The compressibility of silicate liquids containing Fe2O3 and the effect of composition,temperature, oxygen fugacity and pressure on their redox states     

Victor C. Kress  Ian S. E. Carmichael 《Contributions to Mineralogy and Petrology》1991,108(1-2):82-92

Ultrasonic longitudinal acoustic velocities in oxidized silicate liquids indicate that the pressure derivative of the partial-molar volume of Fe₂O₃ is the same in iron-rich alkali-, alkaline earth- and natural silicate melt compositions at 1 bar. The dV/dP for multicomponent silicate liquids can be expressed as a linear combination of partial-molar constants plus a positive excess term for Na₂O−Al₂O₃ mixing. Partial-molar properties for FeO and Fe₂O₃ components allow extension of the empirical expression of Sack et al. (1980) to permit the calculation of Fe-redox equilibrium in a natural silicate liquid as a function of composition, temperature, fo₂ and pressure; a more formal thermodynamic expression is presented in the Appendix. The predicted equilibrium fo₂ of natural silicate melts, of fixed oxygen content, closely parallels that defined by the metastable assemblage fayalite+magnetite+β-quartz (FMQ), in pressure-temperature space. A silicate melt initially equilibrated at 3 GPa and FMQ, will remain within approximately 0.5 log₁₀ units of FMQ during its closed-system ascent. Thus, for magmas closed to oxygen, iron-redox equilibrium in crystal-poor pristine glassy lavas represents an excellent probe of the relative oxidation state of their source regions.  相似文献   

用超速CT机检测99例无症状香港中国人降低钙指数     

吴敬文  戴有鼎 《CT理论与应用研究》1994,3(4):34-34

回顾分析Ｍａｔｉｌｄａ医院超速ＣＴ室筛选首批病人中９９例中国人资料，很明显从通常采用１３０－１００Ｈｏｕｎｓｆｉｅｌｄ单位作为检出冠状血管钙化的基数应用至中国人身上其阈值数目需要降低，同时，我们也发现如果病人年龄按每１０年范围分组（２１－３０，３０－４０，４１－５０，５１－６０）而计算其超速ＣＴ的钙化指数会较随机男女一起按平均计算更易区分其差异．进一步分析显示，男性中年时候超速ＣＴ指数已达最高值，而女性则晚１０年方达最高值，因此，为了更易探测冠脉循环内钙化倾向应作出超速ＣＴ检出钙化的指数数目．这些实践经验对动脉粥样硬化过程的预测或预防有实际意义．  相似文献   

The annual cycle of kiel bight plankton: A long-term analysis     

Victor Smetacek 《Estuaries and Coasts》1985,8(2):145-157

Over the past decade, the annual cycle of the major pelagic processes in relation to environmental factors and species composition of the plankton has been studied intensively at a fixed station in Kiel Bight. A series of sequential phases, differentiated according to characteristic properties, succeed each other in a recurring pattern each year. The following phases have been differentiated: the spring diatom bloom, the late spring copepod maximum, the summer stratification, the fall blooms and the winter dormancy. Each phase represents a particular pattern of biogenous element cycling, both within the pelagic system and between the pelagic and benthic systems. Each phase is also characterized by a spectrum of dominant species, many of which do not recur each year. Greatest variation is found amongst bloom diatoms, whereas large, slow-growing species such as the Ceratia and most metazooplankton are highly recurrent. Variation in species composition is not related to long-term trends since the past century, in spite of the considerable increase in anthropogenic nutrient input to the Bight. Short-term events appear to determine occurrence of fast-growing species, many of which have benthic resting stages in their life histories. It is concluded that more attention should be paid to life history strategies of species if the mechanisms of seasonal succession are to be elucidated. Long-term observations on appearance or absence of the various species in relation to environmental properties can provide clues as to the nature of these life history strategies.  相似文献   

Effect of waves in the redistribution of sediments along the Konkan coast     

G Victor Rajamanickam  P Vethamony  A R Gujar 《Journal of Earth System Science》1986,95(2):237-244

From the wave refraction diagrams it is delineated that the Jaigad Head and Warori Bluff are the zones of wave energy convergence and the Narvan and Ambwah bays the areas of wave energy divergence. The presence of two distinct mineral phases noticed at the Jaigad, Ambwah and Varvade bays shows that there are two different circulations of sediment movements. The presence of natural barriers restricts the movement of sediment along the coast. The sand bar at the mouth of the Jaigad Bay has different orientations during the monsoon and non-monsoon periods causing obstruction to navigation during the former period.  相似文献   

Book reviews     

David M. Nelson  William Berry Lyons  Victor S. Kennedy  Richard Dame 《Estuaries and Coasts》1982,5(4):325-327

  相似文献   

Subtidal distribution of barnacles (Cirripedia: Balanidae) in Chesapeake Bay,Maryland     

Victor S. Kennedy  Jane DiCosimo 《Estuaries and Coasts》1983,6(2):95-101

From 1977 to 1980, samples of barnacles were collected (as opportunities arose) from 61 subtidal locations (mostly oyster beds) around Chesapeake Bay, Maryland. Three species were identified from the area.Balanus improvisus dominated, comprising 83% of the 8,231 barnacles identified, and was collected at all locations but one. It occurred over a collection salinity range of 0.8‰ to 17.9‰.Balanus subalbidus (14% of the barnacles identified) was collected over the same salinity range, but mainly in lower salinity waters.Balanus eburneus was scarce (2% of the barnacles identified) and was collected at higher salinities (8.5‰ to 17.1‰).  相似文献   

On Invisible Trade Relations between Mesopotamian Cities during the Third Millennium B.C.     

