Effect of corona ageing on the structure changes of polyimide and polyimide/Al2O3 nanocomposite films

In order to investigate the corona ageing mechanism of polyimide and polyimide/Al₂O₃ nanocomposites, effects of corona ageing on the structure changes of the two polymers were studied. The physical and chemical changes were studied by Atomic Force Microscope (AFM), Scanning Electron Microscope (SEM) and Fourier Transform Infrared Spectroscope (FTIR) respectively. Modified isothermal discharge current method (MIDC) was used to investigate the trap level distribution before and after corona ageing. AFM images showed that there are large amounts of nano-clusters on the surface of polyimide nanocomposite before corona ageing. The surface roughness parameters of the nanocomposite is much larger than that of the pure polyimide, and that is slightly decreased for polyimide nanocomposite and largely increased for pure polyimide after corona ageing. FTIR spectra analysis showed that possible chemical changes due to the decomposition of C–O–C bond and C–N bond occurred during corona ageing for both polyimide and its nanocomposite. Pulse corona ageing can introduce even larger structure changes than the AC corona ageing for 100HN, while 100CR was just the opposite. IDC measurements showed that the trap level density was increased evidently after corona ageing and become larger for longer ageing time in 100HN film, whereas for 100CR, the trap level density was decreased with ageing time extended. Thus conclusions can be drawn that, corona ageing is a combined process leading to physical and chemical degradation of PI film. The more serious ageing the specimen suffers, the more changes of the trap level density and the surface roughness occurs. The deposition of inorganic nanoparticles on the surface of nanocomposite can form a flat block layer for corona ageing, which can decrease both the surface roughness and the physical trap level density.     

Asymmetric oxadiazole mesogens as candidates for low-temperature biaxial nematics

We report the synthesis and properties of a homologous series of asymmetric, mesogenic derivatives of 2,5-bis-(p-hydroxyphenyl)-1,3,4-oxadiazole (ODBP). Benzyloxy (BnO-), alkoxy benzoate ester derivatives BnO-ODBP-Ph-O-C _n , where n?=?4, 5, 6, 7, 8, 9, 12, were studied by ²H-NMR, X-ray diffraction and polarising microscopy in order to ascertain if the lower temperature nematic phases exhibited biaxiality. Deuterium nuclear magnetic resonance (NMR) of labelled probes in these asymmetric mesogens does not show evidence of biaxiality. The absence of biaxiality is discussed in terms of the statistical non-linearity of these asymmetric ODBP mesogens.     

基于反向撞击法的JB-9014炸药Hugoniot关系测量

为了获得JB-9014未反应炸药的Hugoniot关系,在火炮加载平台上利用反向撞击技术对JB-9014炸药进行一维平面冲击实验。将JB-9014炸药样品作为飞片安装于弹托前表面,将镀膜氟化锂窗口作为装置靶。利用火炮加速弹托,使炸药样品以一定速度撞击镀膜氟化锂窗口,通过光子多普勒测速仪(photonic Doppler velocimetry,PDV)测量炸药样品击靶速度以及炸药/镀膜氟化锂窗口界面粒子速度。最终根据冲击波阵面守恒关系计算获得了JB-9014炸药冲击Hugoniot数据,采用正交回归直线拟合得到了炸药样品在3.1～8.2 GPa压力范围内的冲击Hugoniot关系:D_s=2.417+2.140u_s (D_s和u_s的单位均为km/s)。结果表明:该方法测试精度较高,响应时间快(小于5 ns),同时该方法可以对炸药的反应情况进行检测,便于判断实验是否测得真实的未反应炸药冲击Hugoniot数据。     

氯磺酚s与铝的显色反应及其应用的研究

本文较详细地研究了表面活性剂和有机溶剂存在下,氯磺酚s与铝的显色反应.试验表明:适量Triton X-10。和丙酮对此反应有协同增敏作用,且选择性亦较好.应用铝一抓磺酚S-Triton X-100一丙酮体系,测定了在铝制炊具中煮沸过的水中的铝.     

Oxidative stress-induced circKIF18A downregulation impairs MCM7-mediated anti-senescence in intervertebral disc degeneration

Low back pain, triggered by intervertebral disc degeneration (IVDD), is one of the most common causes of disability and financial expenditure worldwide. However, except for surgical interventions, effective medical treatment to prevent the progression of IVDD is lacking. This study aimed to investigate the effects of circKIF18A, a novel circRNA, on IVDD progression and to explore its underlying mechanism in IVDD. In this study, we found that oxidative stress was positively correlated with nucleus pulposus cell (NPC) senescence in IVDD and that circKIF18A was downregulated in IVDD and attenuated senescent phenotypes such as cell cycle arrest and extracellular matrix degradation in NPCs. Mechanistically, circKIF18A competitively suppressed ubiquitin-mediated proteasomal degradation of MCM7, and the protective effects of circKIF18A on NPCs were partially mediated by MCM7 under oxidative stress. Intradiscal injection of adenoviral circKIF18A ameliorated IVDD in a rat model. This study revealed that circKIF18A regulates NPC degeneration by stabilizing MCM7 and identified a novel signaling pathway, the circKIF18A-MCM7 axis, for anti-senescence molecular therapy in IVDD.Subject terms: Diseases, Ageing     

Determination of Hexabromocyclododecane in Expanded Polystyrene and Extruded Polystyrene Foam by Gas Chromatography-Mass Spectrometry

A gas chromatography-mass spectrometry (GC/MS) method for the determination of hexabromocyclododecane (HBCD) in expanded polystyrene and extruded polystyrene foam (EPS/XPS) was developed. The EPS/XPS samples were ultrasonically extracted with acetone and the extracts were purified by filtration through a microporous membrane (0.22 μm) and solid-phase extraction. The samples were analyzed using a GC/MS using the selected ion monitoring mode. The ions 157, 319 and 401 were selected as the qualitative ions, while ion 239 was chosen as the quantitative ion. An HBCD standard working solution with a concentration range of 1.0–50.0 mg/L showed good linearity. The detection limit of HBCD was 0.5 mg/kg, meeting the LPC limit (<100 or 1000 mg/kg). Six laboratories were selected to verify the accuracy of the method, and 10 samples were tested. The interlaboratory relative standard deviation range was 3.68–9.80%. This method could play an important role in controlling HBCD contamination in EPS/XPS.     

非离子表面活性剂胶束增溶显色反应机理的研究(Ⅱ)——非离子表面活性剂对Me2+-PAN的作用及其增溶萃取公式

本文以分光光度法研究了在TritonX-100胶束存在下,若干二价金属离子(Me²⁺)与1-(2-吡啶偶氮)-2-茶酚(PAN)的络合反应。导出了用聚氧乙烯型非离子表面活性剂增溶萃取Me²⁺-PAN螯合物的通式,并指出了利用此公式发生偏差的原因。