Preliminary results of a non-spherical aerosol method for the retrieval of the atmospheric aerosol optical properties

There is experimental evidence that the non-sphericity of certain atmospheric particles can cause scattering properties different from those predicted by standard Mie theory. Numerous studies indicate the need to consider the presence of non-spherical particles in modeling the optical properties of atmospheric aerosols. On the other hand, natural aerosols show a great variety of shapes, making difficult a realistic choice of a particle shape (or shape mixture) model. In this paper, we test a parameterization of the particle shape in the retrieval of size distribution, phase function, single scattering albedo and asymmetry parameter from direct and sky-radiance measurements. For this purpose we have substituted the Kernel based on the Mie theory included in the model SKYRAD.PACK by one derived for non-spherical particles. The method is applied under different atmospheric conditions, including Saharan dust outbreak, polluted and local mineral episodes. We compare the results with those obtained by the well known spheroids algorithm used in the AERONET network.     

Bifurcation in a coupled logistic map. Some analytic and numerical results

We study the bifurcation pattern, two- and four-cycle generation, and supertrack functions in the case of the coupled logistic system given byX _n+1=x _n (1–2y _n ) +y _n ,Y _n+1=y _n(1-y _n ), which is of immense importance in various biophysical processes. We deduce analytic formulas for the two -and four-cycle fixed points and cross-check them numerically. The agreement is quite good. Next the bifurcation pattern is explained with the help of analytically derived supertrack functions. To discuss the stability of the system in the various zones defined by the parameter values (, ), the Lyapunov exponents are evaluated, showing a nice transition from the stable to the unstable region. An interesting phenomena occurs at=4, where the logistic itself is chaotic. We then show that near the fixed point an analytic solution can be obtained for the renormalization group equation. In the special case=1,=4 a neat analytic formula can be deduced for then-times iterated values of (x _i ,y _i ).     

纳米MgO掺杂聚乙烯微观特性的分子动力学模拟研究

电力系统高压电缆的主要绝缘材料为聚乙烯,为了提升聚乙烯的热稳定性以及减弱水分对其的渗透能力,采用纳米MgO掺杂聚乙烯,利用分子动力学模拟方法建立包含低密度聚乙烯(LDPE)、不同颗粒半径的MgO纳米团簇以及相同质量分数水分的复合模拟模型.研究结果表明,水分会降低复合体系的玻璃化温度,MgO的掺杂则会提高复合体系的玻璃化温度,减弱聚乙烯分子链的运动并减小复合体系的自由体积,使得复合体系结构更加稳定,从而增强了聚乙烯材料的热稳定性能.此外发现水分子的扩散随着温度的上升而增大,纳米MgO的添加会与水分子形成氢键抑制水分子的扩散,同时自由体积的缩减使水分子的溶解度系数与扩散系数都减小,导致水分子的渗透能力减弱,更难以渗透进聚乙烯材料破坏其结构.研究结果可为聚乙烯的水树枝生长以及老化过程的抑制提供有益的参考.     

Influence of local waste burning on atmospheric aerosol properties in urban environment

Aerosols affect the radiative energy budget on both the regional and global scales. The wavelength-dependent aerosol optical depth (AOD) is a fundamental determinant of the amount by which extra-terrestrial incoming sunlight and outgoing terrestrial radiation are being attenuated in the atmosphere. The present study addresses the influence of local waste burning on aerosol characteristics, black carbon (BC) aerosol mass concentration and spectral solar irradiance using ground-based measurements over the tropical urban environment of Hyderabad, India. AOD has been observed to be maximum during burning days compared to normal days. Aerosol size spectra suggest bimodal distributions during pre-and post-burning periods and trimodal distributions during burning periods. Angstrom wavelength exponent estimated from spectral variation of AOD suggested dominance of accumulation mode particle loading during burning days compared to normal days. Diurnal variation of BC on normal days showed a broad nocturnal peak during ∼20:00 to ∼24:00 h with a maximum value of BC aerosol concentration of ∼14,000 ng m⁻³ whereas on local waste burning days enormous increases in BC concentrations have been observed with a peak at ∼60,000 ng m⁻³. Relative attenuation of global solar irradiance during burning days has been found to be of the order of 30% in the visible and 28% in the near-infrared regions. The results are discussed in detail in this paper.     

