Smith (1997) proposes three stages of a situation from the imprefective veiwpoints in English: preliminary, internal and resultant stage and three readings of imperfective aspect. In the essay, the different readings ...Smith (1997) proposes three stages of a situation from the imprefective veiwpoints in English: preliminary, internal and resultant stage and three readings of imperfective aspect. In the essay, the different readings of imperfective aspect in English and Chinese will be explored.展开更多
Addressing the limitations of inadequate stochastic disturbance characterization during wind turbine degradation processes that result in constrained modeling accuracy,replacement-based maintenance practices that devi...Addressing the limitations of inadequate stochastic disturbance characterization during wind turbine degradation processes that result in constrained modeling accuracy,replacement-based maintenance practices that deviate from actual operational conditions,and static maintenance strategies that fail to adapt to accelerated deterioration trends leading to suboptimal remaining useful life utilization,this study proposes a Time-Based Incomplete Maintenance(TBIM)strategy incorporating reliability constraints through stochastic differential equations(SDE).By quantifying stochastic interference via Brownian motion terms and characterizing nonlinear degradation features through state influence rate functions,a high-precision SDE degradation model is constructed,achieving 16%residual reduction compared to conventional ordinary differential equation(ODE)methods.The introduction of age reduction factors and failure rate growth factors establishes an incomplete maintenance mechanism that transcends traditional“as-good-as-new”assumptions,with the TBIM model demonstrating an additional 8.5%residual reduction relative to baseline SDE approaches.A dynamic maintenance interval optimization model driven by dual parameters—preventive maintenance threshold R_(p) and replacement threshold R_(r)—is designed to achieve synergistic optimization of equipment reliability and maintenance economics.Experimental validation demonstrates that the optimized TBIM extends equipment lifespan by 4.4%and reducesmaintenance costs by 4.16%at R_(p)=0.80,while achieving 17.2%lifespan enhancement and 14.6%cost reduction at R_(p)=0.90.This methodology provides a solution for wind turbine preventive maintenance that integrates condition sensitivity with strategic foresight.展开更多
Over-the-air computation(AirComp)enables federated learning(FL)to rapidly aggregate local models at the central server using waveform superposition property of wireless channel.In this paper,a robust transmission sche...Over-the-air computation(AirComp)enables federated learning(FL)to rapidly aggregate local models at the central server using waveform superposition property of wireless channel.In this paper,a robust transmission scheme for an AirCompbased FL system with imperfect channel state information(CSI)is proposed.To model CSI uncertainty,an expectation-based error model is utilized.The main objective is to maximize the number of selected devices that meet mean-squared error(MSE)requirements for model broadcast and model aggregation.The problem is formulated as a combinatorial optimization problem and is solved in two steps.First,the priority order of devices is determined by a sparsity-inducing procedure.Then,a feasibility detection scheme is used to select the maximum number of devices to guarantee that the MSE requirements are met.An alternating optimization(AO)scheme is used to transform the resulting nonconvex problem into two convex subproblems.Numerical results illustrate the effectiveness and robustness of the proposed scheme.展开更多
This study aims to investigate the propagation of harmonic waves in nonlocal magneto-electro-elastic(MEE)laminated composites with interface stress imperfections using an analytical approach.The pseudo-Stroh formulati...This study aims to investigate the propagation of harmonic waves in nonlocal magneto-electro-elastic(MEE)laminated composites with interface stress imperfections using an analytical approach.The pseudo-Stroh formulation and nonlocal theory proposed by Eringen were adopted to derive the propagator matrix for each layer.Both the propagator and interface matrices were formulated to determine the recursive fields.Subsequently,the dispersion equation was obtained by imposing traction-free and magneto-electric circuit open boundary conditions on the top and bottom surfaces of the plate.Dispersion curves,mode shapes,and natural frequencies were calculated for sandwich plates composed of BaTiO3 and CoFe2O4.Numerical simulations revealed that both interface stress and the nonlocal effect influenced the tuning of the dispersion curve and mode shape for the given layup.The nonlocal effect caused a significant decrease in the dispersion curves,particularly in the high-frequency regions.Additionally,compared to the nonlocal effect,the interface stress exerted a greater influence on the mode shapes.The generalized analytical framework developed in this study provides an effective tool for both the theoretical analysis and practical design of MEE composite laminates.展开更多
This study investigates the nonlinear dynamics of geometrically imperfect graphene platelet-reinforced metal foam(GPLRMF)fluid-conveying pipes under the 1:1 internal resonance condition.With simply supported boundary ...This study investigates the nonlinear dynamics of geometrically imperfect graphene platelet-reinforced metal foam(GPLRMF)fluid-conveying pipes under the 1:1 internal resonance condition.With simply supported boundary conditions,the system is subject to the combined external lateral loads and internal pulsating fluid excitations.The nonlinear dynamic model is established with the Euler-Lagrange equations and then systematically discretized via the Galerkin method.The multi-scale analysis reveals how material properties and geometric imperfections influence the internal resonance.Particular emphasis is placed on elucidating,through the modal energy analysis,the energy exchange mechanisms between the first two vibration modes.展开更多
