2,448 research outputs found
Creep and fluidity of a real granular packing near jamming
We study the internal dynamical processes taking place in a granular packing
below yield stress. At all packing fractions and down to vanishingly low
applied shear, a logarithmic creep is evidenced. The experiments are analyzed
under the scope of a visco-elastic model introducing an internal "fluidity"
variable. For all experiments, the creep dynamics can be rescaled onto a unique
curve which displays jamming at the random-close-packing limit. At each packing
fraction, a stress value is evidenced, corresponding to the onset of internal
granular reorganisation leading to a slowing down the creep dynamics before the
final yield
Quantum dot dephasing by fractional quantum Hall edge states
We consider the dephasing rate of an electron level in a quantum dot, placed
next to a fluctuating edge current in the fractional quantum Hall effect. Using
perturbation theory, we show that this rate has an anomalous dependence on the
bias voltage applied to the neighboring quantum point contact, which originates
from the Luttinger liquid physics which describes the Hall fluid. General
expressions are obtained using a screened Coulomb interaction. The dephasing
rate is strictly proportional to the zero frequency backscattering current
noise, which allows to describe exactly the weak to strong backscattering
crossover using the Bethe-Ansatz solution
Understanding Return And Volatility Spillovers Among Major Agricultural Commodities
We provide comprehensive evidence of return and volatility spillovers for the four major agricultural commodities including sugar, wheat, corn and cotton over the recent period 2003-2010. Our results from the recent VAR-GARCH model of Ling and McAleer (2003) that allows for simultaneous shock transmissions of conditional volatilities of returns across commodities show the existence of substantial volatility spillover linkages between agricultural commodity returns and volatilities. Our findings are also particularly insightful for optimal portfolio designs and risk management through the computation of optimal weights and hedge ratios
Efficient caching in content-centric networks using OpenFlow
International audienceContent-Centric Networking (CCN) is designed for efficient content dissemination and supports caching contents on the path from content providers to content consumers to improve user experience and reduce costs. However, this strategy is not optimal inside a domain. In this paper, we propose a solution to improve caching in CCN using a Software-Defined Networking approach
Robust Feedback Linearization Approach for Fuel-Optimal Oriented Control of Turbocharged Spark-Ignition Engines
This chapter proposes a new control approach for the turbocharged air system of a gasoline engine. To simplify the control implementation task, static lookup tables (LUTs) of engine data are used to estimate the engine variables in place of complex dynamical observer and/or estimators. The nonlinear control design is based on the concept of robust feedback linearization which can account for the modeling uncertainty and the estimation errors induced by the use of engine lookup tables. The control feedback gain can be effectively computed from a convex optimization problem. Two control strategies have been investigated for this complex system: drivability optimization and fuel reduction. The effectiveness of the proposed control approach is clearly demonstrated with an advanced engine simulator
Photo-assisted Andreev reflection as a probe of quantum noise
Andreev reflection, which corresponds to the tunneling of two electrons from
a metallic lead to a superconductor lead as a Cooper pair (or vice versa), can
be exploited to measure high frequency noise. A detector is proposed, which
consists of a normal lead--superconductor circuit, which is capacitively
coupled to a mesoscopic circuit where noise is to be measured. We discuss two
detector circuits: a single normal metal -- superconductor tunnel junction and
a normal metal separated from a superconductor by a quantum dot operating in
the Coulomb blockade regime. A substantial DC current flows in the detector
circuit when an appropriate photon is provided or absorbed by the mesoscopic
circuit, which plays the role of an environment for the junction to which it
couples. Results for the current can be cast in all cases in the form of a
frequency integral of the excess noise of the environment weighted by a kernel
which is specific to the transport process (quasiparticle tunneling, Andreev
reflection,...) which is considered. We apply these ideas to the measurement of
the excess noise of a quantum point contact and we provide numerical estimates
of the detector current.Comment: 19 pages, 11 figure
Playing with Burgers's equation
International audienceThe 1D Burgers equation is used as a toy model to mimick the resulting behaviour of numerical schemes when replacing a conservation law by a form which is equivalent for smooth solutions, such as the total energy by the internal energy balance in the Euler equations. If the initial Burgers equation is replaced by a balance equation for one of its entropies (the square of the unknown) and discretized by a standard scheme, the numerical solution converges, as expected, to a function which is not a weak solution to the initial problem. However, if we first add to Burgers' equation a diffusion term scaled by a small positive parameter ǫ before deriving the entropy balance (this yields a non conservative diffusion term in the resulting equation), and then choose ǫ and the discretization parameters adequately and let them tend to zero, we observe that we recover a convergence to the correct solution
Observation of spin-transfer switching in deep submicron-sized and low-resistance magnetic tunnel junctions
The spin-transfer effect has been studied in magnetic tunnel junctions
(PtMn/CoFe/Ru/CoFe/Al2O3/CoFe/NiFe) with dimensions down to 0.1x0.2 um2 and
resistance-area product RA in the range of 0.5-10 Ohm m2 (dR/R=1-20%).
Current-induced magnetization switching is observed with a critical current
density of about 8e6 A/cm2. The attribution of the switching to the
spin-transfer effect is supported by a current-induced dR/R value identical to
the one obtained from the R versus H measurements. Furthermore, the critical
switching current density has clear dependence on the applied magnetic field,
consistent with what has been observed previously in the case of spin-transfer
induced switching in metallic multilayer systems
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