科创中国

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.

In precision machining of complex curved surface parts with high performance, geometry accuracy is not the only constraint, but the performance should also be met. Performance of this kind of parts is closely related to the geometrical and physical parameters, so the final actual size and shape are affected by multiple source constraints, such as geometry, physics, and performance. These parts are rather difficult to be manufactured and new manufacturing method according to performance requirement is urgently needed. Based on performance and manufacturing requirements for complex curved surface parts, a new classification method is proposed, which divided the complex curved surface parts into two categories: surface re-design complex curved surface parts with multi-source constraints(PRCS) and surface unique complex curved surface parts with pure geometric constraints(PUCS). A correlation model is constructed between the performance and multi-source constraints for PRCS, which reveals the correlation between the performance and multi-source constraints. A re-design method is also developed. Through solving the correlation model of the typical part's performance-associated surface, the mapping relation between the performance-associated surface and the related removal amount is obtained. The explicit correlation model and the method for the corresponding related removal amount of the performance-associated surface are built based on the classification of surface re-design complex curved surface parts with multi-source constraints. Research results have been used in the actual processing of the typical parts such as radome, common bottom components, nozzle, et al., which shows improved efficiency and accuracy of the precision machining for the surface re-design parts with complex curved surface.

Natural frequency characteristics of a thin-walled multiple layered cylindrical shell under lateral pressure are studied.The multiple layered cylindrical shell configuration is formed by three layers of isotropic material where the inner and outer layers are stainless steel and the middle layer is aluminum.The multiple layered shell equations with lateral pressure are established based on Love's shell theory.The governing equations of motion with lateral pressure are employed by using energy functional and applying the Ritz method.The boundary conditions represented by end conditions of the multiple layered cylindrical shell are simply supported-clamped(SS-C),free-clamped(F-C)and simply supported-free(SS-F).The influence of different lateral pressures,different thickness to radius ratios,different length to radius ratios and effect of the asymmetric boundary conditions on natural frequency characteristics are studied.It is shown that the lateral pressure has effect on the natural frequency of multiple layered cylindrical shell and causes the natural frequency to increase.The natural frequency of the developed multilayered cylindrical shell is validated by comparing with those in the literature.The proposed research provides an effective approach for vibration analysis shell structures subjected to lateral pressure with an energy method.

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.

As the two most important indexes of bearing raceway,surface roughness and roundness have significant influence on bearing noise.Some researchers have carried out studies in this field,however,reason and extent of the influence of raceway surface geometric characteristics on bearing running noise are not perfectly clear up to now.In this paper,the raceway of 6309 type bearing's inner and outer ring is machined by floating abrasive polishing adopting soft abrasive pad.Surface roughness parameters,arithmetical mean deviation of the profile Ra,the point height of irregularities Rz,maximum height of the profile Rmax and roundness f of raceways,are measured before and after machining,and the change rules of the measured results are studied.The study results show that the floating abrasive polishing can reduce the surface geometric errors of bearing raceway evidently.The roundness error is reduced by 25%,Rmax value is reduced by 35.5%,Rz value is reduced by 22%and Ra value is reduced by 5%.By analyzing the change of the geometrical parameters and the shape difference of the raceway before and after machining,it is found that the floating abrasive polishing method can affect the roundness error mainly by modifying the local deviation of the raceway's surface profile.Bearings with different raceway surface geometrical parameter value are assembled and the running noise is tested.The test results show that Ra has a little,Rmax and Rz have a measurable,and the roundness error has a significant influence on the running noise.From the viewpoint of controlling bearings'running noise,raceway roundness error should be strictly controlled,and for the surface roughness parameters,Rmax and Rz should be mainly controlled.This paper proposes an effective method to obtain the low noise bearing by machining the raceway with floating abrasive polishing after super finishing.

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.

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.

During hard cutting process there is severe thermodynamic coupling effect between cutting tool and workpiece, which causes quenching effect on finished surfaces under certain conditions. However, material phase transformation mechanism of heat treatment in cutting process is different from the one in traditional process, which leads to changes of the formation mechanism of damaged layer on machined workpiece surface. This paper researches on the generation mechanism of damaged layer on machined surface in the process of PCBN tool hard cutting hardened steel Cr12 Mo V. Rules of temperature change on machined surface and subsurface are got by means of finite element simulation. In phase transformation temperature experiments rapid transformation instrument is employed, and the effect of quenching under cutting conditions on generation of damaged layer is revealed. Based on that, the phase transformation points of temperature under cutting conditions are determined. By experiment, the effects of cutting speed and tool wear on white layer thickness in damaged layer are revealed. The temperature distribution law of third deformation zone is got by establishing the numerical prediction model, and thickness of white layer in damaged layer is predicted, taking the tool wear effect into consideration. The experimental results show that the model prediction is accurate, and the establishment of prediction model provides a reference for wise selection of parameters in precise hard cutting process. For the machining process with high demanding on surface integrity, the generation of damaged layer on machined surface can be controlled precisely by using the prediction model.

近年来178Hfm2 31年的同核异能态被认为是用低能X射线触发使其释放储存能量的最合适候选者.为了探讨在178Hf中是否存在触发Kπ=16+同核异能态γ发射的门态,本工作首先用投影壳模型对178Hf的多准粒子态和集体激发态进行了研究,结果表明其它态位于距离16+同核异能态较远的地方.但当用包括γ自由度的组态限制(绝热阻塞)方法计算178Hf的多准粒子激发态时,结果显示有三个能级可能是16+同核异能态光退激的候选者,位能面计算的结果显示178Hf为轴对称硬核.

With the increasing noise pollution,low noise optimization of centrifugal pimps has become a hot topic.However,experimental study on this problem is unacceptable for industrial applications due to unsustainable cost.A hybrid method that couples computational fluid dynamics(CFD)with computational aeroacoustic software is used to predict the flow-induced noise of pumps in order to minimize the noise of centrifugal pumps in actual projects.Under Langthjem's assumption that the blade surface pressure is the main flow-induced acoustic source in centrifugal pumps,the blade surface pressure pulsation is considered in terms of the acoustical sources and simulated using CFX software.The pressure pulsation and noise distribution in the near-cutoff region are examined for the blade-passing frequency(BPF)noise,and the sound pressure level(SPL)reached peaks near the cutoff that corresponded with the pressure pulsation in this region.An experiment is performed to validate this prediction.Four hydrophones are fixed to the inlet and outlet ports of the test pump to measure the flow-induced noise from the four-port model.The simulation results for the noise are analyzed and compared with the experimental results.The variation in the calculated noise with changes in the flow agreed well with the experimental results.When the flow rate was increased,the SPL first decreased and reached the minimum near the best efficient point(BEP);it then increased when the flow rate was further increased.The numerical and experimental results confirmed that the BPF noise generated by a blade-rotating dipole roughly reflects the acoustic features of centrifugal pumps.The noise simulation method in current study has a good feasibility and suitability,which could be adopted in engineering design to predict and optimize the hydroacoustic behavior of centrifugal pumps.