排序方式： 共有71条查询结果，搜索用时 125 毫秒
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汶川地震强震区映秀地区泥石流的危险性 总被引：1，自引：0，他引：1
汶川地震震中四川省汶川县映秀镇及附近于2010-08-14暴发群发性泥石流(简称"8.14"泥石流),造成巨大的人员伤亡和财产损失。地震灾区松散固体物源丰富,泥石流灾害相对活跃,估算未来不同降雨频率下泥石流的暴发规模并评价其危险性,是泥石流灾害风险管制的首要工作。在研究四川省部分地区的泥石流和对应降雨频率资料的基础上,得到泥石流规模和降雨频率之间的关系式。以映秀"8.14"泥石流的暴发规模和降雨频率为基础数据,通过泥石流规模和降雨频率之间的关系式推算得到映秀及附近岷江两岸13条泥石流沟在不同降雨频率下的泥石流规模。以泥石流在堆积扇上的平均堆积厚度(泥石流规模/堆积扇面积)、泥石流发生频率、流域面积、主沟长度、流域相对高度、流域切割密度和不稳定沟床比例为危险性判断因子,分别对映秀及邻近地区的13条泥石流沟在100 a、50 a、20 a、10 a和5 a一遇5种不同频率降雨条件下的泥石流危险性进行评价。结果表明:在5种降雨频率下,8条沟的泥石流危险性为高度,4条沟的为中度到高度,1条沟的为中度。 相似文献
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东南沿海地区新生代火山作用和地幔柱 总被引：17，自引：0，他引：17
通过本文的研究表明 ,东南沿海地区从沿海→内陆 (牛头山→闽清→明溪 )新生代玄武岩的年龄逐渐变小 ,具有火山链的特征 ;微量元素和 Sr- Nd同位素特征与洋岛玄武岩 (OIB)类似 ;上地幔具有过热状态和扰动的热结构 ;地球物理具有低的 Vs 异常及提供了在该区下面具有地幔柱的 CT模式 ;火山岩具有较高的 3He/4He同位素比值 ,因此提出了研究区下面存在地幔柱。进一步根据火山岩的热动力学参数 ,从沿海→内陆 ,随火山岩年龄变小 ,火山岩的碱性程度逐渐增加 ,岩浆起源的深度逐渐变深 ,局部熔融程度逐渐变小等特征 ,提出了地幔柱的形成是由太平洋板块俯冲诱发 ,地幔柱位于俯冲带上面 ,南海的扩张和新生代火山岩的形成是地幔柱作用的结果 ,并提出地幔柱成因演化模式。 相似文献
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The present study evaluated the effects of chilled storage and cryopreservation on sperm motion characteristics, antioxidant enzyme activities, and lipid peroxidation in the Pacific cod Gadus macrocephalus. Sperm motility and the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (Gr), and lipid peroxidation (measured via malondialdehyde (MDA) content) were determined after the milt was stored at 4°C for 12 h, cryopreserved without cryoprotectant in 12% propylene glycol (PG), cryopreserved in 12% PG+0.1 mol/L trehalose, or cryopreserved in 12% PG spermatozoa but centrifuged to decant the supernatant prior to cryopreservation (only sperm cells were cryopreserved). After chilled storage or cryopreservation, the SOD, CAT and GPx activities were reduced in sperm cells and increased in seminal plasma in almost all treatments; sperm motility parameters were also decreased. However, the addition of trehalose into the cryoprotectant could significantly improve the postthaw sperm quality as revealed by the sperm average path velocity. This improvement might be attributed to the function of trehalose in scavenging reactive oxygen species. Chilled storage and cryopreservation had significant effects on sperm motion characteristics, antioxidant enzyme activities, and lipid peroxidation in the Pacific cod. 相似文献
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泥石流形成区沟床宽度和颗粒粒径对沟床起动型泥石流的发生影响很大,在强烈地震影响区内显得尤为突出,但目前的泥石流预报中还没考虑到这两个因素,无法准确预测强震区泥石流的发生.在泥石流10 min和1 h精细化预报模型基础上,通过现场调查群发泥石流事件,结合汶川地震强烈影响区泥石流的演化特点,引入了泥石流形成区沟道宽度和颗粒粒径的影响,建立了改进的精细化泥石流10 min和1 h预报模型,并在贵州望谟打易和四川德昌群发泥石流、汶川地震强烈影响区的文家沟多次泥石流事件中获得了很好的验证结果,得出泥石流形成区的颗粒粒径代表泥石流的地质因子,泥石流形成区沟床宽度代表泥石流的地形因子之一,这2个因子在泥石流发生中的作用都非常重要;改进的精细化10 min和1 h预报模型以及临界值,可以用于强烈地震区和一般的泥石流预报. 相似文献
