180米箱型拱桥的成桥动载试验研究

本文介绍了180米箱型拱桥的成桥动载试验的方法。动载试验研究中,测试了大桥主要控制截面在各工况下的动力应变曲线、动力响应,并通过模态分析,得出大桥的自振特性。试验结果表明主梁的自振特性和动力响应均在正常范围内。     

基于灵敏度分析的车身结构轻量化设计

就轨道车辆而言,车体钢结构是影响整车力学性能的主要承载部件,为避免车体与转向架产生共振,设计时要考虑车体的自振频率和刚度。车体结构的低阶弹性模态参数反映车身的整体动态刚度性能,是控制振动特性的关键指标。因此,本文选取车体结构一阶垂弯模态频率作为约束条件,同时把扭转刚度作为重要评价指标,进行车体的轻量化设计。     

稳定发展粮棉生产 全面发展农村经济

对简支边界条件下以正交铺设层板为面板的复合材料层板的横向振动进行了求解，在求解中包括了面板的耦合和面板与夹芯间的粘结刚度，计算结果表明，当粘结刚度超过某一时，可以认为面板与芯结完好，但当小于这个值时，结刚度对自振频率会产生很大的影响，影响程度与面板铺层、芯性质、板的长宽比及振动模态有关，作为一个特例，对正交铺设层板中间一个间界面存在滑移时其振动频率的变化进行了讨论。     

斜放四角锥网架结构固有振动特性研究

分别采用拟夹层板法、有限元法求解网架固有振动频率。通过拟夹层板法和ANSYS模态分析法,对网架固有振动特性进行了研究,得到网架自由振动的规律。通过两种方法的比较,证实采用ANSYS软件进行网架结构模态分析是可靠的。     

跨径100m刚架系杆拱桥设计

刚架系杆拱桥是在钢管混凝土拱桥中出现的新桥型,刚架系杆拱桥的主要特点是拱肋与桥墩固接,不设支座,采用预应力钢绞线作为拉杆来平衡拱的水平推力,刚架系杆拱为超静定结构,桥梁上部、下部及基础连成一体,结构的超静定次数较多,受力较为复杂。文章详细介绍了某大桥主跨跨径100 m下承式钢管混凝土刚架系杆拱桥的总体布置及结构设计的要点,并采用有限元计算软件Midas Civil进行全桥结构计算分析,按照规范进行了承载能力极限状态和正常使用极限状态验算。     

酷公司

纳米微球 纳米微球是一种粒径在5纳米到1000微米的小颗粒,每个颗粒上还有些更细小的孔径。液晶屏实质是用两块板中间夹着液晶材料,两块板中间的距离要非常均匀。微球的作用,就是被均匀地放置在两块板之间,充当所谓液晶间隔物,确保板间距离的均匀。     

三维探地雷达技术在沉陷成因探测及处治效果评价中的应用

介绍采用三维探地雷达探测沉陷脱空的技术特征、设备和工作原理,详细描述某路段沥青道路存在沉陷脱空的基本情况以及利用三维探地雷达进行无损检测的过程。通过处治前的检测结果,确定脱空程度、位置,并计算沉陷的位置、面积和高程差。通过对比两个具有不同沉陷脱空形成原因的路段,分析沉陷、脱空的形成原因,提出针对性的处治措施。根据处治后的检测结果,对注浆、加铺等病害处治措施的处治效果进行评价。研究结果表明,三维探地雷达系统能够准确地探测沥青路面内部的沉陷脱空病害程度、位置和形成原因。基于探测结果,提出具有针对性的处治措施,并评价处治效果的可行性和有效性。     

高原地区抗滑桩边坡稳定性分析

由于实际环境的复杂性与多变性,边坡自然沉积土体的强度参数均具有各向异性和非均质性,强度参数的改变对边坡安全系数具有影响。基于抗滑桩土拱效应的影响,考虑边坡土体强度参数的各向异性与非均质性,通过编程二次开发有限元软件,建立土体强度各向异性和非均质性的抗滑桩边坡模型,分析土体强度参数各向同性与各向异性条件下边坡安全系数的变化。研究结果表明,各向异性的非均质系数为0.5时,对抗滑桩边坡安全系数影响最大,比各向同性均质的边坡安全系数降低22.9%。与水平向黏聚力强度相比,垂直向对抗滑桩边坡稳定性影响更大,土体各向异性与非均质性对抗滑桩边坡稳定性分析十分重要。     

