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91.
两种求解可靠指标的实用算法 总被引:9,自引:1,他引:8
介绍了基于几何原理求解可靠指标、寻找设计验算点的具有较高实用价值的两种新算法: 图解渐近法和Monte Carlo递进法。推导了由标准正态变量反算常用分布类型的随机变量数值的计算公式,并且通过采取某些改善措施,简化了计算过程,大大提高了问题的求解效率。同时,两种算法可以结合使用,经算例验证,能够快速解决问题且满足高精度要求,说明了本文方法的可行性和有效性。 相似文献
92.
External magnetic disturbance influences the quality of the image obtained with a magnetic resonance imaging (MRI) system because it causes magnetic resonance frequency drift. When a superconducting magnet in persistent current mode operation is exposed to external magnetic disturbance coil current varies to keep linkage flux constant. Conventional analysis is usually formulated with constant current and does not provide correct evaluation of drift of magnetic field in the magnet. This paper proposes a method of numerical analysis of magnetic field considering conservation of linkage flux in a superconducting magnet under a persistent current mode operation. This method is applied to evaluate drift of the magnetic field in a superconducting magnet for magnetic resonance imaging due to external magnetic disturbance. Analysis results show good agreement with the experimental results. 相似文献
93.
A. Giovagnoni E. Paci Paola Ercolani B. Kiefer P. Santino A. Piga 《Magma (New York, N.Y.)》1995,3(3-4):143-150
The aim of this study was to compare conventional spin-echo (CSE)T
2-weighted (T2W) images with turbo spin-echo (TSE) T2W pulse sequences in their ability to detect focal liver lesions. Seventy-eight consecutive patients with focal liver lesions were entered into this study. All patients were imaged using the gradient-echo (GE) sequence with the breath-hold technique forT
1-weighted (T1W) images, and CSE and TSE sequences for T2W images. Qualitative evaluation included lesion detection (number of lesions detected) and conspicuity (extent of visualization of lesional borders); quantitative evaluation included the signal-to-noise (S/N) ratio and the contrast-to-noise (C/N) ratio. TSE showed the best performance in terms of lesion detection; however, the difference between TSE and CSE was significant only in the case of benign cysts (p<0.01). Conspicuity was higher with TSE and CSE, and lower with GE. The S/N and C/N ratios of the two T2W sequences were also comparable, and better than those of GE. However, the combined use of GE and TSE resulted in improved lesion detection. The results show that, because the acquisition time is greatly reduced with TSE sequences, these should be considered as first-line approach to magnetic resonance imaging of the liver for the study of focal lesions. 相似文献
94.
95.
Maha N Hajmeer Imad A Basheer Dean O Cliver 《Journal of the science of food and agriculture》2006,86(14):2337-2344
Reliability analysis is especially important when critical decisions are to be made involving potentially severe adverse consequences such as foodborne illness. Owing to uncertainty associated with the parameters controlling survival of Listeria monocytogenes in chorizo (a Mexican‐style sausage), the time needed to reduce the count by a certain number (n) of logs (tnD) is probabilistic. In this paper the first‐order second‐moment (FOSM) method based on Taylor series expansion is used to derive the expected value and standard deviation of tnD as function of the operating conditions (random variables) affecting survival, namely initial water activity (aw0) of the sausage batter, storage temperature (T) and airflow velocity (F), along with their uncertainties characterised by their means and coefficients of variation. For any given n the derived tnD probability distribution enables one to determine an estimate of tnD for any desired level of reliability or confidence level, such as 50% (median value), 95%, 99%, etc. Among the conclusions drawn were: (i) the variability associated with T and F has a minor effect on estimating uncertainty in tnD, whereas the reliability of tnD estimation is greatly influenced by the uncertainty in aw0; and (ii) the uncertainty in aw0 has the greatest impact when aw0 of the sausage formulation exceeds 0.90. The approach used and discussed in this paper can be applied to any survival/inactivation study to incorporate the effect of uncertainty in the various extrinsic and intrinsic parameters on the survival kinetics of the pathogen in a food system under evaluation. Copyright © 2006 Society of Chemical Industry 相似文献
96.
97.
孔祥辉 《电子产品可靠性与环境试验》2003,(4):55-59
数字电视播出系统的可靠性直接反映整个系统的质量优劣,是确保能否进行安全、可靠的电视播出的关键。为了保障电视播出的安全与可靠性,必须对硬盘化播控系统进行双机熬备扮和使用有RAID技术的硬盘播出系统的数据备份设计;同时还介绍了数字电视播出播出系统软件的设计要求和数字电视设备的寿命分析。 相似文献
98.
99.
100.
从会计信息的质量特征看财务报告的改进 总被引:1,自引:0,他引:1
基于财务报告目标的实现,首先分析了会计信息的两大质量特征——可靠性与相关性。然后对传统财务报告模式的改进提出了看法:不断健全法制以提高可靠性;财务报告后增加预测性财务报表;提供更加丰富的报表附注内容等,目的是为报表使用者做决策提供相关性更强的信息。最后,针对报告的这些改进可能遇到的障碍及如何应对进行了探索和思考。 相似文献