RDFI determination of anisotropic and scattering dependent radiative conductivity tensors in porous media: Application to rod bundles

A radiative conductivity model is developed for porous media with a solid opaque phase and a transparent fluid phase. In a first step, an effective semi transparent medium occupying the volume of the real fluid phase is characterized, assuming the validity of the Beer’s laws. For example, rod bundles in squared or triangular configurations can be directly characterized by effective strongly anisotropic extinction, absorption and scattering coefficients, optical index and phase function, which depends on both the incident and scattering unit vectors, by generalizing the Radiative Distribution Function Identification method of Tancrez and Taine [M. Tancrez, J. Taine, Direct identification of absorption and scattering coefficients and phase function of a porous medium by a Monte Carlo technique, Int. J. Heat Mass Transfer 47 (2004) 373–383]. The validity and accuracy of the associated Beer’s laws are discussed in this case. In a second step, at the limit of an optically thick porous medium, an original model based on a perturbation method of the Radiative Transfer Equation directly leads to the determination, under an accurate validity criterion, of a radiative conductivity tensor for the fluid phase. Examples of results are given in the case of rod bundles versus porosity, specific area and local wall absorptivity.     

Donor‐Stabilized Phosphenium Adducts as New Efficient and Immobilizing Ligands in Palladium‐Catalyzed Alkynylation and Platinum‐Catalyzed Hydrogenation in Ionic Liquids

The straightforward synthesis of a new donor‐stabilized phosphenium ligand 3d by addition of bromodifurylphosphine to 1,3‐dimethylimidazolium‐2‐carboxylate 1 is described. The obtained ligand exhibits a very strong π‐acceptor character, comparable to that of triphenyl phosphite [P(OPh)₃] or of tris‐halogenophosphines, with a ν_CO(A₁) at 2087 cm⁻¹ for its nickel tricarbonyl complex. This ligand, as well as the related 3a which was obtained from chlorodiphenylphosphine, were tested in palladium‐catalyzed aryl alkynylation and in the platinum‐catalyzed selective hydrogenation of chloronitrobenzenes, both in an ionic liquid phase. In C C bond cross‐coupling we observed that the increase of the π‐acceptor character in ligand 3d , due to the introduction of an additional electron‐withdrawing group, provides a very efficient catalyst in the alkynylation reaction of aryl bromides with phenylacetylene, including the deactivated 4‐bromoanisole or the sterically hindered 2‐bromonaphthalene. The catalytic activity decreases with recycling due to the sensitiveness of ligands to protonation in the ionic phase. Conversely, a multiple recycling of the metal/ligand system in non‐acidic media was achieved from platinum‐catalyzed hydrogenation of m‐chloronitrobenzene. The catalytic results obtained by employing the complex of platinum(II) chloride with 3a [trans‐PtCl₂( 3a )₂] in comparison with the non‐ionic related trans‐tris(triphenylphosphine)platinum dichloride [trans‐PtCl₂(PPh₃)₂] complex clearly indicate that the simultaneous existence of a strong π‐acceptor character and a positive charge within the ligand 3a significantly increases the life‐time of the platinum catalyst. The selectivity of the reaction is also improved by decreasing the undesirable formation of dehalogenation products. This cationic platinum complex trans‐PtCl₂( 3a )₂ is the first example of a highly selective catalyst for hydrogenation of chloronitroarenes immobilized in an ionic liquid phase. The system was recycled six times without noticeable metal leaching in the organic phase, and no loss of activity.     

A non-Newtonian model based on Ree-Eyring theory and surface effect to predict friction in elastohydrodynamic lubrication

The traction behaviour of various lubricants is investigated in elastohydrodynamic regime using a tribometre that simultaneously allows the contact visualization and the friction measurement under controlled contact kinematics. First, the film formation capability is determined: although the base oil and the polymer, via their viscosity, govern the film thickness in EHL regime, the additives control the existence of a boundary film at low entrainment speed. Second, the relative role of the additives and of the base oil on the frictional behaviour is studied for various experimental conditions: this clearly demonstrates that the piezo-viscous response of the lubricant controls the Newtonian/non-Newtonian transition and the friction level. The role of thermal effects is discussed. A strong influence of the entrainment speed, over the frictional response is unexpectedly observed, even in full film regime. A rheological model based on Ree-Eyring theory supposing a heterogeneous flow due to adsorbed surface layers, is proposed to discuss the organization of the molecules within the contact and its effect on the frictional response of the contact.     

