瞬变响应与视纵向电导解释方法的对比

从＂等效导电平面原理＂出发,研究瞬变电磁过程中层状介质的视纵向电导的计算方法.在正演过程中引入中心差分算法来求取瞬变响应的导数,利用样条插值方法来代替传统意义上的求解反函数的方法来获取关键值-m,通过计算证明该方法可行.最后在验证视纵向电导解释方法有效性的过程中,采用典型的3层H型和4层HK型地电模型分别进行视纵向电导曲线与瞬变响应曲线的对比,计算结果表明,视纵向电导曲线比瞬变响应曲线能够更好地划分电性层,并能很好的指示电性变化关系,从而达到良好的解释效果.     

公路桥头跳车产生的原因及综合治理措施

结合工程实践,通过对高等级公路桥头跳车产生原因的分析,从设计和施工角度提出具体防治措施。     

短暂性脑缺血发作患者认知能力与单光子发射断层扫描脑血流显像的关系

目的探讨脑单光子发射断层扫描(SPECT)血流检测对短暂性脑缺血发作(TIA)患者认知障碍判断的价值。方法根据简易智力状态量表(MMSE)评估65例最后一次发作在72 h内的TIA患者的认知能力状况,同时用SPECT观察患者TIA发作间歇期的脑血流灌注显像。根据脑SPECT显像特点,比较不同程度低灌注组的TIA发作次数、认知能力及发作时的临床神经功能缺失评分;分析TIA患者脑SPECT、TIA发作次数与患者认知能力的关系。结果①所有患者的脑SPECT灌注显像均有不同程度的低灌注区域,其中轻度、中度、重度低灌注各为21、26、18例,且脑SPECT灌注显像低灌注区范围越大,TIA发作次数越多(rs=0.751,P<0.01),患者的临床神经功能缺损程度越重(rs=0.470,P<0.01);②TIA患者的MMSE评分明显低于对照组,且与脑SPECT灌注显像呈负相关(rs=-0.308,P<0.05)。结论TIA患者存在认知障碍,其程度与TIA发作次数及患者脑血流状况相关;SPECT可作为评价TIA患者认知能力的良好手段。     

浅谈高速公路桥头跳车的原因及防治措施

广州市北二环高速公路路线全长42.5公里,全线结构物较多且填土较高。为尽量避免桥头跳车现象的发生,北二环高速公路项目管理处针对不同的情况,采取相应的处理措施,取得了良好的效果。结合以往工程实例及北二环高速公路工程的实践,就桥头跳车的原因及台背处理问题,从理论与实践上作以下简单探讨。     

3种车桥耦合振动分析模型的比较研究

应用达朗贝尔原理和欧拉-贝努利梁假设，推导了简支梁在移动质量、四分之一车模型和二分之一车模型3种不同车辆模型下的车桥耦合振动方程，比较了在不同速度下的桥梁动态响应，结果表明，3种车辆模型都可以反映出在移动荷载作用下车桥耦合振动的总体规律，但考虑车体弹簧和阻尼的影响能更充分体现车桥耦合效应。     

A simplified calculation method for non-stationary random seismic response of jacket platform

Jacket platform was simulated by non-uniform cantilever beam subjected to axial loading. Based on the Hamilton theory, the equation of bending motion was developed and solved by the classical Ritz method combined with the pseudo-excitation method (PEM) for non-stationary random response with non-classical damping. Usually, random response of this continuous structure is obtained by orthogonality of modes and some normal modes of the structure are needed, causing inconvenience in the analysis of the non-uniform beam whose normal modes are not easy to be obtained. However, if the PEM is extended to calculate random respouse by combining it with the classical Ritz method, the responses of non-uniform beam, such as auto-power spectral density (PSD) function, croes-PSD and higher spectral moments can be solved directly avoiding the calculation of normal modes. The numerical results show that the present method is effective and useful in aseismic design of platforms.     

