Mobile-edge computing(MEC)is a promising technology for the fifth-generation(5G)and sixth-generation(6G)architectures,which provides resourceful computing capabilities for Internet of Things(IoT)devices,such as virtua...Mobile-edge computing(MEC)is a promising technology for the fifth-generation(5G)and sixth-generation(6G)architectures,which provides resourceful computing capabilities for Internet of Things(IoT)devices,such as virtual reality,mobile devices,and smart cities.In general,these IoT applications always bring higher energy consumption than traditional applications,which are usually energy-constrained.To provide persistent energy,many references have studied the offloading problem to save energy consumption.However,the dynamic environment dramatically increases the optimization difficulty of the offloading decision.In this paper,we aim to minimize the energy consumption of the entireMECsystemunder the latency constraint by fully considering the dynamic environment.UnderMarkov games,we propose amulti-agent deep reinforcement learning approach based on the bi-level actorcritic learning structure to jointly optimize the offloading decision and resource allocation,which can solve the combinatorial optimization problem using an asymmetric method and compute the Stackelberg equilibrium as a better convergence point than Nash equilibrium in terms of Pareto superiority.Our method can better adapt to a dynamic environment during the data transmission than the single-agent strategy and can effectively tackle the coordination problem in the multi-agent environment.The simulation results show that the proposed method could decrease the total computational overhead by 17.8%compared to the actor-critic-based method and reduce the total computational overhead by 31.3%,36.5%,and 44.7%compared with randomoffloading,all local execution,and all offloading execution,respectively.展开更多
Complex systems in the real world often can be modeled as network structures,and community discovery algorithms for complex networks enable researchers to understand the internal structure and implicit information of ...Complex systems in the real world often can be modeled as network structures,and community discovery algorithms for complex networks enable researchers to understand the internal structure and implicit information of networks.Existing community discovery algorithms are usually designed for single-layer networks or single-interaction relationships and do not consider the attribute information of nodes.However,many real-world networks consist of multiple types of nodes and edges,and there may be rich semantic information on nodes and edges.The methods for single-layer networks cannot effectively tackle multi-layer information,multi-relationship information,and attribute information.This paper proposes a community discovery algorithm based on multi-relationship embedding.The proposed algorithm first models the nodes in the network to obtain the embedding matrix for each node relationship type and generates the node embedding matrix for each specific relationship type in the network by node encoder.The node embedding matrix is provided as input for aggregating the node embedding matrix of each specific relationship type using a Graph Convolutional Network(GCN)to obtain the final node embedding matrix.This strategy allows capturing of rich structural and attributes information in multi-relational networks.Experiments were conducted on different datasets with baselines,and the results show that the proposed algorithm obtains significant performance improvement in community discovery,node clustering,and similarity search tasks,and compared to the baseline with the best performance,the proposed algorithm achieves an average improvement of 3.1%on Macro-F1 and 4.7%on Micro-F1,which proves the effectiveness of the proposed algorithm.展开更多
Oxidative dehydrogenation of light alkanes to alkenes is an attractive alternative route for industrial direct dehydrogenation because of favorable thermodynamic and kinetic characteristics,but encounters difficulties...Oxidative dehydrogenation of light alkanes to alkenes is an attractive alternative route for industrial direct dehydrogenation because of favorable thermodynamic and kinetic characteristics,but encounters difficulties in selectivity control for alkenes because of over-oxidation reactions that produce a substantial amount of undesired carbon oxides.Recent progress has revealed that boron nitride is a highly promising catalyst in the oxidative dehydrogenation of light alkanes because of its superior selectivity for and high productivity of light alkenes,negligible formation of CO2,and remarkable catalyst stability.From this viewpoint,recent works on boron nitride in the oxidative dehydrogenations of ethane,propane,butane,and ethylbenzene are reviewed,and the emphasis of this viewpoint is placed on discussing the catalytic origin of boron nitride in oxidative dehydrogenation reactions.After analyzing recent progress in the use of boron nitride for oxidative dehydrogenation reactions and finding much new evidence,we conclude that pure boron nitride is catalytically inert,and an activation period is required under the reaction conditions;this process is accompanied by an oxygen functionalization at the edge of boron nitride;the B-O species themselves have no catalytic activity in C-H cleavage,and the B-OH groups,with the assistance of molecular oxygen,play the key role in triggering the oxidative dehydrogenation of propane;the dissociative adsorption of molecular oxygen is involved in the reaction process;and a straightforward strategy for preparing an active boron nitride catalyst with hydroxyl groups at the edges can efficiently enhance the catalytic efficacy.A new redox reaction cycle based on the B-OH sites is also proposed.Furthermore,as this is a novel catalytic system,there is an urgent need to develop new methods to optimize the catalytic performances,clarify the catalytic function of boron species in the alkane ODH reactions,and disclose the reaction mechanism under realistic reaction conditions.展开更多
