中国城镇化的地域非均衡及其动态演进——来自基尼系数及核密度估计的经验证据

基于中国1995-2013年省域数据,采用基尼系数及其分解、核密度估计方法,从人口和土地城镇化入手,系统分析了中国城镇化的地域非均衡及其动态演化规律。结果发现,1.中国人口和土地城镇化分布均呈现出由东往西逐渐降低的规律,城镇化非均衡主要体现在土地城镇化,而人口城镇化则未出现明显分异。2.全国尺度人口城镇化基尼系数随时间不断下降,城镇化非均衡逐渐减小;土地城镇化基尼系数则呈倒"U"型,城镇化非均衡先增后减。3.东中西三大区域内人口城镇化基尼系数均呈直线下降,区域间非均衡东部最大,西部次之,中部最小;土地城镇化非均衡则是东部大于中部和西部,但近年来西部已超过东部。4.人口城镇化非均衡在1995-2001年间主要来自地区间重叠,而后2002-2013年主要由地区间差异驱动;土地城镇化非均衡则主要来源于地区间差异。5.核密度估计显示人口城镇化增速较快,波动较小,而土地城镇化则极化趋势明显,波动较大。新型城镇化的协调推进宜从人口和土地城镇化两方面着手,特别要注意土地城镇化的失衡发展问题。     

Spatial distance and mobile business social network density

Following the increasing adoption of mobile communication, scholars have shown interest in the role of place on the structure of mobile social networks. The purpose of this study is to investigate the association between spatial distance and the closure and diversity of businesses mobile social networks. We used a database that aggregates actual mobile communication patterns of business users of a large Israeli cell phone company (n?= 16,199). Our findings, among a large sample of businesses, provide support for the place and mobile communication perspective. The results reveal a negative association between spatial distance and mobile business communication networks. As spatial distance between business network members increases, business social ties through mobile communication decreases. Furthermore, the results also revealed a negative association between spatial distance and mobile network density. As the spatial distance between business users increases, the density of the mobile communication network diminishes. Physical proximity promotes the development of dense business networks. The implications of the findings are discussed.     

Kernel density estimation on the torus

Kernel density estimation for multivariate, circular data has been formulated only when the sample space is the sphere, but theory for the torus would also be useful. For data lying on a d-dimensional torus (d?1), we discuss kernel estimation of a density, its mixed partial derivatives, and their squared functionals. We introduce a specific class of product kernels whose order is suitably defined in such a way to obtain L₂-risk formulas whose structure can be compared to their Euclidean counterparts. Our kernels are based on circular densities; however, we also discuss smaller bias estimation involving negative kernels which are functions of circular densities. Practical rules for selecting the smoothing degree, based on cross-validation, bootstrap and plug-in ideas are derived. Moreover, we provide specific results on the use of kernels based on the von Mises density. Finally, real-data examples and simulation studies illustrate the findings.     

Lower Risk Bounds and Properties of Confidence Sets for Ill‐Posed Estimation Problems with Applications to Spectral Density and Persistence Estimation,Unit Roots,and Estimation of Long Memory Parameters

Important estimation problems in econometrics like estimating the value of a spectral density at frequency zero, which appears in the econometrics literature in the guises of heteroskedasticity and autocorrelation consistent variance estimation and long run variance estimation, are shown to be “ill‐posed” estimation problems. A prototypical result obtained in the paper is that the minimax risk for estimating the value of the spectral density at frequency zero is infinite regardless of sample size, and that confidence sets are close to being uninformative. In this result the maximum risk is over commonly used specifications for the set of feasible data generating processes. The consequences for inference on unit roots and cointegration are discussed. Similar results for persistence estimation and estimation of the long memory parameter are given. All these results are obtained as special cases of a more general theory developed for abstract estimation problems, which readily also allows for the treatment of other ill‐posed estimation problems such as, e.g., nonparametric regression or density estimation.     

