Global hybrid simulations of soft X-ray emissions in the Earth’s magnetosheath

Earth’s magnetopause is a thin boundary separating the shocked solar wind plasma from the magnetospheric plasmas,and it is also the boundary of the solar wind energy transport to the magnetosphere.Soft X-ray imaging allows investigation of the large-scale magnetopause by providing a two-dimensional(2-D)global view from a satellite.By performing 3-D global hybrid-particle-in-cell(hybrid-PIC)simulations,we obtain soft X-ray images of Earth’s magnetopause under different solar wind conditions,such as different plasma densities and directions of the southward interplanetary magnetic field.In all cases,magnetic reconnection occurs at low latitude magnetopause.The soft X-ray images observed by a hypothetical satellite are shown,with all of the following identified:the boundary of the magnetopause,the cusps,and the magnetosheath.Local X-ray emissivity in the magnetosheath is characterized by large amplitude fluctuations(up to 160%);however,the maximum line-of-sight-integrated X-ray intensity matches the tangent directions of the magnetopause well,indicating that these fluctuations have limited impact on identifying the magnetopause boundary in the X-ray images.Moreover,the magnetopause boundary can be identified using multiple viewing geometries.We also find that solar wind conditions have little effect on the magnetopause identification.The Solar wind Magnetosphere Ionosphere Link Explorer(SMILE)mission will provide X-ray images of the magnetopause for the first time,and our global hybrid-PIC simulation results can help better understand the 2-D X-ray images of the magnetopause from a 3-D perspective,with particle kinetic effects considered.

Hybrid-Vlasov simulation of soft X-ray emissions at the Earth’s dayside magnetospheric boundaries

Solar wind charge exchange produces emissions in the soft X-ray energy range which can enable the study of near-Earth space regions such as the magnetopause,the magnetosheath and the polar cusps by remote sensing techniques.The Solar wind Magnetosphere Ionosphere Link Explorer(SMILE)and Lunar Environment heliospheric X-ray Imager(LEXI)missions aim to obtain soft Xray images of near-Earth space thanks to their Soft X-ray Imager(SXI)instruments.While earlier modeling works have already simulated soft X-ray images as might be obtained by SMILE SXI during its mission,the numerical models used so far are all based on the magnetohydrodynamics description of the space plasma.To investigate the possible signatures of ion-kinetic-scale processes in soft Xray images,we use for the first time a global hybrid-Vlasov simulation of the geospace from the Vlasiator model.The simulation is driven by fast and tenuous solar wind conditions and purely southward interplanetary magnetic field.We first produce global X-ray images of the dayside near-Earth space by placing a virtual imaging satellite at two different locations,providing meridional and equatorial views.We then analyze regional features present in the images and show that they correspond to signatures in soft X-ray emissions of mirrormode wave structures in the magnetosheath and flux transfer events(FTEs)at the magnetopause.Our results suggest that,although the time scales associated with the motion of those transient phenomena will likely be significantly smaller than the integration time of the SMILE and LEXI imagers,mirror-mode structures and FTEs can cumulatively produce detectable signatures in the soft X-ray images.For instance,a local increase by 30%in the proton density at the dayside magnetopause resulting from the transit of multiple FTEs leads to a 12%enhancement in the line-of-sight-and time-integrated soft X-ray emissivity originating from this region.Likewise,a proton density increase by 14%in the magnetosheath associated with mirror-mode structures can result in an enhancement in the soft X-ray signal by 4%.These are likely conservative estimates,given that the solar wind conditions used in the Vlasiator run can be expected to generate weaker soft X-ray emissions than the more common denser solar wind.These results will contribute to the preparatory work for the SMILE and LEXI missions by providing the community with quantitative estimates of the effects of small-scale,transient phenomena occurring on the dayside.

