Hans-Rudolf Wenk

Bio: Hans-Rudolf Wenk is an academic researcher from University of California, Berkeley. The author has contributed to research in topics: Slip (materials science) & Texture (crystalline). The author has an hindex of 75, co-authored 423 publications receiving 21294 citations. Previous affiliations of Hans-Rudolf Wenk include Los Alamos National Laboratory & Princeton University.

Texture and Anisotropy

Abstract: The study of preferred orientation of minerals in rocks dates back to Omalius d’Halloy (1833) who attributes a special significance to the alignment of crystals as an indicator of the formation process. Much later the influence of crystal alignment on physical properties was quantified (e.g., Weissenberg 1922, Voigt 1928, Reuss 1929). Only recently has this field emerged as a coherent part of earth science research linking such branches as mineralogy, petrology, structural geology, geodynamics and seismology. The reason for this was the emergence of quantitative methods to analyze preferred orientation, or “texture” as it was first called by Naumann (1850). These methods were largely developed in collaboration with materials science and mechanics. Quantitative measurements, detailed field studies, rigorous data analysis, theories to predict textures, and improvements in characterizing seismic anisotropy in the Earth are leading to a coherent picture that is now being refined. Though seismologists have long accepted that there is a causal relationship between anisotropic propagation of seismic waves, the deformation field and crystal orientation, the prevailing view is still largely the mythological concept that seismic fast directions align with the flow direction. While this may be approximately the case for olivine deformed under certain conditions, it is certainly no universal law, as we will try to illustrate in this review. The “fast” direction of a crystal depends on the mineral species and its crystal structure. The alignment of crystals depends on microscopic, intra-crystalline deformation systems and the deformation history. Both relationships are complex and not intuitive, but there are well-established theories to compute single crystal physical properties as well as orientation patterns. Simulations can be compared with experimental data and then applied with some caution to the macroscopic Earth. This review is intended to provide a brief introduction, highlighting some of the issues with …

Texture and Anisotropy: Preferred Orientations in Polycrystals and their Effect on Materials Properties

Abstract: Introduction H. Mecking Part I. Description of Textures and Anisotropies: 1. Anisotropy and symmetry U. F. Kocks 2. The representation of orientations and textures U. F. Kocks 3. Determination of the orientation distribution from pole figure data J. S. Kallend 4. Pole figure measurements with diffraction techniques H.-R. Wenk 5. Typical textures in metals A. D. Rollett and S. I. Wright 6. Typical textures in geological materials and ceramics H.-R. Wenk Part II. Anisotropic Mechanical Properties in Textured Polycrystals: 7. Tensor properties of textured polycrystals C. N. Tome 8. Kinematics and kinetics of plasticity U. F. Kocks 9. Simulation of deformation texture development for cubic metals U. F. Kocks 10. Effects of texture on plasticity M. G. Stout and U. F. Kocks 11. Self consistent modeling of heterogeneous plasticity C. N. Tome and G. R. Canova 12. Finite element modeling of heterogeneous plasticity P. R. Dawson and A. J. Beaudoin, Jr. Part III. Some Applications: 13. Finite element simulations of metal forming P. R. Dawson and A. J. Beaudoin, Jr. 14. Plasticity modeling in minerals and rocks H.-R. Wenk Appendix: the elastic inclusion problem C. N. Tome.

Combined texture and structure analysis of deformed limestone from time-of-flight neutron diffraction spectra

Abstract: The orientation distribution of a textured polycrystalline material has been traditionally determined from a few individual pole figures of lattice planes hkl, measured by x-ray or neutron diffraction A new method is demonstrated that uses the whole diffraction spectrum, rather than extracted peak intensities, by combining the orientation distribution calculation with the crystallographic Rietveld method The feasibility of the method is illustrated with time-of-flight neutron diffraction data of experimentally deformed polycrystalline calcite It is possible to obtain quantitative information on texture, crystal structure, microstructure, and residual stress from highly incomplete pole figures and from regions of the diffraction spectrum containing many overlapping peaks The approach provides a key for quantitative texture analysis of low symmetry compounds and of composites with complicated diffraction spectra

