Average cluster sizes and cluster size distributions of superfine nickel particles in light media

Effects of shear rates on average cluster sizes (ACSs) and cluster size distributions (CSDs) in uni- and bi-systems of partly charged superfine nickel particles were investigated by Brownian dynamics, and clustering properties in these systems were compared with those in non-polar systems. The results show that the ACSs in bi-polar systems are larger than those in the non-polar systems. In uni-polar systems the behavior of clustering property differs: at the lower ionic concentration (10%), repulsive force is not strong enough to break clusters, but may greatly weaken them. The clusters are eventually cracked into smaller ones only when concentration of uni-polar charged particles is large enough. In this work, the ionic concentration is 20%. The relationship between ACS and shear rates follows power law in a exponent range of 0.176-0.276. This range is in a good agreement with the range of experimental data, but it is biased towards the lower limit slightly.

Power analysis for stratified cluster randomisation trials with cluster size being the stratifying factor

Stratified cluster randomisation trial design is widely employed in biomedical research and cluster size has been frequently used as the stratifying factor.Conventional sample size calculation methods have assumed the cluster sizes to be constant within each stratum,which is rarely true in practice.Ignoring the random variability in cluster size leads to underestimated sample sizes and underpowered clinical trials.In this study,we proposed to directly incorporate the variability in cluster size(represented by coefficient of variability)into sample size calculation.This approach provides closed-form sample size formulas,and is flexible to accommodate arbitrary randomisation ratio and varying numbers of clusters across strata.Simulation study shows that the proposed approach achieves desired power and type I error over a wide spectrum of design configurations,including different distributions of cluster sizes.An application example is presented.

Kinetics Investigation of Sintering of Nanometer Size Metal Clusters:A Molecular Dynamics Study

纳米尺寸金牌簇的 sintering 过程被在嵌入的原子论的方法的框架使用分子的动力学模拟调查。几种分子的动力学模拟技术被用来观察并且描述 sintering 过程的进化。为单个簇的精力分发被检验，二簇的 sintering 过程的快照被记录。sintering 的进化被与每簇的时间阴谋集体中心变化也描述。变化运动并且势能在 sintering 的过程期间被监视并且测量了从精力观点分析 sintering 的主导的机制。

Clustering properties of partly charged superfine particles in a light medium

This paper investigated average cluster sizes （ACS） and cluster size distributions （CSD） at different shear rates by Brownian dynamics in non-, bi-, and uni-polar systems with partly charged superfine particles, The investigation indicates that clusters in non- polar systems are the weakest and easiest to be damaged by increasing shear stresses; charged particles play important and different roles： in bi-polar system, it intends to strengthen clusters to some extent provided that the sign-like ions homogeneously arranged; in uni-polar system charged particles cracked the clusters into smaller ones, but the small clusters are strong to stand with larger shear stress. The relationship between ACS and shear rates follows power law with exponents in a range 0.18-0.28, these values are in a good agreement with experiment range but at the lower limit compared with other systems of non-metallic cluster particles.

miR-23a/27a/24基因簇g.65307469G>A突变对大白猪产仔数和启动子活性的影响

[目的]本文旨在研究大白猪miR-23a/27a/24基因簇启动子突变位点多态性与产仔数性状的关系及潜在机制,为母猪繁殖性状的分子育种提供新的潜在遗传标记。[方法]利用混池测序技术筛选猪miR-23a/27a/24基因簇启动子突变位点,直接测序法对大白猪群体(n=345)miR-23a/27a/24基因簇突变位点进行基因分型,计算遗传多样性;用线性模型对突变位点多态性与产仔数性状进行关联性分析;构建不同等位基因类型启动子载体,转染猪卵巢颗粒细胞,通过检测荧光素酶活性分析突变对启动子活性的影响;用生物信息学方法预测不同等位基因类型启动子潜在结合的差异转录因子,用荧光素酶活性分析差异转录因子对不同等位基因类型启动子活性的影响。[结果]在猪miR-23a/27a/24基因簇启动子-648 nt(Chr.2,65307469 nt)处发现1个新的G/A突变,命名为g.65307469G>A。在大白猪群体中发现3种基因型(GG、GA和AA),其中GG为优势基因型(89.57%),G等位基因为优势等位基因(94.64%)。关联性分析发现,GA基因型母猪的总产仔数(TNB)比GG基因型母猪每胎高0.56头(P<0.05)。荧光素酶活性分析结果显示G等位基因类型启动子活性显著高于A等位基因类型(P<0.05)。在不同等位基因类型启动子间发现1个潜在结合的差异转录因子死亡相关蛋白1(THAP1),成功构建猪THAP1基因过表达载体,共转试验结果显示转录因子THAP1对不同等位基因类型启动子活性均无显著影响(P>0.05)。[结论]miR-23a、miR-27a和miR-24是大白猪产仔数性状的候选基因,g.65307469G>A突变抑制miR-23a/27a/24基因簇的启动子活性,但与转录因子THAP1无关。

