Geant4 simulation of fast-electron bremsstrahlung imaging at the HL-3 tokamak

To further research on high-parameter plasma,we plan to develop a two-dimensional hard X-ray(HXR)imaging system at the HL-3 tokamak to measure HXRs with energies ranging from 20 to 300 keV.The application of an array-structured detector ensures that this system can measure HXR-radiation spectra from the entire plasma cross section.Therefore,it is suitable for the study of fast-electron physics,such as radio-frequency wave current drives,fast electrons driving instabilities,and plasma disruptions in fusion research.In this study,we develop a simulation for calculating fast-electron bremsstrahlung in the HL-3 tokamak based on the Monte Carlo simulation code Geant4,in which the plasma geometry and forward scattering of fast-electron bremsstrahlung are considered.The preliminary calculation results indicate that the HXR energy deposi-tion on the detector is symmetrically distributed,even though the plasma distribution is asymmetric owing to the toroidal effect.These simulation results are helpful in constructing the relationship between the energy deposition on the detector and parameter distribution on the plasma cross section during HL-3 experiments.This is beneficial for the reconstruction of the fast-electron-distribution function and for optimizing the design of the HXR-imaging system.

A COMPUTER CODE FASTOR-3D FOR TRANSIENT THREE-DIMENSIONAL SIMULATION ON FLOW AND HEAT TRANS-FER WITH POROSITY APPROXIMATION

Upon the conservation of mass, momentum and energy, volume fraction and surface penetrative rate were employed to modify the conservative equations to simulate the effect of blockages on fluid flows and heat transfer. These equations were solved numerically with the finite differential method and the primitive variable approach. This method uses staggered grid and pressure correction schemes. A computer code FASTOR3D integrated the aforementioned algorithm. The preliminary results have been compared with conventional benchmark solutions. With auxiliary software DV, the numerical results were visualized in colorful images to demonstrate the variation of flow patterns and temperature profiles during the transient process. The results of the simulation code for the fluid flows and heat transfer in the sodium pool of a fast breeder reactor are acceptable.

Molecular dynamics simulation of relationship between local structure and dynamics during glass transition of Mg_7Zn_3 alloy

The rapid solidification process of Mg7Zn3 alloy was simulated by the molecular dynamics method. The relationship between the local structure and the dynamics during the liquid-glass transition was deeply investigated. It was found that the Mg-centered FK polyhedron and the Zn-centered icosahedron play a critical role in the formation of Mg7Zn3 metallic glass. The self-diffusion coefficients of Mg and Zn atoms deviate from the Arrhenius law near the melting temperature and then satisfy the power law. According to the time correlation functions of mean-square displacement, incoherent intermediate scattering function and non-Gaussian parameter, it was found that the β-relaxation in Mg7Zn3 supercooled liquid becomes more and more evident with decreasing temperature, and the α-relaxation time rapidly increases in the VFT law. Moreover, the smaller Zn atom has a faster relaxation behavior than the Mg atom. Some local atomic structures with short-range order have lower mobility, and they play a critical role in the appearance of cage effect in theβ-relaxation regime. The dynamics deviates from the Arrhenius law just at the temperature as the number of local atomic structures begins to rapidly increase. The dynamic glass transition temperature （Tc） is close to the glass transition point in structure （TgStr）.

Material driven workability simulation by FEM including 3D processing maps for magnesium alloy

The three-dimensional （3D） processing maps considering strain based on the two-dimensional （2D） processing maps proposed by PRASAD can describe the distribution of the efficiency of power dissipation and flow instability regions at various temperatures, strain rates and strains, which exhibit intrinsic workability related to material itself. Finite element （FE） simulation can obtain the distribution of strain, strain rate, temperature and die filling status, which indicates state-of-stress （SOS） workability decided by die shape and different processing conditions. On the basis of this, a new material driven analysis method for hot deformation was put forward by the combination of FE simulation with 3D processing maps, which can demonstrate material workability of the entire hot deformation process including SOS workability and intrinsic workability. The hot forging process for hard-to-work metal magnesium alloy was studied, and the 3D thermomechanical FE simulation including 3D processing maps of complex hot forging spur bevel gear was first conducted. The hot forging experiments were carried out. The results show that the new method is reasonable and suitable to determine the aoorooriate nrocess narameters.

