14 族元素架橋ビピリジル誘導体の合成と物性

内容の要約広島大学(Hiroshima University)博士(工学)Doctor of Engineeringdoctora

Spherical and Non-spherical Bubble Dynamics in Soft Matter

Cavitation and bubble dynamics play an important role in a wide range of applications including material characterization and therapeutic ultrasound. A specific problem in bubble dynamics is inertially dominated collapse, which occurs when a bubble reaches a critical size compared to its equilibrium size. This inertial collapse of cavitation bubbles enables us to characterize soft materials at high strain-rates or to ablate malignant tissue in therapeutic ultrasound. This thesis contributes to the understanding of spherical and non-spherical bubble dynamics in soft matter relevant to these applications. We first study ultrasound-induced oscillations of a gas bubble in soft matter. Oscillations of a spherical bubble in water are described by a classical Rayleigh-Plesset-type model. Although this model has been extended to include viscoelasticity necessary to represent soft matter, experiments of nonlinear bubble oscillations in soft matter are scarce, thus limiting opportunities for validating the models and understanding the role of viscoelasticity on bubble oscillations. We experimentally and numerically study ultrasound-induced bubble oscillations in a gelatin gel. Comparison of finite-amplitude oscillations between experiments and numerical solutions show good agreement, implying the validity of the viscoelastic modeling. A resonance curve of the ultrasound-induced bubble oscillations is obtained and shows the nonlinear feature of spring softening, where viscoelasticity has an impact on the resonant radius and peak amplitude. Since cavitation bubbles in soft materials consist of a finite amount of non-condensible gas as well as vapor, we investigate the role of gas-vapor mixture transport on the bubble dynamics. From a modeling standpoint, past studies relied on the assumption that the ratios of specific heats are the same for the gas and vapor. We develop a new model that accounts for the mixture with different ratios of specific heats. Numerical solutions show that vapor is trapped by an air shell during inertial collapse. This trapped vapor reduces the bubble collapse velocity and thus energy losses via acoustic radiation, leading to a larger bubble rebound. This analysis is further validated against experiments of laser-induced bubble collapse in glycerol. Comparison between the new and conventional models shows experimentally measurable discrepancies of several percent. Finally, we study the shape stability of a bubble in soft matter. Bubbles deviate from a spherical shape in practice, typically due to one of two mechanisms: parametric instability or Rayleigh-Taylor-type instability. We develop a model for non-spherical bubble dynamics in soft matter by extending classical perturbation analysis on a plane interface to a spherical interface between a gas and a soft solid. Parametric instability occurs during ultrasound-induced oscillations. The natural frequency and a Mathieu equation obtained from the non-spherical model predict unstable modes in parametric instability, which agrees with experimental observations in gelatin gels. Rayleigh-Taylor-type instability is induced by the large acceleration during inertial collapse. Numerical solutions of the non-spherical model show that viscoelasticity influences the bubble wall acceleration and thus is a key factor to determine this instability.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/166150/1/mkazuya_1.pd

Ski jumping flight skill analysis based on high-speed video image

AbstractMages of the initial 40 m part of a flight of 120-m ski jumping were recorded by a fixed high-speed video camera in Hakuba Ski Jumping Stadium. The time variations of the forward leaning angle and the ski angle of attack were measured from the video image and the aerodynamic forces were calculated from kinematic data. Some correlations were investigated between the reduced jumping distance Dr, which is an initial speed corrected flight distance, and some key angles and the initial transition time, as well as those between Dr and the aerodynamic force coefficients. Jumping performance is compared between advanced jumpers and beginner jumpers

Mail-in data collection at SPring-8 protein crystallography beamlines

A mail-in data collection system at SPring-8, which is a web application with automated beamline operation, has been developed

Lipids from Vitellaria paradoxa Gaertn Seeds by Supercritical CO2: Extraction and Optimization of Parameters by Response Surface Methodology

Supercritical carbon dioxide (CO2) was employed to extract lipids from Vitellaria paradoxa Gaertn seeds in semi–batch process at various operating conditions to optimize extraction process. The extraction processes were carried out at 40 – 60 oC and 20 – 40 MPa with 2 – 4 ml min–1 CO2 flow rates. Analysis of variance (ANOVA) with 33 factorial design combined with statistical was used to optimize variables in the process of Vitellaria paradoxa Gaertn seeds lipids extraction with supercritical CO2. The FT–IR spectra indicated that the Vitellaria paradoxa Gaertn seeds components were extracted by supercritical CO2. The SEM images also indicated that the physical changes in the surface of the Vitellaria paradoxa Gaertn seeds occurred after supercritical CO2 extraction treatment. The maximum of extracted lipids was 0.47 g/g–sample when the extraction was conducted at a temperature of 80 oC and pressure of 40 MPa with CO2 flow rate of 3 ml min–1. The GC–MS analysis showed that the extracted lipids mainly composed of palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1), and linoleic acid (C18:2). The analysis of experimental design demonstrated that pressure and temperature were the influential variables on the lipids extraction

The intercapillary space spectrum as a marker of diabetic retinopathy severity on optical coherence tomography angiography

Microcirculatory disturbance plays a pivotal role in the pathogenesis in diabetic retinopathy (DR). We retrospectively quantified the total counts and morphological features of intercapillary spaces, i.e., intercapillary areas and nonperfusion areas (NPAs), on swept-source optical coherence tomography angiography (SS-OCTA) images and to evaluate their associations with DR severity grades. We acquired 3 × 3 mm OCTA images in 75 eyes of 62 diabetic patients and 22 eyes of 22 nondiabetic subjects. In the en-face superficial images within the central 2 mm, the areas enclosed by retinal vessels were automatically detected. Their total numbers decreased in some eyes with no apparent retinopathy and most eyes with DR, which allowed us to discriminate diabetic subjects from nondiabetic subjects [area under the receiver operating characteristic curve (AUC) = 0.907]. The areas and area/perimeter ratios continuously increased in DR, indicating a continuum between healthy intercapillary areas and NPAs. The number of intercapillary spaces with a high area/perimeter ratio increased according to DR severity, which showed modest performance in discriminating moderate NPDR or higher grades (AUC = 0.868). These quantified parameters of intercapillary spaces can feasibly be used for the early detection of microcirculatory impairment and the diagnosis of referable DR