Speed limit measures are ubiquitous due to the complexity of the road environment,which can be supplied with the help of vehicle to everything(V2X)communication technology.Therefore,the influence of speed limit on tra...Speed limit measures are ubiquitous due to the complexity of the road environment,which can be supplied with the help of vehicle to everything(V2X)communication technology.Therefore,the influence of speed limit on traffic system will be investigated to construct a two-lane lattice model accounting for the speed limit effect during the lane change process under V2X environment.Accordingly,the stability condition and the mKdV equation are closely associated with the speed limit effect through theory analysis.Moreover,the evolution of density and hysteresis loop is simulated to demonstrate the positive role of the speed limit effect on traffic stability in the cases of strong reaction intensity and high limited speed.展开更多
We theoretically study the quantum speed limit of a single atom trapped in a Fabry-Perot microresonator.The cavity mode will be squeezed when a driving laser is applied to the second-order nonlinear medium,and the eff...We theoretically study the quantum speed limit of a single atom trapped in a Fabry-Perot microresonator.The cavity mode will be squeezed when a driving laser is applied to the second-order nonlinear medium,and the effective Hamiltonian can be obtained under the Bogoliubov squeezing transformation.The analytical expression of the evolved atom state can be obtained by using the non-Hermitian Schr¨odinger equation for the initial excited state,and the quantum speed limit time coincides very well for both the analytical expression and the master equation method.From the perspective of quantum speed limit,it is more conducive to accelerate the evolution of the quantum state for the large detuning,strong driving,and coupling strength.For the case of the initial superposition state,the form of the initial state has more influence on the evolution speed.The quantum speed limit time is not only dependent on the system parameters but also determined by the initial state.展开更多
Predictive control is an advanced control algorithm,which is widely used in industrial process control.Among them,model predictive control(MPC)is an important branch of predictive control.Its basic principle is to use...Predictive control is an advanced control algorithm,which is widely used in industrial process control.Among them,model predictive control(MPC)is an important branch of predictive control.Its basic principle is to use the system model to predict future behavior and determine the current control action by optimizing the objective function.This paper discusses the application of MPC in the prediction and control of the speed of vehicles to optimize traffic flow.It is a valuable reference for alleviating traffic congestion and improving travel efficiency and smoothness and provides scientific basis and technical support for future highway traffic management.展开更多
Traffic intersections are incredibly dangerous for drivers and pedestrians. Statistics from both Canada and the U.S. show a high number of fatalities and serious injuries related to crashes at intersections. In Canada...Traffic intersections are incredibly dangerous for drivers and pedestrians. Statistics from both Canada and the U.S. show a high number of fatalities and serious injuries related to crashes at intersections. In Canada, during 2019, the National Collision Database shows that 28% of traffic fatalities and 42% of serious injuries occurred at intersections. Likewise, the U.S. National Highway Traffic Administration (NHTSA) found that about 40% of the estimated 5,811,000 accidents in the U.S. during the year studied were intersection-related crashes. In fact, a major survey by the car insurance industry found that nearly 85% of drivers could not identify the correct action to take when approaching a yellow traffic light at an intersection. One major reason for these accidents is the “yellow light dilemma,” the ambiguous situation where a driver should stop or proceed forward when unexpectedly faced with a yellow light. This situation is even further exacerbated by the tendency of aggressive drivers to inappropriately speed up on the yellow just to get through the traffic light. A survey of Canadian drivers conducted by the Traffic Injury Research Foundation found that 9% of drivers admitted to speeding up to get through a traffic light. Another reason for these accidents is the increased danger of making a left-hand turn on yellow. According to the National Highway Traffic Safety Association (NHTSA), left turns occur in approximately 22.2% of collisions—as opposed to just 1.2% for right turns. Moreover, a study by CNN found left turns are three times as likely to kill pedestrians than right turns. The reason left turns are so much more likely to cause an accident is because they take a driver against traffic and in the path of oncoming cars. Additionally, most of these left turns occur at the driver’s discretion—as opposed to the distressingly brief left-hand arrow at busy intersections. Drive Safe Now proposes a workable solution for reducing the number of accidents occurring during a yellow light at intersections. We believe this fairly simple solution will save lives, prevent injuries, reduce damage to public and private property, and decrease insurance costs.展开更多
The maximum delivery pressure and the maximum rotational speed determine the power density of axial piston pumps.However,increasing the speed beyond the limit always accompanies cavitation,leading to the decrease of t...The maximum delivery pressure and the maximum rotational speed determine the power density of axial piston pumps.However,increasing the speed beyond the limit always accompanies cavitation,leading to the decrease of the volumetric efficiency.The pressure loss in the suction duct is considered a significant reason for the cavitation.Therefore,this paper proposes a methodology to optimize the shape of the suction duct aiming at reducing the intensity of cavitation and increasing the speed limit.At first,a computational fluid dynamics(CFD)model based on the full cavitation model(FCM)is developed to simulate the fluid field of the axial piston pump and a test rig is set to validate the model.Then the topology optimization is conducted for obtaining the minimum pressure loss in the suc-tion duct.Comparing the original suction duct with the optimized one in the simulation model,the pressure loss in the suction duct gets considerable reduction,which eases the cavitation intensity a lot.The simulation results prove that the speed limit can increase under several different inlet pressures.展开更多
