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The jetting behaviour and migratory characteristics of a laser-induced cavitation bubble in a rectangular channel are investigated both experimentally and numerically, for various combinations of the geometric and physical parameters of the system. High-speed photography is used to visualize the temporal development of the bubble shape, the formation of liquid jets during bubble collapse, and the bubble displacement in contact with the sidewalls of the channel during two oscillation cycles of the bubble. The bubble profiles, pressure contours and velocity vectors ambient to the bubble are obtained through numerical simulation results by using an Eulerian finite element method with a compressible liquid impact model. The jetting behaviour of the bubble varies between single jet formation and the formation of three liquid jets directed towards each wall of the channel. The numerical calculations indicate that the liquid jets directed towards the sidewalls of the channel reach maximum velocities of 100 m s−1 while the peak velocity of the liquid jet directed towards the channel endwall is about 55 m s−1. A small bubble generated close to a sidewall of the channel develops only a single inclined jet during collapse. Such jets can reach velocities of up to 110 m s−1. A bubble displacement in contact with the sidewalls of the channels of 350 μm was observed during the first two oscillation cycles for a bubble with a maximum diameter slightly smaller than the height of the channel. The results of our investigations are compared to previous results obtained in similar configurations.

Cavitation bubble cloud formation due to the backscattering of high-intensity focused ultrasound (HIFU) from a laser-induced bubble in various water temperatures and dissolved oxygen (DO) has been investigated. A laser-induced bubble generated near the geometrical focus of HIFU is utilized to yield intense negative pressure by the backscattering. Optical observation with a high-speed video camera and pressure measurement with a fiber-optic probe hydrophone are conducted simultaneously to understand the forming process of a bubble cloud and corresponding pressure field by the backscattering. Optical observation shows that a bubble cloud grows stepwise forming multiple layers composed of tiny cavitation bubbles, and the cavitation inception position is consistent with the local minimum pressure position simulated with the ghost fluid method. The bubble cloud grows larger in the opposite direction of HIFU propagation, and the absolute value of the cavitation inception pressure decreases with an increase in water temperature. The linear correlation between cavitation inception pressure and water temperature agrees with that given by Vlaisavljevich, Xu, Maxwell, Mancia, Zhang, Lin, Duryea, Sukovich, Hall, Johnsen, and Cain [IEEE Trans. Ultrason. Ferroelectr. Freq. Control 63, 1064-1077 (2016)]. However DO has minor dependence on the cavitation inception pressure when DO is degassed sufficiently. Furthermore, the gas nucleus size that might exist in the experiment has been estimated by using bubble dynamics.

We used Raman micro-spectroscopy technique to analyze the molecular changes associated with oral squamous cell carcinoma (SCC) cells in the form of frozen tissue. Previously, Raman micro-spectroscopy technique on human tissue was mainly based on spectral analysis, but we worked on imaging of molecular structure. In this study, we evaluated the distribution of four components at the cell level (about 10 μm) to describe the changes in protein and molecular structures of protein belonging to malignant tissue. We analyzed ten oral SCC samples of five patients without special pretreatments of the use of formaldehyde. We obtained cell level images of the oral SCC cells at various components (peak at 935 cm−1: proline and valine, 1004 cm−1: phenylalanine, 1223 cm−1: nucleic acids, and 1650 cm−1: amide I). These mapping images of SCC cells showed the distribution of nucleic acids in the nuclear areas, meanwhile, proline and valine, phenylalanine, and amide I were detected in the cytoplasm areas of the SCC cells. Furthermore, the peak of amide I in the cancer area shifts to the higher wavenumber side, which indicates the α-helix component may decrease in its relative amounts of protein in the β-sheet or random coil conformation. Imaging of SCC cells with Raman micro-spectroscopy technique indicated that such a new observation of cancer cells is useful for analyzing the detailed distribution of various molecular conformation within SCC cells.

