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- 实验方案
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Analysis of Beam Hardening of Modulation Layers for Dual Energy Cone-beam CT
摘要： Dual energy cone-beam CT can distinguish two materials with different atomic compositions. The principle of dual energy cone-beam CT based on modulation layer is that higher energy spectrum can be acquired at blocked x-ray window. To evaluate the possibility of modulation layer based dual energy cone-beam CT, we analyzed x-ray spectrum for various thicknesses of modulation layers by Monte Carlo simulation. To compare with the results of simulation, the experiment was performed on prototype cone-beam CT for 50～100 kVp with CdTe XR-100T detector. As the result of comparing, the mean energy of energy spectrum for 80 kVp are well matched with that of simulation. The mean energy of energy spectrum for 80 and 120 kVp were increased as 1.67 and 1.52 times by 2.0 mm modulation layer, respectively. We realized that the virtual dual energy x-ray source can be generated by modulation layer.
关键词： Dual energy cone-beam CT,Monte Carlo simulation,Beam hardening effect,Modulation layer
更新于2025-09-11 14:15:04
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A simulation tool for better management of retinal services
摘要： Background: Advances in the management of retinal diseases have been fast-paced as new treatments become available, resulting in increasing numbers of patients receiving treatment in hospital retinal services. These patients require frequent and long-term follow-up and repeated treatments, resulting in increased pressure on clinical workloads. Due to limited clinic capacity, many National Health Service (NHS) clinics are failing to maintain recommended follow-up intervals for patients receiving care. As such, clear and robust, long term retinal service models are required to assess and respond to the needs of local populations, both currently and in the future. Methods: A discrete event simulation (DES) tool was developed to facilitate the improvement of retinal services by identifying efficiencies and cost savings within the pathway of care. For a mid-size hospital in England serving a population of over 500,000, we used 36 months of patient level data in conjunction with statistical forecasting and simulation to predict the impact of making changes within the service. Results: A simulation of increased demand and a potential solution of the ‘Treat and Extend’ (T&E) regimen which is reported to result in better outcomes, in combination with virtual clinics which improve quality, effectiveness and productivity and thus increase capacity is presented. Without the virtual clinic, where T&E is implemented along with the current service, we notice a sharp increase in the number of follow-ups, number of Anti-VEGF injections, and utilisation of resources. In the case of combining T&E with virtual clinics, there is a negligible (almost 0%) impact on utilisation of resources. Conclusions: Expansion of services to accommodate increasing number of patients seen and treated in retinal services is feasible with service re-organisation. It is inevitable that some form of initial investment is required to implement service expansion through T&E and virtual clinics. However, modelling with DES indicates that such investment is outweighed by cost reductions in the long term as more patients receive optimal treatment and retain vision with better outcomes. The model also shows that the service will experience an average of 10% increase in surplus capacity.
关键词： Virtual clinics,Retinal services,Discrete event simulation,Treat and extend,Patient flow modelling
更新于2025-09-11 14:15:04
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Influence of surface charge decay on cavity PD frequency at DC voltage
摘要： In this study, two types of samples, i.e. a disc-shaped cavity embedded within solid dielectrics and the other on an electrode surface, were used to investigate partial discharge (PD) behaviours at DC voltage. It has been found that the discharge frequency of the sample with one metallic surface was much larger under a positive voltage than under a negative one, whereas it was not sensitive to voltage polarities for the sample with two insulating surfaces. In order to explain experimental results, a simulation model based on continuity equations was established to obtain PD sequences at DC voltage, in which surface charge decay and discharge time lag were taken into account. Simulation results showed that positive surface charges dissipated faster than the negative, and the discharge time lag kept almost unchanged at the same voltage amplitude. The discharge time interval consisted of field recovery time and discharge time lag, and the former was determined by surface charge decay rate. In terms of these, the effect of surface charge decay on discharge frequency was discussed. The research is helpful to clarify PD mechanism at DC voltage.
关键词： simulation model,partial discharge,discharge frequency,DC voltage,surface charge decay
更新于2025-09-11 14:15:04
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The effect of piezoelectric ceramic volume fraction on the thickness vibration characteristics of 1-3 piezocomposites
摘要： The thickness vibration mode of the piezoelectric composite is the most common operation mode in transducer applications. The study on the thickness vibration characteristics plays a key role in application.In this paper, the influence of volume fraction of piezo-ceramic on the thickness vibration characteristics of 1-3 piezoelectric composites was investigated. Through finite element analysis and simulation, the relationship between vibration performance parameters and the ceramic volume fraction of composites was obtained. The samples with volume fraction of 0.2 (cid:1) 0.6 were prepared by cutting and filling and tested by Impedance Analyzer.Experimental and simulation results were matched by comparison.
关键词： electromechanical coupling factor,finite element simulation,conductance,1-3 piezocomposite
更新于2025-09-11 14:12:44
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[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris, France (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Design and Modelling of a Shunt for Current Measurements at 10 a and up to 1 MHz: A Theoretical Approach
摘要： Electrical current shunts used as resistance standards in metrology laboratories are characterized by a broadband operating frequency bandwidth and are commonly calibrated up to 100 kHz. The use of a current shunt requires the preliminary knowledge of its magnitude deviation from DC and phase angle according to the frequency. The best magnitude performances published so far are limited to 2 μΩ/Ω at 100 kHz. In this paper, we present an innovative shunt design for current measurements at 10 A up to 1 MHz. The relative deviation from DC is less than 0.2 μΩ/Ω and 20 μΩ/Ω in magnitude at 100 kHz and 1 MHz respectively.
