Browsing by Author "Li, J"
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- ItemCrystal growth through progressive densification identified by synchrotron small-angle x-ray scattering(American Chemical Society, 2008-05) Li, J; Cookson, DJ; Gerson, ARFor the first time, evolution of the interfacial structure of aluminum hydroxide nuclei forming within concentrated caustic solutions has been examined in situ in real time. In both dilute and concentrated caustic aluminate solutions (NaOH = 1.0 and 3.0 M, respectively, [NaOH]/[Al] = 1.22), the measured synchrotron small-angle X-ray scattering data indicate distinctly different surface structures throughout the maturation process. In the dilute solution, the data are consistent with a thin layer of less dense, recently accreted material on the surface of large fully dense particles-consistent with the familiar model process of species attachment to well-faceted surfaces. In contrast to this, the data for the concentrated solution are consistent with large diffuse particles growing with a mass fractal dimension of approximately 2.5 which density to form rough surface fractal particles on maturation. This unusual densification crystallization mechanism may occur in analogous concentrated systems where the fractal structures may be entropically stablized. © 2008, American Chemical Society
- ItemThe formation of eutectic phases and hot cracks in one Ni–Mo–Cr superalloy(Elsevier B. V., 2016-03-05) Li, J; Shrestha, SL; Long, Y; Zhijun, L; Xintai, ZThe structure and the formation mechanism of brittle eutectic phases and hot cracks formed at grain boundaries were investigated in two Ni-Mo-Cr superalloys with different silicon contents (0.06 and 0.46 wt.%). The eutectic phases and hot cracks can be observed along the rolling direction in the 0.46 wt.% Si heat when heated to 1335 °C or a higher peak temperature up to 1365 °C. Exposure to the higher peak temperatures resulted in the formation of larger eutectic phases and hot cracks in the higher silicon heat. Conversely, there are fewer eutectic phases and smaller hot cracks forming in the low-silicon heat when heated to 1365 °C. The eutectic phases were identified as γ-M6C′ type. Based on the constitutional liquation theory and thermodynamic calculations, it was found that the formation of the eutectic phases and hot cracks is due to the localized melting of primary M6C carbides and surrounding Si-riched matrix. The degree of elements segregation in liquid films determines whether liquid films solidify into eutectic phases or cause hot cracks. This model can reasonably explain the observed phenomena and contribute to designing appropriate solid-solution treatment process and welding procedure to avoid brittle phases and cracks in the Ni-Mo-Cr superalloy. © 2015 Elsevier B. V.
- ItemAn in vitro model to investigate the interactions between antimicrobial peptides and the outer membrane of gram-negative pathogens(Australian Institute of Nuclear Science and Engineering, 2016-11-29) Han, ML; Shen, HH; Zhu, Y; Le Brun, AP; Holt, SA; Roberts, K; Song, JN; Cooper, MA; Moskowitz, SM; Velkov, T; Li, JIncreasing antibiotic resistance in Gram-negative bacteria led to polymyxins as the last therapy. Polymyxins present their antimicrobial activity through an initial electronical interaction with lipid A in the outer membrane (OM) of GNB, and the most common mechanism of polymyxin resistance is through modifications of lipid A with positively charged groups, such as 4-amino-L-arabinose (L-Aar4N) or phosphoethanolamine (pEtN). However, it is notable that Gram-negative bacteria employ a combination of charge-charge repulsion mechanism and the modification to fatty acyl chains of lipid A to obtain high-level polymyxin resistance. Hence, we designed hydrophobic polymyxin-related lipopeptides in order to overcome modified lipid A to insert into the outer membrane of Gram-negative bacteria. In this study, we employed neutron reflectometry (NR) study to investigate the interactions between lipid A and polymyxins. Lipid A was extracted from polymyxin-susceptible and -resistant pseudomonas aeruginosa strains, and analysed using ESI-MS in the negative ion mode. The asymmetric lipid A: deuterated DPPC bilayers were deposited on SiO2 surfaces by combined Langmuir-Blodgett and Langmuir-Schaefer disposition methods, and characterised by neutron reflectometer. Our results showed L-Ara4N modified lipid A was observed in polymyxin-resistant PAKpmrB6 strain, but not in the wild-type PAK strain. The NR data obtained from unmodified lipid A: DPPC bilayer was fitted into a five-layer model. Whereas, a six-layer model containing an extra outer headgroup was established for L-Ara4N modified lipid A: d-DPPC bilayer. Our results showed a dense of PMB (volume fraction of >20%) bound to the surface of both unmodified and modified lipid A: DPPC bilayers. While it is notable that the significant changes in NR profiles obtained from H2O contrast indicated about 15.8% and 6.1% of PMB penetrated into the wild-type lipid A headgroup and fatty acyl chains, respectively, but without penetration into L-Ara4N-lipid A: d-DPPC bilayer. However, the employment of octpeptin A3 induced higher hydrophobic interactions with L-Ara4N-lipid A: d-DPPC bilayer. Our study provides an in vitro model to investigate the interactions of polymyxins with OM bilayers in GNB, and confirmed that lipid A modification with L-Ara4N was certainly to reduce the penetration of PMB into bacterial membranes. Remarkably, the higher binding affinity between octapeptin A3 and L-Ara4N modified lipid A indicated its potential to be the new generation antibiotics for the therapy of infections caused by multi-drug resistant Gram negative bacteria.
