91,597 research outputs found
Three-Dimensional Phase-Kink State in Thick Stack of Josephson Junctions and Terahertz Radiation
The dynamics of superconductivity phase in thick stack of Josephson junctions
with strong inductive coupling, such as the one realized in layered high-
cuprates and possibly the recently discovered FeAs-based superconductors, is
investigated under a c-axis bias voltage and in the absence of an external
magnetic field. The kink state found previously by the present authors is
extended to three dimensions for both rectangular and cylindrical geometries.
The IV characteristics are calculated and the distributions of electromagnetic
field inside the samples are clarified. The solution for a cylindrical mesa
exhibits a higher resonating frequency than that of a square mesa with the same
linear size by a factor of . More importantly, from the radius
dependence of the resonance frequency for the cylinder geometry it is possible
to confirm directly the kink state, and thus to reveal the mechanism of the
strong radiation discovered in recent experiments.Comment: 6 pages, 8 figures. to be published in Phys. Rev. B. to be published
in Phys. Rev.
NMR Measurements of Power-Law Behavior in the Spin-Wave and Critical Regions of Ferromagnetic EuO
Precision continuous-wave NMR measurements have been carried out over the
entire magnetization curve of EuO and are presented in tabular form. Two very
closely spaced resonances are observed and are attributed to domain and
domain-wall signals. Both of the signals are useful for analysis in the
spin-wave region. Only the domain signal is measurable above ~50K. The latter
is used for fitting Tc and the critical exponent beta. The critical-region fits
agree with previous measurements, within experimental error. The
low-temperature data exhibit a clear-cut T^2 behavior, at variance with the
expectations of conventional spin-wave theory. This result is discussed in
relation to two semi-empirical spin-wave schemes, one formulated by N.
Bykovetz, and one by U. Koebler. The NMR signal at 4.2K gives no indication of
a quadrupole splitting, in contradiction to the interpretation of several
previous spin-echo NMR spectra observed in EuO. This issue remains unresolved.Comment: 3 pages, 2 figures, 3 tables. in Proceedings of the 11TH Joint
MMM-Intermag Conference, Washington, DC, 201
Entanglement creation between two causally-disconnected objects
We study the full entanglement dynamics of two uniformly accelerated
Unruh-DeWitt detectors with no direct interaction in between but each coupled
to a common quantum field and moving back-to-back in the field vacuum. For two
detectors initially prepared in a separable state our exact results show that
quantum entanglement between the detectors can be created by the quantum field
under some specific circumstances, though each detector never enters the
other's light cone in this setup. In the weak coupling limit, this entanglement
creation can occur only if the initial moment is placed early enough and the
proper acceleration of the detectors is not too large or too small compared to
the natural frequency of the detectors. Once entanglement is created it lasts
only a finite duration, and always disappears at late times. Prior result by
Reznik derived using the time-dependent perturbation theory with extended
integration domain is shown to be a limiting case of our exact solutions at
some specific moment. In the strong coupling and high acceleration regime,
vacuum fluctuations experienced by each detector locally always dominate over
the cross correlations between the detectors, so entanglement between the
detectors will never be generated.Comment: 16 pages, 8 figures; added Ref.[7] and related discussion
Three-region inequalities for the second order elliptic equation with discontinuous coefficients and size estimate
In this paper, we would like to derive a quantitative uniqueness estimate,
the three-region inequality, for the second order elliptic equation with jump
discontinuous coefficients. The derivation of the inequality relies on the
Carleman estimate proved in our previous work. We then apply the three-region
inequality to study the size estimate problem with one boundary measurement.Comment: 16 pages, 1 figur
Determination of a set of constitutive equations for an al-li alloy at SPF conditions
© 2015 The Authors.Uniaxial tensile tests of aluminium-lithium alloy AA1420wereconducted at superplastic forming conditions. The mechanical properties of this Al-Li alloy were then modelled by a set of physicallybased constitutive equations. The constitutive equations describe the isotropic work hardening,recovery and damage by dislocation density changes and grain size evolution. Based on a recent upgraded optimisation technique, the material constants for these constitutive equations were determined
Evidence for Differential Rotation on a T Tauri Star
Five years of photometric monitoring of the T Tauri star HBC 338 in NGC 1333
has revealed that it is a periodic variable, but the period has changed
significantly with time. From 2000-2003, a period near 5.6 days was observed,
while in the last two seasons, the dominant period is near 4.6 days. No other T
Tauri star has been seen to change its period by such a large percentage. We
propose a model in which a differentially rotating star is seen nearly
equator-on and a high latitude spot has gradually been replaced by a low
latitude spot. We show that this model provides an excellent fit to the
observed shapes of the light curves at each epoch. The amplitude and sense of
the inferred differential rotation is similar to what is seen on the Sun. This
may be surprising given the likely high degree of magnetic surface activity on
the star relative to the Sun but we note that HBC 338 is clearly an exceptional
T Tauri star.Comment: Acepted for publication in PAS
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