Based on the objective reality of channel estimation error,this paper introduces a novel artificial noise(AN)aided spatial modulation(SM)secrecyenhancing scheme under imperfect channel state information(CSI).In the pr...Based on the objective reality of channel estimation error,this paper introduces a novel artificial noise(AN)aided spatial modulation(SM)secrecyenhancing scheme under imperfect channel state information(CSI).In the proposed scheme,SM is used to activate one antenna from the transmit antennas,and the information symbols will be transmitted with the designed AN at each timeslot.By utilizing the legitimate channel’s imperfect CSI,AN is generated across two adjacent timeslots.Because the CSI is known at the legitimate receiver,then it can perfectly cancel the AN.However,the eavesdropper knows nothing of the legitimate channel’s CSI,so it can not recover any useful information from the AN.At the receiver,a new detection scheme that detects across two adjacent timeslots is also proposed.With imperfect CSI,the secrecy rate of the proposed scheme is derived over Rayleigh fading channels in order to investigate the performance.Moreover,based on the secrecy performance analysis,the lower bound of the ergodic secrecy rate(ESR),the corresponding closed form of the lower bound,and the approximated expression are also derived.The simulation results verified in this paper prove that the proposed scheme with imperfect CSI can achieve satisfactory performance.展开更多
The buckling behavior of stiffened panels is significantly influenced by material and geometric defects,making it a critical factor in ensuring structural integrity and safety.These panels are widely used in mechanica...The buckling behavior of stiffened panels is significantly influenced by material and geometric defects,making it a critical factor in ensuring structural integrity and safety.These panels are widely used in mechanical,aerospace,marine,and civil engineering applications due to their ability to enhance bending stiffness with minimal additional weight.Under high loads or stress concentrations,localized structural failures can initiate global buckling in stiffened panels.This study investigates how such defects affect the critical buckling load,stiffness,and thickness of stiffened panels.Two finite element analyses were conducted:a linear analysis to identify the initial buckling mode and a nonlinear analysis using the Riks algorithm in Abaqus CAE,incorporating localized imperfections.The simulations show that material and geometric defects can reduce buckling resistance depending on their severity.展开更多
Based on the theoretical representation of piezoelectric quasicrystal,a generalized dynamic model is built to represent the transmission of wave aspects in surface acoustic pulse nano-devices.Surface elasticity,surfac...Based on the theoretical representation of piezoelectric quasicrystal,a generalized dynamic model is built to represent the transmission of wave aspects in surface acoustic pulse nano-devices.Surface elasticity,surface piezoelectricity,and surface permittivity help to include the surface effect,which equals additional thin sheets.It is shown that,under certain assumptions,this generalized dynamic model may be simplified to a few classical examples that are appropriate for both macro and nano-scale applications.In the current work,surface piezoelectricity is used to develop a theoretical model for shear horizontal(SH)waves where it contains the surface piezoelectricity theory and a linear spring model to quantitatively and qualitatively explore SH waves in an orthotropic piezoelectric quasicrystal layer overlying an elastic framework(Model I),a piezoelectric quasi-crystal nano substrate,and an orthotropic piezoelectric quasicrystal half-space(Model II).The theoretical model stimulates the numerical results,which establish the critical thickness.As the piezoelectric layer’s thickness gets closer to nanometres,surface energy must be included when analyzing dispersion properties.Furthermore,the effects of surface elasticity and density on wave velocity are investigated individually.The authors establish a parameter,precisely the ratio of the physical modulus along the width direction to along the direction of wave travel.The surface effect’s impact on the general char-acteristics of piezoelectric structures is seen as a spring force acting on bulk boundaries.Analytical presentation of frequency equations for both symmetric and anti-symmetric waves pertains to the case of an electrical short circuit in Model II.The project aims to analyze SH waves in orthogonal anisotropic,transversely isotropic piezoelectric layered nanostructures,providing a practical mathematical tool for surface effects analysis and adaptability to other wave types,including Rayleigh waves and acoustic surface waves.展开更多
