Influence of Mixed Na2O/K2O on Chemical Durability and Spectral Properties of P2O5-Al2O3-BaO-K2O-Na2O-Nd2O3 Phosphate Glasses

A series of 56P₂O₅-7.5Al₂O₃-5.9BaO-(28.56-x)K₂O-xNa₂O-1.51Nd₂O₃ phosphate glasses with different Na/(Na+K) ratios, which were specially designed for high-power laser application, were prepared by a high-temperature melting method. Except for the density, refractive index, glass transition temperature, and DC conductivity, the chemical durability and spectral properties, as emphasized by high-power and high-energy laser material, were further measured and analyzed. Regarding the chemical durability, the dissolution rates of these glasses do not show an evident mixed alkali effect with increasing the Na/(Na+K) ratio, although the effect is obvious for the glass transition temperature and DC conductivity. To better understand the nature of the dissolution mechanism, the ionic release concentrations of every element are determined. Both Na and K undergo ion exchange, but the ion exchange rate of K is much larger than that of Na. In terms of the spectral properties, the J–O parameters, emission cross-section, radiation lifetime, fluorescence lifetime, effective bandwidth, fluorescence branching ratio, and quantum efficiency are determined from absorption and emission spectra. The trend of Ω₂ deviating from linearity indicates that the coordination environment symmetry of Nd³⁺ ions and the covalence of Nd-O also present an evident mixed alkali effect. The most important finding is that the emission cross-section and fluorescence lifetime of Nd³⁺ ions at 1053 nm were not affected by the change in the Na/K ratio. According to the above experimental results, the optimized value of the Na/K ratio was determined, based on which the 56P₂O₅-7.5Al₂O₃-5.9BaO-(28.56-x)K₂O-xNa₂O-1.51Nd₂O₃ glass maintains a high emission cross-section with good chemical durability.     

Electrochemical Reduction of La2O3, Nd2O3, and CeO2 in LiCl-Li2O Melt

The reduction of pellets composed of individual CeO₂, Nd₂O₃ and a La₂O₃-Nd₂O₃-CeO₂ mixture by lithium extracted on a cathode during lithium chloride electrolysis at 650 °C was studied. The methods of cyclic voltammetry, electron microscopy, including determination of the elemental composition of the studied objects, and X-ray diffraction analysis were applied for the present study. The reduction degree of rare-earth metal (REM) oxides was determined using both the bromine method and reduction melting of the samples in the graphite crucible. The formation of the metallic phase composed of the rare-earth elements (REEs) was not observed even at the cathode potentials, corresponding to the formation of the liquid alkali metal phase, and lithium extraction, which, in the quantitative ratio, exceeds greatly the values needed for the reduction reaction. CeO₂ was found to reduce to Ce₂O₃.     

Effects of neuraminidase on O2 consumption and release of O2 and H2O2 from phagocytosing human polymorphonuclear leukocytes

Neuraminidase type X (NMD-type-X, Sigma Chemical Co., St. Louis, Mo.), which is obtained from a further purification of neuraminidase type V (NMD-type-V, Sigma), markedly enhanced the release of O2- and H2O2 from phagocytosing human polymorphonuclear leukocytes (PMN). In contrast, O2 consumption by NMD-type-X-treated PMN was identical to that of untreated PMN. Morphological observations suggested that the enhancement of O2- and H2O2 release was caused by excessive release of the oxygen metabolites into the extracellular medium from incompletely formed phagocytic vacuoles as was observed with cytochalasin-B-treated cells. Our observations are in contrast to the previous reports of Tsan et al. that showed complete inhibition of both O2- and H2O2 release from phagocytosing PMN by the treatment with NMD-type-V.     

Effect of Gd2O3 Addition on the Microstructure and Properties of Gd2O3-Yb2O3-Y2O3-ZrO2 (GYYZO) Ceramics

