Measurement of the Energy Spectrum of a 6 MV Linear Accelerator Using Compton Scattering Spectroscopy and Monte Carlo-Generated Corrections

Purpose: The energy spectrum of a linear accelerator used for dose calculations is determined during beam commissioning by iteratively adjusting the spectrum and comparing calculated and measured percent depth-dose curves. Direct measurement of the energy spectrum using pulse mode detectors is particularly challenging because of the high-energy, high fluence nature of these beams and limitations of the detector systems. This work implements a Compton scattering (CS) spectroscopy setup and presents detector corrections and spectral unfolding techniques to measure the spectrum of a 6 MV linear accelerator using a pulse mode detector. Methods: Spectral measurements were performed using a Varian Clinac 21EX linear accelerator and a high-purity germanium (HPGe) detector. To reduce fluence to the detector, a custom-built lead shield and a CS spectrometry setup were used. The detector was placed at CS angles of 46°, 89°, and 125°. At each of these locations, a detector response function was generated to account for photon interactions within the experimental geometry. Gold’s deconvolution algorithm was used to unfold the energy spectrum. The measured spectra were compared to simulated spectra, which were obtained using an experimentally benchmarked model of the Clinac 21EX in MCNP6. Results: Measurements were acquired and detector response corrections were calculated for all three CS angles. A comparison of spectra for all CS angles showed good agreement with one another. The spectra for all three angles were averaged and showed good agreement with the MCNP6 simulated spectrum, with all points above 400 keV falling within 4%, which was within the uncertainty of the measurement and statistical uncertainty. Conclusions: The measurement of the energy spectrum of a 6 MV linear accelerator using a pulse-mode detector is presented in this work. For accurate spectrum determination, great care must be taken to optimize the detector setup, determine proper corrections, and to unfold the spectrum.

Spectral Imagers with Linear Detector Imager Systems Based on Spectrum Compressed

Traditional spectral imagers require 2-dimensional detectors. We present a new method to implement spectral imagers with linear detector imager systems based on spectrum compressed. Using 1-dimension detectors instead of 2-dimension detectors to get 3-dimensional data cubes, the spectral imagers could get both the spectral information and the spatial information of each ground object. By the method of characteristics decoupling, we make high precision reconstruction of compressed data. Theoretical analysis and simulations show that it not only ensures the imaging quality but also reduces the dimension of the detectors and complexity of imaging system greatly.

QUADRATIC CORRECTION TO THE LINEAR WAVE SPECTRUM OF TWO-DIMENSIONAL RANDOM WAVES

A perturbation expansion method’s first three order solutions of two-dimensional random gravity waves in finite uniform depth were used as bases to derive the quadratic correction to the linear wave spectrum (ie., the quadratic spectrum ). For infinite water depth, the expression of the quadratic spectrum given in this paper is much simpler then that of Sclavounos (1992) and Olemz and Milgram (1995).

Distinction of self-synchronous scrambled linear blockcodes based on multi-fractal spectrum

This study proposes a novel multi-fractal spectrumbasedapproach to distinguish linear block codes from its selfsynchronousscrambled codes. Given that the linear block codeand self-synchronous scrambled linear block code share the propertyof linear correlation, the existing linear correlation-basedidentification method is invalid for this case. This drawback can becircumvented by introducing a novel multi-fractal spectrum-basedmethod. Simulation results show that the new method has highrobustness and under the same conditions of bit error, the lowerthe code rate, the higher the recognition rate. Thus, the methodhas significant potential for future application in engineering.

激光回馈双通道位移测量创新实验平台设计

针对激光回馈技术中多目标同步检测以提高测量效率的问题,提出了一种基于线性调频的测量通道拓展方法。在线性电流注入下,激光器输出的光频率近似线性变化;2个被测物体到激光器距离不同时,回馈信号的频谱中出现分别对应2个物体的独立谱峰,通过全相位频谱分析方法在2个谱峰处进行相位解算可以重构2个物体的运动曲线。基于Python语言构建的仿真模型和相应的双通道位移测量实验系统均证实了该方法的有效性,2个通道的位移测量相对误差小于5%。

