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141.
Point and area inventories of anthropogenic mercury emissions documented by US and Canadian environmental agencies have been aggregated into a single archive for analysis and air pollution modeling work. For 5341 point sources and 1634 aggregated area sources, mercury emissions are apportioned among elemental gaseous [Hg(0)], reactive gaseous[Hg(II)], and particulate [Hg(p)] emissions using speciation factors derived from available monitoring measurements. According to this inventory, 4.82 x 10(5) mol of mercury were emitted in calendar year 1996 in the latitude range 24-51 degrees north, and longitude range 64-91 degrees west, which covers most of North America east of the Mississippi River. Using speciation factors consistent with past emission source studies, we find the relative emission proportions among Hg(0):Hg(II):Hg(p) species are 47:35:18. Maps of the various mercury species' emissions patterns are presented. Gridded emission patterns show local mercury emission extremes associated with individual cement production and municipal incineration facilities, and in contrast to past inventories, population centers do not stand out. Considerable uncertainties are still present in estimating emissions from large point sources, as are methods of apportioning emissions among various mercury species. 相似文献
142.
Studies were carried out to investigate the metabolism of herbicide chlortoluron in the microsomal fractions and whole cells of Saccharomyces cerevisiae expressing human cytochrome P450 3A4. Both whole cells and microsomal fractions of yeast expressing human cytochrome P450 3A4 exhibited a typical dithionite-reduced, CO-difference absorbance spectrum with maximum absorbance at 448 nm. Chlortoluron produced a type I binding spectrum with cytochrome P450 3A4 with a Ks value of 200 μM. Chlortoluron was metabolised into four metabolites; hydroxylated-N-monodemethylated, hydroxylated ring methylated, N-didemethylated and N-monodemethylated products. Chlortoluron metabolism was absolutely dependent on NADPH and no metabolism was observed in control transformants. 相似文献
143.
Reynolds SD Blanchard CL Ziman SD 《Journal of the Air & Waste Management Association (1995)》2003,53(2):195-205
Analyses of ambient measured ozone data were used in conjunction with the application of photochemical modeling to determine the technical feasibility of attaining the federal 8-hr ozone standard in central California. Various combinations of volatile organic compound (VOC) and oxides of nitrogen (NOx) emission reductions were effective in lowering modeled peak 1-hr ozone concentrations. However, VOC emissions reductions were found to have only a modest impact on modeled peak 8-hr ozone concentrations. NOx emission reductions generally lowered 8-hr ozone concentrations, but their effectiveness was partially or, in some cases, wholly offset by the increase in the number of NO cycles and, hence, in the ozone produced per NO. As a result, substantial NOx emission reductions--70 to 90%--were required to reduce peak 8-hr ozone concentrations to the level of the standard throughout the modeling domain. These modeling results provide a possible physical explanation for recent analyses that have reported more prominent trends in peak 1-hr ozone levels than in peak 8-hr ozone concentrations or in occurrences of mid-level (60-90 parts per billion by volume) ozone concentrations. The findings also have serious implications for the feasibility of attaining the 8-hr ozone standard in central California. Further efforts are needed to clarify the applicability of the modeling results to the full set of days with ozone levels exceeding the 8-hr ozone standard, as well as their applicability to other geographical areas. 相似文献
144.
Steven S. Seefeldt Jeffery S. Conn Mingchu Zhang Phil N. Kaspari 《Agriculture, ecosystems & environment》2010,135(1-2):119-126
Over 14 million hectares of erosion prone cropland in the United States has been converted into grasslands through the Conservation Reserve Program (CRP) administered by the United States Department of Agriculture, however, studies of the effects of CRP enrollment on plant communities and subsequent plant succession are largely lacking. In Delta Junction, Alaska plant communities in CRP fields are transitioning from grasslands to shrub dominated plant communities, which are resulting in compliance problems with program regulations that state “fields must be maintained in a condition that permits easy conversion to cropland”. To determine plant succession and how previous land management and soils might influence the transition, we measured plant populations in 20 CRP fields throughout Delta Junction using modified-Whittaker plots. These data were combined with data on current management practices, previous farming history, soils, soil properties, diversity indices, and time since land was cleared and analyzed with nonmetric multidimensional scaling ordination to determine factors that influence plant succession. Time in the CRP was the only factor consistently influencing plant succession. As time in the CRP increased, the planted introduced grasses brome grass (Bromus inermis) and red fescue (Festuca rubra) and the native pteridophyte (Equisetum arvense) decreased, whereas a native grass (Calamigrostis canadensis), five native forb, two native shrub, and three native tree species increased. Plant diversity increased at a rate of more than 2 species per 1000 m2 per year. Regression analyses of plant species and plant groups using time in the CRP as the dependent variable resulted in the identification of outlier CRP fields with significantly more or less than expected covers of vegetation. All fields with these outliers had reasonable explanations for the differences in cover that were unrelated to the overall rate of plant succession. Current management practices will result in incompliant fields and different management practices that result in woody vegetation control is key to maintaining CRP fields in compliance. 相似文献
145.
