Spatial Distribution and Influencing Factors of Urban Shrinkage from the Perspective of Factor Flow - A Case Study of National Urban Agglomerations

This paper examines national urban agglomerations by taking factor flows as the focal point as the research subject.By dividing the stages of urban agglomeration development,a comprehensive framework of urban shrinkage is constructed,encompassing economic,population,and social shrinkage.The study explores the spatial distribution characteristics of urban shrinkage during different stages of urban agglomeration and investigates the influencing factors using a geographic detector model.The findings reveal that urban shrinkage within urban agglomerations is widely spread,predominantly in peripheral areas.During the diffusion stage,urban shrinkage is scattered,with population shrinkage concentrated in peripheral regions,economic shrinkage concentrated on old industrial cities,and social shrinkage concentrated on the northeast.The outcomes of the geographic detector model indicate that traffic flow,capital flow,information flow,node importance,network connectivity,government investment,openness,and environmental regulations all play significant roles in shaping the spatial distribution of urban shrinkage.

Non-Darcy Flow in Molding Sands

Darcy’s law is widely used to describe the flow in porous media in which there is a linear relationship between fluid velocity and pressure gradient. However, it has been found that for high numbers of Reynolds this law ceases to be valid. In this work, the Ergun equation is employed to consider the non-linearity of air velocity with the pressure gradient in casting sands. The contribution of non-linearity to the total flow in terms of a variable defined as a non-Darcy flow fraction is numerically quantified. In addition, the influence of the shape factor of the sand grains on the non-linear flow fraction is analyzed. It is found that for values of the Reynolds number less or equal than 1, the contribution of non-linearity for spherical particles is around 1.15%.

Bulking factor of the strata overlying the gob and a three-dimensional numerical simulation of the air leakage flow field

现在的学习检验与在家和国外执行的嘴 bulking 因素有关的研究的结果。一个三维的嘴 bulking 因素的数学功能基于一个三维的嘴模型被描述。为空隙和渗透比率拿价值的方法也被建议。充分使机械化的最高的煤的空气漏的法律在这研究被研究。结果证明上面、更低的 crossheadings 附近的空气流动的速度在在从工作的脸的一样的距离的嘴的中央节比那高。当在工作的脸的空气的数量超过批评数量时，在上面、更低的 crossheadings 的自燃地区的宽度在中央节也比那大。处于这种状况，钥匙正在阻止从 self-igniting 在上面、更低的 crossheadings 离开的煤。在工作的脸减少空气的数量能减少自燃地区的宽度，特别上面、更低的 crossheadings 附近的宽度。这也在工作的脸的方向移动自燃地区。它能由在惰性的 crossheadings 使煤左并且由有效地在工作的脸控制空气的数量在嘴阻止煤 self-igniting。

Changes in spatial variations of sap flow in Korean pine trees due to environmental factors and their effects on estimates of stand transpiration

It is difficult to scale up measurements of the sap flux density(J_S) for the characterization of tree or stand transpiration(E) due to spatial variations in J_S and their temporal changes.To assess spatial variations in the sap flux density of Korean pine(Pinus koraiensis) and their effects on E estimates,we measured the J_S using Granier-type sensors.Within trees,the J_S decreased exponentially with the radial depth,and the J_S of the east aspects were higher than those of the west aspects.Among trees,there was a positive relationship between J_S and the tree diameter at breast height,and this positive relationship became stronger as the transpiration demand increased.The spatial variations that caused large errors in E estimates(i.e.,up to 110.8 % when radial variation was ignored) had varied systematically with environmental factors systematic characteristics in relation to environmental factors.However,changes in these variations did not generate substantial errors in the E estimates.For our study periods,the differences in the daily E(E_D) calculated by ignoring radial,azimuthal and tree-to-tree variations and the measured E_D were fairly constant,especially when the daily vapor pressure deficit(D_D)was higher than 0.6 k Pa.These results imply that the effect of spatial variations changes on sap flow can be a minor source of error compared with spatial variations(radial,azimuthal and tree-to-tree variations) when considering E estimates.

Influences of nonassociated flow rules on seismic bearing capacity factors of strip footing on soil slope by energy dissipation method

Seismic bearing capacity factors of a strip footing placed on soil slope were determined with both associated and nonassociated flow rules. Quasi-static representation of earthquake effects using a seismic coefficient concept was adopted for seismic bearing capacity calculations. A multi-wedge translational failure mechanism was used to obtain the seismic bearing capacity factors for different seismic coefficients and various inclined angles. Employing the associated flow rule, numerical results were compared with the published solutions. For bearing capacity factors related to cohesion and equivalent surcharge load, the maximum difference approximates 0.1%. However, the difference of bearing capacity factor related to unit weight is larger. With the two flow rules, the seismic bearing capacity factors were presented in the form of design charts for practical use. The results show that seismic bearing capacity factors related to the cohesion, the equivalent surcharge load and the unit weight increase greatly as the dilatancy angle increases, and that the nonassociated flow rule has important influences on the seismic bearing capacity.

