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941.
Visualization of a collapsing vertical packet of patches in a laboratory experiment and the results of acoustical sounding under field conditions allowed us to discriminate the stage of its evolution which was previously unknown. It is defined by the variations of the horizontal dimensions of patches and their effective scattering surface with a period ofT=150–250/N, whereN is the Brunt-Väisälä frequency. The horizontal dimensions of patches can reach 40% of their final dimensions at the evolution stage discriminated.Translated by Mikhail M. Trufanov. 相似文献
942.
Regoli F Gorbi S Frenzilli G Nigro M Corsi I Focardi S Winston GW 《Marine environmental research》2002,54(3-5):419-423
An integrate approach will be discussed for investigations on oxidative stress in xenobiotic toxicity. While the analysis of individual antioxidants is useful for their sensitivity and to understand the mode of action of a stressor, the integration with the analysis of the total antioxidant capacity provides a more holistic assessment of the overall biological significance of such variations. TOSC has a greater predictive value on the health condition of the organisms and allows to discriminate the different role of specific ROS in oxidative stress syndrome. 相似文献
943.
The process of Differential Roughness Secondary Flow (DRSF), hitherto little recognized, recently was demonstrated in a wind
tunnel and in a flume. It is suggested here the DRSF may, in the natural environment, play an important part in the persistence
and sharp definition of sand ribbons, previously initiated by other processes.
In 1980 Karl described a series of sand ribbons, alternating with exposed substrate, which he attributed to the effect of
Langmuir circulations. Although Langmuir Circulation Secondary Flow (LCSF) may indeed, in some cases, initiate sand ribbons,
the sharply-defined edges typical of these features are explained better by DRSF. 相似文献
944.
Adriano Mazzini D. Duranti R. Jonk J. Parnell B. T. Cronin A. Hurst M. Quine 《Geo-Marine Letters》2003,23(3-4):323-339
Petrographic and geochemical analyses performed on a North Sea core from the Gryphon Field reveal the presence of palaeo-degassing features surrounded by injected sandstones in the Eocene interval. The injected sandstones are oil-stained and poorly cemented by carbonate and quartz. 18O isotope analyses indicate that carbonate cementation occurred during shallow burial (likely less than about 300 m). Depleted 13C (around –30 V-PDB) carbonate cement suggests that bicarbonate was derived from the microbial oxidation of oil and gas. Late quartz overgrowths enclose oil present in the injected units. The tubular degassing conduits are composed of zoned cements and have 18O and 13C isotope values similar to the injected sandstones, indicating that oil and gas seepage induced the precipitation of authigenic carbonate in the shallow subsurface. Oil inclusions in inter- and intra-crystal cement sites in both injected sandstones and degassing conduits indicate that oil seepage was an ongoing feature at shallow burial. A proposed model involves oil and gas seepage and the formation of the degassing conduits, followed by a sand injection phase. It seems likely that oil and gas continued to leak towards the seabed by exploiting the network of permeable injected sandstones and the horizons of porous degassing features. 相似文献
945.
X-band sea-clutter nonstationarity: influence of long waves 总被引:1,自引:0,他引:1
In this paper, we deal with the problem of modeling the backscattering from sea surface for low-grazing-angle and high-resolution radar systems. Based on the electromagnetic two-scale model, we analyzed both the amplitude and frequency modulations induced on the small-scale Bragg resonant waves by the large-scale surface tilt and advection due to the swell presence. Evidence of sea-clutter nonstationarity has been verified and the relationship between the variations of clutter spectral features, such as texture, Doppler centroid, and bandwidth, have been studied by processing real sea-clutter data recorded by the IPIX radar of McMaster University, Hamilton, ON, Canada. An autoregressive nonstationary process is proposed and validated to model the physical phenomenon. 相似文献
946.
