4,208 research outputs found
Machine learning techniques for fault isolation and sensor placement
Fault isolation and sensor placement are vital for monitoring and diagnosis. A sensor conveys information about a system's state that guides troubleshooting if problems arise. We are using machine learning methods to uncover behavioral patterns over snapshots of system simulations that will aid fault isolation and sensor placement, with an eye towards minimality, fault coverage, and noise tolerance
Partial breakdown of quantum thermalization in a Hubbard-like model
We study the possible breakdown of quantum thermalization in a model of
itinerant electrons on a one-dimensional chain without disorder, with both spin
and charge degrees of freedom. The eigenstates of this model exhibit peculiar
properties in the entanglement entropy, the apparent scaling of which is
modified from a "volume law" to an "area law" after performing a partial,
site-wise measurement on the system. These properties and others suggest that
this model realizes a new, non-thermal phase of matter, known as a quantum
disentangled liquid (QDL). The putative existence of this phase has striking
implications for the foundations of quantum statistical mechanics.Comment: As accepted to PR
Determination of the phase diagram of the electron doped superconductor Ba(FeCo)As
Systematic measurements of the resistivity, heat capacity, susceptibility and
Hall coefficient are presented for single crystal samples of the electron-doped
superconductor Ba(FeCo)As. These data delineate an
phase diagram in which the single magnetic/structural phase transition that is
observed for undoped BaFeAs at 134 K apparently splits into two
distinct phase transitions, both of which are rapidly suppressed with
increasing Co concentration. Superconductivity emerges for Co concentrations
above , and appears to coexist with the broken symmetry state for
an appreciable range of doping, up to . The optimal
superconducting transition temperature appears to coincide with the Co
concentration at which the magnetic/structural phase transitions are totally
suppressed, at least within the resolution provided by the finite step size
between crystals prepared with different doping levels. Superconductivity is
observed for a further range of Co concentrations, before being completely
suppressed for and above. The form of this phase diagram
is suggestive of an association between superconductivity and a quantum
critical point arising from suppression of the magnetic and/or structural phase
transitions
Bulk Fermi surface coexistence with Dirac surface state in BiSe: a comparison of photoemission and Shubnikov-de Haas measurements
Shubnikov de Haas (SdH) oscillations and Angle Resolved PhotoEmission
Spectroscopy (ARPES) are used to probe the Fermi surface of single crystals of
Bi2Se3. We find that SdH and ARPES probes quantitatively agree on measurements
of the effective mass and bulk band dispersion. In high carrier density
samples, the two probes also agree in the exact position of the Fermi level EF,
but for lower carrier density samples discrepancies emerge in the position of
EF. In particular, SdH reveals a bulk three-dimensional Fermi surface for
samples with carrier densities as low as 10^17cm-3. We suggest a simple
mechanism to explain these differences and discuss consequences for existing
and future transport studies of topological insulators.Comment: 5 mages, 5 figure
- …