The structure optimization design under thermo-mechanical coupling is a difficult problem in the topology optimization field.An adaptive growth algorithm has become a more effective approach for structural topology op...The structure optimization design under thermo-mechanical coupling is a difficult problem in the topology optimization field.An adaptive growth algorithm has become a more effective approach for structural topology optimization.This paper proposed a topology optimization method by an adaptive growth algorithm for the stiffener layout design of box type load-bearing components under thermo-mechanical coupling.Based on the stiffness diffusion theory,both the load stiffness matrix and the heat conduction stiffness matrix of the stiffener are spread at the same time to make sure the stiffener grows freely and obtain an optimal stiffener layout design.Meanwhile,the objectives of optimization are the minimization of strain energy and thermal compliance of the whole structure,and thermo-mechanical coupling is considered.Numerical studies for square shells clearly show the effectiveness of the proposed method for stiffener layout optimization under thermo-mechanical coupling.Finally,the method is applied to optimize the stiffener layout of box type load-bearing component of themachining center.The optimization results show that both the structural deformation and temperature of the load-bearing component with the growth stiffener layout,which are optimized by the adaptive growth algorithm,are less than the stiffener layout of shape‘#’stiffener layout.It provides a new solution approach for stiffener layout optimization design of box type load-bearing components under thermo-mechanical coupling.展开更多
Aluminum-ion batteries(AIBs)have been highlighted as a potential alternative to lithium-ion batteries for large-scale energy storage due to the abundant reserve,light weight,low cost,and good safety of Al.However,the ...Aluminum-ion batteries(AIBs)have been highlighted as a potential alternative to lithium-ion batteries for large-scale energy storage due to the abundant reserve,light weight,low cost,and good safety of Al.However,the development of AIBs faces challenges due to the usage of AlCl_(3)-based ionic liquid electrolytes,which are expensive,corrosive,and sensitive to humidity.Here,we develop a low-cost,non-corrosive,and air-stable hydrated eutectic electrolyte composed of aluminum perchlorate nonahydrate and methylurea(MU)ligand.Through optimizing the molar ratio to achieve the unique solvation structure,the formed Al(ClO_4)_(3)·9H_(2)O/MU hydrated deep eutectic electrolyte(AMHEE)with an average coordination number of 2.4 can facilely realize stable and reversible deposition/stripping of Al.When combining with vanadium oxide nanorods positive electrode,the Al-ion full battery delivers a high discharge capacity of 320 mAh g^(-1)with good capacity retention.The unique solvation structure with a low desolvation energy of the AMHEE enables Al^(3+)insertion/extraction during charge/discharge processes,which is evidenced by in situ synchrotron radiation X-ray diffraction.This work opens a new pathway of developing low-cost,safe,environmentally friendly and high-performance electrolytes for practical and sustainable AIBs.展开更多
In this paper,we consider a downlink non-orthogonal multiple access(NOMA)network assisted by two reconfigurable intelligent surfaces(RISs)over Rician fading channels,in which each user communicates with the base stati...In this paper,we consider a downlink non-orthogonal multiple access(NOMA)network assisted by two reconfigurable intelligent surfaces(RISs)over Rician fading channels,in which each user communicates with the base station by the virtue of a RIS to enhance the reliability of the received signal.To evaluate the system performance of our proposed RIS-NOMA network,we first derive the exact and asymptotic expressions for the outage probability and ergodic rate of two users.Then,we derive the exact and asymptotic upper bound expressions for the ergodic rate of the nearby user.Based on asymptotic analytical results,the diversity orders for the outage probability and the high signal-to-noise ratio(SNR)slopes for the ergodic rate of the two users are obtained in the high SNR regime.Moreover,we derive the system throughputs of the proposed RIS-NOMA network in delay-limited and delay-tolerant transmission modes.Numerical results confirm our analysis and demonstrate that:1)The outage probability and ergodic rate of RIS-NOMA networks are superior to that of RIS-assisted orthogonalmultiple access(OMA)networks;2)The RIS-NOMA networks have ability to achieve a larger system throughput compared to RIS-OMA networks;and 3)The system performance of RIS-NOMA networks can be significantly improved as the number of reflecting elements and Rician factor increases.展开更多
