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Chaotic Dynamics of a Simple Population Model under the Allee Effect
Namjung Hur,Jae Han Choi,Kyoung-Eun Lee,Do-Hun Lee,Areum Kim,Tae-Soo Chon,Jae Woo Lee 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.76 No.6
We look at the population dynamics of an ecological system considering the Allee effect across different levels of population growth rates. The model is described by the growth and degradation of population size by multiplying a threshold term by the Allee effect. When the population of a species is low, the population of the system is not maintained and collapses to extinction. A wide survival region is observed in the dynamics of the Allee effect, and we report a bifurcation diagram for selected control parameters. We identify the chaotic region based on Lyapunov exponents. We obtain a phase diagram distinguishing extinction, periodic oscillation, the chaotic region, and the unstable region in the control parameter space. We observe two sets of chaotic bands one for low and the other for high values of the Allee effect. The Allee effect diversifies the dynamic region in parameter space.
허남정(Namjung Hur) 한국자기학회 2011 韓國磁氣學會誌 Vol.21 No.3
Principles in the synthesis of small-sized high-quality crystals for the experimental condensed matter physics will be discussed in this paper. Synthesis process and cautions will be introduced especially for the synthesis methods which can be easily accessible to researchers. Starting from the solid state reaction which is the most common synthesis method, I will explain the quartz tube sealing that is crucial for making polycrystalline materials as well as single crystals in various conditions. Finally, basics of single crystal growth and various techniques will be introduced on the whole for the researchers who are not familiar with the material synthesis.
이경동(Kyungdong Lee),송기명(Kimyung Song),허남정(Namjung Hur) 한국자기학회 2010 韓國磁氣學會誌 Vol.20 No.6
We have investigated the magnetoresistance effect in Cr?S? single crystals prepared by vapor transport method. Room temperature X-ray diffraction (XRD) study reveals the phase formation of the single crystals with trigonal crystal structure. The magnetization was measured as a function of temperature (5 K~400 K) and applied magnetic field (0.1 T and 5 T). The magnetization curve as a function of temperature reveals the two transition states of Cr?S?: one from antiferromagnetic to ferrimagnetic state at ~150 K and the other from ferrimagnetic to paramagnetic state at ~300 K. Temperature dependent resistivity at 0 T and 5 T magnetic field shows the metallic behavior, showing the transition from antiferromagnetic to ferrimagnetic state at ~150 K. Magnetic field dependence of magnetization was measured at four fixed temperatures viz. 100 K, 150 K, 200 K, and 300 K. It is observed that at 200 K and 300 K it shows well M-H hysteresis behavior, whereas at 100 K and 150 K it shows non-hysteretic nature. A negative magnetoresistance (MR) of ?2% is observed at 5 T for Cr?S? single crystal at 150 K, near the antiferromagnetic transition temperature.
Park Garam,Cho Jaehun,Kim June-Seo,Kim Yonghwan,Jung Jong Hoon,Hur Namjung,Oh In-Hwan,Kim Ki-Yeon 한국물리학회 2022 Current Applied Physics Vol.35 No.-
Critical behavior of quasi two-dimensional organic-inorganic halide perovskites (C6H5CH2CH2NH3)2CuCl4 is investigated using magneto-thermal and isothermal magnetic properties along the easy axis. Banerjee’s criterion indicates that phase transition from paramagnetic to ferromagnetic phases below TC = 9.4 K is of second-order. Scaling analysis reveals that critical exponent β from spontaneous magnetization in the critical region below TC and δ from critical isotherm at TC are found to be 0.22(3) and 9.28–9.4, close to 2D finite XY model. Meanwhile, γ from magnetic susceptibility in the critical region above TC is gradually decreased from 2.4 at high-temperature region. Critical exponents from magneto-thermal properties are found to be consistent with those determined from magnetization isotherms. The reliability of critical values is verified using the scaling hypothesis. Our results evidence that (C6H5CH2CH2NH3)2CuCl4 crossovers from isotropic 2D Heisenberg to anisotropic 3D models towards TC and can be promising candidates for magnetocaloric materials for hydrogen reliquefaction.