基于集聚效应的城市地价分布与城市空间演变

集聚效应导致产出外部性,使不同区位的生产力存在差异,各部门在地区之间的均衡分配即城市分区的形成,有赖于各部门聚集收益的强度以及对区位特征要素的特别需求。本文将集聚效应因素引入生产函数,构建了一个包含集聚效应影响的城市土地市场模型,分析基于集聚效应的各区位生产力差异、就业密度差异、区位成本差异,在此基础上进一步探讨了城市地价分布规律、城市空间演变,以及企业和家庭的选址行为。

以圈层分布制定地价调节标准的相关探索——以武汉市为例

随着房地产市场的快速发展以及城市开发区的快速发展,实现地价的精准调控成为城市管理的重要主题。本文以武汉市为例,从地价圈层分布的视角出发,通过对新城区、开发区地价成交价格的综合分析,提出了当前全市地价存在的问题以及解决问题的有效措施,指明了土地市场调节目标,为武汉市土地地价的制定完善提供了依据。

基于多源数据和集成学习的城市住宅地价分布模拟——以武汉市为例

精准刻画城市住宅地价分布特征,对于科学引导城市空间布局规划、有效实现城市精明增长等具有重要意义。而城市住宅地价与其潜在影响因素之间的复杂非线性关系,给地价分布精细模拟带来了挑战。论文旨在探索基于地理大数据和集成学习的城市住宅地价分布模拟方法体系,以满足快速、精准监测地价动态变化的需要。选取武汉市为典型区,以住宅用地交易样点、兴趣点(points of interest, POI)和夜间灯光影像为数据源,以500 m分辨率网格为估价单元,提取POI核密度和夜间灯光强度作为住宅地价预测变量,采用机器学习算法和bagging、stacking集成方法构建住宅地价预测模型,并对比分析其精度。研究发现:①单个机器学习算法中,支持向量回归(support vector regression, SVR)预测精度最高,接下来依次是k最近邻算法(k-nearest neighbor algorithm, k-NN)、高斯过程回归(Gaussian process regression, GPR)和BP神经网络(back propagation neural networks, BP-NN);②在提升单个算法预测精度方面,stacking方法的性能优于bagging方法,使用stacking集成SVR和k-NN的地价预测模型精度最高,其平均绝对百分误差仅为8.29%,拟合优度R2达0.814;③基于论文所构建模型生成的城市住宅地价分布图能有效表征价格圈层分布特征和局部奇异性。研究结果可为城市住宅地价评估提供新的思路和方法借鉴。

江苏省城市地价影响因素分析与空间结构研究

本文以江苏省68个地级与县级市的城市地价为样本,运用因子分析方法对影响地价的诸多变量进行分析,发现城市集聚规模与城市经济发展水平是影响地价的重要因素。对江苏省城市地价进行地统计分析,发现江苏省城市地价明显表现出区域空间分布规律,表现为江苏省城市地价存在南北、东西两个方向上的梯度变化,运用线性回归方法求得两个方向上的梯度值;江苏省城市地价整体有一定正相关性,但局域自相关性表现不强;地价以南京、苏州为高地价点,省内地价存在沿沪宁铁路与长江的高地价条带区域。结合因子分析结果对以上规律做出解释。

江苏省小城镇地价空间分布与成因研究

以江苏省典型区域的小城镇体系为样本、以城镇平均地价为指标,对江苏省小城镇体系地价进行地统计研究,分析发现江苏省小城镇体系地价表现出明显空间分布特征。研究表明:①小城镇体系地价从中心城市到行政区边缘的变化具有明显阶段性,且不同城镇体系表现出差异特征;②由于发展阶段的不同,小城镇地价结构体系存在较大差异;③小城镇间相互联系强度的不同造成不同地区城镇体系地价的相互关联性表现迥异;④江苏省区域小城镇体系地价总体存在南—北向空间变化趋势。最后,运用因子分析方法揭示出:区别于大中城市地价的主要影响因素是集聚规模,小城镇地价空间差异的主要原因是空间区位差异。

城市地价空间分布的流场理论研究

本文以系统论、信息论为基础,对城市地价空间分析规律进行了理论研究,提出了城市地价空间分布的流场理论,并从地价场、地价梯度、地价势能、地价信息熵等四个方面对该理论进行了阐释。同时,认为该理论的提出为地价系统的定量研究开辟了一条道路,可作为城市土地定级估价的指导工具,可以促进地价杠杆在城市土地资源节约集约利用中调控功能的发挥,也是确定城市合理用地规模的理论依据之一。

