低应变率下混凝土动态拉伸破坏尺寸效应细观模拟

在混凝土静态破坏尺寸效应方面已取得了较完善的成果,而在动态破坏尺寸效应方面,包括其产生机制及对应的尺寸效应律的研究则非常匮乏。为探讨动态荷载作用下混凝土尺寸效应行为,从细观角度出发,结合混凝土细观结构特征,考虑动态加载下细观组分应变率效应的影响,建立了混凝土破坏行为研究的细观力学分析模型与方法。以双边缺口混凝土试件为例,对其在低应变率（10-5 s-1~1 s-1）下混凝土动态拉伸破坏行为及尺寸效应进行细观数值模拟,并分析了应变率效应对动态破坏尺寸效应的影响。最后,结合应变率效应对强度及尺寸效应的影响规律—“强度增强效应”与“尺寸效应削弱效应”,在静态破坏尺寸效应律的基础上,建立了混凝土拉伸强度的“静动态统一”尺寸效应理论公式,并验证了理论公式的准确性和合理性。     

反铁电材料中负电卡效应的研究进展

电卡效应是指电介质材料中由于施加或去除电场导致的材料温度变化的现象, 包括正电卡效应和负电卡效应两种类型。电卡效应作为一种高效率、无噪音、环境友好的制冷效应, 在固态制冷特别是集成电路制冷领域显示出广阔的应用前景, 在过去的几十年中吸引了科研人员广泛的研究兴趣。研究表明, 通过结合正负电卡效应, 可以显著提高电卡效应的制冷能力。与正电卡效应不同, 负电卡效应因其独特的物理起源, 调控手段极为有限。本文以负电卡效应为中心, 重点介绍反铁电材料中负电卡效应的最新研究进展, 具体内容包括以下四个部分: 首先, 从电卡效应的研究历史出发, 介绍了电卡效应的制冷原理, 介绍了一个典型的能将正、负电卡效应结合的双制冷循环; 其次, 介绍了基于Maxwell关系的负电卡效应间接测试方法, 以及几种负电卡效应直接测试方法, 并讨论了不同方法的适用条件和优缺点; 再次, 以典型的负电卡效应材料——反铁电材料为例, 着重介绍了负电卡效应的物理起源, 综述了反铁电薄膜和反铁电块体材料中的负电卡效应, 并对其它铁电材料中的负电卡效应做了简要介绍; 最后, 对负电卡效应的研究进行了总结和展望。     

力敏导电橡胶中的应变和压阻效应及工作原理分析

分析了应变和压阻效应对"负压力-电阻特性"(NPC)的影啊程度,揭示出力敏导电橡胶的工作原理.当填料用量处在渗流区中心时,电阻率的减小在NPC效应中占主导,导电橡胶的工作原理主要为压阻效应.随着填料用量的增多,电阻几何系数的减小在NPC效应中起主导,其工作原理主要为应变效应.在某一特定填料用量范围,力敏导电橡胶的工作原...     

相邻柜体干扰对煤气柜风致基底剪力的影响

通过风洞测力试验,研究了在不同风向角不同净距情况下相邻柜体干扰对煤气柜风致基底剪力的影响。结果表明:顺风向平均基底剪力干扰效应根据风向角可分成遮挡效应、狭缝效应和尾流效应三种情况,其中遮挡效应和狭缝效应均随净距减小而逐渐显著,而尾流效应在净距较小时表现不明显,只有在一定净距内才表现显著;顺风向脉动基底剪力根方差干扰效应在狭缝效应所对应的风向角且净距较小时表现较为显著;横风向脉动基底剪力根方差干扰效应与相邻柜体的位置有关,相邻柜体位于上游的干扰效应普遍大于相邻柜体位于下游的干扰效应,而相邻柜体位于下游时只有在净距很小时干扰效应才表现显著。     

Effect of porosity and tension–compression asymmetry on the Bauschinger effect in porous sintered steels