3-D Simulation of FINFET

An SOI MOSFET with FINFET structure is simulated using a 3 D simulator. I V characteristics and sub threshold characteristics,as well as the short channel effect(SCE) are carefully investigated.SCE can be well controlled by reducing fin height.Good performance can be achieved with thin height,so fin height is considered as a key parameter in device design.Simulation results show that FINFETs present performance superior to conventional single gate devices.

Using 3D TCAD Simulation to Study Charge Collection of a p-n Junction in a 0.18μm Bulk Process

Single event transient of a real p-n junction in a 0.18μm bulk process is studied by 3D TCAD simulation. The impact of voltage, temperature, substrate concentration, and LET on SET is studied. Our simulation results demonstrate that biases in the range 1.62 to 1.98V influence DSET current shape greatly and total collected charge weakly. Peak current and charge collection within 2ns decreases as temperature increases,and temperature has a stronger influence on SET currents than on total charge. Typical variation of substrate concentration in modern VDSM processes has a negligible effect on SEEs. Both peak current and total collection charge increases as LET increases.

基于SolidWorks Simulation的3D打印机机体静力学分析

近年来,3D打印机作为一种高效率的成型设备被广泛的使用,然而,其高速性、高精度与高可靠性与其机体的轻量化设计存在一定的矛盾关系。通过SolidWorks软件对3D打印机机体进行轻量化设计,并使用集成的Simulation仿真软件对设计模型进行快速静态力学分析,参照仿真结果对轻量化设计的模型进行验证与优化。通过集成化的三维建模软件和仿真软件,实现了3D打印机的模型设计和模型力学分析,验证了3D打印机设计的合理性和可靠性,为3D打印机的轻量化设计提供理论指导和修改建议,节省设备的研发周期和研发成本。

基于NS-3网络模拟器的MPQUIC协议仿真研究

随着5G移动视频应用加速落地以及国内视频流需求的迅速激增,迫切需要一种新的数据传输协议来提供可靠的安全性,以保障上层应用处理更多的接入连接以及满足更低的延时需求.多路径QUIC协议(Multipath Quick UDP Internet Connection,MPQUIC)具有拟合多条链路带宽资源、强大连接的容错能力和高可靠性等优点,被认为将在未来移动互联网数据传输中发挥重要的作用.然而,目前国内外研究人员对于MPQUIC协议的相关研究正处于初步阶段,该协议还没有一个普适性的、开源的仿真平台.因此,借助全球网络仿真领域应用最广的NS-3网络模拟器搭建了MPQUIC仿真平台(ns3-mpquic),为相关学者提供研究MPQUIC协议的开源、免费、普适的基础平台,为全球专家学者对MPQUIC协议的模拟部署和优化提供助力.

A Parallel Discrete Event Simulation Engine for the Low-Earth-Orbit Satellite Constellation Networks

Low-Earth-Orbit satellite constellation networks(LEO-SCN)can provide low-cost,largescale,flexible coverage wireless communication services.High dynamics and large topological sizes characterize LEO-SCN.Protocol development and application testing of LEO-SCN are challenging to carry out in a natural environment.Simulation platforms are a more effective means of technology demonstration.Currently available simulators have a single function and limited simulation scale.There needs to be a simulator for full-featured simulation.In this paper,we apply the parallel discrete-event simulation technique to the simulation of LEO-SCN to support large-scale complex system simulation at the packet level.To solve the problem that single-process programs cannot cope with complex simulations containing numerous entities,we propose a parallel mechanism and algorithms LP-NM and LP-YAWNS for synchronization.In the experiment,we use ns-3 to verify the acceleration ratio and efficiency of the above algorithms.The results show that our proposed mechanism can provide parallel simulation engine support for the LEO-SCN.

