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Equation governing the probability density evolution of multi-dimensional linear fractional differential systems subject to Gaussian white noise

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Theoretical & Applied Mechanics Letters 2023年第3期13卷 199-208页

作者： yi luo Meng-Ze Lyu Jian-Bing Chen Pol D.Spanos George R.Brown School of Engineering Rice UniversityHouston 77005TXUSA Institute for Risk&Reliability Leibniz University HannoverHannover 30167Germany College of Civil Engineering Tongji UniversityShanghai 200092China State Key Laboratory of Disaster Reduction in Civil Engineering Tongji UniversityShanghai 200092China

Stochastic fractional differential systems are important and useful in the mathematics,physics,and engineering fields.However,the determination of their probabilistic responses is difficult due to their non-Markovian property.The recently developed globally-evolving-based generalized density evolution equation(GE-GDEE),which is a unified partial differential equation(PDE)governing the transient probability density function(PDF)of a generic path-continuous process,including non-Markovian ones,provides a feasible tool to solve this problem.In the paper,the GE-GDEE for multi-dimensional linear fractional differential systems subject to Gaussian white noise is established.In particular,it is proved that in the GE-GDEE corresponding to the state-quantities of interest,the intrinsic drift coefficient is a time-varying linear function,and can be analytically determined.In this sense,an alternative low-dimensional equivalent linear integer-order differential system with exact closed-form coefficients for the original highdimensional linear fractional differential system can be constructed such that their transient PDFs are identical.Specifically,for a multi-dimensional linear fractional differential system,if only one or two quantities are of interest,GE-GDEE is only in one or two dimensions,and the surrogate system would be a one-or two-dimensional linear integer-order system.Several examples are studied to assess the merit of the proposed method.Though presently the closed-form intrinsic drift coefficient is only available for linear stochastic fractional differential systems,the findings in the present paper provide a remarkable demonstration on the existence and eligibility of GE-GDEE for the case that the original high-dimensional system itself is non-Markovian,and provide insights for the physical-mechanism-informed determination of intrinsic drift and diffusion coefficients of GE-GDEE of more generic complex nonlinear systems.

关键词： Globally-evolving-based generalized density evolution equation(GE-GDEE) Linear fractional differential system Non-Markovian system Analytical intrinsic drift coefficient Dimension reduction

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Competitive role of film-like austenite and transition carbides on hydrogen embrittlement resistance and impact toughness in bainite-containing quenched and partitioned steel

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Journal of Iron and Steel Research(International) 2023年第4期30卷 782-794页

作者： Kai Yang yi luo Wei Li Li Wang Zhong-qu Sun Jun-liang Liu Xue-jun Jin Bao Steel-SJTU Joint Research Center of Future Steels School of Materials Science and EngineeringShanghai Jiao Tong UniversityShanghai 200240China State Key Lab of Metal Matrix Composites School of Materials Science and EngineeringShanghai Jiao Tong UniversityShanghai 200240China State Key Lab of Development and Application Technology of Automotive Steels(Bao Steel) Research Institute(R&D Center)Baoshan Iron&Steel Co.Ltd.Shanghai 200240China

A microstructure composed of martensite matrix,lower bainite,and stable film-like austenite was designed by a quenching and isothermal bainitic holding process in a 0.30C–2.69Mn–1.71Si(wt.%)steel.The yield strength,tensile strength,and ductile-to-brittle transition temperature(DBTT)of the high-strength steel thus obtained were 1263 MPa,1521 MPa,and-33℃,respectively,and at-20℃,it showed superior low-temperature toughness,which reached 77.5 J/cm^(2).Meanwhile,it showed excellent hydrogen embrittlement(HE)resistance,and the total elongation loss is only 3.1%after 15 min of hydrogen charging.The excellent comprehensive performance is attributed to the fact that fine stable austenite with film-like morphology hindered the crack nucleation and propagation,and hindered hydrogen diffusion as a hydrogen trap.However,with a decrease in the isothermal temperature,transition carbide precipitation was accompanied by a further decrease in austenite grain size.For this condition,although transition carbides can act as effective hydrogen traps,excessive precipitation decreased the carbon content of retained austenite and increased the deformation heterogeneity between austenite and martensite matrix,leading to weakened austenite stability and HE resistance,a total elongation loss of approximately 39%(15 min hydrogen charging),a sharp decrease in impact toughness,and an increase in DBTT.The competitive role of film-like austenite and transition carbides on the comprehensive mechanical performance of steel is revealed,especially the suppression of crack nucleation and propagation that will provide a guide for the design of high strength steels with excellent impact toughness and HE resistance.

