多层螺旋CT在诊断中心型肺栓塞的初步应用     

徐凯  李江山  荣玉涛  程广军  任忠清  冯守信 《CT理论与应用研究》2002,11(1):30-33

目的是评价多层螺旋CT诊断中心型肺动脉栓塞的诊断价值。方法：6例肺栓塞病人行多层螺旋CT血管造影检查，结合三维成像技术进行图像分析。结果：6例病人的肺动脉病变以及主肺动脉扩张、肺梗死表现均较好显示，肺动脉病变主要表现为完全性或部分性充盈缺损。结论：多层螺旋CT是一种有效的无创性诊断中心型肺动脉栓塞的检查方法。  相似文献   

The ocean-atmosphere system. A. H. Perry and J. M. Walker,Longman, 1977, no. of Pages: 160     

B. Atkinson 《地球表面变化过程与地形》1979,4(1):91-91

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Morphology and mineralogy of red desert soils in the libyan sahara     

K. Atkinson  B. Waugh 《地球表面变化过程与地形》1979,4(2):103-115

The occurrence of red desert soil profiles developed on Nubian Sandstone in the Libyan Sahara is discussed. From an examination of profile morphology in the field and the position of the soils at 970 m on an old land surface, it would be possible to regard them as desert paleosols formed under a previous humid climatic phase during the Quaternary. However, an investigation of the mineralogy of the soils and the underlying parent rocks strongly suggests that the properties of the soils are largely dependent on the parent material. Both have identical patterns of kaolinite content, haematite as the main ferric oxide, and similar proportions of quartz silt and coarse quartz sand. Therefore, the use of kaolinite and ferric oxides in interpreting past soil-forming climates in arid regions needs to be carried out with caution, for in the present case such an interpretation would be unreliable.  相似文献   

Geotechnology: An Introductory Text for Students and Engineers | A. Roberts. Pergamon Press,Oxford, 1977, 347 pp. £19.50 (hardback), £9.50 (paperback)     

J.H. Atkinson 《Engineering Geology》1979,14(4):286

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High-temperature stress relaxation of synthetic,polycrystalline galena     

Barry Kean Atkinson 《Physics and Chemistry of Minerals》1978,2(4):305-315

Stress relaxation experiments were performed on hot-pressed cylinders of synthetic, polycrystalline galena at temperatures of 500°, 600°, 700° and 800°C at atmospheric pressure after various levels of axial strain, in the range from 2% to 25%, had been imposed at a constant strain rate (?) of 3×10^?4 s^?1. For this study a new apparatus was built which can measure small changes in applied stress (σ), better than ±0.5 × 10⁵ Pa, and which incorporates a facility whereby the composition of the test specimen can be fixed through equilibration with a gas atmosphere of controlled composition. Deformation mechanism maps constructed largely on theoretical grounds predict that, under the conditions studied here, high-temperature dislocation creep, for which ?∝σ⁵, gives way on lowering the applied stress to diffusion creep, for which ?∝σ. The experimental results agree in large measure with these theoretical predictions. However, it is not possible in this preliminary study to conclusively identify the dominant deformation mechanisms.  相似文献   

Studies in speleology,Volume IV,William Pengelly Cave Studies Trust Ltd., London and Buckfastleigh,Devon, 1983     

T. C. Atkinson 《地球表面变化过程与地形》1985,10(1):89-90

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Deformation mechanism maps for polycrystalline galena     

B.K. Atkinson 《Earth and Planetary Science Letters》1976,29(1):210-218

A deformation mechanism map, depicting the fields of stress and temperature in which modes of plastic flow are dominant (i.e. provide the fastest strain rate) has been calculated for polycrystalline, stoichiometric galena for each of two grain sizes; namely, 10 and 10³ μm. The deformation mechanisms considered were dislocation glide, dislocation creep (i.e. creep involving dislocation climb), Nabarro-Herring creep and Coble creep.During folding and related tectonic deformation in the earth's crust steady-state flow of galena may occur by either dislocation or diffusion creep at very low differential stresses (typically ranging from 100 bars down to 10^?2 bar, or less). The dislocation creep field will be enlarged at the expense of that for diffusion creep, however, if (a) the stress dependence of strain rate for dislocation creep decreases at low stresses and if the grain size is greater than 10 μm, or (b) diffusion creep rates decline at high strains due to the presence of second-phase particles in the grain boundaries. It is probable that dislocation glide will be the dominant deformation mechanism in galena only at low temperatures and fast strain rates and it is unlikely to be the dominant mechanism during folding. Kinking may have some potential as an indicator of these temperatures and strain rates.  相似文献   

Orthophosphate in Ground Water, Hall County, Nebraska     

Jon C. Atkinson 《Ground water》1974,12(5):291-295

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Orographic and stability effects on valley-side drainage flows     

B. W. Atkinson 《Boundary-Layer Meteorology》1995,75(4):403-428

The effects of orography and stability on valley-side drainage winds were investigated with the aid of a numerical model. The model is three-dimensional, non-hydrostatic, cast in terrain-following co-ordinates, has a surface energy budget and a 1.5 order TKE closure scheme. Experiments were conducted over a schematic three-dimensional valley to assess the influences on airflow of valley-side slope magnitude, valley cross-section shape, tilt of the valley floor and stability.In drainage flow, magnitudes of horizontal and vertical velocities and heights of their maxima are directly related to slope angle. The velocities are either insensitive to, or slightly inversely related to stability. The cooling which drives the flows is strongest over steep slopes and in large stabilities. The depth of the cooled layer, whilst increasing over steeper slopes, is inversely related to the stability. TKE increases with slope angle and decreases with increasing stability. In the downslope direction, the near-surface cooled layer significantly increases whereas the inversion intensity decreases by about 20%. These two features are due to mixing between the drainage flow and the overlying air. Tha drainage flow accelerates down the slope until it reaches the accumulated pool of cold air in the valley bottom, whereupon it slows down markedly and is accompanied by uplift over the centre of the valley.The cross-valley circulation is influenced by valley-side slope angle, valley cross-section shape and tilt of the valley floor, in addition to the effects of stability. For a given shape, the circulation is a direct function of the valley-side slope and an inverse function of the ambient stability. This relationship is described mathematically.V-shaped valleys generate stronger flows than doU-shaped valleys and a tilted valley floor also leads to a significant increase in velocities.  相似文献   

Alkyl nitrate formation from the atmospheric photoxidation of alkanes; a revised estimation method     

William P. L. Carter  Roger Atkinson 《Journal of Atmospheric Chemistry》1989,8(2):165-173

The available experimental data concerning the yields of alkyl nitrates in the reactions of alkyl peroxy radicals with NO have been used to derive a revised expression for the estimation of alkyl nitrate yields in the atmospheric photooxidation of alkanes as a function of temperature and pressure. This revised expression gives more reasonable predictions of alkyl nitrate yields under high altitude tropospheric conditions than that which has been previously published.  相似文献