1,163 research outputs found
Effects of superâshear rupture speed on the high frequency content of Sâwaves investigated using spontaneous dynamic rupture models and isochrone theory
This paper achieves three goals: 1) It demonstrates that crack tips governed by friction laws including slipâweakening, rateâand stateâdependent laws, and thermal pressurization of pore fluids, propagating at superâshear speed have slip velocity functions with reduced high frequency content compared to crack tips traveling at subâshear speeds. This is demonstrated
using a fully dynamic, spontaneous, 3âD earthquake model, in which we calculate fault slip velocity at nine points (locations) distributed along a quarterâcircle on the fault where the rupture is traveling at superâshear speed in the inâplane direction and subâshear speed in the
antiâplane direction. This holds for a fault governed by the linear slipâweakening constitutive equation, by slipâweakening with thermal pressurization of pore fluid and by rateâ and stateâdependent laws with thermal pressurization. The same is also true even assuming a highly heterogeneous initial shear stress field on the fault. 2) Using isochrone theory we derive a general expressions for the spectral characteristics and geometric spreading of two pulses
arising from superâshear rupture, the wellâknown Mach wave, and a second lesser known
pulse caused by rupture acceleration. 3) The paper demonstrates that the Mach cone
amplification of high frequencies overwhelms the deamplification of high frequency content in the slip velocity functions in superâshear ruptures. Consequently, when earthquake ruptures travel at superâshear speed, a net enhancement of high frequency radiation is expected, and the alleged âlowâ peak accelerations observed for the 2002 Denali and other large earthquakes are
probably not caused by diminished high frequency content in the slip velocity function, as has been speculated
Synthesis of a gene for sensory rhodopsin I and its functional expression in Halobacterium halobium.
A global search inversion for earthquake kinematic rupture history: Application to the 2000 western Tottori, Japan earthquake
We present a two-stage nonlinear technique to invert strong motions records and
geodetic data to retrieve the rupture history of an earthquake on a finite fault. To account
for the actual rupture complexity, the fault parameters are spatially variable peak slip
velocity, slip direction, rupture time and risetime. The unknown parameters are given at
the nodes of the subfaults, whereas the parameters within a subfault are allowed to
vary through a bilinear interpolation of the nodal values. The forward modeling is
performed with a discrete wave number technique, whose Greenâs functions include the
complete response of the vertically varying Earth structure. During the first stage, an
algorithm based on the heat-bath simulated annealing generates an ensemble of models
that efficiently sample the good data-fitting regions of parameter space. In the second
stage (appraisal), the algorithm performs a statistical analysis of the model ensemble and
computes a weighted mean model and its standard deviation. This technique, rather than
simply looking at the best model, extracts the most stable features of the earthquake
rupture that are consistent with the data and gives an estimate of the variability of each
model parameter. We present some synthetic tests to show the effectiveness of the method
and its robustness to uncertainty of the adopted crustal model. Finally, we apply this
inverse technique to the well recorded 2000 western Tottori, Japan, earthquake (Mw 6.6);
we confirm that the rupture process is characterized by large slip (3-4 m) at very shallow
depths but, differently from previous studies, we imaged a new slip patch (2-2.5 m)
located deeper, between 14 and 18 km depth
Internal Motility in Stiffening Actin-Myosin Networks
We present a study on filamentous actin solutions containing heavy meromyosin
subfragments of myosin II motor molecules. We focus on the viscoelastic phase
behavior and internal dynamics of such networks during ATP depletion. Upon
simultaneously using micro-rheology and fluorescence microscopy as
complementary experimental tools, we find a sol-gel transition accompanied by a
sudden onset of directed filament motion. We interpret the sol-gel transition
in terms of myosin II enzymology, and suggest a "zipping" mechanism to explain
the filament motion in the vicinity of the sol-gel transition.Comment: 4 pages, 3 figure
Fluctuating-friction molecular motors
We show that the correlated stochastic fluctuation of the friction
coefficient can give rise to long-range directional motion of a particle
undergoing Brownian random walk in a constant periodic energy potential
landscape. The occurrence of this motion requires the presence of two
additional independent bodies interacting with the particle via friction and
via the energy potential, respectively, which can move relative to each other.