Exhumation of ultrahigh-pressure continental crust in east central China: Late Triassic-Early Jurassic tectonic unroofing

Abstract: The largest tract of ultrahigh-pressure rocks, the Dabie-Hong'an area of China, was exhumed from 125 km depth by a combination of normal-sense shear from beneath the hanging wall Sino-Korean craton, southeastward thrusting onto the footwall Yangtze craton, and orogen-parallel eastward extrusion. Prior to exhumation the UHP slab extended into the mantle a downdip distance of 125–200 km at its eastern end, whereas it was subducted perhaps only 20–30 km at its far western end ∼200 km away. Structural reconstructions imply that the slab was >10 km thick. U/Pb zircon and 40Ar/39Ar geochronology indicate that exhumation up to crustal depths occurred diachronously between 240 and ∼225–210 Ma, reflecting a vertical exhumation rate of >2 mm/yr. The upper boundary of the slab is the Huwan shear zone, a normal-sense detachment that reactivated the plate suture. The lower boundary is represented by the Lower Yangtze fold-thrust belt. NW-trending stretching lineations, NE-vergent, WNW-ESE trending folds, dominant top-NW shear, and conjugate, but overall asymmetric, shear band fabrics, document that exhumation was accomplished by updip and orogen-parallel extrusion accompanied by layer-parallel thinning. The orientation and shape of the folds, and a change from SE to SW flow directions, imply that the slab rotated clockwise about a western pivot during exhumation; this rotation was likely caused by the eastward increasing depth of subduction mentioned above, combined with a possible marginal basin and a weak eastern plate boundary. Exhumation of the slab produced considerable shortening in the Lower Yangtze fold-thrust belt, perhaps producing the foreland orocline.

Preferred orientation in deformed metals and rocks : an introduction to modern texture analysis

Abstract: L.E. Weiss and H.-R. Wenk, An Introduction. H.-R. Wenk, Measurement of Pole Figures. L.E. Weiss and H.-R. Wenk, Symmetry of Pole Figures and Textures. H.J. Bunge, Representation of Preferred Orientations. H.J. Bunge and C. Esling, The Harmonic Method. H. Schaeben, A. Vadon, and H.-R. Wenk, Vector Method. S. Matthies and H.-R. Wenk, ODF Reproduction with Conditional Ghost Correction. D.J. Barber, Dislocations and Microstructures. G. Gottstein and H. Mecking, Recrystallization. T.G. Langdon, Regimes of Plastic Deformation. P. Van Houtte and F. Wagner, Development of Textures by Slip and Twinning. G. Oertel, Reorientation due to Grain Shape. H. Mecking, Textures of Metals. J. Hirsch and K. L cke, Interpretation of the Copper*b1Brass Texture Transition by Quantitative ODF Analysis. H. Kern and A. Richter, Microstructures and Textures in Evaporites. H. Siemes and Ch. Hennig-Michaeli, Ore Minerals. H.-R. Wenk, Carbonates. G.P. Price, Preferred Orientations in Quartzites. J.-C.C. Mercier, Olivine and Pyroxenes. G. Oertel, Phyllosilicate Textures in Slates. J.L. Rosenfeld, Schistosity. B.E. Hobbs, The Geological Significance of Microfabric Analysis. H.C. Heard, Experimental Determination of Mechanical Properties. H.J. Bunge, Physical Properties of Polycrystals. P.R. Morris and J.W. Flowers, Texture and Magnetic Properties of Metals. H. Kern and H.-R. Wenk, Anisotropy in Rocks and the Geological Significance. References. Index.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

The Mechanics of Earthquakes and Faulting

Abstract: This essential reference for graduate students and researchers provides a unified treatment of earthquakes and faulting as two aspects of brittle tectonics at different timescales. The intimate connection between the two is manifested in their scaling laws and populations, which evolve from fracture growth and interactions between fractures. The connection between faults and the seismicity generated is governed by the rate and state dependent friction laws - producing distinctive seismic styles of faulting and a gamut of earthquake phenomena including aftershocks, afterslip, earthquake triggering, and slow slip events. The third edition of this classic treatise presents a wealth of new topics and new observations. These include slow earthquake phenomena; friction of phyllosilicates, and at high sliding velocities; fault structures; relative roles of strong and seismogenic versus weak and creeping faults; dynamic triggering of earthquakes; oceanic earthquakes; megathrust earthquakes in subduction zones; deep earthquakes; and new observations of earthquake precursory phenomena.

