Investigation of redox potential and negative differential resistance behavior of heteropolyacids by scanning tunneling microscopy

Nanoscale images and tunneling spectra of cation-exchanged or polyatom-substituted heteropolyacids (HPAs) were probed by scanning tunneling microscopy (STM) at room temperature. All the HPAs formed two-dimensional ordered arrays on graphite surfaces, and their molecular dimensions were in good agreement with values determined by X-ray crystallography. It was observed that the negative differential resistance (NDR) peak voltage measured by STM was closely related to the reduction potential of the corresponding bulk HPA. The higher the reduction potential of the HPA, the lower the applied voltage at which NDR was observed.     

Processing aids for biodegradable polymers

The melt fracture behavior of several commercial polylactides (PLAs) and poly(ε‐caprolactone) (PCL) is investigated. PLAs and PCL with molecular weights greater than a certain value were found to exhibit melt fracture phenomena in capillary extrusion, which manifests itself as distortions on their surface once the extrusion rate exceeds a critical value. It was found that the addition of a small amount of PCL (typically 0.5 wt %) into the PLA and vice versa is effective in eliminating and delaying the onset of melt fracture to higher shear rates in the capillary extrusion of PLA and PCL, respectively. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Comparisons between unsteady sediment-transport modeling

The comparative study between unsteady flow models in alluvial streams shows a chaotic residue as for the choices of a forecasting model. The difficulty resides in the choice of the expressions of friction resistance and sediment transport. Three types of mathematical models were selected. Models of type one and two are fairly general, but require a considerable number of boundary conditions, which related to each size range of sediments. It can be a handicap during rivers studies which are not very well followed in terms of experimental measurements. Also, the use of complex models is not always founded. But then, the model of type three requires a limited number of boundary conditions and solves only a system of three equations at each time step. It allows a considerable saving in calculating times.     

Effect of probiotic lactobacilli on faecal enzyme and genotoxic activity in human faecal water in the presence of the carcinogen PhIP in vitro

The average β‐glucuronidase activity for children was 0.48 ± 0.04 U/mg, for adults 0.75 ± 0.27 U/mg and for elderly 1.55 ± 0.06 U/mg. For β‐glucosidase, it was 0.19 ± 0.02 U/mg for children, 0.77 ± 0.26 U/mg for adults and 1.18 ± 0.27 U/mg for elderly. In the presence of probiotics, the highest decrease in genotoxicity was observed for Lactobacillus casei 0908 (to 7.99 ± 1.32) and Lactobacillus paracasei 0919 (to 6.19 ± 1.44) for all children. In adults, lower mean genotoxicity was regarded after incubation of PhIP with L. casei 0908 (it was 5.27 ± 1.13) and L. paracasei 0919 (it was o 6.01 ± 1.00). For elderly, statistically significant decrease was maintained after incubation of PhIP with L. casei 0900 (to 6.72 ± 2.67).     

The effect of surface modification on the corrosion protection ability of the passive films of sensitized UNS S31803 duplex stainless steel

ABSTRACT

The influence of sensitisation heat treatment, surface roughness and repetitive cyclic voltammetry (RCV) procedure (that was used to create passive films on the surface of sensitised samples) on the corrosion behaviour of UNS S31803 duplex stainless steel was evaluated using sodium hydroxide etching, double-loop electrochemical potentiodynamic reactivation (DLEPR), potentiodynamic polarisation, Mott–Schottky analysis, X-ray diffraction and optical microscopy techniques. The results showed that prolonged sensitisation time leads to the formation of defective passive films on the surface. In addition, as the substrate surface roughness decreases, the defect concentration in the resulting passive film decreases. Moreover, thick passive films that were created at a high number of RCV cycles contain fewer defects than the thin ones. Finally, the specimens with smooth surfaces, thick passive films and low degree of sensitisation exhibit high corrosion resistance due to their intact passive layers formed on their surfaces.     

