700 research outputs found
Induced order and reentrant melting in classical two-dimensional binary clusters
A binary system of classical charged particles interacting through a dipole
repulsive potential and confined in a two-dimensional hardwall trap is studied
by Brownian dynamics simulations. We found that the presence of small particles
\emph{stabilizes} the angular order of the system as a consequence of radial
fluctuations of the small particles. There is an optimum in the increased
rigidity of the cluster as function of the number of small particles. The small
(i.e. defect) particles melt at a lower temperature compared to the big
particles and exhibit a \emph{reentrant} behavior in its radial order that is
induced by the intershell rotation of the big particles.Comment: 7 pages, 3 figure
Structural transitions in vertically and horizontally coupled parabolic channels of Wigner crystals
Structural phase transitions in two vertically or horizontally coupled
channels of strongly interacting particles are investigated. The particles are
free to move in the -direction but are confined by a parabolic potential in
the -direction. They interact with each other through a screened power-law
potential (). In vertically coupled systems the channels
are stacked above each other in the direction perpendicular to the
-plane, while in horizontally coupled systems both channels are aligned
in the confinement direction. Using Monte Carlo (MC) simulations we obtain the
ground state configurations and the structural transitions as a function of the
linear particle density and the separation between the channels. At zero
temperature the vertically coupled system exhibits a rich phase diagram with
continuous and discontinuous transitions. On the other hand the vertically
coupled system exhibits only a very limited number of phase transitions due to
its symmetry. Further we calculated the normal modes for the Wigner crystals in
both cases. From MC simulations we found that in the case of vertically coupled
systems the zigzag transition is only possible for low densities. A
Ginzburg-Landau theory for the zigzag transition is presented, which predicts
correctly the behavior of this transition from which we interpret the
structural phase transition of the Wigner crystal through the reduction of the
Brillouin zone.Comment: 9 pages, 13 figure
Hysteresis and re-entrant melting of a self-organized system of classical particles confined in a parabolic trap
A self-organized system composed of classical particles confined in a
two-dimensional parabolic trap and interacting through a potential with a
short-range attractive part and long-range repulsive part is studied as
function of temperature. The influence of the competition between the
short-range attractive part of the inter-particle potential and its long-range
repulsive part on the melting temperature is studied. Different behaviors of
the melting temperature are found depending on the screening length ()
and the strength () of the attractive part of the inter-particle potential.
A re-entrant behavior and a thermal induced phase transition is observed in a
small region of ()-space. A structural hysteresis effect is observed
as a function of temperature and physically understood as due to the presence
of a potential barrier between different configurations of the system.Comment: 8 pages, 6 figure
Transition from single-file to two-dimensional diffusion of interacting particles in a quasi-one-dimensional channel
Diffusive properties of a monodisperse system of interacting particles
confined to a \textit{quasi}-one-dimensional (Q1D) channel are studied using
molecular dynamics (MD) simulations. We calculate numerically the mean-squared
displacement (MSD) and investigate the influence of the width of the channel
(or the strength of the confinement potential) on diffusion in finite-size
channels of different shapes (i.e., straight and circular). The transition from
single-file diffusion (SFD) to the two-dimensional diffusion regime is
investigated. This transition (regarding the calculation of the scaling
exponent () of the MSD ) as a
function of the width of the channel, is shown to change depending on the
channel's confinement profile. In particular the transition can be either
smooth (i.e., for a parabolic confinement potential) or rather sharp/stepwise
(i.e., for a hard-wall potential), as distinct from infinite channels where
this transition is abrupt. This result can be explained by qualitatively
different distributions of the particle density for the different confinement
potentials.Comment: 13 pages, 11 figure
Using self-driven microswimmers for particle separation
Microscopic self-propelled swimmers capable of autonomous navigation through
complex environments provide appealing opportunities for localization, pick-up
and delivery of micro-and nanoscopic objects. Inspired by motile cells and
bacteria, man-made microswimmers have been fabricated, and their motion in
patterned surroundings has been experimentally studied. We propose to use
self-driven artificial microswimmers for separation of binary mixtures of
colloids. We revealed different regimes of separation including one with a
velocity inversion. Our finding could be of use for various biological and
medical applications.Comment: 6 pages, 5 figure
A forward genetics approach integrating genome-wide association study and expression quantitative trait locus mapping to dissect leaf development in maize (Zea mays)
The characterization of the genetic basis of maize (Zea mays) leaf development may support breeding efforts to obtain plants with higher vigor and productivity. In this study, a mapping panel of 197 biparental and multiparental maize recombinant inbred lines (RILs) was analyzed for multiple leaf traits at the seedling stage. RNA sequencing was used to estimate the transcription levels of 29\ua0573 gene models in RILs and to derive 373\ua0769 single nucleotide polymorphisms (SNPs), and a forward genetics approach combining these data was used to pinpoint candidate genes involved in leaf development. First, leaf traits were correlated with gene expression levels to identify transcript\u2013trait correlations. Then, leaf traits were associated with SNPs in a genome-wide association (GWA) study. An expression quantitative trait locus mapping approach was followed to associate SNPs with gene expression levels, prioritizing candidate genes identified based on transcript\u2013trait correlations and GWAs. Finally, a network analysis was conducted to cluster all transcripts in 38 co-expression modules. By integrating forward genetics approaches, we identified 25 candidate genes highly enriched for specific functional categories, providing evidence supporting the role of vacuolar proton pumps, cell wall effectors, and vesicular traffic controllers in leaf growth. These results tackle the complexity of leaf trait determination and may support precision breeding in maize
The P gene of Newcastle disease virus does not encode an accessory X protein
Many paramyxoviruses encode non-essential accessory proteins that are involved in the regulation of virus replication and inhibition of cellular antiviral responses. It has been suggested that the P gene mRNA of Newcastle disease virus (NDV) encodes an accessory protein ¿ the so-called X protein ¿ by translation initiation at a conserved in-frame AUG codon at position 120. Using a monoclonal antibody that specifically detected the P and X proteins, it was shown that an accessory X protein was not expressed in NDV-infected cells. Recombinant NDV strains in which the AUG was changed into a GCC (Ala) or GUC (Val) codon were viable but showed a reduction in virulence, probably because the amino acid change affected the function of the P and/or V protein
Low-temperature structural model of hcp solid C
We report intermolecular potential-energy calculations for solid C_ and
determine the optimum static orientations of the molecules at low temperature;
we find them to be consistent with the monoclinic structural model proposed by
us in an earlier report [Solid State Commun. {\bf 105), 247 (1998)]. This model
indicates that the C_5 axis of the molecule is tilted by an angle 18^o
from the monoclinic b axis in contrast with the molecular orientation proposed
by Verheijen {\it et al.} [J. Chem. Phys. {\bf 166}, 287 (1992)] where the C_5
axis is parallel to the monoclinic b axis. In this calculation we have
incorporated the effective bond charge Coulomb potential together with the
Lennard-Jones potential between the molecule at the origin of the monoclinic
unit cell and its six nearest neighbours, three above and three below. The
minimum energy configuration for the molecular orientations turns out to be at
=18^o, =8^o, and =5^o, where , , and
define the molecular orientations.Comment: ReVTeX (4 pages) + 2 PostScript figure
- …