5,686 research outputs found
Student-Faculty Partnership: The European Framework and the Experience of the Italian Project Employability & Competences.
The article describes the European Framework for Improving Quality of Teaching in Europe and the research carried our at Italian University to explore the student voices in higher education
Constraints on Radial Migration in Spiral Galaxies - II. Angular momentum distribution and preferential migration
The orbital angular momentum of individual stars in galactic discs can be
permanently changed through torques from transient spiral patterns.
Interactions at the corotation resonance dominate these changes and have the
further property of conserving orbital circularity. We derived in an earlier
paper an analytic criterion that an unperturbed stellar orbit must satisfy in
order for such an interaction to occur i.e. for it to be in a trapped orbit
around corotation. We here use this criterion in an investigation of how the
efficiency of induced radial migration for a population of disc stars varies
with the angular momentum distribution of that population. We frame our results
in terms of the velocity dispersion of the population, this being an easier
observable than is the angular momentum distribution. Specifically, we
investigate how the fraction of stars in trapped orbits at corotation varies
with the velocity dispersion of the population, for a system with an assumed
flat rotation curve. Our analytic results agree with the finding from
simulations that radial migration is less effective in populations with
'hotter' kinematics. We further quantify the dependence of this trapped
fraction on the strength of the spiral pattern, finding a higher trapped
fraction for higher amplitude perturbations.Comment: 28 pages, 15 figure, accepted for publication in MNRA
Smoothness of definite unitary eigenvarieties at critical points
We compute an upper bound for the dimension of the tangent spaces at
classical points of certain eigenvarieties associated with definite unitary
groups, especially including the so-called critically refined cases. Our bound
is given in terms of "critical types" and when our bound is minimized it
matches the dimension of the eigenvariety. In those cases, which we explicitly
determine, the eigenvariety is necessarily smooth and our proof also shows that
the completed local ring on the eigenvariety is naturally a certain universal
Galois deformation ring.Comment: 29 pages. Updated version of 2015 preprint (previously not arXiv'd
Tuning the Magnetic Ordering Temperature of Hexagonal Ferrites by Structural Distortion Control
To tune the magnetic properties of hexagonal ferrites, a family of
magnetoelectric multiferroic materials, by atomic-scale structural engineering,
we studied the effect of structural distortion on the magnetic ordering
temperature (TN). Using the symmetry analysis, we show that unlike most
antiferromagnetic rare-earth transition-metal perovskites, a larger structural
distortion leads to a higher TN in hexagonal ferrites and manganites, because
the K3 structural distortion induces the three-dimensional magnetic ordering,
which is forbidden in the undistorted structure by symmetry. We also revealed a
near-linear relation between TN and the tolerance factor and a power-law
relation between TN and the K3 distortion amplitude. Following the analysis, a
record-high TN (185 K) among hexagonal ferrites was predicted in hexagonal
ScFeO3 and experimentally verified in epitaxially stabilized films. These
results add to the paradigm of spin-lattice coupling in antiferromagnetic
oxides and suggests further tunability of hexagonal ferrites if more lattice
distortion can be achieved
Magnetothermodynamics: Measuring equations of state in a relaxed magnetohydrodynamic plasma
We report the first measurements of equations of state of a fully relaxed
magnetohydrodynamic (MHD) laboratory plasma. Parcels of magnetized plasma,
called Taylor states, are formed in a coaxial magnetized plasma gun, and are
allowed to relax and drift into a closed flux conserving volume. Density, ion
temperature, and magnetic field are measured as a function of time as the
Taylor states compress and heat. The theoretically predicted MHD and double
adiabatic equations of state are compared to experimental measurements. We find
that the MHD equation of state is inconsistent with our data.Comment: 4 pages, 4 figure
The Minimal Length of a Lagrangian Cobordism between Legendrians
To investigate the rigidity and flexibility of Lagrangian cobordisms between
Legendrian submanifolds, we investigate the minimal length of such a cobordism,
which is a -dimensional measurement of the non-cylindrical portion of the
cobordism. Our primary tool is a set of real-valued capacities for a Legendrian
submanifold, which are derived from a filtered version of Legendrian Contact
