科创中国

根据陕西省17个村庄的农地流转情况的调查资料,采取随机抽样法和问卷调查法,利用Logistic模型对陕西农村农地流转的影响因素进行分析,结果显示农户的个体因素是影响农地流转的主要因素,而一般认为的工资性收入和政策因素对其影响并不显著,由此应调整促进农地流转的长短期政策.文中的"农地流转"是指土地承包经营权的流转,不涉及农村建设用地的流转.

农地流转作为推动我国农业规模经营的有效方式,一直以来得到政府的大力支持,然而长期以来我国农村土地流转率仍然偏低.分析了农地流转中交易费用的存在对农户土地流转行为的影响.从农地产权安排、搜寻交易对象和价格发现、合约谈判以及合约执行4个方面探讨了农地流转中存在的交易费用,并针对流转中不同方面的交易费用提出降低交易费用的相关举措.

以海河流域龙门水库以上流域为研究对象,在对流域下垫面条件进行调查分析的基础上,分析了下垫面条件对流域产汇流特征变化的影响,龙门以上流域降雨产汇流规律在1980年左右发生明显变化,龙门以上流域的土壤含水量消退系数1980年均值为0.91,1980年后均值为0.94,1980年均值后较1980年前均值略增3.3%.对流域下垫面条件变化影响下的洪水变化规律进行了分析和探讨,为流域洪水系列一致性修正奠定了基础,为流域防洪规划和管理提供了技术支撑,为洪水预报方案编制提供了第一手资料.

在中国农村物流发展现状及特点分析的基础上,对中国邮政发展农村物流分销模式进行了研究和探讨,总结出邮政农村分销的四大模式,并对分销模式的进一步推广实施提出了相关建议.

In the prediction of active vibration isolation performance,control force requirements were ignored in previous work.This may limit the realization of theoretically predicted isolation performance if control force of large magnitude cannot be supplied by actuators.The behavior of a feed-forward active isolation system subjected to actuator output constraints is investigated.Distributed parameter models are developed to analyze the system response,and to produce a transfer matrix for the design of an integrated passive-active isolation system.Cost functions comprising a combination of the vibration transmission energy and the sum of the squared control forces are proposed.The example system considered is a rigid body connected to a simply supported plate via two passive-active isolation mounts.Vertical and transverse forces as well as a rotational moment are applied at the rigid body,and resonances excited in elastic mounts and the supporting plate are analyzed.The overall isolation performance is evaluated by numerical simulation.The simulation results are then compared with those obtained using unconstrained control strategies.In addition,the effects of waves in elastic mounts are analyzed.It is shown that the control strategies which rely on unconstrained actuator outputs may give substantial power transmission reductions over a wide frequency range,but also require large control force amplitudes to control excited vibration modes of the system.Expected power transmission reductions for modified control strategies that incorporate constrained actuator outputs are considerably less than typical reductions with unconstrained actuator outputs.In the frequency range in which rigid body modes are present,the control strategies can only achieve 5–10 dB power transmission reduction,when control forces are constrained to be the same order of the magnitude as the primary vertical force.The resonances of the elastic mounts result in a notable increase of power transmission in high frequency range and cannot be attenuated by active control.The investigation provides a guideline for design and evaluation of active vibration isolation systems.

选择IGC(产业梯度系数)作为衡量区域产业梯度水平的指标,通过计算豫沪苏浙产业梯度系数,结合国情、省情,明确在"十二五"期间,河南省宜承接的工业产业.

本文将分税制改革、土地财政和房价水平置于同一框架来研究推动中国城镇房价持续快速上涨的制度性因素.经验事实表明,较高的房价水平总是与较大的土地财政规模相联系,而土地财政的形成与1994年的分税制改革密切相关.在对上述经验事实进行背景分析的基础上,本文运用2000--2008年的省级面板数据进行实证分析,结果表明,在控制了经济基本面、城市化率和地区竞争等潜在影响房价的因素后,分税制背景下逐年扩大的财政分权度是引发地方政府追求土地财政的制度性因素;地方政府的土地财政规模对中国城镇房价水平的高涨具有显著的正向影响,并且这种正向效应会随着财政分权度的扩大而被强化.本文的估计结果对财政分权变量的选取、估计方法的选择和估计函数形式的设定均是非常稳健的.

In piezoceramic ultrasonic devices,the piezoceramic stacks may fail permanently or function improperly if their working temperatures overstep the Curie temperature of the piezoceramic material.While the end of the horn usually serves near the melting point of the molten metal and is enclosed in an airtight chamber,so that it is difficult to experimentally measure the temperature of the transducer and its variation with time,which bring heavy difficulty to the design of the ultrasonic molten metal treatment system.To find a way out,conjugate heat transfer analysis of an ultrasonic molten metal treatment system is performed with coupled fluid and heat transfer finite element method.In modeling of the system,the RNG model and the SIMPLE algorithm are adopted for turbulence and nonlinear coupling between the momentum equation and the energy equation.Forced air cooling as well as natural air cooling is analyzed to compare the difference of temperature evolution.Numerical results show that,after about 350 s of working time,temperatures in the surface of the ceramic stacks in forced air cooling drop about 7 K compared with that in natural cooling.At 240 s,The molten metal surface emits heat radiation with a maximum rate of about 19 036 W/m2,while the heat insulation disc absorbs heat radiation at a maximum rate of about 7922 W/m2,which indicates the effectiveness of heat insulation of the asbestos pad.Transient heat transfer film coefficient and its distribution,which are difficult to be measured experimentally are also obtained through numerical simulation.At 240 s,the heat transfer film coefficient in the surface of the transducer ranges from–17.86 to 20.17 W/(m2?K).Compared with the trial and error method based on the test,the proposed research provides a more effective way in the design and analysis of the temperature control of the molten metal treatment system.

入学数学准备是预测儿童小学学业成绩的有力指标,提高儿童的入学数学准备水平有助于提高儿童入学后的学业成绩、缩小儿童学习与发展的阶层差距和城乡差距.对浙江、江西、四川三省的1181名学前一年幼儿入学数学准备状况的城乡差异比较发现,城乡学前一年幼儿的数学学习与发展普遍存在不同步、不均衡的现象,关系领域的学习落后于数、量、形、空间等领域的学习;总体上,城市幼儿在多个领域的表现都优于乡镇和农村幼儿,城市幼儿与县城幼儿的表现没有显著差异.在普及学前教育发展的过程中,应加强对乡镇和农村幼儿的早期补偿教育,并加强关系领域的教学.

关于我国农民工的福利与社会政策问题,已有的研究多专注于实际状况与问题,从一定的理论视角出发进行的研究并不多.综合考量以往研究成果以及我国农民工面临的问题后建立的农民工社会政策决定分析框架,有助于对我国进入新世纪以来国家关于农民工社会政策的转变进行分析.近年来,我国各级政府在农民工政策选择转向中发挥了较大作用,但中央政府责任承担过少,对于地方政府的激励、约束措施不足,导致政策实施效果差强人意.因此,今后农民工社会政策的实践效果与社会权利的平等获得,在很大程度上取决于中央政府的责任承担,包括在中央层面的组织机构、制度创新以及资源供给上作出适当安排.