Effect of the compositional distribution on the photovoltaic power conversion of SiGe solar cells

Theoretical investigation on the photovoltaic power conversion of SiGe solar cells was carried out focusing on the impact of the compositional distribution. The absorption coefficient and the intrinsic carrier concentration were assumed to be macroscopically uniform parameters controlled by the compositional distribution. Under an assumption with finite minority carrier diffusion length, solar cell based on SiGe was revealed to have power conversion superior to that based on Si in a limited compositional window on the Si-rich side. In the window, the increase in the photocurrent density overcompensates the decrease in the voltage, and controls the overall conversion efficiency. The width of the window was greatly affected by the compositional distribution in SiGe. A comparison was made with experiments to support the existence of such a compositional window.     

Evaluation of the electromagnetic characteristics of type 316L stainless steel welds from the viewpoint of eddy current inspections

This study evaluated the electromagnetic characteristics of austenitic stainless steel welds from the viewpoint of eddy current testing. Seven welded plate specimens, which were welded using JIS Z3221:2010 YS316L welding metals, were prepared. Two welding metals and several welding conditions were adopted to discuss the generality. The results of eddy current examination of the specimens using three different types of eddy current probes, that is, an absolute pancake probe, a differential plus-point probe, and a uniform eddy current probe, confirmed that the welds cause a large noise especially when the absolute pancake probe was used. The analysis of the signals through finite element simulations revealed that the magnetic property of the welds is not negligible from the viewpoint of eddy current testing. Complementary experiments were conducted using a vibrating sample magnetometer to validate the results.     

Study of a methodology of identifying important research problems by the PIRT process

In this paper, we propose a new methodology of identifying important research problems to be solved to improve the performance of some specific scientific technologies by the phenomena identification and ranking table (PIRT) process which has been used as a methodology for demonstrating the validity of the best estimate simulation codes in US Nuclear Regulatory Commission (USNRC) licensing of nuclear power plants. The new methodology makes it possible to identify important factors affecting the performance of the technologies from the viewpoint of the figure of merit and problems associated with them while it keeps the fundamental concepts of the original PIRT process. Also in this paper, we demonstrate the effectiveness of the new methodology by applying it to a task of extracting research problems for improving an inspection accuracy of ultrasonic testing or eddy current testing in the inspection of objects having cracks due to fatigue or stress corrosion cracking.     

Large-scale parallel computation for the reconstruction of natural stress corrosion cracks from eddy current testing signals

An inversion algorithm for the reconstruction of cracks from eddy current signals is developed in this study and applied to the profile evaluation of natural stress corrosion cracks that were found in steam generator tubes of a nuclear power plant. A crack is modeled as an assembly of small regions having conductivities inside so that eddy currents that flow across the cracks are considered. The conductivity of each region, which is assumed to be a discrete value, is reconstructed by means of the algorithm. Since the algorithm is based upon a tabu search that usually requires a large number of evaluating solution candidates, simulations are carried out on a supercomputer with the use of parallel computation using up to 128 CPUs so as to reconstruct the crack profiles within a reasonable computational time. It is demonstrated that the algorithm can estimate the profiles of the natural cracks with sufficient accuracy. The simulations also show that the algorithm is highly compatible with parallel computation. Additional simulations using other models of natural cracks are performed. Reconstructed profiles of the natural cracks, as a notch with zero conductivity, are very different from the true profiles, even though the reconstructed signals agree well with the measured values. This reveals that it is necessary to take the internal conductivity into consideration when dealing with natural cracks.     

Stimuli‐Responsive Liquid Marbles: Controlling Structure,Shape, Stability,and Motion

“Liquid marbles” are liquid‐in‐gas dispersed systems stabilized by hydrophobic solid particles adsorbed at the gas‐liquid interface. The structure, stability and movement of these liquid marbles can be controlled by external stimuli such as pH, temperature, light, magnetic and electric fields, ultrasonic, mechanical stress and organic solvents. Stimuli‐responsive modes can be categorized into five classes: (i) liquid marbles whose stability can be controlled by adsorption/desorption of solid particles to/from liquid surfaces, (ii) liquid marbles that can open and close their particle‐coated surface by moving particles to and from the gas‐liquid surface, (iii) liquid marbles that can move, (iv) liquid marbles that can change their shape and (v) liquid marbles that can be split. As a result of these stimuli‐responsive characteristics, liquid marbles offer potential in the areas of controlled encapsulation, delivery and release.     