Principles of equal-channel angular pressing as a processing tool for grain refinement

Abstract: During the last decade, equal-channel angular pressing (ECAP) has emerged as a widely-known procedure for the fabrication of ultrafine-grained metals and alloys. This review examines recent developments related to the use of ECAP for grain refinement including modifying conventional ECAP to increase the process efficiency and techniques for up-scaling the procedure and for the processing of hard-to-deform materials. Special attention is given to the basic principles of ECAP processing including the strain imposed in ECAP, the slip systems and shearing patterns associated with ECAP and the major experimental factors that influence ECAP including the die geometry and pressing regimes. It is demonstrated that all of these fundamental and experimental parameters play an essential role in microstructural refinement during the pressing operation. Attention is directed to the significant features of the microstructures produced by ECAP in single crystals, polycrystalline materials with both a single phase and multi-phases, and metal–matrix composites. It is shown that the formation of ultrafine grains in metals and alloys underlies a very significant enhancement in their mechanical and functional properties. Nevertheless, it is demonstrated also that, in order to achieve advanced properties after processing by ECAP, it is necessary to control a wide range of microstructural parameters including the grain boundary misorientations, the crystallographic texture and the distributions of any second phases. Significant progress has been made in the development of ECAP in recent years, thereby suggesting there are excellent prospects for the future successful incorporation of the ECAP process into commercial manufacturing operations.

Nature and composition of the continental crust: A lower crustal perspective

Abstract: Geophysical, petrological, and geochemical data provide important clues about the composition of the deep continental crust. On the basis of seismic refraction data, we divide the crust into type sections associated with different tectonic provinces. Each shows a three-layer crust consisting of upper, middle, and lower crust, in which P wave velocities increase progressively with depth. There is large variation in average P wave velocity of the lower crust between different type sections, but in general, lower crustal velocities are high (>6.9 km s−1) and average middle crustal velocities range between 6.3 and 6.7 km s−1. Heat-producing elements decrease with depth in the crust owing to their depletion in felsic rocks caused by granulite facies metamorphism and an increase in the proportion of mafic rocks with depth. Studies of crustal cross sections show that in Archean regions, 50–85% of the heat flowing from the surface of the Earth is generated within the crust. Granulite terrains that experienced isobaric cooling are representative of middle or lower crust and have higher proportions of mafic rocks than do granulite terrains that experienced isothermal decompression. The latter are probably not representative of the deep crust but are merely upper crustal rocks that have been through an orogenic cycle. Granulite xenoliths provide some of the deepest samples of the continental crust and are composed largely of mafic rock types. Ultrasonic velocity measurements for a wide variety of deep crustal rocks provide a link between crustal velocity and lithology. Meta-igneous felsic, intermediate and mafic granulite, and amphibolite facies rocks are distinguishable on the basis of P and S wave velocities, but metamorphosed shales (metapelites) have velocities that overlap the complete velocity range displayed by the meta-igneous lithologies. The high heat production of metapelites, coupled with their generally limited volumetric extent in granulite terrains and xenoliths, suggests they constitute only a small proportion of the lower crust. Using average P wave velocities derived from the crustal type sections, the estimated areal extent of each type of crust, and the average compositions of different types of granulites, we estimate the average lower and middle crust composition. The lower crust is composed of rocks in the granulite facies and is lithologically heterogeneous. Its average composition is mafic, approaching that of a primitive mantle-derived basalt, but it may range to intermediate bulk compositions in some regions. The middle crust is composed of rocks in the amphibolite facies and is intermediate in bulk composition, containing significant K, Th, and U contents. Average continental crust is intermediate in composition and contains a significant proportion of the bulk silicate Earth's incompatible trace element budget (35–55% of Rb, Ba, K, Pb, Th, and U).