Homology. Relationships between capacities of Legendrians at the ends of a
Lagrangian cobordism yield lower bounds on the length of the cobordism. We
apply the capacities to Lagrangian cobordisms realizing vertical dilations
(which may be arbitrarily short) and contractions (whose lengths are bounded
below). We also study the interaction between length and the linking of
multiple cobordisms as well as the lengths of cobordisms derived from
non-trivial loops of Legendrian isotopies.Comment: 33 pages, 9 figures. v2: Minor corrections in response to referee
comments. More general statement in Proposition 3.3 and some reorganization
at the end of Section
Flipping the roles: Analysis of a university course where students become co-creators of curricula
In this paper I present the transformation of a university course inspired by the theoretical
background of the student voice approach (Fielding, 2004a and 2004b; Cook-Sather, 2006) and, in
particular, the ways students are encouraged to be \u201cco-creators of curricula\u201d through partnership
with faculty (Bovill, Cook\u2010Sather & Felten, 2011). I introduce active learning practices centered on
\u201cstudent generated content\u201d (Sener, 2007; Bates et al., 2012), allowing a new rendering of the
traditional lesson cycle: frontal lesson, individual study, and final exam. The change in students\u2019
attitude towards study and final exam support the effectiveness of this methodology
Energy dynamics in a simulation of LAPD turbulence
Energy dynamics calculations in a 3D fluid simulation of drift wave
turbulence in the linear Large Plasma Device (LAPD) [W. Gekelman et al., Rev.
Sci. Inst. 62, 2875 (1991)] illuminate processes that drive and dissipate the
turbulence. These calculations reveal that a nonlinear instability dominates
the injection of energy into the turbulence by overtaking the linear drift wave
instability that dominates when fluctuations about the equilibrium are small.
The nonlinear instability drives flute-like () density
fluctuations using free energy from the background density gradient. Through
nonlinear axial wavenumber transfer to fluctuations, the
nonlinear instability accesses the adiabatic response, which provides the
requisite energy transfer channel from density to potential fluctuations as
well as the phase shift that causes instability. The turbulence characteristics
in the simulations agree remarkably well with experiment. When the nonlinear
instability is artificially removed from the system through suppressing
modes, the turbulence develops a coherent frequency spectrum
which is inconsistent with experimental data
Ordinary Modular Forms and Companion Points on the Eigencurve
We give a new proof of a result due to Breuil and Emerton which relates the
splitting behavior at p of the p-adic Galois representation attached to a
p-ordinary modular form to the existence of an overconvergent p-adic companion
form for f.Comment: 12 pages. Final version. Changes from previous version: expanded on
an argument in section 2.3 and minor correction of typos/languag
Generalized Gauss maps and integrals for three-component links: toward higher helicities for magnetic fields and fluid flows, Part 2
We describe a new approach to triple linking invariants and integrals, aiming
for a simpler, wider and more natural applicability to the search for higher
order helicities of fluid flows and magnetic fields. To each three-component
link in Euclidean 3-space, we associate a geometrically natural generalized
Gauss map from the 3-torus to the 2-sphere, and show that the pairwise linking
numbers and Milnor triple linking number that classify the link up to link
homotopy correspond to the Pontryagin invariants that classify its generalized
Gauss map up to homotopy. This can be viewed as a natural extension of the
familiar fact that the linking number of a two-component link in 3-space is the
degree of its associated Gauss map from the 2-torus to the 2-sphere. When the
pairwise linking numbers are all zero, we give an integral formula for the
triple linking number analogous to the Gauss integral for the pairwise linking
numbers, but patterned after J.H.C. Whitehead's integral formula for the Hopf
invariant. The integrand in this formula is geometrically natural in the sense
that it is invariant under orientation-preserving rigid motions of 3-space,
while the integral itself can be viewed as the helicity of a related vector
field on the 3-torus. In the first paper of this series [math.GT 1101.3374] we
did this for three-component links in the 3-sphere. Komendarczyk has applied
this approach in special cases to derive a higher order helicity for magnetic
fields whose ordinary helicity is zero, and to obtain from this nonzero lower
bounds for the field energy.Comment: 22 pages, 8 figures. arXiv admin note: text overlap with
arXiv:1101.337
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