锥形光纤的偏振特性

随着光通信技术的不断发展，光纤的应用越来越广泛，而锥形光纤以其独特的传光方式越来越多地应用于光纤连接、成像及测量等领域。实验测定了不同锥角和不同长度锥形光纤的偏振特性。理论上，根据麦克斯韦方程组以及边界条件给出了光在理想光纤中的场分布，阐明了实际光纤中光的传输特性。论证了锥形光纤长度与其偏振特性的关系，进而利用几何光学方法对锥形光纤锥角与其偏振特性的关系作了定性说明。并用具体数据进行了定量计算，得出偏振光经锥形光纤传输或耦合后再传输到其终端所得到均是椭圆偏振光的结论。     

短脉冲激光尾流场中的前向Raman散射

用212维粒子模拟分析了前向Raman散射对激光尾流场加速电子的影响.前向Raman散射使脉冲长度在传播方向上被拉长，脉冲后沿变陡，产生的尾流场相速度明显减小，而且超热电子的最大动能明显小于理论估计值.此外激光频率整体向低频移动.     

Lax Pairs for Equations Describing Compatible Nonlocal Poisson Brackets of Hydrodynamic Type and Integrable Reductions of the Lamé Equations

We solve the problem of describing compatible nonlocal Poisson brackets of hydrodynamic type. We prove that for nonsingular pairs of compatible nonlocal Poisson brackets of hydrodynamic type, there exist special local coordinates such that the metrics and the Weingarten operators of both brackets are diagonal. The nonlinear evolution equations describing all nonsingular pairs of compatible nonlocal Poisson brackets of hydrodynamic type are derived in these special coordinates, and the integrability of these equations is proved using the inverse scattering transform. The Lax pairs with a spectral parameter for these equations are found. We construct various classes of integrable reductions of the derived equations. These classes of reductions are of an independent differential-geometric and applied interest. In particular, if one of the compatible Poisson brackets is local, we obtain integrable reductions of the classical Lamé equations describing all orthogonal curvilinear coordinate systems in a flat space; if one of the compatible brackets is generated by a constant-curvature metric, the corresponding equations describe integrable reductions of the equations for orthogonal curvilinear coordinate systems in a space of constant curvature.     

Probing proton halo of the exotic nucleus28S by elastic electron scattering

Elastic electron scattering on the exotic light nucleus²⁸S is investigated in the plane wave Born approximation. The variation of the squared form factors of²⁸S with momentum transfer is compared with that of³²S. It is found that the behavior of the form factors near the second minimum (with a moderate momentum transfer) is sensitive to the alteration of the charge density distribution of halo protons in²⁸S. This indicates that elastic electron scattering can be a good probe of the structure of proton-halo nuclei.     

10-GHz Optical Comb in L-Band Region With Brillouin/Erbium-Doped Fibre Laser

A multiwavelength Brillouin/erbium fibre laser (BEFL) which operates in the long wavelength (L-band) region is demonstrated for potential applications in an L-band wavelength division multiplexing (WDM) communication system. The laser configuration consists of a long erbium-doped fibre to enable L-band amplification where two 3-dB couplers take a portion of the generated BEFL signal and re-inject it into the single mode fibre to seed a cascaded BEFL line in the same direction as the first BEFL line. A stable and strong laser comb of up to five lines with 10-GHz spacing has been obtained with a Brillouin pump (BP) of 9.2 mW and a 980 nm pump of 92 mW. The BEFL has shown a broad tuning range with a tuning characteristic for line #1 which is flat over a range greater than 9.9 nm.     

Molecular dynamics in aqueous solutions of β-cyclodextrin

Water molecule mobility in ion-containing and nonionic aqueous solutions of β-cyclodextrin was studied by quasielastic neutron scattering (QENS). The total self-diffusion coefficients and their components corresponding to the contributions from collective (Lagrange type) and single-particle (jump diffusion) parts of molecular motions were determined. From the data obtained, one can conclude that the molecular mobility of free water in nonionic aqueous solutions of β-cyclodextrin with guest molecules (2-aminopyridine) proceeds by a single-particle mechanism. The addition of Pb²⁺ ions into the solution leads to increase in self-diffusion coefficients and growth of a bound water fraction.     

Furtivity and Masking Problems in Time-Dependent Electromagnetic Obstacle Scattering

In this paper, we consider furtivity and masking problems in time-dependent three-dimensional electromagnetic obstacle scattering. That is, we propose a criterion based on a merit function to minimize or to mask the electromagnetic field scattered by a bounded obstacle when hit by an incoming electromagnetic field and, with respect to this criterion, we drive the optimal strategy. These problems are natural generalizations to the context of electromagnetic scattering of the furtivity problem in time-dependent acoustic obstacle scattering presented in Ref. 1. We propose mathematical models of the furtivity and masking time-dependent three-dimensional electromagnetic scattering problems that consist in optimal control problems for systems of partial differential equations derived from the Maxwell equations. These control problems are approached using the Pontryagin maximum principle. We formulate the first-order optimality conditions for the control problems considered as exterior problems defined outside the obstacle for systems of partial differential equations. Moreover, the first-order optimality conditions derived are solved numerically with a highly parallelizable numerical method based on a perturbative series of the type considered in Refs. 2–3. Finally, we assess and validate the mathematical models and the numerical method proposed analyzing the numerical results obtained with a parallel implementation of the numerical method in several experiments on test problems. Impressive speedup factors are obtained executing the algorithms on a parallel machine when the number of processors used in the computation ranges between 1 and 100. Some virtual reality applications and some animations relative to the numerical experiments can be found in the website http://www.econ.unian.it/recchioni/w10/.     

同步辐射小角x射线散射方法研究由城市固体垃圾制备的活性炭

应用同步辐射小角x射线散射方法研究了由不同城市固体垃圾制备而成的活性炭的孔结构-结果发现利用木类、纸张、塑料这三类典型垃圾组分的热解残余物为原料制备中孔发达的活性炭是可行的-活性炭的形态和结构取决于垃圾热解残余物的组分和热解程度等因素- 关键词： 小角x射线散射 活性炭 分形维数 平均孔径     

Nonequilibrium Statistical Thermodynamics of Two Dissipative Processes in Solids: Energy Losses of Channeled Particles at Low Velocities and Ultrasound Absorption by Conduction Electrons

We use methods of nonequilibrium statistical thermodynamics to investigate two dissipative processes in solids. We find the electron energy losses of a particle moving in a planar channeling regime and the sound absorption coefficient in metals under electron impurity scattering. The oscillator model is used to analyze the contribution from the effect of electron entrainment by a moving scattering center to the total dissipated energy. We investigate the frequency and temperature dependence of energy losses and also the dependence of the absorption coefficient on the sound wave vector.     

Scattering Problem for a Classical Particle with Spin in a Coulomb Field

We investigate the scattering problem for a relativistic electron with spin in a Coulomb field in the framework of pseudoclassical mechanics. We obtain an analytic expression for the scattering angle and limiting estimates for the scattering parameters for the spinless and nonrelativistic cases. For small angles, the pseudoclassical model under consideration leads to the well-known quantum-mechanical Mott formula.