Vortex images on Ba{1-x}KxFe2As2 observed directly by the magnetic force microscopy

The vortex states on optimally doped Ba0.6K0.4Fe2As2 and underdoped Ba0.77K0.23Fe2As2 single crystals are imaged by magnetic force microscopy at various magnetic fields below 100 Oe. Local triangular vortex clusters are observed in optimally doped samples. The vortices are more ordered than those in Ba(Fe{1-x}Co{x})2As2, and the calculated pinning force per unit length is about 1 order of magnitude weaker than that in optimally Co-doped 122 at the same magnetic field, indicating that the Co doping at the Fe sites induces stronger pinning. The proportion of six-neighbored vortices to the total amount increases quickly with increasing magnetic field, and the estimated value reaches 100% at several tesla. Vortex chains are also found in some local regions, which enhance the pinning force as well as the critical current density. Lines of vortex chains are observed in underdoped samples, and they may have originated from the strong pinning near the twin boundaries arising from the structural transition.Comment: 7 pages, 8 figure

Optimal View Angle in Collective Dynamics of Self-propelled Agents

We study a system of self-propelled agents in which each agent has a part of omnidirectional or panoramic view of its sensor disc, the field of vision of the agent in this case is only a sector of a disc bounded by two radii and the included arc. The inclination of these two radii is characterized as the view angle. Contrary to our intuition, we find that, the non-omnidirectional-view for swarm agents with periodic boundary conditions in noiseless Vicsek model can accelerate the transient process of the emergence of the ordered state. One consequent implication is that, there are generally superfluous communications in the Vicsek Model, which may even obstruct the possible fast swarm emergence. This phenomenon may invoke further efforts and attentions to explore the underlying mechanism of the emergence in self-propelled agents.Comment: 4 pages, 6 figure

catena-Poly[[(1,10-phenanthroline)lead(II)]bis­(μ-5-chloro-2-hy­droxy­benzoato)]

In the title polymer, [Pb(C7H4ClO3)2(C12H8N2)]n, the Pb(II) ion displays a distorted pseudo-octa­hedral coordination geometry. The metal center is coordinated by six O atoms from four 5-chloro­salicylate ligands and two N atoms from a chelating phenanthroline ligand. The polymeric structure is built up from bridging carboxyl­ate O atoms, forming chains along [100]. The crystal structure is stabilized by π–π inter­actions between the 1,10-phenanthroline and 5-chloro­salicylate ligands, the shortest centroid–centroid separation between neighbouring aromatic rings being 3.652 (1) Å