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排序方式: 共有185条查询结果,搜索用时 15 毫秒
91.
Timothy Stahl Stefan Winkler Mark Quigley Mark Bebbington Brendan Duffy Daniel Duke 《地球表面变化过程与地形》2013,38(15):1838-1850
Schmidt hammer (SH) R‐values are reported for surface clasts from numerically dated Holocene and Pleistocene fluvial terraces in the South Island of New Zealand. The R‐values are combined with previously obtained weathering rind, radiocarbon, terrestrial cosmogenic nuclide and luminescence terrace ages to derive SH R‐value chronofunctions for greywacke clasts from four distinct locations. Our results show that different weathering rates affect the form of the SH R‐value versus Age curve, however a fundamental dependency between the two remains constant over timescales ranging from 102 to 105 years. Power law scaling constants suggest changes in clast weathering rates are primarily affected by climatic (precipitation and temperature) and sedimentologic variables (source terrane petrology). Age uncertainties of ~22% of the surface age suggest that Schmidt hammer exposure‐age dating (SHD) is a reliable calibrated‐age dating technique for fluvial terraces. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
92.
Comparison of electronic and mechanical Schmidt hammers in the context of exposure‐age dating: are Q‐ and R‐values interconvertible?
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Application of Schmidt‐hammer exposure‐age dating (SHD) to landforms has substantially increased in recent years. The original mechanical Schmidt hammer records R‐(rebound) values. Although the newly introduced electronic Schmidt hammer (SilverSchmidt) facilitates greatly improved data processing, it measures surface hardness differently, recording Q‐(velocity) values that are not a priori interconvertible with R‐values. This study is the first to compare the performance of both instruments in the context of field‐based exposure‐age dating with a particular focus on the interconvertibility of R‐values and Q‐values. The study was conducted on glacially polished pyroxene‐granulite gneiss, Jotunheimen, southern Norway. Results indicate that mean Q‐values are consistently 8–10 units higher than mean R‐values over the range of values normally encountered in the application of SHD to glacial and periglacial landforms. A convenient conversion factor of ±10 units may, therefore, be appropriate for all but the softest rock types close to the technical resolution of the instruments. The electronic Schmidt hammer should therefore be regarded as a useful complement and potential replacement for the mechanical Schmidt hammer. Conversion of published R‐values data to Q‐values requires, however, careful control and documentation of instrument calibration. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
93.
Julie A. Winkler Suzanne Thornsbury Marco Artavia Frank-M. Chmielewski Dieter Kirschke Sangjun Lee Malgorzata Liszewska Scott Loveridge Pang-Ning Tan Sharon Zhong Jeffrey A. Andresen J. Roy Black Robert Kurlus Denys Nizalov Nicole Olynk Zbigniew Ustrnul Costanza Zavalloni Jeanne M. Bisanz Géza Bujdosó Lesley Fusina Yvonne Henniges Peter Hilsendegen Katarzyna Lar Lukasz Malarzewski Thordis Moeller Roman Murmylo Tadeusz Niedzwiedz Olena Nizalova Haryono Prawiranata Nikki Rothwell Jenni van Ravensway Harald von Witzke Mollie Woods 《Climatic change》2010,103(3-4):445-470
A conceptual framework for climate change assessments of international market systems that involve long-term investments is proposed. The framework is a hybrid of dynamic and static modeling. Dynamic modeling is used for those system components for which temporally continuous modeling is possible, while fixed time slices are used for other system components where it can be assumed that underlying assumptions are held constant within the time slices but allowed to vary between slices. An important component of the framework is the assessment of the “metauncertainty” arising from the structural uncertainties of a linked sequence of climate, production, trade and decision-making models. The impetus for proposing the framework is the paucity of industry-wide assessments for market systems with multiple production regions and long-term capital investments that are vulnerable to climate variations and change, especially climate extremes. The proposed framework is pragmatic, eschewing the ideal for the tractable. Even so, numerous implementation challenges are expected, which are illustrated using an example industry. The conceptual framework is offered as a starting point for further discussions of strategies and approaches for climate change impact, vulnerability and adaptation assessments for international market systems. 相似文献
94.
Particle detection by condensation particle counters (CPCs) is ultimately limited by the onset of homogeneous nucleation. At vapour supersaturations around the homogeneous nucleation limit the diameter of critical clusters is typically about 2 nm. It is widely assumed that only particles larger than critical clusters can be activated by vapour condensation and the general detection limit of CPCs is therefore currently accepted to be around 2 nm particle diameter. Using an expansion type CPC with n-propanol as working fluid we investigated the transition from heterogeneous to homogeneous nucleation, clearly showing that particles are activated much before the onset of homogeneous nucleation, even at particle diameters as small as 1.4 nm. For particle diameters below 2 nm we have usually found condensation particle counting to be influenced by the simultaneous presence of ions as generated in a bipolar diffusion charger. In this paper we illustrate how the presence of ions influences particle number concentration measurement and how ions can be removed in order to obtain accurate seed particle number concentrations for particle diameters down to 1 nm. 相似文献
95.
