Multifluid numerical approximations based on a multipressure formulation

In the present work, we consider the numerical approximations of multifluid compressible flows. We suppose that the flow is composed by nonmixing compressible fluids. We propose a dissipative model insuring, for the mixture, the conservation of the mass, the momentum and the total energy. Entropy balances between phases are described by additional nonconservative equations. At the limit of vanishing viscosity the model is still consistent with the entropy balances. The nonlinear projection scheme is used to preserve, at the discrete level, the main properties of the model. Numerical experiments are conducted to validate the proposed models for the multicomponent shock tube, the bubble-shock interaction and the tank filling problems.     

The microbiology of mixed salad containing raw and cooked ingredients without dressing

Growth of aerobic mesophilic bacteria in mixed salad without dressing, containing cooked sweet corn and raw endive, was similar to that of raw endive alone. At 9°C, sweet corn permitted the growth of the lactic acid bacterium Leuconostoc mesenteroides , whenever the bacterium was present on raw endive, whereas no growth of lactic acid bacteria was recorded on raw endive alone. Listeria monocytogenes , artificially inoculated in the samples, grew more in the mixed salad than in the raw endive alone, for products stored at 6°C and 9°C. Acidification of sweet corn to pH 5.0 was proposed to reduce the development of L. monocytogenes in the mixed salad to a level similar to that recorded in the raw endive alone. Acidification with citric acid reduced spoilage of sweet corn, whereas acetic acid caused necrosis on the leaves of raw endive.     

Mécanisme de l’évolution des champs électromagnétiques dans un simulateur de grandes dimensions. Projet d’un simulateur semi-rhombique

The purpose of this paper is to evaluate theoretically and experimentally the transient electric field in anemp simulator. Using a time domain analysis, the mechanism of the field deformation can be analysed and consequently modifications can be introduced in the conception of new simulators (for example: rhombic simulator).     

Physicochemical Properties of Palm Oil-Based Puff Pastry Model Margarines Related to Their Baking Performance in Long-Term Storage

Developing trans-free alternative fat solutions suitable for specific applications remains a challenge in edible fats and other domains. This is particularly true for palm oil-based puff pastry margarines, which suffer from post crystallization problems, leading to dramatic loss of functionality. This research is aimed at investigating the influence of triacylglycerol (TAG) compositions of palm oil-based puff pastry margarines on the physical properties of the fat crystal network, which determine the functionality of such products. Three model puff pastry margarines are produced at pilot scale under the same crystallization conditions. They share the same fatty acid composition and close solid fat content (SFC) profiles, whereas the proportions of major TAG (tripalmitoylglycerol (PPP), 1,3-di-palmitoyl-2-oleoylglycerol (POP), 1,2-di-palmitoyl-3-oleoylglycerol (PPO), 1,2-dioleoyl-3-palmitoylglycerol (POO)) are different. Polymorphism, melting profile, hardness, microscopic structures, and baking performance (puffing effect) of the model fats are examined during a period of 6 months. The following results are obtained: 1) The TAG composition significantly influences the post crystallization processes occurring in palm oil-based margarines. 2) High amounts of POP show negative influences. 3) The proportions of POP, PPO, and PPP should be carefully balanced to prevent detrimental crystal network rearrangements, leading to textural modifications (hardness increase) and significant reduction in baking performance. Practical Applications : The results presented in this work could be helpful for edible fat products developers, especially for roll-in fat applications. This research provides an overview of the relevant properties to study for the assessment of puff pastry margarine functionality. It also highlights the importance of ensuring long-term stability of palm oil-based fat products. Finally, it emphasizes that certain combinations of fat materials should be avoided to maintain the quality of palm oil-based puff pastry margarines.     

