激光烧蚀瑞利泰勒不稳定性数值研究

 介绍了激光烧蚀流体不稳定性计算程序EUL3D,其计算结果与Takabe 公式、FAST2D程序和LASNEX程序的结果以及日本大阪大学激光烧蚀瑞利—泰勒(RT)不稳定性实验,都较好符合,发现了横向电子热传导烧蚀在长波长扰动的非线性瑞利—泰勒不稳定性演变中起重要作用。在合理近似下,得到了烧蚀RT不稳定性线性增长率的预热致稳公式,此公式除包含了烧蚀对流致稳和密度梯度致稳因素外,还包含了Atwood数变小致稳因素,因此与各种情况的二维计算值都很好符合。     

掺铑BaTiO3单晶场致应变特性的研究

系统地研究了掺铑的BaTiO3单晶在老化后的场致应变性能.研究发现,晶体的场致应变随老化时间的增加而增大,在老化27天后,在300V/mm的电场下,其双向场致应变可达1.11%;在较小的测试频率下(0.01Hz)也可得到0.95%的可逆的巨大的单向场致应变,在低频范围内,晶体的单向场致应变随测试频率增大而减小;研究晶体老化后的电滞回线,发现其形状类似于蜂腰磁滞回线.实验结果表明,对BaTiO3单晶掺杂铑元素可以大大改善其电致伸缩性能,可能产生新的在超大应变及非线性驱动器中的应用.     

场致发射的温度效应对微波管爆炸电子发射的影响

为研究场致发射的温度效应对微波管中爆炸电子发射过程的影响,在对比分析低温条件下的场致发射电流密度Fowler-Nordheim（FN）和一般的电子发射电流密度积分公式的基础上,利用细长圆柱形微凸起模型,重点考虑焦耳加热和热传导两个因素,编程计算得到了微凸起内部的温度分布和不同位置处温度随时间的变化。结果表明:场致发射的温度效应是一个重要影响因素,考虑温度对场致发射的影响后,微凸起内部各点的温度随时间呈非线性增长,且增长速率越来越大;在微波电场强度较弱时,若不考虑场致发射的温度效应而直接用FN公式表示的电流密度代入计算,会使爆炸发射延迟时间变短;当微波电场很强时,温度效应对爆炸发射延迟时间的影响则较小。     

非旋波耦合条件下微波控制的光学双稳与多稳

研究了在非旋波耦合条件下微波场建立的原子相干对光学双稳与多稳的控制.通过改变微波场的初始相位,可以有效地控制双稳与多稳的存在与否、迟滞环宽度和阈值强度的高低.旋波和非旋波耦合在物理上可视为双色激发,耦合的能级分裂成无穷多个子能级,原来的裸态跃迁变成无穷多个不同频率的跃迁.这些跃迁的相干叠加决定了介质的非线性吸收与色散,相干叠加的结果取决于微波场的相位. 关键词： 原子相干 非旋波耦合 光学双稳与多稳 相位控制     

非线性光机械系统中的双稳性与纠缠

在含有克尔介质和光学参量放大器(OPA)的光机械系统中,腔中的光学双稳性与纠缠特性会受到这两种介质较大的影响。当调节非线性晶体与腔场的耦合常数时,OPA晶体的非线性增益对系统的双稳性影响与入射光强度对双稳性的影响是相似的,然而克尔介质的三阶非线性系数对系统双稳性却有着明显不同的影响。对系统纠缠特性的研究结果表明:OPA晶体的非线性增益系数对腔场与振动镜之间的纠缠有着增强的作用,而克尔介质的三阶非线性系数对纠缠却有着减弱的效果。     

掺铑BaTiO3单晶场致应变特性的研究

系统地研究了掺铑的BaTiO₃单晶在老化后的场致应变性能.研究发现，晶体的场 致应变随老化时间的增加而增大，在老化27天后，在300V/mm的电场下，其双向场致应变可达1.11％；在较小的测试频率下（0.01Hz）也可得到0.95％的可逆的巨大的单向场致应变，在低频范围内，晶体的单向场致应变随测试频率增大而减小；研究晶体老化后的电滞回线，发现其 形状类似于蜂腰磁滞回线.实验结果表明，对BaTiO₃单晶掺杂铑元素可以大大改 善其电致伸缩性能，可能产生新的在超大应变及非线性驱动器中的应用. 关键词： 3单晶')" href="#">BaTiO₃单晶 掺铑 场致应变 老化     

石英玻璃的电致二阶非线性极化及其热擦除性

本文报导了石英玻璃的电致二阶非线性极化及其热擦除性的实验研究结果。通过电致二次谐波测量发现:在一定的电场极化条件下,石英玻璃的电致二阶非线性极化强度随极化时间的延长而逐渐增强,并渐趋饱和;石英玻璃的电致二阶非线性极化可通过热处理而擦除,并随热擦除时间的延长呈动态衰减趋势。根据玻璃的电致二阶非线性极化的“偶极子取向”模型,对实验结果进行了讨论.     