Such three-body system generalizes the classical Brownian ratchet mechanism,
which requires only two interacting bodies. In particular, we describe a simple
two-level model of fluctuating-friction molecular motor that can be solved
analytically. In our previous work [M.K., L.M and D.P. 2000 J. Nonlinear Opt.
Phys. Mater. vol. 9, 157] this model has been first applied to understanding
the fundamental mechanism of the photoinduced reorientation of dye-doped liquid
crystals. Applications of the same idea to other fields such as molecular
biology and nanotechnology can however be envisioned. As an example, in this
paper we work out a model of the actomyosin system based on the
fluctuating-friction mechanism.Comment: to be published in J. Physics Condensed Matter
(http://www.iop.org/Journals/JPhysCM
Structural Transition of Actin Filament in a Cell-Sized Water Droplet with a Phospholipid Membrane
Actin filament, F-actin, is a semiflexible polymer with a negative charge,
and is one of the main constituents on cell membranes. To clarify the effect of
cross-talk between a phospholipid membrane and actin filaments in cells, we
conducted microscopic observations on the structural changes in actin filaments
in a cell-sized (several tens of micrometers in diameter) water droplet coated
with a phospholipid membrane such as phosphatidylserine (PS; negatively-charged
head group) or phosphatidylethanolamine (PE; neutral head group) as a simple
model of a living cell membrane. With PS, actin filaments are distributed
uniformly in the water phase without adsorption onto the membrane surface
between 2 and 6 mM Mg2+, while between 6 and 12 mM Mg2+, actin filaments are
adsorbed onto the inner membrane surface. With PE, actin filaments are
uniformly adsorbed onto the inner membrane surface between 2 and 12 mM Mg2+.
With both PS and PE membranes, at Mg2+ concentrations higher than 12 mM, thick
bundles are formed in the bulk water droplet accompanied by the dissolution of
actin filaments from the membrane surface. The attraction between actin
filaments and membrane is attributable to an increase in the translational
entropy of counterions accompanied by the adsorption of actin filaments onto
the membrane surface. These results suggest that a microscopic water droplet
coated with phospholipid can serve as an easy-to-handle model of cell
membranes
Attractant and Repellent Signaling Conformers of Sensory RhodopsinâTransducer Complexesâ
ABSTRACT: Attractant and repellent signaling conformers of the dual-signaling phototaxis receptor sensory rhodopsin I and its transducer subunit (SRI-HtrI) have recently been distinguished experimentally by the opposite connection of their retinylidene protonated Schiff bases to the outwardly located periplasmic side and inwardly located cytoplasmic side. Here we show that the pKa of the outwardly located Asp76 counterion in the outwardly connected conformer is lowered by âŒ1.5 units from that of the inwardly connected conformer. The pK a difference enables quantitative determination of the relative amounts of the two conformers in wild-type cells and behavioral mutants prior to photoexcitation, comparison of their absorption spectra, and determination of their relative signaling efficiency. We have shown that the onephoton excitation of the SRI-HtrI attractant conformer causes a Schiff base connectivity switch from inwardly connected to outwardly connected states in the attractant signaling photoreaction. Conversely, a second near-UV photon drives the complex back to the inwardly connected conformer in the repellent signaling photoreaction. The results suggest a model of the color-discriminating dual-signaling mechanism in which phototaxis responses (his-kinase modulation) result from the photointerconversion of the two oppositely connected SRI-HtrI conformers by one-photon and two-photon activation. Furthermore, we find that the related repellent phototaxis SRII-HtrII receptor complex has an outwardly connecte
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