782 research outputs found
Chromosome Oscillations in Mitosis
Successful cell division requires a tight regulation of chromosome motion via
the activity of molecular motors. Many of the key players at the origin of the
forces generating the movement have been identified, but their spatial and
temporal organization remains elusive. The protein complex Kinetochore on the
chromosome associates with microtubules emanating from one of the spindle poles
and drives the chromosome toward the pole. Chromokinesin motors on the
chromosome arms also interact with microtubules, ejecting the chromosome away
from the pole. In animal cells, a monooriented chromosome (associated to a
single pole) periodically switches between phases of poleward and away from the
pole movement[, a behavior tentatively explained so far by the existence of a
complex switching mechanism within the kinetochore itself. Here we show that
the interplay between the morphology of the mitotic spindle and the collective
kinetics of chromokinesins can account for the highly non-linear periodic
chromosome motion. Our analysis provides a natural explanation for the origin
of chromosome directional instability and for the mechanism by which
chromosomes feel their position in space.Comment: http://hogarth.pct.espci.fr/~pierre
Higher order effects in the and transfer reactions
Full Coupled Channels Calculations were performed for the
and transfer reactions at several deuteron incident
energies from MeV up to 3.27 MeV. A strong polarization effect
between the entrance channel and the transfer channels
and was
observed. This polarization effect had to be taken into account in order to
obtain realistic spectroscopic factors from these reactions.Comment: 15 papes, 13 figures, accepted for publication in Phys. Rev.
Force balance and membrane shedding at the Red Blood Cell surface
During the aging of the red-blood cell, or under conditions of extreme
echinocytosis, membrane is shed from the cell plasma membrane in the form of
nano-vesicles. We propose that this process is the result of the
self-adaptation of the membrane surface area to the elastic stress imposed by
the spectrin cytoskeleton, via the local buckling of membrane under increasing
cytoskeleton stiffness. This model introduces the concept of force balance as a
regulatory process at the cell membrane, and quantitatively reproduces the rate
of area loss in aging red-blood cells.Comment: 4 pages, 3 figure
BPS Configurations in Smectics
It is typical in smectic liquid crystals to describe elastic deformations
with a linear theory when the elastic strain is small. We extend the recent,
exact solution of Brener and Marchenko to more general one-dimensional
deformations, including multiple edge dislocations by relying on the
Bogomol'nyi, Prasad and Sommerfield (BPS) decomposition. We introduce an
approximation for the deformation profile far from a spherical inclusion and
find an enhanced attractive interaction at long distances due to the nonlinear
elasticity.Comment: 4 pages, RevTeX, 2 figures, corrected typo
The impact of lepton-flavor violating Z' bosons on muon g-2 and other muon observables
A lepton-flavor violating (LFV) Z' boson may mimic some of the phenomena
usually attributed to supersymmetric theories. Using a conservative model of
LFV Z' bosons, the recent BNL E821 muon g-2 deviation allows for a LFV Z'
interpretation with a boson mass up to 4.8 TeV while staying within limits set
by muon conversion, mu -> e gamma, and mu -> eee. This model is immediately
testable as one to twenty e^+e^- -> mu tau events are predicted for an analysis
of the LEP II data. Future muon conversion experiments, MECO and PRIME, are
demonstrated to have potential to probe very high boson masses with very small
charges, such as a 10 TeV boson with an e-mu charge of 10^-5. Furthermore, the
next linear collider is shown to be highly complementary with muon conversion
experiments, which are shown to provide the strictest and most relevant bounds
on LFV phenomena.Comment: 17 pages, 6 figures, uses feynMF, edited references (v2), corrected
MEGA experimental limit (v3), accepted to Phys. Rev.
Spectroscopy of Na: Bridging the two-proton radioactivity of Mg
The unbound nucleus Na, the intermediate nucleus in the two-proton
radioactivity of Mg, was studied by the measurement of the resonant
elastic scattering reaction Ne(p,Ne)p performed at 4 A.MeV.
Spectroscopic properties of the low-lying states were obtained in a R-matrix
analysis of the excitation function. Using these new results, we show that the
lifetime of the Mg radioactivity can be understood assuming a sequential
emission of two protons via low energy tails of Na resonances
Degradation versus self-assembly of block copolymer micelles
The stability of micelles self-assembled from block copolymers can be altered
by the degradation of the blocks. Slow degradation shifts the equilibrium size
distribution of block copolymer micelles and change their properties.
Quasi-equilibrium scaling theory shows that the degradation of hydrophobic
blocks in the core of micelles destabilize the micelles reducing their size,
while the degradation of hydrophilic blocks forming coronas of micelles favors
larger micelles and may, at certain conditions, induce the formation of
micelles from individual chains.Comment: Published in Langmuir http://pubs.acs.org/doi/pdf/10.1021/la204625
Toward Forecasting Volcanic Eruptions using Seismic Noise
During inter-eruption periods, magma pressurization yields subtle changes of
the elastic properties of volcanic edifices. We use the reproducibility
properties of the ambient seismic noise recorded on the Piton de la Fournaise
volcano to measure relative seismic velocity variations of less than 0.1 % with
a temporal resolution of one day. Our results show that five studied volcanic
eruptions were preceded by clearly detectable seismic velocity decreases within
the zone of magma injection. These precursors reflect the edifice dilatation
induced by magma pressurization and can be useful indicators to improve the
forecasting of volcanic eruptions.Comment: Supplementary information:
http://www-lgit.obs.ujf-grenoble.fr/~fbrengui/brenguier_SI.pdf Supplementary
video:
http://www-lgit.obs.ujf-grenoble.fr/~fbrengui/brenguierMovieVolcano.av
Entropic Tension in Crowded Membranes
Unlike their model membrane counterparts, biological membranes are richly
decorated with a heterogeneous assembly of membrane proteins. These proteins
are so tightly packed that their excluded area interactions can alter the free
energy landscape controlling the conformational transitions suffered by such
proteins. For membrane channels, this effect can alter the critical membrane
tension at which they undergo a transition from a closed to an open state, and
therefore influence protein function \emph{in vivo}. Despite their obvious
importance, crowding phenomena in membranes are much less well studied than in
the cytoplasm.
Using statistical mechanics results for hard disk liquids, we show that
crowding induces an entropic tension in the membrane, which influences
transitions that alter the projected area and circumference of a membrane
protein. As a specific case study in this effect, we consider the impact of
crowding on the gating properties of bacterial mechanosensitive membrane
channels, which are thought to confer osmoprotection when these cells are
subjected to osmotic shock. We find that crowding can alter the gating energies
by more than in physiological conditions, a substantial fraction of
the total gating energies in some cases.
Given the ubiquity of membrane crowding, the nonspecific nature of excluded
volume interactions, and the fact that the function of many membrane proteins
involve significant conformational changes, this specific case study highlights
a general aspect in the function of membrane proteins.Comment: 20 pages (inclduing supporting information), 4 figures, to appear in
PLoS Comp. Bio
- âŠ