科创中国

设计一种基于Howland电流源电路的精密压控电流源,论述了该精密压控电流源的原理.该电路以V/I转换电路作为核心,Howland电流源做为误差补偿电路,进一步提高了电流源的精度,使绝对误差仿真值达到nA级,实际电路测量值绝对误差达到μA级,得到高精度的压控电流源.仿真和实验测试均证明该方案是可行的.

To improve the performance of the positive displacement blower,it is imperative to understand the detailed internal flow characteristics or enable a visualization of flow status.However,the existing two-dimensional unsteady,three-dimensional steady or quasi-unsteady numerical simulation and theoretical analysis cannot provide the detailed flow information,which is unfavorable to improve the performance of positive displacement blower.Therefore,the unsteady flow characteristics in a three-lobe positive displacement blower are numerically investigated by solving the three-dimensional,unsteady,compressible Navier-Stokes equations coupled with RNG k-εturbulent model.In the numerical simulation,the dynamic mesh technique and overset mesh updating method are adopted.Due to the air being compressed in the process of the rotors rotating,the variation of the temperature field in the positive displacement blower is considered.By comparing the experimental measurements and the numerical results on the variation of flow rate with the outlet pressure,the maximum relative error of the flow rate is less than 2.15%even at the maximum outlet pressure condition,which means that the calculation model and numerical computational method used are effective.The numerical results show that in the intake region,the fluctuations of the inlet flow are greatly affected by the direction of the velocity vectors.In the exhaust region,the temperature changes significantly,which leads to the increase of the airflow pulsation.Through analysis on the velocity,pressure and temperature fields obtained from the numerical simulations,three-dimensional unsteady flow characteristics in the positive displacement blower are revealed.The studied results will provide useful reference for improving the performance and empirical correction in the design of the positive displacement blower.

本研究调查了计算机辅助反馈策略对大学技术教育课程的影响.具体来说,研究探讨了计算机辅助反馈策略"对错反馈"(Knowledge of Responses,简称KCOR)和"正确答案反馈"(Knowledge of Correct Responses,简称KCR)的有效性,并与"无反馈"(No Feedback)的学生的学习态度进行了比较.三组学生被分配到三个条件之一:KOR,KCR和NR(对照组).通过四个星期的基于网络的教学实验,研究者获得学习者对计算机辅助反馈教学系略的态度.结果表明,学生对三种反馈显示出相同的态度.计算机辅助反馈策略可能是促进学习的可行的选择.

针对NRA算法和BPA算法查询效率不高、重复访问数据的问题,提出了一种基于三维分档布鲁姆过滤器表(TF)的Top-κ查询算法(TKBFP).该算法使用TF对数据进行处理,以较低的误判率获得较高的访问效率并降低了内存消耗,利用最优位置索引策略,避免重复访问数据对象.对TKBFP算法进行了严格的语义定义,推导出每一维BF中需要的哈希函数个数;以自主开发的Java程序为仿真平台,对TKBFP算法进行了试验,并对算法执行效率和存储性能进行评价.试验结果表明,该算法能够避免重复访问数据对象,并能以较低的误判率实现大规模数据的高效查询处理.与NRA和BPA相比,当属性列表超过4个时,开销明显降低,适合面向大规模数据的查询处理应用.

为了优化生物质能供应链,降低成本,在无扰动因素情况,需求不确定且与价格有关的条件下,研究了由能源公司、基地和农户组成的三级生物质供应链中,奖惩与回馈契约对供应链的协调问题,建立了满足渠道协调的条件和供应链内各级参与者实现互赢的数学模型,最后将其用于数值算例中验证.结果证明契约参数的合理选择可以实现供应链各方利益最大.

首先给出了若干标量Young型不等式.然后在此基础上,建立了相应的矩阵Young型不等式.