The adsorption of uranyl on hydroxylated α-SiO_2(001) in the presence of a series of anionic ligands, i.e. OH^-, CO_3^(2-), NO_3^-, H_2PO_4^-, HPO_4^(2-),CH_3COO^-(Ac^-), C_6H_5COO^-(PhCO_2^-), C_6H_5O^-(PhO^-), was ...The adsorption of uranyl on hydroxylated α-SiO_2(001) in the presence of a series of anionic ligands, i.e. OH^-, CO_3^(2-), NO_3^-, H_2PO_4^-, HPO_4^(2-),CH_3COO^-(Ac^-), C_6H_5COO^-(PhCO_2^-), C_6H_5O^-(PhO^-), was studied by the periodic density functional theory(DFT) implemented in the Vienna ab initio simulation package(VASP). For the ligands other than OH^-and PhO^-, only the bidentate coordination modes to the uranyl were considered. The excess charge effect of a charged system was first evaluated by constructing models with net charge as is or neutralized by creating defect at the bottom of silica, and the results show that a neutralized model, even with defects, is more realistic than the charged ones.All uranyl species prefer to bind with the deprotonated site(—O^-) rather than the protonated one(—O_H), which suggests that the increase of pH,which leads to the deprotonation of the surface, may enhance the uranyl adsorption. On the other hand, the anionic ligands, which are formed at higher pH, have negative effects. The weaker acidic ligands, such as H_2CO_3, H_3PO_4 and H_2O, whose speciation in solutions is sensitive to the fluctuation of pH, have more complex effect on the uranyl adsorption than strong acids or bases. Humic substances may coordinate with uranyl through carboxyl and phenolic groups, with the carboxyl group bound stronger. The ternary complexes with one bidentate(or monodentate)anion and one(or two) H20 as ligands, which leads to the uranyl penta-coordinated in its equatorial plane, are more favorable than other configurations when bound to the same anionic ligand. Both the charged nature and the coordination behavior of an anionic ligand are relevant to its ability to influence the adsorption of uranyl on the mineral surface. In addition, the uranyl species adsorbed at the surface functionalized by anionic ligands were also addressed, and the functionalized surfaces have weaker interaction with hydrated uranyl dication.展开更多
Distributed Denial-of-Service (DDoS) attacks against public web servers are increasingly common. Countering DDoS attacks are becoming ever more challenging with the vast resources and techniques increasingly available...Distributed Denial-of-Service (DDoS) attacks against public web servers are increasingly common. Countering DDoS attacks are becoming ever more challenging with the vast resources and techniques increasingly available to attackers. It is impossible for the victim servers to work on the individual level of on-going traffic flows. In this paper, we establish IP Flow which is used to select proper features for DDoS detection. The IP flow statistics is used to allocate the weights for traffic routing by routers. Our system protects servers from DDoS attacks without strong client authentication or allowing an attacker with partial connectivity information to repeatedly disrupt communications. The new algorithm is thus proposed to get efficiently maximum throughput by the traffic filtering, and its feasibility and validity have been verified in a real network circumstance. The experiment shows that it is with high average detection and with low false alarm and miss alarm. Moreover, it can optimize the network traffic simultaneously with defending against DDoS attacks, thus eliminating efficiently the global burst of traffic arising from normal traffic.展开更多
Secure Coding is an indispensable part of the undergraduate training program for Information Security Major.As a basic course for undergraduates to carry out project engineering,its importance is self-evident.In the a...Secure Coding is an indispensable part of the undergraduate training program for Information Security Major.As a basic course for undergraduates to carry out project engineering,its importance is self-evident.In the actual teaching activities,the program design courses have to be solved in terms of content update,practical ability improvement and scientific research project,so the curriculum reform is imperative.This paper analyses the main problems existing in the Secure Coding course,explores the solution,proposes teaching methods,and gives the evaluation method.The practice shows that the reform exploration can obtain good teaching results.展开更多
