给定度序列图的覆盖成本和反向覆盖成本的研究

具有n个顶点且度序列为(m,2,…,2,1,…,1)(1的重数为m)的连通图不止一个(这些图均为树),而每个树对应唯一一个段序列(l₁,l₂,…,l_m).通过对任意一树移动最长段的悬挂点到最短段悬挂点的方式得到另一树,比较前后两树的覆盖成本和反向覆盖成本,给出了具有最小覆盖成本和反向覆盖成本的极树,并且进一步给出了取得最小覆盖成本和反向覆盖成本的顶点.     

Further results on several types of generalized inverses

Let R be an associative ring with unity 1 and let a,b,c∈R. In this paper, several characterizations for hybrid (b,c)-inverses of a are given. Also, the hybrid (b,c)-inverse of a is characterized by the group inverse of ab, under certain hypothesis. In particular, existence criteria for the the inverse along an element are obtained. Finally, we get the double commutant property and the reverse order law of annihilator (b,c)-inverses.     

Weighted estimates for the multilinear maximal function on the upper half‐spaces

For a general dyadic grid, we give a Calderón–Zygmund type decomposition, which is the principle fact about the multilinear maximal function on the upper half‐spaces. Using the decomposition, we study the boundedness of . We obtain a natural extension to the multilinear setting of Muckenhoupt's weak‐type characterization. We also partially obtain characterizations of Muckenhoupt's strong‐type inequalities with one weight. Assuming the reverse Hölder's condition, we get a multilinear analogue of Sawyer's two weight theorem. Moreover, we also get Hytönen–Pérez type weighted estimates.     

氢气浸泡辐照加速方法在3DG111器件上的应用及辐射损伤机理分析

本文以~(60)Co为辐照源,针对3DG111型晶体管,利用半导体参数分析仪和深能级缺陷瞬态谱仪,研究高/低剂量率和有/无氢气浸泡条件下,电性能和深能级缺陷的演化规律.试验结果表明,与高剂量率辐照相比,低剂量率辐照条件下,3DG111型晶体管的电流增益退化更加严重,这说明该器件出现了明显的低剂量率增强效应;无论是高剂量率还是低剂量率辐照条件下,3DG111晶体管的辐射损伤缺陷均是氧化物正电荷和界面态陷阱,并且低剂量率条件下,缺陷能级较深;氢气浸泡后在高剂量率辐照条件下,与未进行氢气处理的器件相比,辐射损伤程度明显加剧,且与低剂量率辐照条件下器件的损伤程度相同,缺陷数量、种类及能级也相同.因此,氢气浸泡处理可以作为低剂量率辐射损伤增强效应加速评估方法的有效手段.     

A computational foray into the mechanism and catalysis of the adduct formation reaction of guanine with crotonaldehyde

Crotonaldehyde, a common environmental pollutant and product of endogenous lipid peroxidation, reacts with guanine to form DNA adducts with pronounced genotoxicity and mutagenicity. Here, we explore the molecular mechanism of this adduct formation using double-hybrid density functional theory methods. The reaction can be envisaged to occur in a two-step fashion via an aza-Michael addition leading to an intermediate ring-open adduct followed by a cyclization reaction giving the mutagenic ring-closed adduct. We find that (i) a 1,2-type addition is favored over a 1,4-type addition for the aza-Michael addition, and (ii) an initial tautomerization of the guanine moiety in the resulting ring-open adduct significantly reduces the barrier toward cyclization compared to the direct cyclization of the ring-open adduct in its keto-form. Overall, the aza-Michael addition is found to be rate-determining. We further find that participation of a catalytic water molecule significantly reduces the energy barriers of both the addition and cyclization reaction. © 2018 Wiley Periodicals, Inc.     

振型归一化对梁结构柔度曲率损伤指标的影响

结构柔度矩阵需由质量矩阵归一化振型获得,而质量矩阵归一化振型难以直接测得,限制了柔度曲率类损伤指标的应用。为分析振型归一化方法对梁结构柔度曲率类损伤指标的影响,根据梁结构的刚度、弯矩和位移曲率的关系,建立了均布荷载作用下结构损伤前后位移曲率与损伤程度的理论表达式,实现定量分析均匀荷载面曲率结构损伤程度。提出P-范数振型归一化方法,通过均匀荷载面曲率指标推导了振型质量矩阵归一化系数差x_α与损伤程度的关系。以三跨连续梁算例对理论进行了验证,结果表明,损伤程度定量指标效果良好,不同P-范数振型归一化方法下,损伤程度的偏差可由2x_α估算;2-范数振型归一化方法的损伤识别结果与质量矩阵振型归一化结果最接近,故当无法获得质量矩阵归一化振型时,可采用2-范数归一化振型代替。     

