关于门式起重机主要部分杆件应力的测定及分析

本文根据各类型杆件断面在不同载荷作用下的应力分布规律，得出门式起重机主要部件杆件的应力分析和测定方法。从而为门式起重机的拓展应用、性能安全和高效运作提供了技术保证。     

龙门起重机测试结果与分析

龙门起重机测试项目主要是检测其静刚度、动刚度,主要杆件的静应力、动应力、振动等。本文通过对朗乡林业局贮木场龙门起重机的测试及对测试结果的分析,得出该龙门起重机在额定载荷30t·f 下工作,其刚度、主要杆件强度、振动等条件均满足要求。     

树木生长过程中产生的残余应力的测试分析

本文利用将树干视为均质正交各向异性圆柱体推导出的方程,并通过试验确定了树木生长应力。根据大量测试数据的处理结果,得出了实测树干生长应力分布图。同时,对其分布情况进行了讨论与分析。     

用有限元法对热压机机架的应力分析

介绍了应用有限元法对热压机机架进行应力应变计算过程，并对应力、应变进行了分析，提出了改善机架应力状态的措施。     

框架式压机机架应力的有限元分析及结构改进

介绍了应用有限元法对框架式压机机架进行应力、应变的计算和分析,提出了改善机架应力状态的措施.     

木材干燥应力的研究方法与进展

木材干燥应力的研究对丰富和完善木材干燥理论、建立和完善干燥工艺、提高干燥质量和经济效益具有重要意义,许多研究者从不同角度对木材干燥应力应变进行了试验测定及数值计算.本文对其中的主要研究方法进行了较详细的归纳,并对今后的研究提出了看法和建议.     

锯链传动链片的有限元分析

用有限元法对锯链的传动链片进行了应力分析，结果表明：危险剖面上的应力分布是不均匀的，在运转中传动链片所受的应力为变应力，按传统的方法仅计算静强度是不够的，要提高锯链的使用寿命，必须提高锯链零件的疲劳强度。     

基桩动态响应特性分析

通过对基桩做一定的假设后,将其简化为一维弹性杆件,根据基桩埋置于地下后的受力情况,推导了应力波在桩身中传播的阻尼波动方程.分别对完全摩擦桩、端承桩、摩擦端承桩分析了其位移和速度的动态响应,并对其多频谐振特性进行了分析.同时指出,可以在频率域中分析桩身的完整性,并根据桩底的嵌固系数来判断基桩与持力层的接触情况.     

水曲柳木材裂纹尖端应力强度因子研究( 英文)

该文研究了水曲柳 (FraxinusmandshuricaRupr .)木材发生Ⅰ型断裂时裂纹尖端的应力场应力强度因子的情况 .借助美国大型通用有限元分析软件NASTRAN计算出裂纹尖端附近的应力 ,并通过GRAFTOOL软件对数据进行后期处理 ,画出裂纹尖端附近的应力强度因子分布图     

G-300荷载作用下重力式路肩挡土墙基底应力分析

基于挡土墙计算基本理论,阐述了计算步骤与方法,在对计算结果进行分析的基础上,总结出内坡比与基底应力的对应变化规律.文章的分级思维模式、计算步骤和方法以及结论等,对重力式路肩挡土墙基底应力的计算具有较好的借鉴和参考价值.     

白梭梭同化枝对干旱胁迫的生理生态响应

对白梭梭同化枝自然水分胁迫下的季节抗旱特征进行研究。结果表明:自然干旱胁迫条件下,不同生长发育时期同化枝的主导抗旱生理因子不同。5月31日至6月29日盛花期间,同化枝内源ABA含量甚微,气孔导度值与光合强度处于生长发育过程的最高水平,可溶性糖含量呈现下降趋势,而脯氨酸含量略有增加,植物通过渗透调节作用适应此阶段轻度干旱胁迫;6月29日至7月26日盛夏期间,ABA迅速积累,气孔导度值降为生长发育过程的最低值,叶绿素分解,可溶性糖与脯氨酸均呈现快速积累趋势,且可溶性糖积累强度大于脯氨酸;8月9日至8月22日同化枝生长发育后期,ABA急剧积累为生长发育过程的最高浓度,气孔导度值有所增大,脯氨酸和可溶性糖保持在高水平平稳变化。此阶段高浓度ABA调节植物生理过程适应干旱的效应受CTK、IAA两种内源激素的抑制,进而抑制脯氨酸和可溶性糖的继续积累。     

