32,928 research outputs found
Properties of tug-of-war model for cargo transport by molecular motors
Molecular motors are essential components for the biophysical functions of
the cell. Our current quantitative understanding of how multiple motors move
along a single track is not complete; even though models and theories for
single motor chemomechanics abound. Recently, M.J.I. Mller {\em
et al.} have developed a tug-of-war model to describe the bidirectional
movement of the cargo (PNAS(2008) 105(12) P4609-4614). Through Monte Carlo
simulations, they discovered that the tug-of-war model exhibits several
qualitative different motility regimes, which depend on the precise value of
single motor parameters, and they suggested the sensitivity can be used by a
cell to regulate its cargo traffic. In the present paper, we carry out a
thorough analysis of the tug-of-war model. All the stable, i.e., biophysically
observable, steady states are obtained. Depending on several parameters, the
system exhibits either uni-, bi- or tristability. Based on the separating
boundary of the different stable states and the initial numbers of the
different motor species that are bound to the track, the steady state of the
cargo movement can be predicted, and consequently the steady state velocity can
be obtained. It is found that, the velocity, even the direction, of the cargo
movement change with the initial numbers of the motors which are bound to the
track and several other parameters
Hadron Mass Spectrum from Lattice QCD
Finite temperature lattice simulations of quantum chromodynamics (QCD) are
sensitive to the hadronic mass spectrum for temperatures below the "critical"
temperature T_c ~ 160 MeV. We show that a recent precision determination of the
QCD trace anomaly shows evidence for the existence of a large number of hadron
states beyond those known from experiment. The lattice results are well
represented by an exponentially growing hadron mass spectrum up to a
temperature T = 155 MeV. Using simple parametrizations we show how one may
estimate the total spectral weight in these yet undermined states
JPEG2000 Image Compression on Solar EUV Images
For future solar missions as well as ground-based telescopes, efficient ways
to return and process data have become increasingly important. Solar Orbiter,
e.g., which is the next ESA/NASA mission to explore the Sun and the
heliosphere, is a deep-space mission, which implies a limited telemetry rate
that makes efficient onboard data compression a necessity to achieve the
mission science goals. Missions like the Solar Dynamics Observatory (SDO) and
future ground-based telescopes such as the Daniel K. Inouye Solar Telescope, on
the other hand, face the challenge of making petabyte-sized solar data archives
accessible to the solar community. New image compression standards address
these challenges by implementing efficient and flexible compression algorithms
that can be tailored to user requirements. We analyse solar images from the
Atmospheric Imaging Assembly (AIA) instrument onboard SDO to study the effect
of lossy JPEG2000 (from the Joint Photographic Experts Group 2000) image
compression at different bit rates. To assess the quality of compressed images,
we use the mean structural similarity (MSSIM) index as well as the widely used
peak signal-to-noise ratio (PSNR) as metrics and compare the two in the context
of solar EUV images. In addition, we perform tests to validate the scientific
use of the lossily compressed images by analysing examples of an on-disk and
off-limb coronal-loop oscillation time-series observed by AIA/SDO.Comment: 25 pages, published in Solar Physic
“Though this be madness, yet there is method in’t.” A counterfactual analysis of Richard Wagner’s Tannhäuser
Much like Wagner himself, the eponymous hero of Tannhäuser treads a path of stark contrasts and
rapid swings. From Wartburg to the Venusberg and to the Vatican, the gifted bard transforms from
self-centered artist to seduced disciple, disillusioned devotee, hopeful lover, self-loathing pilgrim and
finally redeemed martyr. He tries everything and everything is trying. These contrasts reach a peak in
the opera‟s central episode, the song contest at Wartburg. Tannhäuser has just been welcomed at the
court, received Elisabeth‟s favor and affection, and is ready to compete for the contest‟s prize, one as
lofty as possibly the princess‟ hand. Instead of securing his reintegration to Wartburg with a brilliant
performance, however, he spoils the event with insolent remarks and the exhibitionist disclosure of
his Venusberg experience. His behavior offends his peers, scandalizes the court, breaks Elisabeth‟s
heart, and brings him to the edge of death. Why would Tannhäuser sacrifice everything for nothing
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
Geometric quantum gates with superconducting qubits
We suggest a scheme to implement a universal set of non-Abelian geometric
transformations for a single logical qubit composed of three superconducting
transmon qubits coupled to a single cavity. The scheme utilizes an adiabatic
evolution in a rotating frame induced by the effective tripod Hamiltonian which
is achieved by longitudinal driving of the transmons. The proposal is
experimentally feasible with the current state of the art and could serve as a
first proof of principle for geometric quantum computing.Comment: 7 pages, 5 figure
Butterfly hysteresis loop and dissipative spin reversal in the S=1/2, V15 molecular complex
Time resolved magnetization measurements have been performed on a spin 1/2
molecular complex, so called V. Despite the absence of a barrier,
magnetic hysteresis is observed over a timescale of several seconds. A detailed
analysis in terms of a dissipative two level model is given, in which
fluctuations and splittings are of same energy. Spin-phonon coupling leads to
long relaxation times and to a particular "butterfly" hysteresis loop.Comment: LaTeX/RevTeX, 3 figures.Approved for publication in PR
Microscopic formula for transport coefficients of causal hydrodynamics
The Green-Kubo-Nakano formula should be modified in relativistic
hydrodynamics because of the problem of acausality and the breaking of sum
rules. In this work, we propose a formula to calculate the transport
coefficients of causal hydrodynamics based on the projection operator method.
As concrete examples, we derive the expressions for the diffusion coefficient,
the shear viscosity coefficient, and corresponding relaxation times.Comment: 4 pages, title was modified, final version published in Phys. Rev.
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