Multivariable fractional system approximation with initial conditions using integral state space representation

In this paper, we consider the approximation of general multivariable non commensurate fractional systems by integer order state space models. This work contains two main contributions. First, a new state space representation using the fractional integral operator is introduced. Second, the approximate model carries explicitly the initial conditions of the system. Two examples are given to illustrate the accuracy of the approximation.     

An integrated agro-ecosystem and livelihood systems approach for the poor and vulnerable in dry areas

More than 400 million people in the developing world depend on dryland agriculture for their livelihoods. Dryland agriculture involves a complex combination of productive components: staple crops, vegetables, livestock, trees and fish interacting principally with rangeland, cultivated areas and watercourses. Managing risk and enhancing productivity through diversification and sustainable intensification is critical to securing and improving rural livelihoods. The main biophysical constraints are natural resource limitations and degradation, particularly water scarcity and encroaching desertification. Social and economic limitations, such as poor access to markets and inputs, weak governance and lack of information about alternative production technologies also limit the options available to farmers. Past efforts to address these constraints by focusing on individual components have either not been successful or are now facing a declining rate of impact, indicating the need for new integrated approaches to research for development of dryland systems. This article outlines the characteristics of such an approach, integrating agro-ecosystem and livelihoods approaches and presents a range of empirical examples of its application in dryland contexts. The authors draw attention to new insights about the design of research required to accelerate impact by integrating across disciplines and scales.     

Synthesis and Characterization of Novel Surfactants: Combination Products of Fatty Acids,Hydroxycarboxylic Acids and Alcohols

The reaction of hydroxycarboxylic acids, such as citric, malic and tartaric species with an excess of fatty acid chlorides produces the corresponding O-acylated hydroxycarboxylic anhydrides in one step and in a near quantitative yield. These molecules are excellent electrophiles which react readily with a variety of nucleophiles including alcohols, diols and polyols. Their reaction with triethylene glycol and triethylene glycol monomethyl ether leads to two series of novel anionic surfactants, which are unsymmetrical gemini surfactants. The determination of their properties (CMC, foaming, HLB) revealed that these molecules are—depending on the chain length of the fatty acid—excellent emulsifiers, and that they also display interesting antimicrobial activity. These novel functional surfactants are of interest for applications in food and personal care products and for the formulation of pharmaceuticals.     

Sustainability of a wind power plant: Application to different Moroccan sites

In this paper, three main steps allowing the definition of the sustainability of a wind power plant (WPP) are described in detail. The first step is to choose a site with a good wind potential. In this respect, two approaches have been introduced: traditional wind statistical estimations based on the identification of the Weibull probability density function on specific sites; and an innovative Kriging approach based on artificial neural networks to reconstruct the profile of the mean wind speed of the territory. In the second step, given technical details, the energetic sustainability of a WPP installation is assessed according to a model computing the wind energy production per year, as well as the details of its efficiency. Finally, as third step, a cost/benefit evaluation on the overall reduction in CO₂ emissions with respect to traditional fossil fuel energy plants is reported. From a wind speed characterisation viewpoint, the case study is referred to the overall Moroccan territory. From a WPP model viewpoint, the case study is referred to the installation of a specific WPP, which would allow the production of more than 2 GWh per year in the south Atlantic coast and of nearly 1 GWh per year in the Mediterranean coast in the neighbourhood of Tangier.     

Electrochemical coupling reactions of benzyl halides on a powder cathode and cavity cell

Benzyl halides adsorbed on a cathode made of pure or silver-doped graphite powder were reduced in an undivided cell using an aqueous electrolyte and an inert anode, in the absence or presence of benzaldehyde. The product ratio is influenced by the applied potential, the leaving halide group and presence/absence of silver electrocatalyst. The highest yield of bibenzyl was obtained from the electrolysis of benzyl bromide on silver-doped graphite at a constant potential equal to −1.0 V vs Ag/AgCl (sat. KCl). Benzyl chloride is less prone to dimerization, but undergoes efficient carbonyl addition to benzaldehyde, especially in the presence of silver. The results can be interpreted as a competition of radical and anionic processes.     

