8,451 research outputs found
Return migration in Italy: what do we know?
Return migration is the positive counterpart of brain drain. Human capital accumulation increases in a country if skilled agents go back home after a period spent working abroad. Effects of brain drain in Italy could be negative as highly skilled migrants decide not to come back to their native country. Our simple model shows that if preference for home consumption is balanced by career opportunities and life-style conditions, agents leave Italy and prefer to remain abroad. Data support and policy implications are provided.Return migration; brain drain.
Andreev-Bashkin effect in superfluid cold gases mixture
We study a mixture of two superfluids with density-density and
current-current (Andreev-Bashkin) interspecies interactions. The
Andreev-Bashkin coupling gives rise to a dissipationless drag (or entrainment)
between the two superfluids. Within the quantum hydrodynamics approximation, we
study the relations between speeds of sound, susceptibilities and static
structure factors, in a generic model in which the density and spin dynamics
decouple. Due to translational invariance, the density channel does not feel
the drag. The spin channel, instead, does not satisfy the usual Bijl-Feynman
relation, since the f-sum rule is not exhausted by the spin phonons. The very
same effect on one dimensional Bose mixtures and their Luttinger liquid
description is analysed within perturbation theory. Using diffusion quantum
Monte Carlo simulations of a system of dipolar gases in a double layer
configuration, we confirm the general results. Given the recent advances in
measuring the counterflow instability, we also study the effect of the
entrainment on the dynamical stability of a superfluid mixture with non-zero
relative velocity.Comment: 12 pages, 4 figure
Optimal generation of entanglement under local control
We study the optimal generation of entanglement between two qubits subject to
local unitary control. With the only assumptions of linear control and unitary
dynamics, by means of a numerical protocol based on the variational approach
(Pontryagin's Minimum Principle), we evaluate the optimal control strategy
leading to the maximal achievable entanglement in an arbitrary interaction
time, taking into account the energy cost associated to the controls. In our
model we can arbitrarily choose the relative weight between a large
entanglement and a small energy cost.Comment: 4 page
Spin fluctuations, susceptibility and the dipole oscillation of a nearly ferromagnetic Fermi gas
We discuss the spin fluctuations and the role played by the magnetic
susceptibility in an atomic Fermi gas interacting with positive scattering
length. Both thermal and quantum fluctuations are considered. Using a sum rule
approach and recent {\it ab initio} Monte Carlo results for the magnetic
susceptibility of uniform matter we provide explicit predictions for the
frequency of the spin dipole oscillation of a gas trapped by a harmonic
potential and discuss the deviations from the behaviour of an ideal gas when
the system approaches the ferromagnetic transition. The role of the Landau's
parameters in the characterization of the magnetic properties is also
discussed.Comment: 5 pages, 2 figure
Widely-tunable mid-IR frequency comb source based on difference frequency generation
We report on a mid-infrared frequency comb source of unprecedented tunability
covering the entire 3-10 {\mu}m molecular fingerprint region. The system is
based on difference frequency generation in a GaSe crystal pumped by a 151 MHz
Yb:fiber frequency comb. The process was seeded with Raman shifted solitons
generated in a highly nonlinear suspended-core fiber with the same source.
Average powers up to 1.5 mW were achieved at 4.7 {\mu}m wavelength.Comment: 3 pages, 3 figure
Real-Time Dedispersion for Fast Radio Transient Surveys, using Auto Tuning on Many-Core Accelerators
Dedispersion, the removal of deleterious smearing of impulsive signals by the
interstellar matter, is one of the most intensive processing steps in any radio
survey for pulsars and fast transients. We here present a study of the
parallelization of this algorithm on many-core accelerators, including GPUs
from AMD and NVIDIA, and the Intel Xeon Phi. We find that dedispersion is
inherently memory-bound. Even in a perfect scenario, hardware limitations keep
the arithmetic intensity low, thus limiting performance. We next exploit
auto-tuning to adapt dedispersion to different accelerators, observations, and
even telescopes. We demonstrate that the optimal settings differ between
observational setups, and that auto-tuning significantly improves performance.
This impacts time-domain surveys from Apertif to SKA.Comment: 8 pages, accepted for publication in Astronomy and Computin
Computational analysis of performance deterioration of a wind turbine blade strip subjected to environmental erosion
Wind-turbine blade rain and sand erosion, over long periods of time, can degrade the aerodynamic performance and therefore the power production. Computational analysis of the erosion can help engineers have a better understanding of the maintenance and protection requirements. We present an integrated method for this class of computational analysis. The main components of the method are the streamline-upwind/PetrovâGalerkin (SUPG) and pressure-stabilizing/PetrovâGalerkin (PSPG) stabilizations, a finite element particle-cloud tracking method, an erosion model based on two time scales, and the solid-extension mesh moving technique (SEMMT). The turbulent-flow nature of the analysis is handled with a Reynolds-averaged NavierâStokes model and SUPG/PSPG stabilization, the particle-cloud trajectories are calculated based on the computed flow field and closure models defined for the turbulent dispersion of particles, and one-way dependence is assumed between the flow and particle dynamics. Because the geometry update due to the erosion has a very long time scale compared to the fluidâparticle dynamics, the update takes place in a sequence of âevolution stepsâ representing the impact of the erosion. A scale-up factor, calculated in different ways depending on the update threshold criterion, relates the erosions and particle counts in the evolution steps to those in the fluidâparticle simulation. As the blade geometry evolves, the mesh is updated with the SEMMT. We present computational analysis of rain and sand erosion for a wind-turbine blade strip, including a case with actual rainfall data and experimental aerodynamic data for eroded airfoil geometries
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