Wonju Jeon

A constraint condition for foraging strategy in subterranean termites

Abstract Previous studies have explored the relationship between termite branch tunnel geometry and foraging efficiency in a model simulation in which foraging efficiency, &ggr;, for two termite species, Coptotermes formosanus Shiraki and Reticulitermes flavipes (Kollar) (Isoptera: Rhinotermitidae), was investigated in response to two variables, the probability of tunnel branching (Pbranch) and the probability of tunnel branch termination (Pterm). It was found that simulated tunnel patterns based on empirical data did not have maximum foraging efficiency. We hypothesized that termites could increase their foraging efficiency in response to landscape heterogeneity. The present study investigated how termites could control the two variables, Pbranch and Pterm, in response to the external environment in terms of tunnel network connectivity. It was found that the best simulated strategy for C. formosanus and R. flavipes termites would occur if both Pbranch and Pterm were increased together. This study provides possible mechanisms for foraging strategies in subterranean termites and a baseline for future empirical work.

Suppression of scar formation in a murine burn wound model by the application of non-thermal plasma

Suppression of hypertrophic scar generation in an animal model by treatment with plasma is reported. Contact burn following mechanical stretching was used to induce scar formation in mice. Exposure to the plasma tended to reduce the scar area more rapidly without affecting vitality. The treatment resulted in decreased vascularization in the scar tissue. Plasma-treated scars showed mild decrease in the thickness of hypertrophic tissues as shown by histological assessment. Finally, we showed that plasma treatment induced cell death and reactive oxygen species generation in hypertrophic scar fibroblast. All of the results support that plasma treatment can control scar generation.

Exact and useful formulas of generalized gamma functions occurring in finite diffraction theory

Exact formulas of generalized gamma functions, Γ m (u, z), occurring in finite diffraction theory are derived in closed form for arbitrary m, u=n+1/2 (m and n are non-negative integers), and for both real and complex arguments z. For m=1 and real argument z, the formula consists of polynomials and the complementary error function. And, for m=1 and purely imaginary argument z occurring in the Wiener–Hopf integral equation for a finite diffraction problem, the formula is expressed by polynomials and the Fresnel integral which is a well-known function in mathematical theory of diffraction. The formulas for an arbitrary positive integer m are also obtained simply by differentiating Γ m (u, z) with respect to z. These exact formulas are graphically shown and compared with Kobayashis asymptotic formulas for various m and n values.

Effect of compressibility and non-uniformity in flow on the scattering pattern of acoustic cloak

During the last decade, most of acoustic cloak research has been done within a theoretical framework in which the medium is at rest. However, such an acoustic cloak cannot preserve its unique properties or functions to make an object acoustically invisible in the presence of flow. In this study, we propose a theoretical framework to accurately investigate the effect of compressibility and non-uniformity in flow on the scattering pattern of acoustic cloak. In the formulation, the wave operator is coupled with the non-uniform velocity vector, and the equivalent source terms due to mean flow are divided into the compressibility effect and the non-uniformity effect with their own physical meanings. Numerical simulation shows the difference in far-field directivity between previous and present formulations. The polarity of the equivalent sources in the present formulation shows hexapole and skewed quadrupole patterns for non-uniformity and compressibility effects, respectively, and their magnitudes increase with power laws of Mach number as the Mach number increases. As an application, we make use of the present formulation for predicting the acoustic scattering from newly designed convective cloaks. The simulation results show better performance compared to the existing convective cloak.

Quantitative analysis of fish schooling behavior with different numbers of medaka (Oryzias latipes) and goldfish (Carassius auratus)

Fish form schools of various sizes, according to species or environmental conditions, to attain several advantages, such as protection from predators or to improve efficiency in searching for prey. Thus, quantifying the mechanisms of how group size affects schooling behavior may contribute to better understanding fish biology and the evolution of the collective behavior of fishes. In the present study, we explored how school size affected the behavior of medaka (Oryzias latipes) and goldfish (Carassius auratus). Size groups of 10 to 40 individuals were placed in a circular aquarium (100 cm diameter, 30 cm height, 5 cm water depth) and videoed for 4 hours. Eight to 10 video clips of 3 seconds in length for each group size were evaluated for 6 physical parameters of fish schooling behavior. Regardless of species, the mean distance among individuals increased with increasing school size. However, due to variations in certain physical parameters, the schooling pattern of goldfish was more elongated than medaka, possibly related to body size, or indicating species-specific differences in schooling characteristics. Our experimental datasets could be incorporated into theoretical mathematical models of fish schooling behavior, by contributing new information about school size and species differences.

