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991.
992.
崇明东滩沉积物再悬浮对沉积物-水界面氮、磷交换行为的影响 总被引:33,自引:10,他引:23
2002年7月采集崇明东滩低潮滩沉积物样和水样,运用模拟实验研究沉积物再悬浮作用对沉积物-水界面三态氮和可溶磷交换行为的影响实验发现,在沉积物不断发生再悬浮的过程中,水体中三态氮的含量明显增加,其中NO3--N变化最为显著,升高浓度值达11.869μmol·L-1,NH4+-N增长2.1713μmol·L-1,NO2--N的释放约为0.2μmol·L-1,可溶磷的含量也有少量的增加.同时,再悬浮作用对沉积物-水界面三态氮和可溶磷的环境地球化学行为也有一定的影响,与静置状态相比,NH4+-N和NO3--N表现出与静置状态截然相反的变化规律,NO2--N受多种因素的影响,变化比较复杂,初期与静置状态相反而后表现一致.再悬浮颗粒物浓度也是制约沉积物-水界面三态氮和可溶磷变化的主要因子之一.实验结果显示,NH4+-N在前7h以内的变化和悬浮颗粒物浓度表现出较好的相关关系,后5h呈负相关关系;NO2--N和可溶磷在整个过程中与悬浮颗粒物浓度的变化都有着很好的相关性,只有NO3--N的变化与其关系比较薄弱. 相似文献
993.
优化、RSA和GLUE方法在非线性环境模型参数识别中的比较 总被引:6,自引:2,他引:4
参数识别是数学模型应用的前提,本文对非线性环境模型常用的3种参数识别方法进行了比较分析.优化方法是出现最早、应用最广泛的参数识别方法之一.但在观测误差存在的情况下,采用优化方法识别的最优参数进行模型预测,存在很大的决策风险.考虑到这种不足,RSA方法和GLUE方法摒弃了识别单一最优参数的传统思维,而把识别参数扩大到多点组成的参数集.RSA方法与GLUE方法不同的是,RSA方法把可行的参数点看成是同等接受的,而GLUE方法则根据模拟值与实测值的差别,确定其似然度,代表参数的可信度水平.除参数识别以外,RSA方法和GLUE方法也是全局灵敏度分析的重要工具. 相似文献
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为研究2008年8月北京奥运会1a之后北京市大气颗粒物的污染特征,于2009年8月对北京市大气颗粒物PM10、PM2.5样品进行采集,测量其质量浓度并对其中的水溶性离子组分进行分析.研究发现2009年8月北京市大气颗粒物PM10、PM2.5质量浓度日均值分别为176.9μg/m3和102.5μg/m3.PM10质量浓度比2008年观测值上升了180%,比2007年降低了10%; PM2.5质量浓度比2008年观测值上升了126%,比2007年上升了31%.水溶性离子是大气颗粒物的重要组分,分别占PM10和PM2.5质量浓度的43%和61%.对比发现,污染天气条件下PM2.5/PM10和NO3-/SO42-比值升高,移动源是北京地区主要的污染物来源.风向风速和降水等天气条件对颗粒物质量浓度有很大影响,其中0.5~1.0m/s的东南风条件下大气颗粒物污染最为严重. 相似文献
997.
以互花米草为原料,采用中温(35±1)℃批式发酵的方式,考察了NaOH高温碱间歇式处理对互花米草厌氧消化过程的影响.结果表明,互花米草一次发酵至产气停止,单位TS产气量为263mL/g,发酵过程中出现酸化现象, pH值最低为5.17.二次发酵原料为一次发酵后的固体残余物,主要组分为可分解有机物以及一些难分解有机物,过程中未出现酸化现象, pH值经短暂下降后很快稳定在7.5左右,累积产气量在一次发酵的基础上提高了46%.互花米草单位TS产气量为383mL/g.消化液中有机酸乙酸含量最大,丙酸和丁酸含量相当. 相似文献
998.
Influence of Polyol Plasticizers on the Properties of Polyvinyl Alcohol Films Fabricated by Melt Processing 总被引:1,自引:0,他引:1
In this work, high-alcoholysis polyvinyl alcohol (PVA) films were fabricated by melt processing and the plasticizing effect
of compound polyol plasticizers on PVA were investigated with X-ray diffraction (XRD), differential scanning calorimetry (DSC),
rheological measurements, mechanical tests etc. Hydrogen bonding interactions occurred between PVA and plasticizer. With the
increase of plasticizer, the flowability of PVA was improved and reached the maximum value at the plasticizer of 20%. Glass
transition temperature (T
g) and melting point (T
m) decreased with the increase of plasticizer content. For the heterogeneous nucleation effect of plasticizer, new polymorph
of PVA formed. The viscosity was sensitive to the shear rates. The incorporation of plasticizers into PVA resulted in the
increase of elongation at break and impact strength, as well as the decrease of tensile strength. 相似文献
999.
The main purpose of this study is challenging to dramatically improve the toughness of poly(lactic acid) (PLA)/starch by adding poly (ethylene glycol) (PEG) into the composites and grafting PEG molecules onto the surface of starch particles. It was found that the surface grafting of PEG onto starch induced the presence of PEG-rich regions located around the starch particles, caused by migration and aggregation of free PEG molecules. A novel interphase transition layer between PLA and starch was formed, which showed great ability for cavitation and vested large-scaled plastic deformation to PLA matrix. Further mechanical properties tests indicated the formation of interphase layer significantly increase the elongation at break from 10.2 to 254.5%, and notched impact strength from 1.56 to 2.37?kJ/m2 for PLA/PEG/starch ternary composites. The influence of PEG component, ethanol extraction and annealing was also investigated. 相似文献
1000.
Cadmium (Cd2+), a known carcinogen, mimics the effects of estrogen in the uterus and mammary gland suggesting its possible involvement in the development and progression of breast cancer. This lab showed through analysis of a small set of archival human diagnostic specimens that the third isoform of the classic Cd2+ binding protein metallothionein (MT-3) is not expressed in normal breast tissue, but is expressed in some breast cancers and that expression tends to correlate with a poor disease outcome. The goals of this study were to verify that overexpression of MT-3 in a large set of archival human diagnostic specimens tends to correlate with poor disease outcome and define the mechanism of MT-3 gene regulation in the normal breast epithelial cell. The results showed that MT-3 was expressed in approximately 90% of all breast cancers and was absent in normal breast epithelium. The lack of MT-3 staining in some cancers correlated with a favorable patient outcome. High frequency of MT-3 staining was also found for in situ breast cancer suggesting that MT-3 might be an early biomarker for breast cancer. The study also demonstrated that the MCF-10A cell line, an immortalized, non-tumorigenic model of human breast epithelial cells, displayed no basal expression of MT-3, nor was it induced by Cd2+. Treatment of the MCF-10A cells with the demethylation agent, 5-aza-2′-deoxycytidine, or the histone deacetylase inhibitor, MS-275, restored MT-3 mRNA expression. It was also shown that the MT-3 metal regulatory elements are potentially active binders of protein factors following treatment with these inhibitors suggesting that MT-3 expression may be subject to epigenetic regulation. 相似文献