Al_2O_3颗粒对Al-Zn合金激光快凝组织的影响

通过比较Ａｌ－Ｚｎ合金和Ａｌ_２Ｏ_（３ｐ）／Ａｌ－Ｚｎ复合材料的激光重熔组织。分析Ａｌ_２Ｏ_３颗粒对Ａｌ－Ｚｎ合金激光快凝组织的影响规律。实验结果表明,Ａｌ_２Ｏ_３颗粒可以显著细化激光熔区的晶粒。基于凝固界面与颗粒交互作用的理论分析,给出了晶粒细化的临界条件。     

多晶类窗口材料研究

多晶类窗口材料研究李艺，苏希玉，张冰林（曲阜师范大学物理系，山东曲阜２７３１６５）在光电探测器窗口材料的系列内，多晶窗口材料占有一定地位，如专家们所熟悉的热压多晶材料Ｉｔｒａｎ１、Ｉｔｒａｎ２等。透明Ａｌ２Ｏ３陶资及微晶玻璃陶瓷作为窗口材料也被介绍到...     

陶瓷材料的激光合成工艺研究

采用激光作热源合成了Ａｌ_２Ｏ_３－ＷＯ_３，Ｃｒ_２Ｏ_３－ＷＯ_３，Ｓｂ_２Ｏ_３－ＷＯ_３，ＣｄＯ－ＷＯ_３，Ｆｅ_２Ｏ_３－ＷＯ_３等系列陶瓷材料。测量这些材料的阻温特性，结果表明这些材料都是负温度系数热敏电阻材料。讨论激光合成陶瓷工艺过程中所表现出来的特殊生长形态，这些形态与激光在合成材料中形成的温场分布、材料的导热特性、材料对激光的吸收等有关。通过理论计算得出的温场分布与实验结果很好符合。论述用激光作热源合成陶瓷与传统工艺相比所具有的独特优点，指出该工艺目前尚未解决的问题及今后的研究方向。     

激光合成Al_2O_3-WO_3陶瓷材料的显微分析

用Ｘ射线衍射等技术分析了激光合成Ａｌ２Ｏ３－ＷＯ３陶瓷材料，结果表明在激光合成样品中形成柱状晶，而常规工艺和Ｎ２气氛中烧结样品不含有柱状晶，柱状晶的成分主要是Ａｌ２Ｏ３。进一步的分析表明Ａｌ２Ｏ３－ＷＯ３陶瓷合成样品的导电相是ＡｌｘＷＯ３。     

γ-TiAl金属间化合物合金激光表面合金化制备Al_2O_3/TiAl耐磨复合材料涂层研究

以镍包Ａｌ_２Ｏ_３粉末为原料对γ－ＴｉＡｌ金属间化合物合金进行激光表面合金化,制得无裂纹、表面光滑、内部组织致密、厚度可达１．０ｍｍ、以快速凝固Ａｌ_２Ｏ_３硬质相为增强相的“原位”耐磨复合材料合金层,通过预热及缓冷可以消除涂层开裂现象。涂层与基体的结合为完全冶金结合,激光表面合金化后ＴｉＡｌ合金硬度及在滑动磨损及磨料磨损条件下耐磨性均大幅度提高。     

自锁模Ti：Al_2O_3激光器的像散补偿

提出在自锁模Ｔｉ：Ａｌ_２Ｏ_３激光器激光晶体内部实现像散补偿的方案，并给出了最佳腔型设计和最佳工作点。     

等离子喷涂Al_2O_3陶瓷涂层的激光重熔处理

用Ｘ 射线衍射、扫描电镜和显微硬度研究了等离子喷涂Ａｌ２Ｏ３ 陶瓷涂层激光重熔处理后陶瓷熔化层的组织结构及硬度变化特征。激光重熔区亚稳相γ－ Ａｌ２Ｏ３ 转变成为稳定相α－ Ａｌ２Ｏ３;陶瓷熔化层致密、无孔隙,但存在裂纹;熔化层硬度有较大提高,且随激光能量密度的增大而增大,而与涂层设计几乎无关。此外,激光重熔能较大地提高Ａｌ２Ｏ３ 陶瓷涂层的耐磨性。     