Ecotone or Ecocline: Ecological Boundaries in Estuaries 总被引:1,自引:0,他引:1
Two main ecological boundaries, ecotone and ecocline, have been defined in landscape ecology. At this scale, the estuary represents a boundary between rivers and the sea, but there has been no attempt to fit empirical data for estuaries to these boundary models. An extensive data set from the Thames estuary was analysed using multivariate techniques and species-range analysis, in order to investigate whether the ecocline or the ecotone model was most relevant to this estuary. Data for periods of high and low freshwater flow allowed the impact of large-scale fluctuations implicit in both models to be determined.A continuum of assemblages existed along the salinity gradient from freshwater river to the North Sea, with shifts in the ranges of organisms apparent in response to changes in freshwater flow. This pattern closely fits an ecocline model. However, the estuary differs from previously defined ecoclines in having two overlapping gradients in the major stressor: from river to mid-estuary for freshwater species and from sea to mid-estuary for marine species. We propose, therefore, that the estuary represents a two-ecocline model, with fauna inhabiting the mid-estuary being either freshwater or marine species at the edge of their range, rather than ‘ true estuarine organisms ’. This allows a redefinition of the Remane diagram, with estuarine species removed, and supports previous arguments that brackish-water species do not exist. Such two-ecocline models may also exist in other marine systems, such as rocky shores. 相似文献
947.
J. M. Lort W. Q. Limond J. Segoufin Ph. Patriat J. R. Delteil B. Damotte 《Marine Geophysical Researches》1979,4(1):71-89
This paper presents seismic reflection and refraction data from the Mozambique Channel, collected between 1971 and 1973. A deep sedimentary basin (up to 5 km of sediments) opens southwards to the Mozambique Basin, and is bounded to the east by the Davie Ridge and beyond by the marginal plateau of Malagasy. A continuous reflector (C), possibly of Cretaceous age, is identified between layers having seismic interval velocities of 2.4–2.8 km/s and 3.1–3.4 km/s. The deepest sediments have velocities of 4.5–4.9 km/s and overlie a layer with velocity 5.5 km/s, which may be volcanic in the north-east of the Channel.The crust occupying most of the Channel is probably pre-Cretaceous in age, and may be largely continental in nature. This is supported by subdued magnetic anomalies and the possibility of a continuous Karroo sedimentary section across the northern Channel. The oceanic crust of the Mozambique Basin may extend as far north as 24°S, into the western Channel only. The problem of the origin of the Mozambique Channel remains unresolved, although a long sedimentary history indicates that Malagasy may have separated from Mainland Africa prior to Karroo times. The Davie Ridge may possibly represent a relict strike-slip fault, which permitted movement along a north-south line. 相似文献
948.
V. A. Frol’kis I. L. Karol’ A. A. Kiselev Yu. E. Ozolin V. A. Zubov 《Izvestiya Atmospheric and Oceanic Physics》2007,43(4):413-422
This is a study of the sensitivity of model results (atmospheric content of main gas constituents and radiative characteristics of the atmosphere) to errors in emissions of a number of atmospheric gaseous pollutants. Groups of the model variables most dependent on these errors are selected. Two variants of emissions are considered: one without their evolution and the other with their variation according to the IPCC scenario. The estimates are made on the basis of standard statistical methods for the results obtained with the detailed onedimensional radiative—photochemical model of the Main Geophysical Observatory (MGO). Some approaches to such estimations with models of higher complexity and to the solution of the inverse problem (i.e., the estimation of the necessary accuracy of external model parameters for obtaining the given accuracy of model results) are outlined. 相似文献
949.
Seismic stratigraphic and main lithological features of the sedimentary cover overlying the basement of the Alboran Sea were established via the analysis of commercial multichannel seismic surveys, geophysical well logs, and well data. Six seismic stratigraphics units (VI to I), bounded by unconformities, form the marine sediments that range in age from early Miocene to Quaternary. They are dated by extrapolation of commercial drilling results from the northern Alboran Sea. Volcanic activity is recorded within sedimentary sequences of units V to II. Undercompaction features are detected in the two basal units. 相似文献
950.
Mud and fluid migration in active mud volcanoes in Azerbaijan 总被引:7,自引:2,他引:7
Mud volcanic eruptions in Azerbaijan normally last for less than a few hours, and are characterized by vigorous extrusion of mud breccias, hydrocarbon gases, and waters. Recent fieldwork and mapping on four active mud volcanoes show that dormant period activity ranges from quiet to vigorous flow of mud and fluids. Geochemical analyses of expelled waters show a wide range in solute concentrations, suggesting the existence of a complex plumbing system. The mud and fluids have a deep origin, but are sometimes stored in intermediate-depth mud chambers. A mixing model between deep-seated saline waters and shallow meteoric water is proposed. 相似文献