基于地铁隧道高分辨率图像的裂缝信息提取

随着运营年限的增长,地铁隧道会逐渐产生各类病害,裂缝是一种典型的病害现象。由于大部分裂缝的特征不突出,且受到地铁隧道内部电缆设备、划痕、蜘蛛网等线状干扰物的影响,现有裂缝检测方法在高分辨率图像下效果不佳。本文以衬砌裂缝为研究对象,基于自主研发的隧道相机系统,实现对隧道表面信息的无损数据采集,获取4096×2168像素的高分辨率图像数据;明确裂缝识别的干扰因素,基于病害特性构建干扰数据集及真实纹理数据集;以掩码-区域卷积神经网络(Mask R-CNN)模型为基准框架,采用K-means和遗传算法对区域建议网络(RPN)网络进行参数优化;利用对比试验和消融试验说明本文算法的检测效果和表现性能。结果表明,本文算法能实现高分辨率图像下隧道裂缝的识别和长度测量,漏检和误检概率更低,对细长、特征不太明显的裂缝具有较好的检测性能,裂缝测量值可为地铁的运营维护提供参考。

地理位置对京津冀城市群县域人口规模变动的影响——兼对京津冀协同发展效果的评价

到北京的距离越近越有利于县域地区人口的增加,到省会、港口的距离越近,也越有利于人口的增加。但对于拥有较大人口规模的县域,到省会和最近港口的距离近对人口增加的正向作用没有北京的大,到地级市的距离近,也没有对人口增加产生显著的正向作用。从不同距离上看,在北京周边200公里范围以内的地区,北京对县域人口增加的正向作用大于省会;但超过200公里后,北京的正向作用明显减弱,省会的正向作用大于北京。从不同时段上来看,2010—2014年间,到北京的距离对人口增加的正向作用大于省会;2015—2019年间,到省会的距离对人口增加的正向作用大于北京,到地级市的距离越近,越有利于该地区的人口增加。可见,随着京津冀协同发展的实施,北京对周边地区的虹吸效应在减弱,而省会对周边县域发展的正向影响在增强,这说明京津冀协同发展的机制可能是通过省会进行了中转,而不是直接作用到北京周边的河北地区。

城市群内中小城市更新策略——以京津冀城市群内徐水区公共空间为例

“城市群”是我国城镇化体系的主体形态和城镇人口的主要空间载体,城市群内的中小城市与核心城市一样肩负着重要的时代使命。以徐水区为例,探讨京津冀城市群内的中小城市如何通过城市更新传承保护城市历史文化、优化城市公共空间、提升城市景观风貌。提出徐水公共空间城市更新技术路线,就城市文化在公共空间表达、街道空间优化、口袋公园营建、门户景观提升等4项景观策略进行详尽阐述,并总结出文化传达的独特性、公共空间提升的节约性、城市景观风貌塑造的特色性、科技赋能的示范性等在京津冀城市群内中小城市实施公共空间更新中可推广的景观策略。

Bulk metallic glasses formed by alloying the Cu_6Zr_5 cluster

The bulk metallic glass formation in the Cu-Zr-M ternary systems by alloying of a binary basic Cu6Zr5 cluster was inves- tigated, where M stands for Sn, Mo, Ta, Nb, Ag, Al and Ti. The Cu6Zr5 cluster is a capped Archimedean antiprism that characterizes the local structure of the Cu10Zr7 crystalline phase. This cluster composition almost superposes with Cu-Zr eutectic Cu0.56Zr0.44. A se- ries of alloys along the cluster line (Cu6Zr5)1-xMx were examined for their glass forming abilities. Alloy rods with a diameter of 3 mm were prepared by copper mould suction casting method and analyzed by XRD and thermal analysis. The Cu-Zr based bulk metallic glasses were discovered with minor Nb, Sn, Mo, Ta additions (≤2at%) and Al, Ti, Ag (8at%≤concentration≤9at%). The alloying mechanism was discussed in the light of atomic size, cluster-linking structure and electron concentration factors.

