Digital Twin-based Quality Management Method for the Assembly Process of Aerospace Products with the Grey-Markov Model and Apriori Algorithm

The assembly process of aerospace products such as satellites and rockets has the characteristics of single-or small-batch production,a long development period,high reliability,and frequent disturbances.How to predict and avoid quality abnormalities,quickly locate their causes,and improve product assembly quality and efficiency are urgent engineering issues.As the core technology to realize the integration of virtual and physical space,digital twin(DT)technology can make full use of the low cost,high efficiency,and predictable advantages of digital space to provide a feasible solution to such problems.Hence,a quality management method for the assembly process of aerospace products based on DT is proposed.Given that traditional quality control methods for the assembly process of aerospace products are mostly post-inspection,the Grey-Markov model and T-K control chart are used with a small sample of assembly quality data to predict the value of quality data and the status of an assembly system.The Apriori algorithm is applied to mine the strong association rules related to quality data anomalies and uncontrolled assembly systems so as to solve the issue that the causes of abnormal quality are complicated and difficult to trace.The implementation of the proposed approach is described,taking the collected centroid data of an aerospace product’s cabin,one of the key quality data in the assembly process of aerospace products,as an example.A DT-based quality management system for the assembly process of aerospace products is developed,which can effectively improve the efficiency of quality management for the assembly process of aerospace products and reduce quality abnormalities.

Quantifying urbanization levels on the Tibetan Plateau with high-resolution nighttime light data

The Tibetan Plateau(TP)is undergoing rapid urbanization.To improve urban sustainability and construct eco-logical security barriers,it is essential to quantify the spatial patterns of urbanization level on the TP,but the existing studies on the topic have been limited by the lack of socioeconomic data.This study aims to quantify the urbanization level on the TP in 2018 with Luojia1-01(LJ1-01)high-resolution nighttime light(NTL)data.Specifically,the compounded night light index is used to quantify spatial patterns of urbanization level at mul-tiple scales.The results showed that the TP had a low overall urbanization level with a large internal difference.The urbanization level in the northeast,southeast and south of the TP was relatively high,forming three hotspots centered in Xining City,Lhasa City and Shangri-La City,while the urbanization level in the central and western regions was relatively low.The analysis of influencing factors,based on the random forest model,showed that transportation and topography were the main factors affecting the TP’s spatial patterns of urbanization level.The comparison analysis with socioeconomic statistics and traditional NTL data showed that LJ1-01 NTL data can be used to more effectively quantify the urbanization level since it is more advantageous for reflecting the spatial extent of urban land and describing the spatial structure of socioeconomic activities within urban areas.These advantages are attributed to the high spatial resolution of the data,appropriate imaging time and unaf-fected by saturation phenomena.Thus,the proposed LJ1-01 NTL-based urbanization level measurement method has the potential for wide applications around the world,especially in less-developed regions lacking statistical data.Using this method,we refined the measurement of the TP’s urbanization level in 2018 for multiple scales including the region,basin,prefecture and county levels,which provides basic information for the further urban sustainability research on the TP.

SRIM Scheme： An Impression-Management Scheme for Privacy-Aware Photo-Sharing Users

With the development of online social networks （OSNs） and modern smartphones, sharing photos with friends has become one of the most popular social activities. Since people usually prefer to give others a positive impression, impression management during photo sharing is becoming increasingly important. However, most of the existing privacy-aware solutions have two main drawbacks： Users must decide manually whether to share each photo with others or not, in order to build the desired impression; and users run a high risk of leaking sensitive relational information in group photos during photo sharing, such as their position as part of a couple, or their sexual identity. In this paper, we propose a social rela- tion impression-management （SRIM） scheme to protect relational privacy and to automatically recom- mend an appropriate photo-sharing policy to users. To be more specific, we have designed a lightweight face-distance measurement that calculates the distances between users＇ faces within group photos by relying on photo metadata and face-detection results. These distances are then transformed into relations using proxemics. Furthermore, we propose a relation impression evaluation algorithm to evaluate and manage relational impressions. We developed a prototype and employed 21 volunteers to verify the functionalities of the SRIM scheme. The evaluation results show the effectiveness and efficiency of our proposed scheme.

