84,696 research outputs found
Topological Weyl and Node-Line Semimetals in Ferromagnetic Vanadium-Phosphorous-Oxide -VOPO Compound
We propose that the topological semimetal features can co-exist with
ferromagnetic ground state in vanadium-phosphorous-oxide -VOPO
compound from first-principles calculations. In this magnetic system with
inversion symmetry, the direction of magnetization is able to manipulate the
symmetric protected band structures from a node-line type to a Weyl one in the
presence of spin-orbital-coupling. The node-line semimetal phase is protected
by the mirror symmetry with the reflection-invariant plane perpendicular to
magnetic order. Within mirror symmetry breaking due to the magnetization along
other directions, the gapless node-line loop will degenerate to only one pair
of Weyl points protected by the rotational symmetry along the magnetic axis,
which are largely separated in momentum space. Such Weyl semimetal phase
provides a nice candidate with the minimum number of Weyl points in a condensed
matter system. The results of surface band calculations confirm the non-trivial
topology of this proposed compound. This findings provide a realistic candidate
for the investigation of topological semimetals with time-reversal symmetry
breaking, particularly towards the realization of quantum anomalous Hall effect
in Weyl semimetals.Comment: 5 pages, 4 figure
Tortoise coordinate and Hawking effect in a dynamical Kerr black hole
Hawking effect from a dynamical Kerr black hole is investigated using the
improved Damour-Ruffini method with a new tortoise coordinate transformation.
Hawking temperature of the black hole can be obtained point by point at the
event horizon. It is found that Hawking temperatures of different points on the
surface are different. Moreover, the temperature does not turn to zero while
the dynamical black hole turns to an extreme one.Comment: 7 page
Distributed Clustering in Cognitive Radio Ad Hoc Networks Using Soft-Constraint Affinity Propagation
Absence of network infrastructure and heterogeneous spectrum availability in cognitive radio ad hoc networks (CRAHNs) necessitate the self-organization of cognitive radio users (CRs) for efficient spectrum coordination. The cluster-based structure is known to be effective in both guaranteeing system performance and reducing communication overhead in variable network environment. In this paper, we propose a distributed clustering algorithm based on soft-constraint affinity propagation message passing model (DCSCAP). Without dependence on predefined common control channel (CCC), DCSCAP relies on the distributed message passing among CRs through their available channels, making the algorithm applicable for large scale networks. Different from original soft-constraint affinity propagation algorithm, the maximal iterations of message passing is controlled to a relatively small number to accommodate to the dynamic environment of CRAHNs. Based on the accumulated evidence for clustering from the message passing process, clusters are formed with the objective of grouping the CRs with similar spectrum availability into smaller number of clusters while guaranteeing at least one CCC in each cluster. Extensive simulation results demonstrate the preference of DCSCAP compared with existing algorithms in both efficiency and robustness of the clusters
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