- 标题
- 摘要
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A Functional Expansion Tally Method for Gray Radiative Transfer Equations in Implicit Monte Carlo
摘要： The Implicit Monte Carlo (IMC) method is widely used for solving the nonlinear thermal radiative transport problems. This method often exhibits teleportation error in problems with strong coupling between radiation and matter. In this article, we propose a new Legendre functional expansion tally method to reduce the teleportation error for gray radiative transfer equations in the IMC method. The piecewise functional expansion tallies of absorbed energy in the previous time step is employed for the distribution of emission energy at the current time step within a cell. Numerical simulations show that our method significantly reduces the teleportation error relative to the source tilting method, and enables the use of lower spatial resolutions that would be required to mitigate the teleportation error using the source tilting method.
关键词： teleportation error,Radiative transfer,implicit Monte Carlo,functional expansion tally
更新于2025-09-23 15:22:29
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Terahertz Differential Computed Tomography: a Relevant Nondestructive Inspection Application
摘要： In recent years, tremendous advances have been made in the choice of materials used in the industry. With weight reduction as the goal, composite and polymer materials are more and more popular but they are almost transparent to X-ray. Because of this, interest has grown in other wavelengths like terahertz (THz). Due to a difference in how X-ray and THz propagate, X-ray CT algorithms cannot be directly used. For example, THz induces refraction making the reconstruction problem nonlinear. In this paper, we present a new algorithm which complies with beam profile intensities, refraction, and reflection. It is based on linearizing the reconstruction process around a computer-aided design (CAD) model of the object to be reconstructed. The method we propose computes the deviation between the object and this model.
关键词： Terahertz computed tomography,Inverse problem,Nondestructive testing,Modeling,Monte Carlo,Refraction,Nonlinear problem,Projection simulation
更新于2025-09-23 15:22:29
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[IEEE 2018 26th European Signal Processing Conference (EUSIPCO) - Rome (2018.9.3-2018.9.7)] 2018 26th European Signal Processing Conference (EUSIPCO) - Bayesian Restoration of High-Dimensional Photon-Starved Images
摘要： This paper investigates different algorithms to perform image restoration from single-photon measurements corrupted with Poisson noise. The restoration problem is formulated in a Bayesian framework and several state-of-the-art Monte Carlo samplers are considered to estimate the unknown image and quantify its uncertainty. The different samplers are compared through a series of experiments conducted with synthetic images. The results demonstrate the scaling properties of the proposed samplers as the dimensionality of the problem increases and the number of photons decreases. Moreover, our experiments show that for a certain photon budget (i.e., acquisition time of the imaging device), downsampling the observations can yield better reconstruction results.
关键词： Bayesian statistics,Markov chain Monte Carlo,Inverse problems,Image processing,Bouncy particle sampler,Poisson noise
更新于2025-09-23 15:22:29
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Assessment of Self-Heating Effects Under Lateral Scaling of GaN HEMTs
摘要： The impact on self-heating mechanisms observed in GaN HEMTs fabricated on Si substrates is studied by means of a cellular Monte Carlo particle-based device simulator. Within this framework, the thermal effects are included through an energy-balance equation for phonons allowing for self-consistently coupling the charge and heat transport. First, the advanced electrothermal model of an experimental device is developed and calibrated to measured dc characteristics, showing an accurate description throughout the IDS(VGS?VDS) space, as a result of capturing the temperature dependence of the scattering processes that modify the charge transport. Then, the model is used to assess the effect of lateral scaling, i.e., reducing the source-to-gate LSG and gate-to-drain LGD dimensions, in terms of detailed temperature maps obtained for the acoustic and optical phonon modes as well as the electric field and carrier velocity profiles. It is found that the hot spot in the channel is not located at the peak electric field as predicted by previous methods, but instead, it is shifted toward the drain up to 32 nm. Furthermore, it is shown that, while scaled devices offer improved dc and small-signal ac performance, they are subjected to temperatures up to 15% higher in the channel as compared to the original nonscaled device when dissipating the same dc power, and the temperature distribution throughout the device shows a strong correlation with the scaled layout.
