12,737 research outputs found
Low-momentum ring diagrams of neutron matter at and near the unitary limit
We study neutron matter at and near the unitary limit using a low-momentum
ring diagram approach. By slightly tuning the meson-exchange CD-Bonn potential,
neutron-neutron potentials with various scattering lengths such as
and are constructed. Such potentials are renormalized
with rigorous procedures to give the corresponding -equivalent
low-momentum potentials , with which the low-momentum
particle-particle hole-hole ring diagrams are summed up to all orders, giving
the ground state energy of neutron matter for various scattering lengths.
At the limit of , our calculated ratio of to that of
the non-interacting case is found remarkably close to a constant of 0.44 over a
wide range of Fermi-momenta. This result reveals an universality that is well
consistent with the recent experimental and Monte-Carlo computational study on
low-density cold Fermi gas at the unitary limit. The overall behavior of this
ratio obtained with various scattering lengths is presented and discussed.
Ring-diagram results obtained with and those with -matrix
interactions are compared.Comment: 9 pages, 7 figure
Does a loaded warm-up influence jump asymmetry and badminton-specific change of direction performance?
Purpose: Previously, it has been shown that loaded warm-up (LWU) can improve change of direction speed (CODS) in professional badminton players. However, the effect of asymmetry on CODS in badminton players and the influence of LWU on asymmetry has not been examined.
Methods: Twenty-one amateur badminton players (age: 29.5 ± 8.4; playing experience: 8.4 ± 4.2 years) completed two trials. In the first, they performed a control warm-up (CWU). In the second, they performed the same warm-up but with three exercises loaded with a weight vest (LWU). Following both warm-ups, players completed single leg jump (SLCMJ) and badminton-specific CODS tests.
Results: No significant differences between CWU and LWU were observed for CODS, SLCMJ or SLCMJ asymmetry. However, small effect sizes suggested faster CODS (mean difference: -5%; d = -0.32) and lower asymmetries (mean difference: -3%; d = -0.39) following LWU. Five players (24%) experienced CODS improvements greater than the minimum detectable change whilst two (10%) responded negatively. Asymmetry was not correlated with CODS following CWU (ρ = 0.079; p = 0.733) but was negatively associated with CODS after LWU (ρ = -0.491; p = 0.035).
Conclusion: LWU may prove a strategy to trial on an individual basis but generic recommendations should not be applied
Cauchy boundaries in linearized gravitational theory
We investigate the numerical stability of Cauchy evolution of linearized
gravitational theory in a 3-dimensional bounded domain. Criteria of robust
stability are proposed, developed into a testbed and used to study various
evolution-boundary algorithms. We construct a standard explicit finite
difference code which solves the unconstrained linearized Einstein equations in
the 3+1 formulation and measure its stability properties under Dirichlet,
Neumann and Sommerfeld boundary conditions. We demonstrate the robust stability
of a specific evolution-boundary algorithm under random constraint violating
initial data and random boundary data.Comment: 23 pages including 3 figures and 2 tables, revte
Linearized solutions of the Einstein equations within a Bondi-Sachs framework, and implications for boundary conditions in numerical simulations
We linearize the Einstein equations when the metric is Bondi-Sachs, when the
background is Schwarzschild or Minkowski, and when there is a matter source in
the form of a thin shell whose density varies with time and angular position.
By performing an eigenfunction decomposition, we reduce the problem to a system
of linear ordinary differential equations which we are able to solve. The
solutions are relevant to the characteristic formulation of numerical
relativity: (a) as exact solutions against which computations of gravitational
radiation can be compared; and (b) in formulating boundary conditions on the
Schwarzschild horizon.Comment: Revised following referee comment
Horizon Pretracking
We introduce horizon pretracking as a method for analysing numerically
generated spacetimes of merging black holes. Pretracking consists of following
certain modified constant expansion surfaces during a simulation before a
common apparent horizon has formed. The tracked surfaces exist at all times,
and are defined so as to include the common apparent horizon if it exists. The
method provides a way for finding this common apparent horizon in an efficient
and reliable manner at the earliest possible time. We can distinguish inner and
outer horizons by examining the distortion of the surface. Properties of the
pretracking surface such as its expansion, location, shape, area, and angular
momentum can also be used to predict when a common apparent horizon will
appear, and its characteristics. The latter could also be used to feed back
into the simulation by adapting e.g. boundary or gauge conditions even before
the common apparent horizon has formed.Comment: 14 pages, 8 figures, minor change
High-Order Coupled Cluster Method (CCM) Calculations for Quantum Magnets with Valence-Bond Ground States
In this article, we prove that exact representations of dimer and plaquette
valence-bond ket ground states for quantum Heisenberg antiferromagnets may be
formed via the usual coupled cluster method (CCM) from independent-spin product
(e.g. N\'eel) model states. We show that we are able to provide good results
for both the ground-state energy and the sublattice magnetization for dimer and
plaquette valence-bond phases within the CCM. As a first example, we
investigate the spin-half -- model for the linear chain, and we show
that we are able to reproduce exactly the dimerized ground (ket) state at
. The dimerized phase is stable over a range of values for
around 0.5. We present evidence of symmetry breaking by considering
the ket- and bra-state correlation coefficients as a function of . We
then consider the Shastry-Sutherland model and demonstrate that the CCM can
span the correct ground states in both the N\'eel and the dimerized phases.
Finally, we consider a spin-half system with nearest-neighbor bonds for an
underlying lattice corresponding to the magnetic material CaVO (CAVO).
We show that we are able to provide excellent results for the ground-state
energy in each of the plaquette-ordered, N\'eel-ordered, and dimerized regimes
of this model. The exact plaquette and dimer ground states are reproduced by
the CCM ket state in their relevant limits.Comment: 34 pages, 13 figures, 2 table
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