辐射器漫反射定向管表面热辐射方向性

为了得到辐射能的方向分布特性,利用蒙特卡罗法,研究了定向管内壁面为不等温灰体、其底部假想圆型辐射器为黑体时,管内壁发射率、管长与半径比、管内空气流速等参数的变化对管口表面当量定向发射率的影响,计算结果表明:管长与半径比增加,管口表面较大的当量定向发射率向小角度的天顶角方向移动,空气流速仅影响当量定向发射率数值大小。     

分数阶对数耦合系统在非周期外力作用下的定向输运现象

本文讨论了分数阶对数耦合系统在非周期外力作用情况下, 耦合粒子链的定向输运现象. 由于粒子在黏性介质中的运动具有“记忆性”, 所以本文通过将系统建模为分数阶对数耦合模型来研究各个系统参数对粒子链运动状态的影响. 数值仿真表明: 1)对于此类系统, 只有在存在外力作用的情况下粒子链才能够产生定向输运现象, 并且粒子链平均流速随着外力的增大而增大. 2)对于分数阶阶数较小的系统, 阻尼记忆性对粒子链的运动状态有显著的影响, 具体表现为: 粒子链的平均流速存在上界(这个上界非常小), 无论外力、耦合力以及噪声强度如何变化, 粒子链的平均流速都不会超过这个上界. 当系统的阻尼力很大且外力为零时, 粒子链不会产生定向输运现象. 3) 当系统的阶数与外力较大时, 虽然粒子链能够产生定向流, 但是此时系统对耦合力与噪声具有免疫性. 4) 耦合力与噪声强度对粒子链运动的影响只在外力较小的情况下有所表现. 在这种情况下, 当系统阶数充分大时, 粒子链的平均流速随着耦合力与噪声强度的变化而变化, 并且伴随着定向流的产生.     

抽拉速度对SCN-DC共晶生长形貌的影响

本文采用类金属透明模型合金丁二腈-23.6 wt%樟脑 (SCN-23.6 wt%DC) 合金, 研究了棒状共晶定向凝固组织的演化行为, 考察了抽拉速度对棒状共晶合金组织形貌演化的影响规律. 结果表明, 在共晶生长初期, 共晶组织首先起源于晶粒晶界或者试样盒型壁处, 随后沿液/固界面和平行于热流方向生长; 在较小的抽拉速度 (0.064–0.44 μm/s)下, 棒状共晶界面前沿呈现平界面形态, 内部两相棒状组织平行生长, 并且随着抽拉速度的增大,棒状共晶逐渐细化, 棒状间距减小; 而在较大的抽拉速度 (0.67–1.56 μm/s)下, 共晶界面前沿呈现胞状生长形貌, 胞内的棒状共晶呈放射状生长, 同样, 随着抽拉速度的增大, 胞内棒状共晶逐渐细化, 棒状间距减小. 关键词： 定向凝固 共晶形貌 抽拉速度 共晶间距     

Directional Mode-Locking of Dynamics of Two-Dimensional Superparamagnetic Colloidal System in a Periodic Pinning Array

Using Langevin simulations,we study numerically the directional mode-locking of the dynamics of twodimensional superparamagnetic colloidal system in a periodic pinning array.When the colloidal particles are initially commensurate with the pinning sites,there appear mode-locking steps in the average velocity of colloidal particles along certain directions of the external driving force.With an increase in the pinning strength,the width of the step increases linearly but the velocity at the step decreases parabolically.     

定向结晶条件下聚乙二醇6000的强动力学效应

在单向温度场条件下, 采用不同抽拉速度实现了聚乙二醇6000的定向生长、界面形貌的实时观测及界面温度的测量, 进而揭示了其生长机制. 实验结果表明, 随着抽拉速度的增大, 界面的温度逐渐减小, 过冷度逐渐增大. 运用高聚物结晶的次级形核理论模型, 对实验数据进行了计算, 得到在界面过冷度为13.5 K左右时, 生长机制发生了由区域Ⅱ向区域Ⅲ的转变. 实验数据与等温结晶数据的比较发现等温结晶方法中获得过冷度相对较大, 是因为其包含了热过冷. 聚乙二醇6000定向结晶过程中需要的最大动力学过冷度为20 K, 说明由于高聚物的二维形核, 其生长主要由界面动力学控制, 具有较强的动力学效应.     

