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

Patterns of Striped order in the Classical Lattice Coulomb Gas

We obtain via Monte Carlo simulations the low temperature charge configurations in the lattice Coulomb gas on square lattices for charge filling ratio $f$ in the range $1/3 < f < 1/2$. We find a simple regularity in the low temperature charge configurations which consist of a suitable periodic combination of a few basic striped patterns characterized by the existence of partially filled diagonal channels. In general there exist two separate transitions where the lower temperature transition ($T_p$) corresponds to the freezing of charges within the partially filled channels. $T_p$ is found to be sensitively dependent on $f$ through the charge number density $\nu = p_{1}/q_{1}$ within the channels.Comment: 4 pages, 8 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

Improvement of Riboflavin Production Using Mineral Support in the Culture of Ashbya gossypii

Riboflavin production in a culture of Ashbya gossypii was enhanced by adding mineral support with adsorbed soybean oil. When the support in an amount of 1 % to the amount of medium was added into the culture at agitation intensity corresponding to impeller rotation rate of 600 rpm, the attained riboflavin concentration was 2.5 g/L at the culture time of 4 days, i.e. 1.6 times higher than that in the culture without adding mineral support. Riboflavin yield coefficient based on consumed substrate was also 1.6-fold higher than that in the culture without mineral support. In order to investigate the effect of mineral support on the riboflavin production and mycelial morphology variation, intracellular oil droplets were investigated by staining mycelia with Nile red. The A. gossypii cells, growing in submerged culture using soybean oil as a carbon source, were found to form intracellular micro-lipid bodies. The oil droplets became bigger as the culture time increased, and then the riboflavin leakage began, whereas lipid bodies gradually disappeared. When the soybean oil adsorbed on mineral support was added to the culture, the diameter of A. gossypii mycelia was much thicker and more riboflavin crystals were accumulated than in the pool of culture without mineral support; and what is more, mycelial autolysis was delayed for 2 days due to the presence of mineral support

Structural Relaxation, Self Diffusion and Kinetic Heterogeneity in the Two Dimensional Lattice Coulomb Gas

We present Monte Carlo simulation results on the equilibrium relaxation dynamics in the two dimensional lattice Coulomb gas, where finite fraction $f$ of the lattice sites are occupied by positive charges. In the case of high order rational values of $f$ close to the irrational number $1-g$ ($g\equiv(\sqrt{5} -1)/2$ is the golden mean), we find that the system exhibits, for wide range of temperatures above the first-order transition, a glassy behavior resembling the primary relaxation of supercooled liquids. Single particle diffusion and structural relaxation show that there exists a breakdown of proportionality between the time scale of diffusion and that of structural relaxation analogous to the violation of the Stokes-Einstein relation in supercooled liquids. Suitably defined dynamic cooperativity is calculated to exhibit the characteristic nature of dynamic heterogeneity present in the system.Comment: 12 pages, 20 figure

Ultrasonographic measurement of shoulder subluxation in patients with post-stroke hemiplegia

OBJECTIVE: To evaluate the ultrasonographic measurement of shoulder subluxation in patients with post-stroke hemiplegia. DESIGN: Prospective, single blind study. PATIENTS: A total of 41 patients with post-stroke hemiplegia were included (24 men and 17 women, mean age 56 years (standard deviation 11), age range 34-78 years). METHODS: Clinical evaluation of the affected shoulder was assessed using the Motricity Index scores and the Modified Ashworth Scale. Two ultrasonographic measurements were taken to check intra-rater reliability. The shoulder subluxation ratio was determined as the ratio of the radiographic vertical and horizontal distance, and the ultrasonographic lateral and anterior distances in the affected shoulder divided by that in the unaffected shoulder. RESULTS: Intraclass correlation coefficients of the repeated ultrasonographic lateral/anterior distance measurements in the unaffected and affected shoulders were 0.979/0.969 and 0.950/0.947, respectively. Ultrasonographic lateral/anterior distance ratios were negatively correlated with Motricity Index scores of the affected shoulder abduction (r = -0.490, p < 0.001/ r = -0.671, p < 0.001). Ultrasonographic anterior distance ratio was negatively correlated with Modified Ashworth Scale score of the affected shoulder (r = -0.374, p < 0.05). However, there was no correlation between radiographic distance ratios and clinical evaluation scores. CONCLUSION: We strongly recommend ultrasonography as a diagnostic tool to measure the degree of shoulder subluxation in patients with post-stroke hemiplegia

Coarsening Kinetics of a Two Dimensional O(2) Ginzburg-Landau Model: Effect of Reversible Mode Coupling

We investigate, via numerical simulations, the phase ordering kinetics of a two- dimensional soft-spin O(2) Ginzburg-Landau model when a reversible mode cou- pling is included via the conserved conjugate momentum of the spin order parameter (the model E). Coarsening of the system, when quenched from a dis- ordered state to zero temperature, is observed to be enhanced by the existence of the mode coupling terms. The growth of the characteristic length scale L(t) exhibits an effective super-diffusive growth exponent that can be interpreted as a positive logarithmic-like correction to a diffusive growth, i.e., L(t) ~ (t ln t)^{1/2}. In order to understand this behavior, we introduced a simple phenomenological model of coarsening based on the annihilation dynamics of a vortex-antivortex pair, incorporating the effect of vortex inertia and logarithmically divergent mobility of the vortex. With a suitable choice of the parameters, numerical solutions of the simple model can fit the full simulation results very adequately. The effective growth exponent in the early time stage is larger due to the effect of the vortex inertia, which crosses over into late time stage characterized by positive logarithmic correction to a diffusive growth. We also investigated the non-equilibrium autocorrelation function from which the so called {\lambda} exponent can be extracted. We get {\lambda} = 1.99(2) which is distinctively larger than the value of {\lambda} = 1.17 for the purely dissipative model-A dynamics of non-conserved O(2) models.Comment: 19 pages, 8 figure