The Putative Liquid-Liquid Transition is a Liquid-Solid Transition in Atomistic Models of Water

We use numerical simulation to examine the possibility of a reversible liquid-liquid transition in supercooled water and related systems. In particular, for two atomistic models of water, we have computed free energies as functions of multiple order parameters, where one is density and another distinguishes crystal from liquid. For a range of temperatures and pressures, separate free energy basins for liquid and crystal are found, conditions of phase coexistence between these phases are demonstrated, and time scales for equilibration are determined. We find that at no range of temperatures and pressures is there more than a single liquid basin, even at conditions where amorphous behavior is unstable with respect to the crystal. We find a similar result for a related model of silicon. This result excludes the possibility of the proposed liquid-liquid critical point for the models we have studied. Further, we argue that behaviors others have attributed to a liquid-liquid transition in water and related systems are in fact reflections of transitions between liquid and crystal

Design of variable bandwidth symmetric/anti-symmetric FIR single-band PCLS lowpass and highpass filters

© 2014, Springer-Verlag London. This paper proposes a reconfiguration design of variable bandwidth symmetric/anti-symmetric finite impulse response single-band peak-constrained least squares (PCLS) lowpass and highpass filters. When the bandwidth of the filter changes, a new set of filter coefficients is derived based on the old set of filter coefficients via a modified method of bisection. Since the proposed algorithm is very efficient, the new set of filter coefficients can be obtained in real time. Also, the new set of filter coefficients can be arbitrarily close to the globally optimal solution of the new PCLS optimization problem