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排序方式: 共有128条查询结果,搜索用时 15 毫秒
1.
Rheological behaviour of polysaccharide aqueous solutions 总被引:1,自引:0,他引:1
Several data relative to the viscosity of water-soluble polysaccharide solutions were collected from the literature and processed by different rheological models. Some relationships between the viscosity of these polymer solutions, their molecular weight and their solution concentrations, were established and their validity checked. Thus, an accurate equation correlating the viscosity and both the shear rate and the solution concentration of different water soluble polysaccharides (xanthan, hyaluronan, carboxymethylcellulose) was deduced on the basis of Cross' model which suggests two domains in which the viscosity is constant, i.e. very low and very high shear rate ranges. Then, an expression relating the zero-shear viscosity (A) and the concentration of their solutions was proposed. Finally, an alternative equation to that of Mark–Houwink correlating the molecular weight and the intrinsic viscosity of the water-soluble polysaccharides studied in this paper was found. 相似文献
2.
3.
Margarita Evtiouguina Alessandro Gandini Carlos Pascoal Neto Naceur M Belgacem 《Polymer International》2001,50(10):1150-1155
The reaction of various polyols derived from the oxypropylation of cork with aliphatic and aromatic mono‐ and diisocyanates was studied in solution at room temperature. In all instances, good second‐order kinetics were observed and the corresponding rate constant determined. The reactivity of the aromatic isocyanate was found to be much higher than that of aliphatic counterparts. The ensuing urethanes and polyurethanes were characterised by FTIR and 1H NMR spectroscopy, DSC and sol/gel distribution. © 2001 Society of Chemical Industry 相似文献
4.
Ayman Ben Mabrouk Hamid Kaddami Albert Magnin Mohamed Naceur Belgacem Alain Dufresne Sami Boufi 《Polymer Engineering and Science》2011,51(1):62-70
A one‐step method was used to prepare stable aqueous nanocomposite dispersions based on cellulose whiskers extracted from the rachis of the date palm tree and a poly(styrene‐co‐2‐ethyl hexylacrylate) copolymer via miniemulsion polymerization. A reactive silane, i.e., methacryloxypropyl triethoxysilane was added to stabilize the dispersion and favor the anchoring of the whiskers on polymer particles. Dynamic light scattering was used to study the effect of the silane and whiskers contents on the average particle size of the polymer. Nanocomposites materials were prepared from these dispersions using a casting/evaporation method. The effect of the silane and whiskers contents on the thermal and mechanical properties were studied using differential scanning calorimetry and dynamic mechanical analysis. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers 相似文献
5.
Moncer A. Hariga M. Naceur Azaiez Mohamed Ben Daya 《International Transactions in Operational Research》2006,13(4):353-364
In this paper, we address the problem of determining optimum inspection schedules for a single deteriorating production system with a predetermined replacement cycle. It is assumed that, at different discrete points in time over the fixed planning horizon, the facility is inspected to detect its operating state and then it goes over an imperfect preventive maintenance routine to enhance its operating performance. Moreover, the facility undergoes minimal repair once detected in an “out‐of‐control” state. We also adopt the concept of discounted cash flow analysis to account properly for the effect of time value of money on the inspection policies. Under these settings, we formulate the discounted integrated inspection‐maintenance problem as a dynamic programming model with general time to failure distribution. After illustrating the model with a numerical example, we perform sensitivity analysis to investigate the effects of some input parameters on the expected present worth and the number of inspections. 相似文献
6.