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目前行人航迹推算逐渐成为室内定位研究与应用的热点。针对利用陀螺仪推算行人航向时存在较大累积误差的问题，本文提出了一种基于智能手机传感器的行人航向解算算法。该算法根据陀螺仪输出的角速度数据与手机传感器参数计算合适的阈值，实时调节PI调节器的误差补偿系数，对预处理后加速度计和磁力计数据解算的航向角进行补偿，并与陀螺仪数据互补滤波融合，得到融合后的航向角。试验基于低成本智能手机，分别在磁场强弱环境下采集手机传感器数据，对比分析本文算法与传统互补滤波算法及九轴数据融合算法在推算行人航向时的精度。试验结果表明，在室内磁干扰较强的环境下，本文算法与传统互补滤波算法、九轴数据融合算法相比定位精度分别提升了68.4%和65.9%，平均航向误差分别减小了3.4°和1.8°，验证了本文算法有较好的抗磁干扰性能，提高了行人航向角解算的可靠性。 相似文献
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鞍带石斑鱼仔稚幼鱼骨骼发育与生长特性研究 总被引：1，自引：0，他引：1
骨骼发育对于养殖鱼类苗种培育至关重要,骨骼畸形会影响仔稚幼鱼的外部形态及功能需求。作者利用骨骼染色技术和显微测量的方法对鞍带石斑鱼(Epinepheluslanceolatus)仔稚幼鱼的骨骼发育及生长特性进行连续观察和测量。实验结果表明:鞍带石斑鱼初孵仔鱼不存在骨与软骨结构,鞍带石斑鱼在变态前期和变态早期(长棘期)仔鱼的全长、颅骨长度、脊柱长度及尾鳍复合物的长度增加缓慢,骨骼发育过程中与摄食、呼吸及游泳功能相关的骨骼优先发育,如颅骨(颌骨、鳃)和鳍元件,且骨化顺序与发育顺序基本一致。进入变态晚期(收棘期),营养摄取及利用的器官发育趋于完善,稚鱼进入快速生长阶段。此外,在仔稚鱼发育早期,颅骨、脊柱以及尾鳍复合物中存在异速生长特性,呈现为在变态前期和变态早期(长棘期)颅骨和尾鳍复合物为正异速生长,而脊柱为负异速生长;在变态晚期(收棘期)和变态后期,颅骨为负异速生长,而脊柱和尾鳍复合物为近等速生长。因此,鞍带石斑鱼仔稚幼鱼的颅骨、脊柱及尾鳍复合物骨骼发育的异速生长现象与摄食、呼吸及游泳功能相适应。 相似文献
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Turbots( Schophthalmus maximus), one of the most important economic marine flatfish species, fail to undergo final spawning and spermiation naturally under artificial farming conditions. In vertebrates, reproduction is regulated by the brain-pituitary-gonadal axis(BPG-axis), and gonadotropin releasing hormone(GnRH) is one of its key components. Therefore, to better understand the physiology of reproduction in the turbot, three of the genes encoding GnRH subtypes— sbGnRH, c GnRH-II and sGnRH —were cloned and sequenced by isolating the cDNA sequences. The localizations and patterns of expression of their mRNAs were also evaluated during seasonal gonadal development. All three mRNAs were expressed abundantly in the brain; sbGnRH and sGnRH mRNAs were also detected in the gonads and pituitary gland, and sbGnRH expression was much higher than that of sGnRH, indicating the critical role of sbGnRH in regulating the BPG-axis. Moreover, the brain expression patterns of sbGnRH and sGnRH mRNAs showed an increased trend during gonadal development, peaking in mature stages. This indicated the direct regulation of gonadal development by the GnRH system. In addition, c GnRH-II mRNA expression showed no significant variations, suggesting that c GnRH-II is not critically involved in the control of reproduction. Further, the mRNA abundances of the three GnRH forms in the breeding season were significantly higher than those in immature and post-breeding stages in all analyzed brain areas. Therefore, we propose that sbGnRH is the most important hormone for the regulation of reproduction in turbot via the BPG-axis. These results will help in better understanding the reproductive endocrine mechanisms of turbots and lay the groundwork for additional studies aimed at comparing the reproductive physiology of wild individuals with those raised under artificial conditions. 相似文献
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