Talents through-cultivating of bachelor master and doctor degrees(shortened for throughcultivating)refers to organic integration of the cultivating process of bachelor,master and doctoral students integrating high-qua...Talents through-cultivating of bachelor master and doctor degrees(shortened for throughcultivating)refers to organic integration of the cultivating process of bachelor,master and doctoral students integrating high-quality educational resources,optimizing the talents cultivating model to achieve the goal of cultivating outstanding innovative talents.Analyzing the status of the talents through-cultivating model in universities pointing out the current problems in the talents throughcultivating model,this paper discusses from the perspectives of cultivating system construction,admission of bachelor-master-doctoral students,diversion and elimination mechanism,international exchanges and cooperation,and support policies.展开更多
Soft arms have shown great application potential because of their flexibility and compliance in unstructured environments.However,soft arms made from soft materials exhibit limited cargo-loading capacity,which restric...Soft arms have shown great application potential because of their flexibility and compliance in unstructured environments.However,soft arms made from soft materials exhibit limited cargo-loading capacity,which restricts their ability to manipulate objects.In this research,a novel soft arm was developed by coupling a rigid origami exoskeleton with soft airbags.The joint module of the soft arm was composed of a deployable origami exoskeleton and three soft airbags.The motion and load performance of the soft arm of the eight-joint module was tested.The developed soft arm withstood at least 5 kg of load during extension,contraction,and bending motions;exhibited bistable characteristics in both fully contracted and fully extended states;and achieved a bending angle of more than 240°and a contraction ratio of more than 300%.In addition,the high extension,contraction,bending,and torsional stiffnesses of the soft arm were experimentally demonstrated.A kinematic-based trajectory planning of the soft arm was performed to evaluate its error in repetitive motion.This work will provide new design ideas and methods for flexible manipulation applications of soft arms.展开更多
Calcium carbonate often precipitates in anaerobic reactors treating wastewater with high calcium content.The aim of this paper is to study the effect of wastewater composition on calcium carbonate precipitation in upf...Calcium carbonate often precipitates in anaerobic reactors treating wastewater with high calcium content.The aim of this paper is to study the effect of wastewater composition on calcium carbonate precipitation in upflow anaerobic sludge blanket(UASB)reactors.Two laboratory-scale UASB reactors were operated with calcium-containing influents using acetate and carbohydrate as substrate,respectively.There was an obvious accumulation of inorganic precipitate observed in the biogranules.Observations via scanning electron microscope(SEM)and energy dispersive spectroscopy(EDS)showed that the acclimated biogranules in the two reactors differed in microstructure.Calcium carbonate was found to have precipitated on the surface of acetate-degrading biogranules,but precipitated at the core of the carbohydrate-degrading biogranules.The results indicated that substrates had significant influence on the location of calcium carbonate precipitation in anaerobic granular sludge,which was expected due to the different methanogens distribution and pH gradient within the granular sludge degrading various substrates.Moreover,the location of calcium carbonate precipitation substantially affected the specific methanogenic activity(SMA)of the granular sludge.The SMA of the acetate-degrading biogranules dropped from 1.96 gCODCH4·gVSS^(–1)·d^(–1)to 0.61 gCODCH4·gVSS^(–1)·d^(–1)after 180-d of operation in the reactor.However,the SMA of the carbohydrate-degrading biogranules was not adversely affected by calcium carbonate precipitation.展开更多
Changes in metal concentrations in the litter of Potamogeton crispus were monitored during a consecutive 40-day in situ decomposition experiment using the litterbag method.The accumulation index was calculated and use...Changes in metal concentrations in the litter of Potamogeton crispus were monitored during a consecutive 40-day in situ decomposition experiment using the litterbag method.The accumulation index was calculated and used to indicate the changes in the metals in litter.The results showed that the concentrations of Al,Cd,Cr,Fe,Mn,and Pb in litter increased significantly during the decomposition,while Cu and Zn concentrations decreased dramatically.Significant positive correlations were found between the concentrations of Al,Cr,Fe,and Mn and between Cu and Zn.Moreover,Cu and Zn both negatively correlated with Al and Fe.The remaining dry mass was negatively correlated with Al and Fe concentrations but positively correlated with Cu and Zn concentrations.Generally the accumulation index values of metals other than Al were less than one,indicating that the litter of P.crispus acted as a source of metals to the surrounding water body.Al was the only metal that showed continuous net accumulation in litter.The net accumulation of Fe and Mn in litter during the last 10 days of the experiment may indicate the precipitation of Feand Mn-oxides.It was estimated that 160 g/m^2（dry weight）P.crispus was decomposed in40 days.This was equivalent to releasing the following amounts of metals：0.01 mg Cd,0.03 mg Cr,0.71 mg Cu,0.55 mg Mn,0.02 mg Pb and 13.8 mg Zn into surrounding water,and accumulating 149 mg Al and 11 mg Fe,in a 1 m^2 area.展开更多
