Stochastic optimization based on a novel scenario generation method for midstream and downstream petrochemical supply chain

A two-stage mixed integer linear programming model(MILP)incorporating a novel method of stochastic scenario generation was proposed in order to optimize the economic performance of the synergistic combination of midstream and downstream petrochemical supply chain.The uncertainty nature of the problem intrigued the parameter estimation,which was conducted through discretizing the assumed probability distribution of the stochastic parameters.The modeling framework was adapted into a real-world scale of petrochemical enterprise and fed into optimization computations.Comparisons between the deterministic model and stochastic model were discussed,and the influences of the cost components on the overall profit were analyzed.The computational results demonstrated the rationality of using reasonable numbers of scenarios to approximate the stochastic optimization problem.

1064 nm InGaAsP multi-junction laser power converters

Laser photovoltaic devices converting 1064 nm light energy into electric energy present a promising prospect in wireless energy transmission due to the commercial availability of high power 1064 nm lasers with very small divergence. Besides their high conversion efficiency, a high output voltage is also expected in a laser energy transmission system. Meanwhile,1064 nm InGaAsP multi-junction laser power converters have been developed using p^+-InGaAs/n^+-InGaAs tunnel junctions to connect sub-cells in series to obtain a high output voltage. The triple-junction laser power converter structures are grown on p-type InP substrates by metal-organic chemical vapor deposition(MOCVD), and InGaAsP laser power converters are fabricated by conventional photovoltaic device processing. The room-temperature I–V measurements show that the 1 × 1 cm^2 triplejunction InGaAsP laser power converters demonstrate a conversion efficiency of 32.6% at a power density of 1.1 W/cm^2, with an open-circuit voltage of 2.16 V and a fill factor of 0.74. In this paper, the characteristics of the laser power converters are analyzed and ways to improve the conversion efficiency are discussed.

Research of Insect Recognition Based on Improved YOLOv5

Insects play an important role in the natural ecology,it is of great significance for ecology to research on insects.Nowadays,the invasion of alien species has brought serious troubles and a lot of losses to local life.However,there is still much room for improvement in the accuracy of insect recognition to effectively prevent the invasion of alien species.As the latest target detection algorithm,YOLOv5 has been used in various scene detection tasks,because of its powerful recognition capabilities and extremely high accuracy.As the problem of imbalance of feature maps at different scales will affect the accuracy of recognition,we propose that adding an attention mechanism based on YOLOv5.The channel attention module and the spatial attention module are added to highlight the important information in the feature map and weaken the secondary information,enhancing the recognition ability of the network.Through training on self-made insect data sets,experimental results show that the mAP@0.5 value reaches 92.5%and the F1 score reaches 0.91.Compared with YOLOv5,the map has increased by 1.7%,and the F1 score has increased by 0.02,proving the effectiveness of insect recognition based on improved YOLOv5.In conclusion,we provide effective technical support for insect identification,especially for pest identification.

Temporal-spatial dynamic characteristics of vehicle emissions on intercity roads in Guangdong Province based on vehicle identity detection data

Estimating intercity vehicle emissions precisely would benefit collaborative control in multiple cities.Considering the variability of emissions caused by vehicles,roads,and traffic,the 24-hour change characteristics of air pollutants(CO,HC,NO_(X),PM_(2.5))on the intercity road network of Guangdong Province by vehicle categories and road links were revealed based on vehicle identity detection data in real-life traffic for each hour in July 2018.The results showed that the spatial diversity of emissions caused by the unbalanced economywas obvious.The vehicle emissions in the Pearl River Delta region(PRD)with a higher economic level were approximately 1–2 times those in the non-Pearl RiverDelta region(non-PRD).Provincial roads with high loads became potential sources of high emissions.Therefore,emission control policies must emphasize the PRD and key roads by travel guidance to achieve greater reduction.Gasoline passenger cars with a large proportion of traffic dominated morning and evening peaks in the 24-hour period and were the dominant contributors to CO and HC emissions,contributing more than 50%in the daytime(7:00–23:00)and higher than 26%at night(0:00–6:00).Diesel trucks made up 10%of traffic,but were the dominant player at night,contributed 50%–90%to NO_(X) and PM_(2.5) emissions,with amarked 24-hour change rule of more than 80%at night(23:00–5:00)and less than 60%during daytime.Therefore,targeted control measures by time-section should be set up on collaborative control.These findings provide time-varying decision support for variable vehicle emission control on a large scale.