Dendrite to symmetry-broken dendrite transition in directional solidification of non-axially oriented crystals

In this paper, the morphological transition from dendrite to symmetry-broken dendrite is investigated in the directional ;olidification of non-axially-oriented crystals using a quantitative phase-field model. The effects of pulling velocity and zrystal orientation on the morphological transition are investigated. The results indicate the orientation dependence of the ;ymmetry-broken double dendrites. A dendrite to symmetry-broken dendrite transition is found by varying the pulling telocity at different crystal orientations and the symmetry-broken multiple dendrites emerge as a transition state for the ;ymmetry-broken double dendrites. The state region during the transition can be well characterized through the variations ff the characteristic angle and the average primary dendritic spacing.     

Influence of isothermal approximation on the phase-field simulation of directional growth in undercooled melt

By using the phase-field approach,we have simulated the directional growth of alloys in undercooled moten states under the isothermal and nonisothermal conditions.The influences of the isothermal approximation on simulation results are discussed.We found that for undercooling greater than 25K,the isothermal approximation overestimates the interface growth velocity and reduces a critical velocity for an absolute stable planar interface,thus in this simulation,the uinterface morphology shows the plane-cell-plane transition with increasing initial undercooling of the mele,and the planar interface obtained under a large undercooling is absolutely stable.Whereas in the nonisothermal simulation,only plane-cell transition occures in the same range of the initial undercoolings of the melt,and the planar interface tends to be destabilized and evolve into cells.     

A study on radial directional natural frequency and damping ratio in a vehicle tire

The measurement of radial directional natural frequency and damping ratio in a vehicle tire has been studied. Natural frequencies and damping ratios in the radial direction of various tires, from passenger car tires to truck bus tires, are reported. The radial direction modal parameters of tires subjected to different levels of inflation pressure, have been determined by using a frequency response function method. To obtain the theoretical natural frequency and mode shape, the plane vibration of a tire has been modeled as though it were that of a circular beam. By using the Tielking method that is based on Hamilton’s principle, theoretical results have been determined by considering the rotational velocity, tangential and radial stiffness, radial directional velocity and tension force which is due to tire inflation pressure. The results show that experimental conditions can be considered as the parameters that shift the natural frequency and damping ratio.     

二元合金高速定向凝固过程的相场法数值模拟

利用相场法对二元合金高速定向凝固过程进行了模拟，为简化计算，采用了温度冻结近似.模拟了定向凝固时平界面失稳、界面形态演化、溶质浓度分布以及高速绝对稳定性条件下胞晶向平面晶的转变等，得到了不同抽拉速度下胞晶间距、胞晶尖端温度以及有效溶质分配系数等参数，显示了高速生长条件下的溶质截留效应. 关键词： 定向凝固 相场法 高速绝对稳定性 溶质截留     

Solidification microstructure selection of the peritectic Nd-Fe-B alloys

Bridgman directional solidification and laser remelting experiments were carried out on Nd_11.76Fe_82.36B_5.88 and Nd_13.5Fe_79.75B_6.75 alloys. Microstructure evolutions along with solidification parameters (temperature gradient G, growth velocity V and initial alloy composition C ₀) were investigated. A solidification microstructure selection map was established, based on the consideration of solidification characteristics of peritectic T₁ phase. In Bridgman directional solidification experiments, with the increasing growth velocities, the morphology of T₁ phase changed from plane front or faceted plane front to dendrites. In laser remelting experiments, a transition from primary γ-Fe dendrites to T₁ dendrites was found. Theoretical predictions are in good agreement with experimental results. Supported by the National Natural Science Foundation of China (Grant No. 50395100)     

