聪明的泰勒斯(英文)

)1.Once,Tylers,an ancientGreek businessman,was drivinga group of mules crossing a river.The mules were carrying salt.一次,古希腊商人泰勒斯,赶着一群驮运食盐的骡子过河。2.When the mules came to the middle of the river,one mule accidentally fell down in the     

Multi-objective optimization design method of the high-speed train head

With the continuous improvement of the train speed, the dynamic environment of trains turns out to be aerodynamic domination. Solving the aerodynamic problems has become one of the key factors of the high-speed train head design. Given that the aerodynamic drag is a significant factor that restrains train speed and energy conservation, reducing the aerodynamic drag is thus an important consideration of the high-speed train head design. However, the reduction of the aerodynamic drag may increase other aerodynamic forces （moments）, possibly deteriorating the operational safety of the train. The multi-objective optimization design method of the high-speed train head was proposed in this paper, and the aerodynamic drag and load reduction factor were set to be optimization objectives. The automatic multi-objective optimization design of the high-speed train head can be achieved by integrating a series of procedures into the multi-objective optimization algorithm, such as the establishment of 3D parametric model, the aerodynamic mesh generation, the calculation of the flow field around the train, and the vehicle system dynamics. The correlation between the optimization objectives and optimization variables was analyzed to obtain the most important optimization variables, and a further analysis of the nonlinear relationship between the key optimization variables and the optimization objec- tives was obtained. After optimization, the aerodynamic drag of optimized train was reduced by up to 4.15%, and the load re- duction factor was reduced by up to 1.72%.     

Characteristics of bifurcation and buckling load of space truss in consideration of initial imperfection and load mode

This study investigated characteristics of bifurcation and critical buckling load by shape imperfection of space truss,which were sensitive to initial conditions.The critical point and buckling load were computed by the analysis of the eigenvalues and determinants of the tangential stiffness matrix.The two-free-nodes example and star dome were selected for the case study in order to examine the nodal buckling and global buckling by the sensitivity to the eigen buckling mode and the analyses of the influence,and characteristics of the parameters as defined by the load ratio of the center node and surrounding node,as well as rise-span ratio were performed.The sensitivity to the imperfection of the initial shape of the two-free-nodes example,which occurs due to snapping at the critical point,resulted in bifurcation before the limit point due to the buckling mode,and the buckling load was reduced by the increase in the amount of imperfection.The two sensitive buckling patterns of the numerical model are established by investigating the displaced position of the free nodes,and the asymmetric eigenmode greatly influenced the behavior of the imperfection shape whether it was at limit point or bifurcation.Furthermore,the sensitive mode of the two-free-nodes example was similar to the in-extensional basis mechanism of a simplified model.The star dome,which was used to examine the influence among several nodes,indicated that the influence of nodal buckling was greater than that of global buckling as the rise-span ratio was higher.Besides,global buckling is occurred with reaching bifurcation point as the value of load ratio was higher,and the buckling load level was about 50%-70% of load level at limit point.     

Application of automated image analysis to the identification and extraction of recyclable plastic bottles

An experimental machine vision apparatus was used to identify and extract recyclable plastic bottles out of a conveyor belt. Color images were taken with a commercially available Webcam, and the recognition was performed by our homemade software, based on the shape and dimensions of object images. The software was able to manage multiple bottles in a single image and was additionally extended to cases involving touching bottles. The identification was fulfilled by comparing the set of measured features with an existing database and meanwhile integrating various recognition techniques such as minimum distance in the feature space, self-organized maps, and neural networks. The recognition system was tested on a set of 50 different bottles and provided so far an accuracy of about 97% on bottle identification. The extraction of the bottles was performed by means of a pneumatic arm, which was activated according to the plastic type; polyethylene-terephthalate （PET） bottles were left on the conveyor belt, while non-PET bottles were extracted. The software was designed to provide the best compromise between reliability and speed for real-time applications in view of the commercialization of the system at existing recycling plants.     

Environmental noise beside an elevated box girder bridge for urban rail transit

Noise generated by trains running on elevated lines creates many disturbances to the normal lives of surrounding residents. Investigations have shown that people living along elevated lines complain that the noise is sometimes unbearable. To better control the noise and optimize the acoustic environment, noise spectrum characteristics were analyzed and compared with a field test and a numerical simulation. Through an energy analysis of the noise on the bridge side, the energy distribution characteristics of the noise at specific measuring points in different frequency bands were obtained. The influence of the Doppler effect on frequency shift was analyzed. Based on the partial coherence theory, a multi-input and single-output program was compiled to calculate the correlation and contribution degree of the bridge structure-borne noise and wheel/rail noise at the one-third octave center frequency. The results show that the peak noises of the bridge and the wheel/rail are concentrated at 31.5–63 Hz and 400–800 Hz, respectively. For environmental noise on the bridge side, the frequency band above 250 Hz is mainly affected by the wheel/rail noise. In areas of noise source strength, the relative ratio of noise energy above 250 Hz can reach 83.4%. Noise in the near ground and far bridge area is mainly low-frequency, and the relative energy ratio is about 8.9%. The Doppler effect has an influence of less than 6% on the frequency shift with a speed of 67.9 km/h. In the low-frequency band below 250 Hz, the noise in the acoustic shadow area near the bridge and the ground is mainly contributed to by the vibration-radiated noise of the bridge, of which the contribution of the bottom panel is the most prominent. The noise in the comprehensive noise area of the far bridge is mainly caused by the structure-borne noise of the bridge, and the contribution of each bridge panel is different. This study can provide a reference for finding the source of elevated rail noise in some challenging frequency ranges and for then determining optimal designs and measures for noise reduction.     

