Non-targeted high-resolution mass spectrometry study for evaluation of milk freshness

Milk freshness is an important parameter for both consumers' health and quality of milk-based products. Up to now there have been neither analytical methods nor specific parameters to uniquely define milk freshness from a complete and univocal chemical perspective. In this study, 8 molecules were selected and identified as responsible for milk aging, using a liquid chromatography–high-resolution mass spectrometry approach followed by chemometric data elaboration. For model setup and marker selection, 30 high-quality pasteurized fresh milk samples were collected directly from the production site and analyzed immediately and after storage at 2 to 8°C for 7 d. The markers were then validated by challenging the model with a set of 10 milk samples, not previously analyzed. Our results demonstrated that the markers identified within this study can be successfully used for the correct classification of non-fresh milk samples, complementing and successfully enhancing parallel evaluations obtainable through sensory measures.     

Super high-resolution spaceborne multiple-transit and multiple-receive sliding spotlight SAR imaging

In the Wide-field Super High-resolution Spaceborne Multiple-transit and multiple-receive Sliding Spotlight SAR, the line-of-sight approximation of the curved orbit is not established, so traditional imaging algorithms based on line-of-sight approximation is no longer available. For this problem, a super high-resolution velocity scaling algorithm(SHRVS) is proposed to meet the need of wide-field and super high-resolution. Besides, in the procedure of sub-band assembling, a high level virtual image appears due to the frequency aliasing of adjacent sub-bands. For this problem, an optimized linear FM transmit waveform is proposed, which can depress the virtual image level greatly.     

High-resolution SIMS and analytical TEM evaluation of alumina scales onβ-NiAl containing Zr or Y

High-resolution SIMS and TEM have been used to evaluate growth processes and interfacial segregation occurring in -Al₂O₃ scales grown at 1200°C on -NiAl containing zirconium or yttrium.¹⁸O/SIMS shows that the extent of aluminum diffusion occurring during -Al₂O₃ growth is reduced by the presence of these alloying elements, which are seen by SIMS imaging as oxide particles within the scale. STEM/EDS of the same oxide scales show that zirconium and yttrium also segregated to the oxide-alloy interface to the extent, respectively, of 0.15 and 0.07 of a monolayer and to oxide grain boundaries (0.2 monolayer). The complementary information provided by SIMS, TEM, and STEM provides a better understanding of the role of reactive elements in modifying scale-growth processes.     

A comparison of the microstructure of silicon nitride-silicon carbide composites made with and without deoxidized starting material

Two different types of silicon carbide (SiC) matrix composites, with either 10 wt% or 20 wt% silicon nitride (Si₃N₄) reinforcement, were fabricated to investigate the effect of pretreatment on the resulting composite micro-structure. The first type of composite was prepared from as-received α-SiC and α-Si₃N₄ powders, while the second type was prepared from powder compacts that had been deoxidized to eliminate surface silica on the powder particles. The composites were hot isostatically pressed in tantalum cans at 2373 K for 1h under a pressure of 200 MPa. Density measurements showed that full theoretical density was achieved for the composites prepared from the as-received powders, while much lower densities were obtained for the composites prepared from the deoxidized green compacts. Almost all of the α-SiC transformed into β-SiC, and almost all the α-Si₃N₄ transformed into α-Si₃N₄ in the composites made from the as-received powders, while in the composites made from the deoxidized material the α-SiC remained untransformed and both α-Si₃N₄ and β-Si₃N₄ phases were present in significant quantities. High-resolution transmission electron microscopy and Fresnel fringe imaging were used to identify the grain boundary and interphase boundary structure. Most interfaces were found to be covered with ? 1 nm thick amorphous intergranular films in the composites prepared from as-received powders, whereas most interfaces were found to be free of such amorphous intergranular films in the composites prepared from the deoxidized material. Taken together, the presence of intergranular films at the interfaces and the results from density measurements are consistent with the densification and reverse α → β-SiC transformation taking place in the composites made from as-received powders by a liquid-phase sintering route. An incomplete liquid-phase sintering mechanism is also able to explain the microstructure observed in the composites made from the deoxidized material.     

High-resolution cryo-scanning electron microscopy study of the macromolecular structure of fibronectin fibrils

High-resolution cryo-scanning electron microscopy was used to examine fibronectin fibrils formed in culture by human skin fibroblasts and in a cell-free system by denaturing soluble plasma fibronectin with guanidine. These studies indicate that the conformation of fibrils formed in culture and in a cell-free system appeared to be similar and that fibronectin fibrils have at least two distinct structural conformations. Fibronectin fibrils can be very straight structures with smooth surfaces or highly nodular structures. The average diameter of the nodules in these fibrils is 12 nm. Both conformations can be seen within an individual fibril indicating that they are not different types of fibronectin fibrils but rather different conformational states. Immunolabeling studies with a monoclonal antibody, IST-2, to the heparin II binding domain of fibronectin revealed that the epitope was buried in highly smooth fibrils, but it was readily exposed in nodular fibrils. We propose, therefore, that fibronectin fibrils are highly flexible structures and, depending on the conformation of the fibril, certain epitopes on the surface may be buried or exposed.     

