The development of guidance technology has made it possible for the earth penetration weapons(EPWs)to impact the target repeatedly at a close range. To investigative the damage of single and sequential strike induced ...The development of guidance technology has made it possible for the earth penetration weapons(EPWs)to impact the target repeatedly at a close range. To investigative the damage of single and sequential strike induced by the EPWs, experimental and numerical investigations are carried out in this paper.Firstly, a series of sequential explosion tests are conducted to provide the basic data of the crater size.Then, a numerical model is established to simulate the damage effects of sequential explosions using the meshfree method of Smoothed particle Galerkin. The effectiveness of numerical model is verified by comparison with the experimental results. Finally, based on dimensional analysis, several empirical formulas for describing the crater size are presented, including the conical crater diameter and the conical crater depth of the single explosion, the conical crater area and the joint depth of the secondary explosion. The formula for the single explosion expresses the relationship between the aspect ratio of the charge ranging from 3 to 7, the dimensionless buried depth ranging from 2 to 14 and the crater size. The formula for the secondary explosion expresses the relationship between the relative position of the two explosions and the crater size. All of data can provide reference for the design of protective structures.展开更多
Industrial linear accelerators often contain many bunches when their pulse widths are extended to microseconds.As they typically operate at low electron energies and high currents,the interactions among bunches cannot...Industrial linear accelerators often contain many bunches when their pulse widths are extended to microseconds.As they typically operate at low electron energies and high currents,the interactions among bunches cannot be neglected.In this study,an algorithm is introduced for calculating the space charge force of a train with infinite bunches.By utilizing the ring charge model and the particle-in-cell(PIC)method and combining analytical and numerical methods,the proposed algorithm efficiently calculates the space charge force of infinite bunches,enabling the accurate design of accelerator parameters and a comprehensive understanding of the space charge force.This is a significant improvement on existing simulation software such as ASTRA and PARMELA that can only handle a single bunch or a small number of bunches.The PIC algorithm is validated in long drift space transport by comparing it with existing models,such as the infinite-bunch,ASTRA single-bunch,and PARMELA several-bunch algorithms.The space charge force calculation results for the external acceleration field are also verified.The reliability of the proposed algorithm provides a foundation for the design and optimization of industrial accelerators.展开更多
Gamma-ray imaging systems are powerful tools in radiographic diagnosis.However,the recorded images suffer from degradations such as noise,blurring,and downsampling,consequently failing to meet high-precision diagnosti...Gamma-ray imaging systems are powerful tools in radiographic diagnosis.However,the recorded images suffer from degradations such as noise,blurring,and downsampling,consequently failing to meet high-precision diagnostic requirements.In this paper,we propose a novel single-image super-resolution algorithm to enhance the spatial resolution of gamma-ray imaging systems.A mathematical model of the gamma-ray imaging system is established based on maximum a posteriori estimation.Within the plug-and-play framework,the half-quadratic splitting method is employed to decouple the data fidelit term and the regularization term.An image denoiser using convolutional neural networks is adopted as an implicit image prior,referred to as a deep denoiser prior,eliminating the need to explicitly design a regularization term.Furthermore,the impact of the image boundary condition on reconstruction results is considered,and a method for estimating image boundaries is introduced.The results show that the proposed algorithm can effectively addresses boundary artifacts.By increasing the pixel number of the reconstructed images,the proposed algorithm is capable of recovering more details.Notably,in both simulation and real experiments,the proposed algorithm is demonstrated to achieve subpixel resolution,surpassing the Nyquist sampling limit determined by the camera pixel size.展开更多
In response to the demand for rapid geometric modeling in Monte Carlo radiation transportation calculations for large-scale and complex geometric scenes,functional improvements,and algorithm optimizations were perform...In response to the demand for rapid geometric modeling in Monte Carlo radiation transportation calculations for large-scale and complex geometric scenes,functional improvements,and algorithm optimizations were performed using CAD-to-Monte Carlo geometry conversion(CMGC)code.Boundary representation(BRep)to constructive solid geometry(CSG)conversion and visual CSG modeling were combined to address the problem of non-convertible geometries such as spline surfaces.The splitting surface assessment method in BRep-to-CSG conversion was optimized to reduce the number of Boolean operations using an Open Cascade.This,in turn,reduced the probability of CMGC conversion failure.The auxiliary surface generation algorithm was optimized to prevent the generation of redundant auxiliary surfaces that cause an excessive decomposition of CAD geometry solids.These optimizations enhanced the usability and stability of the CMGC model conversion.CMGC was applied successfully to the JMCT transportation calculations for the conceptual designs of five China Fusion Engineering Test Reactor(CFETR)blankets.The rapid replacement of different blanket schemes was achieved based on the baseline CFETR model.The geometric solid number of blankets ranged from hundreds to tens of thousands.The correctness of the converted CFETR models using CMGC was verified through comparisons with the MCNP calculation results.The CMGC supported radiation field evaluations for a large urban scene and detailed ship scene.This enabled the rapid conversion of CAD models with thousands of geometric solids into Monte Carlo CSG models.An analysis of the JMCT transportation simulation results further demonstrated the accuracy and effectiveness of the CMGC.展开更多
