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1.
Effective dielectric constant model of electromagnetic backscattering from stratified air–sea surface film–sea water medium 下载免费PDF全文
Studies of surface film medium on the sea surface are carried out in this paper for developing the technology to automatically detect and classify sea surface films, and an effective dielectric constant model of electromagnetic backscattering from a stratified air–ocean interface. Numerical results of the new model show the characteristics of effective dielectric constants for the air–sea surface film–sea water medium as follows. The effective dielectric constants decrease with increasing relative dielectric constants of the sea surface films. The effective dielectric constants decrease in horizontal polarization(abbr. HH polarization) and increase in VV vertical polarization(abbr. VV polarization) with increasing radar incident angle. Effective dielectric constants vary with relative sea surface film thickness as a cosinusoidal function of sea surface film thickness. Effective dielectric constant of VV polarization is larger than that of HH polarization. Two potential applications are found with our model, i.e., the retrieval of dielectric constants from the sea surface film, and the film thickness retrieval with our model. Our model has a highly significant influence on improving the technology related to the remote sensing of sea surface films. 相似文献
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Graphene-based heterostructure is one of the most attractive topics in physics and material sciences due to its intriguing properties and applications. We report the one-step fabrication of a novel graphene/Mo_2C heterostructure by using chemical vapor deposition(CVD). The composition and structure of the heterostructure are characterized through energydispersive spectrometer, transmission electron microscope, and Raman spectrum. The growth rule analysis of the results shows the flow rate of methane is a main factor in preparing the graphene/Mo_2C heterostructure. A schematic diagram of the growth process is also established. Transport measurements are performed to study the superconductivity of the heterostructure which has potential applications in superconducting devices. 相似文献
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Effects of tip perturbation and wing locations on rolling oscillation induced by forebody vortices 总被引:1,自引:0,他引:1 下载免费PDF全文
The wing rock motion is frequently suffered by a wing-body configuration with low swept wing at high angle of attack. It is found from our experimental study that the tip perturbation and wing longitudinal locations affect significantly the wing rock motion of a wing-body. The natural tip perturbation would make the wing rock motion of a nondeterministic nature and an artificial mini-tip perturbation would make the wing rock motion deterministic. The artificial tip perturbation would, as its circumferential location is varied, generate three different types of motion patterns: (1) limit cycle oscillation, (2) irregular oscillation, (3) equilibrium state with tiny oscillation. The amplitude of rolling oscillation corresponding to the limit cycle oscillatory motion pattern is decreased with the wing location shifting downstream along the body axis. 相似文献
