蒸汽锅炉安全阀排放量的计算与分析

锅炉安全阀排放量的大小,决定了锅炉非正常情况下蒸汽压力的释放能力.结合催化装置余热锅炉的不同工况,对安全阀排放量进行校核计算,提出了相应对策.     

基于贝叶斯网的交通事故机理分析

针对道路交通事故的形成机理进行定性、定量研究,根据我国道路交通事故记录数据特征,应用贝叶斯网对事故发生概率进行定量分析.引入"驾驶员紧张度"和"道路线形合理度"两个隐节点,建立了事故分析的贝叶斯网多层隐类模型,采用最大似然估计方法确定了模型的边缘概率和条件概率.将贝叶斯网模型应用于国道104二级公路(K1310+000～K1330+000)的事故分析中,运用贝叶斯网分析软件包Netica对其历史事故记录数据进行分析.结果表明: 贝叶斯网不仅可以定量计算某种道路交通状态下的事故发生概率,而且可以找出影响事故概率的关键原因和最不利状态组合(事故概率最大时的道路交通状态).     

内外场综合可靠性试验方法分析与探讨

介绍了常规内场试验采用的一些可靠性评价标准,概括总结了内场与外场可靠性分析与评价中运用的数据处理方法,提出了利用内场数据,收集和分析外场数据的信息融合技术,即内外场可靠性综合分析法,阐述了该技术方法的相关研究内容,最后通过实际应用指出了计算的有关方法和步骤.     

Prenatal ultrasonographic diagnosis of congenital megalourethra

Congenital megalourethra is a rare genital anomaly characterized by dilatation of the penile urethra without evidence of distal obstruction. Reports of the prenatal diagnosis of this condition in the literature are limited. We present a case of congenital megalourethra with obstructive uropathy from the posterior urethra diagnosed prenatally at 18 weeks of gestation. ‘Prune-belly’-like features, colonic malrotation, and imperforate anus were also found on autopsy.     

Early prenatal diagnosis of concordant posterior urethral valves in male monochorionic twins

The association between monozygotic twins and posterior urethral valves (PUV) in postnatal life has been thoroughly described. In the fetus, the prenatal recognition of PUV is feasible. However, it has been repeatedly reported in singletons but never in monochorionic twins. We describe two cases of early prenatal diagnosis of concordant PUVs in monochorionic twins. In one of the sets, the expression of the disease was different for each twin. Copyright © 2006 John Wiley & Sons, Ltd.     

不同恢复模式下红壤区森林植被盖度变化的阈值效应分析

植被恢复过程中乔木层与灌草层变化的阈值效应往往决定着生态恢复工程的成败,若忽视这一效应可能会引发其他生态问题。为了进一步促进我国森林生态系统植被恢复建设,填补相关研究空白,研究了典型红壤区自然和人工恢复模式下乔木层和灌草层盖度的动态变化特征,基于前沿的生态阈值评估框架,利用线性模型和三种阈值模型（包括分段回归模型、阶跃函数模型以及通用模型）评估了不同恢复模式下两种盖度指标之间的阈值效应。模型评估结果的后验分布形式表明：在人工恢复乔木层与灌草层盖度之间存在阈值效应,而在自然恢复模式下则不存在;通过比较各个模型评估结果的精度可知,分段回归模型结果更加准确;进一步利用分段回归模型得出,当前人工恢复样地中乔木层盖度的阈值为42.85%（95%的置信区间为41.57%~44.13%）,此时灌草盖度为58.75%,若超过乔木层盖度阈值会使得灌草层盖度开始降低。研究结果对促进我国红壤区人工林生态系统的结构改善具有较高的参考价值。     

基于BN-CREAM的深水井控压井作业风险诱因研究

深水井控压井作业是有效控制溢流演化为井喷事故的二级井控工艺屏障。为提高深水井控压井作业可靠性,采用 BN-CREAM方法对其风险诱因进行研究。结合深水井控压井作业特点,考虑共因失效等因素,采用贝叶斯网络方法建立深 水井控压井作业风险演化模型。应用人因可靠性分析CREAM法计算深水压井人因失误先验概率,参考海洋可靠性数据手 册OREDA确定深水井控设备失效先验概率。依托贝叶斯网络的逆向推理能力辨识压井作业的主要风险节点,从而实现对 深水井控压井作业风险诱因的有效预测和评估。研究表明:深水井控压井作业共包含6个关键风险根节点,且压井作业人 因可靠性要低于设备可靠性;3级子节点“压井方法选择不合理”对深水压井作业的成功起到至关重要的作用,需进一 步开展风险分析研究。     

Sizing pressure relief valves in flashing and two-phase service: an alternative procedure

In view of the greater accuracy of the ω HEM correlation and the resulting conservative PR valve sizing (relative to the traditional PR valve sizing methods), the ω HEM-based flow calculations are recommended for all situations where flashing or two-phase flow occurs within the PR valve. However, as with any correlation, the accuracy of the ω HEM correlation results drops as the system to which it is applied diverges from the data used to develop it. Analysis of 15 different systems representative of actual refinery streams indicate that for fluids with a wide boiling range and for very non-ideal systems such as those containing hydrogen, the HEM correlation underpredicts the mass flux significantly (i.e. overpredicts the PR valve size). Since the large deviations are on the conservative side, the procedure will result in excessively large PR valves that may cause problems because of chattering of the PR valves, but would not present potential for vessel failure. The majority of the deviations are a result of the fact that the simplifying assumptions built into the correlation for single component do not truly characterize the actual flashing behaviour of many multicomponent fluids. The alternative approach presented, in which the correlation parameter ω is based on the actual flashing behaviour, eliminates nearly all the deviations and significantly improves the results of the correlation regardless of the system analysed. For trouble systems (those containing more than 0.1 wt% hydrogen and for some multicomponent fluids with a nominal boiling range greater than 80°C (150°F), the alternative approach should be used to define the correlation parameter ω. Use of this alternative approach is valid for any system (and will improve the accuracy of the correlation) but does require an additional flash calculation. However, for other systems the original formulation of ω is adequate and can be used.