Vibration and wave propagation analysis of twisted micro-beam using strain gradient theory

In this research, vibration and wave propagation analysis of a twisted micro- beam on Pasternak foundation is investigated. The strain-displacement relations （kine-matic equations） are calculated by the displacement fields of the twisted micro-beam. The strain gradient theory （SGT） is used to implement the size dependent effect at micro-scale. Finally, using an energy method and Hamilton＇s principle, the governing equations of motion for the twisted micro-beam are derived. Natural frequencies and the wave prop- agation speed of the twisted micro-beam are calculated with an analytical method. Also, the natural frequency, the phase speed, the cut-off frequency, and the wave number of the twisted micro-beam are obtained by considering three material length scale parameters, the rate of twist angle, the thickness, the length of twisted micro-beam, and the elastic medium. The results of this work indicate that the phase speed in a twisted micro-beam increases with an increase in the rate of twist angle. Moreover, the wave number is in- versely related with the thickness of micro-beam. Meanwhile, it is directly related to the wave propagation frequency. Increasing the rate of twist angle causes the increase in the natural frequency especially with higher thickness. The effect of the twist angle rate on the group velocity is observed at a lower wave propagation frequency.

An extended displacement discontinuity method for analysis of stress wave propagation in viscoelastic rock mass

An extended displacement discontinuity method (EDDM) is proposed to analyze the stress wave propagation in jointed viscoelastic rock mass (VRM).The discontinuities in a rock mass are divided into two groups.The primary group with an average geometrical size larger than or in the same order of magnitude of wavelength of a concerned stress wave is defined as 'macro-joints',while the secondary group with a high density and relatively small geometrical size compared to the wavelength is known as 'micro-defects'.The rock mass with micro-defects is modeled as an equivalent viscoelastic medium while the macro-joints in the rock mass are modeled explicitly as physical discontinuities.Viscoelastic properties of a micro-defected sedimentary rock are obtained by longitudinally impacting a cored long sedimentary rod with a pendulum.Wave propagation coefficient and dynamic viscoelastic modulus are measured.The EDDM is then successfully employed to analyze the wave propagation across macro-joint in VRM.The effect of the rock viscosity on the stress wave propagation is evaluated by comparing the results of VRM from the presented EDDM with those of an elastic rock mass (ERM) from the conventional displacement discontinuity method (CDDM).The CDDM is a special case of the EDDM under the condition that the rock viscosity is ignored.Comparison of the reflected and transmitted waves shows that the essential rock viscosity has a significant effect on stress wave attenuation.When a short propagation distance of a stress wave is considered,the results obtained from the CDDM approximate to the EDDM solutions,however,when the propagation distance is sufficiently long relative to the wavelength,the effect of rock viscosity on the stress wave propagation cannot be ignored.

<i>In Vitro</i>Direct Organogenesis Protocol for Mass Propagation of an Elite Ethiopian Hot Pepper (<i>Capsicum annuum</i>L.) Cultivar: Mareko Fana

An efficient and reproducible in vitro mass propagation protocol was developed for Mareko Fana cultivar of hot pepper (C. annuum L.) through direct organogenesis using nodal and shoot tip explants. Three percent active chlorine for 20 minutes was found to be optimum treatment combination yielding 82.5% ± 5.00% contaminant-free germinated seedlings. For shoot induction, MS + 4.5 mg/l BAP + 0.5 mg/l IAA and MS medium containing eight mg/l Zeatin were found to be optimum resulting 77.5% ± 5.00% and 67.50% ± 5.00% induction percentage for nodal and shoot tip explants respectively. Maximum shoot multiplication responses were obtained on MS + 3 mg/l BAP + 2 mg/l Kinetin with mean number of 9.2 ± 0.2 and 8.6 ± 0.00 shoots for nodal and shoot tip explants respectively. Best shoot elongation and rooting responses were obtained on MS + 0.5 mg/l IBA resulting mean value of 29.6 ± 0.12 root number, 4.25 ± 0.20 cm root length and 5.12 ± 0.20 cm shoot height. The plantlets showed 77.5% survival during acclimatization and transplanting.

