Resource allocation remains a challenging issue in communication networks,and its complexity is continuously increasing with the densification of the networks.With the evolution of new wireless technologies such as Fi...Resource allocation remains a challenging issue in communication networks,and its complexity is continuously increasing with the densification of the networks.With the evolution of new wireless technologies such as Fifth Generation(5G)and Sixth Generation(6G)mobile networks,the service level requirements have become stricter and more heterogeneous depending on the use case.In this paper,we review a large body of literature on various resource allocation schemes that are used in particular in mobile wireless communication networks and compare the proposed schemes in terms of performance indicators as well as techniques used.Our review shows that among the strategies proposed in the literature,there is a wide variety of optimization targets and combinations thereof,focusing mainly on performance indicators such as energy efficiency,spectral efficiency,and network capacity.In addition,in this paper,selected algorithms for resource allocation are numerically analyzed through simulations to compare and highlight the importance of how the resource algorithms are implemented to achieve efficient usage of the available spectrum.The performance of selected algorithms is evaluated in a multi-cell heterogeneous network and compared to proportional fair and eICIC,a widely-used combination of resource allocation and interferencemitigation techniques used by communication networks.The results show that one approach may performbetter when looking at the individual average user data rate but worse when looking at the overall spectral or energy efficiency,depending on the category of traffic.The results,therefore,confirm that theremay not be a single algorithmthat visibly outperforms other candidates in terms of all performance criteria.Instead,their efficiency is always a consequence of a strategic choice of goals,and the targeted parameters are optimized at a price.Thus,the development and implementation of resource allocation algorithms must follow concrete usage scenarios and network needs and be highly dependent on the requirements and criteria of network performance.展开更多
This paper highlights the statistical procedure used in developing models that have the ability of capturing and forecasting the traffic of mobile communication network operating in Vietnam. To build such models, we f...This paper highlights the statistical procedure used in developing models that have the ability of capturing and forecasting the traffic of mobile communication network operating in Vietnam. To build such models, we follow Box-Jenkins method to construct a multiplicative seasonal ARIMA model to represent the mean component using the past values of traffic, then incorporate a GARCH model to represent its volatility. The traffic is collected from EVN Telecom mobile communication network. Diagnostic tests and examination of forecast accuracy measures indicate that the multiplicative seasonal ARIMA/GARCH model, i.e. ARIMA (1, 0, 1) × (0, 1, 1)24/GARCH (1, 1) shows a good estimation when dealing with volatility clustering in the data series. This model can be considered to be a flexible model to capture well the characteristics of EVN traffic series and give reasonable forecasting results. Moreover, in such situations that the volatility is not necessary to be taken into account, i.e. short-term prediction, the multiplicative seasonal ARIMA/GARCH model still acts well with the GARCH parameters adjusted to GARCH (0, 0).展开更多
The purpose is to explore the effect of the spatial distribution of ground control points （GCPs） on the accuracy of imagery rectification. Both area-distributed and linearly distributed GCPs were used to rectify a L...The purpose is to explore the effect of the spatial distribution of ground control points （GCPs） on the accuracy of imagery rectification. Both area-distributed and linearly distributed GCPs were used to rectify a Landsat TM image of a coastal zone. Rectification accuracy was checked against 99 independent points over the intertidal mudflats with no ground control. Results indicate that the root-mean-square error of residuals over these areas is several times larger than its GCPs-measured counterpart. If the GCPs are spatially dispersed over an area, residuals fluctuate but increase steadily with distance to the source of control in easting （R^2= 0. 827）. in northing they fluctuate around 150 m until 15 km, beyond which they rise steadily at a small range of fluctuation. These residuals are less predictable from distance to the source of control than in easting （R^2= 0.517 ）. If the GCPs are distributed along a control line, residuals rise with distance to it linearly and predictably （R^2 = 0. 877） in the direction perpendicular to it. In a direction parallel to it, the distance has little impact on rectification residuals.展开更多
