Study of cryostructuration of polymer systems. XIV. Poly(vinyl alcohol) cryogels: Apparent yield of the freeze–thaw‐induced gelation of concentrated aqueous solutions of the polymer

Poly(vinyl alcohol) (PVA) cryogels, which are formed as a result of freeze–thaw treatment of concentrated solutions of the polymer, were studied in respect to the amount of gel and sol fractions in these heterogeneous macroporous gel materials depending on the conditions of the thawing step of similar cryotropic gelation. It was shown that the yield of gel fraction (the efficiency of the gelation process) was not quantitative; this was controlled by the initial PVA concentration in the solution to be frozen, and to a higher extent, by the thawing rate, when the yield increased with slowing of the defrostation process. The sol fraction could be extracted from the PVA cryogels by their rinsing with water at room temperature; the extraction of the sol was accompanied with the variations of the swelling parameters of the gels (initial slight upswelling and subsequent gradual deswelling), as well as with analogous, in their character, variations of the gel strength. It was also demonstrated that at the evaluation of the fusion enthalpies of PVA cryogels with the aid of the Eldridge–Ferry equation a consideration of the values of gel‐fraction yield gave rise to the significantly higher ΔH values than in traditional cases commonly used for the thermoreversible gels, where such an yield was not taken into account. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1822–1831, 2000     

Effect of mechanical activation time on the reactivity of wolframite concentrates

A direct method has been tested for evaluating the energy stored during mechanical activation in the wolframite phase of standard and low-grade wolframite concentrates. The activation energy change has been shown to be influenced by the type of energy stored. Our results confirm that the energy stored during mechanical activation in the form of surface energy influences the leaching behavior of the concentrate. We have studied the effect of the surface energy stored in the wolframite phase during mechanical activation on the tungsten extraction into solution through low-temperature alkaline leaching. A relationship has been derived between the tungsten extraction into solution through alkaline leaching and the surface energy stored in the wolframite phase.     

Preliminary reliability assessment and failure physical analysis on AlGaN/GaN HEMTs COTS

GaN based FETs have demonstrated high microwave performance since several years, and exhibit attractive potential for microwave power source in electronic warfare and military radar application, and also for civilian telecommunication applications like wireless basestations, Wi-Max, Wi-Fi as well. Up to now, the main challenge remaining for this technology is the proof of good reliability. The Information Warfare Technology Center (CELAR) launched a GaN COTS assessment campaign in order to achieve a state of the art on this topic. In this paper, we presented and discussed the first results of a life test evaluation on HFET GaN/AlGaN structure on silicon substrate and the first results of investigations by physical analysis on a failed device. These preliminary reliability investigations show all the importance of reliability tests conditions applied in order to compare reliability results and also, the benefits of a screening to obtain representative technology quality of the batch of sample before stress. Our investigations on failure analysis by STEM around the gate area of a failed device show defects which could be responsible of a degradation of the Schottky gate.     

Isoxazole‐Based‐Scaffold Inhibitors Targeting Cyclooxygenases (COXs)

A new set of cyclooxygenase (COX) inhibitors endowed with an additional functionality was explored. These new compounds also contained either rhodamine 6G or 6,7‐dimethoxy‐1,2,3,4‐tetrahydroisoquinoline, two moieties typical of efflux pump substrates and inhibitors, respectively. Among all the synthesized compounds, two new COX inhibitors with opposite selectivity were discovered: compound 8 [N‐(9‐{2‐[(4‐{2‐[3‐(5‐chlorofuran‐2‐yl)‐4‐phenylisoxazol‐5‐yl]acetamido}butyl)carbamoyl]phenyl‐6‐(ethylamino)‐2,7‐dimethyl‐3H‐xanthen‐3‐ylidene}ethanaminium chloride] was found to be a selective COX‐1 inhibitor, whereas 17 (2‐[3,4‐bis(4‐methoxyphenyl)isoxazol‐5‐yl]‐1‐[6,7‐dimethoxy‐3,4‐dihydroisoquinolin‐2‐(1H)‐yl]ethanone) was found to be a sub‐micromolar selective COX‐2 inhibitor. However, both were shown to interact with P‐glycoprotein. Docking experiments helped to clarify the molecular aspects of the observed COX selectivity.     

Dynamics of a reverse osmosis unit with application to pulsating regimes for process optimization

We propose unsteady-state reverse osmosis cell modelling in two dimensions. The convection-diffusion equation describing the concentration of the relevant chemical species is solved by a finite difference technique, while the velocity field is described by empirical expressions for spiral-wound membrane cells. A non-constant permeability is introduced to take into account the effects of membrane compaction at high operating pressures. The role of concentration polarization is discussed for different values of the parameters describing the global process. Finally, the model is applied to predict the effects of a pulsating flow where a cyclic pressure feed is adopted to enhance the permeate flux. In this context, an experimental validation of the model is proposed.     

Chamotte Refractory Materials with a Compound Nitride-Based Bond

The optimum compositions of oxygen-free mixtures for manufacture of nitride-based refractory bonds are reported. A technology for manufacturing chamotte refractory materials with a compound nitride-based bond is developed. The newly designed materials exhibit improved physicomechanical properties and enhanced durability against attack by alkalis and molten slag.