Structural Change in Lipid Bilayers and Water Penetration Induced by Shock Waves: Molecular Dynamics Simulations

科研費報告書収録論文(課題番号:17300168/研究代表者:小玉哲也/マイクロ気泡と超音波を用いた高効率型分子導入法の開発とがん治療法への応用

Cavitation Bubbles in a Starting Submerged Water Jet

The behavior of cavitation bubbles in a starting submerged water jet discharging from a circular nozzle is studied by a simple photography technique in a moderately low range of jet exit velocity. A number of small spherical bubbles are initially generated in a starting vortex formed at the jet tip and often connected circumferentially with each other in the form similar to a vortex ring. Nearly axisymmetric lumps of disconnected bubbles are also observed frequently. By analyzing photographic data acquired from the side and end view pictures of the ring-like bubbles, their average properties, such as trajectory, geometry and size, are evaluated

キャビテーションキホウノホウカイキコウニカンスルケンキュウ

京都大学0048新制・論文博士工学博士乙第4113号論工博第1271号新制||工||473(附属図書館)6300UT51-55-E93(主査)教授 赤松 映明, 教授 森 美郎, 教授 佐藤 俊学位規則第5条第2項該当Kyoto UniversityDA

Molecular dynamics study of kinetic boundary condition at an interface between argon vapor and its condensed phase

The evaporation and condensation at an interface of vapor and its condensed phase is considered. The validity of kinetic boundary condition for the Boltzmann equation, which prescribes the velocity distribution function of molecules outgoing from the interface, is investigated by the numerical method of molecular dynamics for argon. From the simulations of evaporation into vacuum, the spontaneous-evaporation flux determined by the temperature of condensed phase is discovered. Condensation coefficient in equilibrium states can then be determined without any ambiguity. It is found that the condensation coefficient is close to unity below the triple-point temperature and decreases gradually as the temperature rises. The velocity distribution of spontaneously evaporating molecules is found to be nearly a half-Maxwellian at a low temperature. This fact supports the kinetic boundary condition widely used so far. At high temperatures, on the other hand, the velocity distribution deviates from the half-Maxwellian

Linear Analysis of Dispersive Waves in Bubbly Flows Based on Averaged Equations

One-dimensional linear dispersive waves in water flows containing a number of small spherical air bubbles are analytically studied on the basis of a set of averaged equations recently derived by the present authors. The set of equations consists of the conservation laws for gas and liquid phases and the equation of motion of bubble wall. In addition to the volume-averaged pressure in each phase, the surface-averaged liquid pressure at the bubble wall is incorporated. The compressibility of water is taken into account as well as that of gas in bubbles, and a model of virtual mass force is included, although the Reynolds stress, viscosity, heat conductivity, and the phase change across the bubble wall are disregarded. The results are summarized as follows: (i) the waves are decomposed into the fast mode, slow mode, and convection mode (void wave). (ii) In the uniform flows, the three modes stably exist for all real wave numbers. (iii) In the limit of infinitesimal void fraction, the explicit representation of the elementary solution is obtained. (iv) The instability does not appear in the range where the present averaged equations are applicable

Kinetic Boundary Condition at a Vapor-Liquid Interface

By molecular dynamics simulations, the boundary condition for the Boltzmann equation at a vapor-liquid interface is found to be the product of three one-dimensional Maxwellian distributions for the three velocity components of vapor molecules and a factor including a well-defined condensation coefficient. The Maxwellian distribution for the velocity component normal to the interface is characterized by the liquid temperature, as in a conventional model boundary condition, while those for the tangential components are prescribed by a different temperature, which is a linear function of energy flux across the interface. The condensation coefficient is found to be constant and equal to the evaporation coefficient determined by the liquid temperature only

Molecular dynamics study of kinetic boundary condition at an interface between a polyatomic vapor and its condensed phase

The kinetic boundary condition for the Boltzmann equation at an interface between a polyatomic vapor and its liquid phase is investigated by the numerical method of molecular dynamics, with particular emphasis on the functional form of the evaporation part of the boundary condition, including the evaporation coefficient. The present study is an extension of a previous one for argon [Ishiyama, Yano, and Fujikawa, Phys. Fluids 16, 2899 (2004)] to water and methanol, typical examples of polyatomic molecules. As in the previous study, molecular dynamics simulations of vapor–liquid equilibrium states and those of evaporation from liquid into a virtual vacuum are carried out for water and methanol. In spite of the formation of molecular clusters in the vapor phase and the presence of the preferential orientation of molecules at the interface, essentially the same results as in the previous study are obtained. When the bulk liquid temperature is relatively low, the evaporation part is the product of the half range Maxwellian for the translational velocity of molecules of saturated vapor at the temperature of the bulk liquid phase, the equilibrium distribution of rotational energy of molecules at the temperature, and the evaporation coefficient (or the condensation coefficient in the equilibrium state). The evaporation coefficients of water and methanol are determined without any ambiguity as decreasing functions of the temperature, and are found to approach unity with the decrease of the temperature

Structural Change in Lipid Bilayers and Water Penetration Induced by Shock Waves: Molecular Dynamics Simulations

The structural change of a phospholipid bilayer in water under the action of a shock wave is numerically studied with unsteady nonequilibrium molecular dynamics simulations. The action of shock waves is modeled by the momentum change of water molecules, and thereby we demonstrate that the resulting collapse and rebound of the bilayer are followed by the penetration of water molecules into the hydrophobic region of the bilayer. The high-speed phenomenon that occurs during the collapse and rebound of the bilayer is analyzed in detail, particularly focusing on the change of bilayer thickness, the acyl chain bend angles, the lateral fluidity of lipid molecules, and the penetration rate of water molecules. The result shows that the high-speed phenomenon can be divided into two stages: in the first stage the thickness of bilayer and the order parameter are rapidly reduced, and then in the second stage they are recovered relatively slowly. It is in the second stage that water molecules are steadily introduced into the hydrophobic region. The penetration of water molecules is enhanced by the shock wave impulse and this qualitatively agrees with a recent experimental result