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Search Results: 1 - 10 of 65346 matches for " Hong Feng "
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Role of amino acid residues involved in the active cavity of proline iminopeptidase in catalytic activity  [PDF]
Kangkang Xing, Hong Feng
Advances in Biological Chemistry (ABC) , 2013, DOI: 10.4236/abc.2013.33032
Abstract: The proline iminopeptidase (PchPiPA) of the white-rot fungi Phanerochaete chrysosporium is an exopeptidase specific to catalyze hydrolysis of the N-terminal proline of peptides or proteins. Its catalytic cavity is comprised of a catalytic triad (Ser107, Asp264 and His292) and an oxyanion hole (His38, Gly39, Gly40 and Pro41). In this work, several amino acid residues involved in the catalytic cavity were selected for investigation of their influences on the catalytic activity by site-directed mutagenesis. It was shown that mutation of residues (Gly39 and Gly40) involved in oxyanion hole resulted in almost complete loss of catalytic activity largely due to changes in kcat. The other residues (Gly42 and Cys45) lined at the entrance of the active cavity also yielded a profound negative effect on the activity. Mutation of the other two residues Arg130 and Gly131 which were flanked spatially by the nucleophilic attacking active site of Ser107, caused different effects on the activity. R130Aincreased catalytic efficiency due to changes in both kcat and Km; while G131V decreased the value of kcat/Km mainly due to changes in kcat. And T111Aalso caused a negative effect on the kcat. Conclusively, these amino acid residues involved in active cavity were more susceptible to be negatively affected by mutation, suggested that the active cavity of proline iminopeptidase might evolve to be less plausible.
The Analysis of Stiffness for Rubbery Metallic Material Based on Mesoscopic Features  [PDF]
Hong Zuo, Hongbai Bai, Yuhong Feng
Materials Sciences and Applications (MSA) , 2011, DOI: 10.4236/msa.2011.26090
Abstract: In this article, deformation and mechanical response of a rubbery metallic material were investigated. First, the mesoscopic structural properties of the material and its evolution during part producing were analyzed and described in detail. Then the inherence relationship between the macroscopic mechanical properties and mesoscopic structural characteristics were studied, in which the related mesoscopic structural characteristics were limited in the basic unit (mm) scale such as the radius of metal wire and unit coil, etc. Furthermore, according to the mesoscopic properties of the material, a curved beam unit based on the mesoscopic scale and shape factor was introduced to bridge the mechanical response and the mesoscopic parameters such as the beam orientation and spatial distribution. In the end, a mesoscopic stiffness model was proposed, from which the macroscopic mechanical properties of material could be deduced from the mesoscopic characteristic size, shape and the mechanical properties of base metallic material.
Functional Characterization of CRISPR-Cas System in the Ethanologenic Bacterium Zymomonas mobilis ZM4  [PDF]
Ge Dong, Mingxiong He, Hong Feng
Advances in Microbiology (AiM) , 2016, DOI: 10.4236/aim.2016.63018
Abstract: CRISPR-Cas (clustered regularly interspaced short palindromic repeats—CRISPR associated proteins) is a RNA-guided defense immune system that prevents some genetic elements such as plasmids and virus from getting into the bacterial cells. Zymomonas mobilis is an ethanologenic bacterium, which encodes a subtype I-F CRISPR-Cas system containing three CRISPR loci and a far distant cas gene cluster. Reverse transcription (RT)-PCR analysis revealed that the CRISPR loci were transcribed on both strands. The Cas proteins were suggested to be expressed based on the previous transcriptomic analysis. Challenging with the invader plasmids containing the artificial protospacer with the protospacer adjacent motif (PAM) of NGG or GG exhibited immune interference activity. However, PAM motif of GG seems more effective than NGG in interference activity. Further, the artificial CRISPR arrays with the spacer sequences targeting to the specific genome sites could also lead to strong immune activity, resulting in almost no transformant grown on the agar plates. It was suggested that bacteria like Z. mobilis ZM4 are lack of the rejoining function to heal the double breakage of genomic DNA made by the CRISPR system. Conclusively, the Type I-F CRISPR-Cas system in Z. mobilis ZM4 is active to functionally defense the invading DNA elements.
