In recent years,the addition of Ni has been widely acknowledged to be capable of enhancing the mechanical properties of Al-Si alloys.However,the effect of Ni on the wear behaviors of Al-Si alloys and Al matrix composi...In recent years,the addition of Ni has been widely acknowledged to be capable of enhancing the mechanical properties of Al-Si alloys.However,the effect of Ni on the wear behaviors of Al-Si alloys and Al matrix composites,particularly at elevated temperat-ures,remains an understudied area.In this study,Al-Si-Cu-Mg-Ni/20wt%SiC particles(SiCp)composites with varying Ni contents were prepared by using a semisolid stir casting method.The effect of Ni content on the dry sliding wear behavior of the prepared compos-ites was investigated through sliding tests at 25 and 350℃.Results indicated that theθ-Al_(2)Cu phase gradually diminished and eventually disappeared as the Ni content increased from 0wt%to 3wt%.This change was accompanied by the formation and increase inδ-Al_(3)CuNi andε-Al_(3)Ni phases in microstructures.The hardness and ultimate tensile strength of the as-cast composites improved,and the wear rates of the composites decreased from 5.29×10^(−4)to 1.94×10^(−4)mm^(3)/(N∙m)at 25℃and from 20.2×10^(−4)to 7×10^(−4)mm^(3)/(N∙m)at 350℃with the increase in Ni content from 0wt%to 2wt%.The enhancement in performance was due to the presence of strengthening network structures and additional Ni-containing phases in the composites.However,the wear rate of the 3Ni composite was approximately two times higher than that of the 2Ni composite due to the fracture and debonding of theε-Al_(3)Ni phase.Abrasive wear,delamination wear,and oxidation wear were the predominant wear mechanisms of the investigated composites at 25℃,whereas delamination wear and oxid-ation wear were dominant during sliding at 350℃.展开更多
Flexible adaptation to differentiated quality of service(QoS)is quite important for future 6G network with a variety of services.Mobile ad hoc networks(MANETs)are able to provide flexible communication services to use...Flexible adaptation to differentiated quality of service(QoS)is quite important for future 6G network with a variety of services.Mobile ad hoc networks(MANETs)are able to provide flexible communication services to users through self-configuration and rapid deployment.However,the dynamic wireless environment,the limited resources,and complex QoS requirements have presented great challenges for network routing problems.Motivated by the development of artificial intelligence,a deep reinforcement learning-based collaborative routing(DRLCR)algorithm is proposed.Both routing policy and subchannel allocation are considered jointly,aiming at minimizing the end-to-end(E2E)delay and improving the network capacity.After sufficient training by the cluster head node,the Q-network can be synchronized to each member node to select the next hop based on local observation.Moreover,we improve the performance of training by considering historical observations,which can improve the adaptability of routing policies to dynamic environments.Simulation results show that the proposed DRLCR algorithm outperforms other algorithms in terms of resource utilization and E2E delay by optimizing network load to avoid congestion.In addition,the effectiveness of the routing policy in a dynamic environment is verified.展开更多
Spectrum prediction plays an important role for the secondary user(SU)to utilize the shared spectrum resources.However,currently utilized prediction methods are not well applied to spectrum with high burstiness,as par...Spectrum prediction plays an important role for the secondary user(SU)to utilize the shared spectrum resources.However,currently utilized prediction methods are not well applied to spectrum with high burstiness,as parameters of prediction models cannot be adjusted properly.This paper studies the prediction problem of bursty bands.Specifically,we first collect real Wi Fi transmission data in 2.4GHz Industrial,Scientific,Medical(ISM)band which is considered to have bursty characteristics.Feature analysis of the data indicates that the spectrum occupancy law of the data is time-variant,which suggests that the performance of commonly used single prediction model could be restricted.Considering that the match between diverse spectrum states and multiple prediction models may essentially improve the prediction performance,we then propose a deep-reinforcement learning based multilayer perceptron(DRL-MLP)method to address this matching problem.The state space of the method is composed of feature vectors,and each of the vectors contains multi-dimensional feature values.Meanwhile,the action space consists of several multilayer perceptrons(MLPs)that are trained on the basis of multiple classified data sets.We finally conduct experiments with the collected real data and simulations with generated data to verify the performance of the proposed method.The results demonstrate that the proposed method significantly outperforms the stateof-the-art methods in terms of the prediction accuracy.展开更多
Concerned with the surge of contentcentric applications,it is challenging to balance network traffic and cater to low-delay requirements.Hierarchical caching architecture of both edge network(EN)and core network(CN)em...Concerned with the surge of contentcentric applications,it is challenging to balance network traffic and cater to low-delay requirements.Hierarchical caching architecture of both edge network(EN)and core network(CN)emerges and leverages caching resources to reduce the delivery delay of contents.Most previous work takes an impractical assumption to treat the CN as a content provider,which neglects the collaboration by intermediate CN caches.Most importantly,it is still necessary to thoroughly study the tradeoff between CN delay and edge delay for files delivery so as to minimize the overall delivery delay across the network.In this paper,we consider a hierarchical caching network with distributed CN nodes and edge nodes,where cooperative transmission is enabled for edge nodes to transmit multi-files simultaneously.This poses a joint optimization problem of hierarchical file caching and fetching to minimize the overall delivery delay of requests.Since the problem is NP-hard,we decompose the original problem and design an iterative algorithm to address it.Numerical results validate that the proposed scheme can find a balanced solution between lowering edge delay by utilizing coordinated CN caching and lowering CN delay by solely relying on edge caching.展开更多