The Bauschinger effect is a common phenomenon in metallic materials. In this paper, the Bauschinger effect in Fe–0.85Mo–2Ni powder metallurgy (PM) steel was investigated for different porosities and as a function of loading sequence (compression–tension versus tension–compression). Both the porosity and loading sequence had a significant effect on the magnitude and asymmetry of Bauschinger effect. Compression followed by tensile loading lead to a higher Bauschinger effect than tension followed by compression. This asymmetry of Bauschinger effect was more significant for higher porosity. Crack formation and propagation, observed in this study, were the main factors influencing the asymmetry in Bauschinger effect. Finite element analysis, based on the actual microstructure of the steels, yielded good agreement with the experimental stress-strain behavior. FEM showed that both the Bauschinger effect in the steel matrix and porosity contribute to the global Bauschinger effect of the PM steels.     

基于CSI 效应的高耸结构液压驱动ATMD风振控制研究

在高耸结构风振控制中,由于忽略控制系统与结构振动的相互作用（CSI）,造成实际模型与理论模型存在差异,往往造成实际控制效果与理论控制效果不一致,导致控制效果不佳。本文以某电视塔为对象,将CSI 效应考虑在高耸结构模型中,建立了考虑CSI效应的动力特性模型,并与不考虑CSI效应的理想模型进行了对比分析。基于结构动力特性模型,分析了在控制算法中,考虑与不考虑CSI效应对控制效果的影响。为高耸结构ATMD风振控制提供相关的工程建议。     

Optical Response on the Colossal Magnetoresistance Effect in Manganites

The magnetorefractive effect in magnetoreflection and magnetotransmission modes in the optimally doped manganite epitaxial films possessed the colossal magnetoresistance effect was in the wide spectral region studied. The strict correlation between the magnetorefractive effect and colossal magnetoresistance in the middle infrared region for all samples was observed. It was shown that the magnetorefractive effect is an optical response to the colossal magnetoresistance in manganites. The magnetorefractive effect can reach a few tens of percents in the field of 3 kOe near the Curie point and can be explained by the change of ratio of localized and delocalized charge carriers under the magnetic field. On the contrary, in the visible range no direct correlations between magnetorefractive effect and colossal magnetoresistance were detected. The magnetorefractive effect is related with the alteration of the optical density under the magnetic field in the region of interband optical transitions. The magnitude of the effect is at least one order less in comparison with one in the infrared, but exceeds the values of traditional linear magnetooptical phenomena as the Kerr effect. Finally, huge magnetorefractive effect in manganites may be used for creation of various magnetic sensors and light modulation.     

Energy rebound effect in China’s manufacturing sector: Fresh evidence from firm-level data

The rebound effect refers to the phenomenon that individuals tend to consume more energy in the face of energy efficiency improvement, which reduces the expected energy-saving effect. Previous empirical studies on the rebound effect of regions and sectors do not provide microscopic evidence. To fill this gap, we use China’s firm-level data to estimate the rebound effect in China’s manufacturing subsectors, providing a detailed picture of China’s rebound effect across different sectors and different regions in 2001–2008. Results show that a partial rebound effect robustly appears in all industries, and the disparity between sectors is quite broad, ranging from 43.2% to 96.8%. As for the dynamic rebound effect of subsectors, most subsectors present an upward trend, whereas few subsectors show a clear downward trend. As a whole, the declined trend of the rebound effect is driven by the descent of minority sectors with high energy consumption and high energy-saving potential. In addition, we find that the disparity of the rebound effect across sectors is more significant than that across regions.     

