Prediction of interwell tracer flow behaviour in heterogeneous reservoirs

A new numerical approach has been developed for predicting the interwell tracer flow behaviour in heterogeneous porous media typical of water and oil reservoirs. This approach uses a mixed finite-element method with triangular elements to predict pressure and velocity fields, and a novel random walk model to simulate the tracer transport through the reservoir, and to perdict the concentration response at the production well. The mixed finite-element method solves the pressure and velocity simultaneously imposing suitable boundary conditions for both pressure and velocity, which allows the solution of the tracer velocity to be more accurate and to conserve mass more precisely than a standard finite-element method. The random walk model can reflect the tracer flow behaviour directly by tracking the movement of particles representing the tracer input volume.The technique has been validated by comparing the predicted results with analytical solutions of tracer concentration response for a homogeneous five-spot pattern, and with published experimentally observed tracer fronts at breakthrough for homogeneous and three heterogeneous cases of five-spot pattern. Good agreement has been achieved for all cases. The model presented in this paper is general, and can therefore be applied to drive patterns other than the five-spot pattern, and for different types of heterogeneities; it can also include effects such as longitudinal and transverse dispersion and adsorption.     

再循环自净型排风柜检测方法的分析研究

在分析常规检测方法弊端的基础上,提出以环己烷、异丙醇或盐酸溶液代替SF6作为示踪气体,将吸附过滤器吸附量检测和控制浓度检测有机结合起来的一种改良检测方法;并从必要性、技术性和经济性角度分析了该检测方法用以检测再循环自净型排风柜的可行性和合理性。     

High-performance high-resolution semi-Lagrangian tracer transport on a sphere

Current climate models have a limited ability to increase spatial resolution because numerical stability requires the time step to decrease. We describe a semi-Lagrangian method for tracer transport that is stable for arbitrary Courant numbers, and we test a parallel implementation discretized on the cubed sphere. The method includes a fixer that conserves mass and constrains tracers to a physical range of values. The method shows third-order convergence and maintains nonlinear tracer correlations to second order. It shows optimal accuracy at Courant numbers of 10–20, more than an order of magnitude higher than explicit methods. We present parallel performance in terms of strong scaling, weak scaling, and spatial scaling (where the time step stays constant while the resolution increases). For a 0.2° test with 100 tracers, the implementation scales efficiently to 10,000 MPI tasks.     

扩展IP访问列表的访问控制在模拟器CiscoPacketTracer中的仿真设计与实现

目前,通过扩展IP进行访问控制已广泛应用在各行各业的网络中,但在有一部分的学校在教学过程中,由于实训条件的限制,很多实验无法展开。该文以IP访问列表的访问控制为例,利用Cisco Packet Tracer模拟器搭建仿真实验平台,从而保证了实验的正常开展。     

Automated registration of sequential breath-hold dynamic contrast-enhanced MR images: a comparison of three techniques

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is increasingly in use as an investigational biomarker of response in cancer clinical studies. Proper registration of images acquired at different time points is essential for deriving diagnostic information from quantitative pharmacokinetic analysis of these data. Motion artifacts in the presence of time-varying intensity due to contrast enhancement make this registration problem challenging. DCE-MRI of chest and abdominal lesions is typically performed during sequential breath-holds, which introduces misregistration due to inconsistent diaphragm positions and also places constraints on temporal resolution vis-à-vis free-breathing. In this work, we have employed a computer-generated DCE-MRI phantom to compare the performance of two published methods, Progressive Principal Component Registration and Pharmacokinetic Model-Driven Registration, with Sequential Elastic Registration (SER) to register adjacent time-sample images using a published general-purpose elastic registration algorithm. In all three methods, a 3D rigid-body registration scheme with a mutual information similarity measure was used as a preprocessing step. The DCE-MRI phantom images were mathematically deformed to simulate misregistration, which was corrected using the three schemes. All three schemes were comparably successful in registering large regions of interest (ROIs) such as muscle, liver, and spleen. SER was superior in retaining tumor volume and shape, and in registering smaller but important ROIs such as tumor core and tumor rim. The performance of SER on clinical DCE-MRI data sets is also presented.     