风险资产组合的均值—M有效前沿及其实证分析

本文基于由Carlo Acerbi(2002)提出的一类一致性风险度量—谱风险测度M,给出了谱风险测度的一些性质及构造谱密度的一种具体形式;重点讨论了正态情形下风险资产组合的均值—M有效前沿,探讨了其经济含义,并与经典的均值—方差有效前沿进行了对比研究,获得了若干深入的结果。由于期望短缺ES是特殊的谱风险测度,因此其对应的有效前沿是本文结果的特例。最后,本文利用前面的结论对深市和沪市的风险资产组合的均值—M有效前沿作了实证分析。     

芽胞杆菌在南美白对虾高密度养殖中的应用

以南美白对虾为研究对象,研究了芽胞杆菌制剂在低盐度水体对虾高密度养殖生产中对水质的改良效果．结果表明：间隔7d给试验虾塘泼洒0．8g／m^3剂量的芽胞杆菌,在相同的养殖条件下,池水氨氮（NH3-N）、亚硝酸盐（NO2-N）含量以及COD值、BOD值,较对照池均显著降低,对虾养成时的存活率较对照池提高．这说明芽胞杆菌应用于对虾生产可明显改善水质,优化池塘生态条件,减少痛害发生,提高养殖效益．     

一种精确测量周期信号参数的窗口和内插算法

提出了一种基于离散傅里叶变换的改进的周期信号参数的测量算法。该算法通过对时域信号加合适的窗函数,并在频域采用相应的内插算法,可以有效地减小测量过程中信号的频谱泄漏,得到精确的测量结果。仿真实验通过与已有算法的比较证明了该方法的有效性和先进性;噪声分析实验证明了该方法的稳定性。     

《霍小玉传》两个英译本的翻译风格——基于语料库的研究

使用语料库语言学方法对<霍小玉传>两个英译本的译者风格进行了研究.使用语料库检索分析软件WordSmith,对两个英译本以及作为对比使用的英语本族语语料库中的平均词长、词汇密度和文本可读性等多方面数据做了统计和对比.同时,还将定量研究与定性研究相结合,运用相关翻译理论对两个译本中的翻译实例进行对比分析,得出了两个译本译者在翻译风格上的特点.基于语料库的译者风格实证性研究具有科学性,因此其研究结果可以为翻译批评提供可靠的依据,也可用于翻译教学和译者培训中.     

城镇化、水资源消耗的动态演进与门槛效应

基于中国30个省市1998—2015年面板数据,综合利用核密度估计函数、非动态面板门槛回归模型系统考察城镇化与水资源消耗的动态演进过程和非线性关系。研究结果表明:（1）全国城镇化率呈两极分化态势,东部、中部、西部三大区域间城镇化受经济发展等因素影响而存在差异;全国水资源消耗得到控制,但东部、中部、西部水资源消耗高的省份存在增加趋势。（2）全国城镇化对水资源消耗影响存在显著的经济发展和居民收入门槛,并具有显著的抑制效应;东部经济发展门槛具有抑制效应,中部居民收入门槛具有促进效应;西部门槛效应与全国相同,且经济发展抑制作用阶段性增强。（3）居民收入、资本存量、人力资本与水资源消耗正相关,而经济发展与之负相关。     

The product <Emphasis Type="Italic">t</Emphasis> density distribution arising from the product of two Student’s <Emphasis Type="Italic">t</Emphasis> PDFs

The Student’s t distribution has become increasingly prominent and is considered as a competitor to the normal distribution. Motivated by real examples in Physics, decision sciences and Bayesian statistics, a new t distribution is introduced by taking the product of two Student’s t pdfs. Various structural properties of this distribution are derived, including its cdf, moments, mean deviation about the mean, mean deviation about the median, entropy, asymptotic distribution of the extreme order statistics, maximum likelihood estimates and the Fisher information matrix. Finally, an application to a Bayesian testing problem is illustrated.