61,942 research outputs found
Test of shell-model interactions for nuclear structure calculations
The binding energy and excitation spectra of 6Li are calculated in a no-core shell-model space giving encouraging results. The results of this calculation are then treated as a theoretical experiment, against which different effective-interaction approximations are compared. In this way insight into the perturbation expansion for the effective interaction is obtained
The dynamical fate of planetary systems in young star clusters
We carry out N-body simulations to examine the effects of dynamical
interactions on planetary systems in young open star clusters. We explore how
the planetary populations in these star clusters evolve, and how this evolution
depends on the initial amount of substructure, the virial ratio, the cluster
mass and density, and the initial semi-major axis of the planetary systems. The
fraction of planetary systems that remains intact as a cluster member, fbps, is
generally well-described by the functional form fbps=f0(1+[a/a0]^c)^-1, where
(1-f0) is the fraction of stars that escapes from the cluster, a0 the critical
semi-major axis for survival, and c a measure for the width of the transition
region. The effect of the initial amount of substructure over time can be
quantified as fbps=A(t)+B(D), where A(t) decreases nearly linearly with time,
and B(D) decreases when the clusters are initially more substructured. Provided
that the orbital separation of planetary systems is smaller than the critical
value a0, those in clusters with a higher initial stellar density (but
identical mass) have a larger probability of escaping the cluster intact. These
results help us to obtain a better understanding of the difference between the
observed fractions of exoplanets-hosting stars in star clusters and in the
Galactic field. It also allows us to make predictions about the free-floating
planet population over time in different stellar environments.Comment: 14 pages, 9 figures, accepted for publication in MNRA
Phase Ordering Dynamics of Theory with Hamiltonian Equations of Motion
Phase ordering dynamics of the (2+1)- and (3+1)-dimensional theory
with Hamiltonian equations of motion is investigated numerically. Dynamic
scaling is confirmed. The dynamic exponent is different from that of the
Ising model with dynamics of model A, while the exponent is the same.Comment: to appear in Int. J. Mod. Phys.
Distributed coherent manipulation of qutrits by virtual excitation processes
We propose a scheme for the deterministic coherent manipulation of two atomic
qutrits, trapped in separate cavities coupled through a short optical fibre or
optical resonator. We study such a system in the regime of dispersive
atom-field interactions, where the dynamics of atoms, cavities and fibre
operates through virtual population of both the atomic excited states and
photonic states in the cavities and fibre. We show that the resulting effective
dynamics allows for the creation of robust qutrit entanglement, and thoroughly
investigate the influence of imperfections and dissipation, due to atomic
spontaneous emission and photon leakage, on the entanglement of the two qutrits
state.Comment: 15 pages, 4 figure
Achieving control of in-plane elastic waves
We derive the elastic properties of a cylindrical cloak for in-plane coupled
shear and pressure waves. The cloak is characterized by a rank 4 elasticity
tensor with 16 spatially varying entries which are deduced from a geometric
transform. Remarkably, the Navier equations retain their form under this
transform, which is generally untrue [Milton et al., New J. Phys. 8, 248
(2006)]. We numerically check that clamped and freely vibrating obstacles
located inside the neutral region are cloaked disrespectful of the frequency
and the polarization of an incoming elastic wave.Comment: 9 pages, 4 figure
Dynamics of two atoms coupled to a cavity field
We investigate the interaction of two two-level atoms with a single mode
cavity field. One of the atoms is exactly at resonance with the field, while
the other is well far from resonance and hence is treated in the dispersive
limit. We find that the presence of the non-resonant atom produces a shift in
the Rabi frequency of the resonant atom, as if it was detuned from the field.
We focus on the discussion of the evolution of the state purity of each atom.Comment: LaTex, 2 figure
Close encounters involving free-floating planets in star clusters
Instabilities in planetary systems can result in the ejection of planets from
their host system, resulting in free-floating planets (FFPs). If this occurs in
a star cluster, the FFP may remain bound to the star cluster for some time and
interact with the other cluster members until it is ejected. Here, we use
-body simulations to characterise close star-planet and planet-planet
encounters and the dynamical fate of the FFP population in star clusters
containing single or binary star members. We find that FFPs ejected
from their planetary system at low velocities typically leave the star cluster
40% earlier than their host stars, and experience tens of close ( AU)
encounters with other stars and planets before they escape. The fraction of
FFPs that experiences a close encounter depends on both the stellar density and
the initial velocity distribution of the FFPs. Approximately half of the close
encounters occur within the first 30 Myr, and only 10% occur after 100 Myr. The
periastron velocity distribution for all encounters is well-described by a
modified Maxwell-Bolzmann distribution, and the periastron distance
distribution is linear over almost the entire range of distances considered,
and flattens off for very close encounters due to strong gravitational
focusing. Close encounters with FFPs can perturb existing planetary systems and
their debris structures, and they can result in re-capture of FFPs. In
addition, these FFP populations may be observed in young star clusters in
imaging surveys; a comparison between observations and dynamical predictions
may provide clues to the early phases of stellar and planetary dynamics in star
clusters.Comment: Accepted for publication in MNRAS; 18 pages, 12 figure
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