应用蒙特卡罗方法研究医用加速器光子能谱分布

目的研究医用直线加速器在等中心平面的光子能谱分布和次级准直器对光子能谱的影响。方法使用BEAMnrc程序模拟5 cm×5 cm、10 cm×10 cm、15 cm×15 cm和20 cm×20 cm射野下,能量为6 MeV电子和光子在加速器治疗头中的输运行为,在等中心平面处设置相空间记录文件,以记录经过此平面的粒子信息。然后利用BEAMdp程序对相空间文件进行分析,从而获得在等中心平面的光子能谱分布及次级准直器对光子能谱的影响。结果通过分析标称能量为6 MV的医用直线加速器的光子能谱,发现次级准直器对光子能谱影响很小;不同射野具有不同的光子能谱分布;同一射野不同中心区域的光子能谱具有相同的归一化分布。结论在放射治疗的剂量计算中,应仔细考虑光子能谱的影响。

两类非对称双箭型矩阵的广义逆谱问题

针对两类非对称双箭型矩阵的广义逆谱问题,本文先将两类矩阵的两组特征对作为其特征数据,然后利用矩阵元素间具有的函数关系、线性关系及箭型矩阵的相关性质,将两类矩阵的逆谱问题转换为求解线性方程组的问题,进而实现了两类矩阵的重构。本文给出了该问题有唯一解的充分必要条件以及问题构造的算法,并通过相应数值实例验证了所得结果。

A Calibration Method Based on Linear InGaAs in Fiber Grating Sensors Interrogation System

In accordance with the characteristics of wavelength shift detection in fiber grating sensor interrogation system,the wavelength interrogation system which uses linear InGaAs as the spectrum receiver is proposed.Orientation of optic spectrum line affects the silt of volume phase grating and size of InGaAs photosensitive unit,thus the calibration method is needed.Based on an analysis of InGaAs imaging model,least square curve fitting method is proposed to detect spectrum wavelength and InGaAs photosensitive unit position.The experimental results show that the methods are effective and the demodulation system precision is improved.

Linear Support Vector Machine Based Inter-harmonic Modeling and Parameter Estimation

There are often many inter-harmonics in power system.The high measurement accuracy of inter-harmonics order,amplitude and initial phase is needed.A new approach is presented for inter-harmonic modeling and parameter estimation based on linear support vector machine (SVM).Firstly,parameter estimation of linear model is realized based on standard linear SVM.Then,inter-harmonic model is transformed to a linear model according to trigonometric functions.The approach obtains order of inter-harmonic model with windowed Blackman-Tukey (BT) spectrum analysis,and gets number and frequency of harmonics.Finally,the linear SVM is applied to estimate the inter-harmonic parameters,amplitude and initial phase.The simulation results show that the proposed approach has high precision and good antinoise.The accuracy of three parameters are all higher than 98%.

Research of optical rainfall sensor based on CCD linear array

Rainfall monitoring is one of the most important meteorological observation elements for the disaster weather. The maintenance of current tipping bucket rain gauge and weighing type rain gauge is a critical issue. The optical rainfall sensor based on CCD linear array is mainly studied in this paper. Because of the maintenance-free time and good adaptability,it can be widely used in the automatic rainfall monitoring in severe environment and have a good perspective in using.

激光云粒子成像探测仪研制

为了研究云粒子微观特性,采用激光成像技术、高斯光束匀化处理技术、高分辨率阵列探测器以及图像抽帧还原算法,研制出激光云粒子成像仪。通过地面模拟测量及实际飞行试验,对仪器性能进行了测试。结果表明,研制仪器可实现对25μm~1550μm云粒子的成像,分辨率为25μm,粒径测量误差小于9.5%;实测的冰晶粒子形态符合云粒子自然分布规律,粒子尺度谱符合指数分布,决定系数在0.58~0.97之间。该研制仪器可为云降水微物理研究提供基础观测数据。

RELATIVE ESSENTIAL SPECTRA INVOLVING RELATIVE DEMICOMPACT UNBOUNDED LINEAR OPERATORS

In this article, we introduce the concept of demicompactness with respect to a closed densely defined linear operator, as a generalization of the class of demicompact operator introduced by Petryshyn in [24] and we establish some new results in Fredholm theory. Moreover, we apply the obtained results to discuss the incidence of some perturbation results on the behavior of relative essential spectra of unbounded linear operators acting on Banach spaces. We conclude by characterizations of the relative Schechter＇s and approximate essential spectrum.

Suboptimal stochastic H-two/H-infinity design with spectrum constraint

This paper studies the problem of suboptimal state-feedback H-two/H-infinity control of stochastic systems with spectrum constraint. Concretely speaking, a mixed suboptimal H-two/H-infinity controller synthesis together with placing the spectrum into a strip region is considered, which is achieved via solving a convex optimization problem.

