浆固碎石桩成桩注浆渗透影响分析

浆固碎石桩作为一种新型软土地基处理技术,其主要通过注浆改善桩体的加固效果,同时通过浆体渗透来改善桩周土体的物理力学性质,从而减小浆固碎石桩复合地基沉降。针对浆体对桩周土体的渗透作用,按照平面轴对称问题,推导出注浆渗透影响范围的计算方法和浆固区压缩模量计算公式,并通过室内模型试验研究,验证了浆固区压缩模量计算公式的正确性。随后,利用数值计算分析,对浆固区影响范围进行量化分析,并通过数值拟合得到了考虑注浆渗透影响的桩体等效半径计算公式。所得结果对工程设计具有重要的指导意义。     

Perfluorinated compounds in the Antarctic region: Ocean circulation provides prolonged protection from distant sources

In order to investigate the extent to which Perfluorinated Contaminants (PFCs) have permeated the Southern Ocean food web to date, a range of Antarctic, sub-Antarctic and Antarctic-migratory biota were analysed for key ionic PFCs.Based upon the geographical distribution pattern and ecology of biota with detectable vs. non-detectable PFC burdens, an evaluation of the potential contributory roles of alternative system input pathways is made. Our analytical findings, together with previous reports, reveal only the occasional occurrence of PFCs in migratory biota and vertebrate predators with foraging ranges extending into or north of the Antarctic Circumpolar Current (ACC).Geographical contamination patterns observed correspond most strongly with those expected from delivery via hydrospheric transport as governed by the unique oceanographic features of the Southern Ocean. We suggest that hydrospheric transport will form a slow, but primary, input pathway of PFCs to the Antarctic region.     

汽车后排座椅侧气囊仿真系统参数优化研究

为提升侧面碰撞中后排乘员胸腹部保护效果,在国内某款汽车原有侧面碰撞系统模型基础上,构建后排座椅侧气囊(RSAB)仿真试验模型,通过各项零部件试验与气囊模型对标后导入侧面碰撞系统试验模型;分析RSAB及气帘对后排被试的保护性能,针对胸腹部损伤防护优化侧面气囊相关参数,设计正交试验,运用极差分析法,得出最优参数组合,并对比...     

川藏铁路沿线地区夏季气温日较差的影响因素研究

利用ERA5再分析资料,分析了1979—2018年川藏铁路沿线区域气候特征.研究了2014—2018年夏季气温日较差(DTR)的变化趋势,以及2014—2018年夏季DTR与地面太阳辐射(SSR)、总降水量(TP)、总云量(TCC)、海拔(DEM)和地表平均蒸发率(MER)的相关性.结果表明:研究区域气温呈上升趋势,2...     

外来入侵假臭草在中国分布区的预测

假臭草原产南美洲,上世纪80年代首次记载传入中国,是潜在的恶性杂草.为提供其在中国分布区的预测资料,采用397个采集数据和已有的146个分布点数据,利用生态位模型(GARP)和Domain模型对分布区进行预测分析,并通过AUC与MaxKappa进行模型评价.结果显示:近十年,假臭草入侵记录增多,入侵扩散加剧;太阳辐射、水汽压、极端高温、霜日频率和水流方向对假臭草的分布限制较小,雨日频率、坡向、坡度、海拔、年降水、年均温、地形指数和极端低温等8个环境因子对其分布影响显著;入侵的主要植被类型是农田、灌木或草类覆盖嵌合区,常绿、落叶灌木地带,栽培植被及相关联地带等.模型评价表明两种模型预测能力为较好及以上,预测结果显示:假臭草在西藏(除东南小块区域)、新疆、青海、内蒙古、宁夏,陕西和山西北部地区,黑龙江、吉林、辽宁(除辽东半岛小块区域)是不宜生长区;最易入侵广东、广西、海南等地区,其中华中部分省份、华北平原为适生区,还未见有假臭草入侵的报道,相关部门应引起重视,严防入侵.     

Estimating animal densities and home range in regions with irregular boundaries and holes: A lattice-based alternative to the kernel density estimator

Density estimates based on point processes are often restrained to regions with irregular boundaries or holes. We propose a density estimator, the lattice-based density estimator, which produces reasonable density estimates under these circumstances. The estimation process starts with overlaying the region with nodes, linking these together in a lattice and then computing the density of random walks of length k on the lattice. We use an approximation to the unbiased crossvalidation criterion to find the optimal walk length k. The technique is illustrated using walleye (Sander vitreus) radiotelemetry relocations in Lake Monroe, Indiana. We also use simulation to compare the technique to the traditional kernel density estimate in the situation where there are no significant boundary effects.     