Audrey Bossuyt  Laurence Broze  Victor Ginsburgh 《The Professional geographer》2001,53(3):374-383

The idea that the emergence of writing was necessity due to the increase in both the number of economic transactions and political complexity has been recently emphasized by Matthews, who also underlines that writing acted as a feedback in enabling and encouraging the growth of ever more complex modes of exchange. The intertwinement of trade and writing suggests that clay tablets left by the civilizations from the third millennium B.C. in Mesopotamia, where writing was invented, may be considered as traces of trade links and transactions between cities. We estimate a gravity model based on clay tablets, as if they represented trade flows. The parameters lead us to conclude that Mesopotamia formed a strongly integrated market.  相似文献   

Scale Invariances in the Morphology and Evolution of Braided Rivers   总被引：1，自引：0，他引：1  

Efi Foufoula-Georgiou  Victor Sapozhnikov 《Mathematical Geology》2001,33(3):273-291

This paper presents an overview and synthesis of an extensive research effort to characterize and quantify scale invariances in the morphology and evolution of braided rivers. Braided rivers were shown to exhibit anisotropic spatial scaling (self-affinity) in their morphology, implying a statistical scale invariance under appropriate rescaling of the axes along and perpendicular to the main direction of flow. The scaling exponents were found similar in rivers of diverse flow regimes, slopes, types of bed material and braid plain widths, indicating the presence of universal features in the underlying mechanisms responsible for the formation of their spatial structure. In regions where predominant geologic controls or predominant flow paths were present, no spatial scaling was found. Regarding their spatiotemporal evolution, braided rivers were found to exhibit dynamic scaling, implying that a smaller part of a braided river evolves identically to a larger one provided that space and time are appropriately normalized. Based on these findings, and some additional analysis of experimental rivers as they approach equilibrium, it was concluded that the mechanism bringing braided rivers to a state where they show spatial and temporal scaling is self-organized criticality and inferences about the physical mechanisms of self-organization were suggested.  相似文献   

Oxygen and Carbon Isotope Study of Calcite and Dolomite in the Disseminated Au-Ag Telluride Bulawan Deposit, Negros Island, Philippines     

Victor B. MAGLAMBAYAN  Daizo ISHIYAMA  Toshio MIZUTA  Osamu MATSUBAYA  Yohei ISHIKAWA 《Resource Geology》2001,51(2):107-116

Abstract: The disseminated Au‐Ag telluride Bulawan deposit, Negros island, Philippines, is hosted by dacite porphyry breccia pipes which formed in a Middle Miocene dacite porphyry stock. Electrum and Au‐Ag tellurides occur mostly as grains intergrown with or filling voids between sphalerite, pyrite, chalcopyrite, galena and tennantite. Calcite, quartz and rare dolomite are the principal gangue minerals. Four types of alteration were recognized in the deposit, namely; propylitic, K‐feldspar‐sericitic, sericitic and carbonate alteration. Carbonate alteration is correlatable to the gold deposition stage and occurs mostly along fault zones. The δ¹⁸O and δ¹³C compositions of calcite and dolomite in propylite zone and ore‐stage dacite porphyry breccia were determined. The δ¹⁸O values of calcite in propylitized andesite range from +12.2 to +14.7%, and their δ¹³C values range from ‐6.1 to ‐1.0%. The δ¹⁸O values of calcite and dolomite in sericite‐ and carbonate‐altered, mineralized dacite porphyry breccia and dacite porphyry rocks range from +15.1 to +23.1%, and the δ¹³C values of calcite and dolomite range from ‐3.9 to +0.9%. The δ¹⁸O and δ¹³C values of the hydrothermal fluids were estimated from inferred temperatures of formation on the basis of fluid inclusion microthermometry. The δ¹⁸O values of hydrothermal fluid for the propylitic alteration were calculated to be +8.5 ‐ +9.5%, assuming 375°C. On the other hand, the δ¹⁸O values of ore solutions for base metal and Au mineralization were computed to be +13.6 ‐ +14.6%, assuming 270°C. The hydrothermal fluids that formed the Bulawan deposit are dilute and ¹⁸O‐enriched fluids which reacted with ¹⁸O‐ and ¹³C‐rich wallrocks such as limestone.  相似文献   

Computer simulations of the Al-Si disorder in synthetic cordierites: Configuraltional entropy constrained by 29Si NMR data     

Victor L. Vinograd 《Physics and Chemistry of Minerals》1996,23(6):391-401

The published ²⁹Si NMR data on synthetic Mg-cordierites have been used to estimate the changes in configurational Al-Si entropy of the samples due to metastable disorder. The results show that with the increase of the time of annealing in the range of 2 min-2000 h at 1185 °C the entropy of disorder in cordierite decreases from 17.1 to 6.4 J/mol K, while at 1400 °C in the range of 2 min–88 h the entropy changes from 15.4 to 8.8 J/mol K. The decrease in entropy is followed by the appearance and increase of long-range ordering which is reflected in changes of T₁ and T₂ site occupancies, decrease in the number of Si-O-Si and Al-O-Al groupings around O1 oxygens and in a decrease in the number of Al-O-Si-O-Al contacts among hexagonal 6T₂-rings. The derived values of entropy effects together with published calorimetric data suggest that the enthalpy of metastable disordering strongly depends on the temperature of annealing.  相似文献