Seismic displacement demand prediction in non-linear domain: Optimization of the N2 method

In Europe, computation of displacement demand for seismic assessment of existing buildings is essentially based on a simplified formulation of the N2 method as prescribed by Eurocode 8(EC8). However, a lack of accuracy of the N2 method in certain conditions has been pointed out by several studies. This paper addresses the assessment of effectiveness of the N2 method in seismic displacement demand determination in non-linear domain. The objective of this work is to investigate the accuracy of the N2 method through comparison with displacement demands computed using non-linear timehistory analysis(NLTHA). Results show that the original N2 method may lead to overestimation or underestimation of displacement demand predictions. This may affect results of mechanical model-based assessment of seismic vulnerability at an urban scale. Hence, the second part of this paper addresses an improvement of the N2 method formula by empirical evaluation of NLTHA results based on EC8 ground-classes. This task is formulated as a mathematical programming problem in which coefficients are obtained by minimizing the overall discrepancy between NLTHA and modified formula results. Various settings of the mathematical programming problem have been solved using a global optimization metaheuristic. An extensive comparison between the original N2 method formulation and optimized formulae highlights benefits of the strategy.

海上油气田热介质供热设备故障数字化识别技术

海上油气田热介质供热设备长期在高温易燃的环境中运行,其可靠性对油气田开发的安全稳定起到重要作用,有必要研究其故障识别方法。为此,提出海上油气田热介质供热设备故障数字化识别方法。采用线性谱聚类算法对红外设备图像展开超像素分割处理,利用基于最大相似度区域合并算法分割设备目标区域。通过基于梯度变化的补偿算法对目标区域展开盲元块补偿。在核函数估计的基础上提取红外设备图像的温度概率密度函数,采用K均值聚类算法根据温度概率密度划分目标区域,将目标区域分为故障区域和正常区域,实现海上油气田热介质供热设备故障的数字化识别。实验结果表明,所提方法可以准确地完成目标区域分割和过热区域定位、故障识别准确率最低为97.3%、识别时间在2s内。

Non-Frobenius Spectrum-Transformation Method

A method allowing a desirable matrix spectrum to be constructed as an alternative to the method using matrix transformation to the Frobenius form is stated. It can be applied to implement control algorithms for technical systems without executing the variables transformation procedures that are needed for deriving a Frobenius matrix. The method can be used for simulation of systems with different spectrums for choosing an alternative that satisfies to the distinct demands.

1.06μm结构参数最优化非保偏锁模光纤激光器

采用半导体可饱和吸收镜的锁模光纤激光器是构建皮秒脉冲光纤放大器的热门候选种子光源之一。本文利用非线性薛定谔方程从理论上分析了单模传输光纤和单模增益光纤的模场半径、增益光纤的光纤长度、光纤布拉格光栅的反射率、半导体可饱和吸收镜的调制深度、非饱和损耗和饱和通量对输出脉冲特性的影响。对输出激光的脉冲和光谱特性也进行了理论研究。根据仿真结果,搭建了基于非保偏线型腔和SESAM的掺镱锁模光纤激光器系统。在没有任何腔内色散补偿和外部偏振控制的情况下,获得了中心波长为1.06μm、脉冲宽度小于12.51 ps、光谱宽度为0.32 nm、重复频率为37 MHz、输出功率为2 mW的稳定锁模脉冲激光输出。在我们的实验中,激光脉冲的光谱边缘平滑,光谱分布非常接近高斯线型。最后,通过系统的仿真,近红外锁模光纤激光器的整体结构得到了优化。本文介绍的锁模光纤激光器具有紧凑的非保偏光纤结构、精简的腔内配置和较少的元器件、高质量的输出脉冲相关特性,有望为下一代皮秒脉冲光纤激光器提供性能优异的实用化种子光源。

SPECTRUM DISTRIBUTION OF THE SEDOND ORDER GENERALIZED DISTRIBUTED PARAMETER SYSTEMS

Spectrum distribution of the second order generalized distributed parameter system was discussed via the functional analysis and operator theory in Hilbert space. The solutions of the problem and the constructive expression of the solutions are given by the generalized inverse one of bounded linear operator. This is theoretically important for studying the stabilization and asymptotic stability of the second order generalized distributed parameter system.