Standard machine-learning approaches involve the centralization of training data in a data center,where centralized machine-learning algorithms can be applied for data analysis and inference.However,due to privacy res...Standard machine-learning approaches involve the centralization of training data in a data center,where centralized machine-learning algorithms can be applied for data analysis and inference.However,due to privacy restrictions and limited communication resources in wireless networks,it is often undesirable or impractical for the devices to transmit data to parameter sever.One approach to mitigate these problems is federated learning(FL),which enables the devices to train a common machine learning model without data sharing and transmission.This paper provides a comprehensive overview of FL applications for envisioned sixth generation(6G)wireless networks.In particular,the essential requirements for applying FL to wireless communications are first described.Then potential FL applications in wireless communications are detailed.The main problems and challenges associated with such applications are discussed.Finally,a comprehensive FL implementation for wireless communications is described.展开更多
Two major earthquakes in Alaska, namely the 1964 Great Alaska Earthquake and the 2002 Denali Earthquake, occurred in winter seasons when the ground crust was frozen. None of the then-existing foundation types was able...Two major earthquakes in Alaska, namely the 1964 Great Alaska Earthquake and the 2002 Denali Earthquake, occurred in winter seasons when the ground crust was frozen. None of the then-existing foundation types was able to withstand the force from the lateral spreading of frozen crust. This paper presents results from the analysis of pile foundations in frozen ground overlying liquefiable soil utilizing the Beam-on-Nonlinear-Winkler-Foundation (BNWF) (or p-y approach). P-multipliers were applied on traditional sandy soil p-y curves to simulate soil strength degradation during liquefaction. Frozen soil p-y curves were constructed based on a model proposed in a recent study and the frozen soil mechanical properties obtained from testing of naturally frozen soils. Pile response results from the p-y approach were presented along with those from fluid-solid coupled Finite Element (FE) modeling for comparison purpose. Finally, the sensitivity of pile response to frozen soil parameters was investigated and a brief discussion is presented.展开更多
Rechargeable aluminum-sulfur(Al-S)batteries have been considered as a highly potential energy storage system owing to the high theoretical capacity,good safety,abundant natural reserves,and low cost of Al and S.Howeve...Rechargeable aluminum-sulfur(Al-S)batteries have been considered as a highly potential energy storage system owing to the high theoretical capacity,good safety,abundant natural reserves,and low cost of Al and S.However,the research progress of Al-S batteries is limited by the slow kinetics and shuttle effect of soluble polysulfides intermediates.Herein,an interconnected free-standing interlayer of iron sin-gle atoms supported on porous nitrogen-doped carbon nanofibers(FeSAs-NCF)on the separator is developed and used as both catalyst and chemical barrier for Al-S batteries.The atomically dispersed iron active sites(Fe-N_(4))are clearly identified by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption near-edge structure.The Al-S battery with the FeSAs-NCF shows an improved specific capacity of 780 mAh g^(−1)and enhanced cycle stability.As evidenced by experimental and theoretical results,the atomically dispersed iron active centers on the separator can chemically adsorb the polysulfides and accelerate reaction kinetics to inhibit the shuttle effect and promote the reversible conversion between aluminum polysulfides,thus improving the electrochemical performance of the Al-S battery.This work provides a new way that can not only promote the conversion of aluminum sulfides but also suppress the shuttle effect in Al-S batteries.展开更多
In this paper,we propose a two-tiered segment-based Device-toDevice(S-D2D)caching approach to decrease the startup and playback delay experienced by Video-on-Demand(VoD)users in a cellular network.In the S-D2D caching...In this paper,we propose a two-tiered segment-based Device-toDevice(S-D2D)caching approach to decrease the startup and playback delay experienced by Video-on-Demand(VoD)users in a cellular network.In the S-D2D caching approach cache space of each mobile device is divided into two cache-blocks.The rst cache-block reserve for caching and delivering the beginning portion of the most popular video les and the second cacheblock caches the latter portion of the requested video les‘fully or partially’depending on the users’video watching behaviour and popularity of videos.In this approach before caching,video is divided and grouped in a sequence of xed-sized fragments called segments.To control the admission to both cacheblocks and improve the system throughput,we further propose and evaluate three cache admission control algorithms.We also propose a video segment access protocol to elaborate on how to cache and share the video segments in a segmentation based D2D caching architecture.We formulate an optimisation problem and nd the optimal cache probability and beginning-segment size that maximise the cache-throughput probability of beginning-segments.To solve the non-convex cache-throughout maximisation problem,we derive an iterative algorithm,where the optimal solution is derived in each step.We used extensive simulations to evaluate the performance of our proposed S-D2D caching system.展开更多
