Strength-ductility trade-off is a common issue in Mg alloys. This work proposed that a synergistic enhancement of strength and ductility could be achieved through tuning interlayer dwell time(IDT) in the wire and arc ...Strength-ductility trade-off is a common issue in Mg alloys. This work proposed that a synergistic enhancement of strength and ductility could be achieved through tuning interlayer dwell time(IDT) in the wire and arc additive manufacturing(WAAM) process of Mg alloy.The thermal couples were used to monitor the thermal history during the WAAM process. Additionally, the effect of different IDTs on the microstructure characteristics and resultant mechanical properties of WAAM-processed Mg alloy thin-wall were investigated. The results showed that the stable temperature of the thin-wall component could reach 290 ℃ at IDT=0s, indicating that the thermal accumulation effect was remarkable. Consequently, unimodal coarse grains with an average size of 39.6 μm were generated, and the resultant room-temperature tensile property was poor. With the IDT extended to 60s, the thermal input and thermal dissipation reached a balance, and the stable temperature was only 170 ℃, closing to the initial temperature of the substrate. A refined grain structure with bimodal size distribution was obtained. The remelting zone had fine grains with the size of 15.2 μm, while the arc zone owned coarse grains with the size of 24.5 μm.The alternatively distributed coarse and fine grains lead to the elimination of strength-ductility trade-off. The ultimate tensile strength and elongation of the samples at IDT=60s are increased by 20.6 and 75.0% of those samples at IDT=0s, respectively. The findings will facilitate the development of additive manufacturing processes for advanced Mg alloys.展开更多
Train timetables and operations are defined by the train running time in sections,dwell time at stations,and headways between trains.Accurate estimation of these factors is essential to decision-making for train delay...Train timetables and operations are defined by the train running time in sections,dwell time at stations,and headways between trains.Accurate estimation of these factors is essential to decision-making for train delay reduction,train dispatching,and station capacity estimation.In the present study,we aim to propose a train dwell time model based on an averaging mechanism and dynamic updating to address the challenges in the train dwell time prediction problem(e.g.,dynamics over time,heavy-tailed distribution of data,and spatiotemporal relationships of factors)for real-time train dispatching.The averaging mechanism in the present study is based on multiple state-of-the-art base predictors,enabling the proposed model to integrate the advantages of the base predictors in addressing the challenges in terms of data attributes and data distributions.Then,considering the influence of passenger flow on train dwell time,we use a dynamic updating method based on exponential smoothing to improve the performance of the proposed method by considering the real-time passenger amount fluctuations(e.g.,passenger soars in peak hours or passenger plunges during regular periods).We conduct experiments with the train operation data and passenger flow data from the Chinese high-speed railway line.The results show that due to the advantages over the base predictors,the averaging mechanism can more accurately predict the dwell time at stations than its counterparts for different prediction horizons regarding predictive errors and variances.Further,the experimental results show that dynamic smoothing can significantly improve the accuracy of the proposed model during passenger amount changes,i.e.,15.4%and 15.5%corresponding to the mean absolute error and root mean square error,respectively.Based on the proposed predictor,a feature importance analysis shows that the planned dwell time and arrival delay are the two most important factors to dwell time.However,planned time has positive influences,whereas arrival delay has negative influences.展开更多
In this paper, we consider the relation between the switching dwell time and the stabilization of switched linear control systems. First of all, a concept of critical dwell time is given for switched linear systems wi...In this paper, we consider the relation between the switching dwell time and the stabilization of switched linear control systems. First of all, a concept of critical dwell time is given for switched linear systems without control inputs, and the critical dwell time is taken as an arbitrary given positive constant for a switched linear control systems with controllable switching models. Secondly, when a switched linear system has many stabilizable switching models, the problem of stabilization of the overall system is considered. An on-line feedback control is designed such that the overall system is asymptotically stabilizable under switching laws which depend only on those of uncontrollable subsystems of the switching models. Finally, when a switched system is partially controllable (While some switching models are probably unstabilizable), an on-line feedback control and a cyclic switching strategy are designed such that the overall system is asymptotically stabilizable if all switching models of this uncontrollable subsystems are asymptotically stable. In addition, algorithms for designing switching laws and controls are presented.展开更多