Sap Flow of Abies georgei var. smithii and Its Relationship with the Environment Factors in the Tibetan Subalpine Region, China

Abies georgei var. smithii is a dominant species playing an important role in protecting biodiversity and sustaining the forestry ecosystems in Southeastern Tibetan Plateau. Stem sap flows of five different diameters at the breast height(DBH) A. georgei var. smithii samples were monitored continuously with the thermal dissipation probe for the entire growing period in order to understand the water transportation mechanism and the effects of environmental factors on its transpiration and growth. Relative environment factors, temperature and humidity of air, photosynthetically active radiation, rainfall, and wind speed, soil moisture, etc. were measured by the automatic weather stations. Diurnal and seasonal variations in sap flow rate with the different stem diameters and their correlations with meteorological factors were analyzed. The diurnal change in sap flow velocity showed a single-peak curve at the daily time scale, whereas a lower sap flow velocity can be observed in the largest DBH sample tree at night. The maximum average velocity was observed in August, whereas the minimum velocity was observed in January, and a large amount of water evaporated in summer owing to the higher sap flow velocity. In addition, sap flow velocity was closely related to changes in the micrometeorological factors, with average sap flow velocity showing significant linear correlations with air temperature, photosynthetically active radiation, rainfall, and vapor pressure deficit of air and soil moisture. Therefore, some measures, improving the light and temperature conditions, should be taken for protecting A. georgei var. smithii population in the Tibetan Plateau.

Direct Calculation of Unsteady-State Weymouth Equations for Gas Volumetric Flow Rate with Different Friction Factors in Horizontal and Inclined Pipes

Direct calculations of unsteady-state Weymouth equations for gas volumetric flow rate occur more frequently in the design and operation analysis of natural gas systems. Most of the existing gas pipelines design procedures are based on a particular friction factor and steady-state flow analysis. This paper examined the behavior of different friction factors and the need to develop model analysis capable of calculating unsteady-state gas flow rate in horizontal and inclined pipes. The results show different variation in flow rate with Panhandle A and Panhandle B attaining stability in accurate time with initial unsteadiness at the instance of flow. Chen and Jain friction factors have opposition to flow with high flow rate: The prediction also reveals that Colebrook-White degenerated to Nikuradse friction factor at high Reynolds number. The horizontal and inclined flow equations are considerably enhanced on the usage of different friction factors with the aid of Matlab to handle these calculations.

Analysis of Influencing Factors of Silt Solidified Soil in Flowing State

Every year, a large amount of silt is generated by river dredging. For the characteristics of dredging silt, such as high moisture content, low strength and high compressibility, the traditional solidification method can no longer better solve this kind of silt problem.?This paper mainly studies the fluidized solidification treatment of high water content sludge, not only makes the silt soil achieve a good solidification effect, but also the project cost is lower, the construction method is more environmentally friendly and green. The influencing factors of the solidified soil are mainly investigated by the unconfined compression test and the fluidity test. The experiment result shows?1)When the cement to sludge mass ratio (RCS) is 0.09?-?0.16 and the fly ash to cement mass ratio (RFC) is 0.35?-?0.80, as the amount of?RFC?increases, the flow rate of the solidified soil gradually decreases. With the increase of time, the liquidity is significantly reduced, and the influence of cement on the fluidity is greater than that of fly ash.?2) When?RCS?= 0.09?-?0.16, the strength of the sludge solidified soil at 28?d age increased by 4.5?-?6 times. 3)?When?RCS?= 0.09?-?0.16 and?RFC?= 35%?-?80%, the intensity of 14?d increased by 1.23 times than that of 7?d, and the intensity of 28 days increased by 1.29 times than that of 14?d. This experiment can provide the mix ratio design of solidified materials for different needs of the project, which can better provide a basis for engineering application and strength prediction.

Application of Factor Difference Scheme to Solving Discrete Flow Equations Based on Unstructured Grid

A second-order mixing difference scheme with a limiting factor is deduced with the reconstruction gradient method and applied to discretizing the Navier-Stokes equation in an unstructured grid.The transform of nonorthogonal diffusion items generated by the scheme in discrete equations is provided.The Delaunay triangulation method is improved to generate the unstructured grid.The computing program based on the SIMPLE algorithm in an unstructured grid is compiled and used to solve the discrete equations of two types of incompressible viscous flow.The numerical simulation results of the laminar flow driven by lid in cavity and flow behind a cylinder are compared with the theoretical solution and experimental data respectively.In the former case,a good agreement is achieved in the main velocity and drag coefficient curve.In the latter case,the numerical structure and development of vortex under several Reynolds numbers match well with that of the experiment.It is indicated that the factor difference scheme is of higher accuracy,and feasible to be applied to Navier-Stokes equation.

