安宁河谷区粮经作物种植方式的经济效果分析

通过对攀西地区安宁河流域有关农作物种植方式的调查,发现当地的粮—经作物配套种植增产潜力很大。本文对几种作物种植方式的经济效果作了对比分析。     

PEMFC输出功率的二自由度PID控制

为提高质子交换膜燃料电池(PEMFC)的输出性能,对于其输出功率的一阶滞后数学模型,进行二自由度PID控制方案设计.针对二自由度PID控制器参数整定过程中存在的不足,提出一种基于自适应遗传算法的二自由度PID控制器设计.仿真结果表明,经优化整定后的二自由度PID控制器,可使PEMFC的输出功率能较好地跟踪给定期望值的变化,同时也可更好地抑制外扰.     

四程放大激光系统输出能量稳定性研究

 根据原型装置主放大系统组合式四程放大结构的特点,计算分析了放大过程中注入能量、放大增益及损耗的微小起伏对系统输出能量稳定性的影响。根据原型装置集成实验结果,分析了目前原型装置单路输出能量稳定性水平。研究结果表明：注入能量越大,其变化对输出能量影响越小;小信号增益系数对输出能量的影响明显大于注入能量;系统输出能量稳定性对腔内光学元件的透过率变化要求高于腔外光学元件。在3 ns基频光输出达标点处要使输出能量不稳定性控制在5%以内,注入能量起伏要低于10%,腔内放大片小信号增益系数起伏要低于1%,腔内光学系统损耗起伏要低于2%。     

低阈值单谐振周期极化掺镁铌酸锂光参量振荡器

对基于周期极化掺镬铌酸锂晶体的信号光单谐振光学参量振荡器的输出特性进行了实验研究.讨论了光学参量振荡器谐振腔的腔长、周期极化铌酸锂晶体的通光长度、输出镜的透过率以及抽运光的脉冲宽度对光学参量振荡器谐振阈值的影响.光学参量振荡器的抽运源采用输出波长为1 064 nm的声光调Q Nd:YVO_4激光器,在重复频率为2 kHz、周期极化掺镁铌酸锂晶体的温度为30℃的条件下,光学参量振荡器的振荡阈值仅为48 mW.当抽运功率为94 mW时获得了25 mW的信号光输出,其光-光转换效率为26.6%.     

Adjoint-based h–p adaptive discontinuous Galerkin methods for the 2D compressible Euler equations

In this paper, we investigate and present an adaptive Discontinuous Galerkin algorithm driven by an adjoint-based error estimation technique for the inviscid compressible Euler equations. This approach requires the numerical approximations for the flow (i.e. primal) problem and the adjoint (i.e. dual) problem which corresponds to a particular simulation objective output of interest. The convergence of these two problems is accelerated by an hp-multigrid solver which makes use of an element Gauss–Seidel smoother on each level of the multigrid sequence. The error estimation of the output functional results in a spatial error distribution, which is used to drive an adaptive refinement strategy, which may include local mesh subdivision (h-refinement), local modification of discretization orders (p-enrichment) and the combination of both approaches known as hp-refinement. The selection between h- and p-refinement in the hp-adaptation approach is made based on a smoothness indicator applied to the most recently available flow solution values. Numerical results for the inviscid compressible flow over an idealized four-element airfoil geometry demonstrate that both pure h-refinement and pure p-enrichment algorithms achieve equivalent error reductions at each adaptation cycle compared to a uniform refinement approach, but requiring fewer degrees of freedom. The proposed hp-adaptive refinement strategy is capable of obtaining exponential error convergence in terms of degrees of freedom, and results in significant savings in computational cost. A high-speed flow test case is used to demonstrate the ability of the hp-refinement approach for capturing strong shocks or discontinuities while improving functional accuracy.     

