Modeling perceived collision risk in port water navigation

An increase in the likelihood of navigational collisions in port waters has put focus on the collision avoidance process in port traffic safety. The most widely used on-board collision-avoidance system is the automatic radar plotting aid which is a passive warning system that triggers an alert based on the pilot’s pre-defined indicators of distance and time proximities at the closest point of approaches in encounters with nearby vessels. To better help pilot in decision making in close quarter situations, collision risk should be considered as a continuous monotonic function of the proximities and risk perception should be considered probabilistically. This paper derives an ordered probit regression model to study perceived collision risks. To illustrate the procedure, the risks perceived by Singapore port pilots were obtained to calibrate the regression model. The results demonstrate that a framework based on the probabilistic risk assessment model can be used to give a better understanding of collision risk and to define a more appropriate level of evasive actions.     

雷达吸波涂层海洋大气环境适用性试验研究

目的 分析一种雷达吸波隐身涂层在海洋大气自然环境下性能的变化规律。方法 对12个月不同阶段涂层的常规物理性能和电性能进行检测,其中常规物理性能包括宏观形貌、金相形貌、微观性能、附着力、抗冲击强度和红外光谱。结果 从宏观形貌看,涂层明度和色差值呈上升趋势,12个月明度增加1.22,色差值增加2.91,颜色向绿色和蓝色发展,失光率先增大、后减小,最大失光率为9个月时的34%。涂层附着力和试验时间呈现非线性关系,6个月时,附着力降低了18%,12个月时增大了24%。涂层在2～18GHz的频率范围内,吸波曲线大体呈“U”形,最低反射率随时间向低频方向偏移。涂层金相形貌、微观性能、抗冲击强度和红外光谱特征总体变化不明显。结论 在1a内,自然海洋大气环境对雷达吸波隐身涂层常规物理性能和电性能产生了一定影响,但在试验时间相对较短情况下,海洋大气环境对涂层老化的影响作用尚未充分显示,需要结合更长周期的试验数据进一步分析。     

华中地区吸收性气溶胶时空分布特征及类型研究

利用2005-2019年OMI-OMAERUV L2气溶胶数据集,研究了近15年华中地区吸收性气溶胶指数(UVAI)的时空分布特征和主导气溶胶类型,探究下垫面变化和人为及气象因素的影响.结果表明:①在时间分布上,华中地区UVAI的年际变化整体呈波动上升趋势;2005-2008年UVAI波动下降,20092013年逐年增...     

UV-B辐射增强对芦苇生长及生理特性的影响

在UV-B辐射增强条件下,以芦苇为材料,研究了不同辐射梯度对芦苇生长及生理特性的影响.结果表明:与自然光照相比,UV-B辐射增强可显著降低芦苇植株高度、比叶面积、生物量,且高强度辐射处理的影响大于低强度辐射,随辐射时间延长,生物量分配有向地下部分转移的趋势;与自然光照相比,UV-B辐射增强可显著增加芦苇叶片丙二醛(MDA)含量、抗氧化酶活性(SOD、CAT、GR、APX)、抗氧化物质含量(GSH、As A),且随辐射强度增大,MDA含量、酶活性、抗氧化物质含量增强程度加剧,但随辐射时间延长,高辐射处理下,GR酶活显著低于对照,GSH也表现出相应的趋势;UV-B辐射增强条件下,类胡萝卜素含量显著降低,而类黄酮含量较对照组却显著升高,且高强度辐射处理对芦苇叶片紫外吸收物质的影响大于低强度辐射.     

多普勒雷达回波在一次大暴雨中的应用分析

利用多部新一代天气雷达资料结合常规探空资料和逐小时的自动站资料,对2007年7月18日发生在河北省东部平原(以下简称冀东平原)的一次区域性暴雨过程进行分析。结果发现:低层中α尺度切变线的南压、东移及"人"字形辐合线是本次降水过程的主要影响系统;降水发生前西南暖湿气流和冀东平原近地层偏东风是"人"字形辐合线形成的直接原因;在不稳定层结存续条件下,急流方向上上游雷达站中尺度低空急流的脉动对下游台站的短时暴雨预报具有一定时效的指示意义。     

The use of leeches and logit log-linear contingency models to assess and monitor aquatic PCB contamination originating from mid-Canada radar line site 050

Abandoned military sites in northern North America are relics of the Cold War and sources of polychlorinated biphenyls (PCBs). In the late 1990s, the Canadian federal and provincial governments began the cleanup of the mid-Canada radar line in Ontario, Canada. The first site to be remediated was Site 050 (Fort Albany First Nation) in 2001; however, the community remains concerned that contaminants may have moved prior to, during, and after remediation into the Albany River directly adjacent to Site 050. Thus, the Albany River was monitored (1999, 2001, 2002) during the remediation process to determine if the cleanup itself further contaminated the aquatic compartment, using leeches (Haemopis spp.) as bioindicators. Few organochlorines were found in leeches at levels higher than the detection limit, aside from PCBs. Leech data from the present study indicated that PCB levels were significantly higher near Site 050 than the control site upstream, indicating point source contamination from Site 050. The temporal trend in leech contaminant data indicated an increase in PCB contaminant load from 1999 (pre-remediation) to 2001 (immediately post-remediation), but this difference was not statistically significant due to high variances. Nevertheless, logit log-linear contingency modeling did reveal that immediately after cleanup (2001), contaminants (CBs 99, 118, 128, 156, 170, 183) in leeches were detected significantly more frequent than expected. When taken together, leech body burden and frequency of detection data suggest that the remediation process itself further contaminated the aquatic environment, if only temporarily. Lastly, the removal of the terrestrial source of PCBs during remediation did remove the source of aquatic contaminants in that body burden of contaminants in leeches were significantly lower a year after cleanup.     