Stefan Winkler 《Central European Journal of Geosciences》2009,1(3):274-290
This study provides the first attempt to combine terrestrial (in situ) cosmogenic nuclide (10Be) surface exposure dating with Schmidt hammer relative-age dating for the age estimation of Holocene moraines at Strauchon Glacier, Southern Alps, New Zealand. Numerous Schmidt hammer tests enable a multi-ridged lateral moraine system to be related to three late-Holocene ‘Little Ice Age’-type events. On the basis of cosmogenic 10Be ages, those events are dated to c. 2400, 1700, and 1100 years ago. Linear age-calibration curves are constructed in order to relate Schmidt hammer R-values to cosmogenic 10Be ages. The high explanation yielded reveals the causal link between both data sets. The potential of combining both methods in a ‘’multiproxy approach’ is discussed alongside possible future improvements. Terrestrial cosmogenic nuclide dating delivers absolute ages needed as fixed points for Schmidt hammer age-calibration curves. The Schmidt hammer technique can be used to crosscheck the boulder surfaces chosen for surface exposure dating by terrestrial cosmogenic nuclides. It should, therefore, reduce the number of samples necessary and costs. 相似文献
96.
97.
The relative stabilities of orthozoisite, Ca2Al3[O|OH|Si2O7|SiO4], space group Pnma, and the monoclinic polymorph, clinozoisite, space group P21/m, have been investigated using calculations based on density functional theory. It is found that orthozoisite is more stable
than clinozoisite by about 1 kJ mol−1 at zero pressure in the athermal limit. The bulk moduli of the two polymorphs have been calculated to be Bortho=117.5(1.7) GPa and Bclino=136(4) GPa.
Received: 20 March 2000 / Accepted: 26 February 2001 相似文献
98.
A molecular dynamics simulation study of MgSiO3 has been performed using a large sample containing 4096 unit cells. Thermodynamic properties have been extracted using a semiclassical approximation to the correct quantum mechanical treatment, using the calculated density of states and the quantum harmonic formalism for thermodynamic functions. Simulations performed at different temperatures and volumes have given an estimate of the relative contributions due to thermal expansion (quasi-harmonic effects) and direct anharmonic interactions. Comparison of results for mean square atomic displacements with results on smaller samples have shown the limitations of smaller sample sizes. 相似文献
99.
100.
Leonardo Sagnotti Pierre RochetteMike Jackson Fabienne VadeboinJaume Dinarès-Turell Aldo Winkler 《Physics of the Earth and Planetary Interiors》2003,138(1):25-38
Inter-laboratory and absolute calibrations of rock magnetic parameters are fundamental for grounding a rock magnetic database and for semi-quantitative estimates about the magnetic mineral assemblage of a natural sample. Even a dimensionless ratio, such as anhysteretic susceptibility normalized by magnetic susceptibility (Ka/K) may be biased by improper calibration of one or both of the two instruments used to measure Ka and K. In addition, the intensity of the anhysteretic remanent magnetization (ARM) of a given sample depends on the experimental process by which the remanence is imparted. We report an inter-laboratory calibration of these two key parameters, using two sets of artificial reference samples: a paramagnetic rare earth salt, Gd2O3 and a commercial “pozzolanico” cement containing oxidized magnetite with grain size of less than 0.1 μm according to hysteresis properties. Using Gd2O3 the 10 Kappabridges magnetic susceptibility meters (AGICO KLY-2 or KLY-3 models) tested prove to be cross-calibrated to within 1%. On the other hand, Kappabridges provide a low-field susceptibility value that is ca. 6% lower than the tabulated value for Gd2O3, while average high-field susceptibility values measured on a range of instruments are indistinguishable from the tabulated value. Therefore, we suggest that Kappabridge values should be multiplied by 1.06 to achieve absolute calibration. Bartington Instruments magnetic susceptibility meters with MS2B sensors produce values that are 2-13% lower than Kappabridge values, with a strong dependence on sample centering within the sensor. The Ka/K ratio of ca. 11, originally obtained on discrete cement samples with a 2G Enterprises superconducting rock magnetometer and a KLY-2, is consistent with reference parameters for magnetites of grain size <0.1 μm. On the other hand, Ka values from a 2G Enterprises magnetometer and K values from a Bartington Instruments MS2C loop sensor for u-channel and discrete cement samples, will produce average Ka/K values that are unrealistically high if not properly corrected for the nominal volume detected by the sensors for these instruments. Inter-laboratory measurements of K and Ka for standard paleomagnetic plastic cubes filled with cement indicate remarkable differences in the intensity of the newly produced ARMs (with a standard deviation of ca. 21%), that are significantly larger than the differences observed from the calibration of the different magnetometers employed in each laboratory. Differences in the alternating field decay rate are likely the major source of these variations, but cannot account for all the observed variability. With such large variations in experimental conditions, classical interpretation of a “King plot” of Ka versus K would imply significant differences in the determination of grain size of magnetite particles on the same material. 相似文献