Vibration damping using a spiral acoustic black holea)

This study starts with a simple question: can the vibration of plates or beams be efficiently reduced using a lightweight structure that occupies a small space? As an efficient technique to damp vibration, the concept of an acoustic black hole (ABH) is adopted with a simple modification of the geometry. The original shape of an ABH is a straight wedge-type profile with power-law thickness, with the reduction of vibration in beams or plates increasing as the length of the ABH increases. However, in real-world applications, there exists an upper bound of the length of an ABH due to space limitations. Therefore, in this study, the authors propose a curvilinear shaped ABH using the simple mathematical geometry of an Archimedean spiral, which allows a uniform gap distance between adjacent baselines of the spiral. In numerical simulations, the damping performance increases as the arc length of the Archimedean spiral increases, regardless of the curvature of the spiral in the mid- and high-frequency ranges. Adding damping material to an ABH can also strongly enhance the damping performance while not significantly increasing the weight. In addition, the radiated sound power of a spiral ABH is similar to that of a standard ABH.

Simulation study of territory size distributions in subterranean termites.

In this study, on the basis of empirical data, we have simulated the foraging tunnel patterns of two subterranean termites, Coptotermes formosanus Shiraki and Reticulitermes flavipes (Kollar), using a two-dimensional model. We have defined a territory as a convex polygon containing a tunnel pattern and explored the effects of competition among termite territory colonies on the territory size distribution in the steady state that was attained after a sufficient simulation time. In the model, territorial competition was characterized by a blocking probability P(block) that quantitatively describes the ease with which a tunnel stops its advancement when it meets another tunnel; higher P(block) values imply easier termination. In the beginning of the simulation run, N=10, 20,…,100 territory seeds, representing the founding pair, were randomly distributed on a square area. When the territory density was less (N=20), the differences in the territory size distributions for different P(block) values were small because the territories had sufficient space to grow without strong competitions. Further, when the territory density was higher (N>20), the territory sizes increased in accordance with the combinational effect of P(block) and N. In order to understand these effects better, we introduced an interference coefficient γ. We mathematically derived γ as a function of P(block) and N: γ(N,P(block))=a(N)P(block)/(P(block)+b(N)). a(N) and b(N) are functions of N/(N+c) and d/(N+c), respectively, and c and d are constants characterizing territorial competition. The γ function is applicable to characterize the territoriality of various species and increases with both the P(block) values and N; higher γ values imply higher limitations of the network growth. We used the γ function, fitted the simulation results, and determined the c and d values. In addition, we have briefly discussed the predictability of the present model by comparing it with our previous lattice model that had been used to explain the territory size distributions of mangrove termites on the Atlantic coast of Panama.

A mathematical model for the territorial competition of the subterranean termites Coptotermes formosanus and Reticulitermes flavipes (Isoptera: Rhinotermitidae)

The foraging territories of two subterranean termites, Coptotermesformosanus Shiraki and Reticulitermesflavipes (Kollar), were simulated using a two-dimensional model to explore how territorial competition changes according to two variables characterizing territory formation: the total number of territories, and the blocking probability. Meanwhile, the blocking probability quantitatively describes the likelihood that a tunnel will be terminated when another tunnel is encountered. In our previous study, we introduced an interference coefficient γ to characterize territorial competition, and obtained γ as a function of the total number of territories and the blocking probability for a single termite species by model simulation. In the field, the territorial competition of more than two termite species is frequently observed. Here, we extended the γ function to be able to explain the competition between the two species by applying statistical regression to the simulation data. Further, we statistically checked the extended γ function by comparing the γ function for a single species. We also discuss another approach to mathematically derive the extended γ function, which can be easily generalized for use in cases of territorial competition involving more than two termite species.

A Simulation Model for the Study on the Forest Fire Pattern

Because forest fires are predicted to increase in severity and frequency under global climate change with important environmental implications, an understanding of fire dynamics is critical for mitigation of these negative effects. For the reason, researchers with different background, such as ecologists, physicists, and mathematical biologists, have developed the simulation models to mimic the forest fire spread patterns. In this study, we suggested a novel model considering the wind effect. Our theoretical forest was comprised of two different tree species with varying probabilities of transferring fire that were randomly distributed in space at densities ranging from 0.0 (low) to 1.0 (high). We then studied the distributional patterns of burnt trees using a two-dimensional stochastic cellular automata model with minimized local rules. We investigated the time, T, that the number of burnt trees reaches 25% of the whole trees for different values of the initial tree density, fire transition probability, and the degree of wind strength. Simulation results showed that the values of T decreased with the increase of tree density, and the wind effect decreased in the case of too high or low tree density. We believe that our model can be a useful tool to explore forest fire spreading patterns.

Radiation Characteristics of Noise Generated by Steady Loading on Rotating Blade

Loading noise generated by steady aerodynamic force exerted on the rotating body surface is theoretically analyzed and its radiation characteristics is examined as a fundamental research of helicopter rotor noise. For simplicity, the force exerted on each blade is not distributed but concentrated at one point and the noise is evaluated by using Lowson` exact formula with a discussion of the physical meaning of each term in the formula. For a single point force rotating with various angular frequencies, we investigated the radiation characteristics and theoretically explained the physical behavior at near and far-field. By investigating the amplitude of acoustic pressure with various distances, we observed the different decreasing ratio at near- and far-field with the discussion of the effect of acceleration of angular frequency. Finally, the phenomenon that the noise level is reduced everywhere as the number of blade increases is explained with the suggestion of a noise reduction idea, the limitations of this study, and the future research topics.