Stable high-order delta-sigma digital-to-analog converters

Stability analysis of high-order delta-sigma loops is a challenge. In this brief, a sufficient design criterion is presented for high-order multibit error-feedback digital-to-analog converters (DACs) which are especially suitable for high-speed operation. This analytical criterion might be too conservative, but it allows for the design of stable, robust, and high-resolution delta-sigma DACs. Both analytical and numerical analysis are performed for verification. Also, experimental results of a discrete-component multiplier-free prototype demonstrate 10-b operation at a very low oversampling ratio of 4.     

STUDY ON PHASE PERCEPTION IN SPEECH

The perceptual effect of the phase information in speech has been studied by auditory subjective tests. On the condition that the phase spectrum in speech is changed while amplitude spectrum is unchanged, the tests show that: (1) If the envelop of the reconstructed speech signal is unchanged, there is indistinctive auditory perception between the original speech and the reconstructed speech; (2) The auditory perception effect of the reconstructed speech mainly lies on the amplitude of the derivative of the additive phase; (3) td is the maximum relative time shift between different frequency components of the reconstructed speech signal. The speech quality is excellent while td <10ms; good while 10ms< td <20ms; common while 20ms< td <35ms, and poor while td >35ms.     

Positively Thermo‐Sensitive Monodisperse Core–Shell Microspheres

In this paper, we report on a novel family of monodisperse thermo‐sensitive core–shell hydrogel microspheres that is featured with high monodispersity and positively thermo‐responsive volume phase transition characteristics with tunable swelling kinetics, i.e., the particle swelling is induced by an increase rather than a decrease in temperature. The microspheres were fabricated in a three‐step process. In the first step, monodisperse poly(acrylamide‐co‐styrene) seeds were prepared by emulsifier‐free emulsion polymerization. In the second step, poly(acrylamide) or poly[acrylamide‐co‐(butyl methacrylate)] shells were fabricated on the microsphere seeds by free radical polymerization. In the third step, the core–shell microspheres with poly‐ (acrylamide)/poly(acrylic acid) based interpenetrating polymer network (IPN) shells were finished by a method of sequential IPN synthesis. The proposed monodisperse core–shell microspheres provide a new mode of the phase transition behavior for thermo‐sensitive “smart” or “intelligent” monodisperse micro‐actuators that is highly attractive for targeting drug delivery systems, chemical separations, sensors, and so on.     

多目标规划的鞍点准则

本文给出多目标规划有效解适应鞍点准则的一个新的判别法 ,它不使用凸性的几何术语及凸分析中的概念。最后给出单目标规划的一个相应的判别法     

On numerical ranges and roots

Existence of the fractional powers is established in Banach algebra setting, in terms of the numerical ranges of elements involved. The behavior of the spectra and (for Hermitian ∗-algebras satisfying some additional hypotheses) the ∗-numerical range under taking these powers also is investigated.     

离子束混合工艺对材料抗蚀性能的影响

本文介绍了离子束混合工艺方法。与直接注入相比较,离子束混合所使用的设备造价低1/4—1/2,而生产效率可提高1—2个数量级,因而使生产成本大幅度降低,这无疑对离子束工艺的实际应用将产生巨大的促进作用。 通过对轴承材料(GCr15和Cr4Mo4V)经Cr、N、Ta不同元素的混合处理后,在0.5M H_2SO_4和0.1M NaCl的缓冲溶液中的阳极极化曲线表明经混合处理后的两种材料试样,其抗蚀能力和抗点蚀能力均大大提高,这与直接注入的试样效果是一致的。 通过俄歇谱仪和透射电镜的分析结果表明混合是成功的,且在一定的条件下,形成非晶组织。 本文的结论是,无论是离子的直接注入还是离子束混合,对提高轴承材料的抗腐蚀性能都是有效的方法,特别是离子束混合技术具有更大的应用前景。     

光通信用垂直腔面发射激光器的进展

垂直腔面发射激光器(VCSEL)以其优异的性能有望成为信息时代的新光源.文章介绍了用于光通信的VCSEL的开发现状.     

牛顿第二定律实验中的误差分析

本文是通过对加速度的实验值和理论值进行比较和分析，给出误差的合理范围。     

Crystallographic report: Bis(norfloxacin)dilead(II) tetranitrate, [Pb2(H‐Norf)2(ONO2)4]

The centrosymmetric binuclear structure of [Pb₂(H‐Norf)₂(ONO₂)₄]shows the geometry around each lead(II) atom to be distorted trigonal bipyramidal with Pb–O distances ranging from 2.357(3) to 2.769(4) Å. Copyright © 2003 John Wiley & Sons, Ltd.