RS触发器“状态不定”的详细分析与实验验证

基本RS触发器和同步RS触发器都有一个"状态不定"的状态,不同版本的数字电路教材在状态说明部分的解释不尽相同,这给读者,特别是学生的学习造成困难,使大家对此问题的理解产生了混乱,在对时序波形的分析时,出现不同的结果,这是不应该的。教师在教学中讲授这一内容时,为了给学生讲解清楚,需要翻阅多本参考书来了解这一问题。我们应该对此问题进行认真分析与求证,得出正确的结论,并在叙述时统一起来,消除书本上混乱的阐述,进而消除人们理解上的混乱。这是一个看似小但却并不小的问题,因为科学东西就应该有一个清晰的、严谨的、正确的解释,而不是模糊的、模凌两可的表述。

谈基本RS触发器输出不定状态的教学体会

基于多年的教学经验,针对学生对基本RS触发器输出不定状态的模糊认识,总结了一些教学体会和方法。

RS触发器“不定状态”的理解

RS触发器作为时序逻辑电路的基础电路,具有十分重要的作用,表述它的逻辑功能的方法也多种多样,有逻辑函数表示法、波形图表示法、时序图表示法等等.本文通过波形图直观地阐明了各种RS触发器“不定状态”发生的时间段,以加深对RS触发器更进一步了解.

Application of uncertain type of AHP to condition assessment of cable-stayed bridges

In order to guarantee the safety service and life-span of long-span cable-stayed bridges, the uncertain type of analytic hierarchy process （AHP） method is adopted to access the bridge condition. The correlative theory and applied objects of uncertain type of AHP are introduced, and then the optimal transitive matrix method is chosen to calculate the interval number judgment matrix, which makes the weights of indices more reliable and accurate. Finally, with Harbin Songhua River Cable-Stayed Bridge as an example, an index system and an assessment model are proposed for the condition assessment of this bridge, and by using uncertain type of AHP, the weights of assessment indices are fixed and the final assessment results of the bridge are calculated, which proves the feasibility and practicability of this method. The application of this assessment method can provide the scientific basis for maintenance and management of long-span cable-stayed bridges.

利用Multisim实现RS触发器功能仿真测试

针对数字电路中触发器正常工作时出现的无序、不定、空翻等现象,提出了用Multisim软件进行虚拟仿真测试及消除。通过调整基本RS触发器的频率、占空比,仿真测试触发器不定状态的规律。利用同步(时钟)控制、限制RS状态、调整结构等多种仿真测试方法,观测消除无序、不定、空翻现象的效果。实践证明,利用Multisim仿真软件平台,能使理论知识与实际结果相印证,直观有效地测试各种复杂现象,生动形象地辅助课堂教学活动,是电子设计仿真的理想工具。

数字电路教学中几个值得强调的问题

本文对脉冲触发器误触发问题进行了分析总结,对边沿触发器存在的不可靠性问题进行了探讨,强调了SR触发器出现不定状态的时刻,指出了产生不定状态的原因。

Dynamic Instability of Tunnel in Blocky Rock Mass

The displacements and geometry of the rock blocks and the properties of the rock struc-ture play an important role in the stability of tunnels.Based on the key block model,the dynamic instability analysis of underground tunnel subjected to intensive short-time compressional wave was conducted.The instability of the tunnel caused by the spallation and the inertial effect was distin-guished.And the influence of the roof contour curvature of tunnel was also determined.

Laws of motion of particles in a jigging process

The laws of motion of particle groups in a jigging process are studied. These describe the macroscopic phenomena that occur during jigging. During jigging the heavier and bigger particles concentrate at the bed bottom while lighter and smaller particles move to the upper part of the bed. Particles with equivalent properties tend to concentrate at a certain position centered around the inherent height of their distribution. The particle distribution variance gradually diminishes to some asymptotic value. The state equation group of the jigging bed is deduced and a calculation method, called the λ value judgment method, is proposed. The method is used to calculate the layer number and the inherent height of each particle group. A mathematical expression for the particle distribution variance is also given.

Reliability Analysis Based on a Direct Ship Hull Strength Assessment

A method of reliability analysis based on a direct strength calculation employing the von Mises stress failure criterion is presented here. The short term strain distributions of ship hull structural components are identified through the statistical analysis of the wave-induced strain history and the long term distributions by the weighted summation of the short term strain distributions. The wave-induced long term strain distribution is combined with the still water strain. The extreme strain distribution of the response strain is obtained by statistical analysis of the combined strains. The limit state function of the reliability analysis is based on the von Mises stress failure criterion, including the related uncertainties due to the quality of the material and model uncertainty. The reliability index is calculated using FORM and sensitivity analysis of each variable that has effects on the reliability is also discussed.

