9,685 research outputs found
The transport properties of Floquet topological superconductors at the transition from the topological phase to the Anderson localized phase
The Floquet topological superconducting state is a nonequilibrium
time-periodic state hosting Majorana fermions. We study its transport
properties by using the Kitaev model with time-periodic incommensurate
potentials, which experiences phase transition from the Floquet topological
superconducting phase to the Anderson localized phase with increasing driving
strength. We study both the real time dynamics of the current and the
non-analytic behavior of the tunneling conductance at the transition.
Especially, we find that the tunneling conductance changes continuously at the
transition, being a finite value in the presence of Floquet Majorana fermions,
but dropping to zero as the Majorana fermions vanish. For a special choice of
parameters, the Majorana fermions revive at larger driving strength,
accompanied by the revival of conductances.Comment: 8 pages, 5 figure
Higgs amplitude mode in massless Dirac fermion systems
The Higgs amplitude mode in superconductors is the condensed matter analogy
of Higgs bosons in particle physics. We investigate the time evolution of Higgs
amplitude mode in massless Dirac systems, induced by a weak quench of an
attractive interaction. We find that the Higgs amplitude mode in the
half-filling honeycomb lattice has a logarithmic decaying behaviour,
qualitatively different from the decay in the normal
superconductors. Our study is also extended to the doped cases in honeycomb
lattice. As for the 3D Dirac semimetal at half filling, we obtain an undamped
oscillation of the amplitude mode. Our finding is not only an important
supplement to the previous theoretical studies on normal fermion systems, but
also provide an experimental signature to characterize the superconductivity in
2D or 3D Dirac systems.Comment: 6 pages, 8 figure
Experimental Tests of a Resistive SFCL Integrated with a Vacuum Interrupter
A resistive superconducting fault-current limiter (SFCL) has been developed using round magnesium diboride (MgB2) wire. The SFCL coil was wound using an interleaved coil arrangement to minimize the total coil inductance. The SFCL coil demonstrated reliable and repeatable current-limiting properties during testing. However, the wire temperature of the SFCL coil increases quickly during quench tests, and several minutes are required for temperature recovery after the fault is cleared. The SFCL coil therefore was fully integrated with a vacuum interrupter to quickly remove the SFCL coil from the circuit once a fault occurred. This allowed the SFCL coil to recover quickly while a bypass resistor acted as the current limiting resistance. A fast-acting actuator and its control circuit were designed and built to provide automatic control for the operation of the vacuum interrupter. The SFCL with the prototype vacuum interrupter was successfully tested. The energy dissipated in the SFCL coil was significantly reduced by integrating the vacuum interrupter. The fault tests with different potential fault currents also proved that the operation of the vacuum interrupter is independent of the fault current level. This prototype demonstrated the potential of a cost-effective and compact integrated SFCL and vacuum interrupter for power system applications.</p
PADS: A simple yet effective pattern-aware dynamic search method for fast maximal frequent pattern mining
While frequent pattern mining is fundamental for many data mining tasks, mining maximal frequent patterns efficiently is important in both theory and applications of frequent pattern mining. The fundamental challenge is how to search a large space of item combinations. Most of the existing methods search an enumeration tree of item combinations in a depth-first manner. In this paper, we develop a new technique for more efficient max-pattern mining. Our method is pattern-aware: it uses the patterns already found to schedule its future search so that many search subspaces can be pruned. We present efficient techniques to implement the new approach. As indicated by a systematic empirical study using the benchmark data sets, our new approach outperforms the currently fastest max-pattern mining algorithms FPMax* and LCM2 clearly. The source code and the executable code (on both Windows and Linux platforms) are publicly available at http://www.cs.sfu.ca/~jpei/Software/PADS.zip. © Springer-Verlag London Limited 2008
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