AN OSCILLATION PHENOMENON OF REVERBERATION IN THE SHALLOW WATER WITH A THERMOCLINE

An oscillation phenomenon of the reverberation intensity was observed in a recent shallow water reverberation experiment. This phenomenon cannot be explained by the widely used incoherent reverberation theory. In this paper, to explain the observed oscillation phenomenon, the modal interference of reverberation in the shallow water with a thermocline is discussed on the basis of the ray-mode theory. The theoretical analysis and numerical results show that modal interference can cause the regular oscillation phenomenon of the reverberation intensity, and the oscillation phenomenon of the reverberation intensity can be used to test different reverberation models.     

高密度LED显示屏莫尔条纹抑制研究

为了抑制数码相机拍摄LED显示屏时图像中存在的莫尔条纹现象,对莫尔条纹产生的机理及其特性进行了理论分析。提出了利用多层散射膜抑制高密度LED显示屏莫尔条纹的方法。利用光学模拟程序对莫尔条纹抑制装置进行了仿真验证,对其中的关键参数进行了优化。利用优化后的莫尔条纹抑制结果在P2.5 mm 高密度LED显示样箱上进行了实验验证。实验观察结果与理论分析吻合,该装置可大幅度降低莫尔条纹的对比度,证明了方法的有效性。     

Enhancement and weakening of stochastic resonance for a coupled system

In the paper, we investigate the phenomenon of stochastic resonance of a system with finite locally coupled linear elements driven by multiplicative dichotomous noise and temporal periodic signal. It is shown that, for some suitably selected values of the parameters, with increasing the size of the system or the coupling among the nearest elements, the stochastic resonance phenomenon can be enhanced; while for some other suitably selected parameters' values, with the increase of the size or the coupling, the phenomenon of stochastic resonance can be weakened. Our results can provide some useful insights for the investigation of the stochastic resonance phenomenon of the systems with locally (or globally) coupled finite (or infinite) elements.     

Stochastic resonance in an asymmetric bistable system driven by coloured correlated multiplicative and additive noise

This paper investigates the stochastic resonance （SR） phenomenon in an asymmetric system with coupling between multiplicative and additive noise when the coupling between two noise terms is coloured. The approximate expression of signal-to-noise ratio has been obtained by applying the two-state theory and SR exhibits in the bistable system. Moreover, the potential asymmetry r and cross-correlation strength λ can weaken the SR phenomenon, while the cross-correlation time r can strengthen the SR phenomenon.     

Tunable entanglement sudden death and three-partite entanglement in Tavis-Cummings model with an added nonlinear kerr-like medium

We investigate the entanglement dynamics and the phenomenon of entanglement sudden death in the two-photon Tavis-Cummings model with an added nonlinear kerr-like medium. It is shown that the phenomenon of entanglement sudden death can be controlled by the nonlinear kerr-like medium. Furthermore, the influence of dipole-dipole interaction on entanglement between atoms is also discussed. It is found that the phenomenon of entanglement sudden death can be weakened by the dipole-dipole interaction. Finally, we investigate the influence of kerr medium and dipole-dipole interaction on the three-partite entanglement of the system by making use of the state preparation fidelity.     

Observing Zitterbewegung for photons near the Dirac point of a two-dimensional photonic crystal

It is shown, for the first time, that the Zitterbewegung of photons can appear near the Dirac point in a two-dimensional photonic crystal. The superiority of such a phenomenon for photons is that it can be found in different scaling structures with wide frequency regions. It can be observed by measuring the time dependence of the transmission coefficient through photonic crystal slabs. Thus, it is particularly suited for experimentally observing this effect. We have observed such a phenomenon by exact numerical simulations, confirming a long-standing theoretical prediction.     

Delay induced steady-state transition and stochastic resonance for an ecological vegetation growth system subjected to multiplicative and additive noises

In this paper, our aim is to investigate the steady state properties and stochastic resonance (SR) phenomenon for an ecological vegetation growth system with time delay induced by the multiplicative and additive noises. Numerical results show that the SR phenomenon caused by time delay, different noise terms and a weak periodic signal occurs in the vegetation growth model under different values of system parameters. With regard to the stationary state properties of the vegetation system, the results indicate that the terms of different noises and time delay can all accelerate the shift from the substantial state to the barren one of the ecological system, restrain the development of the vegetation system and weaken the stability of the ecological system. On the other hand, the additive noise strength always enhances the SNR and the SR phenomenon, while the intensity of multiplicative noise often reduces the effect of the SR. In particular, time delay can play different roles in exciting the SR phenomenon in different cases.     

