Hybrid gas-to-particle conversion and chemical vapor deposition for the production of porous alumina films

Porous alumina films can be found in a wide variety of materials, including filters, thermal insulation components, dielectrics, biomedical and catalyst supports, coatings and adsorbents. Production methods for these films are as equally diverse as their applications. In this work, a hybrid process based upon chemical vapor deposition and gas-to-particle conversion is presented as an alternative technique for producing porous alumina films, with the main advantages of solvent-free, low substrate-temperature operation. In this process, nanoparticles were produced in the vapor phase by reaction of aluminum acetylacetonate in the presence of oxygen. Downstream of this reaction zone, these nanoparticles were collected via thermophoresis onto a cooled substrate, forming a porous film. Some deposited films were subjected to post-processing in the form of annealing in air. Fourier-transform infrared spectra and X-ray energy-dispersive spectroscopy analysis confirmed the production of alumina at processing temperatures above 973 K. X-Ray diffraction revealed that the films were amorphous. Film thickness, ranging from 30 to 250 μm, and the average deposition rate were determined from scanning electron microscopy results. From transmission electron microscopy, the average primary particle size was determined to be approximately 18 nm and the formation of nanoparticle aggregates was evident. Annealing of the films at temperatures ranging from 523 to 1173 K in the presence of air did not have an effect on particle size. The specific surface area of the powder composing the films ranged from 10 to 185 m² g⁻¹, as determined from nitrogen gas adsorption by the Brunauer–Emmett–Teller method.     

Mössbauer spectroscopic studies of Fe-substituted YIG

Compositional dependence of hyperfine parameters, determined through Mössbauer spectral analysis has been studied for Y_3−xFe_5+xO₁₂ (x = 0.0, 0.1, 0.3 and 0.5) garnet system at 300 K. The Mössbauer spectra have been fitted with three sextets in the ferrimagnetic state corresponding to Fe³⁺ ions at tetrahedral (d), octahedral (a) and dodecahedral (c) sites of the crystal structure. It is observed that isormershift, quadrupole shift and hyperfine field of d-site show no significant variation with Fe³⁺ concentration. The change in hyperfine fields of a- and c-sites with composition (x) has been explained on the basis of strength of exchange integrals, change in isomershift can be understood due to s-electron charge distribution and asymmetric displacement of oxygen ions surrounding the a- and c-sites seems to be responsible for observable quadrupole shift. The magneton number values obtained from magnetization and Mossbauer data are in agreement to those calculated using Neel's three sublattice model of ferrimagnetism.     

利用Hilbert-Huang变换提取地震信号瞬时参数

 通过Hilbert变换求取的信号瞬时参数并非对任何信号都有物理意义，此法通常要求被分析信号是窄带或平稳的，而且对噪声很敏感。而实际地震信号既非平稳又含有噪声，若在实际应用中不加考虑地对地震信号进行Hilbert变换以求取瞬时参数，这种情况下求取的瞬时参数将缺乏物理意义甚至失真。Hilbert-Huang变换是一种新的分析非平稳非线性信号的方法，它先将信号进行经验模态分解（EMD），形成有限个固有模态函数（IMF）之和，再对固有模态函数作Hilbert变换求取时频谱，求取的时频谱在时域和频域都具有较高的分辨率。本文将Hilbert-Huang变换应用于地震瞬时参数的提取，实例表明，对地震剖面做EMD可以得到不同时间尺度上的特征，Hilbert谱比传统的时频谱在时间和频率域上的分辨率都要高，强反射层在第1阶IMF瞬时频率剖面上比原瞬时频率剖面上表现得更为明显。     

Hardware and software architecture for power quality analysis

This paper presents a novel concept for power quality hardware and software architecture. Software tools related to detection, classification and characterization of power quality events can be integrated into a Distribution Control Center in which the interconnection between different subsystems is being carried out through the Internet allowing flexibility to the system. This system is implemented using wavelet analysis applied in all proposed algorithms. Different power quality events are taken as examples to illustrate the capabilities of the proposed method. The obtained results reveal that the proposed architecture is feasible to be implemented as an integral part of a control center system.The proposed system has the property of fast and accurate detection and classification of any power quality disturbance event and introduces a new PQ index determination that allows characterizing any type of disturbance including the non-periodic signals.     

基于纠错编码和小波变换的数字图像水印算法

文章提出了一种基于小波变换和纠错编码的数字图像水印算法,该算法不需要利用原始图像。实验结果表明,该算法较好地保持了图像的质量,并大大提高了检测的可靠性,对常见的图像处理方法显示了较强的鲁棒性。     

Structure modification of rapidly solidified Al-11 wt% Si alloy by the addition of 2 wt% Fe

An investigation of the structure formation of as-cast Al-11 wt% Si (AlSi11) and Al-11 wt% Si-2 wt% Fe (AlSi11Fe2) rapidly solidified (RS) ribbons is performed. Ribbon samples are examined in detail using Auger electron spectroscopy (AES) and transmission electron microscopy (TEM). A nanoscale thickness layer of Si-precipitations, at both Al-grains boundary and oxide/Al-matrix interface, is found to be characteristic for “pure” AlSi11 ribbons. For Fe-doped ribbons, this layer comprises Fe-containing phase also, which appears to possess amorphous nature and is situated between the Si-grains and Al-matrix. A possible mechanism of altering the thermally activated volume diffusion of elements, due to the effect of Fe on the structure modification, is speculated based on the obtained results.     

Secondary ion emission from Ti and Si targets induced by medium energy Ar ion bombardment - Experiment and computer simulation

The paper presents experimental results of secondary ion energy distributions obtained for Ti and Si targets bombarded by 20-30 keV monoisotope Ar⁺ ion beam. The influence of the extraction voltages between target and a slit of the electrostatic energy analyzer entrance on the energy distributions of secondary ions was investigated. After optimization of the secondary ion extraction system, the mass spectra of secondary ions were also measured. The investigations were done using recently built experimental system. Experimental data are compared with the computer simulation results obtained using TRQR and SATVAL codes.     

源气体流量比对F-DLC薄膜结构的影响

以高纯石墨作靶，CHF3/Ar作源气体采用反应磁控溅射法制备出了氟化类金刚石（F-DLC）薄膜。拉曼光谱表明，CHF3相对流量的增加会引起薄膜的D峰与G峰强度之比I（D）/I（G）减小，晶粒增大，芳香环结构出例下降。红外吸收光谱分析证实了这些推论，指出这是由于薄膜中氟含量上升的结果。     

炼油化工装置技术改造的决策与实施

针对炼油和石化工业装置技术改造的特点，系统地总结了技术改造的类型和改造方案的制定、决策及实施的原则、程序和方法，指出对炼化装置实施技术改造是一项极其复杂、极具难度的系统工程，必须结合实际情况，以投资回报最大化为原则，通过深入细致地研究和反复比选优化改造方案，并结合现场情况制定切实、可靠、安全的实施方案。