Coherent transport on Apollonian networks and continuous-time quantum walks

We study the coherent exciton transport on Apollonian networks generated by simple iterative rules. The coherent exciton dynamics is modeled by continuous-time quantum walks and we calculate the transition probabilities between two nodes of the networks. We find that the transport depends on the initial nodes of the excitation. For networks less than the second generation the coherent transport shows perfect revivals when the initial excitation starts at the central node. For networks of higher generation, the transport only shows partial revivals. Moreover, we find that the excitation is most likely to be found at the initial nodes while the coherent transport to other nodes has a very low probability. In the long time limit, the transition probabilities show characteristic patterns with identical values of limiting probabilities. Finally, the dynamics of quantum transport are compared with the classical transport modeled by continuous-time random walks.Comment: 5 pages, 6 figues. Submitted to Phys. ReV.

A Taxonomy Of The Join Operations In The REA Data Model

The Resource-Event-Agent (REA) data model identifies these three categories of entities in business processes and establishes relationships among them based on the rules that underlay actual business practices. The model becomes more efficient when the principle of relational database design, i.e., normalization, is applied. However, the higher the level of normalization in the database, the higher will be the degree of information segregation. Therefore, to ensure the accuracy of the information retrieved, it is crucial to understand the database structure and apply queries with correct join operations. “Join” is one of the fundamental relational database query operations. Join handles the processes that determine how data from two tables will be merged and selected. In this paper, a taxonomy of the join operations applicable to the REA data model is presented: it classifies the combinations of the categorical components in the REA model, identifies the join operation, and links to AIS documents and reports

Correspondence Between DGP Brane Cosmology and 5D Ricci-flat Cosmology

We discuss the correspondence between the DGP brane cosmology and 5D Ricci-flat cosmology by letting their metrics equal each other. By this correspondence, a specific geometrical property of the arbitrary integral constant I in DGP metric is given and it is related to the curvature of 5D bulk. At the same time, the relation of arbitrary functions $\mu$ and $\nu$ in a class of Ricci-flat solutions is obtained from DGP brane metric.Comment: 8 pages, 1 figure, accepted by MPLA, added referenc

The Real Scalar Field Equation for Nariai Black Hole in the 5D Schwarzschild-de Sitter Black String Space

The Nariai black hole, whose two horizons are lying close to each other, is an extreme and important case in the research of black hole. In this paper we study the evolution of a massless scalar field scattered around in 5D Schwarzschild-de Sitter black string space. Using the method shown by Brevik and Simonsen (2001) we solve the scalar field equation as a boundary value problem, where real boundary condition is employed. Then with convenient replacement of the 5D continuous potential by square barrier, the reflection and transmission coefficients ($R, T$) are obtained. At last, we also compare the coefficients with usual 4D counterpart.Comment: 10 pages,6 figures.To appear in Int. J. Mod. Phys.

Skyrmion-skyrmion and skyrmion-edge repulsions in skyrmion-based racetrack memory

Magnetic skyrmions are promising for building next-generation magnetic memories and spintronic devices due to their stability, small size and the extremely low currents needed to move them. In particular, skyrmion-based racetrack memory is attractive for information technology, where skyrmions are used to store information as data bits instead of traditional domain walls. Here we numerically demonstrate the impacts of skyrmion-skyrmion and skyrmion-edge repulsions on the feasibility of skyrmion-based racetrack memory. The reliable and practicable spacing between consecutive skyrmionic bits on the racetrack as well as the ability to adjust it are investigated. Clogging of skyrmionic bits is found at the end of the racetrack, leading to the reduction of skyrmion size. Further, we demonstrate an effective and simple method to avoid the clogging of skyrmionic bits, which ensures the elimination of skyrmionic bits beyond the reading element. Our results give guidance for the design and development of future skyrmion-based racetrack memory.Comment: 15 pages, 6 figure

Quasicoherent nucleation mode in two-phase nanomagnets

Magnetization processes in advanced magnetic nanostructures are investigated. For the case of spherical soft or semihard grains surrounded by a very hard matrix a bulging nucleation mode is discovered. The bulging mode exhibits the radial angular symmetry of the coherent mode, but it is incoherent due to its radial variation. The radial dependence of the bulging mode is obtained by solving a spherical Bessel equation which is subject to appropriate boundary conditions. In contrast to the coherent mode, the bulging mode yields a nucleationfield coercivity which depends on the exchange stiffness and on the size of the grain. There is a critical grain radius 7.869√A/μ0Ms2 above which the bulging mode is replaced by a modified curling mode. The nucleation modes realized in nanostructures affect the demagnetizing-field corrections necessary to account for the external shape of magnetic samples. Since strong but short-range exchange and weak but long-range magnetostatic interactions compete on nanostructural length scales, the sample-shape dependence of the hysteresis loops cannot be mapped onto a purely magnetostatic demagnetizing factor

Transition from negative magnetoresistance behavior to positive behavior in Co\u3csub\u3e20\u3c/sub\u3e (Cu\u3csub\u3e1-x\u3c/sub\u3eGe\u3csub\u3ex\u3c/sub\u3e)\u3csub\u3e80\u3c/sub\u3e ribbons

We report a transition of the giant magnetoresistance (GMR) behavior in nanocrystalline Co20 (Cu1-xGex)80 ribbons from negative to positive, as the semiconductor Ge substitutes for the Cu matrix. The growth of the hexagonal Co3Ge2 compound leads to a change of the physical origin of the GMR. The normal spin-dependent transport behavior in the CoCu granular system evolves into Coulomb blockade behavior of electronic tunneling in ribbons with a Co/Co3Ge2/Co junctionlike configuration

Testing Spatial Noncommutativity via Magnetic Hyperfine Structure Induced by Fractional Angular Momentum of Rydberg System

An approach to solve the critical problem of testing quantum effects of spatial noncommutativity is proposed. Magnetic hyperfine structures in a Rydberg system induced by fractional angular momentum originated from spatial noncommutativity are discussed. The orders of the corresponding magnetic hyperfine splitting of spectrum $\sim 10^{-7} - 10^{-8} eV$ lie within the limits of accuracy of current experimental measurements. Experimental tests of physics beyond the standard model are the focus of broad interest. We note that the present approach is reasonable achievable with current technology. The proof is based on very general arguments involving only the deformed Heisenberg-Weyl algebra and the fundamental property of angular momentum. Its experimental verification would constitute an advance in understanding of fundamental significance, and would be a key step towards a decisive test of spatial noncommutativity.Comment: 11 pages, no figure