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31.
A code of practice for ocean mining has been developed by the International Marine Minerals Society. The code provides general guiding Principles for development of marine mineral resources and delineates Operating Guidelines for application, as appropriate, at specific mining sites. In total 11 operating guidelines are provided to serve as benchmarks for industry and targets for regulatory agencies and other stakeholders. They include the following commitments: •To sustainable development, •To environmentally responsible corporate ethics, •To the development of effective community partnership, •To implementation of environmental risk management, •To the integration of environmental management into all phases of development, •To the establishment of corporate environmental performance targets, •To timely environmental improvements and upgrading, •To responsible rehabilitation of operations sites and decommissioning of facilities, and •To accurate and timely, reporting and documentation, archiving, and performance review. 相似文献
32.
33.
Arnold H. Bouma James M. Coleman Charles E. Stelting Barry Kohl 《Geo-Marine Letters》1989,9(3):161-170
A conceptual sea-level-driven depositional model for individual fanlobes (channel-overbank systems) of the Mississippi Fan
does not permit direct application of the sequence stratigraphic principles of Vail and colleagues. Deep Sea Drilling Project
Leg 96 results suggest that, during initial relative lowering of sea level, the canyon and upper fan channel were formed;
excavated fine-grained slope sediments may have formed a debris flow deposit base for the fanlobe. Continued lowering produced
constructional channel-levee-overbank deposits. Rising relative sea level inhibited input of coarse clastics, and channel
depressions filled with muds. A blanket of (hemi)pelagics represents relative high sea level stand. 相似文献
34.
Simplified limit solutions for the capacity of suction anchors under undrained conditions 总被引:1,自引:0,他引:1
Upper bound plastic limit analyses (PLA) can provide a useful framework for estimating the load capacity of suction caisson anchors in purely cohesive soils. Since arbitrary assumptions regarding the soil stress state are not required in the PLA formulation, it may be used with greater consistency compared to other simplified approaches such as limit equilibrium methods. While PLA methods do not attempt to include all of the complexities of anchor behavior, they can provide a relatively simple framework for visualizing anchor kinematics leading to an understanding of the relative importance of various parameters on suction anchor load capacity. The most rigorous PLA formulations involve postulating a three-dimensional anchor-soil failure mechanism and deriving expressions for internal energy dissipation throughout the mechanism. This approach can involve extensive numerical integrations and a relatively complex scheme for optimizing the failure mechanism to obtain a least upper bound collapse load. Considerable simplification is possible if the problem is formulated in terms of ultimate unit resistances (lateral, axial, and their interaction) that can be exerted by the soil on the caisson. In this case, the caisson failure mechanism can be characterized in terms of one or two optimization variables. Simple expressions for the ultimate unit resistances acting on the caisson can be obtained from several sources including rigorous PLA solutions, finite element techniques, or experimental measurements. General expressions are possible by limiting consideration to common, idealized strength profiles such as uniform or constant gradient. Such simplified formulations are particularly valuable for providing an analysis tool accessible to practicing engineers. Suction caisson anchors can be subjected to a variety of load orientations including nearly vertical uplift forces imposed by the vertical tendons of tension leg platforms, horizontal loads imposed by catenary mooring systems, and inclined loads imposed by taut moorings. Recently, PLA methods have been applied to the analysis of suction caissons subjected to this range of loading conditions. This paper reviews the formulation of these analyses and summarizes the most significant findings. 相似文献
35.
L. I. Kuncheva J. J. Charles N. Miles A. Collins B. Wells I. S. Lim 《Mathematical Geosciences》2008,40(6):639-652
We develop the classification part of a system that analyses transmitted light microscope images of dispersed kerogen preparation. The system automatically extracts kerogen pieces from the image and labels each piece as either inertinite or vitrinite. The image pre-processing analysis consists of background removal, identification of kerogen material, object segmentation, object extraction (individual images of pieces of kerogen) and feature calculation for each object. An expert palynologist was asked to label the objects into categories inertinite and vitrinite, which provided the ground truth for the classification experiment. Ten state-of-the-art classifiers and classifier ensembles were compared: Naïve Bayes, decision tree, nearest neighbour, the logistic classifier, multilayered perceptron (MLP), support vector machines (SVM), AdaBoost, Bagging, LogitBoost and Random Forest. The logistic classifier was singled out as the most accurate classifier, with an accuracy greater than 90. Using a 10 times 10-fold cross-validation provided within the Weka software, we found that the logistic classifier was significantly better than five classifiers (p<0.05) and indistinguishable from the other four classifiers. The initial set of 32 features was subsequently reduced to 6 features without compromising the classification accuracy. A further evaluation of the system alerted us to the possible sensitivity of the classification to the ground truth that might vary from one human expert to another. The analysis also revealed that the logistic classifier made most of the correct classifications with a high certainty. 相似文献
36.