Characteristics of Important Stopover Locations for Migrating Birds: Remote Sensing with Radar in the Great Lakes Basin

Abstract:  A preliminary stage in developing comprehensive conservation plans involves identifying areas used by the organisms of interest. The areas used by migratory land birds during temporal breaks in migration (stopover periods) have received relatively little research and conservation attention. Methodologies for identifying stopover sites across large geographic areas have been, until recently, unavailable. Advances in weather-radar technology now allow for evaluation of bird migration patterns at large spatial scales. We analyzed radar data (WSR-88D) recorded during spring migration in 2000 and 2001 at 6 sites in the Great Lakes basin (U.S.A.). Our goal was to link areas of high migrant activity with the land-cover types and landscape contexts corresponding to those areas. To characterize the landscapes surrounding stopover locations, we integrated radar and land-cover data within a geographic information system. We compared landscape metrics within 5 km of areas that consistently hosted large numbers of migrants with landscapes surrounding randomly selected areas that were used by relatively few birds during migration. Concentration areas were characterized by 1.2 times more forest cover and 9.3 times more water cover than areas with little migrant activity. We detected a strong negative relationship between activity of migratory birds and agricultural land uses. Examination of individual migration events confirmed the importance of fragments of forested habitat in highly altered landscapes and highlighted large concentrations of birds departing from near-shore terrestrial areas in the Great Lakes basin. We conclude that conservation efforts can be more effectively targeted through intensive analysis of radar imagery.     

辐射化学剂量计在强脉冲混合辐射场测定中的应用

本文讨论了将硫酸亚铁剂量计和铜－铁剂量计用于强脉冲混合辐射场测定的实验设计,利用直径２２０毫米的聚乙烯球,将硫酸亚铁剂量计的快中子响应降低到２０％以下,由它和完全暴露在中子、γ混合场中的硫酸亚铁剂量计响应之差,测量中子吸收剂量。这种方法两次实际用于强脉冲混合辐射场中子、γ吸收剂量测量,得到的结果和热释光剂量计、固体径迹探测器的测量结果进行了比较,在±２５％的误差范围内一致     

镍铁合金/铁包云母粉复合吸波涂层材料的频散特性

目的探究不同质量分数配比的镍铁合金/铁包云母粉复合吸波涂层材料的频散特性。方法利用扫描电镜(SEM)观察镍铁合金和铁包云母粉的微观形貌,并使用仪器附带的能谱分析仪对样品所选区域的各元素含量进行测量。用矢量网络分析仪研究了不同质量分数下的镍铁合金/石蜡、铁包云母粉/石蜡同轴样品的介电常数与磁导率。用弓形法测试在2~18 GHz频段内镍铁合金和铁包云母粉以不同质量比加入环氧树脂-聚酰胺体系中制备的不同厚度的单层吸波涂层的反射损耗。结果镍铁合金频散特性较好,对电磁波损耗较大,将其作为吸波涂层的填料,减少吸收剂的用量同时降低了涂层的厚度。铁包云母粉的介电常数的实部较低,与自由空间的阻抗匹配较好,拓宽了吸波频带。镍铁合金和铁包云母粉作为填料,以质量分数30%/30%制备厚度1.2 mm的单层吸波涂层,在2~18 GHz其最小反射值达到了-21.8 d B,小于-10 d B的带宽达到10.5 GHz。结论镍铁合金与铁包云母粉以合适质量比复合,制备的吸波涂层材料厚度薄、吸波频带宽。     

基于空间监视雷达散射回波的电离层电子密度探测方法

目的提高空间监视雷达的电离层电波环境适应性。方法 VHF-L波段大功率雷达信号经过电离层传播时会发生非相干散射,散射回波中包含电离层信息。结合雷达方程和电离层目标特征,基于电离层非相干散射原理,理论分析空间监视雷达用于电离层电子密度非相干散射探测的条件(包括雷达参数设置和波束扫描方式),给出电离层回波功率、自相关函数和电子密度表达式,利用Matlab编程对某大功率空间监视雷达原始数据处理得到电离层散射回波及电子密度。结果给出了空间监视雷达用于电离层电子密度非相干散射探测的基本条件,实测数据发现电离层回波和电子密度符合电离层变化特征。结论利用VHF-L波段大功率雷达空间散射回波探测电离层电子密度是可行的,为空间监视雷达电离层环境感知与传播自适应修正提供了一种可能的新途径。