38,928 research outputs found
A polyphonic acoustic vortex and its complementary chords
Using an annular phased array of eight loudspeakers, we generate sound beams that simultaneously contain phase singularities at a number of different frequencies. These frequencies correspond to different musical notes and the singularities can be set to overlap along the beam axis, creating a polyphonic acoustic vortex. Perturbing the drive amplitudes of the speakers means that the singularities no longer overlap, each note being nulled at a slightly different lateral position, where the volume of the other notes is now nonzero. The remaining notes form a tri-note chord. We contrast this acoustic phenomenon to the optical case where the perturbation of a white light vortex leads to a spectral spatial distribution
Geometric phases and anholonomy for a class of chaotic classical systems
Berry's phase may be viewed as arising from the parallel transport of a
quantal state around a loop in parameter space. In this Letter, the classical
limit of this transport is obtained for a particular class of chaotic systems.
It is shown that this ``classical parallel transport'' is anholonomic ---
transport around a closed curve in parameter space does not bring a point in
phase space back to itself --- and is intimately related to the Robbins-Berry
classical two-form.Comment: Revtex, 11 pages, no figures
Runway grooving project at Chicago Midway Airport
Runway grooving project at Chicago Midway Airpor
Statistical Properties of Many Particle Eigenfunctions
Wavefunction correlations and density matrices for few or many particles are
derived from the properties of semiclassical energy Green functions. Universal
features of fixed energy (microcanonical) random wavefunction correlation
functions appear which reflect the emergence of the canonical ensemble as the
number of particles approaches infinity. This arises through a little known
asymptotic limit of Bessel functions. Constraints due to symmetries,
boundaries, and collisions between particles can be included.Comment: 13 pages, 4 figure
Phase Space Evolution and Discontinuous Schr\"odinger Waves
The problem of Schr\"odinger propagation of a discontinuous wavefunction
-diffraction in time- is studied under a new light. It is shown that the
evolution map in phase space induces a set of affine transformations on
discontinuous wavepackets, generating expansions similar to those of wavelet
analysis. Such transformations are identified as the cause for the
infinitesimal details in diffraction patterns. A simple case of an evolution
map, such as SL(2) in a two-dimensional phase space, is shown to produce an
infinite set of space-time trajectories of constant probability. The
trajectories emerge from a breaking point of the initial wave.Comment: Presented at the conference QTS7, Prague 2011. 12 pages, 7 figure
Berry phase in a non-isolated system
We investigate the effect of the environment on a Berry phase measurement
involving a spin-half. We model the spin+environment using a biased spin-boson
Hamiltonian with a time-dependent magnetic field. We find that, contrary to
naive expectations, the Berry phase acquired by the spin can be observed, but
only on timescales which are neither too short nor very long. However this
Berry phase is not the same as for the isolated spin-half. It does not have a
simple geometric interpretation in terms of the adiabatic evolution of either
bare spin-states or the dressed spin-resonances that remain once we have traced
out the environment. This result is crucial for proposed Berry phase
measurements in superconducting nanocircuits as dissipation there is known to
be significant.Comment: 4 pages (revTeX4) 2 fig. This version has MAJOR changes to equation
Decimation and Harmonic Inversion of Periodic Orbit Signals
We present and compare three generically applicable signal processing methods
for periodic orbit quantization via harmonic inversion of semiclassical
recurrence functions. In a first step of each method, a band-limited decimated
periodic orbit signal is obtained by analytical frequency windowing of the
periodic orbit sum. In a second step, the frequencies and amplitudes of the
decimated signal are determined by either Decimated Linear Predictor, Decimated
Pade Approximant, or Decimated Signal Diagonalization. These techniques, which
would have been numerically unstable without the windowing, provide numerically
more accurate semiclassical spectra than does the filter-diagonalization
method.Comment: 22 pages, 3 figures, submitted to J. Phys.
Nonclassical Degrees of Freedom in the Riemann Hamiltonian
The Hilbert-Polya conjecture states that the imaginary parts of the zeros of
the Riemann zeta function are eigenvalues of a quantum hamiltonian. If so,
conjectures by Katz and Sarnak put this hamiltonian in Altland and Zirnbauer's
universality class C. This implies that the system must have a nonclassical
two-valued degree of freedom. In such a system, the dominant primitive periodic
orbits contribute to the density of states with a phase factor of -1. This
resolves a previously mysterious sign problem with the oscillatory
contributions to the density of the Riemann zeros.Comment: 4 pages, no figures; v3-6 have minor corrections to v2, v2 has a more
complete solution of the sign problem than v
Quantum Spectra of Triangular Billiards on the Sphere
We study the quantal energy spectrum of triangular billiards on a spherical
surface. Group theory yields analytical results for tiling billiards while the
generic case is treated numerically. We find that the statistical properties of
the spectra do not follow the standard random matrix results and their peculiar
behaviour can be related to the corresponding classical phase space structure.Comment: 18 pages, 5 eps figure
Emotional and behavioral reaction to intrusive thoughts.
A self-report measure of the emotional and behavioral reactions to intrusive thoughts was developed. The article presents data that confirm the stability, reliability, and validity of the new seven-item measure. Emotional and behavioral reactions to intrusions emerged as separate factors on the Emotional and Behavioral Reactions to Intrusions Questionnaire (EBRIQ), a finding confirmed by an independent stress study. Test-retest reliability over 30 to 70 days was good. Expected relationships with other constructs were significant. Stronger negative responses to intrusions were associated with lower mindfulness scores and higher ratings of experiential avoidance, thought suppression, and intensity and frequency of craving. The EBRIQ will help explore differences in reactions to intrusive thoughts in clinical and nonclinical populations, and across different emotional and behavioral states. It will also be useful in assessing the effects of therapeutic approaches such as mindfulness
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