22,620 research outputs found
Dynamics of Vortex Core Switching in Ferromagnetic Nanodisks
Dynamics of magnetic vortex core switching in nanometer-scale permalloy disk,
having a single vortex ground state, was investigated by micromagnetic
modeling. When an in-plane magnetic field pulse with an appropriate strength
and duration is applied to the vortex structure, additional two vortices, i.e.,
a circular- and an anti-vortex, are created near the original vortex core.
Sequentially, the vortex-antivortex pair annihilates. A spin wave is created at
the annihilation point and propagated through the entire element; the relaxed
state for the system is the single vortex state with a switched vortex core.Comment: to appear in Appl. Phys. Let
Tunnel splitting and quantum phase interference in biaxial ferrimagnetic particles at excited states
The tunneling splitting in biaxial ferrimagnetic particles at excited states
with an explicit calculation of the prefactor of exponent is obtained in terms
of periodic instantons which are responsible for tunneling at excited states
and is shown as a function of magnetic field applied along an arbitrary
direction in the plane of hard and medium axes. Using complex time
path-integral we demonstrate the oscillation of tunnel splitting with respect
to the magnitude and the direction of the magnetic field due to the quantum
phase interference of two tunneling paths of opposite windings . The
oscillation is gradually smeared and in the end the tunnel splitting
monotonously increases with the magnitude of the magnetic field when the
direction of the magnetic field tends to the medium axis. The oscillation
behavior is similar to the recent experimental observation with Fe
molecular clusters. A candidate of possible experiments to observe the effect
of quantum phase interference in the ferrimagnetic particles is proposed.Comment: 15 pages, 5 figures, acceptted to be pubblished in Physical Review
Digraph-based joint routing and resource allocation in software-defined backhaul networks
By decoupling the control plane from the data plane and providing programmability for network applications, software-defined network (SDN) is positioned to offer more efficient management, higher flexibility and better performance. Routing and resource allocation are two closely related applications in wireless networks. With close cooperation, better performance and lower complexity can be achieved in an SDN architecture. However, work that jointly studies routing and resource allocation is rarely seen. In this paper, the joint routing and resource allocation problem is investigated in OFDMA-based software-defined backhaul networks (SDBN). To exploit the SDN programmability, an SDBN system model is proposed, where the control panel can use high complexity algorithms in configuration phase in order to simplify algorithms in operation phases. Then the joint routing and resource allocation problem is formulated as a system throughput optimization problem. By constructing the interference digraph of the network and analysing the vertex degree characteristics, a digraph-based greedy algorithm (DBGA) is proposed. Simulation results have shown that, the proposed DBGA works well to increase the system throughput
Dressed Polyakov loop and flavor dependent phase transitions
The chiral condensate and dressed Polyakov loop at finite temperature and
density have been investigated in the framework of Nf = 2+1 Nambu-Jona-Lasinio
(NJL) model with two degenerate u, d quarks and one strange quark. In the case
of explicit chiral symmetry breaking with physical quark masses, it is found
that the phase transitions for light u, d quarks and s quark are sequentially
happened, and the separation between the transition lines for different flavors
becomes wider and wider with the increase of baryon density. For each flavor,
the pseudo-critical temperatures for chiral condensate and dressed Polyakov
loop differ in a narrow transition range in the lower baryon density region,
and the two transitions coincide in the higher baryon density region.Comment: 9 pages, 9 figures; Version accepted in Phys. Rev.
Ground state fidelity in bond-alternative Ising chains with Dzyaloshinskii-Moriya interactions
A systematic analysis is performed for quantum phase transitions in a
bond-alternative one-dimensional Ising model with a Dzyaloshinskii-Moriya (DM)
interaction by using the fidelity of ground state wave functions based on the
infinite matrix product states algorithm. For an antiferromagnetic phase, the
fidelity per lattice site exhibits a bifurcation, which shows spontaneous
symmetry breaking in the system. A critical DM interaction is inversely
proportional to an alternating exchange coupling strength for a quantum phase
transition. Further, a finite-entanglement scaling of von Neumann entropy with
respect to truncation dimensions gives a central charge c = 0.5 at the critical
point.Comment: 6 pages, 4 figure
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