Search

Pocket molds are widely applied, whose pockets usually contain many transition corners. The machining efficiency of pocket mold can be improved significantly through deep milling. However, tools are subject to quick wear and damage during corner deep milling. Corner rounding along tool path by different approaches has great influence on the tool wear in deep milling of hardened steel pocket mold. Therefore, conducting related researches on tool wear is of practical significance. Firstly, continuous cutting pocket molds were designed for typical corners of different corner rounding approaches as per the basic theory of tool engagement angle in milling, and then hardened steel was subject to deep milling and the tool was inspected and analyzed; afterwards, tool wear process and mechanism, etc. were studied. The results showed that during the deep milling of hardened steel, adhesion, oxidation, and diffusion wear appeared gradually since the stabilization of tool wear and further aggravated along with the cutting process, which led to wear and peeling of coating as well as highly possible tool damage like tipping and chipping of tool nose in later period. It was easy to generate high tool-chip interface temperature and great tool load in the high-speed deep milling of hardened steel with small corner rounding radius. In this case, the cutting edge was under considerable thermal fatigue and mechanical shock and thus subject to extensive abrasion wear, adhesion wear, and diffusion wear. The tool wear could be reduced notably by increasing the corner rounding radius.

Two genes encoding the maltooligosyltrehalose synthase (MTSase) from Sulfolobus acidocaldarius ATCC 33909 were synthesized: one (designated E-treY) using codons preferred by Escherichia coli and the other (designated P-treY) using codons preferred by Pichia pastoris. E-treY was inserted into pET-24a(+), and the resulting plasmid was used to transform E. coli BL21(DE3). P-treY was inserted into pPIC3.5 K and pGAPZA, and the resulting plasmids were used to transform P. pastoris KM71. The maximum MTSase activity expressed by these E. coli and P. pastoris strains reached 31.6 and 133.0 U mL−1, respectively. The purified MTSases displayed the same pH (pH 5.5) and temperature (75 °C) optima. Both had a half-life of 12 h at 75 °C. The recombinant P. pastoris KM71/pPIC3.5K-treY strain producing the highest enzyme activity was used to optimize the fermentation conditions in a 3.6-L bioreactor. Fermentation for 96 h under optimal conditions yielded an MTSase activity of 747.4 U mL−1.

When machining the pocket of a mould in high-speed milling mode, the tool load at a pocket’s narrow area or corner may sharply increase because of the presence of a higher amount of material to be cut. A trochoidal machining method considering milling force, machining tool, and pocket geometry is proposed in this paper. First, a method for the geometric modeling of the engagement angle in trochoidal machining is proposed. Maximum and mean values of the milling force are analysed; meanwhile, the corresponding relationship between the milling force curve and the engagement angle curve during the trochoidal machining process is analysed. Based on fundamental experiments on trochoidal machining, results for the milling force and tool wear are obtained; then, a proper control strategy for cavity trochoidal milling machining is proposed. Based on this control strategy for trochoidal milling machining, two realisations of cavity trochoidal milling machining are proposed. Finally, comparison experiments on cavity machining are conducted. Compared with the feedrate adjustment method, trochoidal machining provides better control over the milling force and tool wear at corners and narrow slots. The milling force and machining vibrations are smaller, and the tool wear is substantially reduced.

Maltooligosyl trehalose trehalohydrolase (MTHase, EC 3.2.1.141) catalyzes the release of trehalose, a novel food ingredient, by splitting the α-1,4-glucosidic linkage adjacent to the α-1,1-glucosidic linkage of maltooligosyl trehalose. However, the high-yield preparation of recombinant MTHase has not yet been reported. In this study, a codon-optimized synthetic gene encoding Sulfolobus acidocaldarius MTHase was expressed in Escherichia coli. In initial expression experiments conducted using pET-24a (+) and E. coli BL21 (DE3), the MTHase activity was 10.4 U/mL and a large amount of the expression product formed inclusion bodies. The familiar strategies, including addition of additives, co-expression with molecular chaperones, and expression with a fusion partner, failed to enhance soluble MTHase expression. Considering the intermolecular disulfide bond of MTHase, expression was investigated using a system comprising plasmid pET-32a (+) and host E. coli Origami (DE3), which is conducive to cytoplasmic disulfide bond formation. The MTHase activity increased to 55.0 U/mL, a 5.3-fold increase. Optimization of the induction conditions in a 3-L fermentor showed that when the lactose was fed at 0.2 g/L/h beginning at an OD600 of 40 and the induction temperature was maintained at 30 °C, the MTHase activity reached a maximum of 204.6 U/mL. This is the first report describing a systematic effort to obtain high-efficiency MTHase production. The high yield obtained using this process provides the basis for the industrial-scale production of trehalose. This report is also expected to be valuable in the production of other enzymes containing disulfide bonds.

HuanHuan Guo, Shuo Huang, Shuang Li, Hui Yu, ShiXiong Wu, XuHong Zhou Department of Otorhinolaryngology-Head and Neck Surgery, Zhongnan Hospital of Wuhan University, Wuhan, China Background and objective: Nasopharyngeal carcinoma (NPC) is a common head and neck malignancy. Despite recent advances in treatment, the prognosis, particularly for those at the advanced stages, remains poor. Moreover, the underlying genetic and molecular events have remained obscure so far. Recently, increasing evidence has demonstrated that long noncoding RNAs (lncRNAs) could act as either oncogenes or tumor suppressor genes in various cancers depending on their targets. And some lncRNAs have been shown to be aberrantly expressed in NPC. In this meta-analysis, we try to elucidate the possible role of lncRNAs and their expression on prognosis in NPC.Methods: We searched the databases of PubMed, Embase, and Web of Science for relevant articles ranging from January 2000 to December 2017. Pooled hazard ratios (HRs) and 95% confidence intervals (CIs) were used to evaluate the prognostic value of lncRNAs in NPC. Odds ratios (ORs) were used to assess the association between lncRNAs and clinicopathological characteristics.Results: A total of 14 eligible publications including 14 on prognosis and eight on clinicopathological characteristics were identified. Our results demonstrated that the high expression of lncRNAs was related to poor overall survival (OS; HR =1.55; 95% CI =1.01, 2.40; P=0.05) and disease-free survival (DFS; HR =1.83; 95% CI =1.07, 3.13; P=0.03) of NPC. Moreover, the expression of lncRNAs was correlated with male gender (OR =1.42; 95% CI =1.05, 1.91; P=0.02), lymph node status (OR =2.20; 95% CI =1.29, 3.73; P=0.004), and tumor node metastasis (TNM) clinical stage (OR =2.55; 95% CI =1.12, 5.78; P=0.03).Conclusion: This meta-analysis shows that the level of expression of lncRNAs may be a potential prognostic indicator in NPC. Keywords: long noncoding RNAs, nasopharyngeal carcinoma, prognosis, overall survival, meta-analysis