A sonochemical reaction depends on the kind of gas dissolved in the reaction field, namely, in the reactant solution. In former paper, we reported an improvement of sono oxidation rate of KI solution in a CO₂-Ar system. To study the effect of CO₂ existing under alkaline condition, sonication was performed in a NaHCO₃-KI solution. Sonication was carried out in a system with a 200 kHz transducer (KAIJO, QUAVA mini QR003, 50 W). The reactants comprised several concentrations of KI aqueou s solution. Before sonication, the reactor was filled with Ar gas and a certain amount of NaHCO₃ was dosed to the solution. Sono-oxidation rate was evaluated by KI dosimetry (λ_max = 355 nm, JASCO V730). In the cases of no addition of NaHCO₃ a weak absorbance, namely, a slow rate of sono oxidation was observed. On the other hand, in spite of the alkaline solution, the system with dissolved NaHCO₃ had the highe st absorbance We considered sono oxidation activity would be enhanced by CO₂ produced from NaHCO₃. However, effect of KI concentration on sono-oxidation rate in NaHCO₃-KI system was different from that in CO₂-Ar system.

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In this study, 430 kHz of ultrasonication which can simultaneously cause pyrolysis by chemical effect and atomization by physical effect was selected and applied to highly effective decomposition of organic pollutants in water. In order to investigate the influence of physical properties on the degradation rate, three different aldehydes, formaldehyde, acetaldehyde and benzaldehyde, were chosen as model substances. As a result, removal ratio of benzaldehyde reached 100% after 120 min by only US irradiation whereas the removal ratios of formaldehyde and acetaldehyde only reached 21.1%, 53.0%, respectively. On the other hand, in the case of combining the UV irradiation and the ultrasonic atomization, formaldehyde and acetaldehyde with hydrophilic property were effectively decomposed on the mist surface in gas phase. By this combined use of US and UV irradiation, it was confirmed that US irradiation acts on effective degradation of hydrophobic substances and UV irradiation promoted the decomposition and the mineralization of hydrophilic substances including degradation products formed from hydrophobic substances.

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A novel wastewater treatment process, acoustic cavitation assisted plasma (ACAP) is proposed in this study aiming at expanding the treatable range of water pollutants. In this process, the role of acoustic cavitation is not only to provide generation of chemically active radicals, but also to ensure conditions for stable plasma generation in wastewater and, thus, to extend the treatable range of water pollutants. Rhodamine B (RhB) was used as a model pollutant in experiments examining effects of electrical conductivity on the RhB degradation efficiency. A maximum degradation efficiency was observed in ACAP processes. Acoustic cavitation assists a transition of plasma discharge from ineffective streamer type to more effective spark type that further contributes to the improvement of the treatment performance.

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To develop a simple technique for separating submicron particles, aqueous suspensions of silica particle mixtures were ultrasonically atomized and the behavior of particle separation was examined under various conditions. Ultrasonic atomization brought silica particles of a specific size, 100 nm into fog from a suspension containing a mixture of silica particle of 100 and 300 nm. Most of the fog was successfully recovered with liquid nitrogen coldtrap, and the recovery percent of particles reached more than 90 %. In the recovered suspension, enrichment of 100 nm particle was observed and dilution of 300 nm was attained. The result indicated selective transfer of 100 nm silica particle into the fog and rejection of 300 nm silica particle. Interestingly, the separation disappeared after degassing the feedstock. Also, when the gas dissolving in the suspension was changed from air to argon, the rejection of 300 nm silica particle was decreased. The separation, selective transfer of silica particle depending on the size was significantly affected by the amount of dissolving gas as well as type of the gas. The result clearly indicates a strong influence of cavitation on the separation mechanism.

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Noble metal (gold; Au, silver; Ag, copper; Cu, palladium; Pd and platinum; Pt) nanoparticles were deposited on activated carbon in aqueous media by irradiation of high-frequency ultrasound in the absence of any additional reductants (e.g., sodium borohydride). The diameter of nanoparticles deposited on the activated carbon was controlled by the concentration of metal salt in the aqueous metal salt solution. Furthermore, we revealed that the ethylene gas in air was removed by Ag, Pd and Pt nanoparticles-deposited activated carbon while the ethylene gas in air was not removed by Au, and Cu nanoparticles-deposited activated carbon and non-deposited activated carbon.