微电子材料在微塑成形中的尺度效应

微电子材料在微机电系统（MEMS）的发展中越来越受到青睐，但是其工艺加工的不足限制了实际应用的步伐。微塑性成形可以成形微电子器件，由于其尺寸微型化，在微塑性成形中存在一个不可避免的“尺度效应”问题，尺度效应表现在材料的流动行为、成形中摩擦效应和实验结果的分散性上。在介绍尺度效应的基础上对其进行了分类，给出了判断标准，并从流动应力、晶粒尺度、摩擦效应和温度效应等方面综述了尺度效应对微塑性成形的影响。由于基于连续介质的传统塑性力学理论无法解释微塑性成形过程中的尺度效应，因此引入了非均匀介质的塑性应变梯度理论并进行了探讨，最后指出了尺度效应的研究发展方向，从而促进微电子材料的开发应用。     

Does the ripple effect influence the bullwhip effect? An integrated analysis of structural and operational dynamics in the supply chain†

The ripple effect refers to structural dynamics and describes a downstream propagation of the downscaling in demand fulfilment in the supply chain (SC) as a result of a severe disruption. The bullwhip effect refers to operational dynamics and amplifies in the upstream direction as ordering oscillations. Being interested in uncovering if the ripple effect can be a driver of the bullwhip effect, we performed a simulation-based study to investigate the interrelations of the structural and operational dynamics in the SC. The results advance our knowledge about both ripple and bullwhip effects and reveal, for the first time, that the ripple effect can be a bullwhip-effect driver, while the latter can be launched by a severe disruption even in the downstream direction. The findings show that the ripple effect influences the bullwhip effect through backlog accumulation over the disruption time as a consequence of non-coordinated ordering and production planning policies. To cope with this effect, a contingent production-inventory control policy is proposed that provides results in favour of information coordination in SC disruption management to mitigate both ripple and bullwhip effects. The SC managers need to take into account the risk of bullwhip effect during the capacity disruption and recovery periods.     

The effect of traffic policing on road safety in Israel

We use panel data on road sections to investigate the effect of traffic policing on non-urban road accidents in Israel. Traffic policing is measured indirectly by the number of police reports issued for driving offences. Our main findings are: (1) only large-scale enforcement has any measurable effect on road accidents while small-scale enforcement has no apparent effect. (2) The enforcement effect is slightly larger in the long run than it is in the short-run. (3) The effect of enforcement tends to dissipate rapidly after the dosage of enforcement is reduced. (4) Enforcement has no effect on fatal road accidents. (5) The evidence that the effect of policing in one road section spills over onto other road sections is weak.     

Characterization of the size effect in grinding and the sliced bread analogy

The size effect is a well known phenomenon in grinding. The specific energy increases with decreasing depth of cut. A comprehensive explanation is therefore required to explain the size effect. In this paper, the size effect in grinding is reviewed and the proposition investigated that the size effect correlates with chip surface area. This effect is shown to be too large to ignore. It was found that the chip surface area created in grinding may increase by nearly 20% when the depth of cut is reduced by half. The effect of the density of the cutting edge distribution on the wheel surface is taken into account and is shown to be as important as the kinematic conditions of grinding. The density of the cutting edge distribution is influenced by the dressing conditions. A grinding power model is presented taking dressing effects into accounts. Grinding performance is comprehensively explained by the size effect and bluntness of the grinding wheel grains. The size effect is explained by the 'sliced bread analogy'. The characterization of the influence of grinding and dressing conditions on the size effect in grinding provides a basis to achieve improved control of the process.     

基于未确知测度理论的露天矿深孔爆破效果评价

露天矿的爆破效果受众多因素的影响。结合工程实际,从安全、经济、爆破质量三个方面来综合评价露天矿深孔爆破效果。选取了起爆成本、炸药单耗、装运成本和爆破飞石等13个影响因素,基于未确知测度理论,建立露天矿爆破效果评价模型。根据露天矿爆破实测数据,建立了适合各影响因素的未确知测度函数,并对其进行定量分析。利用熵计算各影响因素的指标权重,根据置信度识别准则对爆破效果等价进行判定,并对三种不同爆破方案的爆破效果进行综合评价排序。研究结果表明：方案 II 的爆破效果最好,爆破效果综合评价指数为4.76,与现场实际较为符合。该方法在评价露天矿爆破效果时更具客观性,评价影响因素可根据现场实际情况进行灵活选取,其评价结果能为现场爆破方案的选取提供决策依据。     