多维要素流视角下成渝城市群空间结构特征研究

随着交通、通讯设施的日益完善与经济的快速发展,城市间各类要素流动更为频繁并形成城市网络,促进城市动态“流”数据的分析成为区域空间结构研究新范式。相比单一要素流,多维要素流可以从更加综合的视角刻画城市群内部网络联系,识别城市群空间结构特征。本文通过集成百度迁徙、快递物流线路、百度指数、企业总部—分支、科技论文合作等多元地理流数据建立成渝城市群人流、物流、信息流、资金流、技术流及综合流网络,借助社会网络分析方法识别网络节点特征并结合位序—规模法则评估城市体系规模结构,利用核密度分析法识别多维要素流动主要廊道,结合优势流和DBSCAN聚类分析成渝城市群空间组团特征。结果表明:第一,在多维要素流网络中,各节点层级分化明显,成都市、重庆市是成渝城市群的两大核心,对多维要素流的集聚扩散能力突出,而其他城市普遍发育不足。第二,重庆市—成都市关联区间联系强度最高,成都市、重庆市与14个地级市组成的关联区间次之,14个地级市之间组成的关联区间最低,成渝发展主轴、成德绵乐城市带是要素流动的主要廊道。第三,在优势流约束下,成渝城市群内部形成成都—德阳—眉山、重庆—广安、南充—遂宁、内江—自贡—宜宾—泸州、乐山—雅安共5个空间聚类,其中南充—遂宁、内江—自贡—宜宾—泸州具备培育都市圈的潜力。结合本文分析结果和现有规划,建议将多维要素流网络中心度相对较高的绵阳、南充、宜宾作为次级中心城市培育,在重点发展成都都市圈、重庆都市圈的同时着力培育南充—遂宁、内自宜泸两大都市圈,促进绵阳市、雅安市、乐山市、达州市等圈群空隙城市差异化、特色化发展,强化宜宾—泸州—重庆沿江发展轴,逐步优化成渝城市群空间结构,形成区域协调发展新格局。

Estimation of Attributable Risk from Clustered Binary Data: The Case of Cross-Sectional and Cohort Studies

Effect sizes are estimated from several study designs when the subjects are individually sampled. When the samples are the aggregate cluster of individuals, the within cluster correlation must be accounted for to construct correct confidence intervals, and to conduct valid statistical inference. The purpose of this article is to propose and evaluate statistical procedures for the estimation of the variance of the estimated attributable risk in parallel groups of clusters, and in a design dividing each of k clusters into two segments creating multiple sub-clusters. The estimated variance is the first order approximation and is obtained by the delta method. We apply the methodology and propose a Wald type confidence interval on the difference between two correlated attributable risks. We also construct a test on the hypothesis of equality of two correlated attributable risks. We evaluate the power of the proposed test via Monte-Carlo simulations.

Influence of air masses on particle number concentration and size distribution at Mt. Waliguan, Qinghai Province, China

Particle size distribution of 12-500 nm was measured at Mt. Waliguan, China Global Atmosphere Watch Baseline Observatory, from Aug. in 2005 to May in 2007.72-hr back-trajectories at 100-m arrival height above ground level for the same period were calculated at 6：00, 12：00, and 21：00 （Beijing Time） for each day using the Hybrid Single-Particle Lagrangian Integrated Trajectory （HYSPLIT-4） model developed by NOAA/ARL. It was found that air mass sources significantly impact particle number concentration and size distribution at Mt. Waliguan. Cluster analysis of back-trajectories show that higher Aitken mode particle number concentration was observed when air masses came from or passed by the northeastern section of Mt. Waliguan, with short trajectory length. High number concentration of nucleation mode was associated with air masses from clean regions, with long trajectory length.

Three vertex degree correlations of fixed act-size collaboration networks

A rate equation approach was presented for the exact computation of the three vertex degree correlations of the fixed act-size collaboration networks.Measurements of the three vertex degree correlations were based on a rate equation in the continuous degree and time approximation for the average degree of the nearest neighbors of vertices of degree k,with an appropriate boundary condition.The rate equation proposed can be generalized in more sophisticated growing network models,and also extended to deal with related correlation measurements.Finally,in order to check the theoretical prediction,a numerical example was solved to demonstrate the performance of the degree correlation function.

