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  • 1
    Publication Date: 2021-06-09
    Description: In this study we present dissolved and particulate 230Th and 232Th results, as well as particulate 234Th data, obtained as part of the GEOTRACES central Arctic Ocean sections GN04 (2015) and IPY11 (2007). Samples were analyzed following GEOTRACES methods, and compared to previous results from 1991. We observe significant decreases in 230Th concentrations in the deep waters of the Nansen Basin. We ascribe this non-steady state removal process to a variable release and scavenging of trace metals near an ultra-slow spreading ridge. This finding demonstrates that hydrothermal scavenging in the deep-sea may vary on annual time scales and highlights the importance of repeated GEOTRACES sections
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
    Publication Date: 2016-06-22
    Description: Most lakes in the interior Tibetan Plateau have expanded rapidly since the late 1990s. Because of a lack of observations, lake water balances and their changes are far from well understood. Evaporation is a component of the lake water balance, and this study quantifies its magnitude, decadal change, and its contribution to the water balance changes in Lake Nam Co, one of the largest lakes on the Tibetan Plateau (with an area of approximately 2000 km 2 and a mean depth of approximately 40 m). The lake temperature and the evaporation are simulated by the Flake model. The simulation results are validated against observed lake temperature profile from 2013 and MODIS lake surface temperature data from 2000-2014. The simulated latent heat flux and sensible heat flux are validated against Bowen ratio-derived estimates for 2013. Based on the validated simulation results, the long-term mean annual evaporation is approximately 832 ± 69 mm, and this value is much less than the potential evaporation estimated using the Penman-Monteith equation. The annual evaporation from 1980-2014 displays a complex decadal oscillation, mainly due to the changes in energy-related terms (air temperature and radiation). The mean lake evaporation since the late 1990s is greater than previous periods; thus, this change in evaporation has suppressed the recent expansion of Nam Co.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
    Publication Date: 2019
    Description: Abstract Dynamic changes in soil organic carbon (SOC) have become a popular topic in global research on organic carbon as part of the increasing attention being paid to food security and reducing greenhouse gas emissions. In this paper, the semiarid regions of China were selected as a research focus, and SOC data from 1980–2015 were analyzed using IBM SPSS Statistics 20.0 software. SOC in farmland varied according to cultivated land type, mulching material type, and planting method in the studied regions. The SOC content is 10.3–10.8 g/kg in supplementally irrigated land and flat dry land, 7.1–8.7 g/kg in terraced dry land and river beach land, and 6.2–6.4 g/kg in sloping dry land. The SOC content increased to 16.1–17.4 g/kg when crop stalks were used as mulch. The increase was only 11.5‐13.5 g/kg in soils mulched with film or sandstone. The SOC value in wheat, maize, and potatoes sown on single or double ridges was 2.4–3.2%, 35.7–36.4% and 4.4–4.8%, respectively, which are higher than the values for wheat, maize, and potatoes sown using the flat planting method. The SOC sequestering potential also varied according to the previously noted factors and was improved from 224.1–383.8% depending on cultivated land type, from 96.5–182.3% depending on mulching material type, and from 96.1–191.3% depending on planting method. The SOC sequestering potential can be improved by 453.2–757.4% with the integration of the optimal cultivated land type, mulching material type, and planting method. Thus, there is substantial soil carbon sequestration potential in China's semiarid regions. This article is protected by copyright. All rights reserved.
    Print ISSN: 0266-0032
    Electronic ISSN: 1475-2743
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Wiley
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  • 4
    Publication Date: 2018
    Description: Abstract In this work, we report a lead‐free piezoelectric ceramic of (0.9‐x)NaNbO3‐0.1BaTiO3‐xBaZrO3, and the effects of BaZrO3 on the phase structure, microstructure, electrical properties and temperature stability are investigated. A morphotropic phase boundary‐like region consisting of rhombohedral (R) and tetragonal (T) phases is constructed in the compositions with x = 0.035‐0.04. More importantly, in situ temperature independence of the piezoelectric effect {piezoelectric constant (d33) and strain} can be achieved below the Curie temperature (Tc). Intriguingly, the electric field‐induced strain is still observed at T ≥ Tc due to the combined actions of the electrostrictive effect and the electric field‐induced phase transition. We believe that NaNbO3‐based ceramics of this type have potential for applications in actuators and sensors.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Wiley
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  • 5
    Publication Date: 2016-06-04
    Description: Independent measurements of the volumetric and elastic properties of Columbia River basalt glass were made up to 5.5 GPa by high-pressure X-ray microtomography and GHz-ultrasonic interferometry, respectively. The Columbia River basalt displays P- and S-wave velocity minima at 4.5 and 5 GPa, respectively, violating Birch's Law. These data constrain the pressure dependence of the density and elastic moduli at high pressure, which cannot be modeled through usual equations of state nor determined by step-wise integrating the bulk sound velocity as is common practice. We propose a systematic variation in compression behavior of silicate glasses that is dependent on the degree of polymerization and arises from the flexibility of the aluminosilicate network. This behavior likely persists into the liquid state for basaltic melts resulting in weak pressure dependence for P-wave velocities perhaps to depths of the transition zone. Modeling the effect of partial melt on P-wave velocity reductions suggest that melt fraction determined by seismic velocity variations may be significantly overestimated in the crust and upper mantle.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
    Publication Date: 2012-10-12