The dynamics of a laser-induced cavitation bubble generated in the middle of two parallel horizontal rigid walls which are closed at one end with a vertical rigid wall is investigated experimentally using high-speed photography with 100,000 frames s−1. To gain a better understanding of the physical processes that underlie the bubble motion, numerical simulations are conducted by using a boundary element method with an incompressible formulation. We found a complex jetting behaviour which depends strongly on the relative size of the bubble with respect to the distance between the parallel walls and the initial location of the bubble from the vertical rigid wall. When the bubble is generated far from the vertical rigid wall, a radial jet is formed during bubble collapse leading, in some conditions, to bubble splitting. A bubble generated close to the vertical rigid wall develops a planar jet during its collapse phase, which is directed towards the vertical rigid wall. In the transition region, both a radial and a planar jet are generated. When the bubble diameter at its maximum expansion is much smaller than the distance between the parallel rigid walls, both the penetration of the planar jet on the opposite bubble surface and the formation of the secondary cavitation structure were observed during bubble oscillation. The height of the planar jet increases with increasing the bubble size with respect to the distance between the parallel rigid walls. The jet velocity decreases with increasing the relative bubble size with respect to the distance between the horizontal walls and decreasing the initial location of the bubble from the vertical wall. The complex jetting behaviour is attributed to a difference between the strength of the pressure gradients acting on the bubble motion during its collapse phase.

The motion of mono-dispersed spherical bubbles rising along an inclined flat wall is investigated experimentally. An inclination angle of the flat wall is changed to control the bubble Reynolds number set to be 100. As an experimental condition, the boundary condition on the bubble surface (free-slip and no-slip conditions) is controlled, and its effect on the motion of the bubbles has been analyzed. MgSO4 solution and Triton X-100 solution are used to achieve free-slip and no-slip bubble surfaces, respectively. Bubble coalescences are almost inhibited by using these additives. The bubbles tend to be horizontally arranged in lines and such arrangements pile up to be remarkable bubble clusters. The radial pair distribution function and the conditional average of the relative velocity of two bubbles are calculated to evaluate the spatial distribution and bubble–bubble interaction quantitatively. The results show that the tandem configuration of bubble pair next to each other frequently appears due to the increment in the rising velocity of the trailing bubble; a horizontally-oriented (side-by-side) configuration is stable compared to a vertically-oriented (tandem) one, which leads to a horizontally arranged bubbles in a single line. A similar tendency for the bubble clustering is confirmed for both free-slip bubbles and no-slip bubbles. However, there are some quantitative differences such as the faster approaching velocity of the trailing bubble in wider wake region of the leading bubble for no-slip bubbles, etc. The bubble cluster velocity as a velocity of highly accumulated bubbles is also defined and evaluated.

The behaviour of a laser-induced cavitation bubble near two perpendicular rigid walls and its dependence on the distance between bubble and walls is investigated experimentally. It was shown by means of high-speed photography with $100\,000~\text{frames}~\text{s}^{-1}$ that an inclined jet is formed during bubble collapse and the bubble migrates in the direction of the jet. At a given position of the bubble with respect to the horizontal wall, the inclination of the jet increases with decreasing distance between the bubble and the second, vertical wall. A bubble generated at equal distances from the walls develops a jet that is directed in their bisection. The penetration of the jet into the opposite bubble surface leads to the formation of an asymmetric toroidal bubble that is perpendicular to the jet direction. At a large distance from the rigid walls, the toroidal bubble collapses in the radial direction, eventually disintegrating into tiny microbubbles. When the bubble is in contact with the horizontal wall at its maximum expansion, the toroidal ring collapses in both radial and toroidal directions, starting from the bubble part opposite to the vertical wall, and the bubble achieves a crescent shape at the moment of second collapse. The bubble oscillation is accompanied by a strong migration along the horizontal wall.

Sialoliths are a common occurrence in salivary glands. Here, we report a case of a giant submandibular gland sialolith in a patient presented with dysphagia as the only symptom. The sialolith measured 24 mm in length and weighed 4.7 g. A preoperative computed tomography scan revealed displacement of the hyoid bone at rest position on the non-affected side. The right submandibular gland that contained the sialolith was extirpated under general anesthesia, following which, the symptoms of dysphagia were resolved. However, no improvement in displacement was noted postoperatively. Dysphagia may have occurred due to disturbances in hyoid bone movements caused by the large sialolith. The absence of any changes in the position of the displaced bone at rest after removal of the sialolith may be attributed to the fixation of the bone in the underlying tissues due to the long-term existence of the sialolith.