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Gold nanoparticles have electronic, magnetic and optical characteristics depending on their sizes and shapes. Ultrasonic irradiation to an aqueous solution of gold salt is able to synthesize gold nanoparticles without surfactants and reducers. Previous our study, the diameter of gold nanoparticles decreased and diameter distribution became narrow by the addition of ultrafine bubbles (UFB). In this study, we investigated effect of gas kind in UFB and pulsed ultrasound irradiation. The mean diameter of particles with Air-, Ar-, N₂-, and O₂-UFB are 24.7, 49.4, 73.0, and 43.1 nm, respectively. The standard deviation of particles with Air-, Ar-, N₂-, and O₂-UFB are 8.0, 13.5, 21.2, and 7.7 nm. This is because maximum temperature of cavitation for air is high, and many kinds of reducers (such as, nitrous acid and hydrogen peroxide) are generated since air contain Ar, N₂ and O₂. Compared with continuous wave, it is clear that pulse ultrasound reduces particle size.

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It has been experimentally reported that surface tension is reduced by the presence of ultrafine bubbles (bulk nanobubbles) by about 14 % [A.Ushida et al., J.Surfact.Deterg. 15, 695 (2012)]. In the experiment of Ushida et al., surface tension was measured by the liquid height from a ring to the liquid surface when the liquid film ruptures using the du Nouy ring method. According to the dynamic equilibrium model, an ultrafine bubble is stabilized by partly covered with hydrophobic impurities. In the present study, it is theoretically shown that ultrafine bubbles are concentrated at the liquid surface due to the hydrophobic impurities partly covering the bubbles. It is suggested that rupture of liquid film is accelerated by the presence of the bubbles at the liquid surface. It may be the reason for the reduction of surface tension by the presence of ultrafine bubbles in the du Nouy ring method.

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The ultrasonic cavitating bubble oscillations were numerically investigated through full 3D computational fluid dynamics. The bubble compression was numerically expressed by the compressible fluid dynamics. The Volume of Fluid (VOF) method was adopted for the bubble-liquid multiphase flow. The frequency of pressure oscillation is 20 kHz, and the oscillation amplitudes of pressure wave are 0.5 and 0.9 atm., respectively.
The numerical results show that the bubble oscillates almost linearly at the 0.5 atm. amplitude. However, the oscillations of bubble become non-linear at the 0.9 atm. amplitude. The calculated results correspond well to the results obtained by using the Keller and Rayleigh-Plesset equations.

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The degradation of poly-N-isopropylacrylamide (PNIPAM) was carried out using ultrasonic irradiation in a mixed solvent of water and ethanol. The effects of ultrasonic intensity and reaction temperature on polymer degradation rate were investigated. The starting PNIPAM with high molecular weight was synthesized in water by using chemical initiator, ammonium peroxodisulfate, and accelerator, N,N,N',N'-tetramethylethylenediamine. The obtained polymer was dissolved in 60 vol% ethanol-water mixed solvent, and then ultrasound was irradiated to the solution. Under the ultrasonic irradiation, the number average molecular weight abruptly decreased in the early stage, and then gradually reached a limiting molecular weight. The higher the ultrasonic power intensity, the faster the polymer degradation rate. On the other hand, the higher the reaction temperature, the slower the polymer degradation rate. Since the vapor pressure of the solvent is higher at higher reaction temperature, the more vapor enters the cavitation bubble so that cushioning the bubble collapse and reducing the shear force result in the decrement of the polymer degradation rate.

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As compared with other stimuli such as light and heat, the advantages of US are non-invasiveness and non-ionizing radiation. For drug release applications, drug release control by weak power US is preferable. In the present study, by using nicotine loaded cellulose hydrogels, effect of the US and mechanical strain was investigated on the loaded nicotine for releasing with the triggers. Nicotine loaded cellulose hydrogel was prepared from cotton using phase-inversion process. Then, outernal US or mechanical strain trigger was exposed. The release nicotine efficiencies in the US system were higher than that of the no US system. When 1% strain was exposed during the US operation, the US stimulus effect on the nicotine release was highly enhanced. For example the released nicotine concentration increased to 19 μg /mL when 90 min was operated, indicating twice relative to only US irradiation. This indicated that the combination of US and mechanical strain could well broke the cellulose hydrogel matrix.

