编译原理教学中创造性思维能力的培养

阐述了在编译原理教学中,从调动内驱力、提倡发散思维、提倡探究学习、培养抽象思维四个方面入手,加强学生创造性思维能力的培养,给出了教学实施的具体步骤和方法。多年的教学实践证明,达到了预期的目的。     

舵机控制用PWM信号的研究与实现

当前生成PWM信号的方法繁多,生成的PWM信号的质量也参差不齐。针对这种现象,提出了PWM信号生成方法合理性评价四原则,实现了对各种生成PWM信号的方法具体全面的评价。然后提出了一种分时成组原理,利用这一原理,实现了一种基于C8051F040单片机的舵机控制用PWM信号生成方法。最后利用PWM信号生成方法合理性评价的四条原则,对此方法的合理性进行了评价。在实践中证明了评价结论的正确性。     

用Mathematica解热量传递过程中的数学问题

本文建议用数学软件Mathematica计算热量传递过程,包括用符号运算功能推导保温层临界直径,用曲线拟合法处理传热实验数据,用积分法求取传热系数为温度函数时的换热面积,用Solve等命令求解换热和保温过程所产生的非线性方程,用DSolve命令求解非稳态传热过程产生的微分方程等等。同时绘制出有关函数图形,准确、形象地展示计算过程和结果,方便教师讲解和学生理解,避免复杂、繁琐、耗时的手工计算,提高学生利用计算机解决热量传递问题的能力。     

“数据库原理与应用”课程实践教学的改革与探索

"数据库原理与应用"的实践教学是该课程的一个重要教学环节,对提高教学质量和培养学生能力起着决定性的作用。本文论述了该课程在课堂教学、课程设计和课外活动指导三个方面所作的一些实践教学改革和探索,取得了较好的效果。     

浅析绘画色彩的对比之美

用色彩对比语言用来产生视觉冲突,转换表现空间,树立视觉中心,表现艺术特质,抒发作者心境等,是各种视觉艺术中的重要艺术表现手段。只有达到色彩规律的自如掌握,色彩的组织结构语言纯熟于胸,才能达到"随心所欲而不逾距"的境界,达到色彩艺术的完美境界。     

On mesh restrictions to satisfy comparison principles,maximum principles,and the non-negative constraint: Recent developments and new results

This article concerns mesh restrictions that are needed to satisfy several important mathematical properties—maximum principles, comparison principles, and the nonnegative constraint—for a general linear second-order elliptic partial differential equation. We critically review some recent developments in the field of discrete maximum principles, derive new results, and discuss some possible future research directions in this area. In particular, we derive restrictions for a three-node triangular (T3) element and a four-node quadrilateral (Q4) element to satisfy comparison principles, maximum principles, and the nonnegative constraint under the standard single-field Galerkin formulation. Analysis is restricted to uniformly elliptic linear differential operators in divergence form with Dirichlet boundary conditions specified on the entire boundary of the domain. Various versions of maximum principles and comparison principles are discussed in both continuous and discrete settings. In the literature, it is well-known that an acute-angled triangle is sufficient to satisfy the discrete weak maximum principle for pure isotropic diffusion. Herein, we show that this condition can be either too restrictive or not sufficient to satisfy various discrete principles when one considers anisotropic diffusivity, advection velocity field, or linear reaction coefficient. Subsequently, we derive appropriate restrictions on the mesh for simplicial (e.g., T3 element) and nonsimplicial (e.g., Q4 element) elements. Based on these conditions, an iterative algorithm is developed to construct simplicial meshes that preserve discrete maximum principles using existing open source mesh generators. Various numerical examples based on different types of triangulations are presented to show the pros and cons of placing restrictions on a computational mesh. We also quantify local and global mass conservation errors using representative numerical examples and illustrate the performance of metric.     

