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Developing and evaluating a hybrid wind instrument
A hybrid wind instrument generates self-sustained sounds via a real-time interaction between a computed excitation model (such as the physical model of human lips interacting with a mouthpiece) and a real acoustic resonator. Attempts to produce a hybrid instrument have so far fallen short, in terms of both the accuracy and the variation in the sound produced. The principal reason for the failings of previous hybrid instruments is the actuator which, controlled by the excitation model, introduces a fluctuating component into the air flow injected into the resonator. In the present paper, the possibility of using a loudspeaker to supply the calculated excitation signal is evaluated. A theoretical study has facilitated the modeling of the loudspeaker-resonator system and the design of a feedback and feedforward filter to successfully compensate for the presence of the loudspeaker. The resulting self-sustained sounds are evaluated by a mapping of their sound descriptors to the input parameters of the physical model of the embouchure, both for sustained and attack sounds. Results are compared with simulations. The largely coherent functioning confirms the usefulness of the device in both musical and research contexts
Decoherence of Friedmann-Robertson-Walker Geometries in the Presence of Massive Vector Fields with U(1) or SO(3) Global Symmetries
Retrieval of classical behaviour in quantum cosmology is usually discussed in
the framework of {\em midi}superspace models in the presence of scalar fields
and the inhomogeneous modes corresponding either to gravitational or scalar
fields. In this work, we propose an alternative model to study the decoherence
of homogeneous and isotropic geometries where the scalar field is replaced by a
massive vector field with a global internal symmetry. We study here the cases
with and global internal symmetries. The presence of a mass term
breaks the conformal invariance and allows for the longitudinal modes of the
spin-1 field to be present in the Wheeler-DeWitt equation. In the case of the
U(1) global internal symmetry, we have only one single ``classical'' degree of
freedom while in the case of the SO(3) global symmetry, we are led to consider
a simple two-dimensional minisuperspace model. These minisuperspaces are shown
to be equivalent to a set of coupled harmonic oscillators where the kinetic
term of the longitudinal modes has a coefficient proportional to the inverse of
the scale factor. The conditions for a suitable decoherence process and
correlations between coordinate and momenta are established. The validity of
the semi-classical Einstein equations when massive vector fields (Abelian and
non-Abelian) are present is also discussed.Comment: 26 pages, CERN-TH.7241/94 DAMTP R-94/2
Light with a self-torque: extreme-ultraviolet beams with time-varying orbital angular momentum
Twisted light fields carrying orbital angular momentum (OAM) provide powerful
capabilities for applications in optical communications, microscopy, quantum
optics and microparticle rotation. Here we introduce and experimentally
validate a new class of light beams, whose unique property is associated with a
temporal OAM variation along a pulse: the self-torque of light. Self-torque is
a phenomenon that can arise from matter-field interactions in electrodynamics
and general relativity, but to date, there has been no optical analog. In
particular, the self-torque of light is an inherent property, which is
distinguished from the mechanical torque exerted by OAM beams when interacting
with physical systems. We demonstrate that self-torqued beams in the
extreme-ultraviolet (EUV) naturally arise as a necessary consequence of angular
momentum conservation in non-perturbative high-order harmonic generation when
driven by time-delayed pulses with different OAM. In addition, the
time-dependent OAM naturally induces an azimuthal frequency chirp, which
provides a signature for monitoring the self-torque of high-harmonic EUV beams.
Such self-torqued EUV beams can serve as unique tools for imaging magnetic and
topological excitations, for launching selective excitation of quantum matter,
and for manipulating molecules and nanostructures on unprecedented time and
length scales.Comment: 24 pages, 4 figure
Associative memory storing an extensive number of patterns based on a network of oscillators with distributed natural frequencies in the presence of external white noise
We study associative memory based on temporal coding in which successful
retrieval is realized as an entrainment in a network of simple phase
oscillators with distributed natural frequencies under the influence of white
noise. The memory patterns are assumed to be given by uniformly distributed
random numbers on so that the patterns encode the phase differences
of the oscillators. To derive the macroscopic order parameter equations for the
network with an extensive number of stored patterns, we introduce the effective
transfer function by assuming the fixed-point equation of the form of the TAP
equation, which describes the time-averaged output as a function of the
effective time-averaged local field. Properties of the networks associated with
synchronization phenomena for a discrete symmetric natural frequency
distribution with three frequency components are studied based on the order
parameter equations, and are shown to be in good agreement with the results of
numerical simulations. Two types of retrieval states are found to occur with
respect to the degree of synchronization, when the size of the width of the
natural frequency distribution is changed.Comment: published in Phys. Rev.
Localized Manifold Harmonics for Spectral Shape Analysis
The use of Laplacian eigenfunctions is ubiquitous in a wide range of computer graphics and geometry processing applications. In particular, Laplacian eigenbases allow generalizing the classical Fourier analysis to manifolds. A key drawback of such bases is their inherently global nature, as the Laplacian eigenfunctions carry geometric and topological structure of the entire manifold. In this paper, we introduce a new framework for local spectral shape analysis. We show how to efficiently construct localized orthogonal bases by solving an optimization problem that in turn can be posed as the eigendecomposition of a new operator obtained by a modification of the standard Laplacian. We study the theoretical and computational aspects of the proposed framework and showcase our new construction on the classical problems of shape approximation and correspondence. We obtain significant improvement compared to classical Laplacian eigenbases as well as other alternatives for constructing localized bases
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