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271.
The building of railways on seasonally frozen ground is inevitable as China pursues economic development and the improvement of its citizens' living standards. However, railway construction in seasonally frozen soil areas is often faced with frost heave, leading to uneven subgrades which seriously threaten traffic safety. This article summarizes extant research results on frost heave mechanism, frost heave factors, and anti-frost measures of railway subgrades in seasonally frozen soil areas. 相似文献
272.
采用基于高通量测序平台的SLAF-seq技术开发蓝圆鲹(Decapterus maruadsi)微卫星标记,从获得的1 450个四至六碱基重复微卫星位点中随机挑选93个位点进行引物合成和多态性检测,最终开发出31个多态性微卫星标记.群体遗传学检测结果表明,31个位点的等位基因数为4~29(均值13.48),观测杂合度(Ho)为0.281~0.875(均值0.650),期望杂合度(He)为0.557~0.958(均值0.838),多态信息含量值(PIC)为0.456~0.939(均值0.803),表明所开发的31个微卫星位点均具有较高的多态性.Hardy-Weinberg平衡检测表明,17个位点符合HWE("哈迪-温伯格"平衡),且各位点间不存在连锁不平衡现象.跨物种扩增结果显示,分别有27、20、20、18、9个微卫星标记在颌圆鲹(Decapterus macarellus)、长身圆鲹(Decapterus macrosoma)、无斑圆鲹(Decapterus kurroides)、竹荚鱼(Trachurus japonicus)及金带细鲹(Selaroides leptolepis)中具有较好的通用性.本研究开发的多态性长碱基重复微卫星标记可为蓝圆鲹渔业资源的科学管理和保护提供有力的遗传学评估手段,亦可为圆鲹属和鲹科鱼类系统进化研究提供新的分析手段. 相似文献
273.
目的:观察益气养阴方治疗气阴两虚型慢性功能性便秘的临床疗效。方法:将气阴两虚型慢性功能性便秘患者80例随机分为治疗组与对照组各40例。治疗组采用益气养阴方治疗,对照组采用枸橼酸莫沙必利分散片治疗,比较2组患者临床疗效及临床症状积分变化情况。结果:总有效率治疗组为90.0%,对照组为75.0%,2组比较,差异有统计学意义(P<0.05);2组临床症状积分治疗前后组内比较及治疗后组间比较,差异均有统计学意义(P<0.05)。结论:益气养阴方治疗气阴两虚型慢性功能性便秘有较好的临床疗效。 相似文献
274.
中国沿海常见蜑螺科贝类的DNA条形码 总被引:1,自引:0,他引:1
DNA条形码不仅为物种鉴定提供了有效方法,而且也有助于分类学和生物多样性研究。本研究旨在探讨将COI和16S rRNA基因序列应用于中国沿海蜑螺科贝类物种鉴定的可行性,获得了该科3属7种贝类61个个体的COI和16S rRNA基因序列。基于COI基因序列的种内遗传距离为0.00—1.29%,平均为0.67%;属内种间遗传距离为4.62%—19.25%,平均为13.02%;基于16S rRNA基因序列的种内遗传距离为0.00%—0.48%,平均为0.23%;属内种间遗传距离为2.47%—8.48%,平均为6.37%。两种基因序列在所研究的蜑螺中,种内遗传差异均小于种间遗传差异,存在明显的条形码间隙,所有物种在系统发生树上都表现为独立的单系群。结果表明,线粒体COI和16S rRNA基因序列可以作为DNA条形码标准基因对蜑螺科贝类进行有效地物种鉴定。 相似文献
275.
The Antarctic krill(Euphausia superba) is a key species in the Southern Ocean ecosystem and an important link in the food web of the Antarctic ecosystem. The trophic information for this species during the transition from the austral fall to the winter is important to understand its poorly known overwintering mechanisms. However, the few studies on the topic differ in their results, in terms of both spatial and temporal variables. We investigated the size dependence and monthly and regional variation in δ~(13) C and δ~(15) N values of adult krill in the Antarctic Peninsula, in the austral fall(April to May) and the early winter(June). We aimed to examine the trophic variations of krill occurred during this period, and the relationship between krill and their feeding environment in the Antarctic marine ecosystem. The following results were obtained:(1) no significant relationship was observed between size and the δ13 C value of krill, but the δ15 N value of krill presented a remarkable association with size;(2)the δ13 C values of krill increased during the austral fall, but no remarkable variation existed at the onset of winter,and the δ15 N values were not significant different during this period;(3) mean δ15 N values of krill differed significantly between the Bransfield Strait and the South Shetland Islands. Our data imply that adult krill present size-, season-, and region-dependent trophic variation during the transition from austral fall to early winter in the Antarctic Peninsula. 相似文献
276.