Engineering activities in the salt lake region continue to increase where fresh water resources are scarce.This paper investigates the physical properties of saline soils during mixing with brine.Fine-grained saline s...Engineering activities in the salt lake region continue to increase where fresh water resources are scarce.This paper investigates the physical properties of saline soils during mixing with brine.Fine-grained saline soils with salt content varying from 2.6%to 78.5%were collected along Qarhan-Golmud Highway(QGH)and Sebei-Qarhan Highway(SQH)on the Qinghai-Tibet Plateau to conduct laboratory physical properties tests.Liquid plastic limit tests were conducted.Results show that liquid plastic limit parameters will decrease with an increase of salt content ranging from 2.6% to 78.5%,and the relationship between them is linear.After considering the content ratio of chloride and sulfate,results show that liquid plastic limit parameters will decrease with an increase of the ratio of chloride to sulfate ranging from 0.7% to 7.0%;liquid plastic limit parameters enter a stable period at the ratio of chloride to sulfate ranging from 7.0% to 37.4%;liquid plastic limit parameters enter a decline period at the ratio of chloride to sulfate ranging from 37.4% to 77.2%.After brine and fresh water are separately mixed into saline soil,the optimal moisture content of the soil samples after the brine action is lower than the saline soil under the action of fresh water,and the maximum dry density of the soil sample is higher than that under the action of fresh water.At the same time,these changing laws show a certain correlation with the chloride ion content and the ratio of chloride to sulfate in saline soils.The results are of significance for engineering activities in salt lake regions with extensive saline soil distribution.展开更多
Graduate education is the key support to the national competitive and technological levels. Therefore, the system of granting graduate degree was clearly guaranteed in the national level. For example, there are Educat...Graduate education is the key support to the national competitive and technological levels. Therefore, the system of granting graduate degree was clearly guaranteed in the national level. For example, there are Education Law and Higher Education Law in China; the people＇ s education right is protected by federal constitution in the United States, and also universities or institutes have their own charters to claim the relative rights. The system safeguards the legitimacy of degree granting, but also gives a considerable discretionary power to the granting units who can grant or cancel the degree.展开更多
Based on one-year observation,the concentration,sources,and potential source areas of volatile organic compounds(VOCs)were comprehensively analyzed to investigate the pollution characteristics of ambient VOCs in Haiko...Based on one-year observation,the concentration,sources,and potential source areas of volatile organic compounds(VOCs)were comprehensively analyzed to investigate the pollution characteristics of ambient VOCs in Haikou,China.The results showed that the annual average concentration of total VOCs(TVOCs)was 11.4 ppb V,and the composition was dominated by alkanes(8.2 ppb V,71.4%)and alkenes(1.3 ppb V,20.5%).The diurnal variation in the concentration of dominant VOC species showed a distinct bimodal distribution with peaks in the morning and evening.The greatest contribution to ozone formation potential(OFP)was made by alkenes(51.6%),followed by alkanes(27.2%).The concentrations of VOCs and nitrogen dioxide(NO_(2))in spring and summer were low,and it was difficult to generate high ozone(O_(3))concentrations through photochemical reactions.The significant increase in O_(3)concentrations in autumn and winter was mainly related to the transmission of pollutants from the northeast.Traffic sources(40.1%),industrial sources(19.4%),combustion sources(18.6%),solvent usage sources(15.5%)and plant sources(6.4%)were identified as major sources of VOCs through the positive matrix factorization(PMF)model.The southeastern coastal areas of China were identified as major potential source areas of VOCs through the potential source contribution function(PSCF)and concentration-weighted trajectory(CWT)models.Overall,the concentration of ambient VOCs in Haikou was strongly influenced by traffic sources and long-distance transport,and the control of VOCs emitted from vehicles should be strengthened to reduce the active species of ambient VOCs in Haikou,thereby reducing the generation of O_(3).展开更多
Norovirus(NoV)is an important cause of viral acute gastroenteritis(AGE).To gain insights into the epidemio-logical characteristics and genetic diversity of NoV among children in Hubei,1216 stool samples from children(...Norovirus(NoV)is an important cause of viral acute gastroenteritis(AGE).To gain insights into the epidemio-logical characteristics and genetic diversity of NoV among children in Hubei,1216 stool samples from children(≤5 years)obtained under AGE surveillance from January 2017 to December 2019 were analyzed.The results showed that NoV was responsible for 14.64%of AGE cases,with the highest detection rate in children aged 7-12 months(19.76%).Statistically significant differences were found between male and female infection rates(χ^(2)=8.108,P¼0.004).Genetic analysis of RdRp and VP1 sequences showed that NoV GII