关于用稳恒电流场模拟静电场的对应条件问题

(一) 我们知道,静电场_e和稳恒电流场_i都遵循环路定理∮_L_e·d=0,∮_L_i·d=0它们都有势函数U,使得_e=-▽U,_i=-▽UU是我们熟知的电位。稳恒电流场和静电场就是通过它们的电位建立了对应关系。如果一个稳恒电流场的电位分布等于一个静电场的电位分布,则这个静电场就可以被那个稳恒电流场所模拟。所以,场的模拟问题的本质,就是电位模拟。 (二) 一般的静电场是三维的。但三维空间的电位不便测量。所以我们试图用二维的电流场来     

单模热致超大模场掺镱光纤放大器的数值研究

非线性效应是限制光纤激光器功率提升的重要限制因素,而超大模场光纤对于非线性效应的抑制具有重要意义.热致超大模场光纤是一种新型超大模场光纤,其利用热透镜效应实现低数值孔径波导结构,从而在保证光束质量的前提下实现超大模场输出.不过,现阶段对于热致超大模场光纤激光器的研究较为有限.本文提出了单模超大模场掺镱光纤放大器的速率方程模型,该模型由稳态速率方程和热传导方程组成.利用该模型,对前向抽运单模热致超大模场光纤放大器进行了数值研究.研究表明:信号光模场直径随着信号光功率的增加而增加,这体现了热致超大模场光纤在非线性效应抑制方面的优势.研究还揭示了最佳光纤长度及其产生的物理机制,发现最佳光纤长度与注入抽运光功率有关,其随着注入抽运光功率的增加而减小;不过,当注入抽运光功率足够大时,最佳光纤长度随注入抽运光功率变化不大.此外,还对输出光场的模式进行了探讨,验证了其在保证超大模场输出的同时,实现高斜率效率输出的可行性.相关研究对于热致超大模场光纤放大器的设计具有指导意义.     

平面调制靶瑞利-泰勒不稳定性初步研究

 瑞利-泰勒不稳定性增长的准确估计是激光聚变的重要研究课题。在神光Ⅱ装置上,利用面向背光照相技术对正弦调制平面靶的瑞利-泰勒不稳定性增长进行了实验研究,得到了清晰的时空分辨图像;采用傅里叶变换取基模法和求波峰波谷差值法分析了实验结果;两种方法得到的靶扰动增长因子相同。实验中平面靶扰动增长较小可能是密度梯度致稳和烧蚀致稳抑制了扰动增长,也可能是扰动进入了非线性阶段而使增长不大。     

Stabilization of extra dimensions and the dimensionality of the observed space

We present a simple model for the late time stabilization of extra dimensions. The basic idea is that brane solutions wrapped around extra dimensions, which is allowed by string theory, will resist expansion due to their winding mode. The momentum modes in principle work in the opposite way. It is this interplay that leads to dynamical stabilization. We use the idea of democratic wrapping, where in a given decimation of extra dimensions, all possible winding cases are considered. To further simplify the study we assumed a symmetric decimation in which the total number of extra dimensions is taken to be Np where N can be called the order of the decimation. We also assumed that extra dimensions all have the topology of tori. We show that with these rather conservative assumptions, there exist solutions to the field equations in which the extra dimensions are stabilized and that the conditions do not depend on p. This fact means that there exists at least one solution to the asymmetric decimation case. If we denote the number of observed space dimensions (excluding time) by m, the condition for stabilization is m≥3 for pure Einstein gravity and m≤3 for dilaton gravity massaged by a string theory parameter, namely the dilaton coupling to branes. PACS 98.80.-k; 11.25.Uv     

Classical Description of Intense Field Stabilization Dynamics of 1D Model Atom

Abstract In this paper classical nonlinear dynamics approaches are used to study the intense field stabilization (IFS) for ID model atom according to differential equation (DE) and map approximation (MA). The exact stability boundary and region of I-period fixed points in the parameter space of field strength and frequency are obtained, and the results of MA are in excellent agreement with those of DE. The electrons dynamical behavior in phase space is investigated and the IFS mainly occurring in high frequency regime is confirmed. The stabilization phenomenon connected with the stable fixed points is also examined. In particular it is shown that this phenomenon depends on tightly the KAM tori. It can be predicted that the stabilization probability is just the fraction of initial electrons confined by the KAM tori.     

The Riemann tensor and the Bianchi identity in 5D space–time

The initial assumption of theories with extra dimension is based on the efforts to yield a geometrical interpretation of the gravitation field. In this paper, using an infinitesimal parallel transportation of a vector, we generalize the obtained results in four dimensions to five-dimensional space–time. For this purpose, we first consider the effect of the geometrical structure of 4D space–time on a vector in a round trip of a closed path, which is basically quoted from chapter three of Ref. [5]. If the vector field is a gravitational field, then the required round trip will lead us to an equation which is dynamically governed by the Riemann tensor. We extend this idea to five-dimensional space–time and derive an improved version of Bianchi's identity. By doing tensor contraction on this identity, we obtain field equations in 5D space–time that are compatible with Einstein's field equations in 4D space–time. As an interesting result, we find that when one generalizes the results to 5D space–time, the new field equations imply a constraint on Ricci scalar equations, which might be containing a new physical insight.     