城市电缆隧道中圆形咬合桩深基坑的变形特性研究

圆形基坑因其存在空间拱效应,导致围护结构和周围土体呈现不同于一般基坑的变形特性,而被广泛应用于城市电缆隧道建设中。结合某一采用钻孔咬合桩支护的圆形深基坑工程,对基坑开挖过程中的围护结构受力变形和周围土体变形特性进行了现场观测和分析。结果表明,在坑外荷载不对称的条件下,基坑开挖引起的围护结构水平位移呈现不规则的变形分布,向坑内的最大侧移为11.42mm。围护结构的支撑轴力随着开挖深度的增大而增大,开挖完成时的轴力最大可达1962k N。周围地表沉降呈现"凹槽形"分布,在空间拱效应作用下的最大地表沉降仅为13.52mm,且发生位置与基坑的距离约为0.8倍开挖深度。     

空气放电特性参数间相关性研究分析

通过对同轴圆筒结构在非平衡状态下进行放电实验研究,并对实验数据进行线性拟合分析,探究常温空气放电过程中各特性参数之间的联系.实验发现,在电压满足阈值条件时,频率变化是直接影响等离子射流的主要因素,频率改变会引起射流长度相应的变化.频率的连续变化过程中,因电场驻波的影响存在突变点;而射流温度与频率变化虽受驻波影响,存在极值跳变,但射流长度与射流温度基本成对应关系;在满足阈值条件下,射流温度与电压之间呈线性增长关系;气体流速小于1 L/min时,流速变化对射流温度影响较大;当流速在1～4 L/min时,射流温度随气流速度变化较小.     

On the Major Transformation of the Asia-Pacific Regional Structure北大核心CSSCISSCI

Recent years have witnessedsignificant changes in the Asia-Pacific regionalstructure featuring the shift in power balance among related countries as well as adjust-ments in their respective regional strategies. So what is the prevailing trend in thistransformation and what kind of regional order will likely emerge in the future？ To an-swer these questions, the paper tries to explore the following dimensions： the evolvingregional context, shift in power balance and power conversion, geo-political and geo-e-conomic developments and interactions between them, and evolving regional order. Asthe study shows, the broadening of regional geographical scope, the rise in the numberof actors involved, as well as changesin the relations among them, have combined tocast a pluralistic and complex flavor to the regional structure. While the power balanceamong China, the United States and Japan shifts, and power conversion is also occur-ring. China and Japan are paying increasing attention to their security roles, whereasthe United States under the Obama administration laid more stress on expanding itsgeo-economic clout. In spite of the intensifying geopolitical competition among China,the United States and Japan in recent years, a Sino-US strategic compromise-whichholds the key to regional geopolitics-isother front, some kind of geo-economicmore likely to take place in the future. On thecooperation will probably emerge. In the longerterm, it will be the geo-economic trend thatwill prevail over the geopolitical trend inthe region. Finally, the future evolution of regional order wiI1 mainly follow the eco-nomic logic, accompanied by the dilutionof its hegemonic and hierarchical nature.Hence, a pluralistic and complex regional community will emerge.     

Organization and incentives in the age of sail

The British Navy in the age of sail was the most successful bureaucracy of its time. Its organization and incentive structures differed importantly from contemporaneous private sailing ventures, but closely resembled those of today’s large corporations. To induce efficient effort, the navy used a hierarchical tournament, in which sailors competed for higher pay that came with promotions based on relative performance. Promotion probabilities, the option value of future promotions, and the higher effort required of men in higher ranks and on larger vessels, combined to yield a highly skewed pay structure.     

The German Hanse and Bergen – new perspectives on an old subject

Abstract

The Hanseatic League and her kontors (trading posts) were an integral part of the medieval trade system in Northern Europe. Hanse merchants dominated many markets in this region and managed to maintain a monopoly-like role in towns like Novgorod and Bergen for many centuries. Consequently, one focus of historical research about the Hanseatic League lay on the mechanisms that enabled the Hanse merchants to keep that strong of a position for such a long time.