genotypes were GII.4 Sydney[P31](34.35%),GII.3[P12](25.95%),GII.2[P16](22.90%),GII.4 Sydney[P16](12.98%),GII.17[P17](2.29%),GII.6[P7]and GII.3[P16](each at 0.76%).GII.17[P17]variants were divided into the Kawasaki323-like lineage and the Kawasaki308-like lineage.A unique recombination event was detected between strains of GII.4 Sydney 2012 and GII.4 Sydney 2016.Significantly,all GII.P16 sequences associated with GII.4/GII.2 ob-tained in Hubei were correlated with novel GII.2[P16]variants that re-emerged in Germany in 2016.Antigenic site analysis of complete VP1 sequences from all GII.4 variants from Hubei identified notable variable residues of antibody epitopes.Genotyping under continuous AGE surveillance and observation of the antigenic sites of VP1 are important monitoring strategies for emerging NoV strains.展开更多
This paper investigates the secure transmission for reconfigurable intelligent surface(RIS)-assisted wireless communication systems.In the studied model,one user connects to the access point via a RIS while an eavesdr...This paper investigates the secure transmission for reconfigurable intelligent surface(RIS)-assisted wireless communication systems.In the studied model,one user connects to the access point via a RIS while an eavesdropper eavesdrops on the signal sent from the user to the access point.Therefore,it is necessary to design an appropriate RIS reflection vector to solve the eavesdropping problem.This problem is formulated as an optimization problem whose goal is to maximize the secure energy efficiency which is defined as the ratio of the secure rate to the total energy consumption of the system via jointly optimizing the RIS reflection reflector as well as the number of RIS elements,which results in a non-convex optimization problem that is intractable to solve by traditional methods.To tackle this issue,a new algorithm by leveraging the advance of the established deep learning(DL)technique is proposed so as to find the optimal RIS reflection vector and determine the optimal number of RIS reflection elements.Simulation results show that the proposed method reaches 96%of the optimal secure energy efficiency of the genie-aided algorithm.展开更多
Reconfigurable intelligent surfaces(RISs)are lately being attractive for their great potential in future sixth generation wireless communications(6G),which is attributed to their affordable energy consumption and easy...Reconfigurable intelligent surfaces(RISs)are lately being attractive for their great potential in future sixth generation wireless communications(6G),which is attributed to their affordable energy consumption and easy integration.However,the large numbers of low-cost reflecting elements comprising RISs impose challenges for channel acquisition in various RIS-based wireless applications,such as RIS-enhanced orthogonal frequency-division multiplexing and multi-user multipleinput multiple-output systems.In this article,we first overview the state-of-the-art RIS hardware architectures designed to assist channel estimation for RIS-empowered wireless communication systems.We also overview existing channel estimation approaches,which are categorized into model-based and model-free techniques,and discuss their advantages and limitations depending on the RIS deployment.Design challenges with RIS-empowered systems in terms of hardware and other parameter limitations are presented,together with future research directions for channel estimation in RIS-based wireless systems,such as RISs with extremely large numbers of elements,multi-hop communications with RISs,and frequency division duplexing for high mobility systems.展开更多
基金supported by National Natural Science Foundation of China (No.52075445)Science,Technology and Innovation Commission of Shenzhen Municipality (No.JCYJ20190806151013025).
文摘The structure optimization design under thermo-mechanical coupling is a difficult problem in the topology optimization field.An adaptive growth algorithm has become a more effective approach for structural topology optimization.This paper proposed a topology optimization method by an adaptive growth algorithm for the stiffener layout design of box type load-bearing components under thermo-mechanical coupling.Based on the stiffness diffusion theory,both the load stiffness matrix and the heat conduction stiffness matrix of the stiffener are spread at the same time to make sure the stiffener grows freely and obtain an optimal stiffener layout design.Meanwhile,the objectives of optimization are the minimization of strain energy and thermal compliance of the whole structure,and thermo-mechanical coupling is considered.Numerical studies for square shells clearly show the effectiveness of the proposed method for stiffener layout optimization under thermo-mechanical coupling.Finally,the method is applied to optimize the stiffener layout of box type load-bearing component of themachining center.The optimization results show that both the structural deformation and temperature of the load-bearing component with the growth stiffener layout,which are optimized by the adaptive growth algorithm,are less than the stiffener layout of shape‘#’stiffener layout.It provides a new solution approach for stiffener layout optimization design of box type load-bearing components under thermo-mechanical coupling.
