Modeling Scatter in Multiple Energy Windows to Incorporate Scattered Radiation Information in Single Photon Emission Computed Tomography Imaging

Using scattered radiation as useful information to improve radioisotope image quality is a topic attracting many researchers. Some reports showed that incorporating scattered components offers a possibility to improve image quality. The general method is modeling scatter in multiple energy windows and incorporating that information into the reconstruction process. However, what the performance will be and how noise will behave when using scattered radiation in reconstruction are not yet well answered. In this paper, we investigate a method of modeling scatter in multiple energy windows in cases of a few projection views. The system performance is analyzed using singular value decomposition and resolution kernels. For noise behavior investigation, reconstructions are accomplished by estimating the variance of reconstructed voxel values and the effectiveness of using scatter is evaluated by resolution kernel analysis. The results show there are improvements in normalized mean-square error of the images and the resolution kernels. When photon counts fall below about one million, it is still effective to use scatter for some cases of a few projections     

Air-kerma modulation effects on the energy spectrum of a 137CS irradiator using Monte-Carlo techniques

Calibration of radiation protection instrumentation such as survey meters is typically performed using ¹³⁷Cs irradiators. During calibration, various thicknesses of lead attenuators are added and the source-to-detector distance is adjusted to modulate air-kerma rate. Variations in the energy spectrum as a result of these modulation techniques are unknown, and may affect the response of energy-dependent survey meters during calibration. The purpose of this work was to characterize the spectral changes that result from modulation of the air-kerma rate for the Hopewell Designs G-10 dual source irradiator at the University of Wisconsin Accredited Dosimetry Calibration Laboratory (UWADCL). An experimentally validated Monte-Carlo model of the irradiator geometry was used to investigate energy spectra variations as a function of attenuation and distance. Lead attenuator thicknesses of (0, 0.64, 1.22, 2.22, 4.32, and 5.54) cm were used in this study. The irradiator geometry was modeled using MCNP6 Monte Carlo (MC) transport code and validated by comparing simulated and measured percent depth dose (PDD) curves and cross-field profiles. Spectra were tallied at (100, 200, 300, and 400) cm from the source. The effects of room scatter on the energy spectrum were also investigated. Simulated and measured PDDs agreed within the associated uncertainty and profiles agreed within 3% or 3 mm distance to agreement. The mean energy for simulated spectra at 100 cm from the source varied from 593 keV to 654 keV as attenuation increased from no attenuation to 5.54 cm of lead. The mean energy of the spectra remained consistent at distances ranging from 100 cm to 400 cm for all attenuation thicknesses and for both geometries in which the vault walls were defined and undefined. This study used MC methods to show that the modulation of air-kerma rate using attenuation and source-detector distance significantly changes the energy spectrum. This knowledge may improve the accuracy of any calibrations using this source.     

Influence Function and Efficiency of the Minimum Covariance Determinant Scatter Matrix Estimator

The minimum covariance determinant (MCD) scatter estimator is a highly robust estimator for the dispersion matrix of a multivariate, elliptically symmetric distribution. It is relatively fast to compute and intuitively appealing. In this note we derive its influence function and compute the asymptotic variances of its elements. A comparison with the one step reweighted MCD and with S-estimators is made. Also finite-sample results are reported.     

闪光照相中散射照射量的解析分析

 考虑了光子与物质的三种相互作用方式，用解析分析法确定光子在材料中能量的一次散射转化几率，并由此求得闪光照相系统中成像平面上的散射和最小直散比的表达式。用该公式求得的FTO客体的最小直散比约为1.0，与美国NIH实验结果0.5~1.5近似符合。     

Scatter Search for Network Design Problem

A fixed charge capacitated multicommodity network design problem on undirected networks is addressed. At the present time, there exists no algorithm that can solve large instances, common in several applications, in a reasonable period of time. This paper presents an efficient procedure using a scatter search framework. Computational experiments on a large set of randomly generated problems show that this procedure is capable of finding good solutions to large-scale problems within a reasonable amount of time.     

