Hafnium isotope homogenization during metamorphic zircon growth in amphibolite-facies rocks: Examples from the Shackleton Range (Antarctica)   总被引：2，自引：0，他引：2  

Armin Zeh  Axel Gerdes  Hartwig E. Frimmel 《Geochimica et cosmochimica acta》2010,74(16):4740-4758

Hafnium isotope analyses of a large number of metamorphic zircon grains of two garnet-kyanite-staurolite schist samples from the Shackleton Range yielded ¹⁷⁶Hf/¹⁷⁷Hf of 0.28160 ± 0.00003 and 0.28142 ± 0.00003, respectively. The variations of these analyses are less than ±1.2 epsilon units and indicate that all metamorphic zircon grains in the two rocks formed in environments with nearly homogenous Hf isotopic composition. The metamorphic origin of the zircon grains is constrained by textures as well as by their low Th/U (<0.2), ¹⁷⁶Lu/¹⁷⁷Hf (<0.0003), and ¹⁷⁶Yb/¹⁷⁷Hf ratios (<0.009), indicating that they grew in the presence of garnet. Furthermore, the grains yield Pb-Pb ages of c. 1.7 Ga, which is the time of amphibolite-facies metamorphism. In combination with petrological results, it is suggested that the observed ¹⁷⁶Hf/¹⁷⁷Hf homogeneity was caused by a fluid- and deformation-assisted dissolution of detrital zircon grains, followed by new zircon re-precipitation that was accompanied by Hf transport on at least a hand-specimen scale. This interpretation is supported by results obtained from an additional paragneiss sample that contains zoned zircon grains with xenocrystic cores formed at 2.6-1.8 Ga and metamorphic rims with a U-Pb age of 1.7 Ga. The ¹⁷⁶Hf/¹⁷⁷Hf variation of the zircon rims is mostly at ±0.0003, which is much less than that of the magmatic cores (±0.0019). The metamorphic fluid for the dissolution-homogenization-re-precipitation process most likely resulted from prograde reactions among the minerals chlorite-muscovite-biotite-garnet-staurolite-apatite, in agreement with thin section observations and P-T pseudosection calculations.  相似文献   

Generating extreme ship responses using non-uniform phase distributions     

Laura K. Alford  Armin W. Troesch 《Ocean Engineering》2009,36(9-10):641-649

Modified Gaussian phase distributions are used to generate short time series containing a specific extreme value of a ship response. The corresponding incident wave train is calculated via linear systems theory. Sample response and wave time series are compared to the expected time series as calculated by probabilistic analysis. The average of the sample response time series compares favorably to the expected time series, but the average of the sample wave trains does not, in general, match the expected wave train. These comparisons show the danger in estimating extreme ship responses considering only extreme waves. A sample analysis for a Great Lakes bulk carrier is included for illustration.  相似文献   

Comparative geometric and radiometric evaluation of mobile phone and still video cameras     

Devrim  Akca  Armin  Gruen 《The Photogrammetric Record》2009,24(127):217-245

This paper examines the potential of mobile phones to be used as front-end sensors for photogrammetric procedures and applications. For this purpose, two mobile phone cameras (Sony Ericsson K750i and Nokia N93) were calibrated over an indoor 3D testfield, using a self-calibrating bundle adjustment. Geometric accuracy tests were carried out in order to evaluate their metric performances and to compare the results with respect to two off-the-shelf digital still video cameras (Sony DSC W100 and Sony DSC F828). The geometric accuracy evaluation comprised an absolute accuracy test, JPEG test and temporal stability test. The radiometric capabilities of all cameras (except that the DSC W100 was replaced with a DSC T100 camera) were also evaluated and compared by carrying out modulation transfer function (MTF) analysis, image noise analysis and an operating range test. Substantial systematic errors were diagnosed in some systems. However, with proper calibration it is believed that these devices can be used for many photogrammetric tasks.  相似文献   

Interpretation of Pumping Tests in Heterogeneous Aquifers with Constant Head Boundary     

Armin Pechstein  Nadim K. Copty 《Ground water》2021,59(4):517-523

This paper investigates the impact of heterogeneity of the transmissivity field on the interpretation of steady-state pumping test data from aquifer systems delimited by constant head boundaries such as aquifers adjacent to lakes or rivers. Spatially variable transmissivity fields are randomly generated and used to simulate the drawdown due to a pumping well located at different distances from a constant head boundary. The steady-state drawdown simulated at different observation wells are then interpreted using the Hantush method (Hantush 1959). The numerical simulations show that, in contrast to the case of infinite aquifer domains, the interpreted transmissivity varies depending on well locations and the separation distance between pumping well and boundary relative to the correlation length. The ensemble-averaged estimated transmissivity varies between the geometric mean and the arithmetic mean, and can even exceed the arithmetic mean in a narrow domain adjacent to the boundary. It approaches the geometric mean of the underlying transmissivity field only if the distance between the pumping well is more than 20 times the characteristic length of the transmissivity field.  相似文献   

