C-Fe chains due to segregated carbon impurities on Fe(1 0 0)

Bulk carbon impurities segregate at the Fe(1 0 0) surface and, upon thermal annealing, can form metastable surface phases with local and long range order and peculiar electronic properties. We present a surface science study of C-segregated Fe(1 0 0) with scanning tunneling microscopy, angle resolved photoemission, and ab initio calculations of the surface structure and electron states. In particular the c(3√2 × √2) structure, observed for 0.67 atomic layers of C segregated at the iron surface, is found to be due to self-organized carbon stripes made of zig-zag chains. The strong hybridization between C and Fe was observed in ARPES spectra.     

Property improvement of pulsed laser deposited boron carbide films by pulse shortening

Growth characteristics and surface morphology of boron carbide films fabricated by ablating a B₄C target in high vacuum with a traditional KrF excimer laser and a high brightness hybrid dye/excimer laser system emitting at the same wavelength while delivering 700 fs pulses are compared. The ultrashort pulse processing is highly effective. Energy densities between 0.25 and 2 J cm⁻² result in apparent growth rates ranging from 0.017 to 0.085 nm/pulse. Ablation with nanosecond pulses of one order of magnitude higher energy densities yields smaller growth rates, the figures increase from 0.002 to 0.016 nm/pulse within the 2-14.3 J cm⁻² fluence window. 2D thickness maps derived from variable angle spectroscopic ellipsometry reveal that, when ablating with sub-ps pulses, the spot size rather than the energy density determines both the deposition rate and the angular distribution of film material. Pulse shortening leads to significant improvement in surface morphology, as well. While droplets with number densities ranging from 1 × 10⁴ to 7 × 10⁴ mm⁻² deteriorate the surface of the films deposited by the KrF excimer laser, sub-ps pulses produce practically droplet-free films. The absence of droplets has also a beneficial effect on the stoichiometry and homogeneity of the films fabricated by ultrashort pulses.     

使用超声估计肌肉疲劳的初步研究

表面肌电信号把神经肌肉活动和肌肉收缩联系起来，已被视为一种估计肌肉疲劳比较客观的方法，但也存在一些不足。另一方面，超声已广泛应用于医学诊断和研究，在骨骼肌方面也有不少研究报道，但还未见文献报道超声用于肌肉疲劳的估计。本文介绍一套自行开发的新的同步连续采集B超图像、力矩和肌电信号的采集系统，并利用它对肱二头肌的肌肉疲劳进行了估计。试验表明在30秒的肌肉疲劳过程中，肌肉厚度会以非线性的方式增加。     

Fabrication of material-independent morphology gradients for high-throughput applications

Gradient surfaces allow rapid, high-throughput investigations and systematic studies in many disparate fields, including biology, tribology and adhesion. We describe a novel method for the fabrication of material-independent morphology gradients, involving a two-step process of particle erosion followed by a chemical polishing procedure that preferentially removes features with a small radius of curvature as a function of time. Gradients are fabricated on aluminium surfaces, but they may be readily transferred to other materials via a replication technique, which allows for the production of identical roughness gradient samples with any chosen surface chemistry. The gradients have been characterized by means of scanning electron microscopy and optical profilometry. Standard roughness parameters (Ra, Rq, Rz, Sm and Sk) were calculated from optical profilometry data. The roughness has also been assessed over different wavelength windows by means of a fast Fourier transformation approach.     

Microwave synthesis of magnetic Fe3O4 nanoparticles used as a precursor of nanocomposites and ferrofluids

Methods to synthesize magnetic Fe₃O₄ nanoparticles and to modify the surface of particles are presented in the present investigation. Fe₃O₄ magnetic nanoparticles were prepared by the co-precipitation of Fe³⁺ and Fe²⁺, NH₃·H₂O was used as the precipitating agent to adjust the pH value, and the aging of Fe₃O₄ magnetic nanoparticles was accelerated by microwave (MW) irradiation. The obtained Fe₃O₄ magnetic nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and vibrating sample magnetometer (VSM). The average size of Fe₃O₄ crystallites was found to be around 8–9 nm. Thereafter, the surface of Fe₃O₄ magnetic nanoparticles was modified by stearic acid. The resultant sample was characterized by FT-IR, scanning electron microscopy (SEM), XRD, lipophilic degree (LD) and sedimentation test. The FT-IR results indicated that a covalent bond was formed by chemical reaction between the hydroxyl groups on the surface of Fe₃O₄ nanoparticles and carboxyl groups of stearic acid, which changed the polarity of Fe₃O₄ nanoparticles. The dispersion of Fe₃O₄ in organic solvent was greatly improved. Effects of reaction time, reaction temperature and concentration of stearic acid on particle surface modification were investigated. In addition, Fe₃O₄/polystyrene (PS) nanocomposite was synthesized by adding surface modified Fe₃O₄ magnetic nanoparticles into styrene monomer, followed by the radical polymerization. The obtained nanocomposite was tested by thermogravimetry (TG), differential scanning calorimetry (DSC) and XRD. Results revealed that the thermal stability of PS was not significantly changed after adding Fe₃O₄ nanoparticles. The Fe₃O₄ magnetic fluid was characterized using UV–vis spectrophotometer, Gouy magnetic balance and laser particle-size analyzer. The testing results showed that the magnetic fluid had excellent stability, and had susceptibility of 4.46×10⁻⁸ and saturated magnetization of 6.56 emu/g. In addition, the mean size d (0.99) of magnetic Fe₃O₄ nanoparticles in the fluid was 36.19 nm.     