To evaluate the performance of a photovoltaic panel, several parameters must be extracted from the photovoltaic. These parameters are very important for the evaluation, monitoring and optimization of photovoltaic. Amo...To evaluate the performance of a photovoltaic panel, several parameters must be extracted from the photovoltaic. These parameters are very important for the evaluation, monitoring and optimization of photovoltaic. Among the methods developed to extract photovoltaic parameters from current-voltage (I-V) characteristic curve, metaheuristic algorithms are the most used nowadays. A new metaheuristic algorithm namely enhanced vibrating particles system algorithm is presented here to extract the best values of parameters of a photovoltaic cell. Five recent algorithms (grey wolf optimization (GWO), moth-flame optimization algorithm (MFOA), multi-verse optimizer (MVO), whale optimization algorithm (WAO), salp swarm-inspired algorithm (SSA)) are also implemented on the same computer. Enhanced vibrating particles system is inspired by the free vibration of the single degree of freedom systems with viscous damping. To extract the photovoltaic parameters using enhanced vibrating particles system algorithm, the problem can be set as an optimization problem with the objective to minimize the difference between measured and estimated current. Four case studies have been implemented here. The results and comparison with other methods exhibit high accuracy and validity of the proposed enhanced vibrating particles system algorithm to extract parameters of a photovoltaic cell and module.展开更多
Tropospheric Scattering(Troposcatter) and Tropospheric Ducting are two different mechanisms due to in-homogenoueties in the lower part of the Earths atmosphere.Their common influence in propagation of microwaves is st...Tropospheric Scattering(Troposcatter) and Tropospheric Ducting are two different mechanisms due to in-homogenoueties in the lower part of the Earths atmosphere.Their common influence in propagation of microwaves is studied here in order to achieve a feasible naval communication system.Although not new,Troposcatter together with Tropospheric Ducting communications are regaining popularity in current military and civil applications such as isolated islands and oil extraction facilities in the open sea.The innovation proposed here is the application of such systems in naval communications where at least one of the stations is mobile.Several propagation together with fading models are simulated using appropriate programs and scientific simulation packets in order to predict maximum range of such communication systems in each dominant mode of operation.Then appropriate antenna design proposals are given to overcome the high propagation loss and minimize possible interferences.展开更多
In mmWave massive multiple-input multiple-output(MIMO)communication systems,the extension of low-complexity narrowband precoding schemes to be operated on wideband systems under frequency-selective channels remains an...In mmWave massive multiple-input multiple-output(MIMO)communication systems,the extension of low-complexity narrowband precoding schemes to be operated on wideband systems under frequency-selective channels remains an important challenge at the current time.This paper investigates a low complexity wideband hybrid precoding scheme for mmWave massive MIMO multicarrier systems under a single-user,fully-connected hybrid architecture.We show that the radio frequency(RF)precoding/combining vectors can be directly derived from the eigenvectors of the optimal fully-digital covariance matrix over all subcarriers in order to maximize the sum rate of spectral efficiency.We also suggest a new method that iteratively reduces the residual error between the covariance matrix and the sum of products of precoding matrices over all the subcarriers to improve the performance in the case where the number of RF chains is higher than the number of streams.The results of the simulation show that the proposed schemes’complexity is low compared to the present methods,and their performance can almost reach the upper bound achieved by the optimal full-baseband design.展开更多
In this letter,a new polarization state generator(PSG) is presented,which can generate an output with arbitrary state of polarization(SOP).This PSG consists of a linear polarizer,a rotatable quarter-waveplate,and a ro...In this letter,a new polarization state generator(PSG) is presented,which can generate an output with arbitrary state of polarization(SOP).This PSG consists of a linear polarizer,a rotatable quarter-waveplate,and a rotatable half-waveplate.The PSG can be used to study the polarization-related effects on optical components and on optical fiber communication systems.展开更多
With the help of network densification,network coverage as well as the throughput can be improved via ultra-dense networks(UDNs).In tandem,Unmanned Aerial Vehicle(UAV)communications have recently garnered much attenti...With the help of network densification,network coverage as well as the throughput can be improved via ultra-dense networks(UDNs).In tandem,Unmanned Aerial Vehicle(UAV)communications have recently garnered much attention because of their high agility as well as widespread applications.In this paper,a cognitive UAV is proposed for wireless nodes power pertaining to the IoT ground terminal.Further,the UAV is included in the IoT system as the source of power for the wireless nodes as well as for resource allocation.The quality of service(QoS)related to the cognitive node was considered as a utility function based on pricing scheme that was modelled as a non-cooperative game theory in order to maximise users’net utility function.Moreover,an energy efficiency non-cooperative game theory power allocation with pricing scheme(EE-NGPAP)is proposed to obtain an efficient power control within IoT wireless nodes.Further,uniqueness and existence of the Nash equilibrium have been demonstrated mathematically and through simulation.Simulation results show that the proposed energy harvest algorithm demonstrated considerable decrease in transmitted power consumption in terms of average power reduction,which is regarded to be apt with the 5Gnetworks’vision.Finally,the proposed algorithm requires around 4 iterations only to converge to NE which makes the algorithm more suitable in practical heterogeneous scenarios.展开更多