B级车轮铸钢疲劳可靠性S-N曲线重构方法

为实现任意可靠性水平疲劳强度设计、寿命预测和可靠性评定,提出了B级车轮铸钢疲劳可靠性S-N曲线的重构方法,应用Monte-Carlo模拟技术在可接受误差范围内重构了B级铸钢的疲劳极限和成组法S-N数据,依照常规法测定了B级铸钢中、短寿命范围的可靠性S-N曲线,应用概率疲劳极限外推法获得了包含中、短和长寿命范围的可靠性曲线。在此基础上,考虑工程应用实际情况,推导出了任意概率水平下的里程可靠性曲线。重构获得的疲劳极限及S-N数据最大模拟误差分别只有0.15%和0.07%,较好再现了原始数据,对曲线的外推使其合理性达到生产需要的104km以上,说明曲线重构方法可获得所需疲劳可靠性S-N曲线。     

Parallel processing based on ship maneuvering in identification of interaction force coefficients

The parallel processing based on the free running model test was adopted to predict the interac-tion force coefficients (flow straightening coefficient and wake fraction) of ship maneuvering. And the multi-population genetic algorithm (MPGA) based on real coding that can contemporarily process the data of freerunning model and simulation of ship maneuvering was applied to solve the problem. Accordingly the optimalindividual was obtained using the method of genetic algorithm. The parallel processing of multi-populationsolved the prematurity in the identification for single population, meanwhile, the parallel processing of the dataof ship maneuvering (turning motion and zigzag motion) is an attempt to solve the coefficient drift problem.In order to validate the method, the interaction force coefficients were verified by the procedure and thesecoefficients measured were compared with those ones identified. The maximum error is less than 5%, and theidentification is an effective method.     

Development of 2D hybrid equilibrium elements in large increment method

As a force-based finite element method (FEM), large increment method (LIM) has been developed in recent years. It has been shown that LIM provided prominent advantage of parallel computation with high efficiency and low time consumption for member structural system. To fully utilize its advantage in parallel computation, it is the time to extend LIM to 2D and 3D continua analysis. In this paper, a 2D finite element library with the capability of modeling arbitrary configurations is developed. Some illustrative numerical examples are solved by using the proposed library; the obtained results are compared with those obtained from both traditional displacement-based FEM and analytical solutions, which has clearly shown the advantages of LIM.     

单车荷载作用下T型刚构桥车致振动响应研究

根据车辆-桥梁结构振动特性,研究单车移动荷载作用下,T型刚构桥考虑桥面不平顺影响时桥梁振动响应及冲击特性。通过将T型刚构桥离散为三维梁单元有限元模型,车辆简化为九自由度整车模型（考虑车辆俯仰及侧翻）,桥面不平顺激励采用实测和数值模拟（根据国标GB／T7031—86给定功率谱密度曲线采用三角级数叠加法模拟）两种激励;以车轮与桥面相互接触处保持不脱离为条件,建立车辆与桥梁耦舍振动方程,利用模态综合法并结合Newmark—β数值积分方法进行迭代求解。以乔木湾乐安河T型刚构桥为工程背景,研究了单车荷载下,最不利位置处的冲击系数随桥梁结构阻尼、行车速度、桥面不平顺及车辆特性的变化关系,并将数值模拟结果与实测结果对比。研究结果表明,实测冲击系数与数值模拟的冲击系数较好吻合,乐安河大桥冲击系数满足04《桥规》要求。     

Analysis of arc physical property of pulsed tungsten inert gas welding based on Fowler-Milne method

Pulsed tungsten inert gas (TIG) welding is widely used in industry due to its superior properties, so the measurement of arc temperature is important to analyse welding process. Arc image of spectral line in 794.8 nm is captured by high speed camera; both the Abel inversion and the Fowler-Milne method are used to calculate the temperature distribution of the pulsed TIG welding. Characteristic of transient variation in arc intensity and temperature is analyzed. When the change of current happens, intensity and temperature of arc jump as well, it costs several milliseconds. The further the axial position from the tungsten is, the greater the intensity jumps, and the smaller the temperature changes.     