关键词： Quenched and partitioned steel Isothermal bainite transformation Transition carbide Hydrogen embrittlement Impact toughness

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High-speed optoelectronic devices

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Science China(Information Sciences) 2023年第5期66卷 5-27页

作者： yi luo Changzheng SUN Bing XIONG Jian WANG Zhibiao HAO Yanjun HAN Hongtao LI Lai WANG Beijing National Research Center for Information Science and Technology (BNRist) Department of Electronic Engineering Tsinghua University

High-speed optoelectronic devices are key components of modern fiber communication systems,and the backbone of information technology. In this paper, we present our work on high-speed devices over the past decades, including high-performance semiconductor lasers and integrated light sources, wideband electrooptic modulators, high saturation power photodetectors, and their applications in both fiber communications and microwave photonics. Gain-coupled distributed feedback(DFB) lasers were fabricated with high singlemode yield. Electroabsorption modulated lasers(EMLs) were demonstrated based on identical epitaxial layer integration scheme, including single channel 40 Gb/s EMLs, and 4 × 25 and 4 × 56 Gb/s EML arrays. Both In P and thin-film lithium niobate based low half-wave voltage electro-optic modulators with modulation bandwidth over 40 GHz were demonstrated. Back-illuminated modified uni-traveling-carrier photodetectors(MUTC-PDs) with high saturation power and bandwidth exceeding 100 GHz were developed. Applications of high-speed optoelectronic devices in fiber-optic links and sub-THz wave generation are presented.

关键词： optoelectronic devices semiconductor lasers optical modulators photodetectors integrated photonic circuits

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Transient synchronous stability analysis and enhancement control strategy of a PLL-based VSC system during asymmetric grid faults

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Protection and Control of Modern Power Systems 2023年第2期8卷 304-320页

作者： yi luo Jun Yao Zhaoyang Chen Sen Huang Shiyue Chen Qi Zhang Zhentao Qin State Key Laboratory of Power Transmission Equipment and System Security and New Technology School of Electrical EngineeringChongqing UniversityChongqing 400044China State Grid Changzhou Power Supply Company Changzhou 2131261China

The stability of a voltage source converters(VSC)system based on phase-locked loop(PLL)is very important issue during asymmetric grid faults.This paper establishes a transient synchronous stability model of a dual-sequence PLL-based VSC system during low voltage ride-through by referring to the equivalent rotor swing equation of syn-chronous generators.Based on the model,the synchronization characteristics of the VSC system under asymmetric grid faults are described,and the interaction mechanisms,as well as the transient instability phenomena of positive and negative sequence PLL during asymmetric faults are explained.Using the equal area criterion,the influences of sequence control switching action,detection delay,and interaction between the positive and negative sequence PLL on the transient synchronous stability of the VSC system are analyzed,respectively.In addition,a transient stabil-ity assessment criterion based on the critical fault clearance angle and time and an enhancement control strategy based on the improved positive and negative sequence PLL are proposed.Finally,the analytical results are validated through simulation and experiments.

关键词： Voltage source converters(VSC) Asymmetric grid faults Dual-sequence PLL Transient synchronous

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Probing the ultrafast dynamics in nanomaterial complex systems by femtosecond transient absorption spectroscopy

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High Power Laser Science and Engineering 2016年第3期4卷 13-22页

作者： Qun Zhang yi luo Hefei National Laboratory for Physical Sciences at the Microscale Department of Chemical Physics and Synergetic Innovation Center of Quantum Information & Quantum Physics University of Science and Technology of China

Over the past decade the integration of ultrafast spectroscopy with nanoscience has greatly propelled the development of nanoscience, as the key information gleaned from the mechanistic studies with the assistance of ultrafast spectroscopy enables a deeper understanding of the structure–function interplay and various interactions involved in the nanosystems.This mini-review presents an overview of the recent advances achieved in our ultrafast spectroscopy laboratory that address the ultrafast dynamics and related mechanisms in several representative nanomaterial complex systems by means of femtosecond time-resolved transient absorption spectroscopy. We attempt to convey instructive, consistent information regarding the important processes, pathways, dynamics, and interactions involved in the nanomaterial complex systems,most of which exhibit excellent performance in photocatalysis.