基金supported by the National Natural Science Foundation of China(52274302)。
文摘Aluminum-ion batteries(AIBs)have been highlighted as a potential alternative to lithium-ion batteries for large-scale energy storage due to the abundant reserve,light weight,low cost,and good safety of Al.However,the development of AIBs faces challenges due to the usage of AlCl_(3)-based ionic liquid electrolytes,which are expensive,corrosive,and sensitive to humidity.Here,we develop a low-cost,non-corrosive,and air-stable hydrated eutectic electrolyte composed of aluminum perchlorate nonahydrate and methylurea(MU)ligand.Through optimizing the molar ratio to achieve the unique solvation structure,the formed Al(ClO_4)_(3)·9H_(2)O/MU hydrated deep eutectic electrolyte(AMHEE)with an average coordination number of 2.4 can facilely realize stable and reversible deposition/stripping of Al.When combining with vanadium oxide nanorods positive electrode,the Al-ion full battery delivers a high discharge capacity of 320 mAh g^(-1)with good capacity retention.The unique solvation structure with a low desolvation energy of the AMHEE enables Al^(3+)insertion/extraction during charge/discharge processes,which is evidenced by in situ synchrotron radiation X-ray diffraction.This work opens a new pathway of developing low-cost,safe,environmentally friendly and high-performance electrolytes for practical and sustainable AIBs.
基金supported in part by the Key R&D Program of Zhejiang Province under Grant No.2020C05005in part by the National Natural Science Foundation of China under Grants U2033215,91738301,91538202,and 91638301+7 种基金in part by the Program for New Century Excellent Talents in University under Grant NCET-09-0025in part by the Fundamental Research Funds for the Central Universitiessupported by the China National Key R&D Program under Grant 2021YFA1000500National Natural Science Foundation of China under Grant 62101492Zhejiang Provincial Natural Science Foundation of China under Grant LR22F010002Distinguished Young Scholars of the National Natural Science Foundation of China,Ng Teng Fong Charitable Foundation in the form of ZJU-SUTD IDEA Grant,Zhejiang University Education Foundation Qizhen Scholar FoundationFundamental Research Funds for the Central Universities under Grant 2021FZZX001-21supported by the National Natural Science Foundation of China under Grant 62071052 and the R&D Program of Beijing Municipal Education Commission under Grant KM202011232003.
文摘In this paper,we consider a downlink non-orthogonal multiple access(NOMA)network assisted by two reconfigurable intelligent surfaces(RISs)over Rician fading channels,in which each user communicates with the base station by the virtue of a RIS to enhance the reliability of the received signal.To evaluate the system performance of our proposed RIS-NOMA network,we first derive the exact and asymptotic expressions for the outage probability and ergodic rate of two users.Then,we derive the exact and asymptotic upper bound expressions for the ergodic rate of the nearby user.Based on asymptotic analytical results,the diversity orders for the outage probability and the high signal-to-noise ratio(SNR)slopes for the ergodic rate of the two users are obtained in the high SNR regime.Moreover,we derive the system throughputs of the proposed RIS-NOMA network in delay-limited and delay-tolerant transmission modes.Numerical results confirm our analysis and demonstrate that:1)The outage probability and ergodic rate of RIS-NOMA networks are superior to that of RIS-assisted orthogonalmultiple access(OMA)networks;2)The RIS-NOMA networks have ability to achieve a larger system throughput compared to RIS-OMA networks;and 3)The system performance of RIS-NOMA networks can be significantly improved as the number of reflecting elements and Rician factor increases.
基金This work was supported by research grants from the Engineering and Physical Sciences Research Council(EPSRC),UK(EP/T015985/1)from US National Science Foundation(CCF-1908308).
