Functional expression of recombinant sweet-tasting protein brazzein by Escherichia coli and Bacillus licheniformis

Brazzein is an attractive sweetener candidate because of its sugar-like taste, high sweetness, and good stability at high temperature and wide pH range. This study was aimed to express and purify bioactive recombinant brazzein (rBrazzein). The rBrazzein gene was synthesized according to the preferred codons of Bacillus subtilis and successfully expressed in Escherichia coli and Bacillus licheniformis. In E. coli host, lower induction temperature of 30°C increased soluble rBrazzein (Ebrazzein) at high level. In B. licheniformis host, two signal peptides (Sec type and Tat type) were evaluated for the expression of rBarzzein in B. subtilis and B. licheniformis. However, only the Sec-type signal peptide guided the secretion expression of rBrazzein in B. licheniformis. The rBrazzein was expressed steadily and the highest yield reached about 57 mg/L at 36 h by small-scale fermentation. The purification procedure of rBrazzein by B. licheniformis (Bbrazzein) was thus established. Approximately 5 mg/L purified rBrazzein was obtained and the purity was 85%. The conformational state of rBrazzeins was confirmed by circular dichroism. The bioactivities of rBrazzeins were evaluated by sweet taste testing. The Bbrazzein and Ebrazzein were 266 times and 400 times sweeter than sucrose on a weight basis, respectively. The formation of disulfide bonds were both confirmed by LC/MS/MS and MALDI-TOF. The CD analysis indicated that Ebrazzein has a similar secondary structure with natural brazzein, which explained why Ebrazzein had a higher intensity of sweetness. This study demonstrated that B. licheniformis system is useful to produce active recombinant brazzein, and has potential food industry applications.     

基于Deform 3D的高速车削加工仿真研究

基于有限元分析软件Deform 3D对高速车削加工进行仿真研究,通过实例分析了车削过程中切屑的形成过程,切削力大小、切削温度及应力应变的分布情况。该仿真结果对车削工艺效果的预测和优化具有现实的指导意义。     

Effects of selected water chemistry variables on copper pitting propagation in potable water

The pit propagation behavior of copper (UNS C11000) was investigated from an electrochemical perspective using the artificial pit method. Pit growth was studied systematically in a range of HCO₃⁻, SO₄²⁻ and Cl⁻ containing-waters at various concentrations. Pit propagation was mediated by the nature of the corrosion products formed both inside and over the pit mouth (i.e., cap). Certain water chemistry concentrations such as those high in sulfate were found to promote fast pitting that could be sustained over long times at a fixed applied potential but gradually stifled in all but the lowest concentration solutions. In contrast, Cl⁻ containing waters without sulfate ions resulted in slower pit growth and eventual repassivation. These observations were interpreted through understanding of the identity, amount and porosity of corrosion products formed inside and over pits. These factors controlled their resistive nature as characterized using electrochemical impedance spectroscopy. A finite element model (FEM) was developed which included copper oxidation kinetics, transport by migration and diffusion, Cu(I) and Cu(II) solid corrosion product formation and porosity governed by equilibrium thermodynamics and a saturation index, as well as pit current and depth of penetration. The findings of the modeling were in good agreement with artificial pit experiments. Malachite, bronchantite, cuprite, nantokite and atacamite corrosion products were both observed in experiment and predicted by the model. Stifling and/or repassivation occurred when the resistance of the corrosion product layer became high enough to lower the pit bottom potential and pit current density such as 10^-5 A/cm² could be attained with thick and dense layer. The ramifications of these findings towards pit propagation characteristics in potable waters will be discussed with improved insight into the roles of Cl⁻ and SO₄²⁻ ions.     

The Effect of Silver Chloride Formation on the Kinetics of Silver Dissolution in Chloride Solution

The precipitation and growth of AgCl on silver in physiological NaCl solution were investigated. AgCl was found to form at bottom of scratches on the surface which may be the less effective sites for diffusion or the favorable sites for heterogeneous nucleation. Patches of silver chloride expanded laterally on the substrate until a continuous film formed. The ionic transport path through this newly formed continuous film was via spaces between AgCl patches. As the film grew, the spaces between AgCl patches closed and ion transport was primarily via micro-channels running through AgCl patches. The decrease of AgCl layer conductivity during film growth were attributed to the clogging of micro-channels or decrease in charge carrier concentration inside the micro-channels. Under thin AgCl layer, i.e. on the order of a micrometer, the dissolution of silver substrate was under mixed activation-Ohmic control. Under thick AgCl layer, i.e. on the order of tens of micrometers, the dissolution of silver substrate was mediated by the Ohmic resistance of AgCl layer.     