The dwell time and spin polarization(SP)of electrons tunneling through a parallel doubleδ-magnetic-barrier nanostructure in the presence of a bias voltage is studied theoretically in this work.This nanostructure can ...The dwell time and spin polarization(SP)of electrons tunneling through a parallel doubleδ-magnetic-barrier nanostructure in the presence of a bias voltage is studied theoretically in this work.This nanostructure can be constructed by patterning two asymmetric ferromagnetic stripes on the top and bottom of InAs/AlxIn1-xAs heterostructure,respectively.An evident SP effect remains after a bias voltage is applied to the nanostructure.Moreover,both magnitude and sign of spin-polarized dwell time can be manipulated by properly changing the bias voltage,which may result in an electrically-tunable temporal spin splitter for spintronics device applications.展开更多
Bus rapid transit (BRT) systems have been shown to have many advantages including affordability, high capacity vehicles, and reliable service. Due to these attractive advantages, many cities throughout the world are...Bus rapid transit (BRT) systems have been shown to have many advantages including affordability, high capacity vehicles, and reliable service. Due to these attractive advantages, many cities throughout the world are in the process of planning the construction of BRT systems. To improve the performance of BRT systems, many researchers study BRT operation and control, which include the study of dwell times at bus/BRT stations. To ensure the effectiveness of real-time control which aims to avoid bus/BRT vehicles congestion, accurate dwell time models are needed. We develop our models using data from a BRT vehicle survey conducted in Changzhou, China, where BRT lines are built along passenger corridors, and BRT stations are enclosed like light rails. This means that interactions between passengers traveling on the BRT system are more frequent than those in traditional transit system who use platform stations. We statistically analyze the BRT vehicle survey data, and based on this analysis, we are able to make the following conclusions: ( I ) The delay time per passenger at a BRT station is less than that at a non-BRT station, which implies that BRT stations are efficient in the sense that they are able to move passengers quickly. (II) The dwell time follows a logarithmic normal distribution with a mean of 2.56 and a variance of 0.53. (III) The greater the number of BRT lines serviced by a station, the longer the dwell time is. (IV) Daily travel demands are highest during the morning peak interval where the dwell time, the number of passengers boarding and alighting and the number of passengers on vehicles reach their maximum values. (V) The dwell time is highly positively correlated with the total number of passengers boarding and alighting. (VI) The delay per passenger is negatively correlated with the total number of passengers boarding and alighting. We propose two dwell time models for the BRT station. The first proposed model is a linear model while the second is nonlinear. We introduce the conflict between passengers boarding and alighting into our models. Finally, by comparing our models with the models of Rajbhandari and Chien et al., and TCQSM (Transit Capacity and Quality of Service Manual), we conclude that the proposed nonlinear model can better predict the dwell time at BRT stations.展开更多
This paper will investigate global exponential stability analysis for a class of switched positive nonlinear systems under minimum dwell time switching, whose nonlinear functions for each subsystem are constrained in ...This paper will investigate global exponential stability analysis for a class of switched positive nonlinear systems under minimum dwell time switching, whose nonlinear functions for each subsystem are constrained in a sector field by two odd symmetric piecewise linear functions and whose system matrices for each subsystem are Metzler. A class of multiple time-varying Lyapunov functions is constructed to obtain the computable sufficient conditions on the stability of such switched nonlinear systems within the framework of minimum dwell time switching.All present conditions can be solved by linear/nonlinear programming techniques. An example is provided to demonstrate the effectiveness of the proposed result.展开更多
