Effect of variable particle size reinforcement on mechanical and wear properties of 6061Al–SiCp composite

Abstract

The influence of reinforcement particle size variation plays a major role on the properties of Al–SiC_p composite. Therefore, this study aim to investigate the mechanical and wear performance of single particle size (SPS) and multiple particle size (MPS) Al–SiC_p composite prepared by stir casting process. The SPS comprises three categories; fine (15 μm), intermediate (40 μm) and coarse (80 μm) particle sizes and combination of the three sizes accounts for the MPS in the ratio 1:1:2, respectively. Oxidation of the SiC_p and addition of 1 wt% Mg during composite processing resulted to interface reaction products such as MgO (magnesium oxide) and MgAl₂O₄ (magnesium aluminate) which suppresses the potential formation of undesired Al₃C₄ (aluminium carbide). The study reveals that MPS composite improved the hardness and impact properties with enhanced wear performance compared to SPS composite. Characterization of the composite morphology and phases was performed using scanning electron microscope and X-ray diffraction analysis. This study provides an effective method of optimizing the properties of Al–SiC_p composite by integrating MPS with low volume fraction of reinforcement phase.     

基于近红外光谱和仿生模式识别玉米品种快速鉴别方法

文章提出了一种采用近红外光谱快速鉴别玉米品种的新方法,并对不同品种的玉米种子建立了相应的鉴别模型。对7个玉米品种共140个样本,通过近红外光谱仪扫描获得4 000～12 000 cm-1波段范围内的光谱数据。为了消除噪声、提高数据处理效率,对原始数据进行了归一化预处理,采用固定尺寸移动窗口渐进因子法(fix-sized moving window evolving factor analysis)寻找特征波段,使用主成分分析(PCA)方法得到能反映玉米种子99.96%光谱信息的5个主成分,进而利用仿生模式识别(biomimetic pattern recognition)方法建立玉米品种的鉴别模型。对于每个品种中的20个样本,随机挑选10个样本作为训练样本,其余10个样本作为第一测试集,其他品种共120个样本作为第二测试集。在对第二测试集平均正确拒识率达到99.1%的情况下,对第一测试集中的样本取得了94.3%的平均正确识别率。该方法具有较高的鉴别准确度,可以作为一种快速无损的玉米品种鉴别方法。     

基于最小平均距离免疫算法的模糊红外图像分割

由于犯罪分子利用各种方法来避开传统的刑侦图像技术,因而红外图像逐渐成为获取犯罪现场痕迹的有效手段。然而,从犯罪现场拍摄的红外图像其目标痕迹大多是弱化的,所以在这类红外图像中分割目标是一项具有挑战性的任务。已有基于生物免疫的各类算法尚未明确描述免疫分割作用领域,以及免疫网络算法模型中的免疫识别距离。为实现对目标痕迹弱化红外图像的有效分割,提出了一种新的具有免疫作用领域和最小平均免疫识别距离的人工免疫构架,设计了一种具备最小平均距离免疫域的免疫分割算法。该方法根据红外图像的特点,采用多步分类算法、免疫变异和自适应免疫最小均距识别方法,根据目标区域和背景区域的总体统计特性实现最佳分类。实验结果表明,提出的基于最小平均距离的免疫算法能够有效地分割目标弱化的红外图像。与经典的边缘模板和区域模板方法相比,该算法具有更好的分割效果,尤其是针对目标弱化红外图像的分割,该算法能够较好地给出五个手指的边界轮廓。     

Effects of Metallic Silver Particles on Resonance Energy Transfer Between Fluorophores Bound to DNA

We examined the effects of metallic silver island films on resonance energy transfer (RET) between a donor and acceptor bound to double helical DNA. The donor was 4',6-diamidino-2-phenylindole (DAPI) and the acceptor was propidium iodide (PI). Proximity of the labeled DNA to the silver particles resulted in a dramatic increase in RET as seen from the emission spectra and the donor decay times. Proximity to silver particles results in an increase of the Förster distance from 35 Å an to an apparent value of 166 Å. These results suggest a new type of DNA hybridization assays based on RET over distances much longer than the free-space Forster distance.     