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Recently, we have reported the occurrence of DNA double-strand breaks in different human cell lines which were exposed to ultrasound in vitro with some insight into the subsequent DNA damage response and repair pathways. Although sonochemistry is important to consider when DNA in solution is exposed to ultrasound, sonomechanical effects are critical if DNA exists in chromatin inside the cells. Since ultrasound has been utilized in medical diagnosis and therapy, ultrasound-induced effects on the nucleus and genomic DNA will be much important. Here, historical data on DNA damage induced by ultrasound are presented and the implications from the viewpoint of sonochemistry will be discussed.

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The dynamic behavior of a damped vibration system containing thixotropic material was experimentally investigated. We constructed a device to evaluate vibration and sound in a thin plate structure with a damper containing thixotropic materials. The tests indicated that the damped system containing thixotropic materials had good vibration characteristics. We have performed basic experiments for the purpose of applying onomatopoeia to engineering problems. In these experiments, test subjects were made to perform lifting actions while listening to onomatopoeic utterances.
We investigated how the lifting force is affected depending on whether or not emotion is expressed when uttering the onomatopoeia.

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Application of Au nanoparticles to various fields has been studied actively because of its unique characteristics different from those of bulk. However, the formation mechanism of Au nanoparticles is still unclear. If the formation mechanism of Au nanoparticles was clarified in more details and the size of Au nanoparticles was controlled more precisely, the application range of Au nanoparticles should be expanded dramatically. The reducing radicals formed in the sonolysis of solution containing Au(III) and 1-propanol, result in the formation of Au seed particles via reduction of Au(III). This sonochemical reduction method is quite different from other methods. The synthesis of Au nanoparticle is possible without using any colloid stabilizers. In this study, Au nanoparticles were synthesized by sonochemical reduction method. The reduction behavior of Au(III) and particle diameter change of synthesized Au nanoparticles were measured by ultraviolet-visible (UV-vis) spectrophotometer to clarify the formation mechanism of Au nanoparticles.

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Nanographenes are synthesized from alcohols by in-liquid plasma with ultrahigh rate. When carbon number in an alcohol molecule is high, synthesis rates increase but the crystalline nature of nanographene decreases. To eliminate trade-off between synthesis rates and crystal nature of nanographenes, ultrasound was irradiated to alcohols under in-liquid plasma. Samples were ethanol, 2-propanol, and 1-hexanol. Ultrasonic frequency was 500 kHz and power was 7.5 W. After nanographene synthesis, suspended solids were filtered using 0.45-μm-pore-size filters and treated with 30% hydrogen peroxide solution. Treated nanographene was analyzed by Raman scattering spectroscopy. Sample color was changed from transparent to black by in-liquid plasma and black area spread under ultrasound. The synthesis rate for all alcohol increased by ultrasound. In the case of 1-hexanol, crystal nature of nanographene was improved due to ultrasonic cavitation.

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Nanoparticle alloy which has different redox potential is impossible to synthesize by conventional method, liquid phase reduction. In this study, physical ultrasound effect was focused for synthesis of nanoparticle alloy, and ultrasound effect at the solid-liquid system was investigated.
300 ml methanol and 10.00 g Sn-Bi solder powder were added to 1000 ml beaker and irradiate by ultrasound for 6-24 h (ultrasound condition:1200 W, 28 KHz:75 KHz=50 %:50 %). After ultrasound irradiation, solution was separated the supernatant and the residue by decantation. By ultrasound irradiation, corrosion of starting material surface were observed and it increased with long-time irradiation. It is considered that hotspot and micro jet were occurred by ultrasound irradiation in solid-liquid system, and it promoted corrosion of Sn-Bi particle surface. It found that corroded Sn-Bi by ultrasound effect was nano-size, it was dispersed in methanol as a result.

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Lithium-ion battery has high discharge voltage, high capacity and high energy density. Therefore, it is used for electrical power supply for electro vehicles (EVs). LiFePO₄ (LFP) and iNi_0.5Mn_1.5O₄ (LNMO) have attracted attention as alternate material of LiCoO₂ which is used as a main cathode material. However, electronical conductivity of these materials is lower than that of LiCoO₂. The cathode material of low electronical conductivity is difficult to charge and discharge at high current density. To overcome this drawback, coating the surface of cathode material with an electronically conductive material, such carbon, is desired. In this study, we chose Au NPs as an electrically conductive material, and deposited Au NPs on the carbon layer of surface of carbon coated LNMO (LNMO/C). Amounts of coated carbon and deposited Au NPs for LNMO were 0.54% and 0.89% by weight respectively. The average size of Au NPs deposited on LNMO/C was 4–10 nm. Discharge capacity of LNMO/C·Au was higher than that of LNMO/C at each C rate.