Two Monte Carlo-based simulators for imaging-system modeling and projection simulation of flat-panel X-ray source

The advantages of a flat-panel X-ray source(FPXS)make it a promising candidate for imaging applications.Accurate imaging-system modeling and projection simulation are critical for analyzing imaging performance and resolving overlapping projection issues in FPXS.The conventional analytical ray-tracing approach is limited by the number of patterns and is not applicable to FPXS-projection calculations.However,the computation time of Monte Carlo(MC)simulation is independent of the size of the patterned arrays in FPXS.This study proposes two high-efficiency MC projection simulators for FPXS:a graphics processing unit(GPU)-based phase-space sampling MC(gPSMC)simulator and GPU-based fluence sampling MC(gFSMC)simulator.The two simulators comprise three components:imaging-system modeling,photon initialization,and physical-interaction simulations in the phantom.Imaging-system modeling was performed by modeling the FPXS,imaging geometry,and detector.The gPSMC simulator samples the initial photons from the phase space,whereas the gFSMC simulator performs photon initialization from the calculated energy spectrum and fluence map.The entire process of photon interaction with the geometry and arrival at the detector was simulated in parallel using multiple GPU kernels,and projections based on the two simulators were calculated.The accuracies of the two simulators were evaluated by comparing them with the conventional analytical ray-tracing approach and acquired projections,and the efficiencies were evaluated by comparing the computation time.The results of simulated and realistic experiments illustrate the accuracy and efficiency of the proposed gPSMC and gFSMC simulators in the projection calculation of various phantoms.

Simulations and software development for the Hard X-ray Imager onboard ASO-S

China’s first solar mission,the Advanced Space-based Solar Observatory(ASO-S),is now changing from Phase B to Phase C.Its main scientific objectives are summarized as’1M2B’,namely magnetic field and two types of bursts(solar flares and coronal mass ejections).Among the three scientific payloads,Hard X-ray Imager(HXI)observes images and spectra of X-ray bursts in solar flares.In this paper,we briefly report on the progresses made by the HXI science team(data and software team)during the design phase(till May 2019).These include simulations of HXI imaging,optimization of HXI grids,development of imaging algorithms,estimation of orbital background,as well as in-orbit calibration plan.These efforts provided guidance for the engineering,improved HXI’s imaging capability and reduced the cost of the instrument.

Orthogonal design and numerical simulation of room and pillar configurations in fractured stopes

Room and pillar sizes are key factors for safe mining and ore recovery in open-stope mining. To investigate the influence of room and pillar configurations on stope stability in highly fractured and weakened areas, an orthogonal design with two factors, three levels and nine runs was proposed, followed by three-dimensional numerical simulation using ANSYS and FLAC3~. Results show that surface settlement after excavation is concentrically ringed, and increases with the decrease of pillar width and distances to stope gobs. In the meantime, the ore-control fault at the ore-rock boundary and the fractured argillaceous dolomite with intercalated slate at the hanging wall deteriorate the roof settlement. Additionally, stope stability is challenged due to pillar rheological yield and stress concentration, and both are induced by redistribution of stress and plastic zones after mining. Following an objective function and a constraint function, room and pillar configuration with widths of 14 m and 16 m, respectively, is presented as the optimization for improving the ore recovery rate while maintaining a safe working environment.

Numerical simulation and method study of X-ray litho-density logging

To effectively replace the isotope radiation source in litho-density logging,this study presents a method for measuring the formation density and photoelectric absorption index(Pe)using a switchable X-ray tube.First,the gamma-ray litho-density logging(GLD)method for measuring formation density and Pe using chemical sources is introduced.Then,a benchmark verification based on the X-ray litho-density logging tool prototype and data published by Simon(In:Paper presented at the SPWLA 59th annual logging symposium,London,UK,2018)was carried out using Monte Carlo numerical simulations.Second,the impacts of the photoelectric effect and detector statistical error on the GLD method were analyzed.Finally,based on a theoretical analysis,the formation density and Pe measurement algorithm(double energy window(DEW)method)was improved,which was found to be suitable for X-ray litho-density logging.Moreover,the results obtained using this algorithm were compared with those obtained using the GLD method.The results indicate that owing to the impact of photoelectric effect and detector statistical error on the density energy window,the accuracy of formation density and Pe measurement using the GLD method is relatively low,with the uncertainty in formation density and Pe measurement reaching 2.620±0.047 g/cm3 and 4.090±0.580 b/e,respectively.In comparison,the DEW method can improve the accuracy of density and Pe measurement to 0.006 g/cm3 and 0.065 b/e,respectively,as the photoelectric effect in the density window is corrected using the counts in the lithology window of the energy spectrum.This study aims to provide a new theoretical foundation for processing X-ray litho-density logs in the future.

