Spatial Vulnerability of Network Systems under Spatially Local Hazards.

A hazard is often spatially local in a network system, but its impact can spread out through network topology and become global. To qualitatively and quantitatively assess the impact of spatially local hazards on network systems, this article develops a new spatial vulnerability model by taking into account hazard location, area covered by hazard, and impact of hazard (including direct impact and indirect impact), and proposes an absolute spatial vulnerability index (ASVI) and a relative spatial vulnerability index (RSVI). The relationship between the new model and some relevant traditional network properties is also analyzed. A case study on the spatial vulnerability of the Chinese civil aviation network system is conducted to demonstrate the effectiveness of the model, and another case study on the Beijing subway network system to verify its relationship with traditional network properties.

Distribution and source assessment of polycyclic aromatic hydrocarbons levels from Lake IJssel (the Netherlands) and their responses to hydrology.

Based on field efforts in Lake IJssel (the Netherlands) from 2000 to 2010, dynamics of 15 priority PAHs in suspended particulate matter (SPM) and in seawater were determined. This study examined time-varying changes in PAH concentration and composition, apportioned potential anthropogenic sources, and quantified their linkages to hydrological factors. The sum of individual PAHs (defined as ∑15 PAHs) varied widely throughout the study period in Lake IJssel, ranging from 0.76 to 9.66 mg/kg in SPM and from 0.014 to 0.136 µg/L in seawater. High molecular weight PAHs were the most abundant PAH compounds, responsible for 73%-97%. Seasonal variation in ∑15 PAHs level was distinguished, peaked in late winter and early spring, and reached a minimum in summer. Over site, the heavy contamination was found at the river mouth (e.g., Genemuiden). The driving factors of SPM and water temperature controlled the fate of PAHs. Principal component analysis and diagnostic ratios suggested that PAHs may have been derived from different input sources through various transport pathways, for example, coal combustion source and petroleum source. The findings are useful for filling the knowledge gap of PAH dynamics in Lake IJssel and Wadden Sea, which exerts significant influences on lake's environment. PRACTITIONER POINTS: HMW PAHs (4-6 rings) were the most abundant PAH compounds. Heavy contamination was found in the mouth of IJssel River. Time-varying change in PAHs level was significantly correlated with riverine input. PAHs sources were apportioned via principal component analysis and diagnostic ratios.

A concise equation that captures the essential elements of one-way sensitivity analyses in health economic models.

OBJECTIVE: Sensitivity analyses are often performed on only a limited number of variables without justification of the choice of variables and range of each variable. External parties such as health authorities are increasingly requiring submission of the actual model, often in order to test the robustness of the outcomes of the model by performing additional sensitivity analyses. The objective of this work was to develop an alternative method to capture the critical issues of a sensitivity analysis in a health economic model, especially regarding the selection of variables and determining the range for each variable. Apart from external parties such as health authorities, journal readers who want to perform their own sensitivity analysis but do not have access to the model may find this useful. METHODS AND RESULTS: Statistical methods based on Markov chain modeling and regression analysis, using the framework of the Taylor series expansion around a point, are used to derive an equation for 1-way sensitivity analyses. In particular, equations for costs and effects are being developed, from which the cost-effectiveness ratio is built. The article shows the feasibility of such equations for the execution of 1-way sensitivity analyses. CONCLUSION: An equation that can be derived in the manner described in this article provides a substantial amount of information. The inclusion of such an equation in a report may increase transparency of the reporting of outcomes of health economic models.