图像强度的平方和最大化自聚焦算法

为了获得精确的方位向多普勒调频率参数以提高合成孔径雷达图像的质量,提出了一种新的自聚焦算法,即图像强度的平方和最大化准则的自聚焦算法。该算法基于图像对比度,推导了图像强度的平方和与图像对比度的关系,同时为了提高该算法的计算效率,又提出利用二分法替代通常的进退法。最后,利用实测数据处理,验证了二分法收敛速度较快和本算法的有效性。

有机染料双光子吸收截面与激发光强度的关系

根据激光物理半经典理论,利用量子力学二级含时微扰方法,推导出双光子吸收几率与激发光的强度平方成正比的计算结果,在推导过程中假设入射光是非偏振的,并且简化激发光场为单频电场,这与实验中实际激发光不一致,但对所要计算的结果来说是足够精确的。给出了大分子有机染料双光子吸收截面的表达形式并进行了估算,得出双光子吸收截面的量级约为10-50cm4.s/photon。

Limit equilibrium analysis for rock slope stability using basic Hoek–Brown strength criterion

Hoek–Brown(HB)strength criterion can reflect rock’s inherent failure nature,so it is more suitable for analyzing the stability of rock slopes.However,the traditional limit equilibrium methods are at present only suitable for analyzing the rock slope stability using the linear equivalent Mohr–Coulomb(EMC)strength parameters instead of the nonlinear HB strength criterion.Therefore,a new method derived to analyze directly the rock slope stability using the nonlinear HB strength criterion for arbitrary curve slip surface was described in the limit equilibrium framework.The current method was established based on certain assumptions concerning the stresses on the slip surface through amending the initial normal stressσ0 obtained without considering the effect of inter-slice forces,and it can satisfy all static equilibrium conditions of the sliding body,so the current method can obtain the reasonable and strict factor of safety(FOS)solutions.Compared with the results of other methods in some examples,the feasibility of the current method was verified.Meanwhile,the parametric analysis shows that the slope angleβhas an important influence on the difference of the results obtained using the nonlinear HB strength criterion and its linear EMC strength parameters.Forβ≤45°,both of the results are similar,showing the traditional limit equilibrium methods using the linear EMC strength parameters and the current method are all suitable to analyze rock slope stability,but forβ>60°,the differences of both the results are obvious,showing the actual slope stability state can not be reflected in the traditional limit equilibrium methods,and then the current method should be used.

Simulation of rock deformation and mechanical characteristics using clump parallel-bond models

To properly simulate hard rock with a high ratio of the uniaxial compressive strength to tensile strength(UCS/TS) and realistic strength-failure envelope,the rock deformation and mechanical characteristics were discussed in detail when the particle simulation method with the clump parallel-bond model(CPBM) was used to conduct a series of numerical experiments at the specimen scale.Meanwhile,the effects of the loading procedure and crack density on the mechanical behavior of a specimen,which was modeled by the particle simulation method with the CPBM,were investigated.The related numerical results have demonstrated that:1) The uniaxial compressive strength(UCS),tensile strength(TS) and elastic modulus are overestimated when the conventional loading procedure is used in the particle simulation method with the CPBM; 2) The elastic modulus,strength and UCS/TS decrease,while Poisson ratio increases with the increase of the crack density in the particle simulation method with the CPBM; 3) The particle simulation method with the CPBM can be used to reproduce a high value of UCS/TS(>10),as well as a high friction angle and reasonable cohesion strength; 4) As the confining pressure increases,both the peak strength of the simulated specimen and the number of microscopic cracks increase,but the ratio of tensile cracks number to shear cracks number decreases in the particle simulation method with the CPBM; 5) Compared with the conventional parallel-bond model,the CPBM can be used to reproduce more accurate results for simulating the rock deformation and mechanical characteristics.

Numerical Simulation of Mechanical Behaviors of Degradable Porous Bioceramics with Cracks

Hydroxyapatite bioceramics is simulated by using finite element method （FEM）. The influences of porosity, hole shape, angle of crack and other parameters on the ceramics are analyzed. The results show that with the increase of the angle between crack and horizontal direction, the stress intensity factor KⅠ decreases gradually, but stress intensity factor KⅡ increases at first and then it decreases. The value of KⅡ reaches maximum when the angle between crack and horizontal direction is 45°. KⅠ and KⅡ rise with the increase of porosity, and they are almost the same for the circular and hexagonal holes. For elliptical holes, KⅠ and KⅡ reach maximum when the long axis of ellipse is perpendicular to the loading direction and they reach minimum when the same axis is parallel to the loading direction. Moreover, with the increase of the angle between the long axis and loading direction, KⅠ and KⅡ increase gradually.

Adaptive Rate Control Scheme for H.264/AVC

The purpose of this paper is to improve allocation of the number of bits without skipping the frame by accurately estimating the target bits in H. 264/AVC rate control. The scheme ImPoses an enhancement method of the target frame rate based on H. 264/AVC bit allocation. The enhancement uses a frame complexion estimation to improve the existing Mean Absolute Difference （MAD） complexity measurement. Bit allocation to each frame is not just computed by target frame rote but also adjusted by a combined frame complexity measure. Using the statistical characteristic, the scheme obtains change of occurrence bit about QP to apply the bit amount by QP from the video characteristic and apply it in the estimated bit amount of the current frame. Simulation results show that the proposed rate eontrol scheme achieves time saving of mine than 99% over existing rate control algorithm. Nevertheless, Peak Signal-to-Noise Ration （PSNR） and bit rate were almost the same as the performances.

Modeling stationary and moving cracks in shells by X-FEM with CB shell elements

The continuum-based(CB)shell theory is combined with the extended finite element method(X-FEM)in this paper to model crack propagation in shells under static and dynamic situations.Both jump function and asymptotic crack tip solution are adopted for describing the discontinuity and singularity of the crack in shells.Level set method(LSM)is used to represent the crack surface and define the enriched shape functions.Stress intensity factors(SIFs)are calculated by the displacement interpolation technique to prove the capability of the method and the maximum strain is applied for the fracture criterion.Also,an efficient integration scheme for the CB shell element with cracks is proposed.