Chemical bond characteristics and infrared reflectivity spectrum of a novel microwave dielectric ceramic CaIn2O4 with near-zero τf

Orthorhombic-structured CaIn₂O₄ ceramics with a space group Pca2₁ were synthesized via a solid-state reaction method. A high relative density (95.6 %) and excellent microwave dielectric properties (ε_r ～11.28, Qf = 74,200 GHz, τ_f ～ ?4.6 ppm/°C) were obtained when the ceramics were sintered at 1375 °C for 6 h. The dielectric properties were investigated on the basis of the Phillips–Van Vechten–Levine chemical bond theory. Results indicated that the dielectric properties were mainly determined by the InO bonds in the CaIn₂O₄ ceramics. These bonds contributed more (74.65 %) to the dielectric constant than the CaO bonds (25.35 %). Furthermore, the intrinsic dielectric properties of the CaIn₂O₄ ceramics were investigated via infrared reflectivity spectroscopy. The extrapolated microwave dielectric properties were ε_r ～10.12 and Qf = 112,200 GHz. Results indicated that ion polarization is the main contributor to the dielectric constant in microwave frequency ranges.     

高光谱成像用高帧频CMOS图像传感器北大核心

针对高帧频、全局曝光和光谱平坦等成像应用需求,设计了一款高光谱成像用CMOS图像传感器。其光敏元采用PN型光电二极管,读出电路采用5T像素结构。采用列读出电路以及高速多通道模拟信号并行读出的设计方案来获得低像素固定图像噪声(FPN)和非均匀性抑制。芯片采用ASMC 0.35μm三层金属两层多晶硅标准CMOS工艺流片,为了抑制光电二极管的光谱干涉效应,后续进行了光谱平坦化VAE特殊工艺,并对器件的光电性能进行了测试评估。电路测试结果符合理论设计预期,成像效果良好,像素具备积分可调和全局快门功能,最终实现的像素规模为512×256,像元尺寸为30μm×30μm,最大满阱电子为400 ke^(-),FPN小于0.2%,动态范围为72 dB,帧频为450 f/s,相邻10 nm波段范围内量子效率相差小于10%,可满足高光谱成像系统对CMOS成像器件的要求。     

As the number falls,alternatives to the Hagberg–Perten falling number method: A review

This review examines the application, limitations, and potential alternatives to the Hagberg–Perten falling number (FN) method used in the global wheat industry for detecting the risk of poor end-product quality mainly due to starch degradation by the enzyme α-amylase. By viscometry, the FN test indirectly detects the presence of α-amylase, the primary enzyme that digests starch. Elevated α-amylase results in low FN and damages wheat product quality resulting in cakes that fall, and sticky bread and noodles. Low FN can occur from preharvest sprouting (PHS) and late maturity α-amylase (LMA). Moist or rainy conditions before harvest cause PHS on the mother plant. Continuously cool or fluctuating temperatures during the grain filling stage cause LMA. Due to the expression of additional hydrolytic enzymes, PHS has a stronger negative impact than LMA. Wheat grain with low FN/high α-amylase results in serious losses for farmers, traders, millers, and bakers worldwide. Although blending of low FN grain with sound wheat may be used as a means of moving affected grain through the marketplace, care must be taken to avoid grain lots from falling below contract-specified FN. A large amount of sound wheat can be ruined if mixed with a small amount of sprouted wheat. The FN method is widely employed to detect α-amylase after harvest. However, it has several limitations, including sampling variability, high cost, labor intensiveness, the destructive nature of the test, and an inability to differentiate between LMA and PHS. Faster, cheaper, and more accurate alternatives could improve breeding for resistance to PHS and LMA and could preserve the value of wheat grain by avoiding inadvertent mixing of high- and low-FN grain by enabling testing at more stages of the value stream including at harvest, delivery, transport, storage, and milling. Alternatives to the FN method explored here include the Rapid Visco Analyzer, enzyme assays, immunoassays, near-infrared spectroscopy, and hyperspectral imaging.     

Evolution of core–rim structures and phase transformations in infra-red transmitting Y-α-SiAlON ceramics

Core–rim structures were observed as common features in Y-α-SiAlON ceramics hot-pressed between 1550?1950 °C. We found most dopants were taken into α’-rims, and a transition layer grown first on α-cores from liquid-phase over-saturated with metal solutes. Elongated β’-grain were formed as minor phase with α’- or AlN-cores thus only after the α’ matrix had consumed up all Y solutes, revealing that the α’ → β’ transformation is controlled by the transient liquid-phase and similar defects and dangling bonds could be detected in both SiAlON phases by cathodoluminescence. Quantitative assessment of Y_m/3Si_12?(m+n)Al_m+nO_nN_16?n demonstrates the multiphase evolution, initiated by over-saturation of Y solutes at low temperatures thus retaining α-phase as cores to lower the infra-red transmittance, dictated by homogenization of Al solutes at higher temperature. The elimination of those phase boundaries leads to better dopant and sintering design for achieving transparent and high-performance SiAlON ceramics.     

