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81.
The reaction process of polycarbosilane (PCS) fiber cured by cyclohexene vapor has been studied and compared with that of PCS fiber cured by air. The influence of curing temperature on Si? H bond reaction degree and gel content, the structure and composition of PCS were investigated by FTIR, EA, TGA, NMR, and GC‐MS. The results showed that, Si? H bond in the molecular structure of PCS reacted during cyclohexene curing process and the reaction degree increased when the curing temperature increases. Simultaneously, gel content of PCS fiber rapidly increased till PCS fiber became infusible. Si? H radical and Si? CH2 radicals formed Si? CH2? Si crosslinking of PCS molecules through the agency of cyclohexene. Some cyclohexyls linked to principal chain of PCS, which was proven by 13C‐CPMAS‐NMR, and broke off, and cyclohexane and some monosilane are generated as byproducts when temperature increased. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献
82.
The corrosion inhibition and adsorption characteristics of three selected imidazole derivatives namely, 2-amino-4,5-imidazoledicarbonitril
(AID), 5-amino-4-imidazolecarboxamide (AIC) and imidazole (IM) on aluminum in 1.0 M HCl was investigated at 25 °C. Measurements
were carried out under various experimental conditions using chemical (weight loss), and electrochemical (Tafel polarization
and impedance) methods. Molecular dynamics (MD) method and density functional theory were also applied here for theoretical
study. Results obtained showed that inhibition efficiency of these compounds increases with increase in their concentrations
due to the formation of a surface film on the aluminum surface. Adsorption energy as well as hydrogen bond length calculations
showed that AID was the best corrosion inhibitor among the tested imidazole derivatives. Polarization measurements reveal
that the selected imidazole derivatives function mainly as cathodic-type inhibitors. Physisorption, followed by chemisorption
was proposed as the mechanism for the inhibition process. Adsorption via H-bond formation was also considered here. Results
obtained from theoretical study were found to confirm experimental findings. 相似文献
83.
The corrosion behaviour of steel at various concentrations of perchloric acid was studied by weight loss method in temperature range from 298 to 323 K. Results obtained show that corrosiveness of acid increases with its concentration and temperature. The logarithm of corrosion rate was plotted against the acid concentration and values of Hammett Ho and Strehlow Ro(H) acidity functions. The activation energies, enthalpies and entropies of the corrosion process of steel were also determined and fitted against Ro(H). 相似文献
84.
Khaled Ali Alfadhel 《Chemical engineering science》2005,60(11):2911-2926
We study the development of a mathematical model that describes isothermal microfluidic steady flow in a membrane microreactor, i.e., a silicon microreactor that houses a permeable membrane in one wall. The model employs the Navier-Stokes equation with appropriate boundary conditions for fluid permeation through the membrane and velocity slip at the walls to account for high Knudsen number. The model equations are solved analytically using finite Fourier transforms. The model solution is used to evaluate the effect of fluid permeation through the membrane and the Knudsen number on the velocity profile and pressure drop. For the simplified cases of no permeation and/or no slip, the derived solution is in excellent agreement with published experimental and theoretical results available in the literature. The utility of the model is illustrated by applying the results to a membrane microseparator used to separate hydrogen from the other effluents in a microreformer. 相似文献
85.
86.
Zaynab M. Elhadi Khaled Melghit Issa Al-Amri Mohammed A. Al-Kindi 《Ceramics International》2010,36(2):807-809
A novel layered compound Al0.3V2O5·5H2O was successfully prepared and characterized using powder X-ray diffraction, Thermal analysis, scanning and transmission electron microscopes. The new layered Al0.3V2O5·5H2O has like-nanowires shape and the layered structure was stable until 400 °C. At higher temperature (500 °C), it decomposes to orthorhombic AlxV2O5 and triclinic AlVO4. 相似文献
87.
Gypsum is a bioresorbable material that has been used in many applications such as tissue regeneration. Mechanical properties of gypsum have limited its applications to non-load bearing sites. The current study aimed at studying the compressive strength and behaviour of gypsum–polymer composites in protein-free simulated body fluids (SBF). Polymers studied were poly(vinyl alcohol) (PVA) and its copolymers with vinyl acetate and itaconic acid in addition to vinyl acetate and vinyl chloride. Composites with the highest compressive strength results were chosen for the preliminary in vitro evaluation in protein-free SBF solutions. Changes in the concentrations of Ca2+ and PO43− ions, weight loss and morphology of the solid samples were monitored after soaking them in SBF and 1.5 SBF solutions. Results showed resorption of gypsum, concurrently with deposition of apatite in all composites, including polymer-free gypsum. Mechanical integrities of all samples were maintained, suggesting their stabilities when used as bone cements. 相似文献
88.