Quantum speed limit time and entanglement in a system composed of coupled quantum dots are investigated.The excess electron spin in each quantum dot constitutes the physical system(qubit).Also the spin interaction is ...Quantum speed limit time and entanglement in a system composed of coupled quantum dots are investigated.The excess electron spin in each quantum dot constitutes the physical system(qubit).Also the spin interaction is modeled through the Heisenberg model and the spins are imposed by an external magnetic field.Taking into account the spin relaxation as a non-Markovian process,the quantum speed limit and entanglement evolution are discussed.Our findings reveal that increasing the magnetic field leads to the faster quantum evolution.In addition,the temperature increment causes the longer quantum speed limit time as well as the entanglement degradation.展开更多
The quantum speed limit time for quantum system under squeezed environment is studied.We consider two typical models,the damped Jaynes-Cummings model and the dephasing model.For the damped Jaynes-Cummings model under ...The quantum speed limit time for quantum system under squeezed environment is studied.We consider two typical models,the damped Jaynes-Cummings model and the dephasing model.For the damped Jaynes-Cummings model under squeezed environment,we find that the quantum speed limit time becomes larger with the squeezed parameter r increasing and indicates symmetry about the phase parameter valueθ=π.Meanwhile,the quantum speed limit time can also be influenced by the coupling strength between the system and environment.However,the quantum speed limit time for the dephasing model is determined by the dephasing rate and the boundary of acceleration region that interacting with vacuum reservoir can be broken when the squeezed environment parameters are appropriately chosen.展开更多
The speed of evolution of a qubit undergoing a nonequilibrium environment with spectral density of general ohmic form is investigated. First we reveal non-Markovianity of the model, and find that the non-Markovianity ...The speed of evolution of a qubit undergoing a nonequilibrium environment with spectral density of general ohmic form is investigated. First we reveal non-Markovianity of the model, and find that the non-Markovianity quantified by information backflow of Breuer et al. [Phys. Rev. Lett. 103 210401(2009)] displays a nonmonotonic behavior for different values of the ohmicity parameter s in fixed other parameters and the maximal non-Markovianity can be achieved at a specified value s. We also find that the non-Markovianity displays a nonmonotonic behavior with the change of a phase control parameter. Then we further discuss the relationship between quantum speed limit(QSL) time and non-Markovianity of the open-qubit system for any initial states including pure and mixed states. By investigation, we find that the QSL time of a qubit with any initial states can be expressed by a simple factorization law: the QSL time of a qubit with any qubitinitial states are equal to the product of the coherence of the initial state and the QSL time of maximally coherent states,where the QSL time of the maximally coherent states are jointly determined by the non-Markovianity, decoherence factor and a given driving time. Moreover, we also find that the speed of quantum evolution can be obviously accelerated in the wide range of the ohmicity parameter, i.e., from sub-Ohmic to Ohmic and super-Ohmic cases, which is different from the thermal equilibrium environment case.展开更多
A potential acceleration of a quantum open system is of fundamental interest in quantum computation, quantum communication, and quantum metrology. In this paper, we investigate the "quantum speed-up capacity" which ...A potential acceleration of a quantum open system is of fundamental interest in quantum computation, quantum communication, and quantum metrology. In this paper, we investigate the "quantum speed-up capacity" which reveals the potential ability of a quantum system to be accelerated. We explore the evolutions of the speed-up capacity in different quantum channels for two-qubit states. We find that although the dynamics of the capacity is varying in different kinds of channels, it is positive in most situations which are considered in the context except one case in the amplitude-damping channel. We give the reasons for the different features of the dynamics. Anyway, the speed-up capacity can be improved by the memory effect. We find two ways which may be used to control the capacity in an experiment: selecting an appropriate coefficient of an initial state or changing the memory degree of environments.展开更多
The classical version of Mandelstam-Tamm speed limit based on theWigner function in phase space was reported by Shanahan et al.[Phys.Rev.Lett.120070401(2018)].We present the Margolus-Levitin speed limit across the qua...The classical version of Mandelstam-Tamm speed limit based on theWigner function in phase space was reported by Shanahan et al.[Phys.Rev.Lett.120070401(2018)].We present the Margolus-Levitin speed limit across the quantumto-classical transition in phase space based on the trace distance.The Margolus-Levitin speed limit is set by the Schatten L1 norm of the generator of time-dependent evolution for both the quantum and classical domains.As an example,the time-dependent harmonic oscillator is considered to illustrate the result.展开更多
For a two-level atom in a lossy cavity, a scheme to manipulate the non-Markovian speedup dynamics has been pro- posed in the controllable environment (the lossy cavity field). We mainly focus on the effects of the q...For a two-level atom in a lossy cavity, a scheme to manipulate the non-Markovian speedup dynamics has been pro- posed in the controllable environment (the lossy cavity field). We mainly focus on the effects of the qubit--cavity detuning A and the qubit-cavity coupling strength k on the non-Markovian speedup evolution of an open system. By controlling the environment, i.e., tuning zl and , two dynamical crossovers from Markovian to non-Markovian and from no-speedup to speedup are achieved. Furthermore, it is clearly found that increasing the coupling strength k or detuning A in some cases can make the environmental non-Markovianity stronger and hence can lead to faster evolution of the open system.展开更多
