可调谐高重频高压脉冲驱动模块的设计

设计了一种高重频高压快脉冲驱动模块作用于激光调Q系统。该驱动模块采用零电压准谐振SMPS技术、大功率高速高压固体开关器件多管级联电路、大电流脉冲过驱动技术,获得了频率为1kHz至100kHz可调、高电平0～5000V可调、脉冲宽度0．5肚s、下降沿可达20ns的负脉冲,可靠性强,体积小。     

铜沉淀对直拉硅单晶中洁净区形成的影响

研究普通热处理和快速热处理工艺下直拉单晶硅中过渡族金属铜杂质对洁净区生成的影响. 通过腐蚀和光学显微镜研究发现,常规高-低-高三步洁净区生成热处理样品中, 第一步高温热处理前对样品铜沾污,样品中没有洁净区生成,高密度的铜沉淀布满了样品整个截面. 而第二步、第三步热处理过程中引入铜杂质不影响洁净区的生成. 研究表明,高温热处理过程中生成的铜沉淀不能溶解是导致洁净区不能形成的最主要原因. 另外,由于不同温度下热处理,导致引入铜杂质的平衡浓度不同,会在一定程度上影响洁净区的厚度. 对于快速热处理样品,可以得到相似的结果. 关键词： 直拉单晶硅 铜沉淀 洁净区     

Large negative dispersion in dual-concentric-core photonic crystal fiber with hybrid cladding structure based on complete leaky mode coupling

Considering the optical stability of solution, the sugar-solution is infused into the outer core ring of dual-concentric-core photonic crystal fiber (DCCPCF). The influences of structure parameters and solution concentration on the phase and loss matching are comprehensively analyzed. By choosing the appropriate outer core mode to completely couple with the inner core fundamental mode, the large negative dispersion PCF around 1.55 μm is designed, which has the dispersion value of − 39,500 ps/km/nm as well as bandwidth of 7.4 nm and effective mode area of 28.3 μm². The designed PCF with hybrid cladding structure can effectively compensate the positive dispersion of conventional single mode fiber, and suppress the system perturbation caused by a series of nonlinear effects. Considering the mode field mismatching between the DCCPCF and the tapered fiber, the calculated connection loss around 1.55 μm is below 3 dB. In addition, the equivalent propagation constants of two leaky modes are deduced from the coupled-mode theory, and the complete mode coupling case can be well predicted by comparing the real and imaginary parts of propagation constants.     

螺旋光子筛用于相衬成像的模拟研究

为了提高螺旋波带片用于相衬成像的分辨率和成像对比度,因此本文将螺旋波带片的透光环带替换为透光微孔,以类-贝塞尔函数作为螺旋光子筛透过率的振幅调制窗函数设计了一种螺旋光子筛.在相同的特征尺寸下,螺旋光子筛比螺旋波带片具有更大的数值孔径,因此分辨率更高.同时基于光瞳切趾原理,经过类-贝塞尔振幅调制窗函数对螺旋光子筛透光微孔的分布进行调制,螺旋光子筛的成像对比度将高于螺旋波带片.通过数值计算和仿真分析表明:螺旋光子筛的点扩展函数主瓣宽度相对于螺旋波带片更窄,旁瓣幅值也相对更低.在相衬成像中,螺旋光子筛不仅能够消除螺旋波带片对圆盘状位相物体成像时图像的"浮雕"效应而且能够更为清晰地分辨出位相跳变更为密集的周期矩形条状物体.因此,螺旋光子筛用于相衬成像中将具有更高的成像分辨率和成像对比度,其在医学领域将具有广阔的运用前景.     

双根堆叠YBCO超导带材缺陷状态下失超传播规律研究

因双根并绕堆叠结构的YBCO带材能够进一步增加设备承载电流密度,被广泛应用于大型超导设备线圈绕制中.本文研究了外层有包绕绝缘的双根并绕堆叠YBCO带材有缺陷情况下的失超传播特性,应用有限元法方法,建立了双根YBCO带材堆叠状态下失超仿真模型,研究了存在不同缺陷的情况下双根堆叠超导带材的失超传播特性,探索了堆叠带材在不同工作电流下传播速度(NZPV)等参数的变化趋势,同时探究了不同铜稳定层厚度下并绕堆叠带材失超传播规律.结果表明缺陷区域面积增加以及铜稳定层厚度减小,都将导致双根并绕堆叠结构的二代高温超导带材失超传播速度增加,在带材上的温升增加,增加失超的风险.研究结果可以为超导设备安全稳定运行参数设置提供支持.     

