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1.
D. J. Cherniak 《Physics and Chemistry of Minerals》2008,35(4):179-187
Self-diffusion of Si under anhydrous conditions at 1 atm has been measured in natural zircon. The source of diffusant for
experiments was a mixture of ZrO2 and 30Si-enriched SiO2 in 1:1 molar proportions; experiments were run in crimped Pt capsules in 1-atm furnaces. 30Si profiles were measured with both Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis with the resonant
nuclear reaction 30Si(p,γ)31P. For Si diffusion normal to c over the temperature range 1,350–1,550°C, we obtain an Arrhenius relation D = 5.8 exp(−702 ± 54 kJ mol−1/RT) m2 s−1 for the NRA measurements, which agrees within uncertainty with an Arrhenius relation determined from the RBS measurements
[62 exp(−738 ± 61 kJ mol−1/RT) m2 s−1]. Diffusion of Si parallel to c appears slightly faster, but agrees within experimental uncertainty at most temperatures
with diffusivities for Si normal to c. Diffusion of Si in zircon is similar to that of Ti, but about an order of magnitude faster than diffusion of Hf and two
orders of magnitude faster than diffusion of U and Th. Si diffusion is, however, many orders of magnitude slower than oxygen
diffusion under both dry and hydrothermal conditions, with the difference increasing with decreasing temperature because of
the larger activation energy for Si diffusion. If we consider Hf as a proxy for Zr, given its similar charge and size, we
can rank the diffusivities of the major constituents in zircon as follows: D
Zr < D
Si << D
O, dry < D
O, ‘wet’. 相似文献
2.
介绍了一种电子继电器,具有对恒温系统中加热元件的无触点控制和无级设定功率,以及自动适应电压变化的补偿功能。 相似文献
3.
Dissolved aluminium and the silicon cycle in the Arctic Ocean 总被引：1，自引：0，他引：1
Concentrations of dissolved (0.2 µm filtered) aluminium (Al) have been determined for the first time in the Eurasian part of the Arctic Ocean over the entire water column during expedition ARK XXII/2 aboard R.V. Polarstern (2007). An unprecedented number of 666 samples was analysed for 44 stations along 5 ocean transects. Dissolved Al in surface layer water (SLW) was very low, close to 1 nM, with lowest SLW concentrations towards the Canadian part of the Arctic Ocean and higher values adjacent to and in the shelf seas. The low SLW concentrations indicate no or little influence from aeolian dust input. Dissolved Al showed a nutrient-type increase with depth up to 28 nM, but large differences existed between the different deep Arctic basins. The differences in concentrations of Al between water masses and basins could largely be related to the different origins of the water masses. In the SLW and intermediate water layers, Atlantic and Pacific inflows were of importance. Deep shelf convection appeared to influence the Al distribution in the deep Eurasian Basin. The Al distribution of the deep Makarov Basin provides evidence for Eurasian Basin water inflow into the deep Makarov Basin. A strong correlation between Al and Silicon (Si) was observed in all basins. This correlation and the nutrient-like profile indicate a strong biological influence on the cycling and distribution of Al. The biological influence can be direct by the incorporation of Al in biogenic silica, indirect by preferential scavenging of Al onto biogenic siliceous particles, or by a combination of both processes. From the slope of the overall Al–Si relationship in the intermediate water layer (AIDW; ~ 200–2000 m depth), an Al/Si ratio of 2.2 atoms Al per 1000 atoms Si was derived. This ratio is consistent with the range of previously reported Al/Si uptake ratio in biogenic opal frustules of diatoms. In the deepest waters (>2000 m depth) a steeper slope of the Al–Si relationship of 7.4 to 13 atoms Al per 1000 atoms Si likely results from entrainment of cold shelf water into the deep basins, carrying the signal of dissolution of terrigenous particles with a much higher Al:Si ratio of crustal abundance. Only a small enrichment with such crustal Al and Si component may readily account for the higher Al:Si slope in the deepest waters. 相似文献
4.
