自然地面背景下红外目标检测算法

为了快速准确地检测出以地面物体为背景的红外序列图像中的目标,结合小波变换的特点及其应用于图像边缘检测的优点,提出了一种基于小波技术的图像预处理算法。该方法利用图像边缘在目标识别中的重要作用,讨论了基于小波变换的图像边缘检测方法,并结合地面背景红外图像自身的特点,大大地提高了单帧的检测概率。     

Phase transition and optoelectronic properties of MgH2

In this article, structural and electronic properties of MgH₂ have been studied. The aim behind this study was to find out the ground state crystal structure of MgH₂. For the purpose, density functional theory (DFT)-based full-potential linearized augmented plane wave (FP-LAPW) calculations have been performed in three different space groups: P4₂/mnm (α-MgH₂), Pa3 (β-MgH₂) and Pbcn (γ-MgH₂). It has been found that the ground state structure of MgH₂ is α-MgH₂. The present study shows that α-MgH₂ transforms into γ-MgH₂ at a pressure of 0.41 GPa. After further increase in pressure, γ-MgH₂ transforms into β-MgH₂ at a pressure of 3.67 GPa. The obtained results are in good agreement with previously reported experimental data. In all the studied phases, the behavior of MgH₂ is insulating and its optical conductivity is around 6.0 eV. The α-MgH₂ and γ-MgH₂ are anisotropic materials while β-MgH₂ is isotropic in nature.     

Reference spectra of important adsorbed organic and inorganic phosphate binding forms for soil P speciation using synchrotron‐based K‐edge XANES spectroscopy

Direct speciation of soil phosphorus (P) by linear combination fitting (LCF) of P K‐edge XANES spectra requires a standard set of spectra representing all major P species supposed to be present in the investigated soil. Here, available spectra of free‐ and cation‐bound inositol hexakisphosphate (IHP), representing organic P, and of Fe, Al and Ca phosphate minerals are supplemented with spectra of adsorbed P binding forms. First, various soil constituents assumed to be potentially relevant for P sorption were compared with respect to their retention efficiency for orthophosphate and IHP at P levels typical for soils. Then, P K‐edge XANES spectra for orthophosphate and IHP retained by the most relevant constituents were acquired. The spectra were compared with each other as well as with spectra of Ca, Al or Fe orthophosphate and IHP precipitates. Orthophosphate and IHP were retained particularly efficiently by ferrihydrite, boehmite, Al‐saturated montmorillonite and Al‐saturated soil organic matter (SOM), but far less efficiently by hematite, Ca‐saturated montmorillonite and Ca‐saturated SOM. P retention by dolomite was negligible. Calcite retained a large portion of the applied IHP, but no orthophosphate. The respective P K‐edge XANES spectra of orthophosphate and IHP adsorbed to ferrihydrite, boehmite, Al‐saturated montmorillonite and Al‐saturated SOM differ from each other. They also are different from the spectra of amorphous FePO₄, amorphous or crystalline AlPO₄, Ca phosphates and free IHP. Inclusion of reference spectra of orthophosphate as well as IHP adsorbed to P‐retaining soil minerals in addition to spectra of free or cation‐bound IHP, AlPO₄, FePO₄ and Ca phosphate minerals in linear combination fitting exercises results in improved fit quality and a more realistic soil P speciation. A standard set of P K‐edge XANES spectra of the most relevant adsorbed P binding forms in soils is presented.     

Prediction of Γ-L and L-X crossovers in Ga<Subscript>x</Subscript>Al<Subscript>1-x</Subscript>Sb alloys by empirical pseudopotential method

Using empirical pseudopotential method Γ-L crossover is found for the Ga_0.74Al_0.26Sb. The conduction band minimum is observed to switch at the (0.87, 0, 0) point for Ga_0.51Al_0.49Sb which shifts to the X point for Ga_0.21Al_0.79Sb and remains at X leading finally to indirect band gap in AlSb. Band structure calculations for a large number of alloys are performed and bowing parameters b_X and b_L are proposed for the E_X and E_L respectively. Our findings may serve as directive to select the materials in a range of composition to examine the bowing parameters and thereby effective mass experimentally for the Ga_xAl_1-xSb alloys.     