Understanding of the cavitation inception and the following bubble cloud formation by the high intensity focused ultrasound (HIFU) is important in both physical and medical aspects. The backscattering from a primary cavitation is a key of these phenomena. In the present study, the cavitation inception pressure and the mechanism of bubble cloud formation by the backscattering of HIFU are investigated experimentally and numerically. In the experiment, a laser-induced bubble generated near the HIFU focus is utilized as a primary cavitation, and the optical observation with a high-speed video camera and the pressure measurement with a fiber optic prove hydrophone (FOPH) are conducted simultaneously. It is shown that the bubble cloud grows with forming multiple layers of tiny bubbles, and finally becomes a cone-shaped bubble cloud. The pressure distribution by the backscattering from bubbles simulated with the ghost fluid method reveals the forming process of bubble clouds in the experiment. The pressure measurement shows that the measured pressure has a stronger negative pressure value by the superposition of the incident wave and the backscattered wave from bubble interfaces. The pressure before the cavitation inception occurring at the tip of the cone-shaped bubble cloud is found to be around -26 MPa.Understanding of the cavitation inception and the following bubble cloud formation by the high intensity focused ultrasound (HIFU) is important in both physical and medical aspects. The backscattering from a primary cavitation is a key of these phenomena. In the present study, the cavitation inception pressure and the mechanism of bubble cloud formation by the backscattering of HIFU are investigated experimentally and numerically. In the experiment, a laser-induced bubble generated near the HIFU focus is utilized as a primary cavitation, and the optical observation with a high-speed video camera and the pressure measurement with a fiber optic prove hydrophone (FOPH) are conducted simultaneously. It is shown that the bubble cloud grows with forming multiple layers of tiny bubbles, and finally becomes a cone-shaped bubble cloud. The pressure distribution by the backscattering from bubbles simulated with the ghost fluid method reveals the forming process of bubble clouds in the experiment. The pressure measu...

In this work, we investigate the shock wave–inertial vapor bubble interactions by taking the nonequilibrium phase transition at the interface, fluid compressibility, and axisymmetric bubble deformations including jet penetration into account. We use the level set method (Sussman et al., 1994) and the ghost fluid method (Fedkiw et al., 1999), which were improved so as to consider the nonequilibrium phase transition (Jinbo & Takahira, 2012). The numerical treatments for heat and mass fluxes through interfaces due to the phase transition are implemented, satisfying the conservation laws of mass, momentum, and energy at the interface and preventing the interface from becoming diffused. The influence of surface tension is also considered in the method. The improved method is applied to the shock–bubble interaction under the experimental conditions by Sankin et al. (2005). The pressure waveform of the incident shock wave is comprised of a leading compressive wave with a peak pressure of 39 MPa and a pulse duration of around 1 μs, followed by a trailing tensile wave of −8 MPa in peak pressure with a pulse duration of around 2 μs which is determined from the experiment. The liquid-jet formation and the generation of shock waves from the collapsing nonspherical bubble are simulated successfully by taking the nonequilibrium phase transition and surface tension into account. The validity of the simulation is shown by comparing the numerical results (e.g. the intensity of the shock wave generated by the bubble collapse and displacement of the bubble centroid) with those obtained from the experiments (Sankin et al., 2005; Klaseboer et al., 2007). We investigate the effects of the phase of bubble oscillations when the incident shock wave impinges on the spherically-shrinking bubble, on the shock wave radiated from the bubble collapse. It is also shown that when the nonequilibrium phase transition at the interface of nonspherically collapsing bubbles is considered, the minimum bubble radius and the maximum space-averaged pressure value inside the bubble reached during its collapse decreases and increases, respectively, compared with those in the case without the phase transition.

The present study is concerned with the cavitation inception and the growth of a cavitation bubble cloud by the backscattering of focused ultrasound from a laser-induced bubble. The cavitation inception close to the interface of a laser-induced bubble has been observed by a high-speed video camera with the frame rate of up to 1.25 Mfps, and its location and the successive cavitation cloud growth are discussed for various ultrasound conditions. It is shown that the normalized distance between the cavitation inception location and the bubble interface by the wavelength of ultrasound is an increasing function of η = t0 / ts where the time t0 is the characteristic time for cavitation bubble collapse and the time ts the period of ultrasound. Also the magnitude of the dimensionless distance is about 0.05-0.3 times of the wavelength of ultrasound, and the positive pressure threshold of ultrasound for a cavitation inception is about 35 MPa. It is also shown that the cavitation bubble cloud by the backscattering of the incident ultrasound grows conically along the propagation axis of the focused ultrasound. As the incident focused ultrasound pressure at the focus becomes stronger or the duration of the focused ultrasound becomes longer, the cavitation bubble cloud grows larger. However, even though the ultrasound duration becomes longer, this growth ends up and reaches a limited value when the cavitation bubble cloud grows out of the focal region of the focused ultrasound.