In this article,we study the following fractional Schrodinger equation with electromagnetic fields and critical growth(-Δ)^sAu+V(x)u=|u|^2^*s-2)u+λf(x,|u|^2)u,x∈R^n,where(-Δ)^sA is the fractional magnetic operator...In this article,we study the following fractional Schrodinger equation with electromagnetic fields and critical growth(-Δ)^sAu+V(x)u=|u|^2^*s-2)u+λf(x,|u|^2)u,x∈R^n,where(-Δ)^sA is the fractional magnetic operator with 0<s<1,N>2s,λ>0,2^*s=2N/(N-2s),f is a continuous function,V∈C(R^n,R)and A∈C(R^n,R^n)are the electric and magnetic potentials,respectively.When V and f are asymptotically periodic in x,we prove that the equation has a ground state solution for largeλby Nehari method.展开更多
Applying pre-stress in glulam beam can reduce its deformation and make full use of the compressive strength of wood.However,when the glulam with low strength and the pre-stressed steel with high strength form combined...Applying pre-stress in glulam beam can reduce its deformation and make full use of the compressive strength of wood.However,when the glulam with low strength and the pre-stressed steel with high strength form combined members,materials of high strength can’t be fully utilized.Therefore,this study puts forward the idea of regulating and controlling string beam of pre-stressed glulam.By regulating and controlling the pre-stress,a part of the load borne by the wood is allocated to the pre-stressed tendon,which is equivalent to completing a redistribution of internal force,thus realizing the repeated utilization of the wood strength and the full utilization of the strength of the high-strength pre-stressed tendon.The bending experiments of 10 beams under 5 working conditions are carried out.The failure mode,bearing capacity and deformation of the beams are analyzed.The results show that 90%of beams are deformed under compression.The ultimate load of the regulated and controlled beam is obviously larger than that of the unregulated beam,and the ultimate load of the beam increases with the increase of the degree of regulation and control.Compared with that of the unregulated beams,the ultimate load of beams regulated by 7.5%-30%increases by 25.42%-65.08%,and the regulated and controlled effect is obvious.With the increase of the regulation and control amplitude of pre-stress,the stiffness of string beam of pre-stressed glulam increases.In addition,with the increase of the regulation and control amplitude,the compression height of the beam increases before the failure,and it reaches the state of full-section compression at the time of failure,giving full play to the compressive property of the glulam.At the end of the experiment,the constitutive relation which can reflect the anisotropy of the wood is established combined with the experimental data.The finite element analysis of the beam under 7 working conditions is carried out by using ABAQUS finite element program,and the influence of the regulation and control amplitude on the stress distribution and ultimate bearing capacity of the beam is discussed.展开更多
The mortise-tenon joint is an important hub transmitting and distributing external loads for load-bearing components(beams,columns et al.)in the ancient-timber frame structure system.However,the conventional steel hoo...The mortise-tenon joint is an important hub transmitting and distributing external loads for load-bearing components(beams,columns et al.)in the ancient-timber frame structure system.However,the conventional steel hoop reinforcement methods often insert wood screws into the timber components.When the reinforced joint rotates greatly,the anchoring failure of the screws will cause damage to the timber joint.To solve this problem,this study proposes a detachable and replaceable non-destructive flat-steel jacket reinforcement method in which horizontal flat steel is placed in the center of the joint,and the bolt is extended to the outside of the timber beam.Nine 1:3.52 scaled straight-tenon joint specimens were subjected to monotonic loading of beam ends,including three unreinforced reference joints,three joints with flat-steel jacket and three carbon fiber-reinforced plastic(CFRP)reinforced joints.The mechanical behaviors of the novel joints with flat-steel jacket were experimentally studied by comparing with those of the joints without strengthening and retrofitted with CFRP,based on the failure modes,the initial stiffness,the ultimate bearing capacity,and the moment-rotation relationship curves.Results indicated that the mortise-tenon joints reinforced with flat-steel jackets maintain the original semi-rigid properties of the unreinforced mortise-tenon joints and can effectively prevent the tenon from pulling out.The initial stiffness and ultimate bearing capacity were improved markedly.The column and beam of the reinforced joints remain intact providing the reference for the practical application of joints reinforcement.The mortisetenon joints reinforced with CFRP lose the semi-rigid properties of the unreinforced tenon-mortise joints.The joints reinforced with CFRP have the largest initial stiffness,while the unreinforced joints have the lowest stiffness.The initial stiffness of the proposed joint is in between the joints reinforced with CFRP and unreinforced joints.The ultimate bearing capacity of the joints reinforced with flat-steel jacket is larger than the other two joints,whereas the unreinforced joints have the lowest ultimate bearing capacity.展开更多
