Can farmers extend their cultivation areas in urban agriculture? A contribution from agronomic analysis of market gardening systems around Mahajanga (Madagascar)

The rapid urbanization in developing countries implies an increasing pressure on urban agriculture for production. As most perishable food products come from this agriculture in close proximity to population concentrations, we analysed from an agronomic point of view how market-garden farmers can meet this increasing urban demand. This work took place in the case of Mahajanga, a secondary city with high increasing demographic rate on the Northwest coast of Madagascar. Based on preliminary surveys to characterize the farming systems (on a sample of 91 farms), 11 market-garden farmers chosen in the three main agricultural zones of the urban area were surveyed during two years. Surveys aimed at understanding their decision rules in crop choices, crop allocation to land and resource management, and to estimate their room for manoeuvre to increase their leafy vegetable areas under cultivation. The wholesalers and retailers who buy the farmers’ produce were also surveyed. A previous model of decision rules regarding crop location on farm territory was used to analyse the on-farm surveys and cartographic methods (GIS and on-farm manual representations) were used to quantify the land use. We highlight the following major points. (1) The leafy vegetable production in the surveyed farms already intensively uses land: farmers have complex decision rules largely depending on the water dynamics in the two main environments (lowlands and lakesides) where leafy vegetables are cultivated during the dry season. (2) The scarcity of farmers’ resources (labour money and water) leads to very little internal room for manoeuvre to increase the leafy vegetable production in the farms. (3) At territorial level however, some land reserve exist in one of the lowlands, but not on lakesides. The water availability for agriculture must be better informed through specialized hydrologic studies, as one of the main constraints nowadays to extend the agricultural area. An extrapolation to other cases of urban agriculture is then discussed as well as the role of agronomy to help urban planners to consider the place of agriculture in the urban development.     

城市区位研究的回顾与评述

回顾了中心地理论提出以来国内外学者关于城市区位的相关研究,包括对中心地理论的修正与检验,基于该理论的城市体系空间分布模式研究,及其在聚落体系规划和中心城市服务功能研究中的应用等;总结了空间结构理论对城市区位研究的拓展,以及基于城市区位理论的城市形成发展动力相关研究;对城市区位相关研究的趋势和问题进行了评述.     

大数据背景下区域木材物流配送中心选址

指出了我国木材物流存在的主要问题以及解决方案,结合大数据技术,利用遗传算法进行木材物流配送中心的选址,建立了数学模型并进行了案例分析,以达到对木材物流成本和服务的优化。     

渠道合作情境下合同双元功能对主动和被动投机行为的影响差异研究

基于交易成本理论,在渠道合作情境下,以制造商的合同监督和企业间联合行动为工具测量合同治理的保障功能和协作功能,探讨二者对经销商主动投机行为和被动投机行为的影响差异。通过对512份问卷数据的统计分析,得到以下结论：第一,合同监督有助于抑制经销商的主动投机行为,但对其被动投机行为的影响不显著;第二,企业间联合行动有助于抑制经销商的被动投机行为,但对其主动投机行为的影响不显著;第三,经销商的主动投机行为和被动投机行为均会负向影响合作绩效;第四,经销商的主动投机行为中介合同监督对合作绩效的正向影响,被动投机行为中介企业间联合行动对合作绩效的正向影响。     

出口经验能助推对外直接投资吗?--基于中国与“一带一路”沿线国家宏观数据的实证研究

以"一带一路"沿线45国2003~2014年数据为样本,实证检验了出口经验能否提升对外直接投资。研究结果显示,出口经验显著提升中国对"一带一路"沿线国家的直接投资。在基准模型的基础上,引入公共治理、能源禀赋和地理区位与出口经验交互项的实证结果还显示,出口经验对直接投资的促进效应随着东道国治理水平提升而提高,对陆上丝绸之路国家的作用显著低于海上丝绸之路国家,而能源禀赋并未直接或间接通过出口经验对直接投资产生作用。这些研究结论说明,企业在不确定性外部环境下进行对外直接投资时,倾向于通过建立出口学习曲线并依此进行直接投资决策。     

