The problem of creating a multiuser hands-free immersive telecommunications environment poses many challenges for acoustic signal processing. The most pressing is the creation of a fast multi-channel acoustic echo canceller (MCAEC) to eliminate acoustic feedback created in the speaker-microphone loop. Traditional multi-channel adaptive algorithms for echo cancellation are not fast enough to wor...

We analyze theoretically the subspace best approximating images of a convex Lambertian object taken from the same viewpoint, but under different distant illumination conditions. Since the lighting is an arbitrary function, the space of all possible images is formally infinite-dimensional. However, previous empirical work has shown that images of largely diffuse objects actually lie very close t...

This paper presents a warm bore ferromagnetic shimming design for a high resolution NMR magnet based on spherical harmonic coefficient reduction techniques. The passive ferromagnetic shimming along with the active shimming is a critically important step to improve magnetic field homogeneity for an NMR Magnet. Here, the technique is applied to an NMR magnet already designed and built at the MIT'...

In this paper we describe algorithms for the numerical computation of Fourier transforms of tensor elds on the two-sphere, S. These algorithms reduce the computation of an expansion on tensor spherical harmonics to expansions in scalar spherical harmonics, and hence can take advantage of recent improvements in the eÆciency of computation of scalar spherical harmonic transforms.

Starting from a kinetic model for electrons in a weakly ionized plasma, a spherical harmonic expansion (SHE-) model is derived by a formal asymptotic analysis for strongly disparate masses of electrons and ions. The macroscopic limit of the SHE-model for high elds gives a high eld extension of standard macroscopic models for ionization.

Starting from a kinetic model for electrons in a weakly ionized plasma, a spherical harmonic expansion (SHE-) model is derived by a formal asymptotic analysis for strongly disparate masses of electrons and ions. The macroscopic limit of the SHE-model for high elds gives a high eld extension of standard macroscopic models for ionization.

Estimates for the decay of Fourier transforms of measures have extensive applications in numerous problems in harmonic analysis and convexity including the distribution of lattice points in convex domains, irregularities of distribution, generalized Radon transforms and others. Here we prove that the spherical L-average decay rate of the Fourier transform of the Lebesgue measure on an arbitrary...

Aspects of continuous and discrete harmonic analysis on the circle are generalized to star graphs, and through spherical coordinates to the two sphere. The resulting function theory is used to analyze trapezoidal rule integration on the two sphere. 2000 Mathematics Subject Classification 65D30, 65T99, 34B45

We prove almost sharp upper bounds for the Lp norms of eigenfunctions of the full ring of invariant differential operators on a compact locally symmetric space, as well as their restrictions to maximal flat subspaces. Our proof combines techniques from semiclassical analysis with harmonic theory on reductive groups, and makes use of new asymptotic bounds for spherical functions that are of inde...

We present a method for densely computing local spherical histograms of oriented gradients (SHOG) in volumetric images. The descriptors are based on the continuous representation of the orientation histograms in the harmonic domain, which we compute very efficiently via spherical tensor products and the fast Fourier transformation. Building upon these local spherical histogram representations, ...