电子束驱动的回旋激射不稳定性

对弱相对论性电子束驱动的回旋激射(maser)不稳定性的一般理论作了详细讨论.对在获得增长率实用表达式过程中若干解析表达式的推导与细节做了仔细的补充讨论和说明，还增加了增长率的近似表达式，并由此得到了回旋激射不稳定性主要特征的解析分析以及与精确计算的比较，使整个理论有一个完整的描述.侧重解析讨论，也提供了部分一般性的数值计算结果. 关键词： 回旋激射不稳定性 弱相对论性电子束 增长率     

Experimental investigation of time-dependent cavitation in an oscillatory squeeze film

The occurrence of time-dependent cavitation and tensile stress in an oscillatory oil squeeze film were investigated experimentally. The test apparatus was a simple thrust bearing consisting of two parallel circular plates separated by a thin viscous oil film. During the test, one plate was at rest while the other (transparent) oscillated in a direction normal to its surface. This test configuration was chosen to avoid the rotational motion and complicated geometry of a squeeze film journal bearing. The frequency of oscillation was in the range of 5 to 50 Hz and was controlled by an electro-magnetic exciter. The process of cavity formation and its subsequent development was recorded by a high-speed video camera. Concomitant pressure in the oil film was measured both within and without the cavitation region. It was found that both tensile stress and cavities existed in a squeeze film under certain working conditions.     

浮栅ROM器件辐射效应机理分析

分析了浮栅ROM器件的辐射效应机理，合理地解释了实验中观察到的现象.指出辐射产生的电子空穴对在器件中形成的氧化物陷阱电荷和界面陷阱电荷是导致存储单元及其外围电路出现错误的原因.浮栅ROM器件的中子、质子和⁶⁰Co γ辐射效应都是总剂量效应 . 关键词： FLASH ROM EEPROM 中子 质子 60Co γ')" href="#">⁶⁰Co γ 总剂量效应     

A novel tridentate nitrogen donor as ligand in copper catalyzed ATRP of methyl methacrylate

A tridentate ligand, BPIEP: 2,6‐bis[1‐(2,6‐diisopropyl phenylimino) ethyl] pyridine, having central pyridine unit and two peripheral imine coordination sites was effectively employed in controlled/“living” radical polymerization of MMA at 90°C in toluene as solvent, Cu^IBr as catalyst, and ethyl‐2‐bromoisobutyrate (EBiB) as initiator resulting in well‐defined polymers with polydispersities M_w/M_n ≤ 1.23. The rate of polymerization follows first‐order kinetics, k_app = 3.4 × 10^?5 s^?1, indicating the presence of low radical concentration ([P*] ≤ 10^?8) throughout the reaction. The polymerization rate attains a maximum at a ligand‐to‐metal ratio of 2:1 in toluene at 90°C. The solvent concentration (v/v, with respect to monomer) has a significant effect on the polymerization kinetics. The polymerization is faster in polar solvents like, diphenylether, and anisole, as compared to toluene. Increasing the monomer concentration in toluene resulted in a better control of polymerization. The molecular weights (M_n,SEC) increased linearly with conversion and were found to be higher than predicted molecular (M_n,Cal). However, the polydispersity remained narrow, i.e., ≤1.23. The initiator efficiency at lower monomer concentration approaches a value of 0.7 in 110 min as compared to 0.5 in 330 min at higher monomer concentration. The aging of the copper salt complexed with BPIEP had a beneficial effect and resulted in polymers with narrow polydispersitities and higher conversion. PMMA obtained at room temperature in toluene (33%, v/v) gave PDI of 1.22 (M_n = 8500) in 48 h whereas, at 50°C the PDI is 1.18 (M_n = 10,300), which is achieved in 23 h. The plot of lnk_app versus 1/T gave an apparent activation energy of polymerization as (ΔE^≠_app) 58.29 KJ/mol and enthalpy of equilibrium (ΔH⁰_eq) to 28.8 KJ/mol. Reverse ATRP of MMA was successfully performed using AIBN in bulk as well as solution. The controlled nature of the polymerization reaction was established through kinetic studies and chain extension experiments. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4996–5008, 2005     

