8,008 research outputs found
Lattice stretching bistability and dynamic heterogeneity
A simple one-dimensional lattice model is suggested to describe the
experimentally observed plateau in force-stretching diagrams for some
macromolecules. This chain model involves the nearest-neighbor interaction of a
Morse-like potential (required to have a saturation branch) and an harmonic
second-neighbor coupling. Under an external stretching applied t o the chain
ends, the intersite Morse-like potential results in the appearance of a
double-well potential within each chain monomer, whereas the interaction
between the second neighbors provide s a homogeneous bistable (degenerate)
ground state, at least within a certain part of the chain.
As a result, different conformational changes occur in the chain under the
external forcing. The transition regions between these conformations are
described as topological solitons. With a strong second-neighbor interaction,
the solitons describe the transition between the bistable ground states.
However, the key point of the model is the appearance of a heterogenous
structure, when the second-neighbor coupling is sufficiently weak. In this
case, a part of the chain has short bonds with a single-well potential, whereas
the complementary part admits strongly stretched bonds with a double-well
potential. This case allows us to explain the existence of a plateau in the
force-stretching diagram for DNA and alpha-helix protein. Finally, the soliton
dynamics are studied in detail.Comment: Submitted to Phys. Rev. E, 13 figure
Discovery of TUG-770: a highly potent free fatty acid receptor 1 (FFA1/GPR40) agonist for treatment of type 2 diabetes
Free fatty acid receptor 1 (FFA1 or GPR40) enhances glucose-stimulated insulin secretion from pancreatic β-cells and currently attracts high interest as a new target for the treatment of type 2 diabetes. We here report the discovery of a highly potent FFA1 agonist with favorable physicochemical and pharmacokinetic properties. The compound efficiently normalizes glucose tolerance in diet-induced obese mice, an effect that is fully sustained after 29 days of chronic dosing
Quasiperiodic Solutions of the Fibre Optics Coupled Nonlinear Schr{\"o}dinger Equations
We consider travelling periodical and quasiperiodical waves in single mode
fibres, with weak birefringence and under the action of cross-phase modulation.
The problem is reduced to the ``1:2:1" integrable case of the two-particle
quartic potential. A general approach for finding elliptic solutions is given.
New solutions which are associated with two-gap Treibich-Verdier potentials are
found. General quasiperiodic solutions are given in terms of two dimensional
theta functions with explicit expressions for frequencies in terms of theta
constants. The reduction of quasiperiodic solutions to elliptic functions is
discussed.Comment: 24 page
Stationary and moving breathers in a simplified model of curved alpha--helix proteins
The existence, stability and movability of breathers in a model for
alpha-helix proteins is studied. This model basically consists a chain of
dipole moments parallel to it. The existence of localized linear modes brings
about that the system has a characteristic frequency, which depends on the
curvature of the chain. Hard breathers are stable, while soft ones experiment
subharmonic instabilities that preserve, however the localization. Moving
breathers can travel across the bending point for small curvature and are
reflected when it is increased. No trapping of breathers takes place.Comment: 19 pages, 11 figure
Discovery of the spectroscopic binary nature of six southern Cepheids
We present the analysis of photometric and spectroscopic data of six bright
Galactic Cepheids: GH Carinae, V419 Centauri, V898 Centauri, AD Puppis, AY
Sagittarii, and ST Velorum. Based on new radial velocity data (in some cases
supplemented with earlier data available in the literature), these Cepheids
have been found to be members in spectroscopic binary systems. V898 Cen turned
out to have one of the largest orbital radial velocity amplitude (> 40 km/s)
among the known binary Cepheids. The data are insufficient to determine the
orbital periods nor other orbital elements for these new spectroscopic
binaries.
These discoveries corroborate the statement on the high frequency of
occurrence of binaries among the classical Cepheids, a fact to be taken into
account when calibrating the period-luminosity relationship for Cepheids.
We have also compiled all available photometric data that revealed that the
pulsation period of AD Pup, the longest period Cepheid in this sample, is
continuously increasing with Delta P = 0.004567 d/century, likely to be caused
by stellar evolution. The wave-like pattern superimposed on the parabolic O-C
graph of AD Pup may well be caused by the light-time effect in the binary
system. ST Vel also pulsates with a continuously increasing period. The other
four Cepheids are characterised with stable pulsation periods in the last half
century.Comment: accepted by the MNRAS, 11 pages, 16 figures, 18 tables, a part of the
data can be downloaded from the online version of this articl
Nonlinearity-induced conformational instability and dynamics of biopolymers
We propose a simple phenomenological model for describing the conformational
dynamics of biopolymers via the nonlinearity-induced buckling and collapse
(i.e. coiling up) instabilities. Taking into account the coupling between the
internal and mechanical degrees of freedom of a semiflexible biopolymer chain,
we show that self-trapped internal excitations (such as amide-I vibrations in
proteins, base-pair vibrations in DNA, or polarons in proteins) may produce the
buckling and collapse instabilities of an initially straight chain. These
instabilities remain latent in a straight infinitely long chain, because the
bending of such a chain would require an infinite energy. However, they
manifest themselves as soon as we consider more realistic cases and take into
account a finite length of the chain. In this case the nonlinear localized
modes may act as drivers giving impetus to the conformational dynamics of
biopolymers. The buckling instability is responsible, in particular, for the
large-amplitude localized bending waves which accompany the nonlinear modes
propagating along the chain. In the case of the collapse instability, the chain
folds into a compact three-dimensional coil. The viscous damping of the aqueous
environment only slows down the folding of the chain, but does not stop it even
for a large damping. We find that these effects are only weakly affected by the
peculiarities of the interaction potentials, and thus they should be generic
for different models of semiflexible chains carrying nonlinear localized
excitations.Comment: 4 pages (RevTeX) with 5 figures (EPS
Linear response subordination to intermittent energy release in off-equilibrium aging dynamics
The interpretation of experimental and numerical data describing
off-equilibrium aging dynamics crucially depends on the connection between
spontaneous and induced fluctuations. The hypothesis that linear response
fluctuations are statistically subordinated to irreversible outbursts of
energy, so-called quakes, leads to predictions for averages and fluctuations
spectra of physical observables in reasonable agreement with experimental
results [see e.g. Sibani et al., Phys. Rev. B74:224407, 2006]. Using
simulational data from a simple but representative Ising model with plaquette
interactions, direct statistical evidence supporting the hypothesis is
presented and discussed in this work.
A strict temporal correlation between quakes and intermittent magnetization
fluctuations is demonstrated. The external magnetic field is shown to bias the
pre-existent intermittent tails of the magnetic fluctuation distribution, with
little or no effect on the Gaussian part of the latter. Its impact on energy
fluctuations is shown to be negligible.
Linear response is thus controlled by the quakes and inherits their temporal
statistics. These findings provide a theoretical basis for analyzing
intermittent linear response data from aging system in the same way as thermal
energy fluctuations, which are far more difficult to measure.Comment: 9 pages, 10 figures. Text improve
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