A Model for Mechanical Property Evaluation of the Periodic Porous Low-k Materials by SAW

The influence of the distribution of nano-pores on the mechanical properties evaluation of porous low-k films by surface acoustic waves （SAW） is studied. A theoretical SAW propagation model is set up to characterize the periodic porous dielectrics by transversely isotropic symmetry. The theoretical deductions of SAW propagating in the low-k film/Si substrate layered structure are given in detail. The dispersive characteristics of SAW in differ- ent propagation directions and the effects of the Young＇s moduli E, E′ and shear modulus G′ of the films on these dispersive curves are found. Computational results show that E′ and G′ cannot be measured along the propagation direction that is perpendicular to the nano-pores＇ direction.

Microstructural and mechanical properties of Al-4.5wt% Cu reinforced with alumina nanoparticles by stir casting method

The microstructure and mechanical properties of A1-4.5wt% Cu Mloy reinforced with different volume fractions （1.5vo1%, 3vo1%, and 5vo1%） of alumina nanoparticles, fabricated using stir casting method, were investigated. CMculated amounts of alumina nanoparticles （about ~50 nm in size） were ball-milled with aluminum powders in a planetary ball mill for 5 h, and then the packets of milled powders were incorporated into molten Al-4.5wt% Cu alloy. Microstructural studies of the nanocomposites reveal a uniform distribution of alumina nanoparticles in the A1-4.5wt% Cu matrix. The results indicate an outstanding improvement in compression strength and hardness due to the effect of nanoparticle addition. The aging behavior of the composite is also evaluated, indicating that the addition of alumina nanoparticles can accelerate the aging process of the Mloy, resulting in higher peak hardness values.

Mechanical properties of TiO_2-hydroxyapatite nanostructured coatings on Ti-6Al-4V substrates by APS method

TiO2-hydroxyapatite （HA） nanostructured coatings were produced by atmospheric plasma spray method. The effects of starting powder composition and grain size on their mechanical properties were investigated. The microstructure and morphology were characterized by X-ray diffraction and scanning electron microscopy （SEM）. It is found that the coating with 10% HA has the best mechanical properties. Based on Rietveld refinement method, the mean grain size of the as-received powder （212 nm） extensively decreases to 66.4 nm after 20 h of high-energy ball milling. In spite of grain growth, the deposited coatings maintain their nanostructures with the mean grain size of 112 nm. SEM images show that there is a lower porosity in the coating with a higher HA content. Optical microscopy images show that uniform thickness is obtained for all the coatings.

Driving Mechanism of Cultivated Land Transition in Yantai Proper,Shandong Province,China

Cultivated land transition and its driving mechanism are the hotspots among studies on land use change. In this study, we constructed a framework to study the driving mechanism of cultivated land transition from the quantitative perspective. Based on the vector data of land use in 1990, 2000 and 2009 of Yantai Proper, Shandong Province China, 11 explanatory variables were chosen from two aspects: the elevation, slope, cost distance to major water area and cost distance to minor water area, which presented physical factors; cost distance to district center, cost distance to town center, cost distance to city expansion center, cost distance to major roads, cost distance to city roads, cost distance to county roads and cost distance to rural roads, which presented the socio-economic factors. Combined with spatial analysis tools and Logistic regression analysis model, we construct Logistic regression analyses with four objectives that were urban construction land, rural residential land, orchard and other lands. The results show that, cost distance to district center, cost distance to town center, cost distance to city expansion center and cost distance to city roads are the significant explanatory variables for the transition of cultivated land into urban construction land. The main explained factors on the transition of cultivated land into rural residential land are slope, cost distance to town center, cost distance to county roads and cost distance to rural roads. Slope, cost distance to minor water area, cost distance to town center, cost distance to county roads and cost distance to rural roads are the significant explanatory variables for the transition of cultivated land into orchard land. Elevation, slope, cost distance to major water area and cost distance to minor water area are the main explanatory variables on the transition of cultivated land into other land uses.

