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121.
Fate of PBDEs in juvenile lake trout estimated using a dynamic multichemical fish model 总被引:1,自引:0,他引:1
Biotransformation half-lives (HL) and gut absorption efficiencies (GAE) of PBDE congeners in fish are poorly known and challenging to quantify experimentally. These values are needed in order to accurately assess their food web dynamics, and in turn, for policy development We recently developed a multichemical aquatic food web model, which was used to estimate HL of four PBDE congeners in a simple Arctic food web. However, an application of this model to more complex food webs would dramatically increase the uncertainties in the results due to the large number of unknowns that would need to be considered simultaneously. As such, an in-depth analysis of possible HL and GAE of additional PBDE congeners at the scale of individual fish species would facilitate model application to more complex food webs. For this purpose, we developed a fugacity-based dynamic multichemical fish model and applied it to previously published experimental laboratory data. The model was calibrated by maximizing correspondence between the modeled and observed concentrations for each of the thirteen congeners at two dietary concentrations in juvenile lake trout (Salvelinus namaycush) during uptake and depuration phases mainly by varying HL and GAE. A robust parametrization and calibration procedure gave us confidence in our back-calculated congener-specific HL of 42-420 days and GAE of 20-45%. These values can be used as a starting point for model applications to natural fish populations. The fate/transport results suggest that not only loss of PBDE congeners via degradation, but also input through biotransformation of higher brominated congeners, should be accounted for in order to accurately portray dynamics of PBDEs in fish. 相似文献
122.
We have investigated the utility of a Lau phase interferometer with circular gratings and a white-light source to measure the temperature and temperature profile of an axisymmetric flame. The temperature measured with a Lau phase interferometer is in good agreement with the temperature measured with a thermocouple and multilogger. Detailed theoretical analysis and experimental investigation are presented. 相似文献
123.
Computational Grids are emerging as a new infrastructure for high performance computing. Since the resources in a Grid can
be heterogeneous and distributed, mesh-based applications require a mesh partitioner that considers both processor and network
heterogeneity. We have developed a heterogeneous mesh partitioner, called PaGrid. PaGrid uses a multilevel graph partitioning
approach, augmented by execution time load balancing in the final uncoarsening phase. We show that minimization of total communication
cost (e.g., as used by JOSTLE) can lead to significant load being placed on processors connected by slow links, which results
in higher application execution times. Therefore, PaGrid balances the estimated execution time of the application across processors.
PaGrid performance is compared with two existing mesh partitioners, METIS 4.0 and JOSTLE 3.0, for mapping several application
meshes to two models of heterogeneous computational Grids. PaGrid is found to produce significantly better partitions than
JOSTLE and slightly better partitions than METIS in most cases, in terms of estimated application execution time averaged
over a large number of runs with different random number seeds. 相似文献
124.
Diamond ML Bhavsar SP Helm PA Stern GA Alaee M 《The Science of the total environment》2005,342(1-3):245-259
Elevated concentrations of some persistent organic pollutants (POPs) in fish from arctic and subarctic lakes have been hypothesized to be due to processes within food webs and fish physiology. We investigated limnological processes and contaminant chemistry as explanations of these elevated concentrations by developing and applying fugacity-based mass balance models to a relatively small lake in the high arctic and a series of larger lakes in the southern Yukon River basin. The results indicate that high arctic lakes are transient and inefficient sinks for POPs. The mobility of POPs in high arctic lakes is conferred by their hydrologic regime (i.e. partial through flow of melt water loadings) and minimal scavenging and retention in sediments due to extremely low organic carbon in settling and sediment particles. Contaminant dynamics in lakes of the south Yukon River basin are governed by hydrology (i.e., water residence time), because, similarly to high arctic lakes, most of the contaminant inventory resides in the water column due to inefficient scavenging by settling particles. For the less persistent compounds, long water residence time shifts the major loss process from export to degradation. Model results also suggest relatively short degradative half-lives of the hexachlorocyclohexanes (sum of HCHs) and endosulfan, particularly in high arctic Amituk Lake. 相似文献
125.
Amarendra Matsa Madhuri Avinash Chaudhari Hiralal Muralidhar Suryawanshi 《电力部件与系统》2017,45(8):881-893
This article presents a modified synchronous vector control design of a five-level cascaded H-Bridge inverter for integration of distributed generation (DG) resources to the power grid. The presented control strategy explores the limitations in the conventional synchronous vector control algorithm of grid-connected converter (GCC). The dynamic reference point (DRP) approach is considered to improve the performance of GCC. Compared with conventional control algorithm, DRP based control algorithm exhibits several specific advantages, such as increased reliability of the grid-interfaced converter, more active and reactive power injection capacity of the converter, and reduced cost of the converter. The objectives of control technique of the DG interface system are also employed to enhance the standard of the power grid. The optimized space vector pulse-width modulation (OSVPWM) control technique is used for grid integration. The simulation and experimental results are presented in order to validate the proposed functionalities of the grid-interfaced DG system. The effectiveness of the proposed control scheme is validated with better utilization of DG system, faster dynamics with reduced total harmonic distortion, better power factor, compensated load reactive power, and fault withstanding capability. 相似文献
126.
