Alexandros Soumelidis

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PURPOSE To detect tear film regularity changes in the 15 seconds after a blink, by using a new high-speed videotopographic method. METHODS The new system, based on a standard corneal topograph, allows registration of four photokeratoscopic images per second. Altogether, 15 eyes of 15 healthy volunteers and 7 eyes of 7 patients with dry eye were examined(More)
This paper proposes a new approach to identification of the poles in a linear system from frequency domain data. The discrete rational transfer function is represented in a rational Laguerre–basis, where the basis elements can be expressed by powers of the Blaschke–function. This function can be interpreted as a congruence transform on the Poincaré unit(More)
The design and the initial realization of control on an experimental in-door unmanned autonomous quadrotor helicopter is presented. This is a hierarchical embedded model-based control scheme that is built upon the concept of back-stepping, and is applied on an electric motor-driven quadrotor UAV hardware that is equipped with an embedded on-board computer,(More)
The paper constructs a method for identification of models given in partial fraction representation by using a specific discrete bi-orthogonal system of functions specified by the poles and their multiplicities. Using frequency domain data, an iteration algorithm convergent in second order is given that incorporates procedures for finding not only the pole(More)
The optical behaviour of the (human) cornea is often characterized with the Zernike-coefficients derived via the Zernike-transform of its optical power map. In this paper, a radial transform based on the Chebyshev-polynomials of the second kind is suggested for a surface-based, rather than an optical power map based representation of the cornea. This(More)
The even Chebyshev-polynomials of the second kind – modified with appropriate argument-transforms – were used to describe quasi-hemispherical and calotte-like natural surfaces over a set of discrete points – and via interpolation – between these points. The point-set used was selected in a manner that promotes the proper approximation of such surfaces and(More)
In a recent paper the authors proposed a new frequency-domain approach to identify poles in discrete-time linear systems. The discrete rational transfer function is represented in a rational Laguerre-basis, where the basis elements are expressed by powers of the Blaschke-function. This function can be interpreted as a congruence transform on the(More)
Our topography system is an enhancement of a standard TMS-1 corneal topograph instrument (Computed Anatomy Inc., New York, NY, USA). Topographic images are captured at a rate of 4 s(-1), allowing the recording of a series of 120 images in 30 s after a complete blink. In this prospective preliminary study 15 healthy volunteers were examined. The main outcome(More)
In a series of paper the authors proposed a new frequency-domain approach to identify poles in discrete-time linear systems. The discrete rational transfer function is represented in a rational Laguerre-basis, where the basis elements are expressed by powers of the Blaschke-function. This function can be interpreted as a congruence transform on the(More)