双能CT的基本原理、应用和未来展望(英文)

断层影像(CT)的图像对比度与扫描所用的X光源能谱分布有很大关系。传统CT使用具有能谱分布的一个光源进行成像,有时会出现信息模糊致使两种不同材料在CT图像上完全相同。双能CT使用两个不同分布的能谱对物体进行成像,能够消除单能谱情况下的信息模糊。虽然双能CT的基本概念由来已久,但最近商业系统的出现使双能CT迅速成为一个热点。我们首先概述了双能CT的基本物理原理和双能信号处理方法,包括促使双能CT进入现代医学成像的关键技术。其次,双能CT的应用已非常广泛,本文从其在临床应用角度进行了详细介绍使读者有所了解。最后,我们简要探讨了当前的两个技术发展领域:光子技术探测器和技术合成CT。     

Marine Controlled Source Electromagnetics: Principles,Methodologies, Future Commercial Applications

The exploration community, from the earth scientist to the investment manager, has surely recognized the recent surge of interest in the use of controlled source electromagnetics for offshore hydrocarbon detection and assessment. The targets, petroleum, natural gas and gas hydrate, are resistive zones in an otherwise conductive background. I trace the academic and commercial development of marine methods from basic theory through experimental design to the few published relevant exploration case histories. Invited review paper presented at the 17th Electromagnetic Induction Workshop. Hyderabad, India, 18–23 October, 2004.     

A Grid Framework for Visualization Services in the Earth Sciences

Scientific visualization is an ingredient essential to understanding the large amounts of data generated from large-scale numerical simulations, laboratory experiments and geological surveys. Visualization forms an integral component of any complete framework, together with services to handle mathematical and statistical analysis, storage, feature extraction, and other functions. To support rapid and seamless collaborations and communication between researchers across geographically disparate regions necessitates a distributed infrastructure that supports redundancy, fault tolerance, and most importantly, ease of use. We describe herein an architecture based on Naradabrokering, a publish/subscribe framework that supports the above requirements. We have implemented an initial version of this architecture and describe some initial experiments.     

Intensity Spectra Versus Response Spectra: Basic Concepts and Applications

This paper begins with a critical assessment of the concept of macroseismic intensity, on which traditional scales, such as MSK and EMS, are based. The main shortcoming identified is the model's failure to consider the spectral features of ground motion. This omission may lead to erroneous seismic zonation, as shown in the paper. As a result, the model is of little interest to engineers who must design and build safe structures while adopting economical solutions. The paper presents a way to radically improve this situation. The starting point for this approach was the experience of the destructive Vrancea earthquake of 1977.03.04, which made it clear that intensity appears to be different for structures having natural periods pertaining to different spectral domains. The solution proposed to the shortcomings of the traditional intensity concept is postulated on a system of analytical expressions, covering definitions of global intensities, of intensities related to oscillation frequency and of intensities related to a definite spectral band. The latter definition lies at the basis of a definition of discrete intensity spectra. Illustrative applications are presented, in relation to global intensities and to discrete intensity spectra. We then analyze an illustrative case in which the use of traditional macroseismic survey techniques led to erroneous seismic zonation. Finally, some conclusions and recommendations are presented. Based on the authors?? long-term experience, we strongly recommend close interaction between seismologists and engineers in working groups and joint projects targeted on radical improvement of the basic concepts of seismic intensity and of specific analysis procedures.     