Importance:Central line-associated bloodstream infection(CLABSI)is one of the most serious complications of central venous access devices.Reducing the risk of CLABSI is of utmost significance in efforts to improve neo...Importance:Central line-associated bloodstream infection(CLABSI)is one of the most serious complications of central venous access devices.Reducing the risk of CLABSI is of utmost significance in efforts to improve neonatal mortality rates and enhance long-term prognosis.Objective:To determine the dwell time and incidence of CLABSI of umbilical venous catheterization(UVC)for preterm infants in China.Methods:Preterm infants with UVC admitted to 44 tertiary neonatal intensive care units in 24 provinces in China were enrolled.Study period was from November 2019 to August 2021.The end point of observations was 48 h after umbilical venous(UV)catheter removal.The primary outcomes were dwell time of UV catheter and UVC-associated CLABSI.Data between infants with UV catheter dwell time≤7 days and>7 days,and with birth weight(BW)≤1000 g and>1000 g were compared.Results:In total,2172 neonates were enrolled(gestational age 30.0±2.4 weeks,BW 1258.5±392.8 g).The median UV catheter dwell time was 7(6–10)days.The incidence of UVC-associated CLABSI was 3.03/1000 UV catheter days.For infants with UV catheter dwell time≤7 days and>7 days,the UVC-associated CLABSI incidence was 3.71 and 2.65 per 1000 UV catheter days,respectively,P=0.23.For infants with UVC dwell times of 3–6,7–12,and 13–15 days,the UVC-associated CLABSI rates were 0.14%,0.68%,and 2.48%(P<0.01).The Kaplan–Meier plot of UV catheter dwell time to CLABSI showed no difference between infants with BW≤1000 g and>1000 g(P=0.60).Interpretation:The median dwell time of UV catheter was 7 days,and the incidence of UVC-associated CLABSI was 3.03/1000 catheter days in China.The daily risk of UVC-associated CLABSI and other complications increased with the dwell time.展开更多
To some extent,the operational quickness of semiconductor devices depends on the transmission time of an electron through semiconductor nanostructures.However,the calculation of transmission time is very difficult,tha...To some extent,the operational quickness of semiconductor devices depends on the transmission time of an electron through semiconductor nanostructures.However,the calculation of transmission time is very difficult,thanks to both the contentious definition of the transmission time in quantum mechanics and the complicated effective potential functions experienced by electrons in semiconductor devices.Here,based on an improved transfer matrix method to numerically solve the Schr?dinger equation and H G Winful’s relationship to calculate the dwell time,we develop a numerical approach to evaluate the transmission time of an electron in semiconductor devices.Compared to the exactly resolvable case of the rectangular potential barrier,the established numerical approach possesses high precision and small error,which may be employed to explore the dynamic response and operating speed of semiconductor devices.This proposed numerical method is successfully applied to the calculation of dwell time for an electron in double rectangular potential barriers and the dependence of transmission time on the number of potential barriers is revealed.展开更多
In this paper, the problems of stability for a class of switched positive descriptor systems(SPDSs)with average dwell time(ADT) switching are investigated. First, based on the equivalent switched system and the proper...In this paper, the problems of stability for a class of switched positive descriptor systems(SPDSs)with average dwell time(ADT) switching are investigated. First, based on the equivalent switched system and the properties of the projector matrix, sufficient stabilities are given for the underlying systems in both continuoustime and discrete-time contexts. Then, a sufficient stability condition for the SPDS with both stable and unstable subsystems is obtained. The stability results for the SPDSs are represented in terms of a set of linear programmings(LPs) by the multiple linear co-positive Lyapunov function(MLCLF) approach. Finally, three numerical examples are given to illustrate the effectiveness of the obtained theoretical results.展开更多
This article presents a general evaluation of handoff dwell time distribution based on geometric analysis methods. Considering the geometric characteristic of the deployed sector pattern, and the distribution of the u...This article presents a general evaluation of handoff dwell time distribution based on geometric analysis methods. Considering the geometric characteristic of the deployed sector pattern, and the distribution of the users' position and the moving direction in the given sector, the general formulas of the probability density function of sector handoff dwell time are derived. Some numerical results are also presented for illustration.展开更多