Quantum speed limit and entanglement of a two-spin Heisenberg XYZ system in an inhomogeneous external magnetic field are investigated.The physical system studied is the excess electron spin in two adjacent quantum dot...Quantum speed limit and entanglement of a two-spin Heisenberg XYZ system in an inhomogeneous external magnetic field are investigated.The physical system studied is the excess electron spin in two adjacent quantum dots.The influences of magnetic field inhomogeneity as well as spin-orbit coupling are studied.Moreover,the spin interaction with surrounding magnetic environment is investigated as a non-Markovian process.The spin-orbit interaction provides two important features:the formation of entanglement when two qubits are initially in a separated state and the degradation and rebirth of the entanglement.展开更多
The quantum speed limit(QSL)of the double quantum dot(DQD)system has been theoretically investigated by adopting the detection of the quantum point contact(QPC)in the pure dephasing environment.The Mandelstam–Tamm(MT...The quantum speed limit(QSL)of the double quantum dot(DQD)system has been theoretically investigated by adopting the detection of the quantum point contact(QPC)in the pure dephasing environment.The Mandelstam–Tamm(MT)type of the QSL bound which is based on the trace distance has been extended to the DQD system for calculating the shortest evolving time.The increase of decoherence rate can weaken the capacity for potential speedup(CPS)and delay the evolving process due to the frequently measurement localizing the electron in the DQD system.The system needs longer time to evolve to the target state as the enhancement of dephasing rate,because the strong interaction between pure dephasing environment and the DQD system could vary the oscillation of the electron.Increasing the dephasing rate can sharp the QSL bound,but the decoherence rate would weaken the former effect and vice versa.Moreover,the CPS would be raised by increasing the energy displacement,while the enhancement of the coupling strength between two quantum dots can diminish it.It is interesting that there has an inflection point,when the coupling strength is less than the value of the point,the increasing effect of the CPS from the energy displacement is dominant,otherwise the decreasing tendency of the CPS is determined by the coupling strength and suppress the action of the energy displacement if the coupling strength is greater than the point.Our results provide theoretical reference for studying the QSL time in a semiconductor device affected by numerous factors.展开更多
The lower bounds of the evolution time between two distinguishable states of a system, defined as quantum speed limit time, can characterize the maximal speed of quantum computers and communication channels. We study ...The lower bounds of the evolution time between two distinguishable states of a system, defined as quantum speed limit time, can characterize the maximal speed of quantum computers and communication channels. We study the quantum speed limit time between the composite quantum states and their target states in the presence of nondissipative decoherence.For the initial states with maximally mixed marginals, we obtain the exact expressions of the quantum speed limit time which mainly depend on the parameters of the initial states and the decoherence channels. Furthermore, by calculating the quantum speed limit time for the time-dependent states started from a class of initial states, we discover that the quantum speed limit time gradually decreases in time, and the decay rate of the quantum speed limit time would show a sudden change at a certain critical time. Interestingly, at the same critical time, the composite system dynamics would exhibit a sudden transition from classical decoherence to quantum decoherence.展开更多
We investigate the quantum speed limit time (QSLT) of a two-level atom under quantum-jump-based feedback control or homodyne-based feedback control. Our results show that the two different feedback control schemes h...We investigate the quantum speed limit time (QSLT) of a two-level atom under quantum-jump-based feedback control or homodyne-based feedback control. Our results show that the two different feedback control schemes have different influences on the evolutionary speed. By adjusting the feedback parameters, the quantum-jump-based feedback control can induce speedup of the atomic evolution from an excited state, but the homodyne-based feedback control cannot change the evolutionary speed. Additionally, the QSLT for the whole dynamical process is explored. Under the quantum-jump-based feedback control, the QSLT displays oscillatory behaviors, which implies multiple speed-up and speed-down processes during the evolution. While, the homodyne-based feedback control can accelerate the speed-up process and improve the uniform speed in the uniform evolution process.展开更多
As is well known,the quantum evolution speed of quantum state can never be accelerated in the Markovian regime without any operators on the system.The Hamiltonian corrections induced by the action of coherent driving ...As is well known,the quantum evolution speed of quantum state can never be accelerated in the Markovian regime without any operators on the system.The Hamiltonian corrections induced by the action of coherent driving forces are often used to fight dissipative and decoherence mechanisms in experiments.For this reason,considering three noisy channels(the phase-flip channel,the amplitude damping channel and the depolarizing channel),we propose a scheme of speedup evolution of an open system by controlling an external unitary coherent driving operator on the system.It is shown that,in the presence of the coherent driving,no-speedup evolution can be transformed into quantum speedup evolution in the Markovian dynamics process.Additionally,under the fixed coherent driving strength in the above three noisy channels,the best way to achieve the most degree of quantum speedup for the system has been acquired by rotating the system with appropriate driving direction angles,respectively.Finally,we conclude that the reason for this acceleration is not the nonMarkovian dynamical behavior of the system but due to the oscillation of geometric distance between the initial state and the target final state.展开更多