Research Progress on the Structure of DCAF7 Gene and Its Effects on Growth and Development

DNA damage binding protein 1(DDB1) and CUL4-associated factor 7(DCAF7), also known as WDR68, regulate a series of biological activities such as growth and development of organisms. In this paper, the nucleotide sequence and the secondary structure and tertiary structure of the encoded protein were analyzed by an online bioinformatics program, and the biological function, deletion effects and expression level of the gene in different tissues were reviewed, in order to provide reference for the study of this gene as a genetic marker affecting livestock production performance.

Residents’perceptions of ecosystem services in an urbanizing basin:A case study in the Guanting Reservoir basin,China

Understanding stakeholders’differences in perceptions of ecosystem services(ES)is crucial for guiding ecolog-ical conservation and planning.However,the variations of ES perception amongst different types of residents in urbanizing areas along an urban-rural gradient are still poorly understood.Combining a questionnaire-based survey,redundancy analysis,and statistical tests,we delineated the urban-rural gradient according to local res-idents’socio-economic characteristics,and investigated the differences in local residents’perceptions of ES and potential factors affecting them in the Guanting Reservoir basin,a rapidly urbanizing basin in China.The results showed that residents living in urban-rural transitional areas attached great importance to provisioning services of providing food and domestic water,regulating services of carbon sequestration and air purification,and cul-tural services of providing education and training,which were 0.7%-13.1%,0.7%-9.1%and 2.5%-21.2%higher than that of residents in other areas,respectively.Age and occupation were major factors affecting residents’perceptions.In terms of land-use types that deliver ES,the difference in perceptions of ES delivered by grassland was the greatest amongst residents.Our results support recommendations for policymakers to take into account the stakeholders’diverse perceptions,thus promoting residents’sense of gain on ES.

不同植被恢复类型的沙地土壤中溶解性有机质演变特征

溶解性有机质(dissolved organic matter, DOM)是土壤有机碳的重要组成部分,可以有效地评价干旱区沙漠化土壤植被恢复状况.然而,对于不同恢复方式、不同植被类型(如草地、灌木丛、针叶林、落叶林等)沙地土壤中DOM的演变特征与光谱学特性缺乏认知.本研究以毛乌素沙地为例,采集3种土地利用类型(裸沙地、配土改良地和植被覆盖地)的表层土壤,采用紫外吸收光谱、三维荧光光谱和平行因子模型法,结合主成分分析法探究了不同土地改良措施和植被覆盖类型下土壤中DOM的来源、含量与组分特征.结果表明,不同土地利用类型和不同植被覆盖下土壤DOM含量和溶解性有机碳(DOC)/土壤有机碳(SOC)值存在较大差异,相较于裸沙地,配土改良和植被覆盖显著提高了DOC的含量,但DOC/SOC的比值降低, SOC的稳定性有所提升;且乔木覆盖地中有机碳的稳定性略高于草地及灌木地.平行因子分析(PARAFAC)结果表明,裸沙地DOM主要由类蛋白质(C3)组成,而配土改良和植被覆盖地则以类腐殖酸(C1和C2)为主.相关性分析表明, C1与C3及C2与C3均为极显著负相关关系(P<0.01).这说明C3组分与C1、C2组分的来源不同.在不同的植被类型之间,类腐殖酸物质(C1与C2)的总占比为乔木>草本>灌木,且恢复年限越长,腐殖质类物质的相对含量越高.相比于裸沙地和配土改良地,植被覆盖地土壤DOM的荧光指数(FI值)下降、自生源指数(BIX值)与腐殖化指数(HIX值)显著提高,呈现明显的陆源特征,证实了有机碳稳定性的增强.且乔木区域土壤的腐殖化程度相较于灌木地和草地更高.总之,植被恢复过程,特别是乔木的种植,较配土改良地和裸沙地可有效增加DOM的含量,提高DOM的稳定性,有利于土壤有机碳的固存.本研究为毛乌素沙地的治理改善提供一定的理论支持和参考依据.

