共查询到20条相似文献，搜索用时 841 毫秒
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H. M. Pantin 《地球表面变化过程与地形》1982,7(5):503-505
The experiments of Southard and Mackintosh prove only that autosuspension did not occur under the tested conditions; these were based on the Bagnold (1963) criterion, which is unsound. An alternative criterion is re-emphasized, and a method for testing its validity suggested. Two separate derivations are given for the power required for sediment suspension. 相似文献
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Joyce Vetterlein and Gerald P Roberts describe research in progress on the structural evolution of Cerberus Fossae, Mars, with implications for cryosphere cracking in recent Mars history. 相似文献
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Matthew P. Miller Bailey E. Simone Diane M. McKnight Rose M. Cory Mark W. Williams Elizabeth W. Boyer 《Aquatic Sciences - Research Across Boundaries》2010,72(3):269-275
In their article, “New light on a dark subject: On the use of fluorescence data to deduce redox states of natural organic
matter,” Macalady and Walton-Day (2009) subjected natural organic matter (NOM) samples to oxidation, reduction, and photochemical transformation. Fluorescence spectra
were obtained on samples, which were diluted “to bring maximum uvvisible absorbance values below 1.0.” The spectra were fit
to the Cory and McKnight (2005) parallel factor analysis (PARAFAC) model, and consistent variation in the redox state of quinone-like moieties was not detected.
Based on these results they concluded that fitting fluorescence spectra to the Cory and McKnight (2005) PARAFAC model to obtain information about the redox state of quinone-like moieties in NOM is problematic. Recognizing that
collection and correction of fluorescence spectra requires consideration of many factors, we investigated the potential for
inner-filter effects to obscure the ability of fluorescence spectroscopy to quantify the redox state of quinone-like moieties.
We collected fluorescence spectra on Pony Lake and Suwannee River fulvic acid standards that were diluted to cover a range
of absorbance wavelengths, and fit these spectra to the Cory and McKnight (2005) PARAFAC model. Our results suggest that, in order for the commonly used inner-filter correction to effectively remove inner-filter
effects, samples should be diluted such that the absorbance at 254 nm is less than 0.3 prior to the collection of fluorescence
spectra. This finding indicates that inner-filter effects may have obscured changes in the redox signature of fluorescence
spectra of the highly absorbing samples studied by Macalady and Walton-Day (2009). 相似文献
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This paper reviews the use of the Generalized Likelihood Uncertainty Estimation (GLUE) methodology in the 20 years since the paper by Beven and Binley in Hydrological Processes in (1992), which is now one of the most highly cited papers in hydrology. The original conception, the on‐going controversy it has generated, the nature of different sources of uncertainty and the meaning of the GLUE prediction uncertainty bounds are discussed. The hydrological, rather than statistical, arguments about the nature of model and data errors and uncertainties that are the basis for GLUE are emphasized. The application of the Institute of Hydrology distributed model to the Gwy catchment at Plynlimon presented in the original paper is revisited, using a larger sample of models, a wider range of likelihood evaluations and new visualization techniques. It is concluded that there are good reasons to reject this model for that data set. This is a positive result in a research environment in that it requires improved models or data to be made available. In practice, there may be ethical issues of using outputs from models for which there is evidence for model rejection in decision making. Finally, some suggestions for what is needed in the next 20 years are provided. © 2013 The Authors. Hydrological Processes published by John Wiley & Sons, Ltd. 相似文献
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Ashley G Davies 《Astronomy& Geophysics》2001,42(2):2.10-2.16
Io, Jupiter's innermost Galilean satellite, is the most volcanically active body in the solar system. Ashley Gerard Davies reviews the wealth of data returned by NASA's veteran spacecraft Galileo, that has led to a better understanding of the volcanic processes wracking Io.
Jupiter's moon Io is the only other body in the solar system known to have active, high-temperature volcanism like that found on Earth. The Galileo spacecraft has been observing Io regularly since June 1996, and the data that it has returned have led to many new insights into the volcanic processes that have shaped not only Io, but Earth in its distant past. 相似文献
Jupiter's moon Io is the only other body in the solar system known to have active, high-temperature volcanism like that found on Earth. The Galileo spacecraft has been observing Io regularly since June 1996, and the data that it has returned have led to many new insights into the volcanic processes that have shaped not only Io, but Earth in its distant past. 相似文献
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对今后太湖研究工作的意见 总被引：2，自引：2，他引：0
通过对当前太湖流域治理结果的思考,认为在近的完成１０项工程后,为更好发挥工程效益,有些工作尚需要深入,可能出现的一些新问题要研究解决,提出今后研究的主要课题有：分区国土规划,远景水资源策略,流域水环境调度,水环境与地区经济,太湖和长江关系５个方面。 相似文献
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R. Romano 《Bulletin of Volcanology》1970,34(4):823-832
Several trends of differentiation have been observed in the Etna lavas. Such trends, starting from an olivine basaltic magma, lead to the formation of hawaiites and mugearites, tephrites or latite-andesites. These lavas alternate in time and space, according to variations of the local tectonic conditions connected with the subsidence of the Ionian Sea and the uplift of northeastern Sicily. 相似文献
