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排序方式: 共有112条查询结果,搜索用时 921 毫秒
31.
To reduce both the cost and the environmental impact of copper‐based thermal solar absorbers, we have investigated their possible substitution by bio‐based conductive polymer nanocomposite (CPC) elements. Our results show that carbon nanotubes (CNT) have no significant influence on polymers’ calorimetric properties such as Tm and Tg but lead to a strong increase in crystallinity of poly(lactic acid) (PLA) and to a lesser extent of poly(amide 12) poly(amide 12) (PA12) for 2 and 3 CNT wt % respectively. Percolation thresholds as low as 0.5 and 0.58 were obtained for PA12 and PLA, respectively, and visco‐elastic properties such as η*, G’ and G” were found to increase exponentially with CNT content confirming the formation of a CNT network within the matrix. All CPC are absorbing more energy in the visible and infrared than in the ultraviolet wavelength ranges. Finally, the thermal conductivity k of PLA–CNT and PA12–CNT were increased, respectively, of 85% and 24%, to reach 0.28 W.m?1.K?1 and 0.26 W.m?1.K?1, for only 5 wt% CNT. The figure of merit suggests that PA12 is the polymer which satisfies at best all criteria, particularly combining a lower viscosity at almost equivalent thermal conductivity and absorptivity. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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33.
Raffael Davenport Mattia Silvi Adam Noble Zied Hosni Natalie Fey Varinder K. Aggarwal 《Angewandte Chemie (International ed. in English)》2020,59(16):6525-6528
There are a limited number of ring‐contraction methodologies which convert readily available five‐membered rings into strained four‐membered rings. Here we report a photo‐induced radical‐mediated ring contraction of five‐membered‐ring alkenyl boronate complexes into cyclobutanes. The process involves the addition of an electrophilic radical to the electron‐rich alkenyl boronate complex, leading to an α‐boryl radical. Upon one‐electron oxidation, ring‐contractive 1,2‐metalate rearrangement occurs to give a cyclobutyl boronic ester. A range of radical precursors and vinyl boronates can be employed, and chiral cyclobutanes can be accessed with high levels of stereocontrol. The process was extended to the preparation of benzofused cyclobutenes and the versatility of the boronic ester was demonstrated by conversion to other functional groups. 相似文献
34.
Naifar O. Ben Makhlouf A. Hammami M. A. Ouali A. 《Mediterranean Journal of Mathematics》2016,13(5):2841-2851
The observer design for nonlinear systems with unknown, bounded, time-varying delays, on both input and state, is still an open problem for researchers. In this paper, a new observer design for a class of nonlinear system with unknown, bounded, time-varying delay was presented. For the proof of the observer stability, a Lyapunov–Krasovskii function was chosen. Sufficient assumptions are provided to prove the practical stability of the proposed observer. Furthermore, the exponential convergence of the observer was proved in the case of a constant time delay. Simulation results were shown to illustrate the feasibility of the proposed strategy.
相似文献35.
An analysis of the linear and nonlinear vibration responses of composites with delaminations is presented. The effect of delamination size on the linear and nonlinear vibration response is studied. The composite material used in this paper is a glass fibre reinforced plastic (GFRP) having delaminations at the plies interfaces. The experimental procedure consists in inducing the specimen on its resonance flexural modes with different excitation levels (amplitudes) for six bending modes and for each delamination length. The presence of the nonlinearity introduced by the delamination was clearly identified by the variation of natural frequencies for increasing excitation levels. Then, nonlinear elastic parameters for progressive delamination length were determined and discussed for the first six bending modes. The linear and the nonlinear elastic parameters were compared in their sensitive modes. 相似文献
36.