Since the evolution of a mixed state in a unitary system is equivalent to the joint evolution of the eigenvectors contained in it,we could use the tool of instantaneous angular velocity for pure states to study the qu...Since the evolution of a mixed state in a unitary system is equivalent to the joint evolution of the eigenvectors contained in it,we could use the tool of instantaneous angular velocity for pure states to study the quantum speed limit(QSL)of a mixed state.We derive a lower bound for the evolution time of a mixed state to a target state in a unitary system,which automatically reduces to the quantum speed limit induced by the Fubini–Study metric for pure states.The computation of the QSL of a degenerate mixed state is more complicated than that of a non-degenerate mixed state,where we have to make a singular value decomposition(SVD)on the inner product between the two eigenvector matrices of the initial and target states.By combing these results,a lower bound for the evolution time of a general mixed state is presented.In order to compare the tightness among the lower bound proposed here and lower bounds reported in the references,two examples in a single-qubit system and in a single-qutrit system are studied analytically and numerically,respectively.All conclusions derived in this work are independent of the eigenvalues of the mixed state,which is in accord with the evolution properties of a quantum unitary system.展开更多
Annually, there are over 120,000 crashes in work zones in the United States. High speeds in construction zones are a well-documented risk factor that increases <span style="font-family:Verdana;"><sp...Annually, there are over 120,000 crashes in work zones in the United States. High speeds in construction zones are a well-documented risk factor that increases <span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">the </span></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">frequency and severity of crashes. This study used connected vehicle data to evaluate the spatial and temporal impact that regulatory signs, speed feedback displays, and construction site geometry had on vehicle speed. Over 27,000 unique trips over 2 weeks on a 15-mile interstate construction work zone near Lebanon, IN were analyzed. Spatial analysis over a 0.2-mi segment before and after the posted speed limit signs showed that the regulatory signs had no statistical impact on reducing speeds. A before/after analysis was also conducted to study the impact of radar-based speed feedback that displays the motorists</span></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">’</span></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> speed on a sign below a regulatory speed limit sign. Results showed a maximum drop in median speeds of approximately 5 mph. Speeds greater than 15 mph above the speed limit dropped by 10%</span></span></span></span></span><span><span><span><span><span style="font-family:;" "=""> </span></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">-</span></span></span></span></span><span><span><span><span><span style="font-family:;" "=""> </span></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">15%. The reduction in speeds began approximately 1000 feet ahead of the sign and results were found to be statistically significant. </span></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">The </span></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">analysis also revealed that larger speed drops inside the work zone were due to geometric constraints that required additional driver workloads, especially during shoulder width changes and lane shifts. The results from this study will be helpful for agencies to understand driver behavior in the work zones and to identify proper speed limit compliance techniques that significantly reduce driver speeds in and around work zones.</span></span></span></span></span>展开更多
Historically, researchers and practitioners have utilized spot speeds and microscopic simulation methodologies to evaluate the operational impact of differential or uniform speed limits for trucks and passenger vehicl...Historically, researchers and practitioners have utilized spot speeds and microscopic simulation methodologies to evaluate the operational impact of differential or uniform speed limits for trucks and passenger vehicles. This paper presents a methodology that uses connected truck data to develop a statistical characterization of both passenger car and truck speeds. These techniques were applied to three adjacent states, Illinois, Indiana and Ohio. Illinois and Ohio have 70 mph speed limits for both trucks and cars. Indiana has a differential speed limit for heavy trucks (65 mph) and passenger cars (70 mph). The statistical distribution of truck speeds was then compared among Illinois, Indiana and Ohio. These speeds were derived from over 8 million connected truck records traveling along Interstate 70 in Illinois, Indiana and Ohio during a one-week period from May 8-14, 2022. Statistical test results over selected 20-mile sections in each state showed that median truck speeds in Indiana with its differential speed limit of 65 mph were only 1 - 2 mph lesser than the neighboring states of Illinois and Ohio who observe a uniform speed limit of 70 mph for all traffic.展开更多
Purpose–In service,the periodic clashes of wheel flat against the rail result in large wheel/rail impact force and high-frequency vibration,leading to severe damage on the wheelset,rail and track structure.This study...Purpose–In service,the periodic clashes of wheel flat against the rail result in large wheel/rail impact force and high-frequency vibration,leading to severe damage on the wheelset,rail and track structure.This study aims to analyze characteristics and dynamic impact law of wheel and rail caused by wheel flat of high-speed trains.Design/methodology/approach–A full-scale high-speed wheel/rail interface test rig was used for the test of the dynamic impact of wheel/rail caused by wheel flat of high-speed train.With wheel flats of different lengths,widths and depths manually set around the rolling circle of the wheel tread,and wheel/rail dynamic impact tests to the flats in the speed range of 0–400 km/h on the rig were conducted.Findings–As the speed goes up,the flat induced the maximum of the wheel/rail dynamic impact force increases rapidly before it reaches its limit at the speed of around 35 km/h.It then goes down gradually as the speed continues to grow.The impact of flat wheel on rail leads to 100–500 Hz middle-frequency vibration,and around 2,000 Hz and 6,000 Hz high-frequency vibration.In case of any wheel flat found during operation,the train speed shall be controlled according to the status of the flat and avoid the running speed of 20 km/h–80 km/h as much as possible.Originality/value–The research can provide a new method to obtain the dynamic impact of wheel/rail caused by wheel flat by a full-scale high-speed wheel/rail interface test rig.The relations among the flat size,the running speed and the dynamic impact are hopefully of reference to the building of speed limits for HSR wheel flat of different degrees.展开更多
基金Project supported by the Guangxi Natural Science Foundation,China(Grant No.2022GXNSFDA035080)the Central Government Guidance Funds for Local Scientific and Technological Development,China(Grant No.Guike ZY22096024)the National Natural Science Foundation,China(Grant No.61963008).
