Biomedical subjects

Hyeong-Chai Jeong

Publications and source records attributed to Hyeong-Chai Jeong.

5 recordsLinked to original sources

PubMed2005

Directed polymers in random media under confining force.

The scaling behavior of a directed polymer in a two-dimensional random potential under confining force is investigated. The energy of a polymer with configuration {y(x)} is given by H({y(x)}) = sigma(x=1)(N) eta(x,y(x)) + epsilonW(alpha), where eta(x,y) is an uncorrelated random potential and W is the width of the polymer. Using an energy argument, it is conjectured that the radius of gyration Rg(N) and the energy fluctuation deltaE(N) of the polymer of length N in the ground state increase as Rg(N) approximately N(nu) and deltaE(N) approximately N(omega), respectively, with nu = 1/(1+alpha) and omega = (1+2alpha)/(4+4alpha) for alpha > or = 1/2. An algorithm of finding the exact ground state, with the effective time complexity of O(N3), is introduced and used to confirm the conjecture numerically.

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PubMed2005

Growing network model for community with group structure.

We propose a growing network model for a community with a group structure. The community consists of individual members and groups, gatherings of members. The community grows as a new member is introduced by an existing member at each time step. The new member then creates a new group or joins one of the groups of the introducer. We investigate the emerging community structure analytically and numerically. The group size distribution shows a power-law distribution for a variety of growth rules, while the activity distribution follows an exponential or a power law depending on the details of the growth rule. We also present an analysis of empirical data from online communities the "Groups" in http://www.yahoo.com and the "Cafe" in http://www.daum.net, which show a power-law distribution for a wide range of group sizes.

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PubMed2003

Scaling function for surface width for free boundary conditions.

We study the restricted curvature model with both periodic and free boundary conditions and show that the scaling function of the surface width depends on the type of boundary conditions. When the free boundary condition is applied, the surface width shows a new dynamic scaling whose asymptotic behavior is different from the usual scaling behavior of the self-affine surfaces. We propose a generalized scaling function for the surface width for free boundary conditions and introduce a normalized surface width to clarify the origin of the superrough phenomena of the model.

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PubMed2003

Inflation rule for Gummelt coverings with decorated decagons and its implication for quasi-unit-cell models.

The equivalence between quasi-unit-cell models and Penrose-tile models on the level of decorations is proved using inflation rules for Gummelt coverings with decorated decagons. Owing to overlaps, Gummelt arrangement of decorated decagons gives rise to nine different (context-dependent) decagon decorations in the covering. The inflation rules for decagons for each of nine types are presented and it is shown that inflations from differently typed decagons always produce different decorations of inflated decagons. However, if the original decagon region is divided into 'equivalent' rhombus Penrose tiles, typed-decagon arrangements in the tiles (of the same shape) become identical for the fourfold inflated decagons. This implies that a decagonal quasi-unit-cell model can be reinterpreted as a Penrose-tile model with fourfold deflated supertiles.

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PubMed2002

Restricted curvature model with suppression of extremal height.

A discrete growth model with a restricted curvature constraint is investigated by measuring both the surface width and the height difference correlation function. In our model, where an extremal height is suppressed, the surface width W shows the roughness exponent alpha approximately 0.561 and the dynamics exponent z approximately 1.69 in one substrate dimension. However the correlation function has an unusual scaling behavior and produces different wandering exponent alpha(') approximately 1.33 and its dynamic exponent z(') approximately 4. The discrepancy is due to the fact that the correlation length increases with a power law t(1/z(')) until it reaches the value proportional to Ldelta at time t(s) approximately L(z), where L is the system size and delta is the "window exponent" satisfying the relation delta=z/z(')=alpha/alpha('). delta is a new exponent to characterize the window size of the system.

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