15,240 research outputs found
The energy dependence of the amplitude and the three-nucleon interaction
By calculating the contribution of the three-body force to the
three-nucleon binding energy in terms of the amplitude using
perturbation theory, we are able to determine the importance of the energy
dependence and the contribution of the different partial waves of the
amplitude to the three-nucleon force. A separable representation of the
non-pole amplitude allows us to write the three-nucleon force in terms
of the amplitude for , propagation of the system,
and the amplitude for , with being the
quasi-particle amplitude in a given state. The division of the
amplitude into a pole and non-pole gives a procedure for the determination of
the form factor within the model. The total contribution of the
three-body force to the binding energy of the triton for the separable
approximation to the Paris nucleon-nucleon potential (PEST) is found to be very
small mainly as a result of the energy dependence of the amplitude, the
cancellation between the - and -wave amplitudes, and the soft
form factor.Comment: RevTex file, 36 pages, 10 figures available from authors:
[email protected]
Coupled ion - nanomechanical systems
We study ions in a nanotrap, where the electrodes are nanomechanical
resonantors. The ions play the role of a quantum optical system which acts as a
probe and control, and allows entanglement with or between nanomechanical
resonators.Comment: 4 pages, 2 figures, submitted for publicatio
Degeneracy breaking and intervalley scattering due to short-ranged impurities in finite single-wall carbon nanotubes
We present a theoretical study of degeneracy breaking due to short-ranged
impurities in finite, single-wall, metallic carbon nanotubes. The effective
mass model is used to describe the slowly varying spatial envelope
wavefunctions of spinless electrons near the Fermi level at two inequivalent
valleys (K-points) in terms of the four component Dirac equation for massless
fermions, with the role of spin assumed by pseudospin due to the relative
amplitude of the wave function on the sublattice atoms (``A'' and ``B''). Using
boundary conditions at the ends of the tube that neither break valley
degeneracy nor mix pseudospin eigenvectors, we use degenerate perturbation
theory to show that the presence of impurities has two effects. Firstly, the
position of the impurity with respect to the spatial variation of the envelope
standing waves results in a sinusoidal oscillation of energy level shift as a
function of energy. Secondly, the position of the impurity within the hexagonal
graphite unit cell produces a particular 4 by 4 matrix structure of the
corresponding effective Hamiltonian. The symmetry of this Hamiltonian with
respect to pseudospin flip is related to degeneracy breaking and, for an
armchair tube, the symmetry with respect to mirror reflection in the nanotube
axis is related to pseudospin mixing.Comment: 20 pages, 10 eps figure
Gap opening in graphene by simple periodic inhomogeneous strain
Using ab-initio methods, we show that the uniform deformation either leaves
graphene (semi)metallic or opens up a small gap yet only beyond the mechanical
breaking point of the graphene, contrary to claims in the literature based on
tight-binding (TB) calculations. It is possible, however, to open up a global
gap by a sine-like one-dimensional inhomogeneous deformation applied along any
direction but the armchair one, with the largest gap for the corrugation along
the zigzag direction (~0.5 eV) without any electrostatic gating. The gap
opening has a threshold character with very sharp rise when the ratio of the
amplitude A and the period of the sine wave deformation lambda exceeds
(A/lambda)_c ~0.1 and the inversion symmetry is preserved, while it is
threshold-less when the symmetry is broken, in contrast with TB-derived
pseudo-magnetic field models.Comment: 6 pages, 6 figures; (v2) added figures illustrating opening gap in
Graphene mesh on BN, expanded analysis illustrating absence of
pseudo-magnetic fields in deformed Graphen
Calculation of the Self-energy of Open Quantum Systems
We propose an easy method of calculating the self-energy of semi-infinite
leads attached to a mesoscopic system.Comment: 6 pages, 2 figures, published in J. Phys. Soc. Jp
Energy gap tuning in graphene on hexagonal boron nitride bilayer system
We use a tight binding approach and density functional theory calculations to
study the band structure of graphene/hexagonal boron nitride bilayer system in
the most stable configuration. We show that an electric field applied in the
direction perpendicular to the layers significantly modifies the electronic
structure of the whole system, including shifts, anticrossing and other
deformations of bands, which can allow to control the value of the energy gap.