Physio-ecological response of Haloxylon persicum photosynthetic shoots to drought stress

This paper studied the seasonal characteristics to resist the drought stress of Haloxylon persicum Bge. Ex Boiss. et Buhse photosynthetic shoots at habitat. The results showed that the predominant drought resistance factors were varied at the different stage from growth to development. In the blooming season (from May 31 to June 29), endogenous ABA contents were rare; stomatal conductance and photosynthesis intensity were the highest at the whole stage from growth to development; soluble sugars contents had a decreasing trend and proline contents increased a little that made proline become the predominant factor to resist the drought under this light water stress. In the hot summer (from June 29 to July 26), ABA contents accumulated rapidly; stomatal conductance dropped to the lowest level of the growth and development; chlorophyll was also decomposed; both soluble sugars and proline contents showed the trend of quickly accumulating, but the former was faster than the latter. It was due to stomatal limitation and osmotic organic molecules accumulation that would affect the photosynthetic shoots to resist severe drought stress. At the late period of the development (from Aug 9 to Aug 22), ABA rapidly accumulated, its contents got to the highest level of whole life-span; stomatal conductance increased a little; proline and soluble sugars contents changed little at high level; while the ratios of ABA to CTK content and ABA to IAA content got up obviously, the effect to resist drought stress on high content ABA was inhibited by endogenous plant hormone CTK and IAA, then the continuing accumulation of proline and soluble sugars would be prevented. Osmosis of organic molecules was the most important factor to adjust leaves to severe water stress at this period. __________ Translated from Scientia Silvae Sinicae, 2005, 41(5) [译自, 林业科学 2005, 41(5)]     

不同杨树无性系光合作用与其抗旱能力的初步研究

不同杨树无性系光合作用与其抗旱能力的初步研究刘建伟，刘雅荣，王世绩（中国林业科学研究院林业研究所北京１０００９１）关键词杨树无性系，光合作用，水势补偿点，水分胁迫，抗旱在水分逆境的研究中，净光合速率的降低已成为显著的特征，针叶、阔叶树的种间变化曾有许...     

天然林落叶松锯材机械应力分等法与四点弯曲性能相关性研究

采用机械应力分等法对天然林落叶松锯材进行动态弹性模量EMSR测定，依据美国标准ASTM D 4761-05测量其四点平弯与侧弯的弹性模量E4f、E4s和抗弯强度（MOR），并分析EMSR与E4f、E4s、MOR的相关性。结果显示，EMSR与E4f、E4s相关性存在较大差异，且后者高于前者。相关系数分别为0.555、0.681。 E4f、E4s与MOR相关性高于EMSR与MOR的相关性，E4s与MOR的相关性高于E4f与MOR的相关性。实验表明，采用机械应力分等法提高木材分等准确性还需进一步研究。     

淹水胁迫对南五味子和海南红豆幼苗光合特性的影响

对南五味子和海南红豆的1年生实生苗在不同淹水时间下的叶片的光合特性进行了研究。结果表明:随着淹水时间的持续,南五味子幼苗的净光合速率(Pn)小幅波动后升高,而气孔导度(Gs)、蒸腾速率(Tr)和胞间CO2浓度(Ci)先降后升,至淹水20 d时各指标均高于对照;海南红豆幼苗的Pn、Gs、Ci、Tr先降后升,至淹水20 d没有恢复到对照水平;2种幼苗的气孔限制值(Ls)均为先升高后下降;南五味子和海南红豆都有一定的抗涝性,前者具有更强的耐淹水能力。     

两种地被植物的抗旱性研究

采用盆栽试验研究干旱胁迫下2种地被植物金叶过路黄(Lysimachia nummularia‘Aurea’)、过路黄(Lysi-machia christinaeHance)的抗旱生理表现。结果表明,随着干旱胁迫程度加强,2种植物的叶片相对含水量呈缓慢下降趋势;相对电导率逐渐增大;丙二醛(MDA)含量呈上升趋势。胁迫初期SOD活性、可溶性蛋白含量小幅度增加,随后呈缓慢下降。金叶过路黄可溶性糖含量先升后降,过路黄则一直呈现缓慢上升趋势;综合各项指标,过路黄抗旱性强于金叶过路黄。     