基于K-AP算法的高光谱图像波段选择方法

在高光谱图像分析领域中，波段选择是一种能有效减少高光谱图像维度的方法。K类仿射传播算法是一种高效的聚类算法，已成功地应用于人脸识别和数据分析等领域，但在高光谱图像分析领域还少有成功的应用。提出将K-AP算法应用于高光谱图像波段选择，对高光谱图像进行有效的数据压缩。针对K-AP算法的特点，基于Kullback-Leibler散度定义了新的相似度矩阵，对波段进行度量，再使用K-AP算法进行聚类，选择最有代表性的波段。实验结果表明，与常用的波段选择方法相比，所提出的方法有更好的表现。     

Hydrothermally grown uniform TiO2 coatings on ZrO2 fibers and their infrared reflective and thermal conductive properties

Improving the infrared reflectivity of ZrO₂ polycrystalline fibers is of great benefit to its thermal applications. In the present research, we cast a highly uniform TiO₂ coating with a thickness ranging from dozens to hundreds of nanometers on ZrO₂ fibers by utilizing hydrothermal growth. The coating bonds tightly to the ZrO₂ fibers via Zr–O–Ti chemical linkages, and the thickness of the coating can be tailored by varying the hydrothermal growth time. The TiO₂ coating, acting as a sheath towards electromagnetic radiation, not only reflected light with wavelengths ranging from the visible region to the infrared region and up to 8 μm but also shielded the Raman signals of the ZrO₂ fibers. The present research provides an efficient way to cast controllable and uniform coatings on flexible fiber materials. The obtained ZrO₂ fibers coated with TiO₂ may have applications such as reinforcement for bulk ceramics, thermal barrier coatings, aerogels, etc., thus performing the dual functions of mechanical strengthening and thermal insulation.     

Impact of rare earth europium (RE-Eu3+) ions substitution on microstructural,optical and magnetic properties of CoFe2−xEuxO4 nanosystems

In this study, pure cobalt ferrite (CoFe₂O₄) nanoparticles and europium doped CoFe₂O₄ (CoFe_2−xEu_xO₄; x = 0.1, 0.2, 0.3) nanoparticles were synthesized by the precipitation and hydrothermal approach. The impact of replacing trivalent iron (Fe³⁺) ions by trivalent rare earth europium (RE-Eu³⁺) ions on the microstructure, optical and magnetic properties of the produced CoFe₂O₄ nanoparticles was studied. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectra exposed the consistency of a single cubic phase with the evidence of Eu₂O₃ phases for x ≥ 0.2. FTIR transmittance spectra showed that, the all investigated samples have three characteristic metal-oxygen bond vibrations corresponding to octahedral B-site (υ₁ and υ₂) and tetrahedral A-site (υ₃) around 415 cm⁻¹, 470 cm⁻¹ and 600 cm⁻¹ respectively. XRD and energy dispersive X-ray spectroscopy studies affirmed the integration of RE-Eu³⁺ ions within CoFe₂O₄ host lattice and decrease of average crystals size from 13.7 nm to 4.7 nm. Transmission electron microscopy (TEM) analysis showed the crucial role played by RE-Eu³⁺ added to CoFe₂O₄ in reducing the particle size below 5 nm in agreement with XRD analysis. High resolution-TEM (HR-TEM) analysis showed that the as-synthesized spinel ferrite, i.e., CoFe_2−xEu_xO₄, nanoparticles are single-crystalline with no visible defects. In addition, the HR-TEM results showed that pure and doped CoFe₂O₄ have well-resolved lattice fringes and their interplanar spacings matches that obtained by XRD analysis. Magnetic properties investigated by the vibrating sample magnetometer technique illustrated transformation of magnetic state from ferromagnetic to superparamagnetic at 300 K resulting in introducing RE-Eu³⁺ in CoFe₂O₄ lattice. At low temperature (~5 K) the magnetic order was ferromagnetic for both pure and doped CoFe₂O₄ samples. Substitution of Fe³⁺ ions in CoFe₂O₄ nanoparticles with RE-Eu³⁺ ions optimizes the sample nanocrystals size, cation distribution and magnetic properties for many applications.     

基于高光谱图像的改进SIFT特征提取与匹配

针对尺度不变特征变换(SIFT)算法所提取图像特征点数量少、误匹率高的问题,提出了一种基于高光谱图像的改进SIFT算法。首先,依据传统SIFT算法中高斯金字塔的构造思想,结合在不同波段下的高光谱图像具有相同宏观特征的特点,首次用高光谱图像作为原始算法中经高斯变换产生的图像,使得检测到的具有实际意义的特征点数量大幅增加;其次,传统SIFT算法以及大量的改进方法都只通过目标象元邻域范围内的像素信息来构造特征描述符,而忽略了像素点的位置信息,文中将目标象元的位置信息纳入了特征描述符,在特征描述符的匹配阶段,在利用邻域范围内的像素信息进行粗匹配之后,利用特征描述符中的位置信息进行精细匹配。仿真实验结果表明在限定最优值与次优值之比的情况下,采用高光谱图像构造高斯金字塔的方式能显著增加特征点的提取数量,更多地挖掘出图像中的极值点;在特征描述符中加入目标象元的位置信息作为特征点匹配第二阶段的判断依据,正确匹配数量达到原方法的59倍以上,极大提升了算法的匹配性能。