River Otter (Lutra lutra L.) in Northeastern Siberia: Distribution and Numbers

Russian Journal of Ecology -     

Long-Term Population Changes of Native and Introduced Birds in the Alaka'i Swamp, Kaua'i

Abstract:  Within the last 30 years, five endemic bird species of the Alaka'i Swamp, Kaua'i, Hawai'i, have likely gone extinct. We documented population trends of the remaining avifauna in this time period to identify a common pattern in the Hawaiian Islands: decline of native species and expansion of introduced species. We conducted bird surveys over 100 km² of the Alaka'i and Kōke'e regions of Kaua'i in March–April 2000 to estimate population size, distribution, and range limits of seven native and six introduced forest birds. We compared the results with four previous surveys conducted over the last 30 years. Five of the seven native species we studied have fared well, maintaining sizeable populations (>20,000 individuals) and unchanged or increasing numbers. The endemic 'Akikiki ( Oreomystis bairdi ), however, declined from 6296 (SE ± 1374) to 1472 (SE ± 680) individuals and exhibited range contraction from 88 to 36 km². The 'I'iwi ( Vestiaria coccinea ) also experienced a decline and contraction, though not as severe. Populations of several introduced forest birds are increasing, but all species, excluding the Japanese White-eye ( Zosterops japonicus ), were at low numbers (<5,500 individuals in survey area). One introduced species, the Japanese Bush-Warbler ( Cettia diphone ) recently invaded, whereas another, the Red-billed Leiothrix ( Leiothrix lutea ), has been extirpated. Two hurricanes in the past 20 years appear to have most strongly affected nectarivores and may have contributed to the decline or extinction of several other species. Overall, native bird populations on Kaua'i have exhibited species-specific responses to limiting factors. Although most native populations appear stable, the extant native avifauna is vulnerable as a result of limited distributions and the potential for widespread habitat degradation.     

Host Specificity of Flukes of the Genus Sphaerostomum (Trematoda: Opecoelidae) within Their Geographic Ranges

The host specificity of flukes belonging to the genus Sphaerostomum (S. bramae and S. globiporum) in the center and at the periphery of the genus range is discussed. Both fluke species are specific parasites of cyprinids. However, fish of nine other families and one cyclostome species have also been recorded as their hosts. At the periphery of the range, the spectrum of definitive hosts is broader than in the center owing to a greater number of unspecific hosts. In the center, unspecific hosts are represented by six fish species (Esox lucius, Misgurnus fossilis, Perca fluviatilis, Lota lota, Gymnocephalus cernuus, and Salmo sp.), four of which are predators. At the periphery, 11 fish species, including six predators (Anguilla anguilla, Barbatula barbatula, Cottus gobio, Cobitis taenia, Coregonus lavaretus, Salmo trutta, Alosa sp., Potamoschistus minutus, E. lucius, P. fluviatilis, and L. lota), and the cyclostome Lampetra fluviatilis are unspecific hosts. In the peripheral populations, compared to central, flukes manifest greater adaptive plasticity and can infest new hosts.     

土地利用对流域氮素记忆效应的影响研究

"记忆效应"是一些流域实行了多年的氮污染控制实践却仍未见成效的主要原因之一.然而,目前对流域氮素记忆效应的认识还很有限.本研究利用温州市珊溪水源地13个集水区近5年的河流TN浓度逐月监测数据,运用重标极差(R/S)分析和Spearman秩相关分析方法,探讨了土地利用对流域氮素记忆效应的影响.结果表明,河流TN平均浓度与耕地(r=0.495,p=0.086)和建设用地(r=0.692,p=0.009)面积比例正相关,与林地(r=-0.604,p=0.029)面积比例显著负相关,与园地(r=-0.039,p=0.900)、未利用地(r=-0.176,p=0.566)、集水区面积(r=-0.335,p=0.263)和河网密度(r=0.148,p=0.629)的相关性不显著.13条入库支流TN浓度序列的Hurst指数变异范围为0.33~0.72,意味着其中11个集水区具有显著的氮素记忆效应(0.5Hurst指数1.0),而其余2个集水区不显著(0Hurst指数0.5).Hurst指数与耕地(r=-0.482,p=0.095)和建设用地(r=-0.311,p=0.301)面积比例均负相关,而与园地(r=0.479,p=0.098)和林地(r=0.510,p=0.075)面积比例正相关.同时,Hurst指数与集水区面积大小(r=0.118,p=0.700)和未利用地面积比例(r=0.032,p=0.917)的相关性不显著,而与河网密度负相关(r=-0.529,p=0.063).流域内"源"功能为主土地利用面积的增加和氮输移效率的提高加剧了河流氮污染,而对氮素记忆效应的作用则相反.因此,尽管增加"汇"景观面积、降低氮输移效率能缓解河流氮污染,但"汇"景观中截留的遗留氮对河流氮浓度会造成更长时间的影响.