Testing different sorting techniques in macroinvertebrate samples from running waters     

Peter Haase  Steffen Pauls  Andrea Sundermann  Armin Zenker 《Limnologica》2004,34(4):366-378

With the aim of finding an efficient, standardised and practical protocol for sorting macroinvertebrate samples for water management practice, three different sorting techniques were tested: RIVPACS sorting, a modified AQEM/STAR (MAS) sorting protocol and a Live-sorting method. Based on the same AQEM/STAR sample to ensure comparable results, we compared RIVPACS and MAS sorting for 20 samples, and Live-sorting and MAS for a different set of 20 samples. Comparisons were based on both ecological and financial parameters relevant for the implementation of the EU Water Framework Directive in Germany. Parameters include recently developed multimetric assessment indices, their stream type specific core metric results, time effort and costs. While RIVPACS and MAS sorting produced similar results in terms of ecological assessment, time effort and costs, Live-sorting differed notably in all three respects. Live-sorting is the quickest and least expensive protocol, but shows higher variability than the other protocols. We discuss the differences and the level of standardisation for each of these methods.  相似文献   

Green Hydropower: The contribution of aquatic science research to the promotion of sustainable electricity     

Bernhard Truffer  Christine Bratrich  Jochen Markard  Armin Peter  Alfred Wüest  Bernhard Wehrli 《Aquatic Sciences - Research Across Boundaries》2003,65(2):99-110

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Entrance of hot pyroclastic flows into the sea: experimental observations   总被引：1，自引：0，他引：1  

Armin Freundt 《Bulletin of Volcanology》2003,65(2-3):144-164

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Decline of fish catch in Switzerland     

Patricia Burkhardt-Holm  Armin Peter  Helmut Segner 《Aquatic Sciences - Research Across Boundaries》2002,64(1):36-54

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Interannual-decadal variability of wintertime mixed layer depths in the North Pacific detected by an ensemble of ocean syntheses     

Toyoda  Takahiro  Fujii  Yosuke  Kuragano  Tsurane  Kosugi  Naohiro  Sasano  Daisuke  Kamachi  Masafumi  Ishikawa  Yoichi  Masuda  Shuhei  Sato  Kanako  Awaji  Toshiyuki  Hernandez  Fabrice  Ferry  Nicolas  Guinehut  Stéphanie  Martin  Matthew  Andrew Peterson  K.  Good  Simon A.  Valdivieso  Maria  Haines  Keith  Storto  Andrea  Masina  Simona  Köhl  Armin  Yin  Yonghong  Shi  Li  Alves  Oscar  Smith  Gregory  Chang  You-Soon  Vernieres  Guillaume  Wang  Xiaochun  Forget  Gael  Heimbach  Patrick  Wang  Ou  Fukumori  Ichiro  Lee  Tong  Zuo  Hao  Balmaseda  Magdalena 《Climate Dynamics》2017,49(3):891-907

Climate Dynamics - The interannual-decadal variability of the wintertime mixed layer depths (MLDs) over the North Pacific is investigated from an empirical orthogonal function (EOF) analysis of an...  相似文献   

The experimental and theoretical evaluation of a twin-flap wave-energy absorbing device     

Robert M. Scher  Armin W. Troesch  Guojun Zhou 《Ocean Engineering》1983,10(5):325-345

A series of model experiments with a twin-flap wave-energy absorbing device is described, and the results compared with numerical predictions based on theoretical work reported by Srokosz and Evans (1979). Measurements were made of absorption efficiency, flap motion responses, and total flap forces (mooring forces), all with the supporting structure held fixed, with normal wave encounter. Both 2-D and finite-length flap experiments were conducted.Generally, fair agreement was obtained between theory and experiments with regard to efficiency vs wavenumber and applied damping coefficient was generally matched by apparent from these experiments. Maximum efficiencies approaching 100% (as predicted analytically) were confirmed by experiments. Further, the predicted behavior of curves of efficiency vs wave number and applied damping coefficient was generally matched by experimental results.Results for flap motion responses and forces showed good agreement with theory.Some basic conclusions are drawn with regard to practical design and economic considerations for a twin-flap power generating system.  相似文献