The problem of stabilizing switched linear systems under asynchronous switching is addressed.The admissible edge-dependent average dwell time method is applied to design a switching signal that comprises slow admissib...The problem of stabilizing switched linear systems under asynchronous switching is addressed.The admissible edge-dependent average dwell time method is applied to design a switching signal that comprises slow admissible edge-dependent average dwell time and fast admissible edge-dependent average dwell time.Under this switching signal,the restriction that the maximum delay of asynchronous switching is known in advance is removed.The constructed Lyapunov function is associated with both the system mode and controller mode.The stabilization criteria and the corresponding algorithm are presented to obtain the controller gains and to design the switching signal.Finally,two examples are given to demonstrate the effectiveness of the proposed results.展开更多
The influences of strain amplitude ranges and dwell time at peak strains on the low cycle fatigue (LCF) properties at 600℃ of a new near α high temperature titanium alloy containing rare earth Nd are investigated. ...The influences of strain amplitude ranges and dwell time at peak strains on the low cycle fatigue (LCF) properties at 600℃ of a new near α high temperature titanium alloy containing rare earth Nd are investigated. The creep fatigue interaction behavior is discussed in this paper in terms of a creep fatigue interaction cumulative law and fatigue crack propagation model. The results show that the creep fatigue interaction is largely dependent on the strain amplitude range, and the tensile dwell periods, as well as compressive dwell periods, have a great influence on the LCF life of this alloy.展开更多
Two algorithms for dwell time adjustment are evaluated under the same polishing conditions that involve tool and work distributions.Both methods are based on Preston’s hypothesis.The first method is a convolution alg...Two algorithms for dwell time adjustment are evaluated under the same polishing conditions that involve tool and work distributions.Both methods are based on Preston’s hypothesis.The first method is a convolution algorithm based on the Fast Fourier Transform.The second is an iterative method based on a constraint problem,extended from a one-dimensional formulation to address a two-dimensional problem.Both methods are investigated for their computational cost,accuracy,and polishing shapes.The convolution method has high accuracy and high speed.The constraint problem on the other hand is slow even when it requires larger memory and thus is more costly.However,unlike the other case a negative region in the polishing shape is not predicted here.Furthermore,new techniques are devised by combining the two methods.展开更多
Regulatory molecules present on the core promoter of a gene interact often in a dynamic,highly combinatorial and possibly energy-dependent manner, leading to complex promoter structure and even complex global dynamics...Regulatory molecules present on the core promoter of a gene interact often in a dynamic,highly combinatorial and possibly energy-dependent manner, leading to complex promoter structure and even complex global dynamics. The authors analyze dynamics of an arbitrarily complex promoter from the view of thermodynamics combined with statistic physics. First, the authors formulize transcription factors-mediated promoter kinetics in terms of energy. Then, the authors analyze energetic cost in several representative cases of promoter structure, deriving useful analytical results. Third, the authors derive analytical expressions for mean dwell times of the promoter activity states, experimentally measurable quantities related to the energy cost of promoter dynamics. The overall framework lays a theoretical foundation for analysis of complex promoter kinetics and gene expression dynamics.展开更多
Introduction: Because establishing venous access in patients can be difficult and time consuming, the use of ultrasound to guide the insertion of peripheral intravenous catheters has become more common. Anecdotal evid...Introduction: Because establishing venous access in patients can be difficult and time consuming, the use of ultrasound to guide the insertion of peripheral intravenous catheters has become more common. Anecdotal evidence indicates ultrasound-guided catheter insertion may result in decreased catheter survival in the vein (dwell-time), but there is little evidence to support this observation. The purpose of this study was to compare dwell-times for peripheral intravenous catheters placed with ultrasound guidance with intravenous catheters placed by means of traditional anatomic insertion in patients in an acute care hospital. Methods: This secondary data analysis examined outcomes of 298 patients who received ultrasound-guided catheter insertion and 299 patients who received traditionally placed intravenous catheters. Multivariable linear regression was used to identify significant predictors of dwell-time for both the traditional and US-guided catheters. Results: The average dwell-times for ultrasound-guided and traditionally placed catheters were significantly different (p 2 = 0.22). Discussion: Dwell-times of catheters placed with ultrasound guidance are shorter than traditionally placed catheters. Ultrasound-guided catheters should be monitored closely for inadvertent removal or infiltration. A plan to place a more permanent type of intravenous access should be considered for patients admitted for patients longer than 24 hours.展开更多
