数字音频压缩（AC—3）（五）（摘译）

数字音频压缩（ＡＣ－３）（五）（摘译）７．２比特指派７．２．１概述比特指派程序对在进行编码的音频信号，从掩盖效应分析它的频谱包络，以确定将需要的比特数分派给各变换系数的尾数。在编码器中，把所有声道作为一个整体，从一个公共比特区对它实行总的比特指派，没...     

数字音频磁带（DAT）技术（三）

数字音频磁带（ＤＡＴ）技术（三）陈贵民（广播电影电视部１００８６６）６数字音频磁带（ＤＡＴ用）６．ＩＤＡＴ磁带一般性能数字记录用磁带与以往的模拟型盒式磁带相比，录音和重放的频带明显变宽。通常模拟型磁带音频的记录上限频率为２０ｋＨＺ。但是ＤＡＴ数字记录...     

因特网（Internet）操作指南（四）

因特网（Ｉｎｔｅｒｎｅｔ）操作指南（四）张连杰（大连港香炉礁港务公司，大连，１１６０１１）１１．Ｖｏｉｃｅ、Ｔｅｌ＆Ｖｉｄｅｏ我们可以在Ｉｎｔｅｒｎｅｔ上相互交谈，其优点是免去了昂贵的长话费。取代电话的是ＰＣ、Ｍｏｄｅｍ、ＭＩＣ和全双工声卡。１１．１...     

通信局（站）接地系统新观念（上）

根据相关国际标准（IEC,ITU）和我国标准（GB,YD）,阐述通信局（站）接地系统的新观念和实施原则,介绍联合接地、接地电阻、等电位连接和接地的实施方法、防雷接地、交流和直流配电系统的接地等方面的技术。此外,分析了当前实际工程中存在的问题并提出改进建议。     

异步转移模式（ATM）（续）

异步转移模式（ＡＴＭ）（续）电子科技大学刘荣富孝感师范专科学院叶建勇七、ＡＴＭ交换机的组成实现Ｂ—ＩＳＤＮ的技术难点是研制高性能、大容量的ＡＴＭ交换机。ＡＴＭ交换机主要由输入模块（ＩＭ）、交换结构（ＳＦ）、输出模块（ＯＭ）和控制模块（ＣＭ）等部分组成...     

因特网（Internet）操作指南（六）

因特网（Ｉｎｔｅｒｎｅｔ）操作指南（六）张连杰（大连港香炉礁港务公司，大连，１１６０１１）１７．部分中文ＷＷＷ站点举例ｈｔｐ：∥ｇｂｃｈｉｎｅｓｅ．ｙａｈｏｏ．ｃｏｍ简体中文雅户ｈｔｐ：∥ｗｗｗ．ｇｏｙｏｙｏ．ｃｏｍ台湾搜索引擎ｈｔｐ：∥ｗｗｗ．ｃｈ...     

因特网（Internet）操作指南（九）

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因特网（Internet）操作指南（二）

5.弹出式菜单(鼠标右键)(1)Back(orBackinFrame)(SameasGoBackitem):回退(2)Forward(orForwardinFrame)(SameasGoForwarditem):前进(3)OpenthisLink(filename):打开此地址(4)AddBookmarkforthisLink:做个书签(5)NewWindwoswiththisLink:开辟新窗口并调此连接项(6)SavethisLinkas…另存为…(7)SavethisLinkLocation:复制此Link(8)OpenthisImage(filename):打开此图像(9)SavethisImageas…另存图像为…(10)CopythisImage(Macintoshonly):拷贝该图像(11)CopythisImageLocation:拷贝该图像的地址(12)LoadthisImage:载入此图像(1…     

Miniband spectra of (AlAs)M(GaAs)N(111) superlattices

Semiconductors - Electron states in the conduction band of (111)-oriented (AlAs)M(GaAs)N superlattices (SLs) with M≥N and N&;lt;10 are considered. The properties of such SLs are mainly...     

(Sr_(0.5)Ba_(0.5))_(1.9)Ca_(0.1)NaNb_(5–x)TaxO_(15)陶瓷的介电性能

通过Ta掺杂改性钨青铜陶瓷(Sr0.5Ba0.5)1.9Ca0.1NaNb5–xTaxO15(x=0～0.30),分析了Ta掺杂量对其烧结性能、微观结构及介电性能的影响。陶瓷的烧结温度随x的增大略有提高。当x<0.10时,陶瓷的tC和弛豫性变化不大;当x≥0.10时,tm(1kHz)明显降低,从270℃(x=0)降低至231℃(x=0.30)。且tm随频率增加向高温移动,弛豫性明显增强。认为Ta掺杂引起其性能变化是由于Ta—O键与Nb—O键键能的差异,导致陶瓷氧八面体中心离子位移量以及A位离子有序程度的变化所致。     

Theoretical studies of poly(para-phenylene vinylene) (PPV) and poly(para-phenylene) (PPP)

The electroluminescence from PPV and the blue light emission from PPP constitute exciting subjects of study. The band gap of these semiconducting polymers can be engineered in a wide range from red to ultraviolet by structural changes made on them. In the present work, we present a theoretical approach based on semiempirical and ab initio total energy and force calculations of PPV and PPP. We perform a conformational analysis in order to investigate the connection between their structural, optical and electronic properties. We use the large cell approach, in connection with the semiempirical quantum method Extended Hückel (BICON-CEDiT code) and the density functional theory (DFT) within the full-potential linearized augmented-plane-wave method (FPLAPW) as implemented in the computational code WIEN2k. Our results are compared to other calculations and to optical absorption measurements.     

