Shock compression of deuterium to 900 Kbar     

M. Van Thiel  L.B. Hord  W.H. Gust  A.C. Mitchell  M. D&#x;Addario  K. Boutwell  E. Wilbarger  B. Barrett 《Physics of the Earth and Planetary Interiors》1974,9(1):57-77

An experimental program to compress liquid deuterium with a two-stage gun is described. A xenon standard was used to check the adequacy of the EOS of the Dural container in the 7000 (1.7 Mbar) to 3000° K (0.0 Mbar) range. The agreement is reasonable. Further work on this standard is in progress to improve the accuracy. The target design parameters were checked with some sound speed measurements which confirm the liquid-like behavior of Dural at the temperatures, pressures, and strain rates of these experiments. The uncertainties of the results are analyzed and tabulated with the data. Comparison between the molecular and the metallic equations of state indicates a small volume change on metallization due to the high compressibility of the molecular phase vis-a-vis the metallic phase.  相似文献   

Frequency-dependent Shear-wave Q Models for the Crust of China and Surrounding Regions     

Alemayehu L. Jemberie  Brian J. Mitchell 《Pure and Applied Geophysics》2005,162(1):21-36

— Starting with fundamental-mode Rayleigh-wave attenuation coefficient values (_R) predicted by previously determined frequency-independent models of shear-wave Q (Q), we have obtained frequency-dependent Q models that explain measured values of _R as well as of Lg coda Q and its frequency dependence at 1 Hz (Q_o and , respectively) for China and some adjacent regions. The process combines trial-and-error selection of a model for the depth distribution of the frequency dependence parameter () for Q with a formal inversion for the depth distribution of Q at 1 Hz. Fifteen of the derived models have depth distributions of that are constant, or nearly constant, between the surface and a depth of 30 km. distributions that vary with depth in the upper 30 km are necessary to explain the remaining seven models. values for the depth-independent models vary between 0.4 and 0.7 everywhere except in the western portion of the Tibetan Plateau where they range between about 0.1 and 0.3 for three paths. These low values lie in a region where Q_Lg and crustal Q are very low and suggest that they should also be low for high-frequency propagation. The models in which varies with depth all show a decrease in that value ranging between 0.55 and 0.8 in the upper 15 km of the crust and (with two exceptions where =0.0) between 0.3 and 0.55 in the depth range 15–30 km. The distribution of values between 0.6 and 0.8 (the higher part of the range) in the upper crust indicates that high-frequency waves will propagate most efficiently, relative to low-frequency waves, in a band that includes, and strikes north-northeastward from the path between event 212/97 and KMI to the path between event 180/95 and station HIA in the north.Acknowledgement. We thank Lianli Cong for providing his code for plotting crustal Q models and Robert Herrmann for writing the mode summation code for computing Lg synthetics used in this study. Our work benefited from helpful discussions with Jack Xie at Lamont-Doherty Earth Observatory of Columbia University. This research was sponsored by the Defense Threat Reduction Agency Contract No. DTRA-01-00-C-0213.  相似文献   

Solid solution of rare earth elements in synthetic titanite: a reconnaissance study     

R. P. Liferovich  R. H. Mitchell 《Mineralogy and Petrology》2005,83(3-4):271-282

Summary Titanite varieties doped with rare earth elements (REE) have been prepared by ceramic synthesis and quenching in air. Their crystal structure was determined by Rietveld analysis of the powder X-ray diffraction patterns. Two different substitution schemes, Ca_1–xNa_x/2Sm_x/2TiSiO₅ and Ca_1–xDy_xTi_1–x SiO₅, are studied at x=0.2. Both synthetic varieties of titanite adopt space group A2/a. This implies that both single-site and complex multivalent substitutional schemes destroy the coherence of the off-centering of octahedral chains in the titanite structure resulting in a P2₁/aA2/a phase transition. Unit cell dimensions obtained for the REE-bearing titanite varieties are as follows: a=7.0541(1)Å; b=8.7247(1)Å; c=6.5664(1)Å; =113.732(1)° for Ca_0.8Na_0.1Sm_0.1TiSiO₅; and a=7.0021(1)Å; b=8.7256(1)Å; c=6.5427(1)Å; =113.294(1)° for . Both REE-doped titanite samples and a control sample of the pure titanite end member have similar unit cell parameters and consist of polyhedra distorted to a similar extent with the exception of more-distorted SiO₄ tetrahedron in CaSiTiO₅. The structural data suggest that the Ca_1–xNa_x/2Sm_x/2TiSiO₅ and Ca_1–xDy_xTi_1–xFe_xSiO₅ solid solutions adopting the titanite structure might extend to x sufficiently greater than 0.2 and involve both heavier and lighter trivalent rare earth elements.Permanent address: Geological Institute KSC RAS, 14 Fersmana St., Apatity, 184200 Russia  相似文献   