Passive variable stiffness joints have unique advantages over active variable stiffness joints and are currently eliciting increased attention.Existing passive variable stiffness joints rely mainly on sensors and spec...Passive variable stiffness joints have unique advantages over active variable stiffness joints and are currently eliciting increased attention.Existing passive variable stiffness joints rely mainly on sensors and special control algorithms,resulting in a bandwidth-limited response speed of the joint.We propose a new passive power-source-free stiffness-self-adjustable mechanism that can be used as the elbow joint of a robot arm.The new mechanism does not require special stiffness regulating motors or sensors and can realize large-range self-adaptive adjustment of stiffness in a purely mechanical manner.The variable stiffness mechanism can automatically adjust joint stiffness in accordance with the magnitude of the payload,and this adjustment is a successful imitation of the stiffness adjustment characteristics of the human elbow.The response speed is high because sensors and control algorithms are not needed.The variable stiffness principle is explained,and the design of the variable stiffness mechanism is analyzed.A prototype is fabricated,and the associated hardware is set up to validate the analytical stiffness model and design experimentally.展开更多
Variable Stiffness Actuator(VSA)is the core mechanism to achieve physical human–robot interaction,which is an inevitable development trend in robotic.The existing variable stiffness actuators are basically single deg...Variable Stiffness Actuator(VSA)is the core mechanism to achieve physical human–robot interaction,which is an inevitable development trend in robotic.The existing variable stiffness actuators are basically single degree-of-freedom(DOF)rotating joints,which are achieving multi-DOF motion by cascades and resulting in complex robot body structures.In this paper,an integrated 2-DOF actuator with variable stiffness is proposed,which could be used for bionic wrist joints or shoulder joints.The 2-DOF motion is coupling in one universal joint,which is different from the way of single DOF actuators cascade.Based on the 2-DOF orthogonal motion generated by the spherical wrist parallel mechanism,the stiffness could be adjusted by varying the effective length of the springs,which is uniformly distributed in the variable stiffness unit.The variable stiffness principle,the model design,and theoretical analysis of the VSA are discussed in this work.The independence of adjusting the equilibrium position and stiffness of the actuator is validated by experiments.The results show that the measured actuator characteristics are sufficiently matched the theoretical values.In the future,VSA could be used in biped robot or robotic arm,ensuring the safety of human–robot interaction.展开更多
This study investigated the dry and wet deposition fluxes of atmospheric polycyclic aromatic hydrocarbons （PAHs） in Shanghai, China. The flux sources were traced based on composition and spatio-temporal variation. T...This study investigated the dry and wet deposition fluxes of atmospheric polycyclic aromatic hydrocarbons （PAHs） in Shanghai, China. The flux sources were traced based on composition and spatio-temporal variation. The results show that wet deposition concentrations of PAHs ranged from 0.07 to 0.67 μg·L-1 and were correlated with temperature （P 〈 0.05）. Dry deposition of PAHs concentrations ranged from 3.60-92.15 μg·L-1 and were higher in winter and spring than in summer and autumn. The annual PAH average fluxes were 0.631 μg·m-2·d-1 and 4.06 μg.m·d-1 for wet and dry deposition, respectively. The highest wet deposition of PAH fluxes was observed in summer, while dry deposition fluxes were higher in winter and spring. Atmospheric PAHs were deposited as dry deposition in spring and winter, yet wet deposition was the dominant pathway during summer. Total atmospheric PAH fluxes were higher in the northern areas than in the southern areas of Shanghai, and were also observed to be higher in winter and spring. Annual deposition of atmospheric PAHs was about 10.8 t in across all of Shanghai. Wet deposition of PAHs was primarily composed of two, three, or four rings, while dry deposition of PAHs was composed of four, five, or six rings. The atmospheric PAHs, composed of four, five, or six rings, primarily existed in the form of particulates. Coal combustion and vehicle emissions were the dominant sources of PAH in the observed area of downtown Shanghai. In suburban areas, industrial pollution, from sources such as coke oven, incinerator, and oil fired power plant, was as significant as vehicle emissions in contributing to the deposition of PAHs.展开更多
基金supported by the National Natural Science Foundation of China(62162050)the Fundamental Research Funds for the Central Universities(No.N2217002)the Natural Science Foundation of Liaoning ProvincialDepartment of Science and Technology(No.2022-KF-11-04).
