Study on Antibacterial Effects of Extracts from Pinus massoniana Lamb.Needles

[Objectives]To study the antibacterial effects of extracts from Pinus massoniana Lamb.needles.[Methods]In this experiment,the components from Pinus massoniana Lamb.needles were extracted by systematic solvent extraction method,and the antibacterial activity against four common bacteria,Escherichia coli,Staphylococcus aureus,Bacillus subtilis,Aspergillus flavus and the antibacterial active component were examined for by punch method.[Results]Different solvent extraction rate was different,the rates of petroleum ether,chloroform,ethyl acetate,n-butanol,water extracts were 4.2%,16.7%,17.4%,21.1%,40.6%.All extracts showed inhibitory effect against test bacteria.It was observed that the inhibition of G+was stronger than G-,and the extracts had the best antibacterial activity to Staphylococcus aureus while the weakest to Aspergillus flavus.The antibacterial activity of the components decreased in the order:ethyl acetate extract>n-butanol extract>chloroform extract>petroleum ether extract>aqueous phase.The extracts were stable under ultraviolet radiation(UV)light and long term storage.The antibacterial activity of the extracts was weaker with the increase of pH value when the pH value≤8.[Conclusions]It is inferred that the antibacterial components in the extract of Pinus massoniana needles are widely distributed,and the components with medium polarity or above are the main antibacterial components.

Branching and growth of plantings in fifth year of a seedling seed orchard of Masson pine (Pinus massoniana Lamb.)

The features of branching and growth studied included height, diameter at breast height (DBH), total number of branches, annual height growth, annual branch elongation in the year of elongating, annual branch number for four consecutive years, diameter of branches of different ages, and diameter of stem where branch-whorl originates. For features of total growth and overall branching, no significant differences were found between families, except for DBH. For annual features, no significant differences were found in annual stem height growth, annual branch elongation in the year of elongation and diameter of branches. In the last four years, differences in number of branches were not significant in the first two years but were significant in the last two year; differences in stem diameter where branch-whorls grow were significant for the four consecutive years. Trend of annual growth and branching features of families can be divided into three types as increasing type, stable type and fluctuating type. Most of families have an increasing type with respect of annual height growth and annual branch elongation, while most families belong to a fluctuating type with annual branch number. The results indicated that in the fifth year after planted in seedling seed orchard, differences between families were mostly insignificant. This result may have two main explanations: one is the growth rhyme in early ages of Masson pine, the other one is the complex paternal components to form the open-pollinated families. Family selection seemed to be not useful based on the result. It is suggested to select some of families in the nursery instead of to use all the families when establishing seedling seed orchards with open-pollinated families from plus-trees.

Metal pollution in relation to mass outbreaks of Dendrolimus punctatus Walker on Pinus massoniana Lamb.in China

Insects with their ecological superpower have enormous capacity to transform small pollution damage in forests to full scale calamities. Acid rain resulting from extensive coal burning is the chief pollutant in China. Acid rain activates from soil deposits toxic metals, which are transferred to trees and further to insects eating them. We studied the levels of the toxic Cd, its antagonists Zn and Cu, and acid rain indicators Fe and Mn in the forest pest moth Dendrolimus punctatus Walker (Lepidoptera:Lasiocampidae) in variously polluted Pinus massoniana Lamb forests in China.\; The highest density of D. punctatus , as well as the highest Cd levels developed in the moderately polluted forests. Possibly Cd had there broken down the pest resistance of the pines. The paradoxical coexistence of high Cd level and elevated population density of the pest seems to result from the high accumulation of Cd in its ichneumonid parasitoid. In the most heavily polluted forests the Cd level in needles was low, possibly because the strong acid rain had washed away most of the Cd deposit in the soil. It existed there no D.punctatus population. Absence of pest insects from the most heavily polluted areas is a common phenomenon.

Plantlet regeneration from mature zygotic embryos andembryonic explants of masson pine (Pinus massoniana Lamb.)