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.

2D hydrodynamic simulation of a line-focused plasma in Ni-like Ag x-ray laser research

In most collisional schemes of x-ray laser （XRL） experiments, a bow-like intensity distribution of XRL is often observed, and it is generally ascribed to the two-dimensional hydrodynamic behaviour of expanding plasma. In order to better understand its essence in physics, a newly developed two-dimensional non-equilibrium radiation hydrodynamic code XRL2D is used to simulate a quasi-steady state Ni-like Ag XRL experiment on ShenGuang-Ⅱfacility. The simulation results show that the bow-like distribution of Ni-like ions caused by over-ionization in the central area of plasma is responsible for the bow-like shape of the XRL intensity distribution observed.

Simultaneous fluorescence and Compton scattering computed tomography based on linear polarization X-ray

Purpose To propose a method for simultaneous fluorescence and Compton scattering computed tomography by using linearly polarized X-rays.Methods Monte Carlo simulations were adopted to demonstrate the feasibility of the proposed method.In the simulations,the phantom is a polytetrafluoroethylene cylinder inside which are cylindrical columns containing aluminum,water,and gold(Au)-loaded water solutions with Au concentrations ranging between 0.5 and 4.0 wt%,and a parallel-hole collimator imaging geometry was adopted.The light source was modeled based on a Thomson scattering X-ray source.The phantom images for both imaging modalities were reconstructed using a maximumlikelihood expectation maximization algorithm.Results Both the X-ray fluorescence computed tomography(XFCT)and Compton scattering computed tomography(CSCT)images of the phantom were accurately reconstructed.A similar attenuation contrast problem for the different cylindrical columns in the phantom can be resolved in the XFCT and CSCT images.The interplay between XFCT and CSCT was analyzed,and the contrast-to-noise ratio(CNR)of the reconstruction was improved by correcting for the mutual influence between the two imaging modalities.Compared with K-edge subtraction imaging,XFCT exhibits a CNR advantage for the phantom.Conclusion Simultaneous XFCT and CSCT can be realized by using linearly polarized X-rays.The synergy between the two imaging modalities would have an important application in cancer radiation therapy.

Three-dimensional spatial structure of the macro-pores and flow simulation in anthracite coal based on X-ray μ-CT scanning data

The three-dimensional(3 D) structures of pores directly affect the CH4 flow.Therefore,it is very important to analyze the3 D spatial structure of pores and to simulate the CH4 flow with the connected pores as the carrier.The result shows that the equivalent radius of pores and throats are 1-16 μm and 1.03-8.9 μm,respectively,and the throat length is 3.28-231.25 μm.The coordination number of pores concentrates around three,and the intersection point between the connectivity function and the X-axis is 3-4 μm,which indicate the macro-pores have good connectivity.During the single-channel flow,the pressure decreases along the direction of CH4 flow,and the flow velocity of CH4 decreases from the pore center to the wall.Under the dual-channel and the multi-channel flows,the pressure also decreases along the CH4 flow direction,while the velocity increases.The mean flow pressure gradually decreases with the increase of the distance from the inlet slice.The change of mean flow pressure is relatively stable in the direction horizontal to the bedding plane,while it is relatively large in the direction perpendicular to the bedding plane.The mean flow velocity in the direction horizontal to the bedding plane(Y-axis) is the largest,followed by that in the direction horizontal to the bedding plane(X-axis),and the mean flow velocity in the direction perpendicular to the bedding plane is the smallest.

