连锁企业的物流配送问题研究——以国美物流为例

针对我国连锁企业的配送现状及问题,比较分析目前四种主要配送模式的特点,并通过国美物流配送的实例分析,得出我国连锁企业长远发展的几点建议。     

逆向物流中基于均匀分布的库存控制策略研究

库存管理是逆向物流的重要研究内容。假定销售商允许顾客退货,退回物品可如新以原价卖出,且顾客的需求与退货均服从独立的均匀分布;在此条件下,提出了一个最优订货模型,并进行了求解分析。研究结果表明,退货率对销售商的订货数量和期望收益都有影响,销售商应采取有效的措施尽量降低退货率。     

刍议工程招标中拦标价的设立

针对目前工程量清单招标项目中设立拦标价的做法是否合法合理,以及如何准确计算拦标价仍存在一定的争议。论述了拦标价设立的目的、作用、法规依据和造价依据以及拦标价在应用中存在的一些问题,提出了一种基于概率论的知识来确定拦标价上浮比例的方法,并指出拦标价在招标和评标应用中需要注意的问题。     

连锁超市生鲜加工配送中心的物流绩效评价

分析了连锁超市生鲜加工配送中心的定位,建立了连锁超市生鲜加工配送中心物流绩效评价体系;并选取模糊综合评价法对其进行综合评价。     

Fractals in trade duration: capturing long-range dependence and heavy tailedness in modeling trade duration

Several studies that have investigated a few stocks have found that the spacing between consecutive financial transactions (referred to as trade duration) tend to exhibit long-range dependence, heavy tailedness, and clustering. In this study, we empirically investigate whether a larger sample of stocks exhibit those characteristics. We do so by comparing goodness of fit in modeling trade duration data for stable distribution and fractional stable noise based on a procedure applying bootstrap methods developed by the authors with several alternative distributional assumptions in modeling trade duration data. The empirical results suggest that the autoregressive conditional duration model with stable distribution fits better than other combinations, while fractional stable noise itself fits better for the time series of trade duration. Our result is consistent with the general findings in the literature that trade duration is informative and that short trade durations move prices more than long trade duration. In addition, our result confirms the advantage of fractal models in the study of roughness in trade duration and provides some evidence for duration dependence. S. Rachev’s research was supported by grants from the Division of Mathematical, Life and Physical Science, College of Letters and Science, University of California, Santa Barbara, and the Deutschen Forschungsgemeinschaft. W. Sun’s research was supported by grants from the Deutschen Forschungsgemeinschaft. P.S. Kalev’s research was supported with a NCG grant from the Faculty of Business and Economics, Monash University. Data are supplied by Securities Industry Research Center of Asia-Pacific (SIRCA) on behalf of Reuters. The first draft of this paper was presented at the International Conference on High Frequency Finance 2006; the authors would like to thank the conference participants for their valuable comments.     

草原荒漠区红砂和珍珠猪毛菜群落分布特征分析

为探究影响红砂和珍珠猪毛菜群落空间分布的主要环境因子,采用点格局分析方法和冗余分析(RDA),分析了植物种的空间分布格局及其与环境因子之间的关系。研究结果显示：多年平均降水量的减少地点,红砂种群、珍珠猪毛菜种群的空间聚集程度减弱,向随机分布趋势转化,表现出种内促进关系逐渐减弱的适应策略;种间关联性也表现出随降水的减少物种之间的促进关系逐渐减弱。消除生境异质性后,红砂种群、珍珠猪毛菜种群均在>30 m尺度下随机分布,种群内部表现为相互独立;空间关联性整体均呈现为负相关,种间关系表现为相互竞争,降水减少的地点存在向无相关性转变的趋势。利用冗余分析识别出导致群落植被特征产生差异的主要因素是气候、土壤、海拔,因此在制定更为有效的荒漠灌木多样性保育措施时不仅要考虑植被本身的特性,也要加强对荒漠土壤环境的保护。     

Analysis of the correlations between environmental factors and rare cranes in the Poyang Lake region of China