Excised zygotic embryos, cotyledons and hypocotyls of juvenile seedlings of masson pine were grown on DCR medium supplemented with several concentrations of various plant phytohormones. BA (1.0 mg/ L) in combination with NAA (0.05 mg/L)in DCR medium was found to increase the formation of adventitious buds from mature zygotic embryos, but most of them were formed at the tips of embryonic cotyledons. Adventitious buds were obtained from cotyledons and hypocotyls from juvenile seedlings when they were cultured on DCR medium containing BA 3-5 mg/L and NAA 0.1-0.2 mg/L. Elongation of buds were observed on hormone-free DCR medium with or without activated charcoal (0.5%). Root initiation was achieved with full or half strength DCR inedium supplemented with IBA 1.0 mg/L and NAA 0.25-0.5 mg/L. Approximately 11-20 axillary buds formed on each explant when juvenile seedling explants were treated (3-20h) with BA 50-100 mg/L, followed by transfer to hormone-free DCR medium. The maximum number of shoots obtained per explant within six months was 33.

Patterns of variation in chemical compositions of wood from natural populations of Pinus manssoniana Lamb.in Guizhou Province,China

Patterns of variation in the chemical composition of wood, i.e., holocellulose, cellulose and lignin contents and 1% NaOH extractives were studied in 12 natural populations of Pinus manssoniana Lamb. in Guizhou Province, China, using wood cores as experiment material. The results show statistically significant differences among provenances in holocellulose, cellulose and 1% NaOH extractive contents. The largest coefficient of variation among the provenances was found in the 1% NaOH extractive content and the smallest in the holocellulose content. Variation of lignin content occurred within provenances. Correlations between chemi- cal compositions of wood and factors of local geography and meteorology were largely insignificant. The chemical composition of wood presented patterns of random variation. The correlation of 1% NaOH extractive content with holocellulose content was sig- nificant （r = -0.68）. There was also significantly negative correlation （r = -0.62） between cellulose and lignin content. On the basis of a UPGMA cluster analysis, we identified three provenances of masson pine among the 12 studied, i.e., those of Wengan, Tongzi and Luodian with high cellulose contents, low levels of 1% NaOH extractive and moderate lignin contents, which we recommend as promising provenances for growing of pulp wood and the manufacture of paper in Guizhou Province.

基于Barker码脉冲压缩技术的钢板多阵元Lamb波电磁超声换能器设计与优化

为了解决传统Barker码脉冲压缩技术受脉冲功率放大器额定参数(占空比,最大脉冲宽度等)限制而导致的脉冲压缩效果下降、检测速度降低等问题,提出一种基于Barker码脉冲压缩技术的多阵元Lamb波电磁超声换能器(EMAT)。建立了基于tone-burst信号激励-Barker码脉冲压缩技术的多阵元Lamb波EMAT检测过程的有限元模型,分析了永磁体的配置形式、阵元序列长度、激励信号周期数、曲折线圈匝数等因素对脉冲压缩后的主旁瓣比和主瓣宽度的影响,并进行了实验验证。结果表明:曲折线圈匝数为4和Barker码序列长度为13位的多阵元EMAT在配置3对外置永磁体后,其信噪比(SNR)可提高9.8 dB。综合考虑检测回波的空间分辨率和SNR,多阵元Lamb波EMAT最佳参数为:曲折线圈匝数为10、激励信号周期数为11、Barker序列为13位,并配置3对外置永磁体。

基于Lamb波损伤特征融合模型的金属结构件疲劳裂纹扩展预测

针对动态载荷环境下机械装备金属结构件疲劳裂纹扩展延伸问题,提出一种基于Lamb波损伤特征融合的疲劳裂纹扩展预测模型。首先从Lamb波信号传播特性出发,分析对比对称模式下Lamb波损伤信号和基准信号传播过程中的特性变化,在此基础上提取能够敏感表达结构损伤的相关系数和相位差异特征,通过变量标准化变换后进一步构建出疲劳裂纹扩展预测模型,最后利用金属结构件全寿命周期疲劳实验数据对模型进行验证。结果表明:所提模型能够准确预测动态载荷环境下疲劳裂纹扩展过程,与其他预测模型相比优势明显,可为机械装备关键结构件合理检修计划制定提供一定参考借鉴。

