2,313 research outputs found
Thermal inclusions: how one spin can destroy a many-body localized phase
Many-body localized (MBL) systems lie outside the framework of statistical
mechanics, as they fail to equilibrate under their own quantum dynamics. Even
basic features of MBL systems such as their stability to thermal inclusions and
the nature of the dynamical transition to thermalizing behavior remain poorly
understood. We study a simple model to address these questions: a two level
system interacting with strength with localized bits subject to
random fields. On increasing , the system transitions from a MBL to a
delocalized phase on the \emph{vanishing} scale , up to
logarithmic corrections. In the transition region, the single-site eigenstate
entanglement entropies exhibit bi-modal distributions, so that localized bits
are either "on" (strongly entangled) or "off" (weakly entangled) in
eigenstates. The clusters of "on" bits vary significantly between eigenstates
of the \emph{same} sample, which provides evidence for a heterogenous
discontinuous transition out of the localized phase in single-site observables.
We obtain these results by perturbative mapping to bond percolation on the
hypercube at small and by numerical exact diagonalization of the full
many-body system. Our results imply the MBL phase is unstable in systems with
short-range interactions and quenched randomness in dimensions that are
high but finite.Comment: 17 pages, 12 figure
Determining North Atlantic meridional transport variability from pressure on the western boundary: a model investigation.
In this paper we investigate the possibility of determining North
Atlantic meridional transport variability using pressure on the western boundary, focusing on the 42degN latitude of the Halifax WAVE array. We start by
reviewing the theoretical foundations of this approach. Next we present results from a model analysis, both statistical and dynamic, that demonstrate
the feasibility of the approach. We consider how well we can quantify the meridional transport variability at 42degN given complete knowledge of bottom pressure across the basin, and to what degree this quantification is degraded by first ignoring the effect of intervening topography, and then by using only bottom pressure on the western boundary. We find that for periods of greater
than one year we can recover more than 90% of the variability of the main
overturning cell at 42degN using only the western boundary pressure, provided
we remove the depth-average boundary pressure signal. This signal arises from
a basin mode of bottom pressure variability, which has power at all timescales,
but that does not in truth have a meridional transport signal associated with
it, and from the geostrophic depth-independent compensation of the Ekman
transport. An additional benefit of the removal of the depth-average pressure is that this high-frequency Ekman signal, which is essentially noise as
far as monitoring the MOC for climatically important changes is concerned,
is clearly separated from other modes
Estruturação do Complexo Xisto-Grauváquico num conjunto areno-quartzítico da região de Ázere-S. Paio (Tábua, Portugal central)
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