In the upcoming 5 G heterogeneous networks, leveraging multiple radio access technologies(RATs) shows to be a crucial issue in achieving RAT multiplexing gain to meet the explosive traffic demand. For always best conn...In the upcoming 5 G heterogeneous networks, leveraging multiple radio access technologies(RATs) shows to be a crucial issue in achieving RAT multiplexing gain to meet the explosive traffic demand. For always best connection(ABC), users tend to activate parallel transmission across all available RATs. However from a system-wide perspective, this might not be optimal given the context of network load, interference and diverse service requirements. To intelligently determine how to use these multi-RAT access resources concurrently, this paper proposes a joint multi-RAT user association and resource allocation strategy with triple decision and integrated context awareness of users and networks. A dynamic game based ant colony algorithm(GACA) is designed to simultaneously maximize the system utility and the fairness of resource allocation. Simulation results show that it's more reasonable to make multi-RAT association decision from a system-wide viewpoint than from an individual one. Compared to max-SNR based and ABC based strategies, the proposed method alleviates network congestion and optimizes resource allocation. It obtains 39%~70% performance improvement.展开更多
Source localization plays an indispensable role in many applications.This paper addresses the directional source localization problem in a three-dimensional(3D)wireless sensor network using hybrid received-signal-stre...Source localization plays an indispensable role in many applications.This paper addresses the directional source localization problem in a three-dimensional(3D)wireless sensor network using hybrid received-signal-strength(RSS)and angle-of-arrival(AOA)measurements.Both the position and transmission orientation of the source are to be estimated.In the considered positioning scenario,the angle and range measurements are respectively corresponding to the AOA model and RSS model that integrates the Gaussian-shaped radiation pattern.Given that the localization problem is non-convex and the unknown parameters therein are coupled together,this paper adopts the second-order cone relaxation and alternating optimization techniques in the proposed estimation algorithm.Moreover,to provide a performance benchmark for any localization method,the corresponding Cramer-Rao lower bounds(CRLB)of estimating the unknown position and transmission orientation of the source are derived.Numerical and simulation results demonstrate that the presented algorithm effectively resolves the problem,and its estimation performance is close to the CRLB for the localization with the hybrid measurements.展开更多
A series of chitosan/attapulgite (CTS/APT) hybrid microspheres were prepared by a facile spray-drying technique. The developed hybrid microspheres were characterized by Fourier transform infrared spectra (FTIR), X-ray...A series of chitosan/attapulgite (CTS/APT) hybrid microspheres were prepared by a facile spray-drying technique. The developed hybrid microspheres were characterized by Fourier transform infrared spectra (FTIR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and the zeta potential. The encapsulation efficiency and in vitro controlled release properties of the microspheres for drug were evaluated using diclofenac sodium (DS) as a model drug. Results indicated that the introduction of APT into crosslinked CTS microspheres can achieve narrow size distribution and make them more uniform. The isoelectric point of the microspheres increased from 8.14 to 9.18 with increasing the content of APT to 10 wt.%. DS loaded in hybrid microspheres is hardly released in simulated gastric fluid, but quickly released in simulated intestinal fluid. The electrostatic interaction between hybrid microspheres and DS can improve the encapsulation efficiency and controlled release behavior of CTS/APT microspheres, and the release mechanism fits Fickian diffusion.展开更多
A distributed reinforcement learning(RL)based resource management framework is proposed for a mobile edge computing(MEC)system with both latency-sensitive and latency-insensitive services.We investigate joint optimiza...A distributed reinforcement learning(RL)based resource management framework is proposed for a mobile edge computing(MEC)system with both latency-sensitive and latency-insensitive services.We investigate joint optimization of both computing and radio resources to achieve efficient on-demand matches of multi-dimensional resources and diverse requirements of users.A multi-objective integer programming problem is formulated by two subproblems,i.e.,access point(AP)selection and subcarrier allocation,which can be solved jointly by our proposed distributed RL-based approach with a heuristic iteration algorithm.The proposed algorithm allows for the reduction in complexity since each user needs to consider only its own selection of AP without knowing full global information.Simulation results show that our algorithm can achieve near-optimal performance while reducing computational complexity significantly.Compared with other algorithms that only optimize either of the two sub-problems,the proposed algorithm can serve more users with much less power consumption and content delivery latency.展开更多
Keloids are a notorious fibroproliferative disorder that may cause cosmetic concerns and life inconvenience.Various methods such as surgery,injection,and laser have been used;however,single treatments are at risk of r...Keloids are a notorious fibroproliferative disorder that may cause cosmetic concerns and life inconvenience.Various methods such as surgery,injection,and laser have been used;however,single treatments are at risk of recurrence;therefore,comprehensive therapy is the better solution.Here,we focused on the management of different medical interventions according to subjective and objective conditions of keloid patients and summarized several clinical comprehensive strategies based on our clinical experience.One original concept of laser combined with radiotherapy was also introduced as a promising method,especially for wide-based pathological scars.展开更多