The cylindrical virtual cathode reflex triode is a new type of pulsed hard X-ray load,which has the advantages of simple structure,high radiation conversion efficiency,and simplicity in seriesparallel operation.This p...The cylindrical virtual cathode reflex triode is a new type of pulsed hard X-ray load,which has the advantages of simple structure,high radiation conversion efficiency,and simplicity in seriesparallel operation.This paper presents a method to reduce the impedance of the triode using a multiring cathode.The average electric field on the ring-cathode emission surface is enhanced due to edge effect,and the beam intensity is greatly increased in proportion to the square of the electric field strength.Multi-ring cathode is used to enlarge the emission area.Therefore,the reflex triode can work at lower impedance and generate a stronger beam under the same anode-cathode gap.In addition,the electric field enhancement of the cathode reduces the cathode emission stabilization time and enhances the operation stability of the triode.The effects of parameters such as ring width and ring gap on the triode impedance are simulated and studied.The cathode emission stabilization time and the X-ray conversion efficiency are compared.The design basis of cathode structure parameters and the impedance control method of the cylindrical virtual cathode reflex triode are given according to the simulations.展开更多
Stripping injection overcomes the limitations of Liouville's theorem and is widely used for beam injection and accumulation in high-intensity synchrotrons.The interaction between the stripping foil and beam is cru...Stripping injection overcomes the limitations of Liouville's theorem and is widely used for beam injection and accumulation in high-intensity synchrotrons.The interaction between the stripping foil and beam is crucial in the study of stripping injection,particularly in low-energy stripping injection synchrotrons,such as the XiPAF synchrotron.The foil thickness is the main parameter that affects the properties of the beam after injection.The thin stripping foil is reinforced with collodion during its installation.However,the collodion on the foil surface makes it difficult to determine its equivalent thickness,because the mechanical measurements are not sufficiently reliable or convenient for continuously determining foil thickness.We propose an online stripping foil thickness measurement method based on the ionization energy loss effect,which is suitable for any foil thickness and does not require additional equipment.Experimental studies were conducted using the XiPAF synchrotron.The limitation of this method was examined,and the results were verified by comparing the experimentally obtained beam current accumulation curves with the simulation results.This confirms the accuracy and reliability of the proposed method for measuring the stripping foil thickness.展开更多
A half-size prototype of the multi wire drift chamber for the cooling storage ring external-target experiment(CEE)was assembled and tested in the 350 MeV/u Kr+Fe reactions at the heavy-ion research facility in Lanzhou...A half-size prototype of the multi wire drift chamber for the cooling storage ring external-target experiment(CEE)was assembled and tested in the 350 MeV/u Kr+Fe reactions at the heavy-ion research facility in Lanzhou.The prototype consists of six sense layers,where the sense wires are stretched in three directions X,U,and V;meeting 0?,30?,and-30?,respectively,with respect to the vertical axis.The sensitive area of the prototype is 76 cm×76 cm.The amplified and shaped signals from the anode wires were digitized in a serial capacity array.When operating at a high voltage of 1500 V on the anode wires,the efficiency for each layer is greater than 95%.The tracking residual is approximately 301±2μm.This performance satisfies the requirements of CEE.展开更多
In the paper,we discuss the development of the multigap resistive plate chamber time-of-fight(TOF)technology and the production of the solenoidal tracker at RHIC(STAR)TOF detector in China at the beginning of the twen...In the paper,we discuss the development of the multigap resistive plate chamber time-of-fight(TOF)technology and the production of the solenoidal tracker at RHIC(STAR)TOF detector in China at the beginning of the twenty-frst century.Subsequently,recent experimental results from the frst beam energy scan program(BES-I)at the Relativistic Heavy Ion Collider(RHIC)pertaining to measurements of collectivity,chirality,criticality,global polarization,strangeness,heavy favor,dilepton and light nuclei productions are reviewed.展开更多
Since the first demonstrations of nuclear magnetic resonance (NMR) in condensed matter in 1946, the field of NMR has yielded a continuous flow of conceptual advances and methodological innovations that continues today...Since the first demonstrations of nuclear magnetic resonance (NMR) in condensed matter in 1946, the field of NMR has yielded a continuous flow of conceptual advances and methodological innovations that continues today. Much progress has been made in the utilization of solid-state NMR to illuminate molecular structure and dynamics in systems not controllable by any other way. NMR deals with time-dependent perturbations of nuclear spin systems and solving the time-dependent Schrodinger equation is a central problem in quantum physics in general and solid-state NMR in particular. This theoretical perspective outlines the methods used to treat theoretical problems in solid-state NMR as well as the recent theoretical development of spin dynamics in NMR and physics. The purpose of this review is to unravel the versatility of theories in solid-state NMR and to present the recent theoretical developments of spin dynamics.展开更多
The key plasma parameters under different discharge modes, such as heavy-particle and electron temperatures, electron number density, and nonequilibrium volume of plasmas, play important roles in various applications ...The key plasma parameters under different discharge modes, such as heavy-particle and electron temperatures, electron number density, and nonequilibrium volume of plasmas, play important roles in various applications of gas discharge plasmas. In this study, a self-consistent two-dimensional nonequilibrium fluid model coupled with an external circuit model is established to reveal the mechanisms related to the discharge modes, including the normal glow, abnormal glow,arc, and glow-to-arc transition modes, with an atmospheric-pressure direct-current(DC) argon discharge as a model plasma system. The modeling results show that, under different discharge modes, the most significant difference between the preceding four discharge modes lies in the current and energy transfer processes on the cathode side. On one hand, the current to the cathode surface is mainly delivered