Aoyama Gakuin University

About: Aoyama Gakuin University is a education organization based out in Tokyo, Japan. It is known for research contribution in the topics: Superconductivity & Thin film. The organization has 3494 authors who have published 6419 publications receiving 115648 citations. The organization is also known as: Aoyama gakuin daigaku.

Synthesis of ammonia in high-frequency discharges

Abstract: The synthesis of ammonia from nitrogen-hydrogen plasma prepared using radiofrequency discharge and microwave discharge was studied under the same experimental conditions except the driving frequency. Twice larger amounts of ammonia were adsorbed on zeolite used as adsorbent in the microwave discharge than in the radiofrequency discharge. Relative intensities of NH band head (A3Π−X3Σ−,0−0) as well as hydrogen atomic line (H\) observed in the plasma prepared using microwave discharge were one order of magnitude larger than those in the plasma prepared using radiofrequency discharge. Since NHx radicals and H atoms are considered ammonia precursors, the advantage of microwave discharge over radiofrequency discharge on ammonia synthesis is discussed from the results obtained above and from the plasma parameters,kT e andn e , obtained by the electric double probe technique.

Efficient algorithms for dualizing large-scale hypergraphs

Abstract: A hypergraph F is a set family defined on vertex set V. The dual of F is the set of minimal subsets H of V such that F ∩ H ≠ p for any F ∈ F. The computation of the dual is equivalent to many problems, such as minimal hitting set enumeration of a subset family, minimal set cover enumeration, and the enumeration of hypergraph transversals. In this paper, we introduce a new set system induced by the minimality condition of the hitting sets, that enables us to use efficient pruning methods. We further propose an efficient algorithm for checking the minimality, that enables us to construct time efficient and polynomial space dualization algorithms. The computational experiments show that our algorithms are quite fast even for large-scale input for which existing algorithms do not terminate in practical time.

Critical behaviors of sheared frictionless granular materials near the jamming transition.

Abstract: Critical behaviors of sheared dense and frictionless granular materials in the vicinity of the jamming transition are numerically investigated. From the extensive molecular dynamics simulation, we verify the validity of the scaling theory near the jamming transition proposed by Otsuki and Hayakawa [Prog. Theor. Phys. 121, 647 (2009)]]. We also clarify the critical behaviors of the shear viscosity and the pair correlation function based on both a mean field theory and the simulation.

Efficient discovery of influential nodes for SIS models in social networks

Abstract: We address the problem of discovering the influential nodes in a social network under the susceptible/infected/susceptible model that allows multiple activation of the same node, by defining two influence maximization problems: final-time and integral-time. We solve this problem by constructing a layered graph from the original network with each layer added on top as the time proceeds and applying the bond percolation with two effective control strategies: pruning and burnout. We experimentally demonstrate that the proposed method gives much better solutions than the conventional methods that are based solely on the notion of centrality using two real-world networks. The pruning is most effective when searching for a single influential node, but burnout is more powerful in searching for multiple nodes which together are influential. We further show that the computational complexity is much smaller than the naive probabilistic simulation both by theory and experiment. The influential nodes discovered are substantially different from those identified by the centrality measures. We further note that the solutions of the two optimization problems are also substantially different, indicating the importance of distinguishing these two problem characteristics and using the right objective function that best suits the task in hand.