Scaling theory for unipolar resistance switching

We investigate a reversible percolation system showing unipolar resistance switching in which percolating paths are created and broken alternately by the application of an electric bias. Owing to the dynamical changes in the percolating paths, different from those in classical percolating paths, a detailed understanding of the structure is demanding and challenging. Here, we develop a scaling theory that can explain the transport properties of these conducting paths; the theory is based on the fractal geometry of a percolating cluster. This theory predicts that two scaling behaviors emerge, depending on the topologies of the conducting paths. We confirm these theoretical predictions experimentally by observing material-independent universal scaling behaviors in unipolar resistance switching.     

Surface reconstructions of the Si(100)–Ge system

The surface reconstruction of epitaxial Ge layer on Si(100) was studied with ultrahigh vacuum scanning tunneling microscopy. The surface with 0.8 ML Ge grown in the presence of a hydrogen surfactant reveals the same structures as found in chemical-vapor-deposited Ge on Si(100): (i) defective (2×1) structure at 290°C, (ii) irregular (2×N) in Ge layer and defective (2×1) in bare Si regions at 420°C, and (iii) (2×N) in Ge-covered regions and c(4×4) in bare Si regions at 570°C. The morphology of step edges does not change with temperature, implying that the c(4×4) reconstruction is anisotropic in nature.     

Fluctuation-driven dynamics of the internet topology

We study the dynamics of the Internet topology based on empirical data on the level of the autonomous systems. It is found that the fluctuations occurring in the stochastic process of connecting and disconnecting edges are important features of the Internet dynamics. The network's overall growth can be described approximately by a single characteristic degree growth rate g(eff) approximately 0.016 and the fluctuation strength sigma(eff) approximately 0.14, together with the vertex growth rate alpha approximately 0.029. A stochastic model which incorporates these values and an adaptation rule newly introduced reproduces several features of the real Internet topology such as the correlations between the degrees of different vertices.     

Dynamics of kaleidoscopic maps

First, we introduce a certain class of piecewise affine elliptic rotation maps on , called the kaleidoscopic maps, and describe its importance.And then, we concentrate our efforts on a special case, when the rotation angle θ of a kaleidoscopic map is , . For the special case, we answer the conjectures regarding the periodicity and the singularity structure of such (kaleidoscopic) dynamics. In the process, we prove the partial riddling of the regular orbits that gives rise to the classification of periodic sets, and estimate the Hausdorff dimension of the singular set.Finally, we study the dynamics of such kaleidoscopic maps restricted within the singular set, and answer conjectures concerning the chaos, the local chaos, and the ergodicity with respect to the normalized Hausdorff measure of the singular set.     

Multi-component static model for social networks

The static model was introduced to generate a scale-free network. In the model, N number of vertices are present from the beginning. Each vertex has its own weight, representing how much the vertex is influential in a system. The static model, however, is not relevant, when a complex network is composed of many modules such as communities in social networks. An individual may belong to more than one community and has distinct weights for each community. Thus, we generalize the static model by assigning a q-component weight on each vertex. We first choose a component among the q components at random and a pair of vertices is linked with a color according to their weights of the component as in the static model. A (1-f) fraction of the entire edges is connected following this way. The remaining fraction f is added with (q + 1)-th color as in the static model but using the maximum weights among the q components each individual has. The social activity with such maximum weights is an essential ingredient to enhance the assortativity coefficient as large as the ones of real social networks.Received: 27 October 2003, Published online: 17 February 2004PACS: 89.65.-s Social and economic systems - 89.75.Hc Networks and genealogical trees - 89.75.Da Systems obeying scaling laws     

Packet transport along the shortest pathways in scale-free networks

We investigate a problem of data packet transport between a pair of vertices on scale-free networks without loops or with a small number of loops. By introducing load of a vertex as accumulated sum of a fraction of data packets traveling along the shortest pathways between every pair of vertices, it is found that the load distribution follows a power law with an exponent . It is found for the Barabási-Albert-type model that the exponent changes abruptly from for tree structure to as the number of loops increases. The load exponent seems to be insensitive to different values of the degree exponent as long as .Received: 4 February 2004, Published online: 14 May 2004PACS: 89.75.Fb Structures and organization in complex systems - 05.65. + b Self-organized systems - 02.10.Ox Combinatorics; graph theory     

Paired gap states in a semiconducting carbon nanotube: deep and shallow levels

Several paired, localized gap states were observed in semiconducting single-wall carbon nanotubes using spatially resolved scanning tunneling spectroscopy. A pair of gap states is found far from the band edges, forming deep levels, while the other pair is located near the band edges, forming shallow levels. With the help of a first-principles study, the former is explained by a vacancy-adatom complex while the latter is explained by a pentagon-heptagon structure. Our experimental observation indicates that the presence of the gap states provides a means to perform local band-gap engineering as well as doping without impurity substitution.     

Supramolecular Cl⋅⋅⋅H and O⋅⋅⋅H Interactions in Self‐Assembled 1,5‐Dichloroanthraquinone Layers on Au(111)

The role of halogen bonds in self‐assembled networks for systems with Br and I ligands has recently been studied with scanning tunneling microscopy (STM), which provides physical insight at the atomic scale. Here, we study the supramolecular interactions of 1,5‐dichloroanthraquinone molecules on Au(111), including Cl ligands, by using STM. Two different molecular structures of chevron and square networks are observed, and their molecular models are proposed. Both molecular structures are stabilized by intermolecular Cl???H and O???H hydrogen bonds with marginal contributions from Cl‐related halogen bonds, as revealed by density functional theory calculations. Our study shows that, in contrast to Br‐ and I‐related halogen bonds, Cl‐related halogen bonds weakly contribute to the molecular structure due to a modest positive potential (σ hole) of the Cl ligands.