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大迎角细长体绕流背涡结构与气动特性分析 总被引:5,自引:0,他引:5
结合实验成果,对大迎角细长体绕流结构及其气动特征进行了分析。利用势流理论,探讨了大迎角下非对称侧向力沿物体轴线的变化特征与分离背涡结构之间的关系,得出截面侧向力系数沿轴向呈现正弦型曲线的变化特征是由轴向旋涡不断脱落所形成的多涡系统诱导的结果。对于三涡以上的多涡系统中,对称的物面压强分布并非一定对应对称的涡结构。 相似文献
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用示踪原子方法,研究了磷(Na2HP32O4)在p型硅表面氧化层中的扩散。硅单晶的电阻率为5—6欧姆·厘米。氧化层是在高温下水汽中生长的,其厚度为0.5—0.6微米,是用灵敏度为10-5克/刻度的微量天平测定的。发现在1245℃时氧化层的生长规律服从X1.85=1.4×10-2t,其中X为氧化层的厚度,单位为微米;t为氧化层的生长时间,单位为分钟。其红外吸收的测量结果与文献中的数据基本一致。扩散是在充满空气的封闭石英管中进行的,扩散温度为700—1250℃,扩散时间从4分钟到5小时。实验结果表明,磷在SiO2层中的浓度分布不能直接用菲克第二定律描述,它可以看成是一个均匀分布和一个遵守菲克第二定律的分布的迭加。按后一种分布得到在700—1200℃范围内的扩散系数的温度依赖关系:D=1.9×10-9exp(-1.1/kT)厘米2/秒。均匀分布部分的浓度为(1—8)×1019原子/厘米3。大中对所用方法和所得结果作了简单讨论. 相似文献
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用中子激活方法,对气态P2O5在SiO2-Si系统中的扩散分布进行了直接测量。样品为p型Si单晶,电阻率为3—5欧姆·厘米,氧化层是在1250℃下水汽中生长的,其厚度为0.45—0.47微米。实验结果表明:对于完全掩蔽的样品,磷在SiO2层中的浓度分布有个陡峭的边界;对于掩蔽失效情形,在靠近SiO2-Si交界面约0.1微米的SiO2层内,磷的浓度显著地降低,出现一个明显的交界层,在交界层以外的SiO2层中磷的浓度是均匀的和恒定的,而交界层中磷的浓度及磷在Si中的表面浓度都随时间的延长而显著地升高,文中对所得的结果作了简单讨论。 相似文献
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目的通过大蒜素和蒜氨酸+蒜氨酸酶混合物处理高血脂小鼠,比较了它们对高血脂小鼠体重、肝重、肝脏细胞形态和脂肪变性的影响.方法大蒜素与蒜氨酸+蒜氨酸酶混合物处理高血脂小鼠,8周后称量小鼠体重和肝重.制作小鼠肝脏细胞石蜡切片和冰冻切片观察的细胞形态.结果大蒜活性物质大蒜素与蒜氨酸+蒜氨酸酶混合物能抑制高血脂小鼠体重和肝重的增加,降低肝系数,并且具有剂量依赖性.组织学观察表明高剂量大蒜素与蒜氨酸+蒜氨酸酶混合物均能减轻脂质对肝细胞形态的改变.与高血脂模型组相比,高剂量大蒜素与蒜氨酸+蒜氨酸酶混合物处理组肝索排列呈放射状,肝细胞排列较为紧密、规则,细胞核位置接近中央,有细胞界限.细胞内颗粒、脂滴和炎性细胞浸润和肝细胞坏死较少.结论大蒜素和蒜氨酸+蒜氨酸酶混合物能减轻高血脂小鼠脂肪对肝细胞的浸润和脂肪变性,并减轻脂肪对肝小叶和细胞形态的改变.蒜氨酸+蒜氨酸酶混合物在降低高血脂小鼠体重和肝重的效果优于大蒜素. 相似文献
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Asymmetric vortices flow over slender body and its active control at high angle of attack 总被引:5,自引:0,他引:5
The studies of asymmetric vortices flow over slender body and its active control at high angles of attack have significant
importance for both academic field and engineering area. This paper attempts to provide an update state of art to the investigations
on the fields of forebody asymmetric vortices. This review emphasizes the correlation between micro-perturbation on the model
nose and its response and evolution behaviors of the asymmetric vortices. The critical issues are discussed, which include
the formation and evolution mechanism of asymmetric multi-vortices; main behaviors of asymmetric vortices flow including its
deterministic feature and vortices flow structure; the evolution and development of asymmetric vortices under the perturbation
on the model nose; forebody vortex active control especially discussed micro-perturbation active control concept and technique
in more detail. However present understanding in this area is still very limited and this paper tries to identify the key
unknown problems in the concluding remarks.
The project supported by the National Natural Science Foundation of China (10172017), Aeronautical Science Foundation of China
(02A51048) and Foundation of National Key Laboratory of Aerodynamic Design and Research (51462020504HK0101) 相似文献
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A critical pattern of crossflow around a slender 总被引:1,自引:0,他引:1
IntroductionModernhigh_performancefightersoftenrequiretobeoperatedunderafairlylargeangleofattacksoastoachieveexcellentmaneuverabilityandagility .Atsuchlargeangleofattack ,asymmetricallee_sidevortexflowwillformatthefrontpartofthefuselage .Sothatsuchagreats… 相似文献