基于纳米天线的多通道高强度定向表面等离子体波激发

设计了一种带有纳米天线的金属微腔结构, 以实现高强度表面等离子的定向激发. 在利用双狭缝结构实现表面等离子体波定向激发的基础上, 分别结合共振增强和干涉相长原理, 在传统结构的入射端面上添加纳米天线结构, 并增加狭缝通道数, 实现了定向激发的表面等离子体波的能量增强. 基于纳米天线的多通道高强度定向表面等离子体波激发装置结构简单, 系统紧凑, 并能够有效提高定向传播的表面等离子体波的能量密度和传播距离, 其对微纳光学传输和高密度光学集成领域等方面的研究具有重要意义.     

有限点方法研究

在二维散乱离散点集上研究一类无网格方法——有限点方法(Finite Point Method,简称FPM),建立方法的基础.采用方向微商和方向差商讨论有限点方法,建立各阶各方向微商间的关系式.利用这些关系式,根据被逼近点的邻点数目差异,分别建立数值方向微商的五点公式及少点(两点、三点、四点)公式;研究五点公式的可解性条件与可允许邻点集;获得典型微分算子的数值方向微商公式等.理论分析和数值试验表明,随着邻点数目的增加,相应数值公式的逼近精度随之提高.这类近似公式不仅为在散乱离散点集上构造各类偏微分方程的格式奠定了基础,同时,也可应用于偏微分方程非结构网格计算方法,提高方法的精度.     

Directional growth of Al-Mg2Si eutectic alloy in the SZ2 unmanned spaceship

This paper reports the investigation results on directional growth of Al-Mg2Si eutectic alloy in the SZ2 unmanned spaceship. The analysis shows that microgravity has influence on the directional growth of Al-Mg2Si eutectic alloy. The eutectic colony in space-grown sample is larger than that in ground-grown sample, and the directional effect is not so good as that of terrestrial sample. But there is no obvious difference in the lamellar thickness between these samples, and lamellar interspacing in space sample is smaller than that grown on the ground. A simple discussion is done on the gravity effect on the directional growth of Al-Mg2Si eutectic alloy.     

晶体取向对定向凝固平界面失稳行为的影响

采用丁二腈-丙酮透明模型合金研究了不同晶体取向的晶粒在定向凝固条件下的平界面失稳过程.实验选择了三个界面失稳后具有不同生长形态的典型晶粒作为研究对象, 分别为择优生长枝晶、倾斜枝晶和海藻晶.结果表明可发展为择优生长枝晶的晶粒的平界面失稳孕育时间和初始扰动波长最小,海藻晶次之, 倾斜枝晶最大,这与以往的解析结果和相场模拟结果一致. 同时,实验观察发现可发展为择优生长枝晶和倾斜枝晶的晶粒的界面非稳态演化过程与海藻晶显著不同,这表明平界面失稳的非稳态演化过程与晶体取向相关.     

Graphical Representation of the Supermode Theory of a Waveguide Directional Coupler

A novel graphical representation of the supermode theory of a waveguide directional coupler based on phasor analysis is described. Following this approach, dependence of the magnitudes and phases of the output fields on the splitting ratio of a directional coupler is discussed. Both the cases of phase-matched (identical) and non-phase-matched (non-identical) waveguides constituting a directional coupler are investigated. This approach directly illustrates the fact that the phase shift suffered by the coupled light relative to the throughput light is π/2, regardless of the splitting ratio for identical guides, which is not the case for couplers with non-identical waveguides. It also yields additional information about the phases of the output fields of a directional coupler. The usefulness of this approach in the context of wavelength-flattened couplers, wavelength division multiplexing couplers, and polarization effects in directional couplers is also discussed. This approach should also be helpful in the analysis of guided wave interferometric devices such as wavelength interleave filters and modulators, based on concatenated directional couplers.     

