Analysis of the Influence Factors of Grain Supply-Demand Gap in China

Based on the analysis of the grain supply and demand gap’s current situation in China, this paper establishes an indicator system for the influence factors of grain supply and demand gap. Then this paper calculates the correlation degree between the main grain varieties’ supply and demand gap and its influence factors. The results show that sown area and unit yield have the greatest impact on wheat supply and demand gap;per capita disposable income and unit yield have the greatest impact on corn supply and demand gap;per capita disposable income and agricultural mechanization level have the greatest impact on the supply and demand gap of soybean and rice. From the analysis results, we can obtain the difference between the factors affecting the grain supply and demand gap, and provide a certain theoretical basis and new ideas for the balance of grain supply and demand in China.

The Supply-Demand Analysis and Mechanism Innovation of Chinese Rural Public Goods

The connotation of rural public goods is expounded.The rural public goods refer to the products and labors that satisfy the production and living of rural residents,economic growth and social progress.The rural public goods is characterized by non-excludability,non-competitiveness and indispensability of other general public goods.The supply situation of Chinese government to rural public goods is analyzed,as well as the demand situation of rural public goods,which includes farmers' demand on training,the assistance demand of rural weak groups,farmers' demand on comfortable living conditions and farmers' demand on "soft" public goods.The paths for innovating the supply mechanism of rural public goods are put forward,which cover perfecting the decision mechanism of public goods supply;scientifically distributing the supply responsibility of rural public goods;facilitating the reform of each supporting equipment and exploring the multiple capital collecting channels of rural public goods.

Clinical features of multiple gastrointestinal stromal tumors:A pooling analysis combined with evidence and gap map

BACKGROUND Multiple gastrointestinal stromal tumors(MGISTs)are a very rare type of gastrointestinal stromal tumor(GIST)and are usually observed in syndrome.AIM The paper aimed to describe the clinical and oncological features of MGISTs and to offer evidence for the diagnosis and treatment.METHODS Data of consecutive patients with MGISTs who were diagnosed at Peking University People’s Hospital(PKUPH)from 2008 to 2019 were retrospectively evaluated.Further,a literature search was conducted by retrieving data from PubMed,EMBASE,and the Cochrane library databases from inception up to November 30,2019.RESULTS In all,12 patients were diagnosed with MGISTs at PKUPH,and 43 published records were ultimately included following the literature review.Combined analysis of the whole individual patient data showed that female(59.30%),young(14.45%),and syndromic GIST(63.95%)patients comprised a large proportion of the total patient population.Tumors were mainly located in the small intestine(58.92%),and both CD117 and CD34 were generally positive.After a mean 78.32-mo follow-up,the estimated median overall survival duration(11.5 years)was similar to single GISTs,but recurrence-free survival was relatively poorer.CONCLUSION The clinical and oncological features are potentially different between MGISTs and single GIST.Further studies are needed to explore appropriate surgical approach and adjuvant therapy.

Band gap analysis of periodic structures based on cell experimental frequency response functions(FRFs)

An approach is proposed to estimate the transfer function of the periodic structure, which is known as an absorber due to its repetitive cells leading to the band gap phenomenon. The band gap is a frequency range in which vibration will be inhibited. A transfer function is usually performed to gain band gap. Previous scholars regard estimation of the transfer function as a forward problem assuming known cell mass and stiffness matrices. However, the estimation of band gap for irregular or complicated cells is hardly accurate because it is difficult to model the cell exactly. Therefore, we treat the estimation as an inverse problem by employing modal identification and curve fitting. A transfer matrix is then established by parameters identitled through modal analysis. Both simulations and experiments have been performed. Some interesting conclusions about the relationship between modal parameters and band gap have been achieved.

An Analysis of Structural-Acoustic Coupling Band Gaps in a Fluid-Filled Periodic Pipe

A periodic pipe system composed of steel pipes and rubber hoses with the same inner radius is designed based on the theory of phononic crystals. Using the transfer matrix method, the band structure of the periodic pipe is calculated considering the structural-acoustic coupling. The results show that longitudinal vibration band gaps and acoustic band gaps can coexist in the fluid-filled periodic pipe. The formation of the band gap mechanism is further analyzed. The band gaps are validated by the sound transmission loss and vibration-frequency response functions calculated using the finite element method. The effect of the damp on the band gap is analyzed by calculating the complex band structure. The periodic pipe system can be used not only in the field of vibration reduction but also for noise elimination.

