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861.
Eric D. Wachsman Sai Boyapati Michael J. Kaufman Naixiong Jiang 《Journal of the American Ceramic Society》2000,83(8):1964-1968
Stabilized bismuth oxides undergo a decay in conductivity when subjected to annealing at temperatures of <600°C, because of the formation of an ordered superstructure, which is observed in transmission electron microscopy (TEM) diffraction patterns. Neutron-diffraction studies of the aged samples indicate that there is a displacement of almost all the anions, from the regular 8c sites to interstitial 32f sites. Based on the TEM patterns and the displacement of the oxygen ions, various structural models for the superstructure have been analyzed. From this work, it can be deduced that the observed decay in conductivity is due to the ordering of the oxygen sublattice, along with a possible concomitant ordering of cations. 相似文献
862.
863.
Eric N. Kaufman Mark H. Little Punjai T. Selvaraj 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1996,66(4):365-374
A combined chemical and biological process for the recycling of flue gas desulfurization (FGD) gypsum into calcium carbonate and elemental sulfur is demonstrated. In this process, a mixed culture of sulfate-reducing bacteria (SRB) utilizes sewage digest as its carbon source to reduce FGD gypsum to hydrogen sulfide. The sulfide is then oxidized to elemental sulfur via reaction with ferric sulfate, and accumulating calcium ions are precipitated to calcium carbonate using carbon dioxide. Employing anaerobically digested-municipal sewage sludge (AD-MSS) medium as a carbon source, SRB in serum bottles demonstrated an FGD gypsum reduction rate of 8 mg dm−3 h−1 (109 cells)−1. A chemostat with continuous addition of both AD-MSS medium and gypsum exhibited sulfate reduction rates as high as 1·3kg FGD gypsumm−3 day−1. The increased biocatalyst density afforded by cell immobilization in a columnar reactor allowed a productivity of 152 mg SO4 dm−3 h−1 or 6·6kg FGD gypsum m−3 day−1. Both reactors demonstrated 100% conversion of sulfate, with 75–100% recovery of elemental sulfur and as high as 70% COD utilization. Calcium carbonate was recovered from the reactor effluent upon precipitation using carbon dioxide. The formation of two marketable products—elemental sulfur and calcium carbonate—from FGD gypsum sludge, combined with the use of a low-cost carbon source and further improvements in reactor design, promises to offer an attractive alternative to the landfilling of FGD gypsum. 相似文献
864.
MD Simms M Freundlich ES Battistelli ND Kaufman 《Canadian Metallurgical Quarterly》1999,78(1):166-183
As the 20th century draws to a close, fundamental changes in the organization, financing, and delivery of health care and welfare services, principally directed at poor families, are likely to result in an increased number of children entering out-of-home care. These children typically have significant physical, mental health, and developmental problems. Whether the quality of health care services they receive will improve as a result of health care reform efforts and new approaches to service delivery remains to be seen. This article addresses some of the major changes wrought by welfare and health care reform and describes the essential features of a health care system that can meet the special needs of children in care. 相似文献
865.
L Kaufman AF Vargas CE Coimbra Júnior RV Santos FM Salzano MH Hutz 《Canadian Metallurgical Quarterly》1999,71(1):87-98
We analyzed tissue samples from bottlenose dolphins (Tursiops truncatus) that had stranded on beaches in Texas and Florida over a 1-year period starting in September 1991. The concentrations of 10 elements plus methyl mercury (MeHg) were determined in brain, kidney, and liver, and we examined these results for differences based upon age, site, sex, and tissue type. A strong inverse relationship between total mercury (Hg) and the percentage that was MeHg was found in liver, kidney, and brain tissue, presumably due to demethylation of MeHg. A threshold concentration was found for total Hg in brain tissue, indicating that most Hg was present as MeHg up to about 8 years of age. Increases in total Hg after this age were accompanied by an increase in the ratio of total Hg to MeHg, indicating demethylation. Strong relationships were found between total Hg in liver and age and between total Hg and selenium in liver, which have been observed before in many fish- and squid-eating marine mammals. The only difference based on sex of the animals was observed for MeHg, which was higher in females and contrary to the pattern often observed for organic contaminants. Several elements (copper, Hg, lead, zinc) exhibited intersite differences, which were not consistent. Bottlenose dolphin from Florida exhibited the highest levels of MeHg and total Hg, while animals from Texas exhibited the highest levels of lead, copper, and zinc. The essential elements copper and zinc were expected to be the same for the Texas and Florida animals; however, observed differences may indicate population differences in basic physiological levels, dietary intake, or health status. 相似文献
866.
Eric N Kaufman Abhijeet P Borole Robert Shong Jerry L Sides Cliff Juengst 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1999,74(10):1000-1004
Biological removal of organic sulfur from petroleum feedstocks may offer an attractive alternative to conventional thermochemical treatment due to the mild operating conditions and greater reaction specificity afforded by the nature of biocatalysis. Previous investigations have either reported the desulfurization of model sulfur compounds in organic solvents or gross desulfurization of crude oil without data on which sulfur species were being removed. This study reports initial sulfur speciation data for thiophenic sulfur compounds present in crude oil which may be used as a guide both as to which species are treated by the biocatalyst investigated as well as to where biocatalyst development is needed to improve the extent of biological desulfurization when applied to whole crudes. Biodesulfurization of two different crude oils in the 22–31 ° API specific gravity range with total sulfur contents between 1 and 2% is demonstrated in 1‐dm3 batch stirred reactors using wild type Rhodococcus sp IGTS8. While analysis of the crudes before and after biodesulfurization did not reveal a decrease in total sulfur, GC–MS did reveal significant (43–99%) desulfurization of dibenzothiophenes (DBT) and substituted DBTs. Fractionation of the whole crude, followed by analysis using gas chromatography–sulfur chemiluminescence detection (GC–SCD) of the aromatic fraction of the Van Texas crude oil, demonstrated a reduction of sulfur in this fraction from 3.8% to 3.2%. This research indicates that IGTS8 may be capable of biodesulfurization of refined products such as gasoline and diesel whose predominant sulfur species are dibenzothiophenes. Further biocatalyst development would be needed for effective treatment of the spectrum of sulfur‐bearing compounds present in whole crudes. 相似文献
867.
Construction of an enzymatically active ribonuclease H domain of human immunodeficiency virus type 1 reverse transcriptase 总被引:1,自引:0,他引:1
868.
Eran Y. Bellin William T. Markis Alice M. Hellebrand Christine M. Busby Katy A. Wane Camille R. Jordan Jordan G. Ledvina Steven M. Kaplan Todd R. Metzroth Greg S. Williams Arif Nazir Nathan W. Levin Allen M. Kaufman 《Hemodialysis international. International Symposium on Home Hemodialysis》2023,27(4):465-474