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41.
Mohamed Kameche Mohamed Feham 《International Journal of Infrared and Millimeter Waves》2006,27(5):687-705
Simple techniques for determining the broadband small signal equivalent circuit (SSEC) of MESFETs are presented in this paper.
The intrinsic elements are calculated using two-dimensional method from the Y parameters, which are obtained from the Fourier
analysis of the device transient response to voltage-step perturbations at the drain and gate electrodes. Whereas, the parasitic
external elements are determined by simple approximations used in transmission line modeling. In addition, a new technique
is also proposed to determine the source and drain series resistances. A comparison of the SSEC of three different MESFETs
technologies shows that the MESFETs on GaN and 4H-SiC are suitable for high power applications. The method used to determine
the intrinsic elements is validated with simulated data obtained by Monte Carlo method. 相似文献
42.
M.M. El-Nahass M.A.M. Seyam H.E.A. El-Sayed A.M. Abd El-Barry 《Applied Surface Science》2006,252(18):6218-6227
Thin films of samples of the glassy SxSe100−x system with 0 ≤ x ≤ 7.28 have been prepared by thermal evaporation technique at room temperature (300 K). X-ray investigations show that the structure of pure selenium (Se) does change seriously by the addition of small amount of sulphur S ≤7.28%. The lattice parameters were determined as a function of sulphur content. Results of differential thermal analysis (DTA) of the glassy compositions of the system SxSe100−x were discussed. The characteristic temperatures (Tg, Tc and Tm) were evaluated. Dark electrical resistivities, ρ, of SxSe100−x thin films with different thicknesses from 100 to 500 nm, were measured in the temperature range from 300 to 423 K. Two distinct linear parts with different activation energies were observed. The variation of electrical resistivity of examined compositions has been discussed as a function of the film thickness, temperature and the sulphur content. The application of Mott model for the phonon assisted hopping of small polarons gave the same two activation energies obtained from the resistivity temperature calculations. 相似文献
43.
44.
M. S. Sakr A. A. El-Shazly M. M. Mostafa H. A. El-Sayed A. A. Mohamed 《Czechoslovak Journal of Physics》1988,38(11):1255-1259
Transient creep of Cd-2 wt. % Zn and Cd-17·4 wt. % Zn alloys has been studied under different constant stresses ranging from 6·4 MPa to 12·7 MPa near the transformation temperature. The results of both compositions showed two transient deformation regions, the low temperature region (below 483 K) and the high temperature region (above 483 K). From the transient creep described by the equation
tr=Bt
n, where
tr andt are the transient creep strain and time. The parametersB andn were calculated. The parameterB was found to change with the applied stress from 0·3×10–4 to 3×10–4 and from 0·6×10–4 to 18×10–4 for Cd-2 wt. % Zn and Cd-17·4 wt. % Zn, respectively. The exponentn was found to change from 0·8 to 0·95 for both alloys. The parameterB was related to the steady state creep rate
through the equation
, the exponent was found to be 0·5 for Cd-2 wt. % Zn and 0·6 for the eutectic composition. The activation energies of transient creep in the vicinity of the transformation regions (above 483 K) were found to be 50·2 kJ/mole for Cd-2 wt. % Zn and 104·7 kJ/mole for the eutectic composition characterizing the mechanisms of grain boundary diffusion and volume diffusion in Cd, respectively. 相似文献
45.
46.
Abdel -Aziz M. Wahbi Mona M. Bedair Shereen M. Galal Mohamed H. Abdel-Hay Azza A. Gazy 《Mikrochimica acta》1993,111(1-3):83-91
A sensitive and rapid Spectrofluorimetric method for the determination of guanethidine sulphate, guanfacine hydrochloride, guanoclor sulphate and guanoxan sulphate in tablets and spiked human serum and urine samples is described. The method is based on the reaction of monosubstituted guanidino compounds in an aqueous potassium hydroxide solution with benzoin, in the presence of -mercaptoethanol and sodium sulphite. Highly fluorescent derivatives were obtained, with excitation and emission maximum wavelengths around 325 and 430 nm, respectively. In optimal reaction conditions, the linearity ranges were 0.04–0.28 g/ml, with relative standard deviations less than 2%. The method has been successfully applied to the determination of these drugs in tablets. The results are highly correlated with the B.P. method. Chloroform (or for guanoxan dichloromethane) was used to extract the drugs from serum and urine at basic pH, followed by the proposed fluorimetric method. The limit of detection is 0.02 g/ml for the selected drugs. 相似文献
47.
48.
Unusual Formation and Structure of a O‐Sulfinato Zinc Complex Whereas the reaction between hydrotris[(N‐xylyl)‐thioimidazolyl]borato‐zinc perchlorate ([ L· Zn‐OClO3]) and ethanethiolate under an inert atmosphere leads to the thiolate complex [ L· Zn‐SC2H5], the same reaction in air produces the sulfinato complex [ L· Zn‐O‐S(O)‐C2H5] ( 1 ). 1 is the first fully characterized sulfinato‐zinc complex. Its structure determination has confirmed the unusual coordination of the sulfinato ligand via one of its oxygen atoms. 相似文献
49.
I. K. Battisha A. El Beyally S. Abd El Mongy A. M. Nahrawi 《Journal of Sol-Gel Science and Technology》2007,41(2):129-137
Structural characteristics of pure silica gel (silica-xerogel, SiO2) and silica gel doped with some rare earth elements (REEs) such as, praseodymium Pr3+, and Europium Eu3+, Erbium Er3+ and Holmium Ho3+ ions, with different concentrations ranging from 1 up to 6%, in the form of monolith materials were prepared by sol-gel technique,
Using tetra-ethoxysilane as precursor materials, which are of particular interest for sol-gel integrated optics applications.
Some structural features of sol-gel derived monolith are analyzed, namely the structure of nano-particle momolith samples,
based on X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR). We show that the XRD spectra of α-crystobalite are
obtained for the pure samples at 1100°C and even by doping with the four REEs ions. 相似文献
50.
Loganin ( 1 ), loganic acid ( 2 ), and periclymenoside ( 3 ) have been isolated from Lonicera periclymenum L . The structure of the new compound 3 and the identity of the others have been determined by chemical transformations and interpretation of the spectral data. 相似文献