3,599 research outputs found
Bosons Doubling
It is shown that next-nearest-neighbor interactions may lead to unusual
paramagnetic or ferromagnetic phases which physical content is radically
different from the standard phases. Actually there are several particles
described by the same quantum field in a manner similar to the species doubling
of the lattice fermions. We prove the renormalizability of the theory at the
one loop level.Comment: 12 page
Semiclassical Dynamics of Electrons in Magnetic Bloch Bands: a Hamiltonian Approach
y formally diagonalizing with accuracy the Hamiltonian of electrons
in a crystal subject to electromagnetic perturbations, we resolve the debate on
the Hamiltonian nature of semiclassical equations of motion with Berry-phase
corrections, and therefore confirm the validity of the Liouville theorem. We
show that both the position and momentum operators acquire a Berry-phase
dependence, leading to a non-canonical Hamiltonian dynamics. The equations of
motion turn out to be identical to the ones previously derived in the context
of electron wave-packets dynamics.Comment: 4 page
Development of UHF measurements
Collector gauge and orbitron gauge for ultrahigh vacuum measurement
From Feynman Proof of Maxwell Equations to Noncommutative Quantum Mechanics
In 1990, Dyson published a proof due to Feynman of the Maxwell equations
assuming only the commutation relations between position and velocity. With
this minimal assumption, Feynman never supposed the existence of Hamiltonian or
Lagrangian formalism. In the present communication, we review the study of a
relativistic particle using ``Feynman brackets.'' We show that Poincar\'e's
magnetic angular momentum and Dirac magnetic monopole are the consequences of
the structure of the Lorentz Lie algebra defined by the Feynman's brackets.
Then, we extend these ideas to the dual momentum space by considering
noncommutative quantum mechanics. In this context, we show that the
noncommutativity of the coordinates is responsible for a new effect called the
spin Hall effect. We also show its relation with the Berry phase notion. As a
practical application, we found an unusual spin-orbit contribution of a
nonrelativistic particle that could be experimentally tested. Another practical
application is the Berry phase effect on the propagation of light in
inhomogeneous media.Comment: Presented at the 3rd Feynman Festival (Collage Park, Maryland,
U.S.A., August 2006
Berry Curvature in Graphene: A New Approach
In the present paper we have directly computed the Berry curvature terms
relevant for Graphene in the presence of an \textit{inhomogeneous} lattice
distortion. We have employed the generalized Foldy Wouthuysen framework,
developed by some of us \cite{ber0,ber1,ber2}. We show that a non-constant
lattice distortion leads to a valley-orbit coupling which is responsible to a
valley-Hall effect. This is similar to the valley-Hall effect induced by an
electric field proposed in \cite{niu2} and is the analogue of the spin-Hall
effect in semiconductors \cite{MURAKAMI, SINOVA}. Our general expressions for
Berry curvature, for the special case of homogeneous distortion, reduce to the
previously obtained results \cite{niu2}. We also discuss the Berry phase in the
quantization of cyclotron motion.Comment: Slightly modified version, to appear in EPJ
Noncommutative Quantum Mechanics Viewed from Feynman Formalism
Dyson published in 1990 a proof due to Feynman of the Maxwell equations. This
proof is based on the assumption of simple commutation relations between
position and velocity. We first study a nonrelativistic particle using Feynman
formalism. We show that Poincar\'{e}'s magnetic angular momentum and Dirac
magnetic monopole are the direct consequences of the structure of the sO(3) Lie
algebra in Feynman formalism. Then we show how to extend this formalism to the
dual momentum space with the aim of introducing Noncommutative Quantum
Mechanics which was recently the subject of a wide range of works from particle
physics to condensed matter physics.Comment: 11 pages, To appear in the Proceedings of the Lorentz Workshop
"Beyond the Quantum", eds. Th.M. Nieuwenhuizen et al., World Scientific,
Singapore, 2007. Added reference
Renormalization Group in Quantum Mechanics
We establish the renormalization group equation for the running action in the
context of a one quantum particle system. This equation is deduced by
integrating each fourier mode after the other in the path integral formalism.
It is free of the well known pathologies which appear in quantum field theory
due to the sharp cutoff. We show that for an arbitrary background path the
usual local form of the action is not preserved by the flow. To cure this
problem we consider a more general action than usual which is stable by the
renormalization group flow. It allows us to obtain a new consistent
renormalization group equation for the action.Comment: 20 page
Kinematic design of a finger abduction mechanism for an anthropomorphic robotic hand
This paper presents the kinematic design of an abduction mechanism for the fingers of an underactuated anthropomorphic robotic hand. This mechanism will enhance the range of feasible grasps of the underactuated hand without significantly increasing its complexity. The analysis of the link between the index finger and the third finger is first assessed, where the parameters are studied in order to follow the amplitude constraint and to minimize the coordination error. Then, the study of the mechanism joining the third finger and the little finger is summarized. Finally, a prototype of the finger's abduction system is presented. <br><br> <i>This paper was presented at the IFToMM/ASME International Workshop on Underactuated Grasping (UG2010), 19 August 2010, Montréal, Canada.</i>
Characterisation of the transmissivity field of a fractured and karstic aquifer, Southern France
International audienceGeological and hydrological data collected at the Terrieu experimental site north of Montpellier, in a confined carbonate aquifer indicates that both fracture clusters and a major bedding plane form the main flow paths of this highly heterogeneous karst aquifer. However, characterising the geometry and spatial location of the main flow channels and estimating their flow properties remain difficult. These challenges can be addressed by solving an inverse problem using the available hydraulic head data recorded during a set of interference pumping tests.We first constructed a 2D equivalent porous medium model to represent the test site domain and then employed regular zoning parameterisation, on which the inverse modelling was performed. Because we aim to resolve the fine-scale characteristics of the transmissivity field, the problem undertaken is essentially a large-scale inverse model, i.e. the dimension of the unknown parameters is high. In order to deal with the high computational demands in such a large-scale inverse problem, a gradient-based, non-linear algorithm (SNOPT) was used to estimate the transmissivity field on the experimental site scale through the inversion of steady-state, hydraulic head measurements recorded at 22 boreholes during 8 sequential cross-hole pumping tests. We used the data from outcrops, borehole fracture measurements and interpretations of inter-well connectivities from interference test responses as initial models to trigger the inversion. Constraints for hydraulic conductivities, based on analytical interpretations of pumping tests, were also added to the inversion models. In addition, the efficiency of the adopted inverse algorithm enables us to increase dramatically the number of unknown parameters to investigate the influence of elementary discretisation on the reconstruction of the transmissivity fields in both synthetic and field studies.By following the above approach, transmissivity fields that produce similar hydrodynamic behaviours to the real head measurements were obtained. The inverted transmissivity fields show complex, spatial heterogeneities with highly conductive channels embedded in a low transmissivity matrix region. The spatial trend of the main flow channels is in a good agreement with that of the main fracture sets mapped on outcrops in the vicinity of the Terrieu site suggesting that the hydraulic anisotropy is consistent with the structural anisotropy. These results from the inverse modelling enable the main flow paths to be located and their hydrodynamic properties to be estimated
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