Exact solutions for the incompressible viscous magnetohydrodynamic fluid of a rotating-disk flow with Hall current

The focus of the present study is to obtain exact solutions for the flow of a viscous hydromagnetic fluid due to the rotation of an infinite disk in the presence of an axial uniform steady magnetic field with the inclusion of Hall current effect. In place of the traditional von Karman's axisymmetric evolution of the flow, the rotational non-axisymmetric stationary conducting flow is taken into consideration here, whose governing equations allow an exact solution to develop bounded everywhere in the normal direction to the wall.The three-dimensional equations of motion are treated analytically yielding derivation of exact solutions, which differ from those of corresponding to the classical von Karman's conducting flow. Making use of this solution, analytical formulas for the angular velocity components, for the current density field as well as for the wall shear stresses are extracted. The critical peripheral locations at which extrema of the local skin friction occur are also determined. It is proved from the analytical results that for the specific flow the properly defined thicknesses decay as the magnetic field strength increases in magnitude, approaching their hydrodynamic value in the limit of large Hall numbers.Interaction of the resolved flow field with the surrounding temperature is further analyzed via the energy equation. The temperature field is shown to accord with the dissipation function. According to the Fourier's heat law, a constant heat transfer from the disk to the fluid occurs, though it increases by the presence of magnetic field, the increase is slowed down by the Hall effect eventually reaching its hydrodynamic limit.     

Study on the dynamical characteristics of a supersonic high pressure ratio underexpanded impinging ideal gas jet through numerical simulations

The impingement of an axisymmetric underexpanded ideal gas jet on a flat surface is investigated through numerical simulations. Different injection conditions, characterized by the nozzle pressure ratio (NPR), have been considered and for each, several standoff distances were studied. The study was conducted using the commercial finite volume general purpose code Fluent^®. The numerical results are presented in terms of Mach number and static pressure to characterize the structure of the flow. Furthermore, the influence of the standoff distance upon the position and diameter of Mach disk is analysed. Some results are compared with literature data and good agreement is obtained.     

大口径薄片激光器中的谐振模式及光束质量诊断

基于自再现原理,利用菲涅耳-基尔霍夫衍射积分方程,引入腔镜失调、激光介质上的增益分布以及光阑口径,采用本征矢量法分析了大口径平凹腔薄片激光器的本征模式,并计算了相应的光束质量因子M2.建立了千瓦级薄片激光系统和光纤扫描光斑诊断装置,开展了高功率激光输出特性研究.结果表明,在大口径高功率平凹腔中多个本征模式可同时起振,获...     

碳纤维超微盘电极的制备及对单囊泡胞吐动力学的高分辨研究

利用改良的电化学腐蚀方法制备了碳纤维超微盘状电极,具有方法简便,电极尺寸可控、可多次使用等优点.扫描电镜和伏安表征实验表明电极密封效果良好、电化学性能优良.在鼠嗜铬神经瘤PC12细胞上,用超微盘电极实现了高时空分辨、高保真度的单囊泡胞吐测定.与常规微电极相比,能更准确地反应囊泡融合这一超快过程(毫秒级)的动力学过程.     

Film-thickness Error Analysis of Optical Disk Systems

1　Ｉｎｔｒｏｄｕｃｔｉｏｎ　　Ｒｅｃｅｎｔｌｙｏｐｔｉｃａｌｄｉｓｋｓａｂｌｅｔｏｓｔｏｒｅａｌａｒｇｅｑｕａｎｔｉｔｙｏｆｉｎｆｏｒｍａｔｉｏｎｈａｖｅｂｅｅｎｕｓｅｄａｓｃｏｍｐａｃｔｄｉｓｋ (ＣＤ ) ,ｄｉｇｉｔａｌｖｅｒｓａｔｉｌｅｄｉｓｋ(ＤＶＤ) ,ａｎｄｔｈｅｉｒｒｅｃｏｒｄａｂｌｅｏｒｒｅｗｒｉｔａｂｌｅｔｙｐｅｓ(ｓｕｃｈａｓＣＤ Ｒ ,ＣＤ ＲＷ ,ＤＶＤ Ｒ ,ａｎｄＤＶＤ ＲＡＭ ) [1 ] .Ａｎｏｐｔｉｃａｌｄｉｓｋｉｓａｋｉｎｄｏｆｍｕｌｔｉｌａｙｅｒｓｙｓｔｅｍｄｅｐｏｓｉｔｅｄｏｎａ…     

