Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) Production in Recombinant Aeromonas hydrophila 4AK4 Harboring phbA,phbB and vgb Genes

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx), a copolyester consisting of 3-hydroxybutyrate (3HB) and 3-hydroxyhexanoate (3HHx), can be synthesized by Aeromonas hydrophila strain 4AK4 using long chain fatty acids as the carbon source. The wild type A. hydrophila 4AK4 accumulated PHBHHx consisting of 12-15 mol% 3HHx regardless of growth conditions. When phbA, phbB and vgb genes encoding β-ketothiolase, acetoacetyl-CoA reductase and vitreoscilla hemoglobin, respectively, were introduced together into A. hydrophila 4AK4, the recombinant strain grew to over 20 g/L cell dry weight (CDW) after 48 h of shake flask cultivation in co-substrates of dodecanoate and gluconate (weight ratio 1:1), and the CDW contained 50% PHBHHx consisting of 9 mol% 3HHx. Under similar conditions, the wild type strain produced only 12 g/L CDW containing 32% PHBHHx with 15 mol% 3HHx. In comparison, recombinant harboring phbA and phbB produced 35% PHBHHx with 9 mol% 3HHx in 15 g/L CDW under the same conditions. The obvious differences in terms of the cell growth and PHBHHx production were attributed to the expression of vgb in A. hydrophila 4AK4, which was clearly observed in carbon monoxide difference spectra. The expression of vgb in the recombinant not only improved cell growth and PHBHHx accumulation, but also increased the plasmid stability during cell growth, especially under low dissolved oxygen tension in fermentors. PHBHHx production could be further increased to over 60% of the CDW by the over expression of phaC and phaJ from Aeromonas caviae encoding PHBHHx synthase and (R)-specific enoyl-CoA hydratase, respectively. Over expression of phaC, phaJ and phaP, alone or in various combinations, also increased the 3HHx content of PHBHHx from 14-34%. The above results showed that A. hydrophila was amenable to genetic manipulation, and that these modifications could be exploited to produce compounds with different properties for commercial and research applications.     

非线性数值流形方法的变分原理与应用

针对非线性力学问题,根据数值流形方法的特点及相应的位移模式,得到了面向物理覆盖的非线性数值流形方法的变分原理,详细推导了基于变分原理的非线性数值流形方法的理论计算公式,建立了非线性数值流形方法的理论体系和控制方程。作为实际应用,给出了相应的数值算例,结果表明,求解精度和效益令人满意。     

Influence of sodium dodecyl sulfate on the physicochemical properties of whey protein-stabilized emulsions

The influence of sodium dodecyl sulfate (SDS) on the flocculation of droplets in 20 wt.% soybean oil-in-water emulsions stabilized by whey protein isolate (WPI) was investigated by light scattering, rheology and creaming measurements. The SDS concentrations used were low enough to prevent depletion flocculation by surfactant micelles and extensive protein displacement. In the absence of SDS, emulsions were prone to droplet flocculation near the isoelectric point of the proteins (4<pH<6), but were stable at a higher and lower pH. Flocculation led to an increase in emulsion viscosity, pronounced shear thinning behavior and accelerated creaming. When the surfactant-to-protein molar ratio was increased from 0 to 10, the emulsion instability range shifted to lower pH values due to binding of the negatively charged SDS molecules to the droplets. Our results indicate that the physicochemical properties of protein-stabilized emulsions can be modified by utilizing surfactant–protein interactions.     

Expanding the utility of proteases in synthesis: broadening the substrate acceptance in non-coded amide bond formation using chemically modified mutants of subtilisin

The strategy of combined site directed mutagenesis and chemical modification creates chemically modified mutants (CMMs) with greatly broadened substrate specificities. We have previously reported that the CMMs of subtilisin Bacillus lentus (SBL) are efficient catalysts for the coupling of both l- and d-amino acids. We now report that these powerful catalysts also allow amide bond formation between a variety of non-coded carboxylic acids, including β-alanine and β-amino homologues of phenylalanine, with both l- and d-amino acid nucleophiles. As a guide to enzyme efficiency, a hydrolysis assay indicating pH change has been employed. CMMs selected by this screen furnished higher yields of coupling products compared to the wild-type enzyme (WT). Furthermore, both WT and CMM enzymes allow highly stereoselective aminolysis of a meso diester with an amino acid amine. These results highlight the utility of CMMs in the efficient formation of non-coded amides as potential peptide isosteres.     

