基于实验模态分析理论的木／竹复合板物理参数识别试验研究

基于实验模态分析(EMA)理论,利用脉冲激励试验和CRAS V5.1分析软件得出木/竹复合客车底板的物理参数,为木/竹复合客车底板的动态设计和动力特性改进提供依据.     

大跨度钢管混凝土拱桥空间地震响应分析

建立了四川白日坝大桥的空间有限元模型,研究了该桥的自振特性并讨论了结构主要参数对其动力特性的影响,然后对该桥在一致激励、行波效应、多点激励下的结构响应进行了分析,并考虑了几何非线性对结构地震响应的影响.得出了一些有益于工程的结论.     

略论中国股票期权激励的有效性

股票期权激励的目标在于统一经营者与股东利益，解决委托代理问题。文章在阐述股票期权激励影响因素的基础上，对中国股票期权激励的有效性进行了概要性分析，认为中国上市公司治理结构中的股票期权激励是弱有效的。     

脉冲磁场对葡萄座腔菌生长及侵染的影响

利用脉冲磁场研究在固定脉冲前沿宽度10ms条件下,不同脉冲时间对葡萄座腔菌生长及侵染的影响。结果表明:短时间内的脉冲磁场处理即可有效抑制葡萄座腔菌的生长及侵染能力,处理时间越长,抑制作用越强。当脉冲处理45min时,菌落生长48h的抑菌率为54.11%,接种葡萄座腔菌的毛白杨愈伤组织72h后的褐化指数仅为26.89%。当脉冲处理60min时,抑菌效果最好,菌落全部死亡。扫描电镜观察结果可知:与对照相比,脉冲磁场处理的葡萄座腔菌的菌丝粗细不均,表面皱缩;菌丝体之间相互粘连,部分菌丝分枝、干瘪。透射电镜观察可知:脉冲处理后菌丝的细胞壁变薄,细胞内部组成紊乱、降解,细胞结构破坏严重,胞内空腔增多;同时毛白杨愈伤组织的细胞结构受到葡萄座腔菌不同程度的破坏,细胞壁变形、解体,中胶层分解,质膜断裂,质壁分离;细胞器分解沉积于细胞壁附近,细胞内菌丝降解,管腔空化。脉冲磁场对葡萄座腔菌的生长及侵染具有较强的抑制作用,可改变菌丝超微结构。     

简支梁在动载荷作用下竖向动挠度的计算理论研究

本文对简支梁在匀速常量力和匀速脉冲力的作用下，应用结构动力学理论，对梁的动力响应给出了近似解答。     

林业发展与政策困境:国家政策与森林

森林与用于影响国家社会、政治和经济关系的总的政策结构密切相关。这种政策结构对全国范围内的森林利用产生了不同的激励作用和机会。     

数控木工加工中心伺服进给系统设计与仿真

根据数控木工加工中心伺服进给系统的特点,通过对其机械传动机构进行设计计算确定其主要结构尺寸和选择驱动元件;并建立了伺服驱动系统数学模型,对此非线性离散控制系统进行了仿真,得出了数字控制器的脉冲传递函数.     

大跨度步行桥人行激励的 TMD 水平向减振

大跨度步行桥在人行激励下的水平振动将引起行人不适和结构损坏,为了对大跨度步行桥人行激励水平振动进行减震控制,以某大跨度景观步行桥为例研究了人行激励的特征和步行桥的振动特性,以人行桥舒适度为目标进行了TMD控制设计,通过数值分析进行了减振控制研究。研究结果表明,TMD质量比取1%~3%时有明显的减震效果,且TMD质量块越大,控制效果越好;TMD水平减振对大跨度步行桥人行激励引起的水平振动减震效果明显,位移和加速度控制效果分别达到21.3%和20.2%;MTMD的控制效果要比单个TMD的控制效果要好,但当数目超过5个时,随着TMD的个数增多,控制效果增加的并不明显。     

二.脉冲式烟雾机的构造和工作原理

烟雾机是森林病虫害烟雾载药防治技术的配套设备。按照产生烟雾的方式，烟雾机分为常温烟雾机和热烟雾机两种。热烟雾机采用高速气体的动能和热能使油烟剂雾化，脉冲式烟雾机是其中的一种。该机（以下简称烟雾机）用脉冲喷气式发动机为动力，它有结构简单，重量轻，操作容易的特点。1烟雾机的构造烟雾机由脉冲喷气式发动机、供药系统、操作部件及机架四部分构成。图1示6HY～25型烟雾机，今以此机为例说明其构造。1．1脉冲喷气式发动机脉冲喷气式发动机是产生高速、高温燃气的装置。发动机产牛的燃气本面给药液雾化提供能量，一小部分气流从…     

定向结构板热物理特性的研究

采用热脉冲法测定杨木定向结构板的热物理特性,研究板材的密度、含水率对其热物理特性的影响,获得了绝干、气干及高湿度状态下各种不同密度的定向结构板的热导率、热扩散率、比热容的变化规律,以此为建筑热工设计提供依据。通过对不同材料建筑物的采暖能耗的对比分析得出,定向结构板具有良好的保温隔热性能,用作墙体材料可达到节能目的。     

Can the impulse propagation speed from cross-section tomography explain the conditioned density of wood?

