Geochemical Fingerprinting of Coltan Ores by Machine Learning on Uneven Datasets     

Christian Savu-Krohn  Gerd Rantitsch  Peter Auer  Frank Melcher  Torsten Graupner 《Natural Resources Research》2011,20(3):177-191

Two modern machine learning techniques, Linear Programming Boosting (LPBoost) and Support Vector Machines (SVMs), are introduced and applied to a geochemical dataset of niobium–tantalum (“coltan”) ores from Central Africa to demonstrate how such information may be used to distinguish ore provenance, i.e., place of origin. The compositional data used include uni- and multivariate outliers and elemental distributions are not described by parametric frequency distribution functions. The “soft margin” techniques of LPBoost and SVMs can be applied to such data. Optimization of their learning parameters results in an average accuracy of up to c. 92%, if spot measurements are assessed to estimate the provenance of ore samples originating from two geographically defined source areas. A parameterized performance measure, together with common methods for its optimization, was evaluated to account for the presence of uneven datasets. Optimization of the classification function threshold improves the performance, as class importance is shifted towards one of those classes. For this dataset, the average performance of the SVMs is significantly better compared to that of LPBoost.  相似文献   

Magnetic aggregation: II. Laboratory and microgravity experiments     

Henrik Nübold  Torsten Poppe  Carsten Dominik 《Icarus》2003,165(1):195-214

In a previous publication (Dominik and Nübold, 2002, Icarus 157, 173-186), we presented analytical expressions and theoretical considerations concerning preplanetary dust aggregation with magnetized grains in the solar nebula. The present work is dedicated to the experimental study of magnetic aggregation in a ground-based laboratory as well as under microgravity conditions on parabolic flights. We conducted aggregation experiments with dust analogues in order to study the temporal evolution and the structural outcome of grain growth processes dominated by or comprising exclusively magnetic grains. Within aggregation times ranging from a couple of seconds to a few minutes only, formation of huge chain-like and/or web-like dust aggregates was observed. After aggregate retrieval we were able to study the sizes and structures of the aggregates in great detail. We established the fractal dimension of the aggregates as D_fs=1.20±0.05 for single chains and D_fc=1.50±0.21 for inter-connected web-like structures. This is considerably lower than for non-magnetic grain growth. The dynamic exponent z for the mass increase with time according to t^z was found to be z=2.7 from in-situ video images of the microgravity aggregation runs. The results are compared with the theoretical considerations presented earlier as well as with previous experimental work on the same and on related topics, respectively.  相似文献   

Monotonic and cyclic tests on kaolin: a database for the development,calibration and verification of constitutive models for cohesive soils with focus to cyclic loading     

Torsten Wichtmann  Theodoros Triantafyllidis 《Acta Geotechnica》2018,13(5):1103-1128

A database with about 60 undrained monotonic and cyclic triaxial tests on kaolin is presented. In the monotonic tests, the influences of consolidation pressure, overconsolidation ratio, displacement rate and sample cutting direction have been studied. In the cyclic tests, the stress amplitude, the initial stress ratio and the control (stress vs. strain cycles) have been additionally varied. Isotropic consolidation leads to a failure due to large strain amplitudes with eight-shaped effective stress paths in the final phase of the cyclic tests, while a failure due to an excessive accumulation of axial strain and lens-shaped effective stress paths was observed in the case of anisotropic consolidation with \(q^{\text{ ampl }}< |q^{\text{ av }}|\). The rate of pore pressure accumulation grew with increasing amplitude and void ratio (i.e. decreasing consolidation pressure and overconsolidation ratio). The “cyclic flow rule” well known for sand has been confirmed also for kaolin: With increasing value of the average stress ratio \(|\eta ^{\text{ av }}| = |q^{\text{ av }}|/p^{\text{ av }}, \) the accumulation of deviatoric strain becomes predominant over the accumulation of pore water pressure. The tests on the samples cut out either horizontally or vertically revealed a significant effect of anisotropy. In the cyclic tests, the two kinds of samples exhibited an opposite inclination of the effective stress path. Furthermore, the horizontal samples showed a higher stiffness and could sustain a much larger number of cycles to failure. All data of the present study are available from the homepage of the first author. They may serve for the examination, calibration or improvement in constitutive models dedicated to cohesive soils under cyclic loading, or for the development of new models.  相似文献   