The design, production and characterization of tailored printable optical filters for visible optical communications are demonstrated. As result, the average color difference between the specified and the produced fil...The design, production and characterization of tailored printable optical filters for visible optical communications are demonstrated. As result, the average color difference between the specified and the produced filters is 32.6, quantified in terms of CIELAB coordinates.展开更多
This study investigates the properties of exciton-polaritons in a two-dimensional(2D)hybrid organic-inorganic perovskite microcavity in the presence of optical Stark effect.Through both steady and dynamic state analys...This study investigates the properties of exciton-polaritons in a two-dimensional(2D)hybrid organic-inorganic perovskite microcavity in the presence of optical Stark effect.Through both steady and dynamic state analyses,strong coupling between excitons of perovskite and cavity photons is revealed,indicating the formation of polaritons in the perovskite microcavity.Besides,it is found that an external optical Stark pulse can induce energy shifts of excitons proportional to the pulse intensity,which modifies the dispersion characteristics of the polaritons.展开更多
Purpose-In order to solve the problem of inaccurate calculation of index weights,subjectivity and uncertainty of index assessment in the risk assessment process,this study aims to propose a scientific and reasonable c...Purpose-In order to solve the problem of inaccurate calculation of index weights,subjectivity and uncertainty of index assessment in the risk assessment process,this study aims to propose a scientific and reasonable centralized traffic control(CTC)system risk assessment method.Design/methodologylapproach-First,system-theoretic process analysis(STPA)is used to conduct risk analysis on the CTC system and constructs risk assessment indexes based on this analysis.Then,to enhance the accuracy of weight calculation,the fuzzy analytical hierarchy process(FAHP),fuzzy decision-making trial and evaluation laboratory(FDEMATEL)and entropy weight method are employed to calculate the subjective weight,relative weight and objective weight of each index.These three types of weights are combined using game theory to obtain the combined weight for each index.To reduce subjectivity and uncertainty in the assessment process,the backward cloud generator method is utilized to obtain the numerical character(NC)of the cloud model for each index.The NCs of the indexes are then weighted to derive the comprehensive cloud for risk assessment of the CTC system.This cloud model is used to obtain the CTC system's comprehensive risk assessment.The model's similarity measurement method gauges the likeness between the comprehensive risk assessment cloud and the risk standard cloud.Finally,this process yields the risk assessment results for the CTC system.Findings-The cloud model can handle the subjectivity and fuzziness in the risk assessment process well.The cloud model-based risk assessment method was applied to the CTC system risk assessment of a railway group and achieved good results.Originality/value-This study provides a cloud model-based method for risk assessment of CTC systems,which accurately calculates the weight of risk indexes and uses cloud models to reduce uncertainty and subjectivity in the assessment,achieving effective risk assessment of CTC systems.It can provide a reference and theoretical basis for risk management of the CTC system.展开更多
We investigate the negative refraction effect at a planar interface of a highly absorptive material,where the direct experimental verification is difficult because of the loss-induced skin depth effect. An apparent co...We investigate the negative refraction effect at a planar interface of a highly absorptive material,where the direct experimental verification is difficult because of the loss-induced skin depth effect. An apparent contradiction occurs when we try to determine the group velocity direction by the method of equifrequency contours(EFCs) in detail. This contradiction forbids any physical solution to be found for negative refraction.We conclude that this paradox is mainly caused by the definition of complex wavevector ■which is conventionally adopted in the case of complex permittivity. The complex wavevector may result in ambiguously defined optical path, which limits the application of the classical Snell’s law. We propose a bold suggestion that the complex wavevector■ should be replaced by a complex frequency■ . Therefore, the optical path can always be defined as real. The proposed hypothesis is capable of resolving the contradiction about the loss-induced negative refraction,and the obtained theoretical prediction fits well with the reported experimental results.展开更多