关键词： nanomaterials time-resolved femtosecond pump-probe transient absorption spectroscopy ultrafast dynamics

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基于IWOA-Transformer的磨煤机故障预警

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动力工程学报 2024年第6期44卷 939-946页

作者：罗毅段明达华北电力大学控制与计算机工程学院北京102206

提出了一种基于改进鲸鱼算法优化Transformer网络超参数(IWOA-Transformer)的故障预警方法。该方法利用非线性收敛系数和高斯变异对鲸鱼算法(WOA)进行改进,以提高WOA的收敛速度和避免其陷入局部最优;再采用改进鲸鱼算法(IWOA)优化Transf... 详细信息

提出了一种基于改进鲸鱼算法优化Transformer网络超参数(IWOA-Transformer)的故障预警方法。该方法利用非线性收敛系数和高斯变异对鲸鱼算法(WOA)进行改进,以提高WOA的收敛速度和避免其陷入局部最优;再采用改进鲸鱼算法(IWOA)优化Transformer的超参数,建立磨煤机故障预警模型;然后,通过预测值和实际值的相似度函数确定自适应阈值,结合专家系统判断故障类型并提出解决方案,实现磨煤机故障预警;最后,以某350 MW热电机组中速磨煤机为例进行故障预警试验。结果表明:所提IWOA-Transformer模型可显著提高预警速度和准确率,具有工程实用价值。

关键词： Transformer神经网络鲸鱼优化算法磨煤机故障预警专家系统

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The influence of adding niobium and vanadium on hydrogen diffusion in 22MnB5 hot stamping steel

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Journal of Iron and Steel Research(International) 2023年第10期30卷 2031-2042页

作者： Peng-wei Zhou Zhi-yi Yan Ke Wang Tao Liu Si-jia Chen Zhen Ma Ju-sha Ma Wei Ding yi luo Bing-gang Liu Wei Li Shanghai Institute of Space Power-Sources Shanghai 200245China State Key Lab of Metal Matrix Composites School of Materials Science and EngineeringShanghai Jiao Tong UniversityShanghai 200245China

Adding alloying elements is always considered as an effective method to enhance the resistance against hydrogen embrittlement in steels.Nb and V were added into 22MnB5 hot stamping steel,and then their influences on hydrogen permeation of 22MnB5 steel suffering from corrosion in 3.5%NaCl aqueous solution were investigated.The results showed that the addition of Nb/V could reduce the hydrogen permeation content due to solution corrosion.Electrochemical techniques including electrochemical impedance spectroscopy and overpotential stepping hydrogen permeation test con-firmed that compared to the original 22MnB5 steel,22MnB5-NbN steel owned a higher corrosion resistance and a higher hydrogen diffusion resistance.Furthermore,it was confirmed that Nb-V-alloyed 22MnB5 steel showed higher resistance against hydrogen embrittlement than the Nb-V-free counterpart,which should be related to the presentence of nanoscaled Nb/V-containing precipitates as the irreversible trapping sites for hydrogen detected by thermal desorption spectroscopy.Finally,the lattice diffusion coefficient of hydrogen DL was determined in steels with and without Nb and V.

关键词： Hydrogen permeation Corrosion Hot stamping steel Niobium Vanadium Thermal desorption spectroscopy

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Development of a roof bolter drilling control process to reduce the generation of respirable dust

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International Journal of Coal Science & Technology 2021年第2期8卷 199-204页

作者： Hua Jiang yi luo Centers for Disease Control and Prevention National Institute for Occupational Safety and HealthPittsburghPAUSA Department of Mining Engineering West Virginia UniversityMorgantownWVUSA

