Excess phase in oscillators or phase locked loops is a very important design specification typically modelled as a continuous time signal. In this paper we explain why, when the quantity of interest is jitter, excess phase should be treated as a discrete quantity. This treatment helps explaining noise folding in frequency dividers and analyse its consequences in Phase Locked Loops.
This paper describes the design and operation of a high output impedance tissue current driver circuit, for use in medical electronics, such as Electrical Impedance Tomography (EIT). This novel architecture was designed for implementation in bipolar technology, to meet the specifications for EIT, namely operating frequency range 10 kHz–1 MHz with a target output resistance of 16 MW. Simulation results are presented, showing that the current source more than met the minimum specification for EIT.
In this article, we present a reconstruction method for the inverse conductivity problem suitable for smooth conductivity distributions. The inverse problem is reformulated in terms of a pair of coupled integral equations, one of which is of the first kind which we regularize using mollifier methods. An interesting feature of this method is that the kernel of this integral equation is not given, but can be modified for the choice of mollifier. We are able to obtain conductivity reconstructions rapidly and without relying on accurate a priori information.
Oxford Brookes has been collaborating with the University of Mainz in Germany to develop an alternative breast cancer detection technique.
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 l1-regularization term. The functional is minimized with an iterative soft shrinkage-type algorithm.
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.
The forward problem for complex electrical impedance tomography (EIT) is solved by means of a meshless method, namely the method of fundamental solutions (MFS). The MFS for the complex EIT direct problem is numerically implemented, and its efficiency and accuracy as well as the numerical convergence of the MFS solution are analysed when assuming the presence in the medium (i.e. background) of one or two inclusions with the physical properties different from those corresponding to the background. Four numerical examples with inclusion(s) of various convex and non-convex smooth shapes (e.g. circular, elliptic, peanut-shaped and acorn-shaped) and sizes are presented and thoroughly investigated.
In this paper the authors analyze the conventional current-feedback operational amplifier (CFOA) in terms of common-mode-rejection ratio (CMRR) performance, and having identified the mechanism primarily responsible for the CMRR, they propose two new architecture CFOAs. These new CFOAs are further developed, and modified to provide improved bandwidth, AC gain accuracy and high CMRR performance. The key features of the two proposed new CFOAs are the designs of the internal voltage followers which have two separate biasing currents with a similar dynamic architecture to that of the conventional CFOA. The magnitude of one bias current determines the value of the maximum CMRR, and the second can be used to maximize bandwidth.
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.
We describe a method by which the reactions in a metabolic system may be grouped hierarchically into sets of modules to form a metabolic reaction tree. In contrast to previous approaches, the method described here takes into account the fact that, in a viable network, reactions must be capable of sustaining a steady-state flux. In order to achieve this decomposition we introduce a new concept—the reaction correlation coefficient, φ, and show that this is a logical extension of the concept of enzyme (or reaction) subsets. In addition to their application to modular decomposition, reaction correlation coefficients have a number of other interesting properties, including a convenient means for identifying disconnected subnetworks in a system and potential applications to metabolic engineering. The method computes reaction correlation coefficients from an orthonormal basis of the null-space of the stoichiometry matrix. We show that reaction correlation coefficients are uniquely defined, even though the basis of t…