干旱胁迫对麻栎无性系蒸腾作用的影响

以13个3年生麻栎无性系为研究对象,采用盆栽试验方法,研究了在持续干旱胁迫条件下的麻栎无性系土壤水势、叶片水势光合速率和蒸腾速率变化规律及其关系。结果表明,随着干旱胁迫的加剧,13个麻栎无性系土壤水势呈现出不断下降的变化趋势,叶片水势的变化无一致规律,光合速率则先下降而后上升,蒸腾速率的变化规律不尽相同。在13个麻栎无性系中,2、4、5、7、9和16号无性系的蒸腾速率、叶片水势和光合速率具有相同规律,随着干旱胁迫的加剧先下降而后上升,具有较强的适应干旱逆境的能力。对不同干旱条件下无性系的蒸腾速率、土壤水势、叶片水势和光合速率的相关性分析发现,干旱胁迫7天时,蒸腾速率和光合速率达极显著正相关;干旱胁迫12天时,蒸腾速率和土壤水势间呈极显著负相关,光合速率与土壤水势呈显著负相关;干旱胁迫17天时,蒸腾速率与光合速率呈显著正相关。     

人工林马尾松晚材率、年轮宽度和组织比量变异研究

对22年生人工林马尾松木材年轮宽度、晚材率和组织比量进行系统的测量、统计和分析，结果表明，年轮宽度随树龄增加先增加后减小，而随树干高度的增加先减小后增加。晚材率随着树龄增加呈波动增大，而随树干高度的增加呈逐渐减小趋势。木射线比量和树脂道比量随树龄增加呈波动增大，但总体变幅不大，而前者随树干高度的增加呈波动减小，后者先减小再增大。管胞比量随树龄增加呈波动减小，而随树干高度的增加先增加，达到一定值后减小，然后再增加。方差分析表明，年轮宽度、晚材率、组织比量在各年轮间、各高度间差异显著或极显著。     

干旱胁迫对黄山紫荆生长形态和生理特性的影响

采用盆栽控水法研究黄山紫荆Cercis chingii 1年生幼苗在干旱胁迫下的形态变化和生理响应机制.结果表明,随着干旱胁迫时间的增加,黄山紫荆的叶片、嫩枝逐渐出现萎蔫、枯落;在干旱胁迫15 d时,叶片中的可溶性糖、可溶性蛋白、丙二醛(MAD)含量和抗氧化酶活性开始升高;持续干旱胁迫20 d时,抗氧化酶的活性如CAT...     

Influences of Thinning and Prescribed Fire on Water Relations of Jeffrey Pine I. Xylem and Soil Water Potentials

Abstract

Forest thinning accomplished with cut-to-length and whole-tree harvesting systems, and prescribed underburning were assessed for their impacts on water relations in eastern Sierra Nevada Jeffrey pine (Pinus Jeffreyi Grev. & Balf.) during a period of extended drought. Predawn and midday measurements of xylem water potential in dominant and codominant crown class trees more than a century old were made on six days spread over three growing seasons, accompanied by measurements of soil water potential completed between the predawn and midday sessions of each day. With the exception of a single predawn session, the only one of a total of 12 in which xylem water potentials did not differ among treatments, the potentials in trees of thinned stand subunits were 0.67 MPa higher on average during predawn sessions and 0.71 MPa higher during midday sessions than those in trees of the unthinned treatment. Differences between the cut-to-length and whole-tree treatments were marginal and uncommon, but when they occurred, potentials were higher in the former. Prescribed fire effects on xylem water potential were also uncommon, but when occurring generally indicated lower stress levels in the burned than in the unburned treatment. Soil water potentials largely coincided with those of xylem water, with higher potentials in either the cut-to-length or whole-tree treatments, and usually both, than in the unthinned treatment on each of the six days of measurement. Underburning influences on soil water were rare, but when evident, potentials were higher in the burned than in the unburned treatment by substantial margins. For a majority of the measurement sessions, xylem water potential was found to be negatively correlated with residual basal area but positively correlated with soil water potential. In turn, coarse fragments and organic matter in the soil profile intermittently influenced soil water potential, with the former a negative factor while the latter was positive. Overall, results of this study suggest that substantial ecophysiological advantages can be derived from density management in older, dry site forests, which at minimum are not compromised by subsequent implementation of controlled underburning.