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The variation in point precipitation with elevation is investigated using an event-based stochastic model of thunderstorm rainfall and empirical data. Parameters of the model correspond to the number of events per unit of time and the depth of rainfall per event. An increase in precipitation with elevation may be due to an increase in the number of events, in the amount of rainfall per event or to some combination of both possibilities. The distribution of the number of events per season is assumed to be a Poisson variate while the distribution of point rainfall depths may be taken as geometric. The summation of a random number of random variables is used to represent seasonal point precipitation. Assuming that the two parameters of the model increase linearly with elevation, then total seasonal rainfall increases as a quadratic polynomial with elevation. The use of the model allows one to obtain the return period of storm rainfall of a given magnitude despite a short historical record. An independent set of data was used to verify the procedure. 相似文献
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Sheppard C 《Marine pollution bulletin》2003,46(12):1517-1518
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Tariq Alkhalifah 《Geophysical Prospecting》2016,64(2):505-513
While velocity contrasts are responsible for most of the events recorded in our data, the long wavelength behavior of the velocity model is responsible for the geometrical shape of these events. For isotropic acoustic materials, the wave dependency on the long (wave propagation) and short (scattering) wavelength velocity components is stationary with the propagation angle. On the other hand, in representing a transversely isotropic with a vertical symmetry axis medium with the normal moveout velocity, the anellepticity parameter η, the vertical scaling parameter δ, and the sensitivity of waves vary with the polar angle for both the long and short wavelength features of the anisotropic dimensionless medium parameters (δ and η). For horizontal reflectors at reasonable depths, the long wavelength features of the η model is reasonably constrained by the long offsets, whereas the short wavelength features produce very week reflections at even reasonable offsets. Thus, for surface acquired seismic data, we could mainly invert for smooth η responsible for the geometrical shape of reflections. On the other hand, while the δ long wavelength components mildly affects the recorded data, its short wavelength variations can produce reflections at even zero offset, with a behavior pattern synonymous to density. The lack of the long wavelength δ information will mildly effect focusing but will cause misplacement of events in depth. With low enough frequencies (very low), we may be able to recover the long wavelength δ using full waveform inversion. However, unlike velocity, the frequencies needed for that should be ultra‐low to produce long‐wavelength scattering‐based model information as δ perturbations do not exert scattering at large offsets. For a combination given by the horizontal velocity, η, and ε, the diving wave influence of η is absorbed by the horizontal velocity, severely limiting the η influence on the data and full waveform inversion. As a result, with a good smooth η estimation, for example, from tomography, we can focus the full waveform inversion to invert for only the horizontal velocity and maybe ε as a parameter to fit the amplitude. This is possibly the most practical parametrization for inversion of surface seismic data in transversely isotropic with vertical symmetry axis media. 相似文献
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Constantine C. Spyrakos Charilaos A. Maniatakis John Taflambas 《Soil Dynamics and Earthquake Engineering》2008,28(9):738-753
The study presents the results of an investigation that identifies among the available records in Greece those that reveal near-source characteristics, using a procedure based on damage potential parameters. The findings reaffirm the opinion that earthquakes with magnitude less than M=6.0 present near-source phenomena that can cause severe damage to relatively stiff structures, common in urban areas. Spectra from selected accelerograms of near-source records are compared with the corresponding elastic spectra of the current Greek Seismic Code, (EAK 2000), the impulsive character of the Greek near-source records is ascertained and shortcomings of EAK 2000 to account for near-source effects are demonstrated.Based on records from seismic events in Greece and records from international earthquakes of small-to-moderate magnitude, the study demonstrates that there exists a near-source magnitude-distance region, where the velocity pulses have smaller amplitude and period in comparison with earthquakes of great magnitude. A simplified representation of three pulse types is, also, adopted for near-source events. It is found that the type-A pulse related to permanent displacement phenomena does not characterize Greek records. In addition a simple criterion is developed to identify the most appropriate simplified pulse type for near-source seismic events independently of magnitude. 相似文献
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A considerable amount of research has been conducted on the impacts of recreational boating activities on fishes but little or no synthesis of the information has been undertaken. This review shows that motor boats impact on the biology and ecology of fishes but the effects vary according to the species and even particular size classes. Direct hits on fishes by propellers are an obvious impact but this aspect has been poorly documented. Alterations in the wave climate and water turbidity may also influence fishes and their habitats, especially submerged and emergent plant beds. Sound generated by boat motors can also influence the communication and behaviour of certain species. Pollution arising from fuel spillages, exhaust emissions and antifouling paints all have detrimental effects on fishes. Finally, the use of recreational boats as vectors of aquatic invasive organisms is very real and has created major problems to the ecology of aquatic systems. 相似文献
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利用Cluster卫星数据,选取2001—2010年期间的616个极尖区穿越事件,研究了行星际磁场（IMF）的大小和方向对极尖区位形的影响.结果表明：当Bz为北向时,随着Bx负向的增大,极尖区的磁不变纬度向高纬方向（极区）移动;当Bz为南向时,随着Bx负向增大,极尖区的磁不变纬度略微向低纬度方向（赤道）移动.Bx正向增大时,极尖区并没有明显移动.Bx对极尖区影响在南半球较为显著,在北半球没有明显规律性变化.此外,随着行星际磁场锥角的增大（>90°）,极尖区也随之向高纬移动.当Bz南向时,随着By的负向增大,极尖区在北半球向晨侧移动,在南半球向昏侧移动.而当Bz南向增加时,南北半球两个极尖区的磁不变纬度都朝赤道方向移动;但北向Bz时几乎没有移动. 相似文献