The uplink massive multiple-input multiple-output(MIMO)status update system is very concerned about information freshness performance,especially for some central control Internet of Things(IoT)applications.In this con...The uplink massive multiple-input multiple-output(MIMO)status update system is very concerned about information freshness performance,especially for some central control Internet of Things(IoT)applications.In this context,age of information(AoI),as the metric of information freshness,gets more and more recognition,and simultaneously,the status packet blocklength plays an important role in improving the information freshness.In this work,we firstly consider a case with perfect channel state information(CSI)at the base station(BS),and derive the closed-form expression of the average AoI by using the Shannon theory.Guided by this,we obtain the tradeoff relationship among the status packet blocklength,transmission time and transmission failure probability.Accordingly,we optimize the status packet blocklength to minimize the average AoI.Then,we consider a more practical case with finite blocklength and imperfect CSI at the BS.In this case,we exploit pilot sequence to assist channel estimation,and derive an approximated closed-form expression of the average AoI according to short packet communication theory.It is found that increasing pilot block-length can improve the accuracy of channel estimation but reduce the frequency of status updates.Hence,we jointly optimize the pilot blocklength and status packet blocklength to improve the AoI performance.Extensive simulation results validate that the proposed methods can achieve almost the same performance as the exhaustive search methods.展开更多
The access of massive Internet of Things(IoT)users poses several challenges for Unmanned Aerial Vehicle(UAV)-aided communications,particularly in terms of security and reliability.This paper investigates a secure and ...The access of massive Internet of Things(IoT)users poses several challenges for Unmanned Aerial Vehicle(UAV)-aided communications,particularly in terms of security and reliability.This paper investigates a secure and robust power allocation scheme for UAV-aided IoT Non-Orthogonal Multiple Access(NOMA)downlink networks with a potential eavesdropper,considering imperfect Channel State Information(CSI).Given the noise uncertainty caused by the UAV’s mobility and the statistical channel estimation error,we formulate a robust optimization problem to maximize the total covert rate of all NOMA users,subject to covertness and rate-based reliability constraints.To solve this optimization problem,we first derive the minimum detection error rate and utilize the statistical characteristics(i.e.,the mean and variance of channel gain errors)to obtain the deterministic covertness and reliability constraints,respectively.We then prove that the problem is concave and determine the optimal power allocation algorithm using the Karush–Kuhn–Tucker conditions.Extensive numerical simulations validate the effectiveness of the proposed algorithm and demonstrate its ability to realize more secure and robust UAV-aided IoT systems.展开更多
According to the failure characteristics of aircraft structure, a delay-time model is an effective method to optimize maintenance for aircraft structure. To imitate the practical situation as much as possible, imperfe...According to the failure characteristics of aircraft structure, a delay-time model is an effective method to optimize maintenance for aircraft structure. To imitate the practical situation as much as possible, imperfect inspections, thresholds and repeated intervals are concerned in delay-time models. Since the suggestion by the existing delay-time models that the inspections are implemented in an infinite time span lacks practical value, a de- lay-time model with imperfect inspection within a finite time span is proposed. In the model, the nonhomogenous Poisson process is adopted to obtain the renewal probabilities between two different successive inspections on de- fects or failures. An algorithm is applied based on the Nelder-Mead downhill simplex method to solve the model. Finally, a numerical example proves the validity and effectiveness of the model.展开更多
A two-period model is developed to investigate the competitive effects of targeted advertising with imperfect targeting in a duopolistic market. In the first period, two firms compete in price in order to recognize cu...A two-period model is developed to investigate the competitive effects of targeted advertising with imperfect targeting in a duopolistic market. In the first period, two firms compete in price in order to recognize customers. In the second period, targeted advertising plays an informative role and acts as a price discrimination device. The firms＇ optimal advertising and pricing strategies under imperfect targeting are compared with those under perfect targeting. Equilibrium decisions show that, under imperfect targeting, when the advertising cost is low enough, both firms will choose to target ads at the rivals＇ old segments. This equilibrium, which could not exist under perfect targeting, results in two opposite results. When cost is high, the effect of mis-targeting will soften price competition and increase profits; on the contrary, when cost is low enough, it will lead to aggressive price competition and profit loss with the increase of imperfect targeting, so firms may have incentives to reduce the mis- targeting degree.展开更多
The concept of the imperfection sensitive region is given. The advanced stochastic imperfection method is used to research the imperfection sensitive region of single-layer latticed domes. Taking a K6 single-layer lat...The concept of the imperfection sensitive region is given. The advanced stochastic imperfection method is used to research the imperfection sensitive region of single-layer latticed domes. Taking a K6 single-layer latticed dome with a diameter of 50 m as an example, its imperfection sensitive region is made up of the first 12 kinds of joints. The influence of the imperfections of support joints on the stability of the K6 single-layer latticed dome is negligible. Influences of the joint imperfections of the main rib and the secondary rib on the structural stability are similar. The initial deviations of these joints all greatly lower the critical load of the dome. Results show that the method can analyze the structural imperfection sensitive region quantitatively and accurately.展开更多