省域数字经济对共同富裕的影响研究--基于要素流动视角的空间计量检验

在信息化时代,数字经济如何促进共同富裕具有重要的现实意义。基于2011―2021年31个省份面板数据,测算数字经济指数和共同富裕指数,选取人才和资本要素流动为中介变量,数据要素流动环境为调节变量,运用空间杜宾模型(SDM)实证检验数字经济发展对共同富裕的影响。结果表明:数字经济发展能明显促进共同富裕,对邻边地区存在显著的正向的空间溢出效应,且在地理分布上呈现明显的区域异质性。机制分析发现,数字经济能够通过人才和资本要素流动影响共同富裕;数字经济对共同富裕存在倒“U”型的非线性效应,且人才和资本要素流动对数字经济影响共同富裕起到“边际效应递增”作用;数据要素流动环境能合理调节数字经济对共同富裕的影响。据此,应大力发展数字经济,促进人才与资本要素的流动和精准匹配,形成优势互补、区域协调发展的新格局。

数字经济对城市创新效率影响的实证研究

创新是推动经济增长的重要引擎。探讨数字经济能否成为提升城市创新效率的驱动力,对我国实现高质量发展具有重要意义。为深入理解这一关系,利用2011—2021年我国278个地级及以上城市的面板数据并构建计量模型,实证检验数字经济对城市创新效率的影响。研究发现:数字经济总体上有效促进城市创新效率的提升,且创新要素流动有效增强这一促进作用;数字经济对城市创新效率的影响具有空间溢出效应,且这种溢出效应在不同的空间权重矩阵下具有差异性;数字经济因为经济发展水平的不同对城市创新效率的影响也不同。

国家高新区对提升区域综合竞争力的影响研究

为检验国家高新区对提升区域全面竞争力的实际影响效果,文章选用全国29个省份国家高新区2016—2021年的面板数据进行实证分析。结果显示,国家高新区在促进创新能力方面具有显著的正面作用,且对环境规制和要素流动性的影响在不同地域表现出明显的异质性:西部地区国家高新区在激发创新活力方面更显著,东部地区则在环境规制和要素流动性方面呈现多样化的表现;相较北部地区而言,南部地区国家高新区在提升创新能力方面成效更为显著。

流通数字化赋能全国统一大市场建设的机理与效应研究

建设全国统一大市场是加快构建新发展格局的基础支撑和内在要求。本文聚焦流通数字化发展对全国统一大市场建设的影响,实证检验流通数字化赋能全国统一大市场建设的传导机制和异质特征。研究发现,流通数字化发展能够显著促进全国统一大市场建设,且该研究结论具有较强的稳健性。机制检验结果表明,流通数字化发展能够通过加快创新要素流动、扩大企业规模、释放消费潜力等途径促进全国统一大市场建设。异质性检验结果表明,在基础设施水平、城镇化率和人口集聚程度较高地区,流通数字化对全国统一大市场建设的促进作用较为明显。进一步研究发现,流通数字化与统一大市场之间存在基于基础设施、城镇化率和人口集聚水平的门槛效应。本文研究结论为我国进一步加快流通产业的数字化转型、破除区域间要素流动壁垒、推进统一大市场建设提供了经验证据。

基于要素的城乡融合识别研究——以重庆永川南大街街道为例

科学理解城乡融合发展状态,对于实现乡村振兴、建立良性的城乡关系有着重大作用。城乡融合的实质是城乡要素的融合,本文从资源禀赋、人口、经济、文化、生态、政治6个方面构建城乡融合水平评价指标体系,并对重庆市永川区南大街街道城乡融合程度加以识别,将南大街区分为高融合度区域(中心城区、小南村)、中融合度区域(大南村、代家店村、黄瓜山村)、低融合度区域(谭家坝村、八角寺村、兴隆村),并针对不同的城乡融合度区域提出未来发展方向。研究可为我国城乡融合发展与乡村转型发展的研究与实践提供借鉴。

非遗文化旅游FLOW体验影响因素模型构建——以敦煌非遗演艺体验项目为例

FLOW体验状态下主体的心理幸福感水平很高,已有研究多关注户外探险等领域,对非遗文化领域旅游者如何进入FLOW体验状态关注较少。本研究以扎根理论为指导,选取敦煌三大非遗演艺的网络文本为基本数据库,选择其中旅游者进入FLOW体验状态的文本进行三级编码分析,结合其游览故事线构建进入FLOW体验状态的影响因素模型,发现基础因素旅游者“技能”、核心因素积极情感的生成及中介因素身体感知参与可以共同促使非遗文化旅游者进入FLOW体验状态。