纳米复合(Nd,Pr)FeTiBC永磁合金的结构与磁性能

采用熔体快淬法制备了纳米复合(Nd1-xPrx)9.4Fe75.6Ti4B10.5C0.5(x为0,0.2,0.4,0.6,0.8和1.0)合金薄带,研究了Pr对合金薄带结构与磁性能的影响规律。结果表明:Pr降低了合金薄带的晶化温度,使合金薄带晶粒变得粗大,不利于合金矫顽力的提高。Pr对合金薄带磁性能的影响不大,不同Nd和Pr比例的合金薄带在最佳热处理条件下,剩磁Br在0.86 T与0.90 T之间,内禀矫顽力Hcj在1 000 kA/m左右,最大磁能积(BH)max介于130 kJ/m3与136 kJ/m3之间。     

sol-gel法制备Ba_(3.99)Sm_(9.34)Ti_(18)O_(54)微波介质陶瓷

以柠檬酸为络合剂,通过sol-gel法制备了Ba3.99Sm9.34Ti18O54陶瓷前驱体;经1100℃预烧2h压片成型后,再在1300℃保温3h,即得到了烧结致密的陶瓷样品。与传统固相法相比,其烧结温度降低了50℃,且陶瓷晶粒细小,晶粒分布均匀,具有更加优良的微波介电性能:εr=79.56,Q·f=9636GHz(4.71GHz),τf=–1.23×10–6/℃。     

High-resolution transmission electron microscopy study of Ca(3)Co(4)O(9)

The crystal structure of Ca(3)Co(4)O(9) was investigated using high-resolution transmission electron microscopy (HRTEM) and the image-simulation method. The c(*) was 10.8A and the b parameters were 4.56A for the Ca(2)CoO(3) block and 2.82A for the CoO(2) sheet. The [110] zone axis HRTEM images confirmed that Ca(3)Co(4)O(9) has a modulated layered structure with modulation. For the first time, the atomic positions of the Ca and Co atoms in the Ca(2)CoO(3) block were identified, corresponding to three rows of dark spots in the [110] direction. The observed HRTEM images for Ca(2)CoO(3) agreed well with the calculated images based on the structural model obtained by the Rietveld refinement method.     

单层超晶格Ga_(0.47)In_(0.53)As/InP(110)及半导体合金Ga_(0.235)In_(0.765)P_(0.5)As_(0.5)的状态密度及介电常数(英文)

The DOS, JDOS and ε2(Ω) of monolayer superlattice Ga0.47ln0.53As/ InP(110) have been calculated by a tight-binding approach and compared with that of alloy Ga0.235ln0.765P0.5As0.5 which has the same stoi-chiometric composition as the monolayer superlattice. By using the techniques of the group theory we have obtained the expressions of momentum matrix elements between valence band states and conduction band states with four adjustable parameters. These parameters are determined by fitting the calculated values of ε2(Ω) with the experimental values for InP, GaAs and InAs. Our results show that the superlattice periodicity makes its DOS, JDOS and ε2(Ω) different from those of alloy in varying degree. Due to the folding of Brillouin zone, the JDOS of superlattice turns round in comparison with that of alloy. The momentum matrix elements have different effects for the superlattices and alloys.For the alloys, they can only change the amplitudes of peaks but not the positions of peaks; however, for the superlattices both amplitude and position can be changed.     

Electron-phonon interaction in short-period (GaAs) m (AlAs) n (001) superlattices

The deformation potentials of electron scattering at short-wavelength phonons for intervalley transitions in the conduction band of short-period (GaAs) _m (AlAs) _n (001) (m, n = 1, 2, 3) superlattices are determined by the electron density functional method. The dependences of the electron and phonon states and deformation potentials on the layer thickness in the superlattices are analyzed. The results of ab initio calculations are in good agreement with the data of empirical calculation of the deformation potentials integrated over phonons, but differ from data on the corresponding potentials for partial scattering channels because of approximations of the phenomenological model of interatomic binding.     

The growth of (InGa)As quantum wells on GaAs(111)A, (211)A and (311)A substrates

The ability to grow high quality (InGa)As on the (111)A surface is essential for the production of a wide range of optoelectronic devices, but the topic has so far received little attention. What work there has been shows it to be highly problematic, reflected in the very broad photoluminescence (PL) peaks observed for GaAs:(InGa)As multiple quantum well structures. The origin of this broadening is unclear but is certainly related to the difficulty in choosing appropriate conditions for the growth of III-Vs on the (111)A surface. We have undertaken a study of the growth of (InGa)As on the GaAs(111)A, (211)A and (311)A surfaces with the goal of achieving high quality quantum well structures, the test being the ability to obtain narrow PL line widths. We have demonstrated that 80 Å 15% InGaAs(111)A single quantum wells with 12K PL peak widths of less than 8 meV can be obtained by growth at 400°C under a V:III ratio of 5:1.     

Sm~(3+)掺杂Co_(0．6)Zn_(0．4)Ni_(0．8)Fe_(1．2)O_4红外辐射陶瓷材料的研究

用常规固相合成法成功地制备出Sm3 掺杂Co0.6Zn0.4Ni0.8Fe1.2O4红外辐射陶瓷材料,并通过XRD、FT-IR和IRE-2型红外发射率测量仪测试了材料的微观结构,分析了材料的结构特征与红外辐射性能的关系,发现Sm3 的掺杂导致Sm3 以一定的配位形式进入Co0.6Zn0.4Ni0.8Fe1.2O4体系中,并形成了有限置换型固溶体结构.数据分析可知,Sm3 掺杂浓度对材料的红外辐射性能存在一定的影响,样品Sm0.1在全波段的积分发射率为0.74,而在>8μm波段的平均发射率最高值可达0.94.