4,746 research outputs found
Interface relaxation in electrophoretic deposition of polymer chains: Effects of segmental dynamics, molecular weight, and field
Using different segmental dynamics and relaxation, characteristics of the
interface growth is examined in an electrophoretic deposition of polymer chains
on a three (2+1) dimensional discrete lattice with a Monte Carlo simulation.
Incorporation of faster modes such as crankshaft and reptation movements along
with the relatively slow kink-jump dynamics seems crucial in relaxing the
interface width. As the continuously released polymer chains are driven (via
segmental movements) and deposited, the interface width grows with the
number of time steps , (--,
which is followed by its saturation to a steady-state value . Stopping the
release of additional chains after saturation while continuing the segmental
movements relaxes the saturated width to an equilibrium value ().
Scaling of the relaxed interface width with the driving field , remains similar to that of the steady-state width. In
contrast to monotonic increase of the steady-state width , the relaxed
interface width is found to decay (possibly as a stretched exponential)
with the molecular weight.Comment: 5 pages, 7 figure
Possible singlet to triplet pairing transition in NaxCoO2 H2O
We present precise measurements of the upper critical field (Hc2) in the
recently discovered cobalt oxide superconductor. We have found that the
critical field has an unusual temperature dependence; namely, there is an
abrupt change of the slope of Hc2(T) in a weak field regime. In order to
explain this result we have derived and solved Gor'kov equations on a
triangular lattice. Our experimental results may be interpreted in terms of the
field-induced transition from singlet to triplet superconductivity.Comment: 6 pages, 5 figures, revte
Charge-ordering, commensurability and metallicity in the phase diagram of layered Na(x)CoO(2)
The phase diagram of non-hydrated Na(x)CoO(2) has been determined by changing
the Na content x using a series of chemical reactions. As x increases from 0.3,
the ground state goes from a paramagnetic metal to a charge-ordered insulator
(at x=1/2) to a `Curie-Weiss metal' (around 0.70), and finally to a weak-moment
magnetically ordered state (x>0.75). The unusual properties of the state at 1/2
(including particle-hole symmetry at low T and enhanced thermal conductivity)
are described. The strong coupling between the Na ions and the holes is
emphasized.Comment: 4 pages with 3 figures, changed conten
Pressure effects in the triangular layered cobaltites NaxCoO2
We have measured transport properties as a function of temperature and
pressure up to 30GPa in the NaxCoO2 system. For the x=0.5 sample the transition
temperature at 53K increases with pressure, while paradoxically the sample
passes from an insulating to a metallic ground state. A similar transition is
observed in the x=0.31 sample under pressure. Compression on the x=0.75 sample
transforms the sample from a metallic to an insulating state. We discuss our
results in terms of interactions between band structure effects and Na+ order.Comment: 18 pages, 5 figure
Accelerating boundary analog of a Kerr black hole
An accelerated boundary correspondence (i.e. a flat spacetime accelerating
mirror trajectory) is derived for the Kerr spacetime, with a general formula
that ranges from the Schwarzschild limit (zero angular momentum) to the extreme
maximal spin case (yielding asymptotic uniform acceleration). The beta
Bogoliubov coefficients reveal the particle spectrum is a Planck distribution
at late times with temperature cooler than a Schwarzschild black hole, due to
the "spring constant" analog of angular momentum. The quantum stress tensor
indicates a constant emission of energy flux at late times consistent with
eternal thermal equilibrium.Comment: 7 pages, 6 figure
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