Structural purity of magnetite nanoparticles in magnetotactic bacteria

Magnetosome biomineralization and chain formation in magnetotactic bacteria are two processes that are highly controlled at the cellular level in order to form cellular magnetic dipoles. However, even if the magnetosome chains are well characterized, controversial results about the microstructure of magnetosomes were obtained and its possible influence in the formation of the magnetic dipole is to be specified. For the first time, the microstructure of intracellular magnetosomes was investigated using high-resolution synchrotron X-ray diffraction. Significant differences in the lattice parameter were found between intracellular magnetosomes from cultured magnetotactic bacteria and isolated ones. Through comparison with abiotic control materials of similar size, we show that this difference can be associated with different oxidation states and that the biogenic nanomagnetite is stoichiometric, i.e. structurally pure whereas isolated magnetosomes are slightly oxidized. The hierarchical structuring of the magnetosome chain thus starts with the formation of structurally pure magnetite nanoparticles that in turn might influence the magnetic property of the magnetosome chains.     

Effects of mechanical force on crystalline structure of electrospun poly(1‐butene) membranes

Fibrous poly(1‐butene) membranes were prepared from solutions using mixed solvents via electrospinning. The electrospun fibrous poly(1‐butene) membranes were stretched at elongations of 8, 16 and 24%, respectively. Scanning electron microscopy and stress–strain analysis showed that the deformation was elastic at an elongation of 8%, while plastic deformation occurred above 16%. The crystalline transformation induced by mechanical stretching was investigated using wide‐angle X‐ray diffraction. The poly(1‐butene) membrane stretched at 24% exhibited decreased diffraction intensity at 2θ = 11.8° and 18.3°, corresponding to the (200) and (213) crystalline reflections, indicating that crystalline transformation from metastable form II to either stable form I or I′ occurred due to mechanical stretching. Copyright © 2011 Society of Chemical Industry     

储油罐变位识别与罐容表标定的数学建模

针对2010年数模竞赛A题,使用二重积分、近似积分及坐标变换方法,求出储油罐发生变位时储油量与油面高度的函数关系.利用最小二乘法原理建立了求解最优参数和的约束规划模型,进而对罐容表重新标定.     

A Material Model for TRIP‐Steels and its Application to a CrMnNi Cast Alloy

A material model is presented that accounts for strain rate dependent inelastic deformation and strain‐induced phase transformation in TRIP‐steels. Modifications for the kinetics equations of the strain‐induced phase transformation, introduced by Stringfellow, are proposed to overcome a drawback of Stringfellow's model. A parameter identification strategy that relies on Gauss‐Markov estimates is used to determine the model parameters from experimental data of a recently developed cast TRIP‐steel. Good agreement is observed between experimental results of the compression test and the corresponding finite element simulation employing the proposed model. This forms the basis for future applications of the material model in the design of composites and structures.     

A reduced mechanism for ethylene/methane mixtures with excessive NO enrichment

A detailed mechanism for methane–ethylene mixtures enriched with excessive amount of NO was systematically reduced for efficient numerical simulations of flames in arc-heated co-flowing air. Methane and ethylene were selected as the surrogate fuel in the present study due to their drastically different features of ignition and extinction properties and flame propagation speeds, such that the mixtures of them may be utilized to mimic practical hydrocarbon fuels with various kinetic properties in experiments. The recently released USC Mech-II for C1–C4 was grafted with the NO_x sub-mechanism in GRI-Mech 3.0 with updated reaction parameters for prompt NO formation. The resulting detailed mechanism with 129 species and 900 reactions was first validated against experiments involving NO_x enrichment and reasonably good agreements were observed. The detailed mechanism was then employed as the starting mechanism for the reduction. A skeletal mechanism with 44 species and 269 reactions was derived using the methods of directed relation graph (DRG) and DRG-aided sensitivity analysis (DRGASA); a 39-species reduced mechanism with 35 semi-global reaction steps was further obtained using the linearized quasi steady state approximations (LQSSA). Five species related to prompt NO were retained in the reduced mechanism because of their significant impacts on the fuel oxidation. The reduced mechanism closely agrees with the detailed mechanism for ignition and extinction of homogenous mixtures, as well as selected 1-D flames over a wide range of parameters with NO concentrations between 0% and 3%. The observed worst-case relative error of the reduction is approximately 20%. The reduced mechanism was further validated with experiments involving excessive NO_x enrichment.     

内环线浦东段快速化改建工程中道路绿化建设

分析、总结了在市政道路改造中道路绿化的二次建设面临的主要不利因素。在内环线浦东段快速化工程(龙阳路段)道路绿化建设设计原则中着重介绍了绿化景观总体定位、设计策略、种植设计,并对4个路段的绿化建设条件和绿化改建方案进行了设计。     

Phase and Microstructural Analysis of Hot Rolled FeNi42 Sheet,its Response in Magnetic and Mechanical Properties

Inclusions unavoidably existing in steels and consequently also in final products obtained by e.g. rolling markedly affects the physical properties. This paper is devoted to investigation of FeNi42 steel hot rolled into a sheet form. The structural and phase analysis is done by scanning electron microscopy, X‐ray diffraction, and Mössbauer spectroscopy completed by magnetic and hardness measurements. The results yield an inhomogeneous nickel distribution in the sheet resulting in a formation of the intermetallic Ni₃Fe phase. A depletion of sheet surface by nickel leads to an intensive surface oxidation; its thickness increases in the direction of sheet edges. The non‐metallic oxide inclusions are concentrated predominantly at grain boundaries, which contribute to an easier cracking. The formation of Ni₃Fe affects a small increase in saturation magnetization. The oxides and consequently cracks formation cause magnetic hardening as can be seen on an increase of the structurally sensitive remnant magnetization. The hard oxide inclusions evoke also the hardening of material, rise brittleness and crack liability.     

Collective tracking control for multi‐agent system on balanced graphs

In this paper, we consider a collective tracking problem of a multi‐agent system which has a varying‐velocity leader and evolves on balanced information topologies. First, we propose a coordination‐variable‐based control strategy for every agent to track the leader whose state may not be measured. Moreover, from a collective behavior perspective, a new decomposition method is utilized to decompose the resulting closed‐loop system into two subsystems, and a novel measure also is introduced to characterize collective tracking performance of the system. Finally, we prove that the proposed control strategy can not only estimate the tracking errors but also increase the introduced measure to improve collective tracking performance even under the case of balanced information topologies. Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

基于改进HMM的潜在电子故障状态识别模型

针对复杂电子装备隐性故障难以诊断的难题,在深入分析隐马尔可夫模型的核心问题及基本算法的基础上,探讨了其在故障诊断应用中存在的主要问题,建立了多状态电子装备可靠性评估模型,利用系统可靠性评估结果作为隐马尔可夫模型的初始模型特征量,改进了传统的隐马尔可夫模型,并对Baum-Welch训练算法进行了优化,形成了一套适于复杂电子装备潜在故障状态跟踪识别的数学模型.实验结果显示,理论方法及模型能够更好地识别潜在故障状态,加快了模型训练速度,提高了故障状态识别率.