Controlling microstructure and film growth of relaxor-ferroelectric thin films for high break-down strength and energy-storage performance

The relaxor ferroelectric Pb_0.9La_0.1(Zr_0.52Ti_0.48)O₃ (PLZT) thin films were deposited using pulsed laser deposition, and their microstructures, break-down field strengths and energy storage performances were investigated as a function of the buffer layer and electrode. A large recoverable energy-storage density (U_reco) of 23.2 J/cm³ and high energy-storage efficiency (η) of 91.6% obtained in the epitaxial PLZT film grown on SrRuO₃/SrTiO₃/Si are much higher than those in the textured PLZT film (U_reco = 21.9 J/cm³, η = 87.8%) on SrRuO₃/Ca₂Nb₃O₁₀-nanosheet/Si and the polycrystalline PLZT film (U_reco = 17.6 J/cm³, η = 82.6%) on Pt/Ti/SiO₂/Si, under the same condition of 1500 kV/cm and 1 kHz, due to the slim polarization loop and significant antiferroelectric-like behavior. Owing to the high break-down strength (BDS) of 2500 kV/cm, a giant U_reco value of 40.2 J/cm³ was obtained for the epitaxial PLZT film, in which U_reco values of 28.4 J/cm³ (at BDS of 2000 kV/cm) and 20.2 J/cm³ (at BDS of 1700 kV/cm), respectively, were obtained in the textured and polycrystalline PLZT films. The excellent fatigue-free properties and high thermal stability were also observed in these films.     

发展工业锅炉专用洁净型煤

分析了中国工业锅炉的特殊性及其人对层燃用煤的要求，评介了关于独特的板栗型煤和炉前成型技术及设备的研究，为工业锅炉改变原煤直接散烧的落后状况探索一条可行的途径。     

ADHESION OF ELASTOMER LAYERS TO AN INTERPOSED LAYER OF FILLER PARTICLES

Adhesion of elastomers to filler particles was studied by interposing a single layer of particles between two layers of a crosslinked elastomer and peeling the sandwich apart. Carbon black particles increased the peel strength by up to 100% compared with autohesion of the elastomer layers. Silica particles also increased the adhesion, but by a smaller factor, and there were significant differences using different elastomers. Also, the strength of adhesion depended on the degree of crosslinking of the elastomer layers: at higher levels of crosslinking, both self-adhesion and adhesion to particles were reduced. Nevertheless, this simple experiment gives an indication of the relative strength of adhesion for different combinations of elastomer and reinforcing filler.     

Two ways of synthesis of polymer networks based on diglycidyl ether of bisphenol A,bisphenol A,and sulfanilamide: Kinetics study

The kinetics of reactions of ternary systems based on bisphenol A diglycidyl ether, bisphenol A, and a sulfanilamide curing agent were investigated using HPLC, during two different synthesis paths. The influence of tetrabutylphosphonium tetrafluoroborate as a catalyst for the epoxy–phenol reaction was studied. For the same initial composition, polymers differing by the crosslink point distribution and the chain length between crosslinks were synthesized. Different solid‐state behavior is expected in these two categories of networks. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 580–591, 2001     

Properties of PVA-PSA hybrid materials prepared through the incorporation of polysilicic acid (PSA) into polyvinyl alcohol

A quick method of preparing transparent organic-inorganic hybrid material was studied. The hybrid, PVA/PSA, was prepared through incorporating the nanoscaled polysilicic acid (PSA) obtained through hydrolysis and condensation of metasilicate salt directly into a polyvinyl alcohol (PVA). The interfacial force, microstructure, and dynamic mechanical property of the hybrid were studied by means of spectroscopy (FTIR, X-ray diffraction and solid-state ²⁹Si NMR) and dynamic mechanical analysis, and the results were compared with that of the hybrids, PVA/TEOS, prepared through the traditional sol-gel process. It was found that the microstructure of PVA/PSA was different from that of PVA/TEOS because of the different preparation methods. The structures of the crystals in both hybrids were similar to that of the pure PVA. Other physical properties, such as T_g, storage modulus, tensile strength and solvent resistance of the PVA/PSA hybrid, were improved significantly with the addition of the silica content. The extent of improvement was a little lower than that for the PVA/TEOS.     

Preparation and characterization of ordered mesoporous Mg–Al–Co hydrotalcite based catalyst for decarboxylation of jatropha oil

This paper reported preparation of novel order mesoporous Mg–Al–Co hydrotalcite based catalysts through sol–gel procedure using precursors such Mg(NO₃)₂, Al(NO₃)₃ and Co(NO₃)₂ and Na₂CO₃. The catalyst also contained both acidity and basicity being very convenient for decarboxylation process of vegetable oil to green hydrocarbons. The alkaline media was maintained at pH 10 during the processes. Molar ratio of metal cations and temperature of the sol–gel processes were investigated for their effect in the mesoporous structure formation. The results showed that the procedure should be established at 70 °C with the molar Mg/Al/Co ratio of 1/5/0.2. Acidity and basicity of the mesoporous hydrotalcite based catalyst were demonstrated for their co-existence. The as-synthesized material at the suitable conditions was used as catalyst for decarboxylation of jatropha oil to obtain green hydrocarbons mainly belonging to diesel fraction. The decarboxylation was carried out at 400 °C for 3 h in closed auto-pressurized reactor exhibiting a yield of diesel involving hydrocarbons of over 70% after distillation and analysis. The result also confirmed that the acidity and basicity greatly accelerated the activity of the catalyst. Some techniques were used to characterizing the catalyst including XRD, SEM, TEM, TGA, NH₃-TPD, CO₂-TPD and BET, and GC–MS was also used to analyze the main product composition.