Three-dimensional finite element simulation and reconstruction of jointed rock models using CT scanning and photogrammetry

The geometry of joints has a significant influence on the mechanical properties of rocks.To simplify the curved joint shapes in rocks,the joint shape is usually treated as straight lines or planes in most laboratory experiments and numerical simulations.In this study,the computerized tomography (CT) scanning and photogrammetry were employed to obtain the internal and surface joint structures of a limestone sample,respectively.To describe the joint geometry,the edge detection algorithms and a three-dimensional (3D) matrix mapping method were applied to reconstruct CT-based and photogrammetry-based jointed rock models.For comparison tests,the numerical uniaxial compression tests were conducted on an intact rock sample and a sample with a joint simplified to a plane using the parallel computing method.The results indicate that the mechanical characteristics and failure process of jointed rocks are significantly affected by the geometry of joints.The presence of joints reduces the uniaxial compressive strength (UCS),elastic modulus,and released acoustic emission (AE) energy of rocks by 37%–67%,21%–24%,and 52%–90%,respectively.Compared to the simplified joint sample,the proposed photogrammetry-based numerical model makes the most of the limited geometry information of joints.The UCS,accumulative released AE energy,and elastic modulus of the photogrammetry-based sample were found to be very close to those of the CT-based sample.The UCS value of the simplified joint sample (i.e.38.5 MPa) is much lower than that of the CT-based sample (i.e.72.3 MPa).Additionally,the accumulative released AE energy observed in the simplified joint sample is 3.899 times lower than that observed in the CT-based sample.CT scanning provides a reliable means to visualize the joints in rocks,which can be used to verify the reliability of photogrammetry techniques.The application of the photogrammetry-based sample enables detailed analysis for estimating the mechanical properties of jointed rocks.

Simulation Study of Quantitative X-Ray Fluorescence Analysis of Ore Slurry Using Partial Least-Squares Regression

X-ray fluorescence （XRF） in combination with partial least-squares （PLS） regression was employed to analyze the ore slurry grade. Using the Monte Carlo simulation code PENELOPE, X-ray fluorescence spectra of ore samples were obtained. Good accuracy was achieved when this method was used to analyze elements with concentrations of several percent or above. It was demonstrated that the more the number of X-ray fluorescence spectra used to calibrate, the better the obtained accuracy. In this method detector resolution was found to have little or no effect on the results of quantitative analysis. The effect of the concentration of water was investigated as well, and it was found to have little influence on the results.

GEANT4 simulation study of over-response phenomenon of fiber x-ray sensor

The purpose of this article is to explore the cause of the over-response phenomenon of fiber x-ray sensor.The sensor is based on a length of PMMA fiber,whose end is filled with the scintillation material Gd_(2)O_(2)S:Tb.The Monte Carlo simulation software GEANT4 uses the phase space file provided by the International Atomic Energy Agency(IAEA),by irradiating the fiber x-ray sensor in the water phantom,counting the fluorescence signal of the optical fiber x-ray sensor after propagation through the fiber.In addition,the number of Cerenkov photons propagating through the fiber is also counted.Comparing this article with previous research,we believe that one of the reasons for the over-response of the fiber x-ray sensor is the non-linear response of the deposition energy of the scintillator to the fluorescence.By establishing a region of interest and counting the x-rays in this region,the simulation results show that the counted number of x-rays that may affect the fiber x-ray sensor is the biggest in the area of interest at a water depth of 5 cm.This result is close to the maximum dose point of the experimental and simulated percentage depth dose(PDD) curve of fiber x-ray sensor.Therefore,the second reason of the over-response phenomenon is believed to be fact that the inorganic materials such as Gd_(2)O_(2)S:Tb have larger effective atomic numbers,so the fiber x-ray sensors will cause more collisions with x-ray in a low energy region of 0.1 MeV-1.5 MeV.

A computer simulation model for room sound field considering diffuse reflection

A multiple random ray tracing model was developed for predicting the distribution of sound pressure levels in an enclosed space of any shape. This model considered two diffuse factors of a room:diffuse reflection due to room surfaces and scattering due to objects. The surface diffusion was treated by two different methods on the basis of probability analysis, and the scattering was simulated by a multiple random ray tracing process. Thus the sound pressure level distribution in a diffuse sound filed can be calculated more precisely.

Computer Simulation and X-ray Diffraction of Nanocrystals

X-ray diffraction of structure in nanocrystalline alpha -Fe and Cu was studied by atomistic simulation. Atomic position equilibrium was reached by using molecular dynamics method to simulate nanocrystalline structure with Finnis potentials to model interatomic interactions. It was found that the boundary component exhibits short-range order, and the distortion in crystalline component increases with the decrease of grain size.