基金the support from Projects of Major Innovation Platforms for Scientific and Technological and Local Transformation of Scientific and Technological Achievements of Xi’an (No.20GXSF0003)the Higher Education Institution Discipline Innovation and Intelligence Base of Shaanxi Provincial (No.S2021-ZC-GXYZ0011)National Natural Science Foundation of China (Grants No.51801154)。
文摘Strength-ductility trade-off is a common issue in Mg alloys. This work proposed that a synergistic enhancement of strength and ductility could be achieved through tuning interlayer dwell time(IDT) in the wire and arc additive manufacturing(WAAM) process of Mg alloy.The thermal couples were used to monitor the thermal history during the WAAM process. Additionally, the effect of different IDTs on the microstructure characteristics and resultant mechanical properties of WAAM-processed Mg alloy thin-wall were investigated. The results showed that the stable temperature of the thin-wall component could reach 290 ℃ at IDT=0s, indicating that the thermal accumulation effect was remarkable. Consequently, unimodal coarse grains with an average size of 39.6 μm were generated, and the resultant room-temperature tensile property was poor. With the IDT extended to 60s, the thermal input and thermal dissipation reached a balance, and the stable temperature was only 170 ℃, closing to the initial temperature of the substrate. A refined grain structure with bimodal size distribution was obtained. The remelting zone had fine grains with the size of 15.2 μm, while the arc zone owned coarse grains with the size of 24.5 μm.The alternatively distributed coarse and fine grains lead to the elimination of strength-ductility trade-off. The ultimate tensile strength and elongation of the samples at IDT=60s are increased by 20.6 and 75.0% of those samples at IDT=0s, respectively. The findings will facilitate the development of additive manufacturing processes for advanced Mg alloys.
基金This work was supported by the National Natural Science Foundation of China(No.71871188).
文摘Train timetables and operations are defined by the train running time in sections,dwell time at stations,and headways between trains.Accurate estimation of these factors is essential to decision-making for train delay reduction,train dispatching,and station capacity estimation.In the present study,we aim to propose a train dwell time model based on an averaging mechanism and dynamic updating to address the challenges in the train dwell time prediction problem(e.g.,dynamics over time,heavy-tailed distribution of data,and spatiotemporal relationships of factors)for real-time train dispatching.The averaging mechanism in the present study is based on multiple state-of-the-art base predictors,enabling the proposed model to integrate the advantages of the base predictors in addressing the challenges in terms of data attributes and data distributions.Then,considering the influence of passenger flow on train dwell time,we use a dynamic updating method based on exponential smoothing to improve the performance of the proposed method by considering the real-time passenger amount fluctuations(e.g.,passenger soars in peak hours or passenger plunges during regular periods).We conduct experiments with the train operation data and passenger flow data from the Chinese high-speed railway line.The results show that due to the advantages over the base predictors,the averaging mechanism can more accurately predict the dwell time at stations than its counterparts for different prediction horizons regarding predictive errors and variances.Further,the experimental results show that dynamic smoothing can significantly improve the accuracy of the proposed model during passenger amount changes,i.e.,15.4%and 15.5%corresponding to the mean absolute error and root mean square error,respectively.Based on the proposed predictor,a feature importance analysis shows that the planned dwell time and arrival delay are the two most important factors to dwell time.However,planned time has positive influences,whereas arrival delay has negative influences.
基金This work was supported by the National Natural Science Foundation of China(No.60343001, 60221301) and the Foundation of Harbin EngineeringUniversity.
