Node discovery in a networked organization

In this paper, I present a method to solve a node discovery problem in a networked organization. Covert nodes refer to the nodes which are not observable directly. They affect social interactions, but do not appear in the surveillance logs which record the participants of the social interactions. Discovering the covert nodes is defined as identifying the suspicious logs where the covert nodes would appear if the covert nodes became overt. A mathematical model is developed for the maximal likelihood estimation of the network behind the social interactions and for the identification of the suspicious logs. Precision, recall, and F measure characteristics are demonstrated with the dataset generated from a real organization and the computationally synthesized datasets. The performance is close to the theoretical limit for any covert nodes in the networks of any topologies and sizes if the ratio of the number of observation to the number of possible communication patterns is large

Transition into a low temperature superconducting phase of unconventional pinning in Sr_2RuO_4

We have found a sharp transition in the vortex creep rates at a temperature T^\ast=0.05 T_c in a single crystal of Sr_2RuO_4 (T_{c}=1.03 K) by means of magnetic relaxation measurements. For T<T^\ast, the initial creep rates drop to undetectable low levels. One explanation for this transition into a phase with such extremely low vortex creep is that the low-temperature phase of Sr_2RuO_4 breaks time reversal symmetry. In that case, degenerate domain walls separating discreetly degenerate states of a superconductor can act as very strong pinning centers.Comment: 3 pages, 2 figure

Mineral composition of ores and silicagel quality

Mineral composition and silica hydrogel properties of Japanese acid clay or

Transport properties of Ag5Pb2O6: a three-dimensional electron-gas-like system with low-carrier-density

We report normal-state transport properties of the single-crystalline samples of the silver-lead oxide superconductor Ag5Pb2O6, including the electrical resistivity, magnetoresistance, and Hall coefficient. From the Hall coefficient measurement, we confirmed that the carrier density of this oxide is as low as 5x10^{21} cm^{-3}, one order of magnitude smaller than those for ordinary alkali metals and noble metals. The magnetoresistance behavior is well characterized by the axial symmetry of the Fermi surface and by a single relaxation time. The T^2 term of the resistivity is scaled with the specific heat coefficient, based on the recent theory for the electron-electron scattering. The present results provide evidence that Ag5Pb2O6 is a low-carrier-density three-dimensional electron-gas-like system with enhanced electron-electron scatterings.Comment: 7 pages, 4 figures. Accepted for publication in Phys. Rev.

Analyzing covert social network foundation behind terrorism disaster

This paper addresses a method to analyze the covert social network foundation hidden behind the terrorism disaster. It is to solve a node discovery problem, which means to discover a node, which functions relevantly in a social network, but escaped from monitoring on the presence and mutual relationship of nodes. The method aims at integrating the expert investigator's prior understanding, insight on the terrorists' social network nature derived from the complex graph theory, and computational data processing. The social network responsible for the 9/11 attack in 2001 is used to execute simulation experiment to evaluate the performance of the method.Comment: 17pages, 10 figures, submitted to Int. J. Services Science