Vacuum pyrolysis characteristics of waste epoxy printed circuit boards

Vacuum pyrolysis was employed to dispose scrap brominated epoxy printed circuit boards (PCBs). Pyrolysis characteristics of waste PCBs under normal pressure and vacuum were investigated in this paper. A detailed study on the analysis of the elemental composition of PCBs and the pyrolysis products was performed. The thermal decomposition kinetics was measured by a thermogravimetric (TG) analyzer. The activation energy of pyrolysis under nitrogen atmosphere and vacuum were 193 kJ/mol to 206 kJ/mol and 145 kJ/mol to 165 kJ/mol, respectively. The composition of materials was analyzed by elemental analyzer. The pyrolysis products were analyzed by GC (gas chromatograph), GC-MS (chromatography and mass spectrometry) and FT-IR (Fourier transform infrared spectroscopy). Vacuum helped to increase the yield of pyrolysis oil. The liquid yield of PCBs pyrolysis at 15 kPa and normal pressure were 31.3? and 23.5?, respectively. The main components in pyrolysis oils were phenol, isopropyl-phenol, and their brominated substitution.     

没人让我讲话

One of the qualities that most people admire in others is the willingness to admil one‘s mistakes. It is extremely hard sometimes to say a simple thing like“I was wrong about that” ,and it is even harder to say, “I was wrong, and you were right about that. ”Perhaps the reason we admire this.     

Tissue-engineered graft constructed by self-derived cells and heterogeneous acellular matrix

Background： Endothelial and smooth muscle cells were used as seeding cells and heterogeneous acellularized matrix was used as scaffold to construct the tissue-engineered graft. Methods： A 2 weeks piglet was selected as a donor of seeding cells. Two-centimetre length of common carotid artery was dissected. Endothelial cells and smooth muscle cells were harvested by trypsin and collagenase digestion respectively. The isolated cells were cultured and expanded using routine cell culture technique. An adult sheep was used as a donor of acellularized matrix. The thoracic aorta was harvested and processed by a multi-step decellularizing technique to remove the original cells and preserve the elastic and collagen fibers. The cultured smooth muscle cells and endothelial cells were then seeded to the acellularized matrix and incubated in vitro for another 2 weeks. The cell seeded graft was then transplanted to the cell-donated piglet to substitute part of the native pulmonary artery. Results： The cultured cells from piglet were characterized as endothelial cells by the presence of specific antigens vWF and CD31, and smooth muscle cells by the presence of specific antigen a-actin on the cell surface respectively with immunohistochemical technique. After decellularizing processing for the thoracic aorta from sheep, all the cellular components were extracted and elastic and collagen fibers kept their original morphology and structure. The maximal load of acellular matrix was decreased and 20% lower than that of untreated thoracic aorta, but the maximal tensions between them were not different statistically and they had similar load-tension curves. Three months after transplantation, the animal was sacrificed and the graft was removed for observation. The results showed that the inner surfaces of the graft were smooth, without thrombosis and calcification. Under microscopy, a great number of growing cells could be seen and elastic and collagen fibers were abundant. Conclusion： Cultured self-derived endothelial and smooth muscle cells could be used as seeding cells and heterogeneous acellularized matrix could be used as scaffold in constructing tissue-engineered graft.     

Using fracture grouting to lift structures in clayey sand

An inclined seven-story reinforced concrete building was leveled by a fracture grouting technique with quick-setting grout on a differential thickness of a clayey sand layer. The permeability and strength of clayey sand were controlled by clay content, although sand was the primary component of the foundation soil. The elevations of the building columns at basement level were closely monitored to record both the heaved volume of mat foundation after grouting and the settled volume during pore pressure dissipation. During the stabilizing stage of grouting, the foundation soil was densified by the repetitive fracturing process, which resulted in the lateral movement of the foundation soil. When the grout is less able to push soil laterally than upwards, the building starts to lift, the so-called lifting stage of grouting. The grouting efficiency is influenced by soil type, soil stress history, and foundation pressure. A final grouting efficiency of 27% and a linear relationship between grout use and percentage of elevation were obtained when this building was successfully and permanently leveled.     