Long-term environmental fate of perfluorinated compounds after accidental release at Toronto airport 总被引:1,自引:0,他引:1
Awad E Zhang X Bhavsar SP Petro S Crozier PW Reiner EJ Fletcher R Tittlemier SA Braekevelt E 《Environmental science & technology》2011,45(19):8081-8089
Perfluorooctane sulfonate (PFOS; a perfluorinated compound or PFC), its salts, and perfluorooctane sulfonyl fluoride have recently been listed in Annex B of the Stockholm Convention due to their widespread presence, persistence, and toxicity. Because of the persistent nature of PFCs, it is generally presumed that the impact of direct discharges of these chemicals on a receiving environment would be long-lasting. However, long-term environmental fate studies based on field measurements are rare. We examined spatial and long-term (9 year) temporal trends of PFCs in water, sediment, fish, and fish liver collected in 2003, 2006, and 2009 from 10 locations spanning ~20 km in Etobicoke and Spring Creeks, where an accidental release of fire fighting foam containing PFOS from nearby Toronto International Airport occurred in 2000. Even a decade after the spill, sediment PFOS concentrations are still elevated in Spring Creek Pond which received the foam discharge; however, the major impact is relatively localized likely due to the stormwater management nature of the pond and the diluting effect of Etobicoke Creek. Fish and fish liver PFOS concentrations at a Spring Creek location downstream of Spring Creek Pond declined by about 70 and 85%, respectively, between 2003 and 2009. PFOS in water at locations further downstream in Etobicoke Creek have declined by >99.99% since the spill; however, the 2009 water and fish levels were ~2-10 times higher than upstream locations likely due to the long-term impact of the spill as well as urbanization. The decrease in the upstream PFOS concentrations likely reflects the reduction of PFOS sources due to phased out production by 3M and regulations on the use of PFOS in fire fighting foams. Field-based sediment/water distribution coefficients (K(D)) and bioaccumulation factors (BAF) were calculated from environmental measurements. Log K(D) values were 0.54-1.65 for perfluoroalkyl sulfonates (PFASs) and 1.00-1.85 for perfluorocarboxylates (PFCAs). Log BAF(fish) ranged from 1.85 to 3.24 for PFASs and 0.88-3.47 for PFCAs, whereas log BAF(fish liver) ranged from 2.1-4.3 for PFASs and 1.0-5.0 for PFCAs. 相似文献
127.
Dr. Madhuri Gade Dr. Jasmine M. Gardner Dr. Prashant Jain Prof. Paola Laurino 《Chembiochem : a European journal of chemical biology》2023,24(22):e202300094
We have studied the adenosine binding specificities of two bacterial DNA methyltransferases, Taq methyltransferase (M.TaqI), and HhaI methyltransferase (M.HhaI). While they have similar cofactor binding pocket interactions, experimental data showed different specificity for novel S-nucleobase-l -methionine cofactors (SNMs; N=guanosyl, cytidyl, uridyl). Protein dynamics corroborate the experimental data on the cofactor specificities. For M.TaqI the specificity for S-adenosyl-l -methionine (SAM) is governed by the tight binding on the nucleoside part of the cofactor, while for M.HhaI the degree of freedom of the nucleoside chain allows the acceptance of other bases. The experimental data prove catalytically productive methylation by the M.HhaI binding pocket for all the SNMs. Our results suggest a new route for successful design of unnatural SNM analogues for methyltransferases as a tool for cofactor engineering. 相似文献
128.
Faiz Almansour Monica Alberto Rupesh S. Bhavsar Xiaolei Fan Peter M. Budd Patricia Gorgojo 《Frontiers of Chemical Science and Engineering》2021,15(4):872-881
Physical aging is currently a major obstacle for the commercialization of PIM-1 membranes for gas separation applications. A well-known approach to reversing physical aging effects of PIM-1 membranes at laboratory scale is soaking them in lower alcohols, such as methanol and ethanol. However, this procedure does not seem applicable at industrial level, and other strategies must be investigated. In this work, a regeneration method with alcohol vapors (ethanol or methanol) was developed to recover permeability of aged PIM-1 membranes, in comparison with the conventional soaking-in-liquid approach. The gas permeability and separation performance, before and post the regeneration methods, were assessed using a binary mixture of CO2 and CH4 (1:1, v:v). Our results show that an 8-hour methanol vapor treatment was sufficient to recover the original gas permeability, reaching a CO2 permeability>7000 barrer. 相似文献