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31.
采用HF酸刻蚀和紫外激光预处理相结合的方式提升熔石英元件的负载能力,用质量分数为1%的HF缓冲溶液对熔石英刻蚀1~100 min,综合透过率、粗糙度和损伤阈值测试结果,发现刻蚀时间为10 min的熔石英抗损伤能力最佳。采用355 nm紫外激光对HF酸刻蚀10 min的熔石英进行预处理,结果表明:紫外预处理能量密度在熔石英零损伤阈值的60%以下时,激光损伤阈值单调递增;能量到达80%时,阈值反而低于原始样片的损伤阈值。适当地控制酸蚀时间和紫外激光预处理参数能有效提高熔石英的抗损伤能力。 相似文献
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Reaction of Amino Acids,Di‐ and Tripeptides with the Environmental Oxidant NO3.: A Laser Flash Photolysis and Computational Study 下载免费PDF全文
Absolute rate coefficients for the reaction between the important environmental free radical oxidant NO3. and a series of N‐ and C‐protected amino acids, di‐ and tripeptides were determined using 355 nm laser flash photolysis of cerium(IV) ammonium nitrate in the presence of the respective substrates in acetonitrile at 298±1 K. Through combination with computational studies it was revealed that the reaction with acyclic aliphatic amino acids proceeds through hydrogen abstraction from the α‐carbon, which is associated with a rate coefficient of about 1.8×106 m ?1 s?1 per abstractable hydrogen atom. The considerably faster reaction with phenylalanine [k=(1.1±0.1)×107 m ?1 s?1] is indicative for a mechanism involving electron transfer. An unprecedented amplification of the rate coefficient by a factor of 7–20 was found with di‐ and tripeptides that contain more than one phenylalanine residue. This suggests a synergistic effect between two aromatic rings in close vicinity, which makes such peptide sequences highly vulnerable to oxidative damage by this major environmental pollutant. 相似文献
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Firas Awaja Benedicta Arhatari Elisabeth Leiss 《Polymer Degradation and Stability》2009,94(10):1814-1824
Epoxy resin composites reinforced with hollow glass microspheres, microlight microspheres, 3D parabeam glass, and E-Glass individually were subjected to accelerated thermal degradation conditions. X-ray microcomputed tomography (XμCT) was used to evaluate density changes, reinforcement filler damage, homogeneity, cracks and microcracks in the bulk of the different epoxy resin composites. XμCT 3D images, 2D reconstructed images and voids calculations revealed microspheres damage, filler distributions and showed cracks in all composites with different shapes and volume in response to the thermal degradation conditions. In addition, expansion of air bubbles/voids was observed and recorded in the microsphere and microlight epoxy composite samples. In a complementary way, optical coherence tomography (OCT) was used as a novel optical characterisation technique to study structural changes of the surface and near-surface regions of the composites, uncovering signs of surface shrinkage caused by the thermal treatment. Thus, combining XμCT and OCT proved useful in examining epoxy resin composites' structure, filler-resin interface and surface characteristics. 相似文献
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35.
《Electrophoresis》2018,39(12):1474-1477
DNA gel electrophoresis is a standard tool of biochemistry and molecular biology laboratories. The common dye ethidium bromide suffers from toxicity concerns and requires the use of damaging ultraviolet light. We observe that exposing plasmid DNA to a UV transilluminator for only 1 s results in detectable loss of colonies following transformation, suggesting rapid accumulation of DNA damage. SYBR Safe, a commercial product, is marketed as a safe alternative to ethidium bromide and has excellent sensitivity with nondamaging blue light, but suffers from prohibitively high costs. We show that thiazole orange, the parent compound of SYBR Safe, is an excellent, simple, and inexpensive alternative to these dyes. It is excitable with safe blue light or UV light, with DNA detection limits in agarose gels similar to ethidium bromide and SYBR Safe (1–2 ng/lane). Thiazole orange safely allows the use of nondamaging blue light at the same cost as ethidium bromide. 相似文献
36.
塑性损伤本构模型的自由能势函数研究 总被引:1,自引:1,他引:0
自由能势函数是不可逆热力学量及其共轭量的标量泛函,是广义标准材料模型的重要组成.论文根据损伤状态、过程、作用和伪势的定义和定理,分析了损伤耗散势的数学和物理含义,探讨了损伤耗散势的理论基础和描述耗散势的一般理论方法.研究了耗散势、损伤作用和自由能势函数的相互关系,给出了满足上述基本原理的自由能表达式,基于增量最小原理的变分形式得到了损伤理论基本方程的数值离散方程,实验模拟验证了该文理论和数值方法的正确性和有效性. 相似文献
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A new series of photoactivated DNA oxidizing agents in which an acridine moiety is covalently linked to viologen by an alkylidene spacer was synthesized, and their photophysical properties and interactions with DNA, including DNA cleaving properties, were investigated. The fluorescence quantum yields of the viologen-linked acridines were found to be lower than that of the model compound 9-methylacridine (MA). The changes in free energy for the electron transfer reactions were found to be favorable, and the fluorescence quenching observed in these systems is explained by an electron transfer mechanism. Intramolecular electron transfer rate constants were calculated from the observed fluorescence quantum yields and singlet lifetime of MA and are in the range from 1.06x10(10) s(-1) for 1 a (n=1) to 6x10(8) s(-1) for 1 c (n=11), that is, the rate decreases with increasing spacer length. Nanosecond laser flash photolysis of these systems in aqueous solutions showed no transient absorption, but in the presence of guanosine or calf thymus DNA, transient absorption due to the reduced viologen radical cation was observed. Studies on DNA binding demonstrated that the viologen-linked acridines bind effectively to DNA in both intercalative and electrostatic modes. Results of PM2 DNA cleavage studies indicate that, on photoexcitation, these molecules induce DNA damage that is sensitive to formamidopyrimidine DNA glycosylase. These viologen-linked acridines are quite stable in aqueous solutions and oxidize DNA efficiently and hence can be useful as photoactivated DNA-cleaving agents which function purely by the co-sensitization mechanism. 相似文献
39.
<正>An electrochemical sensor for the detection of the natural double-stranded DNA(dsDNA) damage induced by PbSe quantum dots(QDs) under UV irradiation was developed.The biosensing membranes were prepared by successively assembling 3- mercaptopropionic acid,polycationic poly(diallyldimethyl ammonium) and dsDNA on the surface of the gold electrode.Damage of dsDNA was fulfilled by immersing the sensing membrane electrode in PbSe QDs suspension and illuminating it with an UV lamp. Cyclic voltammetry was utilized to detect dsDNA damage with Co(phen)_3~(3+) as the electroactive probe.The UV irradiation,Pb~(2+) ions liberated from the PbSe QDs under the UV irradiation and the reactive oxygen species(ROS) generated in the presence of the PbSe QDs also under the UV irradiation were the three factors of inducing the dsDNA damage.The synergistic effect of the three factors might dramatically enhance the damage of dsDNA.This electrochemical sensor provided a simple method for detecting DNA damage,and may be used for investigating the DNA damage induced by other QDs. 相似文献
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