Hypernuclear Magnetic Moments and λ--N Interaction in 17λO
中国物理快报 , 2007,
Abstract: Hypernuclear magnetic moment and λ--N interaction in 17λO has been studied within relativistic mean field theory. Without core polarization, the relativistic results are found to fit the Schmidt value well and not be sensitive to λ--N interaction. The relativistic magnetic moment is enhanced with nearly equal contributions of the relativistic and free masses. When λ hyperon occupies the l=0 or l=1 orbit, the effect of λ--N interaction on the magnetic moment of valence proton is different.
An Analysis on the Importance of Motivation and Strategy in Postgraduates English Acquisition
Ruizhen Feng,Hong Chen
English Language Teaching , 2009, DOI: 10.5539/elt.v2n3p93
Abstract: Postgraduates’ English acquisition is an intriguing but complex process. A lot of factors have contributed to the outcome of a learner’s acquisition, among them, motivation and strategy are playing a crucial role. Motivation is the driving force to encourage the learner to learn, while strategy being the techniques or devices for a learner to use for gaining knowledge. Since both belong to learner factors that may account for individual differences in postgraduates’ English acquisition process, it is essential to discuss and analyze them for Postgraduates’ English achievement.
Coupling of magnetization and structural distortions in multiferroic BiFeO3 : an ab initio density functional theory study
Hong-Jian Feng
Physics , 2007, DOI: 10.1088/0256-307X/25/2/086
Abstract: This paper has been withdrawn by the author due to a crucial citing error in equation 4.
Electronic structures and lattice dynamics of BaTiO3 and BiFeO3 : a comparative first-principles study
Hong-Jian Feng
Physics , 2007,
Abstract: First-principles calculations were performed to investigate the ferroelectric properties of barium titanate and bismuth ferrite, as well as phonon dispersion of BaTiO3, using density functional theory and density functional perturbation theory. Results show that the strong hybridization of Ti-O and Bi-O lead to the corresponding mechanisms for stabilizing the distorted structure. The spontaneous polarization of 59.4 \mu C/cm2 and 27.6 \mu C/cm2 were calculated for BiFeO3 and BaTiO3 respectively, using berry phase method within the modern theory of polarization. The stereochemical activity of Bi-6s long-pair, which was the driven mechanism for ferroelectricity in BiFeO3, was able to produce greater polarization than the Ti off-centring displacement in BaTiO3. New multiferroic perovskite type materials combined with these two ferroelectric instabilities were predicted to have a better ferromagnetic ordering in comparison with BiFeO3.
Spin transfer in ultrathin BiFeO3 film under external electric field
Hong-Jian Feng
Physics , 2012, DOI: 10.1209/0295-5075/101/67007
Abstract: First-principals calculations show that up-spin and down-spin carriers are accumulating adjacent to opposite surfaces of BiFeO3(BFO) film with applying external bias. The spin carriers are equal in magnitude and opposite in direction, and down-spin carriers move to the direction opposing the external electric field while up-spin ones along the field direction. This novel spin transfer properties make BFO film an intriguing candidate for application in spin capacitor and BFO-based multiferroic field-effect device.
Magnetism and electronic properties of BiFeO3 under lower pressure
Hong-Jian Feng
Physics , 2012, DOI: 10.1016/j.jmmm.2010.07.034
Abstract: Ab initio calculations show an antiferromagnetic-ferromagnetic phase transition around 9-10 GPa and a magnetic anomaly at 12 GPa in BiFeO3. The magnetic phase transition also involves a structural and insulator-metal transition. The G-type AFM configuration under pressure leads to an increase of the y component and decrease of the z component of the magnetization, which is caused by the splitting of the dz2 orbital from doubly degenerate eg states. Our results agree with recent experimental results.
The role of Coulomb and exchange interaction on the Dzyaloshinskii-Moriya interaction(DMI) in BiFeO3
Hong-Jian Feng
Physics , 2012, DOI: 10.1016/j.jmmm.2009.12.025
Abstract: Ab initio calculations show that the Dzyaloshinskii-Moriya interaction(DMI)and net magnetization per unit cell in BiFeO3 are reduced when U is increasing from 0 to 2.9 eV, and independent of $J$. Interestingly, the DMI is even destroyed as $U$ exceeds a critical value of 2.9 eV. We propose a simple model to explain this phenomenon and present the nature of the rotation of the magnetization corresponding to altered antiferrodistortive distortions under DMI in BiFeO3.
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