Al_2O_3-WO_3材料的激光合成研究

采用大功率ＣＯ２激光器合成出了Ａｌ２Ｏ３－ＷＯ３陶瓷材料。测量其阻－温特性表明合成样品具有线性的ＮＴＣ热敏电阻特性，微观分析结果证明激光合成样品由Ａｌ２Ｏ３、ＷＯ３、Ａｌ２（ＷＯ４）３、ＡｌｘＷＯ３四相组成，而起导电作用的是ＡｌｘＷＯ３这一非平衡反应产物。常规烧结工艺合成Ａｌ２Ｏ３－ＷＯ３陶瓷材料所得试样没有线性的ＮＴＣ热敏电阻特性。     

等离子喷涂Al2O3+13wt%TiO2陶瓷涂层的 激光重熔处理

本文用Ｘ射线衍射、扫描电镜和显微硬度研究了等离子喷涂Ａｌ２Ｏ３＋１３ｗｔ％ＴｉＯ２陶瓷涂层激光重熔处理后陶瓷熔化层的组织结构及硬度变化特征。激光重熔区亚稳相Ｙ－Ａｌ２Ｏ３转变成为稳定相α－Ａｌ２Ｏ３：ＴｉＯ２与Ａｌ２Ｏ３反应生成ＴｉＡｌ２Ｏ３陶瓷熔化层致密,无孔隙、少裂纹或无裂纹;熔化层硬度有较大提高,且随激光能量密度的增大而增大,而涂层设计对其影响很小。此外,激光重熔能极大地提高陶瓷的涂层的耐磨     

SiCp/6061Al金属基复合材料激光焊接研究

采用高能ＣＯ_２激光束对 ＳｉＣ颗粒增强 ６０６１铝基复合材料 ＳｉＣｐ／６０６１ＡＩＭＭＣ进行激光焊接、研究激光焊接工艺参数及填充材料对焊缝显微组织的影响。结果表明,对 ＳｉＣｐ／６０６１Ａｌ复合材料进行激光焊接,可以获得气孔很少、质量较高的焊接接头,但在激光直接熔化焊接焊缝中形成针状Ａｌ_４Ｃ_３脆性相,脆性相Ａｌ_４Ｃ_３的数量与尺寸随激光束功率密度增加而增大,随焊接速度增大而减少。激光焊接时加入０．３ｍｍ厚的金属钛片作为填充材料,在焊缝中形成ＴｉＣ增强相,从而抑制了脆性相Ａｌ_４Ｃ_３的形成。     

白宝石窗口增透膜的研究

对白宝石 (Al2 O3)和石英 (SiO2 )窗口的性能进行了比较 ,并在白宝石上镀制增透膜 ,进行初步的判断实验 ,取得了良好的效果 ,同时对存在的问题进行了分析 ,指出白宝石是一种比较有前途的高功率激光窗口材料。     

指数遗忘分布性能分析

该文分析讨论了指数遗忘变换(EFT)的信号瞬时频率表示性能。EFT采用单边指数窗口对信号进行采样和加权,因而可以利用迭代运算提高计算效率。与其他时频表示方法相比,EFT在处理较大长度的数据时具有优势,且更易于利用硬件实现。该文对EFT的瞬时频率表示偏差、均方差值的统计特性与信噪比及遗忘系数的关系进行了分析,给出了相应的仿真结果。同时为克服单边指数窗口的缺陷,提出了采用对称窗口的双边指数遗忘分布的计算形式,该方法在保持原有指数遗忘分布计算效率较高的优点的同时能够大大减小瞬时频率的表示偏差。     

Electromagnetic Analysis and Cold Test of a Distributed Window for a High Power Gyrotron

A novel distributed window for output radiation from a high power 110 GHz gyrotron is made of thin slats of sapphire interleaved and brazed to hollow metal vanes. We report the results of electromagnetic theory and cold test of this distributed window. We calculate the frequency dependence of the reflectivity of a Gaussian beam from the window. The theory indicates a significant frequency shift of the minimum reflectivity with temperature rise of the sapphire slab. This effect is of great importance for high power operation. In cold test, the distributed window reflectivity was measured while the window was heated. The cold test results are in good agreement with the theory.     