Simulation of 1,3-Butadiene Production Process by Dimethylfomamide Extractive Distillation

Nowadays, extractive distillation is the main technique to produce 1,3-butadiene. This study simulated the 1,3-butadiene production process with DMF extractive distillation by Aspen Plus. The solvent ratio is the most important parameter to the extractive distillation process. The article has given out the proper solvent ratios, reflux ratios, distillate ratios, and bottom product ratios of the columns. It also discusses the thermal loads of several columns. The results of simulation are consequently compared with the plant data, which shows good accordance with each other.

Numerical simulation of 3D-microstructures in solidification processes based on the CAFE method

It was analyzed that the finite element-cellular automaton （CAFE） method was used to simulate 3D-microstructures in solidification processes. Based on this method, the 3D-microstructure of 9SMn28 free-cutting steel was simulated in solidification processes and the simulation results are consistent with the experimental ones. In addition, the effects of Gaussian distribution parameters were also studied. The simulation results show that the higher the mean undercooling, the larger the columnar dendrite zones, and the larger the maximum nucleation density, the smaller the size of grains. The larger the standard deviation, the less the number of minimum grains is. However, the uniformity degree decreases first, and then increases gradually.

Numerical simulation of a combined oxidation ditch flow using 3D k-ε turbulence model

The standard three dimensional（3D） k-ε turbulence model was applied to simulate the flow field of a small scale combined oxidation ditch. The moving mesh approach was used to model the rotor of the ditch. Comparison of the computed and the measured data is acceptable. A vertical reverse flow zone in the ditch was found, and it played a very important role in the ditch flow behavior. The flow pattern in the ditch is discussed in detail, and approaches are suggested to improve the hydrodynamic performance in the ditch.

Surface Air Temperature Simulations over China with CMIP5 and CMIP3

Historical simulations of annual mean surface air temperature over China with 25 CMIP5 models were assessed.The observational data from CRUT3v and CN05 were used and further compared with historical simulations of CMIP3.The results show that CMIP5 models were able to simulate the observed warming over China from 1906 to 2005(0.84 C per 100 years)with a warming rate of 0.77 C per 100 years based on the multi-model ensemble(MME).The simulations of surface air temperature in the late 20th century were much better than those in the early 20th century,when only two models could reproduce the extreme warming in the 1940s.The simulations for the spatial distribution of the 20-yearmean(1986–2005)surface air temperature over China fit relatively well with the observations.However,underestimations in surface air temperature climatology were still found almost all over China,and the largest cold bias and simulation uncertainty were found in western China.On sub-regional scale,northern China experienced stronger warming than southern China during 1961–1999,for which the CMIP5 MME provided better simulations.With CMIP5 the diference of warming trends in northern and southern China was underestimated.In general,the CMIP5 simulations are obviously improved in comparison with the CMIP3 simulations in terms of the variation in regional mean surface air temperature,the spatial distribution of surface air temperature climatology and the linear trends in surface air temperature all over China.

SIMULATION OF 3-D DEFORMATION AND MATERIAL FLOW DURING ROLL FORGING PROCESS USING SYSTEM OF OVAL-ROUND GROOVE

Basing on the analysis of the traits of the roll forging process, a system-model of computer simulation has been established. Three-dimensional rigid-plastic FEM has been used for the simulation of the deformation process in the oval and round pass rolling, including the entering, rolling, and separating stages. The analysis was conducted using the Deform-3D ver.5.0 code. The important information concerned with the deformation area characteristic, material flow, and velocity field has been presented. Otherwise, the location of the neutral plane in the deformation area was shown clearly.

