5,148 research outputs found
Statistical Analysis of the Metropolitan Seoul Subway System: Network Structure and Passenger Flows
The Metropolitan Seoul Subway system, consisting of 380 stations, provides
the major transportation mode in the metropolitan Seoul area. Focusing on the
network structure, we analyze statistical properties and topological
consequences of the subway system. We further study the passenger flows on the
system, and find that the flow weight distribution exhibits a power-law
behavior. In addition, the degree distribution of the spanning tree of the
flows also follows a power law.Comment: 10 pages, 4 figure
Sleepless in Seoul: `The Ant and the Metrohopper'
One of Aesop's (La Fontain's) famous fables `The Ant and the Grasshopper' is
widely known to give a moral lesson through comparison between the hard working
ant and the party-loving grasshopper. Here we show a slightly different version
of this fable, namely, "The Ant and the Metrohopper," which describes human
mobility patterns in modern urban life. Numerous real transportation networks
and the trajectory data have been studied in order to understand mobility
patterns. We study trajectories of commuters on the public transportation of
Metropolitan Seoul, Korea. Smart cards (Integrated Circuit Cards; ICCs) are
used in the public transportation system, which allow collection of transit
transaction data, including departure and arrival stations and time. This
empirical analysis provides human mobility patterns, which impact traffic
forecasting and transportation optimization, as well as urban planning.Comment: to be appeared in Journal of the Korean Physical Societ
Nearly Massless Electrons in the Silicon Interface with a Metal Film
We demonstrate the realization of nearly massless electrons in the most
widely used device material, silicon, at the interface with a metal film. Using
angle-resolved photoemission, we found that the surface band of a monolayer
lead film drives a hole band of the Si inversion layer formed at the interface
with the film to have nearly linear dispersion with an effective mass about 20
times lighter than bulk Si and comparable to graphene. The reduction of mass
can be accounted for by repulsive interaction between neighboring bands of the
metal film and Si substrate. Our result suggests a promising way to take
advantage of massless carriers in silicon-based thin-film devices, which can
also be applied for various other semiconductor devices.Comment: 4 pages, 4 figures, accepted for publication in Physical Review
Letter
Effect of sintering temperature under high pressure in the uperconductivity for MgB2
We report the effect of the sintering temperature on the superconductivity of
MgB2 pellets prepared under a high pressure of 3 GPa. The superconducting
properties of the non-heated MgB2 in this high pressure were poor. However, as
the sintering temperature increased, the superconducting properties were vastly
enhanced, which was shown by the narrow transition width for the resistivity
and the low-field magnetizations. This shows that heat treatment under high
pressure is essential to improve superconducting properties. These changes were
found to be closely related to changes in the surface morphology observed using
scanning electron microscopy.Comment: 3 Pages including 3 figure
Microstructure and pinning properties of hexagonal-disc shaped single crystalline MgB2
We synthesized hexagonal-disc-shaped MgB2 single crystals under high-pressure
conditions and analyzed the microstructure and pinning properties. The lattice
constants and the Laue pattern of the crystals from X-ray micro-diffraction
showed the crystal symmetry of MgB2. A thorough crystallographic mapping within
a single crystal showed that the edge and c-axis of hexagonal-disc shape
exactly matched the (10-10) and the (0001) directions of the MgB2 phase. Thus,
these well-shaped single crystals may be the best candidates for studying the
direction dependences of the physical properties. The magnetization curve and
the magnetic hysteresis for these single crystals showed the existence of a
wide reversible region and weak pinning properties, which supported our single
crystals being very clean.Comment: 5 pages, 3 figures. submitted to Phys. Rev.
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