Self-similarity of complex networks

Complex networks have been studied extensively owing to their relevance to many real systems such as the world-wide web, the Internet, energy landscapes and biological and social networks. A large number of real networks are referred to as 'scale-free' because they show a power-law distribution of the number of links per node. However, it is widely believed that complex networks are not invariant or self-similar under a length-scale transformation. This conclusion originates from the 'small-world' property of these networks, which implies that the number of nodes increases exponentially with the 'diameter' of the network, rather than the power-law relation expected for a self-similar structure. Here we analyse a variety of real complex networks and find that, on the contrary, they consist of self-repeating patterns on all length scales. This result is achieved by the application of a renormalization procedure that coarse-grains the system into boxes containing nodes within a given 'size'. We identify a power-law relation between the number of boxes needed to cover the network and the size of the box, defining a finite self-similar exponent. These fundamental properties help to explain the scale-free nature of complex networks and suggest a common self-organization dynamics.     

浅议工程量清单计价的造价管理

《工程量清单计价规范》从2003年7月1日推行至今已经1年多了。这项被称为工程造价管理走向市场化的重大步骤,已经在市场上取得一定的成效。但值得重视的是,由于人们对这个问题认识的偏差和市场客观环境的支持度不高,以及相关政策不完善等诸多原因,目前这项强制性规范实际上还很不“强”。     

空气粘滞阻尼对g的影响

在气垫导轨上测重力加速度时,空气粘滞阻尼力是产生误差的主要原因。在实验数据中考虑空气粘滞阻尼力的影响,可使实验误差从4.3%降低到0.3%。     

十水草酸澜的热分解

本文用热分析的方法─—热重（ＴＧ），差热分析（ＤＴＡ）对十水草酸镧的热分解机理进行研究。提出其热分解过程的五个步骤：＋水物→九水物→二水物→无水物→一碳酸二氧盐→氧化物。在热分解阶段的中间产物（一碳酸二氧盐）用红外光谱和ｘ－射线衍射仪进行了测定。     

一个生物化学反应的振荡现象

本文讨论生物化学反应中的一类模型:运用定性分析方法及Hopf分枝理论,对系统(?)进行研究,得到了系统(?)的极限环存在性及不存在性条件.最后对所得结果给出了实际解释.     

车床刀架系统动力设计

对Φ４００普通车床的刀架系统进行了动态特性研究，以主要模态柔度及各阶模态能量分布为判据，进行了动力修改设计，获得较高的静、动态特性。     

锰结构钢中的脆化元素和铈

本文通过系列冲击试验和俄歇谱仪等试验,较系统地探讨了磷、锑、铋在晶界上偏聚脆化锰结构钢的能力,以及铈在晶界上偏聚韧化锰结构钢的作用。结果表明,按单位原子百分比计算,对锰结构钢脆化的能力从大到小的顺序是秘、锑、磷;铈韧化含磷锰结构钢的作用最强,韧化含锑锰结构钢的作用居中,韧化含铋锰结构钢的作用最弱。     

De novo mutations revealed by whole-exome sequencing are strongly associated with autism

Multiple studies have confirmed the contribution of rare de novo copy number variations to the risk for autism spectrum disorders. But whereas de novo single nucleotide variants have been identified in affected individuals, their contribution to risk has yet to be clarified. Specifically, the frequency and distribution of these mutations have not been well characterized in matched unaffected controls, and such data are vital to the interpretation of de novo coding mutations observed in probands. Here we show, using whole-exome sequencing of 928 individuals, including 200 phenotypically discordant sibling pairs, that highly disruptive (nonsense and splice-site) de novo mutations in brain-expressed genes are associated with autism spectrum disorders and carry large effects. On the basis of mutation rates in unaffected individuals, we demonstrate that multiple independent de novo single nucleotide variants in the same gene among unrelated probands reliably identifies risk alleles, providing a clear path forward for gene discovery. Among a total of 279 identified de novo coding mutations, there is a single instance in probands, and none in siblings, in which two independent nonsense variants disrupt the same gene, SCN2A (sodium channel, voltage-gated, type II, α subunit), a result that is highly unlikely by chance.     

β-羟基亚胺类化合物的合成及其锂化合物催化异氰酸酯三聚反应

以苯乙酮和芳香胺化合物通过缩合反应合成相应的亚胺化合物,再用二异丙胺基锂去质子后与二苯甲酮反应,然后水解,合成了三个β-羟基亚胺类化合物.进一步研究了β-羟基亚胺锂化合物对芳香异氰酸酯三聚合成异氰脲酸酯的催化效果.实验结果表明,在室温条件下,当催化剂用量为0.1％,反应时间为2h时,催化剂1有较好的催化效果,芳香异氰酸酯苯环上有吸电子的取代基时,催化效果最好,产率可达到96％以上.     

二元混合型偏微分方程的Frankl问题和Tricomi问题

研究一个二元混合型偏微分方程的Frankl问题解的存在惟一性,并讨论此方程的Frankl问题的解如何趋向于其对应的Tricomi问题的解.此混合型方程的系数在双曲型区域与椭圆型区域的连接线上是间断的.主要结果是:此方程的Frankl问题在H1中存在惟一的解;当Frankl问题的边界条件给法趋向于Tricomi问题的边界条件给法时,该方程的Frankl问题的解也在H1中趋近于其对应的Tricomi问题的解.