文摘Speed limit measures are ubiquitous due to the complexity of the road environment,which can be supplied with the help of vehicle to everything(V2X)communication technology.Therefore,the influence of speed limit on traffic system will be investigated to construct a two-lane lattice model accounting for the speed limit effect during the lane change process under V2X environment.Accordingly,the stability condition and the mKdV equation are closely associated with the speed limit effect through theory analysis.Moreover,the evolution of density and hysteresis loop is simulated to demonstrate the positive role of the speed limit effect on traffic stability in the cases of strong reaction intensity and high limited speed.
基金Project supported by the National Natural Science Foundation of China(Grant No.12175029)the Fundamental Research Program of Shanxi Province,China(Grant No.20210302123063)。
文摘We theoretically study the quantum speed limit of a single atom trapped in a Fabry-Perot microresonator.The cavity mode will be squeezed when a driving laser is applied to the second-order nonlinear medium,and the effective Hamiltonian can be obtained under the Bogoliubov squeezing transformation.The analytical expression of the evolved atom state can be obtained by using the non-Hermitian Schr¨odinger equation for the initial excited state,and the quantum speed limit time coincides very well for both the analytical expression and the master equation method.From the perspective of quantum speed limit,it is more conducive to accelerate the evolution of the quantum state for the large detuning,strong driving,and coupling strength.For the case of the initial superposition state,the form of the initial state has more influence on the evolution speed.The quantum speed limit time is not only dependent on the system parameters but also determined by the initial state.
文摘Predictive control is an advanced control algorithm,which is widely used in industrial process control.Among them,model predictive control(MPC)is an important branch of predictive control.Its basic principle is to use the system model to predict future behavior and determine the current control action by optimizing the objective function.This paper discusses the application of MPC in the prediction and control of the speed of vehicles to optimize traffic flow.It is a valuable reference for alleviating traffic congestion and improving travel efficiency and smoothness and provides scientific basis and technical support for future highway traffic management.
文摘Traffic intersections are incredibly dangerous for drivers and pedestrians. Statistics from both Canada and the U.S. show a high number of fatalities and serious injuries related to crashes at intersections. In Canada, during 2019, the National Collision Database shows that 28% of traffic fatalities and 42% of serious injuries occurred at intersections. Likewise, the U.S. National Highway Traffic Administration (NHTSA) found that about 40% of the estimated 5,811,000 accidents in the U.S. during the year studied were intersection-related crashes. In fact, a major survey by the car insurance industry found that nearly 85% of drivers could not identify the correct action to take when approaching a yellow traffic light at an intersection. One major reason for these accidents is the “yellow light dilemma,” the ambiguous situation where a driver should stop or proceed forward when unexpectedly faced with a yellow light. This situation is even further exacerbated by the tendency of aggressive drivers to inappropriately speed up on the yellow just to get through the traffic light. A survey of Canadian drivers conducted by the Traffic Injury Research Foundation found that 9% of drivers admitted to speeding up to get through a traffic light. Another reason for these accidents is the increased danger of making a left-hand turn on yellow. According to the National Highway Traffic Safety Association (NHTSA), left turns occur in approximately 22.2% of collisions—as opposed to just 1.2% for right turns. Moreover, a study by CNN found left turns are three times as likely to kill pedestrians than right turns. The reason left turns are so much more likely to cause an accident is because they take a driver against traffic and in the path of oncoming cars. Additionally, most of these left turns occur at the driver’s discretion—as opposed to the distressingly brief left-hand arrow at busy intersections. Drive Safe Now proposes a workable solution for reducing the number of accidents occurring during a yellow light at intersections. We believe this fairly simple solution will save lives, prevent injuries, reduce damage to public and private property, and decrease insurance costs.
基金Supported by National Key R&D Program of China(Grant No.2019YFB2004504).
文摘The maximum delivery pressure and the maximum rotational speed determine the power density of axial piston pumps.However,increasing the speed beyond the limit always accompanies cavitation,leading to the decrease of the volumetric efficiency.The pressure loss in the suction duct is considered a significant reason for the cavitation.Therefore,this paper proposes a methodology to optimize the shape of the suction duct aiming at reducing the intensity of cavitation and increasing the speed limit.At first,a computational fluid dynamics(CFD)model based on the full cavitation model(FCM)is developed to simulate the fluid field of the axial piston pump and a test rig is set to validate the model.Then the topology optimization is conducted for obtaining the minimum pressure loss in the suc-tion duct.Comparing the original suction duct with the optimized one in the simulation model,the pressure loss in the suction duct gets considerable reduction,which eases the cavitation intensity a lot.The simulation results prove that the speed limit can increase under several different inlet pressures.