基于Lamb波与虚拟时间反转的延时叠加成像算法

针对传统的延时叠加成像容易产生伪像而导致缺陷不易识别且成像清晰度差的问题,提出采用虚拟时间反转技术与椭圆定位法初步定位损伤区域,进而在对应的时间窗内截取差信号,最后结合延时叠加成像技术解决了伪像和清晰度问题。以ABAQUS软件仿真的方式模拟Lamb波在损伤铝板中的传播过程,首先利用虚拟时间反转法对初次响应信号进行处理而获得聚焦重构信号,然后利用准确的时间延时作椭圆以初步定位范围,从而得到对应的时间窗来截取差信号,最后结合延时叠加成像技术对损伤进行成像。仿真和试验结果表明:该方法降低了操作难度,提高了成像清晰度,能准确有效地识别损伤位置,提高了铝板的损伤定位检测精度。

融合Radon变换的孔边裂纹Lamb波定位成像研究

基于不同模态Lamb波与孔边裂纹相互作用的基本原理,聚焦不同模态Lamb波波包飞行时间精确检测问题,以各向同性板中的孔边裂纹为研究对象,开展了融合Radon变换的孔边裂纹Lamb波定位成像研究。首先,使用宽频chirp信号激励稀疏传感器阵列产生Lamb波,并采集通孔散射信号作为基线信号,采集孔边裂纹散射信号作为缺陷信号。其次,对chirp响应信号进行滤波处理,优化选取窄带单音频脉冲响应信号的中心频率和调制周期数。然后,对基线单音频脉冲响应信号进行Radon变换,得到优化后的群速度和偏移时间,并计算出Lamb波波包飞行时间。最后,使用椭圆定位成像算法对孔边裂纹进行定位成像,并将成像结果与名义群速度法的结果进行对比。结果表明,使用Radon变换可以准确获取Lamb波波包飞行时间,提升了不同模态Lamb波对孔边裂纹缺陷的检测能力。

基于混叠模态Lamb波能量衰减特性的液位检测研究

提出了一种利用混叠模态Lamb波检测液位的方法。利用具有单侧液体负载的Lamb波的频散方程求得了相速度频散曲线,分析了波的离面位移和接收信号能量衰减的关系,选择激励了对液位变化敏感的Lamb波模态。仿真计算了不同角度入射波对应的混叠接收时域信号及其对应的能量。实验测试结果表明,包含B4模态波为主的混叠波的检测区分度远高于其他模态混叠波和纵波,该结果与理论计算相符。

利用Lamb波时间反转法的套筒灌浆连接缺陷位置检测

针对装配式建筑中套筒灌浆连接件缺陷位置难确定的问题,建立套筒灌浆连接结构有限元模型,采用Lamb波研究套筒灌浆连接结构中的传播规律.在确定最佳激励信号的基础上,检测出灌浆料损伤缺陷位置,同时设置无损伤测区与有损伤测区.结果表明,有损伤测区聚焦峰值与无损伤测区聚焦峰值均值相比下降11.70%,说明采用Lamb波时间反转法可实现预埋状态下套筒灌浆连接结构内部缺陷位置的判断.其对套筒灌浆连接缺陷定位是有效的,在结构无损检测领域具有良好的应用前景.