The drilling operation in the roof bolting process,especially in hard rock,generates excessive respirable coal and quartz dusts,which could expose the roof bolting operator to continued health risks.Previous research has shown that the amount of respirable dust produced is dependent on the main drilling parameters,specifically the drilling rotational and penetration rate.In this paper,a roof bolter drilling control process was proposed to reduce the generation of respirable dust.Based on the analysis of laboratory drilling test results,a rational drilling control process(adjusting rotational and penetration rates)to achieve the optimal drilling parameter for different rock types was proposed.In this process,the ratio between specific energy and rock uniaxial compressive strength was used as the index to determine the optimal operation point.The recommended drilling operation range for the rock type used in the experiment was provided,and the reduction in respirable dust generation was demonstrated.By following this control process,the drilling efficiency can be monitored in real time,so the system can stay in a relatively high-energy efficiency with less respirable dust production from the drilling source.This algorithm is targeted to be incorporated into the current roof bolter drilling control system for drilling automation so that a safe and productive drilling operation can be conducted in a healthy working environment.

关键词： Roof bolter Drilling control Respirable dust Specific energy

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Plasmon-exciton interaction in colloidally fabricated metal nanoparticlequantum emitter nanostructures

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Nano Research 2019年第9期12卷 2164-2171页

作者： yi luo Jing Zhao Department of Chemistry University of Connecticut55 North Eagleville RoadStorrs06269USA Institute of Materials Science University of Connecticut97 North Eagleville RoadStorrs06269USA

When quantum emitters and plasmonic nanoparticles are in close vicinity,the energy exchange,termed as plasmon-exciton coupling,can make the absorption and emission behavior of the hybrid structure very different from those of the two constituents alone.The coupling strength between the two constituents highly depends on how the hybrid structure is constructed.As a result,a diverse range of coupling effect arise including plasmon induced fluorescence quenching/enhancing (weak coupling),Fano interference (intermediate coupling),Rabi-splitting and lasing (strong coupling).The emergence of different coupling behavior can be controlled by the different combinations of quantum emitters and plasmonic nanoparticles as well as the spatial arrangement of the individual components.Colloidal assembly/synthesis methods are essentially delicate strategies that can build the hybrid nanostructures with nanometer precision and allow for large-scale processing.In this review,we discuss the theoretical models that apply to different coupling behaviors,the optical properties of the hybrid systems,and the advancement of colloidal methods to manipulate the plasmon-exciton in the hybrid structures.We also provide perspectives on the challenges and future directions of the research in coupled plasmon-exciton nanosystems.

关键词： quantum emitter metal nanoparticles plasm on-exciton coupling colloidal assembly Purcell effect Rabi-splitting

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Effect of tempering on carbides and hydrogen embrittlement in E690 high strength marine structural steel

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Journal of Iron and Steel Research(International) 2022年第10期29卷 1669-1682页

作者： yi luo Wei Li Peng-wei Zhou Yuan-tao Xu Hui-yong Pang Ning Zhong Hui-sheng Jiao Xue-jun Jin Shanghai Key Laboratory of Materials Laser Processing and Modification School of Materials Science and EngineeringShanghai Jiao Tong UniversityShanghai200240China Institute of Advanced Steels and Materials School of Materials Science and EngineeringShanghai Jiao Tong UniversityShanghai200240China China Wuyang Iron and Steel Co. Ltd.Pingdingshan462500HenanChina School of Materials Science and Engineering Shanghai Maritime UniversityShanghai200120China TESCAN CHINA Shanghai200240China

The effect of tempering on carbides and hydrogen embrittlement in E690 high strength marine structural steel has been investigated.The steel was tempered at 600℃ for 1–3 h.Detailed characterization was carried out to characterize the microstructure,especially the dislocation density and grain size.The hydrogen permeation test and thermal desorption spectroscopy test were also implemented.The dislocation density decreases,the amount of carbide increases,and carbides(M_(23)C_(6) and MX)coarsen with the tempering time increasing.After tempered at 600℃ for 3 h,the diffusible hydrogen trapped by lattice and dislocation decreases while the non-diffusible hydrogen trapped by carbides increases,leading to the best hydrogen embrittlement resistance,although hydrogen diffuses rapidly due to the reduction of dislocation density.And the fracture mode changes from a combination of brittle cleavage and ductile dimpled fracture to fully ductile dimple fracture under hydrogen charging condition.Moreover,a phenomenon that hydrogen accelerates the dislocations movement of the steel during deformation was observed,which is related to the fact that hydrogen enhanced localized plasticity mechanism.

关键词： High strength marine structural steel Carbide Tempering Hydrogen embrittlement Thermal desorption spectroscopy

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