Unperturbed dimensions and the g factor of a star-shaped polystyrene

Unperturbed dimensions of a star-shaped polystyrene near the θ temperatures, 25°C, 35°C and 45°C were determined by the measurement of intrinsic viscosity of the polymer in poor solvents. It was found that the inferred mean square radius of gyration of the star-shaped polystyrene, while much smaller than that of the linear polystyrene, as expected, changes much faster with the increase of temperature. The geometric factor g of the star-shaped polystyrene was found to be temperature-dependent.     

Synthesis,structural and magnetic properties of self-organized single-crystalline nanobricks of chalcopyrite CuFeS2

A thermal pyrolysis method has been developed to synthesize the tetragonal phase of chalcopyrite magnetic semiconductor CuFeS₂ nanoparticles. All nanoparticles have the same anisotropic brick-like shape, and the “bricks” are self-organized in a certain orientation, creating well-ordered nanocomposites. High-resolution transmission electron microscopy and electron diffraction data show that every nanobrick is a single crystal with a layered atomic structure and characteristic dimensions of about 5 nm × 20 nm in plane. Magnetic measurements support the antiferromagnetic spin structure and reveal the appearance of a small ferromagnetic component below 60 K. Magnetic anomalies observed in the zero-field cooled magnetization curves at low temperatures may be related to an appearance of magnetic moment at the Cu ion site. The Mössbauer spectra show that only about 50% of Fe atoms are in the magnetically ordered α-phase of chalcopyrite. The remaining Fe is non-magnetic and may be located either in the γ-phase of chalcopyrite or in isocubanite.     

国产立体测图卫星典型冰川区高精度DEM生产及质量对比

数字高程模型（Digital Elevation Model, DEM）是开展青藏高原冰川研究的重要基础数据。随着国产立体测图卫星的快速发展,自主可控地获取青藏高原冰川区高精度DEM成为可能。该研究综合采用资源三号、高分七号卫星的立体影像和激光测高数据,分别生成冰川区域5 m和2 m格网的DEM,并选择岗钦及普若岗日等两处冰川为实验区,将国产卫星DEM与国外的AW3D、SRTM、TanDEM、HMA DEM等多种开源数字高程模型进行对比分析,并采用ICESat-2星载激光测高数据开展DEM绝对高程精度验证。结果表明：与中等空间分辨率的开源DEM相比,基于国产立体测图卫星影像生产的DEM高程精度更优,且格网更精细、更能详细描述冰川末端纹理特征;与高空间分辨率数据集HMA DEM对比高程精度,资源三号DEM略差、高分七号DEM更优,且在覆盖完整性方面国产卫星DEM均优于HMA DEM。综上所述,基于国产立体测图卫星可以实现冰川区高精度DEM的获取,能够为青藏高原冰川研究提供自主可控、精度可靠的地形参考数据。     

Characterisation of Mechanical Properties of Magnetite‐Polymer Composite Films

Abstract: Time dependent mechanical properties of magnetic polymer films were investigated. These polymer films, synthesised by using solution polymerisation followed by the inverse emulsion process, consist of poly (MMA‐co‐MAA‐co‐BA) and different weight ratios of magnetite nano‐particles. This study deals with the influence of weight ratios of magnetite nano‐particles on the time dependent mechanical properties of hybrid copolymer films. The viscoelastic properties of aforementioned polymer films with 0, 20 and 40% of magnetite nano particles were studied. Ramp‐hold experiments were performed by using a custom‐made tension testing apparatus to evaluate the time dependent stress‐strain behaviour of magnetic polymer films under uniaxial tensile load at different loading strain rates. It can be seen that the magnetite nano‐particles weight percentage of polymer has a strong effect on the stress‐strain relations of polymer films. The polymer with a higher weight ratio of magnetite nano‐particles can sustain higher stress under the same test condition. Experimental data were fitted into 3, 5 and 7 parameter linear viscoelastic models. It is shown that the 7‐parameter Wiechert model leads to better curve‐fitting results for the magnetic polymer material under ramp‐hold experiments.     

Water permeation analysis on gas diffusion layers of proton exchange membrane fuel cells for Teflon-coating annotation

This study presents an analysis of water permeation of a polytetrafluoroethylene (PTFE)-coated gas diffusion layer (GDL) to determine the influence of hydrophobic treatment on the GDL for diagnosis of water flooding. It is found that the behaviour of water drainage is controlled by the pore configuration instead of the hydrophobicity in GDL. Better water drainage is achieved by the action of the Teflon coating in modulating the GDL pore configuration to give both a larger average pore size and a wider distribution of pore size. The results show that water penetration through the GDL must overcome a threshold surface tension defined by the largest pore range. A 30 wt.% PTFE coating of a GDL is shown to generate a satisfactory pore configuration, explaining the improved cell polarization performance with a lower driven pressure (∼1.91 kPa) and a higher rate of water drainage.     