Deformation,yield and fracture of polymers at high pressure

The effects of hydrostatic pressure on the shear, compressive, and tensile stress-strain behavior of both amorphous and crystalline polymers are reviewed and illustrated. For polymers with T_g near to but below ambient temperature, there is a steep increase of modulus with pressure and, above some critical pressure, there is a lower rate of increase. The critical pressure is a linear function of the test temperature and, from its slope, one can deduce the pressure coefficient of T_g. For many other polymers, there is a linear increase, over a wide pressure range, of elastic and shear moduli with pressure, and this is in accord, to a first approximation, with predictions of finite strain theory. Most all polymers investigated show a strong pressure coefficient of yield stress and in many cases this variation is linear over a wide pressure range, in accord with several pressure dependent yield criteria. To a considerable extent, the yield stress rise with pressure parallels that of the modulus, and this behavior is predicted by some yield theories. The effects of pressure on fracture stress and fracture strain are discussed. The results obtained depend on the polymer composition and structure and on the pressure medium. Consideration is also given to the effects of pressure on crazing and stress-whitening.     

Influence of molecular weight on fatigue behavior of polyethylene and polystyrene

Fatigue tests in reversed tension-compression have been carried out on samples of polyethylene and polystyrene of widely varying molecular weights, extending up to 2, 000, 000. All tests on polystyrene specimens were made at 1600 rpm. For polyethylene, tests speeds had to be reduced to 100 rpm in order to avoid serious temperature effects. For both materials, increasing molecular weight leads to improved resistance to alternating loading. For polystyrene, this improvement in ultimate properties even continued well beyond molecular weight values where T_g, becomes effectively independent of molecular weight. For polyethylene, samples of high molecular weight did not fail even after 10⁷ cycles of alternating loading at a stress level of 3000 psi.     

Structures and morphologies of cast and plastically strained polyamide 6 films as evidenced by confocal Raman microspectroscopy and atomic force microscopy

Both confocal Raman microspectroscopy and atomic force microscopy (AFM) have been undertaken to study the crystalline and the morphological aspects of cast PA 6 films at a sub-microscopic scale. The percentages of the different crystalline structures present within PA 6 cast films, i.e. the monoclinic α, the pseudo-hexagonal β, and the monoclinic γ, have been measured by confocal Raman microspectroscopy. In cast films, the prevailing structure is the β one. AFM has been used to characterize the morphology of the PA 6 films. Simultaneously, the deformed state has been considered as well. Our main interest has been to follow the evolution of the percentage of each crystalline structure as a function of the plastic deformation mechanisms which are responsible of the yielding of PA 6 films: shear banding for temperatures T lower than 160 °C and formation of fibrils for      

Frictional wear in high temperature thermotropic liquid crystalline polymers: correlation with glass transitions

Wholly aromatic thermotropic main chain liquid crystalline copolymers (LCPs) with varying glass transitions (T_g) were tested for wear resistance, particularly under high friction conditions, where surface temperatures can rise. Dynamic mechanical spectroscopy and DSC were used to characterize molecular relaxations. Three copolyester LCPs which all contain a substantial fraction of main chain 1,4-phenyl groups were chosen for this study. These included semi-crystalline Vectra^® A900, a semi-crystalline LCP containing phenyl hydroquinone (phHQ-LCP), and a low crystallinity LCP containing t-butyl substituted hydroquinone (t-butylLCP). These have glass transitions of 100, 160 and 175 °C, respectively, and heat deflection temperatures (HDTs) of 170, 260 and 174 °C, respectively. HDT is dependent in part on crystallinity. The wear performance was found to depend mainly on T_g and not HDT, suggesting a microscopic failure mechanism related to the amorphous phase. This is supported by the relatively poor elevated temperature wear performance of Vectra^® compared to the higher T_g LCPs. Shear strength measurements on the neat LCP resins did not correlate with wear properties of the blends, most likely because the measurements were made at room temperature and not elevated temperatures.     

The effect of water on the tensile yield of polystyrene

When PS is tested in tension but immersed in water the yield stress is unchanged and the crazing stress is increased, as compared with tests conducted in air. The crazing pattern is otherwise unchanged. If the PS is first equilibrated with water and then tested under water, both crazing stress and yield stress are reduced. A very large number of small crazes are generated which result in a 23% increase in the fracture strain.