文摘Mobile-edge computing(MEC)is a promising technology for the fifth-generation(5G)and sixth-generation(6G)architectures,which provides resourceful computing capabilities for Internet of Things(IoT)devices,such as virtual reality,mobile devices,and smart cities.In general,these IoT applications always bring higher energy consumption than traditional applications,which are usually energy-constrained.To provide persistent energy,many references have studied the offloading problem to save energy consumption.However,the dynamic environment dramatically increases the optimization difficulty of the offloading decision.In this paper,we aim to minimize the energy consumption of the entireMECsystemunder the latency constraint by fully considering the dynamic environment.UnderMarkov games,we propose amulti-agent deep reinforcement learning approach based on the bi-level actorcritic learning structure to jointly optimize the offloading decision and resource allocation,which can solve the combinatorial optimization problem using an asymmetric method and compute the Stackelberg equilibrium as a better convergence point than Nash equilibrium in terms of Pareto superiority.Our method can better adapt to a dynamic environment during the data transmission than the single-agent strategy and can effectively tackle the coordination problem in the multi-agent environment.The simulation results show that the proposed method could decrease the total computational overhead by 17.8%compared to the actor-critic-based method and reduce the total computational overhead by 31.3%,36.5%,and 44.7%compared with randomoffloading,all local execution,and all offloading execution,respectively.
基金This work was supported by the Key Technologies Research and Development Program of Liaoning Province in China under Grant 2021JH1/10400079the Fundamental Research Funds for the Central Universities under Grant 2217002.
文摘Complex systems in the real world often can be modeled as network structures,and community discovery algorithms for complex networks enable researchers to understand the internal structure and implicit information of networks.Existing community discovery algorithms are usually designed for single-layer networks or single-interaction relationships and do not consider the attribute information of nodes.However,many real-world networks consist of multiple types of nodes and edges,and there may be rich semantic information on nodes and edges.The methods for single-layer networks cannot effectively tackle multi-layer information,multi-relationship information,and attribute information.This paper proposes a community discovery algorithm based on multi-relationship embedding.The proposed algorithm first models the nodes in the network to obtain the embedding matrix for each node relationship type and generates the node embedding matrix for each specific relationship type in the network by node encoder.The node embedding matrix is provided as input for aggregating the node embedding matrix of each specific relationship type using a Graph Convolutional Network(GCN)to obtain the final node embedding matrix.This strategy allows capturing of rich structural and attributes information in multi-relational networks.Experiments were conducted on different datasets with baselines,and the results show that the proposed algorithm obtains significant performance improvement in community discovery,node clustering,and similarity search tasks,and compared to the baseline with the best performance,the proposed algorithm achieves an average improvement of 3.1%on Macro-F1 and 4.7%on Micro-F1,which proves the effectiveness of the proposed algorithm.
基金supported by State Key Program of the National Natural Science Foundation of China(21733002)the National Natural Science Foundation of China(U1462120,21403027)Cheung Kong Scholars Programme of China(T2015036)~~
文摘Oxidative dehydrogenation of light alkanes to alkenes is an attractive alternative route for industrial direct dehydrogenation because of favorable thermodynamic and kinetic characteristics,but encounters difficulties in selectivity control for alkenes because of over-oxidation reactions that produce a substantial amount of undesired carbon oxides.Recent progress has revealed that boron nitride is a highly promising catalyst in the oxidative dehydrogenation of light alkanes because of its superior selectivity for and high productivity of light alkenes,negligible formation of CO2,and remarkable catalyst stability.From this viewpoint,recent works on boron nitride in the oxidative dehydrogenations of ethane,propane,butane,and ethylbenzene are reviewed,and the emphasis of this viewpoint is placed on discussing the catalytic origin of boron nitride in oxidative dehydrogenation reactions.After analyzing recent progress in the use of boron nitride for oxidative dehydrogenation reactions and finding much new evidence,we conclude that pure boron nitride is catalytically inert,and an activation period is required under the reaction conditions;this process is accompanied by an oxygen functionalization at the edge of boron nitride;the B-O species themselves have no catalytic activity in C-H cleavage,and the B-OH groups,with the assistance of molecular oxygen,play the key role in triggering the oxidative dehydrogenation of propane;the dissociative adsorption of molecular oxygen is involved in the reaction process;and a straightforward strategy for preparing an active boron nitride catalyst with hydroxyl groups at the edges can efficiently enhance the catalytic efficacy.A new redox reaction cycle based on the B-OH sites is also proposed.Furthermore,as this is a novel catalytic system,there is an urgent need to develop new methods to optimize the catalytic performances,clarify the catalytic function of boron species in the alkane ODH reactions,and disclose the reaction mechanism under realistic reaction conditions.