Hybrid ferromagnetic/semiconductor heterostructures for spintronics

Heterostructures that integrate conventional semiconductors with ferromagnetic semiconductors and ferromagnetic metals are important for developing a framework for semiconductor spintronics. We describe recent efforts to study ‘hybrid’ ferromagnetic/semiconductor heterostructures that combine conventional III-V and II-VI semiconductors with the ferromagnetic semiconductor (Ga,Mn)As and the ferromagnetic metal MnAs. We focus on the characteristics of two novel classes of heterostructures: (a) (Ga,Mn)As/AlAs/MnAs magnetic tunnel junctions (MTJs) that provide an all-electrical scheme for probing spin injection from metals into GaAs and (b) n-ZnSe/(Ga,Mn)As heterojunction diodes that surprisingly exhibit a magnetically-driven photoconductivity.     

Performance of Distributed Fiber Raman Amplifier Based on Hybrid Cladding Photonic Crystal Fiber

Abstract

This article presents a feasibility study for using a hybrid cladding photonic crystal fiber as a distributed fiber Raman amplifier based transmission link with negligible confinement losses and flattened dispersion characteristics. The simulation results clearly indicate that a bit error rate of 10^?9 can be maintained at the end of a (4 × 170)-km distributed fiber Raman amplifier link operating with 40 Gbps and 0.6 dBm transmit power if 20 dBm of pump power is used for each span.     

Insulating ferromagnetism in La4Ba2Cu2O10: an Ab initio wannier function analysis

Microscopic mechanisms of the puzzling insulating ferromagnetism of half-filled La4Ba2Cu2O10 are elucidated with energy-resolved Wannier states. The dominant magnetic coupling, revealed through evaluated parameters (t, U, and J), turns out to be the intersite direct exchange, a currently ignored mechanism that overwhelms the antiferromagnetic superexchange. By contrast, the isostructural Nd4Ba2Cu2O10 develops the observed antiferromagnetic order via its characteristics of a 1D chain. Surprisingly, the in-plane order of both cases is not controlled by coupling between nearest neighbors. An intriguing pressure-induced ferromagnetic to antiferromagnetic transition is predicted.     

Diffraction of evanescent waves and nanomechanical displacement detection

Sensitive displacement detection has emerged as a significant technological challenge in mechanical resonators with nanometer-scale dimensions. A novel nanomechanical displacement detection scheme based upon the scattering of focused evanescent fields is proposed. The sensitivity of the proposed approach is studied using diffraction theory of evanescent waves. Diffraction theory results are compared with numerical simulations.     

Two-proton correlations in the decay of 45Fe

The decay of extremely neutron-deficient 45Fe has been studied in detail by means of a novel type of a gaseous detector employing digital imaging to record tracks of charged particles. The two-proton radioactivity channel was clearly identified. For the first time, the angular and energy correlations between two protons emitted from the nuclear ground state were determined, indicating the genuine three-body character of this decay. The half-life of 45Fe was found to be 2.6+/-0.2 ms and the observed 2p decay branching ratio is 70+/-4%.     

Dynamic electromagnetic processes in micro-wires inferred from GMI-characteristics

The penetration depth of the skin-effect has been calculated for a specimen in the form of a piece of amorphous glass-coated magnetic micro-wire of the “non-magnetostrictive” composition Co₆₇Fe_3.85Ni_1.45Mo_1.7Si_14.5B_11.5 displaying large GMI effect. For these calculations a simple model was applied in which a rough assumption was made that the changes of the real component of the impedance are due only to changes in the effective cross-section of the wire for the AC-current. The evolution of the penetration depth with the applied DC-axial field and frequencies of the AC-current, flowing along the wire, is presented. The so-called Cole–Cole diagrams were also plotted for the same specimen. These diagrams, representing the measured impedance plotted in the complex plane, were obtained for axial DC-magnetic field of selected intensities and circular AC-field generated by an AC-current of various frequencies (1–30 MHz) flowing along the wire specimen. Analysis of the diagrams enabled one to characterize magnetization processes within the wire specimen and also to estimate the median relaxation time of these processes as well as a relative measure of the distribution of relaxation times.