Scattering loss in Nd-doped silica based optical fibers

Rare-earth doped fibers suffer from relatively high attenuation in comparison to conventional communication fibers. In order to improve the properties of such fibers, understanding of the mechanisms involved in scattering effects is of great importance. The effect of Nd-doping, Al-codoping and of the drawing temperature on the scattering effect was investigated for several different optical fibers. To this end a measuring setup was realized which allows absolute measurements of the scattering coefficient at different positions along a fiber. Also separation of total attenuation and scattering effects is possible. The presented results indicate scattering effects as primary source for increased attenuation compared with undoped fibers.     

石油醚在流体静高压下的超声声速、衰减、密度和绝热压缩系数

 专门设计了用脉冲-回波-重合法在不同静水压下测量液体声速的装置，并对石油醚在0.1~650 MPa流体静压力范围内测量了其超声声速和衰减系数。还通过测量体积压缩量和质量得到石油醚密度ρ随流体静压力的变化。最后，给出了石油醚的绝热压缩系数β与流体静压力的关系。     

Correction for Shift-variant Characteristics of Single Photon Emission Computed Tomography Acquisition System Using Sensitivity Functions

The single photon emission computed tomography (SPECT) imaging system has shift-variant characteristics due to non-uniform attenuation of gamma-ray, collimator design, scattered photons, etc. In order to provide quantitatively accurate SPECT images, these characteristics should be compensated in the reconstruction. This paper presents a new method to correct the shift-variant characteristics, which is based on a continuous-discrete mapping model and filtered backprojection (FBP) method, in which the projection data are assumed to be acquired by narrow ray sum beams in the FBP method and the assumed data set is expressed as a linear combination of the actual projection data. Narrow ray sum beams are approximated by a weighted sum of the original sensitivity functions. Thus, at the reconstruction the projection data are first modified using an approximation and the FBP method is then applied to the corrected projection data and a SPECT image is reconstructed. We further propose a technique that requires the inversion of smaller matrices than the conventional algebraic method; the amount of calculation and memory space become smaller and the stability of the calculation is greatly improved as well. The results of the numerical simulations are also demonstrated.     

Stability of surface waves at magnetized plasma – metal interface

The stability of high‐frequency potential surface waves at a dense magnetized plasma – metal interface with respect to a low‐frequency plasma density modulation is studied in the point of view of the surface waves control. The discussion is addressed to the situation, when an external steady magnetic field is directed perpendicularly to the interface. The nonlinear interaction process of the high‐frequency surface wave, its satellites and the low‐frequency plasma density perturbation is investigated. It is shown that the low‐frequency plasma density perturbation can be represented as a superposition of forced waves of surface and volume types and can lead to an additional attenuation of the surface waves. This attenuation arises when the surface wave amplitude exceeds the threshold value. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Attenuation Characteristics of Corrugated Circular Groove Waveguide

When neglecting space harmonics and higher-order slot modes, the attenuation characteristic of corrugated circular groove waveguide has been investigated. It is shown that under certain conditions, the attenuation coefficient of HE ₁₁ mode will be lower than that of dominant TE ⁽¹⁾ ₁₁ mode of circular groove waveguide with same radius.     

基于分光链路模拟的曲面量子雷达散射截面研究

量子雷达基于量子态特性对目标探测识别,可有效克服复杂电磁环境和目标隐身特性影响。针对光量子在大气中传播时易受介质吸收和散射影响的问题,提出利用分光链路模拟大气介质的方法,对目标量子雷达散射截面进行了研究。通过引入单光子波动方程,采用分光链路模拟大气介质,得到衰减条件下光子波函数,推导衰减条件下量子雷达散射截面公式,并对衰减条件下单曲面量子雷达散射截面进行仿真。仿真证明,在不同入射角条件下,量子雷达散射截面主瓣峰值随衰减系数增加而减小,入射角对量子雷达散射截面无影响;在0 ℃、能见度30 m条件下,目标量子雷达散射截面主瓣峰值随波长增加。     

MTO联合装置急冷塔管道及其大型拉杆补偿器黏滞性阻尼减振技术研究

新疆某大型煤化工企业的68万t/a煤制烯烃项目于2016年建成,其中甲醇制烯烃（MTO）联合装置中甲醇-反应气进急冷塔的DN1800管道及大型拉杆横向补偿器存在剧烈振动问题,由于振动过大无法开车,安装普通液压阻尼器等设备后,问题依然存在。通过对管线结构特点、介质参数、拉杆补偿器特性等的分析,运用有限元软件对该管线进行模态、热位移计算及阻尼减振模拟计算,提出了进塔管线振动抑制控制的解决方案。在不更改管线结构的情况下,在管线的适当位置安装适当数量的黏滞阻尼器,有效降低了DN1800大型管线的振动,保障了生产安全并成功开车,为特大型管线减振提供了工程经验。     

基于深度学习的材料超声回波衰减预测方法

材料超声回波衰减是评价材料均匀一致性的常用方法, 针对具有复杂结构的航空发动机盘件难以进行材料底面超声回波衰减评价的问题, 本文提出了利用超声背散射波信号直接预测底面回波衰减的方法。采用10MHz聚焦探头进行超声背散射波数据的采集, 利用深度学习技术构建和训练模型,建立了基于深度学习的材料底面回波衰减预测方法, 同时讨论了采用不同信号形式的超声波信号分类识别模型的准确率差异。研究发现：基于深度学习技术可实现通过超声背散射波预测材料的底面回波衰减, 预测结果和实际底面回波衰减试验结果具有良好的一致性。     

A model for dependent default with hyperbolic attenuation effect and valuation of credit default swap

A hyperbolic function is introduced to reflect the attenuation effect of one firm's default to its partner.If two firms are competitors(copartners),the default inten- sity of one firm will decrease(increase)abruptly when the other firm defaults.As time goes on,the impact will decrease gradually until extinct.In this model,the joint distri- bution and marginal distributions of default times are derived by employing the change of measure,and the fair swap premium of a credit default swap(CDS)can be valued.     

Attenuation of shock waves propagating over arrayed baffle plates

The paper reports results of shock tube experiments of the attenuation of shock waves propagating over arrayed baffle plates, which is motivated to simulate shock wave attenuation created accidentally at the acoustic delay line in synchrotron radiation factory upon the rupture of a metal membrane separating the acceleration ring at high vacuum and atmospheric test chambers. Experiments were carried out, by using double exposure holographic interferometry with double path arrangement, in a 100 mm×180 mm shock tube equipped with a test section of 180 mm×1100 mm view field. Two baffle plate arrangements were tested: Oblique and staggered baffle plates; and vertical symmetric ones. Pressures were measured along the shock tube sidewall at individual compartments for shock Mach numbers ranging from 1.2 to 3.0 in air. The results were compared with a numerical simulation. The rate of shock attenuation over these baffle plates was compared for vertical and oblique baffle plates. Shock wave attenuation is more pronounced in the oblique baffle plate arrangements than in the vertical ones. PACS 47.40.Nm; 42.40.Kw Communicated by C. Needham