A mathematical mechanism for instabilities in stripe formation on growing domains

A cascade process involving stripe splitting in reaction-diffusion systems with isotropically growing one-dimensional domains is studied. Such cascades, propagating from a smaller domain to a larger domain, have been proposed as an answer to the criticism that the Turing mechanism lacks robustness because many stable patterns can coexist on a large domain and, therefore, the final state is very sensitive to the initial conditions. In contrast, if the system starts with a small domain, very few stable patterns are possible, which limits the sensitivity to the initial conditions. In order to show the validity and limitations of this scenario, we clarify the underlying mathematical mechanism that drives various types of stripe-splitting via a reduction from partial differential equations to ordinary differential equations, as well as investigating global arrangements of the set of n-mode stripe branches with D_n-symmetry of the stripe locations. The mathematical simplification above allows us to reveal how each n-mode stripe branch is destabilized as the domain grows and to characterize the associated eigenprofiles that actually determine the manner of splitting at the infinitesimal level. We find that all the D_n-symmetry-breaking instabilities typically occur simultaneously up to leading order before the saddle-node point of the n-mode stripe branch is reached. The instability with the largest real part is of the alternate type: every other peak splits at the infinitesimal level. A symmetry-preserving instability appears at the saddle-node point, which drives the simultaneous type of splitting, i.e., mode-doubling. Due to competition between these two types of instabilities, the problem depends subtly on the growth speed. Alternate splitting typically arises for slow growth and simultaneous splitting for fast growth. For intermediate growth rates, the manner of splitting becomes mixed and sensitive to fluctuations.     

Low-energy structure in the ionization of argon: Comparison of experiment with theory

The above-threshold ionization of argon in an intense 70-fs,400-nm linearly polarized laser pulse has been investigated by the velocity map imaging techniques,combined with an attosecond-resolution quantum wave packet dynamics method.There is a quantitative agreement in all dominant features between the experiment and the theory.Moreover,a peak-splitting phenomenon in the first energy peak has been observed at high pulse intensity.Further,through the theoretical analysis,an ac Stark splitting with evident resonant and nonresonant ionization pathways has been found to be the physical reason for the experimental observations.     

虚拟流体方法的显隐算法

基于算子分裂,把欧拉方程分裂成对流项和非对流项两部分,建立一种基于原始变量的二阶显隐算法.由通常的虚拟流体方法显式地预估流场,用隐式的压力修正对预估解进行修正.计算结果表明,这样可以有效增大时间步长,提高计算效率.     

Progress in spintronics

The discovery of the giant magnetoresistance (GMR) by Peter Grünberg and Albert Fert in 1988, which was awarded with the Nobel Prize for Physics in 2007, initiated an upsurge of experimental and theoretical investigations on spin dependent transport phenomena. Since then, spin valves have been introduced, switching via spin torque was proposed and confirmed, the tunneling magneto-resistance effect has matured to marketability, and magnetic domain walls and their propagation are being developed for memory storage devices with enhanced density. This field, which embraces spin-structures and spin-transport on the nanoscale, was coined spin electronics or short spintronics. A brief overview on the development of spintronics from the early discovery of the GMR effect to the present activities is provided.     

Stable loosely-coupled-type algorithm for fluid–structure interaction in blood flow

We introduce a novel loosely coupled-type algorithm for fluid–structure interaction between blood flow and thin vascular walls. This algorithm successfully deals with the difficulties associated with the “added mass effect”, which is known to be the cause of numerical instabilities in fluid–structure interaction problems involving fluid and structure of comparable densities. Our algorithm is based on a time-discretization via operator splitting which is applied, in a novel way, to separate the fluid sub-problem from the structure elastodynamics sub-problem. In contrast with traditional loosely-coupled schemes, no iterations are necessary between the fluid and structure sub-problems; this is due to the fact that our novel splitting strategy uses the “added mass effect” to stabilize rather than to destabilize the numerical algorithm. This stabilizing effect is obtained by employing the kinematic lateral boundary condition to establish a tight link between the velocities of the fluid and of the structure in each sub-problem. The stability of the scheme is discussed on a simplified benchmark problem and we use energy arguments to show that the proposed scheme is unconditionally stable. Due to the crucial role played by the kinematic lateral boundary condition, the proposed algorithm is named the “kinematically coupled scheme”.     

Tunneling of Dirac Particles from a Double Myers-Perry Black Hole in?Five?Dimensions

Motivated by the fermions tunneling formalism of Kerner and Mann, we attempt to investigate quantum tunneling of Dirac particles from a five dimensions double Myers-Perry black hole, which describes the superposition of two Myers-Perry black holes, each with a single angular momentum parameter and both in the same plane. After introducing several appropriate Gamma matrixes for the covariant Dirac equation, we obtain the tunneling probability of Dirac particles from the double Myers-Perry black hole, which gives the expected emission temperature as the case of scalar particles that obtained by others.     

Bisplitting an Arbitrary <Emphasis Type="Italic">N</Emphasis>-Qubit State with a Class of Asymmetric Three-Qubit W States

We propose a tripartite scheme for bisplitting an arbitrary single-qubit quantum information (QI) by using a class of asymmetric three-qubit W state as quantum channels. In the scheme, the sender Alice first performs a Bell-state measurement on her two qubits and then publishes her measurement result via a public classical channel. Based on Alice’s message, if the two receivers Bob and Charlie collaborate together, they can retrieve the QI, i.e., they can deterministically recover the QI in one receiver’s site by first performing a two-qubit unitary operation and then executing a single-qubit unitary operation. Afterwards, we sketch the extension of the single-qubit QI splitting to an arbitrary N-qubit QI splitting.     

Focal depth and focal splitting of truncated hyperbolic-cosine-Gaussian beam induced by phase plate

Focal depth and focal splitting of hyperbolic-cosine-Gaussian beams induced by a phase plate were investigated. The pure phase plate consists of three concentric zones: a center circle zone, an inner annular zone and an outer annular zone. The phase variance of the inner annular zone is adjustable. Simulation results show that the focal depth can be adjusted by changing the radii of zones. With the increase of the inner radius of the outer annular zone, the focal spot broadens along the optical axis and splits into two peaks. Then the two peaks combine back into one peak. There are two critical values for the inner radius of the outer annular zone, at which focal spot changes sharply. The tunable range of the focal depth varies considerably. The phase variance of the inner annular zone affects focal depth also; when the phase variance is π, the effect attains maximum. The parameters of cosh parts of the beam affect both focal splitting and focal depth evidently; focal splitting disappears with increasing parameters of cosh parts, and focal depth increases with increasing the parameters of cosh parts in both the low and the high numerical-aperture optical systems.     

光子数分束攻击对星地量子密钥分配系统安全的影响

由于仪器设备性能的不完美和信道传输损耗的存在,光子数分束(PNS)攻击对采用弱相干脉冲(WCP)光源的量子密钥分配(QKD)系统的安全性构成重大威胁.以基于WCP光源的星地QKD系统为研究对象,推导了在PNS攻击者采用最佳窃听策略进行窃听时,保证密钥绝对安全的最大天顶角和可采用的平均光子数之间的关系.理论分析和计算结果表明,星地QKD系统的最大安全传输天顶角和可使用的平均光子数等重要系统参数的取值上限均受PNS攻击的限制,最终系统的密钥交换速率和系统容量受到限制.对星地QKD系统的传输容量来说,天顶角和平均光子数是一对矛盾的影响因素.提供了一种对实际星地QKD系统的天顶角和平均光子数参数进行估算的方法.