基于近似非凸RPCA的Lamb波损伤监测

在结构健康监测(Structural Health Monitoring,SHM)技术中,基于Lamb波的损伤监测方法在板状结构中显示出了巨大的潜力。提出了一种基于近似非凸鲁棒主成分分析(Approximate Non-Convex Robust Principal Component Analysis,ANC-RPCA)的异常值分析方法。该算法对于高维测量信号,能够在降维条件下实现有效的损伤诊断。通过使用秩近似函数逼近矩阵的秩,采用非凸惩罚函数逼近?_(0)范数,非凸惩罚函数在一定条件下可以保证稀疏解的唯一性。随着数据矩阵规模的扩大,传统的RPCA采用核范数近似时,奇异值分解的计算复杂度也会上升。新的近似方法能在使计算效率更高的情况下,针对波场图像能够在更低秩的水平下保留有效信息,识别出异常值。将该算法运用到基于Lamb波的波场图像中,通过仿真和实验数据验证其有效性,使用非精确增广拉格朗日乘子(Inexact Augmented Lagrange Multiplier,IALM)法求解,并与目前使用较多的主流RPCA算法进行了效果对比。实验结果表明ANC-RPCA算法在异常值识别中具有良好的性能,相较于其他算法,在计算效率和低秩性等方面具有巨大的优势,证明了所提算法的可靠性和完整性。

基于PVDF梳状换能器的零群速度Lamb波层合板损伤检测的数值研究

为提高层合板损伤检测的准确性与灵敏度,基于聚偏二氟乙烯(polyvinylidene fluoride,PVDF)梳状换能器激发的零群速度(zero group velocity,ZGV)Lamb波,提出了一种层合板损伤的检测方法。采用二维时域有限元方法,研究了PVDF梳状换能器对零群速度Lamb波的激励,通过改变层合板中铝层杨氏模量来表征不同的损伤程度,分析了PVDF梳状换能器电压响应特性与层合板损伤程度之间的关系。结果表明:采用PVDF梳状换能器能够有效激励零群速度Lamb波,并获得层合板内部的状态信息。随着损伤程度的增加,PVDF梳状换能器响应的零群速度共振峰频域幅值随着铝层杨氏模量的减小而显著减少,进而灵敏地评价层合板损伤变化。研究结果说明优化设计的PVDF梳状换能器在零群速度Lamb波的激发与接收性能上都具有优越性,能够有效检测层合板损伤情况。

基于Lamb波的CFRP层合板损伤类型检测和成像研究

采用数值分析方法对Lamb波两种不同的波模态传播特性进行分析,并利用其振动特性对CFRP(carbon fibre reinforced plastics)层合板中不同类型的损伤进行成像及识别。通过采用延时累加算法与缺陷概率检测重构算法相结合的成像算法对损伤进行成像研究。最后通过试验进行验证。研究表明:S0模态对于复合材料中的裂纹损伤更为敏感,而A0模态更适用于检测分层损伤;在实现Lamb波不同模态的单独激励后进行损伤检测成像,可根据损伤检测敏感性不同的特性对层合板中同时存在的损伤进行类型识别。成像结果表明所提出的方法能有效地检测出复合材料中存在的损伤并判断损伤类型。

用于ZGV Lamb波检测的PVDF梳状换能器及性能研究

能够准确激励与响应零群速度(ZGV)Lamb波的换能器是ZGV Lamb波检测应用的重要支撑。现有用于ZGV Lamb波检测的换能器存在信号弱、信噪比低等问题,为此,本文设计了一种柔性好、灵敏度高的聚偏二氟乙烯(PVDF)梳状换能器,并研究了换能器对ZGV Lamb波的激发响应性能。首先,分析了梳状换能器的工作特性,根据薄铝板的ZGV模式设计制作了PVDF梳状换能器;其次,在不同中心频率的脉冲信号下通过PVDF梳状换能器激发ZGV Lamb波,并与PVDF方形电极换能器做了性能对比实验;最后,分析了PVDF梳状换能器电压响应特性与附着层厚度之间的关系。实验结果表明,设计制作的PVDF梳状换能器能够精准的激励与响应ZGV Lamb波,其响应信号的ZGV频域幅值相对大小随着附着层厚度的增加显著减小。

