碳纳米管辐射太赫兹波的理论分析与数值验证

基于简单紧束缚方法理论,利用一维碳纳米管的量子化周期边界条件得到了碳纳米管的电子能级结构关系.并结合已报道的碳纳米管中电子与声子相互作用的实验结果,得到了碳纳米管能够辐射太赫兹波的结论.通过数值结果验证了碳纳米管在外场作用下能够产生太赫兹波,并对数值计算结果中太赫兹波的振荡现象给予合理的解释.其结果为进行碳纳米管产生太赫兹辐射的实验研究提供深入的理论基础. 关键词： 太赫兹波 碳纳米管     

Simplified expressions of the T-matrix integrals for electromagnetic scattering

The extended boundary condition method, also called the null-field method, provides a semianalytic solution to the problem of electromagnetic scattering by a particle by constructing a transition matrix (T-matrix) that links the scattered field to the incident field. This approach requires the computation of specific integrals over the particle surface, which are typically evaluated numerically. We introduce here a new set of simplified expressions for these integrals in the commonly studied case of axisymmetric particles. Simplifications are obtained using the differentiation properties of the radial functions (spherical Bessel) and angular functions (associated Legendre functions) and integrations by parts. The resulting simplified expressions not only lead to faster computations, but also reduce the risks of loss of precision and provide a simpler framework for further analytical work.     

Modification of Spalart-Allmaras model with consideration of turbulence energy backscatter using velocity helicity

The correlation between the velocity helicity and the energy backscatter is proved in a DNS case of 256³-grid homogeneous isotropic decaying turbulence. The helicity is then proposed to be employed to improve turbulence models and SGS models. Then Spalart-Allmaras turbulence model (SA) is modified with the helicity to take account of the energy backscatter, which is significant in the region of corner separation in compressors. By comparing the numerical results with experiments, it can be concluded that the modification for SA model with helicity can appropriately represent the energy backscatter, and greatly improves the predictive accuracy for simulating the corner separation flow in compressors.     

π π andK¯K channel coupling

We investigate the origin of the attraction in theK¯K channel around the threshold by introducing an additional channel to theππ andK¯K channels in a separable potential formalism assuming, in general, no direct interaction in theK¯K channel. To reproduce the features of the data, we find that the threshold of the additional channel is much above thef ₀(975) meson position. We show that this three-channel problem can be reduced to an effective two-channel problem where thef ₀(975) behaves as if it were aK¯K molecule bound by the coupling to the exotic channel. This picture is also supported by the fact that a single pole only, in the complexK¯K momentum plane, is associated to thef ₀(975) meson. Various physical observables, like the decay branching ratio and theK¯K scattering length, are then discussed in an effective two-channel framework.     

磁绝缘传输线电压的初步测量

针对快脉冲直线变压器驱动源装置上的真空磁绝缘传输线（MITL)电压测量的需求,开展了微分型电容分压器和电感分压器的设计、标定和实验。通过不同的电压值、负载阻抗的装置实验中探头输出结果的分析和比较,讨论了测量方法的可行性和适用范围。实验结果表明：微分型电容分压器能够应用于完全磁绝缘状态下的MITL电压测量,但容易受阴极电子发射的影响导致探头输出波形发生畸变。电感分压器受分布电容和电感的影响导致输出信号存在寄生振荡,采用波形重建的方法初步获得了合理的测量结果。     

Facile synthesis of SnO2–ZnO core–shell nanowires for enhanced ethanol-sensing performance

The design of core–shell heteronanostructures is powerful tool to control both the gas selectivity and the sensitivity due to their hybrid properties. In this work, the SnO₂–ZnO core–shell nanowires (NWs) were fabricated via two-step process comprising the thermal evaporation of the single crystalline SnO₂ NWs core and the spray-coating of the grainy polycrystalline ZnO shell for enhanced ethanol sensing performance. The as-obtained products were investigated by X-ray diffraction, scanning electron microscopy, and photoluminescence. The ethanol gas-sensing properties of pristine SnO₂ and ZnO–SnO₂ core–shell NW sensors were studied and compared. The gas response to 500 ppm ethanol of the core–shell NW sensor increased to 33.84, which was 12.5-fold higher than that of the pristine SnO₂ NW sensor. The selectivity of the core–shell NW sensor also improved. The response to 100 ppm ethanol was about 14.1, whereas the response to 100 ppm liquefied petroleum gas, NH₃, H₂, and CO was smaller, and ranged from 2.5 to 5.3. This indicates that the core–shell heterostructures have great potential for use as gas sensing materials.     

Design of an insensitive-polarization all-optical switch based on multimode interference structures

This paper presents a new design for an insensitive-polarization all-optical switch using 2 × 2 multimode interference (MMI) couplers. The switching structure can operate at central operating wavelength 1550 nm for both polarizations. A nonlinear directional coupler is used to realize the phase shifter and therefore switching mechanism is obtained. The transfer matrix method and beam propagation method are used to design and optimize the whole device structure.     

聚变实验堆真空室壳体成型残余应力分析

为了了解聚变实验堆真空室壳体表面残余应力的分布以及退火工艺对残余应力的影响,通过模拟分析和实验检测两种方式对不锈钢316LN冷压曲面和热压曲面残余应力进行研究,获得退火前后曲面表面残余应力的大小,得到冷压曲面和热压曲面残余应力的分布以及退火工艺对残余应力分布的影响。研究结果为分析成型工艺提供数据支撑,对中国聚变工程实验堆真空室的研究与制造具有重要意义。