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601.
Iftheker A. Khan Nirupam Aich A.R.M. Nabiul Afrooz Joseph R.V. Flora P. Ariette Schierz P. Lee Ferguson Tara Sabo-Attwood Navid B. Saleh 《Chemosphere》2013
Aggregate structure of covalently functionalized chiral specific semiconducting single-walled carbon nanotubes (SWNTs) was systematically studied employing static light scattering (SLS). Fractal dimensions (Df) of two specific chirality SWNTs—SG65 and SG76 with (6, 5) and (7, 6) chiral enrichments—were measured under four biological exposure media conditions, namely: Dulbecco’s Modified Eagle Medium (DMEM), Minimum Essential Medium (MEM), Roswell Park Memorial Institute (RPMI) 1640 medium, and 0.9% saline solution. The SWNTs exhibited chiral dependence on Df with SG65 showing more fractal or loosely bound aggregate structures, i.e., lower Df values (range of 2.24 ± 0.03 to 2.64 ± 0.05), compared to the SG76 sample (range of 2.58 ± 0.13 to 2.90 ± 0.08). All the Df values reported are highly reproducible, measured from multiple SLS runs and estimated with ‘random block-effects’ statistical analysis that yielded all p values to be <0.001. The key mechanism for such difference in Df between the SWNT samples was identified as the difference in van der Waals (VDW) interaction energies of these samples, where higher VDW of SG76 resulted in tighter packing density. Effect of medium type showed lower sensitivity; however, presence of di-valent cations (Ca2+) in DMEM and MEM media resulted in relatively loose or more fractal aggregates. Moreover, presence of fetal bovine serum (FBS) and bovine serum albumin (BSA), used to mimic the in vitro cell culture condition, reduced the Df values, i.e., created more fractal structures. Steric hindrance to aggregation was identified as the key mechanism for creating the fractal structures. Also, increase in FBS concentration from 1% to 10% resulted in increasingly lower Df values. 相似文献
602.
Hang Wang Joseph Holden Kandice Spera XinHua Xu ZaoDe Wang JingHua Luan Xin Xu ZhiJian Zhang 《Chemosphere》2013,90(6):1794-1804
Global warming is increasingly challenging for wetland ecological function. A temperature controlled microcosm system was developed to simulate climate change scenarios of an ambient temperature (control) and an elevated temperature (+5 °C). The effects and associated mechanisms of warming on phosphorus (P) fluxes at the sediment–water interface of six subtropical wetlands were investigated. The results indicated that P fluxes were generally enhanced under the experimental warming as measured by higher P concentrations in the porewater and overlying water as well as higher benthic P fluxes. The release of P from sediment to porewater occurred more strongly and quickly in response to experimental warming compared to the subsequent upward transfer into overlying water. The average accumulative benthic P output from the tested wetlands under the experimental warming was greater by 12.9 μg cm?2 y?1 (28%) for total P and 8.26 μg cm?2 y?1 (25%) for dissolved reactive P, compared to the ambient scenarios. Under warming the redistribution of P fractions in sediments occurred with greater NH4Cl–P and lower BD–P (extracted by a bicarbonate buffered dithionite solution) accompanied by greater NaOH–P. The higher temperature enhanced total phospholipid fatty acids. A shift in the microbial community was also observed with a relative dominance of fungi (a 4.7% increase) and a relative decline (by 18%) in bacterial abundance, leading to the higher secretion of phosphatase. Comparing between wetlands, the potential P fluxes in the nutrient-enriched wetlands were less impacted by warming than the other wetland types investigated. Thus wetlands characterized by low or medium concentrations of P in sediments were more susceptible to warming compared to P-rich wetlands. 相似文献
603.
Max Eisenberg Joseph J. Topping 《Journal of environmental science and health. Part. B》2013,48(6):729-742
Abstract Organochlorine pesticide and herbicide levels were monitored in samples of a variety of edible finfish harvested from the Maryland section of the Chesapeake Bay and its tributaries over a five‐year period (1976–80). Qualitative and quantitative information was obtained for the various polychlorinated biphenyls (PCB's), heptachlor, α‐BHC, chlordane, DDD, DDE, DDT, dieldrin, endrin, heptachlor‐epoxide, lindane, mirex, methoxychlor, aldrin, toxaphene, hexachlorobenzene, kepone and dacthal. In addition to analyses of the flesh of the animals, organochlorine residue levels were determined in roe or gonad tissue of several samples. Striped bass, white perch and yellow perch samples showed significantly higher concentrations of certain of these substances in roe or gonad tissue, especially PCB's, chlordane, DDD and dieldrin. Significantly higher levels of six organochlorine residues were found in the gonad tissue of striped bass; however, similar studies on gonad tissue of American Shad, harvested from the same region, show no such enhancement. Rather, the reverse is true; levels of certain organochlorine residues are higher in flesh tissue. All mean values, and virtually all individual values of organochlorine concentrations in the edible portion of the fish were within the U.S. Food and Drug Administration guideline, where such guidelines have been established. 相似文献
604.