The Blacktail Creek Tuff: an analytical and experimental study of rhyolites from the Heise volcanic field,Yellowstone hotspot system     

Torsten Bolte  Francois Holtz  Renat Almeev  Barbara Nash 《Contributions to Mineralogy and Petrology》2015,169(2):15

The magma storage conditions of the 6.62 Ma Blacktail Creek Tuff eruption, belonging to the Heise volcanic field (6.62–4.45 Ma old) of the Yellowstone hotspot system, have been investigated by combining thermobarometric and experimental approaches. The results from different geothermometers (e.g., Fe–Ti oxides, feldspar pairs, apatite and zircon solubility, and Ti in quartz) indicate a pre-eruptive temperature in the range 825–875 °C. The temperature estimated using two-pyroxene pairs varies in a range of 810–950 °C, but the pyroxenes are probably not in equilibrium with each other, and the analytical results of melt inclusion in pyroxenes indicate a complex history for clinopyroxene, which hosts two compositionally different inclusion types. One natural Blacktail Creek Tuff rock sample has been used to determine experimentally the equilibrium phase assemblages in the pressure range 100–500 MPa and a water activity range 0.1–1.0. The experiments have been performed at fluid-present conditions, with a fluid phase composed of H₂O and CO₂, as well as at fluid-absent conditions. The stability of the quartzo-feldspathic phases is similar in both types of experiments, but the presence of mafic minerals such as biotite and clinopyroxene is strongly dependent on the experimental approach. Possible explanations are given for this discrepancy which may have strong impacts on the choice of appropriate experimental approaches for the determination of magma storage conditions. The comparison of the composition of natural phases and of experimentally synthesized phases confirms magma storage temperatures of 845–875 °C. Melt water contents of 1.5–2.5 wt% H₂O are required to reproduce the natural Blacktail Creek Tuff mineral assemblage at these temperatures. Using the Ti-in-quartz barometer and the Qz–Ab–Or proportions of natural matrix glasses, coexisting with quartz, plagioclase and sanidine, the depth of magma storage is estimated to be in a pressure range between 130 and 250 MPa.  相似文献   

Hydraulic fracturing in unconventional gas reservoirs: risks in the geological system, part 2   总被引：2，自引：2，他引：0  

Alexander Kissinger  Rainer Helmig  Anozie Ebigbo  Holger Class  Torsten Lange  Martin Sauter  Michael Heitfeld  Johannes Klünker  Wiebke Jahnke 《Environmental Earth Sciences》2013,70(8):3855-3873

Hydraulic fracturing is a method used for the production of unconventional gas resources. Huge amounts of so-called fracturing fluid (10,000–20,000 m³) are injected into a gas reservoir to create fractures in solid rock formations, upon which mobilised methane fills the pore space and the fracturing fluid is withdrawn. Hydraulic fracturing may pose a threat to groundwater resources if fracturing fluid or brine can migrate through fault zones into shallow aquifers. Diffuse methane emissions from the gas reservoir may not only contaminate shallow groundwater aquifers, but also escape into the atmosphere where methane acts as a greenhouse gas. The working group “Risks in the Geological System” as part of ExxonMobil’s hydrofracking dialogue and information dissemination processes was tasked with the assessment of possible hazards posed by migrating fluids as a result of hydraulic fracturing activities. In this work, several flow paths for fracturing fluid, brine and methane are identified and scenarios are set up to qualitatively estimate under what circumstances these fluids would leak into shallower layers. The parametrisation for potential hydraulic fracturing sites in North Rhine-Westphalia and Lower Saxony (both in Germany) is derived from literature using upper and lower bounds of hydraulic parameters. The results show that a significant fluid migration is only possible if a combination of several conservative assumptions is met by a scenario.  相似文献   