基金financially supported by the National Natural Science Foundation of China to Z.Chai(91026000) to D.Wang(91226105)by the CAS Hundred Talents Program to D.Wang(Y2291810S3)
文摘The adsorption of uranyl on hydroxylated α-SiO_2(001) in the presence of a series of anionic ligands, i.e. OH^-, CO_3^(2-), NO_3^-, H_2PO_4^-, HPO_4^(2-),CH_3COO^-(Ac^-), C_6H_5COO^-(PhCO_2^-), C_6H_5O^-(PhO^-), was studied by the periodic density functional theory(DFT) implemented in the Vienna ab initio simulation package(VASP). For the ligands other than OH^-and PhO^-, only the bidentate coordination modes to the uranyl were considered. The excess charge effect of a charged system was first evaluated by constructing models with net charge as is or neutralized by creating defect at the bottom of silica, and the results show that a neutralized model, even with defects, is more realistic than the charged ones.All uranyl species prefer to bind with the deprotonated site(—O^-) rather than the protonated one(—O_H), which suggests that the increase of pH,which leads to the deprotonation of the surface, may enhance the uranyl adsorption. On the other hand, the anionic ligands, which are formed at higher pH, have negative effects. The weaker acidic ligands, such as H_2CO_3, H_3PO_4 and H_2O, whose speciation in solutions is sensitive to the fluctuation of pH, have more complex effect on the uranyl adsorption than strong acids or bases. Humic substances may coordinate with uranyl through carboxyl and phenolic groups, with the carboxyl group bound stronger. The ternary complexes with one bidentate(or monodentate)anion and one(or two) H20 as ligands, which leads to the uranyl penta-coordinated in its equatorial plane, are more favorable than other configurations when bound to the same anionic ligand. Both the charged nature and the coordination behavior of an anionic ligand are relevant to its ability to influence the adsorption of uranyl on the mineral surface. In addition, the uranyl species adsorbed at the surface functionalized by anionic ligands were also addressed, and the functionalized surfaces have weaker interaction with hydrated uranyl dication.
文摘Distributed Denial-of-Service (DDoS) attacks against public web servers are increasingly common. Countering DDoS attacks are becoming ever more challenging with the vast resources and techniques increasingly available to attackers. It is impossible for the victim servers to work on the individual level of on-going traffic flows. In this paper, we establish IP Flow which is used to select proper features for DDoS detection. The IP flow statistics is used to allocate the weights for traffic routing by routers. Our system protects servers from DDoS attacks without strong client authentication or allowing an attacker with partial connectivity information to repeatedly disrupt communications. The new algorithm is thus proposed to get efficiently maximum throughput by the traffic filtering, and its feasibility and validity have been verified in a real network circumstance. The experiment shows that it is with high average detection and with low false alarm and miss alarm. Moreover, it can optimize the network traffic simultaneously with defending against DDoS attacks, thus eliminating efficiently the global burst of traffic arising from normal traffic.
文摘Secure Coding is an indispensable part of the undergraduate training program for Information Security Major.As a basic course for undergraduates to carry out project engineering,its importance is self-evident.In the actual teaching activities,the program design courses have to be solved in terms of content update,practical ability improvement and scientific research project,so the curriculum reform is imperative.This paper analyses the main problems existing in the Secure Coding course,explores the solution,proposes teaching methods,and gives the evaluation method.The practice shows that the reform exploration can obtain good teaching results.
文摘Talents through-cultivating of bachelor master and doctor degrees(shortened for throughcultivating)refers to organic integration of the cultivating process of bachelor,master and doctoral students integrating high-quality educational resources,optimizing the talents cultivating model to achieve the goal of cultivating outstanding innovative talents.Analyzing the status of the talents through-cultivating model in universities pointing out the current problems in the talents throughcultivating model,this paper discusses from the perspectives of cultivating system construction,admission of bachelor-master-doctoral students,diversion and elimination mechanism,international exchanges and cooperation,and support policies.