by the ions coming from the plasma column under the glow discharge mode due to the low temperature of the solid cathode, whereas the thermionic and secondary electrons emitted from the hot cathode surface play a very important role under the arc mode with a higher cathode surface temperature and higher ion flux toward the cathode. On the other hand, the energy transfer channel on the cathode side changes from mainly heating the solid cathode under the glow mode to simultaneously heating both the solid cathode and plasma column under the arc mode with an increase in the discharge current. Consequently, the power density in the cathode sheath(P_c) was used as a key parameter for judging different discharge modes, and the range of(0.28–1.2) × 10^(12) W m^(-3) was determined as a critical window of P_c corresponding to the glow-to-arc-mode transition for the atmospheric-pressure DC argon discharge, which was also verified by comparison with the experimental results in this study and the data in the previous literature.展开更多
Pedestrian self-organizing movement plays a significant role in evacuation studies and architectural design.Lane formation,a typical self-organizing phenomenon,helps pedestrian system to become more orderly,the majori...Pedestrian self-organizing movement plays a significant role in evacuation studies and architectural design.Lane formation,a typical self-organizing phenomenon,helps pedestrian system to become more orderly,the majority of following behavior model and overtaking behavior model are imprecise and unrealistic compared with pedestrian movement in the real world.In this study,a pedestrian dynamic model considering detailed modelling of the following behavior and overtaking behavior is constructed,and a method of measuring the lane formation and pedestrian system order based on information entropy is proposed.Simulation and analysis demonstrate that the following and avoidance behaviors are important factors of lane formation.A high tendency of following results in good lane formation.Both non-selective following behavior and aggressive overtaking behavior cause the system order to decrease.The most orderly following strategy for a pedestrian is to overtake the former pedestrian whose speed is lower than approximately 70%of his own.The influence of the obstacle layout on pedestrian lane and egress efficiency is also studied with this model.The presence of a small obstacle does not obstruct the walking of pedestrians;in contrast,it may help to improve the egress efficiency by guiding the pedestrian flow and mitigating the reduction of pedestrian system orderliness.展开更多
The four-color three-step selective photoionization process of atom is very important in laser isotope separation technology.The population trapping phenomena and their influences are studied theoretically in monochro...The four-color three-step selective photoionization process of atom is very important in laser isotope separation technology.The population trapping phenomena and their influences are studied theoretically in monochromatic and non-monochromatic laser fields based on the density matrix theory in this work.Time evolutions of the photoionization properties of the four-color,three-step process are given.The population trapping effects occur intensely in monochromatic excitation,while it gradually turns weak as the laser bandwidth increases.The effects of bandwidth,Rabi frequency,time delay,and frequency detuning on the population trapping effect are investigated in monochromatic and non-monochromatic laser fields.The effects of laser process parameters and atomic parameters on the effective selective photoionization are also discussed.The ionization probability and selectivity factors,as evaluation indexes,are difficult to improve synchronously by adjusting systematic parameters.Besides,the existence of metastable state may play a negative role when its population is low enough.展开更多
An accurate assessment of the evacuation efficiency in case of disasters is of vital importance to the safety design of buildings and street blocks.Hazard sources not only physically but psychologically affect the ped...An accurate assessment of the evacuation efficiency in case of disasters is of vital importance to the safety design of buildings and street blocks.Hazard sources not only physically but psychologically affect the pedestrians,which may further alter their behavioral patterns.This effect is especially significant in narrow spaces,such as corridors and alleys.This study aims to integrate a non-spreading hazard source into the social force model following the results from a previous experiment and simulation,and to simulate unidirectional pedestrian flows over various crowd densities and clarity–intensity properties of the hazard source.The integration include a virtual repulsion force from the hazard source and a decay on the social force term.The simulations reveal(i)that the hazard source creates virtual bottlenecks that suppress the flow,(ii)that the inter-pedestrian push forms a stabilisation phase on the flow-density curve within medium-to-high densities,and(iii)that the pedestrians are prone to a less orderly and stable pattern of movement in low clarity–intensity scenarios,possibly with lateral collisions passing the hazard source.展开更多
In recent years,attacks against crowded places such as campuses and theaters have had a frequent and negative impact on the security and stability of society.In such an event,the crowd will be subjected to high psycho...In recent years,attacks against crowded places such as campuses and theaters have had a frequent and negative impact on the security and stability of society.In such an event,the crowd will be subjected to high psychological stress and their emotions will rapidly spread to others.This paper establishes the attack-escape evacuation simulation model(AEES-SFM),based on the social force model,to consider emotion spreading under attack.In this model,(1)the attack-escape driving force is considered for the interaction between an attacker and evacuees and(2)emotion spreading among the evacuees is considered to modify the value of the psychological force.To validate the simulation,several experiments were carried out at a university in China.Comparing the simulation and experimental results,it is found that the simulation results are similar to the experimental results when considering emotion spreading.Therefore,the AEES-SFM is proved to be effective.By comparing the results of the evacuation simulation without emotion spreading,the emotion spreading model reduces the evacuation time and the number of casualties by about 30%,which is closer to the real experimental results.The results are still applicable in the case of a 40-person evacuation.This paper provides theoretical support and practical guidance for campus response to violent attacks.展开更多