We have demonstrated the first carrier density model for AlGaN channel with AlN buffer using spontaneous and piezoelectric polarization comparison with experimental and theoretical results. From the results we proved ...We have demonstrated the first carrier density model for AlGaN channel with AlN buffer using spontaneous and piezoelectric polarization comparison with experimental and theoretical results. From the results we proved that the formation of 2DEG in undoped structure relied both on spontaneous and piezoelectric polarization. The electron distribution of Al concentration (0 < x < 0.5) was measured for both AlGaN channel and barrier. Barrier thickness assumed between 20 and 25 nm for validating the experimental results. The carrier concentration was observed at the specific interface of the N- and Ga-face by assuming x1, x2 = 0. The model results are verified with previously reported experimental data.展开更多
With the development of optical communication systems in high bandwidth fiber, various degradations affect the propagation of light signals such as polarization mode dispersion which represents a temporal pulse broade...With the development of optical communication systems in high bandwidth fiber, various degradations affect the propagation of light signals such as polarization mode dispersion which represents a temporal pulse broadening, it becomes troublesome from long and long distances for this, it is necessary to regenerate the signal optically, that is to say, the amplified （1R regeneration） , the reshaping （2R regeneration） and sometimes resynchronize to overcome the phenomenon of jitter time （3R regeneration）. In this paper we study the contribution of 2R optical regenerator self-modulation to combat the phenomenon of polarization mode dispersion. The experiment is simulated with optisystem.展开更多
Owing to the enormously enhanced oscillating wave,a minute variation of the incident light intensity will give rise to a change in the dielectric constant of the Kerr nonlinear medium and lead to a bistable reflection...Owing to the enormously enhanced oscillating wave,a minute variation of the incident light intensity will give rise to a change in the dielectric constant of the Kerr nonlinear medium and lead to a bistable reflection with an ultra-low threshold intensity,which is closely related to the angle of incidence and the thickness of the Kerr nonlinear medium.The criterion for the existence of optical bistability is derived.Our bistability scheme is simple and not limited to the TM-polarization.展开更多
In African countries,regulations on the management of WTE(Waste from Information Technology Equipment)are non-existent or sometimes insufficient,if they exist.This study shows how to mention waste from information tec...In African countries,regulations on the management of WTE(Waste from Information Technology Equipment)are non-existent or sometimes insufficient,if they exist.This study shows how to mention waste from information technology equipment in a country that does not have a regulatory legislative framework or organized management channels.A methodological approach based on documentary research and semi-directed interviews was adopted in this work.The results showed that 54.55%of institutional managers are unaware of the existence of regulations for the management of WTE,both at the national and international levels;72.72%of these managers do not have a specific implementing text for this management;72.73%of institutions have adopted an acquisition policy based on the needs of workers and 81.82%of institutions store WTE in warehouses.Relations with waste collection SMEs(Small and Midsize Enterprises),especially for IT equipment,are limited for 72.73%of institutions.In terms of improving the capacity to manage WEEE(Waste Electrical and Electronic Equipment),90.91%of institutions do not offer training or awareness raising.Overall,no significant indicators are in place to assess WEEE management in institutions,which reflects a lack of commitment and awareness among institutional managers.In addition,there are no financial means for ecological and sustainable management.Although 27.27%of managers are aware of the dangers to human health and the environment related to IT equipment,they are often unaware of the harmful consequences of abandoning it in nature.展开更多
This paper discusses issues regarding the operation of algorithms for VolP （voice over intemet protocol） signaling. The resulting data include jitter, packet delays, delays related to signalization, distribution of ...This paper discusses issues regarding the operation of algorithms for VolP （voice over intemet protocol） signaling. The resulting data include jitter, packet delays, delays related to signalization, distribution of packets in protocols and relative assessments of QoS （quality of service） and MOS （mean opinion score）.展开更多
基金supported by the Slovenian Research and Innovation Agency(ARIS)within the Research Program P2-0425:“Decentralized Solutions for the Digitalization of Industry and Smart Cities and Communities”supported by the Ministry of Education,Science,Technology and Innovation of Republic of Kosovo through the annual small grant projects.
