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排序方式: 共有488条查询结果,搜索用时 31 毫秒
51.
This study presents an easy and cost-effective flow-based cloud point extraction (CPE) method for determining partial amounts of two organophosphorus pesticides (phosalone and ethion) in seawater by HPLC–UV–Vis. In continues CPE methodology, the effect of the different column packing type such as carbon nanotube, polyacrylonitrile nanofiber and fiberglass on pesticide extraction was investigated. The Triton X-100 was utilized as nonionic surfactant, and moreover, effect of different parameters such as pH, temperature, extraction time, surfactant concentration, type and volume of the eluent solution on the extraction efficiency was optimized. Under optimum conditions, the figures of merit of the method for phosalone and ethion were obtained as: the enrichment factor (172 and 166), line range (0.8–300 and 0.5–300 µg L?1, R 2 = 0.9973 and 0.9982), relative standard deviation in concentration of 200 µg L?1 (%RSD = %5.4 and %7.99, N = 5) and limit of detection (LOD = 0.24 and 0.14 µg L?1). The suggested method was successfully used for determination of phosalone and ethion in Chabahar Bay seawaters with satisfactory results. 相似文献
52.
Formation of Phosphorylated 3H‐Pyrroles from NefIsocyanidePerkow Adducts and Tosylmethyl Isocyanide 下载免费PDF全文
Imidoyl chlorides, generated from isocyanides and acyl chlorides, react with trialkyl phosphites, in a Perkow‐type reaction, to afford 3‐(alkylimino)‐2‐[(dialkyloxyphosphoryl)oxy]acrylates, which undergo a smooth reaction with tosylmethyl isocyanide (TsMIC) to furnish 4‐(alkylamino)‐3‐[(dialkyloxyphosphoryl)oxy]‐5‐[(4‐methylphenyl)sulfonyl]‐3H‐pyrrole‐3‐carboxylates in moderate‐to‐good yields. 相似文献
53.
A theoretical study of the thermal decomposition kinetics of ethane halides(C2H6-nXn(n = 1~3);X = F,Cl,Br) has been carried out at the B3LYP/6-31++G** and B3PW91/631++G** levels of theory.Among these methods and comparison of activation parameters with available experimental values,the B3PW91/6-31++G** method is in good agreement with the experimental data.The analysis of bond order and natural bond orbital(NBO) charges,bond indexes,and synchronicity parameters suggest the elimination of HX in reactions 1~9(HF:compounds 1~3,HCl:compounds 4~6,and HBr:compounds 7~9) occur through a concerted and slightly asynchronous four-membered cyclic transition state type of mechanism. 相似文献
54.
Ehsan Jazaeri Liyuan Zhang Xungai Wang Takuya Tsuzuki 《Cellulose (London, England)》2011,18(6):1481-1485
The possibility of fabricating carbon nanofibers from cellulose nanofibers was investigated. Cellulose nanofiber of ~50 nm
in diameter was produced using ball milling in an eco-friendly manner. The effect of the drying techniques of cellulose nanofibers
on the morphology of carbon residue was studied. After pyrolysis of freeze-dried cellulose nanofibers below 600 °C, amorphous
carbon fibers of ~20 nm in diameter were obtained. The pyrolysis of oven-dried precursors resulted in the loss of original
fibrous structures. The different results arising from the two drying techniques are attributed to the difference in the spatial
distance between cellulose nanofiber precursors. 相似文献
55.
A local herb, Kacip Fatimah, is famous amongst Malay women for its uses in parturition; however, its phytochemical contents have not been fully documented. Therefore, a study was performed to evaluate the phenolics, flavonoids, and total saponin contents, and antibacterial and antifungal properties of the leaf, stem and root of three varieties of Labisia pumila Benth. Total saponins were found to be higher in the leaves of all three varieties, compared to the roots and stems. Leaves of var. pumila exhibited significantly higher total saponin content than var. alata and lanceolata, with values of 56.4, 43.6 and 42.3 mg diosgenin equivalent/g dry weight, respectively. HPLC analyses of phenolics and flavonoids in all three varieties revealed the presence of gallic acid, caffeic acid, rutin, and myricetin in all plant parts. Higher levels of flavonoids (rutin, quercitin, kaempferol) were observed in var. pumila compared with alata and lanceolata, whereas higher accumulation of phenolics (gallic acid, pyrogallol) was recorded in var. alata, followed by pumila and lanceolata. Antibacterial activities of leaf, stem and root extracts of all varieties determined against both Gram positive (Micrococcus luteus, Bacillus subtilis B145, Bacillus cereus B43, Staphylococcus aureus S1431) and Gram negative (Enterobacter aerogenes, Klebsiella pneumonia K36, Escherichia coli E256, Pseudomonas aeruginosa PI96) pathogens showed that crude methanolic extracts are active against these bacteria at low concentrations, albeit with lower antibacterial activity compared to kanamycin used as the control. Antifungal activity of methanolic extracts of all plant parts against Fusarium sp., Candida sp. and Mucor using the agar diffusion disc exhibited moderate to appreciable antifungal activities compared to streptomycin used as positive control. 相似文献
56.