商业办公用地地价水平分布规律研究——以上海静安区为例

以静安区商业办公用地为例实证探究商业办公用地地价水平分布规律,得到以下结论:(1)静安区样本商业办公楼租金水平呈现近似同心圆分布,中心地价高,向两侧递减。(2)静安区样本商业办公楼租金分布受到交通干线的影响。(3)静安区样本商业办公楼租金在各同心圆内呈现不均质分布。(4)商业办公楼对区位因素较敏感。因此,静安区商业办公用地地价水平分布规律近似符合阿朗索克竞标地租理论。

Identification of agricultural systems in the mountains of Northeast Thailand

Agricultural systems in Thailand's northeastern mountains are described in terms of their type of crops, marketing channels, and labor requirements. Five distinctive systems are identified: The Field crop system, Fruit tree system, Industrial tree plantation system, Specialty crop system and Agro-tourism system. The different systems are compared with each other in order to identify their respective strengths and weaknesses as development models. The Field crop system covers the largest area of agricultural land and is found in all mountainous villages but it generates very low net profits per hectare. The Specialty crop system and Agro-tourism system generate very high net profits per hectare but cover only a small land area and have a restricted spatial distribution. Expansion of these high value systems may be limited because they are capital and labor intensive and require highly skilled farmers to manage them successfully. If these constraints can be overcome, they may offer a useful model for mountain agricultural development.

A Preliminary Study on The Medicinal Plants of Euphorbia in Gansu Province

Seventeen species and two varieties of Euphorbia,including one new variety,were found inGansu Province.They belong to three sections,viz.Sect.Anisophyllum:Euphorbia bumifusaWilld.;Sect.Petaloma:E.marginata Pursh;Sect.Tithymalus:E.micractina Boiss.,E.wangiiOudejans,E.heishuiensis W.T.Wang,E.hylonoma Hand.-Mzt.,E.ekinensis

Role of Buffalo in International Trade

The study analyzed the foreign trade performance of buffalo products using several indicators. These are the foreign trade structure by product and by Geographic distribution, time trend, instability, the free on board or freight on board （FOB） price ratio of buffalo to cattle revealed comparative advantage of tradable buffalo products. Thailand has the highest buffalo exports of live animals and hides. India exports the highest share of buffalo meat. Buffalo dairy products exports are rare due to lack of expanded dairy processing industries of buffalo milk and lacking of awareness towards the buffalo milk quality, which limits the demand for buffalo dairy products and shortage in supply beyond the domestic consumption. While buffalo stock all over the world represents 12% of the world bovine stock, its share in buffalo exports of meat is around 27% of the world bovine exports measured in tons in 2007. Such share shrinkages to 13.2% when measured in dollars. This shrinkage is due to lower prices of buffalo products than cattle products. The ratio of annual average ＂FOB price＂ of buffalo meat to bovine price was about one-half and for hides was about 40%, and for live buffalo was 14%. Reasons of the apparent lower FOB price of buffalo Exported Products than cattle are the low carcass weight of buffalo exported mainly for processing, low quality and limited demand for buffalo hides, and commonly, exporting live buffalo as weaned calves. Expansion in exports of buffalo products requires expansion in supply, through the potentiality of higher productivity, rather than stock size, to reach in balance with available feeds.

Occurrence Probability Evaluation of the Maximum Potential Earthquake on the Faults in Zhengzhou City

According to the results of estimation of the maximum potential earthquake in the project of ＂The Active Fault Detection and Seismic Risk Evaluation （Phase H） of Zhengzhou City＂, the near east-west trending Laoyachen fault and Shangjie fault are developed in the urban area. The Laoyachen fault was not active in the Quaternary, but the Shangjie fault may have the potential of generating M5.0 - 5.5 earthquakes. In order to get the probability of occurrence of maximum potential earthquakes, we delineate the statistical areas and the potential source areas and calculate the seismicity parameters and the space distribution functions. Our study shows that the probability of occurrence of an earthquake with M〉 5.0 on the faults in Zhengzhou city is 6% in the next 50 years and 11% in the next 100 years.

