3,222 research outputs found
Cooperative transport by small teams of molecular motors
Molecular motors power directed transport of cargoes within cells. Even if a
single motor is sufficient to transport a cargo, motors often cooperate in
small teams. We discuss the cooperative cargo transport by several motors
theoretically and explore some of its properties. In particular we emphasize
how motor teams can drag cargoes through a viscous environment.Comment: 9 pages, 1 figure, uses ws-brl.cls, presented at Bio-Systems
conference, Berlin, June 200
Tug-of-war as a cooperative mechanism for bidirectional cargo transport by molecular motors
Intracellular transport is based on molecular motors that pull cargos along
cytoskeletal filaments. One motor species always moves in one direction, e.g.
conventional kinesin moves to the microtubule plus end, while cytoplasmic
dynein moves to the microtubule minus end. However, many cellular cargos are
observed to move bidirectionally, involving both plus-end and minus-end
directed motors. The presumably simplest mechanism for such bidirectional
transport is provided by a tug-of-war between the two motor species. This
mechanism is studied theoretically using the load-dependent transport
properties of individual motors as measured in single-molecule experiments. In
contrast to previous expectations, such a tug-of-war is found to be highly
cooperative and to exhibit seven different motility regimes depending on the
precise values of the single motor parameters. The sensitivity of the transport
process to small parameter changes can be used by the cell to regulate its
cargo traffic.Comment: 17 pages, latex, 11 figures, 4 tables, includes Supporting
Informatio
Two-Photon Excitation of Low-Lying Electronic Quadrupole States in Atomic Clusters
A simple scheme of population and detection of low-lying electronic
quadrupole modes in free small deformed metal clusters is proposed. The scheme
is analyzed in terms of the TDLDA (time-dependent local density approximation)
calculations. As test case, the deformed cluster is considered.
Long-living quadrupole oscillations are generated via resonant two-photon
(two-dipole) excitation and then detected through the appearance of satellites
in the photoelectron spectra generated by a probe pulse. Femtosecond pump and
probe pulses with intensities and
pulse duration fs are found to be optimal. The modes of
interest are dominated by a single electron-hole pair and so their energies,
being combined with the photoelectron data for hole states, allow to gather new
information about mean-field spectra of valence electrons in the HOMO-LUMO
region. Besides, the scheme allows to estimate the lifetime of electron-hole
pairs and hence the relaxation time of electronic energy into ionic heat.Comment: 4 pages, 4 figure
The FFLO state in the one-dimensional attractive Hubbard model and its fingerprint in the spatial noise correlations
We explore the pairing properties of the one-dimensional attractive Hubbard
model in the presence of finite spin polarization. The correlation exponents
for the most important fluctuations are determined as a function of the density
and the polarization. We find that in a system with spin population imbalance,
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-type pairing at wavevector
Q=|k_{F,\uparrow}-k_{F,\downarrow}| is always dominant and there is no
Chandrasekhar-Clogston limit. We then investigate the case of weakly coupled 1D
systems and determine the region of stability of the 1D FFLO phase. This
picture is corroborated by density-matrix-renormalization-group (DMRG)
simulations of the spatial noise correlations in uniform and trapped systems,
unambiguously revealing the presence of fermion pairs with nonzero momentum Q.
This opens up an interesting possibility for experimental studies of FFLO
states.Comment: 8 pages, 4 figure
New effective interactions in RMF theory with non-linear terms and density-dependent meson-nucleon coupling
New parameter sets for the Lagrangian density in the relativistic mean field
(RMF) theory, PK1 with nonlinear sigma- and omega-meson self-coupling, PK1R
with nonlinear sigma-, omega- and rho-meson self-coupling and PKDD with the
density-dependent meson-nucleon coupling, are proposed. They are able to
provide an excellent description not only for the properties of nuclear matter
but also for the nuclei in and far from the valley of beta-stability. For the
first time in the parametrization of the RMF Lagrangian density, the
center-of-mass correction is treated by a microscopic way, which is essential
to unify the description of nuclei from light to heavy regions with one
effective interaction.Comment: 22 pages, 16 EPS figures, RevTeX
Two-dimensional solitons on the surface of magnetic fluids
We report an observation of a stable soliton-like structure on the surface of
a ferrofluid, generated by a local perturbation in the hysteretic regime of the
Rosensweig instability. Unlike other pattern-forming systems with localized 2D
structures, magnetic fluids are characterized by energy conservation; hence
their mechanism of soliton stabilization is different from the previously
discussed gain/loss balance mechanism. The radioscopic measurements of the
soliton's surface profile suggest that locking on the underlying periodic
structure is instrumental in its stabilization.Comment: accepted for publication by Physical Review Letter
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