Intraplate processes,such as continental surface uplift and intraplate volcanism,are enigmatic and the underlying mechanisms responsible are not fully understood.Central Mongolia is an ideal natural laboratory for stu...Intraplate processes,such as continental surface uplift and intraplate volcanism,are enigmatic and the underlying mechanisms responsible are not fully understood.Central Mongolia is an ideal natural laboratory for studying such processes because of its location in the continental interior far from tectonic plate boundaries.展开更多
Whole-lithosphere structure has direct implications for both the genesis of minerals and the locations of mineral emplacement;thus knowledge of the deep structural framework of the lithosphere can advance understandin...Whole-lithosphere structure has direct implications for both the genesis of minerals and the locations of mineral emplacement;thus knowledge of the deep structural framework of the lithosphere can advance understanding of the development and evolution of mineral systems.展开更多
In this article,discrete variants of several results from vector calculus are studied for clas-sical finite difference summation by parts operators in two and three space dimensions.It is shown that existence theorems...In this article,discrete variants of several results from vector calculus are studied for clas-sical finite difference summation by parts operators in two and three space dimensions.It is shown that existence theorems for scalar/vector potentials of irrotational/solenoidal vector fields cannot hold discretely because of grid oscillations,which are characterised explicitly.This results in a non-vanishing remainder associated with grid oscillations in the discrete Helmholtz Hodge decomposition.Nevertheless,iterative numerical methods based on an interpretation of the Helmholtz Hodge decomposition via orthogonal projections are pro-posed and applied successfully.In numerical experiments,the discrete remainder vanishes and the potentials converge with the same order of accuracy as usual in other first-order partial differential equations.Motivated by the successful application of the Helmholtz Hodge decomposition in theoretical plasma physics,applications to the discrete analysis of magnetohydrodynamic(MHD) wave modes are presented and discussed.展开更多
We recorded continuous seismic noise close and around two wind parks with different geological site conditions in order to investigate the effects of wind turbines on seismic signals in the frequency interval between ...We recorded continuous seismic noise close and around two wind parks with different geological site conditions in order to investigate the effects of wind turbines on seismic signals in the frequency interval between 1 and 10 Hz. In wind park Fraureuth-Beiersdorf (5 turbines, 11 km south from Zwickau, Saxony), we used small seismic networks, with 3 to 5 stations for 1 - 2 weeks. In Heinde (2 turbines, close to Hildesheim, Lower Saxony), we recorded 1 week with one station around 1 km away from the wind turbines and some additional stations for several hours only. With the spectrogram analysis of the data, we clearly identify the diurnal variation on the spectral amplitude separately from the noise generated by the turbines. The turbine noise appears at certain frequency bands around 2.2, 2.7, 3.3, 4.5, 5.2 and 6.6 Hz. A linear relation between the spectral amplitudes of these frequency bands and the wind velocity or rotation velocity of the turbines is clearly identified. The seismic signals produced by the operation of the wind turbines are not peaks at single frequencies, but look more like frequency bands with increased noise amplitudes. They could be identified up to at least 10 km in the case of Fraureuth-Beiersdorf. These bands depend on numerous parameters, i.e. wind turbine height, weight and construction, number of turbines, geology, etc. In both wind parks we also recorded along profiles with increasing distances from the wind turbines. With the analysis of these data, we propose an amplitude attenuation model for the wind park Fraureuth-Beiersdorf to a distance of 9 km, and for Heinde to a distance of 4 km. The attenuation models for both wind parks are quite different, depending probably on the local geology and topography.展开更多
