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A STOCHASTIC TRUST-REGION FRAMEWORK FOR POliCY OPTIMIZATION

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Journal of Computational Mathematics 2022年第6期40卷 1004-1030页

作者： Mingming Zhao Yongfeng Li Zaiwen Wen Beijing International Center for Mathematical Research Peking UniversityBeijing 100871China

In this paper,we study a few challenging theoretical and numerical issues on the well known trust region policy optimization for deep reinforcement learning.The goal is to find a policy that maximizes the total expected reward when the agent acts according to the policy.The trust region subproblem is constructed with a surrogate function coherent to the total expected reward and a general distance constraint around the latest policy.We solve the subproblem using a preconditioned stochastic gradient method with a line search scheme to ensure that each step promotes the model function and stays in the trust region.To overcome the bias caused by sampling to the function estimations under the random settings,we add the empirical standard deviation of the total expected reward to the predicted increase in a ratio in order to update the trust region radius and decide whether the trial point is accepted.Moreover,for a Gaussian policy which is commonly used for continuous action space,the maximization with respect to the mean and covariance is performed separately to control the entropy loss.Our theoretical analysis shows that the deterministic version of the proposed algorithm tends to generate a monotonic improvement of the total expected reward and the global convergence is guaranteed under moderate assumptions.Comparisons with the state-of-the–art methods demonstrate the effectiveness and robustness of our method over robotic controls and game playings from OpenAI Gym.

关键词： Deep reinforcement learning Stochastic trust region method Policy optimization Global convergence Entropy control

Evaluation of Holstein cows with different tongue‑rolling frequencies:stress immunity,rumen environment and general behavioural activity

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Journal of Animal Science and Biotechnology 2023年第6期14卷 2686-2700页

作者： Fuyu Sun Xiaoyang Chen Yongfeng Li Guangyong Zhao Xianhong Gu State Key Laboratory of Animal Nutrition Institute of Animal ScienceChinese Academy of Agricultural SciencesHaidian DistrictNo.2 Yuanmingyuan West RoadBeijingChina. College of Animal Science and Technology China Agricultural UniversityHaidian DistrictNo.2 Yuanmingyuan West RoadBeijingChina. Agricultural Information Institute Chinese Academy of Agriculture SciencesHaidian DistrictNo.12 Zhongguancun South StreetBeijingChina

Background The tongue-rolling behaviour of cows is regarded as an outward sign of stressed animals in a low welfare status.The primary aim of this observational study was to evaluate the association between the frequency of tongue-rolling behaviour and its physiological function.The secondary aim was to explore the relationship between general activities and the frequency of tongue-rolling behaviour of cows.A total of 126 scan sampling behavioural observations were collected over 7 d on 348 Holstein cows with the same lactation stage in the same barn.The tongue-rolling frequency was defined as the number of tongue-rolling observations as a percentage to the total observations per individual cow.According to their tongue-rolling frequency,the cows were grouped into the CON(no tongue-rolling),LT(frequency 1%),MT(frequency 5%),and HT(frequency 10%)groups.Six cows from each group were randomly selected for sampling.Serum samples,rumen fluid,milk yield,and background infor-mation were collected.The general behaviour data during 72 continuous hours of dairy cows,including eating time,rumination time,food time(eating time+rumination time),and lying time,were recorded by the collar sensor.Results Cortisol(P=0.012),γ-hydroxybutyric acid(P=0.008),epinephrine(P=0.030),and dopamine(P=0.047)levels were significantly higher in tongue-rolling groups than in the CON group.Cortisol levels and tongue-rolling frequency had a moderate positive correlation(linearly r=0.363).With the increase in tongue-rolling frequency,the rumen pH decreased first and then increased(P=0.013),comparing to the CON group.HT cows had significantly less food time than CON cows(P=0.035).The frequency of tongue-rolling had a moderate negative relationship with rumination time(r=-0.384)and food time(r=-0.492).Conclusions The tongue-rolling behaviour is considered as a passive coping mechanism,as the stress response in cows with high tongue-rolling frequency increased.Food intake and rumination activities were all closely related to the occurrence of tongue-r

关键词： General activity Holstein cow Rumen fermentation Stress immunity Tongue rolling

High mass loading NiCo_(2)O_(4) with shell-nanosheet/core-nanocage hierarchical structure for high-rate solid-state hybrid supercapacitors

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Green Energy & Environment 2022年第4期7卷 723-733页