Fluorinated Phosphorene: Electrochemical Synthesis,Atomistic Fluorination,and Enhanced Stability

Phosphorene has attracted great interest due to its unique electronic and optoelectronic properties owing to its tunable direct and moderate band‐gap in association with high carrier mobility. However, its intrinsic instability in air seriously hinders its practical applications, and problems of technical complexity and in‐process degradation exist in currently proposed stabilization strategies. A facile pathway in obtaining and stabilizing phosphorene through a one‐step, ionic liquid‐assisted electrochemical exfoliation and synchronous fluorination process is reported in this study. This strategy enables fluorinated phosphorene (FP) to be discovered and large‐scale, highly selective few‐layer FP (3?6 atomic layers) to be obtained. The synthesized FP is found to exhibit unique morphological and optical characteristics. Possible atomistic fluorination configurations of FP are revealed by core‐level binding energy shift calculations in combination with spectroscopic measurements, and the results indicate that electrolyte concentration significantly modulates the fluorination configurations. Furthermore, FP is found to exhibit enhanced air stability thanks to the antioxidation and antihydration effects of the introduced fluorine adatoms, and demonstrate excellent photothermal stability during a week of air exposure. These findings pave the way toward real applications of phosphorene‐based nanophotonics.     

产品细节形态设计探究

目的探究产品细节形态设计中的设计原则和方法。方法结合现有产品的调研汇总、基本模型的建立分析以及问卷调查的结果,对影响产品外观细节形态的两个基本要素——圆角和分割线的属性对产品视觉美感的影响进行研究,并给出相关实例验证。结论分析了产品细节形态中圆角和分割线两个视觉元素对产品视觉感受的影响,提出了在产品细节形态设计中合理设计圆角和分割线的原则和方法,给出了从圆角和分割线两个方面提升整体产品视觉美感的优化方案。     

不同浓度Cu掺杂SnO2材料电学和力学性质的研究

为研究Cu掺入对SnO_2性能的影响,本文采用密度泛函理论和平面波赝势法,建立了未掺杂SnO_2和不同比例Cu掺杂的SnO_2晶胞模型,对Sn_(1-x)Cu_xO_2(x=0、0.083、0.125、0.167、0.25、0.5)超晶胞体系进行优化计算、能量计算和弹性模量计算,得到晶格常数、弹性模量、电荷分布、能带结构和态密度图.研究表明:掺杂能够使得材料的弹性模量大幅减小,对应的硬化函数值降低,易于材料加工;在电性质方面,掺杂后,材料均属于直接带隙半导体材料.当x0.25时,由于掺杂浓度过高使得晶格发生畸变,电性质与未掺杂情况类似;当x0.25时,随着掺杂浓度的降低,导带收缩加剧,局域性增强,禁带宽度变窄,使得电子从价带受激跃迁所需能量降低,故掺杂后材料表现出半金属性,导电性增强.     

Jumps and logic in the law

The main stream of legal theory tends to incorporate unwritten principles into the law. Weighing of principles plays a great role in legal argumentation, inter alia in statutory interpretation. A weighing and balancing of principles and other prima facie reasons is a jump. The inference is not conclusive.To deal with defeasibility and weighing, a jurist needs both the belief-revision logic and the nonmonotonic logic. The systems of nonmonotonic logic included in the present volume provide logical tools enabling one to speak precisely about various kinds of rules about rules, dealing with such things as applicability of rules, what is assumed by rules, priority between rules and the burden of proof. Nonmonotonic logic is an example of an extension of the domain of logic. But the more far-reaching the extension is, the greater problems it meets. It seems impossible to make logical reconstruction of the totality of legal argumentation.The lawyers' search for reasons has no obvious end point. Ideally, the search for reasons may end when one arrives at a coherent totality of knowledge. In other words, coherence is the termination condition of reasoning. Both scientific knowledge and knowledge of legal and moral norms progresses by trial and error, and that one must resort to a certain convention to define what error means. The main difference is, however, that conventions of science are much more precise than those of legal scholarship.Consequently, determination of error in legal science is often holistic and circular. The reasons determining that a legal theory is erroneous are not more certain than the contested theory itself. A strict and formal logical analysis cannot give us the full grasp of legal rationality. A weaker logical theory, allowing for nonmonotonic steps, comes closer, at the expense of an inevitable loss of computational efficiency. Coherentist epistemology grasps even more of this rationality, at the expense of a loss of preciseness.