高三语文复习创新实践二则

笔者找到了仅仅针对高考且仅仅适用于高考的某些技巧。笔者提出的"《评分细则》的模拟策略"和"‘分数时间化’的目标管理策略",就是此类技巧化的东西。它们强调了两个词:实战、实效;有一个共同点,就是强化复习的主体色彩,增强学生的应试能力。

Spectrum Allocation for Cognitive Radio Networks with Non-Deterministic Bandwidth of Spectrum Hole

The spectrum allocation for cognitive radio networks(CRNs) has received considerable studies under the assumption that the bandwidth of spectrum holes is static. However, in practice, the bandwidth of spectrum holes is time-varied due to primary user/secondary user(PU/SU) activity and mobility, which result in non-determinacy. This paper studies the spectrum allocation for CRNs with non-deterministic bandwidth of spectrum holes. We present a novel probability density function(PDF) through order statistics as well as its simplified form to describe the statistical properties of spectrum holes, with which a statistical spectrum allocation model based on stochastic multiple knapsack problem(MKP) is formulated for spectrum allocation with non-deterministic bandwidth of spectrum holes. To reduce the computational complexity, we transform this stochastic programming problem into a constant MKP through exploiting the properties of cumulative distribution function(CDF), which can be solved via MTHG algorithm by using auxiliary variables. Simulation results illustrate that the proposed statistical spectrum allocation algorithm can achieve better performance compared with the existing algorithms when the bandwidth of spectrum holes is time-varied.

Coefficient of retardation time found out by polynomial fitting to predict creep behaviour of polystyrene

The universal creep function is successful in relating the creep （ε） to the ageing time （ta）, coefficient of retardation time （β）, and intrinsic time （t0）. The relation was used to treat the creep experimental data for polystyrene （PS） specimens at a given aged time and different stress levels. Comparing with “middle-point” method reported in the literatures, β is found out by another method “polynomial fitting” in this work. Then unified master lines were constructed with the treated data and curves according to the universal equation. The master lines can be used to predict the long-term creep behaviour and lifetime by extrapolating to a required ultimate strain.

A Learning Evasive Email-Based P2P-Like Botnet

Nowadays, machine learning is widely used in malware detection system as a core component. The machine learning algorithm is designed under the assumption that all datasets follow the same underlying data distribution. But the real-world malware data distribution is not stable and changes with time. By exploiting the knowledge of the machine learning algorithm and malware data concept drift problem, we show a novel learning evasive botnet architecture and a stealthy and secure C&C mechanism. Based on the email communication channel, we construct a stealthy email-based P2 P-like botnet that exploit the excellent reputation of email servers and a huge amount of benign email communication in the same channel. The experiment results show horizontal correlation learning algorithm is difficult to separate malicious email traffic from normal email traffic based on the volume features and time-related features with enough confidence. We discuss the malware data concept drift and possible defense strategies.

A modified highly precise direct integration method for a class of linear time-varying systems

It is always a bottleneck to design an effective algorithm for linear time-varying systems in engineering applications.For a class of systems,whose coefficients matrix is based on time-varying polynomial,a modified highly precise direct integration(VHPD-T method)was presented.Through introducing new variables and expanding dimensions,the system can be transformed into a timeinvariant system,in which the transfer matrix can be computed for once and used forever with a highly precise direct integration method.The method attains higher precision than the common methods(e.g.RK4 and power series)and high efficiency in computation.Some numerical examples demonstrate the validity and efficiency of the method proposed.

Lie Symmetries,Conservation Laws and Explicit Solutions for Time Fractional Rosenau–Haynam Equation

Under investigation in this paper is the invariance properties of the time fractional Rosenau-Haynam equation, which can be used to describe the formation of patterns in liquid drops. By using the Lie group analysis method, the vector fields and symmetry reductions of the equation are derived, respectively. Moreover, based on the power series theory, a kind of explicit power series solutions for the equation are well constructed with a detailed derivation. Finally, by using the new conservation theorem, two kinds of conservation laws of the equation are well constructed with a detailed derivation.

Effect of Pore Distribution on Melting Behavior of Paraffin in Fractal Metal Foam

An unsteady model of melting heat transfer in metal foam filled with paraffin is developed and numerically analyzed. In the model, the pore distribution of metal foam is described by Sierpinski fractal. By this fractal description,six types of metal foams with the identical porosity, different pore distributions are reconstructed. The effect of pores distribution on the heat transfer performance of the paraffin/copper foam composite is emphatically investigated. The solid-liquid distribution, the evolution of the melting front, the dynamic temperature response and the total melting time in these six fractal structures are all examined and analyzed. The results indicate that, the pores distribution has a significant impact on the melting heat transfer of the paraffin in the metal foam. When the first-level fractal pore is located near the heat source boundary, the thermal hysteresis effect of the paraffin on the solid matrix heat transfer is more significant. If the cross-sectional length of the pores along the normal direction of heat transfer is larger, the heat transfer barrier of the solid matrix is greater. It is favorable for the paraffin heat transfer when the pores specific surface area is larger.

Numerical analysis on shock-cylinder interaction using immersed boundary method

The problem of shock interaction with a rigid circular cylinder has been investigated using a compressible immersed boundary method coupled with high-order weighted-essentially non-oscillatory(WENO) scheme.First,the accuracy of the developed code is validated.Then,influences of the incident shock Mach number on the flow-field structure and dynamic drag coefficient,as well as time evolution of the flow field are studied.For different shock Mach number,the flow structure shows very different features.At a given dimensionless time,both the normalized shock detachment distance and the normalized vertical distance from the highest point of the primary reflected shock to the centerline of the cylinder decreases with increasing shock Mach number.However,location of the upper triple point varies non-monotonically with shock Mach number.For a case with given shock Mach number,the trajectory of the upper triple point and the time evolution of the normalized vertical distance from the highest point of the primary reflected shock to the centerline of the cylinder can both be predicted by linear correlation.Nevertheless,the time evolution of the normalized shock detachment distance is biased to be non-linear.Meanwhile,time evolution of force exerted on the cylinder is quite unsteady for a case with given shock Mach number and given cylinder diameter.For small shock Mach number,there exists a negative valley,and it disappears when the incident shock Mach number increases to a large value,e.g.,1.7.Furthermore,correlations to predict the occurrence of the peak drag and its value under different shock Mach numbers have been proposed.