Two-Dimensional Rossby Waves: Exact Solutions to Petviashvili Equation

The two-dimensional (2D) nonlinear Rossby waves described by the Petviashvili equation, which has been invoked as an ageostrophic extension of the barotropic quasi-geostrophic potential vorticity equation, can be investigated through the exact periodic-wave solutions for the Petviashvili equation, while the exact analytical periodic-wave solutions to the Petviashvili equation are obtained by using the Jacobi elliptic function expansion method. It is shown that periodic-wave 2D Rossby solutions can be obtained by this method, and in the limit cases, the 2D Rossby soliton solutions are also obtained.     

Influence of Generalized (r, q) Distribution Function on Electrostatic Waves

Non-Maxwellian particle distribution functions possessing high energy tail and shoulder in the profile of distribution function considerably change the damping characteristics of the waves. In the present paper Landau damping of electron plasma (Langmuir) waves and ion-acoustic waves in a hot, isotropic, unmagnetized plasma is studied with the generalized (r,q) distribution function. The results show that for the Langmuir oscillations Landau damping becomes severe as the spectral index r or q reduces. However, for the ion-acoustic waves Landau damping is more sensitive to the ion temperature than the spectral indices.     

等离子体隐身技术的WKB方法

研究了非磁化等离子体的碰撞吸收隐身技术机理。用WKB方法给出了垂直入射、斜入射情况下,非磁化不均匀等离子体密度覆盖导体平板的等离子体对不同频率电磁波的反射系数。给出了不均匀非磁化等离子体密度、等离子体碰撞频率、电磁波频率与碰撞吸收的关系。     

Supernovae and the Arrow of Time

Supernovae are explosions of stars and are a central problem in astrophysics. Rayleigh–Taylor (RT) and Richtmyer–Meshkov (RM) instabilities develop during the star’s explosion and lead to intense interfacial RT/RM mixing of the star materials. We handle the mathematical challenges of the RT/RM problem based on the group theory approach. We directly link the conservation laws governing RT/RM dynamics to the symmetry-based momentum model, derive the model parameters, and find the analytical solutions and characteristics of RT/RM dynamics with variable accelerations in the linear, nonlinear and mixing regimes. The theory outcomes explain the astrophysical observations and yield the design of laboratory experiments. They suggest that supernova evolution is a non-equilibrium process directed by the arrow of time.     

Millimeter-Wave Spectroscopy of Methylfuran Isomers: Local vs. Global Treatments of the Internal Rotation

Methylfurans are methylated aromatic heterocyclic volatile organic compounds and primary or secondary pollutants in the atmosphere due to their capability to form secondary organic aerosols in presence of atmospheric oxidants. There is therefore a significant interest to monitor these molecules in the gas phase. High resolution spectroscopic studies of methylated furan compounds are generally limited to pure rotational spectroscopy in the vibrational ground state. This lack of results might be explained by the difficulties arisen from the internal rotation of the methyl group inducing non-trivial patterns in the rotational spectra. In this study, we discuss the benefits to assign the mm-wave rotational-torsional spectra of methylfuran with the global approach of the BELGI-Cs code compared to local approaches such as XIAM and ERHAM. The global approach reproduces the observed rotational lines of 2-methylfuran and 3-methylfuran in the mm-wave region at the experimental accuracy for the ground vt=0 and the first torsional vt=1 states with a unique set of molecular parameters. In addition, the V3 and V6 parameters describing the internal rotation potential barrier may be determined with a high degree of accuracy with the global approach. Finally, a discussion with other heterocyclic compounds enables the study of the influence of the electronic environment on the hindered rotation of the methyl group.     

TRANSIENT TORSIONAL WAVE IN FINITE HOLLOW CYLINDER WITH INITIAL AXIAL STRESS

An analytical solution is obtained for transient torsional vibration of a finite hollow cylinder with initial axial stress. The cylinder is subjected to dynamic shearing stress at the internal surface and is fixed at the external surface. The basic equations are presented and the solution is obtained by means of Fourier series expansion technique and the separation of variables method. The effects of the initial stress on the natural frequencies and transient torsional responses are presented and discussed.     

波导参数和传播常数对光折变表面波的影响

基于质点振荡的模型和数值模拟的方法,研究了波导参数和传播常数对光折变晶体与线性电介质界面光折变表面波类型和局域表面波模的影响。当波导参数大于传播常数时,在光折变晶体与线性电介质界面可以产生非局域表面波。当波导参数小于传播常数时,在光折变晶体与线性电介质界面可以产生振荡表面波和局域表面波。在局域表面波形成的系统内,正波导参数的光波能量比负波导参数的光波能量在光折变晶体内聚集得多。在给定一个局域表面波形成的物理系统,传播常数越大,表面波在线性电介质和光折变晶体中衰减就越快,对应表面波模的波峰离界面就越近。     

激光多普勒扭转振动测试技术的研究

提出了一种差动式可辨向激光多普勒扭转振动测试仪 ,计算并分析了激光多普勒技术的双相检测和矩形光栅的衍射光强分布。采用相位光栅作为光学混频器件 ,提高了测量的信噪比并充分地利用了光能。实验表明 ,该系统能有效地实现旋转轴可辨向扭转振动的测量 ,并可获得较高的精度     

自聚焦介质波导中的新型导波

本文给出了导波层为自聚焦介质平板波导波方程的特殊精确解,得到了具有非线性导波层的波导归一化色散方程及场分布,并对得出的结果进行了讨论。     

(n,n)-(2n, 0)碳纳米管异质结的扭转力学特性

相近直径的锯齿型和扶手椅型碳纳米管可以共轴组合形成5-7碳环交替出现的柱形对称异质结. 本文利用分子动力学方法研究了直径相近且等长锯齿型和扶手椅型碳纳米管形成的(n, n)-(2n, 0)结在扭转过程中的扭矩和轴向应力随扭转角度的变化规律以及应力传递过程. 研究发现, (n, n)-(2n, 0)结扭转应变在达弹性限度内不会产生轴向应力, 该效应对基于碳纳米管扭转特性的纳米振荡器件的设计具有重要意义.