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831.
832.
833.
Hein J.W. De Baar Peter G. Brewer Michael P. Bacon 《Geochimica et cosmochimica acta》1985,49(9):1961-1969
We have measured profiles of the rare earth elements (REE) in Atlantic and Pacific Ocean waters. The data, normalized versus shales, exhibit a pronounced anomaly in Gd relative to its neighbors Eu and Tb in the REE series such that the Gd concentrations are high by 30–50%. Closer inspection reveals that the anomaly is made up of both elevated Gd and depressed Tb concentrations, likely associated with solution chemistry shifts in the transition from an exactly half filled 4f electron shell. Anomalies in Gd and Tb solution complexation are also indicated by the Turner-Whitfield-Dickson speciation model. The overall trend of heavy REE(III) enrichment in seawater and the anomaly described here tend to support scavenging as an important removal mechanism for the REE from seawater. 相似文献
834.
Microearthquake digital data collected at Campi Flegrei during the recent (1982–1985) ground uplift episode have been analyzed in order to infer source and medium seismic properties. The main results obtained from these analyses are:
- Hypocenter distribution and the size of the seismic zone do not change with time and do not depend on the ground uplift rate. Events occurred clustered in time with no simple causal relations between the cluster occurrences and their energy.
- Anelastic attenuation does not depend strongly on frequency, showing a constant pattern at high frequencies. The observed values of low and high frequency attenuation, due to the short source receiver distances, do not seriously affect the spectral content of signals radiated by the sources.
- A constant Brune stress drop pattern (~4–5 bars) as a function of seismic moment is observed. This indicates that the manner of fracturing is almost independent on magnitude of earthquakes (hypothesis of self-similarity (Aki, 1967)). Seismic processes in a prefractured medium can explain the observed small stress drop values.
- Focal mechanisms from moment tensor estimates show that radiation patterns are mostly well interpreted in terms of double couple source models.
- The scaling of peak ground motion parameters (A max andV max vs seismic moment) can be explained by an ω2 source model (constant stress drop) multiplied by an exponential function with a small decay parameter, which takes into account the measured attenuation.
835.
Peter A. E. M. Janssen Gerbrand J. Komen Willem J. P. De Voogt 《Boundary-Layer Meteorology》1987,38(1-2):29-35
This note is devoted to the problem of the appropriate scaling of parameters relevant for sea waves, such as wave height, peak frequency, duration, and fetch. In the past, the growth of sea waves has often been analysed in terms of the wind velocity at a fixed height, despite the fact that many authors have stressed the importance of scaling with the friction velocity. This problem would be immaterial if the ratio between the friction velocity and the wind speed at a fixed height were a constant. There is, however, ample evidence that this ratio increases with wind speed (Smith and Banke, 1975; Smith, 1980), in agreement with dimensional considerations by Charnock (1955) on the friction height. As a result, the scaling problem is an important one. In this note we conjecture that the correct procedure is to scale wave parameters with friction velocity, and we discuss experimental evidence for the correctness of this conjecture. Comparing two independent datasets (JONSWAP and KNMI), we find some evidence supporting our ideas. Further confirmation remains desirable, however, and suggestions are made as to how this might be obtained. 相似文献
836.
In order to get a better insight into the role of hydrologic regime components in an Alpine environment, runoff characteristics were analysed in relation to atmospheric circulation types over a 23-yr. period. For this purpose, atmospheric circulation types were classified into hydrologically relevant classes of weather types using Schüepp's classification which was developed for the European Alpine region. It is found that the magnitude of runoff during each particular class of weather types is largely governed by autocorrelation (related to the characteristic times of the systems active during preceding classes and thus related to the preceding weather types) and by antecedent conditions, rather than by the weather types themselves. The influence of a weather class displays a distinct dependency of the time elapsed since the start of the particular class. This influence does not become manifest until after a 2–3-day period on the average. 相似文献
837.
838.
For several reasons the fate and effects of oil pollution are not easily studied in natural ecosystems. Furthermore, the results of laboratory tests cannot easily be extrapolated to natural systems. A logical objective of ecotoxicological research is, therefore, to simulate natural systems in model ecosystem experiments. A one-year feasibility study was carried out with MOdel TIdal Flat ecosystems (MOTIFs), designed to represent tidal flat systems typical of the Wadden Sea and other temperate estuarine areas. During the first 6 months the 4 MOTIFs studied developed very similarly. After this period an oil spill was simulated by exposing two of the four MOTIFs to a floating oil mousse for one week. During this week part of the oil was buried in the sediment by bioturbation. This sediment-bound fraction caused a prolonged exposure of the MOTIFs to oil compounds. Short- and long-term effects resulted in large differences between oil-treated and control MOTIFs. These differences persisted to the end of the experiment, 7 months after the removal of most of the oil. 相似文献
839.
The standard deviation of temperature
T
is proposed as a temperature scale and
as a velocity scale to describe the behaviour of turbulent flows in the Atmospheric Surface Layer (ASL), instead of
* andu
* of the Monin—Obukhov similarity theory, and ofT
f
andU
f
used for free convection stability conditions. On the basis of experimental evidence reported in the literature, it is shown that
T
T
f
andv
* U
f
in the free convection region, and
T
* andv
* U
* in nearneutral and stable conditions. This implies that the proposed scales can be applied for all stabilities. Furthermore, a new length scale is proposed and its relation with Obukhov length is given. Also, a simple semi-empirical expression is presented with which
T
andv
* can be evaluated in a rather simple way. Some examples of practical applications are given, e.g., a stability classification for unstable conditions. 相似文献
840.
Shear‐wave polarization and time delay are attributes commonly used for fracture detection and characterization. In time‐lapse analysis these parameters can be used as indicators of changes in the fracture orientation and density. Indeed, changes in fracture characteristics provide key information for increased reservoir characterization and exploitation. However, relative to the data uncertainty, is the comparison of these parameters over time statistically meaningful? We present the uncertainty in shear‐wave polarization and time delay as a function of acquisition uncertainties, such as receiver and source misorientation, miscoupling and band‐limited random noise. This study is applied to a time‐lapse borehole seismic survey, recorded in Vacuum Field, New Mexico. From the estimated uncertainties for each survey, the uncertainty in the difference between the two surveys is 31° for the shear‐wave polarization angle and 4 ms for the shear‐wave time delay. Any changes in these parameters greater than these error estimates can be interpreted with confidence. This analysis can be applied to any time‐lapse measurement to provide an interval of confidence in the interpretation of shear‐wave polarization angles and time splitting. 相似文献