熔石英玻璃激光损伤的三维应力场研究

为了研究CO₂激光损伤后熔石英玻璃内部的三维应力场分布,采用脉冲CO₂激光与熔石英玻璃相互作用的有限元数值模型,计算了脉冲激光停止时熔石英玻璃内部的温度分布,并研究了材料冷却后的内部三维应力分布和表面初始损伤形貌,计算结果与实验结果吻合。以该模型为基础,详细分析了径向和环向应力的三维分布,结果表明,在损伤凹坑附近,径向应力表现为压应力,且在凹坑底部附近取得最大值后,径向应力沿深度方向逐渐转化为拉应力;损伤凹坑附近的环向应力与径向应力相似,均表现为压应力,但压应力沿径向逐渐转化为拉应力,不同深度处的环向应力沿轴向增至最大后逐渐减小。另外,脉冲激光能量的增大导致径向应力与环向应力及其影响范围均有明显增加。研究结果有助于分析激光损伤熔石英玻璃内部的三维应力场,为CO₂激光修复工艺的改进提供了理论依据。     

基于NCC的图像匹配快速算法

在图像匹配过程中,针对传统归一化积相关（NCC）算法计算量大的问题,提出一种对NCC进行改进的图像匹配快速算法。该算法首先使用差分求和定理改造NCC相似度量函数,以降低匹配计算量。然后提出模板区域分割,设定阈值,进一步去除大量不必要的计算,优化匹配搜索过程,实现了快速匹配。实验结果证明,与传统的匹配算法相比,在保证精度的前提下,计算复杂度大大降低。     

无像散场曲的衍射机理及其计算研究

首先由衍射成像原理出发得到用波像差函数表示的有像差像点的光强分布的积分式,再由仅有无像散场曲的像点光强分布的积分式推导出其解析计算式,进而分析了无像散场曲产生的衍射机理.模拟实验表明了这一计算和分析是有效而可靠的,有助于像差检测与校正中对场曲进行分析与处理.     

EPCs与NSCs共移植对MCAO模型大鼠神经功能缺损恢复影响

目的：将体外培养的EPCs与NSCs共移植体移入MCAO模型大鼠脑内,观察缺血区血管新生和神经功能缺损修复情况。方法;选择240只SD大鼠随机分为假手术组、MCAO组、MCAO＋NSCs组、MCAO＋EPCs组、MCAO＋EPCs和NSCs共移值体组,在1d、3d、7d、14d、30d、60d各时间点观察各组脑缺血半暗区微血管密度和大鼠的电生理指标（运动诱发电位）及行为学（mNSS改良神经功能评分）。结果：MCAO＋NSCs组的微血管密度与MCAO组在各时间点无差别;MCAO＋EPCs组、MCAO＋EPCs和NSCs共移值体组的微血管密度除1d外其他各时间点均高于MCAO组。在7d后MCAO＋NSCs组、MCAO＋EPCs组、MCAO＋共移植体组运动诱发电位与缺血对照组有差异,MCAO＋共移植体组差异最大。MCAO＋EPCs组、MCAO＋共移值体组与MCAO照组相比在3d后有差异,MCAO＋共移植体组差异最大。结论：EPCs与NSCs共移植体移入MCAO模型大鼠脑内,可增加其缺血半暗区血管新生,促进神经功能的进一步恢复。     

红外人脸隐蔽性三维测量

提出了一种利用近红外结构光对人脸进行隐蔽性三维测量的方法。将波长为850nm的红外结构光条纹投影到人脸表面,利用相位测量轮廓术获取人脸的三维数据。用频谱分析的方法讨论了皮肤对结构照明光场的影响,通过实验给出了系统等效的传递函数,并计算分析了皮肤对红外正弦条纹对比度的影响.由于皮肤的透射和散射等特性,在设计人脸三维测量系统时,必须使用较低空间频率和较高对比度的结构光。实验结果表明,文中提出的方法是可行的,满足人脸隐蔽性三维测量的要求,在医学美容、人脸识别等领域具有广阔的应用前景。     

Empirical analysis of strategy selection for the technology leading and technology catch-up in the IT industry

R&D strategies of companies with low and high technological levels are discussed based on the concept of technology convergence and divergence. However, empirically detecting enterprise technology convergence in the distribution of enterprise technology (total productivity increase) over time and identifying key change factors are challenging. This study used a novel statistical indicator that captures the internal technology distribution change with a single number to clearly measure the technology distribution peak as a change in critical bandwidth for enterprise technology convergence and presented it as evidence of each technology convergence or divergence. Furthermore, this study applied the quantitative technology convergence identification method. Technology convergence appeared from the separation of total corporate productivity distribution of 69 IT companies in Korea in 2019–2020 rather than in 2015–2016. Results indicated that when the total technological level was separated from the technology leading and technology catch-up, IT companies were found to be pursuing R&D strategies for technology catch-up.     

