To address the problems of severe machined surface defects and serious material breakage in unidirectional C/C composites (UD-C/C), this study investigates a UD-C/C composite removal mechanism using ...ultrasonic-assisted orthogonal cutting technology. A solid cemented carbide cutting edge is used. This study focuses on the chip formation, cutting forces, and morphology of the machined surface in different directions between the tool feed and fiber, including perpendicular to the fiber, along the fiber, along the fiber cross section, and different fiber orientation angles, recorded simultaneously using a high-speed camera. The experimental results indicated that, in the perpendicular direction, damage in the interfacial phase and crack extension in the matrix dominated the chip generation process. The cracks formed during cutting along the fiber direction were relatively short, thus producing continuous segmentation chips. Owing to the accumulation and extrusion of chips, the measured cutting force remained low rather than zero. In the fiber direction, the extension of interfacial cracks in the direction of the fiber and the bending fracture of the fiber dominate in the process of material removal. The matrix was first removed, and the fiber was bent and clung to the rank face, producing a continuous band of chips. The measured cutting force remained stable. In the cross-sectional fiber direction, crack propagation results from interlayer separation, fiber yield, and matrix breakage caused by tool extrusion. The cracks expanded along the interface to the inner part of the material, and discontinuous powders were formed during the cutting process. Moreover, for different fiber orientation angles, the machining quality of the acute cutting zone was significantly better than that of the obtuse cutting zone. Second, the surface topographies of the workpieces were evaluated using a 3D surface-measuring instrument and scanning electron microscopy (SEM). Owing to the occurrence of secondary cutting, the quality of surface topographies cutting perpendicular to the fiber direction improves with increasing cutting depths. The surface topographies cutting along the fiber direction present numerous craters on the surface of the specimen as well as regional surface damage. The surface topographies cutting along the fiber cross-sectional direction show relatively serious machining damage and poor surface machining quality.
Machinability of γ-TiAl: A review XIA, Ziwen; SHAN, Chenwei; ZHANG, Menghua ...
Chinese journal of aeronautics,
07/2023, Letnik:
36, Številka:
7
Journal Article
Recenzirano
Odprti dostop
Owing to its outstanding mechanical properties, γ-TiAl is desirable materials for cross-generation aero-engines. Nearly 70 years of exploration have made it into the initial application. However, the ...intrinsic brittleness of γ-TiAl is still a critical obstacle to its large-scale applications. In this context, researchers have made many attempts to study the machinability of γ-TiAl. At present, existing relevant reviews have mostly discussed the processing methods of γ-TiAl. Hence, there is still a lack of a perspective on material properties to analyze the cutting mechanism. Herein, this paper provides the systematic review of such perspectives. Above all, the developmental process, phase transformation, and microstructural evolution of γ-TiAl are discussed, as well as its deformation mechanism at quasi-static. These topics can provide a materials science foundation for the machining of γ-TiAl. And then, the review focuses on the cutting mechanism and surface integrity of γ-TiAl. Moreover, special attention is paid to the microscope deformation mechanism and surface defects evolution of γ-TiAl during cutting. Finally, the review indicates that the high-performance machining technology of γ-TiAl faces challenges and proposes potential future research directions. Solving the difficulties during machining γ-TiAl aero-engine components will accelerate the development of new aero-engines.
Ultrasonic-assisted machining of silicon carbide (SiC) ceramic matrix composites (CMCs) has the ability to decrease grinding force and improve processing quality. The machining process often produces ...large cutting forces which cause defects, such as delamination and burrs, due to the brittleness and high hardness of the material. Therefore, it is significant to precisely predict the grinding force. In published literature, the modelling of cutting force has been investigated based on brittle removal assumption. However, a ductile flow phenomenon exists simultaneously during the micro-grinding of CMCs. Hence, in this paper, we present an analytical model of grinding force with the consideration of ductile–brittle transition. Additionally, the critical cutting depth for removal mode transition can be applied to distinguish the ductile and brittle fracture removal processes. The establishment of the analytical model was on the basis of the research of single abrasive grain, including motion trajectory, micromechanical analysis, cutting time, and removal volume in ductile and brittle fracture processes during one cutting cycle. Thereafter, the final model was proposed with respect to the quantity of active abrasive grains in the cutting area. The trend of the experiment results was in good agreement with the predicted values of the analytical model.