改善Si3N4俘获层过擦现象的第一性原理研究

采用第一性原理方法对如何改善电荷俘获存储器的过擦现象进行了研究. 过擦是由于氮空位中Si原子对电荷的局域能力弱导致, 因此, 在Si₃N₄超胞中分别建立了以C, N, O替换氮空位中的Si原子的缺陷结构作为本文的研究模型. 分别计算了擦写之后体系的巴德电荷分布、相互作用能、态密度, 借以分析替位原子对过擦的影响. 巴德电荷分布的计算结果表明, Si₃N₄在O替位128号Si后的过擦现象被明显改善; C替位128号Si也可以改善过擦, 但由于C替位对电荷的局域作用变弱, 不利于电荷的存储实现; N替位128号Si则不能改善过擦; 而在162和196号Si位置, 三种原子的替换均无法改善过擦现象. 相互作用能的研究表明, 在128号Si位置, 三种原子都能够和氮空位形成团簇, 在体系中稳定存在. 特别地, O替位Si后, 体系中两缺陷的相互吸引作用最弱, 从而写入的电荷能够短暂的打破O团簇的稳定性, 实现电荷重构, 将电荷局域在O团簇周围. 此外, 态密度的分析结果表明O在128号Si位置能够在Si₃N₄禁带中引入深能级缺陷, 深能级局域电荷的能力强. 以上分析证明, O替位可以很好的改善Si₃N₄中的过擦现象. 本文的研究结果为电荷俘获存储器改善过擦提供了一种方法, 对提高器件的电荷保持特性和优化存储窗口具有指导意义.     

光的偏振演示仪的制作

针对现行教材的内容制作了光的偏振演示仪.该演示仪既可以真实的演示光的偏振现象,又可以通过在形成驻波的弦上放置狭缝,模拟演示光的偏振现象,且驻波的振动频率连续可调.     

On/off spin-crossover phenomenon and control of the transition temperature in assembled Iron(II) complexes

The present study reveals the on/off of spin-crossover (SCO) phenomenon in assembled Fe(II) complexes bridged by bis(pyridyl) type ligand. Whether SCO phenomenon occurs or not in assembled Fe(II) complexes bridged by bis(pyridyl) type ligand is determined by local structure around iron atom. SCO phenomenon occurs when the coordinating pyridines facing to each other across the iron atom are propeller type, while the phenomenon does not occur when they are parallel type or distorted propeller type. DFT calculation explained that, in the shortening of Fe-pyridine bonds when changing from high-spin state to low-spin state, the pyridines of propeller type can approach the iron atom with smaller steric hindrance than those of parallel and distorted propeller type complexes. The local structure is controlled by introducing methyl substituent and introducing π-system, changing SCO phenomenon. And the transition temperature of SCO is also controlled in assembled complexes bridged by 1,2-bis(4-pyridyl)ethane by mixing anionic ligand.     

A scaling phenomenon for the cross section of fragment produced in projectile fragmentation reactions

A scaling phenomenon has been found for the cross section of a fragment, which is defined as a "square" cross section(SCS).This phenomenon can unify the cross sections of fragments in projectile fragmentation(PF) reactions. An empirical formula is proposed to calculate SCSfor a fragment with parameters determined by an extensive investigation of measured reactions ranging from Fermi energies to relativistic energies. The scaling phenomenon of SCShas been verified using different techniques,showing that the scaling of SCSgenerally exists in PF reactions. The concept of SCS, which can be assumed as a standard value for a fragment, is shown to accurately predict the cross sections of isotopes in PF reactions with incident energies ranging from tens of A MeV to approximately 1000 A MeV.     