Minimizing Labor Requirements in a Periodic Vehicle Loading Problem

In this paper, we address a logistics problem that a manufacturer of auto parts in the north of Spain described to the authors. The manufacturer stores products in its warehouse until customers retrieve them. The customers and the manufacturer agree upon an order pickup frequency. The problem is to find the best pickup schedule, which consists of the days and times during the day that each customer is expected to retrieve his/her order. For a given planning horizon, the optimization problem is to minimize the labor requirements to load the vehicles that the customers use to pick up their orders. Heuristically, we approach this situation as a decision problem in two levels. At the first level, customers are assigned to a calendar, consisting of a set of days with the required frequency during the planning horizon. Then, for each day, the decision at the second level is to assign each customer to a time slot. The busiest time slot determines the labor requirement for a given day. Therefore, once customers have been assigned to particular days in the planning horizon, the second-level decision is a multiprocessor scheduling problem, where each time slot is the equivalent of a processor, and where the objective is to minimize the makespan. A metaheuristic procedure is developed for the problem of minimizing labor requirements in this periodic vehicle-loading problem and artificial as well as real data are used to assess its performance.     

统计深度函数及其应用

次序统计量在一维统计数据分析中起着很重要的作用．多年来,人们一直在商维数据处理和分析中寻找“次序统计量”,却没有得到很满意的结果．由于缺少自然而有效的高维数据排序方法,因而象一维“中位数”的概念很难推广到高维．统计深度函数则提供了高维数据排序的一种工具,其主要思想是提供了一种从高维数据中心(最深点)向外的排序方法．不仅如此,统计深度函数已经在探索性高维数据分析,统计判决等方面带给我们一种全新的前景,并在工业、工程、生物医学等诸多领域得到很好的应用．本文介绍了统计深度函数概念及其应用,讨论了位置深度函数的标准,介绍了几种常用的统计深度函数．给出了由深度函数特别是由投影深度函数所诱导的位置和散布阵估计,介绍了它们的诸多优良性质,如极限分布,稳健性和有效性．由于在大多数场合下,高崩溃点的估计不是较有效的估计,而由统计深度函数所诱导的估计具有多元仿射不变性,并能提供理想的稳健性与有效性之间的平衡,本文还讨论了基于深度的统计检验和置信区域,介绍了统计深度函数的其他应用,如多元回归、带有变量误差模型、质量控制等,以及实际计算问题．指出了统计深度函数领域有关进一步的工作和研究方向．     

Statistical analysis of HDPE fatigue lifetime

Fatigue lifetime of HDPE structures such as pipes is recognized to show a large scatter. This study aims to compare different statistical methods and distributions, in order to give convenient modeling of tensile and fatigue test results of commercially available polyethylene compression molded sheets. The median rank, the maximum likelihood and the Kolmogorov-Smirnov fitting are compared for the estimation of Weibull parameters. The choice of the best distribution to fit fatigue lifetime is discussed on the basis of the goodness-of-fit results. It is found that whether the three-parameter distributions of Weibull and lognormal types are suitable for lifetime prediction, the two-parameter Weibull is more conservative for probabilistic fatigue design.     

密频子空间的可控度与可观度

首先提出了频率组的分散度和密集度的概念,从而可以在整体上把握一个频率组的接近程度,然后对于二阶的弹性结构系统,分别在可控性和可观性的意义下,引入了两个同维数的一阶系统,分别以该一维系统为基础,利用小参数方法,以频率组的分散度为参数,分析了密集频率子空间的可控度和可观度,给出了可控度和可观度的一阶近似解。     

天津高村井水位主要周期成分的干扰因素及特征分析

以天津高村井水位与气压观测数据及理论固体潮为研究对象,首先利用别尔采夫滤波滤除其日波、半日波;其次利用一般多项式分段曲线拟合(按月分段),将周期在1-2个月内的月波滤除;再次利用小波分析研究高村井水位分钟值与气压、理论固体潮的关系,结果表明:1)高村井水位观测主要周期有日波、半日波、1-2月的月波及年周期;2)高村井水位的日波、半日波主要的影响因素为固体潮,它们之间为线性关系;3)高村井水位1-2月的月波频段受气压影响较显著,井水位与气压呈线性关系;4)小波分析结果表明,在64-256min频段高村井水位与气压线性相关程度较高,受气压影响显著.