Development of Translucent Aluminum Nitride (AIN) Using Microwave Sintering Process

Pure aluminum nitride (AIN) has been successfully sintered to highly translucent form by microwave sintering at 1850°C with a dwelling time of 30–60 minutes. The results showed that the sintering temperature should be at least 1850°C or higher to get reasonable translucency in the AIN sample by the microwave sintering process. On the other hand, the conventional sintering method requires much longer sintering time to obtain a translucent AIN ceramics.     

Synthesis of Glass-like Cordierite from Metal Alkoxides and Characterization by 27Al and 29Si MASNMR

A sol-gel process for the preparation of glass-like cordierite and ceramic oxide powder is described. Metal alkoxide precursors were dissolved in 2-methoxyethanol and the metal cations were complexed using 2,4-pentanedione to overcome different hydrolysis rates of metal alkoxides which lead to microscopic inhomogeneities during gelation. Heating the gel in an aerated furnace resulted in ultrafine cordierite powder of stoichiometric composition at a relatively low temperature. Cordierite gel and glass were also prepared by other methods and compared with the above gel. The environments of aluminum and silicon in the glass and gels heated at various temperatures were studied using ²⁷Al and ²⁹Si magic angle spinning nuclear magnetic resonance (MASNMR) spectroscopy. Most of the heated gels and the glass showed resonances due to pentacoordinated aluminum along with 4- and 6-coordinated aluminum. The homogeneities of the resulting gels and glass are compared using the MASNMR data.     

Application of Compositionally Diphasic Xerogels for Enhanced Densification: The System Al2O3-SiO2

Stoichiometric mullite (71.38 wt% Al₂O₃-28.17 wt% SiO₂) and 80 wt% Al₂O₃-20 wt% SiO₂ gels were prepared by the single-phase and/or diphasic routes. Dense sintered bodies were prepared from both sets of gels in the Al₂O₃-SiO₂ system. Apparent densities of 96% and 97% of theoretical density were measured for the diphasic (using two sols) mullite samples sintered at 1200° and 1300°C for 100 min, respectively; this compared with 85% and 94% for the single-phase xerogels under the same conditions, and to much lower values for mullite prepared from conventional mixed powders. The microstructure of the mullite pellets from diphasic xerogel precursors is also considerably finer.     

Potential Role of Selenium in the Treatment of Cancer and Viral Infections

Selenium has been extensively evaluated clinically as a chemopreventive agent with variable results depending on the type and dose of selenium used. Selenium species are now being therapeutically evaluated as modulators of drug responses rather than as directly cytotoxic agents. In addition, recent data suggest an association between selenium base-line levels in blood and survival of patients with COVID-19. The major focus of this mini review was to summarize: the pathways of selenium metabolism; the results of selenium-based chemopreventive clinical trials; the potential for using selenium metabolites as therapeutic modulators of drug responses in cancer (clear-cell renal-cell carcinoma (ccRCC) in particular); and selenium usage alone or in combination with vaccines in the treatment of patients with COVID-19. Critical therapeutic targets and the potential role of different selenium species, doses, and schedules are discussed.     

Cellular determinants of resistance to indolocarbazole analogue 6-N-formylamino-12,13-dihydro-1,11-dihydroxy-13(beta-D-glucopyranosyl)- 5H-indolo[2,3-alpha]pyrrolo[3,4-c]carbazole-5,7(6H)-dione (NB-506), a novel potent topoisomerase I inhibitor, in multidrug-resistant human tumor cells

1. In this study we hypothesized that in individuals with certain genetic makeup, MTBE, benzene or their metabolites act as adducts and may induce programmed cell death. 2. Our study involved a group of 60 male and female subjects who were exposed to MTBE and benzene-contaminated water concentrations up to 76 PPB for MTBE and 14 PPB for benzene, for a period of 5 to 8 years. For comparison, we recruited a control group consisting of 32 healthy males and females with similar age distribution and without a history of exposure to MTBE or benzene. 3. Peripheral blood lymphocytes (PBL) of both groups were tested for the percentage of apoptotic cells and cell cycle progression using flow cytometry. 4. When apoptotic lymphocytes from exposed individuals were compared to apoptotic lymphocytes from the control group, statistically-significant differences between each mean group were detected (26.4 +/- 1.8 and 12.1 +/- 1.3, respectively), indicating an increased rate of apoptosis in 80.5% of exposed individuals (P < 0.0001, Mann-Whitney U-Test). MTBE and benzene-induced apoptosis is attributed to a discrete block within the cell cycle progression. Because cell cycle analysis showed that in PBL from chemically-exposed individuals, between 20-50% of cells were accumulated at the S-G2/M boundaries. 5. One of the signaling molecules which mediates programmed cell death is nuclear factor Kappa-B (NF-kappa B). NF-kappa B was examined as one of the many molecular mechanisms for mediating cell death by MTBE and benzene. Indeed, addition of inhibitors of NF-kappa B activation pyrrolidine dithiocarbamate (PDTC), to the lymphocytes of the chemically-exposed group was capable of inhibiting programmed cell death by 40%. This reversal of apoptosis almost to the control level by inhibitor of NF-kappa B activation may indicate involvement of this signaling molecule in MTBE and benzene induction of programmed cell death.     

Combustion Synthesis of Hexaaluminate Phosphors

Green phosphors of the composition Ce_{1- x} Tb _x MgAl₁₁O₁₉ (0.1 < x < 0.6) were prepared via self-propagating (combustion) synthesis, using urea as a fuel. The phosphors that were produced via the combustion route were fine powders and produced a luminous intensity of 72%, compared to an optimized commercial phosphor. The excitation spectra were characteristic of the Ce³⁺ cation; however, no Ce³⁺ emission was observed. Energy transfer from the Ce³⁺ cation to the Tb³⁺ cation was complete, and only the 542 nm Tb³⁺ emission was observed. Concentration quenching occurred with x > 0.5. Scanning electron microscopy images showed a well-crystallized, platelike morphology, with a particle size of 10-20 µm.     

Crystal chemistry and luminescence of the Eu-activated alkaline earth aluminate phosphors

Alkaline earth monoaluminate phosphors activated with Eu²⁺ were synthesized by microwave processing and alkaline earth hexaaluminate phosphors activated by Eu²⁺ were synthesized by hydrothermal reactions. The emission spectra of the monoaluminates are similar to phosphors prepared by high-temperature firing except for BaAl₂O₄ which emits farther in the blue. The spectra of the hexaaluminate phosphors in general have their emission peak at different wavelengths than what are nominally the same compositions prepared by high-temperature firing.