考虑蠕变特性的航空发动机阀门用非金属垫片的密封性能研究

The valve gasket for aero-engine is prone to creep under extreme conditions such as high temperature and high pressure.The creep failure of the gasket leads to valve leakage,which seriously threatens the safe and reliable operation of aero-engine.Aiming at the creep failure of FEP gasket in use,a timehardening creep model of valve gasket seal is established.The effects of time,operating pressure,material and structural parameters on the creep and sealing properties of FEP gaskets are analyzed.The results show that the compression rebound rate of gaskets decreases with the increase of time,and small compression rebound rate will decrease the sealing performance.The creep behavior of FEP gasket increases with the increase of operating pressure.Reducing the fillet radius can reduce the probability of shear failure,but also reduce the contact stress.Increasing the height of the boss can reduce the deformation behavior of the gasket,but reduce the contact stress on the sealing surface.When the gasket bevel angle is 85°,the creep property and contact stress of the gasket are higher than those of other sizes.But large bevel angle leads to the gasket unsticking.Replacing the FEP material with the polyimide material can improve the creep resistance of gaskets and the contact stress of sealing surface.Considering the service life and sealing effect of gasket,the material is replaced with polyimide plastic,the fillet radius is 0.20mm,the bevel angle is 85°and the boss height is 0.2mm.

红光闪烁治疗仪联合红色视力表远距离视功能训练对儿童近视性弱视的影响

目的:探讨红光闪烁治疗仪联合红色视力表远距离视功能训练对儿童近视性弱视的影响。方法:将我院收治的112例近视性弱视患儿分组,对照组予短小遮盖+近距离功能性视力训练,观察组在此基础上予红光闪烁治疗仪联合红色视力表远距离视功能训练。比较两组患儿临床疗效和治疗前后屈光动态变化、BCVA、弱视复发率。结果:观察组的临床总有效率高于对照组(P<0.05)。治疗后,观察组近视性屈光度与治疗前对比无差异(P>0.05),而对照组随时间延长逐渐升高(P<0.05);观察组治疗1a后的近视性屈光度、年均屈光度变化值和弱视复发率低于对照组(P<0.05)。两组患儿治疗后BCVA优于治疗前,治疗1a时优于治疗6mo(P<0.05)。结论:红光闪烁治疗仪联合红色视力表远距离视功能训练治疗儿童近视性弱视可有效降低年平均屈光度变化值,矫正最佳视力,降低弱视复发率。

曲安奈德联合黄斑区格栅样光凝治疗BRVO继发黄斑水肿的疗效

目的:分析曲安奈德(TA)联合黄斑区格栅样光凝治疗视网膜分支静脉阻塞(BRVO)继发黄斑水肿(ME)的疗效及安全性。方法:将2016-01/2020-01在本院诊治的BRVO继发ME患者147例147眼随机分为观察组(73眼)和对照组(74眼),观察组接受玻璃体腔注射TA联合黄斑区格栅样光凝治疗,对照组接受玻璃体腔注射康柏西普联合黄斑区格栅样光凝治疗。随访6mo,比较两组的疗效及安全性指标。结果:治疗后两组最佳矫正视力(BCVA,LogMAR)均较治疗前改善;治疗后1mo时观察组BCVA优于对照组(0.22±0.15 vs 0.27±0.13,P<0.05);治疗后6mo时观察组中年龄<50岁患者BCVA显著优于对照组中年龄<50岁患者(0.09±0.04 vs 0.14±0.06,P<0.05),两组中浆液性视网膜脱离(SRD)型患者BCVA均显著优于囊样水肿(CME)型与混合型患者,CME型患者BCVA均显著优于混合型患者(P<0.05),但两组之间各ME分型亚组患者BCVA均无差异(P>0.05)。治疗后两组黄斑中心凹视网膜厚度(CMT)均较治疗前明显下降;治疗后3mo时观察组CMT高于对照组(309.76±84.24μm vs 258.75±88.76μm,P<0.01)。治疗后1wk,1、3、6mo时观察组眼压均高于对照组(P<0.01)。治疗后6mo时,两组浅层毛细血管(SCP)血流密度较治疗前明显上升(P<0.05),深层毛细血管(DCP)血流密度、中心凹无血管区(FAZ)面积则未见明显改变(P>0.05)。观察组眼压升高发生率高于对照组(28.8%vs 14.9%),玻璃体腔注射次数低于对照组(1.21±0.74次vs 3.62±2.08次)。结论:TA联合黄斑区格栅样光凝治疗BRVO继发ME可短期内将视力维持在一定水平,在视力、CMT上的获益与康柏西普联合黄斑区格栅样光凝治疗相当,但存在眼压升高现象,需加强眼压监测。

Coevality of the sea-level fall and main mass extinction in the Permian-Triassic transition in Xiushui, Jiangxi Province, southern China

A continuous Permian-Triassic boundary （PTB） section has been found and studied for the first time in Xiushui, Jiangxi Province, South China. Evidence for a large sealevel fall has been found in the horizon of 0.8 m below the PTB, from the beginning of Hindeodus changxingensis zone （correlatable to Hindeodus typicalis Zone of the Meishan section）. Sedimentary record indicates that the sea level kept at Iowstand, or occasionally rose slowly during the whole Hindeodus parvus zone, except another substantial sea-level fall in early H. parvus zone. It began a quick rise from the beginning of Isarcicella staeschei zone, kept rising for the whole/, staeschei zone, and probably caused the stagnation of sea water. The first severe change in the biota, marked by the sudden disappearance of all steno- tropic organisms such as fusulinids and dasycladacians, happened at the same time as the first sea-level fall, and is regarded as the first and main episode of the end-Permian mass extinction in this area. A microbe-dominated biota followed the first extinction, and spanned the late H. changxingensis zone and the whole H. parvus zone. All the microbes and some other eurytropic organisms including gastropods and ostracods disappeared at the end of the H. parvus zone, and the following biota in the/. staeschei zone is very simple. The coevality of the main sea-level fall and the main extinction episode might be causal： both of them might be caused by a drastic climatic cooling.

Synthesis,characterization and optical studies on Sm2+-doped CdSe nanocrystals:a blueshift and fixed emission with high quantum yields

CdSe:Sm nanocrystals(NCs) were synthesized by a water phase method,and their structures,shapes and optical properties were further characterized.X-ray diffraction(XRD) analysis suggested that both the CdSe and CdSe:Sm NCs contained(111),(220) and(311) lattice planes in the zinc blende structure overlapped with the(002),(110) and(112) lattice planes in the wurtzite structure,and the diameters were about 4.2,3.3 and 2.3 nm for CdSe,CdSe:Sm(8%) and CdSe:Sm(10%) NCs,respectively.All of the CdSe:Sm NCs were monodispersed and uniform spherical nanocrystals.The CdSe:Sm(10%) NCs prepared with different reaction times exhibited constant absorption spectra at 430 nm and a fixed emission peak at581 nm.Compared with those of pure CdSe NCs,the fluorescence emission of CdSe:Sm(10%) NCs blueshifted 20-36 nm,and the absorption peak initially redshifted and then blueshifted with the prolongation of reaction time.In addition,the Sm^2+ doping decreased the fluorescence lifetime and increased the quantum yields(QYs) of CdSe NCs.The QYs of CdSe:Sm NCs increased initially and then decreased with the increase in the amount of doped Sm2+.The initial pH and charge compensator concentration also exhibited significantly enhanced fluorescence emission of CdSe:Sm NCs.