It is shown that band structure of biased system may be tailored for specific
requirements of nanoelectronics applications. The carriers' mobilities are
expected to be higher than in the bilayer graphene devices.Comment: 10 pages, 7 figures, submitted to Physical Review
Hot nuclear matter in the modified quark-meson coupling model with quark-quark correlations
Short-range quark-quark correlations in hot nuclear matter are examined
within the modified quark-meson coupling model (MQMC) by adding repulsive
scalar and vector quark-quark interactions. Without these correlations, the bag
radius increases with the baryon density. However when the correlations are
introduced the bag size shrinks as the bags overlap. Also as the strength of
the scalar quark-quark correlation is increased, the decrease of the effective
nucleon mass with the baryonic density is slowed down and tends to
saturate at high densities. Within this model we study the phase transition
from the baryon-meson phase to the quark-gluon plasma (QGP) phase with the
latter modeled as an ideal gas of quarks and gluons inside a bag. Two models
for the QGP bag parameter are considered. In one case, the bag is taken to be
medium-independent and the phase transition from the hadron phase to QGP is
found to occur at 5-8 times ordinary nuclear matter density for temperatures
less than 60 MeV. For lower densities, the transition takes place at higher
temperature reaching up to 130 MeV at zero density. In the second case, the QGP
bag parameter is considered medium-dependent as in the MQMC model for the
hadronic phase. In this case, it is found that the phase transition occurs at
much lower densities.Comment: 8 pages, latex, 4 eps figure
Bulge RR Lyrae stars in the VVV tile
The VISTA Variables in the V\'ia L\'actea (VVV) Survey is one of the six ESO
public surveys currently ongoing at the VISTA telescope on Cerro Paranal,
Chile. VVV uses near-IR () filters that at present provide
photometry to a depth of mag in up to 36 epochs spanning
over four years, and aim at discovering more than 10 variable sources as
well as trace the structure of the Galactic bulge and part of the southern
disk. A variability search was performed to find RR Lyrae variable stars. The
low stellar density of the VVV tile , which is centered at
() (), makes it suitable to search for
variable stars. Previous studies have identified some RR Lyrae stars using
optical bands that served to test our search procedure. The main goal is to
measure the reddening, interstellar extinction, and distances of the RR Lyrae
stars and to study their distribution on the Milky Way bulge. A total of 1.5 sq
deg were analyzed, and we found 39 RR Lyrae stars, 27 of which belong to the
ab-type and 12 to the c-type. Our analysis recovers all the previously
identified RR Lyrae variables in the field and discovers 29 new RR Lyrae stars.
The reddening and extinction toward all the RRab stars in this tile were
derived, and distance estimations were obtained through the period--luminosity
relation. Despite the limited amount of RR Lyrae stars studied, our results are
consistent with a spheroidal or central distribution around and
kpc. for either the Cardelli or Nishiyama extinction law.Comment: 10 pages, 8 figures, accepted for publication in Astronomy and
Astrophysic
Stochastic Approach to Enantiomeric Excess Amplification and Chiral Symmetry Breaking
Stochastic aspects of chemical reaction models related to the Soai reactions
as well as to the homochirality in life are studied analytically and
numerically by the use of the master equation and random walk model. For
systems with a recycling process, a unique final probability distribution is
obtained by means of detailed balance conditions. With a nonlinear
autocatalysis the distribution has a double-peak structure, indicating the
chiral symmetry breaking. This problem is further analyzed by examining
eigenvalues and eigenfunctions of the master equation. In the case without
recycling process, final probability distributions depend on the initial
conditions. In the nonlinear autocatalytic case, time-evolution starting from a
complete achiral state leads to a final distribution which differs from that
deduced from the nonzero recycling result. This is due to the absence of the
detailed balance, and a directed random walk model is shown to give the correct
final profile. When the nonlinear autocatalysis is sufficiently strong and the
initial state is achiral, the final probability distribution has a double-peak
structure, related to the enantiomeric excess amplification. It is argued that
with autocatalyses and a very small but nonzero spontaneous production, a
single mother scenario could be a main mechanism to produce the homochirality.Comment: 25 pages, 6 figure
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