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排序方式: 共有206条查询结果,搜索用时 156 毫秒
71.
W. Trabelsi P. Cecílio M.G.S. Ferreira K. Yasakau M.L. Zheludkevich M.F. Montemor 《Progress in Organic Coatings》2007
The present work aims at evaluating the surface morphology and the corrosion resistance of galvanised steel substrates pre-treated with bis-[triethoxysilylpropyl] tetrasulfide silane (BTESPT) solutions doped with cerium nitrate or zirconium nitrate. The silane pre-treatment leads to the formation of a silane coating in the metallic surface. The surface morphology of this coating was studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM). 相似文献
72.
G Kvam H Dahle JE Nordrehaug TI Randa T Tillung 《Canadian Metallurgical Quarterly》1997,38(3):391-399
PURPOSE: To evaluate the mean shortening fraction and its SD through the wall calculated from multiple cine-MR views, as an estimate of left ventricular globar function. MATERIAL AND METHODS: The average myocardial fiber shortening fraction was calculated by means of a simple truncated ellipsoid nested shell model. Left ventricular parameters, acquired by cine-MR imaging, from 20 healthy volunteers served as input. Fiber angles, ventricular torsion and a gradient increase in wall thickening from epicard to endocard were part of the model. RESULTS: The average fiber shortening fraction was 0.203 (0.158-0.246) +/- 0.021 diastolic lengths. It varied only moderately with variations in fiber angle values and not at all when the torsion angles were varied within physiological limits. The average shortening fraction correlates well with the systolic increase in chamber oblonguity (k = 0.837), with the ejection fraction (k = 0.877), and even better with the calculated wall thickening (k = 0.973). The average epicardial shortening fraction 0.169 (0.142-0.202) +/- 0.016 increased gradually through the wall to the endocardial value 0.250 (0.212-0.290) +/- 0.024. The increase in chamber length-width ratio from diastole to systole reduced the SD of the shortening fraction through the wall layers to a minimum. CONCLUSION: The fiber shortening fraction expresses the layered contraction of the myocardial wall, the wall thickening, and also the endocardial wall motion. The ejection fraction expresses only the latter. The shortening fraction and its SD through the wall may prove a valuable additional tool for estimating ventricular globar function. 相似文献
73.
Randa Herzallah Author Vitae 《Automatica》2007,43(8):1355-1362
In this paper, a novel dual heuristic programming (DHP) adaptive-critic-based cautious controller is proposed. The proposed controller avoids the pre-identification training phase of the forward model by taking into consideration model uncertainty when calculating the control law. It is suitable for linear and nonlinear, deterministic and stochastic control systems that are characterized by functional uncertainty. Convergence of the proposed DHP adaptive critic method to the correct value of the cost function is proven by evaluating analytically the correct value of the cost function, which satisfies the Bellman equation, and compares it to that calculated by the proposed method in a simple linear quadratic example. Moreover, the performance of the proposed cautious controller is demonstrated on linear one-dimensional and multidimensional examples. 相似文献
74.
Static and low-frequency noise characterization in submicron MOSFETs for memories cells applications
In this paper, we present the extraction of oxide traps properties of n-metal-oxide-semiconductor (N-MOS) field effect transistors with W×L=0.5×0.1 μm2 using low-frequency (LF and random telegraph signal) noise and static I(V) characterizations. The impact of oxide thickness, on static and noise parameters is analyzed. Static measurements on N-MOS devices with different tunnel oxide thickness show anomalies (a significant increase in Vt values for low temperature and kink effect) attributed to traps located in the oxide. From LF noise analysis we find that 1/f noise stems from carrier number fluctuations. The slow oxide trap concentration deduced from the noise data is about 1015 eV/cm3 in agreement with the state-of-the-art gate oxides. Finally, drain current RTS amplitude as large as 10% have been observed. 相似文献
75.
