X－CT检查与X线摄影的区别     

朱事芳  叶琴  高艳 《CT理论与应用研究》1995,(3)

本文列出ＣＴ检查与Ｘ线摄影的成像原理，及各自优缺点，提示临床正确应用ＣＴ检查与Ｘ线摄影，使得诊断更加正确有效，并节省患者的的检查费。  相似文献   

NUMERICAL STUDY OF OROGRAPHIC INFLUENCE ON LOW FREQUENCY OSCILLATION     

张勤  朱育峰  倪允琪  林武银 《热带气象学报(英文版)》1995,1(1):67-74

Orographic effects on monthly-and seasonal-scale low frequency oscillation are investiged in terms of a five-level global spectral model with a triangle truncation at wavenumber 10 that contains relatively full physical parameterization, followed by analysis and comparison of the lowpass filtered data separately obtained from models with and without orography. Results show that remarkable seasonal characteristics are displayed in the orographic forcing-generated low frequency wavetrain on monthly and seasonal scales. It is found that the Northern Hemisphere summer orography-produced tropical heating acts as source of the low-frequency wavetrain for both hemispheres. Besides, the simulations indicate that the orographic wavetrain perturbation can give rise to the anomaly in the equatorial zonal flow, whose transient forcing will cause a new wavetrain in the Southern Hemisphere, thus completing the cross-equatorial propagation of the northern wave in interhemispheric action.  相似文献   

NUMERICAL STUDY ON NONLINEAR INTERACTION BETWEEN TROPICAL CYCLONE AND SEA^*          下载免费PDF全文

Qin Zenghao  Zhu Jianrong 《Acta Meteorologica Sinica》1995,9(1):13-25

Given time-independent monthly mean sea temperature,numerical simulation was done of the path of the tropicalcy clone Forrest and its related physical quantity field in terms of the improved version of the σ-coordinate 10-level primitive equation model for tropical cyclones developed by the Guangzhou Institute of Marine Meteorology.Result ssuggest the similarity between the simulated and observed physical quantity fields except that the simulated path was to the right of the observed,with the deviation increasing with time.Sea and tropical cyclone,in effect,interact mutually.In an attempt to compare the results from coupling and uncoupling experiments,an oceanic mixed layer model was formulated based on experiments with sea response to cyclone and integrated in synchronous coupling with the aforementioned version of tropical cyclones,the computational domain covering the western North Pacific with the coastal configuration involved.The coupling experiment shows that the negative feedback of the interaction between sea and mature cyclone leads to weaker sea response as compared to the uncoupling case.Except for the location of the divergence core of oceanic current,the mixed layer depth and inhomogeneous distribution of sea surface temperature (SST) caused by the cyclone-core position and intensity,the values of the maximum oceanic current,departure of the mixed layer depth and SST drop were smaller in the coupling than in the uncoupling case,and so was the maximum wind near the cyclone core.The path from the coupling run is to the left of the course in the uncoupling experiment but closer to the observed one though remaining somewhat leftward.Even on a scale of less than 3 days,the effects of sea and sea-cyclone interaction on the cyclone were by no means negli-gible.  相似文献   

QBO Features of Tropical Pacific wind Stress Field with the Relation to El Nino     

Zhang Qin  Zhu Yufeng  Ni Yunqi 《大气科学进展》1995,12(1):87-94

Analysis has been implemented of 1970-1992 tropical Pacific wind stress anomaly and sea surface temperature anomaly (SSTA) datasets, indicating that quasi-biennial oscillation (QBO) of the tropical Pacific WS and SSTA is featured both by a standing and a progressive form, the former emerging in the most intense centers of action and the latter travelling east- or west-ward out of the SSTA sources. Results show that the SSTA is in the warm (cold) phase as zonal component of euqatorial wind stress anomaly gets weakened (reinforced) and the QBO of wind stress anomaly is well related to the El Nino cycle.  相似文献   

DETERMINATION OF AERODYNAMIC PARAMETERS OF CROP CANOPIES WITH A CENTER-OF-PRESSURE METHOD          下载免费PDF全文

Qin Wenhan 《Acta Meteorologica Sinica》1995,9(1):78-86

Using data on leaf area density and wind profiles above and within canopies of wheat,rice,soybean and corn,thecenter-of-pressure method (CPM),originally proposed by Thom (1971),is first validated in the field.Aphysically-based model for directly calculating zero-displacement height (d) is derived.The comparison between thefriction velocity (u_*) estimated with CPM and that with eddy correlation technique shows that CPM not only works wellin the field,but also produces more steady and accurate estimates of aerodynamic parameters (which are hardly affectedby atmospheric thermal stability),than those with the widely-used log-profile fitting method in diabatic atmosphere.The results presented in this paper also demonstrate that the ratios of d,z_0 to crop height h usually vary with canopy ar-chitecture,atmospheric stratification and turbulent exchange intensity,and are not just constants as commonly assumedor used.d/h raises with an increase of relative height of the maximum foliage layer and wind extinction coefficientwithin the canopy.Only for crops with short stem and moderate foliage density,can the relations d= 0.64h,z_0=0.08hkeep stable.In addition,for long stem crops or sparse canopies,the fairly large shear stress at the soil surface and the va-riation of the exponent in the relationship between drag coefficient and wind speed undoubtedly influence the accuracyof CPM to a certain extent.  相似文献   