Rapid metastasis to vital organs such as the lung,liver,and brain is responsible for the vast majority of pancreatic cancer deaths.Liver metastasis of pancreatic cancer accounts for the high mortality rate in patients...Rapid metastasis to vital organs such as the lung,liver,and brain is responsible for the vast majority of pancreatic cancer deaths.Liver metastasis of pancreatic cancer accounts for the high mortality rate in patients.Exosomes derived from pancreatic cancer cells tend to be enriched in proteins that are anchored to the cell membrane,supporting the reprogramming of the tumor microenvironment and the progression of distant metastatic lesions.For the first time,our study has demonstrated that cluster of differentiation 44(CD44),a transmembrane glycoprotein delivered by exosomes,is involved in the metastatic process of pancreatic cancer.Moreover,CD44 was found to interact with integrin a6b4 to form a complex,thereby remodeling intracellular skeleton proteins,and to promote tumor cell motility through the activation of the Src and Ras signaling cascades.Notably,we also demonstrated that the CD44–a6b4 complex can be delivered to the target region via the paracrine effects of exosomes.The selective uptake of CD44-competent tumor exosomes by liver cells activated fibrotic pathways and generated a pre-metastatic niche by stimulating the cytokines,proinflammatory factors,and growth factors that ultimately support tumor metastasis.Our results suggest the potential application of exosomal CD44 as a biomarker for the clinical diagnosis of and therapy for pancreatic cancer.展开更多
Cloud computing.based heterogeneous networks(C.Het Nets) have been considered as promising network architecture of future wireless communication systems. However, its performance is constrained by the capability of fr...Cloud computing.based heterogeneous networks(C.Het Nets) have been considered as promising network architecture of future wireless communication systems. However, its performance is constrained by the capability of fronthaul. To study the performance limit of C.Het Nets, the coverage performance of the open access strategy in C.Het Nets is analyzed in this paper. In particular, the non.ideal condition of fronthaul in C.Het Nets is characterized by establishing a stochastic geometry.based model, and a tight lower bound on coverage probability is derived for downlink transmissions. Based on the derived results, the constraint of the fronthaul is given to ensure that open access strategy can achieve the best coverage performance. Finally, the simulation results are provided to verify the theoretical results and show the impact of fronthaul constrains.展开更多
In this paper, we investigate nonlinear Hamiltonian elliptic system {-△u＋b（x）· u＋（V（x）＋τ）u=K（x）g（v） in R^N,-△u-b（x）· v＋（V（x）＋τ）v=K（x）f（u） in R^N,u（x）→ and v（x）→0 as ｜x｜...In this paper, we investigate nonlinear Hamiltonian elliptic system {-△u＋b（x）· u＋（V（x）＋τ）u=K（x）g（v） in R^N,-△u-b（x）· v＋（V（x）＋τ）v=K（x）f（u） in R^N,u（x）→ and v（x）→0 as ｜x｜→∞2,where N ≥ 3, τ 〉 0 is a positive parameter and V, K are nonnegative continuous functions,f and g are both superlinear at 0 with a quasicritical growth at infinity. By establishing avariational setting, the existence of ground state solutions is obtained.展开更多
[Objective] This study was conducted to investigate the pollution caused by staphylococcal enterotoxins(SE) in raw milk and the safety of dairy products in Jinan, and to provide a scientific basis for food safety risk...[Objective] This study was conducted to investigate the pollution caused by staphylococcal enterotoxins(SE) in raw milk and the safety of dairy products in Jinan, and to provide a scientific basis for food safety risk analysis. [Method] A total of 130 raw milk samples were collected from different regions of Jinan, and detected for Staphylococcus aureus by referring to GB4789.10-2010. Then, enzyme-linked immunosorbent assay was performed to detect whether the S.aureus strains produced enterotoxins, and the enterotoxin type was identified using colloidal gold-based immunochromatographic test strips. [Result] Fiftyseven of the raw milk samples were polluted by S.aureus, so the detection rate of S.aureus was 43.85%; and 11 of the strains produced enterotoxins. Among the 11 enterotoxin-producing strains, seven produced SEB, only one produced SEC, and the SE type of other three strains was not identified. [Conclusion] Enzyme-linked immunosorbent assay and colloidal gold-based immunochromatographic test strips can be used in combination to rapidly detect staphylococcal enterotoxins and identify enterotoxin type, although there are some limitations. SEB is the main type of staphylococcal enterotoxin causing pollution in milk of Shandong Province.展开更多
In the application of large-scale ancient site protection, it is necessary to continuously monitor the ambient light, temperature, humidity and so on. However, it is impractical to frequently replace the nodes’ batte...In the application of large-scale ancient site protection, it is necessary to continuously monitor the ambient light, temperature, humidity and so on. However, it is impractical to frequently replace the nodes’ battery in the protected areas. So, the key methods to prolong the network lifetime are to aggregate the collected data and reduce the number of transferring messages. In this paper a Lightweight Data Aggregation Protocol (LDAP) based on the characteristics of the environmental changes in ancient sites is proposed. It has been implemented in the Lab with a dozen of MICAz motes and deployed in the real ancient sites. The result shows that LDAP is effective in reducing the number of transferring packets and satisfies the real application requirements.展开更多
Energy efficiency and enhanced backbone capacity is obtained by exploiting the geometric orientation of cooperative nodes in wireless sensor network. The cooperative communication in wireless sensor networks (WSN) giv...Energy efficiency and enhanced backbone capacity is obtained by exploiting the geometric orientation of cooperative nodes in wireless sensor network. The cooperative communication in wireless sensor networks (WSN) gives us leverage to get the inherent advantages of its random node’s locations and the direction of the data flow. Depending on the channel conditions and the transmission distance, the number of cooperative nodes is selected, that participate in an energy efficient transmission/reception. Simulation results show that increasing the cooperative receive diversity, decreases the energy consumption per bit in cooperative communications. It has also been shown that the network backbone capacity can be increased by controlled displacement of antennas at base station at the expense of energy per bit.展开更多
基金the financial support from Ningbo Institute of Technology, Beihang University
