共查询到16条相似文献,搜索用时 0 毫秒
1.
测量了6种东海常见的浮游植物在两个温度(20℃,15℃)、三个光照(7000Lux,4100Lux,1100Lux)下的不同生长期的三维激发/发射荧光光谱,研究了光谱特征提取方法。对去除散射干扰后的三维光谱进行了奇异值分解,得到的相应于激发光谱的第一主成分具有区分藻种的能力,可作为三维光谱的特征光谱。分析结果表明,实验条件下,等鞭金藻(Isochrysis galbana)、岛国大扁藻(Platymonas helgolanidica)和中肋骨条藻(Skeletonema costatuma)的特征光谱相似度高,塔玛亚历山大藻(Alexandrium tamarense)、东海原甲藻(Prorocentrum dentatum)和尖刺拟菱形藻(Pseudo—nitzschia pungens)光谱相似度稍差。 相似文献
2.
Michael T. Barry Roberto Rusconi Jeffrey S. Guasto Roman Stocker 《Journal of the Royal Society Interface》2015,12(112)
Fluid flow, ubiquitous in natural and man-made environments, has the potential to profoundly impact the transport of microorganisms, including phytoplankton in aquatic habitats and bioreactors. Yet, the effect of ambient flow on the swimming behaviour of phytoplankton has remained poorly understood, largely owing to the difficulty of observing cell–flow interactions at the microscale. Here, we present microfluidic experiments where we tracked individual cells for four species of motile phytoplankton exposed to a spatially non-uniform fluid shear rate, characteristic of many flows in natural and artificial environments. We observed that medium-to-high mean shear rates (1–25 s−1) produce heterogeneous cell concentrations in the form of regions of accumulation and regions of depletion. The location of these regions relative to the flow depends on the cells'' propulsion mechanism, body shape and flagellar arrangement, as captured by an effective aspect ratio. Species having a large effective aspect ratio accumulated in the high-shear regions, owing to shear-induced alignment of the swimming orientation with the fluid streamlines. Species having an effective aspect ratio close to unity exhibited little preferential accumulation at low-to-moderate flow rates, but strongly accumulated in the low-shear regions under high flow conditions, potentially owing to an active, behavioural response of cells to shear. These observations demonstrate that ambient fluid flow can strongly affect the motility and spatial distribution of phytoplankton and highlight the rich dynamics emerging from the interaction between motility, morphology and flow. 相似文献
3.
Shovonlal Roy Shubha Sathyendranath Trevor Platt 《Journal of the Royal Society Interface》2011,8(58):650-660
The absorption coefficient of a substance distributed as discrete particles in suspension is less than that of the same material dissolved uniformly in a medium—a phenomenon commonly referred to as the flattening effect. The decrease in the absorption coefficient owing to flattening effect depends on the concentration of the absorbing pigment inside the particle, the specific absorption coefficient of the pigment within the particle, and on the diameter of the particle, if the particles are assumed to be spherical. For phytoplankton cells in the ocean, with diameters ranging from less than 1 µm to more than 100 µm, the flattening effect is variable, and sometimes pronounced, as has been well documented in the literature. Here, we demonstrate how the in vivo absorption coefficient of phytoplankton cells per unit concentration of its major pigment, chlorophyll a, can be used to determine the average cell size of the phytoplankton population. Sensitivity analyses are carried out to evaluate the errors in the estimated diameter owing to potential errors in the model assumptions. Cell sizes computed for field samples using the model are compared qualitatively with indirect estimates of size classes derived from high performance liquid chromatography data. Also, the results are compared quantitatively against measurements of cell size in laboratory cultures. The method developed is easy-to-apply as an operational tool for in situ observations, and has the potential for application to remote sensing of ocean colour data. 相似文献
4.
海洋浮游植物生长过程中溶解有机物质的三维荧光光谱研究 总被引:7,自引:1,他引:7
利用三维激发-发射矩阵荧光光谱技术,监测了赤潮异弯藻和中肋骨条藻培养过程中产生的溶解有机物,分析了三维荧光光谱图中的荧光峰位置、数量及荧光强度的变化情况.结果表明,微藻生长过程中会产生类蛋白和类腐殖质两类荧光有机物质,这两类有机物的荧光峰的位置及荧光强度有较大差异.在不同生长期,两类荧光有机物的产生机制不同.在指数生长期,两类有机物的荧光强度与藻密度成正相关,说明浮游植物释放了一定量的荧光物质;在平稳期和衰亡期,两类有机物的荧光强度迅速增加,这可能由于衰老、死亡藻细胞的破碎释放出大量的荧光有机物质所致,此外细菌对非荧光有机物进一步降解,也可能是产生该现象的一个原因. 相似文献
5.