Application of the Conditional Nonlinear Optimal Perturbations Method in a Theoretical Grassland Ecosystem

Using a simplified nonlinearly theoretical grassland ecosystem proposed by Zeng et al.,we study the sensitivity and nonlinear instability of the grassland ecosystem to finiteamplitude initial perturbations with the approach of conditional nonlinear optimal perturbation （CNOP）.The results show that the linearly stable grassland （desert or latent desert） states can turn to be nonlinearly unstable with finite amplitude initial perturbations.When the precipitation is between the two bifurcation points,a large enough finite amplitude initial perturbation can induce a transition between the grassland statethe desert state or the latent desert.

Asymmetric Effects on Escape Rates of Bistable System

The asymmetric effects on the escape rates from the stable states x±in the bistable system are analyzed. The results indicate that the multiplicative noise and the additive noise always enhance the particle escape from stable states x±of bistable.However,the asymmetric parameter r enhances the particle escape from stable state x_+,and holds back the particle escape from stable state x_-.

KRAS mutation testing in metastatic colorectal cancer

The KRAS oncogene is mutated in approximately 35%-45% of colorectal cancers, and KRAS mutational status testing has been highlighted in recent years. The most frequent mutations in this gene, point substitutions in codons 12 and 13, were validated as negative predictors of response to anti-epidermal growth factor receptor antibodies. Therefore, determining the KRAS mutational status of tumor samples has become an essential tool for managing patients with colorectal cancers. Currently, a variety of detection methods have been established to analyze the mutation status in the key regions of the KRAS gene; however, several challenges remain related to standardized and uniform testing, including the selection of tumor samples, tumor sample processing and optimal testing methods. Moreover, new testing strategies, in combination with the mutation analysis of BRAF , PIK3CA and loss of PTEN proposed by many researchers and pathologists, should be promoted. In addition, we recommend that microsatellite instability, a prognostic factor, be added to the abovementioned concomitant analysis. This review provides an overview of KRAS biology and the recent advances in KRAS mutation testing. This review also addresses other aspects of status testing for determining the appropriate treatment and offers insight into the potential drawbacks of mutational testing.

Robust stabilization and disturbance attenuation for a class of underactuated mechanical systems

The robust control problem for a class of underactuated mechanical systems called acrobots is addressed. The goal is to drive the acrobots away from the straight-down position and balance them at the straight-up unstable equilibrium position in the presence of parametric uncertainties and external disturbance. First, in the swing-up area, it is shown that the time derivative of energy is independent of the parameter uncertainties, but exogenous disturbance may destroy the characteristic of increase in mechanical energy. So, a swing-up controller with compensator is designed to suppress the influence of the disturbance. Then, in the attractive area, the control problem is formulated into a H~ control framework by introducing a proper error signal, and a sufficient condition of the existence of Hoo state feedback control law based on linear matrix inequality （LMI） is proposed to guarantee the quadratic stability of the control system. Finally, the simulation results show that the proposed control approach can simultaneously handle a maximum ±10% parameter perturbation and a big disturbance simultaneously.

风险小论

风险是保险研究和处理的主要对象,因此,要了解保险必先了解风险.关于风险,有多种理解和表述,如:“风险为可测定的不确定性;对发生某一经济损失的不确定性;风险是一种无法预料的、其实际后果可能不同于预测后果的倾向;损失的可能即为风险;对特定情况下关于未来结果的客观疑虑;风险即损失的不确定性.”(《新编保险学》陈继儒编著,)我基本上同意最后一种看法,因为它揭示了风险的本质特征.下面我就谈一谈我对“风险是损失的不确定性”的理解.一、风险与损失风险首先与损失相连。

The identification algorithm for commensurate order linear time-invariant fractional systems

An efficient identification algorithm is given for commensurate order linear time-invariant fractional systems. This algorithm can identify not only model coefficients of the system, but also its differential order at the same time. The basic idea is to change the system matrix into a diagonal one through basis transformation. This makes it possible to turn the system’s input-output relationships into the summation of several simple subsystems, and after the identification of these subsystems, the whole identification system is obtained which is algebraically equivalent to the former system. Finally an identification example verifies the effectiveness of the method previously mentioned.

Effect of discontinuities characteristics on coal mine stability and sustainability： A rock fall prediction approach

Rock fall related accidents continue to occur in coal mines,although artificial support mechanisms have been used extensively. Roof stability is primarily determined in many underground mines by a limited number of methods that often resort to subjective criteria. It is argued in this paper that stability conditions of mine roof strata,as a key factor in sustainability in coal mines,must be determined by a survey which proactively investigates fundamental aspects of said mine. Failure of rock around the opening happens as a result of both high rock stress conditions and the presence of structural discontinuities. The properties of such discontinuities affect the engineering behavior of rock masses causing wedges or blocks to fall from the roof or sliding out of the walls. A practical rule-based approach to assess the risk of a roof fall is proposed in the paper. The method is based on the analysis of structural data and the geometry and stability of wedges in underground coal mines. In this regard,an accident causing a huge collapse in a coal mine leading to 4 fatalities is illustrated by way of a case study. Horizontal and vertical profiles are prepared by geophysical methods to define the falling zone and its boundaries. The collapse is then modeled by the use of sophisticated computer programs in order to identify the causes of the accident.