Most umami substances were developed in aqueous extracts. In this study, we compared the molecular weight distributions and sensory characteristics of ethanol and aqueous Takifugu obscurus muscle ...extracts, and assessed their taste-related metabolites and peptide profile (<3 kDa) using nuclear magnetic resonance and nano liquid chromatography-mass spectrometry. The potential antioxidant peptide in ethanolic fraction was screened using Peptide Ranker, BIOPEP and quantum chemical simulations. The results indicated that 60% ethanolic extract fraction (60%-F) had the highest umami intensity and more palatable overall taste among all pufferfish extracts. It can be caused by more umami enhancing components such as Asp, Asn, Ala and 5′-AMP, and considerable umami-potential smaller peptides in 60%-F. 60%-F also showed an antioxidant activity, and several antioxidant peptides was screened. The present study indicated the relationship between extract solution and taste characterization, which provided more possibility for the exploitation of umami substances and screening potential activity peptides.
Intensifying urban stormwater runoff and pollution caused by urbanization and climate change threatens property and lives in cities around the world. Low-impact development (LID) is an effective ...approach to improve urban flood resistance, but there is a lack of quantitative evaluation criteria to determine the best scenario in the newly built and built-up urban areas. In this study, based on the Fuzzy Comprehensive Evaluation method (FCE), a multi-index evaluation system is established to quantify the LID performance for the environment, technology, economy, and society. For overcoming subjective arbitrariness, the Criteria Importance Though Intercriteria Correlation (CRITIC) and Analytical Hierarchy Process (AHP) methods are used to evaluate the weight of each evaluation index. The proposed method is demonstrated for the Xi’an City, China. Results show that the integrated configuration of green roof, infiltration pavement and grass swale has the best comprehensive efficiency under the proposed method. More specifically, the allocation of different LID combinations in the newly built area can effectively manage the flooding in this area. However, the comprehensive efficiency of increasing the diameter of the storm sewer is optimal in the built-up area. The increased pipe diameter can discharge more rainwater through the urban storm sewer and mitigate overflow. A multi-index evaluation framework beyond the traditional subjective evaluation standard is established, which can quantitatively evaluate the effectiveness of LID facilities. The proposed quantification evaluation method can provide an efficient recommendation for sponge city construction and evaluation.
Regulation of prodigiosin biosynthesis is received wide attention due to the antimicrobial, immunosuppressive and anticancer activities of prodigiosin. Here, we constructed a transposon mutant ...library in
S. marcescens
FS14 to identify genes involved in the regulation of prodigiosin biosynthesis. 62 strains with apparently different colors were obtained. Identification of the transposon insertion sites revealed that they are classified into three groups: the coding region of
cyaA
and two component system
eepS/R
and the promoter region of
rpoH
. Since the effect of
cyaA
and
eepS/R
genes on prodigiosin was extensively investigated in
Serratia marcescens
, we chose the mutant of
rpoH
for further investigation. Further deletion mutation of
rpoH
gene showed no effect on prodigiosin production suggesting that the effect on prodigiosin production caused by transposon insertion is not due to the deletion of RpoH. We further demonstrated that multicopy expression of RpoH reduced prodigiosin biosynthesis indicating that transposon insertion caused RpoH enhanced expression. Previous results indicate that RpoS is the sigma factor for transcription of
pig
gene cluster in FS14, to test whether the enhanced expression of RpoH prevents prodigiosin by competing with RpoS, we found that multicopy expression of RpoS could alleviate the prodigiosin production inhibition by enhanced RpoH. We proposed that multicopy expressed RpoH competes with RpoS for core RNA polymerase (RNAP) resulting in decreased transcription of
pig
gene cluster and prodigiosin production reduction. We also demonstrated that RpoH is not directly involved in prodigiosin biosynthesis. Our results suggest that manipulating the transcription level of sigma factors may be applied to regulate the production of secondary metabolites.