Truth-conditional approaches to tense and other temporal expressions have relied on both linear-time and branching-time frameworks as needed. However, in the truth-conditional enterprise generally, it seems advisable ...Truth-conditional approaches to tense and other temporal expressions have relied on both linear-time and branching-time frameworks as needed. However, in the truth-conditional enterprise generally, it seems advisable to settle on a single depiction of time. Linear time is the simpler framework, and branching time faces difficulties for which we seem to have no immediate solutions. This paper defends the applicability of linear time. The apparent branching of time results from the use of speech acts other than factual assertion. Truth in correspondence with specific conditions is relevant when making factual assertions. However, we are in no epistemic position to advance factual assertions about the future, but only suppositions and predictions. For these, the truth-conditional content is employed differently. For suppositions and predictions, we only ＂pretend＂ to reference things, to assert facts, and to accept them as ＂true.＂ There is a wide array of alternatives about what we can suppose or predict, giving the impression of branching options. Suppositions and predictions under active consideration are often marked with present tense, whereas those that are inactive （not presently under active consideration but nonetheless relevant） are often marked with past tense.展开更多
Mesqan is a South Ethio-Semitic tongue which is mainly worn in day-to-day message by a people of 179,737 communities in the Gurage Zone,Ethiopia,whose linguistic skin was not well expressed.The inner aspire of this pa...Mesqan is a South Ethio-Semitic tongue which is mainly worn in day-to-day message by a people of 179,737 communities in the Gurage Zone,Ethiopia,whose linguistic skin was not well expressed.The inner aspire of this paper is to offer a complete account of tense,aspect,mood and aktionsart structures of the Mesqan tongue.The paper is expressive in character,as the lessons are mostly worried with telling what is really being in the tongue,and mostly rely on main linguistic facts.The linguistic facts,i.e.the elicited grammatical facts regarding tense,aspect,mood and aktionsart,were composed from local speakers of the tongue during 12 months of fieldwork mannered among 2011 and 2012 in four Mesqan villages and in Butajira,the managerial hub of the Mesqan Woreda.The perfective aspect in the tongue emphasizes the endpoint of the oral state with dynamic verbs,but the imperfective aspect relates with the lexical semantics of the verb,which can be practical when their purposes with stative and dynamic verbs are evaluated.Concerning tense,the past and the non-past tense in the tongue are distinguished by assisting verbs and a verb in the imperfective aspect is able to happen with states in the past and in the non-past,i.e.present or future.Future time can also be uttered by an anticipated act throughout the grouping of the future.In addition,an action happening in the past and still around in the tongue is marked by a zero morpheme in the present perfect.Concerning mood,the language has agent-oriented moods that are articulated by verb inflection,and speaker-oriented moods that are articulated by a periphrastic structure.Regarding aktionsart that denotes a specific phase in a verbal condition,like period,regularity,etc.Mesqan has two aktionsarten which are noticeable by periphrastic structures,that is the progressive and the prospective.展开更多
To investigate the effects of initial geometric imperfection and material nonlinearity on the stability analysis of the suspen-dome, the steel roof of Jiangsu Culture Sports Center Gymnasium was utilized as a numerica...To investigate the effects of initial geometric imperfection and material nonlinearity on the stability analysis of the suspen-dome, the steel roof of Jiangsu Culture Sports Center Gymnasium was utilized as a numerical model, and modal analyses were performed. Then, linear buckling analysis,geometric nonlinear stability analysis, geometric nonlinear stability analysis with initial imperfection, and double nonlinear analysis considering material nonlinearity and geometric nonlinearity were discussed in detail to compare the stability performance of the ellipse-like suspen-dome and the single-layer reticulated shell. The results showthat the cable-strut system increases the integrity of the suspen-dome, and moderates the sensibility of the single-layer reticulated shell to initial geometric imperfection. However, it has little influence on integral rigidity, fundamental vibration frequencies, linear ultimate live loads, and geometric nonlinear ultimate live loads without initial imperfection. When considering the material nonlinearity and initial imperfection, a significant reduction occurs in the ultimate stability capacities of these two structures. In this case, the suspen-dome with a lowrise-span ratio is sensitive to the initial imperfection and material nonlinearity. In addition, the distribution pattern of live loads significantly influences the instability modes of the structure, and the uniform live load with full span is not always the most dangerous case.展开更多
文摘Smith (1997) proposes three stages of a situation from the imprefective veiwpoints in English: preliminary, internal and resultant stage and three readings of imperfective aspect. In the essay, the different readings of imperfective aspect in English and Chinese will be explored.
