Reconfigurable intelligent surface(RIS)for wireless networks have drawn lots of attention in both academic and industry communities.RIS can dynamically control the phases of the reflection elements to send the signal ...Reconfigurable intelligent surface(RIS)for wireless networks have drawn lots of attention in both academic and industry communities.RIS can dynamically control the phases of the reflection elements to send the signal in the desired direction,thus it provides supplementary links for wireless networks.Most of prior works on RIS-aided wireless communication systems consider continuous phase shifts,but phase shifts of RIS are discrete in practical hardware.Thus we focus on the actual discrete phase shifts on RIS in this paper.Using the advanced deep reinforcement learning(DRL),we jointly optimize the transmit beamforming matrix from the discrete Fourier transform(DFT)codebook at the base station(BS)and the discrete phase shifts at the RIS to maximize the received signal-to-interference plus noise ratio(SINR).Unlike the traditional schemes usually using alternate optimization methods to solve the transmit beamforming and phase shifts,the DRL algorithm proposed in the paper can jointly design the transmit beamforming and phase shifts as the output of the DRL neural network.Numerical results indicate that the DRL proposed can dispose the complicated optimization problem with low computational complexity.展开更多
Acoustic holograms can recover wavefront stored acoustic field information and produce high-fidelity complex acoustic fields. Benefiting from the huge spatial information that traditional acoustic elements cannot matc...Acoustic holograms can recover wavefront stored acoustic field information and produce high-fidelity complex acoustic fields. Benefiting from the huge spatial information that traditional acoustic elements cannot match, acoustic holograms pursue the realization of high-resolution complex acoustic fields and gradually tend to high-frequency ultrasound applications. However, conventional continuous phase holograms are limited by three-dimensional(3D) printing size, and the presence of unavoidable small printing errors makes it difficult to achieve acoustic field reconstruction at high frequency accuracy. Here, we present an optimized discrete multi-step phase hologram. It can ensure the reconstruction quality of image with high robustness, and properly lower the requirement for the 3D printing accuracy. Meanwhile, the concept of reconstruction similarity is proposed to refine a measure of acoustic field quality. In addition, the realized complex acoustic field at 20 MHz promotes the application of acoustic holograms at high frequencies and provides a new way to generate high-fidelity acoustic fields.展开更多
The vapor diffusion and transport resulting from steam generator tube rupture(SGTR)accidents are a major concern threatening lead-based reactor core safety.In this study,a high-parameter SGTR experimental platform and...The vapor diffusion and transport resulting from steam generator tube rupture(SGTR)accidents are a major concern threatening lead-based reactor core safety.In this study,a high-parameter SGTR experimental platform and the multi-phase multi-physics processes numerical simulation were developed to investigate the phase behavior and interaction mechanisms.This study revealed the interaction mechanisms of lead-bismuth liquid metal and water driven by flash vaporization,jet impingement boiling,and moderate boiling.The migration and evolution of the discrete phases(vapor-water mixture)were inferred from the temperature transient laws and a numerical simulation.The results revealed that the evolution of the discrete phases consists of three stages:cavity formation,flanking diffusion,and stable up-floating.The jet pressure significantly extended the disturbance period.Variations in the water temperature mainly affected the depressurization boiling process,altering the diffusion region of the discrete phases.The temperature of the liquid metal and the duration of the jet had a minimal impact on the behavior of the discrete phases.This study provides a crucial reference for constructing a complete picture of accident evolution.展开更多
The objective of this research is to track the phase changes in Binary Phase Shift Keying (BPSK) modulated signal in ZigBee communication systems using discrete Kalman Filter (KF). Therefore, Kalman Filtering is used ...The objective of this research is to track the phase changes in Binary Phase Shift Keying (BPSK) modulated signal in ZigBee communication systems using discrete Kalman Filter (KF). Therefore, Kalman Filtering is used to estimate and optimize the carrier phase of BPSK modulated signal, in the presence of Additive White Gaussian Noise (AWGN) channel, by minimizing the phase deviation error. Therefore, a simulation model, using MATLAB, will be created to demonstrate ZigBee transmission system with the impact of the integrated filter. The expected results will show that Kalman Filter tracks the phase of BPSK modulated signal correctly and the performance of tracking will be measured by Mean Square Error (MSE) with respect to Signal to Noise Ratio (SNR). This study proposes a new method of phase tracking in ZigBee receivers in the presence of AWGN channel which can be extended to Internet of Things (IoT) applications.展开更多
Chokes are one of the most important components of downhole flow-control equipment. The particle erosion mathematical model, which considers particle-particle interaction, was established and used to simulate solid pa...Chokes are one of the most important components of downhole flow-control equipment. The particle erosion mathematical model, which considers particle-particle interaction, was established and used to simulate solid particle movement as well as particle erosion characteristics of the solid-liquid two-phase flow in a choke. The corresponding erosion reduction approach by setting ribs on the inner wall of the choke was advanced. This mathematical model includes three parts： the flow field simulation of the continuous carrier fluid by an Eulerian approach, the particle interaction simulation using the discrete particle hard sphere model by a Lagrangian approach and calculation of erosion rate using semiempirical correlations. The results show that particles accumulated in a narrow region from inlet to outlet of the choke and the dominating factor affecting particle motion is the fluid drag force. As a result, the optimization of rib geometrical parameters indicates that good anti-erosion performance can be achieved by four ribs, each of them with a height （H） of 3 mm and a width （B） of 5 mm equaling the interval between ribs （L）.展开更多