Preparation of a DNA aptamer-Pt complex and its use in the colorimetric sensing of thrombin and anti-thrombin antibodies

DNA aptamers carrying Pt nanoparticles were prepared by the reaction of DNA aptamers (without functionalization with biotin, thiol, or other reactive groups) with K 2[PtCl 4] in solution at 60-90 degrees C. The DNA-Pt complexes possessed peroxidase enzymatic activity while retaining the specific binding ability of the aptamers. The enzymatic reaction of these complexes obeyed Michaelis-Menten kinetics. K M for the DNA-Pt complex was found to be on the same order as K M for hemin and hemin-DNA complex but 1 or 2 orders of magnitude higher than that of horseradish peroxidase. The rate of the reaction catalyzed by the DNA-Pt complex, k cat, was found to be on the same order as that of hemin and hemin-DNA complex but 2 or 3 orders of magnitude lower than that of horseradish peroxidase. Two types of DNAzyme-linked aptamer assays (DLAAs) were developed using these complexes, which successfully detected target proteins, with the sandwich type of DLAA targeting thrombin and the competitive type of DLAA targeting anti-thrombin IgA/G/M in serum. The DNA-Pt complexes retained their peroxidase enzymatic activity even after heat treatment. DLAAs having high thermal stability were developed using these complexes, which were free of animal and plant matter because neither antibodies nor horseradish peroxidase were used in their synthesis.     

The Effects of Solid-State Aging on the Intermetallic Compounds of Sn-Ag-Bi-In Solders on Cu Substrates

The growth behavior of the intermetallic compounds that formed at the interfaces between Sn-Ag-Bi-In solders and Cu substrates during solid-state aging is investigated. The compositions of the intermetallic compounds are Cu₃(Sn,In) near the Cu substrates and Cu₆(Sn,In)₅ near the solders; very little Bi or Ag was dissolved in the compounds. The aging temperatures were 120°C, 150°C, and 180°C for 5 days, 10 days, 20 days, and 40 days. The change in the morphology of Cu₆(Sn,In)₅ from scallop type to layer type was prominent at the aging temperature of 180°C. The thickness of the compound layers did not vary much at the lower aging temperatures but followed the diffusion- controlled mechanism at 180°C. Massive Kirkendall voids were observed in Cu₃(Sn,In) layers at the aging temperature of 180°C.     

航空轮胎胎面胶等效工况磨损特性研究

使用自主研制的航空轮胎等效摩擦磨损试验平台对航空轮胎不同服役工况下的摩擦行为进行等效拆解,研究加载条件对加速起飞、着陆瞬间和制动滑行摩擦工况对胎面胶磨损特性的影响。结果表明：3种工况中,制动滑行是航空轮胎胎面胶快速磨损的主要工况,制动滑行工况下胎面胶磨损率明显大于加速起飞和着陆瞬间工况下;等效摩擦磨损试验平台可实现航空轮胎胎面胶摩擦行为的模拟,可作为高耐磨胎面胶配方开发的评价工具。     

The dielectric property and phase transition of Sr-doping effect of Ba1−xSrxTi0.9Mn0.1O3-δ ceramic

In this work, we prepare Ba_1−xSr_xTi_0.9Mn_.01O_3-δ (x = 0.00, 0.01, 0.03, 0.05, and 0.07) ceramics by the mixed oxide method and study the relationship between phase transition and dielectric property of the ceramics. The phase of the samples transformed from a hexagonal phase to mixed phases due to the increase in Sr doping amount. The X-ray diffraction (XRD) profiles and Raman spectra of the samples also show the same phase transformation due to increasing Sr doping amount. The XRD pattern of the undoped sample indicates a single h-BaTiO₃ phase with P6₃/mmc symmetric space group, while the samples with high Sr doping amounts have a mixed phase with t-BaTiO₃ with P₄mm symmetric space group. The scanning electron microscopy images show two types of BaTiO₃ grains, which grew with increasing sintering temperature. With increasing Sr concentration, the K-values (relative dielectric constant) of the ceramics increased, while the Q_xf values (the quality factor multiplied by frequency) decreased, which indicate that the microwave dielectric property is related to phase transformation.