New ternary superconducting compound LaRu2As2： Physical properties from density functional theory calculations

In this paper, we perform the density functional theory （DFT） -based calculations by the first-principles pseudopo- tential method to investigate the physical properties of the newly discovered superconductor LaRu2As2 for the first time. The optimized structural parameters are in good agreement with the experimental results. The calculated independent elas- tic constants ensure the mechanical stability of the compound. The calculated Cauchy pressure, Pugh＇s ratio as well as Poisson＇s ratio indicate that LaRu2As2 should behave as a ductile material. Due to low Debye temperature, LaRu2As2 may be used as a thermal barrier coating （TBC） material. The new compound should exhibit metallic nature as its valence bands overlap considerably with the conduction bands. LaRu2As2 is expected to be a soft material and easily machinable because of its low hardness value of 6.8 GPa. The multi-band nature is observed in the calculated Fermi surface. A highly anisotropic combination of ionic, covalent and metallic interactions is expected to be in accordance with charge density calculation.

Deep Learning Applied to Computational Mechanics:A Comprehensive Review,State of the Art,and the Classics

Three recent breakthroughs due to AI in arts and science serve as motivation:An award winning digital image,protein folding,fast matrix multiplication.Many recent developments in artificial neural networks,particularly deep learning(DL),applied and relevant to computational mechanics(solid,fluids,finite-element technology)are reviewed in detail.Both hybrid and pure machine learning(ML)methods are discussed.Hybrid methods combine traditional PDE discretizations with ML methods either(1)to help model complex nonlinear constitutive relations,(2)to nonlinearly reduce the model order for efficient simulation(turbulence),or(3)to accelerate the simulation by predicting certain components in the traditional integration methods.Here,methods(1)and(2)relied on Long-Short-Term Memory(LSTM)architecture,with method(3)relying on convolutional neural networks.Pure ML methods to solve(nonlinear)PDEs are represented by Physics-Informed Neural network(PINN)methods,which could be combined with attention mechanism to address discontinuous solutions.Both LSTM and attention architectures,together with modern and generalized classic optimizers to include stochasticity for DL networks,are extensively reviewed.Kernel machines,including Gaussian processes,are provided to sufficient depth for more advanced works such as shallow networks with infinite width.Not only addressing experts,readers are assumed familiar with computational mechanics,but not with DL,whose concepts and applications are built up from the basics,aiming at bringing first-time learners quickly to the forefront of research.History and limitations of AI are recounted and discussed,with particular attention at pointing out misstatements or misconceptions of the classics,even in well-known references.Positioning and pointing control of a large-deformable beam is given as an example.

高性能机油净化碳基复合定型滤芯研制与应用

针对目前机油滤清器滤芯存在的机油净化性能差、使用寿命短等问题,通过活性炭与聚氨酯经插嵌微发泡复合定型,研发首创出具有开孔型微泡网状结构碳基复合定型滤芯,并研究其性能。结果表明,碳基复合定型滤芯属于过滤-吸附双效深层体型滤材,阻力小、流量大;通过开孔型微泡网状结构过滤作用和碳材料吸附作用的协同效应,显著提升机油净化性能、延长使用寿命;与德国马勒纸质滤清器相比,碳基复合滤清器在汽车90 km/h等速行驶测试中节约燃油达3.80%,4辆实车、累计66801公里行驶验证,碳基复合滤清器节约燃油3.17~3.33%。碳基复合滤清器节油效果显著,大规模推广与应用将产生巨大的经济效益和社会效益。

基于条件对抗增强的Transformer煤矿微震定位方法

随着人工智能技术的发展以及煤矿微震监测系统的广泛应用,越来越多的深度学习模型被应用到煤矿微震事件震源定位问题的求解上。然而,由于目前的微震数据量小且数据单一不足以训练大且深的神经网络模型,而小且浅的神经网络模型也不足以表征受多方因素影响的微震事件的震源,因而导致了定位模型定位精度低和鲁棒性弱,在实际生产生活中表现较差,严重地阻碍了深度学习模型在微震定位领域上的发展。针对上述问题,提出一种基于条件对抗增强的Transformer煤矿微震定位方法CGAN-Transformer,该方法首先通过一个CGAN架构的网络模型将数据量少且单一的微震数据增强成数据量庞大且具有一定多样性的微震数据;其次,利用Transformer编码器层将微震波形数据转换为特征数据后再利用其注意力机制进一步学习微震波形数据深层次特征和复杂的站间依赖关系,同时也利用高斯分布随机变量抵消了不同地质条件对定位精度的影响;最后,通过引入混合密度输出层获取高斯分布参数,计算最优的震源位置。在智利和辽宁某矿数据集上的实验结果验证了该方法的有效性,结果表明该方法所获得的震中误差与震源误差均优于其他方法,在两个数据集上的定位误差分别降低了38%和12%,达到了提高震源定位精度和定位模型鲁棒性的目的。

