Partition of proteins in the aqueous guar/dextran two-phase system

The partition of proteins (bovine serum albumin, β-lactoglobulin, micellar casein) has been examined in the guar/dextran aqueous two-phase system. The influence of parameters like pH, ionic strength (NaCl), and polymer concentration has been investigated while the protein concentration was increased up to 2% w/w. For globular proteins (bovine serum albumin, β-lactoglobulin) the general trends of partitioning established in the literature with other systems like polyethyleneoxide/dextran were nearly verified. The dextran-rich bottom phase was found to be slightly more concentrated in protein than the guar-enriched top one. However, micellar casein displayed a different behavior, giving a more uneven partition and phase separation phenomena at concentrations above 0.5% w/w. This difference has been attributed to the larger size of the particle. Meanwhile, the modifications of the guar/dextran phase diagram have been investigated. It was shown that the addition of globular protein or micellar casein up to 2% w/w did not affect the thermodynamic features of this system.     

Large-eddy simulation of a turbulent jet and wake vortex interaction

In this study, temporal large-eddy simulations of the interaction between a turbulent jet flow and a trailing vortex are described. Three cases are analyzed: in the first one, the jet and the vortex axes are sufficiently well separated to not interact immediately, while in the second case, the distance between the jet and the vortex is reduced by half. In the last case the jet blows in the vortex core. In the two first cases, as the jet spreads it is progressively deflected by the continuous input of crossflow momentum. Thus it acquires azimuthal and radial components of velocity, causing the emergence of three-dimensional structures of azimuthal vorticity around it. When the jet and the vortex are superimposed, the turbulent kinetic energy does not increase, the vortex core is very buffeted. Numerical simulation results of the convection-diffusion of a passive scalar show that its distribution (initially in the jet) cannot penetrate inside the vortex core due to its solid rotation. For the cases where the jet is initially outside the vortex and when it is injected in the vortex wake, its value remains very high and cannot get out of the vortex core. This phenomenon confirms the existence of a stabilizing “dispersion buffer”, adjacent to the core, which prevents amplification of the turbulence generated inside the core.     

Coin-operated dry cleaning machines may be responsible for acute tetrachloroethylene poisoning: report of 26 cases including one death

It appears from the evidence documented in this Commentary that the neonatal period is another critical stage in the process of sexual, behavioural and immune system development and maturation in primates. Interference with normal brain-pituitary-gonadal function during this period (e.g. with a GnRH analogue in monkeys) appears to impact adversely on subsequent reproductive, immunological and behavioural function. These data further emphasize the importance of fully understanding the regulatory mechanisms that govern neonatal gonadal function in the primate, if we are to eliminate, control or minimize the potential risk resulting from its disruption in humans. Given the recent evidence that the reproductive potential of the human male has declined rather dramatically over the last 50 years, and that clinical conditions associated with abnormal testicular function are on the rise, continued investigation in this area would appear to be imperative.     

Deciphering the biology of Mycobacterium tuberculosis from the complete genome sequence

Countless millions of people have died from tuberculosis, a chronic infectious disease caused by the tubercle bacillus. The complete genome sequence of the best-characterized strain of Mycobacterium tuberculosis, H37Rv, has been determined and analysed in order to improve our understanding of the biology of this slow-growing pathogen and to help the conception of new prophylactic and therapeutic interventions. The genome comprises 4,411,529 base pairs, contains around 4,000 genes, and has a very high guanine + cytosine content that is reflected in the biased amino-acid content of the proteins. M. tuberculosis differs radically from other bacteria in that a very large portion of its coding capacity is devoted to the production of enzymes involved in lipogenesis and lipolysis, and to two new families of glycine-rich proteins with a repetitive structure that may represent a source of antigenic variation.     

Analyse ultrasonore du temps de prise de bétons compactés au rouleau

Résumé Dans les structures multicouches construites en Bétons Compactés Roulés (BCR), la détermination du Temps de Prise (TP) permet d'assurer la qualité des liaisons mécaniques et donc physiques à l'interface. Afin de pouvoir définir et suivre en temps réel un paramètre significatif, nous utilisons la propagation des ondes ultrasonores à travers une éprouvette de BCR et nous considérons le béton comme un filtre fréquentiel et énergétique évolutif. Le traitement du signal ultrasonore transmis nous permet, par une décomposition fréquentielle, de déterminer le maximum d'amplitude du signal sur une bande passante limitée. Ce paramètre est représentatif des évolutions de la microstructure du béton. Au moyen d'essais mécaniques et d'observations au microscope électronique à balayage, nous vérifions que le Temps de Prise correspond à une transformation microstructurale liée à la formation massive d'hydrates du type CSH. Cette définition, issue de l'évolution du maximum d'amplitude du signal ultrasonore transmis, nous permet de situer temporellement le TP. Des essais réalisés sur des éprouvettes identiques permettent d'étudier la répétabilité et la sensibilité de la méthode.