一个特殊6点图Q与nK_1,P_n及C_n的联图交叉数

图的交叉数是图的一个重要参数,研究图的交叉数问题是拓扑图论中的前沿难题.确定图的交叉数是NP-难问题,因为其难度,能够确定交叉数的图类很少.通过圆盘画法途径,确定了一个特殊6点图与n个孤立点nK_1,路P_n及圈C_n的联图的交叉数分别是cr(Q+nK_1)=Z(6,n)+2[n/2],cr(Q+P_n)=Z(6,n)+2[n/2]+1及cr(Q+C_n)=Z(6,n)+2[n/2]+3.     

Graphene‐based solid‐phase extraction disk for fast separation and preconcentration of trace polycyclic aromatic hydrocarbons from environmental water samples

Graphene has great potentials for the use in sample preparation due to its ultra high specific surface area, superior chemical stability, and excellent thermal stability. In our work, a novel graphene‐based SPE disk was developed for separation and preconcentration of trace polycyclic aromatic hydrocarbons from environmental water samples. Based on the strong π–π stacking interaction between the analytes and graphene, the analytes extracted by graphene were eluted by cyclohexane and then determined by GC‐MS. Under the optimized conditions, high flow rate (30 mL/min) and sensitivity (0.84–13 ng/L) were achieved. The proposed method was successfully applied to the analysis of real environmental water samples with recoveries ranging from 72.8 to 106.2%. Furthermore, the property of anticlogging and reusability was also improved. This work reveals great potentials of graphene‐based SPE disk in environmental analytical.     

K3 surfaces,Picard numbers and Siegel disks

If a K3 surface admits an automorphism with a Siegel disk, then its Picard number is an even integer between 0 and 18. Conversely, using the method of hypergeometric groups, we are able to construct K3 surface automorphisms with Siegel disks that realize all possible Picard numbers. The constructions involve extensive computer searches for appropriate Salem numbers and computations of algebraic numbers arising from holomorphic Lefschetz-type fixed point formulas and related Grothendieck residues.     

一套新型基于物理放大原理的微小长度测量工具的设计

设计了一套利用圆盘放大和普通长度测量工具相结合的测量微小长度的工具,分别利用该设计装置和螺旋测微器对钢丝的直径和普通A4纸张的厚度进行了测量。结果显示了新设计的可行性、创新性和数据的高精度性、准确性。     

盘型激光焊金属蒸汽特征色调-色饱和度-亮度分析法研究

对于大功率盘型激光焊,金属焊件表面在激光束辐射下强烈汽化并形成等离子体状的金属蒸汽羽状物. 该金属蒸汽羽状物可逆向激光束传输,对激光有明显的屏蔽作用, 降低激光辐射至焊件的能量密度,影响焊接效率和质量. 因此研究金属蒸汽特征变化规律及其与焊接质量之间的关联 ,可实现由金属蒸汽特征实时监测激光焊接状态. 以10 kW大功率盘型连续激光焊接304不锈钢钢板为试验对象, 应用高速摄像机摄取金属蒸汽动态图像,将其转换至色调-色饱和度-亮度空间, 提取金属蒸汽面积、激光束受影响路径长度等相关特征量, 以焊缝熔宽的变化作为衡量焊接状态稳定性的参数. 通过金属蒸汽特征值的均值统计和方差分析,试验证明根据金属蒸汽面积和激光束受影响路径长度等金属蒸汽特征可有效地反映熔宽质量, 从而对焊接状况做出动态评估.