17,106 research outputs found
Intermittency in two-dimensional Ekman-Navier-Stokes turbulence
We study the statistics of the vorticity field in two-dimensional
Navier-Stokes turbulence with a linear Ekman friction. We show that the
small-scale vorticity fluctuations are intermittent, as conjectured by Nam et
al. [Phys. Rev. Lett. vol.84 (2000) 5134]. The small-scale statistics of
vorticity fluctuations coincides with the one of a passive scalar with finite
lifetime transported by the velocity field itself.Comment: 4 pages, 7 figure
Heavy pseudoscalar-meson decay constants with strangeness from the extended nonlocal chiral-quark model
We study the weak-decay constants for the heavy pseudoscalar mesons, D, Ds,
B, and Bs. For this purpose, we employ the extended nonlocal chiral-quark model
(ExNLChQM), motivated by the heavy-quark effective field theory as well as the
instanton-vacuum configuration. In addition to the heavy-quark symmetry and the
nonlocal interactions between quarks and pseudoscalar mesons in ExNLChQM, a
correction for the strange-quark content inside Ds and Bs is also taken into
account and found to be crucial to reproduce the empirical values. From those
numerical results, we obtain f_{D,Ds,B,Bs}=(207.53, 262.56, 208.13, 262.39)
MeV, which are in good agreement with experimental data and other theoretical
estimations. Using those numerical results, we compute the CKM matrix elements
and the Cabibbo angle, using various mesonic and leptonic heavy-meson decay
channels, resulting in
(|V_{cd}|,|V_{cs}|,|V_{ub}|,|V_{td}|/|V_{ts}|)=(0.224,0.968,<5.395*10^{-3},0.215)
and theta_C=12.36^o which are well compatible with available data.Comment: 12 pages, 7 figures, accepted for publication in Mod. Phys. Lett.
Helices at Interfaces
Helically coiled filaments are a frequent motif in nature. In situations
commonly encountered in experiments coiled helices are squeezed flat onto two
dimensional surfaces. Under such 2-D confinement helices form "squeelices" -
peculiar squeezed conformations often resembling looped waves, spirals or
circles. Using theory and Monte-Carlo simulations we illuminate here the
mechanics and the unusual statistical mechanics of confined helices and show
that their fluctuations can be understood in terms of moving and interacting
discrete particle-like entities - the "twist-kinks". We show that confined
filaments can thermally switch between discrete topological twist quantized
states, with some of the states exhibiting dramatically enhanced
circularization probability while others displaying surprising
hyperflexibility
Free Energy Approach to the Formation of an Icosahedral Structure during the Freezing of Gold Nanoclusters
The freezing of metal nanoclusters such as gold, silver, and copper exhibits
a novel structural evolution. The formation of the icosahedral (Ih) structure
is dominant despite its energetic metastability. This important phenomenon,
hitherto not understood, is studied by calculating free energies of gold
nanoclusters. The structural transition barriers have been determined by using
the umbrella sampling technique combined with molecular dynamics simulations.
Our calculations show that the formation of Ih gold nanoclusters is attributed
to the lower free energy barrier from the liquid to the Ih phases compared to
the barrier from the liquid to the face-centered-cubic crystal phases
Inverse velocity statistics in two dimensional turbulence
We present a numerical study of two-dimensional turbulent flows in the
enstrophy cascade regime, with different large-scale forcings and energy sinks.
In particular, we study the statistics of more-than-differentiable velocity
fluctuations by means of two recently introduced sets of statistical
estimators, namely {\it inverse statistics} and {\it second order differences}.
We show that the 2D turbulent velocity field, , cannot be simply
characterized by its spectrum behavior, . There
exists a whole set of exponents associated to the non-trivial smooth
fluctuations of the velocity field at all scales. We also present a numerical
investigation of the temporal properties of measured in different
spatial locations.Comment: 9 pages, 12 figure
Propagation of Exchange Bias in CoFe/FeMn/CoFe Trilayers
CoFe/FeMn, FeMn/CoFe bilayers and CoFe/FeMn/CoFe trilayers were grown in
magnetic field and at room temperature. The exchange bias field
depends strongly on the order of depositions and is much higher at CoFe/FeMn
than at FeMn/CoFe interfaces. By combining the two bilayer structures into
symmetric CoFe/FeMn()/CoFe trilayers, and
of the top and bottom CoFe layers, respectively, are both enhanced.
Reducing of the trilayers also results in enhancements of
both and . These results evidence the propagation of
exchange bias between the two CoFe/FeMn and FeMn/CoFe interfaces mediated by
the FeMn antiferromagnetic order
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