A high‐precision unstructured adaptive mesh technique for gas–liquid two‐phase flows

Adaptive mesh techniques are used widely in the numerical simulations of fluid flows, and the simulation results with high accuracies are obtained by appropriate mesh adaptations. However, gas–liquid two‐phase flows are still difficult to be simulated on adaptive meshes, especially on unstructured adaptive meshes, because the physical phenomena near gas–liquid interfaces are highly complicated and in general, not modeled appropriately on adaptive meshes. In this paper, a high‐precision unstructured adaptive mesh technique for gas–liquid two‐phase flows is developed and verified/validated. In the unstructured adaptive mesh technique, the PLIC algorithm is employed to simulate interfacial dynamic behaviors and, therefore, the reconstruction method for the interfaces in refined cells is developed, which satisfies the gas and liquid volume conservations and geometrical conservations of interfaces. In addition, the physics‐based consideration is performed on the momentum calculations near interfaces, and the calculation method with gas and liquid momentum conservations is developed. For verification, the slotted‐disk revolution problem is solved. As a result, the unstructured adaptive mesh technique succeeds in reproducing the slotted‐disk shape accurately and well maintaining the shape after one full‐revolution. The dam‐break problem is also simulated and the momentum conservative calculation method succeeds in providing physically appropriate results, which show good agreements with experimental data. Therefore, it is confirmed that the developed unstructured adaptive mesh technique is very efficient to simulate gas–liquid two‐phase flows accurately. Copyright © 2010 John Wiley & Sons, Ltd.     

Energetically deep defect centers in vapor-phase grown zinc oxide

Vapor-phase grown ZnO crystals were investigated by means of DLTS measurements. The generation of defect center E4 subsequent to annealing in different ambients was monitored. By conducting electron irradiations with energies, where either both the Zn- and O-sublattice are damaged or according to [1] only the Zn-lattice, a chemical assignment to the defect centers E4 and E3 could be accomplished. DLTS investigations of ZnO samples under illumination give evidence that E4 is a negative-U center. PACS 71.55.-i; 71.55.Gs     

Nano- and macro-geometrical structural change of caffeine and theophylline anhydrate tablets during hydration process by using X-ray computed tomography

The effects of nano- and macro-geometrical factors on the hydration kinetics of caffeine (CA) and theophylline anhydrate (TA) tablets at high humidity were investigated using X-ray high-resolution computed tomography (CT). Hydration profiles of CA and TA tablets obtained at 25 and 50 MPa, 96% relative humidity, and 20 °C were measured by weight and X-ray CT. The total tablet volume (G-V) and average tablet density (G-D) calculated based on the volume and weight of tablets, and tablet volume (CT-V) and tablet density (CT-D) were evaluated by X-ray CT. The hydration kinetics of CA and TA tablets followed two-dimensional growth of nuclei (Avrami-Erofee) and three-dimensional phase boundary equations, respectively. The increase in the G-V of TA tablets was initially more than, but later less than, that of CA tablets. The G-D of CA tablets varied extensively and was constant initially, whereas that of TA tablets decreased significantly in the initial stage. The CT-V of CA tablets gradually increased initially, but that of TA tablets increased significantly early on. The inter-granular volume (IG-V) of both tablets decreased initially with large fluctuations, but then increased. The CT-D of CA tablets decreased significantly, but that of TA tablets did not decrease. The hydration kinetics of CA and TA tablets was affected by changes in the geometrical structure of the tablets. X-ray CT is a powerful tool for evaluating dynamic changes inside tablets.     

Influence of 0.03?wt.% Carbon Black Addition on the Performance of Sn-3.5Ag Lead-Free Solder

In an effort to improve the performance of lead-free solder, Sn-3.5?wt.%Ag (Sn-3.5Ag) solder alloy with 0.03?wt.% carbon black was prepared under high pressure (5.5?GPa) and high temperature (1200°C). We have investigated the microstructure, melting behavior, and mechanical properties of the alloy using x-ray diffraction, differential scanning calorimetry (DSC), Vickers hardness testing, tensile testing, and scanning electron microscopy (SEM). The melting point was found to be unchanged, while the hardness and the tensile strength increased with the addition of carbon black. SEM images showed that the average thickness of the intermetallic compound (IMC) layer decreased with the addition of carbon black, indicating improvement in solder joint reliability.     

Microwave-assisted deacylation of unactivated amides using ammonium-salt-accelerated transamidation

The combination of an ammonium salt and ethylenediamine promotes deacylation of a variety of unactivated amides to give the corresponding amines in high yields without the use of strong acids or bases. The reactions proceed without special care regarding air and moisture, and tolerate a wide range of functional groups.     

IR-extended photoluminescence mapping of single-wall and double-wall carbon nanotubes

A simple and efficient technique is described for measuring photoluminescence (PL) maps of carbon nanotubes (NTs) in the extended IR range (1-2.3 mum). It consists of preparing an NT/surfactant/gelatin film and measuring PL spectra using a combination of a tunable Ti-sapphire laser excitation and FTIR detection. This procedure has been applied to a wide range of single- and double-wall NTs unveiling chirality and diameter distributions that have so far been very difficult to measure. The problems associated with deducing these distributions are discussed by comparing absorption and PL mapping data for NT samples prepared under different conditions.     

Electrophoresis of soft particles: analytic approximations

An approximate analytic expression is derived for the electrophoretic mobility of a weakly charged spherical soft particle (i.e., a hard particle covered with a weakly charged polyelectrolyte layer) on the basis of the general mobility expression for soft particles (Ohshima, H., J. Colloid Interface Sci. 2000, 228, 190-193). The obtained mobility expression, which reproduces various approximate results so far derived and gives some new mobility formulas, covers all types of weakly charged soft particles with arbitrary values of the thickness of polymer layer, the radius of the particle core, the electrophoretic softness, and the Debye length, including spherical polyelectrolytes with no particle core as well as spherical hard particles with no polyelectrolyte layer.     

Polarized target asymmetry in π+ photoproduction between 0.3 and 1.0 GeV at 130°

The polarized target asymmetry for γ + p → π⁺ + n was measured at c.m. angles around 130° for the energy range between 0.3 and 1.0 GeV. A magnetic spectrometer system was used to detect π⁺ mesons from the polarized butanol target. The data show two prominent positive peaks at 0.4 and 0.8 GeV and a deep minimum at 0.6 GeV. These features are well reproduced by the phenomenological analysis made by us.