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Chatter causes machining instability and reduces productivity in the metal cutting process. It has negative effects on the surface finish, dimensional accuracy, tool life and machine life. Chatter identification is therefore necessary to control, prevent, or eliminate chatter and to determine the stable machining condition. Previous studies of chatter detection used either model-based or signal-based methods, and each of them has its drawback. Model-based methods use cutting dynamics to develop stability lobe diagram to predict the occurrence of chatter, but the off-line stability estimation couldn't detect chatter in real time. Signal-based methods apply mostly Fourier analysis to the cutting or vibration signals to identify chatter, but they are heuristic methods and do not consider the cutting dynamics. In this study, the modelbased and signal-based chatter detection methods were thoroughly investigated. As a result, a hybrid model- and signal-based chatter detection method was proposed. By analyzing the residual between the force measurement and the output of the cutting force model, milling chatter could be detected and identified efficiently during the milling process.
The in uence of granular friction on the mechanical behaviors of a granular system is a typical research realm that is still not yet fully understood because of the complexities and the discreteness of the granular system. In this study, a two-dimensional model of a granular system with biaxial compression is established by using the discrete element method (DEM). Using this DEM model, we investigate the macroscopic mechanical behaviors, the microscopic mechanical responses and the force chain distributions of a granular system in uenced by granular friction. Simulation results show that the granular friction has a prominent in uence on the stress-strain response, dilatancy behaviors, and peak strength of the granular system. The microscopic mechanical behaviors of the coordination number, the sliding fraction, and the mean mobilized friction coecient of the granular system are also shown to be markedly in uenced by the granular friction. The force chains in the granular system form an inhomogeneous distribution, and their intensities increase with increasing granular friction.
( Yan Yu Zhao ), ( Kun Meng ), ( Hui Ying Luo ), ( Pei Long Yang ), ( Peng Jun Shi ), ( Huo Qing Huang ), ( Ying Guo Bai ), ( Bin Yao ) 한국미생물 · 생명공학회 2011 Journal of microbiology and biotechnology Vol.21 No.8
A xylanase gene, xyn7c, was cloned from Paenibacillus sp. 12-11, an alkalophilic strain isolated from the alkaline wastewater sludge of a paper mill, and expressed in Escherichia coli. The full-length gene consists of 1,296 bp and encodes a mature protein of 400 residues (excluding the putative signal peptide) that belongs to the glycoside hydrolase family 10. The optimal pH of the purified recombinant XYN7C was found to be 8.0, and the enzyme had good pH adaptability at 6.5-8.5 and stability over a broad pH range of 5.0-11.0. XYN7C exhibited maximum activity at 55℃ and was thermostable at 50℃ and below. Using wheat arabinoxylan as the substrate, XYN7C had a high specific activity of 1,886 U/mg, and the apparent Km and Vmax values were 1.18 mg/ml and 1,961 ?mol/mg/min, respectively. XYN7C also had substrate specificity towards various xylans, and was highly resistant to neutral proteases. The main hydrolysis products of xylans were xylose and xylobiose. These properties make XYN7C a promising candidate to be used in biobleaching, baking, and cotton scouring processes.
Background: The prevalence and incidence of latent tuberculosis infection (LTBI) in patients with kidney transplant remains unclear. Methods: In this prospective study, we enrolled kidney transplant candidates (KTCs) and recipients (KTRs) from 2014 to 2018. We defined LTBI as a positive result of QuantiFERON-TB Gold In-tube (QFT). We analyzed the predictors for LTBI acquisition and followed QFT test for 2 years among those initially without LTBI. Results: Of 425 patients enrolled, 305 (71.8%) patients belonged to the KTC group and 120 (28.2%) to the KTR group. The initial QFT showed positive results in 33 (10.8%) and 25 (20.8%) in the KTC and KTR groups, respectively (p=0.007). The QFT response value in LTBI patients was higher in the KTR group than in the KTC group (1.85 vs. 1.06 IU/ml, p=0.046). Multivariate logistic regression showed that old age, absence of Bacillus Calmette-Guerin scar, and KTR group were independent factors for positive LTBI. For participants with initial negative QFT, positive QFT conversion within 2-year follow-up was higher after kidney transplantation (20%) than in KTCs (5.5%) (p=0.032). Conclusion: This study is the first cohort to follow up LTBI status in patients with kidney transplant and shows its higher prevalence and incidence in those belong to KTR. It indicates that surveillance of LTBI after renal transplantation is important.
A model of process damping in milling was developed in this study. The process damping is a critical parameter to increasethe stable cutting region at low cutting speed to avoid chatter. The previous studies conducted experiments to estimate theprocess damping. Nevertheless, it is time and cost consuming. A model of dynamic cutting force was employed in this study. The plowing force generated by the fl ank-wave contact is considered as the main source of process damping to dissipatevibratory energy during cutting. In addition to the material properties and plowing force, the eff ects of chatter amplitudeand wavelength, which result in the various indentation conditions and aff ect the coeffi cient of process damping, were alsoconsidered. The consideration of wavy contact surface and indentation area in this model allows quick determination of cuttingstability conditions with high accuracy. The process damping coeffi cient estimated by the proposed model successfullyrepresented the eff ect of the tool wear on chatter because of the change of tool geometry. Experiments were conducted toverify the new model.
