对ORL人脸数据库识别过程中的参数选择策略

对ORL人脸数据库的识别大致分为两步骤:使用PCA对训练集降维提取特征向量和使用KNN对样本集进行分类。在该过程中,有两个参数直接影响着人脸识别的准确率:PCA选取的特征向量数目n和KNN中的k值。如果对它们的选取没有一个良好的策略,就会出现正确率太低、时间复杂度太高、过拟合等问题。文章采用状态空间搜索找到准确率与时间复杂度中的平衡点,得到了有效的搜索结果。     

叶绿素荧光量子产量的MODIS遥感算法

从荧光量子产量的原理出发,利用 MODIS 卫星数据建立了一种估算量子产量的算法--φ算法.通过 2006 年 3 月 23 日渤海和北黄海的 MODIS 数据计算了荧光量子产量,并与叶绿素荧光效率(cFE)产品进行了比较.结果表明,φ算法是一种更精确的荧光量子产量的估算算法,它有效地避免了 CFE 存在的几个误差来源:包括未考虑浮游植物的"包裹效应"、使用 412nm 的离水辐亮度反演的浮游植物吸收系数以及积分深度过浅.CFE在大部分海域出现负值,还出现了某些高估点;在有效数据范围内,两者存在明显的线性相关关系.φ算法估算的量子产量最高值在0.05左右,这与其它海区测量的值域范围基本一致.除辽东湾东北部和部分近岸水域外,大部分离岸水域在0.001～0.02的范围内.通过对φ算法的误差来源分析,认为发展一种新的反演 678nm 比吸收系数和平均吸收系数的波段比值算法是可行的,也是改进φ算法精度的有效方法.     

On the Diversity Order of a General Cooperative Relaying Communication System

Cooperative communication technology exploiting distributed spatial diversity is a promising solution for the future high data-rate cellular and ad-hoc wireless communications. To characterize the performance of a cooperative network, the cooperative diversity is commonly used. In this paper, we revisit the concept of diversity and look into the essence of cooperative diversity. We analyze the diversity performance of a general cooperative relaying system with multiple branches. Moreover, each branch consists of one or more hops. Unlike in other analyses, the assumptions that each node being only equipped with a single antenna and that all channel characteristics belonging to the same family are NOT required in our study. Using the decode-and-forward (DF) relaying protocol as an illustration, we provide analytical results on the diversity gain and the coding gain. The results also encompass most of the existing results as special cases. We further show the relationship between the diversity order of a branch and those of the constituent links; and the relationship between the diversity order of the network and those of the constituent branches. In particular, we show that for the uncoded DF protocol, the full diversity order can be achieved by using simple hard-decision detection at the destination. The requirement is to set appropriate signal-to-noise-ratio (SNR) thresholds for the multi-hop branches. To improve the bandwidth efficiency, we also randomly select one branch, among those branches satisfying the SNR-threshold requirement, for the transmission. We show that such a scheme accomplishes the full diversity order and produces a good error performance.     

Influence of N2 and O2 annealing treatment on the optical bandgap of polycrystalline Ga2O3:Cu films

Cu-doped Ga₂O₃ thin films were deposited by electron beam evaporation with subsequent annealing at 1000 °C in N₂ and O₂ for 1 h. The influence of the annealing atmosphere on the crystal structure, surface morphology and optical properties of Ga₂O₃:Cu films was investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), and transmittance and photoluminescence (PL) spectroscopy. The optical bandgap deduced from the absorption spectrum was greater for the O₂ annealed than for N₂ annealed samples. In both cases the bandgap was wider than for bulk β-Ga₂O₃. The grain size and surface roughness were sensitive to the annealing atmosphere. Results confirmed that the annealed samples were polycrystalline β-Ga₂O₃ with some amorphous phase. We hypothesize that annealing in oxygen led to recrystallization of the Ga₂O₃:Cu film. Annealing treatment improved the crystal quality of Ga₂O₃:Cu films and the PL intensity of the samples increased.     

室内MIMO ACO-OFDM可见光通信系统接收机设计

设计了一种在室内可见光MIMO通信系统(MIMO-VLC)中使用具有两个不同视场角(FOV)的光电二极管(PD)的角度分集光接收机(2FOV-ADR),其兼具两个不同视场角的接收机(2-FOV)和传统角度分集接收机(ADR)的优点,实现了更优的接收性能。对将LED灯用作数据发射器的典型室内可见光通信场景进行仿真,结果表明,2FOV-ADR均衡器输出端的最小信噪比(minSNR)要高于2-FOV接收机和传统ADR,实现了室内97%的位置的minSNR在45 dB以上,相比于前两种接收机,这一比例分别提高了96%和32%。最后,对使用非对称限幅光正交频分复用(ACO-OFDM)作为调制方案的系统,计算总误码率(BER),给出了迫零和最小均方误差均衡器的结果。结果表明,对于所考虑的室内位置,2FOV-ADR都具有最低的误码率。     

Concurrent Blind Channel Equalization in Impulsive Noise Environments

In some communication systems the trans- mitted signal is contaminated by impulsive noise with a non-Gaussian distribution. Non-Gaussian noise caused significant performance degradation to communication re- ceivers. The new constant modulus blind equalizer based on Fractional lower-order statistics of the equalizer input, which is defined as FLOS_CMA, is able to mitigate impul- sive channel noise while restoring the constant modulus character of the transmitted communication signal. How- ever, like the Constant modulus algorithm （CMA）, the steady-state Mean square error （]VISE） of the FLOS_CMA algorithm may not be sufficient low for the system to ob- tain adequate performance. This paper proposes a con- current equalizer, in which a Decision-directed least mean p norm （DD_LMP） equalizer operates cooperatively with a FLOS_CMA equalizer, controlled through a non-linear link. Simulation results using M-QAM and 8-PSK signal- ing have shown that besides the capability of compensating the phase offset, the proposed concurrent FLOS_CMA and DD_LMP blind equalizer has faster convergence rate and lower steady-state MSE than the FLOS_CMA approach.     

L-乳酸和α-苯丙氨酸聚酯酰胺共聚物的合成表征及降解

以直接熔融缩聚法成功制备了L-乳酸和α-苯丙氨酸聚酯酰胺共聚物.采用红外光谱、核磁共振、凝胶色谱、差示扫描量热仪和X射线衍射等对共聚物结构和性能进行了分析测试,重点考察了投料比对产物组成、分子量及其热性能和结晶性能的影响,并对共聚物的降解性能进行了初步试验.随着α-苯丙氨酸含量增加,相应共聚物的分子量明显下降,结晶性下...     

热解含硫金属有机配合物法合成亮紫色发光的α-ZnS:Cu纳米荧光粉

以硝酸锌、硝酸铜和二乙基二硫代氨基甲酸钠为原料,制得含硫金属有机配合物.将含硫金属有机配合物在200℃进行热解,制备了亮紫色发光的ZnS： Cu纳米荧光粉.XRD检测结果显示,荧光粉样品为六方晶系的高温相α-ZnS.根据TEM结果,样品为均匀的球形粒子,其粒子尺寸在30nm左右.室温下,样品的激发光谱峰值位于235nm...