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排序方式: 共有659条查询结果,搜索用时 15 毫秒
61.
Alireza Ahadpour Shal Atefeh Jafari 《Journal of Superconductivity and Novel Magnetism》2014,27(6):1531-1538
In this work, Fe3O4–ZnO core–shell nanoparticles have been successfully synthesized using a simple two-step co-precipitation method. In this regard, Fe3O4 (magnetite) and ZnO (zincite) nanoparticles (NPs) were synthesized separately. Then, the surface of the Fe3O4 NPs was modified with trisodium citrate in order to improve the attachment of ZnO NPs to the surface of Fe3O4 NPs. Afterwards, the modified magnetite NPs were coated with ZnO NPs. Moreover, the influence of the core to shell molar ratio on the structural and magnetic properties of the core–shell NPs has been investigated. The prepared nanoparticles have been characterized utilizing transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and vibrating sample magnetometer (VSM). The results of XRD indicate that Fe3O4 NPs with inverse spinel phase were formed. The results of VSM imply that the Fe3O4–ZnO core–shell NPs are superparamagnetic. The saturation magnetization of prepared Fe3O4 NPs is 54.24 emu/g and it decreases intensively down to 29.88, 10.51 and 5.75 emu/g, after ZnO coating with various ratios of core to shell as 1:1, 1:10 and 1:20, respectively. This reduction is attributed to core–shell interface effects and shielding. TEM images and XRD results imply that ZnO-coated magnetite NPs are formed. According to the TEM images, the estimated average size for most of core–shell NPs is about 12 nm. 相似文献
62.
A new brachytherapy (125)I source has been investigated at Iranian Agricultural, Medical and Industrial Research School. Dosimetric characteristics [dose-rate constant Λ, radial dose function g(l)(r) and anisotropy function F(r,)] of IRA-(125)I were theoretically determined in terms of the updated AAPM task group 43 (TG-43U1) recommendations. Versions 5 and 4C of the Monte Carlo radiation transport code were used to calculate the dosimetry parameters around the source. The Monte Carlo calculated dose-rate constant of the (125)I source in water was found to be 92×10(-4) Gy h(-1) U(-1) with an approximate uncertainty of ±3 %. Brachytherapy seed model, 6711-(125)I, carrying (125)I radionuclides, was modelled and benchmarked against previously published values. Finally, the calculated results were compared with the published results of those of other source manufacturers. 相似文献
63.
64.
A density-based fuzzy clustering technique for non-destructive detection of defects in materials 总被引:1,自引:1,他引:0
Hasanzadeh P.R. Reza A.H. Rezaie S.H.H. Sadeghi M.H. Moradi M. Ahmadi 《NDT & E International》2007,40(4):337-346
In non-destructive testing and evaluation of materials, defects contain visible aggregations of similar levels of brightness with large scale of correlation between them. In most cases, these brightnesses have no notable contrast relative to non-defect counterparts. However, the density and the size of the defect are visually the most notable features. In this paper, we have utilized human conception for classifying defects by the fusion of fuzzy clustering method and fuzzy logic rules based on the density and the size of the defect. The probability of detection and the probability of error are compared with the Bayes classifier. The proposed approach shows that there is less dependency between the variation of density and size of a defect and variations of noise density and distribution. Experimental images from eddy current, ultrasonic and radiography techniques are investigated. It is shown that the new approach reduces the noise and drift, leading to a better detection of defects. 相似文献
65.
66.
Gity Mir Mohamad Sadeghi Jalil Morshedian Mehdi Barikani 《Polymer International》2003,52(7):1083-1087
Polybutadiene‐ol was synthesized by solution radical polymerization of 1,3‐butadiene in the presence of hydrogen peroxide as initiator and 2‐propanol as solvent. The ratio of initiator to monomer molar concentration, [I0]/[M0], was varied while temperature, reaction time and the type and amount of solvent were kept constant. The effects on the Mn; Mw; Mv; PDI, OH‐number and functionality of the synthesized polyols were studied. By taking several samples during a polymerization batch and analyzing them, the time of reaction was chosen as 100 min, after which the PDI changed dramatically. Mn decreased exponentially with increasing [I0]/[M0] according to the relationship Mn = 565.55 ([I0]/[M0])?0.7553. The decrease observed in Mw gradually levelled off with increasing [I0]/[M0] and molecular weight distribution broadened at larger values of [I0]/[M0]. The OH‐number increases with [I0]/[M0]. In addition to the number‐average molecular weight, functionality is dependent on the number of hydroxyl‐terminated chain radicals in the reaction medium. Copyright © 2003 Society of Chemical Industry 相似文献
67.
Rahmat Sadeghi 《Chemical engineering science》2006,61(23):7786-7794
A new model for representation of the excess Gibbs energy of polymer-electrolyte solutions is proposed. The excess Gibbs energy of a polymer-electrolyte solution is expressed as a sum of contributions of a combinatorial, a long-range and a short-range excess Gibbs energy term. The Flory-Huggins expression and the Pitzer's extension of Debye-Hückel function are used, respectively, as a combinatorial and a long-range contribution to the excess Gibbs energy. A new expression based on the local composition concept, which is the modified nonrandom two-liquid (NRTL) model, is developed to account for the short-range contribution to the excess Gibbs energy. The model provides a versatile and flexible thermodynamic framework for both correlating and predicting the phase equilibrium of electrolyte solutions, polymer solutions and complex systems containing both electrolytes and polymers. The utility of the model is demonstrated with successful representation of vapor-liquid equilibrium of several PEG or PPG-salt-H2O systems at different polymer molar masses. Results are compared with those obtained from the NRTL model. 相似文献
68.
69.
An optimal proportional-plus-integral/tracking control law is formulated. The control law has a command augmentation system configuration suitable for implementation on a digital computer on-board an aircraft. The proposed configuration offers the flexibility for choosing a feedforward matrix incorporating a set of additional control elements and for shaping the transient response without affecting the steady-state tracking property. Assuming the system is open-loop stable, then in the presence of a "jam" the disengaged system will maintain the steady-state tracking property which is desirable for aircraft continuing their mission. 相似文献
70.
This note describes a method for producing cubic curves made up from Bézier functions on an oscilloscope screen using simple analogue techniques. Ruled surface patches are illustrated in a simple extension of the method. It also indicates how generalized Bézier patches could be produced. 相似文献