The librational dynamics of deformable bodies     

T. P. Mitchell  J. Lingerfelt 《Celestial Mechanics and Dynamical Astronomy》1970,1(3-4):289-296

The volume average of the strain tensor in a body moving in an inverse-square force field is evaluated. The calculation is carried out assuming the satellite to be an isotropic elastic body whose center of mass moves in a planar orbit. An approximate expression, in terms of its volume and elastic properties, is presented for the strain energy in the satellite. Using this expression the equation of planar librational motion is written explicity. This equation is discussed for both circular and elliptic orbits and is modified to include the effects of energy dissipation in the body. It is shown that the concept of Adiabatic Invariants allows one to analyze the influence of slow changes in the material volume and elasticity.This work was supported by NASA Grant No. NGR 05-010-020.  相似文献   

XMM-EPIC observation of MCG–6-30-15: direct evidence for the extraction of energy from a spinning black hole?     

Jörn Wilms  Christopher S. Reynolds †  Mitchell C. Begelman  James Reeves  Silvano Molendi  Rüdiger Staubert  Eckhard Kendziorra 《Monthly notices of the Royal Astronomical Society》2001,328(3):L27-L31

We present XMM-Newton European Photon Imaging Camera (EPIC) observations of the bright Seyfert 1 galaxy MCG–6-30-15, focusing on the broad Fe K α line at ∼6 keV and the associated reflection continuum, which is believed to originate from the inner accretion disc. We find these reflection features to be extremely broad and redshifted, indicating an origin in the very central regions of the accretion disc. It seems likely that we have caught this source in the 'deep minimum' state first observed by Iwasawa et al. The implied central concentration of X-ray illumination is difficult to understand in any pure accretion disc model. We suggest that we are witnessing the extraction and dissipation of rotational energy from a spinning black hole by magnetic fields connecting the black hole or plunging region to the disc.  相似文献   

Limb darkening in the solar ultraviolet     

Walter E. Mitchell Jr. 《Solar physics》1981,69(2):391-398

New photoelectric limb-darkening data are given for 38 of the windows in the UV solar spectrum in which Houtgast has supplied absolute energy measurements. The region, 4000 Å to 3000 Å, is marked by unaccounted opacity. Results are given also for 13 longer wavelengths. The measurements are fully corrected for atmospheric seeing and scattering. The corrected drift curves exhibit a quasi-periodic character suggestive of the supergranulation.  相似文献   

Crustal structure and possible anisotropy in Turkey from seismic surface wave dispersion   总被引：2，自引：0，他引：2  

Oznur Y. Mindevalli  Brian J. Mitchell 《Geophysical Journal International》1989,98(1):93-106

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Palaeomagnetism and isotopic age data from Upper Cretaceous igneous rocks of W. Portugal; geological correlation and plate tectonic aspects     

K. M. Storetvedt  H. Mogstad  M. C. Abranches  J. G. Mitchell  A. Serralheiro 《Geophysical Journal International》1987,88(1):241-263

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A Back-Projection Method For Imaging Large-Scale Lateral Variations of Lg Coda Q With Application to Continental Africa   总被引：4，自引：0，他引：4  

J. Xie  B. J. Mitchell 《Geophysical Journal International》1990,100(2):161-181

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Anelasticity of the Crust and Upper Mantle beneath the Pacific Ocean from the Inversion of Observed Surface Wave Attenuation     

Brian J. Mitchell 《Geophysical Journal International》1976,46(3):521-533

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