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正1引言Kaczmarz算法[8]是求解超定相容线性方程组的最受欢迎的方法之一,Ax=b,(1.1)其中矩阵A=(a_(ij))∈C~(m×n)(m≥n),b=(b_1,b_2,…,b_m)~T∈C~m,a_i~T(i=1,2,…,m)表示矩阵A的行.由于其简单且收敛速度快,Kaczmarz算法的应用范围非常广泛,最早是被 相似文献
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Peptide backbone-copper ring structure: A molecular insight into copper-induced amyloid toxicity 下载免费PDF全文
Copper ions can promote amyloid diseases that are associated with amyloid peptides, such as type 2 diabetes (T2D), Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). However, the underlying molecular mechanism remains obscure. Here we present that Cu2+ is able to specifically bind to the backbone of T2D-related human islet amyloid polypeptide (hIAPP) by forming a ring structure, which causes the reduction of Cu2+ to Cu+ to produce reactive oxygen species (ROS) and the modulation of hIAPP aggregation. Nuclear magnetic resonance spectroscopy showed that Cu2+ bound to the backbone of a turn region, His18—Ser21, which is critical for hIAPP aggregation. Ab initio calculations and x-ray absorption fine structure analyses revealed that Cu2+ simultaneously bound with both the amide nitrogen and carbonyl oxygen on the peptide backbone, resulting in a ring structure, and causing the reduction of Cu2+ to Cu+ to form a hIAPP-Cu+ complex. 2',7'-dichlorodihydrofluorescin diacetate fluorescence measurements further indicated that this complex led to enhanced ROS levels in rat insulinoma cells. Additionally, thioflavin T fluorescence and atomic force microscopy measurements denoted that the backbone-Cu ring structure largely modulated hIAPP aggregation, including the inhibition of hIAPP fibrillation and the promotion of peptide oligomerization. These findings shed new light on the molecular mechanism of Cu2+-induced amyloid toxicity involving both the enhancement of ROS and the modulation of hIAPP aggregation. 相似文献
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The eccentricity of the centre of mass from the geometric centre of a spherical attracting mass in determining the Newtonian gravitational constant G is tested by means of an electronic balance. The experimental result shows that the eccentricity of the sample is about 0.31 μm with uncertainty of 0.05μm. Two density distribution models are discussed to estimate the uncertainty to G by the eccentricities of the attracting masses. 相似文献
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稀土/高分子杂化发光材料的研究 总被引:11,自引:1,他引:10
用SiO2为无机组份和以与SiO2具有相似折射率和优良力学性能的丙烯酸类如甲基丙烯酸甲酯(MMA)和甲基丙烯酸羟乙酯(HEMA),在交联剂3-(三甲氧基硅)丙基甲基丙烯酸酯(MSMA)存在下,快速制备了两种杂化基质材料SiO2/P(MMA-MSMA)和SiO2/P(HEMA-MSMA)。分别以盐酸和六次甲基四胺作为酸性催化剂和碱性催化剂,建立了快速制备透明凝胶的两步溶胶-凝胶法,大大缩短了溶胶的成胶时间,所得杂化材料具有良好的光学透明性,利用此方法制备了掺杂稀土配合物的多种发光杂化材料。采用组装的方法,得到了稀土配合物与层次化合物α-磷酸氢锆(α-ZrP)及中孔分子筛材料MCM-41的组装体,并对所制备的杂化材料进行了表征。另外,将稀土配合物通过共价键嫁接于无机SiO2基质中,得到了含有稀土配合物的分子杂化材料。 相似文献
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通过测量荧光寿命和荧光光谱,研究了1,2-苯并蒽(BA),9,10-二甲基-1,2-苯并蒽(DMBA)与β-环糊精(β-CD)络合过程及荧光猝灭。计算出络合平衡常数和猝灭常数。结果表明,BA与β-CD发生了络合作用,DMBA几乎不与β-CD络合。加入β-CD可使荧光分子的,聚集态与单体间的平衡向生成单体的方向移动,碘离子对BA的猝灭作用也明显减弱。 相似文献
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