Indication of high pore-fluid pressures in a seismically-active fault zone   总被引：12，自引：0，他引：12  

Stuart Crampin  Theodora Volti  Sebastien Chastin  Agust Gudmundsson  Ragnar Stefánsson 《Geophysical Journal International》2002,151(2):F1-F5

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Effects of oxygen and redox oscillation on degradation of cell-associated lipids in surficial marine sediments   总被引：2，自引：0，他引：2  

Ming-Y.i Sun  Robert C. AllerCindy Lee  Stuart G. Wakeham 《Geochimica et cosmochimica acta》2002,66(11):2003-2012

Degradation patterns of sedimentary algal lipids were tracked with time under variable redox treatments designed to mimic conditions in organic-rich, bioturbated deposits. Uniformly ¹³C-labeled algae were mixed with Long Island Sound surface muddy sediments and exposed to different redox regimes, including continuously oxic and anoxic, and oscillated oxic: anoxic conditions. Concentrations of several ¹³C-labeled algal fatty acids (16:1, 16:0 and 18:1), phytol and an alkene were measured serially. Results showed a large difference (∼10×) in first-order degradation rate constants of cell-associated lipids between continuously oxic and anoxic conditions. Exposure to oxic conditions increased the degradation of cell-associated lipids, and degradation rate constants were positive functions (linear or nonlinear) of the fraction of time sediments were oxic. Production of two new ¹³C-labeled compounds (iso-15:0 fatty acid and hexadecanol) further indicated that redox conditions and oxic: anoxic oscillations strongly affect microbial degradation of algal lipids and net synthesis of bacterial biomass. Production of ¹³C-labeled iso-15:0 fatty acid (a bacterial biomarker) was inversely proportional to the fraction of time sediments were oxic, rapidly decreasing after 10 days of incubation under oxic and frequently oscillated conditions. Turnover of bacterial biomass was faster under continuously or occasionally oxic conditions than under continuously anoxic conditions. ¹³C-labeled hexadecanol, an intermediate degradation product, accumulated under anoxic conditions but not under oxic or periodically oxic conditions. The frequency of oxic: anoxic oscillation clearly alters both the rate and pathways of lipid degradation in surficial sediments. Terminal degradation efficiency and lipid products from degradation of algal material depend on specific patterns of redox fluctuations.  相似文献   

多震相层析成像与在介质中的多波型射线跟踪     

毛伟健  ＧｒａｈａｍＷ．Ｓｔｕａｒｔ 《CT理论与应用研究》1996,(4)

本文介绍了多震相的层析成像的思路和算法，通过穿透和反射走时可以同时作出２维和３维慢度（速度的倒数）重建。我们分析了在穿透和反射数据中确定速度和深度的不确定性，并认识到深度扰动对反射走时异常比慢度扰动更敏感。由不同波类型所提供的对速度和深度的约束，这个算法实际上减少了在一般反射层析成像在速度和深度之间的不确定性，并且也避免了在穿透层析成像中的不确定问题。线性化反演是通过从反射界面深度由分离速度参数迭代进行的。使用一个快速的２－Ｄ和３－Ｄ射线跟踪算法来计算穿透和反射走时和对幔度及反射界面深度的偏导数。深度和速度都用立方Ｂ样条函数来进行参数化。合成例子表明，当同时考虑穿透和反射时间，层析成像的结果得到改进。这个方法也应用到英国煤炭测量局（ＢｒｉｔｉｓｈＣｏａｌＭｅａｓｕｒｅｓ）沿跨线排列所记录的逆ＶＳＰ数据组。通过使用波形配合技术，用同时确定时间延迟和叠加权，可以自动拾取旅行时间。所观察到的逆ＶＳＰ层析成像可比周围介质具有较低速度的两个断层区域成像。断层的位置由附近的反射测线所确定。本文还讨论了在复杂２－Ｄ和３－Ｄ非均匀各向同性介质中地震射线跟踪方法。界面的几何形状和水平速度场都通过使用非均匀步长立方Ｂ－样条节点  相似文献   

Air-sea fluxes: 25 years of progress   总被引：3，自引：0，他引：3  

Stuart D. Smith  Christopher W. Fairall  Gerald L. Geernaert  Lutz Hasse 《Boundary-Layer Meteorology》1996,78(3-4):247-290

During the past quarter century the study of air-sea interaction has evolved from a small branch of marine climatology to play a key role in the modelling of the coupled system of ocean and atmosphere. Knowledge of air- sea fluxes has grown, based on Monin-Obukhov similarity theory for surface boundary layers and on direct and indirect techniques of measuring the fluxes. This has been the basis for providing boundary conditions needed to couple atmospheric and oceanic circulation models that are used to forecast weather and climate. An overview of current understanding is followed by a discussion of parameterisation schemes and a chronicle of some of the experimental work that has tested theories and quantified their conclusions.  相似文献   

Shear-wave anisotropy and the stress field from borehole recordings at 2.5 km depth at Cajon Pass     

Yun Liu  Stuart Crampin  Rachael E. Abercrombie 《Geophysical Journal International》1997,129(2):439-449

