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51.
Trifolium repens and Lolium perenne were exposed as both monocultures and two-species mixtures to an episodic rural ozone regime in large, well-watered containers within solardomes for 12 weeks. There were reductions in biomass for T. repens, but not L. perenne, and the proportion of T. repens decreased in ozone-exposed mixtures compared to the control. In addition, leaf biomass of T. repens was maintained at the expense of biomass partitioning to the stolons. The decreased growth corresponded with decreased photosynthetic capacity for T. repens, however, by the end of the exposure there was also decreased photosynthetic capacity of L. perenne, a species previously considered insensitive to ozone. The observed decreases in photosynthetic efficiency and capacity in elevated ozone indicate that the ability of such ubiquitous vegetation to act as a sink for atmospheric carbon may be reduced in future climates. 相似文献
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Pankiw T 《Die Naturwissenschaften》2004,91(4):178-181
The evolution of sociality has configured communication chemicals, called primer pheromones, which play key roles in regulating the organization of social life. Primer pheromones exert relatively slow effects that fundamentally alter developmental, physiological, and neural systems. Here, I demonstrate how substances extracted from the surface of foraging and young pre-foraging worker bees regulated age at onset of foraging, a developmental process. Hexane-extractable compounds washed from foraging workers increased foraging age compared with controls, whereas extracts of young pre-foraging workers decreased foraging age. This represents the first known direct demonstration of primer pheromone activity derived from adult worker bees. 相似文献
55.
Molecular structures and associations of humic substances in the terrestrial environment 总被引:4,自引:0,他引:4
Simpson AJ Kingery WL Hayes MH Spraul M Humpfer E Dvortsak P Kerssebaum R Godejohann M Hofmann M 《Die Naturwissenschaften》2002,89(2):84-88
Here we show, for the first time, evidence of the primary molecular structures in humic substances (HS), the most abundant naturally occurring organic molecules on Earth, and their associations as mixtures in terrestrial systems. Multi-dimensional nuclear magnetic resonance (NMR) experiments show us that the major molecular structural components in the mixtures operationally defined as HS are aliphatic acids, ethers, esters and alcohols; aromatic lignin derived fragments; polysaccharides and polypeptides. By means of diffusion ordered spectroscopy, distinct diffusion coefficients consistent with relatively low molecular weight molecules were observed for all the components in the mixtures, and saccharides were the largest single class of component present. Liquid chromatography NMR confirmed that HS components can be easily separated and nuclear Overhauser effect (NOE) enhancements support the finding that the components are of relatively low molecular weight <~2,000 Da. The widely recognized properties of HS, i.e., characteristics indicative of crosslinked, macromolecular networks, can now be explained as aggregation of mixtures, most likely instigated by complexation with metal cations. 相似文献
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The success of a species depends on its ability to assess its environment and to decide accordingly which behaviors are most appropriate. Many animal species, from bacteria to mammals, are able to communicate using interspecies chemicals called pheromones. In addition to exerting physiological effects on individuals, for social species, pheromones communicate group social structure. Communication of social structure is important to social insects for the allocation of its working members into coordinated suites of behaviors. We tested effects of long-term treatment with brood pheromone on suites of honey bee brood rearing and foraging behaviors. Pheromone-treated colonies reared significantly greater brood areas and more adults than controls, while amounts of stored pollen and honey remained statistically similar. Brood pheromone increased the number of pollen foragers and the pollen load weights they returned. It appeared that the pheromone-induced increase in pollen intake was directly canalized into more brood rearing. A two-way pheromone priming effect was observed, such that some workers from the same age cohorts showed an increased and extended capacity to rear larvae, while others were recruited at significantly younger ages into pollen-specific foraging. Brood pheromone affected suites of nursing and foraging behaviors allocating worker and pollen resources associated with an important fitness trait, colony growth. 相似文献
57.
The modelling of skin permeability is important for transdermal drug delivery, in the cosmetic industry and for risk assessment attendant on dermal exposure to toxic substances. The two principal methods currently used are quantitative structure-activity relationships (QSARs), used in the main to predict permeability coefficients, and mathematical modelling based on analytical or numerical solutions to the relevant partition and transport equations and used to predict the amount of a substance permeating through the skin. This paper will assess recent progress in this area and suggest what will be needed for future advancements. The considerable effort invested in the development of QSARs during the past decade has resulted in only rather modest progress. Further significant improvement in our ability to predict percutaneous permeability is likely to require the measurement of new data under carefully controlled conditions and its fitting to new QSAR equations. Reliable assessments of risks following dermal exposures will demand new integrated mathematical models that include the variables associated with the exposure and penetration processes as well as the factors that control the subsequent passage of the penetrant into the systemic system. 相似文献
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A novel method to remediate dense nonaqueous phase liquid (DNAPL) source zones that incorporates in situ density conversion of DNAPL via alcohol partitioning followed by displacement with a low interfacial tension (IFT) surfactant flood has been developed. Previous studies demonstrated the ability of the density-modified displacement (DMD) method to recover chlorobenzene (CB) and trichloroethene (TCE) from heterogeneous porous media without downward migration of the dissolved plume or free product. However, the extent of alcohol (n-butanol) partitioning required for in situ density conversion of high-density NAPLs, such as tetrachloroethene (PCE), could limit the utility of the DMD method. Hence, the objective of this study was to compare the efficacy of two n-butanol delivery approaches: an aqueous solution of 6% (wt) n-butanol and a surfactant-stabilized macroemulsion containing 15% (vol) n-butanol in water, to achieve density reduction of PCE-NAPL in two-dimensional (2-D) aquifer cells. Results of liquid-liquid equilibrium studies indicated that density conversion of PCE relative to water occurred at an n-butanol mole fraction of 0.56, equivalent to approximately 5 ml n-butanol per 1 ml of PCE when in equilibrium with an aqueous solution. In 2-D aquifer cell studies, density conversion of PCE was realized using both n-butanol preflood solutions, with effluent NAPL samples exhibiting density reductions ranging from 0.51 to 0.70 g/ml. Although the overall PCE mass recoveries were similar (91% and 93%) regardless of the n-butanol delivery method, the surfactant-stabilized macroemulsion preflood removed approximately 50% of the PCE mass. In addition, only 1.2 pore volumes of the macroemulsion solution were required to achieve in situ density conversion of PCE, compared to 6.4 pore volumes of the 6% (wt) n-butanol solution. These findings demonstrate that use of the DMD method with a surfactant-stabilized macroemulsion containing n-butanol holds promise as an effective source zone remediation technology, allowing for efficient recovery of PCE-DNAPL while mitigating downward migration of the dissolved plume and free product. 相似文献
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S.R. Hayes 《Journal of the Air & Waste Management Association (1995)》2013,63(8):840-843
Because of the increasing demand for energy, construction of a number of large power plants is planned, particularly in the southwestern U.S. Before construction of a plant can begin, however, it must be shown that its emissions will not degrade air quality beyond certain acceptable limits. A new plant must undergo not only a New Source Review1 to demonstrate compliance with New Source Performance Standards,2 but also an analysis to show that it will not produce significant deterioration of air quality in designated pristine areas (often these areas are state or federal parks.) Further, as a result of the 1977 amendments3 to the Clean Air Act, visibility must not be impaired where impairment is defined as a reduction in visual range or as atmospheric discoloration. Plume visual impact must thus be considered before permission for construction will be granted. Because of these requirements, it is important to be able to visualize the plume from a power plant as it travels through surrounding terrain. 相似文献