Output feedback stabilization for a class of nonlinear time-evolution systems

A variety of problems in nonlinear time-evolution systems such as communication networks, computer networks, manufacturing, traffic management, etc., can be modelled as min–max-plus systems in which operations of min, max and addition appear simultaneously. Systems with only maximum (or minimum) constraints can be modelled as max-plus system and handled by max-plus algebra which changes the original nonlinear system in the traditional sense into linear system in this framework. Min-max-plus systems are extensions of max-plus systems and nonlinear even in the max-plus algebra view. Output feedback stabilization for min–max-plus systems with min–max-plus inputs and max-plus outputs is considered in this paper. Max-plus projection representation for the closed-loop system with min–max-plus output feedback is introduced and the formula to calculate the cycle time is presented. Stabilization of reachable systems with at least one observable state and a further result for reachable and observable systems are worked out, during which max-plus output feedbacks are used to stabilize the systems. The method based on the max-plus algebra is constructive in nature.     

不确定离散时间输入饱和系统的鲁棒预见控制

本文研究一类具有输入饱和的不确定离散时间系统的鲁棒预见控制问题.与以往对误差信号和系统方程取差分不同,本文引入状态辅助变量,利用系统状态向量与辅助变量之差代替通常的状态差分,使得输入饱和不确定离散系统的扩大误差系统的构造成为可能.另外,本文推导的扩大误差系统不再包含误差向量,这不仅降低系统的阶数而且允许输出矩阵带有不确...     

高校考核教师应该依据净效益

目前全国高校都对教师的考核给予了高度重视,进行了积极有益的探索和实践。但是,考核的标准仅根据教师的产出量。到目前为止,几乎所有学校的考核标准中都没有考虑学校或政府的投入,这样的考核标准不能发挥其应有的作用。本文提出学校考核教师应该以净效益为依据,制定合理的考核标准,才能正确评价教师。     

An incremental variational approach to coupled thermo-mechanical problems in anelastic solids. Application to shape-memory alloys

We study the coupled thermo-mechanical problem that is obtained by combining generalized standard materials with Fourier’s law for heat conduction. The analysis is conducted in the framework of non-smooth mechanics in order to account for possible constraints on the state variables. This allows models of damage and phase-transformation to be included in the analysis. In view of performing numerical simulations, an incremental thermo-mechanical problem and corresponding variational principles are introduced. Conditions for existence of solutions to the incremental problem are discussed and compared with the isothermal case. The numerical implementation of the proposed approach is studied in detail. In particular, it is shown that the incremental thermo-mechanical problem can be recast as a concave maximization problem and ultimately amounts to solve a sequence of linear thermal problems and purely mechanical (i.e. at a prescribed temperature field) problems. Therefore, using the proposed approach, thermo-mechanical coupling can be implemented with low additional complexity compared to the isothermal case, while still relying on a sound mathematical framework. As an application, thermo-mechanical coupling in shape memory alloys is studied. The influence of the loading strain-rate on the phase transformation and on the overall stress–strain response is investigated, as well as the influence of the thermal boundary conditions. The numerical results obtained by the proposed approach are compared with numerical and experimental results from the literature.     

A Flow feature detection framework for large-scale computational data based on incremental proper orthogonal decomposition and data mining

ABSTRACT

A framework based on incremental proper orthogonal decomposition (iPOD) and data mining to perform large-scale computational data analysis is presented. It includes iPOD to incrementally reduce data dimensions and decouple dynamic flow structures in massive CFD data; data mining to classify and identify candidate global regions of interest (ROIs) for focused analysis; feature detection to capture key flow features and ultimate ROIs (UROIs); and targeted data storage and visualisation. Quantitative results show that iPOD is able to process large datasets that overwhelm the batch-POD, leading to 4–16× data reduction in the temporal domain. Data mining and feature detection algorithms, respectively, identify 50–70% of the spatial domain with high probability of flow feature occurrence and only 2–30% containing key flow features. The UROI and associated data can be selectively stored and visualised. In contrast to batch-POD, iPOD reduces memory usage by more than 10× and time by up to 75%.