Momentum-resolved EELS and EMCD spectra from the atomic multiplet theory: Application to magnetite

While the energy loss near edge structures of metallic crystals can be calculated with a good accuracy using density functional theory based codes, core-level spectra of transition metal oxides show pronounced multiplet effects which are better described by atomic multiplet codes. We describe the formalism which allows to calculate momentum-resolved electron energy loss spectra in the electric dipole approximation from the atomic multiplet theory, and we apply this formalism to the calculation of energy loss magnetic chiral dichroic spectra of magnetic transition metal oxides. Explicit results are given for magnetite Fe₃O₄.     

Ba原子6pnd自电离态实验研究

采用三步孤立实激发与偏振光激发相结合的技术将 Ba原子分别从中间态6snp1 D2 (n=7～ 41 )和 6snp3D2 (n=7～ 2 9)激发到 6p1 / 2 nd以及 6p3/ 2 nd自电离态 ,从而获得了这 4个系列的自电离光谱。采用 Lorentz线型拟和的方法对这 4个系列的光谱所展现的不同的光谱特性及其所反映的物理意义做了详细的分析     

TM影像水体的提取研究

针对现有基于TM影像的水体提取方法存在耗时、准确率低及通用性不强等问题,应用主成分分析法（principal component analysis,PCA）,并结合徐涵秋改进的归一化差异水体指数（modified normalized difference water index,MNDwI）构建了便于提取水体的假彩色合成图,通过分析水体在该合成图中的光谱特征,建立水体提取模型,从而实现基于TM影像的水体提取。比较本文方法与MNDWI、谱间关系（TM2＋TM3）-（TM4＋TM5）和新型水体指数等几种常见的水体提取方法分别在太原市城区、山区的水体提取效果,结果表明：本文提出的方法更能快速、高效地提取TM影像水体,其精度高达94．03％。此外,该方法不需要对阈值进行人工选择,达到了高自动化的研究要求。     

Energy-loss near-edge structure (ELNES) and first-principles calculation of electronic structure of nickel silicide systems

The electronic structures of nanometre-sized nickel silicide systems, Ni(2)Si and NiSi, have been studied by energy-loss near-edge structure (ELNES) and first-principles band structure calculations. Experimental ELNES of Ni L(3)- and Si L(2,3)-edges could be explained well using theoretical spectra calculated for the ground state without the core hole, suggesting metallic properties for both silicides. It was shown that a slight difference in ELNES spectra of Ni(2)Si and NiSi comes from the coupling among the Ni d and Si p, d states in the unoccupied bands. The density of states and the contour plots of all the valence electron densities for Ni(2)Si, NiSi together with NiSi(2) show that Ni(2)Si has the bond with the strongest covalent character between Ni and Si atoms and the most transition metal-like character of the Ni 3d band among the three silicides.     

First-principles calculation of electronic properties of N-and X(X=S,Se,Te)-codoped anatase TiO2

本文运用密度泛函理论系统地研究了N和X(X=S,Se,Te)共掺杂锐钛矿TiO2时电子特性所受的影响。优化后的结构表明,在锐钛矿TiO2共掺杂时,由于掺杂原子有较大的原子半径而引起了大的晶格膨胀。从计算的替换能结果看,当X(X=S,Se,Te)掺杂到有N原子存在的TiO2时,若替换Ti原子,则不能很好地促进与N的协同作用,若替换O原子,则相反。从总态密度图和分态密度图来看,替换O原子后的N2p轨道和其他杂质带S 3p,Se 4p,Te 5p杂化在一起;同时替换Ti原子后,导带主要由Ti 3d轨道所占据,从而形成了S 3p(Se 4p or Te 5p)-N2p-Ti 3d杂化态。从Bader电荷的结果可知,替换O原子,电子转移是由N到X(X=S,Se,Te),而替换Ti原子后,电子转移是由X(X=S,Se,Te)到N。     

Modelling of extrusion force using the surface response method

Due to the complexity of bulk metal forming processes, the establishment of theoretical models for these processes is prohibitively difficult and frequently impossible. Consequently, empirical models attained by means of experimental research are habitually used to replace the theoretical models. This paper describes the application of the surface response method in an attempt to define a relationship between the maximum extrusion force and three process parameters; namely, the conical die angle γ, die land height, h and die exit diameter, d. An extensive experimental program of aluminium extrusion was undertaken in parallel with the empirical modelling. An adequacy test was made on the analysed models to determine the accuracy with which the model predicted data obtained by experimental methods.     

