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391.
Relative growth rate (RGR) is currently the most commonly used method for measuring and comparing species' intrinsic growth potential. Comparative studies have, for example, revealed that small-seeded species have higher RGR, leading to the common belief that small-seeded species possess physiological adaptations for rapid growth that would allow them to outgrow large-seeded species, given sufficient time. We show that, because RGR declines as individual plants grow, it is heavily biased by initial size and does not measure the size-corrected growth potential that determines the outcome of competition in the long-term. We develop a daily growth model that includes a simple mechanistic representation of aboveground and belowground growth and its dependency on plant size and environmental factors. Intrinsic growth potential is encapsulated by the size-independent growth coefficient, G. We parameterized the model using repeated-harvest data from 1724 plants of nine species growing in contrasting nutrient and temperature regimes. Using information-theoretic criteria, we found evidence for interspecific differences in only three of nine model parameters: G, aboveground allocation, and frost damage. With other parameters shared between species, the model accurately reproduced above- and belowground biomass trajectories for all nine species in each set of environmental conditions. In contrast to conventional wisdom, the relationship between G and seed size was positive, despite a strong negative correlation between seed size and average RGR, meaning that large-seeded rather than small-seeded species have higher size-corrected growth potential. Further, we found a significant positive correlation between G and frost damage that, according to simulations, causes rank reversals in final biomass under daily temperature changes of +/- 5 degrees C. We recommend the wider use of this new kind of plant growth analysis as a better way of understanding underlying differences in species' physiology; but we recognize that RGR is still a useful metric if considering the potential rate of population increase in empty habitats.  相似文献   
392.
Environmental Fluid Mechanics - The paper reports on the development of an explicit, algebraic model for the turbulent scalar fluxes which properly reflects the dependence of these fluxes on the...  相似文献   
393.
In many vertebrate species, we find temporally stable traditions of socially learned behaviors. The social structure of animal populations is highly diverse and it has been proposed that differences in the social organization influence the patterns of information propagation. Here, we provide results of a simulation study of information propagation on real-life social networks of 70 primate groups comprising 30 different species. We found that models that include the social structure of a group differ significantly from those that assume random associations of individuals. Information spreads slower in the structured groups than in the well-mixed groups. While we found only a minor effect on the path lengths of the transmission chains, robustness against information extinction was strongly influenced by the group structure. Interestingly, robustness against information loss was not correlated with propagation speed but could be predicted reasonably well by relative strength assortativity—a structural network metric. In those groups where highly pro-social individuals preferentially interact with other pro-social individuals, information was more likely to be lost. Our results show that incorporating group structure in any social propagation model significantly alters predictions for spreading patterns, speed, and robustness of information.  相似文献   
394.
Males discriminate between the single most important individual component of the sex pheromone of the female cabbage looper, Trichoplusia ni (Hübner), (Z)-7-dodecenyl acetate (Z7-12:Ac), and a mixture containing Z7-12:Ac and the other five putative components. The manifestation of discrimination is not an enhancement of captures by the mixture, rather, it is a reduction of captures in a paired trap baited with Z7-12:Ac by itself. Previous experiments showed that either or both of (Z)-7-tetradecenyl acetate (Z7-14:Ac) and (Z)-9-tetradecenyl acetate (Z9-14:Ac) were responsible for this discrimination. This report provides evidence that Z7-14:Ac is more active than Z9-14:Ac, which appears to have no demonstrable effect on behavior. The results are discussed with reference to the behavior that is effected by the above three components, the composition of the native sex pheromone, and whether or not Z7-12:Ac might be a supernormal releaser of behavior.  相似文献   
395.
396.
