On the Integrability of the Bukhvostov-Lipatov Model

The integrability of the Bukhvostov-Lipatov four-fermion model is investigated. It is shown that the classical model possesses a current of Lorentz spin 3, conserved both in the bulk and on the half-line for specific types of boundary actions. It is then established that the conservation law is spoiled at the quantum level -- a fact that might indicate that the quantum Bukhvostov-Lipatov model is not integrable, contrary to what was previously believed.Comment: 11 pages, 1 figure, LaTeX2e, AMS; new references adde

Inversion of Gamow's Formula and Inverse Scattering

We present a pedagogical description of the inversion of Gamow's tunnelling formula and we compare it with the corresponding classical problem. We also discuss the issue of uniqueness in the solution and the result is compared with that obtained by the method of Gel'fand and Levitan. We hope that the article will be a valuable source to students who have studied classical mechanics and have some familiarity with quantum mechanics.Comment: LaTeX, 6 figurs in eps format. New abstract; notation in last equation has been correcte

Large Eddy Simulation study on the structure of turbulent flow in a complex city

Abstract Large Eddy Simulation (LES) of atmospheric flows has become an increasingly popular modelling approach within the last years, as it has the potential to provide deeper insight into unsteady flow phenomena. LES can be improved and validated using specifically designed and well documented wind tunnel datasets. In this work, we evaluate the performance of LES against a wind tunnel experiment in a semi-idealized city (Michel-Stadt; CEDVAL-LES database) and use the LES results to study the structure of the turbulent flow at the particular urban area. The first, second and third order statistics are presented, as well as velocity frequency distributions and energy spectra. The results compare well with the experimental values. Information about special features of the flow field is also provided. A particular focus of this work is put on the influence of grid resolution on the results. Five different grids are examined and the required resolution for turbulent flow within the canopy layer is evaluated. This study reveals the strong potential of LES for urban flow simulations. It is shown that LES can assess highly non-Gaussian flow behaviour in street canyons, which has implications for urban ventilation, wind comfort assessment and urban design

Comparative evaluation of image reconstruction methods for the siemens PET-MR scanner using the stir library

With the introduction of Positron Emission Tomography - Magnetic Resonance (PET-MR) scanners the development of new algorithms and the comparison of the performance of different iterative reconstruction algorithms and the characteristics of the reconstructed images data is relevant. In this work, we perform a quantitative assessment of the currently used ordered subset (OS) algorithms for low-counts PET-MR data taken from a Siemens Biograph mMR scanner using the Software for Tomographic Image Reconstruction (STIR, stir.sf.net). A comparison has been performed in terms of bias and coefficient of variation (CoV). Within the STIR library different algorithms are available, such as Order Subsets Expectation Maximization (OSEM), OS Maximum A Posteriori One Step Late (OSMAPOSL) with Quadratic Prior (QP) and with Median Root Prior (MRP), OS Separable Paraboloidal Surrogate (OSSPS) with QP and Filtered Back-Projection (FBP). In addition, List Mode (LM) reconstruction is available. Corrections for attenuation, scatter and random events are performed using STIR instead of using the scanner. Data from the Hoffman brain phantom are acquired, processed and reconstructed. Clinical data from the thorax of a patient have also been reconstructed with the same algorithms. The number of subsets does not appreciably affect the bias nor the coefficient of variation (CoV=11%) at a fixed sub-iteration number. The percentage relative bias and CoV maximum values for OSMAPOSL-MRP are 10% and 15% at 360 s acquisition and 12% and 15% for the 36 s, whilst for OSMAPOSL-QP they are 6% and 16% for 360 s acquisition and 11% and 23% at 36 s and for OSEM 6% and 11% for the 360 s acquisition and 10% and 15% for the 36 s. Our findings demonstrate that when it comes to low-counts, noise and bias become significant. The methodology for reconstructing Siemens mMR data with STIR is included in the CCP-PET-MR website

A non-standard matter distribution in the RS1 model and the coupling constant of the radion

In the zero mode approximation we solve exactly the equations of motion for linearized gravity in the Randall-Sundrum model with a non-standard distribution of matter in the neighbourhood of the negative tension brane. It is shown that the form of this distribution can strongly affect the coupling of the radion to matter. We believe that such a situation can arise in models with a realistic mechanisms of matter localization.Comment: 12 pages, LaTe

