Effects of Tearing Conditions on the Crack Propagation in a Monolayer Graphene Sheet

The path of crack propagation in a graphene sheet is significant for graphene patterning via the tearing approach. In this study, we evaluate the fracture properties of pre-cracked graphene during the tearing process, with consideration of the effects of the aspect ratio, loading speed, loading direction, and ambient temperatures on the crack propagation in the monolayer sheet. Some remarkable conclusions are drawn based on the molecular dynamic simulation results, i.e., a higher loading speed may result in a complicated path of crack propagation, and the propagation of an armchair crack may be accompanied by sp carbon links at high temperatures. The reason for this is that the stronger thermal vibration reduces the load stress difference near the crack tip and, therefore, the crack tip can pass through the sp link. A crack propagates more easily along the zigzag direction than along the armchair direction. The out-of-plane tearing is more suitable than the in-plane tearing for graphene patterning. The path of crack propagation can be adjusted by changing the loading direction, e.g., a rectangular graphene ribbon can be produced by oblique tearing. This new understanding will benefit the application of graphene patterning via the tearing approach.     

Nanoscale Calculation of Proton-Induced DNA Damage Using a Chromatin Geometry Model with Geant4-DNA

Monte Carlo simulations can quantify various types of DNA damage to evaluate the biological effects of ionizing radiation at the nanometer scale. This work presents a study simulating the DNA target response after proton irradiation. A chromatin fiber model and new physics constructors with the ELastic Scattering of Electrons and Positrons by neutral Atoms (ELSEPA) model were used to describe the DNA geometry and the physical stage of water radiolysis with the Geant4-DNA toolkit, respectively. Three key parameters (the energy threshold model for strand breaks, the physics model and the maximum distance to distinguish DSB clusters) of scoring DNA damage were studied to investigate the impact on the uncertainties of DNA damage. On the basis of comparison of our results with experimental data and published findings, we were able to accurately predict the yield of various types of DNA damage. Our results indicated that the difference in physics constructor can cause up to 56.4% in the DNA double-strand break (DSB) yields. The DSB yields were quite sensitive to the energy threshold for strand breaks (SB) and the maximum distance to classify the DSB clusters, which were even more than 100 times and four times than the default configurations, respectively.     

实测卫星频谱占用状态拟合与预测方法

由于在不同时间、不同空间卫星接收数据底噪是动态起伏的,传统建模固定门限的方法存在缺陷。本文在时间维度上对卫星频谱感知数据的频谱占用模型进行分析,利用自适应阈值法确定噪声门限,对卫星频谱数据进行预处理,得到卫星频谱占用长度序列。为对卫星频谱的态势进行有效的统计分析,利用泊松分布和指数分布方法对频谱占用时间长度序列的概率密度曲线进行拟合,得到了适用于卫星频谱占用时间序列的概率分布模型。基于所得的卫星频谱占用状态模型,通过两状态马尔可夫链计算出卫星信道某一频点的状态转移矩阵,从而预测出信道占用和空闲的概率。利用卫星频谱感知数据构建的数据集进行反向传播(BP)神经网络训练,预测某一频点的占用长度。通过计算BP神经网络与传统的长短期记忆(LSTM)神经网络预测法的均方根误差(RMSE),得到LSTM神经网络的RMSE为2.208 1,BP神经网络的RMSE为0.172 8。评估结果表明,BP神经网络准确度高。     

电动机固态节能起动器在皮带输送机上的应用

文中介绍了固态节能起动器的工作原理,并在某港务公司的3台皮带运输机上分别对它们进行了安装固态节能起动器前后功耗的对比现场测试,结果显示,安装节能起动器后,可降低起动电流、减少有功损耗和无功损耗,提高了功率因数。     