文摘In this paper, we consider the relation between the switching dwell time and the stabilization of switched linear control systems. First of all, a concept of critical dwell time is given for switched linear systems without control inputs, and the critical dwell time is taken as an arbitrary given positive constant for a switched linear control systems with controllable switching models. Secondly, when a switched linear system has many stabilizable switching models, the problem of stabilization of the overall system is considered. An on-line feedback control is designed such that the overall system is asymptotically stabilizable under switching laws which depend only on those of uncontrollable subsystems of the switching models. Finally, when a switched system is partially controllable (While some switching models are probably unstabilizable), an on-line feedback control and a cyclic switching strategy are designed such that the overall system is asymptotically stabilizable if all switching models of this uncontrollable subsystems are asymptotically stable. In addition, algorithms for designing switching laws and controls are presented.
基金the National Natural Science Foundation of China(Grant No.11864009).
文摘The dwell time and spin polarization(SP)of electrons tunneling through a parallel doubleδ-magnetic-barrier nanostructure in the presence of a bias voltage is studied theoretically in this work.This nanostructure can be constructed by patterning two asymmetric ferromagnetic stripes on the top and bottom of InAs/AlxIn1-xAs heterostructure,respectively.An evident SP effect remains after a bias voltage is applied to the nanostructure.Moreover,both magnitude and sign of spin-polarized dwell time can be manipulated by properly changing the bias voltage,which may result in an electrically-tunable temporal spin splitter for spintronics device applications.
基金supported by the National Scienceand Technology Support Program of China (No.2009BAG17B01)
文摘Bus rapid transit (BRT) systems have been shown to have many advantages including affordability, high capacity vehicles, and reliable service. Due to these attractive advantages, many cities throughout the world are in the process of planning the construction of BRT systems. To improve the performance of BRT systems, many researchers study BRT operation and control, which include the study of dwell times at bus/BRT stations. To ensure the effectiveness of real-time control which aims to avoid bus/BRT vehicles congestion, accurate dwell time models are needed. We develop our models using data from a BRT vehicle survey conducted in Changzhou, China, where BRT lines are built along passenger corridors, and BRT stations are enclosed like light rails. This means that interactions between passengers traveling on the BRT system are more frequent than those in traditional transit system who use platform stations. We statistically analyze the BRT vehicle survey data, and based on this analysis, we are able to make the following conclusions: ( I ) The delay time per passenger at a BRT station is less than that at a non-BRT station, which implies that BRT stations are efficient in the sense that they are able to move passengers quickly. (II) The dwell time follows a logarithmic normal distribution with a mean of 2.56 and a variance of 0.53. (III) The greater the number of BRT lines serviced by a station, the longer the dwell time is. (IV) Daily travel demands are highest during the morning peak interval where the dwell time, the number of passengers boarding and alighting and the number of passengers on vehicles reach their maximum values. (V) The dwell time is highly positively correlated with the total number of passengers boarding and alighting. (VI) The delay per passenger is negatively correlated with the total number of passengers boarding and alighting. We propose two dwell time models for the BRT station. The first proposed model is a linear model while the second is nonlinear. We introduce the conflict between passengers boarding and alighting into our models. Finally, by comparing our models with the models of Rajbhandari and Chien et al., and TCQSM (Transit Capacity and Quality of Service Manual), we conclude that the proposed nonlinear model can better predict the dwell time at BRT stations.
基金supported by the National Natural Science Foundation of China(61673198)the Provincial Natural Science Foundation of Liaoning Province(20180550473)
文摘This paper will investigate global exponential stability analysis for a class of switched positive nonlinear systems under minimum dwell time switching, whose nonlinear functions for each subsystem are constrained in a sector field by two odd symmetric piecewise linear functions and whose system matrices for each subsystem are Metzler. A class of multiple time-varying Lyapunov functions is constructed to obtain the computable sufficient conditions on the stability of such switched nonlinear systems within the framework of minimum dwell time switching.All present conditions can be solved by linear/nonlinear programming techniques. An example is provided to demonstrate the effectiveness of the proposed result.
