Length scale of interface heterogeneities selects propagation mechanism of frictional slip fronts

We present three-dimensional finite-element simulations showing the propagation of slip fronts at striped heterogeneous interfaces. The heterogeneous area consists of alternating stripes of weaker and stronger frictional properties, which is equivalent to a lower and higher fracture energy, respectively. By comparing the slip front propagation at interfaces that differ solely by the length scale of the heterogeneous pattern, we illustrate that two different propagation regimes exist. Interfaces with wide stripes present slip fronts with propagation speeds that transition from sub-Rayleigh to inter-sonic. Thinner stripes are, however, characterized by the propagation of sub-Rayleigh slip fronts, which are preceded by slip pulses of negligible slip in the weaker stripes. From a macroscopic point of view, an interface with a smaller heterogeneous pattern appears to be stronger than the equivalent coarser interface even though both have the same average properties. The numerical results as well as a theoretical approach based on fracture-mechanics considerations suggest that the origin of these two distinct propagation mechanisms lies in the interaction between the length scales of the cohesive zone and the heterogeneous configuration. We further show by estimating the relevant length scales that the occurring propagation mechanism is influenced by the friction weakening rate of the interface as well as the shear modulus of the bulk material.     

Inventory competition in a dual-channel supply chain with delivery lead time consideration

Aimed at the inventory competition of perishable products in a dual-channel supply chain with consideration of the delivery lead time in the online direct channel, we extend the Newsvendor model considering stock-out-based consumer switching behavior to include the delivery lead time. We examine the retailer's optimal order quantity decision in the retail channel and the manufacturer's optimal inventory level decision in the online direct channel, explore the manufacturer's optimal delivery lead time decision in the online direct channel, discuss the impact of the product price and consumer switching behavior on the optimal decisions of supply chain members, and compare the optimal decisions between decentralized and centralized scenarios. The results show that, compared with the centralized scenario, at least one of the supply chain members will overstock in the decentralized scenario and that consumers in the online direct channel enjoy a shorter delivery lead time and hence better service in the decentralized scenario. Finally, we present numerical examples to analyze the impact of relevant parameters on the supply chain members’ profits and the supply chain efficiency.     

自由场中液氮单空泡动力学特性的实验研究

本文专门设计搭建了低温介质空泡演化实验测试平台, 对液氮单空泡非定常演化过程和动力学特性开展了实验研究. 实验中利用电火花瞬态放电激发液氮汽化形成单空泡, 通过高速摄影系统对单空泡的瞬态特征进行了精细化捕捉. 为了进一步揭示低温介质独特的物理性质以及强热力学效应对单空泡演化过程的影响机制, 对比分析了在相同环境压力下, 77.41 K液氮和298.36 K水单空泡的演化过程和动力学特性. 基于实验得到空泡半径与界面速度等定量数据, 阐明了液氮单空泡球形与非球形演化阶段的非定常特性. 研究结果表明: (1) 在相同输入电压下, 液氮单空泡的整体尺寸比常温水更小, 当输入电压为400 V时, 液氮空泡的最大半径约为常温水空泡的0.69倍; 同时, 液氮单空泡经历了膨胀阶段?收缩阶段?振荡阶段以及上升阶段的演化过程. (2)液氮空泡的收缩过程主要由相界面的热传导主导, 没有明显的塌陷现象, 收缩阶段液氮空泡的最小收缩半径约为常温水的5.5倍. (3)在液氮空泡振荡初期, 空泡相界面传热增强, Rayleigh-Taylor不稳定与热力学效应共同引起了空泡界面的表面粗化效应; 在整个振荡阶段, 空泡界面附近存在破碎的小泡. 当输入电压较高时, 空泡底部的小泡数量显著增多. (4)由于液氮空泡浮力系数较大, 液氮空泡在演化后期空泡整体向上迁移显著, 液氮空泡底部收缩更快产生凹陷, 促使空泡变为环状.      

电感耦合等离子体原子发射光谱法测定铂铑合金中铑

提出了电感耦合等离子体原子发射光谱法测定铂铑合金中铑含量的方法。含铑(wRh≤40%)的铂铑合金称样0.1000 g,用盐酸-硝酸(3+1)溶液10 mL和氢氟酸(ρ=1.18 g·mL-1)0.5 mL于微波消解仪中消解完全。选择波长为343.489 nm的谱线作为测定铑的分析线。方法的检出限为0.029 mg·L-1。方法用于分析5个铂铑合金样品,测定值与国家标准方法测定值的相对误差在0.10%~0.40%之间,回收率在99.6%~101.0%之间。     

A parallel system for adaptive optics based on parallel mutation PSO algorithm

Wavefront sensor-less adaptive optics technology has a much higher requirement for the processing speed than ever before. To improve the efficiency of particle swarm optimization (PSO), this paper proposes a novel parallel mutation particle swarm optimization (PMPSO) algorithm based on a master-slave model. The parallel system based on PMPSO algorithm is applied in a 61-element adaptive optics system to control the deformable mirror. The experimental results show that the parallel system based on PMPSO algorithm has a rapid convergence speed, which can effectively correct the wavefront aberration.     