53 local earthquakes recorded at 2.5 km depth in the Cajon Pass scientific borehole are analysed for shear-wave splitting. The time delays between the split shear waves can be positively identified for 32 of the events. Modelling these observations of polarizations and time delays using genetic algorithms suggests that the anisotropic structure near Cajon Pass has orthorhombic symmetry. The polarization of the shear waves and the inferred strike of the stress-aligned fluid-filled intergranular microcracks and pores suggests that the maximum horizontal compressional stress direction is approximately N13°W. This is consistent with previous results from earthquake source mechanisms and the right-lateral strike-slip motion on the nearby San Andreas Fault, but not with stresses measured within the uppermost 3 km of the borehole. This study suggests that the San Andreas Fault is driven by deeper tectonic stresses and the present understanding of a weak and frictionless San Andreas Fault may need to be modified. The active secondary faulting and folding close to the fault are probably driven by the relatively shallow stress as measured in the 3.5 km deep borehole.  相似文献   

Measurement of PAN in the Polluted Boundary Layer and Free Troposphere Using a Luminol-NO2 Detector Combined with a Thermal Converter     

Chloe Nikitas  Kevin C. Clemitshaw  David E. Oram  Stuart a. Penkett 《Journal of Atmospheric Chemistry》1997,28(1-3):339-359

Peroxyacetyl nitrate (PAN,CH³C(O)O₂NO₂) has been measured inthe polluted boundary layer and free troposphere by thermal conversion tonitrogen dioxide (NO₂) followed by detection of thedecomposition product with a Scintrex LMA-3 NO₂-luminolinstrument. Following laboratory tests of the efficiency of PAN conversionand investigations of possible interferences, the technique was evaluated atthe West Beckham TOR (Tropospheric Ozone Research) Station near the northNorfolk coast in Eastern England between September 1989 and August 1990. PANmeasured by the new technique was reasonably well correlated with PANrecorded using electron capture gas chromatography (EC/GC). PAN was alsowell correlated with ozone (O³) in the summer months. Springand autumn episodes of simultaneously high concentrations of PAN andO³ were examined in conjunction with air parcelback-trajectories and synoptic- and local-scale meteorology in a study ofthe sources of photooxidants on the east coast of England. Spring-timemeasurements of PAN made in the free troposphere in a light aircraft ataltitudes up to 3.1 km showed the presence of 0.54 and 0.26 ppbv PAN inpolar maritime and mid-latitude oceanic air masses, respectively. Thetechnique is particularly suited to airborne applications because potentialinterferences are minimised and the frequency of measurements is higher thangenerally achieved with EC/GC methods.  相似文献   

Evaluating the science behind the management advice for North Sea cod   总被引：1，自引：3，他引：1  

Reeves  Stuart A.; Pastoors  Martin A. 《ICES Journal of Marine Science》2007,64(4):671-678

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A synthesis of the early life history of the anglerfish, Lophius piscatorius (Linnaeus, 1758) in northern British waters   总被引：1，自引：0，他引：1  

Hislop  John R.G.; Gallego  Alejandro; Heath  Michael R.; Kennedy  Fiona M.; Reeves  Stuart A.; Wright  Peter J. 《ICES Journal of Marine Science》2001,58(1):70-86

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Electron spin resonance spectra of marine and fresh-water manganese nodules     

Stuart Wakeham  Roy Carpenter 《Chemical Geology》1974,13(1):39-47

Eighty ferromanganese nodules from a wide variety of marine and fresh-water environments have been analyzed by electron spin resonance spectroscopy. The purpose has been to gain information on the forms in which the major constituents of manganese nodules are present. Contributions to ESR spectra of the nodules come mainly from Mn²⁺ and Fe³⁺. Deep-sea samples generally showed only broad resonance lines, and those with larger peaks close to g = 2.0 are believed to contain more Mn²⁺ than others. Some Antarctic and fresh-water nodules lack a strong Mn²⁺ resonance and have a peak around g = 4.0 which is most likely tetrahedral Fe³⁺. A number of smaller peaks in several samples could not be readily interpreted in terms of contributions from individual ionic species because of fundamental problems in preparing standards having the ion of interest in the same micro-environment as it experiences in the nodules.  相似文献   

Physical processes determining the chromospheric temperature distribution     

Stuart D. Jordan 《Solar physics》1977,51(1):51-59

Calculations performed with several models of the solar chromosphere support Ulmschneider's conclusion that relatively short period acoustic waves heat the low chromosphere in the region just above the temperature minimum. However, these same short period waves (10 period P80 s) are not able to maintain chromospheric temperatures at heights where _5000Å(normal) < 10^-6. The calculations also show that an earlier conjecture stating that the H₂ population might influence the non-LTE chromospheric H^- population is probably not correct, due to lower values of the ratio n _e/n _H inferred from more recent observations. Finally, the calculations support Athay's contention that the Cayrel mechanism alone cannot produce the observed temperature rise, because the magnitude of the radiative cooling in the lines is too great.  相似文献