Comparison of void volume, mobile phase volume and accessible volume determined from retention data for oligomers in reversed-phase liquid chromatographic systems

The experimental technique of mass spectrometric tracer pulse chromatography was used to determine the void volume, i.e., the total volume of eluent in the column, and the volume of eluent moving freely through the column, i.e., mobile phase volume, for a series of eluents with a C(18)-bonded RPLC column. The interstitial volume of the column was determined by size exclusion chromatography. In order to evaluate the utility of the accessible volumes determined from the retention volumes of homologous solutes, the accessible volume of the column was determined as a function of eluent composition and temperature with polystyrene and polyethylene glycol samples using Martin's Rule. Comparison of these four measured volumes indicated that the experimentally measured accessible volumes did not correspond to either the void volumes, mobile phase volumes or interstitial volumes.     

Monoclonal Antibody-Based Fluorescence Polarization Immunoassay for Furazolidone in Feed

A rapid, specific, and sensitive fluorescence polarization immunoassay (FPIA) method was developed to detect residues of furazolidone, a forbidden drug in feed. An immuno-hapten was designed for monoclonal antibody preparation. Furthermore, seven novel tracers were synthesized and the “heterology tracer” could improve the sensitivity of FPIA significantly. An optimized FPIA method was established with a cross-reactivity of less than 0.1%, IC₅₀ of 5.5 ng/mL. The limits of detection (LOD) calculated from feed samples were 0.5–0.9 ng/mL. Recoveries of fortified samples at levels of 5, 20, and 50 ng/mL ranged from 79.0% to 85.0%. The coefficients of variation were less than 12%.     

Hamiltonian Dynamics of a Particle Interacting with a Wave Field

We study the Hamiltonian equations of motion of a heavy tracer particle interacting with a dense weakly interacting Bose-Einstein condensate in the classical (mean-field) limit. Solutions describing ballistic subsonic motion of the particle through the condensate are constructed. We establish asymptotic stability of ballistic subsonic motion.     

Packet Tracer在“计算机网络”课程教学中的应用研究

文章指出在"计算机网络"课程教学中,网络分层体系结构及网络协议较为抽象,导致学生理解困难。通过将Cisco Packet Tracer网络模拟工具引入计算机网络教学,以浏览器访问Web服务器这一典型网络应用场景为示例,演示Packet Tracer在理论教学中的应用。网络模拟工具的应用,使得学生易于理解网络概念,有较好的教学效果。     

Mineralogical characteristics of soil dust from source regions in northern China

Mineral compositions of aerosol particles were investigated at four sites （Aksu, Dunhuang, Zhenbeitai, and Tongliao） in desert regions of northern China from March to May in 2001 and 2002 during the intensive field campaign period of ACE-Asia （Aerosol Characterization Experiments-Asia）. The X-ray diffraction （XRD） results show the main minerals for Asian dust are illite, chlorite, kaolinite, quartz, feldspar, calcite, and dolomite. Gypsum, hornblende, and halite are also detected in several samples. Semi-quantitative mineralogical data of aerosol samples show that carbonate content decreases from western to eastern source areas; that is, soil dust collected at western source area sites of Dunhuang and Aksu are enriched with carbonate, while northeastern source area site of Tongliao is associated with low carbonate content. But the spatial distribution of feldspar exhibits a different pattern as compared to carbonate, increasing from the western to the eastern sources. The total clay content is significantly higher （73% in average） at the deposition site of Changwu than those at source areas. Air-mass back trajectory studies for the three dust storm events observed at Changwu, showed that soil dust transport pathways were as expected from carbonate content for the source identification, further demonstrating that carbonate was a useful tracer for eolian dust on regional scale in northern China.