Detection of charged particles with charge injection devices

A method for using charge injection devices (CIDs) for detection of high-energy charged particles from inertial-confinement fusion reactions is described. Because of the relatively small depletion region of the CID camera (depletion depth of approximately 7 mum), aluminum foils are placed in front of the device to reduce the energy of the charged particles and maximize the energy deposited in the CID. Simultaneous measurements of (2)H(d,p)(3)H protons with a CID and a surface barrier detector indicate that the CID is an efficient detector of charged fusion products. Tests using high energy alpha particles emitted from a radium-226 source are also reported.     

非异常区TM偏振波宽波段特性在激光器调谐光栅设计中的应用

通过刻划工艺控制光栅槽形零级面宽度,使-1级和0级衍射效率同时达到期望值是激光器调谐光栅研制中的技术难题。基于光栅电磁场理论,利用光栅非异常区入射波长与光栅周期之比λ/d≈1.414附近较宽波段范围内TM偏振波的衍射效率变化梯度小,而且同一波长的衍射效率随闪耀角增大呈单调递增或随槽顶角增大呈单调递减趋势的特性,给出了-1级振荡0级输出激光器调谐光栅的全三角槽形模型及设计方法。该方法用常规三角槽形光栅即可实现任意比值的-1级与0级衍射能量分布,避免了以往通过控制类梯形槽形零级面宽度来制作此类光栅的工艺不确定性,降低了制作难度。应用该模型设计并制作了-1级衍射效率为65%的0级输出激光器调谐光栅,其在10.6μm处的衍射效率误差为0.6%。该方法还适用于-1级振荡-1级输出激光器调谐光栅的设计,实现了两类激光器谐振光栅在设计方法以及制作工艺上的统一。     

Comparative wear in titanium diboride coatings on steel using high energy density processes

A comparison between the tribological properties of titanium diboride (TiB₂) deposited using high energy density processes such as Pulse Electrode Surfacing (PES) and Laser Surface Engineering (LSE) has been made. The wear resistance of TiB₂ coated surface is higher than AISI 1010 steel. The wear resistance of the LSE coated TiB₂ coating is even better than that of the PES deposited TiB₂ coating. Coefficient of friction values for LSE coated TiB₂ coating (μ=0.6) are lower than PES deposited TiB₂ coating (μ=0.7). Wear occurs in PES deposited TiB₂ coating by brittle fracture and attrition type mechanisms whereas mixed adhesive–abrasive wear in LSE deposited TiB₂ coating occurs by localized plastic deformation of the soft matrix phase Fe from a “composite” layer on the surface.     

弹性流体静压轴承

The elasto-hydraustatic bearing is a new type of hydraustatic bearing. In action, it is similar to some conventional type of hydraustatic bearing The difference lies in the fact that in a Conventional hydraustatic bearing, the inside surface of the bearing shell must bs made to a certain configuration to prodvce the by dravstatic action. In this new type of bearing, the bearing shell is made to the form of a plain cylindrical bushing with a circumferential groove in the middle. (Fig 3-1) when the oil pressure is low, it will function as a plain sliding bearing. But when the pressure of oil is high, the bearing Shell, mostly made of some elastomer, will deform and the diameter of the bearing at the middle will be larger than the diameter at both ends. As is well known, this taper shaped bearing shell will have hydracstatic action, (Fig 3-2) Experiments show that the load carrying capacity of this kind of hrdravstatic bearing can be computed by the following empirical formula;W=0.12xDxL when the bearing bushing is made of metal, the outside of the bushing must be hollowed out(Fig3-3) to make it easier to deform.There are many advantage of this type of hydraustatic bearing. It is simple in form and very easy to make. When the pressure of the oil drops, it will foction as a plain bearing and hence is very safe and reliable. As there is no groove at the inside of the bearing shell, it will function as a squeeze film bearing under shock or vibrating load and has a high capacity.     