Multiaxial neutron/x-ray imaging and three-dimensional (3D) reconstruction techniques play a crucial role in gaining valuable insights intothe generation and evolution mechanisms of pulsed radiation sources. Owing to ...Multiaxial neutron/x-ray imaging and three-dimensional (3D) reconstruction techniques play a crucial role in gaining valuable insights intothe generation and evolution mechanisms of pulsed radiation sources. Owing to the short emission time (∼200 ns) and drastic changes of thepulsed radiation source, it is necessary to acquire projection data within a few nanoseconds in order to achieve clear computed tomography3D imaging. As a consequence, projection data that can be used for computed tomography image reconstruction at a certain moment are oftenavailable for only a few angles. Traditional algorithms employed in the process of reconstructing 3D images with extremely incomplete datamay introduce significant distortions and artifacts into the final image. In this paper, we propose an iterative image reconstruction methodusing cylindrical harmonic decomposition and a self-supervised denoising network algorithm based on the deep image prior method. Weaugment the prior information with a 2D total variation prior and a 3D deep image prior. Single-wire Z-pinch imaging experiments have beencarried out at Qin-1 facility in five views and four frames, with a time resolution of 3 ns for each frame and a time interval of 40 ns betweenadjacent frames. Both numerical simulations and experiments verify that our proposed algorithm can achieve high-quality reconstructionresults and obtain the 3D intensity distribution and evolution of extreme ultraviolet and soft x-ray emission from plasma.展开更多
High-purity germanium(HPGe)detectors,which are used for direct dark matter detection,have the advantages of a low threshold and excellent energy resolution.The surface passivation of HPGe has become crucial for achiev...High-purity germanium(HPGe)detectors,which are used for direct dark matter detection,have the advantages of a low threshold and excellent energy resolution.The surface passivation of HPGe has become crucial for achieving an extremely low energy threshold.In this study,first-principles simulations,passivation film preparation,and metal oxide semiconductor(MOS)capacitor characterization were combined to study surface passivation.Theoretical calculations of the energy band structure of the -H,-OH,and -NH_(2) passivation groups on the surface of Ge were performed,and the interface state density and potential with five different passivation groups with N/O atomic ratios were accurately analyzed to obtain a stable surface state.Based on the theoretical calculation results,the surface passivation layers of the Ge_(2)ON_(2) film were prepared via magnetron sputtering in accordance with the optimum atomic ratio structure.The microstructure,C-V,and I-V electrical properties of the layers,and the passivation effect of the Al/Ge_(2)ON_(2)/Ge MOS were characterized to test the interface state density.The mean interface state density obtained by the Terman method was 8.4×10^(11) cm^(-2) eV^(-1).The processing of germanium oxynitrogen passivation films is expected to be used in direct dark matter detection of the HPGe detector surface passivation technology to reduce the detector leakage currents.展开更多
The Doppler backscattering(DBS)diagnostic is widely used to measure the localized density fluctuations and the propagation velocity of turbulent structures.Microwave is launched at a frequency that approaches a cutoff...The Doppler backscattering(DBS)diagnostic is widely used to measure the localized density fluctuations and the propagation velocity of turbulent structures.Microwave is launched at a frequency that approaches a cutoff layer in the plasma at an angle oblique to the cutoff layer.A new Q-band multichannel DBS system based on a comb generator has been designed and tested for application on the HL-3 tokamak.With the comb generator and heterodyne scheme,the stability and flexibility of the new DBS system are improved.The new DBS diagnostic has a high output power(~10 dBm),good power flatness(<5 dB in Q-band),and frequency stability,and the inter-frequency separation is tunable remotely.This article introduces the system design,laboratory test results,and initial experimental results from the HL-3 tokamak.With the help of the newly developed multichannel DBS,the turbulence information can be studied with high temporal and spatial resolution.展开更多
Track reconstruction algorithms are critical for polarization measurements.Convolutional neural networks(CNNs)are a promising alternative to traditional moment-based track reconstruction approaches.However,the hexagon...Track reconstruction algorithms are critical for polarization measurements.Convolutional neural networks(CNNs)are a promising alternative to traditional moment-based track reconstruction approaches.However,the hexagonal grid track images obtained using gas pixel detectors(GPDs)for better anisotropy do not match the classical rectangle-based CNN,and converting the track images from hexagonal to square results in a loss of information.We developed a new hexagonal CNN algorithm for track reconstruction and polarization estimation in X-ray polarimeters,which was used to extract the emission angles and absorption points from photoelectron track images and predict the uncer-tainty of the predicted emission angles.The simulated data from the PolarLight test were used to train and test the hexagonal CNN models.For individual energies,the hexagonal CNN algorithm produced 15%-30%improvements in the modulation factor compared to the moment analysis method for 100%polarized data,and its performance was comparable to that of the rectangle-based CNN algorithm that was recently developed by the Imaging X-ray Polarimetry Explorer team,but at a lower computational and storage cost for preprocessing.展开更多
