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881.
Frank?M.?FlockeEmail author Andrew?J.?Weinheimer Aaron?L.?Swanson James?M.?Roberts Rainer?Schmitt Stephen?Shertz 《Journal of Atmospheric Chemistry》2005,52(1):19-43
A fast, automated, gas chromatographic system for the airborne measurement of PAN and a series of its homologues is described
and its performance is evaluated. Response factors for PAN, PPN, APAN, PiBN, and MPAN have been determined and are discussed
with regard to ECD response and to potential losses in the analytical system. Calibration methods used for these tasks are
described and compared. The results from this work should help investigators who are employing the widely used GC/ECD method
for the measurement of peroxyacyl nitrates to evaluate peaks of PAN homologues that cannot be calibrated for by using the
reported response factors. 相似文献
882.
Mineral-potential mapping is the process of combining a set of input maps, each representing a distinct geo-scientific variable, to produce a single map which ranks areas according to their potential to host mineral deposits of a particular type. The maps are combined using a mapping function that must be either provided by an expert (knowledge-driven approach), or induced from sample data (data-driven approach). Current data-driven approaches using multilayer perceptrons (MLPs) to represent the mapping function have several inherent problems: they are highly sensitive to the selection of training data; they do not utilize the contextual information provided by nondeposit data; and there is no objective interpretation of the values output by the MLP. This paper presents a new approach by which MLPs can be trained to output values that can be interpreted strictly as representing posterior probabilities. Other advantages of the approach are that it utilizes all data in the construction of the model, and thus eliminates any dependence on a particular selection of training data. The technique is applied to mapping gold mineralization potential in the Castlemaine region of Victoria, Australia, and results are compared with a method based on estimating probability density functions. 相似文献
883.
A computationally efficient method to direct and evaluate the sufficiency of site characterization data is demonstrated on two synthetic subsurface geometries. This method, entitled reliability-based exploration (RBE), combines three-dimensional subsurface analysis and uncertainty in the geologic data to produce a quantifiable measure of data sufficiency, which is directly related to the probability of project success. The RBE approach is illustrated with a three-dimensional finite element soil deformation model, where interfaces separating geologic units are the subsurface data of interest. The RBE method begins with a prior model of the subsurface, which can include geologic judgement. As new information is collected at a site, the prior subsurface model is updated with site data. During the RBE analysis, both a probability of project success and the location of the next boring are computed. The robustness of this computation is illustrated with a practical example of the automatic exploration of two different pinching geometries. The subsurface geometry is imposed on these two sites to demonstrate the importance of geology on the computed results. A comparison of the modeled subsurface and the true (or defined) subsurface at each site shows a close match directly below the proposed structure, where calculated settlement is most sensitive to uncertainty in geology. The study demonstrated that to achieve the same exploration sufficiency more data are required at the site with abruptly changing subsurface geometry than at the site with gradually changing geometry. 相似文献
884.
885.
Haiyu Gao Zhuoheng Chen Kirk G. Osadetz Peter Hannigan Cameron Watson 《Mathematical Geology》2000,32(6):725-749
An approach is proposed to predict the spatial distributions of undiscovered petroleum resources. Each pool is parameterized as a marked-point. The independence chain of the Hastings algorithm is used to generate an appropriate structure for pool combinations in a play. Petroleum-bearing favorability estimated from geological observations is used to represent the sampling probabilities of pool locations. An objective function measuring the distance between characteristics of the realization and constraints is constructed from both the pool size distribution and entropy maximum criterion, in which the entropy criterion places all undiscovered pools in the most favorable positions. The geometrical convergence property of the proposed Hastings algorithm is presented. The method is illustrated by a case study from the Western Canada Sedimentary Basin. 相似文献
886.
Cochran Anita Veverka Joseph Bell James Belton Michael Benkhoff Johannes Benkhoff Andrew Clark Benton Feldman Paul Kissel Jochen Mahaffy Paul Malin Michael Murchie Scott Neimann Hasso Owen Tobias Robinson Mark Schwehm Gerhard Squyres Steve Thomas Peter Whipple Fred Yeomans Donald 《Earth, Moon, and Planets》2000,89(1-4):289-300
In 1997, the COmet Nucleus TOUR (CONTOUR) was selected byNASA for a new start as part of the Discovery line. In this paper, we review the status of the mission, the mission timeline and the instruments to be flown. Detail is given of the science goals and how they are to be accomplished. 相似文献
887.
888.
889.
The state and future of Mars polar science and exploration. 总被引:1,自引:0,他引:1
S M Clifford D Crisp D A Fisher K E Herkenhoff S E Smrekar P C Thomas D D Wynn-Williams R W Zurek J R Barnes B G Bills E W Blake W M Calvin J M Cameron M H Carr P R Christensen B C Clark G D Clow J A Cutts D Dahl-Jensen W B Durham F P Fanale J D Farmer F Forget K Gotto-Azuma H J Zwally 《Icarus》2000,144(2):210-242
As the planet's principal cold traps, the martian polar regions have accumulated extensive mantles of ice and dust that cover individual areas of approximately 10(6) km2 and total as much as 3-4 km thick. From the scarcity of superposed craters on their surface, these layered deposits are thought to be comparatively young--preserving a record of the seasonal and climatic cycling of atmospheric CO2, H2O, and dust over the past approximately 10(5)-10(8) years. For this reason, the martian polar deposits may serve as a Rosetta Stone for understanding the geologic and climatic history of the planet--documenting variations in insolation (due to quasiperiodic oscillations in the planet's obliquity and orbital elements), volatile mass balance, atmospheric composition, dust storm activity, volcanic eruptions, large impacts, catastrophic floods, solar luminosity, supernovae, and perhaps even a record of microbial life. Beyond their scientific value, the polar regions may soon prove important for another reason--providing a valuable and accessible reservoir of water to support the long-term human exploration of Mars. In this paper we assess the current state of Mars polar research, identify the key questions that motivate the exploration of the polar regions, discuss the extent to which current missions will address these questions, and speculate about what additional capabilities and investigations may be required to address the issues that remain outstanding. 相似文献
890.
Andrew Steele David t. Goddard Dave Stapleton Jan k. w. Toporski Vanessa Peters Virginia Bassinger George Sharples David d. Wynn‐Williams David s. Mckay 《Meteoritics & planetary science》2000,35(2):237-241
Abstract— Examination of fracture surfaces near the fusion crust of the martian meteorite Allan Hills (ALH) 84001 have been conducted using scanning electron microscopy (SEM) and atomic force microscopy (AFM) and has revealed structures strongly resembling mycelium. These structures were compared with similar structures found in Antarctic cryptoendolithic communities. On morphology alone, we conclude that these features are not only terrestrial in origin but probably belong to a member of the Actinomycetales, which we consider was introduced during the Antarctic residency of this meteorite. If true, this is the first documented account of terrestrial microbial activity within a meteorite from the Antarctic blue ice fields. These structures, however, do not bear any resemblance to those postulated to be martian biota, although they are a probable source of the organic contaminants previously reported in this meteorite. 相似文献