Gd and Yb elements have high chemical stability, which can stabilize the solid solution in ZrO₂. Gd₂O₃ and Yb₂O₃ have high melting points, and good oxidation resistance in extreme environments, stable chemical properties. Therefore, Gd₂O₃ and Yb₂O₃ were added to ZrO₂ to stabilize oxides, improve the high temperature stability, and effectively decrease the thermal conductivity at high temperature. In this work, 5 wt% Yb₂O₃ and 5 wt%, 10 wt%, 15 wt% Gd₂O₃ were doped into 8 wt% Y₂O₃ stabilized ZrO₂ (8YSZ) powders as thermal barrier coating materials, and sintered at 1650 °C for 6 h, 12 h, 24 h. The effects of Gd₂O₃ addition on the microstructure, density, thermal conductivity, hardness, and fracture toughness of Gd₂O₃-Yb₂O₃-Y₂O₃-ZrO₂ (GYYZO) bulk composite ceramics were investigated. It was found that the densification of the 8YSZ bulk and GYYZO bulk with 15 wt% Gd₂O₃ reached 96.89% and 96.22% sintered at 1650 °C for 24 h. With the increase of Gd₂O₃ addition, the hardness, elastic modulus and fracture toughness of the GYYZO bulk increased and the thermal conductivity and thermal expansion coefficient of the GYYZO bulk decreased. GYYZO bulk with 15 wt% Gd₂O₃ sintered at 1650 °C for 24h had the highest hardness, elastic modulus and fracture toughness of 15.61 GPa, 306.88 GPa, 7.822 MPa·m^0.5, and the lowest thermal conductivity and thermal expansion coefficient of 1.04 W/(m·k) and 7.89 × 10⁻⁶/°C at 1100 °C, respectively. The addition of Gd₂O₃ into YSZ could not only effectively reduce the thermal conductivity but also improve the mechanical properties, which would improve the thermal barrier coatings’ performances further.     

Drastic Dependence of the pH Sensitivity of Fe2O3-Bi2O3-B2O3 Hydrophobic Glasses with Composition

Fe₂O₃-Bi₂O₃-B₂O₃ (FeBiB) glasses were developed as novel pH responsive hydrophobic glasses. The influence of the glass composition on the pH sensitivity of FeBiB glasses was investigated. The pH sensitivity drastically decreased with decreasing B₂O₃ content. A moderate amount of Fe₂O₃ and a small amount of B₂O₃ respectively produces bulk electronic conduction and a pH response on glass surfaces. Because the remaining components of the glass can be selected freely, this discovery could prove very useful in developing novel pH glass electrodes that are self-cleaning and resist fouling.     

Influence of Li2O Incrementation on Mechanical and Gamma-Ray Shielding Characteristics of a TeO2-As2O3-B2O3 Glass System

According to the Makishema–Mackenzie model assumption, the dissociation energy and packing density for a quaternary TeO₂-As₂O₃-B₂O₃-Li₂O glass system were evaluated. The dissociation energy rose from 67.07 to 71.85 kJ/cm³, whereas the packing factor decreased from 16.55 to 15.21 cm³/mol associated with the replacement of TeO₂ by LiO₂ compounds. Thus, as a result, the elastic moduli (longitudinal, shear, Young, and bulk) were enhanced by increasing the LiO₂ insertion. Based on the estimated elastic moduli, mechanical properties such as the Poisson ratio, microhardness, longitudinal velocity, shear velocity, and softening temperature were evaluated for the investigated glass samples. In order to evaluate the studied glasses’ gamma-ray shield capacity, the MCNP-5 code, as well as a theoretical Phy-X/PSD program, were applied. The best shielding capacity was achieved for the glass system containing 25 mol% of TeO_2, while the lowest ability was obtained for the glass sample with a TeO₂ concentration of 5 mol%. Furthermore, a correlation between the studied glasses’ microhardness and linear attenuation coefficient was performed versus the LiO₂ concentration to select the glass sample which possesses a suitable mechanical and shielding capacity.     

Peroxone chemistry: formation of H2O3 and ring-(HO2)(HO3) from O3/H2O2

The recent observation [Wentworth, P., Jones, L. H., Wentworth, A. D., Zhu, X. Y., Larsen, N. A., Wilson, I. A., Xu, X., Goddard, W. A., Janda, K. D., Eschenmoser, A. & Lerner, R. A. (2001) Science 293, 1806-1811] that antibodies form H(2)O(2) from (1)O(2) plus H(2)O was explained in terms of the formation of the H(2)O(3) species that in the antibody reacts with a second H(2)O(3) to form H(2)O(2). There have been few reports of the chemistry for forming H(2)O(3), but recently Engdahl and Nelander [Engdahl, A. & Nelander, B. (2002) Science 295, 482-483] reported that photolysis of the ozone-hydrogen peroxide complex in argon matrices leads to significant concentrations of H(2)O(3). We report here the chemical mechanism for this process, determined by using first-principles quantum mechanics. We show that in an argon matrix it is favorable (3.5 kcal/mol barrier) for H(2)O(2) and O(3) to form a [(HO(2))(HO(3))] hydrogen-bonded complex [head-to-tail seven-membered ring (7r)]. In this complex, the barrier for forming H(2)O(3) plus (3)O(2) is only 4.8 kcal/mol, which should be observable by means of thermal processes (not yet reported). Irradiation of the [(HO(2))(HO(3))-7r] complex should break the HO-OO bond of the HO(3) moiety, eliminating (3)O(2) and leading to [(HO(2))(HO)]. This [(HO(2))(HO)] confined in the matrix cage is expected to rearrange to also form H(2)O(3) (observed experimentally). We show that these two processes can be distinguished isotopically. These results (including the predicted vibrational frequencies) suggest strategies for synthesizing H(2)O(3) and characterizing its chemistry. We suggest that the [(HO(2))(HO(3))-7r] complex and H(2)O(3) are involved in biological, atmospheric, and environmental oxidative processes.     