    Description: Ultrasonic interferometry measurements in conjunction with in situ X-ray techniques have been used to measure compressional and shear wave velocities and densities of MgSiO3 perovskite (Mg-Pv) and Mg0.95Fe0.042+Fe0.013+SiO3 perovskite ((Mg, Fe)-Pv) in the multianvil at pressures up to 25 GPa and temperatures to 1200 K. Data for Mg-Pv are consistent with previous studies and the (Mg, Fe)-Pv sample has almost identical shear properties to Mg-Pv. The adiabatic bulk modulus, Ks, for (Mg, Fe)-Pv, however, is found to be substantially lower than Mg-Pv, with a refined value of 236 GPa and a pressure derivative of 4.7. It is proposed that this low KS value result from a change in the elasticity of Fe-bearing perovskite at low pressures
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
    Publication Date: 2013-01-19
    Description: [1]  Phase relations in harzburgite have been determined between 14 and 24 GPa and 1473 and 1673 K. At 1673 K, harzburgite transformed to wadsleyite + garnet + clinopyroxene below 19 GPa and decomposed into an assemblage of ringwoodite + garnet + stishovite above 20 GPa. Certain amounts of akimotoite were produced at still higher pressures (22–23 GPa). Finally perovskite and magnesiowüstite were found to coexist with garnet at 24.2 GPa. Compositions of all the phases were analyzed and elemental partitioning coefficients were determined among co-existing phases. Combining our experimental data with available thermoelastic properties of major minerals in the earth's mantle, we modeled the velocity and density signatures of the stagnated oceanic slabs in the mantle transition zone (MTZ) under eastern China, based on kinematic slab thermal structure analysis. We examined two end-member slab models: a conventional straight slab with deformation thickening, and an undulated slab with an oscillating wavelength of 200 km. We found that an undulated (buckled) slab model yields velocity anomalies (about 1–2% for Vp) that are consistent with seismic tomography models, taking into account of low-pass filtering effects in seismic tomography studies. On the other hand, straight slab models yield velocity anomalies that are too high comparing with seismic tomography models. Our models provide important constraints on the thermal structure, mineralogy, composition, density, and velocities of slab materials in the MTZ.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
    Publication Date: 2012-05-18
    Description: We use receiver functions calculated for data collected by the INDEPTH-IV seismic array to image the three-dimensional geometry of the crustal and upper mantle velocity discontinuities beneath northeastern Tibet. Our results indicate an average crustal thickness of 65 to 70 km in northern Tibet. In addition, we observe a 20 km Moho offset beneath the northern margin of the Kunlun Mountains, a 10 km Moho offset across the Jinsha River Suture and gently northward dipping Moho beneath the Qaidam Basin. A region in the central Qiangtang Terrane with higher than normal crustal Vp/Vs ratio of ∼1.83 can be the result of the Eocene magmatic event. In the Qiangtang Terrane, we observe a significant lithospheric mantle discontinuity beneath the Bangong-Nujiang Suture at 80 km depth which dips ∼10° to the north, reaching ∼120 km depth. We interpret this feature as either a piece of Lhasa Terrane or remnant oceanic slab underthrust below northern Tibet. We detect a ∼20 km depression of the 660-km discontinuity in the mantle transition zone beneath the northern Lhasa Terrane in central Tibet, which suggests this phase transition has been influenced by a dense and/or cold oceanic slab. A modest ∼10 km depression of the 410-km discontinuity located beneath the northern Qiangtang Terrane may be the result of localized warm upwelling associated with small-scale convection induced by the penetration of the sinking Indian continental lithosphere into the transition zone beneath the central Tibetan Plateau.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
    Publication Date: 2019
    Description: Abstract Although the impact of El Niño–Southern Oscillation on the Tibetan Plateau (TP) is reflected through stable isotopes of precipitation and ice cores, the hydroclimate response of TP lakes to El Niño–Southern Oscillation is seldom investigated. Here we show that significant lake water deficit occurred on the central TP (CTP) due to a dramatic decrease in precipitation 2016 El Ni/2016 El Niño event, followed by extreme lake water surplus in 2016 and 2017 over most of the TP (except the eastern CTP). Similar but weaker lake shrinkage and afterward expansion can also be found during historical El Niño events. Further exploration reveals that the CTP dry anomaly during El Niño events tends to bridge the dry anomalies over India and northern China, thereby forming a dry zone along the northwestern edge of the Asian monsoon domain. This study may shed light on the prediction of lake level changes on the TP.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
    Publication Date: 2019
    Description: ABSTRACT Numerical simulation in coupled elastic and poroelastic media is important in oil and gas exploration. However, the interface between elastic and poroelastic media is a challenge to handle. In order to deal with the coupled model, the first‐order velocity–stress wave equations are used to unify the elastic and poroelastic wave equations. In addition, an arbitrary high‐order discontinuous Galerkin method is used to simulate the wave propagation in coupled elastic–poroelastic media, which achieves same order accuracy in time and space domain simultaneously. The interfaces between the two media are explicitly tackled by the Godunov numerical flux. The proposed forms of numerical flux can be used efficiently and conveniently to simulate the wave propagation at the interfaces of the coupled model and handle the absorbing boundary conditions properly. Numerical results on coupled elastic–poroelastic media with straight and curved interfaces are compared with those from a software that is based on finite element method and the interfaces are handled by boundary conditions, demonstrating the feasibility of the proposed scheme in dealing with coupled elastic–poroelastic media. In addition, the proposed method is used to simulate a more complex coupled model. The numerical results show that the proposed method is feasible to simulate the wave propagation in such a media and is easy to implement.
    Print ISSN: 0016-8025
    Electronic ISSN: 1365-2478
    Topics: Geosciences , Physics
    Published by Wiley
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