Heteroscedasticity-robust estimation of autocorrelation

This paper proposes estimators of the first-order autocorrelation that are based on suitably transformed ratios of successive observations. The new estimators are given by simple functions of the observations. Numerical optimization is not required. Simulations show that they are highly robust against extreme values and clusters of high volatility and are therefore particularly useful for the estimation of serial correlation in return series. Besides, the results of the simulation study also call into question the common practice of correcting the small-sample bias of conventional estimators.     

Locative Mobile Social Networks: Mapping Communication and Location in Urban Spaces

Abstract

This study conceptualizes the new spatial logic created by the social use of location aware mobile technologies, analyzing how mobile communities are formed by the mapping of social networks in urban spaces. It explores two main areas with the goal of understanding how locative mobile social networks (LMSNs) challenge the traditional logic of networks. First, it conceptualizes LMSNs by comparing them to (1) traditional transportation and communication networks, and (2) mobile social networks (MSNs). Second, the paper discusses potential social implications of LMSNs, such as privacy, surveillance, and social exclusion.     

宁夏产业结构及其区位优势变化(1978～2003)

本文在已有的区位商分析方法基础上,提出了“产业综合区位商”概念,并以此作为衡量地区产业综合区位优势的尺度。借助于计量模型,分析了1978～2003年宁夏回族自治区六部门(农业、工业、建筑业、交通通讯业、商业、其他服务业)综合区位商变化趋势。结果如下:第一,宁夏产业综合区位商变化带有明显的阶段性特征。20世纪90年代初以来全面推行的市场化改革,提高了宁夏各产业部门的资源配置效率及其综合区位优势。第二,农村剩余劳动力向具有比较优势的非农产业转移,有利于优化地区产业结构。第三,各部门对宁夏产业综合区位优势变化有着不同的影响。建筑业影响力最大,其余依次是:其他服务业、农业、交通通讯业、商业、工业。工业的影响力最弱。如何加快工业化和工业部门优势产业的发展,是宁夏产业结构调整的关键。     

试论湘西民族地区交通经济带的评价与构建

本文从交通经济带的传统构成要素入手,对湘西民族地区交通基础设施、城镇综合实力、产业状况等进行了评价,提出了以民族文化为纽带构筑民族地区交通经济带的模式,认为该地区可以形成一纵一横两条沿路型经济子带,并提供具体设计思路。     

C型主轴端部短锥法兰式联接分析

关于短锥法兰式C型主轴端部与花盘等机床附件的联接定位问题,目前尚未有统一的解释和确切的结论.本文对此联接状态进行定位分析和尺寸分析,得出正确结论.     

Investigating the European perception of food using moments obtained from non-symmetrical correspondence analysis

The perception of food in Europe has been a topic of research for many years due to its importance in better understanding the role of food in helping to define the culture of a country. It is also important from a marketing perspective for identifying how consumers relate to food. Recently, this topic was discussed by Guerrero et al. (2010) who used a graphical statistical technique called correspondence analysis to identify the association between the countries that participated in the study and words that were linked with “Traditional” food. This paper explores the use of non-symmetrical correspondence analysis and provides an interpretation of the configuration of points in the graphical display in terms of its first four moments. In particular, we will focus on the skewness and kurtosis of such a configuration. Such measure's provide further detail on the nature of the association between the countries studied and the words linked with “Traditional” food.     

Heuristic Procedures for Practical-Sized Uncapacitated Location-Capacitated Routing Problems*

Facility location and vehicle routing are two important logistical problems closely interrelated in many real-world applications where locating facilities and determining the associated multi-stop vehicle routes are required simultaneously. Previous research has found that using the classical facility location models on these location-routing problems (LRPs) may lead to suboptimal solutions. We propose an approximate approach for the LRPs, which first generates and improves feasible location/allocation schemes with the associated multi-stop routing costs approximated using some route length estimators. We then design the minimum-cost routes based on the location/allocation results. We review two estimators that can provide accurate approximations to the multi-stop route distances; define the uncapacitated location-capacitated routing problem; and evaluate several heuristic procedures for approximately solving the problem. Computational results show that when vehicle capacities are not too restrictive, the sequential procedures that incorporate the two robust route length estimators can produce good solutions to practical-sized problems with a reasonable amount of computational efforts.     

The cost of not knowing the radius

Robust Statistics considers the quality of statistical decisions in the presence of deviations from the ideal model, where deviations are modelled by neighborhoods of a certain size about the ideal model. We introduce a new concept of optimality (radius-minimaxity) if this size or radius is not precisely known: for this notion, we determine the increase of the maximum risk over the minimax risk in the case that the optimally robust estimator for the false neighborhood radius is used. The maximum increase of the relative risk is minimized in the case that the radius is known only to belong to some interval [r _l ,r _u ]. We pursue this minmax approach for a number of ideal models and a variety of neighborhoods. Also, the effect of increasing parameter dimension is studied for these models. The minimax increase of relative risk in case the radius is completely unknown, compared with that of the most robust procedure, is 18.1% versus 57.1% and 50.5% versus 172.1% for one-dimensional location and scale, respectively, and less than 1/3 in other typical contamination models. In most models considered so far, the radius needs to be specified only up to a factor , in order to keep the increase of relative risk below 12.5%, provided that the radius–minimax robust estimator is employed. The least favorable radii leading to the radius–minimax estimators turn out small: 5–6% contamination, at sample size 100.      

流通厂商的空间区位决定及其投资选择

流通产业较之于制造业在许多方面有着异同点,当注重考察它们在空间区位决定上的相异之处时,我们就会追溯到对流通厂商投资选择的分析。本文把流通厂商以利润最大化为目标所采取的商业网点和仓储的布局、运输路线和商业业态等的规划,理解为流通产业的空间区位决定,而将流通厂商在这一决定过程中所采取的手段、步骤和谋略等,解释为流通厂商的空间区位决定过程中的选择。文章的分析脉络和着重点在很大程度上是把流通厂商的空间区位决定,看成是商业网点和仓储布局、要素流动、运输路线和商业业态等规划的函数,试图通过对这种函数关系的分析,揭示出流通厂商投资选择的一般行为,从而在理论上为政府规制政策的制定提供一些有价值的思路。     

唐代西受降城、天德军的置废和建制沿革考述

为了应对北方游牧民族的威胁,唐朝在河套地区先后修建了西受降城和天德军等两座军事城镇。两城设立之初,在唐朝的北疆防御体系中占有重要的地位。西受降城建成后不久即因水患而遭废弃并在旧址以东另筑新城,天德军也因在安史之乱中遭到破坏而一度被废弃并移至西受降城。后来设立天德镇专门负责河套西部地区的防务,其辖区几经变化,最后领有天德...