HATO机械感度和热感度的影响因素研究

为了研究5,5'-联四唑-1,1'-二氧二羟铵(HATO)机械感度、热感度的影响因素,利用机械球磨法制备了4种不同粒度的HATO颗粒。利用激光粒度分析仪和扫描电子显微镜对HATO的粒度和表观形貌进行了表征;利用X射线衍射仪对HATO的晶体结构进行了表征;采用BAM撞击感度仪及BAM摩擦感度仪对不同粒度、不同温度HATO的撞击感度和摩擦感度进行了研究;采用差示扫描量热仪对不同粒度HATO的热分解情况进行了分析。结果表明:小粒度HATO的X射线衍射峰的位置与HATO原料的保持一致,证明小粒度HATO的晶体结构没有发生改变。随着粒度的减小,HATO的机械感度先升高、后降低。认为机械球磨法得到的小粒度HATO表面缺陷增多、结构完整性降低,受到外力作用时,样品内部的活性中心增多,提高了热点产生的概率。但随着粒度的进一步减小,HATO颗粒之间的孔穴及孔隙率也急剧减小,颗粒结构越来越密实,形状更加规则,减少了热点源和热点产生的机率。因此,当HATO粒度过小时,机械感度反而降低了。此外,随着温度的升高,HATO的机械感度增高,但撞击感度与摩擦感度随温度的变化规律并不相同。热感度方面,小颗粒HATO的起始分解温度提前,活化能减小,热稳定性降低。

高速激光熔覆铁基TY-2合金组织及力学性能分析

目的通过与激光熔覆进行对比,探究高速激光熔覆铁基TY-2合金的显微组织及力学性能。方法采用高速激光熔覆技术在27SiMn不锈钢基体上制备铁基TY-2合金熔覆层。利用扫描电子显微镜、X射线衍射仪、显微硬度计,对熔覆层的显微组织、物相结构及力学性能进行分析测试,对比研究高速激光熔覆与激光熔覆铁基TY-2合金熔覆层的显微组织和力学性能。结果与激光熔覆层相比,获得的高速激光熔覆层均匀致密,无裂纹,孔隙与夹杂较少,与基体形成良好的冶金结合。激光熔覆层的组织以粗大的柱状晶为主,高速激光熔覆层的组织以尺寸为5~10μm的细小晶粒为主。高速激光熔覆层与原始粉末的物相一致,包含(Fe,Ni)、Cr_(0.19)Fe_(0.7)Ni_(0.11)和Fe-Cr等相。激光熔覆层与原始粉末的物相有所差别,高能量密度导致CaNi_(3)C_(0.5)金属间化合物的生成。高速激光熔覆层的平均硬度为604HV_(0.3),相比激光熔覆层(543HV_(0.3))提高了9.4%。结论高速激光熔覆的总能量较低,为激光熔覆总能量的77.9%,其中高速粒子携带的动能占高速激光熔覆总能量的17.7%。高速激光熔覆可实现低能量下的高效熔覆,熔覆层的组织更加细小,成分更加均匀,硬度更高。

冷拉变形对7050铝合金丝材组织与性能的影响

对7050铝合金丝材经冷拉变形后过时效态以及冷加工变形态的组织与性能进行了研究。结果表明,随着冷变形量的增加,晶粒拉长,屈服强度、抗拉强度和剪切强度增大。与冷拉态相比较,过时效态丝材的这些指标增加不明显;晶粒越均匀细小,合金丝材冷镦时越不易发生开裂。