Mode-I-crack compression modeling and numerical simulation for evaluation of in-situ stress around advancing coal workfaces

The relatively high stress probably leads to generation of a fractured or even instable area around a working coalface. Also, the generated weak area often evolves into an easy-infiltrating field of water/gas to greatly increase probability of accident occurrence. To reveal the distribution of high stress around working faces, we put forward the mode-I-crack compression model. In this model, the goaf following a working face is regarded as a mode-I crack in an infinite plate, and the self-gravity of overlaying strata is transformed into an uniform pressure applied normal to the upper edge of the model crack. Solving this problem is based on the Westergaard complex stress function. For comparison, the software RFPA-2D is also employed to simulate the same mining problem, and furthermore extendedly to calculate the stress interference induced by the simultaneous advances of two different working faces. The results show that, the area close to a working face or the goaf tail has the maximum stress, and the stress is distributed directly proportional to the square root of the advance and inversely proportional to the square root of the distance to the working face. The simultaneous advances of two neighboring working faces in different horizontals can lead to extremely high resultant stress in an interference area.

Distributed Estimation and Analysis of Precipitation Recharge Coefficient in Strongly-exploited Beijing Plain Area, China

The precipitation recharge coefficient(PRC), representing the amount of groundwater recharge from precipitation, is an important parameter for groundwater resources evaluation and numerical simulation. It was usually obtained from empirical knowledge and site experiments in the 1980 s. However, the environmental settings have been greatly modified from that time due to land use change and groundwater over-pumping, especially in the Beijing plain area(BPA). This paper aims to estimate and analyze PRC of BPA with the distributed hydrological model and GIS for the year 2011 with similar annual precipitation as long-term mean. It is found that the recharge from vertical(precipitation + irrigation) and precipitation is 291.0 mm/yr and 233.7 mm/yr, respectively, which accounts for 38.6% and 36.6% of corresponding input water. The regional mean PRC is 0.366, which is a little different from the traditional map. However, it has a spatial variation ranging from –7.0% to 17.5% for various sub-regions. Since the vadose zone is now much thicker than the evaporation extinction depth, the land cover is regarded as the major dynamic factor that causes the variation of PRC in this area due to the difference of evapotranspiration rates. It is suggested that the negative impact of reforestation on groundwater quantity within BPA should be well investigated, because the PRC beneath forestland is the smallest among all land cover types.

Quantitative and Qualitative Analysis of Groundwater in Aguanaval and Chupaderos Aquifers （Mexico）

Adequate regional groundwater assessment studies are essential for the correct groundwater management by policy/decision makers; increased use of groundwater resources and drought have led to concern about the future availability of groundwater to meet domestic, agricultural, industrial, and environmental needs. Deep understanding of spatial and temporal water table dynamics together with transport processes is required. This paper gathers historical geological, hidrological and chemical information for quantitative and qualitative as well as spatial and temporal evolution of groundwater for Aguanaval and Chupaderos aquifers, both surrounding Calera aquifer in Mexico. Historical databases were employed to determine temporal trends of water levels and values were projected for years 2010, 2030 and 2050. Potential recharge sites were also identified through water level-topography correlation. The water quality analysis was completed by obtaining, through geostatistics, spatial distributions for bicarbonate, chloride, sulfate, total dissolved solids, temperature, and sodium, employing databases generated in recent sampling campaigns. This analysis provided additional elements to help understand the functioning of groundwater in studied aquifers. Finally, results were compared with permissible values established in the Mexican norm.

Performance Comparison of Distributed State Estimation Algorithms for Power Systems

A newly proposed distributed dynamic state estimation algorithm based on the maximum a posteriori(MAP) technique is generalised and studied for power systems. The system model involves linear time-varying load dynamics and nonlinear measurements. The main contribution of this paper is to compare the performance and feasibility of this distributed algorithm with several existing distributed state estimation algorithms in the literature. Simulations are tested on the IEEE 39-bus and 118-bus systems under various operating conditions. The results show that this distributed algorithm performs better than distributed quasi-steady state estimation algorithms which do not use the load dynamic model. The results also show that the performance of this distributed method is very close to that by the centralized state estimation method. The merits of this algorithm over the centralized method lie in its low computational complexity and low communication load. Hence, the analysis supports the efficiency and benefits of the distributed algorithm in applications to large-scale power systems.