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Search Results: 1 - 10 of 602248 matches for " R. A. Lambert "
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Stability of Wavelengths and Spatiotemporal Intermittency in Coupled Map Lattices
A. Lambert,R. Lima
Physics , 1994, DOI: 10.1016/0167-2789(94)90006-X
Abstract: In relation to spatiotemporal intermittency, as it can be observed in coupled map lattices, we study the stability of different wavelengths in competition. Introducing a two dimensional map, we compare its dynamics with the one of the whole lattice. We conclude a good agreement between the two. The reduced model also allows to introduce an order parameter which combines the diffusion parameter and the spatial wavelength under consideration.
Hamiltonian analysis of the double null 2+2 decomposition of Ashtekar variables
R. A. d'Inverno,P Lambert,J. A. Vickers
Physics , 2006, DOI: 10.1088/0264-9381/23/11/005
Abstract: We derive a canonical analysis of a double null 2+2 Hamiltonian description of General Relativity in terms of complex self-dual 2-forms and the associated SO(3) connection variables. The algebra of first class constraints is obtained and forms a Lie algebra that consists of two constraints that generate diffeomorphisms in the two surface, a constraint that generates diffeomorphisms along the null generators and a constraint that generates self-dual spin and boost transformations.
Hamiltonian analysis of the double null 2+2 decomposition of General Relativity expressed in terms of self-dual bivectors
R. A. d'Inverno,P. Lambert,J. A. Vickers
Physics , 2006, DOI: 10.1088/0264-9381/23/13/014
Abstract: In this paper we obtain a 2+2 double null Hamiltonian description of General Relativity using only the (complex) SO(3) connection and the components of the complex densitised self-dual bivectors. We carry out the general canonical analysis of this system and obtain the first class constraint algebra entirely in terms of the self-dual variables. The first class algebra forms a Lie algebra and all the first class constraints have a simple geometrical interpretation.
Boundary conditions for quasiclassical equations in the theory of superconductivity
C. J. Lambert,R. Raimondi,V. Sweeney,A. F. Volkov
Physics , 1996, DOI: 10.1103/PhysRevB.55.6015
Abstract: In this paper we derive effective boundary conditions connecting the quasiclassical Green's function through tunnel barriers in superconducting - normal hybrid (S-N or S-S') structures in the dirty limit. Our work extends previous treatments confined to the small transparency limit. This is achieved by an expansion in the small parameter $r^{-1}=T/2(1-T)$ where T is the transparency of the barrier. We calculate the next term in the $r^{-1}$ expansion for both the normal and the superconducting case. In both cases this involves the solution of an integral equation, which we obtain numerically. While in the normal case our treatment only leads to a quantitative change in the barrier resistance $R_b$, in the superconductor case, qualitative different boundary conditions are derived. To illustrate the physical consequences of the modified boundary conditions, we calculate the Josephson current and show that the next term in the $r^{-1}$ expansion gives rise to the second harmonic in the current-phase relation.
Phase coherent transport in hybrid superconducting structures: the case of d-wave superconductors
P. M. A. Cook,R. Raimondi,C. J. Lambert
Physics , 1996, DOI: 10.1007/BF02583830
Abstract: We examine the effect of d-wave symmetry on zero bias anomalies in normal-superconducting tunnel junctions and phase-periodic conductances in Andreev interferometers. In the presence of d-wave pairing, zero-bias anomalies are suppressed compared with the s-wave case. For Andreev interferometers with aligned islands, the phase-periodic conductance is insensistive to the nature of the pairing, whereas for non-aligned islands, the nature of the zero-phase extremum is reversed.
