5,747 research outputs found
Selection of dune shapes and velocities. Part 2: A two-dimensional modelling
We present in this paper a simplification of the dune model proposed by
Sauermann et al. which keeps the basic mechanisms but allows analytical and
parametric studies. Two kinds of purely propagative two dimensional solutions
are exhibited: dunes and domes, which, by contrast to the former, do not show
avalanche slip face. Their shape and velocity can be predicted as a function of
their size. We recover in particular that dune profiles are not scale invariant
(small dunes are flatter than the large ones), and that the inverse of the
velocity grows almost linearly with the dune size. We furthermore get the
existence of a critical mass below which no stable dune exists. However, the
linear stability analysis of a flat sand sheet shows that it is unstable at
large wavelengths and suggests a mechanism of dune initiation.Comment: submitted to Eur. Phys. J. B, 13 pages, 17 figure
The first coefficients of the asymptotic expansion of the Bergman kernel of the spin^c Dirac operator
We establish the existence of the asymptotic expansion of the Bergman kernel
associated to the spin-c Dirac operators acting on high tensor powers of line
bundles with non-degenerate mixed curvature (negative and positive eigenvalues)
by extending the paper " On the asymptotic expansion of Bergman kernel "
(math.DG/0404494) of Dai-Liu-Ma. We compute the second coefficient b_1 in the
asymptotic expansion using the method of our paper "Generalized Bergman kernels
on symplectic manifolds" (math.DG/0411559).Comment: 21 pages, to appear in Internat. J. Math. Precisions added in the
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Transition from viscous to inertial regime in dense suspensions
Non-Brownian suspensions present a transition from Newtonian behavior in the
zero-shear limit to a shear thickening behaviour at a large shear rate, none of
which is clearly understood so far. Here, we carry out numerical simulations of
such an athermal dense suspension under shear, at an imposed confining
pressure. This set-up is conceptually identical to the recent experiments of
Boyer and co-workers [Phys. Rev. Lett. 107,188301 (2011)]. Varying the
interstitial fluid viscosities, we recover the Newtonian and Bagnoldian regimes
and show that they correspond to a dissipation dominated by viscous and contact
forces respectively. We show that the two rheological regimes can be unified as
a function of a single dimensionless number, by adding the contributions to the
dissipation at a given volume fraction.Comment: 4 pages, 3 figure
Droplets move over viscoelastic substrates by surfing a ridge
Liquid drops on soft solids generate strong deformations below the contact
line, resulting from a balance of capillary and elastic forces. The movement of
these drops may cause strong, potentially singular dissipation in the soft
solid. Here we show that a drop on a soft substrate moves by surfing a ridge:
the initially flat solid surface is deformed into a sharp ridge whose
orientation angle depends on the contact line velocity. We measure this angle
for water on a silicone gel and develop a theory based on the substrate
rheology. We quantitatively recover the dynamic contact angle and provide a
mechanism for stick-slip motion when a drop is forced strongly: the contact
line depins and slides down the wetting ridge, forming a new one after a
transient. We anticipate that our theory will have implications in problems
such as self-organization of cell tissues or the design of capillarity-based
microrheometers.Comment: 9 pages, 5 figure
Flow rule, self-channelization and levees in unconfined granular flows
Unconfined granular flows along an inclined plane are investigated
experimentally. During a long transient, the flow gets confined by quasistatic
banks but still spreads laterally towards a well-defined asymptotic state
following a nontrivial process. Far enough from the banks a scaling for the
depth averaged velocity is obtained, which extends the one obtained for
homogeneous steady flows. Close to jamming it exhibits a crossover towards a
nonlocal rheology. We show that the levees, commonly observed along the sides
of the deposit upon interruption of the flow, disappear for long flow
durations. We demonstrate that the morphology of the deposit builds up during
the flow, in the form of an underlying static layer, which can be deduced from
surface velocity profiles, by imposing the same flow rule everywhere in the
flow.Comment: 4 pages, 5 figure
Erosion waves: transverse instabilities and fingering
Two laboratory scale experiments of dry and under-water avalanches of
non-cohesive granular materials are investigated. We trigger solitary waves and
study the conditions under which the front is transversally stable. We show the
existence of a linear instability followed by a coarsening dynamics and finally
the onset of a fingering pattern. Due to the different operating conditions,
both experiments strongly differ by the spatial and time scales involved.
Nevertheless, the quantitative agreement between the stability diagram, the
wavelengths selected and the avalanche morphology reveals a common scenario for
an erosion/deposition process.Comment: 4 pages, 6 figures, submitted to PR
Reflections on symmetries and asymmetries in the internationalization of higher education in Brazil and Canada
In this article we reflect on how internationalization is articulated in different ways within the context of a relatively new global educational credentials export industry (GEEI). This industry emerged largely as a response to decreased public funding of higher education in specific \u27education export\u27 countries. We take Canada as an example of one of these countries, to illustrate how the marketization of internationalization in higher education is reproduced and contested within that context. We contrast how internationalization is articulated in Canada with the context of internationalization in Brazil. We offer the case of a Brazilian university - UNILA, the Federal University for Latin American Integration, as an example of internationalization that attempts to challenge the global credentials export industry. mple. The example of UNILA shows how a commitment to international public service stands in contrast to transactional internationalization processes that sustain dominant trends of student and knowledge flows in North-South asymmetrical engagements
Esperienze di didattica della fisica in diversi livelli del sistema educativo
The growing interest of people in science events, the projects supported by
the Italian Ministry of Education, University and Research to foster STEM
teaching in different levels of the education system and the introduction of
modern physics in some Italian high schools, contributed to the strengthening
of interaction between schools, universities and research centers. This
interaction realized in dedicated activities characterized by innovative
communication and education strategies.This paper presents the events of
science dissemination organized in the last years by the University of Ferrara
and the National Institute for Nuclear Physics taking into account some case
study differentiated by contents, recipients and education strategies.Comment: The article is written in Italia
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