纳米Al_(2)O_(3)/h-BN复配改性对环氧树脂复合材料电热性能的影响

提升环氧树脂的电、热性能对固封极柱、干式变压器等中低压电气设备的长期安全稳定运行意义重大。文中采用偶联剂KH550对纳米Al_(2)O_(3)以及经羟基化处理的纳米h-BN粒子进行表面接枝后填充入环氧树脂基体,研究了填料纳米Al_(2)O_(3)、纳米h-BN对环氧树电热性能的影响。结果表明,纳米Al_(2)O_(3)/h-BN混合填充能够形成良好的协同效应,复合材料在电绝缘参数大幅提升的同时,热性能也得到明显改善。Al_(2)O_(3)填充质量分数为2%、h-BN填充质量分数为1%时,复合材料的介电性能最优,同时,击穿电压相较未改性提升了27.1%;Al_(2)O_(3)和h-BN填充质量分数均为1.5%时,复合材料的热导率最高,绝缘失效温度至351.5℃。这一结果可为高温强电场下环氧树脂固封设备高可靠性运行提供参考。

An Overview and Experimental Study of Learning-Based Optimization Algorithms for the Vehicle Routing Problem

The vehicle routing problem(VRP)is a typical discrete combinatorial optimization problem,and many models and algorithms have been proposed to solve the VRP and its variants.Although existing approaches have contributed significantly to the development of this field,these approaches either are limited in problem size or need manual intervention in choosing parameters.To solve these difficulties,many studies have considered learning-based optimization(LBO)algorithms to solve the VRP.This paper reviews recent advances in this field and divides relevant approaches into end-to-end approaches and step-by-step approaches.We performed a statistical analysis of the reviewed articles from various aspects and designed three experiments to evaluate the performance of four representative LBO algorithms.Finally,we conclude the applicable types of problems for different LBO algorithms and suggest directions in which researchers can improve LBO algorithms.

Simulation research on collisions between highway corrugated beam guardrails and vehicles based on LS-DYNA

To explore the safety of highway traffic operations,the vehicle state and guardrail deformation during highway guardrail collisions are simulated and analyzed.The vehicle-guardrail collision is simulated by finite element software such as LS-DYNA and HyperMesh.The vehicle speed settings are 60,80,100 and 120 km/h,and the collision angles are 5°,10°,15°and 20°.The guardrail deformation,vehicle acceleration and energy changes under different collision speeds and angles are studied.The research results show that at the same collision speed,an increase in the collision angle causes more serious damage to the vehicle,a greater transverse displacement of the guardrail,and a greater range of car acceleration fluctuations.When the collision angle is the same,an increase in the collision speed causes greater lateral displacement of the guardrail,a greater vehicle acceleration fluctuation range,and more serious vehicle damage.The results of the study can provide a reference for demonstrating highway guardrail safety.

Natural gas density under extremely high pressure and high temperature: Comparison of molecular dynamics simulation with corresponding state model

This work applied molecular dynamics(MD)simulation to calculate densities of natural gas mixtures at extremely high pressure(>138 MPa)and high temperature(>200℃)conditions(x HPHT)to bridge the knowledge and technical gaps between experiments and classical theories.The experimental data are scarce at these conditions which are also out of assumptions for classical predictive correlations,such as the Dranchuk&Abou-Kassem(DAK)equation of state(EOS).Force fields of natural gas components were carefully chosen from literatures and the simulation results are validated with experimental data.The largest relative error is 2.67%for pure hydrocarbons,2.99%for C1/C3 mixture,7.85%for C1/C4 mixture,and 8.47%for pure H2S.These satisfactory predictions demonstrate that the MD simulation approach is reliable to predict natural-and acid-gases thermodynamic properties.The validated model is further used to generate data for the study of the EOS with pressure up to 276 MPa and temperature up to 573 K.Our results also reveal that the Dranchuk&Abou-Kassem(DAK)EOS is capable of predicting natural gas compressibility to a satisfactory accuracy at x HPHT conditions,which extends the confidence range of the DAK EOS.

Residual coronary artery tree description and lesion EvaluaTion(CatLet)score,clinical variables,and their associations with outcome predictions in patients with acute myocardial infarction

Background:We have recently developed a new Coronary Artery Tree description and Lesion EvaluaTion(CatLet)angiographic scoring system.Our preliminary studies have demonstrated its superiority over the the Synergy between percutaneous coronary intervention(PCI)with Taxus and Cardiac Surgery(SYNTAX)score with respect to outcome predictions for acute myocardial infarction(AMI)patients.The current study hypothesized that the residual CatLet(rCatLet)score predicts clinical outcomes for AMI patients and that a combination with the three clinical variables(CVs)-age,creatinine,and ejection fraction,will enhance its predicting values.Methods:The rCatLet score was calculated retrospectively in 308 consecutively enrolled patients with AMI.Primary endpoint,major adverse cardiac or cerebrovascular events(MACCE)including all-cause mortality,non-fatal AMI,transient ischemic attack/stroke,and ischemia-driven repeat revascularization,was stratified according to rCatLet score tertiles:rCatLet_low≤3,rCatLet_mid 4-11,and rCatLet_top≥12,respectively.Cross-validation confirmed a reasonably good agreement between the observed and predicted risks.Results:Of 308 patients analyzed,the rates of MACCE,all-cause death,and cardiac death were 20.8%,18.2%,and 15.3%,respectively.Kaplan-Meier curves for all endpoints showed increasing outcome events with the increasing tertiles of the rCatLet score,with P values<0.001 on trend test.For MACCE,all-cause death,and cardiac death,the area under the curves(AUCs)of the rCatLet score were 0.70(95%confidence intervals[CI]:0.63-0.78),0.69(95%CI:0.61-0.77),and 0.71(95%CI:0.63-0.79),respectively;the AUCs of the CVs-adjusted rCatLet score models were 0.83(95%CI:0.78-0.89),0.87(95%CI:0.82-0.92),and 0.89(95%CI:0.84-0.94),respectively.The performance of CVs-adjusted rCatLet score was significantly better than the stand-alone rCatLet score in terms of outcome predictions.Conclusion:The rCatLet score has a predicting value for clinical outcomes for AMI patients and the incorporation of the three CVs into the rCatLet score will enhance its predicting ability.Trial Registration:http://www.chictr.org.cn,ChiCTR-POC-17013536.

The prediction of spontaneous oil-water imbibition in composite capillary

In view of the classical Lucas-Washburn equation,which can only describe the spontaneous imbibition of single wetted capillary,a tilted composite capillary model with circular cross section,composed of different wettability capillary wall was established.The model can describe the spontaneous oil-water imbibition of water-wet capillary,oil-wet capillary and mixed wetting capillary.Through numerical solution of the model equation,it is found that the component content of the capillary walls,the capillary radius and the oil-water viscosity ratio have great effects on the spontaneous oil-water imbibition.Effects of capillary inclination angle and inertia force on spontaneous oil-water imbibition are related to the capillary scale.Effects of capillary inclination angle and inertia force can be ignored in small radius capillary,while effects of inclination angle and inertia force can not be ignored in large radius capillary.