Considering the current disadvantages of present offshore wind turbine foundations, a novel anchor foundation with skirt and branches is proposed, called offshore umbrella suction anchor foundation (USAF). A series of experiments and numerical simulations were performed to explore the bearing capacity of the USAF under various kinds of loading modes. The bearing characteristics and the anchor–soil interactions are described in detail for horizontal static loading, horizontal cyclic loading, and an antidrawing (pullout) test in silty soil. In the static loading test, the load–deflection of the anchor under step loading was analyzed and the normalized curve of the load–deflection was obtained to determine the ultimate horizontal bearing capacity of the anchor under normal working conditions. Under horizontal cyclic loading, the relationship between the plastic cumulative deformation and cyclic number was determined. In addition, the responses of USAF were investigated for a low wave frequency and storm surges. In the drawing test, it was found that a “segmentation phenomenon” occurred during the test. Moreover, a method to identify the maximum antidrawing load of USAF was provided based on dynamic mechanics. The numerical results show that the use of anchor branches and skirt can enhance the bearing performance of USAF to a certain degree. However, the anchor branch has a slight positive influence on the bearing performance improvement. The USAF is not only similar to a stiff short pile, but a rotation occurs. The failure envelope under composite loading (V-M) was obtained and the changes associated with changes in the aspect ratio of the internal compartment were clarified. 相似文献
277.
介绍捷联式航空重力矢量测量的基本原理,利用波数相关滤波(WCF)、比力线性校正的方法对重力扰动的水平和垂向分量进行误差补偿,评定内符合精度。对国产捷联式航空重力矢量仪的某次试验数据进行处理,以验证和评估航空重力矢量仪的性能。结果表明,在半波长分辨率为7.5 km时,6条重复测线的重力扰动水平分量经波数相关滤波处理后,东、北向分量的平均内符合精度分别从9.77 mGal、9.18 mGal提高到5.95 mGal、3.83 mGal;对比力的垂向分量线性校正后,将解算的重力扰动垂向分量再用WCF方法处理,其平均内符合精度从1.27 mGal提高到0.59 mGal。 相似文献
278.
It is well known that pitting corrosion occurring on surface of hull structural plate will surely result in a significant degradation of the ultimate strength of the hull structural plate. This report aims at development of an assessing formula for ultimate strength of hull plate with pitting corrosion damage under the biaxial in-plane compression loading. The ultimate strength assessment model that is in terms of the corroded volume loss was deduced in theory, and which was then completed through numerical experiment by employing nonlinear finite element analyses for series of corroded plate models. Meanwhile, pitting corrosion in actual ship hull was analyzed and simulated, which ensured that all the assumptions for the finite element model parameters were in accord with the actual hull plate with pitting corrosion damage. Furthermore, the effects of plate slenderness, the linear factors at the plate edges and the ratio between the transverse and the longitudinal in-plane stresses on the ultimate strength reduction related to the corroded volume loss were discussed. The ultimate strength assessment formula being in terms of corroded volume loss developed in this research is expected to be applicable to assess the ultimate strength of the hull structural plate with pitting corrosion damage. 相似文献
279.
This paper proposes a scheme of axial triple-well optical dipole trap by employing a simple optical system composed of a circular cosine grating and a lens. Three optical wells separated averagely by ~37 μm were created when illuminating by a YAG laser with power 1 mW. These wells with average trapping depth ~0.5 μK and volume ~74 μm3 are suitable to trap and manipulate an atomic Bose--Einstein condensation (BEC). Due to a controllable grating implemented by a spatial light modulator, an evolution between a triple-well trap and a single-well one is achievable by adjusting the height of potential barrier between adjacent wells. Based on this novel triple-well potentials, the loading and splitting of BEC, as well as the interference between three freely expanding BECs, are also numerically stimulated within the framework of mean-field treatment. By fitting three cosine functions with three Gaussian envelopes to interference fringe, the information of relative phases among three condensates is extracted. 相似文献
280.
海洋青鳉鱼专用型基因芯片的设计及其在生态毒理学上的应用研究 总被引:3,自引:0,他引:3
以生物芯片技术为核心,结合生态毒理学与功能基因组学的方法,制备了海洋青鳉鱼专用型生物芯片,包含180个与细胞分裂、解毒反应、缺氧反应、氧化应激反应、凋亡、生长和发育、性别决定和性腺分化以及生殖激素分泌等功能相关的基因.我们提取了雌性海洋青鳉鱼成体在正常培养和缺氧处理12周后的肝脏和卵巢组织总RNA,利用自制的基因芯片进行了基因表达谱分析,结果显示海洋青鳉鱼在缺氧压力环境下,肝脏和卵巢组织的差异性表达基因分别检测出9个和6个,表明应用此类自制良好的芯片可有效获得海洋青鳉鱼的组织特异性基因表达图谱,也将加强对海洋缺氧状态、氧化应激等反应的分子生物学机制的理解.本研究对于识别异常环境状态下的基因表达模式和组织特异性标志物,进一步开展监测海洋生态毒理因素的研究奠定良好的基础. 相似文献