梯度嵌入与数字反哺：数字乡村建设中新农人的数字转化逻辑

作为乡村振兴的战略方向,数字乡村建设的讨论往往突出自上而下的数字构建,常常忽视自下而上的数字转化,因而也就难以解释“脱嵌与嵌入共存,赋能与祛能相生”的建设悖论。以数字新农人作为研究对象,探讨数字乡村建设的后半篇文章,理解数字转化的内在逻辑。研究发现：从流量竞争到公益反哺,数字嵌入乡村的程度不断加深并呈现梯度特征。数字在文化编码与行动反哺的推动下,逐步从“作为流量的数字”向“作为文化的数字”“作为发展的数字”“作为公益的数字”转化。数字的不断转化,使作为政策的数字乡村建设不断向下扎根,从而实现数字对乡村的反哺。     

A gradient Markov chain Monte Carlo algorithm for computing multivariate maximum likelihood estimates and posterior distributions: mixture dose-response assessment

Multivariate probability distributions, such as may be used for mixture dose‐response assessment, are typically highly parameterized and difficult to fit to available data. However, such distributions may be useful in analyzing the large electronic data sets becoming available, such as dose‐response biomarker and genetic information. In this article, a new two‐stage computational approach is introduced for estimating multivariate distributions and addressing parameter uncertainty. The proposed first stage comprises a gradient Markov chain Monte Carlo (GMCMC) technique to find Bayesian posterior mode estimates (PMEs) of parameters, equivalent to maximum likelihood estimates (MLEs) in the absence of subjective information. In the second stage, these estimates are used to initialize a Markov chain Monte Carlo (MCMC) simulation, replacing the conventional burn‐in period to allow convergent simulation of the full joint Bayesian posterior distribution and the corresponding unconditional multivariate distribution (not conditional on uncertain parameter values). When the distribution of parameter uncertainty is such a Bayesian posterior, the unconditional distribution is termed predictive. The method is demonstrated by finding conditional and unconditional versions of the recently proposed emergent dose‐response function (DRF). Results are shown for the five‐parameter common‐mode and seven‐parameter dissimilar‐mode models, based on published data for eight benzene–toluene dose pairs. The common mode conditional DRF is obtained with a 21‐fold reduction in data requirement versus MCMC. Example common‐mode unconditional DRFs are then found using synthetic data, showing a 71% reduction in required data. The approach is further demonstrated for a PCB 126‐PCB 153 mixture. Applicability is analyzed and discussed. Matlab^® computer programs are provided.     

新疆高等教育对区域经济发展的适应性分析——以高教发展规模、速度为视角

高等教育发展的规模、速度对经济发展的适应性是判断高等教育发展适应性的重要方面。该文通过对新疆高等教育和全国高等教育的相关指标分析,认为新疆高等教育发展规模偏小、速度较慢,不适应新疆区域的经济发展。     

英语成分感知凸显

英语成分感知凸显分为结果和过程,产生其凸显有可能性和必要性。该过程的主要途径有:语境作用;形成并增强要凸显的语言成分与其语境之间的刺激梯度,这主要依赖于产生异质性和突变、给语言接受者直接提醒、提出特定的任务要求、满足其需要、提高同一个语言成分的刺激密度;特定的语法手段。英语成分感知凸显有重要的美学、社会学和心理学意义。     

修正共轭梯度恒模阵列算法研究

提出一种基于修正共轭梯度算法的恒模(MCG-CMA)盲干扰抑制算法,该算法将修正共轭梯度方法引入到恒模算法中,克服了传统恒模算法收敛缓慢、LS-CMA运算量大的缺点,保留了较好的计算复杂度和数值稳定性,理论推导了算法失调量的显式表达式。仿真结果表明该算法不需要波达方向估计,与传统的LS-CMA算法、SCG-CMA算法相比,具有较好的收敛性能和输出信干噪比(SINR)。     

A conceptual framework for the study of human ecosystems in urban areas

The need for integrated concepts, capable of satisfying natural and social scientists and supporting integrated research, motivates a conceptual framework for understanding the role of humans in ecosystems. The question is how to add humans to the ecological models used to understand urban ecosystems. The ecosystem concept can serve as the basis, but specific social attributes of humans and their institutions must be added. Learning and feedback between the human and natural components of urban ecosystems are key attributes of the integrated model. Parallels with familiar ecological approaches can help in understanding the ecology of urban ecosystems. These include the role of spatial heterogeneity and organizational hierarchies in both the social and natural components of urban ecosystems. Although urban watersheds are commonly highly altered, the watershed approach can serve as a spatial basis for organizing comparative studies of ecosystems exhibiting differing degrees of urbanization. The watershed concept can also spatially organize the hierarchically scaled linkages by which the integrated human ecosystem model can be applied. The study of urban ecosystems is a relatively new field, and the questions suggested by the integrated framework can be used to frame ecosystem research in and associated with urban and metropolitan areas.     

OPTIMIRUS. Simulating Population Change in the Russian Far East

This article examines the population trends in the cities of the Russian Far East between the two census years 1989 and 2002. Three geographical models – Rank-Size Rule, Temperature per Capita and a simple gravity model – are used to describe the direction of these population trends. An economic efficiency function is constructed from the three models to simulate an ideal population distribution for the Russian Far East. The heart of the simulation is a conjugate gradient optimisation of the economic efficiency function. The results serve as an important backdrop to discussions of current population trends and serve as an important backdrop to discussions of current population trends and as basis for recommendations concerning future changes in the spatial distribution of population in the region.Mueller, K., et Bradshaw M. J., 2006. OPTIMIRUS. Une simulation des variations de population dans l’Extrême-Orient russe. Revue européenne de démographie, 22:105–126.     

基于梯度法的OD矩阵估计和应用研究

以交通规划软件EMME／2为平台，在拥有合理的原始矩阵和一定数量的路段实测流量数据的基础上，运用梯度法(最速下降法)求出OD矩阵估计．结合具体的课题研究应用情况，证明该方法适用于大规模实际路网．     

基于小波神经网络的基建投资预测研究

基建投资预测是基建部门急需解决的问题之一,本文在分析已有预测技术的基础上,建立了相应的小波神经网络模型。运用历年天津市基建投资数据进行实证研究,为政府相关部门编制基建投资的规划提供有效的理论支持。     

Partially projected gradient algorithms for computing nonparametric maximum likelihood estimates of mixing distributions

There exist primarily three different types of algorithms for computing nonparametric maximum likelihood estimates (NPMLEs) of mixing distributions in the literature, which are the EM-type algorithms, the vertex direction algorithms such as VDM and VEM, and the algorithms based on general constrained optimization techniques such as the projected gradient method. It is known that the projected gradient algorithm may run into stagnation during iterations. When a stagnation occurs, VDM steps need to be added. We argue that the abrupt switch to VDM steps can significantly reduce the efficiency of the projected gradient algorithm, and is usually unnecessary. In this paper, we define a group of partially projected directions, which can be regarded as hybrids of ordinary projected gradient directions and VDM directions. Based on these directions, four new algorithms are proposed for computing NPMLEs of mixing distributions. The properties of the algorithms are discussed and their convergence is proved. Extensive numerical simulations show that the new algorithms outperform the existing methods, especially when a NPMLE has a large number of support points or when high accuracy is required.