庆阳驴体尺指标的相关性、聚类和主成分分析

为了明确庆阳驴各体尺指标间的关系,对成年庆阳驴(公驴31头、母驴47头)的12项体尺指标进行了测定统计,并采用SPSS 19.0软件对体尺指标进行了相关性、聚类和主成分分析。结果表明,公驴组的各体尺指标均略高于母驴,各指标间的相关性大多大致相同,少数呈现差异性。公母驴体高与部分体尺指标间均存在不同程度的正相关,其中,公驴体高与十字部高呈极显著正相关(P<0.01);母驴体高与腰角宽和十字部高呈极显著正相关(P<0.01),胸围与腰角宽和头长呈极显著相关(P<0.01)。公母驴各体尺指标聚类分析(当类间距等于13时)与主成分分析的结果基本一致,其所有体尺指标区分为4个相对独立的主成分,公驴累计贡献率为93.934%,其中第一个贡献率为45.403%,可分为高度因子、宽度因子、头部因子和长度因子;母驴累计贡献率为92.740%,其中第一个贡献率为47.132%,可分为胸围因子、管围因子、胸深因子和头部因子。综上,公驴体尺指标均略高于母驴;公母驴体高与部分体尺指标间存在不同程度的正相关,且12项体尺指标均可区分为4个相对独立的主成分。

Unimolecular Dissociation of H⁺<sub style="margin-left:-6px;">2n+1</sub>Hydrogen Clusters: Measured Cross Sections and Theoretically Calculated Rate Constants

In this paper, we studied the process of dissociation unimolecular of the evaporation of H+2n+1 hydrogen clusters according to size, using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The rate constants k(E) were determined with the use of statistical theory of unimolecular reactions using various approximations. In our work, we used the products frequencies instead of transitions frequencies in the calculation of unimolecular dissociation rates obtained by three models RRKM. The agreement between the experimental cross section ratio and calculated rate ratio with direct count approximation seems to be reasonable.

产业集群视角下中小企业绿色技术创新协同策略博弈研究

学界对于政府补贴在扭转绿色技术创新的技术与环境双重市场失效中具有关键作用,并且协同创新有助于企业抵御绿色技术创新的研发风险与需求不足已达成共识,但同时考虑政府补贴与绿色技术协同创新的研究尚不足,因此,为进一步探究中小企业绿色技术创新决策与绿色生产决策以及政府创新补贴之间的影响机制,以产业集群绿色发展为背景,结合古诺(Cournot)模型与斯塔克尔伯格(Stackelberg)模型,将政府补贴与绿色技术协同创新纳入模型中,构建由一个领军企业、两个中小企业构成的三阶段三寡头绿色技术协同创新博弈模型,其中第一阶段为政府绿色技术创新补贴决策、第二阶段为企业绿色技术创新决策、第三阶段为企业绿色生产决策,通过模型求解分析以及数值算例分析,研究基于中小企业绿色技术创新的研发阶段和生产阶段不同协同创新策略情形下的决策均衡解。结果发现:基于研发阶段合作的部分协同创新策略可以在适当降低创新补贴标准情况下有效缩小中小企业的绿色技术创新绩效差距;基于创新和生产两阶段合作的全面协同创新策略配合创新补贴标准提高,中小企业可以在市场份额和创新绩效两方面同时赶超领军企业。为此,建议政府相关部门制定创新标准时应与中小企业的协同创新策略进行协同,且应积极推动绿色技术创新共享,从共同利润最大化角度进行创新决策与生产决策的优化协同。

网格尺寸对识别循环流化床上升管中颗粒聚团特性的影响研究

采用LES-DSMC方法模拟了循环流化床上升管中气固两相流动特性,并基于颗粒聚团识别准则,考察了网格尺寸对识别上升管中心和壁面区域内颗粒聚团特性的影响规律。结果表明,采用独立的聚团识别网格可有效消除对气相计算网格的尺度限制,减小识别网格尺寸可提高聚团识别精度并获得聚团的详细特性。在上升管中心区域,床层平均聚团特性几乎随网格尺寸线性变化;而在近壁区域,随着识别网格尺寸的增加,可获得的数据点减少,数均聚团特性与实际值的偏差越来越大。此外,提出了计算近壁区域聚团平均颗粒浓度和沉降速度的方法,计算结果与实验结果较吻合。

中小机场群跨节点网络调度优化

目前我国的西南地区有50个民用机场,中小机场群的出现使机场空域冲突增多,使得管制协调量增大,出现航班延误等问题。为了解决中小机场群的管制协调问题,论文重新定义了延误的概念,通过模拟仿真航班的运行情况,使用一种基于航空器累积延误的联合跨节点网络调度方法,采用西南地区中小机场群航班运行情况为例,建立网络调度模型,对航空器的进离场进行合理的规划,本质上对累积了高延误的航班进行合理的优先排序来降低航班延误的方差的调度方法。