基金supported in part by the National Natural Science Foundation of China(No.52467008)Gansu Provincial Depatment of Education Youth Doctoral Suppo Project(2024QB-051).
文摘Addressing the limitations of inadequate stochastic disturbance characterization during wind turbine degradation processes that result in constrained modeling accuracy,replacement-based maintenance practices that deviate from actual operational conditions,and static maintenance strategies that fail to adapt to accelerated deterioration trends leading to suboptimal remaining useful life utilization,this study proposes a Time-Based Incomplete Maintenance(TBIM)strategy incorporating reliability constraints through stochastic differential equations(SDE).By quantifying stochastic interference via Brownian motion terms and characterizing nonlinear degradation features through state influence rate functions,a high-precision SDE degradation model is constructed,achieving 16%residual reduction compared to conventional ordinary differential equation(ODE)methods.The introduction of age reduction factors and failure rate growth factors establishes an incomplete maintenance mechanism that transcends traditional“as-good-as-new”assumptions,with the TBIM model demonstrating an additional 8.5%residual reduction relative to baseline SDE approaches.A dynamic maintenance interval optimization model driven by dual parameters—preventive maintenance threshold R_(p) and replacement threshold R_(r)—is designed to achieve synergistic optimization of equipment reliability and maintenance economics.Experimental validation demonstrates that the optimized TBIM extends equipment lifespan by 4.4%and reducesmaintenance costs by 4.16%at R_(p)=0.80,while achieving 17.2%lifespan enhancement and 14.6%cost reduction at R_(p)=0.90.This methodology provides a solution for wind turbine preventive maintenance that integrates condition sensitivity with strategic foresight.
文摘Over-the-air computation(AirComp)enables federated learning(FL)to rapidly aggregate local models at the central server using waveform superposition property of wireless channel.In this paper,a robust transmission scheme for an AirCompbased FL system with imperfect channel state information(CSI)is proposed.To model CSI uncertainty,an expectation-based error model is utilized.The main objective is to maximize the number of selected devices that meet mean-squared error(MSE)requirements for model broadcast and model aggregation.The problem is formulated as a combinatorial optimization problem and is solved in two steps.First,the priority order of devices is determined by a sparsity-inducing procedure.Then,a feasibility detection scheme is used to select the maximum number of devices to guarantee that the MSE requirements are met.An alternating optimization(AO)scheme is used to transform the resulting nonconvex problem into two convex subproblems.Numerical results illustrate the effectiveness and robustness of the proposed scheme.
基金supported by the Ministry of Science and Technology Taiwan under Grant No.MOST 109-2628-E-009-002-MY3.
文摘This study aims to investigate the propagation of harmonic waves in nonlocal magneto-electro-elastic(MEE)laminated composites with interface stress imperfections using an analytical approach.The pseudo-Stroh formulation and nonlocal theory proposed by Eringen were adopted to derive the propagator matrix for each layer.Both the propagator and interface matrices were formulated to determine the recursive fields.Subsequently,the dispersion equation was obtained by imposing traction-free and magneto-electric circuit open boundary conditions on the top and bottom surfaces of the plate.Dispersion curves,mode shapes,and natural frequencies were calculated for sandwich plates composed of BaTiO3 and CoFe2O4.Numerical simulations revealed that both interface stress and the nonlocal effect influenced the tuning of the dispersion curve and mode shape for the given layup.The nonlocal effect caused a significant decrease in the dispersion curves,particularly in the high-frequency regions.Additionally,compared to the nonlocal effect,the interface stress exerted a greater influence on the mode shapes.The generalized analytical framework developed in this study provides an effective tool for both the theoretical analysis and practical design of MEE composite laminates.