Based on theoretical analysis and numerical calculations, this study systematically investigated the changes in rice tillering dynamics and the simulation of stem tiller growth during the tillering ...stage using the farm water level as a regulation index for rice irrigation and drainage. Based on pit testing, the results of this study show that both flooding and drought in the tillering stage suppress the tiller output of rice and have a certain compensating effect following rehydration. Heavy drought during the tillering period reduced the effective tiller rate, while flooding and light drought had little effect on the effective tiller rate. Flooding and maintaining a high infiltration rate also increased the effective tiller rate. The primary kinetic model of tiller elongation (DMOR) was a good fit for the tiller elongation process (coefficients of determination of 0.99 or higher). In addition, the growth and extinction rates of the stem tiller extinction curves were fitted. The maximum growth rate of the stem tiller growth segment was ranked as CK > L1 > H1 > L2 > H2, and the maximum extinction rate of the stem tiller extinction segment was ranked as CK > H2 > H1 > L2 > L1, indicating that both flooding and drought during the tillering stage could reduce the growth and extinction rates of the stem tiller. This shows that both flooding and drought can reduce the growth and extinction rates of tillers.
Abstract
The National Genomics Data Center (NGDC), part of the China National Center for Bioinformation (CNCB), provides a family of database resources to support global research in both academia and ...industry. With the explosively accumulated multi-omics data at ever-faster rates, CNCB-NGDC is constantly scaling up and updating its core database resources through big data archive, curation, integration and analysis. In the past year, efforts have been made to synthesize the growing data and knowledge, particularly in single-cell omics and precision medicine research, and a series of resources have been newly developed, updated and enhanced. Moreover, CNCB-NGDC has continued to daily update SARS-CoV-2 genome sequences, variants, haplotypes and literature. Particularly, OpenLB, an open library of bioscience, has been established by providing easy and open access to a substantial number of abstract texts from PubMed, bioRxiv and medRxiv. In addition, Database Commons is significantly updated by cataloguing a full list of global databases, and BLAST tools are newly deployed to provide online sequence search services. All these resources along with their services are publicly accessible at https://ngdc.cncb.ac.cn.
Ti
2
AlNb has much application potential in the aerospace sector thanks to its outstanding material characteristics. Poor wear resistance, however, blocks its development. This study used LTUAM ...(longitudinal-torsional ultrasonic-assisted milling) to get the surface micro-texture of Ti
2
AlNb in order to address the issue. By comparing traditional milling (CM), the surface micro-texture and tribological characteristics were studied. On this basis, the kinematic characteristics of the elliptical vibration were explored, introducing the critical condition of the separated pattern. In addition, the torsion-rotation ratio was put forward to understand the separation characteristics. The corresponding finite element model exhibited these kinematic characteristics. The model also looked into how the cutting parameters affected the way surface microtexture was generated. Experimental results indicated that machined surfaces with uniform micro-texture were seen in LTUAM, whereas scratches predominated in CM. The variation of micro-texture and surface roughness was discussed in respect to cutting parameters. It has been demonstrated that a machined surface with uniform micro-texture had superior tribological properties. The friction coefficient under LTUAM was approximately 27.08% less than that in CM.
Vibrio cholerae is the causative bacteria of the diarrheal disease cholera, but it also persists in aquatic environments, where it displays an expression profile that is distinct from that during ...infection. Upon entry into the host, a tightly regulated circuit coordinates the induction of two major virulence factors: cholera toxin and a toxin-coregulated pilus (TCP). It has been shown that a set of bile salts, including taurocholate, serve as host signals to activate V. cholerae virulence through inducing the activity of the transmembrane virulence regulator TcpP. In this study, we investigated the role of calcium, an abundant mental ion in the gut, in the regulation of virulence. We show that whereas Ca
alone does not affect virulence, Ca
enhances bile salt-dependent virulence activation for V. cholerae The induction of TCP by murine intestinal contents is counteracted when Ca
is depleted by the high-affinity calcium chelator EGTA, suggesting that the calcium present in the gut is a relevant signal for V. cholerae virulence induction in vivo We further show that Ca
enhances virulence by promoting bile salt-induced TcpP-TcpP interaction. Moreover, fluorescence recovery after photobleaching (FRAP) analysis demonstrated that exposure to bile salts and Ca
together decreases the recovery rate for fluorescently labeled TcpP, but not for another inner membrane protein (TatA). Together, these data support a model in which physiological levels of Ca
may result in altered bile salt-induced TcpP protein movement and activity, ultimately leading to an increased expression of virulence.
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