电视天气预报制作系统     

泰祥士  杨玉真  叶阿庆 《气象》1995,21(5):25-30

电视气象服务是气象服务的重要窗口之一。电视天气预报制作系统将计算机技术，电视技术和气象预报产品有机地结合起来融为一体，该文介绍了国家气象中心电视天气预报制作系统的系统设计思想，系统结构、系统分析，计算机动画技术和音／视频技术，节目内容及取得的效益，同时提出了我国气象部门国家，省，地三级电视气象服务系统的发展方向。  相似文献   

金顶铅锌矿床流体包裹体地球化学特征   总被引：28，自引：1，他引：28  

温春齐  覃功炯 《矿物岩石》1995,15(4):78-84

金顶超大型铅锌矿床主要工业矿体形成于热卤水成矿期。本文通过对流体包裹体的温度、压力、盐度、密度、成分、氢氧同位素及流体性质等地球化学研究表明，金顶矿床具有浅成中－低温、中－低盐度矿化的特点，成矿流体源于沉积盆地热卤水和古大气降水的混合，部分源于深部，从热卤水矿化的早期到晚期，随着古大气降水的加入，流体的Ｔ，ｐ，Ｓ，δ＾１８Ｏ，δＤ，ｆｏ２，ｆｃｏ２，ｆｓ２均具降低趋势，而ＰＨ，Ｅｈ值略有增大。  相似文献   

NUMERICAL STUDY ON THE INTERANNUAL OSCILLATION OF SEA SURFACE TEMPERATURE IN THE SOUTH CHINA SEA   总被引：5，自引：0，他引：5  

王东晓  周发琇  傅刚  秦曾灏 《中国海洋湖沼学报》1996,14(1):61-67

A two and a half layer oceanic model of wind-driven, thermodynamical general circulation is appliedto study the interannual oscillation of sea surface temperature (SST) in the South China Sea (SCS). Themodel consists of two active layers: the upper mixed layer (UML) and the seasonal thermocline, with themotionless abyss beneath them. The governing equations which include momentum, continuity and sea.temperature for each active layer, can describe the physics of Boussinseq approximation, reduced gravityand equatorial β-plane. The formulas for the heat flux at the surface and at the interface between twoactive layers are designed on the Haney scheme. The entrainment and detrainment at the bottom of theUML induces vertical transport of mass,momentum and heat, and couples of dynamic andthermodynamic effect.Using leap-frog integrating scheme and the Arakawa-C grid the model is forced bya time-dependent wind anomaly stress pattern obtained from category analysis of COADS. The numerical results indicate that t  相似文献   

异类矿物结构基元层间层矿物及墨铜矿的研究   总被引：1，自引：0，他引：1  

曹正民  秦善  王启明 《岩石矿物学杂志》1995,14(1):52-56

本文提出了“异类矿物结构基元层间层矿物”这一新概念，从五个方面限定了其含义，扩展了“间层矿物”的内涵。对其典型矿物墨铜矿进行了Ｘ射线，电子探针和高分辨透射电镜的初步研究，取得了一些新认识，墨铜矿在ｃ方向有序，重复周期为１１．４５Ａ，在ａ，ｂ方向无序，不存在超晶胞。  相似文献   

山高水长路漫漫——纪念丁文江先生     

张进  曲军峰  王勤  程弘毅 《地质学报》2022,96(5):1524-1543

丁文江先生是我国近代地质学的奠基人之一，也是中国地质学会的主要创始人之一。他在地质学的诸多领域都开展了卓有成效的工作，组建了我国最早的地质调查和科研机构，立德树人，培养了第一代地质学家，主导了前中央研究院的重大机构改革，为地质甚至科学事业在中国的落地生根起到了决定性的作用。同时他也积极参与到当时的社会和政治活动中，践行自己报效国家的理念。他是在我国开展系统性区域地质调查的第一人，开启了中国人系统地质填图的先河，先后填制了诸多不同比例尺的地质图，为后世我国构造地质界奠定了研究传统。他填图的区域从克拉通到造山带，从弱变形区到强变形带，填制的地质图也从简单到复杂，从关注地层到构造内容的逐步增加，不仅体现了一个地质学家野外填图经验和技术的逐步成熟，也体现了我国构造地质学逐渐从地层学中独立出来的过程。这个过程与国际上构造地质作为一个独立的专业从地层学中分离出来的阶段一致。因此丁文江先生不仅仅是我国地质学的奠基人之一，更是我国构造地质学的开山宗师。丁文江先生始终怀揣科学救国的信念，将自己的一生融入到科学救国、传播科学思想的过程中，将自己的科研活动与当时的国家建设联系，积极参与多项铁路选址、矿产调查与开发以及生态环境变迁等工作，这永远值得我们学习。他为中国地质学乃至科学发展做出的贡献永载史册。  相似文献