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101.
Mohamed Afqir A. Tachafine D. Fasquelle M. Elaatmani J. C. Carru A. Zegzouti M. Daoud 《Moscow University Physics Bulletin》2017,72(2):196-202
The SrBi2 – x Sm x Nb2O9 (x = 0, 0.4, 0.5) structure were synthesized by a conventional solid-state method. The X-ray diffraction shows an orthorhombic at room temperature. Dielectric constant, loss tangent and Ac conductivity of Sm-doped SrBi2Nb2O9 were carried out, as well. A higher concentration of samarium (x = 0.4 and 0.5) doping leads to a significant reduction in dielectric constant and in Curie temperature. Rather relaxor type of behaviour took place. 相似文献
102.
103.
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
104.
An idea to design a new converging collimator for cold neutron time-of-flight measurements is presented. Using this new facility in combination with a neutron time-of-flight spectrometer, we may have neutron intensity gain factors about three times that obtained using the conventional straight slit collimators. Expressions for calculating the collimators dimensions as well as the intensity gain and the time resolution broading were presented. 相似文献
105.
The main purpose of this article is to study the L
p
-boundedness of linear and bilinear multiplier operators for the Dunkl transform in the one dimensional case. 相似文献
106.
Boumediene Abdellaoui Tarik Mohamed Touaoula 《NoDEA : Nonlinear Differential Equations and Applications》2010,17(3):271-288
In this paper we consider age structured equation with diffusion under nonlocal boundary condition and nonnegative initial
data. We prove existence, uniqueness and the positivity of the solution to the above problem. Our main result is to get an
exponential decay of the solution for large times toward such a study state. To this end we prove a weighted Poincaré–Wirtinger’s
type inequality in unbounded domain. 相似文献
107.
】Nd1+ x Ba2 - x Cu3Oy超导体以其良好的 Jc- B特性倍受人们注目。文中用区域熔炼技术在空气下制备出取向良好的 Nd1+ x Ba2 - x Cu3Oy 块材 ,采用纯氩下高温退火的办法抑制固溶体的形成 ,得到了零电阻温度 94K、临界电流密度达 540 0 A/cm2 的超导体。讨论了进一步提高 Jc的可能途径是减少液相的流失并使 Nd4 Ba2 Cu2 O10 相均匀分布。 相似文献
108.
109.
Mohamed Saleh Rogelio Oliva Christian Erik Kampmann Pål I. Davidsen 《European Journal of Operational Research》2010
Formal tools to link system dynamics model’s structure to the system modes of behavior have recently become available. In this paper, we aim to expand the use of these tools to perform the model’s policy analysis in a more structured and formal way than the exhaustive exploratory approaches used to date. We consider how a policy intervention (a parameter change) affects a particular behavior mode by affecting the gains of particular feedback loops as well as how it affects the presence of that mode in the variable of interest. The paper demonstrates the utility of considering both of these aspects since the analysis provides an assessment of the overall impact of a policy on a variable and explains why the impact occurs in terms of structural changes in the model. Particularly in the context of larger models, this method enables a much more efficient search for leverage policies, by ranking the influence of each model parameter without the need for multiple simulation experiments. 相似文献
110.
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