The forces on rigid particles moving in relation to fluid having been studied and the equation of modifications of their expressions under different flow conditions discussed, a general form of equation for discrete p...The forces on rigid particles moving in relation to fluid having been studied and the equation of modifications of their expressions under different flow conditions discussed, a general form of equation for discrete particles' motion in arbitrary flow field is obtained. The mathematical features of the linear form of the equation are clarified and analytical solution of the linearized equation is gotten by means of Laplace transform. According to above theoretical results, the effects of particles' properties on its motion in several typical flow field are studied, with some meaningful conclusions being reached.展开更多
Basing on discrete event simulation, a reliability simulation algorithm of the phased-mission system with multiple states is put forth. Firstly, the concepts and main characters of phasedmission system are discussed, ...Basing on discrete event simulation, a reliability simulation algorithm of the phased-mission system with multiple states is put forth. Firstly, the concepts and main characters of phasedmission system are discussed, and an active and standby redundancy (AS) tree structure method to describe the system structure of each mission phase is brought forward. Secondly, the behavior of the phased-mission system with multiple states is discussed with the theory of state chart. Thirdly, basing on the discrete event simulation concept, a simulation algorithm to estimate reliability parameters of the phased-mission system with multiple states is explored. Finally, an example is introduced and analyzed, and the analysis result verifies the algorithms. The simulation algorithm is practical and versatile, for it can model complex behavior of phased-mission system flexibly, and more reliability parameters to understand system operation can be attained.展开更多
This paper takes further insight into the sparse geometry which offers a larger array aperture than uniform linear array(ULA)with the same number of physical sensors.An efficient method based on closed-form robust Chi...This paper takes further insight into the sparse geometry which offers a larger array aperture than uniform linear array(ULA)with the same number of physical sensors.An efficient method based on closed-form robust Chinese remainder theorem(CFRCRT)is presented to estimate the direction of arrival(DOA)from their wrapped phase with permissible errors.The proposed algorithm has significantly less computational complexity than the searching method while maintaining similar estimation precision.Furthermore,we combine all phase discrete Fourier transfer(APDFT)and the CFRCRT algorithm to achieve a considerably high DOA estimation precision.Both the theoretical analysis and simulation results demonstrate that the proposed algorithm has a higher estimation precision as well as lower computation complexity.展开更多
In this paper, we propose a combination of discrete elements for the soil and finite elements for the fluid flow field inside the pore space to simulate the triggering of landslides. We give the details for the implem...In this paper, we propose a combination of discrete elements for the soil and finite elements for the fluid flow field inside the pore space to simulate the triggering of landslides. We give the details for the implementation of third order finite elements (“P<sub>2</sub> with bubble”) together with polygonal discrete elements, which allows the formulation with a minimal number of degrees of freedom to save computer time and memory. We verify the implementation with several standard problems from computational fluid dynamics, as well as the decay of a granular step in a fluid as test case for complex flow.展开更多
As a third generation light source, Shanghai Synchrotron Radiation Facility (SSRF) has up to 140 beam position monitors (BPM) installed to monitor the beam dynamics on its storage ring. Once the operation mode is chos...As a third generation light source, Shanghai Synchrotron Radiation Facility (SSRF) has up to 140 beam position monitors (BPM) installed to monitor the beam dynamics on its storage ring. Once the operation mode is chosen, the betatron functions are determined. Since the sinusoidal betatron oscillation is the dominant component of the transverse motion, these BPMs can be used to measure the motion to get the betatron functions. Three methods are compared to calculate the phase advance among the BPMs in this paper, aiming to find one or more feasible ways to check the beam optics in SSRF. Some experiments have also been made to verify the practicality of the phase information.展开更多
Switching current distributions of an Nb/Al-AlO2/Nb Josephson junction are measured in a temperature range from 25 mK to 800 mK. We analyse the phase escape properties by using the theory of Larkin and Ovchinnikov （L...Switching current distributions of an Nb/Al-AlO2/Nb Josephson junction are measured in a temperature range from 25 mK to 800 mK. We analyse the phase escape properties by using the theory of Larkin and Ovchinnikov （LO） which takes discrete energy levels into account. Our results show that the phase escape can be well described by the LO approach for temperatures near and below the crossover from thermal activation to macroscopic quantum tunneling. These results are helpful for further study of macroscopic quantum phenomena in Josephson junctions where discrete energy levels need to be considered.展开更多
文摘Reconfigurable intelligent surface(RIS)for wireless networks have drawn lots of attention in both academic and industry communities.RIS can dynamically control the phases of the reflection elements to send the signal in the desired direction,thus it provides supplementary links for wireless networks.Most of prior works on RIS-aided wireless communication systems consider continuous phase shifts,but phase shifts of RIS are discrete in practical hardware.Thus we focus on the actual discrete phase shifts on RIS in this paper.Using the advanced deep reinforcement learning(DRL),we jointly optimize the transmit beamforming matrix from the discrete Fourier transform(DFT)codebook at the base station(BS)and the discrete phase shifts at the RIS to maximize the received signal-to-interference plus noise ratio(SINR).Unlike the traditional schemes usually using alternate optimization methods to solve the transmit beamforming and phase shifts,the DRL algorithm proposed in the paper can jointly design the transmit beamforming and phase shifts as the output of the DRL neural network.Numerical results indicate that the DRL proposed can dispose the complicated optimization problem with low computational complexity.
