19,842 research outputs found
Maghiel van Crevel. Language shattered : contemporary Chinese poetry and Duoduo
This article reviews the book Language Shattered: Contemporary Chinese Poetry and Duoduo written by Maghiel van Crevel
How to model quantum plasmas
Traditional plasma physics has mainly focused on regimes characterized by
high temperatures and low densities, for which quantum-mechanical effects have
virtually no impact. However, recent technological advances (particularly on
miniaturized semiconductor devices and nanoscale objects) have made it possible
to envisage practical applications of plasma physics where the quantum nature
of the particles plays a crucial role. Here, I shall review different
approaches to the modeling of quantum effects in electrostatic collisionless
plasmas. The full kinetic model is provided by the Wigner equation, which is
the quantum analog of the Vlasov equation. The Wigner formalism is particularly
attractive, as it recasts quantum mechanics in the familiar classical phase
space, although this comes at the cost of dealing with negative distribution
functions. Equivalently, the Wigner model can be expressed in terms of
one-particle Schr{\"o}dinger equations, coupled by Poisson's equation: this is
the Hartree formalism, which is related to the `multi-stream' approach of
classical plasma physics. In order to reduce the complexity of the above
approaches, it is possible to develop a quantum fluid model by taking
velocity-space moments of the Wigner equation. Finally, certain regimes at
large excitation energies can be described by semiclassical kinetic models
(Vlasov-Poisson), provided that the initial ground-state equilibrium is treated
quantum-mechanically. The above models are validated and compared both in the
linear and nonlinear regimes.Comment: To be published in the Fields Institute Communications Series.
Proceedings of the Workshop on Kinetic Theory, The Fields Institute, Toronto,
March 29 - April 2, 200
Gravity, antimatter and the Dirac-Milne universe
We review the main arguments against antigravity, a different acceleration of
antimatter relative to matter in a gravitational field, discussing and
challenging Morrison's, Good's and Schiff's arguments. Following Price, we show
that, very surprisingly, the usual expression of the Equivalence Principle is
violated by General Relativity when particles of negative mass are supposed to
exist, which may provide a fundamental explanation of MOND phenomenology,
obviating the need for Dark Matter. Motivated by the observation of repulsive
gravity under the form of Dark Energy, and by the fact that our universe looks
very similar to a coasting (neither decelerating nor accelerating) universe, we
study the Dirac-Milne cosmology, a symmetric matter-antimatter cosmology where
antiparticles have the same gravitational properties as holes in a
semiconductor. Noting the similarities with our universe (age, SN1a luminosity
distance, nucleosynthesis, CMB angular scale), we focus our attention on
structure formation mechanisms, finding strong similarities with our universe.
Additional tests of the Dirac-Milne cosmology are briefly reviewed, and we
finally note that a crucial test of the Dirac-Milne cosmology will be soon
realized at CERN next to the ELENA antiproton decelerator, possibly as early as
fall 2018, with the AEgIS, ALPHA-g and Gbar antihydrogen gravity experiments.Comment: Proceedings of the Low Energy Antiproton Physics Conference (LEAP),
Sorbonne University, Paris, March 12th to 16th, 201
Polynomial Chaos-Based Tolerance Analysis of Microwave Planar Guiding Structures
This paper focuses on the derivation of an enhanced transmission-line model allowing to describe a realistic microwave interconnect with the inclusion of external uncertainties, like tolerances or process variations. The proposed method, that is based on the expansion of the well-known telegraph equations in terms of orthogonal polynomials, turns out to be accurate and more efficient than alternative solutions like Monte Carlo method in determining the transmission-line response sensitivity to parameters variability. An application example involving the analysis of the S-parameters of a realistic PCB coplanar waveguide concludes the pape
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