基金supported by the Shanghai Shuguang Program(No.18SG36)。
文摘This study investigates the nonlinear dynamics of geometrically imperfect graphene platelet-reinforced metal foam(GPLRMF)fluid-conveying pipes under the 1:1 internal resonance condition.With simply supported boundary conditions,the system is subject to the combined external lateral loads and internal pulsating fluid excitations.The nonlinear dynamic model is established with the Euler-Lagrange equations and then systematically discretized via the Galerkin method.The multi-scale analysis reveals how material properties and geometric imperfections influence the internal resonance.Particular emphasis is placed on elucidating,through the modal energy analysis,the energy exchange mechanisms between the first two vibration modes.
基金supported in part by the Natural Science Project of Hubei Province under Grant 2023AFB383in part by the Open Foundation of Hubei Key Laboratory for High-Efficiency Utilization of Solar Energy and Operation Control of Energy Storage System under Grant HBSEES202107.
文摘Based on the objective reality of channel estimation error,this paper introduces a novel artificial noise(AN)aided spatial modulation(SM)secrecyenhancing scheme under imperfect channel state information(CSI).In the proposed scheme,SM is used to activate one antenna from the transmit antennas,and the information symbols will be transmitted with the designed AN at each timeslot.By utilizing the legitimate channel’s imperfect CSI,AN is generated across two adjacent timeslots.Because the CSI is known at the legitimate receiver,then it can perfectly cancel the AN.However,the eavesdropper knows nothing of the legitimate channel’s CSI,so it can not recover any useful information from the AN.At the receiver,a new detection scheme that detects across two adjacent timeslots is also proposed.With imperfect CSI,the secrecy rate of the proposed scheme is derived over Rayleigh fading channels in order to investigate the performance.Moreover,based on the secrecy performance analysis,the lower bound of the ergodic secrecy rate(ESR),the corresponding closed form of the lower bound,and the approximated expression are also derived.The simulation results verified in this paper prove that the proposed scheme with imperfect CSI can achieve satisfactory performance.
文摘The buckling behavior of stiffened panels is significantly influenced by material and geometric defects,making it a critical factor in ensuring structural integrity and safety.These panels are widely used in mechanical,aerospace,marine,and civil engineering applications due to their ability to enhance bending stiffness with minimal additional weight.Under high loads or stress concentrations,localized structural failures can initiate global buckling in stiffened panels.This study investigates how such defects affect the critical buckling load,stiffness,and thickness of stiffened panels.Two finite element analyses were conducted:a linear analysis to identify the initial buckling mode and a nonlinear analysis using the Riks algorithm in Abaqus CAE,incorporating localized imperfections.The simulations show that material and geometric defects can reduce buckling resistance depending on their severity.
文摘Based on the theoretical representation of piezoelectric quasicrystal,a generalized dynamic model is built to represent the transmission of wave aspects in surface acoustic pulse nano-devices.Surface elasticity,surface piezoelectricity,and surface permittivity help to include the surface effect,which equals additional thin sheets.It is shown that,under certain assumptions,this generalized dynamic model may be simplified to a few classical examples that are appropriate for both macro and nano-scale applications.In the current work,surface piezoelectricity is used to develop a theoretical model for shear horizontal(SH)waves where it contains the surface piezoelectricity theory and a linear spring model to quantitatively and qualitatively explore SH waves in an orthotropic piezoelectric quasicrystal layer overlying an elastic framework(Model I),a piezoelectric quasi-crystal nano substrate,and an orthotropic piezoelectric quasicrystal half-space(Model II).The theoretical model stimulates the numerical results,which establish the critical thickness.As the piezoelectric layer’s thickness gets closer to nanometres,surface energy must be included when analyzing dispersion properties.Furthermore,the effects of surface elasticity and density on wave velocity are investigated individually.The authors establish a parameter,precisely the ratio of the physical modulus along the width direction to along the direction of wave travel.The surface effect’s impact on the general char-acteristics of piezoelectric structures is seen as a spring force acting on bulk boundaries.Analytical presentation of frequency equations for both symmetric and anti-symmetric waves pertains to the case of an electrical short circuit in Model II.The project aims to analyze SH waves in orthogonal anisotropic,transversely isotropic piezoelectric layered nanostructures,providing a practical mathematical tool for surface effects analysis and adaptability to other wave types,including Rayleigh waves and acoustic surface waves.