GPU-based Monte Carlo(MC)simulations are highly valued for their potential to improve both the computational efficiency and accuracy of radiotherapy.However,in proton therapy,these methods often simplify human tissues...GPU-based Monte Carlo(MC)simulations are highly valued for their potential to improve both the computational efficiency and accuracy of radiotherapy.However,in proton therapy,these methods often simplify human tissues as water for nuclear reactions,disregarding their true elemental composition and thereby potentially compromising calculation accuracy.Consequently,this study developed the program g MCAP(GPU-based proton MC Algorithm for Proton therapy),incorporating precise discrete interactions,and established a refined nuclear reaction model(REFINED)that considers the actual materials of the human body.Compared to the approximate water model(APPROX),the REFINED model demonstrated an improvement in calculation accuracy of 3%.In particular,in high-density tissue regions,the maximum dose deviation between the REFINED and APPROX models was up to 15%.In summary,the g MCAP program can efficiently simulate 1 million protons within 1 s while significantly enhancing dose calculation accuracy in high-density tissues,thus providing a more precise and efficient engine for proton radiotherapy dose calculations in clinical practice.展开更多
文摘The development of guidance technology has made it possible for the earth penetration weapons(EPWs)to impact the target repeatedly at a close range. To investigative the damage of single and sequential strike induced by the EPWs, experimental and numerical investigations are carried out in this paper.Firstly, a series of sequential explosion tests are conducted to provide the basic data of the crater size.Then, a numerical model is established to simulate the damage effects of sequential explosions using the meshfree method of Smoothed particle Galerkin. The effectiveness of numerical model is verified by comparison with the experimental results. Finally, based on dimensional analysis, several empirical formulas for describing the crater size are presented, including the conical crater diameter and the conical crater depth of the single explosion, the conical crater area and the joint depth of the secondary explosion. The formula for the single explosion expresses the relationship between the aspect ratio of the charge ranging from 3 to 7, the dimensionless buried depth ranging from 2 to 14 and the crater size. The formula for the secondary explosion expresses the relationship between the relative position of the two explosions and the crater size. All of data can provide reference for the design of protective structures.
基金supported by the National Key Research and Development Program(No.2022YFC2402300)。
文摘Industrial linear accelerators often contain many bunches when their pulse widths are extended to microseconds.As they typically operate at low electron energies and high currents,the interactions among bunches cannot be neglected.In this study,an algorithm is introduced for calculating the space charge force of a train with infinite bunches.By utilizing the ring charge model and the particle-in-cell(PIC)method and combining analytical and numerical methods,the proposed algorithm efficiently calculates the space charge force of infinite bunches,enabling the accurate design of accelerator parameters and a comprehensive understanding of the space charge force.This is a significant improvement on existing simulation software such as ASTRA and PARMELA that can only handle a single bunch or a small number of bunches.The PIC algorithm is validated in long drift space transport by comparing it with existing models,such as the infinite-bunch,ASTRA single-bunch,and PARMELA several-bunch algorithms.The space charge force calculation results for the external acceleration field are also verified.The reliability of the proposed algorithm provides a foundation for the design and optimization of industrial accelerators.
基金supported by the National Natural Science Foundation of China(Grant No.12175183)。
文摘Gamma-ray imaging systems are powerful tools in radiographic diagnosis.However,the recorded images suffer from degradations such as noise,blurring,and downsampling,consequently failing to meet high-precision diagnostic requirements.In this paper,we propose a novel single-image super-resolution algorithm to enhance the spatial resolution of gamma-ray imaging systems.A mathematical model of the gamma-ray imaging system is established based on maximum a posteriori estimation.Within the plug-and-play framework,the half-quadratic splitting method is employed to decouple the data fidelit term and the regularization term.An image denoiser using convolutional neural networks is adopted as an implicit image prior,referred to as a deep denoiser prior,eliminating the need to explicitly design a regularization term.Furthermore,the impact of the image boundary condition on reconstruction results is considered,and a method for estimating image boundaries is introduced.The results show that the proposed algorithm can effectively addresses boundary artifacts.By increasing the pixel number of the reconstructed images,the proposed algorithm is capable of recovering more details.Notably,in both simulation and real experiments,the proposed algorithm is demonstrated to achieve subpixel resolution,surpassing the Nyquist sampling limit determined by the camera pixel size.
基金supported by the National Natural Science Foundation of China(No.U23B2067)Innovation Program of CAEP(No.CX20210045)。
文摘In response to the demand for rapid geometric modeling in Monte Carlo radiation transportation calculations for large-scale and complex geometric scenes,functional improvements,and algorithm optimizations were performed using CAD-to-Monte Carlo geometry conversion(CMGC)code.Boundary representation(BRep)to constructive solid geometry(CSG)conversion and visual CSG modeling were combined to address the problem of non-convertible geometries such as spline surfaces.The splitting surface assessment method in BRep-to-CSG conversion was optimized to reduce the number of Boolean operations using an Open Cascade.This,in turn,reduced the probability of CMGC conversion failure.The auxiliary surface generation algorithm was optimized to prevent the generation of redundant auxiliary surfaces that cause an excessive decomposition of CAD geometry solids.These optimizations enhanced the usability and stability of the CMGC model conversion.CMGC was applied successfully to the JMCT transportation calculations for the conceptual designs of five China Fusion Engineering Test Reactor(CFETR)blankets.The rapid replacement of different blanket schemes was achieved based on the baseline CFETR model.The geometric solid number of blankets ranged from hundreds to tens of thousands.The correctness of the converted CFETR models using CMGC was verified through comparisons with the MCNP calculation results.The CMGC supported radiation field evaluations for a large urban scene and detailed ship scene.This enabled the rapid conversion of CAD models with thousands of geometric solids into Monte Carlo CSG models.An analysis of the JMCT transportation simulation results further demonstrated the accuracy and effectiveness of the CMGC.