关键词： reliability,HEMTs,Monte Carlo methods,self-heating,scaling,GaN
更新于2025-09-23 15:22:29
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Dosimetric verification of lung phantom calculated by collapsed cone convolution: A?Monte Carlo and experimental evaluation
摘要： OBJECTIVE: To evaluate the dose calculation accuracy in the Prowess Panther treatment planning system (TPS) using the collapsed cone convolution (CCC) algorithm. METHODS: The BEAMnrc Monte Carlo (MC) package was used to predict the dose distribution of photon beams produced by the Oncor? linear accelerator (linac). The MC model of an 18 MV photon beam was verified by measurement using a p-type diode dosimeter. Percent depth dose (PDD) and dose profiles were used for comparison based on three field sizes: 5 × 5, 10 × 10, and 20 × 20cm2. The accuracy of the CCC dosimetry was also evaluated using a plan composed of a simple parallel-opposed field (11 × 16cm2) in a lung phantom comprised of four tissue simulating media namely, lung, soft tissue, bone and spinal cord. The CCC dose calculation accuracy was evaluated by MC simulation and measurements according to the dose difference and 3D gamma analysis. Gamma analysis was carried out through comparison of the Monte Carlo simulation and the TPS calculated dose. RESULTS: Compared to the dosimetric results measured by the Farmer chamber, the CCC algorithm underestimated dose in the planning target volume (PTV), right lung and lung-tissue interface regions by about –0.11%, –1.6 %, and –2.9%, respectively. Moreover, the CCC algorithm underestimated the dose at the PTV, right lung and lung-tissue interface regions in the order of –0.34%, –0.4% and –3.5%, respectively, when compared to the MC simulation. Gamma analysis results showed that the passing rates within the PTV and heterogeneous region were above 59% and 76%. For the right lung and spinal cord, the passing rates were above 80% for all gamma criteria. CONCLUSIONS: This study demonstrates that the CCC algorithm has potential to calculate dose with sufficient accuracy for 3D conformal radiotherapy within the thorax where a significant amount of tissue heterogeneity exists.
关键词： 3D conformal radiotherapy,Monte Carlo,treatment planning,collapsed cone convolution
更新于2025-09-23 15:22:29
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G4Linac_MT, an easy-to-use Geant4-based code for modeling medical linear accelerator
摘要： In this paper, we present G4Linac_MT, a simple-to-use open source code developed to facilitate the use of the Geant4 C++ toolkit for the simulation of a medical linear accelerator (linac). This multithreaded code encapsulates several well-developed C++ modules serving to handle the complexity of coding geometry and material, to easy plot histograms of various physics quantities, to auto-merge output data created by all working threads into a single file, to well-estimate the number of simulated primary particles required to achieve data with a statistical uncertainty < 1% and also the CPU time required for, to use a set of variance reduction techniques as bremsstrahlung splitting, particle recycling, particle rotational splitting and stacking mechanism, to use a new format of phase space file based on HDF5-C++ scientific library which has been developed specially for this code. In order to minimize human effort required by Geant4 coding and validating of a linac, the code comes with a Java-based GUI application which contains separated GUI modules for linac head simulation, dose calculation, data analysis, geometry modeling and gamma index calculation. Results from Monte Carlo simulations of linac head of a Saturne 43 12 MV configuring a 10 × 10 cm2 radiation field are showed in order to demonstrate the G4Linac_MT capabilities. Thus, comparisons between simulated dosimetric functions and measured ones in a water phantom have been established by using a gamma index method and the results show a good agreement within 2.6%-1 mm accuracy. In addition, after optimizing variance reduction techniques, the overall CPU time spent by this multithreaded code has been decreased by a factor of 7.
