Photoluminescence Analysis of Iron Contamination Effect in Multicrystalline Silicon Wafers for Solar Cells

We investigated the effect of Fe contamination on the electronic properties of dislocation clusters in relation to oxygen precipitation in multicrystalline silicon (mc-Si). Photoluminescence (PL) spectroscopy and mapping were performed at room and liquid-He temperatures on mc-Si wafers before and after Fe contamination. PL spectra consisted of the band-edge emission, the 0.78-eV emission associated with oxygen precipitates, and the dislocation-related D-lines. The Fe contamination increased the electrically active dislocation clusters. Part of these clusters acted as preferential oxygen precipitation sites, and their electronic properties were not further influenced by the Fe contamination.     

Metastatic Voyage of Ovarian Cancer Cells in Ascites with the Assistance of Various Cellular Components

Epithelial ovarian cancer (EOC) is the most lethal gynecologic malignancy and has a unique metastatic route using ascites, known as the transcoelomic root. However, studies on ascites and contained cellular components have not yet been sufficiently clarified. In this review, we focus on the significance of accumulating ascites, contained EOC cells in the form of spheroids, and interaction with non-malignant host cells. To become resistant against anoikis, EOC cells form spheroids in ascites, where epithelial-to-mesenchymal transition stimulated by transforming growth factor-β can be a key pathway. As spheroids form, EOC cells are also gaining the ability to attach and invade the peritoneum to induce intraperitoneal metastasis, as well as resistance to conventional chemotherapy. Recently, accumulating evidence suggests that EOC spheroids in ascites are composed of not only cancer cells, but also non-malignant cells existing with higher abundance than EOC cells in ascites, including macrophages, mesothelial cells, and lymphocytes. Moreover, hetero-cellular spheroids are demonstrated to form more aggregated spheroids and have higher adhesion ability for the mesothelial layer. To improve the poor prognosis, we need to elucidate the mechanisms of spheroid formation and interactions with non-malignant cells in ascites that are a unique tumor microenvironment for EOC.     

c-axis oriented ZnO formed in a rotating magnetic field with various rotation speeds

A rotating magnetic field was used to fabricate c-axis oriented zinc oxide. The influence of rotating speed on orientation structure was also examined. The aligned axes had the largest diamagnetic susceptibility, which axis was difficult to align with a static magnetic field. In c-axis oriented ZnO, the degree of orientation (Lotgering factor) in the green compact ranged from 0.2 to 0.5 along c-axis. The Lotgering factor increased with rotating speed. For all samples with the rotating magnetic field, the degrees of orientation increased up to above 0.9 after sintering at 1573 K.     

Star-shaped poly(lactic acid) with carboxylic acid terminal groups via poly-condensation

A series of star-shaped poly(lactic acid)s with carboxylic acid terminal groups have been synthesized by direct poly-condensation of lactic acid in the presence of a poly-carboxylic acid core molecule with triphenylphosphonium trifluoromethanesulfonate (TPP-T) catalyst.These star-polymers had thermal properties not very much different from those of star-shaped poly(lactic acid) with hydroxyl terminal groups and linear poly(lactic acid), irrespective of the structure of the core molecule and number of polymer arms. Solubility and degradability of these star-polymers were, however, greatly enhanced compared to those of star-polymers with hydroxyl terminal groups and increased depending on the number of polymer arms. From the star-shaped polymers, a variety of ammonium salts and the corresponding carboxyamides were successfully prepared.     

Numerical simulation of critical current performance in Nb3Sn strand subjected to periodic bending deformation

In the ITER Engineering Design Activity (EDA), four NB₃Sn model coils were developed and successfully tested. However, it was revealed that the critical current of the conductor degraded with the increase of electromagnetic force. One of the explanations of this phenomenon is a strand bending caused by enormous electromagnetic force. The authors therefore developed a simulation code using the distributed circuit model to investigate dependency of the critical current performance on the periodic bending deformation. The simulation results were in good agreement with the experiments. The dependence of the critical current on the periodic transverse load, temperature, periodic load pitch, thickness of Ta barrier which prevents Cu stabilizer from being contaminated by Sn, twist pitch of the strand, and RRR of the bronze matrix was investigated using the developed code. The results showed that the critical current degraded less with decreasing the pitch of the transverse load and increasing the Ta barrier thickness. It suggests that the shorter cabling pitch and the larger bending stiffness prevent the critical current degradation. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(3): 7–15, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20923     