基金supported by National Natural Science Foundation of China (Grants No. 62122094 and No.62171464)
文摘The uplink massive multiple-input multiple-output(MIMO)status update system is very concerned about information freshness performance,especially for some central control Internet of Things(IoT)applications.In this context,age of information(AoI),as the metric of information freshness,gets more and more recognition,and simultaneously,the status packet blocklength plays an important role in improving the information freshness.In this work,we firstly consider a case with perfect channel state information(CSI)at the base station(BS),and derive the closed-form expression of the average AoI by using the Shannon theory.Guided by this,we obtain the tradeoff relationship among the status packet blocklength,transmission time and transmission failure probability.Accordingly,we optimize the status packet blocklength to minimize the average AoI.Then,we consider a more practical case with finite blocklength and imperfect CSI at the BS.In this case,we exploit pilot sequence to assist channel estimation,and derive an approximated closed-form expression of the average AoI according to short packet communication theory.It is found that increasing pilot block-length can improve the accuracy of channel estimation but reduce the frequency of status updates.Hence,we jointly optimize the pilot blocklength and status packet blocklength to improve the AoI performance.Extensive simulation results validate that the proposed methods can achieve almost the same performance as the exhaustive search methods.
基金supported in part by the National Natural Science Foundation of China(No.62403500)in part by the Hubei Provincial Natural Science Foundation,China(No.2023AFB202)+4 种基金in part by the Fundamental Research Funds for the Central Universities,South-Central Minzu University,China(No.CZQ23016)in part by the Chunhui Program of Ministry of Education(No.HZKY20220331)in part by the Research Start-up Funds of South-Central Minzu University,China(Nos.YZZ18006,YZY23001)in part by the Fund for Academic Innovation Teams and Research Platform of South-Central Minzu University,China(Nos.XTZ24003,PTZ24001)in part by the Research Matching Grant Scheme from the Research Grants Council of Hong Kong。
文摘The access of massive Internet of Things(IoT)users poses several challenges for Unmanned Aerial Vehicle(UAV)-aided communications,particularly in terms of security and reliability.This paper investigates a secure and robust power allocation scheme for UAV-aided IoT Non-Orthogonal Multiple Access(NOMA)downlink networks with a potential eavesdropper,considering imperfect Channel State Information(CSI).Given the noise uncertainty caused by the UAV’s mobility and the statistical channel estimation error,we formulate a robust optimization problem to maximize the total covert rate of all NOMA users,subject to covertness and rate-based reliability constraints.To solve this optimization problem,we first derive the minimum detection error rate and utilize the statistical characteristics(i.e.,the mean and variance of channel gain errors)to obtain the deterministic covertness and reliability constraints,respectively.We then prove that the problem is concave and determine the optimal power allocation algorithm using the Karush–Kuhn–Tucker conditions.Extensive numerical simulations validate the effectiveness of the proposed algorithm and demonstrate its ability to realize more secure and robust UAV-aided IoT systems.
基金Supported by the National Natural Science Foundation of China(61079013)the Natural Science Fund Project in Jiangsu Province(BK2011737)~~
文摘According to the failure characteristics of aircraft structure, a delay-time model is an effective method to optimize maintenance for aircraft structure. To imitate the practical situation as much as possible, imperfect inspections, thresholds and repeated intervals are concerned in delay-time models. Since the suggestion by the existing delay-time models that the inspections are implemented in an infinite time span lacks practical value, a de- lay-time model with imperfect inspection within a finite time span is proposed. In the model, the nonhomogenous Poisson process is adopted to obtain the renewal probabilities between two different successive inspections on de- fects or failures. An algorithm is applied based on the Nelder-Mead downhill simplex method to solve the model. Finally, a numerical example proves the validity and effectiveness of the model.
基金The National Natural Science Foundation of China(No.71371050)
文摘A two-period model is developed to investigate the competitive effects of targeted advertising with imperfect targeting in a duopolistic market. In the first period, two firms compete in price in order to recognize customers. In the second period, targeted advertising plays an informative role and acts as a price discrimination device. The firms＇ optimal advertising and pricing strategies under imperfect targeting are compared with those under perfect targeting. Equilibrium decisions show that, under imperfect targeting, when the advertising cost is low enough, both firms will choose to target ads at the rivals＇ old segments. This equilibrium, which could not exist under perfect targeting, results in two opposite results. When cost is high, the effect of mis-targeting will soften price competition and increase profits; on the contrary, when cost is low enough, it will lead to aggressive price competition and profit loss with the increase of imperfect targeting, so firms may have incentives to reduce the mis- targeting degree.
