电路分析中的等效概念及其应用

应用等效的理论,通过实例,阐述了等效变换在电路分析和计算中的应用,从而将复杂电路通过等效变换变成简单电路,方便了分析和计算。     

创设旅行社"第二代"特许经营战略模式

在我国旅行社业内,目前普遍采用的扩张战略主要有以下三种模式:在异地设立非法人分社;参股、控股异地旅行社;实行特许经营。以特许经营战略来拓展业务网络的规模具有无法比拟的优越性,但其局限性制约了旅行社扩张战略的进一步实施,通过创设“第二代”旅行社特许经营战略模式力图解决上述问题。     

蠕变条件下完整岩石的起裂和扩展准则

The mechanism and criterion of crack initiation and propagation of rocks were investigated by many researchers,And the creep behaviour of rocks was also theoretically and experimentally studied by some scientists and engineers.The characteristics of crack initation and propagation of rocks under creep condition.however,are very improtant for rock engineering and still not paid enough attention by researchers,In this paper,the criterion and mechanism of crack initiation and propagation under creep condition were investigated using specimens collected from sandstone rock formations outcropping in the Emei Mountain,the Sichuan Province of China.Cuboid specimens under three point bending were used in this investigation.All specimens were classified into four sorts and used for Mode-I fracutre of creep frcture tests.The experimental result shows that due to creep deformation.rock crack will inevitably initialt and propagate under a load of KI,which is less than fracture toughness KIC but not less than a constant(marked as KIC2),KIC2 indicates the ability of rock to resist crack initiation and propagation under creep conditions and is less than fracture tough ness KIC.defined as creep fracture toughness in this paper,KIC2 should be considered as an importnat parameter on design and computation of rock engineering.The microstructureal mechanism for crack initiation and propagation of rock materials under creep condition was introduced based on competitive model between softening effect and hardening effect,and the validity of test result was explained.The test result was also verified in rheological theory.When KI is more than KIC2 but less than KIC,rock crack will initiate and propagate after a time interval of sustained loading under creep condition.In order to find the relation between duration of sustained lading.which can lead to crack initiation and propagation,and the initial stress intensity factor KI,an unequal0interval time sequence forecasting and predicting model was introduced,and the relation was obtained for homogeneous and isotropic fine-grained red sandstone.Finally a modified fracture toughness formula was given,in which the influence of fracture process zone(FPZ) was fully considered.     

The Relationship between Students’ Characteristics and Their Impressions of Online Courses

This study explored relationship between students’ conscientiousness and motivation, their impressions of the online environment, and their learning. Also examined were relationships between their impressions of the online environment and their sense of community and their interactions with others. Questionnaires were completed by 84 students at a private college. Students who were more conscientious and intrinsically motivated had more favorable impressions of online courses. They were engaged, and perceived value in the course, and were less anxious or frustrated when taking online courses. Those students who perceived a sense of community, or social presence, also had more favorable impressions. These relationships and their implications are discussed.