一种厚铜刚挠结合印制板渗胶改善

厚铜刚挠结合板的生产中一般采用普通流胶半固化片制作,在满足厚铜填胶的同时也导致窗口渗胶的问题越发突出,严重影响弯折性能,本研究选取一款应用于电源模块的105μm厚铜刚挠结合板,结合半固化片类型、压合参数、保护胶带类型、窗口设计等,极大程度的克服了窗口渗胶问题.     

Investigation of alternative window materials for GaAs solar cells

The optimum window material for surface passivation of GaAs solar cells is investigated using theoretical analysis of optical losses due to window bandgap energy and thickness. A simplified expression is developed to calculate the effective surface recombination velocity in terms of lattice mismatch between the window layer and GaAs, which suggests using a window material with and indirect bandgap energy greater than 2.0 eV, a thickness of less than 0.05 μm, and a lattice mismatch of less than 0.05%. Experimental GaAs solar cells were fabricated and quantum efficiency measurements were made using no window (bare GaAs), Al_0.7Ga_0.3As, Na₂S, and ZnSe/Na₂S windows. The Al_0.7Ga_0.3As and Na₂S windows are shown to passivate the GaAs surface and reduce the surface recombination velocity to less than 10⁵ cm/s, while the ZnSe encapsulating layer was used to permanently maintain the temporary surface passivation effects from Na₂S     

余弦窗DFT递推算法

本文分析了DFT递推算法的窗谱特性及其对信号频谱精度的影响,给出了余弦窗DFT递推算法及其实现方法,介绍了算法的初始化方法及局部频域的频谱分析算法,分析了算法的复杂性进行了仿真分析。     

Compensating for window effects in the calculation of spectrographic instantaneous bandwidth

Exact results derived by Cohen and Lee are used to study the distortion induced by the window in the computation of instantaneous bandwidth via the spectrogram. These concepts have been recently used in an interesting study regarding lesion-induced blood flow disturbances, where an approximation was made to compensate for the window effects. We show that this compensation is accurate for stationary signals, but becomes increasingly poorer as the signal becomes less stationary (e.g., large frequency modulations). We propose an alternative technique to reduce the window distortions, and point out the use of other time-frequency distributions that do not suffer such distortions.     

Comparison of Model Prediction With Measurements of Galactic Background Noise at L-Band

The spectral window at L-band (1.413 GHz) is important for passive remote sensing of surface parameters such as soil moisture and sea surface salinity that are needed to understand the hydrological cycle and ocean circulation. Radiation from celestial sources (mostly galactic) is strong in this window, and an accurate accounting of this background radiation is often needed for calibration. This paper presents a comparison of the background radiation predicted by a model developed from modern radio astronomy measurements with measurements made with several modern L-band remote sensing radiometers. The comparison validates the model and illustrates the magnitude of the correction necessary in remote sensing applications.     

无线信道上的语音抗阻塞传输算法

阻塞干扰是无线信道上数据传输面临的棘手问题。抗阻塞干扰的“滑动窗”语音传输算法将传输码流均匀地分成若干片段,用定长的“滑动窗”在码流上滑动并截取其中的一段连续片段作为某跳频点的数据。接收端比较连续若干跳的重叠部分,判断并恢复“坏跳”数据;对每个片段进行差错控制保护,通过“联合最大后验概率译码”方法抵抗更高误码率的影响。测试表明,在有阻塞干扰的跳频信道上,“滑动窗”算法的性能远远优于传统的RS码纠错算法。     

A computer analysis of Ga1-xAlxAs-GaAs solar cells with multilayered window structure

Numerical calculations have been made of the spectral response and conversion efficiency of Ga1-xAlxAs-GaAs solar cells with multilayered window structures. Maximum conversion efficiencies of about 20 percent are predicted, equaling those achieved with graded band-gap solar cells, for the case of three-layered window structures.