Propagation of the polyamorphic transition of ice and the liquid-liquid critical point

Water has a rich metastable phase behaviour that includes transitions between high- and low-density amorphous ices, and between high- and low-density supercooled liquids. Because the transitions occur under conditions where crystalline ice is the stable phase, they are challenging to probe directly. In the case of the liquids, it remains unclear whether their mutual transformation at low temperatures is continuous, or discontinuous and terminating at a postulated second critical point of water that is metastable with respect to crystallization. The amorphous ices are more amenable to experiments, which have shown that their mutual transformation is sharp and reversible. But the non-equilibrium conditions of these studies make a firm thermodynamic interpretation of the results difficult. Here we use Raman spectroscopy and visual inspection to show that the transformation of high-density to low-density amorphous ices involves the propagation of a phase boundary-a region containing a mixture of both ices. We find that the boundary region becomes narrower as the transformation progresses, and at higher transformation temperatures. These findings strongly suggest that the polyamorphic ice transition is discontinuous; a continuous transformation should occur uniformly over the entire sample. Because the amorphous ices are structurally similar to their supercooled liquid counterparts, our results also imply that the liquids transform discontinuously at low temperatures and thus support the liquid-liquid critical-point theory.     

脑磁扫描反应与从自相关和双耳互相关函数中得到的因子的关系

利用脑电磁图示（MEG）的方法对听觉诱发磁场（AEFs）与由自相关系数（ACF）以及由双耳互相关系数（IACF）中导出的因子的关系加以检验．首先，检验ACF，φ1的峰值对AEFs的影响，发现音调的强度与φ1良好相关，而当刺激开始后大约100ms时在左右颞叶上发现的N1m的振幅则随φ1的增加而增大．此结果表明较强声调感的声音导致N1m幅值的增加．此外，对IACC以及τIACC对AEFs的作用也加以检验，发现人类侧向声音定位的能力随IACC的减小而变差．当IACC为0．95时，N1m幅值随τIACC的增加而增加，而当IACC为0．5时，τIACC对N1m幅值的作用不显著．此结果表明侧向声音定位的能力可由N1m的幅值来反映．