高纵横比单层MoS_(2)纳米-微米带的可控合成及其在高性能光电晶体管中的应用

本文报道了一种快速、可控合成单层MoS_(2)纳米-微米带的方法:通过在蓝宝石衬底上旋涂Na_(2)MoO_(4)和NaOH的混合溶液后一步化学气相沉积硫化的方式进行生长.其中,通过改变NaOH的浓度,对气-液-固生长过程中的反应物液滴流动性进行调控,我们实现了对所获得的MoS_(2)的形貌和取向的调控;同时,通过改变生长时间,可以实现对MoS_(2)层数的调控.利用这种方法,我们获得了最窄宽度仅为200 nm,纵横比超过100的单层MoS_(2)纳米-微米带,且表征证明其具有很高的晶体质量.同时,我们还用该MoS_(2)纳米带作为沟道材料,制备了光电晶体管,测试表明其具有高达9×10^(5)的电流开/关比、超过10^(5)的光暗电流比以及高达8.6 A W^(-1)的响应度,展现了其在电子和光电子器件中的应用潜力.

Integrating 2D layered materials with 3D bulk materials as van der Waals heterostructures for photodetections:Current status and perspectives

In the last decade,two-dimensional layered materials(2DLMs)have been drawing extensive attentions due to their unique properties,such as absence of surface dangling bonds,thickness-dependent bandgap,high absorption coeffi-cient,large specific surface area,and so on.But the high-quality growth and transfer of wafer-scale 2DLMs films is still a great challenge for the commerciali-zation of pure 2DLMs-based photodetectors.Conversely,the material growth and device fabrication technologies of three-dimensional(3D)semiconductors photodetectors tend to be gradually matured.However,the further improvement of the photodetection performance is limited by the difficult heterogeneous inte-gration or the inferior crystal quality via heteroepitaxy.Fortunately,2D/3D van der Waals heterostructures(vdWH)combine the advantages of the two types of materials simultaneously,which may provide a new platform for developing high-performance optoelectronic devices.Here,we first discuss the unique advantages of 2D/3D vdWH for the future development of photodetection field and simply introduce the structure categories,working mechanisms,and the typical fabrication methods of 2D/3D vdWH photodetector.Then,we outline the recent progress on 2D/3D vdWH-based photodetection devices integrating 2DLMs with the traditional 3D semiconductor materials,including Si,Ge,GaAs,AlGaN,SiC,and so on.Finally,we highlight the current challenges and pros-pects of heterointegrating 2DLMs with traditional 3D semiconductors toward photodetection applications.

Characterizations of high-voltage vertically-stacked GaAs laser power converter

Six-junction vertically-stacked Ga As laser power converters（LPCs） with n^＋-Ga As/p^＋-Al0.37 Ga0.63 As tunnel junctions have been designed and grown by metal-organic chemical vapor deposition for converting the power of 808 nm lasers. The LPC chips are characterized by measuring current–voltage（I–V） characteristics under 808 nm laser illumination, and a maximum conversion efficiency ηc of 53.1% is obtained for LPCs with an aperture diameter of 2 mm at an input laser power of 0.5 W. In addition, the characteristics of the LPCs are analyzed by a standard equivalent-circuit model, and the reverse saturation current, ideality factor, series resistance and shunt resistance are extracted by fitting of the I–V curves.

Four-junction AlGaAs/GaAs laser power converter

Four-junction A1GaAs/GaAs laser power converters （LPCs） with n＋-GaAs/p＋-A10.37Ga0.63As hetero- structure tunnel junctions （TJs） have been designed and grown by metal-organic chemical vapor deposition （MOCVD） for converting the power of 808 nm lasers. A maximum conversion efficiency ηc of 56.9% ＋ 4% is obtained for cells with an aperture of 3.14 mm2 at an input laser power of 0.2 W, while dropping to 43.3% at 1.5 W. Measured current-voltage （I-V） characteristics indicate that the performance of the LPC can be further improved by increasing the tunneling current density of TJs and optimizing the thicknesses of sub-cells to achieve current matching in LPC.