文摘Resource allocation remains a challenging issue in communication networks,and its complexity is continuously increasing with the densification of the networks.With the evolution of new wireless technologies such as Fifth Generation(5G)and Sixth Generation(6G)mobile networks,the service level requirements have become stricter and more heterogeneous depending on the use case.In this paper,we review a large body of literature on various resource allocation schemes that are used in particular in mobile wireless communication networks and compare the proposed schemes in terms of performance indicators as well as techniques used.Our review shows that among the strategies proposed in the literature,there is a wide variety of optimization targets and combinations thereof,focusing mainly on performance indicators such as energy efficiency,spectral efficiency,and network capacity.In addition,in this paper,selected algorithms for resource allocation are numerically analyzed through simulations to compare and highlight the importance of how the resource algorithms are implemented to achieve efficient usage of the available spectrum.The performance of selected algorithms is evaluated in a multi-cell heterogeneous network and compared to proportional fair and eICIC,a widely-used combination of resource allocation and interferencemitigation techniques used by communication networks.The results show that one approach may performbetter when looking at the individual average user data rate but worse when looking at the overall spectral or energy efficiency,depending on the category of traffic.The results,therefore,confirm that theremay not be a single algorithmthat visibly outperforms other candidates in terms of all performance criteria.Instead,their efficiency is always a consequence of a strategic choice of goals,and the targeted parameters are optimized at a price.Thus,the development and implementation of resource allocation algorithms must follow concrete usage scenarios and network needs and be highly dependent on the requirements and criteria of network performance.
文摘This paper highlights the statistical procedure used in developing models that have the ability of capturing and forecasting the traffic of mobile communication network operating in Vietnam. To build such models, we follow Box-Jenkins method to construct a multiplicative seasonal ARIMA model to represent the mean component using the past values of traffic, then incorporate a GARCH model to represent its volatility. The traffic is collected from EVN Telecom mobile communication network. Diagnostic tests and examination of forecast accuracy measures indicate that the multiplicative seasonal ARIMA/GARCH model, i.e. ARIMA (1, 0, 1) × (0, 1, 1)24/GARCH (1, 1) shows a good estimation when dealing with volatility clustering in the data series. This model can be considered to be a flexible model to capture well the characteristics of EVN traffic series and give reasonable forecasting results. Moreover, in such situations that the volatility is not necessary to be taken into account, i.e. short-term prediction, the multiplicative seasonal ARIMA/GARCH model still acts well with the GARCH parameters adjusted to GARCH (0, 0).
基金financially supported by a grant from the joint key project of National Natural Science Foundation of China under contract(No.50339010)the National"211"Key Project of China.
文摘The purpose is to explore the effect of the spatial distribution of ground control points （GCPs） on the accuracy of imagery rectification. Both area-distributed and linearly distributed GCPs were used to rectify a Landsat TM image of a coastal zone. Rectification accuracy was checked against 99 independent points over the intertidal mudflats with no ground control. Results indicate that the root-mean-square error of residuals over these areas is several times larger than its GCPs-measured counterpart. If the GCPs are spatially dispersed over an area, residuals fluctuate but increase steadily with distance to the source of control in easting （R^2= 0. 827）. in northing they fluctuate around 150 m until 15 km, beyond which they rise steadily at a small range of fluctuation. These residuals are less predictable from distance to the source of control than in easting （R^2= 0.517 ）. If the GCPs are distributed along a control line, residuals rise with distance to it linearly and predictably （R^2 = 0. 877） in the direction perpendicular to it. In a direction parallel to it, the distance has little impact on rectification residuals.
