共查询到20条相似文献,搜索用时 109 毫秒
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快波加热算法,一般都是假定托卡马克中粒子为麦克斯韦分布.其实由于准线性扩散效应,共振粒子的平行温度与垂直温度不相等,这样必然产生一定的计算误差.针对这种情况,本文引入FokkerPlanck方程,采用叠代算法较好地解决了这一问题 相似文献
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如何解决粒子的退化问题和提高算法对突变状态的跟踪能力,是粒子滤波算法研究和应用中需要考虑的两个主要因素.传统的再采样算法虽然可以解决退化问题,但是容易导致粒子耗尽;扩展粒子滤波算法虽然可在一定程度上解决粒子耗尽问题,但其对突变状态的跟踪能力却不近人意;强跟踪粒子滤波算法可以提高对突变状态的跟踪能力,但却未能较好地改善粒子退化问题.针对上述问题,本文将随机摄动再采样方法引入强跟踪粒子滤波算法,提出了一种随机摄动强跟踪粒子滤波算法.当粒子退化问题严重时,对权值最大的粒子迭加随机摄动,用摄动粒子替换退化粒子以解决粒子退化问题,同时由于摄动粒子的加入增加了粒子集的多样性,可在一定程度上缓解粒子耗尽问题,提高算法对突变状态的跟踪能力.利用标准验证模型和分时恒定系统对所提出的算法进行了仿真验证,仿真结果证明了该算法的可行性和有效性. 相似文献
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在双温聚变燃烧点模型框架下,对比D-T等离子体聚变燃烧过程中α粒子能量逐步沉积与瞬时沉积两种描述的等离子体温度、离子数密度随时间的变化,在不同的密度条件下作了计算,考察了α粒子的慢化过程对D-T聚变点火的影响.发现考虑α粒子的慢化过程后,D-T等离子体峰值温度的出现将会推迟若干皮秒甚至几十皮秒,在较低的初始温度密度条件下,时间推迟得更多些.等离子体的峰值温度比α粒子能量瞬时沉积描述也会下降13keV左右.
关键词:
α粒子
聚变燃烧
能量沉积
慢化过程 相似文献
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针对粒子算法存在的问题,提出了辅助粒子算法.该算法在重采样算法基础上,引进辅助变量,对粒子的权2次计算,可使粒子权值比重采样的粒子权值变化更稳定,最后给出了红外目标模型和均方根误差函数.仿真结果表明该算法对运动目标跟踪的均值和方差上均优于标准粒子滤波、重采样粒子滤波,且提高了计算效率. 相似文献
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应用小角x射线散射技术分析了Al-Zn-Mg-Cu-Li合金在130,150和160℃温度时效24 h析出粒子的微结构参数的变化情况. 粒子的半径随着时效温度的增高而增加,它的比内表面积和体积百分数随着时效温度的增高而减小. 对Porod曲线q3J(q)-q2的分析表明,析出粒子与基体之间有明显的界面.
关键词:
小角x射线散射
Al-Zn-Mg-Cu-Li合金
时效
析出粒子 相似文献
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《物理学报》2017,(5)
标准粒子滤波容易出现粒子贫化问题,滤波精度不稳定,并且需要大量粒子才能对非线性系统进行准确估计,降低了算法的综合性能.针对该问题,本文提出了一种基于蝙蝠算法的新型粒子滤波算法.该算法用粒子表征蝙蝠个体,模拟蝙蝠群体搜索猎物的过程,粒子群体通过调整频率、响度、脉冲发射率,追随当前最优粒子在解空间中进行搜索,并可以动态控制全局搜索及局部搜索的相互转换,进而提髙粒子整体的质量和分布的合理性;此外,改进算法引入Levy飞行策略,从而避免局部极值的不良吸引.实验表明新型粒子滤波方法提高了粒子多样性和滤波预测精度,同时大大降低了对非线性系统进行状态预测所需的粒子数量. 相似文献
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In this paper, distribution of suspended micrometer-size particles in magnetic fluids is investigated. Microstructure formation of particles in magnetic fluids is simulated by using the discrete particle method based on the simplified Stokes dynamics. Not only magnetic particles but also nonmagnetic particles are rearranged in the field direction and form chain-like clusters due to the apparent magnetization in magnetic fluids in the presence of magnetic field. When the diameter of nonmagnetic particles is smaller than that of magnetic particles, nonmagnetic particles move into the empty space of microstructure of magnetic particles, and they are rearranged in the field direction. Uniformity of distribution of particles on the plane perpendicular to the field direction is maintained even after microstructure formation. 相似文献
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针对自然界中多数沙尘、烟煤粒子的非球形问题, 在球形粒子偏振特性的基础上, 进一步研究非球形椭球粒子的折射率、有效半径、粒子形状等参数变化对光偏振特性的影响, 采用基于T矩阵的非球形粒子仿真方法, 模拟非偏振光经椭球粒子传输后光的偏振特性及其与球形粒子间的差异, 并以实际沙尘、海洋、烟煤三种气溶胶粒子为例说明结果的正确性. 结果表明: 当折射率实部越小, 虚部越大时, 球形粒子与非球形粒子的偏振差异越不明显; 当粒子有效半径增加时, 球形粒子偏振度的变化比非球形粒子更为明显, 且最大值分别出现在散射角为150°和120°的位置; 当粒子形状不同时, 不同形状椭球及球形粒子的差异在散射角小于60° 时并不明显, 且当椭球粒子纵横比互为倒数时, 两种粒子的偏振特性近似相同. 通过以上分析可知, 在光传输过程中, 椭球粒子多数情况下无法被近似为球形粒子进行计算. 相似文献
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A. Vatry A. MarchandPh. Delaporte D. GrojoC. Grisolia M. Sentis 《Applied Surface Science》2011,257(12):5384-5388
The removal of metallic and carbon particles is a great issue in the framework of the ITER (International Thermonuclear Experimental Reactor) project. Indeed, the presence of these particles in the vessel of a tokamak leads to safety risks.The laser process seems to be a very promising solution for this cleaning. However, the process optimization requires a good knowledge of the removal mechanisms. For this purpose, we investigated the influence of beam parameters, such as laser pulse duration and wavelength, on the cleaning efficiency. In this paper, two kinds of particles are chosen to be studied, carbon aggregates and tungsten droplets, because they are typical of dust collected in tokamak.The results show an influence of beam parameters on the tungsten particles removal efficiency (PRE), whereas this influence is not significant for carbon particles.To help the understanding of the removal mechanisms, substrates and particles were inspected by scanning electron microscopy, before and after the irradiation.We will see on this paper that even if carbon and tungsten particles strongly absorb the different laser wavelength used, the removal mechanisms of these particles are very different. 相似文献