Cross-linking mechanisms of arginine and lysine with α,β-dicarbonyl compounds in aqueous solution 总被引:1,自引:0,他引:1
Nasiri R Field MJ Zahedi M Moosavi-Movahedi AA 《The journal of physical chemistry. A》2011,115(46):13542-13555
Cross-linking in proteins by α,β-dicarbonyl compounds is one of the most damaging consequences of reactive carbonyl species in vivo and in foodstuffs. In this article we investigate computationally the cross-linking of glyoxal and methylglyoxal with lysine and arginine residues using density functional theory and the wB97XD dispersion-corrected functional. Five pathways, A-E, have been characterized. In pathways A and B, the reaction proceeds via formation of the Schiff base, aldimine, followed by addition of arginine. In contrast, in pathways C-E, direct addition of arginine to the dicarbonyl compounds occurs first, leading to a dihydroxyimidazolidine intermediate, which then reacts with lysine after dehydration and proton transfer reactions. The results reveal that pathways A, C, and E are competitive whereas reactions via pathways B and D are much less favorable. Inclusion of up to five explicit water molecules in the proton transfer and dehydration steps is found to lower the energy barriers in the feasible pathways by about 5-20 kcal/mol. Comparison of the mechanisms of methylglyoxal-derived imidazolium cross-linking (MODIC) and glyoxal-derived imidazolium cross-linking (GODIC) shows that the activation barriers are lower for GODIC than MODIC, in agreement with experimental observations. 相似文献
57.
M. Abdolzadeh M.A. MehrabianG. Zahedi A. Soltani Goharrizi 《International Journal of Heat and Fluid Flow》2011,32(3):670-679
In this study a modified version of v2-f turbulence model (φ-α), is applied to simulate a non-isothermal air-flow. The φ-α model and a two-phase Eulerian approach complement each other to predict the rate of particle deposition on a tilted surface. The φ-α model can accurately calculate the normal fluctuations, which mainly represent the non-isotropic nature of turbulence regime near the wall. The Eulerian model was modified considering the most important mechanism in the particle deposition rate when compared to the experimental data. The model performance is examined by comparing the rate of particle deposition on a vertical surface with the experimental data in a turbulent channel flow available in the literature. The effects of lift force, turbophoretic force, thermophoreric force, electrostatic force, gravitational force and Brownian/turbulent diffusion were examined on the particle deposition rate. The results show that, using the φ-α model predicts the rate of deposition with reasonable accuracy. The results of modified particle model are in good agreement with the experimental data. This study highlights the paramount effect of thermophoretic force on the particle deposition rate and clearly shows that when the temperature difference exceeds a certain limit, the electrostatic force has insignificant effect on the particle deposition rate. Furthermore, it is indicated that even at small temperature differences, the effect of tilt angle on the particle deposition rate for intermediate-size particles is negligible. 相似文献
58.
Mohammadhassan Vasheghani Ehsan Marzbanrad Cyrus Zamani Mohamed Aminy Babak Raissi Toraj Ebadzadeh Hadi Barzegar-Bafrooei 《Heat and Mass Transfer》2011,47(11):1401-1405
Thermal conductivity of α-Al2O3 was measured using hot wire method. α-Al2O3 (20 nm in size) was synthesized by microwave method for which, the results were compared with commercially available γ-Al2O3. Thermal conductivity of nanofluids was investigated considering, it is dependency on Al2O3 phase. It was observed that by adding 3 wt% of nano γ-Al2O3 and α-Al2O3 to the engine oil, thermal conductivity increases by 37 and 31%, respectively. The corresponding viscosity increase for the
same amount of nano γ-Al2O3 and α-Al2O3 were 36 and 38%, respectively. It was concluded that the differences in thermal conductivity originate from higher specific
surface area of γ-Al2O3 compared to the α-Al2O3 which is the result of porosity difference, obtained during the synthesis process. 相似文献
59.
In the present study the effects of surface tension on the growth and collapse stages of cavitation bubbles are studied individually for both spherical and nonspherical bubbles. The Gilmore equation is used to simulate the spherical bubble dynamics by considering mass diffusion and heat transfer. For the collapse stage near a rigid boundary, the Navier–Stokes and energy equations are used to simulate the flow domain, and the VOF method is adopted to track the interface between the gas and the liquid phases. Simulations are divided into two cases. In the first case, the collapse stage alone is considered in both spherical and nonspherical situations with different conditions of bubble radius and surface tension. According to the results, surface tension has no significant effects on the flow pattern and collapse rate. In the second case, both the growth and collapse stages of bubbles with different initial radii and surface tensions are considered. In this case surface tension affects the growth stage considerably and, as a result, the jet velocity and collapse time decrease with increasing surface tension coefficient. This effect is more significant for bubbles with smaller radii. 相似文献
60.
Meccanica - In the present study, the two-phase gas–liquid convective heat transfer is numerically studied inside uniformly heated wavy micro-tubes in the Taylor flow regime. Both Newtonian... 相似文献