14,590 research outputs found
Kicked Burgers Turbulence
Burgers turbulence subject to a force ,
where the 's are ``kicking times'' and the ``impulses'' have
arbitrary space dependence, combines features of the purely decaying and the
continuously forced cases. With large-scale forcing this ``kicked'' Burgers
turbulence presents many of the regimes proposed by E, Khanin, Mazel and Sinai
(1997) for the case of random white-in-time forcing. It is also amenable to
efficient numerical simulations in the inviscid limit, using a modification of
the Fast Legendre Transform method developed for decaying Burgers turbulence by
Noullez and Vergassola (1994). For the kicked case, concepts such as
``minimizers'' and ``main shock'', which play crucial roles in recent
developments for forced Burgers turbulence, become elementary since everything
can be constructed from simple two-dimensional area-preserving Euler--Lagrange
maps.
One key result is for the case of identical deterministic kicks which are
periodic and analytic in space and are applied periodically in time: the
probability densities of large negative velocity gradients and of
(not-too-large) negative velocity increments follow the power law with -7/2
exponent proposed by E {\it et al}. (1997) in the inviscid limit, whose
existence is still controversial in the case of white-in-time forcing. (More in
the full-length abstract at the beginning of the paper.)Comment: LATEX 30 pages, 11 figures, J. Fluid Mech, in pres
On the third order structure function for rotating 3D homogeneous turbulent flow
A form for the two-point third order structure function has been calculated
for three dimensional homogeneous incompressible slowly rotating turbulent
fluid. It has been argued that it may possibly hint at the initiation of the
phenomenon of two-dimensionalisation of the 3D incompressible turbulence owing
to rotation.Comment: This revised version corrects some serious flaws in the discussions
after the equation (2) and the equation (13) of the earlier version. Some
typos are also correcte
Stiff polymer in monomer ensemble
We make use of the previously developed formalism for a monomer ensemble and
include angular dependence of the segments of the polymer chains thus
described. In particular we show how to deal with stiffness when the polymer
chain is confined to certain regions. We investigate the stiffness from the
perspectives of a differential equation, integral equations, or recursive
relations for both continuum and lattice models. Exact analytical solutions are
presented for two cases, whereas numerical results are shown for a third case.Comment: 10 pages, including 6 figure
An H-Theorem for the Lattice Boltzmann Approach to Hydrodynamics
The lattice Boltzmann equation can be viewed as a discretization of the
continuous Boltzmann equation. Because of this connection it has long been
speculated that lattice Boltzmann algorithms might obey an H-theorem. In this
letter we prove that usual nine-velocity models do not obey an H-theorem but
models that do obey an H-theorem can be constructed. We consider the general
conditions a lattice Boltzmann scheme must satisfy in order to obey an
H-theorem and show why on a lattice, unlike the continuous case, dynamics that
decrease an H-functional do not necessarily lead to a unique ground state.Comment: 6 pages, latex, no figures, accepted for publication in Europhys.
Let
First principles structures and circular dichroism spectra for the close-packed and the 7/2 motif of collagen
The recently proposed close-packed motif for collagen is investigated using
first principles semi-empirical wave function theory and Kohn-Sham density
functional theory. Under these refinements the close-packed motif is shown to
be stable. For the case of the 7/2 motif a similar stability exists. The
electronic circular dichroism of the close-packed model has a significant
negative bias and a large signal. An interesting feature of the close-packed
structure is the existence of a central channel. Simulations show that, if
hydrogen atoms are placed in the cavity, a chain of molecular hydrogens is
formed suggesting a possible biological function for molecular hydrogen.Comment: 12 pages, 3 figures; 3(PPG)_6 xyz file attached; v2: minor
modification
Narrow-line magneto-optical trap for erbium
We report on the experimental realization of a robust and efficient
magneto-optical trap for erbium atoms, based on a narrow cooling transition at
583nm. We observe up to atoms at a temperature of about
. This simple scheme provides better starting conditions for direct
loading of dipole traps as compared to approaches based on the strong cooling
transition alone, or on a combination of a strong and a narrow kHz transition.
Our results on Er point to a general, simple and efficient approach to laser
cool samples of other lanthanide atoms (Ho, Dy, and Tm) for the production of
quantum-degenerate samples
Material studies related to lunar surface exploration. Volume 4 - Preliminary studies for the design of engineering probes Final report, 6 Mar. 1967 - 30 Jun. 1968
Preliminary design of engineering probes for studying lunar surface material propertie
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