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We introduce a one-dimensional model involving the nucleation and the drift of many particles. The model originates from interacting kink systems and simulates time evolution in modulated systems. In this model the nucleation rate of a particle depends nonlocally on the density of preexisting particles and the drift of particles is due to a weak and repulsive interaction among them. We first study the statistics of this model in the case that the drift of particles is negligible, and then consider the effects of the drift of particles. 相似文献
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B. H. A. A. van den Brule R. J. J. Jongschaap 《Journal of statistical physics》1991,62(5-6):1225-1237
The constitutive equation of a concentrated suspension of spherical particles in a Newtonian medium is derived. To this end the method of local volume averaging is employed. To calculate the contribution of the particles to the stress tensor it is assumed that the stress generated in the interstitial holes between the particles is negligible compared to the stress generated in !he narrow gaps separating the particles. The use of the resulting expression is demonstrated with two examples on a cubical arrangement of particles: pure shear and simple shear. Furthermore, the validity of the lubrication approximation employed in this work is checked against the results derived by Nunan and Keller for periodic suspensions. 相似文献
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Sabrina Reuter Marek A. Smolarczyk André Istock Uh-Myong Ha Olga Schneider Natalie Worapattrakul Safoura Nazemroaya Hai Hoang Ludmilla Gomer Frank Pilger Markus Maniak Hartmut Hillmer 《Journal of nanoparticle research》2017,19(5):184
Nanoimprinting enables the implementation of nanoparticle shapes with complex 2D shapes involving different materials. In addition to these objects, this article presents 3D-shaped nanoparticles fabricated by substrate conformal imprint technique. The imprint polymer AMONIL is used either in pure form or in combination with fluorescent dyes for the preparation of particles. The substrate conformal imprint lithography process, including etching and particle release, is conducted for both materials in a similar fashion. In this work, cuboidal particles with a high aspect ratio (1:120) are compared to particles with a T-shaped cross section with respect to their abilities to enhance or reduce their stiffness. Additionally, particles with a high aspect ratio are compared to particles with a lower aspect ratio (1:20). The local stiffness is found to depend strongly on the particle thickness and the geometry of their cross section. Thicker and 3D T-shaped particles present higher local stiffness than thinner and 2D cuboidal-shaped particles. The local bending angle was determined to be 77° for 2D-shaped particles and 83° for 3D-shaped particles, of the same total height of 176 nm. Very thin particles (<50 nm) of high aspect ratio prefer to curl finally forming loops. 相似文献
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Dino Bacci Alessio Baron Toaldo Manuela Scaini 《Journal of Macromolecular Science: Physics》2013,52(10):1438-1452