Jay S. Gregg Steven J. Smith 《Mitigation and Adaptation Strategies for Global Change》2010,15(3):241-262
As co-products, agricultural and forestry residues represent a potential low cost, low carbon, source for bioenergy. A method
is developed for estimating the maximum sustainable amount of energy potentially available from agricultural and forestry
residues by converting crop production statistics into associated residue, while allocating some of this resource to remain
on the field to mitigate erosion and maintain soil nutrients. Currently, we estimate that the world produces residue biomass
that could be sustainably harvested and converted into nearly 50 EJ yr−1 of energy. The top three countries where this resource is estimated to be most abundant are currently net energy importers:
China, the United States (US), and India. The global potential from residue biomass is estimated to increase to approximately
50–100 EJ yr−1 by mid- to late- century, depending on physical assumptions such as of future crop yields and the amount of residue sustainably
harvestable. The future market for biomass residues was simulated using the Object-Oriented Energy, Climate, and Technology
Systems Mini Climate Assessment Model (ObjECTS MiniCAM). Utilization of residue biomass as an energy source is projected for the next century under different climate
policy scenarios. Total global use of residue biomass is estimated to be 20–100 EJ yr−1 by mid- to late- century, depending on the presence of a climate policy and the economics of harvesting, aggregating, and
transporting residue. Much of this potential is in developing regions of the world, including China, Latin America, Southeast
Asia, and India. 相似文献
146.
Keeping the blood flowing—plasminogen activator genes and feeding behavior in vampire bats 总被引:1,自引:0,他引:1
Tellgren-Roth A Dittmar K Massey SE Kemi C Tellgren-Roth C Savolainen P Lyons LA Liberles DA 《Die Naturwissenschaften》2009,96(1):39-47
The blood feeding vampire bats emerged from New World leaf-nosed bats that fed on fruit and insects. Plasminogen activator,
a serine protease that regulates blood coagulation, is known to be expressed in the saliva of Desmodus rotundus (common vampire bat) and is thought to be a key enzyme for the emergence of blood feeding in vampire bats. To better understand
the evolution of this biological function, we studied the plasminogen activator (PA) genes from all vampire bat species in
light of their feeding transition to bird and subsequently mammalian blood. We include the rare species Diphylla ecaudata and Diaemus youngi, where plasminogen activator had not previously been studied and demonstrate that PA gene duplication observed in Desmodus is not essential to the vampire phenotype, but relates to the emergence of predominant mammalian blood feeding in this species.
Plasminogen activator has evolved through gene duplication, domain loss, and sequence evolution leading to change in fibrin-specificity
and susceptibility to plasminogen activator inhibitor-1. Before undertaking this study, only the four plasminogen activator
isoforms from Desmodus were known. The evolution of vampire bat plasminogen activators can now be linked phylogenetically to the transition in feeding
behavior among vampire bat species from bird to mammalian blood.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
147.
湖泊热结构和蒸发的模拟计算 总被引:9,自引:0,他引:9
应用一维涡扩散模型计算一年内不同时期的湖泊垂直温度分布和湖水蒸发率。主管方程是同一水平面内均温的一维非定常热传导方程。模型不要求特定的湖泊拟合参数。模型中涡扩散系数通过Richardsono数计算,水面热交换用能量平衡法计算,湖底假定为绝热,主管方程用有限差分法求解。对Colorado City湖和Calhoun湖的模拟计算表明:水面温度和温度剖面的计算值与实测值吻合很好,最大差值均在2℃范围内。 相似文献
148.
Two potential mechanisms for reducing the level of inbreeding, sex-biased dispersal and kin avoidance, were examined in the
Australian sleepy lizard, Tiliqua rugosa. The home range centres, and the genotypes at four polymorphic microsatellite DNA loci were determined for adult lizards
in a 70-ha study area near Mount Mary, South Australia. From estimates of genetic relatedness, females were as closely related
to other females as they were to males, both within the whole study area, and within home ranges. Similarly, males were as
closely related to other males as they were to females. This suggests that dispersal in the population is not sex-biased.
Sleepy lizards form monogamous pairs during the spring. Partners were less closely related to each other than to other potential
partners in the home range area. This suggests active choice of unrelated partners. The mechanism for recognising related
from unrelated individuals is unknown, but the behaviour could reduce inbreeding.
Received: 7 November 1998 / Accepted: 30 May 1999 相似文献
149.
150.
Peng Liu Xiaoliang Liang Yanliu Dang Junkai He Alireza Shirazi-Amin Laura A. Achol Shanka Dissanayake Hanlin Chen Mingli Fu Daiqi Ye Steven L. Suib 《环境科学学报(英文版)》2021,33(3):293-303
Ceria is widely used as a catalyst for soot combustion, but effects of Zr substitution on the reaction mechanism is ambiguous. The present work elucidates effects of Zr substitution on soot combustion over cubic fluorite-structured nanoceria. The nanostructured CeO2, Ce0.92Zr0.08O2, and Ce0.84Zr0.16O2 composed of 5–6 nm crystallites display Tm-CO2 (the temperature at maximum CO2 yield) at 383, 355, and 375°C under 10 vol.% O2/N2, respectively. The size of agglomerate decreases from 165.5 to 51.9–57.3 nm, which is beneficial for the soot-ceria contact. Moreover, Zr increases the amount of surface oxygen vacancies, generating more active oxygen (O2? and O?) for soot oxidation. Thus, the activities of Ce0.92Zr0.08O2 and Ce0.84Zr0.16O2 in soot combustion are better than that of CeO2. Although oxygen vacancies promote the migration of lattice O2?, the enriched surface Zr also inhibits the mobility of lattice O2?. Therefore, the Tm-CO2 of Ce0.84Zr0.16O2 is higher than that of Ce0.92Zr0.08O2. Based on reaction kinetic study, soot in direct contact with ceria preferentially decomposes with low activation energy, while the oxidation of isolated soot occurs through diffusion with high activation energy. The obtained findings provide new understanding on the soot combustion over nanoceria. 相似文献