高速柔性容差机构抑振研究及其最优驱动设计

智能建造中需要引入钢筋自动捆扎设备,以提高捆扎效率及质量,降低工人劳动强度,为人机协作提供新的应用场景。针对现阶段钢筋自动捆扎设备视觉定位精度不高的技术瓶颈问题,引入容差机构,利用容差机构欠驱动的特性弥补视觉定位误差。但欠驱动中的弹性构件在运动平台高速运行时会因惯性力导致系统振动,影响捆扎精度并限制工作效率。针对这一问题,运用最优化动态控制理论,确定了控制运动规律和关键的系统结构设计参数,旨在减少非稳定过渡时间、能量消耗和稳态误差。对研究结果进行了数字仿真与实验验证,结果显示:与传统驱动方法相比,经最优控制设计的驱动方式在非稳定过渡时间和稳态误差方面具有明显的综合优势。

美国“海洋自由”观念的欧洲源头(1643—1785)

作为美国外交政策原则的重要组成部分,“海洋自由”观念并非完全由美国人“原创”,而是有着深刻的欧洲理论源头和国家实践印记。在革命年代,美国开国先辈在设计国家外交政策的过程中,基于中立国国家角色定位,“舶来”了欧洲的“自由船所载货物自由”原则,主要体现在“1776年条约计划”中。而在争取加入1780年“武装中立”联盟,以及与欧洲国家的谈判中,富兰克林、亚当斯等人借鉴并阐发了源自欧洲启蒙思想家的“海上私人财产免于捕获”理念,将其确认为美国的外交政策原则之一,并落实在1785年与普鲁士签订的双边条约之中。作为具有美国特色的海洋自由观念,海上私人财产豁免原则具有理想主义和现实主义的双重属性,反映了美国建国之初海军力量弱小的现实,其式微是历史发展的必然趋势。

伪装遮障材料耐老化性能与机理分析

目的 研究伪装遮障材料在实用期的老化机理,获悉伪装遮障材料失效的主要环境因素。方法 通过分析伪装遮障材料在自然环境和实验室单因素环境中的性能变化,得出影响伪装遮障材料老化失效的主要因素。采用扫描电子显微镜、红外光谱仪、X射线光电子能谱仪表征材料的微观形貌、化学结构和化学成分变化,解释伪装遮障材料的老化机理。结果 获得了在不同自然环境、实验室单因素环境下,伪装遮障材料颜色外观和力学性能的变化规律,得到了伪装遮障材料在老化过程中发生的微观形貌、化学结构和化学成分变化。结论 伪装遮障材料在西双版纳自然环境下的老化程度最大,在济南自然环境下的老化程度最小。光照是导致伪装遮障材料颜色外观及力学性能降低的主要因素。老化过程中,主要是材料表面的聚氨酯发生老化、脱落,导致材料的力学性能下降。伪装遮障材料破坏时,纤维有2种失效形式,一种是纤维脱黏、直接断裂;另一种是纤维脱黏,拔出,或者拔出过程中断裂。

“套路鉴”案件的定性——以诈骗罪的认定为切入的思考

“套路鉴”案件罪与非罪争议的背后涉及诈骗罪认定的刑法理论问题,而实务中有关司法机关对此尚未予以充分认识,由此导致诈骗罪的成立范围不当地得以扩大。因此,有必要从欺骗行为的认定、认识错误与动机错误的区分、财产损失的认定、非法占有目的的认定等方面对“套路鉴”案件中诈骗罪的成立范围进行合理限缩。就判断交易型诈骗罪是否成立而言,主要应当关注两个核心问题:一是交易是否真实存在,二是交易是否为被害人所需要。在“套路鉴”案件中,如果鉴定公司提供了真实的鉴定服务,就可以认定交易是真实存在的;如果鉴定公司的宣传涉及一些价值判断的表述,应当认为被害人申请做鉴定是基于自身动机,可以认定交易是被害人所需要的。因此,对“套路鉴”案件能否以诈骗罪定性,不能一概而论。

淬火热处理对马氏体不锈钢组织和性能的影响

马氏体不锈钢以其优异的强度和硬度特性,在许多工业应用中占据重要地位,尤其是在耐磨性和抗腐蚀性要求极高的环境中。为了进一步满足该试验材料在高压高温条件下的服役性能,试验提出研究淬火热处理对06Cr11Ni2MoVNb2马氏体不锈钢微观组织和宏观性能的影响,通过微观组织、拉伸性能和力学性能3个方面对比分析了不同冷却方式与淬火温度对试验钢组织与性能的影响。结果表明:对钢体进行淬火后得到的钢组织主要为板条状的马氏体、冷却奥氏体以及碳化物,淬火温度为1 040℃时,试验钢的综合性能最为优越,说明不同冷却方式与淬火温度对试样钢的性能和组织有着十分显著的影响。