文摘Quantum speed limit time and entanglement in a system composed of coupled quantum dots are investigated.The excess electron spin in each quantum dot constitutes the physical system(qubit).Also the spin interaction is modeled through the Heisenberg model and the spins are imposed by an external magnetic field.Taking into account the spin relaxation as a non-Markovian process,the quantum speed limit and entanglement evolution are discussed.Our findings reveal that increasing the magnetic field leads to the faster quantum evolution.In addition,the temperature increment causes the longer quantum speed limit time as well as the entanglement degradation.
基金Project supported by the National Natural Science Foundation of China(Grant No.11775040)the Scientific and Technological Innovation Program of the Higher Education Institutions of Shanxi Province,China(Grant No.2019L0527).
文摘The quantum speed limit time for quantum system under squeezed environment is studied.We consider two typical models,the damped Jaynes-Cummings model and the dephasing model.For the damped Jaynes-Cummings model under squeezed environment,we find that the quantum speed limit time becomes larger with the squeezed parameter r increasing and indicates symmetry about the phase parameter valueθ=π.Meanwhile,the quantum speed limit time can also be influenced by the coupling strength between the system and environment.However,the quantum speed limit time for the dephasing model is determined by the dephasing rate and the boundary of acceleration region that interacting with vacuum reservoir can be broken when the squeezed environment parameters are appropriately chosen.
基金supported by the National Natural Science Foundation of China(Grants Nos.61505053 and 61475045)the Natural Science Foundation of Hunan Province,China(Grant No.2015JJ3092)+2 种基金the School Foundation from the Hunan University of Arts and Science(Grant No.14ZD01)the Fund from the Key Laboratory of Photoelectric Information Integration and Optical Manufacturing Technology of Hunan Province,Chinathe Construction Program of the Key Discipline in Hunan University of Arts and Science(Optics)
文摘The speed of evolution of a qubit undergoing a nonequilibrium environment with spectral density of general ohmic form is investigated. First we reveal non-Markovianity of the model, and find that the non-Markovianity quantified by information backflow of Breuer et al. [Phys. Rev. Lett. 103 210401(2009)] displays a nonmonotonic behavior for different values of the ohmicity parameter s in fixed other parameters and the maximal non-Markovianity can be achieved at a specified value s. We also find that the non-Markovianity displays a nonmonotonic behavior with the change of a phase control parameter. Then we further discuss the relationship between quantum speed limit(QSL) time and non-Markovianity of the open-qubit system for any initial states including pure and mixed states. By investigation, we find that the QSL time of a qubit with any initial states can be expressed by a simple factorization law: the QSL time of a qubit with any qubitinitial states are equal to the product of the coherence of the initial state and the QSL time of maximally coherent states,where the QSL time of the maximally coherent states are jointly determined by the non-Markovianity, decoherence factor and a given driving time. Moreover, we also find that the speed of quantum evolution can be obviously accelerated in the wide range of the ohmicity parameter, i.e., from sub-Ohmic to Ohmic and super-Ohmic cases, which is different from the thermal equilibrium environment case.
基金supported by the EU FP7 Marie–Curie Career Integration Fund(Grant No.631883)the Royal Society Research Fund(Grant No.RG150036)the Fundamental Research Fund for the Central Universities,China(Grant No.2018IB010)
文摘A potential acceleration of a quantum open system is of fundamental interest in quantum computation, quantum communication, and quantum metrology. In this paper, we investigate the "quantum speed-up capacity" which reveals the potential ability of a quantum system to be accelerated. We explore the evolutions of the speed-up capacity in different quantum channels for two-qubit states. We find that although the dynamics of the capacity is varying in different kinds of channels, it is positive in most situations which are considered in the context except one case in the amplitude-damping channel. We give the reasons for the different features of the dynamics. Anyway, the speed-up capacity can be improved by the memory effect. We find two ways which may be used to control the capacity in an experiment: selecting an appropriate coefficient of an initial state or changing the memory degree of environments.
基金Project supported by the National Natural Science Foundation of China(Grant No.11775040)the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi Province of China(Grant No.2019L0527)the Fundamental Research Fund for the Central Universities of China(Grant No.DUT18LK45).
文摘The classical version of Mandelstam-Tamm speed limit based on theWigner function in phase space was reported by Shanahan et al.[Phys.Rev.Lett.120070401(2018)].We present the Margolus-Levitin speed limit across the quantumto-classical transition in phase space based on the trace distance.The Margolus-Levitin speed limit is set by the Schatten L1 norm of the generator of time-dependent evolution for both the quantum and classical domains.As an example,the time-dependent harmonic oscillator is considered to illustrate the result.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11647171,61675115,and 91536108)
文摘For a two-level atom in a lossy cavity, a scheme to manipulate the non-Markovian speedup dynamics has been pro- posed in the controllable environment (the lossy cavity field). We mainly focus on the effects of the qubit--cavity detuning A and the qubit-cavity coupling strength k on the non-Markovian speedup evolution of an open system. By controlling the environment, i.e., tuning zl and , two dynamical crossovers from Markovian to non-Markovian and from no-speedup to speedup are achieved. Furthermore, it is clearly found that increasing the coupling strength k or detuning A in some cases can make the environmental non-Markovianity stronger and hence can lead to faster evolution of the open system.