SOIL EROSION ESTIMATION USING THE EPM MODEL

Στην παρούσα εργασία γίνεται προσπάθεια εκτίμησης της εδαφικής διάβρωσης σε ορεινές υδρολογικές λεκάνες Μεσογειακού τύπου, με τη χρήση του ομοιώματος EPM (Erosion Potential Model). Η περιοχή μελέτης περιλαμβάνει τις λεκάνες των ποταμών Βενέτικου, Καλαμά, Άνω Ρου Αχελώου και Αράχθου (8 υπολεκάνες συνολικά). Το ομοίωμα εφαρμόζεται τόσο σε ετήσιο όσο και σε υπέρ-ετήσιο χρονικό βήμα, σε περιβάλλον GIS, λαμβάνοντας υπόψη τη χωρική κατανομή των επιμέρους παραγόντων του καθώς και την εξέλιξη του φαινομένου εντός της λεκάνης. Τα αριθμητικά αποτελέσματα αξιολογούνται αρχικά ως προς τις παρατηρημένες τιμές στερεοαπορροής (προκύπτουν από τις μετρήσεις στερεοπαροχής της ΔΕΗ στην έξοδο κάθε λεκάνης). Το ομοίωμα υποεκτιμά σημαντικά τις παρατηρημένες τιμές και στις δυο χρονικές κλίμακες. Η αμφιλεγόμενη αξιοπιστία των παρατηρημένων τιμών οδήγησε στην αντικατάσταση τους από προσομοιωμένες (μεθοδολογία καμπυλών παροχής στερεοπαροχής). Ως προς αυτές, το ομοίωμα συμπεριφέρεται καλύτερα, εξακολουθώντας όμως να υποεκτιμά τα αποτελέσματα. Εν τούτοις, η χωρική αποτύπωση του φαινομένου κρίνεται αξιόπιστη. Η φτωχή επίδοση του ομοιώματος αποδίδεται στα ιδιαίτερα χαρακτηριστικά του καθώς επίσης στις συνθήκες και το ιδιαίτερο καθεστώς στερεοπαροχής της περιοχής μελέτης.The study aims to evaluate soil erosion and investigate its spatial distribution by applying the empirical EPM (i.e. Erosion Potential Model) at mountainous Mediterranean type catchments. Study area includes the catchments of Venetikos; Kalamas; Upper Acheloos and Arachthos Rivers (eight subcatchments in total), very important aquatic systems of NW Greece. The model was implemented both annually and inter-annually. A GIS-based approach was adopted, considering the spatial variation of its factors, as well as the erosion processes occurring in a catchment. The results were initially validated by being compared to the observed sediment yield values (based on the sediment discharge measurements conducted by the PPC). The model’s performance was poor, significantly underestimating the results at both time scales. The ambiguous reliability of the PPC measurements led to their replacement by simulated ones, estimated using the sediment discharge rating curves methodology. Regarding the latter, the model performed better, attributing more accurate results, yet anew underestimated. However, it managed to identify the most susceptible to erosion areas. The poor performance is mainly attributed to its inherent shortcomings along with the specific characteristics and sedimentary regime of the study area