文摘In recent years,the addition of Ni has been widely acknowledged to be capable of enhancing the mechanical properties of Al-Si alloys.However,the effect of Ni on the wear behaviors of Al-Si alloys and Al matrix composites,particularly at elevated temperat-ures,remains an understudied area.In this study,Al-Si-Cu-Mg-Ni/20wt%SiC particles(SiCp)composites with varying Ni contents were prepared by using a semisolid stir casting method.The effect of Ni content on the dry sliding wear behavior of the prepared compos-ites was investigated through sliding tests at 25 and 350℃.Results indicated that theθ-Al_(2)Cu phase gradually diminished and eventually disappeared as the Ni content increased from 0wt%to 3wt%.This change was accompanied by the formation and increase inδ-Al_(3)CuNi andε-Al_(3)Ni phases in microstructures.The hardness and ultimate tensile strength of the as-cast composites improved,and the wear rates of the composites decreased from 5.29×10^(−4)to 1.94×10^(−4)mm^(3)/(N∙m)at 25℃and from 20.2×10^(−4)to 7×10^(−4)mm^(3)/(N∙m)at 350℃with the increase in Ni content from 0wt%to 2wt%.The enhancement in performance was due to the presence of strengthening network structures and additional Ni-containing phases in the composites.However,the wear rate of the 3Ni composite was approximately two times higher than that of the 2Ni composite due to the fracture and debonding of theε-Al_(3)Ni phase.Abrasive wear,delamination wear,and oxidation wear were the predominant wear mechanisms of the investigated composites at 25℃,whereas delamination wear and oxid-ation wear were dominant during sliding at 350℃.
基金supported by the 2020 National Key R&D Program"Broadband Communication and New Network"special"6G Network Architecture and Key Technologies"(2020YFB1806700)。
文摘Flexible adaptation to differentiated quality of service(QoS)is quite important for future 6G network with a variety of services.Mobile ad hoc networks(MANETs)are able to provide flexible communication services to users through self-configuration and rapid deployment.However,the dynamic wireless environment,the limited resources,and complex QoS requirements have presented great challenges for network routing problems.Motivated by the development of artificial intelligence,a deep reinforcement learning-based collaborative routing(DRLCR)algorithm is proposed.Both routing policy and subchannel allocation are considered jointly,aiming at minimizing the end-to-end(E2E)delay and improving the network capacity.After sufficient training by the cluster head node,the Q-network can be synchronized to each member node to select the next hop based on local observation.Moreover,we improve the performance of training by considering historical observations,which can improve the adaptability of routing policies to dynamic environments.Simulation results show that the proposed DRLCR algorithm outperforms other algorithms in terms of resource utilization and E2E delay by optimizing network load to avoid congestion.In addition,the effectiveness of the routing policy in a dynamic environment is verified.
基金supported in part by the China National Key R&D Program(no.2020YF-B1808000)Beijing Natural Science Foundation(No.L192002)+2 种基金in part by the Fundamental Research Funds for the Central Universities(No.328202206)the National Natural Science Foundation of China(No.61971058)in part by"Advanced and sophisticated"discipline construction project of universities in Beijing(No.20210013Z0401)。
文摘Spectrum prediction plays an important role for the secondary user(SU)to utilize the shared spectrum resources.However,currently utilized prediction methods are not well applied to spectrum with high burstiness,as parameters of prediction models cannot be adjusted properly.This paper studies the prediction problem of bursty bands.Specifically,we first collect real Wi Fi transmission data in 2.4GHz Industrial,Scientific,Medical(ISM)band which is considered to have bursty characteristics.Feature analysis of the data indicates that the spectrum occupancy law of the data is time-variant,which suggests that the performance of commonly used single prediction model could be restricted.Considering that the match between diverse spectrum states and multiple prediction models may essentially improve the prediction performance,we then propose a deep-reinforcement learning based multilayer perceptron(DRL-MLP)method to address this matching problem.The state space of the method is composed of feature vectors,and each of the vectors contains multi-dimensional feature values.Meanwhile,the action space consists of several multilayer perceptrons(MLPs)that are trained on the basis of multiple classified data sets.We finally conduct experiments with the collected real data and simulations with generated data to verify the performance of the proposed method.The results demonstrate that the proposed method significantly outperforms the stateof-the-art methods in terms of the prediction accuracy.
基金supported by National Key R&D Program of China under grant No.2021YFB2900200China Postdoctoral Science Foundation under grant No.2022M713475。
文摘Concerned with the surge of contentcentric applications,it is challenging to balance network traffic and cater to low-delay requirements.Hierarchical caching architecture of both edge network(EN)and core network(CN)emerges and leverages caching resources to reduce the delivery delay of contents.Most previous work takes an impractical assumption to treat the CN as a content provider,which neglects the collaboration by intermediate CN caches.Most importantly,it is still necessary to thoroughly study the tradeoff between CN delay and edge delay for files delivery so as to minimize the overall delivery delay across the network.In this paper,we consider a hierarchical caching network with distributed CN nodes and edge nodes,where cooperative transmission is enabled for edge nodes to transmit multi-files simultaneously.This poses a joint optimization problem of hierarchical file caching and fetching to minimize the overall delivery delay of requests.Since the problem is NP-hard,we decompose the original problem and design an iterative algorithm to address it.Numerical results validate that the proposed scheme can find a balanced solution between lowering edge delay by utilizing coordinated CN caching and lowering CN delay by solely relying on edge caching.