Application of method of fundamental solutions in solving potential flow problems for ship motion prediction

A novel panel-free approach based on the method of fundamental solutions (MFS) is proposed to solve the potential flow for predicting ship motion responses in the frequency domain according to strip theory. Compared with the conventional boundary element method (BEM), MFS is a desingularized, panel-free and integration-free approach. As a result, it is mathematically simple and easy for programming. The velocity potential is described by radial basis function (RBF) approximations and any degree of continuity of the velocity potential gradient can be obtained. Desingularization is achieved through collating singularities on a pseudo boundary outside the real fluid domain. Practical implementation and numerical characteristics of the MFS for solving the potential flow problem concerning ship hydrodynamics are elaborated through the computation of a 2D rectangular section. Then, the current method is further integrated with frequency domain strip theory to predict the heave and pitch responses of a containership and a very large crude carrier (VLCC) in regular head waves. The results of both ships agree well with the 3D frequency domain panel method and experimental data. Thus, the correctness and usefulness of the proposed approach are proved. We hope that this paper will serve as a motivation for other researchers to apply the MFS to various challenging problems in the field of ship hydrodynamics.     

快速多极多域虚边界元法解不同材料组合结构

将快速多极算法和广义极小残值法（GMRES）的基本思想运用于虚边界元法的方程求解中,并构造了多域组合问题虚边界元法的快速多极展开的实施思路,且将此方法用于不同材料组合结构问题的求解.采用此方法能够使得原问题方程组求解的计算耗时量和储存量降至与所求问题的计算自由度数成线性比例.数值算例验证了方法的可行性、计算精度和计算效率.     

混合动力轿车后舱热分析

热管理影响混合动力电动轿车的性能、安全和寿命,热分析为热管理提高了基础和依据.根据后舱关键部件的热特性以及车用环境,采用有限元方法对一混合动力电动轿车后舱的温度场进行了分析计算.通过试验验证了仿真的正确性,为热管理系统集成和优化提供了依据.     

Back-analysis of the response of shield tunneling by 3D finite element method

This paper presents a numerical back-analysis of the response of a shield tunnel during construction. An important issue in the construction of shallow tunnels, especially in soft ground conditions, is the surface settlement caused by shield tunneling. The tunnel test system with 10 m length, 7 m width and 6.7 m height, which was completed in China in 2009, is a research shield tunnel system. Using shield tunneling technique known as earth pressure balance (EPB) and slurry shield method, it could be excavated in a region consisting of original soft soils, such as silty clay, and different types of underlain soft soils. Based on the test results, the real-life tunnel response can be analyzed by back-analysis technique. The back-analysis technique is adapted to the three-dimensional finite element method (FEM). Parameter analyses are calibrated to study the behavior of the multi-scale diameter tunnel under various conditions. The suggested multi-scale model results show a well agreement between the prediction and the measurement.     

Asymmetric PCR method in generation of HBV ssDNA for pyrosequencing

Objective To explore the optimal primer ratio and concentration of asymmetric polymerase chain reaction (A-PCR) in producing hepatitis B virus (HBV) single-stranded DNA (ssDNA) for pyrosequencing. Methods A-PCR was carried out to generate HBV ssDNA with forward to reverse primers of different ratios (50 : 1, 100 : 1) and concentrations (13. 0 pmol/25μL and 0.14 pmol/25μL, 19. 5 pmol/25μL and 0. 21 pmol/25μL), and the product yield and quality were compared respectively. Results The forward to reverse primer ratio of 50 : 1 provided better yield and concentration of 19. 5 pmol/25μL and 0. 21 pmol//25μL generated a clearer band. Conclusion A simple and feasible method to produce HBV ssDNA for pyrosequencing in batch is established.     

