BENTLY现场动平衡技术在风机减振方面的运用

对于运行多年的加热炉引风机,现场检修后,开机试运行,经常振动偏大,给现场检修工作造成困扰。通过原因分析,在确认为转子不平衡的原因后,采取现场动平衡的方法,降低了振动值,满足了现场长周期运行的要求,其方法可推广解决风机等转动设备类似振动问题。     

四维彩超在诊断胎儿畸形中的应用研究

目的探讨四维彩超在诊断胎儿畸形中的应用。方法对近3年来在本院使用四维彩超检查的2760例孕16～30周之间的孕妇进行胎儿产前诊断检查,检出各类异常胎儿39例,并经引产证实。结果脑积水6例,脑积水合并脊柱裂4例;无脑儿4例;全前脑5例;颈部水囊瘤2例;唇裂8例;四肢发育异常4例;内脏外翻3例;多系统复合畸形3例。结论四维彩超在孕期保健中,筛查胎儿畸形是安全、可靠、诊断符合率高的检查手段之一。     

基于多层领域本体的知识表示通用模型研究

随着复杂信息系统涉及的知识领域越来越广泛,传统的基于领域本体以及基于关键词的知识表示模型,当处理多领域异构知识的共享与重构时,表现出异构信息有效组织及准确检索的不足。针对此问题,提出了基于多层领域本体的知识表示通用模型,借鉴顶层本体提供的上层语义知识,整合各领域的本体知识,并详细分析了由顶层本体、上层本体、应用本体、实例本体组成的多层领域本体的各层本体的构建流程。仿真实验通过与基于传统领域本体以及基于关键词的知识表示模型的对比分析,分别于一个以及多个领域知识的视角下,验证了基于多层领域本体的知识表示通用模型的有效性。     

Fatigue Strength and Crack Initiation Mechanism of Very-High-Cycle Fatigue for Low Alloy Steels

The fatigue strength and crack initiation mechanisms of very-high-cycle fatigue (VHCF) for two low alloy steels were investigated. Rotary bending tests at 52.5?Hz with hour-glass type specimens were carried out to obtain the fatigue propensity of the test steels, for which the failure occurred up to the VHCF regime of 10⁸ cycles with the S-N curves of stepwise tendency. Fractography observations show that the crack initiation of VHCF is at subsurface inclusion with ??fish-eye?? pattern. The fish-eye is of equiaxed shape and tends to tangent the specimen surface. The size of the fish-eye becomes large with the increasing depth of related inclusion from the surface. The fish-eye crack grows faster outward to the specimen surface than inward. The values of the stress intensity factor (K _I ) at different regions of fracture surface were calculated, indicating that the K _I value of fish-eye crack is close to the value of relevant fatigue threshold (??K _th ). A new parameter was proposed to interpret the competition mechanism of fatigue crack initiation at the specimen surface or at the subsurface. The simulation results indicate that large inclusion size, small grain size, and high strength of material will promote fatigue crack initiation at the specimen subsurface, which are in agreement with experimental observations.     

固定式放映机光学还音系统的技术检测(上)

本文叙述了固定式放映机还音速度稳定装置的工作原理，光学还音系统的检验与。调整、技术要求及还音系统主要指标的检测。     

Preparation and photocatalysis of TiO2 nanoparticles co-doped with nitrogen and lanthanum

Nanoparticles of TiO₂ powder co-doped with La and N were prepared using a coprecipitation method followed by being two hours calcinated at a temperature ranging from 500 to 600°C in NH₃/Ar atmosphere. Uniformly co-doped TiO₂ nanocrystalline was 5–15 nm with surface area 65–125 m²/g. Optical absorption along with the microstructural investigation for monodoped and co-doped catalyst provided that a part of O vacancy of Ti₅O₉ was occupied by N, which is responsible for the band-gap narrowing of TiO₂, while La³⁺ doping prevents the aggregation of powder in process of nitrification. Superior catalytic activity was observed in the co-doped TiO₂ under visible light (350 < < 450 nm). 20 mg/l methyl orange solution could be docomposed completely within 1 h using the 0.5 at.% La³⁺ doped TiO₂ calcinated in NH₃ for 2 h.     

Highly Surface‐roughened “Flower‐like” Silver Nanoparticles for Extremely Sensitive Substrates of Surface‐enhanced Raman Scattering

Surface‐enhanced Raman scattering (SERS) is a new optical spectroscopic analysis technique with potential for highly sensitive detection of molecules. Recently, many efforts have been made to find SERS substrates with high sensitivity and reproducibility. In this Research News article, we provide a focused review on the synthesis of monodispersed silver particles with a novel, highly roughened, “flower‐like” morphology by reducing silver nitrate with ascorbic acid in aqueous solutions. The nanometer‐scale surface roughness of the particles can provide several hot spots on a single particle, which significantly increases SERS enhancement. The incident polarization‐dependent SERS of individual particles is also studied. Although the different “hot spots” on a single particle can have a strong polarization dependency, the total Raman signals from an individual particle usually have no obvious polarization dependency. Moreover, these flower‐like silver particles can be measured by SERS with high enhancement several times, which indicates the high stability of the hot spots. Hence, the flower‐like silver particles here can serve as highly sensitive and reproducible SERS substrates.     

环境介质对40Cr结构钢高周和超高周疲劳行为的影响

选用40Cr结构钢,分别在空气、水和3.5%NaCl水溶液中进行旋转弯曲疲劳实验,研究环境介质对该结构钢高周和超高周疲劳特性的影响.结果表明,40Cr钢在水环境中的疲劳强度比在空气中明显降低;在3.5%NaCl水溶液环境中的疲劳强度比在水中低.断面观察显示,在水和3.5%NaCl水溶液中,疲劳裂纹多源萌生;在稳态扩展阶段,裂纹沿品界扩展并存在广泛分布的沿晶二次裂纹.     

SHORT FATIGUE CRACK BEHAVIOUR IN ISO-STRESS SPECIMENS

Fatigue tests were made on a vibration machine using specially designed specimens to investi-gate the initiation and propagation features of short fatigue cracks in a weld metal.The spec-imens were triangular in shape so that when loaded as a cantilever beam the surface tensilestress is constant.Test results show that short fatigue cracks mainly originate from slip bandswithin ferrite grains.The development of short fatigue cracks is marked by a gradual increasein crack density with fatigue cycles.Coalescence of short cracks leads to crack propagationand the crack path is predominantly transgranular.     

自然有机物对地下水混凝除铁的影响试验研究

通过模拟试验,考察了自然有机物的浓度、分子质量以及溶液的pH、温度对地下水混凝除铁的影响,并研究了预氧化在混凝除铁中的作用.结果表明,有机物的浓度越高、分子质量越大,有机铁的去除率越高.当Fe2 与分子质量＞10 ku的有机物络合时,用混凝除铁能取得良好的效果;当Fe2 与分子质量＜4 ku的有机物络合时,采用预氧化混凝工艺能达到较好的除铁效果.在pH6.0～7.5的范围内,降低pH有利于混凝除铁.温度升高对混凝除铁有利.