Recent advances toward high voltage,EC-free electrolytes for graphite-based Li-ion battery

Lithium-ion batteries are a key technology in today’s world and improving their performances requires, in many cases, the use of cathodes operating above the anodic stability of state-of-the-art electrolytes based on ethylene carbonate (EC) mixtures. EC, however, is a crucial component of electrolytes, due to its excellent ability to allow graphite anode operation–also required for high energy density batteries–by stabilizing the electrode/electrolyte interface. In the last years, many alternative electrolytes, aiming at allowing high voltage battery operation, have been proposed. However, often, graphite electrode operation is not well demonstrated in these electrolytes. Thus, we review here the high voltage, EC-free alternative electrolytes, focusing on those allowing the steady operation of graphite anodes. This review covers electrolyte compositions, with the widespread use of additives, the change in main lithium salt, the effect of anion (or Li salt) concentration, but also reports on graphite protection strategies, by coatings or artificial solid electrolyte interphase (SEI) or by use of water-soluble binder for electrode processing as these can also enable the use of graphite in electrolytes with suboptimal intrinsic SEI formation ability.     

Residual stresses in thin polymer films cause rupture and dominate early stages of dewetting

In attempting to reduce the size of functional devices, the thickness of polymer films has reached values even smaller than the diameter of the unperturbed molecule. However, despite enormous efforts for more than a decade, our understanding of the origin of some puzzling properties of such thin films is still not satisfactory and several peculiar observations remain mysterious. For example, under certain conditions, such films show negative expansion coefficients or show undesirable rupture although energetically they are expected to be stable. Here, we demonstrate that many of these extraordinary effects can be related to residual stresses within the film, resulting from the preparation of these films from solution by fast evaporation of the solvent. Consequently, depending on thermal history and ageing time, such films show significant changes even in the glassy state, which we quantify by dewetting experiments and corresponding theoretical studies. Identifying the relevance of frozen-in polymer conformations gives us a handle for manipulating and controlling properties of nanometric thin polymer films.     

Isolation, molecular characterization and antimicrobial resistance patterns of Salmonella and Escherichia coli isolates from meat-based fast food in Lebanon

The aim of this study was to characterize at the molecular level the different stains of Salmonella spp. and Escherichia coli that were isolated from meat-based fast food in Lebanon. In addition, this study evaluated the resistance of those strains to different antimicrobials that are commonly used. The foods included were Lahm-bi-Ajeen (LBA, meat pies) and Shawarma (Lebanese meat sandwiches similar to Gyros and Donairs, containing meat, vegetables, and sesame seeds-oil-based sauce). Polymerase chain reaction (PCR) was used to characterize and identify the strains of both bacteria. Salmonella species characterization was performed using rfb genes cluster genetic marker, while that of E. coli strains were carried out based on stx1, stx2, eaeA, fliC, and ehlyA virulence markers. The characterized strains were then tested for their response to various antimicrobials. The results showed that the tested foods were contaminated with Salmonella paratyphi (serogroup A) and Shiga Toxin (Stx)-producing E. coli (STX-EC). The PCR showed that 75% of E. coli tested strains was positive in PCR performed with stx1 primers, one of which was eaeA positive. Two of the tested strains were positive using PCR with fliC primers. The resistances of the various strains were evaluated using the following antimicrobials: Oxacillin, Teicoplanin, Trimethoprim/sulfamethoxazole, Gentamicin, Clindamycin, Cefotaxime, Cefuroxime, Erythromycin, and Vancomycin. Bacteria were highly resistant to one or more of the tested antimicrobials. Approximately 69% of E. coli and 77.8% of Salmonella spp. exhibited resistance. Salmonella spp. were shown to be 100% resistant to four antimicrobials: Oxacillin, Teicoplanin, Clindamycin, Vancomycin, and Erythromycin, while E. coli was 100% resistant to Teicoplanin and Trimethoprim/sulfamethoxazole. The most interesting findings were the high susceptibility of the E. coli to Gentamicin (100%). Highest resistance in the case of Salmonella spp. was seen against Cefotaxime (74%). Those two antimicrobials are commonly used for the treatment of enteric infections caused by gram-negative bacteria. The results showed that meat-based fast foods in Lebanon could be a public health hazard, especially Shawarma, as they may act as a potential vehicle for many antimicrobial-resistant pathogenic organisms. Improper hygienic standards and indiscriminate use of antimicrobials are two of the main causes for the prevalence of these pathogenic resistance strains in Lebanon. These results will emphasize the need to implement protective measures and more emphasis will be placed on the application of hygienic practices to reduce the levels of food contamination.     

Discovering relationship types between users using profiles and shared photos in a social network

In this paper, we propose a new approach to discover the relationship types between a user and her contacts in a social network. This is of key importance for many applications in the domain of photo sharing, privacy protection, information enriching, etc. Our approach is based, on one hand, on information extracted from users’ profiles and their shared photos, and, on the other hand, on a set of predefined rules validated by the main user before being mined and derived according to her preferences and social network content. The contribution of our method is twofold: 1) it is user-based enabling the user to set her preferences and give her feedbacks on the derived rules and results, and 2) it is multi-criteria that exploits and combines several attributes and features from user profiles and shared photos respectively. It also allows the user to define new relationship types. We conducted a set of experiments to validate our approach. The obtained results show the accuracy of our approach in different scenarios.