Comment on "A 3-hydroxypropionate/4-hydroxybutyrate autotrophic carbon dioxide assimilation pathway in Archaea"

Berg et al. (Reports, 14 December 2007, p. 1782) reported the discovery of an autotrophic carbon dioxide-fixation pathway in Archaea and implicated a substantial role of this pathway in global carbon cycling based on sequence analysis of Global Ocean Sampling data. We question the validity of the latter claim.     

不同NH4＋/NO3-配比作用下红松幼苗的氮吸收和同化特征

采用营养液培养法,研究不同NH4＋/NO3-配比供氮模式下红松幼苗的氮素吸收水平、主要氮同化酶活性及苗木生长水平。结果表明：红松幼苗在NH4＋占优势的营养条件下吸收氮素能力较强、总生物量较大。苗木根系中硝酸还原酶（NR）活性较强,营养液中的NO3-对NR活性有明显的促进作用,且随其中供NO3-比例的增加而增强。谷氨酰胺...     

Dispersion polymerizations in supercritical carbon dioxide

Conventional heterogeneous dispersion polymerizations of unsaturated monomers are performed in either aqueous or organic dispersing media with the addition of interfacially active agents to stabilize the colloidal dispersion that forms. Successful stabilization of the polymer colloid during polymerization results in the formation of high molar mass polymers with high rates of polymerization. An environmentally responsible alternative to aqueous and organic dispersing media for heterogeneous dispersion polymerizations is described in which supercritical carbon dioxide (CO(2)) is used in conjunction with molecularly engineered free radical initiators and amphipathic molecules that are specifically designed to be interfacially active in CO(2). Conventional lipophilic monomers, exemplified by methyl methacrylate, can be quantitatively (>90 percent) polymerized heterogeneously to very high degrees of polymerization (>3000) in supercritical CO(2) in the presence of an added stabilizer to form kinetically stable dispersions that result in micrometer-sized particles with a narrow size distribution.     

Cavitation-induced reactions in high-pressure carbon dioxide

The feasibility of ultrasound-induced in situ radical formation in liquid carbon dioxide was demonstrated. The required threshold pressure for cavitation could be exceeded at a relatively low acoustic intensity, as the high vapor pressure of CO2 counteracts the hydrostatic pressure. With the use of a dynamic bubble model, the formation of hot spots upon bubble collapse was predicted. Cavitation-induced radical formation was used for the polymerization of methyl methacrylate in CO2, yielding high-molecular-weight polymers. These results show that sonochemical reactions can be performed in dense-phase fluids, which allows the environmentally benign CO2 to replace conventional organic solvents in many reaction systems.     

Synthesis of fluoropolymers in supercritical carbon dioxide

Fluoropolymers are used in many technologically demanding applications because of their balance of high-performance properties. A significant impediment to the synthesis of variants of commercially available amorphous fluoropolymers is their general insolubility in most solvents except chlorofluorocarbons (CFCs). The environmental concerns about CFCs can be circumvented by preparing these technologically important materials in supercritical fluids. The homogeneous solution polymerization of highly fluorinated acrylic monomers can be achieved in supercritical carbon dioxide by using free radical methods. In addition, detailed decomposition rates and efficiency factors were measured for azobisisobutyronitrile in supercritical carbon dioxide and were compared to those obtained with conventional liquid solvents.     

Variations in the isotopic composition of carbon in urban atmospheric carbon dioxide

Measurement of the abundance of atmospheric carbon dioxide as an indicator of air pollution has been of very limited value because of variations in urban areas in the substantial concentration of natural carbon dioxide produced from combustion and noncombustion (natural) sources. A solution to this problem is the use of precise isotopic assay of ratios of carbon-13 to carbon-12 in atmospheric carbon dioxide. There is very little variation of carbon isotopic composition in samples taken over rural or urban areas where rapid mixing and diffusion of gaseous combustion products is possible. Significant differences in this composition in samples taken at centrally located points at street level in the lower Manhattan business district show an increase in concentration of atmospheric carbon dioxide of roughly 20 percent produced primarily by automobile exhaust.     

Use of carbon dioxide in enhanced oil recovery

Large volumes of oil will remain in U.S. oil reservoirs when standard recovery methods have been completed. Supercritical carbon dioxide can be used to recover part of that remaining oil. If carbon dioxide is dense enough, it extracts hydrocarbons from the oil to make a mixture miscible with crude oil. Such a mixture can recover 95 percent of the oil in controlled laboratory flow settings. Heterogeneity of reservoir rocks and the low viscosity of carbon dioxide reduce the fraction of oil recovered in projects to lower but still significant levels. With the construction of three pipelines to carry naturally occurring carbon dioxide from Colorado and New Mexico to Permian basin oil fields, large-scale implementation of enhanced oil recovery by carbon dioxide flooding is now beginning.     

