Crustal Anisotropy from the Birefringence of P-to-S Converted Waves: Bias Associated with P-Wave Anisotropy

Many researchers have used the birefringence of P‑to‑S converted waves from the Moho discontinuity to constrain the anisotropy of Earth’s crust. However, this practice ignores the substantial influence that anisotropy has on the initial amplitude of the converted wave, which adds to the splitting acquired during its propagation from Moho to the seismometer. We find that large variations in Ps birefringence estimates with back-azimuth occur theoretically in the presence of P‑wave anisotropy, which normally accompanies S‑wave anisotropy. The variations are largest for crustal anisotropy with a tilted axis of symmetry, a geometry that is often neglected in birefringence interpretations, but is commonly found in Earth’s crust. We simulated globally-distributed P‑coda datasets for 36 distinct 4‑layer crustal models with combinations of elliptical shear anisotropy or compressional anisotropy, and also incorporated the higher-order anisotropic Backus parameter C. We tested both horizontal and tilted symmetry-axis geometries and tested the birefringence tradeoff associated with Ps converted phases at the top and bottom of a thin high‑ or low‑velocity basal layer. We computed composite receiver functions (RFs) with harmonic regression over back azimuth, using multipletaper correlation with moveout corrections for the epicentral distances of 471 events, to simulate a realistic data set. We estimate Ps birefringence from the radial and transverse RFs, a strategy that is similar to previous studies. We find that Ps splitting can be a useful indicator of bulk crustal anisotropy only under restricted circumstance, either in media with no compressional anisotropy, or if the symmetry axis is horizontal throughout. In other, more-realistic cases, the inferred fast polarization of Ps birefringence estimated from synthetic RFs tends either to drift with back-azimuth, form weak penalty-function minima, or return splitting times that depend on the thickness of an anisotropic layer, rather than the birefringence accumulated within it.

The crustal structure of the western Himalayas and Tibet

We present new, high-resolution, shear velocity models for the western Himalayas and West Tibet from the joint inversion of P receiver functions recorded using seismic stations from four arrays in this region and fundamental mode Rayleigh wave group velocity maps from 5–70 s covering Central and Southern Asia. The Tibetan Plateau is a key locality in understanding large-scale continental dynamics. A large number of investigations has examined the structure and processes in eastern Tibet; however, western Tibet remains relatively understudied. Previous studies in this region indicate that the western part of the Tibetan Plateau is not a simple extension of the eastern part. The areas covered by these arrays include the Karakoram and Altan-Tagh faults, and major terrane boundaries in West Tibet and the Himalayas. The arrays used include broadband data collected by the West Tibet Array, a U.S.-China deployment on the western side of the Tibetan Plateau between 2007 and 2011. We use the shear wave velocity models to obtain estimates of Moho depth. The Moho is deep (68–84 km) throughout West Tibet. We do not observe significant steps within the Moho beneath West Tibet. A large step in Moho depth is observed at the Altyn-Tagh fault, where Moho depths are 20–30 km shallower to the north of the fault compared to those to the south. Beneath the Lhasa Terrane and Tethyan Himalayas, we observe a low-velocity zone in the midcrust. This feature is not interrupted by the Karakoram Fault, suggesting that the Karakoram Fault does not cut through the entire crust

Subduction beneath Laurentia modified the eastern North American cratonic edge : Evidence from P wave and S wave tomography

Funding Information: NERC Doctoral Training Partnership: Science and Solutions for a Changing Planet and Leverhulme Trust Acknowledgments A.B. is funded by the NERC Doctoral Training Partnership: Science and Solutions for a Changing Planet. I.B. is funded by the Leverhulme Trust. F.D. acknowledges funding from NSERC through their Discovery grants and Canada Research Chairs program. We thank J. VanDecar for use of his tomographic inversion and MCCC codes. SAC [Helffrich et al., 2013] and GMT [Wessel and Smith, 1995] software were also used to process seismic data obtained from the IRIS DMC and from the Canadian National Data Centre (Natural Resources Canada). A digital supplement is also available to download containing models and the processed relative arrival‐time data set, additional information is available from A.B. (email: [email protected]). Discussing the implications of our tomographic results with S. Goes and A. Hynes provided great motivation for this manuscript. Two anonymous reviewers helped clarify our interpretations.Peer reviewedPublisher PD

Lithospheric deformation in the Canadian Appalachians : evidence from shear wave splitting

This work was funded by Leverhulme Trust research project grant RPG-2013-332. Imperial College Maritimes network stations were provided through Natural Environment Research Council (NERC) Geophysical Equipment Facility loan 986. Logistical field support was provided by D. Heffler, D. Simpson, and residents of Nova Scotia and New Brunswick. Data for Portable Observatories for Lithospheric Analysis and Research Investigating Seismicity (POLARIS) and Canadian National Seismograph Network stations were downloaded from the Canadian National Data Centre. POLARIS stations were funded by the Canadian Foundation for Innovation, Natural Resources Canada and Industry Canada. FD is supported by Natural Sciences and Engineering Research Council of Canada through the Discovery Grants and Canada Research Chair programmes. AB is funded by the NERC Doctoral Training Partnership: Science and Solutions for a Changing Planet. We thank Thomas Plenefisch and an anonymous reviewer for their comments on this manuscript.Peer reviewedPublisher PD