作者： Wang Yang liqiang Hou Peng Wang Yun li Rui li Bo Jiang Fan Yang Yongfeng Li State Key Laboratory of Heavy Oil Processing China University of Petroleum(Beijing)Changping102249China

Rational design of advanced structure for transition metal oxides(TMOs) is attractive for achieving high-performance supercapacitors.However, it is hampered by sluggish reaction kinetics, low mass loading, and volume change upon cycling. Herein, hierarchical Ni Co_(2)O_(4) architectures with 2D-nanosheets-shell and 3D-nanocages-core(2D/3D h-NCO) are directly assembled on nickel foam via a facile one-step way.The 2D nanosheets are in-situ generated from the self-evolution of initial NCO nanospheres. This 2D/3D hierarchical structures ensure fast ion/electron transport and maintain the structural integrity to buffer the volume expansion. The 2D/3D h-NCO electrode with an ultrahigh mass loading(30 mg cm^(-2)) achieves a high areal capacity of 4.65 C cm^(-2)(equivalent to 1.29 mAh cm^(-2)) at a current density of 4 mA cm^(-2), and retains 3.7 C cm^(-2) even at 50 mA cm^(-2). Furthermore, the assembled solid-state hybrid supercapacitor yields a high volumetric energy density of 4.25 mWh cm^(-3) at a power density of 39.3 mW cm^(-3), with a high capacity retention of 92.4% after 5000 cycles. Therefore, this work provides a new insight to constuct hierarchical electrodes for energy storage application.

关键词： Transition-metal oxides Hierarchical structure High mass loading Free-standing Supercapacitors

Tailoring circular dichroism via the Born-Kuhn model for meta-holograms

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Science China(Physics,Mechanics & Astronomy) 2022年第10期65卷 83-92页

作者： He Wang Hongqiang Zhou Tianhao li Zhe Qin Chenchen li Xin li Yongfeng Li Jieqiu Zhang Shaobo Qu lingling Huang Department of Basic Sciences Air Force Engineering UniversityXi’an 710051China Beijing Engineering Research Center of Mixed Reality and Advanced Display School of Optics and PhotonicsBeijing Institute of TechnologyBeijing 100081China Department of Physics and Optoelectronics Faculty of ScienceBeijing University of TechnologyBeijing 100124China

Chirality, as one of the ubiquitous properties in nature, has aroused striking attention in the fields of physics and materials sciences. For tailoring of light with more degree of freedom, circular dichroism has been considered as the auxiliary dimension to improving such an issue. Inspired by the Born-Kuhn plasmonic oscillation model, we demonstrate and discuss a chiral resonator to reveal reverse circular dichroism within two separate frequency bands in the microwave regime. The underlying physical mechanisms of bonding and anti-bounding modes are analyzed via transmission/reflection spectra and surface current distributions for different chiral enantiomers. To leverage the proposed paradigm to the application levels, especially for metaholography, we conduct the numerical simulation and experimental demonstration of two proofs of principles. Based on the Pancharatnam-Berry phase/amplitude modulation and complex-amplitude manipulation, respectively, the meta-holograms with independent targets of reconstructing images in full-space and reflected regions are achieved. Significantly, our paradigm may promise further applications in spin-controlled meta-devices for image processing, information encryption, anti-counterfeiting,remote sensing, and radar systems.

关键词： circular dichroism Born-Kuhn model meta-hologram electromagnetic manipulation

Electrochemical synthesis of Ni doped carbon quantum dots for simultaneous fluorometric determination of Fe^(3+)and Cu^(2+)ion facilely

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Green Chemical Engineering 2023年第1期4卷 115-122页

作者： Siyuan Sun Yang Sun Fan Yang Sai Che Xiaoyun Zhang Ge Zhang Yongfeng Li State Key Laboratory of Heavy Oil Processing China University of PetroleumBeijing102249China

