6,096 research outputs found
Thin-film flow in helically wound rectangular channels with small torsion
Laminar gravity-driven thin-film flow down a helically-wound channel of rectangular cross-section with small torsion in which the fluid depth is small is considered. Neglecting the entrance and exit regions we obtain the steady-state solution that is independent of position along the axis of the channel, so that the flow, which comprises a primary flow in the direction of the axis of the channel and a secondary flow in the cross-sectional plane, depends only on position in the two-dimensional cross-section of the channel. A thin-film approximation yields explicit expressions for the fluid velocity and pressure in terms of the free-surface shape, the latter satisfying a non-linear ordinary differential equation that has a simple exact solution in the special case of a channel of rectangular cross-section. The predictions of the thin-film model are shown to be in good agreement with much more computationally intensive solutions of the small-helix-torsion Navier–Stokes equations. The present work has particular relevance to spiral particle separators used in the mineral-processing industry. The validity of an assumption commonly used in modelling flow in spiral separators, namely that the flow in the outer region of the separator cross-section is described by a free vortex, is shown to depend on the problem parameters
Measuring atomic NOON-states and using them to make precision measurements
A scheme for creating NOON-states of the quasi-momentum of ultra-cold atoms
has recently been proposed [New J. Phys. 8, 180 (2006)]. This was achieved by
trapping the atoms in an optical lattice in a ring configuration and rotating
the potential at a rate equal to half a quantum of angular momentum . In this
paper we present a scheme for confirming that a NOON-state has indeed been
created. This is achieved by spectroscopically mapping out the anti-crossing
between the ground and first excited levels by modulating the rate at which the
potential is rotated. Finally we show how the NOON-state can be used to make
precision measurements of rotation.Comment: 14 preprint pages, 7 figure
Weather modification by carbon dust absorption of solar energy
July, 1974.Includes bibliographical references
Hamiltonian effective field theory study of the resonance in lattice QCD
We examine the phase shifts and inelasticities associated with the
Roper resonance and connect these infinite-volume observables to
the finite-volume spectrum of lattice QCD using Hamiltonian effective field
theory. We explore three hypotheses for the structure of the Roper resonance.
All three hypotheses are able to describe the scattering data well. In the
third hypothesis the Roper resonance couples the low-lying bare basis-state
component associated with the ground state nucleon with the virtual
meson-baryon contributions. Here the non-trivial superpositions of the
meson-baryon scattering states are complemented by bare basis-state components
explaining their observation in contemporary lattice QCD calculations. The
merit of this scenario lies in its ability to not only describe the observed
nucleon energy levels in large-volume lattice QCD simulations but also explain
why other low-lying states have been missed in today's lattice QCD results for
the nucleon spectrum.Comment: 14 pages, 14 figures; version to be published in Phys. Rev.
Hamiltonian effective field theory study of the resonance in lattice QCD
Drawing on experimental data for baryon resonances, Hamiltonian effective
field theory (HEFT) is used to predict the positions of the finite-volume
energy levels to be observed in lattice QCD simulations of the lowest-lying
nucleon excitation. In the initial analysis, the phenomenological
parameters of the Hamiltonian model are constrained by experiment and the
finite-volume eigenstate energies are a prediction of the model. The agreement
between HEFT predictions and lattice QCD results obtained on volumes with
spatial lengths of 2 and 3 fm is excellent. These lattice results also admit a
more conventional analysis where the low-energy coefficients are constrained by
lattice QCD results, enabling a determination of resonance properties from
lattice QCD itself. Finally, the role and importance of various components of
the Hamiltonian model are examined.Comment: 5 pages, 2 figures; version published in Phys. Rev. Let
Order parameters in the Verwey phase transition
The Verwey phase transition in magnetite is analyzed on the basis of the
Landau theory. The free energy functional is expanded in a series of components
belonging to the primary and secondary order parameters. A low-temperature
phase with the monoclinic P2/c symmetry is a result of condensation of two
order parameters X_3 and \Delta_5 . The temperature dependence of the shear
elastic constant C_44 is derived and the mechanism of its softening is
discussed.Comment: 4 pages, 1 figur
Normalized Double-Talk Detection Based on Microphone and AEC Error Cross-correlation
In this paper, we present two different double-talk detection schemes for Acoustic Echo Cancellation (AEC). First, we present a novel normalized detection statistic based on the cross-correlation coefficient between the microphone signal and the cancellation error. The decision statistic is designed in such a way that it meets the needs of an optimal double-talk detector. We also show that the proposed detection statistic converges to the recently proposed normalized cross-correlation based double-talk detector, the best known cross-correlation based detector. Next, we present a new hybrid double-talk detection scheme based on a cross-correlation coefficient and two signal detectors. The hybrid algorithm not only detects double-talk but also detects and tracks any echo-path variations efficiently. We compare our results with other cross-correlation based double-talk detectors to show their effectiveness
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