Thermal radiation effects on Williamson fluid flow due to an expanding/contracting cylinder with nanomaterials: Dual solutions

The phenomena of heat and mass transfer during the flow of non-Newtonian transfer are amongst the core subjects in mechanical sciences. Recently, the nanomaterials are among the eminent tools for improving the low thermal conductivity of working fluids. Therefore, in view of the existing contributions, this article presents a two-dimensional numerical simulation for the transient flow of a non-Newtonian nanofluid generated by an expanding/contracting circular cylinder. This critical review further explores the impacts of variable magnetic field, thermal radiation, velocity slip and convective boundary conditions. The basic governing equations for Williamson fluid flow are formulated with the assistance of boundary layer approximations. The non-dimensional form of partially coupled ordinary differential equations has been tackled numerically by utilizing versatile Runge–Kutta integration scheme. The momentum, thermal and concentration characteristics are investigated with respect to several critical parameters, like, Weissenberg number, unsteadiness parameter, viscosity ratio parameter, slip parameter, suction parameter, magnetic parameter, thermophoresis parameter, Brownian motion parameter, Prandtl number, Lewis number and Biot number. The outcomes of the systematic reviews of these parameters and forest plots are illustrated. The study reveals that multiple solutions for the considered problem occurs for diverse values of involved physical parameters. The computed results indicate that the friction and heat transfer coefficients are significantly raised by the magnetic parameter for upper branch solutions.     

Bright‐Dark Rogue Waves

During the last two decades, revealing mechanisms of origin waves with anomalous amplitude (rogue waves) have been in the focus of researchers from different fields ranging from oceanography to laser physics. Mode‐locked lasers, as a test bed system, provide a unique opportunity to collect more data on rogue waves in the form of random pulses (soliton rain) and to clarify the mechanisms of rogue‐wave emergence caused by soliton–soliton and soliton–dispersive wave interactions. Here, for the first time, for an Er‐doped mode‐locked laser, a new type of vector rogue waves is demonstrated experimentally and theoretically, which is driven by desynchronization of the orthogonal linear states of polarization, so leading to output power oscillations in the form of anomalous spikes‐dips (bright‐dark rogue waves). The results can pave the way to unlocking the universal nature of the origin of rogue waves and thus can be of interest to the broad scientific community.     

基于表面增强拉曼光谱技术的金表面耐腐蚀性分析

金属表面耐腐蚀性能与其微观结构密切相关。以金为分析对象,采用不同粒径氧化铝抛光粉抛光处理金片表面,经扫描电镜和原子力显微镜观察,表明金片表面具备与实际工件类似的微观结构,在此基础上,研究金片表面微观划痕结构对表面增强拉曼散射(SERS)以及耐腐蚀性能的影响。以罗丹明B为探针分子,对不同特征尺寸的微观划痕进行SERS分析,获得了罗丹明B的SERS信号强度随划痕平均特征尺寸的变化规律。通过改变拉曼激发光偏振方向与划痕方向的夹角大小,发现SERS信号主要归因于激发光与划痕相互作用产生的横向表面等离激元。划痕平均特征尺寸在50 nm附近时,横向表面等离激元最强,之后随着划痕平均特征尺寸增加,横向表面等离激元逐渐变弱。另一方面,对具有不同特征尺寸微观划痕的金片进行电化学极化测试,获得了各样品的自腐蚀电位,发现金片的自腐蚀电位随着划痕平均特征尺寸增大而降低。结果表明,当划痕平均特征尺寸大于50 nm,金表面的SERS信号与自腐蚀电位间存在良好的线性对应关系,这为SERS技术用于工件耐蚀性分析提供了依据。通过在工件表面滴涂探针分子并使用便携式拉曼光谱仪测量有望可以对工件耐蚀性进行现场快速预判。     

新型静态偏振风成像干涉仪理论探测误差的分析与计算

简述了新型静态偏振风成像干涉仪的原理,推导出一般情况下系统的Jones矩阵.在此基础上计算了系统中各偏振器件重要参数在非理想情况下对风速和温度探测结果的影响.利用计算机模拟对探测误差进行了分析,并按照系统精度要求从理论上提出了各重要参数的误差容限.该研究为新型静态偏振风成像干涉仪的研制、定标及后期数据处理提供了理论依据. 关键词： 静态偏振风成像干涉仪 Jones矩阵 方位角误差 相位延迟量误差     