Nizar Tlili Hajer Trabelsi Justin Renaud Abdelhamid Khaldi Paul M. Mayer Saîda Triki 《Journal of the American Oil Chemists' Society》2011,88(11):1787-1793
The goal of this study is to evaluate for the first time the composition of triacylglycerols (TAG) using ESI-TOF-MS and phospholipids
species using HPLC–ESI-TOF-MS of two Capparis spinosa seed oil populations. Results show that LOO, LOP, LLO, OOO, PLL and POO were the major molecular species of triacylglycerol
detected in caper seeds; where L represents linoleic acid; O, oleic acid; and P, palmitic acid. The TAG composition was significantly
different among the two C. spinosa populations. In Ghar el Melh population, LOO (15.7%) was detected as the dominant TAG molecular species, followed by LOP
(13.2%), LLO (12.0%) and OOO (11.4%); while, the dominant fraction was LLO (14.2%) followed by LOO (14.1%), LOP (11.5%) and
PLL (10.5%) in Chouigui samples. The major component in the phospholipids fraction was phosphatidylinositol (ca. 54–91%),
followed by phosphatidylglycerol, phosphatidylethanolamine and phosphatidic acid. A variety of molecular species within each
class were identified. The major component in all phospholipids species contains a C-18:1 lipid chain. C16:0/C18:2-PI (ca.
28–31%) was the most abundant PI. PG species were mainly C18:2/C18:1-PG (25–32%). The major PE was C18:1/C18:1-PE (44–75%).
The major PA species was C18:1/C18:1-PA (22–24%). 相似文献
76.
Sana Toumi Seifeddine Benelghali Mohamed Trabelsi Elhoussin Elbouchikhi Yassine Amirat 《电力部件与系统》2017,45(7):715-725
This paper deals with the modeling and simulation of a permanent magnet synchronous generator (PMSG)-based marine current turbine (MCT) under faulty rectifier conditions. The modeling of the generator is established in the synchronous rotating d-q reference frame. The control of the speed, the d-axis current, and the q-axis current are achieved using proportional integral (PI) correctors. The faulty mode deals with the study of single and multiple open-switch damages appearing in the pulse width modulation (PWM) power rectifier. Simulations are carried out to highlight the proposed PMSG-based MCT performance in both cases using MATLAB/Simulink environment. 相似文献
77.
Nehla Abdellatif Nejmeddine Chorfi Sihem Trabelsi 《Journal of scientific computing》2011,47(3):419-440
We consider the Stokes problem in a three-dimensional axisymmetric bounded domain with non standard conditions which involve
the normal component of the velocity and tangential component of the vorticity. We reduce the three-dimensional problem into
a two-dimensional one and we write a variational formulation of it with three independent unknowns: the vorticity, the velocity
and the pressure. Then we propose a discretization by spectral methods which relies on this formulation. A detailed numerical
analysis leads to optimal error estimates for the three unknowns and numerical experiments confirm the interest of the discretization. 相似文献
78.
Tunisian acid activated clay was investigated as catalyst in the esterification of stearic acid with ethyl alcohol, carried out in a semi-continuous reactor. Kinetic study shows that the reaction is first order with respect to acid concentration. The activation energy found was 21 kJ/mol. This result suggests that the reaction process was controlled by a diffusional step. A kinetic model, giving the apparent constant rate as a function of temperature and catalyst concentration, has been established. This equation has been then successfully applied for a complex mixture of fatty acid. 相似文献
79.
80.
Voluntary boards composed primarily of industry practitioners who give aid and advice are almost universal in engineering education programs, though there has been little published research on this subject. Based on a survey of 90 engineering school directors and advisory board members, this research characterizes the operation, makeup, and effectiveness of advisory boards. The study shows that effective boards have a clear understanding of their role and limitations in influencing curriculum, encourage engagement with students, have formal procedures for involvement in ABET accreditation, and are well coordinated with the larger educational institution. Boards can be effective with or without involvement in fundraising, but it is essential that fundraising expectations be clearly understood and agreed upon by the school and the board. Boards composed largely of members with close ties to the institution, generally alumni, will be more engaged as advocates of the program and will contribute more financially. 相似文献