基金supported in part by the NationalNatural Science Foundation of China(11801153,11501403,11701322,11561072)the Honghe University Doctoral Research Programs(XJ17B11,XJ17B12,DCXL171027,201810687010)+4 种基金the Yunnan Province Applied Basic Research for Youths(2018FD085)the Yunnan Province Local University(Part)Basic Research Joint Project(2017FH001-013)the Natural Sciences Foundation of Yunnan Province(2016FB011)the Yunnan Province Applied Basic Research for General Project(2019FB001)Technology Innovation Team of University in Yunnan Province。
文摘In this article,we study the following fractional Schrodinger equation with electromagnetic fields and critical growth(-Δ)^sAu+V(x)u=|u|^2^*s-2)u+λf(x,|u|^2)u,x∈R^n,where(-Δ)^sA is the fractional magnetic operator with 0<s<1,N>2s,λ>0,2^*s=2N/(N-2s),f is a continuous function,V∈C(R^n,R)and A∈C(R^n,R^n)are the electric and magnetic potentials,respectively.When V and f are asymptotically periodic in x,we prove that the equation has a ground state solution for largeλby Nehari method.
基金In the process,this project was supported by the Fundamental Research Funds for the Central Universities(2572017DB02)Natural Science Foundation of Heilongjiang Province(JJ2019LH0696)by Postdoctoral Scientific Research Developmental Fund of Heilongjiang Province in 2016(LBH-Q16011).
文摘Applying pre-stress in glulam beam can reduce its deformation and make full use of the compressive strength of wood.However,when the glulam with low strength and the pre-stressed steel with high strength form combined members,materials of high strength can’t be fully utilized.Therefore,this study puts forward the idea of regulating and controlling string beam of pre-stressed glulam.By regulating and controlling the pre-stress,a part of the load borne by the wood is allocated to the pre-stressed tendon,which is equivalent to completing a redistribution of internal force,thus realizing the repeated utilization of the wood strength and the full utilization of the strength of the high-strength pre-stressed tendon.The bending experiments of 10 beams under 5 working conditions are carried out.The failure mode,bearing capacity and deformation of the beams are analyzed.The results show that 90%of beams are deformed under compression.The ultimate load of the regulated and controlled beam is obviously larger than that of the unregulated beam,and the ultimate load of the beam increases with the increase of the degree of regulation and control.Compared with that of the unregulated beams,the ultimate load of beams regulated by 7.5%-30%increases by 25.42%-65.08%,and the regulated and controlled effect is obvious.With the increase of the regulation and control amplitude of pre-stress,the stiffness of string beam of pre-stressed glulam increases.In addition,with the increase of the regulation and control amplitude,the compression height of the beam increases before the failure,and it reaches the state of full-section compression at the time of failure,giving full play to the compressive property of the glulam.At the end of the experiment,the constitutive relation which can reflect the anisotropy of the wood is established combined with the experimental data.The finite element analysis of the beam under 7 working conditions is carried out by using ABAQUS finite element program,and the influence of the regulation and control amplitude on the stress distribution and ultimate bearing capacity of the beam is discussed.
基金This research was funded by the National Natural Science Foundation of China No.51908291Nanjing Forestry University Youth Science and Technology Innovation Fund No.CX2019002.
文摘The mortise-tenon joint is an important hub transmitting and distributing external loads for load-bearing components(beams,columns et al.)in the ancient-timber frame structure system.However,the conventional steel hoop reinforcement methods often insert wood screws into the timber components.When the reinforced joint rotates greatly,the anchoring failure of the screws will cause damage to the timber joint.To solve this problem,this study proposes a detachable and replaceable non-destructive flat-steel jacket reinforcement method in which horizontal flat steel is placed in the center of the joint,and the bolt is extended to the outside of the timber beam.Nine 1:3.52 scaled straight-tenon joint specimens were subjected to monotonic loading of beam ends,including three unreinforced reference joints,three joints with flat-steel jacket and three carbon fiber-reinforced plastic(CFRP)reinforced joints.The mechanical behaviors of the novel joints with flat-steel jacket were experimentally studied by comparing with those of the joints without strengthening and retrofitted with CFRP,based on the failure modes,the initial stiffness,the ultimate bearing capacity,and the moment-rotation relationship curves.Results indicated that the mortise-tenon joints reinforced with flat-steel jackets maintain the original semi-rigid properties of the unreinforced mortise-tenon joints and can effectively prevent the tenon from pulling out.The initial stiffness and ultimate bearing capacity were improved markedly.The column and beam of the reinforced joints remain intact providing the reference for the practical application of joints reinforcement.The mortisetenon joints reinforced with CFRP lose the semi-rigid properties of the unreinforced tenon-mortise joints.The joints reinforced with CFRP have the largest initial stiffness,while the unreinforced joints have the lowest stiffness.The initial stiffness of the proposed joint is in between the joints reinforced with CFRP and unreinforced joints.The ultimate bearing capacity of the joints reinforced with flat-steel jacket is larger than the other two joints,whereas the unreinforced joints have the lowest ultimate bearing capacity.