Numerical study of growth competition between twin grains during directional solidification by using multi-phase field method

A multi-phase field model is established to simulate the growth competition and evolution behavior between seaweed and columnar dendrites during directional solidification.According to the effects of surface tension and interfacial energy,we quantitatively analyze the influences of factors such as inclination angles,pulling velocity,and anisotropic strength on twin growth.The results demonstrate that the pulling velocity and anisotropic strength have an important influence on the morphology and evolution of the seaweed and dendritic growth.The low pulling velocity and anisotropic strength are both key parameters for maintaining the stable morphology of seaweed during competitive growth in a bicrystal,showing that the lateral branching behavior is the root of the dendrites that can ultimately dominate the growth.And it is clarified that the lateral branching behavior and lateral blocking are the root causes of the final dominant growth of dendrites.With the increase of anisotropy strength,the seaweed is eliminated fastest in case 1,the seaweed is transformed into degenerate dendritic morphology,and eliminates the seaweed by promoting the generation and lateral growth of the lateral branches of the dendrites.The increase of pulling velocity is to increase the undercooling of favorable oriented grain and accelerate the growth rate of dendrites,thus producing more new primary dendrites for lateral expansion and accelerating the elimination rate of unfavorable oriented grain.     

Slow-wave directional coupler and its applications

The directional coupler and the traveling-wave directional filter made of coupled slow-wave microstrip lines are proposed and their characteristics discussed. These structures exhibit interesting characteristics not readily available in conventional transmission lines.This work is supported by U.S. Army Research Office contract DAAG29-84-K-0076.     

Switchable directional scattering based on spoof core—shell plasmonic structures

Manipulating directional electromagnetic scattering plays a crucial role in the realization of exotic optical phenomenon. Here, we show that the spoof plasmonic structure is able to achieve the switching of directional scattering direction on a subwavelength scale by inserting a perfect electric conductor (PEC) cylinder into the hollow of the spoof plasmonic structure. Based on the modal analysis, it is found that the electromagnetic response of the core-shell structure not only is well excited, but also exhibits the directional scattering by interference between the electric and magnetic dipolar resonances. We also discuss the influence of PEC cylinder radius on the performance of the directional scattering. Finally, the active tunable directional scattering is realized by switching between the two states. This work provides a feasible pathway to the subwavelength manipulation of electromagnetic wave. Moreover, it offers a simple method to switch the directional scattering direction. The proposed design approach can be easily applied to digital electromagnetic wave communication and associated applications.     

二维正方晶格Compass-XY模型的方向序和拓扑序

采用Monte Carlo方法研究二维正方晶格Compass-XY模型,通过调节过渡参量α,计算了降低交换相互作用的阻挫对方向序和拓扑序的影响.结果表明,方向序和拓扑序之间的转变是一个逐渐过渡的过程,并不存在明显的界限.在某一范围内,这两种序是相互重叠的,难以区分.阻挫的降低,易于形成拓扑序,同时会抑制方向序.当阻挫变得足够弱时,方向序被破坏.     

温度梯度区域熔化作用下熔池迁移的元胞自动机模拟

本文采用耦合凝固和熔化效应的二维元胞自动机(cellular automaton, CA)模型,对温度梯度区域熔化(temperature gradient zone melting, TGZM)效应引起的熔池在固液两相区中的迁移现象进行模拟研究.模拟分析了抽拉速度、熔池初始位置、温度梯度和合金成分等因素对TGZM动力学的影响,并将模拟结果与解析模型的预测结果进行比较验证.通过模拟发现,在温度梯度作用下,熔池总是向着高温方向迁移;当抽拉速度低于或高于临界抽拉速度时,熔池朝向移动的液相线或固相线迁移;对于给定的抽拉速度,位于糊状区内临界位置以上的熔池会迁移进入液相,而位于临界位置以下的熔池会逐步靠近固相线.此外,温度梯度越高,合金成分越低,熔池的迁移速度越快.