通过细菌16S rRNA基因(16S rDNA)文库方法研究了1至7天近海浸海玻片附着细菌的多样性和群落演替特征.从1至7天3个基因文库中共筛选了269个克隆、144个有效分类操作单元 (OUT)并对其全部测序.16S rDNA序列系统进化分析发现,这些细菌主要归属于8个细菌门类:变形菌门(Proteobacteria)(α-、γ-和δ-亚群)、拟杆菌门(Bacteroidetes)、芽单胞菌门(Gemmatimonadetes)、厚壁菌门(Firmicutes)、浮霉菌门(Planctomycetes) 、光合细菌门(Cyanobacteria)、放线菌门(Actinobacteria)和酸杆菌门(Acidobacter ia).由此可知1周内变形菌门的α-亚群、γ-亚群和拟杆菌门的细菌是常见的附着类群;α-变形菌亚群中的玫瑰杆菌族(Roseobacter clade)是海洋环境中比较常见的早期附着种类;由聚类分析显示3天和7天细菌的群落结构相似.这些实验结果为了解海水附着细菌生物膜形成的演替过程提供了理论基础,并为海水微生物腐蚀控制提供了生物学线索. 相似文献
6.
It is notoriously difficult to predict the behaviour of a complex self-organizing system, where the interactions among dynamical units form a heterogeneous topology. Even if the dynamics of each microscopic unit is known, a real understanding of their contributions to the macroscopic system behaviour is still lacking. Here, we develop information-theoretical methods to distinguish the contribution of each individual unit to the collective out-of-equilibrium dynamics. We show that for a system of units connected by a network of interaction potentials with an arbitrary degree distribution, highly connected units have less impact on the system dynamics when compared with intermediately connected units. In an equilibrium setting, the hubs are often found to dictate the long-term behaviour. However, we find both analytically and experimentally that the instantaneous states of these units have a short-lasting effect on the state trajectory of the entire system. We present qualitative evidence of this phenomenon from empirical findings about a social network of product recommendations, a protein–protein interaction network and a neural network, suggesting that it might indeed be a widespread property in nature. 相似文献
7.
Klaus Marhold 《Industry and innovation》2017,24(2):122-142
This research proposes internal and external determinants that influence the diversity of a firm’s alliance portfolio. Focusing on technological aspects of the firm as well as investigating internal and external factors, we suggest that the internal technological diversity of the focal firm, as well as the technological uncertainty of the industry, affects the technological diversity of the alliance portfolio. The hypotheses are tested on a sample of U.S.-listed semiconductor firms’ global R&D alliances from 1990 to 2010. We find that the internal technological diversity of a firm has a negative influence on its technological alliance portfolio diversity. However, technological alliance portfolio diversity seems unaffected by the uncertainty of the firm’s environment. This study contributes to prior literature which has extensively studied the effects of alliance portfolio diversity on firm performance but has paid little attention to its determinants. 相似文献
8.
Christopher A Gilligan James E Truscott Adrian J Stacey 《Journal of the Royal Society Interface》2007,4(16):925-934
We use a spatially explicit, stochastic model to analyse the effectiveness of different scales of local control strategies in containing the long-term, multi-seasonal spread of a crop disease through a dynamically changing population of susceptible crops in which there is cryptic infection. The model distinguishes between susceptible, infested and symptomatic fields. It is motivated by rhizomania disease on sugar beet in the UK as an exemplar of a spatially structured and partially asymptomatic epidemic. Our results show the importance of matching the scales of local control strategies to prevent intensification and regional spread of disease with the inherent temporal and spatial scales of an epidemic. A simple field-scale containment strategy, whereby the susceptible crop is no longer grown on fields showing symptoms, fails for this system with cryptic infection because the locally applied control lags behind the epidemic. A farm-scale strategy, whereby growers respond to the disease status of neighbouring farms by transferring their quota for sugar beet to farmers in regions of reduced risk, succeeds. We conclude that a soil-borne pathogen such as rhizomania could be managed by movement of susceptible crops in the landscape using a strategy that matches the temporal and spatial scales of the epidemic and which take account of risk aversion among growers. We show some parallels and differences in effectiveness between a 'culling' strategy involving crop removal around emerging foci and the local deployment of partially resistant varieties that reduce amplification and transmission of inoculum. Some relationships between the control of plant and livestock diseases are briefly discussed. 相似文献
9.
生物入侵及其对农田生态系统中生物多样性的影响 总被引:2,自引:0,他引:2
综述了生物入侵的途径及其对农田生态系统的危害,主要从遗传多样性、物种多样性、生态系统多样性三个方面讨论生物入侵对农田生态系统中生物多样性的影响. 相似文献
10.
