1,550 research outputs found
Topological thermal instability and length of proteins
We present an analysis of the effects of global topology on the structural
stability of folded proteins in thermal equilibrium with a heat bath. For a
large class of single domain proteins, we computed the harmonic spectrum within
the Gaussian Network Model (GNM) and determined the spectral dimension, a
parameter describing the low frequency behaviour of the density of modes. We
find a surprisingly strong correlation between the spectral dimension and the
number of amino acids of the protein. Considering that larger spectral
dimension value relate to more topologically compact folded state, our results
indicate that for a given temperature and length of the protein, the folded
structure corresponds to the less compact folding compatible with thermodynamic
stability.Comment: 15 pages, 6 eps figures, 2 table
Thermally induced directed currents in hard rod systems
We study the non equilibrium statistical properties of a one dimensional
hard-rod fluid undergoing collisions and subject to a spatially non uniform
Gaussian heat-bath and periodic potential. The system is able to sustain finite
currents when the spatially inhomogeneous heat-bath and the periodic potential
profile display an appropriate relative phase shift, . By comparison with
the collisionless limit, we determine the conditions for the most efficient
transport among inelastic, elastic and non interacting rods. We show that the
situation is complex as, depending on shape of the temperature profile, the
current of one system may outperform the others.Comment: 5 pages, 2 figure
Female fertility and environmental pollution
A realistic picture of our world shows that it is heavily polluted everywhere. Coastal regions and oceans are polluted by farm fertilizer, manure runoff, sewage and industrial discharges, and large isles of waste plastic are floating around, impacting sea life. Terrestrial ecosystems are contaminated by heavy metals and organic chemicals that can be taken up by and accumulate in crop plants, and water tables are heavily contaminated by untreated industrial discharges. As deadly particulates can drift far, poor air quality has become a significant global problem and one that is not exclusive to major industrialized cities. The consequences are a dramatic impairment of our ecosystem and biodiversity and increases in degenerative or man-made diseases. In this respect, it has been demonstrated that environmental pollution impairs fertility in all mammalian species. The worst consequences are observed for females since the number of germ cells present in the ovary is fixed during fetal life, and the cells are not renewable. This means that any pollutant affecting hormonal homeostasis and/or the reproductive apparatus inevitably harms reproductive performance. This decline will have important social and economic consequences that can no longer be overlooked
N-tree approximation for the largest Lyapunov exponent of a coupled-map lattice
The N-tree approximation scheme, introduced in the context of random directed
polymers, is here applied to the computation of the maximum Lyapunov exponent
in a coupled map lattice. We discuss both an exact implementation for small
tree-depth and a numerical implementation for larger s. We find that the
phase-transition predicted by the mean field approach shifts towards larger
values of the coupling parameter when the depth is increased. We conjecture
that the transition eventually disappears.Comment: RevTeX, 15 pages,5 figure
Refurbishing Voyager 1 & 2 Planetary Radio Astronomy (PRA) Data
Voyager/PRA (Planetary Radio Astronomy) data from digitized tapes archived at
CNES have been reprocessed and recalibrated. The data cover the Jupiter and
Saturn flybys of both Voyager probes. We have also reconstructed
goniopolarimetric datasets (flux and polarization) at full resolution. These
datasets are currently not available to the scientific community, but they are
of primary interest for the analysis of the Cassini data at Saturn, and the
Juno data at Jupiter, as well as for the preparation of the JUICE mission. We
present the first results derived from the re-analysis of this dataset.Comment: Accepted manuscript for PRE8 (Planetary Radio Emission VIII
conference) proceeding
A vigorous activity cycle mimicking a planetary system in HD200466
Stellar activity can be a source of radial velocity (RV) noise and can
reproduce periodic RV variations similar to those produced by an exoplanet. We
present the vigorous activity cycle in the primary of the visual binary
HD200466, a system made of two almost identical solar-type stars with an
apparent separation of 4.6 arcsec at a distance of 44+/-2 pc. High precision RV
over more than a decade, adaptive optics (AO) images, and abundances have been
obtained for both components. A linear trend in the RV is found for the
secondary. We assumed that it is due to the binary orbit and once coupled with
the astrometric data, it strongly constrains the orbital solution of the binary
at high eccentricities (e~0.85) and quite small periastron of ~21 AU. If this
orbital motion is subtracted from the primary radial velocity curve, a highly
significant (false alarm probability <0.1%) period of about 1300 d is obtained,
suggesting in a first analysis the presence of a giant planet, but it turned
out to be due to the stellar activity cycle. Since our spectra do not include
the Ca~II resonance lines, we measured a chromospheric activity indicator based
on the Halpha line to study the correlation between activity cycles and
long-term activity variations. While the bisector analysis of the line profile
does not show a clear indication of activity, the correlation between the
Halpha line indicator and the RV measurements identify the presence of a strong
activity cycle.Comment: Accepted on Astronomy and Astrophysics Main Journal 2014, 16 pages,
18 figure
Sensorless variable speed single-phase induction motor drive system based on direct rotor flux orientation
The single-phase induction motor (SPIM) is one of the electrical machines more used in the World, and can be found in several fractional and sub-fractional horsepower applications in houses, offices, shoppings, farms, and industries. The introduction of more sophisticated applications has required the use of variable speed drives for SPIM, where the adoption of sensorless techniques is the more reasonable option for speed control due to the low cost of this electrical machine. A proposal for sensorless variable speed SPIM drive based on direct rotor field orientation techniques is presented in this paper. None transformation is used in order to eliminate the asymmetry of the stator windings of the SPIM. The rotor speed is estimated from an flux observer, which is based on two independent linear feedback control systems. The speed and flux estimatives are used in two control loop based on PID regulators, which determine the voltages to be applied to the SPIM windings by a three-legs VSI inverter. Using computer simulations, two situations are considered in order to demonstrate the satisfactory performance of the proposed sensorless speed control for SPIM drives: variations on rotor speed reference and the application of mechanical load
Comparison of voter and Glauber ordering dynamics on networks
We study numerically the ordering process of two very simple dynamical models
for a two-state variable on several topologies with increasing levels of
heterogeneity in the degree distribution. We find that the zero-temperature
Glauber dynamics for the Ising model may get trapped in sets of partially
ordered metastable states even for finite system size, and this becomes more
probable as the size increases. Voter dynamics instead always converges to full
order on finite networks, even if this does not occur via coherent growth of
domains. The time needed for order to be reached diverges with the system size.
In both cases the ordering process is rather insensitive to the variation of
the degreee distribution from sharply peaked to scale-free.Comment: 12 pages, 12 figure
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