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251.
The trends of distribution, translocation and seasonal change of heavy metal Pb were studied based on the surface and bottom water sampling in Jiaozhou Bay in 1979, and compared with those in 1990's. The results showed that the source of Pb in the bay was from wastewater and sewage in the east of Jiaozhou Bay from ocean vessels. Pb concentration was higher in spring and lower in summer and autumn, and remained stable through sedimentation in the bottom layer. The overall water quality was good in 1970's. Compared with the environmental monitoring data of 1995-1999, Pb pollution had become serious. Therefore, more efforts should be made to protect the bay from Pb pollution. 相似文献
252.
Reversible protein phosphorylation, catalyzed by protein kinases and phosphatases, is an important and versatile mechanism by which eukaryotic cells regulate almost all the signaling processes. Protein phosphatase 1 (PP1) is the first and well-characterized member of the protein serine/threonine phosphatase family. In the present study, a full-length cDNA encoding the beta isoform of the catalytic subunit of protein phosphatase l(PPlcb), was for the first time isolated and sequenced from the skin tissue of flatfish turbot Scophthalmus maximus, designated SmPPlcb, by the rapid amplification of cDNA ends (RACE) technique. The cDNA sequence of SmPPlcb we obtained contains a 984 bp open reading frame (ORF), flanked by a complete 39 bp 5' untranslated region and 462 bp 3' untranslated region. The ORF encodes a putative 327 amino acid protein, and the N-terminal section of this protein is highly acidic, Met-Ala-Glu-Gly-Glu-Leu-Asp-Val-Asp, a common feature for PP1 catalytic subunit but absent in protein phosphatase 2B (PP2B). And its calculated molecular mass is 37 193 Da and pI 5.8. Sequence analysis indicated that, SmPPlcb is extremely conserved in both amino acid and nucleotide acid levels compared with the PPlcb of other vertebrates and invertebrates, and its Kozak motif contained in the 5'UTR around ATG start codon is GXXAXXGXXATGG, which is different from mammalian in two positions A6 and G3, indicating the possibility of different initiation of translation in turbot, and also the 3'UTR of SmPPlcb is highly diverse in the sequence similarity and length compared with other animals, especially zebraf'lsh. The cloning and sequencing of SmPPlcb gene lays a good foundation for the future work on the biological functions of PP1 in the flatfish turbot. 相似文献
253.
GPS���ٶ�λ�в�̬�����������ⷨ 总被引:1,自引:1,他引:0
???GPS?????λ??????????????????????????????????????????????M??????????????μ??????????????????????????????????????????????е????????????????????????÷??????п??????????????????????????? 相似文献
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256.
利用DEM提取坡度具有明显的尺度依赖性,探求DEM在不同尺度下表现出的规律关系,建立多尺度变换模型,以实现不同尺度间的转换是地形分析研究的热点和难点。本文阐释了DEM表面与地表粗糙度分形维数值的地学意义及内在关系,并利用分形对象的自相似性原理,建立了一种基于DEM分形特征的坡度尺度变换模型。选取四川丘陵地区某小流域为研究区,进行坡度尺度变换实验和误差分析,结果表明该模型能有效实现坡度尺度变换:在非平坦地区(坡度>1°)一般重采样方法变换得到的坡度误差为该方法的1.86倍;从信息熵理论分析,经该方法转换后的坡度信息得到了显著恢复。对于无1︰1万及以上精度地形数据的西南山区,利用该方法获取高精度坡度数据具有重要的理论价值和现实意义。 相似文献
257.
