3,887 research outputs found
Cascading failures in coupled networks with both inner-dependency and inter-dependency links
We study the percolation in coupled networks with both inner-dependency and
inter-dependency links, where the inner- and inter-dependency links represent
the dependencies between nodes in the same or different networks, respectively.
We find that when most of dependency links are inner- or inter-ones, the
coupled networks system is fragile and makes a discontinuous percolation
transition. However, when the numbers of two types of dependency links are
close to each other, the system is robust and makes a continuous percolation
transition. This indicates that the high density of dependency links could not
always lead to a discontinuous percolation transition as the previous studies.
More interestingly, although the robustness of the system can be optimized by
adjusting the ratio of the two types of dependency links, there exists a
critical average degree of the networks for coupled random networks, below
which the crossover of the two types of percolation transitions disappears, and
the system will always demonstrate a discontinuous percolation transition. We
also develop an approach to analyze this model, which is agreement with the
simulation results well.Comment: 9 pages, 4 figure
Dilute magnetic semiconductor and half metal behaviors in 3d transition-metal doped black and blue phosphorenes: a first-principles study
We present first-principles density-functional calculations for the
structural, electronic, and magnetic properties of substitutional 3d transition
metal (TM) impurities in two-dimensional black and blue phosphorenes. We find
that the magnetic properties of such substitutional impurities can be
understood in terms of a simple model based on the Hund's rule. The TM-doped
black phosphorenes with Ti, V, Cr, Mn, Fe and Ni impurities show dilute
magnetic semiconductor (DMS) properties while those with Sc and Co impurities
show nonmagnetic properties. On the other hand, the TM-doped blue phosphorenes
with V, Cr, Mn and Fe impurities show DMS properties, those with Ti and Ni
impurities show half-metal properties, whereas Sc and Co doped systems show
nonmagnetic properties. We identify two different regimes depending on the
occupation of the hybridized electronic states of TM and phosphorous atoms: (i)
bonding states are completely empty or filled for Sc- and Co-doped black and
blue phosphorenes, leading to non-magnetic; (ii) non-bonding d states are
partially occupied for Ti-, V-, Cr-, Mn-, Fe- and Ni-doped black and blue
phosphorenes, giving rise to large and localized spin moments. These results
provide a new route for the potential applications of dilute magnetic
semiconductor and half-metal in spintronic devices by employing black and blue
phosphorenes.Comment: 9 pages, 7 figure
A Wideband Printed Directional Antenna Array with Impedance Regulating Load
We proposed a broadband directional antenna array working at mobile communication frequency band, which achieves a relative bandwidth of 50.7%. This binary antenna array is fed by two branches of the balanced microstrip. To enhance the antenna bandwidth, we introduced a section of loading metal strip. The antenna prototype has a S11 lower than −10 dB within the 1.5 GHz to 2.52 GHz frequency band, particularly from 2.01 GHz to 2.50 GHz, the S11 is lower than −15 dB. The gain varies with relatively small variation within the working band, which is 5.4 dBi to 8.7 dBi
Observation of Majorana fermions with spin selective Andreev reflection in the vortex of topological superconductor
Majorana fermion (MF) whose antiparticle is itself has been predicted in
condensed matter systems. Signatures of the MFs have been reported as zero
energy modes in various systems. More definitive evidences are highly desired
to verify the existence of the MF. Very recently, theory has predicted MFs to
induce spin selective Andreev reflection (SSAR), a novel magnetic property
which can be used to detect the MFs. Here we report the first observation of
the SSAR from MFs inside vortices in Bi2Te3/NbSe2 hetero-structure, in which
topological superconductivity was previously established. By using
spin-polarized scanning tunneling microscopy/spectroscopy (STM/STS), we show
that the zero-bias peak of the tunneling differential conductance at the vortex
center is substantially higher when the tip polarization and the external
magnetic field are parallel than anti-parallel to each other. Such strong spin
dependence of the tunneling is absent away from the vortex center, or in a
conventional superconductor. The observed spin dependent tunneling effect is a
direct evidence for the SSAR from MFs, fully consistent with theoretical
analyses. Our work provides definitive evidences of MFs and will stimulate the
MFs research on their novel physical properties, hence a step towards their
statistics and application in quantum computing.Comment: 4 figures 15 page
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