压制观瞄系统多光谱光轴平行性调校技术研究

鉴于压制观瞄系统光轴平行性是实现精确压制的一项指标,其特殊性在于保证回转机械轴、可见光轴、激光光轴的平行性,提出一种采用双光楔对压制观瞄系统光轴进行调校的方法, 通过转动双光楔,使光轴发生偏转,从而完成各光轴的平行。通过分析压制观瞄系统的结构,重点介绍了双光楔调校的原理与方法,并建立数学模型。采用Matlab对数学模型进行仿真,基于该调校原理搭建实验装置进行试验,试验结果表明,采用双光楔进行光轴调校方法可使三轴调校后的平行度误差不超过0.1 mrad。     

Readout circuit with dual switching mode design for infrared focal plane arrays

The paper proposes a readout circuit architecture with adjustable integration time for dual-band infrared detectors. The readout circuit uses direct injection to be combined with a capacitive trans-impedance amplifier. The amplifier is sharing between two pixels to reduce the complexity of the readout circuit. The proposed device reduces power consumption and area overhead compared to traditional structures. An experimental chip was fabricated using the TSMC 0.35 μm 2P4 M 5 V process. The resulting unit pixel layout area is 40 μm × 40 μm with input photocurrent ranging from 0.11 pA to 50 nA. CTIA mode is applicable from 0.11 pA to 10 nA, while DI mode is applicable from 3.3 pA to 50 nA. The maximum operating frequency of the chip are 4 MHz. The CTIA output swing is 1.2 V, the DI output swing is 2 V. The signal to noise ratio of the readout circuit is 65 dB and power consumption is less than 9.6 mW.     

第一原理研究界面弛豫对InAs/GaSb超晶格界面结构、能带结构和光学性质的影响

通过广义梯度近似的第一原理全电子相对论计算, 研究了不同界面类型InAs/GaSb超晶格的界面结构、电子和光吸收特性. 由于四原子界面的复杂性和低对称性, 通过对InAs/GaSb超晶格进行电子总能量和应力最小化来确定弛豫界面的结构参数. 计算了InSb, GaAs型界面和非特殊界面(二者交替)超晶格的能带结构和光吸收谱, 考察了超晶格界面层原子发生弛豫的影响.为了证实能带结构的计算结果, 用局域密度近似和Hartree-Fock泛函的平面波方法进行了计算. 对不同界面类型InAs/GaSb超晶格的能带结构计算结果进行了比较, 发现界面Sb原子的化学键和离子性对InAs/GaSb超晶格的界面结构、 能带结构和光学特性起着至关重要的作用.     

基于像素灰阶熵的自适应增强算法在乳腺CR图像中的应用

乳腺完全是由密度接近软组织构成,因此乳腺CR(Computed Radiography)放射图像对比度小,轻微的差别变化都可能是肿瘤的表现,要对其进行增强处理方能满足医生临床诊断的需要。而目前通用的乳腺CR图像增强算法对比度和噪声增强过度,丢失细节,为此提出了采用一种基于像素灰阶熵的自适应边缘增强算法对乳腺CR图像进行增强。该算法使用模糊影像增加对选择空间频率的响应,以增强乳腺CR图像结构边缘和细节;算法能根据乳腺CR图像灰度特性即像素灰阶熵来自适应的调节增强程度的加权因数K。实验证明,该算法处理后的乳腺CR图像细节丰富,信噪比高,增强后的图像具有良好的视觉效果,该算法是一种有效的适合乳腺CR医学图像的边缘细节增强算法。     

Ni、Co/AAO纳米有序阵列复合结构光吸收特性的比较研究

在多孔阳极氧化铝(AAO)模板中分别沉积金属镍(Ni)、钴(Co),制备了Ni／AAO和Co／AAO纳米有序阵列复合结构,对其光吸收特性进行了比较研究。实验结果表明．相同结构参量的模板中,Ni、Co纳米粒子的表观形状随沉积时间的变化规律基本一致．但Co/AAO及Ni／AAO复合结构的光吸收特性却有较大差异。Ni／AAO复合结构表现出间接带隙半导体的光学特征．而Co／AAO复合结构具有直接带隙半导体的光学特征。同时,随金属沉积量的增加,Ni／AAO吸收边的红移量仅约为13nm．而Co/AAO复合结构的吸收边红移量却超过了80nm。用Maxwell-Garnett(M-G)理论分析了导致二者光吸收特性存在较大差异的主要原因。     

Synchrotron XANES and ED‐XRF analyses of fine‐paste ware from 13th to 14th century maritime Southeast Asia

The combination of energy dispersive X‐ray fluorescence (ED‐XRF) and synchrotron X‐ray absorption near‐edge structure (XANES) provides the detailed composition of fine‐paste ware (FPW) kendis, dated back to 13th–14th century maritime Southeast Asia. Sources of clay and production sites were classified according to Al₂O₃, SiO₂, α‐Fe₂O₃ and γ‐Fe₂O₃ as well as trace elements. The similarities based on these components provided another evidence of a trade route between Kota Cina in North Sumatra of Indonesia and Kok Moh on Satingphra Peninsula, a well‐known production area in present‐day Thailand. In additions, the uniquely large contribution of α‐Fe₂O₃ in XANES spectra suggests that Nakhon Si Thammarat province of Thailand could also be one of FPW production areas in maritime Southeast Asia. Copyright © 2017 John Wiley & Sons, Ltd.