- ItemNarrowed bandgaps and stronger excitonic effects from small boron nitride nanotubes(Elsevier, 2009-07-16) Yu, J; Yu, DH; Chen, YS; Chen, H; Lin, MY; Cheng, BM; Li, J; Duan, WThe bandgap of boron nitride nanotubes (BNNTs) is generally considered to be independent on tube radius and chirality. However, we have observed that the bandgaps of BNNTs do depend on the tube size. Photoluminescence excitation spectroscopy with variable photon energies in vacuum ultraviolet (VUV) range revealed that the bandgap becomes smaller when the tube diameter decreases. This is consistent with red-shifted luminescent emissions. The strong interactions between excitons and phonons are possibly responsible for the bandgap narrowing as the function of nanotube size. © 2009, Elsevier Ltd.
- ItemPolymyxin-induced lipid A deacylation in pseudomonas aeruginosa perturbs polymyxin penetration and confers high-level resistance(ACS Publications, 2017-11-28) Han, ML; Velkov, T; Zhu, Y; Roberts, KD; Le Brun, AP; Chow, SH; Gutu, AD; Moskowitz, SM; Shen, HH; Li, JPolymyxins are last-line antibiotics against life-threatening multidrug-resistant Gram-negative bacteria. Unfortunately, polymyxin resistance is increasingly reported, leaving a total lack of therapies. Using lipidomics and transcriptomics, we discovered that polymyxin B induced lipid A deacylation viapagL in both polymyxin-resistant and -susceptible Pseudomonas aeruginosa. Our results demonstrated that the deacylation of lipid A is an “innate immunity” response to polymyxins and a key compensatory mechanism to the aminoarabinose modification to confer high-level polymyxin resistance in P. aeruginosa. Furthermore, cutting-edge neutron reflectometry studies revealed that an assembled outer membrane (OM) with the less hydrophobic penta-acylated lipid A decreased polymyxin B penetration, compared to the hexa-acylated form. Polymyxin analogues with enhanced hydrophobicity displayed superior penetration into the tail regions of the penta-acylated lipid A OM. Our findings reveal a previously undiscovered mechanism of polymyxin resistance, wherein polymyxin-induced lipid A remodeling affects the OM packing and hydrophobicity, perturbs polymyxin penetration, and thereby confers high-level resistance. © 2017 American Chemical Society
- ItemStructural evolution and high-voltage structural stability of Li(NixMnyCoz)O2 electrodes(American Chemical Society, 2018-12-17) Goonetilleke, D; Sharma, N; Pang, WK; Peterson, VK; Petibon, R; Li, J; Dahn, JRPositive electrode materials remain a limiting factor for the energy density of lithium-ion batteries (LIBs). Improving the structural stability of these materials over a wider potential window presents an opportune path to higher energy density LIBs. Herein, operando neutron diffraction is used to elucidate the relationship between the structural evolution and electrochemical behavior for a series of Li-ion pouch cells containing Li(NixMnyCoz)O2 (x + y + z = 1) electrode chemistries. The structural stability of these electrodes during charge and discharge cycling across a wide potential window is found to be influenced by the ratio of transition-metal atoms in the material. Of the electrodes investigated in this study, the Li(Ni0.4Mn0.4Co0.2)O2 composition exhibits the smallest magnitude of structural expansion and contraction during cycling while also providing favorable structural stability at high voltage. Greater structural change was observed in electrodes with a higher Ni content, while decreasing inversely to the Ni and Co content in the positive electrode. The combination of structural and electrochemical characterization of a wide range of NMC compositions provides useful insight for the design and application of ideal electrode compositions for long-term cycling and structural stability during storage at the charged state. © 2018 American Chemical Society
- ItemThree-dimensional stress distribution of surplus assembled 7050Al alloy ring and plug determined by neutron diffraction(Science China Press Co., Ltd, 2013-01-01) Sun, GA; Wang, XL; Wu, ED; Li, J; Chen, YZ; Chen, B; Sheng, LS; Luzin, V; Gyula, TThe hoop, radial and axial stress and strain distribution of surplus assembled 7050Al alloy ring and plus were investigated by neutron diffraction method. The measured results from crystal planes (200) and (311) are coincided with the data obtained by analytical calculation and international standard sample experiment. The discontinuous stress and strain at the interference of ring and plug can be clearly shown by the neutron diffraction method. Monte Carlo method was used to simulate the neutron diffraction process to reduce the deviation of the stress at the surface. The results show that the measured accuracy can be improved when the slits are substituted by the radial collimation. Compared the results obtained from (311) and (200) with analytical calculation, it reveals that the stress distribution among crystal planes will cause system deviation. Therefore the experiment accuracy may be further improved if the inner plane stress could be evaluated. The results also indicate that the strain accuracy will be affected by microstress and texture, and the gauge volume should be reduced as small as possible at the region where the stress distribution is steep. ©2020 Science China Press Co. Ltd.