农机化对农业经济发展影响程度的分析

本文利用统计数据，对影响农业经济发展的诸因素进行了分段关联分析。结果表明了农业机械化对农业经济发展的作用逐步增大。根据关联度所确定的判断矩阵进行层次分析，也得出同样的结论。     

颗粒材料上运动物体所受摩擦力的数值模拟

通过数值模拟,考察一定重量的平板在水平颗粒物质层上做匀速运动所引起的剪切颗粒流,并关注其与平板的摩擦力及等效摩擦系数.数值结果表明,等效摩擦系数不是常数,与平板的运动速度有关.这与通常的固体与固体之间剪切作用时所满足的摩擦定律不同,体现了颗粒系统的特殊力学行为.     

A Comparison and Unification of Ellipsoidal Statistical and Shakhov BGK Models

The Ellipsoidal Statistical model (ES-model) and the Shakhov model (S-model) were constructed to correct the Prandtl number of the original BGK model through the modification of stress and heat flux. With the introduction of a new parameter to combine the ES-model and S-model, a generalized kinetic model can be developed. This new model can give the correct Navier-Stokes equations in the continuum flow regime. Through the adjustment of the new parameter, it provides abundant dynamic effect beyond the ES-model and S-model. Changing the free parameter, the physical performance of the new model has been tested numerically. The unified gas kinetic scheme (UGKS) is employed for the study of the new model. In transition flow regime, many physical problems, i.e., the shock structure and micro-flows, have been studied using the generalized model. With a careful choice of the free parameter, good results can be achieved for most test cases. Due to the property of the Boltzmann collision integral, the new parameter in the generalized kinetic model cannot be fully determined. It depends on the specific problem. Generally speaking, the S-model predicts more accurate numerical solutions in most test cases presented in this paper than the ES-model, while ES-model performs better in the cases where the flow is mostly driven by temperature gradient, such as a channel flow with large boundary temperature variation at high Knudsen number.     

镁合金在含F－的NaOH溶液中钝化行为的电化学研究

采用极化曲线、电容-电位曲线、Mott-Schottky分析以及电化学阻抗(EIS)等电化学方法研究了镁合金在含F^－ NaOH溶液中的阳极钝化行为. 结果表明, 在－1.2～1.8 V的电位范围内, 镁合金在含F^－的NaOH溶液中发生阳极钝化. 所形成的钝化膜表现出n型半导体的导电特性. 在0.7～1.8 V的电位范围内, 随着F^－浓度增大, 镁合金的阳极极化电流密度呈现出随着电位升高而逐渐增大的趋势, 随着F^－浓度增大这一趋势逐渐减弱. 并且F^－浓度的增大使得镁合金表面空间电荷层电容和钝化膜的载流子密度都不断减小. 通过极化曲线和电化学阻抗共同说明, 在5%的Na₂SO₄溶液中, NaOH溶液中阳极钝化后的镁合金随着钝化体系中F^－浓度的增加其耐蚀性逐渐减弱.     

水的汽化热实验研究

利用质量、电功率及时间等基本量便于测定的特点、测定水的汽化热、方法新颖，简便可靠，减少了误差。该方法也可用来测一些无毒液体的汽化热。     

Ladder-Type Heteroheptacenes with Different Heterocycles for Nonfullerene Acceptors

The design, synthesis, and characterization of two novel nonfullerene acceptors (M8 and M34) based on ladder-type heteroheptacenes with different heterocycles are reported. Replacing the furan heterocycles with the thiophene heterocycles in the heteroheptacene backbone leads to a hypsochromically shifted absorption band and greatly improved carrier transport for the resulting nonfullerene acceptor (M34) although the π–π-stacking distances are barely affected. Bulk-heterojunction polymer solar cells fabricated from M34 and a wide band gap polymer (PM6) as the donor showed a best power conversion efficiency (PCE) of 15.24 % with an open circuit voltage (V_OC) of 0.91 V, much higher than a PCE of 4.21 % and a V_OC of 0.83 V for the counterparts based on M8:PM6. These results highlight the importance of key atoms in the construction of high-performance nonfullerene acceptors.