Smoothing estimation of rate function for recurrent event data with informative censoring

This paper proposes kernel estimation of the occurrence rate function for recurrent event data with informative censoring. An informative censoring model is considered with assumptions made on the joint distribution of the recurrent event process and the censoring time without modeling the censoring distribution. Under the validity of the informative censoring model, we also show that an estimator based on the assumption of independent censoring becomes inappropriate and is generally asymptotically biased. To investigate the asymptotic properties of the proposed estimator, the explicit form of its asymptotic mean squared risk and the asymptotic normality are derived. Meanwhile, the empirical consistent smoothing estimator for the variance function of the estimator is suggested. The performance of the estimators are also studied through Monte Carlo simulations. An epidemiological example of intravenous drug user data is used to show the influence of informative censoring in the estimation of the occurrence rate functions for inpatient cares over time.     

Influence of transition metal ions on the textural properties of alumina and aluminasilicates

Accelerated phase transformations and chemical reactions of metastable aluminas and kaolinite, doped with Cu^{2 +}, Mn^{3 +}/Mn^{2 +} and Fe^{3 +}/Fe^{2 +} ions, are accompanied with accelerated decrease of surface area and pore volume values. The phenomena in metal ion doped samples are explained by a catalytic mechanism, in terms of the Jahn-Teller effect. This revised version was published online in June 2006 with corrections to the Cover Date.     

Anti-BZ-Structure in Effect Algebras

The definitions of sharply approximating effect algebras, anti-BZ-effect algebras, central approximating effect algebras, and S-anti-BZ-effect algebras are given, the relationships between sharply approximating effect algebras and anti-BZ-effect algebras, between central approximating effect algebras and anti-BZ-effect algebras are established, and the set of anti-BZ-sharp elements in S-anti-BZ-effect algebras is proved to be an orthomodular lattice.     

Bounds to optimal burn‐in and optimal work size

Burn‐in is a widely used method to improve the quality of products or systems after they have been produced. In this paper, we consider the problem of determining the optimal burn‐in time and optimal work size maximizing the long‐run average amount of work saved per time unit in the computer applications. Assuming that the underlying lifetime distribution of the computer has an initially decreasing or/and eventually increasing failure rate function, an upper bound for the optimal burn‐in time is derived for each fixed work size and a uniform (with respect to the burn‐in time) upper bound for the optimal work size is also obtained. Furthermore, it is shown that a non‐trivial lower bound for the optimal burn‐in time can be derived if the underlying lifetime distribution has a large initial failure rate. Copyright © 2005 John Wiley & Sons, Ltd.     

Photorefractive Four-Wave Mixing Switches Utilizing Pockels Effect -Longitudinal and Lateral Switches-

We carried out detailed calculations for photorefractive wave-mixing switches based on one of three crystals with high electro-optic coefficients, namely, BaTiO₃, Strontium Barium Niobate (SBN (0.75)), and Potasium Sodium Strontium Barium Niobate (KNSBN). A comparison of results for the three crystals shows that a 0_-cut BaTiO³ crystal is suitable for a longitudinal switch and requires a voltage of about 80 for a 2-mm-thick crystal to induce sufficient phase mismatch. The electrodes must be transparent for the incident and diffracted beams. A 45_-cut SBN (0.75) crystal, however, is suitable for a lateral switch and requires a voltage of about 150 for a 1-mm-wide crystal. The electrodes do not need to be transparent.     

Negative luminescence in semiconductors: a retrospective view

Twenty-five years ago, we introduced the phenomenon of negative luminescence (NL) into semiconductor physics. This paper provides an overview of work conducted to develop this fundamental concept. Initially, we consider the first-principle approach to radiation interaction with basic matter and the major properties of NL. Then we describe the problems of NL direct measurements in homogeneous materials and structures. Finally, we emphasize the use of NL approach in applications involving devices for infrared (IR) wavelength (3–12 μm) high-temperature (300–400 K) optoelectronics. Our subjects will include NL IR emitting diodes, radiative coolers, IR dynamic scene simulators, light up-conversion devices, and the Stealth effect in IR.