舰船机电设备在冲击环境下的离散模型 总被引:4,自引:1,他引:4
在强冲击作用下,舰船设备与冲击限位块可能发生碰撞,从而导致破坏,本文采用不对称四点带限位器弹性元件支撑的单铡体模型,模拟简单设备--支撑保护系统,并采用经典的碰撞理论直接导出该系统的映射方程,建立其冲击后振动的离散动力学模型。经过对某实船设备在冲击作用后的振动响应调查指出,由于可能发生碰撞,该系统在共振区附近呈现复杂的非线性特性。该结论对如何正确设计设备支撑保护系统提供了理论参考依据。 相似文献
11.
Dinis Gkaydin Jos B Oliveira-Martins Isabel Gordo M. Gabriela M Gomes 《Journal of the Royal Society Interface》2007,4(12):137-142
The awareness that pathogens can adapt and evolve over relatively short time-scales is changing our view of infectious disease epidemiology and control. Research on the transmission dynamics of antigenically diverse pathogens is progressing and there is increasing recognition for the need of new concepts and theories. Mathematical models have been developed considering the modelling unit in two extreme scales: either diversity is not explicitly represented or diversity is represented at the finest scale of single variants. Here, we use an intermediate approach and construct a model at the scale of clusters of variants. The model captures essential properties of more detailed systems and is much more amenable to mathematical treatment. Specificities of pathogen clusters and the overall potential for transmission determine the reinfection rates. These are, in turn, important regulators of cluster dynamics. Ultimately, we detect a reinfection threshold (RT) that separates different behaviours along the transmissibility axis: below RT, levels of infection are low and cluster substitutions are probable; while above RT, levels of infection are high and multiple cluster coexistence is the most probable outcome. 相似文献
12.
Zoubeir L Adeline S Laurent CS Yoann C Truc HT Benoît le G Federico A 《Journal of hazardous materials》2007,148(3):606-612
The work presented in this article concerns polluted marine sediments. The article is divided into three parts. The first part discusses existing industrial procedures of treatment. The second part introduces the Novosol((R)) process, which was used for the treatment of polluted marine sediments. This process is based on the stabilization of heavy metals in the solid matrix by phosphatation and the destruction of organic matter by calcination. Finally, after a comparison had been made between environmental results obtained on both polluted marine sediments and inert ones, treated sediments were introduced in the production of clay bricks. The results obtained show that the Novosol process leads to the immobilization of most heavy metals and can be considered as an efficient tool for the stabilisation of polluted marine sediment. Thus, the results of physical and mechanical tests as compressive strength and water absorption indicate that performances obtained were comparable to standard brick values. These results confirm that, once treated, polluted sediments can be recycled. 相似文献
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14.
Porous materials are processed in various areas of material science and manufacturing. Furthermore, the varieties of porous materials ensure great advantages to designers. This paper proposes a decision aid mechanism based on fuzzy axiomatic design (FAD) to select adequate form of porous materials in marine systems design. It enables elimination and choice of suitable material alternatives in respect to two sets of attributes: generic material selection attributes (GMSA) and specific material selection attributes (SMSA). Furthermore, the paper specifically addressed use of porous materials in plate type heat exchanger design to demonstrate the proposed model. It is expected that the paper ensures a novel procedure for marine engineers and naval architectures in conceptual design process of marine systems. 相似文献
15.
The impact of subsidiary top management team national diversity on subsidiary performance: Knowledge and legitimacy perspectives 总被引:1,自引:0,他引:1
Yaping Gong 《Management International Review》2006,46(6):771-790
Abstract and Key Results
相似文献
– | This study examines the impact of nationality composition within subsidiary top management teams (STMTs) on subsidiary performance. It first gives a review of the multinational team literature. It concludes that nationality diversity is beneficial when it is relevant to a multinational team’s task. The study then draws upon two complementary theoretical perspectives: knowledge and legitimacy. |
– | It proposes that a heterogeneous STMT nationality composition may enhance subsidiary performance with the effect being stronger in subsidiaries of longer years of operation. Hypotheses were tested in a sample of STMTs from Japanese Multinational Corporations. The study finds that STMT nationality heterogeneity was positively related to subsidiary labor productivity. An interaction effect was also found. As the number of years a subsidiary had been in operation increased, so did the effect of STMT nationality heterogeneity on subsidiary performance. |
16.
A quenched and tempered marine steel has been cooled at different rates after tempering and low frequency fatigue crack growth rates in air and seawater compared. Water quenching was shown to result in significantly lower fatigue crack growth rates compared to furnace cooling. The likely causes and the implications of the results are discussed. 相似文献