8,221 research outputs found
Dynamical Properties of Multi-Armed Global Spirals in Rayleigh-Benard Convection
Explicit formulas for the rotation frequency and the long-wavenumber
diffusion coefficients of global spirals with arms in Rayleigh-Benard
convection are obtained. Global spirals and parallel rolls share exactly the
same Eckhaus, zigzag and skewed-varicose instability boundaries. Global spirals
seem not to have a characteristic frequency or a typical size ,
but their product is a constant under given experimental
conditions. The ratio of the radii of any two dislocations (,
) inside a multi-armed spiral is also predicted to be constant. Some of
these results have been tested by our numerical work.Comment: To appear in Phys. Rev. E as Rapid Communication
Local interaction scale controls the existence of a non-trivial optimal critical mass in opinion spreading
We study a model of opinion formation where the collective decision of group
is said to happen if the fraction of agents having the most common opinion
exceeds a threshold value, a \textit{critical mass}. We find that there exists
a unique, non-trivial critical mass giving the most efficient convergence to
consensus. In addition, we observe that for small critical masses, the
characteristic time scale for the relaxation to consensus splits into two. The
shorter time scale corresponds to a direct relaxation and the longer can be
explained by the existence of intermediate, metastable states similar to those
found in [P.\ Chen and S.\ Redner, Phys.\ Rev.\ E \textbf{71}, 036101 (2005)].
This longer time-scale is dependent on the precise condition for
consensus---with a modification of the condition it can go away.Comment: 4 pages, 6 figure
Cavity optomechanical coupling assisted by an atomic gas
We theoretically study a cavity filled with atoms, which provides the
optical-mechanical interaction between the modified cavity photonic field and a
movable mirror at one end. We show that the cavity field ``dresses'' these
atoms, producing two types of polaritons, effectively enhancing the radiation
pressure of the cavity field upon the end mirror, as well as establishing an
additional squeezing mode of the end mirror. This squeezing produces an
adiabatic entanglement, which is absent in usual vacuum cavities, between the
oscillating mirror and the rest of the system. We analyze the entanglement and
quantify it using the Loschmidt echo and fidelity.Comment: 8 pages, 4 figure
Investigation of infrared phonon modes in multiferroic single-crystal FeTeOBr
Reflection and transmission as a function of temperature (5--300 K) have been
measured on single crystals of the multiferroic compound FeTeOBr
utilizing light spanning the far infrared to the visible portions of the
electromagnetic spectrum. The complex dielectric function and optical
properties were obtained via Kramers-Kronig analysis and by fits to a
Drude-Lortentz model. Analysis of the anisotropic excitation spectra via
Drude-Lorentz fitting and lattice dynamical calculations have lead to the
observation of all 52 IR-active modes predicted in the plane and 43 or the
53 modes predicted along the b axis of the monoclinic cell. Assignments to
groups (clusters) of phonons have been made and trends within them are
discussed in light of our calculated displacement patterns.Comment: 9 pages, 7 figure
The NN phase shifts in the extended quark-delocalization, color-screening model
An alternative method is applied to the study of nucleon-nucleon(NN)
scattering phase shifts in the framework of extended quark delocalization,
color-screening model(QDCSM), where the one-pion-exchange(OPE) with short-range
cutoff is included.Comment: 5 pages, 3 figures, two-colum
Hole Doping Dependence of the Coherence Length in Thin Films
By measuring the field and temperature dependence of magnetization on
systematically doped thin films, the critical current
density and the collective pinning energy are determined in
single vortex creep regime. Together with the published data of superfluid
density, condensation energy and anisotropy, for the first time we derive the
doping dependence of the coherence length or vortex core size in wide doping
regime directly from the low temperature data. It is found that the coherence
length drops in the underdoped region and increases in the overdoped side with
the increase of hole concentration. The result in underdoped region clearly
deviates from what expected by the pre-formed pairing model if one simply
associates the pseudogap with the upper-critical field.Comment: 4 pages, 4 figure
Wess-Zumino-Witten model off criticality
We study the renormalization group flow properties of the Wess-Zumino-Witten
model in the region of couplings between and , by
evaluating the two-loop Zamolodchikov's -function. We also discuss the
region of negative couplings.Comment: 8 page
Signatures of a Pressure-Induced Topological Quantum Phase Transition in BiTeI
We report the observation of two signatures of a pressure-induced topological
quantum phase transition in the polar semiconductor BiTeI using x-ray powder
diffraction and infrared spectroscopy. The x-ray data confirm that BiTeI
remains in its ambient-pressure structure up to 8 GPa. The lattice parameter
ratio c/a shows a minimum between 2.0-2.9 GPa, indicating an enhanced c-axis
bonding through pz band crossing as expected during the transition. Over the
same pressure range, the infrared spectra reveal a maximum in the optical
spectral weight of the charge carriers, reflecting the closing and reopening of
the semiconducting band gap. Both of these features are characteristics of a
topological quantum phase transition, and are consistent with a recent
theoretical proposal.Comment: revised final versio
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