172 resultados para 617.574


Relevância:

10.00% 10.00%

Publicador:

Resumo:

Epitaxial crystallization of trans-1,4-polybutadiene (PBD) on highly oriented isotactic poly(propylene) (iPP) has been investigated at different crystallization temperatures and rates. From electron microscopy and electron diffraction, it is confirmed that epitactic growth of the low-temperature modification (monoclinic) with microcrystals of PBD on the iPP films takes place with their chain directions about +/- 50-degrees apart. No epitaxial relationship occurs between the high-temperature modification (hexagonal) of PBD and the iPP substrate. Thermal analyses of PBD-PP layered films indicate that the epitaxy has an important effect on the formation of the high-temperature modification of PBD.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

本文介绍了利用自装的时间分辨激光荧光光谱装置对混合稀土中铽的测定方法。装置采用氮分子激光器为激发光源,Boxcar积分器为信号处理系统,选择了Tb-Sal-乙醇溶液为荧光体系,用标准加入法对样品进样行了测定。并将已知样品的测定结果与其它方法测定结果进行了比较。本法测定铽的相对标准偏差为7.4%,检出限为1.3×10~(-4)μg/ml。

Relevância:

10.00% 10.00%

Publicador:

Resumo:

本文对 LB 膜修饰电极特点、电化学行为及其在光电化学,电催化,传感器等方面的应用进行了综述。

Relevância:

10.00% 10.00%

Publicador:

Resumo:

本文评述了天然水样品中PPb级的Cu、Pb、Zn、Cd、Cr~(3+)、Cr~(6+)、Ni、Co、Mn、Fe、As~(3+)、As~(5+)、Se~(4+)、Se~(6+)、Hg、F-的保存条件。如水样的pH值,金属离子的初始浓度,容器的材料,保存的时间和温度等等。建议水样经0.45微米泸膜过泸后。用硝酸酸化至pH≤1.5(As、Se用硫酸酸化),对于Hg不仅酸化,还应加入半胱氨酸、氯金酸或重铬酸钾等保护剂。水样贮存在干净的高密度聚乙烯或聚四氟乙烯(特氟隆)容器中,在4℃的条件下为最佳。

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Toll-like receptors (TLRs) are an evolutionarily ancient family of pattern recognition receptors (PRRs), playing a crucial role in innate immune responses. Here we present a Toll homolog from Chinese shrimp Fenneropenaeus chinensis, designated FcToll. The full-length cDNA of FcToll is 4115 bp including a poly A-tail of 16 bp, encoding a putative protein of 931 amino acids. The predicted protein consists of an extracellular domain with a potential signal peptide, 16 leucine-rich repeats (LRR), two LRR-C-terminal (LRR-CT) motifs, and two LRR-N-terminal (LRR-NT) motifs, followed by a transmembrane segment of 23 amino acids, and a cytoplasmic Toll/Interteukin-IR (TIR) domain of 139 residues. Genomic structure of FcToll gene contains five exons and four introns. Phylogenetic analysis revealed that it belongs to insect-type invertebrate Toll family. Transcripts of FcToll gene were constitutively expressed in various tissues, with predominant level in lymphoid organ. Real-time PCR assays demonstrated that expression patterns of FcToll were distinctly modulated after bacterial or viral stimulation, with significant enhancement after 5 h post-Vibrio anguillorum challenge but markedly reduced levels immediately after white spot syndrome virus (WSSV) exposure. These results suggest that FcToll might be involved in innate host defense, especially against the pathogen V. anguillarum. (c) 2008 Elsevier Ltd. All rights reserved.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

A group of statistical algorithms are proposed for the inversion of the three major components of Case-H waters in the coastal area of the Huanghai Sea and the East China Sea. The algorithms are based on the in situ data collected in the spring of 2003 with strict quality assurance according to NASA ocean bio-optic protocols. These algorithms are the first ones with quantitative confidence that can be applied for the area. The average relative error of the inversed and in situ measured components' concentrations are: Chl-a about 37%, total suspended matter (TSM) about 25%, respectively. This preliminary result is quite satisfactory for Case-H waters, although some aspects in the model need further study. The sensitivity of the input error of 5% to remote sensing reflectance (Rrs) is also analyzed and it shows the algorithms are quite stable. The algorithms show a large difference with Tassan's local SeaWiFS algorithms for different waters, except for the Chl-a algorithm.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