基金the National Natural Science Foundation of China(Grant Nos.51975566,61821005,and U1908214)the Key Research Program of Frontier Sciences,CAS,China(Grant No.ZDBS-LY-JSC011).
文摘Soft arms have shown great application potential because of their flexibility and compliance in unstructured environments.However,soft arms made from soft materials exhibit limited cargo-loading capacity,which restricts their ability to manipulate objects.In this research,a novel soft arm was developed by coupling a rigid origami exoskeleton with soft airbags.The joint module of the soft arm was composed of a deployable origami exoskeleton and three soft airbags.The motion and load performance of the soft arm of the eight-joint module was tested.The developed soft arm withstood at least 5 kg of load during extension,contraction,and bending motions;exhibited bistable characteristics in both fully contracted and fully extended states;and achieved a bending angle of more than 240°and a contraction ratio of more than 300%.In addition,the high extension,contraction,bending,and torsional stiffnesses of the soft arm were experimentally demonstrated.A kinematic-based trajectory planning of the soft arm was performed to evaluate its error in repetitive motion.This work will provide new design ideas and methods for flexible manipulation applications of soft arms.
基金the National Science and Technology Major Special“Water Pollution Control and Governance”of China(No.2009ZX07212-002-002)the National Natural Science Foundation of China(Grant No.20946001)+1 种基金the Science and Technology Development Program of Shanxi Province in China(No.2006kz08-G2)the Fundamental Research Funds for the Central Universities.
文摘Calcium carbonate often precipitates in anaerobic reactors treating wastewater with high calcium content.The aim of this paper is to study the effect of wastewater composition on calcium carbonate precipitation in upflow anaerobic sludge blanket(UASB)reactors.Two laboratory-scale UASB reactors were operated with calcium-containing influents using acetate and carbohydrate as substrate,respectively.There was an obvious accumulation of inorganic precipitate observed in the biogranules.Observations via scanning electron microscope(SEM)and energy dispersive spectroscopy(EDS)showed that the acclimated biogranules in the two reactors differed in microstructure.Calcium carbonate was found to have precipitated on the surface of acetate-degrading biogranules,but precipitated at the core of the carbohydrate-degrading biogranules.The results indicated that substrates had significant influence on the location of calcium carbonate precipitation in anaerobic granular sludge,which was expected due to the different methanogens distribution and pH gradient within the granular sludge degrading various substrates.Moreover,the location of calcium carbonate precipitation substantially affected the specific methanogenic activity(SMA)of the granular sludge.The SMA of the acetate-degrading biogranules dropped from 1.96 gCODCH4·gVSS^(–1)·d^(–1)to 0.61 gCODCH4·gVSS^(–1)·d^(–1)after 180-d of operation in the reactor.However,the SMA of the carbohydrate-degrading biogranules was not adversely affected by calcium carbonate precipitation.
基金supported by the National Natural Science Foundation of China(Nos.41401563,41301544,41201094)the Natural Science Foundation of Shandong Province(Nos.ZR2014JL028+2 种基金ZR2012DQ003)the China Postdoctoral Science Foundation(No.2015M571830)the Taishan Scholar Program of Shandong Province for supporting his research
文摘Changes in metal concentrations in the litter of Potamogeton crispus were monitored during a consecutive 40-day in situ decomposition experiment using the litterbag method.The accumulation index was calculated and used to indicate the changes in the metals in litter.The results showed that the concentrations of Al,Cd,Cr,Fe,Mn,and Pb in litter increased significantly during the decomposition,while Cu and Zn concentrations decreased dramatically.Significant positive correlations were found between the concentrations of Al,Cr,Fe,and Mn and between Cu and Zn.Moreover,Cu and Zn both negatively correlated with Al and Fe.The remaining dry mass was negatively correlated with Al and Fe concentrations but positively correlated with Cu and Zn concentrations.Generally the accumulation index values of metals other than Al were less than one,indicating that the litter of P.crispus acted as a source of metals to the surrounding water body.Al was the only metal that showed continuous net accumulation in litter.The net accumulation of Fe and Mn in litter during the last 10 days of the experiment may indicate the precipitation of Feand Mn-oxides.It was estimated that 160 g/m^2（dry weight）P.crispus was decomposed in40 days.This was equivalent to releasing the following amounts of metals：0.01 mg Cd,0.03 mg Cr,0.71 mg Cu,0.55 mg Mn,0.02 mg Pb and 13.8 mg Zn into surrounding water,and accumulating 149 mg Al and 11 mg Fe,in a 1 m^2 area.
