用电子束CT作冠状动脉血管造影

本文介绍用电子束ＣＴ作冠状动脉可视化造影的方法,说明本项成就的特征和在应用这项技术的局限性,并指出这种技术在临床上,可能成为新无创伤性的诊断工具。     

Lattice-preferred orientation and microstructure of peridotites from ODP Hole 1274A (15°39′N), Mid-Atlantic Ridge: Testing models of mantle upwelling and tectonic exhumation

Eleven harzburgites and one dunite from Ocean Drilling Program Leg 209 Hole 1274A preserve high-temperature mantle textures. Electron backscatter diffraction (EBSD) analysis shows moderately developed crystal lattice preferred orientations (LPOs) in olivine and orthopyroxene (M-indices ≈ 0.1) indicative of crystal-plastic deformation at ~ 1250 °C. These rocks preserve a protogranular texture with a weak olivine foliation, a very weak or absent orthopyroxene foliation that may be decoupled from the orthopyroxene LPO, and minor interstitial clinopyroxene and spinel. Olivine grain size distributions, along with melt-related microstructures in orthopyroxene, clinopyroxene and spinel suggest that high-temperature deformation textures have been overprinted by pervasive post-deformation melt-rock interaction. Paleomagnetic data constrain the olivine [100] axes to be subhorizontal and oriented at low angle (≤ 28.6° ± 10.6°) to the ridge axis at the onset of serpentinization. This orientation is consistent with either complex 3-D mantle upwelling or 2-D mantle upwelling coupled with complex 3-D tectonic emplacement to the seafloor.     

Love waves excited by discontinuous propagation of a rupture front

Summary. Analytical results are presented for Love waves generated by sudden changes of the rate of advance of a curved rupture front in an inclined fault plane that is embedded in an elastic half-space. The boundary condition at the surface of the half-space approximates the presence of an overlying layer. The calculation consists of two parts. First, ray theory is used to calculate far-field approximations to the horizontally polarized wavefields which are emitted when the speed of the rupture front suddenly changes. These fields can be expressed as products of emission coefficients (which govern the angular dependence) and propagation terms. Secondly, a representation integral for the Love wave over a surface enclosing the rupture front is constructed, using the emitted signal and an appropriate Green's function. This integral is evaluated asymptotically. The resulting approximate Love-wave spectrum shows an explicit dependence on the nature of the rupture process, on the rupture-front and fault-plane geometry, and on the magnitude of a sudden change in the rate of advance of the rupture front.     

New findings concerning the Pleistocene Glaciation of the Leh Basin,Ladakh (34°03′ N/77°38′ E)

Like for most parts of High Asia, researches concerning the Pleistocene landscape evolution of the Leh Basin (34°03′ N/77°38′ E) have also left contradictions. To push this topic, three up to now unexplored Ladakh Range tributaries of the Leh Basin (Stagmo-, Arzu- and Nang-Valley) have been investigated. U-shaped profiles, transfluence passes, moraine mantled and glacially rounded peaks and ridges, roches moutonnées, glacial flank polishings and ground moraines document the former glaciation of the study area. The ice fillings of these tributaries reached a minimum thickness up to 540 m. Even at the valley outlets and on the orographic right side of the Leh Basin, the glaciation was more than 350 m thick. Based on these empirically extracted results, theoretical snow line considerations lead to the conclusion that the whole Leh Basin was filled up by a former Indus-Valley glacier. An ice injection limited to the nourishment areas of the Ladakh Range valleys could not have caused the reconstructed ice cover (down to 3236 m a.s.l.), which is proved by extended ground moraine complexes. Only an Indus ice stream network (most likely during the LGP), nourished by inflowing glaciers of the Ladakh- and Stok Range, explains the widespread existence of the glacial sediments at the outlets of the investigated valleys.     

Reflection and transmission of plane waves by a layer of compact inhomogeneities

Reflection and transmission of elastic wave motion by a layer of compact inhomogeneities has been analyzed. For identical inhomogeneities whose geometrical centers are periodically spaced, the problem has been formulated and solved rigorously. The reflected and transmitted longitudinal and transverse wave motions have been expressed as superpositions of wavemodes, where each wavemode has its own cut-off frequency. At its cut-off frequency a mode converts from a standing into a propagating wavemode. The standing wavemodes decay exponentially with distance to the plane of the centers of the inhomogeneities. At small frequencies only the lowest order modes of longitudinal and transverse wave motion are propagating. Reflection and transmission coefficients have been defined in terms of the coefficients of the zeroth-order scattered wavemodes. These coefficients have been computed by a novel application of the Betti-Rayleigh reciprocal theorem. They are expressed as integrals over the surface of a single inhomogeneity, in terms of the displacements and tractions on the surface of the inhomogeneity. The system of singular integral equations for the surface fields has been solved numerically by the boundary integral equation method. Curves show the reflection and transmission coefficients for the reflected and transmitted longitudinal and transverse waves as functions of the frequency. Some results are also presented for planar distributions of cracks whose spacing and size are random variables. Finally, dispersion relations are discussed for solids which are completely filled with periodically spaced inhomogeneities.     

New findings concerning the Pleistocene Glaciation of the Leh Basin,Ladakh(34°03'N/77°38'E)

Like for most parts of High Asia,researches concerning the Pleistocene landscape evolution of the Leh Basin(34°03' N/77°38' E) have also left contradictions.To push this topic,three up to now unexplored Ladakh Range tributaries of the Leh Basin(Stagmo-,Arzu-and Nang-Valley) have been investigated.U-shaped profiles,transfluence passes,moraine mantled and glacially rounded peaks and ridges,roches moutonnées,glacial flank polishings and ground moraines document the former glaciation of the study area.The ice fillings of these tributaries reached a minimum thickness up to 540 m.Even at the valley outlets and on the orographic right side of the Leh Basin,the glaciation was more than 350 m thick.Based on these empirically extracted results,theoretical snow line considerations lead to the conclusion that the whole Leh Basin was filled up by a former Indus-Valley glacier.An ice injection limited to the nourishment areas of the Ladakh Range valleys could not have caused the reconstructed ice cover(down to 3236 m a.s.l.),which is proved by extended ground moraine complexes.Only an Indus ice stream network(most likely during the LGP),nourished by inflowing glaciers of the Ladakh-and Stok Range,explains the widespread existence of the glacial sediments at the outlets of the investigated valleys.