The effects of acoustic flow and mechanical flow on the sonochemical efficiency in a rectangular sonochemical reactor

Visualization of cavitation behavior in a rectangular sonochemical reactor at 490 kHz was carried out by a laser sheet technique and the distribution of liquid flow was measured by a laser Doppler velocimeter. The pattern of liquid flow and distribution of acoustic pressure of the rectangular sonochemical reactor were investigated as a function of the input power from 10 to 50 W. The liquid moved upward above the transducer at every power. As increasing the input power, the random flow out side the cylindrical part above the transducer changed into the convective one and the region of the visualized standing wave which was formed in the cylindrical part changed with the input power. The position showing the sonochemical luminescence exists inside or near the region where the standing wave was visualized. Introduction of a stirrer resulted in disturbance of liquid flow and expanded the position showing the sonochemical luminescence, but the luminescence intensity was weakened. The sonochemical efficiency was enhanced by about twice by introduction of the stirrer. From these results, we discussed the effects of liquid flow on sonochemical efficiency with and without a stirrer.     

Influence of a buried misfit dislocation network on the pyramid-to-dome transition size of Ge self-assembled quantum dots on Si(0 0 1)

The critical sizes of the pyramid-to-dome transition of Ge self-assembled quantum dots (SAQDs) grown on relaxed SiGe buffer layers were investigated for the relationship between the misfit strain built in dots and nucleation sites. The strain field of arrays of buried dislocations in a relaxed SiGe buffer layer provided preferential nucleation sites for quantum dots. Burgers vector analysis using plan-view transmission electron microscopy verified that the preferential nucleation sites of Ge SAQDs depended on the Burgers vector direction of corresponding dislocations. The measurement of the lateral distance between SAQDs and dislocations clarified that the location of SAQDs was at the intersection of the dislocation slip plane and the top surface. The samples are fabricated to contain low dislocation densities. The average dislocation spacing is larger than the surface migration length of Ge adatoms, resulting in two groups of SAQDs, those that are located along the dislocations, and those that are not. Atomic force microscopy observations showed a distinctively larger critical size for Ge SAQDs grown over the intersection of the dislocation slip plane and the top surface than those grown in regions between dislocations. These experimental observations indicate that the critical size of the pyramid-to-dome transition is strongly dependent on misfit strain in SAQDs with lower strain being associated with a larger critical size.     

Microwave-assisted preparation and enhanced photocatalytic activity of Bi2WO6/BiOI heterojunction for organic pollutants degradation under visible-light irradiation

In this research, we adopted morphology control and constructing p-n heterojunction to boost the photocatalytic performance of BiOI. BiOI with three morphologies (nanoplate, micro-flower, microsphere) was fabricated via a wet-chemical method at room temperature using different solvents. And Bi₂WO₆/BiOI microspheres were successfully prepared by a microwave-assisted synthetic method. The as-synthesized samples were characterized by X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), Energy Dispersive Spectroscopy (EDS) and High-resolution Transmission Electron Microscopy (HRTEM). The results of photo-degradation experiment demonstrated that BiOI-3 and BWOI-3 show high photocatalytic performance towards methyl orange (MO) and bisphenol A (BPA) degradation due to the high specific surface area, synergistic effect between p-type BiOI and n-type Bi₂WO₆ and high separation efficiency of electron-hole pairs, which is verified by Brunauer-Emmett-Teller (BET), Photocurrent (PC) and Electrochemical Impedance Spectroscopy (EIS) analysis. Moreover, the repeated photocatalytic experiment was carried out by using MO as the representative organic pollutant, manifesting the good durability of the sample.     

Compositional analysis of UV-cured acrylic ester resins by pyrolysis–gas chromatography in the presence of organic alkali

Compositional analysis of UV-cured resins consisting of multi-component acrylic esters was studied by pyrolysis–gas chromatography (Py–GC) in the presence of organic alkali, tetramethylammonium hydroxide (TMAH). The pyrograms of the UV-cured resins formed from ethylene oxide modified bisphenol A diacrylate (EBADA) contained specific products such as methyl acrylate (MA) and various dimethyl ethers of ethylene oxide modified bisphenol A reflecting the numbers of ethylene oxide units in the original EBADA. Meanwhile the pyrograms of the UV-cured resins comprised of acrylated polyfunctional aliphatic alcohols such as pentaerythritol triacrylate (PETA) and dipentaerythritol hexacrylate (DPEHA) contained methyl ethers reflecting the structure of the original alcohols. In addition, considerable amounts of pyrolyzates with non-methylated hydroxyl groups were also detected for aliphatic alcohol moieties. The compositions of the UV-cured resins containing multi-component acrylic esters were also analyzed based on the relative yields of the characteristic pyrolyzates of each acrylic ester. For calibration purpose, a series of UV-cured standard samples, which contained known amounts of the individual acrylic ester and neopentylglycol diacrylate (NPGDA) used as an internal standard, were measured. The compositions of the multi-component UV-cured resins determined using this approach showed good agreement with the theoretical values estimated from the feed composition.     