The Portevin–Le Chatelier effect: a review of experimental findings

Abstract

The Portevin–Le Chatelier (PLC) effect manifests itself as an unstable plastic flow during tensile tests of some dilute alloys under certain regimes of strain rate and temperature. The plastic strain becomes localized in the form of bands which move along a specimen gauge in various ways as the PLC effect occurs. Because the localization of strain causes degradation of the inherent structural properties and surface quality of materials, understanding the effect is crucial for the effective use of alloys. The characteristic behaviors of localized strain bands and techniques commonly used to study the PLC effect are summarized in this review. A brief overview of experimental findings, the effect of material properties and test parameters on the PLC effect, and some discussion on the mechanisms of the effect are included. Tests for predicting the early failure of structural materials due to embrittlement induced by the PLC effect are also discussed.     

浅述城市热岛效应的形成原因及其对策

在全球气候变暖和高速城市化的大背景下,世界上许多城市都出现了高强度的城市热岛效应,城市热环境质量日趋恶化。分析和评价城市热岛效应已经成为当前城市气候与环境研究的重要内容之一,也是全球变化研究的重要方面。介绍了城市热岛效应的定义,接着说明了城市热岛效应的形成原因,进一步说明了城市热岛效应对人们及周围环境带来的影响,最后提出了改善城市热岛效应的措施。     

应用边界元法模拟厅堂中座席低谷效应

座席低谷效应是坐席中声波为掠入射时声场在低频段出现的选择性吸收的现象，它会影响厅堂中低频声的听感。文章用边界元法模拟了坐席低谷效应，考查影响座席低谷效应的因素。计算结果表明了坐席低谷效应在座席不同位置处的变化情况。最后列举了一些降低座席低谷效应的办法。     

弯曲缩短对杆件结构非线性分析的影响

为了考察弯曲缩短对杆件结构非线性分析的影响(弓形效应),利用ANSYS用户可编程特性(UPFs)研究了考虑弓形效应的实用方法,采用ANSYS数值模拟方法对若干杆件结构算例进行了弹性及弹塑性大位移分析。算例分析结果表明:对于扁平刚架等易发生跃越失稳的结构,弯曲缩短的影响大,分析时应予以考虑;而对于普通矩形框架结构,弯曲缩短的影响可以忽略不计。采用弓形函数的近似表达式可有效考虑弯曲缩短效应。     

一维声子晶体中弹性波的全反射贯穿效应

为了研究一维声子晶体中弹性波的全反射贯穿效应,利用转移矩阵法计算了弹性波在大于全反射角入射一维声子晶体的透射率。在透射波中发现了两条透射峰带,即出现了全反射贯穿效应。得出了贯穿效应随入射角的变化规律、贯穿效应随介质厚度的变化规律以及贯穿效应随周期数的变化规律。并利用波的量子理论和渐逝波的理论对一维声子晶体的贯穿效应作出了定性的理论解释     

六流道喷嘴涡流管能量分离特性的研究

涡流管具有结构简单、无运动部件、价格低廉、可靠性高等优点,但管内发生的能量转换却极为复杂。以压缩空气为工作介质,对涡流管能量分离特性进行了实验研究,获得了涡流管制冷、制热效应随入口压力、冷端流率之间的关系,研究结果表明,进口压力越高,六流道喷嘴涡流管的制冷、制热效应越好,但获得最大制冷、制热效应时的冷端流率均有减小的趋势。     

硫硒化镉微晶玻璃制备和非线性光学性质研究

具有明显量子尺寸效应和较大三阶非线性光学效应的CdSxSe1-x(O相似文献