Some theoretical and numerical results for delayed neural field equations

In this paper we study neural field models with delays which define a useful framework for modeling macroscopic parts of the cortex involving several populations of neurons. Nonlinear delayed integro-differential equations describe the spatio-temporal behavior of these fields. Using methods from the theory of delay differential equations, we show the existence and uniqueness of a solution of these equations. A Lyapunov analysis gives us sufficient conditions for the solutions to be asymptotically stable. We also present a fairly detailed study of the numerical computation of these solutions. This is, to our knowledge, the first time that a serious analysis of the problem of the existence and uniqueness of a solution of these equations has been performed. Another original contribution of ours is the definition of a Lyapunov functional and the result of stability it implies. We illustrate our numerical schemes on a variety of examples that are relevant to modeling in neuroscience.     

Low frequency scattering through an aperture in a rigid screen—Some numerical results

The penetration of a plane wave through an aperture in a rigid screen is investigated. The first three terms of the low frequency expansion are evaluated numerically for both simply connected and annular apertures. In the numerical method use is made of a division of the aperture into arbitrary triangles. The singular behaviour at the edges is incorporated in the shape functions, which yields good accuracy and fast convergence. Special attention has been given to the thin ring which can serve as a model for, e.g., imperfectly shielded windows.     

Rotational motions of optically trapped microscopic particles by a vortex femtosecond laser

The rotational motions of the optically trapped microscopic particles by the vortex femtosecond laser beam are investigated in this paper.Black particles can be trapped and rotated by a vortex femtosecond laser beam very effectively because the vortex beam carries orbital angular momentum due to the helical wave-front structure in assoication with the central phase singularity.Trapped black particles rotate in the vortex beam due to the absorption of the angular momentum transferred from the vortex beam.The rotating directions of the trapped particles can be modulated by reversing the topological charge of the optical vortex in the vortex femtosecond beam.And the rotating speeds of the trapped microscopic particles greatly depend on the topological charges of the vortex tweezer and the used pulse energies.     

Filtration of aerosol particles by elliptical fibers: a numerical study

Filtration is an important technology for nanoparticle control and reduction of human exposure to nanoparticles. Filtration by non-circular fibers is gaining more attention in search for better filter quality; elliptical fibers have extra significance because they may be used in simple models of dust loading. We carry out numerical simulation to investigate filtration by fibers with elliptical cross-sections. The drag force on individual fibers is in good agreement with analytical solutions for elliptical fibers obtained from the cell model. Our simulation covers mechanisms for particle capture due to interception, inertial impaction, and diffusion. Single-fiber efficiencies of different elliptical fibers are computed. The figure of merit, which is an indicator of the ratio of the collection efficiency to the pressure drop, is used to evaluate the performance of different elliptical fibers. It is found that blunt and close to circular fibers perform better for particles dominated by the effects of interception and inertial impaction, whereas long and slim fibers perform better for particles dominated by the diffusion effect. For very small nanoparticles, the diffusion effect is important and long and slim elliptical fibers may improve the filter performance.     

Dynamic compaction of copper powder: 2D numerical simulation and experimental results

Abstract

A method for plate-impact dynamic compaction of copper powder has been developped. The optimization of the experimental set-up (impedance adjustments, tensile wave traps, relative thickness of impactor and target,…) is presented.

2D axisymetrical numerical simulations have been performed with a Lagrangian finite element code. Geometrical characteristics of the experimental set-up as well as the dynamic response of the powder (Reaugh equation of state) and of the material of the set-up have been taken into account. These simulations show that, due to the difference in shock velocities in the container and in the powder, the powder is submitted to 2D loading waves. As a matter of fact the powder may be loaded by a non-planar shock wave propagating in the as-expected direction, as well as by a sweeping wave initiated at the bottom of the powder container, and propagating obliquely from the bottom-up. This second wave loads the bottom of the powder first. The influence of the impactor thickness as well as its material on the shock front shape and on the shock density-pressure history of the material has been studied. 1D simulations are shown not to evaluate properly the stress history and the energy deposition in the powder sample.

