1,069 research outputs found
Thermodynamical properties of a mean-field plus pairing model and applications for the Fe nuclei
A mean-field plus pairing model for atomic nuclei in the Fe region was
studied using a finite-temperature quantum Monte-Carlo method. We present
results for thermodynamical quantities such as the internal energy and the
specific heat. These results give indications of a phase transition related to
the pairing amongst nucleons, around temperatures of 0.7 MeV. The influence of
the residual interaction and of the size of the model space on the nuclear
level densities is discussed too.Comment: 23 pages, including 17 eps figure
Bosons Confined in Optical Lattices: the Numerical Renormalization Group revisited
A Bose-Hubbard model, describing bosons in a harmonic trap with a
superimposed optical lattice, is studied using a fast and accurate variational
technique (MF+NRG): the Gutzwiller mean-field (MF) ansatz is combined with a
Numerical Renormalization Group (NRG) procedure in order to improve on both.
Results are presented for one, two and three dimensions, with particular
attention to the experimentally accessible momentum distribution and possible
satellite peaks in this distribution. In one dimension, a comparison is made
with exact results obtained using Stochastich Series Expansion.Comment: 10 pages, 15 figure
Consequences of the Pauli exclusion principle for the Bose-Einstein condensation of atoms and excitons
The bosonic atoms used in present day experiments on Bose-Einstein
condensation are made up of fermionic electrons and nucleons. In this Letter we
demonstrate how the Pauli exclusion principle for these constituents puts an
upper limit on the Bose-Einstein-condensed fraction. Detailed numerical results
are presented for hydrogen atoms in a cubic volume and for excitons in
semiconductors and semiconductor bilayer systems. The resulting condensate
depletion scales differently from what one expects for bosons with a repulsive
hard-core interaction. At high densities, Pauli exclusion results in
significantly more condensate depletion. These results also shed a new light on
the low condensed fraction in liquid helium II.Comment: 4 pages, 2 figures, revised version, now includes a direct comparison
with hard-sphere QMC results, submitted to Phys. Rev. Let
Integrable two-channel p_x+ip_y-wave superfluid model
We present a new two-channel integrable model describing a system of spinless
fermions interacting through a p-wave Feshbach resonance. Unlike the BCS-BEC
crossover of the s-wave case, the p-wave model has a third order quantum phase
transition. The critical point coincides with the deconfinement of a single
molecule within a BEC of bound dipolar molecules. The exact many-body
wavefunction provides a unique perspective of the quantum critical region
suggesting that the size of the condensate wavefunction, that diverges
logarithmically with the chemical potential, could be used as an experimental
indicator of the phase transition.Comment: 4 pages, 4 figure
Existence of Density Functionals for Excited States and Resonances
We show how every bound state of a finite system of identical fermions,
whether a ground state or an excited one, defines a density functional.
Degeneracies created by a symmetry group can be trivially lifted by a
pseudo-Zeeman effect. When complex scaling can be used to regularize a
resonance into a square integrable state, a DF also exists.Comment: 4 pages, no figure
Ultracold atoms in one-dimensional optical lattices approaching the Tonks-Girardeau regime
Recent experiments on ultracold atomic alkali gases in a one-dimensional
optical lattice have demonstrated the transition from a gas of soft-core bosons
to a Tonks-Girardeau gas in the hard-core limit, where one-dimensional bosons
behave like fermions in many respects. We have studied the underlying many-body
physics through numerical simulations which accommodate both the soft-core and
hard-core limits in one single framework. We find that the Tonks-Girardeau gas
is reached only at the strongest optical lattice potentials. Results for
slightly higher densities, where the gas develops a Mott-like phase already at
weaker optical lattice potentials, show that these Mott-like short range
correlations do not enhance the convergence to the hard-core limit.Comment: 4 pages, 3 figures, replaced with published versio
Integrable models for asymmetric Fermi superfluids: Emergence of a new exotic pairing phase
We introduce an exactly-solvable model to study the competition between the
Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) and breached-pair superfluid in
strongly interacting ultracold asymmetric Fermi gases. One can thus investigate
homogeneous and inhomogeneous states on an equal footing and establish the
quantum phase diagram. For certain values of the filling and the interaction
strength, the model exhibits a new stable exotic pairing phase which combines
an inhomogeneous state with an interior gap to pair-excitations. It is proven
that this phase is the exact ground state in the strong coupling limit, while
numerical examples demonstrate that also at finite interaction strength it can
have lower energy than the breached-pair or LOFF states.Comment: Revised version accepted for publicatio
Monograph No. 5: Drug law enforcement: The evidence
This monograph (No. 05) provides an annotated bibliography of all the relevant drug law enforcement literature. The team at Griffith University have collated and summarised the extant research literature and completed two systematic reviews – a narrative review and a meta-analytic review. These have both been published in peer review journals. This monograph provides the reader with a detailed list of all the published law enforcement literature, broken down into categories of: international/national interventions; reactive/aggressive interventions; proactive/partnership interventions; individualised interventions; and combination of reactive/aggressive & proactive/partnership interventions
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