Chinese summer extreme rainfall often brings huge economic losses, so the prediction of summer extreme rainfall is necessary. This study focuses on the predictability of the leading mode of Chinese summer extreme rainfall from empirical orthogonal function(EOF) analysis. The predictors used in this study are Arctic sea ice concentration(ASIC) and regional sea surface temperature(SST) in selected optimal time periods. The most important role that Arctic sea ice(ASI) plays in the appearance of EOF1 may be strengthening the high pressure over North China, thereby preventing water vapor from going north. The contribution of SST is mainly at low latitudes and characterized by a significant cyclone anomaly over South China. The forecast models using predictor ASIC(PA), SST(PS), and the two together(PAS) are established by using data from 1980 to 2004. An independent forecast is made for the last 11 years(2005-2015). The correlation coefficient(COR) skills between the observed and cross-validation reforecast principal components(PC) of the PA, PS, and PAS models are 0.47, 0.66, and 0.76, respectively. These values indicate that SST is a major cause of Chinese summer extreme rainfall during 1980-2004. The COR skill of the PA model during the independent forecast period of 2004-2015 is 0.7, which is significantly higher than those of the PS and PAS models. Thus, the main factor influencing Chinese summer extreme rainfall in recent years has changed from low latitudes to high latitudes. The impact of ASI on Chinese summer extreme rainfall is becoming increasingly significant. 相似文献
258.
HU Huiqin HUANG Fei ZHANG Shaoqing RUAN Chengqing GAO Shanhong LI Pengyuan 《中国海洋大学学报(英文版)》2019,(2):271-281
Fog has recently become a frequent high-impact weather phenomenon along the coastal regions of North China. Accurate fog forecasting remains challenging due to limited understanding of the predictability and mechanism of fog formation associated with synoptic-scale circulation. One frequent synoptic pattern of fog formation in this area is associated with cold front passage(cold-front synoptic pattern, CFSP). This paper explored the predictability of a typical CFSP fog event from the perspective of analyzing key characteristics of synoptic-scale circulation determining fog forecasting performance and the possible mechanism. The event was ensemble forecasted with the Weather Research and Forecasting model. Two groups of ensemble members with good and bad forecasting performance were selected and composited. Results showed that the predictability of this case was largely determined by the simulated strengths of the cold-front circulation(i.e., trough and ridge and the associated surface high). The bad-performing members tended to have a weaker ridge behind a stronger trough, and associated higher pressure over land and a weaker surface high over the sea, leading to an adverse impact on strength and direction of steering flows that inhibit warm moist advection and enhance cold dry advection transported to the focus region. Associated with this cold dry advection, adverse synoptic conditions of stratification and moisture for fog formation were produced, consequently causing failure of fog forecasting in the focus region. This study highlights the importance of accurate synoptic-scale information for improved CFSP fog forecasting, and enhances understanding of fog predictability from perspective of synoptic-scale circulation. 相似文献
259.
长三角地区民宿的空间分布及影响因素 总被引:5,自引:0,他引:5
近年来,民宿作为旅游业发展的新兴模式,日益受到关注,并呈现蓬勃发展状态。以民宿业发展最为成熟的长三角地区为研究对象,基于去哪儿网相关民宿数据,采用空间最邻近分析、密度分析等空间分析方法,研究民宿的空间分布格局与特征,并基于逐步回归分析,探讨影响民宿分布的因素,得出以下结论:① 长三角地区民宿呈现高度集聚的状态,整体上表现为多核心分布,并形成一、二、三级组团,密度由核心向外围递减。② 民宿集聚分布在经济较为发达的城市和核心景区周边,具有明显的中心性。③ 基于对经济基本状况、交通状况、人口条件、居民消费能力、旅游市场状况、旅游资源与环境条件等方面共15个影响因素分析,发现单位面积旅游收入、A级景区数量、人口密度、地区国内生产总值四个指标对民宿密度有显著正向影响,其中,影响力单位面积旅游收入>A级景区数量>人口密度>地区国内生产总值。 相似文献
260.
基于敏感性-稳定性-响应3维要素构建指标体系,运用熵值法和ARIMA-BP组合预测模型研究中国人海经济系统环境适应性的演化及预警。结果表明:① 2001~2016年中国人海经济系统环境适应性呈稳定上升态势,总体集中于中警状态,期间经历了“人海环境系统比较优势阶段→耦合协调阶段→人海经济系统比较优势阶段”的双螺旋适应过程,预计2017~2020年再次进入相互契合的轻警状态;② 16 a间中国人海经济系统环境适应性波动存在上升期短-衰退期长现象,预计未来4 a人海经济系统环境适应性在经济下行和生态约束背景下的速率不容乐观;③ 权衡人海经济系统和人海环境系统的关系,追求总体效益最大化,延长适应性周期波动中扩张期活动,差别化和灵活性的适应行为是未来主要排警对策。 相似文献