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991.
Electrolyte powders with low sintering temperature and high-ionic conductivity can considerably facilitate the fabrication and performance of solid oxide fuel cells (SOFCs). Gadolinia-doped ceria (GDC) is a promising electrolyte for developing intermediate- and low-temperature (IT and LT) SOFCs. However, the conventional sintering temperature for GDC is usually above 1200 °C unless additives are used. In this work, a nanocrystalline powder of GDC, (10 mol% Gd dopant, Gd0.1Ce0.9O1.95) with low-sintering temperature has been synthesized using ammonium benzoate as a novel, environmentally friendly and cost-effective precursor/precipitant. The synthesized benzoate powders (termed washed- and non-washed samples) were calcined at a relatively low temperature of 500 °C for 6 h. Physicochemical characteristics were determined using thermal analysis (TG/DTA), Raman spectroscopy, FT-IR, SEM/EDX, XRD, nitrogen absorptiometry, and dilatometry. Dilatometry showed that the newly synthesized GDC samples (washed and non-washed routes) start to shrink at temperatures of 500 and 600 °C (respectively), reaching their maximum sintering rate at 650 and 750 °C. Sintering of pelletized electrolyte substrates at the sintering onset temperature for commercial GDC powder (950 °C) for 6 h, showed densification of washed- and non-washed samples, obtaining 97.48 and 98.43% respectively, relative to theoretical density. The electrochemical impedance spectroscopy (EIS) analysis for the electrolyte pellets sintered at 950 °C showed a total electrical conductivity of 3.83 × 10?2 and 5.90 × 10?2 S cm?1 (under air atmosphere at 750 °C) for washed- and non-washed samples, respectively. This is the first report of a GDC synthesis, where a considerable improvement in sinterability and electrical conductivity of the product GDC is observed at 950 °C without additives addition. 相似文献
992.
Robert E. Goldstein Giora Z. Feuerstein Linda M. Bradley Joseph J. Stambouly Francisco R. M. Laurindo Nancy J. Davenport 《Lipids》1991,26(12):1250-1256
Sudden release of platelet-activating factor (PAF) into the circulation can cause hypotension, tachycardia, and circulatory
collapse. To further examine this response, we performed detailed studies of cardiovascular function after PAF administration
to young domestic pigs and newborn piglets. Our results indicate that circulatory dysfunction after PAF reflects severe constriction
of pulmonary resistance vessels and consequent acute right ventricular failure. Although PAF-induced coronary artery constriction
and contractile depression may be complicating problems, left ventricular underperfusion and dysfunction after PAF are mainly
the result of systemic arterial hypotension and diminished left ventricular filling. The adverse hemodynamic effects of PAF
are accompanied by substantial release of thromboxane A2 (TxA2). These effects are mimicked by the TxA2 agonist U-46619 and partially blocked by specific and nonspecific inhibitors of TxA2 synthesis (OKY-046 and indomethacin). Even more potent blockade of PAF action is exerted by the TxA2 receptor blocker, SQ 29,548. Taken together, these findings indicate that severe pulmonary vascular constriction and hemodynamic
collapse soon after intravenous PAF are at least partially mediated by PAF-induced TxA2 release.
Tachyphylaxis to PAF influence has been observed in studies of leukocyte and platelet function. We hypothesized that tachyphylaxis
to PAF might also occur in our studies of constrictor responses in pulmonary vessels. Recently, we have examined the capacity
of PAF to produce sustained pulmonary vasoconstriction in openchested, anesthetized newborn piglets. Infusions sufficient
to produce 100% increase in mean pulmonary artery pressure after 3 min showed no loss of efficacy when sustained for 30 min.
The same was true for infusions of U-46619. Thus, the pulmonary vasoconstrictor influence of PAF or U-46619 is not readily
diminished by tachyphylaxis. These findings favor the viewpoint that PAF or TxA2 release during inflammatory processes could have prolonged adverse actions on pulmonary and systemic circulations.
Based on a paper presented at the Third International Conference on Platelet-Activating Factor and Structurally Related Alkyl
Ether Lipids, Tokyo, Japan, May 1989.
The opinions or assertions contained here are those of the authors. They do not reflect the views of the Department of Defense
or the Uniformed Services University of the Health Sciences. The experiments reported here were conducted according to the
principles set forth in the “Guide for the Care and Use of Laboratory Animals,” Institute of Laboratory Animal Resources,
U.S. Department of Health and Human Services (NIH Publ. 85-23, 1985). 相似文献
993.
Single crystals of CaO-stabilized ZrO2 containing between 15.3 and 18.9 mol% CaO were heat-treated for 5000 h at 1200°C to study the stability of the ordered defect-fluorite phase, CaZr4 O9 (φ1 ). Subsequent TEM analysis of the equiaxed φ1 domains in samples richer than approximately 18 mol% in CaO showed a random distribution of φ1 variants, with no preferred interfacial habit planes. A critical review of the literature, combined with the new data, supports the Stubican-Hellmann-Hannon version of the phase diagram in the region 15 to 26 mol% CaO and 1000° to 1400°C and strongly suggests that φ1 is a stable phase in the ZrO2 -CaO systems. 相似文献
994.
Niobium pentoxide (T form, orthorhombic system) was utilized to promote devitrification in Li2 O · Al2 O3 · 6SiO2 glasses. Two or more mole percentage of this nucleating dopant enhanced crystallization in these glasses. Glasses containing 4.0 and 8.0 mol% T-Nb2 O5 exhibited a high tendency to form dispersed TT-Nb2 O5 (monoclinic system) precipitates during the glass quenching process. The crystallization process in glasses containing 2.0 or 4.0 mol% T-Nb2 O5 occurred as microphase separation, followed by the formation of dispersed TT-Nb2 O5 crystalline precipitates (760°C), followed by β-quartz solid-solution ( ss ) formation (850° to 900°C) heterogeneously nucleated from the precipitates. β-quartz( ss ) transformed to β-spodumene( ss ), along with a polymorphic transition from the TT-Nb2 O5 to M-Nb2 O5 (tetragonal system) crystalline phase. 相似文献
995.