动态事件触发机制下二阶多智能体系统完全分布式控制

本文研究了无向通信拓扑下二阶多智能体系统的一致性问题, 分别针对有领导者和无领导者的情形, 设计 了一类基于辅助动态变量的完全分布式事件触发控制策略, 该策略具有参数较少且易调等特点. 智能体自身的触 发函数满足条件时才向邻居广播自身的状态信息, 有效避免了连续通信, 减少了系统能量耗散. 每个智能体的控制 协议和触发函数都只用到自身的状态和邻居触发时刻的状态, 不涉及邻居的实时状态信息, 也不依赖通信拓扑网络 的任何全局信息. 利用代数图论以及Lyapunov稳定性理论, 证明在所提出的控制策略下, 二阶多智能体系统能够实 现渐近一致性, 且不存在Zeno行为. 仿真示例进一步验证了理论结果的有效性.     

Molecular Identification of the G-Protein Genes and Their Expression Profiles in Response to Nitrogen Deprivation in Brassica napus

Heterotrimeric guanine nucleotide binding protein (G-protein) consisting of Gα, Gβ, and Gγ subunits is one of the key signal transducers in plants. Recent studies indicated that G-protein has been proposed as an important mediator of nitrogen responses in rice, wheat, and Arabidopsis. However, little is known about these G-proteins in Brassica napus (B. napus), except for three identified G-proteins, BnGA1, BnGB1, and BnGG2. Therefore, the aim of the present study is to characterize the members of the G-protein gene family in allotetraploid B. napus and to analyze their expression profiles in response to nitrogen deprivation. In total, 21 G-protein family members were identified in B. napus, encoding two Gα, six Gβ, and 13 Gγ. Sequence and phylogenetic analyses showed that although genome-wide triploid events increased the number of genes encoding Gα, Gβ, and Gγ subunits, the gene structure and protein properties of the genes encoding each G-protein subunit were extremely conserved. Collinearity analysis showed that most G-protein genes in B. napus had syntenic relationships with G-protein members of Arabidopsis, Brassica rape (B. rapa), and Brassica oleracea (B. oleracea). Expression profile analysis indicated that Gα and C-type Gγ genes (except BnGG10 and BnGG12 were highly expressed in flower and ovule) were barely expressed in most organs, whereas most Gβ and A-type Gγ genes tended to be highly expressed in most organs. G-protein genes also showed various expression patterns in response to nitrogen-deficient conditions. Under nitrogen deficiency, Gα and five C-type Gγ genes were upregulated initially in roots, while in leaves, Gα was downregulated initially and five C-type Gγ genes were highly expressed in different times. These results provide a complex genetic dissection of G-protein genes in B. napus, and insight into the biological functions of G-protein genes in response to nitrogen deficiency.     

Cryogenic Exfoliation of 2D Stanene Nanosheets for Cancer Theranostics

Stanene(Sn)-based materials have been extensively applied in industrial production and daily life,but their potential biomedi-cal application remains largely un...     

四川盆地剑阁地区多层系储层叠前描述

近期龙岗62井长兴组及剑门102井须家河组须三段获得重大突破,证实长兴组生物礁储层及须家河组碎屑岩储层均具有较大的勘探潜力。通过对研究区资料特征进行分析对比,在攻关中采用了纵横波阻抗叠前同时反演、体曲率属性、瞬时振幅属性等针对性技术,准确地刻画了生物礁台缘发育相带,预测了碎屑岩裂缝发育和油气有利聚集区,为研究区下一步井位部署提供了准确的资料基础,并形成了一套有效的技术流程。     

一种新型的适应于MANET的基于移动代理的对等入侵检测系统

移动自组织网络(Mobile Ad hoc Networks,MANET)是一种开放性的媒介系统,从而很容易受到黑客的入侵.提出了一种有效的适应于MANET的入侵检测系统,叫做MAPIDS(Mobile Agent-based Peer-to-peer Intrusion Detection System).该系统一旦发现网络中的可疑行为,就会引发一次集体投票过程,以确定该可疑行为是否是入侵行为,并根据投票结果作出相应的进一步处理.相比于其他同样基于集体决策机制的入侵检测系统,MAPIDS节省了更多的网络带宽和电池能耗,并且该系统不存在稀疏节点问题.