基于GIS的漳州市松岭村乡村旅游适宜性评价及GAP分析

以“全国乡村旅游扶贫重点村”漳州市松岭村为研究对象,借助地理信息系统(GIS),从资源禀赋潜力出发,构建乡村旅游适宜性评价体系,利用地理探测器计算各旅游适宜性影响因子的权重,基于乡村旅游适宜性评价结果对旅游空间进行开发空缺(GAP)分析,并提出旅游规划优化策略。旨在优化景观资源在空间整体布局中的合理利用,为乡村旅游规划提供新思路。研究结果表明:(1)松岭村旅游适宜性受基础设施因子影响最大,受坡向因子影响最小;(2)松岭村旅游适宜等级可分为高适宜、较高适宜、中适宜、较低适宜、低适宜区5类,其中高适宜区面积最小,仅占松岭村总面积的4.64%,低适宜区面积最大,占总面积的58.00%;(3)借鉴GAP分析思路,识别松岭村景观资源点开发潜力分级区块,各适宜等级区均存在较多景观资源点未开发。建议结合现有特色景观资源点,优先开发较高及高潜力区块、积极开发中潜力区、适度开发较低及低潜力区,以期在保留旅游资源特色的同时最大化利用其景观资源。

GAP STRUCTURE ANALYSIS OF FOREST TRANSECT USINGTHE 1-D DISCRETE WAVELET TRANSFORM

Wavelets is a very effective technique for time-frequency analysis with the ability of preserving loeal information, applied to many areas such as nonlinear science, information processing.quantum physics etc.. In this paper. from the view of ecology spatial pattern, the authors try to process the sample data of Larix forest transects to identify the canopy gap structures by wavelet analysis. The caleulation of wavelet variance, derived from the transtform facilitates comparison based on dominant scale of pattern between multiple datasets such as the stands described.

An Informative System Based on the Skill Gap Analysis to Planning Training Courses

By using the skill gap analysis we propose a new quantitative method to plan training courses. By comparing the differences between the competences needed to cover a position and the ones possessed, it is possible to find the cases that need to be trained. According to different situations we propose some algorithms to plan courses and to find the subjects that require to be trained.

Analysis and Prediction of Residents' Income Gap in Poverty-stricken Areas of Yunnan Province

Taking Ludian County in Zhaotong City of Yunnan Province for example,according to the data on residents'income gap in Ludian County during the period 2002-2011,we analyze the residents'income gap in Ludian County,and offer the forecast value of residents'income gap in Ludian County during the period 2012-2015,using Compertz curve model and Eviews software for fitting.The forecast value shows that the residents'income gap will continue to widen in Ludian County.Finally we put forth the recommendations for bridging the residents'income gap in Ludian County,in order to provide a reference for settling the problems concerning residents'income gap in other state-level povertystricken counties of Yunnan Province.

Modeling and analysis of piezoelectric beam with periodically variable cross-sections for vibration energy harvesting

A bimorph piezoelectric beam with periodically variable cross-sections is used for the vibration energy harvesting. The effects of two geometrical parameters on the first band gap of this periodic beam are investigated by the generalized differential quadrature rule （GDQR） method. The GDQR method is also used to calculate the forced vibration response of the beam and voltage of each piezoelectric layer when the beam is subject to a sinusoidal base excitation. Results obtained from the analytical method are compared with those obtained from the finite element simulation with ANSYS, and good agreement is found. The voltage output of this periodic beam over its first band gap is calculated and compared with the voltage output of the uniform piezoelectric beam. It is concluded that this periodic beam has three advantages over the uniform piezoelectric beam, i.e., generating more voltage outputs over a wide frequency range, absorbing vibration, and being less weight.

Analysis of limitations on recovery of gravity field based on satellite gravity gradient data

Although satellite gravity gradient data plays a great role in determining short-wavelength part of static gravity field model,accuracy of the long-wavelength part of gravity field model recovered by them are poor,which leads to only a few applications in time-variable gravity investigation.The reason is that some factors limit the accuracy of the gravity field recovered using gradient data,including accuracy of the gravity gradient observations,measurement bandwidth(MBW)of gradiometer,satellite inclination,etc.This paper aims at analyzing the influence of these limitations on gravity field recovery and discusses the possibility of time-variable gravity field detection by using gravity gradient observations.Firstly,for arbitrary satellite orbit inclination,we give the frequency distributions of all the components of gravity gradients(i.e.Txx;Tyy;Tzz;Txy;Txz and Tyz,).The results show that the maximum frequency of each component of the gravity gradients is the same,i.e.l=Ts(l is degree of the gravity field model,Ts is the orbital periods),and it is not influenced by the inclination of the satellite orbits.Secondly,the paper gives a theory proof to explain why only the low orders of the coefficients are influenced by polar gaps.Big polar gaps are experimented by a numerical test with inclination of 45°.Finally,considering that the measurement bandwidth can be expanded and accuracy of gradient observations can be improved by superconducting gravity gradiometer(SGG)compared to gradiometer used in Gravity field and steadystate Ocean Circulation Explorer(GOCE),the possibility of detecting time-variable gravity using gravity gradient observations is discussed.The results show that the SGG creates errors in MBW with magnitude of 0.014 m E,which is smaller than the magnitude of the time-variable gravity gradient signals(i.e.,0.02 m E)derived from Gravity Recovery and Climate Experiment(GRACE)gravity field models.This indicates the potential of SGG in time-variable gravity detection.