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When ultrasonic waves are irradiated to liquid, micro bubbles which called cavitation bubbles are formed. When this bubble collapses adiabatically, the temperature of bubbles instantaneously reaches more than several thousand degrees and several hundred atmospheres. This unique field is expected to be used for decomposition of organic compounds and synthesis of metal nanoparticles. Although the temperature of bubbles is one of the most important parameters to control chemical reactions, the temperature of bubbles formed under air atmosphere has hardly been investigated so far. Therefore, in this study, the temperature of bubbles was estimated under various mixed atmospheres of nitrogen and oxygen. From experiments, the temperature of bubbles was estimated to be lower under nitrogen atmosphere than that under oxygen atmosphere.

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In this presentation, we report influences of concentration of KI and frequency on the rate of sono-oxidation in a CO₂-Ar atmosphere. Sonication was performed using an ultrasonic irradiator (Shinka, 200 kHz, 100 W and Honda, 2.4 MHz, 15 W) at 25 ℃. The rate of sono-oxidation was evaluated by KI dosimetry using UV-Vis spectrophotometer (JASCO V-650, measuring wavelength is 355 nm). The rate difference between with and without CO₂ in an Ar atmosphere was indicated as Improvement index. The index means the ratio of absorbance in a CO₂-Ar atmosphere to that in Ar atmosphere. Sono-oxidation rate of NaI solution increased by introduction of CO₂ as same as KI. The Improvement index increased with decreasing KI concentration not only at 200 kHz but also at 2.4 MHz.

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Intensification of sonochemical reaction is necessary to put sonochemical process into industrial application. To evaluate the rate of sonochemical reaction, we choose sonochemical efficiency because this method has high quantitative performance, do not use hazardous chemical material, and is simple to operate. In this study, factor that influence of sonochemical efficiency is investigated. A Langevin and disc type transducers were used at 129 and 488 kHz, respectively. A circulating water bath was connected to the annular section of the vessel to maintain the sample temperature at 298 ± 1 K. Sample was aqueous solution of 0.1 M potassium iodide and volume was 100 ml. At 488 kHz, sonochemical efficiency increased with ultrasonic power until 5 W after that becomes constant. This is because sonochemical reaction fields are not enough to spread in the reactor. On the other hand, at 129 kHz, as ultrasonic power becomes higher, sonochemical efficiency increased until 1 W after that decreased. The sonochemical efficiency at 1 W is 1.5 times higher than that at 500 kHz.

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Nano/micro-structured conducting polymeric materials are of great importance for the significant range of applications such as energy storage and sensors.
In this work, we wish to report an electropolymerization in the acoustically prepared foam to obtain polyaniline (PANI) film with microporous structure on an electrode surface. In this process, ultrasonication was used to foam the electrolyte solution containing surfactant and the foamy electrolyte was employed as soft template for the polymer growth. SEM analysis revealed that the obtained PANI film possessed a porous structure composed of a number of micropores. In addition, it was also found that the porous PANI film exhibited a faster electrochemical response compared to that of the ordinary flat PANI film. Since no hard templates and cumbersome procedures are require for this synthetic method, it is advantageous in respect of environmental and economic sustainability.

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Among the nanoparticles, hollow particles are particularly attractive materials due to their unique structure. In this work, we have successfully carried out size-controlled synthesis of polymer hollow nanoparticles using tandem acoustic emulsification. In this process, the acoustic emulsification is used to produce emulsion droplets of perfluoromethylcyclohexane (PFMCH) which are used as templates for the following polymer capsule synthesis. Since the size of the droplets can be changed by the number of steps in tandem acoustic emulsification, the capsules size can also be controlled. TEM-EDS analysis revealed that the core of the obtained polymer capsules filled with PFMCH. Furthermore, the core solvent could be removed by heating treatment, and consequently hollow nanoparticles are obtained. In addition, we confirmed that the obtained polymer capsules could be filed with solutions by penetration through their shell.

