642 research outputs found
Twin-free YBa2Cu3O7 films on (001) NdGaO3 showing isotropic electrical behaviour
Investigating the epitaxial nature of YBa2Cu3O7 films on NdGaO3 (001) by Rutherford backscattering (RBS) and X-ray diffraction (XRD) texture measurements we find that the films are almost single crystalline, in the sense that the a, b and c axes are uniquely defined with respect to those of NdGaO3. The crystalline perfection is, however, not reflected in the electrical properties of the films. Although we measure a Tc of 89.7 K, we did not observe the expected anisotropy in the resistivity. We interpret this to be due to Ga diffusion from the substrate into the film, which effectively blocks the chain conductivity
The ab-anisotrophy of twinfree YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub> films above and below T<sub>c</sub>
High quality twin-free c-axis oriented YBa2Cu3O7 films were grown by pulsed laser deposition on NdGaO3. We find resistive anisotropies between 1 < a/b < 1.6. The resistive anisotropy above Tc appears to be correlated to the anisotropy in the critical current below Tc. The normal state properties of the chains along b seem to have a significant influence on the superconducting properties of YBa2Cu3O7
Extreme hydrogen plasma densities achieved in a linear plasma generator
A magnetized hydrogen plasma beam was generated with a cascaded arc, expanding in a vacuum vessel at an axial magnetic field of up to 1.6 T. Its characteristics were measured at a distance of 4 cm from the nozzle: up to a 2 cm beam diameter, 7.5×1020 m-3 electron density, ~2 eV electron and ion temperatures, and 3.5 km/s axial plasma velocity. This gives a 2.6×1024 H+ m-2 s-1 peak ion flux density, which is unprecedented in linear plasma generators. The high efficiency of the source is obtained by the combined action of the magnetic field and an optimized nozzle geometry. This is interpreted as a cross-field return current that leads to power dissipation in the beam just outside the source
From thermal rectifiers to thermoelectric devices
We discuss thermal rectification and thermoelectric energy conversion from
the perspective of nonequilibrium statistical mechanics and dynamical systems
theory. After preliminary considerations on the dynamical foundations of the
phenomenological Fourier law in classical and quantum mechanics, we illustrate
ways to control the phononic heat flow and design thermal diodes. Finally, we
consider the coupled transport of heat and charge and discuss several general
mechanisms for optimizing the figure of merit of thermoelectric efficiency.Comment: 42 pages, 22 figures, review paper, to appear in the Springer Lecture
Notes in Physics volume "Thermal transport in low dimensions: from
statistical physics to nanoscale heat transfer" (S. Lepri ed.
Measurement of the B0-anti-B0-Oscillation Frequency with Inclusive Dilepton Events
The - oscillation frequency has been measured with a sample of
23 million \B\bar B pairs collected with the BABAR detector at the PEP-II
asymmetric B Factory at SLAC. In this sample, we select events in which both B
mesons decay semileptonically and use the charge of the leptons to identify the
flavor of each B meson. A simultaneous fit to the decay time difference
distributions for opposite- and same-sign dilepton events gives ps.Comment: 7 pages, 1 figure, submitted to Physical Review Letter
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
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