62,942 research outputs found
Axioms for consensus functions on the n-cube
An elementary general result is proved that allows for simple
characterizations of well-known location/consensus functions (median, mean and
center) on the n-cube. In addition, alternate new characterizations are given
for the median and anti-median functions on the n-cube.Comment: 12 page
Superconducting weak links in YBa2Cu3O7-δ an AC magnetic susceptibility study
AC magnetic susceptibility, X' and X'', and ac resistivity, ρ, of two different samples of superconducting YBa2Cu3O7-δ have been measured. The results show a strong non-linear behaviour and are very sensitive to the exciting amplitudes. From the analysis of the data and comparison with appropriate models and other superconducting compounds, evidence for the existence of weak superconducting links is inferred. Finally, the utility of acX measurements for detection of different superconducting phases is made evident. \u
Non-linear response of single-molecule magnets: field-tuned quantum-to-classical crossovers
Quantum nanomagnets can show a field dependence of the relaxation time very
different from their classical counterparts, due to resonant tunneling via
excited states (near the anisotropy barrier top). The relaxation time then
shows minima at the resonant fields H_{n}=n D at which the levels at both sides
of the barrier become degenerate (D is the anisotropy constant). We showed that
in Mn12, near zero field, this yields a contribution to the nonlinear
susceptibility that makes it qualitatively different from the classical curves
[Phys. Rev. B 72, 224433 (2005)]. Here we extend the experimental study to
finite dc fields showing how the bias can trigger the system to display those
quantum nonlinear responses, near the resonant fields, while recovering an
classical-like behaviour for fields between them. The analysis of the
experiments is done with heuristic expressions derived from simple balance
equations and calculations with a Pauli-type quantum master equation.Comment: 4 pages, 3 figures. Submitted to Phys. Rev. B, brief report
Advection-Dominated Accretion and Black Hole Event Horizons
The defining characteristic of a black hole is that it possesses an event
horizon through which matter and energy can fall in but from which nothing
escapes. Soft X-ray transients (SXTs), a class of X-ray binaries, appear to
confirm this fundamental property of black holes. SXTs that are thought to
contain accreting black holes display a large variation of luminosity between
their bright and faint states, while SXTs with accreting neutron stars have a
smaller variation. This difference is predicted if the former stars have
horizons and the latter have normal surfaces.Comment: 11 pages, including 2 tables and 2 figures. To appear in The
Astrophysical Journal Letter
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