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排序方式: 共有235条查询结果,搜索用时 15 毫秒
41.
Parviz Aberoomand Azar Mohammad Saber Tehrani Sirwan Mohammadiazar Syed Waqif Husain 《Journal of separation science》2012,35(23):3354-3360
In the present work, the effect of substrate porosity for preparation of solid‐phase microextraction (SPME) fibers was investigated. The fibers were prepared by electrodeposition of sol‐gel coatings using negative potentials on porous Cu wire and compared with previous reported technique for preparation of SPME fibers using positive potentials on smooth gold wire. Porous substrate was prepared by electrodeposition of a thin layer of Cu on a Cu wire. The extraction capability of prepared fibers was evaluated through extraction of some aromatic hydrocarbons from the headspace of aqueous samples. The effect of substrate porosity and some operating parameters on extraction efficiency was optimized. The results showed that extraction efficiency of SPME fibers highly depends on porosity of the substrate. The LOD ranged from 0.005 to 0.010 ng/mL and repeatability at the 1 ng/mL was below 12%. Electrodeposited films were characterized for their surface morphology and thermal stability using SEM and thermogravimetric analysis, respectively. SEM analysis revealed formation of porous substrate and subsequently porous coating on the wire surface and thermogravimetric analysis showed high thermal stability of the prepared fiber. 相似文献
42.
We found that elemental iodine and bromine are converted to trihalide nucleophiles (triiodine and tribromide anion, respectively) in the presence of catalytic amounts of meso-tetraphenylporphyrins (H2TPP). Therefore a highly regioselective method for the synthesis of beta-haloalcohols through direct ring opening of epoxides with elemental iodine and bromine in the presence of H2TPPs as new catalysts is described. At room temperature a series of epoxide derivatives were converted into the corresponding halohydrins resulting from an attack of trihalide species anion atoms at the less substituted carbon atom. This method occurs under neutral and mild conditions with high yields in various aprotic solvents, even when sensitive functional groups are present. 相似文献
43.
Mohammad Ali Rasouli Mohammad Mahdavi Parviz Rashidi Ranjbar Mina Saeedi Abbas Shafiee Alireza Foroumadi 《Tetrahedron letters》2012,53(52):7088-7092
This work describes a green and efficient one-pot synthesis of N-alkyl-2-(2-oxoazepan-1-yl)-2-arylacetamide derivatives via an Ugi four-center, three-component reaction of 6-aminohexanoic acid, aromatic aldehydes, and isocyanide derivatives in water under reflux conditions in the absence of a catalyst. 相似文献
44.
Hu Zhang ** Sally Lamping Parviz Ayazi ShamlouAdvanced Biochemical Engineering Centre University College London Torrington Place London WCE JE 《高等学校化学研究》2002,18(2):113-116
IntroductionShakeflasksareusedroutinelyinthepharmaceu tical,biochemicalandmedicalfieldsforcellgrowthculture ,mediascreeningandforcellexpansion .Shakeflaskfermentationrequiresrelativelysmallamountsofmaterial,typicallybetween 5 0and 5 0 0mL ,andreliesonahorizon… 相似文献
45.
ZHANGHu ParvizAyaziShamlou 《高等学校化学研究》2004,20(4):489-493
Three approaches based on computational fluid dynamics(CFD) techniques have been assessed for their ability to describe the engineering flow environment in a miniaturized mechanically agitated bioreactor. The three approaches tested were the source-sink(SS), the multiple reference frames (MRF) and the sliding grids(SG). In all the cases, the predictions of the velocity components agree with reported experimental data. However, the analysis of the results of the turbulent intensities predicted by the three approaches indicates the MRF and the SG techniques under predicted turbulent intensities are comparable to both experimental measurements and the SS method. The predicted power number and pumping number based on the SS ap-proach are closer to typical reported experimental values compared to those obtained from the MRF and SG methods. 相似文献
46.
Mahmoudan Alireza Samadof Parviz Sadeghzadeh Milad Jalili Mohamad Sharifpur Mohsen Kumar Ravinder 《Journal of Thermal Analysis and Calorimetry》2021,145(3):1163-1189
Journal of Thermal Analysis and Calorimetry - Waste heat recovery systems are proposed to be an environmentally benign and a cost-effective application for efficiency improvement of energy... 相似文献
47.
Parviz Ghandforoush James C. Loo 《The Journal of the Operational Research Society》1992,43(11):1087-1093
This paper presents a procurement model for a multinational oil company with affiliate plants located worldwide. The proposed model uses a quantity discount relationship to reduce the total procurement cost. We use a non-linear programming method to solve the model and make comparisons with the current approach used by the oil company. The proposed approach has several distinct advantages: assured minimum cost, ease of data management, flexibility in design, and accuracy in results. 相似文献
48.
Tarun K. Sen Parviz Ghandforoush Charles T. Stivason 《Journal of Applied Mathematics and Decision Sciences》2004,8(4):219-233
Neural networks are excellent mapping tools for complex financial data. Their mapping capabilities however do not always result in good generalizability for financial prediction models. Increasing the number of nodes and hidden layers in a neural network model produces better mapping of the data since the number of parameters available to the model increases. This is detrimental to generalizability of the model since the model memorizes idiosyncratic patterns in the data. A neural network model can be expected to be more generalizable if the model architecture is made less complex by using fewer input nodes. In this study we simplify the neural network by eliminating input nodes that have the least contribution to the prediction of a desired outcome. We also provide a theoretical relationship of the sensitivity of output variables to the input variables under certain conditions. This research initiates an effort in identifying methods that would improve the generalizability of neural networks in financial prediction tasks by using mergers and bankruptcy models. The result indicates that incorporating more variables that appear relevant in a model does not necessarily improve prediction performance. 相似文献
49.
50.
Mohammad Reza Ganjali Parviz Norouzi Masoud Salavati-Niasari 《Analytica chimica acta》2006,567(2):196-201
In this work, a highly selective and sensitive monohydrogen phosphate membrane sensor based on a molybdenum bis(2-hydroxyanil) acetylacetonate complex (MAA) is reported. The sensor shows a linear dynamic range between 1.0 × 10−1 and 1.0 × 10−7 M, with a nice Nernstian behavior (−29.5 ± 0.3 mV decade−1) in pH of 8.2. The detection limit of the electrode is 6.0 × 10−8 M (∼6 ppb). The best performance was obtained with a membrane composition of 32% poly(vinyl chloride), 58% benzyl acetate, 2% hexadecyltrimethylammonium bromide and 8% MAA. The sensor possesses the advantages of short response time, low detection limit and especially, very good selectivity towards a large number of organic and inorganic anions including salicylate, citrate, tartarate, acetate, oxalate, fluoride, chloride, bromide, iodide, sulfite, sulfate, nitrate, nitrite, cyanide, thiocyanate, perchlorate, metavanadate, and bicarbonate ions. The electrode can be used for at least 10 weeks without any considerable divergence in its slope and detection limit. It was used as an indicator electrode in potentiometric titration of monohydrogenphosphate ion with barium chloride. The proposed sensor was successfully applied to direct determination of monohydrogenphosphate in two fertilizer samples (NPK). 相似文献