Spectral Features of Magnetic Fluctuations at Proton Scales from Fast to Slow Solar Wind

This Letter investigates the spectral characteristics of the interplanetary magnetic field fluctuations at proton scales during several time intervals chosen along the speed profile of a fast stream. The character of the fluctuations within the first frequency decade, beyond the high frequency break located between the fluid and the kinetic regime, strongly depends on the type of wind. While the fast wind shows a clear signature of both right handed and left handed polarized fluctuations, possibly associated with KAW and Ion-Cyclotron waves, respectively, the rarefaction region, where the wind speed and the Alfv\'{e}nicity of low frequency fluctuations decrease, shows a rapid disappearance of the ion-cyclotron signature followed by a more gradual disappearance of the KAWs. Moreover, also the power associated to perpendicular and parallel fluctuations experiences a rapid depletion, keeping, however, the power anisotropy in favour of the perpendicular spectrum.Comment: 10 pages, 5 figures, to be published in ApJ

A note on some homology spheres which are 2-fold coverings of inequivalent knots

We construct a family of closed 3--manifolds $M_{\alpha,r}$, which are  homeomorphic to the Brieskorn homology spheres $\Sigma(2, \alpha+1, q+2r-1)$,  where $q=\alpha(r-1)$ and both $\alpha \ge 1$ and $q \ge 3$ are odd. We show  that $M_{\alpha,r}$ can be represented as 2--fold covering of the 3--sphere  branched over two inequivalent knots. Our proofs follow immediately from two  different symmetries of a genus 2 Heegaard diagram of $\Sigma(2, \alpha+1,  q+2r-1)$, and generalize analogous results proved in [BGM], [IK], [SIK] and  [T]

Cyclic Branched Coverings Over Some Classes of (1,1)-Knots

We construct a 4-parametric family of combinatorial closed 3-manifolds, obtained by glueing together in pairs the boundary faces of polyhedral 3-balls. Then, we obtain geometric presentations of the fundamental groups of these manifolds and determine the corresponding split extension groups. Finally, we prove that the considered manifolds are cyclic coverings of the 3-sphere branched over well-specified -knots, including torus knots and Montesinos knots

Re-design of digital tasks: the role of automatic and expert scaffolding at university level

In this study we present the re-design of a digital task for university students attending to a probability course. The re-design, directed toward the overcoming of specific critical issues highlighted in previous studies, is mainly aimed at providing students (in particular low achievers) with hints and feedback as tools of scaffolding and meta- scaffolding. Thanks to the analysis of a low achiever’s interaction with the re-designed task, we investigated the limits of the automatic scaffolding and the key- role of expert’s interventions in fostering students’ overcoming of possible impasses

The role of formative assessment in fostering individualized teaching at university level

International audienceIn this paper we present the design of individualized online teaching/learning paths at university level, within a formative assessment frame. Moreover, we discuss the preliminary results of a pilot study aimed at investigating the students’ perception of the impact of these online paths to support their learning, their elaboration of the external feedback that the digital environment provides and their awareness about their difficulties and the strategies they could activate to overcome them

Exceptional surgeries on certain (1,1)(1,1)-knots

We determine certain exceptional surgeries on a 3--parametric family of hyperbolic 1--bridge genus one knots ((1,1)-knots, in short). In particular, we show that such knots admit two infinite series of lens space surgeries. Our work is related to a nice paper of Teragaito [16], since we represent his toroidal manifolds as 2--fold coverings of the 3-sphere branched over well--specified links

Levels of generalization in the objectification of the recursion step

In this study, we focus on the students’ objectification of the recursion step, intended as a process of generalization in the sense of Radford (2001). Building on Radford’s model, we elaborate levels of generalization of the recursion step and use them to analyze the processes activated by secondary school students during collaborative activities with geometric recursive sequences. The analysis allows us to identify different levels reached by the students in grasping the recursion step and their transitions between these levels

Topology of compact space forms from Platonic solids. I.

AbstractThe problem of classifying, up to isometry, the orientable 3-manifolds that arise by identifying the faces of a Platonic solid was completely solved in a nice paper of Everitt [B. Everitt, 3-manifolds from Platonic solids, Topology Appl. 138 (2004) 253–263]. His work completes the classification begun by Best [L.A. Best, On torsion-free discrete subgroups of PSL2(C) with compact orbit space, Canad. J. Math. 23 (1971) 451–460], Lorimer [P.J. Lorimer, Four dodecahedral spaces, Pacific J. Math. 156 (2) (1992) 329–335], Prok [I. Prok, Classification of dodecahedral space forms, Beiträge Algebra Geom. 39 (2) (1998) 497–515], and Richardson and Rubinstein [J. Richardson, J.H. Rubinstein, Hyperbolic manifolds from a regular polyhedron, Preprint]. In this paper we investigate the topology of closed orientable 3-manifolds from Platonic solids. Here we completely recognize those manifolds in the spherical and Euclidean cases, and state topological properties for many of them in the hyperbolic case. The proofs of the latter will appear in a forthcoming paper