文摘Quantum speed limit and entanglement of a two-spin Heisenberg XYZ system in an inhomogeneous external magnetic field are investigated.The physical system studied is the excess electron spin in two adjacent quantum dots.The influences of magnetic field inhomogeneity as well as spin-orbit coupling are studied.Moreover,the spin interaction with surrounding magnetic environment is investigated as a non-Markovian process.The spin-orbit interaction provides two important features:the formation of entanglement when two qubits are initially in a separated state and the degradation and rebirth of the entanglement.
基金the National Natural Science Foundation of China(Grant No.11974217)。
文摘The quantum speed limit(QSL)of the double quantum dot(DQD)system has been theoretically investigated by adopting the detection of the quantum point contact(QPC)in the pure dephasing environment.The Mandelstam–Tamm(MT)type of the QSL bound which is based on the trace distance has been extended to the DQD system for calculating the shortest evolving time.The increase of decoherence rate can weaken the capacity for potential speedup(CPS)and delay the evolving process due to the frequently measurement localizing the electron in the DQD system.The system needs longer time to evolve to the target state as the enhancement of dephasing rate,because the strong interaction between pure dephasing environment and the DQD system could vary the oscillation of the electron.Increasing the dephasing rate can sharp the QSL bound,but the decoherence rate would weaken the former effect and vice versa.Moreover,the CPS would be raised by increasing the energy displacement,while the enhancement of the coupling strength between two quantum dots can diminish it.It is interesting that there has an inflection point,when the coupling strength is less than the value of the point,the increasing effect of the CPS from the energy displacement is dominant,otherwise the decreasing tendency of the CPS is determined by the coupling strength and suppress the action of the energy displacement if the coupling strength is greater than the point.Our results provide theoretical reference for studying the QSL time in a semiconductor device affected by numerous factors.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61178012 and 11304179)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant Nos.20123705120002 and 20133705110001)+1 种基金the Natural Science Foundation of Shandong Province of China(Grant No.ZR2014AP009)the Scientific Research Foundation of Qufu Normal University
文摘The lower bounds of the evolution time between two distinguishable states of a system, defined as quantum speed limit time, can characterize the maximal speed of quantum computers and communication channels. We study the quantum speed limit time between the composite quantum states and their target states in the presence of nondissipative decoherence.For the initial states with maximally mixed marginals, we obtain the exact expressions of the quantum speed limit time which mainly depend on the parameters of the initial states and the decoherence channels. Furthermore, by calculating the quantum speed limit time for the time-dependent states started from a class of initial states, we discover that the quantum speed limit time gradually decreases in time, and the decay rate of the quantum speed limit time would show a sudden change at a certain critical time. Interestingly, at the same critical time, the composite system dynamics would exhibit a sudden transition from classical decoherence to quantum decoherence.
基金Project supported by the National Natural Science Foundation of China(Grant No.11374096)Hunan Provincial Innovation Foundation for Postgraduate,China(Grant No.CX2017B177)the Scientific Research Project of Hunan Provincial Education Department,China(Grant No.16C0949)
文摘We investigate the quantum speed limit time (QSLT) of a two-level atom under quantum-jump-based feedback control or homodyne-based feedback control. Our results show that the two different feedback control schemes have different influences on the evolutionary speed. By adjusting the feedback parameters, the quantum-jump-based feedback control can induce speedup of the atomic evolution from an excited state, but the homodyne-based feedback control cannot change the evolutionary speed. Additionally, the QSLT for the whole dynamical process is explored. Under the quantum-jump-based feedback control, the QSLT displays oscillatory behaviors, which implies multiple speed-up and speed-down processes during the evolution. While, the homodyne-based feedback control can accelerate the speed-up process and improve the uniform speed in the uniform evolution process.