融合反距离加权和矩阵填充的位置指纹库构建

为解决位置指纹定位在离线阶段构建位置指纹库时耗费的人力和时间成本较大,构建指纹库效率低和利用空间插值法构建的指纹库精度不高的问题,提出了一种融合反距离加权和矩阵填充的位置指纹库构建算法。该算法仅需人工采集定位区域内少量参考点的接收信号强度值用作信标点指纹信息,结合反距离加权算法特性计算出次信标点指纹信息,根据位置指纹库数据矩阵的低秩性,应用奇异值阈值矩阵填充算法构建出位置指纹数据库。仿真实验结果表明,所提算法有效降低了矩阵填充算法构建位置指纹库所需的人工和时间成本,构建出的位置指纹库定位性能优于反距离加权和克里金空间插值法,接近传统人工采集法,显著地提高了位置指纹库的构建效率。     

论国土空间生态修复基本逻辑

研究目的:阐释国土空间生态修复的基本逻辑,支撑新时期国土空间生态修复从区域自主治理向全域空间设计的战略转型。研究方法:文献综述分析法,逻辑推理法,系统回顾法。研究结果:基于国土空间"要素—格局—过程—服务"级联框架及全域耦合关联,针对目标、对象、区位及途径厘清国土空间生态修复的基本逻辑:以提升人类生态福祉而非生态系统服务潜在供给增长为核心修复目标,国土空间社会—生态要素为基本修复对象,构建多尺度协同的生态安全格局识别重点修复地域,秉承多层级协同次优而非单层级最优的主导修复途径。研究结论:国土空间生态修复的本质在于修复人地冲突、强化人地协同,"修"的是人与自然不和谐的相处方式,"复"的是生态系统退化或受损的结构、过程、功能及服务;国土空间生态修复的对象、区位及途径均以修复目标为导向。     

城市建筑空地遗留与区位建设——以北京市为例

现代城市问题,归根到底是人与地的关系问题,疏浚和控制人口密度是当前城市发展所不容忽视的重要课题.通过实地考察和对北京市区位建设相关数据的理论分析,认为在旧城改造和新城建设中,为有效控制人口聚集的密度,当前应主要致力于:一是重视建筑高度和密度的控制,为其设定具有法律效力的底线标准;二是在遵循市场运行规律的前提下,合理划分城市区位,引导进行多核心的数量、品位、质量、规模大致相同的功能分布体的区位建设.     

Do satisfying walking and cycling trips result in more future trips with active travel modes? An exploratory study

Previous studies have indicated that travel satisfaction - the experienced emotions during, and cognitive evaluation of, a trip - can be affected by travel mode choice and other trip characteristics. However, as satisfactory trips might improve a person's attitude towards the used mode, persons may be more likely to use that same mode for future trips of the same kind. Hence, a cyclical process between travel mode choice and travel satisfaction might occur. In this paper we begin to analyse this process—using a structural equation modelling approach on cross-sectional data—for people who engage in walking and cycling for leisure trips in the Belgian city of Ghent. The focus on walking and cycling reflects recent studies indicating that active travel is often associated with the highest levels of travel satisfaction. Results of this exploratory analysis offer tentative support for the idea of a cyclical process: the evaluation of walking and cycling trips positively affects the respondents' attitude towards the respective mode, which in turn has a positive effect on choosing that mode.     

我国原材料工业发展环境及其布局区位选择

加入WTO后,国内外经济环境和较大需求对我国重要原材料工业的发展比较有利;将规模大、运量大、用地多、用水多、污染重的钢铁和石油化工等原材料工业布局在滨海地区是一种国际性选择趋势;随着我国原材料工业原料和产品市场的国际化．方便利用国内和国外铁矿石和石油资源的滨海地区成为我国钢铁和石油化工布局的主要考虑区位;在考虑资源安全和少占可耕地的前提下,我国铁矿和石油资源的主要富集地区又具备建设大型深水港口的滨海地区是建设布局大型钢铁和石化企业的首选区位。