基于POD与机器学习的综掘工作面流场快速预测算法

针对综掘工作面降尘措施难以合理利用的问题,提出了一种基于本征正交分解(POD)与机器学习的综掘工作面流场快速预测算法。利用计算流体力学(CFD)技术对多种工况下的综掘工作面风流场和粉尘浓度场进行模拟,获得高维度流场数据;利用POD对高维度流场数据进行降维,提取能够反映流场主要特性的核心模态,得到流场工况的基函数模态与模态系数;通过机器学习方法预测不同工况下占总能量达到90%以上的模态系数,从而对未知工况的模态系数进行预测,利用预测的模态系数与基函数模态进行重构,得到未知工况的风流场数据或粉尘浓度场。研究结果表明:综掘工作面数值模拟模型的相对误差在3%以内,能够准确反映实际的风流和粉尘分布状况;风流场选择前5阶模态,粉尘浓度场选择前7阶模态,即可兼顾POD重构精度与效率;支持向量机(SVM)模型对模态系数的预测能力优于随机森林及神经网络模型,针对60种不同工况,基于POD和SVM预测的风流速度、粉尘浓度与数值模拟结果之间的相对误差分别为0.36 m/s,86.24 mg/m^(3),风流场及粉尘浓度场平均预测耗时为73 s,实现了对矿井综掘工作面风流场和粉尘浓度场的高精度快速预测。

Influence of Nano-Al_2O_3 on Properties of Magnesia Chrome Refractories

Magnesia chrome bricks were prepared with fiLsed MgO- Cr2 O3 synthesized material, fused magnesite and ：hrome ore as main starting materials. Nano-Al2O3 was tdded into refractories （ 2% , 4% and 6% in mass ） ;ubstit,ting for Al203 micropowder. After m＆ing and ;haping, the bricks were fired at 1 550 ℃, 1 600 91℃, t 650 ℃ and 1 750℃, respectively. The microstruc-ure , sintering property, mechanical properties, thermal ;kock resistance and shtg resistance of the specimens with he addition of nano-Al2O3 were investigated. The results indicate that the performance of brick with 4 mass% of nano-Al2O3 is greatly improred afier firing at 1 650 ℃.

Mechano-chemical selections of two competitive unfolding pathways of a single DNA i-motif

The DNA i-motif is a quadruplex structure formed in tandem cytosine-rich sequences in slightly acidic conditions. Besides being considered as a building block of DNA nano-devices, it may also play potential roles in regulating chromo- some stability and gene transcriptions. The stability of i-motif is crucial for these functions. In this work, we investigated the mechanical stability of a single i-motif formed in the human telomeric sequence 51-（CCCTAA）3CCC, which revealed a novel pH and loading rate-dependent bimodal unfolding force distribution. Although the cause of the bimodal unfolding force species is not clear, we proposed a phenomenological model involving a direct unfolding favored at lower loading rate or higher pH value, which is subject to competition with another unfolding pathway through a mechanically stable inter- mediate state whose nature is yet to be determined. Overall, the unique mechano-chemical responses of i-motif-provide a new perspective to its stability, which may be useful to guide designing new i-motif-based DNA mechanical nano-devices.

热处理工艺对TB9钛合金棒材组织和性能的影响

文章借助光学显微镜、扫描电镜和室温拉伸机,研究了不同固溶和时效温度对TB9钛合金棒材显微观组织、力学性能及断口形貌的影响。结果表明:在时效温度相同的条件下,随着固溶温度的升高,β相晶粒尺寸增加,抗拉强度和屈服强度呈下降趋势,延伸率和面缩率变化较小;在相同固溶处理工艺条件下,随着时效温度的升高,β相晶粒尺寸增加,在高于510℃时效后,β相晶内和晶界处出现了大量α析出相,抗拉强度和屈服强度显著降低,延伸率和面缩率显著提高;随着固溶温度的增加,相同时效温度处理的断口形貌由韧窝状塑性断裂逐渐向脆性断裂转变,韧窝含量减小,沿晶断裂的含量增加。