Stabilization of a class of nonlinear discrete time systems with time varying delay

The stability and stabilization of a class of nonlinear discrete time delayed systems(NDTDS) with time-varying delay and norm-bounded nonlinearity are investigated. Based on discrete time Lyapunov–Krasovskii functional method, a sufficient delaydependent condition for asymptotic stability of nonlinear systems is offered. Then, this condition is used to design a new efficient delayed state feedback controller(DSFC) for stabilization of such systems. These conditions are in the linear matrix inequality(LMI) framework. Illustrative examples confirm the improvement of the proposed approach over the similar cases. Furthermore, the obtained stability and stabilization conditions will be extended to uncertain discrete time delayed systems(UDTDS) with polytopic parameter uncertainties and also with norm-bounded parameter uncertainties.

Effect of acupuncture on rabbit bladder with urodynamic indexes

OBJECTIVE： To study the effect of acupuncture on rabbit bladder with urodynamic indexes. METHODS： New Zealand male rabbits were divid ed into control group, model group, treatment group 1 treated by acupuncture at Shenshu （BL 23） and treatment group 2 treated by acupuncture at Zhongji （CV 3）. The urine dynamic parameters through the urethral catheter were detected in each group in order： fluctuation of pressure at fill ing phase of urinary bladder and flow rate in urina tion phase, which were used as quantification in dexes of urinary bladder function. The urinary blad der abnormal model was prepared by administra tion of cholinergic stimulant; Regulatory effects of acupuncture at Shenshu （BL 23） and Zhongji （CV 3） on the abnormal state of the urinary bladder were respectively observed. RESULTS： 1） In the filling phase of urinary bladder and in the urination phase, the intravesical pres sure wave in infilling （IPWI） and intravesical dis charge rate （IDR） could be respectively recorded. 2） IPWI and IDR could become abnormality by neo stigmine methyl sulfate [stability type IPWh the con trol group （n=20, 80%） vs the model group （n=15, 14.3%）, P〈0.01; IDR and time regression equation： the control group （n=20, y=24.3 0.878x） vs the model group （n=15, y=40.0 5.15x）, P〈0.01]. 3） Ab normal IPWI＇s could be normalized respectively by acupuncture at Shenshu （BL 23） and Zhongji （CV 3） [the stability type IPWl wave： the model group （n= 2, 14.3%） vs the treatment group 1 （n=3, 30%）, P〉 0.05; the instability type IPWl wave： the model group （n=13, 85.7%） in vs the treatment group 2 （n=6, 60%）, P〉0.05]; 4） Abnormal IDR also could be turned to normality by acupuncture at Shenshu （BL 23） and Zhongji （CV 3）, respectively [IDR and the time regression equation： the model group （n=15, y=40.0 5.15x） vs the treatment group 1 （n=10, y= 18.9 0.499x）, P〈0.01; the model group （n=15, y= 40.0 5.15x） vs the treatment group 2 （n=10, y= 17.5 0.251x）, P〈0.01]. CONCLUSION： 1） Urodynamic indexes can be used for study of mechanism of acupuncture effects; 2） The effect of acupuncture in the bladder filling phase is smaller than that in the urination phase; 3） Acupuncture has a very obvious effect on intravesi cal discharge rate.

A new alternative approach for investigating acidization dissolution front propagation in fluid-saturated carbonate rocks

The natural phenomenon associated with the chemical dissolution of dissolvable minerals of rocks can be employed to develop innovative technology in mining and oil extracting engineering. This paper presents a new alternative approach for theoretically dealing with chemical dissolution front （CDF） propagation in fluid-saturated carbonate rocks. Note that the CDF is represented by the porosity front in this study. In this new approach, the porosity, pore-fluid velocity and acid concentration are directly used as independent variables. To illustrate how to use the present new approach, an aeidization dissolution system （ADS） consisting of carbonate rocks, which belongs to one of the many general chemical dissolution systems （CDSs）, is taken as an application example. When the acid dissolution capacity （ADC） number （that is defined as the ratio of the volume of the carbonate rock dissolved by an acid to that of the acid） approaches zero, the present new approach can be used to obtain analytical solutions for the stable ADS. However, if the ADC number is a nonzero finite number, then numerical solutions can be only obtained for the ADS, especially when the ADS is in an unstable state. The related theoretical results have demonstrated that： （1） When the ADS is in a stable state and in the case of the ADC number approaching zero, the present new approach is mathematically equivalent to the previous approach, in which the porosity, pore-fluid pressure and acid concentration are used as independent variables. However, when the ADS is in an unstable state, the use of the present new approach leads to a free parameter that needs to be determined by some other ways. （2） The existence of a non-step-type dissolution front within a transient region should at least satisfy that none of the ADC number, injected acid velocity and reciprocal of the dissolution reaction rate is equal to zero in the stable ADS.