Compositional contrast of uncoated fungal spores and stained section-face by low-loss backscattered electron imaging

Comparative surface imaging was performed on uncoated fungal spores and stained section-face by field emission scanning electron microscopy with an in-column energy-selective backscattered electron detector. Epoxy resin thin sections (ca. 200 and 500 nm thick) of the osmicated and uranyl acetate/lead citrate-stained fungus were examined with the microscope. Topographical contrast was evident in secondary electron imaging by either a below-lens or an in-lens detector. Meanwhile, low-loss backscattered electron images showed mainly compositional contrast at low accelerating voltages (mostly below 1 kV). With attenuated topographical contrast, several different electron densities could be detected, exhibiting several levels of electron density even on a flat plane of spines. Minute differences in topography on epoxy resin sections as seen by secondary electron imaging represented the periphery of the fungal spores and hyphae. On the other hand, the compositional contrast could be retrieved from stained section-face in low-loss BSE imaging, revealing subcellular entities after contrast inversion. The resolution of low-loss BSE imaging was sufficient to resolve plasma membrane, and various types of vacuoles and vesicles. These results suggest that low-loss backscattered electron imaging could potentially provide compositional information to resolve surface chemical features of uncoated microbial cells and stained section-face with heterogeneous surface compositions.     

S/X波段低损耗波导真空窗技术研究

低损耗波导真空窗具有优异的微波特性和真空密封性能,是高灵敏度致冷接收机的关键部件.文中介绍了波导真空窗的工作原理和应用场合,给出了详细的设计模型和性能指标.     

Microwave dielectric properties of BaO−2CeO2−nTiO2 ceramics

The BaO-2CeO₂-nTiO₂ ceramics with n=3, 4 and 5 have been prepared with CeO₂ as starting material. The ceramics have been characterized using scanning electron microscopy, X-ray diffraction, Raman and X-ray photoelectron spectroscopy techniques. The microwave dielectric properties have been measured using standard dielectric resonator techniques. BaO-2CeO₂-3TiO₂ (123), BaO-2CeO₂-4TiO₂ (124) and BaO-2CeO₂-5TiO₂ (125) ceramics showed dielectric constants of 38, 27 and 32, respectively. All the ceramics showed fairly good unloaded Q-factors. 124 and 125 compounds exhibited low τ_f values, while 123 showed a high τ_f value.     

The effect of glass additives on the microwave dielectric properties of Ba(Mg1/3Ta2/3)O3 ceramics

The effect of glass additives on the densification, phase evolution, microstructure and microwave dielectric properties of Ba(Mg_1/3Ta_2/3)O₃ (BMT) was investigated. Different weight percentages of quenched glass such as B₂O₃, SiO₂, B₂O₃-SiO₂, ZnO-B₂O₃, 5ZnO-2B₂O₃, Al₂O₃-SiO₂, Na₂O-2B₂O₃·10H₂O, BaO-B₂O₃-SiO₂, MgO-B₂O₃-SiO₂, PbO-B₂O₃-SiO₂, ZnO-B₂O₃-SiO₂ and 2MgO-Al₂O₃-5SiO₂ were added to calcined BMT precursor. The sintering temperature of the glass-added BMT samples were lowered down to 1300 °C compared to solid-state sintering where the temperature was 1650 °C. The formation of high temperature satellite phases such as Ba₅Ta₄O₁₅ and Ba₇Ta₆O₂₂ were found to be suppressed by the glass addition. Addition of glass systems such as B₂O₃, ZnO-B₂O₃, 5ZnO-2B₂O₃ and ZnO-B₂O₃-SiO₂ improved the densification and microwave dielectric properties. Other glasses were found to react with BMT to form low-Q phases which prevented densification. The microwave dielectric properties of undoped BMT with a densification of 93.1% of the theoretical density were ε_r=24.8, and Q_u×f=80,000. The BMT doped with 1.0 wt% of B₂O₃ has Q_u×f=124,700, ε_r=24.2, and . The unloaded Q factor of 0.2 wt% ZnO-B₂O₃-doped BMT was 136,500 GHz while that of 1.0 wt% of 5ZnO-2B₂O₃ added ceramic was Q_u×f=141,800 GHz. The best microwave quality factor was observed for ZnO-B₂O₃-SiO₂ (ZBS) glass-added ceramics which can act as a perfect liquid-phase medium for the sintering of BMT. The microwave dielectric properties of 0.2 wt% ZBS-added BMT dielectric was Q_u×f=152,800 GHz, ε_r=25.5, and .     

Microprism for Wide-Angle Low-Loss Y-Junction Waveguide

A wide-angle low-loss Y-branch waveguide with butterfly-shaped microprisms is designed. The microprisms not only compensate the phase difference but enhance the mode-conversion evolution in the branching region. Simulation results predict that a mode separation with low branching losses can be achieved in the wide-angle Y-branch. The transmitted power efficiency can be as high as 89 % for the branching angle up to 20 .