This article is part of the discussion about this topic. Based on Lübeck merchants with business interest in the Norwegian town of Bergen, the so-called Bergenfahrers (Bergen travellers), it will give new insights into the Hansards' economical and social organization. The three main points are (a) the integration of the Bergen market in the Hanseatic trade network as an intermediary trading place on the vivid East–West route of Hanse trade; (b) the importance of the Bergenfahrers within the Hanse merchants' economical, social and political networks; and (c) the structure of the Bergenfahrers network patterns in the late Middle Ages.

In addition to new insights into the important role of Bergen and the Bergenfahrers within Lübeck's and the other Wendish Hanse towns' trading system, this articles provides further proof for the usefulness of the methods of Social Network Analysis in medieval economic research.     

Financial Reporting and Trade Credit: Evidence from Mandatory IFRS Adoption*

We investigate the effect of mandatory IFRS adoption on trade credit. We document that firms in countries that adopt IFRS receive more trade credit from their suppliers, consistent with improved financial reporting quality and comparability playing a role in facilitating informal financing. This increase is larger for countries with a low level of societal trust, a poor pre‐IFRS‐adoption information environment, and stronger legal enforcement. These cross‐sectional results suggest that the conditions under which higher‐quality information is made publicly available affect suppliers' decisions to provide trade credit. This increase is also larger for firms with greater exposure to foreign markets, a finding that highlights the importance of more comparable international financial reporting standards in facilitating cross‐country trade credit. We also find that IFRS adoption has a stronger positive effect on trade credit for firms with greater liquidity needs. Finally, we find that firms in countries that adopt IFRS also extend more trade credit to their customers. Overall, our results support the notion that financial reporting can have a causal effect on trade credit.     

区域工业产业竞争力指标体系的构建及其评价方法研究

文章通过建立省级区域工业产业竞争力评价指标体系,设计竞争力模型,利用SPSS统计软件,对各省工业产业竞争力进行了评价测定。     

Penetration and Post-infection Development of Meloidogyne Incognita on Tobacco as Treated by Rhizobacteria Pseudomonas Fluorescens Strain P-72-10

The bio-control potential of rhizospere bacteria Pseudomonas fluorescens against plant-parasite nematode had been demonstrated. P. fluorescens had shown the effect to enhance tobacco resistance to root-knot nematode Meloidogyne incognita. Inoculation with P. fluoreseens in tobacco could lead to significant reductions in the number of juveniles that penetrated tobacco root and further life stage development of the juveniles. The number of juveniles penetrated into tobac- co root in treatment with P. fluorescens is significantly different from CK at 2DAI, 6DAI, 8DAI and 10DAI. Significant reduction and delayed development of juveniles that penetrated into tobacco root and treated were observed in treatment at 14DAI, 21DAI, 28DAI and 35DAI. In addition, P. fluoreseens treatment leads to a significant reduction in the number of eggs per egg-mass at 35 DAI. The results show P. fluorescens induced a continuously suppression on root-knot nema- tode M. incognita throughout their entire early infection phase of root penetration, subsequent life stage development and reproduction.     

文化传播中电视暴力对青少年侵犯行为的影响

伴随当代传媒产业的蓬勃发展,暴力也成为影视艺术基本的叙事类型及消费主义文化日趋盛行的现实语境。＂电视暴力＂是作为＂媒介暴力＂的一个子概念存在的;从文化传播看电视暴力,其覆盖面大,且易于接触;电视暴力对受众特别是青少年的影响巨大而深刻。要从制作者、传播者和观众三个方面的自律出发,建立适应我国国情的影视分级制。     

理性与先验的完美整合——论笛卡尔的"上帝"观

笛卡尔是西方近代主体性哲学的先驱,是近代唯理论学说的创始人,他使人们从中世纪宗教势力的禁锢中解放了出来.虽然"上帝"这个被人们视为理性最大敌人的概念在他的哲学中大量存在,但他极力证明上帝存在的最终目的却是为了证明理性的伟大;作为真理化身的上帝,归根到底是为他的理性主义服务的.