土壤胡敏素的自由基特性、氧化还原性及其影响因素

采用电子顺磁共振波谱技术研究了10种代表性土壤胡敏素中持久性自由基(persistent free radicals,PFRs)的类型与浓度.结果表明10种土壤提取的胡敏素中均检测到PFRs,浓度范围为0.11×10^(16)~5.79×10^(16)spins/g,其g因子均<2.0030,属于以碳为中心的"芳香族"类自由基.傅里叶变换衰减全反射红外光谱、紫外可见漫反射光谱及酸性基团分析表明,胡敏素的芳香结构有利于PFRs的形成,且PFRs浓度与酚羟基含量呈负相关关系(P<0.05),但与羧基含量呈正相关关系(P<0.05).自旋捕获法测定了胡敏素诱导产生活性氧物种(reactive oxygen species,ROS)的能力,10种胡敏素中均检测到超氧自由基(平均浓度达5.25×10^(13)spins/g),仅在部分样品(如红壤、黑土、栗钙土和褐土提取的胡敏素)中检测到羟基自由基.通过二硫苏糖醇(DTT)和1,1-二苯基-2-三硝基苯肼(DPPH)方法测定了胡敏素的氧化还原性,其氧化能力范围为24~376 nmol/(min g),还原能力IC50的范围为0.19~1.83 g/mL.相关分析结果表明,胡敏素的氧化能力与其促使产生ROS的性能直接相关,而酚羟基是其还原能力的主要贡献基团.进一步以双酚A(BPA)为目标污染物,研究了不同来源胡敏素促使BPA转化的性能.结果显示,BPA去除率与胡敏素氧化能力呈正相关关系(P<0.05),而氧化能力与ROS呈正相关关系(P<0.05),证实了ROS对BPA去除率的贡献.这些结果为评价不同类型土壤中胡敏素的生态环境效应提供了理论依据.

Stochastic Dynamic Economic Dispatch of Wind-integrated Electricity and Natural Gas Systems Considering Security Risk Constraints

As the proportion of wind power generation increases in power systems,it is necessary to develop new ways for wind power accommodation and improve the existing power dispatch model.The power-to-gas technology,which offers a new approach to accommodate surplus wind power,is an excellent way to solve the former.Hence,this paper proposes to involve power-to-gas technology in the integrated electricity and natural gas systems(IEGSs).To solve the latter,on one hand,a new indicator,the scale factor of wind power integration,is introduced into the wind power stochastic model to better describe the uncertainty of grid-connected wind power;on the other hand,for quantizing and minimizing the impact of the uncertainties of wind power and system loads on system security,security risk constraints are established for the IEGS by the conditional value-at-risk method.By considering these two aspects,an MILP formulation of a security-risk based stochastic dynamic economic dispatch model for an IEGS is established,and GUROBI obtained from GAMS is used for the solution.Case studies are conducted on an IEGS consisting of a modified IEEE 39-bus system and the Belgium 20-node natural gas system to examine the effectiveness of the proposed dispatch model.