有限元模型修正研究进展:从线性到非线性

有限元分析在实际工程中得到了广泛应用.然而有限元模型由于受到网格划分、边界条件和材料物理参数不确定性等的影响,与真实结构有差异. 因此须通过试验数据加以修正,使其尽可能接近实际结构,以保证之后的结构动力模拟分析和监测等具有实际意义. 经过多年发展,有限元模型修正技术已经能够成功应用于一些实际工程,但现代工程技术的进步对有限元模型修正提出了更高要求,修正后的有限元模型不仅要有较高的精确度,还需要为后续应用给出具有指导意义的置信度.而现有的有限元模型修正、确认方法多基于结构线性的假设,而未能考虑实际结构中广泛存在的非线性.因此本文以土木工程结构模型修正的一些研究成果为例,通过对传统有限元模型修正的发展历程进行全面回顾;总结评述传统有限元修正技术的主要方法,以及包括有限元模型确认在内的最新研究进展;重点探讨有限元模型修正技术向非线性发展的技术路线和目前主要研究成果,展望其未来发展方向, 并提出值得研究的问题.      

Electrocatalytic and Photocatalytic CO2 Methanation: From Reaction Fundamentals to Catalyst Developments

Transitioning from fossil fuels to renewable energy sources is demanded due to the gradual depletion of petroleum oil/gas and the environmental impact of carbon dioxide (CO₂) emissions into the atmosphere. Electrocatalytic and photocatalytic CO₂ reduction to methane (CH₄) using renewable energy sources is crucial for sustainable chemical/fuel production and greenhouse gas reduction. In recent years, extensive research has focused on understanding the fundamental aspects of the two approaches, such as reaction mechanisms and active sites, and exploring/designing novel catalytic materials. This review initially discusses the reaction fundamentals, including performance evaluation indexes, reactors, and mechanisms, to understand the catalytic reactions. Subsequently, various catalyst preparation strategies and characterization methods are summarized, trying to outline the catalyst design principle based on the obtained understanding of the reaction mechanisms. Finally, research challenges and perspectives for future development in this area are discussed and presented. It is expected to provide a comprehensive understanding of the photo/electrocatalytic CO₂ methanation, valuable knowledge to novice researchers, and a helpful reference for future research endeavors.     

High resolution Si 2p gas phase photoelectron spectra of model silicon compounds: implications for hydrogen adsorbed on a silicon surface

High resolution Si 2p gas phase photoelectron spectroscopy has been used to measure the vibrational energy spacing in SiH₄ (0.295 eV) and SiD₄ (0.212 eV). These values are compared with those measured for the chemical shift (0.30 eV/hydrogen atom) of model compounds which mimic the effects of zero, one, two and three hydrogen atoms bonded to a silicon atom on a silicon surface. Implications for the interpretation of surface photoelectron spectra are discussed.     

Free vibration characteristics of sectioned unidirectional/bidirectional functionally graded material cantilever beams based on finite element analysis

Advancements in manufacturing technology, including the rapid development of additive manufacturing (AM), allow the fabrication of complex functionally graded material (FGM) sectioned beams. Portions of these beams may be made from different materials with possibly different gradients of material properties. The present work proposes models to investigate the free vibration of FGM sectioned beams based on onedimensional (1D) finite element analysis. For this purpose, a sample beam is divided into discrete elements, and the total energy stored in each element during vibration is computed by considering either the Timoshenko or Euler-Bernoulli beam theory. Then, Hamilton's principle is used to derive the equations of motion for the beam. The effects of material properties and dimensions of FGM sections on the beam's natural frequencies and their corresponding mode shapes are then investigated based on a dynamic Timoshenko model (TM). The presented model is validated by comparison with three-dimensional (3D) finite element simulations of the first three mode shapes of the beam.