Multicarrier constant envelope OFDM signal design for radar applications

Orthogonal frequency division multiplexing (OFDM) radar signals have been introduced for high range resolution radars. These signals have prominent properties such as favorable ambiguity function, high bandwidth efficiency, and possibility of use in dual mode radar/communication systems. But the large amplitude fluctuations of the OFDM signal make it susceptible to system nonlinearities. To alleviate this problem, constant envelope OFDM (CE-OFDM) signal has been introduced which combines orthogonal frequency division multiplexing and phase modulation or frequency modulation. Although several works have been reported on OFDM radar signal design, there is no a systematic approach for designing CE-OFDM signals for radar applications. In this paper we will focus on CE-OFDM signal design for radar applications. Two different methods for designing a CE-OFDM signal with favorable ambiguity functions are introduced. The first one is based on modulating a complementary set of sequences on different sub-carriers while the second is based on using a proper single carrier coded signal and then extracting its most similar multicarrier OFDM or CE-OFDM coded signal.     

Dielectric response and electric properties of organic semiconducting phthalocyanine thin films

The dielectric function of some phthalocyanine compounds (ZnPc, H₂Pc, CuPc, and FePc) were investigated by analyzing the measured capacitance and loss tangent data. The real part of the dielectric constant, ε₁, varies strongly with frequency and temperature. The frequency dependence was expressed as: ε₁ = Aωⁿ, where the index, n, assumes negative values (n < 0). In addition, the imaginary part of the dielectric constant, ε₂, is also frequency and temperature dependent. Data analysis confirmed that ε₂ = Bω^m with values of m less than zero. At low frequencies and all temperatures, a strong dependence is observed, while at higher frequencies, a moderate dependence is obvious especially for the Au-electrode sample. Qualitatively, the type of electrode material had little effect on the behavior of the dielectric constant but did affect its value. Analysis of the AC conductivity dependence on frequency at different temperatures indicated that the correlated barrier hopping (CBH) model is the most suitable mechanism for the AC conduction behavior. Maximum barrier height, W, has been estimated for ZnPc with different electrode materials (Au and Al), and had values between 0.10 and 0.9 eV. For both electrode types, the maximum barrier height has strong frequency dependence at high frequency and low temperatures. The relaxation time, τ, for ZnPc and FePc films increases with decreasing frequency. The activation energy was derived from the slopes of τ versus 1/T curves. At low temperatures, an activation energy value of about 0.01 eV and 0.04 eV was estimated for ZnPc and FePc, respectively. The low values of activation energy suggest that the hopping of charge carriers between localized states is the dominant mechanism.     

基于SPWVD的频率编码脉冲信号的检测与参数估计

运用SPWVD对脉内频率编码信号进行检测与参数估计,根据SPWVD的真边缘性实现了对频率编码信号的识别、突变点的检测以及瞬时频率的估计。该算法在低信噪比下,可以准确地提取出信号的脉内调制特征,有较好的应用价值。     

Performance and Modeling of the MWIR HgCdTe Electron Avalanche Photodiode

The operation of the mid-wave infrared (MWIR) HgCdTe cylindrical electron injection avalanche photodiode (e-APD) is described. The measured gain and excess noise factor are related to the collection region fill factor. A two-dimensional diffusion model calculates the time-dependent response and steady-state pixel point spread function for cylindrical diodes, and predicts bandwidths near 1 GHz for small geometries. A 2 μm diameter spot scan system was developed for point spread function and crosstalk measurements at 80 K. An electron diffusion length of 13.4 μm was extracted from spot scan data. Bandwidth data are shown that indicate bandwidths in excess of 300 MHz for small unit cells geometries. Dark current data, at high gain levels, indicate an effective gain normalized dark density count as low as 1000 counts/μs/cm² at an APD gain of 444. A junction doping profile was determined from capacitance–voltage data. Spectral response data shows a gain-independent characteristic.