基于方向权值标签传播的微学习单元聚类算法

为帮助学习者从大量在线学资源中找到适合自身个性化的学习资源及顺序集合,提出了一种基于有向边方向权值的标签传播算法(label propagation algorithm on directed edge weights,LPADEW)用于发现适合特定学习者并属于同一学习周期的微学习单元序列簇群。该算法对标签传播算法进行两个改进:根据单元节点的利用度确定标签的更新顺序,降低在节点更新顺序上的随机性;利用当前单元节点的前置邻居和后置邻居的有向边权累加值进行标签更新,并将标签权重引入标签更新策略,既可降低标签更新的随机性,也可避免形成巨型簇群。实验结果表明,LPADEW算法在微学习真实数据集和人工数据集中均取得了较好的结果。

微时代党的创新理论高校传播问题研究

推动党的创新理论的传播和普及是党的思想建设的重要内容。如何让高校大学生从党的创新理论中获取思想资源、精神动力和奋进力量,是高校思想政治教育的需要解决的一大问题。微媒体时代,党的创新理论在高校的传播存在传播内容的话语形式僵硬呆板、传播的方式过于单一以及传播平台与“微媒体”联动不足等问题。秉持党的创新理论传播的指导思想和基本原则,针对当代大学生思想开放、学习方式多样、网络社交泛化等特点,在党的创新理论传播的过程中,可以“微表达”来构建党的创新理论传播话语体系,打造“微阵地”来拓宽党的创新理论传播路径;用微力量来实现党的创新理论的联动传播。

借助微媒体平台传播革命老区红色文化的策略探索

微媒体平台对弘扬革命老区红色文化精神具有十分积极的作用,不仅为红色文化精神的更好传播开辟了新的“窗口”,而且有助于强固主流文化意识形态,增强红色文化的趣味性。借助微媒体平台传播革命老区红色文化需特别关注以下几个问题:活用“互联网+”思维;注重传播环境的规范性;加强红色文化在微媒体传播的广度和深度。借助微媒体平台传播革命老区红色文化,一需创建以手机为重要载体和平台的红色文化阵地;二需创建“三微一端”多元化的红色文化宣传渠道,并加强信息审核;三需培育一支得力精干的红色文化宣传管理队伍;四需加强对红色文化的学习、研究,多和自媒体等其他相关媒体宣传平台进行交流合作。

Multi-modality measurement and comprehensive analysis of hepatocellular carcinoma using synchrotron-based microscopy and spectroscopy

The visualization and data mining of tumor multidimensional information may play a major role in the analysis of the growth,metastasis,and microenvironmental changes of tumors while challenging traditional imaging and data processing techniques.In this study,a general trans-scale and multi-modality measurement method was developed for the quantitative diagnosis of hepatocellular carcinoma(HCC)using a combination of propagation-based phase-contrast computed tomography(PPCT),scanning transmission soft X-ray microscopy(STXM),and Fourier transform infrared micro-spectroscopy(FTIR).Our experimental results reveal the trans-scale micro-morpho-logical HCC pathology and facilitate quantitative data analysis and comprehensive assessment.These results include some visualization features of PPCT-based tissue microenvironments,STXM-based cellular fine structures,and FTIR-based bio-macromolecular spectral characteris-tics during HCC tumor differentiation and proliferation.The proposed method provides multidimensional feature data support for constructing a high-accuracy machine learning algorithm based on a gray-level histogram,gray-gradient co-occurrence matrix,gray-level co-occurrence matrix,and back-propagation neural network model.Multi-dimensional information analysis and diagnosis revealed the morphological pathways of HCC pathological evolution and we explored the relationships between HCC-related feature changes in inflammatory microenviron-ments,cellular metabolism,and the stretching vibration peaks of biomolecules of lipids,proteins,and nucleic acids.Therefore,the proposed methodology has strong potential for the visualization of complex tumors and assessing the risks of tumor differentiation and metastasis.

Effect of Ultrasonic Vibration on Deformation in Micro-blanking Process with Copper Foil

Effect of ultrasonic vibration on deformation in micro-blanking was investigated with copper foils of different grain sizes using a developed device. It is found that maximum shearing strength is decreased by ultrasonic vibration, and this effect becomes bigger for coarse grain than that for fine grain, which can be attributed to acoustic softening effect considering the absorbed acoustic energy. Surface roughness R_a of smooth zone decreases for the polishing effect of vibration at the lateral contact surface. When ultrasonic vibration is applied, the sheared deformation area becomes relatively narrow, and it leads to the reduction of radius of rollover. The analysis of cross section in sheared deformation area shows that the crack initiation is inhabited for the existence of acoustic softening, and the proportion of smooth zone is increased. Also, angle of crack propagation becomes smaller because of periodic strain, and the angle of facture surface is decreased. As a result, the quality of micro-sheet parts is improved by applying ultrasonic vibration.

Experimental investigation on microstructure behavior of premixed methane-air flame-flow interaction in a semi-vented chamber

To explore the premixed methane-air flame microstructure behavior and the flame-flow interaction, the premixed methane/air flame was studied in a semi-vented chamber. A high speed camera and schlieren images methods were used to record the processes of interaction between rare- faction wave and flame. Meanwhile, a pressure sensor was utilized to catch the pressure variation in the process of flame propagation. The experiment results showed that the interference of rarefaction wave on flame caused the flame front structure change, which led to the flame transition from lami- nar to turbulent quickly. The rarefaction wave intervened in the flame by turning the flame front sur- face into dentiform structure. The violent turbulent combustion began to appear in part of the flame front and spreaded to the whole flame front surface. The rarefaction also decreased the flame propa- gation speed.

