Por que consumir pescado é estratégico para o Brasil?

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Vortex ratchet reversal: The role of interstitial vortices

Triangular arrays of Ni nanotriangles embedded in superconducting Nb films exhibit unexpected dynamical vortex effects. Collective pinning with a vortex lattice configuration different from the expected fundamental triangular "Abrikosov state" is found. The vortex motion which prevails against the triangular periodic potential is produced by channelling effects between triangles. Interstitial vortices coexisting with pinned vortices in this asymmetric potential, lead to ratchet reversal, i.e. a DC output voltage which changes sign with the amplitude of an applied alternating drive current. In this landscape, ratchet reversal is always observed at all magnetic fields (all numbers of vortices) and at different temperatures. The ratchet reversal is unambiguously connected to the presence of two locations for the vortices: interstitial and above the artificial pinning sites.Comment: 21 pages, 4 figures, 1 Tabl

PT-symmetry from Lindblad dynamics in a linearized optomechanical system

We analyze a lossy linearized optomechanical system in the red-detuned regime under the rotating wave approximation. This so-called optomechanical state transfer protocol provides effective lossy frequency converter (quantum beam-splitter-like) dynamics where the strength of the coupling between the electromagnetic and mechanical modes is controlled by the optical steady-state amplitude. By restricting to a subspace with no losses, we argue that the transition from mode-hybridization in the strong coupling regime to the damped-dynamics in the weak coupling regime, is a signature of the passive parity-time (PT) symmetry breaking transition in the underlying non-Hermitian quantum dimer. We compare the dynamics generated by the quantum open system (Langevin or Lindblad) approach to that of the PT-symmetric Hamiltonian, to characterize the cases where the two are identical. Additionally, we numerically explore the evolution of separable and correlated number states at zero temperature as well as thermal initial state evolution at room temperature. Our results provide a pathway for realizing non-Hermitian Hamiltonians in optomechanical systems at a quantum level

Axial Multicentric Osteosarcoma in an English Cocker Spaniel

No abstract available

Modelling and analysis of traffic networks based on graph transformation

This is an electronic version of the paper presented at the Symposium on Formal Methods for Automation and Safety in Railway and Automotive Systems, FORMS/FORMATS 2004 , held in Braunschweig on 2004We present the formal definition of a domain specific visual language (Traffic) for the area of traffic networks. The syntax has been specified by means of meta-modelling. For the semantics, two approaches have been followed. In the first one, graph transformation is used to specify an operational semantics. In the second one we include timing information and a denotational semantics is defined in terms of Timed Transition Petri Nets (TTPN). The transformation from the Traffic formalism into TTPN was also defined by graph transformation. Both approaches have been used for the analysis of Traffic models. The ideas have been implemented in the AToM3 tool and are illustrated with examples.Juan de Lara’s work has been partially sponsored by a grant from the E.U. SEGRAVIS research network (HPRN-CT-2002-00) and the Spanish Ministry of Science and Technology (TIC2002-01948). Hans Vangheluwe gratefully acknowledges partial support for this work by a National Sciences and Engineering Research Council of Canada (NSERC) Individual Research Grant

Ca impurity in small mixed 4^4He-3^3He clusters

The structure of small mixed helium clusters doped with one calcium atom has been determined within the diffusion Monte Carlo framework. The results show that the calcium atom sits at the $^4$He-$^3$He interface. This is in agreement with previous studies, both experimental and theoretical, performed for large clusters. A comparison between the results obtained for the largest cluster we have considered for each isotope shows a clear tendency of the Ca atom to reside in a deep dimple at the surface of the cluster for $^4$He clusters, and to become fully solvated for $^3$He clusters. We have calculated the absorption spectrum of Ca around the $4s4p \leftarrow 4s^2$ transition and have found that it is blue-shifted from that of the free-atom transition by an amount that depends on the size and composition of the cluster.Comment: 24 pages, 11 figures. Accepted on Journal of Chemical Physic