A novel Ni doped carbon quantum dots(Ni-CQDs)fluorescence probe was synthesized by facile electrolysis of monoatomic Ni dispersed porous carbon(Ni–N–C).The obtained Ni-CQDs showed a high quantum yield of 6.3%with the strongest excitation and emission peaks of 360 nm and 460 nm,and maintained over 90%of the maximum fluorescence intensity in a wide p H range of 3–12.The metal ions detectability of Ni-CQDs was enhanced by Ni doping and functional groups modification,and the rapid and selective detection of Fe^(3+)and Cu^(2+)ions was achieved with Ni-CQDs through dynamic and static quenching mechanism,respectively.On one hand,the energy band gap of Ni-CQDs was regulated by Ni doping,so that excited electrons in Ni-CQDs were able to transfer to Fe^(3+)easily.On the other hand,the abundant functional groups promoted the generation of static quenching complexation between Cu^(2+)and Ni-CQDs.In metal ions detection,the linear quantitation range of Fe^(3+)and Cu^(2+)were 100–1000μM(R^(2)=0.9955)and 300–900μM(R^(2)=0.9978),respectively.The limits of detection(LOD)were calculated as 10.17 and 7.88μM,respectively.Moreover,the fluorescence quenched by Cu^(2+)could be recovered by EDTA2-due to the destruction of the static quenching complexation.In this way,NiCQDs showed the ability to identify the two metal ions to a certain degree under the condition of Fe^(3+)and Cu^(2+)coexistent.This work paves the way of facile multiple metal ion detection with high sensitivity.

关键词： Electrolysis Ni doped CQDs Fe^(3+)detection Cu^(2+)detection Ions distinction

Multiscale structure and interface engineering of Fe/Fe_(3)C in situ encapsulated in nitrogen-doped carbon for stable and efficient multi-band electromagnetic wave absorption

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Journal of Materials Science & Technology 2023年第27期158卷 9-20页

作者： Bo Jiang Wang Yang Hengxuan Bai Chen Zhang Siyuan li Shaoxiong Du Ye Wang li Sun Xiaobai Wang Yongfeng Li State Key Laboratory of Heavy Oil Processing China University of Petroleum(Beijing)Changping 102249China Department of Materials Application Research AVIC Manufacturing Technology InstituteBeijing 100024China

Most reported electromagnetic wave absorption(EWA)materials show significant effective absorption in a certain frequency range,but their performances deteriorate dramatically as the frequency changes.As the range of working frequencies for electronic devices is gradually widening,it is of great interest to explore frequency-insensitive EWA materials that can achieve efficient absorption in every waveband by simply changing the absorption thickness.To this end,a multi-scale absorber(Fe/Fe_(3) C@NC)is rationally synthesized by chemical foaming and in-situ growth strategy.By controlling the growth of carbon nan-otubes,the Fe/Fe_(3) C@NC-2 exhibits a well-constructed 3D multi-scale architecture.Thanks to dipole po-larization,interface polarization and magnetic-dielectric energy conversion,the Fe/Fe_(3) C@NC-2 overcomes the frequency dispersion behavior and keeps a stable dielectric attenuation capability across the entire frequency range.Consequently,it delivers a superb full-band absorption of-50.1,-59.83,-55.87 and-51.91 dB in the S,C,X and Ku bands,respectively.The maximum radar cross-sectional reduction reaches 35.44 dB m^(-2) when the incidentθis 20°,testifying its impressive performance.Surprisingly,this EWA material also shows a remarkable resistance to oxidation and corrosion derived from the tightly coated carbon layers.This work provides new insight into the design of multi-band and stable EWA materials for practical application.

关键词： Multi-scale structure Heterogeneous interface Multiple bands Magnetic-dielectric composites Electromagnetic waves absorption

CLE14 functions as a "brake signal" to suppress age-dependent and stress-induced leaf senescence by promoting JUB1-mediated ROS scavenging in Arabidopsis

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Molecular Plant 2022年第1期15卷 179-188页

作者： Zenglin Zhang Cheng liu Kui li Xiaoxu li Mengmeng Xu yongfeng Guo Tobacco Research Institute Chinese Academy of Agricultural SciencesQingdaoShandong 266101China