基金supported by the National Natural Science Fund of China(Grant NO.61771065,Grant NO.61571054 and Grant NO.61631005)Beijing Nova Program(NO.Z151100000315077)
文摘In the upcoming 5 G heterogeneous networks, leveraging multiple radio access technologies(RATs) shows to be a crucial issue in achieving RAT multiplexing gain to meet the explosive traffic demand. For always best connection(ABC), users tend to activate parallel transmission across all available RATs. However from a system-wide perspective, this might not be optimal given the context of network load, interference and diverse service requirements. To intelligently determine how to use these multi-RAT access resources concurrently, this paper proposes a joint multi-RAT user association and resource allocation strategy with triple decision and integrated context awareness of users and networks. A dynamic game based ant colony algorithm(GACA) is designed to simultaneously maximize the system utility and the fairness of resource allocation. Simulation results show that it's more reasonable to make multi-RAT association decision from a system-wide viewpoint than from an individual one. Compared to max-SNR based and ABC based strategies, the proposed method alleviates network congestion and optimizes resource allocation. It obtains 39%~70% performance improvement.
基金supported in part by Beijing Natural Science Foundation(No.19L2002)in part by the National Natural Science Foundation of China(No.61631004)in part by BUPT Excellent Ph.D.students Foundation(No.CX2019312).
文摘Source localization plays an indispensable role in many applications.This paper addresses the directional source localization problem in a three-dimensional(3D)wireless sensor network using hybrid received-signal-strength(RSS)and angle-of-arrival(AOA)measurements.Both the position and transmission orientation of the source are to be estimated.In the considered positioning scenario,the angle and range measurements are respectively corresponding to the AOA model and RSS model that integrates the Gaussian-shaped radiation pattern.Given that the localization problem is non-convex and the unknown parameters therein are coupled together,this paper adopts the second-order cone relaxation and alternating optimization techniques in the proposed estimation algorithm.Moreover,to provide a performance benchmark for any localization method,the corresponding Cramer-Rao lower bounds(CRLB)of estimating the unknown position and transmission orientation of the source are derived.Numerical and simulation results demonstrate that the presented algorithm effectively resolves the problem,and its estimation performance is close to the CRLB for the localization with the hybrid measurements.
文摘A series of chitosan/attapulgite (CTS/APT) hybrid microspheres were prepared by a facile spray-drying technique. The developed hybrid microspheres were characterized by Fourier transform infrared spectra (FTIR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and the zeta potential. The encapsulation efficiency and in vitro controlled release properties of the microspheres for drug were evaluated using diclofenac sodium (DS) as a model drug. Results indicated that the introduction of APT into crosslinked CTS microspheres can achieve narrow size distribution and make them more uniform. The isoelectric point of the microspheres increased from 8.14 to 9.18 with increasing the content of APT to 10 wt.%. DS loaded in hybrid microspheres is hardly released in simulated gastric fluid, but quickly released in simulated intestinal fluid. The electrostatic interaction between hybrid microspheres and DS can improve the encapsulation efficiency and controlled release behavior of CTS/APT microspheres, and the release mechanism fits Fickian diffusion.
基金supported in part by the National Natural Science Foundation of China under Grant 61671074in part by Project No.A01B02C01202015D0。
文摘A distributed reinforcement learning(RL)based resource management framework is proposed for a mobile edge computing(MEC)system with both latency-sensitive and latency-insensitive services.We investigate joint optimization of both computing and radio resources to achieve efficient on-demand matches of multi-dimensional resources and diverse requirements of users.A multi-objective integer programming problem is formulated by two subproblems,i.e.,access point(AP)selection and subcarrier allocation,which can be solved jointly by our proposed distributed RL-based approach with a heuristic iteration algorithm.The proposed algorithm allows for the reduction in complexity since each user needs to consider only its own selection of AP without knowing full global information.Simulation results show that our algorithm can achieve near-optimal performance while reducing computational complexity significantly.Compared with other algorithms that only optimize either of the two sub-problems,the proposed algorithm can serve more users with much less power consumption and content delivery latency.
基金This study is supported by the National Nature Science Foundation of China(81101432 and 81272036).
文摘Keloids are a notorious fibroproliferative disorder that may cause cosmetic concerns and life inconvenience.Various methods such as surgery,injection,and laser have been used;however,single treatments are at risk of recurrence;therefore,comprehensive therapy is the better solution.Here,we focused on the management of different medical interventions according to subjective and objective conditions of keloid patients and summarized several clinical comprehensive strategies based on our clinical experience.One original concept of laser combined with radiotherapy was also introduced as a promising method,especially for wide-based pathological scars.
基金This work was sponsored by grants from the National Natural Science Foundation of China(81803269 and 81427805)the Science and Technology Commission of Shanghai Municipality(18YF1412100 and 2019Y0150)+2 种基金the National Key Research and Development Program of China(2018YFC2000700)the Key Research Program of the Chinese Academy of Sciences(ZDRW-ZS-2017-1)Shanghai Municipality Health Commission(GWV-10.2-YQ17 and 2019Y0150).