文摘Standard machine-learning approaches involve the centralization of training data in a data center,where centralized machine-learning algorithms can be applied for data analysis and inference.However,due to privacy restrictions and limited communication resources in wireless networks,it is often undesirable or impractical for the devices to transmit data to parameter sever.One approach to mitigate these problems is federated learning(FL),which enables the devices to train a common machine learning model without data sharing and transmission.This paper provides a comprehensive overview of FL applications for envisioned sixth generation(6G)wireless networks.In particular,the essential requirements for applying FL to wireless communications are first described.Then potential FL applications in wireless communications are detailed.The main problems and challenges associated with such applications are discussed.Finally,a comprehensive FL implementation for wireless communications is described.
基金funding from Alaska University Transportation Center (AUTC)the State of Alaska Department of Transportation and Public Facilities (ADOT&PF) under projects AUTC Projects #309011 and #510021
文摘Two major earthquakes in Alaska, namely the 1964 Great Alaska Earthquake and the 2002 Denali Earthquake, occurred in winter seasons when the ground crust was frozen. None of the then-existing foundation types was able to withstand the force from the lateral spreading of frozen crust. This paper presents results from the analysis of pile foundations in frozen ground overlying liquefiable soil utilizing the Beam-on-Nonlinear-Winkler-Foundation (BNWF) (or p-y approach). P-multipliers were applied on traditional sandy soil p-y curves to simulate soil strength degradation during liquefaction. Frozen soil p-y curves were constructed based on a model proposed in a recent study and the frozen soil mechanical properties obtained from testing of naturally frozen soils. Pile response results from the p-y approach were presented along with those from fluid-solid coupled Finite Element (FE) modeling for comparison purpose. Finally, the sensitivity of pile response to frozen soil parameters was investigated and a brief discussion is presented.
基金financially supported by the National Natural Science Foundation of China (No.51874197)Natural Science Foundation of Shanghai (Nos.21ZR1429400,22ZR1429700)
文摘Rechargeable aluminum-sulfur(Al-S)batteries have been considered as a highly potential energy storage system owing to the high theoretical capacity,good safety,abundant natural reserves,and low cost of Al and S.However,the research progress of Al-S batteries is limited by the slow kinetics and shuttle effect of soluble polysulfides intermediates.Herein,an interconnected free-standing interlayer of iron sin-gle atoms supported on porous nitrogen-doped carbon nanofibers(FeSAs-NCF)on the separator is developed and used as both catalyst and chemical barrier for Al-S batteries.The atomically dispersed iron active sites(Fe-N_(4))are clearly identified by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption near-edge structure.The Al-S battery with the FeSAs-NCF shows an improved specific capacity of 780 mAh g^(−1)and enhanced cycle stability.As evidenced by experimental and theoretical results,the atomically dispersed iron active centers on the separator can chemically adsorb the polysulfides and accelerate reaction kinetics to inhibit the shuttle effect and promote the reversible conversion between aluminum polysulfides,thus improving the electrochemical performance of the Al-S battery.This work provides a new way that can not only promote the conversion of aluminum sulfides but also suppress the shuttle effect in Al-S batteries.
基金The author F.W.would like to express their gratitude to the Baihang university,Beijing,China for their nancial and technical support under Code No.BU/IFC/INT/01/008.
文摘In this paper,we propose a two-tiered segment-based Device-toDevice(S-D2D)caching approach to decrease the startup and playback delay experienced by Video-on-Demand(VoD)users in a cellular network.In the S-D2D caching approach cache space of each mobile device is divided into two cache-blocks.The rst cache-block reserve for caching and delivering the beginning portion of the most popular video les and the second cacheblock caches the latter portion of the requested video les‘fully or partially’depending on the users’video watching behaviour and popularity of videos.In this approach before caching,video is divided and grouped in a sequence of xed-sized fragments called segments.To control the admission to both cacheblocks and improve the system throughput,we further propose and evaluate three cache admission control algorithms.We also propose a video segment access protocol to elaborate on how to cache and share the video segments in a segmentation based D2D caching architecture.We formulate an optimisation problem and nd the optimal cache probability and beginning-segment size that maximise the cache-throughput probability of beginning-segments.To solve the non-convex cache-throughout maximisation problem,we derive an iterative algorithm,where the optimal solution is derived in each step.We used extensive simulations to evaluate the performance of our proposed S-D2D caching system.
基金jointly supported by grants from the National Natural Science Foundation of China(No.41501062)the Longyuan Youth Innovation and Entrepreneurship Talent(Team)Project of Gansu Province and Natural Science Foundation of Gansu Province(No.20JR10RA227).