More than a decade of dedicated experimental work on the collisional physics of protoplanetary dust has brought us to a point at which the growth of dust aggregates can - for the first time - be self-consistently and ...More than a decade of dedicated experimental work on the collisional physics of protoplanetary dust has brought us to a point at which the growth of dust aggregates can - for the first time - be self-consistently and reliably modeled. In this article, the emergent collision model for protoplanetery dust aggregates, as well as the numerical model for the evolution of dust aggregates in protoplanetary disks, is reviewed. It turns out that, after a brief period of rapid collisional growth of fluffy dust aggregates to sizes of a few centimeters, the protoplanetary dust particles are subject to bouncing collisions, in which their porosity is considerably decreased. The model results also show that low-velocity fragmentation can reduce the final mass of the dust aggregates but that it does not trigger a new growth mode as discussed previously. According to the current stage of our model, the direct formation of kilometer-sized planetesimals by collisional sticking seems unlikely, implying that collective effects, such as the streaming instability and the gravitational instability in dust-enhanced regions of the protoplanetary disk, are the best candidates for the processes leading to planetesimals.展开更多
We investigate sedimentological and tectonic processes at the central High Atlas, in order to understand their functioning and to build a geodynamic model that placed the area in its current geological frame.The analy...We investigate sedimentological and tectonic processes at the central High Atlas, in order to understand their functioning and to build a geodynamic model that placed the area in its current geological frame.The analysis used here is based on the numerical enhancement of a Landsat image where the main goal is to map surface sedimentary deposits throughout the central High Atlas in order to delimit the large geological structures. The sediment distribution throughout central High Atlas indicates that this one is a large tectonic subsiding basin, where the ongoing tectonic events and the geodynamical evolution remain to be explained by other prospecting techniques.3-D structure velocities obtained by local seismic tomography and enhancement techniques of gravimetric anomalies are used to explore and define deep structure beneath the central High Atlas. The goal is to establish the evolution of the deep structure related to the geodynamical processes. Modest crustal thickness variation beneath the central High Atlas(~20-~40 km) define by local tomography and gravimetric anomalies, confirms that, a major part of the lower crust is detached into the lithosphere by delamination. Gravimetric anomaly, local seismic tomography and vertical cross sections throughout the central High Atlas, suggest that the lower crust detached is related to the broken slab of remain northward subduction beneath High and Middle Atlas. Meanwhile, extrusions of heated Asthenosphere materials induce the rifting stage concomitant to tectonic subsidence of the basin.展开更多
基金part of the research project"Crustmantle interactions beneath the Hangai Mountains in western Mongolia"the financial support of the DFG and the SNF,awarded through the DACH program
文摘Intraplate processes,such as continental surface uplift and intraplate volcanism,are enigmatic and the underlying mechanisms responsible are not fully understood.Central Mongolia is an ideal natural laboratory for studying such processes because of its location in the continental interior far from tectonic plate boundaries.
基金part of the research project"Crustmantle interactions beneath the Hangai Mountains in western Mongolia"the financial support of the DFG and the SNF,awarded through the DACH program
文摘Whole-lithosphere structure has direct implications for both the genesis of minerals and the locations of mineral emplacement;thus knowledge of the deep structural framework of the lithosphere can advance understanding of the development and evolution of mineral systems.
文摘In this article,discrete variants of several results from vector calculus are studied for clas-sical finite difference summation by parts operators in two and three space dimensions.It is shown that existence theorems for scalar/vector potentials of irrotational/solenoidal vector fields cannot hold discretely because of grid oscillations,which are characterised explicitly.This results in a non-vanishing remainder associated with grid oscillations in the discrete Helmholtz Hodge decomposition.Nevertheless,iterative numerical methods based on an interpretation of the Helmholtz Hodge decomposition via orthogonal projections are pro-posed and applied successfully.In numerical experiments,the discrete remainder vanishes and the potentials converge with the same order of accuracy as usual in other first-order partial differential equations.Motivated by the successful application of the Helmholtz Hodge decomposition in theoretical plasma physics,applications to the discrete analysis of magnetohydrodynamic(MHD) wave modes are presented and discussed.
