded from the synonymy of Drepanophycus gaspianus (Dawson) Stockmans, F., 1939. Thus their re-examination was required. It allowed to assert the assignation of F. Crépin's specimens to D. gaspianus and to set aside A. Gilkinet's specimen. On the other hand special attention is drawn on D. gaspianus leaves morphology.Certains spécimens, parmi ceux décrits par F. Crépin en 1875 et, la même année, par A. Gilkinet (1875) sont inclus, ou exclus de la synonymie de Drepanophycus gaspianus (Dawson) Stockmans, F., 1939. Leur réexamen s'imposait donc. Il a permis de justifier l'attribution des spécimens de F. Crépin au D. gaspianus et d'écarter celui étudié par A. Gilkinet. Par ailleurs, la morphologie des feuilles de D. gaspianus fait l'objet d'une attention particulière.Fairon-Demaret M. À propos de certains spécimens de Drepanophycus gaspianus (Dawson) Stockmans, F., 1939, du Dévonien inférieur de Belgique. In: Bulletin de la Classe des sciences, tome 63, 1977. pp. 781-790