Abrasive flow polishing plays an important role as a type of precision nanomachining technology. In this study, the polishing mechanism of abrasive flow was studied using numerical simulations based on molecular dynamics. In order to study the polishing mechanism of polycrystalline materials, the molecular dynamics simulation of three kinds of polycrystalline materials was carried out. The cutting force, energy, friction coefficient, and surface morphology (during the microcutting process) of the three workpiece materials were analyzed. The analysis shows that the adhesion of atoms in the contact area on the workpiece surface will be affected by liquid phase and the type of abrasive particles, and then the surface quality polished by the abrasive flow will also be influenced. The onset of an abrasive flow polishing process involving plastic deformation (including the nucleation and migration of dislocations, grain boundary shape deformation, and deformation twinning) was observed on the workpiece surface. Defects strongly competed with each other in the form of interactions of dislocations and the grain boundaries, resulting in the migration of twin boundaries. A further analysis of the numerical results for different cutting depths and abrasive properties of the workpiece materials will be useful for understanding the different cutting effects.
Kiwifruits (Actinidia chinensis cv. Hongyang) were treated by direct cooling and gradual cooling to investigate the effect of cooling treatment on chilling injury. The direct cooling fruits were immediately cooled at 0℃ after harvest. The gradual cooling fruits were held for 3 days at 5℃ (from 5℃ to 0℃), or for 7 days at 2℃(from 2℃ to 0℃), or decreased in temperature from 15℃ to 5℃ by 5℃ at 1 days intervals and then maintained at 5℃ for 3 days plus a subsequent period of of 7 days at 2℃ (from 15℃ to 0℃). After the above treatments, then those fruit were stored at 0 ± 0.5℃, 90% to 95% RH for 80 days. Gradual cooling (from 15℃ to 0℃) significantly maintained higher percentage of accepted fruit and lower chilling injury index and chilling injury incidence of fruit compared with the direct cooling. Some attributes were then assayed in the fruits treated with gradual cooling (from 15℃ to 0℃). Gradual cooling (from 15℃ to 0℃) inhibited increases in membrane permeability, malondialdehyde content, superoxide anion production rate, and H2O2 content. At the same time, fruit cooled gradually (from 15℃ to 0℃) exhibited higher superoxide dismutase, catalase, ascorbate peroxidase, and peroxidase activities than those treated by direct cooling during storage. The present study indicated that enhancement in antioxidant enzyme activity may be attributed to the reduction in CI symptoms by the gradual cooling treatment (from 15℃ to 0℃).
( Yan An Li ), ( Pei Long Yang ), ( Kun Meng ), ( Ya Ru Wang ), ( Hui Ying Luo ), ( Ning Feng Wu ), ( Yun Liu Fan ), ( Bin Yao ) 한국미생물 · 생명공학회 2008 Journal of microbiology and biotechnology Vol.18 No.1
A DNA fragment containing 2,079 base pairs from Bacillus circulans CGMCC 1416 was cloned using degenerate PCR and inverse PCR. An open reading frame containing 981 bp was identified that encoding 326 amino acids residues, including a putative signal peptide of 31 residues. The deduced amino acid sequence showed the highest identity (68.1%) with endo-β-1,4-D-mannanase from Bacillus circulans strain K-1 of the glycoside hydrolase family 5 (GH5). The sequence encoding the mature protein was cloned into the pET-22b(+) vector and expressed in Escherichia coli as a recombinant fusion protein containing an N-terminal hexahistidine sequence. The fusion protein was purified by Ni2+ affinity chromatography and its hexahistidine tag cleaved to yield a 31-kDa β-mannanase having a specific activity of 481.55 U/mg. The optimal activity of the purified protein, MANB48, was at 58℃ and pH 7.6. The hydrolysis product on substrate locust bean gum included a monosaccharide and mainly oligosaccharides. The recombinant MANB48 may be of potential use in the feed industry.
Based on the theory of porous media, an interaction system of a floating pile and a saturated soil in cylindrical coordinates subjected to vertical harmonic load is presented in this paper. The surrounding soil is separated into two distinct layers. The upper soil layer above the level of pile base is described as a saturated viscoelastic medium and the lower soil layer is idealized as equivalent spring-dashpot elements with complex stiffness. Considering the cylindrically symmetry and the pile-soil compatibility condition of the interaction system, a frequency-domain analytical solution for dynamic impedance of the floating pile embedded in saturated viscoelastic soil is also derived, and reduced to verify it with existing solutions. An extensive parametric analysis has been conducted to reveal the effects of the impedance of the lower soil base, the interaction coefficient and the damping coefficient of the saturated viscoelastic soil layer on the vertical vibration of the pile-soil interaction system. It is shown that the vertical dynamic impedance of the floating pile significantly depends on the real stiffness of the impedance of the lower soil base, but is less sensitive to its dynamic damping variation; the behavior of the pile in poro-visco-elastic soils is totally different with that in single-phase elastic soils due to the existence of pore liquid; the effect of the interaction coefficient of solid and liquid on the pile-soil system is limited.