Grindability and Surface Integrity of Cast Nickel-based Superalloy in Creep Feed Grinding with Brazed CBN Abrasive Wheels

AbstractThe technique of creep feed grinding is most suitable for geometrical shaping, and therefore has been expected to improve effectively material removal rate and surface quality of components with complex profile. This article studies experimentally the effects of process parameters (i.e. wheel speed, workpiece speed and depth of cut) on the grindability and surface integrity of cast nickel-based superalloys, i.e. K424, during creep feed grinding with brazed cubic boron nitride (CBN) abrasive wheels. Some important factors, such as grinding force and temperature, specific grinding energy, size stability, surface topography, microhardness and microstructure alteration of the sub-surface, residual stresses, are investigated in detail. The results show that during creep feed grinding with brazed CBN wheels, low grinding temperature at about 100 °C is obtained though the specific grinding energy of nickel-based superalloys is high up to 200-300 J/mm3. A combination of wheel speed 22.5 m/s, workpiece speed 0.1 m/min, depth of cut 0.2 mm accomplishes the straight grooves with the expected dimensional accuracy. Moreover, the compressive residual stresses are formed in the burn-free and crack-free ground surface

Identification of sucrose synthase from Micractinium conductrix to favor biocatalytic glycosylation

Sucrose synthase (SuSy, EC 2.4.1.13) is a unique glycosyltransferase (GT) for developing cost-effective glycosylation processes. Up to now, some SuSys derived from plants and bacteria have been used to recycle uridine 5′-diphosphate glucose in the reactions catalyzed by Leloir GTs. In this study, after sequence mining and experimental verification, a SuSy from Micractinium conductrix (McSuSy), a single-cell green alga, was overexpressed in Escherichia coli, and its enzymatic properties were characterized. In the direction of sucrose cleavage, the specific activity of the recombinant McSuSy is 9.39 U/mg at 37°C and pH 7.0, and the optimum temperature and pH were 60°C and pH 7.0, respectively. Its nucleotide preference for uridine 5′-diphosphate (UDP) was similar to plant SuSys, and the enzyme activity remained relatively high when the DMSO concentration below 25%. The mutation of the predicted N-terminal phosphorylation site (S31D) significantly stimulated the activity of McSuSy. When the mutant S31D of McSuSy was applied by coupling the engineered Stevia glycosyltransferase UGT76G1 in a one-pot two-enzyme reaction at 10% DMSO, 50 g/L rebaudioside E was transformed into 51.06 g/L rebaudioside M in 57 h by means of batch feeding, with a yield of 76.48%. This work may reveal the lower eukaryotes as a promising resource for SuSys of industrial interest

Recent progress in electrochemical synthesis of ammonia from nitrogen: strategies to improve the catalytic activity and selectivity

The modern ammonia synthesis industry founded by Haber-Bosch in 1913 has successfully altered the history of food production, fed explosive population growth, and laid the foundation of heterogeneous catalysis and chemical engineering as well. However, its reliance on fossil fuels for reactant H-2 production consumes 1-3% of the world's electric energy and 2-5% of the world's natural gas, accompanied by more than 400 million tons of CO2 emission annually. Making use of water as the proton source and electric energy to drive the ammonia synthesis reaction will reduce the fossil fuel consumption and CO2 emission and is thus regarded as a green and sustainable alternative to the conventional Haber-Bosch process. To date, some excellent reviews on electrochemical ammonia synthesis have been published, but most of them were organized according to the type of catalyst. A systematic summary of the performance-improving strategies of the electrocatalyst for ammonia synthesis is rarely reported and therefore highly desirable. In this review, the nitrogen reduction reaction mechanisms and recent theoretical advances are briefly outlined first. Then, strategies for both reactivity and selectivity enhancement of catalysts and catalytic systems are methodically discussed. Last, criteria for the electrochemical nitrogen reduction reaction, ammonia quantification methods, and an outlook for further research are also concluded. This review aims to provide systematic and concise guidance for the design of highly efficient and selective electrochemical ammonia synthesis systems

Original speech and its echo are segregated and separately processed in the human brain.

Speech recognition crucially relies on slow temporal modulations (<16 Hz) in speech. Recent studies, however, have demonstrated that the long-delay echoes, which are common during online conferencing, can eliminate crucial temporal modulations in speech but do not affect speech intelligibility. Here, we investigated the underlying neural mechanisms. MEG experiments demonstrated that cortical activity can effectively track the temporal modulations eliminated by an echo, which cannot be fully explained by basic neural adaptation mechanisms. Furthermore, cortical responses to echoic speech can be better explained by a model that segregates speech from its echo than by a model that encodes echoic speech as a whole. The speech segregation effect was observed even when attention was diverted but would disappear when segregation cues, i.e., speech fine structure, were removed. These results strongly suggested that, through mechanisms such as stream segregation, the auditory system can build an echo-insensitive representation of speech envelope, which can support reliable speech recognition

FBXL5 Inhibits Metastasis of Gastric Cancer Through Suppressing Snail1

Background/Aims: The Snail family of transcription factors controls epithelial to mesenchymal transition (EMT), a process associated with tumorigenesis originated from epithelial cells. Snail1 is a member from Snail family and upregulation of Snail1 has been detected in gastric cancer (GC), suggesting a potential role of Snail1 in GC metastasis. We have recently reported that FBXL5 regulates cortactin by inducing its ubiquitylation and subsequent proteasomal degradation, resulting in inhibition of metastasis of GC. However, a role of FBXL4 in regulation of other EMT-associated proteins is not unknown. Methods: The levels of FBXL5 and Snail1 as well as their relationship were determined in GC specimen. Co-immunoprecipitation (IP) was performed to detect the interaction between Snail1 and FBXL5 in GC cells. The effects on Snail1 by FBXL5 were examined by overexpression of depletion of FBXL5 in GC cells. The invasiveness of the FBXL5-modified GC cells was examined in both scratch wound healing assay and transwell matrix penetration assay. Results: FBXL5 also physiologically interacted with Snail1. FBXL5 inhibited Snail1 to suppress GC cell invasiveness. Conclusion: FBXL5 negatively regulates several EMT-enhancing factors. FBXL5 is an attractive novel target for inhibiting invasion and metastasis of GC cells

Discussion of skill improvement in marine ecosystem dynamic models based on parameter optimization and skill assessment

Shen C, Shi H, Liu Y, Li F, Ding D. Discussion of skill improvement in marine ecosystem dynamic models based on parameter optimization and skill assessment. Chinese Journal of Oceanology and Limnology. 2016;34(4):683-696