Tomography is a wave-based technique used to depicture tree cross-sections; specifically, impulse tomography uses data given by the passage of impulse waves, which were primarily influenced by density, modulus of elasticity, and moisture content of wood. The influence of wood characteristics on various kinds of waves has been extensively studied, allowing the establishment of statistical correlations between wave behavior and wood properties. In this context, the relationship between impulse speed from cross-section tomography and conditioned density that was obtained on diametrical sample by X-ray densitometry was analyzed using logs of three tree species with different densities that were air dried to 12 % moisture content. For each species, means from 5 mm length intervals of conditioned density profile graph (ρ _12%) and impulse speed distribution graph (S _12%) on the same diametrical sample are used to fit models. Joining data from all species, the exponential model \( \ln \rho_{12\% } = - 4.32822 + 1.67894 *\ln S_{12\% } \) was obtained with correlation coefficient of 0.85 and highly significant parameters. The results indicate that conditioned density could be explained by impulse speed on the cross-section, but research is necessary to make a useful tool out of it.     

古建筑木结构的无损检测新技术

将三维应力波断层扫描仪和阻力仪应用于古建筑木结构的勘查中.试验室预试验及现场勘查实例证明,三维应力波断层扫描仪完全适用于木构件的勘查,与阻力仪结合使用,可使勘查操作更便捷,结果更准确.     

Effect of electric impulse on sporocarp formation of ectomycorrhizal fungusLaccaria laccata in Japanese red pine plantation

We examined the effect of electric impulses on sporocarp formations of ectomycorrhizal fungus in a Japanese red pine (Pinus densiflora) plantation.Laccaria laccata was the dominant species in this study plantation. Spatial distribution concentrated in the electric impulse treatment zone, and recorded a markedly larger number of sporocarps compared with untreated control plots. The effect of electric impulses was also recognized onL. laccata fruiting with a mycorrhizal sapling in a pot. Sporocarp production ofL. laccata was strongly promoted by the electric impulse in experiments bothin vivo natural plantation stands andin vitro pot saplings. Our work indicates the possibility of enhancement of sporocarp production of the mycorrhizal fungi with electric impulses in the nursery and plantation. This work was partly supported by a grant from the Kyushu Electric Power Company.     

水泥刨花板制作轻质条板工艺技术的研究

根据我国水泥刨花板在建筑上的应用情况 ,研究以水泥刨花板为原料 ,加工制作轻型墙体条板的结构及生产工艺技术 ,这种轻质条板的开发与应用必将推动水泥刨花板在墙体材料方面的应用     

Effect of thermal high-frequency surface hardening on the hardness and microstructure of bandsaw teeth

Summary Examination of the bandsaw teeth (1) untreated, (2) swaged and (3) treated by thermal high-frequency surface hardening method has shown that their average microhardness is 473 DPN (<46 R_c), 502 DPN (<49 R_c) and 836 DPN (>62 R_c) respectively.Scanning electron microscopy revealed that no significant change occurred within the crystalline microstructure of untreated and swaged specimens. The high-frequency treated specimen, however, has shown a definite structural modification of a very finely grained martensitic type, extending from the apex for a distance of 0.24 mm.The relationship between DPN microhardness distribution throughout the bandsaw steel and the range of H.F. impulse times from 24/50 to 36/50 of a second was also investigated, and depth of the hardened zone determined.The optimal H.F. impulse time length corresponding to the optimal tooth hardness appears to lie between 32 and 33/50 of a second. Operating with 32/50 impulse time on a conventional 2.41 mm thick SANDVIK bandsaw with 0.73 mm side swage, it was found that the average hardness of a H.F. treated tooth apex is about 905 DPN (>64 R_c) to a depth of 415 m and in practical terms approaches the estimated optimum for high-speed cutting.     

Excitation wavelength-specific changes in lignocellulosic autofluorescence

Lignocellulose (paper sheets of thermomechanical pulp) was irradiated with specific wavelengths in an epifluorescence microscope equipped with filter cubes with excitation and emission filters commonly used for excitation of fluorophores with blue, green, and red emissions. The irradiation was shown to affect the relative autofluorescence intensity over time. Shorter wavelength excitation (λ_ex = 340–380 nm) induced photoyellowing that increased the autofluorescence. Filter cubes allowing irradiation at longer wavelengths (λ_ex = 450–490 nm and λ_ex = 515–560, respectively) caused photobleaching and a decrease in lignocellulosic autofluorescence. The increase and decrease in autofluorescence was reversible; prephotoyellowed samples could be photobleached and prephotobleached samples regained autofluorescence by shorter wavelength irradiation. Thus, the specificity of the excitation wavelength and the time-dependent autofluorescence might affect long-term imaging experiments of lignocellulose-based samples.     

配电系统中浪涌保护器的选择和安装

随着电子信息设备的大量应用,雷击电磁脉冲和雷电过电压对设备和系统所造成的损坏日显严重。因此,解决雷击对建筑物电子信息和配电系统所造成的损害变得十分重要。本文简要阐述了在配电系统设计中如何选择浪涌保护器。     

冲击条件对原木孔洞缺陷检测效果影响的研究

应用摆锤敲击装置,在实验室条件下研究冲击条件对原木内部孔洞缺陷检测效果的影响。摆锤冲击装置能以不同的速度敲击测试传感器,得到扰动信号在试样内的平均传播速度及原木孔洞缺陷区域的识别质量系数。研究结果表明,适当提高摆锤冲击速度,能够提高原木孔洞缺陷的检测效果。     

基于磁流变液阻尼器的半主动悬挂式座椅性能的评价

对安装磁流变液阻尼器的悬挂式座椅的挡板冲击和减震性能进行评价,并与安装传统阻尼器的同样悬挂式座椅的性能进行对比。在振动实验台上通过分别给座椅阻尼器施加临近主频的瞬态激励、连续随机激励EM1以及放大150%的EM1激励进行性能测试。