Experimental Investigation of Radiation Shielding Competence of Bi2O3-CaO-K2O-Na2O-P2O5 Glass Systems

The gamma-ray shielding features of Bi₂O₃-CaO-K₂O-Na₂O-P₂O₅ glass systems were experimentally reported. The mass attenuation coefficient (MAC) for the fabricated glasses was experimentally measured at seven energy values (between 0.0595 and 1.33 MeV). The compatibility between the practical and theoretical results shows the accuracy of the results obtained in the laboratory for determining the MAC of the prepared samples. The mass and linear attenuation coefficients (MACs) increase with the addition of Bi₂O₃ and A4 glass possesses the highest MAC and LAC. A downward trend in the linear attenuation coefficient (LAC) with increasing the energy from 0.0595 to 1.33 MeV is found. The highest LAC is found at 1.33 MeV (in the range of 0.092–0.143 cm⁻¹). The effective atomic number (Z_eff) follows the order B1 > A1 > A2 > A3 > A4. This order emphasizes that increasing the content of Bi₂O₃ has a positive effect on the photon shielding proficiencies owing to the higher density of Bi₂O₃ compared with Na₂O. The half value layer (HVL) is also determined and the HVL for the tested glasses is computed between 0.106 and 0.958 cm at 0.0595 MeV. The glass with 10 mol% of Bi₂O₃ has lower HVL than the glasses with 0, 2.5, 5, and 7.5 mol% of Bi₂O₃. So, the A4 glass needs a smaller thickness than the other glasses to shield the same radiation. As a result of the reported shielding parameters, inserting B₂O₃ provides lower values of these three parameters, which in turn leads to the development of superior photons shields.     

Comparison of formation of reactive conformers for the SN2 displacements by CH3CO2- in water and by Asp124-CO2- in a haloalkane dehalogenase

The S(N)2 displacement of Cl(-) from 1,2-dichloroethane by acetate (CH(3)CO(2)(-)) in water and by the carboxylate of the active site aspartate in the haloalkane dehalogenase of Xanthobacter autothropicus have been compared by using molecular dynamics simulations. In aqueous solution, six families of contact-pair structures (I-VI) were identified, and their relative concentrations and dissociation rate constants were determined. The near attack conformers (NACs) required for the S(N)2 displacement reaction are members of the IV (CH(3)COO(-)...CH(2)(Cl)CH(2)Cl) family and are formed in the sequence II-->III-->IV-->NAC. The NAC subclass is defined by the COO(-)...CCl contact distance of < or = 3.41 A and the COO(-)...CCl angle of 157-180 degrees. The mole percentage of NACs is 0.16%, based on the 1 M standard state. This result may be compared with 13.4 mole percentage of NACs in the Michaelis complex in the enzyme. It follows that NAC formation in the enzyme is favored by 2.6 kcal/mol. Because reaction coordinates from S to TS, both in water and in the enzyme, pass via NAC (i.e., S --> NAC --> TS), the reduction in the S --> NAC barrier by 2.6 kcal/mol accounts for approximately 25% of the reduction of total barrier in the S --> TS (10.7 kcal/mol). The remaining 75% of the advantage of the enzymatic reaction revolves around the efficiency of NAC --> TS step. This process, based on previous studies, is discussed briefly.     

Microcirculatory effects of total triterpenic fraction of Centella asiatica in chronic venous hypertension: measurement by laser Doppler, TcPO2-CO2, and leg volumetry

The aim of this prospective, randomized study was to demonstrate whether an oral preparation of TTFCA was effective in improving the microcirculation and edema (leg volume) in venous microangiopathy. Forty patients with venous hypertension were included. Treatment was prescribed for 6 weeks (tablets, 60 mg twice daily). Patients were randomized into a treatment and a placebo group. There were 20 patients in each group. In the treatment group the mean age was 42 (SD 7; M:F = 10:10); in the placebo group, the mean age was 40 (SD 9; M:F = 10:10). Tolerability and compliance were very good; there were no dropouts. At inclusion there were no differences between placebo and treatment group. After treatment there was a decrease in resting flux (29%) and an improvement (increase) in venoarteriolar response (52%); PO2 was increased (7.2%) and PCO2 decreased (9.6%). There was an important decrease in leg volume (66 mL decrease; 1.3% volume variation). The difference in flux, O2-CO2 and volume parameters were significant and clinically important at 6 weeks in the treatment group. In conclusion, TTFCA improves microcirculation and leg volume in venous hypertension. The effects of TTFCA are observed even in a limited sample of patients.     