SOIL EROSION ESTIMATION USING THE EPM MODEL

Στην παρούσα εργασία γίνεται προσπάθεια εκτίμησης της εδαφικής διάβρωσης σε ορεινές υδρολογικές λεκάνες Μεσογειακού τύπου, με τη χρήση του ομοιώματος EPM (Erosion Potential Model). Η περιοχή μελέτης περιλαμβάνει τις λεκάνες των ποταμών Βενέτικου, Καλαμά, Άνω Ρου Αχελώου και Αράχθου (8 υπολεκάνες συνολικά). Το ομοίωμα εφαρμόζεται τόσο σε ετήσιο όσο και σε υπέρ-ετήσιο χρονικό βήμα, σε περιβάλλον GIS, λαμβάνοντας υπόψη τη χωρική κατανομή των επιμέρους παραγόντων του καθώς και την εξέλιξη του φαινομένου εντός της λεκάνης. Τα αριθμητικά αποτελέσματα αξιολογούνται αρχικά ως προς τις παρατηρημένες τιμές στερεοαπορροής (προκύπτουν από τις μετρήσεις στερεοπαροχής της ΔΕΗ στην έξοδο κάθε λεκάνης). Το ομοίωμα υποεκτιμά σημαντικά τις παρατηρημένες τιμές και στις δυο χρονικές κλίμακες. Η αμφιλεγόμενη αξιοπιστία των παρατηρημένων τιμών οδήγησε στην αντικατάσταση τους από προσομοιωμένες (μεθοδολογία καμπυλών παροχής στερεοπαροχής). Ως προς αυτές, το ομοίωμα συμπεριφέρεται καλύτερα, εξακολουθώντας όμως να υποεκτιμά τα αποτελέσματα. Εν τούτοις, η χωρική αποτύπωση του φαινομένου κρίνεται αξιόπιστη. Η φτωχή επίδοση του ομοιώματος αποδίδεται στα ιδιαίτερα χαρακτηριστικά του καθώς επίσης στις συνθήκες και το ιδιαίτερο καθεστώς στερεοπαροχής της περιοχής μελέτης.The study aims to evaluate soil erosion and investigate its spatial distribution by applying the empirical EPM (i.e. Erosion Potential Model) at mountainous Mediterranean type catchments. Study area includes the catchments of Venetikos; Kalamas; Upper Acheloos and Arachthos Rivers (eight subcatchments in total), very important aquatic systems of NW Greece. The model was implemented both annually and inter-annually. A GIS-based approach was adopted, considering the spatial variation of its factors, as well as the erosion processes occurring in a catchment. The results were initially validated by being compared to the observed sediment yield values (based on the sediment discharge measurements conducted by the PPC). The model’s performance was poor, significantly underestimating the results at both time scales. The ambiguous reliability of the PPC measurements led to their replacement by simulated ones, estimated using the sediment discharge rating curves methodology. Regarding the latter, the model performed better, attributing more accurate results, yet anew underestimated. However, it managed to identify the most susceptible to erosion areas. The poor performance is mainly attributed to its inherent shortcomings along with the specific characteristics and sedimentary regime of the study area

Form factors in the Bullough-Dodd related models: The Ising model in a magnetic field

We consider particular modification of the free-field representation of the form factors in the Bullough-Dodd model. The two-particles minimal form factors are excluded from the construction. As a consequence, we obtain convenient representation for the multi-particle form factors, establish recurrence relations between them and study their properties. The proposed construction is used to obtain the free-field representation of the lightest particles form factors in the $\Phi_{1,2}$ perturbed minimal models. As a significant example we consider the Ising model in a magnetic field. We check that the results obtained in the framework of the proposed free-field representation are in agreement with the corresponding results obtained by solving the bootstrap equations.Comment: 20 pages; v2: some misprints, textual inaccuracies and references corrected; some references and remarks adde

Integration of a Spanish-to-LSE machine translation system into an e-learning platform

The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-642-21657-2_61This paper presents the first results of the integration of a Spanish-to-LSE Machine Translation (MT) system into an e-learning platform. Most e-learning platforms provide speech-based contents, which makes them inaccessible to the Deaf. To solve this issue, we have developed a MT system that translates Spanish speech-based contents into LSE. To test our MT system, we have integrated it into an e-learning tool. The e-learning tool sends the audio to our platform. The platform sends back the subtitles and a video stream with the signed translation to the e-learning tool. Preliminary results, evaluating the sign language synthesis module, show an isolated sign recognition accuracy of 97%. The sentence recognition accuracy was of 93%.Authors would like to acknowledge the FPU-UAM grant program for its financial support. Authors are grateful to the FCNSE linguistic department for sharing their knowledge in LSE and performing the evaluations. Many thanks go to María Chulvi and Benjamín Nogal for providing help during the imple-mentation of this system. This work was partially supported by the Telefónica Móviles España S.A. project number 10-047158-TE-Ed-01-1

Quantum Calogero-Moser Models: Integrability for all Root Systems

The issues related to the integrability of quantum Calogero-Moser models based on any root systems are addressed. For the models with degenerate potentials, i.e. the rational with/without the harmonic confining force, the hyperbolic and the trigonometric, we demonstrate the following for all the root systems: (i) Construction of a complete set of quantum conserved quantities in terms of a total sum of the Lax matrix (L), i.e. (\sum_{\mu,\nu\in{\cal R}}(L^n)_{\mu\nu}), in which ({\cal R}) is a representation space of the Coxeter group. (ii) Proof of Liouville integrability. (iii) Triangularity of the quantum Hamiltonian and the entire discrete spectrum. Generalised Jack polynomials are defined for all root systems as unique eigenfunctions of the Hamiltonian. (iv) Equivalence of the Lax operator and the Dunkl operator. (v) Algebraic construction of all excited states in terms of creation operators. These are mainly generalisations of the results known for the models based on the (A) series, i.e. (su(N)) type, root systems.Comment: 45 pages, LaTeX2e, no figure