Dilaton Brane Cosmology with Second Order String Corrections and the Cosmological Constant

We consider, in five dimensions, the effective action from heterotic string which includes quantum gravity corrections up to (a')^2. The expansion, in the string frame, is in terms of |a'R|, where R is the scalar curvature and uses the third order Euler density, next to the Gauss-Bonnet term. For a positive tension brane and infinite extra dimension, the logarithmic class of solutions is less dependent from fine-tuning problems than in previous formulations. More importantly, the model suggests that in the full non-perturbative formulation, the string scale can be much lower than the effective Planck mass, without the string coupling to be vanishingly small. Also a less severe fine-tuning of the brane tension in needed.Comment: 19 pages, 5 figures LaTeX. Accepted for publication in IJMP

Optimal two-stage filtering of elastograms

In ultrasound elastography, tissue axial strains are obtained through the differentiation of measured axial displacements. However, during the measurement process, the displacement signals are often contaminated with de-correlation noise caused by changes in the speckle pattern in the tissue. Thus, the application of the gradient operator on the displacement signals results in the presence of amplified noise in the axial strains, which severely obscures the useful information. The use of an effective denoising scheme is therefore imperative. In this paper, a method based on a two-stage consecutive filtering approach is proposed for the accurate estimation of axial strains. The presented method considers a cascaded system of a frequency filter and a time window, which are both designed such that the overall system operates optimally as a minimum variance estimator. Experimentation on simulated signals shows that the two-stage scheme employed in this study has good potential as a denoising method for ultrasound elastograms

Alfven modes driven non-linearly by metric perturbations in anisotropic magnetized cosmologies

We consider anisotropic magnetized cosmologies filled with conductive plasma fluid and study the implications of metric perturbations that propagate parallel to the ambient magnetic field. It is known that in the first order (linear) approximation with respect to the amplitude of the perturbations no electric field and density perturbations arise. However, when we consider the non-linear coupling of the metric perturbations with their temporal derivatives, certain classes of solutions can induce steeply increasing in time electric field perturbations. This is verified both numerically and analytically. The source of these perturbations can be either high-frequency quantum vacuum fluctuations, driven by the cosmological pump field, in the early stages of the evolution of the Universe or astrophysical processes or a non-linear isotropization process of an initially anisotropic cosmological spacetime.Comment: 7 pages, RevTex, 3 figures ps, accepted for publication to IJMP

Investigation of Themes about the Design and the Operation of a Freight Rail Station inside port

145 σ.Σκοπός της παρούσας διπλωματικής εργασίας είναι η διερεύνηση θεμάτων που σχετίζονται με την χωροθέτηση των εμπορευματικών σιδηροδρομικών εγκαταστάσεων εντός των λιμένων, καθώς επίσης και με την οργάνωση, την λειτουργία και την εκμετάλλευση των συναρτώμενων σιδηροδρομικών μεταφορών. Συλλέχτηκαν στοιχεία από Ευρωπαϊκούς λιμένες και έγινε κατηγοριοποίηση των υφιστάμενων σιδ. εγκαταστάσεων σε 5 κατηγορίες: α) φορτοεκφόρτωση κάτω από τα σκέλη της γερανογέφυρας κρηπιδώματος β) σιδ. εγκατάσταση εντός του χώρου στοιβασίας γ) σιδ. εγκατάσταση στα όρια του λιμένα, δ) ανεξάρτητη σιδ. εγκατάσταση σε μικρή απόσταση και ε) ανεξάρτητη απομακρυσμένη σιδ. εγκατάσταση. Δημιουργήθηκε μια εφαρμογή σε περιβάλλον Google η οποία επιτρέπει τον εντοπισμό των ανωτέρω σιδηροδρομικών εγκαταστάσεων μέσω κριτηρίων αναζήτησης καθώς επίσης και ένα έμπειρο σύστημα για την επιλογή της κατάλληλης σιδηροδρομικής διάταξης με βάση κριτήρια που ορίστηκαν. Ένα βασικό συμπεράσματα της σχετικής ανάλυσης είναι ότι τα περισσότερα λιμάνια της Ευρώπης ανήκουν στις κατηγορίες {β} και {γ}.The purpose of this thesis is to investigate issues related to the positioning of rail freight facilities in ports , as well as the organization , function and operation of rail -linked transportations. There has been collected data from European ports and has been done a categorization of the existing railway facilities in 5 categories : a) connection under the legs of the gantry , b )railway connection next to storage space , c ) railway connection on the edge of the port , d ) independent connection adjacent to the port and e) independent remote railway connection. There has been created an application on Google environment which allows the identification of these rail facilities through search criteria as well as an expert system for the selection of the appropriate railway layout based on defined criteria. A key conclusion for the analysis is that most European ports in categories { b } and { c } .Απόστολος Κ. Αργυρείου-Ευαγγελούδη

An application of the theory of intutionistic fuzzy multigraphs

In a recent paper by one of the authors it has been shown that there is a relationship between algebraic structures and labeled transition systems. Indeed, it has been shown that an algebraic structures can be viewed as labeled transition systems, which can also be viewed as multigraphs. In this paper, we extend this work by providing an estimation of the transition possibilities between vertices that are connected with multiarcs