基金Project supported by the Shandong Provincial Natural Science Foundation,China(Grant No.ZR2020MA086)the National Natural Science Foundation of China(Grant Nos.61675115 and 11974209)。
文摘As is well known,the quantum evolution speed of quantum state can never be accelerated in the Markovian regime without any operators on the system.The Hamiltonian corrections induced by the action of coherent driving forces are often used to fight dissipative and decoherence mechanisms in experiments.For this reason,considering three noisy channels(the phase-flip channel,the amplitude damping channel and the depolarizing channel),we propose a scheme of speedup evolution of an open system by controlling an external unitary coherent driving operator on the system.It is shown that,in the presence of the coherent driving,no-speedup evolution can be transformed into quantum speedup evolution in the Markovian dynamics process.Additionally,under the fixed coherent driving strength in the above three noisy channels,the best way to achieve the most degree of quantum speedup for the system has been acquired by rotating the system with appropriate driving direction angles,respectively.Finally,we conclude that the reason for this acceleration is not the nonMarkovian dynamical behavior of the system but due to the oscillation of geometric distance between the initial state and the target final state.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11664018,12174247,and U2031145)。
文摘Since the evolution of a mixed state in a unitary system is equivalent to the joint evolution of the eigenvectors contained in it,we could use the tool of instantaneous angular velocity for pure states to study the quantum speed limit(QSL)of a mixed state.We derive a lower bound for the evolution time of a mixed state to a target state in a unitary system,which automatically reduces to the quantum speed limit induced by the Fubini–Study metric for pure states.The computation of the QSL of a degenerate mixed state is more complicated than that of a non-degenerate mixed state,where we have to make a singular value decomposition(SVD)on the inner product between the two eigenvector matrices of the initial and target states.By combing these results,a lower bound for the evolution time of a general mixed state is presented.In order to compare the tightness among the lower bound proposed here and lower bounds reported in the references,two examples in a single-qubit system and in a single-qutrit system are studied analytically and numerically,respectively.All conclusions derived in this work are independent of the eigenvalues of the mixed state,which is in accord with the evolution properties of a quantum unitary system.
文摘Annually, there are over 120,000 crashes in work zones in the United States. High speeds in construction zones are a well-documented risk factor that increases <span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">the </span></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">frequency and severity of crashes. This study used connected vehicle data to evaluate the spatial and temporal impact that regulatory signs, speed feedback displays, and construction site geometry had on vehicle speed. Over 27,000 unique trips over 2 weeks on a 15-mile interstate construction work zone near Lebanon, IN were analyzed. Spatial analysis over a 0.2-mi segment before and after the posted speed limit signs showed that the regulatory signs had no statistical impact on reducing speeds. A before/after analysis was also conducted to study the impact of radar-based speed feedback that displays the motorists</span></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">’</span></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> speed on a sign below a regulatory speed limit sign. Results showed a maximum drop in median speeds of approximately 5 mph. Speeds greater than 15 mph above the speed limit dropped by 10%</span></span></span></span></span><span><span><span><span><span style="font-family:;" "=""> </span></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">-</span></span></span></span></span><span><span><span><span><span style="font-family:;" "=""> </span></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">15%. The reduction in speeds began approximately 1000 feet ahead of the sign and results were found to be statistically significant. </span></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">The </span></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">analysis also revealed that larger speed drops inside the work zone were due to geometric constraints that required additional driver workloads, especially during shoulder width changes and lane shifts. The results from this study will be helpful for agencies to understand driver behavior in the work zones and to identify proper speed limit compliance techniques that significantly reduce driver speeds in and around work zones.</span></span></span></span></span>
文摘Historically, researchers and practitioners have utilized spot speeds and microscopic simulation methodologies to evaluate the operational impact of differential or uniform speed limits for trucks and passenger vehicles. This paper presents a methodology that uses connected truck data to develop a statistical characterization of both passenger car and truck speeds. These techniques were applied to three adjacent states, Illinois, Indiana and Ohio. Illinois and Ohio have 70 mph speed limits for both trucks and cars. Indiana has a differential speed limit for heavy trucks (65 mph) and passenger cars (70 mph). The statistical distribution of truck speeds was then compared among Illinois, Indiana and Ohio. These speeds were derived from over 8 million connected truck records traveling along Interstate 70 in Illinois, Indiana and Ohio during a one-week period from May 8-14, 2022. Statistical test results over selected 20-mile sections in each state showed that median truck speeds in Indiana with its differential speed limit of 65 mph were only 1 - 2 mph lesser than the neighboring states of Illinois and Ohio who observe a uniform speed limit of 70 mph for all traffic.
基金by CHINA RAILWAY Scientific and Technological Research and Development Project(contract no.2015J007-E and 2016J007-H)which the authors hereby express their appreciation.
文摘Purpose–In service,the periodic clashes of wheel flat against the rail result in large wheel/rail impact force and high-frequency vibration,leading to severe damage on the wheelset,rail and track structure.This study aims to analyze characteristics and dynamic impact law of wheel and rail caused by wheel flat of high-speed trains.Design/methodology/approach–A full-scale high-speed wheel/rail interface test rig was used for the test of the dynamic impact of wheel/rail caused by wheel flat of high-speed train.With wheel flats of different lengths,widths and depths manually set around the rolling circle of the wheel tread,and wheel/rail dynamic impact tests to the flats in the speed range of 0–400 km/h on the rig were conducted.Findings–As the speed goes up,the flat induced the maximum of the wheel/rail dynamic impact force increases rapidly before it reaches its limit at the speed of around 35 km/h.It then goes down gradually as the speed continues to grow.The impact of flat wheel on rail leads to 100–500 Hz middle-frequency vibration,and around 2,000 Hz and 6,000 Hz high-frequency vibration.In case of any wheel flat found during operation,the train speed shall be controlled according to the status of the flat and avoid the running speed of 20 km/h–80 km/h as much as possible.Originality/value–The research can provide a new method to obtain the dynamic impact of wheel/rail caused by wheel flat by a full-scale high-speed wheel/rail interface test rig.The relations among the flat size,the running speed and the dynamic impact are hopefully of reference to the building of speed limits for HSR wheel flat of different degrees.