Tarek Elesseily Tamer Ali Khaled Sharaf 《Analog Integrated Circuits and Signal Processing》2010,63(2):143-159
This paper presents the design of a dual-band L1/L2 GPS receiver, that can be easily integrated in portable devices (mainly
GSM mobile phones). For the ease of integration with GSM wireless systems the receiver can tolerate most of the common GSM
crystals, besides the GPS crystals, this will eliminate the need to use another crystal on board. A new frequency plan is
presented to satisfy this requirement. A low-IF receiver architecture is used for dual-band operation with analog on-chip
image rejection. The receiver is composed of a narrow-band LNA for each band, dual down-conversion mixers, a variable-gain
channel filter, a 2-bit analog-to-digital converter, and a fully integrated frequency synthesizer including an on-chip VCO
and loop filter. The complex filter can accept IF frequency variation of 10% around 4.092 MHz which allows the use of the
commonly used 10/13/26 MHz GSM crystals and all the GPS crystals. The synthesizer generates the LO signals for both L1/L2
bands with an average phase noise of −95 dBc/Hz. The receiver exhibits maximum gain of 112 and 115 dB, noise figures of 4
and 3.6 dB, and input compression points of −76 and −79 dBm for L1 and L2, respectively. An on-chip variable-gain channel
filter provides IF image rejection greater than 25 dB and gain control range over 80 dB. The receiver is designed in 0.13 μm
CMOS technology and consumes 18 mW from a 1.2-V supply. 相似文献
89.
Khaled Elbanna Adel M. A. Assiri Monier Tadros Manal Khider Abdelrahaman Assaeedi Adel A. A. Mohdaly Mohamed Fawzy Ramadan 《Sensing and Instrumentation for Food Quality and Safety》2018,12(3):1601-1609
The aim of this work was to investigate cold-pressed rosemary oil (RO) for its lipid classes, subclasses, fatty acid composition, tocochromanols and total phenolics amount. Antiradical activity against 1,1-diphenyl-2-picrylhydrazyl (DPPH?) and galvinoxyl radicals, antioxidant activity, as measured by the Rancimat test, as well as antimicrobial activity against food-borne bacteria, and dermatophytic fungi of RO were evaluated. In RO, the amount of neutral lipids was highest (ca. 86%), followed by phospholipids (0.92%) and glycolipids (0.88%). The percentages of monounsaturated, polyunsaturated, and saturated fatty acids were 41.7, 42.3, and 15.8%, respectively. Linoleic acid (41.7%) and oleic acid (41.2%) were the major fatty acids while linolenic acid accounted for 1.3% of total fatty acids. The following tocochromanols were detected: α-, β-, γ- and δ-tocopherols, which accounted for 291, 22, 1145, and 41 mg/100 g oil, respectively, as well as α-, β-, γ- and δ-tocotrienols, which accounted for 18, 12, 29, and 158 mg/100 g oil, respectively. RO also contained high levels of phenolic compounds (7.2 mg GAE/g). After 60 min of reaction with free radicals, 67% of DPPH? and 55% of galvinoxyl radicals were quenched by RO. Rancimat test showed that blending RO with sunflower oil increased the induction period (IP) for blends. The IP of the RO: sunflower oil blend (1:9, v/v) was 390 min, and RO: sunflower oil blend (2:8, v/v) was longer (540 min). RO exhibited high antimicrobial potential against food-borne pathogenic bacteria (E. coli, S. enteritidis, and L. monocytogenes) and high antifungal potential against dermatophyte fungi (T. mentagrophytes, and T. rubrum). RO had unique high level of γ-tocopherol, which is a scavenger of reactive nitrogen species making it a promising material in the food, cosmetic and pharmaceutical applications. 相似文献
90.
Khaled Yahia Antonio J. Marques Cardoso Adel Ghoggal Salah-Eddine Zouzou 《电力部件与系统》2014,42(7):682-692
Abstract—In this article, a method based on the application of the discrete wavelet transform to the instantaneous reactive power signal, for diagnosing the occurrence of broken rotor bars in induction motors operating under time-varying load conditions, is presented. This method is based on the decomposition of the instantaneous reactive power signal, from which wavelet approximation and detail coefficients are extracted. The energy evaluation of known bandwidths permits to de?ne a fault severity factor. This method has been tested through the simulation of an induction motor using a mathematical model based on the winding-function approach. These simulation results are complemented by experimental tests conducted on an induction motor with several faulty rotors that can be interchanged and both simulation and experimental results have shown the effectiveness of the proposed method for broken rotor bars diagnosis in induction motors even under time-varying load conditions. 相似文献