Selection of optimal process parameters in WEDM while machining Al7075/SiCp metal matrix composites

Aluminium metal matrix composites (MMCs) reinforced with silicon carbide particulate (SiCp) find several applications due to their improved mechanical properties over the conventional metals for a wide variety of aerospace and automotive applications. However, the presence of discontinuously distributed hard ceramic in the MMCs made them as difficult-to-cut materials for conventional machining methods. The wire electrical discharge machining (WEDM), as a widely adopted non-traditional machining method for difficult-to-cut precision components, found an appropriate metal removal process for MMCs to enhance quality of cut within the stipulated cost. While machining the advanced materials like MMCs, a clear understanding into the machining performance of the process for its control variables could make the process uncomplicated and economical. In light of the growing industrial need of making high performance-low cost components, the investigation aimed to explore the machining performance characteristics of SiCp reinforced Al7075 matrix composites (Al7075/SiCp) during WEDM. While conducting the machining experiments, surface roughness, metal removal rate, and wire wear ratio are considered the responses to evaluate the WEDM performance. Response surface methodology is used to develop the empirical models for these WEDM responses. SiC particulate size and volume percentages are considered the process variables along with pulse-on time, pulse-off time, and wire tension. Analysis of variance (ANOVA) is used to check the adequacy of the developed models. Since the machining responses are conflicting in nature, the problem is formulated as a multi-objective optimization problem and is solved using the Non-dominated Sorting Genetic Algorithm-II to obtain the set of Pareto-optimal solutions. The derived optimal process responses are confirmed by the experimental validation tests, and the results are analyzed by SEM.     

Fe3Al金属间化合物的有序度截留与力学性能

运用固体与分子经验电子理论(EET)对Fe3Al的两种晶体结构DO3和B2的滑移能进行了计算,结果表明B2结构在室温下具有较好的塑性和较低的强度.据此对长程有序金属间化合物Fe3Al进行有序度截留(淬火处理)研究.X射线衍射和强度试验表明有序度截留可以明显截留Fe3Al的有序度,截留后的试样强度和硬度下降,材料的力学性能得到改善.     

A simple method to deposit palladium doped SnO2 thin films using plasma enhanced chemical vapor deposition technique

This work presents a simple method to deposit palladium doped tin oxide (SnO(2)) thin films using modified plasma enhanced chemical vapor deposition as a function of deposition temperature at a radio frequency plasma power of 150 W. Stannic chloride (SnCl(4)) was used as precursor and oxygen (O(2), 100 SCCM) (SCCM denotes cubic centimeter per minute at STP) as reactant gas. Palladium hexafluroacetyleacetonate (Pd(C(5)HF(6)O(2))(2)) was used as a precursor for palladium. Fine granular morphology was observed with tetragonal rutile structure. A peak related to Pd(2)Sn is observed, whose intensity increases slightly with deposition temperature. Electrical resistivity value decreased from 8.6 to 0.9 mΩ cm as a function of deposition temperature from 400 to 600 °C. Photoelectron peaks related to Sn 3d, Sn 3p3, Sn 4d, O 1s, and C 1s were detected with varying intensities as a function of deposition temperature.     

空气孔硅光子晶体偏振无关3 dB分光器

提出并成功设计了基于自准直马赫-曾德尔干涉仪(SMZI)的空气孔硅光子晶体偏振无关3dB分光器。介绍了采用偏振透射谱匹配的方法,SMZI可以实现偏振无关分束的基础理论。通过连续改变SMZI两臂的光程差,基于匹配两个偏振的透射谱,成功实现了在归一化频率下将TE偏振和TM偏振的入射自准直光束进行1∶1分光。最后,利用时域有限差分数值模拟软件计算出来的TE偏振瞬时磁场分布图和TM偏振瞬时电场分布图验证了自准直光束的分光情况。结果显示:如果将工作波长定在1 550nm,该偏振无关3dB分光器大小仅为16.7μm×16.7μm。由于具有尺寸微小、结构简单并使用单一硅材料等特性,该分光器有望应用于集成光路中。     

Adaptive sparsest narrow-band decomposition method and its applications to rotor fault diagnosis