基金Capital’s Funds for Health Improvement and Research,Grant/Award Number:2022-2-2095。
文摘Importance:Central line-associated bloodstream infection(CLABSI)is one of the most serious complications of central venous access devices.Reducing the risk of CLABSI is of utmost significance in efforts to improve neonatal mortality rates and enhance long-term prognosis.Objective:To determine the dwell time and incidence of CLABSI of umbilical venous catheterization(UVC)for preterm infants in China.Methods:Preterm infants with UVC admitted to 44 tertiary neonatal intensive care units in 24 provinces in China were enrolled.Study period was from November 2019 to August 2021.The end point of observations was 48 h after umbilical venous(UV)catheter removal.The primary outcomes were dwell time of UV catheter and UVC-associated CLABSI.Data between infants with UV catheter dwell time≤7 days and>7 days,and with birth weight(BW)≤1000 g and>1000 g were compared.Results:In total,2172 neonates were enrolled(gestational age 30.0±2.4 weeks,BW 1258.5±392.8 g).The median UV catheter dwell time was 7(6–10)days.The incidence of UVC-associated CLABSI was 3.03/1000 UV catheter days.For infants with UV catheter dwell time≤7 days and>7 days,the UVC-associated CLABSI incidence was 3.71 and 2.65 per 1000 UV catheter days,respectively,P=0.23.For infants with UVC dwell times of 3–6,7–12,and 13–15 days,the UVC-associated CLABSI rates were 0.14%,0.68%,and 2.48%(P<0.01).The Kaplan–Meier plot of UV catheter dwell time to CLABSI showed no difference between infants with BW≤1000 g and>1000 g(P=0.60).Interpretation:The median dwell time of UV catheter was 7 days,and the incidence of UVC-associated CLABSI was 3.03/1000 catheter days in China.The daily risk of UVC-associated CLABSI and other complications increased with the dwell time.
基金supported jointly by the National Natural Science Foundation of China(11864009 and 62164005)the Guangxi Natural Science Foundation of China(2021JJB110053)
文摘To some extent,the operational quickness of semiconductor devices depends on the transmission time of an electron through semiconductor nanostructures.However,the calculation of transmission time is very difficult,thanks to both the contentious definition of the transmission time in quantum mechanics and the complicated effective potential functions experienced by electrons in semiconductor devices.Here,based on an improved transfer matrix method to numerically solve the Schr?dinger equation and H G Winful’s relationship to calculate the dwell time,we develop a numerical approach to evaluate the transmission time of an electron in semiconductor devices.Compared to the exactly resolvable case of the rectangular potential barrier,the established numerical approach possesses high precision and small error,which may be employed to explore the dynamic response and operating speed of semiconductor devices.This proposed numerical method is successfully applied to the calculation of dwell time for an electron in double rectangular potential barriers and the dependence of transmission time on the number of potential barriers is revealed.
基金the National Natural Science Foundation of China(Nos.61374070 and 61374154)the Fundamental Research Funds for the Central Universities of China(Nos.DUT14QY14 and DUT14QY31)
文摘In this paper, the problems of stability for a class of switched positive descriptor systems(SPDSs)with average dwell time(ADT) switching are investigated. First, based on the equivalent switched system and the properties of the projector matrix, sufficient stabilities are given for the underlying systems in both continuoustime and discrete-time contexts. Then, a sufficient stability condition for the SPDS with both stable and unstable subsystems is obtained. The stability results for the SPDSs are represented in terms of a set of linear programmings(LPs) by the multiple linear co-positive Lyapunov function(MLCLF) approach. Finally, three numerical examples are given to illustrate the effectiveness of the obtained theoretical results.
文摘This article presents a general evaluation of handoff dwell time distribution based on geometric analysis methods. Considering the geometric characteristic of the deployed sector pattern, and the distribution of the users' position and the moving direction in the given sector, the general formulas of the probability density function of sector handoff dwell time are derived. Some numerical results are also presented for illustration.