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Ultrasonically assisted polymerization of NIPAM (N-Isopropylacrylamide) in water and water-ethanol mixture was carried out in the ethanol concentration range of 0-80 v/v% at 20 kHz and 500 kHz, and the effects of solvent composition and frequency on polymer yield, weight average molecular weight (Mw), polydispersity(PD) were investigated. When ultrasonically assisted polymerization of NIPAM was performed in water-ethanol in the ethanol concentration range of 0-80 v/v% at 20 kHz and 14 W, the highest polymerization rate of NIPAM and the lowest PD were obtained for water-2.0 v/v% ethanol. For ultrasonically assisted polymerization of NIPAM in water-2.0 v/v% ethanol at 8.5 W, the polymerization rate of NIPAM at 20 kHz was higher than that at 500 kHz. To the contrary, for water-60 v/v% ethanol, the higher polymerization rate of NIPAM was obtained at 500 kHz compared to that at 20 kHz.

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When ultrasound is irradiated into the liquid, positive and negative pressure are alternately applied to the gas molecules in the liquid, and as the bubbles repeatedly compress and expand to about several μm to 100 μm, at the limit of high pressure during compression. Micro bubbles bursts, resulting in”shock wave” and ”local high temperature and high pressure field”. This is called ultrasonic cavitation. At this time, ”physical action by shock wave” and ”chemical action by OH radical generated by thermal decomposition of water at local high temperature and high pressure field” occur. On the other hand, in recent years, ultrafine bubbles have been paid attention which are bubbles of 10 to 100 nm size. Unlike microbubbles of 1 μm size or more, this ”nanobubble” exists stably in water. We set up a working hypothesis that this ultrafine bubble will be the core of ultrasound cavitation. We hypothesize that combination of ultrafine bubbles and ultrasound irradiation can synergistically increase ”physical effect by shock wave” and ”chemical effect by OH radical generated by thermal decomposition of water in a local high temperature and high pressure field” upon ultrasonic cavitation. The combination of ultrafine bubble and ultrasound synergistically improved the generation of OH radicals and the inactication of E. coli.

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In this study, for the evaluation of ultrafine bubbles (UFB) which is important in fine bubble research, a method to use hydroxyl (OH) radicals or luminescence phenomenon (sonoluminescence) generated by the collapse of UFB when applying ultrasonic wave to UFB as an indicator was verified. Electron spin resonance method and potassium iodide (KI) method were used for the evaluation of OH radicals, and photomultiplier tubes were used for the evaluation by sonoluminescence. OH radicals by the collapse of UFB were observed from the result of OH radical measurement by ESR. And, even in the KI method which is a simple OH radical evaluation, it was shown that the same evaluation can be made from the difference in absorbance when ozone is used for the inclusion gas. On the other hand, in the sonoluminescence measurement, it was confirmed that the luminescence intensity in water to which inorganic particles of the same amount as that of UFB was added was smaller than in the case of UFB water.

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In this study, based on the report that the photocatalyst was driven by ultrasonic irradiation under dark conditions, the decomposition ratios of two types of aldehydes with different physical properties, such as benzaldehyde and formaldehyde, were evaluated using various visible-light-driven photocatalysts under ultrasonic irradiation condition. From the results of this experiment, the removal ratio of formaldehyde using US+Pd/WO₃ which is visible-light-driven photocatalyst increased approximately 7 % over that of using TiO₂. This reason is that Pd/WO₃ can effectively utilize SL emission compared to TiO₂. In addition, sono-photocatalytic degradation using Pd/WO₃ had the highest removal ratio for both formaldehyde and benzaldehyde meaning that the active species generated from Pd/WO₃ were the largest. Also, it was confirmed that the performance of Pd as a promoter was higher than that of Cu. From these results, it was suggested that the relationship between the absorption wavelength of the catalyst and the SL wavelength is important in the sono-photocatalytic degradation utilizing SL emission.

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Since sodium percarbonate (SPC) contains three molecules of hydrogen peroxide (H₂O₂), we used it as a source of OH radicals in this study. Decomposition experiments of toluene gas on SPC were performed using UV irradiation and ultrasonication. Experimental results showed that the toluene concentration decreased slightly by the reaction with SPC under UV irradiation. On the other hand, when the ultrasonication was applied to the SPC, the toluene concentration decreased faster and reached about 30% of removal ratio after 120 minutes. It was suggested that ultrasonic irradiation was transmitted inside the SPC solid and its energy contributed to the generation and dissolution of H₂O₂. By using UV irradiation and ultrasonication at a constant temperature condition of 80℃, the highest removal ratio of about 70% after 120 min was obtained. These results suggested that effective use of ultrasonication could achieve effective VOC gas decomposition on SPC.