Prediction and Measurement of Apparent Heat Transfer Coefficient by Condensation in Finned-Tube Heat Exchangers

The apparent heat transfer coefficient by condensation in finned-tube heat exchangers is determined experimentally and numerically in this paper. The film method is used to predict the partial or total condensation of the water vapor contained in the humid air over the smooth or finned tube-heat recuperators. Based on this method, a computer code is developed here. The mathematical formulation is validated by our experimental results, using tube bundles in staggered and aligned arrangements. The determination of the fin portion, which functions in wet regime, is carried out by the prediction of thermal field over a circular fin. The condensation of the water vapor contained in the humid air is done preferentially with the last rows of the heat exchanger. The heat flux is predicted in a range of 20% and 5% in wet and dry regimes, respectively. The apparent heat transfer coefficient by condensation can exceed 10 times the value of the air-side heat transfer coefficient in dry regime.     

Thermosolutal Convection During Melting in a Porous Medium Saturated with Aqueous Solution

The thermosolutal convection in a porous medium saturated with an aqueous solution near the temperature of the density maximum is studied. The fixed temperatures applied to vertical walls include the density maximum. The formulation of the problem is based on the Darcy-Brinkman model and the density variation is governed by a nonlinear approximation. The equations are solved by a finite-volume method. The numerical model is validated through experimental results. We show that the nonlinear variation of the density influences strongly the flow structure and the heat transfer. The structures of this flow show that the density maximum generates a complex flow structure of two contrarotating cells of unequal importance.     

Catalytic Partial Oxidation of Methanol and Methyl Mercaptan: Studies on the Selectivity of TiO2 and CeO2 Supported V2O5 Catalysts

Catalyst samples based on vanadium, cerium and titanium oxides were prepared using sol–gel method and wet impregnation. Several analytical techniques were used to characterize catalysts. The best activity and selectivity in the partial oxidation of methanol and methyl mercaptan were observed for the catalyst sample with the composition of 3 % V₂O₅/Ti_0.1–Ce_0.9O₂.     

Tool wear mechanisms of PcBN in machining Inconel 718: Analysis across multiple length scale

Recently, PcBN tooling have been successfully introduced in machining Ni-based superalloys, yet our knowledge of involved wear mechanisms remains limited. In this study, an in-depth investigation of PcBN tool degradation and related wear mechanisms when machining Inconel 718 was performed. Diffusional dissolution of cBN is an active wear mechanism. At high cutting speed oxidation of cBN becomes equally important. Apart from degradation, tool protection phenomena were also discovered. Oxidation of Inconel 718 resulted in formation of γ-Al₂O₃ and (Al,Cr,Ti)₃O₄ spinel that were deposited on the tool rake. Also on the rake, formation of (Ti,Nb,Cr)N takes place due to cBN-workpiece interaction. This creates a sandwich tool protection layer forming continuously as tool wear progresses. Such in operando protection enabled counterbalancing tool wear mechanisms and achieved high performance of PcBN in machining.     

Specific signatures of α-alumina powders prepared by calcination of boehmite or gibbsite

The specific signatures of α-Al₂O₃ powders by a combination of X-ray diffraction (Rietveld analysis), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, thermal analysis (TG-DTA) and cathodoluminescence (CL) were investigated. Thus, α-alumina was prepared by calcination of boehmite or gibbsite at 1573 K for 24 h. The size of α-alumina crystallites obtained using boehmite precursor was smaller than that obtained using gibbsite precursor. The difference in oxygen vacancies (F⁺-centers) amount between α-Al₂O₃ powder obtained by calcination of gibbsite and boehmite was confirmed by CL spectra. Furthermore, the Ti³⁺ emission at 1.71 eV is absent in α-Al₂O₃ powder obtained by calcination of gibbsite. CL has been demonstrated as a possible method for differentiation between the various α-alumina powders.