基于近似黎曼求解器的三维浅水方程组求解方法

将求解平面二维浅水方程组的Godunov型有限体积法扩展至求解三维浅水方程组,建立具有激波捕捉特性的三维数学模型,将扩大三维浅水方程数学模型的应用范围。模型中湍流封闭采用非线性K-ε模型,水平方向数值通量采用HLLC近似黎曼求解器计算。为改善数值格式稳定性,垂向扩散项采用隐式离散,且在局部小水深处将三维模型退化为水深平均平面二维模型,所开发的模型在形式上具有时、空二阶精度。随后采用水跃、干河床溃坝洪水演进等算例对模型进行检验,结果表明:该模型具有较好的稳定性,能保证静水平衡,在间断解处能给出高分辨率的数值解,并具有较好的干湿边界模拟能力。     

Unprecedented Surface Plasmon Modes in Monoclinic MoO2 Nanostructures

Developing stable plasmonic materials featuring earth-abundant compositions with continuous band structures, similar to those of typical metals, has received special research interest. Owing to their metal-like behavior, monoclinic MoO₂ nanostructures have been found to support stable and intense surface plasmon (SP) resonances. However, no progress has been made on their energy and spatial distributions over individual nanostructures, nor the origin of their possibly existing specific SP modes. Here, various MoO₂ nanostructures are designed via polydopamine chemistry and managed to visualize multiple longitudinal and transversal SP modes supported by the monoclinic MoO₂, along with intrinsic interband transitions, using scanning transmission electron microscopy coupled with ultrahigh-resolution electron energy loss spectroscopy. The identified geometry-dependent SP energies are tuned by either controlling the shape and thickness of MoO₂ nanostructures through their well-designed chemical synthesis, or by altering their length using a developed electron-beam patterning technique. Theoretical calculations reveal that the strong plasmonic behavior of the monoclinic MoO₂ is associated with the abundant delocalized electrons in the Mo d orbitals. This work not only provides a significant improvement in imaging and tailoring SPs of nonconventional metallic nanostructures, but also highlights the potential of MoO₂ nanostructures for micro–nano optical and optoelectronic applications.     

Edge-Mediated Annihilation of Vacancy Clusters in Monolayer Molybdenum Diselenide (MoSe2) under Electron Beam Irradiation

Annihilation of vacancy clusters in monolayer molybdenum diselenide (MoSe₂) under electron beam irradiation is reported. In situ high-resolution transmission electron microscopy observation reveals that the annihilation is achieved by diffusion of vacancies to the free edge near the vacancy clusters. Monte Carlo simulations confirm that it is energetically favorable for the vacancies to locate at the free edge. By computing the minimum energy path for the annihilation of one vacancy cluster as a case study, it is further shown that electron beam irradiation and pre-stress in the suspended MoSe₂ monolayer are necessary for the vacancies to overcome the energy barriers for diffusion. The findings suggest a new mechanism of vacancy healing in 2D materials and broaden the capability of electron beam for defect engineering of 2D materials, a promising way of tuning their properties for engineering applications.     

一种正前视宽扇区高分辨雷达扫描成像方法

合成孔径雷达（Synthetic Aperture Radar,SAR）只有照射到飞行方向左、右两侧的感兴趣成像区域时才能处理出高分辨率SAR图像,飞行方向正前方的成像区域就成为了SAR成像的固有盲区。三通道（和、方位差、俯仰差）毫米波单脉冲成像雷达能够实现对正前视场景的二维成像,获取单脉冲图像。提出对SAR/单脉冲图像进行图像配准和融合拼接的方法：首先利用多尺度多方向二维Gabor滤波器组分别对SAR/单脉冲图像进行特征提取,然后对两组特征矩阵进行归一化互相关匹配,对匹配好的图像进行像素级融合处理,得到完整的正前视宽扇区高分辨雷达图像。试验数据成像处理结果表明,所提复合成像算法能够对飞行正前方宽扇区范围内进行高分辨成像,有效解决了工程实际中碰到的正前视高分辨成像盲区的难题,对于前视雷达成像侦察、弹载雷达目标区域景象匹配、飞行器夜航、盲降等具有一定的工程实际意义。