关键词： calibration,AC–DC transfer,Current shunts,3D thermal simulation,current measurement,3D electromagnetic simulation,uncertainty,AC current,modeling
更新于2025-09-10 09:29:36
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Unsteady pressure estimation and compensation capabilities of the hybrid simulation combining PIV and DNS
摘要： The hybrid unsteady-flow simulation, which has been developed to assimilate the Navier–Stokes simulation into a time-resolved particle image velocimetry (PIV) field by synchronizing the frame rate with the direct-numerical-simulation time step, can simultaneously produce an unsteady pressure field. The hybrid process typically introduces a ‘patch function’, which transplants the PIV fields inside the camera window into a larger computational domain. This study evaluates the pressure fields produced by the hybrid simulation inside the patch function (i.e. estimation) and outside of it (i.e. compensation). We take time-resolved planar PIV data of a separated flow past the NACA 0012 airfoil at an angle of attack of 30° in a water tunnel as an example. First, an unsteady pressure field produced from the hybrid simulation is compared with other existing pressure-estimation methods in two dimensions over the entire domain of the camera window. The results of the two-dimensional (2D) hybrid simulation are found to agree best with those of the sequential-integration method with much lower noise levels in time and space. Next, the domain of the forcing is reduced by truncating the patch function in the hybrid simulation, and the pressure fields in the missing parts of the patch function are compared with those solved using the full patch function. When at least the regions in which 2D vortical structures collapse are included in the patch function downstream, the rest of the pressure fields can be compensated for relatively well. In contrast, the forces acting on the airfoil can be estimated accurately only if it is enclosed by the camera window.
关键词： hybrid simulation,data assimilation,pressure estimation,particle image velocimetry
更新于2025-09-10 09:29:36
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Weak Target Tracking Based on Improved Particle Filter Algorithm
摘要： The traditional particle filter detection algorithm cannot detect weak targets efficiently in the face of the current complex environment. To solve that problem, an improved particle filtering algorithm is proposed in this paper. Firstly, the basic theory of particle filter is introduced, the defects of particle filter method are pointed out. Utilizing auxiliary particle filter and resampling in filtering algorithm is proposed in this paper. So that particle degeneration can be solved which is the significant problem in particle filtering algorithm. A simulation experiment has been conducted to verify the effectiveness of the algorithm.
关键词： simulation,target detection,track-before-detect,particle filter
更新于2025-09-10 09:29:36
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Performances of the Rotating Fanbeam Scatterometer on Cfosat
摘要： The Ku-band rotating fan-beam scatterometer (RFSCAT) onboard the China-France Oceanography Satellite (CFOSAT) is dedicated to the measurement of sea surface wind vectors. The flight model of RFSCAT has been assembled and tested, and the data processing algorithms have been developed. This paper provides an overview of the design and characteristics of RFSCAT instrument, and then a prelaunch analysis is carried out to estimate the scatterometer backscatter and wind accuracy. The overall study includes two parts: first, a forward model is developed to simulate the ocean backscatter signals under certain wind conditions; second, a wind inversion processor is used to retrieve sea surface wind vectors from the outputs of the forward model. Simulations show that the backscatter accuracy and the retrieved wind quality of RFSCAT are quite promising and meet the scientific requirements of the mission.
关键词： Scatterometer,simulation,quality control,wind
更新于2025-09-10 09:29:36
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - The Decomposition-Reconstitution Theorem for Scattering Computation from Random Rough Surface
摘要： In this paper, the decomposition-reconstitution theorem is introduced to solve the electromagnetic scattering field from the random rough surface. The random rough surface is decomposed into a series of fractal described by sinusoidal basis functions and the scattering fields are computed for each fractal. The scattering field of surface is reconstituted by vector-superposing the scattering fields of fractal. The theorem is demonstrated by the numerical simulation using FDTD. It shows that the difference of both results is a little in the range of the calculation error. This theorem was applied to solving the backscattering coefficient of the soil surface of Qionglai Sichuan, the result generally coincides with the ground-based scatter-meter measurement data and AIEM.
关键词： Fractal,Decomposition-Reconstitution Theorem,Numerical Simulation,Electromagnetic Scattering
更新于2025-09-10 09:29:36
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Forward Modeling of Cloud Shadows And the Impact of Cloud Shadows On Remote Sensing Data Products
摘要： This paper will discuss the use of the MODTRAN (MODerate spectral resolution TRANsmittance) code to simulate shadows on terrain created by broken cloud fields. Under partially cloudy conditions, there are two main cloud-induced effects: shadowing, which results in diminished and spectrally altered ground illumination, and illumination enhancement of sunlit areas due to the photons scattered from the clouds into these areas. The work presented here will focus on the effects of cloud shadows on the retrieval of reflectance signatures for target detection applications. The impact of cloud shadows is examined using forward simulations of fully and partly shadowed scenes based on the Rochester Institute of Technology Target Detection Self-Test reflectance scene. A blue roof spectral signature extracted from the scene was used as a target signature. The roof signature was randomly embedded back into the scene at subpixel levels. The scene radiance is then modeled for a low altitude sensor flying below uniform and broken cloud fields, as well as under clear sky conditions. Target detection is performed on these radiance scenes after atmospheric correction. Preliminary detection results show significant performance loss when scenes include a combination of cloud shadows and sunlit areas.
关键词： simulation,infrared,shadow,clouds,Spectral,visible
更新于2025-09-10 09:29:36