Metallographic observations as well as X-ray tomography experiments have been performed on consolidated samples. A very good agreement has been found between results of 2D numerical simulations and the observed final shape and density maps of the samples. The shape of deformed powder particles are also in agreement with the expected shock history.     

辐射烧蚀CH薄膜非平衡理论计算与实验比对分析

用一维非平衡辐射输运程序和实验提供的黑腔辐射流,对CH薄膜靶的辐射烧蚀进行了数值模拟计算。计算结果表明,非平衡的黑腔辐射场对CH薄膜靶辐射烧蚀的影响十分明显。出靶外界面的辐射流总强度、等效辐射温度随时间变化、400eV光子出界面延迟时间随靶厚度变化规律等方面的数值模拟结果与实验结果基本符合。     

Thermorefractive noise in whispering gallery mode microresonators: Analytical results and numerical simulation

We demonstrate numerical finite element simulation of thermorefractive noise in whispering gallery mode cavities and compare the results with known experimental data and analytical derivations. We show that thermal interaction of the microcavity with environment is very significant, making particular geometry significant for the noise spectral density at low frequencies.     

Rod-pinch 二极管理论及数值模拟

 介绍了Rod-pinch二极管的基本结构和工作原理，采用Laminar模型分析了Rod-pinch二极管中的粒子运动过程及其阻抗特性。考虑背景空间离子电荷的影响，用1维Laminar方程分析Rod-pinch二极管中电子的自箍缩过程，并且利用Magic程序对其中的粒子运动进行数值模拟，求解二极管中的电压和电流，最终得出二极管的阻抗特性，在较低电压下，负极性RPD的性能明显不如正极性RPD。根据临界电流经验公式，初步验证Laminar理论模型的可行性。     

辐射烧蚀CH薄膜非平衡理论计算与实验比对分析

 用一维非平衡辐射输运程序和实验提供的黑腔辐射流，对CH薄膜靶的辐射烧蚀进行了数值模拟计算。计算结果表明，非平衡的黑腔辐射场对CH薄膜靶辐射烧蚀的影响十分明显。出靶外界面的辐射流总强度、等效辐射温度随时间变化、400eV光子出界面延迟时间随靶厚度变化规律等方面的数值模拟结果与实验结果基本符合。     

Rod-pinch 二极管理论及数值模拟

介绍了Rod-pinch二极管的基本结构和工作原理,采用Laminar模型分析了Rod-pinch二极管中的粒子运动过程及其阻抗特性。考虑背景空间离子电荷的影响,用1维Laminar方程分析Rod-pinch二极管中电子的自箍缩过程,并且利用Magic程序对其中的粒子运动进行数值模拟,求解二极管中的电压和电流,最终得出二极管的阻抗特性,在较低电压下,负极性RPD的性能明显不如正极性RPD。根据临界电流经验公式,初步验证Laminar理论模型的可行性。     

Constraints on the universe as a numerical simulation

The level scheme above the proton threshold in ²⁶Si is crucial for evaluating the ²⁵Al(p, γ)²⁶Si stellar reaction, which is important for understanding the astrophysical origin of the long-lived cosmic radioactivity ²⁶Al(T _1/2 = 7.17 × 10⁵ y) in the Galaxy. The excited states in ²⁶Si have been studied using an in-beam γ-ray spectroscopy technique with the ²⁴Mg(³He, nγ)²⁶Si reaction. γ-rays with energies up to 4.6 MeV emitted from excited states in ²⁶Si have been measured using large volume HPGe detectors. The spin-parity of one of the most important states reported recently at 5890.0keV has been assigned as 0⁺ by γ-γ angular correlation measurements in this work.     

改进型磁绝缘线振荡器的设计和数值模拟

 综合两种现有磁绝缘线振荡器的优点，对器件进行改进，将双渐变结构、轭流片和阻抗渐变三种增大功率的机制综合考虑，利用二维半全电磁PIC程序进行数值模拟，设计了一种新的改进型磁绝缘线振荡器，当外加电压为550kV，电流为35kA左右时，在L波段获得了6GW的峰值输出功率。     

衍射图样的数值模拟

介绍了平面波角谱理论中得到衍射积分公式的方法.用Matlab计算了15×15矩孔阵列近场区域的衍射图样,在距离周期衍射屏特定距离处出现衍射屏的自成像.