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991.
本文观察分析了肝癌侵犯门静脉,在门脉分支及主干内形成癌栓后的CT影像特征。发现46例中有41例(91%)有门脉增宽,此征象在CT图像上容易发现和测量出,可作为门脉癌栓的辅助诊断依据;同时CT平扫可以发现早期新形成的栓子,其特点是增宽的门脉内高密度结节影,CT值平均56±7·8Hu;另外增强扫描可显示出平扫低密度而无增强表现的癌栓影。同时对上述各征象的产生机制进行了分析。 相似文献
992.
甘、宁、青地区地震孕育的力源环境 总被引:2,自引:0,他引:2
从3个方面讨论了甘、宁、青三省区地震孕育的力源环境。①从强震震源机制、地震形变带、断层滑移特征和现代形变、地应力实地测量等几个不同侧面,讨论了区域构适应力场的分布规律。指出,甘、宁、青现今区域构造应力场以水平为主,主压应力方向从地区的西部到东南部,由NNE逐渐转为近EW向,且在地壳的深部、浅部和地表,方向有较好的一致性。它是印度板块向青藏块体碰撞、挤压,使青藏块体向北东方向推济,同时向东蠕散的结果。②通过讨论发展断层的错动形式以及部分前兆资料所反映的应力特征,揭示了地震孕育过程中震源及周围地区处于一种更高的应力状态。这是该地区地震前兆具有普遍性的根本原因。③讨论了甘、宁、青现今地震的孕育方式。指出,6级以上地震基本上以先存断层重新活动或相互沟通为主要活动形式。 相似文献
993.
本文采用解析方法,给出了感应测井中当介质可表示成v(x,y,z)=Σ↓k,fvk,j^x^ky^j时的反演公式,并讨论了径向浸入深度γ0的反演。 相似文献
994.
The effect of employing flux adjustments on the climatic response of an idealized coupled model to an imposed radiative forcing
is investigated with two coupled models, one of which employs flux adjustments. A linear reduction (to the planetary longwave
flux) of 4 W/m2 is applied over a 70 y period and held constant thereafter. Similar model responses are found (during the initial 70 y period)
for global-scale diagnostics of hemispheric air temperature due to the nearly linear surface-air temperature response to the
radiative forcing. Significant regional scale differences do exist, however. As the perturbation away from the present climate
grows, basin-scale diagnostics (such as meridional overturning rates) begin to diverge between flux adjusted and non-flux
adjusted models. Once the imposed radiative forcing is held constant, differences in global mean air temperature of up to
0.5 °C are found, with large regional-scale differences in air temperature and overturning rates within the North Atlantic
and Southern Ocean. Two additional experiments with the flux adjusted model (beginning from points further along the control
integration) suggest that the elimination of much of the coupling shock before the radiative forcing is applied leads to results
slightly closer to the non-flux adjusted case, although large differences still persist. In particular a dipole structure
indicating an enhanced warming within the Pacific sector of the Southern Ocean, and cooling within the Atlantic sector is
not reproduced by the flux adjusted models. This disparity is intimately linked to the Southern Ocean overturning cell along
with the flux adjustments employed as well as the drift arising from coupling shock. If a similar form of sensitivity exists
in more realistic coupled models, our results suggest: (1) perturbation experiments should not be undertaken until after the
coupled model control experiment is carried out for several hundred years (thereby minimizing the coupling shock); (2) care
should be exercised in the interpretation of regional-scale results (over the ocean) in coupled models which employ flux adjustments;
(3) care should also be taken in interpreting even global-scale diagnostics in flux adjusted models for large perturbations
about the present climate.
Received: 15 November 1996 / Accepted: 4 June 1997 相似文献
995.
TH. Blumenstock H. Fisher A. Friedle F. Hase P. Thomas 《Journal of Atmospheric Chemistry》1997,26(3):311-321
During SESAME phase I ground-based FTIR measurements were performed atEsrange near Kiruna, Sweden, from 28 January to 26 March 1994. Zenith columnamounts of ClONO2, HCl, HF, HNO3,O3, N2O, CH4, and CFC-12 werederived from solar absorption spectra. Time series of ClONO2and HCl indicate a chlorine activation at the end of January and around 1March. On 1 March a very low amount of HCl of 2.09times; 1015molec. cm-2 was detected, probably caused by a second chlorineactivation phase starting from an already decreased amount of HCl. The ratioof column amounts of HCl to ClONO2 decreased inside the vortexfrom about 1 in January to 0.4 in late March compared to values of about 2outside the vortex. Although the Arctic stratosphere was rather warm in winter1993/94 and PSCs occurred seldom, chlorine partitioning into its reservoirspecies HCl and ClONO2 changed during that winter andClONO2 is the major chlorine reservoir at the end of thewinter as in cold winters like 1991/92 and 1994/95. 相似文献
996.
S. Solberg T. Krognes F. Stordal OØ Hov H. J. Beine D. A. Jaffe K. C. Clemitshaw S. A. Penkett 《Journal of Atmospheric Chemistry》1997,28(1-3):209-225
Simultaneousindependent measurements of NOy and NOx(NOx= NO + NO2) by high-sensitivitychemiluminescence systems and of PAN (peroxyacetylnitrate) and PPN (peroxypropionyl nitrate) by GC-ECDwere made at Spitsbergen in the Norwegian Arcticduring the first half year of 1994. The average mixingratio of the sum of PAN and PPN (denoted PANs)increased from around 150 pptv in early winter to amaximum of around 500 pptv in late March, whereasepisodic peak values reached 800 pptv. This occurredsimultaneously with a maximum in ozone which increasedto 45–50 ppbv in March–April. The average NOxmixing ratio was 27 pptv and did not show any cyclethrough the period. The NOy mixing ratio showeda maximum in late March, while the difference betweenNOy and PAN decreased during spring. This is anindication of the dominance of PAN in the NOybudget in the Arctic, but possible changes in theefficiency of the NOy converter could alsocontribute to this. Although most PAN in theArctic is believed to be due to long range transport,the observations indicate local loss and formationrates of up to 1–2 pptv h-1 in April–May.Measurements of carbonyl compounds suggest thatacetaldehyde was the dominant, local precursor ofPAN.Now at 1. 相似文献
997.
Summary The relation between the air temperature and the global solar radiation, which can be conveniently represented by the three characteristics: mean, amplitude and phase lag of the first harmonic of global radiation and air temperatures. A good correlation between the air temperature and the solar radiation has been found when the phase lag between them is nearly of 30 days.With 6 Figures 相似文献
998.
Geophysical variables are orthogonally decomposed by averaging timeseries using different averaging lengths, referred to as a (Haar)multiresolution decomposition. This simple and economic decomposition isassociated with cospectra that formally satisfy Reynolds averaging rules foreach averaging length. The multiresolution decomposition provides a naturalestimate of the random error in estimating a mean turbulent flux. The Fourierand multiresolution decompositions are compared using aircraft data fromBOREAS. 相似文献
999.
1000.