文摘Engineering activities in the salt lake region continue to increase where fresh water resources are scarce.This paper investigates the physical properties of saline soils during mixing with brine.Fine-grained saline soils with salt content varying from 2.6%to 78.5%were collected along Qarhan-Golmud Highway(QGH)and Sebei-Qarhan Highway(SQH)on the Qinghai-Tibet Plateau to conduct laboratory physical properties tests.Liquid plastic limit tests were conducted.Results show that liquid plastic limit parameters will decrease with an increase of salt content ranging from 2.6% to 78.5%,and the relationship between them is linear.After considering the content ratio of chloride and sulfate,results show that liquid plastic limit parameters will decrease with an increase of the ratio of chloride to sulfate ranging from 0.7% to 7.0%;liquid plastic limit parameters enter a stable period at the ratio of chloride to sulfate ranging from 7.0% to 37.4%;liquid plastic limit parameters enter a decline period at the ratio of chloride to sulfate ranging from 37.4% to 77.2%.After brine and fresh water are separately mixed into saline soil,the optimal moisture content of the soil samples after the brine action is lower than the saline soil under the action of fresh water,and the maximum dry density of the soil sample is higher than that under the action of fresh water.At the same time,these changing laws show a certain correlation with the chloride ion content and the ratio of chloride to sulfate in saline soils.The results are of significance for engineering activities in salt lake regions with extensive saline soil distribution.
文摘Graduate education is the key support to the national competitive and technological levels. Therefore, the system of granting graduate degree was clearly guaranteed in the national level. For example, there are Education Law and Higher Education Law in China; the people＇ s education right is protected by federal constitution in the United States, and also universities or institutes have their own charters to claim the relative rights. The system safeguards the legitimacy of degree granting, but also gives a considerable discretionary power to the granting units who can grant or cancel the degree.
基金supported by the Major Program of Science and Technology of Hainan Province,China(No.ZDKJ202007)the Special Foundation of Government Financial of Hainan Province,China(No.ZC2018-196)the Youth Innovation Foundation of Hainan Research Academy of Environmental Sciences,China(No.QNCX2021002)。
文摘Based on one-year observation,the concentration,sources,and potential source areas of volatile organic compounds(VOCs)were comprehensively analyzed to investigate the pollution characteristics of ambient VOCs in Haikou,China.The results showed that the annual average concentration of total VOCs(TVOCs)was 11.4 ppb V,and the composition was dominated by alkanes(8.2 ppb V,71.4%)and alkenes(1.3 ppb V,20.5%).The diurnal variation in the concentration of dominant VOC species showed a distinct bimodal distribution with peaks in the morning and evening.The greatest contribution to ozone formation potential(OFP)was made by alkenes(51.6%),followed by alkanes(27.2%).The concentrations of VOCs and nitrogen dioxide(NO_(2))in spring and summer were low,and it was difficult to generate high ozone(O_(3))concentrations through photochemical reactions.The significant increase in O_(3)concentrations in autumn and winter was mainly related to the transmission of pollutants from the northeast.Traffic sources(40.1%),industrial sources(19.4%),combustion sources(18.6%),solvent usage sources(15.5%)and plant sources(6.4%)were identified as major sources of VOCs through the positive matrix factorization(PMF)model.The southeastern coastal areas of China were identified as major potential source areas of VOCs through the potential source contribution function(PSCF)and concentration-weighted trajectory(CWT)models.Overall,the concentration of ambient VOCs in Haikou was strongly influenced by traffic sources and long-distance transport,and the control of VOCs emitted from vehicles should be strengthened to reduce the active species of ambient VOCs in Haikou,thereby reducing the generation of O_(3).
基金the sub-project of Major National Science and Technology Projects(grant number 2017ZX10103005)the Natural Science Foundation of Hubei Province(grant number 2018CFB716,2022CFB015)the Health and Family Planning Scientific Research Project of Hubei Province(grant number WJ2017M137,WJ2023M107).