Service‐level assurance in high‐availability multi‐unit systems using the M‐for‐N backup scheme

In this paper, we investigate service‐level assurance in high‐availability multi‐unit systems using the M‐for‐N backup scheme. M‐for‐N shared protection (backup) systems with priority control (i.e. prioritized protection switching and prioritized re‐housing of repaired units) can be applied to actual telecommunication devices that are subject to service‐level agreement (SLA) involving reliability measures. A priority level is assigned to each end user in such a system and the switching and unit re‐housing process is subject to the priority. The main contribution of this paper is to give a practical computation method of the user‐perceived availability under the priority control. Our case studies for real telecommunication systems reveal the effect of priority control on the user‐perceived availability. Copyright © 2011 John Wiley & Sons, Ltd.     

New technique for bonding hydroxyapatite ceramics and magnesium alloy by hydrothermal hot-pressing method

The solidification of hydroxyapatite (HA:Ca₁₀(PO₄)₆(OH)₂) and its bonding with Magnesium (Mg) alloys (AZ31; Mg–3Al–1Zn) were achieved simultaneously by using a hydrothermal hot-pressing method at a low temperature as low as 150 °C with no special surface treatment of Mg alloy. A mixture of calcium hydrogen phosphate dihydrate and calcium hydroxide was used as a starting powder material for solidifying HA. 3-point bending tests were conducted to obtain an estimate of the fracture toughness for the HA/Mg interface as well as for the HA ceramics only. The fracture toughness tests showed that the induced crack from the pre-crack tip deviated from the HA/Mg interface and propagated into the HA. The fracture toughness determined on the bonded HA/Mg specimen was close to that of the HA ceramics only (0.30 MPam^1/2).     

Colorless polyimides derived from 1S,2S,4R,5R-cyclohexanetetracarboxylic dianhydride,self-orientation behavior during solution casting,and their optoelectronic applications

A novel cycloaliphatic monomer for polyimides (PI), 1S,2S,4R,5R-cyclohexanetetracarboxylic dianhydride (H′-PMDA) is proposed in this work. H′-PMDA shows high polymerizability with various diamines in contrast to its isomer, i.e., conventional hydrogenated pyromellitic dianhydride (H-PMDA) and leads to highly flexible and colorless PI films with very high T_g's. In particular, the combinations with rigid structures of diamines give rise to PIs with significantly decreased coefficients of thermal expansion (CTE) owing to high extents of in-plane chain orientation induced by thermal imidization, whereas the H-PMDA-based counterparts do not. The decreased CTE reflects structural rigidity/linearity of the H′-PMDA-based diimide units as supported by liquid crystallinity observed in the corresponding model compound. Solution casting of a chemically imidized PI derived from H′-PMDA and 2,2′-bis(trifluoromethyl)benzidine (TFMB) results in a lower CTE than that of the thermally imidized counterpart, suggesting the presence of a self-orientation phenomenon during solvent evaporation. The mechanism is proposed in this work. H′-PMDA/TFMB and its copolymer systems can be useful as plastic substrates in image display devices and/or novel coating-type optical compensation films.     

Behavior of composite segment for shield tunnel

Composite segment has been developed for obtaining high capacity in lining of shield tunnel subject to high hydraulic pressure and earth pressure in deep underground, which is made of steel plates connected to an infill of high fluidity concrete with shear connectors. However, a rational design method for composite segments can not be established, because the behavior of composite segments is not clarified. The purpose of this paper is to study the behavior of the most complicated composite segment with six steel plates using finite element method and the four-point bending tests. The effects of the shear studs and the thicknesses of steel plates were verified and estimated quantitatively. Meanwhile, the failure modes of composite segments were investigated. Comparisons show that the finite element model is suitable for composite segments and predicts the behavior of composite segments accurately.