基金Project supported by the China Postdoctoral Science Foundation (Grant No.2023M732745)the National Natural Science Foundations of China (Grant Nos.61974110 and 62104177)+1 种基金the Fundamental Research Funds for the Central Universities,China (Grant Nos.QTZX23022 and JBF211103)the Cooperation Program of XDU– Chongqing IC Innovation Research Institute (Grant No.CQ IRI-2022CXY-Z07)。
文摘Acoustic holograms can recover wavefront stored acoustic field information and produce high-fidelity complex acoustic fields. Benefiting from the huge spatial information that traditional acoustic elements cannot match, acoustic holograms pursue the realization of high-resolution complex acoustic fields and gradually tend to high-frequency ultrasound applications. However, conventional continuous phase holograms are limited by three-dimensional(3D) printing size, and the presence of unavoidable small printing errors makes it difficult to achieve acoustic field reconstruction at high frequency accuracy. Here, we present an optimized discrete multi-step phase hologram. It can ensure the reconstruction quality of image with high robustness, and properly lower the requirement for the 3D printing accuracy. Meanwhile, the concept of reconstruction similarity is proposed to refine a measure of acoustic field quality. In addition, the realized complex acoustic field at 20 MHz promotes the application of acoustic holograms at high frequencies and provides a new way to generate high-fidelity acoustic fields.
基金supported by the National Natural Science Foundation of China(Nos.U20B2011 and 123B2086)。
文摘The vapor diffusion and transport resulting from steam generator tube rupture(SGTR)accidents are a major concern threatening lead-based reactor core safety.In this study,a high-parameter SGTR experimental platform and the multi-phase multi-physics processes numerical simulation were developed to investigate the phase behavior and interaction mechanisms.This study revealed the interaction mechanisms of lead-bismuth liquid metal and water driven by flash vaporization,jet impingement boiling,and moderate boiling.The migration and evolution of the discrete phases(vapor-water mixture)were inferred from the temperature transient laws and a numerical simulation.The results revealed that the evolution of the discrete phases consists of three stages:cavity formation,flanking diffusion,and stable up-floating.The jet pressure significantly extended the disturbance period.Variations in the water temperature mainly affected the depressurization boiling process,altering the diffusion region of the discrete phases.The temperature of the liquid metal and the duration of the jet had a minimal impact on the behavior of the discrete phases.This study provides a crucial reference for constructing a complete picture of accident evolution.
文摘The objective of this research is to track the phase changes in Binary Phase Shift Keying (BPSK) modulated signal in ZigBee communication systems using discrete Kalman Filter (KF). Therefore, Kalman Filtering is used to estimate and optimize the carrier phase of BPSK modulated signal, in the presence of Additive White Gaussian Noise (AWGN) channel, by minimizing the phase deviation error. Therefore, a simulation model, using MATLAB, will be created to demonstrate ZigBee transmission system with the impact of the integrated filter. The expected results will show that Kalman Filter tracks the phase of BPSK modulated signal correctly and the performance of tracking will be measured by Mean Square Error (MSE) with respect to Signal to Noise Ratio (SNR). This study proposes a new method of phase tracking in ZigBee receivers in the presence of AWGN channel which can be extended to Internet of Things (IoT) applications.