正交异性钢桥面板横梁切口裂纹的Lamb波监测分析

为探究钢桥面板横梁切口裂纹的Lamb波技术监测效果,设计了2个钢桥面板足尺模型,通过循环加载使其横梁切口处发生疲劳开裂,利用Lamb波监测裂纹扩展情况,进而从波信号中提取标准化特征,用于评估裂纹扩展.建立并验证了钢桥面板有限元模型,进行了裂纹长度、传感器位置等各种参数分析,以确定最佳传感器布置.试验结果表明:当裂纹扩展长度与波传播路径垂直时,标准化特征增大;当两者路径平行时,标准化特征减小.参数化分析结果确定了切口处裂纹监测的最佳传感器位置,建议在选定横梁切口区域,预先布置1个激励器和4个接收器,激励器位于距切口50 mm处,接收器位于距离切口50 mm处或距顶板50~100 mm处.

基于Lamb波的损伤铝板信号获取仿真研究

为了分析Lamb波在健康铝板和通孔铝板上的传播规律,提出基于Lamb波的损伤信号获取仿真方法。首先绘制3 mm铝板的群速度和相速度频散曲线,然后调制激励信号,在有限元软件Abaqus中建模仿真,获得Lamb波在铝板上的信号,最后再将各信号带入损伤因子公式中计算SDC值。研究结果表明:距离激励点的位置越远,Lamb波衰减的越厉害;相同位置,接收到完整板的信号幅值大于损伤板;传感器距离损伤位置越近,损伤因子越大。研究结果为无损检测成像技术提供理论支持。

北极冰层反射系数与Lamb波频散的关系

为获得北极冰层反射系数与Lamb波的关系,应用传递矩阵法分析了冰层反射系数实虚部、模值范围与冰层自由Lamb波、漏Lamb波频散的关系。获得了冰层自由Lamb波频散曲线与反射系数的对应关系;针对漏Lamb波相速度大于冰层纵波声速,振动模态无法识别的现象,通过调整冰−水界面耦合条件,得到改进后的漏Lamb波频散方程,获得小角度入射时冰层漏Lamb波振动模态与反射系数的关系,并结合北极跨冰层检波实验数据进行了验证。结果表明,反射系数小于1的频段声波激发了相应频段的冰层Lamb波。此外,根据改进的漏Lamb波频散方程进一步获得了多层冰层漏Lamb波频散曲线。

套管中弯曲型Lamb波数值仿真和物理模拟

低密度水泥在低压易漏复杂井固井中的广泛应用使得声阻抗类测井方法难以准确、有效地评价固井质量。基于套管中传播的弯曲型Lamb波对套后介质的声学参数和胶结状况的敏感性,该文通过理论计算和实验测量研究了不同频率下弯曲型Lamb波衰减与水泥声学性质的关系,较低的工作频率会使得不同水泥阻抗下的衰减动态变化范围降低,且对水泥环第I界面的窜槽厚度也有很高的灵敏度;利用套管外胶结流体和固体时衰减的差异,还可较好地区分套管外声阻抗接近的流体和固体;但弯曲型Lamb波的同一个衰减值可与两个水泥声阻抗值相对应,因此需通过建立弯曲型Lamb波的衰减与水泥声阻抗的解释图版以提高低密度水泥固井质量评价的可信度。该文的计算分析结果对进一步应用弯曲型Lamb评价低密度水泥具有指导意义。

稀疏阵列下基于机器学习多模Lamb波损伤监测

复合材料结构损伤机理复杂,形式多样,对工程结构的安全带来潜在的风险,也使得结构健康监测研究中的损伤程度辨识存在很大的困难。针对上述问题与实际工程应用场景,研究基于稀疏阵列的多模态Lamb波损伤识别方法。分析多模态Lamb波在复合材料结构中的传播过程及损伤作用机理;设计稀疏压电阵列,提高工程应用实用性;采用Fisher线性判别原理,分析提取识别损伤区域下的最优监测路径;最后,基于损伤机理分析,提取Lamb波结构响应时域、频域、时频域多特征参数,建立基于支持向量机的损伤监测与评估模型。实验验证表明,基于稀疏阵列的多模态Lamb波损伤辨识技术能够识别任意区域、不同程度的损伤,识别率为93.75%。