文摘To evaluate the performance of a photovoltaic panel, several parameters must be extracted from the photovoltaic. These parameters are very important for the evaluation, monitoring and optimization of photovoltaic. Among the methods developed to extract photovoltaic parameters from current-voltage (I-V) characteristic curve, metaheuristic algorithms are the most used nowadays. A new metaheuristic algorithm namely enhanced vibrating particles system algorithm is presented here to extract the best values of parameters of a photovoltaic cell. Five recent algorithms (grey wolf optimization (GWO), moth-flame optimization algorithm (MFOA), multi-verse optimizer (MVO), whale optimization algorithm (WAO), salp swarm-inspired algorithm (SSA)) are also implemented on the same computer. Enhanced vibrating particles system is inspired by the free vibration of the single degree of freedom systems with viscous damping. To extract the photovoltaic parameters using enhanced vibrating particles system algorithm, the problem can be set as an optimization problem with the objective to minimize the difference between measured and estimated current. Four case studies have been implemented here. The results and comparison with other methods exhibit high accuracy and validity of the proposed enhanced vibrating particles system algorithm to extract parameters of a photovoltaic cell and module.
文摘Tropospheric Scattering(Troposcatter) and Tropospheric Ducting are two different mechanisms due to in-homogenoueties in the lower part of the Earths atmosphere.Their common influence in propagation of microwaves is studied here in order to achieve a feasible naval communication system.Although not new,Troposcatter together with Tropospheric Ducting communications are regaining popularity in current military and civil applications such as isolated islands and oil extraction facilities in the open sea.The innovation proposed here is the application of such systems in naval communications where at least one of the stations is mobile.Several propagation together with fading models are simulated using appropriate programs and scientific simulation packets in order to predict maximum range of such communication systems in each dominant mode of operation.Then appropriate antenna design proposals are given to overcome the high propagation loss and minimize possible interferences.
文摘In mmWave massive multiple-input multiple-output(MIMO)communication systems,the extension of low-complexity narrowband precoding schemes to be operated on wideband systems under frequency-selective channels remains an important challenge at the current time.This paper investigates a low complexity wideband hybrid precoding scheme for mmWave massive MIMO multicarrier systems under a single-user,fully-connected hybrid architecture.We show that the radio frequency(RF)precoding/combining vectors can be directly derived from the eigenvectors of the optimal fully-digital covariance matrix over all subcarriers in order to maximize the sum rate of spectral efficiency.We also suggest a new method that iteratively reduces the residual error between the covariance matrix and the sum of products of precoding matrices over all the subcarriers to improve the performance in the case where the number of RF chains is higher than the number of streams.The results of the simulation show that the proposed schemes’complexity is low compared to the present methods,and their performance can almost reach the upper bound achieved by the optimal full-baseband design.
基金Supported by State"10-5"Project :"40 Gb/s SDH(STM-256)Optical Fiber Communications Equipments and Systems"( No.2002BA106B07-5)
文摘In this letter,a new polarization state generator(PSG) is presented,which can generate an output with arbitrary state of polarization(SOP).This PSG consists of a linear polarizer,a rotatable quarter-waveplate,and a rotatable half-waveplate.The PSG can be used to study the polarization-related effects on optical components and on optical fiber communication systems.
基金supported by the School of Computing,Faculty of Engineering,Universiti Teknologi Malaysia(UTM)and funded by the PRGS Project(Grant ID:R.J130000.7806.4L706).
文摘With the help of network densification,network coverage as well as the throughput can be improved via ultra-dense networks(UDNs).In tandem,Unmanned Aerial Vehicle(UAV)communications have recently garnered much attention because of their high agility as well as widespread applications.In this paper,a cognitive UAV is proposed for wireless nodes power pertaining to the IoT ground terminal.Further,the UAV is included in the IoT system as the source of power for the wireless nodes as well as for resource allocation.The quality of service(QoS)related to the cognitive node was considered as a utility function based on pricing scheme that was modelled as a non-cooperative game theory in order to maximise users’net utility function.Moreover,an energy efficiency non-cooperative game theory power allocation with pricing scheme(EE-NGPAP)is proposed to obtain an efficient power control within IoT wireless nodes.Further,uniqueness and existence of the Nash equilibrium have been demonstrated mathematically and through simulation.Simulation results show that the proposed energy harvest algorithm demonstrated considerable decrease in transmitted power consumption in terms of average power reduction,which is regarded to be apt with the 5Gnetworks’vision.Finally,the proposed algorithm requires around 4 iterations only to converge to NE which makes the algorithm more suitable in practical heterogeneous scenarios.