Preparation and properties of Tung oil-based polyurethane

Tung oil-based polyols were synthesized by the esterification and transesterification between Tung oil-based anhydride and butanediol. The hydroxyl values of the polyols prepared were tested and discussed. Polyurethane was prepared by using Tung oil-based polyols and/or poly （propylene glycol） as polyols and by using isophorone diisocyanate as isocyanate. The effect of the ratio of Tung oil-based polyols to poly （propylene glycol） on the proper- ties of polyurethane prepared was investigated by the water resistance, alcohol resistance and hardness tests. The results show that Tung oil-based polyols are effective to improve the hardness, water resistance and alcohol resistance of polyurethane.     

神秘的中国西羌丝绸之路

在中国四川经松潘草地至西藏出雅鲁藏布大峡谷到印度,有一条中国历史上最早唯一对外的文化、经贸窗口,这条神秘的中线商道两千多年来由于种种原因隐藏进了岁月的迷雾中而鲜为人知,它为中西方文化、经济的交流发挥了极其重要的作用。唐时这条至关重要的商道被吐蕃占领,宋朝重新开通茶马古道而兴盛一时,新中国建立后修通了公路,汽车代替了当年的骡马,这条繁荣的商道才正式退出了历史舞台。     

南下平卢的马匹

平卢军驻北方时,得马非常便利,而广征西北马、突厥马、护真马为坐骑,军事实力雄厚。浮海南下后,沿用北方优良马种。同时,引进渤海马,又培养了汝南马,甚至训骡为骑。马匹品种的改良,巩固了平卢诸藩镇的军事地位。在黄淮畜牧业的发展中,南下平卢贡献卓著,影响及于后世。朱温在争霸战争中,逐步吸收平卢诸镇军队与马匹,军事实力大增,从而为统一北方打下了良好的基础。平卢军的南下,促进了农牧业的交流与发展。     

三十姓达怛与室韦的关系

古突厥文碑铭中的三十姓达怛,与汉文文献记载的室韦的地域分布相吻合,部落数略等,尤其是汉文史籍对室韦屡次或附或叛突厥的记载正好与突厥碑文把三十姓达怛或作为属部或看成敌人的记载相合不悖,证明三十姓达怛就是指室韦人     

“幽默”与“讽刺”并举——论梁实秋小品散文的艺术风格

梁实秋先生是中国现代散文创作的一代宗师,其小品散文呈现出一种独特的幽默与讽刺并举的艺术风格。其作品或针砭时弊风情,或揭露人性弱点,或抒发生活感悟,或体察世态人生,诙谐幽默中展示着作者对于社会人生的真知灼见。这种幽默与讽刺并举的艺术风格的形成与梁实秋先生的出身、经历、文学观有着直接的关系。     

陶诗的生命意识感

陶渊明的《咏怀》、《咏史 )诗 ,与正始时期阮籍的《咏怀诗》所抒写的“忧生之嗟”相比 ,体现出更丰富、更强烈的生命意识感。诗中 ,有时是壮志不能实现所激起的伤感 ,有时则是历史的永存与人生短促所触发的悲感 ,有时是对时间的高度敏感。这焦灼不安、苍凉忧伤的情惑 ,使陶诗在审美视域中具有了悲剧美的特质。     

革命与改良之问：严复对辛亥革命的态度

通过对进化论的独特理解,严复提出了文明排外和发展民力民智民德的社会改良之路来解除中国的生存危机,因而他坚决反对辛亥革命所提出的暴力排满的主张,也很反对暴力革命的手段,但他对辛亥革命所提出的建立民主共和国的主张既有反对的一面。又有可以接受的一面。由此可见,革命和改良的关系是相当复杂的,而不是简单的二元对立关系。     

"一+量+名"作"把"的介引对象的指称性的若干验证——兼与张济卿同志商榷

六种“把“字句类型的验证,认为“一 量 名“作“把“的介引对象时,并不一定是语境现场原已存在的非照应性事物,它可能是泛指性事物,也可能是照应性事物,也有可能是隐含某种条件的事物.     

论艺术歌曲《声声慢》的演唱特征

李清照晚年的作品《声声慢》,这首词押入声韵,并屡用叠字和双声字,节奏舒缓而急促、哀婉、凄厉。表现了作者孤独寂寞的忧郁情绪和动荡不安的心境。正因为这首词艺术特征鲜明,著名作曲家黄永熙先生予以谱曲,赋予了这首词新的艺术生命。在解析《声声慢》词曲艺术的基础上,重点从歌词、伴奏、情感、音准、音色、演唱方法等几个方面进行分析与探讨,研究其演唱规律与特征。     

电视节目主持人的语言风格

电视节目主持人的语言总是首先受到电视话语、栏目特点的约束,在此基础上又要凸显个人的风格。白岩松、崔永元等优秀节目主持人,其语言或理智深刻、尖锐犀利,或新颖独特、融情于理,或温文尔雅、细腻真挚,或机智幽默、平中见奇,都具有迷人的个人魅力和独特的语言风格,应认真总结优秀语言风格的内在规律及培养途径。