Review of the Anisotropic Interface Ray Propagator: Symplecticity,Eigenvalues, Invariants and Applications

A review of the 6 × 6 anisotropic interface ray propagator matrix in Cartesian coordinates and within the framework of the Hamiltonian formalism shows that there is one unique propagator satisfying the symplectic property. This is essential, since the symplecticity furnishes an exact inverse, while an eigenvalue analysis indicates that the propagator may be arbitrarily ill-conditioned. As such, the symplectic interface propagator naturally connects to symplectic ray integration algorithms for smooth media, designed to maintain accuracy. Moreover, several ray invariants for smooth media remain invariant across interfaces. It is straightforward to derive expressions for the interface propagator, both explicit and implicit. Symplecticity is equivalent to the condition that the propagator preserves the eikonal constraint across the interface. The symplectic interface propagator complies with phase matching of the incident and reflected/transmitted ray field, and is therefore in accordance with the earlier derived 4 × 4 matrix in ray-centred coordinates. The symplectic property is related to the symmetry of the second derivative matrix of the reflected/transmitted traveltime field. Thanks to the analytic expression of the symplectic interface propagator, relating interface curvature directly to second derivatives of traveltimes observed at a datum level, numerous applications are available in the area of processing and inversion.     

"数字地球"在我国地震信息系统与地球科学发展中的地位和作用

从“数字地球”出发,以我国２１世纪地球科学发展的战略目标为例,以地震信息系统为例,简要阐述了“数字地球”在地震信息与地球科学发展中的地位和作用。     

Cosmogenic and radiogenic noble gases in the Dhajala chondrite

Whole rock and chondrules of the Dhajala chondrite were analyzed for Ne, Ar, Kr and Xe by total melting as well as by stepwise heating techniques. The cosmic ray exposure ages for the whole rock and the chondrules are6.2 ± 0.8 and6.3 ± 1.0m.y. as determined by the²¹Ne method and4.8 ± 1.5 and4.2 ± 2.0m.y. by the³⁸Ar method, respectively. The K-Ar age of the whole rock is4.2 ± 0.4b.y. The elemental composition of the trapped gas in this chondrite is of “planetary” type. The radiogenic¹²⁹Xe contents in the whole rock and chondrules are similar and this component is very retentively sited in the chondrules.     

美国国家科学基金地球科学领域的研究新机遇

引言地球有一套复杂的动力地质系统,它控制着这个星球及整个人类所经历的过去的演化、现在的状态和未来的状况。由于地球科学在过去两个世纪已变得成熟,发展中的各分支学科可以稳步完善地解答构造、作用和历史等各方面的具体问题,各个动力地质系统的多学科特性受到越来越多的关注。持续的理论和技术改进使得地球科学的所有分支学科有能力解释地球变化的地质记录,并可观测今天的地球从地表到内核正在发生的作用,更逼真地模拟复杂的动力作用,所有这些工作都还需要继续进行。但是本次报告所     

地球系统科学与社会可持续发展--青年科学家论坛第76次活动

由中国科学技术协会主办的“青年科学家论坛”第 76次活动于 2 0 0 3年 8月 2 1～ 2 2日在北京中国科技会堂举行。活动的主题是“地球系统科学与社会可持续发展”。 4 2位来自全国各地的青年科学家和研究生参加了此次活动 ,代表中包括多位“中国青年科技奖”获得者 ,中国科学院“百人计划”、国家“百千万人才工程”等的入选者 ,以及“国家杰出青年科学基金”项目、国家“86 3项目”、国家“973项目”的项目或课题负责人。中国科学技术协会学术部部长、“青年科学家论坛”活动组委会常务副主任马阳出席了论坛活动。这次活动得到国际科联环境…     

Turbulent transport of the Earth magnitisphere: Review of the results of observations and modeling

The results of observations of turbulent transport in the Earth’s magnetosphere tail are summarized. The results of recent works on the projection of the auroral oval onto the equatorial plane, according to which the main part of the oval is not projected onto the plasma sheet, are taken into account. Analysis of the eddy diffusion coefficient dependences on the geocentric distance and on the phase of a magnetosphere substorm, both across the sheet and in the azimuthal direction, is carried out. The role of eddy diffusion in the creation of quasi-equilibrium plasma structures and in the plasma transport from the magnetospheric flanks into the plasma sheet is considered. The transport along the sheet is discussed. The problems of turbulent transport that can be solved by analysis the data of multisatellite projects are indicated.