基金supported by National Natural Science Foundation of China(Nos.12027811 and 12275222)。
文摘The cylindrical virtual cathode reflex triode is a new type of pulsed hard X-ray load,which has the advantages of simple structure,high radiation conversion efficiency,and simplicity in seriesparallel operation.This paper presents a method to reduce the impedance of the triode using a multiring cathode.The average electric field on the ring-cathode emission surface is enhanced due to edge effect,and the beam intensity is greatly increased in proportion to the square of the electric field strength.Multi-ring cathode is used to enlarge the emission area.Therefore,the reflex triode can work at lower impedance and generate a stronger beam under the same anode-cathode gap.In addition,the electric field enhancement of the cathode reduces the cathode emission stabilization time and enhances the operation stability of the triode.The effects of parameters such as ring width and ring gap on the triode impedance are simulated and studied.The cathode emission stabilization time and the X-ray conversion efficiency are compared.The design basis of cathode structure parameters and the impedance control method of the cylindrical virtual cathode reflex triode are given according to the simulations.
文摘Stripping injection overcomes the limitations of Liouville's theorem and is widely used for beam injection and accumulation in high-intensity synchrotrons.The interaction between the stripping foil and beam is crucial in the study of stripping injection,particularly in low-energy stripping injection synchrotrons,such as the XiPAF synchrotron.The foil thickness is the main parameter that affects the properties of the beam after injection.The thin stripping foil is reinforced with collodion during its installation.However,the collodion on the foil surface makes it difficult to determine its equivalent thickness,because the mechanical measurements are not sufficiently reliable or convenient for continuously determining foil thickness.We propose an online stripping foil thickness measurement method based on the ionization energy loss effect,which is suitable for any foil thickness and does not require additional equipment.Experimental studies were conducted using the XiPAF synchrotron.The limitation of this method was examined,and the results were verified by comparing the experimentally obtained beam current accumulation curves with the simulation results.This confirms the accuracy and reliability of the proposed method for measuring the stripping foil thickness.
基金supported by the National Natural Science Foundation of China(Nos.11927901,11875301,11875302,U1867214,U1832105,U1832167)the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDB34000000)+2 种基金the National Key R&D Program of China(No.2018YFE0205200)the CAS"Light of West China"Programthe Tsinghua University Initiative Scientific Research Program。
文摘A half-size prototype of the multi wire drift chamber for the cooling storage ring external-target experiment(CEE)was assembled and tested in the 350 MeV/u Kr+Fe reactions at the heavy-ion research facility in Lanzhou.The prototype consists of six sense layers,where the sense wires are stretched in three directions X,U,and V;meeting 0?,30?,and-30?,respectively,with respect to the vertical axis.The sensitive area of the prototype is 76 cm×76 cm.The amplified and shaped signals from the anode wires were digitized in a serial capacity array.When operating at a high voltage of 1500 V on the anode wires,the efficiency for each layer is greater than 95%.The tracking residual is approximately 301±2μm.This performance satisfies the requirements of CEE.
基金National Key Research and Development Program of China(No.2022YFA1604900)National Natural Science Foundation of China(No.12025501)Strategic Priority Research Program of Chinese Academy of Sciences(No.XDB34000000)。
文摘In the paper,we discuss the development of the multigap resistive plate chamber time-of-fight(TOF)technology and the production of the solenoidal tracker at RHIC(STAR)TOF detector in China at the beginning of the twenty-frst century.Subsequently,recent experimental results from the frst beam energy scan program(BES-I)at the Relativistic Heavy Ion Collider(RHIC)pertaining to measurements of collectivity,chirality,criticality,global polarization,strangeness,heavy favor,dilepton and light nuclei productions are reviewed.
文摘Since the first demonstrations of nuclear magnetic resonance (NMR) in condensed matter in 1946, the field of NMR has yielded a continuous flow of conceptual advances and methodological innovations that continues today. Much progress has been made in the utilization of solid-state NMR to illuminate molecular structure and dynamics in systems not controllable by any other way. NMR deals with time-dependent perturbations of nuclear spin systems and solving the time-dependent Schrodinger equation is a central problem in quantum physics in general and solid-state NMR in particular. This theoretical perspective outlines the methods used to treat theoretical problems in solid-state NMR as well as the recent theoretical development of spin dynamics in NMR and physics. The purpose of this review is to unravel the versatility of theories in solid-state NMR and to present the recent theoretical developments of spin dynamics.