四合木(Tetraena mongolica)的潜在适生区预测及其与自然保护区GAP分析

明晰物种的潜在分布区及其与当前自然保护区的空缺,对于合理高效地开展濒危物种保护具有重要的意义。为了预测四合木(Tetraena mongolica)在当代(2020s)及未来(2060s、2100s)的分布范围,以及自然保护区对四合木的保护现状,以四合木为对象,利用最大熵模型(The maximum entropy model software,MaxEnt)结合23个环境变量预测其在内蒙古自治区西鄂尔多斯与宁夏回族自治区的潜在适生区,并与当前四合木自然保护区进行了保护空缺分析。结果表明:(1)MaxEnt模型的受试者工作特征曲线下的面积为0.977,表明预测结果准确。(2)影响四合木分布的主要环境因子是最湿月降水量,其次是最干月降水量、距道路距离、等温性、最冷季平均温度、坡度。(3)研究区内四合木当前适生面积为4717 km2;2020s—2100s四合木潜在分布区退缩,并向西北部偏移。(4)基于保护空缺分析,当前仅有14.88%四合木的适宜生境位于保护区内,大面积的四合木适生区未设立自然保护区,这些地区主要集中在内蒙古乌海市和鄂尔多斯市杭锦旗。研究结果旨在为四合木保护及其自然保护区建设提供科学指导。

中国数字经济空间动态演进的区域现状

数字经济已成为引领我国经济一体化高质量发展的主要驱动力,立足于国家整体经济及区域经济稳步协调发展的战略。文章基于中国2013—2020年省级数据,运用主成分分析法对中国数字经济进行测度,并运用社会网络分析及核密度等方法对我国数字经济动态演化的空间关联及区域差异进行研究。研究发现:(1)2013—2020年我国数字经济发展整体网络密度稳步提升但依旧处于低水平。(2)中国各省份数字经济发展两极分化,东部与西北、东北等边缘地区存在“数字经济鸿沟”,加之整体关联水平低,分化严重,发达地区对边缘地区的辐射效应较低,差距可能愈发扩大。(3)将其划分为四个板块,发现存在“弱关联”板块,板块间溢出关系及关联度差异悬殊,进一步研究各省份数字经济发展的“中间人”作用,发现各省份承担角色更是“极化”严重。研究结果可为我国持续深化数字经济建设,推动经济协调、稳定、高质量发展提供参考。

P-GMAW起弧过程特征分析及稳定性判别方法

脉冲熔化极气体保护焊(pulsed gas metal arc welding,P-GMAW)起弧过程易产生不稳定现象,会严重影响电弧传感焊缝跟踪精度.针对这一问题,对摆动电弧窄间隙P-GMAW不稳定起弧过程的成因进行了研究,发现送丝速度对起弧过程稳定性具有重要影响.通过对电弧图像与电信号特征进行对比分析,提取了表征电弧稳定性的电信号特征变量;为减小变量冗余性和过拟合,采用最大似然估计法筛选并提取了8个变量,并通过主成分分析法(principal component analysis,PCA)对变量进行融合,提取了方差贡献率最高的前两个主成分;根据因子载荷发现,相比熔滴过渡阶段和基值阶段,脉冲峰值阶段是电弧更易发生不稳定现象的阶段.结合提取的主成分变量与二分类Logistic回归模型建立了起弧过程电弧稳定性判别模型.通过受试者工作特征(receiver operating characteristic,ROC)曲线得到了模型的最佳阈值.结果表明,该模型对脉冲稳定性判别准确率达到了80%以上,表明模型具有良好的判别性能.该模型对提高窄间隙高低跟踪精度、保证焊接质量具有一定应用价值.

高铁建设是否缩小了区域创新差距?——基于多期差分法和社会网络分析

基于我国2005-2019年的城市面板数据,从高铁开通和高铁网络两个视角,实证检验高铁建设对区域创新差距的影响。结果显示,高铁开通对区域创新差距具有显著的缩小效应。区域异质性分析发现,高铁开通对区域创新差距的缩小效应对西部地区的作用更大,且在二线以上城市更为明显;机制分析表明,人力资本和物质资本是高铁建设影响区域创新差距的中介路径,且后者的作用更大;社会网络分析则认为,城市在高铁网络中的联系广度和中心性越高,高铁对区域创新差距的缩小效应越强。基于此,文章从优化高铁网络配置、改善要素流动机制和制定区域创新发展策略三方面提出了相应的政策建议。