文摘We recorded continuous seismic noise close and around two wind parks with different geological site conditions in order to investigate the effects of wind turbines on seismic signals in the frequency interval between 1 and 10 Hz. In wind park Fraureuth-Beiersdorf (5 turbines, 11 km south from Zwickau, Saxony), we used small seismic networks, with 3 to 5 stations for 1 - 2 weeks. In Heinde (2 turbines, close to Hildesheim, Lower Saxony), we recorded 1 week with one station around 1 km away from the wind turbines and some additional stations for several hours only. With the spectrogram analysis of the data, we clearly identify the diurnal variation on the spectral amplitude separately from the noise generated by the turbines. The turbine noise appears at certain frequency bands around 2.2, 2.7, 3.3, 4.5, 5.2 and 6.6 Hz. A linear relation between the spectral amplitudes of these frequency bands and the wind velocity or rotation velocity of the turbines is clearly identified. The seismic signals produced by the operation of the wind turbines are not peaks at single frequencies, but look more like frequency bands with increased noise amplitudes. They could be identified up to at least 10 km in the case of Fraureuth-Beiersdorf. These bands depend on numerous parameters, i.e. wind turbine height, weight and construction, number of turbines, geology, etc. In both wind parks we also recorded along profiles with increasing distances from the wind turbines. With the analysis of these data, we propose an amplitude attenuation model for the wind park Fraureuth-Beiersdorf to a distance of 9 km, and for Heinde to a distance of 4 km. The attenuation models for both wind parks are quite different, depending probably on the local geology and topography.
基金funded by the German Space Agency (DLR) under grant Nos. 50WM0336, 50WM0636 and 50WM0936the Deutsche Forschungsgemeinschaft (DFG) under grant No. Bl298/7-1
文摘More than a decade of dedicated experimental work on the collisional physics of protoplanetary dust has brought us to a point at which the growth of dust aggregates can - for the first time - be self-consistently and reliably modeled. In this article, the emergent collision model for protoplanetery dust aggregates, as well as the numerical model for the evolution of dust aggregates in protoplanetary disks, is reviewed. It turns out that, after a brief period of rapid collisional growth of fluffy dust aggregates to sizes of a few centimeters, the protoplanetary dust particles are subject to bouncing collisions, in which their porosity is considerably decreased. The model results also show that low-velocity fragmentation can reduce the final mass of the dust aggregates but that it does not trigger a new growth mode as discussed previously. According to the current stage of our model, the direct formation of kilometer-sized planetesimals by collisional sticking seems unlikely, implying that collective effects, such as the streaming instability and the gravitational instability in dust-enhanced regions of the protoplanetary disk, are the best candidates for the processes leading to planetesimals.
基金supported by the Institut Scientifique, Rabat, Morocco
文摘We investigate sedimentological and tectonic processes at the central High Atlas, in order to understand their functioning and to build a geodynamic model that placed the area in its current geological frame.The analysis used here is based on the numerical enhancement of a Landsat image where the main goal is to map surface sedimentary deposits throughout the central High Atlas in order to delimit the large geological structures. The sediment distribution throughout central High Atlas indicates that this one is a large tectonic subsiding basin, where the ongoing tectonic events and the geodynamical evolution remain to be explained by other prospecting techniques.3-D structure velocities obtained by local seismic tomography and enhancement techniques of gravimetric anomalies are used to explore and define deep structure beneath the central High Atlas. The goal is to establish the evolution of the deep structure related to the geodynamical processes. Modest crustal thickness variation beneath the central High Atlas(~20-~40 km) define by local tomography and gravimetric anomalies, confirms that, a major part of the lower crust is detached into the lithosphere by delamination. Gravimetric anomaly, local seismic tomography and vertical cross sections throughout the central High Atlas, suggest that the lower crust detached is related to the broken slab of remain northward subduction beneath High and Middle Atlas. Meanwhile, extrusions of heated Asthenosphere materials induce the rifting stage concomitant to tectonic subsidence of the basin.
文摘本文简要介绍了多重网格方法的基本思想和原理,然后应用多重网格（MG）方法求解三维泊松方程,网格尺度从17×17×17逐次增加至257×257×257,并与不完全Chelesky共轭梯度法（ICCG）、Gauss直接解法进行比较.结果表明,MG方法计算速度明显优于ICCG、Gauss方法,对于129×129×129网格的三维数值模拟费时43s,比ICCG法快7倍,而对于257×257×257超大型网格的三维数值模拟也仅需412 s.