In this paper, we present two classification approaches based on Rough Sets (RS) that are able to learn decision rules from uncertain data. We assume that the uncertainty exists only in the decision attribute values of the Decision Table (DT) and is represented by the belief functions. The first technique, named Belief Rough Set Classifier (BRSC), is based only on the basic concepts of the Rough Sets (RS). The second, called Belief Rough Set Classifier, is more sophisticated. It is based on Generalization Distribution Table (BRSC-GDT), which is a hybridization of the Generalization Distribution Table and the Rough Sets (GDT-RS). The two classifiers aim at simplifying the Uncertain Decision Table (UDT) in order to generate significant decision rules for classification process. Furthermore, to improve the time complexity of the construction procedure of the two classifiers, we apply a heuristic method of attribute selection based on rough sets. To evaluate the performance of each classification approach, we carry experiments on a number of standard real-world databases by artificially introducing uncertainty in the decision attribute values. In addition, we test our classifiers on a naturally uncertain web usage database. We compare our belief rough set classifiers with traditional classification methods only for the certain case. Besides, we compare the results relative to the uncertain case with those given by another similar classifier, called the Belief Decision Tree (BDT), which also deals with uncertain decision attribute values. 相似文献
37.
This paper deals with the problem of the global stabilization for a class of cascade nonlinear control systems. It is well
known that, in general, the global asymptotic stability of the cascaded subsystems does not imply the global asymptotic stability
of the composite closed-loop system. In this paper, we give additional sufficient conditions for the global stabilization
of a cascade nonlinear system. In particular, we consider a class of Takagi–Sugeno (TS) fuzzy cascaded systems. Using the
so-called parallel distributed compensation (PDC) controller, we prove that this class of systems can be globally asymptotically
stable. An illustrative example is given to show the applicability of the main result. 相似文献
38.
Brahmi Khaled Bouguerra Wided Hamrouni Béchir Elaloui Elimame Loungou Mouna Tlili Zied 《Arabian Journal of Chemistry》2019,12(8):1848-1859
This study investigates the effect of reactor design parameters on cadmium removal from industrial wastewater discharged by the Tunisian Chemical Group (TCG) to improve as much as possible efficiency and cost of electrocoagulation (EC) process. Based on an examination of the design parameters one by one, the best cadmium removal was achieved for an inter-electrode distance (die) of 0.5 cm, monopolar connection mode, stirring speed of 300 rev min?1, surface-area-to-volume ratio (S/V) of 13.6 m?1, and an initial temperature of 50 °C. These operating conditions are allowed to achieve efficient removal in a relatively short operating time with the lowest energy consumption and cost possible. The present study proved that the parameters that have an effect on the operating cost are the electrode configuration, inter-electrode distance and S/V ratio. The energy consumption, the pH evolution, and the treatment cost were studied. The investigation of the effect of all the selected optimum EC design parameters together on the removal of cadmium from the TCG wastewater proved that the treatment was highly efficient; 100% of cadmium removal was reached in 5 min, with a very low power consumption (1.6 kW h m?3) and very low cost (0.116 TND m?3). Moreover, EC was found to be capable of removing cadmium as well as other pollutants at the same time from the case-study industrial wastewater. The investigation carried out in this work explores and proposes a very cost-effective treatment method to remove heavy metals from industrial wastewater if compared to results reported about cost of this treatment process through other widely used technologies such as coagulation (4.36 Tunisian National Dinar (TND) m?3) and precipitation (9.96 TND m?3) employed in previous studies. 相似文献
39.
A. Loghman M. Hammami E. Loghman 《Journal of Applied Mechanics and Technical Physics》2017,58(3):443-453
The history of stresses and creep strains of a rotating composite cylinder made of an aluminum matrix reinforced by silicon carbide particles is investigated. The effect of uniformly distributed SiC micro- and nanoparticles on the initial thermo-elastic and time-dependent creep deformation is studied. The material creep behavior is described by Sherby’s constitutive model where the creep parameters are functions of temperature and the particle sizes vary from 50 nm to 45.9 μm. Loading is composed of a temperature field due to outward steady-state heat conduction and an inertia body force due to cylinder rotation. Based on the equilibrium equation and also stress-strain and strain-displacement relations, a constitutive second-order differential equation for displacements with variable and time-dependent coefficients is obtained. By solving this differential equation together with the Prandtl–Reuss relation and the material creep constitutive model, the history of stresses and creep strains is obtained. It is found that the minimum effective stresses are reached in a material reinforced by uniformly distributed SiC particles with the volume fraction of 20% and particle size of 50 nm. It is also found that the effective and tangential stresses increase with time at the inner surface of the composite cylinder; however, their variation at the outer surface is insignificant. 相似文献
40.