Reduction in greenhouse effect gases emission is a major source of concern nowadays. Internal combustion engines, as the most widely used power generation mean for transportation, represent a large share of such gases, which motivates active research efforts for alternative solutions. In this regard, PEM fuel cells represent a promising prospect and are thoroughly investigated, whether experimentally or through numerical simulation. The present work presents a simulation of the power potential of a PEM fuel cell, which is integrated to the full power electric traction chain of a medium size car. The cell potential is modelled by taking into account the different types of polarization. The driving performances of the vehicle and its hydrogen consumption are evaluated through a simple mathematical model and an application is performed for the New European Driving Cycle (NEDC) standard driving cycle. A preliminary sizing of the proton exchange membrane fuel cell (PEMFC) membrane area for the chosen vehicle is presented, along with that of a hydrogen storage tank for a typical autonomy. The main goal of the simulation is to estimate CO2 indirect emissions due to the production of the needed hydrogen for the cycle via an electrolyser, compared with the case of a gasoline fueled vehicle. This is performed solely on a ‘fuel tank to wheel’ basis in order to have comparable figures. The results indicate that the environmental advantage of hydrogen cars is quite questionable if hydrogen is produced using carbon‐based energy sources. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
7.
Wiem Jebri Jemai Houssem Jerbi Mohamed Naceur Abdelkrim 《International Journal of Control, Automation and Systems》2011,9(3):566-573
The objective of this paper is to simplify the complexity of practical implementation of the input-state feedback linearization
technique for the control of input-affine systems. A polynomial approach which makes use of the Taylor series expansion and
the Kronecker product is developed. Our work aims to address the problem of synthesizing a polynomial control via a nonlinear
analytical coordinates transformation. To check the effectiveness of the investigated approach, we consider the control problem
of a series DC motor. A comparative study with the input-state feedback linearization control is developed. 相似文献
8.
Paola Fabbri Graldine Champon Maila Castellano Mohamed Naceur Belgacem Alessandro Gandini 《Polymer International》2004,53(1):7-11
Various lignocellulosic substrates, including microcrystalline cellulose, pinewood and hemp fibres, were treated with triethylaluminium and triethylboron in suspensions, in non‐swelling media. Chemical and spectroscopic analyses show that coupling surface reactions took place between one or two metal‐to‐carbon (Mt–C) bonds and the OH groups of the natural polymers. The remaining unreacted Mt–C bonds were exploited to graft numerous molecular structures derived from alcohols and amines. The occurrence of the second reaction was proved by Fourier‐transform infrared spectroscopy, elemental analyses, X‐ray photoelectron spectroscopy and contact angle measurements. Copyright © 2004 Society of Chemical Industry 相似文献
9.
In this review, an overview is given on the last development of catalytic methods for the preparation of substituted furans from carbohydrates and ensuing polymers. The review starts with the recent aspects in the synthesis of some key furan monomers in the presence of solid catalysts. In the second part, selected examples are given of polymerization systems leading to furan-based materials with promising properties, thus constituting a serious alternative to petroleum-based counterparts. Finally, a short examination is given on what could be the future of furan chemistry with the recent development of ionic liquids as solvents. 相似文献
10.
Naceur Etteyeb Leila Dhouibi Mercedes Sanchez Cruz Alonso Carmen Andrade Ezzeddine Triki 《Journal of Materials Science》2007,42(13):4721-4730
The aim of this study is to investigate the viability of use of sodium phosphate (Na3PO4: SP), tetrasodium pyrophosphate (Na4P2O7: TSPP) and hydroxyethylidene-diphosphonic acid (C2H8O7P2: HEDP) as a non-toxic corrosion inhibitors of steel bars in alkaline media which simulate the electrolyte in the concrete
pores. The effectiveness of these phosphate compounds as corrosion inhibitors was investigated by measuring the corrosion
potentials, the polarization curves, the corrosion current densities, and the electrochemical impedance spectroscopy of steel
bars immersed for 30 days in saturated Ca(OH)2 solutions with and without chlorides. At the completion of the tests, the mass losses were determined in order to verify
the reliability of the electrochemical results. The results showed that phosphate compounds form a protective layer on the
steel surface when immersed in alkaline solution without chlorides. In the presence of chloride ions, the SP acts as an anodic
inhibitor and reduces the corrosion activity on steel. The HEDP shows lower efficiency, probably due to the decrease of the
pH and to the high [Cl−]/[inh] ratio used. Results obtained by electrochemical and gravimetric methods are in quite reasonable agreement. 相似文献