Organizer:

Lei Zhang (BICMR, PKU)

Speaker list:

Huijing Du, Dept. of Math, University of Nebraska-Lincoln

Man Fang, School of Music, University of South Carolina

Yi Sun, Dept. of Math, University of South Carolina

Yanxiang Zhao, Dept. of Math, George Washington University

Program:

1:30-2:10, Huijing Du,

Gene regulation and spatial mechanisms control layer formation in epidermis

2:10-2:50, Yi Sun

Kinetic Monte Carlo Simulations of Traffic and Pedestrian Flows

2:50-3:30, Yanxiang Zhao

Bubble Assemblies in Ternary Systems with Long Range Interaction

3:30-4, Tea break

4-5, Man Fang

Color, Drama & Symmetry

Abstract:

Gene regulation and spatial mechanisms control layer formation in epidermis

Huijing Du, Dept. of Math, University of Nebraska-Lincoln

Abstract: Epidermal morphogenesis, which occurs during the second half of embryogenesis, is the developmental process that generates a skin permeability barrier essential for terrestrial survival. Defects with this barrier are associated with common skin disorders such as atopic dermatitis. Study of mechanisms that control epidermal development and differentiation is therefore highly relevant to human health. Motivated by recent experimental observations on the role of Ovol transcription factors in regulating epidermal development, we developed a multiscale model to investigate the underlying mechanisms responsible for epidermal layer formation and homeostasis. We report that regulation of proliferation and differentiation by Ovol plays an important role in epidermal development. In addition, our computational analysis shows that asymmetric cell division, selective cell adhesion, and morphogen regulation work in a synergetic manner to produce the well-stratified epidermal layers. Taken together, our results demonstrate that robust epidermal morphogenesis involves a balance between proliferation and differentiation, and an interplay between short- and long-range spatial control mechanisms. This principle may also be applicable to other complex systems of tissue development or regeneration.

Kinetic Monte Carlo Simulations of Traffic and Pedestrian Flows

Yi Sun, Dept. of Math, University of South Carolina

Abstract: We employ an efficient list-based kinetic Monte Carlo (KMC) method to study 1D and 2D traffic flow models and 2D pedestrian flow models based on the exclusion principle and Arrhenius microscopic dynamics. 1) The traffic flow model implements stochastic rules for cars' movement based on the configuration of the traffic ahead of each car. In particular, we compare two different look-ahead rules: one is based on the distance from the car under consideration to the car in front of it, the other one is based on the density of cars ahead. The 1D numerical results of these two rules suggest different coarse-grained macroscopic limits in the form of integro-differential Burgers equations. The 2D results of both rules exhibit a sharp phase transition from freely flowing to fully jammed, as a function of initial density of cars. However, the look-ahead rule based on the density of the traffic produces more realistic results. 2)  The pedestrian flow model implements stochastic rules for pedestrians' movements based on the configuration of the surrounding conditions of each pedestrian. The rules can reflect the pedestrians' decisions of action such as moving forward, stopping to wait, lane switching, back stepping, etc. The simulation results of both two-way and four-way flows exhibit a state transition from freely flowing to fully jammed, as a function of initial density of pedestrians. At different states the relationships of density-flow and density-velocity are different from each other.

Bubble Assemblies in Ternary Systems with Long Range Interaction

Yanxiang Zhao, Dept. of Math, George Washington University

Abstract: A nonlocal diffuse interface model, based on the Nakazawa-Ohta density functional theory for triblock copolymers, is used to study bubble assemblies in ternary systems. The model has three parameters weighing three types of long range interaction and two parameters that fix the total area of each constituent. As the parameters vary, a large number of morphological phases appear as stable stationary states. One open question related to the polarity direction of double bubble assemblies is answered numerically. Moreover, it is shown that the average size of bubbles in a single bubble assembly depends on the sum of the minority constituent areas and the long range interaction coefficients. One further identifies the ranges for area fractions and the long range interaction coefficients for double bubble assemblies.

Color, Drama & Symmetry

Man Fang, School of Music, University of South Carolina

Abstract: Composer Fang Man introduces her musical compositions through three important elements that drive her creative mind: color, drama and symmetry.  She has done interdisciplinary projects with various artists and scientists. For instance, Noir for orchestra is a collaborative work with visual artist Michael Wyshock; Ambush from Ten Sides for Guitar and Electronics is an experimental work, which she collaborated with scientists at IRCAM (Institute for Research and Coordination in Acoustics Music)-Centre Pompidou in Paris. She adapts symmetrical construction for the pitch and harmonic organizations in her recent works, which include Earth a song cycle for sextet and modern dancers, and her Guggenheim Fellowship project: a full length opera Golden Lily.