对自行研制开发的气升式藻类光生物反应器的特性和应用进行了研究。反应器的主体包括主筒、导流筒和通气管,有10升和100升两种容积;二氧化碳配气装置由气体配制、配气罐和气体过滤装置三部分组成。反应器与配气装置均已申报国家专利。通过冷模实验,比较通气管和导流筒设置对气升式反应器的气含率、上升时间、下降时间、循环时间和导流筒内流体雷诺数的影响;提供提高二氧化碳传递速率和通气效率的理论论据。以小球藻和海带雌配子体无性繁殖系为研究对象,对光衰减规律进行了初步研究,建立了数学模型。用小球藻为材料,对100升反应器进行了应用研究。结果表明这台反应器可长期连续稳定运转,占地面积小,具有较高的传质、光能传输和利用效率,小球藻密度达到6.09 * 10~7cell/ml时,光照尚未成为生长的限制因子。以占地面积计,小球藻25天平均产量达到293.94g/(m~2 · d)。在小球藻密度提高时,无机碳源供应成为限制因子,补充CO_2可明显提高生长速率。利用10升反应器,分别对海带雌、雄配子体无性繁殖系进行培养,每天短时间通入二氧化碳混合气体,使海带无性繁殖系的对数生长期延长,雌配子体无性繁殖系日产量达到35.3mgDCW/(L · d)。

Relevância:

10.00% 10.00%

Publicador:

Resumo:

太平洋磷虾(Euphausia pacifica Hansen)作为目前已开发利用的6种主要磷虾资源之一,广泛分布于北太平洋北部及其临近近岸海域。在黄海,太平洋磷虾是黄海海洋生态系统中大型浮游动物的优势种和重要功能群的组成种类,它还是黄海生态系统中鱼类等上层营养级生物的重要饵料。太平洋磷虾的种群组成以及数量变化会直接影响到黄海经济鱼类的资源动态,从而影响到整个黄海海洋生态系统的变化。 本论文依托国家重点基础研究发展计划项目(973-II)——“我国近海生态系统食物产出的关键过程及其可持续机理”和国家自然科学基金40306021号——“黄、东海太平洋磷虾种群补充机制研究”,在2006年4月到2007年8月的八个黄海调查航次中,通过网采固定样品和现场培养实验相结合的方法,对黄海海域太平洋磷虾的种群生态分布和补充、繁殖和发育策略、以及成体的摄食、代谢进行了较为全面、细致的研究。 种群生态分布:本文根据2006年4月(春季)和10月(秋季)两次黄海大面调查和2006年9月-2007年8月六次黄海断面调查所获得的样品,研究了太平洋磷虾在南黄海的种群生态分布和补充机制,并探讨了其生态分布与环境因子的关系。 春季,南黄海太平洋磷虾种群主要分布在33 °N-36 °N、50 m-75 m等深线之间的海域,种群总丰度(不包括卵)为152.90 ind. m-3,卵丰度非常高,成体丰度较低,仅占种群总数量的8.72%。调查海域的平均成体丰度为0.35 ind. m-3。种群组成以幼体为主,占到种群的90.85%。春季是太平洋磷虾种群补充的高峰期。秋季,种群主要分布在黄海冷水团海域,种群总丰度(不包括卵)为335.38 ind. m-3,成体丰度显著高于春季,调查海区成体的平均丰度为7.73 ind. m-3。成体和未成体以99.5%的总比例在种群中占绝对数量优势,卵和幼体都非常少。秋季太平洋磷虾种群处于稳定期。春季成体的体长显著大于秋季,春季成体全长以13-18 mm为主,而秋季成体的全长主要是9-13 mm。 春季,太平洋磷虾成体具有昼夜垂直迁移行为,白天主要停留在底层水域,夜间少部分成体会上升到中上层水域,但是大部分成体仍然停留在深层。幼体从C3期开始就具有一定昼夜垂直迁移行为,F2—F5期幼体的昼夜垂直迁移行为已经非常明显。由于从表层到底层叶绿素a浓度逐渐降低,因此,太平洋磷虾的昼夜垂直迁移行为可能与摄食有关。 太平洋磷虾成体的分布是与海水温度紧密相关,南黄海太平洋磷虾成体比较适宜生活的水温是8-16 °C。春、冬季水温较低,成体分布范围较广。夏、秋季表层水温急剧升高到20 °C以上,太平洋磷虾成体主要分布在黄海冷水团海域,丰度也达到一年中的最高值。另外,秋季在近长江口的北部海域有大量成体分布。 繁殖和发育:自2006年9月到2007年8月的一年内,在黄海进行了七个航次的太平洋磷虾现场培养产卵实验,结果表明:在南黄海,太平洋磷虾在3月—6月份都具有产卵行为,4月份达到产卵高峰期。单个雌体的最大产卵量为617 egg female-1,出现在4月份。8月、9月和12月在南黄海均未发现太平洋磷虾的产卵行为。太平洋磷虾具有二次产卵行为,并且第一次产卵量要高于第二次。太平洋磷虾的产卵行为与其干湿重紧密相关。成体干重低于5.0 mg,湿重低于26.0 mg,均不具有产卵能力。在产卵高峰期,太平洋磷虾的干湿重达到一年中的最高值。 在南黄海,太平洋磷虾的幼体发育主要遵循下面的发育途径:卵 → 无节幼体 → 后期无节幼体 → 原溞状幼体 → 溞状幼体F1(0' 7, 1' 7) → 溞状幼体F2(1' 4'' 7, 3' 1'' 7) → 溞状幼体F3(5'' 7) → 溞状幼体F4(5'' 5) → 溞状幼体F5(5'' 3) → 溞状幼体F6(5'' 1)。太平洋磷虾在15 °C下的幼体发育速度明显快于4 °C。15 °C下幼体发育到C1期只需5.6 d,而4 °C下则需要16.1 d。 摄食和代谢:2006年9、10、12月和2007年3、8月,在南黄海的五个断面调查航次中,在S1-4站进行了太平洋磷虾成体摄食实验,结果表明:太平洋磷虾在8月和9月份对水体中浮游植物的摄食率比较低,主要摄食水体中的微型浮游动物,从而由于营养级级联作用,致使水体中叶绿素a浓度升高。12月和3月,太平洋磷虾对水体中浮游植物有着很强的摄食活动,使得水体的叶绿素a浓度大量降低,当然太平洋磷虾也可能会同时摄食水体中微型浮游动物。 2006年9、12月和2007年3月,在南黄海的三个断面调查航次中,在S1-4站进行了太平洋磷虾现场耗氧率和排氨率实验,结果表明:太平洋磷虾在3月份的耗氧率是172.92 μg ind.-1 d-1,是9月份和12月份的6倍还要多。太平洋磷虾在9月和12月的耗碳率和体碳日损耗量相近,且都较低。3月份太平洋磷虾的代谢非常旺盛,体碳日损耗量达到2.70 % d-1,每日的耗碳率为62.9 µg C ind-1 d-1。9月和12月份太平洋磷虾代谢的氧氮比都较低,分别是11.3和7.0,太平洋磷虾成体的主要代谢基质是蛋白质。3月份的氧氮比为35.1,太平洋磷虾成体代谢主要以脂肪及碳水化合物为主。