Ultra high-speed micron-resolution particle tracking velocimetry (UH-μPTV) technique has been developed to advance the novel method to generate microbubbles using a T-shaped microchannel. The method can produce microbubbles with 10-μm order diameter by applying the gas pressure of several tens of kilopascal and injecting the deionized water with the speed of a few meters per second. The conventional μPTV was restricted to the velocity measurement of the order of millimeter per second due to a few kilohertz frame rate CMOS camera. On the other hand, the present UH-μPTV technique achieves to measure the liquid velocity of the order of meter per second by combining the bright-field microscopy and the ultra high-speed camera with 1 MHz frame rate. For improving the spatial resolution, the phase sampling method has been introduced and results in 10 velocity vectors in 20 μm × 20 μm area. The validation of the velocity measurement using UH-μPTV has been conducted through the comparison with the theoretical solution, and it has been shown that the proposed technique can capture the velocity vector field higher than 1 m/s. Furthermore, from the 1-μs time-series imaging, the microbubble generation process has been classified into two stages: the intruding stage and the growing stage. It has been shown that the bubble diameter becomes smaller by increasing the liquid velocity with reducing the period of the growing stage. In addition, from the velocity-vector maps, the normal components of velocities to the gas–liquid interface in the intruding stage are compared with those in the growing stage, and it has been observed that the velocity amplitudes in the growing stage are much larger than those in the intruding stage. This fact suggests that the high-speed liquid flow normal to the gas–liquid interface plays an important role in microbubble generation process.

The formation of a cavitation bubble cloud due to the high intensity focused ultrasound (HIFU) with a laser-induced bubble near the focus has been investigated experimentally. The backscattering of HIFU having the nonlinear pressure waveform from the interface of a laser-induced bubble forms stronger tensile pressure field near the interface, which leads to the cavitation inception and the following cavitation bubble cloud formation. In the present study, the optical observation by the high-speed video camera with a frame rate up to 1.25 Mfps and the pressure measurement by the fiber-optic prove hydrophone (FOPH) are carried out simultaneously to analyse the cavitation bubble cloud formation. The pressure field with the stronger negative pressure is formed by the backscattering of HIFU, and the minimum negative pressure is measured at a distance of 0.3 times of the wavelength of ultrasound from the interface of a laser-induced bubble. It is also found that the cavitation bubble cloud grows conically along with the propagation axis of the incident wave. The cloud is composed of some layers of small bubbles and these layers appear stepwise in time. Thus, the growth of the cavitation bubble cloud is accompanied by multiple sudden increments of bubbles on the axial dimension leading to the multilayer formation of cavitation bubbles. The measurement by the FOPH reveals that when a laser-induced bubble exists, a stronger negative pressure than the incident wave is measured due to the backscattering of the incident ultrasound from the bubble interface. Negative peaks in the pressure waveform have a long-term fluctuation, and are correlated with the growth of the bubble cloud. The minimum negative pressure measured in the vicinity of the borderline for the growth of the bubble cloud is considered to be the pressure threshold of the cavitation inception, and is −24 MPa in the present experiment.

本稿では，意思決定において多角的な視点からのデータ分析と，相補 / 非相補的な意思決定方略に対応できる，関連バランス制御機能を備えたキーワードマップを提案する．キーワードマップは，オブジェクト（キーワード）間の関連度に応じて，キーワードを２次元平面上に配置する汎用的な情報可視化システムであり，ユーザ意図を強調するマップの編集機能が備わっている．しかしながら，従来システムは，キーワード間の関連性に複数の属性が含まれている場合でも，関連度はそれらを包含し１種類の属性とみなすため，１つの視点からしかデータ分析できない．そのため意思決定支援へ応用する場合に，データを様々な視点から分析できない問題と，任意の属性を重要視するなどの意思決定方略を支援できない問題がある．本稿では，関連度を複数の重み付き属性値の線形結合と再定義し，ユーザがそれらの重みを制御することが可能な関連バランス調整機能をキーワードマップに導入する．属性の重み付け設定に応じたユーザのマップの解釈の仕方の違いを検証する被験者実験と，意思決定方略に応じた提案システムの使われ方の違いを検証する被験者実験を行った結果，提案システムは多角的な視点をユーザに提供し，また相補 / 非相補的な意思決定方略に対応可能であることを示す．

