基于校园网的嵌入式广播系统设计

建立基于校园网的嵌入式广播系统,可以克服传统广播系统的许多缺陷。通过共享校园网网络系统的硬件资源,建立嵌入式广播系统,通过VLAN划分实现广播系统动态分区管理,扩展广播系统的功能。该方案可以大大节约校园广播系统的建设成本。     

利用HVS特性与混沌映射的图像水印算法

提出一种基于混沌序列的图像空域水印算法。首先通过亮度、边缘、纹理特性计算出每象素视觉因子;然后由视觉因子和混沌映射确定每象素水印嵌入比特位;最后通过替换方式嵌入水印。水印提取时不需原始图像的参与,实验表明算法具有较好的水印透明性,并对一般信号处理攻击是鲁棒的。     

基于紫外光刻的双轴张应变Ge/SiGe多量子阱电吸收调制器北大核心CSCD

采用紫外光刻工艺(ultraviolet lithography technique,UVL),在互补金属氧化物半导体(complementary metal oxide semiconductor,CMOS)兼容的硅基平台上制作了基于悬空微桥结构在Ge/SiGe多量子阱材料中引入双轴张应变的低偏振相关电吸收调制器。利用拉曼光谱测试了器件引入双轴张应变的大小,并对器件在横电(transverse electric,TE)偏振和横磁(transverse magnetic,TM)偏振下的光电流响应、调制消光比和高频响应等性能进行了测试。器件的低偏振相关消光比在0 V/4 V工作电压下可达5.8 dB,3 dB调制带宽在4 V反向偏置电压时为8.3 GHz。与电子束光刻工艺(electron beam lithography technique,EBL)相比,采用UVL制作的器件在调制消光比、高频响应带宽等性能上略差一点,但具有曝光时间短、成本低和可大批量生产等优势,应用前景广阔。     

LTE系统中下行预编码技术

长期演进技术（LTE,Long Term Evolution）采用正交频分复用（Orthogonal Frequency Division Multiplexing）和多输入多输出（Multiple-Input Multiple-Output）相关技术作为其无线网络演进的标准。MIMO是下一代无线移动通信的关键技术之一,它通过使用多天线来抑制信道衰落,能够获得比传统单输入单输出（Single Input,Single Output）系统更高的信道容量,在实际中有广泛的应用。文中主要研究了LTE系统中MIMO下行链路的预编码技术以及相关仿真算法。仿真结果表明了LTE系统中预编码技术的有效性。     

多重分数傅里叶变换全息防伪术

基于分数傅里叶变换全息图 (FRTH)的记录和再现的特殊性 ,提出一种记录多重全息图的新方法 ,可发展一种多重FRTH防伪术。即利用简单的分数傅里叶变换系统 ,并改变其分数阶 ,就可以很方便地在一块感光板上分别记录多个物体 (或同一物体的不同部分 )在不同位置上的不同阶的FRTH。制作了多重分数傅里叶变换全息图 ,讨论了其防伪特性 ,并获得了满意的再现结果     

功率型LED封装键合材料的有限元热分析

建立了功率型LED结构,分析了其热阻模型,对采用高导热导电银胶、纳米银焊膏、大功率芯片键合胶、Sn70Pb30四种键合材料的LED进行了ANSYS有限元软件仿真对比研究。结果表明,纳米银焊膏具有最优的传热特性。采用了正向电压法对3W蓝光LED进行了热阻测量,其数值与仿真结果基本相符,验证了模拟仿真结果的真实性。     

电厂空预器吹灰改造与研究

空预器作为我国大型火力发电厂重要组成部分,其高效、稳定的运行对于火电机组而言具有十分重大的意义.当前,我国大部分火电机组均存在空预器堵塞现象,严重影响到锅炉安全、经济运行,为此,本文基于宝庆发电公司660MW机组三分仓容克氏空预器吹灰改造展开研究,对变工况下空预器吹灰改造前后差压变化做出对比分析,以及对定工况下空预器烟...     

慢化体材料对加速器BNCT束流装置中子品质影响研究

基于加速器中子源的硼中子俘获治疗（BNCT）是一种较好的肿瘤治疗技术,通过慢化得到的超热中子可用于非浅表肿瘤BNCT治疗.本文以2.3 MeV、10 mA质子流强的7Li（p,n）7Be中子源为对象,建立了加速器BNCT束流装置模型,采用中子输运程序MCNP研究了慢化体材料对超热中子束流品质的影响.结果表明：采用重水作为慢化体材料可有效的提高束流出口处超热中子水平,对于2.3 MeV、10 mA质子流强的7Li（p,n）7Be中子源,超热中子束流水平为0.669×109n/（cm2.s）,超热中子与快中子产额比达62.3,基本达到临床治疗所需109n/（cm2.s）的超热中子水平.     

Raman spectra,bond characteristics,and microwave dielectric properties of Gd2Mo3O12 ceramics

Gd₂Mo₃O₁₂ ceramics were prepared using the traditional solid-phase reaction method. All samples were found to possess an orthorhombic crystal structure with a space group of Pba2, as revealed by refined XRD results. The ceramic sintered at 1000 °C exhibited a high relative density of 96.95 % and superior microwave dielectric properties, including ε_r of 9.42 ± 0.05,  × f of 49258 ± 1200 GHz, and τ_f of −71.8 ± 0.7 ppm/°C. The results suggest a correlation between an increase in ε_r and higher relative density, and a more compact and uniform microstructure can lead to higher  × f value. Chemical bonding theories and Raman spectroscopy analysis reveal that Mo-O bonds, rather than Gd-O bonds, dominate the microwave dielectric properties. Furthermore, the ε_r of Gd₂Mo₃O₁₂ ceramic was closely related to bond ionicity, while  × f and τ_f were mainly determined by lattice energy and bond energy, respectively.     

Investigation of the structure and mechanical properties of a novel dental graded glass/zirconia ceramic

Constructing graded structure is a promising solution to reduce the occurrence of cracking and delamination of bilayered zirconia prosthesis. In this work, a novel graded glass/zirconia ceramic was developed by utilizing the interdiffusion between dense zirconia and a novel lithium disilicate glass in the SiO₂-Li₂O-Al₂O₃ system. Results demonstrated that a graded glass/zirconia structure with a depth of about 300 µm was constructed, which exhibited obviously gradient characteristics in microstructure, glass content and mechanical properties. The hardness (H) and elastic modulus (EM) values at the surface reduced significantly (64% for H and 79% for EM), and increased gradually with depth of graded layer. When the graded layer was subjected to loading force, the biaxial flexural strength increased. The mechanism of the evolution of graded structure and change of strength were also elucidated in detail. This study provides a promising strategy to improve the interface stability of bilayered zirconia restoration.