Failure analysis of a blower fan at a petrochemical plant

The catastrophic failure of the main blower of a petroquimical plant boiler is discussed. The preliminary analysis of all the damage suffered by the machine indicated that the rotor was subject to strong unbalanced forces due to the breakage of one or more blades. Root Cause Analysis (RCA) was employed to determine the events responsible for failure. It could be established the bearing box nearest to the gearbox was damaged first, and the consequent displacement that was transmitted through the coupling, tore the gearbox out of its base. The reconstruction and analysis of the deformations of the analyzed parts allowed identifying the initiation of the fracture at the cone rotor. Manufacture defects contributed to the occurrence of the failure due to an excess rotating speed overload.     

Socio-Economic Demands,Ecological Conditions and the Power of Tradition: Past Woodland Management Decisions in a Central European Landscape

Humans have managed European landscapes, including woodlands, for millennia. Prior to the birth of modern forestry in the eighteenth and nineteenth centuries, there existed two basic management forms for lowland broadleaved woods: coppicing and wood pasture. While the existence and characteristics of these two basic management types are well-known, the reasons why particular woods were coppiced while others pastured are little investigated. As a case-study, we chose two large ancient woods in the southern Moravian region of Central Europe. One was managed as coppice, while the other as wood pasture for most of their histories. The woods are similar in size, location, climate and vegetation. We examined several potential explanations (terrain morphology, soil productivity, abundance of woodland, ownership and economy) for past management decisions in these woods. We found that the links between soil productivity, economic demands and ownership were of key importance. Other factors were less significant, for example woodland abundance played no detectable role in spite of the decreasing availability of woodland resources. We also found that tradition mattered; it took a major shift in ideology to change entire management strategies. In sum, management decisions were driven by a complex network of multiple interactions among the individual factors.     

Adsorption layer and foam film properties of mixed solutions containing β-casein and C12DMPO

The interrelations between adsorption layer properties and surface forces in thin foam films of protein/surfactant mixtures were investigated. The adsorption from β-casein/dodecyl dimethyl phosphine oxide (C₁₂DMPO) mixed solutions was studied by Profile Analysis Tensiometry (PAT). The adsorption of protein/surfactant mixtures at the air/water interface is of competitive nature. The obtained adsorption isotherms suggest a gradual displacement of the protein molecules from the interface with increasing surfactant concentration. Foam films were studied by microinterferometry, originally introduced by Scheludko and Exerowa. The obtained experimental results show that the composition of the mixed adsorption layers changes with increasing amount of added surfactant. At a certain mixing ratio the corresponding foam film thickness decreases dramatically. This change happens above the surfactant concentration where the surface tension of the protein–surfactant mixtures approaches the values obtained for the respective pure surfactant solutions. The thickness, refractive index and adsorbed amount of the respective adsorption layers were determined by ellipsometry. These results correlate with the above-mentioned PAT and foam film data. The refractive index and adsorbed amount decrease monotonically and reach values close to those for pure surfactant solutions. On the contrary, a continuous increase can be observed in the layer thickness up to the above-mentioned concentration, indicating the formation of a more diffuse layer at the air–water interface formed by β-casein and C₁₂DMPO molecules upon increase of surfactant concentration. For foam films the electrolyte concentration can change the equilibrium thickness of the films and the Π(h)-isotherms significantly.     

Inertia force effects in the non-Newtonian couple stress squeeze film between a sphere and a flat plate

On the basis of the Stokes micro-continuum theory together with the method of mean averaged inertia, the influences of fluid inertia forces on the non-Newtonian squeeze film characteristics between a sphere and a flat plate have been presented. Comparing with the case of a non-inertia non-Newtonian lubricant, the consideration of fluid inertia forces provides a longer squeeze film time especially for the squeeze film operating with a lower film height, and a larger non-Newtonian parameter and density parameter. It prolongs the life of squeeze films.     

4-硝基苯乙烯基吡啶类氢键液晶的合成及表征

该文用4-硝基苯甲醛和4-甲基吡啶合成了质子受体4-硝基苯乙烯基吡啶,用无水乙醇重结晶得黄色固体,其熔点126.8～128.9℃,产率27%。用4-羟基苯甲酸和1-溴代正烷合成了质子供体4-烷氧基苯甲酸,用体积分数为95%的乙醇重结晶,所得4种中间体产率都在20%左右。最后,以上述两个中间体为原料,制备了系列4-硝基苯乙烯基吡啶类氢键型液晶。IR和1H NMR证实了各中间体结构。POM、IR、DSC检测了各复合物。POM拍摄的向列相、近晶相液晶织构表明,3种该氢键复合物均呈现明显的液晶态,且n=3时为向列相,n=5、8时为近晶相;IR图谱3500～2500cm-1处峰的变化及羰基向高波数位移,证明了羧基和吡啶间的分子间氢键代替了羧基间的分子间氢键。各复合物的液晶区间范围比各相应单体增大了1倍,表明羧酸吡啶间氢键起到了稳定液晶态的作用。     

试论技术经济学的学科性质与理论基础

本文从技术经济的研究对象和研究角度出发,论述了技术经济学的学科性质属于经济学;技术经济学的理论基础是生产力经济学和政治经济学;在此基础之上,论述明确技术经济学学科属性及理论基础对推动技术经济研究和技术经济人才培养的重要意义.     

一种新的端铣力计算模型

根据铣削和车削的相似性原理，通过对切削机理和切削几何关系的分析，建立了—个以车削力经验公式为基础的多齿铣刀端铣力计算模型．试验结果表明：铣削力的计算值和实测值有着很好的一致．     

关于离散系统的动力学方程

本文对处于复杂运动中的离散系统的动力学方程进行了详细的推导,并讨论了在微幅运动假定下,方程线化后的形式。最终给出了一般意义上的非定常系统的动力学方程式的正确表达式。     

三相交流电路非同期短路时电动力的计算

本文计算了三相交流电路非同期短路时作用在水平布置的三相载流导体上的电动力,计算表明,在最严重的情况下,作用在左边,中间和右边各相导体上最大电动力的方向分别为向左、向左和向右,而最大电动力的数值分别为三相同期短路时的1.2,1.4和1.4倍,为此,作者建议,在设计高压电器时,应按非同期短路时的情况来考虑其电动稳定性,     

球壳轴对称问题的加权残值解

本文以一半球壳为例,对球壳在轴对称边界力作用下弯曲的微分方程采用加权残值方法求解,并给出了对比的计算误差。