Intrinsic background radiation of LaBr3(Ce)detector via coincidence measurements and simulations

The LaBr3(Ce)detector has attracted much attention in recent years because of its superior characteristics compared with other scintillating materials in terms of resolution and efficiency.However,it has a relatively high intrinsic background radiation because of the naturally occurring radioisotopes in lanthanum,actinium,and their daughter nuclei.This limits its applications in low-counting rate experiments.In this study,we identified the radioactive isotopes in theφ3"x 3"Saint-Gobain B380 detector by a coincidence measurement using a Clover detector in a low-background shielding system.Moreover,we carried out a Geant4 simulation of the experimental spectra to evaluate the activities of the main internal radiation components.The total activity of the background radiation of B380 is determined to be 1.523(34)Bq/cm^3.The main sources include 138La at 1.428(34)Bq/cm^3,207Tl at 0.0135(13)Bq/cm^3,211Bi at 0.0136(15)Bq/cm^3,215Po at 0.0135(3)Bq/cm^3,219Rn at 0.0125(12)Bq/cm^3,223Fr at 0.0019(11)Bq/cm^3,223Ra at 0.0127(10)Bq/cm^3,227Th at 0.0158(22)Bq/cm^3,and 227Ac at 0.0135(13)Bq/cm^3.Of these,the activities of 207Tl,211Po,215Po,223Fr,and 227Ac are deduced for the first time from the secular equilibrium established in the decay chain of 227Ac.

Dynamic simulations of the late MIS 3 transgressions in the East China Sea and southern Yellow Sea,China

Abundant evidences of higher sea levels from Jiangsu and Fujian coasts have proved a marine transgression event during 30–40 ka BP, suggesting that there was a stage with high sea level and a warm climate when ice sheets shrank in the Northern Hemisphere. The duration of 30–40 ka BP spanned a period in the late Marine Isotope Stage 3（MIS 3） and was in nature an interstadial epoch during the Last Glacial period of the Quaternary. Different from the glacial period with a cold climate, this marine transgression considered as a penultimate higher sea level during the Quaternary remains a puzzle that why the evidence is contrary to the Quaternary glacial theory. It is important to understand sea level rise for these areas sensitively responding to the global changes in the future. To recognize the key issues on sea level changes, the eustatic sea level（H_S） was defined as the glaciation-climateforced sea levels, and the relative sea level change（H_R） was defined as that a sea level record was preserved in sediment that experienced multiple secondary actions of land and sea effects. On the basis as defined above, we constructed multi-level models of climate-driven glacio-eustatic changes and land-sea systems. By integrating data sets from eight borehole cores and prescribing the boundary conditions, we simulated the changes of HS and HR in the East China Sea and southern Yellow Sea areas in the late MIS 3. The marine transgression strata from the borehole core data was identified at ca. 30 m below present sea level as a result of the collective influence of ice melting water, neotectonic subsidence, sediment compaction and terrestrial sediment filling since ca. 35 ka ago,whereas the simulated relative sea-levels turned out to be –26.3––29.9 m a.s.l. The small error involved in the simulation results of ±（2.5–4.5） m demonstrated the credibility of the results. Our results indicated that sea level change in the late MIS 3 was dominated by glacial effects, in which the eustatic sea-level was between –19.2––22.1m a.s.l. The study sheds light on the nature of sea-level changes along the east coast of China in the late MIS 3 and contributes to understanding the characteristics of marine transgression under the effects of multiple complex land-sea interactions.

Numerical simulations of full-wave fi elds and analysis of channel wave characteristics in 3-D coal mine roadway models

