C. Sebu

Sparse 3D reconstructions in electrical Impedance Tomography using real data

Abstract We present a 3D reconstruction algorithm with sparsity constraints for electrical impedance tomography (EIT). EIT is the inverse problem of determining the distribution of conductivity in the interior of an object from simultaneous measurements of currents and voltages on its boundary. The feasibility of the sparsity reconstruction approach is tested with real data obtained from a new planar EIT device developed at the Institut für Physik, Johannes Gutenberg Universität, Mainz, Germany. The complete electrode model is adapted for the given device to handle incomplete measurements and the inhomogeneities of the conductivity are a priori assumed to be sparse with respect to a certain basis. This prior information is incorporated into a Tikhonov-type functional by including a sparsity-promoting -regularization term. The functional is minimized with an iterative soft shrinkage-type algorithm.

QCD condensates from τ-decay data: a functional approach

Abstract We study a functional method to extract the V − A condensate of dimension 6 from a comparison of τ -decay data with the asymptotic space-like QCD prediction. Our result is in agreement within errors with that from conventional analyses based on finite energy sum rules.

Critical review of the circuit architecture of CFOA

This study investigates the closed-loop performance of the basic current feedback operational amplifier (CFOA), with particular emphasis on its dynamic response. It also focuses on the design, performance and advantages of the CFOA in its ability to provide a substantially constant closed-loop bandwidth for closed-loop voltage gain. Furthermore, an improved CFOA with wide bandwidth and common-mode-rejection ratio (CMRR) performance is also presented. The design presented in this article uses a bootstrapping technique with Quasi-Darlington in the input stage to reduce the influence of the Early effect which results in improved performance. Another advantage of this design is that the inverting input impedance is reduced significantly, which leads to further improvement in bandwidth and CMRR.

An integral equation method for the inverse conductivity problem

We present an image reconstruction algorithm for the inverse conductivity problem based on reformulating the problem in terms of integral equations. We use as data the values of injected electric currents and of the corresponding induced boundary potentials, as well as the boundary values of the electrical conductivity. We have used a priori information to find a regularized conductivity distribution by first solving a Fredholm integral equation of the second kind for the Laplacian of the potential, and then by solving a first order partial differential equation for the regularized conductivity itself. Many of the calculations involved in the method can be achieved analytically using the eigenfunctions of an integral operator defined in the Letter.

On the resolving power of electrical impedance tomography

The resolving power of data is an essential question in most inverse problems and in many cases it can be estimated by very simple, often well-known, methods. In this paper the resolving power of measurements on the boundary of a domain is estimated for electrical impedance tomography. The data used are the values of a single pair of injected electric current and the corresponding induced boundary potential, together with the boundary values of the electrical conductivity. We apply a linear analysis to an integral equation method recently introduced in the study of this inverse conductivity problem.

Conductivity imaging with interior potential measurements

In this article, we present two reconstruction methods intended to be used for conductivity imaging with data obtained from a planar electrical impedance tomography device for breast cancer detection. The inverse problem to solve is different from the classical inverse conductivity problem. We reconstruct the electrical conductivity of a two-dimensional domain from boundary measurements of currents and interior measurements of the potential. One reconstruction algorithm is based on a discrete resistor model; the other one is an integral equation approach for smooth conductivity distributions.

Conductivity reconstructions using real data from a new planar electrical impedance tomography device

Abstract In this paper, we present results of reconstructions using real data from a new planar electrical impedance tomography device developed at the Institut für Physik, Johannes Gutenberg Universität, Mainz, Germany. The prototype consists of a planar sensing head of circular geometry, and it was designed mainly for breast cancer detection. There are 12 large outer electrodes arranged on a ring of radius cm where the external currents are injected, and a set of 54 point-like high-impedance inner electrodes where the induced voltages are measured. Two direct (i.e. non-iterative) reconstruction algorithms are considered: one is based on a discrete resistor model, and the other one is an integral equation approach for smooth conductivity distributions.

A mollifier method for the inverse conductivity problem

In this paper we present an integral equation formulation of the inverse conductivity problem that is regularised using mollifier methods.

Stable Lagrange points of large planets as possible regions where WIMPs could be sought

In this paper we show that the physical properties of the Lagrange points of large planets could provide an effective mechanism for trapping dark matter, if dark matter really exists in our solar system. Certainly, the familiar trapping mechanism of a potential well combined with some dissipative processes is not a good candidate for particles like WIMPs which are supposed to be very slippery. However, in each of the Lagrange regions, L4 and L5, of large planets the potential has a maximum which together with the Coriolis force provides an effective trapping mechanism without the need of any kind of friction. This is a purely inertial and gravitational mechanism with no assumptions on other possible interactions. Hence if the density of dark matter is not negligible in this part of the universe, a direct experiment to be considered is the establishment of a satellite in orbit around one of the stable Lagrange points, L4 or L5, of Jupiter.

A three-dimensional image reconstruction algorithm for electrical impedance tomography using planar electrode arrays

We present a three-dimensional non-iterative reconstruction algorithm developed for conductivity imaging with real data collected on a planar rectangular array of electrodes. Such an electrode configuration as well as the proposed imaging technique is intended to be used for breast cancer detection. The algorithm is based on linearizing the conductivity about a constant value and allows real-time reconstructions. The performance of the algorithm was tested on numerically simulated data and we successfully detected small inclusions with conductivities three or four times the background lying beneath the data collection surface. The results were fairly stable with respect to the noise level in the data and displayed very good spatial resolution in the plane of electrodes.