Leaf senescence is an important developmental process in the plant life cycle and has a significant impact on agriculture.When facing harsh environmental conditions,monocarpic plants often initiate early leaf senes-cence as an adaptive mechanism to ensure a complete life cycle.Upon initiation,the senescence process is fine-tuned through the coordination of both positive and negative regulators.Here,we report that the small secreted peptide CLAVATA3/ESR-RELATED 14(CLE14)functions in the suppression of leaf senescence by regulating ROS homeostasis in Arabidopsis.Expression of the CLE14-encoding gene in leaves was signifi-cantly induced by age,high salinity,abscisic acid(ABA),salicylic acid,and jasmonic acid.CLE14 knockout plants displayed accelerated progression of both natural and salinity-induced leaf senescence,whereas increased CLE14 expression or treatments with synthetic CLE14 peptides delayed senescence.CLE14 pep-tide treatments also delayed ABA-induced senescence in detached leaves.Further analysis showed that over-expression of CLE14 led to reduced.ROS levels in leaves,where higher expression of ROS scavenging genes was detected.Moreover,CLE14 signaling resulted in transcriptional activation of JUB1,a NAC family tran-scription factor previously identified as a negative regulator of senescence.Notably,the delay of leaf senes-cence,reduction in H202 level,and activation of ROS scavenging genes by CLE14 peptides were dependent on JUB1.Collectively,these results suggest that the small peptide CLE14 serves as a novel"brake signal"to regulate age-dependent and stress-induced leaf senescence through JUB1-mediated ROS scavenging.

关键词： CLE14 peptide signal leaf senescence salt stress ABA ROS JUB1

Blockchain-based Privacy-Preserving Group Data Auditing with Secure User Revocation

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Computer Systems Science & Engineering 2023年第4期45卷 183-199页

作者： Yining Qi Yubo Luo yongfeng Huang Xing li Tsinghua University Beijing100084China Beijing National Research Center for Information Science and Technology Beijing100084China University of North Carolina at Chapel Hill North Carolina27599USA

Progress in cloud computing makes group data sharing in outsourced storage a reality.People join in group and share data with each other,making team work more convenient.This new application scenario also faces data security threats,even more complex.When a user quit its group,remaining data block signatures must be re-signed to ensure security.Some researchers noticed this problem and proposed a few works to relieve computing overhead on user side.However,considering the privacy and security need of group auditing,there still lacks a comprehensive solution to implement secure group user revocation,supporting identity privacy preserving and collusion attack resistance.Aiming at this target,we construct a concrete scheme based on ring signature and smart contracts.We introduce linkable ring signature to build a kind of novel meta data for integrity proof enabling anonymous verification.And the new meta data supports secure revocation.Meanwhile,smart contracts are using for resisting possible collusion attack and malicious re-signing computation.Under the combined effectiveness of both signature method and blockchain smart contracts,our proposal supports reliable user revocation and signature re-signing,without revealing any user identity in the whole process.Security and performance analysis compared with previous works prove that the proposed scheme is feasible and efficient.

关键词： Provable data possession data integrity blockchain ring signature

Flexible and densified graphene/waterborne polyurethane composite film with thermal conducting property for high performance electromagnetic interference shielding

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Nano Research 2022年第11期15卷 9926-9935页

作者： Wang Yang Hengxuan Bai Bo Jiang Chaonan Wang Weimin Ye Zhengxuan li Chong Xu Xiaobai Wang Yongfeng Li State Key Laboratory of Heavy Oil Processing China University of PetroleumBeijing 102249China Department of Materials Application Research AVIC Manufacturing Technology InstituteBeijing 100024China

High-performance electromagnetic interference(EMI)shielding materials with flexibility,excellent mechanical property,and thermal conductivity are highly desired for fifth-generation communications devices.Graphene exhibits tremendous potential due to its high electrical conductivity and unique lamellar structure.However,the construction of densified graphene structure in polymer matrix is still challenging.Herein,we develop a graphene/waterborne polyurethane(G/WPU)flexible film with densified and ordered layer-structure for using as an EMI shielding material.By virtue of the polyvinylpyrrolidone modified strategy and facile liquid phase ball-milling treatment,the graphene nanosheets can be efficiently dispersed into the WPU substrate and tightly connected between each other via internal interactions.Benefiting from the relatively low defects and densified structure of graphene,the resultant G/WPU film yields a high electrical conductivity of 1,004.5 S/m,and a tensile strength of around 48.5 MPa.As a consequence,it achieves an average EMI shielding effectiveness of over 30 dB in the X-band with a thickness of merely 0.15 mm and the value is further enhanced to 73.4 dB at 0.9 mm with a low density of 1.4 g/cm^(3),offering over 99.99999%shielding of incident electromagnetic waves.More importantly,this G/WPU film also exhibits a high cross-plane thermal conductivity of about 1.13 W/(m·K).Thus,this work develops a high-performance EMI shielding material with both good capacity of heat transmission,but also provides a facile strategy for designing next-generation advanced,lightweight,flexible,and multifunction shielding materials.

关键词： electromagnetic interference shielding graphene densification flexible thermal conductivity