一种利用多带激励模型改进的低速率线性预测语音编码算法

提出了一种利用多带激励（ＭＢＥ）模型改进的低速率线性预测（ＬＰＣ）语音编码算法．文中介绍了该算法的参数提取、量化编码及语音合成的具体方案,并用Ｃ语言构造了一个基于该算法的速率为１,６ ｋｂ／ｓ的语音编码／解码系统．主观测听表明,该系统性能与 ２．４ ｋｂ／ｓ的 ＭＥＬＰ算法接近或相当。     

半导体黄光发光二极管新材料新器件新设备

在可见光范围内,半导体发光二极管(LED)发展很不平衡,黄光LED光效(光功率效率)长期远低于其他颜色光效.本文基于GaN/Si体系,从材料生长、芯片制造、器件物理和专用装备等方面进行了系统研究,解决了外延膜龟裂、位错过多、量子阱应力过大、InGaN黄光阱材料相分离、空穴浓度不足、阱材料生长温度过低、衬底吸光、电极挡光等问题,率先实现了高光效黄光LED关键性突破.所研制的黄光LED器件,在20 A/cm~2驱动下波长565 nm黄光LED光效达26.7%,对应164 lm/W;在1 A/cm~2驱动下波长577 nm黄光LED光效达42.8%,对应248 lm/W.基于高光效黄光LED,开发了无荧光粉、多基色LED照明新光源,实现了纯LED照明光源在路灯、氛围灯等方面应用.     

Effects of Hydrogen Treatment in Barrier on the Electroluminescence of Green InGaN/GaN Single-Quantum-Well Light-Emitting Diodes with V-Shaped Pits Grown on Si Substrates

Effect of hydrogen(H_2) treatment during the GaN barrier growth on the electroluminescence performance of green In GaN/GaN single-quantum-well light-emitting diodes(LEDs) grown on Si substrates is experimentally investigated. We prepare two LED samples with different carrier gas compositions during the growth of GaN barrier. In the H_2 free LED, the GaN barrier is grown in full nitrogen(N_2) atmosphere. For the other H_2 treated LED, a mixture of N_2 and H_2 was used as the carrier gas. It is observed that V-shaped pits decrease in size after H_2 treatment by means of the scanning electron microscope. Due to the fact that the p–n junction interface would be closer to the p-GaN as a result of smaller V-shaped pits, the tunneling barrier for holes to inject into the In GaN quantum well would become thicker after H_2 treatment. Hence, the external quantum efficiency of the H_2 treated LED is lower compared to the H_2 free LED. However, LEDs would exhibit a better leakage behavior after H_2 treatment during the GaN barrier growth because of more effective blocking of the threading dislocations as a result of the H_2 etching at V-shaped pits.     

多孔泡沫镍分液隔板的气液分离性能研究

本文通过水与空气模拟两相流来探究多孔泡沫镍分液隔板的分液性能,测试不同工况下分液隔板分液能力的大小,总结分液隔板分液性能随入口空气流量以及水流量的变化规律,并且用达西渗流定律对多孔材料的渗流率进行了分析,从而对分液隔板的设计起到一定的指导意义。     

铁路围岩分类专家系统中的不确定性推理问题

本文将专家的经验分类标准与需要评判的围岩用模糊数学中择近原则的方法进行模糊模式识别,对专家评判中有关因素采用因素关系图描述,将被评定的围岩视为论域上的一个模糊子集,把推理过程抽象为多维论域上确定隶属度的过程,进而提出用连续隶属函数进行围岩类别的模糊推理。最后,以隶属度的形式,给出评判的分类结果。     

从珠心算起步 走上多彩多姿的人生路——记珠心算选手吴宇恩清华园生活剪影

吴宇恩,小时是广西少数民族珠心算选手,现清华大学在读博士研究生。他是广西龙胜各族自治县侗族人家的子弟,今年26岁,在清华园里他已住了长长的八个年头。回顾曾经走过的路,他感慨万千,常常会回想,自己是怎样走进清华园这个科学知识殿堂的。在一次历届同学的座谈会上,同学们很想分享吴宇恩的成长体会,向他提出:你为什么会选择学习珠     

课外练习

初一年级1.已知:x=2000/2001,y=2001/2002,试比较x与y的大小.     

Dependence of Structure and Haemocompatibility of Amorphous Carbon Films on Substrate Bias Voltage

Tetrahedral amorphous hydrogenated carbon (ta-C:H) films on Si(lO0) substrates were prepared by using a magnetic-field-filter plasma stream deposition system. Samples with different ratios of sp^3-bond to sp^2-bond were obtained by changing the bias voltage applied to the substrates. The ellipsometric spectra of various carbon films in the photon energy range of 1.9-5.4eV were measured. The refractive index n and the relative sp^3 C ratio of these films were obtained by simulating their ellipsometric spectra using the Forouhi-Bloomer model and by using the Bruggeman effective medium approximation, respectively. The haemocompatibility of these ta-C:H films was analysed by observation of platelet adhesion and measurement of kinetic clotting time. The results show that the sp^3 C fraction is dependent on the substrate bias voltage, and the haemocompatibility is dependent on the ratio of sp^3-bond to sp^2-bond. A good haemocompatibility material of ta-C:H films with a suitable sp^3 C fraction can be prepared by changing the substrate bias voltage.     

巧用特殊法 妙解课本题

根据题目条件的信息,选用恰当的化简技巧,是解决课本二次根式题的关键.一、变换所求,以简驭繁例1已知x=1/2(7~(1/2)+5~(1/2)),y=1/2(7~(1/2)-5~(1/2)),求x2-xy+y2的值.解当x=1/2(7~(1/2)+5~(1/2)),y=1/2(7~(1/2)-5~(1/2))时,有x-y=5~(1/2),xy=1/2.∴原式=(x-y)2+xy=(5~(1/2))2+1/2=11/2.二、化简变形,化难为易例2已知x=(3~(1/2)+2)/(3~(1/2)-2),y=(3~(1/2)-2)/(3~(1/2)+2),求