TRANSIENT THERMOELASTIC PROBLEM FOR AN INFINITE PLATE CONTAINING A PENNY-SHAPED CRACK AT AN ARBITRARY POSITION

This article deals with the transient thermoelastic problem for an infinite plate containing a penny-shaped crack that is parallel to the surfaces of the plate but at an arbitrary position of the plate. The transient thermal stresses are set up by the heat generation on the surfaces and the sudden heat exchange on the surfaces. By using the finite difference method for the time variable, the analytical solution for spatial variables can be obtained. The numerical results for the temperature and stress intensity factor are obtained, and results are shown in graphs.     

Oxidative decomposition of dichlorodifluoromethane (CFC-12) in the presence of butane over Tungsten(VI) oxide catalysts supported on alumina–zirconia

The oxidative decomposition of dichlorodifluoromethane (CFC-12) in the presence of butane was investigated with tungsten(VI) oxide catalyst supported on alumina–zirconia. In this reaction, it is considered that CFC-12 might react with water formed by the combustion of butane at high temperatures above 773 K, and that most of CFC-12 might react directly with oxygen at low temperatures below 723 K. The CFC-12 conversion over the tungsten(VI) oxide catalyst decreased with the passage of time on stream at low temperatures below 673 K. This deactivation of the catalyst was attributed to the coke deposition on the acid sites of the catalyst as well as to the fluorination of the acid sites. The CFC-12 conversion at 4 h on stream became higher when the catalyst was loaded with platinum or palladium, but the butane conversion was not changed by loading. The amount of the coke deposited on platinum- or palladium-loaded tungsten(VI) oxide catalysts, which exhibited a high CFC-12 conversion at 4 h on stream, was very small. Accordingly, the depression of the catalyst deactivation might be caused by the combustion of the coke deposited on the acid sites due to the catalysis of platinum and palladium.     

Preparing activated carbon from various nutshells by chemical activation with K2CO3

We have prepared activated carbons by chemical activation with K₂CO₃ from five kinds of nutshells: almond shell (AM), coconut shell (CN), oil palm shell (OP), pistachio shell (PT) and walnut shell (WN). When prepared at 1073 K, the activated carbons from all the nutshells had the maximum specific surface areas. According to the maximum values of specific surface areas, the activated carbons prepared were classified into two groups: Group-L and Group-S; the former group included activated carbons with high specific surface area and the latter included those with lower specific surface area, respectively. It was found that K₂CO₃ effectively worked as an activation reagent, but differently in the temperature ranges below 800 and above 900 K. Due to impregnation, cellulose and hemi-cellulose were modified by K₂CO₃ and accordingly the weight loss behaviors of the nutshells were changed in the temperature range below 800 K. In the temperature range above 900 K, carbon in the chars was removed as CO gas by the reduction of K₂CO₃ to increase the specific surface area and the pore volume. It was deduced that the difference between the specific surface areas of Group-L and those of Group-S correspond to the difference between weight loss behaviors in the temperature range above 900 K.     

Ca-vacancy effect on the stability of substitutional divalent cations in calcium-deficient hydroxyapatite

First-principles calculations were performed to reveal an effect of Ca vacancies on the stability of substitutional divalent cations M²⁺ (M = Mg, Zn, Sr) in Ca-deficient hydroxyapatite (dHAp). M²⁺ concentrations up to 20 mol% in dHAp were considered, and the most stable substitutional sites and their lowest energy configurations in the dHAp lattice were examined with the aid of a generic algorithm method. It was found that defect formation energies of substitutional M²⁺ are lower in dHAp than in stoichiometric HAp (sHAp) at all M²⁺ concentrations. This indicates that these M²⁺ ions are more favorably involved in dHAp than in sHAp, which is in reasonable agreement with experiment. Detailed analyses on atomic structures in dHAp show that the presence of a Ca vacancy varies its surrounding Ca–O bond lengths over a wide area so that Ca–O polyhedrons with various sizes are produced. As a result, M²⁺ ions can predominantly occupy Ca sites at which M²⁺ fits better, depending on the ionic radii of M²⁺. For Zn²⁺ substitution in dHAp, its defect formation energy decreases more with the increasing concentrations and has the minimum value at 15 mol%. Such a trend can be understood from changes in effective coordination numbers of Zn in dHAp.     

Elevation of Chemosensitivity of Lung Adenocarcinoma A549 Spheroid Cells by Claudin-2 Knockdown through Activation of Glucose Transport and Inhibition of Nrf2 Signal

Claudin-2 (CLDN2), a tight junctional protein, is involved in the chemoresistance in a three-dimensional spheroid culture model of human lung adenocarcinoma A549 cells. However, the mechanism has not been fully clarified. We found that the knockdown of CLDN2 expression by siRNA in the spheroid reduces the expression of glucose transporters and metabolic enzymes. In a two-dimensional culture model, the expression of these proteins was increased by glucose deprivation or fasentin, an inhibitor of glucose transporter. In addition, the expression levels of nuclear factor erythroid 2-related factor 2 (Nrf2) and antioxidant enzymes including heme oxygenase-1, NAD(P)H:quinone oxidoreductase-1, and a glutamate–cysteine ligase modifier subunit were increased by fasentin. The fluorescence intensities of JC-1, a probe of mitochondrial membrane potential, and MitoROS 580, a probe of mitochondrial superoxide production, were increased by fasentin. These results suggest that mitochondrial production of reactive oxygen species is increased by glucose deficiency. The knockdown of CLDN2 enhanced the flux of 2-deoxy-2-[(7-nitro-2,1,3-benzoxadiazol-4-yl)amino]-D-glucose (2-NBDG), a fluorescent deoxyglucose derivative, in a transwell assay, and the accumulation of glucose and 2-NBDG in spheroid cells. The expression of Nrf2 was decreased by CLDN2 knockdown, which was inhibited by fasentin and sulforaphane, a typical Nrf2 activator, in spheroid cells. The sensitivity of spheroid cells to doxorubicin, an anthracycline antitumor antibiotic, was enhanced by CLDN2 knockdown, which was inhibited by fasentin and sulforaphane. We suggest that CLDN2 induces chemoresistance in spheroid cells mediated through the inhibition of glucose transport and activation of the Nrf2 signal.