基于半解析涡环模型的农用单旋翼直升机流场快速计算

农业航空领域中,定量获取风场(流场)速度分布对单旋翼直升机辅助授粉作业、农药施用效率提升具有重要意义。基于此提出一种半解析理论方法能够快速完整计算单旋翼流场速度。以涡环模型为基础,将农用直升机旋转桨盘下的尾涡系等效为涡环连续叠加所形成的圆柱涡面,再由涡环速度诱导公式半解析计算直升机旋翼空间各点速度。理论模型与仿真和文献试验数据比较,结果表明:涡环模型简单快速,普通计算机(CPU 2 GHz,内存2 GB)上2.8 s完成计算;悬停时与计算流体力学仿真结果下洗速度径向平均误差小于1.9 m/s,平均相对误差小于39.1%,轴向平均误差小于2.26 m/s,平均相对误差小于54.6%;悬停时,诱速从中央往桨尖递增;前飞时,平飞速度越大诱速越小;流场主要影响因素依次为前飞速度、旋翼半径、飞机总重、空气密度。为定量计算农用直升机旋翼风场、辅助授粉作业和田间施药喷头布置提供一种快速方法和参考。

数据要素流动对城市创新活跃度的影响研究

如何发挥好数据要素的创新引擎作用是缓解城市创新能力分化的重要手段。文章基于2005—2020年284个地级市面板数据,运用时空双固定的空间杜宾模型来实证分析数据要素流动与城市创新活跃度之间的关系。结果表明:数据要素流动可以显著提升本地区和周边地区的创新活跃度,具体为数据要素流动规模每提高1%,本地区和周边地区的创新活跃度便分别上升0.022%和0.197%。机制分析表明,数据要素流动能够通过提升地区创新要素集聚水平、创新质量以及激发创新精神来提升城市创新活跃度。进一步研究发现,以市场化水平和知识产权保护水平为代表的制度环境在数据要素流动影响城市创新活跃度的过程中发挥完全中介调节作用和双重门槛效应。

从同步数据分析乔木树干液流与气象因子的关系

[目的]树干液流是研究植物蒸腾耗水的重要生理指标,树种和气象因子均是其关键影响因素。本文旨在消除树种因素限制,探讨树干液流与气象因子之间的关系。[方法]以哈尼梯田水源区3种林分中10种乔木树种为研究对象,采用Granier热扩散探针技术测定其树干液流速率,将其同步数据与气象因子进行关联分析。[结果]从次生落叶阔叶林和原生常绿阔叶林的7779条乔木树干液流速率数据中发现7条异常数据,且这些异常数据在各个树种中都表现出同步一致性;进一步关联分析表明,太阳辐射的突然增加是产生乔木树干液流数据同步上升的主要原因,而降雨则是产生树干液流数据同步下降的主要原因,两者的变化可导致其他气象因子发生变化,从而影响树干液流速率;树干液流与气象因子存在一定的时滞效应,在发生同步异常数据的气候条件下,树干液流滞后太阳辐射0~30 min,提前于饱和水汽压差、气温和湿度0~60 min,滞后或提前时间远小于正常气候条件下各树种的时滞时间。[结论]乔木树干液流受到太阳辐射和降雨等气象因子的综合调节,其中太阳辐射的影响最为显著。研究结果可为从生理生态角度探究乔木的蒸腾作用与气象因子的关系提供科学依据。

数字技术与政府治理有效性:来自285个城市的经验证据

政府治理有效性是对治理能力予以定量识别的重要参考。本文基于2003—2021年我国285个城市的面板数据,实证检验了数字技术对提升政府治理有效性的作用。研究发现:数字技术能够提升政府治理有效性。进一步将政府治理有效性细分为经济治理有效性和社会治理有效性发现,数字技术既能够通过要素流动机制让企业信息获取能力提升和重资产比重降低,提升经济治理有效性,也能通过政治参与机制增强民众政治效能感和政府信息处理水平,帮助政府提升社会治理有效性。在高数字基础设施建设水平城市、适度数字人才集聚度城市、超特大城市、副省级以上城市、资源型城市以及市场化程度和财政透明度高的城市中,数字技术对政府治理有效性的作用更强。同时,数字技术对政府治理有效性的影响在东部沿海、黄河中游等人口密集地区显著为正,在西北地区显著为负。数字技术对政府治理有效性存在正向空间溢出,本地数字技术发展也能促进相邻城市政府治理有效性提升。对此,政府应制定企业数字化转型的激励政策,加强民众数字素养教育,制定全国性的数字治理发展规划,构建地区间协同互通的数字政务体系。