关键词： Multi-threading,G4Linac_MT,Monte Carlo,Geant4,Linac
更新于2025-09-23 15:22:29
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[IEEE 2018 International Multi-Conference on Industrial Engineering and Modern Technologies (FarEastCon) - Vladivostok, Russia (2018.10.3-2018.10.4)] 2018 International Multi-Conference on Industrial Engineering and Modern Technologies (FarEastCon) - Numerical Simulation of Low-Coherence Radiation Propagation in Turbid Media and Structural Image Reconstruction in Endoscopic Optical Coherence Tomography with Allowance for Speckle Fluctuations
摘要： A method of Monte Carlo simulation of low-coherence radiation propagation in turbid media with consideration of speckle noise (the result of mutual interference of secondary spherical waves) is described. The process of photon propagation within investigated object, such as biological tissue, includes the following steps: the photon injection, mean free path determination, the verification of the fulfillment of the boundary condition, the absorption and scattering. Structural image reconstruction in optical coherence tomography (OCT) with consideration of speckle fluctuations is made by summation the statistical weight of the beam coming out of the investigated object inside the detector area with the intensity of a series of pixels of the current A-scan. The key feature of the presented method is the description of the investigated object geometry. Three-dimensional array of voxels combined into parallelograms, and the border cross checking is carried out by using an improved Smith algorithm. The described method can be used to obtain high-quality endoscopic structural OCT images of body cavities and tracts (diagnosis of the respiratory tract, cardiovascular system, gastrointestinal tract, genitourinary system, etc.).
关键词： coherence probing depth,Monte Carlo simulation,optical coherence tomography,voxel based model,speckle fluctuations,structural image
更新于2025-09-23 15:22:29
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Monte Carlo Analysis of Orbital Station Motion Parameter Errors Influence on Sar Azimuth Resolution Degradation
摘要： Orbital stations can be an alternative platform choice for SAR payloads besides professional remote sensing satellite platform. However, such platform cannot provide as precision motion parameters as remote sensing satellite platform for SAR imaging due to its unique structure. The influence of motion parameter errors on SAR azimuth resolution degradation should be taken into consideration. Selecting the second order phase error caused by Doppler frequency rate with error as intermediate variable between motion parameter errors and SAR azimuth resolution, this paper proposed a Monte Carlo simulation model has been set up to obtain the specific probability distribution of SAR azimuth resolution degradation. A typical Monte Carlo simulation result is given to show the effectiveness of the method and may help actual SAR payload system design.
关键词： Orbital Station,Monte Carlo,SAR,Azimuth Resolution Degradation,Motion Parameter Errors
更新于2025-09-23 15:22:29
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Uncertainty Analysis and Experimental Design in the Monte Carlo Ray-Trace Environment
摘要： Despite the dominant role of the Monte Carlo ray-trace (MCRT) method in modern radiation heat transfer analysis, the contemporary literature remains surprisingly reticent on the uncertainty of results obtained using it. After first identifying the radiation distribution factor as a population proportion, standard statistical procedures are used to estimate its mean uncertainty, to a stated level of confidence, as a function of the number of surface elements making up the enclosure and the number of rays traced per surface element. This a priori statistical uncertainty is then shown to compare favorably with the observed variability in the distribution factors obtained in an actual MCRT-based analysis. Finally, a formal approach is demonstrated for estimating, to a prescribed level of confidence, the uncertainty in predicted heat transfer. This approach provides a basis for determining the minimum number of rays per surface element required to obtain the desired accuracy.
关键词： Monte Carlo ray-trace,uncertainty analysis,experimental design,radiation heat transfer,distribution factor
更新于2025-09-23 15:22:29
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Half-metallic ferromagnetic behavior in (Ga, Cr)N and (Ga, Cr, V)N compounds for spintronic technologies: Ab-initio and Monte Carlo methods
摘要： In this article, we investigate the magnetic- and electronic-proprieties of GaN doped with simple- and double-impurities utilizing Ab-initio and Monte Carlo studies. We have predicted that (Ga, Cr)N and (Ga, Cr, V)N compounds exhibit ferromagnetic- and halfmetallic-behavior with 100% spin-polarization at the Fermi-level. Moreover, we have found that Ga1-xCrxN and Ga1-2xCrxVxN (x = 0.04, 0.05 and 0.06) show a 2nd order ferromagnetic transition and that their Tc is above room temperature. These predictions make (Ga, Cr)N and (Ga, Cr, V)N compounds strong-candidates for spintronic-technologies.
关键词： Ab-initio calculations,Monte Carlo method,Diluted magnetic semiconductors,Spintronic,Gallium Nitride
更新于2025-09-23 15:22:29