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251.
Contourites within a deep-water sequence stratigraphic framework 总被引：2，自引：2，他引：0
Rachel Brackenridge Dorrik A. V. Stow F. Javier Hern��ndez-Molina 《Geo-Marine Letters》2011,31(5-6):343-360
Sequence stratigraphy has proven to be an extremely useful predictive tool in the search for hydrocarbons along the continental margins. However, of the several models in use, none includes the effects of alongslope processes in deep-water. This paper, therefore, is a first attempt to place contourite depositional systems (CDSs) firmly within a sequence stratigraphic framework, based on detailed examination of over 20 CDSs worldwide. It also presents a new view of how sea level variation influences bottom current generation and intensity. Two key controls on contourite drift formation are identified: sediment influx and bottom current velocity. Sea level directly influences the sediment influx to a basin and, therefore, the contourite response fits nicely into the downslope sequence stratigraphy model. Bottom current velocity variations in response to sea level are more complex, and two key controls are identified: (1) oceanic gateways can effectively constrict and accelerate water masses and are therefore closely associated with CDS evolution; fluctuating sea level will affect the water exchange through a gateway; (2) changing rates of bottom-water generation: some water masses appear more vigorous during periods of lowstand, whereas others appear more sluggish. In order to accommodate this variation, two new sequence stratigraphy models are herein presented, comprising both downslope and alongslope processes. The first model reveals a CDS where bottom current activity is markedly more vigorous during times of sea level highstand, whereas the second model indicates margin evolution where bottom-water currents are most vigorous during times of sea level lowstand. It is recognised that there are additional controlling factors linked to sea level variation which can significantly modify the distribution and development of contourite elements. 相似文献
252.
We consider some practical issues of the determination of the b-value of sequences of magnitudes with the bootstrap method for short series of length L and various quantization levels $\Updelta m$ of the magnitude. Preliminary Monte Carlo tests performed with $\Updelta m = 0$ demonstrate the superiority of the maximum likelihood estimator b MLE, and the inconsistency of the, yet often used, b LR estimator defined as the least-squares slope of the experimental Gutenberg?CRichter curve. The Monte Carlo tests are also applied to an estimator, b KS, which minimizes the Kolmogorov?CSmirnov distance between the cumulative distribution of magnitudes and a power-law model. Monte Carlo tests of discrete versions of the b MLE and b KS estimators are done for $\Updelta m = \{0.1, 0.2, 0.3 \}$ and used as reference to evaluate the performance of the bootstrap determination of b. We show that all estimators provide b estimates within 10?% error for L????100 and if a large number, n?=?2?×?105, of bootstrapped sample series is used. A resolution test done with $\Updelta m = 0.1$ reveals that a clear distinction between b?=?0.8, 1.0, and 1.2 is obtained if L????200. 相似文献
253.
Mauricio Cataldo Fabiola Ar��valo Patricio Mella 《Astrophysics and Space Science》2011,333(1):287-293
It is well known that Kasner-type cosmologies provide a useful framework for analyzing the three-dimensional anisotropic expansion because of the simplification of the anisotropic dynamics. In this paper relativistic multi-fluid Kasner-type scenarios are studied. We first consider the general case of a superposition of two ideal cosmic fluids, as well as the particular cases of non-interacting and interacting ones, by introducing a phenomenological coupling function q(t). For two-fluid cosmological scenarios there exist only cosmological scaling solutions, while for three-fluid configurations there exist not only cosmological scaling ones, but also more general solutions. In the case of triply interacting cosmic fluids we can have energy transfer from two fluids to a third one, or energy transfer from one cosmic fluid to the other two. It is shown that by requiring the positivity of energy densities there always is a matter component which violates the dominant energy condition in this kind of anisotropic cosmological scenarios. 相似文献
254.
A. Dizi��re C. Michaut M. Koenig C. D. Gregory A. Ravasio Y. Sakawa Y. Kuramitsu T. Morita T. Ide H. Tanji H. Takabe P. Barroso J.-M. Boudenne 《Astrophysics and Space Science》2011,336(1):213-218
In this paper, recent results obtained on highly radiative shocks generated in a xenon filled gas cell using the GEKKO XII laser facility are presented. Data show extremely high shock velocity (??150 km/s) never achieved before in gas. Preliminary analyses based on theoretical dimensionless numbers and numerical simulations suggest that these radiative shocks reach a new radiative regime where the radiative pressure plays a role in the dynamics and structure of the shock. A major effect observed is a strong anisotropic emission in the downstream gas. This unexpected feature is discussed and compared to available 2D radiation hydrodynamic simulations. 相似文献
255.
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256.
Pablo E. S. Oliveira Ot��vio C. Acevedo Osvaldo L. L. Moraes Hans R. Zimermann Claudio Teichrieb 《Boundary-Layer Meteorology》2013,146(1):45-64
A 1-year set of measurements of CO2 and energy turbulent fluxes above and within a 25-m pine forest in southern Brazil is analyzed. The study focuses on the coupling state between two levels and its impact on flux determination by the eddy-covariance method. The turbulent series are split in their typical temporal scales using the multiresolution decomposition, a method that allows proper identification of the time scales of the turbulent events. Initially, four case studies are presented: a continually turbulent, a continually calm, a calm then turbulent, and an intermittent night. During transitions from calm to turbulent, large scalar fluxes of opposing signs occur at both levels, suggesting the transference of air accumulated in the canopy during the stagnant period both upwards and downwards. Average fluxes are shown for the entire period as a function of turbulence intensity and a canopy Richardson number, used as an indicator of the canopy coupling state. Above the canopy, CO2 and sensible heat fluxes decrease in magnitude both at the neutral and at the very stable limit, while below the canopy they increase monotonically with the canopy Richardson number. Latent heat fluxes decrease at both levels as the canopy air becomes more stable. The average temporal scales of the turbulent fluxes at both levels approach each other in neutral conditions, indicating that the levels are coupled in that case. Average CO2 fluxes during turbulent periods that succeed very calm ones are appreciably larger than the overall average above the canopy and smaller than the average or negative within the canopy, indicating that the transfer of air accumulated during calm portions at later turbulent intervals affects the flux average. The implications of this process for mean flux determination are discussed. 相似文献