Molecular dynamics simulation study on the transient response of solvation structure during the translational diffusion of solute

The transient response function of the density profile of the solvent around a solute during the translational diffusion of the solute is formulated based on the generalized Langevin formalism. The resultant theory is applied to both neat Lennard-Jones fluids and cations in liquid water, and the response functions are obtained from the analysis of the molecular dynamics simulations. In the case of the self-diffusion of Lennard-Jones fluids, the responses of the solvation structures are in harmony with conventional pictures based on the mode-coupling theory, that is, the binary collision in the low-density fluids, the backflow effect from medium to high density fluids, and the backscatter effect in the liquids near the triple point. In the case of cations in water, the qualitative behavior is strongly dependent on the size of cations. The pictures similar to simple dense liquids are obtained for the large ion and the neutral molecule, while the solvent waters within the first solvation shell of small ions show an oscillatory response in the short-time region. In particular, the oscillation is remarkably underdumped for lithium ion. The origin of the oscillation is discussed in relation to the theoretical treatment of the translational diffusion of ions in water.     

K-edge angiography utilizing a tungsten plasma X-ray generator in conjunction with gadolinium-based contrast media

The tungsten plasma flash X-ray generator is useful in order to perform high-speed enhanced K-edge angiography using cone beams because K-series characteristic X-rays from the tungsten target are absorbed effectively by gadolinium-based contrast media. In the flash X-ray generator, a 150 nF condenser is charged up to 80 kV by a power supply, and flash X-rays are produced by the discharging. The X-ray tube is a demountable diode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Since the electric circuit of the high-voltage pulse generator employs a cable transmission line, the high-voltage pulse generator produces twice the potential of the condenser charging voltage. At a charging voltage of 80 kV, the estimated maximum tube voltage and current were approximately 160 kV and 40 kA, respectively. When the charging voltage was increased, the characteristic X-ray intensities of tungsten K_α lines increased. The K_α lines were clean, and hardly any bremsstrahlung rays were detected. The X-ray pulse widths were approximately 110 ns, and the time-integrated X-ray intensity had a value of approximately 0.35 mGy at 1.0 m from the X-ray source with a charging voltage of 80 kV. Angiography was performed using a film-less computed radiography (CR) system and gadolinium-based contrast media. In angiography of non-living animals, we observed fine blood vessels of approximately 100 μm with high contrasts.     

Study of particle size distribution and formation mechanism of radioactive aerosols generated in high-energy neutron fields

The size distributions of ³⁸Cl, ³⁹Cl, ⁸²Br and ⁸⁴Br aerosols generated by irradiations of argon and krypton gases containing di-octyl phthalate (DOP) aerosols with 45 MeV and 65 MeV quasi-monoenergetic neutrons were measured in order to study the formation mechanism of radioactive particles in high energy radiation fields. The effects of the size distribution of the radioactive aerosols on the size of the added DOP aerosols, the energy of the neutrons and the kinds of nuclides were studied. The observed size distributions of the radioactive particles were explained by attachment of the radioactive atoms generated by the neutron-induced reactions to the DOP aerosols.     

Caltrop particles synthesized by photochemical reaction induced by X‐ray radiolysis

X‐ray radiolysis of a Cu(CH₃COO)₂ solution was observed to produce caltrop‐shaped particles of cupric oxide (CuO, Cu₂O), which were characterized using high‐resolution scanning electron microscopy and micro‐Raman spectrometry. X‐ray irradiation from a synchrotron source drove the room‐temperature synthesis of submicrometer‐ and micrometer‐scale cupric oxide caltrop particles from an aqueous Cu(CH₃COO)₂ solution spiked with ethanol. The size of the caltrop particles depended on the ratio of ethanol in the stock solution and the surface of the substrate. The results indicated that there were several synthetic routes to obtain caltrop particles, each associated with electron donation. The technique of X‐ray irradiation enables the rapid synthesis of caltrop cupric oxide particles compared with conventional synthetic methods.