BaMgAl10O17:Eu2+,Mn2+中Eu2+→Mn2+的能量传递

在还原气氛下采用高温固相法合成了BaMgAl10O17:Mn2 ,BaMgAl10O17:Eu2 ,BaMgAl10O17:Eu2 ,Mn2 粉末样品,测量并研究了它们的激发光谱和发射光谱性质.结果表明:BaMgAl10O17:Eu2 ,Mn2 中,Eu2 的发射光谱和Mn2 的吸收光谱之间的光谱交叠范围较大,两种离子之间发生了明显的交叉弛豫过程,即有较强的共振能量传递过程,导致在紫外光的激发下,样品BaMgAl10O17:Eu2 ,Mn2 发射光谱中以蓝光和绿光为主.     

汉语儿童情感语声合成

情感语声合成技术对于人机交互具有重要的意义。面对儿童情感语声合成所需汉语语声数据资源缺乏以及模型训练时长较长等问题,该文提出利用迁移学习实现汉语儿童情感语声合成的方法。首先基于汉语语声数据库训练深度学习模型实现中文语声端到端合成模型,再使用高质量大样本的中文情感语料库完成情感语声合成模型,最后利用自行采样的小样本汉语儿童情感语料对模型进行迁移学习实现低资源的语声合成。客观实验结果中梅尔倒谱失真指标为4.91,主观听辨实验指标分别为3.61和4.17。通过实验对比表明,该文的方法在情感语声合成技术的应用上具有良好的性能表现,并且优于现有先进的低资源情感语声合成方法。     

非线性一维光子晶体特性的动态调制

对含有非线性材料的一维光子晶体带隙结构进行了数值计算.在外部入射光强调制下,非线性缺陷层折射率的改变会引起禁带内缺陷模的移动,而光子晶体禁带位置与宽度基本保持不变;若基本周期层取非线性材料,随入射光强的改变,禁带内部缺陷模发生相同的移动,同时,禁带位置和禁带宽度也会发生移动.利用这一性质可以对光子晶体进行动态外部调制,在此基础上对非线性一维光子晶体动态滤波选频进行了实验设计.     

Effect of the interface on separation in multicapillary gas chromatography-based hyphenated techniques for speciation analysis of organometallic compounds

This paper reports the effect of transfer line (TL) internal diameter (i.d.) on gas chromatographic separation characteristics such as efficiency and speed, when a multicapillary (MC) column is used for speciation analysis of mercury. Five different TL consisting of fused-silica capillaries with 0.15, 0.20, 0.25, 0.32, and 0.53 mm i.d. are compared. The separation efficiency and total chromatographic run time are critically affected by the i.d. of the TL. Narrow capillaries (i.d.0.20 mm) produce minimum peak dispersion whereas wide capillaries result in narrow peaks and shorter chromatographic analysis times. A thermodynamic approach is proposed to describe the motion of the analytes through the separation column and TL. The model provides good agreement with the experimental data for high pressures (35 psig) and wide TL (0.25 mm i.d.).Dedicated to the memory of Wilhelm Fresenius     

MICROEMULSION SYSTEMS WITH A NONIONIC COSURFACTANT

The conditions to obtain W/0 microemulsions using ionic surfactants and a nonionic cosurfactant, a polyoxyethylene alkyl ether, were investigated. The length of the polyoxyethylene chain was critical to obtain the typical water solubilization maximum

The variation of the W/0 microemulsion region with hydrocarbon content was different from that of the usual type of microemulsions having a medium chain length alcohol as cosurfactant. In the present systems the W/0 microemulsion region was not a direct continuation of the inverse micellar area at zero content of hydrocarbon. Addition of hydrocarbon was necessary for the formation of inverse micelles

The microemulsion regions were sensitive to the kind of hydrocarbon used; a sign of the importance of the nonionic surfactant for the stability of this kind of microemulsions.     

Turbulence Closure with a Topography-parameter-free Single Equation Model

A new topography-parameter-free turbulence closure, based on a transport equation for the pseudo eddy viscosity, is described. The model is tested against experimental data of several flow cases across the Mach number range and compared to Menter's single equation model and to the Spalart-Allmaras model. The main conclusion is that the new closure outperforms the other two models in both low and high speed flows.     

Recurring angular distribution patterns in resonant heavy-ion reactions

It has been noticed that a distinct resemblance exists at large angles among angular distributions measured for reaction channels at the energies of some resonance-like structures in the ¹²C+¹²C and ¹⁴C+¹⁶O systems. It is pointed out that such forms are typical of a diffraction pattern of a broad band of coherent partial waves. Received: 5 October 1998 / Revised version: 8 December 1998     

低温液体输送系统间歇泉现象机理分析与消除措施

在低温液体输送系统的垂直管路中有可能发生间歇泉现象 ,对管路系统和液体储存都会产生不利影响。文中从气泡动力学、间歇泉循环过程、管路结构等方面对低温液体输送系统中出现的间歇泉现象进行了机理分析 ,介绍了几种消除间歇泉现象的措施 ,为进一步研究间歇泉现象提供了理论基础     

Transfer functions of US transducers for harmonic imaging and bubble responses

Current medical diagnostic echo systems are mostly using harmonic imaging. This means that a fundamental frequency (e.g., 2 MHz) is transmitted and the reflected and scattered higher harmonics (e.g., 4 and 6 MHz), produced by nonlinear propagation, are recorded. The signal level of these harmonics is usually low and a well-defined transfer function of the receiving transducer is required. Studying the acoustic response of a single contrast bubble, which has an amplitude in the order of a few Pascal, is another area where an optimal receive transfer function is important.

We have developed three methods to determine the absolute transfer function of a transducer. The first is based on a well-defined wave generated by a calibrated source in the far field. The receiving transducer receives the calibrated wave and from this the transfer functions can be calculated. The second and third methods are based on the reciprocity of the transducer. The second utilizes a calibrated hydrophone to measure the transmitted field. In the third method, a pulse is transmitted by the transducer, which impinges on a reflector and is received again by the same transducer. In both methods, the response combined with the transducer impedance and beam profiles enables the calculation of the transfer function.

The proposed methods are useful to select the optimal piezoelectric material (PZT, single crystal) for transducers used in reception only, such as in certain 3D scanning designs and superharmonic imaging, and for selected experiments like single bubble behavior.

We tested and compared these methods on two unfocused single element transducers, one commercially available (radius 6.35 mm, centre frequency 2.25 MHz) the other custom built (radius 0.75 mm, centre frequency 4.3 MHz). The methods were accurate to within 15%.