Currently, numerical simulations of seismic channel waves for the advance detection of geological structures in coal mine roadways focus mainly on modeling two- dimensional wave fields and therefore cannot accurately simulate three-dimensional （3-D） full-wave fields or seismic records in a full-space observation system. In this study, we use the first-order velocity-stress staggered-grid finite difference algorithm to simulate 3-D full-wave fields with P-wave sources in front of coal mine roadways. We determine the three components of velocity Vx, Vy, and Vz for the same node in 3-D staggered-grid finite difference models by calculating the average value of Vy, and Vz of the nodes around the same node. We ascertain the wave patterns and their propagation characteristics in both symmetrical and asymmetric coal mine roadway models. Our simulation results indicate that the Rayleigh channel wave is stronger than the Love channel wave in front of the roadway face. The reflected Rayleigh waves from the roadway face are concentrated in the coal seam, release less energy to the roof and floor, and propagate for a longer distance. There are surface waves and refraction head waves around the roadway. In the seismic records, the Rayleigh wave energy is stronger than that of the Love channel wave along coal walls of the roadway, and the interference of the head waves and surface waves with the Rayleigh channel wave is weaker than with the Love channel wave. It is thus difficult to identify the Love channel wave in the seismic records. Increasing the depth of the receivers in the coal walls can effectively weaken the interference of surface waves with the Rayleigh channel wave, but cannot weaken the interference of surface waves with the Love channel wave. Our research results also suggest that the Love channel wave, which is often used to detect geological structures in coal mine stopes, is not suitable for detecting geological structures in front of coal mine roadways. Instead, the Rayleigh channel wave can be used for the advance detection of geological structures in coal mine roadways.

Device simulation of lead-free CH_3NH_3SnI_3 perovskite solar cells with high efficiency

The lead-free perovskite solar cells(PSCs) have drawn a great deal of research interest due to the Pb toxicity of the lead halide perovskite.CHNHSnIis a viable alternative to CHNHPbX,because it has a narrower band gap of 1.3 eV and a wider visible absorption spectrum than the lead halide perovskite.The progress of fabricating tin iodide PSCs with good stability has stimulated the studies of these CHNHSnIbased cells greatly.In the paper,we study the influences of various parameters on the solar cell performance through theoretical analysis and device simulation.It is found in the simulation that the solar cell performance can be improved to some extent by adjusting the doping concentration of the perovskite absorption layer and the electron affinity of the buffer and HTM,while the reduction of the defect density of the perovskite absorption layer significantly improves the cell performance.By further optimizing the parameters of the doping concentration(1.3 × 10cm~3) and the defect density(1 × 10cm~3) of perovskite absorption layer,and the electron affinity of buffer(4.0 eV) and HTM(2.6 eV),we finally obtain some encouraging results of the Jof 31.59 mA/cm~2,Vof 0.92 V,FF of 79.99%,and PCE of 23.36%.The results show that the lead-free CHNHSnIPSC is a potential environmentally friendly solar cell with high efficiency.Improving the Snstability and reducing the defect density of CHNHSnIare key issues for the future research,which can be solved by improving the fabrication and encapsulation process of the cell.

Numerical Simulation of the Protective Effect of Complex Boundaries Toward Shock Waves in a 3D Explosive Field

A numerical method is presented that simulates 3D explosive field problems. A code MMIC3D using this method can be used to simulate the propagation and reflected effects of all kinds of rigid boundaries to shock waves produced by an explosive source. These numerical results indicate that the code MMIC3D has the ability in computing cases such as 3D shock waves produced by air explosion, vortex region of the shock wave, the Mach wave, and reflected waves behind rigid boundaries.

Prediction and Simulation of Microstructure of Ti-15-3 Alloy

Ti-15-3 alloy is a new metastableβ-type titanium. The influence of hot deformation parameters on the microstructureof Ti-15-3 alloy after solution treatment has been studied by isothermal compression tests as well as quantitativemetallographic analysis. On the basis of the data obtained from the tests, predicting models for equivalent grainsize and recrystallization volume fraction have been established with an artificial neural network method. An FEnumerical simulation system has been developed to simulate the distribution of microstructure in Ti-15-3 alloy afterhot back extrusion and solution treatment by combining the neural network model with thermal-mechanical coupledrigid-viscoplastic FE model. Corresponding experimental research is performed. The agreement of the simulatedresults with measured ones shows that the simulation system is reliable.