Investigation of some copolymers based on acrylic salts as circulation loss control agents

In this work, six copolymers were prepared from sodium and potassium acrylate. Both salts individually were copolymerized with acrylamide, methacrylic acid and acrylic acid at different ratios. The monomer reactivity ratios for copolymerization reactions of both of acrylate salts with acrylamide, methacrylic acid and acrylic acid, in solution with azobisisobutyronitrile (AIBN) as an initiator, were estimated by atomic adsorption analyser. The chemical structure was confirmed by atomic adsorption spectroscopy and FT-IR spectroscopy.The prepared copolymers were investigated as loss circulation control materials by measuring different filtration parameters such as; spurt loss, fluid loss and permeability plugging tester value according to the American Petroleum Institute (API) standard. From the obtained data, it was found that the 0.6% from the poly[PA-co-AM]_(0.4:0.6) exhibited the best results of the filtration parameters among the other copolymers. At the same time all the studied copolymers enhanced the rheological properties of the drilling mud. These results were discussed on the light of the swelling capacity of the copolymers.     

Phase transformations and structural changes in the course of the high-temperature superplastic deformation of aluminum alloys

Phase and structural transformations, which develop under conditions characteristic of high-temperature superplasticity in matrix multicomponent aluminum alloys, have been investigated. It has been shown that the appearance of a metastable liquid phase is in principle possible in the structure of such alloys in the process of the establishment of the equilibrium state during their heating to the temperature of tests and in the course of superplastic deformation. The characteristic properties of the structural changes that occur in the course of the superplastic deformation of such alloys have been studied. The basic conditions that lead to the origin and the development of fibrous species in the course of the high-temperature superplastic deformation have been determined. The determining role of magnesium in the process of origin and development of such fibrous formations is shown.     

Regulation of exocytosis by cyclin-dependent kinase 5 via phosphorylation of Munc18

Munc18a, a mammalian neuronal homologue of Saccharomyces cerevisiae Sec1p protein, is essential for secretion, likely as a result of its high affinity interaction with the target SNARE protein syntaxin 1a (where SNARE is derived from SNAP receptor (the soluble N-ethylmaleimide-sensitive fusion protein)). However, this interaction inhibits vesicle SNARE interactions with syntaxin that are required for secretory vesicles to achieve competency for membrane fusion. As such, regulation of the interaction between Munc18a and syntaxin 1a may provide an important mechanism controlling secretory responsiveness. Cyclin-dependent kinase 5 (Cdk5), a member of the Cdc2 family of cell division kinases, co-purifies with Munc18a from rat brain, interacts directly with Munc18a in vitro, and utilizes Munc18a as a substrate for phosphorylation. We have now demonstrated that Cdk5 is capable of phosphorylating Munc18a in vitro within a preformed Munc18a.syntaxin 1a heterodimer complex and that this results in the disassembly of the complex. Using site-directed mutagenesis, the Cdk5 phosphorylation site on Munc18a was identified as Thr574. Stimulation of secretion from neuroendocrine cells produced a corresponding rapid translocation of cytosolic Cdk5 to a particulate fraction and an increase of Cdk5 kinase activity. Inhibition of Cdk5 with olomoucine decreased evoked norepinephrine secretion from chromaffin cells, an effect not observed with the inactive analogue iso-olomoucine. The effects of olomoucine were independent of calcium influx as evidenced by secretory inhibition in permeabilized chromaffin cells and in cells under whole-cell voltage clamp. Furthermore, transfection and expression in chromaffin cells of a neural specific Cdk5 activator, p25, led to a strong increase in nicotinic agonist-induced secretory responses. Our data suggest a model whereby Cdk5 acts to regulate Munc18a interaction with syntaxin 1a and thereby modulates the level of vesicle SNARE interaction with syntaxin 1a and secretory responsiveness.     

Magneto-Caloric Effect in Ge0.95Mn0.05 Films

In this paper, a phenomenological model is used to calculate magneto-caloric properties of Ge_0.95Mn_0.05 films fabricated with substrate temperatures of 85, 100, and 120 ^°C. Calculations showed that the ferromagnetic Mn₅Ge₃ phase improves magneto-caloric properties of the Ge_0.95Mn_0.05 films. It is suggested that Ge_0.95Mn_0.05 films are suitable candidates as refrigerants near room-temperature region.