Acousto-optical diagnostics of Gulyaev-Bleustein waves under Fresnel reflection conditions

Diffraction of light by ultrasonic Gulyaev-Bleustein waves is studied under Fresnel reflection conditions. It is shown that Gulyaev-Bleustein waves propagating in GaAs-AlGaAs structures can be detected by acousto-optic methods under conditions for Fresnel reflection of diffracted waves. It has been established that the considered structures are promising for design of multichannel acousto-optical deflectors and modulators. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 4, pp. 583–587, July–August, 2008.     

最小二乘法在铜电阻测量实验数据处理中的应用

文介绍了最小二乘法的原理,给出了用最小二乘法对铜电阻测量数据处理的实例。     

Design of the low energy beam transport line for the China spallation neutron source

The design of the China Spallation Neutron Source (CSNS) low-energy beam transport (LEBT) line, which locates between the ion source and the radio-frequency quadrupole (RFQ), has been completed with the TRACE3D code. The design aims at perfect matching, primary chopping, a small emittance growth and sufficient space for beam diagnostics. The line consists of three solenoids, three vacuum chambers, two steering magnets and a pre-chopper. The total length of LEBT is about 1.74 m. This LEBT is designed to transfer 20 mA of H-pulsed beam from the ion source to the RFQ. An induction cavity is adopted as the pre-chopper.The electrostatic octupole steerer is discussed as a candidate. A four-quadrant aperture for beam scraping and beam position monitoring is designed.     

Sodium transport in polyimide-SiO2 systems

The use of polyimide (PI) in integrated circuits either as a passivant or as an interlevel dielectric requires an understanding of the potential for transfer of contaminant ions, always present to some degree in device-grade PI, from the PI to other device constituents. Sodium, in particular, if transferred from PI to SiO₂ where it is relatively mobile at typical device operating temperatures, could affect device thresholds and create a reliability problem. In this paper, the quasistatic Q-V technique of Brown using metal-PI-SiO₂-Si structures has been applied to the quantitative study of the transfer of Na between PI and SiO₂. Removal of the PI after cure or after application of bias-temperature stress has been used to demonstrate that (1) quantitative, reversible ion transfer between PI and SiO₂ does occur at temperatures above 200°C in the presence of an applied bias, but (2) in the absence of an applied bias, Na ions are not transferred from PI to SiO₂ during PI cure at 350°C. It is also shown that the kinetics of Na transfer from PI to SiO₂ in the presence of a bias are dominated by an activated diffusion process, with an activation energy on the order of 2.0eV and a prefactor on the order of 2x10⁹ cm²/s.     

在“画法几何及机械制图”课程教学中如何培养学生的能力

本文从高等教育必须加强学生各种能力培养的观点出发，阐述了在“画法几何及机械制图”课程教学活动中如何培养大学生的自学能力、空间想象能力、逻辑思维能力、读图和绘图能力的途径和方法上所作的探索和体会。     

差分方程解对初值连续性问题

本文讨论了差分方程的解对初值的连续性问题，对较一般的方程给出了保证解对初值连续的充分条件，对线性方程（组）利用系数矩阵的特征值给出其解对初值连续的条件．     

On a class of signals and matrices giving very fast algorithms for linear problems

In this paper is presented a class of stochastic signals and of correlation matrices introducing very fast algorithms for solving linear problems. These signals are derived from white noise by using three kinds of operations combined in various orders: summation, difference and instantaneous modulation. The discrete time Brownian motion is a particular example of such signals.     

NMOSFET characteristics on a double hetero-epitaxial Si/γ-Al2O3/Si structure fabricated by a new MBE growth method

A new MBE growth method for the fabrication of a high-quality double hetero-epitaxial Si/γ-Al₂O₃/Si structure was recently developed. In the present work, characteristics of NMOSFETs fabricated on the Si/γ-Al₂O₃/Si structure were investigated, and compared with those on a Si/MgAl₂O₄/Si structure. A γ-Al₂O₃ layer was created from a MgAl₂O₄ layer by reaction with Si beams as follows: MgAl₂O₄ + Si → γ-Al₂O₃ + SiO ↑ + Mg ↑. The MBE growth of Si on the effectively restructured γ-Al₂O₃ layer was then performed at a substrate temperature of 700° C, 150° C lower than for the MBE growth of Si on a MgAl₂O₄/Si substrate. The electron field effect mobility and leakage current between source and drain for the NMOSFETs fabricated on Si/γ-Al₂O₃/Si structures were 660 cm²/V · s and 2.8 pA/μm respectively, and exhibited a higher level of performance than those on a Si/MgAl₂O₄/Si structure. In the Si/MgAl₂O₄/Si, SIMS measurements confirmed that autodoped Al and Mg atoms near the interface between the Si epi-layer and MgAl₂O₄/Si substrate diffused anomalously and accumulated at the surface during device fabrication processes. These autodoped Al and Mg atoms acted as ionized impurities during test operation. Suppression of autodoping from insulator layers during the MBE growth of Si was thus deemed essential to the improvement of NMOSFET characteristics. In the Si/γ-Al₂O₃/Si structure, autodoped atoms were scarcely detectable. It was therefore concluded that the Si/γ-Al₂O₃/Si structure under study was very promising for SOI device applications.     

The lion and man problem revisited

A pursuerP, whose speed is bounded by 1, wants to get closer to an evaderE, whose speed is bounded by >1.P wants to reduce his distancePE fromE below the capture radius . Both players are confined to a circular arena. This problem is equivalent to a problem discussed by Flynn, who characterized and gave numerical bounds to the least upper boundd* on the values ofPE thatE can maintain. He used direct methods and did not use Isaacs' theory.We solve our problem relying on the theory of singular surfaces in differential games. We construct and investigate barriers of the game of kind, and we replace Flynn's bounds ond* by analytical (exact) values for various speeds .The support of the TW Department of THT, Enschede, Holland, is gratefully acknowledged.     

Asymptotic distribution of the increase of the largest canonical correlation when one of the vectors is augmented

Let r₁ > r₂ > … be the sample canonical correlations in a sample of size n from a multivariate normal population partitioned into two subvectors with population canonical correlations ₁ > ₂ > …. Let one of the subvectors be augmented by adding one or more variables to it. For the increase in the largest canonical correlation, Δr in the sample and Δ in the population, it is shown that √n(Δr − Δ) → ^DN(0, σ²) and a formula for σ² is derived.