When an inverse problem can be formulated so the data are minima of one of the variational problems of mathematical physics, feasibility constraints can be found for the nonlinear inversion problem. These constraints guarantee that optimal solutions of the inverse problem lie in the convex feasible region of the model space. Furthermore, points on the boundary of this convex region can be found...

The theory of twistors, developed by Penrose’,2,3) gives an alternative geometry of Minkowski space. It is therefore remarkable that the symmetry group of compactified Minkowski space, the conformal group C, is different from the symmetry group of twistor space, which is SU(2,2). The relation between these two groups is that SU(2,2) is 4: 1 homomorphic to C,, the identity-connected component of...

We apply a regularization method for the optical inversion of SAGE II aerosol extinction profiles and derive the particle number density N , the mode radius ρ and width σ of an effective lognormal aerosol size distribution. The constraint applied to the inversion scheme allows us to appreciably enhance the stability of the solution. Therefore, because of the disposal of a more stable inversion ...

Speech inversion is a well-known ill-posed problem and addition of speaker differences typically makes it even harder. This paper investigates a vocal tract length normalization (VTLN) technique to transform the acoustic space of different speakers to a target speaker space such that speaker specific details are minimized. The speaker normalized features are then used to train a feed-forward ne...

This study examined the effects of frontal lobe lesions on the control of movements during motor learning. We compared the performance of patients with unilateral frontal or temporal excisions and controls in two-dimensional aiming movements during adaptation to a transformed visuomotor mapping. Subjects tried to reach a fixed target on a graphics tablet using indirect visual control from a mon...

The goal of this work is to recover articulatory information from the speech signal by acoustic-to-articulatory inversion. One of the main difficulties with inversion is that the problem is underdetermined and inversion methods generally offer no guarantee on the phonetical realism of the inverse solutions. A way to adress this issue is to use additional phonetic constraints. Knowledge of the p...

The goal of this work is to recover articulatory information from the speech signal by acoustic-to-articulatory inversion. One of the main difficulties with inversion is that the problem is underdetermined and inversion methods generally offer no guarantee on the phonetical realism of the inverse solutions. A way to adress this issue is to use additional phonetic constraints. Knowledge of the p...

We present a multigrid algorithm for the solution of distributed parameter inverse problems constrained by variable-coefficient linear parabolic partial differential equations. We consider problems in which the inversion variable is a function of space only; for stability we use an L2 Tikhonov regularization. The main feature of our algorithm is that its convergence rate is mesh-independent—eve...

Seismic inversion is a method that extracts acoustic impedance data from the seismic traces. Source wavelets are band-limited, and thus seismic traces do not contain low and high frequency information. Therefore, there is a serious problem when the deterministic seismic inversion is applied to real data and the result of deterministic inversion is smooth. Low frequency component is obtained fro...

The aim of seismic inversion is mapping all of the subsurface structures from seismic data. Due to the band-limited nature of the seismic data, it is difficult to find a unique solution for seismic inversion. Deterministic methods of seismic inversion are based on try and error techniques and provide a smooth map of elastic properties, while stochastic methods produce high-resolution maps of el...