Orbital order in bilayer graphene at filling factor $ν=-1 $
R. C?té,Jules Lambert,Yafis Barlas,A. H. MacDonald
Physics , 2010, DOI: 10.1103/PhysRevB.82.035445
Abstract: In a graphene bilayer with Bernal stacking both $n=0$ and $n=1$ orbital Landau levels have zero kinetic energy. An electronic state in the N=0 Landau level consequently has three quantum numbers in addition to its guiding center label: its spin, its valley index $K$ or $K^{\prime}$, and an orbital quantum number $n=0,1.$ The two-dimensional electron gas (2DEG) in the bilayer supports a wide variety of broken-symmetry states in which the pseudospins associated these three quantum numbers order in a manner that is dependent on both filling factor $\nu $ and the electric potential difference between the layers. In this paper, we study the case of $\nu =-1$ in an external field strong enough to freeze electronic spins. We show that an electric potential difference between layers drives a series of transitions, starting from interlayer-coherent states (ICS) at small potentials and leading to orbitally coherent states (OCS) that are polarized in a single layer. Orbital pseudospins carry electric dipoles with orientations that are ordered in the OCS and have Dzyaloshinskii-Moriya interactions that can lead to spiral instabilities. We show that the microwave absorption spectra of ICSs, OCSs, and the mixed states that occur at intermediate potentials are sharply distinct.
Transition to Chaos in a Shell Model of Turbulence
L. Biferale,A. Lambert,R. Lima,G. Paladin
Physics , 1994, DOI: 10.1016/0167-2789(95)90065-9
Abstract: We study a shell model for the energy cascade in three dimensional turbulence at varying the coefficients of the non-linear terms in such a way that the fundamental symmetries of Navier-Stokes are conserved. When a control parameter $\epsilon$ related to the strength of backward energy transfer is enough small, the dynamical system has a stable fixed point corresponding to the Kolmogorov scaling. This point becomes unstable at $\epsilon=0.3843...$ where a stable limit cycle appears via a Hopf bifurcation. By using the bi-orthogonal decomposition, the transition to chaos is shown to follow the Ruelle-Takens scenario. For $\epsilon > 0.3953..$ the dynamical evolution is intermittent with a positive Lyapunov exponent. In this regime, there exists a strange attractor which remains close to the Kolmogorov (now unstable) fixed point, and a local scaling invariance which can be described via a intermittent one-dimensional map.
Transition to Chaos in a Shell Model of Turbulence
L. Biferale,A. Lambert,R. Lima,G. Paladin
Physics , 1994,
Abstract: We study a shell model for the energy cascade in three dimensional turbulence at varying the coefficients of the non-linear terms in such a way that the fundamental symmetries of Navier-Stokes are conserved. When a control parameter $\epsilon$ related to the strength of backward energy transfer is enough small, the dynamical system has a stable fixed point corresponding to the Kolmogorov scaling. This point becomes unstable at $\epsilon=0.3843...$ where a stable limit cycle appears via a Hopf bifurcation. By using the bi-orthogonal decomposition, the transition to chaos is shown to follow the Ruelle-Takens scenario. For $\epsilon > 0.3953..$ the dynamical evolution is intermittent with a positive Lyapunov exponent. In this regime, there exists a strange attractor which remains close to the Kolmogorov (now unstable) fixed point, and a local scaling invariance which can be described via a intermittent one-dimensional map.
Conductance suppression in normal metal-superconductor mesoscopic strucutres
C. J. Lambert,R. Seviour,A. F. Volkov
Physics , 1998,
Abstract: Using a scattering matrix approach and quasiclassical Green's function technique, we calculate the conductance of the S/N system (see Fig.1). We establish that the difference between the superconducting and normal state conductance $(\delta G = G_s - G_n)$ is negative for large S/N interface resistances $(R_{S/N})$ and changes sign with decreasing $R_{S/N}$. The comparision of the result obtained with experimental data is carried out.
Sub-gap conductance in ferromagnetic-superconducting mesoscopic structures
M. Leadbeater,C. J. Lambert,R. Raimondi,A. F. Volkov
Physics , 1998, DOI: 10.1103/PhysRevB.59.12264
Abstract: We study the sub-gap conductance of a ferromagnetic mesoscopic region attached to a ferromagnetic and a superconducting electrode by means of tunnel junctions. In the absence of the exchange field, the ratio $r= \gamma / \epsilon_T$ of the two tunnel junction resistances determines the behaviour of the sub-gap conductance which possesses a zero-bias peak for $r\gg 1$ and for $r\ll 1$ a peak at finite voltage. We show that the inclusion of the exchange field leads to a peak splitting for $r\ll 1$, while it shifts the zero-bias anomaly to finite voltages for $r\gg 1$.
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