文摘Rapid metastasis to vital organs such as the lung,liver,and brain is responsible for the vast majority of pancreatic cancer deaths.Liver metastasis of pancreatic cancer accounts for the high mortality rate in patients.Exosomes derived from pancreatic cancer cells tend to be enriched in proteins that are anchored to the cell membrane,supporting the reprogramming of the tumor microenvironment and the progression of distant metastatic lesions.For the first time,our study has demonstrated that cluster of differentiation 44(CD44),a transmembrane glycoprotein delivered by exosomes,is involved in the metastatic process of pancreatic cancer.Moreover,CD44 was found to interact with integrin a6b4 to form a complex,thereby remodeling intracellular skeleton proteins,and to promote tumor cell motility through the activation of the Src and Ras signaling cascades.Notably,we also demonstrated that the CD44–a6b4 complex can be delivered to the target region via the paracrine effects of exosomes.The selective uptake of CD44-competent tumor exosomes by liver cells activated fibrotic pathways and generated a pre-metastatic niche by stimulating the cytokines,proinflammatory factors,and growth factors that ultimately support tumor metastasis.Our results suggest the potential application of exosomal CD44 as a biomarker for the clinical diagnosis of and therapy for pancreatic cancer.
基金supported in part by the National Natural Science Foundation of China (Grant 61501045)in part by State Major Science and Technology Special Projects (Grant 2016ZX03001017-004)
文摘Cloud computing.based heterogeneous networks(C.Het Nets) have been considered as promising network architecture of future wireless communication systems. However, its performance is constrained by the capability of fronthaul. To study the performance limit of C.Het Nets, the coverage performance of the open access strategy in C.Het Nets is analyzed in this paper. In particular, the non.ideal condition of fronthaul in C.Het Nets is characterized by establishing a stochastic geometry.based model, and a tight lower bound on coverage probability is derived for downlink transmissions. Based on the derived results, the constraint of the fronthaul is given to ensure that open access strategy can achieve the best coverage performance. Finally, the simulation results are provided to verify the theoretical results and show the impact of fronthaul constrains.
基金partially supported by the Honghe University Doctoral Research Program(XJ17B11)Yunnan Province Applied Basic Research for Youthsthe Yunnan Province Local University(Part)Basic Research Joint Project(2017FH001-013)
文摘In this paper, we investigate nonlinear Hamiltonian elliptic system {-△u＋b（x）· u＋（V（x）＋τ）u=K（x）g（v） in R^N,-△u-b（x）· v＋（V（x）＋τ）v=K（x）f（u） in R^N,u（x）→ and v（x）→0 as ｜x｜→∞2,where N ≥ 3, τ 〉 0 is a positive parameter and V, K are nonnegative continuous functions,f and g are both superlinear at 0 with a quasicritical growth at infinity. By establishing avariational setting, the existence of ground state solutions is obtained.
文摘[Objective] This study was conducted to investigate the pollution caused by staphylococcal enterotoxins(SE) in raw milk and the safety of dairy products in Jinan, and to provide a scientific basis for food safety risk analysis. [Method] A total of 130 raw milk samples were collected from different regions of Jinan, and detected for Staphylococcus aureus by referring to GB4789.10-2010. Then, enzyme-linked immunosorbent assay was performed to detect whether the S.aureus strains produced enterotoxins, and the enterotoxin type was identified using colloidal gold-based immunochromatographic test strips. [Result] Fiftyseven of the raw milk samples were polluted by S.aureus, so the detection rate of S.aureus was 43.85%; and 11 of the strains produced enterotoxins. Among the 11 enterotoxin-producing strains, seven produced SEB, only one produced SEC, and the SE type of other three strains was not identified. [Conclusion] Enzyme-linked immunosorbent assay and colloidal gold-based immunochromatographic test strips can be used in combination to rapidly detect staphylococcal enterotoxins and identify enterotoxin type, although there are some limitations. SEB is the main type of staphylococcal enterotoxin causing pollution in milk of Shandong Province.
文摘In the application of large-scale ancient site protection, it is necessary to continuously monitor the ambient light, temperature, humidity and so on. However, it is impractical to frequently replace the nodes’ battery in the protected areas. So, the key methods to prolong the network lifetime are to aggregate the collected data and reduce the number of transferring messages. In this paper a Lightweight Data Aggregation Protocol (LDAP) based on the characteristics of the environmental changes in ancient sites is proposed. It has been implemented in the Lab with a dozen of MICAz motes and deployed in the real ancient sites. The result shows that LDAP is effective in reducing the number of transferring packets and satisfies the real application requirements.
文摘Energy efficiency and enhanced backbone capacity is obtained by exploiting the geometric orientation of cooperative nodes in wireless sensor network. The cooperative communication in wireless sensor networks (WSN) gives us leverage to get the inherent advantages of its random node’s locations and the direction of the data flow. Depending on the channel conditions and the transmission distance, the number of cooperative nodes is selected, that participate in an energy efficient transmission/reception. Simulation results show that increasing the cooperative receive diversity, decreases the energy consumption per bit in cooperative communications. It has also been shown that the network backbone capacity can be increased by controlled displacement of antennas at base station at the expense of energy per bit.