Dissolved aluminium (Al) is generally at low concentrations in neutral freshwater due to its insolubility. However, a fall in pH resulting from acid deposition and mining alters the mobility of Al and so entry to adjacent neutral waters. The present study examines the environmental behaviour, cell-associated surface adsorption/absorption and toxicity of Al at neutral pH to the alga Chlamydomonas gigantea in the presence and absence of the key Al-binding ligand silica. We then examined transfer of Al from C. gigantea to the planktonic crustacean Daphnia pulex. Finally, the effect of Al on the elemental composition (and hence nutritional value) of the two organisms was compared to unexposed controls. C. gigantea increased the amount of Al in the algal culture medium. Binding of Al to extracellular glycoprotein is probably the reason why only one-third of the biosorbed Al was absorbed (accumulated) by C. gigantea. Aluminium concentrations between 50 and 500 μg l−1 reduced growth of C. gigantea at 16 days exposure to the metal. Silica reduced biosorption, accumulation and toxicity of Al by C. gigantea. The concentration of Al in D. pulex fed Al-contaminated C. gigantea for 16 days did not differ from those fed alga grown in the absence of added Al. C. gigantea contaminated with Al contained less sulphur, magnesium, potassium and sodium although only sulphur fell in D. pulex subsequently fed the contaminated alga. Chloride, calcium, iron and silicon were significantly higher in D. pulex. 相似文献
5.
Governing a city of unicorns: technology capital and the urban politics of San Francisco 总被引：1，自引：1，他引：0
Donald McNeill 《Urban geography》2016,37(4):494-513
San Francisco is now widely considered to be the most important city in the world for the location of new technology start-up firms, especially high valuation “unicorns,” and is increasingly seen as both a locational and metaphorical extension of Silicon Valley. In this paper, I trace some of the political strategies and tensions that have accompanied the city’s prominence in this area, and in particular the distinctive role of technology and venture capital in the political economy of urban development. The paper has four empirical sections. It describes (1) the political machinations surrounding the 2011 and 2015 municipal elections, which saw the election of Ed Lee as Mayor with significant support from individual technology investors such as Ron Conway and Marc Benioff, and accompanied by various “tech-friendly” policy shifts; (2) the foundation of the “tech chamber of commerce” sf.citi as a means of enhancing the policy influence of the tech industry in San Francisco; (3) the introduction of a low taxation regime in the city’s Central Market area that has attracted technology companies such as Twitter as tenants; and (4) the urban policy tensions associated with the evolution of new “sharing economy” firms such as Uber and Airbnb, which have aggressively challenged municipal regulations in the taxi and property rental fields. Throughout these machinations, we can see a reshaping of capital fractions, with venture and angel capital increasingly involved in reengineering the labor, housing, and public transport markets of the city in order to circumvent the accumulation problems that tech investors had suffered in the earlier dot.com failures. 相似文献
6.
Mathieu Mongin David M. Nelson Philippe Pondaven Mark A. Brzezinski Paul Trguer 《Deep Sea Research Part I: Oceanographic Research Papers》2003,50(12):1445-1480
We report the first application of a biogeochemical model in which the major elemental composition of the phytoplankton is flexible, and responds to changing light and nutrient conditions. The model includes two phytoplankton groups: diatoms and non-siliceous picoplankton. Both fix C in accordance with photosynthesis-irradiance relationships used in other models and take up NO3− and NH4+ (and Si(OH)4 for diatoms) following Michaelis-Menten kinetics. The model allows for light dependence of photosynthesis and NO3− uptake, and for the observed near-total light independence of NH4+ uptake and Si(OH)4 uptake. It tracks the resulting C/N ratios of both phytoplankton groups and Si/N ratio of diatoms, and permits uptake of C, N and Si to proceed independently of one another when those ratios are close to those of nutrient-replete phytoplankton. When the C/N or Si/N ratio of either phytoplankton group indicates that its growth is limited by N, Si or light, uptake of non-limiting elements is controlled by the content of the limiting element in accordance with the cell-quota formulation of Droop (J. Mar. Biol. Ass. U.K 54 (1974) 825).We applied this model to the Bermuda Atlantic Time-series Study (BATS) site in the western Sargasso Sea. The model was tuned to produce vertical profiles and time courses of [NO3−], [NH4+] and [Si(OH)4] that are consistent with the data, by adjusting the kinetic parameters for N and Si uptake and the rate of nitrification. The model then reproduces the observed time courses of chlorophyll-a, particulate organic carbon and nitrogen, biogenic silica, primary productivity, biogenic silica production and POC export with no further tuning. Simulated C/N and Si/N ratios of the phytoplankton indicate that N is the main growth-limiting nutrient throughout the thermally stratified period and that [Si(OH)4], although always limiting to the rate of Si uptake by diatoms, seldom limits their growth rate. The model requires significant nitrification in the upper 200 m to yield realistic time courses and vertical profiles of [NH4+] and [NO3−], suggesting that NO3− is not supplied to the upper water column entirely by physical processes. A nitrification-corrected f-ratio (fNC), calculated for the upper 200 m as: (NO3− uptake—nitrification)/(NO3− uptake+NH4+ uptake) has annual values ranging from only 0.05–0.09, implying that 90–95% of the N taken up annually by phytoplankton is supplied by biological regeneration (including nitrification) in the upper 200 m. Reported discrepancies between estimates of organic C export based on seasonal chemical changes and POC export measured at the BATS site can be almost completely resolved if there is significant regeneration of NO3− via organic-matter decomposition in the upper 200 m. 相似文献
7.