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Ionic surfactant accumnlates at the gas-liquid interface of cavity because of their amphipathicity and extremely low vapor pressure, it is difficult to diffuse into the interior of the gas phase region of cavity. On the basis of this property, the sonolysis of the ionic surfactant supposed to be occurred at interfacial region of cavity. In this research, ionic surfactants with different carbon chain lengths were ultrasonically decomposed and the decomposition rate and the amount of gaseous hydrocarbons produced were compared in order to elucidate the molecular behavior and reaction in the interface region of cavity. The effect of the surface potential of cavity on the sonolysis of surfactants was also investigated.

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Degradation of many kinds of environmental pollutants such as dyes, malodorous substances, PCB and environmental hormones using ultrasonic cavitation bubble's high temperature and high pressure chemical reaction field has been reported. However, the reaction mechanism and the predominant factors of the reactivity have not been completely clarified. In this study, sonolysis of aqueous solutions of two kinds of azo dyes, methyl orange and methyl red was investigated. The degradation products and their concentration change with time were analyzed using high performance liquid chromatograph with photodiode array detector. The decomposition reaction mechanism and its dominant factors were examined.

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By using an ultrasonic atomization and AOP techniques, VOC gas can be decomposed and mineralized effectively. However, in this flow system, there was a problem that the mist leaked out of the reactor. Therefore, we investigated the degradation of toluene gas which is typical VOC gas using AOP, ultrasonic mist and a porous poly tetra fluoro ethylene (PTFE) tube. The PTFE tube was installed as a flow path in the AOP reactor by the UV₂₅₄/H₂O₂ method with ultrasonic mist to prevent the release of secondary particles and ozone to the outlet of the reactor. As a result of the experiment, the removal ratio of 22.0% was obtained under the condition of UV₂₅₄/H₂O₂/mist/PTFE tube. In order to improve the removal rate, UV_254+185 with higher energy was replaced in the reactor. When UV_254+185 was used, removal ratio of toluene reached 83.7% under condition of UV_254+185/mist/PTFE tube. In the case of installing the PTFE tube, the release of secondary generated particles to the outside of the reactor was suppressed. Also, it was confirmed that ozone leakage could be suppressed to about 60%. From these results, it was shown that introduction of ultrasonic mist and PTFE tube can inhibit re-release of degradation products while maintaining sufficient decomposition reaction in the reactor.

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Efficient removal technology of arsenic (As) from polluted soil harvested in Japan is described in the present work by using high power ultrasound (US) washing. The critical experimental parameters including US powers, exposure time and acid/base additives were systematically varied in the US treatment process. In conclusion, high power US treatment was efficient in releasing As from polluted soil in alkali medium.

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CCS (carbon dioxide capture and storage) is a technology of recovering carbon dioxide (CO₂) from exhaust gas such as fired power plant, and storing it in underground. Monoethanolamine (MEA) is widely used as a chemical absorbent in CCS technology. However, it is difficult to desorbed CO₂ from MEA solution without heating at high temperature of 120℃. In this study, we used ultrasound irradiation to desorbed CO₂ from amine solution at low temperature. Furthermore, we focused on the class and dissociation constant (pKa) of amine for increase of CO₂ desorption amount using ultrasound irradiation. As a result, tertiary amine of low pKa value showed the large CO₂ desorption amount using ultrasound irradiation at low temperature.

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A drug delivery system (DDS) helps to suppress damage to a patient's body via targeted therapy. These systems use microcapsules as one of the forms of drug delivery carriers, and ultrasound waves are used to trigger drug release from the capsules. Ultrasonic destruction of capsules has been well documented, and it is generally known that the main factor inducing destruction is cavitation bubbles.
In this study, we examined the influence of external factors on ultrasonic destruction of microcapsules. We added various organic compounds to suspensions containing the capsules and irradiated the samples with ultrasonic waves at 430 kHz and 950 kHz.