The subject of this paper is the impact modification of polymers with elastomers via melt blending. A mathematical model was developed to account for the shape of the Izod S-curves (Izod values versus impact modifier content). Wu introduced the critical ligament thickness concept to explain the Brittle/Ductile Transition of polymers modified with elastomers: only when the ligament thickness (surface to surface distance of two rubber particles) is smaller than a critical value can the rubber particles promote toughness. In an ideal model with rubber particles distributed in an ordered lattice this transition would be a 90-degree step, whereas in practice this transition curve is more or less rounded. The smoothness of this transition is attributed in the present paper to the random distribution of rubber particles inside the polymer matrix: from this concept, an equation for the B/D Transition part of the S-curve was developed. This equation introduces the concept of the critical number of rubber particles, that is the number of particles within the ligament thickness distance necessary to trigger the toughness. The polymers investigated were polypropylene (PP) of different viscosity, polyamide (PA), polystyrene (PS), and polycarbonate (PC). 相似文献
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In this article we investigate charged particles in gauge theories. After reviewing the physical and theoretical problems,
a method to construct charged particles is presented. Explicit solutions are found in the abelian theory and a physical interpretation
is given. These solutions and our interpretation of these variables as the true degrees of freedom for charged particles,
are then tested in the perturbative domain and are demonstrated to yield infra-red finite, on-shell Green’s functions at all
orders of perturbation theory. The extension to collinear divergences is studied and it is shown that this method applies
to the case of massless charged particles. The application of these constructions to the charged sectors of the standard model
is reviewed and we conclude with a discussion of the successes achieved so far in this programme and a list of open questions.
An erratum to this article is available at . 相似文献
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This paper presents the effects of density difference on
the three-dimensional (3D) distribution of random mixed packing. The
random mixed packing dynamics of particles of two different
densities are simulated. The initial state is homogeneous, but the
final packing state is inhomogeneous. The segregation phenomenon
(inhomogeneous distribution) is also observed. In the final state,
the top layers are composed of mostly light particles. The several
layers beneath the top contain more heavy particles than light
particles. At the bottom, they also contain more heavy particles
than light particles. Furthermore, at both the top and the bottom,
particle clustering is observed. The current study also analyses the
cause of this inhomogeneity in detail. The main cause of this
phenomenon is the velocity difference after collision of these two
types of particles induced by the density difference. The present
study reveals that even if particles were perfectly mixed, the
packing process would lead to the final inhomogeneous mixture. It
suggests that special treatment may be required to get the true
homogeneous packing. 相似文献
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The collective diffusion of anisotropic particles in liquids plays a crucial role in many processes, such as self-assembly. The patchy particle, which is usually nearly spherical in shape, is an important anisotropic particle with different properties from other anisotropic particles like the ellipsoid liquid crystal particles. In the present study, molecular dynamics simulations are performed to study the collective diffusion of a two-dimensional anisotropic liquid system composed of Janus particles. The static structures and diffusion behaviours of anisotropic and isotropic Lennard-Jones liquids are compared. The long-time diffusion behaviour of an anisotropic liquid of nearly spherical Janus particles is found to be similar to that of an isotropic liquid because the orientation of the particles disappears over long-term averaging. The anisotropic properties of the Janus particles are mainly reflected in the spatial correlation of particle orientations and mid-time diffusion behaviour. The difference between nearly spherical anisotropic particles and rod-like particles is also discussed in this paper. 相似文献