当前应坚定实行扩张性宏观经济政策

GDP增速面临下行压力和物价水平持续处于低位,本应促使决策者采取扩张性财政货币政策以刺激有效需求,但在许多行业存在“产能过剩”的情况下,消除“过剩产能”成为宏观经济政策的突出目标。实际上,宏观层面的“产能过剩”和有效需求不足是等价概念,即便考虑产业层面的结构失衡,政府在决定是否应该实行扩张性宏观经济政策时,依然应该看通胀和经济增速变化,而不应该受“产能过剩”的干扰。当前,中国经济既面临周期性问题,也存在结构性矛盾,实行扩张性宏观经济政策同结构性改革并不矛盾,而是相辅相成。目前来看,2024年实现GDP增长5%左右的目标面临较大挑战,为完成全年经济社会发展目标任务,应实行更具扩张性的财政货币政策,特别是财政政策。

森林康养消费意愿—行为与服务质量期望—感知调查及差距分析

基于对森林康养实际消费者问卷调查,发现森林康养消费者消费意愿—行为差距和森林康养服务质量期望—感知差距,根据差距分析提出以需求为导向的森林康养供给侧改革方向。研究表明,森林康养消费意愿强烈,森林康养潜在市场空间巨大,在消费次数、消费金额和消费时长等方面均远未达到消费者的预期,可以成为森林康养产业发展的增长点。配套设施、管理服务的期望—感知差距最大,因此,完善配套设施、提升管理服务成为森林康养项目重点改进方向。应从丰富自然资源多样性着手减少自然生态类因素的期望—感知差距,提高康养项目体验性与多样性,为消费者提供高性价比的森林康养产品,重点提升消费者的身心愉悦感。

基于声子晶体的周期性基础机器振动波衰减性能分析

文章利用COMSOL多物理场程序计算不同参数周期性基础的衰减域特性,探讨周期性基础对机器振动波的衰减和阻隔作用。利用商业有限元ABAQUS软件建立周期性基础机器振动有限元模型,对不同厚度、材料的周期性基础模型进行频域分析,得到周期性基础的频散关系;通过时程分析研究周期性基础机器的动力响应和振动衰减效果。结果表明:当输入波的频率处于周期性基础频率带隙内时,可以有效地减小上部机器的动力响应;当输入波的主频处于周期性基础频率带隙外时,无法减小上部机器的动力响应;不同厚度和材料的周期性基础的带隙以及对于上部机器振动的减振效果不同。研究结果为周期性基础在工业厂房机器减振中的应用提供了新的思路和方法。

双调制式轴向永磁齿轮电动机气隙磁场与转矩计算

针对轴向永磁齿轮电动机(Axial Magnetic Gear Motor,AMGM)整体尺寸偏大导致的转矩密度偏低(≤70 kN·m/m^(3))等缺陷,提出了一种双调制式轴向永磁齿轮电动机(Dual-modulation Axial Magnetic Gear Motor,DAMGM)。采用高速侧及低速侧两个调磁环对DAMGM低速转子进行调制,且两个调磁环中的非导磁部分均为永磁体,有效提高了低速转子的输出转矩;另外,与现有AMGM相比,将驱动电动机置于DAMGM高速永磁转子内部,减小了整体轴向尺寸,大幅提高了低速转子的转矩密度(150 kN·m/m^(3))。针对现有3D有限元计算时间长、计算机资源浪费严重等问题,给出一种基于圆柱坐标系的DAMGM三维分析方法。根据调磁环的3种边界条件,建立了调制后DAMGM气隙磁场及电磁转矩的数理模型,不仅计算结果准确(与3D有限元相比,平均计算误差≤5%),而且计算时间短(仅为3D有限元的1/10),便于DAMGM不同参数结构的分析、比较与优化。

基于振幅放大机制的无砟轨道周期结构弯曲波调控研究

【目的】轨道结构的振动一直是相关领域亟待研究和解决的问题。传统减隔振装置受到自身重量与列车行车安全性的限制,难以实现对轨道结构弯曲波的宽频调控。【方法】通过引入振幅放大机制,设计了一种杠杆式轨道综合减隔振装置。以CRTSⅢ型板式无砟轨道结构为研究对象,采用能量泛函变分法和人工弹簧技术建立了配置有轨道综合减隔振装置的周期性轨道结构波动分析模型和振动响应分析模型,研究了轨道综合减隔振装置对弯曲波的调控能力,并分析了轨道综合减隔振装置工作能力与振幅放大系数的关系。【结果】结果表明:采用振幅放大机制,能够有效增大减隔振装置的惯性质量,增强减隔振装置的阻尼特性和刚度特性,进而显著提升其工作能力。【结论】实现了轨道综合减隔振装置“低频隔振高频吸振”的超宽频弯曲波调控设计目标。