各向异性对平板裂纹扩展路径的影响研究

近场动力学理论克服了经典连续介质力学在模拟裂纹扩展方面的不足。本文基于微梁键构建了一般各向异性近场动力学平面模型,并探讨了各向异性对于裂纹扩展路径的影响。首先,建立一般各向异性的微梁键,并基于插值法建立了一般各向异性近场动力学平面模型的应变能密度表达式;然后,利用应变能密度互等原理求解出近场动力学平面本构模型的一般各向异性参数;最后,通过带初始切口的平板断裂实验研究了不同各向异性参数对于平板裂纹扩展路径的影响。

基于分布位错法研究多条微裂纹对偏折主裂纹的影响

目的 采用理论方法求解多条微裂纹对偏折主裂纹的影响,重点分析偏折主裂纹尖端的力学行为及微裂纹对主裂纹扩展角度和闭合区域的影响等问题,为实际的工程应用提供理论依据。方法 运用叠加原理将主问题分解成2个子问题,通过材料力学方法求解子问题一;基于分布位错方法求解子问题二。进一步建立关于位错密度的奇异积分方程,利用Gauss-Chebyshev数值求积分法解决位错密度方程的奇异性问题,并通过计算机编写程序,最终得到相关力学参量的数值解。结果 得到了偏折主裂纹附近的应力场以及微裂纹长度、微裂纹个数对偏折主裂纹尖端应力强度因子的影响等相关力学参量。分析了主裂纹不同偏折角度时的闭合区域,以及微裂纹的方位角、微裂纹个数等对偏折主裂纹扩展角度的影响。结论 裂纹面对拉应力有屏蔽作用,导致拉应力在裂纹面附近应力松弛,而裂纹尖端对拉应力有放大作用,随着应力增加将导致裂纹的扩展。一条微裂纹位于主裂纹尖端约–30°<θ<50°时,将使主裂纹尖端应力强度因子增加,促进主裂纹的扩展,而微裂纹位于50°<θ<90°或–90°<θ<–30°时,将使主裂纹尖端应力强度因子减小,抑制主裂纹的扩展。主裂纹尖端应力强度因子随微裂纹长度的增加而变大,随微裂纹与主裂纹间距离的增加而减小。

预腐蚀7050-T7651铝合金微裂纹的萌生与扩展

开展不同预腐蚀时间下7050-T7651铝合金的扫描电子显微镜原位拉伸实验,利用扫描电子显微镜观原位、在线测试件表面微观裂纹的萌生、扩展,分析腐蚀对铝合金微裂纹行为的影响。结果表明:随着腐蚀程度加剧,试件表面腐蚀坑密度增大,形成腐蚀坑群,试件的承载能力也随之下降。微裂纹主要萌生于试件缺口粗糙表面和试件表面蚀坑处,微裂纹数量随着腐蚀时间的延长而增多;缺口产生的微裂纹与相邻的蚀坑微裂纹相互联结形成主裂纹,主导试件的损伤失效过程。腐蚀损伤较轻时,主裂纹尖端附近的蚀坑会引起裂纹分支;腐蚀损伤较重时,腐蚀坑诱导的多条微裂纹与主裂纹发生多次联合,影响了主裂纹的扩展方向与路径;切应力在裂纹扩展过程中也起到了重要作用,开裂模式为Ⅰ/Ⅱ混合断裂模式。

焊接微裂纹缺陷对顶板与纵肋构造疲劳性能影响研究

为研究焊接微裂纹缺陷对正交异性钢桥面板顶板与纵肋构造疲劳性能的影响,首先采用扫描电子显微镜对实际桥梁结构的焊接断面进行缺陷检测,统计分析微裂纹尺寸和分布特性,然后基于既有试验和有限元分析方法,结合断裂力学理论,评估不同微裂纹缺陷对构造细节劣化效应的影响,并分析焊接微裂纹关键特征参数对构造细节疲劳性能的影响。结果表明:顶板与纵肋构造的焊趾及焊根处普遍存在微裂纹缺陷,焊根处微裂纹尺寸(平均值150.7μm、标准差100.8μm)大于焊趾处(平均值29.8μm、标准差17.4μm);顶板与纵肋构造细节主导失效模型主要由微裂纹尺寸决定;构造细节疲劳寿命直接由焊接微裂纹尺寸决定,其疲劳强度为100~200 MPa;疲劳裂纹最终扩展方向与焊接微裂纹初始角度无关,仅受实际受力状态影响。