人工神经网络预测非环状亚硝胺急性毒性的QSAR研究

在DFT-B3LYP/6-311+G(d,p)水平对60种非环状亚硝胺分子结构进行几何全优化,通过多元逐步线性回归(MSR)分析筛选出9个量子化学描述符作为自变量,log LD50(lethal dose 50％,LD50:大鼠口服急性毒性)作为因变量,采用人工神经网络(ANN)方法构建QSAR模型.经Levenber...     

In situ fabrication of lithium polymer battery basing on a novel electro-polymerization technique

Electro-polymerization technology is proposed for the in situ fabrication of polymer lithium secondary battery and exciting results have been obtained. The polymerization starts from a common used electrolyte of 1 M LiTFSI in DOL/DME (2:1 by weight) with no initiator addition through a routine charge–discharge treatment under some appointed current rate. It is found that once an appropriate current is applied in the charging–discharging of Li/1 M LiTFSI in DOL + DME/LiCoO₂ cell, the original liquid electrolyte polymerizes readily during the first several cycles in an irreversible mode, and thus the desired polymer electrolyte obtained. SEM observation indicates that unlike previous report, the designed electro-polymerization does not result in destructive local break and then turnoff of the circuit, just the reverse, it helps to the formation of a smooth polymer layer, which can effectively protect the lithium substrate from corrosion and dendrite growth. Detailed examination shows that the in situ electro-polymerization does not disturb the electrochemical behavior of the cell, the cycleabilty, internal resistance are all comparable to that of a normal Li/LiCoO₂ liquid secondary battery.     

ZrO2包覆高镍LiNi0.8Co0.1Mn0.1O2正极材料提高其循环稳定性的作用机理

高镍三元材料作为一种锂离子电池正极材料,因其较高的放电比容量而得到科学界和工业界的广泛关注。研究表明,高镍三元材料的比容量与材料中的Ni含量呈正相关,但Ni含量的增加也会加剧循环过程中的界面副反应,材料表面释氧以及结构转变等问题。本文采用ZrO₂包覆LiNi_0.8Co_0.1Mn_0.1O₂材料,利用X射线衍射证明,在高温处理下ZrO₂包覆物中的Zr⁴⁺会掺杂进LiNi_0.8Co_0.1Mn_0.1O₂材料表面晶格中,使得X射线衍射谱中的(003)衍射峰左移。电化学测试证明在4.3和4.5 V的截止电压下,改性最优的材料在1C循环100周后容量保持率分别从84.89%和75.60%提高到97.61%和81.37%,同时发现循环稳定性的提升主要来自材料表面的Zr⁴⁺掺杂。X射线光电子能谱证明Zr⁴⁺表层掺杂后材料的Ni化合价由Ni3+向Ni²⁺转变,透射电子显微镜观察到Zr⁴⁺的表层掺杂使得材料表面的层状结构发生重构,从而稳定了材料体相结构,提高了材料整体的循环稳定性。     

Reversible adhesion surface coating proppant

Proppant is a key material in the hydraulic fracturing process,which has been widely used in unconventional oil exploitation.Normal proppants are easy to sedimentate and accumulate at the entrance of shale fracture,which will block the diversion of water,oil and gas.Coated proppants(CPs) are fabricated by coating resin on normal ceramic proppants through a simple method,which is dramatically enhanced the supporting properties in shale fracture and easy to scale up.Compared with uncoated ceramic proppants,the self-suspension ability of CPs is ~11 times higher,which are able to migrate and distribute farther and deeper inside the fracture.At the same time,Coating enhanced the 23.7% of adhesive force in maximum,which makes the CPs easier to adhere on the fracture surface to supportthe shale fracture.Besides,the liquid conductivity of CPs is 60% higher than uncoated ceramic proppants at13.6 MPa pressure.This method is expected to fabricated varieties of proppantsfor shale fracture supporting to improve the exploration of unconventional oil and gas resources.     

高职“三进阶”高端技能人才培养模式设计与实施——以工业分析与检验专业为例

从高等职业院校定位出发,明晰了高职人才培养模式的定义。考虑到社会需求、企业要求和新生学情,具体以高职工业分析与检验专业为例,设计出一套既适用于高职学生学习又符合社会对高端技能人才要求的基于认知顺序的三进阶人才培养模式。