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Within multi-layered structures built with rolledcompacted concrete (RCC), the determination of the setting time (ST) helps insure the quality of both the mechanical and physical linkages located at the interface. In order to define and follow-up in real time the evolution of a significant parameter, we use herein the propagation of ultrasonic waves passing through an RCC test specimen, and we consider the concrete as a frequency and energy evolutive filter. Processing the ultrasonic wave transmitted enables us, by means of a speed and frequency spectrum, to ascertain the maximum amplitude of the wave on a limited bandwidth. This parameter is representative of the concrete's microstructural evolutions. Through mechanical testing and scanning electron microscope observations, we have been able to verify that the setting time corresponds to the microstructural transformation linked to the massive formation of CSH-type hydrates. This definition, resulting from the evolution of the maximum amplitude of the ultrasonic wave being transmitted, allows us to position the ST as a function of time. Tests carried out on identical samples have enabled assessing the potential reuse and the sensitivity of the method employed.

     

Rheology and microstructure of κ-carrageenan under different conformations induced by several concentrations of potassium ion

Rheology, micro-DSC and confocal microscopy were used to study the effect of potassium ion on the viscoelastic behavior, disorder–order transition and microstructure, respectively, of κ-carrageenan in solution under different conformations at 60, 25 and 9 °C. At 60 and 25 °C the rheological behavior of 0.5% κ-carrageenan with 0–80 mmol/dm³ and 0–5 mmol/dm³ KCl, respectively, was typical of viscoelastic solutions of random coiled polymers. At 9 °C and below a critical ionic concentration of about 7.0 mmol/dm³, κ-carrageenan adopted an ordered conformation in which helical structures did not aggregate and hence did not form self-supporting gels. Changes in polysaccharide stiffness were estimated from intrinsic viscosity variations as a function of ionic content. In the ordered state, the stiffness was higher than in the disordered state, whereas a liquid-like viscoelastic behavior was still exhibited. In 0.5% κ-carrageenan at 25 °C, increasing KCl from 0 to 300 mmol/dm³ produced gels of increasing rigidity. However, above 100 mmol/dm³ such increase was marginal. Confocal images evidenced a three-dimensional network whose continuity depends on polysaccharide and salt concentrations. These observations are consistent with the rheological behavior of the self-supporting gels obtained with κ-carrageenan concentrations in the range of 0.05–1%.     

Physicochemical Properties of Dietary Fibres Prepared from Ambarella (Spondias cytherea) and Mango (Mangifera indica) Peels

The preparation of fibres from mango and ambarella peels can offer a way to upgrade by-products. Comparatively to lime, ambarella and mango fibres were prepared from their corresponding peels using ethanolic treatment (85% at 70 °C/5 min). The peels were characterised for their dry matter content, pH and apparent viscosity. The soluble dietary fibre (SDF) and insoluble dietary fibre (IDF) contents of the samples were determined. Hydration capacity of these fibres was evaluated. Results showed that the ethanolic treatment of the peels (85% at 70 °C/5 min) had significant (p?<?0.05) effects on the contents of neutral sugars and uronic acid (from 105 to even 203 mg/g in case of mango fibre). For ambarella fibres, the proportion of IDF (51%) was highest and that of SDF (34%) was lowest. Mango and lime fibres exhibited similar values of IDF (40–43%) and SDF (50–57%). Mango peel fibres had higher hydration capacities than ambarella and lime fibres. The best dietary fibres content and the high hydration capacities of mango peel fibres favour their exploitation in dietary fibre-rich foods preparation.     

Rheological behaviour of low-methoxyl pectin gels over an extended frequency window

The rheological behaviour of biopolymer gels is commonly investigated by means of small amplitude oscillatory measurements. This consolidated approach was used in the present paper to characterize the influence of ionic strength and temperature on the gelation of commercial low-methoxyl pectin (LMP) (DE = 22.5%). The main results showed that the sol/gel transition is very sensitive to the ionic strength of the medium, while the viscoelastic properties of the gel structure, developed over 8 h cure test, were retained up to 60 °C. The soft material under study displays the typical rheological behaviour of a solid-like material, in good agreement with results previously reported in the literature. It is known that the best time or frequency window useful to explore in dynamic mode the viscolelastic behaviour of complex materials such as a gel would range over several decades of frequency. The possibility to extend the frequency domain of the dynamic tests in the region of the lower frequencies (10⁻⁵–10² rad s⁻¹) was therefore investigated by matching information coming from dynamic and transient rheological tests and converting data from time domain into frequency domain throughout the discrete retardation spectrum of the material, as described by Kaschta [Kaschta, J., & Schwarzl, F. R. (1994). Calculation of discrete retardation spectra from creep data - I. Method. Rheologica Acta, 33, 517-529.].