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71.
In this paper, Fourier cosine series are proposed for representing the hard nonlinear dependence of the permittivity and conductance
of a ferroelectric material on the DC bias voltage. Using these Fourier series representations closed-form expressions are
obtained for the amplitudes of the fundamental and third-order intermodulation products generated when a exposing ferroelectric-based
varactor to a DC bias voltage plus an equal-amplitude two-sinusoids signal. The results clearly show the strong and complicated
dependence of the third-order intermodulation performance on the DC bias voltage, the temperature and the amplitude of the
sinusoid. The results obtained suggest that the DC bias voltage and/or the temperature play an important role in deciding
the nonlinear performance of the ferroelectric-based varactors. 相似文献
72.
Using a unified representation for a class of buffered-outlet two current-feedback operational amplifier (CFOAs)-based sinusoidal
oscillators, new circuits of this type can be systematically discovered. A catalogue of four circuit structures, each structure
realizing nine oscillator circuits, is presented. Moreover, using the RC:CR transformation, additional nine oscillator circuits
can be obtained from each structure. While each circuit requires five passive elements, some of the circuits enjoy one or
more of the following attractive features: use of grounded capacitors, feasibility of absorbing the parasitic components of
the CFOAs and orthogonal tuning of the frequency and the startup condition of oscillation. 相似文献
73.
Taher Yousefi Reza Davarkhah Ahmad Nozad Golikand Mohammad Hossein Mashhadizadeh 《Materials Science in Semiconductor Processing》2013,16(3):868-876
One-dimensional manganese (IV) oxide (MnO2) (~20 nm in average diameter) were synthesized by cathodic electrodeposition and heat treatment. The mechanism of electrodeposition and nanowire formation were discussed. The product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR). Nanowires with varying lengths and diameters were found in TEM and SEM images of the sample. The results of N2 adsorption–desorption analysis indicated that the BET surface area of the MnO2 nanowires was 157 m2 g?1 and the pore size distributions were 2.5 and 4.5 nm. The electrochemical performances of the prepared MnO2 as an electrode material for supercapacitors were evaluated by cyclic voltammetry and galvanostatic charge/discharge measurements in a solution of 0.5 M Na2SO4. The higher specific capacitance of 318 F g?1 and good capacity retention of 86% were achieved after 1000 charge–discharge cycles had been observed for the MnO2 nanowires electrode. 相似文献
74.
Hoda H. M. Fadel Mohamed S. Taher Ahmed M. Gad Eman M. Kandil Fatma Sh Abd El-Aleem 《International Journal of Food Properties》2013,16(4):796-807
The main objective of the present study was to evaluate the release of aroma compounds from a banana soft drink complex model system in comparison with their release from simple model systems, each contains individual food ingredients. The effect of different food ingredients (sweeteners and thickeners at different concentrations), used in formulation of the soft drinks, on flavor release from simple model systems containing banana flavor was evaluated separately. The optimum release of isoamyl acetate (the most potent odorant of banana aroma) was observed at a concentration of 10% of each investigated sweetener (sucrose, glucose, and corn syrup). Pectin and xanthane showed the highest release at a concentration of 2.5 and 0.8% w/w, respectively. The level of each ingredient that showed the optimum release of isoamyl acetate was selected and used in formulation of a banana soft drink complex model system. The released volatiles were trapped by tenax and activated carbon. The gas chromatographic-mass spectrometric analysis revealed a gradual decrease (p < 0.05) in the volatile compounds release from the complex banana soft drink model system during storage for 90 days. However, the total content of the volatiles adsorbed by activated carbon trap was higher than that trapped by tenax. The percentage of isoamyl acetate to total volatiles (isoamyl acetate/total volatiles %) was calculated for each sample during storage. A distinct linear correlation was found between the calculated values and storage time (r = 0.97 and 0.92 for volatiles trapped by tenax and activated carbon, respectively). Sample stored for 60 days showed the highest value. These findings confirmed the results of aroma sensory evaluation. 相似文献
75.
Muhammad Taher Abuelma'atti 《International Journal of Electronics》2013,100(6):665-675
This paper discusses the large signal performance of CMOS analogue-functional elements. Fourier-series approximations are obtained for the transfer functions of the basic building blocks such as the linear CMOS transconductance element and the CMOS full-wave rectifier. Using these Fourier-series approximations, simple closed-form analytical expressions are obtained for the amplitudes of the harmonics at the output of a basic building block excited by a sinusoidal input signal. The analysis shows that, while the performance of the basic building blocks is near ideal at relatively small input amplitudes, performance degradation increases as the input amplitudes increase. On the other hand, since these expressions ignore the distortion mechanisms resulting from body effect and channel-length modulation, they cannot reliably predict the performance at small input signal levels. It appears, therefore, that body-effect and channel-length modulation must be taken into consideration for small-signal analysis. 相似文献
76.
Muhammad Taher Abuelma'atti 《International Journal of Electronics》2013,100(12):1229-1240
Large signal analysis of mixers excited by three tone signals is presented. The special case of two equal-amplitude sinusoids plus a difference-frequency injection is considered in detail and the results are compared, whenever possible, with previously published results. Contrary to previously published results, it is shown that even under large signal conditions and strong nonlinearity it is possible, at least in theory, to totally eliminate the third-order intermodulation when the amplitudes of the equal-amplitudes input sinusoids and the difference-frequency injection are equal. 相似文献
77.
Kamel Abboudi Lassâad Walha Yassine Driss Mohamed Maatar Taher Fakhfakh Mohamed Haddar 《Mechanism and Machine Theory》2011,46(12):1888-1900
The dynamic behavior of a two stage spur gear system used in a typical wind turbine is investigated in this paper. With the purpose of having an accurate simulation, for a given excitations, of the dynamic response of bearings, shafts and teeth in contact.In this study, we developed a lamped mass dynamic model with 12 DOFs. This model is excited by external and internal issues sources. The main factors of these excitations are the variability in the wind resource and the time varying mesh stiffness fluctuation.The aerodynamic torque is calculated from an empirical approach of the power coefficient. The incoming flow is modeled by an analytic equation test varies with time. The differential equations governing the system motion are solved by an implicit Newmark algorithm. 相似文献
78.
79.
Muhammad Taher Abuelma'atti 《Journal of Infrared, Millimeter and Terahertz Waves》1992,13(11):1795-1800
A new empirical formula is presented for the normalised capacitance of microstrip lines. The formula uses a single equation to represent the microstrip line capacitance over the useful range of the aspect ratio. The maximum error of the new formula is contained within 0.8 percent and the relative root-mean-square error is contained within 0.55 percent. The new formula can be easily implemented in computeraided design and analysis as well as in hand calculations using pocket calculators. 相似文献
80.
A Fourier-series model describing the current-voltage characteristic of a quantum-well diode (QWD) is presented. Using this model, closed-form expressions are obtained for the harmonic and intermodulation performance of a QWD excited by a multisinusoidal voltage superimposed on a dc voltage. 相似文献