H.-r. Wenk

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—Anisotropy in clay-rich sedimentary rocks is receiving increasing attention. Seismic anisotropy is essential in the prospecting for petroleum deposits. Anisotropy of diffusion has become relevant for environmental contaminants, including nuclear waste. In both cases, the orientation of component minerals is a critical ingredient and, largely because of(More)
Magnesium silicates are the dominant minerals in the earth's mantle. Their preferred orientation is important for understanding the rheology and seismic anisotropy in the deep earth. Here we report results of radial synchrotron diffraction diamond anvil cell (DAC) experiments on San Carlos olivine, axially compressed to 50 GPa. Experiments were performed at(More)
Mechanical twinning in polycrystalline quartz was investigated in situ with time-of-flight neutron dif-fraction and a strain diffractometer. Dauphiné twinning is highly temperature sensitive. It initiates at a macroscopic differential stress of 50–100 MPa and, at 500°C, saturates at 400 MPa. From normalized diffraction intensities the patterns of preferred(More)
Ringwoodite Mg 2 SiO 4 with spinel structure is an important phase in the earth's mantle transition zone. Controlled deformation experiments showed that ringwoodite underwent ductile deformation when compressed axially at 6–10 GPa and at room temperature in a multianvil D-DIA deformation apparatus. Texture evolution during cyclic compression has been(More)
Acetylcholinesterase (AChE) and choline acetyltransferase (CHAc) activities were studied by quantitative histochemical (AChE) as well as biochemical methods (AChE, ChAc) in certain cortical brain areas in rats after stereotaxic lesions had been placed in several structures of the basal forebrain. After lesioning the magnocellular nuclei of the substantia(More)
Large meteorite impacts cause great changes to geologic features on Earth, ranging from cratering and ejecta blankets to phase transformations in minerals. In this report we describe the effect of a shock wave on the crystallographic orientation of quartz crystals in quartzite from the Vredefort impact site in South Africa. Preferred orientation of bulk(More)
Preferred orientation in granitic mylonites from the Santa Rosa mylonite zone in Southern California is investigated with time-of-flight neutron diffraction. Quartz and biotite display strong preferred orientation, whereas, feldspar alignment is weak. For quartz, a c-axis maximum in the intermediate fabric direction is consistent with dynamic(More)
aBStract The full elastic tensors of the sheet silicates muscovite, illite-smectite, kaolinite, dickite, and nacrite have been derived with first-principles calculations based on density functional theory. For muscovite, there is excellent agreement between calculated properties and experimental results. The influence of cation disorder was investigated and(More)