Relevância:

10.00% 10.00%

Publicador:

Resumo:

虾青素是一种具有极强抗氧化活性的类胡萝卜素,具有广泛的应用价值。雨生红球藻是一种单细胞绿藻,在逆境胁迫条件下能够大量合成并迅速积累虾青素,其积累量最高可达细胞干重的4%,从而成为目前首选的天然虾青素合成工具。但是,虾青素的大量积累总是发生在不适于生物量积累的环境胁迫条件下,虾青素积累与生物量积累之间成为一对矛盾,制约着虾青素大量生产。 异戊烯焦磷酸异构酶(IPI)、β-胡萝卜素酮化酶(BKT)和β-胡萝卜素氧化酶(CRTO)是虾青素合成过程中的相关酶。已有研究结果表明,这些酶基因的表达调控至少是部分发生在转录水平上的,这就为我们从转录水平上研究虾青素生物合成关键酶基因的调控机制提供了重要线索。 本文研究结果如下: 1. 利用基因组步移的方法克隆了两条异戊烯焦磷酸异构酶基因(ipi)的5’上游侧翼序列(1.8kb和2.5kb),预示着ipi的转录由不止一个启动子调控。 2. 利用上述方法克隆了两条β-胡萝卜素氧化酶基因(crtO)5'上游侧翼序列(1kb和2kb)。以lacZ为报告基因的瞬间表达实验结果表明,长度为320bp(-682/-363)的crtO 5'上游侧翼序列具有很强的启动转录活性,提示这段序列包含了启动子的结构。 3. 利用凝胶阻滞的方法研究了雨生红球藻中bkt强启动转录活性区域,即 309bp(-617/-309)启动子区域的转录因子结合位点,并发现在-396/-338的59bp区域内存在特异的核蛋白结合位点。通过序列分析,发现此59bp区域并不包含TATA或者CAAT-box,而是存在对光、缺氧、p-香豆酸及激素反应的G-box。 4. 根据国外已经获得的ipi和crtO全长cDNA序列,利用长距离PCR法从红球藻基因组中扩增到基因组序列。发现ipi和crtO均包含6个外显子和5个内含子,内含子的剪切位点基本符合GU-AG规律。并通过似然比检验(Likelihood ratio test)的方法发现两基因在进化过程中存在着正选择现象。 这些工作为下一步继续寻找与上述特定DNA调控区域特异结合的反式作用因子(蛋白质因子)奠定了基础。

