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Second Blows in the Head-on Collisions of Spherical Nano Polymer Droplets
김상락 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.5
We report observations of a weird but interesting phenomenon from molecular dynamics simulations:the occurrence of second blows in head-on collisions of two equal-sized spherical nanopolymer droplets. In head-on collisions, we usually expect single-peak impact forces between thetwo colliding droplets. However, a second peak of the impact force is actually observed in thesimulations. Its underlying mechanisms on a molecular scale are proposed.
김상락,장선아,양재군,배재학 한국산업경영시스템학회 2010 한국산업경영시스템학회 학술대회 Vol.2010 No.춘계
In cloud computing environment, service contracts between service providers and customers should be monitored in real-time. In the current paper-based service contract environment, service providers and customers cannot monitor service levels in real-time. Moreover, if a service failure occurs, there is no compensation system for the failure. Therefore, it is necessary to develop an automated administrative tool to support overall cloud services. The proposed intelligent framework is a document containing information processing knowledge which is used whenever information-processing demand occurs. It can be an important technology for service extension.
Elastic Behavior of Spherical Nanodroplets in Head-on Collisions
김상락 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.3
Simulation results for head-on collisions of equal-sized spherical polymer nanodroplets, which were obtained by using molecular dynamics, are presented. The elastic behavior of an initial compressed phase for the colliding droplets is analyzed. Deformations and contact radii of the nanodroplets are compared with the Hertzian model of elastic solid balls. At least the initial phase of the collision could be explained by this continuum model, except at the very beginning of the collision.
Generation of Transverse Velocities in a Head-on Collision of Two Nanodroplets
김상락 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.6
We will report molecular-dynamic simulation results for the velocity fields generated in a headon collision of two equal-sized spherical nanodroplets. The results show the detailed motion of the molecules of the colliding droplets during the collision. We also discuss the generation of transverse velocities due to the collision, and we analyze the underlying mechanism at a molecular scale. We, thus, get some intuition into nanodroplet collision.
Molecular Dynamics Study of Soft Matter: Potential Dependence of Depletion Forces
김상락 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.7
Depletion forces of colloids in a polymer solution in two dimension are investigated by employing molecular dynamics simulations for different soft potential models between a colloid and a polymer and between two polymers. In order to see the local distributions of solvent particles, centro-symmetry parameters around a colloid and pair correlation functions between a colloid and a polymer are calculated. In order to see the direct effects of the solvent particles on the depletion forces, the volume fractions in the depletion zone are also calculated. Changes regarding depletion forces with gaps between two colloids can be understood with the introduction of these quantities. When the interaction between a colloid and a polymer is attractive, the gap between colloids acts as a shelter for the polymers and a layer is made in the gap and thus these particles in the layer exert strong repulsive forces to the colloids. It is found that the layer of polymers formed in the depletion zone plays a dominant role on the behaviors of depletion forces between colloids.
Molecular Dynamics Study of Nanodroplets: Initial Compressed Phase of Collisions Against a Flat Wall
김상락 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.3
Collisions of spherical nanodroplets against a flat wall are studied using molecular dynamics simulations. The initial compressed phase of the collisions is focused on to illuminate the elastic behavior of the droplet. The normal forces Fz between the droplet and the wall are calculated at varying impact velocities u along the <i>z</i>-direction and fitted to a power law of the form <i>F<sub>z</sub></i> ∝ ζ<sup>n</sup>, where ζ denotes a deformation. If <i>u</i> is less than 0.2 and ζ < 0.8, then the normal forces all together satisfy a power law with exponent <i>n</i> ∽ 1.5, corresponding to the Hertz law. However, if <i>u</i> is greater than 0.3, then the exponent <i>n</i> changes to around 2.0 ∼ 2.4.
Formulation of Statistical Mechanics in Terms of Information Theory
김상락 한국물리학회 2017 새물리 Vol.67 No.2
We present a new formulation of statistical mechanics based on information theory. Starting from completely independent systems, we increase the level of dependency between the systems step-by-step and extend the dimensionality of the system and the number of particles. The number of accessible states for a single particle in occupying the states plays a central role in the particle statistics of many identical particles. The corresponding expressions for the Shannon entropy of many identical particles are naturally derived from this building block for the cases of indistinguishable/distinguishable and/or interacting/noninteracting systems. We employ the concepts of coarse-graining and mutual information. The counting factor $N!$ can be regarded as a coarse-graining factor. The interaction between particles implies mutual information between locations of the particles.
김상락,김종훈,김풍호 경기대학교 1996 論文集 Vol.38 No.2
A simple one-dimensional dynamical system of a ball colliding with a periodically vibrating table is considered. It is assumed that the ball is a granular particle and the table is sinusoidally vibrating. The collision is characterized by a coefficient of restitution at each impact. The coefficient of restitution and the frequency of the table is fixed. For given values of initial position and velocity of a ball, we investigated the behavior from periodic to chaotic motion by changing table's amplitude A. We observed the distinct regions of period doubling, chaos, crisis and sticking.