Ship appearance optimal design on RCS reduction using response surface method and genetic algorithms

Radar cross section (RCS) reduction technologies are very important in survivability of the militarynaval vessels. Ship appearance shaping as an effective countermeasure of RCS reduction redirects the scatteredenergy from one angular region of interest in space to another region of little interest. To decrease the scatteringelectromagnetic signals from ship scientifically, optimization methods should be introduced in shaping design.Based on the assumption of the characteristic section design method, mathematical formulations for optimalshaping design were established. Because of the computation-intensive analysis and singularity in shapingoptimization, the response surface method (RSM) combined genetic algorithm (GA) was proposed. The poly-nomial response surface method was adopted in model approximation. Then genetic algorithms were employedto solve the surrogate optimization problem. By comparison RCS of the conventional and the optimal design,the superiority and effectiveness of proposed design methodology were verified.Ky words: radar cross section (RCS); characteristic section design method; response surface method; genetic algorithm (GA) was proposed. The polynomial response surface method was adopted in model approximation. Then genetic algorithms were employed to solve the surrogate optimization problem. By comparison RCS of the conventional and the optimal design, the superiority and effectiveness of proposed design methodology were verified.     

Time-series forecasting using autoregression enhanced k-nearest neighbors method

This study proposes two metrics using the nearest neighbors method to improve the accuracy of time-series forecasting. These two metrics can be treated as a hybrid forecasting approach to combine linear and non-linear forecasting techniques. One metric redefines the distance in k-nearest neighbors based on the coefficients of autoregression (AR) in time series. Meanwhile, an improvement to Kulesh’s adaptive metrics in the nearest neighbors is also presented. To evaluate the performance of the two proposed metrics, three types of time-series data, namely deterministic synthetic data, chaotic time-series data and real time-series data, are predicted. Experimental results show the superiority of the proposed AR-enhanced k-nearest neighbors methods to the traditional k-nearest neighbors metric and Kulesh’s adaptive metrics.     

CXCL12/CXCR4轴在胰腺癌-神经交互作用中的研究

目的本研究旨在阐述CXCLl2/CXCR4轴对胰腺癌神经相互作用的影响,探讨CXCLl2/CXCR4在胰腺癌嗜神经过程中的相关分子机制。方法体外培养胰腺癌Panc-1、Miapaca-2细胞,实验分为空白对照组、外源性CXCLl2组及CXCR4受体特异性阻断剂AMD3100组。采用RT-PCR检测胰腺癌细胞CXCR4及CXCL12mRNA的表达,检测基质金属蛋白酶-2(matrix metalloproteinase-2,MMP-2)、基质金属蛋白酶-9(matrix metalloproteinase-9,MMP-9)及人尿激酶型纤溶酶原激活物(human urokinase plasminogen activator,uPA)mRNA的表达;采用Transwell侵袭实验观察各实验组中细胞侵袭性的变化;提取大乳鼠脊髓背根神经节,建立胰腺癌细胞Miapaca-2与脊髓背根神经节(DRG)共培养模型,倒置显微镜成像系统动态观察不同实验组中神经轴突生长差异。结果胰腺癌细胞Panc-1、Miapaca-2细胞存在CXCR4mRNA的表达,而CXCL12mRNA无表达;两种胰腺癌细胞之MMP-2、MMP-9及uPAmRNA在AMD3100组、对照组、CXCLl2组中的表达差异具有统计学意义(P<0.01);Transwell细胞侵袭性实验中,外源性CXCLl2明显增强Panc-1、Miapaca-2细胞的侵袭性,而AMD3100有效抑制肿瘤细胞的侵袭能力,组间存在显著差异(P<0.05)。胰腺癌细胞与脊髓背根神经节共培养模型中,外源性CXCLl2明显增强神经轴突的生长,促使胰腺癌细胞与神经轴突接触,而AMD3100有效抑制神经轴突生长及与肿瘤细胞接触;细胞共培养144h后各组神经生长轴突数差异有统计学意义(P<0.01)。结论 CXCLl2/CXCR4一方面增强胰腺癌细胞的侵袭能力,促进胰腺癌细胞神经浸润;另一方面,神经元与施万细胞等构成神经纤维分泌CXCL12并通过化学趋化作用,诱导表达CXCR4的胰腺癌细胞向神经迁移,导致神经浸润的发生。