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Accumulation and distributions of aliphatic and polyaromatic hydrocarbons (PAHs) and heavy metals were measured in tissues of the clam Ruditapes philippinarum collected from 5 sites in Jiaozhou Bay, Qingdao, China. The concentrations of total aliphatic hydrocarbon and PAHs ranged from 570 to 2 574 ng/gdw (gram dry weight) and from 276 to 939 ng/gdw, in the most and least polluted sites, respectively. The bio-accumulation of hydrocarbons and PAHs in the clams appeared to be selective. Aliphatic hydrocarbons were predominantly represented by short chain (< nC(23)) n-alkanes, suggesting that petroleum hydrocarbons were likely the major contamination source. The selective uptake of 3 and 4 ring PAHs, such as naphthalene, fluorene, phenanthrene, fluoranthene and pyrene, by the clams was probably related to the physiological and bio-kinetic processes that were energetically favorable for uptake of compounds with fewer rings. Accumulation of the metals Cd, Cu, Zn, Pb, Cr, Hg, and As in the clam tissues also showed high variability, ranging from 0.043 to 87 A mu g/gdw. Among the 7 detected metals, Zn, Cd, Cu, and As had a particularly high potential of accumulation in R. philippinarum. In general, a positive correlation was found between the tissue concentrations and sediment concentrations of hydrocarbons and of some metals. Our study suggests that moderate contamination with polyaromatic hydrocarbons, and low to moderate contamination with metals, currently exists for clam R. philippinarum in Jiaozhou Bay, in comparison with other regional studies. A long-term monitoring program is certainly needed for assessment of the potential ecological influence and toxicity of these contaminants of R. philippinarum in Jiaozhou Bay.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Surface modification of montmorillonite by means of Mg2+ insertion reaction has been studied and a positively charged montmorillonite has been prepared. The effects of preparation temperature and Mg2+ concentration on the positive charge property of the clay and on the clay coagulating Heterosigma akashiwo have been studied. The results showed that the modified clay enhanced the coagulation and the used amount decreased to 1/5-1/10 of the original. The removal rates of Heterosigma akashiwo were correlated positively with positive charge on the clay in accordance with theoretical model.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

An elemental carbon (EC) record, covering the last 420 ka, was reconstructed using chemical oxidation method on a loess and paleosol sequence from the Lingtai section on the Chinese Loess Plateau. The EC record reveals the paleofire history and its relationship with climate and vegetation changes on the Chinese Loess Plateau. Our results show that the EC abundance is generally higher in the paleosols than in the loess layers, showing a glacial/interglacial pattern, which is coincident with biomass changes. This variation pattern indicates that paleofires were intensified when biomass accumulated and climate changed abruptly especially from wet to dry conditions. The EC abundance increases sharply at similar to 130 kaB.P., indicating a dramatic change in the vegetation and climate variation patterns. The occurrence of a peak value with the highest average EC abundance in the Holocene may reflect the occurrence of a major climate event at similar to 6 kaB.P., and may also be partly due to more frequent anthropogenic fire usages. (c) 2007 Elsevier B.V. All rights reserved.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Parkinson's disease is a neurodegenerative disorder of uncertain pathogenesis characterized by a loss of dopaminergic neurons in substantia nigra pars compacta, and can be modeled by the neurotoxin 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP). Oxidative stress may contribute to MPTP- and Parkinson's disease-related neurodegeneration. Fucoidan is a sulfated polysaccharide extracted from brown seaweeds which possesses a wide variety of biological activities including potent antioxidative effects. Here we investigated the effect of fucoidan treatment on locomoter activities of animals, striatal dopamine and its metabolites and survival of nigral dopaminergic neurons in MPTP-induced animal model of Parkinsonism in C57/BL mice in vivo and on the neuronal damage induced by 1-methyl-4-phenylpyridinium (MPP+) in vitro, and to study the possible mechanisms. When administered prior to MPTP, fucoidan reduced behavioral deficits, increased striatal dopamine and its metabolites levels, reduced cell death, and led to a marked increase in tyrosine hydroxylase expression relative to mice treated with MPTP alone. Furthermore, we found that fucoidan inhibited MPTP-induced lipid peroxidation and reduction of antioxidant enzyme activity. In addition, pre-treatment with fucoidan significantly protected against MPP+-induced damage in MN9D cells. Taken together, these findings suggest that fucoidan has protective effect in MPTP-induced neurotoxicity in this model of Parkinson's disease via its antioxidative activity. (C) 2009 Elsevier B.V. All rights reserved.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Studies were carried out to optimize the conditions for the recovery of protein. The results showed that pH of 6.00 for wastewater, the dosage of 1% chitosan solution in 1% acetic acid aqueous solution of 2.0 ml for 50 ml wastewater and 1% FeCl3 aqueous solution of 2 ml for 50 ml wastewater, the flocculation time of 4.0 h were the optimal conditions for the recovery of protein. The obtained protein sediment contained abundant amino acids, especially isoleucine, methione and lysine that are absent in other protein resource. (c) 2007 Elsevier Ltd. All rights reserved.