碳钢二氧化碳腐蚀研究现状

二氧化碳腐蚀是油气中的二氧化碳（ＣＯ２）溶解于水后生成碳酸后引起的腐蚀。综述了在二氧化碳环境中,碳钢金属表面有产物膜和无产物膜存在的情况下腐蚀机理。分析了温度、二氧化碳分压、流速、ｐＨ值及腐蚀产物膜对二氧化碳腐蚀的影响。认为碳钢的二氧化碳腐蚀机理因金属是否形成碳酸铁（ＦｅＣＯ３）膜而不同,二氧化碳分压和洗速影响着腐蚀的阴极过程,而温度主要是影响腐蚀产物膜的形成条件。在局部腐蚀领域内开展基础性和应用     

A large terrestrial carbon sink in north america implied by atmospheric and oceanic carbon dioxide data and models

Atmospheric carbon dioxide increased at a rate of 2.8 petagrams of carbon per year (Pg C year-1) during 1988 to 1992 (1 Pg = 10(15) grams). Given estimates of fossil carbon dioxide emissions, and net oceanic uptake, this implies a global terrestrial uptake of 1.0 to 2. 2 Pg C year-1. The spatial distribution of the terrestrial carbon dioxide uptake is estimated by means of the observed spatial patterns of the greatly increased atmospheric carbon dioxide data set available from 1988 onward, together with two atmospheric transport models, two estimates of the sea-air flux, and an estimate of the spatial distribution of fossil carbon dioxide emissions. North America is the best constrained continent, with a mean uptake of 1.7 +/- 0.5 Pg C year-1, mostly south of 51 degrees north. Eurasia-North Africa is relatively weakly constrained, with a mean uptake of 0.1 +/- 0.6 Pg C year-1. The rest of the world's land surface is poorly constrained, with a mean source of 0.2 +/- 0.9 Pg C year-1.     

Land floras: the major late phanerozoic atmospheric carbon dioxide/oxygen control

Since at least the late Mesozoic, the abundance of terrestrial vegetation has been the major factor in atmospheric carbon dioxideloxygen fluctuations. Of modern ecosystem types occupying more than 1 percent of the earth's surface, productivity/area ratios of terrestrial ecosystems (excepting tundra and alpine meadow, desert scrub, and rock, ice, and sand) exceed those of marine ecosystems and probably have done so for much of late Phanerozoic time. Reduction of terrestrial ecosystems during marine transgression would decrease the world primary productivity, thus increasing the atmospheric carbon dioxide concentration and decreasing the oxygen concentration. Regression would produce opposite effects.     

Use of an organic carbon dioxide buffer in vivo

The compound 2-amino-2(hydroxymethyl)1,3-propane diol was administered intravenously to apneically oxygenated dogs over a 1-hour period. Arterial blood pH remained normal, and an estimated 18 to 28 percent of the CO(2) produced during apnea was recovered in the urine.     

Free-radical side-chain bromination of alkylaromatics in supercritical carbon dioxide

Free-radical side-chain brominations of alkylaromatics in supercritical carbon dioxide (SC-CO(2)) are reported. Direct bromination of toluene and ethylbenzene form the corresponding benzyl bromides in high yield. The observed selectivity in SC-CO(2) is similar to that observed in conventional organic solvents. Also, SC-CO(2) is an effective alternative to carbon tetrachloride for use in the classical Ziegler bromination with N-bromosuccinimide. Reaction yields are high, side products are minimized, and bromine-atom selectivities are observed. Thus, SC-CO(2) must be useful as a viable, environmentally benign substitute for many of the solvents typically used for free-radical reactions.     

Responses to elevated carbon dioxide in artificial tropical ecosystems

Carbon, nutrient, and water balance as well as key plant and soil processes were simultaneously monitored for humid tropical plant communities treated with CO(2)-enriched atmospheres. Despite vigorous growth, no significant differences in stand biomass (of both the understory and overstory), leaf area index, nitrogen or water consumption, or leaf stomatal behavior were detected between ambient and elevated CO(2) treatments. Major responses under elevated CO(2) included massive starch accumulation in the tops of canopies, increased fine-root production, and a doubling of CO(2) evolution from the soil. Stimulated rhizosphere activity was accompanied by increased loss of soil carbon and increased mineral nutrient leaching. This study points at the inadequacy of scaling-up from physiological baselines to ecosystems without accounting for interactions among components, and it emphasizes the urgent need for whole-system experimental approaches in global-change research.     

Receptors sensitive to carbon dioxide in lungs of chicken

Receptors responsive to the removal of carbon dioxide from ventilatory gas were demonstrated in the lungs of the chicken. Apnea was induced in 0.64 second after rapid lowering of respired carbon dioxide in the absence of blood flow through the lungs. Afferent impulses from the receptors are conducted centrally in the vagi.     

Enzymatic oxidation of cholesterol aggregates in supercritical carbon dioxide

Fundamental studies of enzyme-solvent interactions can be conducted with supercritical fluids because small changes in pressure or temperature may bring about great changes in the properties of a single solvent near its critical point. Cholesterol oxidase is active in supercritical carbon dioxide and supercritical carbon dioxide-cosolvent mixtures. Variations in solvent power caused by pressure changes or by the addition of dopants affected the rate of enzymatic oxidation of cholesterol by altering the structure of cholesterol aggregates.