文摘The concept of the imperfection sensitive region is given. The advanced stochastic imperfection method is used to research the imperfection sensitive region of single-layer latticed domes. Taking a K6 single-layer latticed dome with a diameter of 50 m as an example, its imperfection sensitive region is made up of the first 12 kinds of joints. The influence of the imperfections of support joints on the stability of the K6 single-layer latticed dome is negligible. Influences of the joint imperfections of the main rib and the secondary rib on the structural stability are similar. The initial deviations of these joints all greatly lower the critical load of the dome. Results show that the method can analyze the structural imperfection sensitive region quantitatively and accurately.
文摘Truth-conditional approaches to tense and other temporal expressions have relied on both linear-time and branching-time frameworks as needed. However, in the truth-conditional enterprise generally, it seems advisable to settle on a single depiction of time. Linear time is the simpler framework, and branching time faces difficulties for which we seem to have no immediate solutions. This paper defends the applicability of linear time. The apparent branching of time results from the use of speech acts other than factual assertion. Truth in correspondence with specific conditions is relevant when making factual assertions. However, we are in no epistemic position to advance factual assertions about the future, but only suppositions and predictions. For these, the truth-conditional content is employed differently. For suppositions and predictions, we only ＂pretend＂ to reference things, to assert facts, and to accept them as ＂true.＂ There is a wide array of alternatives about what we can suppose or predict, giving the impression of branching options. Suppositions and predictions under active consideration are often marked with present tense, whereas those that are inactive （not presently under active consideration but nonetheless relevant） are often marked with past tense.
文摘Mesqan is a South Ethio-Semitic tongue which is mainly worn in day-to-day message by a people of 179,737 communities in the Gurage Zone,Ethiopia,whose linguistic skin was not well expressed.The inner aspire of this paper is to offer a complete account of tense,aspect,mood and aktionsart structures of the Mesqan tongue.The paper is expressive in character,as the lessons are mostly worried with telling what is really being in the tongue,and mostly rely on main linguistic facts.The linguistic facts,i.e.the elicited grammatical facts regarding tense,aspect,mood and aktionsart,were composed from local speakers of the tongue during 12 months of fieldwork mannered among 2011 and 2012 in four Mesqan villages and in Butajira,the managerial hub of the Mesqan Woreda.The perfective aspect in the tongue emphasizes the endpoint of the oral state with dynamic verbs,but the imperfective aspect relates with the lexical semantics of the verb,which can be practical when their purposes with stative and dynamic verbs are evaluated.Concerning tense,the past and the non-past tense in the tongue are distinguished by assisting verbs and a verb in the imperfective aspect is able to happen with states in the past and in the non-past,i.e.present or future.Future time can also be uttered by an anticipated act throughout the grouping of the future.In addition,an action happening in the past and still around in the tongue is marked by a zero morpheme in the present perfect.Concerning mood,the language has agent-oriented moods that are articulated by verb inflection,and speaker-oriented moods that are articulated by a periphrastic structure.Regarding aktionsart that denotes a specific phase in a verbal condition,like period,regularity,etc.Mesqan has two aktionsarten which are noticeable by periphrastic structures,that is the progressive and the prospective.
基金The National Key Technology R&D Program of China(No.2012BAJ03B06)the National Natural Science Foundation of China(No.51308105)+1 种基金the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)the Fundamental Research Funds for the Southeast University(No.KYLX_0152,SJLX_0084,KYLX_0149)
文摘To investigate the effects of initial geometric imperfection and material nonlinearity on the stability analysis of the suspen-dome, the steel roof of Jiangsu Culture Sports Center Gymnasium was utilized as a numerical model, and modal analyses were performed. Then, linear buckling analysis,geometric nonlinear stability analysis, geometric nonlinear stability analysis with initial imperfection, and double nonlinear analysis considering material nonlinearity and geometric nonlinearity were discussed in detail to compare the stability performance of the ellipse-like suspen-dome and the single-layer reticulated shell. The results showthat the cable-strut system increases the integrity of the suspen-dome, and moderates the sensibility of the single-layer reticulated shell to initial geometric imperfection. However, it has little influence on integral rigidity, fundamental vibration frequencies, linear ultimate live loads, and geometric nonlinear ultimate live loads without initial imperfection. When considering the material nonlinearity and initial imperfection, a significant reduction occurs in the ultimate stability capacities of these two structures. In this case, the suspen-dome with a lowrise-span ratio is sensitive to the initial imperfection and material nonlinearity. In addition, the distribution pattern of live loads significantly influences the instability modes of the structure, and the uniform live load with full span is not always the most dangerous case.
