基于形式化B方法的因子网络模型构建探讨

形式化方法中的B方法与B语言在工业领域获得了广泛的应用,将其用于因子网络模型构建中,可以有效提高模型的正确性。基于此,笔者从形式化方法、B方法以及因子网络的概念入手,分析了传统因子网络模型的弊端,然后提出了基于形式化B方法的因子网络模型,最后对该模型系统的分析与描述、验证以及模拟仿真流程进行了阐述,意在为相关人员构建因子网络模型提供帮助。

基于交通因子状态网络的城市交叉口交通流预测

信息技术的快速发展,为交通研究和城市交通管理提供了大规模、多样化的数据资源,并为城市交通状态估计和交通流预测方法的研究提供了有力支持。将城市交叉口视为一个微观交通系统,采用数据驱动与领域知识结合的方式,建立微观层次的交通因子状态网络模型(Traffic Factor State Network, TFSN),考察交通因素之间的相互关联,并考虑环境因素的影响。该模型结合交通因子和环境影响因子的影响,通过对交通流数据进行聚类分析,估算出对应于环境影响因子的交通状态,并通过实际案例验证其物理意义以及与交通流实际状态的对应关系。进一步地,基于不同交通状态下的交通流数据建立高阶多元马尔可夫链,进行交通流预测,并根据交通流时间序列的聚类性能指标提高模型的预测准确性。对数据序列马氏性强弱、马尔可夫模型阶数与模型预测准确性之间关系进行分析。研究结果表明:根据马氏性合理选择马尔可夫模型的阶数可以提升模型预测准确性;直接对原始交通流数据进行预测的平均绝对百分比误差为24.61%,而不同交通状态下交通流预测的平均绝对百分比误差为16.99%,相比直接预测误差下降了7.62%,验证了所提出的微观交通因子状态网络的有效性和可用性。

Pore-scale simulation of gas-water flow in low permeability gas reservoirs

A novel method was developed to establish a realistic three dimensional(3D) network model representing pore space in low permeability sandstone.Digital core of rock sample was established by the combination of micro-CT scanning and image processing,then 3D pore-throat network model was extracted from the digital core through analyzing pore space topology,calculating pore-throat parameters and simplifying the shapes of pores and throats.The good agreements between predicted and measured porosity and absolute permeability verified the validity of this new network model.Gas-water flow mechanism was studied by using pore-scale simulations,and the influence of pore structure parameters,including coordination number,aspect ratio and shape factor,on gas-water flow,was investigated.The present simulation results show that with the increment of coordination number,gas flow ability in network improves and the effect of invading water on blocking gas flow weakens.The smaller the aspect ratio is,the stronger the anisotropy of the network is,resulting in the increase of seepage resistance.It is found that the shape factor mainly affects the end points in relative permeability curves,and for a highly irregular pore or throat with a small shape factor,the irreducible water saturation(Swi) and residual gas saturation(Sgr) are relatively high.

EXPRESSION OF PEDF mRNA AND PROTEIN IN NORMAL MOUSE RETINA AND EXPERIMENTAL CHOROIDAL NEOVASCULARIZATION TISSUES

Objective To study the expression of pigment epithelium derived factor (PEDF) in normal mouse retina and experimental choroidal neovascularization (CNV) tissues. Methods CNV mouse models were induced by diode laser. The expression of PEDF mRNA and protein in normal mouse retina and CNV tissues were detected by in situ hybridization and immunohistochemical study. Results In normal mouse retina, PEDF mRNA was observed in the ganglion cell layer, inner nuclear layer and RPE cell layer, and PEDF protein was observed mainly in the nerve fiber layer, ganglion cell layer, photoreceptor cell layer and RPE cell layer, and lower level expression of PEDF protein was also observed in the inner plexiform layer and outer plexiform layer. In CNV tissues, the expression of PEDF mRNA and protein was also observed. 3d and 1 week after photocoagulation, the expression level of PEDF was relatively lower, and increased following the development of CNV. The level was the highest 2 weeks after photocoagulation, then decreased at 3 weeks. Conclusion PEDF was expressed in different layers of retina and was obviously expressed in the CNV tissues induced by laser photocoagulation. These findings suggest that PEDF may participate and modulate the development of CNV.