Fluidic control of wake-flow behind a two-dimensional square back bluff body

This experimental study deals with wake-flow fluidic control behind a two-dimensional square back geometry positioned close to the ground. The fluidic control system is made of pulsed jets positioned at the upper edge of the model base. The objective of the fluidic action is to modify the wake-flow development, and as a consequence the static pressure distribution over the model base and hence the pressure drag. The main concern of this study is to determine to what extent the presence of a flow confined between the model and the floor influences the effectiveness of the control. Static pressure measurements at the model base and wake-flow characteristics derived from PIV measurements at a high acquisition frequency indicate global similarities between a case where an underbody flow exists and a case where this underbody flow is absent. For low actuation frequencies, discrepancies in the way the coherent structures due to the control develop in the shear layer appear.     

Dynamics of fronts in optical media with linear gain and nonlinear losses

The dynamics of fronts, or kinks, in dispersive media with gain and losses is considered. It is shown that the front parameters, such as the velocity and width, depend on initial conditions. This result is not typical for dissipative systems. For exponentially decreasing initial conditions, the relations for the front parameters are found. A presence of the global bifurcation, when a soliton solution is replaced by the front solution, is demonstrated. It is also shown that in order to observe fronts, the front velocity should be larger than the characteristic velocity of the modulational instability.     

Wave Front Tracking in Systems of Conservation Laws

This paper contains several recent results about nonlinear systems of hyperbolic conservation laws obtained through the technique of Wave Front Tracking.     

谱负Lévy过程位势测度的推广

位势测度在占位时的求解过程中是一个重要的工具,对谱负Lévy过程的位势测度进行了推广.在目前已有位势测度结论的基础上运用维纳-霍夫分解方法,求出了谱负Lévy过程X在0ab时,形式为Ex∫τ+bτ+ae-qt1{Xt∈dy,tτ}dt的位势测度.其表达式用谱负Lévy过程的尺度函数和拉普拉斯的逆函数表示.这些表达式可以应用到一些Lévy风险过程相关的破产时间问题的研究中.     

Algorithms and Identities for(q,h)-Bernstein Polynomials and(q,h)-Bézier Curves–A Non-Blossoming Approach

We establish several fundamental identities,including recurrence relations,degree elevation formulas,partition of unity and Marsden identity,for quantum Bernstein bases and quantum Bézier curves.We also develop two term recurrence relations for quantum Bernstein bases and recursive evaluation algorithms for quantum Bézier curves.Our proofs use standard mathematical induction and other elementary techniques.     

Fréchet-Riesz表示定理的两种证明

基于Hilbert空间正规正交基,本文给出了Fréchet-Riesz表示定理的新证明,明确写出连续线性泛函对应元的表达式。此外,在实Hilbert空间情形下,本文基于变分原理证明了Fréchet-Riesz表示定理。     

Fejér不等式加强形式的推广

通过建立积分恒等式,将一个关于4阶可微函数的Fejér不等式的加强形式推广到关于2n-1(n≥2)阶可微函数的Fejér型不等式.对此新推广的不等式还给出了若干误差估计.     

二帧变换光源阴影莫尔技术研究

为了快速测量物体表面三维轮廓,提出一种变换光源位置的相移阴影莫尔技术.该方法通过控制两个光源的亮灭,将相移引入测量视场.使用二维经验模式分解法对条纹图进行正则化,结合螺旋相位变换方法和二帧相移算法对测量高度进行估计,利用发展的迭代自调算法提取精确测量相位.计算机仿真和光学实验结果表明,该方法的解调准确度优于现有的二帧相移解调算法,同时,由于消除了测量过程中必要的机械运动,只需要二帧条纹图进行相位解调,节约了测量时间.     

繁星无法超越——三体问题溯源

三体问题是一个困扰学术界多年的难题.自牛顿在《自然哲学的数学原理》中首次定义三体问题开始,人们已经在这个问题上努力了300年之久.欧拉和拉格朗日先后研究了一些较为简单的三体系统问题,而庞加莱首先考虑了限制性的三体问题,但发现其轨迹十分复杂而无法描绘.他转而证明了三体问题不存在解析解,并着手创立了一门崭新的学科——非线性动力学.充满生命力的非线性动力学或能为人们解决这个问题提供不同的思路.