Recommendation for the discrimination of human-related and natural seismicity   总被引：1，自引：1，他引：0  

T. Dahm  D. Becker  M. Bischoff  S. Cesca  B. Dost  R. Fritschen  S. Hainzl  C. D. Klose  D. K��hn  S. Lasocki  Th. Meier  M. Ohrnberger  E. Rivalta  U. Wegler  Stephan Husen 《Journal of Seismology》2013,17(1):197-202

Various techniques are utilized by the seismological community, extractive industries, energy and geoengineering companies to identify earthquake nucleation processes in close proximity to engineering operation points. These operations may comprise fluid extraction or injections, artificial water reservoir impoundments, open pit and deep mining, deep geothermal power generations or carbon sequestration. In this letter to the editor, we outline several lines of investigation that we suggest to follow to address the discrimination problem between natural seismicity and seismic events induced or triggered by geoengineering activities. These suggestions have been developed by a group of experts during several meetings and workshops, and we feel that their publication as a summary report is helpful for the geoscientific community. Specific investigation procedures and discrimination approaches, on which our recommendations are based, are also published in this Special Issue (SI) of Journal of Seismology.  相似文献   

Inversion of Scholte wave dispersion and waveform modeling for shallow structure of the Ninetyeast Ridge     

Xuan Nhi Nguyen  Torsten Dahm  Ingo Grevemeyer 《Journal of Seismology》2009,13(4):543-559

The construction of S-wave velocity models of marine sediments down to hundreds of meters below the seafloor is important in a number of disciplines. One of the most significant trends in marine geophysics is to use interface waves to estimate shallow shear velocities which play an important role in determining the shallow crustal structure. In marine settings, the waves trapped near the fluid–solid interface are called Scholte waves, and this is the subject of the study. In 1998, there were experiments on the Ninetyeast Ridge (Central Indian Ocean) to study the shallow seismic structure at the drilled site. The data were acquired by both ocean bottom seismometer and ocean bottom hydrophone. A new type of seafloor implosion sources has been used in this experiment, which successfully excited fast and high frequency (>500 Hz) body waves and slow, intermediate frequency (<20 Hz) Scholte waves. The fundamental and first higher mode Scholte waves have both been excited by the implosion source. Here, the Scholte waves are investigated with a full waveform modeling and a group velocity inversion approach. Shear wave velocities for the uppermost layers of the region are inferred and results from the different methods are compared. We find that the full waveform modeling is important to understand the intrinsic attenuation of the Scholte waves between 1 and 20 Hz. The modeling shows that the S-wave velocity varies from 195 to 350 m/s in the first 16 m of the uppermost layer. Depths levels of high S-wave impedance contrasts compare well to the layer depth derived from a P-wave analysis as well as from drilling data. As expected, the P- to S-wave velocity ratio is very high in the uppermost 16 m of the seafloor and the Poisson ratio is nearly 0.5. Depth levels of high S-wave impedance contrasts are comparable to the layer depth derived from drilling data.  相似文献   

Energy dissipation within the wave run-up at stepped revetments     

Nils B. Kerpen  Daniel B. Bung  Daniel Valero  Torsten Schlurmann 《中国海洋大学学报(英文版)》2017,16(4):649-654

To understand the processes and energy dissipation performance caused by turbulence during the wave run-up over a stepped revetment, hydraulic model tests with steady flow conditions are conducted and correlated with unsteady flow conditions of the wave run-up within a short time frame. Under irregular waves, the run-up reduction over a stepped revetment is dependent on the Iribarren number and decreases for decreasing Iribarren numbers. Velocity gradients are found to be similar in a steady and unsteady flow regime near the pseudo-bottom.  相似文献   