基金supported by National Natural Science Foundation of China (No. 12075132)。
文摘The key plasma parameters under different discharge modes, such as heavy-particle and electron temperatures, electron number density, and nonequilibrium volume of plasmas, play important roles in various applications of gas discharge plasmas. In this study, a self-consistent two-dimensional nonequilibrium fluid model coupled with an external circuit model is established to reveal the mechanisms related to the discharge modes, including the normal glow, abnormal glow,arc, and glow-to-arc transition modes, with an atmospheric-pressure direct-current(DC) argon discharge as a model plasma system. The modeling results show that, under different discharge modes, the most significant difference between the preceding four discharge modes lies in the current and energy transfer processes on the cathode side. On one hand, the current to the cathode surface is mainly delivered by the ions coming from the plasma column under the glow discharge mode due to the low temperature of the solid cathode, whereas the thermionic and secondary electrons emitted from the hot cathode surface play a very important role under the arc mode with a higher cathode surface temperature and higher ion flux toward the cathode. On the other hand, the energy transfer channel on the cathode side changes from mainly heating the solid cathode under the glow mode to simultaneously heating both the solid cathode and plasma column under the arc mode with an increase in the discharge current. Consequently, the power density in the cathode sheath(P_c) was used as a key parameter for judging different discharge modes, and the range of(0.28–1.2) × 10^(12) W m^(-3) was determined as a critical window of P_c corresponding to the glow-to-arc-mode transition for the atmospheric-pressure DC argon discharge, which was also verified by comparison with the experimental results in this study and the data in the previous literature.
基金Project supported by the National Natural Science Foundation of China(Grant No.71603146).
文摘Pedestrian self-organizing movement plays a significant role in evacuation studies and architectural design.Lane formation,a typical self-organizing phenomenon,helps pedestrian system to become more orderly,the majority of following behavior model and overtaking behavior model are imprecise and unrealistic compared with pedestrian movement in the real world.In this study,a pedestrian dynamic model considering detailed modelling of the following behavior and overtaking behavior is constructed,and a method of measuring the lane formation and pedestrian system order based on information entropy is proposed.Simulation and analysis demonstrate that the following and avoidance behaviors are important factors of lane formation.A high tendency of following results in good lane formation.Both non-selective following behavior and aggressive overtaking behavior cause the system order to decrease.The most orderly following strategy for a pedestrian is to overtake the former pedestrian whose speed is lower than approximately 70%of his own.The influence of the obstacle layout on pedestrian lane and egress efficiency is also studied with this model.The presence of a small obstacle does not obstruct the walking of pedestrians;in contrast,it may help to improve the egress efficiency by guiding the pedestrian flow and mitigating the reduction of pedestrian system orderliness.
文摘The four-color three-step selective photoionization process of atom is very important in laser isotope separation technology.The population trapping phenomena and their influences are studied theoretically in monochromatic and non-monochromatic laser fields based on the density matrix theory in this work.Time evolutions of the photoionization properties of the four-color,three-step process are given.The population trapping effects occur intensely in monochromatic excitation,while it gradually turns weak as the laser bandwidth increases.The effects of bandwidth,Rabi frequency,time delay,and frequency detuning on the population trapping effect are investigated in monochromatic and non-monochromatic laser fields.The effects of laser process parameters and atomic parameters on the effective selective photoionization are also discussed.The ionization probability and selectivity factors,as evaluation indexes,are difficult to improve synchronously by adjusting systematic parameters.Besides,the existence of metastable state may play a negative role when its population is low enough.
基金Project supported by National Key Research and Development Program of China(Grant Nos.2022YFC3320800 and 2021YFC1523500)the National Natural Science Foundation of China(Grant Nos.71971126,71673163,72304165,72204136,and 72104123).
文摘An accurate assessment of the evacuation efficiency in case of disasters is of vital importance to the safety design of buildings and street blocks.Hazard sources not only physically but psychologically affect the pedestrians,which may further alter their behavioral patterns.This effect is especially significant in narrow spaces,such as corridors and alleys.This study aims to integrate a non-spreading hazard source into the social force model following the results from a previous experiment and simulation,and to simulate unidirectional pedestrian flows over various crowd densities and clarity–intensity properties of the hazard source.The integration include a virtual repulsion force from the hazard source and a decay on the social force term.The simulations reveal(i)that the hazard source creates virtual bottlenecks that suppress the flow,(ii)that the inter-pedestrian push forms a stabilisation phase on the flow-density curve within medium-to-high densities,and(iii)that the pedestrians are prone to a less orderly and stable pattern of movement in low clarity–intensity scenarios,possibly with lateral collisions passing the hazard source.
基金Project supported by the National Natural Science Foundation of China(Grant No.72274208)。
文摘In recent years,attacks against crowded places such as campuses and theaters have had a frequent and negative impact on the security and stability of society.In such an event,the crowd will be subjected to high psychological stress and their emotions will rapidly spread to others.This paper establishes the attack-escape evacuation simulation model(AEES-SFM),based on the social force model,to consider emotion spreading under attack.In this model,(1)the attack-escape driving force is considered for the interaction between an attacker and evacuees and(2)emotion spreading among the evacuees is considered to modify the value of the psychological force.To validate the simulation,several experiments were carried out at a university in China.Comparing the simulation and experimental results,it is found that the simulation results are similar to the experimental results when considering emotion spreading.Therefore,the AEES-SFM is proved to be effective.By comparing the results of the evacuation simulation without emotion spreading,the emotion spreading model reduces the evacuation time and the number of casualties by about 30%,which is closer to the real experimental results.The results are still applicable in the case of a 40-person evacuation.This paper provides theoretical support and practical guidance for campus response to violent attacks.
基金supported partially by a grant from NNSFC No.12027811.