一类二元相关威布尔分布的可靠性问题

本文考虑生存函数为${\ol{F}(x_{1},x_{2})}=\exp\{-[(x_{1}^{1/\alpha}/\theta_{1})^{1/\delta}+(x_{2}^{1/\alpha}/\theta_{2})^{1/\delta}]^{\delta}\},\;x_{i}>0,\;\alpha>0$, $1\geq\delta>0,\;\theta_{i}>0\;(i=1,2)$的二元威布尔分布的两种可靠性问题, 提出可靠度$\pr$的估计并讨论了它们的渐近性, 最后还作了模拟计算.     

ALICE实验中光子谱仪的触发选判机制的模拟研究

对ALICE实验光子谱仪的触发选判机制进行了模拟研究, 内容包括: 1) 对光子谱仪的能量重建性能进行了研究, 通过计算机模拟检验光子谱仪探测器对大横动量范围的入射粒子的能量重建性能; 2) 对光子谱仪探测器的事件触发效率进行了研究, 通过计算机模拟分析触发阈值的选取并计算触发效率; 3) 对光子谱仪探测器的事件触发频率进行了研究, 通过计算机模拟对p-p和Pb-Pb两种碰撞模式下的触发频率分别进行了估算和讨论.     

SSIMS analysis of organics, polymer blends and interfaces

This paper gives a critical review on the applications of ToF SIMS in the areas of polymer additive characterization and in the study of polymer blends and interfaces. Polymer additives can readily be identified by ToF SIMS using their parent molecular ions or characteristic fragments. This analytical capability has been successfully applied to monitor the migration or segregation of additives during polymer processing. ToF SIMS is an ideal analytical tool for the study of polymer blends and interfaces because it is able to provide information on both surface composition and morphology. In combination with other analytical techniques such as AFM and XPS, ToF SIMS chemical imaging capability has opened up new horizons in the investigation of complex polymer blend systems. Finally the main advantages and limitations of ToF SIMS in these application areas are also discussed.     

Electron beam induced modification of poly(ethylene terephthalate) films

Electron beam processing of poly(ethylene terephthalate) (PET) films is found to promote significant changes in the melting heat, intrinsic viscosity and polymer film-liquid (water, isooctane and toluene) boundary surface tension. These properties are featured with several maximums depending on the absorbed dose and correlating with the modification of PET surface functionality. Studies using adsorption of acid-base indicators and IR-spectroscopy revealed that the increase of PET surface hydrophilicity is determined by the oxidation of methylene and methyne groups. Electron beam treatment of PET films on the surface of N-vinylpyrrolidone aqueous solution provided graft copolymerization with this comonomer at optimum process parameters (energy 700 keV, current 1 mA, absorbed dose 50 kGy).     

CuPc molecules adsorbed on Au(1 1 0)-(1 × 2): growth morphology and evolution of valence band states

We present the growth morphology, the long-range ordering, and the evolution of the valence band electronic states of ultrathin films of copper phthalocyanine (CuPc) deposited on the Au(1 1 0)-(1 × 2) reconstructed surface, as a function of the organic molecule coverage. The low energy electron diffraction patterns present a (5 × 3) reconstruction from the early adsorption stages. High-resolution UV photoelectron spectroscopy data show the disappearance of the Au surface states related to the (1 × 2) reconstruction, and the presence of new electronic features related to the molecule-substrate interaction and to the CuPc molecular states. The CuPc highest occupied molecular orbital gradually emerges in the valence band, while the interface electronic states are quenched, upon increasing the coverage.