Light-induced variation in environmentally persistent free radicals and the generation of reactive radical species in humic substances

Environmentally persistent free radicals(EPFRs)in humic substances play an essential role in soil geochemical processes.Light is known to induce EPFRs formation for dissolved organic matter in aquatic environments;however,the impacts of light irradiation on the variation of EPFRs in soil humic substances remain unclear.In this study,humic acid,fulvic acid,and humin were extracted from peat soil and then in situ irradiated using simulated sunlight.Electron paramagnetic resonance spectroscopy results showed that with the increasing irradiation time,the spin densities and g-factors of humic substances rapidly increased during the initial 20 min and then gradually reached a plateau.After irradiation for 2h,the maximum spin density levels were up to 1.63×10^17,2.06×10^17,and 1.77×10^×10^17 spins/g for the humic acid,fulvic acid,and humin,respectively.And the superoxide radicals increased to 1.05×10^l4-1.46×10^14spins/g while the alkyl radicals increased to 0.47×10^14-1.76×10^14 spins/g.The light-induced EPFRs were relatively unstable and readily returned back to their original state under dark and oxic conditions.Significant positive correlations were observed between the concentrations of EPFRs and reactive radical species(R2=0.65-0.98,/?<0.05),which suggested that the newly produced EPFRs contributed to the formation of reactive radical species.Our findings indicate that under the irradiation humic substances are likely to be more toxic and reactive in soil due to the formation of EPFRs.

Surface hydrophobic modification enhanced catalytic performance of electrochemical nitrogen reduction reaction

Electrocatalytic nitrogen reduction reaction(NRR)is a sustainable approach for NH_(3)production with low energy consumption.However,competing hydrogen reduction reaction(HER)in aqueous solution results in low NH_(3)production and Faraday efficiency(FE).Here,MoS_(2)nanostructures with a hydrophobic surface are synthesized by alkyl thiols modification.Aerophilic and hydrophobic surface facilitates an efficient three-phase contact of N_(2),H_(2)O,and catalyst.Thus,localized concentrated N_(2)molecules can overcome the mass transfer limitation of N2 and depress the HER due to lowering the proton contacts.Although the active-sites decrease with the increase of the alkyl chain since the thiol may cover the active site,the optimized electrocatalyst achieves NH_(3)yield of 12.86×10^(-11)mol·cm^(-2)·s^(-1)at-0.25 V and 22.23%FE,which are 4.3 and 24 times higher than those of MoS2-CP electrocatalyst,respectively.The increased catalytic performance is attributed to the high N_(2)adsorption and depressed HER.

Comprehensive Control Scheme for an Interlinking Converter in a Hybrid AC/DC Microgrid

This paper presents a comprehensive control scheme for the interlinking converter(ILC)in a hybrid AC/DC microgrid consisting of the outer loop flexible power sharing control and the improved robust inner loop control.The outer loop power control of ILC is presented to achieve flexible power sharing of distributed generations(DGs)in the hybrid microgrid,depending on different power management objectives,which is realized based on the deduced balance state equation,and regulating the frequency and DC voltage at the same time.The improved robust inner loop control of ILC is also presented to suppress external disturbance and system model uncertainties with the improved dynamic response.This improved inner loop control which includes a disturbance observer link,can force the converter current to track the reference value with no steady error and improve the dynamic stability of the microgrid・With the proposed outer loop power sharing control and improved inner loop control,the comprehensive control scheme for the ILC is presented・Simulations cases show the effectiveness and superiority of the proposed comprehensive control scheme.

Emergency laparoscopic pancreatoduodenectomy as treatment for pancreatic head cancer-induced acute gastrointestinal hemorrhage,safe or not?

We have read with great interests the article by Jin and colleagues entitled“Laparoscopic pancreaticoduodenectomy for pancreatic cancer:a hope or hype?”recently published in HepatoBiliary Surgery and Nutrition(1).They came out with a conclusion that Laparoscopic pancreaticoduodenectomy(LPD)could be a safe and feasible approach for the patients with pancreatic cancers even at their advanced stage,and may also obtain comparable long-term oncologic outcomes.We really agree with this conclusion.We would here also like to report one of our experiences of an emergency LPD case of the treatment of pancreatic head cancer induced acute gastrointestinal hemorrhage,which could be the first case to the best of our knowledge based on literature research.