Lake Bonneville marl provides a stratigraphic record of lake history preserved in its carbonate minerals and stable isotopes. We have analyzed the marl in shallow cores taken at three localities in the Bonneville basin. Chronology for the cores is provided by dated volcanic ashes, ostracode biostratigraphy, and a distinctive lithologic unit believed to have been deposited during and immediately after the Bonneville Flood.A core taken at Monument Point at the north shore of Great Salt Lake encompasses virtually the entire Bonneville lake cycle, including the 26.5 ka Thiokol basaltic ash at the base and deposits representing the overflowing stage at the Provo shoreline at the top of the core. Two cores from the Old River Bed area near the threshold between the Sevier basin and the Great Salt Lake basin (the main body of Lake Bonneville) represent deposition from the end of the Stansbury oscillation ( 20 ka) to post-Provo time ( 13 ka), and one core from near Sunstone Knoll in the Sevier basin provides a nearly complete record of the period when Lake Bonneville flooded the Sevier basin (20–13 ka).In all cores, percent calcium carbonate, the aragonite to calcite ratio, and percent sand were measured at approximately 2-cm intervals, and 18O and 13C were determined in one core from the Old River Bed area. The transgressive period from about 20 ka to 15 ka is represented in all cores, but the general trends and the details of the records are different, probably as a result of water chemistry and water balance differences between the main body and the Sevier basin because they were fed by different rivers and had different hypsometries. The Old River Bed marl sections are intermediate in position and composition between the Monument Point and Sunstone Knoll sections. Variations in marl composition at the Old River Bed, which are correlated with lake-level changes, were probably caused by changes in the relative proportions of water from the two basins, which were caused by shifts in water balance in the lake.This is the second paper in a series of papers published in this issue on Climatic and Tectonic Rhythms in Lake Deposits. 相似文献
37.
The discovery of large, solid particles in the clouds of Venus is one of the most significant findings of Pioneer Venus because it means that a substantial mass of the clouds is composed of a material other than sulfuric acid. The evidence which suggests that solid particles form a distinctive size mode is reexamined. The mode is defined by a discontinuity between two size ranges of the Pioneer Venus particle size spectrometer. This discontinuity could represent a real size mode. However, it could also be an artifact of the measurement technique. R. G. Knollenberg (1984) discusses several possible instrumental effects which might have caused this discontinuity. It is hypothesized herein that such effects did occur and that the large particles are really the tail of the mode 2 sulfuric acid particle size distribution and are not a separate mode of solid particles. Using such a revised size distribution, it is shown that all of the Pioneer Venus and Venera optical data from the lower clouds can be explained with sulfuric acid droplets without introducing any solid particles. As a by-product of this analysis, it is also found that the upper clouds of Venus must contain a material with a higher refractive index than sulfuric acid. A small quantity of sulfur could account for this observation. 相似文献
38.
Charles L. Wolff 《Solar physics》1984,93(1):1-13
Solar irradiance measurements from the ACRIM experiment show a clear response to the rotation periods of g-mode oscillations (l = 1, 2, and 3) and their first harmonics. Peaks in the ACRIM spectrum at 16.6, 18.3, 20.7, 36.5, and - 71 days all lie within about 1% of periods arising from g-mode rotation. This means that the g-modes are a fundamental cause of irradiance fluctuations. On time scales of months and less they modulate the irradiance by means of transient flows of global scale which they stimulate in the Sun's convective envelope. Dimensional arguments indicate that the flows carry up heat at an average rate 10-3
L
which is not in conflict with observed changes in the irradiance. Five additional tests for g-modes and large-scale convection are given. An instability is described which undermines diffusion models of sunspot energy storage. 相似文献
39.
A mission out of the planetary system, launched about the year 2000, could provide valuable data concerning characteristics of the heliopause, the interstellar medium, stellar distances (by parallax measurements), low-energy cosmic rays, interplanetary gas distribution, and mass of the solar system. Secondary objectives include investigation of Pluto. Candidate science measurements, instruments, and instrument development needs are discussed. The mission should extend from 400 to 1000 AU from the Sun. A heliocentric hyperbolic escape velocity of 50–100 km/sec or more is needed to attain this distance within a reasonable mission duration (20–50 years). The trajectory should be toward the incoming interstellar gas. For a year 2000 launch, a Pluto encounter and orbiter can be included. A second mission targeted parallel to the solar axis would also be worthwhile. 相似文献
40.
A comparison is made between the plane-parallel approximation and the more realistic spherical shell approximation for the radiance reflected from a planetary atmosphere. In this paper we have considered a planet of radius 6371 km (the Earth) with a homogeneous, conservative, Rayleigh scattering atmosphere extending to a height of 100 km. We have found significant departures from the plane-parallel approximation. Radiance versus height distributions for both single and multiple scattering are presented. Results are presented for the fractional radiance from altitudes in the atmosphere which contribute to the total unidirectional reflected radiance at the top of the atmosphere. We have referred to this as the radiance versus height distribution in the sequel. These data will be very useful for both remote sensing applications and planetary spectroscopy. We have also found that gross violations of the principle of reciprocity do occur in the spherical shell approximation. 相似文献