2,191 research outputs found
X-ray variance method to determine the domain size and lattice distortion of ground kaolinite samples
On the decay of Burgers turbulence
This work is devoted to the decay ofrandom solutions of the unforced Burgers
equation in one dimension in the limit of vanishing viscosity. The initial
velocity is homogeneous and Gaussian with a spectrum proportional to at
small wavenumbers and falling off quickly at large wavenumbers. In physical
space, at sufficiently large distances, there is an ``outer region'', where the
velocity correlation function preserves exactly its initial form (a power law)
when is not an even integer. When the spectrum, at long times, has
three scaling regions : first, a region at very small \ms1 with a
time-independent constant, stemming from this outer region, in which the
initial conditions are essentially frozen; second, a region at
intermediate wavenumbers, related to a self-similarly evolving ``inner region''
in physical space and, finally, the usual region, associated to the
shocks. The switching from the to the region occurs around a wave
number , while the switching from to
occurs around (ignoring logarithmic
corrections in both instances). The key element in the derivation of the
results is an extension of the Kida (1979) log-corrected law for the
energy decay when to the case of arbitrary integer or non-integer .
A systematic derivation is given in which both the leading term and estimates
of higher order corrections can be obtained. High-resolution numerical
simulations are presented which support our findings.Comment: In LaTeX with 11 PostScript figures. 56 pages. One figure contributed
by Alain Noullez (Observatoire de Nice, France
Level attraction in a microwave optomechanical circuit
Level repulsion - the opening of a gap between two degenerate modes due to
coupling - is ubiquitous anywhere from solid state theory to quantum chemistry.
In contrast, if one mode has negative energy, the mode frequencies attract
instead. They converge and develop imaginary components, leading to an
instability; an exceptional point marks the transition. This, however, only
occurs if the dissipation rates of the two modes are comparable. Here we expose
a theoretical framework for the general phenomenon and realize it
experimentally through engineered dissipation in a multimode superconducting
microwave optomechanical circuit. Level attraction is observed for a mechanical
oscillator and a superconducting microwave cavity, while an auxiliary cavity is
used for sideband cooling. Two exceptional points are demonstrated that could
be exploited for their topological properties.Comment: 5 pages, 4 figures; includes Supplementary informatio
Addendum to "Sufficient conditions for three-particle entanglement and their tests in recent experiments"
A recent paper [M. Seevinck and J. Uffink, Phys. Rev. A 65, 012107 (2002)]
presented a bound for the three-qubit Mermin inequality such that the violation
of this bound indicates genuine three-qubit entanglement. We show that this
bound can be improved for a specific choice of observables. In particular, if
spin observables corresponding to orthogonal directions are measured at the
qubits (e.g., X and Y spin coordinates) then the bound is the same as the bound
for states with a local hidden variable model. As a consequence, it can
straightforwardly be shown that in the experiment described by J.-W. Pan et al.
[Nature 403, 515 (2000)] genuine three-qubit entanglement was detected.Comment: Two pages, no figures, revtex4; minor changes before publicatio
Global MHD simulations of Saturns's magnetosphere at the time of Cassini approach
We present the results of a 3D global magnetohydrodynamic simulation of the magnetosphere of Saturn for the period of Cassini's initial approach and entry into the magnetosphere. We compare calculated bow shock and magnetopause locations with the Cassini measurements. In order to match the measured locations we use a substantial mass source due to the icy satellites (\sim1 x 10^{28} s^{-1} of water product ions). We find that the location of bow shock and magnetopause crossings are consistent with previous spacecraft measurements, although Cassini encountered the surfaces further from Saturn than the previously determined average location. In addition, we find that the shape of the model bow shock and magnetopause have smaller flaring angles than previous models and are asymmetric dawn-to-dusk. Finally, we find that tilt of Saturn's dipole and rotation axes results in asymmetries in the bow shock and magnetopause and in the magnetotail being hinged near Titan's orbit (\sim20 R _S)
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