基金Project supported by the National Natural Science Foundation of China(Nos.61873331,61773236,and 61773235)the Natural Science Foundation of Shandong Province,China(No.ZR2020YQ48)。
文摘The problem of stabilizing switched linear systems under asynchronous switching is addressed.The admissible edge-dependent average dwell time method is applied to design a switching signal that comprises slow admissible edge-dependent average dwell time and fast admissible edge-dependent average dwell time.Under this switching signal,the restriction that the maximum delay of asynchronous switching is known in advance is removed.The constructed Lyapunov function is associated with both the system mode and controller mode.The stabilization criteria and the corresponding algorithm are presented to obtain the controller gains and to design the switching signal.Finally,two examples are given to demonstrate the effectiveness of the proposed results.
文摘The influences of strain amplitude ranges and dwell time at peak strains on the low cycle fatigue (LCF) properties at 600℃ of a new near α high temperature titanium alloy containing rare earth Nd are investigated. The creep fatigue interaction behavior is discussed in this paper in terms of a creep fatigue interaction cumulative law and fatigue crack propagation model. The results show that the creep fatigue interaction is largely dependent on the strain amplitude range, and the tensile dwell periods, as well as compressive dwell periods, have a great influence on the LCF life of this alloy.
文摘Two algorithms for dwell time adjustment are evaluated under the same polishing conditions that involve tool and work distributions.Both methods are based on Preston’s hypothesis.The first method is a convolution algorithm based on the Fast Fourier Transform.The second is an iterative method based on a constraint problem,extended from a one-dimensional formulation to address a two-dimensional problem.Both methods are investigated for their computational cost,accuracy,and polishing shapes.The convolution method has high accuracy and high speed.The constraint problem on the other hand is slow even when it requires larger memory and thus is more costly.However,unlike the other case a negative region in the polishing shape is not predicted here.Furthermore,new techniques are devised by combining the two methods.
基金supported by Science and Technology Department under Grant No.2014CB964703the Natural Science Foundation under Grant Nos.91530320 and 11761025
文摘Regulatory molecules present on the core promoter of a gene interact often in a dynamic,highly combinatorial and possibly energy-dependent manner, leading to complex promoter structure and even complex global dynamics. The authors analyze dynamics of an arbitrarily complex promoter from the view of thermodynamics combined with statistic physics. First, the authors formulize transcription factors-mediated promoter kinetics in terms of energy. Then, the authors analyze energetic cost in several representative cases of promoter structure, deriving useful analytical results. Third, the authors derive analytical expressions for mean dwell times of the promoter activity states, experimentally measurable quantities related to the energy cost of promoter dynamics. The overall framework lays a theoretical foundation for analysis of complex promoter kinetics and gene expression dynamics.
基金supported by the National Natural Science Foundation of China under Grant Nos.61473189 and 61621003the National Key Basic Research Program of China(973 program)under Grant No.2014CB845302
文摘Introduction: Because establishing venous access in patients can be difficult and time consuming, the use of ultrasound to guide the insertion of peripheral intravenous catheters has become more common. Anecdotal evidence indicates ultrasound-guided catheter insertion may result in decreased catheter survival in the vein (dwell-time), but there is little evidence to support this observation. The purpose of this study was to compare dwell-times for peripheral intravenous catheters placed with ultrasound guidance with intravenous catheters placed by means of traditional anatomic insertion in patients in an acute care hospital. Methods: This secondary data analysis examined outcomes of 298 patients who received ultrasound-guided catheter insertion and 299 patients who received traditionally placed intravenous catheters. Multivariable linear regression was used to identify significant predictors of dwell-time for both the traditional and US-guided catheters. Results: The average dwell-times for ultrasound-guided and traditionally placed catheters were significantly different (p 2 = 0.22). Discussion: Dwell-times of catheters placed with ultrasound guidance are shorter than traditionally placed catheters. Ultrasound-guided catheters should be monitored closely for inadvertent removal or infiltration. A plan to place a more permanent type of intravenous access should be considered for patients admitted for patients longer than 24 hours.