基金supported by the National Key R&D Program of China(Grant No.2018YFB1304600)the National Natural Science Foundation of China(Grant Nos.51975566 and 61821005)the CAS Interdisciplinary Innovation Team(Grant No.JCTD-2018-11).
文摘Passive variable stiffness joints have unique advantages over active variable stiffness joints and are currently eliciting increased attention.Existing passive variable stiffness joints rely mainly on sensors and special control algorithms,resulting in a bandwidth-limited response speed of the joint.We propose a new passive power-source-free stiffness-self-adjustable mechanism that can be used as the elbow joint of a robot arm.The new mechanism does not require special stiffness regulating motors or sensors and can realize large-range self-adaptive adjustment of stiffness in a purely mechanical manner.The variable stiffness mechanism can automatically adjust joint stiffness in accordance with the magnitude of the payload,and this adjustment is a successful imitation of the stiffness adjustment characteristics of the human elbow.The response speed is high because sensors and control algorithms are not needed.The variable stiffness principle is explained,and the design of the variable stiffness mechanism is analyzed.A prototype is fabricated,and the associated hardware is set up to validate the analytical stiffness model and design experimentally.
基金This work was supported by the National Key R&D Program of China(2018YFB1304600)National Natural Science Foundation of China(51605474,61821005)+1 种基金Key Research Program of Frontier Sciences,CAS,Grantno.ZDBS-LY-JSCollLiaoning RevitalizationTalents Program(XLYC1807090).
文摘Variable Stiffness Actuator(VSA)is the core mechanism to achieve physical human–robot interaction,which is an inevitable development trend in robotic.The existing variable stiffness actuators are basically single degree-of-freedom(DOF)rotating joints,which are achieving multi-DOF motion by cascades and resulting in complex robot body structures.In this paper,an integrated 2-DOF actuator with variable stiffness is proposed,which could be used for bionic wrist joints or shoulder joints.The 2-DOF motion is coupling in one universal joint,which is different from the way of single DOF actuators cascade.Based on the 2-DOF orthogonal motion generated by the spherical wrist parallel mechanism,the stiffness could be adjusted by varying the effective length of the springs,which is uniformly distributed in the variable stiffness unit.The variable stiffness principle,the model design,and theoretical analysis of the VSA are discussed in this work.The independence of adjusting the equilibrium position and stiffness of the actuator is validated by experiments.The results show that the measured actuator characteristics are sufficiently matched the theoretical values.In the future,VSA could be used in biped robot or robotic arm,ensuring the safety of human–robot interaction.
基金This work was jointly supported by the National Natural Science Foundation of China （Grant Nos. 41271472, 41473094 and 41671467）, Natural Science Foundation of Shanghai Municipality （Grant Nos.14ZR1412100 and 12ZR1409000）. Authors also acknowledge J. Lv and J. Han for their assistance with field work and in the laboratory.
文摘This study investigated the dry and wet deposition fluxes of atmospheric polycyclic aromatic hydrocarbons （PAHs） in Shanghai, China. The flux sources were traced based on composition and spatio-temporal variation. The results show that wet deposition concentrations of PAHs ranged from 0.07 to 0.67 μg·L-1 and were correlated with temperature （P 〈 0.05）. Dry deposition of PAHs concentrations ranged from 3.60-92.15 μg·L-1 and were higher in winter and spring than in summer and autumn. The annual PAH average fluxes were 0.631 μg·m-2·d-1 and 4.06 μg.m·d-1 for wet and dry deposition, respectively. The highest wet deposition of PAH fluxes was observed in summer, while dry deposition fluxes were higher in winter and spring. Atmospheric PAHs were deposited as dry deposition in spring and winter, yet wet deposition was the dominant pathway during summer. Total atmospheric PAH fluxes were higher in the northern areas than in the southern areas of Shanghai, and were also observed to be higher in winter and spring. Annual deposition of atmospheric PAHs was about 10.8 t in across all of Shanghai. Wet deposition of PAHs was primarily composed of two, three, or four rings, while dry deposition of PAHs was composed of four, five, or six rings. The atmospheric PAHs, composed of four, five, or six rings, primarily existed in the form of particulates. Coal combustion and vehicle emissions were the dominant sources of PAH in the observed area of downtown Shanghai. In suburban areas, industrial pollution, from sources such as coke oven, incinerator, and oil fired power plant, was as significant as vehicle emissions in contributing to the deposition of PAHs.
