Safety of child passengers who ride to school on a motorcycle: An observational study in two Argentine cities

In low- and middle-income countries, the motorcycle has increasingly become a means of family transportation due to its low cost and the poor quality of public transportation. Consequently, many child motorcycle passengers are at an elevated risk of serious injury in the event of a traffic crash. The available research on child safety devices is scarce and focused mainly on helmet use, while other devices (e.g. high-visibility clothing) have received little attention. This observational study documented the safety conditions and related factors of primary schoolchildren who rode to school as motorcycle passengers in two cities of Argentina.Data was obtained in the vicinity of 27 public primary schools in two cities of Argentina (one mid-sized city and the other a small city by the country's standards) between May 2018 and September 2019. A total of 1440 motorcycle occupants (656 drivers and 784 child passengers) were observed.The use of an adequate helmet was lower among children (vs. drivers). Most of the children were unable to reach the motorcycle's footrests, did not use high-visibility clothing or a fastening device, carried a backpack, and mounted and dismounted the motorcycle in an unsafe place. Some children rode in front of the driver or in a motorcycle with three or four occupants. Use of helmet by drivers and driver sex (woman) were related with an increase in safety in children. The indicators were worse in the larger city.The results revealed a low level of adoption of safety measures in children as well as in adults in both cities. This suggests that motorcycle travel is unsafe. Greater effort is needed to improve motorcycle safety, especially for children. It is important to debate regulatory details such as a minimum age for passengers, a limit on the number of passengers, and other safety criteria. It is also important to conduct educational campaigns that include the distribution of safety devices.     

Network representation,continuum approximations and a solution to the spatial aggregation problem of traffic assignment

This paper complements the preceding one, which showed how one could modify equilibrium traffic assignment algorithms for networks with many centroids. In this one it is shown how one can substitute centroids by zones with continuous population densities. The technique, which is mathematically guaranteed to approximate a flow pattern in accordance with Wardrop's user equilibrium criterion, requires some geometrical calculations which can be handled off-line. With the suggested approach, it is possible to represent the spatial distribution of trip ends more realistically and this allows traffic assignment models to capture the effects of short and intrazonal trips in a way previously impossible. The method is shown to be computationally feasible.     

Flexible long range planning using low cost information

Contemporary transport planning requires a flexible modelling approach which can be used to monitor the implementation of a long term plan checking regularly its short term performance with easily available data; the original model is periodically updated using low cost information and this allows the evaluation of the changes to the plan which may be required. Such an approach requires models suited to regular updating and to the use of data from different sources. Models to update trip matrices from traffic counts have been available for some time; however, the estimation and/or updating of other model stages with low cost data has escaped analytical treatment. The paper discusses this idea and formulates the updating problem for an example involving a joint destination/mode choice model under various assumptions about the nature of the available data. Analytical solutions are proposed as well as some general conclusions.requests for offprints     

Correcting injection pressure maladjustments to reduce NOX emissions by marine diesel engines

Emissions from the exhausts of marine diesel engines comprises several different gases including NO_X. These are currently regulated at the international level under Regulation 13 of ANNEX VI of MARPOL 73/78, but this regulation only applies to new engines and is based on bench tests, for only a single engine designated the “parent engine”. Here, the need to take measurements from across their whole range and once in operation on board a vessel is examined. This would not only improve assessment of new equipment against the current regulation, but would also detect defects in the functioning of the engine.     

Surface patterns of zooplankton spatial variability detected by high frequency sampling in the NW Mediterranean. Role of density fronts

High frequency sampling was performed in daylight hours along a 35 km transect in the Ligurian Sea to investigate the upper layer zooplankton distribution during the spring phytoplankton bloom. The results show detailed spatial structure and biomass of key zooplankton functional groups, copepods, salps and krill larvae, within the different water masses characterizing this region. Although observed values of total copepod biomass distribution were rather constant along the transect, species-specific patterns were observed in the copepod spatial distribution. The larger species Calanus helgolandicus, as well as Centropages typicus, Oithona spp., and Oncaea spp., were associated with the frontal zone. However, Acartia spp. had a scattered distribution, and Clausocalanus/Paracalanus did not have a clear pattern. In addition, krill larvae were concentrated in the frontal area and salps had a scattered pattern. The cross-shore zooplankton distribution appeared strongly influenced by both the Northern Ligurian current governing inshore waters, which acts as a major flushing forcing, and the Ligurian front, which governs offshore waters and may act as retention area for zooplankton.     

Can mixed logit reveal the actual data generating process? Some implications for environmental assessment

Recent advances in the specification of the utility function of mixed logit models allow the analyst, in principle, to consider a vast variety of individual heterogeneity. Nevertheless, when estimating the model it is common practice to experience severe difficulties in discriminating between different specifications to infer the “true” data generating process. We investigate possible sources for this difficulty focusing on the confounding effects inherent in two basic assumptions of discrete choice model utilities: linearity in the parameters and added error terms. We analyse the role of these assumptions in giving rise to confounding effects and why this increases the difficulty of discriminating among different structures. Finally, we investigate how these problems may affect benefit appraisal using these models. Empirical evidence is provided for two different environmental contexts and a more typical transport context using various kinds of data.     

桥梁支座典型病害分析及对策

随着桥梁建设的飞速发展和荷载等级的不断提高,支座也被广泛地使用于桥梁中,同时也出现了支座使用、安装和耐久性问题等等,这些问题都是影响结构安全性和耐久性的重要因素,需要通过科学手段、方法加以诊断、评价。     

二尖瓣脱垂综合征患者QT离散度分析

测定了30例二尖瓣脱垂综合征伴室性心律失常患者的QTd。结果发现，二尖瓣脱垂组QTd、QTcd、JTd显著延长，说明心室肌复极有局部的不均一性和电不稳定性，离散度与室性心律失常的发生密切相关，可能是室性心律失常发生的机理之一。QTd不仅能预测室性心律失常及猝死，而且能指导临床用药，是一很好的临床观察指标。     

结合均值导纳法的声呐腔自噪声统计能量分析

讨论了湍流边界层激励下声呐腔自噪声统计能量分析.采用圆柱一圆板组合结构模拟艏部声呐罩,重点讨论了湍流边界层输入功率计算,及利用均值导纳法求解多耦合结构之间的直接耦合损耗因子及间接耦合损耗因子,给出了详细的理论推导,最后给出了具体的算例.分析结果可作为湍流边界层激励下声呐腔自噪声工程估算的参考.     

Review and assessment of the nested logit model

The popular hierarchical or nested logit model that has been the recent source of heated discussions in the literature is reviewed and critically examined. The fundamental underpinnings of the model are first presented in a concise and easy-to-understand fashion and then used to assess each controversy in turn. Monte Carlo simulation is also used to examine some problems that are not possible to address by just resorting to the theory. The main conclusion is that all the model hypotheses are both essential and unambiguous and should not be ignored for a correct use of the model in practice.