7,578 research outputs found
Strain-rate development between a co-rotating Lamb-Oseen vortex pair of unequal strength.
To date, several investigations have considered the prospect of enhanced dissipation of a vortex pair due to elliptic (short wave) instabilities. Recent studies indicate that these modes have the potential to significantly reduce the time taken to dissipate vortex pairs. This has generated interest in the aviation industry, where aircraft trailing wakes pose a significant hazard for nearby aircraft. Of note, recent studies have indicated that the growth rate of these short-wave instability modes depends strongly on the strain-rate developed within the core of each vortex. This strainrate has been shown to develop naturally simply due to the presence of both vortices. Studies to date have concentrated on vortex pairs where each vortex has the same magnitude of circulation. We extend this by varying the circulation ratio of the two vortices; the circulation of one vortex is varied while the circulation of the other remains constant. The effect on the strain-rate which develops within each core is considered. Of particular interest are the time-scales involved in both the strain-rate development and in the twodimensional merging process, as sufficient time is required for short-wavelength instabilities to occur prior to merging for the process to successfully reduce dissipation time. A spectral-element method is used to conduct the DNS investigation at a circulation Reynolds number of ReÎ = 20,000
Thermodynamics of Cu47Ti34Zr11Ni8, Zr52.5Cu17.9Ni14.6Al10Ti5 and Zr57Cu15.4Ni12.6Al10Nb5 bulk metallic glass forming alloys
The differences in the thermodynamic functions between the liquid and the crystalline states of three bulk metallic glass forming alloys, Cu47Ti34Zr11Ni8, Zr52.5Cu17.9Ni14.6Al10Ti5, and Zr57Cu15.4Ni12.6Al10Nb5, were calculated. The heat capacity was measured in the crystalline solid, the amorphous solid, the supercooled liquid, and the equilibrium liquid. Using these heat capacity data and the heats of fusion of the alloys, the differences in the thermodynamic functions between the liquid and the crystalline states were determined. The Gibbs free energy difference between the liquid and the crystalline states gives a qualitative measure of the glass forming ability of these alloys. Using the derived entropy difference, the Kauzmann temperatures for these alloys were determined
On the complementarity of the quadrature observables
In this paper we investigate the coupling properties of pairs of quadrature
observables, showing that, apart from the Weyl relation, they share the same
coupling properties as the position-momentum pair. In particular, they are
complementary. We determine the marginal observables of a covariant phase space
observable with respect to an arbitrary rotated reference frame, and observe
that these marginal observables are unsharp quadrature observables. The related
distributions constitute the Radon tranform of a phase space distribution of
the covariant phase space observable. Since the quadrature distributions are
the Radon transform of the Wigner function of a state, we also exhibit the
relation between the quadrature observables and the tomography observable, and
show how to construct the phase space observable from the quadrature
observables. Finally, we give a method to measure together with a single
measurement scheme any complementary pair of quadrature observables.Comment: Dedicated to Peter Mittelstaedt in honour of his eightieth birthda
Low-density, one-dimensional quantum gases in a split trap
We investigate degenerate quantum gases in one dimension trapped in a
harmonic potential that is split in the centre by a pointlike potential. Since
the single particle eigenfunctions of such a system are known for all strengths
of the central potential, the dynamics for non-interacting fermionic gases and
low-density, strongly interacting bosonic gases can be investigated exactly
using the Fermi-Bose mapping theorem. We calculate the exact many-particle
ground-state wave-functions for both particle species, investigate soliton-like
solutions, and compare the bosonic system to the well-known physics of Bose
gases described by the Gross-Pitaevskii equation. We also address the
experimentally important questions of creation and detection of such states.Comment: 7 pages, 5 figure
Detection of quantum light in the presence of noise
Detection of quantum light in the presence of dark counts and background
radiation noise is considered. The corresponding positive operator-valued
measure is obtained and photocounts statistics of quantum light in the presence
of noise is studied.Comment: 4 pages, 1 figure; misprints correcte
Differences in long-term physical activity trajectories among individuals with chronic widespread pain : A secondary analysis of a randomized controlled trial
Funding Sources: The MUSICIAN trial was funded by Arthritis Research UK, Chesterfield, UK (Grant award number 17292) and the MELODIC study was funded by NHS Grampian Endowment Grant, Project No: 14/40.Peer reviewedPostprin
A new model for the double well potential
A new model for the double well potential is presented in the paper. In the
new potential, the exchanging rate could be easily calculated by the
perturbation method in supersymmetric quantum mechanics. It gives good results
whether the barrier is high or sallow. The new model have many merits and may
be used in the double well problem.Comment: 3pages, 3figure
Measurement uncertainty relations
Measurement uncertainty relations are quantitative bounds on the errors in an
approximate joint measurement of two observables. They can be seen as a
generalization of the error/disturbance tradeoff first discussed heuristically
by Heisenberg. Here we prove such relations for the case of two canonically
conjugate observables like position and momentum, and establish a close
connection with the more familiar preparation uncertainty relations
constraining the sharpness of the distributions of the two observables in the
same state. Both sets of relations are generalized to means of order
rather than the usual quadratic means, and we show that the optimal constants
are the same for preparation and for measurement uncertainty. The constants are
determined numerically and compared with some bounds in the literature. In both
cases the near-saturation of the inequalities entails that the state (resp.
observable) is uniformly close to a minimizing one.Comment: This version 2 contains minor corrections and reformulation
Remote state preparation and teleportation in phase space
Continuous variable remote state preparation and teleportation are analyzed
using Wigner functions in phase space. We suggest a remote squeezed state
preparation scheme between two parties sharing an entangled twin beam, where
homodyne detection on one beam is used as a conditional source of squeezing for
the other beam. The scheme works also with noisy measurements, and provide
squeezing if the homodyne quantum efficiency is larger than 50%. Phase space
approach is shown to provide a convenient framework to describe teleportation
as a generalized conditional measurement, and to evaluate relevant degrading
effects, such the finite amount of entanglement, the losses along the line, and
the nonunit quantum efficiency at the sender location.Comment: 2 figures, revised version to appear in J.Opt.
Trap Loss in a Dual-Species Rb-Ar* Magneto-Optical Trap
We have investigated trap loss in a dual-species magneto-optical trap (MOT) comprised of 85Rb and metastable 40Ar. We measure the trap loss rate coefficients for each species due to the presence of the other as a function of trap light intensity. We clearly identify both Penning ionization of Rb by Ar* and associative ionization to form the molecular ion RbAr+ as two of the trap loss channels. We have also measured the trap loss rate coefficient for the Ar* MOT alone and observe production of Ar+ and Ar2+ ions
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