Southern hemispheric westerlies control the spatial distribution of modern sediments in Laguna Potrok Aike,Argentina     

Stephanie Kastner  Christian Ohlendorf  Torsten Haberzettl  Andreas Lücke  Christoph Mayr  Nora I. Maidana  Frank Schäbitz  Bernd Zolitschka 《Journal of Paleolimnology》2010,44(4):887-902

We studied the internal lake processes that control the spatial distribution and characteristics of modern sediments at the ICDP (International Continental Scientific Drilling Program) deep drilling site in Laguna Potrok Aike, southern Patagonia, Argentina. Sediment distribution patterns were investigated using a dense grid of 63 gravity cores taken throughout the lake basin and 40 additional shoreline samples. Analysis of the surficial sediment distribution points to distinct internal depositional dynamics induced by wind-driven lake internal currents. Distribution maps illustrate that the spatial characteristics of analysed variables are linked to high erosional wave activity. Persistent wave action and littoral erosion along all shores, especially the eastern shore, is caused by prevailing Southern Hemispheric Westerlies. Several sediment variables (grain size, benthic diatoms, total inorganic carbon and calcium) indicate re-suspension of littoral sediment followed by re-distribution to profundal accumulation areas near the eastern shore. Variations within the catchment influence sediment characteristics in the north-eastern bay. That area is characterized by different mineralogical and sedimentological conditions as well as greater accumulation of pollen, inorganic carbon and diatoms. These findings are related to the influence of episodic inflow into this bay. Spatial differences in stable isotope values throughout the lake suggest that ephemeral tributaries around the lake basin may also contribute to the detected spatial sediment variations.  相似文献   

Carbon and oxygen isotope zoning around Carlin-type gold deposits: a reconnaissance survey at Twin Creeks, Nevada     

David P. Stenger  Stephen E. Kesler  Torsten Vennemann 《Journal of Geochemical Exploration》1998,63(2):105-121

This study was undertaken to determine whether wallrocks around the Twin Creeks Carlin-type gold deposits exhibit oxygen isotope haloes similar to those found around other types of hydrothermal deposits. Mineralization at Twin Creeks is hosted by Ordovician Sequence shales containing some carbonate minerals and by Pennsylvanian–Permian Etchart Formation limestone. Analysis of orthophosphate-soluble carbonate from these rocks shows that oxygen isotope haloes are detectable in Ordovician Sequence shales but not in Etchart Formation limestone. The soluble fraction of Ordovician Sequence shales at Twin Creeks has δ¹⁸O values of 12 to 24‰ and δ¹³C values of 0 to −10‰. Most samples fall along a poorly defined trend that extends from δ¹⁸O of about 24‰ and δ¹³C values of about 0, which are typical of unaltered limestones, toward lower values for both isotope systems, which are typical of rocks that have undergone alteration by hydrothermal fluids. Plots of these values along two sections through the ore body show that δ¹⁸O values of wallrocks are lowest in the ore zone and increase outward, forming a halo several hundred meters in size. In the same plots, δ¹³C values of the wallrocks do not show systematic spatial variations. The soluble fraction of Etchart Formation limestones at Twin Creeks have δ¹⁸O values of 25 to 5‰ and δ¹³C values of 4 to −10‰, but do not show any systematic spatial variation relative to mineralization at the scale of our samples. Failure of the Etchart Formation samples to show detectable haloes is probably related to deposition of post-ore carbonate minerals or lower ore fluid : rock ratios. Material balance calculations used to model the isotopic composition of average Ordovician Sequence shales indicate that changes in temperature and water : rock ratio were probably not sufficient to account for the wide range of isotope compositions observed in these rocks. The most likely additional factor contributing to this range of values was a change in the composition of the altering fluid, probably by mixing of the ore fluid with surrounding meteoric water. These results suggest that Carlin-type gold deposits are surrounded by haloes of low δ¹⁸O values, but that detection of these haloes could be complicated by local compositional variations and post-ore modification of the wallrocks.  相似文献