文摘Multiaxial neutron/x-ray imaging and three-dimensional (3D) reconstruction techniques play a crucial role in gaining valuable insights intothe generation and evolution mechanisms of pulsed radiation sources. Owing to the short emission time (∼200 ns) and drastic changes of thepulsed radiation source, it is necessary to acquire projection data within a few nanoseconds in order to achieve clear computed tomography3D imaging. As a consequence, projection data that can be used for computed tomography image reconstruction at a certain moment are oftenavailable for only a few angles. Traditional algorithms employed in the process of reconstructing 3D images with extremely incomplete datamay introduce significant distortions and artifacts into the final image. In this paper, we propose an iterative image reconstruction methodusing cylindrical harmonic decomposition and a self-supervised denoising network algorithm based on the deep image prior method. Weaugment the prior information with a 2D total variation prior and a 3D deep image prior. Single-wire Z-pinch imaging experiments have beencarried out at Qin-1 facility in five views and four frames, with a time resolution of 3 ns for each frame and a time interval of 40 ns betweenadjacent frames. Both numerical simulations and experiments verify that our proposed algorithm can achieve high-quality reconstructionresults and obtain the 3D intensity distribution and evolution of extreme ultraviolet and soft x-ray emission from plasma.
基金supported by the National Natural Science Foundation of China(No.12005017).
文摘High-purity germanium(HPGe)detectors,which are used for direct dark matter detection,have the advantages of a low threshold and excellent energy resolution.The surface passivation of HPGe has become crucial for achieving an extremely low energy threshold.In this study,first-principles simulations,passivation film preparation,and metal oxide semiconductor(MOS)capacitor characterization were combined to study surface passivation.Theoretical calculations of the energy band structure of the -H,-OH,and -NH_(2) passivation groups on the surface of Ge were performed,and the interface state density and potential with five different passivation groups with N/O atomic ratios were accurately analyzed to obtain a stable surface state.Based on the theoretical calculation results,the surface passivation layers of the Ge_(2)ON_(2) film were prepared via magnetron sputtering in accordance with the optimum atomic ratio structure.The microstructure,C-V,and I-V electrical properties of the layers,and the passivation effect of the Al/Ge_(2)ON_(2)/Ge MOS were characterized to test the interface state density.The mean interface state density obtained by the Terman method was 8.4×10^(11) cm^(-2) eV^(-1).The processing of germanium oxynitrogen passivation films is expected to be used in direct dark matter detection of the HPGe detector surface passivation technology to reduce the detector leakage currents.
基金supported by National Natural Science Foundation of China(Nos.12105087,12275096,and 11922503)the Joint Funds of the National Natural Science Foundation of China(No.U21A20440)the Science and Technology Planning Project of Sichuan Province(No.2023YFG0139)。
文摘The Doppler backscattering(DBS)diagnostic is widely used to measure the localized density fluctuations and the propagation velocity of turbulent structures.Microwave is launched at a frequency that approaches a cutoff layer in the plasma at an angle oblique to the cutoff layer.A new Q-band multichannel DBS system based on a comb generator has been designed and tested for application on the HL-3 tokamak.With the comb generator and heterodyne scheme,the stability and flexibility of the new DBS system are improved.The new DBS diagnostic has a high output power(~10 dBm),good power flatness(<5 dB in Q-band),and frequency stability,and the inter-frequency separation is tunable remotely.This article introduces the system design,laboratory test results,and initial experimental results from the HL-3 tokamak.With the help of the newly developed multichannel DBS,the turbulence information can be studied with high temporal and spatial resolution.
基金supported by the National Natural Science Foundation of China(No.12025301)the Tsinghua University Initiative Scientific Research Program.
文摘Track reconstruction algorithms are critical for polarization measurements.Convolutional neural networks(CNNs)are a promising alternative to traditional moment-based track reconstruction approaches.However,the hexagonal grid track images obtained using gas pixel detectors(GPDs)for better anisotropy do not match the classical rectangle-based CNN,and converting the track images from hexagonal to square results in a loss of information.We developed a new hexagonal CNN algorithm for track reconstruction and polarization estimation in X-ray polarimeters,which was used to extract the emission angles and absorption points from photoelectron track images and predict the uncer-tainty of the predicted emission angles.The simulated data from the PolarLight test were used to train and test the hexagonal CNN models.For individual energies,the hexagonal CNN algorithm produced 15%-30%improvements in the modulation factor compared to the moment analysis method for 100%polarized data,and its performance was comparable to that of the rectangle-based CNN algorithm that was recently developed by the Imaging X-ray Polarimetry Explorer team,but at a lower computational and storage cost for preprocessing.
文摘GPU-based Monte Carlo(MC)simulations are highly valued for their potential to improve both the computational efficiency and accuracy of radiotherapy.However,in proton therapy,these methods often simplify human tissues as water for nuclear reactions,disregarding their true elemental composition and thereby potentially compromising calculation accuracy.Consequently,this study developed the program g MCAP(GPU-based proton MC Algorithm for Proton therapy),incorporating precise discrete interactions,and established a refined nuclear reaction model(REFINED)that considers the actual materials of the human body.Compared to the approximate water model(APPROX),the REFINED model demonstrated an improvement in calculation accuracy of 3%.In particular,in high-density tissue regions,the maximum dose deviation between the REFINED and APPROX models was up to 15%.In summary,the g MCAP program can efficiently simulate 1 million protons within 1 s while significantly enhancing dose calculation accuracy in high-density tissues,thus providing a more precise and efficient engine for proton radiotherapy dose calculations in clinical practice.
