横向声波扰动下的乙醇燃烧火焰结构和振荡特性

为研究声波灭火的机理,分析声波对非封闭火焰的具体控制行为,对3、4和5 cm直径油池火焰在30 ~ 90 Hz声波作用下的火焰形态及燃烧特征进行了分析。对火焰图像的分析发现,横向声波加剧了涡旋的不稳定运动,声强迫下的火焰形态可归结为间歇截断、偏转和稳定燃烧三种状态。火焰几何尺寸的数值分析表明:间歇截断和偏转状态下的火焰表面高度扭曲皱褶,具有更高的分形维数。对火焰面积、高度和宽度的频域信号分析表明:在间歇截断状态下火焰信号极不稳定,频域峰值集中在0 ~ 10 Hz之间,声频率在火焰宽度信号的频域分布中始终突出。基于火焰倾角和Richardson数的关系提出了Ri数在声波作用下的形式,Richardson数分析表明:在50 ~70 Hz之间,火焰对声波频率的响应尤为显著,声频高于或低于该段频率时对火焰的影响存在边际效应,间歇截断和偏转状态的临界Ri_a?1数（声波作用下的火焰Richardson数的倒数）分别为10.32和2.92。      

Retrograde solubility in semiconductors

The origin ofretrograde solubility has been an enigma since its discovery decades ago. Systems with a eutectic invariant which have retrograde solubility display a maximum in solidus concentration above the eutectic temperature. Many solutes used as dopants in silicon and germanium exhibit retrograde solubility, and as this phenomenon severely limits solute concentrations in solids, it has been of great concern in semiconductor processing. It is shown that previous explanations for ret-rograde solubility are insufficient, as they are based on circuitous arguments which describe only theeffects of retrograde solubility and never the origin of this phenomenon. An original derivation is presented here, which shows retrograde solubility to be caused by a miscibility gap in the free energy of mixing during solidification.