草莓微繁殖苗及其后代性状表观遗传变异研究

为揭示微繁殖导致表观遗传变异的表现特点,以草莓品种佐贺清香和全明星为试材,研究了微繁殖导致草莓表观遗传变异的生物学性状表现和生理生化变化。草莓微繁殖原种苗和一代苗繁殖匍匐茎子苗的能力明显高于普通苗,其中佐贺清香微繁殖原种苗繁苗能力比普通苗高1倍以上。微繁殖苗后代与普通苗在物候期上没有明显差异,同样在叶片形态和发育上也没有明显差异。在果实成熟期,微繁殖苗后代的生长势强旺,佐贺清香二代苗和全明星二代苗分别比普通苗增产49.8%和9.7%;微繁殖苗后代叶片中可溶性糖含量、可溶性蛋白质含量、苯丙氨酸解氨酶活性、几丁质酶活性和β-1,3-葡聚糖酶活性明显低于普通苗,这意味着微繁殖可能导致草莓的抗病性降低。

兔眼越橘茎段快繁高效技术研究

为获取兔眼越橘微体快繁高效技术体系,以越橘幼嫩茎段为试材,通过改变初代培养基、增殖培养基、生根培养基和炼苗基质的组分对24种介质进行了筛选。结果表明,初代培养基WPM+10mg/LZT能显著提高外植体的萌芽率和>1cm的枝条数;增殖培养基WPM+5mg/LZT能使新梢增殖率提高12倍;散射光处理下,生根培养基1/2WPM+0.1mg/LIBA能使试管苗生根率达到97%;草炭∶石英砂=2～3∶1的炼苗基质可以使幼苗的成活率达到99%。

基于微博传播信息流的微博效果评价模型及实证研究

基于用户行为视角,根据微博传播信息流,结合PageRank算法思想和用户行为权值,提出一种评价企业微博博文营销效果的量化方案。以当当网发布的微博博文及其转发与评论作为研究样本,依据评价方案筛选出营销效果排名前八的博文并作进一步分析,进而给出提升企业微博运营效果的策略建议。实验结果表明并不是博文转发数越多,营销效果就越好;互动影响力大的用户进行博文转发能够有效提升企业的微博营销效果。

西南桦组培苗培育的轻基质筛选

西南桦（Betula alnoides Buch.-Ham.ex D.Don）是我国热带、南亚热带地区的一个乡土珍贵用材树种,其适应性强、生长迅速、材质优良,深受林农、私营投资商、林业企事业单位的喜爱,已在该地区广为栽培[1],近10余年来推广面积达8万hm2。由于采用实生苗造林出现林分参差不齐、

白刺组培快繁的研究

验选用唐古特白刺嫩茎作为试验材料 ,来研究白刺的组培快繁技术。试验结果表明 ,白刺的启动最适培养基是 :MS+IBA0 .5 mg· L- 1 ;最适增殖、壮苗培养基是 :MS+ 6-BA0 .5 mg· L- 1 + NAA1.0 mg· L- 1 + GA32 .0 mg· L- 1 ;最适生根培养基是 :1/ 2 MS+ IBA0 .5 mg·L- 1。

中国甘草的组织培养研究进展

概述了国内在甘草植株再生、快速繁殖和毛状根培养方面的研究进展情况。甘草组织培养的基本培养基为MS,诱导培养基主要附加激素为2,4-D、6-BA和NAA,其中6-BA(0.2￣1.0mg/L)必不可少;分化培养基以MS无机元素和B5的有机成分为基本培养基,并附加ZT、BA、KT,三者可单独使用或配合NAA使用;生根培养基主要是添加NAA(0.05￣0.01mg/L)。能分化成苗的外植体仅有下胚轴,而且分化率极低,仅为3%￣6%。快速繁殖方法有腋芽丛状茎生根成苗和带叶茎段直接生根成苗两种,其中带2叶茎段成苗繁殖系数最高,达到98%。发根农杆菌ATCC15834感染甘草下胚轴诱导产生毛状根效果最好,诱导率高达30%。毛状根的最佳培养条件是:50mg/LKNO3,100mg/LCaCl2·2H2O,0￣225mg/LKH2PO4,640mg/LMgSO4·7H2O,微量元素及有机物质采用B5水平,32.5g/L蔗糖,转速100r/min,pH6.2左右,通过毛状根的培养可获得原植物中含有的或者不含有的化合物。

洋桔梗叶片培养不定芽发生和微繁研究

以洋桔梗叶片为材料,建立了洋桔梗叶片高效不定芽发生、植株再生体系。研究了不同激素及其组合对外植体不定芽发生、壮苗和生根的效应。结果显示,MS+BA 1mg/L是叶片不定芽发生的适宜培养基;MS+BA 0.1mg/L+NAA 0.05mg/L是试管嫩梢形成壮苗的适宜培养基;MS+IAA 0.1mg/L培养基是壮苗生根的适宜培养基。草炭珍珠岩基质是生根苗移栽的适宜基质。