Developmental patterns of O2 consumption,heart rate and O2 pulse in unturned eggs

The effects of failure to turn eggs on the developmental patterns of oxygen consumption (Ṁ_O2), heart rate (fh) and O₂ pulse during the second half of incubation of individual chicken eggs were examined. The Ṁ_O2 of unturned eggs increased at a significantly lower rate than the control toward the end of prenatal incubation, and the plateau Ṁ_O2 between day 17 and 19 was significantly lower than the control. Lack of turning also resulted in significant changes in the developmental patterns of fh and O₂ pulse. It is suggested that the effects of lack of egg-turning on the developmental patterns of Ṁ_O2 may be attributable to lower embryonic growth rate in addition to impairment of gas exchange through the chorioallantoic gas exchanger.     

Effect of the curvature of the O2 equilibrium curve on alveolar O2 uptake: theory

The effect of the curvature of the O2 equilibrium curve (OEC), in the range between mixed venous and alveolar PO2, on alveolar O2 uptake was quantitatively investigated in a simple homogeneous lung model. The O2 uptake achieved with a linear OEC (Mlin) was subtracted from the O2 uptake (M) attained with the physiologically curved, sigmoid OEC, and the relative difference was considered as the 'curvature effect', CE [= (M - Mlin)/M], indicating, if positive, the enhancement of O2 uptake by the non-linearity of the OEC. Calculations show CE to be close to nil (less than 1%) in normal lungs during rest both in normoxia and in hypoxia. CE is more important in heavy exercise both in normoxia (CE less than 19%) or slight hypoxia (CE less than 15%). In deep hypoxia, CE is negligible again even during exercise. Thus, the simplified approach to the analysis of alveolar O2 uptake using a linear OEC, in the mixed venous-to-alveolar PO2 range, constitutes in most cases a valid approximation.     

Blood flow, O2 extraction and O2 consumption along the rat small intestine

Differences in O2 delivery and consumption along the fed and fasted small intestine are described. Total wall blood flow was determined in sequential segments of small intestine from 5 to 6-month-old male, anesthetized Fischer 344 rats either 75-80 min before or after feeding, using radioactive microspheres. Oxygen saturation in submucosal arterioles and venules (50-60 micron diam) was determined throughout the intestine, using a microspectrophotometric technique. Venous O2 saturations showed considerable heterogeneity in all regions, and ranged from 0 to 77%. Arterial-venous O2 content differences (CaO2-CvO2) did not change along the fasted rat intestine, and averaged 8.2 ml O2/100 ml blood. However, CaO2-CvO2 followed a small proximal to distal gradient (proximal greater than distal) in the fed rats. Larger proximal to distal gradients (proximal greater than distal) occurred in both blood flow and O2 consumption in both groups. Feeding did not change intestinal average CaO2-CvO2. However, feeding induced a 53% increase in average O2 consumption, with the greatest increase (130%) occurring in the middle third of the intestine. Feeding induced a 42% increase in average blood flow, with the greatest increase (70%) occurring in the distal third of the intestine. The increased O2 used by the fed intestine was primarily provided by the increased blood flow. The O2 consumption gradient is assumed to reflect differences in mucosal mass along the intestine and/or differences in metabolic activity.     

Relationship between O2 delivery and O2 consumption in the adult respiratory distress syndrome

We evaluated the relationship between O2 delivery and oxygen consumption (VO2) in ten patients with the adult respiratory distress syndrome (ARDS) over the course of their illness (mean 7 +/- 5 days) while they were receiving positive mechanical ventilation with varying levels of positive end-expiratory pressure (PEEP). Mean values and standard deviations for O2 delivery and VO2 were 15.2 +/- 4.8 ml/min/kg and 4.1 +/- 1.2 ml/min/kg, respectively. In our ten patients, below an O2 delivery of 21 ml/min/kg, VO2 was linearly related to O2 delivery (VO2 = 0.32 X O2 delivery--0.53, n = 83, r = 0.76). However, at an O2 delivery rate higher than 21 ml/min/kg, there was no correlation between VO2 and O2 delivery. Mixed venous O2 content (CvO2) and arteriovenous oxygen content difference (C(a-v)O2) did not correlate with O2 delivery, nor was there a significant correlation between cardiac output (Qt) and mixed venous O2 tension (PvO2) or saturation (SvO2). We conclude that in patients with ARDS on mechanical ventilation with PEEP, VO2 and O2 delivery are linearly related except at high levels of O2 delivery. PvO2 and (C(a-v)O2) do not correlate with O2 delivery and are not sensitive indicators of tissue oxygenation in ARDS.