α—较多最优解的梯度特性

对于多目标规划的α—较多最优解,本文给出目标函数的梯度特性.     

宅基地城乡间流转研究——基于T县城镇化的调查简

T县宅基地流转市场不活跃,交易方式单一,交易价格偏低,与大城市周边农村地区宅基地交易市场的火热场面迥异。“同心圆梯度差”现象客观存在．城郊农村与偏远农村之间的差异不容忽视,偏远农村宅基地城乡间流转的条件尚不成熟。偏远农村地区宅基地向城市居民流转的渠道不畅通,相关政策和规定的限制、农村地区基础建设落后、熟人社会的排外意识、农村居民对房宅的惜售心理构成了宅基地流转的主要障碍。宅基地的使用价值优先于财产价值,保障作用重要于融资作用,宅基地城乡间流转的必要性不充分、效率性不显著。宅基地制度改革需稳妥推进．宅基地城乡间流转应以大城市周边农村地区为试点,从城郊农村向偏远农村逐步推进。同时,要借鉴土地发展权制度,对尚未实施宅基地城乡间流转政策的农村地区的居民予以补贴。对于宅基地所具有的财产价值,主要通过放开抵押、担保、出租等与宅基地的居住保障功能较为兼容的财产收益方式给予保障。     

A proposal for categorizing the severity of non uniform differential item functioning: The polytomous case

Abstract

Differential item functioning (DIF) is present when something about the characteristics of a test taker interferes with the relationship between ability and item response. Non uniform DIF (NUDIF) exists when there is interaction between ability level and group membership. The aim of this study is to propose guidelines to evaluate the severity of NUDIF, taking into account the family of Rasch models. The severity of NUDIF is evaluated trying to quantify the overall biasing impact of the presence in the test of NUDIF items, on the estimated measure of the latent trait of interest.     

位移边界对2D-FGM板热应力影响研究

考虑不同的位移边界条件,建立了常物性2D-FGM板研究模型,并采用有限元法,得到其冷却瞬态热应力场分布图形。位移边界条件对常物性2D-FGM平面区域冷却瞬态热应力分布影响颇大,在简支和一端固定情况下,2D-FGM板自由边界上的热应力σ_x=0;两端固定情况下,其左右两边界均形成上中下三个应力聚集,应力分布形状和数值都发生了巨大的变化;将四周均设置呈固定约束后,热应力数值增长幅度较两端固定情况时更为明显。此结果为该材料的设计、制备提供了准确的理论计算依据。     

Forest leaf litter quantity and seedling occurrence along an urban-rural gradient

Leaf litter, by modifying microenvironmental conditions, can alter plant population distributions and is considered to be a major force in structuring many plant communities. Comparative studies of urban, suburban, and rural forests in the New York City (NYC) metropolitan area have identified numerous biotic and abiotic differences among these forests, including several involved in leaf litter decomposition. These differences in decomposition among the forests could result in differences in litter quantity on the forest floor and hence microenvironmental conditions and safe sites for germination of different plant species. We conducted a survey of forest floor leaf litter quantity in forests located along an urban-to-rural land-use gradient originating in urban NYC and extending to rural Connecticut. Mean litter depth, mass, and density increased significantly with increased distance of the forest from NYC.We also surveyed woody seedlings and compared the litter depth in which they naturally occurred to the mean litter depth of the surrounding forest. Seedlings of small-seeded species were much more likely to be located in litter shallower than mean forest litter depth than were seedlings of large-seeded species. Taken together, these results suggest that environmental changes associated with urbanization may have profound effects on long-term patterns of forest regeneration.     

高知大龄未婚女性的婚恋问题浅析

在男女性别比居高不下。男性人口远远高于女性人口的当今中国,却出现了高知大龄未婚女性婚恋难问题,这一奇特的社会现象引起人们广泛的关注和热议。本文认为高知大龄未婚女性婚恋问题主要源于“结构性剩余”,在对高知大龄未婚女性婚恋难问题已有的多角度理论研究回顾的基础上．主要从人口与经济的视角对高知大龄未婚女性“结构性剩余”现象的原因进行深入发掘。最后提出一些解决问题的举措。     

用于RBF-SVM参数搜索的伪梯度动态步长算法

针对基于径向基核函数(RBF)的支持向量机(SVM)超参数选择问题,提出了一种基于差分方程的新算法——伪梯度动态步长算法。该算法根据径向基核函数的特点提出由训练集的空间特性确定的核参数搜索范围,并采用对数刻度表示搜索空间;利用参数空间中SVM在两个临近点的分类精度的变化估计参数的搜索方向,并且随着搜索方向的变化动态调整搜索步长,从而实现较快的搜索。通过与Grid和PSO方法的对比实验,表明该算法具有良好的性能。     

Development of an urban intensity index to facilitate urban ecosystem studies in Trinidad and Tobago

Urban ecosystems, considered centres of economic, social and cultural development, face a multitude of environmental and socio-economic challenges, which impact on quality of life. Effective management of the urbanization process is believed critical to improving quality of life and realizing sustainable development. The ecosystem perspective provides a holistic approach, needed to address the complexly interconnected issues, which arise from urban development. Central to the mapping and characterization of urban ecosystems is the delineation of their boundaries, which are made less transparent by growing urbanization. This exposes the limitations of a dichotomous approach. An urban intensity index is a critical tool which supports urban ecosystem studies by facilitating analysis of effects along the urban–rural gradient. In this study, Urban Intensity is estimated and ranked from most to least intense for communities across Trinidad and Tobago, using multivariate statistical analysis of physical data from the built environment. This statistically validated index, designed for Trinidad and Tobago, should have wider applicability to other disciplines and countries.     

On parallel policies for ranking and selection problems

In this paper we develop and test experimental methodologies for selection of the best alternative among a discrete number of available treatments. We consider a scenario where a researcher sequentially decides which treatments are assigned to experimental units. This problem is particularly challenging if a single measurement of the response to a treatment is time-consuming and there is a limited time for experimentation. This time can be decreased if it is possible to perform measurements in parallel. In this work we propose and discuss asynchronous extensions of two well-known Ranking & Selection policies, namely, Optimal Computing Budget Allocation (OCBA) and Knowledge Gradient (KG) policy. Our extensions (Asynchronous Optimal Computing Budget Allocation (AOCBA) and Asynchronous Knowledge Gradient (AKG), respectively) allow for parallel asynchronous allocation of measurements. Additionally, since the standard KG method is sequential (it can only allocate one experiment at a time) we propose a parallel synchronous extension of KG policy – Synchronous Knowledge Gradient (SKG). Computer simulations of our algorithms indicate that our parallel KG-based policies (AKG, SKG) outperform the standard OCBA method as well as AOCBA, if the number of evaluated alternatives is small or the computing/experimental budget is limited. For experimentations with large budgets and big sets of alternatives, both the OCBA and AOCBA policies are more efficient.     

具有最优学习率的RBF神经网络及其应用

传统固定学习率的RBF神经网络在金融时间序列预测方面已经有比较成功的应用,但网络学习率的选择问题却给传统RBF神经网络的使用带来了不便.利用梯度下降法及优化方法推导出了RBF神经网络的动态最优学习率并将其应用于网络学习算法,具有最优学习率的RBF神经网络能够在保证网络稳定学习的同时兼顾网络的收敛速度.为了检验具有动态最优学习率的RBF神经网络的预测效果,对沪深300指数波动率进行了预测实验.实验结果表明,具有动态最优学习率的RBF神经网络比传统的固定学习率的RBF神经网络有着更快的收敛速度,同时也避免了人为选定学习率的不便.