Using survey data during 2001–2013 from a total of 38 lakes in the Poyang Lake region of China, we analyzed the inter-annual change in crane populations and the spatial distribution of crane species. Across the study sites, the total crane population was 6400 ± 2620 individuals during the period 2001–2013. Crane populations varied widely across the study sites: the largest crane population was observed on Bang Lake with an annual average of 2373, followed by Qi Lake, Dacha Lake, and Zhu Lake. The four main crane species, which were active on 50–80% of study lakes during the period of investigation, were G. leucogeranus, G. monacha, G. vipio, and G. grus. In particular, G. leucogeranus, G. monacha, and G. vipio were observed mainly in Poyang Lake National Nature Reserve and nearby lakes. G. grus was mostly observed in Poyang County. The largest populations of G. leucogeranus, G. vipio, and G. monacha were observed on Bang Lake, with annual averages of 1229, 985, and 88 birds, respectively. The largest G. grus population was observed on Qi Lake, with an annual average of 756 birds. We found that habitats for G. leucogeranus, G. monacha, and G. vipio were defined by similar environmental factors. In particular, increasing distance from roads had a positive impact on populations of these three species. By contrast, sedimentary total phosphorus content showed negative correlations with populations of all four main crane species, which implied that eutrophication could pose a threat to these rare crane species.     

基于高维Gaussian Copula函数的区域农田灌溉需水分析

以广东省农田灌溉需水为例,构建了分区降水的8维联合分布模型,提出了给定全省降水频率的全省及分区农田灌溉需水分析思路,采用同频、典型年和最大权函数3种方法对区域需水、分区降水频率及需水进行了分析计算和对比。结果显示:Gaussian Copula函数能够很好地模拟广东省8个分区年降水联合分布,单变量最优分布主要为广义极值分布和广义正态分布。3种方法之间的全省农田灌溉需水相差甚小,但是各分区需水差别相对较大。典型年法推求的分区降水频率差异最明显,最大权函数法推求的大部分分区降水频率处于同频位置附近,其中分区Ⅷ的降水频率在特枯和特丰时明显偏离同频位置,而且其置信区间范围明显大于其它分区,表明分区Ⅷ不确定性更大。由于基于高维Copula函数联合分布模拟既考虑了分区降水的独立分布,又考虑了它们之间的相依性,而且能够给出分区需水的置信范围,因此认为最大权函数法推求区域农田灌溉需水更为合理。     

基于Bayes理论的田间层状土壤水分运动参数识别及不确定性分析

土壤水分运动参数是非饱和带水分及污染物运移研究的核心参数,根据点尺度土壤样本的室内稳态试验得到的水分运动参数往往不能准确反映天然条件下田间尺度土壤水分运动特征。本文基于为时2年的田间土壤含水量观测数据(2013年为率定期,2014年为验证期),通过土壤转换函数得到了VGM(van Genuchten-Mualem)模型水力参数的先验分布,建立了反演层状土壤持水和导水特征的贝叶斯模型,采用自适应差分演化(DREAMZS)的采样方法,结合Hydrus_1d模型,对田间尺度土壤水分含量预测模型进行优化及不确定性分析,获得了水分特征参数的后验分布,分析了最优参数组的模拟效果及模型预测的95%的置信区间。结果表明,基于DREAMZS采样的Bayes方法可以实现田间尺度层状土壤水分特征参数的率定及土壤水分动态的模拟预测。率定结果显示饱和导水率Ks最不敏感,饱和含水量θs最为敏感,可识别性较高,室内试验反演得到θs可用于田间土壤水分运动的模拟。随着土壤含水量模拟深度的增加,PUCI(单位平均相对宽度所包含的实测点数据比例)值越大,模型预测的性能越高。模拟结果的不确定性主要由模型结构所引起,所以对模型结构的修改完善是未来提高模型预测的关键。     

整流罩在泵站肘形进水流道中的应用效果分析

肘形进水流道广泛应用于大型低扬程泵站,其弯曲段的内侧与外侧曲率半径相差较大,故流道出口存在较严重的流动不均匀性,从而影响泵站工作效率。针对此问题,本文设计了一种装在肘形进水流道末端的整流罩,并采用计算流体力学方法对传统肘形进水流道和加装整流罩的进水流道进行了对比分析。研究发现,传统肘形进水流道在弯曲段内,内侧流速比外侧流速高28.4%。在进水流道末端加装整流罩之后,进水流道出口速度分布均匀度基本保持不变,但设计工况下出口水流平均偏流角由原来的13.1°减小至4.3°,降低70%以上,水泵扬程增加2.3%,水泵效率增大2.5%。上述结果表明,整流罩在减小了进水流道出口水流平均偏流角之后,使水泵进口流态得到改善,从而降低了泵内流动损失,提高了水泵扬程和效率。该项研究工作对改善大型泵站水力设计,提高泵站运行效率具有参考价值。