基金The financial support of“Scientific and technological collaboration Portugal/China 2010/2012.Proc.0 441.00”is gratefully acknowledged.
文摘The design, production and characterization of tailored printable optical filters for visible optical communications are demonstrated. As result, the average color difference between the specified and the produced filters is 32.6, quantified in terms of CIELAB coordinates.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11974071 and 62375040)the Sichuan Science and Technology Program(Grant Nos.2022ZYD0108 and 2023JDRC0030).
文摘This study investigates the properties of exciton-polaritons in a two-dimensional(2D)hybrid organic-inorganic perovskite microcavity in the presence of optical Stark effect.Through both steady and dynamic state analyses,strong coupling between excitons of perovskite and cavity photons is revealed,indicating the formation of polaritons in the perovskite microcavity.Besides,it is found that an external optical Stark pulse can induce energy shifts of excitons proportional to the pulse intensity,which modifies the dispersion characteristics of the polaritons.
基金National Natural Science Foundation of China under Grant 62203468Technological Research and Development Program of China State Railway Group Co.,Ltd.under Grant J2023G007+2 种基金Young Elite Scientist Sponsorship Program by China Association for Science and Technology(CAST)under Grant 2022QNRC001Youth Talent Program Supported by China Railway SocietyResearch Program of Beijing Hua-Tie Information Technology Corporation Limited under Grant 2023HT02.
文摘Purpose-In order to solve the problem of inaccurate calculation of index weights,subjectivity and uncertainty of index assessment in the risk assessment process,this study aims to propose a scientific and reasonable centralized traffic control(CTC)system risk assessment method.Design/methodologylapproach-First,system-theoretic process analysis(STPA)is used to conduct risk analysis on the CTC system and constructs risk assessment indexes based on this analysis.Then,to enhance the accuracy of weight calculation,the fuzzy analytical hierarchy process(FAHP),fuzzy decision-making trial and evaluation laboratory(FDEMATEL)and entropy weight method are employed to calculate the subjective weight,relative weight and objective weight of each index.These three types of weights are combined using game theory to obtain the combined weight for each index.To reduce subjectivity and uncertainty in the assessment process,the backward cloud generator method is utilized to obtain the numerical character(NC)of the cloud model for each index.The NCs of the indexes are then weighted to derive the comprehensive cloud for risk assessment of the CTC system.This cloud model is used to obtain the CTC system's comprehensive risk assessment.The model's similarity measurement method gauges the likeness between the comprehensive risk assessment cloud and the risk standard cloud.Finally,this process yields the risk assessment results for the CTC system.Findings-The cloud model can handle the subjectivity and fuzziness in the risk assessment process well.The cloud model-based risk assessment method was applied to the CTC system risk assessment of a railway group and achieved good results.Originality/value-This study provides a cloud model-based method for risk assessment of CTC systems,which accurately calculates the weight of risk indexes and uses cloud models to reduce uncertainty and subjectivity in the assessment,achieving effective risk assessment of CTC systems.It can provide a reference and theoretical basis for risk management of the CTC system.
基金the Fundamental Research Funds for the Central Universities of China(No.2017B14914)the Postdoctoral Science Foundation of China(No.2016M601586)+1 种基金the National Natural Science Foundation of China(No.11874140)the Science and Technology Project of Changzhou(No.CJ20180048)
文摘We investigate the negative refraction effect at a planar interface of a highly absorptive material,where the direct experimental verification is difficult because of the loss-induced skin depth effect. An apparent contradiction occurs when we try to determine the group velocity direction by the method of equifrequency contours(EFCs) in detail. This contradiction forbids any physical solution to be found for negative refraction.We conclude that this paradox is mainly caused by the definition of complex wavevector ■which is conventionally adopted in the case of complex permittivity. The complex wavevector may result in ambiguously defined optical path, which limits the application of the classical Snell’s law. We propose a bold suggestion that the complex wavevector■ should be replaced by a complex frequency■ . Therefore, the optical path can always be defined as real. The proposed hypothesis is capable of resolving the contradiction about the loss-induced negative refraction,and the obtained theoretical prediction fits well with the reported experimental results.