绿政是在全球金融危机、气候危机和能源危机背景下，世界各国为契合可持续发展战略，借鉴历史危机应对经验的一种对全球未来发展模式的探索与尝试，硅谷作为世界科技创新中心，以其极强的创新能力和探索精神，持续主导全球经济发展方向。近10年来，硅谷创新的理论和实践重点正向以绿色科技和清洁能源开发为主的绿政之路布局，被美国各级政府2008年后针对金融危机所采取的一系列经济复苏刺激政策推波助澜，成为推动硅谷地区各企业、政府和学术界不断互动与创新的主导趋势，不断刷新硅谷的经济繁荣和科技进步，引领着全球创新的未来。本文详细分析硅谷该轮绿政探索的思考与实践及其对我国的启示，以期为我国经济的可持续发展提供借鉴。 相似文献
8.
氮磷硅对咖啡双眉藻和缢缩菱形藻繁殖速度和油脂积累的影响 总被引：1，自引：0，他引：1
采用光密度法和尼罗红染色法,探索了氮、磷、硅对从温州海区分离出的底栖硅藻咖啡双眉藻(Amphora coffeaeformis)和缢缩菱形藻(Nitzschia constricta)的繁殖速度和油脂积累的影响。结果显示,2种底栖藻在NO3-N质量浓度为1.746 mg/L时,细胞均不繁殖,且在实验第7天开始死亡,当NO3-N质量浓度再升高后,细胞繁殖速度开始加快,质量浓度达8.820 mg/L后,藻细胞的繁殖速度不再明显加快;2种藻类的繁殖速度均随H2PO4-P质量浓度升高而加快,但当质量浓度达到0.884 mg/L后,藻细胞的繁殖速度不再明显加快;2种底栖藻类均随Si O3-Si质量浓度增加而加快,但质量浓度对2种底栖硅藻细胞繁殖速度影响并不显著。3种元素对2种底栖硅藻繁殖速度的影响力:NPSi。实验期间,2种底栖硅藻的油脂含量均呈先降后升的变化规律,油脂的积累主要集中在实验后期,氮磷硅限制均能促进2种底栖硅藻细胞油脂的积累,对2种硅藻细胞油脂积累的影响程度,氮限制比磷和硅限制都要大。 相似文献
9.
介绍了晶安高科污染源的来源、采取的措施及综合治理、利用方法.使废水指标由PH11～12;SS<1000mg/l;CODcr≤200mg/l;氨氮≤200mg/l降到PH6～9;SS<70mg/l;CODcr≤100mg/l;氨氮≤15mg/l;酸雾指标由HCl500～800mg/m3达到小于25～40mg/m3;炉窑烟气由林格曼黑度5,烟尘浓度2700～5191mg/Nm3降到林格曼黑度1,烟尘浓度小于200mg/Nm3;硅渣可生产复合絮凝剂和白炭黑,不仅可改善环境影响,而且可回收盐酸和利用废资源,可给企业带来经济效益. 相似文献
10.
滤光罩是地球辐射表的关键部件, 其性能直接影响着该仪器的性能与质量.利用LOWTRAN 7和国产各种滤光罩实测的光谱透射比数据, 对不同的模式大气下各滤光罩有效透射比等性能指标进行计算, 并与Eppley罩的研究情况作了对比.结果表明, 国产罩的各项性能指标并不次于Eppley罩. 相似文献