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SUMMARY:Equilibrium and nonequilibrium description of negative temperature
  states in a one-dimensional lattice using a wave kinetic approach - David
 e Proment (University of East Anglia)
DTSTART:20221017T153000Z
DTEND:20221017T160000Z
UID:TALK182492@talks.cam.ac.uk
DESCRIPTION:We predict negative temperature states in the discrete nonline
 ar Sch&ouml\;dinger (DNLS) equation as exact solutions of the associated w
 ave kinetic equation. Within the wave kinetic approach\, we define an entr
 opy that results monotonic in time and reaches a stationary state\, that i
 s consistent with classical equilibrium statistical mechanics. We also per
 form a detailed analysis of the fluctuations of the actions at fixed wave 
 numbers around their mean values. We give evidence that such fluctuations 
 relax to their equilibrium behavior on a shorter timescale than the one ne
 eded for the spectrum to reach the equilibrium state. Numerical simulation
 s of the DNLS equation are shown to be in agreement with our theoretical r
 esults. The key ingredient for observing negative temperatures in lattices
  characterized by two invariants is the boundedness of the dispersion rela
 tion.\n(Based on the joint work M. Onorato\, et al.\, PRE 105\, 014206\, 2
 022)
LOCATION:Seminar Room 1\, Newton Institute
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