微波辅助对生物溶液超滤过程的影响

为验证微波场强化植物提取的膜超滤假说机理,以聚醚砜超滤膜为研究对象,以膜通量为考察指标,结合膜和黄芪饮片显微结构的扫描电镜(SEM)表征,讨论了微波辐射对黄芪水提液超滤过程的影响。结果表明,驱动压力相同,微波辅助超滤30 min时,膜通量下降到初始值的57.36%,且膜表面观察不到凝胶层;而常规超滤30 min,膜通量已下降到初始值的30.29%,且膜表面覆盖一层约20μm的凝胶层。说明微波辐射能够减弱浓差极化现象,促进膜超滤过程中的物质传递。     

Spin-polarizing properties of heterostructures with magnetic nano elements

The problem of electron resonant and non-resonant scatterings on two magnetized barriers is studied in the one-dimension. The transfer-matrix is built up to exactly calculate the coefficient of the electron transmittance through the system of two magnetic barriers with non-collinear magnetizations. The polarization of the transmitted electron wave for resonance and non-resonance transmittances is calculated. The transmittance coefficient and spin polarization can be drastically enhanced and controlled by the angle between the barrier magnetizations.     

Second-harmonic wave induced by vortex beams with radial and azimuthal polarizations

The author investigated second-harmonic (SH) wave patterns generated by focused vortex beams with radial and azimuthal polarizations. Expressions for electric field components near the focus through a dielectric interface were obtained based on vector diffraction theory. Furthermore, the (110) and (001) planes of a crystal classified in the symmetry group 4?3m were considered as second order nonlinear optical medium to analyze nonlinear polarization and the intensity distributions of the SH wave in the far-field were simulated for topological charge m = 1 and 2. Numerical simulations indicated that the intensity and emission pattern of the SH wave depended principally on the electric field component and distribution near the focus. In particular, for the (001) plane, the intensity of the SH wave was strongly correlated with the existence of a longitudinal electric field.     

Periodic intensity variations on the pulse-train of a passively mode-locked fiber ring laser

We investigate the evolvement of the periodic intensity variations of the pulse-train in a fiber ring laser mode-locked by the nonlinear polarization rotation technique. It is found that the phenomenon of such intensity fluctuations is related to the orientation of the polarization controllers when the pump power is fixed. The numerical results show that the mechanism of the periodic intensity variations is caused by the interaction of the nonlinear polarization rotation and the passive polarizer in the cavity.     

An angle-resolved laser incident beam detector based on a pair ofFabry-Perot etalons

An angle-resolved laser detector based on a pair of a non-mechanical scanning Fabry-Perot cavities is described. The differential signal from the two cavities is approximately independent from the polarization of the incident laser beam and it is used to determine the angle of incidence of the beam on the Fabry-Perot cavities. The F-P etalon is made of interferometric filter combination. A laser incident angle sensor experimental platform is built up, and the experiment is carried out with a given laser range finder. When the incident angle is less than 5°, the transmission difference measured by the laser angle sensor is significantly lower than theoretical value, and deviation is more than 10%. When the incident angle is greater than 10°, the deviation is much lower than that of the situation of the incident angle is lower than 10°.     

Changes in the intensity distribution and polarization of non-uniformly polarized beams focused by a spherically aberrated lens with annular aperture

Based on the generalized Huygens-Fresnel diffraction integral and beam coherence polarization (BCP) matrix formulation, the focusing properties of a type of non-uniformly polarized (NUP) beam through a spherical aberrated lens with annular aperture are studied. The dependence of focal shift, intensity distribution, power in the bucket (PIB) and degree of polarization on the spherical aberration coefficient, obscure ratio and polarization parameters is illustrated numerically. The focusing of NUP beams by a spherically aberrated lens with circular aperture is treated as a special case, where the inner radius of the aperture is equal to zero.