An Ultra-Wideband Janus Metastructure with Graphene for Detector Based on Anapole Mode in the Terahertz Region

In this paper, an ultra-wideband Janus metastructure (MS) utilizing anapole mode for detector in the terahertz (THz) range by graphene is proposed. Specifically, when Fermi level (E_f) is set to 0.9 eV, the MS demonstrates ultra-broadband absorption exceeding 0.9 from 0.754 to 5 THz in the −z-direction with a relative bandwidth of 147.6 %, in which perfect absorption of over 98% develops from 3.24 to 5 THz. In the case of the +z-direction, the absorptivity maintains around 0.6 within the 0.745 ∼ 5 THz range. As E_f equals 0 eV, the difference in absorption between the −z-direction and +z-direction exceeds 0.9 from 4.49 to 4.76 THz. The study also explores the MS for refractive index sensing near 3.71 THz by a unique difference detection, measuring two refractive index ranges: 1.2 ∼ 2.6 and 4.5 ∼ 4.7, with corresponding sensitivities of 0.0450 and 0.0304, respectively. Owing to its highly symmetrical structure, the MS is insensitive to the polarization state of the electromagnetic (EM) waves, performing remarkable angular stability as the incident angle varies from 0 to 60 degrees in the −z-direction. These splendid properties make the design a good candidate for biomedical sensing, EM cloaking, and full-space EM wave control.     

Fluctuations in nonequilibrium systems and broken supersymmetry

The fluctuation-dissipation theorem is not expected to hold for systems that either violate detailed balance or have time-dependent or nonpotential forces. Therefore the relation between response and correlation functions should have contributions due to the nonequilibrium nature. An explicit formula for such a contribution is calculated, which in the present derivation appears as a historydependent term. These relations are the Ward-Takahashi identities of a supersymmetric formulation of the Langevin models, and the new term results from a broken supersymmetry.     

Raman spectra of crystalline iron perchlorate hexahydrate

Raman studies of crystalline iron perchlorate hexahydrate (Fe(ClO₄)₂·6H₂O) in the region of lattice and anion internal modes were carried out in the temperature range 80–385 K. The temperature‐dependent Raman results are consistent with those from previous works, showing that two phase transitions occur around 336 and 245 K. The transition at 336 K may be considered as an order–disorder transformation, while the one at 245 K is associated with the configurational disorder of the tetrahedron of the perchlorate ions. Copyright © 2008 John Wiley & Sons, Ltd.     

正三角形及正方形微光学腔模式特性研究

微谐振腔模式特性研究是利用微腔研制新型光电器件的基础．为了研制出能采用平面工艺制作的定向输出的微腔激光器，文章采用解析和数值模拟方法深入研究了正三角形及正方形光学微腔的模式特性，并得到与数值模拟结果符合非常好的解析场分布及模式波长．对正方形光学微腔，把模式组合成满足正方形对称性的场分布，发现其类WG模式只存在品质因子比它小一个数量级以上的偶然简并模式，因此正方形微腔有利于实现真正的单模工作．     

THE DEVELOPMENT OF NATIONAL ZHOU PEIYUAN COMPETITION ON MECHANICS

全国周培源大学生力学竞赛为《力学与实践》编委会发起并承办的一项大学生科技赛事,经过三十多年的发展,已经成功举办了12届,也成为展示高校力学教学水平的一个窗口。在《力学与实践》创刊40周之际,本文对全国周培源大学生力学竞赛的发展历程和组织模式进行了较为系统的回顾和梳理;对各届的组织规模和创新形式进行归纳与汇总;并通过案例说明力学竞赛对力学教学和人才培养所发挥的作用。     

Condensed Mode Cooling of Ethylene Polymerization in Fluidized Bed Reactors

This review gives an overview of the evolution of the technology of condensed mode cooling, primarily for the case of ethylene polymerization on supported catalysts in fluidized bed reactors. It is well known that this mode of heat removal is quite effective in allowing polyolefin manufacturers to increase significantly production rates. What is perhaps less well understood are all of the issues that, in addition to the effect of the latent heat of vaporization of injected liquid components, also have an impact on the rate of production and behavior of the reactor. However, the liquid components injected into the reactor can vaporize rapidly under full‐scale conditions, leaving behind several heavy components (with respect to ethylene) that have numerous effects on how the particles behave, on the reaction rate, and on fluidization, fouling, and other parameters related to reactor and process performance.     

On the use of edge cracked short bend beam specimen for PMMA fracture toughness testing under mixed-mode I/II

In this paper an inclined edge cracked short beam specimen subjected to symmetric three-point bend loading was designed and examined for conducting mixed-mode I/II fracture toughness experiments. The aspect ratio (i.e. length to width ratio) and the loading span distance are considered much lower than the other conventional cracked bend beam samples. Crack tip parameters such as stress intensity factors and T-stress were computed numerically for this specimen by several finite element analyses and it was demonstrated that the specimen is able to produce full combinations of mode I and II including pure mode II. The practical capability of the short bend beam specimen was studied experimentally by conducting a set of mixed-mode fracture tests on PolymethylMethacrylate (PMMA) as a well-known model brittle material. The critical stress intensity factors, the direction of fracture kinking and the path of fracture trajectory were investigated both experimentally and theoretically using two stress and strain-based fracture criteria. The fracture toughness of tested PMMA was decreased by moving towards mode II case due to the effect of T-stress on the fracture mechanism of the short bend beam specimen.     

腔镜形变对圆筒组合型CO2激光器模式的影响

针对具有锁相结构的圆筒组合型CO2激光器,分析了其注入锁定的原理,利用等价条形腔理论,建立了分析其输出基模的数学模型。利用该模型,研究了不同形变量对圆筒形腔输出基模的影响。结果表明,为了获得与注入光束模式类似的光场分布,复曲面镜与圆筒形谐振腔中平面镜镜面中心的形变量应控制在0.07倍波长以内。同时,分析在不同腔镜参数情况下腔镜形变对输出模式造成的影响,其结果有利于进一步优化谐振腔的参数设计。     

Soft mode dynamics of perovskite type crystals

The soft mode dynamics and related properties of perovskite, ABO₃-type crystals have been studied using the operator form of the model Hamiltonian proposed by Pytte. The correlations have been evaluated using the double time thermal Green’s function technique and Dyson’s equation. Without any decoupling, the higher order correlations, appearing in the dynamical equation, have been evaluated using the renormalized Hamiltonian. The dielectric properties are directly related to the optical soft mode. The phonon width and shift have been calculated for different structural phases. The analysis of the temperature dependence of microwave loss tangent and dielectric constant explains the experimental results.     

Performance Analysis of High-speed Optical Pulse Transmission in Dispersion-managed Nonlinear Birefringent Fiber Using Quantum Well Laser Diode Sources

This paper analyzes the high bit-rate optical pulse trasmission in single mode optical fiber with chromatic dispersion, polarization mode dispersion (small random birefringence) and nonlinearity. Numerical method employed can precisely describe their interactive effect on transmission performance. Different dispersion maps and the related performance are analysed. Various simulation results and discussion are given. The results show that chromatic dispersion compensation should be carefully designed. Appropriate dispersion management can also alleviate the effect of polarization mode dispersion.