文摘We have demonstrated the first carrier density model for AlGaN channel with AlN buffer using spontaneous and piezoelectric polarization comparison with experimental and theoretical results. From the results we proved that the formation of 2DEG in undoped structure relied both on spontaneous and piezoelectric polarization. The electron distribution of Al concentration (0 < x < 0.5) was measured for both AlGaN channel and barrier. Barrier thickness assumed between 20 and 25 nm for validating the experimental results. The carrier concentration was observed at the specific interface of the N- and Ga-face by assuming x1, x2 = 0. The model results are verified with previously reported experimental data.
文摘With the development of optical communication systems in high bandwidth fiber, various degradations affect the propagation of light signals such as polarization mode dispersion which represents a temporal pulse broadening, it becomes troublesome from long and long distances for this, it is necessary to regenerate the signal optically, that is to say, the amplified （1R regeneration） , the reshaping （2R regeneration） and sometimes resynchronize to overcome the phenomenon of jitter time （3R regeneration）. In this paper we study the contribution of 2R optical regenerator self-modulation to combat the phenomenon of polarization mode dispersion. The experiment is simulated with optisystem.
基金Projected supported by the Open Fund by State Key Laboratory of Advanced Optical Communication Systems and Networks(Grant No.2017GZKF18)the National Natural Science Foundation of China(Grant Nos.12064017,61765008,11764020,11864017,11804133,and 51567011)+3 种基金the Jiangxi Provincial Natural Science Foundation(Grant No.20181BAB206034)the Fundamental Research Funds for the Central Universities of China(Grant No.2017B14914),the Postdoctoral Science Foundation of China(Grant No.2016M601586)the Science and Technology Project of Changzhou(Grant No.CJ20180048)Scientific Research Fund of Jiangxi Provincial Education Department(Grant Nos.GJJ150313,GJJ160273,and GJJ170184).
文摘Owing to the enormously enhanced oscillating wave,a minute variation of the incident light intensity will give rise to a change in the dielectric constant of the Kerr nonlinear medium and lead to a bistable reflection with an ultra-low threshold intensity,which is closely related to the angle of incidence and the thickness of the Kerr nonlinear medium.The criterion for the existence of optical bistability is derived.Our bistability scheme is simple and not limited to the TM-polarization.
文摘In African countries,regulations on the management of WTE(Waste from Information Technology Equipment)are non-existent or sometimes insufficient,if they exist.This study shows how to mention waste from information technology equipment in a country that does not have a regulatory legislative framework or organized management channels.A methodological approach based on documentary research and semi-directed interviews was adopted in this work.The results showed that 54.55%of institutional managers are unaware of the existence of regulations for the management of WTE,both at the national and international levels;72.72%of these managers do not have a specific implementing text for this management;72.73%of institutions have adopted an acquisition policy based on the needs of workers and 81.82%of institutions store WTE in warehouses.Relations with waste collection SMEs(Small and Midsize Enterprises),especially for IT equipment,are limited for 72.73%of institutions.In terms of improving the capacity to manage WEEE(Waste Electrical and Electronic Equipment),90.91%of institutions do not offer training or awareness raising.Overall,no significant indicators are in place to assess WEEE management in institutions,which reflects a lack of commitment and awareness among institutional managers.In addition,there are no financial means for ecological and sustainable management.Although 27.27%of managers are aware of the dangers to human health and the environment related to IT equipment,they are often unaware of the harmful consequences of abandoning it in nature.
文摘This paper discusses issues regarding the operation of algorithms for VolP （voice over intemet protocol） signaling. The resulting data include jitter, packet delays, delays related to signalization, distribution of packets in protocols and relative assessments of QoS （quality of service） and MOS （mean opinion score）.