Color coherent phenomena on nuclei and the QCD evolution equation

We review the phenomenon of color coherence in quantum chromodynamics (QCD), its implications for hard and soft processes with nuclei, and its experimental manifestations. The relation of factorization theorems in QCD with color coherence phenomena in deep inelastic scattering (DIS) and color coherence phenomena in hard exclusive processes is emphasized. Analyzing numerically the QCD evolution equation for conventional and skewed parton densities in nuclei, we study the onset of generalized color transparency and nuclear shadowing of the sea quark and gluon distributions in nuclei as well as related phenomena. Such novel results as the dependence of the effective coherence length on $Q^2$ and general trends of the QCD evolution are discussed. The limits of the applicability of the QCD evolution equation at small Bjorken $x$ are estimated by comparing the inelastic quark-antiquark- and two gluon-nucleon (nucleus) cross sections, calculated within the DGLAP approximation, with the dynamical boundaries, which follow from the unitarity of the $S$ matrix for purely QCD interactions. We also demonstrate that principles of color coherence play an important role in the processes of soft diffraction off nuclei.Comment: 58 pages, 19 figures, Revtex. Minor editor's changes, final version published in J.Phys. G27 (2001) R23-6

Commercial articulated collaborative in situ 3D bioprinter for skin wound healing

In situ bioprinting is one of the most clinically relevant techniques in the emerging bioprinting technology because it could be performed directly on the human body in the operating room and it does not require bioreactors for post-printing tissue maturation. However, commercial in situ bioprinters are still not available on the market. In this study, we demonstrated the benefit of the originally developed first commercial articulated collaborative in situ bioprinter for the treatment of full-thickness wounds in rat and porcine models. We used an articulated and collaborative robotic arm from company KUKA and developed original printhead and correspondence software enabling in situ bioprinting on curve and moving surfaces. The results of in vitro and in vivo experiments show that in situ bioprinting of bioink induces a strong hydrogel adhesion and enables printing on curved surfaces of wet tissues with a high level of fidelity. The in situ bioprinter was convenient to use in the operating room. Additional in vitro experiments (in vitro collagen contraction assay and in vitro 3D angiogenesis assay) and histological analyses demonstrated that in situ bioprinting improves the quality of wound healing in rat and porcine skin wounds. The absence of interference with the normal process of wound healing and even certain improvement in the dynamics of this process strongly suggests that in situ bioprinting could be used as a novel therapeutic modality in wound healing.publishersversionPeer reviewe

La nuova Russia. Dibattito culturale e modello di società in costruzione

Una radiografia del dibattito culturale della Russia che illustra i tanti problemi con cui si deve confrontare la costruzione di una nuova società. Modernizzazione, tradizionalismo, nuovo corporativismo, privatizzazioni, nazionalismo e religione sono solo alcuni degli elementi che compongono un quadro ricco di conflittualità e foriero di grandi trasformazioni.- Indice #5- Radiografia del dibattito culturale: modernizzazione e tradizionalismo nello scontro tra gli “addetti ai lavori”, Ilja Levin #9- Partiti e società: evoluzione e prospettive della differenziazione politica ed ideologica nella Russia postsovietica, Kirill Kholodkovski #29- Dal “collettivismo” all’individualismo: l’uomo nella società deistituzionalizzata, Guerman Diliguenski #45- Gruppi direttivi regionali: trasformazione dei meccanismi organizzativi e relazionali del potere, Mikhail Afanasjev #63- L’”oligarchia” e la crisi in atto nel postcomunismo russo, Alexeij Zudin #81- Il nuovo corporativismo russo all’interno del contesto globale: il ruolo in via di cambiamento dell’élite settoriale, Sergei Peregudov #107- La formazione di nuovi mercati e lo Stato nella Russia postcomunista, Vadim Radaev #133- Stabilizzazione macroeconomica e mutamenti strutturali nell’economia nazionale russa: deindustrializzazione o sfondamento verso una società postindustriale?, Vladimir Mau e Irina Starodubrovskaja #163- Dopo la privatizzazione: alla ricerca di un modello ottimale di società, Viktor Studentsov #187- Fondamenta e principi dello Stato accentratore in Russia, Igor Pantin #217- Nazionalismo liberale o idea imperiale? La consapevolezza degli interessi e degli orientamenti nazionali in Russia, Vladimir Kolossov #233- Il primo quinquennio della repubblica di dicembre in Russia: come si costruiscono gli istituti e si strutturano gli interessi, Petr Fedossov #257- Lo stato attuale e le prospettive della Chiesa ortodossa in Russia, P. Innokentij Pavlov #272- La nuova influenza dei valori religiosi sull’intellighenzia russa (tendenze attuali), Andrei B. Zubov #295- La religiosità postsovietica: dall’eclettismo religioso alle fedi nazionali, Sergei Filatov #32