Sialoliths, a cause of the salivary gland infection, are reported to be composed of inorganic and organic substances. However, the precise mechanism of sialolith formation remains unclear. The purpose of this report is to elucidate this mechanism by analyzing the precise distribution of phosphate (an inorganic substance) and amide III (an organic substance) in sialoliths by using Raman microspectroscopy. Sialoliths from the submandibular gland duct were analyzed by this form of observation and by a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectroscope (EDX). In Raman microspectroscopy we analyzed the spectral peak of the phosphate (PO4 3− ) symmetric stretching vibrational mode (u1) at 960 cm −1 and that of amide III at 1265 cm −1 to demonstrate the mapping of an image of these elements showing a semiquantitative distribution of phosphate and amide III in the sialoliths. It was found that phosphate and amide III were concentrated at the center of the sialoliths, and the phosphate distribution in the sialoliths showed concentric laminations. These results indicated the possibility that the sialoliths originated from a nidus of organic materials and progressively grew by the deposition of layers of organic and inorganic materials. Copyright  2008 John Wiley & Sons, Ltd.

We employed Raman microspectroscopy to measure the Raman spectra of phosphate in sound and carious tooth substance. The peak intensity at 960 cm−1 of the phosphate (PO43−) symmetric stretching vibrational mode (υ1) in sound enamel was stronger than that of sound dentin, which indicated that sound enamel contained more phosphate than sound dentin. Furthermore, the element analysis of phosphate in sound teeth substance, measured using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectroscope (EDX), gave similar results to those of the Raman measurement. In addition, the border between sound enamel and dentin was clearly demonstrated by mapping the image of the Raman spectrum of phosphate. The mapping image of phosphate in the carious enamel region revealed a heterogeneous low Raman spectrum intensity of phosphate in the area surrounding carious enamel; this finding indicates that phosphate had dissolved from the tooth substance in such areas. In contrast with the decrease in the Raman spectrum intensity of phosphate, the intensity of amide I increased mainly in the low-phosphate area. Although it remains very difficult to clinically identify the accurate border between sound and carious tooth substance, this distinction may be enabled by using the Raman spectrum of carious tooth substance. Copyright © 2008 John Wiley & Sons, Ltd.

A rare case of simple bone cyst in the mandibular condyle of a 33-year-old woman is reported. The condition was difficult to diagnose because the cyst was accompanied by severe osteoarthritis. T1-weighted magnetic resonance (MR) images revealed a cystic lesion with intermediate signal intensity within the condylar head and an irregular margin with intermediate signal intensity on the superior surface of the condyle. The patient was treated by high condylectomy, discectomy and reconstruction by sagittal split ramus osteotomy. Histopathological examination showed a simple bone cyst in the condylar head and erosion of the anterior articular surface due to degenerative changes.

The interactions between a microbubble and ultrasound in an elastic tube are investigated to understand the bubble dynamics in a blood vessel. The tube wall is modeled with a spring-mass system. A simple bubble model for investigating bubble oscillations in the tube is introduced and is combined with the spring-mass system of the tube: the bubble is represented by a point source for the bubble volume oscillation and a dipole for the translational motion. The natural frequencies of the system are derived by linearizing the governing equations. The influences of an elastic tube on a bubble are mainly discussed by using eigenvalue analysis in the present work. It is shown that the resonance frequency of a bubble in the tube decreases with increasing the mass of the tube wall. The effects of the tube length and the initial location of a bubble are also investigated. The results show that although the resonance frequency decreases monotonically with increase in the tube length when the wall mass is large, it is not changed when the mass is sufficiently small. It is also shown that the resonance frequency is decreased with decreasing the distance between the bubble centroid and the tube wall when the mass is large. However, when the mass is small enough, it is increased with decreasing the distance. We also investigate the influence of the characteristics of an elastic tube on nonlinear oscillations of a bubble. The condition that the harmonic oscillation is enhanced is discussed.Copyright © 2015 by JSME