The localization of antigens and other substances in cells and tissues by electron microscopy is usually performed by immunohistochemical techniques employing labelled conventional or monoclonal antibodies. For the ultrastructural localization of the antibodies, they are coupled to electron-dense labels like gold or ferritin. Here, we demonstrate a novel method to localize antigens in cells, tissues, and on other supports. By electron energy loss spectroscopy (EELS) it is possible to directly analyze the distribution of antigens, metabolites or other substances without the use of labelled antibodies: as an example we demonstrate the distribution of the immunomodulator lipopeptide in B lymphocytes and macrophages. EELS represents a novel, sensitive, and generally applicable method for the detection and localization of antigens and other substances in biology and medicine.  相似文献   
397.
In 1994, the U.S. Department of Energy (DOE) initiated a contract reform program intended to strengthen oversight capabilities and encourage the creation of contract and incentive structures, which would effectively facilitate the treatment of onsite contamination and waste. The remedia‐tion and disposal of these legacy wastes is the core of the Department's environmental manage‐ment mission (Government Accountability Office [GAO], 2003). Despite a concerted effort toward achieving the goals of the reform, progress has been slow. Many projects continue to necessitate cost and time extensions above those originally agreed upon. Although the Department insti‐tuted an accelerated cleanup program in 2002, promising to shave some $50 billion and 35 years from its earlier cost and schedule projections, there have been delays in critical project areas that call into question the attainability of the proposed reductions (GAO, 2005). Numerous explana‐tions have been offered as to why achieving these goals has proven so difficult, many of which have concluded that flawed contracting practices are to blame. This article concludes that the root of the problem is much deeper and that the organizational criticisms aimed at DOE are as much a legacy as the waste itself. Although the focus of this article is on large former nuclear weapons sites, these types of contracting and organizational issues are often found at other gov‐ernment and private complex hazardous waste sites. © 2006 Wiley Periodicals, Inc.  相似文献   
398.
The Consortium for Risk Evaluation with Stakeholder Participation (CRESP) was asked by the United States Department of Energy (US DOE) to consider the root causes of remediation projects that fail to entirely achieve their goals and then to offer suggestions to assist the Department. To begin this project, CRESP held several meetings at which the group defined problematic outcomes, the early symptoms of problematic outcomes, and the root causes of failing to meet expectations. The five root causes are complex science, engineering, and technology; ambiguous economics; project management shortcomings; political processes and credibility; and history and organizational culture. This article, while focusing on the US DOE, provides a larger context for many remediation projects that have failed to entirely live up to their sponsors' expectations. © 2007 Wiley Periodicals, Inc.  相似文献   
399.
Low-temperature alteration reactions on uranium phases may lead to the mobilization of uranium and thereby poses a potential threat to humans living close to uranium-contaminated sites. In this study, the surface alteration of uraninite (UO2) and uranium tetrachloride (UCl4) in air atmosphere was studied by confocal laser scanning microscopy (CLSM) and laser-induced fluorescence spectroscopy using an excitation wavelength of 408 nm. It was found that within minutes the oxidation state on the surface of the uraninite and the uranium tetrachloride changed. During the surface alteration process U(IV) atoms on the uraninite and uranium tetrachloride surface became stepwise oxidized by a one-electron step at first to U(V) and then further to U(VI). These observed changes in the oxidation states of the uraninite surface were microscopically visualized and spectroscopically identified on the basis of their fluorescence emission signal. A fluorescence signal in the wavelength range of 415–475 nm was indicative for metastable uranium(V), and a fluorescence signal in the range of 480–560 nm was identified as uranium(VI). In addition, the oxidation process of tetravalent uranium in aqueous solution at pH 0.3 was visualized by CLSM and U(V) was fluorescence spectroscopically identified. The combination of microscopy and fluorescence spectroscopy provided a very convincing visualization of the brief presence of U(V) as a metastable reaction intermediate and of the simultaneous coexistence of the three states U(IV), U(V), and U(VI). These results have a significant importance for fundamental uranium redox chemistry and should contribute to a better understanding of the geochemical behavior of uranium in nature. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   
400.
Environmental Science and Pollution Research - Human biomonitoring studies are of increasing importance in regulatory toxicology; however, there is a paucity of human biomonitoring data for the...  相似文献   
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