基金supported by the Fund of Innovation Research Group of National Natural Science Foundation of China (Grant NO.5052160450323001)Major Program of National Natural Science Foundation of China (Grant No.50536020)
文摘Chokes are one of the most important components of downhole flow-control equipment. The particle erosion mathematical model, which considers particle-particle interaction, was established and used to simulate solid particle movement as well as particle erosion characteristics of the solid-liquid two-phase flow in a choke. The corresponding erosion reduction approach by setting ribs on the inner wall of the choke was advanced. This mathematical model includes three parts： the flow field simulation of the continuous carrier fluid by an Eulerian approach, the particle interaction simulation using the discrete particle hard sphere model by a Lagrangian approach and calculation of erosion rate using semiempirical correlations. The results show that particles accumulated in a narrow region from inlet to outlet of the choke and the dominating factor affecting particle motion is the fluid drag force. As a result, the optimization of rib geometrical parameters indicates that good anti-erosion performance can be achieved by four ribs, each of them with a height （H） of 3 mm and a width （B） of 5 mm equaling the interval between ribs （L）.
文摘The forces on rigid particles moving in relation to fluid having been studied and the equation of modifications of their expressions under different flow conditions discussed, a general form of equation for discrete particles' motion in arbitrary flow field is obtained. The mathematical features of the linear form of the equation are clarified and analytical solution of the linearized equation is gotten by means of Laplace transform. According to above theoretical results, the effects of particles' properties on its motion in several typical flow field are studied, with some meaningful conclusions being reached.
基金supported by the Natural Science Foundation of China(61174156 61273189+5 种基金 61174035 61374179 U1435218 6140340171401168)the Army Equipment Research Foundation(012016012600B12507)
文摘Basing on discrete event simulation, a reliability simulation algorithm of the phased-mission system with multiple states is put forth. Firstly, the concepts and main characters of phasedmission system are discussed, and an active and standby redundancy (AS) tree structure method to describe the system structure of each mission phase is brought forward. Secondly, the behavior of the phased-mission system with multiple states is discussed with the theory of state chart. Thirdly, basing on the discrete event simulation concept, a simulation algorithm to estimate reliability parameters of the phased-mission system with multiple states is explored. Finally, an example is introduced and analyzed, and the analysis result verifies the algorithms. The simulation algorithm is practical and versatile, for it can model complex behavior of phased-mission system flexibly, and more reliability parameters to understand system operation can be attained.
基金supported by the Fund for Foreign Scholars in University Research and Teaching Programs(the 111 Project)(B18039)
文摘This paper takes further insight into the sparse geometry which offers a larger array aperture than uniform linear array(ULA)with the same number of physical sensors.An efficient method based on closed-form robust Chinese remainder theorem(CFRCRT)is presented to estimate the direction of arrival(DOA)from their wrapped phase with permissible errors.The proposed algorithm has significantly less computational complexity than the searching method while maintaining similar estimation precision.Furthermore,we combine all phase discrete Fourier transfer(APDFT)and the CFRCRT algorithm to achieve a considerably high DOA estimation precision.Both the theoretical analysis and simulation results demonstrate that the proposed algorithm has a higher estimation precision as well as lower computation complexity.
文摘In this paper, we propose a combination of discrete elements for the soil and finite elements for the fluid flow field inside the pore space to simulate the triggering of landslides. We give the details for the implementation of third order finite elements (“P<sub>2</sub> with bubble”) together with polygonal discrete elements, which allows the formulation with a minimal number of degrees of freedom to save computer time and memory. We verify the implementation with several standard problems from computational fluid dynamics, as well as the decay of a granular step in a fluid as test case for complex flow.
基金Supported by National Natural Science Foundation of China (No.11075198)
文摘As a third generation light source, Shanghai Synchrotron Radiation Facility (SSRF) has up to 140 beam position monitors (BPM) installed to monitor the beam dynamics on its storage ring. Once the operation mode is chosen, the betatron functions are determined. Since the sinusoidal betatron oscillation is the dominant component of the transverse motion, these BPMs can be used to measure the motion to get the betatron functions. Three methods are compared to calculate the phase advance among the BPMs in this paper, aiming to find one or more feasible ways to check the beam optics in SSRF. Some experiments have also been made to verify the practicality of the phase information.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.10534060 and 10874231)National Basic Research Program of China (Grant Nos.2006CB601007,2006CB921107,and 2009CB929102)
文摘Switching current distributions of an Nb/Al-AlO2/Nb Josephson junction are measured in a temperature range from 25 mK to 800 mK. We analyse the phase escape properties by using the theory of Larkin and Ovchinnikov （LO） which takes discrete energy levels into account. Our results show that the phase escape can be well described by the LO approach for temperatures near and below the crossover from thermal activation to macroscopic quantum tunneling. These results are helpful for further study of macroscopic quantum phenomena in Josephson junctions where discrete energy levels need to be considered.