Quantum Inequality Bounds for Free Rarita-Schwinger Field in Flat Spacetime

Although quantum field theory allows the local energy density negative, it also places severe restrictions on the negative energy. One of the restrictions is the quantum energy inequality (QEI), in which the energy density is averaged over time, or space, or over space and time. By now temporal QEIs have been established for various quantum fields, but less work has been done for the spacetime quantum energy inequality. In this paper we deal with the free Rarita-Schwinger field and present a quantum inequality bound on the energy density averaged over space and time.Comparison with the QEI for the Rarita-Schwinger field shows that the lower bound is the same with the QEI. At the same time, we find the quantum inequality for the Rarita-Schwinger field is weaker than those for the scalar and Dirac fields. This fact gives further support to the conjecture that the more freedom the field has, the more easily the field displays negative energy density and the weaker the quantum inequality becomes.     

A multi-band atomic candle with microwave-dressed Rydberg atoms

Stabilizing important physical quantities to atom-based standards lies at the heart of modern atomic, molecular and optical physics, and is widely applied to the field of precision metrology. Of particular importance is the atom-based microwave field amplitude stabilizer, the so-called atomic candle. Previous atomic candles are realized with atoms in their ground state, and hence suffer from the lack of frequency band tunability and small stabilization bandwidth, severely limiting their development and potential applications. To tackle these limitations, we employ microwave-dressed Rydberg atoms to realize a novel atomic candle that features multi-band frequency tunability and large stabilization bandwidth. We demonstrate amplitude stabilization of microwave field from C-band to Ka-band, which could be extended to quasi-DC and terahertz fields by exploring abundant Rydberg levels. Our atomic candle achieves stabilization bandwidth of 100 Hz, outperforming previous ones by more than two orders of magnitude. Our simulation indicates the stabilization bandwidth can be further increased up to 100 kHz. Our work paves a route to develop novel electric field control and applications with a noise-resilient, miniaturized, sensitive and broadband atomic candle.     

Relativistic description of single-particle resonances via phase shift analysis

Single-particle resonant states in spherical nuclei are studied by the real stabilization method in coordinate space within the framework of self-consistent relativistic mean field theory. Taking 122Zr as an example, the resonant parameters, including the energies and widths are extracted by fitting energy and phase shift. Good agreement with the previous calculations has been found. The details of single-particle resonant states are analysed.     

Relativistic description of single-particle resonances via phase shift analysis

Single-particle resonant states in spherical nuclei are studied by the real stabilization method in coordinate space within the framework of self-consistent relativistic mean field theory. Taking 122Zr as an example, the resonant parameters, including the energies and widths are extracted by fitting energy and phase shift. Good agreement with the previous calculations has been found. The details of single-particle resonant states are analysed.     

Intercalation of magnesium–urea complex into swelling clay

N fertilization is considered as a main source of N₂O and NO emission from agricultural soils. Especially, it is a great challenge to enhance urea efficiency without any deleterious effects on the environment because of massive application of urea. In this study, we attempted to stabilize urea in the interlayer space of montmorillonite (MMT) in order to reduce urea loss from soils. Urea was successfully intercalated in the form of urea–magnesium complexes. The stabilization of urea–magnesium complexes within the interlayer space was confirmed by a significant expansion of the interlayer space and the presence of urea–magnesium complexes. Urea degradation in soils was significantly delayed by application of the urea–magnesium complex intercalated into MMT. It is highly feasible that stabilization of urea within nanosized interlayer space would lead to considerable improvement of nitrogen efficiency in soils.     

Magnetic aftereffects and the barkhausen effect in a magnesium manganese ferrite single crystal

The temperature dependence of the critical magnetic field [H₀(T)] of a magnesium manganese ferrite single crystal is analyzed, together with the changes taking place in the critical magnetic field with time, H₀(t), the temperature dependence of the domain-boundary stabilization field H_st(T), and the time required to establish the equilibrium state of the domain boundaries; the domain structure is examined, and the induced anisotropy constant is calculated; so is the activation energy of the process leading to the stabilization of the domain boundaries. The magnetic aftereffects and the Barkhausen jumps accompanying them are of a diffusion nature.     

A Note on the Problem of Proper Time in Weyl Space–Time

We discuss the question of whether or not a general Weyl structure is a suitable mathematical model of space–time. This is an issue that has been in debate since Weyl formulated his unified field theory for the first time. We do not present the discussion from the point of view of a particular unification theory, but instead from a more general standpoint, in which the viability of such a structure as a model of space–time is investigated. Our starting point is the well known axiomatic approach to space–time given by Elhers, Pirani and Schild (EPS). In this framework, we carry out an exhaustive analysis of what is required for a consistent definition for proper time and show that such a definition leads to the prediction of the so-called “second clock effect”. We take the view that if, based on experience, we were to reject space–time models predicting this effect, this could be incorporated as the last axiom in the EPS approach. Finally, we provide a proof that, in this case, we are led to a Weyl integrable space–time as the most general structure that would be suitable to model space–time.