A spatio-temporal analysis of academic performance at the Basic Education Certificate Examination in Ghana

Over the last decade, Ghana has more than tripled investment in its basic education system. Consequently, the country has made huge educational gains, primarily in providing universal access to basic education. However, many stakeholders are worried that academic performance is lagging because of disproportional attention to accessing basic education. Discussion of these concerns is hampered by ongoing disagreement about the true trajectory of academic performance at the basic education level and the widespread nature of students' lagging academic performance. In part, this disagreement stems from the failure of empirical studies to comprehensively examine trends in academic performance standards at the basic education level by concurrently considering a geographical and longitudinal perspective. Thus, this study examines the spatio-temporal trends of academic performance at the junior high school level since 2009 by using multilevel growth curve modeling, spatial statistics, and district-level longitudinal data. Results reveal 3 statistically distinct trajectories of academic performance: erratic, accelerating, and decelerating changes. Results also show that rural–urban gaps explain 31% of the performance trajectories, a trend which is expected to persist in the long term. In addition, we find extreme variations in academic performance within rural areas. Given the varying trajectories and geographical variability in academic performance, we suggest a localized approach to addressing challenges of low academic achievement at the basic education level in Ghana.     

环境库兹涅茨曲线在文山县城的应用

环境库兹涅茨曲线认为随着经济发展，环境质量先下降后改善，环境质量与收入之间表现为倒U形曲线，这意味着经济发展最终会解决环境问题。应用这一思想，根据1991～2000年文山县城区大气污染指数及1998～2002年盘龙河水污染物浓度与同期人均居民收入进行了回归分析，发现对多数污染物而言，表现为N形的高次曲线能很好的拟合两者之间的关系，据此提出一种简单但普遍的机理来解释EKC曲线，即经济发展对环境质量的正负反馈作用决定其在涨落中演变。     

基于空间公平理论的公共交通服务评价——以深圳市为例

使用空间无关的公平性衡量指数评价公交服务时,会忽视公交服务需求与供给的空间分布特征.为解决此问题,论文提出基于空间公平理论的公交服务评价框架,即通过构建综合基尼系数与莫兰指数的空间公平评价方法,实现整体尺度公交服务评价;通过对分析单元上相对需求与相对供给变量的匹配关系、空间差距进行分析,实现局部尺度公交服务评价,对整体...     

国家需求结构演变理论及其应用——以中俄北极合作为例

首先,提出国家需求概念,在总结国家需求结构及其演变特点的基础上,提出双边关系中国家需求结构演变的三个模型：相对稳定型、合作优化型、关系紧张型。认为国家需求和人的需求一样,存在由低层次向高层次跃升的演变趋势。“低层次需求得到满足”是需求层次升级的前提条件,但这种满足具有方向性、主观性、阶段性。其次,运用国家需求结构演变模型分析了中俄北极开发合作的地缘政治环境,提出了维持中俄北极合作良好态势的对策建议：美国是中俄北极合作发生变数的能动力量,妥善处理好中美关系是重中之重;政治互信是中俄北极合作的决定性因素,加强双方在国际关系理论研究领域的合作是行之有效的政策工具;提高合作项目的透明度,向国际社会分享项目对生态环境和原住民影响的相关数据;加强战略沟通扩大共同利益,维持与美国盟友的合作伙伴关系;作为非北极国家,中国应该坚持对北极事务“有所为有所不为”的原则。最后,本研究得出如下几点结论：国家需求结构演变理论能够解释西方国际关系理论三大学派的核心观点;双边国家需求结构演变模型关注国际关系发生突变的规律性;国家需求结构演变理论能够为不同层次不同规模国家制定外交政策提供理论参考。     

Multivariate adaptive regression splines for estimating riverine constituent concentrations

Regression-based methods are commonly used for riverine constituent concentration/flux estimation, which is essential for guiding water quality protection practices and environmental decision making. This paper developed a multivariate adaptive regression splines model for estimating riverine constituent concentrations (MARS-EC). The process, interpretability and flexibility of the MARS-EC modelling approach, was demonstrated for total nitrogen in the Patuxent River, a major river input to Chesapeake Bay. Model accuracy and uncertainty of the MARS-EC approach was further analysed using nitrate plus nitrite datasets from eight tributary rivers to Chesapeake Bay. Results showed that the MARS-EC approach integrated the advantages of both parametric and nonparametric regression methods, and model accuracy was demonstrated to be superior to the traditionally used ESTIMATOR model. MARS-EC is flexible and allows consideration of auxiliary variables; the variables and interactions can be selected automatically. MARS-EC does not constrain concentration-predictor curves to be constant but rather is able to identify shifts in these curves from mathematical expressions and visual graphics. The MARS-EC approach provides an effective and complementary tool along with existing approaches for estimating riverine constituent concentrations.     

测井解释中煤层含气量评价方法对比研究

随着煤层气勘探的不断深入,对煤层含气量预测精度提出了更高的要求。基于煤层含气量测井响应特征,分析测井参数与含气量的相关性,提出MIV（Mean Impact Value）技术与LSSVM（Least Squares Support Vector Machine）结合的测井参数优选策略,优选最优测井参数作为网络建模的输入自变量组合,通过粒子群算法优化LSSVM网络核心参数,最后构建一套适用于煤层含气量预测的MIV-PSO-LSSVM模型。在此基础上,分别对比分析LSSVM、PSO-LSSVM、MIV-LSSVM和MIV-PSO-LSSVM模型对煤层含气量的预测性能,并与传统多元回归方法进行了对比,利用拟合优度和均方根误差对此5类模型进行评价。结果表明：PSO优化下的LSSVM模型预测精度得到有效提升,结合MIV方法优选测井参数可大幅度改善神经网络建模性能,MIV-PSO-LSSVM模型可实现煤层含气量高精度预测,为煤层气勘探及其储层评价提供新的技术支撑,且本研究的建模策略及思想可广泛应用于其他机器学习建模研究领域。     

Modelling load–displacement response of driven piles in cohesionless soils under tensile loading

A new methodology for deriving the uplift load–displacement response of long driven piles in cohesionless soils is proposed. This method accounts for the effects of the friction fatigue processes during pile driving and the existence of locked-in residual stresses at the end of pile driving before commencing the pile load test. A hyperbolic formulation is utilized to simulate the nonlinear load transfer curves (the so-called t–z curves). The utility of this technique is demonstrated for a field pullout load test on a driven pile in sand. Predicted and measured load–displacement curves showed good agreement, indicating that this approach yields reasonable results as long as representative input parameters are employed.     

地震多属性拟测井多参数反演预测煤层顶底板岩石赋水性研究

通过实例介绍利用地震多属性与测井成果联合反演,获得表征煤层顶底板岩石赋水性强弱的拟测井参数体,进而对其进行赋水性分析：首先利用伽马-伽马测井及视电阻率曲线重构岩石视孔隙度曲线,以获得研究区岩石视孔隙度成果;利用测井成果合成地震记录进行精细的地震地质层位标定及采区地震数据的保幅、保真处理;在测井成果约束下进行地震多属性拟测井多参数反演,利用反演成果的高低异常区评价煤层顶底板赋水强弱分区——低波阻抗、低电阻率、高孔隙度分布的区域对应赋水性强的区域,反之为赋水性弱的区域。