Simulation of X-ray Diffraction Line Broadening Caused by Stress Gradients and Determination of Stress Distribution by Fourier Analysis

Different physical, mechanical and chemical processes, such as： ion implantation, oxidation, nitridation and others create on the surface of materials residual stress state, characterized by high level and strong gradient. X-ray diffraction method widely used for stress measurements has some difficulties in interpretation of experimental data, when the depth of X-ray penetration is compared with thickness of surface layer where inhomogeneous stress distribution is localized. Early it has been shown by authors that diffraction line broadening occurs when analyzed surface is characterized by strong gradient. The interest to study the diffraction line broadening is connected to the possibility of obtaining information about parameters of surface stress distribution. In the present paper the convolution and deconvolution concepts of Fourier analysis were applied to study X ray diffraction line broadening caused by surface stress gradients. Developed methodology allows determining of stress distribution in superficial layers of materials.

IDENTIFICATION AND SIMULATION OF X-RAY POWDER DIFFRACTION PATTERN

A new method for pattern identification and simulation of X-ray powder diffraction data is described, which can give definite phase composition of the unknown rapidly and correctly. The method is implemented in Microsoft Fortran 77 for the IBM PC/XT/AT personal computer or their compatibles.

Numerical simulation of asphalt mixture based on three-dimensional heterogeneous specimen

In order to verify the validity of finite element numerical simulation method for asphalt mixture, which consists of aggregates, mastic （where mastic is a kind of fine mixture composed of asphalt binder mixed with fines and fine aggregates） and air voids, based on three-dimensional （3D） heterogeneous specimen, X-ray computerized tomography （X-ray CT） was used to scan the asphalt specimens to obtain the real internal microstrnctures of asphalt mixture. CT images were reconstructed to build up 3D digital specimen, and the viscoelastic properties of mastic were described with Burgers model The uniaxial creep numerical simulations of three different levels of aggregate gradation were conducted. The simulation results agree well with the experimental results. The numerical simulation of asphalt mixture incorporated with real 3D microstructure based on finite element method is a promising application to conduct research of asphalt concrete. Additionally, this method can increase the mechanistic understanding of global viscoelastic properties of asphalt mixtures by linking the real 3D microstructure.

Overlying strata movement of recovering standing pillars with solid backfilling by physical simulation

To analyze the overlying strata movement law of recovering room mining standing pillars with solid backfilling.Physical simulation experiments with sponge and wood as the backfilling simulation material were tested.The results show that:(i) The covering-rock mechanics of the overly strata comes from "two-arch structures + hinged girder + bend beam" to "backfilling material + hinged girder + bent beam" by increasing the fill ratio from 0%to 85%,the beginning of overlying strata movement appears later and the total duration of subsidence velocity increased from zero to the highest value increases.The trend of "single polarization" of the subsidence velocity curves becomes noticeable and the velocity variation trend becomes stable,(ii) The equiponderate aeolian sand was added to improve the anti-pressure ability of the loess,and the corresponding ground processing & transportation system was designed.

Personalized cardiovascular intervention simulation system

Background This study proposes a series of geometry and physics modeling methods for personalized cardiovascular intervention procedures,which can be applied to a virtual endovascular simulator.Methods Based on personalized clinical computed tomography angiography(CTA)data,mesh models of the cardiovascular system were constructed semi-automatically.By coupling 4 D magnetic resonance imaging(MRI)sequences corresponding to a complete cardiac cycle with related physics models,a hybrid kinetic model of the cardiovascular system was built to drive kinematics and dynamics simulation.On that basis,the surgical procedures related to intervention instruments were simulated using specially-designed physics models.These models can be solved in real-time;therefore,the complex interactions between blood vessels and instruments can be well simulated.Additionally,X-ray imaging simulation algorithms and realistic rendering algorithms for virtual intervention scenes are also proposed.In particular,instrument tracking hardware with haptic feedback was developed to serve as the interaction interface of real instruments and the virtual intervention system.Finally,a personalized cardiovascular intervention simulation system was developed by integrating the techniques mentioned above.Results This system supported instant modeling and simulation of personalized clinical data and significantly improved the visual and haptic immersions of vascular intervention simulation.Conclusions It can be used in teaching basic cardiology and effectively satisfying the demands of intervention training,personalized intervention planning,and rehearsing.