A test of Rasmussen's risk management framework in the food safety domain: BSE in the UK

In 1986, bovine spongiform encephalopathy (BSE) was identified in the UK. Millions of BSE-infected cows were slaughtered and over 150 people contracted variant Creutzfeldt–Jakob disease, an inevitably fatal human form of BSE. Tragic incidents such as this provide valuable opportunities to understand and improve the safety of complex socio-technical systems. By studying accidents, knowledge can be gained that can improve system safety. The purpose of this article is to test the usefulness of Rasmussen's risk management framework for explaining how and why accidents occur in the food production domain. This was accomplished by using the framework to retrospectively investigate how and why BSE was transmitted through the human and animal food supply in the UK from 1986 to 1996. More specifically, an AcciMap and Conflict Map were constructed to represent contributing factors of the epidemic according to the structure of Rasmussen's framework. These factors were used to test the seven predictions made by the framework. All seven predictions were supported by the evidence, indicating that Rasmussen's risk management framework shows promise as a theoretically driven explanation of how and why accidents happen in complex socio-technical systems, particularly in the food production domain.     

Risk assessment for prion protein reduction under the conditions of the biodiesel production process

Due to the increased demand for biofuels, all different feedstocks from oils and fats have to be considered for biodiesel production. Animal fats have proved to be excellent sources for biodiesel due to their high cetane number and good stability. Large amounts of fat from so‐called high‐risk material, possibly contaminated with infectious prions, are available for biodiesel production. In this paper, the grade of destruction of prions during the biodiesel production process, including pre‐esterification with conc. sulfuric acid followed by KOH‐catalyzed transesterification, was studied. The starting material of the different production steps was spiked with purified and highly infectious prion rods, and the destruction of these prions was determined by gel electrophoresis (SDS‐PAGE) and Western blot. The pre‐esterification step led to a destruction factor of at least 100, the transesterification led to a factor of at least 250, and the distillation of the final biodiesel showed a destruction factor of at least 1000. During all experiments, no traces of prions could be detected after the different reaction steps. Based on these data, a complete and unequivocal risk assessment regarding the industrial process of biodiesel production was carried out, leading to a calculated overall risk of 5.8×10^?15 ID₅₀ units/person and year, which means that a hypothetical BSE contamination from biodiesel is more than 10⁹ times lower than the background risk.     

Detection and survival of prion agents in aquatic environments

Environmental contamination is considered a potential mechanism of transmission of prion diseases. Sheep scrapie and cervid chronic wasting diseases (CWD) epizootics are thought to be maintained by natural horizontal transmission through the environment. Here, we describe a method for the detection of prion proteins (PrPres) in aquatic environments. The procedure is based on a glycine buffer-mediated extraction, sonication, and an ultracentrifugation step. The detection limit of the method was estimated to be over 5-10 microg of infected tissue. In order to determine the inactivation of these agents, we spiked infected brain tissue in urban sewage, seawater and a buffered solution (final concentrations of 0.1-0.2% brain in matrix), and studied the decay of BSE- and scrapie-associated PrPres over time (up to 265 days). Densitometric data from Western blots were plotted in logarithmic scale against time. Reduction of PrPres titer in sewage was quantified in one logarithm after 13.5 days for BSE, 27.9 days for mouse-passaged scrapie and 32.6 days for sheep scrapie. In the buffered solution, a logarithm of BSE-associated PrPres also disappeared earlier than that of scrapie (113.9 and 214.3 days, respectively). By means of the covariance analysis, these differences in the inactivation patterns were shown to be statistically significant. According to the data, prions may be stable for extended periods of time in buffered solutions like PBS, but would show limited survival in aquatic environmental matrices.     

基于广义自相关的两步盲提取算法

盲提取算法在信号处理和分析中逐步成为一项重要的方法,因为它利用信号的先验特性只提取感兴趣的信号,这样就可以节约大量的计算时间和资源.提出了时序结构信号的两步盲提取算法,第一步,利用信号所具有的广义自相关特性粗提取信号,第二步利用信号的高阶统计特性精提取信号.计算机仿真和实际的胎儿心电实验表明了提出算法的正确性,与基于广义自相关的盲提取算法相比,提出算法具有较好的性能和对时延估计偏差具有更强的健壮性.     

盲信号提取算法研究与分析*

盲信号提取主要研究如何把源信号逐个从观察信号中提取出来。以矩阵理论为基础,推证了在病态条件下逐个从观察信号中提取出主要源信号的可行性,并对给出的BSE学习算法,在病态条件下进行分析仿真。     

导弹天线罩电性能测试系统集成与实现

为满足导弹天线罩电性能测试的需要,设计了一套功能强大的自动测试系统;在硬件方面采用了分布式、多通道的搭建形式,而在软件方面则使用了Visual Basic和Measurement Studio语言并采用模块化、层次化的软件集成方式.提高了软件的可维护性,缩短了开发周期;该系统实现了在0.1～40GHz频带下,使用比幅、比相、寻零等多种方法,对导弹天线罩的数个电性能参数进行高精度测试,并同时进行效据的处理、分析与显示;该系统丰富的功能为导弹天线罩电性能测试提供了强大的测试平台。     

Atrial fibrillatory signal estimation using blind source extraction algorithm based on high-order statistics

The analysis and the characterization of atrial fibrillation （AF） requires, in a previous key step, the extraction of the atrial activity （AA） free from 12-lead electrocardiogram （ECG）. This contribution proposes a novel non-invasive approach for the AA estimation in AF episodes. The method is based on blind source extraction （BSE） using high order statistics （HOS）. The validity and performance of this algorithm are confirmed by extensive computer simulations and experiments on realworld data. In contrast to blind source separation （BSS） methods, BSE only extract one desired signal, and it is easy for the machine to judge whether the extracted signal is AA source by calculating its spectrum concentration, while it is hard for the machine using BSS method to judge which one of the separated twelve signals is AA source. Therefore, the proposed method is expected to have great potential in clinical monitoring.     

Detection of central nervous system tissue in meat and meat products with a newly developed immunoassay selective for Myelin proteolipid protein

Bovine spongiform encephalopathy (BSE) is most likely transmitted by the consumption of central nervous system (CNS) tissue of infected animals. In this study, an immunochemical assay for CNS in meat and meat products was developed using an antibody against Myelin proteolipid protein (PLP), which is very specifically expressed in the CNS. Solvent extraction of CNS-contaminated meat yielded a highly enriched PLP fraction. Subsequent Western blot analysis specifically detected the PLP band at 29 kDa. The detection limit for unprocessed CNS in raw meat was less than 0.025% and the quantification limit was calculated to be 0.049%. The PLP epitope was relatively stable during storage at 5 °C or –21 °C and during heating at 75 °C and 95 °C. Amounts of 0.1% CNS could be reliably detected in cooked bologna type sausage, cooked liver sausage and fermented sausage. Thus, the new assay allows highly specific and sensitive determination of CNS contaminations in meat and meat products.