Scaling laws and internal structure for characterizing electrospun poly[(R)-3-hydroxybutyrate] fibers

Using chloroform/dimethylformamide (CF/DMF) co-solvent, electrospinning of poly[(R)-3-hydroxybutyrate] (PHB) solutions was carried out at ambient temperature. The effects of the applied voltage (V), flow-rate (Q), and solution viscoelastic properties on the Taylor cone, electrified jet, and fiber morphology were investigated. In addition, the electric field developed by the needle-plate electrode configuration was calculated using a finite element analysis to reveal the tip-to-collector (H) effect. Among the processing parameters (V, Q and H), it was found that Q played a key role in determining the jet diameter (d_j) and electrospun fiber diameter (d_f), and scaling laws existed between them, i.e., d_j-Q^0.61 and d_f-Q^0.33. The diameter reduction ratios of D_o/d_j (D_o is the needle diameter) and d_j/d_f were measured as 50-120 and 5-10, respectively; it suggested that major jet stretching took place in the straight electrified jet region, and further chain orientation could be gained by the subsequent process of jet whipping. By changing PHB concentrations from 5 to 15 wt%, the solution viscosity (η_o) was increased from 100 to 4900 cP, whereas the surface tension and solution conductivity remained unchanged; it provided a good model solution to exclusively reveal the η_o effect on the electrospinning process. Our results showed that the η_o-dependence of d_j and d_f also followed simple scaling laws: d_j-η_o^0.06, and d_f-η_o^0.39, with a prefactor depending on the processing variables, mainly the flow-rate. Regardless of the PHB concentrations used, the obtained PHB fibers showed a similar crystallinity fraction of ca. 0.63 and possession of major α-crystals together with a small amount of β-crystals with zigzag chain conformation.     

Towards a new definition of EPOC parameters for anionic electrochemical catalysts: case of propene combustion

The electrochemical promotion of catalysis (EPOC) of propene combustion was investigated using Pt sputtered thin film on an O²⁻ conductor, 8 mol% Y₂O₃-stabilized-ZrO₂ (YSZ). In order to separate the influence of the thermal migration of the O²⁻ oxide ions from the electrolyte to the catalyst surface and the impact of an electrical polarization on the catalytic activity, several light-off experiments (cool down and heat up procedures) were successively performed under different polarizations, i.e. OCV, +2 and −2 V. These experiments have clearly shown that the presence of O²⁻ (thermally or electrochemically induced) inhibits the catalytic activity of the platinum for the propene deep oxidation. These results demonstrate the importance to define a normalized rate enhancement ratio, ρ _n , from a reference value of the catalytic rate corresponding to a Pt surface state free of O²⁻ ions.     

ΝΗ<Subscript>3</Subscript> decomposition in a proton conducting solid electrolyte cell

The reaction of NH₃ decomposition was studied on Ag in a proton conducting double chamber cell-reactor. The proton conductor was a strontia-ceria-ytterbia (SCY) perovskite of the form SrCe_0.95Yb_0.05O_3−α. The reaction was studied at 350–700 °C and atmospheric total pressure. The proton transference number (PTN) was calculated by simultaneous measurement of the imposed current and the proton flux and it was found to vary between 0.5 and 0.7. The effects of imposed current, temperature and inlet gas composition on the reaction rate and the PTN, were examined. Although the faradaic efficiency (Λ) remained near unity in all experiments, reaction rate enhancements (ρ) as high as 57 were achieved. An up to 90% decrease in the activation energy of the reaction was observed when protons were electrochemically “pumped” away from the catalyst.     

Al2O3对唐钢高炉炉渣性能的影响

针对唐钢近2年提高进口矿配比后，Al2O3含量升高对炉渣流动性带来的不利影响，对唐钢高炉的炉渣性能进行了试验研究。并结合国内同行业的生产实践经验，从理论上分析了炉渣中Al2O3及MgO的适宜含量范围，着重论述了唐钢所处冀东矿区条件下降低Al2O3的主要途径及适应高Al2O3炉渣的具体措施。     

Effect of 3D lip deformations on elastohydrodynamic lip seals behaviour

The numerical simulation of comparative elastohydrodynamic lubrication between axisymmetrical and 3D elastic approaches on the radial lip seals is presented in order to determine the 3D effect of the elastic aspect of the seal lip. Indeed, the consideration of 3D model in other words the circumferential variation of the lip elastic deformation indicated a difference in the deformation distribution of the lip compared to the axisymmetrical approach. Consequently, the results show that the presence of the circumferential variation of the seal lip deformation has a significant effect on the pumping rate values.     

Epitaxial growth of GaN on (0001) Al<Subscript>2</Subscript>O<Subscript>3</Subscript> via solution-cast seed layer formation process using Ga(mDTC)<Subscript>3</Subscript>

This paper reports an alternative method for the growth of GaN epitaxial layer on (0001) Al₂O₃ substrate by hot-wall vapor phase epitaxy technique. Tris (N,N-dimethyldithiocarbamato)-gallium (III), Ga(mDTC)₃ was introduced as a precursor material for the seed layer formation in the growth of GaN. Optimal growth conditions with seed layers formed by the Ga(mDTC)₃ concentration of 0.047 mol/L were identified: Growth temperature was found to be 850 °C, and optimal distance between the reactant outlet and substrate was determined to be 12.5 cm. Characterization results showed that this growth method produce high-crystallinity GaN epitaxial layers at a relatively lower growth temperature compared to the existing growth techniques and simplify the growth process.     

The determinants of heat-shock element-directed lacZ expression in Saccharomyces cerevisiae.

Heat-shock induction of heat-shock protein genes is due to a specific promoter element (the heat-shock element, HSE). This study used lacZ under HSE control (HSE-lacZ) to characterize HSE activity in Saccharomyces cerevisiae cells of different physiological states and differing genetic backgrounds. In batch fermentations HSE-lacZ induction by heat shock was maximal in exponential growth, and showed marked decline with the approach to stationary phase. Expression in the absence of heat shock was unaffected by growth phase, indicating that the growth-dependent expression of many yeast heat-shock genes uses promoter elements in addition to the HSE. Heat-induced expression was strongly influenced by the temperature at which cultures were grown. While basal, uninduced expression was constant during growth at different temperatures to 30 degrees C, induction by transfer to 39 degrees C was reduced by increases in growth temperature as low as 18-24 degrees C. Maximal HSE-lacZ induction (30- to 50-fold) was in cultures grown at low temperatures (18-24 degrees C), then heat shocked at 39 degrees C. Ethanol was a poor inducer. Mutations having little effect on HSE-lacZ expression included a respiratory petite; ubi4 (which inactivates the poly-ubiquitin gene); also ubc4 and ubc5 (which each inactivate one of the ubiquitin ligases involved in degradation of aberrant protein). pep4-3 increased both basal and induced beta-galactosidase about two-fold, probably because of slower turnover of this enzyme in pep4-3 strains.