Flexible varieties and automorphism groups

Given an irreducible affine algebraic variety X of dimension n≥2 , we let SAut(X) denote the special automorphism group of X , that is, the subgroup of the full automorphism group Aut(X) generated by all one-parameter unipotent subgroups. We show that if SAut(X) is transitive on the smooth locus X reg , then it is infinitely transitive on X reg . In turn, the transitivity is equivalent to the flexibility of X . The latter means that for every smooth point x∈X reg the tangent space T x X is spanned by the velocity vectors at x of one-parameter unipotent subgroups of Aut(X) . We also provide various modifications and applications.

RADIX: a minimal-resources rapid-access drilling system

Determining the expected age at a potential ice-core drilling site on a polar ice sheet generally depends on a combination of information from remote-sensing methods, estimates of current accumulation and modelling. This poses irreducible uncertainties in retrieving an undisturbed ice core of the desired age. Although recently perfected radar techniques will improve the picture of the ice sheet below future drilling sites, rapid prospective drillings could further increase the success of deep drilling projects. Here we design and explore a drilling system for a minimum-size rapid-access hole. The advantages of a small hole are the low demand for drilling fluid, low overall weight of the equipment, fast installing and de-installing and low costs. We show that, in theory, drilling of a 20mm hole to a depth of 3000m is possible in ~4 days. First concepts have been realized and verified in the field. Both the drill cuttings and the hole itself can be used to characterize the properties of the ice sheet and its potential to provide a trustworthy palaeo-record. A candidate drilling site could be explored in ~2 weeks, which would enable the characterization of several sites in one summer season.

Erkenntnisfortschritt durch Problematisierung

In diesem Beitrag wird das Problem behandelt, wie methodisch kontrollierter Erkenntnisfortschritt in der Erziehungswissenschaft theoretisch bestimmt werden kann. Hierzu wird der Lösungsansatz der erziehungswissenschaftlichen Komplexitätsforschung vorgestellt. Diese beschreibt Forschung als ein irreduzibles Wechselspiel von Perspektiven und sieht in der gegenseitigen Problematisierung theoretischer Standpunkte das Medium des methodisch kontrollierten Erkenntnisfortschritts. Anhand des Diskurses um die Begriffe ‚Bildung´ und ‚Subjektivation´ werden die Überlegungen konkretisiert. Es wird darauf aufmerksam gemacht, dass eine wechselseitige Problematisierung theoretischer Standpunkte in diesem Kontext nicht auszumachen ist. Aus diesem Grund werden mögliche bildungstheoretische Einsätze markiert, die es erlauben, subjektivationstheoretische Problematisierungen ihrerseits zu problematisieren. Statt Resignifizierung vorschnell als eine Form von Bildung zu bestimmen, wird die Auffassung vertreten, dass ein Bildungsbegriff entwickelt werden müsse, der subjektivationstheoretischen Problematisierungen ebenso Rechnung trägt wie einem bereits erreichten bildungstheoretischen Problembewusstsein.

Measurement of the intrinsic electron neutrino component in the T2K neutrino beam with the ND280 detector

The T2K experiment has reported the first observation of the appearance of electron neutrinos in a muon neutrino beam. The main and irreducible background to the appearance signal comes from the presence in the neutrino beam of a small intrinsic component of electron neutrinos originating from muon and kaon decays. In T2K, this component is expected to represent 1.2% of the total neutrino flux. A measurement of this component using the near detector (ND280), located 280 m from the target, is presented. The charged current interactions of electron neutrinos are selected by combining the particle identification capabilities of both the time projection chambers and electromagnetic calorimeters of ND280. The measured ratio between the observed electron neutrino beam component and the prediction is 1.01±0.10 providing a direct confirmation of the neutrino fluxes and neutrino cross section modeling used for T2K neutrino oscillation analyses. Electron neutrinos coming from muons and kaons decay are also separately measured, resulting in a ratio with respect to the prediction of 0.68±0.30 and 1.10±0.14 , respectively.