Plants were examined at three different locations in the eastern part of the United States to determine whether damage from air pollution had occurred. This paper discusses sulfur dioxide damage in the metropolitan New York City area; hydrogen fluoride damage near a glass fiber manufacturing plant in the midwest; and hydrochloric acid mist and chlorine damage from a manufacturing operation in an eastern state. The symptoms that developed in vegetation were often found to be similar. Chemical and microscopical analyses were helpful in diagnosing the toxicants. 相似文献
605.
606.
Aristides Stamulis Joseph K. Thompson Harold F. Bogardus 《Journal of the Air & Waste Management Association (1995)》2013,63(11):709-712
Activated charcoal is widely used for the purification of air. Charcoal has a large surface area (ca. 1000 square meters per gram) and acts to purify air by adsorbing gaseous pollutants on its surface. When the capacity of the surface is exhausted, the charcoal is no longer effective and must be replaced. The carbon dioxide (CO2) pulse technique, developed at NRL, is a non-destructive method by which one can determine the remaining capacity, or the residual life of a charcoal bed before it has become exhausted. A dose of CO2 is injected into the air stream ahead of the charcoal bed and is eluted through the bed. The shape of the emerging CO2 elution peak is determined by the condition of the charcoal bed. For a new, unused charcoal bed the CO2 elution peak is considerably dispersed (flattened and broadened) due to adsorption and desorption at the charcoal surface. For a partially spent bed the elution peak is dispersed to a degree proportional to the remaining capacity of the bed. For a fully spent bed the CO2 elution peak is little affected by passage through the bed. The carbon dioxide puise technique has been shown to be indicative of charcoal capacity for a wide range of non-polar materials (such as hydrocarbons, alcohols, etc.), which are taken up primarily by physical adsorption. The method is essentially insensitive to relative humidity in the range between 10 and 70%. An adaptation of the method has been used for detection of leaks in a charcoal bed, such as those caused by channeling, faulty packing, etc. 相似文献
607.
608.
Donald L. Fox Joseph E. Sickles Michael R. Kuhlman Parker C. Reist William E. Wilson 《Journal of the Air & Waste Management Association (1995)》2013,63(10):1049-1053
Recent investigations of ambient aerosol behavior over urban areas have pointed out the need for controlled experimental data to link together field investigation results and computer simulation studies. This paper describes the design considerations, construction details and operating parameters of a large (8000 ft3) outside reaction chamber constructed in rural North Carolina. The chamber is triangular in cross-section, 20 ft wide, 20 ft high and 40 ft long, and is covered with clear 5 ml Teflon film. The outdoor location of the chamber permits the reaction volume to be exposed to the natural conditions of temperature and solar radiation. A recirculating air system allows the air in the chamber to be passed through an “absolute” fiberglas filter for adjustment of condensation nuclei concentration and also through driers for humidity adjustment. Internal fans are provided for mixing of the chamber contents without use of the recirculating system so that various degrees of turbulence can be approximated. A sampling line from the chamber passes directly to an instrument room, located directly under the chamber, where direct analyses for particle composition, concentration, and size, and gas composition and concentration are carried out. Parameters which can be varied in this system include number, size, distribution, and chemical composition of pre-existing nuclei, as well as humidity, solar radiation, temperature, and trace gas concentration and composition. 相似文献
609.
Joseph B. Knox 《Journal of the Air & Waste Management Association (1995)》2013,63(7):660-664
There is an emerging need to develop understanding and predictive capability for the transport, diffusion, and deposition of pollutants on regional and extended spatial scales. Some recent developments in the numerical simulation of pollutant transport and diffusion are reviewed and summarized herein, including case studies of model validation whenever’available. The efforts reported include: (a) the development and verification of a Lagrangian large-cloud diffusion code for intermediate to extended scales; (b) a hybrid Lagrangian-Eulerian transport-diffusion code for simulating pollutant distributions in transient stratified shear flow; (c) a meteorological submodel for determining a mass-consistent wind field on a regional scale suitable as input to a regional air pollution model; and (d) the development and initial verification of a multi-box regional air pollution model for the San Francisco Bay Area utilizing a mass-consistent wind field submodel. 相似文献
610.
Joseph R. Visalli 《Journal of the Air & Waste Management Association (1995)》2013,63(12):1451-1463
Dioxin, furan and combustion gas data from test programs conducted at the Pitts field, Prince Edward Island, and Peekskill municipal solid waste incinerators were compared to identify similar and discrepant results. Dioxin and furan concentrations sampled upstream of air pollution control devices are related to a variety of combustion gas variables monitored in the high temperature zones of the incinerators. The effects of temperature, excess oxygen, carbon monoxide, hydrochloric acid gas, flue gas moisture, particulate loading and refuse moisture and PVC content are discussed. Conclusions are made and future research needs are discussed. 相似文献