In the course of isolating and analyzing the fatty acid methyl esters (FAME) from steelhead trout (Salmo gairdneri) eggs and sac fry, a component was found on gas liquid chromatography to have a retention time longer than any characteristic
polyunsaturated fatty acid previously encountered in trout. Subsequent purification and analysis demonstrated this component
to be cholesterol. Thus, cholesterol and related compounds can interfere in the analysis of FAME when the methyl esters are
prepared by transesterification. 相似文献
996.
X-ray Photoelectron Spectroscopy (XPS) was used to study mineral, synthetic and coal-associated pyrites, oxidized for various time intervals at low temperatures with humid air or oxygen. This was done to find out if XPS could detect, monitor and clarify pyrite surface-oxidative changes that influence surface-dependent coal-cleaning methods such as froth flotation, and could provide a means of directly analysing coal sulphur, by determining if oxidizing conditions existed which would effectively eliminate the surface pyrite whose XPS peak may occur at the same energy as the organic sulphur peak of coal. The conditions of study were as follows: a mineral and two coals containing pyrite were exposed to air at 24 ± 3 ° C and 33 ± 8% relative humidity up to 600 h; two mineral pyrites were exposed to oxygen at 100% relative humidity and 35 ° C for up to 200 h; and the two mineral and a synthetic pyrite were exposed to oxygen at 100% relative humidity and 55 ° C for up to 300 h and at 72°C for 25 h. The results indicated that the XPS S2p pyrite peak at ≈169 eV and the surface-oxidation-product(s) peak(s) at ≈163 eV could be detected and followed with XPS, although no conclusions could be made about the oxidation mechanism. The pyrite XPS peak became small compared to that of its oxidation products when the synthetic and mineral pyrites were exposed to 55 ° C oxygen at 100% relative humidity for 300 h. These conditions may prove useful in trying to determine directly the organic sulphur in coal. 相似文献
997.
Stephen S. Chang Robert J. Peterson Chi-Tang Ho 《Journal of the American Oil Chemists' Society》1978,55(10):718-727
Deep-fat frying is one of the most commonly used procedures for the preparation and manufacture of foods in the world. During
deep-fat frying, oxidative and thermal decompositions may take place with the formation of volatile and nonvolatile decomposition
products, some of which in excessive amounts are harmful to human health. A limited survey of frying fats used in commercial
operations indicated that some were maintained at good quality and others were overused or abused. The volatile decomposition
products produced by corn oil, hydrogenated cotton-seed oil, trilinolein, and triolein, under simulated commercial frying
conditions, were collected, fractionated, and identified. A total of 211 compounds were identified. The nonvolatile decomposition
products produced by trilinolein, triolein, and tristearin under simulated commercial frying conditions were collected and
characterized. After being treated under deep-fat frying conditions at 185 C for 74 hr, trilinolein yielded 26.3% non-urea-adduct-forming
esters, triolein yielded 10.8%, and tristearin also yielded 4.2%. 相似文献
998.
999.
Aldo M. Crugnola Eric L. Radin Robert M. Rose Igor L. Paul Sheldon R. Simon Mark B. Berry 《应用聚合物科学杂志》1976,20(3):809-812
Currently there is widespread use of ultrahigh molecular weight polyethylene (UHMWPE) acetabular components in total joint replacement prostheses. What has been most surprising about the wear of UHMWPE under such circumstances is the occurrence of brittle fracture. Such fracture had not been observed in the usual engineering tests done in the laboratory on UHMWPE. It was only when prosthese which had been removed from patients were examined or run in hip joint simulators with serum or synovial fluid as the lubricant, that brittle fracture was encountered. The problem of environment-enhanced brittle fracture in plastics dates back to 1946. Interestingly, the phenomenon was first described in polyethylene. The prime variables involved are polymer molecular weight, sensitizing environment, stress filed, and temperature. Other things being equal, brittle behavior in polyethylene is extremely sensitive to the amount of low molecular weight polymer present. In the light of the foregoing we have studied the molecular weight distribution in six commercially available UHMWPE components. These were obtained from six different manufacturers. The specimens were characterized both on their bearing (wear) surfaces and in their interior bulk. The results obtained indicate that:
- 1 The UHMWPE components contain substantial amounts of low molecular weight polymer.
- 2 The UHMWPE components differ significantly in molecular weight distribution.
- 3 The UHMWPE components contain substantial amounts of crosslinked polymer.
1000.
Abstract. A generalized autoregressive (GAR) process {Z ( t ) ; t = 0 , ±1, …} is defined to satisfy the recurrence relation Z(t) = Aθ (t)Z (t -l)+ u( t ), where {Aθ (t); t = 0,±1, …} is itself a stochastic process depending on a vector parameter θ and where {u( t ); t = 0, ±1, …} is white noise with Eu 2 ( t ) = a 2 . This paper develops theory and methodology and implementing the class of GAR processes for time series modeling and forecasting. Conditions on the 'parameter process' { A θ ( t ); t = 0, ±1, …} are obtained for the existence of a GAR process; necessary and sufficient conditions on { Aθ ( t ) ; t = 0, ±1, …} for existence of a stationary GAR process are also obtained. Procedures are developed for computing maximum likelihood estimates of the parameters 0 and u2 and for computing the minimum mean squared error forecasts for GAR processes. 相似文献