文摘Norovirus(NoV)is an important cause of viral acute gastroenteritis(AGE).To gain insights into the epidemio-logical characteristics and genetic diversity of NoV among children in Hubei,1216 stool samples from children(≤5 years)obtained under AGE surveillance from January 2017 to December 2019 were analyzed.The results showed that NoV was responsible for 14.64%of AGE cases,with the highest detection rate in children aged 7-12 months(19.76%).Statistically significant differences were found between male and female infection rates(χ^(2)=8.108,P¼0.004).Genetic analysis of RdRp and VP1 sequences showed that NoV GII genotypes were GII.4 Sydney[P31](34.35%),GII.3[P12](25.95%),GII.2[P16](22.90%),GII.4 Sydney[P16](12.98%),GII.17[P17](2.29%),GII.6[P7]and GII.3[P16](each at 0.76%).GII.17[P17]variants were divided into the Kawasaki323-like lineage and the Kawasaki308-like lineage.A unique recombination event was detected between strains of GII.4 Sydney 2012 and GII.4 Sydney 2016.Significantly,all GII.P16 sequences associated with GII.4/GII.2 ob-tained in Hubei were correlated with novel GII.2[P16]variants that re-emerged in Germany in 2016.Antigenic site analysis of complete VP1 sequences from all GII.4 variants from Hubei identified notable variable residues of antibody epitopes.Genotyping under continuous AGE surveillance and observation of the antigenic sites of VP1 are important monitoring strategies for emerging NoV strains.
基金China National Key R&D Program(2021YFA1000500)National Natural Science Foundation of China(62101492)+7 种基金Zhejiang Provincial Natural Science Foundation of China(LR22F010002)Natural Science Foundation of Jiangsu Province of China(BK20210641)Natural Science Foundation of Jiangsu Province of China(BK20210641)Engineering and Physical Sciences Research Council(EPSRC)(EP/P022723/1)National Natural Science Foundation of China(62271094)Key Fund of Natural Science Foundation of Chongqing(CSTB2022NSCQLZX0009)Scientific and Technological Research Program of Chongqing Municipal Education Commission(KJZD-K202200601)China Postdoctoral Science Foundation(2022MD723725)。
文摘This paper investigates the secure transmission for reconfigurable intelligent surface(RIS)-assisted wireless communication systems.In the studied model,one user connects to the access point via a RIS while an eavesdropper eavesdrops on the signal sent from the user to the access point.Therefore,it is necessary to design an appropriate RIS reflection vector to solve the eavesdropping problem.This problem is formulated as an optimization problem whose goal is to maximize the secure energy efficiency which is defined as the ratio of the secure rate to the total energy consumption of the system via jointly optimizing the RIS reflection reflector as well as the number of RIS elements,which results in a non-convex optimization problem that is intractable to solve by traditional methods.To tackle this issue,a new algorithm by leveraging the advance of the established deep learning(DL)technique is proposed so as to find the optimal RIS reflection vector and determine the optimal number of RIS reflection elements.Simulation results show that the proposed method reaches 96%of the optimal secure energy efficiency of the genie-aided algorithm.
基金supported by the China National Key R&D Program(2021YFA1000500)National Natural Science Foundation of China(62101492)+4 种基金Zhejiang Provincial Natural Science Foundation of China(LR22F010002)Zhejiang University Global Partnership Fund,Zhejiang University Education Foundation Qizhen Scholar Foundation,and Fundamental Research Funds for the Central Universities(2021FZZX001-21)supported in part by the European Commission through the H2020 ARIADNE project(871464)and through the H2020 RISE-6G project(101017011)by the Agence Nationale de la Recherche(ANR)through the PEPR-5G projectThis research is supported by the Ministry of Education,Singapore,under its MOE Tier 2(Award number MOE-T2EP50220-0019).
文摘Reconfigurable intelligent surfaces(RISs)are lately being attractive for their great potential in future sixth generation wireless communications(6G),which is attributed to their affordable energy consumption and easy integration.However,the large numbers of low-cost reflecting elements comprising RISs impose challenges for channel acquisition in various RIS-based wireless applications,such as RIS-enhanced orthogonal frequency-division multiplexing and multi-user multipleinput multiple-output systems.In this article,we first overview the state-of-the-art RIS hardware architectures designed to assist channel estimation for RIS-empowered wireless communication systems.We also overview existing channel estimation approaches,which are categorized into model-based and model-free techniques,and discuss their advantages and limitations depending on the RIS deployment.Design challenges with RIS-empowered systems in terms of hardware and other parameter limitations are presented,together with future research directions for channel estimation in RIS-based wireless systems,such as RISs with extremely large numbers of elements,multi-hop communications with RISs,and frequency division duplexing for high mobility systems.