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Micro samples (bacteria, algae, microcapsules, etc.) are required as probes for checking abilities of ultrasonic cavitation. Ultrasonic waves are one of the mechanisms by which microscopic specimens are destroyed, and it has been reported that microscopic specimens in the vicinity of cavitation bubbles that experience repeated expansion and contraction synchronously with the excitation frequency are destroyed as a result of resonance with the vibration. Past reports have observed that samples subjected to ultrasonic irradiation were most often ruptured or broken by the resonance and destroyed. Further, small holes (pits) were observed on the surfaces of small-diameter samples. It is well known that relatively minute air bubbles in a sample can sense asymmetry and generate a micro jet shock wave.
The purpose of this study was to investigate ultrasonic pitting effects on fine samples. A starch sample was irradiated with ultrasonic waves in a broadband frequency range of 26 kHz to 3.6 MHz. We then measured the number of pits on the surface of the sample at various frequencies and observed the surface using a scanning electron microscope. We further investigated the stress imparted by cavitation bubbles, which were destroyed near the sample, to the sample.

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Water washing process on the contaminated surface was investigated with flowing ultrasound (US) at 430kHz. The US effect was tested when water flowing, US was irradiated towards the glass surface having marker stain adhered. the effect of washing flow without and with US operation on the cleaning was examine to remove the marker stain at several conditions; flow rate and US output power. In addition, fluorometry diagnostic was applied for detection to OH radical in the US flowing, when aqueous coumarin was exposed for checking the fluorescence of umbelliferone.

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Studies on ultrasonic reaction fields in organic solvents leave much room for clarification because the decomposition products of the solvents themselves are complicated and the decomposition products have a large influence on the cavitation bubbles. In lubricating oils used in hydraulic equipment, some products which are supposed to be derived from the high temperature and high pressure field of cavitation phenomenon has been reported. In this study, linear alkanes (C₉ to C₁₆) and squalane (C₃₀) were sonicated as a model solvent for lubricating base oils, and the formation of lower fatty acids was confirmed by using ion chromatograph. The average temperature of ultrasonic cavitation bubbles (cavities) was estimated by methyl radical recombination method via determining the amount of gaseous hydrocarbon produced using a gas chromatograph. Furthermore, the influence of physical properties such as vapor pressure and viscosity of solvents on cavity temperature was discussed.

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Ultrasonic atomization is a method to produce very fine droplets from bulk liquid with irradiating ultrasound of MHz frequency[1, 2]. The droplet size distribution has two peaks, the one is in the range of micrometers and the other one is sub micrometers. Even for the peak in the micrometer range, the width is much narrower than that for the droplets produced by conventional spraying with two-fluid. Thus, ultrasonic atomization produces well-tailored fine droplets including nanodroplets. These droplets potentially accommodate solutes or solid nanoparticles of specific size, and bring them to gas phase. Such a selective transfer of solutes or particles will achieve separation.
Our past study on separating submicron particles in aqueous suspensions by ultrasonic atomization proved the silica particles of 100 nm was brought into the fog from the mixture of silica of 100 and 300 nm[3]. Improvement of the fog recovery unit allowed recovering more than 90 % fog. Furthermore, 100 nm silica particles were enriched in the recovered liquid. The present study aims to enhance the understanding of this enrichment of a specific particle with ultrasonic atomization. Under various operating parameters, enrichment behavior was examined with silica as well as polystyrene particles.
No effect was found of the type of particles on the enrichment, but the degassing of sample suspension had a strong influence, which is a loss of enrichment. The result indicates the close relation with cavitation on the enrichment effect.

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Nicotine, which is a potential medicine for neurodegenerative diseases, was loaded in biopolymer hydrogels of cellulose or chitin. Here, the nicotine-loaded hydrogel prepared was exposed to ultrasound (US) at 30 W with 43kHz frequency at 25℃. By the US exposure, it was noted that nicotine release from the hydrogel matrix was enhanced. The comparison in the loaded cellulose and chitin hydrogels was shown to be different release behavior, meaning that the durg release depended upon the hydorgel chemical structure having interaction with the drug.

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High frequency ultrasound brings particles to pressure node of standing wave and also provides strong shear in liquids. Because of the shorter wavelength, density of the events in the sound field is higher than those in the lower frequency ultrasound. Although the strength of cavitaion phenomena might be less than lower frequency ultrasound, high frequency ultrasound has a strong potential on applications for flow chemistry system and micro channels. As one example of applying high frequency ultrasound on sonocrystallization, glycine crystals were formed under irradiation of 1.6 MHz ultrasound. The irradiation narrowed crystal size distribution and enhanced growth of the crystal. Also, submicron silica particles of specific size range were selectively transferred into the mist generated from ultrasonic atomization of silica suspension.

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