64,466 research outputs found

    Regional mapping of the crustal structure in southern California from receiver functions

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    Lateral variations of the crustal structure in southern California are determined from receiver function (RF) studies using data from the Southern California Seismic Network broadband stations and Los Angeles Regional Seismic Experiment surveys. The results include crustal thickness estimates at the stations themselves, and where possible, cross sections are drawn. The large-scale Moho depth variation pattern generally correlates well with the current status of the Mesozoic batholith: Deep Moho of 35–39 km is observed beneath the western Peninsula Ranges, Sierra Nevada, and San Bernardino Mountains, where the batholith is relatively intact, and shallow Moho of 26–32 km is observed in the Mojave Desert, where the batholith is highly deformed and disrupted. High-resolution lateral variations of the crustal structure for individual geographic provinces are investigated, and distinctive features are identified. The crustal structure is strongly heterogeneous beneath the central Transverse Ranges, and deep Moho of 36–39 km is locally observed beneath several station groups in the western San Gabriel Mountains. Moho is relatively flat and smooth beneath the western Mojave Desert but gets shallower and complicated to the east. Anomalous RFs are observed at two stations in the eastern Mojave Desert, where a Moho step of ∼8–10 km is found between the NW and SE back-azimuthal groups of station DAN in the Fenner Valley. Asymmetric extension of the Salton Trough is inferred from the Moho geometry. Depth extension of several major faults, such as the San Andreas Fault and San Gabriel Fault, to the Moho is inferred

    Ab Initio Studies of Cellulose I: Crystal Structure, Intermolecular Forces, and Interactions with Water

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    We have studied the structural, energetic, and electronic properties of crystalline cellulose I using first-principles density functional theory (DFT) with semiempirical dispersion corrections. The predicted crystal structures of both Iα and Iβ phases agree well with experiments and are greatly improved over those predicted by DFT within the local and semilocal density approximations. The cohesive energy is analyzed in terms of interchain and intersheet interactions, which are calculated to be of similar magnitude. Both hydrogen bonding and van der Waals (vdW) dispersion forces are found to be responsible for binding cellulose chains together. In particular, dispersion corrections prove to be indispensable in reproducing the equilibrium intersheet distance and binding strength; however, they do not improve the underestimated hydrogen bond length from DFT. The computed energy gaps of crystalline cellulose are 5.7 eV (Iα) and 5.4 eV (Iβ), whereas localized surface states appear within the gap for surfaces. The interaction of cellulose with water is studied by investigating the adsorption of a single water molecule on the hydrophobic Iβ(100) surface. The formation of hydrogen bond at the water/cellulose interface is shown to depend sensitively on the adsorption site for example above the equatorial hydroxyls or the CH moieties pointing out of the cellulose sheets. VdW dispersion interactions also contribute significantly to the adsorption energy

    Long-Range Coulomb Effect on the Antiferromagnetism in Electron-doped Cuprates

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    Using mean-field theory, we illustrate the long-range Coulomb effect on the antiferromagnetism in the electron-doped cuprates. Because of the Coulomb exchange effect, the magnitude of the effective next nearest neighbor hopping parameter increases appreciably with increasing the electron doping concentration, raising the frustration to the antiferromagnetic ordering. The Fermi surface evolution in the electron-doped cuprate Nd2x_{2-x}Cex_xCuO4_4 and the doping dependence of the onset temperature of the antiferromagnetic pseudogap can be reasonably explained by the present consideration.Comment: 4 pages, 4 figure

    A First Experimental Limit on In-matter Torsion from Neutron Spin Rotation in Liquid He-4

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    We report the first experimental upper bound to our knowledge on possible in-matter torsion interactions of the neutron from a recent search for parity violation in neutron spin rotation in liquid He-4. Our experiment constrains a coefficient ζ\zeta consisting of a linear combination of parameters involving the time components of the torsion fields TμT^\mu and AμA^\mu from the nucleons and electrons in helium which violates parity. We report an upper bound of ζ<9.1x1023|\zeta|<9.1x10^{-23} GeV at 68% confidence level and indicate other physical processes that could be analyzed to constrain in-matter torsion.Comment: 12 pages, typo correcte