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魁蚶(Anadara broughtonii)是我国北方重要的经济贝类,筏式养殖是其主要的生产方式。2014年5月至2015年1月,测定了不同季节灵山湾筏式养殖魁蚶及其3种潜在食物源(表层颗粒有机物SPOM、底层颗粒有机物BPOM和附着微藻AM)的碳氮稳定同位素(δ13C和δ15N),结合胃含物分析研究了海区食物源结构的季节变化对魁蚶食物组成的影响。结果显示,魁蚶及其食物源的稳定同位素比值均存在明显的季节差异,魁蚶的δ13C值(-19.6‰~-19.2‰)介于SPOM (-23.3‰~-21.8‰)、BPOM (-22.1‰~-21.2‰)和AM(-17.0‰~-16.0‰)之间,δ15N值范围集中在8.7‰~9.9‰。冬季魁蚶的δ13C值最低,δ15N值则最富集。水体颗粒有机物(主要由浮游植物组成)是魁蚶的主要食物来源(60.0%~77.8%),以夏季的饵料贡献率最高;海区再悬浮作用使BPOM的贡献率始终维持在较高水平(30.8%~47.1%);而养殖网笼上的附着微藻也可为魁蚶提供约22.1%~40.0%的食物。研究揭示了筏式养殖魁蚶可以混合滤食颗粒有机物和附着微藻,附着微藻是其重要的食物补充。 相似文献
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根据广州国家基本气象站1951—2020年的逐日气温资料,采用线性趋势法、距平及累积距平法和Mann-Kendall检验法,对WMO推荐的16种极端气温指数中的13种以及2种结合本地实际的新的极端气温指数共计15种指数进行计算,从月尺度和年尺度分析广州地区各极端气温指数随时间变化的趋势和突变年份,并对以往研究中较少探究的基期的选择对相对极端气温指数的结果影响进行了对比分析。(1)从年尺度看,广州地区近70 a的夏日日数SU25、酷热日数SU35、热夜日数TR20、非常热夜日数TR26、最高气温TXx、最低气温TNn、最低气温最大值TNx、相对暖夜日数TN90p、暖昼日数TX90p、显著偏暖持续指数WSDI均呈现明显的上升趋势,相对冷夜日数TN10p、冷昼日数TX10p和偏冷持续指数CSDI呈现下降趋势,气温日较差DTR和最高气温最小值TXn变化趋势不明显;(2)新的极端气温指数SU35和TR26的上升速率明显大于SU25和TR20的上升速率,能更好地反映近70 a昼夜体感炎热日数呈现极显著的上升趋势,更加符合评估气候变化对当地生产生活的影响;(3)从月尺度来看近70 a广州地区的暖系列... 相似文献
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Sea surface temperature(SST) data obtained from coastal stations in Jiangsu, China during 2010–2014 are quality controlled before analysis of their characteristic semidiurnal and seasonal cycles, including the correlation with the variation of the tide. Quality control of data includes the validation of extreme values and checking of hourly values based on temporally adjacent data points, with 0.15°C/h considered a suitable threshold for detecting abnormal values. The diurnal variation amplitude of the SST data is greater in spring and summer than in autumn and winter. The diurnal variation of SST has bimodal structure on most days, i.e., SST has a significant semidiurnal cycle. Moreover, the semidiurnal cycle of SST is negatively correlated with the tidal data from March to August, but positively correlated with the tidal data from October to January. Little correlation is detected in the remaining months because of the weak coastal–offshore SST gradients. The quality control and understanding of coastal SST data are particularly relevant with regard to the validation of indirect measurements such as satellitederived data. 相似文献
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为研究工程区海域水沙特征的时空分布、运动规律,采用不同时期的现场水文泥沙资料,对射阳港拦门沙航道工程建设前后的水流、含沙量、悬沙粒径和底质特征进行了对比分析。研究表明:射阳港一期航道工程建设后航道内潮波发生变形,涨潮流速大、历时短;落潮流速小、历时长,进入到航道内泥沙很难被带出航道,容易导致航道淤积。工程区海域整体含沙量较大,一期工程建设后导堤内涨潮含沙量明显增大,口门净输沙向口内,通过口门进入到航道的高含沙水体是航道淤积的重要沙源之一。导堤间边滩表层存在部分淤泥,且具有一定流动性,在水流及自身重力作用下,边滩淤泥可归入航道内。 相似文献
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如何使传统神经网络算法对遥感影像典型目标检测表现出良好的适应性是当前遥感领域的一项难点.在深入解析最新YOLOv4网络结构及算法核心思想前提下,首先通过增加104×104的特征层尺度并嵌入SE模块进行网络结构改进;继而根据待检测目标尺度特点调整锚点框,提高YOLOv4算法对遥感影像典型目标检测性能;最后设计对照实验进行... 相似文献
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Stick–Slip and the Transition to Steady Sliding in a 2D Granular Medium and a Fixed Particle Lattice
We report an experimental study of the stick–slip to steady sliding behavior of a solid object pulled, via a spring, across
2D granular substrates of photoelastic disks that are either fixed in a solid lattice (granular solid) or unconstrained, forming
a granular bed. We observe a progression of friction regimes with increasing sliding speed, including single-slip, double-slip,
and mixed stick–slip regimes, steady sliding, and inertial oscillations. For the case of the granular bed, we report a detailed
analysis of frictional behavior for the low speed stick–slip regime, including spring and elastic energy dependencies during
the stick and slip portions of the motion. For the case of the granular solid, we explore friction in the presence and absence
of externally applied vibrations, and compare it with sliding on a granular bed, which is intrinsically disordered. We observe
that external vibration reduces transition values for both the single-slip to double-slip transition and the stick–slip to
steady sliding transition. Moreover, we observe that the effect of packing disorder on granular friction seems similar to
the effect of vibration-induced disorder, a result that, to our knowledge, has not been reported previously in the experimental
literature. 相似文献
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通过工程实例,介绍CFG桩在大型油罐地基局部处理中,既有效提高软弱地基强度,又最大限度保持不同地基变形协调一致的处理方法.针对油罐体型的特殊性,采用了沿油罐圆心环形布桩,并且根据不同地段地基土性质的纵横向差异采用不等距布桩的方案.复合地基处理效果理想,达到了预期的设计目的,为类似工程的地基处理提供了一种新的设计理念,供类似工程参考. 相似文献