Enlightened by empirical mode decomposition (EMD) and matching pursuit (MP), adaptive sparsest narrow-band decomposition (ASNBD) method is proposed in this paper. The main idea of the method is to obtain the sparsest representation of a signal by constraining the components to be local narrow-band signals. In ASNBD, an optimized filter must be established at first. The parameters of the filter are determined by solving a nonlinear optimization problem. A regulated differential operator is used as the objective function so that each component is constrained to be a local narrow-band signal. Afterwards, the signal is filtered by the optimized filter to generate a single component. ASNBD is superior to matching pursuit in both the adaptivity and the physical meaning of the components. And problems such as mode mixing and end effect in EMD are alleviated in ASNBD as the computing of extremas is avoided. As it is robust and adaptive to non-stationary signals, artificial chemical reaction optimization algorithm (ACROA) is chosen to solve the optimization problems in ASNBD. Compared with GA, ACROA can reach a global optimum in a shorter time while the classification result is the same. Comparisons are made between ASNBD optimized by ACROA, ASNBD optimized by genetic algorithm and empirical mode decomposition (EMD) by analyzing simulation and experimental signals. The results indicate that ASNBD–ACROA is superior to the other two methods at least in restraining boundary effect, gaining more accurate components in the presence of noise and showing better orthogonality; moreover, it performs better in the analysis of experimental data.     

Friction reduction by metal sulfides in boundary lubrication studied by XPS and XANES analyses

In this work, the antiwear action of zinc dithiophosphate (ZnDTP) in combination with friction modifier agent molybdenum dithiocarbamate (MoDTC) has been investigated. A Cameron-Plint friction machine was used to generate large tribofilm areas in mild tribological conditions. Two analytical techniques, X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES) spectroscopy, have been employed to characterize the chemical species in tribofilms. XANES spectroscopy at the P K and L-edge, Mo L and M-edge and S K-edge was carried out in order to investigate phosphates and sulfides species in the tribofilms This was followed by XPS analysis in the same location in the tribofilms. Special attention has been paid to the peak fitting of Fe 2p, Zn 2p, S 2p, Mo 3d and O 1s photopeaks and Auger ZnLMM lines. The combined analyses have shown that the MoDTC+ZnDTP containing oil produces mainly shorter chain metal polyphosphate material in addition to ZnS and MoS₂. No zinc sulfate has been detected. XPS confirms that the formation of MoS₂ is enhanced by the presence of ZnDTP. For all additives combinations; no iron has been detected in the tribofilms. Analytical results are discussed and compared with theoretical predictions from the Chemical Hardness model for ZnDTP, MoDTC and ZnDTP+MoDTC tribofilms formation.     

Selective coupling of HE11 and TM01 modes into microfabricated fully metal-coated quartz probes

We report computational and experimental investigations on injection and transmission of light in microfabricated fully Aluminum-coated quartz probes. In particular, we show that a selective coupling of either the HE(11) or the TM(01) mode can be carried out by injecting focused linearly or radially polarized beams into the probe. Optical fields, emitted by the probe after a controlled injection, are characterized in intensity and phase with the help of an interferometric technique. With the help of near-field measurement, we finally demonstrate that a longitudinally polarized spot localized at the tip apex is actually produced when the TM(01) mode is coupled into the probe.     

电液位置伺服系统的计算机辅助设计

利用面向对象编程的思想对电液位置伺服系统CAD软件进行开发.该软件以中文WindowsXP为操作平台,用MicrosoftAccess建立的数据库为基础,以Autodesk公司的AutoCAD2005和MathWorks公司的Matlab7.0为支撑软件,利用VisualBasic6.0开发语言,将系统原理图绘制、参数计算、元件选取、动态仿真集成于一体.使用该软件进行电液位置伺服系统的设计,可获得工程上直接可用的系统原理图.     

采用子滑窗技术的修正剔除平均恒虚警检测算法

在雷达系统中用来进行目标检测的恒虚警技术,常采用的方法有单元平均（CA）方法,但这种方法在杂波背景的均匀性受到破坏时性能会恶化,1983年罗林教授提出了有序统计（OS）方法,这种方法具有较强的多目标分辨能力,Gandhi和Kassam又提出了剔除平均（TM）方法,CA和OS可看作是TM的特例。本文基于子滑窗技术提出了一种修正的剔除平均（MTM－CFAR）检测方法,它将检测单元附近杂波样本所形成的参滑窗分为前、后滑子滑窗,分别采用TM产生局部估计,再对二者求和来实现对杂波功率水平的估计。本文在SwerlingⅡ型目标假设下,出了它的平均虚警概率Pfa、平均检测概率Pd和平均判决门限ADT的角析表达式,并与基它检测方案进行了比较。分析结果表明,MTM在均匀背景及多目标引起的非均匀背景中,它的性能比OS,TM和GOSCA获得了改善,它的样本排离时间会比TM减少一半,CA,GOSCA和MCM均可看成MTM的特例。