一种光电载荷非线性隔振装置的研究

针对光电载荷对隔振性能的需求,提出一种采用菱形连杆机构作为负刚度组件,具有高静、低动刚度特点的非线性隔振器（简称菱形HSLDS隔振器）。采用静力学分析方法,建立了隔振器数学模型,研究了刚度参数设定以及非线性调节方法;利用谐波平衡法（HBM）求解动力学方程,分析了各参数对隔振性能的影响关系;采用动力学仿真软件ADAMS及实物样机对理论模型与结论进行了验证。测试结果表明:菱形HSLDS隔振器具有较方便的参数调整能力,零位刚度及刚度非线性可通过拉簧参数与连杆参数进行设定、优化,隔振的刚度非线性优化程度受主隔振器阻尼以及零位刚度参数影响。相比于传统线性隔振器,菱形HSLDS具有显著的非线性隔振优势,可较好地满足光电载荷隔振需求。     

Effects of W~(6+) occupying Sc~(3+) on the structure,vibration, and thermal expansion properties of scandium tungstate

We experimentally investigate effects of W~(6+)occupying the sites of Sc~(3+)in the unit cell of Sc_2 W_3 O_(12)(Sc_8 W_(12) O_(48))on the structure, vibration and thermal expansion. The composition and structure of the doped sample(Sc_6 W_2)W_(12) O_(48±δ)(with two W~(6+)occupying two sites of Sc~(3+)in the unit cell of Sc_8 W_(12) O_(48)) are analyzed and identified by combining the x-ray photoelectron spectroscopy and the synchronous x-ray diffraction with first-principles calculations based on density functional theory. Results show that the crystal with even W~(6+)occupying even Sc~(3+)in the unit cell is stable and maintains the orthorhombic structure at room temperature. The structure of the doped sample is similar to that of Sc_2 W_3 O_(12), and with even W occupying even positions of Sc in the unit cell and constituting the WO_6 octahedra. Raman analyses show that the doped sample possesses stronger W–O bonds and wider Raman linewidths than those of Sc_2 W_3 O_(12). The sample doped with W also exhibits intrinsic negative thermal expansion in the measured range of 150 K–650 K.     

Magneto-transport properties of thin flakes of Weyl semiconductor tellurium

As an elemental semiconductor, tellurium has recently attracted intense interest due to its non-trivial band topology, and the resulted intriguing topological transport phenomena. In this study we report systematic electronic transport studies on tellurium flakes grown via a simple vapor deposition process. The sample is self-hole-doped, and exhibits typical weak localization behavior at low temperatures. Substantial negative longitudinal magnetoresistance under parallel magnetic field is observed over a wide temperature region, which is considered to share the same origin with that in tellurium bulk crystals, i.e., the Weyl points near the top of valence band. However, with lowering temperature the longitudinal magnetoconductivity experiences a transition from parabolic to linear field dependency, differing distinctly from the bulk counterparts. Further analysis reveals that such a modulation of Weyl behaviors in this low-dimensional tellurium structure can be attributed to the enhanced inter-valley scattering at low temperatures. Our results further extend Weyl physics into a low-dimensional semiconductor system, which may find its potential application in designing topological semiconductor devices.     

On completely hyperexpansive operators

We introduce and discuss a class of operators, to be referred to as the class of completely hyperexpansive operators, which is in some sense antithetical to the class of contractive subnormals. The new class is intimately related to the theory of negative definite functions on abelian semigroups. The known interplay between positive and negative definite functions from the theory of harmonic analysis on semigroups can be exploited to reveal some interesting connections between subnormals and completely hyperexpansive operators.

     

Chaotic Motion Generated by Delayed Negative Feedback Part II: Construction of Nonlinearities

We construct a smooth function g* : IR ? IR with such that the equation has a slowly oscillating periodic solution y, and a slowly oscillating solution z* whose phase curve is homoclinic with respect to the orbit o of y in the space C = C⁰([1,0],IR). For an associated Poincaré map we obtain a transversal homoclinic loop. The proof of transversality employs a criterion which uses oscillation properties of solutions of variational equations. The main result is that the trajectories (ψn)^∞_-∞ of the Poincaré map in a neighbourhood of the homoclinic loop form a hyperbolic set on which the motion is chaotic.