弱耦合LC电路节拍振荡的实验现象

对弱耦合LC电路的节拍振荡现象进行了计算机模拟研究,由此可以加深学生对这一物理现象的现解。     

GaN发光二极管表观电容极值分析

利用正向交流(ac)小信号方法对GaN发光二极管的电容-电压特性进行测量,可以观察到GaN发光二极管中的负电容现象。正向偏压越大,测试频率越低,负电容现象越明显。测量到的负电容现象是表象,不存在负电容;提出GaN发光二极管p-n结的结电容在特定的正向电压范围内等效于可变电容。分析可变电容对正向交流小信号响应得到:特定参数的可变电容使结电容电流相位落后于交流小信号电压相位π/2,使得在测量中表现为负电容。发现表观电容-正向电压曲线的极值点与理论模型相吻合,证明了该理论模型的正确性。     

An oscillation phenomenon of low frequency reverberation in the shallow water and its physical explanation

~~An oscillation phenomenon of low frequency reverberation in the shallow water and its physical explanation1 Zhang, R.. Jin. G. Normal-mode theory of average reverberation intensity in shallow water, Journal of Sound and Vibration, 1987 19(2):215-223 2. Ellis, D. D., A shallow-water normal-mode reverberation model, J. Acoust. Soc, Am., 1995, 97(5): 2804-2814. 3. McDaniel, S. T., Seafloor reverberation fluctuations, J. Acoust. Soc. Am., 1990, 88(3): 1530-1535. 4. Abraham, …     

分光仪调整中干涉现象的分析与应用

描述了在分光仪调整实验中观察到的干涉条纹现象,并且当转动平行平板玻璃时,该干涉条纹有粗细疏密变化.本文从理论上分析了产生干涉条纹及干涉条纹疏密粗细变化的原因.在已知平行平板玻璃的厚度和光的波长的情况下,可应用该现象测量平行平板玻璃折射率,给出了折射率的计算方法,对结果进行了数据处理及误差分析.     

ErYb:氟氧化物玻璃陶瓷的上转换发光特征饱和现象的综合分析

研究了Er3+和Yb3+双掺的氟氧化物玻璃陶瓷在966 nm激光激发下的上转换发光的饱和现象。详细的分析发现了它存在一种能量扩展导致的“特征饱和现象”,也就是说上转换发光强度I随激光功率P而改变的双对数曲线的斜率随着激光光斑的增大而明显增大至正常的多光子关系。还发现布居耗空所导致的“典型饱和现象”也有较大的影响,它导致了logI-logP曲线会随着激光功率的增加而逐渐弯曲,而激光功率的减小会导致“典型饱和现象”也减小甚至完全消失。     

Decapitation of tungsten field emitter tips during sputter sharpening

The sharpening of tungsten tips by sputtering with neon ions shows a surprising phenomenon when the tip radius is smaller than about 20 nm: the gas ions produce a neck in the tip which becomes thinner until it breaks due to the electrostatically induced stress. This decapitation phenomenon limits the attainable tip sharpness to a radius of about 4 nm. The process can repeat in a regular, oscillating manner and is probably at the origin of the unreliability often mentioned in connection with this sharpening method. The effect can be used to determine experimentally the theoretical shear stress of refractory metals.     

On the detection of closed orbits in time-dependent systems by using double-pulse lasers

In the photodetachment of atoms or negative ions by a double-pulse laser, the first pulse of the double-pulse laser generates waves and the delayed second pulse may detect them. The phenomenon of the excitation and detection of waves by a double-pulse laser can be used to identify the closed orbits in the system. We demonstrate this phenomenon with a negative hydrogen ion (H⁻) by analyzing the total population excited by a double-pulse laser in a time-dependent field for different physical parameters. By analyzing the total excited population using a double-pulse laser, we can uncover all the closed orbits existing in the system. We demonstrate that this can be realized by scanning the first pulse position and the time delay between the two pulses.     

快重离子引起的塑性形变现象

非晶材料在快重离子轰击下显示了奇异的各向异性的塑性形变 ,这是电子能损所引起的宏观可见的剧烈的原子重排 .这个效应不能发生在具有晶态结构的材料中 ,但发生于所有的非晶材料中 .这一宏观现象隐含了寻找原子尺度上电子激发转换成原子位移的潜在线索 ,因而受到广泛的关注 .在回顾了现象发现的历史之后 ,综述了离子束引起的塑性形变的基本规律、最新结果、实验方法和技术新的进展 ,最后讨论了相关的物理机制和唯象模型. A very peculiar effect occurring when an amorphous material is irradiated with swift heavy ion is the giant plastic deformation phenomenon discovered in the eighties by Klaumunzer[DD(-8/9]¨ It is macroscopically visible atomic rearrangements induced by electronic energy loss. This effect occurs only in truly amorphous solids and can not occur in a crystalline material. This phenomenon gives rise to a wide ranging and lasting research in the field of the interaction of swift heavy...