Three-dimensional fabrication on GaAs surfaces using electron-beam-induced carbon deposition followed by wet chemical etching

We propose a method for fabricating three-dimensional structures on GaAs surfaces using electron beam (EB) irradiation followed by wet chemical etching. An etch-resistant hydrocarbon layer forms on the GaAs surface with the EB irradiation. Structures can be fabricated after etching using the hydrocarbon layer to block the etching. The height dependence on the irradiation and etching conditions was investigated as a means of controlling the height of the structures. A higher structure was fabricated at higher doses. The etching selectivity changed with the concentration of the etchant. A three-dimensional structure was fabricated based on these results, demonstrating the possible use of this method as a novel three-dimensional fabrication method for GaAs surfaces.     

Imaging of local stiffness of damaged polycrystalline copper: nondestructive evaluation by resonance ultrasound microscopy

The distribution of the local stiffness of a polycrystalline copper exposed to a creep test was studied by resonance ultrasound microscopy. The local effective modulus was evaluated from the resonance frequency of the isolated langasite oscillator touching the specimen. Defects appeared predominantly on grain boundaries, and they were clearly visualized by the stiffness microscopy through the significant decrease of the effective stiffness. The stiffness within the grains becomes lower regardless of invisible defects. The stiffness distribution was quantitatively analyzed by the contact model between two anisotropic bodies and by the micromechanics modeling. The microscopic stiffness shows much higher sensitivity to the defects than the macroscopic stiffness.     

Porphyromonas gingivalis Components/Secretions Synergistically Enhance Pneumonia Caused by Streptococcus pneumoniae in Mice

Streptococcus pneumoniae is an important causative organism of respiratory tract infections. Although periodontal bacteria have been shown to influence respiratory infections such as aspiration pneumonia, the synergistic effect of S. pneumoniae and Porphyromonas gingivalis, a periodontopathic bacterium, on pneumococcal infections is unclear. To investigate whether P. gingivalis accelerates pneumococcal infections, we tested the effects of inoculating P. gingivalis culture supernatant (PgSup) into S. pneumoniae-infected mice. Mice were intratracheally injected with S. pneumoniae and PgSup to induce pneumonia, and lung histopathological sections and the absolute number and frequency of neutrophils and macrophages in the lung were analyzed. Proinflammatory cytokine/chemokine expression was examined by qPCR and ELISA. Inflammatory cell infiltration was observed in S. pneumoniae-infected mice and S. pnemoniae and PgSup mixed-infected mice, and mixed-infected mice showed more pronounced inflammation in lung. The ratios of monocytes/macrophages and neutrophils were not significantly different between the lungs of S. pneumoniae-infected mice and those of mixed-infected mice. PgSup synergistically increased TNF-α expression/production and IL-17 production compared with S. pneumoniae infection alone. We demonstrated that PgSup enhanced inflammation in pneumonia caused by S. pneumoniae, suggesting that virulence factors produced by P. gingivalis are involved in the exacerbation of respiratory tract infections such as aspiration pneumonia.     

Prediction of long-term settlement and evaluation of pore water pressure using particle filter

The present paper showcases a numerical simulation of the long-term behavior of a foundation and an evaluation of the pore water pressure on Kobe Airport Island. To calculate the behavior of the ground and the pore water pressure, a numerical analysis is implemented using an elasto-plastic FEM for soil–water coupled problems with the Cam-clay model. However, numerical difficulties still remain in estimating the elasto-plastic parameters because of the nonlinearity of the materials and the uncertainty of the initial/boundary conditions. To account for these difficulties, a data assimilation technique, the particle filter, is adopted to identify the soil parameters using field measurements. The numerical simulation is carried out with the identified parameters to predict the long-term settlement and to evaluate the pore water pressure of the improved ground for two cases of boundary conditions. The outcomes show a good agreement with the direct measurements of the long-term settlement and the observed pore water pressure.