Cold,warm, and hot programming of shape memory polymers

In this article, programming is classified as hot, warm, and cold, based on the temperature zone within which the programming is conducted. The strain and stress locking and releasing mechanisms are discussed within the thermodynamics framework. A new formula is developed for quantifying the strain recovery ratio of cold-programmed SMPs. Stress fixity ratio and stress recovery ratio are also defined based on the understanding of stress locking and recovery mechanisms. State-of-the-art literature on warm and cold programming is reviewed. Well-controlled programming as well as free strain recovery test and constrained stress recovery test are conducted, in order to validate the memory mechanisms discussed in this study. It is found that, while programming temperature has an insignificant effect on the final free shape recovery, it has a significant effect on the stress recovery. The recovery stress programmed by cold programming may be lower, equal to, or higher than that by hot programming, due to the different stress locking mechanisms and other factors such as damage during the thermomechanical cycle. Cold, Warm, and Hot Programming of Shape Memory Polymers © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1319–1339     

循环孔隙水压下混凝土常规三轴压缩损伤破坏特性分析

本文进行了孔隙水压不同循环次数(0次,10次,50次,100次和200次)以及不同应变速率下(10~(-5)/s,10~(-4)/s,10~(-3)/s和10~(-2)/s)混凝土常规三轴压缩试验,分析了混凝土峰值应变的变化规律、应力-应变曲线及损伤特性。结果表明:相同循环次数孔隙水压下,峰值应变随应变速率增加,整体呈现出增加的趋势;而相同应变速率下,峰值应变随孔隙水压循环次数的变化规律并不明显;在中低应变速率(10~(-5)~10~(-3)/s)下,混凝土的损伤变化受孔隙水压循环次数影响较大;当循环次数达到200次时,孔隙水压作用对混凝土产生较大的损伤。通过对循环孔隙水作用下混凝土动态损伤破坏机理的分析可知:混凝土的破坏过程实际上是内部裂纹不断形成、扩展、贯通,材料损伤不断产生、累积的过程;当损伤达到一定程度,混凝土发生宏观破坏,失去承载力。     

综合考虑宏细观缺陷的岩体动态损伤本构模型

针对节理岩体同时含有节理、裂隙等宏观缺陷及微裂隙、微孔洞等细观缺陷的客观事实, 提出了在节理岩体动态损伤本构模型中应同时考虑宏细观缺陷的观点。为此, 首先对基于细观动态断裂机理的经典岩石动态损伤本构模型—TCK(Taylor-Chen-Kuszmaul)模型进行了阐述, 其次基于Lemaitre等效应变假设推导了综合考虑宏细观缺陷的复合损伤变量(张量), 进而在此基础上建立了相应的节理岩体动态损伤本构模型, 并利用该模型讨论了载荷应变率及节理条数对岩体动态力学特性的影响规律。结果表明, 在不同载荷应变率下试件在变形初始阶段是重合的, 而后随着应变的增加, 试件峰值强度、峰值应变及总应变均随载荷应变率的增加而增加; 随着节理条数的增加, 试件峰值强度逐渐降低, 但降低趋势逐渐变缓并趋于某一定值。上述研究结论与目前的理论及实验研究结果的基本规律是一致的, 说明了本模型的合理性。     

Radiation damage in polymer films from grazing‐incidence X‐ray scattering measurements

Grazing‐incidence X‐ray scattering (GIXS) is widely used to analyze the crystallinity and nanoscale structure in thin polymer films. However, ionizing radiation will generate free radicals that initiate crosslinking and/or chain scission, and structural damage will impact the ordering kinetics, thermodynamics, and crystallinity in many polymers. We report a simple methodology to screen for beam damage that is based on lithographic principles: films are exposed to patterns of X‐ray radiation, and changes in polymer structure are revealed by immersing the film in a solvent that dissolves the shortest chains. The experiments are implemented with high throughput using the standard beam line instrumentation and a typical GIXS configuration. The extent of damage (at a fixed radiation dose) depends on a range of intrinsic material properties and experimental variables, including the polymer chemistry and molecular weight, exposure environment, film thickness, and angle of incidence. The solubility switch for common polymers is detected within 10–60 s at ambient temperature, and we verified that this first indication of damage corresponds with the onset of network formation in glassy polystyrene and a loss of crystallinity in polyalkylthiophenes. Therefore, grazing‐incidence X‐ray “patterning” offers an efficient approach to determine the appropriate data acquisition times for any GIXS experiment. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1074–1086