声底醇厚、韵味飘逸的胆前级的制作

放音系统中前级放大器的重要作用是众所周知的。一般合并式功率放大器输入端的电压放大级，又称前置放大级，此级的位置虽然很重要，但在合并式放大器中，设计者往往注意力多集中到功率放大级上，而前置电压放大级就显得不重要了，所以对前置放大级的投入也较少。并且，因功放级的影响，B 电压也不够稳定(有     

Infinitely Many Sign-changing Solutions for a Schr(o)dinger Equation in RN

We consider the existence of infinitely many sign-changing solutions for the nonlinear timeindependent schr(o)dinger equations of the form {-△u+Vλ(x)u=f(u), u∈H1(RN), (1.1) where Vλ(x) = λα(x) + 1.     

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Energy Density in Quark-Gluon Plasma

We study the energy density in quark-gluon plasma. At the very high temperature, the quark matter is a hot and dense matter in the colour deconfinement condition, and quarks can coalescent diquarks. Energy density of this system is worked out and compared with the energy density in the other two kinds of situations. Possible energy density is about ε0≈2.4 GeV/fm^3 according to our estimation for quark matter including diquarks.     

Self-assembly behaviour of amphiphilic diblock copolymer in selective solvents studied by synchrotron small-angle x-ray scattering

The aggregation behaviour of styrene-vinyl benzoic acid (PSm-b-PVBAn) amphiphilic diblock copolymers in selective solvents with different m and n was investigated by synchrotron small-angle x-ray scattering (SAXS). We have carried out a detailed analysis of scattering intensity, dimension, shape and microstructure of the diblock copolymers of narrow distribution in water, methanol, ethanol and isopropanol selective solvents, respectively. We have found that the aggregation behaviour of the copolymer depends on the nature of the solvent and the micelle forms fiat disc objects with the ratio of radius ω=0.4. The average radius gyration Rg of the copolymer decreases as solvents change from isopropanol to ethanol and to methanol, and increases with increasing pH in aqueous solution, but decreases with the addition of COCl2 in ethanol solvent. The scattering intensity of diblock copolymer micelle follows I(h) ∝ h^-α in different selective solutions, suggesting that the PSm-b-PVBAn coils have self-similar structure behaviour or a fractal structure in the selective solvents. All of these revealed that the aggregation behaviour of the diblock copolymer changes dramatically with experimental condition in the selective solvent. The increase of mass fractal dimension (Dm) from 2.12 to 2.47 indicates that the copolymer chain changes from a swollen coil to a rather compact disc in the course of changing solvents, decreasing surface fractal dimension (Ds) from 2.98 to 2.58 indicates that the copolymer micelle change from a rather rough surface to a smooth form in the course of increasing pH in aqueous solutions, and increasing Dm and Ds from 2.29 to 2.35 and 2.70 to 2.90, respectively, indicates the shrinkage of copolymer micelle to a rather compact and rough disc form by adding COCl2 in ethanol solvents.     

立方相GaN的持续光电导

研究了金属有机物化学气相外延 (MOVPE)方法生长的非故意掺杂的立方相 Ga N的持续光电导效应 .在六方相 Ga N中普遍认为持续光电导效应与黄光发射有关 ,而实验则显示在立方 Ga N中 ,持续光电导效应与其中的六方相 Ga N夹杂有关系 ,而与黄光发射没有关系 .文中提出 ,立方相 Ga N与其中的六方相 Ga N夹杂之间的势垒引起的空间载流子分离是导致持续光电导现象的物理原因 .通过建立势垒限制复合模型 ,解释了立方相 Ga N的持续光电导现象的物理过程 ,并对光电导衰减过程的动力学作了分析 .对实验数据拟合的结果证明以上的模型和推导是与实验相符的 .     

通信电源的集中监控与安全生产

通信电源的集中监控与安全生产杨世忠编者按：本刊和《电信商情》杂志于５月２５日～２８日在北京举办了“’９６通信电源研讨（展示）会。”有近２００名代表和７０多个电源厂家参加了会议。会议期间，不但展示了各种通信电源新产品，还举办了多场技术讲座，介绍了当前通...