微带型光导开关的电压转换效率

采用微带测试电路对光导开关电压转换效率进行了测试。依据传输线理论,考虑微带传输电路的端点反射,计算给出了光导开关导通电阻不为0的情况下,微带测试电路电压转换效率的解析结果。计算表明：对窄脉宽的线性电脉冲输出,电压转换效率将小于50%;对lock-on模式下的宽脉冲输出,电压转换效率可以超过50%,在理想情况下达到100%;在临界状态下,形成双峰电脉冲输出。结果表明,存在端点反射且光导开关产生电脉冲脉宽达到一定值时,微带线可以起到倍压传输线的作用。     

Adsorption and desorption characteristics of barium oxide at high temperature

Oxygen-selective adsorbents were prepared by two different methods, hydrothermal and sol-gel methods. The adsorption and desorption characteristics of these adsorbents were compared in terms of stability and sorption capacity. The sorbents prepared by the sol-gel method showed better cyclic stability and higher adsorption capacity than that prepared by the hydrothermal method because the sol-gel method entrapped well the barium peroxide.Relaxation time for adsorption ranged from 4 to 9 min depending on the preparation methods and that for desorption was 6 min regardless of the preparation methods. Breakthrough experiment with the sorbent prepared by the sol-gel method was performed. The adsorption breakthrough curves at 600 °C showed two plateau regions. One was at about 3.5%, and the other was 20%. The first plateau region is related to the sharp transition point of the oxygen adsorption isotherm. Though the relaxation time for adsorption was 6 min, the time required from the end of the first plateau to the beginning of the second plateau was just 2 min. During the desorption, a plateau region at 3.5% of oxygen concentration was observed regardless of the desorption flow rate.     

Development of nitride-layer of AISI 304 austenitic stainless steel during high-temperature ammonia gas-nitriding

Ammonia-gas nitriding of AISI 304 austenitic stainless steel was studied at temperatures higher than 800 °C using SEM and X-ray diffraction. The result showed that S-phase, an expanded austenite, was formed even at such high temperatures due to a high nitriding potential of ammonia gas. The equilibrium phase, CrN was formed through a decomposition of S-layer in two different modes; the one was through continuous precipitation of particles at the surface-side of S-layer due to a higher nitriding potential; the other through a discontinuous(-like) precipitation at the austenite interface-side, producing a fine lamellar structure of austenite and CrN. The γ-phase in the surface-side resulting from the precipitation of CrN particles subsequently transformed into Fe₄N because of a fast enrichment of N atoms and a limited mobility of Cr atoms at the surface-side. A coarse lamellar structure made of austenite and Cr₂N was developed in front of fine lamellae composed of austenite and CrN by the decomposition of supersaturated austenite through a discontinuous precipitation via grain boundary movement.     

Quantitative assessment of motion correction for high angular resolution diffusion imaging

Several methods have been proposed for motion correction of high angular resolution diffusion imaging (HARDI) data. There have been few comparisons of these methods, partly due to a lack of quantitative metrics of performance. We compare two motion correction strategies using two figures of merit: displacement introduced by the motion correction and the 95% confidence interval of the cone of uncertainty of voxels with prolate tensors. What follows is a general approach for assessing motion correction of HARDI data that may have broad application for quality assurance and optimization of postprocessing protocols. Our analysis demonstrates two important issues related to motion correction of HARDI data: (1) although neither method we tested was dramatically superior in performance, both were dramatically better than performing no motion correction, and (2) iteration of motion correction can improve the final results. Based on the results demonstrated here, iterative motion correction is strongly recommended for HARDI acquisitions.     

3-Band theory of Fe pnictide superconductors

For the Fe pnictide superconductors, band features important for superconductivity (SC) in the neighborhood of ε_F are mimicked by tight-binding bands with bases of Fe d_xz, d_yz and d_xy orbitals. In terms of this 3-band model, effective pair transfer processes originating from Coulombic integrals are shown to be largely enhanced due to the nesting between electron and hole pockets by explicitly summing up ladder diagrams. Obtained coupled gap equations lead to s^±-type SC. This framework are argued to provide a scheme for discussing important elements working for the high T_c SC, although its validity is restricted to the case where Dirac cones are away from ε_F. Experimental results on Fe pnictides are discussed in terms of the present results. The pair transfer process explicitly due to the exchange-like integral is suggested to be considerably important for the high T_c in MFeAsO_1−xF_x to occur.     

Integrable boundary conditions for the B_2 model

New integrable B_2 model with off-diagonal boundary reflections is proposed. The general solutions of the reflection matrix for the B_2 model are obtained by using the fusion technique. Wefind that the reflection matrix has 7 free boundary parameters, which are used to describe the degree of freedom of boundary couplings, without breaking the integrability of the system. The new quantization conditions will induce the novel structure of the energy spectrum and the boundary states. The corresponding boundary effects can be studied based on the results in this paper. Meanwhile, the reflection matrix of high rank models associated with Bnalgebra can also be obtained by using the method suggested in this paper.     

Size reduction of “reformed casein micelles” by high-power ultrasound and high hydrostatic pressure

We investigated the effect of ultrasound (US) and high hydrostatic pressure (HHP) on the size of reformed casein micelles (RMCs) obtained by titrating calcium and phosphorous solution into sodium caseinate solutions. Both US and HHP reduced the size of the RMCs. A decrease in size from ~200 nm to ~170 nm when US (20 kHz, 0.46 W/mL) was applied for 30 min; and down to ~85 nm when HHP was applied 500 MPa for 15 min. Electron microscopic analysis showed that the RMCs before and after US are similar to milk native casein micelles, and that HHP extensively disintegrated the RMCs. Small angle X-ray scattering and SDS-PAGE showed that the internal structure of the RMCs as well as the casein molecules are not affected by the US and HHP treatments.     

LiF∶F_2晶体中实现三维光数据存储的实验研究

基于LiF∶F2晶体在近红外飞秒脉冲激光作用下产生F2色心向F3 色心的转变,以及两种色心荧光光谱的不同,实现了荧光反射共焦读出和多光子写入的三维光数据存储的原理性实验.钛宝石再生放大器输出的脉冲宽度100fs、中心波长800nm、重复频率1kHz的超短脉冲激光束,用数值孔径0.68的显微物镜聚焦到LiF:F2晶体内部,通过移动晶体实现了三维逐位式数据写入;用405nm的连续蓝光激发存储位,通过探测F3 色心产生的540nm荧光,实现了对信息位进行快速非破坏性的反射共焦读出.与多光子三维存储的透射共焦散射读出和相衬读出相比,格式与现存光盘技术兼容,结构简单;更重要的是,存储信息位是依靠荧光光谱的变化,折射率变化很小,可以有效增加读出层数.     

Effects of doping on the surface energies of nanocrystals and evidence from studies at high pressure

Zn_1−XMn_XS (X=0.85% and 1.26%) nanoparticles have been synthesized using a specially designed equipment and we have studied the influence of doping Mn²⁺ on the surface energy of ZnS. The high pressure behaviors of ZnS nanocrystals with different dopant contents have been investigated using angle-dispersive synchrotron X-ray powder diffraction up to 45.1 GPa. Theoretical calculations show that doping with Mn²⁺ increases the surface energy of the nanocrystals. The theoretical result has been further corroborated by our experimental observation of an increase in the phase transition pressure of Mn²⁺ doped ZnS nanocrystals in diamond-anvil-cell studies.